Q: What's Filter Efficiency Filtration Class based on ASHRAE Standard 52.2-2007, EN779-2012,EN1822-2009

Filter Class ASHRAE Standard 52.2-2007, EN779-2012,EN1822-2009

Question 1

Inner Analysis Report for Industrial Wet Scrubber-A Probe In Wet Dust Collector with Calculation

Accepted Answer

Inner Analysis Report for Industrial Wet Scrubber-A Probe In Wet Dust Collector with Calculation

Wet dust removal is also called Wet Scrubber. It is a dust removal method that uses water (or other liquids) to contact each other with dusty gas, accompanied by heat and mass transfer, and separates dust particles from gas after washing. This method has been used in the iron and steel industry since the end of the 19th century to remove large particles of dust. The advantages and disadvantages of wet dust removal and dry dust removal are shown in Table 2-1

Table 2-1 Comparison between wet dust removal and dry dust removal

Wet Dust Collector

Dry Dust Collector

advantage:

1. Can capture gas and dust at the same time

2. Recovered soluble matter can be pumped to another device

proceed to the next step

3. It can cool and wash high-temperature gas

4. Can recycle and neutralize corrosive gas and liquid droplets

5. Use water as washing liquid to prevent fire and explosion

6. Less equipment investment, relatively simple structure and small body

shortcoming:

1. To consume a certain amount of water (or other liquids), the sewage needs to be treated after dust removal to prevent secondary pollution

2. Dust recovery is difficult

3. Viscous dust is prone to clogging and hanging ash

4. Antifreeze needs to be considered in winter

5. After washing, the exhaust humidity is high and the dew point is low

6. Ultrafine particles are not easy to wet and can pass through the scrubber

advantage:

1. The recovered dry material does not need to be reprocessed

2. Corrosion can be avoided in most cases

3. High-efficiency dust collectors can be produced

4. Radioactive dust can use combustible filter material

shortcoming:

1. Hygroscopic substances will cake and be difficult to remove

2. Equipment maintenance and dust disposal will endanger the operation

3. High temperature may limit dust removal methods

4. For some dust collectors (such as filter bag dust collectors), the use of corrosive liquid beads is limited

5. The problem of regenerated dust will be encountered when disposing of the collected dust

Mechanism of wet dust removal

The catch in wet dust removal is water or other liquids. According to its different forms when collecting dust particles: liquid droplets, liquid film, and liquid layer, wet dust removal can be divided into three types accordingly. Among them, the dust removal method using liquid droplets as dust collectors is the most widely used, and it can be subdivided into several types due to the different ways of generating liquid droplets.

1) Droplet wet dust removal

Droplet wet dedusting mainly depends on the full contact between the dust-containing gas and the evenly dispersed droplets in a closed space, and the capture of the droplets on the dust particles is realized through the effects of inertial collision, interception, diffusion, gravity, electrostatic force, etc., such as As shown in Figure 2-1.

The basic inertial collision, interception and diffusion effects will be described below. It is assumed that dust particles are captured as soon as they contact the capture body.

(1)Inertial collision

Inertial collision is the most common dust removal effect in wet dust removal. The inertial collision effect only considers the mass of dust particles and not its volume.

As shown in Figure 2-2, there is a droplet in front of the dust-laden airflow, and the streamline of the airflow is deflected in front of the droplet. The deflection of the streamline varies with the air velocity. When the velocity is high, the streamline should be close to the surface of the droplet. The front end deflects around the catcher, and at lower speeds the streamline deflects farther away from the catcher. Because the density of the dust particles in the airflow is much higher than that of the gas, under the action of inertial force, their trajectory deviates from the flow line of the airflow and moves towards the direction close to the trapping body. The farthest trajectory where collective collisions occur is called the limit trajectory. Within the range b shown in the figure, all dust particles with a mass not less than m particles will be trapped due to inertial collision with the capture body.Define the inertial collision factor as：

The collision factor φ varies between 0 and 1. The larger the collision factor, the greater the probability of dust being trapped due to inertial collision. The inertial parameter Ψ, also known as the Stokes number, is defined as:

d1—droplet diameter, μm.

In the formula: C—Cunningham sliding correction coefficient

v0—the relative velocity of dust particles and droplets, m/s;

ρp—dust particle density, kg/m3;

dp—diameter of dust particle, μm;

μg—gas dynamic viscosity, Pa s;dl—droplet diameter, μm.

In the formula: C—Cunningham sliding correction coefficient

v0—the relative velocity of dust particles and droplets, m/s;

ρp—dust particle density, kg/m3;

dp—diameter of dust particle, μm;

μg—gas dynamic viscosity, Pa s;

It can be seen from Figure 2-3 that the collision factor φ has a dependence on the inertia parameter Ψ, and the parameter Rer is the Reynolds number.

In the above definition, ρg is the gas density, kg/m3.

Therefore, with the increase of relative velocity v0 between dust particles and liquid droplets, dust particle density ρp, and dust particle diameter dp, due to the effect of inertia, the collision factor will increase, and the probability of dust being trapped will increase; and when the gas viscosity When the μg droplet diameter dl increases, the collision force and friction force dominate, and the dust will bypass the droplet without being trapped.

For a single droplet, the inertial collision trapping efficiency is defined as the percentage of the number of dust particles that have inertial collision with the droplet to the initial number of dust particles in the dusty airflow passing around the droplet. Many scholars at home and abroad have studied the collection efficiency of single droplet inertial collision.

Wong and Johnstone, for the condition of potential flow and inertial parameter Ψ>0.2, proposed a single droplet inertial collision trapping efficiency as:It can be seen from Figure 2-3 that the collision factor φ has a dependence on the inertia parameter Ψ, and the parameter Rer is the Reynolds number.

In the above definition, ρg is the gas density, kg/m3.

Therefore, with the increase of relative velocity v0 between dust particles and liquid droplets, dust particle density ρp, and dust particle diameter dp, due to the effect of inertia, the collision factor will increase, and the probability of dust being trapped will increase; and when the gas viscosity When the μg droplet diameter dl increases, the collision force and friction force dominate, and the dust will bypass the droplet without being trapped.

For a single droplet, the inertial collision trapping efficiency is defined as the percentage of the number of dust particles that have inertial collision with the droplet to the initial number of dust particles in the dusty airflow passing around the droplet. Many scholars at home and abroad have studied the collection efficiency of single droplet inertial collision.

Wong and Johnstone, for the condition of potential flow and inertial parameter Ψ>0.2, proposed a single droplet inertial collision trapping efficiency as:

Sell.W et al. conducted experiments to study the longitudinal sections of water streamlines passing through objects of different shapes (the diameters of balls, columns and flat plates are all 10cm), and obtained the relationship curve between the inertial collision capture efficiency ηp and the inertial parameter Ψ as shown in Figure 2-4 Show.

（2）to intercept

Contrary to the inertial impact effect, the interception effect only considers the volume of dust particles, but ignores their mass. Since there is no inertial force without mass, particles of different sizes flow around the trapping body along the streamline. If the minimum distance between the streamline where the particle is located and the surface of the trapping body is less than or equal to the particle radius, the particle will come into contact with the trapping body. And being captured, this is the interception effect.

As shown in Figure 2-5, at a position b away from the horizontal centerline of the trapping body, a particle approaches the trapping body along the airflow streamline at a velocity v0. Before approaching the trapping body, the airflow streamline deflects, because the mass of the particle , so the particles are also deflected by the streamline around the capture body. If the shortest distance between the streamline and the surface of the capture body is dp/2, the particles shown in the figure just come into contact with the capture body and are trapped. The trajectory of the particle That is, the limit trajectory of particles of the same size. Within the range of b, particles with a diameter not smaller than dp will contact with the trapping body and be trapped.

The dimensionless interception factor characterizing the interception is defined asAs shown in Figure 2-5, at a position b away from the horizontal centerline of the trapping body, a particle approaches the trapping body along the airflow streamline at a velocity v0. Before approaching the trapping body, the airflow streamline deflects, because the mass of the particle , so the particles are also deflected by the streamline around the capture body. If the shortest distance between the streamline and the surface of the capture body is dp/2, the particles shown in the figure just come into contact with the capture body and are trapped. The trajectory of the particle That is, the limit trajectory of particles of the same size. Within the range of b, particles with a diameter not smaller than dp will contact with the trapping body and be trapped.

The dimensionless interception factor characterizing the interception is defined as：

The interception efficiency of a single droplet is：

For potential flow around a sphere at rest, the flow function is：

Divide both sides of formula (2.8) by ，And simplify, that is, the interception efficiency of a single spherical droplet:

For viscous flow around a sphere at rest, the flow function is:

According to the above steps, the interception efficiency of a single spherical droplet is obtained as:

The calculation formula of interception efficiency obtained above can be simplified as follows for viscous flow around a sphere at rest, the flow function is:

According to the above steps, the interception efficiency of a single spherical droplet is obtained as:

The calculation formula of interception efficiency obtained above can be simplified as follows:

For potential flow, the Ranz formula is：

The Reynolds number of the droplet flow is defined as:

In the formula：R—gas constant，J/(kg·K)；

m—gas molar mass，kg；

p—gas pressure，Pa。

Johnstone and RobertsThe diffusion and sedimentation efficiency of a single droplet proposed in 1949 is：

In 1976，Crawford exports in Re_D<1，Pe<1 In the viscous flow of , the diffusion and sedimentation efficiency of a single droplet is:

Also，Pfeffer-The calculation formula is:

In the actual wet dust removal process, the inertial collision, interception and diffusion effects exist at the same time, and the three mechanisms interact and work together. At this time, the dust removal efficiency cannot be directly obtained through the theoretical calculation formula.

Wet Scrubber Overview

The self-initated dust collector relies on the dust-laden airflow hitting the liquid film or the free liquid surface to form a large number of droplets or water curtains to capture dust particles. The diameter of the droplets produced by this dust collector is small, and the relative velocity between the droplets and the airflow is relatively large, so it has a high dust removal efficiency.

The self-initated dust collector on the driving face as shown in Figure 2-10. After the dust-laden air enters the air inlet chamber I, it hits the free liquid surface, and larger dust particles fall into the water due to inertia during this process. The dust-laden airflow and the aroused water droplets are fully mixed in the curved channel II, and the droplets trap dust particles through inertial collision, interception and diffusion. The purified gas is dehydrated by the dehydrator and then discharged from the dust collector.

Figure 2-11 is a vortex self-initated wet dust collector. The dust-laden gas and the aroused liquid droplets are fully mixed in the vortex channel to complete the purification work.

Dust removal mechanism of self-initated water curtain and influencing factors of dust removal efficiency

The dust removal process of the self-initated water curtain dust collector is as follows：

The induced draft fan provides power for the whole system, so that a negative pressure environment is formed at the air inlet, and the outside dust-laden airflow is sucked into the air inlet chamber of the dust collector. Under the action of the throttle baffle, the flow area of the dust-laden airflow is rapidly reduced. The speed is small, so the speed is getting bigger and bigger, and reaches the maximum when it flows through the end of the throttle baffle, where the high-speed airflow forms a strong impact on the liquid surface, and the larger particles of dust fall directly into the water due to inertia. The rest of the dust continues to enter the mixing chamber composed of the throttle baffle and the deflector with the airflow. The liquid surface at the end of the throttle baffle is strongly impacted by the airflow and separates a large number of droplets. It sprays into the mixing chamber at a high speed and performs a similar parabolic motion. A large number of droplets complete this action without interruption, forming a water curtain with a certain shape in the mixing chamber, and the droplets are dispersed in the entire airflow. Dust particles are collected comprehensively and efficiently, and the purified airflow entrains a large number of small droplets. When passing through the water barrier, due to the sharp change of the airflow direction, the droplets are separated from the air flow line and collected by the water barrier. Finally The purified air is discharged through the outlet of the induced draft fan.

The mixing of dust-laden airflow and liquid droplets in the mixing chamber is the most important stage in the whole dust removal process, which plays a decisive role in the dust removal efficiency of the dust collector. Figure 2-16 is a schematic diagram of the fluid flow state in the mixing chamber.

In the mixing chamber, the trapping body mainly exists in the form of water droplets, and the dust removal mechanism at this time mainly considers inertial collision and interception. From the formula and relationship curve given in 2.1, it can be seen that under the condition of a certain dust density, the dust removal efficiency of a single water droplet is inversely proportional to the diameter of the water droplet, and proportional to the diameter of the dust particle and the relative speed between the dust particle and the water droplet, while for For the whole dust removal system, firstly, the dust removal efficiency of individual water droplets should be improved, and secondly, the number of water droplets in the mixing chamber should be increased, so that the overall dust removal efficiency of the dust collector can be improved. On the other hand, in order to improve the dust removal efficiency of the whole dust removal system, one must increase the relative velocity between the dust particles and the liquid droplets, and second, the diameter of the water droplets forming the water curtain in the mixing chamber shall be as small as possible and the number shall be as large as possible.

The generation of water droplets in the mixing chamber is due to the impulsive action of the dust-laden airflow on the liquid surface. During the impulsive process, the airflow transfers the inertial kinetic energy to the water droplets, making them break away from the shackles of the liquid surface and move with the airflow. The diameter of the water droplets produced is larger. The smaller the number, the larger the number, the more energy the airflow transmits. Therefore, the inertial kinetic energy of the dusty airflow itself determines the size and number of water droplets that are stirred up.

The inertial kinetic energy of the airflow when it hits the water surface at the end of the throttle baffle can be regarded as the sum of the following two parts: one is the energy of the airflow itself after entering the dust collector due to the negative pressure of the air inlet, which is called the initial inertia ; The second is the change from pressure energy to kinetic energy caused by the sharp reduction of air flow area due to baffle throttling, which is called inertial increment. In the case of a certain structure of the dust collector, the initial inertia of the airflow is proportional to the air volume of the dust collector.

and the air volume of the dust collector is jointly determined by the induced fan and the dust removal device. As the load of the induced draft fan, the dust removal device can only be changed by adjusting the throttling baffle or valve. For the induced draft fan (determined by model) equipped with the dust removal device, the control can only be controlled by changing the operating frequency. The higher the operating frequency of the induced draft fan, the greater the processing air volume and the greater the initial inertia of the airflow, and vice versa. The change of the height of the throttle baffle directly affects how much the pressure energy of the airflow can be converted into kinetic energy. The more obvious the throttling effect is, that is, the lower the height of the throttle baffle, the greater the inertial increase of the airflow. On the contrary, the higher the height, the greater the inertial increase. The smaller the amount.

The relationship curve between the operating frequency of the induced draft fan and the dust removal efficiency is shown in Figure 2-17.

The curve in Figure 2-17 is drawn from the data obtained by adjusting the operating frequency of the induced draft fan sequentially under the same self-initated water curtain dust collector test model at different throttle baffle heights. It can be seen from the figure that the dust removal efficiency With the increase of the operating frequency of the induced draft fan, there is a trend of increasing first and then stabilizing.

Taking the h=50mm curve as an example, when the fan runs between 25~45Hz, the dust removal efficiency increases with the increase of frequency, and the change is most obvious before 35Hz; when the fan is running at 45~50Hz, the dust removal efficiency tends to be stable. At 25Hz, because the initial inertia obtained by the airflow is too small, the energy transferred to the liquid surface is too small when it hits the liquid surface, so that sufficient water droplets cannot be aroused, so the airflow bypasses the throttle baffle and enters the mixing chamber. The dust particles cannot be captured in large quantities, and the dust removal efficiency is not high; as the operating frequency of the fan increases, before 40Hz, the initial inertia obtained by the airflow entering the dust collector increases accordingly, and at the end of the throttling baffle The energy transmitted to the liquid surface increases when the liquid surface is impacted, and more and more water droplets break free from the shackles of the liquid surface and enter the mixing chamber with the airflow, and the diameter of the water droplets is also getting smaller and smaller, and the initial inertia of the airflow The increase in itself directly leads to the increase of dust particles falling into the water due to inertia during the process of circumventing the throttling baffle. In addition, it increases the number of water droplets in the mixing chamber and reduces the particle size. In the mixing chamber due to The dust particles captured by inertial collision and interception will also increase accordingly, and the dust removal efficiency will inevitably increase significantly; when the frequency continues to increase to 45Hz, at this stage, when the airflow hits the liquid surface, it will fall into the water due to the inertial effect The dust particles in the airflow continue to increase, although the number of water droplets in the mixing chamber continues to increase with the increase of the frequency, the particle size continues to decrease, and the condition of the water curtain is getting better and better, but because the dust particles in the air flow decrease with the particle size, the trapping The difficulty of collection increases obviously, and the increase of dust removal efficiency in the mixing chamber becomes insignificant, which leads to the slowdown of the increase of dust removal efficiency of the whole dust collector. The dust particles entering the water still continue to increase, and the excessive impulse energy makes the diameter of the water droplets that are partly separated from the liquid surface too small, so that after the dust is captured, they cannot freely settle into the water or be removed by the water barrier, but are separated by the airflow. It is discharged from the outlet of the dust collector, and the originally collected dust particles are released into the environment again, so the dust removal efficiency of the dust collector will no longer increase.

h=30mm In the curve, when the frequency is 25~35Hz, the dust removal efficiency increases with the increase of the frequency; 35~45Hz, the dust removal efficiency is basically stable at the highest value; while 45~50Hz, the dust removal efficiency has a slow downward trend.

The change trend of the first two stages is the same as the change of the h=50mm curve, and the reason is the same, so I won’t go into details here. At the stage of 45~50Hz, with the increase of the initial inertia of the airflow, although the number of particles falling into the water due to the inertial effect when the airflow hits the liquid surface increases, the excessive impulse energy makes the diameter of the excited water droplets too small, and the fog If the pollution is serious, there will be more and more small droplets carrying the collected dust particles through the water barrier to the outlet of the dust collector with the airflow. Because of this, the dust removal efficiency will slowly decline.

For the two curves h=80mm and h=100mm in the figure, in the frequency range of 25~50Hz, the dust removal efficiency has been increasing with the increase of frequency, and there is no stable section in the h=50mm curve, which is Because the height of the throttle baffle is too high at this time, the inertia increment obtained by the dust-laden airflow passing through the throttle baffle is not large. Even if the induced draft fan operates at a high frequency, the water curtain in the mixing chamber cannot be fully spread. The state, so it can not reach the highest dust removal efficiency. Obviously, if we can continue to increase the processing air volume of the dust collector at this time, so that the initial inertia of the dusty airflow continues to increase, the maximum dust removal efficiency at this baffle height will be reached like other curves.

The relationship curve between throttle baffle height and dust removal efficiency is shown in Figure 2-18

As mentioned above, the height of the throttle baffle directly affects the size of the inertial increment after the airflow passes through the baffle. The smaller the size, the less water droplets will leave the liquid surface, and the larger the particle size, the worse the condition of the water curtain in the mixing chamber, and the lower the dust removal efficiency; on the contrary, the lower the baffle height, the greater the energy obtained by the liquid surface. The better the condition of the water curtain in the mixing chamber, the higher the dust removal efficiency; however, if the height of the baffle is too low, the particle size of the water droplets will be too small, and the dust will be discharged from the outlet with the airflow bypassing the water barrier, thereby reducing the dust removal efficiency. . Therefore, there must be an optimal throttle baffle height hm, so that the dust removal efficiency of the dust collector at a certain frequency can reach the highest.

Take the f=50Hz curve in Figure 2-18 as an example, the curve as a whole shows a trend of rising first and then falling, and reaches the maximum value at h=50mm, that is to say, when the operating frequency of the induced draft fan is 50Hz, the optimal throttle gear Board height hm=50mm. At this time, reducing the height of the baffle will lead to severe water discharge at the outlet of the dust collector, and the dust removal efficiency will decrease; if the height of the baffle is increased, the inertia increment will decrease after the airflow bypasses the baffle, and the condition of the water curtain in the mixing chamber will deteriorate, reducing the dust removal efficiency. For the two cases of frequency f=25 and 30Hz, there is only a descending section in Fig. 2-18. This is because the initial inertia of the airflow in these two cases is too small, so under this test condition, there is no water droplet size that is too small. In the case of severe water discharge at the outlet, the hm at these two frequencies should be less than or equal to 30mm.

The aroused water droplets break away from the air flow line in the mixing chamber and collide with the water film formed on the deflector, which also has a trapping effect on the dust particles. The capture effect of water film on dust is very complex, and its capture efficiency is related to factors such as dust particle size, dust concentration, wettability of dust, and stability of water film.

The larger the particle size of the dust, the greater the degree of separation from the streamline when the airflow encounters the deflector and the deflection of the streamline, so the greater the probability of hitting the water film and being captured. In addition, the dust is captured by the liquid film. In fact, the gas-solid interface on the outer wall of the dust particle is replaced by the liquid-solid interface, and the dust particle breaking through the outer gas film is the prerequisite for this replacement. The particles are not easy to break through because they are tightly wrapped by the air film, and it is difficult to be captured by the water film.

Excessive dust particle concentration will reduce the dust removal efficiency of the water film. Excessive particle concentration may cause the dust particles that escape from the air flow line and hit the water film to collide with the dust particles suspended in the water film and be bounced back into the air flow.

The wettability of dust refers to the degree of affinity between liquid and dust. The affinity of the same dust to different liquids is different; the affinity of different dust to the same liquid is also different. The wettability of dust is related to the type, particle size, shape, generation conditions, components, temperature, moisture content, surface roughness and chargeability of the dust, and is also related to the surface tension of the liquid and the viscosity between the dust particles and the liquid. Adhesion is related to contact mode [31]. The degree to which a liquid wets a solid surface depends on the force exerted by the liquid molecules on the solid surface molecules. The size of wettability is often expressed by wetting angle. The wetting angle means that when solid particles are immersed in the liquid, the surface tension of the liquid acts on the tangent of the solid-liquid contact point, and the angle θ between the tangent and the surface of the dust particle is called the wetting angle. For hydrophobic dust particles, the liquid shrinks on the dust particle surface, θ>90°, as shown in Figure 2-19a; for hydrophilic dust particles,As mentioned above, the height of the throttle baffle directly affects the size of the inertial increment after the airflow passes through the baffle. The smaller the size, the less water droplets will leave the liquid surface, and the larger the particle size, the worse the condition of the water curtain in the mixing chamber, and the lower the dust removal efficiency; on the contrary, the lower the baffle height, the greater the energy obtained by the liquid surface. The better the condition of the water curtain in the mixing chamber, the higher the dust removal efficiency; however, if the height of the baffle is too low, the particle size of the water droplets will be too small, and the dust will be discharged from the outlet with the airflow bypassing the water barrier, thereby reducing the dust removal efficiency. . Therefore, there must be an optimal throttle baffle height hm, so that the dust removal efficiency of the dust collector at a certain frequency can reach the highest.

Take the f=50Hz curve in Figure 2-18 as an example, the curve as a whole shows a trend of rising first and then falling, and reaches the maximum value at h=50mm, that is to say, when the operating frequency of the induced draft fan is 50Hz, the optimal throttle gear Board height hm=50mm. At this time, reducing the height of the baffle will lead to severe water discharge at the outlet of the dust collector, and the dust removal efficiency will decrease; if the height of the baffle is increased, the inertia increment will decrease after the airflow bypasses the baffle, and the condition of the water curtain in the mixing chamber will deteriorate, reducing the dust removal efficiency. For the two cases of frequency f=25 and 30Hz, there is only a descending section in Fig. 2-18. This is because the initial inertia of the airflow in these two cases is too small, so under this test condition, there is no water droplet size that is too small. In the case of severe water discharge at the outlet, the hm at these two frequencies should be less than or equal to 30mm.

The aroused water droplets break away from the air flow line in the mixing chamber and collide with the water film formed on the deflector, which also has a trapping effect on the dust particles. The capture effect of water film on dust is very complex, and its capture efficiency is related to factors such as dust particle size, dust concentration, wettability of dust, and stability of water film.

The larger the particle size of the dust, the greater the degree of separation from the streamline when the airflow encounters the deflector and the deflection of the streamline, so the greater the probability of hitting the water film and being captured. In addition, the dust is captured by the liquid film. In fact, the gas-solid interface on the outer wall of the dust particle is replaced by the liquid-solid interface, and the dust particle breaking through the outer gas film is the prerequisite for this replacement. The particles are not easy to break through because they are tightly wrapped by the air film, and it is difficult to be captured by the water film.

Excessive dust particle concentration will reduce the dust removal efficiency of the water film. Excessive particle concentration may cause the dust particles that escape from the air flow line and hit the water film to collide with the dust particles suspended in the water film and be bounced back into the air flow.

The wettability of dust refers to the degree of affinity between liquid and dust. The affinity of the same dust to different liquids is different; the affinity of different dust to the same liquid is also different. The wettability of dust is related to the type, particle size, shape, generation conditions, components, temperature, moisture content, surface roughness and chargeability of the dust, and is also related to the surface tension of the liquid and the viscosity between the dust particles and the liquid. Adhesion is related to contact mode [31]. The degree to which a liquid wets a solid surface depends on the force exerted by the liquid molecules on the solid surface molecules. The size of wettability is often expressed by wetting angle. The wetting angle means that when solid particles are immersed in the liquid, the surface tension of the liquid acts on the tangent of the solid-liquid contact point, and the angle θ between the tangent and the surface of the dust particle is called the wetting angle. For hydrophobic dust particles, the liquid shrinks on the dust particle surface, θ>90°, as shown in Figure 2-19a; for hydrophilic dust particles，The liquid expands on the surface of the dust particle, θ<90°, as shown in Figure 2-19b.

The stability of the water film mainly refers to the stability of the thickness of the water film. If the thickness of the water film is too small, it will be pulled into small water droplets by the airflow, which will obviously reduce the collection efficiency of dust particles. The water film on the deflector of the shock-type water curtain dust collector is definitely not stable compared with the general water film dust collector, but due to the large amount of water droplets being excited in the mixing chamber, it can ensure that the water film on the deflector is stable. A certain thickness of the water film.

Based on the wetting angle, it is judged whether the dust particles are captured in the water film dust removal. In the research, it is assumed that the dust particles are captured when they are immersed in the liquid, and the calculation formula of the wetting angle at this time is obtained:

μ_l—Dynamic viscosity coefficient of water，（Pa·s）；

　　　 v_r—The velocity of dust particles in the vertical direction of the water film，m/s。

The wetting angle of dust particles in the actual environment is recorded asθ'，if θ'<θ，Dust particles can be immersed in the water film to reach or exceed ’s deep，thereby being captured；if θ'>θ，The ability of the water film to capture dust particles is reduced.

2.3 Force and Motion Analysis of dust particles

The flow field area in the mixing chamber of the self-initated water curtain dust collector is a gas-liquid-solid three-phase flow, the gas is the continuous phase, and the liquid droplets and dust particles are the dispersed phase. Dust particles interact with gas, liquid droplets and other particles in this three-phase flow, and the stress conditions are very complicated. However, since the interaction between particles and gas plays a dominant role in particle motion, only Briefly analyze the force condition of a single dust particle in the gas.

The shapes of dust particles in the airflow are various, and it is most convenient to use spherical particles when analyzing the force on the particles. Therefore, the concept of "equivalent diameter" is introduced for the calculation of irregular particles. The stress situation is the same as that of spherical particles with equivalent diameter. The equivalent diameter is divided into volume equivalent diameter dv and surface area equivalent diameter ds, which are defined as follows:The flow field area in the mixing chamber of the self-initated water curtain dust collector is a gas-liquid-solid three-phase flow, the gas is the continuous phase, and the liquid droplets and dust particles are the dispersed phase. Dust particles interact with gas, liquid droplets and other particles in this three-phase flow, and the stress conditions are very complicated. However, since the interaction between particles and gas plays a dominant role in particle motion, only Briefly analyze the force condition of a single dust particle in the gas.

The shapes of dust particles in the airflow are various, and it is most convenient to use spherical particles when analyzing the force on the particles. Therefore, the concept of "equivalent diameter" is introduced for the calculation of irregular particles. The stress situation is the same as that of spherical particles with equivalent diameter. The equivalent diameter is divided into volume equivalent diameter dv and surface area equivalent diameter ds, which are defined as follows:

The forces experienced by particles in the airflow include: drag resistance, pressure gradient force、Magnus force、Saffman force、additional mass force、Basset force、gravity、Buoyancy etc.

1）Drag resistance F_D

The drag resistance is the force that the airflow acts on the particles when the particles are moving in the airflow. As long as there is relative motion between the particles and the airflow, the drag resistance exists. It is the force that pushes the particles to move forward with the airflow. one of the most important.

laminar flow zone（Stokes区）：10^-4<Re_p<0.3，C_D=24/Re_p

Transition zone（Allen区）：0.3<Re_p<500，C_D=10/(Re_p)^1/2

Turbulent zone（Newton区）：500<Re_p<10³，C_D=0.44

The relationship curve between the two is shown in Figure 2-20

2）pressure gradient force F_P

In a flow with a pressure gradient, particles will always be affected by a resultant force that is not zero. This resultant force is the pressure gradient force. FP is opposite to the direction of the pressure gradient, and its size is equal to the product of the particle volume and the pressure gradient.

3）Magnus Force F_M

The dust particles in the airflow are due to the vorticity of the airflow and the collision with other particles or walls

The rotation of the particles causes the surrounding fluid to produce a resultant force perpendicular to the direction of motion. The resultant force is Magnus Force。F_MThe size and direction of are affected by the relative velocity of the particle and the airflow and the angular velocity of the particle's rotation. The definition formula is as follows:

ω—particle rotation angular velocity, rad/s

4）Saffman Force F_S

In addition to the rotation of the particle itself will generate a force perpendicular to the direction of motion, the existence of the velocity gradient in the flow field makes the flow velocity on both sides of the particle different, and will also generate a force from the low-speed side to the high-speed side,即Saffman force，It is the result of the combined action of slip (relative motion) and shear, and its direction always points to the high-speed side, that is, the center of the flow field, so it is also called slip-shear lift.

5）additional mass force F_vm

When the particle moves at a variable speed in the airflow, it will drive the surrounding fluid to move at a variable speed, which requires the particle to exert a force on the surrounding fluid. According to Newton's third law, the surrounding fluid must also have a reaction force on the particle. This The force is called the added mass force. The additional mass is half the mass of the fluid with the same volume as the particle.

6）Basset forceF_B

When the particle is moving at a variable speed, in addition to the additional mass force of the surrounding fluid, it will also receive an additional resistance. This is due to the fact that the fluid layer attached to the particle will generate fluidity and viscosity when it is moving at a variable speed. deformation. This time-varying fluid force due to the instability of the fluid layer on the particle surface is called the Basset force.

At this time, the particles decelerate in the vertical direction, and the resulting force is

Although the forces acting on particles are quite complicated, not all forces are equally important in general. Many scholars have studied and calculated the forces on particles in airflow, but due to different experimental conditions, it is concluded that The results vary. In most areas of the flow field, the Magnus force is at least an order of magnitude smaller than the Saffman force and drag resistance, and for mineral powder particles, the Basset force can also be ignored. it concluded that when the rotation speed of pulverized coal particles is 1800 rpm, the Magnus force is about 1% of the drag resistance. Cen Kefa came to the following conclusion: Under various conditions of pulverized coal particles, the order of magnitude of additional mass force, pressure gradient force, and Saffman force is very small and generally negligible, but in the boundary layer, due to The velocity gradient is very large, so the Saffman force cannot be ignored at this time; the magnitude of the Magnus force is equal to the gravity at each particle size, which plays a role in balancing gravity; in turbulent flow motion, Basset force is a very important force; drag resistance It is the maximum force acting on the pulverized coal particles, which plays the role of accelerating the particles.

The following discusses the movement state of dust particles with the dust-laden airflow around the end of the throttling baffle. According to the conclusions of the above-mentioned scholars, only the drag resistance FD and gravity Fg are considered here.

When the dust-laden airflow passes through the throttling baffle, the airflow streamline is compressed and the direction changes sharply. The particles that originally moved along the streamline direction gradually depart from the original streamline, and then intersect with other airflow streamlines. At this time, the velocity of the particles and the airflow It is no longer in the same direction, as shown in Figure 2-22, so the direction of its drag resistance also changes, as shown in Figure 2-23.At this time, the particles decelerate in the vertical direction, and the resulting force is

Although the forces acting on particles are quite complicated, not all forces are equally important in general. Many scholars have studied and calculated the forces on particles in airflow, but due to different experimental conditions, it is concluded that The results vary. In most areas of the flow field, the Magnus force is at least an order of magnitude smaller than the Saffman force and drag resistance, and for mineral powder particles, the Basset force can also be ignored. Literature [43] concluded that when the rotation speed of pulverized coal particles is 1800 rpm, the Magnus force is about 1% of the drag resistance. Cen Kefa came to the following conclusion in literature [44]: Under various conditions of pulverized coal particles, the order of magnitude of additional mass force, pressure gradient force, and Saffman force is very small and generally negligible, but in the boundary layer, due to The velocity gradient is very large, so the Saffman force cannot be ignored at this time; the magnitude of the Magnus force is equal to the gravity at each particle size, which plays a role in balancing gravity; in turbulent flow motion, Basset force is a very important force; drag resistance It is the maximum force acting on the pulverized coal particles, which plays the role of accelerating the particles.

The following discusses the movement state of dust particles with the dust-laden airflow around the end of the throttling baffle. According to the conclusions of the above-mentioned scholars, only the drag resistance FD and gravity Fg are considered here.

When the dust-laden airflow passes through the throttling baffle, the airflow streamline is compressed and the direction changes sharply. The particles that originally moved along the streamline direction gradually depart from the original streamline, and then intersect with other airflow streamlines. At this time, the velocity of the particles and the airflow It is no longer in the same direction, as shown in Figure 2-22, so the direction of its drag resistance also changes, as shown in Figure 2-23.

From the analysis of the comprehensive formula (2.38) and section 2.2.2, it can be obtained that with the increase of the particle diameter dp, the inertial energy of the particle in the vertical direction will be greater, and the acceleration of deceleration motion in this direction will decrease. To obtain vertical upward velocity with the airflow into the mixing chamber requires a greater vertical distance, and the distance between the end of the baffle and the water surface is almost constant, so the particles fall into the water below more easily.

In the mixing chamber, the movement of dust particles in the airflow near the surface of the water droplet is shown in Figure 2-24. After analysis by the above method, the same conclusion is reached, that is, the larger the particle size, the easier it is to break away from the streamline and hit the surface of the water droplet to be trapped.2

Question 2

How To Design Dust Extraction System for Multi Dust Emission Points-Tablet Coating Pans As Example?

Accepted Answer

How To Design Dust Extraction System for Multi Dust Emission Points-Tablet Coating Pans As Example

The production workshop of a pharmaceutical factory has a construction area of about 3240m². It is a single-story building with partial 2 floors. The building height is about 10m. The indoor ceiling height is 2.7m. The upper part is the equipment pipeline layer, and the partial 2-story building is the air-conditioning machine room. Area H is the sugar coating packaging workshop with a total of 12 sugar coating machines.

During the pharmaceutical production process in the sugar-coating workshop of a pharmaceutical factory, a large amount of process talc dust will escape, and effective dust removal measures need to be taken. If dust removal measures are not handled properly, the dust will pollute the indoor air, block and contaminate the purification air-conditioning system, affect the physical and mental health of the staff, thereby destroying the requirements for a clean production environment in the production room and the quality of pharmaceuticals;

And it causes pollution to the outdoor atmospheric environment.

Energy Saving Consideration

Since the dust generation points of process dust are concentrated near the process equipment in the clean room, in order to save energy (such as purifying air conditioning system energy: power supply, exhaust, cooling, heat load, etc.) and saving production space, the layout of the production process is generally considered. , the area of the dust-producing production area should be minimized. Therefore, the room ventilation air volume per unit time is smaller (relatively

For the dust removal system, the available exhaust air volume is also small, and it is necessary to reasonably select the air volume, wind speed, dust collection device and dust removal equipment).

Local ventilation is is better than whole room ventilation

External suction hood. When the production equipment cannot be sealed due to limitations of process conditions, the exhaust hood can be placed near the source of harmful substances. The suction effect of the hood can be used to create a certain air flow at the point where the pollution source emanates, and the harmful substances can be removed. Suction into hood.

In this design, the pollution source produces light mineral talc dust, which disperses into the above-mentioned calm air at a slight speed. Therefore, the control speed of the pollution source can be obtained from the control air speed table of the control point in "Industrial Ventilation", which is 0.5m/s~1.0 m/s. This design uses v=0.6m/s.

Determination of exhaust volume and size of suction hood

1): Top Design

The exhaust hood is located above the sugar coating machine. Due to equipment limitations, gas can only flow into the hood from the side, as shown in Figure 3.2. In order to avoid cross-air flow interference, it is required that H should be ≤0.3L as much as possible (the long side dimension of the cover mouth), take H=0.4m, therefore, L≥1.33m, take L=1.4m.

2): Suction hood size:

The diameter of the umbrella-shaped suction cover is: 0.56+2×0.4H=0.56+2×0.4×0.4=0.88(m)

The perimeter of the suction hood is: 3.14×0.88=2.76(m)

3) In order to ensure the uniform inhalation speed of the mask mouth, a is set to 60° in this design.

4) The exhaust air volume is calculated according to the following formula:

Q=KPHvx

=1.4×2.76×0.4×0.6

=0.93(m²/s)=3348(m³/h)

In the formula: P --- perimeter of the open surface of the hood, m;

H---- distance from the mask mouth to the pollution source, m;

vx-----Control speed, m/s;

K----Considering the uneven velocity distribution along the height, the safety factor is usually taken as K=1.4.

Pipe design

First, design the layout position of the pipeline, then number each pipe section, and select the calculation loop according to the principle of maximum pressure loss.

Determination of the minimum speed in the pipeline

In this design, the pollutant is light mineral powder. According to the "Ventilation and Dust Removal Equipment Design Manual", the minimum flow velocity in the horizontal pipe is 14m/s and the vertical pipe is 12m/s.

Minimum air flow velocity in dust removal ventilation duct (m/s)

Dust properties	Vertical pipe	Horizontal Pipe	Dust properties	Vertical pipe	Horizontal Pipe
	m/s			m/s
Powdered clay and sand	11	13	Iron and steel (chips)	19	23
Fire clay	14	17	dust	16	18
heavy mineral dust	14	16	sawdust, chippings	12	14
light mineral dust	12	14	Large dry sawdust	14	15
dry sand	11	13	dry dust	8	10
coal ash	10	12	fuel dust	14-16	16-18
Wet soil (less than 2% moisture)	15	18	Large pieces of wet sawdust	18	20
Iron and steel (dust)	13	15	grain dust	10	12
cotton	8	10	Hemp, short fiber dust	8	12

Pipe material Choosing

In the dust removal system of a pharmaceutical factory's clean room, materials such as pipes and fittings and valves should be selected based on the physical and chemical properties of the materials being transported and the working conditions. The materials and valves used should meet the process requirements and should not adsorb or pollute the media. The exposed pipelines introduced into the medical clean room (area) should be made of stainless steel or other materials that do not pollute the environment. Air ducts in pharmaceutical factories are usually made of SUS materials (high-quality galvanized steel plates can also be used). The material thickness is determined according to the corrosiveness and abrasion of the dust. For smaller dust removal systems, a plate thickness of 1.2mm to 2mm is generally sufficient. This design uses thin steel plate because its advantages are that it is easy to be processed and manufactured industrially, easy to install, and can withstand higher temperatures.

Selection of air duct cross-section shape

The cross-sectional shapes of air ducts are round and rectangular. Compared with the two, when the cross-sectional area is the same, the circular air duct has less resistance, saves material, and has greater strength; when the diameter of the circular air duct is smaller, it is easier to manufacture and is more convenient for thermal insulation. However, it is more difficult to lay out and make circular air duct fittings than rectangular air ducts; it is not easy to coordinate with the building and structure when laying out, and it is not easy to arrange beautifully when exposed. When the flow velocity in the air duct is high and the diameter of the air duct is small, a circular air duct is usually used, so a round air duct is selected here.

The flow rate in the air duct should be determined from both technical and economic aspects. Judging from the actual engineering situation, it is appropriate to choose a lower flow rate (selectable lower limit of flow rate) for the dust removal system in the pharmaceutical factory's clean room, and should be combined with reasonable air duct layout, which can save energy consumption. With appropriate technology, it will not Cause dust precipitation and blockage. After the flow rate and flow rate of the air duct are determined, the cross-sectional size of the duct can be calculated as follows:

Q=(π d²V)/4 gets:

d=√4Q/πV

d—Duct diameter m

Q—Dust gas flow rate m³/s

V—dust gas flow velocity m/s

Determination of elbow

When laying out pipes, try to keep straight lines and reduce elbows. The radius of curvature of circular air duct elbows should generally be greater than (1~2) times the pipe diameter. Therefore, a 90° elbow is taken here. Due to the erosion and wear of the elbow by the dusty airflow in the pipeline, it is easy to wear through and leak air, which affects the normal dust collection effect. Therefore, wear-resistant facilities must be installed on the elbow.

Determination of three links

The collision between two airflows with different flow speeds in the tee and the formation of vortices when the airflow speed changes causes local resistance. In order to reduce the local resistance of the tee, the ejector phenomenon should be avoided, and attention should be paid to the connection between the branch pipe and the main pipe to reduce the angle. Therefore, the angle between the branch pipe and the main pipe is a=30; at the same time, the branch pipe should also be as close as possible to the main pipe. Maintain the same flow rate as the flow rate in the main pipe. Like elbows, tee fittings should also be equipped with wear-resistant facilities.

Using 30° converging tee: resistance coefficient ξ=0.20 force coefficient ξ=0.18.

Then use a "Pipe pressure calculator" App to calculate the pressure loss. If you do not have, please ask ACMAN for help:

Dust Collector Choosing

When selecting a dust collector, the properties and particle size distribution of the dust, the temperature and properties of the gas, and the dust concentration of the gas should be considered.

Factors such as the degree of dust removal and the problem of handling dust removed by the dust collector.

The properties of dust have a great influence on the performance of the dust collector. For example, dust with greater viscosity is easy to adhere to the surface of the dust collector and is not suitable for dry dust removal; dust with too large or too small specific resistance is not suitable for electrostatic dust removal. When dealing with abrasive dust, the bag dust collector should use wear-resistant filter media. Different dust collectors have completely different dust removal efficiencies for dust with different particle sizes.

Similarly, when choosing a dust collector, you must first understand the particle size distribution of the dust to be processed and the classification efficiency of various dust collectors.

During the sugar-coating packaging process in the sugar-coating workshop, talc dust will be emitted, affecting the personal health of employees and the air quality in the workshop. In severe cases, the accumulation of a large amount of dust may cause an explosion and affect production. Therefore, the dusty air needs to be purified after being collected. Allowed to vent to atmosphere. Since the collected talc dust has a small particle size between 0.5 and 1.0 μm, and it also contains certain medicinal ingredients, it needs to be recycled. The cartridge dust collector has an efficiency of up to 1.0 μm for dust.

98%～99%. Therefore, the choice of cartridge dust collector has a small footprint and high cost performance.

Blower Choosing

Select the appropriate fan and motor based on the air volume and total resistance of the system.

1) Determine the type of fan based on the properties of the transported gas, the air volume and resistance of the system.

This fan transports talc dust. Due to the fluidity of the dust, static electricity will be generated and cause an explosion. Therefore, an explosion-proof fan is selected.

2) Taking into account the air leakage and resistance calculation of air ducts and equipment, the air volume and air pressure should be selected according to the following formula:

machine:

P_f=KpΔP (Pa)

In the formula, P_f——the wind pressure of the fan;

Kp additional coefficient of wind pressure, general air supply and exhaust system Kp=1.1~1.15; dust removal system Kp=1.15~1.20;

ΔP——the total resistance of the coefficient;

LF=K_LL (m³/h)

In the formula,LF—the air volume of the fan;

K_L——Additional coefficient of air volume, general air supply and exhaust system K₁=1.1; dust removal system K₁=1.1～1.15

L——The total air volume of the coefficient.

Fan wind pressure P_f=KpΔP=1.15×1609.3=1850.7Pa

Fan air volume L_F=K_LL=1.15×42336=48686.4m³h

select 4-68No.10 fan, its performance is

P_f=2030 Pa L_F=49040 m3/h

Fan speed: n=2300r/min.

Equipped with YZ25S-4 motor, the power of the motor is N=40KW.

Conclusion

At last, You can Find the suitable dust collector in ACMAN product list:

https://www.acman-dustcollector.com/products-list.htm

Question 3

How to Design Dust Collection and Ventilation System for Pharmaceutical Cleanroom?

Accepted Answer

How to Design Dust Collection and Ventilation System for Pharmaceutical Cleanroom?

Dust pollution is a pollution problem that many production companies such as chemical industry, medicine, light industry, etc. may encounter.

Dust pollution caused by pharmaceutical companies in the production of solid preparations not only has the characteristics and hazards of general dust, but also contains the toxic hazards of medicine. Mixing of medicine or cross-contamination will occur through the purification air-conditioning system, which will also affect human health and the environment. It is also relatively large and must be effectively captured and controlled before it can be discharged after effective treatment. In particular, with the implementation of the revised Environmental Protection Law, the requirements for the treatment and emission of air pollutants have become more stringent. In environmental management, dust emissions at the boundaries of pharmaceutical factories should usually meet the comprehensive emission standards for air pollution and the concentration limits for unorganized emission monitoring, that is, ≤1.0 mg/m3.

According to the particularity of pharmaceutical production, how can its dust emissions meet the "Good Manufacturing Practice for Pharmaceuticals" (referred to as GMP) and "Pharmaceutical Industry Clean Factory Design Specifications" while achieving effective control of pollutants and environmentally friendly emissions to ensure that pharmaceuticals Improving production quality, preventing the occurrence of contamination and cross-contamination, and protecting the health of company employees are important issues that must be solved during the design and production process of pharmaceutical clean plants, and are also a vital task for engineering designers.

This article combines the actual production, starting from the dust generation link in pharmaceutical production, and discusses how to choose a reasonable, effective and easy-to-operate dust removal system in the dust operation room of pharmaceutical clean plants.

1: Which process points generate dust?

In the production of solid preparations, the processes that generate large amounts of dust and are most prone to dust flying and spreading are: weighing, crushing, sieving, granulating, drying, granulating, mixing, tableting, coating, filling and other processes.

Although in the design and selection of equipment for these processes, in order to effectively prevent the generation of dust during the production process, production equipment that meets the requirements of "GMP" has been selected, and unit equipment should work under negative pressure or in a closed environment as much as possible, and some even Dust-producing equipment is also equipped with dust suction devices and other measures, but it is still unavoidable that a large amount of dust will be generated during the feeding, unloading and equipment cleaning of each process. If effective collection, control and cleaning are not carried out, Clear, there will be mixing or cross-contamination problems through the purification air conditioning system

2: Dust removal and ventilation principles in the operating rooms

According to GMP Article 53: Dust-producing operation rooms (such as sampling, weighing, mixing, packaging, etc. of dry materials or products) should maintain a relative negative pressure or take special measures to prevent the spread of dust and avoid cross-contamination. , and easy to clean.

Generally, the measures taken for dust-generating operation rooms are as follows: First, install external dust hoods in local locations, especially for equipment that generates large amounts of dust, to achieve local dust exhaust; Second, when local dust exhaust cannot be achieved for dust sources, , the dust source equipment is isolated with enclosure facilities within a wide range, and different air purification schemes are designed according to the air cleanliness requirements of the process; third, the pressure difference between inside and outside the workshop is used to suppress the flow of airflow and prevent the spread of dust. , avoid cross-contamination and facilitate cleaning; fourth, adopt new ventilation and full exhaust measures for the production of solid preparation workshops with high drug sensitivity and drug activity.

3: Dust removal and ventilation design in operation room

After taking the above measures, the dust-laden air in the dust-producing operation room needs to be purified by dust removal equipment, and can only be discharged to the outdoors after meeting the standards. Therefore, exploring the dust removal and ventilation technology and equipment is a prerequisite for achieving dust removal and ventilation in dust-producing operation rooms to comply with relevant GMP regulations and meet environmental protection emission requirements.

3.1 Selection of dust removal equipment

When selecting dust removal equipment, in addition to considering the equipment structure and its dust removal efficiency, it should also be based on the properties of the dust (bulk density, hydrophilicity, adhesion, specific resistance and particle size) and the properties of the gas (temperature, humidity, chemical properties, etc.) and indoor and outdoor operating conditions and other comprehensive considerations.

Dust collectors can usually be divided into two types: dry dust collectors and wet dust collectors. There are two types of dry dust collectors: filter type (cartridge dust collector, bag dust collector, etc.) and mechanical type (inertial dust collector, settling chamber, cyclone dust collector, etc.).

According to practical experience, filter-type dry dust collectors are mainly used as dust collectors in solid preparation workshops of pharmaceutical factories. Commonly used ones include the following:

1) Cartridge dust collector.

Using the method of combining gravity and filter material, large particle size powder from dusty air enters the box. Under the action of its own weight, it is separated from the dusty air and settles into the dust drawer. The remaining dust particles are filtered by the filter element. Collision, hooking, static electricity and other effects are retained on the outer wall of the filter element to achieve purification purposes. At the same time, it is also equipped with an automatic pulse backflush self-cleaning device.

The cartridge dust collector has the advantages of stable technical performance, low noise, low power consumption, beautiful appearance, flexible use, small footprint, wide application range, and high dust removal efficiency (99.99%).

2) Bag dust collector.

It is a dry high-efficiency dust collector that separates and captures dust in dust-containing gas through filter materials. It is not suitable to purify dusty gas containing oil mist, condensation water and high dust cohesion, as well as smoke with explosion hazard or sparks. For example: dust removal in coating room.

3) Primary, medium and high-efficiency fan boxes.

The basic components consist of a fan, air filter, air volume regulating valve and box. Has the following characteristics:

①Capture 1~5μm particle dust and various suspended matter;

② Using hot melt process, the structure is stable and the risk of leakage is reduced;

③Large air volume;

④Small resistance;

⑤High dust holding capacity;

⑥Can be cleaned and used repeatedly;

⑦Efficiency: 60%~95%.

Disadvantages: When the amount of dust is large, the fan box needs to be cleaned manually, which greatly increases the labor of employees.

3.2 Dust collector settings

There are two basic forms of dust collector settings. One is stand-alone dust removal. That is, one piece of equipment is equipped with a dust collector, and its exhaust air can be circulated indoors, such as a separate dust collector for a tablet press.

The other is centralized dust removal. That is, multiple dust-producing equipment share one dust collector, such as the crusher and oscillating screen in the powder screen room share one dust collector. The air suction, discharge and installation in the dust-producing operation room are all in the dust removal machine room in the non-purification area. After being processed by the dust collector, it is discharged from the workshop through the exhaust port.

3.3 Selection of dust removal process system

Choosing an appropriate dust removal process system needs to be determined based on the specific production process. The general principles are: ① Set up a system when the production process is the same, the work is synchronized, the dust points are not far apart, and different dust types are allowed to be mixed and recycled or have no recycling value;

② If the dust-containing gases have different temperatures and humidity and condensation will occur in the air duct after mixing, separate systems should be installed.

3.4 Reasonable process layout

Under the condition that the workshop layout meets the relevant conditions of process production, specifications and regulations, people and logistics should be separated and not crossed as much as possible, the process route should be smooth, the logistics route should be short and quick, and there should be no backflow or detours. Reduce the flying and spreading of dust from the source and reduce mutual influence. Centrally arrange process areas with large amounts of dust and noise to facilitate dust treatment.

Project cases

Design of the solid preparation workshop of a pharmaceutical factory in Kunming.

First of all, based on the above principles and combined with the production process, we rationally layout and organize the air flow and air volume distribution. Centrally arrange the weighing and batching room, mixing room and tablet pressing room to avoid cross-contamination and facilitate cleaning; the design considers only one dust removal system and sharing a dust removal machine room; adopt local fresh air exhaust measures, and clean the air according to the process According to the requirements of the degree, the dust removal standards in other areas of the workshop are maintained by designing a purification air conditioning scheme. In accordance with the requirements of environmental management, the emission standards of the dust removal machine room meet the requirements of the unorganized emission monitoring concentration limit of "GB16297-1996 Comprehensive Air Pollution Emission Standard".

The detailed layout of the ventilation and dust removal in the solid preparation workshop of this pharmaceutical factory is shown in Figure 1.

Secondly, two different ventilation and dust removal methods were compared and selected for the dust removal process system, and finally the second method was adopted as the design solution.

Method 1: Local dust exhaust plus environmental dust removal method, see Figure 2 for details.

Figure 2 Partial dust exhaust plus environmental dust removal method

A dust collection hood is installed above the equipment in the dust production room for local dust exhaust. The suction hood and the inside of the dust hood are in a negative pressure state. The dust-containing gas is transported to the dust removal machine room through the negative pressure of the pipeline, and is dusted by the cartridge dust collector. After reaching the standard, it is directly discharged to the outdoor atmosphere through the chimney.

If some dust still exists in the dust-producing room environment after partial dust removal, air supply from above the dust-producing room and side exhaust are used to transport the dust-containing gas in the dust-producing room environment to the dust removal machine room through negative pressure pipes. After dust removal treatment in the medium-efficiency fan box, it will be directly discharged to the atmospheric environment through the chimney after reaching the standard.

Above the equipment in the dust-producing operation room, a dust collection hood is installed for local dust exhaust. The suction hood and the inside of the dust hood are in a negative pressure state, and the dust-containing gas is transported to the dust removal machine room through the negative pressure of the pipeline, and is dusted by the cartridge dust collector. After reaching the standard, it is directly discharged to the outdoor atmosphere through the chimney.

If some dust still exists in the dust-producing room environment after partial dust removal, air supply from above the dust-producing room and side exhaust are used to transport the dust-containing gas in the dust-producing room environment to the dust removal machine room through negative pressure pipes. After dust removal treatment in the medium-efficiency fan box, it will be directly discharged to the atmospheric environment through the chimney after reaching the standard.

Method 2: Only environmental dust removal method is provided, see Figure 3 for details.

Figure 3 Only environmental dust removal method

Dust removal is only carried out for the space environment in the dust-producing operation room, and no local dust exhaust is performed. That is: increase the air supply and exhaust volume, and still use air supply from above the dust-generating operation room. The side exhaust method transports the dust-laden gas in the dust-producing operation room to the dust removal machine room through negative pressure pipes, where it is removed by the cartridge dust collector and then directly discharged to the outdoor atmospheric environment through the chimney.

The choice of method two in this case is mainly determined based on the production process and the amount of dust generated by the specific process. Compared with method one, method two has the characteristics of short process, easy adjustment of air pressure and air volume in the clean area of the workshop, and simple process operation. At the same time, the cartridge dust collector is equipped with an automatic pulse backflush dust cleaning device, which has high dust removal efficiency. The equipment is also arranged to operate in a non-clean area, which can save labor costs and reduce energy consumption.

The design scheme has been proven in practice that the dust removal effect is very obvious, which not only meets the requirements of the new version of GMP, but also meets the requirements of the unorganized emission monitoring concentration limit of the comprehensive emission standard of air pollution.

Conclusion

The production dust in the dust operation room of a pharmaceutical clean factory has its own uniqueness. The two dust removal process systems in this case are often used in the design, each with its own advantages and disadvantages. The key is to fully understand the properties of dust and gas at each dust generation point and the operating conditions, flexibly choose economical and applicable dust removal measures, and design the best dust removal plan.

Question 4

How to Clean the Sinter Plate Filter? Herding Delta 2 Plastic PE+PTFE Filter Element

Accepted Answer

How to Clean the Sinter Plate Filter? -Herding Delta 2 Plastic PE+PTFE Filter Element

Sinter plate filter elements feature a PTFE-coating that is embedded into the matrix of the rigid body. This leads to a consequent surface filtration and an effective protection against damage and / or penetrations into the filter media.

That means the sinter plate filter do not need manually cleaning?

In some occasions, the sinter plate need to washing and cleaning, here we give the ways to clean the plastic porous sinter plate filter.

Structure of the Filter

How to Washing the Sinter-plate Filters

1. Take out the sintered plate in the dust collector and place it on the tray horizontally, as shown in the figure.

Lay horizontally, stacked end to end, with padding (cardboard strips) between each other.

If there is no suitable place to place it, it is recommended to take out one piece and clean one piece.

2. Take a sintered plate and place it vertically, use a soft brush to remove the dust on the surface of the sintered plate.

Rinse the filter element from top to bottom with clean water at room temperature, so that the dust on the surface of the sintered plate is washed away with the water flow.

3. Under normal circumstances, the above steps can clean the sintered plate.

4. If there is residual dust on the surface of the sintered plate, it may be caused by dust crusting. The whole sintered plate needs to be immersed in water to loosen the dust on the filter plate。

5. The soaked sintered plate needs to be washed and then rinsed twice.

6. Dry or air dry the sintered plate. The drying time is at least 8 hours, and the temperature of the drying room is about 50~60 degrees; the drying time requires at least 16 hours of sunshine time.

After the above is completed, the sintered plate can be used again

Question 5

What is Electrostatic electret air filter?

Accepted Answer

What is Electrostatic electret air filter

Electrostatic electret air filter for dust collector

Electrostatic electret air filter material, which uses the electrostatic force of electric charge to trap dust particles, and is made of small strips of polypropylene film.

Electrostatic electret air filter material: referred to as electret, refers to those dielectric materials that can store space charge and dipole charge for a long time, that is, in terms of time span, their charge decay time constant is longer than the period formed by electret. many. The electret charge can be a real charge (or space charge), a dipole charge, or both. Electret air filter material uses the electrostatic force of electric charge to capture dust particles.

Material

In recent years, the development of polymer chemical fiber production technology has enabled the production of HEPA and ULPA filters with electret fibers; materials used as electret air filters require excellent dielectric properties, such as high bulk resistance and surface resistance , high dielectric breakdown strength, low hygroscopicity and air permeability, etc. Such materials are mainly organic electret materials based on polymers, such as non-polar materials: polypropylene, PTFE, hexafluoroethylene/polytetrafluoroethylene copolymer, etc.; polar materials or weak polar materials Material: Teflon, polypropylene (blended) and polyester, etc.

Synthetic fiber filter material

Electret electrostatic synthetic fiber filter material is to electrostatically charge polypropylene fibers in the melt-blown manufacturing process to make them electrostatic electret melt-blown non-woven fabrics (filter paper), with a fiber diameter of 2-5 μm. This filter material not only utilizes the filtering mechanism of traditional air filter materials, but also utilizes the Coulomb force of charged fibers to capture particles, so the efficiency is increased and the resistance is decreased. At present, this filter material is used in the 3M surgical masks (N95, N97, N99) that have the function of preventing viruses (including SARS virus) in the world, and the anti-SARS air filter launched in the United States in April 2003 also uses this filter material Material.

Because this filter material has high efficiency, low resistance and low price, this material is used in air filters for general air conditioning and ventilation. When the wind speed on the windward side is 0.5m/s, the dust filtration efficiency of 0.5μm is obtained. It can reach more than 95%, and the air resistance is only 40Pa, which is incomparable to the traditional cabinet air conditioner unit air filter (usually nylon mesh). This air filter has been used in large shopping malls, supermarkets, and hospital air conditioning systems for nearly 10 years, and has been applied to homes, such as Fairway air purifiers, which have achieved good air purification effects.

The production process has been comprehensively improved. At present, it has been able to produce electret electrostatic filter materials with a sodium flame method efficiency of 99.9999%. At the same time, it also solves the shortcomings of poor uniformity and low strength of this filter material. Air filters provide an ideal filter material. The commercialization of electret electrostatic synthetic fiber filter material has largely solved the contradiction between air filter efficiency and resistance.

Question 6

What are the categories of air filter materials?

Accepted Answer

What are the categories of air filter materials?

1. Chemical fiber non-woven filter material: scientific name polyester fiber, commonly known as non-woven fabric, non-woven fabric has the technical characteristics of wide application, mature technology, good stability, etc. typical filter media. The production process is made of meltblown, acupuncture, spunlace, spunbond and other processes through multiple processes. Compared with other filter materials of the same level, it has stable quality, larger dust holding capacity, strong moisture resistance, long service life, economical and durable Etc.

Non-woven fabrics are the earliest filter materials with mature technology and low production costs. Although new filter materials have emerged in an endless stream in recent years, due to high production costs and high technical standards, it is difficult to popularize

2. Synthetic fiber filter material: Synthetic fiber filter material can completely replace non-woven fabrics and glass fiber covering a full range of filter products with coarse, medium and high efficiency (G3-H13) in general filtration environments. It is an emerging filter material. The main development direction of filter materials in the future. Compared with other filter materials of the same level, it has the advantages of low resistance, light weight, large capacity, environmental protection (can be incinerated), and moderate price. Due to the relatively backward domestic processing technology and technical means in the 1990s, the synthetic fiber filter materials at that time were mainly imported.

3. Glass fiber filter material: Glass fiber filter material is mainly made of glass fibers of various thicknesses and lengths through special processing technology. Because glass fiber has the characteristics of high temperature resistance, high efficiency, long service life and environmental protection. And in some special circumstances, only the wave line can be competent. Widely used in bag filters and high efficiency filters for general ventilation systems. Glass fiber filter materials and synthetic fiber filter materials are mainly imported, and although the performance is good, there is an actual situation that the price is high.

4. Imported cotton fiber: Imported cotton fiber is actually a new type of filter material that is mixed with chemical fiber and cotton fiber. It is mainly used in pre-filtration of coarse efficiency and general air-conditioning systems. Fully imported filter media. It has the characteristics of small resistance, large dust capacity, light weight, stable performance, economical and environmental protection and so on. It is an ideal product to replace non-woven fabrics in future filter equipment.

5. Activated carbon filter material: The characteristic of activated carbon is to remove peculiar smell in the air. Activated carbon filter material refers to the activated carbon used in coarse, medium and high-efficiency air filters. There are two main forms of activated carbon filter media - granular and activated carbon filter cotton. Because the function of activated carbon is to remove odors, the filtration efficiency is not emphasized. in use. Generally, it must be used with independent coarse and medium efficiency filters.

6. Long fiber series: chemical fiber, synthetic and glass fiber filter materials all have corresponding long fiber varieties, which are mainly used for filtration of 10μm large particles (such as dust) in special occasions (such as spraying workshop). Large dust holding capacity, high capture rate, can be made into filter pad or flat structure, easy to pave and replace, glass fiber and a small amount of chemical fiber varieties can withstand high temperature.

Question 7

Current Situation and Development Trend of Air Purification Technology

Accepted Answer

Current Situation and Development Trend of Air Purification Technology

In recent years, due to the development of science and technology and the progress of society, industrial emissions such as factories and automobiles have intensified the deterioration of air quality across the country, and severe weather has occurred frequently. In order to reduce energy consumption and improve the airtightness of the building, the ventilation volume in the building is reduced, and the indoor air environment is further deteriorated. Under this circumstance, people have begun to pay attention to the impact of gradually deteriorating air pollution on their own health and daily life. How to deal with and deal with this problem is a topic that must be studied and explored.

At present, the components and sources of indoor pollutants are mainly divided into three categories. The first type of pollutant is particulate matter, especially fine particulate matter led by PM2.5. Because of its extremely small diameter, it can even penetrate deep into human bronchioles and alveoli to deposit, which is extremely harmful to the human respiratory system. The main sources of particulate pollutants are exhaust emissions from automobiles and smoke from incomplete combustion of fuel, as well as kitchen fumes, cigarette smoke and pollutants released from building materials. The second type of pollutants are microorganisms, mainly including bacteria, molds and viruses that are harmful to the human body. Such air pollutants mainly come from damp and moldy walls, domestic garbage, pets, indoor flowers, carpets, and air conditioning filters in the room. Wait. The third type of pollutants are gas pollutants, which are mainly divided into organic pollutants and inorganic pollutants. Organic pollutants include various gas pollutants headed by TVOCs, including alkanes, aldehydes, esters and aromatic hydrocarbons. The main sources are building materials, cleaning agents, wax products, carpets, furniture, adhesives and paints, etc.; inorganic pollutants include carbon monoxide, nitrogen oxides, ammonia, ozone, hydrogen sulfide, radon, etc. The sources include construction, toilets, etc. Sewers, industrial and automotive exhaust, etc. Existing air purification technologies mainly deal with three types of particulate matter, microorganisms and gas pollutants.

The author introduces the single air purification technology applied in recent years and the principle of collaborative air purification technology with development potential, and summarizes the purification range, characteristics and development direction of various air purification technologies, and finally looks forward to the future air purification technology.

1 The principle of a single air purification technology

1.1 Fiber Filtration Technology

Fiber filters can be divided into coarse-efficiency filters, medium-efficiency filters, high-efficiency filters, sub-high-efficiency filters and high-efficiency filters according to filtration efficiency. The filter material of the coarse-efficiency filter is mainly wire mesh, coarse-pored cloth, foam plastic, etc. which are easy to clean and replace, and its filtration efficiency is evaluated based on particles with a particle size of 5 μm; The filter materials are mainly medium and fine-pored foam plastics, composite non-woven fabrics, glass fibers, etc., and the filtration efficiency is evaluated based on particles with a particle size of 1 μm; high-efficiency filters are similar to medium-efficiency filters; sub-high-efficiency filters are mainly Glass fiber filter paper, cotton short fiber filter paper, etc. are used, and the filtration efficiency is evaluated based on particles with a particle size of 0.5 μm; high-efficiency filter (HEPA) filter materials are mainly ultra-fine glass fiber paper, synthetic fiber paper and asbestos fiber paper. Filtration efficiency was evaluated based on particles with a particle size of 0.3 μm.

The polluted air passes through the fiber filter material, which is mainly affected by the interception effect, inertial collision, diffusion effect, gravity effect and electrostatic effect. The mechanism of action is as follows: the particles move along the streamline to the vicinity of the fiber surface, when the distance from the movement to the fiber surface is equal to or less than the particle radius, the particles will be intercepted by the fiber surface, which is the interception effect (see Figure 1); When the fiber layer passes through, during the violent turning process of the streamline, the particles break away from the streamline due to inertia and collide with the fibers and stay, that is, inertial collision (see Figure 2); for particles with smaller diameters, the Brownian motion is more intense, and this Irregular motion makes the particles have a greater chance of contacting and depositing on the surface of the fiber, that is, diffusion effect (see Figure 3); The electric charge can produce adsorption, and the particles are adsorbed to the fibers, that is, the electrostatic effect.

1.2 Activated carbon and similar materials

Adsorption is caused by the force between the adsorbent and the adsorbate molecules. This adsorption force can generally be divided into two categories: one is the interaction force between molecules caused by van der Waals force; the other is chemical bond force. , including electron transfer between solids and gases. These two forces exist at the same time, depending on which force is dominant. Physical adsorption is dominated by the van der Waals molecular interaction force, and the adsorbate is adsorbed on the surface of the adsorbent, which is a reversible process. Chemisorption relies on the chemical bond force between the solid surface and the adsorbed gas molecules, which is the result of chemical action, and its force far exceeds the van der Waals force of physical adsorption, which is often an irreversible process.

At present, the commonly used adsorption materials mainly include activated carbon, activated carbon fiber materials and related derivative materials (such as carbon nanotubes, graphene, etc.):

1) Activated carbon is one of the most common adsorption materials, and has a wide range of applications in industrial and daily fields. The raw materials for preparing activated carbon can be mainly divided into plants and minerals: plants include sawdust, coconut shell, walnut shell, etc.; minerals mainly include coal with various degrees of coalification, such as peat, lignite, bituminous coal, anthracite, etc.

2) Activated carbon fiber materials have gradually attracted attention due to their better adsorption effect and better physical properties. Different from the structure of activated carbon, activated carbon fibers contain a large number of micropores that open directly on the surface of the fibers. The diffusion path of adsorbate to the adsorption site is shorter than that of activated carbon, and it has a larger surface area (1 000~3 000 m2/g), and the adsorption and desorption is very good. The attachment rate is fast and the adsorption capacity is large. In Figure 4, the left part is the microstructure of activated carbon, and the right side is the microstructure of activated carbon fiber.

3) Materials such as carbon nanofibers, carbon nanotubes and graphene are generally not used as the main material of adsorption filter elements in air purification applications due to material costs and other reasons, but are used in some special applications, such as gas sensors, for example A PAN carbon nanofiber/ZnO2/SnO2 composite material can be used as a gas sensor for nerve-like gas DMMP; some foreign scholars have made relevant discussions on the use of carbon nanotubes to prepare gas sensors and detect trace pollution gases; domestic scholars from Tsinghua University The application of such carbonaceous materials in air purification is also described more fully.

4) Adsorbents similar to activated carbon materials (such as activated alumina, silica gel and molecular sieves, etc.) are also widely used in industry. For example, gamma alumina is generally used for adsorbents, catalysts and catalyst carriers in petrochemical industries, and macroporous silica gel is generally used for catalyst carriers, matting agents, etc., and the most commonly used adsorbent in the field of air purification is activated carbon.

1.3 Electrostatic Precipitation

The principle of electrostatic precipitator technology is to use a high-voltage electric field to form a corona, and to pass the polluted air through the corona area, so that the particles in the polluted air are charged, and then under the action of the electric field force, they are adsorbed to the collection area with opposite polarity and deposited. , so as to achieve the effect of purifying particulate matter in the air.

The working principle of the commonly used electrostatic precipitator is shown in Figure 5. Generally, the polluted air will pass through a pre-filter to remove large particle pollutants and aerosols, and then pass through the ionization section and the dust collection section to finally obtain purified air.

The function of the ionization section is to charge the particles, and the charging process is divided into two stages: corona discharge and charging according to the sequence of the process. In the corona discharge area, because the air molecules will naturally radiate electrons, the electrons are accelerated to a high speed under the action of the electric field force and hit the air molecules, thereby generating positive ions and free electrons. This process is completed instantaneously in the ionization zone, and the free electrons will continue to hit the air molecules, forming a layer of electron cloud or positive ion cloud around the ionization wire.

After corona discharge, a large number of positive ions have been generated. The particles and positive ions are mixed together. Due to the Brownian motion of the positive ions, they will hit the particles, and the particles will be positively charged, which is diffusion charging. Diffusion charging does not require an electric field and is independent of the type of particle. As the positive charge on the particle increases, the particle creates an electric field that repels other positive ions, thereby weakening subsequent impacts. When the charge on the particle increases to a certain level, no positive ions can overcome the repulsive force to hit the particle, and the charge ends.

The positively charged aerosol particles enter the dust collecting section with the air, are adsorbed by the electric field force, and are adsorbed on the dust collecting plate, thus completing the electrostatic dust removal work.

1.4 Low temperature plasma

Low-temperature plasma is a partially ionized gas that can be generated by applying a high-voltage discharge between two electrodes. It is rich in charged particles, high-energy electrons, and active particles, such as free radicals, excited atoms and molecules. Atoms or molecules in excited states generate various light radiations during electronic transitions. Plasma is generated by high-voltage discharge, and these chemical effects are accompanied by physical effects such as strong electromagnetic fields, thermal effects, and shock waves. Such physical and chemical characteristics can generate huge energy to break chemical bonds and do many complex chemical reactions. Low-temperature plasma shows that it can quickly and efficiently sterilize and deal with complex pollution.

There are many methods for generating low temperature plasma, the common ones are electron beam radiation method, low pressure glow discharge method, dielectric barrier discharge method, pulse corona discharge method, DC corona discharge method and so on. The discharge will generate a large number of high-energy electrons and ions to bombard VOCs molecules, and through a series of complex chemical reactions, the pollutant molecules will be decomposed, which can theoretically be finally degraded into harmless products such as CO2 and H2O.

1.5 Photocatalytic Technology

At present, the commonly used photocatalysts are mainly semiconductor materials represented by TiO2. Taking TiO2 as an example to introduce the principle of photocatalytic air purification technology: when light waves greater than or equal to 3.2 eV (wavelength less than 380 nm) are irradiated on the surface of TiO2, some valence band electrons absorb energy and undergo energy level transitions, and the electrons transition to the conduction band Then, a hole will be generated in the valence band accordingly, thereby forming an electron-hole pair. At this time, the electrons on the conduction band can be used as reducing agents because of their higher energy, and the holes with lower energy can be used as oxidants. When the electron-hole pair has a long enough existence time, it can undergo a redox reaction with the VOCs pollutants adsorbed on the surface of TiO2, so as to achieve the purpose of degrading the pollutants. If nano-TiO2 particles are used, due to the quantum size effect of ultra-fine particles, the photocatalytic activity of the catalyst can be improved. At the same time, the nano-sized particles are small, the surface atoms are many, and the specific surface area is large, and the ability of the photocatalyst to adsorb organic substances is enhanced. The oxidative decomposition of pollutants is more sufficient and effective.

The specific reaction of the degradation is described as follows. The holes act as a strong oxidant to oxidize the hydroxyl groups (OH-) and water (H2O) adsorbed on the surface of TiO2 to hydroxyl radicals ( OH), while the conduction band electrons act as a strong reducing agent, which will be absorbed by the TiO2 surface. The dissolved oxygen adsorbed on the surface of TiO2 is captured to form superoxide anion radicals (O-2); some superoxide anion radicals (O-2) can continue to generate hydroxyl radicals (·OH) through chain reaction. The generated superoxide anion free radicals and hydroxyl free radicals have strong oxidizing properties, which can attack the unsaturated bonds of pollutants, or extract hydrogen atoms to generate new free radicals, stimulate chain reactions, oxidize them, and finally cause pollutants. Degrades into harmless substances.

1.6 Other purification technologies

There are also some purification technologies, which have low market application rate and little research value due to large defects or narrow scope of application. For example, the principle of negative ion technology is similar to that of plasma and electrostatic precipitator, but it has the defect of high ozone generation, and it has almost no purification effect on gas pollutants; ultraviolet technology and ozone technology only have good effects on sterilization, and have good effects on particulate matter and gas pollution. Things are powerless; water washing is effective for some gas pollutants that are easily soluble in water, but there are problems such as high air humidity and few types of pollutants.

In addition, there is a special kind of purification technology - ozone purification technology. Since technologies such as electrostatic precipitator will produce ozone as a by-product, it is generally necessary to use an ozone purification module when using this type of technology, that is, to eliminate ozone through a catalyst to achieve the effect of purification.

2 Introduction of synergistic air purification technology

The synergistic technology of air purification generally refers to a type of composite technology in which two or more purification technologies combine and promote each other. Different purification technologies can play a synergistic role due to the complementarity of purification mechanisms, and generally have better purification efficiency than the original single technology, so they have strong research value. At present, the more common synergistic technologies include adsorption-photocatalysis technology and low-temperature plasma-photocatalysis technology.

2.1 Adsorption-photocatalysis technology

Adsorbent materials such as activated carbon have the advantages of strong adsorption of low-concentration pollutants, but at the same time they have the disadvantage that they can only enrich and cannot degrade pollutants and need to be replaced regularly. However, photocatalytic technology is limited by the problem of reaction contact area and cannot be used for low-concentration pollutants. Contaminants are rapidly degraded. The advantages and disadvantages of the two can be complementary. The adsorption principle is used to enrich the pollutants on the surface of the adsorption material, and then the pollutants are degraded by catalytic technology, which avoids the disadvantage that the adsorption material cannot degrade the pollutants and needs to be replaced regularly. , and avoids the problem that the electrocatalytic technology has a slow rate of treating low-concentration pollutants.

In 1997, a Japanese scholar proposed a composite material in which photocatalyst TiO2 was attached to activated carbon particles. After that, some researchers expounded the mechanism of the mutual enhancement of the purification ability of photocatalysts and activated carbon, and prepared different purification materials through different methods and raw materials. For example, a thin layer of TiO2 was formed on the activated carbon carrier by dip coating, and an activated carbon-nano-TiO2 composite photocatalytic air purification net was developed; a Fe-TiO2-zeolite composite material was prepared by a sol-gel method, which was verified by tests. It has high removal efficiency of formaldehyde under visible light; a series of TiO2-molecular sieve/corrugated ceramic fiber composite photocatalyst materials were prepared by dipping and calcination method, and the optimal molecular sieve loading was verified; electrospun nanofiber membrane was used as the Attachment, electrospray technology is used to deposit photocatalyst and activated carbon on the surface of fiber, and further composite multilayer film is obtained by electrospinning technology.

2.2 Low temperature plasma-photocatalytic technology

Both plasma technology and photocatalytic technology are mainly aimed at purifying gaseous pollutants (such as VOCs, etc.) in the air, and the combination of the two can play a role in promoting each other. Experimental studies have compared the purification effects of the two technologies synergistically, low-temperature plasma alone, and photocatalytic technology alone on pollutant formaldehyde.

There are many types of low-temperature plasma-photocatalytic coupled reactors currently used for air purification. According to the discharge form, it can be divided into dielectric barrier discharge reactor, creeping discharge reactor, pulse corona discharge reactor, etc. According to the electrode structure, it can be divided into needle plate type, wire plate type, flat plate type, bobbin type, etc. According to the different placement positions of the photocatalyst in the reactor, that is, in the discharge region (in-plasma catalysis, IPC) and the afterglow region (post plasma catalysis, PPC), the reaction system can be divided into two categories. According to this, some researchers refer to them as single-stage plasma catalysis (SPC) and two-stage plasma catalysis (TPC) or plasma-driven catalysis. catalysis, PDC) and plasma-assisted catalysis (plasma-assisted catalysis, PAC. At present, there are many researches on PPC technology. Starting from the principle of low-temperature plasma-photocatalysis technology, it is believed that the catalyst can form a more obvious synergistic effect in the discharge region. A large number of active ions, electrons, free radicals, etc. generated by the plasma generator can, on the one hand, stimulate the particles to transition downward with high energy to generate ultraviolet light, and activate the photocatalyst to produce a catalytic reaction. On the other hand, the plasma discharge has a direct activation effect on the photocatalyst, which can enhance the Its catalytic performance. In addition, the combined action of the two is conducive to the deep reaction of the by-products generated by the reaction, so that they can be completely degraded into harmless products such as H2O and CO2, which effectively improves the degradation efficiency.

3 Air purification technology purification range and advantages and disadvantages

Each air purification technology has its applicable purification range, advantages and disadvantages. When applying purification technology, it is necessary to reasonably consider the characteristics of different purification technologies, make full use of strengths and avoid weaknesses, and play its due role. The following is a brief description and summary of the purification range and characteristics of various purification technologies:

1) Fiber filtration technology has a good filtering effect on particulate matter. Since microorganisms such as bacteria and viruses are generally attached to suspended particulate matter, it also has a filtering effect on microorganisms, but it has little effect on gas pollutants. Its advantages lie in mature industrial production, safe use, convenient maintenance, and extremely high filtering effect on particulate matter. The disadvantage is that it belongs to non-renewable consumables and needs to be replaced regularly, and it is easy to cause secondary pollution of adsorbed microorganisms in an environment with high humidity. Especially when used in places with serious pollution, its service life is shorter and the maintenance cost is higher. In addition, the high-efficiency filter has a large wind resistance, which requires high static pressure and noise control of the fan.

2) Activated carbon adsorption technology has adsorption effect on pollutants, but particulate matter is easy to block the micropores of activated carbon, so that the adsorption force quickly fails, and microorganisms are easy to enrich and reproduce on the adsorption matrix, resulting in secondary pollution, so it is generally used for gas pollutants. purification. Its advantages are that it has a broad spectrum of adsorption capacity, has a certain purification efficiency for almost all gas pollutants, and is the same as the fiber filter, which is safe to use, easy to maintain, and has a large adsorption capacity. It is the most widely used purification material. The disadvantage is that there is a limitation of adsorption capacity, which needs to be replaced regularly, and due to its non-targeted adsorption, it also has adsorption effect on harmless substances in the air (such as water vapor, etc.), which will lead to a decrease in its effective adsorption capacity; no degradation of adsorbed pollutants It is easy to breed microorganisms in a wet environment, causing secondary pollution.

3) Electrostatic dust removal technology is mainly used for the purification of various particulate matter, and because the generated charged ions and ozone can effectively destroy the biological structure of bacteria and viruses, it has a good microbial purification effect, but it has almost no effect on gas pollutants. . Its advantages are that compared with high-efficiency fiber filters, the wind resistance is smaller, the filter material is not consumed, the dust collecting board is easy to clean and can be reused, and the sterilization ability is strong, which will not cause secondary pollution. The disadvantage is that the principle of the equipment is complex, there is a high-voltage area, and the maintenance is highly specialized; it is greatly affected by factors such as ambient temperature, humidity and dust specific resistance, and cannot maintain a high purification efficiency; although the generated ozone has a bactericidal effect, it is necessary to prevent In a closed environment, the increased ozone concentration is harmful to human health.

4) The application of low-temperature plasma technology in the field of air purification has its unique advantages. The use of high-voltage discharge reaction can degrade VOCs without frequent replacement and low secondary pollution. In addition, the generated high-energy particles, ozone and ultraviolet rays can all play a role in sterilization. However, in actual engineering, there are some problems if the low-temperature plasma technology is used alone. The higher the plasma power, the higher the degradation efficiency of VOCs, but the more toxic by-products. Degradation efficiency will decrease. Low-temperature plasma technology is also less effective for the degradation of inorganic pollutants such as nitrogen oxides. It is also worth mentioning that because the discharge area is filled with a large number of high-energy electrons and ions, as well as by-products such as ozone, it also has a strong killing effect on microorganisms such as bacteria and viruses in the air.

5) Photocatalytic technology has development potential in the field of air purification. It reacts at room temperature and pressure, has low energy consumption, and is more energy-saving and safe than low-temperature plasma technology; as a type of catalytic reaction, it can degrade VOCs quickly, effectively and renewable. It does not need to be replaced as frequently as activated carbon; the material has strong plasticity and is easy to use, such as all kinds of tile coatings can be applied. Relevant studies have shown that TiO2 photocatalyst can not only degrade toxic compounds produced by harmful microorganisms, but also directly act on the biological macromolecules of bacteria and viruses to promote their destruction and decomposition to achieve sterilization. However, in the process of research, it was found that the photocatalytic technology represented by TiO2 currently has defects that hinder its industrial application. TiO2 has better catalytic activity mainly at ultraviolet wavelengths and lower efficiency at visible light wavelengths, which may require additional ultraviolet lamps to promote photocatalysis in practical applications. Aromatic VOCs have a low reaction rate under the photocatalysis of TiO2 and can lead to catalyst deactivation. In practical applications, photocatalytic treatment is limited by many factors and the degradation rate is slow. In addition, the incomplete photocatalytic reaction may produce toxic intermediates such as acetaldehyde. For inorganic pollutants such as oxides with relatively stable chemical bonds and radon, the degradation effect of photocatalytic technology is very limited.

4 Development direction of air purification technology

1) The fiber filtration technology represented by HEPA is a commonly used particle purification technology, and its market application is very mature. At present, the main development directions are various, mainly reflected in the development of high-fiber nano-molecular materials represented by electrospinning, and the expansion research on this basis. For example, gradient composite filter materials with different densities and pores can filter particles of different diameters in layers to improve filtration efficiency; fuse or coat various catalytic materials, so that fibers have certain sterilization ability or gas pollutant purification function. In addition, there is another type of electret filter material worth mentioning. Electret refers to a dielectric material with a long-term charge storage function. It has the characteristics of being able to generate electrostatic force by itself in the absence of an external electric field. Directly relying on electrostatic force to directly attract charged particles in the air and capture them, or induce neutral particles in the air to generate polarity and then capture them, compared with conventional materials, it has the characteristics of high filtration efficiency and low resistance.

2) Activated carbon adsorption technology is one of the most commonly used purification technologies for gas pollutant purification. There are three main development directions: the first is to make new breakthroughs in adsorption strength and adsorption capacity by developing new adsorption materials; Targeted modification treatments such as surface impregnation or halogenation make it characterized by strong adsorption of target gas pollutants; the last one is synergistic with photocatalytic technology, using activated carbon to adsorb and enrich pollutants , to promote the photocatalytic reaction, and achieve a benign purification cycle of adsorption-degradation-adsorption.

3) Electrostatic precipitator technology is one of the commonly used particle purification technologies, which has unique advantages compared to HEPA. In practical applications, the main defect that limits its application is that it will generate ozone and cause secondary pollution. Its main development directions: First, by studying the principle of discharge, improving the discharge equipment and reducing the amount of ozone released. For example, the ozone generation rate is related to voltage and discharge structure, and is affected by temperature, and the ozone generation concentration is reduced by technologies such as corona wire heating. The second direction is to achieve the purpose of ozone purification through the coupling of ozone elimination technology and electrostatic dust removal. Some researchers have summarized and compared the methods of controlling ozone concentration. Generally, the methods of eliminating ozone include heating, adsorption, and catalytic reaction. However, both heating and adsorption have various defects, while the catalytic decomposition method has high decomposition rate and long validity period. And other advantages, there is a greater potential for development. For example, the combination of photocatalytic technology and high-voltage static electricity can not only eliminate ozone but also complete the removal of pollutants such as VOCs.

4) Plasma purification technology is another kind of potential purification technology. For some complex application environments, such as ship cabins, due to the narrow space, dense personnel and equipment, and insufficient endurance of adsorbent materials, plasma purification technology with strong degradation ability is suitable. The theoretical reaction of plasma purification technology is complex, and the influencing factors are diverse, so it has strong research value. Its development direction: one is to improve the degradation efficiency through rational design of generating equipment; the other is to couple with various catalysts, such as adsorbents, metal catalysts and photocatalysts, etc., the purpose is to improve the degradation efficiency of pollutants.

Photocatalytic technology is limited by factors such as catalyst contact area, surface wind speed and pollutant concentration, and its purification efficiency is poor when used alone. However, its material has strong plasticity and mild catalytic conditions, and is suitable for use in synergistic coupling with other gas purification technologies.

There are three main research directions in adsorption-photocatalysis technology research: First, the selection of catalyst types. At present, for indoor air purification, most of the research still uses TiO2 with broad spectrum purification ability as the test object, and a small amount of other catalyst types and purification methods are used. The second is the selection of adsorbents, which are generally still based on conventional adsorbent materials, such as activated carbon, activated carbon fibers, zeolite, molecular sieves, etc. There are some ceramic carriers and metal-organic frameworks (MOFs), etc.; the third is the way of compounding the two. Taking activated carbon and TiO2 as an example, there are mainly mechanical mixing, carbon dispersed in TiO2 bulk, carbon-coated TiO2 particles, etc., and TiO2 in TiO2. Load on activated carbon. The loading of TiO2 on activated carbon is the most common, and its preparation methods mainly include direct dip coating method, sol-gel method, sputtering method, direct hydrolysis method, solution method, chemical vapor deposition method, etc.

The research on low-temperature plasma-photocatalysis technology is still immature and still in the laboratory research stage. Most of the current research on VOCs degradation reactors only selects a specific organic waste gas, and then studies its degradation characteristics under a specific power supply and reactor. The conclusions about the discharge form and reactor structure are often only applicable to the researched exhaust gas or specific applications. Therefore, it is necessary to further optimize the structure of the discharge power source and the reactor, and explore the matching method with general guiding significance between the two. At present, there are many factors that affect the synergistic photocatalytic purification of VOCs by low-temperature plasma, including the structure and parameters of the ion reactor, and the different types of VOCs and catalysts, which all affect the purification efficiency. Therefore, it is necessary to study the purification reaction more systematically, and it is necessary to expand the technology for processing various types of VOCs so as to be closer to practical applications. It is also necessary to analyze the factors affecting purification, and to promote the research and development of reactor structural parameters and new catalysts. Further improve the purification efficiency.

Question 8

What's Filter Efficiency Filtration Class based on ASHRAE Standard 52.2-2007, EN779-2012,EN1822-2009

Accepted Answer

Filter Class ASHRAE Standard 52.2-2007, EN779-2012,EN1822-2009

Question 9

What is the ADVANTAGES of ACMAN Pulse dust collector?

Accepted Answer

What is the ADVANTAGES of ACMAN Pulse dust collector?

Advantages of ACMAN Explosion Proof

Dust Collector

1: The dust collector adopts advanced anti-static filter cartridge type, and the dust removal efficiency is as high as 99.9% (0.5um).

2:Advanced control technology realizes single-channel and multi-channel backflushing, excellent cleaning effect and beautiful appearance.

3:Professionally designed and customized high-speed and large-volume explosion-proof centrifugal fans and advanced impeller design enable each dust collection equipment to generate flow and negative pressure that meet the needs of on-site working conditions, and can meet the continuous and stable dust collection effect in industrial environments. . Low noise, standard flow and pressure, good dynamic balance, no risk of equipment jitter;

4:The electric control box adopts well-known explosion-proof electric control box and electrical components, and has the functions of phase loss, overload and overheating protection;

5:The anti-static filter element is made of polyester-coated microporous material, which has the characteristics of waterproof, oil-proof and high-temperature resistance. The cylindrical pleated design has the advantages of small volume and large filtering area.

6:The solenoid valve adopts explosion-proof solenoid valve, which realizes comprehensive explosion-proof in electrical aspect;

7:The quick-release filter element design device makes maintenance and replacement very simple and easy to use, and the selection of filter elements is very diverse, and anti-static film, nanofiber, etc. can be selected according to the requirements of use.

8:It has compact structure, beautiful appearance, convenient installation, simple maintenance and high dust collection efficiency.

9:The whole machine is equipped with an anti-static grounding device, which can conduct static electricity more effectively, avoid the generation of static sparks, and is safe and reliable.

10:There are remote model ports, which can be connected to remote control to realize linkage control with factory equipment.

Big Airflow

Comparison with other dust collector

ACMAN stainless steel dust collector

ACMAN Carbon steel dust collector

1: Production based on ISO9001 quality system standards, in line with national HJ/T328 standards;

Standard national standard cold-rolled sheet laser production, 304 stainless steel δ1.5-2mm, carbon steel δ2mm;

2: Outer surface: stainless steel brushed and polished; carbon steel sprayed with plastic, durable;

3: The door frames are designed with reinforced pressure resistance, and the 6 access doors all use automotive industry sealing strips;

4: The electrical control is carried out in accordance with the GB/T4942 standard, neat and standardized;

5: The design of the injection system is perfect, and the injection effect is good;

6: One-year warranty for the whole machine, lifetime maintenance, long-term provision of accessories

Other brands of dust collector

Other brands Dust Collector

Other brands bag dust collector

1: No production standards and specifications, plate splicing production;

2: Non-polishing plate, lower tolerance is too large, inferior 304 stainless steel; carbon steel is only artificially painted;

3: The door frame sealing strips do not meet the pressure resistance and leakage rate standards, and there is a risk of powder running;

4: The production does not meet the electrical specification standards, and there is a risk of leakage;

5: Many manufacturers do not make pulse jet systems,

6: One-time sale, no after-sale;

ACMAN Pulse Dust Collector Details

1: Multiple filter cartridges, larger filter area and higher efficiency;

2: Multiple filter cartridges are sprayed in sections, with good cleaning effect and stable resistance;

3: The fan is dynamically balanced and calibrated, with low noise, and the overall feeling of welding and polishing is delicate;

4: Laser cutting, welding, CNC bending, electrical standardized production;

5: The materials are abundant, the accessories are high-quality, the equipment is solid, and the pressure resistance is strong;

6: The injection system is professionally designed, the risk of leakage is guaranteed, and the pressure is stable;

Other Brand Dust Collector Detail

1: Single filter cartridge, small filter area and low efficiency;

2: The design of the injection system is simple, and there is a risk of air leakage and uneven injection. The injection pipe is simply made of pvc, with obvious vibration and short life;

3: The fan has no dynamic balance sign, there is a risk of jitter, and the actual air volume differs greatly from the marked air volume, poor welding, and high air leakage rate;

4: The wiring is messy, there are potential safety hazards, and the service life is short;

Question 10

How many types of FILTER ELEMENTS in Industrial dust collectors?

Accepted Answer

How many types of FILTER ELEMENTS in Industrial dust collectors?

Without Filters-Cyclone

Cyclone is the most simple dust and gas separation device without filters in dust collection methods

Advantage: 1: simple structure;

2: easy to cleaning;

3: used for powder recycling;

4: used for pre-treatment collection;

5: cheap;

Disadvantage: 1: efficiency not so high;

2: big size for big airflow;

Cartridge Filters

Advantage: 1: Big filter area;

2: PTFE filter high efficiency;

3: Low price;

4: Easy to install;

Disadvantage: 1: Not suitable for abrasive dust ;

2: Not suitable for high concentration dust ;

Filter Bags

Advantage: 1: Cheap;

2: Sustain high temperature

over 280 centigrade ;

Disadvantage: 1: Small filter area, big machine space ;

2: Not suitable for high concentration dust ;

3: Efficiency not so high;

4: hard to replace the filters;

5: short life span;

Sinter-plate Filter Elements

Advantage: 1: long life span, over 10 years;

2: Ultra-high efficiency ;

3: FDA:used for powder recycling;

4: Washable;

5: Anti-acid and alkali;

Disadvantage: 1: Can not sustain high temperature;

less than 80 centigrade.

Water-Wet Scrubber

Advantage: 1: catch sticky dust;

2: catch dust with sparks ;

3: catch explosion/flammable dust;

4: catch odor;

Disadvantage: 1: need waste water treatment;

Question 11

What is the WORKING PRINCIPLE of ACMAN Dust Collector?

Accepted Answer

What is the WORKING PRINCIPLE of ACMAN Dust Collector?

ACMAN Industrial Dust Collectors has a compact design which make the blower, pulse-jet reverse cleaning system, filter elements and dust drawer/dust bin together.

When the raw gas come into the air inlet of dust collector, the gas is expanding in the filtration room, and the dust velocity became slow. Because of the gravity, some heavy dust fall into the dust bin; Thanks to the high efficiency filter elements（sinter-plated filters, cartridge PTFE filters, filter bags), the dust is crashed on the filters' surface, and blocked by the filter elements, 0.3-1um dust could be catched by the filters. then the clean air come out of the filters, and then extracted by the centrifugal fan which provide high air flow and high pressure.

when the differential pressure between filter surface and atmosthere became high, the filter ventilation quantity became small, the pulse-jet reverse cleaning system start to work, the compressed air backflow sharply in the inner filters, and the dust on the surface of filters is falling down to the dust bin.

This is the one working circle of the dust collector machine.

Filtration steps

Online reverse pulse steps