With the development of the benefits of production and the continuous improvement of the technical level, the clean technology of compressed air has become more and more important. Especially in recent years, various famous brands of compressors, compressed air dryers and filters in the international market have poured in. To a certain extent, the country has promoted or promoted the development and improvement of the application level of compressed air clean technology in China. For the advanced technology in the world, it not only absorbs but also transforms into our own things, and at the same time, develops our own brand products.

1Compressed air pollution and its hazards 1.1 Contaminants in compressed air systems It is well known that air can be compressed, so no matter what kind of compressor we use, in the process of air compression, atmospheric pollutants, oil (coal Pollutants of smoke, sulfur dioxide, carbon monoxide, nitrogen oxides and carbonammonium, as well as microorganisms such as bacteriophage; at the same time, the air also contains a certain amount of water vapor, so the air inhaled by the compressor already contains a certain amount. Solid, liquid, or even solid-liquid mixed contaminants. Take a compressed air system with a pressure of 0.8Mpa as an example. The amount of pollutants and atmospheric (free air) is simultaneously enhanced by 8 times. The water will be condensed after the water vapor is compressed; there are also a large number of oil-lubricated compressors, which also produce waste pollution to the compressed gas. These pollutants are mainly carbonized after the compression of high temperature. Particles and lubricant particles, etc.; for non-lubricated compressors, metal piston rings or plastic piston rings and cylinder walls

1.2 The hazards of pollutants in compressed air systems are summarized. There are two main types of pollutants in compressed air. One is the atmospheric pollutants that are sucked into the air compressor, and the 80G diameter is 2! The following is the m; the other is that the oil from the compressor is in a smoke state, and it spreads to become 0.01-0.8! An aerosol of m. In this way, all contaminants mix with the dirt in the pipe to form rust, solid particles, and latex-like emulsifiable concentrate.

If the unclean compressed air is not used in any effective removal method, it can be directly applied to occasions or places where the temperament is high, which will pollute the clean production environment and even contaminate the product and cause unqualified. Therefore, in some gas departments, such as large-scale, ultra-large-scale integrated circuit production process gas, air-floating gyro, air-floating bearing inflation, rocket and spacecraft production, processing control, inspection, test gas, etc. The quality of compressed air is very high. In addition, various kinds of gas, such as various jet technology, pneumatic devices, precision instruments, etc., also put forward corresponding cleaning requirements.

☆ Zhang Hongyan male, born in February 1940, a university researcher.

100071 Beijing West Fourth Ring Road, No. 83 (010) 58749507 received the deadline for March 3, 2003. Therefore, in order to avoid waste of manpower, financial resources and time, it is necessary to fully understand the system pollution situation and make reasonable use of the compressed air system. The decontamination, degreasing, drying and other purification facilities are configured to optimize the clean compressed air supply system, so as to provide users with reliable technical support conditions.

2 Filtering mechanism of compressed air and its performance and classification In the revised design code of compressed air station-2002, the filter is clearly defined: "When users have requirements for compressed air quality, they should be in front of the air drying device. After that, use a gas to set the sound, etc., and set the filter with the corresponding precision. "When the compressed air needs to be dried, the compressed air should be effectively degreased before entering the drying device".

It is relatively easy to remove larger contaminant particles, and to remove those that are invisible to the naked eye, generally 0.3-5! The dust particles of m have certain difficulty. The filter is used to remove pollutant particles, but if it is used or improperly set, it can not only remove the pollution. On the contrary, the filter itself becomes a typical source of particle pollution. Therefore, we should understand and be familiar with the distribution of particles and their filtration mechanism. A clean piping system can be properly designed, installed and used.

General-purpose filtration can remove most of the liquid and solid particles, and its particle size is generally greater than 1! m, and to remove very small solid particles and oil-water aerosols, high-efficiency filters must be used. However, with its method and mechanism, it is impossible to make very strict physical classification, such as gravity separation, centrifugal separation, inertia. Impact, direct interception, Brownian diffusion, eddy current diffusion, thermal condensation, electrostatic deposition, magnetic deposition, Brown condensation, acoustic condensation, turbulent deposition, etc.

In some cases, only one mechanism plays a dominant role for a particular particle, but in most cases it is a combination of multiple mechanisms. Generally speaking, it mainly relies on direct interception, inertial impact, diffusion or Brownian motion, thermal condensation and the like.

Direct interception, that is, to create a solid, liquid contaminant particles subject to the physical barrier of the filter material, mainly for the particle size in the airflow! Larger particles above m, during the interception process, inertial impact also occurs simultaneously, because the airflow entraining solid and liquid particles, when flowing through the filter material, due to the weight and speed, the particles cannot change direction rapidly in synchronization with the airflow. Therefore, it is impossible to pass the passage of the filter material to the filter material, so that the filter material captures the particles, and therefore, the larger solid particles in the air flow end up. Diffusion and Brownian motion dominate the extremely small particles that act on the intermolecular gravitational and electrostatic forces, causing the particles to circulate in the airflow while simultaneously squeezing and pasting each other, increasing the effective diameter of the particles. Larger particles make it easier to remove. The liquid particles are not all the same. When flowing through the filter material, the tiny particles tend to gather, and finally gather at one place to form a larger droplet and push it toward the outside of the filter to form a larger liquid saturation region. And then outside the ejector, this is condensed filtration. This way you can clear more than 0.01! The solid particles of m, if the pollutants are less than 0.Olppm, then the solid and liquid contaminant particles in the gas stream can be completely removed.

2 Performance of compressed air filter For a group of filters with good performance, the filtration efficiency should be high, generally should reach 99.99% or more; the resistance is small, and the pressure and flow rate of the filtered gas are not changed much; the filter material itself must have a certain sound. Mechanical strength, not only can withstand a certain pressure, but also can withstand the impact of airflow, no rupture, no lint, no slag in dynamic airflow; no oxidation or surface peeling, long life of filter media, cleaning, replacement Convenience.

Withstand pressure, and the rigor is good, the inner wall is smooth, so that the droplets and solid particles are not easy to stay and adhere on the surface, and the wear resistance is extremely low, and metal particles are not generated under the airflow.

According to the structure of the filter material, it can be divided into a 'deep layer' filter, a mesh "filter" or a deep "mesh" combined filter.

2.31 "Deep" filter filter material is chaotic fiber, sintered powder metallurgy and porous ceramics, etc. Its function is to set up a tortuous curved airflow path, so that the filter material can capture the dust when the airflow passes. Particles such as: This kind of filter element is used more and is widely used. Generally, it does not consider reverse purging or repeated use, and is basically a disposable filter element.

The main materials are rayon, nylon yarn, polypropylene fiber, glass fiber and so on. Since the mechanical winding is not used, the adhesive is more adaptable to the medium and is inexpensive. Because it belongs to deep filtration, the dust content is generally large, but the filtration precision is not high. Due to the quality of the winding, when the initial operation is started, there is a possibility that the fiber is taken out under the flushing of the airflow.

Powder metallurgy porous filter material is a porous metal or porous alloy prepared by metallurgical sintering process with metal powder. Therefore, it has the filtering property of ordinary porous material due to porosity and sound, and has the complete processing property of metal. A large class of materials.

Powder metallurgy porous materials of bronze, low carbon steel, stainless steel, titanium, nickel, and alloys thereof are currently used. They have excellent gas permeability and high filtration rate. For example, the filter material made by sintering bronze powder can be 4 times of the flow of the folded paper filter and 6 times of the cotton filter. However, the area of ​​the origami and cotton yarn is smaller than that of the powder metallurgy. Bigger. In special filtration applications, such as aircraft, tanks, warships and other liquid fuels, oils and lubricants, 5 -10 is not required! m solid residue; liquid metal nano, lithium filtration, neutron emission device in nuclear technology; used in the medical and health industry to filter viruses, bacteria, produce sterile air and isolate penicillin, streptomycin and other antibacterial crystals from mother liquor Environmentally friendly recycling of radioactive dust, blast furnace exhaust gas collection; as a flame retardant for ammonia, acetylene and other flammable and explosive gases; as a compressed gas for gas-water separation and gas emission silencer, etc., the application range is extremely wide.

However, due to the sintering technology, individual devices have their own powder peeling and loss under the scouring of the airflow during use.

This kind of filter appeared earlier. Porous ceramics is a kind of filter material with high pressure resistance. In recent years, it has been in a rising state in use. To ensure the reliability of use, two stages are generally used, such as the American PARKER porous ceramics. Filter, the housing is 316L stainless steel, the inner surface roughness of the housing is less than 0.8! m, under pressure 22MPa, is the ultra-clean series used for terminal gas points.

Due to materials such as porous ceramics and glass, the use of materials such as porous ceramics and thermal shock resistance is poor, and welding is not possible, and a large amount of use is limited to some extent.

3.2 "Mesh" filter, generally consists of porous metal, plastic, various fiber fabrics and microporous membranes as the main filter material. The filter material has a relatively uniform porosity and a high porosity, and any fine dust particles larger than a certain pore can be removed. For example, the filter element is mainly processed into a cylindrical filter element using a porous film of vinyl cellulose, polypropylene, polytetrafluoroethylene and a reinforcing material. Most of the filters currently on the market are combinations of such filter elements. The biggest advantage of this kind of filter element is that when the airflow passes, the filter element will often have an electrostatic charge. This static charge can prevent the suspended particles from entering the depth of the filter element and blocking the filter element, and can make the dust appear soft and deposited in the filter. The surface of the component is easily removed or easy to clean. For example: cellulose acetate and nitrocellulose and two kinds of mixed materials of folded filter paper microporous filter, not susceptible to corrosion by dilute acid, dilute alkali and non-polar liquid, but the use temperature can not be higher than 755. PTFE filter It is made of pure Teflon. It is suitable for organic solvents, strong acids and strong alkalis. It is chemically erotic and its temperature is stable from -100 to 2005.

PVC filter has high strength, toughness and medium strength acid and alkali. The use temperature should not be higher than 655, otherwise it will soften and be toxic. Therefore, it should be applied in food processing, pharmaceutical, beverage industry, and even domestic water. Be cautious. 5! The filter, the liquid, the gas can be removed more than 0. 5! The working pressure of m dust particles is generally 0.8-1.0 MPa. Since the micropore distribution is much denser than that of ordinary filters, the number of micropores in the unit filtration area is considerable, which means that the maximum number of micropores is reduced. Ordinary membrane filters have a maximum pore size of 0.3! m, while the hollow fiber is only 0.1! m, which also means that the hollow fiber has a long service life and safety and reliability of gas filtration. Woven metal mesh, etched metal mesh: various woven metal mesh, metal etched mesh, although strong in strength and good in air permeability, the mesh is easily deformed at high temperature and seriously affects the filtering precision, especially the processing technology is complicated, and the price is relatively high. High, so it can only be used in a few special departments and special processes.

2.4 Evaluation of various compressed air filters It is not easy to fully evaluate various filters, because it is sometimes impossible to separate them in a series of complicated and interrelated situations for research and discussion. In some cases, direct Judgment is also difficult, so you can only make a corresponding comment on some specific examples of sounding. It is a combined filter produced by MASTERPNEUMATIC-DETROITINC in the United States. It can remove liquid pollutants such as liquid and smoke in compressed air. At the same time, it can completely clean the gas filter and remove the particle size in the airflow! The filtration efficiency of particle contaminants above m is above 99.57.

This kind of filter, because the gas inlet and outlet are located on the same axis, is easy to install in the pipeline system, and the filter element is replaced at the top of the filter, which is convenient and simple. However, since the solid-liquid residue stopped at the discharge port is always in the disturbance of the air flow of the air inlet, the liquid impurities are not easily aggregated, and the pollutants easily block the filter element, resulting in a decrease in the life of the filter element.

Eliminate more than 0.3! The solid pollution particles of m, the life of the filter element can be more than 6 months, which is a typical oil mist filter in the instrument gas. It is characterized by small size, threaded connection, easy to use and reasonable price. However, due to the small size, the effective flow area at the gas inlet and outlet cannot be ensured, and the resistance increases rapidly after a short period of use.

The company also produces a horizontal filter that removes solid-liquid residues from the gas stream and has a particle size greater than 3! m!, the removal efficiency can reach 1007 particle size greater than 0. 5! When m is used, the removal efficiency is over 997. This is a typical horizontal filter. Obviously, the sound height is lower than that of the vertical type. Therefore, it is very convenient to replace the filter on the side in places or places where there is a high demand. However, the floor space is large. Due to the influence of the gravity of the filter element, the fixing and sealing of the filter element and the flower plate are difficult and difficult to be reliable, and the accuracy of the filtration is affected to some extent.

5! A high-efficiency filter produced by Domnnik Filter Ltd, can be removed more than 0. l! m solid contaminant particles, if the pollutants are less than 0.01ppm (m / m), can remove all liquid water and oil. It is suitable for gas that generates a large amount of condensate and solid particles when compressed. Moreover, as long as the filter element is pre-aligned and the filter element can be replaced in a short time, the length and the number of the filter element can be combined according to the amount of gas, so the diameter of the casing of the filter is usually large.

The setting of the compressed air drying device 5 prevents the pollution of the system from increasing during drying. The air removal measures should be taken. "When oil-lubricated compressors are used, the content of pollutants in the compressed air after the compressor is higher than that of the compressor. The gas port will increase by 50ppm (m/m), which is caused by the pollution of the compressor and oil. After the drying device is added, the significance of the system purification is more prominent, because the control unit is equipped with a reasonable drying device. The content of the impurity atmosphere and the high dryness can achieve the desired effect, but it also brings some undesired negative effects. For example, in terms of use, due to malfunction of the adsorption drying device switching procedure, untimely action Leakage caused by electric valves, pipes, and even cross-diffusion caused by de-diffusion of desiccant powder will cause clean gas to be contaminated again. Of course, such situations are mostly caused by improper installation and use.

Seriously, the drying device itself, especially the adsorbent used, has low mechanical strength, unstable performance, poor thermal stability, easy pulverization under pressure shock, and generation of fine dust, which often causes secondary pollution of dry gas.

The results of the gas measurement before and after the dryer are used to illustrate: Table 1: Before and after the clean compressed air passes through the dryer, the gas dust content is compared with the gas before entering the molecular sieve dryer, and the gas passes through the molecular sieve dryer 0.3! The number of particles of dust particles per liter is visible, and the number of particles after passing through the dryer is 0.5-4 times that before entering the dryer. Practice has shown that this phenomenon is more obvious in the case of high flow rate and high pressure. This is not ruled out for aluminum gel and silica gel desiccant. Therefore, before and after the dryer, effective pre-filtering is generally configured. And the post-filter, which prevents the poisoning of the adsorbent, while preventing the desiccant from causing secondary pollution to the clean gas.

Adsorption is an exothermic process and therefore low temperature is advantageous for adsorption. Table 2 clearly reflects this characteristic. Therefore, the sound setting sequence in the station room should be the compressor, the gas storage tank, the freeze dryer, the adsorption dryer, and the station outlet filter, so as to form a good job for the dryer and the station outlet filter. condition.

Table 2 The effect of temperature on the adsorption amount of various desiccants. Temperature molecular sieve alumina silica gel For the compressed air with low dryness requirement, as the pre-process of the adsorption dryer, it is appropriate to use the freeze dryer, and it is set in the gas storage. Behind the tank, adsorb the position in front of the dryer. In this way, the airflow from the compressor aftercooler can be raked in the tank, allowing the condensate to be analyzed and discharged out of the tank. At the same time, low temperature is advantageous for adsorption, so that the temperature of the compressed air at the inlet of the dryer is lower, thereby reducing the power consumption of the freeze dryer, so the capacity of the dryer does not have to be too large. The buffer of the large volume of the gas tank is buffered and stabilized to make the load of the dryer uniform, so that a relatively stable pressure dew point is obtained at the outlet of the dryer. At this moment, the adsorption drying device can obtain a better drying effect. The compressed air after drying, in fact, contains very little oil mist and fine dust particles, and will not cause the burden of the system high-precision filter 1994 "ChinaAcademicournalElectronicPubli overweight, so that the end filter filter material life increases, while filtering It will also be more effective and reliable.

4 The reasonable setting of the compressed air station system is to make the compressed air station reach a higher standard, the system should be free of leakage, install competent compressors, dryers, high-efficiency filters, and make the gas reasonable in production. Process flow characteristics, accompanied by an online dew point meter, particle counter, etc., to monitor the dynamic gas operation at any time, then it will be able to meet the needs of any 'high, fine, sharp' production technology. High cleanliness, high dryness (Double high) compressed air system, it is extremely important to configure the sound according to a reasonable process program. Generally it should be a compression grip 1I cooler (2I degreaser (3) - gas tank U) - freeze dryer (5) - Pre-degreasing filter (6)-Adsorption dryer (7)-Post filter (8)-High-precision filter for station exit (9 at the end of the compressed air system at the air compressor station (at the exit of the station), configuration An effective compressed air filter is effective for ensuring the quality of compressed air, and has a greater significance for preventing pollution, with air compressors, dryers, and process systems that constitute air compressor stations.

Because the temperature of the oil contained in the compressed air determines the efficiency of the high-precision filter. When the temperature is 302, the oil flowing through the filter is 5 times that of the temperature 202. When the temperature rises to 402, the oil flowing through the filter is 10 times when the temperature is 202. Therefore, for high-precision filtration, it needs to be installed at the lowest temperature of the compressed air system, that is, the outlet of the compressed air system of the station, and the high-precision filtering device used in combination with the degreasing filter can ensure Filtration accuracy extends the life of the filter.

2 High-performance degreaser setting Although the compressor is not more likely to ignite than other machines, the oil is often running under pressure. If the maintenance, operation measures are improper, or the oil that does not meet the requirements is used, it will increase. The deposition of aging materials of large oil formation increases the probability of carbon deposition, which may lead to fire and even bursting of weak links such as pipelines or gas storage tanks. This is the specification of the storage drying of oil-lubricated air compressors. The sorbent of the unit is “poisoned” and we have to set up a high-performance degreaser at the compressor outlet (the piston cooler outlet).

3 Reasonable setting of clean compressed air system gas storage tank For the smooth and normal operation of pneumatic tools, pulseless and non-fluctuating pressure gas should be used as the power source. The function of the compressed air storage tank is to overcome the gas pulse and pressure fluctuation caused by the operation of the piston compressor, as well as to separate the condensed water and store the compressed air. For the screw compressor and the centrifugal compressor, the gas storage tank is first stored in the air, followed by the separation of the condensed water. When there is a large gas load in a short time, the auxiliary gas supply can be supplemented by the gas storage tank, so that the pressure drop in the pipe network does not fluctuate greatly, so that the compressor starting frequency or the load regulating frequency is always allowed and reasonable. Within the scope, the gas tank is an important part of the station process system.

For the gas storage tank of the clean compressed air system, it should be placed at the position of the compressor (the cooler X is de-oiled before the freeze-drying, and should not be placed at the very end of the station piping system like the ordinary compressed air system). .

5 The effect of vibration on the quality of a clean compressed air system The shutdown or start-up during dynamic gas motion results in a sudden increase in the number of particles in a clean compressed air system. This is because the impact and disturbance of the airflow are equivalent to the tapping and vibration of the pipeline system itself. The particles are released from the detention wall of the pipe wall, valves, flanges, filters, dryers, gas storage tanks, etc., and are entrained by the moving airflow. At this moment, the pipeline system may be several times or even several times larger than the filter precision. Particles appear. Moreover, through diffusion, gravity sedimentation and contact adhesion between particles, after a long time, the suspended particles are retained by the pipe wall, the gas tank wall, the dead angle of the valve, etc., and the suspended particle concentration decreases and the system returns to the normal state.

1 The influence of vibration and other factors on the filter can be clearly understood through the test of the three sets of filters. See Table 3. Table 3 Changes in the number of particles after the filter Filter filter element structure Increase the flow rate of the pressure air flow without the bandage The increase in the number of glass particles is not significantly increased by a tens of times. The increase in external use is reduced by several tens of times. The increase in the standard membrane over/h filter is slightly increased.

Reducing the impact of 2 vibrations on the gas storage tanks. Because of the disturbance of the airflow, the adhesion, release, sedimentation, impact, etc. of the inner wall of the ordinary gas storage tank frequently occur, and this situation depends on the gas pressure and the inherent nature of the particles. The density, the shape of the particles, and the operating state of the compressor, etc., are greater than 1 in the static state where the gas tank is neither air-in nor out! In less than 16 hours, the particles settled to the bottom of the tank, and 0.1! The particles can only be fully settled within two weeks. In the dynamic gas condition during operation, the particles in the tank are always suspended, and the particle concentration distribution is uneven. Gravity sedimentation makes the particle concentration at the top of the tank far lower than the particle concentration at the bottom of the tank, and the diffusion causes There is a low particle concentration near the gas tank wall. The impact process mainly occurs in the gas tank inlet and outlet. At this moment, the particles released in the tank are concentrated near the impact point, especially the relatively heavy particle liquid in the suspended particles cannot move to the gas. The top of the can. The gas tank itself is the distribution center of the particles, which can also be said to be the source of the particles. Such a sound setting at the end of the station system will cause the various purification means in the station to lose meaning. When the gas storage tank is set in the compressor cooling After the device, before drying and purifying the sound, the particles in the can, which are generated for whatever reason, can be removed by the subsequent clean sound.

Sounds such as compressors, dryers, and high-precision filters maintain an important production relationship in the production of compressed air stations. On the macro level, the drying and purification of compressed air must be improved by the improvement of each set of sounds and every drop of the system, which is very difficult. Practice has shown that large-capacity tanks and system pipelines have regulators and valves, which are more polluting than gas itself. Nearly 95% of all pollution is directly related to system assembly and operation, including gas itself. The most influential factors are corrosion of gas tanks, valves, flanges, etc., combined with inconsistent assembly, resulting in the penetration of gas inside and outside. Gas moisture is a key factor in the pollution of the whole system. Flanges, gaps in valves, even pipes and inner surfaces and gas tanks without any treatment. Potential metal corrosion caused by gas moisture and oxygen. Therefore, when the airflow passes, all of these pollutions can be released, and the quality of the gas is destroyed.

In view of this situation, for a clean compressed air system, if a tank is provided at the end of the station system, the inner surface of the pipe should be smooth and clean. Of course, the pipe is at least stainless steel, and the inner surface of the tank should be polished. Roughness is 1! ) Below, this is very difficult to implement. Therefore, for the compression of the space (down to page 59) but its imaginary share of the full day of 15%%20, NO and RSP not only generally exceed the standard and the higher share of the market is said to be harsh. If it can improve the environment of the hall, it is of great significance to reduce the amount of exposure of the main pollutants that are gambling.

Although Chinese-style restaurants in Hong Kong are equipped with sound-proof air-conditioning air supply and exhaust systems, they are often subject to conditions and airflow organization is not ideal. The air-conditioning air outlets in the restaurant are basically uniform, and the air outlets are not only small, but some are not even set. In most restaurants, in order to prevent the smell of kitchen overflow and improve the utilization of cold source, most of the exhaust in the restaurant flows to the kitchen as a supplement to the kitchen, and is exhausted from the exhaust hood of the cooktop. Therefore, the pollutants generated by the smoking and fire in the restaurant are not discharged outside the room, but the room is swept to the kitchen. Therefore, the air quality in the whole room is poor and the air quality in the kitchen is worse.

In order to improve the indoor air quality, in addition to increasing the amount of fresh air at the peak of the flow of people, it is advisable to distribute the direct exhaust vents at the top of the restaurant to remove pollutants on the spot. If used as a kitchen air supply, pipes and fans should also be used to change the existing unorganized ventilation. Kitchens with common exhaust hoods should be replaced with direct air vents. The opening of the restaurant to the kitchen (doors, transfer windows, hoist openings, etc.) should be provided with an air curtain to reduce and block air circulation.

Adding better performance filters to air conditioning units to reduce indoor RSP concentration is also an important aspect of improving indoor air quality.

4.3 Minimize the pollution of the restaurant. The source restaurant clearly divides the smoking and non-smoking areas, and sets a special smoking place in the indoor downwind. At the top of the area, there are more exhaust vents to discharge the flue gas on site; reduce or cancel the furnace in the restaurant. fire. The fixed part fire can be replaced by electric stove, and the mobile food car replaces the fire insulation with hot water cover heat preservation; strengthen the publicity to protect indoor air quality, gradually reduce the number of people smoking in the restaurant, or open a smoking place outside the restaurant to avoid pollution. restaurant.

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