Development and design of coalescing filters

Abstract: This paper focuses on the development and design of the coalescing filter and its performance in comparison with the original products of the air compressor plant. The new coalescing filter enables tangential air intake of compressed air, replacing the original ceramic tube packing filter and felt winding filtration method with a wire mesh demister and a fine filter element. It has certain advantages in performance such as filtration accuracy, airflow uniformity resistance characteristics, and low cost, long life, and economical and practical.
Key words: compressed air; coalescing filter; tangential air intake; centrifugal separation 1 Introduction Compressed air is widely used in petrochemical, textile, biochemical, national defense and other fields. However, compressed air contains impurities. These impurities are derived from the atmosphere, the compressor itself, and the piping. According to scientific statistics, there are about 140 million particles per cubic meter in the atmosphere, and 80% of the particles are less than 2 mm in size, and the suction filtration of such small particle compressors cannot be eliminated; working with oil-lubricated compressors The waste generated by the process itself also contaminates the finished gas. Depending on the operating conditions and model of the compressor, the pollutants usually vary between 5 and 50 mg/m3. At present, most of the oil-free lubricating compressors commonly used in China are only semi-oil-free. Due to the large amount of splash lubrication at the connection between the crankshaft and the piston rod, the working part of the oil vapor will still be carried into the cylinder along the piston rod, resulting in the presence of trace oil in the gas. In addition, the gas coming out of the compressor will precipitate with the temperature and will accumulate with the long-term deposits in the pipeline to form impurities such as rust and solid particles. Therefore, it is necessary to purify the compressed air.
2 Gas compressor original air filter structure, principle Air compressor GYF-3/8, GYF-6/8 oil-water separator used in air compressor factory to purify the air, its structure diagram As shown in Figure 1, its working principle is: the compressed air coming out through the compressor and the cooler enters from the intake pipe of the device. After the spiral separation, the larger particles and droplets are thrown to the wall of the cylinder, and are discharged through the drain valve. After the gas travels to the conical cover on the upper part of the head, the gas flows in a collision to deflect into the chaotic ceramic ring (Rasi ring). The gas continuously breaks between the ceramic rings, so that the oil and water continue to separate. The gas continues to pass upward through the coarse filter element, the fine filter element, and the exhaust pipe through the exhaust pipe. The function of the oil drain pipe is to discharge the oil, water, dust, etc. from the coarse and fine filtration. Air treated by the device, oil content (5mg/m3, dust-containing particle diameter (5um, such dust-containing indicators can only meet the general requirements, for biochemical, pharmaceutical, scientific research and other industries that have high requirements for compressed air) Not satisfied.

3 Design of the coalescing filter This paper attempts to develop a new schematic diagram of the structure of the coalescing filter as shown in Figure 2. Its working principle is: after the gas discharged from the oil-lubricated compressor is cooled by the rear cooler, it is tangentially entered into the cylinder of the device, and a high-speed rotating airflow is forced in the annular chamber of the cylinder and the inner cylinder to be suspended in the air. The medium coarse particles and the coarse oil and water droplets are separated by centrifugation and thrown to the wall of the cylinder. Under the action of self-weight, they sink along the inner wall of the cylinder through the gap between the cone cover and the cylinder, and are deposited on the bottom of the vessel and discharged through the automatic drain valve. . The airflow is swirled to the lower part of the cylinder and meets the conical cover, changing the flow direction and blunging into the stainless steel flat screen. The wire mesh is a mesh belt structure woven from a very thin flat stainless steel wire like a sock tube. The mesh is connected in a ring shape, which can be separated by gas and liquid, gas and solid, and can be partially particulate. As the generation of these particles and droplets grows, they are discharged on the smooth surface of the screen and discharged. After the gas passes through the fine filter core, the aerosol condensation growth and gravity drop are continued, and the oil water in the concave portion of the deposition filter element is discharged through the oil discharge pipe.
4 Performance analysis of coalescing filter The oil-water separator of this structure integrates three processes of centrifugal separation, coarse filtration and fine filtration, which can effectively remove impurities such as dust, moisture and oil mist of compressed air. The quantity is ≤1mg/m (the dust-containing particle size is ≤1μm. It can provide pureness for the industry with oil and dust index greater than or equal to the performance index of JB/T5967-97 "Pneumatic components and air medium quality grading" Air source.
The development of this new type of filter eliminates the original old product and has the following advantages:
First, in the centrifugal separation method, it changed the former spiral welded structure and adopted the current tangential intake. The surface of the spiral sheet which is caused by the limited processing method is not uneven, and the deformation amount after welding is large, and it is difficult to process and weld. The new structure simplifies the process, reduces costs, and significantly improves separation.
Secondly, the ceramic tube stacking filtration method was replaced by the domestically successful mesh demister element. The short-section ceramic tubes are piled up in a disorderly manner. When the airflow passes through, many times of baffles and collisions can separate a part of oil, water and dust. However, due to the flow of high-pressure gas, the ceramic tubes collide with each other, and broken particles appear. And easy secondary pollution of air. The stainless steel flat screen has no pollution problem, and it is easy to clean, and the separation effect is excellent, which reduces the load of the rear fine filter element and prolongs the life of the fine filter.
Third, the original felt-wound filtration method of the old product was replaced by an approved fine filter. Felt filtration will be saturated by impurities when it is extended over time, which will easily block the felt hole, greatly reduce the filtration area and increase the pressure loss. More seriously, if the impurities of the felt hole are not removed in time, the impurities are mixed with the product gas after passing through the hole, so that the original design index cannot be realized. The precision filter used in the new product is a high-tech product, which can be compared with the precision filter elements of western industrial developed countries. The filter mechanism of the filter element is a combination of direct, inertial collision, diffusion (Brown) motion, and agglomeration. The filter material adopts a regular distribution arrangement of non-woven fabric woven with microfibers and reinforced filter paper. Because the surface of the filter material is smooth, impurities are easily collected on the surface and then discharged outside the ejector to make the product gas The quality is guaranteed.
Fourth, the original manual sewage is changed to have both manual and automatic sewage. Under normal circumstances, the manual drain valve is closed and the automatic drain valve works. If the automatic drain valve fails or repairs it can be turned off and manual draining is used. The reason for this design is that although there are many automatic sewage disposal valves produced in China, the quality is not satisfactory. Although the quality of foreign automatic sewage traps is reliable, its cost is high. From the economic point of view, imported valves are not used. Therefore, the use of manual and automatic sewage discharge is both reliable and economical.
5 Conclusion In summary, the design of the new coalescing filter is successful, in line with the filter design specifications and principles. The utility model has the advantages of high filtering precision, accurate and reliable, uniform gas flow, no retention, small volume, large dust holding capacity, easy replacement of the filter element, small resistance, long service life, low cost and high work automation degree. However, with the higher requirements of compressed air in various industries, the design of air filters with higher precision will be a new topic and new challenge.

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