Development and design of coalescing filters

**Abstract:** This paper presents the development and design of an advanced coalescing filter, comparing its performance with that of the original air compressor plant filters. The new coalescing filter introduces a tangential air intake system, replacing the traditional ceramic tube packing and felt winding filtration methods with a wire mesh demister and a fine filter element. It offers improved performance in terms of filtration accuracy, airflow uniformity, and resistance characteristics, along with advantages such as low cost, long service life, and practicality. **Keywords:** compressed air; coalescing filter; tangential air intake; centrifugal separation **1. Introduction** Compressed air is widely used across various industries, including petrochemical, textile, biochemical, and defense sectors. However, it often contains impurities that originate from the atmosphere, the compressor itself, and the piping system. Scientific data indicates that there are approximately 140 million particles per cubic meter in the atmosphere, with 80% being smaller than 2 micrometers. These tiny particles cannot be fully removed by standard suction filtration. Additionally, oil-lubricated compressors generate waste that contaminates the final gas. Depending on the compressor type and operating conditions, contamination levels typically range between 5 and 50 mg/m³. Most oil-free compressors in China are only partially oil-free, as lubrication at the crankshaft-piston rod interface can still introduce trace amounts of oil into the compressed air. Moreover, temperature fluctuations cause condensation, and over time, deposits in the pipeline can lead to rust and solid particles. Therefore, effective purification of compressed air is essential. **2. Original Air Filter Structure and Working Principle** The GYF-3/8 and GYF-6/8 oil-water separators used in the air compressor factory have been designed to purify compressed air. As shown in Figure 1, their working principle involves the intake of compressed air through an inlet pipe, followed by spiral separation to remove larger particles and droplets, which are then discharged via a drain valve. The gas then flows upward through a conical cover, colliding with ceramic rings (Rasi rings) to further separate oil and water. After passing through coarse and fine filter elements, the purified air exits through the exhaust pipe. While this system meets general requirements, it falls short for high-purity applications such as pharmaceuticals, biotechnology, and scientific research, where oil content should be below 5 mg/m³ and particle size less than 5 μm. **3. Design of the New Coalescing Filter** This paper proposes a new coalescing filter design, as illustrated in Figure 2. Compressed air, after cooling, enters the device tangentially, creating a high-speed rotating airflow in the annular chamber. Centrifugal force separates larger particles and oil droplets, which settle along the cylinder wall and are drained automatically. The gas then moves downward, collides with a conical cover, and passes through a stainless steel flat screen. This mesh structure effectively separates gas and liquid or solid particles. After passing through a fine filter core, aerosols continue to coalesce and drop due to gravity, while oil and water are drained through an outlet pipe. **4. Performance Analysis of the Coalescing Filter** The new coalescing filter integrates centrifugal separation, coarse filtration, and fine filtration, significantly improving the removal of dust, moisture, and oil mist. It achieves a dust particle size of ≤1 μm and oil content of ≤1 mg/m³, meeting the standards set by JB/T5967-97 for air quality in pneumatic components. Compared to the original design, the new filter offers several advantages: - **Improved Separation:** Replacing the spiral structure with a tangential intake simplifies manufacturing, reduces costs, and enhances efficiency. - **Better Filtration:** The wire mesh demister eliminates secondary pollution and improves separation, reducing the load on the fine filter. - **Longer Lifespan:** The fine filter replaces the old felt-winding method, preventing clogging and extending the filter's life. - **Dual Drainage System:** Combining manual and automatic drainage ensures reliability and cost-effectiveness, avoiding the high cost of imported valves. **5. Conclusion** In conclusion, the new coalescing filter has been successfully designed and meets all necessary specifications. It provides high filtration precision, reliable operation, uniform airflow, and a long service life, making it both economical and efficient. As industrial demands for higher-quality compressed air increase, future developments will focus on even more precise and advanced filtration systems.

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