Development and design of coalescing filters

**Abstract:** This paper presents the development and design of an improved coalescing filter, comparing its performance with 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 enhanced performance in terms of filtration accuracy, airflow uniformity, and reduced resistance, while also providing cost-effectiveness, durability, and practicality. **Keywords:** compressed air; coalescing filter; tangential air intake; centrifugal separation **1. Introduction** Compressed air is extensively used across various industries such as petrochemicals, textiles, biotechnology, and defense. 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 fine particles are difficult to remove through standard suction filtration. Additionally, oil-lubricated compressors generate waste that contaminates the final gas. Depending on the operating conditions, pollutants can range between 5 and 50 mg/m³. Most oil-free compressors in China are only semi-oil-free, as oil vapor can still be carried into the cylinder via the piston rod. Moreover, temperature fluctuations cause condensation and accumulation of impurities like rust and solid particles in the pipeline, necessitating effective purification systems. **2. Original Air Filter Structure and Working Principle** The GYF-3/8 and GYF-6/8 oil-water separators commonly used in air compressor plants are designed to purify compressed air. As shown in Figure 1, the process involves the compressed air entering the device through an inlet pipe, where spiral separation causes larger particles and droplets to be thrown against the cylinder wall and discharged through a drain valve. The gas then flows into a conical cover and collides with a ceramic ring (Rasi ring), causing further separation of oil and water. After passing through coarse and fine filter elements, the purified gas exits through the exhaust pipe. However, this system only meets general standards, with an oil content of up to 5 mg/m³ and dust particles of 5 µm, which is insufficient for high-purity applications in pharmaceuticals, biotechnology, and research. **3. Design of the New Coalescing Filter** This paper introduces a redesigned coalescing filter, as illustrated in Figure 2. The compressed air, after being cooled by a rear cooler, enters the device tangentially, creating a high-speed rotating airflow in the annular chamber. Centrifugal force separates large particles and oil/water droplets, which settle along the cylinder walls and are discharged via an automatic drain valve. The gas then swirls downward, hits the conical cover, and enters a stainless steel flat screen. This mesh structure effectively separates gas and liquid or solid particles. As the particles accumulate, they are removed from the screen surface. After passing through a fine filter core, any remaining aerosols are collected and discharged through an oil drain pipe, ensuring high-quality output. **4. Performance Analysis of the New Coalescing Filter** The new coalescing filter integrates three stages: centrifugal separation, coarse filtration, and fine filtration, effectively removing dust, moisture, and oil mist from compressed air. It achieves a particle size of ≤1 µm and oil content ≤1 mg/m³, meeting or exceeding the requirements outlined in JB/T5967-97 for pneumatic components and air quality. Compared to the original system, the new filter offers several advantages: - **Improved Centrifugal Separation:** Replacing the old spiral welded structure with a tangential intake simplifies the manufacturing process, reduces costs, and enhances efficiency. - **Enhanced Filtration:** The wire mesh demister replaces the ceramic tubes, eliminating secondary pollution and improving cleaning efficiency. - **Advanced Fine Filtration:** The new precision filter uses advanced mechanisms such as inertial collision, diffusion, and agglomeration, ensuring reliable and long-lasting performance. - **Dual Drainage System:** Combining manual and automatic drainage ensures reliability and cost-effectiveness, avoiding the drawbacks of imported valves. **5. Conclusion** The new coalescing filter has been successfully designed and implemented, meeting all necessary specifications and performance criteria. It offers high filtration accuracy, uniform airflow, low resistance, and a long service life at a lower cost. While current standards are met, the increasing demand for higher purity in industrial applications means that future developments in air filtration will continue to be a critical challenge and opportunity.

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