Jiangsu Huachang Chemical Co., Ltd. Xue Jun 215600 Wenzhou Ruide Valve Co., Ltd. Shao Xiaoguang 325038
Abstract: By modifying the material of the sixth and seventh piston rings of the Shenyang 6M50 compressor, the maintenance cost has been reduced, the stable operation of the compressor has been ensured, the output of synthetic ammonia has been increased, and greater economic benefits have been achieved.​

Keywords: 6M50 compressor piston ring polyetheretherketone (PEEK)



Jiangsu Huachang Chemical Co., Ltd. was formerly known as Zhangjiagang Fertilizer Factory. In February 2004, it was approved and renamed Jiangsu Huachang Chemical Co., Ltd. and moved to the Yangtze River International Chemical Industrial Park in Jiangsu Province. The company is a basic chemical enterprise with synthetic ammonia as its leading product. In the newly relocated synthetic ammonia production unit, the 6M50 large-scale compressors produced by Shenyang Compressor Co., Ltd. and Shanghai Compressor Co., Ltd. were selected for the compressors that directly determine the synthetic ammonia production capacity. Reciprocating compressor, the synthetic ammonia production capacity of a single unit of this machine is: 40ktNH3/a, so the stability of the compressor operation directly affects the output of synthetic ammonia. After more than a year of operation, some existing problems were exposed and solved. One of the more successful ones was the transformation of the material of the sixth and seventh piston rings of the Shenyang 6M50 compressor.​



The six- and seven-stage piston rings originally designed for this machine were copper piston rings. After more than a year of operation, they generally reached the replacement cycle. However, the service life of the replaced piston rings gradually became shorter. When the transformation was completed, the operating time In about 15 days, it seriously affects the stability of the compressor operation, reduces the output of synthetic ammonia, and greatly increases the maintenance workload and maintenance costs.​

Analyzing this problem, the main reasons are as follows:

1. There is an elliptical phenomenon on the outer circumference of the replaced piston ring, and its light leakage in the cylinder is out of tolerance. The outer circumferential surface of the piston ring and the cylinder mirror surface cannot fully fit and are all in contact. This results in eccentric wear of the piston ring, severe local thinning, reduced strength and fracture. Looking from the side of the broken piston ring, there is still flash around it, indicating that the piston ring material is soft.​

2. The cylinder mirror also suffered a small amount of slight wear during the friction process with the piston ring. However, when the piston ring continued to operate after the piston ring was broken, the performance was more serious, with scratches and reduced roughness on the cylinder mirror. , also affects the service life of piston rings.​

3. Lubrication in the cylinder. Since the six- and seven-stage cylinder is a high-pressure cylinder, the working pressure is about 12MPa to 30MPa. Although it is designed with two oil injection points, the oil injection amount may decrease and the oil check valve may malfunction. The amount of lubricating oil entering the cylinder is reduced, resulting in less oil in the piston ring and increased wear, thereby reducing the service life of the piston ring.​

4. The seventh-stage inlet temperature of the compressor is high. Due to the influence of the front section, the temperature of the seventh-stage gas entering the compressor is high. Moreover, the company adopts the alcoholization process of Anchun Company to replace the original copper ammonia acetate solution copper washing process. , so the gas also contains methanol vapor that has not been completely separated, and it will condense after being compressed by the compressor, and part of it will stay in the cylinder, affecting the quality of the lubricating oil in the cylinder, reducing the lubrication performance, and affecting the operation of the piston ring and cylinder. Deterioration of the condition will also cause the service life of the piston ring to be reduced.​

In response to the above possible factors, corresponding measures have been taken: improve the manufacturing quality and processing accuracy of piston rings; increase the amount of oil injection in the cylinder, from two oil injectors to three oil injectors, and increase the oil injection amount by 50%; try to reduce the seven level inlet temperature to improve the separation effect of the seven-level inlet gas; strengthen operation and patrol inspection to ensure that the oil injector operates well. However, the results were all ineffective and failed to effectively extend the service life of the piston ring.​

In view of the fact that the service life of the piston ring is getting shorter and shorter and the production is passive, it was decided to make the piston ring according to the characteristics of the polyether ether ketone (PEEK) resin valve plate used in the machine without changing the original structure of the piston body. Try using polyetheretherketone (PEEK) resin material to make piston rings of the same size for trial use.​

Polyetheretherketone (PEEK) resin is a new type of special engineering plastic successfully developed in the UK. Main properties: melting point: 334°C, glass transition temperature: 143°C, flexural strength: 134MPa, tensile strength: 97.38MPa. Main physical properties: Heat resistance: According to the evaluation method of long-term continuous use temperature, the UL temperature index value is 250 degrees. Chemical resistance: Polyetheretherketone (PEEK) resin is only soluble in concentrated sulfuric acid and has good chemical resistance, especially acid and alkali resistance at high temperatures, and methanol has a small impact on it. Therefore, polyetheretherketone (PEEK) resin has good physical and chemical properties and should be suitable for the working characteristics of the six- and seven-stage cylinders.​

Then we contacted Wenzhou Ruide Valve Co., Ltd., a manufacturer of polyether ether ketone (PEEK) valves, and made the six- and seven-grade piston rings according to our drawings and related technical parameters and requirements, and made them as early as March 2007. On 21st and March 23, 2007, they were replaced with cylinders with bore diameters of Φ205 and Φ195 respectively. After monitoring their use, the gas pressure and temperature of these two stages were in line with the designed process indicators, and the use effect was good. When the vehicle was stopped for maintenance on November 8, 2007, the Φ205 piston rings installed on March 21, 2007 were disassembled and inspected. It was found that only 2 of the 20 piston rings were broken, and the remaining 18 were basically intact, with almost the same overall dimensions. No change has occurred, except for slight scratches left on the outer periphery of the piston ring after friction with the cylinder mirror. At present, the piston rings of several other Φ205 cylinders are still in use.​

Economic benefit analysis:

1. Maintenance cost: The cost of replacing each set of piston rings (20 pieces) and support rings (2 pieces) is: 18,360 yuan. In addition, part of the sealing packing must be replaced when replacing the piston rings, the total cost is approximately: 19,000 yuan. The average life span is about 15 days. Calculated as 330 days a year, it needs to be replaced 22 times. The cost is: 418,000 yuan. The company has 5 Shenyang 6M50 compressors and a total of 10 six- and seven-stage cylinders. Therefore, Total maintenance cost saved in one year: ~4.18 million yuan. If the cylinder liner is damaged due to excessive wear due to broken piston rings, the related costs of inserting the cylinder liner will also need to be added. The cost of replacing the polyetheretherketone (PEEK) piston ring is only 10,800 yuan/set.​

2. Indirect costs affected by maintenance: The replacement time of each set of piston rings is about 4 hours, and the cumulative maintenance time in a year is about: ~880 hours. If the piston rings are damaged at night, the parking time will increase, and the cumulative parking time in a year will be at least More than 1,000 hours. According to the synthetic ammonia production capacity of a single unit of this machine is 40ktNH3/a, that is: 5tNH3/h. Just replacing the six or seven piston rings in one year will affect more than 5,000 tons of synthetic ammonia. This does not include the electricity and gas consumption caused by additional driving and parking.​

Summary: Through the transformation of the six- and seven-stage piston rings of the Shenyang 6M50 compressor, and after more than a year of successful operation, a large amount of maintenance costs have been saved, the impact of shutdown maintenance on synthetic ammonia production has been reduced, and the stable operation of the compressor has been ensured. , and achieved obvious economic benefits.