Application of oil-free lubrication technology in the cylinder of the high-pressure section of the piston-type nitrogen-hydrogen compressor

Application of oil-free lubrication technology in the cylinder of the high-pressure section of the piston-type nitrogen-hydrogen compressor
1. Raising the problem
　　 Compressor oil-free lubrication technology, as a new energy-saving technology, has been developed and applied to various compressors in various industries for more than 60 years. At present, my country has good applications in oxygen compressors, hydrogen compressors, air compressors and nitrogen-hydrogen compressors. As oxygen compressor cylinders, oil-free lubrication technology must be used. Then as nitrogen-hydrogen compressors widely used in the fertilizer industry , How much benefit can be gained by adopting oil-free lubrication technology? Will the working cycle of wearing parts and the air volume of the machine be affected by the compressor with oil-free lubrication? This is a problem that often arises when preparing to adopt this technology. This article explains the necessity of applying oil-free lubrication technology in the cylinders of nitrogen-hydrogen compressors and the benefits that can be obtained to illustrate the necessity of the application of oil-free lubrication technology. The feasibility of applying oil-free lubrication technology to compressors.
　　 Second, the necessity of using oil-free lubrication technology for the cylinders of the high pressure section of the nitrogen-hydrogen compressor
　　 1. The use of oil-free lubrication technology can effectively stabilize the working cycle of the cylinder piston ring in the high pressure section:
The working pressure of the cylinders in the high-pressure section of the nitrogen-hydrogen compressor is very high, generally reaching 13-31 MPa. The actual situation is that the working life of the piston rings of these high-pressure cylinders is often problematic during oil filling work, and wear occurs after 1-2 months of operation. , It is not uncommon for a large number of leaks to be shut down for replacement. Obviously, the existence of this situation has a great negative impact on the production rate of machines and the stability of the company's production conditions, seriously jeopardizing the improvement of the company's production capacity, and affecting the economic benefits of the company.
　　Analyze the important reason why the working life of the piston ring of these cylinders is difficult to reach the expected working cycle stably is the failure of the high-pressure cylinder oil injection system. Because the back pressure of the cylinder piston ring in the high pressure section is very huge, it can be hundreds of times the back pressure of the cylinder piston ring in the low pressure section. Under such a large back pressure value, the cylinder oil injection system must be required to work In good condition, there must be sufficient lubricating oil in the cylinder to reduce the friction coefficient between the ring and the cylinder wall to avoid short-term excessive wear when the piston ring is working. This puts forward very high requirements on the oil injection system of the high-pressure cylinder. The pressure of the oil injector must exceed the working pressure of the cylinder before the lubricating oil can enter the cylinder. Therefore, the oil injector of the high-pressure cylinder has a heavy workload and high repair requirements. In actual production, the oil injector often fails. If you do not pay attention to the oil injector, you will not inject oil, which will seriously affect the working life of the piston ring in the high pressure section.
　　 Correspondingly, the piston ring in the non-lubricated cylinder has good self-lubricating performance. There is no need to inject oil into the cylinder during operation, and the piston ring can maintain good friction conditions and work normally. At present, oil-free piston rings in high-pressure cylinders are generally made of FH-1A metal plastic composite material. This material has good self-lubricating performance, good wear resistance and sealing performance, ensuring that it is oil-free in the 31 MPa high-pressure cylinder The working cycle under lubrication conditions can reach 4000 hours. For certain cylinders with special structures, such as high-pressure balanced cylinder pistons, the working period of oil-free lubrication can even reach about 8000 hours. This is because the operating performance of the piston assembly with no oil lubrication structure has got rid of the dependence on lubricating oil, so the impact of the failure of the high-pressure oil injection system on its operating cycle is effectively avoided.
　　 This is the reason why the oil-free lubrication technology can effectively stabilize the working life of the piston ring of the high-pressure cylinder, and it is also a major advantage of the oil-free lubrication technology for the high-pressure cylinder.
2. Save oil:
In piston compressors, when cast iron is used as the piston, the high-grade mechanical oil that is injected into the cylinder by the ring material for lubrication consumes a large amount. For a fertilizer company with an annual output of 100,000 tons of synthetic ammonia, the lubrication added to the compressor high-pressure cylinder The quantity of oil can reach 20 tons per year, and the single value can reach 200,000 yuan. In addition, my country's petroleum resources are not rich. If the compressor is operated without oil lubrication, it will save a lot of petroleum resource consumption, and its significance will be even greater.
　　3. Purify gas, reduce production cost, realize production increase and save:
When lubricating oil is injected into the compressor cylinder during operation, the lubricating oil will inevitably be atomized and sent out along with the compressed gas. Although the outlet of the high-pressure machine is generally equipped with an oil separator, the separation effect of the separator is absolutely absolute. It is impossible to reach 100%, so oil mist is often entrained in the outlet gas of the oil-filled cylinder. The oil mist entrained at the outlet of the nitrogen-hydrogen compressor used for fertilizer production will enter the refining system, the synthetic ammonia system or the methanol system, and the high-pressure methanation system, which will cause great harm to the production system.
　　 For example, the compressor six-stage cylinder outlet gas is sent to the refining system. If the gas is entrained in the copper acetate ammonia solution, the quality of the copper solution will be deteriorated, and the gas trace index cannot be guaranteed. The funds spent on cleaning up oil pollution or updating the copper liquid will obviously greatly increase the cost of synthetic ammonia production.
Another example: the outlet gas of the seventh stage of the compressor is sent to the synthetic ammonia production system. If the oil content in this supplementary fresh gas is high, then the gas will bring the oil into the catalyst basket after the gas enters the synthesis tower, and the oil will be wrapped on the surface of the catalyst when it contacts the catalyst. , Make it permanently poisoned and lose its activity. As a result, the hot spot of the synthesis reaction moves down, the production capacity of the synthesis tower decreases and the catalyst is replaced earlier. Some companies reported that more than 30 kg of lubricating oil was discharged from the lower part of the synthesis tower when the catalyst was replaced at a time, which shows that the gas entrains a lot of oil mist.
　　 Another example: In the methanol production enterprises, because the methanol catalyst is more sensitive and the catalyst is more prone to poisoning and aging, the purification gas is of greater significance to the methanol production system. A company used to replace the methanol catalyst in 4 months. After all the compressor high-pressure cylinders were lubricated without oil, the catalyst life cycle was extended to 12 months. It can be clearly seen that the use of oil-free lubrication technology to purify gas is indeed very effective in reducing production costs, improving production efficiency, increasing production and reducing consumption.
　　 Finally, fertilizer manufacturers are currently carrying out a series of production process reforms, the purpose of which is naturally to further save energy and reduce consumption. For example, the use of high-pressure methanation process to eliminate the refining process is one of them. High-pressure methanation is to convert trace amounts of carbon monoxide and carbon dioxide into methane under high pressure. The conversion is completed by catalysts, which are more sensitive, and the gas with oil content will make the traces unqualified. Therefore, the high-pressure cylinder of the compressor is required to run without oil injection when using this process.
　　 To sum up, the purification of the gas compressed by the nitrogen-hydrogen compressor, especially the purification of the high-pressure gas, has a series of benefits for fertilizer production, which will further save energy and reduce consumption, increase benefits, and enhance vitality for enterprises. The oil-free lubrication of the compressor high-pressure cylinder is not optional, but imperative.
　　 3. The feasibility of using oil-free lubrication technology for the cylinders in the high pressure section of the compressor
　　1. The oil-free piston ring has good sealing performance during operation to ensure the air volume of the machine:
　　 When the piston is running in the cylinder, it relies on the sealing effect of the piston ring to prevent the compressed gas from leaking, thereby ensuring the machine's gas delivery volume and reaching a certain production capacity. The airtight performance of the oil-free piston is carefully considered when the structure is designed, and the leakage during operation is reduced to about 2% of the allowable level. Therefore, there is no need to add lubricating oil in the cylinder during operation, and the oil film is used to assist air tightness. Practical application shows that the oil-free lubrication machine has good air tightness, small leakage, and guaranteed air delivery.
　　 Example 1: Shandong Hengtong Chemical Co., Ltd. fertilizer plant, the compressor high-pressure cylinder is implemented without oil lubrication as follows.
　　①. Compressor configuration:
MH92/31.4
(Seven-level compression)
Qitai
M73/31.4
(Six-level compression)
Two sets
4M8K4-36/320
(Six-level compression)
　　②. The high-pressure cylinder adopts oil-free technology:
　　 The high-pressure sections of 14 compressors (MH92 six-seventh section, 4M8K4, M73 five-sixth section) were all completed without oil lubrication in 2002 and have been in operation until now. The average working life of the piston ring is 4000 hours, of which the MH92 seven-stage working life is over 8000 hours.
③. Machine production rate after implementing oil-free lubrication:
Comparison of machine yield before and after using oil-free lubrication technology

　Note: The number of starting units is converted into 4M8K4, and the output of amino alcohol is calculated as 1:1.

　　From the above machine output rate, after all the machine high pressure cylinders were operated without oil lubrication in 2002, the average machine output rate was not lower than when using oil injection operation, indicating that the air tightness of the oil-free piston ring was good.
　　 Example 2: Shanxian Jinmao Chemical Co., Ltd., Henan Province, oil-free lubrication transformation.
　　①. There are five M73/31.4 compressors, five and six-stage cylinders with the structure of canceling the balance section.
②. Before 2001, the five and six-segment cylinders of five M73 machines were running with oil. Due to the poor wear resistance and sealing performance of the piston ring, leakage often occurred during operation. The piston ring will be replaced in one month.
　　 ③. In 2001, the oil-free lubrication technology was adopted in the five and six cylinders of the M73 machine.
Because the oil-free piston ring has good wear resistance and air tightness, the piston ring still maintains a good seal after half a year of operation. After all the five and six-stage cylinders of the five machines are changed to oil-free operation, the five-stage overpressure is completely eliminated . When measuring the temperature of the fifth-stage outlet valve with an infrared thermometer, it was found that its working temperature was 5C lower than that during oil injection, which proved that the high-temperature gas leaking to the fifth-stage during the sixth-stage compression was greatly reduced, which made the fifth-stage outlet temperature drop.
　　④. The company is very satisfied with the use of oil-free lubrication technology for the cylinder of the M73 engine with the cancellation of the balance section, which improves the air-tightness of the piston ring, thereby reducing the internal leakage of the equipment and increasing the machine output rate.
　　 From the above two cases, it can be clearly seen that the oil-free lubrication technology used in the high-pressure cylinder of the compressor can fully guarantee the air tightness of the piston ring and the machine output rate.
　　 2. The oil-free piston ring has good wear resistance, so that the air tightness of the piston assembly can be maintained for a long time:
As a compressor piston ring, it must not only have sufficient air tightness but also good wear resistance to maintain air tightness for a long enough time. Practical application shows that the oil-free piston ring we use now has the above performance.
At present, the oil-free lubrication piston ring material of the high-pressure cylinder adopts FH-1A metal plastic material, which is impregnated with polytetrafluoroethylene material in the porous copper powder layer formed by sintering, so that it has low friction coefficient of polytetrafluoroethylene , It also has the advantages of good heat transfer, small thermal expansion coefficient and good thermal strength of metal materials. The allowable PV value of this material is 10 times that of filled PTFE. The "back pressure" value (the positive pressure value of the piston ring close to the cylinder wall when working) of the piston ring of the high pressure section cylinder is relatively large, and only materials with high allowable PV value will be more wear-resistant. Nowadays, we use FH-1A material as the high-pressure cylinder piston ring, so that the wear of the piston ring is very small, so that it can still maintain good air tightness after 4000 hours of operation, thereby stably extending its effective working life.
　　3. The PTFE pre-filmed cylinder liner and the gold-plastic piston ring form a good friction pair to ensure the working life of the piston ring:
　　 In the cylinder, the piston ring and the cylinder liner are a pair of friction pairs. To ensure a good self-lubricating condition of the piston ring, it is a very important part of the performance of the grinding parts. We use a pearlitic ductile iron cylinder liner with a certain degree of roughness, and use an extrusion process to hang a layer of polytetrafluoroethylene film on the inner hole, which can further reduce the friction coefficient between the ring and the cylinder wall and reduce the piston during operation. Ring wear and stable piston ring life play a very important role.
　　 The above examples prove that it is not only necessary to implement oil-free operation of the cylinder in the high-pressure section of the compressor, but also the effect is good and feasible.
　　 IV. Conclusion
　　At present, the oil-free lubrication technology we have mastered has enabled the piston ring to have good sealing performance and can operate stably in the high-pressure cylinder. Judging from the operating results of more than 30 models that have been promoted and implemented on more than 300 machines in more than 50 enterprises, various cylinders with cylinder diameters ranging from 48 to 220 operate under normal working conditions without oil lubrication, and continuous The operating cycle has reached more than 4000 hours.
The implementation of oil-free lubrication operation in the cylinder of the high-pressure section of the compressor can not only save oil, stabilize the working life of the piston ring, reduce machine leakage and increase the output rate, but also purify the gas, improve the production process conditions, and realize the increase in production and consumption. This is a new technology that can be achieved in one fell swoop.
　　The application of oil-free lubrication technology in the cylinder of the high-pressure section of the nitrogen-hydrogen compressor has been very mature, and it can be promoted and applied.