Discussion on Waterless Lubrication Modification of Nitrogen Compressor

Discussion on Waterless Lubrication Modification of Nitrogen Compressor

With the rapid development of industry, nitrogen has been widely used in the fields of chemical industry, electronics, metallurgy, food, machinery and other fields. my country's demand for nitrogen is increasing at a rate of about 20% every year. Nitrogen is chemically inactive, and it is very inert under normal conditions, and it is not easy to chemically react with other substances. Therefore, nitrogen is widely used as protective gas and sealing gas in metallurgical industry, electronics industry, and chemical industry. Its purity requirement is above 99.99%, and some requirements are even above 99.999%.

Hangzhou Zheqi Gas Co., Ltd. has three 3Z3.5-1.67/150 gas compressors. The compressors are vertical three-stage compressors. Two of them are used to compress nitrogen gas. The working feature is to use softened water as lubrication. To reduce the friction and the temperature in the cylinder, however, due to the use of this lubrication method, there are many shortcomings, mainly caused by the excessive moisture content in the compressed gas. In the compressed nitrogen cylinder, some even The free water reaching about 100ml seriously reduces the quality of nitrogen. In some demanding production processes, it cannot be used at all, and even leads to the production of defective products. In view of the above situation, the company decided to apply waterless lubrication technology to the nitrogen compressor Transform to improve the quality of products and meet the requirements of various production processes. The main links of technical transformation are introduced as follows.

1. Selection of piston ring:

The material used for the piston ring of a general gas compressor is polytetrafluoroethylene. Although it has good self-lubricating properties, it has poor thermal conductivity, corrosion resistance, and morphological stability. In the compression process without water lubrication, The temperature in the cylinder rises significantly, which greatly reduces the service life of the piston ring. Therefore, it is necessary to find a way to solve the above problems. According to the experience of other gas manufacturers and many experiments by piston ring manufacturers, the materials used in the production of piston rings are used. The method of adding fillers to improve the shortcomings of polytetrafluoroethylene is called filled polytetrafluoroethylene. Piston rings made of filled polytetrafluoroethylene have their wear resistance and service life depend on the composition of the material. The selection of the ratio and the structure of the piston ring, and the ratio of the filling components of the PTFE filler is mainly based on the comprehensive consideration of the compressed medium, the structure of the compressor, and the speed of the machine. It is found through experiments that graphite is the main filler. To increase the lubricity of the piston ring, and then add a certain amount of bronze powder to increase the mechanical strength of the piston ring. The piston ring made of the above-mentioned material filled with PTFE has a greatly reduced friction coefficient and a correspondingly extended service life. ；

2. Improvement of piping system:

In order to improve the purity of the compressed gas and improve the working conditions of the compressor, a balance gas tank is added between the front stage of the compressor and the fractionation tower, with a volume of about 0.5-1.0 cubic meters to meet the needs. The air pipe port is changed to perforate the first-stage valve cover, and the pipe is directly connected to the balance gas tank, and the diameter of the inlet pipe is thickened, which can reduce the resistance of the pipe to the gas, increase the gas flow rate, and improve the compressor The amount of intake air when the first-stage piston inhales. The original air inlet of the compressor and the balance gas tank are connected by a pipeline. When the sealing performance of the sealing box is not very good, the pipeline provides a certain pressure to prevent air from leaking from the gap between the sealing box and the piston rod. Into the cylinder, thereby ensuring the purity of the compressed nitrogen, the working conditions of the compressor after the above improvements have been greatly improved;

3. Improvement of cylinder heat dissipation performance:

Due to the non-water lubrication method, the temperature of each cylinder of the compressor has a certain degree of rise, and the temperature rise of the three-stage cylinder is z*. In order to improve the heat dissipation of the cylinder, avoid excessive temperature rise, In the case of a three-stage cylinder, the manufacturer of the cylinder is required to design its outer wall into a fin type, and the inner wall is inlaid with a copper sleeve with good thermal conductivity and wear resistance. The performance and life of the cylinder produced by the above method are greatly improved;

Fourth, the improvement of the control system:

The control system of this kind of gas compressor is generally relatively simple. Some compressors with an earlier age usually use a winding motor, and the starting method is a frequency-sensitive rheostat. In recent years, they have basically changed to use squirrel-cage motors. Many of them use direct start mode, but the start current of this start mode is too large, there is a big safety hazard, and it brings many disadvantages in terms of safety and operation. In order to improve these problems, we changed the motor control system to star-delta starting mode to reduce the starting current, and added interlock and alarm functions to the entire control system, mainly for the equipment’s oil supply system and water supply system. Interlocking and alarm functions, and alarm functions are set for the three-stage exhaust temperature and exhaust pressure. Once there is a shortage of oil or water, the control system will give an alarm indication and delay the shutdown to protect the nitrogen compressor. When the three-stage exhaust temperature and pressure exceed the setting, the system will also sound an alarm to remind the operator to troubleshoot the problem in time and avoid safety accidents;

5. Summary:

The nitrogen compressor that has undergone the entire system transformation, after a period of operation, it is found that all aspects of its operating parameters meet the operating requirements of the machine itself, and the output of the nitrogen compressor has been increased, and the quality of the nitrogen has also been improved. The improvement of the system, the equipment can be used to compress high-purity nitrogen, which improves the practicability of the machine. At the same time, the transformation of the control interlock system of the machine has greatly improved the safety and operation of the equipment.