Introduction To Completely Oil-free Oxygen Compressor

Introduction to completely oil-free oxygen compressor

With the rapid development of modern industrial technology, some industrial processes have increasingly high requirements for the cleanliness of medium compression, and completely oil-free compressors have emerged.

In the mid-19th century, the emergence of new materials - self-lubricating materials - led to a new development direction in the lubrication of compressors. That is, filling polytetrafluoroethylene - a self-lubricating material was used to modify the compressor, reducing its impact on the oil purity of the compressed medium to zero, thereby expanding the application of traditional reciprocating piston compressors in today's industrial process field

1. Introduction to completely oil-free reciprocating piston compressors
   

2. Structural design of a fully oil-free reciprocating piston high-pressure oxygen compressor

3. Adaptability of a fully oil-free reciprocating piston high-pressure oxygen compressor on board ships

   
   

Introduction to completely oil-free reciprocating piston compressors

The traditional thin oil lubrication reciprocating piston compressor contains thin oil in the body, which is transported to various lubrication points by oil pumps or power splashes to lubricate the rotating and reciprocating linear motion of the compressor against the grinding surface. The piston ring and packing sealing ring of this compressor are made of metal material, and the compression work is carried out under the anti wear effect of the oil film. Oil and gas molecules inevitably mix into the compressed medium, changing the purity of the compressed medium. This is not allowed in some high demand process, forcing the compressor to change the lubrication method to meet the requirements.

For example, helium is very expensive, mostly produced in the United States, with scarce resources and political factors that increase prices and restrict sales. In order to improve the utilization rate of helium, the domestic helium recovery industry has emerged, which uses compressors to boost the used helium, purify it through molecular sieves, and obtain high-purity helium. If compressor oil is mixed into the molecular sieve without treatment during the recycling and compression process, it will cause the molecular sieve to get drunk and lose its purification function.

Similarly, sulfur hexafluoride, a protective gas in the power industry, is also required to be recycled and reused due to its high cost and destructive effect on the atmosphere. If sulfur hexafluoride gas is mixed with compressor oil during the recycling process, it will also have a serious impact on subsequent purification. If the sulfur hexafluoride mixture mixed with oil molecules is directly injected into the high-voltage electrical cabinet, it cannot extinguish the arc and will burn out the high-voltage electrical appliances, causing accidents.

In the chemical industry, if the gas involved in the reaction contains oil, it may lead to catalyst poisoning and failure, causing the entire reaction process to be interrupted. So, in the process of gas compression and pressure increase in the process flow, it is necessary to strictly control the compressor oil.

In order to achieve oil-free gas compression, compressor designers have come up with many methods, such as:

1. Water circulation compressor. Change oil lubrication to water lubrication, water is easier to remove than oil. Typical compressors include water lubricated screw compressors, liquid ring compressors, etc.

In 1969, France invented the first highly sealed and efficient water lubricated screw compressor. The compressor produced by this technology was used in military technology on warships, which had long been a blockade on developing countries.

Today's compressor technology, completely dry friction, completely oil-free screw compressors have been designed and manufactured, with oil-free and anhydrous compression, achieving clean gas compression within a certain range, but at a slightly higher price.

2. Diaphragm compressor. A specially designed diaphragm will separate the compressed medium from the outside, achieving clean compression within a small flow rate and high pressure range.

In the two types of oil-free compressors mentioned above, the pressure range of water lubricated and screw compressors is in the low pressure range, at most achieving medium pressure and not high pressure; The diaphragm can withstand high pressure, but it must first increase the oil pressure before driving the diaphragm to compress the gas medium. The machine structure is relatively complex and the cost is high.

3. Oil free reciprocating piston compressor. Due to the emergence of a new material - polytetrafluoroethylene, the reciprocating piston compressor has changed from a metal sealing ring to a non-metallic ring, achieving a qualitative change in lubrication methods. That is, the lubrication of the cylinder and packing no longer requires lubricating oil, resulting in a new completely oil-free reciprocating piston compressor that achieves complete oil-free compression of gas media.

In the mid-19th century, a completely oil-free reciprocating piston compressor was designed and manufactured. The crankcase of the machine is a dry structure, and the connecting rod, small hole, and front and rear main bearings of the crankshaft are all sealed with grease ball bearings with dual ports. Due to the lack of lubricating oil in contact with the compressed medium during operation, the discharged compressed medium gas does not contain oil or gas, which is a new exploration of reciprocating piston compressor technology and has been welcomed by users since its launch.

Structural design of a fully oil-free reciprocating piston high-pressure oxygen compressor

Oxygen compressors are required to be oil-free and non combustible.

In terms of oil-free and compressor structure, as mentioned earlier, there is no oil lubrication in the reciprocating piston compressor structure. The crankcase is a dry structure, and the large and small ends of the connecting rod, as well as the front and rear main bearings of the crankshaft, all use sealed rolling bearings to ensure that there is no contact between lubricating oil and the compressed medium during compressor operation.

When using oil-free reciprocating piston compressors to compress oxygen, the bearings use perfluoroether grease, which is a chemically inert grease that does not burn in a high-purity oxygen environment.

The sealing ring and support ring of a completely oil-free reciprocating piston compressor move at high speed inside the compressor and are filled with polytetrafluoroethylene material. Filled with polytetrafluoroethylene, chemically inert and non combustible in a high-purity oxygen environment.

So, although oxygen is a strong oxidizing agent and may burn with oil and some materials at appropriate temperatures during compression and pressure increase, the fully oil-free lubrication designed for oxygen is safe for oxygen compression in a reciprocating plug oxygen compressor, regardless of high, medium, and low pressure.

There are also drawbacks to completely oil-free reciprocating piston compressors. For example, the lubricating grease sealed in the bearings will evaporate and oxidize during long-term operation due to temperature rise, and the thickening agent in the grease will also lose its thickening effect due to deterioration. Due to changes in the performance of lubricating grease, the effectiveness of use decreases sharply. If new lubricating grease is not added in a timely manner or new bearings are replaced, the machine will malfunction and cannot be used normally. In addition, lubricating grease also has a certain working period and harsh operating conditions, which will affect the lifespan of lubricating grease. Therefore, after using the compressor without oil lubrication for a period of time, it is necessary to consider replacing the bearings or adding new lubricating grease.

The bearings of a completely oil-free reciprocating piston compressor are different from the two disc sliding bearings of the bearing shell, which are full circle type. It is difficult to replace the bearings or add new lubricating grease. To replace bearings or add new grease, the operator must possess certain professional knowledge and skills

Adaptability of a fully oil-free reciprocating piston high-pressure oxygen compressor on board ships

Completely oil-free reciprocating piston compressors are suitable for use on ships for the following reasons:

1.The biggest difference between marine compressors and land compressors is the swaying of the ship's hull. In order to cope with the swaying, oil-free lubricated compressors have inherent advantages, that is, there is no thin lubricating oil inside the compressor body, eliminating the need for oil shaking control.

2. The various components of the compressor should be able to work in swaying sea conditions. Based on Figure 1, the crankshaft assembly is located on the crankcase, with only one degree of freedom for rotation restricted by bearing seats and end caps at the left and right ends. The large end of the connecting rod is fixed on the crankshaft, with only one degree of freedom. The small end of the connecting rod is limited by the small end bearings and piston, with only one degree of freedom for rotation, meaning that all components are controlled.

3. The heat exchange of the compressor is guaranteed. Reasonably determining the compression stage of the compressor, the heat exchange area of the heat exchanger, and the calculation of the fan air volume can effectively solve the problems of compression process and exhaust gas temperature.

4. The indicators that characterize the performance of the compressor meet the requirements. This provides comprehensive values on flow rate, pressure, power consumption, and vulnerable parts in the standard for fully oil-free reciprocating piston high-pressure oxygen compressors, designed and manufactured according to the standard, with no performance issues.

5. Meet the requirements for salt spray prevention. Stainless steel is widely used in the material of oil-free lubrication oxygen compressors, and with targeted surface spraying treatment, salt spray prevention is no longer a problem. Therefore, it is suitable for use on ships.

6. Precautions for use. Specifically, when using compressors on ships, shock absorbers should be installed under the compressor base to isolate the vibration transmission between the compressor and the hull.

7. When using oil-free reciprocating piston high-pressure oxygen compressors on ships, they must also comply with the "Classification Specification for Steel Seagoing Ships" and can only be used on ships after meeting the requirements of ship inspections, such as using marine motors.