How to select oil for compressor--refrigeration compressor lubricating oil

Relationship between hydrocarbon gas and oil at different temperatures

Dilution degree of propane to ISO 220 polypropylene glycol at different temperatures and pressures. The dilution degree of hydrocarbon gas to oil increases with the increase of pressure at a certain temperature, and decreases with the increase of temperature at a certain pressure. Hydrocarbon gas dissolves in oil, reducing the viscosity of oil. Based on these characteristics of hydrocarbon gas, synthetic oil is increasingly used in hydrocarbon gas compressor, including garbage compressor, oil well compressor, various high boiling point steam recovery compressors (such as gasoline, butene and hexane steam) and natural gas pipeline booster compressor. The synthetic oil suitable for various hydrocarbon compressors is briefly introduced

For low boiling point hydrocarbon gas, Pao is a better choice for lubricating oil, especially for waste gas containing a small amount of strong acid and chlorine impurities. Proper antiwear and antioxidant should be added to the lubricating oil of garbage compressor.    

The oil well gas contains low and high boiling point hydrocarbon, water and hydrogen sulfide mixture. The PAG prepared for these compressors can provide good water resistance and dilution resistance, as well as prevent corrosion caused by high concentration hydrogen sulfide.    

PAG has strong ability to prevent dilution of hydrocarbon gas and is suitable for steam recovery compressor. The cost of a large screw rod compressor for the recovery of hexane and butene steam is up to US $5000 / day. PAG provides excellent performance, with little carrying and replenishment of oil. Only need to change the lubricant once a year to maintain the equipment.    

Alkyl methyl silicone oil mixture is used for cylinder lubrication of large natural gas pipeline supercharger because of its good oil film retention ability. The oil supply system of the cylinder needs to be improved. The cost of system improvement is offset in less than one year due to the improvement of the efficiency of the used lubricating oil and the reduction of maintenance, and the consumption of lubricant is reduced by 20 times.     

Natural gas and other hydrocarbon gases are also used as fuel for gas turbine engines. The compressor provides the gas with proper flow rate and pressure for the continuous operation of the turbine. In this case, even if the gas carries a small amount of mineral oil, the carbon will form in the gas input hole of the turbine, which will block the flow and cause fire break. Therefore, synthetic oil must also be used.

The application of synthetic oil in refrigeration compressor.

lubricating oil used in refrigeration system and heat pump plays an important role in the effectiveness of the system. Because of the possible reaction between lubricating oil and refrigerant in compressor, it is very important to choose the right lubricating oil for refrigerator.

(1) Propane and mineral oil are mutually soluble in the compressor with propane as refrigerant, resulting in the decrease of viscosity of compressor oil and the decrease of oil film thickness; the erosion of gas in cylinder to lubricant or the absorption of lubricant to gas phase lead to insufficient lubrication. PAG has low pour point, high viscosity index, excellent lubricity, especially good low hydrocarbon solubility, so it is widely used in propane refrigerator. The application of PAG in screw compressor shows that the volumetric efficiency of PAG is 18% higher than that of mineral oil, and the adiabatic efficiency increases by 5% ~ 8% when the pressure ratio is 2 ~ 10. The application in the high pressure compressor shows that the sealing life of the oil is prolonged by 20 times when the oil input speed is reduced compared with the mineral oil. 

(2) Compressor with ammonia as refrigerant

PAO and HVI hydroisomers are widely used as lubricating oil in ammonia refrigeration system because of their obvious performance advantages. 

PAO and HVI hydrocarbons have many branched chains, which can provide "three-dimensional" thick oil film and improve lubricity. The wear value of Pao is lower than that of naphthenic base oil in the presence of ammonia. The use experience of ammonia refrigeration system manufacturer proves that PAO and HVI refrigeration oil have better antiwear performance and longer service life than mineral oil. Because PAO and HVI lubricating oil are composed of highly saturated molecules, they have excellent thermochemical stability, thus prolonging the working life of lubricating oil and reducing sludge and carbon deposit.    

PAO has good viscosity temperature performance, which meets the application standard of low temperature ammonia of many refrigeration system manufacturers. HVI oil has better viscosity temperature performance than mineral oil, but additives need to be added to reduce pour point and improve viscosity temperature performance.    

PAO and HVI lubricants have low solubility, less foam and good oil and gas separation. Experience shows that oil carrying capacity can be reduced by 30% ~ 90% by using suitable separator and Pao or HVI oil. The result is a cleaner cooling system and improved heat transfer efficiency. In the use of reciprocating and rotary screw compressors, HVI oil consumption is reduced by 64% - 83%. In addition, the other advantages of Pao and HVI oil are low initial water content and good compatibility with plastic materials.     

The compatibility between ester and ammonia is not good. Ester lubricants produce sludge in the use of ammonia refrigeration system and become solid after long-term use. 

(3) compressor with halogenated hydrocarbon as refrigerant

Sealed tube test showed that PAO was very stable in CFC refrigerant environment. The high viscosity index of PAO can improve the cold start of refrigeration system. PAO does not contain wax, has no flocculation point, and has no possibility of wax blocking expansion valve and control pipe.     

PAO has a wide viscosity range, and the appropriate viscosity grade can compensate for the dilution when contacting with soluble refrigerant, such as R-12 CFC refrigeration system in oil injection screw compressor. R-12 is soluble in most of the oils, and the initial viscosity of naphthenic mineral oil is not high, so PAO is widely used in R-12 screw compressors. Pao has a high critical dissolution temperature (36.7 ℃), and is not used in most R-22 CFC refrigeration systems. However, as other properties of PAO meet the lubrication requirements of compressor, it can be used in R-22 system with special design. The ester oil prepared for R-22 system has excellent thermal stability, solubility as low as - 37.8 ℃ and good chemical stability. This kind of ester is in the range of ISO 200 viscosity, but its price is relatively expensive (35-70 USD / gallon). 

R-114 refrigerant has special significance in the application of heat pump. Experience in the United States and Europe shows that Pao is especially suitable for industrial heat pump operation at high temperature. PAO has been used in r-114 system with compression temperature up to 120 ℃. The reason why Pao is selected is that it has excellent stability, availability of viscosity grade, good low temperature characteristics and high viscosity index when used in r-114 refrigeration system. The use report shows that PAO has worked for thousands of hours, the compressor is not worn, and the lubricating oil is not invalid.    

Low viscosity PAO provides excellent performance in low temperature r-13 and r-503 refrigeration systems, and the evaporator temperature is as low as - 46 ℃.