Traditional compressor cylinder designs require cooling water jackets to promote uniform distribution of heat created by gas compression and friction. Some of the perceived advantages of water-cooled cylinders are reduced suction gas preheat, better cylinder lubrication, prolonged parts life, and reduced maintenance.
Operating experience during the last 30 years has proven that compressor cylinders designed without cooling water jackts (non-cooled) can successfully operate in most natural gas compression applications. Some of the perceived advantgaes of non-cooled cylinders are simplified cylinder designs that reduce cost and improve efficiency, reduced initial system costs due to reductions in the cooling water system, improved valve accessibility, and reduced weight.
Many manufacturers, users, and compressor applications still require that compressor cylinders be supplied with liquid-cooled cylinders. Figure 11-21 includes schematics of several types of liquid coolant systems.
In static systems, the cooling jackets are normally filled with a glycol and water mixture to provide for uniform heat distribution within the cylinder. This system may be used where the AT of the gas is less than 150°F and discharge gas temperature is less than 190°F.
Thermal siphons use the density differences between the hot and the cold coolants to establish flow. This system may be used where the AT of the gas is less than 150°F and discharge gas temperature is less than 210°F.
Forced coolant systems using a mixture of glycol and water are the most common for natural gas compressors. Normally, the compressor cylinder cooling system and compressor frame lube oil cooling system is combined. A single pump is used to circulate the coolant through the cylinders and the lube oil heat exchanger and then to an aerial cooler where the heat is dissipated.
When forced coolant systems are used, care must be taken to provide the coolant at the proper temperature. If the cylinder is too cool, liquids could condense from the suction gas stream. Thus, it is desirable to keep the coolant temperature 10°F higher than that of the suction gas. If the cylinder is too hot, gas throughput capacity is lost due to the gas heating and expanding. Therefore, it is desirable to limit the coolant temperature to less than 30°F above that of the suction gas.