Compressors cylinder cooling

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. 

Another feature necessary to the reciprocating compressor is cylinder cooling. Most process compressors are furnished with water jackets as an integral part of the cylinder. Alternatively, particularly in the smaller size compressors, the cylinder can be designed for air cooling. 

Why use an adiabatic relationship with a compressor whose cylinder is almost always cooled An assumption made in Chapter 2 on adiabatic isentropic relationships was that heat transfer was zero. In practical applications, however, the cooling generally offsets the effect of efficiency. As a side note, cylinder cooling is as much cylinder stabilization for the various load points as it is heat removal. 

As in most jacket-cooled compressors, the cooling acts as a heat sink to stabilize the cylinder dimensionally. The jacket outlet temperature should be around 115 F and be controlled by an automatic temperature regulator if the load or the water inlet temperature are prone to change. 

Compressor cylinders [dry or water-cooled) of cast iron, nodular iron, or forged steel are engineered to suit required pressures and capacities. 

Suction scrubbers are required on the unit suction to catch any liquid carry-overs from the upstream equipment and any condensation caused by cooling in the lines leading to the compressor. They are also required on all the other stages to remove any condensation after cooling. On each suction scrubber a high level shut-down is required so that if any liquids do accumulate in the suction scrubber, the compressor will automatically shut down before liquids carry-over to the compressor cylinders. 

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. 

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. 

Most installations use water-cooled compressor cylinder jackets however, some use air cooling (usually small horsepower units), and a few use no cooling. For water cooling of the cylinder ... 

Most compressors use some method to dissipate a portion of this heat to reduce the cylinder wall and discharge gas temperatures. The following are advantages of cylinder cooling ... 

Fig. 4.1-35. Diaphragm compressor (HOFER). a, Diaphragm b, Gas space c, Discharge valve d, Suction valve e, Diaphragm cover f, Perforated plate g, Hydraulic cylinder h, Oil overflow valve i, Oil return j, Cylinder cooling k, Check valve 1, Crank drive m, Cooling-water in/out n, Oil-cooling coil o, Oil chamber p, Oil injection (leakage compensation) q, Compensation pump r, Check valve s, Oil supply.

The exchangers used to cool the gas and the circulating lubricating oil are of standard construction and usually operate on plant cooling water. Compressor cylinders frequently also are jacketed and cooled. Water used in the jackets should be clean, and frequently its source is something other than plant cooling water. One must be careful not to cool the gas enough to condense water in the cylinders. At startup, it may even be necessary to heat the cylinders. 

A V-belt-driven, force-fed oil lubrication system is used on water-cooled compressors. Oil goes to both bearings and to several points in the cylinder. Ten times as much oil is recommended to lubricate the rotary cylinder as is required for the cylinder of a corresponding reciprocating compressor. The oil carried over with the gas to the line may be reduced 50 per cent with an oil separator on the discharge. Use of an aftercooler ahead of the separator permits removal of 85 to 90 per cent of the entrained oil. 

In piston-type compressors, the oil serves three functions in addition to the main one of lubricating the bearings and cylinders. It helps to seal the fine clearances around piston rings, piston rods and valves, and thus minimizes blow-by of air (which reduces efficiency and can cause overheating). It contributes to cooling by dissipating heat to the walls of the crankcase and it prevents corrosion that would otherwise be caused by moisture condensing from the compressed air. 

Cold suction gas provides cooling for the compressor and is sufficient to keep small machines at an acceptable working temperature. Refrigerantshaving high discharge temperatures (mainly ammonia) require the use of water-cooled cylinder heads. Oil coolers are needed under some working conditions which will be specified by the manufacturer. These maybe water cooled or take refrigerant from the system. 

Better balance between cooling capacity and load can be obtained by capacity control of the compressor (s). Targe systems will have a number of compressors, or built-in capacity control on the cylinders. A central condensing unit of this sort may be coupled to several fan-coils, each with its own thermostat and liquid solenoid value. The COP is good at all but the lowest load levels. 

In practice the cylinders are usually water-cooled. The work of compression is thereby reduced though the effect is usually small. The reduction in temperature does, however, improve the mechanical operation of the compressor and makes lubrication easier. 

A two-stage double-acting compressor with water cooled cylinder jackets and intercooler is shown in Figure 7.18(c). Selected dimensional and performance data are in Table 7.7. Drives may be with steam cylinders, turbines, gas engines or electrical motors. A specification form is included in Appendix B. Efficiency data are discussed in Section 7.6, Theory and Calculations of Gas Compression Temperature Rise, Compression Ratio, Volumetric Efficiency. 

Figure 1. Supercritical flow reactor. Key (I) Mettler balance (2) flask with 1 0 (filtered and deaerated) (3) HPLC pump (4) bypass (three-way) valve (5) feed cylinder (6) weather balloon with feed solution (7) probe thermocouple (type K) (8) ceramic annulus (9) Hastelloy C-276 tube (10) entrance cooling jacket (11) entrance heater (12) furnace coils (13) quartz gold-plated IR mirror (14) window (no coils) (15) guard heater (16) outlet cooling jacket (17) ten-port dualloop sampling value (18) product accumulator (19) air compressor (20) back-pressure regulator and (21) outflow measuring assembly.

Fuel and air or nitrous oxide flow stabilities must be adequate for good precision. Intermediate balast tanks help to smooth out fluctuations caused by compressors.3 As mentioned in Chapter 2, section 5, nitrous oxide cools when it is subjected to a sharp pressure drop, which results in cooling of the cylinder head, and sometimes in instability. The effect is not as important if the nitrous oxide operating pressure... 

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