Reciprocating compressors efficiency

Figure 3 gives reciprocating compressor efficiencies (see Tables 1 and 2 for conection factors). 

Figure 3-6. Reciprocating compressor efficiencies plotted against pressure ratio with a valve velocity of 3,(M)0 fpm and a mechanical efficiency of 95%.

Coker, FCU, Crude Fractionators Reciprocating Compressor Efficiency... 

Gas turbine driven centrifugal compressors are very efficient under the right operating conditions but require careful selection and demand higher levels of maintenance than reciprocating compressors. Compression facilities are generally the most expensive item in an upstream gas process facility. 

Mechanical Expanders Reciprocating expanders are very similar in concept and design to reciprocating compressors. Generally these units are used with inlet pressures of 4 to 20 MPa. These machines operate at speeds up to 500 rpm. The thermal efficiencies (actual enthalpy difference/maximum possible enthalpy difference) range from about 75 percent for small units to 85 percent for large machines. 

Here are some approximate efficiencies to use for centrifugal, axial flow, and reciprocating compressors. 

The reciprocating compressor is generally in the lower flow end of the compressor spectrum. Inlet flows range from less than 100 to approximately 10,000 cfm per cylinder. It is particularly well-suited for high-pressure service. One of the highest pressure applications is at a discharge pressure of 40,000 psi. Above approximately a 1.5-to- i pressure ratio, the reciprocating compressor is one of the most efficient of all the compressors. 

Hartwick, W Efficiency Characteristics of Reciprocating Compressors, ASME 68-WA /DGP-3, New York, NY American Society of Meciwnical tingineers, 1968. 

Because there is no clearance volume expansion, as in the reciprocating compressor, the volumetric efficiency is a function of the rotor slip. This is the internal leakage from the higher pressure to the lower pressure side, reducing potential volume capacity of the compressor. 

There is a disadvantage in centrifugal machines in that they are low efficiency. This means it requires more brake horsepower (bhp) to compress the same flow rate than would be required for a reciprocating compressor. If the compressor is driven with a turbine, there is even a greater disadvantage because the turbines are low in fuel efficiency. The net result is that turbine-driven centrifuea machines do not use fuel very... 

Rotary Compressor. Inherently a rotary compressor is more efficient than the current reciprocating compressor, (room air-conditioners have been using rotary compressors for decades.) Several manufacturers in the U.S. and Japan have produced refrigerators with rotary compressors, but experienced long-term quality problems. 

Figure 12-16D illustrates the type of reciprocating compressor performance problems that can develop from various mechanical details. To maintain peak efficiency in a compressor cylinder, a pressure-time indicator card of the cylinder during operation can be quite helpful in pointing to a problem and its nature. ... 

Figure 12-17B. Effects of clearance volume on performance efficiency of reciprocating compressor cylinder (valve design effect). (Used by permission Livingston, E. H. Chemical Engineering Progress, V. 89, No. 2, 1993. American Institute of Chemical Engineers, Inc. All rights reserved.)...

Figure 12-25. Combined compression and mechanical efficiency of reciprocating compressors. (Used by permission Campbell, J. M. Oil and Gas Journal and Ridgway, R. S. California Natural Gasoline Association Meeting, 1945. All rights reserved.)...

In many instances, the design of suction and discharge pulsation dampening drums (or bottles) for reciprocating compressors is based on piston displacement and volumetric efficiency, and this design normally will suffice to reduce peak pulsation to approximately 5% of the line pressure. In special or other cases, experience has shown that operational difficulties (vibrations, meter pulsations, etc.) may indicate that the peak pulse pressure of 5% line pressure is inadequate. Thus, the pressure in pulsation-reduction design selection is... 

Reciprocating compressors are classified as constant-volume, variable-pressure machines. They are the most efficient type of compressor and can be used for partial-load, or reduced-capacity, applications. 

The isentropic efficiency (see Appendix B) is a function of the machine design and pressure ratio (Pout/Pm) A first estimate of the isentropic efficiency of a reciprocating compressor can be obtained from ... 

Estimate the compressor efficiency. Compressor manufacturer s data should be used where possible. If this is not available, then for a reciprocating compressor, the isentropic efficiency can be estimated from Equation 13.17 ... 

Introducing the isentropic compression efficiency gives Equation B.15, the same result for a reciprocating compressor. In a reciprocating compressor, the net effect of the cycle is a flow process, even though intermittent nonflow steps are involved. 

Whereas reciprocating compressors are normally designed on the basis of adiabatic work (together with an isentropic efficiency), centrifugal compressors are usually designed on the basis of polytropic work. By analogy with Equation B.15, the work required for a poly tropic compression is given by ... 

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