Reciprocating compressors design

Figure 12-5F. Lubricated and nonlubricated balanced opposed process reciprocating compressors, designed to API 618 code. Fixed- and variable-speed drives using gas or diesel engines, steam or gas turbines, or electric motor. Note power drive to connect to right side of cross-head box in center. (Used by permission Bui. PROM 635/115/95-11. Nuovo Pignone S. P. A., Florence, Italy New York Los Angeles and Houston, Texas. All rights reserved.)...

When properly designed, installed, and operated, these compressors serve well. However, there are stories about problems with liquids from condensation of saturated vapor streams entering the suction side of the compressor. The typical reciprocating compressor design is not very tolerant of an accumulation of liquids in the suction. There is the possibility of blowing the compressor heads off if the compressors are subjected to incompressible fluids. 

Design The economics usually work out in the favor of gas coolers when the centrifugal machines flow rate reaches about 5000 scfm. The pressure loss can Be kept to 7.0 kPa in most cases. When the ratio of A(ht lo Ajhs is 20 1, is another point to consider these plate-fin designs. Vibration is practically impossible with this design, and uses in reciprocating compressors are possible due to this. 

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. 

Vlanv process machines operate at speeds diFFerent From the one oF their drivers. Typical oF cases where the machine rotates. dower than the driver are reciprocating compressors typical examples oF machines rotating/ js / er than the drivers are centriFiigal compressors driven bv electric motors. In either case, ear. are used to match the two speeds, (iears can also be designed to accommodate shaFts that... 

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. 

Davis, H., Effects of Reciprocating Compressor Valve Design on Performance and Reliability, Presented at Mechanical Engineers, London, England, October 13, 1970 (Reprint, Worthington Corp., Buffalo, NY). 

Foundation designers, particularly ones who are familiar with reciprocating compressors, will often ask about the shaking forces exhibited by... 

Non-lubricated screw compressors have very close clearances and thus they are designed for limited ranges of discharge temperature, temperature rise, compression ratio, etc., all of which can cause changes in thesc clearances. Lubricated compressors have a somewhat broader tolerance to changes in operating conditions, but they are still more limited than reciprocating compressors. 

End view showing male and female rotors and slide valve on an 85-ton intermediate compressor. The robust design of the Series R compressor can ingest amounts of liquid refrigerant that would severely damage reciprocating compressor valves, piston rods, and cylinders. (Used by permission Cat. RLC-DS-2, Aug. 1995. The Trane Company.)... 

Piston displacement is the actual volume of the cylinder displaced as the piston travels its stroke from the start of the compression (condition (1)) to the end of the stroke (condition (e)) of Figure 12-12 expressed as fF of volume displaced per minute. Displacement values for specific cylinder designs are available from the manufacturers, Table 12-6. Neerken is a useful reference. Reciprocating compressors are usually rated in terms of piston displacement, which is the net volume in ft per minute displaced by the moving piston. Note that the piston does not move through the clearance volume of Figure 12-12 therefore this volume is not displaced during the stroke. 

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.)...

The fundamental characteristics of compression are the same for centrifugal and reciprocating compressors. The manner in which these fundamentals are interpreted must be adapted to the particular machine type and operating characteristics, and this accounts for the difference in design procedures. 

More recently, the Southern Gas Association s Gas Machinery Research Council and Pipeline and Compressor Research Council cooperated with Southwest Research Institute to develop a software package that enhances reciprocating compressor operation. Several major American and foreign compressor manufacturers (and some other interested companies) have cooperated with Southwest Research Institute or developed their own proprietary pulsation-reduction design computer programs. 

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... 

In general, only the reciprocating compressor allows for reliable flexibility in applying variable volumetric flowrate and variable pressure ratio in an operation. The rotary compressor does not allow for variation in either (except that of pressure through the decompression of the air or gas if the system back pressure is below the design pressure of the machine). The dynamic compressors are designed for specific volumetric flowrates and pressure ratios and are not very useful when these design limits are altered. 

The only other variables that affect performance are the inlet-discharge valves, which control flow into and out of each cylinder. Although reciprocating compressors can use a variety of valve designs, it is crucial that the valves perform reliably. If they are damaged and fail to operate at the proper time or do not seal properly, overall compressor performance will be substantially reduced. 

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 ... 

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