Process centrifugal compressors

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. 

Compressor Configuration To propeny design a centrifugal compressor, one must know the operating conditions—the type of gas, its pressure, temperature, and molecular weight. One must also know the corrosive properties of the gas so that proper metallurgical selection can be made. Gas fluctuations due to process instabilities must be pinpointed so that the compressor can operate without surging. 

Turboexpanders with Dry Gas Seals. As mentioned above, the application of dry gas seals in centrifugal compressors dates back to the early 1980s. They are useful in process compressors because seal gas leakage is considerably reduced. Also, the contact of process gas and other constituents that may dilute lubricating oil is minimized. 

Most centrifugal compressors in service in petroleum or petrochemical processing plants use vane less diffusers. A vaneless diffuser is generally a simple flow channel with parallel walls and does not have any elements inside to guide the flow. 

The radial-flow, or centrifugal compressor is a widely used comj sor and is probably second only to the reciprocating compressor in usage in the process industries. A typical multistage centrifugal compressor can he seen in Figure 1-11. The compressor uses an impeller consisting of... 

Historically, the most popular driver for the centrifugal compressor has been the steam turbine. Steam turbines can readily be speed matched to the compressor. Prior to the upsurge in energy costs, reliability, simplicity, and operational convenience were the primary factors in driver selection. The steam turbine, with its ability to operate over a relatively wide speed range, was ideal for the centrifugal compressor, which could be matched to the process load by speed modulation. 

Th chapter presents an overview of the types of compresL . ,. eratic i for selecting a type of compressor, a procedure for estimating hors iwer and number of stages, and some process considerations for both ciprocating and centrifugal compressors. Chapter 11 discusses... 

Figure 10-16. Example process flow diagram of centrifugal compressor.

A superheat exchanger is not needed for a centrifugal compressor system as far as gas condition is concerned. It may be a good unit as fer as other aspects of the process are involved. The centrifugal compressor requires only a suction knock-out drum to remove entrained liquid and foreign particles. 

The centrifugal compressor is well established for the compression of gases and vapors. It has proven its economy and uniqueness in many applications, particularly in which large volumes are handled at medium pressures. This compressor is particularly adaptable to steam turbine or other continuous speed change drives, as the two principles of operation and control are quite compatible. It is also adaptable to the electric motor, gas engine, and gas turbine with each installation being specific to a particular problem or process. Installation as well as operating costs can be quite reasonable. 

Centrifugal compressors are not items that the process company or its mgineers should attempt to design in great detail. Rather, it is more important that they be in a strong position to (a) specify what is needed for the process, (b) understand the manufacturer s recommendations, and (c) evaluate the recommended design and performance in the process situation. Also see reference 117. 

Used by permission Koch, D. T. Centrifugal Compressor Shaft Seals, ref. 35, Jan. 3, 1958. Cooper-Cameron Corp. Reprinted with permission Nelson, W. E. Hydrocarbon Processing, V. 5, No. 2, p. 91 [97], 1977. Gulf Publishing Co., Houston, Texas. All rights reserved. 

The need for and use of multiple inlets/oudets for centrifugal compressors becomes apparent when balancing process flow and pressure requirements. See the later discussion, and also refer to Figures 12-40B and 12-40D. 

Several other types of compressors are used in the process industries for a wide variety of special applications that may not fit the larger reciprocating or centrifugal compressor selections. One of the smaller compressors is a diaphragm compressor. Figures 12-116 and 12-117 and Table 12-10. 

Lapina, R. P, Estimating Centrifugal Compressor Performance, Process Compressor Technology, V. 1, Gulf Publishing Co., Book Div., Houston, TX. 

Karassik, 1. J., Process Engineers Guide to the Centrifugal Compressor, Parts 1 through V.RP-339, Worthington Corp., reproduction reserved by the author. 

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