Centrifugal compressor performance curve

The Operating System. Regardless of calculated centrifugal compressor performance, the machine will operate only on or along its operating curve to fit the system of which it is a part. This is quite similar to the system performance of a centrifugal pump. Friction, other pressure drops of the system, and how friction varies with operating conditions determine machine performance. 

Caution should be taken to prevent excessive acceleration. One solution is to provide for opening of the compressor discharge vent valve to increase the compressor flow and increase blower horsepower. This is effective with a centrifugal compressor, however, not with an axial compressor unless the compressor is provided with adjustable stator vanes that are reliable. This can be seen from the performance curve. The head versus flow curve for a given vane setting is extremely steep and opening the vent valve is ineffective. However, if the vanes operate fully open and the vent valve opens, the combined effect is satisfactory. The vent valve must not be oversized. 

Figure 1-3 presented a general form performance curve for each of the compressors. The centrifugal compressor exhibited a relatively flat curve compared to the other machines. Flat is defined as a relatively low head rise for a volume change. Translated to pressure terms, it means a relatively low pressure change for a given volume change. It is important to understand some of the basics that contribute to the curve shape. 

This provides curves for cooling tower performance and typical off design performance of centrifugal compressor chilled water systems. These graphs show typical coincident wet and dry bulb temperatures, in... 

Compressors are gas movers and devices where mechanical work is done on the gas resulting in an increased pressure. Centrifugal compressors are used in a variety of chemical process industries (CPI). Their performance often varies with changes in process conditions. Sometimes the performance curves supplied by the manufacturer as discharge pressure and power requirement against an inlet volumetric flow may not be valid for variations in process conditions. Lapina [1] has provided a technique of obtaining a usable performance curve that is valid for the actual process conditions. Gas compressor applications are employed in the following duties ... 

Figure 19-3 Typical constant spaed performance curves for a centrifugal compressor.

Figure 19-5 Typical variable speed performance curves for centrifugal compressor.

When a variable-speed centrifugal compressor starts to surge, should its speed be increased or decreased to stop the surging Figure 25-3 shows a set of performance curves for a centrifugal (not an axial) blower. This... 

The performance of centrifugal conpressors is somewhat analogous to that of centrifugal punps. There is a characteristic performance curve, supplied by the manufacturer, that defines how the outlet pressure varies with flowrate. However, compressor behavior is far more conplex than that for punps because the fluid is conpressible. 

As we will discuss in Chap. 41, increasing the compression ratio is a small effect on compressor workload as compared to decreasing the vapor flow as long as we are operating on the flat part of the compressor s flow vs. the head performance curve, which is almost always the case for a centrifugal machine. Hence, suction throttling will significantly reduce the horsepower load on the compressor, as well as increase the evaporator temperature for a motor-driven compressor. 

When 1 describe how to save compressor horsepower by suction throttling later in this chapter, you will understand the importance of the shape of the performance curve. The concept of the suction throttle valve, in fixed-speed centrifugal compressors, is the least understood aspect of all process equipment. 

A typical performance curve of a centrifugal compressor in terms of head against flow is shown in Figure 6. Typical performance curves for axial compressor and reciprocating or rotary compressor are also shown in Figure 6. 

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