Centrifugal surge

The compressors operating range is between two major regions as seen in Fig. 10-74, which is a performance map of a centrifugal compressor. These two regions are. surge, which is the lower flow limit of... 

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. 

The performance of a centrifugal compressor (discharge to suction-pressure ratio vs. the flow rate) for different speeds is shown in Fig. 11-87. Lines of constant efficiencies show the maximum efficiency. Unstable operation sequence, called surging, occurs when compressors fails to operate in the range left of the surge envelope. It is characterized by noise and wide fluctuations of load on the compressor and the motor. The period of the cycle is usually 2 to 5 s, depending upon the size of the installation. 

Table 18-15 summarizes the several types of commercial centrifuges, their manner of liquid and solids discharge, their unloading speed, and their relative volumetric capacity. When either the liquid or the solids discharge is not continuous, the operation is said to be cycHc. Cyclic or batch centrifuges are often used in continuous processes by providing appropriate upstream and downstream surge capacity. 

Boyce, Meherwan P., et al. Practical Aspects of Centrifugal Compressor Surge, and Surge Control, Proceedings of the 12th Turbomachinery S ni-posium, Purdue University, West Lafayette, IN, 1983, pp. 147-173. 

Brown, Royce N., An Experimental Investigation of a Pneumatic Closcrt Loop Anti-Surge Control for Centrifugal and Axial Flow Compressors Master s Thesis, University of Wisconsin, Madison, Wisconsin, 1966,... 

The dynamic compressors, axial and centrifugal, exhibit one other non-steady force, which is often questioned by foundation designers. This is the torque reaction force at the casing feet and, thus, the foundation due to surge. As a rule of thumb, a value of A the maximum steady-state torque reaction at the casing feet can be used. The frequency is the surge frequency, which is less than operating speed but not readily predictable, because it is heavily dependent on the connected system. 

PR valve capacity should be equal to the compressor capacity at the emergency conditions. For centrifugal compressors, the combination of PR valve set point and relieving capacity should be such as to avoid surge conditions over... 

Figure 10-14. Typical centrifugal compressor curve showing surge.

Figure 12-61D. Centrifugal compressor surge control schematic diagram shows instrumentation required when primary flow-measuring device is located in centrifugal compressor discharge line. Symbols T = temperature P = pressure A = differential across compressor outlet to inlet. See Reference 89 for a detailed discussion. (Used by permission White, M. H. Chemical Engineering, p. 54, Dec. 25,1972. McGraw-Hill, Inc. All rights reserved.)...

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