Motor-driven, fixed-speed, centrifugal

Fiqure 41.1 A motor-driven, fixed-speed centrifugal compressor. 

Here is a problem that came up on a sulfur recovery facility in Punto Fijo, Venezuela. The combustion air blower, shown in Fig. 28.8, was a fixed-speed, motor-driven centrifugal machine. The air intake filters were severely fouled. They had a pressure drop of about 8 in H/). The atmospheric vent valve, used to control the discharge pressure at a constant 12 psig, was 50 percent open. The unit engineer had been asked to calculate the incentive in electrical power savings that would result from cleaning the filters. 

Whereas energy can be saved by running steam pumps at a reduced speed, conventional motor-driven centrifugal pumps run at a constant speed. The electricity used by a motor does not depend on the motor horsepower rating but is a function of the head and flow developed by the pump. The pump curve supplied by the vendor (see Fig. 9-1) fixes this relationship for a particular-sized impeller. 

Installation only of a larger control valve, or larger valve trim, will save zero energy regardless of the result of the above calculation. In addition to modification of the control valve, the upstream centrifugal pump must also be modified. Assuming that the pump is driven by a fixed-speed AC motor, the size of the pump s impeller has to be reduced. The smaller impeller plus the larger control valve will result in ... 

Here is a problem that came up on a sulfur recovery facility in Punto Fijo, Venezuela. The combustion air blower, shown in Fig. 35.8, was a fixed-speed, motor-driven centrifugal machine. The air intake filters... 

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