Motor-driven compressor, pressure

The motor-driven compressor boosts the pressure of the refrigerant vapors from the evaporator pressure, up to the condenser pressure. 

Motor-driven, multistage reciprocating compressors have reportedly been the most popular choice for aeroderivatives. Motor-driven, oil-fiooded screw compressors are also used in some cases. High horsepower, multistage centrifugal compressors, similar to those used at many pipeline compressor stations, may be required for the newer heavy-duty units if the distribution pipeline pressure is insufficient (see Pipelines). Gas turbines have more stringent fuel-gas specifications in terms of cleanliness than do gas-fired boilers. Thus oil- and water-knockout systems, coalescing filters, and fine-mesh filters are used. 

On a typical pipeline, compressor stations are located at 81—161-km intervals and may contain up to 15 compressors. These stations may use either gas-turbine, reciprocating-engine, and/or motor-driven centrifugal compressors capable of boosting pipeline pressure and keeping gas moving at an average speed of about 24 km/h. Gas-turbine-driven units are the most popular. 

Throughout our discussion of motor-driven, constant-speed centrifugal compressors, I have assumed that the suction temperature was constant. But let s refer back to Fig. 28.1. Assume that the temperature in the drum increases. How will this affect the pressure in the drum ... 

It is easier to carry than other portable artificial heart systems. It combines two traditional methods to drive pump air-driven and electric motor-driven. The motor-driven actuator generates air pressure necessary to pump blood without any additional air compressor or vacuum pump. 

This story only makes engineering sense when one knows that both the motor and compressor were constant-speed machines. For motor-driven centrifugal compressors that are oversized for a particular service, throttling the compressor suction is the most energy-efficient method to control the discharge pressure. 

Frequently, a major unit shuts down when a compressor trips off. The cause may be low lube- or seal-oil pressure. The pumps providing the lube- and seal-oil pressure are typically spared (backed up). A steam turbine-driven pump is normally backed up by a motor-driven spare. The motor-driven pump should come on when the lube-oil pressure drops below a preset point. 

Low-pressure feed heater, the deaerator and the high-pressure feed heaters Three main feedwater pumps Two start-up feedwater pumps Switchgear rooms Electrical equipment room Lube oil storage tanks Motor-driven fire pumps Air compressors... 

In RELAP5-3D, the compressor model is similar to the pump model. It performs the same function on a gas as the pump performs on fluids. It can be driven by a shaft or use the other capabilities available to a pump (speed table, motor torque table and/or the coastdown feature). The homologous head and torque curves required for a pump are replaced with compressor pressure ratio and efficiency appropriate for the compressor as a function of mass flow rate for up to 99 different shaft speeds. The compressor component consists of an inlet junction, a single volume and optionally an exit junction. Similar to TRACE, the turbine component in RELAP5-3D extracts momentum and energy. 

A compressor driven by a J h.p. electric motor and giving a pressure above atmospheric of 10 Ib/in. is adequate for all normal glassworking operations, including those with a small lathe (Chapter 6). A filter should be fitted on the suction side of the compressor. 

The three main compressor types are rotary, reciprocating, and centrifugal. The compressor drives can be constant or variable speed, and can be driven by electric motors, steam turbines, gas turbines, gasoline, or diesel engine drives. For a particular application, the type of compressor is selected by considering the required capacity and discharge pressure. 

Because high pressure reactant flows are concentrated over the area of the catalyst gauze, there are more layers of gauze required to permit sufficient contact time for the reactant molecules on the catalytic surface. Typically, the air is compressed by a centrifugal compressor, either operated by a turbine driven by tail gases augmented by steam or by a compressor driven by an electric motor. 

To make up the difference between the expected expander returned power and the required compressor input power. Meruit designed an air system using a commercially available positive-displacement compressor driven by an electric motor in tandem with Meruit s turbocompressor. Meruit designed a family of compressor and expander wheels with var5dng characteristics (specific speed, dimensional ratios, etc.) representing different compromises in providing performance compatible with the DOE specifications. After extensive evaluation, a compressor wheel was chosen to provide a desired pressure curve over a wide range of mass flows, and a turbine wheel was matched to it. The chosen compressor wheel is intended to trade peak efficiency for extended turndown performance. 

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