Expander/blower train

The expander train supplier shall assist with the selection of the expander inlet and bypass valve configurations and closure rates by performing an open loop dynamic simulation study. For a main air blower train dais could be closed loop. 

A power recovery train—occasionally called a string—(Figure 4-53) employing a turboexpander usually consists of four main elements or casings the expander, a motor-generator, an air blower, and a steam turbine. The steam turbine is used primarily for startup and often to supplement the expander for generation of energy. This topic will be discussed in more detail later in this chapter. 

The motor-generator ean either produee or absorb power. In some FCC units, the expander horsepower exeeeds the power needed to drive the air blower. In this ease, the exeess power is transmitted to the refinery power grid. If the expander generates less power than required by the blower, the motor-generator provides the power to hold the entire train at the desired speed. 

The second step in developing the process air train is selecting the air blower main driver. This step includes many alternatives such as power recovery expanders, steam turbines, and electric motors. The following example illustrates these alternatives. 

For Main Air Blower serviee without a steam turbine in the string, the unit shall be started by first applying windage steam and then aeeelerating the train to rated speed using the eleetrie motor. After aehieving stable rated speed, the expander inlet valve will be... 

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