Expander-generator

It is advantageous to have the expander generate its refrigeration at the lowest possible temperature in the process (see Fig. 29-45), and this frequently encounters the condensation temperature of the pi ocess stream. Steam-turbine pracrice advises against operating on... 

Expander-Generator Manufacturer Rotoflow Corporation Inc.. Los Angeles. C4. 

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. 

Load sharing or selective load shedding is of interest to many users of hot gas expanders. A particularly successful European FCC application is illustrated in Figure 6-43. The addition of an expander-generator set to the FCC unit at a major refinery presented a challenge because a trip of the expander could upset the process. The company that is the subject of this application case study, GHH Borsig, solved this problem with the installation of a computerized control system and through computer simulation of trips. 

A speed controller synchronizes the expander/generator with the electricity supply grid, and actuates the inlet trip valve to its fully open position. 

Most ethylene plants operate continuously with the expander functioning at or near design point. However, by using inlet guide vanes, the expander can still provide optimum performance at off-design conditions. Also, the expansion process generates power, which is used by the compressor. The ethylene enters the expanders at approximately 26 bar (377 psia) and exits at approximately 6 bar (87 psia). The expanders generate over 2,000 hp for gas compression. 

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