In general, compressors for plants are driven by steam turbines, which convert steam energy to rotational energy by means of rotor blades. Unlike the turbines used for power generation, which rotate at a constant speed, these turbines can be operated at variable speeds.
Steam Turbines are well suited as a prime mover for driving boiler feedback pumps, forced or induced-draft fans, blowers, air compressors, and other rotating equipment. This service generally goes with the back-pressure noncondensing steam turbines. The low-pressure steam turbine exhaust is available for Feedwater heating, preheating of deaerator makeup water, and/or process requirements. In operations where it is possible to reduce the steam pressure to a lower level, it may be advantageous to run the turbine in basic operation, thereby reducing the power consumption.
Drive Steam Turbines are equipped with throttling valves or nozzle governors to balance steam flow and achieve variable speed operation. Thus, the steam turbine is very much capable just like serving the same function as an induction motor coupled to an inverter or adjustable speed drive. Drive Steam Turbine does not fail when overloaded and can operate over a wide speed range. They also give high starting torque required for constant torque loads such as positive displacement pumps.
Steam Turbines are inherently rugged and reliable low-maintenance devices. They are easy to control and offer enclosed, non-sparking operations suitable for use in explosive atmospheres or highly corrosive environments. Steam turbine drives may be installed for continuous duty under severe operating conditions, or used for load shaping (eg. Demand limiting) , standby, or emergency service. Steam turbines provide fast, reliable starting capability and are particularly adaptable for direct connection to equipment that rotates at high speed.
Equipment redundancy and improved reliability can be obtained by mounting a steam turbine drive and electric motor on opposite ends of the driven-equipment shaft. You can then select either motor or turbine as the prime mover by increasing or decreasing the turbine speed relative to the synchronous speed of the motor.

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