Induction steam turbines

Larger steam turbine or bootstrap required Expander and generator part of process Addition of expander requires prior planning Induction M/G decreases power factor Loss of production on loss of generator or expander... 

Direct Material Costs — Major Equipment Motor — Induction Type Steam Turbine Driven Air Blower Motor Driven Air Blower One Stage Expander Driven Air Blower Two Stage Expander Driven Air Blower... 

Steam turbine, 53, 146, 282-92, 179 back pressure, 282 blade deposits, 479 condensing, 282 efficiency, 288 extraction, 282 induction-type, 282 paitial admission, 288 rating, 290 reliability, 478 selecuon variable, 275, 285 speed, 278 stage losses, 286 steam temperatures, 284 steam velocity, 288 trip and throttle valve. 479 Step unloading system, 80 Stiffness coefficients, 385 Stodola slip, 153, 155 Stonewall, 186 Straight labyrinth. seal leakage, 532... 

Figure 23.9d shows an induction turbine. Induction turbines work like extraction machines, except in reverse. Steam at a higher pressure than the exhaust is injected into the turbine to increase the flow part way through the machine and to increase the power production. In a situation like the one shown in Figure 23.9d, an excess of medium-pressure (MP) steam generation over and above that for process heating is used to produce power and exhaust into a low-pressure steam, where there is a demand for the low-pressure steam for process heating. 

Automatic-Extraction-Induction Turbine, Condensing or Noncondensing Steam is extracted from or inducted into one or more stages with means for controUing the pressures of the extrac tiou and/or induc tion steam. 

Sometimes, conventional techniques do not produce a satisfactory steam balance for all operating modes. Options are available for steam drives for flexibility, such as extraction and induction turbines. Extraction turbines are widely used. In these, an intermediate pressure steam is removed or extracted from an intermediate turbine stage with the extraction flow varying as required over preset limits. Induction turbines are not as widely used as extraction turbines, but are a very satisfactory application... 

The driver is a prime mover capable of developing the required torque at a constant speed or over a range of speeds. The driver s energy source can be either electrical or mechanical. Electrical energy is used by motors, either of the induction or synchronous type, while the mechanical covers a multitude of sources. It may be a fuel, as in internal or external combustion engines, or it may be a gas, such as steam or process gas used in a turbine or expander. 

The induction-type turbine is selected when excess steam is available at an intermediate pressure. 

Process steam requirements can be controlled at a suitable pressure and volume required by the process and maintained at these conditions by extraction or induction turbines. 

Any given machine will have minimum and maximum allowable steam flows. In the case of extraction and induction machines, there will be minimum and maximum flows allowable in each turbine section. These minimum and maximum flows are determined by the physical characteristics of individual turbines and specified by the turbine manufacturer. 

Induction generators are simpler and lower in initial cost than synchronous generators. They have been applied to recover power by expanding waste-gas streams and low-pressure steam. In some applications an energy-recovery turbine or expander drives an induction generator-motor and another pump or compressor on the same shaft. The generator-motor can either supply or absorb torque when the power of the other two devices is out of balance. 

A related type of turbine, the so-called mixed-flow or induction turbine, with provision for the use of high-pressure and low-pressure steam in proportion to the available supply, may also be mentioned in this cormection. Generally, the low-pressure steam is expected to carry normal load, and high-pressure steam is admitted only in case of a defldency of low-pressure steam. Even in case of complete failure of the low-pressure supply the turbine may be designed to carry the load with good economy on high-pressure steam alone. 

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