Steam injection turbine plants

A commercial combustion turbine with the provision to inject, at any point upstream of the combustor, the externally supplied humidified and preheated supplementary compressed air. Engineering and mechanical aspects of the air injection for the compressed air injection plant concepts are similar to the steam injection for the power augmentation, which has accumulated significant operating experience. 

The code provides for the testing of gas turbines supplied with gaseous or liquid fuels (or solid fuels converted to liquid or gas prior to entrance to the gas turbine). Test of gas turbines with water or steam injection for emission control and/or power augmentation are included. The tests can be applied to gas turbines in combined-cycle power plants or with other heat recovery systems. 

The turbine temperature, flow, and speed increases in a very short time of about three to five minutes to the full rated parameters. There is usually a short period of time where the temperature may overshoot. If supplementary firing or steam injection for power augmentation is part of the plant system, these should be turned on only after the gas turbine has reached full flow. The injection of steam for power augmentation, if done before full load, could cause the gas turbine compressor to surge. 

Fig. 6.1a shows diagrammatically the steam injection gas turbine (STIG) plant steam. raised in a heat recovery steam generator (HRSG) downstream of the turbine, is injected into the combustion chamber or into the turbine nozzle guide vanes. 

A Comparison of Steam-Injected Gas Turbine and Combined-Cycle Power Plants Technology Assessment. Palo Alto, California Electric Power Research Institute, June 30, 1989. GS-6415s. 

As of the mid-1990s, many older conventional steam plants have been converted to combined cycle. The old boiler is removed and replaced by a combustion turbine and heat recovery steam generator. Although the cycle efficiency is not as high as completely new plants, substantial capital cost is avoided by the modification and reuse of existing steam turbine and auxiHary equipment. In many combined cycle power plants, steam is injected into the combustors of the combustion turbine to lower peak flame temperatures and consequendy lower NO. ... 

Lloyd argues that for a plant with fixed pressure ratio and top temperature, the turbine work output (and hence the net work output) is increased linearly with the. steam quantity 5 that is injected, but the (2n and Qa terms increase more slowly. Thus, the efficiency similarly increases with S. but also more slowly. 

Consider next a recuperative STIG plant (Fig. 6.5, again after Lloyd [2]). Heat is again recovered from the gas turbine exhaust but firstly in a recuperator to heat the compressed air, to state 2A before combustion and secondly in an HRSG, to raise steam S for injection into the combustion chamber. 

Dry steam power plants The geothermal steam goes directly to a turbine, where it expands and produces power. The expanded steam is injected into the geothermal well. This was first done at Lardarello in Italy in 1904. The world s largest geothermal power is at The Geysers in northern California. 

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