Closed-Cycle Gas Turbine Process with Steam Injection

Besides the combined cycle systems, which consist of a cascade of gas and steam turbines and offer the highest efficiency for thermal electric generation, there is also the principle of steam injection into the gas turbine itself of interest. Steam is generated in a heat recovery steam generator, which is then injected superheated behind the compressor, in other words in front of the combustion chamber, as indicated in the previous section. The steam injected in this way performs additional work without extra loading the compressor. When the steam generation potential of turbine waste heat is used to the full, the output at the generator terminals can be roughly doubled. However, the steam, which is only partly superheated with waste heat in the heat recovery steam generator, must be further superheated to the hot gas temperature using additional fuel in the combustion chamber. Although the additional power achieved by steam injection is around twice as much as in case of a combined cycle plant, but the increase in efficiency is only half as much.