Performance of water/steam injected gas turbine power plants consisting of standard gas turbines and turbo expanders

The present study was done to investigate the performance differences in terms of thermal efficiency and specific power output of: combined cycle power plants with integration of low temperature regenerative heat, standard gas turbines operated in wet cycle mode, turbo expanders and steam turbines (here: alternatives); combined cycle power plants with integration of low temperature regenerative heat, wet cycle adjusted gas turbines and steam turbines (here: basic power plants or basic cycles); standard combined cycles. The term "adjusted" means that the blading of either the compressor or the turbine of a standard gas turbine was modified to accommodate the mass flow difference between the two. The analysis shows that in terms of thermal efficiency the alternatives are equal to or better by about 5%-points than the basic power plants. On the other hand, the corresponding specific outputs are lower by about 25 to 30%. But the gas turbines of the alternatives are the existing standard designs (see above) and, therefore, less expensive. Comparing the alternatives with the standard combined cycles, it is observed that the alternatives have a thermal efficiency advantage of up to 20%-points and a specific output advantage of up to 50%. Both of them are due to the integration of low temperature regenerative heat by injection of hot water into the alternative cycles and the definition of the thermal efficiency as based on the fuel burnt.