Economic analysis of retrofitting existing gas turbine power plants with cogeneration facility

Cogeneration refers to the generation of combined heat and power (CHP), which is more efficient than a central power plant generating only electricity. The proportion of power generation using CHP is growing world-wide due to efficiency improvements and environmental benefits. Exhaust heat from GT power plants can be fed to boilers for producing steam. Steam is used for reservoir flooding, petrochemical industries, food processing etc. Operational gas turbine power generation plants can be retrofitted to co-generation power plant to produce steam in addition to electrical power. A computational preliminary economic feasibility study of retrofitting a given existing gas turbine power generation plant into a co-generation power plant is presented in this paper. A 80 MW GE-6111FA frame has been selected for the present study. The work includes the effect of relative humidity (RH), ambient air temperature, etc., on economics of the power plant. GTPRO/PEACE software has been used for carrying out the analysis. The RH and temperature have been varied from 30 to 45 % and from 80 to 100° F, respectively. For a decrease of inlet air temperature by 10 °F, net plant output and efficiency have been found to increase by 4.3 and 1.4 %, respectively for GT only situation. However, for GT with cogeneration scenario, for a decrease of inlet air temperature by 10 °F, net plant efficiency has been found to be increased from 33.3 % (GT only) to 63.4 % (cogeneration). For situations with and without cogeneration, break even fuel price has been found to vary from 2.6 to 3.0 USD/MMBTU respectively and break even electricity price have been found to vary from 0.018 to 0.022 USD/kWh respectively. For the simulation conducted, emission has been found to be 344352 ton/year.