Comprehensive evaluation of a CO2‐capturing NOx‐free repowering system with utilization of middle‐pressure steam in a thermal power plant

Abstract A CO2‐capturing NOx‐free H2O turbine power generation system is proposed in which middle‐pressure steam produced in a thermal power plant is utilized to increase generated power when demand for electricity is large. The proposed system can capture all the generated CO2 based on the oxygen combustion method and emits no NOx, so that it causes no urban or global environmental problems. A combined cycle power generation system with 200 MW gas turbine power output is adopted as an example of a thermal power plant. It was assumed that 32 t/h of steam with 25kg/cm2 pressure produced by the waste heat recovery boiler was utilized in the proposed system. It has been shown through simulation study that increase of power output by 11.8 MW or 4.51% of the rated output is possible with no efficiency decrease. The amount of CO2 emission reduction is estimated to be 19,600 t/y. The unit cost of generated power is estimated to be 8.38 yen/kWh, annual gross profit of the proposed system 271 million yen, depreciation year 4.87, and thus the proposed system is estimated to be economically feasible. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(4): 34–40, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10356