4-E (Energy, Exergy, Environment, and Economic) analysis of solar thermal aided coal-fired power plants

Abstract

Solar aided feedwater heating (SAFWH) appears to be a prospective option for using solar thermal energy in existing or new coal-fired thermal power plants. This article deals with the 4-E (namely energy, exergy, environment, and economic) analysis of solar thermal aided coal-fired power plants to establish their techno-economic viability. An operating coal-fired subcritical (SubC) and the first supercritical (SupC) power plant being commissioned in India are considered as reference power plants for SAFWH. The 4-E analysis is reported assuming operation of coal-fired power plants with SAFWH for 8 h/day in either fuel conservation or power boosting mode. An instantaneous reduction of about 14–19% in coal consumption is observed by substituting turbine bleed streams to all the feedwater heaters including deaerator with SAFWH in “fuel conservation mode”. The substitution of turbine bleed stream to high pressure feedwater heater alone with SAFWH results in about 5–6% instantaneous improvement in coal consumption and additional power generation for the fuel conservation and power boosting modes, respectively compared with the same values in reference power plants. The annual savings in fuel cost alone correspond to Indian Rupee (INR) 73.5–74.5 millions. The performance of solar thermal aided coal-fired power plants is also measured in terms of energy and exergy performance index and it is observed that the utilization of solar energy for feedwater heating is more efficient based on exergy rather than energy. The environmental analysis shows that about 62,000 and 65,000 t of CO 2 are reduced annually from 500 MWe SubC and 660 MWe SupC coal-fired power plants, respectively using the best possible SAFWH option. However, the cost/tonne of CO 2 avoided is about 7775–8885 and 8395–9790 INR (~ 200 USD) for solar thermal aided coal-fired SubC and SupC power plants, respectively far higher than the most mitigation measures under consideration today. Furthermore, SAFWH is found to be a not very cost effective measure based on the cost of saved fuel (coal).