Performance Improvement of Power Plant at Aberrant Steam Temperature Condition through E3 Analysis

Abstract

Energy efficient and environment friendly power generation is the primary goal for any power generating industries. This paper proposes a thermodynamic approach based on E³ (energy, exergy and environment) analysis for performance improvement of power plant during low main steam and high reheater (RH) temperature conditions through a suitable operation technique. Thermodynamic modeling of a 500 MW Subcritical (SubC) coal based thermal power plant is carried in “Cycle-Tempo” at different conditions. Partial withdrawl of final feed water heater (high pressure heater—HPH-6) from service without RH spray condition during low main steam (MS) temperature and high RH steam temperature condition will help to increase the MS temperature by about 0.85–1.00°C and thereby, the net plant energy and exergy efficiency will be improved by about 0.09 and 0.08% point, respectively. Partial withdrawl of HPH-6 with RH spray condition will deteriorate the plant energetic and exergetic plant performance and this will guide the operation engineer for which extend withdrawl of HPH-6 can be done for getting higher plant performance. The net energy efficiency of turbogenerator (TG) cycle decreases with partial withdrawl of HPH-6 due to decrease in the feed water temperature by about 7°C and more relative energy rejection of the cycle. The net exergy efficiency of TG cycle increases due to less relative exergy destruction rate causing from improvement in steam quality. However, the use of RH spray increases the irreversiblities in the plant and the spray does not expand in high pressure turbine (HPT) which in turn decrease the exergy efficiency. The boiler energy efficiency increases due to decrease in fluegas exit loss as the fluegas exit temperature drops from about 140 to 133°C due to partial withdrawl of HPH-6. The exergy efficiency of boiler also decreases due to increase in exergy destruction in final super heater (FSH), reheater and economizer. For a 500 MW SubC coal power plant, hourly about 930 kg of coal and about 1183 kg of CO₂ emission can be saved and reduced through this operation technique namely, partial withdrawl of HPH-6 without RH spray condition for controlling low MS temperature. Hence, the proposed analysis will help to take proper operational technique for mitigating coal crisis and safeguarding the environment as well.