2 Heat recovery steam cycle Text

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COURSE OF ENERGY CONVERSION A 2015/2016 Prof. G. Valenti 2nd Project Analysis of a one-pressure level heat recovery steam cycle Consider a simple cycle gas turbine having the following technical characteristics: - exhaust gases mass flow rate: 657.15 kg/s - exhaust gases temperature: 544.6 °C - electric power at the generator: 235.57 MW - electric efficiency at generator (LHV): 33.82 % Assume a molar mass for the exhaust gases of 28.4 kg/kmol. Moreover, consider the fourth order polynomial coefficients for c0p respectively equal to: c 0p= a0+a1T1+a2T2+a3T3+a4T4 where T is expressed in K and c0p in J/kgK. The aim of the project is to design a heat recovery steam cycle with one evaporation level, whose plant configuration is reported in the figure, which exploits the energy available in the gas turbine exhaust gases in order to produce additional electric energy. The following assumptions apply: Ambient temperature: 15 °C ηad,ST : see below Ambient pressure: 101325 Pa ηaux : 0.96 Maximum steam temperature: 538 °C ηad,pump : 0.8 Condensing pressure: 0.05 bar ηel,ST : 0.985 Deareator pressure: 2.0 bar ηo,ST : 0.995 Maximum steam pressure: 200 bar ηth,steam gen: 0.99 ∆Tpp : 10 °C ηoel,pump : 0.93 ∆Tap : 25 °C ηel,GT : 0.99 ∆Tsc : 10 °C ηo,GT : 0.995 ∆PHRSG : 3000 Pa ηad,GT : 0.925 ∆P/Peconomiser: 10 % As far as the steam turbine isoentropic efficiency (η ad,ST) is concerned, two options shall be considered: a) Constant isoentropic efficiency equal to 0.93 b) Isoentropic efficiency corrected as a function of the outlet steam fraction. The efficiency is constant and equal to 0.93 until the steam fra ction equals 0.98. The subsequent expansion process is characterised by a nominal isoentropic efficiency (0.93) reduced by a percentage point per each percentage point of outlet…