Question

Question A.1 A schematic of a gas turbine combined cycle generating plant is shown in Figure A1.1 on the next page. Exhaust gas from the gas turbine generator pass througha heat recovery steam generator (HRSG) which generates steam to drive a steam turbine generator. The following data is provided for the plant: Gas turbine 18.9:1 Pressure ratio Compressor air inlet temperature Turbine inlet temperature 15°C t 273 288 1350°C +273- 1623 588 kg/s T, T3 Exhaust gas mass flow Isentropic efficiency of compressor Isentropic efficiency of gas turbine 90% 90% HRSG 120°C Exhaust gas outlet temperature Ts Steam outlet temperature 500°C Steam outlet pressure Condenser pressure 50 bar 0.1 bar Steam turbine isentropic efficiency 80% Take Cp and y for the combustion gasses to be 1.11 kJ/kg.K and 1.33 respectively. Take Cp and y for air to be 1.005 kJ/kg.K and 1.4 respectively. For the plant, determine: The gas turbine power output. The gas turbine cycle efficiency. The steam mass flow and draw an annotated sketch of the HRSG indicating the energy flow. [16 marks] [4 marks] i. [9 marks] [9 marks] [4 marks] Breifly discuss what modifications could be made to the steam plant design to increase the power The steam turbine power output. iv. The overall efficiency of the combined cycle. V vi. output. Explain what characteristic of the gas turbine exhaust make this modification possible. [8 marks]

Answer 1

:0 Drant nninlr raL.In Solution.- T3=1623 K combustoi 161.8.35 2 goof. I So TOYbine Compreuor Wout 1 4 Ti-288 K Ts-120c S 393k T7-SOOC P= Sobar Tuibine 8 = Ostl Ph-S0bor 6 Pc= 0-lbor Conden sor Combinad gas-Sleam Powor Plant

Galculation ol enholpy al diffr poinls h Gpax T-1.005X288 = 2.89.44 K coe nave K.9 i) 1 D0SX6 29.0S 632 h3-CpgxT3 1.RX 16 2.3=1801-53 from cii) (금) (음)부 ()-G IxT# 14-1 2-88 hy111x866.73 T= 666.95k XTSI11 X 393 But we have Is0ontopic 타fueney 아 comp. 436.23 KT 11 Adual T ISo leam power plant at point 7 0.90=T-288 66695-288 PE SUba T- S0 O'c Ts-a 63.90 Steam is Supo haated 629.05 ng+cps (Tup T)sober uoe have b7 2794-2 +d1 (soo-263 .9) 1-3290 ET (품)- C18-9) 133-1 1623 T4 Ty-782-71 But T3 -Ty T3-Ty T 866-1 0-90

Enthalry at 8 et Assome iti wer Sw Ssup= e, o.1bor O. 50b이 bw191-8 +6-812x23 92-9) bw =2134-83 S.974+a1 n/S00t273-0 649 +ax 263+273 ㅋ.502 C 2- 0.812- But we have 1s00nropic ASsomption Is nght effices grureine =0.80 84-E녀 3230-hg =0.80 3290-2134 &3 hel 2365.86 KT hg = he e 0lbar ha = 191.8 Considenng pump w Ch6-19)- x CSo-01)A1Co1be 9-44- 0.000050-01)x1o2 h6-h9= 5.039 FJla h6-196.83 K

bine pouor out put Ch3hy- C180153-362-07-63220 20944 496.70 C Amount of fual pplied in the ga eohora macpa = mgcpa bina cye Efficioy Chg-hJ-b- 496.70 18053-632-20 42.47 1

he cleam mau how teat gained b slom-haal tott by gas n HE mg.cpg -S)s cha-hi) 586.x1.11 (86673-393) ms (3290-196 3) OS=99.8881 Steam Tuibine pouso ou put [ch1-he)-Cheha -2365 84) -5039 =M 2-a61e)] p566 Ws 91.78 Mu