Question

A combined cycle power plant consists of two gas turbines; cach produces a net power of 160 MW, and a 70 MW steam power cycle. The combustion of the fuel in the combustion chamber produces hot gases at 1400°C. The hot gases leaving the gas turbines are used to generate steam through the heat recovery steam generator (Boiler). The hot gases enter the heat recovery steam generator at 880°C and leaves at 660°C. Water enters the isentropic pump as saturated liquid at a pressure of 10 kPa. The pump increases the water pressure to 8 MPa at which it enters the heat recovery steam generator (the boiler). The steam enters the turbine (that has an isentropic efficiency of 90 % ) at a temperature of 400 c. The steam then enters the condenser through which latent heat is lost to circulating water from a nearby reservoir that enters at 20°C and leaves at 30°C. Assume no pressure losses occur through the heat recovery steam gencrator and the condenser. Also, hot gases can be treated as air. Take the ambient temperature as 20°C. Determine the following: The specific enthalpy of the steam between the 4 elements of the steam cycle. The specific entropy of the steam before and after the condenser The mass flow rate of the steam in the steam cycle. The rate of heat transfer between the hot gases and the water in the heat recovery steam generator. The mass flow rate of the hot gases through the heat recovery steam generator The rate of heat transfer between the steam and the circulating cooling water in the condenser The power consumed by the pump The steam cycle efficiency (including the heat recovery steam generator) The gas turbines thermal efficiency The plant overall thermal efficiency The second law efficiency of the combined cycle. Boiler Point 3 Point 2 Seam Turbine w W. Pumg Condenser Point Point 4 Q Heat Sisa

Answer 1

CI Soluhon 3 (400c) = 8obar 45.8390 A A0kpa = 0 10 ba9 S1=S S3=Sy a) Spefic Enthalpy o Steam betweon the four Elomun t of tbe Steam.yue 1 0.10bar191-5 Kg Cbetwean condansor &pump) Ch2-hi) xlo (Po-Pe) o.1obar 0.001010x10(80-0.10) 8.06 KT kg. 8-064 191-8- 199.86 KS KS Cbetusaon Aunp & boiles) sup- hgtcps CTBup-3)0 2759.9+2.1C400-295) h3 2980.401319 Cbetwcon Tosbina boile)

C2) S3= Sy 54191-84 0.72x 2392 9 Ssup= Sw by O.1o ba 1914.68 KJ Tsup Cbetwaon TOibine & tondonso1) 673 0 649+xx7-502 S.747 42.11n awe have Isoonhopic Eficieuy 568 LsJTOMIN h3-141 bs-hy O.g0= 2980-h4 29 So-1914.68 202I 21 S 4 Cbetuweon Toibine fiondonso) winth condonsor 4be C2 Specific Entropy o steam before and fte Co1obar S O1Obar TS Su Ts 191.8 ase3+273) 2021 21 (45.83+279) 6.33 LT kg.K Sy CAFt Condani) CBefore condonso) Steam in be eyue plow rate o masi C3) capasity of Ston pouor yue = msCb3-h4) Fox10 2.980.40-2021-21) ms Ms= 72.97 cg

(4) 3) erale of hoat transpor beluooon the hot and the eoaler in the haal rocover sem genoraY Fms Ch3-br) =72.97 (2g 80.40 -199 202-89 mu 202.89 mw. flow rate of hot gaty through Steam generator the hoal rocoveny heat gained by steam (water) heal Lost by ga 202.89x1o 202.89xo X1-005 ( 680-660) $16309-416 and tbe 6 The Tae of hoat transfer betwoon the Steam Circulating cooling oorter in tbe condonsor ms Cnyhi) 72-93 (2021-21-191 8) 133.49 nw

(a) poun (8) Consomad by be pump Tmς Cb -hι) (90 8)t6-71 = WP Stam cyue Efffciuny s-R 202.09-133 41 = 34.20-1 202-89