Question

Steam enters the turbine of a power plant operating on the Rankine cycle at 3300 kPa and exhausts at 50 kPa. To show the effect of superheating on the performance of the cycle, calculate the thermal efficiency of the cycle and the quality of the exhaust steam from the turbine for turbine-inlet steam temperature of 550°C. The Rankine cycle is shown in the following figure: The thermal efficiency of the cycle is O The quality of the exhaust steam is O . .

Answer 1

Initial pressure of steam 3300 kPa Exhaust pressure = 50 kPa There will be saturated liquid at soklat at the outlet from the turbine, from steam table for saturated steam atsokke P = 50 kPa H4 = 340.564 ks/ng Ve 1.030 unity Enthalpy of vapour at sokra= 2646-0 hy/ Entropy of Vapour at 30kPa = 7.5947 ks/nak Entropy of liquid at 30 kPa = 1-0912 ks/gk

T= 550° Wpump a V4 P4 P.) 31-030 cm x com x10004 3300kPa-sokea) CU = 3-34 Euthalpy at boiler, H, = Hut Wpump = 340.564 kJ 13:348 KI kg ? 343.911 kufreg From steam table for T:ssooc e Pu: 3300kPa - H₂2 3565-3 ks/Rg Sa = 7.3282 ks/agk o Step 2-3 is iso entropic Quality of exhaust steam, X = 7.3282 - 1.0912 - 7.5947 - 1.0912 = 0.989

Enthalpy of state - 3 Hg = Hig t X3 (Hump-Hig) = 340.564 +0.959 (2646.0 - 340.564) = 2551.48 kJ/kg turbine = H₂ Ha = 2551.48 kJ/29 - 3565.3 ks/pg a - 1013.82 kJ/ko Qu = H₂ Hi = 3565.3 kJ/kg - 343-911 kJ/kg = 3221.389 kJ/Rq kilpg Efficiency, n = Wrarbine t W pump QH = -1013.82 k5/hey + 3:348 kJ/kg 3221.389 kilka 0-314

Thermal efficiency of cycle = 0.314

Quality of exhaust steam = 0.959