Question

A combined gas-steam power plant uses a simple gas turbine for the topping cycle and a simple Rankine cycle for the bottoming cycle. Atmospheric air enters the compressor at 101 kPa and 20 °C, and the maximum gas cycle temperature is 1100 °C. The
compressor pressure ratio is 8. The gas stream leaves the heat exchanger at the saturation temperature of the steam flowing through the heat exchanger. Steam enters the heat exchanger at a pressure of 6 MPa and leaves at 320 °C. The condenser in the steam cycle operates at 20 kPa. By using cold air-standard assumptions, determine
(a) the mass flow rate of air through the compressor required for this system to
produce 100 MW of power,
(b) the mass flow rate of steam through the heat exchanger,
(c) the mass flow rate of cooling water through the condenser,
(d) thermal efficiency of the combined cycle. (35%)

00 Combustion chan be 7 GAS CYCLE Compressor Gas turbine Air Heat exchanger 8 9 Exhaust gases w w 2 3 STEAM CYCLE Pump Stcam turbine Condenser Oost

If the cooling water (cp = 4180 J/kg·ºC) from the above problem is to be provided evenly by 10 cooling towers. Humid air enters each tower at 1 atm, 15 ºC and 20% relative humidity, and leaves at 20 ºC and 0.014 kg of water/kg of dry air. Determine the required volume flow rate of air through each cooling tower.

Answer 1

combined cycle 7 T-s W op 5 Given data ja s cycle :- 15 20°c, P = lot kPa 11оос, Стр) Т? () (-) То (7) T5 І. 530 75 к | | (-) т. Та от А) (тр) E 18 К% 158 k Tsat — Ta Обоо) ЕРО 548:6 Е.

At P = 20 kpa 251-42 h, = he kJ/kg 0.001017 milkg Vi - f Wp = Ve [P2-P,] wp نا 0.001017 [ 6000 - 20) = خبر) 6.08 kJ/kg P 257.5 hitop. h2= kulkg 320°C AL P= 6000 kpa, kpa, T = h₂= 2953-5 kJ/kg 6.187 kilig-k as S = 3 At P = 20 kpa, kJ/kg ha 2035.8 Gas cycle = > Cp CT-T8] w Turbine 1.005 ( 1373- 758] 619.075 KJ /kg. Woorb

compressoo work Wc cp[To-T5] 1.005 ( 530.75- 293] kJ 1 kg Wc 238.93 379.14 kJ w w wc - T kg Net gaş steam cycle 6.08 we KI kg - wi ha - h4 917.7 kJ lkg 911-62 kulkg w Whet ste om in heat heat exchger balonce 7 Energy mxcp [Tg-Tq J = mx Cha-ha] 1.005 [ 758 - 54806] mia X mg [2953-5- 257.5) ms 0.07805 ma That is Ikg of exhaust gases kg of can heat only 0 0 7805 water

Net) Net ( 1x wret) + (0-07805* w gas steom mo xwo تی Net Net Net wNet a no whet 3 KJls 100 x 10 moi (Ix 379.14) + (0.07805*911-62) KJ kg air mass flow rate of air -) (a) mia 222.07 kgls. . (b) mass flow rate flow rate of sleom 17. . 33 mis kgls in condensed balonce (c) Energy mg { by hq ] = max ex ot 17:33(2035.8-251-42] miw 4.18% (20-15) miw = 1479.58 kg's.

(d) Heat addition Qen m. [Cp] [ Tz -To] air Qin 222:07 x 1.005 [1373- 530-75] Qin 187973.64 kW whet with Thermal effociency Qin 53.19 % wth