Combustor Gas turbine Air inlet Exhaust -a n on n Heat recovery Steam generator
ID: 2327836 • Letter: C
Question
Combustor Gas turbine Air inlet Exhaust -a n on n Heat recovery Steam generator Turbine Vapor cycle i 11 Condenser Pump I 10 Cooling A combined gas turbine vapor power plant has a net heat rate transfer in combustor, Qin 100 Mw. Air enters the compressor of the gas turbine at 100 kPa, 300K, and is compressed to 1200kpa. The isentropic efficiency of the compressor is 8496. The condition at the inletto the turbine is 1200 kPa, 1400 K. Alr expands through the turbine, which has an isentropic efficiency of 88%, to a pressure of 100kpa. The air then passes through interconnecting heat-recovery steam generator and is finally discharged at 400 K. Steam enters the turbine of the vapor power cycle at 8 Mpa, 400 °C, and expands to condenser pressure of 8 kPa. Water enters the pump as saturated liquid at 8 kParThe turbine and pump of the vapor cycle have isentropic efficiency of 90 and 80% respectively. (a) Determine the mass flowrates of air and the team, each in kg/s the net power developed by gas turbine and vapor power cycle, each in MW; and thermal efficiency. (b) For gas turbine only, using the same conditions and discharging combustion products at state 4, determine the mass flow rate of air in kg/s; the net power developed by gas turbine in Mw; and thermal efficiency.Explanation / Answer
solution:
1)here for brayton cycle following ags turbine powerplant we have as following for compresor
T2/T1=(P2/P1)^(k-1/k)
k=1.4
here we get that
t2=610.18 K
but efficiency relation for compressor
nc=T2-T1/T2'-t1
T2'=669.26 k
where for turbine it is given by
T3/T4=(P3/P4)^.4/1.4
T4=688.32 k
where from efficiency we write
nt=T3-T4'/T3-T4
T4'=773.72 k
where for combustor
Qs'=ma'Cp(T3-T2')
ma'=136.1673 kg/s
2)where for combined cycle
T5=400 K
hence heat rejected is
Qr=ma'Cp(T4'-T5)
Qr=51143.10 kw
for vapor steam power plant
Pb=80 bar
Pc=.08 bar
where for saturation at Pc=.08 bar
T9=314.53 k
h9f=173.9 kj/kg
where pump work=wp=Pb-Pc/10*.8=h9-h6=9.99 kj/kg
h6=183.99 kj/kg and temperature as T6=315.2 k
here for combustor
Qr=mw*Cpw(T7-T6)
51143.10=mw*4.5737*(673-315.2) at mean temp cp=4.5737
mw'=31.25 kg/s
where pump work
Wp=mw*wp=312.20kw
here T7=673 k
h7=3138.89 kj/kg
and sf7=6.3604=sf8=.593+x(7.637)
x=.7558
h8=173.9+x(2403.2)
h8=1990.23 kj/kg
here turbine work=mw(h7-h8)=wt2
wt2=32305.78 kw
net power=wt2-Wp=31993.58 kw
4)here for turbine cycle
wt=maCp(T3-T4')=85705.25 kw
wc=mcp(T2'-T1) =50532.54 kw
net power in gas turbine cycle=wt-wc=35172.70 kw
6)net power=wt2+wt=31993.58+35172.70=67166.28 kw
Qs=100000 kw
efficiency=wt/Qs=.6716 =67.16% for combined cycle with regeneration
5)for alone vapor power plant where Qs=Qr=100000kw
Qr=mw'*Cpw(T7-T6)
same condition flow rate would be
mw'=61.10 kg/s
here then pump work=610.46 kw
wt=70183.126 kw
hence net power=69572.60kw
and efficiency=wn/Qs=69572.66/100000=.6957