Not to argue, but the design conditions appear to be with some condensation. And the operating data suggests that the exhaust is somewhat superheated.
That is right, but I took that into account.
To calculate the turbine efficiency one needs a detailed steam table and a Mollier diagram.
The design data are theoretical (calculated) data, so those data must be consistent, unless Sakthi made a typing error above.
Design case:
Steam flow rate = 11.7 mt/h = 3.25 kg/s
Steam enthalpy at 320 oC & 35 barg is 3027 kJ/kg
Steam entropy at 320 oC & 35 barg is 6.52 kJ/kg.K
Water enthalpy at 45.5 oC & 0.10 bara is 188 kJ/kg
Isentropic expansion down to 0.10 bara would result in a mixed phase with an enthalpy of 2065 kJ/kg (and an entropy of 6.52 kJ/kg.K)
Design condenser duty can be calculated from the chilling water data:
Q = (550/3.6) kg/s * 4.19 kJ/kg.K * (39 - 27)K = 7682 kW
So the enthalpy drop of the turbine exhaust over the condenser is: 7682 kW / 3.25 kg/s = 2364 kJ/kg
and the enthalpy of the turbine exhaust must be: 188 + 2364 = 2552 kJ/kg (mixed phase)
Therefor, in the design case the (isentropic) efficiency of the turbine must be:
(3027 - 2552) / (3027 - 2065) = 0.49 = 49 %
Design turbine power (excluding bearing losses) must be:
3.25 kg/s * (3027 - 2552) kJ/kg = 1544 kW
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Actual 2015 Operation:
Steam flow rate = 14.8 mt/h = 4.11 kg/s
Steam enthalpy at 343 oC & 36 barg is 3082 kJ/kg
Steam entropy at 343 oC & 36 barg is 6.60 kJ/kg.K
Isentropic expansion down to 0.42 bara would result in a mixed phase with an enthalpy of 2270 kJ/kg (and an entropy of 6.60 kJ/kg.K)
Real expansion is to 83 oC at 0.42 bara, so turbine exhaust enthalpy is 2650 kJ/kg (this is steam only, as it is above the dewpoint of 77 oC at 0.42 bara).
Therefor, in actual operation the (isentropic) efficiency of the turbine must be:
(3082 - 2650) / (3082 - 2270) = 0.53 = 53 %
Actual turbine power (excluding bearing losses) must be:
4.11 kg/s * (3082 - 2650) kJ/kg = 1776 kW
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The turbine is not the cause of the high exhaust pressure. If there is no air leakage, as Sakthi seems to be convinced of, then the condenser must be the problem.
Note also that the 27 % higher-than-design steam consumption in actual operation is not only caused by the higher-than-design exhaust pressure, but also by the 15 % higher-than-design turbine power. Assuming of course that the steam flow measurement of 14.8 mt/h is correct.