A calculation based on enthalpy so as to attemperate steam to a turbine. The calculation has the following formula which I can´t understand.
Flow = m x(Enthalpy (HPT)- Enthalpy (CRH) /Enthalpy (CRH) - 764.8) kg/s
Enthalpy (HPT) = High pressure turbine. Enthalpy calculated from presssure and temperature before HP turbine
Enthalpy (CRH) = Enthalpy calculated from pressure and temperature before reheater, to where the HP steam is bypassed.
m = mass flow according to Steam valve opening, using pressure and temperature before Bellow Seal valve.
(Enthalpy (HPT)- Enthalpy (CRH) /Enthalpy (CRH) - 764.8)?
You have stream IN with enthalpy equal to enthalpy (HPT).
You have stream OUT with enthalpy equal to enthalpy (CRH)
The value 764.8, I presume expressed in kJ/kg, should be the specific water enthalpy at saturation pressure (9.08 barg) or saturation temperature (180.344 °C) before reheater. What works here is the enthalpy of evaporation, which is the difference between the specific enthalpy of steam and the specific enthalpy of water.Just rearrange the terms and end up with the first law  balance across the spray station:(Whpt+Ws)*Hcrh = Whpt*Hhpt+Ws*Hs,where Hs= spray water enthalpy

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