# Turbine Steam Consumption Calculations

The usual way of representing the steam consumption of a turbine is the willans line, for example... Often, a willans line for a specific turbine is not available, and one only has has incomplete information about an installed steam turbine; namely the rated power and (perhaps a guesstimate) the isentropic efficency or specific steam consumption at full load. But what you need and don't have is the steam consumption at the turbine operating load.

## Background Information

Isentropic efficiency η by definition is given by

η = (hHP - hLP) / (hHP - hLPisen)

where

• hHP is the specific enthalpy of the steam at the turbine inlet
• hLP is the specific enthalpy of the steam at the turbine exhaust
• hLPisen is the specific enthalpy of the steam at turbine exhaust pressure but after isentropic expansion from the HP conditions

We define the ratio

m = ηFL/(1 - ηFL)

where ηFL is the turbine isentropic efficiency at full load

The isentropic efficiency η at load P can be estimated by

η = m·P / (PR + m·P)

where PR is the rated turbine power.

The specific enthalpy at the turbine exhaust conditions is then

hLP = hHP - η·(hHP - hLPisen)

The steam consumption at operating load P is given by

ms = P / (hHP - hLP)

Do these calculations online