The Sugar Engineers

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 = (h_HP - h_LP) / (h_HP - h_LPisen)

where

• h_HP is the specific enthalpy of the steam at the turbine inlet
• h_LP is the specific enthalpy of the steam at the turbine exhaust
• h_LPisen is the specific enthalpy of the steam at turbine exhaust pressure but after isentropic expansion from the HP conditions

We define the ratio

m = η_FL/(1 - η_FL)

where η_FL is the turbine isentropic efficiency at full load

The isentropic efficiency η at load P can be estimated by

η = m·P / (P_R + m·P)

where P_R is the rated turbine power.

The specific enthalpy at the turbine exhaust conditions is then

h_LP = h_HP - η·(h_HP - h_LPisen)

The steam consumption at operating load P is given by

m_s = P / (h_HP - h_LP)