Handbook of Electrical Engineering

36 HANDBOOK OF ELECTRICAL ENGINEERING

Figure 2.11 Heat rate and efficiency versus power rating.

The reduction in output power is typically 0.5 to 0.8%/◦C.

The fuel consumption can be calculated approximately from,

Fuel consumption=

Power output×Heat rate

Fuel LHV

m^3 /h(or kg/h)

For situations where there is a mixture of gases it is advisable to consult the manufacturer
of the gas turbine, since he will have a data bank containing all kinds of fuel compositions and
heating values.

The heat rate and overall thermal efficiencies for typical modern gas turbines in the range
of ISO power ratings 1 MW to 200 MW are shown in Figure 2.11. The data were derived from
Reference 6.

2.3 Power Output from a Gas Turbine

In sub-section 2.2 the performance of a gas turbine was determined as the energy obtainable at the
output shaft coupling. The energy equations are based on a unit of mass flow, 1.0 kg/s, of the fluid
passing through the gas turbine i.e. from the air intake to the exhaust aperture.

The mass flow through the turbine is about 1% higher than that through the compressor because
of the presence of the burnt fuel. Hence the mass flow rate (m) to produce the output power is,

m=

Output power to the generator

Output energy per unit mass

kg/s

=

Wout

Uout

(

kW kg

kj

=kg/s

)