Handbook of Electrical Engineering

GAS TURBINE DRIVEN GENERATORS 35

2.2.5 Heat rate and fuel consumption

The heat rate is the ratio of heat given up by the fuel, in terms of its lower calorific or heating value
(LHV), to the power available at the gas turbine coupling to its generator. It has the SI units of
kJ/kWh. The lower heating value of typical fuels is given in Table 2.3.

The heat rate for a particular gas turbine will be given by its manufacturer at ISO conditions,
and at various ambient temperatures. The typical variation of heat rate and power output, in relation to
their ISO values, are shown in Figure 2.10. For a definition of ISO conditions see sub-section 2.3.2.

Table 2.3. Lower heating values of fuels

Fuel Lower heating value (LHV)

MJ/m^3 for gases

MJ/kg for liquids

Btu/ft^3 for gases

Btu/lb for liquids

GASES

Natural gas 35.40 to 39.12 950 to 1050

Methane 33.94 911

Ethane 60.77 1,631

Propane 87.67 2,353

Butane 115.54 3,101

Hydrogen 10.17 273

Hydrogen sulphide 23.14 621

LIQUIDS

Diesel oil 45.36 19,500

Kerosene 41.87 18,000

Distillate 44.89 19,300

Crude oil 44.66 19,200

Figure 2.10 Power output and heat rate versus ambient air temperature.