Gas turbine unit for combined production of electricity and heat and method for operating such unit

Claim 1

Method in operating a gas turbine unit for combined production of electricity and heat comprising a combustion chamber (16), a high pressure turbine (10) driven by gas from the combustion chamber, a low pressure turbine (13) driven by the exhaust gas from the high pressure turbine, a low pressure compressor (14) driven by the low pressure turbine, a high pressure compressor (11) connected in series with the low pressure compressor and driven by the high pressure turbine for the supply of pressurized air to the combustion chamber, a generator (12) driven by the high pressure turbine for producing electricity, a recuperator (18) for heat exchange between exhaust gas and pressurized air from the compressors, an intermediate cooler (22) for producing hot water between the low pressure and the high pressure compressors, and an exhaust gas heat exchanger (19) for producing hot water, characterized in that the electric power is adjusted to the desired value by changing the geometry of the low pressure turbine in order to change the rotational speed thereof at constant temperature in the combustion chamber, and that the heat power is adjusted to the desired value by controlling a flow bypassing the recuperator.