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In a reheat gas turbine engine for power generation, fuel is burnt with compressed air from a compressor in a first or primary combustor, the combustion products are passed through a high pressure turbine, the exhaust of the high pressure turbine is then burnt together with further fuel in a reheat

In a reheat gas turbine engine for power generation, fuel is burnt with compressed air from a compressor in a first or primary combustor, the combustion products are passed through a high pressure turbine, the exhaust of the high pressure turbine is then burnt together with further fuel in a reheat combustor to consume the excess air, and the exhaust of the second combustor is passed through a lower pressure turbine. Excess air is supplied to the first combustor, thereby enabling so-called “lean burn” combustion for production of low levels of pollutants in the exhaust of the engine. Some turbine components of the turbines, e.g., blades or vanes, are cooled by cooling air supplies tapped off from the compressor. The operating cycle of the gas turbine engine is modified by returning at least some of the spent cooling air from the low pressure turbine to the reheat combustor, where it is burnt with additional fuel to produce a greater volume of exhaust gases, thereby increasing the torque on a shaft and boosting the power output of the generator.

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1. A gas turbine engine comprising, in flow series:a) a multi-stage compressor for compressing air to a high pressure,b) a first combustor having fuel injection means for burning fuel together with the high pressure air supplied from the compressor to form combustion products, the air supplied to th

1. A gas turbine engine comprising, in flow series:a) a multi-stage compressor for compressing air to a high pressure,b) a first combustor having fuel injection means for burning fuel together with the high pressure air supplied from the compressor to form combustion products, the air supplied to the first combustor during operation of the engine being in excess of that required for complete combustion of the fuel,c) a high pressure turbine for being driven by the combustion products from the first combustor to form exhaust gases,d) a second combustor having fuel injection means for burning further fuel together with the exhaust gases of the high pressure turbine to form combustion products, thereby to consume the excess air,e) a lower pressure turbine comprising turbine components that require cooling during operation of the engine,f) means for tapping off a supply of cooling air from an intermediate stage of the compressor and supplying it to the turbine components that require cooling in the lower pressure turbine without first passing the cooling air through components in the high pressure turbine,g) means for supplying the second combustor with at least a portion of the cooling air after it has passed through the lower pressure turbine components, andh) means for supplying sufficient fuel to the second combustor to burn therein with the portion of cooling air. 2. The gas turbine engine according to claim 1, and a heat exchanger arrangement for cooling the cooling air before it is supplied to the turbine components. 3. The gas turbine engine according to claim 2, in which the heat exchanger arrangement comprises means for putting the cooling air in heat exchange relationship with the fuel before injection of the fuel into one of the first and the second combustors. 4. The gas turbine engine according to claim 2, in which the heat exchanger arrangement comprises means for putting the cooling air in heat exchange relationship with the fuel before injection of the fuel into at least the second combustor. 5. The gas turbine engine according to claim 1, in which the cooled turbine components comprise stator blades in at least one stage of turbine blading. 6. The gas turbine engine according to claim 1, in which the cooled turbine components comprise nozzle guide vanes before a first stage of the lower pressure turbine. 7. An operating cycle for a gas turbine engine comprising a multi-stage compressor, first and second combustors, a high pressure turbine and a lower pressure turbine, the operating cycle comprising the steps of:a) burning fuel and excess air together in a first combustor to form combustion products;b) passing the first combustor combustion products through the high pressure turbine, the high pressure turbine forming an exhaust;c) burning the high pressure turbine exhaust together with further fuel in the second combustor to consume the excess air and form further combustion products;d) passing the further combustion products through the lower pressure turbine;e) tapping off cooling air from an intermediate stage of the compressor;f) supplying the cooling air to components requiring cooling in the lower pressure turbine without first passing the cooling air through components in the high pressure turbine;g) supplying the second combustor with at least some of the cooling air after it has passed through the turbine components; andh) supplying sufficient fuel to the second combustor to burn therein with the cooling air. 8. The gas turbine engine operating cycle according to claim 7, which the cooling air is cooled before it is supplied to the turbine components. 9. The gas turbine engine operating cycle according to claim 8, in which the cooling air is cooled by being put into heat exchange relationship with the fuel, thereby to heat the fuel before injection of the fuel into one of the first and the second combustors. 10. The gas turbine engine operating cycle according to claim 8, in which the cooling air is cool ed by being put into heat exchange relationship with the fuel, thereby to heat the fuel before injection of the fuel into at least the second combustor. 11. The gas turbine engine operating cycle according to claim 7, in which the cooling air is passed through stator blades in at least one stage of turbine blading. 12. The gas turbine engine operating cycle according to claim 7, in which the cooling air is passed through nozzle guide vanes constituting a first stage of the lower pressure turbine.