| CPC F02C 6/18 (2013.01) [F02C 3/22 (2013.01); F02C 3/30 (2013.01); F02C 9/28 (2013.01); F05D 2240/35 (2013.01)] | 9 Claims | 

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               1. A method of operating a gas turbine cogeneration system, the gas turbine cogeneration system comprising: 
            a gas turbine including a compressor, a combustor, and a turbine; 
                a first fuel supply facility for supplying a first fuel to the combustor; 
                a second fuel supply facility for supplying a second fuel to the combustor, the second fuel having a calorific value per mass that is lower than that of the first fuel; 
                a heat recovery steam generator for generating steam using exhaust gas discharged from the turbine; 
                a steam supply line for supplying the steam discharged from the heat recovery steam generator to a steam consumer; and 
                a steam extraction line for supplying steam extracted from the steam supply line to both a head end side of the combustor and a turbine side of the combustor, the turbine side of the combustor being closer to the turbine than the head end, 
                the method comprising; 
              acquiring a consumer steam increase command to increase a consumer steam supply amount, the consumer steam supply amount being a supply amount of the steam supplied to the steam consumer; 
                  controlling the steam supply line to achieve the consumer steam supply amount indicated by the consumer steam increase command; 
                  controlling the steam extraction line to reduce an extraction amount of the steam extracted by the steam extraction line in response to the increased consumer steam supply amount; 
                  controlling the first fuel supply facility so that a supply amount of the first fuel decreases in response to the decrease in the extraction amount of the steam by the steam extraction line; and 
                  controlling the second fuel supply facility so that a supply amount of the second fuel increases in response to the decrease in the extraction amount of the steam by the steam extraction line. 
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               3. A gas turbine cogeneration system, comprising: 
            a gas turbine including a compressor, a combustor, and a turbine; 
                a first fuel supply facility for supplying a first fuel to the combustor; 
                a second fuel supply facility for supplying a second fuel to the combustor, the second fuel having a calorific value per mass that is lower than that of the first fuel; 
                a heat recovery steam generator for generating steam using exhaust gas discharged from the turbine; 
                a steam supply line for supplying the steam discharged from the heat recovery steam generator to a steam consumer; 
                a steam extraction line for supplying steam extracted from the steam supply line to both a head end side of the combustor and a turbine side of the combustor, the turbine side of the combustor being closer to the turbine than the head end; and 
                a controller comprising a processor communicatively coupled with a memory, the memory having instructions programmed therein which, when executed by the processor, cause the controller to: 
              acquire a consumer steam increase command to increase a consumer steam supply amount, the consumer steam supply amount being a supply amount of the steam supplied to the steam consumer; 
                  control the steam supply line to achieve the consumer steam supply amount indicated by the consumer steam increase command; 
                  control the steam extraction line to reduce an extraction amount of the steam extracted by the steam extraction line in response to the increased consumer steam supply amount; 
                  control the first fuel supply facility so that a supply amount of the first fuel decreases in response to a decrease in the extraction amount of the steam by the steam extraction line; and 
                  control the second fuel supply facility so that a supply amount of the second fuel increases in response to the decrease in the extraction amount of the steam by the steam extraction line. 
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