Method and arrangement for controlling fuel supply for a gas turbine

A method of controlling a supply of a fuel to a combustor of a gas turbine comprising a compressor up-stream of the combustor, the method comprising:

• supplying the fuel to the combustor;
• obtaining a property value of at least one physical property (PT8, PT7, Tinlet, THBOV) of air used for burning the fuel in the combustor;
• estimating a heat input (HIengmodel) of the fuel supplied to the combustor based on the property value;
• measuring a Caloric Value (LCVmea) of the fuel upstream of the combustor;
• adjusting the estimated heat input (HIengmodel) based on the measured Caloric Value (LCVmea) to obtain an adjusted estimated heat input (HIexpected);
• and
• controlling a fuel valve regulating the supply of the fuel to the combustor based on the adjusted estimated heat input (HIexpected) and a demanded heat input (FFDEM),
• wherein an update interval of estimating the heat input is shorter than an update interval of measuring the Caloric Value;
• wherein the at least one physical property of air comprises:
• an inlet air pressure (PT7) at a compressor inlet;
• an inlet air temperature (Tinlet) at the compressor inlet;
• and
• an outlet air pressure (PT8) at a compressor outlet,
• wherein estimating the heat input comprises:
• forming a pressure ratio (PRC87) between the outlet air pressure (PT8) and the inlet air pressure (PT7) and
• estimating the heat input (HIengmodel) based on the pressure ratio (PRC87),
• wherein estimating the heat input based on the pressure ratio (PRC87) comprises using at least one curve fit based on plural measurements performed on at least one gas turbines, the curve fit relating measured pressure to measured heat input.

An arrangement for controlling a supply of a fuel to a combustor of a gas turbine comprising a compressor upstream of the combustor, the arrangement comprising:

• a fuel valve adapted to supply the fuel to the combustor;
• a processor adapted to
• obtain a property value of at least one physical property (PT8, PT7, Tinlet, THBOV) of air used for burning the fuel in the combustor;
• estimate a heat input (HIengmodel) of the fuel supplied to the combustor based on the property value;
• receive a measured Caloric Value (LCVmea) of the fuel upstream of the combustor;
• adjust the estimated heat input (HIengmodel) based on the measured Caloric Value or Wobbe index;
• and
• control the fuel valve regulating the supply of the fuel to the combustor based on the adjusted estimated heat input (HIexpected) and a demanded heat input (FFDEM),
• wherein an update interval of estimating the heat input is shorter than an update interval of measuring the Caloric Value;
• wherein the at least one physical property of air comprises:
• an inlet air pressure (PT7) at a compressor inlet;
• an inlet air temperature (Tinlet) at the compressor inlet;
• and
• an outlet air pressure (PT8) at a compressor outlet,
• wherein estimating the heat input comprises:
• forming a pressure ratio (PRC87) between the outlet air pressure (PT8) and the inlet air pressure (PT7) and
• estimating the heat input (HIengmodel) based on the pressure ratio (PRC87),
• wherein estimating the heat input based on the pressure ratio (PRC87) comprises using at least one curve fit based on plural measurements performed on at least one gas turbines, the curve fit relating measured pressure to measured heat input.