| CPC F02C 7/224 (2013.01) [F02C 6/08 (2013.01); F02C 7/18 (2013.01); F05D 2220/72 (2013.01); F05D 2260/213 (2013.01); F05D 2260/22141 (2013.01); F05D 2260/232 (2013.01); F05D 2260/606 (2013.01)] | 16 Claims |
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1. A combined cycle power plant comprising:
a gas turbine engine comprising:
a compressor configured to produce compressed gas;
a combustor configured to produce combustion gas from the compressed gas and a fuel; and
a turbine configured to receive the combustion gas to produce rotational shaft power;
a steam system configured to generate steam from water using the combustion gas exiting the turbine;
a first stage fuel-gas heater configured to receive the fuel before entering the combustor and receive feedwater from the steam system to transfer heat from the feedwater to the fuel;
a second stage fuel-gas heater configured to receive at least a portion of the fuel from the first stage fuel-gas heater to transfer heat to the fuel from a heat transfer medium before the fuel enters the combustor, wherein the heat transfer medium comprises compressed air from the compressor of the gas turbine engine;
a bypass system to selectively control a proportion of the fuel that flows through each of the first stage fuel-gas heater and the second stage fuel-gas heater;
a fin-fan heat exchanger in the second stage fuel-gas heater, the fin-fan heat exchanger having a first fan; and
a controller configured to operate the bypass system and the first fan to control temperature of the fuel entering the combustor, wherein the controller is configured to modulate the bypass system and the first fan to heat the fuel with partial heat input from the first stage fuel-gas heater;
wherein the controller is further configured to:
heat the fuel with water below a critical temperature of water in the first stage fuel-gas heater;
heat the fuel with compressed air to temperatures above the critical temperature of water in the second stage fuel-gas heater;
control an amount of compressed air extracted from the compressor to provide a heat input to the second stage fuel-gas heater based on operating needs of the gas turbine engine for compressed air; and
operate the first fan of the second stage fuel-gas heater to control an amount of heat from the compressed air transferred to the fuel based on operating needs of the gas turbine engine for fuel;
wherein the critical temperature of water corresponds to temperatures where water changes phase from liquid to gas.
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