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A clearance control apparatus providing compressed cooling air to a turbine casing in a gas turbine, the apparatus including: a cooling gas passage extending through an inner annular shell of the turbine casing; a cooling gas conduit connected to a compressor of the gas turbine and to the turbine ca

A clearance control apparatus providing compressed cooling air to a turbine casing in a gas turbine, the apparatus including: a cooling gas passage extending through an inner annular shell of the turbine casing; a cooling gas conduit connected to a compressor of the gas turbine and to the turbine casing, wherein the cooling gas conduit receives compressed air from the compressor and delivers the compressed air to the turbine casing, and wherein the cooling gas conduit is in fluid communication with the cooling gas passage, and a heat exchanger connected to the cooling gas conduit and to a fuel conduit delivering fuel to a combustor of the gas turbine, wherein the heat exchanger transfers heat from the cooling gas to the fuel.

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1. A gas turbine comprising: a turbine casing enclosing a rotating turbine in the gas turbine;a fuel conduit connectable to a supply of fuel and to a combustor of the gas turbine, wherein fuel flows through the fuel conduit from the fuel supply to the combustor at a fuel flow rate;a cooling gas cond

1. A gas turbine comprising: a turbine casing enclosing a rotating turbine in the gas turbine;a fuel conduit connectable to a supply of fuel and to a combustor of the gas turbine, wherein fuel flows through the fuel conduit from the fuel supply to the combustor at a fuel flow rate;a cooling gas conduit connected to a compressor of the gas turbine and to the turbine casing, wherein the cooling gas conduit receives compressed air from the compressor and delivers the compressed air to an internal passage in the turbine casing;a heat exchanger connected to the fuel conduit and to the cooling gas conduit, wherein the heat exchanger transfers heat from the compressed air to the fuel flow to form a cooling gas to be delivered to the turbine casing, anda modulation valve configured to modulate the cooling gas flowing into the heat exchanger and into the internal passage in the turbine casing, wherein the modulation valve is at a first setting during a full-speed, full load (FSFL) operational stage of the gas turbine and at a second setting during a full-speed, no load (FSNL) operational stage of the gas turbine, such that the modulation valve receives compressed air from the compressor and delivers the compressed air into the heat exchanger at a cooling gas flow rate during both the FSNL operational stage and the FSFL operational stage, anda computer controller configured to operate the modulation valve during a transition from the FSNL operational stage to the FSFL operational stage, wherein both the cooling gas flow rate into the heat exchanger and the internal passage in the turbine casing and the fuel flow rate increase during said transition, such that a rate of increase of the cooling gas flow rate is controlled to be less than a rate of increase of the fuel flow rate during said transition. 2. The gas turbine of claim 1 wherein the fuel conduit includes a main conduit and a bypass conduit, wherein the bypass conduit is coupled to the heat exchanger and forms a passage for the fuel flowing through the heat exchanger, and the bypass conduit has an inlet and an outlet for the fuel with are both connected to the main conduit. 3. The gas turbine of claim 1 wherein the heat exchanger is a doubled tube heat exchanger including a first tube connected to the fuel conduit and forming a passage for the fuel flowing through the heat exchanger and a second tube connected to the cooling gas conduit and forming a passage for the cooling gas flowing through the heat exchanger. 4. The gas turbine of claim 1 wherein the heat exchanger is a doubled wall heat exchanger including at first and second wall separating the fuel flowing through the heat exchanger from the cooling gas flowing through the heat exchanger. 5. The gas turbine of claim 1 further comprising an inlet duct having an outlet configured to direct air into the compressor, and an inlet bleed heat (IBH) conduit coupled to the compressor and the inlet duct, wherein the IBH conduit is configured to direct compressed air from the compressor to the inlet duct. 6. The gas turbine of claim 1 wherein the internal passage is a passage in an inner annular shell of the turbine casing. 7. The gas turbine of claim 6 wherein the internal passage extends at least one-half of a length of the inner annular shell. 8. A clearance control apparatus providing compressed cooling air to a turbine casing in a gas turbine, the apparatus comprising: a cooling gas passage extending through an inner annular shell of the turbine casing;a cooling gas conduit connected to a compressor of the gas turbine and to the turbine casing, wherein the cooling gas conduit receives compressed air from the compressor and delivers the compressed air as a cooling gas to the turbine casing, and wherein the cooling gas conduit is in fluid communication with the cooling gas passage;a heat exchanger connected to the cooling gas conduit and to a fuel conduit delivering fuel at a fuel flow rate to a combustor of the gas turbine, wherein the heat exchanger transfers heat from the compressed air to the fuel to form the cooling gas to be delivered to the turbine casing, anda modulation valve configured to modulate the compressed air flowing into the heat exchanger and into the cooling gas passage extending through the inner annular shell, wherein the modulation valve is at a first setting during a full-speed, full load (FSFL) operational stage of the gas turbine and at a second setting during a full-speed, no-load (FSNL) operational stage of the gas turbine, such that the modulation valve receives compressed air from the compressor and delivers the compressed air into the heat exchanger at a cooling gas flow rate during both the FSNL operational stage and the FSFL operational stage, anda computer controller configured to control the modulation valve during a transition from the FSNL operational stage to the FSFL operational stage, wherein both the cooling gas flow rate into the heat exchanger and the internal passage in the turbine casing and the fuel flow rate increase during the transition, such that a rate of increase of the cooling gas flow rate is controlled to be less than a rate of increase of the fuel flow rate during the transition. 9. The clearance control apparatus of claim 8 wherein the fuel conduit includes a main conduit and a bypass conduit, wherein the bypass conduit is coupled to the heat exchanger and forms a passage for the fuel flowing through the heat exchanger, and the bypass conduit has an inlet and an outlet for the fuel with are both connected to the main conduit. 10. The clearance control apparatus of claim 8 wherein the heat exchanger is a doubled tube heat exchanger including a first tube connected to the fuel conduit and forming a passage for the fuel flowing through the heat exchanger and a second tube connected to the cooling gas conduit and forming a passage for the cooling gas flowing through the heat exchanger. 11. The clearance control apparatus of claim 8 wherein the heat exchanger is a doubled wall heat exchanger including at first and second wall separating the fuel flowing through the heat exchanger from the cooling gas flowing through the heat exchanger. 12. The clearance control apparatus of claim 8 wherein the gas turbine includes an inlet duct having an outlet configured to direct air into the compressor, and an inlet bleed heat (IBH) conduit coupled to the compressor and the inlet duct, wherein the IBH conduit is configured to direct compressed air from the compressor to the inlet duct. 13. The clearance control apparatus of claim 8 wherein the cooling gas passage extends at least one-half of a length of the inner annular shell. 14. A method for clearance control in a gas turbine having a compressor, combustor, turbine, modulation valve and a turbine casing housing the turbine, the method comprising: extracting compressed air from the compressor;cooling the compressed air in a heat exchanger to form a cooled compressed air, wherein heat from the compressed air is transferred to fuel flowing at a fuel flow rate to the combustor;modulating a gap between the turbine casing and a rotating section of the turbine by passing the cooled compressed air through a passage in the turbine casing, wherein the modulation of the gap includes increasing a rate of the compressed air passing into the heat exchanger and into the turbine casing during a first operational mode of the gas turbine and reducing the rate of compressed air passing through the heat exchanger and the turbine casing during a second operational mode of the gas turbine, wherein the first operational mode is while the gas turbine operates at full-speed, full load (FSFL) and the second operational mode is while the gas turbine operates at full speed, no-load (FSNL), whereinthe modulation valve receives the compressed air from the compressor and delivers the received compressed air to the heat exchanger during both the FSNL and the FSFL operation stage to form the cooled compressed air to be delivered to the turbine casing,wherein during a transition from the second operational mode to the first operational mode, the fuel flow rate is increased; andusing a computer controller configured to operate the modulation valve during the transition from the second operational mode to the first operational mode such that a rate of increase of the rate of the compressed air passing into the heat exchanger and into the turbine casing is controlled to be less than a rate of increase of the fuel flow rate during said transition. 15. The method of claim 14 wherein the passage in the turbine casing is a passage through an inner annular shell and the passage extends at least one-half a length of the annular shell. 16. The method of claim 14 wherein the method further comprises transitioning the gas turbine from the full speed, no load condition to the full speed, full load condition while performing the steps of extraction, cooling and modulating. 17. The method of claim 16 further comprising diverting compressed air output by the compressor from the combustor and to an inlet duct for the compressor during the full speed, no load condition and not diverting the compressed air to the inlet duct during the transition. 18. The method of claim 14 wherein the cooling of the compressed air is performed with a portion of the fuel flowing to the combustor, and the method further comprises diverting the portion of the fuel from a main fuel conduit into a bypass conduit, wherein the bypass conduit is coupled to the heat exchanger and forms a passage for the fuel flowing through the heat exchanger. 19. The method of claim 18 wherein the portion of the fuel diverted to the heat exchanger remains proportionately constant with respect to a total fuel flow to the combustor during operation of the gas turbine. 20. The method of claim 14 wherein the first operational mode corresponds to an operational mode of the gas turbine where the gap is expected to be at a minimum.