This invention was made with Government support under Government Contract No. DE-FG36-05G015023, awarded by the United States Department of Energy. The Government has certain rights in the invention.
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OF THE INVENTION
The invention relates generally to a fuel reformer system based on pre-mixed catalytic partial oxidation, and more particularly to a gas turbine system employing the fuel reformer system.
Fuel injection and mixing are critical to achieving efficient and clean combustion in gas turbine engines. In the case of gaseous fuels, it is desirable to obtain an optimal level of mixing between air, fuel, and combustion products in a combustion zone.
Exhaust gases from gas turbine engines contain substances such as nitrogen oxides (NOx) that are harmful regulated emissions. Hence, there has been increased demand for gas turbines that operate in partially pre-mixed (PP) or lean, pre-mixed (LP) modes of combustion in an effort to meet increasingly stringent emissions goals. PP and LP combustion reduces harmful emissions of NOx without loss of combustion efficiency.
However, combustion instabilities, also known as combustion dynamics, are commonly encountered in development of low emissions gas turbine engines. Combustion dynamics in the form of fluctuations in pressure, heat-release rate, and other perturbations in flow may lead to problems such as lean blow out, structural vibration, excessive heat transfer to a chamber, and consequently lead to failure of the system.
Reforming part of the fuel to hydrogen rich syngas, and then mixing the syngas into the fuel before the turbine combustion chamber is a solution to enhance the gas turbine turn capability by improving the combustion dynamics. One method employs a rich catalytic system to reform the fuel just prior to gas turbine premixing and is further integrated into the gas turbine fuel skid.
BRIEF DESCRIPTION OF THE INVENTION
Briefly, according to one embodiment, a gas turbine system is provided. The gas turbine system includes a fuel reformer system comprising: a fuel inlet configured to receive a fuel stream; an oxygen inlet configured to introduce an oxygen-containing gas; a pre-mixing zone configured to mix the fuel stream and the oxygen-containing gas in a pre-mixing device to form a gaseous pre-mix; wherein the pre-mixing device comprises a flow conditioning device configured to pre-condition the fuel stream, wherein the flow conditioning device is disposed upstream of the oxygen inlet; a diffuser disposed downstream of and in fluid communication with the flow conditioning device, wherein the diffuser is configured to provide a thermal shield to the gaseous pre-mix in the pre-mixing zone; a catalytic partial oxidation zone disposed downstream of and in fluid communication with the diffuser and configured to receive the gaseous pre-mix, wherein the catalytic partial oxidation zone comprises a catalyst composition configured to react the fuel and the oxygen to generate a syngas; and a dilution zone disposed downstream of and in fluid communication with the reaction zone and configured to mix the fuel back into the syngas to form a hydrogen-enriched fuel mixture a gas turbine pre-mixer configured to mix a oxygen-containing gas from a gas turbine compressor with the hydrogen-enriched fuel mixture; and a gas turbine combustor configured to combust the hydrogen-enriched fuel mixture.
In another embodiment, a method of operating a gas turbine system includes introducing a portion of a fuel stream into a pre-mixing zone of a fuel reformer system; introducing an oxygen-containing gas to the fuel stream in a flow conditioning device to facilitate pre-mixing of the fuel stream and oxygen to form a gaseous pre-mix; reacting the gaseous pre-mix in the presence of a catalyst composition in a catalytic partial oxidation zone to form a syngas through catalytic partial oxidation; introducing the syngas stream into the fuel stream to form a hydrogen-enriched fuel mixture; mixing the hydrogen-enriched fuel mixture with an oxygen-containing gas in a gas turbine pre-mixer; combusting the hydrogen-enriched fuel mixture in a gas turbine combustor; and producing electrical power with a gas turbine in operative communication with an electrical generator.
In yet another embodiment, a fuel reformer system comprises: a fuel inlet configured to receive a fuel stream; an oxygen inlet configured to introduce a first oxygen-containing gas; a pre-mixing zone configured to mix a first portion of the fuel stream and the oxygen-containing gas in a pre-mixing device to form a gaseous pre-mix; a diffuser disposed downstream of and in fluid communication with the pre-mixing zone, wherein the diffuser is configured to provide a thermal shield between the pre-mixing zone and a catalytic partial oxidation zone; a catalytic partial oxidation zone disposed downstream of and in fluid communication with the pre-mixing zone and configured to receive the gaseous pre-mix, wherein the catalytic partial oxidation zone comprises a catalyst composition configured to react the fuel and the oxygen to generate a syngas from the gaseous pre-mix; and a dilution zone disposed downstream of and in fluid communication with the catalytic partial oxidation zone and configured to mix the syngas into a second portion of the fuel stream to form a fuel mixture.
BRIEF DESCRIPTION OF THE DRAWINGS
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Referring now to the Figures, which are exemplary embodiments, and wherein the like elements are numbered alike:
FIG. 1 is a diagrammatical illustration of an exemplary embodiment of a gas turbine system having a pre-mix catalytic partial oxidation fuel reformer system;
FIG. 2 is a diagrammatical illustration of an exemplary embodiment of the pre-mix catalytic partial oxidation fuel reformer system of FIG. 1;
FIG. 3 is a diagrammatical illustration of another exemplary embodiment of the fuel reformer system of FIG. 1;
FIG. 4 is a schematic illustration of an exemplary embodiment of a pre-mixing device from the fuel reformer system of FIG. 3;
FIG. 5 is a cross-sectional view of another exemplary configuration of the pre-mixing device from the fuel reformer system of FIG. 3 comprising a plurality of counter swirling vanes;
FIG. 6 is another cross-sectional view of the exemplary embodiment of the pre-mixing device of FIG. 5;
FIG. 7 is a cross-sectional view of the fuel reformer system of FIG. 3, specifically showing the catalytic partial oxidation zone and the reaction zone; and
FIG. 8 is a cross-sectional view of an exemplary embodiment of a gas turbine combustor of the gas turbine system of FIG. 1.
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OF THE INVENTION
As described in detail below, embodiments of the present disclosure provide a gas turbine system incorporating a fuel reformer system and a method of providing the same. The gas turbine system utilizes syngas formed by catalytic partial oxidation. The syngas is generated by mixing and reacting a portion of the natural gas or fuel with air to increase a concentration of hydrogen. The syngas can then be mixed with the natural gas or fuel and sent to the gas turbine combustor. Introduction of hydrogen into the natural gas or fuel allows lowering of a lean blow out point and enhances the combustion dynamics. Gas turbine turndown can be reduced below 40% by the addition of hydrogen to the fuel as compared to a system that does not introduce additional hydrogen to the fuel.
Lowering of the lean blow out point permits the flow rate to the gas turbine to be further turned down when demand for electricity is low, thereby saving fuel and reducing emissions. The term “lean blow out point” used herein refers to a point of loss of combustion in a combustor. Variations in fuel composition and flow disturbances result in a loss of combustion in sufficiently lean flames. The term “combustion dynamics” used herein refers to fluctuations in air pressure, temperature, heat release and unsteady flow oscillations that affect operation of the gas turbine. It is desirable to operate the gas turbine system with a highly reactive fuel component, such as hydrogen, to help limit loss of combustion. Moreover the fuel reformer system disclosed herein is compact in size and of reduced complexity. Existing gas turbine systems, therefore, can easily be retrofitted to include the generator at a low cost and without significantly impacting the size of the gas turbine system.
Turning now to FIG. 1, a block diagram illustrating an exemplary embodiment of a gas turbine system 10 is shown. The gas turbine system 10 includes a fuel reformer system 12 for doping the hydrogen into the fuel of the gas turbine. A compressor 14 is in fluid communication with both the fuel reformer system 12 and the gas turbine pre-mixers 16. The compressor 14 is configured to supply air to both the fuel reformer system 12 and the pre-mixers 16. A fuel stream 18 is also in fluid communication with the fuel reformer system 12. As will be discussed in greater detail below, the fuel and air combine and react in the fuel reformer system 12 to form the syngas, which can then be combined with more fuel and sent to the gas turbine pre-mixers 16. The syngas and fuel is further mixed with air from the compressor 14, and the entire pre-mixed fuel is fed to a combustor 20. The pre-mixed fuel is combusted in the combustor 20 and expanded in the gas turbine 22. The turbine is driven by the combustion and expansion, and the energy is converted to electricity, where it can be sent to a power grid 24 to provide power, or can be stored and used at a later time.
FIG. 2 further illustrates an exemplary embodiment of the fuel reformer system 12 of FIG. 1. A fuel slipstream 30 is split from the main fuel stream 18 is combined with a slipstream of oxygen-containing gas 32 from the gas turbine compressor 14 and sent to a premixing zone 34 of the fuel reformer system 12. As used herein, the term “oxygen-containing gas” is generally used to refer to any oxidant suitable for mixing with the fuel to form a hydrogen-enriched fuel mixture. Exemplary oxygen-containing gases can include, without limitation, air, pure oxygen (O2), oxygen-enriched air, oxygen and steam containing combustion exhaust, and the like.
In an optional embodiment, the fuel slipstream 30 can be combined with steam 36 and fed through a heat exchanger 38 configured to pre-heat the fuel slipstream 30 prior to mixing with the oxygen-containing gas slipstream 32 in the premixing zone 34. The pre-heated fuel slipstream 30, with optional steam 36, can then be premixed with the oxygen-containing gas 32 in the premixing zone 34. In another embodiment, the steam can be a component of the fuel slipstream 30 or the oxygen-containing gas slipstream 32, rather than being a separate supply stream as illustrated in FIG. 2.
The fuel and oxygen-containing gas are mixed to form a gaseous premix, which is immediately fed into a catalytic partial oxidation reactor 40. The gaseous premix undergoes a catalytic partial oxidation reaction and a syngas 42 is formed. The syngas 42 can be cooled when it is diluted with the fuel stream 18 to form a hydrogen-enriched fuel mixture, or it can be cooled with steam. When the optional heat exchanger 38 is present in the fuel reformer system 12, the syngas 42 can be cooled by passing through the heat exchanger down to a temperature of about 250 degrees Celsius (° C.) to about 450° C., specifically about 325° C. to about 375° C. Cooling the syngas 42 is particularly advantageous when an optional water gas shift (WGS) reactor 44 is present in the fuel reformer system 12. The WGS reactor 44 can be disposed downstream of the catalytic partial oxidation reactor 40, and in this case, downstream of the heat exchanger 38. The WGS reactor 44 can be configured to further increase a concentration of hydrogen in the syngas by reacting steam with carbon monoxide in the syngas to form more hydrogen. The hydrogen-enriched syngas 46 can then be recombined with the fuel stream 18 to form a fuel mixture 48, which can be fed to the combustor 20 of the gas turbine system 10.
FIG. 3 is another block diagram illustrating another exemplary embodiment of the fuel reformer system 12 of FIG. 1. The fuel reformer system 12 includes a pre-mixing zone 110, a selective catalytic partial oxidation (SCPO) zone 112, a CPO zone 114, and a dilution zone 116. The fuel stream 18, which can be pressurized before entering the gas turbine system, can be preconditioned in a pretreatment zone 118. In various embodiments, the fuel can be pre-mixed with water or steam, can be preheated, can be preconditioned by means of a fuel swirler, flow enhancer, turbulence generator, or the like, disposed in the zone, can be filtered to reduce the level of impurities, such as sulfur, in the fuel, and other like preconditioning means in the pretreatment zone 118. A fuel bypass valve 120 can be disposed in fluid communication between the fuel stream source 18 and the fuel pretreatment zone 118. The fuel bypass valve 120 can be configured to send a desired portion 121 of the fuel stream to pretreatment and pre-mixing zones of the syngas generator to be used in generation of hydrogen content in the system. The remainder 124 of the fuel stream 18 can be directed by the fuel bypass valve 120 to the dilution zone 116, where the remainder of the fuel stream 124 can combine with the syngas 126 generated in the CPO zone 114.