Patent Application
20070130956
This invention generally relates to a fuel delivery system for an energy conversion device. More particularly, this invention relates to a fuel delivery system including a fuel deoxygenator for removing dissolved oxygen providing for vaporizing fuel to improve combustion.
A gas turbine engine is an energy conversion device commonly used in aircraft and power generation applications. A gas turbine engine typically includes a compressor, a combustor and a turbine. Oxidizer entering the compressor is compressed and directed toward a combustor. Fuel is combined with the high-pressure oxidizer and ignited. Combustion gases produced in the combustor drive the turbine.
Turbine engines that burn liquid fuel produce emissions that can include oxides of nitrogen (NOx), carbon monoxide (CO), unburned hydrocarbons (UHC) and other particulates. It is desirable to reduce the level of these elements emitted from the engine. Using fuel in a gas form such as natural gas that is premixed to form a lean mixture substantially reduces emission of undesirable elements. Vaporization and premixing of a liquid fuel also provide for the reduction of undesirable emissions.
However, heating to vaporize a liquid hydrocarbon fuel can result in the production of undesirable insoluble materials commonly known as “coking”. Coking can cause formation of coke deposits within the fuel system, clogging passages and degrading overall engine performance. The formation of coke deposits is dependent on the amount of dissolved oxygen present within the fuel due to prior exposure to oxidizer. Reducing the amount of oxygen dissolved within the fuel decreases the rate of coke deposition and increases the maximum allowable temperature in which the fuel can be heated without forming coke deposits.
Further, adding additional compounds to a vaporized fuel can provide a lean mixture for burning in the combustor that provides for reduced emissions. The addition of an oxidizer within a catalytic reactor provides a reformed fuel that improves the combustion process. It is therefore desirable to develop a process and design a system for improving combustion that provides for the vaporization of a liquid fuel without generating undesirable coke deposits.
An example low emission rich catalytic combustion system according to this invention removes dissolved oxygen from a liquid fuel to allow vaporization without the undesirable production of insoluble materials and byproducts.
The example fuel transforming system conditions fuel to optimize the combustion process and includes a fuel deoxygenator, a heat transfer device and a catalytic reactor. The fuel deoxygenator removes dissolved oxygen from liquid hydrocarbon fuel, allowing the fuel to be vaporized without the detrimental effects and production of unmanageable amounts of insoluble materials. The vaporized fuel is then mixed with oxidizers and reformed in the catalytic reactor. The resulting reformed fuel mixed with more oxidizer provides for low temperature sustained combustion with reduced emission of undesirable byproducts. The vaporization of the liquid fuel improves the combustion process by improving mixing of oxidizer and fuel, that in turn provides improved flame stabilization and a more complete and efficient burn.
Accordingly, the fuel transforming system and method of this invention improves combustion by providing for the vaporization of a liquid fuel without generating undesirable by-products.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
Referring to
The gas turbine engine 10 includes a compressor 12 that compresses intake air 14, a combustor 18 for igniting a fuel oxidizer mixture and a turbine 16 that turns in response to a flow of exhaust gases 15 produced in the combustor 18.
The gas turbine engine 10 of this invention includes a fuel transforming system 26 that includes a fuel deoxygenator 20, a heat transfer device 22 and a catalytic reactor 24. Hydrocarbon fuel typically includes dissolved oxygen due to exposure with oxidizer during transport and storage. Dissolved oxygen within the fuel combines with other compounds within the fuel at elevated temperatures. The resulting interactions produce undesirable insoluble materials commonly referred to as “coke”. The insoluble materials that build up due to these interactions can build up on the interior walls of the fuel transforming system 26 and combustor 18 causing an undesirable degradation in performance.
Removal of dissolved oxygen from the hydrocarbon fuel increases the temperature at which formation of insoluble materials begins appreciably, along with reducing the amount of insoluble material produced. The deoxygenator 20 removes dissolved oxygen from the fuel without significantly interfering with fuel.
In many combustion processes the fuel oxidizer mixture is a critical component to engine efficiency and emissions. A mixture including a greater percentage of fuel than that in stoichiometric mixture is known as a rich mixture and can be ignited and sustained at relatively lower combustion temperatures compared to stoichiometric combustion temperature. A mixture with a greater percentage of oxidizer than that in stoichiometric mixture is known as a lean mixture and operates at lower temperatures compared to stoichiometric combustion temperature. Operating the combustor at lower temperatures is preferable in some applications to produce lower level of oxides of nitrogen and to avoid the heat management devices and structures required to sustain high temperature combustion. However, combustion with too low temperature produces emissions with undesirable levels of byproducts such as carbon monoxides and unburned hydrocarbons and various other undesirable substances. The lean mixture operating at moderately low temperatures does not produce the high levels of NOx, CO and UHC. However, such lean mixtures are currently practical only with fuel in a gas state and are not practical utilizing common liquid hydrocarbon fuels.
The fuel transforming system 26 of this invention removes dissolved oxygen from a liquid hydrocarbon fuel supplied from a fuel source 25, allowing the fuel to be vaporized without the appreciable detrimental effects and production of unmanageable amounts of insoluble materials. The vaporized fuel is then mixed with oxidizers 21 in premixer 29 to form a rich mixture and reformed in the catalytic reactor 24 which may need cooling as is schematically indicated by arrow 23 to ensure durability. The resulting vaporized fuel provides for low temperature sustained reaction that reduces the production of NOx in the catalytic reactor 24. The vaporization of the liquid fuel improves the combustion process by improving mixing of oxidizer and fuel that in turn improves reaction in the catalytic reactor 24. The transformed fuel processed in fuel transforming system 26 is then mixed with proper amount of oxidizer 19 in a post-mixer 28, and becomes a lean mixture and reacted in combustor stably with minimal NOx, CO and UHC. Oxidizer 19 can be partly or fully supplied by part or all the cooling flow 23.
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The permeable membrane 60 is supported along a porous substrate 66. A vacuum source 70 creates an oxygen partial pressure differential across the permeable membrane 60 such that dissolved oxygen 68 is driven from the fuel 25 on a continual basis. The dissolved oxygen is then exhausted overboard or to other systems that may utilize it. Although an example of a permeable membrane is illustrated, it should be understood that it is within the contemplation of this invention that other known mechanisms that remove oxygen from fuel or other methods enabling liquid fuel being vaporized without appreciable coking are within the contemplation of this invention.
Referring to
The vaporized fuel is then reformed within the catalytic reactor 24 as indicated at 36. The catalytic reactor 24 includes materials that cause favorable reactions within the fuel in preparation for combustion. Reform products emitted from the catalytic reactor 24 can then be mixed with additional oxidizer as indicated at 38. The mixed fuel and oxidizer is then injected into the combustor 18 for combustion as is indicated at 40.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
