HK1115914B - System for vaporization of liquid fuels for combustion and method of use - Google Patents

Description

System for vaporizing liquid fuel for combustion and method of use thereof

This application claims priority to U.S. provisional application 60/417,184 filed on 10/2002 and 60/430,653 filed on 4/12/2002. The entire contents of these two provisional applications are incorporated herein by reference.

Technical Field

The present invention relates to a method and apparatus for properly vaporizing, mixing and delivering liquid fuels or liquefied gases in a combustion device.

Background

Combustion devices, such as gas turbine engines used for power generation, typically use natural gas as a fuel (e.g., compressed natural gas or CNG). Typically, natural gas consists of about 90-98% methane (CH) by volume₄) Composition, although some gases containing as little as 82% methane are also referred to as natural gas. In addition to methane, natural gas may be containedComprises CO₂、O₂、N₂And higher hydrocarbon gases such as C2 (ethane, ethylene, acetylene), C3 (propane), C4 (butane) and C5 (pentane).

In recent studies on combustion systems for gas turbine engines, significant improvements in exhaust emissions have been achieved by using lean premixed combustion in the case of natural gas. In this combustion mode, the natural gas is premixed with the combustion air before reaching the flame front. The lean mixture of natural gas and air is combusted at a lower temperature than conventional diffusion flame combustors, thereby causing pollutants, including oxides of Nitrogen (NO), in the exhaust stream_X) Lower content). For example, maximum allowable NO for diffusion flame combustors_XLevels were typically 42ppm @ 15% O₂And maximum allowable NO of lean premixed combustion gas turbine engine_XLevels are currently typically 15ppm @ 15% O₂. 42ppm NO for diffusion flame combustor_XLevels can usually only be achieved by adding large amounts of water vapor or water to the combustion chamber to reduce the flame temperature.

Lean premixed combustion devices have been attempted for burning alternative higher hydrocarbon liquid fuels such as oil and diesel fuel and higher hydrocarbon fuel gases such as propane (C3) and butane (C4). Herein, "higher hydrocarbon fuel" refers to a fuel in which at least 50% by weight of the hydrocarbon molecules in the fuel have at least two carbon atoms. Unfortunately, these combustion devices are difficult to operate in a lean premixed pre-gasification (LPP) combustion mode when alternative fuels are used. To produce a lean premixed pre-gasification flame using a liquid fuel or liquefied gas (herein, the term "liquid fuel" is to be understood to include fuels that are typically liquid at room temperature and atmospheric pressure, and gases that are liquefied by cooling and/or pressurization), the liquid must first be evaporated into a carrier gas (typically air) to produce a fuel gas (i.e., a fuel vapor/air mixture) and then mixed with additional combustion air before reaching the flame front. However, a phenomenon known as auto-ignition (auto-ignition) may occur using such a vaporized liquid fuel/liquefied gas and air mixture. Auto-ignition is the spontaneous ignition of fuel prior to a predetermined flame location in a combustion device. When the fuel is fed into the combustion device, pre-ignition may occur, for example, due to the fuel being heated, typically, prematurely, or otherwise. Auto-ignition reduces the efficiency of and damages the combustion device, thereby reducing the useful life of the combustion device and/or increasing undesirable emissions.

Various attempts have been made to avoid auto-ignition of higher hydrocarbon liquid fuels in such lean premixed combustion devices, but none have met with full success. Thus, "dual fuel" combustion devices, such as gas turbine engines, that can use natural gas and higher hydrocarbon liquid fuels typically operate in a lean, premixed mode when using natural gas and a diffusion mode when using higher hydrocarbon liquid fuels. Combusting liquid fuels in a diffusion mode is undesirable because it increases NO as compared to natural gas combusted in a lean, premixed mode_XAnd other emissions.

Another issue of increasing importance in recent times is related to the use of liquefied natural gas. Liquefied natural gas has recently become more common due to insufficient supply of domestic natural gas. When transporting liquefied natural gas, typically by tanker (tanker), higher hydrocarbon gases have a higher boiling point. When liquid natural gas is revaporized for use as a gaseous fuel, a higher percentage of higher hydrocarbon fuels is contained in the final portion of the liquefied natural gas withdrawn from the storage vessel. This portion of lng cannot be used in many existing lean premixed natural gas combustors due to the auto-ignition problem described above.

Combustion devices similar to those using natural gas are also used in boilers, incinerators, and turbine engines, as well as other combustion engines, including applications other than power generation, such as for propulsion of warships. Problems encountered in the use of turbine engines for naval vessels include the need for large spaces to accommodate conventional compressed gas fuels and the large amounts of emissions produced by the use of alternative liquid fuels in conventional turbine engines. These emissions can be environmentally damaging and can present a hazard, for example, visible emissions can be generated that can expose the location of the vessel.

There is therefore still a need to develop new combustion devices (e.g. turbine engines, etc.) that can burn both natural gas and higher hydrocarbon liquid fuels using lean premixed pre-evaporation. The satisfactory dual fuel option of such a combustion device allows considerable flexibility in cost control and fuel selection for a variety of applications, including power generation.

Summary of The Invention

Embodiments of the present invention solve the above and other problems by providing, among other things, a mechanism for producing a pre-vaporized fuel gas having an oxygen content less than ambient air from a plurality of liquid fuels or liquefied gases, which can be fed to a combustion device as a gaseous fuel. In a preferred embodiment, this pre-vaporized fuel gas can be used in existing natural gas fired lean premixed combustion devices. Such gaseous fuels may be used in turbine engines, diesel and gasoline engines, such as for supplying energy to naval vessels, locomotives, aircraft and automobiles. The present invention is also applicable to a variety of other combustion devices, particularly those that have high requirements for ignition control and/or emissions control. For example, NO reduction can be achieved using the present invention even in diffusion flame combustors_X. Emissions can be reduced by increasing the heat capacity of the reduced oxygen stream/fuel gas mixture because the added inert gas can be used to lower the flame temperature and thereby reduce NO_X。

In one embodiment of the invention, an inert gas stream or other gas stream containing less oxygen than ambient air is used to vaporize a liquid fuel or a liquefied higher hydrocarbon natural gas and the resulting reduced oxygen vaporized fuel gas is fed to a combustion unit. By mixing the fuel with a gas stream having an appropriately reduced oxygen concentration, the reaction of the vaporized fuel can be prevented or sufficiently retarded, thereby avoiding auto-ignition. The advanced ignition control described below and other features of the present invention may be used to reduce or control emissions or combustion instabilities.

A variety of devices or systems known in the art may be used to supply the inert gas stream, and a variety of inert gases may be used in the present invention. For example, in one embodiment of the invention, a low oxygen gas stream for vaporizing liquid fuels or liquified gases may be provided by foul exhaust gas from a pre-burner or downstream of a combustion device, thereby avoiding auto-ignition. By appropriately conditioning such an exhaust stream, the exhaust stream may be used to vaporize any liquid fuel or liquefied gas that, once appropriately treated and mixed with the exhaust stream, may be directly fed to the combustion device as a gaseous fuel. In another embodiment of the invention, the reduced oxygen gas stream is supplied to a liquid fuel or liquefied gas vaporizer using an air separator unit.

Advantageously, this makes it a stand-alone unit for the preparation of pre-vaporized fuels from various liquid fuels or liquefied gases and compressed air, which, once appropriately treated and mixed, can be supplied directly into existing turbine engines adapted to burn natural gas. The resulting mixture is then combusted in a lean, premixed manner, thereby enhancing engine performance. For example, such improvements may include, but are not limited to, improving exhaust emissions and/or increasing flame stability, including reducing instability of the combustion device.

The air separator unit used in the embodiments of the present invention separates oxygen and nitrogen from air. The output of the air separator includes two streams, a first stream that is high in oxygen and low in nitrogen ("oxygen-rich stream"), and a second stream that is low in oxygen and high in nitrogen (the reduced-oxygen stream obtained in this embodiment, and other reduced-oxygen streams in other embodiments, are referred to as "oxygen-reduced streams" or "reduced-oxygen streams"). In one embodiment of the invention, the air separator uses what is known in the art as an "adsorption process" to produce the gas stream.

The reduced oxygen gas stream may then be mixed with a vaporized liquid fuel or liquefied gas prior to being fed to the combustion device. Since vaporized fuel requires a sufficient amount of oxygen to combust, by mixing the vaporized fuel with a low oxygen stream (e.g., mixed with a low level of oxygen and a suitable level of non-combustible nitrogen), combustion of the vaporized fuel can be prevented or sufficiently retarded to avoid auto-ignition. The mixture of fuel and reduced oxygen gas stream is then fed as a gaseous fuel to a combustion device where the fuel/reduced oxygen gas stream may be mixed with an oxygen source (e.g., intake air) for combustion in the engine.

In one embodiment of the invention, the air separator uses compressed air supplied from a turbo compressor. Alternatively or additionally, the air separator may use compressed air supplied from any compressed air source.

In one embodiment of the invention, the oxygen-rich stream produced by the air separator may be supplied to the combustion device downstream of the fuel combustion zone to reduce emissions from the turbine engine. Supplying the oxygen-rich gas stream to the post-combustion exhaust stream can reduce pollutants produced by the combustion device, such as by promoting oxidation of unburned fuel and/or carbon monoxide in the exhaust stream.

In one embodiment of the invention, the oxygen-enriched stream produced by the air separator may be fed to the combustion device to broaden the range of use of the combustion device.

Many liquid hydrocarbon fuels are suitable for use in the present invention. These liquid fuels or liquefied gases include, but are not limited to, diesel fuel, #2 fuel oil, gasoline, liquefied natural gas with an increased content of higher hydrocarbons, other liquefied gases (including liquefied C2, C3, C4, C5, etc.), and combustible liquid waste streams (such as waste streams obtained during manufacture).

In one embodiment of the invention, the heating value, by mass or volume of the fuel gas stream, may be controlled by mixing the appropriate proportion of the reduced oxygen stream. This facilitates the supply of fuel gas to the combustion device, for example by means of an existing natural gas fuel system.

Additional advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the following specification or may be learned by practice of the invention.

Drawings

FIG. 1(a) is a block diagram of an embodiment of the present invention;

FIGS. 1(b) and 1(c) are block diagrams of different types of combustors suitable for use in the embodiment of FIG. 1 (a);

FIG. 2 is a flow chart illustrating a method of using a liquid fuel or liquefied gas and a combustion device according to an embodiment of the present invention;

FIG. 3 is a block diagram of a gas turbine engine equipped with a liquid fuel or liquefied gas combustion device according to an embodiment of the present invention;

FIG. 4 is a flow chart illustrating a method of using a liquid fuel or liquefied gas and a gas turbine engine according to an embodiment of the present invention;

FIG. 5(a) is a block diagram of a gas turbine engine equipped with a liquid fuel or liquefied gas combustion device according to an embodiment of the present invention;

FIGS. 5(b), (c), (d), and (e) are block diagrams of various combustor configurations of the gas turbine engine of FIG. 5 (a); and

fig. 6 is a flow chart illustrating a method of using a liquid fuel or liquefied gas and a gas turbine engine according to an embodiment of the present invention.

Detailed Description

The invention is discussed in connection with preferred combustion system embodiments. Specific details are set forth, such as fuel type and oxygen content of the gas stream, in order to provide a more thorough understanding of the present invention. The preferred embodiments discussed herein should not be construed as limiting the invention. Furthermore, for ease of understanding, certain processing steps are divided into several steps; however, these steps should not be construed as being distinct or related in their performance.

Herein, "vaporizing" should be understood to be different from "gasifying". Gasification refers to the process of: the process of converting a non-gaseous fuel, such as coal, into a gaseous fuel by partially reacting (e.g., combusting) the non-gaseous fuel with ambient air or an oxygen-rich gas stream. In contrast, the reaction of the liquid fuel is substantially suppressed during the vaporization process of the present invention due to the presence of the gas stream having a reduced oxygen content relative to the ambient air.

The present invention is believed to be particularly useful in lean premixed pre-evaporative combustion devices and is therefore discussed primarily in this context. However, the present invention should not be construed as being so limited. For example, the present invention may also be used in RQL (rich-fuel-rapid-quench-lean) combustion devices, partially premixed combustion devices, or diffusion flame combustion devices.

Fig. 1(a) is a block diagram of a combustion system according to one embodiment of the present invention, which includes a conventional combustor 5 (also referred to herein as a "combustion device") for use as a combustor for combusting liquid fuels or liquified gases, such as, but not limited to, a turbine engine or a spark-ignition or compression-ignition engine. As shown in fig. 1(a), the liquid fuel/liquefied gas vaporization unit 1 is connected to a combustion chamber 5. A reduced oxygen vaporized fuel stream 8 is supplied from the vaporization unit 1 to the combustor 5. An oxygen-containing gas stream 9 is also supplied to the combustion chamber 5, such as from an air supply. In one embodiment, the combustor 5 has the effect of properly mixing the vaporized fuel stream 8 with the oxygen-containing gas stream 9.

The vaporization unit 1 includes a reduced oxygen gas stream source 2, a liquid fuel/liquefied gas source 3 (also referred to herein as "liquid fuel" and/or "liquefied fuel"), and a vaporizer unit 4. The liquid fuel/liquified gas vaporization unit 4 mixes and vaporizes the supply streams 6 and 7 from the liquid fuel/liquified gas source 3 and the reduced oxygen gas stream source 2, respectively. A variety of different methods may be used to vaporize the liquid fuel stream 6 and the reduced oxygen gas stream 2. The order of mixing and vaporisation is not critical. In certain embodiments, mixing and vaporization occur simultaneously, such as when the reduced oxygen gas stream is preheated to a temperature sufficient to vaporize the liquid fuel. In other embodiments, the liquid fuel stream 6 is partially or fully vaporized, for example, by heating liquid fuel, prior to mixing with the reduced oxygen gas stream 7. In certain embodiments, the reduced oxygen gas stream 7 is pressurized and/or heated prior to mixing and vaporization. The vaporized fuel stream 8, which is capable of avoiding auto-ignition by mixing with the oxygen-reduced stream, is then fed into the combustion chamber 5 for use in the combustion process.

In certain embodiments, the temperature of the vaporized fuel stream 8 is sufficiently high such that the vaporized fuel stream 8 remains above the dew point during delivery to the combustion chamber 5. In other embodiments, the temperature of the vaporized fuel stream 8 may be reduced below the dew point if the distance that the vaporized fuel stream 8 must travel before reaching the combustion chamber 5 is short enough that there is insufficient time for significant condensation to occur. In other embodiments, the vaporized fuel stream 8 is heated between the vaporizer 4 and the combustion chamber 5.

The reduced oxygen gas stream source 2 produces a gas stream having a reduced oxygen content relative to ambient air, typically containing about 21% O₂. In certain embodiments of the invention, the oxygen content of the reduced oxygen gas stream is below the limiting oxygen index. The Limiting Oxygen Index (LOI) is the concentration of oxygen in the local environment below which the material does not support combustion and varies from liquid fuel to liquid fuel. LOI is typically about 10% to 14%, for many higher hydrocarbon fuels about 13%. The greater the reduction in oxygen content of the gas stream source 2, the greater the suppression of auto-ignition. However, more work (i.e., energy) is required to produce the low oxygen content gas stream. This work will reduce the overall efficiency of the system. Thus, in certain embodiments, the oxygen content of the gas stream source 2 is just low enough to inhibit the amount required for auto-ignition, and may be above or below LOI. In other embodiments of the invention, the reduced oxygen gas stream source 2 is free of oxygen. In some embodiments, the gas supplied by the hypoxic gas stream source 2 is inert; in other embodiments, the gas from gas stream source 2 contains hydrocarbons (e.g., methanol)Such as methane and/or higher hydrocarbons).

The amount of reduction in oxygen content in the gas stream source 2 that is required to sufficiently suppress auto-ignition depends on the particular application, and in particular depends on the following factors: such as fuel quality, mixing/vaporization process, distance traveled by the vaporized gas stream to the combustion chamber, heat of the vaporized gas stream as it exits the vaporizer, heat of the reduced oxygen gas stream/fuel mixture in the combustion chamber prior to combustion, distance from the pre-mix zone to the combustion zone in the combustion chamber.

As described above, the combustor 5 of fig. 1(a) may be a premix combustor as shown in fig. 1 (b). The premix combustor generally includes a premix zone 5b-1, a main combustion zone 5b-2, an intermediate zone 5b-3, and a dilution zone 5 b-4. In a premixed combustor, the low oxygen vaporized fuel gas stream 8 is supplied to the premixing zone 5b-1 where it is premixed with an oxygen containing gas stream 9a (e.g., air). The oxygen containing gas stream 9a is typically supplied to some or all of the other zones 5b-2, 5b-3, 5 b-4. In the RQL combustor, a low oxygen vaporized fuel gas stream 8 is supplied to the intermediate zone 5 b-3. Alternatively, the combustion chamber 5 of FIG. 1(a) may be a diffusion combustion chamber as shown in FIG. 1(c) which includes a main combustion zone 5c-1, an intermediate zone 5c-2 and a dilution zone 5 c-3. In a typical diffusion combustor, a low oxygen vaporized fuel stream 8 is supplied to the primary combustion zone 5c-1 where it is combusted in the presence of an oxygen containing stream 9 a.

Fig. 2 is a flow chart of a method of operating a liquid fuel/reduced oxygen gas vaporization system in accordance with one embodiment of the present invention. In step 10, both the oxygen-reduced gas stream and a fuel stream from a liquid fuel source are supplied to a liquid fuel vaporization unit. In step 11, the liquid fuel vaporization unit mixes and vaporizes the supply streams. The vaporization energy may be supplied by the reduced oxygen stream or other energy source. A vaporized fuel stream that avoids auto-ignition by mixing with the reduced oxygen gas stream is then supplied to the combustor in step 12. In step 13, the combustor uses the produced liquid fuel/reduced oxygen gas stream and an oxygen source to produce a combustible mixture.

Another embodiment of the combustion system of the present invention is shown in fig. 3. The combustion system of FIG. 3 includes a conventional gas turbine engine 14 including an air compressor 15 (connected to a source of combustion air, not shown in FIG. 3), a combustor 5 (which may be a premix or diffusion combustor, as described above), a turbine 16, and a passage 17 for releasing emissions. The turbine engine 14 may be connected to any device, such as, for example, to a generator 18 or other output, such as a naval vessel propeller. In this embodiment, a partial exhaust gas flow 20 from the passage 17 is used to supply the reduced oxygen gas flow to the liquid fuel/liquified gas vaporization unit 21. The liquid fuel/liquified gas vaporization unit 21 is coupled to a conventional gas turbine engine 14. The vaporization unit 21 includes a compressor 19 for pressurizing the channel exhaust gas stream 20, a fuel vaporizer 4, and a liquid fuel/liquified gas source 3, which may be included in the unit 21 or alternatively not included in the unit 21 but connected thereto.

Fig. 4 is a flow chart of a method of operating a liquid fuel/reduced oxygen gas vaporization system for use with a turbine in accordance with an embodiment of the present invention. In step 25, the low oxygen content turbine exhaust gas stream is supplied to the compressor. In step 26, the compressor pressurizes a gas turbine engine exhaust stream. In step 27, the compressor output reduced oxygen gas stream and the liquid fuel stream are supplied to a liquid fuel vaporizer. In step 28, the compressor output is mixed with the liquid fuel stream to vaporize the liquid fuel. The reduced oxygen vaporized liquid fuel stream is then supplied to the combustor of the gas turbine engine in step 29.

In certain preferred embodiments, the turbine engine 14 is an existing lean, premixed device using natural gas and the liquid fuel 3 is a higher hydrocarbon liquid fuel. In addition to the above auto-ignition problems, a second problem is caused by the use of higher hydrocarbon fuels in combustion devices using natural gas, since higher hydrocarbon fuels have a higher energy content than natural gas, and therefore the fuel gas distribution and dosing system of engines using natural gas typically needs to be changed to use higher hydrocarbon fuel gas. However, in a preferred embodiment, the gas vaporization unit 21 is used to supply the reduced oxygen vaporized fuel gas to the turbine engine 14, thus eliminating the need to modify the fuel gas distribution system of the engine 14. This may be accomplished by mixing the vaporized fuel with an amount of reduced oxygen gas such that the energy content of the reduced oxygen vaporized fuel gas from the vaporizer 4 is comparable to the energy content of natural gas. The energy content may be measured by volume or mass, depending on the fuel dosing method used by the engine 14. In other embodiments, the low-oxygen fuel gas has an energy content higher or lower than natural gas, and the fuel distribution system is configured to combust such higher or lower energy content gas.

For example, the heating value of fuel gas is approximately proportional to the number of carbon atoms in the gas molecules. Accordingly, pentane (C)₅H₁₂) Has a calorific value of about methane (CH) which is a main component of natural gas₄) 5 times of the total weight of the powder. If liquefied pentane is used as the liquid fuel in the system of FIG. 3, the vaporizer 4 needs to be configured to output a fuel gas stream comprising one part vaporized pentane gas and four parts reduced oxygen gas by volume for use with an engine 14 equipped with a fuel gas distribution system for a fixed amount of methane.

FIG. 5a shows another embodiment of the combustion system of the invention comprising a gas turbine engine 14 comprising a compressor 15, a combustion chamber 5, a turbine 16 and a passage 17 for the release of emissions. The turbine 16 may be connected to a generator 18 or any other device, such as a naval vessel propeller. A liquid fuel/liquified gas vaporization unit 31 of one embodiment of the present invention is coupled to the gas turbine engine 14. The turbine may also drive a compressor. In the embodiment shown in fig. 5a, the unit 31 comprises an air separator 32, an auxiliary compressor 33, a second compressor 34, a fuel vaporizer 4 and a liquid fuel/liquefied gas source 3, which may be included in the unit 31 or alternatively not included in the unit 31 but connected thereto.

The compressor 15 has a compressed gas output which can be supplied to the air separator 32. The air separator 32 draws a compressed air stream (or other source of compressed air) from the compressor 15 of the engine 14 and outputs an oxygen-rich stream 41 and a reduced oxygen stream 42, the latter typically containing a significant amount of nitrogen relative to air. Various air separators are known in the art. In certain embodiments, compressed air may be drawn from an intermediate stage of the compressor and sent to the air separator. In certain embodiments, the air separation unit uses a process known as adsorption to produce the oxygen-enriched gas stream 41 and the reduced oxygen gas stream 42. In this embodiment, the air stream may be compressed to 3 atmospheres to facilitate separation.

In the embodiment of FIG. 5a, the oxygen-enriched gas stream 41 is compressed and the compressed oxygen-enriched gas stream 43 is injected into the combustor 5. The reduced oxygen stream 42 is supplied to the auxiliary compressor 33 where it is pressurized. The resulting compressed reduced oxygen gas stream 45 is then supplied to the liquid fuel/liquified gas vaporization unit 4. The liquid fuel/liquified gas vaporization unit 4 mixes the liquid fuel/liquified gas feed 6 from the liquid fuel/liquified gas source 3 with the compressed reduced oxygen gas stream 45 at an elevated temperature to vaporize the liquid fuel/liquified gas. The mixing ratio of the compressed reduced oxygen gas stream 45 and the gaseous feed 6 depends on the liquid fuel 3 and the configuration of the engine 14. As described above, the blend ratio may be selected to use the higher hydrocarbon liquid fuel 3 for a natural gas burning engine 14 without altering the fuel distribution system of the engine 14. The vaporized fuel/reduced oxygen stream 8 is then supplied to the combustor 5.

Fig. 6 is a flow chart of a method of operation of a liquid fuel/reduced oxygen gas vaporization system for a turbine in accordance with an embodiment of the present invention. As shown in FIG. 6, in step 51, compressed air is extracted from the air compressor of the gas turbine engine at a suitable stage/pressure for use in the air separation unit. In step 52, the air separation unit takes in a compressed air stream and generates an oxygen-rich stream and a low-oxygen stream. In one embodiment, the oxygen-rich gas stream is supplied to a first auxiliary compressor in step 53, the first auxiliary compressor pressurizes the oxygen-rich gas stream in step 54, and the pressurized oxygen-rich gas stream is then injected into the combustor in step 55. In certain embodiments 01, the oxygen-rich fuel stream is injected below the flame front of combustor 5Downstream (e.g., an intermediate or dilution zone of a combustion chamber (e.g., a premixed combustion chamber as shown in fig. 5(b) and 5 (c)), or a diffusion combustion chamber) to reduce the amount of pollutants generated by the engine 14. In other embodiments, the oxygen-rich fuel stream is mixed with combustion air from the compressor 15, which is supplied into the main combustion zone of the combustor 5 as shown in fig. 5(d) (premix combustor) and fig. 5(e) (diffusion combustor). This widens the operating range of the combustor, allowing combustion to be carried out at low equivalence ratios (i.e., lean combustion), thereby reducing pollutants such as NO_XAnd (4) discharging. In other embodiments, the oxygen-rich fuel stream is simply mixed with air from the compressor 15 and supplied to all zones of the combustor.

In step 56, the reduced oxygen gas stream from the air separation unit is supplied to a second auxiliary compressor, which pressurizes the reduced oxygen gas stream in step 57. The resulting compressed reduced oxygen gas stream and a liquid fuel/liquefied gas stream from the liquid fuel source are then supplied to a liquid fuel vaporization unit in step 58. In step 59, the liquid fuel vaporization unit mixes the supplied liquid fuel/liquefied gas stream and the compressed reduced oxygen gas stream at an elevated temperature to vaporize the liquid fuel/liquefied gas. In one embodiment of the invention, the degree of mixing of the reduced oxygen gas stream and the liquid fuel/liquefied gas is adjusted to accommodate various liquid fuel/liquefied gas specific heat values and/or mass or volumetric flow rate specifications. The vaporized fuel/reduced oxygen stream is then supplied to the combustor, such as by an existing natural gas fuel system for a turbine, in step 60.

As described above, certain embodiments of the present invention may produce a reduced oxygen fuel gas stream from a liquid fuel that may be supplied to an existing combustion device, such as a gas turbine engine, for combusting other fuels, such as natural gas, without modifying the existing combustion device. This can be accomplished by mixing the fuel gas with an inert, low oxygen stream to maintain the energy content of the fuel gas equal to the energy content of the natural gas, either by volume or by mass, depending on the dosing method used by the combustion device. In most of the known combustion apparatuses, the fuel gas can be controlledCombustion air ratio to make the mixture leaner (lean) or leaner. Other advantages of the present invention are that a variety of reduced oxygen vaporized higher hydrocarbon fuels can be combusted under the same conditions (i.e., same temperature, same combustion air (or other oxygen-containing gas) supply, etc.) at an equivalence ratio lower (leaner) than that of methane. For example, the minimum equivalence ratio of methane in air is typically about 0.5, while many higher hydrocarbon fuels can be combusted when the equivalence ratio in air is about 0.45. Using low equivalence ratios can reduce contaminants such as NO_XAnd (4) discharging. As noted above, in embodiments in which the operating range is widened by adding an oxygen-rich stream from the air separator to the combustion air stream, the operating equivalence ratio of the combustion device may be lower.

In other embodiments of the invention, a reduced oxygen fuel gas having a higher or lower energy content than natural gas may be produced. In this embodiment, if a combustion device for burning natural gas is used, the fuel distribution/dosing system of the combustion device needs to be appropriately changed.

Embodiments of the present invention have now been described in conjunction with the above advantages. It is to be understood that these examples are merely illustrative of the present invention. Many modifications and variations will be apparent to practitioners skilled in the art.

Claims (18)

1. A method of operating a combustion apparatus, the method comprising the steps of:

producing a fuel gas using a liquid fuel containing hydrocarbon molecules and a diluent gas;

premixing the fuel gas and a second gas comprising oxygen to produce a gas mixture in a premixing zone located upstream of a combustion zone of a combustion apparatus; and

combusting a gas mixture in a combustion zone of the combustion device;

wherein the gas mixture auto-ignites in the absence of a diluent gas and the diluent gas is inert and present in an amount such that reaction of the fuel gas upstream of the combustion zone is inhibited.

2. The method of claim 1, wherein the oxygen content of the gas mixture is sufficient to support combustion of the gas mixture.

3. The method of claim 1, wherein the gas mixture is a lean mixture having an equivalence ratio less than 1.

4. The method of claim 1, wherein at least 50 weight percent of the hydrocarbon molecules in the liquid fuel have at least two carbon atoms.

5. The method of claim 1, wherein the oxygen content of the diluent gas is below the limiting oxygen index of the liquid fuel.

6. The method of claim 1, wherein the combustion device comprises a fuel dosing system for natural gas.

7. The method of claim 1, wherein the equivalence ratio of the gas mixture is below the minimum equivalence ratio at which methane can be combusted under the same operating conditions.

8. The method of claim 1, wherein the combustion device is a gas turbine engine.

9. The method of claim 1, wherein the liquid fuel is a liquefied gas that is a composition that is gaseous at room temperature and atmospheric pressure.

10. A combustion apparatus, comprising:

a burner having: a first inlet for receiving a fuel gas; a second inlet receiving an oxygen-containing gas for supporting combustion of the fuel gas; a combustion zone and a pre-mix zone upstream of the combustion zone; the combustion apparatus is designed to premix the fuel gas and an oxygen-containing gas in a premixing zone to produce a gas mixture and to combust the gas mixture in a combustion zone; and

a fuel vaporization unit fluidly connected to the first inlet of the combustion device, the fuel vaporization unit designed to produce a fuel gas using a liquid fuel comprising hydrocarbon molecules and a diluent gas;

wherein the gas mixture auto-ignites in the absence of a diluent gas, and the diluent gas is inert and present in the fuel gas in an amount such that reaction of the fuel gas upstream of the combustion zone is inhibited.

11. The combustion apparatus of claim 10, further comprising a fuel gas dosing device for controlling the supply of fuel gas to the first inlet, the fuel gas dosing device being designed for natural gas.

12. The combustion apparatus of claim 10, wherein the combustion apparatus is designed for combusting a gas mixture having an equivalence ratio of less than 1.

13. The combustion apparatus of claim 10, wherein at least 50 weight percent of the hydrocarbon molecules in the liquid fuel have at least two carbon atoms.

14. The combustion apparatus of claim 10, wherein the oxygen content of the dilution gas is below the limiting oxygen index of the liquid fuel.

15. The combustion apparatus of claim 10, wherein the equivalence ratio of the gas mixture is below the minimum equivalence ratio at which methane can be combusted under the same operating conditions.

16. The combustion apparatus of claim 10, wherein said liquid fuel is a liquefied gas which is a composition that is gaseous at room temperature and atmospheric pressure.

17. The combustion apparatus of claim 10, wherein the combustion apparatus is a gas turbine engine.

18. The combustion apparatus of claim 10, wherein the combustion apparatus is designed such that an amount of oxygen-containing gas sufficient to support combustion is premixed with fuel gas in a premixing zone.