Patent Grant
11415315
This invention pertains to a combustor apparatus for burning a hydrocarbon fuel with an oxidant for the purpose of producing a clean and durable combustion process while providing heat efficiently to a downstream application, for example, a heater head of an external combustion engine.
Stable, non-catalytic combustion of a hydrocarbon fuel, like natural gas, at ambient pressure in a single stage combustor requires a near-stoichiometric ratio of the oxidant relative to the hydrocarbon fuel. The term “stoichiometric ratio” refers herein to an exact ratio of moles of oxidant to moles of hydrocarbon fuel that are required to convert all of the fuel to complete (or deep) oxidation products, namely, carbon dioxide and water. For methane, the stoichiometric ratio equals 2 moles molecular oxygen (O2) per mole methane (CH4). “Near-stoichiometric” molar ratios for methane combustion could range from about 1.6 moles molecular oxygen per mole methane (1.6:1) to about 2.4:1, which ratios correlate to a phi (φ) of 0.8:1 to about 1.2:1, where phi compares the actual molar ratio employed to the stoichiometric ratio. Such high ratios of oxidant to fuel result in a flame temperature exceeding 1,200° C., which is too hot for most metallic materials of construction. Under those circumstances, the combustor is required to be constructed from ceramic materials capable of withstanding the higher temperatures, but potentially more fragile and less efficient in transferring heat to a downstream application, such as the heater head of an external combustion engine (e.g., Stirling engine).
Moreover, while combustion in the presence of a catalyst in a single stage combustor is useful in promoting complete conversion of the fuel and improved selectivity to deep oxidation products, catalyst lifetime is greatly reduced in an oxidizing environment at temperatures exceeding 1,200° C. Generally, catalyst lifetime is lengthened as temperature decreases. Moreover, at temperatures exceeding 1,200° C. the catalyst may be lost through volatilization.
In view of the above, it would be desirable to design an improved combustor apparatus that provides for a clean and complete combustion of a hydrocarbon fuel at about ambient pressure and at a temperature less than about 1,400° C. The combustor should provide for complete combustion of the hydrocarbon fuel into a mixture of carbon dioxide and water with minimal, if any, emissions of NOx and hydrocarbons. The design should accommodate a variety of materials of construction depending upon operating temperature. At combustion temperatures up to about 1,200° C., for example, the combustor should be constructed desirably from a metallic material or cermet, so as to provide for durability and efficient heat transfer. Above about 1,200° C., the combustor should be constructed from a durable ceramic material. If such a combustor were to employ an oxidation catalyst for improved conversion and selectivity, then under operating conditions the catalyst should exhibit an acceptable durability with little if any volatilization as well as exhibiting an acceptable lifetime before requiring replacement. Finally, in order to provide further improvements, the design should incorporate specific structural features for transferring heat in an efficient manner to any downstream application, such as to the heater head of an external combustion engine (e.g. Stirling engine), without undue losses of heat to the surrounding environment.
In one aspect, this invention provides for a two-stage combustor comprising a housing having disposed therein:
(a) a partial oxidation reactor comprising the following components:
(b) a deep oxidation reactor comprising the following components:
The two-stage combustor of this invention functionally splits the combustion of a hydrocarbon fuel into two process segments. A first stage of the combustor comprises a partial oxidation reactor wherein under operating conditions a catalytic partial oxidation (POX) occurs, such that a hydrocarbon fuel is partially oxidized into a gaseous partial oxidation product comprising predominantly carbon monoxide and hydrogen. A second stage of the combustor comprises a deep oxidation reactor wherein under operating conditions complete combustion occurs, either catalytically or non-catalytically, so as to convert the gaseous partial oxidation product cleanly into complete oxidation products of carbon dioxide and water with low levels of undesirable emissions. Moreover, heat generated in the two-stage combustor is efficiently transferred to a heat spreader and thereafter to a downstream heat acceptor.
Several advantages accrue from the two-stage combustor design of this invention. In one advantageous embodiment, the catalyst is disposed within the partial oxidation reactor; whereas the deep oxidation reactor does not contain a catalyst. Suitable partial oxidation catalysts, including those of the noble metal family, are able to withstand temperatures of catalytic partial oxidation processes, which are generally less than 1,200° C. and, more likely, between 750° C. and about 1,100° C. The CPOX process and its lower operating temperatures provide for catalyst durability and longevity with little, if any, volatilization. Correlated therewith, the second stage deep oxidation reactor is operated non-catalytically allowing for higher temperatures up to 1,400° C. resulting in more complete combustion while avoiding catalyst degradation problems. In a second advantageous embodiment, when both stages are intended to be operated at a temperature less than 1,200° C., an appropriate catalyst can be selected in each of the first and second stages, if desired, to optimize reactions therein.
As another advantage, the generation of hydrogen in the first stage CPOX reactor provides for improved combustion stability in the deep oxidation reactor, while aiding in reducing the operating temperature therein. This advantage allows for use of durable and thermally efficient metallic materials of construction; whereas higher temperatures generally impose a requirement for ceramic materials of construction. Moreover, the combustor of this invention provides for a clean and durable combustion process with little, if any, NOx and undesirable hydrocarbons emissions. As yet another advantage, specific structural features of the apparatus of this invention, notably, the particular structure of the heat spreader, result in efficient heat transfer to a heat acceptor, such as the heater head of an external combustion engine, without undue heat losses to the environment.
In one application, this invention provides for an improved Stirling engine having a piston undergoing reciprocating linear motion within an expansion cylinder containing a working fluid, wherein the working fluid is heated through a heater head. The improvement specifically comprises disposing the heater head in thermal communication with the aforementioned two-stage combustor, which functions to generate heat and transfer said heat to the heater head (heat acceptor) of the Stirling engine.
In one embodiment, this invention provides for a two-stage combustor comprising a housing defining a longitudinal axis and having disposed therein:
(a) a partial oxidation reactor comprising the following components:
(b) a deep oxidation reactor comprising the following components:
The term “upstream end”, as used herein, signifies a side of a specified component in the two-stage combustor wherein a fluid flow enters the component. The term “downstream end” signifies a side of a specified component in the two-stage combustor wherein a fluid flow exits the component. In one embodiment, fluids flow through the two-stages of the combustor in a direction parallel to the longitudinal axis of the combustor from the inlets of the catalytic partial oxidation reactor to the outlet of the deep oxidation reactor. It should be appreciated, however, that other operable flow patterns can be envisioned by the person of skill in the art.
In another embodiment, the foam matrix of the heat spreader is provided in an annular shape defined by an inner diameter and an outer diameter.
In another related embodiment, under operating conditions, heat transmitted to and generated within the deep oxidation reactor is transferred radially inward into a heat acceptor disposed within a cylindrical volume defined by the length and the inner diameter of the annular-shaped heat spreader. The two-stage combustor is insulated appropriately to facilitate heat transfer in a radially inward direction. Notably, interior surfaces of the combustor housing are lined with a thermal insulator material. In one embodiment, the heat acceptor comprises the heater head of a Stirling engine.
In one embodiment, the deep oxidation reactor does not comprise a catalyst; accordingly, the combustion process occurring within the deep oxidation reactor functions non-catalytically, which allows for operating temperatures up to 1,400° C. By avoiding the use of a catalyst in the deep oxidation reactor where temperatures are at their highest, the apparatus avoids the problems of catalyst degradation including catalyst volatilization and loss of catalyst lifetime.
In another embodiment, the deep oxidation reactor comprises an oxidation catalyst, and the combustion process occurring within the deep oxidation reactor functions catalytically. Such an embodiment is intended for use at temperatures typically not exceeding 1,200° C., and preferably, not exceeding 900° C.
In one embodiment, the premixer plenum does not contain a foam matrix. In this embodiment, functionally, a non-catalytic combustion occurs with a diffusion flame stabilized within the premixer plenum.
In another embodiment, the premixer plenum contains a high density foam matrix, the density thereof being higher than the density of the foam matrix provided as the heat spreader. In this embodiment, functionally, a non-catalytic flameless combustion is stabilized within the foam matrix of the heat spreader.
The invention is further described and illustrated in the following figures and embodiments. Reference is made to
Further to
In the embodiments of the invention illustrated in
Each component of the two-stage combustor apparatus of this invention is constructed from a material capable of withstanding the temperature to which the part is to be exposed. Moreover, each part is designed to maximize heat transfer downstream into an associated heat acceptor, more specifically, a heat acceptor positioned within the interior space (
The partial oxidation reactor beneficially employed in the process of this invention comprises any one of those partial oxidation (POX) reactors known in the art that provides for conversion of a mixture of the hydrocarbon fuel and the first oxidant into a gaseous partial oxidation product predominantly comprising hydrogen and carbon monoxide. Non-limiting examples of suitable partial oxidation reactors include those described in the following patent documents: U.S. Pat. Nos. 7,976,594, 8,557,189, WO 2004/060546, and US 2011/0061299, incorporated herein by reference.
According to the invention, under operating conditions a hydrocarbon fuel is fed from a fuel supply, such as a fuel tank, through a first inlet pathway into the partial oxidation reactor, preferably, into a mixer within the partial oxidation reactor. The fuel inlet pathway comprises any known inlet device for feeding the hydrocarbon fuel to the partial oxidation reactor, for example, a nozzle, atomizer, vaporizer, injector, mass flow meter, or any other suitable flow control device. The injector also functions to quantify (or meter) the fuel fed to the partial oxidation reactor. Likewise, the first supply of oxidant is fed into the partial oxidation reactor, preferably, into the mixer section of the partial oxidation reactor, through the primary oxidant inlet comprising any conventional inlet device, for example, a nozzle, injector, or mass flow meter capable of feeding the first supply of oxidant into the partial oxidation reactor.
In one embodiment, the mixer of the partial oxidation reactor comprises swirler vanes and baffles to facilitate mixing the hydrocarbon fuel and the first supply of oxidant as well as to facilitate atomization of any liquid fuel, when a liquid fuel is employed. In one other embodiment, the mixer comprises a combination of a pulsed electromagnetic liquid fuel injector and a pulsed oxidant injector, which feed the liquid fuel and the first oxidant, respectively, into an atomizer that thoroughly atomizes the liquid fuel and mixes it with the oxidant. This combined dual injector-atomizer device is described in U.S. Pat. No. 8,439,990, incorporated herein by reference. If a gaseous hydrocarbon fuel is employed, there is no requirement to provide an atomizer.
In one embodiment, the hydrocarbon fuel is fed to the mixer at ambient temperature without preheating. In another embodiment, the hydrocarbon fuel is preheated prior to being fed to the mixer. In the event that a liquid hydrocarbon fuel is employed, we have found that heat generated in the reaction zone of the partial oxidation reactor is sufficient to support liquid fuel vaporization at a level required for stable partial oxidation throughout the partial oxidation catalyst. As a consequence, the partial oxidation reactor and POX process therein are capable of providing gasification of a liquid fuel without a requirement for supplying external heat or steam to the POX reactor. The first supply of oxidant is generally fed into the mixer without preheating, but variations in temperature may be implemented as desired.
The partial oxidation reactor comprises a catalytic reaction zone having disposed therein a porous substrate onto which a partial oxidation catalyst is supported, such porous substrate configured to provide thorough mixing of the fuel and oxidant passing there through. To achieve this goal, in one embodiment the porous substrate is provided as a mesh substrate structured in the form of a reticulated net or screen comprising a plurality of pores or cells or channels. Preferably, the pores, cells, or channels of the porous mesh have an ultra-short-channel-length, as noted hereinafter. In one embodiment the mesh is suitably provided in a coiled configuration of cylindrical shape having an inner diameter and a larger outer diameter such that reactants flowing there through move along a radial flow path from an inlet along the inner diameter to an outlet along the outer diameter of the coil. In another embodiment the mesh is suitably provided as one mesh sheet or a plurality of stacked mesh sheets with a bulk flow from an inlet end of the stack to an outlet end of the stack. In any embodiment, the bulk configuration of the substrate provides for a plurality of void volumes in random order, that is, empty spaces having essentially no regularity along the flow path from the partial oxidation reactor upstream inlets to the partial oxidation reactor downstream outlet.
The porous substrate is typically constructed from any material capable of withstanding the temperature at which the partial oxidation reactor operates, generally, in a range from about 750° C. to about 1,200° C. Such materials include metals and ceramic materials of suitable temperature durability. Suitable metal meshes include, without limitation, those constructed from nickel-chromium-iron alloys, iron-chromium alloys, and iron-chromium-aluminum alloys of the kind previously disclosed herein. The term “ceramic” refers to inorganic non-metallic solid materials with prevalent covalent bonds, including but not limited to metallic oxides, such as oxides of aluminum, silicon, magnesium, zirconium, titanium, niobium, and chromium, as well as zeolites and titanates. Reference is made to U.S. Pat. Nos. 6,328,936 and 7,141,092, detailing insulating layers of ultra-short-channel-length ceramic mesh comprising woven silica, both patents incorporated herein by reference.
In one exemplary embodiment, the porous substrate comprises an ultra-short-channel-length mesh; in a more preferred embodiment thereof a MICROLITH® brand ultra-short-channel-length mesh available from Precision Combustion, Inc., North Haven, Conn., USA. A description of the ultra-short-channel-length mesh is found, for example, in U.S. Pat. No. 5,051,241, incorporated herein by reference. Generally, the mesh comprises short channel length, low thermal mass monoliths, which contrast with prior art monoliths having longer channel lengths. For purposes of this invention, the term “ultra-short-channel-length” refers to a channel length in a range from about 25 microns (μm) (0.001 inch) to about 500 μm (0.02 inch). In contrast, the term “long channels” pertaining to prior art monoliths refers to channel lengths of greater than about 5 mm (0.20 inch) upwards of 127 mm (5 inches). In this invention the term “channel length” is taken as the distance along a pore or channel from inlet to outlet, for example, as measured from an inlet on one side of a sheet of mesh to an outlet on the opposite side of the sheet. (This measurement is not to be confused with the overall length of the flow path through the entire mesh substrate from the upstream inlet of the substrate to the downstream outlet of the substrate.) In another embodiment, the channel length is not longer than the diameter of the elements from which the mesh is constructed; thus, the channel length may range from 25 μm (0.001 inch) up to about 100 μm (0.004 inch) and preferably not more than about 350 μm (0.014 inch). In view of this ultra-short channel length, the contact time of reactants with the mesh and catalyst supported thereon advantageously ranges from about 5 milliseconds (5 msec) to about 350 msec.
The MICROLITH brand ultra-short-channel-length mesh typically comprises from about 100 to about 1,000 or more flow channels per square centimeter. More specifically, each layer of mesh typically is configured with a plurality of channels or pores having a diameter ranging from about 0.25 millimeters (mm) to about 1.0 mm, with a void space greater than about 60 percent, preferably up to about 80 percent or more. A ratio of channel length to diameter is generally less than about 2:1, preferably less than about 1:1, and more preferably, less than about 0.5:1. MICROLITH brand meshes can be manufactured in the form of woven wire screens, woven ceramic fiber screens, pressed metal or ceramic screens; or they can be manufactured by perforation and expansion of a thin metal sheet as disclosed in U.S. Pat. No. 6,156,444, incorporated herein by reference; or alternatively manufactured by 3-D printing or by a lost polymer skeleton method.
The MICROLITH brand mesh having the ultra-short-channel-length facilitates packing more active surface area into a smaller volume and provides increased reactive area and lower pressure drop, as compared with prior art monolithic substrates. Whereas in prior art honeycomb monoliths having conventional long channels where a fully developed boundary layer is present over a considerable length of the channels, in contrast, the ultra-short-channel-length characteristic of the mesh of this invention avoids boundary layer buildup. Since heat and mass transfer coefficients depend on boundary layer thickness, avoiding boundary layer buildup enhances transport properties. Employing the ultra-short-channel-length mesh, such as the MICROLITH brand thereof, to control and limit the development of a boundary layer of a fluid passing there through is described in U.S. Pat. No. 7,504,047, which is a Continuation-In-Part of U.S. Pat. No. 6,746,657 to Castaldi, both patents incorporated herein by reference. The preferred MICROLITH brand of ultra-short-channel-length mesh also advantageously provides for a light-weight portable size, a high throughput, a high one-pass yield of hydrogen-containing partial oxidation product, a low yield of coke and coke precursors, and an acceptably long catalyst lifetime, as compared with alternative substrates including ceramic monolith and pelleted substrates.
In another exemplary embodiment, the porous substrate is constructed of an analogous porous structure of metal or ceramic comprising an interconnected network of solid struts defining a plurality of pores of an open-cell configuration. The pores can have any shape or diameter; but typically, a number of pores that subtend one inch designate a “pore size,” which for most purposes ranges from about 5 to about 80 pores per inch. The relative density of such structures, taken as the density of the structure divided by the density of solid parent material of the struts, typically ranges from about 2 to about 15 percent. Manufactured or structured ultra-short-channel-length substrates are commercially available in a variety of materials capable of withstanding the operating temperature of the partial oxidation reactor.
The porous substrate disposed within the partial oxidation reactor supports a catalyst capable of facilitating partial oxidation reactions, wherein a mixture of the hydrocarbon fuel and the first supply of oxidant are converted to partially-oxidized products, specifically, a synthesis gas comprising hydrogen and carbon monoxide. A suitable partial oxidation catalyst comprises at least one metal of Group VIII of the Periodic Table of the Elements, including iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum, and mixtures thereof. The deposition of the Group VIII metal(s) onto the porous substrate is implemented by methods well known in the art. Alternatively, finished catalysts comprising Group VIII metal(s) supported on the MICROLITH brand mesh substrate are available from Precision Combustion, Inc., North Haven, Conn.
In the reforming process, in one embodiment, the porous substrate supporting the partial oxidation catalyst is initially heated using a commercial ignition device, for example a resistive glow plug heating element, disposed within the partial oxidation reactor in close proximity to the substrate. The hydrocarbon fuel fed to the partial oxidation reactor is likewise heated via the ignition device. The ignition device is energized until temperature sensors located within the partial oxidation reactor indicate a temperature sufficient to initiate catalytic activity (“light-off temperature”). Once the catalyst is ignited, the ignition device is de-energized, and energy from the resulting exothermic partial oxidation reaction sustains catalytic operation without a need for inputting external heat. The ignition device allows for start-up from cold or ambient fuel conditions without a need for a fuel vaporizer or other external source of heat.
The porous heat spreader of the deep oxidation reactor comprises any porous solid material that is capable of retaining thermal energy and supporting combustion therein. In one preferred embodiment, the porous heat spreader comprises a foam matrix constructed of a plurality of struts defining a plurality of open-celled pores and channels. For this invention, the porous heat spreader should be sufficiently durable to withstand prolonged periods at operating temperatures ranging up to about 1,400° C. Accordingly, the porous heat spreader is suitably provided as a metallic, ceramic, or cermet composition appropriate to the operating temperatures. Metallic heat spreaders can be constructed, for example, from iron-chromium alloys, including FeCrAlY iron-chromium alloys or similar iron-chromium-aluminum alloys, examples of such alloy materials being described hereinabove. Ceramic heat spreaders can be constructed, for example, from alumina, aluminosilicates, and mullite, examples of such ceramic materials being described hereinabove as well. Cermets comprise a combination of the suitable ceramic material with the suitable metallic material. In one embodiment, the foam matrix has a regular or periodic distribution of like-sized open-cells. In another embodiment, the porous heat spreader, preferably the foam matrix, has an irregular or asymmetric distribution of different-sized cells winding through the strut structure in serpentine fashion. Typically, the porous heat spreader has a pore density ranging from about 10 to about 30 pores per inch (10-30 ppi).
In one embodiment the premixer comprises an open-spaced plenum, more specifically, an open-spaced plenum absent a foam matrix. In this embodiment, the premixer plenum functions to mix the partial oxidation products and the incoming secondary supply of oxidant, and thereafter combust the resulting mixture in a diffusion flame within the plenum. The combustion is lean based on employing an excess of secondary supply of oxidant relative to partial oxidation product, thereby resulting in complete conversion of the partial oxidation products, namely carbon monoxide and hydrogen, to deep oxidation products of carbon dioxide and water. Heat from the combustion flame is transferred downstream to the porous heat spreader, wherein the heat is transferred radially inwardly to any associated heat acceptor. In another exemplary embodiment, a distribution plate (
In another embodiment, the premixer plenum is filled partially or completely with a foam matrix of a higher pore density as compared with the pore density of the porous heat spreader (e.g., the foam matrix heat spreader). Typically, the foam matrix disposed within the premixer plenum has a pore density ranging from greater than about 60 pores per inch (60 ppi) to about 100 ppi. The premixer plenum containing the high-pore density foam matrix functions to provide improved mixing of the partial oxidation product with the secondary supply of oxidant. Moreover, in this instance combustion of the partial oxidation product is forced downstream into the porous heat spreader. If employed, the foam matrix disposed within the premixer plenum is suitably constructed from any of the heat spreader materials described hereinbefore, such as the iron-chromium alloys (FeCrAlY). Other suitable materials of construction include ceramic foams, such as, mullite aluminosilicate.
The hydrocarbon fuel fed to the partial oxidation reactor is selected from any gaseous or liquid hydrocarbon fuel capable of being converted into a syngas mixture comprising carbon monoxide and hydrogen. Suitable gaseous hydrocarbon fuels include, without limitation, methane, natural gas, ethane, propane, butane, ethylene, propylene, fuel gas, bio fuel gas, and mixtures thereof; methane and natural gas being preferred. Suitable liquid hydrocarbon fuels include, without limitation, gasoline, kerosene, diesel, jet propulsion fuels, such as Jet A and Jet X, biomass fuels, and synthetic fuels obtained from Fisher-Tropsch processes.
The first supply of oxidant fed to the partial oxidation reactor comprises any chemical capable of partially oxidizing the hydrocarbon fuel selectively to a gaseous partial oxidation product comprising hydrogen and carbon monoxide (syngas). Suitable oxidants include, without limitation, essentially pure molecular oxygen, mixtures of oxygen and nitrogen, such as air, and mixtures of oxygen with one or more inert gases, such as helium and argon.
The hydrocarbon fuel and first supply of oxidant are provided to the partial oxidation reactor in a “fuel-rich” ratio such that there is insufficient amount of oxidant present to convert all of the fuel to complete oxidation products of carbon dioxide and water. The quantities of first supply of oxidant and hydrocarbon fuel are best described in terms of an O:C ratio, wherein “O” refers to atoms of oxygen in the first supply of oxidant and “C” refers to atoms of carbon in the hydrocarbon fuel. Generally, the O:C ratio of oxidant to hydrocarbon fuel fed to the POX reactor is greater than about 0.5:1 and less than about 1.2:1.
The reforming process desirably involves contacting the hydrocarbon fuel and the first supply of oxidant in the absence of co-fed external water, steam or mixture thereof. In this instance, the term “co-fed external water, steam or mixture thereof” refers to co-feeding, with the supplies of hydrocarbon fuel and first supply of oxidant, a supply of water, steam, or such mixture thereof as is imported from an external source, for example, an on-board water tank or steam generator or vaporizer. While this application broadly does not prohibit co-feeding water and/or steam to the reforming process, and while partial oxidation product yields can be enhanced by the addition of co-fed water and/or steam, in the present process co-feeding external water and/or steam might add an unnecessary burden.
The reforming process typically operates at a temperature greater than about 700° C. and less than about 1,100° C. and a pressure ranging from sub-ambient to about 1 psig (6.9 kPa). A suitable gas hourly space velocity measured at 21° C. and 1 atm (101 kPa) ranges from about 10,000 liters of combined supply of hydrocarbon fuel and first supply of oxidant per liter of catalyst bed volume per hour (10,000 hr−1) to about 750,000 hr−1 which allows for high throughput. A reforming efficiency of greater than about 75 percent and, preferably, greater than about 80 percent relative to equilibrium is achievable. The partial oxidation reactor is capable of operating for greater than about 1,000 hours essentially without indications of coke production and catalyst deactivation.
The partial oxidation product exiting the POX reactor is passed into the premixer plenum where the product is supplemented with the second supply of oxidant fed through the second oxidant inlet. The second supply of oxidant supplied to the premixer comprises any chemical capable of fully combusting the partial oxidation product to complete combustion products of carbon dioxide and water, such chemicals to include air and essentially pure oxygen. In one exemplary embodiment, the first and second supplies of oxidants are identical, and preferably, comprise air. If desired, however, the first supply of oxidant supplied to the POX reactor may be different from the second supply of oxidant supplied to the premixer plenum. The partial oxidation product and second supply of oxidant are provided in quantities sufficient to convert the partial oxidation product (hydrogen, carbon monoxide, and any unconverted hydrocarbon fuel) completely to carbon dioxide and water. Such quantities refer to a “fuel-lean” condition wherein the quantity of second supply of oxidant exceeds a stoichiometric ratio that balances the combustion reaction.
Temperatures within the deep oxidation reactor range from 950° C. to about 1,400° C. Heat of combustion is transferred to a heat acceptor disposed in contact with or in close proximity to the porous heat spreader, reducing the temperature of the exhausting combustion gases to a range between about 250° C. and about 350° C. In one exemplary embodiment, the exhausting combustion gases are passed through a recuperator structure (
“Superficial velocity” is defined as the standardized volumetric flowrate (equivalent volumetric flow of gas at 0° C. and 1 bar) through the heat spreader matrix divided by cross-sectional area of the heat spreader matrix perpendicular to direction of flow. An optimal superficial velocity is dependent upon operating temperature, inlet gas composition and combustion stoichiometry. In order to maintain combustion within the heat spreader matrix, it was found experimentally that a “superficial velocity” of the gas flowing through the heat spreader matrix is best maintained from about 20 cm/s to about 60 cm/s. At lower velocities, the gas may combust at the entry region of the matrix. At higher velocities, the gas may combust downstream of the matrix. Space velocity through the heat spreader matrix, defined as combined flows of reformate (obtained from the partial oxidation reactor) and second supply of oxidant per unit of matrix volume per standard conditions of 21° C. and 1 atm (101 kPa), is maintained in a range from about 10,000 hr−1 to about 50,000 hr−1. Optimal heat transfer into the heat acceptor occurs when the combustion is distributed evenly throughout the heat spreader matrix.
An apparatus was constructed to test the efficiency of combustion and heat transfer from the deep oxidation reactor component of the instant apparatus invention to a heat acceptor simulating a heater head of a Stirling engine. With reference to the process schematic of
A metal test bar was positioned within the annulus of the foam matrix heat spreader. The top of the metal test bar was positioned in solid-to-solid contact with the heat spreader. The bottom of the test bar extended beyond the downstream end of the heat spreader. A water line brought water into thermal contact with the lower end of the test bar for cooling purposes. Thermocouples were placed on the heat spreader and along the test bar at its head (high top), top (lower top), mid-section, and bottom section.
A full scale two-stage combustor was constructed and tested in accordance with this invention. The combustor featured all components of the design illustrated in
The two-stage combustor 10 was tested with up to 3.4 kWth natural gas input as fuel to the partial oxidation reactor. Air was employed to both the primary oxidant inlet 6 of the partial oxidation reactor 3 and the secondary oxidant inlet 20 to the premixer plenum 18. The partial oxidation reactor zone 8 was operated at a fuel-rich O:C ratio sufficient to maintain a temperature of 950° C., providing for a partial oxidation product composition comprising hydrogen and carbon monoxide. The deep oxidation reactor 5 was operated lean, with excess air relative to partial oxidation product so as to provide for complete conversion of partial oxidation product to CO2 and H2O. The combustion within the deep oxidation reactor 5 was flameless, with no detectable emissions of NOx or hydrocarbons.
A metallic test bar simulating a heat acceptor was placed within the cylindrical space 25 defined by the inner diameter 24 of the heat spreader 28, in solid-to-solid contact with the heat spreader. Under operation at 3.4 kWth input of natural gas to the partial oxidation reactor, the temperature of the test bar increased to 822° C. providing proof of concept.
Thereafter, the metallic test bar was removed and the metal foam matrix heat spreader 28 was brazed onto the heater head of a Stirling engine. The resulting heat spreader-heater head combination was positioned within the housing 2 as illustrated in
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions, or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
This application claims the benefit of U.S. provisional patent application No. 62/813,785, filed Mar. 5, 2019.
This invention was made with support from the U.S. government under Contract No. DE-AR0000604, sponsored by the Department of Energy. The U.S. Government holds certain rights in this invention.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4027476 | Schmidt | Jun 1977 | A |
| 5051241 | Pfefferle | Sep 1991 | A |
| 6270336 | Terashima | Aug 2001 | B1 |
| 8784515 | Roychoudhury | Jul 2014 | B2 |
| 8795398 | Roychoudhury | Aug 2014 | B2 |
| 9903585 | Crowder | Feb 2018 | B1 |
| 10001278 | Roychoudhury | Jun 2018 | B1 |
| 20030000145 | Salemi | Jan 2003 | A1 |
| 20080078175 | Roychoudhury | Apr 2008 | A1 |
| 20090113889 | Roychoudhury | May 2009 | A1 |
| 20100126165 | Roychoudhury | May 2010 | A1 |
| 20110146264 | Roychoudhury | Jun 2011 | A1 |
| 20110165300 | Roychoudhury | Jul 2011 | A1 |
| Number | Date | Country |
|---|---|---|
| WO2004060546 | Jul 2004 | WO |
| WO2008048353 | Apr 2008 | WO |
| WO2012106048 | Aug 2012 | WO |
| Entry |
|---|
| Co-Pending U.S. Appl. No. 16/798,630, filed Feb. 24, 2020, entitled “Two-Stage Combustor for Thermophotovoltaic Generator,” Applicant: Precision Combustion, Inc. |
| Number | Date | Country | |
|---|---|---|---|
| 62813785 | Mar 2019 | US |
