Abstract: An apparatus for combustion of a fuel in stages having at least one wall enclosing a chamber and forming at least one fuel inlet opening, at least one oxidant inlet opening and a plurality of fuel/oxidant outlet openings. A recirculation sleeve is disposed on the fuel/oxidant outlet side of the chamber and is coaxially aligned with the center axis of the apparatus. A plurality of fuel distributors are disposed within the chamber, each fuel distributor having a fuel inlet and a plurality of fuel outlets, each of the fuel outlets being aligned with a corresponding one of the fuel/oxidant outlet openings. Also disclosed is a method for combustion of a fuel in stages.

Abstract: In a gas burner for introducing a fuel/air mixture into a combustion chamber, a tube is provided for introducing a source of primary air into a core portion of the fuel air mixture. The resulting secondary flame that is produced within the primary flame causes a reduction of NOX gases, which can be attributed to the dispersion of combustion byproducts within the primary flame. In one embodiment, the air supply tube enters the area of the fuel air mixture radially and then turns and extends axially along an extended axis of the burner.

Abstract: An oxy-fuel burner generates a long, luminous, stable and adjustable flame temperature profile flame by incorporating separate, fuel and oxygen jets oriented in a unique geometry. In one preferred embodiment, the fuel is injected horizontally at medium injection velocity (50-200 m/s) while primary oxygen is injected underneath the fuel jet at supersonic velocity (300-500 m/s). The supersonic velocity oxygen jet (20 to 50% required for stoichiometric combustion) entrains fuel and furnaces gases in it's core for the primary flame development over the furnace load. The subsequent mixing of the fuel, primary oxygen and entrained furnace gases establish a low NOx, stable, long and luminous primary flame. The secondary oxidant, preferably air or low purity oxygen (50 to 80% of stoichiometric needs), is injected above the flame using one or more oxygen jets to create an oxy-fuel flame with adjustable flame characteristics.

Abstract: A tubular burner for industrial furnaces is capable of achieving a good mixing of combustion gas and fuel. This burner contains an end section projecting into a combustion zone supplied with secondary combustion air, and several separate annular feed ducts for combustion gas and fuel bounded by tubular walls arranged coaxially one inside the other, individual nozzles being arranged in approximately annular distribution in the end wall of the combustion gas feed duct facing into the combustion zone. To achieve a good mixing of combustion gas/combustion air and fuel, at least one outer annular feed duct is constructed essentially as fuel feed duct, whilst the combustion gas feed duct equipped with individual nozzles is arranged radially inside this fuel feed duct.

Abstract: A method of mixing two or more dissimilar fluids such a gas and a liquid is provided. The method includes the steps of introducing one fluid into the other to form a mixture, inducing cavitation in the mixture to reduce at least one of the fluids to a large number of relatively small units, and distributing the small units uniformly throughout the mixture. In a preferred embodiment, the step of inducing cavitation comprises introducing the mixture into a chamber having a rotating disk formed with a plurality of irregularities such as bores. The irregularities on the rotating disk induce cavitation in the mixture. The cavitation also breaks down van der Waals attractions within the mixture to enhance mixing.

Abstract: An ultra low NOx burner for process heating is provided which includes a fluid based flame stabilizer which provides a fuel-lean flame at an equivalence ratio in the range of phi=0.05 to phi=0.3 and fuel staging lances surrounding the flame stabilizer in circular, flat, or load shaping profiles, each lance comprising a pipe having a staging nozzle at a firing end thereof, each lance having at least one hole for staging fuel injection, and each hole having a radial divergence angle and an axial divergence angle. The at least one hole and the divergence angles provide circular, flat or load shaping flame pattern. The burner provides NOx emissions of less than 9 ppmv at near stoichiometry combustion conditions.

Abstract: There is provided methods and systems for the reduction of nitrogen oxides and carbon loss from carbonaceous fuel combustion flue emissions. The preferred carbonaceous fuel is coal. The invention provides methods and systems comprising the use of coal as a reburn fuel for coal combustion systems. The invention comprises low temperature pyrolysis producing gaseous hydrocarbons for the reduction of nitrogen oxides and treatment of char with resulting reduction of carbon loss.

Abstract: To provide a burner for a hydrogen generation system having an excellent combustion stability which can be achieved at low costs, and a hydrogen generation system having such a burner.

Abstract: An oxy-fuel burner is set forth for providing combustion energy to a glass furnace via the mixing and combustion of a fuel stream and an oxidizer stream. The burner is divided into at least two sections, a substantially vertical section beginning at the bottom or feed end of the burner and a generally shorter, substantially horizontal section terminating at the opposite or discharge end of the burner. In a key embodiment, the vertical section of the burner protrudes into the furnace atmosphere through the underside of an air port, while the horizontal section is pointed toward the interior of the furnace. Depending on the number of burners installed, this allows from partial to full conversion of an air fuel furnace to an oxy-fuel furnace. Also, in a key embodiment, the burner includes an oxidant staging means to introduce oxidizer through a staging conduit running beneath and collateral with the outer conduit.

Abstract: A low emissions burner includes a diffusion burner surrounded by an annular array of premix burners. The diffusion burner operates at maximum swirl air flow and at a low constant fuel rate to reduce NOx emissions. The diffusion burner provides a stable swirling diffusion flame. An annular array of premix burners surrounds the diffusion burner and provides a non-swirling premix flame about the diffusion flame to advantageously provide a higher heat content about the periphery of the burner flame to facilitate industrial drying processes using the burner. The diffusion burner flame maintains the premixed flame stabilized. Water injection nozzles are provided each of the premix and diffusion burners.

Abstract: NOx formation in the combustion of solid hydrocarbonaceous fuel such as coal is reduced by obtaining, from the incoming feed stream of fuel solids and air, a stream having a ratio of fuel solids to air that is higher than that of the feed steam, and injecting the thus obtained stream and a small amount of oxygen to a burner where the fuel solids are combusted.

Abstract: NOx emissions from combustion are reduced, NOx reduction efficiency by SNCR is improved, and other efficiencies are realized, by injecting oxygen into a fuel-rich combustion zone under controlled conditions.

Abstract: A furnace that combusts fuel, such as coal, of a given minimum energy content to obtain a stated minimum amount of energy per unit of time is enabled to combust fuel having a lower energy content, while still obtaining at least the stated minimum energy generation rate, by replacing a small amount of the combustion air fed to the furnace by oxygen. The replacement of oxygen for combustion air also provides reduction in the generation of NOx.

Abstract: Improved operational characteristics such as improved fuel efficiency, reduction of NOx formation, reduction of the amount of unburned carbon in the ash, and lessened tendency to corrosion at the tube wall, in a multi-burner furnace are obtained by reducing the flow rate of combustion air to the burners and selectively individually feeding oxidant to only some of the burners.

Abstract: Methods and apparatus for combusting a fuel with an oxidant are described, the apparatus comprising a ceramic burner block, the burner block having a back face and a front face. The burner block has at least one oxidant cavity in an upper portion of the burner block, and at least one fuel cavity in a lower portion of the burner block, each cavity extending from the back face to the front face. The at least one oxidant cavity has positioned therein a fuel supply conduit, the fuel supply conduit having a fuel supply conduit exit positioned a sufficient distance from the front face to allow combustion of at least a portion of fuel exiting the fuel supply conduit exit with at least some of the oxidant traversing the oxidant cavity, and the least one fuel cavity having connected thereto, near the back face, an oxidant conduit, thereby allowing mixing of a minor portion of the oxidant with the fuel.

Abstract: An improved combustion system for reducing NOx in a furnace 10 is provided having a primary flame zone 12. The primary flame zone 12 includes a plurality of burners 14 located therein which are operated on a sub-stoichiometric level thereby producing uncombusted natural gas (or hydrocarbon). The burners 14 also facilitate the passage of the uncombusted natural gas (or hydrocarbon) from the primary flame zone 12 into a secondary flame zone 18 above the primary flame zone. The secondary flame zone 18 is provided with a natural draft port 20, having a predetermined cross-sectional area, formed therein at a predetermined distance above the primary flame zone 12. As a result, air of a predetermined volume is induced into the secondary flame zone 18 so that uncombusted natural gas (or hydrocarbon) in the secondary flame zone is combusted thereby reducing NOx emissions from the furnace 10.

Abstract: An oxy-fuel burner generates a long, luminous, stable and adjustable flame temperature profile flame by incorporating separate, fuel and oxygen jets oriented in a unique geometry. In one preferred embodiment, the fuel is injected horizontally at medium injection velocity (50-200 m/s) while primary oxygen is injected underneath the fuel jet at supersonic velocity (300-500 m/s). The supersonic velocity oxygen jet (20 to 50% required for stoichiometric combustion) entrains fuel and furnaces gases in it's core for the primary flame development over the furnace load. The subsequent mixing of the fuel, primary oxygen and entrained furnace gases establish a low NOx, stable, long and luminous primary flame. The secondary oxidant, preferably air or low purity oxygen (50 to 80% of stoichiometric needs), is injected above the flame using one or more oxygen jets to create an oxy-fuel flame with adjustable flame characteristics.

Abstract: An anti-condensation device for a flame sensor (10) of a combustion chamber (12), wherein the sensor (10) is disposed outside the combustion chamber (12) and determines the presence of the combustion flame by means of an aperture (14) provided in a wall of the chamber (12); the device comprises at least two tubular structures (22, 24), one of which (24) surrounds the other (22) at least partially, an annular space in which air flows being provided between these two structures (22, 24).

Abstract: In a gas burner for introducing a fuel/air mixture into a combustion chamber, a tube is provided for introducing a source of primary air into a core portion of the fuel air mixture. The resulting secondary flame that is produced within the primary flame causes a reduction of NOX gases, which can be attributed to the dispersion of combustion byproducts within the primary flame. In one embodiment, the air supply tube enters the area of the fuel air mixture radially and then turns and extends axially along an extended axis of the burner.

Abstract: The invention is a method and apparatus for use therewith for a main burner of a gas turbine. The method employs catalytic combustion to support main combustion. More specifically, a rich fuel/air mixture is catalytically oxidized with the resulting reacted mixture being made lean by having additional air added thereto. The resulting lean mixture is then combusted in the presence of the main mixture that is also lean thereby supporting combustion of the main mixture. The method allows for enhanced turndown of a lean main mixture.

Abstract: A gas burner assembly, including its gas intake manifold, in combination with upper and lower tiered baffles, and includes the side chambers for regulation of flow if air through a draw in and through type of burner assembly, to provide heated air for a building. Various slots are provided in both the side chambers, and are custom designed for application to select tiers of the upper and lower baffles, to precisely regulate the flow of air into the combustion chamber, and regulate the type of flame generated, to furnish very precise generation of heat, and BTU output for the various sized burner assemblies.

Abstract: A process and furnace for melting glass is set forth wherein the majority of the combustion energy over the melting zone of the furnace is provided by oxy-fuel combustion while a majority of the combustion energy over the fining zone of the furnace is provided by air-fuel combustion. In many cases, it will be preferable to provide greater than 70% and up to and including 100% of the combustion energy over the melting zone by oxy-fuel combustion and greater than 70% and up to and including 100% of the combustion energy over the fining zone by air-fuel combustion. By proper tailoring of the combustion space atmosphere through oxy-fuel and air-fuel firing, the present invention can result in an improvement in glass productivity and quality. The present invention can be applied in the construction of a new furnace or can be applied to existing air-fuel furnaces.

Abstract: A combustor having a combustion liner and at least one combustor orifice assembly, the combustor orifice assembly comprising a boss, an orifice plate that defines an orifice, the orifice plate having a bottom surface that is adapted to be received by the boss, and a retaining ring, whereby the orifice plate is retained between the retaining ring and the boss.

Abstract: A NOx reduction burner system and process. Fuel modification and fuel rich reactor zone gases are brought together with products from a fuel lean reactor zone in a low temperature burnout and NOx reduction reactor zone. The fuel modification fuel rich reactor stabilizes combustion through recirculation of hot gases to the reactants. Nitrogenous species decay reactions in the fuel rich zone controls the production of NOx. The nitrogenous species from the fuel rich zone and the NOx from the fuel lean zone then react in the burnout zone at an optimal temperature and nitrogenous species mix where NOx is minimized. Temperature in all zones, and in particular the burnout zone, can be controlled by furnace gas entrainment, induced flue gas recirculation, forced flue gas recirculation and active cooling by radiative and/or convective heat transfer. NOx can be even further reduced by introducing ammonia, or a like amine species, into the low temperature burnout zone.

Abstract: In a method for reducing the content of polychlorinated dibenzodioxins and -furans in the exhaust gas of chemical high temperature processes handling process materials, amides or organic oxides are made available to the process under the conditions under which the polychlorinated dibenzodioxins and -furans are generated, which amides comprise of at least one of the group consisting of amidosulfonic acid, hydroxyl amino sulfonic acid and sulfamid in an amount of 0.5 to 10% of the process material.

Abstract: Various methods for decreasing the amount of nitrogen oxides released to the atmosphere as a component of combustion gas mixtures are provided. The methods specifically provide for the removal of nitric oxide and nitrogen dioxide (NOx) from gas mixtures emitted from stationary combustion systems. In particular, methods for improving efficiency of nitrogen oxide reduction from combustion systems include injecting metal-containing compounds into the main combustion zone and/or the reburning zone of a combustion system. The metal containing compounds react with active combustion species, and these reactions change radical concentrations and significantly improve NOx conversion to molecular nitrogen. The metal-containing additives can be injected with the main fuel, in the main combustion zone, with secondary or reburning fuel addition, or at several locations in the main combustion zone and reburning zone.

Abstract: A flat-flame burner for reheat, holding, and heat-treatment furnaces for treating iron and steel products. It has at least one fuel-injection pipe lying along the axis of the body of the burner, a combustion tunnel and a combustion-air feed, the air being distributed in and by the body. The fuel is introduced via the injection pipe or pipes through at least one axial orifice lying in a plane close to the external plane of the combustion tunnel, into the combustion products. This produces a first dilution of the fuel in these combustion products, the fuel/combustion products mixture thus obtained being diluted further in the combustion air.

Abstract: Methods and apparatus for combustion of a hydrocarbon fuel in a combustion chamber of a furnace or boiler are presented, the combustion normally using only air as an oxidant, part of the air entering the combustion chamber through one or more burners, and a remaining portion of air entering the combustion chamber at a plurality of locations downstream of the burners. The methods comprise injecting oxygen-enriched gas through a plurality of lances into the combustion chamber at a plurality of downstream locations, the oxygen-enriched gas injected at a velocity ranging from subsonic to supersonic, and the oxygen-enriched gas being present in an amount sufficient to provide an oxygen concentration of no more than 2% on a volume basis greater than when air is used alone as oxidant.

Abstract: Fuel such as coal is combusted in a staged combustion device in a method comprising feeding into a first combustion stage of said furnace said fuel and gaseous oxidant containing more than 21 vol. % oxygen, and preferably 21.8 to 29 vol. % oxygen, at a stoichiometric ratio below that which, if the stage were operated with air as the only oxidant, would produce the same amount of NOx, and combusting said fuel with said gaseous oxidant in said combustion stage to produce combustion products and unburned fuel.

Abstract: In order to create a process for the economical production of cement clinker in a cement clinker production line with a raw meal preheater, a precalcination stage, a rotary tubular kiln and a clinker cooler, in which the total oxygen excess required for all firing points, i.e., the ratio of total oxygen to total fuel, also designated as &lgr; value, is to lie as low as possible, it is proposed according to the invention, to continuously measure the content of CO and/or (unburned) hydrocarbons and/or other combustion products in the exhaust gas path of the precalcination stage and, in dependence on this measurement value, to perform a regulating intervention on the amount of an oxidation agent and/or catalyst to be injected into the precalcination stage.

Abstract: There is provided methods and systems for the reduction of nitrogen oxides and carbon loss from carbonaceous fuel combustion flue emissions. The preferred carbonaceous fuel is coal. The invention provides methods and systems comprising the use of coal as a reburn fuel for coal combustion systems. The invention comprises low temperature pyrolysis producing gaseous hydrocarbons for the reduction of nitrogen oxides and treatment of char with resulting reduction of carbon loss.

Abstract: A fuel being primarily a liquid fuel is ejected through a fuel ejection pipe having an annular ejection opening; primary air is ejected through primary air-ejecting openings arranged on outer and inner sides of the fuel ejection opening, to form outer and inner primary air-ejection straight stream openings between which the fuel ejection stream is interposed, and to burn the fuel ejection stream. The fuel-spraying openings are arranged on the same circumference. The outer and inner primary air-ejecting openings, respectively, are each arranged on a respective concentric circumference having a center point identical to the center of the circumference on which the fuel-spraying openings are arranged. When a power fuel is used, optionally a liquid fuel is further ejected and mixed with the primary air stream, and the liquid and power fuels are burnt together.

Abstract: Low NOx apparatus and methods for burning liquid and gaseous fuels are provided by the present invention. The apparatus of the invention is basically comprised of a housing having an open discharge end attached to a furnace space, means for introducing a controlled quantity of air into the housing and into the furnace space, a combustion compartment disposed within the housing for providing a primary combustion zone therein having an open inlet end for receiving a portion of the air introduced into the housing and an open discharge end, a liquid fuel nozzle attached to the housing for discharging liquid fuel into the primary combustion zone, at least one primary gaseous fuel nozzle for discharging primary gaseous fuel into the primary combustion zone and at least one secondary gaseous fuel nozzle for discharging secondary gaseous fuel into the furnace space.

Abstract: A low NOx and CO emission heating apparatus provides for substantially separate fuel and combustion air feeds into a combustion chamber provided at one end with an exhaust gas opening and, at an opposite end with an elongated porous air distributor through which air is fed into the combustion chamber and into jets of fuel directed into the space between the air distributor and the side wall of the combustion chamber. Both air and fuel may be subjected to swirl to improve the combustion, by adjusting the inclination of the fuel nozzles.

Abstract: A liquid fuel burner comprising a burner tip outputs a thin ring of oil that may be more easily atomized by the flow of atomizing oxidant at lower pressures. The liquid fuel burner comprises a fuel conduit and an atomizing oxidant conduit coaxial about the fuel conduit. The fuel conduit and atomizing oxidant conduit output fuel and oxidant into a furnace through the burner tip. The burner tip includes a central dispersion head in the output end of the fuel conduit which operates to fan the liquid fuel oil outward into a thin fan shaped ring that then is atomized by the surrounding flow of high velocity oxidant.

Abstract: Methods are presented to increase the throughput of a recovery boiler equipped with at least primary and secondary levels of injection of air. The methods comprise operating the recovery boiler with a third level of oxidant injection below or at the same level as the secondary level, and oxygen enrichment applied to at least the secondary level and said third level.

Abstract: A method of combustion and an apparatus therefor in which separate streams of very lean and very rich fuel/oxidant mixture are combusted separately, the products of combustion therefrom being thoroughly mixed before final combustion takes place. The lean/rich primary combustion minimizes combustion temperatures and pollutant formation, whilst the final combustion is substantially stoichiometric.

Abstract: A combustion method for carrying out combustion with reduced generation of NOx wherein high velocity fuel and oxidant in a very low substoichiometric ratio are combusted and thereafter secondary oxidant mixes and combusts with the resulting combustion reaction products.

Abstract: In a method of, and an appliance for, operating a burner (26), in which a combustion air flow (14) transports fuel into a combustion chamber (28) where the fuel is burnt, the formation of coherent flow instabilities of the combustion air flow (15) after emergence into the combustion chamber (28) is prevented by perturbation air (22) being injected into the combustion air flow (15).

Abstract: An apparatus for producing the glass soot used in the formation of optical fiber includes a burner with an internal atomizer. The atomizer includes an outer tube having a nozzle at an end thereof, and an inner tube located within the outer tube and having a closed end restricting fluid flow therethrough and defining a cylindrical sidewall having radially extending apertures spaced there along. The outer tube receives the glass-forming mixture in liquid form and the inner tube receives an atomizing gas which flows through the apertures in the sidewall of the inner tube and atomizes the glass-forming mixture as the glass-forming mixture travels through the outer tube.

Abstract: Combustion assembly adapted to be placed in a wall of a furnace including an axis having at least one pair of burners with axes, one oxidant lance arranged between the burners of the pair and having a lance axis and a source of oxidant connected to the burners and to the lance.

Abstract: A burner assembly having improved flame length and shape control is presented, which includes in exemplary embodiments at least one fuel fluid inlet and at least one oxidant fluid inlet, means for transporting the fuel fluid from the fuel inlet to a plurality of fuel outlets, the fuel fluid leaving the fuel outlets in fuel streams that are injected into a combustion chamber, means for transporting the oxidant fluid from the oxidant inlets to at least one oxidant outlet, the oxidant fluid leaving the oxidant outlets in oxidant fluid streams that are injected into the combustion chamber, with the fuel and oxidant outlets being physically separated, and geometrically arranged in order to impart to the fuel fluid streams and the oxidant fluid streams angles and velocities that allow combustion of the fuel fluid with the oxidant in a stable, wide, and luminous flame. Alternatively, injectors may be used alone or with the refractory block to inject oxidant and fuel gases.

Abstract: Dilution sleeves are provided in radially aligned openings in the combustion liner and flow sleeve of a combustor for a gas turbine. The sleeves have a flange for seating on a collar of the flow sleeve about the opening therethrough enabling the dilution sleeve to extend through the aligned openings. A cover is removably mounted on the outer casing and a spring bears between the cover and the dilution sleeve flange to maintain the dilution sleeve in the openings. Dilution sleeves having different cross-sectional flow areas may be provided in lieu of initially installed dilution sleeves upon comparing measured emission levels with desired emission levels and ascertaining the desired increase or decrease in cross-sectional flow area through the dilution sleeves.

Abstract: An air heating burner having improved CO emissions across a broad range of heat inputs. The burner incorporates wings which cover portions of mixing plates associated with low to medium-low fire. The wings reduce air flow velocity to eliminate quenching during such conditions, thereby increasing combustion temperature and reducing CO emissions. The wings also form pre-heat chambers which further increase combustion temperature. The burner produces a substantially consistent level of CO emissions across the range of inputs, regardless of the pressure drop across the burner.

Abstract: A method for reducing NOx emissions from the combustion of carbonaceous fuels using three stages of oxidation and second stage in-situ furnace flue gas recirculation. In the first stage, a partial oxidation combustor is used to partially combust the fuel in the presence of preheated combustion air. The fuel gas produced in the partial oxidation process is passed to a second stage partial oxidation combustor while molten slag is removed and disposed of. Preheated combustion air also is introduced into the second stage of combustion to produce a slightly reducing flue gas and is injected into the furnace in such a way as to create the desired in-situ furnace flue gas recirculation. In the upper part of the furnace a third combustion air is mixed with the flue gas in a third stage of combustion to substantially complete the combustion process. Preheated steam may be added to the first or second stages of combustion.

Abstract: A method for reducing NOx emissions from the combustion of carbonaceous fuels using two sequential stages of partial oxidation followed by a final oxidation stage. In the first stage, substoichiometric air condition of about 0.55 to 0.75 is used in a plug flow fashion, while second stage combustion is performed at a stoichiometric ratio of about 0.80 to 0.99. As the second stage combustion products are cooled by radiant heat transfer to the boiler furnace walls, overfire air is added to produce an stoichiometric ratio of about 1.05 to 1.25 to complete the combustion process. In this manner, the formation of thermal NOx is reduced.

Abstract: A combustion method and burner system are disclosed herein. The burner system comprises: a fuel manifold comprising a housing, the housing defining an interior area comprising a chamber. The burner system comprises a set of injectors for injecting a fuel from the chamber into a stream of air to pre-mix the fuel and the air, the set of injectors disposed radially inward from the fuel manifold. The system includes a refractory located downstream of the fuel manifold, the refractory to shape a flame and the refractory comprising a plurality of channels for at least one of introducing air and combustion product into a combustion chamber, the combustion chamber located downstream of the refractory. The system can also include steam and/or water injection.

Abstract: A burner (10) for reducing NOx emissions where supply fuel (16) and supply air (20) are supplied to a combustion tunnel (52) at high and low velocities and secondary air (26) is supplied to a secondary combustion zone (60), wherein products of combustion (59) exiting into the secondary combustion zone (60) from the combustion tunnel (52) are drawn back into the combustion tunnel (52) and back into the secondary air conduit (54).

Abstract: Method and apparatus for continuation of combustion with an oxy-fuel combustion system when the supply of oxygen is temporally reduced or stopped. Air or oxygen enriched air and fuel are introduced into the device being heated in place of the oxy-fuel mixture to effect combustion and maintain the heating level in the furnace. Water cooling of the furnace gases is used to reduce the volume of exhaust gases when operating in the air or oxygen enriched air mode.

Abstract: A multi-stage heating apparatus having a first stage combustion chamber, a second stage combustion chamber, a primary porous matrix chamber disposed between the first and second stage combustion chambers, a secondary porous matrix chamber, heat exchanger tubes for transfer of heat from the combustion products to a working fluid, a recirculation device for recirculating combustion products in the first and second stage combustion chambers to the root of flames therein. A mixture of fuel and primary oxidant is introduced into the first stage combustion chamber, and the products of combustion therein are conveyed to the porous matrix chamber disposed between the first and second stage combustion chambers. After undergoing intensive heat transfer in the porous matrix chamber, the cooler products of combustion flow into the second stage combustion chamber forming additional products of combustion.