Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C9/00—Combustion apparatus characterised by arrangements for returning combustion products or flue gases to the combustion chamber
  • F23C9/08—Combustion apparatus characterised by arrangements for returning combustion products or flue gases to the combustion chamber for reducing temperature in combustion chamber, e.g. for protecting walls of combustion chamber
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23D—BURNERS
  • F23D11/00—Burners using a direct spraying action of liquid droplets or vaporised liquid into the combustion space
  • F23D11/36—Details, e.g. burner cooling means, noise reduction means
  • F23D11/38—Nozzles; Cleaning devices therefor
  • F23D11/383—Nozzles; Cleaning devices therefor with swirl means
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23D—BURNERS
  • F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
  • F23D14/20—Non-premix gas burners, i.e. in which gaseous fuel is mixed with combustion air on arrival at the combustion zone
  • F23D14/22—Non-premix gas burners, i.e. in which gaseous fuel is mixed with combustion air on arrival at the combustion zone with separate air and gas feed ducts, e.g. with ducts running parallel or crossing each other
  • F23D14/24—Non-premix gas burners, i.e. in which gaseous fuel is mixed with combustion air on arrival at the combustion zone with separate air and gas feed ducts, e.g. with ducts running parallel or crossing each other at least one of the fluids being submitted to a swirling motion
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C2201/00—Staged combustion
  • F23C2201/20—Burner staging
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C2202/00—Fluegas recirculation
  • F23C2202/30—Premixing fluegas with combustion air
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C2202/00—Fluegas recirculation
  • F23C2202/50—Control of recirculation rate
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C2900/00—Special features of, or arrangements for combustion apparatus using fluid fuels or solid fuels suspended in air; Combustion processes therefor
  • F23C2900/09002—Specific devices inducing or forcing flue gas recirculation

Definitions

• the industrial fuel burners are used in the metallurgical field, for example in the combustion chambers, in fume scrubbers, in forging furnaces, heat treatment furnaces, furnaces for heating and melting, in a continuous or discontinuous cycle, for the processing of ferrous and non-ferrous metallic materials.
• US-A-5092761 and EP 1 20 188 B1 disclose methods for the reduction of nitrogen oxides by a partial recirculation of the combustion fumes, withdrawn directly from the combustion chamber of a burner and re-supplied into a fuel flow.
• the premixing of combustion fumes with the fuel fluid involves a dilution and dispersion of the fuel itself and of the flame and, consequently, a lowering of the combustion temperature, known as the "flameless" combustion effect.
• the object of the present invention is to provide a combustion method and an industrial burner for the above-mentioned applications, having such characteristics as to obviate the drawbacks mentioned with reference to the prior art.
• a particular object of the invention is to provide a combustion method and an industrial burner, particularly for the above-mentioned applications, having an improved energy efficiency and such characteristics as to reduce the NOx formation.
• - Fig. 1 is a schematized partial sectional view of an industrial burner according to an embodiment of the invention
• Fig. 2 illustrates the flows of oxidizing agent, fuel, and combustion fumes, as well as the formation of a flame in the burner of Fig. 1 , in accordance with an embodiment.
• FIG. 3 is a schematized partial sectional view of an industrial burner according to a further embodiment of the invention.
• FIG. 4 and 5 are schematized views of an industrial burner according to embodiments of the invention.
• an industrial burner 1 comprises a combustion chamber 2, a fuel duct 3 in fluidic connection with the combustion chamber 2, an oxidizing agent duct 4 in fluidic connection with the combustion chamber 2, and a discharge duct 5 in fluidic connection with the combustion chamber 2.
• the industrial burner 1 further comprises means (e.g., a fan or a pump 6) for conveying a fuel flow 7 through the fuel duct 3 into the combustion chamber 2, means (e.g., a fan 8 or a pump) for conveying an oxidizing agent flow 9 (e.g., air, air mixed with oxygen or only oxygen) through the oxidizing agent duct 4 into the combustion chamber 2, as well as ignition means 10 for ignition, where in the combustion chamber 2 there are not the conditions for a self-ignition, a combustion reaction of the fuel 7 with the oxidizing agent 9 within the combustion chamber 2, so that the combustion generates hot combustion gases/fumes 11 that, possibly after aver giving at least part of the heat, are removed from the combustion chamber 2 through the above- mentioned discharge duct 5.
• means e.g., a fan or a pump 6
• an oxidizing agent flow 9 e.g., air, air mixed with oxygen or only oxygen
• the burner 1 further comprises one or more first recirculation ducts 12 that put in fluidic communication a withdrawing point 13 of the combustion chamber 2 (Fig. 4) or of the discharge duct 5 downstream of the combustion chamber 2 (Fig.
• the oxidizing agent duct 4 is configured as a Venturi tube, so that the oxidizing agent flow 9 acts as the driving fluid, generating a recirculation of a first partial flow 15 of combustion gas withdrawn from the combustion chamber 2 or from the discharge duct 5 and suctioned through the first recirculation duct(s) 12 into the oxidizing agent duct 4, where the first partial flow 15 of combustion gases/fumes mixes with the oxidizing agent flow 9.
• the burner 1 may comprise a mixing and injection body 16 defining:
• the at least one oxidizing agent inlet opening 19 can be formed in a tubular collector 20 projecting in the inner chamber 18 and having a narrow flow cross- section to accelerate the oxidizing agent flow 9 at the outlet from the collector 20 and generate the Venturi effect that is necessary for suctioning the first partial flow 15 of combustion gases/fumes in the oxidizing agent flow 9.
• the part of the mixing and injection body 16 forming the oxidizing agent 21 and fuel 23 output openings directly opens into the combustion chamber 2 and it can be made of a refractory and/or thermal insulation material or, alternatively, of stainless steel, to withstand high thermal stresses.
• the combustion chamber 2 itself may form an annular, e.g., converging or diverging frusto-conical diffusion surface 26, about the oxidizing agent 21 and fuel 23 output openings of the mixing and injection body 16.
• Fig. 2 illustrates the operation of the burner 1 in accordance with an embodiment.
• the flow of oxidizing agent, passing through the collectors 20, is accelerated and suctions the first partial flow 15 of combustion gases/fumes through the fumes inlet aperture 17 in the inner chamber 18, where it mixes with the flow of oxidizing agent in a mixing zone 24 downstream of the collectors 20.
• the oxidizing agent-fumes/gases mixture then passes through a diffuser zone 25, which may have a frusto-conical profile, of the oxidizing agent outlet opening 21 from which it reaches the combustion chamber 2.
• the fuel outlet opening may comprise a centrifugal end dispenser 27 so shaped as to induce a centrifugal acceleration and to further promote the mixing of the fuel with the oxidizing agent/fumes mixture in the zone (14).
• the burner may comprise a second recirculation duct 28, extending for example externally along the fuel passage duct 22, from a fuel withdrawing point 30 adjacent to the fuel outlet opening 23 up to the re-input point 14 (at the exit of the oxidizing agent from the collectors 20) so as to withdraw a second partial flow of fuel 29 from the combustion chamber 2 in the fuel withdrawing point 30 and re-input the second partial flow 29 at the re-input point 14 into the oxidizing agent duct, by using the oxidizing agent flow 9 as the driving fluid to suction also the second partial flow 29 of fuel.
• This allows to stabilizing and controlling the flame shape by virtue of a "pilot flame” effect, and carrying out the two-stage combustion.
• the second recirculation duct 28 allows exploiting the depression created by the motion of the oxidizing agent to suction small amounts of fuel, for example, to a max. 30% of the total flow rate of the fuel.
• the fuel suctioned mixes with the oxidizing agent and the fumes, giving rise to a low-temperature partial combustion, which is completed upon combining with the remaining fuel when the oxidizing agent exits the oxidizing agent outlet opening 21.
• the burner 1 hereto described by way of exemplary embodiment example can be used and further adapted and configured to carry out a method for burning a fuel, which generally speaking comprises:
• [0034] withdrawing a first partial flow 15 of combustion gases/fumes 11 from the combustion chamber 2 and supplying the first partial flow 15 of combustion gases/fumes into the oxidizing agent duct 4 in a re-input point 14 upstream of the combustion chamber 2, to mix the first partial flow 15 of combustion gases/fumes with the oxidizing agent flow 9, [0035] - configuring the oxidizing agent duct 4 at the re-input point 14 as a Venturi tube, and using the oxidizing agent flow as the driving fluid for suctioning the first partial flow 15 of combustion gases/fumes.
• the oxidizing agent flow 9 is conveyed by a conveyor of oxidizing agent fluid, for example, air, 8, particularly a fan or pump, which is arranged in the oxidizing agent duct 4, and the first partial flow 15 of combustion gases/fumes is supplied into the oxidizing agent duct 4 downstream of the conveyor 8.
• a conveyor of oxidizing agent fluid for example, air, 8, particularly a fan or pump, which is arranged in the oxidizing agent duct 4, and the first partial flow 15 of combustion gases/fumes is supplied into the oxidizing agent duct 4 downstream of the conveyor 8.
• the method provides for conveying the oxidizing agent flow 9 without fuel at , the re-input point 14 of the oxidizing agent duct 4, so as to pre- mix the first partial flow 15 of combustion gases/fumes only with the oxidizing agent.
• the method provides for using, as the driving fluid for suctioning and recirculating the first partial flow 15 of the combustion gases/fumes, more than 80% of the total volume, preferably substantially the whole total volume, of the oxidizing agent supplied into the combustion chamber 2.
• the method may comprise the step of withdrawing the first partial flow 15 of combustion gases/fumes directly from the combustion chamber 2 (hence, still upstream of the fumes duct 11) and re- inputting the first partial flow 15 at the re-input point 14 into the oxidizing agent duct 4, by using the oxidizing agent flow 9 as the driving fluid for suctioning the first partial flow 15 of combustion gases/fumes.
• the first recirculation duct 12 can extend from the combustion chamber 2 (upstream of the fumes duct 11) up to the re-input point 14 of the oxidizing agent duct 4.
• the first partial flow 15 of combustion gases/fumes is withdrawn from the discharge duct 5 at a withdrawing point 13 downstream of the combustion chamber 2.
• the oxidizing agent flow has, at the Venturi tube (when it exits the collectors 20) a speed ranging between 100 m/s and 270 m/s.
• the speed of the flow oxidizing agent at the Venturi tube ranges between 70 and 270m/s.
• the oxidizing agent- combustion gases/fumes mixture is output from the oxidizing agent outlet opening 21 (and then re-input into the combustion chamber 2) at a speed ranging between 30 m/s and 150 m/s.
• these values may sensibly vary based on the actual constructive embodiment.
• the oxidizing agent duct 4 is configured and supplied so as to create, at the re-input point 14, a depression ranging from 0 to 200 mmH 2 0, preferably 0 to 90 mmH 2 0.
• the flow rate of the re-circulated combustion fumes may range, during the carrying out of the method, from 0 to beyond 100% of the volume of the fumes produced by the combustion.
• the volume of the combustion gases/fumes produced by the combustion does not include also the volume of the fumes already recirculated before into the combustion chamber. Therefore, a part of the fumes that are present within the combustion chamber is always removed definitively from the process.
• the (Vfumi/Vcomb) ratio between the flow rate of the recirculated combustion fumes and the flow rate of the oxidizing agent 9 may vary or be varied or adjusted from 0:1 up to beyond 1 :1.
• the method comprises the step of recirculating the first partial flow 15 of combustion gases/fumes without interposing filters, so as to recirculate and re-burn also the dusts and the solid particulate which are contained in the combustion fumes. This allows reducing also the particulate emissions.
• the method provides for adjusting the flame shape within the combustion chamber 2, adjusting the mutual inclination of the axes 36 of the fuel outlet openings 23 and the axis of the oxidizing agent outlet opening 21.
• the first partial flow 15 of combustion gases/fumes has a temperature higher than 750° C, preferably higher than 1250° C, and a mixing of the first partial flow 15 of combustion gases/fumes with the oxidizing agent 9 increases the temperature of the oxidizing agent 9 to beyond 600°C, preferably beyond 1000°C.
• the fuel flow 7 may comprise a solid fuel, for example, in powder form, carried by a carrier fluid, for example, a gaseous or liquid fuel.
• a carrier fluid for example, a gaseous or liquid fuel.
• an end portion of the fuel duct, opening into the combustion chamber 2 may form a distributor 27 so shaped as to create a centrifugal acceleration of the fuel flow that promotes the distribution and mixing thereof with the oxidizing agent and with the fumes recirculated within the combustion chamber 2.
• the method may comprise the step of conveying into the oxidizing agent duct 4 all the oxidizing agent necessary to the process (hot or cold, such as, for example, atmospheric air, or mixtures thereof), withdrawn from the environment or from a passive mixing duct, without the aid of mechanical pumping means (e.g., fans, pumps, or compressors), by connecting an outlet end of the oxidizing agent duct 4 to the fuel duct 3 at an oxidizing agent suctioning point upstream of the combustion chamber 2, and configuring the fuel duct 3 at the oxidizing agent suctioning point as a Venturi tube, so as to use (preferably only) the fuel flow (for example, methane gas, GPL gas, coke oven gas, liquid fuels or mixtures thereof) as the driving fluid to suction and, hence, conveying the oxidizing agent flow 9.
• the fuel flow for example, methane gas, GPL gas, coke oven gas, liquid fuels or mixtures thereof
• the at least one collector 20 in order to increase the stability of the burner 1 in the initial steps, can be displaced (for example, translatable) between a closure position (Fig. 6, forward position), in which the opening section of the re-input point 14 is closed or highly narrowed, and an opening position (Fig. 7, retracted position), in which the opening section of the re-input point 14 is at its maximum.
• a closure position Fig. 6, forward position
• Fig. 7, retracted position in which the opening section of the re-input point 14 is at its maximum.
• the invention has a number of advantages. It allows suctioning, through a system of the Venturi type supplied by a pressurized fluid, high amounts of one or more passive fluids that are necessary to the technological process. By virtue of the suctioning through the Venturi effect, the need to have mechanical pumps, blowers, or fans at certain points along the fluid supply lines is obviated. This allows intaking hot or cold fluids, corrosives, oxidizing agents, fuels, inerts, or mixtures thereof.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
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• General Engineering & Computer Science (AREA)

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Cited By (6)

Citations (10)

• 2013
  • 2013-09-11 IT IT001507A patent/ITMI20131507A1/it unknown
• 2014
  • 2014-09-09 RS RS20190612A patent/RS58795B1/sr unknown
  • 2014-09-09 ES ES14786310T patent/ES2730887T3/es active Active
  • 2014-09-09 EP EP14786310.4A patent/EP3044509B1/de active Active
  • 2014-09-09 WO PCT/IB2014/064339 patent/WO2015036914A1/en active Application Filing

Patent Citations (10)

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