US20110094340A1 - Combustion of co and combustibles in steel furnace offgases - Google Patents

Combustion of co and combustibles in steel furnace offgases Download PDF

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Publication number
US20110094340A1
US20110094340A1 US12/602,627 US60262709A US2011094340A1 US 20110094340 A1 US20110094340 A1 US 20110094340A1 US 60262709 A US60262709 A US 60262709A US 2011094340 A1 US2011094340 A1 US 2011094340A1
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Prior art keywords
offgas
stream
hot oxygen
fed
hot
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US12/602,627
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English (en)
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Kuang Tsai Wu
Euan John Evenson
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Praxair Technology Inc
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Praxair Technology Inc
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Priority to US12/602,627 priority Critical patent/US20110094340A1/en
Assigned to PRAXAIR TECHNOLOGY, INC. reassignment PRAXAIR TECHNOLOGY, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: EVENSON, EUAN JOHN, WU, KUANG TSAI
Publication of US20110094340A1 publication Critical patent/US20110094340A1/en
Priority to US13/458,423 priority patent/US20120213684A1/en
Priority to US14/087,679 priority patent/US20140076106A1/en
Abandoned legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/62—Carbon oxides
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/52—Manufacture of steel in electric furnaces
    • C21C5/5211—Manufacture of steel in electric furnaces in an alternating current [AC] electric arc furnace
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D17/00—Arrangements for using waste heat; Arrangements for using, or disposing of, waste gases
    • F27D17/008—Arrangements for using waste heat; Arrangements for using, or disposing of, waste gases cleaning gases
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/50—Carbon oxides
    • B01D2257/502—Carbon monoxide
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C2100/00—Exhaust gas
    • C21C2100/02—Treatment of the exhaust gas
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/28—Manufacture of steel in the converter
    • C21C5/30—Regulating or controlling the blowing
    • C21C5/305—Afterburning
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/52—Manufacture of steel in electric furnaces
    • C21C5/527—Charging of the electric furnace
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/40—Capture or disposal of greenhouse gases of CO2
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/10—Reduction of greenhouse gas [GHG] emissions
    • Y02P10/122—Reduction of greenhouse gas [GHG] emissions by capturing or storing CO2
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • This invention relates to treatment of offgas streams produced by steel furnaces.
  • EAF electric arc furnace
  • combustible gases such as carbon monoxide (CO) and hydrogen (H 2 )
  • CO carbon monoxide
  • H 2 hydrogen
  • This off-gas can reach a temperature of 3000 F or higher, and CO and H2 peak concentrations in the off-gas can reach up to 60% and 35%, respectively.
  • the thermal energy contained in the EAF off-gas needs to be recovered as much as possible inside the EAF vessel.
  • One way is to recover chemical heat of CO and H 2 combustion using oxygen lances for combustion of the combustibles inside the vessel.
  • Another way to recover the energy from the off-gas stream is to use the heat of the stream to preheat scrap that is going to be fed into the EAF.
  • the EAF off-gas is piped into a conduit where the scrap is moving counter current to the direction of the off-gas flow, and the hot off-gas preheats the scrap by direct heat transfer.
  • Air is injected into the scrap preheating conduit to provide oxygen for the combustion of the CO and H 2 .
  • the conduit may have auxiliary burners installed to augment the heating of the scrap to a desired preheat temperature.
  • the remaining energy contained in the unburned CO, H 2 , and other combustibles may or may not be recovered.
  • the remaining gaseous combustibles in the off-gas are burned to sufficiently complete levels, so that the thus-treated off-gas can then be further cleaned downstream in the duct and discharged into the atmosphere.
  • high temperature combustibles such as CO and H 2 in the off-gas are typically burned with air introduced from an “air gap” in a water-cooled exhaust duct connecting to the “fourth hole” of the EAF furnace (herein called “EAF exhaust duct”).
  • a “dropout box” Downstream of the EAF exhaust duct, a “dropout box” may also function as a post combustion chamber for additional CO and H 2 combustion. Combustion air for the dropout box may be introduced upstream of the box or in the box by lancing. Part of the flue gas stream exiting from the dropout box may be recycled back into the EAF vessel, if the operator wishes to recover the flue gas energy for melting purpose.
  • EAF operators may opt to operate their furnaces conservatively in order to meet the emissions limits, but at the expense of furnace energy efficiency. For example, an operator may set the furnace or the exhaust duct pressures low to induce excessive amount of air infiltration for completing CO burnout. This excess amount of air can increase the total flue gas volume and the heat loss associated with the off-gas, thus decreasing the furnace thermal efficiency.
  • the production capacity of an EAF furnace can be substantially limited by the ability of the downstream ducts or dropout box to complete the combustion of the CO, H 2 , and other combustibles. If scrap preheating is used, EAF operators may also face the issue of containing fugitive odors and limiting the formation of undesired byproducts such as dioxins in the flue gas ducts.
  • BOF basic oxygen furnaces
  • ladle refining furnaces ladle refining furnaces
  • argon-oxygen decarburizing furnaces are also applicable to other apparatus used in steelmaking, such as basic oxygen furnaces (BOF), ladle refining furnaces, and argon-oxygen decarburizing furnaces.
  • a method for treating an offgas stream from a steel furnace comprises
  • step (B) mixing fuel and oxygen and combusting a portion of the oxygen in the mixture with said fuel in a chamber to form a hot oxygen stream emerging from an outlet in said chamber that contains oxygen, wherein the residence time of said combustion in said chamber is long enough that said hot oxygen stream has a temperature higher than the temperature of the offgas stream to which it is added in step (C) and said residence time is short enough that said hot oxygen stream contains products of said combustion including radicals selected from the group consisting of radicals corresponding to the formulas O, H, OH, C 2 H, CH 2 , C j H 2j+1 or C j H 2j ⁇ 1 wherein j is 1-4, and mixtures of two or more of such radicals;
  • step (C) feeding the hot oxygen stream formed in step (B) into the offgas stream provided in step (A) to raise the temperature of the offgas in said provided stream to a temperature higher than 1100 F that is higher than the temperature of the offgas to which said hot oxidant stream is added, wherein the hot oxygen stream is added at a rate sufficient to convert carbon monoxide in the offgas to which it is added to carbon dioxide, thereby lowering the carbon monoxide content of said offgas.
  • metal such as scrap metal is fed into one of the aforementioned furnaces, and before said metal is fed into the furnace it is contacted in direct heat transfer with said offgas obtained from said furnace to heat the metal and to cool said obtained offgas.
  • said scrap metal contains organic material that is volatilized into said obtained offgas by said heat transfer with said obtained offgas stream, and said hot oxygen stream is mixed together with said cooled offgas stream at a rate sufficient to convert said organic material to carbon dioxide and water vapor.
  • This invention involves injecting a stream or streams of high-momentum hot oxygen to destroy low concentration levels of off-gas combustibles, particularly where the off-gas temperature is already below the spontaneous ignition temperature of the off-gas combustibles. Because the injected oxygen is hot and the jet momentum is high, the hot oxygen will mix rapidly with the offgas, thus enhancing the ability of the radicals in the hot oxygen stream to destroy combustibles in the offgas even though the offgas temperature is below the combustibles' ignition temperatures.
  • These streams of high momentum hot oxygen are produced by the hot oxygen generator described herein.
  • FIG. 1 is a flowsheet showing a typical steel furnace system with which the present invention can be practiced.
  • FIG. 2 is a schematic representation of a hot oxygen generator useful in the present invention.
  • FIG. 3 is a cross-sectional view of a hot oxygen generator useful in the present invention.
  • FIG. 4 is a flowsheet of a portion of an alternate embodiment of the present invention.
  • FIG. 5 is a flowsheet of yet another embodiment of the present invention.
  • FIG. 6 is a flowsheet of another embodiment of the present invention.
  • FIG. 1 illustrates several different possible applications of this invention to control CO emissions from steelmaking furnaces. Any one or more of these applications can be practiced, separately or as an overall system for controlling CO emissions.
  • offgas 10 is generated in an electric arc furnace (“EAF”) 20 which has electrodes 24 over molten steel 22 . While three electrodes 24 are shown, other numbers of electrodes can be employed, and the EAF can be operated with alternating current or direct current.
  • the offgas stream 10 flows through an outlet (sometimes referred to as a “4 th hole”) 25 into a conduit (or duct) 26 , and then through air gap 27 which is an opening in duct 26 through which air from the surrounding atmosphere can enter into duct 26 .
  • Air is admitted into the offgas stream, preferably via air gap 27 and/or other inlets in the duct that carries the offgas.
  • the air can be admitted into the offgas with or without the aid of a fan or impeller, preferably without.
  • the offgas stream downstream of air gap 27 passes into dropout box 50 .
  • Larger particulate material entrained in the offgas is separated from the offgas in the dropout box 50 .
  • Stream 52 is the offgas stream exiting from the dropout box 50 .
  • the dropout box 50 may be used as a combustion chamber for combustion of combustible products in the offgas, if lances for combustion oxidant injection and/or burners are installed (not shown).
  • the offgas is preferably at a temperature of 2000 F or lower when a hot oxygen stream is fed into the offgas as described herein. If the offgas as formed is already 2000 F or cooler, then the offgas does not need to be cooled. If the offgas temperature is above 2000 F, then cooling of the offgas is necessary. Typically, offgas as recovered from steel furnace atmospheres such as an EAF is hotter than 2000 F. The admission of air into the offgas stream via the air gap 27 and any other air inlets cools the offgas. Additional cooling as necessary can be provided by passing the duct in which the offgas is flowing through a water jacket or other equivalent mechanism that withdraws heat from the offgas through and away from the wall of the duct. Cooling of the offgas can also be provided by radiative and/or convective cooling of the duct to the ambient atmosphere.
  • Hot oxygen stream 56 which can be produced by hot oxygen generator 54 as described herein, is fed into stream 52 to form stream 53 .
  • Offgas 10 formed in furnace 20 can also be recovered by rising into canopy 30 and into canopy duct 31 .
  • air is drawn into duct 31 from the surrounding atmosphere.
  • Hot oxygen stream 33 which can be produced by hot oxygen generator 32 as described herein, is fed into stream 31 to form stream 34 .
  • Offgas streams that are advantageously treated by this invention can also come from other sources in a steel plant, such as ladle refining furnaces and/or argon-oxygen decarburizing furnaces.
  • Stream 42 represents any such offgas stream, which can also be a stream formed by combining the offgas streams from two or more ladle refining furnaces, two or more argon-oxygen decarburizing furnaces, or from both types of furnaces.
  • Hot oxygen stream 48 which can be produced by hot oxygen generator 46 as described herein, is fed into stream 42 to form stream 49 .
  • any one of these hot oxygen generators and streams can be employed, or several can be employed to treat CO content of several different offgas streams.
  • a second (or additional) hot oxygen generator can be employed to feed a hot oxygen stream into an offgas stream downstream from a location where a hot oxygen stream has already been fed.
  • hot oxygen stream 36 from hot oxygen generator 35 can be fed even where a hot oxygen stream such as streams 33 and/or 48 have been fed upstream.
  • a hot oxygen stream that is fed as stream 36 is, downstream from where another hot oxygen stream is fed, can be fed continuously, or can be turned off and on intermittently as a backup source of hot oxygen where needed to provide sufficient CO destruction during a specific time period of the heat cycle where CO contents are elevated above their normal levels.
  • streams 34 and 49 combine to form stream 38 into which hot oxygen stream 36 can be optionally continuously or intermittently fed, forming stream 39 .
  • streams such as 39 and 53 can be fed separately to baghouse 60 , or can be fed to separate baghouses.
  • Stream 64 exiting from baghouse 60 is drawn by a fan, such as induced draft fan 80 , and the cleaned offgas is discharged into the atmosphere through opening 120 at the top of stack 100 .
  • the fan 80 if present, can also help draw offgas streams into duct 26 , and/or canopy 30 and/or into stream 42 , as the case may be, as depicted in FIG. 1 .
  • hot oxygen stream such as streams 56 , 33 , 48 and/or 36 , formed from its corresponding hot oxygen generator, is described with reference to FIGS. 2 and 3 , using hot oxygen generator 54 as an example.
  • Stream 202 of oxidant having an oxygen concentration of at least 30 volume percent and preferably at least 85 volume percent is provided into hot oxygen generator 54 which is preferably a chamber or duct which communicates through a suitable opening in generator 54 with the duct that carries the offgas stream into which the hot oxygen is to be fed.
  • the oxidant 202 is technically pure oxygen having an oxygen concentration of 99.5 volume percent or more.
  • the oxidant 202 fed to the hot oxygen generator has an initial velocity which is generally within the range of from 50 to 300 feet per second (fps) and typically will be less than 200 fps.
  • Stream 204 of fuel is provided to hot oxygen generator 54 through a suitable fuel nozzle which may be any suitable nozzle generally used for fuel injection.
  • the fuel may be any suitable combustible fluid examples of which include natural gas, methane, propane, hydrogen, refinery fuel gas, landfill offgas, syngas, carbon monoxide, and coke oven gas.
  • the presence of hydrogen in the fuel fed to the hot oxygen generator 54 is advantageous in assisting conversion of CO to CO 2 evidently because the combustion that forms the hot oxygen stream promotes the formation of (nonionic) OH and O radicals in the hot oxygen stream.
  • the fuel is a gaseous fuel. Liquid fuels such as number 2 fuel oil may also be used, although it would be harder to maintain good mixing and reliable and safe combustion with the oxygen with a liquid fuel than with a gaseous fuel.
  • the fuel 204 provided into the hot oxygen generator 54 combusts there with oxidant to produce heat and combustion reaction products such as carbon dioxide and water vapor.
  • oxidant to produce heat and combustion reaction products such as carbon dioxide and water vapor.
  • no more than about 35 percent of the oxygen of the oxidant combusts with the fuel. If more than about 35 percent of the oxygen combusts with the fuel in the hot oxygen generator, then appropriate measures should be taken such as using refractory materials of construction and/or employing a heat removal feature such as a water wall to keep the temperature of the remaining oxygen from increasing to undesirable levels.
  • the combustion reaction products generated in the hot oxygen generator 54 may mix with some of the remaining oxygen of the oxidant 202 , thus providing heat to the remaining oxygen and raising its temperature.
  • the fuel is provided into the hot oxygen generator 54 at a high velocity, typically greater than 200 fps and generally within the range of from 500 to 1500 fps. The high velocity serves to entrain oxidant into the combustion reaction products thus promoting combustion of the fuel in the chamber.
  • the temperature of remaining oxidant within the oxidant supply duct is raised by at least about 500 F, and preferably by at least about 1000 F. It is preferred that the temperature of the remaining oxygen not exceed about 3000 F to avoid overheating problems with supply ducts and nozzles.
  • the requisite supply pressure of the oxygen to achieve any given oxygen injection velocity into the offgas decreases.
  • the requisite pressure exceeds 7 pounds per square inch gauge (psig) in order to inject the oxygen into the offgas at a velocity of 800 fps.
  • psig pounds per square inch gauge
  • the requisite pressure decreases sharply.
  • the requisite pressure is 1.65 psig and at a temperature of 3000 F the requisite pressure is only 0.91 psig.
  • temperatures exceeding 3000 F there is little additional benefit, thus providing another reason for not exceeding 35 percent oxygen combustion with the fuel.
  • generation of hot oxygen in this manner can provide a high velocity hot oxygen stream 56 to the offgas without the need for a high supply pressure thus reducing or eliminating the need for compressing oxygen prior to passing it into the offgas which would otherwise be necessary if the oxygen source pressure is not high.
  • the combustion that occurs in hot oxygen generator 54 should be carried out in a manner such that the hot oxygen stream 56 that emerges from generator 54 contains one or more radicals corresponding to the formulas O, H, OH, C 2 H, CH 2 , C j H 2j+1 or C j H 2j ⁇ 1 wherein j is 1-4, and mixtures of two or more of such radicals.
  • This can be achieved by providing that the residence time of the reactants (fuel and oxygen) within the hot oxygen generator is long enough to enable combustion reaction of fuel and oxygen to occur in the hot oxygen generator producing a stream having a temperature higher than the temperature of the offgas into which the stream is to be fed, and simultaneously providing that said residence time is short enough that at least some of the above-mentioned radicals are present.
  • the residence time is determined by the volume of the space within generator 54 , by the feed rates of fuel stream 204 and of oxidant stream 202 into generator 54 , and by the size of the exit orifice through which the hot oxygen stream 56 emerges from generator 54 .
  • Preferred residence times are about 1 to 2 msec.
  • the combination of the dimensions of a hot oxygen generator, the fuel and oxygen feed rates to that generator, and the exit orifice dimensions, that provide residence time which can produce a hot oxygen stream that has the desired temperature and the desired content of combustion radicals so as to reduce the CO content of an offgas stream into which the hot oxygen stream is fed includes the following:
  • the hot oxygen stream 56 preferably contains at least 75% (volume) O 2 .
  • a typical composition for this stream is about 80% O 2 , 12% H 2 O, 6% CO 2 , some highly reactive radicals such as (nonionic) OH, O, and H which are particularly effective to initiate and oxidize CO to CO 2 , and the aforementioned radicals.
  • the hot oxygen stream 56 exits through orifice 201 and is fed into the offgas at high velocity and momentum, which results in accelerated mixing between the hot gas and the offgas.
  • the hot oxygen stream 56 (as well as streams 33 , 36 and/or 48 , and other streams generated and used in the practice of this invention) obtained in this way typically has a temperature of at least 1600 F and preferably at least 2000 F.
  • the velocity of the hot oxygen stream will be within the range of from 500 to 4500 feet per second (fps), preferably 800 to 2000 or to 2500 fps, and will exceed the initial velocity by at least 300 fps. In a preferred embodiment this velocity is at Mach 1.
  • the high velocity hot oxygen stream is believed to entrain the offgas into which it is fed through jet boundaries by velocity gradients or fluid shear, and by turbulent jet mixing.
  • the gaseous stream that is formed upon combining the offgas and the hot oxygen stream, which mixture may include reaction products of the hot oxygen and the offgas, has a temperature of at least 1000 F, preferably at least 1250 F, although advantages can be realized when the temperature of this mixture is above 1400 F.
  • stream 56 is fed at high momentum into the steel furnace offgas.
  • the desired reaction of the hot oxygen with the offgas is enhanced by increasing the intimacy of mixing between the hot oxygen and the offgas.
  • the intimate mixing can be promoted by dividing the hot oxygen into a plurality of streams and feeding these streams into the offgas, or by feeding the hot oxygen across or countercurrent to the offgas.
  • the intimate mixing is promoted by providing physical structure, within the duct such as the duct carrying offgas stream 52 , that promotes contact between the hot oxygen and the offgas. Examples of such structure include wire mesh that the gases have to flow through, or baffles.
  • the hot oxygen and the offgas mix, during which the hot oxygen burns CO in the offgas to CO 2 .
  • the resulting gas mixture such as stream 53 comprises the products of these reactions between the hot oxygen and the offgas.
  • the preferred location to place a hot oxygen generator is so that the hot oxygen stream is fed into the offgas where the temperature of the offgas is too low for injection of air alone to be effective in destroying sufficient amounts of CO in the offgas.
  • the hot oxygen generator can effectively be used where it feeds the hot oxygen stream to regions where the temperature of the offgas is up to 1800 F, such as 1000 F to 1800 F, preferably 1100 F to 1600 F or even up to 1500 F or even 1400 F. Even at these temperatures, destruction of CO can occur to lower the CO content of the offgas to less than 500 ppm and even to 100 ppm or less.
  • the combined stream preferably has a temperature of 1350 to 1450 F.
  • Typical injection velocities of the hot oxygen stream can be 500 to 3500 fps, preferably 1000 to 2800 fps.
  • FIGS. 4 , 5 and 6 illustrate embodiments of this invention in which feed material for the steel furnace, such as scrap metal, is preheated by offgas from the furnace before the feed material is fed into the furnace.
  • feed material for the steel furnace such as scrap metal
  • EAF offgas 10 flows through a 4 th hole 25 and subsequently a conduit 26 , then through an air gap 27 .
  • the offgas stream splits into two streams 436 and 438 .
  • Stream 436 goes into a preheater 440 such as a so-called bucket preheater, whereas stream 438 bypasses preheater 440 .
  • the preheater 440 is periodically charged with feed material such as scrap charge 442 , which is preheated by the hot offgas stream 436 when it flows through the scrap charge.
  • the offgas which has been cooled by the heat transfer to the charge 442 , flows out of the preheater 440 as stream 437 . Heated charge 442 is fed to EAF 20 .
  • Hot oxygen generator 450 configured and operated as described herein with respect to generator 54 , is installed to feed hot oxygen stream 452 into stream 437 downstream of preheater 440 .
  • the hot oxygen contained in hot oxygen stream 452 mixes rapidly with stream 437 , and destroys CO in stream 437 .
  • the resulting stream 439 combines with stream 438 to form stream 454 , which in turn can optionally be combined with stream 31 from the EAF canopy 30 , to form stream 58 .
  • Off-gas streams 454 and 58 can be processed by downstream pollution control equipment, as described herein.
  • FIG. 5 illustrates another embodiment of the use of a hot oxygen stream formed as described herein, here to control gaseous emissions inside a continuously operating preheater of feed material such as scrap metal.
  • scrap charge 535 is fed continuously by a feeder 540 through preheater 530 which can be an enclosed space such as a pipe, equipped with a conveyor for the feed material.
  • Offgas stream 10 flows through preheater 530 in a direction countercurrent to the charge 535 , wherein the charge material is heated by heat transfer from offgas 10 and offgas 10 is cooled.
  • Air is admitted through one or more openings or vents 527 provided in the preheater and/or in the passage in which the offgas flows going to the preheater.
  • Hot oxygen generator 550 configured and operated as described herein with respect to generator 54 , is installed close to the end of the scrap feeder 540 and generates hot oxygen stream 552 which is fed into offgas stream 10 in preheater 530 .
  • the hot oxygen contained in stream 552 mixes rapidly with stream 10 , to destroy CO in the offgas.
  • the resulting stream 554 flows out of the preheater 530 and can optionally combine with, for instance, stream 31 from the EAF canopy 30 to form stream 58 which can be further processed as described herein.
  • FIG. 6 shows yet another application of this invention, namely, to a shaft furnace 620 equipped with a shaft section 642 positioned over the furnace to receive offgas from the furnace, and hood section 646 positioned over shaft section 642 to receive offgas from shaft section 642 .
  • feed material such as scrap metal is charged into the hood and the shaft sections through door 647 .
  • the charged scrap 641 (represented as solid dots as is feed material 535 in FIG. 5 ) is held in place by plates 640 and 644 (commonly called “fingers”) which have openings through which the offgas can flow.
  • Offgas 10 flows through the charged scrap 641 and preheats the charged scrap as it flows through the scrap.
  • Hot oxygen stream 656 from hot oxygen generator 654 configured and operated as described herein with respect to generator 54 , is injected into and mixes with the offgas stream 10 at the top of the hood section 646 .
  • a hot oxygen generator 650 can also be installed to feed a hot oxygen stream 652 into the offgas 10 after the offgas 10 leaves the hood section 646 . Air is admitted into the offgas through openings in shaft section 642 and/or in hood section 646 and/or where either of those sections joins the plates 640 or 644 .
  • the feed material may contain organic material such as residues or waste material.
  • organic material such as residues or waste material.
  • the preheating of the feed material as described herein may create gasified emissions, by which is meant the gaseous state of organic material that was in or on the feed material, or gaseous organic byproducts formed by exposing said organic material to the temperatures encountered in bringing the feed material into heat transfer contact with the offgas, or mixtures thereof.
  • gaseous emissions may contain chemical components which can cause unpleasant odors, or which can be harmful if the components include hazardous substances such as dioxins or if the components can form into hazardous substances when exposed to the usual preheating conditions.
  • Feeding the hot oxygen stream formed as described herein either into the offgas stream within the apparatus in which the offgas preheats feed material, or downstream of the apparatus in which the off gas preheated feed material, has the additional benefit of removing or even completely eliminating chemical (organic) components by converting them into carbon dioxide and water.
  • the following three criteria are important: (1) achieve good mixing between the hot oxygen stream and the offgas; (2) the temperature of the mixture that is formed of the hot oxygen stream and the offgas is in the proper range; and (3) the mixture has enough residence time for completing CO burnout to CO 2 . Operating within the conditions described herein satisfies these criteria.
  • the use of the hot oxygen stream as described herein has the following advantages:
  • This invention enables the capacity of an existing furnace to be boosted if the production rate of that furnace is constrained by high off-gas CO emissions. If an EAF furnace increases its production rate, more offgas volume will be generated. Due to this increased offgas volume, air-based CO burnout measures installed upstream of the ducts may not be able to combust CO to a level that meets emissions limits at the baghouse. The other possible outcome with the increased production rate is that the EAF ducts may become limited by the capacity of the fan, meaning that there is a maximum amount of air that an existing fan can process for CO combustion. With this invention, an operator can let the existing air-based CO burnout system operate at its maximum ability to destroy CO. He can then use a hot oxygen generator installed downstream of the air systems for final burnout of the CO, where air based systems are no longer effective for CO destruction.
  • furnace operators control their furnaces in very conservative ways to try to be sure that all CO and other combustibles in plant effluent meet regulatory emissions limits. For example, an operator may increase duct suction pressure to introduce excessive amounts of air into the duct for post combustion of CO, H 2 , and other combustibles. By supplying high percentages of excess air for post combustion, the furnace may meet CO emissions limits but at the expense of its thermal efficiency. This is because high air infiltration increases offgas volume and its total heat contents. Without external flue gas recirculation, the available heat contained in the offgas is a heat loss. Higher offgas volume also increases operating costs in downstream off-gas cleaning equipments.
  • This invention provides a simple and effective way for furnace operators to meet their specific CO emissions goals.
  • the hot oxygen generator becomes an assuring device for the furnace where the operating environment is dynamic and transient in nature.
  • operators can operate their furnaces with more flexibility to meet changing process needs, knowing that any CO slip to downstream ducts will be destroyed by the hot oxygen stream whether that stream is fed continuously or periodically when the need arises.

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  • Oil, Petroleum & Natural Gas (AREA)
  • Biomedical Technology (AREA)
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  • General Engineering & Computer Science (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Waste-Gas Treatment And Other Accessory Devices For Furnaces (AREA)
  • Furnace Details (AREA)
  • Combustion Of Fluid Fuel (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Carbon Steel Or Casting Steel Manufacturing (AREA)
  • Incineration Of Waste (AREA)
  • Manufacture Of Iron (AREA)
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US12/602,627 2008-06-26 2009-06-23 Combustion of co and combustibles in steel furnace offgases Abandoned US20110094340A1 (en)

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US12/602,627 US20110094340A1 (en) 2008-06-26 2009-06-23 Combustion of co and combustibles in steel furnace offgases
US13/458,423 US20120213684A1 (en) 2008-06-26 2012-04-27 Combustion of co and combustibles in steel furnace offgases
US14/087,679 US20140076106A1 (en) 2008-06-26 2013-11-22 Combustion of co and combustibles in steel furnace offgases

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US7595808P 2008-06-26 2008-06-26
PCT/US2009/048211 WO2009158320A1 (en) 2008-06-26 2009-06-23 Combustion of co and combustibles in steel furnace offgases
US12/602,627 US20110094340A1 (en) 2008-06-26 2009-06-23 Combustion of co and combustibles in steel furnace offgases

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US20130195138A1 (en) * 2010-09-23 2013-08-01 Tenova S.P.A. Heat exchanger for the rapid cooling of flue gas of ironwork plants, apparatus for the treatment of flue gas of ironwork plants comprising such a heat exchanger and relative treatment method
US20130328252A1 (en) * 2012-06-12 2013-12-12 SSAB Enterprises, LLC Furnace direct evacuation system

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US8753108B2 (en) * 2012-03-30 2014-06-17 Alstom Technology Ltd Method and apparatus for treatment of unburnts
CN104121581B (zh) * 2014-07-23 2016-06-29 华东理工大学 一种高效低NOx管式加热炉低浓度富氧燃烧系统及燃烧器
CN109028106B (zh) * 2018-08-28 2020-03-31 中石化（洛阳）科技有限公司 一种降低催化裂化非完全再生烟气NOx的方法
CN109234490B (zh) 2018-11-07 2020-06-26 北京科技大学 一种提钒-脱碳双联转炉高效长寿喷吹方法及系统
CN109971914B (zh) * 2019-03-26 2020-04-14 东北大学 一种利用高温转炉废气的垃圾焚烧系统及方法
CN109971916B (zh) * 2019-04-01 2020-04-14 东北大学 一种利用转炉废气预热废钢的装置及方法

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US5400358A (en) * 1992-10-13 1995-03-21 Consteel, S.A. Continuous scrap preheating
US5572544A (en) * 1994-07-21 1996-11-05 Praxair Technology, Inc. Electric arc furnace post combustion method
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US20130328252A1 (en) * 2012-06-12 2013-12-12 SSAB Enterprises, LLC Furnace direct evacuation system

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ATE544505T1 (de) 2012-02-15
EP2313179A1 (de) 2011-04-27
JP5398090B2 (ja) 2014-01-29
CN102076399B (zh) 2013-08-28
MX2010013940A (es) 2011-03-21
CN102076399A (zh) 2011-05-25
US20120213684A1 (en) 2012-08-23
BRPI0914420A2 (pt) 2015-10-20
US20140076106A1 (en) 2014-03-20
ZA201009049B (en) 2011-09-28
EP2313179B9 (de) 2012-09-26
KR20110022623A (ko) 2011-03-07
KR101635229B1 (ko) 2016-06-30
EP2313179B1 (de) 2012-02-08
WO2009158320A1 (en) 2009-12-30
CA2729114C (en) 2013-05-14
CA2729114A1 (en) 2009-12-30
JP2011526354A (ja) 2011-10-06
ES2381930T3 (es) 2012-06-01

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