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WO2001091929A1 - Dispositif et procede d'elimination sequentielle d'oxydes d'acier - Google Patents

Dispositif et procede d'elimination sequentielle d'oxydes d'acier Download PDF

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Publication number
WO2001091929A1
WO2001091929A1 PCT/US2001/017523 US0117523W WO0191929A1 WO 2001091929 A1 WO2001091929 A1 WO 2001091929A1 US 0117523 W US0117523 W US 0117523W WO 0191929 A1 WO0191929 A1 WO 0191929A1
Authority
WO
WIPO (PCT)
Prior art keywords
reducing
metal
gas
reducing gas
compartment
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US2001/017523
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English (en)
Inventor
Stephen L. Feldbauer
Brian H. Braho
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Danieli Technology Inc
Original Assignee
Danieli Technology Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US09/584,931 external-priority patent/US6406550B1/en
Application filed by Danieli Technology Inc filed Critical Danieli Technology Inc
Priority to AU2001265218A priority Critical patent/AU2001265218A1/en
Publication of WO2001091929A1 publication Critical patent/WO2001091929A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G5/00—Cleaning or de-greasing metallic material by other methods; Apparatus for cleaning or de-greasing metallic material with organic solvents

Definitions

  • TITLE APPARATUS AND METHOD FOR SEQUENTIAL REMOVAL OF OXIDES FROM STEEL
  • This invention relates to the reduction and removal of oxides from the surface of metal.
  • the metal containing surface oxides is passed into or through an enclosure, continuously, intermittently, or batchwise, in which it is heated and contacted with reducing
  • Hydrogen and other reducing gases such as carbon monoxide have been used for the reduction of oxides in ores, where they are substantially consumed within a reducing furnace or vessel. Hydrogen is readily burned and can cause explosions under certain circumstances, and carbon monoxide is poisonous and generally considered dangerous unless confined and reacted in a vessel of the type generally contemplated in ore reduction. Moreover, steel strip and many other metal products made continuously move at a rapid pace, increasing the difficulty of conducting the oxide removal process with gases within the time constraints normally imposed. Thus, while the elementary chemical principles of oxide removal and/or reduction by reducing gases are known, an acceptable continuous surface oxide reduction system employing reducing gases has not been forthcoming in the art.
  • Our process and apparatus provide for three stages or zones for the processing of the moving metal, which may be any metal having oxide on its surface, in any commercially common shape, such as strip or rod.
  • the three basic stages are heating, reducing, and cooling. All three steps take place within an enclosure of the type to be described in more detail below, and under the conditions to be described in more detail below. Heating in the heating zone is accomplished by a combination of a heating element or device to be described below and post-combustion of unreacted reducing gas.
  • Reduction of the oxide scale in the reduction zone is accomplished by assuring a turbulent and/or vigorous application of reducing gas to the surface of the metal, preferably in the presence of elemental carbon; cooling of the metal in the cooling zone prior to its exit from the enclosure is accomplished by the introduction of inert gas along with the unheated reducing gas to contact the reduced surface of the metal just prior to its exit from the enclosure.
  • the metal surface should preferably be cooled to a temperature at which reoxidation is unlikely to occur; in the case of steel strip, this is 500°F or lower.
  • Figure 1 is a more or less diagrammatic side sectional view of a preferred configuration of the enclosure including all three zones included in our invention, as applied to steel strip.
  • Figure 2 is an overhead view from within the same enclosure.
  • Figure 3 shows a preferred device for distributing carbon on the strip surface.
  • Figure 4 is a more or less diagrammatic side view of a further preferred separate enclosure for the reducing zone.
  • Figure 5 is an overhead view of the reducing zone enclosure of Figure 4.
  • Figure 6 is a side sectional view of a preferred exhaust trap for waste gases.
  • the oxide layer on steel strip may contain Fe 2 O 3 , Fe O , and/or FeO, or various ratios of the three oxide forms depending on the conditions in which the product is made and conducted to the next processing stage.
  • Fe 3 O may pass through the Fe 2 O 3 stage before it is further reduced to FeO and then completely reduced to iron.
  • hydrogen is the reducing agent
  • water is produced
  • carbon is the reducing agent
  • carbon monoxide is first produced
  • carbon monoxide is the reducing agent
  • carbon dioxide results.
  • Our invention contemplates the use of either hydrogen or carbon monoxide, or any other commercially feasible reducing gas, in the absence of or together with elementary carbon as a supplementary reductant.
  • the hydrogen may be manufactured within the enclosure or in its immediate vicinity.
  • Examples of the manufacture of hydrogen include known processes for accomplishing the dissociation of methane, and the combustion of methane or other hydrocarbons in such a way as to produce excess hydrogen.
  • Figure 1 illustrates the invention applied to steel strip 1 from which mill scale, or a layer of oxide, must be removed.
  • Steel strip 1 is caused to pass into enclosure 2 in the direction, as depicted, from left to right. It may be held in enclosure 2 for a period of time or moving at a speed up to as fast as 2000 feet per minute.
  • the strip 1 may be preheated before entering enclosure 2, but is heated within enclosure 2 by heating elements 3, preferably radiant heaters, to ensure that the temperature of its surfaces is at least 752°F (400°C) by the time it leaves the heating zone, which is designated by the numeral 4.
  • the oxide surface should be heated to at least 300°F.
  • a flame 13 and a flue 9 for conducting exhaust gases out of the system.
  • the heating of strip 1 is assisted by the post- combustion of the unconsumed reducing gases by air optionally introduced through inlets 14 in the heating zone 4. Introduction of the air through inlets 14 will cause immediate combustion of whatever reducing gas, usually hydrogen, remains in the atmosphere moving from right to left, as depicted.
  • the flow of air will be directed at the strip so as to ensure the most efficient use of the thermal energy generated by the combustion, that is, to heat the strip.
  • the action of the flame 13 creates a draft continuously moving gases from right to left, as depicted - from the enclosure strip exit 15 to the strip entrance 16, thus providing a constant countercurrent contact of gas to the strip.
  • Rolls 5 and 6 may be replaced by any suitable support, and also may be replaced by graphite or carbon blocks of a consistency so that a thin film of elemental carbon is deposited or rubbed onto the strip surface, preferably both the top side and the under side.
  • Reducing gas 11, usually hydrogen is continuously introduced through small apertures 7 (see Fig. 2) in manifolds 10, and directed, preferably at a slight angle of 5-30 degrees, in the direction of the oncoming strip 1 at a velocity to create turbulence on impact with the strip 1.
  • the deposition preferably occurs in the upstream half of the reducing zone 7, so there will be time for it to react with the oxides on the surface of strip 1.
  • This zone is called the reducing zone because a large part of the reduction of the oxides occurs in this zone, but it should be understood that some oxide may be reduced in the heating zone 4 due to the continued presence there of at least some reducing gas, and in the cooling zone 8 in part because of the continued presence of reducing gas carried into the cooling zone 8 by strip 1.
  • the temperature of the surfaces of the strip is maintained at the temperature necessary for the reducing reaction to take place. In the case of steel strip, this is at least 400°C (752°F). In the case of copper and other metals, the surface should have a temperature of at least 300°F.
  • the strip 1 passes into the cooling zone 8.
  • the strip 1 is caused to cool by the introduction of new reducing gases through manifolds 10.
  • the reducing gases introduced separately through manifolds 10 may be mixed with inert gases introduced through separate inlets 21 or premixed with the reducing gases. Introduction of inert gases here will minimize the possibility of mixing air with the reducing gases.
  • inert gases may be mixed with the reducing gas in volume ratios of from 1:99.9 to 99.9:1.
  • the strip then passes out of enclosure 2 through fabric curtain 12 and may be coiled or further processed in a hot or cold rolling mill, a slitting station, a galvanizing line, or it may be oiled, otherwise processed, or simply coiled.
  • FIG. 2 illustrates the parts of enclosure 2 from above heating elements 3 and manifolds 10.
  • Strip 1 is underneath heating elements 3 and manifolds 10.
  • Manifolds 10 are seen to have a plurality of gas apertures 17 for releasing gas. These are on the underside of the manifolds 10 and aimed so the reducing gas may be directed with force toward the strip 1, preferably in the direction from which the strip 1 is traveling.
  • Heating elements 3 have electrical connections 16.
  • divider 18 appears only on the top side of strip 1 (see Fig 1); dividers 19 and 20 are above and below the strip 1.
  • the reducing gas manifolds 10 have one or two lengths 28 within enclosure 2 before releasing gas through apertures 17, so the gas can be partially preheated before being released.
  • Figure 3 is an optional device for depositing elemental carbon on both sides of strip 1.
  • the device includes carbon blocks 23 and 24 secured to bases 25 and 26, which in turn are connected to pneumatic cylinder 27 made to urge the carbon blocks 23 and 24 toward strip 1.
  • the carbon blocks 23 and 24 may be made of graphite, anode pitch, or any other convenient composition substantially of carbon which will deposit a thin film of carbon on the strip as it passes between the blocks 23 and 24. Alternatively, only one block may be used; in either case the carbon blocks may to some extent replace or supplement the supporting function of rolls 5 and 6 (Fig. 1).
  • steel strip will have an oxide layer about 0.009 inch thick, commonly from 0.005 to 0.015 inch, and contain about 1 mole to about 1400 moles of oxygen per square meter of surface. Thus, about 1.1 moles to about 1400 moles of hydrogen, will be required for complete reduction of the oxides.
  • the oxide layer on copper is generally from about 0.0005 to 0.025 inch. It is known that the microstructure of the scale on the surface of steel shows numerous small crevices between adherent particles of iron oxide, and a significant portion of the oxide is effectively undermined and loosened by the effect of the reducing fluid. This is true also of copper and other metals.
  • Our invention therefore requires that the reducing gas is contacted with the oxide layer in a vigorous, turbulent manner to assure the continuous replenishment of reactants to the metal/oxide surface and continuous convection of the reaction products, i.e. especially water, away from the gas/solid interface.
  • This vigorous, turbulent contacting to enhance the gas phase mass transfer is preferably accomplished by introducing the gas through ports directed toward the surface from which the oxide is to be removed.
  • reducing gas may be introduced directly to the reducing zone after first being preheated. Because gas in the cooling zone is employed partly to cool the strip, the gas introduced there is not to be preheated. Preheating of gas for introduction to the reducing zone may desirably be to a temperature of 900 to 2000°F, and can be accomplished at least partially by directing the fresh reducing gas through extra lengths 28 of manifolds 10 within enclosure 2, where it will pick up heat energy from the environment. Prior to passing into such pipes within the enclosure, the gas may be partially preheated by any suitable means.
  • Suitable devices for heating are radiant tubes, induction coils, and gas burners.
  • heating of the surface we mean the oxide layer, which may be from 0.005 inch thick to 0.01 inch thick, on steel strip, and seldom more than 0.015 inch.
  • temperatures of 752°F (for steel) need not extend to a depth of more than 0.017 inch and, in most cases, 0.015 inch will be sufficient.
  • the heating to 300°F need not extend below the oxide layer.
  • heating of the reducing gas may be accomplished by passing it through passages in heated carbon blocks.
  • our invention contemplates a use of the reducing gases to a such degree of efficiency that no recycling is necessary. Recycling of the exhausted reducing gas stream would require removal of the chief reduction product, water, from the gas to be recycled, which is very difficult to do to the extent necessary. Likewise, it would mean cooling the recycled reducing gas, thus setting up a continuous process of heating and cooling of the reducing gas. Rather, our invention contemplates the efficient use of the reducing gas in enclosure 2 by inducing turbulence and direction of the gas onto the surface of the metal to assure continuing contact and replacement of gas and reduction products on the surface. Preferably at least 5%, more preferably at least 50%, and most preferably at least 90%, of the reducing gas introduced to the enclosure is consumed in the reduction reaction, and the rest is consumed in flame curtain 13.
  • hot rolled steel strip 30 is seen moving from right to left.
  • the steel strip 30 emerges from a furnace 34 where it was heated to at least 400°C (about 750°F). Although there is no need to heat it above 750°C (about 1380°F), our process will accommodate temperatures up to about 2400°F.
  • the heated strip 30 first passes through sealing rolls 31 to enter initial reducing compartment 32.
  • the sealing rolls 31 are configured and installed to seal off the front end 33 of reducing compartment 32, to minimize the escape or leakage of hydrogen and other gases into furnace 34 or into the atmosphere.
  • Radiant tubes 35 may be used to further heat the strip 30 or maintain it at a desired temperature.
  • the reducing zone may comprise one reducing compartment but preferably comprises at least two reducing compartments 32 and 37, positioned in tandem so the strip 30 will pass directly from one to the other.
  • the compartments 32 and 37 are each sealed enclosures except for the provisions for entrance and exit of the strip 30 and reducing gas to be explained below. Compartments 32 and 37 may have a common wall.
  • Reducing gas preferably hydrogen
  • Reducing gas is introduced near the strip exit 44, in this case into the second reducing compartment 37. As illustrated, it is preferably introduced to reducing compartment 37 prior to the point where the strip 30 leaves reducing compartment 37.
  • An inert gas preferably nitrogen, may be introduced to provide a positive pressure in a chamber 29 also near the strip exit. Radiant heaters 45 may be employed for the strip because the hydrogen is normally not heated.
  • the reducing gas flows generally from left to right, as depicted, countercurrently to the strip 30, through reducing compartment 37 where it continually contacts strip 30, through passage 43 to reducing compartment 32, where it again continually contacts strip 30 moving countercurrently, and proceeds to exhaust trap 46, to be explained in detail in Figure 6.
  • the gas is contacted with strip 30 and reacts with the mill scale on the strip 30, manufacturing water (where hydrogen is the reducing gas) from the combination of hydrogen and oxygen from the mill scale.
  • hydrogen the reducing gas
  • the reducing gas will be entirely consumed by the time it reaches the safety trap 46, but in practice as little as five percent is consumed, and provisions must be made for assuring that no hydrogen or other reducing gas escapes to the atmosphere, where it could cause a fire or explosion.
  • composition of the reducing gas in reducing compartment 32 is somewhat different from that of reducing compartment 37.
  • the reducing gas in reducing compartment 37, particularly near strip exit 44, may be relatively pure, or at least have a high concentration, while that in reducing compartment 32 has a lower concentration, having already reduced a large portion of the mill scale on strip 30.
  • the strength of the reducing gas in reducing compartment 37 is substantially greater than that of reducing compartment 32.
  • the compartmentalization illustrated by the use of reducing compartments 37 and 32 is utilized to maintain the concentration of hydrogen or other reducing gas at a higher level in compartment 37 than it would otherwise be throughout an equivalent length of strip 30 if the reducing zone were not compartmentalized.
  • the concentration of hydrogen or other reducing gas be maintained at least at 2% in the gaseous atmosphere of reducing compartment 37, preferably at least 25%, and at least 2%, preferably at least 10%, in compartment 32.
  • the gas entering exhaust trap 46 will contain at least 0.001% water vapor and, where hydrogen is used as the reducing gas, no more than 99% hydrogen.
  • the balance of the gas entering exhaust trap 46 may include carbon monoxide, nitrogen, and methane.
  • Passage 43 which contributes to the maintenance of the higher concentration of reducing gas in reducing compartment 37 than in compartment 32, may include a small diameter pipe connecting compartments 37 and 32.
  • Fans 48 are placed in both reducing compartments 32 and 37 to provide turbulence for assuring good contact of the reducing gas with the strip 30, and to mix the reducing atmosphere so there will be no pockets of very low active reducing gas concentration in the atmosphere contacting the strip 30. Intakes for fans 48 are within the reducing compartments 32 and 37. Fans 48 are placed to assure turbulence in the reducing atmosphere both above and below the strip 30. As seen in Figure 5, an overhead view of a preferred configuration of reducing zone 36, the fans 48 are preferably placed so the strip 30 is exposed to alternating gas flow in alternate directions as it proceeds through the reducing compartment 37. A similar configuration of fans is in reducing compartment 32.
  • Exhaust trap 46 comprises a hood 50 having a gas exit 51. Gas exit 51 leads to a duct 52 of a higher elevation than hood 50, which leads to a downcomer 53 terminating at an elbow 54 positioned lower than hood 50. Elbow 54 leads in turn to damper 55 and thence to chamber 56 which contains at least one constantly lit burner 57.
  • Combustion in burner 57 may be assisted by air introduced through inlet 59.
  • Chamber 56 has a flue 58 to atmosphere.
  • used or substantially exhausted reducing gas from reducing compartment 32 is led, by a negative pressure from flue 58, through gas exit 51, to hood 50. Pressure differences will cause the exhaust gas to descend into elbow 54 from downcomer 53, and immediately into chamber 56 where it is burned at burner 57.
  • the configuration of the duct 52 and downcomer 53 tends to stabilize the flow of gas.
  • Damper 55 may be adjusted either automatically as a function of flow, or manually as conditions may dictate. Damper 55 may also be used to shut off the flow of gas and/or to prevent the backflow of air into downcomer 53. Heat generated by burner 57 and/or the combustion of the used or substantially exhausted reducing gas may be conserved and used in any known manner to assist in the heating of strip 30, either in furnace 34 or elsewhere.
  • our invention may utilize a single reducing compartment but includes a variation in which the reducing zone comprises at least two sealed reducing compartments in tandem.
  • the reducing gas preferably hydrogen
  • the reducing gas is passed turbulently and countercurrently to the moving steel strip containing mill scale, or other oxied-covered metal, at a first relatively high concentration in a first reducing compartment and at a second, lower, concentration in a second reducing compartment.
  • An exit is provided for the exhaust reducing gas, wherein any remaining combustible component is combusted after passing through an inverted U shaped duct to minimize surges and the risk of explosion.
  • strip 30 After emerging from sealing rolls 36, strip 30 is typically still covered by a sponge layer - that is, a thin layer substantially of iron (in the case of steel), the remains of the mill scale.
  • the strip or other metal is then led to a cooling zone, not shown, where it may be cooled by any effective means to a temperature preferably no higher than 150°C, preferably within an inert or slightly reducing atmosphere during the cooling process, to minimize reoxidation after the process is finished.
  • a preferred method of cooling is to spray or otherwise contact the surface of the strip or other metal with cooling water containing a corrosion inhibitor such as sodium nitrite. To preserve the neutral or slightly reducing atmosphere, the entrance and exit to the cooling zone should be sealed with fabric or any other other effective sealing means.
  • the cooling zone is preferably followed by scrubbing by a brush scrubber or other effective scrubber means for mechanically removing foreign matter and/or the reduced mill scale or sponge layer, and/or polishing or retexturing the surface.
  • a brush scrubber or other effective scrubber means for mechanically removing foreign matter and/or the reduced mill scale or sponge layer, and/or polishing or retexturing the surface.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)

Abstract

L'invention concerne un procédé visant à réduire les oxydes présents sur des surfaces métalliques, qui comporte l'étape consistant à diriger sur celles-ci des gaz de réduction sous forte pression et de manière à produire des turbulences. Dans une version préférée, on fait passer le gaz à travers au moins deux zones (32, 37) de réduction conçues pour maintenir, dans au moins une d'entre elles, une concentration plus élevée de gaz de réduction que s'il n'y avait qu'une seule zone de réduction. La surface oxydée est chauffée au début du procédé (34).
PCT/US2001/017523 2000-06-01 2001-05-31 Dispositif et procede d'elimination sequentielle d'oxydes d'acier Ceased WO2001091929A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2001265218A AU2001265218A1 (en) 2000-06-01 2001-05-31 Apparatus and method for sequential removal of oxides from steel

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US09/584,931 US6406550B1 (en) 1998-08-31 2000-06-01 Apparatus and method for sequential removal of oxides from steel
US09/584,931 2000-06-01

Publications (1)

Publication Number Publication Date
WO2001091929A1 true WO2001091929A1 (fr) 2001-12-06

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PCT/US2001/017523 Ceased WO2001091929A1 (fr) 2000-06-01 2001-05-31 Dispositif et procede d'elimination sequentielle d'oxydes d'acier

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AU (1) AU2001265218A1 (fr)
WO (1) WO2001091929A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107695044A (zh) * 2017-11-27 2018-02-16 李姗姗 一种冷轧带肋钢筋的高效除鳞装置
CN110227316A (zh) * 2019-06-18 2019-09-13 江苏科沃纺织有限公司 一种棉布加工输送除尘箱

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2437528A (en) * 1945-06-08 1948-03-09 Surface Combustion Corp High-temperature cleaning of steel strip, including removing ferrous chloride therefrom
US2625495A (en) * 1948-06-04 1953-01-13 Surface Combustion Corp High-temperature cleaning of ferrous metal
US3320085A (en) * 1965-03-19 1967-05-16 Selas Corp Of America Galvanizing
US3941359A (en) * 1974-12-12 1976-03-02 Northwestern Steel And Wire Company Apparatus for direct reduction of iron oxides
US4389254A (en) * 1978-10-27 1983-06-21 Centre De Recherches Metallurgiques-Centrum Voor Research In De Metallurgie Continuous treatment of steel sheet
US5118357A (en) * 1991-03-20 1992-06-02 Finishing Equipment, Inc. Treatment fluid application and recovery apparatus and method
US6217666B1 (en) * 1998-08-31 2001-04-17 Danieli Technology, Inc. Countercurrent reduction of oxides on moving metal

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2437528A (en) * 1945-06-08 1948-03-09 Surface Combustion Corp High-temperature cleaning of steel strip, including removing ferrous chloride therefrom
US2625495A (en) * 1948-06-04 1953-01-13 Surface Combustion Corp High-temperature cleaning of ferrous metal
US3320085A (en) * 1965-03-19 1967-05-16 Selas Corp Of America Galvanizing
US3941359A (en) * 1974-12-12 1976-03-02 Northwestern Steel And Wire Company Apparatus for direct reduction of iron oxides
US4389254A (en) * 1978-10-27 1983-06-21 Centre De Recherches Metallurgiques-Centrum Voor Research In De Metallurgie Continuous treatment of steel sheet
US5118357A (en) * 1991-03-20 1992-06-02 Finishing Equipment, Inc. Treatment fluid application and recovery apparatus and method
US6217666B1 (en) * 1998-08-31 2001-04-17 Danieli Technology, Inc. Countercurrent reduction of oxides on moving metal

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107695044A (zh) * 2017-11-27 2018-02-16 李姗姗 一种冷轧带肋钢筋的高效除鳞装置
CN110227316A (zh) * 2019-06-18 2019-09-13 江苏科沃纺织有限公司 一种棉布加工输送除尘箱

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