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WO2005118890A2 - Recuperation d'acier dans de la ferraille a trier - Google Patents

Recuperation d'acier dans de la ferraille a trier Download PDF

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Publication number
WO2005118890A2
WO2005118890A2 PCT/GB2005/002130 GB2005002130W WO2005118890A2 WO 2005118890 A2 WO2005118890 A2 WO 2005118890A2 GB 2005002130 W GB2005002130 W GB 2005002130W WO 2005118890 A2 WO2005118890 A2 WO 2005118890A2
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WIPO (PCT)
Prior art keywords
scrap
steel
liquid
gas
melt
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PCT/GB2005/002130
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WO2005118890A3 (fr
Inventor
Noel Warner
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Priority to US10/590,409 priority Critical patent/US20070180955A1/en
Priority to GB0623373A priority patent/GB2437374B/en
Publication of WO2005118890A2 publication Critical patent/WO2005118890A2/fr
Publication of WO2005118890A3 publication Critical patent/WO2005118890A3/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/04—Refining by applying a vacuum
    • 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
    • C21C5/56—Manufacture of steel by other methods
    • C21C5/562—Manufacture of steel by other methods starting from scrap
    • 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
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B15/00—Obtaining copper
    • C22B15/0026—Pyrometallurgy
    • C22B15/0056—Scrap treating
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
    • C22B7/001—Dry processes
    • C22B7/003—Dry processes only remelting, e.g. of chips, borings, turnings; apparatus used therefor
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/05—Refining by treating with gases, e.g. gas flushing also refining by means of a material generating gas in situ
    • 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 a method and apparatus for recovering value-added steel from steel scrap contaminated principally with zinc, copper and tin and also possibly other deleterious non-ferrous metal impurities. It also relates to steel contaminated with carbonaceous material either because it stems from organic coated steel substrates either alone or in composite coatings comprised of organic coating in combination with zinc or other non-ferrous metal coating of such steel substrate material or, alternatively, carbonaceous material that is present adventitiously due to contamination with unconsumed foodstuffs or other vegetable matter.
  • the aforementioned examples of contaminated scrap may be treated individually in isolation if sufficient quantities are readily available. More generally, to save labour intensive and thus costly sorting, the termixed scrap materials constitute the feed for the method of this invention for recovery of high quality steel along with a range of valuable by-products.
  • Copper creates a serious problem during mechanical working at high temperatures such as hot rolling and forging, which is well documented and is referred to as hot shortness.
  • copper causes cracks to form on the steel surface during networking by a mechanism involving enrichment of copper at the steel/scale interface by selective oxidation of iron.
  • the copper enriched phase liquefies and penetrates into austenite grain boundaries under stress during hotrolling or forging to initiate surface cracking.
  • surface hot shortness is generally regarded as the most serious problem.
  • tin accelerates this deleterious influence of copper and therefore there are strict limitations on the permitted copper and tin contents in each kind of steel.
  • the inventor has had a long-standing involvement with the fundamental aspects of ironmaking and steelmaking and can rightly claim major contributions in both areas.
  • As long ago as 1964 he successfully challenged a series of papers emanating from the US Steel Corporation Research Laboratory on the kinetics of the gaseous reduction of hematite and in 1966 he was co-recipient in New York of the Robert W. Hunt Award of the AIME.
  • the Hunt Award paper unequivocally demonstrated the central role of gaseous diffusion in the primary steelmaking reaction. Since then he has witnessed countless unsuccessful attempts to introduce continuous steelmaking over the decades, yet has remained convinced that the best way forward for dealing with steel scrap contaminated with non-ferrous metals was to focus on truly continuous steelmaking and the immediate benefits that success in this area would confer on the steel industry.
  • a key feature of truly continuous processing which is just not available with present steelmaking technology, is the ability to in-line continuously incorporate impure steel scrap directly within the overall steelmaking circuit without prior treatment, except perhaps simple physical segregation atpoint of origin. This mustsecure a valuable competitive advantage.
  • Boom and Steffen R. Boom and R. Steffen: Steel Research, 2001, vol. 72 (3), pp. 91-96 recycling for high quality steel products has been the focus recently of group of steel producers and research institutes in the European Union.
  • pre- treatment of steel scrap away from the steelplant, other than simple physical segregation at point of origin is considered by the applicant to be unnecessary and counter-productive.
  • a method of recovering a high quality steel product from contaminated steel scrap from a high temperature steelmaking circuit from which said steel can be produced continuously comprising the steps of:
  • the tin impurity is regenerated to metallic tin within the process.
  • the zinc is principally converted to a liquid zinc byproduct and the balance to a low-iron zinc sulphide concentrate, ideal to supplement natural zinc concentrates for a Primary Zinc producer.
  • the copper impurity is recovered in metallic form, which will yield on fire refining a high quality ingot copper as a by-product.
  • the other two loops continuously refine the solid metallized material produced in the ironmaking loop down to molten low carbon steel with in-line desulphurization and dephosphorization using in situ generated fluxes.
  • the charge progresses in a straight line, initially as a sheet of composite material floating on the circulating Fe-C of the first loop, and is transported along as it is transformed in the first instance into a sintered raft of partially reacted solid material with the thermal and chemical reaction fronts progressing upwards from the charge/liquid metal interface.
  • the first of the two steelmaking loops is top-blown on both arms, whilst the second is merely two open channels. Both are carefully designed so that the supply of oxidant to the liquid metal surface balances the liquid phase mass transfer of carbon from the bulk to the interface. By so doing, sub-surface nucleation and growth of CO bubbles are precluded, making it possible to sustain zero ejection of micro-spray and fume formation right down from say a nominal 4 percent Fe-C melt to 0.03 percent carbon in the open channel loop. Further details concerning the proposed continuous steelmaking process are given in PCT/GB2003/003065 and PCT/GB2003/003069.
  • Liquid steel scrap may be introduced into the melt circulation circuit of the above at two distinctly different locations. If tin is to be removed, then sulphur containing gas initially derived from the ironmaking loop is contacted with the tin containing melt to enable continuous vacuum desorption of volatile stannous sulphide before the liquid scrap enters the primary steelmaking loop so that in-line desulphurization can be effected in concert with the virgin iron produced in the ironmaking loop.
  • steel scrap is melted and then introduced into an overall steelmaking circuit by a further adaptation of melt circulation technology.
  • a melting loop similar to the main steelmaking loops described above, has preheated scrap melting on one arm and on the other radiant heat input either by natural gas combustion with air, if a zero gas emission scenario is not being pursued or alternatively, if zero gas emission is the ultimate objective and integrated ironmaking and steelmaking the preferred way forward, then the scrap melting loop utilizes the oxidizing gases exiting the post combustion arm of the ironmaking loop.
  • convective mass transfer is restricted to ensure liquid scrap oxidation is insignificant on the heat transfer arm, while maintenance of an argon or other protective atmosphere on the melting arm avoids yield losses by oxidation.
  • the protective atmosphere extends from the molten bath right back through charge preheating, initially by radiation and then at the feed end by convection. Scrap addition to the convective preheater is via initial submergence in a water seal so that air ingress is precluded. This means that the recirculating protective atmosphere has to be de-watered and dried, probably using pressure swing adsorption as, for example, patented for maintaining the protective atmosphere in float glass technology.
  • Another closed loop melt circulation loop employing molten aluminum as a heat transfer medium with electromagnetic melt circulation as used extensively in the secondary aluminum industry, coupled with the well- established mechanical rotor/splash system developed for the zinc blast furnace, will provide the high intensity liquid-metal based convective heat transfer to the recirculating argon to sustain scrap preheating and melting under benign conditions.
  • a thin floating layer of calcium chloride flux for example, prevents the hot combustion gases from oxidizing the molten aluminum, while considerably enhancing radiative heat ⁇ ansier.
  • the emissivily of liquid aluminum at its melting point is about 0.03 whereas that of fused halide is typically around 0.7 to 0,75.
  • Liquid metal irrigation of a packed bed for the ultimate refining step is a preferred way forward for removing non- ferrous metal contaminants from liquid scrap, because it has many attributes to commend it. There is no slag and the dissolved gas content is relatively small, so a fixed bed rather than a moving bed is a realistic option. Also because of its inherent simplicity this could be exchanged periodically with a replacement unit as demanded by accretion build up or other adverse operating factors. Accordingly, the overflow from the scrap-melting loop feeds directly by gravity, is transmitted by a hot metal siphon or is gas-lift pumped to a packed bed contactor, in which the continuous stream of liquid scrap is contacted with argon or other appropriate inert gas at reduced pressure. The non-ferrous metal dissolved in the melt diffuses to the large gas-liquid interfacial area characteristic of non-wetting liquid metal irrigation of a packed bed and is then desorbed into the gas phase.
  • the gas phase is maintained as a continuum and high intensity heat and mass transfer are achieved by allowing the liquid-metal stream to disintegrate and flow downwards as droplets or rivulets by gravity countercurrentto an upward flow of gas within a bed of solid packing material.
  • This of course is what happens in the lower regions of a blast furnace.
  • Formation of accretions within the bed normally has little effect on the operability of the blast-furnace process, because the bed material is ultimately melted or consumed while being continuously replenished from above.
  • potential accretion formation dictates either a readily replaceable fixed bed or alternatively a moving bed configuration with solid packing elements being cleaned externally. Because the downward movement is relatively slow in comparison with the velocities of the upward flowing gas and the droplets ⁇ f fivuiets of liquid metal irrigating the solid packing, quantitative treatment for the latter can be based also on fixed- bed behaviour.
  • Equation 1 the mass transfer correlations are given in Equation 1 for liquid-phase mass transfer and Equation 2 for gas-phase mass transfer.
  • the fluid properties are expressed in terms of viscosity ⁇ and density p.
  • the flow rates used are the mass velocity of the liquid L and the true gas velocity v g .
  • the correlations apply to non-wetting conditions of the type likely to be encountered in advanced continuous steelmaking, but should in principle only be used within the experimentally verified range of the dimensionless groups. However, in the present case, this was not always possible, so extrapolation was unavoidable. It should also be bome in mind that the correlations are not dimensionless but are expressed in SI units.
  • the correlating modulus is seen to be the dimensionless Reynolds Number.
  • the dimensionless Schmidt Number (Sc) and the exponents of -1/2 and -2/3 reflect usage in other well-established mass transfer correlations for liquid-phase and gas-phase mass transfer, respectively.
  • the characteristic dimension ds defined as the diameter of a sphere having the same surface area as the packing element in the gas-phase correlations, covers a range of packing elements including 1/4 inch and 1/2 inch Raschig rings and 10 mm, 20 mm and 45 mm diameter spheres. For liquid-phase mass transfer 20 mm, 45 mm and 150 mm spheres were used.
  • volumetric flux L expressed as m 3 /(s)(m 2 ) and empirically the exponent is determined as -0.23.
  • the heights of transfer units H h and H G are in metres.
  • Zinc not removed from galvanized scrap during preheating in argon and "sweated out” immediately as a liquid zinc by-product can be removed from liquid scrap in two stages. Firstly, within the scrap melting loop on the charge arm downstream from the zone in which preheated solid scrap is being assimilated, profiling the roof so that the freeboard is reduced to about 0.1m allows a controlled addition of purge gas to readily desorb zinc from the melt surface such that the steady-state concentration of zinc throughout the melting loop is in the region of 500ppm. This means that for a raw scrap feed containing 1% zinc initially, some 95% of the zinc is either "sweated out” or desorbed at atmospheric pressure into a purge gas as zinc vapour.
  • the overflow from the melting loop is removed continuously, perhaps by a hot metal siphon into a countercurrent contactor.
  • a hot metal siphon into a countercurrent contactor.
  • One option for this is an irrigated packed tower in which a small amount of purge gas is used to strip the zinc from say 500ppm to 5 ⁇ pm, again at atmospheric pressure.
  • the de-zinced liquid scrap then flows directly into the main continuous steelmaking circuit.
  • the above arrangement becomes a direct contact iron vapour condenser.
  • the electric current supply is reduced or switched off altogether and iron vapour condensation commenced, steady state steam generation will be established and the shells of the retained solid should last indefinitely, provided the melt temperature is maintained at the liquidus temperature and the placing of the boiler tubes was correct in the first place, taking into account the various heat flow terms in the heat balance. This, of course, is only an option for a truly continuous steelmaking process.
  • tin plate represents a very low carbon content steel sheet coated with an average of 5g Sn m 2 and tin plate scrap contains an average 0.2 to 0.4% Sn.
  • an in-line desuphurization step has to be introduced into the flowsheet.
  • Desulphurization is not needed when processing very low tin scrap. This is a special case in thattin contamination is assessed to be at an acceptable level after dilution with the total iron units charged (virgin plus scrap). Clearly, the total amount of tin charge has to be restricted but the advantage of this approach is twofold. Firstly, stannous sulphide does not have to be vaporized so the precision of the process engineering design is not corrupted by possible interracial kinetics exerting an influence on the otherwise straightforward and entirely predictable process of physical desorption involved in both zinc and copper elimination. Secondly, sulphur does not have to be added to the liquid scrap, so possibly it can be merely combined with the continuous output of the virgin steelmaking circuit before the combined output goes to continuous casting. Alternatively, the addition of the liquid scrap to the main steelmaking circuit can be delayed to the ULC tower refiner, withoutincreasing the mass flow through decarburization, desulphurization and dephosphorization.
  • coal gasification associated with combined cycle_power generation still costs significantly more than pulverized coal-fired boilers with advanced steam turbines.
  • Natural gas turbines are forecast to take up more than 80% of new generating capacity in the United States over the next 10 to 15_years.
  • the current state of the art for natural gas-fuelled combined cycle power generation is a net thermal efficiency of about 60%, if the latest General Electric Series H (1500°C Class) as turbine is used, for example.
  • General Electric Series H (1500°C Class) as turbine is used, for example.
  • HBI produced with their FINMET process reached a grand total figure exceeding 5Mt during 2003.
  • Atpresent HBI is compacted at temperatures in excess of 650°C, but for local proximity use, clearly the reduced material before briquetting could be fed directly at 650°C into the melting loop of the current proposal. In effect this would capture the benefits of integrated iron and steelmaking with both scrap and virgin iron units feeding the operation, depending entirely on economic considerations. Also of course, this is a very effective way of very substantially reducing greenhouse gas emissions.
  • melt circulation In a melt circulation system, non-agglomerated reduced iron materials, such as FINMET, on being distributed across the width of a moving liquid iron surface will be immediately either "flash melted” or alternatively, larger material will be coated with a frozen layer of solidified iron bath material to form aggregates that will sink to the bottom of the bath, whilst undergoing transient heat transfer back to the melting point.
  • melt circulation affords an appropriate mechanism to ensure that such material does not accumulate in the immediate vicinity of the charging location.
  • saltation velocity any solidified material can be swept downstream clear of the charging area, whilst it is being assimilated into the melt. Such phenomena are readily quantified and should proceed smoothly without the need for extensive piloting and development expenditure.
  • EAF performance is claimed not to suffer unduly but at higher rates, electricity consumption increases significantly due to the lower metallization and higher gangue content of DRI/HBI.
  • slag makes also increase significantly, approximately doubling for an HB ⁇ lncreast from 20 to 60%.
  • Electric arc steelmaking with recycled steel scrap would be truly sustainable, if powered by electricity generated entirely from renewable energy resources.
  • carbonaceous materials could include, for example, metropolitan solid waste (MSW), biomass or scrap tyres.
  • MSW metropolitan solid waste
  • scrap tyres a more direct linkage is already available, namely organic coated steel scrap.
  • the new continuous steelmaking process must be able to accept the aforementioned composite scrap input without attracting expensive pre-treatment charges or high labour-cost sorting as a pre-requisite to securing its financial competitive advantage.
  • its environmental credentials must be superlative.
  • the iron and steel industry mustnotgetembroiled with the issues, which rightly or wrongly have been a major disruptive influence on the more widespread introduction of advanced incineration technology for the treatment of MSW and tfther more specialist waste arisings. Recyclability is steel's major asset and this most definitely must not be put at risk.
  • the protective gas atmosphere in the melting loop and scrap preheater is now recirculated pyrolysis gas as opposed to argon previously. Also now that the protective gas is being generated in-situ continuously, the need for a small bleed to remove accumulated impurities no longer exists, butrather superimposed on the massive circulation of protective gas as the vehicle for sensible heat transfer for scrap preheating, withdrawal of pyrolysis gas at a relatively small rate in comparison with that being recirculated must be undertaken atthe same rate as it is formed.
  • Figure 1 relates to relevant prior art showing continuous steelmaking starting with virgin iron ore and coal in combination with three processing loops in series in which ferrous melt is force circulated in closed loops firstly one for ironmaking followed then by two for steelmaking in which oxygen is not permitted to directly contact iron- carbon melts atany stage.
  • Figure 2 summarizes in block diagram format the various sub-systems of the present invention for continuous oxygen steelmaking based on charging contaminated steel scrap with primary energy input from oxygen fuel combustion based on natural gas, synthesis gas, pyrolysis gases derived from biomass or solid waste arisings either associated with the steel scrap or independently generated, coke oven gas, blast-furnace gas or other primary ironmaking- derived fuel gas.
  • Figure 3 is an overall flow diagram of a steel plant in which the method of the present invention can be performed starting with scrap feed and fmishing with refined liquid steel ready for continuous casting. It also represents the simplest case applicable to scrap with only a single non-ferrous metal contaminant at an appreciable concentration level.
  • Figure 4 shows a schematic arrangement in elevation and plan of two melt circulation loops which process preheated solid scrap, firstly in a melting loop, followed then by continuous liquid scrap withdrawal to vacuum desorbers arranged in parallel for stripping volatile non-ferrous metals or associated gaseous compounds using an appropriate strip gas, then discharging continuously into a steelmaking loop for adjusting the composition of the liquid steel to its product specification, both within the channel arms comprising the loop and in the associated RH-type degasser, which functions in a refining role as well as providing melt circulation.
  • Figure 5 shows a schematic arrangement of melt circulation loops and associated vacuum desorbers necessary to treat an unsegregated scrap charge containing relatively large concentrations of both copper and tin, which is to be refined to liquid steel in two steelmaking loops to a high purity product specification in advance of continuous casting.
  • Figure 6 is a sectional elevation and sectional plan view of a vacuum desorber with provision for radiative preheating of liquid scrap pumped up from the melting loop prior to its entry into the top of the reduced pressure packed bed contactor, in which liquid scrap irrigates the packing in counterflow to an upward rising strip gas.
  • Figure 7 shows an alternative method of preheating the liquid scrap referred to in Figure 6 using externally cooled current input connectors for an electrical conductive heating system comprising a horizontal strip channel of melt inside the vacuum desorber, arranged so that the channel remains full of liquid strip by conttolling the rate of central discharge during operation, but empties out fully once supply is terminated.
  • an electrical conductive heating system comprising a horizontal strip channel of melt inside the vacuum desorber, arranged so that the channel remains full of liquid strip by conttolling the rate of central discharge during operation, but empties out fully once supply is terminated.
  • a sectional elevation and sectional end elevation are shown in this drawing.
  • Figure 8 illustrates the front or charge end of the argon/inert gas recirculating scrap-melting system.
  • Figure 9 is a schematic sectional elevation of the iron vapour condensation system.
  • steel scrap 1 is deposited or charged continuously onto the lower submerged end of an inclined conveyor 2, which traverses upwards through a water bath (not shown) thereby creating a water seal between the surrounding atmosphere and the contents of an extensive gas-tight envelope comprising a horizontal conveyor system 3 heated from above by tubular radiators 4 to effect drying, preheating as well as pyrolysis of any organic material associated with the steel scrap.
  • a horizontal conveyor system 3 heated from above by tubular radiators 4 to effect drying, preheating as well as pyrolysis of any organic material associated with the steel scrap.
  • the water-laden charge is dewatered as it falls from the inclined conveyor onto the horizontal conveyor and in addition optionally by an "air- knife" system or similar device located above the first section of the horizontal conveyor and based on cooled compressed argon, other inert gas or pyrolysis gas depending on the particular application and the nature of the charge material.
  • the objective here is to remove as much liquid water as possible from the scrap and return it to the water bath before it enters the scrap prehe
  • Galvanized steel material is heated under benign non-oxidizing conditions so that the zinc or zinc alloy coating is "sweated off as liquid zinc (melting point 420°C) and separated from scrap as itfails and then progresses along a vibratory screen/feeder 5 discharging scrap onto a second horizontal conveyor 6 whilst recovering molten zinc into a sump 7 for either intermittent or continuous tapping of a liquid zinc by-product 8.
  • the scrap is further heated to about 500"C as it progresses along the second horizontal conveyor 6, which discharges hot scrap via a chute 9 into the top of the convective reheater 10 comprising a moving packed bed of scrap material in which convective heat transfer is accomplished by countercurrent contacting with highly preheated argon inert gas or pyrolysis gas.
  • Any aluminium associated with the scrap is melted (melting point 660°C) under benign conditions and trickles down to the bottom of the packed bed from where is separated from scrap using a trommel screen 11 or similar device to recover a molten aluminium by-product 12.
  • the preheated scrap at about 900°C falls or is distributed onto the moving surface of the charge arm 13 of the melt circulation melting loop.
  • the gas protective atmosphere extends rightthrough this scrap preheating circuit from the charge arm just referred to back to the top of the convective preheater.
  • VOC volatile organic compounds
  • this gas at about 550 U C is recirculated in a closed loop system with a high temperature fan or gas booster 14 which discharges the possibly contaminated gas to a molten aluminium-based heat exchanger and chemical reactor system.
  • This comprises a closed loop melt circulation arrangement with molten aluminium force circulated either with a gas lift RH-type system 15 or alternatively, by an electromagnetic liquid metal pump of the type now widely used in the secondary aluminium industry.
  • One side 16 of the molten aluminium melt circulation loop receives heat from the hot gases emerging from the combustion arm 17 of the scrap melting loop to which is added a stream of cooler recirculated gas to moderate its temperature from around 1780 U C to about 1100°C before its admission to the aluminium melt circulation loop.
  • a stream of cooler recirculated gas to moderate its temperature from around 1780 U C to about 1100°C before its admission to the aluminium melt circulation loop.
  • This heat input is picked up by the circulating molten aluminium and transferred on the other side of the loop 18 to the mcoming recirculating protective gas atmosphere so that its temperature is raised from around 550°C to about 950°C using an adaptation of commercially well proven technology, initially developed in the U.K. as the basis of the then new zinc blast furnace, the Imperial Smelting Furnace (ISF), employing what has now become known as a mechanical rotor splash system.
  • ISF Imperial Smelting Furnace
  • Mechanical rotors just dipping into a pool of melt throw up a vast amount of mechanical spray into the gas space above providing a very large gas/liquid interracial area, ideal for intensive heat and mass transfer.
  • the two chemical reactions of prime significance between molten aluminium and recirculating protective gas are those involving the removal of both hydrogen chloride and water vapour from the gas phase.
  • the gas emerging from the aluminium splash system containing variable amounts of aluminium chloride in the gaseous state depending on the chloride content of the original scrap feed as well as the associated hydrogen reaction product is next scrubbed free of halide content by chemical reaction with sodium carbonate contained in a binary melt with sodium chloride in a countercurrent gas/liquid contactor 19 probably of the fixed packed bed type to which is added a solid feed of soda ash or the naturally occurring mineral trona 20.
  • a slurry of aluminium oxide dispersed in the binary fused salt is removed from the bottom 21 either continuously or intermittently depending on the level of halide contamination, for subsequent downstream processing for alumina and salts recovery.
  • the combustion gases leaving the heat input side 16 of the aluminium melt circulation loop at about 1000°C provide the thermal input to the tubular radiative system 4, which supplies the energy requirements for radiative charge preheating to about 500°C, zinc melting, pyrolysis of organic components associated with the charge scrap as well as the initial drying out of residual water retained by the scrap feed after de-watering.
  • the exit gas at 22 can be used for fuel gas and oxygen preheating separately and to supplement thermal requirements associated with electricity generation, if so required.
  • Liquid scrap is pumped using inert gas injection from the melting loop by an air-lift type system 23 to the top of the vacuum desorber 24, optionally via an external high-level sump 25 incorporating radiative heating elements to raise the hquid scrap temperature up 1780°C or thereabouts to facilitate stripping of copper or stannous sulphide from the liquid scrap into the strip gas.
  • the refined liquid scrap is removed continuously from a low-level sump 26 at near atmospheric pressure by a siphon 27 to a liquid steel melt circulation loop comprising two arms 28 and 29, probably open channels, for desulphurization and dephosphorization, if needed, as well as final composition adjustmentusing both the RH 15 and the two arms 28 and 29 for these purposes.
  • Liquid steel is removed either continuously or intermittently at30 for transmission to a continuous casting facility, it being recognized that there is adequate melt storage capacity in a melt circulation loop to absorb interruptions to continuity.
  • the arrangement shows the disposition of a bank of four vacuum desorbers 24, each typically about 4 m in diameter, arranged in parallel in between the scrap melting melt circulation loop with arms 13 and 17 and a liquid steel loop with arms 28 and 29 each containing an RH 15 and a melt circulation siphon 31.
  • Liquid scrap is pumped to the top of the desorbers by "air-lift" type pumps 23 discharging optionally into high level sumps 25, if radiative heating is employed to raise the liquid scrap temperature prior to its admission to the top of the packed beds inside the desorbers.
  • the product steel siphons 27 continuously transfer the liquid steel from each of the vacuum desorbers 24 via the low-level sumps 26 to the steel melt circulation loop with arm 28, from which product liquid steel can be withdrawn either intermittently or continuously to a continuous casting facility (not shown).
  • FIG. 5 of the drawings this embodiment shown depicts a steel plant in which the method of the present invention can be performed to recover continuously a liquid steel product with a high grade purity specification from unsegregated scrap containing appreciable levels of both copper and tin contamination.
  • the scrap melting loop, air-lifrtype pump and the firstvacuum desorber are identical to those described in Figure 4.
  • This first vacuum desorber is where copper is removed but little elemental tin is desorbed into the strip gas.
  • the second in-line "air-lift" pump and vacuum desorber are marked accordingly in this figure.
  • a sulphur containing gas is used as the lift gas for the "air-lift" pump 23 and is injected at 32 or alternatively the sulphur requirements for stannous sulphide volatilization in the vacuum desorber 24 are injected into the liquid scrap in the high-level sump 25 in advance of or during transmission of the melt to the top of the backed bed inside the vacuum desorber.
  • two steel melt circulation loops are provided with arms 28, 29, 32 and 33. Final high-grade liquid steel product is withdrawn either continuously or intermittently via 34 for transmission to a continuous casting facility as before.
  • this shows one of the alternative options for elevating the liquid scrap temperature prior to its admission to a vacuum desorber 24 as well as details of the arrangement of the desorber internals in terms of refractory linings and provision of the submerged entry means 35 for admission of liquid scrap to the central raised overflow port 36 for discharge and distribution of high temperature liquid scrap onto the top of the packing elements (not shown) within the desorber.
  • Liquid scrap arrives at the upper-level sump 25 via the upleg 38 of the "air-lift" type pump from the scrap melting arm 13 with its exit 39 not submerged in the liquid scrap maintained as a pool 37 by the centrally located and raised overflow spout 36.
  • the perforations are to provide low pressure drop strip gas flow from the packed bed (not shown) below within the desorber 24 to the gas offtake 46 leading to the reduced pressure strip gas recirculation means (not shown) and also its associated vacuum pumping arrangement to maintain the desired reduced pressure in the recirculating strip gas loop by leading off a small fraction of the strip gas for removal of gaseous infiltration into the reduced pressure circuit.
  • the reduced pressure strip gas recirculation means not shown
  • an appropriate level of hydrogen is maintained within the strip gas to react with infiltrated oxygen and thus prevent oxidation of the liquid steel or being instrumental in causing uncontrolled evolution of carbon monoxide within the desorber and its ancillaries.
  • the liquid strip constituting the circuit for electrical conductive heating is maintained at a predetermined depth by the control rod assemblies 47 depicted schematically in the drawing. Also shown is the low-level liquid sump 26 into which the downflow of liquid steel product is accommodated, in this example by an upleg and a downleg from the reduced pressure desorber 24 in order to induce melt circulation by RH action between the vacuum desorber 24 and the low-level sump 26, which is maintained close to atmospheric pressure.
  • This melt circulation is to combat perceived difficulties in withdrawing continuously the relatively small product flowrate of liquid steel in the face of possible excessive carbon monoxide evolution, which may occur if a single offtake without melt circulation were used, as discussed more fully elsewhere in the description of this invention. Whether or not this enhancement is really necessary would depend on the particular concentration levels of dissolved carbon and oxygen in the liquid steel at this juncture and is thus subject to a measure of control by the process operator.
  • the electrical current input to conductively heat the strip of liquid scrap within the desorber is achieved by cooling the exposed external steel sections of the strip 50 and 51 in direct contact with liquid steel at the liquidus temperature well removed from the high temperature region itself but part of the same physical and electrical circuit, fashioned so that the exposed ends can be sealed using conventional vacuum technology practice to afford a means for connection to the AC electrical power supply.
  • a variable low voltage heavy currenttransformer arrangement will be used for this purpose with possible phase balancing by interconnection of adjacent units to form an overall supply circuit.
  • FIG. 8 of the drawings shows a simplified schematic arrangement for preheating clean scrap without organic contamination and without the necessity to recover an intermediate zinc by-product.
  • the preferred inert gas is argon as no pyrolysis gas is formed in the system and the only real concern is water vapour pickup after physical de-watering (not shown) to remove excess liquid water.
  • Scrap 1 is charged through the water seal 52 onto the inclined conveyor 2, which after passage through the water seal 2 discharges its scrap load onto a single horizontal conveyor 3. After initial de-watering (not shown) the scrap passes under a bank of tubular radiant heaters 4 so thatits temperature is gradually raised to about 500 U C before discharge into the top of the scrap convective heater 10.
  • the principal gas offtake for the closed loop argon recirculati ⁇ n system is at 53, which leads to the high temperature fan or booster for argon recirculation and the closed loop melt circulation system employing molten aluminium both as a heat transfer medium for preheating the argon to about 950 U C while comprehensively reducing the water vapour content of the argon before its entry into the base of the convective scrap preheater 10.
  • the scrap is preheated under benign non-oxidizing conditions without yield loss to about 900 U C before admission to the scrap melting arm of the scrap melting melt circulation loop.
  • a small purge of argon is taken off at 54 to a gas purification system in order to control the build-up of nitrogen in the recirculating argon system.
  • a gas purification system in order to control the build-up of nitrogen in the recirculating argon system.
  • Nitrogen contamination of the argon arises from air infiltration throughout the system butprincipally associated with the scrap charged containing inaccessible porosity, which is not displaced by water as the charge material progresses through the water seal.
  • the associated oxygen reacts in the liquid aluminium splash system used for argon preheating and therefore problems with oxygen build-up and steel yield losses due to oxidation do not arise with the system under discussion.
  • iron vapour saturated strip gas 55 from the vacuum desorber enters the condenser through a number of ceramic pipes 56 extending through an annular packed bed 57 to the gas space beneath the bed 58.
  • Liquid iron 59 close to its liquidus temperature is forced to irrigate the packing using a gas lift principle with the inert gas 60, probably argon, being injected from the top again by a number of ceramic pipes 61.
  • the whole assembly is formed by utilizing the residual unmelted steel shell 62 and electrical conductive heating approach advocated by the applicant in International Publication Number WO 2004/007778 Al, which relies on heat extraction from liquid steel already close to its liquidus temperature, using computer assisted location of steam raising tubes 63 such that the desired thickness of retained unmelted steel is maintained at the appropriate location.
  • liquid steel close to its hquidus temperature is an ideal medium for ensuring highly efficient condensation of iron vapour without effecting to any significant extent copper or stannous sulphide vapour condensation so that these passthrough the condenser in an unchanged condition.
  • Mtpa steel is produced from 500,000 tpa Fe virgin and 1,500,000 tpa Fe scrap.
  • the liquid scrap can be refined in-line with copper being recovered continuously to yield immediately a high quality ingot copper as a by-product.
  • sulphur must be added and stannous sulphide desorbed.
  • the tin sulphide vapour can be absorbed in molten tin, for example, with metallic zinc addition to regenerate metallic tin in a closed loop system producing a low-iron zinc sulphide by-product and the liquid metal overflow cast into tin ingots also as a by-product.
  • Liquid scrap mass velocity (L) 0.561 kg/s m 2
  • V g Mean true gas velocity
  • a typical vacuum pumping system such as that associated with a recirculating degassing system was assumed to exist in an established steelmaking site, but in a preferred embodiment ata greenfield site for example, stripping volatile impurities from liquid scrap into a reduced pressure gas does not need the energy and cost penalties associated with compressing the strip gas atsay 1 mbar level to discharge at atmospheric pressure.
  • a far better approach is to recirculate the strip gas in a closed circuit once the contaminants have been removed either by physical or chemical means. Under these conditions the vacuum system pressure ratio rather than being in the region of 1000 to 1 is reduced down to be no more than say 5 to 1 or even less.
  • the theoretical energy consumption is thus reduced by a factor of In (1000/5) equals 5.3 if both compressions are conducted under isothermal conditions and about 15.8 for the usual industrial case of polytropic compression at say a polytropic efficiency of 80% for a diatomic strip gas, such as nitrogen, if multistage compression from the reduced pressure region back to atmospheric pressure is undertaken without heat dissipation between stages.
  • Electric arc steelmaking with recycled steel scrap would be truly sustainable, if powered by electricity generated entirely from renewable energy resources.
  • an ideal objective is more likely to be attainable by direct fuel firing based on pyrolysis of renewable carbonaceous materials as the prime energy source.
  • carbonaceous materials could include, for example, metropolitan solid waste (MSW), biomass or scrap tyres.
  • MSW metropolitan solid waste
  • scrap tyres a more direct linkage is already available, namely organic coated steel scrap.
  • VOC volatile organic compounds
  • MSW treatment with what is known as Thermoselect high temperature gasification technology would appear to be highly relevant in the present context.
  • MSW has a low density and requires a great deal of space.
  • Thermoselect Process compacts this material to about 10% of its original volume using standard in-line scrap metal processes to produce highly compressed packets of waste which are pushed mechanically directly into an externally heated pyrolysis channel where the material is thermally cracked in the absence of air to form hot carbon packets and gaseous compounds, principally water, carbon monoxide, carbon dioxide, hydrogen and hydrocarbon gases.
  • Organic coatings for external building apphcations are typically of the order of 200 ⁇ m in thickness as opposed to 10 - 25 ⁇ m more typical for internal cladding purposes.
  • Weaver et al. R.W. Weaver, J. Edmundson and K. Williams, Ironmaking and Steelmaking, Vol.26, No.4, AugustT999, pp.285-290
  • heating PVC coated steel up to 200 U C results in polymer degradation, achieving a decrease in molecular mass of around 70,000 withoutrelease of significant VOC, indicating that with thermal treatment the polymer chain is broken down to a less complex organic compound by the time is has reached 200 U C. If PVC is heated at 5 u C/min (i.e.
  • Chlorine must be present for dioxins to form in industrial processes and it can be generally stated that increased chlorine concentrations in feed materials enhance the prospects of dioxins formation and thus the prospects for very harmful emission scenarios.
  • the steel scrap charged to the new process contains organic coated steel based on PVC, the hydrogen chloride evolved on pyrolysis needs to be removed from the pyrolysis gas to a very large degree within the process before attempting to recover its fuel energy content.
  • this is accomplished by contacting the gas emerging from the apatinium splash contacting system which results in volatile aluminium chloride gas being generated along with a small amount of residual hydrogen chloride, in a packed bed trickle-irrigated with a fused salt system that preferably fluxes or wets the entire packing surface and contains at least one chemical compound that is capable of reacting with and absorbing gaseous cWorine-containing gases, such as aluminium chloride or indeed residual hydrogen chloride that escaped reaction in the aluminium splash system.
  • gaseous cWorine-containing gases such as aluminium chloride or indeed residual hydrogen chloride that escaped reaction in the aluminium splash system.
  • a preferred reagent for this chlorine scrubbing system is sodium carbonate (soda ash) or perhaps the naturally occurring mineral, "trona". This is the ⁇ nodynamically capable of removing both gaseous aluminium chloride and hydrogen chloride down to very low levels in the carrier gas.
  • the sodium chloride which is one of the products of reaction is miscible with sodium carbonate in all proportions below 858°C in the fused salt binary system, which percolates by gravity through the packed bed countercurrent to the upward flow of pyrolysis gas as the continuous phase.
  • the binary system forms a eutectic at 642 U C, while sodium chloride itself has a melting point of 801 U C.
  • a melt circulation rate of 20 t/min has been commercially demonstrated as a means of overcoming difficulties associated with transporting a carbon and oxygen containing steel melt through a barometric seal, also known as a barometric leg, from a vacuum back to atmospheric pressure for conditions typical of the then Fuji RH operation, which pertain to before degassing melt analyses of 0.055% carbon and 500 ppm oxygen with internal diameters of 200 and 150mm for the upflow and downflow snorkels, respectively and a circulation rate of 20 tmin.
  • the driving force for mass transfer at the top of the contactor is limited to that induced by the exit concentration of refined melt leaving the reservoir vessel, whereas for a once-through or in-line countercurrent contact without backmixing the driving force at the top of the contactor is many times greater as itreflects, in the present case, the relatively high inlet concentrations of copper and tin in the scrap feed material.
  • Some carbon monoxide released in the upleg of an RH is seen as a positive contribution to the gas flow required to effect high circulation rates.
  • a gas-lift pumping device demands the liquid phase to be the continuous phase and ideally, for homogeneous two-phase flow, the gas should be dispersed uniformly throughout the liquid.
  • Most air-lift pumps do undeah ' ze this ideal objective, butare more prone to a degree of slug-flow.
  • Provision of a multiplicity of back-mixed hquid sumps to accommodate large recirculation rates between the various processing stages, with superimposed product flowrate entry and discharge as implied above, is a viable approach, which in certain circumstances may be the only realistic option available, because of process constraints overriding other considerations. For example, it may be that the process chemistry demands high levels of dissolved carbon on therm ⁇ dynamic grounds, while interfacial chemical kinetics are favoured by having at least a certain minimum dissolved oxygen concentration. However, in many cases a far simpler option may be available, in which case the preferred embodiment may turn outto be along the lines now to be developed.
  • one preferred embodiment must focus on decreasing the propensity for CO generation, which essentially means establishing either or both low levels of dissolved carbon or oxygen before any reduped pressure continuous refining for removal of copper and tin on steel stream flow rates typical of actual steel production rates. Even so it would seem prudent in the first instance not to attempt these procedures for relatively small-scale processing, but rather attention should be focused on continuous processing of hquid scrap at rates of say 0.5 Mpta or greater, so thatat least some carbon monoxide evolution can be tolerated without such evolution totally disrupting the continuity of liquid scrap flowing through the various subsystems involved.
  • a preferred embodiment would incorporate decarburization to a very low level using either an ultra low carbon (ULC) refining step or alternatively deoxidation by an addition of metallic or alloy reagents via the RH melt circulation system.
  • ULC ultra low carbon
  • Decarburization of liquid scrap occurs spontaneously during scrap melting based on melt circulation. Some carbon is introduced into the system over and above the carbon content of the steel itself, because of extraneous carbonaceous contamination derived from pyrolysis of oil, grease, plastics, vegetable matter and residual foodstuffs originally in the charge material on the inert gas side of the melt circulation loop. Natural gas or other combustible gas firing on the other arm of the melting loop to provide the energy requirements for melting, automatically establishes open channel decarburization in which dissolved carbon is oxidized in preference to iron at a rate controlled principally by liquid phase mass transfer of solute carbon to the free surface from the bulk of the hquid scrap, once a relatively low steady state carbon level is established throughout the scrap melting loop. Melt circulation based on RH degasser technology contributes to further continuous decarburization with the proportion of the total decarburization due to the RH-type unit capable of being varied at will by controlling the degree of vacuum applied.
  • the oxygen content of the hquid scrap should in most cases should be relatively low, provided there is enough solute carbon in the liquid scrap to sustain liquid phase mass transfer to the liquid/gas interface to satisfy the diffusional supply of oxidant by gas phase mass transfer to the free melt surface on the heat input arm of the melting loop.
  • pgh is equivalent to the hydrostatic pressure, sometimes called the ferrostatic pressure, and 2 ⁇ /r is the excess pressure across the bubble surface. If pco is greater than the carbon monoxide equihbrium pressure, a bubble could not form irrespective of issues relating to homogenous or heterogeneous nucleation. Thus for a ULC meltwith say 20 ppm carbon, it can be shown that with 300 ppm dissolved oxygen, a bubble could not form any deeper than 3 cm from the free melt surface.

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Abstract

L'invention concerne un procédé permettant de contrer les effets indésirables de la désintégration de flux d'acier en fusion dus à la croissance sous-jacente de bulles d'oxyde de carbone lorsque les flux d'acier en fusion sont exposés à des pressions réduites et qui permet ainsi de raffiner la ferraille liquide sensiblement de la même façon que s'il s'agissait d'un liquide de repos en fusion. La ferraille d'acier contaminée par du cuivre, de l'étain, du zinc et des substances organiques, telles qu'un revêtement de PVC, est préchauffée et fondue en continu au moyen de la circulation du liquide en fusion, puis raffinée en continu en ligne de façon à obtenir un acier liquide de haute qualité et des sous-produits métalliques non ferreux séparés par désorption physique simple à une pression réduite au moyen d'un gaz d'extraction inerte dans un désorbeur, puis par condensation de vapeur de fer par contact direct avec de l'acier liquide, enfin par condensation sélective du cuivre et par récupération de l'étain. La formation de dioxines dans de la ferraille contenant du chlore est évitée par épuration en ligne de gaz de pyrolyse formés pendant le préchauffage de la ferraille. La fusion initiale de ferraille préchauffée utilise la du liquide en fusion et la combustion de gaz au lieu de l'électricité dérivée des combustibles fossiles et, par conséquent, elle est éconergétique.
PCT/GB2005/002130 2004-05-29 2005-05-26 Recuperation d'acier dans de la ferraille a trier Ceased WO2005118890A2 (fr)

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WO2008017797A1 (fr) * 2006-08-11 2008-02-14 Noel Warner Post-combustion avec radiation
ES2457140A1 (es) * 2013-12-11 2014-04-24 La Farga Lacambra, S.A.U. Sistema y procedimiento de carga de horno de fusión y refino de chatarras de cobre y horno asociado
WO2018083433A1 (fr) * 2016-11-07 2018-05-11 Warner Noel A Production d'acier sans émission de dioxyde de carbone sur site
CN108070716A (zh) * 2016-11-15 2018-05-25 江苏凯力克钴业股份有限公司 一种从负载有机相中脱除水相的装置
CN109628746A (zh) * 2019-01-03 2019-04-16 江西铜业技术研究院有限公司 一种分银渣中锡的提取方法
CN111693559A (zh) * 2020-06-22 2020-09-22 中国核动力研究设计院 气相混合物的蒸汽液滴质量流量分离测量装置及测量方法
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GB2438570A (en) * 2005-03-02 2007-11-28 Noel Alfred Warner Process and plant for gas-based direct steelmaking
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WO2008017797A1 (fr) * 2006-08-11 2008-02-14 Noel Warner Post-combustion avec radiation
ES2457140A1 (es) * 2013-12-11 2014-04-24 La Farga Lacambra, S.A.U. Sistema y procedimiento de carga de horno de fusión y refino de chatarras de cobre y horno asociado
WO2018083433A1 (fr) * 2016-11-07 2018-05-11 Warner Noel A Production d'acier sans émission de dioxyde de carbone sur site
CN108070716A (zh) * 2016-11-15 2018-05-25 江苏凯力克钴业股份有限公司 一种从负载有机相中脱除水相的装置
CN109628746A (zh) * 2019-01-03 2019-04-16 江西铜业技术研究院有限公司 一种分银渣中锡的提取方法
CN109628746B (zh) * 2019-01-03 2021-02-26 江西铜业技术研究院有限公司 一种分银渣中锡的提取方法
CN111693559A (zh) * 2020-06-22 2020-09-22 中国核动力研究设计院 气相混合物的蒸汽液滴质量流量分离测量装置及测量方法
CN111693559B (zh) * 2020-06-22 2022-04-01 中国核动力研究设计院 气相混合物的蒸汽液滴质量流量分离测量装置及测量方法
CN112111624A (zh) * 2020-08-18 2020-12-22 含山县龙顺机械配件厂 一种利用废铁屑废钢生产铸件的再利用装置
CN112111624B (zh) * 2020-08-18 2021-10-26 含山县龙顺机械配件厂 一种利用废铁屑废钢生产铸件的再利用装置

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GB0412105D0 (en) 2004-06-30
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WO2005118890A3 (fr) 2006-04-27
GB2437374A (en) 2007-10-24

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