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
  • C22B1/00—Preliminary treatment of ores or scrap
  • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
  • C22B1/24—Binding; Briquetting ; Granulating
  • C22B1/242—Binding; Briquetting ; Granulating with binders
• • 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
  • C22B1/00—Preliminary treatment of ores or scrap
  • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
  • C22B1/16—Sintering; Agglomerating
  • C22B1/22—Sintering; Agglomerating in other sintering apparatus
• • 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

• Iron-Containing Particles The invention relates to the production of hardened granules from iron-containing dusts, wherein the iron-containing dusts are mixed with at least one binder and water to obtain a mix, the mix is formed to granules, the granules are introduced into a fluidized-bed reactor for hardening, and the hardened granules are subjected to a reduction.
• the iron-containing material is introduced in the form of fine-grained particles.
• An example for such a process is the so-called SL/RN process, a combination of the Stelco-Lurgi process and the Republic Steel-National Lead process (RN).
• the Stelco-Lurgi process is a direct reduction process, which originally was directed to the production of sponge iron for steel furnaces and the use of ores rich in iron.
• the Republic Steel National-Lead process also is a direct reduction process, in which after the reduction iron ores are decomposed into their components metallic iron and gangue. In this connection, gangue is understood to be non-ferrous rocks which are present in iron ores.
• the SL/RN process was developed in 1964, in which iron oxides are reduced in the rotary kiln with solid reducing agents.
• ores or so-called green pellets together with coal, in particular lignite are introduced in excess as reducing agent and dolomite is introduced for desulfurization.
• the furnace output is cooled indirectly in a tube cooler and there- after is separated into sponge iron, excess, coal and ash by screening, magnetic separation and mineral coal separation.
• lump ores with a grain size of 5-18 mm or pellets with 9-16 mm usually are employed. What is also used are iron sands or ilmenites with a grain size preferably larger than 160 ⁇ . Particles with a diameter ⁇ 63 ⁇ are not suitable for use in an SL/RN process, since they lead to sticking and thus to the formation of crusts in the rotary kiln, which can lead to interruptions of operation.
• the granules here can be designed such that the formation of dust during their production remains low ( ⁇ 10 wt-%).
• WO 98/49352 A1 the granulation of fine-grained iron ore fractions is known, in which for example bentonite is used as binder material.
• Bentonite is a rock which contains a mixture of various clay minerals, with montmorillonite being the most important constituent (60 to 80 wt-%).
• US 6,024,790 describes that it may be expedient to activate this binder material bentonite for its intended uses by ion exchange with the intercalated cations.
• An activated bentonite generally has a better swelling capacity as well as a higher thermal stability.
• the activation process described in US 6,024,790 must be carried out over a period of several hours to a few days, in order to ensure a sufficient ion exchange.
• DE 25 175 43 discloses a process for agglomerating metallurgical dusts, in which the metallurgical dust is mixed with 2 to 20 wt-% binder and about 0.5 to 5 wt-% silicon-containing material, this mixture is formed to pellets or granules and subsequently hardened. It is also known to add further additives to the binder, such as sodium hydroxide, sodium carbonate and sodium bicarbonate in quantities of about 3 wt-%. From EP 1 290 232 B1 , there is known a process for producing metallized iron agglomerates from fine iron-containing particles by means of a binder, wherein cellulose fibers are used as binder. When forming the particles, the cellulose fibers act as binder, but due to their high carbon content they can also be used as reduc- ing agent in the downstream reduction process.
• EP 0 916 742 also discloses a process in which the reducing agent is already incorporated in the iron-containing granules.
• the iron-oxide- containing raw material is mixed with a carbonaceous material, an organic binder and an inorganic coagulating agent and subsequently mixed with water.
• a dispersing agent As dispersing agent, sodium hydroxide solution can also be used, for example. Due to the processing in a rotary kiln, together with the solid reducing agent and comparatively long retention times, an increased formation of fine abrasion is observed, however, in the further processing in all these processes, in particular in the SL/RN process, when using green pellets. A high abrasion requires a high processing expenditure, in order to be able to recover these dusts such that a valuable product can be produced from them. Otherwise, the material contained in the dusts gets lost.
• the ultrafine-grained Fe concentrate is supplied to a mixing unit and mixed there with at least one binder and water.
• further aggregates can also be added in this mixing unit.
• the mix thus obtained then is formed to granules in a microcoagulator.
• the granules are introduced into a preferably circulating fluidized bed, with the introduction being effected at the hottest point of the fluidized bed. This sudden change in temperature leads to a rapid sintering of the small granules and hence to a sufficient strength of the grain for the subsequent reduction in a rotary kiln.
• the heat exchange is particularly good due to the high flow velocities, so that the sintering process is accelerated further.
• This process contradicts the usual procedure, according to which the introduction of the material to be processed into the fluidized bed is effected in a region in which the material is not exposed to high temperature gradients, as in particular with larger particles a high temperature difference can lead to stresses in the material and consequently to cracks and deformations.
• higher demands must be imposed on the material of the supply conduit. Dosing therefore also becomes more expensive.
• the hottest point of the fluidized bed is located at the point where the combustion takes place or where the hot gases enter.
• the iron-containing particles have an iron content of at least 30 wt-%, preferably at least 50 to 80 wt-%, so that the processing expenditure remains economic.
• An advantageous aspect of the invention provides that the Fe concentrate has a grain size of max. 5 wt-% coarser than 100 ⁇ and about 55 to 60 wt-% smaller than 32 ⁇ , as with diameters larger on average a direct processing may be economically more expedient.
• the ultrafine-grained concentrate can be present as filter cake or as dry powdery bulk material.
• the specific surface of the particles lies between 1 ,600 and 4,000 cm 2 /g, depending on the mineralogy or the mineral composition of the iron concentrate used.
• a preprocessing, e.g. in the form of grinding, may be expedient for a more homogeneous grain size.
• an inorganic binder such as e.g. bentonite is suited best, since unde- sired side reactions can thereby be excluded with the abrupt increase in temperature during hardening.
• the added quantity of this binder should lie between 0.25 and 1 .5 wt-%, and in principle it is dependent on the mineral composition and the specific surface of the iron concentrate.
• the mix formed to granules in the microgranulator favorably should have a grain size between 0.1 and 6 mm, as with this particle size it is ensured that during the introduction into the hottest stage of the reactor virtually the entire grain is homogeneously heated up and there are no significant temperature gradients within the individual particles.
• a water content of 8 to 14 wt-% was found to be particularly favorable, with the same in principle depending on the respective mineral composition.
• the optimum hardening temperature lies between 850 and 1 ,050 °C and within this range likewise has a dependence on the mineral composition.
• a maximum of about 5 wt-% of the granules are obtained as abrasion during the thermal hardening, wherein here the grain fraction ⁇ 100 ⁇ was defined as abrasion.
• natural gas or light fuel oil can be burnt directly in the fluidized-bed reactor or in a hot gas generator. If a hot gas generator is used, the hot gas is supplied to the fluidized-bed reactor.
• a hot gas generator is used, the hot gas is supplied to the fluidized-bed reactor.
• coal can be used as fuel, wherein the coal is carbonized in a separate reactor at temperatures between 650 and 950 °C, the carbonization gases are introduced as fuel into the hardening reactor, and the hot carbonization coke is introduced as reducing agent into downstream process stages, preferably into a reduction taking place in a rotary kiln.
• Fe 2 O3 x H 2 O ⁇ Fe 2 O3 + H 2 O (elimination of the crystal water of e.g. goethite).
• the hardened microgranules subsequently are subjected to a reducing treatment with coal in a rotary kiln, wherein the oxygen of the iron oxide is decomposed and the iron passes over into the metallic phase.
• the ratio between carbon and iron (C f i X : Fe) is 0.3 - 0.7 : 1 .
• the invention furthermore comprises a plant with the features of claim 9, which is suitable for carrying out the process according to the invention.
• Such plant includes an apparatus for intermixing iron-containing particles with at least one binder and water to obtain a mix.
• This apparatus is followed by an apparatus for granulating the mix to granules.
• This is followed by a reactor with a circulating fluidized bed for hardening the granules.
• the fluidized-bed reactor is designed such that the supply conduit of the granules opens into the lower region of the fluidized-bed reactor and hence the hottest point of the fluidized bed.
• the material of this supply conduit and a dosing means provided there must be designed such that it permanently withstands these temperatures.
• the fluidized bed is fed with hot gas and the supply conduit of the granules opens in the region of this feed conduit, since at this point the hot gases have not yet lost any thermal energy to the fluidized bed.
• At least one return conduit is provided from the fluidized- bed reactor and/or a downstream reduction apparatus into the apparatus for intermixing and/or the apparatus for microgranulation.
• microgranules hardened according to the invention have a greater porosity as compared to lump ores and therefore can be reduced faster and better than lump ores and the classically burnt pellets, which have been hardened at over 1 ,300 °C.
• the hot output from the hardening furnace can be charged directly into the rotary kiln in the hot condition. Thermal energy thereby is saved and the specific throughput capacity of the rotary kiln is increased.
• the process according to the invention also allows that all dusts generated, wet or dry, are recirculated into the microgranulation process, whereby a completely closed material cycle is ensured.
• the fine-grained iron ore is introduced into a mixing device 1 .
• a mixing device 1 Into this mixing device 1 at least one supply conduit 2 opens in addition, via which a mixture at least consisting of binder and water is introduced. It is of course also possible to provide separate supply conduits for each individual additive.
• the mix thus produced is introduced from the mixing device 1 into the granulating device 4. From the mix, granules with a mean grain diameter of 0.1 to 6 mm are formed there (microgranulation), which are introduced into the fluid- ized-bed reactor 10 via conduit 5.
• fluidizing gas is injected via conduit 1 1 , so that a circulating fluidized bed 14 is formed over a grate 13. Shortly above the grate 13 hot gas enters via conduit 12, by which the fluidized bed 14 is heated.
• fuel can also be introduced into the fluidized-bed reactor 10 via conduit 12 or an additional, non-illustrated conduit.
• the supply conduit 5 of the granules ends in direct vicinity of the supply conduit 12.
• the hardened granules containing iron oxide are supplied to a reduction stage, in particular a rotary kiln 16, in which they are reduced for example by means of an SL/RN process.
• a conduit 17 e.g. coal therefore is introduced into the rotary kiln 16 as reducing agent.
• the dust generated in the fluidized-bed reactor 10 is guided into a cyclone 21 , in which it is separated from the gas stream.
• the solids content is recirculated into the mixing device 1 and/or into the granulating device 4, in order to again be processed to granules.
• the gas withdrawn from the fluidized-bed reactor 10 is supplied to a waste gas aftertreatment 31 .
• the purified gas then can be discharged into the atmosphere via conduit 32 and/or be used as process gas.
• the moisture content of the granules thus obtained should be about 10 wt-%; the grain size of the granules is 0.1 to 3 mm.
• the granules thus obtained subsequently are hardened in a fluidized-bed reactor in continuous operation at about 980 °C and then cooled to about 30 °C.
• the throughput capacity of the plant used is about 14 kg/h.
• magnetite is oxidized up to hematite, so that thermal energy is released in addition. Reduction of the hardened microgranules in a short rotary furnace:
• the ratio C f i X : Fe to t is 0.60.
• the charge was treated at 1 ,020 to 1 ,050 °C for about 4 hours. After cooling under a nitrogen atmosphere, an average sample is taken and charged to a weak-field magnetic separator, in order to separate the residual coal and ash.
• the magnetic product, sponge iron has the following analysis:
• the amount of particles with a diameter ⁇ 0.1 mm in the magnetic product was about 4.5 wt-%.

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• Engineering & Computer Science (AREA)
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• Manufacturing & Machinery (AREA)
• Geochemistry & Mineralogy (AREA)
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• Life Sciences & Earth Sciences (AREA)
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• Organic Chemistry (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Devices And Processes Conducted In The Presence Of Fluids And Solid Particles (AREA)
• Carbon And Carbon Compounds (AREA)

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Citations (9)

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• 2012
  • 2012-03-20 DE DE102012005454.8A patent/DE102012005454B4/de not_active Expired - Fee Related
• 2013
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  • 2013-03-07 CN CN201380015110.9A patent/CN104204244B/zh active Active
  • 2013-03-07 WO PCT/EP2013/054558 patent/WO2013139606A1/en not_active Ceased
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• 2014
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