WO1999063119A1

WO1999063119A1 - Sustainable steelmaking by intensified direct reduction of iron oxide and solid waste minimisation

Info

Publication number: WO1999063119A1
Application number: PCT/AU1999/000418
Authority: WO
Inventors: Louis James Wibberley
Original assignee: Bhp Innovation Pty Ltd
Priority date: 1998-05-29
Filing date: 1999-05-31
Publication date: 1999-12-09
Also published as: KR20010074502A; JP2002517607A

Abstract

A method of processing iron oxide, the method including heating composite agglomerates formed from the iron oxide, and a solid carbonaceous reductant on a grate (27) in a furnace (20), whereby the agglomerates form a moving bed on the grate. Hot gases are directed (downwardly and/or upwardly) through the grate and the bed of agglomerates in a first zone (21) of the furnace (20) for drying and/or preheating the agglomerates of the bed as they traverse the first zone (21). Cold or preheated air and/or oxidant is directed upwardly through the grate (27) and the preheated agglomerates in a second zone (23) of the furnace (20). Reduction of the iron oxide of said agglomerates is effected in said second zone (23) to form a direct reduced iron product, whereby the upwardly directed air and/or oxidant is effective to combust, in the interstices of the bed, volatiles including carbon monoxide emanating from the reducing agglomerates.

Description

SUSTAINABLE STEELMAKING BY INTENSIFIED DIRECT REDUCTION OF IRON OXIDE AND SOLID WASTE MINIMISATION

Field of the Invention

This invention relates generally to iron and steelmaking and in particular is concerned with a process incorporating direct reduction of iron oxides (DRI) for producing an iron product such as steel, semi-steel or pig iron in a manner favourable from an environmental perspective. More favourable environmental performance preferably includes minimising the consumption of energy and maximising the credits from the production of by-products.

Background Art

A variety of processes have been proposed in which iron ore in a raw or prepared form is pre-reduced and treated in a furnace to produce a sponge iron or pig iron for melting in a range of furnaces, especially electric arc furnaces. An example is the Midrex DRI process developed by Midrex Corporation, where pellets of iron ore concentrates are direct reduced using reformed natural gases to produce direct reduced iron, which is used as a direct feed for a variety of melter furnaces including blast furnaces and electric arc furnaces. A similar pellet based process is Hyl III. In other processes fine iron ore concentrates are pre-reduced in a fluidised bed or circulating fluidised bed. In both types of processes the product may be transferred directly to the melting furnace, or hot briquetted to allow transportation and storage without oxidation and self heating.

The Fastmet™ process developed by Midrex Corporation and described, for example, in Metallurgical Plant and Technology International 2/1991 , at page 36 and in Steel Times, December 1994, at page 91 , is a DRI process whose product is proposed as a direct feed for a variety of melter furnaces including blast furnaces and electric arc furnaces. In this process, composite green pellets, formed from iron ore concentrate, pulverised coal or similar solid reductant and a binder, are passed as a layer one pellet deep through a rotary hearth furnace. The layer is heated mainly by radiation from the hot combustion gases. Average heat transfer rates are around 130kW/m² of bed and typical production rates are 100kg of DRI product/hour.m² of bed facial area. The FASTMET furnace is therefore large in relation to most smelters. The degree of metallisation (expressed as the percentage of the total iron converted to metallic iron) of the product can be varied to suit the end use. The product is either hot briquetted (to obtain hot briquetted iron - HBI) or conveyed as hot DRI direct to an adjacent iron or steelmaking furnace. The above mentioned references suggest that this furnace may be a blast furnace, an electric arc furnace (EAF), a submerged arc furnace (SAF), or an energy optimising furnace (EOF). In a specific development of this integration, the melting furnace is a submerged arc furnace followed by an EAF.

In the Inmetco™ process developed by the International Metals Reclamation Company, coal and pulverised stainless steel mill wastes are processed into green pellets which are pre-reduced in a rotary hearth furnace. The product of this furnace is discharged as hot DRI pellets, via transfer bins, into an electric arc furnace. This process has many similarities with the Fastmet process.

The SL/RN™ process developed by Lurgi entails feeding iron ore fines and pulverised coal directly without pelletisation to a rotary kiln furnace to produce a DRI product which again is transferred to a range of melting furnaces.

A more specialised variant of the SL/RN process is the Waeltz kiln. This is used for reprocessing ferruginous dusts containing a high zinc content, and especially those dusts produced from electric arc furnaces using scrap from galvanised steel products. The dust is charged to the kiln as a composite green pellet. During heating to 1000^QC to 1250°C, the zinc is volatilised and then captured as zinc oxide and further reprocessed to produce either zinc metal or a concentrated zinc dust. The iron content of the ferruginous dust is converted to either a high iron slag or DRI which may be further reduced and melted to form liquid iron products using a range of furnaces including blast furnace and BOF.

Another specialised variant of the SL/RN process is the Combismelt process developed by Lurgi and Mannesmann Demag and as described in SEAISI Quarterly Journal, October 1986 page 29. The process uses a SL/RN kiln to produce either pellet or fine DRI which is melted in a submerged arc furnace. The submerged arc furnace can be fed with either hot or cold DRI with a degree of reduction of 80 to 90% (the percentage removal of oxygen from the iron oxides present in the ore). This is equivalent to a degree of metallisation of 70 to 80%. In the case of hot DRI charging, the DRI is transferred by skips or hoppers to the submerged arc furnace.

The Hismelt™ process uses coal as the main energy source and reductant. The process entails an integrated combination of a smelting vessel and a pre-reducing tower or circulating fluidised bed configuration in which top gas from the smelter vessel ascends against a descending iron ore charge in the pre-reducing unit. This arrangement results in a relatively low pre-reduction of the ore from the pre- reduction unit - in the order of about 30% degree of reduction, with the result that the smelter must operate with a high energy input. This requires high post- combustion (expressed as the percentage of carbon monoxide which is combusted to carbon dioxide) in the smelter requiring a high volume of injected air, and a highly turbulent environment. At the necessary temperature in the bath and gas space of the smelter vessel, significant difficulties with refractory degradation may arise, and the slag will be relatively high in FeO compared to the blast furnace or smelters using a higher degree of pre-reduction. The high levels of FeO in the slag preclude direct processing by grinding of the large volumes of slag produced to replace cement and decreases both the economic and environmental credits from slag by-products.

The McDowell-Wellmann process develops an approach disclosed in US patent 2806779, with further refinements described in US patents 3264092, 3304168 and 3495971. A bed of coal-ore-limestone composite pellets is heated on a travelling grate to produce DRI with metallisation up to 90% for a smelter furnace. In this process, hot gases from a combustion hood are drawn downwards through the bed of pellets, which is 125-250mm deep. There are 3 zones in the process. The first is a drying zone in which hot gases are drawn down through the pellet layer bed at 150-300°C for several minutes. These hot gases are obtained by mixing ambient air with recycled hot gases from below the adjacent carbonising zone. In the carbonising zone, hot combustion gases are drawn through the bed, heating the bed to around 980-1200°C: US patent 3264092 suggests either direction for this flow but downwards is preferred and illustrated. A later improvement was to reverse this flow in a final portion of the bed to obtain a more uniform treatment.

In general, there has been considerable interest since the 1970's in developing a steelmaking process which is less capital intensive than traditional integrated steelmaking and which eliminates the need for coke and allows direct use of fine iron ores. More recently, there is a growing recognition in the steel industry that steel as a product is being seen in some quarters as environmentally undesirable because of the high energy consumption and greenhouse gas emissions from its production, relative to competing materials.

The most successful low capital cost processes for steel production are presently based on electric arc furnaces. These are commonly known as mini mills and are fed by scrap iron and, increasingly, by DRI and HBI from DRI plants. EAF mini- mills have disadvantages of requiring high grade feed materials including electricity, scrap and highly reduced DRI or HBI (typically with degree of reduction of 87 to 95%, or degree of metallisation of 87 to 94%). The DRI and HBI plants in turn require large amounts of low cost natural gas which is a rather high grade energy source compared to coal, and is less flexible as natural gas is less readily transported and stored than coal, thereby making efficiency improvements by integration between DRI and steelmaking more difficult (especially hot charging to the EAF). In addition, the energy reserves of natural gas are less than 10% those of coal. When electric arc furnaces use a high proportion of scrap the steel product may contain high levels of deleterious residual elements such as copper, arsenic and tin which report to the steel product and adversely affect the steel's mechanical properties. Control of this contamination requires dilution of scrap using sufficient amounts of DRI or HBI produced from iron ores. However the production of DRI and HBI is capital intensive and leads to only small improvements in the overall energy consumption and greenhouse gas emissions to produce the steel. A further disadvantage of EAF processes using high levels of DRI and HBI is that a large volume of slag is produced which is generally not suitable for direct processing by grinding to make cement replacement due to a high FeO content (typically >10%) and the presence of free or undissolved fluxes. This material is usually used for lower value road aggregate after a long period of weathering in the open atmosphere. Use of slag as a cement replacement decreases the effective greenhouse gas emissions by 0.8 to 1.2 ton C0₂ eq/t slag.

Disclosure of the Invention

The present invention entails two significant concepts in addressing these issues.

(i) Using a grate-type furnace with provision to draw hot furnace gases down through the grate in a drying and preheating section, and to blow cold or preheated air up through the grate in a pre-reducing zone to maximise heat transfer along the grate.

(ii) Adapting segregated layers on the bed of the grate furnace. In one variation, a segregated bed of fuel (eg. coal, coke, charcoal or wood particles/chips) is provided on the bottom layer against the grate, and composite coal-ore agglomerates, eg pellets, on the top layer. Other options involve a relatively unreactive layer on the grate, and a top layer of fluxes or the like on top of the pellet bed.

In an advantageous application of these concepts, it is proposed to enhance the integration between the pre-reducing and smelting steps by carrying out the pre- reduction in the grate-type furnace to produce a relatively highly reduced hot feed for the smelter furnace, and simultaneously to derive heat for the pre-reducing step, at least in part, from the sensible heat and combustion of gases from the smelter furnace.

In a first aspect, the invention therefore provides a method of processing iron oxide, the method including: heating composite agglomerates formed from the iron oxide, and a solid carbonaceous reductant on a grate in a furnace, whereby the agglomerates form a moving bed on the grate;

directing hot gases through the grate and the bed of agglomerates in a first zone of the furnace for drying and/or preheating the agglomerates of the bed as they traverse the first zone;

directing cold or preheated air and/or oxidant upwardly through the grate and the preheated agglomerates in a second zone of the furnace; and

effecting reduction of the iron oxide of said agglomerates in said second zone to form a direct reduced iron product, whereby said upwardly directed air and/or oxidant is effective to combust, in the interstices of the bed, volatiles including carbon monoxide emanating from the reducing agglomerates.

A recycled off-gas from the top of the moving bed or a fuel gas may be directed upwardly through the grate and the preheated agglomerates in the second zone of the furnace.

The hot gases are directed in a direction selected from the group consisting of downwards, upwards, and a combination of downwards and upwards.

The degree of reduction is preferably greater than 60% (equivalent to a degree of metallisation of 65%).

Accordingly to one option, a relatively less reactive layer may be provided as an intermediate layer between the agglomerate bed and the grate, to protect the grate from excessive temperatures, provide an insulating barrier between the grate and the hot bed, improve gas distribution, and improve release of the product after processing. This layer may comprise, for example, unburnt fluxes, burnt fluxes or ore.

Alternatively, and usually preferably, the method includes providing said moving bed of agglomerates with an intermediate layer of solid carbonaceous fuel disposed between said grate and said moving bed of pellets. Advantageously, then, the carbonaceous reductant of said agglomerates is consumed primarily for said reduction of the agglomerates, and said carbonaceous fuel of the intermediate layer is consumed primarily in combustion of volatiles and gaseous substances below and within said bed of composite agglomerates.

In a second aspect, the invention provides a method of processing iron oxide, the method including:

passing composite agglomerates formed from the iron oxide and a solid carbonaceous reductant along a grate in a furnace, whereby the agglomerates form a moving bed through the furnace;

providing an intermediate layer of solid carbonaceous fuel between said grate and said moving bed of agglomerates; and

effecting reduction of the iron oxide of said agglomerates to form a direct reduced iron product of a predetermined degree of reduction;

wherein said carbonaceous reductant of said agglomerates is consumed primarily for said reduction of the iron oxide of said agglomerates, and said carbonaceous fuel of the intermediate layer is consumed primarily in combustion of volatiles and gaseous substances below and within said bed of composite agglomerates.

The agglomerates are preferably composite pellets, but in general agglomeration may be by pelletising, briquetting, rolling, extrusion or otherwise.

The reductant content of the pellets is preferably about 15-30% by weight in the case of washed coal. The pellets may optionally include fluxes.

Preferably, a further overlying layer of fluxes is provided on the bed of agglomerates. The fluxes may be unburnt (eg. limestone or dolomite) or burnt (eg. lime or burnt dolomite). It is believed that this layer is effective to recoup in situ energy from the hot gases leaving the top of the pellet bed, and to absorb radiant energy from the combustion space above. In the drying/preheating first zone, a further benefit of this overlying layer is to temper hot gases drawn through the bed.

In a particularly advantageous application of the invention, the aforesaid furnace is a pre-reduction furnace, the direct reduced iron product is delivered to a smelter furnace at a temperature in the range 700° to 1300°C, preferably 800° to 1100°C, and the method further includes melting the direct reduced iron product with added oxygen in the smelter furnace to form an iron melt containing carbon, a slag, and a top gas including carbon monoxide, and recovering the iron melt from the smelter furnace.

The grate furnace may be, eg. travelling, rotary, tripping or fixed.

Preferably, the heat for the pre-reduction furnace is provided at least in part by combustion of the top gas from the smelter furnace using air or oxygen.

Preferably, gas composition in the pre-reduction furnace minimises, or avoids excessive, reoxidation of reduced pellets.

Bed moisture in the grate furnace is preferably sufficiently, lowered to control the rate of spread of flame front in the pre-reduction zone, and to substantially prevent decrepitation.

Preferably, off gases from the pre-reduction furnace are recovered in means for generating energy from the off gases, preferably a waste heat boiler or gas turbine.

Preferably, one or more raw materials for fluxes are also delivered to the pre- reduction furnace, prepared for melting therein, and then passed hot to the smelter furnace. In one embodiment, the fluxes include raw limestone and/or dolomite, and the preparation comprises calcining the limestone and/or dolomite. In another, the fluxes include burnt flux, which is prepared by precalcining in another plant.

The degree of reduction of the intermediate DRI product is preferably at least 50%, eg. in the range 80 to 90% (equivalent to a degree of metallisation of 73- 86%). By maximising the extent of pre-reduction, the post-combustion energy requirement in the smelter is drastically decreased, thus allowing the melting process to be less intensive, less critical, less turbulent and with a relatively lower level of oxygen or air consumption compared to prior processes such as e.g. DIOS or Hismelt, or electricity consumption where the smelter is an oxygen blown EAF. Moreover, the energy content of the top gas (not needed to the same extent to supply heat to the smelter by post-combustion) is available for combustion to supply heat to the pre- reduction furnace and waste heat boiler or gas turbine.

The invention also provides, in its first aspect, apparatus for processing iron oxide, including:

a furnace including a travelling or rotating grate on which may be passed composite agglomerates eg pellets formed from the iron oxide and a solid carbonaceous reductant, whereby the agglomerates form a moving bed on the grate;

means for directing hot gases downwardly through the grate and the bed of agglomerates in a first zone of the furnace for drying and/or preheating the agglomerates of the bed as they traverse the first zone; and

means for directing cold or preheated air and/or oxidant upwardly through the grate and the preheated agglomerates in a second zone of the furnace in which the iron oxide of the agglomerates is reduced during operation of the furnace to form a direct reduced iron product, whereby said upwardly directed air and/or oxidant is effective to combust, in the interstices of the bed, volatiles including carbon monoxide emanating from the reducing agglomerates.

In the preferred application of its first aspect, the invention also provides integrated apparatus for processing iron oxide into an iron product, including:

a pre-reduction furnace comprising the aforesaid processing apparatus;

a smelter furnace having a melting chamber and means to deliver oxygen to the melting chamber;

means for delivering the direct reduced iron product from the pre-reduction furnace to the smelting chamber at a temperature in the range 700 to 1400°C, and preferably 800 to 1100°C, wherein the smelter furnace is operable to melt the direct reduced iron product with added oxygen, and optionally electrical energy, in the melting chamber to form an iron melt containing carbon, a slag and a top gas with a carbon monoxide:carbon dioxide ratio greater than 1.0 on a volumetric basis; and

means to recover the iron melt from the melting chamber.

Preferably, said integrated apparatus further includes means to provide heat for the pre- reduction furnace at least in part from sensible heat and combustion of said top gas from the smelter furnace.

Because the iron oxide is fed as composite agglomerates such as eg. pellets to the pre-reduction furnace, the top gas of the smelter furnace can be utilised for combustion to provide heat to the pre-reduction furnace, rather than used as the reducing atmosphere as in some prior art processes.

The method may include the step of forming said composite agglomerates, eg. by pelletising, briquetting, rolling or extrusion.

The iron oxide is preferably iron ore concentrate. In an alternative application, the feed may be steelworks solids waste including, eg iron oxide containing dusts and dusts collected and recycled from the present process.

The solid carbonaceous reductant of the pellets is preferably coal or charcoal, and/or also biomass substances such as wood wastes. The carbonaceous fuel of the intermediate layer may be coal, coke, char, charcoal, petroleum coke or wood or green wastes.

The composite pellets are preferably 15 to 40% w/w coal (or equivalent reductant), most preferably 20 to 30% w/w coal.

The carbon content of the direct-reduced iron product is preferably about 5 to 15% w/w. The direct-reduced iron product (with a degree of reduction of 80-90%), and the pretreated fluxes where included, are preferably delivered direct to the smelter furnace and the top gases reused for heating and combustion, in an integrated facility in which the two furnaces are in mutual proximity, eg bridged by a linking enclosure or ducting. Delivery is typically in such a manner, as to feed directly reduced iron product at the indicated temperature range. Alternatively, the pre- reduced iron product and pretreated fluxes may (for operational convenience) be recovered from the pre-reduction furnace, stored and perhaps transported hot, eg in bins, and then delivered at the preferred time to the smelter furnace. In this case, some cooling and reheating may be required but is preferably minimised.

The maximum temperature in the second zone of the travelling grate furnace is preferably in the range 800° to 1300°C but is typically maintained in the vicinity of 1050 to 1250°C. The necessary heat is supplied by sensible heat and said combustion of the top gas, augmented as necessary eg by coal or natural gas fired burners.

The smelter furnace may be any suitable furnace with an oxygen addition facility. A variety of conventional furnaces are suitable, e.g. oxygen blown electric arc furnace (EAF), submerged arc furnace (SAF), blast furnace, energy optimised furnace (EOF), a basic oxygen steelmaking (BOS) vessel and a ROMELT furnace. Of these, those thought particularly suitable include the EOF-style side blown hearth furnace and the ROMELT furnace. The elongated arrangement of the last- mentioned smelter would be suited to liquid steel production by allowing two melting zones with respect to composition and temperature. Most of the slag would be removed from the high C end to ensure lower slag iron (<5% FeO). The smelting furnace may also allow addition of more reductant as lump and/or injection.

The iron melt may be steel, semi-steel or pig iron.

Preferably, the slag from the smelter furnace has an Fe content less than 5% expressed as FeO, and preferably less than 1.5%, measured as FeO, whereby it is suitable for processing into cement. In its preferred embodiment as an integrated steel making process, the invention preferably further includes recovery and processing or transporting the slag for this purpose. Processing steps typically necessary would include rapid cooling or granulation to ensure a high glass content (ie non-crystalline) and then grinding. The slag has an Fe content preferably no greater than 5% measured as FeO, most preferably less than 1.5%. Preferably, this is achieved in part by controlling the carbon content of the bath, the relative intensity of oxygen blowing and mixing between the molten metal and slag phases, and, when necessary the injection of carbon reductants into the slag phase.

In a preferred embodiment as an integrated steelmaking process, the method preferably further includes tapping the melt and delivering it to a further, preferably nearby, plant for further refining using additional fluxes and oxygen as required. Preferably, the slag wastes of such further plants are fed back to the smelter furnace leading to "zero" solid waste generation.

Preferably, the top gas wastes of such further plants are also fed back to the reduction furnace or waste heat recovery system.

In another embodiment, one or multiple smelter furnaces are used, all being directly connected to the pre-reduction furnace. Each smelter furnace would operate with a 2 stage cycle; the first stage being charging with hot DRI and smelting to produce liquid metal of 1 to 4.5% carbon content, and a second stage wherein the slag from the first stage is removed and then the liquid metal is refined and decarburised by the addition of fluxes and oxygen injection. During this second stage the pre-reduction furnace continues to produce hot DRI which is diverted to either other smelter vessel(s) or a hot holding bin.

Preferably, the apparatus further includes a waste boiler or gas turbine for generating electricity or mechanical power using off-gas from the pre-reduction furnace: it is thought that this would provide sufficient power for generating the oxygen for the smelter furnace and all associated plant up to a caster. The hot gases may be supplied directly from the rotary kiln and/or the preheating grate furnace.

Exemplary Embodiment

The invention will now be further described by way of example only, with respect to the accompanying drawing which is a block diagram of an integrated coal based iron ore processing plant in accordance with an embodiment of both aspects of the invention.

The integrated coal based iron ore processing plant 10 illustrated in Figure 1 includes a preheating and prereduction furnace in the form of an inclined travelling grate furnace 20 of generally conventional configuration, and a smelter furnace provided by a side blown hearth furnace 30. The two furnaces are directly linked by a link enclosure 25 between the lower, discharge end 22 of furnace 20 and the central upper feed port 32 of the smelter.

Composite pellets are formed in a pelletiser 40 from a feed of iron ore concentrate, coal and binder, and optionally fluxes, to a product specification of about 15 to 40%, and preferably 20 to 30%, coal. The pellets are fed to furnace 20 along with raw fluxes, eg limestone, and passed along travelling grate 27 as a bed 28 of the pellets. Disposed between the bed and the grate is an intermediate layer 29 of solid carbonaceous fuel.

In furnace 20, there are two distinct zones. In a first, preheating zone 21 , hot furnace gas is drawn downwardly through the bed of pellets and the grate, as indicated by arrows 50, for preheating the pellets as they traverse zone 21. In a second, prereduction zone 23 which commences where the pellet temperature reaches about 250°C, ie. when the coal just starts volatilising, air 52 is blown upwardly through the grate and pellet bed as the iron oxide is substantially reduced to form a direct-reduced iron (DRI) product. Several individual wind boxes may be used. The degree of reduction is about 80 to 90% (equivalent to a degree of metallisation of 73-86%), and carbon content is about 12%. This DRI product at about 1050°C exits from furnace 20 and is dropped through link enclosure 25 into smelter 30. The limestone fluxes are also calcined in furnace 20 and are delivered to the smelter.

Here, oxygen is side injected at peripherally spaced locations 31 , and the DRI is smelted to form a liquid iron melt or semi-steel having a carbon content less than 5%, and a slag having an iron content less than 5%, measured as FeO. Oxygen injection is from the sides into the melt. Because of the high prereduction of the DRI feed to smelter 30, oxygen injection is correspondingly reduced and post combustion can be controlled at a relatively low 20-30%. The top gas, which includes carbon monoxide, is fed (eg at about 1600°C) through link enclosure 25 into furnace 20, where it is combusted with air to provide a portion of the heat for maintaining the furnace temperature and to provide additional reducing potential.

Drawing hot gas down through grate 27 in zone 21 provides most efficient heat transfer from the smelter offgases in the cooler end of furnace 20 and facilitates drying and pre-heating of the entire bed. Passing air up through the preheated bed in zone 23 combust CO emanating from the hot pellets in the upper bed, and from the coal volatiles and chars in the lower bed. The in-situ heating greatly supplements the radiant and convective heat transfer to the top of the bed from the combustion of the hot smelter gases in the free space above the bed. This inset heating assists in maintaining control of the temperature, oxygen, fuel and moisture content of the air passing up through the grate, so as to ensure that different levels of the bed have sufficient time at temperature to achieve the required degree of reduction and the required degree of sintering or clustering, while minimising reductant/fuel consumption and excessive grate temperature. For example, a small addition of water vapour or mist is very effective in decreasing grate temperature and controlling ignition of coal layered against the grate. It is believed average heat absorption by the bed is significantly higher than for radiative and convective heating to the top of the bed alone as in the aforementioned FASTMET process, and may be up to 500kWh/m². This reduces the size of the process considerably, and improves thermal efficiency and greenhouse gas emissions by decreasing energy losses from the walls.

Additional preheated air may be injected above the bed, at low speed and low turbulence, to generate a combustion zone for CO and volatiles immediately above the bed. This provision also reduces the incidence of dust accretions in enclosure 25.

A significant advantage of the upward gas in zone 23 is that the most metallised product in the top sub-layer of the pellet bed is in contact with the less oxidising gas.

The bed composition is such that approximately sufficient carbons are added to the pellets to satisfy reduction to the required degree of metallisation, typically 20 to 30% by weight for washed coal. The remaining carbons are added directly to the grate as intermediate layer 29. This allows combustion of the volatiles and gasified chars to occur below and within the overlying composite pellet bed 28.

The carbonaceous materials remaining on the grate fall into the smelter furnace along with the reduced pellets (DRI).

These features combine the advantages of composite coal-ore pellets with increased process intensification, decreased process size, increased process thermal efficiency and decreased greenhouse gas emissions, together with increased fuel flexibility (the fuel layer may include a wide range of coals, cars and even dry wood). Not all of the carbons required for reduction and the smelter are required in the pellet. This enables easier use of charcoal, for which it is difficult to produce strong pellets.

Further, advantages of the process include the following: 1. The pellets do not have to be as strong, as the physical environment of a travelling grate is less demanding than some other furnace types. Accordingly, there is less decrepitation and less dust, and less binder is required.

2. The coke layer protects the grate from the higher temperature of the pellet layer and any slagging reactions which occur in the pellet layer.

3. The fuel layer is a thicker bed than the single thickness layer necessary in, eg. rotary hearths. The result here is again a much smaller moving volume of fuel bed.

A suitable smelter furnace 30 is of 8m diameter. The slag is recovered, and conveyed to a pulveriser/grinding plant 50 for conversion to cement clinker. The melt is tapped as a hot metal or semi-steel for further refining as required. Slag wastes from such further refining plants are recycled to smelter 30 and off-gases recycled to either the prereducer furnace 20 or the waste heat recovery unit 60. Alternatively slag wastes are used by other value add applications such as soil ameliorant or slow release fertilizers.

Useful melt products from smelter 30 include semi-steel (2% carbon), low silicon hot metal (3.5% carbon) or a steel (0.1 % carbon), although the latter is preferably best produced using a 2-zone smelter of ROMELT configuration, or by operating the smelter as a 2 stage process as previously discussed.

It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Claims

1. A method of processing iron oxide, the method including:

heating composite agglomerates formed from the iron oxide, and a solid carbonaceous reductant on a grate in a furnace, whereby the agglomerates form a moving bed on the grate;

2. A method according to claim 1. wherein the degree of reduction of the iron oxide is greater than 60%.

3. A method according to claim 1 or 2, further including providing an intermediate layer between the agglomerate bed and the grate.

4. A method according to claim 3, wherein the intermediate layer includes unburnt fluxes, burnt fluxes or ore.

5. A method according to claim 3, including providing said moving bed of agglomerates with an intermediate layer of solid carbonaceous fuel disposed between said grate and said moving bed of agglomerates.

6. A method according to claim 5, wherein the carbonaceous reductant of said agglomerates is consumed primarily for said reduction of the agglomerates, and said carbonaceous fuel of the intermediate layer is consumed primarily in combustion of volatiles and gaseous substances below and within said bed of composite agglomerates.

7. A method according to any preceding claim, wherein the hot gases are directed in a direction selected from the group consisting of downwards, upwards, and a combination of downwards and upwards.

8. A method according to any preceding claim, wherein a recycled off-gas from the top of the moving bed or a fuel gas is directed upwardly through the grate and the preheated agglomerates in the second zone of the furnace.

9. A method of processing iron oxide, including:

10. A method according to any one of claims 5 to 9, wherein the carbonaceous fuel of the intermediate layer is coal, coke, char, charcoal, petroleum coke or wood or green wastes.

1 1. A method according to any preceding claim, wherein the solid carbonaceous reductant of the pellets is coal or charcoal, and/or also biomass substances such as wood wastes.

12. A method according to any preceding claim, wherein agglomeration is by pelletising, briquetting, rolling, extrusion or the like.

13. A method according to any preceding claim, further including the step of forming said composite agglomerates, eg. by pelletising, briquetting, rolling or extrusion

14. A method according to any preceding claim, wherein the agglomerates are composite pellets.

15. A method according to claim 14, wherein the reductant content of the pellets is about 15 to 40% by weight.

16. A method according to claim 15, wherein the reductant content of the pellets is about 20 to 30% by weight.

17. A method according to any one of claims 14 to 16, wherein the pellets include fluxes.

18. A method according to any preceding claim, including providing an overlying layer of fluxes on the bed of agglomerates.

19. A method according to claim 17 or 18, wherein the fluxes are unburnt.

20. A method according to claim 17 or 18, wherein the fluxes are burnt.

21. A method according to any preceding claim, wherein the grate furnace is a travelling, rotary, tripping or fixed furnace.

22. A method according to any preceding claim, wherein bed moisture in the grate furnace is sufficiently lowered to control the rate of spread of flame front in the pre-reduction zone, and to substantially prevent decrepitation.

23. A method according to any preceding claim, wherein the furnace is a prereduction furnace.

24. A method according to claim 23, wherein the direct reduced iron product is delivered to a smelter furnace at a temperature in the range 700┬░C to 1300┬░C.

25. A method according to claim 24, wherein the direct reduced iron product is delivered to a smelter furnace at a temperature in the range 800┬░C to 1100┬░C.

26. A method according to claim 24 or 25, further including melting the direct reduced iron product with added oxygen in the smelter furnace to form an iron melt containing carbon, a slag, and a top gas including carbon monoxide, and recovering the iron melt from the smelter furnace.

27. A method according to any one of claims 24 to 26, wherein the heat for the pre-reduction furnace is provided at least in part by combustion of the top gas from the smelter furnace using air or oxygen.

28. A method according to any one of claims 23 to 27, wherein the gas composition in the pre-reduction furnace minimises, or avoids excessive, reoxidation of reduced pellets.

29. A method according to any one of claims 23 to 28, wherein off gases from the pre-reduction furnace are recovered in means for generating energy from the off gases.

30. A method according to claim 29, wherein the means for generating energy is a waste heat boiler or gas turbine.

31. A method according to any one of claims 23 to 30, wherein one or more raw materials for fluxes are also delivered to the pre-reduction furnace, prepared for melting therein, and then passed hot to the smelter furnace.

32. A method according to claim 31 , wherein the materials for the fluxes include raw limestone and/or dolomite, and the preparation includes calcining the limestone and/or dolomite.

33. A method according to claim 31 , wherein the materials for the fluxes include burnt flux, which is prepared by precalcining in another plant.

34. A method according to any one of claims 23 to 33, further including tapping the melt and delivering it to a further plant for further refining using additional fluxes and oxygen as required.

35. A method according to claim 34, wherein the slag wastes of such further plants are fed back to the smelter furnace leading to "zero" solid waste generation.

36. A method according to claim 34 or 35, wherein the top gas wastes of such further plants are also fed back to the reduction furnace or a waste heat recovery system.

37. A method according to any preceding claim, wherein the iron oxide is iron ore concentrate.

38. A method according to any one of claims 1 to 36, wherein the iron oxide is steelworks solids waste including iron oxide dust.

39. Apparatus for processing iron oxide, including:

means for directing hot gases downwardly through the grate and the bed of agglomerates in a first zone of the furnace for drying and/or preheating the agglomerates of the bed as they traverse the first zone; and means for directing cold or preheated air and/or oxidant upwardly through the grate and the preheated agglomerates in a second zone of the furnace in which the iron oxide of the agglomerates is reduced during operation of the furnace to form a direct reduced iron product, whereby said upwardly directed air and/or oxidant is effective to combust, in the interstices of the bed, volatiles including carbon monoxide emanating from the reducing agglomerates.

40. Apparatus according to claim 39, wherein a recycled off-gas from the top of the moving bed or a fuel gas is directed upwardly through the grate and the preheated agglomerates in the second zone of the furnace.

41. Integrated apparatus for processing iron oxide into an iron product, including:

a pre-reduction furnace including the processing apparatus of claim 39;

means for delivering the direct reduced iron product from the pre-reduction furnace to the melting chamber at a temperature in the range 700┬░C to 1300┬░C, wherein the smelter furnace is operable to melt the direct reduced iron product with added oxygen, and optionally electrical energy, in the melting chamber to form an iron melt containing carbon, a slag and a top gas with a carbon monoxide:carbon dioxide ratio greater than 1.0 on a volumetric basis; and

means to recover the iron melt from the melting chamber;

42. Apparatus according to claim 41 , wherein the direct reduced iron product is delivered to the melting chamber at a temperature in the range 800┬░C to 1100┬░C.

43. Apparatus according to claim 41 or 42, further including means to provide heat for the pre-reduction furnace at least in part from sensible heat and combustion of said top gas from the smelter furnace.

44. Apparatus according to any one of claims 40 to 43, wherein the iron oxide is iron ore concentrate.

45. Apparatus according to any one of claims 40 to 43, wherein the iron oxide is steelworks solids waste including iron oxide dusts.

46. Apparatus according to any one of claims 40 to 45, wherein the composite pellets are 15 to 40% w/w reductant.

47. Apparatus according to claim 46, wherein the composite pellets are 20 to 30% w/w reductant.

48. Apparatus according to any one of claims 40 to 47, wherein the carbon content of the direct reduced iron product is about 5 to 15% w/w.

49. Apparatus according to any one of claims 40 to 48, wherein the maximum temperature in the second zone of the travelling grate furnace is in the range 800┬░C to 1300┬░C.

50. Apparatus according to claim 49, wherein the maximum temperature in the second zone of the travelling grate furnace is in the range 1050┬░C to 1250┬░C.

51. Apparatus according to claim 41 , wherein the iron melt is steel, semi-steel or pig iron.

52. Apparatus according to claim 41 , wherein the slag from the smelter furnace has an Fe content less than 5% expressed as FeO.

53. Apparatus according to claim 52, wherein the slag from the smelter furnace has an Fe content less than 1.5%, measured as FeO, whereby it is suitable for processing into cement.

54. Apparatus according to claim 53, further including recovery and processing or transporting the slag for processing into cement.

55. Apparatus according to claim 41 , including one or multiple smelter furnaces, all being directly connected to the pre-reduction furnace.

56. Apparatus according to claim 55, wherein each smelter furnace operates with a 2 stage cycle; the first stage being charging with hot direct reduced iron product and smelting to produce liquid metal of 1 to 4.5% carbon content, and a second stage wherein the slag from the first stage is removed and then the liquid metal is refined and decarburised by the addition of fluxes and oxygen injection.

57. Apparatus according to any one of claims 40 to 56, further including a waste boiler or gas turbine for generating electricity or mechanical power using off- gas from the pre-reduction furnace.