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 111. 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 Fastmetz 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 degree of metallisation of the product (expressed as the percentage of the total iron converted to metallic iron) 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 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 SURNT 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 SURN 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 galvanise steel products. The dust is charged to the kiln as a composite green pellet. During heating to 1000 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 a blast furnace and a BOF.

Another specialised variant of the SURN 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 SURN 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.

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 such as wood or concrete.

The most successful low capital cost processes for steel production are presently based on electric arc furnaces. These are known as steel mills or mini

mills and are fed by scrap iron and, increasingly, by DRI and HBI from DRI plants.

EAF mini-mil plants have disadvantages of requiring high grade feed materials including electricity, scrap and highly reduced DRI or HBI (typically with degree of reduction of 90 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 high grade energy source compared to 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 (ie a cement clinker replacement) due to a high FeO content (typically >10%) and the presence of free or undissolved fluxes. These slags are usually used for road aggregate which has substantially lower economic and environmental benefits.

Summary of the Invention The present invention entails two significant concepts in addressing these issues for processes using self reducing pellets such as coal-ore composite pellets. The first relates to the interaction between the pre-reducing step and the smelting step: it is proposed to enhance the integration between these steps by carrying out the pre-reduction in plant such as a rotary kiln, travelling hearth, rotary hearth or travelling grate 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. Secondly, attention is directed to the slag component of the smelter product and it is proposed to provide for this slag to be a high value material which when ground can substantially replace Portland or similar cements for concrete production.

From another view, the invention, in its preferred embodiment, discards the traditional concepts of minimising smelter slag and off-gases, and instead seeks to produce useful slag and to utilise directly the off-gases, with the preferred aim to be self sufficient in terms of electrical and/or mechanical energy. Also discarded is the traditional objective of seeking a high degree of post-combustion in the smelter furnace.

From another view, the invention, in its preferred embodiment, discards the need for coke or low ash coals, and also allows effective use of reductants produced from renewable fuels such as charcoal produced from wood, timber wastes, or green wastes.

From another view, the invention, in its preferred embodiment, discards the need for flux kilns and allows burning of raw fluxes in the pre-reduction step.

In a first aspect, the invention provides a method of processing iron oxide into an iron product, including: treating composite pellets formed from the iron oxide and a solid carbonaceous reductant (preferably including where possible charcoal) in a pre- reduction furnace to form a direct reduced iron product in which the degree of reduction is greater than 75% (equivalent to a degree of metallisation of >65%); delivering the direct reduced iron product to a smelter furnace at a temperature in the range 700° to 1400°C, preferably 800° to 1100°C; melting the direct reduced iron product with added oxygen or oxygen/air mixtures 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; wherein heat for the pre-reduction furnace is provided at least in part by combustion of said 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.

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 slag 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 pre-heating in other plant.

The degree of reduction of the intermediate DRI product is preferably 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 greatly decreased, thus allowing the melting process to be less intensive, less critical, less turbulent, less erosive to refractories, 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 integrated apparatus for processing iron oxide into an iron product, including: a pre-reduction furnace operable to treat composite pellets formed from iron oxide and a solid carbonaceous reductant to form a direct reduced iron product in which the degree of reduction is greater than 75% (equivalent to a degree of metallisation of >65%) and the pellets contain residual carbon;

a smelter furnace having a melting chamber and means to deliver oxygen or oxygen/air mixtures 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; means to recover the iron melt from the melting chamber; and 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.

Preferably, the combustion of the top gas is effected in the interior of the pre-reduction furnace, in the case of a rotary kiln or rotary hearth furnace, and is introduced at a plurality of locations spaced about the furnace, eg spaced along a rotary kiln furnace. It is further preferred that the combustion is with air rather than oxygen: the air can be drawn in from the surroundings and the capital and operating expense of an oxygen plant can thereby be avoided for a major part of the overall combustion processes compared eg. to DIOS. It is possible to use air rather than oxygen because the nitrogen content has no adverse consequences either due to its volume or reaction with the composite pellets. Relative to prior processes with a low level of pre-reduction and high post-combustion of CO in the smelter, the present invention has thus partially replaced the relatively expensive oxygen requirement at the smelter with inexpensive ambient air at the pre- reduction stage.

Because the iron oxide is fed as composite 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 being necessary to provide the reducing atmosphere as in some prior art processes.

The method may include the step of forming said composite pellets.

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 is preferably coal or charcoal, and/or also biomass substances such as wood wastes.

The composite pellets are preferably 20 to 40% w/w coal (or equivalent reductant), most preferably 25 to 30% w/w coal. Additional reductant may be added separately to the direction reduction furnace and some added or injected directly to the smelter.

The carbon content of the direct-reduced intermediate 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 transported hot, eg in refractory lined bins, and then delivered at the preferred time to the smelter furnace. In this case, some cooling may occur but is preferably minimise.

The pre-reduction furnace is preferably a rotary kiln with a travelling grate preheater (to dry and indurate the pellets), although any furnace that achieves the indicated product conditions will be acceptable. A travelling grate kiln may be suitable alone. Preferably, however, the green pellets (ie undried directly from pelletising drum or wheel) are delivered from a pelletising plant to a rotary kiln via a travelling grate. The maximum temperature in the kiln is preferably in the range 900° to 1400°C but is typically maintained in the vicinity of 1150 to 1300°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 an elongated furnace. Of these, those thought particularly suitable include the EOF-style side blown hearth furnace and the elongated furnace. The elongated arrangement of the last-mentioned smelter could 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 by grinding. 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, liquid holdup volume, 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 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. Steel contaminants such as S and P are preferably bled from the process in the slag stream.

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 supplie directly from the rotary kiln and/or the preheating gate furnace.

Brief Description of the Drawings The invention will now be further described by way of example only, with respect to the accompanying drawings, in which: Figure 1 is a block diagram of an integrated coal based iron ore processing plant in accordance with a first embodiment of both aspects of the invention, utilising a rotary kiln for the pre-reduction step; and Figure 2 is a similar diagram of a second embodiment that utilises a shaft furnace for the pre-reduction step.

Preferred Embodiments The integrated coal based iron ore processing plant 10 illustrated in Figure 1 includes a pre-reduction furnace in the form of an inclined rotary kiln 20 and travelling grate 21 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 rotary kiln prereducer and the central upper feed port 32 of the smelter.

Composite pellets are formed in a pelletier 40 from a feed of iron ore concentrate, coal and binder, to a product specification of about 20 to 35%, and preferably 25 to 30%, coal. The pellets are fed to a grate drier, induration and preheating stage, along with raw fluxes, eg limestone. The preheated pellets are feed directly to the rotary kiln prereducer 20.

In the rotary kiln, natural gas burners initiate and augment heat for maintaining an enclosure temperature of about 1250°C over most of the kiln length, whereby to substantially reduce the iron ore to form a direct-reduced iron (DRI) product at the feed end in which 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 kiln 20 and is dropped through link enclosure 25 into smelter 30. The limestone fluxes are also calcine in the rotary kiln 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 pre-reduction 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 rotary kiln 20, where it is combusted with air to provide a portion of the heat for maintaining the kiln temperature and to provide additional reducing potential. Combustion is spaced out along the kiln to maintain heat flux using a number of shell air injectors 23, where air is drawn in from the surroundings.

A suitable preheater 21 and prereducer 20 is a similar to the rotary kiln and grate combination used in a pellet plant. A typical residence time is in the range 45 to 60mins.

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 20 or 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.

In an exemplary operation of the plant shown in Figure 1, the feed per hour to rotary kiln 20 is: ore 160 tonnes-as composite pellets coal 60tonnes-as composite pellets raw fluxes 40 tonnes plus binder added during green pelletising.

At furnace 30, oxygen required is 25 tonnes per hour (tph), for hot metal recovery of 100tph and slag of 30tph.

The off-gases from rotary kiln 20 are directly passed through the preheater 21 and then to a waste heat boiler 60. At the above noted processing rate, such a boiler may generate 40 MW (or 150 GJ/hr), which will produce 15 MW electrical power.

The smelter may be fed by either batch or continuous operation, the former, for example, by means of two parallel rotary kiln feeds to each furnace. Total energy is approximately 15GJ/t. Greenhouse gases are approximately 1500kg/t liquid metal, using coal; zero or slightly negative using charcoal.

Figure 2, in which like components are indicated by like primed reference numerals, depicts an alternative embodiment 10'in which the generally horizontally extending rotary kiln 20 is replaced by a shaft furnace 20'. This shaft furnace preferably has multiple bussle rings to avoid a thermal pinch point, and heated by partial oxidation of natural gas or smelter gases at each bussle ring.

The atmosphere is reducing at bottom and neutral at the top. Natural gas is preferred to avoid shaft dust problems, while some recycled off-gas via link enclosure 25'is used to control temperatures. Natural gas supply is of the order of 2GJ/t HM. Solids residence time is typically around 60 to 90min.

An alternative means of providing a portion of the enthalpy for the shaft is to use shaft top gases are reheated and injected into the bussle rings using compressed gas injectors or mechanical blowers.

A suitable temperature profile for shaft furnace 20'is indicated in Figure 2.

Cleaned off-gas from the smelter furnace 30 is used to heat the shaft furnace. Offgas from the smelter furnace can also directly fire the burners on the waste heat boiler 50, after being pre-scrubbed if necessary to remove chlorine compounds to decrease dioxin formation.

Preliminary calculations suggest that the greenhouse gas emissions for the integrated configuration illustrated in Figure 2 may be as little as about 1500 kg/tonne, compared with around 2500 kg/tonne for most conventional blast furnace-basic oxygen furnace integrated steelmaking plants. The relative capital cost is much less, in part through the substitution of the illustrated facilities for all of the conventional lime kiln, coke ovens, pellet plant, blast furnace, stoves, BOF and power plant, and by displacing substitutions for cement produced from conventional processes.

The process of the preferred embodiment would be ideal for charcoal based steelmaking avoiding the low strength problems of charcoal in blast furnaces. Other advantages include the high reactivity, low sulphur and low ash content of charcoal. As the process would consume only renewable energy, it would give low or even negative greenhouse gas emissions (negative due to credits from wood tars and other by-products from charcoal production).