implementation of the first commercial scale t dc smelter for … · 2011. 1. 27. · yuzhural...

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Introduction

Yuzhural Nickel, part of the Mechel group,produces nickel from locally mined laterite orein shaft furnaces. The ore is mixed with cokeand pyrites before being sintered in Dwight-Lloyd type sinter machines to produce a lumpy

material with the necessary permeabilitycharacteristics required by the shaft furnaceoperation. The hot sinter is transferred to thesmelter building in railway wagons, unloaded,elevated to the furnace charge floor and tippedsideways into the top of the furnaces. Largevolumes of air are blown through the furnaceto sustain the process conditions, and asynthetic matte is periodically tapped. The slagis water granulated and removed from the siteby rail. The plant is environmentallyunfriendly due to the multiple handling of thesinter, and the discharge of raw furnace off-gas. Much of the heat content in the sintermaterial is lost during transportation to thesmelter, reducing the overall thermalefficiency. The cost of metallurgical coke andlow process efficiency makes the planteconomically uncompetitive compared tomodern rotary hearth—electric furnace (RKEF)smelting operations.

Mechel approached Bateman in early 2006to undertake various studies in order toestablish the economic feasibility of convertingthe Yuzhural Nickel Plant to DC arc smeltingintegrated with the existing sinter plant oralternatively employing modern flashpreheaters. This process route, a competitor toRKEF smelting was preferred because thetechnology is able to smelt raw material with awide particle size distribution range andvariable chemical composition, producing aferronickel alloy of consistent grade andmetallurgical recovery. This has beendemonstrated several times at small scale1,2.Falconbridge have developed a flowsheetincorporating a flash preheater, fluid bed pre-reduction stage and 2 x 80 MW DC furnaces,for their Koniambo project in New Caledonia3.

Implementation of the first commercial scaleDC smelter for ferronickel production fromlow grade laterite ores—technology buildingblocks and lessens learnedby C.P. Naudé* and M.D. Shapiro*

SynopsisMechel, a large, integrated steel, stainless steel, and ferroalloyproducer in Russia is committed to upgrading its facilities to worldclass pyrometallurgical process and environmental practice.Yuzhural Nickel currently uses shaft furnaces to produce a mattecontaining iron, nickel and traces of cobalt. This rather oldtechnology is thermally inefficient and is characterized by highoperating costs. Mechel has investigated suitable equipment andprocesses to upgrade the plant, and awarded a contract for theconstruction of a 12 MW DC smelter, located near the town of Orsk,to Bateman Engineering Projects in June 2008. The selection of DCfurnace technology for laterite smelting can be considered as astrategic highlight for the pyrometallurgical treatment of low-gradelateritic ores, and could be the first industrial-scale implementationof this technology.

This project has been designed to achieve multiple goalsincluding the demonstration of the process and associatedequipment technology at commercial scale, to confirm the scale-updesign parameters of the forthcoming 2 x 90 MW, twin electrode DCfurnaces, and to prove the environmental emission superiority ofclosed furnaces. It also provides a valuable operator trainingplatform. This paper deals with the process design, key technologybuilding blocks and design features which have been incorporatedto produce a pyrometallurgical vessel capable of (i) resisting slagsuperheat and chemical aggressiveness, (ii) process fine materialwithout pre-agglomeration, (iii) achieve high nickel recoveries and(iv) being tolerant to the variations in chemical composition oflaterite ore. The approach to increasing campaign lives betweenpartial and complete rebuilds, through the use of composite furnacemodule (CFM) technology originally developed and patented by theUniversity of Melbourne, is also followed in more detail.Unfortunately, results from hot commissioning and lessons learnedfrom initial operation are not available because the projectcompletion has been delayed due to the worldwide downturn indemand for commodities.

KeywordsDC furnace, ferronickel laterite smelting, corrosive slag, coppercooler technology.

* Bateman Engineering Projects, PyrometallurgyTechnologies, South Africa.

© The Southern African Institute of Mining andMetallurgy, 2010. SA ISSN 0038–223X/3.00 +0.00. This paper was first presented at the,Infacon 2010 Congress, 6–9 June 2010, Helsinki,Finland.

725The Journal of The Southern African Institute of Mining and Metallurgy VOLUME 110 DECEMBER 2010 ▲

Implementation of the first commercial scale DC smelter for ferronickel

This culminated in a decision by Mechel to proceed to aDC arc demonstration smelter project with an installed powerof 12 MW. The factors influencing the decision included thegeneration of acceptable scale-up parameters to the finalplant capacity of 2 x 90 MW based on the capacity of theexisting sinter machines; verification of all process designcriteria; an opportunity to produce saleable product to recoverthe capital costs of the facility; representative production ofalloy to develop downstream refining and extractionprocesses; and provision of an operator training platform todevelop the operational skills necessary for the conversion ofthe plant from thermal to electric smelting.

The project constraints included the location of thedemonstration smelter within an existing building, which isequipped with an electric overhead travelling crane, to savecapital and reduce the construction duration in harsh Russianclimatic conditions; interface with sinter handling logisticsand slag disposal systems within the existing plant; andmake use of existing plant utility infrastructure. The plantwas designed to comply with all regional heath, safety andenvironmental legislation, and demonstrate compliance withfuture western emission standards which are anticipated tobecome more stringent.

The contract was awarded in April 2008, and wasscheduled for commissioning in early 2010. Design andequipment procurement was carried out on a fast-track basisto match the tight schedule, and provide the necessary datafor regulatory authority approval, customs classification anddesign data for Mechel’s structural, civil and electricalconsultants. All equipment will be delivered by the end of2009. Unfortunately, the construction of the project has beendelayed due to the downturn in the worldwide commoditymarket and is now due for commissioning late 2010/early2011. The planned report on lessons learned from thecommissioning and performance testing are thereforedeferred to a future paper.

Raw material selection

The demonstration plant will utilize sinter diverted from thenormal feed stream to the blast furnaces, anthracite anddolomite to produce a crude ferronickel product (Table I).

The sinter will be stored on a stockpile prior to crushingin a jaw crusher to obtain the required particle size distri-bution for which the furnace feed system has been designedto handle. A decision was made not to reheat the crushedsinter to the temperatures anticipated in the futurecommercial plant (600ºC–900ºC) as the effect of hot feed onthe process specific energy requirement (SER) can beestimated directly without the need for demonstration. Theresidence time on the stockpile and significant changes inambient conditions throughout the year have made it difficultto predict the sinter feed temperature. The sinter-to-powerratio (SPR) control algorithm has been designed tocompensate for this variable over a range of 0ºC–200ºC.

The sinter contains significant amounts of carbon;therefore, accurate control of the anthracite-to-sinter ratio(ASR) is required to maintain a balance between productgrade/recovery and the optimum slag conditions. As the ASRis increased, the slag becomes depleted of nickel (and anycobalt present) and reduction of iron oxide increases (seeFigure 1). This causes a marginal increase in nickel recovery

which is then offset by the decrease in alloy grade, reducingthe effective value of the product. Also, the slag liquidustemperature will increase, resulting in a high viscosity slagwhich is difficult to tap and more prone to foaming. Adecrease in the ASR will improve the alloy grade which inturn is offset by low nickel and iron recoveries. The slagliquidus temperature will decrease as the iron oxide increaseswhich will assist slag tapping; however, the slag freeze liningis at risk of dissolving and exposing the lower side wallfurnace containment components to the aggressive slag.

The addition of flux (dolomite) has been allowed for inthe design to modify the slag properties in order to obtain thenecessary viscosity and liquidus temperature withoutcompromising product grade.

Flowsheet development

The smelting of low grade laterite ores using DC furnacetechnology is well established1,2. The process principles andgrade-recovery performance are similar to the cobalt fromslag recovery process which has been in commercial scaleoperation at Chambishi (PLC), Zambia for some eight years4.

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726 DECEMBER 2010 VOLUME 110 The Journal of The Southern African Institute of Mining and Metallurgy

Table I

Guaranteed sinter, anthracite and dolomiteparameters

Item Unit Sinter Anthracite Dolomite

Ni Mass % (Dry) > 1.1 - -Fe Mass % (Dry) 22.15–23.7 - -SiO2 Mass % (Dry) 43.5–45 - -MgO Mass % (Dry) 9.59–10.25 - 19CaO Mass % (Dry) - - 30C Mass % (Dry) 1.47–1.6 79.59–80.44 -Ash Mass % (Dry) - 17.18–18.02 -Volatiles Mass % (Dry) - 2.82–2.92 -LOI Mass % (Dry) 0.6–0.7 - -Size mm < 30 1–10 5–25Temperature Deg C < 200 Ambient Ambient

Figure 1—Relationship between Ni, Co and Fe recoveries and alloy Nicontent2,4

The future smelting facility will utilize, together with the DCfurnace, the latest proven technology in the field of lateritesmelting which includes the following key technologybuilding blocks:

➤ Wet scrubber technology to cool and clean the furnaceoff gas and recover the energy contained in the gas byutilizing it as fuel source to the driers, preheaters andother possible consumers.

➤ Alloy granulation of the refined FeNi product.➤ Slag granulation, since slag pot hauling is an

impractical option due to the harsh climatic conditionsand high slag volumes produced.

The design of the demonstration plant was kept assimilar as possible to the design envisaged for the futureexpansion project; however, due to several constraints (asdiscussed in subsequent sections) the design in some of theareas was revised, which resulted in new designs that mayprove advantageous in the future.

Key technology building blocks

Feed system

Conventional feed system design incorporates elevation of theraw materials to furnace intermediate storage bins within thesmelter building followed by feed rate (dosing) control andfinal distribution over the molten bath area of the furnacevessel by gravity. The design of the feed system for thedemonstration furnace was constrained by the existingbuilding height and the requirement to reuse the existingfeed conveyor gantry of the crushing plant previously housedin this building. Preliminary layout work established that oneelevation stage and gravity feed for raw material distributionwould not be possible within the available height. Thisresulted in the need to transfer the blended material to theelevated final feed distribution system above the furnace byconveyor. The feed is distributed to two ports in therefractory dome adjacent to the electrode by means ofvibratory feeders. The feed system therefore requires twofeed controls systems—one to obtain the desired feed recipe,and one to maintain the level in the feed distribution hopper.The residence time in the distribution hopper and the transfertime across the conveyor have necessitated minor time delaycompensation algorithms for both SPR and ASR control. Thislevel of complexity was unavoidable for the demonstrationplant, and will not be repeated in the commercial installation.

The electrical isolation dome of the furnace containing theelectrode port and the two feed ports is a high wear itemwhich requires periodic replacement. This is caused bythermal radiation exposure to the superheated slag poolassociated with the arc attachment point, as well as blow-back of high temperature gases deflected towards the roof bythe saucer shaped arc depression zone in the slag. A solutionwas sought to avoid excessive dismantling of the feed systemin order for the building crane hook to gain unobstructedaccess to the roof, thereby allowing the spent dome to berapidly lifted out and new dome to be installed. The designwhich evolved incorporates a gantry on wheels whichsupports the transfer conveyor, blended feed hopper anddistribution vibratory feeders. The feed system is discon-nected from the batching hoppers and the furnace feed ports,

and the entire structure is winched away from the furnace,providing clear access to the roof. The performance of thisconcept during operation will provide valuable guidelines forthe design of a removable feed system for the commercialunit (Figure 2).

Furnace vessel design

The critical area of the process containment vessel is thelower side wall in contact with the molten contents of thefurnace. The slag produced by the process is unsaturated inmagnesite (MgO), and contains between 200ºC and 400ºC ofsuperheat above its solidification temperature. The open bathoperation associated with DC smelting allows fresh,unsaturated slag to wash against the refractory lining,resulting in continuous dissolution of any MgO refractorylining constituents into the slag. A ceramic lining capable ofresisting this condition for acceptable vessel campaigndurations has not been established.

A recent example is the slag cleaning furnace at BHPBilliton’s Olympic Dam Operation (ODO), which produces aslag with similar chemical composition to that of lateritesmelting. The MgO lining cooled by means of an externalfalling film was achieving campaign lives of 11–13 months5.Different formulations of MgO bricks produced incrementalimprovements, and an alternative solution was sought.

The University of Melbourne developed a copper paneland refractory composite, later named composite furnacemodule (CFM) technology, which was demonstrated to becapable of resisting the corrosive slag during trial tests in theODO slag cleaning furnace5. The module consists of a copperbase panel incorporating water cooling passages. Pins arecast onto the hot face of the panel, and refractory is cast intothe space between the pins. The resulting composite is

Implementation of the first commercial scale DC smelter for ferronickelTransaction

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727The Journal of The Southern African Institute of Mining and Metallurgy VOLUME 110 DECEMBER 2010 ▲

Figure 2—3D CAD rendering of the furnace feed system


capable of conducting a heat flux of such a magnitude thatthe temperature in the slag boundary layer adjacent to the hotface of the panel is depressed to its solidification temperature.This causes a freeze lining comprised of slag constituents toform on the refractory, thereby protecting the refractory fromfurther corrosion. Experience has demonstrated that thefreeze lining is vulnerable to periodic, localized failure causedby thermal gradient induced stresses in the plane of thelining, as well as process disturbances including chemicalcomposition changes and process temperature fluctuations.However, the sudden increase in heat flux when the liningbreaks away results in the rapid formation of a new layer,thereby forming a refractory lining of virtually unlimited life.The trial panel was ultimately commercialized when the lowersidewall lining was replaced with CFMs fitted with cast-inmonel water passages during the 2003 shutdown, and thereplacement refractory lining is still in operation.

The major advantages of the CFM concept are thecustomization of the pin configuration to suit the heat fluxcapacity and freeze lining formation in different zones of thefurnace, customization to suit different processes, virtuallyuniform temperature distribution in the plane of the hot facewhich limits thermally induced stress failure in both thefreeze lining and the underlying refractory matrix, andgeometric configurability to suit a wide range of applicationincluding slag tapholes, metal tapholes, and off gas ports.This was further demonstrated when a lower sidewall CFMlining was designed and installed in a trial furnace for theShevchenko laterite ore smelting campaign at Mintek in2005, which formed part of a definitive feasibility study(DFS) to facilitate Oriel Resource’s attempt to advance theexploitation of laterite orebodies in Kazakhstan6. The autopsyof the trial furnace lining at the end of the campaign clearlydemonstrated the suitability of CFM technology for lateriteprocessing.

The lessons learned from this campaign as well as theoperational data available from ODO were used to design thelower side wall of the Mechel 12 MW demonstration smelter.

The iterative design procedure and computational fluiddynamics (CFD) conjugate heat transfer analysis to achievethe simultaneous convergence of layout, thermal duty andproject schedule constraints is documented in another InfaconXII paper7.

The Mechel lower side wall is comprised of 16 panels,each covering a 22.5 degree arc segment. Two panels havecut-outs for the slag taphole inserts and two panels have cut-outs for the alloy tapholes. All the panels are fitted with dualcooling coils, each capable of operation at the maximumdesign heat flux to provide online back-up if one coildevelops a leak. Dual thermocouples are installed in sleevescast into the core of strategically selected pins which facilitateheat flux and lining status monitoring, providing theoperators with an early warning of incipient lining failure andprocess disturbances. The panels are designed to support theupper side wall without assistance from a conventional, fullcylindrical shell, so the backs of the panels are completelyexposed to the outside. This combined with the wedgeshaped coolers installed between the top of the panels andthe upper side wall refractory support beam facilitate easyreplacement of an individual cooler without a majorshutdown in the unlikely event of a catastrophic localizedfailure (typically stray arc strike or metal ingress into a waterpassages). The panels are supported from two brick courseswhich are primarily in contact with the alloy. Finite elementanalysis (FEA) was used to demonstrate that this is theoptimal configuration to prevent excessive heating of thepanel footings by contact with the alloy, while providingsufficient cooling to prevent excessive corrosive and erosivewear from the movement of the slag-metal interface. Theweight of the coolers, the entire upper sidewall and roof areapplied to the hearth skew back bricks, thereby maximizingstability of the hearth, and ensuring tight joints betweenadjacent refractory courses.

Slag is tapped directly through the slag taphole insert.The pins of the insert are configured to follow the anticipatedwear profile of the taphole as it ages. Experience confirmedby CFD analysis has shown that this provides the optimaltrade-off between wear, ease of tapping, and taphole stabilityafter plugging by the clay gun. The cooling coils of the insertare configured in an inverted ‘U’ shape around the taphole toprovide security against slag burn through into the waterpassages caused by downward migration of the tap channelas the insert wears. The insert is designed to facilitate ease ofreplacement without disturbing the main panel whichsupports it.

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Figure 3—3D CAD rendering of the removal gantry in the maintenanceposition

Figure 4—Shop assembly of the 12 MW DC furnace CFM sidewallcooling panels

The alloy taphole insert is configured in the shape of adoor frame, and houses conventional refractory tapholeblocks. The design philosophy for cooling coil configurationand replacement is similar to that of the slag taphole insert.The geometry of the opening is designed to interface withstandard block shapes, allowing a suitable margin for partialrepair from the outside, while ensuring a tight fit to provideadequate cooling of the refractory composite. The alloytaphole is fitted with an external copper block housing areplaceable, conical shaped silicon carbide insert. The block isfitted with an inverted ‘U’ shaped cooling coil to protect thesilicon carbide. The entire taphole assembly is designed sothat first line maintenance is carried out on the siliconcarbide insert and taphole block, second line maintenance onthe refractory taphole blocks in the front of the insert, andthird line maintenance by removal of the taphole insertwithout disturbing the panel which supports the tapholeassembly. This is designed to maximize the campaign life ofthe highest wearing component of the furnace containmentsystem.

Anode

The anode is based on the design originally developed andpatented by ABB/Concast Standard. It forms the hearth(bottom) of the furnace and takes the form of a sphericaldish. In vertical cross-section, working from the outside tothe inside through the conductive portion of the hearth, theanode is comprised of the primary structural supportsteelwork dish, strengthened by radial beams, to which thecopper current collector dish and anode terminals aremounted. The safety lining conductive refractory bricks, inthis case carbon impregnated magnesite bricks, are placed incontact with the copper collector plate on a bed of graphitepowder which simultaneously smoothes out constructiontolerance irregularities and ensures electrical continuity. Theworking lining is comprised of double taper magnesite bricksground to tight tolerances with a stainless steel plate (or clad)bent in an ‘L’ shape attached to one vertical face and thebottom of the brick. These bricks are placed on top of thesafety lining on a layer of graphite powder, analogous to thedescription of the back-up lining.

In the radial direction, the central core of the anode isconstructed of electrically isolating bricks of the samegeometry as the conducting bricks. The core is surrounded bya doughnut shaped ring of conducting bricks. The spacebetween the edge of the conducting bricks and the peripheryof the hearth is filled with non-conducting bricks similar tothe core of the hearth. This ensures that the electrically activeportion of the anode is isolated from the hearth periphery andshell. The transition from the dish shaped refractory materialto a cylindrical ring of bricks is formed by the so-called skewback bricks, which transfer thermal expansion forces fromthe tangent to the dish to tensile circumferential forces in thelower shell. The peripheral brick ring is separated from thelower furnace shell by a layer of refractory with a specificcrushing characteristic. All bricks are installed in a regularpattern, including provision for expansion papers. Thethickness and intervals of the papers, together with the crushzone allow for absorption of 90% of the overall expansion ofthe refractory material hot face. The balance of the expansioncauses tension in the cylindrical shell and provides thebinding force to close the vertical gaps between the bricks, aswell as a certain amount of downward pressure through thecross-section of the hearth to promote electrical continuity.Maintaining tight vertical joints is critical to preventing metalpenetration into the refractory composite which increaseswear and inhibits arch buckling instability promoted bybuoyancy forces generated if the bricks become effectivelyimmersed in a metal bath.

The bottom of the anode is force air cooled to remove theheat conducted through the refractory composite andmaintain the freeze isotherm of the alloy as close to therefractory hot face as practicable to limit wear of the lining.This anode configuration provides uniform current distri-bution across the hearth coupled with even heat flux distri-bution from the process to the cooling air. This avoids theformation of hot spots, formation of thermally induced stressconcentrations and ensures that the arc does not favour aparticular radial deflection towards a zone of lowest electrical


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Figure 5—3D CAD rendering of the cooling water piping around theCFM

Figure 6—3D CAD rendering of the 12 MW DC furnace


resistance. The edges of the stainless steel plates in contactwith the process are gradually replaced by alloy to the level ofthe freeze isotherm, which protects the rest of the claddingfrom further attack.

Slag granulation

Processing of low grade laterite ores is similar to slagcleaning operations in which slag handling dominates metal/alloy production rates. A key technology building block whichrequires operational demonstration in the variable Russianclimate is a continuous slag granulation system. AlthoughMechel currently granulate the slag produced by the blastfurnaces using water, the specific technology proposed for thefuture plant was incorporated within the space constraints ofthe existing plant to verify granulate particle size distributionand product dewatering performance (Figure 7).

The furnace is equipped with one duty and one standbytaphole. They will be swapped over approximately once perday to allow for self repair of the taphole freeze lining andplanned maintenance (depending on operational experience).The slag from each taphole is directed to the granulationlaunder via inclined, water cooled slag launder which issupported on a hydraulically actuated mechanism to allow forrapid changeover from normal to emergency slag ladleoperation. Two granulation launders (also used alternatively)are provided which enter the primary granulation tanktangentially. As the slag is discharged from the water cooledlaunders, it is contacted with high pressure water flowingfrom two horizontal nozzle slots, located one above the other.The top water jet facilitates primary granulation, and thelower jet granulates any slag which breaks through the upperjet and simultaneously provides the sluicing water totransport the slurry into the tank. The tangential flow ofwater into the tank promotes a cyclonic action whichenhances solid separation. Warm water is discharged undergravity flow to the return water pumps via the centrallylocated, baffled overflow pipe. This arrangement maximizesthe initial solid-liquid separation. The granulation thermalenergy is dissipated in conventional open circuit coolingtowers equipped with clog resistant packing material.

The slurry concentrated in the lower conical section of thegranulation tank is fluidized by auxiliary water jets, anddischarged to the dewatering screen equipped with 250micron slotted type screen panels by the slurry extractionpumps. Previous test work has demonstrated that theautogenous filter bed forming on the screen is capable ofdewatering the screen overflow to 8–10% water content whileonly allowing particles < 50 micron to report to theunderflow. The dewatered granulate is discharged from thesmelter via a conveyor installed in the tunnel previously usedto discharged crusher product. The screen underflow ispumped to a hydrocyclone. The dirty water from the cycloneoverflow is discharged back into the granulation tank, andthe underflow is discharged on top of the filter bed on thescreen.

Alloy granulation

Alloy granulation of refined FeNi alloy is proposed for theproduction of saleable product in the future plant. Hence agranulation process demonstrating the ability to producealloy nodules of the required particle size distribution without

the excessive fines generation was included in the smelterdesign. Refining (typically sulphur and phosphate removal)was not included for demonstration as third party technologyis available and the granulation performance of crude andrefined alloy is anticipated to be similar. Although the plantcompactness is important for countries with harsh climates tosave building sizes and costs, particular attention was paid tothe layout of this area of the smelter because of spaceconstraints in the existing building. In addition, optimizationof alloy ladle handling logistics also influenced the layout anddesign of equipment (Figure 8).

Alloy is tapped from one of two tapholes alternatively byconventional drilling and oxygen lancing in batches, andflows under gravity via refractory lined runners into the alloyladle. The alloy ladle is supported on a combined tiltingmachine-transfer car, normally located in one of fourpositions—the ladle preheater station, below either of the twoalloy runners, or in the granulation position. The layoutincludes provision for alloy discharge under variousemergency scenarios including self-tapping and emergencydumping. This design was developed to avoid the need tomove and accurately position the ladle by means of the

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Figure 7—3D CAD rendering of the slag granulation area

Figure 8—3D CAD rendering of the alloy granulation area

overhead crane in the restricted space available. This keepsthe ladle handling time between end of tap and start ofgranulation to a minimum, thereby limiting the tapped alloysuperheat required to minimize residual ladle scrap, andprolonging the vessel refractory life by limiting the averageprocess operating temperature.

Once the taphole is closed by means of the conventionalclay gun, the transfer car is aligned with the granulationrunner. The ladle is tilted at high speed until molten materialis first discharged into the runner, after which the ladle istilted at slow speed to achieve the design granulation flowrate. The alloy flows under gravity to the end of thebifurcated runner, terminating in two streams discharginginto the granulation sump filled with water. The drop heightis optimized to allow for initial fragmentation and air coolingof the stream before the droplets contact the water surface,while limiting the entry velocity. The sump depth is designedto allow for outer layer solidification of the largest noduleswhile in free fall to the bottom of the sump. Nozzlespositioned strategically within the sump discharge recooled,high pressure water to increase the effective free-fallretention time, increase heat transfer between the nodulesand the water, and promote vapour release, while turbulencegeneration is minimized to avoid excessive fines generation.Monitoring the sump water temperature is critical to ensuresafe operation; safety interlocks in the control algorithm willautomatically prevent further granulation should an unsafecondition develop.

The nodules are collected in a stainless steel hopperwhich is submerged in the sump by the overhead crane priorto the start of a granulation run. The bifurcated runner isremoved for cleaning and maintenance at the end of agranulation run, and allows for the extraction of the loadedgranulate collection hopper by the crane. Water drains fromthe hopper through nozzles equipped with fines retentionbaffles when the hopper is lifted clear of the water surface.Granulate is discharged by tilting the hopper with theauxiliary crane hoist.

The granulation cooling process water is cooled inconventional, open circuit cooling towers. Cooling ismaintained after the end of a batch to the lowest temperaturepossible in the prevailing ambient conditions which providesa thermal safety reservoir for the next batch.

Off-gas treatment

Wet scrubber technology will be required to flash cool andclean the CO produced by the reduction process, therebyrendering it suitable for use as a heating and drying fuel inthe future plant, thus improving the overall thermal efficiencyof the plant. This technology was not included as it is wellevolved and readily available, and because the volume of COgenerated cannot be economically recovered in thedemonstration plant (Figure 9).

A conventional combustion process was designed. Hot COoff-gas from the furnace and ambient air is drawn into thewater cooled, refractory lined combustion chamber under theaction of the induced draught extraction fan. The CO entersfrom below while the air enters tangentially. The COcombusts to CO2 and is cooled by the excess air drawn intothe process. The combustion products are further cooled inwater-cooled ducts followed by cooling in a radiant

(trombone) cooler before the particulates are removed in abag house filter. Protection has been provided for bothundercooling to avoid condensation formation and high inletgas temperature to prevent damage to the bags. The treatedfurnace off-gas is discharged to atmosphere in a stacktogether with the cleaned taphole fume.

Auto-changeover to an emergency stack has beenprovided in case the treatment plant unexpectedly becomesunavailable. A safety burner has been provided to initiatecombustion when the CO concentration is too low, partic-ularly when the furnace is switched out in an emergency.

Conclusion

Mechel, a large, stainless steel and ferroalloy producer inRussia have embarked on an upgrade and expansionprogramme at their Yuzhural Nickel Plant located in Orsk,Southern Russia. They ultimately plan to convert the plantfrom the thermal production of ferronickel matte to 2 x 90MW DC arc furnaces producing ferronickel alloy from lateriteore. A 12 MW demonstration plant is being built in anexisting building on the site to confirm process and scale-upparameters, produce saleable product, produce alloy forrefining test work, and train operators for the future plantconversion.

The demonstration plant will utilize sinter diverted fromthe normal feed stream to the blast furnaces, anthracite, anddolomite to produce a crude ferronickel product. Theproduction for the demonstration plant is summarized inTable II.

The design of the demonstration plant was kept assimilar as possible to the design envisaged for the futureexpansion project; however, the design was customized tosuit physical space constraints, and focused on criticaltechnology packages which need to be demonstrated atcommercial scale to ensure satisfactory operation of thefuture full sized plant. These included performanceassessment of the anode and composite furnace module(CFM) lower sidewall furnace containment components forlaterite ore processing which are associated with chemicalcorrosion of magnesite refractory materials, a continuousslag granulation system for convenient disposal of the majorfurnace by-product, and an alloy granulation process capableof producing granulate with the required particle size distri-


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Figure 9—3D CAD rendering of the off-gas and fume extraction area


bution and without excessive fines generation. Sinter/orepre-heating was not included, as these parameters do notrequire demonstration. The off gas plant utilizes conventionalCO2 combustion, cooling and baghouse filter technology toavoid the cost and complexity of including a wet CO scrubberto recover the relatively small volume of CO as a fuel. Wetscrubbing is also considered an established technology andtherefore does not require demonstration. This philosophyproduced a cost-effective plant which will enable bothdesigners and operators to gain the required information forsuccessful execution and commissioning of the full-scaleexpansion project.

References

1. LAGENDIJK, H. and JONES, R.J. Production of Ferronickel from NickelLaterites in a DC-Arc Furnace, Nickel/ Cobalt ‘97. 36th Annual Conferenceof Metallurgists, Sudbury, August 1997 orhttp://www.mintek.co.za/Pyromet/Laterite/Laterite.htm.

2. REINECKE, I.J. and LAGENDIJK, H. A twin-cathode DC Arc Smelting Test atMintek to Demonstrate the Feasibility of Smelting FeNi from CalcinePrepared from Siliceous Laterite Ores from Kazakhstan for Oriel Resourcesplc, Infacon XI, 2007, pp. 781–797.

3. KING, M.G., GRUND, G., and SCHONEWILLE, R., A Mid-term Report onFalconbridge's 15 Year Technology Plan for Nickel, Proceedings of EMC(European Metallurgical Conference) 2005, 18 to 21 September 2005,Dresden, Germany, pp. 935–954.

4. Jones, R.T., et al., Recovery of Cobalt from Slag in a DC Arc Furnace atChambishi, Zambia, Cobalt Nickel Copper and Zinc Conference, 16 to 18July 2001, Victoria Falls, Zimbabwe. Also at http://www.mintek.co.za/Pyromet/Chambishi/Chambishi.htm.

5. KYLLO, A.K. AND GRAY, N.B. Composite Furnace Module Cooling Systems inElectric Arc Slag Cleaning Furnace, Proceedings of EMC (EuropeanMetallurgical Conference) 2005, 18 to 21 September 2005, Dresden,Germany, pp. 1027–1034.

6. MARX, F., SHAPIRO, M., and FOWLER, N. Composite Furnace Modules—Application in DC Furnaces for FeNi Alloy Production, Proceedings of EMC(European Metallurgical Conference) 2009, 28 June–1 July 2009,Innsbruck, Austria, pp. 877–888.

7. HENNING, B., SHAPIRO, M., MARX, F., PIENAAR, D., and NEL, H. Evaluating ACand DC Furnace Water-Cooling Systems using CFD Analysis, Infacon XII,2010. ◆

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Table II

Estimated furnace production summary

Item Consumed/produced Temperature Ni Feunit ton/year (ton/day) Deg C Mass % % Recovery Mass % % Recovery

Sinter 119520 (327.5) < 200 1.1 - 22.93 -Anthracite 663.5 (1.8) < 25 - - - -Dolomite TBA < 25 - - - -Alloy 5300 (14.5) 1550 21.6 88 77.4 15Slag 99325 (272.1) 1650 0.1 9 18.4 82

Dr Cuthbert Musingwini, a member of the SAIMMPublications Committee and Senior Lecturer at theUniversity of the Witwatersrand, was this year arecipient of the Wits Faculty of Engineering and BuiltEnvironment (FEBE) Best Researcher Award. Hewalked away with a R20 000 research grant to fundhis research activities. The award is given to anacademic who has produced the highest improvementin the weighted average research output based on

journal publications, international conferenceproceedings publications, and postgraduate researchstudents graduated by the academic among the sevenSchools within the FEBE. Cuthbert is grateful for theassistance and advice given by Mike Rogers andGordon Smith of Anglo Platinum towards his researchefforts. The Publications Committee is delighted withthe honour bestowed on Cuthbert and wishes him wellfor the future. ◆

SAIMM Publications Committee memberreceives Wits Faculty of Engineering Best

Research Award

implementation of the first commercial scale t dc smelter for … · 2011. 1. 27. · yuzhural...

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