8/19/2019 Factors Affecting Silicomanganese Production Using Manganese Rich Slag in the Charge

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FACTORS AFFECTING SILICOMANGANESE PRODUCTION

USING MANGANESE RICH SLAG IN THE CHARGE

Silicomanganese is widely used as a complex reducer and an alloying addition in the production ofvarious grades of steel due to its economic and metallurgical advantages. It is also used as a semi-product in the manufacture of medium- and low-carbon ferromanganese and metallic manganese.

Manganese-rich slag, resulting from high carbon ferromanganese production, has the advantages ofhigh manganese content, high Mn/Fe ratio, low excess oxygen, low phosphorus content, low finecontent and low cost. Such slag seems to be very attractive to use as raw materials for the production of silicomanganese alloys.

In the present study, experimental heats were designed and carried out to optimise the factors affectingthe production process of silicomanganese using manganese rich slag in the charge.

he results of pilot plant experimental heats showed that the optimum metallic yield and recoveries ofmanganese and silicon are obtained with initial slag basicity, !"a# $ Mg#% / !&l'#(%, e)uals *.+ byusing dolomite as fluxing material and charging )uartite and fluorspar in percentage of ' and ofthe blend, respectively. he results showed also that an amount of (0 of co1e in excess of thestoichiometric amount should be added. hese results are relative for the specific high &l'#( ores used.

he main source of Mn in raw materials for SiMn production is Mn-ore and Mn-rich slag from the highcarbon FeMn production. he amount of slag per tonne of SiMn metal is mainly determined by theore/slag ratio. Increasing share of FeMn slag at expense of Mn-ore will lead to larger slag/metal ratio inthe SiMn process. 2igh volume of slag leads to an increased consumption of energy and probably tohigher losses of metal inclusions in the final slag.

3xcavation of a SiMn furnace has shown that only modest pre-reduction of Mn-ore with "# gas seemsto be obtained. 4early all reduction of Mn# was finished at the top of the co1ebed. 5issolution andreduction of )uart obviously ta1es place in the co1ebed one after the main reduction of manganeseoxide is finished. 6robably the 7pic1 up7 of Si in the metal is )uite fast and ta1es place as the metaltric1les down through the co1ebed towards the metal bath.

he distribution of Si between SiMn alloys and multicomponent Mn#-Si#'-"a#-&l'#(-Mg# slags ismainly determined by the process temperature, the silica content of the slag and its 8-ratio 9!"a#$Mg#%/&l'#(. &s an example, the e)uilibrium content of Si in the alloy will increase by about : if the 8-ratio is reduced from ' to *, provided constant temperature and silica content. he effect oftemperature is also considerable. he e)uilibrium content of silicon will increase by approximately : per 0;" in the temperature range *0;" to *<00;".

he e)uilibrium content of Mn# in SiMn slags depends first of all on the temperature and secondly onthe silica content of the slag. &t *:00;" the Mn# content decreases from about = at silica saturationto a minimum of about (- when the silica content is reduced to about 0-.

3M"# has been producing manganese ferroalloys in submerged arc electric furnaces for over 0years. he furnace linings all along have been of conventional insulation type until '00* when a freeelining of >"&8 concept was installed for a '0 M? Furnace.

"ontinuous improvement of furnace lining performance has been a 1ey component in improving thebusiness competitiveness of 3M"#. he expected minimum campaign life of the freee lining is fifteenyears as compared to the ten years of the conventional linings.

he success of the freee lining is very critical to the )uanta and direction of heat flow through the liningthat control the freee protection. >nder freee protection can lead to reduced lining life and over freeeprotection, on the other hand, can lead to operating difficulties and loss of smelting efficiency. It was,therefore, necessary to develop a computer based system to monitor and control the freee protection.

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he computer based monitoring and control system uses the basic principles of heat transfer, active@

obAect and heat f lux from dual thermocouples and that is reviewed.

Since *==, when Bfreee liningB refractory systems were introduced to the ferroalloy industry, they havegained in popularity, due to the freee lining7s reputation for reliability, safety, and the contribution itma1es to profitability.

 &s with many popular and effective technologies, however, the freee lining has spawned low-costpretenders that claim the Bfreee liningB name. #n the surface they appear to contain some of thecomponents of the technology, such as thermally conductive materials, but they fail to incorporate all ofthe principles that define a true Freee Cining.

he term Bfreee liningB refers to the refractory system7s ability to maintain a temperature profile that islow enough to freee a layer of process material on its hot face, which insulates the refractory andprevents direct contact with molten metal and slag. In doing so, the common wear mechanisms found inthe submerged arc furnace - chemical attac1, erosion, and thermal stress - can be prevented. hesewear mechanisms are all related to high temperatureD thus, they are prevented by maintaining lowtemperatures.

"ertain refractory properties and design concepts are absolutely necessary for the lining system tofunction as a true Freee Cining. he paper explains these re)uirements and why they are important -the ruth of freee linings - and further explains why systems that ignore one or more of thesere)uirements cannot claim to be freee linings, thereby exposing the Myths.

he lining, together with the electrodes, forms the heart of the operation of a submerged arc furnace.Subse)uent to a lining failure on M*' furnace during the early *=+0s, Metalloys was active ininvestigating the concept of thermally efficient BfreeeB linings for its furnaces. he theory revolvedaround that, not only would, thermally efficient linings result in significant cost savings, but they wouldalso last longer as a result of being subAected to less harsh operational conditions. &fter having provedthe concept on the BsmallerB furnaces, Metalloys decided to implement the concept on its largest

submerged arc furnace, M*'.

Subse)uent to having recovered from an impending failure of a lining installed in *=+* in M*' in the mid*=+0s, Metalloys managed, through rigid lining management, to extend the life of this lining to *===. &tthe end of *=== the decision to replace the lining in the furnace with a BfreeeB lining was made andplanning and design proceeded in earnest. his paper discusses the options considered in ma1ing thefinal decision. he features of the design of the lining are also discussed. "onsideration is given to thefurnace shell cooling system as a result of its importance in maintaining the thermal e)uilibrium in thelining.

4ote is made of the fact that the purchase of a BfreeeB lining is an expensive exercise but that the timesavings in the installation of the lining and the efficiency improvements during operation far outweigh theadditional capital cost. he experience on M*' has been that the paybac1 period of the marginal capitalexpenditure is less than three years.

 &s a result of the opportunity to reline a furnace the sie of M*' not presenting itself very often, thelearning points from the installation of the lining and the operational advantages and disadvantages aresignificant.

Finally, the point is made that the proAect had its pros and cons but overall the success of the proAect hasbeen evident and, as such, the BfreeeB lining is li1ely to become the norm at Metalloys.

BRIQUETTED CHROME ORE FINES UTILISATION IN

FERROCHROME PRODUCTION AT ZIMBABWE ALLOYS

he ever-increasing pressure on the profit margins of ferro-chrome producers and the gradual depletionof deposits of rich hard lumpy chrome ores calls for the ferrochrome industry to maximise the use of finefractions of concentrates and friable chromite ores. Eimbabwe is endowed with huge deposits ofrefractory and friable ores that occur on and off the reat 5y1e complex. he conventional metallurgicalprocess of smelting of chromite ores in submerged arc furnaces is favoured by the use of refractoryhard lumpy ores. he re)uirement to use all lumpy ore has been circumvented to a large extent at

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Eimbabwe &lloys. he use of bri)uetted chrome ore fines in the production of Ferrosilicon "hrome and

2igh "arbon Ferrochrome has yielded positive results over a period in excess of twenty-five years.

#f the three industrially used methods of agglomeration of chromite oresD sintering, pelletisation andbri)uetting, bri)uetting is preferred because the other two are associated with higher capital andoperational cost.

Eimbabwe &lloys has developed operational and technical expertise on the bri)uetting and utilisation ofchromite ore fines and concentrates. Gariations in the )uality of available chromite ore fines imply thattheir amenability to bri)uetting is a dynamic problem. &ppropriate bri)uetting parameters to guarantee)uality bri)uettes are essential to the successful use of bri)uetted chromite ore fines.

In developing a technology for bri)uetting of chromite ores, it is important not only to study themineralogical and grain-sie characteristics of the chromite ore fines but also to ma1e an informedchoice of the type and )uantity of the binder and the conditions for producing a physically andchemically competent green and cured bri)uette.

his paper discusses Eimbabwe &lloys7 experience on the bri)uetting process and the advantagesderived in the smelting of the bri)uetted chromite ore fines in comparison to the use of conventionallumpy chromite ore with respect to improvements in chromium recovery and as a conse)uence relatedefficiencies and unit cost of production.

3nergy consumption, being a large proportion of the input of the ferroalloy production process, can bemeasured in terms of the efficiency with which the energy is utilied and the effectiveness with which it

is used. he efficiency of the usage of energy revolves around the specific consumption of the energyfor the production of the alloy, which encompasses the thermodynamic aspects of the process and ismore of a metallurgical function that will not be addressed further in this paper. he effectiveness withwhich the energy is utilied is determined by the optimisation of the electricity supply from the utility !inthis case 3s1om%.