Title of Invention

A TREATMENT OF HIGH VOLATILE AND DECREPITABLE MANGANESE ORES IN A VERTICAL FURNACE BY PARTIAL REDUCTION ROASTING UTILIZING OFF-GAS EMITS FROM SUB-MERGED ARC FURNACE FOR PRODUCTION OF FERRO-MANGANESE

Abstract

This invention relates to a process of upgradation of high volatile and decrepitatable managanese ores in a vertical shaft furnace by partial reduction roasting utilising sub-merged are furnace (SAF) off-gas for production of ferromanganese comprising the steps of charging the cleaned and warm off-gas from a sub-merged are furnace (SAF) in the gaseous reduction zone of a vertical shaft furnace charged with decrepitable manganese ores to simultaneously accomplish cooling of the outgoing charge material and pre reduce it partially by dint of carbon monoxide containing in the charged ore, the said upcoming gas is carried through the dissociation zone of the shaft furnace wherein the MnO2 content of the ore is dissociated to Mn3O4 at 570-600° C and liberates free oxygen which is autogenously utilized for combusting the residual carbon monoxide and hydrogen gases available in the off-gas of the sub-merged are furnace (SAF) in the combustion zone maintained at 600-900° C, the heat produced in the combustion zone being utilized for drying, preheating and dissociation of the ores, the ores discharged at the bottom of the furnace being screened to separate fines which are briquetted and sintered and the dried partially reduced manganese pre obtained, to be charged in the sub-merged are furnace (SAF) for producing Ferromanganese optimisingly.

Full Text

-2- FIELD OF THE INVENTION The present invention relates to uprgradation of high volatile and decrepitatable manganese ores in vertical shaft furnace by partial reduction roasting utilizing off-gas of sub-merged arc furnace (SAF) for producing ferro-manganese. BACKGROUND OF THE INVENTION In the existing practice ferromanganese is produced from high grade to low grade manganese ores and manganeseferrous iron ores. Most of those manganese ores are susceptible to decrepitation. Another disadvantage associated with the said ore is due to dissociation of MnO2 to Mn3O4 liberating free oxygen upon heating to as low temperature as 550° C. -3- Chemical Equations & Heat Reactions in the Dissociation of MnO2 into Mn3O4 is explained as follows: Although the exhaust gas coming from the reaction zone rises the charge temperature in top zone, which is common phenomenon, the main reason for overheating and sintering of charge is due to the type of Mn-ore used in the process. The mineral pyrolusite (MnO2) is major constituent in MnO. Thermodynamically MnO2 is not stable at high temperature and in reducing atmospheres, and decomposes into sub-oxides via following reactions: In sub-merged arc furnace (SAF) top zone, atmosphere is highly reducing as exhaust gas coming from reaction zone is CO. The reducing atmosphere further enhances the decomposition of MnO2 in the ore. -4- The oxygen formed during decomposition reacts instantly with CO in exhaust gas in the sub-merged arc furnace (SAF) top zone and combustion of CO gas generates excessive heat in the top zone. Decomposition of MnO2 liberates 9.2 % oxygen in reaction (1) at 600 C temperature. The calculation of thermal energy generated by these reactions revealed that decomposition of 1 tonne Mn-ore at 600 C temperature and burning of CO gas by liberated oxygen generates ~ 300 kWh i.e. - 1080 MJ energy. This localized generation of excessive energy increases the temperature of the charge surface and trigger the sintering of charge by forming siliceous liquid phase with gangues. Thermodynamics of reactions of MnO2 with CO gas: -5- The aforesaid two disadvantageous properties of manganese ores as envisaged from the above reaction behaviours spose problem in their direct use in a submerged arc furnace (SAF) due to generation of ultrafine materials inside the furnace and as a consequence overheating the charge materials at the furnace top due to combustion of the upcoming hot carbon monoxide gas with pure oxygen freed at high temperatures. This reaction involved in sintering result further disadvantage by diminishing the reduction potential of the carbon monoxide gas and masks the natural potential of the ores to lose oxygen. -6- The production of ferro manganese is further aggravated due to the use of as received wet ore which generate series of problems due to its moisture content which besides demanding additional heat, results in the formation of cold lumps at the top most layer due to its recondensation, thus additionally reducing a permeability of the bed and causes channeling. DESCRIPTION OF THE INVENTION To remove the above disadvantages of prior art associated with ferromanganese production in sub-merged arc furnace (SAF) a novel method has been developed with main aim to remove the moisture as well as fines from manganese ores in a separate installation. Another main objective of the invention is to develop and supply slightly preheated and pre-reduced charge material to the sub-merged arc furnace (SAF). -7- A further objective of the invention is to eliminate disadvantages associated with increased temperature at the furnace top while processing low Sio2 containing manganese ores, which have high loss on ignition (LOI), mainly in the form of oxygen, which is liberated at around 550° C and generates large amounts of heat at higher temperatures. A still further objective of the invention is to reduce significant amount of electricity as well as coke consumption in the production of ferromanganese in the sub-merged arc furnace (SAF) by using prepared burden suitable for the sub-merged arc furnace (SAF). A yet another objective of the invention is the optimized use of a sub-merged arc furnace (SAF) by eliminating shut down for dust clean-ups and gas cleaning plant (GCP). -8- A still another objective of the invention is to improve productivity of a submerged arc furnace (SAF) by using pre-reduced charge and increased power input by minimization of the dangers of sintering and channeling at top causing sudden eruptions. According to the invention there is provided a process of upgradation of high volatile and decrepitatable manganese ores in a vertical shaft furnace by partial reduction roasting utilizing sup-merged are furnace sub-merged arc furnace (SAF) off-gas during production of ferromanganese comprising the steps of charging the cleaned and warm off-gas from a sub-merged arc furnace (SAF) in the gaseous reduction zone of a vertical shaft fu rnace charged with decrepitatable manganese ores to simultaneously accomplish cooling of the outgoing charge material and pre reduce it partially by dint of carbon monoxide containing in the charged ore, the said upcoming gas is carried through the dissociation zone of the shaft furnace wherein the MnO2 -9- content of the ore is dissociated to Mn3O4 at 570-600° C and liberates free oxygen which is autogenously utilized for combusting the residual carbon monoxide and hydrogen gases available in the off-gas of the sub-merged arc furnace (SAF) in the combustion zone maintained at 600-900° C, the heat produced in the combustion zone being utilized for drying, preheating and dissociation of the ores, the ores discharged at the bottom of the furnace being screened to separate fines which are briquetted and sintered and the dried partially reduced manganese ore obtained to be charged in the submerged arc furnace (SAF) for producing ferromanganese optimizingly. The present invention is developed by combustion of off-gas of submerged arc furnace for production of ferromanganese with pure oxygen available at high temperature around 600° C from the manganese ore charged in an external vertical shaft furnace instead of combustion by atmospheric air associated with nitrogen. The decreptatable manganese ore is upgraded by preheating the ore in a vertical shaft furnace thus taking care of fines -10- generated outside the sub-merged arc furnace (SAF) and separating the fines easily and utilizing the fines by agglomerating and charging in the submerged arc furnace (SAF). The natural property of the manganese ore is exploited optimizingly in the shaft furnace by utilizing the natural dissociation property of manganese oxide (MnO2) to lose oxygen (around 25 % of its total oxygen) on simply heating the manganese ore without consuming any reductant upto the stage of conversion to Mn2O3. A vertical shaft furnace is equipped with a skip / belt / bucket charging arrangement from the top and a bottom discharge device coupled with a screen is provided at the bottom of the shaft furnace to screen out fines from partially pre reduced Fe-Mn ores. The said fines are briquetted and sintered to be used as a charge material in a sub-merged arc furnace (SAF). The submerged arc furnace (SAF) off-gas and composition at the furnace sub-merged -11- arc furnace (SAF) top is admitted into the vertical shaft furnace which cool the charge materials and at the same time partially pre reduce the charge materials by carbon monoxide emitted form the charge itself. Remaining carbon monoxide content in the upcoming gas combines with the oxygen liberated from the down coming Mn-ores and generates the major portion of heat required for the drying, preheating and dissociation process. The present invention will be better understood from the following description with the help of the accompanying drawing in which Figure 1 represents a flow sheet for partial reduction roasting of high volatile and decrepitatable manganese ores in a vertical shaft furnace utilizing the sub-merged arc furnace (SAF) off-gas. The charge materials are passed through seven zones of the shaft furnace as shown in the flow sheet namely drying zone (100-200° C), preheating zone (300-500° C), combustion zone (600-900° C), dissociation zone (570-600° C), gaseous reduction zone (400-500° C), cooling zone (400-500° C) and discharge zone (100-300° C). -12- The shaft furnace is equipped with skip / belt / bucket charging facility from the top and bottom discharge device coupled with -5mm screen below the furnace such that screening is accomplished in one go and double handling of the material is avoided. Gas seal valves are provided at the materials charging as well as discharge points to prevent the furnace gases to come out of the system unabated. The sub-merged arc furnace (SAF) off-gas at the available temperature and composition at the sub-merged arc furnace (SAF) top is dry cleaned and boosted and the clean and warm gas (100-300° C) is fed in the gaseous reduction zone as shown in the flow sheet. For this purpose dry type electrostatic precipitator (ESP) wherein doubly sealed gas boasters are employed. The admitted cleaned gas accomplish cooling of the outgoing charge materials and simultaneously pre reduce the charge partially by dint of carbon monoxide content in it. Moist waste gas escapes from the chimney after passing through streams of water to separate out the fines with the gases. The shaft furnace operates on counter current flow of gases from the bottom. -13- In the dissociation zone the MnO2 content of the ores is dissociated into Mn3O4 liberating free oxygen which is autogenously utilized for combusting the residual carbon monoxide and hydrogen gases available in the off-gas from semi closed or closed type sub-merged arc furnace (SAF) treating ferromanganese ore and fed in the gaseous reduction zone of the shaft furnace. Supplementary combustion air via combustion air fan is fed at the combustion zone to provide the heat requirement of the process and such supplementary atmospheric air is necessary largely during start-up of the process. The carbon monoxide content in the up coming gas combines with the oxygen liberated from the down-coming MnO at about 600-700° C and generates major portion of the heat required for the drying, preheating and dissociation process. -14- The process becomes almost autogenous with regard to the oxygen requirement and very little amount of it have to be supplemented from fresh combustion air. The invention as described and illustrated hereinabove should not be read in a restrictive manner as various modifications, alternations and changes are possible within the scope and limit of the invention as encampused in the appended claims. -15- WE CLAIM 1. A process of upgradation of high volatile and decrepitatable managanese ores in a vertical shaft furnace by partial reduction roasting utilising sub-merged are furnace (SAF) off-gas for production of ferromanganese comprising the steps of charging the cleaned and warm off-gas from a sub-merged are furnace (SAF) in the gaseous reduction zone of a vertical shaft furnace charged with decrepitatable manganese ores to simultaneously accomplish cooling of the outgoing charge material and pre reduce it partially by dint of carbon monoxide containing in the charged ore, the said upcoming gas is carried through the dissociation zone of the shaft furnace wherein the MnO2 content of the ore is dissociated to Mn3O4 at 570-600° C and liberates free oxygen which is autogenously utilized for combusting the residual carbon monoxide and hydrogen gases available in the off-gas of the sub-merged are furnace (SAF) in the combustion zone maintained at 600-900° C, the heat produced in the combustion zone being utilized for drying, preheating and dissociation of the ores, the ores discharged at the bottom of the furnace . being screened to separate fines which are briquetted and sintered and the dried partially reduced manganese ore obtained, to be charged in the submerged are furnace (SAF) for producing Ferromanganese optimisingly. -16- 2. A process as claimed in Claim-1, wherein the charge materials in the shaft furnace are passed through seven zones namely drying zone (100-200° C), pre-heating zone (300-500° C), combustion zone (600-900° C), dissociation zone (570-600° C), gaseous reduction zone (400-500° C), cooling zone (400- 500° C) and discharge zone (100-300° C). 3. A process as claimed in Claim-1, wherein the shaft furnace is equipped with skip / belt / bucket charging facility from the top and bottom discharge device coupled with -5 mm screen such that screening of resulted partially reduced ore and fines are carried out in one go through the screen, 4. A process as claimed in claim 1, wherein the bottom discharge device is coupled with -5 mm screen below the shaft furnace and gas valves and the sintered fines are charged with the manganese ores in the sub-merged are furnace (SAF). -17- 5. A process as claimed in the predeeding claims, wherein Off gas of the sub merged are furnace (SAF) before admitting in the shaft furnace is cleaned in a dry type electrostatic precipitator, 6. A process as claimed in the preceeding claims, wherein supplementary atmospheric air is fed at the combustion zone via combustion air fan during start up of the process. 7. A process as claimed in the preceeding claims, wherein moist waste gas from the top of the furnace escapes in the atmosphere via GCP. 8. A process of upgradation of high volatile and decrepitatable manganese ores in a vertical shaft furnace by partial reduction roasting utilizing sub-merged arc furnace (SAF) off-gas as herein described.

Documents:

01217-kol-2006 abstract.pdf

01217-kol-2006 claims.pdf

01217-kol-2006 correspondence others.pdf

01217-kol-2006 drawings.pdf

01217-kol-2006 form-1.pdf

01217-kol-2006 form-2.pdf

01217-kol-2006 form-3.pdf

01217-kol-2006 gpa.pdf

01217-kol-2006-correspondence-1.1.pdf

01217-kol-2006-form-1-1.1.pdf

01217-kol-2006-form-9.pdf

1217-KOL-2006-(29-02-2012)-AMANDED CLAIMS.pdf

1217-KOL-2006-(29-02-2012)-CORRESPONDENCE.pdf

1217-KOL-2006-(30-03-2012)-ABSTRACT.pdf

1217-KOL-2006-(30-03-2012)-AMANDED CLAIMS.pdf

1217-KOL-2006-(30-03-2012)-AMANDED PAGES OF SPECIFICATION.pdf

1217-KOL-2006-(30-03-2012)-CORRESPONDENCE.pdf

1217-KOL-2006-(30-03-2012)-FORM-1.pdf

1217-KOL-2006-(30-03-2012)-FORM-2.pdf

1217-KOL-2006-(30-12-2011)-ABSTRACT.pdf

1217-KOL-2006-(30-12-2011)-CLAIMS.pdf

1217-KOL-2006-(30-12-2011)-CORRESPONDENCE.pdf

1217-KOL-2006-(30-12-2011)-OTHERS.pdf

1217-KOL-2006-ABSTRACT 1.1.pdf

1217-KOL-2006-ABSTRACT 1.2.pdf

1217-KOL-2006-AMANDED CLAIMS.pdf

1217-KOL-2006-AMANDED PAGES OF SPECIFICATION.pdf

1217-KOL-2006-CLAIMS.pdf

1217-KOL-2006-CORRESPONDENCE 1.1.pdf

1217-KOL-2006-DESCRIPTION (COMPLETE) 1.1.pdf

1217-KOL-2006-DRAWINGS 1.1.pdf

1217-KOL-2006-EXAMINATION REPORT REPLY RECIEVED.pdf

1217-KOL-2006-FORM 1 1.1.pdf

1217-KOL-2006-FORM 1 1.2.pdf

1217-KOL-2006-FORM 13.pdf

1217-KOL-2006-FORM 2 1.1.pdf

1217-KOL-2006-FORM 2 1.2.pdf

1217-KOL-2006-OTHERS.pdf

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