Title of Invention	PROCESS FOR CARBOTHERMIC REDUCTION OF IRON OXIDE IN AN IMMISCIBLE FLOW WITH CONSTANT DESCENT IN VERTICAL RETORT OF SILICON CARBIDE
Abstract	A carbothermic process of reduction in an externally heated vertical shaft furnace of iron ore to PM grade sponge iron using coke and lime stone as reductant mixture wherein the ore and the reductant mixture are charged from t~e top of the furnace through a co-axial double hopper arrangement having flexibility of changing cross- section with different profiles in an immiscible way thereby avoiding intimate contact between them, the said charge, gravity aided, descending at a constant speed, regulatable, through a preheating zone and subsequently through three reduction zones at optimal temperatures to undergo desired degree of reduction for conversion into PM grade iron powder, encountering no possibility of reverse reaction to be withdrawn along with excess, partially reusable coke through a cooling channel after it has been cooled below the oxidation temperature of the sponge briquette, the withdrawal throughout the shaft being regulated at constant speed, to be discharged out of the axis of the furnace system as handleable pieces using shearing mechanism such that the charge above is not disturbed, the shearing and discharge out of the furnace is hydraulically automated.

Title of Invention

PROCESS FOR CARBOTHERMIC REDUCTION OF IRON OXIDE IN AN IMMISCIBLE FLOW WITH CONSTANT DESCENT IN VERTICAL RETORT OF SILICON CARBIDE

Abstract

A carbothermic process of reduction in an externally heated vertical shaft furnace of iron ore to PM grade sponge iron using coke and lime stone as reductant mixture wherein the ore and the reductant mixture are charged from t~e top of the furnace through a co-axial double hopper arrangement having flexibility of changing cross- section with different profiles in an immiscible way thereby avoiding intimate contact between them, the said charge, gravity aided, descending at a constant speed, regulatable, through a preheating zone and subsequently through three reduction zones at optimal temperatures to undergo desired degree of reduction for conversion into PM grade iron powder, encountering no possibility of reverse reaction to be withdrawn along with excess, partially reusable coke through a cooling channel after it has been cooled below the oxidation temperature of the sponge briquette, the withdrawal throughout the shaft being regulated at constant speed, to be discharged out of the axis of the furnace system as handleable pieces using shearing mechanism such that the charge above is not disturbed, the shearing and discharge out of the furnace is hydraulically automated.

Full Text	FIELD OF INVENTION The present invention relates to the process and equipment for preparation of high purity sponge iron from iron oxide. The invention particularly relates to an improved and novel process to produce a particular quality of sponge iron that can be converted into PM grade iron powder. More particularly the invention relates to a particular metallurgical processing of blue dust and coke in a vertical shaft furnace with a regulated downward movement to convert blue dust which is a mine burden to high purity sponge iron which can be converted to PM grade iron powder. The invention more particularity relates to carbothermic reduction in a vertical shaft to produce PM grade sponge iron BACKGROUND OF INVENTION High Purity Sponge Iron finds number of applications. India is bestowed with high purity iron ore (blue dust) existing in the form of Hematite in millions of tons which is a mine burden. This blue dust cannot be used in blast furnace as such and could be advantageously harnessed by evolving a reduction process using blue dust with solid reductant mixture i.e. mixture of coke breeze, a by-product of coke ovens of steel plants, and calcium carbonate of metallurgical grade available in abundance. A wide range of applications exist for use of iron powders produced from high purity sponge: Powder metallurgy industry, wherein a wide variety of structural parts are produced by 'press-sinter' route and a variety of frictional components like brake pads which are produced by pressure sintering route; Pharmaceutical industry wherein iron powder is used as a catalyst; Welding electrode industry wherein iron powder is an important ingredient in the coating applied on the metallic wire; Food preservative industry wherein preferential oxidation of high purity iron powder preserves food; * India, which is bestowed with abundant blue dust resources, depends on imports for PM grade sponge iron. To reduce such dependence on imports and to convert and add value to the mine burden (blue dust) a technology to indigenously produce sponge iron suitable for production of PM grade iron powder, research work was carried out to develop a process which is capable of economically converting the blue dust to sponge iron with a flexibility and automation which makes the equipment a precious research tool on semi-commercial scale in addition to being ready for scaling up to suitable for producing PM grade iron powder on commercial scale. RELATED PRIOR ART * The production of sponge iron by direct reduction of the ore with coke is a process that has been known since ancient times. There are no available Indian Patent as prior art to this invention. The other patents reported are the US patent 4242125 and the equivalent patent AT369035, AU 4093578, AU 523769 and US 4189313. The process for US 4189313 is for the production of the sponge iron and not the powder metallurgy grade Sponge Iron (low carbon) as claimed in my invention. The charge withdrawn contains the contamination of the residuals of reducing agents including Coal and Coke & other additives. Whereas in our process the low carbon Sponge Iron brickett is free of any of the reducing agents which are discharged free of the brickett. Then the brickett is of high purity Sponge Iron (Powder Metallurgy grade with carbon less than 0.2 % ) The descent of the material in the process of US 4189313 is by the screw discharge mechanism and the free movement downwards of the reduced material cannot be controlled as by the gravity discharge being independent of consolidation, the crumbling of the reduced material cannot be free of carbon . Whereas in the process claimed by us the iron ore and the reducing agent are immissible from the feeding point to the discharge. While the material is descending the hydraulic prop at the bottom supports the total burden in a consolidated position making the distinction between the sponge iron brickett as reduced and the reducing agent surrounded the brickett in free flow conditions even at the temperature of 1250°c. This is the claim novel to our process as compared to any other process available in the world The claim made in process states "that the charge which is which is introduced descends at the first constant speed and afterwards descends at a second speed which has a constant function of the reduction of the speed substantially coincide with the condition prescribed are mechanical and chemical. The control on the movement in theoretical while in our process the material movement in controlled from the bottom depending upon the length of the charge at first, second and third phases. The temperature control and holding at a stoichiometric balance is maintained by not disturbing the movement continuously. But a periodic intervals of 8 hours in our process which can be regulated by increasing the retard height and the cooling zone to the required levels of output. This feature is also an innovation in our process of carbothermic process. In other innovation in our process is the fuel viz., LPG / natural gas burnt in a chamber away from the retard so that retard get the uniform heating by regulating the valve provided in the exhaust line before the chimney. Where as in the process US 4189313 the heating is made directly to the retard where in the hot spots near the flame and away from the flame develops difference in temperatures and thus the retard is charged with thermal shocks and the heating would not be uniform The sponge iron extracted is contaminated with ash, un-burnt coal and other reducing agents if any for de-sulfur sing. This calls separating the pure iron from non-magnetics which is a cumbersome process in which the possibility of coal an ash being carried along with metal may not be desirable. Then the sponge iron in question is ok as it is not low carbon but goes in to the production of steel or cast iron where in the presence of carbon up to 3% is desirable. Metallisation wouldn’t be more than 85-87 %, whereas in our process the material being immissible the high grade sponge iron brickett as discharged in free of lose, coke or reducing agents since the brickett is consolidated, sintered with metallisation of over 97% the process of low carbon process. It doesn't require any further operation except powdering and annealing for direct component manufacturing which is the order of the day. However, the known processes, involve notable shortcomings, and heretofore none of the known processes has been successfully used on an industrial scale to obtain sponge iron suitable for conversion into PM grade iron powder, the sole exception being M/s Hoeganas Corporation, Sweden, who produce such sponge iron using an equipment and a process entirely different from the present case, the equipment being horizontal as against vertical and the starting material- being magnetite as against Haematite (blue dust). M/s Hoeganas corporation, introduced the pattern of loading coke and ore such that they are immiscible in Silicon Carbide saggers, each sager containing a number of vertical reaction chambers of circular cross-section, wherein the coke and ore are loaded in concentric cylindrical pattern, coke being fed at the center followed concentrically by a column of iron ore and finally another column of coke being fed around the iron ore. As compared to M/s. Hoeganas, investment levels are less, process of loading and unloading is not as cumbersome and breakage of Silicon Carbide saggers is a disadvantage, which is overcome by our Silicon Carbide vertical retort. Through the present process the inventor has improved the cost effectiveness of low carbon PM grade sponge iron production using indigenously available raw material with automated and integrated operations involving control on movement of material, temperatures at various reaction zones on continuous basis and also keeping the option of material discharge at will without disturbing the descending material. SUMMARY OF THE INVENTION Carbothermic process for reducing iron ore in an externally heated Silicon Carbide vertical shaft is characterized by charging the reaction mixture (ore and reductant mixture) in a double hopper system which facilitates immiscibility of ore and the reductant mixture while the reaction mixture descends through four different heating zones, i,e, preheating, first, second and third zones, the first, second and third zones of the vertical Silicon Carbide shaft obtaining thermal input through external heating through burners, while the thermal input to preheating zone is from the flue gases from the burners and also from reduction reaction in the shaft which evolves hot gases/ Unlike existing methods, the unique feature herein is gravity aided constant rate of descent, and as it descends from the said hopper system through the vertical shaft, the reaction mixture is pre-heated while descending through the said pre-heating zone and progressively achieves the reduction reaction temperatures while descending through 1®* and 2" zones such that as the reaction mixture traverses through 3^^ zone, the reduction reaction is completed. The temperature in the third zone is kept lower than that of the second zone not only to obtain the said desired degree of reduction reaction, but also to prevent backward reactions, over-sintering which would adversely affect the sponginess of the said briquette of the sponge and thermal shock to the reduced sponge iron briquette. As the sponge iron briquette descends out of the third zone into the cooling system, the heat generated from the hot gases, which is a reaction bye-product, is withdrawn through ducting from below the third zone to the flue gas channel at S"^ zone for better heat utilization. Sponge Iron briquette as a descending continuum and excess reductant mixture are drawn out of the third zone to a cooling system where the temperature is gradually cooled by circulating water during descent. It is ensured that the speed of descent is so controlled that the material i.e. the said continuum of sponge iron has been cooled sufficiently below the oxidation temperature of 50 - 150°C of the sponge iron, and the continuum cut into dischargeable pieces by a shearing mechanism consisting of high-strength blades which support the material above including the one in the cooling system and the time of discharge is so controlled that the original support table regulating the downward movement of briquette is placed in position & downward movement is restarted. DESCRIPTION OF THE DRAWINGS Fig 1 of the drawing shows the cross section of schematic diagram of the furnace along with front view. In the diagram, 1 is the inner hopper, 2 is the outer hopper, 3 is the chute for gas outlet, 4 is the furnace shaft, 5 is the heating channel, 6 is the outlet for gases, 7 is the cooler, 8 is shear blades, 9 is the support table, 10 is the flute for coke collection, 11 is the container for coke collection, 12 is the hydraulic support cylinder, 13 is the iron ore concentrate, 14 is coke breeze, 15 is the electric hoist, 16 is the LPG burners, 17 is the sponge iron briquette, 18 is the hydraulic shear cylinders, 19 is the hydraulic cylinder for pusher, 20 is the container, 21 is the table for briquette cleaning, 22 is container for material lift. DESCRIPTION OF THE INVENTION Detailed description of the equipment and the process is given herein. The stabilized process parameters to produce sponge iron suitable to make PM grade iron powder have been given at the end. Equipment construction The equipment, a typical Vertical shaft furnace with outside dimensions of 2060 mm X 3305 mm x 5600 mm having a capacity of 500 kg/day, consists of material feeding system (1,2,13,14), furnace section (4,9,17), a heating system (5,16), heat exchanger system(6), a cooling system(7), discharge System(8,18,19), briquette receiving system(10,11,20,21), flue gas exhaust system(3) and material handling system(15,22). The charge is fed into the furnace shaft (4) which is Vertical Rectangular Shaft furnace of 280 x 1200 mm cross-section and about 5000 mm height through the co-axial hopper system (1,2), the said furnace shaft being constructed using Silicon Carbide refractory bricks surrounded by hot face and cold face refractory bricks (alumina or illuminate) and the said refractory bricks are arranged in such a way that three independent rectangular spiral channels for flue gases (5) to pass through are created at different heights to form three different and distinct temperature zones. Provision is made in the refractory brick work to incorporate three pairs of gas fuel based burners e.g., LPG (16) located on one side of the shaft, each pair distributed along height of 385mm, 2065mm and 3745mm from the bottom of the shaft such that the flue gases from the burning fuel follow the said spiral paths available in the refractory bricks passing on heat to the charge through the Silicon Carbide shaft. Provision is also made in the refractory brick work to incorporate one pair of Chromel-Alumel thermocouple at 1235mm to measure the temperature in the preheating zone and three pairs of Platinum - Platinum-Rhodium thermocouples to monitor temperatures in the three heating zones at 1625mm, 3305mm and 4990mm from the top of the furnace. The upper part of the shaft is equipped with two co-axial rectangular hoppers (1,2) for charging of blue dust (13) through the inner hopper (1) and the reductant mixture consisting of coke breeze and lime stone (14) through the outer hopper (2). Refractory brick work is developed on a metallic platform, which, in turn, is secured to concrete columns while another set of concrete columns support the upper charging platform. The cooling section (7) is a metallic chamber and is an extension of the furnace shaft (4) and it is surrounded by a water jacket in the form of rectangular spiral and is fastened to the lower part of the furnace. The sponge iron briquette (17) gets cooled in this cooling channel and comes out into the discharge system (8,18,19) where it is sheared (8)into pieces of 800mm and unloaded. The discharging system (8,18,19) consists of the following sub-systems which are actuated hydraulically: Support table (9): The total column of charge is supported by a specially made support table (9) attached to the piston of a hydraulic support cylinder (12) and the rate of movement of the piston can be regulated anywhere 'between 50mm to 300mm per hour. Hydraulic Shears (8): The hydraulic shear system consisting of shearing blades (8), operated by hydraulic shear cylinders (18), is used to cut the sponge iron briquette (17) coming out of the cooling channel (7) into pieces of 800mm height. Unloading system (19): This system is used to unload the sheared piece out of the furnace into the briquette receiving system (10,11, 20,21) Heat exchange system (6): To tap the thermal energy going out of the furnace, via flue gases, a heat exchange system (6) is provided wherein, the thermal energy is transferred to preheat the air that is fed into the gas burners (16) which are used to heat the vertical shaft. Exhaust SvstemO): The top of the furnace is connected to the chimney through a chute(3) to let out the flue gases coming out of the furnace after preheating the charge. Process description with ungues features of processing: The reaction mixture of blue dust and reductant mixture are at a ratio of 1:1 to 2:1 are fed through the inner(1) and outer(2) hoppers of the co-axial hopper system so as to ensure the immiscibility of blue dust and the reductant mixture as they descend into the furnace shaft(4) and said immiscible pattern of loading is a unique feature of this process. The usual practice in sponge iron production in vertical shaft furnaces is to mix ore with coke and charge in required quantities into furnace. Because of the intimate contact between the reactants, high reaction rates are obtained and productivity increases. Since most of the output of these plants goes for steel melting, high degree of reduction is not attempted. Hence reaction times are deliberately kept shorter to keep the carbon pick-up to minimum, while, in the present case for which patent is being applied, the objective is to make high purity sponge to be converted into PM grade iron powder the reaction times have to be necessarily longer to achieve high degree of molecular reduction. Yet another objective of this invention is to avoid excessive carbon pick-up during prolonged reduction phase by eliminating intimate contact between coke and iron ore. In the present case for which patent is being applied, the charge is being gravity fed into the shaft (4) through the said hopper arrangement with hydraulic platform at the bottom to support and regulate downward movement at desired speeds. The hopper arrangement extends into the retort by 250 mm for guiding the material being fed into the shaft. The outer hopper(2) extends beyond the inner hopper(1) which ensures that first the ore gets released out of hopper into the shaft(4). The ore, being heavier than the reductant mixture maintains integrity of its cross-section as it moves down by gravity through the shaft creating a rectangular annular space around it for the reductant mixture to flow out of hopper and any possible spread of reductant mixture inwards into the ore is avoided and thus immiscibility maintained. However, if the rectangular annular space around the ore is not filled up fast, the ore, after travelling some distance down through the shaft, tends to spread outwards blocking the flow of the reductant mix downward which results in improper reduction because of non- availability of required stochiometric quantity of the reductant mixture. This problem is overcome by controlled matching of flows of the ore and the reductant mixture, another unique feature. This is done by selecting appropriate particle morphology size fractions and other physical properties of ore and reductant mixture. The average size of blue dust is 100-300 lam and that of reductant mixture, 1- 8mm.The selected reductant mixture coke having rounded edges to increase its flowability, blue dust having irregular shape with an apparent density(A,D) of 1.5- 2.5 g/cc and flow of 30-50 sec/50g, the moisture content and its loss on Ignition (LOI) being maintained between 1-4% to make it free flowing. Further, to match the flows, coke is filled in the outer hopper to its brim while ore is filled at a level of 25cm -200cm from the top edge of the inner hopper. To coritrol the productivity arid the degree of reduction, the hopper design has inbuilt flexibility. The sizes of hopper are big enough to accommodate another smaller hopper in the middle of the inner hopper if required to obtain different reductant mixture - ore - reductant mixture patterns of loading. This is realized as the hoppers are flanged at the bottom and are easily detachable. By changing the surface profile of the bottom flange of the inner hopper(1), it is possible to change or reduce the quantities of ore or reductant mix in different cross-sections. -It is also possible to provide different profiles (other than rectangular profile) to the ore such that its surface area and reactivity can be increased. Yet another feature of the flexible hopper arrangement is to maintain the correct ratio of layer thickness of ore to reductant mixture. The said reaction mixture of blue dust and reductant mixture in the ratio of 1:1 to 2:1 are gravity fed into the stationary Silicon Carbide shaft with the consequent advantage of long life. The reason for use of Silicon Carbide are its high thermal conductivity (11 W/mK) with required porosity and high resistance to refractoriness under load. An important requirement of the Silicon Carbide bricks used to build the shaft is porosity to relieve the internal pressure of gases formed in the shaft during the reduction reaction. The reduction reaction goes through the following three steps: ■ 3Fe203 + CO o 2Fe304+ CO2+ heat Fe304 + CO o 3FeO + C02 - heat FeO + CO All these reactions are reversible and reaction products (gases) at high pressures and temperatures will bring about this reversibility. Thus, the absolute pressure of reaction products inside the shaft cannot be more than 1200-1400 mmWC. The actual value was measured inside the shaft by regulating the outlet butterfly valve and found to be varying from 1400 mmWC to 1800 mmWC. Based on the actual value of the pressure measured, the opening of butterfly valve was fixed to ensure only forward reaction. The maximum pressure developed by the reaction products varies depending on the configuration of the reaction chamber, amount of reaction mixture, temperature etc. This, in turn has a bearing on the amount of porosity required in the Silicon Carbide shaft. The porosity of Silicon Carbide bricks selected for VSRF ranged between 22% to 25%. As the reaction mixture enters the Silicon Carbide shaft with an internal pressure of 1400 to 1800 mmWG to prevent the backward reactions, it crosses the pre-heating zone at 400-800°C which gets thermal input internally from hot gases evolving out of reduction reaction as well as externally from the flue gases coming from the three heating zones which circulate in rectangular spiral channels around the said preheating zone of the furnace shaft(4). After preheating the charge descends subsequently into three reductions zones which are located one below the other which are maintained at different temperatures by means of externally located burners(16). As the charge enters the first zone where the temperature is maintained at 1000-1 OSO the reduction reaction is initiated. A second and progressive heating of said reaction mixture in the second temperature zone takes place at a temperature range of 1060-1120°C. A third and constant heating of said reaction mixture takes place in the third zone at temperatures of 1000-1100°C of the shaft following the said progressive heating so as to complete the reduction process. The rate of descent of the said reaction mixture is controlled such that the thermal charge moves at a constant speed anywhere set between 50-300mm/h throughout the process till it is completed. The said constant speed is achieved inside the shaft through a hydraulically actuated support table(9), 250mm thick. The speed of descent of the charge can be adjusted between 50 to 300 mm/h, through inbuilt control systems. The regulation of speed of descent, which is another unique feature, is required to arrive at a) optimum speed to ensure desired degree of reduction b) to combat the problems of expansion during phase transformations as shown below thereby avoiding cutting into the reductant mixture cross-section adversely affecting the stochiometric ratio of reductant mixture(14) and blue dust(13) for ensuring proper reduction. c) to prevent damage to the SILICON CARBIDE shaft as a result of briquette expansion and to have control of productivity and hence economies on process cost. In addition this facilitates adjustment of reaction times in the reduction zones. Thus if necessary, and during downtimes it is possible to make other grades of sponge iron that can be used either for remelting purposes or as a charge for atomization. As the reduction process attains desired degree of reduction, the remnant reaction gases which carry sufficient thermal energy are led out through a port located below the third zone into the flue gas chamber of 3^^ zone such that thermal efficiency of the furnace increases. As the reduced sponge iron briquette(17) comes out of the shaft, it enters a metallic, water cooled, cooling chamber of 800 mm length which is an extension of the shaft wherein it gets cooled by circulating water through cooling channels(7) to almost ambient temperature. After the cooling, material is drawn to discharge collection zone where in the briquette is sheared(8) and unloaded though a discharging systemic, 10,18,19). The said arrangement as described below is novel and completely automated. The system consists of the following: 1. Hydraulically actuated shearing mechanism(8,18) 2. 'Briquette holder' that holds the sheared briquette with a hydraulically actuated door and a piston to push(19) out the briquette 3. A briquette receiver(20) hydraulically actuated into horizontal and vertical positions resting on a platform(21) outside the furnace(4) system. The briquette comes out of the cooling chamber (7) and traverses 800 mm supported by the support table (9). After this, the shearing mechanism (8) gets hydraulically actuated (18) and the briquette is sheared into an 800 mm long piece. At that juncture the shearing blades (8) support the total charge inside the shaft and the actual support table (9) moves doWn at the rate of 215 mm/h in a jerk, thereby loosening the coke and ash around the cut briquette such that they can flow out into bins through ports (10) provided for that purpose. After the discharge of the coke and ash, the sheared briquette enters the briquette holder’ whose door is closed. After a time delay of 30s the hydraulically actuated door opens. The briquette receiver then moves from horizontal to vertical position. Next, a hydraulically operated pusher (19) pushes the briquette onto the briquette receiver (20), which gradually comes to its horizontal position carrying the briquette with it after which it is unloaded onto the briquette cleaning table (21). Simultaneously the door of the briquette holder gets closed and within a time span of 15s the charge support table (9) moves up fast to support the entire charge inside the shaft of the furnace which was being supported by shearing blades (8) till then. This whole process cycle is unique. It is fully automated and sequenced gets completed in a minute. Typical properties of raw materials and the output from VSRF Blue dust: To produce PM grade iron powder, beneficiated blue dust is used We claim, 1. A carbothermic process of reduction in an externally heated vertical shaft furnace of iron ore to PM grade sponge iron using coke and lime stone as Reductant mixture wherein the ore and the reductant mixture are charged from the top of the furnace through a co-axial double hopper arrangement having flexibility of changing cross-section with different profiles in an immiscible way * thereby avoiding intimate contact between them, the said charge, gravity aided, descending at a constant speed, regulatable, through a preheating zone and subsequently through three reduction zones at optimal temperatures to undergo desired degree of reduction for conversion into PM grade iron powder, encountering no possibility of reverse reaction to be withdrawn along with excess, partially reusable coke through a cooling channel after it has been cooled below the oxidation temperature of the sponge briquette, the withdrawal throughout the shaft being regulated at constant speed, to be discharged out of the axis of the furnace system as handle able pieces using shearing mechanism such that the charge above is not disturbed, the shearing and discharge out of the furnace is hydraulically automated. 2. A process as claimed in claim 1 wherein the reductant mixture includes a 'reaction initiation' agent. 3. A process as claimed in claim 1, wherein the reductant mixture includes an agent for desulphurising coke. 4. A process as claimed in claims 1, wherein the reaction mixture comprising of ore and the reductant mixture is fed, gravity-aided, as a continuous flow into the furnace. 5. A process as claimed in claim 1, wherein the said reaction mixture is fed through a double hopper arrangement to render its constituents immiscible to avoid extra carbon pick-up. 6. A process as claimed in claim 1 wherein the said double hopper feed arrangement allows the heavier ore to flow out first initially creating an annulus for reductant flow around it thereby ensuring the withdrawal of ore and reductant mixture separately into different collection chambers to facilitate partial reuse of coke. • 7. A process as claimed in claim 1 wherein the said double hopper feed arrangement allows inherent flexibility of changeable cross sections with different profiles thereby allowing the regulation of i) ratio of the constituents of the reaction mixture i) ratio of the layer thickness of the ore to the reductant mixture iii) different levels of productivity 8. A process as claimed in claim 1 wherein the reaction mixture continuously descends through the shaft a constant rate of 80-130mm/h. 9. A process as claimed in claim 1 wherein the said constant rate of descent can be adjusted any where between 50-300mm/h. 10. A process as claimed in claim 1 wherein the said constant rate of descent is attained by an hydraulically operated support table. 11. A process as claimed in claim 1 wherein the said support table, located at the bottom of the furnace, supports the total column of reaction mixture inside the shaft. 12. A process as claimed in claim 1 wherein the said double hopper feed arrangement in conjunction with the constant rate of descent ensures the desired degree of reduction of the iron ore. 13. A process as claimed in claim 1 wherein the said degree of reduction is obtained by allowing the reaction mixture to reside in each reduction zone, its residence time in each zone decided by the length of that zone. 14. A process as claimed in claim 1 wherein the length of the pre-heating zone is 600 to 800 mm, 1®* zone is 700 to 1000mm, 2" zone is 1200 to 1900 mm and 3' zone is 1200 to 2000 mm. 15. A process as claimed in claim 1 wherein the said degree of reduction is attained by maintaining different temperatures in fog different zones -preheating, zones 16. A process as claimed in claim 1 wherein the said temperature in the preheating zone is maintained at 400 to 800°C 17. A process as claimed in claim 1 wherein the said temperature in the 1®^ zone is maintained at 1000-1060 °C 18. A process as claimed in claim 1 wherein the said temperature in the 2^^^ zone is maintained at 1020-1120°C 19. A process as claimed in claim 1 wherein the said temperature in the 3'^ zone is maintained at 1000-1100°C 20. A process as claimed in claim 1 wherein the said temperatures in 1®\ 2" and 3 zones are obtained through independently controllable external burners, a pair of them for each zone, the thermal energy input into each zone being 10,000 to 30,000 KCl/h 21. A process as claimed in claim 1 wherein thermal input to the said preheating zone is through hot reaction gases from inside the shaft and also from the flue gases from the burners 22. A process as claimed in claim 1 wherein the remnant thermal energy of the hot reaction gases in the shaft is recovered and utilized in the heating zones. 23. A process as claimed in claim 1 wherein the reverse reactions in the reduction zones are prevented by maintaining 1200 -1800mmWC inside the shaft. 24. A process as claimed in claim 1 wherein the separation of the parallel flows of the sponge iron bracket and the reductant mixture is effected by means of a sudden jerk actuated by the movement of the support table. 25. A process as claimed in claim 1 with an automated mechanism of cutting the sponge iron briquette and its unloading being completed within a minute without affecting the continuity. 26. A process as claimed in claim 1 wherein the withdrawal rate is between 80-130mm/h * 27. A process as claimed in claim 1 wherein the size range of the ore is > 100- 250\|am, apparent density ranges from 1.4-2.2g/cc, flowability of 20-50s/50g, size range of coke being 1-7 mm and size range of calcium carbonate 1-4 mm. 28. A process as claimed in claim 1 wherein the morphology of iron ore and the reductant mixture are irregular and round- edged respectively. 29. A process as claimed in claim 1 wherein the Silicon carbide refractory bricks of 20-75% porosity to relieve pressures generated by the .reaction and product gases inside the shaft. 30. A process as claimed in claim 1 wherein the constant rate of descent effectively combats the problems of expansion during phase transformations during reduction reaction. 31. A process as claimed in claim 1 where productivity can be increase times by increasing the length and the width of the vertical shaft.

Full Text

FIELD OF INVENTION
The present invention relates to the process and equipment for preparation of high purity sponge iron from iron oxide. The invention particularly relates to an improved and novel process to produce a particular quality of sponge iron that can be converted into PM grade iron powder. More particularly the invention relates to a particular metallurgical processing of blue dust and coke in a vertical shaft furnace with a regulated downward movement to convert blue dust which is a mine burden to high purity sponge iron which can be converted to PM grade iron powder. The invention more particularity relates to carbothermic reduction in a vertical shaft to produce PM grade sponge iron
BACKGROUND OF INVENTION
High Purity Sponge Iron finds number of applications. India is bestowed with high purity iron ore (blue dust) existing in the form of Hematite in millions of tons which is a mine burden.
This blue dust cannot be used in blast furnace as such and could be advantageously harnessed by evolving a reduction process using blue dust with solid reductant mixture i.e. mixture of coke breeze, a by-product of coke ovens of steel plants, and calcium carbonate of metallurgical grade available in abundance.
A wide range of applications exist for use of iron powders produced from high purity sponge:
Powder metallurgy industry, wherein a wide variety of structural parts are produced by 'press-sinter' route and a variety of frictional components like brake pads which are produced by pressure sintering route;
Pharmaceutical industry wherein iron powder is used as a catalyst;

Welding electrode industry wherein iron powder is an important ingredient in the coating applied on the metallic wire;
Food preservative industry wherein preferential oxidation of high purity iron powder preserves food;
* India, which is bestowed with abundant blue dust resources, depends on imports for PM grade sponge iron.
To reduce such dependence on imports and to convert and add value to the mine burden (blue dust) a technology to indigenously produce sponge iron suitable for production of PM grade iron powder, research work was carried out to develop a process which is capable of economically converting the blue dust to sponge iron with a flexibility and automation which makes the equipment a precious research tool on semi-commercial scale in addition to being ready for scaling up to suitable for producing PM grade iron powder on commercial scale.
RELATED PRIOR ART
* The production of sponge iron by direct reduction of the ore with coke is a process
that has been known since ancient times. There are no available Indian Patent as
prior art to this invention.
The other patents reported are the US patent 4242125 and the equivalent patent AT369035, AU 4093578, AU 523769 and US 4189313.
The process for US 4189313 is for the production of the sponge iron and not the powder metallurgy grade Sponge Iron (low carbon) as claimed in my invention.
The charge withdrawn contains the contamination of the residuals of reducing agents including Coal and Coke & other additives.
Whereas in our process the low carbon Sponge Iron brickett is free of any of the
reducing
agents which are discharged free of the brickett. Then the brickett is of high purity
Sponge Iron (Powder Metallurgy grade with carbon less than 0.2 % )

The descent of the material in the process of US 4189313 is by the screw discharge
mechanism and the free movement downwards of the reduced material cannot be
controlled as by the gravity discharge being independent of consolidation, the
crumbling
of the reduced material cannot be free of carbon .
Whereas in the process claimed by us the iron ore and the reducing agent are immissible from the feeding point to the discharge. While the material is descending the hydraulic prop at the bottom supports the total burden in a consolidated position making the distinction between the sponge iron brickett as reduced and the reducing agent surrounded the brickett in free flow conditions even at the temperature of
1250°c.

This is the claim novel to our process as compared to any other process available in the world
The claim made in process states "that the charge which is which is introduced descends at the first constant speed and afterwards descends at a second speed which has a constant function of the reduction of the speed substantially coincide with the condition prescribed are mechanical and chemical. The control on the movement in theoretical while in our process the material movement in controlled from the bottom depending upon the length of the charge at first, second and third phases. The temperature control and holding at a stoichiometric balance is maintained by not disturbing the movement continuously.
But a periodic intervals of 8 hours in our process which can be regulated by increasing the retard height and the cooling zone to the required levels of output. This feature is also an innovation in our process of carbothermic process.
In other innovation in our process is the fuel viz., LPG / natural gas burnt in a chamber away from the retard so that retard get the uniform heating by regulating the valve provided in the exhaust line before the chimney. Where as in the process US 4189313 the heating is made directly to the retard where in the hot spots near the flame and away from the flame develops difference in temperatures and thus the retard is charged with thermal shocks and the heating would not be uniform
The sponge iron extracted is contaminated with ash, un-burnt coal and other reducing agents if any for de-sulfur sing. This calls separating the pure iron from non-magnetics which is a cumbersome process in which the possibility of coal an ash being carried along with metal may not be desirable.
Then the sponge iron in question is ok as it is not low carbon but goes in to the production of steel or cast iron where in the presence of carbon up to 3% is desirable.
Metallisation wouldn’t be more than 85-87 %, whereas in our process the material being immissible the high grade sponge iron brickett as discharged in free of lose, coke or reducing agents since the brickett is consolidated, sintered with metallisation of over 97% the process of low carbon process. It doesn't require any further

operation except powdering and annealing for direct component manufacturing which is the order of the day.
However, the known processes, involve notable shortcomings, and heretofore none of the known processes has been successfully used on an industrial scale to obtain sponge iron suitable for conversion into PM grade iron powder, the sole exception being M/s Hoeganas Corporation, Sweden, who produce such sponge iron using an equipment and a process entirely different from the present case, the equipment being horizontal as against vertical and the starting material- being magnetite as against Haematite (blue dust). M/s Hoeganas corporation, introduced the pattern of loading coke and ore such that they are immiscible in Silicon Carbide saggers, each sager containing a number of vertical reaction chambers of circular cross-section, wherein the coke and ore are loaded in concentric cylindrical pattern, coke being fed at the center followed concentrically by a column of iron ore and finally another column of coke being fed around the iron ore. As compared to M/s. Hoeganas, investment levels are less, process of loading and unloading is not as cumbersome and breakage of Silicon Carbide saggers is a disadvantage, which is overcome by our Silicon Carbide vertical retort.
Through the present process the inventor has improved the cost effectiveness of low carbon PM grade sponge iron production using indigenously available raw material with automated and integrated operations involving control on movement of material, temperatures at various reaction zones on continuous basis and also keeping the option of material discharge at will without disturbing the descending material.
SUMMARY OF THE INVENTION
Carbothermic process for reducing iron ore in an externally heated Silicon Carbide vertical shaft is characterized by charging the reaction mixture (ore and reductant mixture) in a double hopper system which facilitates immiscibility of ore and the reductant mixture while the reaction mixture descends through four different heating zones, i,e, preheating, first, second and third zones, the first, second and third zones of the vertical Silicon Carbide shaft obtaining thermal input through external heating

through burners, while the thermal input to preheating zone is from the flue gases from the burners and also from reduction reaction in the shaft which evolves hot gases/
Unlike existing methods, the unique feature herein is gravity aided constant rate of descent, and as it descends from the said hopper system through the vertical shaft, the reaction mixture is pre-heated while descending through the said pre-heating zone and progressively achieves the reduction reaction temperatures while descending through 1®* and 2" zones such that as the reaction mixture traverses through 3^^ zone, the reduction reaction is completed. The temperature in the third zone is kept lower than that of the second zone not only to obtain the said desired degree of reduction reaction, but also to prevent backward reactions, over-sintering which would adversely affect the sponginess of the said briquette of the sponge and thermal shock to the reduced sponge iron briquette. As the sponge iron briquette descends out of the third zone into the cooling system, the heat generated from the hot gases, which is a reaction bye-product, is withdrawn through ducting from below the third zone to the flue gas channel at S*"^ zone for better heat utilization.
Sponge Iron briquette as a descending continuum and excess reductant mixture are drawn out of the third zone to a cooling system where the temperature is gradually cooled by circulating water during descent. It is ensured that the speed of descent is so controlled that the material i.e. the said continuum of sponge iron has been cooled sufficiently below the oxidation temperature of 50 - 150°C of the sponge iron, and the continuum cut into dischargeable pieces by a shearing mechanism consisting of high-strength blades which support the material above including the one in the cooling system and the time of discharge is so controlled that the original support table regulating the downward movement of briquette is placed in position & downward movement is restarted.
DESCRIPTION OF THE DRAWINGS
Fig 1 of the drawing shows the cross section of schematic diagram of the furnace along with front view.

In the diagram, 1 is the inner hopper, 2 is the outer hopper, 3 is the chute for gas
*
outlet, 4 is the furnace shaft, 5 is the heating channel, 6 is the outlet for gases, 7 is the cooler, 8 is shear blades, 9 is the support table, 10 is the flute for coke collection, 11 is the container for coke collection, 12 is the hydraulic support cylinder, 13 is the iron ore concentrate, 14 is coke breeze, 15 is the electric hoist, 16 is the LPG burners, 17 is the sponge iron briquette, 18 is the hydraulic shear cylinders, 19 is the hydraulic cylinder for pusher, 20 is the container, 21 is the table for briquette cleaning, 22 is container for material lift.
DESCRIPTION OF THE INVENTION
Detailed description of the equipment and the process is given herein. The stabilized process parameters to produce sponge iron suitable to make PM grade iron powder have been given at the end.
Equipment construction
The equipment, a typical Vertical shaft furnace with outside dimensions of 2060
mm X 3305 mm x 5600 mm having a capacity of 500 kg/day, consists of material
feeding system (1,2,13,14), furnace section (4,9,17), a heating system (5,16), heat
exchanger system(6), a cooling system(7), discharge System(8,18,19), briquette
receiving system(10,11,20,21), flue gas exhaust system(3) and material handling
system(15,22).
The charge is fed into the furnace shaft (4) which is Vertical Rectangular Shaft furnace of 280 x 1200 mm cross-section and about 5000 mm height through the co-axial hopper system (1,2), the said furnace shaft being constructed using Silicon Carbide refractory bricks surrounded by hot face and cold face refractory bricks (alumina or illuminate) and the said refractory bricks are arranged in such a way that three independent rectangular spiral channels for flue gases (5) to pass through are created at different heights to form three different and distinct temperature zones.
Provision is made in the refractory brick work to incorporate three pairs of gas fuel based burners e.g., LPG (16) located on one side of the shaft, each pair distributed

along height of 385mm, 2065mm and 3745mm from the bottom of the shaft such that the flue gases from the burning fuel follow the said spiral paths available in the refractory bricks passing on heat to the charge through the Silicon Carbide shaft.
Provision is also made in the refractory brick work to incorporate one pair of Chromel-Alumel thermocouple at 1235mm to measure the temperature in the preheating zone and three pairs of Platinum - Platinum-Rhodium thermocouples to monitor temperatures in the three heating zones at 1625mm, 3305mm and 4990mm from the top of the furnace.
The upper part of the shaft is equipped with two co-axial rectangular hoppers (1,2) for charging of blue dust (13) through the inner hopper (1) and the reductant mixture consisting of coke breeze and lime stone (14) through the outer hopper (2).
Refractory brick work is developed on a metallic platform, which, in turn, is secured to concrete columns while another set of concrete columns support the upper charging platform.
The cooling section (7) is a metallic chamber and is an extension of the furnace shaft (4) and it is surrounded by a water jacket in the form of rectangular spiral and is fastened to the lower part of the furnace. The sponge iron briquette (17) gets cooled in this cooling channel and comes out into the discharge system (8,18,19) where it is sheared (8)into pieces of 800mm and unloaded.
The discharging system (8,18,19) consists of the following sub-systems which are actuated hydraulically:
Support table (9): The total column of charge is supported by a specially made support table (9) attached to the piston of a hydraulic support cylinder (12) and the rate of movement of the piston can be regulated anywhere 'between 50mm to 300mm per hour.

Hydraulic Shears (8): The hydraulic shear system consisting of shearing blades (8), operated by hydraulic shear cylinders (18), is used to cut the sponge iron briquette (17) coming out of the cooling channel (7) into pieces of 800mm height.
Unloading system (19): This system is used to unload the sheared piece out of the furnace into the briquette receiving system (10,11, 20,21)
Heat exchange system (6): To tap the thermal energy going out of the furnace, via flue gases, a heat exchange system (6) is provided wherein, the thermal energy is transferred to preheat the air that is fed into the gas burners (16) which are used to heat the vertical shaft.
Exhaust SvstemO): The top of the furnace is connected to the chimney through a chute(3) to let out the flue gases coming out of the furnace after preheating the charge.
Process description with ungues features of processing:
The reaction mixture of blue dust and reductant mixture are at a ratio of 1:1 to 2:1 are fed through the inner(1) and outer(2) hoppers of the co-axial hopper system so as to ensure the immiscibility of blue dust and the reductant mixture as they descend into the furnace shaft(4) and said immiscible pattern of loading is a unique feature of this process. The usual practice in sponge iron production in vertical shaft furnaces is to mix ore with coke and charge in required quantities into furnace. Because of the intimate contact between the reactants, high reaction rates are obtained and productivity increases. Since most of the output of these plants goes for steel melting, high degree of reduction is not attempted. Hence reaction times are deliberately kept shorter to keep the carbon pick-up to minimum, while, in the present case for which patent is being applied, the objective is to make high purity sponge to be converted into PM grade iron powder the reaction times have to be necessarily longer to achieve high degree of molecular reduction. Yet another objective of this invention is to avoid excessive carbon pick-up during prolonged reduction phase by eliminating intimate contact between coke and iron ore.

In the present case for which patent is being applied, the charge is being gravity fed into the shaft (4) through the said hopper arrangement with hydraulic platform at the bottom to support and regulate downward movement at desired speeds. The hopper arrangement extends into the retort by 250 mm for guiding the material being fed into the shaft. The outer hopper(2) extends beyond the inner hopper(1) which ensures that first the ore gets released out of hopper into the shaft(4). The ore, being heavier than the reductant mixture maintains integrity of its cross-section as it moves down by gravity through the shaft creating a rectangular annular space around it for the reductant mixture to flow out of hopper and any possible spread of reductant mixture inwards into the ore is avoided and thus immiscibility maintained.
However, if the rectangular annular space around the ore is not filled up fast, the ore, after travelling some distance down through the shaft, tends to spread outwards blocking the flow of the reductant mix downward which results in improper reduction because of non- availability of required stochiometric quantity of the reductant mixture. This problem is overcome by controlled matching of flows of the ore and the reductant mixture, another unique feature. This is done by selecting appropriate particle morphology size fractions and other physical properties of ore and reductant mixture. The average size of blue dust is 100-300 lam and that of reductant mixture, 1- 8mm.The selected reductant mixture coke having rounded edges to increase its flowability, blue dust having irregular shape with an apparent density(A,D) of 1.5- 2.5 g/cc and flow of 30-50 sec/50g, the moisture content and its loss on Ignition (LOI) being maintained between 1-4% to make it free flowing. Further, to match the flows, coke is filled in the outer hopper to its brim while ore is filled at a level of 25cm -200cm from the top edge of the inner hopper.
To coritrol the productivity arid the degree of reduction, the hopper design has inbuilt flexibility. The sizes of hopper are big enough to accommodate another smaller hopper in the middle of the inner hopper if required to obtain different reductant mixture - ore - reductant mixture patterns of loading. This is realized as the hoppers are flanged at the bottom and are easily detachable. By changing the surface profile of the bottom flange of the inner hopper(1), it is possible to change or reduce the

quantities of ore or reductant mix in different cross-sections. -It is also possible to provide different profiles (other than rectangular profile) to the ore such that its surface area and reactivity can be increased. Yet another feature of the flexible hopper arrangement is to maintain the correct ratio of layer thickness of ore to reductant mixture.
The said reaction mixture of blue dust and reductant mixture in the ratio of 1:1 to 2:1 are gravity fed into the stationary Silicon Carbide shaft with the consequent advantage of long life. The reason for use of Silicon Carbide are its high thermal conductivity (11 W/mK) with required porosity and high resistance to refractoriness under load.
An important requirement of the Silicon Carbide bricks used to build the shaft is porosity to relieve the internal pressure of gases formed in the shaft during the reduction reaction.
The reduction reaction goes through the following three steps:
■
3Fe203 + CO o 2Fe304+ CO2+ heat
Fe304 + CO o 3FeO + C02 - heat
FeO + CO All these reactions are reversible and reaction products (gases) at high pressures and temperatures will bring about this reversibility. Thus, the absolute pressure of reaction products inside the shaft cannot be more than 1200-1400 mmWC. The actual value was measured inside the shaft by regulating the outlet butterfly valve and found to be varying from 1400 mmWC to 1800 mmWC. Based on the actual value of the pressure measured, the opening of butterfly valve was fixed to ensure only forward reaction.
The maximum pressure developed by the reaction products varies depending on the configuration of the reaction chamber, amount of reaction mixture, temperature etc. This, in turn has a bearing on the amount of porosity required in the Silicon

Carbide shaft. The porosity of Silicon Carbide bricks selected for VSRF ranged between 22% to 25%.
As the reaction mixture enters the Silicon Carbide shaft with an internal pressure of 1400 to 1800 mmWG to prevent the backward reactions, it crosses the pre-heating zone at 400-800°C which gets thermal input internally from hot gases evolving out of reduction reaction as well as externally from the flue gases coming from the three heating zones which circulate in rectangular spiral channels around the said preheating zone of the furnace shaft(4).
After preheating the charge descends subsequently into three reductions zones which are located one below the other which are maintained at different temperatures by means of externally located burners(16). As the charge enters the first zone where the temperature is maintained at 1000-1 OSO the reduction reaction is initiated. A second and progressive heating of said reaction mixture in the second temperature zone takes place at a temperature range of 1060-1120°C. A third and constant heating of said reaction mixture takes place in the third zone at temperatures of 1000-1100°C of the shaft following the said progressive heating so as to complete the reduction process.
The rate of descent of the said reaction mixture is controlled such that the thermal charge moves at a constant speed anywhere set between 50-300mm/h throughout the process till it is completed. The said constant speed is achieved inside the shaft through a hydraulically actuated support table(9), 250mm thick. The speed of descent of the charge can be adjusted between 50 to 300 mm/h, through inbuilt control systems. The regulation of speed of descent, which is another unique feature, is required to arrive at
a) optimum speed to ensure desired degree of reduction

b) to combat the problems of expansion during phase transformations as shown
below

thereby avoiding cutting into the reductant mixture cross-section adversely affecting the stochiometric ratio of reductant mixture(14) and blue dust(13) for ensuring proper reduction.
c) to prevent damage to the SILICON CARBIDE shaft as a result of briquette expansion and to have control of productivity and hence economies on process cost.
In addition this facilitates adjustment of reaction times in the reduction zones. Thus if necessary, and during downtimes it is possible to make other grades of sponge iron that can be used either for remelting purposes or as a charge for atomization.
As the reduction process attains desired degree of reduction, the remnant reaction gases which carry sufficient thermal energy are led out through a port located below the third zone into the flue gas chamber of 3^^ zone such that thermal efficiency of the furnace increases.
As the reduced sponge iron briquette(17) comes out of the shaft, it enters a metallic, water cooled, cooling chamber of 800 mm length which is an extension of the shaft wherein it gets cooled by circulating water through cooling channels(7) to almost ambient temperature. After the cooling, material is drawn to discharge collection zone where in the briquette is sheared(8) and unloaded though a discharging systemic, 10,18,19). The said arrangement as described below is novel and completely automated. The system consists of the following:
1. Hydraulically actuated shearing mechanism(8,18)
2. 'Briquette holder' that holds the sheared briquette with a hydraulically
actuated door and a piston to push(19) out the briquette

3. A briquette receiver(20) hydraulically actuated into horizontal and vertical positions resting on a platform(21) outside the furnace(4) system.
The briquette comes out of the cooling chamber (7) and traverses 800 mm supported by the support table (9). After this, the shearing mechanism (8) gets hydraulically actuated (18) and the briquette is sheared into an 800 mm long piece.
At that juncture the shearing blades (8) support the total charge inside the shaft and the actual support table (9) moves doWn at the rate of 215 mm/h in a jerk, thereby loosening the coke and ash around the cut briquette such that they can flow out into bins through ports (10) provided for that purpose.
After the discharge of the coke and ash, the sheared briquette enters the briquette holder’ whose door is closed. After a time delay of 30s the hydraulically actuated door opens. The briquette receiver then moves from horizontal to vertical position. Next, a hydraulically operated pusher (19) pushes the briquette onto the briquette receiver (20), which gradually comes to its horizontal position carrying the briquette with it after which it is unloaded onto the briquette cleaning table (21). Simultaneously the door of the briquette holder gets closed and within a time span of 15s the charge support table (9) moves up fast to support the entire charge inside the shaft of the furnace which was being supported by shearing blades (8) till then.
This whole process cycle is unique. It is fully automated and sequenced gets completed in a minute.
Typical properties of raw materials and the output from VSRF
Blue dust: To produce PM grade iron powder, beneficiated blue dust is used

We claim,
1. A carbothermic process of reduction in an externally heated vertical shaft
furnace of iron ore to PM grade sponge iron using coke and lime stone as
Reductant mixture wherein the ore and the reductant mixture are charged from
the top of the furnace through a co-axial double hopper arrangement having
flexibility of changing cross-section with different profiles in an immiscible way *
thereby avoiding intimate contact between them, the said charge, gravity aided, descending at a constant speed, regulatable, through a preheating zone and subsequently through three reduction zones at optimal temperatures to undergo desired degree of reduction for conversion into PM grade iron powder, encountering no possibility of reverse reaction to be withdrawn along with excess, partially reusable coke through a cooling channel after it has been cooled below the oxidation temperature of the sponge briquette, the withdrawal throughout the shaft being regulated at constant speed, to be discharged out of the axis of the furnace system as handle able pieces using shearing mechanism such that the charge above is not disturbed, the shearing and discharge out of the furnace is hydraulically automated.
2. A process as claimed in claim 1 wherein the reductant mixture includes a 'reaction initiation' agent.
3. A process as claimed in claim 1, wherein the reductant mixture includes an agent for desulphurising coke.
4. A process as claimed in claims 1, wherein the reaction mixture comprising of ore and the reductant mixture is fed, gravity-aided, as a continuous flow into the furnace.
5. A process as claimed in claim 1, wherein the said reaction mixture is fed through a double hopper arrangement to render its constituents immiscible to avoid extra carbon pick-up.

6. A process as claimed in claim 1 wherein the said double hopper feed
arrangement allows the heavier ore to flow out first initially creating an annulus
for reductant flow around it thereby ensuring the withdrawal of ore and
reductant mixture separately into different collection chambers to facilitate
partial reuse of coke.
•
7. A process as claimed in claim 1 wherein the said double hopper feed
arrangement allows inherent flexibility of changeable cross sections with
different profiles thereby allowing the regulation of
i) ratio of the constituents of the reaction mixture
i) ratio of the layer thickness of the ore to the reductant mixture
iii) different levels of productivity
8. A process as claimed in claim 1 wherein the reaction mixture continuously descends through the shaft a constant rate of 80-130mm/h.
9. A process as claimed in claim 1 wherein the said constant rate of descent can be adjusted any where between 50-300mm/h.
10. A process as claimed in claim 1 wherein the said constant rate of descent is attained by an hydraulically operated support table.
11. A process as claimed in claim 1 wherein the said support table, located at the bottom of the furnace, supports the total column of reaction mixture inside the shaft.
12. A process as claimed in claim 1 wherein the said double hopper feed arrangement in conjunction with the constant rate of descent ensures the desired degree of reduction of the iron ore.

13. A process as claimed in claim 1 wherein the said degree of reduction is obtained by allowing the reaction mixture to reside in each reduction zone, its residence time in each zone decided by the length of that zone.
14. A process as claimed in claim 1 wherein the length of the pre-heating zone is 600 to 800 mm, 1®* zone is 700 to 1000mm, 2" zone is 1200 to 1900 mm and 3' zone is 1200 to 2000 mm.
15. A process as claimed in claim 1 wherein the said degree of reduction is attained by maintaining different temperatures in fog different zones -preheating, zones
16. A process as claimed in claim 1 wherein the said temperature in the preheating zone is maintained at 400 to 800°C
17. A process as claimed in claim 1 wherein the said temperature in the 1®^ zone is maintained at 1000-1060 °C
18. A process as claimed in claim 1 wherein the said temperature in the 2^^^ zone is maintained at 1020-1120°C
19. A process as claimed in claim 1 wherein the said temperature in the 3'^ zone is maintained at 1000-1100°C
20. A process as claimed in claim 1 wherein the said temperatures in 1®\ 2" and 3 zones are obtained through independently controllable external burners, a pair of them for each zone, the thermal energy input into each zone being 10,000 to 30,000 KCl/h
21. A process as claimed in claim 1 wherein thermal input to the said preheating zone is through hot reaction gases from inside the shaft and also from the flue gases from the burners

22. A process as claimed in claim 1 wherein the remnant thermal energy of the hot reaction gases in the shaft is recovered and utilized in the heating zones.
23. A process as claimed in claim 1 wherein the reverse reactions in the reduction zones are prevented by maintaining 1200 -1800mmWC inside the shaft.
24. A process as claimed in claim 1 wherein the separation of the parallel flows of the sponge iron bracket and the reductant mixture is effected by means of a sudden jerk actuated by the movement of the support table.
25. A process as claimed in claim 1 with an automated mechanism of cutting the sponge iron briquette and its unloading being completed within a minute without affecting the continuity.
26. A process as claimed in claim 1 wherein the withdrawal rate is between 80-130mm/h
*
27. A process as claimed in claim 1 wherein the size range of the ore is > 100-
250|am, apparent density ranges from 1.4-2.2g/cc, flowability of 20-50s/50g, size range of coke being 1-7 mm and size range of calcium carbonate 1-4 mm.
28. A process as claimed in claim 1 wherein the morphology of iron ore and the reductant mixture are irregular and round- edged respectively.
29. A process as claimed in claim 1 wherein the Silicon carbide refractory bricks of 20-75% porosity to relieve pressures generated by the .reaction and product gases inside the shaft.
30. A process as claimed in claim 1 wherein the constant rate of descent effectively combats the problems of expansion during phase transformations during reduction reaction.

31. A process as claimed in claim 1 where productivity can be increase times by increasing the length and the width of the vertical shaft.

Documents:

546-che-2003-abstract.pdf

546-che-2003-claims filed.pdf

546-che-2003-claims granted.pdf

546-che-2003-correspondnece-others.pdf

546-che-2003-correspondnece-po.pdf

546-che-2003-description(complete) filed.pdf

546-che-2003-description(complete) granted.pdf

546-che-2003-drawings.pdf

546-che-2003-form 1.pdf

546-che-2003-form 19.pdf

546-che-2003-form 26.pdf

546-che-2003-form 3.pdf

546-che-2003-form 5.pdf

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Patent Number

205728

Indian Patent Application Number

546/CHE/2003

PG Journal Number

26/2007

Publication Date

29-Jun-2007

Grant Date

09-Apr-2007

Date of Filing

01-Jul-2003

Name of Patentee

HYTECH BLUE METAL POWDER ALLOYS (P) LTD

Applicant Address

KAKATI HOUSE NACHARAM INDUSTRIAL AREA, HYDERABAD-500 007.

Inventors:

#	Inventor's Name	Inventor's Address
1	Mr.JANGITI PANDURANGAM	1-4-1,NEW FOUND LAND CO-OPERATIVE SOCIETY, STREET NO.7,HABSIGUDA, HYDERABAD-500 007.
2	MS. MALABIKA KARANJAI	ADVANCED RESEARCH CENTERE INTERNATIONAL BALAPUR,HYDERABAD,A.P

PCT International Classification Number

C 21 B 13/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA