FIELD OF THE INVENTION This invention relates to an ore processing furnace used in the production of metals and their alloys and more particularly, but not exclusively, this invention relates to an ore processing furnace for reducing ore. This invention further extends to an ore processing furnace for pre-heating ore before further processing thereof. BACKGROUND TO THE INVENTION

Oxide bearing materials, such as iron, chromium and manganese ores, have to be reduced to liberate valuable elements from the oxides in which they are located. Traditionally, iron oxides such as hematite or magnetite have been processed in blast furnaces to produce raw iron (or pig iron), containing excess carbon. This raw iron is then further processed in steel plants, typically in electric arc or oxygen furnaces, to reduce the amount of carbon and to form steel. Iron ore is converted into iron through reduction, which is the process in which oxygen in the iron oxide is caused to react with a reductant, normally hydrogen (H ₂ ), methane (CH ₄ ) and/or carbon monoxide (CO) in the gaseous form and to a lesser degree by carbon (C) in the solid form. Typically, carbon monoxide is the dominant species, which could be produced from carbon in the form of coal or any other carbonaceous material. This causes oxygen to disassociate from the iron oxide and leave the elemental iron, which normally contains other unwanted matter, gangue elements, for further treatment. When carbon is used as a reductant, the oxygen in the ore combines with the carbon monoxide to form carbon dioxide gas. The carbon dioxide reacts with carbon to form carbon monoxide to sustain the reduction reactions. The reaction to reduce the oxides from a metal oxide, such as iron oxide, requires a reductant and heat.

Blast furnaces require specific feedstock to operate optimally. Specifically, in the case of iron oxide, the oxides have to be either ore lumps or in indurated pellet form of specific size or sintered form. Blast furnaces cannot handle fine materials ("fines"), which would block the flow of gasses through the process reactor (blast furnace). The blast furnace has been the leading method of iron production over the past century.

It is possible to circumvent the use of blast furnaces through direct reduction processes in which oxides are reduced by reducing gasses at specific temperatures. In a typical direct reduction process the load is first preheated, then reduced. Heat is supplied to the load through gas which, is burned in close proximity to the load. The reduced material is then fed to an electrical arc furnace where it is then melted. The liquid metal is transferred to final purification and alloying stages and cast into ingots or billets.

Direct reduction processes are used in many types of furnaces, including rotary kilns in which lumps or hard pellets of iron oxide are tumbled together with coal while combusting the gasses so formed to provide heat to sustain the reactions. Conventional direct reduction furnaces, such as rotary kilns, cannot handle fine particles since the air blown into the kiln and the gas formed in the kiln is at such velocity that it blows the particles away. In another configuration, a rotary hearth supporting a bed of metal oxides is rotated on a disc and exposed to different reaction zones in which the material is preheated, reduced and cooled. These furnaces are very expensive and are not generally used for reducing iron ore, this function is mainly carried out in blast furnaces. In yet another configuration, particles are fed onto a bath of liquid metal and exposed to heat in the presence of a reducing agent. After being reduced, the reduced metal would be melted into the bath from where it could be transported for further use. A problem with such an arrangement is that the electrical power consumption is extremely high, rendering the process uneconomical.

Partly for this reason, a characteristic of the prior art processes is that they either comprise heaps of metal oxide material which, are exposed to heat, or pellets of the metal oxide which are individually exposed to a reducing atmosphere. The relatively recent increase in the number of "mini mills" (electric arc furnaces fed primarily with steel scrap), which represent relatively low capital investment costs when compared to the blast furnace, has lead to the curtailment of investment in new blast furnace capacity in first world producing countries. However, countries such as India and China, for example, continue to invest in new blast furnace capacity. Mini mills, which were previously competitive, are now being faced with rising electrical power costs and rising scrap prices. Scrap shortages have been caused by rising steel demand and by scrap consumption exceeding the natural recycle rate of the existing "in use" steel inventory.

The combination of higher energy costs, high capital costs, carbon footprint reduction regulations, shortage and high cost of coking coal, shortage of good quality ores and low profit margins of steel producers has focused the need for new technologies to find solutions to the current challenges faced by the industry.

Over the past twenty or so years, the steel industry has applied significant resources to research and development aimed at reducing production costs and carbon footprint. The prime focus of cost reduction has been on:

a) Use of cheaper "soft" non-metallurgical coal;

b) Use of cheaper "fine" ores;

c) Use of cheaper coal fines;

d) Eliminating production steps (e.g. sintering, pelletizing);

e) Reducing energy per unit of production;

f) Improving the efficiency and costs of blast furnace production; and

g) Pre-heating of ores to reduce the energy requirements of downstream processing The blast furnace continues to benefit from operational improvements, however, as the blast furnace has been continuously optimised over a century of use, recent improvements in equipment modifications and operational methods provide very small efficiency gains.

The focus of new technologies has mainly been on solid-state reduction, primarily in rotary hearth furnaces (ITmk3, HiQip), shaft type furnaces (Midrex, HYL), and fluidized beds (Circored, Finmet) and direct smelting (HiSmelt, Auslron). These technologies have targeted the use of cheaper thermal coal and iron ore fines as the rationale for their production cost reduction. These technologies have all been proven in pilot plants and in some production sized units to be capable of producing high quality iron from cheaper input feedstock (thermal coal, ore fines). The fundamental chemistry and physics applicable to these processes is established and documented thereby eliminating process risk.

The following factors have been identified as limitations to the widespread adoption of these new technologies in large-scale commercial applications:

a) High capital cost per unit of output;

b) High maintenance and refractory replacement costs;

c) Difficult to achieve close operational conditions (process control);

d) Scale up challenges (difficult to achieve large commercial production levels); e) Energy savings benefits not proven on large scale;

f) Very large plant required as direct reduction capacity is a function of reaction surface area; and g) Huge engineering challenges caused by the very large mass of rotating equipment associated with rotary hearths of commercial size.

The fluctuating temperature profile (heating, reduction, cooling) in some processes leads to less than optimal use of heat energy.

South African patent 2010/04810 in the name of Price, Christopher James describes a "Static Slope Reduction Furnace". The specification of this patent application is included herewith in its entirety, by way of reference.

OBJECT OF THE INVENTION

It is an object of this invention to provide an ore processing furnace which, at least partially alleviates some of the abovementioned difficulties, and or to provide an ore processing furnace which is a useful alternative to known ore processing furnaces.

SUMMARY OF THE INVENTION

An ore processing furnace comprising:

- a furnace compartment having an inclined ore processing member therein;

- an ore inlet at an operatively higher end of the ore processing member for feeding ore onto that end of the ore processing member; and

- a heat source in the furnace compartment for providing heat energy to ore on the ore processing member. The furnace may further include an ore outlet at an operatively lower end to the ore processing member through which ore discharges from the furnace.

The ore processing member may be an ore reduction member defining a reduction surface on an operatively upper surface thereof.

The ore processing member may be a planar member, generally in the form of at least one of a base, hearth, bed, plate and the like. There is provided for inclination of the ore processing member to be adjustable with inclination adjustment means.

The inclination adjustment means may include one or more actuators which simultaneously adjust the inclination of the furnace compartment and the ore processing member by being associated with the furnace compartment. Alternatively, the inclination adjustment means may include one or more actuators which adjust the inclination of the ore processing member only by being associated with the ore processing member. The at least one or more actuators may be hydraulically operated and telescopically extendible and retractable.

The ore processing member may have an inclination which is close to the angle of repose of the ore on it.

There is further provided for the furnace compartment to be pivotally supported whereby it is pivotally displaceable. The ore processing member may be supported at opposing higher and lower ends thereof by side walls of the furnace compartment.

The heat source may be located operatively underneath the ore processing member. Alternatively, the heat source may be located operatively above the ore processing member. Further alternatively, the heat source may be located operatively underneath and above the ore processing member.

The heat source may be in the form of a flame emitted by one or more burners. Alternatively, the heat source may be in the form of hot air introduced into the furnace compartment by one or more vents. Further alternatively, the heat source may be in the form of hot gas generated by ore on the ore processing member.

The furnace may also include at least one or more temperature sensors in the furnace compartment. The at least one or more temperature sensors may measure the temperature of the gas inside the furnace compartment. Alternatively, the at least one or more temperature sensors may measure the temperature of the ore on the ore processing member. Further alternatively, the at least one or more temperature sensors may measure the temperature of the gas inside the furnace compartment and the ore on the ore processing member.

The at least one or more temperature sensors may be located operatively underneath the ore processing member. Alternatively, the at least one or more temperature sensors may be located operatively above the ore processing member. Further alternatively, the at least one or more temperature sensors may be located operatively underneath and above the ore processing member.

The furnace may further include at least one or more gas analysers for analyzing and measuring one or more gasses in the furnace compartment. The gasses may be selected from the group comprising carbon monoxide, carbon dioxide, hydrogen, water, methane, oxygen, and the like. The at least one or more gas analysers may be located operatively above the ore processing member. The furnace may yet further include at least one or more pressure sensors for measuring the gas pressure inside the furnace compartment. The at least one or more pressure sensors may be located operatively underneath the ore processing member. Alternatively, the at least one or more pressure sensors may be located operatively above the ore processing member. Further alternatively, the at least one or more pressure sensors may be located operatively underneath and above the ore processing member.

The furnace may also include visual inspection means for visually inspecting ore on the ore processing member. The visual inspection means may include at least one or more cameras located operatively above the ore processing member. Alternatively, the visual inspection means may include at least one or more sight ports located operatively above the ore processing member. Further alternatively, the visual inspection means may include at least one or more cameras and at least one or more sight ports located operatively above the ore processing member. A further feature of the invention provides for ore feeding means to be located at an operatively upper end of the ore processing member for providing ore to the ore inlet. The ore feeding means may be in the form of an ore feeder, such as a hopper. There is provided for ore receiving means to be located at an operatively lower end of the ore processing member for receiving ore leaving the ore processing member. The ore receiving means may be a rotatable drum. There is further provided for the rotatable drum to include ore receiving containers. A yet further feature of the invention provides for the furnace to include a briquette making device for making briquettes from reduced product received from the ore receiving means.

There is also provided for a plurality of ore processing members to be stacked above each other.

In the stacked configuration, the heat released from ore being processed on the ore processing member is used assist to heat the ore processing member immediately above.

The ore may include oxide bearing materials.

These and other features of the invention are described in more detail below. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described below, by way of non-limiting examples only, and with reference to the accompanying drawings in which:

Figure 1 shows a schematic cross-sectional side view of an ore processing furnace in accordance with a first aspect of the invention; and

Figure 2 shows a schematic cross-sectional side view of an ore processing furnace in accordance with a second embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

With reference to the drawings, in which like features are indicated by like numerals, an ore processing furnace in accordance with a first embodiment of the invention is generally indicated by reference numeral 1 0 in figure 1 and an ore processing furnace in accordance with a second embodiment of the invention is generally indicated by reference numeral 10A in figure 2. One of the primary uses of the furnace 10 is for it to operate as a reduction furnace for ore. Other uses of the furnace 10 may include, for example, pre-heating of ore before it is further processed. For ease of description, the furnace 10 will hereinafter be referred to as a reduction furnace 10, without limiting its scope as to further applications thereof. The reduction furnace 10 consists of a furnace compartment, including upper and lower compartments 12 and 14, having an inclined ore processing or reduction member 16 therein defining a reduction surface on an operatively upper surface thereof. The reduction member 16 divides the furnace compartment into its upper compartment and lower compartments 12 and 14. The ore reduction member 16 is a planar member, generally in the form of a base, hearth, bed, plate, or the like. An ore inlet 18 or aperture is located at an operatively higher end of the reduction member 16 for feeding ore 20 onto that end of the reduction member 16 and an ore outlet 22 is located at an operatively lower end of the reduction member 16 through which the ore 20 discharges from the furnace 10. Generally in use, the ore 20 would be oxide bearing materials such as iron, chromium and manganese ores.

The furnace compartments 12 and 14 are defined by a roof 24, floor 26 and opposing side walls 28. Front and rear walls are not shown in the schematic drawings. The reduction member 16 is inclined from the ore inlet 18 in one of the side walls 28 towards the ore outlet 22 in the opposing side wall 28. The reduction member 16 is supported at opposing higher and lower ends thereof by the side walls 28.

Ore feeding means in the form of an ore feeder 30 or hopper is located at an operatively higher end of the reduction member 16 and approximate the inlet 18 to feed ore 20 from stored ore 32 to the inlet 18 and thus onto that higher end of the reduction member 16. The stored ore 32 will flow, under force of gravity, from the feeder 30 through the ore inlet 18 onto the reduction member 16. The inclination of the reduction member 16 is at an angle close to the angle of repose of the ore 20, thus allowing the ore 20 to move down the member 16 under the force of gravity.

An ore feed gate 34 is provided adjacent the inlet 18 for regulating the depth of the ore 20 on the reduction member 16. The gate 34 is linearly displaceable between higher and lower positions to so regulate the ore 20 depth. The gate 34 also assists with at least partially sealing off the inlet 18 which reduces the amount of heat escaping from the upper compartment 12. It should be appreciated that in other embodiments of the invention, the gate 34 could also tilt to regulate the ore depth. Also, a flexible curtain could be used in other embodiments of the invention.

Inclination of the reduction member 16 is adjustable with inclination adjustment means which consists of one or more hydraulically operated actuators 36. The actuators 36 would typically be in the form of pistons or rams which are telescopically extendible and retractable. According to this example embodiment of the invention, the actuators 36 are connected to the floor 26 so to simultaneously adjust the inclination of the furnace 10 and reduction member 16. Adjustment in the inclination of the furnace 10 is further assisted by the furnace 10 being pivotally supported 38 and thus pivotally displaceable about the support 38 under the influence of the actuators 36.

It is foreseen that any number of actuators 36 could be provided and they could be connected in any way to the furnace 10 to permit pivotal displacement thereof. It should be appreciated that in other embodiments of the invention, the inclination adjustment means only has to act directly onto the reduction member 16 so to alter its inclination and not on the furnace 10 as a whole as the case is with the embodiment described herein.

The furnace 10 further includes heat sources for providing heat energy to the ore 20. A first type of heat source is flames which are emitted and introduced into the upper compartment 12 by means of a plurality of burners 40, more particularly liquefied petroleum gas burners. As shown in figure 1 , the burners 40 are located above the reduction member 16 and spaced along the length thereof. A second type of heat source is hot air or gas which is introduced into the upper and lower compartments 12 and 14 by means of a plurality of vents 42 or ports. The vents 42 are spaced along the length of the reduction member 16. At least some of the vents 42 are located in close proximity to the burners 40 so to enhance the heating effect and distribution of the heat in furnace 10. It should be appreciated that a further form of heat source is hot gasses which are generated and emitted by the ore 20 on the reduction member 16.

The furnace 10 also includes temperature and pressure sensors 44 and 46 in both its upper and lower compartments 12 and 14 for respectively measuring the temperature and pressure of the gas in the furnace. In addition, at least some of the temperature sensors 44 measures the temperature of the ore 20 on the reduction member 16. These temperature sensors 44 are spaced along the length (and width) of the reduction member 16 and are thus able to measure the temperature of the ore 20 at various locations as it moves along the reduction member 16 and also at different depths in the layer of ore 20. One or more gas analysers 48 are provided in the upper compartment 12 for measuring and analyzing the concentration of one or more of carbon monoxide, carbon dioxide, hydrogen, water, methane and oxygen. Other gases may also be measured. These analysers 48 are generally a located at different positions along the length of the reduction member 16 so to be able to obtain an accurate reading of what the concentrations of these gases are at different positions. Furthermore, the analysers 48 are positioned to obtain readings in the proximity of the ore 20.

Visual inspection means in the form of a camera 50 and a sight port 52 in one of the side walls 28 are provided in the upper compartment 12 for visually inspecting the ore 20. In some embodiments of the invention, the camera 50 could be located outside the upper compartment 12 and be able to visuals of the ore 20 through a similar sight port in the side wall 28 or roof 24. An outlet gate 54 is provided adjacent the outlet 22 and is linearly displaceable between higher and lower positions. The gate 54 also assists with at least partially sealing off the outlet 22 which reduces the amount of heat escaping from the upper compartment 12. It should be appreciated that in other embodiments of the invention, the gate 54 could also tilt to regulate the ore depth. Also, a flexible curtain could also be used in another embodiment of the invention.

According to the example embodiment shown, a lower free end of the reduction member 16 extends through the ore outlet 22 and terminates above an ore receiving means, in the form of a rotatable drum 56. The drum 56 and lower free end of the member 16 are located in an outlet chamber 58. The outlet chamber 58 includes a discharge opening 60 in its base. The discharge opening 60 terminates above briquette press wheels 62 that compress reduced product into briquettes 64. The briquette press wheels 62 from part of a briquette making device (not shown). The drum 56 is rotatable with a variable speed drive 66. The drum 56 includes a plurality of radially spaced ore receiving containers or compartments for receiving reduced product from the lower free end of the member 16. As stated, the containers are spaced about the axis of the drum 56 so that discreet quantities of reduced product are dropped, under force of gravity, onto the briquette press wheels 62, as the drum 56 rotates. In other embodiments of the invention, the drum 56 may, for instance, include a uniform outer surface such that gravity and friction between such drum surface and the reduced material is sufficient to remove the material from the lower end of the inclined member 16. In use, stored ore 32 is fed through from the feeder 30 through the inlet 18 onto the member 16 whilst the burners 40 are operating. When the burners 40 have generated sufficient heat inside the furnace 10, the vents 42 also introduce hot air into the upper and lower compartments 12 and 14. According to an example embodiment, this could occur by air being withdrawn from the furnace 10 and passing it through a heat exchanger (not shown) which heats new air before it is introduced into the furnace 10. The member 16 is generally thin and the heat from the vents 42 below the member 16 is thus easily transferred through the member 16 to the ore 20. Also, a thin layer of ore 20 is easier to reduce whilst it is moving down the member 16. The object is to reduce the ore 20 just prior to it exiting through the outlet 22. The process is controlled by lowering or increasing the angle of inclination of the member 16 using the one or more actuators 36. The ore 20 temperature is used to assist in this control process. The speed of the rotation of the drum 56 will also be adjustable with the variable speed drive 66 to accommodate changes in the angle of the member 16 and thus the flow rate of ore 20 from the member 16 onto the drum 56.

Figure 2 shows a second embodiment of the reduction furnace 10A. The furnace 10A is similar to the furnace 10 described above, apart from the differences highlighted below. It is envisaged that the height of the furnace 10A could be increased to accommodate a plurality of reduction members 16 therein, in a stacked configuration. It will be appreciated that, although only two reduction members 16 are shown, it is envisaged that any number of reduction members 16 could be stacked on top of each other in a similar fashion. In the configuration of figure 2, the further upper reduction member 16 will thus define a further compartment 68 within the furnace 10A. In the stacked configuration, heat released from ore 20 being reduced on the lower reduction member 16 is used to heat the upper reduction member.

It is envisaged that the above configurations will provide improved reduction furnaces 10 and 10A in that heat is easily transferred through the use of thin member(s) 16 and the material bed thickness and the production rate of the end product is controllable through adjustment of the angle of inclination of the member(s) 16. The speed of rotation of the drum 56 is adaptable to match different material bed thickness and angles of inclination of the member(s) 16. Furthermore, only a thin layer of ore 20 is reduced on a continuous basis, this thin layer is adjustable by varying the horizontal aperture formed by the inlet 18. The following is a further description of one of the processes which could be facilitated by the furnaces 10 and 10A:

The ore feeder 30 is filled with a blend of ore and coal in a ratio close to the stoichiometric ratio of oxygen to carbon in the material. The furnace 10 is pre- heated via the one or more burners 40.

The member 16 is charged with cold material by opening the feed gate 34 to allow the stored ore 32 to slide down to the drum 56 which provides a foot on which the material backs up at it's natural angle of repose until the slope has been "filled" all the way back to the ore feeder 30.

The temperature in the furnace 10 is monitored via thermocouple and an infrared thermometer or any other temperature sensing device 44. The product bed will begin to give off combustible gases as its temperature rises, initially the off-gas will comprise volatiles in the coal followed by CO once reduction commences.

Combustion oxygen will then be introduced into the free-board to allow post- combustion of the gasses (CH ₄ to CO ₂ and H ₂ O, CO to CO ₂ , and H ₂ to H ₂ O). Post combustion energy will cause high temperatures on the freeboard roof and walls which, in turn radiate energy back onto the material being reduced. Wall/roof temperatures of 1250 - 1500 degrees Celsius are envisaged. As the reduction process is endothermic it is envisaged that the material bed 20 will be maintained at circa 1 100 - 1 150 degrees Celsius (at which temperature rapid reduction rates occur).

As maximum reduction is approached, the endothermic effect reduces resulting in an initial slight drop in temperature (possibly associated with commencement of melting) followed by a rise in temperature of the material bed, this temperature deflection point is a primary method of the process control. This temperature profile can be measured with sensors 44, even as the angle of inclination of the member 16 changes.

The discharge drum 56 rotates in the direction of the feed material movement down the reduction member 16, effectively the drum 56 lifts material out from under the foot of the slope thereby undermining the slope which allows fresh material to enter the top of the slope. The rotational speed of the drum 16 is achieved via variable speed drive 66 which receives instructions based on the temperature of the material at the foot of the slope from sensors 44 (the temperature is maintained at slightly above the deflection temperature), alternatively the speed of the rotation may be derived from other sensing equipment, such as gas analysis instruments or it may be set at a fixed speed once stable operating conditions have been established.

The rate of introduction of post-combustion oxygen through vents 42 is controlled via input from the gas analysers 48, the objective being to keep the exhaust gas oxygen component as low as possible, this will minimise excess oxygen which may cause re-oxidation whilst ensuring good post combustion and hence energy efficiency of the process. A flow control valve or damper (not shown) may be provided in the vents 42. It is proposed to cool the material (discharge temperature circa 1 150 degrees Celsius) to approximately between 500 and 750 degrees Celsius before compressing into briquettes 64 (a high temperature it is desirable to compress the reduced material while it is still relatively soft which allows a high relative density, over 5, to be achieved in the briquette). Cooling water may be discharged externally onto the floor of the outlet chamber 58. Varying the cooling water flow to the cooling/discharge drum relative to the measured material discharge temperature will control cooling. Any other suitable cooling method may also be used.

The material bed thickness can be accurately varied by adjusting the position of the ore inlet 18. Bed depths of between 20mm and 50mm are proposed, competing rotary hearth technologies employ bed depths of 40-50mm. Thick bed depths slow the production rate while thin bed depth can lead to insufficient off-gas of CO and CO ₂ (which forms a protective blanket which prevents re-oxidation of the bed material).

Production rates of 100kg/hr/m ² of surface area appear to be the expected norm for rotary hearth based iron reduction processes.

The primary advantages arising as a result of the elegantly simple equipment design are: There are no moving parts within the hot zone of the furnace 10, material movement is accomplished via gravity. The use of light weight materials speeds up construction time and reduces cost (no heavy support steel and large foundations for large refractory weights required). Full post combustion within the free-board ensures maximum use of energy input (competing technologies require a degree of reducing gas in the exhaust to ensure reducing conditions throughout the process (e.g. direct reduced iron kilns and blast furnaces). No preparation of feed materials is required (gas based reduction processes and some rotary hearth technologies require energy intensive and expensive pellet feeds). Extremely low coal consumption is achieved via (a) full combustion and (b) as a result of volatile coal gas initiating and taking part in the process. In addition it is speculated that some of the products of reduction exit the bed as CO ₂ thereby reducing coal consumption to below stoichiometric.

Low feed costs (fine ore and fine thermal coal). Very low capital cost (lowest cost of any technology). Dual hearth heating (top and bottom heating) leads to higher production rates per square meter of plant footprint area compared with competing technology. Ability to add layers of reduction slopes one above the other thereby increasing plant capacity without increasing plant footprint, this will bring greater energy efficiencies and lower capital costs. Simple to control process has distinct advantages over the competition. Not dependant on the electrical power grid. Largest beneficiation "value add" for lowest expenditure. Negligible wear on refractory materials (refractory surfaces do not come into contact with the product). Size scale up is easy to achieve. Modular concept allows for increased plant operational flexibility. It will be appreciated by those skilled in the art that various other embodiments of the invention are possible without departing form the scope of the appended claims. For example, and as set out above, the reduction furnace 10 could be used for other purposes. Further, different inclination adjustment means could be provided for tilting the furnace 10 and/or the member 16. Also, there could also be one or more burners 40 located below the member 16. The amount of burners 40, vents 42, sensors 44 and 46, gas analysers 48, and camera 50 is not limited to the amounts and positions shown in the accompanying drawings.