DESCRIPTION

The present invention relates to a reduction furnace method and apparatus. Reduction furnaces are used for the reduction of metal oxides to extract metals.

The oxides are first heated at reduced pressures so that the metals vaporize, followed by condensation of the metals on a cool surface. The metals can then be recovered from the cool surface. Various types of metals can be produced by reduction furnaces, including the alkali metals, alkaline earth metals such as magnesium, and other metals of relatively high volatility.

Silicon is commonly used as a reducing agent within such furnaces to cause a silico-thermic reaction for extracting metal vapours. The silico-thermic reaction typically takes place at high temperatures of 800 - 1600°C. Examples of these types of devices are disclosed in US 4,264,778, and US 4,238,223. Various processes using silico-thermic reactions are known in the art, including the Pidgeon Process, the Bolzano Process, & the Magnatherm Process.

The overall metal extraction process comprises several steps:

1 . Preparation of the block feed material for the furnace.

2. Processing in the furnace, wherein the block feed material is heated and cooked to draw metal out of the blocks and into a condenser using a

vacuum.

3. Emptying & recharging the furnace.

4. Processing the recovered metal in the refinery.

5. Cooling & disposing of the furnace residues.

The early existing art Bolzano furnaces for Magnesium recovery had a cycle time of approx. 23 - 24 hours, and produced 2 tonnes of metal per cycle per furnace per day. In these furnaces, the details of the steps 1 to 5 above were as follows: 1 . Preparation of the block feed material for the furnace:

a) Dolomite is crushed and then calcined to a low LOI (loss on ignition) to drive out CO2 (carbon dioxide). The calcined material is referred to as Dolime.

b) The Dolime is then sintered at 1200°C.

c) The Dolime is cooled & then pulverized or milled into a powder of a

predetermined size.

d) Ferro Silicon 75% (FeSi 75) is also milled to predetermined size, and is mixed with the Dolime powder, and pressed into a block.

e) The block is dried for use in the furnace.

f) The dried block is stacked into a conductor cage, the conductor cage

having heating elements for electrically heating the blocks. The heating elements are typically in the form of a plurality of rings, plurality of helical coils, or circular disk plates.

g) The conductor cage is placed and sealed in the furnace, in preparation for heating

2. Processing in the furnace wherein metal is drawn out of the blocks and into a condenser:

a) The blocks in the furnace are pre-heated up to the reaction temperature as soon as possible, which may take several hours.

b) Once hot, the blocks, which have suffered re-carbonation during and after their manufacturing, have to undergo a period of polish calcining to precondition them. This polish calcining is intended to polish off the calcining that was carried out on the dolomite, by breaking down any carbonate compounds that may have reformed, then driving out the CO2 reabsorbed by the blocks following their manufacture. Full calcination usually occurs at a temperature of 900°C, but the calcination is a two stage process. Carbonates (CaCO3) undergo phase transition from above 400°C to 750°C; and the remaining calcites have usually completed calcination at 900°C & the CO2 removed. Since the silico-thermic reaction begins at 700°C, metal vapour is available to be recovered. The silico- thermic reaction only fully occurs when a vacuum is applied to the furnace to extract the metal vapour, but the reaction temperature is present at 700°C and losing the silicon in the reductant (FeSi 75) to oxidation with air in the furnace before the full reaction can be initiated has to be avoided. As metal is available for recovery during this entire function, and the destruction of the reductant has to be avoided, vacuum has to be applied so the metal can be recovered into a condenser. This brings about the problems of controlling other phase transitions that can occur in the reaction and the contamination by the products of the calcining process with the metal vapour, as both are being processed at the same

temperatures. As this is to be avoided as much as possible, most of the polish calcining is conducted at lower temperatures until temperatures have to be elevated to drive out the last of the C02. It is desirable to keep the reaction as slow as possible for as long as possible to limit the production of metal vapour, the side reactions and the contamination effects until optimum conditioning of the blocks is achieved and the temperature of the furnace can be raised to the full reaction temperature. This takes many hours to complete. The polish calcining step can take 5 - 6 hours.

c) Once the polish calcining has completed, the condenser is changed

(approximately half the metal will have been recovered at this stage). d) The furnace is raised to the full operating temperature of 1 150°C, or more if required, and the remaining metal is drawn off in the next 2½ -3 hours, completing the processing stage. ptying the furnace.

a) The conductor cage and residues from the reactions are removed from the furnace and allowed to cool.

b) The furnace is re-charged and returned to production.

The conductor cage, once cooled, is refurbished and recharged for

next use. ocessing the recovered metal in the refinery.

a) The magnesium crowns are removed from the condenser

b) The magnesium crowns are processed for onward delivery 5. Cooling and disposing of the furnace residues. Usually no attempt is made to value add to the residues. They are typically:

a) Discarded at cost to process, or

b) Used or sold as a low grade fertiliser.

The residues are essentially a Belite cement or a pozzolanic silica, but also contain up to 35% un-reacted FeSi. FeSi is one of the most expensive ingredients in the process. These residues are unsuitable for direct cement use because of their chemistry, but can be sold for use in decorative stuccos and plasters. No attempt to recover the FeSi is usually made.

The Pidgeon process differs from the Bolzano process, in that the Pidgeon process has no conductor cage arrangement for heating and containing the blocks, since the heating of the furnaces is external. This creates material handling issues as well as energy loss issues. The Magnatherm process furnace differs even more from the Bolzano process, and is an electric arc furnace with a batch condenser system.

The Inventor has identified various problems with the above known furnace processes. In particular:

1 . Hot Dolime is cooled for making the blocks. This wastes energy.

2. The Dolime when cold starts to re-carbonate, adding time back into the cycle for the polish calcining that then has to take place in the furnace.

3. The blocks are manufactured cold and have to be heated up in the furnace, which adds time to the cycle, and requires more energy.

4. The heating in the furnace for the recovery of 1 tonne of metal is around 3 hrs in perfect conditions. Due to the pre-heating and pre-conditioning that has to occur in the cycle, the 1 st tonne of metal can take up to 8 hrs to be recovered.

5. The products in the residues are valuable and should be better recovered.

6. Usually the conductor cage and the residues are removed hot from the furnace and cooled separately over a long period, so they can be re-used.

However this wastes a lot of energy.

It is an aim of the present invention to provide a method of operating reduction furnaces, which overcomes one or more of the above problems. Specifically, the present invention aims to provide a more efficient & cost effective method of extracting metals of relatively high volatility from compounds containing oxides of the metals, compared to known furnace devices of the type suitable for silico-thermic reduction. Shortening the processing time in the furnaces would save electrical heating costs. For the extraction of Magnesium using the Bolzano Process, the shortest theoretical processing time is 2½ -3 hours, as that is the time it takes to recover half of the metal when the conditions in the furnace substantially meet the best theoretical conditions for the reaction. The best practice processing time for the reaction should thus be between 3 - 6 hours. The prior art furnaces have processing cycles that are treated as a single operation for the extraction for metal vapour, however, this is not actually the case, and breaking the processing cycle down helps identify where processing time saving may be made. To help reduce the processing time towards the shortest theoretical processing time, and save energy in electric heating costs, according to a first aspect of the invention there is provided a method of extracting metal from metal oxides in a reduction furnace. The method comprises calcining the metal oxide to reduce loss on ignition, forming into blocks a mixture of the calcined metal oxide and a reductant (and optionally binder materials and/or slag conditioning materials) and placing the blocks into a reduction furnace for extracting metal from the blocks. Then the blocks are maintained in a controlled atmosphere that is substantially free of carbon dioxide during the forming of the blocks and the placing of the blocks into the furnace, to minimise re-absorption of carbon dioxide in the block once it has been formed.

According to a second aspect of the invention, there is provided an apparatus for extracting metal from metal oxides, the apparatus comprising a calciner for calcining the metal oxide to reduce loss on ignition, a block press for forming into blocks a mixture of the calcined metal oxide and a reductant, and a reduction furnace for extracting metal from the blocks, wherein the apparatus further comprises a storage facility where blocks are stored in a controlled atmosphere that is substantially free of carbon dioxide, prior to placing the blocks into the reduction furnace. The storage facility may for example be a storage bin. Since the blocks are maintained in a controlled atmosphere that is substantially free of carbon dioxide prior to being placed in the furnace, the re-carbonation of the calcined metal oxide does not happen, and so polish calcining does not need to be done in the furnace during the processing time, and so the processing time can be substantially shortened and adjusted for maximum metal vapour extraction. Therefore, less furnaces are needed for any given rate of production, and surplus furnaces that would normally be available in a traditional plant can be re-directed and used to parallel and sequence other activities in the process thus increasing the versatility and flexibility of the process. Also, since the polish calcining step does not need to be carried out, electricity use is greatly reduced, thereby reducing operating costs.

Preferably, the blocks are maintained in the controlled atmosphere for substantially all of the time between the forming of the blocks and the placing of the blocks into the furnace. The calcined metal oxide may also be maintained in the controlled atmosphere for substantially all of the time between calcining of the metal oxide and the forming of the blocks.

The blocks may be arranged in a conductor cage and the conductor cage with the blocks may be placed into the furnace using an automated conductor cage loading machine. The automated conductor cage loading machine may comprise an enclosed cavity filled with the controlled atmosphere that is substantially free of carbon dioxide. The furnace may also be filled with the controlled atmosphere, so that the blocks do not begin to re-carbonise once they are placed in the furnace. The controlled atmosphere is preferably also free of oxygen, so that oxygen does not begin to react with the reductant of the blocks and degrade the reductant. Accordingly, the controlled atmosphere may be an inert gas, for example Argon.

Argon in particular has been found to be a particularly suitable gas for preserving the blocks prior to placing them into the furnace. Argon in particular has also been found to be a particularly suitable gas for controlling aspects of the phase transitions that occur in the reaction as the blocks undergo pre-heating to the full reaction temperature once in the furnace. The use of Argon in this way can also increase yield levels of recovered metal vapour. Alternatively, other types of inert gas such as Nitrogen could be used. A discussion of the use of Argon during silico-thermic reduction is given in the paper "SILICOTHERMIC REDUCTION OF DOLOMITE ORE UNDER INERT ATMOSPHERE", of I.M. Morsi; K.A. El Barawy; M.B. Morsi; S.R. Abdel-Gawad, Canadian Metallurgical Quarterly, Vol 41 , No 1 pp 15-28, 2002. Furthermore, the blocks may be maintained at a temperature of greater than

100°C between the forming of the blocks and the placing of the blocks into the furnace. Due to the high temperatures required for calcination of the metal oxide, the blocks are hot once they have been formed, and maintaining them hot until they are placed into the furnace means that they do not have to be re-heated once they enter the furnace, and so time and energy is saved in the furnace.

In the case of Dolomite, the resulting Dolime from the calcination process may be at a temperature of 1200°C, and so this heat can be used to create the blocks at a high temperature. The heat of the blocks will also prevent re-carbonation of the blocks to help remove any need for polish calcining in the furnace. Preferably, the blocks are maintained at a temperature of greater than 300°C between the forming of the blocks and the placing of the blocks into the furnace.

The temperature of the mixture of the calcined metal oxide and the reductant may need to be below a certain level in order for blocks to be pressed from the mixture, for example the mixture may need to be no hotter than 500°C in order for the particles to adhere to one another well enough for blocks to be formed.

Accordingly, the calcined metal oxide may be cooled by a coolant prior to its pressing into blocks with the reductant, the coolant harvesting heat from the calcined metal oxide. This harvested heat can be used in several applications, for example preheating of the initial metal oxide to reduce its residency time in the calciner; furnace heating, electric power generation, or internal heating of buildings. Due to the hot feeding of the blocks into the furnace and the use of the controlled atmosphere, the optimum conditions are achieved more quickly for an efficient reaction to take place in the furnace. Therefore, the processing time in the furnace is shortened and becomes closer to the minimum theoretical reaction time. The reduction furnace may be a first reduction furnace of a plurality of reduction furnaces, and the blocks may be a first set of blocks of a plurality of sets of blocks. The reduction furnaces may be operated out of synchronisation with one another, so that each respective furnace has a set of the blocks placed within it at a respective time. Preferably, the respective times are at regular time intervals to one another.

Then, the furnaces are all equally out of synchronisation with one another.

Therefore, a JIT (just-in-time) process for block preparation and introduction into the furnace becomes possible, whereby heat is conserved from the calcined metal oxide when it exits the calciner, which then undergoes heat harvesting in an inert atmosphere, which partially cools the calcined metal oxide to a temperature suitable for hot block manufacture. In the case of Dolomite, the blocks are prepared from hot Dolime and cold Reductant (such as Ferro Silicon FeSi) in the same inert atmosphere, and kept in the same inert atmosphere, but as one of the ingredients is colder than the other, the resulting combination will be at a slightly lower temperature for immediate transfer to the next available furnace. The blocks are sealed in the next available furnace, which is filled with the same inert atmosphere and readied for the metal extraction cycle. In prior art methods of operating furnaces, the furnaces all process blocks at the same time as one another time, with only an hour down time to empty and recharge the furnaces before another processing cycle is started. Removing the preheating, and polish calcining steps according to an embodiment of the invention means that the time to extract the metal is significantly reduced, for example halved, so that only half the furnaces are extracting metal at any one time for the same overall production levels of metal. The time duration for which a furnace performs metal extraction is referred to as the cooking time, and the other half of the furnaces that are not cooking can be used for performing other tasks, such as heating of the blocks and cooling of the residues once cooking has been completed.

The ability to cool the residues down whilst still inside the furnace means that any unreacted reductant is not exposed to oxygen outside of the furnace whilst still hot, preventing the unreacted reductant from oxidising and meaning that it can be recovered. In the case of Ferro Silicon reductant, there may be as much as 35% of the original weight of Ferro Silicon left behind after the cooking time, and so enabling recovery of this Ferro Silicon by allowing the residues to cool inside the furnace rather than exposing them to the outside atmosphere whilst still hot can significantly save on the cost of the process. In the prior art, the residue is typically cooled outside of the furnace to free up the furnace for another processing cycle, and so the unreacted Ferro Silicon reacts with oxygen whilst cooling in the outside atmosphere and is lost.

According to a third aspect of the invention, there is provided a method of operating reduction furnaces that extract metal from material placed in the furnaces, wherein the furnaces heat the material in a heating stage, extract metal from the material in a cooking stage, and cool the material in a cooling stage. The method comprises harvesting heat from one or more furnaces in the cooling stage and imparting the heat to one or more furnaces in the heating stage. The heat that is harvested from the furnaces in the cooling stage is used to heat the furnaces in the heating stage, and so the additional energy required to heat up the furnaces in the heating stage is greatly reduced compared to in the prior art, saving heating costs.

According to a fourth aspect of the invention, there is provided an apparatus comprising a plurality of reduction furnaces for extracting metal from material placed in the furnaces, the material comprising metal oxide. The furnaces are configured to heat the material in a heating stage, extract metal from the material in a cooking stage, and cool the material in a cooling stage. The apparatus comprises a heat transfer apparatus for harvesting heat from one or more furnaces in the cooling stage and imparting the heat to one or more furnaces in the heating stage.

The heat transfer apparatus may be any known apparatus for transferring heat from one location to another location, for example via gases or liquids, or hybrid devices. In one example a long pipe could be coiled around both a furnace to be cooled and a furnace to be heated, and liquid circulated through the pipe to transfer the heat. In another example a long duct could connect both a furnace to be cooled and a furnace to be heated, and gases circulated through the duct to transfer the heat. Some intermediate heat storage could also be implemented, for example by pooling hot fluid from the furnace that is being cooled in a storage container until the fluid is required to be pumped to the furnace that is being heated.

The furnaces of the third and fourth aspects of the invention may be the furnaces as the furnaces of the first and second aspects of the invention.

As well as allowing heat recovery, cooling the residues inside of the furnace whilst the furnace is still sealed assures an oxygen free environment to preserve the unreacted reductant until it is cool enough to be chemically stable and to be

recovered. Once cooling has completed the residues (pozzolanic materials) may be cool to handle. By being able to re-claim reductant, a valuable end product is added to the process for sale or for re-cycling in the process. Accordingly, the process adds value to waste or by-products, helps negate waste disposal costs, increases sustainability, improves statutory compliances, and can add substantial revenue to the overall process.

The cooling stage may comprise passing a first gas though at least one furnace in the cooling stage to heat the first gas and thereby harvest the heat from the at least one furnace in the cooling stage. Accordingly, inlet and outlet ports may be provided in each furnace for in-letting and out-letting the first gas from the furnace. Preferably the first gas is free of oxygen to preserve the unreacted reductant until cooling has completed. For example, the first gas may be carbon dioxide. In one embodiment, to further increase the efficiency of the process, the first gas is waste carbon dioxide that is collected from the calciner during the calcination process.

The heating stage may comprise passing a second gas though at least one furnace in the heating stage, the second gas having a higher temperature than the at least one furnace in the heating stage to impart heat to the at least one furnace in the heating stage. Accordingly, inlet and outlet ports may be provided in each furnace for in-letting and out-letting the second gas from the furnace. The inlet and outlet ports may be the same inlet and outlet ports as are used for passing the first gas in the cooling stage. The first gas may be the same gas as the second gas, for example the first and second gas may be Argon, so that the gas can be passed directly from a furnace that is being cooled to a furnace that is being heated. Alternatively, the first gas may be a different gas to the second gas, and the heat may be passed from the first gas to the second gas via a heat exchanger. This enables carbon dioxide to be used for the first gas; carbon dioxide cannot be used for the second gas since then re-carbonisation of the blocks would occur.

The second gas may provide the controlled atmosphere in the furnace being heated, and so the second gas should also be free of oxygen to prevent reactions with the reductant occurring before the furnace has been heated.

During the heating of the furnace, both the metal oxide and the reductant will sharply increase in their capacity to react before the cooking stage commences. Due to the nature of the Silico-thermic reaction in the case of Ferro Silicon reductant, the reaction is substantially dormant until a vacuum is applied in the cooking stage to draw out metal vapour into a condenser.

Advantageously, the reduction furnaces may be operated out of

synchronisation with one another such that at least one of the furnaces is in the heating stage whilst at least another one of the furnaces is in the cooling stage, and wherein the heat is harvested from one of the furnaces in the cooling stage and immediately imparted to one of the furnaces in the heating stage. Then, there is no need for storage of heat between the cooling and heating stages, increasing efficiency.

The heating stage may comprise a plurality of sub-stages that are ranked from lower temperature intervals to higher temperature intervals, each furnace moving from a lowest ranked one of the heating sub-stages to a highest ranked one of the heating sub-stages during its heating. Furthermore, the cooling stage may comprise a plurality of sub-stages that are ranked from lower temperature intervals to higher temperature intervals, each furnace moving from a highest ranked one of the cooling sub-stages to a lowest ranked one of the cooling sub-stages during its cooling. To help assure efficient heat transfer from the furnaces being cooled to the furnaces being heated, heat is harvested from furnaces in cooling sub-stages corresponding to higher temperature intervals and imparted to furnaces in heating sub-stages corresponding to relatively lower temperature intervals. It is recognised that furnaces in the cooling stage will not yield heat at a sufficiently high temperature to efficiently heat the furnaces in the heating stage up to the final temperature need for the cooking stage. Accordingly, the furnaces in the lowest ranked heating sub-stage may be heated by heat harvested from other furnaces, and furnaces in the highest ranked heating sub-stage may be heated by electrical heating. In particular, once the temperature of a furnace in the heating stage matches the temperature of the harvested heat from a furnace in the highest ranked one of the cooling sub-stages, the furnace in the heating stage may switch to electrical heating to achieve the required temperature for cooking.

Since the furnaces in the cooling stage may be cooled to below 100°C, or even room temperature, and the furnaces in even the lowest ranked heating sub-stage may already be above 100°C if the blocks are fed into the furnaces hot, the furnaces in the lower ranking cooling sub-stages may be used to harvest heat for other purposes such as electrical power generation or utility heating of rooms.

The cooling sub-stages may for example comprise a highest ranking sub-stage for recovering high grade (high temperature) heat, and middle ranking sub-stage for recovering middle grade (middle temperature) heat, and a lowest ranking sub-stage for recovering low grade (low temperature) heat. The high grade heat may be recycled to the furnaces in the heating stage, the medium grade heat could be used for electricity power generation, and the lower grade heat could be used for other process needs and utilities.

The furnaces in the heating stage may be transitioned from lower ranking heating sub-stages to higher ranking heating sub-stages at substantially the same time as furnaces in the cooling stage are transitioned from higher ranking cooling sub- stages to lower ranking cooling sub-stages, so that a continuous cycle of heating and cooling of furnaces may be maintained. Preferably the transitions are at regular time intervals to one another, so maintain a constant input rate of blocks and a constant output rate of metal, enabling just-in-time processing to be effectively implemented. The cooking stage may comprise a plurality of sub-stages, and the furnaces may transition between the cooking sub-stages at the same times as the transitions between the heating sub-stages and the cooling sub-stages.

These regular transitions mean that a consistent heat profile is recovered from the furnaces in the cooling stage so that the different heat levels recovered can be easily managed and allocated back into the production cycle. Each transition may comprise moving the furnace from a station associated with the current sub-stage of the furnace to a station associated with the next sub- stage of the furnace. Accordingly, furnaces may be moved around in a carousel arrangement to incrementally step through the heating, cooking, and cooling sub- stages.

Each transition may comprise uncoupling a hood associated with the current sub-stage of the furnace from the furnace, and coupling a hood associated with the next sub-stage of the furnace to the furnace, each hood having manifolds for connecting to ports of the furnace when the hood is coupled to the furnace.

Accordingly, each station may have a hood configured to perform the required operations on the furnace at that station. Alternatively, the hoods may be moved around instead of the furnaces, or a combination of moving furnaces and moving hoods could be implemented. Or, the hoods may stay attached to the furnaces and the manifolds may be moved in the fashion described for the hoods.

The transitions may be achieved with the furnaces in fixed positions and the systems for the different functions and activities may be governed by a computerised controller, with carriers for unloading and charging of the furnaces after cooling is completed and prior to the subsequent heating stage.

Although, to achieve efficient paralleling of the activities and functions needed to be performed alongside the cooking stage, it is desirable if the furnaces have the availability and capacity to move between the stations on production line(s). Then furnaces could be emptied and recharged off the production line(s) and be returned to the production lines for the heating, cooking, and cooling stages.

For avoidance of any doubt, it is noted that the temperature of a furnace is considered to be the temperature inside of the furnace, or more specifically the temperature of the materials inside of the furnace.

The techniques of hot feeding the blocks into the furnace and recovering heat from the furnaces being cooled are expected to result in large energy savings since in a 24 furnace plant only 50% of the furnaces on the production line require electricity at any one time to produce the same amount of metal as the prior art.

The time interval between each transition may be set by dividing the total number of furnaces operating on the production line by the total time for each furnace to go through its cycle. For example, if there are 24 furnaces and each furnace goes through the cycle in 12 hours, then the time interval between transitions can be as little as 30 minutes. Similarly, if there are 12 furnaces and each furnace goes through the cycle in 6 hours, then the time interval between transitions can also be as little as 30 minutes.

For a given number of furnaces the present invention may substantially double the output compared to prior art Bolzano furnaces, because the time when the furnaces are under electrical heating may be substantially halved. The activities in the reaction that are not part of the cooking stage, where metal is produced under electric heating, may be allocated to furnaces that are not under electrical heating, and may be paralleled and synchronized to each other to achieve the production advantage. To achieve these advantages, changes are made in the preparations stages for the furnace feed blocks. Power use is drastically reduced by the number of furnaces in actual production and altering the process to become heavily dependant on recovered energy.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Fig. 1 shows a schematic block diagram of a material preparation process according to a first embodiment of the invention;

Fig. 2 shows a schematic diagram comparing a prior art processing method to a processing method according to the first embodiment wherein production activities are performed in parallel to one another;

Fig. 3 shows a schematic diagram of the processing method of the first embodiment in more detail;

Fig. 4 shows a schematic block diagram of a configuration of the furnaces in the first embodiment, and an alternate configuration of the furnaces in a second embodiment of the invention; and

Fig. 5 shows a schematic diagram of an apparatus according to the first embodiment.

The first embodiment of the invention will now be described. The first embodiment includes novel block preparation, furnace scheduling, and heat recovery elements, although alternate embodiments may implement only one or two of these elements without implementing the other elements.

The block preparation element of the first embodiment will now be described with reference to Fig. 1 , which shows a block preparation process. As shown, the initial step in the process is to receive Dolomite which has been crushed and milled into a powder having a particle size of below 200 pm. This powdered Dolomite is then heated to a temperature of 300°C by a Dolomite Pre-heater Bed, and then passed to first stage Calix Calciner.

The first stage Calix Calciner heats the Dolomite to a temperature of 750°C, to phase change the CaCO3 to CaO & CO2. And then the Dolomite is further heated up to 900°C in a second stage Calix Calciner to concentrate the CaO levels in the finished Dolime as the CaO is needed in the reaction as a flux. At the same time the CO2 is evaporated out from the Dolomite. The first and second stage Calix Calciners are both heated by a burner, and excess heat from the burner which is not given up to the first stage Calix Calciner is passed to Other use Heat Exchangers, for example power generation or materials preheating or central heating. The C02 which is evaporated out from the second stage calciner is at high temperature, and this heat can be harvested for uses elsewhere in the process.

Specifically, in this embodiment the Dolomite pre-heater bed receives its heat from a heat exchanger, and this heat exchanger receives heat from the C02 which is evaporated out from the calciner tubes; and from part of the exhaust gases from the rising heat used for the sintering of the Dolime.

Once the calcinated Dolomite exits the second stage Calix Calciner it is referred to as Dolime, and the Dolime is then sintered at 1200°C using another burner to glaze and seal the surface of the dolime to slow down the rate of evaporation of the metal vapor during cooking so that the blocks do not explode or break apart and restrict the reaction by hampering the contact between the surface areas of the reactants. The furnace scheduling element of the first embodiment will now be described with reference to Fig. 2, which shows a timing diagram comparing two common prior art processes to the process according to the first embodiment. The time axis is labelled from 0 to 24, corresponding to the hours in any given production day, and the diagram shows what happens during each of the hours in the prior art processes and processes of the first embodiment. For illustratory purposes, only three furnaces of the first embodiment are shown in Fig. 2, although there are a number of possible multiple combinations of furnaces that can occur apart from the practical number herein illustrated of 24 furnaces all operated out of sequence with one another in any day. Firstly looking at the prior art processes, it can be seen from the cycle analysis of the prior art on Fig. 2 that the pre-heating and polish calcining that occur is the majority of the cycle time for the processing of metal vapour and that the processing of metal vapour in optimized conditions is considerably less by comparison. If the preheating and polish calcining are removed from the prior art in-furnace activities then a shorter processing time is possible in the furnace and for furnaces engaged in actual metal production. This is possible because these activities can be performed out of the cooking process and parallel with it. By employment of the paralleling function of the scheduling element of the 1 st embodiment the electricity use is substantially halved for the same number of furnaces in a 24 furnace system and the production time available for metal vapour is substantially doubled.

Further details of the scheduling element will now be described with reference to Fig. 3, which shows the scheduling of all 24 of the furnaces with respect to one another. In addition to the paralleling of the process activities, the furnaces can also be operated out of synchronization with each other. By operating each furnace out of synchronization with the others by a set and consistent time interval a consistent and defined heat profile is available over the production process, which can be

manipulated for harvesting waste heat from the process. By operating each furnace out of synchronization with the others by a set and consistent time interval, more even production flows are achieved. It should be noted that a set and predictable rotation has to be established for the operation of furnaces in the cooking (production) function as well as for the furnaces in the separate rotation required for the functions paralleled to it. The time axis is labelled from 0 to 24, corresponding to the hours in any given production day, and the diagram shows what happens during each of the hours in the day for a 24 furnace system.

Furnaces 1 to 12 are for purposes of illustration designated as furnaces in the cooking (production) function and on power & with a condenser fitted and that are recovering metal. From Fig. 3 it is clear that there are 6 hour cooking (production) periods, and that there are 4 equal 6 hours production periods per day for each of these furnaces dedicated to the cooking function. The paralleling aspect of the scheduling element makes possible the shortened production periods. By then also scheduling these furnaces out-of-synchronization with each other by a set time interval it means that at each time interval 1 furnace goes into the cooking function and another comes out of it. This makes it possible to create the rotation required for the furnaces in the paralleled functions so they can interface with the cooking (production) function.

For the purpose of illustration in Fig. 3, furnaces 13 - 22 illustrate the paralleled activities and how they fit in relation to the cooking function. In Fig. 3, furnace 1 has been chosen to show how this is performed and typically details the cooling function and the harvested heat transfer pathways (furnaces 13 - 17); the empty and fill functions (furnaces 18 - 19): the pre-heating function (furnaces 20 - 22); and then the return of the furnace into the next available cooking function (illustrated at furnace 2).

As illustrated, once furnace 1 finishes cooking it moves to the cooling function, which for illustration purposes is furnace 13. The vertical column illustrated at furnace 13 details the paralleled functions of all the furnaces not directly involved in production activities in turn for a set time interval. It should be noted that each of furnaces 13-22 has its own progression of functions to complete when not in production. In Fig. 3 these are illustrated by the horizontal lines, which also show the time intervals required for each of the different sub-functions. These are then scheduled out-of- synchronization with each other by a set time interval to create the furnace rotation and achieve the interface with the cooking function, which in turn creates the process flow (as illustrated by the vertical column highlighted in the Fig. 3 at furnace 13). It is clear that various production algorithms may be implemented, largely dependent on the time interval. This is the set and consistent time that each furnace has to conduct each function in the process. It can be deduced by dividing the number of producing furnaces into the cycle time, and is a determining factor for making the synchronization & the paralleling work together. For example, in the first embodiment there are 12 producing furnaces and a 6 hour production cycle time. The time interval is 30 minutes. Every 30 minutes a furnace is finishing its production function and has to be moved to a new function station, or undergo a function transition on the production line(s). Fig. 3 also shows how heat can be exchanged between furnaces in cooling and heating stages, in accordance with the heat recovery element of the first embodiment. Fig. 3 details 5 furnaces in the cooling function 'h' & Y; 3 furnaces in the pre-heating function 'w' and 2 furnaces in the empty 'e' and fill T functions. Each furnace is governed by the same time interval as the furnaces in the cooking function. Note that this is where the harvested heat from the furnaces in the cooling function is transferred to the pre-heating furnaces. Note that the highest grade heat from furnace 13 is used in furnace 22 as that furnace will have to be the hottest when it goes back into the cooking function (for purposes of illustration, this is the move from furnace 22 back to furnace 2). Similarly, furnace 14 transfers heat to furnace 21 and furnace 15 transfers heat to furnace 20.

In this fashion the hot blocks, which are already at 300°C when introduced into the furnace at function T, are gradually raised in temperature in stages from the different heat levels available in the furnaces being cooled until a temperature of 800°C is achieved, which is the optimum temperature for the blocks to go into the cooking function. At that point they go back onto electric heating 'p' and are fitted with a condenser and are on vacuum as the temperature in the furnace is very rapidly raised to the reaction temperatures. The reaction temperatures start at 1 150°C, but depending on the composition of the block feed, may need to be raised as high as 1300°C. Note that the hot blocks are introduced into the furnaces at furnace 19. In the same vertical column, furnaces 13 - 15 & furnaces 20 - 22 illustrate the pre-heating function of the blocks by direct and simultaneous heat transfer. Furnaces 16 -17 are further cooling and the harvesting of the remaining medium and low grade heat for other use.

The parallel processing of the furnaces may be realised using various different configurations. A conveyor system to move the furnaces is desirable, but not essential. The detail of this will depend on the configuration of the process and the facilities it will be in. Fig. 4 lists the main functions that have to be satisfied in the production process to achieve metal recovery to the point where it can then be refined and finished. These functions are steps in the process of which functions 1 & 2 relate to the preparation of the blocks prior to introduction into the furnaces; while functions 4 - 6 are functions that are performed in the furnace. Depending on the configuration of the production line(s) these in-furnace functions can represent production activities in a static furnace, or a different station to which the furnace moves to and where a nominated function can be performed. The first embodiment uses a Circuit, or Carousel concept, as shown in the upper part of Fig. 4. In this configuration considerable movement of furnaces is required so that the paralleled functions can be performed in different stations, or locations in the production line(s) and away from the cooking function. The advantage of this is in having smaller, task specific equipment available in the stations to perform the nominated functions. It also allows more flexibility in the lay-out of the production line(s), which may be a consideration in the facility it is in.

The configuration should not be constrained by physical shape as it could be circular, square or rectangular. For example, the lower part of Fig. 4 shows a linear arrangement in a second embodiment where the furnaces only have to shuffle back and forth, or stay in position and be serviced by a moving unloading and loading device. Other irregular shapes are also possible. What needs to be recognized is that some movement of the furnaces is desirable; the rest of the paralleling and

synchronization elements of the scheduling element can be done by sequencing the process through IT means. The paralleling & synchronizing of the scheduling elements in the process is what counts, rather than if and how the furnaces are moved about to enable the paralleling & synchronizing to be achieved. Some form of IT control will be desirable for any production layout that is chosen.

In the illustrated embodiments, a heat exchanger is provided for each furnace in the production line. A gas-to-gas system is recommended for achieving the transfer of the very high temperatures needed. The amount of ducting, piping and auxiliary equipment needed will depend on the amount of movement the furnaces will perform. Less movement, means a bigger system.

A gas circulation pipe is mounted on, or in each furnace during the cooling and heating stages. This is needed to manage the inert gas flows in the furnaces during the cooling and pre-heating stages of the process.

Referring to Fig. 5, the gas circulation pipe is a pipe in the centre of the furnace top shell portion (hood), which reaches down through the centre of the conductor cage to around 500mm from the furnace bottom. The pipe has a diameter of 300mm, although alternate diameters could also be used. Alternatively, the gas circulation pipe could be a pipe running outside the furnace shell with entry and exit points through the lower shell portion at the bottom, and through the top shell portion at the top. In another alternative implementation, a spacer manifold a few hundred mm thick and the diameter of the furnace can be used between the top and lower shells of the furnace, and an external or internal circulation tube fitted as described.

The transfer of heat between the cooling and heating stages will now be described with reference to the schematic diagram of Fig. 5. For clarity, Fig. 5 only shows one furnace in the cooling stage and one furnace in the heating stage, although all 24 furnaces, or furnace positions are present in practice.

In the first and second embodiments, 12 furnaces are dedicated to the cooking function at any 1 time; and as 2 furnaces are in the empty and fill functions; and as there are 2 spare furnaces and furnace spaces available in the production line(s); there are 8 furnaces available to the heating and cooling functions over the entire system.

Fig. 5 relates to a static furnace system configuration and how a possible arrangement could typically be applied for connecting all the furnace spaces and then operating all the furnaces in the production line(s) as required in the methods described in the embodiments. It should be noted that the arrangement disclosed can be applied as a whole, or in part as several different sub-systems or combinations of sub-systems dependent on the amount of furnace movement that is subsequently introduced into the production line(s).

In Fig. 5, the cooling function circulates a 1 st gas, which in the example is designated as CO2 that is captured from the Calix Calciner and stored, then delivered to a reticulation main for distribution into the production line(s). At any one time there will be 5 furnaces engaged in the cooling function and circulating the 1 st gas. This means that 5 furnaces will be doing what furnace 1 of 24 is doing in Fig. 5 at any time, but they will be separated by 1 time interval. This means that every furnace in this function has 5 time intervals (sub-stages) to divest its heat. In this example that is 2.5 hours for each furnace. Consequently, with every time interval, 1 furnace will enter the cooling function and 1 furnace will move out of the cooling function (stage). The 1 st gas continually circulates in the furnace for the entire 5 time intervals and continually harvests heat from the contents of the furnace and imparts it to a dedicated heat exchanger attached to each individual furnace position.

The gas pathway in the cooling function can be seen by following the arrows in the figure. The 1 st gas system is a closed system that circulates only through the furnace and its dedicated heat exchanger.

The heating function is illustrated in Fig. 5 by furnace 2 of 24. At any one time there will be 3 furnaces engaged in the heating function and that will be receiving heat directly and simultaneously from 3 of the 5 furnaces in the cooling function. The time interval each furnace spends in each one of the three heating function sub-stages is 30 minutes, the same time as the time each furnace spends in each cooling function sub-stage (30 minutes, 2.5hr to undergo all 5 sub-stages). A 2nd gas distributes the heat from the heat exchanger to the furnaces being heated. The gas pathway in the heating function can be seen by following the arrows in the figure.

Portions A and B in the figure are distribution manifolds that consist of 5 ducts or pipes that transfer the 2nd gas to any desired furnace. This is possible because there are only 5 furnaces in the cooling function at any one time and each of them is able to select 1 of the 5 ducts or pipes in portion B. The selected duct or pipe can then select any of the other furnaces to circulate the 2nd gas into. The 2nd gas then circulates out of the furnace to portion A where 1 of the 5 ducts or pipes in that portion can be selected to return the gas to the heat exchanger.

The importance of IT (computerized) controls will now be discussed. The target temperature for the next hot furnace to go into the cooking stage is 800°C. The blocks enter the furnace at 300°C. The hottest furnace coming off cooking will impart its heat to the next furnace to go into cooking to bring its temperature up to 800°C. Once that temperature is reached, or the system achieves its heat balance, IT control will reallocate the remaining degraded heat potential to the next furnace in the heating function. Once the heat balance in that furnace is achieved with the available heat in the system, the IT control will switch the heat to the lowest temperature furnace until the heat balance is similarly achieved.

Then the IT control will close the furnace heat exchanger and 2nd gas system and reallocate the C02 flow to the other use heat exchangers. First to the power generation heat exchanger, then when the residual heat has dropped below the threshold temperature (250°C) for that heat exchanger, it will switch to the utilities heat exchanger to complete the cooling of the furnace contents. The gas from either of these lower grade heat exchangers is returned to the furnace via a duct or pipe in portion A.

Various other embodiments falling within the scope of the appended claims will also be apparent to those skilled in the art.