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METHOD AND APPARATUS TO REDUCE METALLIFEROUS MATERIAL TO A
REDUCTION PRODUCT
DESCRIPTION OF THE INVENTION The present invention relates to a method for reducing metalliferous material to a reduction product. The invention also relates to an apparatus for reducing metalliferous material to a reduction product. The reduction of metalliferous materials such as metal-oxygen compounds, metal oxides such as, for example, iron oxides has been carried out in large-scale reduction furnaces. For the reduction of iron-oxygen compounds, the blast furnace has been the workhorse for the production of high carbon raw iron from metalliferous material such as iron-oxygen or iron ore compounds for more than a century. The primary reducer and a chemical energy source in these blast furnaces has been coke. The coke is produced when baking coal in the absence of oxygen in order to separate volatile hydrocarbons and provide the coke with the critical properties for a stable operation in a blast furnace. Coke production is problematic from an environmental perspective since many of the volatile hydrocarbons are hazardous.
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Also not all types of coal are suitable for the manufacture of coke. In addition, the demand for secondary coke products has decreased. Therefore, the main focus of recent developments has been the decrease in coke consumption and the overall fuel consumption of blast furnaces. One of these developments is the injection of coal directly into the blast furnace. In addition, new technologies have been developed that do not take into account the blast furnace process, such as the direct reduction of iron ore. Direct reduction involves the production of iron by reduction of iron ore with a reducing agent which can be a solid reducing agent or a gaseous reducing agent at temperatures below the iron melting point. Solid reducing agents can be coal of any size, instead of coke. Examples of gaseous reducing agents are natural gas, hydrogen and carbon monoxide (CO). The direct reduction of iron ore can generate a final reduction product in the form of solid iron reduced directly or, in combination with a melting device, a liquid product. The final reduction product of a direct reduction process can be discharged into a second reactor for optional further melting and refining or can be cooled and stored
- - for later use. Currently, the dust and mud from integrated steel works is recycled as untreated material in the ore preparation stage. These waste materials, often referred to as "fines" may contain iron-containing compounds such as iron oxides. However, due to the content of metals such as zinc or zinc compounds in these fines, the accumulation of these elements and the limitations of the amount of these metals to be loaded in a blast furnace, often these waste materials must be recycled. otherwise discarded or resulting in additional costs or burden to the environment. From WO2005 / 116273 a method is known for reducing iron ore based on the supply of solid carbonaceous material such as coal and a gas containing oxygen in a fluidized bed in a first vessel and generation of heat, conversion of carbon in coal and discharge a hot gas discharge stream containing CO formed by partially oxidizing the coal. The CO, hard coal and solid particles are unavoidable remnants (such as ash) then placed in a second container where at least partially metalliferous material is reduced. The solid reduction product containing ore fines from
- - iron reduced at least partially can be processed additionally as required, for example, in a fluidized bed during a second reduction stage to obtain a greater degree of reduction. As a result of the high process temperatures of at least 900 ° C, iron ore fines have a tendency to form accretions and agglomerates. This adherent behavior is controlled by forming excess amounts of coal in the first container. An additional disadvantage is the development of large volumes of complex and dangerous hydrocarbons. The condensation of these hydrocarbons should be avoided, which requires separation or post-combustion of the gas discharges and at the same time the reoxidation of the metal should be avoided. In addition, due to the high operating temperature and the consequent heat losses, the energy efficiency of the generally poor direct reduction procedures results in a high carbon consumption rate. High operating temperatures also result in the formation of significant amounts of harmful nitrogen-oxygen compounds (NOx gases) or, in a reducing atmosphere, ammonia-type compounds. In addition, direct reduction technologies based on the direct use of coal need to take into account the higher sulfur concentrations
- - due to the presence of sulfur in the coal. The document of E.U.A. 3,788,835 describes an iron ore reduction process wherein the main portion of the reduction is carried out with a gaseous reductant, for example methane which dissociates into hydrogen and CO at high temperature. The reduction of the iron ore by the gaseous reductant is carried out until a metallization of about 85 to 90% is obtained. In the area where the largest portion of the metallization is obtained, the carbon is deposited on the ore while the ore is reduced. After having reached the degree of metallization of approximately 85 to 90%, the carbon deposited subsequently is allowed to interact with any remaining oxide in a separate inert stage which results in an increase of metallization of between 0.5 and 2.5%. EP 1 568 793 describes a method for reducing metal-oxygen compounds in a reduction reaction in which carbon is used to reduce metal-oxygen compounds wherein a metal acts as a catalyst for the reduction reaction. EP 1 568 793 discloses types of reactors for carrying out the method involving extruder-type screws as a means of transportation for solid reagents. An object of the invention is to provide a
- - method and apparatus for direct reduction of metalliferous material using solid carbon as a reducer. An object of the invention is also to provide a method and apparatus for reducing metal-oxygen compounds which can operate at relatively low temperatures to increase energy efficiency and / or produce lower volumes of dangerous gas discharges such as, for example, hydrocarbons and / or N0X gases. It is also an object of the invention to provide a method and apparatus for reducing metal-oxygen compounds which can result in increased carbon efficiency per unit weight of reduced metal. To obtain one or more of these objectives a method of reducing metalliferous material to a reduction product is provided, the method comprising the steps of: providing a gaseous phase comprising gaseous CO when gasifying a carbon containing compound using a gas flow which contains oxygen; providing the metalliferous metal in a reaction chamber of a fluidized bed reactor; provide gaseous CO in the reaction chamber of the fluidized bed reactor and convert the CO
- - gaseous in solid carbon and gaseous carbon dioxide, causing the solid carbon to precipitate on the metalliferous material and / or on the reduction product; reducing at least partially the metalliferous material by the solid carbon to the reduction product whereby the metalliferous material and / or the reduction product is used as a promoter of the conversion of the gaseous CO into solid carbon and gaseous carbon dioxide; discharging a final reduction product from the reaction chamber, wherein the final reduction product is further reduced in a final stage reactor to a higher degree of metallization by a substantially solid-solid reaction between the solid carbon and the reduced portion of incomplete way of the reduction product. Solid carbon is referred to as Boudouard carbon and typically has a crystal structure of graphite with a very high ratio of surface to volume. For purposes of clarity, it is noted that any other form of carbonaceous compound such as carbon or charcoal is not considered solid carbon in the context of this description, although the carbon content of these solid compounds is very high. CO can be substantially pure CO, but it can also be part of a gas mixture comprising CO. The carbon
- - solid is generated by dissociation of carbon monoxide by the Boudouard reaction: 2C0 - C + C02 This reaction, which is an equilibrium reaction, it moves to the right under correct conditions such as temperature and pressure so that carbon can be formed. Furthermore, it has been found that the metalliferous material or the reaction product also promotes the formation of the solid carbon by the Boudouard reaction. It is emphasized that the reduction product in the context of this invention is not a product with a defined degree of reduction, but it is used to express any reduction state between the reduction state of the metalliferous material, which has a degree of reduction of zero and the final reduction product, which has a desired degree of reduction. This means that during the process according to the invention, reduction products of different degree of reduction will coexist. The degree of reduction of the final reduction product is therefore the average degree of reduction of the various fractions of reduction product that constitute the final reduction product. The degree of metallization of a reduction product in the case of reduction of iron ore (as a non-limiting example) as the initial metalliferous material is defined as the
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ratio between the number of iron atoms in carbide-iron and metallic iron with respect to the total number of iron atoms in the reduction product. The ratio between metallic iron and iron carbide depends on the process conditions in the reaction chamber. It is considered that the reduction of the metalliferous material may involve the existence of a meta-stable carbide. Solid carbon or Boudouard carbon can react with the metalliferous material resulting in a meta-stable carbide, carbide which eventually disintegrates in the metal of metalliferous material and carbon dioxide. Thus, in the context of this invention, the solid carbon includes Boudouard carbon and meta-stable metal carbide. This procedure is represented schematically and is simplified by the following reactions: MeO + 2CO - »MeC + Co2 MeC? Me + C As regards the selection of the appropriate conditions in the reaction chamber, it is considered within the abilities of a person skilled in the art to select these appropriate conditions. It is known that small amounts of hydrogen promote the condition of solid carbon and carbon dioxide from CO by the Boudouard reaction. In case of using CO
- - pure, therefore small amounts of hydrogen must be added to the CO. In the invention typically more than 50%, preferably more than 70%, more preferably more than 80%, even more preferably more than 90% of the oxygen of the metal-oxygen compounds is attached to the solid carbon deposited after of the final reduction in the final stage reactor. If the gaseous mixture comprising CO is produced, for example, by gasifying coal, the gas mixture may also comprise hydrogen. Preferably, the amount of hydrogen is less than 40% by volume, preferably less than 30% by volume, in the case where technically pure oxygen is used as the flow of oxygen-containing gas in the gasifier and preferably lower at 8% by volume, more preferably less than 6% by volume in case air is used as the gas flow containing oxygen in the gasifier. Hydrogen does not play a significant role in the reduction of metal-oxygen compounds due to the operating conditions chosen. Preferably, the complete process of gasification, reduction and final reduction is carried out at a super-atmospheric pressure. The inventors found that an overpressure of at least 3 bar (g) and preferably about 5 bar (g) is desirable. Due to the
- - loss of pressure on the process, the gasifier must be operated at a pressure of 8 bar (g) to ensure an overpressure of 5 bar (g) in the FB. This allows smaller reactor vessels to be used and may have a beneficial effect on the process conditions in the vessels. It is noted that it is also possible to operate only the gasification and reduction at a super-atmospheric pressure and the final reduction at a much lower pressure, preferably at a subatmospheric pressure but this results in a significantly larger final stage reactor and therefore higher costs of both capital and operation. It should be noted that in the method according to the invention it is essential that the carbon, which is formed from gaseous CO in the reaction chamber, must be carried into the reaction chamber in gaseous form and converted to solid carbon in the reaction chamber. reaction chamber by the reaction of Boudouard. Therefore, the invention can be characterized by the absence of any addition of carbon in solid form to the reaction chamber unless the solid carbon has passed through the gaseous state as a carbon oxide and has precipitated into the reaction chamber , preferably on the metalliferous material or the reaction product formed by the reduction of the metalliferous material, optionally through a carbide form
- - of the metal of the metalliferous material or on carbon precipitated beforehand, by the reaction of Boudouard. It is noted that during the start of the reaction, there may still be no reduction product present. This will only be present after a certain reduction of the metalliferous material has been carried out. The prereduced reduction product can also be added to stimulate a faster start of the procedure. The formation of solid carbon from carbon monoxide is an exothermic reaction under the conditions in the reaction chamber. The energy which is released by that exothermic reaction can advantageously be applied to the reduction reaction in the reaction chamber of the metalliferous material by the solid carbon to reduce a reduction product. The use of a fluidized bed is fundamental due to the high thermal and mass transfer coefficients that can be obtained there, due to the high proportion of surface area to volume of the particles. Since, in the method according to the invention, the reagents are placed very close to each other, and are very reactive and the formation of one of the reactants, i.e., solid carbon is exothermic, the conditions in the fluidized bed are optimal for the reduction of the particle of metalliferous material. Is
- - evident that the metalliferous material must also be of a certain morphology to allow fluidization. The maximum particle size of metalliferous material which can still be housed depends on the design and operational parameters of the fluidized bed. The method according to the invention has the advantage that the solid carbon necessary for the reduction of the metalliferous material is formed in situ, in a very reactive form and by an exothermic reaction. This avoids the introduction of material containing solid carbon of a less reactive nature or even of an altering nature, into the reaction chamber or of material which does not contribute in any way to the reduction, such as ash. This altering nature can manifest itself in contamination of the reduction product, for example by sulfur in an alteration of the reduction reaction of the metalliferous material by the solid carbon or possibly by an alteration of the formation of the solid carbon. Since the metalliferous material is provided in a reaction chamber of a fluidized bed and the solid carbon precipitates from gaseous carbon monoxide in the reaction chamber, preferably directly on the metalliferous material or the reduction product, there is no danger of formation of accretions and agglomerates.
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In one embodiment of the invention, the final reduction product after discharges from the chamber. of the reaction of the fluidized-bed reactor has a degree of reduction of at least 50%. This amount provides a good starting point for the reduction in the final stage reactor. In one embodiment, the reduction in the final stage reactor is carried out in a non-inert atmosphere. The non-inert atmosphere is important to create the appropriate reactive conditions so that the final reduction product is further reduced in the final stage reactor to the desired degree of metallization reduction at the end of the process. In one embodiment a flow of hot gas comprising gaseous CO is fed into the final stage reactor. It has been found that the introduction of a flow of hot gas comprising gaseous CO, for example originating from the gasifier or a recycled process gas results in the appropriate reactive conditions in the final stage reactor. In one embodiment, a CO / C02 and / or a gas containing oxygen is provided within the final stage reactor, preferably wherein the gas containing C0 / C02 is fresh synthesis gas and / or recycled process gas and / or wherein the gas containing oxygen is technically pure air or oxygen. The final stage reactor is fed with the
- - reduction product of the last CFB together with fresh synthesis gas or recycled process gas comprising CO and technically pure oxygen or air which is injected into the final stage reactor. The reaction in the final stage reactor is endothermic and the heat released as a result of the oxygen injection, preferably by injection in the bottom in the final stage reactor, facilitates the conditions that allow to reach the degree of reduction or metallization desired end of the procedure. In one embodiment of the invention, the fluidized bed is of rapid fluidization or pneumatic transport or a type of toroidal fluidized bed reactor. These types of fluidized bed reactor allow the formation of a fast fluidized bed that provides a high reaction rate for gasification and a sufficient residence time of solids to complete the reactions. In one embodiment of the invention, the method is carried out as a continuous process wherein the metalliferous material and the gaseous CO are continuously or batch-fed to the reaction chamber of the fluidized-bed reactor so as to continuously produce the product of reduction and where the final reduction product can be downloaded
- - continuously or in batches of the reaction chamber. In this embodiment, the exothermic nature of the formation of the solid carbon can be used optimally and the process can be carried out more economically. The capacity of the reactor, in terms of unit mass per unit time, of reduction product is one of the parameters with which an optimum process efficiency can be achieved and therefore an economy in the process. The final reduction product, which is discharged from the reaction chamber, is in solid form and has a degree of reduction which, in the usual manner, is greater than that of the metalliferous material which is provided in the reaction chamber as the feeding material. It should be noted that the final reduction product can be used as a metalliferous material in a subsequent process that is to be reduced to an even greater degree of reduction. In the latter case, the degree of reduction must be determined with respect to the degree of reduction of the metalliferous material before the first reduction procedure, which is generally assumed to be 0. A degree of reduction of 50% of the reduction product indicates that 50% The oxygen of the metalliferous material has separated from the metalliferous material. 50% metallization means that 50% of the metal atoms originally present in the material
Metals are found in metallic form and / or as metal carbide. The other 50% is still in a more or less oxidized state. For purposes of clarity, a degree of reduction of 50% may mean that the metallization degree is still 0 if (for example) the entire Me02 has been reduced to MeO. It should be noted that the advantages of the invention are fully exploited when the initial metalliferous material has a degree of reduction of 0%, but it will be clear that, when the degree of reduction of the initial metalliferous material is greater in advance, for example due to a preliminary reduction operation, the degree of initial reduction can be greater than 0. In case of iron ore, 100% Fe203 will have a degree of reduction of 0%. Preferably, this degree of initial reduction of the metalliferous material is less than 25%, preferably less than 15%, more preferably less than 5% and much more preferably less than 0%. In a preferred embodiment, the final reduction product after discharge from the reaction chamber of the fluidized bed reactor has a degree of reduction of at least 50%, preferably at least 60%, more preferably at least 70%. %. Although the degree of optimal reduction can be towards full reduction, that is, at least a degree of reduction of 90% or 95% or even higher and technically it is affordable
- - a substantially complete reduction or complete metallization in a fluidized bed reactor, it is probably not the most economical procedure to do it this way. In addition, the tendency of adherence of the reduced particles increases with increasing the degree of metallization. It has been found that it is preferable to aim for a somewhat lower degree of reduction of the final reduction product of at least 50%, preferably at least 60%, more preferably at least 70%, and to perform the final stage towards a substantially complete degree of at least 90 or 95% reduction in a dedicated process step in a final stage reactor. In a preferred embodiment of the invention, the metalliferous material is an iron compound, preferably iron ore. The inventors found that the process according to the invention can be advantageously carried out by using an iron compound, preferably iron ore as a metalliferous material, because the advantageous temperature range of the formation of solid carbon from of gaseous CO and the advantageous temperature range for the reduction of the iron compound, preferably iron ore in metallic iron coincide at least partially. This results in a very economical procedure for the production of a product from
final reduction with a high degree of reduction or metallization or even substantially metallic iron. In one embodiment of the invention, the maximum temperature in the reaction chamber, particularly when an iron compound is used as a metalliferous material is 875 ° C, preferably 845 ° C, more preferably 825 ° C and even more preferably 800 ° C or 790 ° C. It has been found that even at these low temperatures in the reaction chamber the reduction of the metalliferous material by the solid carbon to produce a reduction product can be carried out. The exothermic reaction of the solid carbon formation is able to sustain the reaction to a large extent and the low temperature has the beneficial consequences that the energy loss due to the high process temperatures is limited and the formation of harmful compounds is prevented. nitrogen-oxygen (NOx gases). Another advantage of low operating temperatures is that the solubility of various elements in a metal decreases with temperature, whereby a metal with a higher purity is obtained. It has been found that at temperatures in the reaction chambers below 400 ° C no significant reduction can be observed. At approximately 450 ° C and above, for example 500 ° C, the rate of reduction is significantly increased. A temperature
- - Minimal suitable for the reaction chamber has been found to be 640 ° C, preferably 690 ° C. However, although a significant reduction can not be observed at temperatures below 500 ° C, the deposition of carbon occurs very easily at a temperature between 400 and 500 ° C due to the presence of metalliferous material or the reaction product formed by the reduction of metalliferous material that promotes the precipitation of solid carbon from gaseous CO, optionally through a carbide form of the metal of the metalliferous material or over the already precipitated carbon, by the Boudouard reaction. The balance of the Boudouard reaction will shift to the left (CO side) at a higher temperature and this displacement becomes noticeable above 600 ° C. It has been found that at these temperatures and upper carbon it is deposited only when solid carbon already exists in advance. In one embodiment of the invention, the promoter of the conversion of gaseous CO into solid carbon and gaseous carbon dioxide also acts as a promoter of the reduction of the metalliferous material. This promoter has the function of causing the formation of solid carbon from gaseous carbon monoxide and / or the reduction of the metalliferous material so that it is carried out more rapidly, more completely or at a lower temperature (or
- - combinations of any of these) either by catalysis or by another reaction mechanism. It is noted that the process according to the invention is suitable for a process wherein the metalliferous material is a nickel compound, preferably a nickel ore, a cobalt compound, preferably a cobalt ore or mixtures thereof, which is an inexpensive way to produce metallic cobalt, nickel or alloys thereof. In one embodiment of the invention, the metalliferous material, or more particularly the iron compound or the iron ore is provided in the form of a fine compound or ore, preferably wherein the grain size of the compound or ore is between 0.1 and 5000 μp ?. A suitable maximum grain size is 200 μp ?, preferably 100 μp ?. Preferably, the grain size is at least 5 μp? and preferably at most 50 μp ?, and much more preferably between 5 and 50 μp ?. The use of these types of ores is particularly attractive from an economic point of view, since fine ores are generally cheaper than lumpy iron and also because these fine ores are suitable for processing in fluidized beds. Since the solubility of various elements, for example carbon in the ferritic morphology of iron
it decreases strongly with temperature and for carbon is about 0.02% at 720 ° C, the resulting final reduction product in the form of iron contains very small amounts of possibly undesirable elements. According to one embodiment of the invention, the metalliferous material is a mixture of at least two compounds from the group of compounds comprising a nickel compound such as a nickel ore or a cobalt compound such as a cobalt ore, a compound of iron such as an iron ore. By using said mixture of compounds, the resulting (final) reduction product after complete reduction of the metalliferous material is a mixture of the respective metals and therefore an inexpensive and simple way to produce alloys is provided. In one embodiment of the invention, the solid carbon precipitates on the metalliferous material and / or on the reduction product in the form of carbon nanotubes. The inventors surprisingly found that the solid carbon that is formed from gaseous CO has the morphology of carbon nanotubes. By means of the appropriate design, the reaction chamber and the appropriate selection of the process parameters, the method according to the invention can, as an alternative to the
- - production of a metal as the reduction product by reducing the particles of metalliferous material, can also be used to produce solid carbon in the form of carbon nanotubes by persisting in the formation of solid carbon from gaseous CO and use of the material metalliferous and / or reducing product as a substrate for, and / or promoter of, carbon formation. In a subsequent process, the solid carbon can be separated from the substrate. The substrate can then be reused in the process and the nanotubes can be used for various purposes. In one embodiment of the invention, the gaseous CO which is provided in the reaction chamber of the fluidized bed reactor is prepared by gasifying a carbon containing compound using a flow of oxygen-containing gas, preferably wherein the gas flow is a flow of hot gas. Preferably, the flow of oxygen-containing gas is technically pure oxygen, for example having an oxygen content of at least 85%, preferably at least 90%, more preferably at least 95%. The advantage of using oxygen with respect to air is that the reactors can be made smaller and that the procedure is more efficient in terms of energy, because the air contains 80% inert nitrogen which must be heated
- - and cooled. By using a separate gasification step the gaseous CO which is supplied to the reaction chamber can be cleared of undesirable components such as volatile hydrocarbons or sulfur compounds which are present in the carbon-containing compound or which are formed at the gasify the carbon-containing compound. The gasification step can be carried out in a standard gasifier, but it is preferable to use a drag-flow gasifier because most of the ash is extracted as a slag because the operating temperature of the entrained flow gasifier is well above the ash melting temperature. It will be clear that, depending on how the gasifier is operated, this will determine the amount of gaseous CO in the gas leaving the gasifier (ie, gasifier exhaust or "synthesis gas"). The synthesis gas may comprise, for example, varying concentrations of CO, C02, H2, H20 and N2. The amount of gaseous CO in the exhaust gas of the gasifier also depends on the nature of the gas which is fed into the gasifier for coal gasification. If pure oxygen is used, the CO concentration in the exhaust gas is higher than when air is used. Preferably, the amount of gaseous CO in the exhaust gas of the gasifier is at least 10%
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(% in volume) The CO / C02 equilibrium in the exhaust gas of the gasifier is at least 2, preferably at least 5, more preferably at least 10. The CO / H2 must be at least 1, preferably higher than 3. The carbon-containing compound can be cokes, coal, charcoal, petroleum, polymers, natural gas, paper, biomass, tar sands or energy sources containing highly contaminated carbon. In this way, the process according to the invention can contribute to an efficient use of waste materials or other carbon sources that are otherwise not economical. It should be noted that the exhaust gas temperature of the gasifier can be very high, for example between 1300 and 1600 ° C or about 1500 ° C. In order to be suitable for introduction into the fluidized bed reactor to reduce the initial metalliferous material, the exhaust gas of the gasifier must be cooled. The exhaust gas of the gasifier is preferably cooled by mixing it with a cooled recycled process gas or cooled fresh synthesis gas or by cooling it in a heat exchange unit. The resulting gas phase has a temperature of about 800 ° C and is fed to the FB where the gas phase enters the reduction process. It will be clear that the composition of the gas phase may have changed as
- - result of mixing with the recycled gas because the recycle process gas is the gaseous phase which may have been cleaned and removed from CO after leaving FB after having interacted with the initial metalliferous material in the FB. In one embodiment of the invention, the exhaust gas is discharged from the reaction chamber where at least part of the remaining gaseous CO and / or C02 are separated from the exhaust gas for reintroduction of the gaseous remnant of CO and / or C02. in the reaction chamber of the gasifier. C02 can be used as a source to provide CO by the inverse Boudouard reaction by reacting with the carbon of the carbon-containing compound in the gasifier. It is also possible only to reuse the CO compound of the exhaust gas. This implies that the CO must be separated from the exhaust gas, for example by using a separating means such as a scavenger. The recycled CO gas can be reintroduced into the reaction chamber of the fluidized bed, either directly or after passing through the gasifier or a heat exchanger unit. Instead of recycling carbon from the exhaust gas, it is also possible to recycle any remaining chemical and / or thermal energy still present from the exhaust gas by burning the exhaust gas and / or using the energy
thermal, for example, to reheat the flow of oxygen-containing gas entering the gasifier, for example, by feeding the hot exhaust gas leaving the reaction chamber through a heat exchanger unit to reheat the gas flow which contains oxygen before it enters the gasifier. In a preferred embodiment, the reduction of the metalliferous material by the solid carbon is carried out in a circulating fluidized bed reactor (CFB), the reactor comprises an ascending part and a return leg, wherein the metalliferous material and the gaseous CO are provided within the ascending part of the CFB, and wherein a gas stream comprising the gaseous CO moves the metalliferous material in a substantially upward direction, through the ascending part of the CFB and wherein the gaseous CO conversion in solid carbon and gaseous carbon dioxide is carried out at least partially during the substantially upward movement of the metalliferous material and gaseous CO. By using a CFB, the reagents circulate through the reaction chamber, the reaction chamber comprises the rising part and the return leg of CFB and the conversion of gaseous CO into solid carbon and gaseous carbon dioxide is considered it is carried
- - runs out, at least partially, during a substantially upward movement of the metalliferous material and the gaseous CO and that the reduction of the metalliferous material is carried out substantially during a more or less stagnant phase in the return leg before being reintroduced in the ascending part. Accordingly, in one embodiment of the invention, the metalliferous material and the reduction product resulting from the reduction of the metalliferous material and the solid carbon are discharged into the return leg of CFB and the metalliferous material and the reduction product as well as the solid carbon move in a substantially downward direction through the return leg of the CFB and wherein the reduction of the metalliferous material and the reduction product by the solid carbon is carried out at least partially, and preferably substantially in the return leg of the CFB. Since the reduction of the metalliferous material by solid carbon is a solid-solid reaction, the reaction rates are lower than those of a gas-solid reaction of solid carbon formation from gaseous CO. The difference in the residence times in the ascending part and the return leg take these different reaction rates into consideration. The dwell time of the metal particle in the CFB is selected so that it is
- - perform a large number of circulations, which depend on the desired reduction or metallization. The CFB can be provided with a separation medium, such as a cyclone, to separate the solid parts such as the metalliferous material, the reduction product resulting from the reduction of the metalliferous material and the solid carbon from the gas stream that is moving upwards, the gas stream comprises gaseous CO and gaseous carbon dioxide. This separation is preferably performed near the top of the ascending part of the CFB, preferably by one or more cyclones. The process according to the invention can be carried out as a batch process so that, when the reduction of the product has reached the desired degree of reduction or metallization, it is discharged from the reaction chamber as a final reduction product. This final reduction product can be provided in the next process step for further reduction or metallization. In one embodiment of the invention, the reduction of the metalliferous material is carried out in a plurality of fluidized bed reactors (for example 2 or more), wherein the final reduction product of a preferred fluidized bed reactor (i) is discharge and is passed to a subsequent fluidized bed reactor (i + 1) to
- - further reduction to an even greater degree of reduction or metallization. The temperature in the fluidized bed (i + 1) reactor is preferably greater than that of the i-th fluidized bed reactor. In this embodiment, the process conditions and the FB design can be optimized to obtain the respective degree of reduction or metallization of the final reduction product. It can also be designed in such a way that the above reactor or fluidized bed reactors can be optimized for solid carbon production and that the subsequent reactor or reactors can be optimized to obtain a desired degree of reduction or metallization of the metalliferous material. In a preferred embodiment, the gaseous phases discharged from a subsequent fluidized bed are discharged into a preceding fluidized bed reactor for further processing. In this way a backflow method is obtained for the gas phases and in this way a more economical use of the heat present in the gas is obtained, and the CO gas in the gas phases. The gaseous phases having a higher concentration of CO are therefore introduced into the fluidized bed reactor containing the reduction product with the highest degree of reduction or metallization. Therefore, this mode is characterized by a general counterflow of gas phases and metal particles, although
- in a fluidized bed reactor the gas phases and the metal particles are not counterflow but flow in the same direction. In one embodiment of the invention, the final reduction product of further reduces, to an even greater degree of reduction or metallization of at least 90%, preferably at least 95%, more preferably at least 98% in a final stage reactor to a final reduction product by a substantially solid-solid reaction between the remaining solid carbon and the incompletely reduced portion of the reduction product, wherein the end stage reactor is preferably a rotary kiln, an oven of rotary heart or a fluidized bed reactor. It has been found that a process involving 4, preferably 3 subsequent fluidized beds, preferably CFB, is sufficient to reduce an initial metalliferous material having an initial degree of reduction of less than 25%, preferably less than 15%, more preferably lower to 5% and much more preferably 0%, in an economical manner to a reduction degree or metallization and a quantity of deposited solid carbon suitable to obtain the final reduction in a final stage reactor for directly reduced metal, such as DRI .
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In this embodiment, the metalliferous material has been reduced almost completely to the respective metal. It has been found beneficial to perform the final reduction in a final stage reactor reduced to a reduction or metallization degree greater than at least 90%, preferably at least 95%, more preferably at least 98%. Ideally, the degree of metallization could still be higher, that is, greater than 99% or even higher than 99.5%. A further reduction has been shown to be advantageous in a rotary kiln, rotary core furnace or other fluidized bed reactor. It is also possible to obtain a higher degree of metallization by subjecting the reduction product to a melting operation. The final reduction product, as provided by the process according to the invention, has a large surface area as a direct consequence of the process. When iron-oxygen or less iron compounds are used as the metalliferous material, the intermediate and / or final reduction product will comprise metallic iron or strongly reduced iron-oxygen compounds. In the process according to the invention, iron is obtained with very few contaminants and with a very large specific area. This makes the reduction product extremely suitable for an iron sponge (SIP) process
- - for the production of hydrogen. The sponge process is iron is a well-known technology for the production of hydrogen. It comprises a stage where iron or reduced iron oxide is oxidized again with steam to form magnetite and hydrogen. The hydrogen produced has a degree of high purity, in compliance with the requirements of noble metal fuel cell catalysts. Therefore, the process is very interesting for the production and purification of hydrogen for use in high and low temperature fuel cells. Of course, hydrogen can also be used for other purposes. The final reduction product in the form of iron or in the form of strongly reduced iron-oxygen compounds with a very large specific surface area as provided by the process according to the invention is used as a fuel in a vehicle wherein the The reduction product is oxidized by steam to form oxygen which, for example, can be used to supply energy to a fuel cell and to propel the vehicle or to propel an engine or a device. Hydrogen which can be produced using a final reduction product in the form of iron or strongly reduced iron-oxygen compounds produced by the process according to the invention
It is cheaper than that produced, for example, from natural gas and also produces less carbon dioxide. The final reduction product can be subjected to a separation treatment to separate the metal part from a non-metallic part such as a gangue or slag. This separation treatment may comprise techniques such as gravimetric treatments, particle size treatments or a magnetic treatment. The final reduction product can be further processed by compacting the product in a compacted product, preferably when making briquettes or by rolling in a rolled product. This product in briquettes or laminate can be used in a casting operation. The rolled product can be used as a feed material in an additional rolling operation or can even be used for direct application with the condition that the rolled product has the properties desired for such direct application. According to a second aspect of the invention there is provided an apparatus for reducing metalliferous material to a reduction product according to the method of the invention, comprising: - at least one fluidized bed reactor comprising a reaction chamber; - a gasifier to produce a gas phase
- - comprising gaseous CO when gasifying a carbon-containing compound using an oxygen-containing gas flow comprising an inlet to provide an oxygen-containing gas, an inlet to provide the carbon-containing compound, an outlet for the gas phase which it comprises gaseous CO and an optional outlet for solid waste materials such as slag, - a first entrance to the reaction chamber for introducing the metalliferous material; - a second entry to introduce the gaseous CO into the reaction chamber; - means for generating a fluidized bed comprising the metalliferous material and the gaseous CO in the reaction chamber; - a means for obtaining an adequate temperature in the reaction chamber to allow the conversion of gaseous CO into solid carbon and gaseous carbon dioxide and precipitation of the solid carbon on the metalliferous material and / or on the reduction product and to reduce the material metalliferous by solid carbon to produce a reduction product; - a means for directing at least part of the constituents of the fluidized bed towards the separation means for separating the reduction product from the fluidized bed and optionally a means for directing the gas from the fluidized bed.
- - escape from the fluidized bed to the recycling medium; - a return part for returning at least part of the reduction product separated from the gas stream to the reaction chamber and an outlet for discharging the remaining reduction product from the reaction chamber as a final reduction product. The fluidized bed reactor provides a very efficient device to allow the metalliferous material to operate in places where solid carbon can precipitate due to the high thermal as well as mass transfer coefficients due to the high surface area to volume ratio. the particles . Since the reagents are placed very close to each other and are very reactive and the formation of one of the reactants, that is, the solid carbon is exothermic, the conditions in the fluidized bed are optimal for the reduction of the metalliferous particle material. It is clear that the particle of metalliferous material can also be of a certain size to allow fluidization. The maximum particle size can still be adapted and depends on the design and operational parameters of the fluidized bed. In addition, since the solid carbon precipitates from the gaseous carbon monoxide in the reaction chamber in the fluidized bed, preferably directly on the metalliferous material or metalliferous material at least
- - partially reduced, there is no danger of forming accretions and agglomerates. The inlet to provide the oxygen containing gas and the inlet to provide the carbon containing compound in the gasifier can be combined in one inlet. In a preferred embodiment, the fluidized bed reactor is a circulating fluidized bed (CFB) comprising: an ascending part for housing a substantially upward movement of the fluidized bed, the fluidized bed comprising the metalliferous material and the gaseous CO; - a means for directing the constituents of the fluidized bed towards the separation medium when it reaches the upper part of the rising part to separate the reduction product from the fluidized bed and a means for directing the gaseous phases of the fluidized bed to the recycling medium and a means for directing the reduction product to the return leg; - a return leg for accommodating a substantially downward movement of the reduction product; - means for discharging the exhaust gas from the fluidized bed for further processing; - means for returning at least part of the reduction product of the return leg to the camera
The reaction also comprises an outlet to discharge the remaining reduction product as the final reduction product from the reaction chamber. In time of permanence of the metal particle in the CFB is such that a large amount of circulations are made, depending on the desired degree of metallization of the reduction product. The CFB can be provided with a separation medium such as one or more cyclones to separate the solid parts such as the metalliferous material, the reaction product and the solid carbon that are separated from the rising gas stream, the flow of Gas comprises gaseous CO and gaseous carbon dioxide. This separation is preferably performed near the top of the ascending part of the CFB, preferably by one or more cyclones. In one embodiment of the invention, the means for returning at least part of the reduction product from the return leg to the reaction chamber is a circuit seal or a circuit seal valve. The advantage of a circuit seal is that it can be used to selectively allow portions of the reduction process within the reaction chamber. By using a multiple circuit seal, the portions of the reduction product can also be allowed to be discharged as a final reduction product.
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In one embodiment, the apparatus according to the invention comprises a plurality of connected fluidized-bed reactors wherein a means is provided for transporting the final reduction product from a preceding fluidized bed to the reaction chamber of a subsequent fluidized-bed reactor. for additional reduction or to a greater degree of reduction. In the context of this description it is understood that a plurality means: two or more. In this way, two, three, four or more connected fluidized bed reactors can be used. A means is also provided for providing the gaseous phases discharged from a subsequent fluidized bed for further processing in a preceding fluidized bed reactor and thus allowing the creation of a general counterflow gas stream. In one embodiment, means are provided for operating a fluidized bed reactor subsequent to a higher temperature than a preceding fluidized bed reactor, preferably wherein any subsequent reactor operates at a higher temperature than any preceding fluidized bed reactor. In one embodiment, an apparatus is provided with a recycling means for separating at least part of the remaining CO and / or C02 gaseous from the exhaust gas, for example, for reintroduction thereof into the reaction chamber of the fluidized bed reactor or inside of
- - reaction chamber of one or more fluidized bed reactors or within the gasifier or within a heat exchange unit to recover at least part of the thermal or chemical energy still present in the exhaust gas, for example when burning the combustible components and use the heat to preheat a gaseous phase that enters the apparatus or by reintroduction of CO and / or C02 into the gasifier to use it as a carbon source. In one embodiment the apparatus is provided with a final stage reactor to reduce the final reduction product to an even greater degree of reduction or metallization by a substantially solid-solid reaction of the solid carbon with the incompletely reduced portion of the reduction product. , preferably wherein the final stage reactor is a rotary kiln, a rotary core furnace or a fluidized bed reactor. The solid carbon preferably passes from the fluidized bed reactors where it is formed with the reduction product to the final stage reactor, although the solid carbon can also be added to the reduction product before the introduction of the reduction product into the reactor. final stage in case the amount of solid carbon transferred from the fluidized bed is insufficient to obtain the desired degree of reduction or metallization of the final reduction product
- - after leaving the final stage reactor. In one embodiment the apparatus according to the invention comprises means for separating the metal part of the final reduction product from the remaining part, for example, by gravimetric, magnetic or particle size means. In a preferred embodiment, the apparatus for carrying out the process according to the invention comprises a gasifier, preferably of the entrained flow type, three consecutive CFB reactors and a final stage reactor of the rotary kiln type or of the FB type, preferably of the type of bubbling FB. The method is described for the reduction of iron ore, but the description is equally valid for the reduction of other metalliferous materials that require only minor corrections of the process parameters. The gasifier is provided with technically pure oxygen and coal dust. In the entrained flow gasifier, dry pulverized coal is gasified with technically pure oxygen in co-current flow. The gasification reactions are carried out in a dense cloud of fine particles. The high temperatures and pressures mean that a higher yield can be obtained and that there are not present in the exhaust gas of the tar gasifier and volatile hydrocarbons such as methane. A drag flow gasifier eliminates most of the
- - the ash as slag when the operating temperature is well above the ash melting temperature. A smaller fraction of the ash is produced as a very fine dry fly ash which is transported with the gaseous CO to the last CFB. The exhaust gas from the gasifier comprising CO has a very high temperature at the gasifier outlet of about 1300 to 1600 ° C, preferably about 1400 to 1500 ° C. Optionally cold gas containing C02 can be provided as a moderator to control the temperature in the gasifier. Conventionally used steam is not preferred as a moderator because this impairs the CO / H2 ratio. The exhaust gas of the gasifier is cooled, preferably by mixing it with recycled cooling process gas or cooled synthesis gas, or in a heat exchange unit. The resulting cooled gasifier exhaust gas has a temperature of about 800 ° C and is fed to the last CFB where the exhaust gas from the gasifier (the synthesis gas) enters the reduction process. Prior to introduction to the last CFB, the exhaust gas from the gasifier may have been treated to remove sulfur from the gas, for example by a treatment with calcium to form CaS. The iron compound or the iron ore
- - provide in the form of a fine or ore compound, which preferably has a grain size between 5 and 200 m. This material is provided to the CFBs against backflow with respect to the exhaust gas from the gasifier and therefore enters the apparatus in the first CFB. The temperature in this first CFB is the lowest and is optimized for the purpose of deposition of solid carbon on the compound or ore. The temperature in the first CFB is controlled to be between 350 and 600 ° C, preferably between 400 and 500 ° C so as to form solid carbon (ie, Boudouard carbon and / or iron carbide). Iron ore, particularly the reduction of hematite to magnetite is initiated in advance as these low temperatures begin to form iron carbide (Fe, C). The iron compound and / or the products of the reduction thereof act as a catalyst for the formation of solid carbon at these low temperatures. The conditions in the return leg of the CFB are such that the following reaction becomes possible:
When the last CFB is abandoned (which, due to the counter-flow principle is the first for the solid phases and the last for the gas phase), the reduction product has reached the desired degree of reduction by
- - at least 50%, preferably at least 60%, more preferably at least 70% and / or charged with sufficient solid carbon to allow the final reduction to DRI in the final stage reactor to a degree reduction or metallization of at least 90%, preferably at least 95%, more preferably at least 98%. In this way, the process parameters can be such that they are selected so that the iron ore has not reached the desired degree of 50% reduction when it leaves the last CFB, instead it is loaded with enough solid carbon to allow the final reduction to DRI with the degree of reduction or metallization of at least 90%. In this case, the CFB reactors are used to produce the solid carbon necessary to reduce the iron ore, instead of reducing the iron ore and reducing the iron ore accordingly it is carried out in the stage reactor final. The final stage reactor is fed with the last CFB reduction product together with fresh synthesis gas or recycled process gas comprising CO and technically pure oxygen or air, which is injected into the final stage reactor. The reaction in the final stage reactor is endothermic and the heat released as a result of oxygen injection,
- - preferably by injection at the bottom in the final stage reactor, and facilitates the conditions to allow the final reduction mentioned above. Since the final stage reactor is a fluidized bed, the local hot spots are avoided and the risks of sealing the process by coagulation of fine particles in the reactor are minimized. If necessary, the risk of obturation can be further reduced by the addition of additives to the fluidized bed, as described in the document of E.U.A. 3,615,352. The temperature in the final stage reactor is preferably between 680 and 850 ° C, for example between about 750 ° C ± 20 °. Most of the reduction reactions in the last stage reactor are considered to be solid-solid net reactions and not gas-solid reactions. The present gases only help to create the conditions to allow solid-solid reactions to be carried out by manipulating the stability diagram CO-C02-T for iron and its oxides. The inventors found that the post-combustion ratio of the gas phase entering the reactor in the final stage is substantially the same as the post-combustion ratio.
C0 ^ H '°) C02 + CO + H20 + H2
- - of the gas phase leaving the reactor in the final stage as a result of CO generation during the final reduction. It is noted thatAlthough the modality is described with 3 CFB, it is also possible to use 2, 4, 5 or more CFB. The inventors found that the use of 3 or 4 CFB provides a good combination of a low temperature CFB to deposit carbon on the initial metalliferous material, a medium temperature CFB for additional carbon deposition and a final CFB of "high" temperature for reducing the reduction of the initially metalliferous material to the degree of reduction or metallization desired and the amount of solid carbon deposited to provide a good reduction product for introduction into the final stage reactor. The final reduction product leaving the final stage reactor may also comprise gangue, slag, CaS or other undesirable substances and these may be separated from the metal phase in a magnetic separation operation. The final process exhaust gas, which can no longer be introduced into the process, can still retain some chemical substances or thermal energy that can be used, for example, for its burning and / or heat utilization. In one embodiment the apparatus comprises a unit
- - of recycling to recycle Zn and / or Pb and / or Cd from metalliferous materials containing Zn and / or Pb and / or Cd, the unit comprises a means to enable the reduction of compounds containing Zn, Pb and / or Cd by the solid carbon to Zn, Pb and / or Cd metallic and to evaporate Zn, Pb and / or Cd to produce Zn, Pb and / or Cd gaseous. In one embodiment the apparatus comprises: - a condensation means for condensing and / or solidifying Zn, Pb and / or Cd gas in Zn, Pb and / or liquid and / or solid Cd, or - an oxidation medium for oxidizing the Zn, Pb and / or gaseous Cd to zinc-oxygen compounds, lead-oxygen compounds and / or cadmium-oxygen compounds. The modality allows the processing, for example, of waste material with high iron concentration of the steel industry. These materials, such as the powder with high concentration of iron from the production of steel can be used as a metalliferous material in the process and apparatus according to the invention. In addition to the iron-oxygen compounds, these materials also comprise zinc-oxygen compounds, lead-oxygen compounds or cadmium-oxygen compounds. These compounds are recycled from the metalliferous material by reducing the iron-oxygen compounds to iron compounds. The Zn, Cd or Pb also
- - reduce in the course of the procedure and reach a gaseous state. The reduction of zinc-oxygen compounds, lead-oxygen compounds or cadmium-oxygen compounds can be carried out by the solid carbon or by direct reaction with gaseous CO or H2. Subsequently, the metals of Zn, Cd or Pb can be condensed from gaseous states or can be oxidized and collected as zinc-oxygen compounds, lead-oxygen compounds and / or cadmium-oxygen. In a preferable embodiment, the apparatus comprises a zinc scavenging unit, the zinc scavenging unit comprises a heating means for heating the metalliferous material or the reduction product or the final reduction product to reduce the compounds containing Zn to Zn metal and evaporating Zn to produce gaseous Zn or to oxidize Zn to produce a zinc-oxygen compound such as ZnO or Zn (OH) 2- This mode is particularly advantageous for processing waste material with high concentration of Zn of which the content Zn is too high to be used, for example, in the conventional production of iron and steel. The process can also be adapted to extract Zn, Cd and / or Pb from the fines and use the fines in a conventional iron production path involving a blast furnace. In one embodiment the apparatus comprises a means of
- - condensation to condense and / or solidify the gaseous Zn in liquid and / or solid Zn. The invention will now be explained further by means of the following non-limiting figures. In Figure 1 the basic distribution of the fluidized bed reactor is shown. In Figure 2 the basic distribution of the complete apparatus for carrying out the method of the invention is shown. Figure 3 shows the basic distribution of the apparatus for carrying out the method of the invention comprising at least two circulating fluidized bed reactors and a final stage reactor. In Figure 4 the basic distribution of the apparatus according to Figure 2 is shown comprising a recycling unit for recycling Zn from metalliferous material containing Zn. Figures 5 and 6 show alternative embodiments of Figures 2 and 3, respectively. In Figure 1, the fluidized bed reactor, in this example a circulating fluidized bed 1 is provided with metalliferous material 2 and a gas stream 3 comprising gas CO. After the upward movement through the rising portion of the circulating fluidized bed 1 of the metalliferous material 2 and a gas flow comprising gaseous CO, the material is directed towards the medium 5 for separation of gas particles and
- - solid. The exhaust gas is allowed to move away from the medium 5, which is indicated by the arrow pointing up from the middle 5. The solid parts that comprise the solid carbon which is formed from gaseous CO and the metalliferous material react in a manner that reduces the metalliferous material to a product of reduction. This reduction product descends through the return leg to the medium 7 such as a circuit seal, to return at least part of the reduction product to the reaction chamber of the circulating fluidized bed during one or more additional cycles. Alternatively, at least part of the reduction product can be discharged as a final reduction product, which is indicated by the arrow pointing to the right of the medium 7. In Figure 2, the part of the reduction product is which can be discharged from medium 7 is provided in medium 4. This medium 4 can be a final stage reactor such as a rotary kiln, a rotary core furnace or a fluidized bed reactor. Alternatively, the medium 4 can be one or more additional cycles comprising the parts 1, 5, 6 and 7 wherein 6 is the schematic representation of the return leg of the circulating fluidized bed reactor, 1 is the ascending part and 5 is the means of separation, such as
- - a cyclone. This situation is indicated schematically in Figure 3. The medium 4 may also be present in one or more circulating fluidized bed reactors and a final stage reactor. In Figures 2 and 3, the gas flows are indicated schematically with arrows by points or with ions ("g") and the flows that are not gas are indicated by continuous arrows ("s"). The gaseous products separated by the medium 5 can be directed towards the gas cleaning unit 11 and subsequently exit or be directed from the gas cleaning unit 11 to the gas source 12 such as a gasifier, for gas reuse and / or for reheating purposes. In figure 2, the gas comprising the gas CO is produced in the gas source 12, for example when gasifying coal and the flow 8 of hot gas comprising the gaseous CO is fed through the medium 4 in general or total countercurrent. with respect to the metalliferous material and / or the reduction product. This is indicated by the gas flow 3. Within the upstream part of the circulating fluidized bed the flow of the metalliferous material and / or the intermediate reduction product travels in the same direction as the gas flow, as indicated by the fat arrow in the ascending part 1 and the. In Figure 4, the apparatus of Figure 2 is combined with a unit for recycling Zn and / or Pb and / or Cd a
- - starting from metalliferous material containing Zn and / or Pb and / or Cd. The final reduction product 9 which still comprises the metalliferous material containing Zn and / or Pb and / or Cd is placed in the medium 13 together with a flow 8 of hot gas comprising gaseous CO, which is used to reduce zinc-oxygen compounds or lead-oxygen compounds or cadmium-oxygen compounds to lead, zinc or metallic cadmium. This metallic lead, zinc or cadmium can be brought to a gaseous state and is provided to the medium 15. In the medium 15 metals can be condensed from gaseous states or can be oxidized and collected as zinc-oxygen compounds, lead compounds -oxigen and / or cadmium-oxygen. In Figure 5 an alternative embodiment of the one shown in Figure 2 is presented, wherein the synthesis gas of the gasifier, after being cooled to approximately 800 ° C, is introduced into the CFB. The synthesis gas is separated from the solid particles in the medium 5 and the recycled gas is cleaned in the gas cleaning unit 11. After the gas cleaning unit, the recycled process gas can be directed to the final stage reactor 4 or the gasifier 12. The recycled gas can be directed directly to the gasifier or can be used to cool the fresh synthesis gas produced by the gas. the gasifier at approximately 800 ° C. The medium 4 can have
the same alternative system to that presented for Figure 2. The alternative gas flow as shown in Figure 5 can also be applied to the embodiment of Figure 3 (see Figure 6) and Figure 4.