GB2150590A

GB2150590A - Method and plant for reducing oxidic material

Info

Publication number: GB2150590A
Application number: GB08427966A
Authority: GB
Inventors: Sven Santen; Bjorn Hammarskog; Goran Mathisson
Original assignee: SKF Steel Engineering AB
Current assignee: SKF Steel Engineering AB
Priority date: 1983-12-02
Filing date: 1984-11-05
Publication date: 1985-07-03
Also published as: IT1177075B; DE3441355A1; IT8423368A1; PL250670A1; AU3525084A; IT8423368A0; FR2556001A1; DE3441355C2; NO844802L; BR8406067A; DD229426A5; GB8427966D0; BE901161A; ES8605454A1; ES538142A0

Abstract

The invention relates to a method and a plant for reducing oxidic material. A reduction gas (18) is produced containing mainly carbon monoxide and hydrogen from carbonaceous or hydrocarbon- containing material by means of thermal energy from at least one plasma generator (10) in a separate gas-generating shaft (11). The reduction gas thus produced, after optional sulphur separation (22) and after temperature adjustment, is conducted to a reduction shaft (1) containing the oxidic material. The partially spent reduction gas (4) withdrawn from the shaft is freed from water and dust-like particles (5), after which a part-flow of the return-gas is returned to the process and a small part-flow of the return gas is removed from the system (at 6) for pressure regulation. A small part-flow of said partially spent gas intended for re-use in the process is caused to pass through a CO2 scrubber (23) and is then used to adjust the H2/CO ratio in the final reduction gas. <IMAGE>

Description

SPECIFICATION A method and plant for reducing oxidic material The present invention relates to a method and plant for reducing oxidic material.

The object of the invention is to effect an optimal reduction process with respect to process-technology as well as from the energy point of view, including a particularly easily controlled gas-generating system, the process being so flexible that the main part of the reduction gas initially used for reducing the oxidic material, can be re-used to generate new reduction gas.

This is achieved according to the invention in the manner described in the introduction comprising the steps of a) producing a reduction gas mainly containing carbon monoxide and hydrogen from a carbonaceous and/or hydrocarbon-containing starting material, wherein said starting material, together with an oxidizing agent and optionally also a slag-former, is introduced into a gasification zone or gasification chamber while simultaneously supplying thermal energy from at least one plasma generator; b) bringing the reduction gas thus produced to a temperature suitable for the subsequent reduction process and thereafter introducing said gas into a shaft furnace containing the oxidic material to be reduced, said gas being caused to flow in counter-current to said material to be reduced;; c) thereafter removing substantially all water and dust-like particles from the reduction gas, said gas being partially spent with respect to its reduction ability after reduction of the oxidic material and containing oxidizing components such as carbon dioxide and water as well as dust-like particles, the reduction gas then being mainly returned to the process; d) removing from the system at least a small part-flow of the said partially spent gas intended for re-use in the process, in order to effect pressure regulation of the total gas flow, and e) causing at least a small part-flow of said partially spent gas intended for re-use in the process, to pass a CO2 scrubber in order to adjust the H2/CO ratio in the finished reduction gas.

According to a suitable embodiment of the invention, the pressure in the system is regulated by a small discharge of gas. The gas flow withdrawn to regulate the pressure is then suitably burned off or used in other ways, for instance to dry the carbonaceous material used in the process.

According to a preferred embodiment of the invention, the gas-flow can be withdrawn after the gas leaving the reduction stage has been at least partially freed from water vapour and/or dust-like impurities.

According to a suitable embodiment of the invention, the oxidizing agent used consists of oxygen and/or water and/or recycled gas, supplied to the reaction zone wholly or partially through the plasma generator. The oxidizing agent may optionally be pre-heated.

According to a suitable embodiment of the invention the carbonaceous and/or hydrogencontaining starting material used for generating the reduction gas is in pulverulent and/or liquid form and/or as lump material.

According to the invention, a combustion zone is suitable generated in the lower portion of a shaft filled with solid carbonaeous material in lump form, coke being preferably used as carbonaceous filler in the shaft.

According to the invention, a part-flow of the partially spent gas withdrawn from the reduction shaft is also used, said part-flow of the partially spent reduction gas, which also contains CO2, with the use of a generating shaft filled with lump reduction material, is introduced into the shaft above and at a suitable distance from the combustion zone to make use of the heat in the shaft filling for conversion of the H20 to H2 + CO and the carbon dioxide in the part-flow to carbon monoxide. A part-flow of this return-flow of spent reduction gas from the shaft furnace may also be used as carrier gas for the introduction of a pulverulent, carbonaceous material and/or slag-former, together with optional sulphur acceptors immediately before the plasma generator.A part-flow of this return-flow of spent reduction gas from the shaft furnace is also used as carrier gas for the thermal energy supplied through the plasma generator.

According to a preferred embodiment of the invention, the carbon dioxide content in the return-gas flow intended for re-use in the process is regulated by causing a desired quantity of the return-gas flow to pass a CO2 scrubber.

According to a suitable embodiment of the invention the reduction gas generated in the gas-generating shaft may be freed from any sulphur impurities by providing suitable sulphur acceptors in the shaft filling and/or by causing the gas withdrawn from the shaft to pass a sulphur filter. Alternatively, sulphur acceptors may be injected into the gasification zone.

According to a further embodiment of the invention the temperature of the reduction gas withdrawn from the combustion zone in the gas-generating shaft is regulated to a final temperature of between 700 and 1 000 C, a/ by mixing with a suitable quantity of the partially spent reduction gas withdrawn from the reduction shaft and/or b/ by subjection to cooling and/or c/ by adding a suitable quantity of water and/or water vapour If only a small quantity of this partially spent reduction gas is used for temperature regulation-this partially spent reduction gas has been cooled upon passage through the scubber located immediatly after the gas outlet in the upper portion of the reduction shaft-the desired final temperature of the gas mixture can easily be achieved.However, if a large return-flow is used for mixing with the reduction gas generated, this may suitably be heated before being mixed with the newly generated reduction gas, for instance using a plasma generator.

According to a preferred embodiment of the invention the CO2 content of the part-flow of recycled shaft gas to be used for regulating the temperature of the reduction gas generated in the gas-generating shaft is regulated before being mixed into the reduction gas.

According to another embodiment of the invention, a carbon-carrier such as methane, methanol and/or propane may suitably be added to control the carburization potential of the reduction gas and to counteract methanization.

According to a further embodiment of the invention, H2S may be added to the final reduction gas in order to counter the formation of soot deposits.

According to a preferred embodiment of the invention, the reduction gas can suitably be generated by means of two-step gasification, the starting material being partially combusted and at least partially gasified in a gasification chamber, whereupon the gas mixture thus obtained is introduced into a shaft accommodating a bed of carbonaceous lump material, and the physical thermal content in the gas from the gasification chamber being utilized in the coke bed to reduce the content of carbon dioxide and water in the gas, the gas-generating process thus being controlled so that the gas withdrawn has a temperature and a composition suitable for a subsequent process step.

The invention also comprises a plant for reducing oxidic material while simultaneously generating a gas suitable for recycling, according to the method of this invention. This plant substantially comprises a generating means for reduction gas including a reaction chamber, at least one plasma generator with its orifice in the reaction chamber, a shaft furnace connected to the gas-generating means, optionally via a sulphur filter, said furnace containing said oxidic material to be reduced, a gas outlet means arranged in the upper part of said shaft furnace and a separator means located adjacent to said gas outlet means and arranged to remove from the exiting gas flow any water and dust-like particles contained therein, and a subsequent gas out let means for the purpose of pressure regulation and a main supply line for recycling the main gas flow to the gas-generating means and/or controlling the temperature of the reduction gas produced in the gas-generating means, optionally via a CO2 scrubber.

According to one embodiment of the invention, at least one compressor is provided in the main supply line.

According to a suitable embodiment of the invention, the main supply line is connected to a CO2 scrubber. The CO, scrubber is in this case suitably provided with a by-pass conduit opening into a direct extension of the main supply line for the supply of return gas to the gas-generating means and also into a second main supply line for the provision of return gas, substantially free from carbon dioxide. to be mixed into the freshly generated reduction gas with the object of temperature regulation.

Other features of the invention will be revealed in the accompanying claims.

In the following the invention will be described more fully with reference to two embodiments shown in the accompanying drawings, in which Figure 1 is a diagrammatic sketch of a plant according to the invention, having a singlestep gasifier. and Figure 2 is a diagrammatic sketch of an alternative embodiment of the plant according to the invention, having a two-step gasifier In Fig. 1 a reduction shaft for reducing oxidic lump material is designated 1. The shaft 1 is provided with a means 2 for feeding in the oxidic lump material for reducing. At the bottom of the shaft is an inlet pipe 3 for hot reduction gas, consisting primarily of carbon monoxide and hydrogen, said gas being passed in countercurrent through the reduction shaft 1 and withdrawn thereafter through an upper gas outlet means 4.The outlet line 4 is connected to a separator 5 for dust-like particles and water, known as a scrubber, from whence the gas cleaned from water and dust particles, and at the same time cooled, passes a gas outlet 6 provided for the purpose of pressure regulation, and is then returned via supply line 7 to the process for re-use, as described in more detail below. The supply line 7 is provided with at least one compressor 8.

At least one plasma generator 10 opens into the gas-generating shaft 11. 1 2 denotes a lance for the supply of material required for the gas generation and 1 3 denotes a means for tapping slag from the gas-generating shaft.

After the compressor 8, the main supply line 7 is connected to a CO2 scrubber. This arrangement also comprises a bypass conduit 7a for the supply of return gas to the gasgenerating means 11 and also into a second main supply line 14 for providing return gas, substantially free of carbon dioxide, to the freshly generated reduction gas for the pur pose of regulating its temperature.

In principle this arrangement offers the fol lowing function facilities: -Via a first branch conduit 16 the line 14 can be connected to the upper part of the gas-generating shaft; -the main supply line 7 can be connected via additional branch lines 1 5 and 1 spa, to the gasification zone in the lower part of the shaft 11, i.e. return gas can be sup plied in front of the plasma generator via the pipe 1 5 and, after compression in the compressor 27 the return gas can be brought via pipe 1 5a to pass through the plasma generator;; -via a further branch conduit 1 7 the branch line 14 can be connected to the reduction gas withdrawn from the gas-generator and leaving the upper part of the gas-generator via an outlet pipe 18, and -via a further branch conduit 19, the supply line 14 can be connected via a mixing chamber 20 to the reduction gas flowing out of a sulphur filter 22 through a pipe 21, and finally the supply line 14 can be connected to the reduction gas pipe 21 immediately before the reduction gas en ters the reduction shaft 1.

The CO2 content in the return gas supplied can thus be regulated throughout.

A supply line 9 for the oxidizing agent, in the form of oxygen and/or water and/or air and/or recycled gas, for instance, is connected directly to the plasma generator 10.

After optional pre-heating the oxidizing agent can be conveyed to the reaction zone in the bottom of the shaft 11.

The plant shown in Fig. 1 functions in principle as follows: The reduction gas for reducing the oxidic material in the shaft 1, which gas is introduced into the shaft 1 via gas inlet 3, is in principle produced in the gas-generator 11 by supplying a carbonaceous and/or hydrocarbon-containing starting material, together with oxidizing agent and optionally slag-former, to a gasification zone in the lower part of the gas-generating shaft 11, while simultaneously supplying thermal energy from at least one plasma generator 10. The reduction gas thus produced is then in principle brought to a temperature suitable for the subsequent reduction of the oxidic material in the shaft furnace 1 and caused to flow in countercurrent to the material to be reduced.After reduction of the oxidic material containing oxidizing constituents, e.g. preferably carbon dioxide and water as well as dust-like particles, and thus partially spent with respect to its reduction ability, the reduction gas is withdrawn via the gas outlet means 4 from the top of the reduction shaft and thereafter freed from water and dust-like particles in the scrubber 5. A small portion of the gas treated in this manner in the scrubber 5, and thus also cooled, is then removed from the system via the gas outlet pipe 6 for the purposes of temperature-regulation, while the main flow can be returned to the process via supply line 7, i.e. it can be re-used to generate reduction gas.

The gas generation in shaft 11 can be achieved in a number of alternative ways.

Pulverulent and/or liquid carbonaceous and or hydrocarbon-containing starting material can be blown into the gasification zone through supply line 12, for instance, in which case oxidizing agent such as oxygen or water vapour can be introduced into the reaction zone through the plasma generator. Recycled gas can be supplied to the reaction zone in front of the plasma burner via pipe 15, or said gas may be supplied through the plasma generator via pipe 1 spa. The carbonaceous and/or hydrocarbon-containing starting material may also be supplied in lump form via the upper part of the gas-generating shaft, so that the gasification zone is produced in the lower part of the shaft filled with solid carbonaceous material in lump form. Coke is suitably used as carbonaceous filler in the shaft.

Furthermore, water or part of the partially spent reduction gas withdrawn from the reduction shaft 1 via supply line 7 and branch pipe 1 6 can also be introduced into the gasgenerating shaft 11, which in the case is filled with lump reduction material. The water or spent reduction gas is introduced above and at a distance from the gasification zone itself, thus making use of the heat in the shaft filler to convert H20 to H2 + CO and carbon dioxide to carbon monoxide.

The gas generation in the shaft 11 can also be achieved by injecting pulverulent, carbonaceous material, optionally with sulphur acceptors, and/or slag-former, by means of water vapour or a carrier gas consisting of said partially spent part-flow of reduction gas withdrawn from the reduction shaft, or of oxygen or a mixture of oxygen and water vapour.

The reduction gas generated in the shaft 11 can be desulphurized by including a suitable sulphur acceptor in the shaft filling or by injecting sulphur acceptors in the gasification zone or by leading the gas produced in the shaft via the outlet pipe 1 8 to a sulphurseparating filter 22. Any sulphur impurities will be absorbed by the reduced metal oxide in the lower part of the reduction shaft.

The reduction gas is generally kept within a temperature range of between 1000-1500"C. However, such a hot reduction gas cannot be used directly for reduction in the reduction shaft and its temperature must thus be reduced before it is introduced into the shaft furnace 1. This can be achieved in various ways within the scope of the invention.

For instance, the reduction gas withdrawn from the gas-generating shaft 11 via the pipe 1 8 may be mixed with a suitable part-flow of recycled gas from the shaft furnace. This is achieved via pipe 14 so that the temperature of the gas mixture lies between 700 and 1000"C. Alternatively, this mixing with a partflow recycled from the reduction shaft 1 can be achieved by mixing the reduction gas after it has passed the sulphur filter 22, i.e. on its way from pipe 3. If a small part-flow of return gas is used via branch line 14, it should be sufficient to effect the desired cooling of the reduction gas generated. However, if an exceptionally large quantity of return gas is mixed into the reduction gas generated, such a large flow should be preferably be heated to the correct temperature in the mixing chamber designated 20.This heating may be effected by a plasma generator, for instance.

The temperature adjustment can also be achieved by allowing a part-flow of the gas generated to flow through pipes 21 and 19 and via a mixing chamber 20 acting as cooler.

The requisite temperature adjustment can also be at least partially achieved by the supply of water and/or water vapour via the supply pipe 24. This also prevents the formation of soot deposits.

In order to control the carburizing potential of the reduction gas generated, and to prevent methanization, suitable carbonaceous material, such as methane, methanol and/or propane, might be supplied via pipe 25.

Soot deposits can also be counteracted by the supply of H2S via pipe 26.

An important feature of the invention is that the CO2 content in the return gas used to regulate the temperature of the reduction gas, can be continuously regulated by means of the CO2 scrubber arrangement.

The generation of reduction gas in shaft 11 described above can also be performed by means of two-step gasification.

The gas generation according to the invention offers important technical advantages.

The gas generation can be effected at such temperatures that the ash forms a manageable slag which is tapped off without causing clogging problems in the process. The hydrogen content in the reduction gas can be controlled to a percentage suitable for the reduction process, by controlled injection of water and/or oxygen at the gas-generating stage and at the temperature regulating stage.

From the energy point of view also, an optimal reduction process and an easily controlled gas-generating system are achieved. The control of H20 and CO2 contents in the pipe 3 can thus be carried out by adjusting the flow in the pipes 14 and 18 and 21 and 3, respectively, and also in pipe 24.

As mentioned, with respect to desulphurization, instead of a separate sulphur filter, this function may be built in to the gas-generating shaft itself by providing the coke bed with suitable material, for instance, or by injection in the gasification zone.

Fig. 2 shows an alternative embodiment of the plant according to the invention which, in place of the single-step gas generator shown in Fig. 1, comprises a two-step gas-generator.

The plant is otherwise constructed according to the same principles as the embodiment shown in Fig. 1.

The two-step gas-generator shown in Fig. 2 comprises a gasfication chamber designated 29 and a shaft 30 with coke filler 31.

The gasification chamber 29 is provided with an outer, water-cooled casing 32, and a refractory lining 33 and is preferably substantially cylindrical. Several gasification chambers are preferably arranged around one shaft.

The shaft 30 has a lower slag outlet 34 and an upper gas outlet 35. Coke in lump form is supplied to the shaft through a gas-tight supply means 36 at the top of the shaft. The orifice of the gasification chamber 29 is in the lower part of the shaft and the gas passes up through the coke bed and out through the gas outlet. In the embodiment shown, the slag outlet 34 is common to both gasification chamber and shaft.

At least one burner is arranged in conjunction with the gasification chamber, consisting of a plasma generator 37 in the embodiment shown. The plasma generator is connected to the gasification chamber via a valve means 38. Oxidizing agent is introduced into the plasma generator through a supply pipe 9, or alternatively it may be supplied in front of the plasma generator through a supply pipe 39.

The oxidizing agent may consist of carrier gas which is led through the plasma generator. or a recycled gas may be supplied through pipe 15a. The hot, turbulent gas generated in the plasma generator is introduced into the gasification chamber through the orifice 40 of the plasma generator. The carbonaceous fuel, preferably in pulverulent form, is introduced through a supply pipe 41 into an annular space 42 arranged concentrically around the orifice of the plasma generator, and/or through a lance 43 which can also be used for the supply of optional additives such as slag-former.

Lances 44, 45 are also arranged in the shaft for the optional supply of additional oxidizing agent, such as H20, CO2, to make use of the physical surplus heat in the gas.

This also enables regulation of the temperature and composition of the gas.

A first sensing means 46 is arranged at the end of the gasification chamber located by the coke filler, and a second sensing means 47 in the gas outlet 35 from the shaft. These are for temperature measurment and/or gas analysis.

These two sensing means enable the process to be controlled by regulating the external energy supplied and/or the material flows supplied.

Fig. 2 shows only one embodiment of a suitable two-step gasifier in a plant for performing the process according to the invention and many other solutions are feasible. For instance the plasma generators may be arranged tangentially on the periphery of the gasification chamber, in such a way that a circulating flow is achieved in the gasification chamber. Furthermore, in order to facilitate slag separation, the gasification chamber may be vertical, or the gasification chamber and shaft may be provided with separate slag outlets.

With the two-step gasification plant shown in Fig. 2, therefore, the starting material is partially combusted and at least partially gasified in the gasification chamber and the mixture thus obtained is introduced into a shaft containing a bed of carbonaceous material in lump form. The physical heat content of the gas mixture coming from the gasification chamber is thus utilized in the coke bed to reduce the content of carbon dioxide and water in the gas. The gas-generating process can thus be controlled so that the gas leaving has a temperature and composion well compatible with the subsequent process step.

The hot carrier gas coming from the plasma generator may then suitably be given a rotary motion before being introduced into the gasification chamber and the pulverulent, carbonaceous fuel may be introduced concentrically around the hot gas flowing into the gasification chamber. The material in the gasification chamer having a rotary motion ensures that a protective layer of slag is formed on the inner walls of the gasification chamber.

However, the invention is not limited to the embodiments described above, but can be varied in many ways within the scope of the following claims. For example, additional external thermal energy may be supplied for the gas-generation, by pre-heating the oxidizing agent.

Claims

1. A method for reducing oxidic material comprising the steps of a) producing a reduction gas mainly containing carbon monoxide and hydrogen, from a carbonaceous and/or hydrocarbon-containing starting material, wherein said starting material, together with an oxidizing agent and optionally also a slag-former, is introduced into a gasification zone or gasification chamber while simultaneously supplying thermal energy from at least one plasma generator; b) bringing the reduction gas thus produced to a temperature suitable for the subsequent reduction process and thereafter introducing said gas into a shaft furnace containing the oxidic material to be reduced, said gas being caused to flow in counter-current to said material to be reduced;; c) removing substantially all water and dustlike particles from the reduction gas, said gas being partially spent with respect to its reduction ability after reduction of the oxidic material and containing ozidizing, such as carbon dioxide and water as well as dust-like particles, and then being mainly returned to the process; d) removing from the system at least a small part-flow of the said partially spent gas intended for re-use in the process, in order to effect pressure regulation of the total gas flow, and e) causing at least a small part-flow of said partially spent gas intended for re-use in the process, to pass a CO2 scrubber in order to adjust the H2/CO ratio in the finished reduction gas.

2. A method according to claim 1, wherein the gas flow withdrawn for pressure regulation is burned off or used for external purposes.

3. A method according to claim 1 or claim 2, wherein the gas flow is withdrawn after the gas leaving the reduction step has been freed from water vapour and dust-like impurities.

4. A method according to any one of claims 1 to 3, wherein the oxidizing agent used for the gas-generation consists of oxygen and/or water and/or recycled gas, supplied to the gasification zone wholly or partially through the plasma generator.

5. A method according to claim 4, wherein said oxidizing agent supplied via the plasma generator is preheated before entering the plasma generator.

6. A method according to any one of claims 1 to 5, wherein the carbonaceous and/or hydrogen-containing starting material used or generating the reduction gas is in pulverulent form and/or liquid form and/or in the form of lump material.

7. A method according to any one of claims 1 to 6, wherein the gasification zone is generated in the lower portion of the shaft filled with solid carbonaceous material in lump form.

8. A method according to claim 7, wherein coke is used as a carbonaceous filler in the shaft.

9. A method according to any one of claims 1 to 8, wherein water or a part-flow of the partially spent reduction gas in introduced into the shaft filled with reduction material in lump form, above and at a suitable distance from the gasification zone to make use of the heat in the shaft filling for conversion of the H20 to H2 + CO and the carbon dioxide to carbon monoxide.

10. A method according to any of claims 1 to 9, wherein pulverulent carbonaceous material and/or slag-former, optionally together with sulphur acceptors is injected into the system immediately before the plasma generator with the aid of water or steam, or a carrier gas consisting of a part-flow of said partially spent reduction gas withdrawn from the reduction shaft, or oxygen or air.

11. A method according to any one of claims 1 to 10, wherein the carbon-carrying starting material required for generation of the reduction gas is introduced into the gasification zone immediately before the plasma generator.

12. A method according to any one of claims 1 to 11, wherein optionally additional oxidizing agent for generating the reduction gas and optionally also slag-formers and/or sulphur acceptors and introduced into the gasification zone before the plasma generator.

1 3. A method according to any one of claims 1 to 1 2, wherein a mixture of carbonaceous lump material and a suitable sulphur acceptor is used as shaft filler after the gasification zone.

1 4. A method according to any one of claims 1 to 13, wherein any sulphur impurities are removed from the reduction gas generated in the gasification zone before it is introduced into the reduction shaft.

1 5. A method according to any one of claims 1 to 14, wherein the newly generated reduction gas has a temperature of between 1000-1500"C.

1 6. A method according to any one of claims 1 to 15, wherein the temperature of the reduction gas generated is regulated to between 700-1000"C, preferably 825 C, before being introduced into the reduction shaft.

1 7. A method according to claim 1 6, wherein the temperature of the hot reduction gas leaving the gas-generator, possibly after desulphurization, is regulated a) by mixing with a quantity of the partially spent reduction gas withdrawn from the reduction shaft and/or b) by subjection to cooling and/or c) by adding a quantity of water and/or water vapour such that the final temperature of the gas is between 700 and 100O'C.

1 8. A method according to any one of the preceding claims, wherein a large part-flow of recirculating shaft gas intended for temperature regulation of the reduction gas if necessary is heated before being added to the reduction gas.

1 9. A method according to claim 18, wherein said heating is performed using heatexchangers in the top gas supply line.

20. A method according to any one of the preceding claims, wherein the part-flow of recycled shaft gas used for temperature regulation of the reduction gas generated in the gas-generating shaft is regulated with respect to its CO2 content before being mixed with the reduction gas.

21. A method according to any one of claims 1 to 20, wherein the partially recycled, spent part-flow of reduction gas from the reduction shaft is brought to the pressure required by the process, e.g. using at least one compressor.

22. A method according to any one of claims 1 to 21, wherein a carbon-carrier such as methane, methanol and/or propane, is supplied in order to control the carburizing potential of the reduction gas generated, and to counteract methanization.

23. A method according to any one of the preceding claims, wherein H2S is supplied in order to counteract soot deposits.

24. A method according to any one of claims 1 to 23, wherein the reduction gas is generated by means of two-step gasification, the starting material being partially combusted and at least partially gasified in a gasification chamber, and the gas mixture thus obtained is introduced into a shaft accommodating a bed of carbonaceous lump material, whereupon the physical thermal content in the mixture obtained from the gasification chamber is utilized in the bed of carbonaceous lump material to reduce the content of carbon dioxide and water in the gas, and the gas-generating process is controlled so that the gas leaving has a temperature and a composition suitable for a subsequent process step.

25. A plant for reducing oxidic material according to the method of claim 1, comprising means for a generating reduction gas including a reaction chamber, at least one plasma generator with its orifice in the reaction chamber, a shaft furnace connected to the gas-generating means, optionally via a sulphur-filter, said shaft furnace containing said oxidic material to be reduced, a gas outlet means arranged in the upper part of said shaft furnace and a separator means located adjacent to said gas outlet means and arranged to remove from the exiting gas flow any water and dust-like particles contained therein, and a subsequent gas outlet means for pressure regulation, and a main supply line for recycling the main gas flow to the gasgenerating means and/or for temperature control of the reduction gas produced in the gas-generating means.

26. A plant according to claim 25, wherein the main supply line is provided with at least one compressor means.

27. A plant according to claim 25 or claim 26, wherein said main supply line is connected to a CO2 scrubber.

28. A plant according to any one of claim 27, wherein the CO2 scrubber is provided with a by-pass conduit leading into a direct extension of the main supply line for the supply of return-gas to the gas-generating means, and also leading to a second main supply line for the supply of carbon dioxide regulated return gas to be mixed into the freshly generated reduction gas in order to regulate the temperature thereof.

29. A plant according to any one of claims 25 to 28, wherein the main supply line is connected to the upper part of the generat ing shaft via the by-pass conduit and a first branch.

30. A plant according to any one of claims 25 to 29, wherein the main supply line is connected via the by-pass conduit and a second branch-line to the reaction zone in the lower part of the gas-generating shaft.

31. A plant according to any one of claims 25 to 30, wherein the plasma generator is connected to a supply means for oxidizing agent allowing optionally pre-heated oxidizing agent, to pass directly through the plasma generator to the reaction zone.

32. A plant according to any one of claims 26 to 31, wherein the gas-generating shaft is provided with a tapping means for slag.

33. A plant according to any one of claims 26 to 32, wherein the gas-generating shaft accomodates a filling of carbonaceous lump material, optionally containing sulphur acceptors.

34. A plant according to any one of claims 25 to 33, wherein the gas-supply line between the gas-generating shaft and the sulphur filter is connectable to a part-flow of return gas via a pipe and a branch-pipe.

35. A plant according to any one of claims 25 to 34, wherein the reduction-gas line between the sulphur separator and the gas inlet of said reduction shaft is connectable to a temperature-regulating part-flow of gas from the pipe via a cooling means in the form of a mixing chamber.

36. A plant according to claim 35, wherein heating of the part-gas flow of return gas in the mixing chamber is achieved by the use of heat-exchangers arranged in the top gas supply line.

37. A plant according to any one of claims 25 to 36, wherein the supply line for water vapour opens into the supply line.

38. A plant according to any one of claims 25 to 37, wherein a supply line for a carbon-carrier, e.g. methane, propane and/or methanol, opens into the supply line.

39. A plant according to any one of claims 25 to 28, wherein a supply line for H25 opens into the supply line.

40. A method for reducing oxidic material according to claim 1 and substantially as herein described with reference to the drawings.

41. A plant for reducing oxidic material according to claim 1 and substantially as herein described with reference to the drawings.