LU500891B1 - Double shaft furnace arrangement and method for operating a double shaft furnace arrangement - Google Patents

Abstract

Double shaft furnace arrangement (10) for the direct reduction of metallic oxides, the double shaft furnace arrangement (10) comprising: - at least a first shaft (11) and a second shaft (21) extending along a vertical direction (Z); wherein each shaft (11; 21) has a cooling zone (C) in a bottom portion (12, 22) of each shaft (11; 21), a regenerative zone (A) in a top portion of each shaft, and a high temperature reduction zone (B) arranged between the regenerative zone (A) and the cooling zone (C); - a connection channel (30) connecting the first shaft (11) with the second shaft (21), wherein the connection channel (30) extends along a horizontal direction (X), wherein the connection channel (30) is arranged at a lower end of the high temperature reduction zone (B) and at an upper end of the cooling zone (C) of each of the first shaft (11) and the second shaft (21); and wherein - at least one injector assembly (31) protruding laterally into the connection channel (30).

Description

DOUBLE SHAFT FURNACE ARRANGEMENT AND METHOD FOR OPERATING A

DOUBLE SHAFT FURNACE ARRANGEMENT

TECHNICAL FIELD

[0001] The invention relates to a double shaft furnace arrangement, in particular a metallurgical double shaft furnace arrangement for producing direct reduced iron (DRI) and a method for operating said double shaft furnace arrangement.

BACKGROUND OF THE INVENTION

[0002] Industrial metallurgical reduction plants for producing direct reduced iron, such as for example plants using a so-called Midrex or Energiron process, use a single shaft furnace for the direct reduction process. Such a shaft furnace is usually connected to an external reformer, respectively a heater.

[0003] The reformer, for example a COz-natural gas reformer, produces syngas, i.e. a gas comprising high amounts of hydrogen and carbon monoxide based on an endothermic reaction of hydrocarbons with CO» on a catalyst. In the reformer, respectively during the process of heating said gas, energy is set free due to a combustion, wherein a part of the combustion energy is "lost", respectively dissipated, due to the release of flue gases.

[0004] The so called "top gas", i.e. a gas having a temperature that usually exceeds 300- 350°C, is released from the top of said shaft (furnace). The top gas, which comprises hydrogen, steam, carbon monoxide and carbon dioxide, must usually be quenched during a top gas cleaning process before it can be made available for reuse.

[0005] Due to these operations linked to the process (i.e. reforming, respectively heating, the process gas and quenching the top gas), energy is lost.

[0006] In case the process gas composition is not managed accurately in the heater, the injected natural gas can generate soot or carbon deposition leading to the clogging or to the destruction of the heater by a so-called metal dusting reaction.

In addition, industrial reduction shaft furnaces generally foresee the injection of hot gas at merely one (single) level. Due to such constructional arrangements, in the surrounding of the injection zone solids are overheated regularly. As a result, solids start to melt. As a consequence, sticking phenomena occur, which harm the productivity of the furnace.

OBJECT OF THE INVENTION

[0007] The object of the present invention is to provide an apparatus and method for reducing metallic oxides being less energy consuming and which further allow to reduce the occurrence of sticking phenomena. This object is achieved by the double shaft furnace and the method for operating the same according to the independent claims.

GENERAL DESCRIPTION OF THE INVENTION

[0008] The proposed double shaft furnace arrangement for the direct reduction of metallic (iron) oxides comprises at least a first shaft and a second shaft extending along a vertical direction, wherein each shaft has a cooling zone in a bottom portion of each shaft, a regenerative zone in a top portion of each shaft, and a high temperature reduction zone arranged between the regenerative zone and the cooling zone. The double shaft furnace arrangement comprises further a connection channel connecting the first shaft with the second shaft, wherein the connection channel extends along a horizontal direction. The connection channel is arranged at a lower end of the high temperature reduction zone and at an upper end of the cooling zone of each of the first shaft and the second shaft. The double shaft furnace arrangement comprises further at least one injector assembly protruding laterally into the connection channel.

[0009] The present invention is based on the finding that this particular arrangement of the elements of a double shaft furnace arrangement provide advantageous effects and a solution to the above object.

[0010] Contrary to any other known prior art apparatus or method, the invention provides a solution without a hot gas injection from a separate heater or reformer for generating a hot reducing gas. Due to the absence of an external (gas-fired) heater or external (gas fired) reformer, the energy efficiency is significantly improved and common problems related to this equipment as soot accumulation, carbon deposition, metal dusting and catalyst poisoning are avoided. The heating of the metallic ores to be treated and the hot reducing gas generation is entirely carried out within the double shaft furnace arrangement, which significantly improves energy efficiency.

[0011] In addition, the solids, respectively the metallic ores, present in the regenerative zone at and/or below the top of the shafts, are caused to function as a regenerative heat exchanger, since the solids accumulate heat from the gas after the reduction has been performed during a first step, and "give back" the heat to the recirculation gas during a second, subsequent step.

The top gas temperature is significantly reduced. As a consequence, less energy is lost during (subsequent) gas quenching step and a better energy efficiency is achieved. In addition, and also in order to avoid overheating, the solids are cooled during at least one of the two steps of the operating method by means of the recirculating gas.

[0012] The proposed arrangement and method also provide a solution for reducing the risk of solids sticking in a shaft. In the proposed double shaft furnace arrangement and the corresponding operating method, the temperature of the reducing gas is among others influenced by the position of the injectors, which are located at at least two different heights,

respectively height levels of the respective shaft, which prevents the solids from overheating and thus form sticking.

[0013] Furthermore, because fuel and oxygen are injected in the high temperature zone of a respective shaft, soot or carbon depositions are less likely to appear or form. In other words, soot or carbon depositions may even be entirely avoided. Even in cases where soot or carbon depositions might yet still form, said soot or carbon deposition will at least not accumulate in the regenerative zone where the double shaft furnace functions as a heat exchanger since the solids are permanently replaced during the production cycle.

[0014] Furthermore, carbon dioxide (COz) generated from the double shaft furnace arrangement may be captured at a CO, removal plant, respectively removal apparatus. Since the CO» is not vented in the atmosphere, said amounts of CO. can be sold for industrial applications or sequestrated.

[0015] Typical data/ parameter that may be expected when using the proposed arrangement and method in the context of the production of direct reduced iron (DRI) at a metallization of 93% w/w with natural gas are: Natural gas: 10.3 GJ/t.DRI, export gas: 3.2 GJ/t.DRI having a low calorific value (LCV) after CO, removal: 10.7 MJ/Nm°, net gas consumption: 7.1 GJA.DRI, and oxygen consumption: 180 Nm°/t.DRI. In cases where the arrangement uses an electrical heating device for heating the gas (e.g. an electric heating device arranged at or within the connection channel, an input of 60 kWh/t.DRI (0.22 GJ/t.DRI) may decrease the net gas consumption to 6.8 GJ/t.DRI and oxygen consumption to 160 Nm“t.DRI. It had been found that compared to a commonly known Energiron or Midrex apparatus, the proposed apparatus and method reduce the amount of emitted CO. in kg/tDRI by approximately 18 %. This amount may even be further raised up to 23% when the connection channel of the double shaft furnace is equipped with an electric heating device. The following table illustrates the advantage in an exemplary manner: e [ee | en |S

Midrex Energiron HYL Double shaft electric heating (60 kWh/tDRI)

TAT IEEE

[Neimput | 105 | ses | 98 | 5 | 103 | sw | o | se [Epongas | 0 | 6 | 0 | 0 | a1 | m6 | — | 6. [retgas | 105 | 565 | es | ws | 72 | ae | 68 | s [renom | 25 | @ | 185 | ow [greccoz | | aes || ass | | aoe || ou mE 1 ew | [ow Jam

[0016] "Metallic oxides", or "solids", generally refer to materials to be processed in a reduction apparatus like a blast-furnace or a shaft furnace or a direct reduction furnace or a similar furnace. Metallic oxides may e.g. consist of or comprise lump ore(s), pellets, sinter, briquettes, similar materials or mixtures thereof. The solids may be charged at the top of the shafts and extracted after reduction at the bottom of the shafts. The shafts are usually fully filled with solids and may be operated in two alternative modes, respectively in an alternating manner. It is understood, that the volume of solids within the shafts may be varied according to required process conditions.

[0017] "Double shaft fumace" generally refers to a fumace arrangement which has at least two shafts connected to one another by at least one constructional means, such as e.g. a connection channel. In any case, the double shaft furnace comprises a first shaft and a second shaft arranged in parallel to the first shaft.

[0018] "Vertical direction" may generally refer to a direction perpendicular to the ground. In particular, the vertical direction may be defined by a length dimension of at least one of the shafts.

[0019] "Horizontal direction" may generally refer to a direction parallel to the ground and/or perpendicular to the vertical direction. In particular, the horizontal direction may be defined by a length dimension between the shafts. The connection channel extends along the horizontal direction.

[0020] "Top gas" generally refers to a gas which can be extracted from a top portion of a shaft in operation. For example, a top gas may comprise at least (in terms of molar percent) approximately 16 % carbon monoxide (CO), 12 % carbon dioxide (CO2), 52 % hydrogen (Hz) and 20% water (H20). Top gas composition can vary according the type of fuel. "Export gas" generally refers to the part of the top gas that has passed a gas cleaning apparatus and that may be exported to a different (industrial) facility.

[0021] "Recirculation gas", respectively syngas or reducing gas, generally refers to a gas mixture which is recycled, respectively which is used for initiating a reduction of the metallic ores. For example, a recirculation gas typically comprises at least (in terms of molar percent) approximately 22 % carbon monoxide (CO), 1 % carbon dioxide (CO), 74 % hydrogen (H2) and 3% water (H:O). Recirculation gas composition can vary according the type of fuel.

[0022] The double shaft furnace arrangement may be operated as a recycling arrangement, the term "gas" may thus generally refer to all sorts of gases or gas compounds mentioned above, especially in view of the fact that said gases are created, conducted, treated and/or changed in their composition during their passage through the double shaft furnace arrangement.

[0023] Each shaft of the double shaft furnace arrangement may be described by the structure of its inner zones, wherein each zone performs different reactions, respectively has different functions / purposes. The shaft of each furnace substantially has at least 3 different zones, one above the other. The lowest zone, which is a zone located in or at, respectively above, the bottom of the shaft, is referred to as the cooling zone. Above the cooling zone, the high temperature reduction zone begins. The regenerative zone is situated above the high temperature reduction zone, at the top of the furnace. A shaft may have a height of 20 meters to 40 meters, preferably 26 to 30 meters. Each shaft may comprise one or a plurality of oxy- fuel injectors, respectively injecting devices, having outlets defining the junction level between the regenerative zone and the high temperature reduction zone. Each oxy-fuel injector may at least extend partially along the vertical direction. The vertical direction is a direction perpendicular to the ground.

[0024] The terms "upper", "lower", "bottom" or "top" refer to positions with respect to the vertical direction extending from the ground / bottom. For example, a lower section of a furnace may be a section or portion that is at or near the ground or the bottom of the shaft.

[0025] "Cooling zone" may generally refer to an area and/or volume inside a shaft, in particular at a "lower" end portion of the shaft.

[0026] "Bottom portion" generally refers to a lower portion, respectively section, of the shaft.

The bottom portion comprises the cooling zone of the shaft.

[0027] "Regenerative zone" generally denotes an area or volume inside the shaft at or below a top portion of said shaft. In other words, the top portion of the shaft comprises the regenerative zone.

[0028] "High temperature reduction zone", respectively "reduction zone", generally denotes the area or volume between the regenerative zone and the cooling zone. At the beginning of the high temperature reduction zone, respectively at or in vicinity to the height / level were the reduction zone borders the regenerative zone, which is also referred to as "junction level", fuel and oxygen may be injected through injectors or gas lances of an injectors or preferably oxy- fuel injectors in order to form the "hot reducing gas", which allows to heat up the metallic oxides.

The reducing gas thereby supplies the energy required for the reduction reaction(s). The partial oxidation of the hydrocarbon fuel(s) and or the recirculation gas in turn generates mostly carbon monoxide (CO) and hydrogen (Hz).

[0029] The positions of the oxy-fuel injectors, respectively the outlets of each oxy-fuel injector of the plurality of oxy-fuel injectors may define the height / level of the regenerative zone with respect to a bottom (level). The position of the outlet may thus allow to control the residence time in the respective zones and determine the amount of heat transferred between gas and solids.

[0030] The injected oxygen volume may be adjusted to obtain a reducing gas temperature in the range of 800°C to 1050°C and preferably in the range of 920°C to 950 °C, which has been found to prevent or at least to significantly reduce iron oxide melting and sticking. The solids (passing down through the regenerative zone) enter the high temperature reduction zone whilst having a temperature in a range of 650°C to 850°C. This temperature level is high enough to prevent soot or carbon deposition, which might otherwise cause blockages after a period of time. At the lower portion of the reduction zone, respectively when entering the cooling zone, the solids generally have a temperature in a range of 800°C to 950°C.The temperature should be adapted to the characteristics of the solids. At the end of the reduction zone, respectively the height / level where the upper portion of the cooling zone contacts the lower portion of the reduction zone, the hot reducing gas coming from the top, may mix with the warmed (recirculation) gas coming from the bottom and pass through a connection channel.

[0031] "Connection channel" may generally refer to a constructional element that is arranged between the first shaft and the second shaft. The connection channel may for example be configured to put the first shaft in communication with the second shaft. In other words, gases flow through the first shaft to the second shaft via the connection channel, and vice versa. The connection channel extends in a generally horizontal direction and may at least be partially arranged at the lower end of the reduction zone of each of the first shaft and the second shaft.

In other words, the connection channel may be so as to have one end portion partially overlapping with a "lower" portion of the high temperature reduction zone as well as an upper portion of the "cooling zone" of the first shaft, whilst the other end portion partially overlaps with a lower portion of the high temperature reduction zone as well as an upper portion of the cooling zone of the second shaft.

[0032] The connection channel may be provided with at least one injector assembly. The injector assembly may consist of or comprise e.g. an oxy-fuel injector, such that additional reducing gas and heat may be introduced into the gas passing through the connection channel.

Additionally or alternatively (as a variant), the injector assembly, respectively "injector", may consist of or comprise an electric heated syngas injector and/or a plasma torch for injecting hot syngas and/or recirculation gas into the connection channel. Additionally some electric heating devices as for example electric radiant tubes can be arranged in the connection channel. Additionally or alternatively, the injector assembly may consist of or comprise at least one oxygen injector and at least one fuel injector arranged in proximity to each other.

[0033] Due to the injector assembly, the gas passing through the connection channel may be further heated, whereby its ability for performing reduction reactions increases. This arrangement allows in particular to control and/or influence the process parameters, such as the temperature and/or the composition and/or the volume of the gas flowing into one of the shafts. As a result, the process conditions of the shaft into which the gas is conducted are precisely controllable due to the oxy-fuel injector. In other words, due to the connection channel and the oxy-fuel injector, the process conditions and parameters of at least one of the shafts, in particular the shaft wherein the gas flows after passing the oxy-fuel injector, may be controlled such that they are different to the process conditions and parameters of the shaft, from which the gas has been conducted. It should be noted that also the arrangement of one or more electric heating devices such as electric radiant tubes further contribute to precisely control, respectively influence, the process conditions and parameters.

[0034] The term "Injector", respectively "injecting device" or "injector assembly", may generally refer to a device for introducing/ injecting a medium, such as e.g. a gas, a liquid, a powder, a fuel or a fluid. The injector may for example be configured to inject oxygen and/or fuel and/or a reducing agent such as CO or H at a specific temperature. Additionally or alternatively, an injector may also be configured to inject nitrogen or other substances. For example, the connection channel may be equipped with one or more injector assemblies, preferably with one or more injectors that protrude laterally into the connection channel at, from or through a side or wall section of the connection channel into, respectively forward, an inner volume of the channel. Further for example, in particular an injector arranged at the top portion of a respective shaft may comprise a feeder, for example a feeder that protrudes laterally or substantially along a horizontal direction into the shaft, wherein such an injector may further comprise a gas lance connected to or that is integral with the feeder, wherein the gas lance may extend along a direction different to the horizontal direction, e.g. the vertical direction.

[0035] "Fuel" may generally refer to a combustible medium comprising at least one of the following: hydrogen, hydrocarbon, alcohol, ammonia or compounds derived from those, or mixtures thereof.

[0036] Due to the injector assembly protruding laterally into the connection channel, a further injection of fuel and oxygen may be performed that is different from the first fuel and oxygen injection level caused at the outlets of the plurality of oxy-fuel injectors extending vertically within each of the shafts. The injections at these different locations and height levels allow to generate and control parameters of the reducing gas quantity, temperature and composition.

In addition, the reducing gas temperature may be adjusted and/or controlled particularly quickly and efficiently. The gas temperature and gas composition within the connection channel may in particular be adjusted for controlling the conditions and process parameters at which the reduction reaction of the metal oxides takes place in the adjacent shafts.

[0037] The at least one injector assembly protruding into the connection channel may be arranged laterally of the connection channel. For example, the injector assembly may be arranged at a top portion of the connection channel, yet it should be noted that the placement of the injector assembly or its different elements is not restricted to the top portion. The injector assembly may comprise at least one oxy-fuel injector and/or an electric heated syngas injector and/or a plasma torch.

[0038] An oxy-fuel injector may for example consist of or comprise an assembly of one or more pairs of lances. A "pair of lances" generally refers to a combination consisting or comprising at least one fuel lance and at least one oxygen lance. Preferably, a pair of lances may be formed of or comprise coaxial lances, in particular two coaxial lances, wherein the coaxial lances form an assembly of two pipes, wherein one small diameter pipe, respectively a first lance, is inserted in a bigger diameter pipe, respectively a second lance. The coaxial lances may particularly improve the partial combustion of fuel and oxygen in comparison to a two single injection lance system. In this context, the term "coaxial" refers to a common axe of the two lances. In other words, the two pipes share one common axis.

[0039] In a first embodiment, the injector assembly consists of or comprises at least one of the following: one electric heated syngas injector, a plasma torch for injecting hot syngas, an oxyfuel injector. An electric heated syngas injector may refer to an apparatus that is configured to heat a medium, such as syngas, by means of electrical power. "Plasma torch" generally refers to a plasma generating apparatus configured to inject hot syngas and/or recirculation gas into the channel. "Oxyfuel injector" generally refers to an injector that injects a mixture of oxygen and fuel — or that allows to inject oxygen and fuel at the same time.

[0040] In another embodiment, the double shaft furnace further comprises an electric heating device consisting of or comprising of a plurality of electric radiant heating tubes, wherein the electric heating tubes are arranged within the connection channel. The tubes may for example be essentially cylindric or have a round cross-sectional shape. It is understood that the tubes may also present in other forms. The electric heating device, respectively the electric radiant heating tubes allow that the gas mixture passing through the connection channel may be further heated. In particular, the electric heating device allow that the process parameters of the gas mixture as well as the process parameters of the shaft in which the gas mixtures streams may be further and more precisely controlled. In addition, the radiant heating tubes also allow to influence the reaction of the fuel and oxygen combustion taking place within the connection channel.

[0041] In another embodiment, each shaft comprises at least one bottom recirculation gas inlet and at least one top recirculation gas inlet. "Inlet" may generally refer to an opening or an injector or a similar structure configured to conduct and/or inject the recirculation gas into a respective shaft. The top recirculation gas inlet may consist of or comprise an opening at the top of the shaft. The free space at the top portion of a respective shaft allows to distribute the top recirculation gas evenly before said gas flows through the solids.

[0042] "Recirculation gas" generally refers to a gas that may be rich in CO and/or H close to ambient temperature. The recirculation gas may have a temperature in a range between 40°C to 80°C. The recirculation gas may in particular, when injected at the top of a shaft reheat itself when it contacts the solids. The (recirculation) gas may also be heated when entering the high temperature reduction zone due to the injected fuel and oxygen. The reducing gas may also be heated when passing the connection channel due to the injected fuel and oxygen and/or due to the hot syngas from an electric heated injector and/or due to the hot syngas from plasma torch and/or the electric radiant tubes inside in the connection channel.

[0043] In another embodiment, each one of the first shaft and the second shaft has a plurality of oxy-fuel injectors arranged at least partially along the vertical direction for injecting oxygen and fuel into the high temperature reduction zone of each shaft. In other words, each one of the first shaft and the second shaft have a plurality of oxy-fuel injectors for injecting oxygen and fuel into a respective shaft. The oxy-fuel injectors may comprise lances that inject the oxygen and fuel into the high temperature reduction zone. In particular, each oxy-fuel injector of the plurality of oxy-fuel injectors may further comprise an oxygen feeder and a fuel feeder, wherein the feeders protrude horizontally into the top portion (i.e. the free space) above the regenerative zone of said respective shaft. An (oxyfuel) lance that extends along a vertical direction may be connected at an upper portion to both, the fuel feeder as well as the oxygen feeder. The oxyfuel lances may be provided with an opening at their tip, respectively end section, wherein the opening is arranged at the beginning of high temperature reduction zone, such that oxygen and fuel are injected into the high temperature reduction zone. The feeder, which may be formed as pipelines, may be integral with a respective oxyfuel lance or feed a plurality of connected oxyfuel lances. Due to the oxyfuel injectors, the oxygen and fuel may be dissipated at or near the center of the shaft, or at different locations of the shaft, such that the reducing gas is evenly distributed and the generation of hot spots and/ or cold areas may be prevented efficiently. Since the lances are arranged along a vertical axis of each shaft, there is no mechanical constrain induced by the passing burden along the lance, except for minor frictions. In order to further lessen the effect of frictions of the descending burden, respectively the solids, the lances may have a particularly thin form, i.e. a particularly small diameter.

[0044] In other words, each shaft may have a plurality of oxy-fuel injectors extending at least partially through the regenerative zone along the vertical direction, wherein each oxy-fuel injector of the plurality of oxy-fuel injectors has an outlet arranged at an upper end portion of the high temperature reduction zone. Due to the oxy-fuel injectors, the fuel and oxygen may be dissipated at different locations at the same height level. In addition, the oxy-fuel injector tips specifically define the height level of the junction level, respectively the border between the high temperature reduction zone and the regenerative zone.

[0045] In another embodiments, each oxy-fuel injector of the plurality of oxy-fuel injectors is fluidly and/or gas-tightly connected to an oxygen feeder and a fuel feeder. It is understood that the oxy-fuel injectors arranged at the top of a respective shaft furnace as well as an oxy-fuel injector arranged at the channel may be fluidly and/or gas-tightly connected to the one or more oxygen feeder(s) and fuel feeder(s). The term "gas-tight" generally refers to a connection configured for providing a closed fitting which prevents that pressurized, harmful and/or explosive gases may quit said connection.

[0046] In another embodiment, a first gas-tight valve is arranged upstream of the fuel feeder and downstream of a fuel supply, wherein a second gas-tight valve is arranged upstream of the fuel feeder and downstream of a recirculation gas supply, wherein a third gas-tight valve is arranged upstream of the oxygen feeder and downstream of an oxygen supply, and optionally, wherein a fourth gas-tight valve is arranged upstream of the oxygen feeder and downstream of a nitrogen supply and a fifth gas-tight valve is arranged upstream of the oxygen feeder and downstream of the recirculation gas supply.

[0047] "Recirculation gas supply" may refer to a recirculation gas pipeline or a similar apparatus stocking recirculation gas. Due to this arrangement, an oxyfuel injector may inject alternatingly or simultaneously fuel and/or oxygen and/or recirculation and/or nitrogen gas. It should be noted that the injection of recirculation gas may in particular have the purpose to protect, respectively cool down, the lances when the shaft is in regenerative mode.

Alternatively, or additionally, the recirculation gas may be injected at the top of a respective shaft. It should be noted that when the operation mode of a shaft switches, nitrogen may be injected into the feeders during a short time period, whereby the injectors are flushed, which in turn prevents hazards.

[0048] In another embodiment, each oxygen feeder is fluidly and/or gas-tightly connected to an oxygen supply, and each fuel feeder is fluidly and/or gas-tightly connected to a fuel supply, wherein each oxygen feeder and each fuel feeder are fluidly and/or gas-tightly connected to the at least one recirculation gas top inlet or at least a recirculation gas pipeline.

[0049] In another embodiment, each one of the first shaft and the second shaft has at least one gas vent connected to at least one top gas pipeline for conducting the top gas to a gas cleaning apparatus, wherein each gas vent is arranged at a top portion of the respective shaft and wherein said top gas pipeline has a gas outlet connected to said gas cleaning apparatus. "Gas vent" may generally referto any sort of constructional element permitting the gas to leave a shaft. For example, a gas vent may have the form of a pipeline. The double shaft furnace arrangement may comprise or be connected to a gas cleaning apparatus. "Gas cleaning apparatus" may generally refer to a gas cleaning plant comprising of a dust catcher and/or a bag filter and/or an electrostatic precipitator and/or a wet scrubber which remove solids / dusts from the top gas and cools the top gas down to 25-50°C. The cooling of top gas also to reduce the water content.

[0050] In another embodiment, the gas cleaning apparatus comprises: a wet scrubber for capturing the top gas dust for quenching the gas and (thus) removing water; and optionally, a dry dust capturing unit arranged upstream of the wet scrubber, wherein the dry dust capturing unit comprises at least one of the following: a dust catcher, a cyclone, a bag filter, an electrostatic precipitator. The wet scrubber allows that the top gas dust is captured and evacuated in, respectively as, sludge.

[0051] In another embodiment, the double shaft furnace arrangement further comprises a CO: removal apparatus (for) removing carbon dioxide from gases discharged by the gas cleaning apparatus, wherein the removal apparatus is gas-tightly connected to and arranged downstream of the gas cleaning apparatus. The double shaft furnace arrangement may comprise a CO» removal apparatus for removing carbon dioxide from the gas discharged by the gas cleaning apparatus, wherein the removal apparatus is gas-tightly arranged downstream of the gas cleaning apparatus. The COz removal plant may have two exit streams.

One stream conducts the recirculation gas rich in CO and Hz, the second stream conducts the captured CO». The captured CO» gas may be sold for industrial applications, sequestrated, stored or, if necessary, vented to the atmosphere.

[0052] In another embodiment, the removal apparatus and/or a compression unit for compressing the recirculation gas arranged downstream of the removal apparatus discharge(s) a recirculation gas having a temperature in a range of 40°C to 120°C, wherein a recirculation pipeline (for) conducting the recirculation gas is connected to and/or integral with each bottom recirculation gas inlet and/or each top recirculation gas inlet and/or the oxygen feeder and/or the fuel feeder. The double shaft fumace arrangement may comprise a compression unit arranged downstream the CO. removal apparatus. Due to the compression performed by the compression unit, the recirculation gas can be brought to a temperature in a range of 40°C to 120°C. The recirculation pipeline collecting the recirculation gas is connected to and/or integral with the bottom recirculation gas inlet and/or the top recirculation gas inlet and/or the oxygen feeder and/or the fuel feeder.

[0053] The invention also concerns a method for operating a double shaft furnace arrangement. The method comprises in a first step: injecting oxygen and fuel into the high temperature reduction zone of the first shaft, injecting recirculation gas into the top portion of the first shaft, injecting oxygen and fuel into the connection channel by at least one injector assembly protruding laterally into the connection channel, charging metallic oxides into the second shaft, extracting top gas at the top portion of the second shaft, extracting metallic products from the bottom portion of the second shaft; and in a second step: injecting oxygen and fuel into the high temperature reduction zone of the second shaft, injecting recirculation gas into the top portion of the second shaft, injecting oxygen and fuel into the connection channel by the at least one injector assembly, charging metallic oxides into the first shaft, extracting top gas at the top portion of the first shaft, and extracting metallic products from the bottom portion of the first shaft.

[0054] In other words, in the first step, the recirculation gas is injected at the top of the first shaft. Oxygen and fuel are injecting into the high temperature reduction zone of the first shaft.

At the same time, a small volume of recirculation gas is injected through the lances of the second shaft and the produced top gas is collected from second shaft. Oxygen and fuel are injected into the connection channel. The metallic oxides are charged into the second shaft and metallic products are extracted from the bottom portion of the second shaft. In the second step, the recirculation gas is injected at the top of the second shaft, oxygen and fuel are injected into the high temperature reduction zone of the second shaft, and recirculation gas is injected through the lances of the first shaft. In the second step, the top gas is collected from the first shaft. Like in the first step, oxygen and fuel are injected into the connection channel. The metallic oxides are charged into the first shaft and metallic products are extracted from the bottom portion of the first shaft.

[0055] The aforementioned improvements and embodiments of the dual shaft furnace arrangement also apply to the method for operating a double shaft furnace arrangement.

[0056] Since the method for operating a double shaft fumace is carried out based on two steps, the two shafts are operated in an alternating manner.

[0057] In an embodiment, the method further comprises in the first step and the second step heating a gas passing through the connection channel by the electric heating device. The gas mixture passing through the connection channel may be further heated by the electric heating device, respectively the electric radiant tubes, which allows to more precisely control the temperature of the gas mixture passing the connection channel as well as the process conditions and parameters of the shaft in which the gas mixture is conducted.

[0058] In an embodiment, the metallic oxides have a temperature in a range of -15°C to 40°C, preferably in a range of 15°C to 30°C, most preferred a temperature of 25°C; and/or wherein the metallic products have a temperature in a range of 120°C to 700°C; wherein the top gas has a temperature in a range of 80°C to 250°C, preferably in a range of 130°C to 170°C, most preferred a temperature of 150°C.

[0059] In another embodiment, in the first step, the recirculation gas may be injected at the top of the first shaft with a first pressure and the top gas may be vented at the top of the second shaft with a second pressure, and wherein, in the second step, the recirculation gas may be injected at the top of the second shaft with the first pressure and vented at the top of the first shaft with the second pressure, wherein the first pressure is higher than the second pressure; and wherein, optionally, the pressure difference, first pressure minus second pressure, may be in a range of 1.5 to 3.5 bar, preferably 2.0 to 2.5 bar. The pressure difference is mainly affected by the permeability of the burden, the size distribution of the solids.

[0060] In another embodiment, the method further comprises: conducting the top gas via top gas pipeline to the gas cleaning apparatus arranged downstream of the plurality of shafts, conducting the (cleaned) top gas from the gas cleaning apparatus to the CO. removal apparatus arranged downstream the gas cleaning apparatus, and conducting the recirculation gas via a recirculation pipeline into the plurality of shafts.

[0061] In another embodiment, the method further comprises: compressing the recirculation gas by a compression unit arranged downstream of the CO» removal apparatus and upstream of the recirculation pipeline.

[0062] Further aspects and features of the present invention derive from the dependent claims, the attached drawing and the following description of the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Embodiments of the invention are now described by way of example and with reference to the attached drawings, wherein

FIG. 1: is a schematic view of a double shaft furnace arrangement according to an embodiment, wherein the double shaft furnace arrangement performs the first step of the method;

FIG. 2: is a schematic view of a double shaft furnace arrangement according to an embodiment, wherein the double shaft furnace arrangement performs the second step of the method;

FIG. 3: is a schematic illustration in form of a Chaudron equilibria diagram illustrating the reducing gas evolution of the H2-H2O atmosphere;

FIG. 4: is a schematic illustration in form of a Chaudron equilibria diagram illustrating the CO-COz atmosphere;

FIG. 5: is a schematic illustration in form of a Chaudron equilibria diagram demonstrating that the oxidation degree of the gas is significantly reduced when the recirculation gas rate is doubled;

FIG. 6: is a schematic illustration of the evolution of the temperature of a piece of solid passing one of the shafts.

DESCRIPTION OF EMBODIMENTS

[0064] FIG. 1 shows a schematic view of a double shaft furnace arrangement 10 according to an embodiment, wherein the double shaft furnace arrangement 10 performs the first step of the method, whilst Fig. 2 illustrates schematically the second step.

[0065] As can be derived from Figs. 1 and 2, the double shaft fumace arrangement 10 comprises two shafts 11, 21, wherein reference sign 11 refers to the first shaft and reference sign 21 refers to the second shaft. Both shafts 11, 21 extend along the vertical direction Z.

Each shaft has three different zones consisting of a regenerative zone A, a cooling zone C, and a high temperature reduction zone B above the cooling zone C and below the regenerative zone A. As illustrated, the cooling zone C is partially delimited by the bottom portion 12 of shaft 11 and the bottom portion 22 for shaft 21. The regenerative zone A is delimited by a top portion 13 for shaft 11 and a top portion 23 for shaft 21.

[0066] The connection channel 30 connects a bottom portion, respectively lower section, of the high temperature reduction zone B of the first shaft 11 with a bottom portion, respectively lower section, of the high temperature reduction zone B of the second shaft 21 along a horizontal direction X. As illustrated, at least one injector assembly comprising an oxy-fuel injector 31 protrudes laterally into the connection channel 30. It should be noted that the connection channel 30 can be further provided with an electric heating device comprising a plurality of electric radiant tubes 32 (which is schematically illustrated in Figs. 1 and 2). The injector assembly may further comprise an electric heated syngas injector (not shown). In addition, the injector assembly may further comprise a plasma torch 33 for injecting hot syngas and/or recirculation gas.

[0067] As further illustrated in Fig. 1, each shaft 11, 21 comprises one or more bottom recirculation gas inlets 14, 24 and top recirculation gas inlets 15, 25.

[0068] In addition, each shaft 11 and 21, has a plurality of (oxy-fuel) injectors, wherein each injector comprises a feeder and a lance connected to the feeder. The oxygen feeders 16, 26 and fuel feeders 17, 27 protrude along a horizontal direction X in the free space above the regenerative zone À and thus in a zone above the burden at the top of each shaft along. The lances 18, 28 extend along the vertical direction Z through the regenerative zone A. The oxy- fuel injectors, respectively the lances 18, 28 of the oxy-fuel injectors, have their respective outlets at the upper end of the high temperature reduction zone B.

[0069] As can be derived from Fig. 1 and Fig. 2, each shaft 11, 21 has also a gas vent 19, 29 connected to atop gas pipeline 41 conducting the top gas to a gas cleaning apparatus 42. The gas vent 19, 29 is arranged/located at the top portion 13, 23 of a respective shaft 11, 21.

[0070] The reference sign 51 refers to a COz removal apparatus for removing the carbon dioxide from gases discharged by the gas cleaning apparatus 42. The CO. removal apparatus 51 is gas-tightly connected with the cleaning apparatus 42 by a pipeline 43. The CO, removal apparatus 51 is located/ arranged downstream of the gas cleaning apparatus 42. The CO: apparatus 51 discharges the CO; free gas (rich in CO and H2) in the pipeline 52 and the CO: gas in the CO; gas pipeline 53. In addition, a compression unit 61 arranged downstream the

CO» removal apparatus 51 is connected by the CO; free gas pipeline 52 to the CO, removal apparatus 51 and discharges the recirculation gas having a temperature in a range of 40°C to 80°C. In this context, an export gas pipeline 54 is connected to the CO; free gas pipeline 52 arranged between the CO» removal apparatus 51 and the compression unit 61, which allows in case of necessity to evacuate the gas in excess. A recirculation gas pipeline 62, which collects the discharged recirculation gas from the compression unit 61, is connected to the bottom recirculation gas inlets 14, 24 as well as to the top recirculation gas inlets 15 and 25 as well as the oxygen feeders 16, 26 and fuel feeders 17, 27. It should be noted that a connection between the nitrogen supply and the oxygen feeders 16, 26 is not illustrated in Fig.1.

[0071] In a first step, as illustrated by Fig. 1, metallic oxides are poured through the top portion 23 of the second shaft 21 into the second shaft 21. Recirculation gas conducted from the compression unit 61 is injected through the gas inlet 15 at the top of the first shaft 11. Oxygen and fuel are injected respectively in oxygen feeder 16 and fuel feeder 17 of shaft 11. The lances 18 of the injectors conduct the oxygen and the fuel to the top, respectively the upper portion, of the high temperature reduction zone B of the first shaft 11 where they ignite. The gas generated at, respectively near, the opening of the lances 18 dilutes in the recirculation gas, whereby the hot reducing gas is generated. In the first step, recirculation gas is also injected into the cooling zone C above the bottom portion 12 of the first shaft 11 and also into the cooling zone C above the bottom portion 22 of the second shaft 21. At the same time, a small quantity of recirculation gas is injected in the oxygen feeder 26 and fuel feeder 27 of the second shaft 21, whereby the corresponding injectors, respectively the lances 28 connected to the feeders 26, 27 are cooled and thus protected against heat and internal clogging. It should be noted that the "small quantity” of recirculation gas injected via the fuel feeders 26 and 27 is lesser in comparison to the quantity of gas injected via the oxygen feeder 16 and 17.

[0072] After reacting with the metallic oxides in the high temperature reduction zone B of first shaft 11, the hot reducing gas mixes with the recirculation gas leaving the cooling zone C of the first shaft 11. The mixture enters the connection channel 30. Due to injector assembly comprising the oxy-fuel injector 31, further amounts of oxygen and fuel are injected into the connection channel 30, which allows in particular to adjust the temperature and the composition of the hot reducing gas before entering the second shaft 21 high temperature reduction zone B.

[0073] At the bottom of the high temperature reducing zone B of the second shaft 21, the hot reducing gas leaving the connection channel 30 mixes with the recirculation gas coming from the cooling zone C of shaft 21. The hot reducing gas traverses the high temperature reduction zone B of shaft 21 whilst reducing iron oxides to metallic iron. While streaming upward the second shaft 21 into the regenerative zone A, the hot reducing gas reacts with the iron oxide by making a preliminary step of reduction and transferring its heat to the solids. During the first step, the developing / respectively the reducing gas is extracted at the top portion 23 of the second shaft. At the end of the first step, the metallic products are extracted, respectively poured, from the bottom portion 22 of the second shaft 21.

[0074] It should be noted that the injector assembly comprising the oxy-fuel injector 31 in the connection channel 30 is controlled such that the passing reducing gas is heated to a preset temperature before the gas enters the second shaft 21. This control may be achieved, for example, by measuring the temperature at both ends of the connection channel 30 and/ or by precisely defining the amount of fuel and/or oxygen injected into the connection channel 30.

The process conditions in the second shaft 21 may thus be influenced, respectively precisely adjusted, by the injection of fuel and oxygen into the connection channel 30. In this context, the plasma torch 33 and/or the electric heated syngas injector as well as the electric heating device comprising the radiant rubes 32 allow to further adjust the process parameters and conditions of the passing gas.

[0075] It should be noted that the same applies for the first shaft 11 during the second step.

At the end of the first step, a transition to the second step is carried out. In other words, after a predefined amount of time, for example 20 to 60 minutes, the operation mode of the double shaft furnace arrangement is switched from the first step to the second step. In other words, the two steps are performed in an alternating manner.

[0076] In the second step, as illustrated by Fig. 2, metallic oxides are poured through the top section of the first shaft 11. In the second step, the solids in the regenerative zone of the first shaft 11 will accumulate the heat transferred from the reducing gas before the gas leaves at the top the shaft 11, whilst the second shaft 21 is operated to heat in its regenerative zone A the recirculation gas injected at its top portion 23. Oxygen and fuel are injected through the oxy-fuel injectors, respectively the lances 28 of the oxy-fuel injectors at the top of the high temperature reduction zone B of the second shaft 21. Recirculation gas is also injected into the cooling zone C above the first shaft bottom 12 and above the second shaft bottom portion 22. At the same time, a small quantity of recirculation gas is injected in the oxygen feeder 16 and fuel feeder 17 of the first shaft 21 to protect the oxy-fuel injectors 18 against heat and internal clogging. Like in the first step, oxygen and fuel are injected into the connection channel by the injector assembly 31 and the passing gas is may be further heated by hot gas injected with the plasma torch 33 and/or by the radiant tubes 32, which allows to adjust and/or control parameters of the hot reducing gas, such as the temperature of the gas, as well as to adjust and/or control process parameters in the first shaft 11. In the second step, the top gas is extracted at the top portion 13 of the first shaft 11, whilst the metallic products are poured from the bottom portion 12 of the first shaft 11.

[0077] Before they are charged in one of the shafts, the metallic oxides are at ambient temperature of approximately 25°C, whilst the metallic products poured from the shafts have a temperature in a range of 120°C to 700°C. The metallic products are usually cooled down to about 120°C and then stored for further use. In some cases, however, the metallic products may be extracted at about 700°C and then used directly at that temperature to produce hot briquetted iron (HBI) or hot direct reduced iron (HDRI) which may be fed directly into a smelter.

When the top gas is extracted during the first or second step, the top gas has merely a temperature of approximately 150°C.

[0078] One further advantage of the present installation and process is therefore that no hot items (gas or solids) are introduced into the furnace and no hot items (gas or solids) are extracted from the furnace, except for the case where HBI or HDRI is produced.

[0079] In both steps, the first step and the second step, the top gas is conducted via the top gas pipeline 41 to the gas cleaning apparatus 42 arranged downstream the shafts 11, 21. After the gas has been cleaned and discharged from the gas cleaning apparatus 42, said gas, which is often referred to as "clean top gas" is further conducted to the CO. removal apparatus 51.

The CO» removal apparatus 51 is thus arranged downstream the gas cleaning apparatus 42.

In the CO2 removal apparatus 51, carbon dioxide is removed, such that the remaining gas, referred to as (re-)circulation gas, is conducted through a compressor unit 61 via recirculation pipeline 62 to the shafts 11, 21.

[0080] After having passed the high temperature reduction zone B, the solids enter the cooling zone C and leave the shaft furnace at the targeted temperature for the next, subsequent process. The temperature of the solids exiting the shaft furnace is adjusted by injecting at the bottom portion 12, 22 of a respective shaft via the bottom recirculation gas inlets 14, 24 the right quantity of recirculation gas.

[0081] After a period of time, the solids in the regenerative zone A of the second shaft 21 will have captured enough heat and the top gas temperature at the upper portion of the second shaft 21 will exceed a certain limit. At this point, a transition from the first step to the second step is initiated. A transition may occur after 20 minutes to 60 minutes.

[0082] During the first and/or second step, the oxygen volume is adjusted above partial oxidation stoichiometry, which allows obtaining a reducing gas temperature in the preferred range of 920°C to 950°C and to further prevent the soot generation and carbon deposition.

Yet, the oxidation degree of the gas given by the ratio CO,/(CO+CO;) and H20/(H2+H20) should be low enough to respect the reduction conditions according Chaudron equilibria diagram as illusted in Fig. 3 and Fig. 4. According the illustrated Chaudron equilibria diagrams, the complete reduction of iron oxides can be achieved at 950°C if the ratio COz/(CO+CO2) is less 0.3 and the ratio H:0/(H2+H20) is less than 0.4 in the reduction gas. Therefore, the amount of CO or Hz introduced in the shaft furnace should be much higher than the stoichiometric demand for the chemical reactions of the reduction of the metallic oxides. In other words, CO» and H>O produced during the reduction reaction should remain sufficiently diluted. The CO: and H-O dilution factor is kept high by increasing the quantity of recirculation gas (rich in CO and Hy) injected at the top of the shaft. Therefore, a major portion of the top gas is recirculated after removing H20 in the gas cleaning apparatus and after removing the CO2 in the CO2 removal apparatus. The driving force for the reduction reaction kinetic is the oxidation degree deviation of the reducing gas to the equilibrium shown by the diagrams.

[0083] Fig. 5 shows that the oxidation degree of the gas is significantly reduced when the recirculation gas rate injected at the top is doubled. It had been surprising found that when the recirculation gas rate injected at the top is doubled, the net energy consumption increases only by 1.4%.

[0084] One further advantage of the regenerative double shaft reduction furnace is, that it can recirculate a considerable quantity of gas without affecting the energy consumption of the furnace. Indeed, the necessary energy for heating an extra volume of recirculation gas injected at the top of the, e.g., first shaft 11 is recovered in the regenerative zone A of the, e.g., second shaft 21 before the gas exits the furnace 10.

[0085] Fig. 6 describes the temperature of a piece of solid traversing a shaft from the top portion to the bottom. As can be derived, the piece of solid has a starting temperature (at the top portion) of approximately 25°C, whilst the gas may have a temperature of approximately 100°C in said top section. Within the regenerative zone A, the piece of solid is heated.

[0086] Depending on the number of (operation) cycles performed by the double shaft furnace as well as the gas quantity, composition and temperature, a generally increasing, saw-blade- shaped temperature curve results for the solid passing the regenerative zone À as well as for the gas. It should be noted that the two curves thus represent a function of the distance between the starting point of the solid part and its actual position in the shaft. While passing through the high temperature reduction zone B, the temperature of the solid piece as well as the gas temperature fluctuate around a temperature between 800°C and 900°C, which results in another saw-blade shaped temperature curve. The fluctuation is likewise caused by the number of switching operation cycles of the double shaft furnace. When entering the cooling zone C, the solid piece generally has a temperature about 850°C to 880°C. In the cooling zone

C, the solid piece is cooled down constantly, such that the solid piece has a temperature of about 100°C to 130°C at the bottom (portion) of the shaft. The temperature of the surrounding gas in the cooling zone C increases with rising distance to the bottom of the shaft, respectively decreases steadily with decreasing distance to the bottom of the shaft. The surrounding gas in the cooling zone C has a temperature below that of the solid piece.

[0087] The discussed embodiments are examples of the invention. The components of the respective embodiment(s) each represent individual features of the invention which are to be considered independently of each other and which also further develop the invention independently of each other. The features are thus also to be regarded as components of the invention individually or in a combination other than the combination shown. Furthermore, the described embodiments can also be supplemented by further features of the invention already described. Further features and embodiments of the invention result for the skilled person in the context of the present disclosure and the claims.

REFERENCE SIGNS

A regenerative zone

B high temperature reduction zone

C cooling zone double shaft furnace arrangement 11,21 first shaft, second shaft 12,22 shaft bottom 13,23 shaft top portion 14,24 recirculation gas bottom inlet 15,25 recirculation gas top inlet 16,26 oxygen feeder 17,27 fuel feeder 18,28 oxy-fuel injector 19,29 top gas vent connection channel 31 oxy-fuel injector 32 electric radiant heating tubes 33 electric heated syngas injector and/or syngas plasma torch 41 top gas pipeline 42 gas cleaning apparatus 43 clean top gas pipeline 51 CO. removal apparatus 52 CO» free gas pipeline 53 CO» gas pipeline 54 export gas pipeline 61 compression unit 62 recirculation gas pipeline

Claims (17)

1. Double shaft furnace arrangement (10) for the direct reduction of metallic iron oxides, the double shaft furnace arrangement (10) comprising: - at least a first shaft (11) and a second shaft (21) extending along a vertical direction (2); wherein each shaft (11; 21) has a cooling zone (C) in a bottom portion (12, 22) of each shaft (11; 21), a regenerative zone (A) in a top portion of each shaft, and a high temperature reduction zone (B) arranged between the regenerative zone (A) and the cooling zone (C); - a connection channel (30) connecting the first shaft (11) with the second shaft (21), wherein the connection channel (30) extends along a horizontal direction (X), wherein the connection channel (30) is arranged at a lower end of the high temperature reduction zone (B) and at an upper end of the cooling zone (C) of each of the first shaft (11) and the second shaft (21); and wherein - at least one injector assembly (31) protruding laterally into the connection channel (30).

2. Double shaft furnace arrangement (10) according to claim 1, wherein the injector assembly consists of or comprises at least one of the following: an electric heated syngas injector, a plasma torch, an oxyfuel injector.

3. Double shaft furnace arrangement (10) according to any one of the preceding claims, wherein the double shaft furnace further comprises an electric heating device (32) consisting of or comprising of a plurality of electric radiant heating tubes (32), wherein the electric heating tubes (32) are arranged within the connection channel (30).

4. Double shaft furnace arrangement (10) according to any one of the preceding claims, wherein each shaft (11; 21) comprises at least one bottom recirculation gas inlet (14; 24) and at least one top recirculation gas inlet (15, 25).

5. Double shaft furnace arrangement (10) according to any one of the preceding claims, wherein each one of the first shaft (11) and the second shaft (21) has a plurality of oxy-fuel injectors (18; 28) arranged at least partially along the vertical direction (2) for injecting oxygen and fuel into the high temperature reduction zone (B) of each shaft (11; 21).

6. Double shaft fumace arrangement (10) according to claim 5, wherein each oxy-fuel injector (18; 28) of the plurality of oxy-fuel injectors is fluidly and/or gas-tightly connected to an oxygen feeder (16; 26) and a fuel feeder (17; 27).

7. Double shaft furnace arrangement (10) according to claim 6, wherein a first gas-tight valve is arranged upstream of the fuel feeder (17; 27) and downstream of a fuel supply; wherein a second gas-tight valve is arranged upstream of the fuel feeder (17; 27) and downstream of a recirculation gas supply; wherein a third gas-tight valve is arranged upstream of the oxygen feeder (16; 26) and downstream of an oxygen supply; and optionally, wherein a fourth gas-tight valve is arranged upstream of the oxygen feeder (16, 26) and downstream of a nitrogen supply and a fifth gas-tight valve is arranged upstream of the oxygen feeder (16, 26) and downstream of the recirculation gas supply.

8. Double shaft furnace arrangement (10) according to any one of the preceding claims, wherein each oxygen feeder (16, 26) is fluidly and/or gas-tightly connected to an oxygen supply; and wherein each fuel feeder (17, 27) is fluidly and/or gas-tightly connected to a fuel supply; and wherein each oxygen feeder (16, 26) and each fuel feeder (17, 27) are fluidly and/or gas- tightly connected to the at least one recirculation gas top inlet (15; 25) or at least a recirculation gas pipeline (62).

9. Double shaft furnace arrangement (10) according to any one of the preceding claims, wherein each one of the first shaft (11) and the second shaft (21) has at least one gas vent (19, 29) connected to at least one top gas pipeline (41) for conducting top gas to a gas cleaning apparatus (42); wherein each gas vent (19; 29) is arranged at a top portion (13; 23) of the respective shaft (11; 21); and wherein said top gas pipeline (41) has a gas outlet connected to said gas cleaning apparatus (42).

10. Double shaft fumace arrangement according to claim 9, wherein the gas cleaning apparatus (42) comprises: - a wet scrubber for capturing the top gas dust for quenching the gas and removing water; and - optionally, a dry dust capturing unit arranged upstream of the wet scrubber, wherein the dry dust capturing unit comprises at least one of the following: a dust catcher, a cyclone, a bag filter, an electrostatic precipitator.

11. Double shaft furnace arrangement (10) according to any one of the preceding claims further comprising a CO. removal apparatus (51) for removing carbon dioxide from gases discharged by the gas cleaning apparatus (42), wherein the removal apparatus (51) is gas- tightly connected to and arranged downstream of the gas cleaning apparatus (42).

12. Double shaft furnace arrangement (10) according to claim 11, wherein the removal apparatus (51) and/or a compression unit (61) for compressing the recirculation gas arranged downstream of the removal apparatus (51) discharge(s) a recirculation gas having a temperature in a range of 40°C to 120°C, and wherein a recirculation pipeline (62) for conducting the recirculation gas is connected to and/or integral with each bottom recirculation gas inlet (14; 24) and/or each top recirculation gas inlet (15; 25) and/or the oxygen feeder (16; 26) and/or the fuel feeder (17; 27).

13. Method for operating a double shaft furnace arrangement (10) according to any one of the preceding claims, wherein the method comprises in a first step: injecting oxygen and fuel into the high temperature reduction zone (B) of the first shaft (11); injecting recirculation gas into the top portion (13) of the first shaft (11); injecting oxygen and fuel into the connection channel (30) by at least one injector assembly (31) protruding laterally into the connection channel (30); charging metallic oxides into the second shaft (21): extracting top gas at the top portion (23) of the second shaft (21); extracting metallic products from the bottom portion (22) of the second shaft (21); and in a second step: injecting oxygen and fuel into the high temperature reduction zone (B) of the second shaft (21); injecting recirculation gas into the top portion (23) of the second shaft (21); injecting oxygen and fuel into the connection channel (30) by the at least one injector assembly (31); charging metallic oxides into the first shaft (11); extracting top gas at the top portion (13) of the first shaft (11); extracting metallic products from the bottom portion (12) of the first shaft (11).

14. Method according to claim 13 further comprising, in the first step and the second step heating a gas passing through the connection channel (30) by the electric heating device 32.

15. Method according to any one of claims 13 to 14, wherein the metallic oxides have a temperature in a range of -15°C to 40°C, preferably in a range of 15°C to 30°C, most preferred a temperature of 25°C; and/or wherein the metallic products have a temperature in a range of 120°C to 700°C; wherein the top gas has a temperature in a range of 80°C to 250°C, preferably in a range of 130°C to 170°C, most preferred a temperature of 150°C.

16. Method according to any one of the preceding claims 13 to 15, wherein the method further comprises: conducting the top gas via top gas pipeline (41) to the gas cleaning apparatus (42) arranged downstream of the plurality of shafts (11, 21): conducting the top gas from the gas cleaning apparatus (42) to the CO; removal apparatus (51) arranged downstream the gas cleaning apparatus (42); and conducting the recirculation gas via a recirculation pipeline (62) into the plurality of shafts (11, 21).

17. Method according to claim 16, wherein the method further comprises: compressing the recirculation gas by a compression unit (61) arranged downstream of the CO. removal apparatus (51) and upstream of the recirculation pipeline (62).