A direct reduction shaft arrangement and a process for producing direct reduced iron

Abstract

The disclosure relates to a direct reduction shaft arrangement (1) comprising at least one ore charging arrangement (3) and a direct reduction shaft (5). Each ore charging arrangement comprises an ore charging vessel (7) and an ore feed pipe arrangement (9). The ore feed pipe arrangement comprises at least one lower pipe section (93) arranged internal to the direct reduction shaft (5). Each lower pipe section (93) of the ore feed pipe arrangement is further equipped with an adjustable pipe section (95). Each adjustable pipe section (95) is translationally extendible and / or retractable in relation to its respective lower pipe section (93). The disclosure further relates to a process for producing direct reduced iron from iron ore. Elected for publication:

Description

TECHNICAL FIELD The present disclosure relates to a direct reduction shaft arrangement and a process for producing direct reduced sponge iron from iron ore. More specifically, the disclosure relates to a direct reduction shaft arrangement and a process for producing direct reduced sponge iron from iron ore as defined in the introductory parts of the independent claims. BACKGROUND ART Prior art in the field of technology related to direct reduction of iron ore to sponge iron, in which a direct reduction shaft is used and in which the flow of material goes vertically downwards while meeting a counterflow of a reduction gas, preferably hydrogen gas, uses a feeding pipe, which extends from the top of the shaft into the shaft and which is fed with iron ore through a hopper arrangement. In shafts for direct reduction of iron ore to sponge iron, there is a need of controlling the residence time of the material that is to be reduced in a reduction zone in the shaft. Since the outcome of the reduction processes is dependent on factors such as reduction gas temperature, pressure, reduction gas composition, etc, the residence time of the iron ore in the shaft is crucial if a high degree of reduction, metallization, is to be achieved for given values of said other factors. The residence time can be controlled by controlling the height of the bed of the material that undergoes reduction inside the shaft. Differences in reaction thermodynamics and kinetics are expected to lead to differences in optimal residence time, and, as a result thereof, differences in optimal bed height. The bed height may to some degree be controlled by control of the rate with which iron ore is fed into the shaft. The feeding rate may be controlled by controlling the rate with which a hopper delivers iron ore to a feeding pipe. But, with a fixed position of a lower end of a feeding pipe the bed height cannot be higher than approximately the level the lower end of the feeding pipe. Bed height may be determined by the level of the feed pipe outlets in the shaft. Each feed pipe may contain a standing column of ore that is continuously or batchwise replenished from the ore charging vessel. Bed height is maintained in the shaft by the passive escape of ore from the outlet of each feed pipe as direct reduced iron is discharged from the bottom of the shaft and material descends in the shaft. Thus, in conventional direct reduction shafts for the production of sponge iron, the bed height is essentially constant and is not adjusted. The level of the lower end of the feed pipe decides the maximum upper level of the bed height. However, if a lower level of the bed height is required, this can only be done by emptying the feed pipe from material and let the bed height gradually sink to a lower level as a result of the out-take of sponge iron from the bottom of the shaft. In such a case, the bed height is not given by the position of the lower end of the feed pipe and has to be determined in some other way. This means that in direct reduction shafts of prior art, the bed height cannot be optimally adapted to prevailing conditions in the shaft. This is a shortcoming in particular when the composition or nature of the ingoing materials to the shaft is altered, for example in transitioning from a fossil-based reductant gas to a hydrogen reductant gas. Even if the shaft is not intended to be operated under varying conditions, a fixed bed height is also a shortcoming since it is desirable to be able to determine an optimal bed height empirically for the shaft, rather than bed height being a fixed parameter of the shaft as commissioned. SUMMARY OF THE INVENTION It would be advantageous to achieve a means of overcoming, or at least alleviating, at least some of the above-mentioned drawbacks. It would be desirable to enable a means of performing direct reduction that permits a greater degree of optimisation to prevailing operating conditions. It is an objective to provide continuous control of the bed height that alleviates the above-mentioned drawbacks of prior art, especially during lowering of the bed height, for controlling the residence time. The objective of the invention is achieved by means of a direct reduction shaft arrangement for producing direct reduced sponge iron from iron ore comprising: - a direct reduction shaft, - at least one ore charging arrangement, a sponge iron outlet at a bottom of the direct reduction shaft, wherein each ore charging arrangement comprises an ore charging vessel and an ore feed pipe arrangement, wherein the ore feed pipe arrangement comprises an upper pipe section and at least one lower pipe section, wherein the upper pipe section is arranged in communication with an ore outlet of the ore charging vessel, wherein the at least one lower pipe section is arranged internal to the direct reduction shaft, wherein the upper pipe section and the lower pipe section are arranged in communication such that the ore feed pipe arrangement may convey ore from the ore charging vessel to the direct reduction shaft, wherein each lower pipe section of the ore feed pipe arrangement is further equipped with a vertically adjustable pipe section, wherein each adjustable pipe section is translationally extendible and / or retractable in relation to its respective lower pipe section, wherein the direct reduction shaft arrangement further comprises measuring means for determining a discharge rate of sponge iron through the sponge iron outlet, drive means for driving the adjustable pipe section in a vertical direction, a control unit, which is operatively connected to said measuring means and to said drive means, said control unit being configured to - determine a set bed height on basis of one or more process parameters, - compare the actual bed hight with the set bed height, and, if the set bed is lower than the actual bed height, controlling the drive means to extend the adjustable pipe section downwards until the set bed height is obtained, the arrangement being characterised in that the control unit is configured to determine a bed height decrease rate corresponding to the determined discharge rate, and to control the drive means to extend the adjustable with a velocity that corresponds to the determined bed height decrease rate. The invention enables the maintenance of a column of iron ore in the feed pipe arrangement during increase as well as decrease of the bed height. No emptying of the feed pipe arrangement is needed before actual decrease of bed height is performed, since the adjustable feed pipe section (or sections) follows the motion downwards of the upper surface of the bed because of the discharge of sponge iron. No filling of the feed pipe arrangement from the bottom of the pipes is thus needed after decrease of the bed height. Preferably, temperature and pressure inside the shaft may thereby be maintained during bed height increase as well as during bed height increase. The invention thus contributes to a very stable process. The control unit may comprise any kind of control system configured to deciding the bed height and to control the motion of the adjustable on basis of the sponge discharge rate. It may comprise software / hardware, it may be a part of a control system for the whole direct reduction shaft, or it may comprise any kind of suitable electric circuit for the control of the drive means based on the data from the measuring means. The measuring means may comprise any kind of out-feed mechanism for the out-feed of sponge iron, whereby a measurable operation parameter of the out-feed mechanism is proportional to the sponge iron discharge rate. The determined bed height decrease rate is thus the height decrease rate that the bed will have as a direct consequence of the discharge rate, with no iron ore added to the bed. According to some embodiments, the control unit is configured compare the actual bed hight with the set bed height, and, if the set bed is higher than the actual bed height, controlling the drive means to retract the adjustable pipe section(s) upwards while feeding iron ore through the vertically adjustable feed pipe section(s) until the set bed height is obtained. According to some embodiments, the arrangement comprises a sensor for sensing presence of iron ore at a predetermined level in the feed pipe arrangement, wherein, said sensor is connected to the control unit and wherein the control unit is configured to control the ore charging vessel to fill the feed pipe arrangement with iron ore pellets up to said predetermined level and maintain a column of iron ore inside the feed pipe arrangement up to at least that level during said extension of the adjustable pipe section downwards. Preferably, said predetermined level is a level on an upper part of the feed pipe arrangement. According to some embodiments, the arrangement comprises a sensor for sensing presence of iron ore at a predetermined level in the feed pipe arrangement, wherein, said sensor is connected to the control unit and wherein the control unit is configured to control the ore charging vessel to fill the feed pipe arrangement with iron ore pellets up to said predetermined level and maintain a column of iron ore inside the feed pipe arrangement up to at least that level during said retraction of the adjustable pipe section upwards. According to some embodiments, said one or more process parameters comprises one or more of the following parameters: -    a composition of the reducing gas, -    a temperature of the reducing gas, - a flow rate of the reducing gas, -     a composition of the iron ore, -    a temperature of the iron ore. According to some embodiments, said one or more process parameters comprises each of the following parameters: -    a composition of the reducing gas, -    a temperature of the reducing gas, - a flow rate of the reducing gas, -     a composition of the iron ore, -    a temperature of the iron ore. Preferably, the parameters refer to the respective parameter value upon entrance of the reducing gas and iron ore into the direct reduction shaft. According to some embodiments, the adjustable pipe section is an adjustable sleeve arranged coaxially around the lower pipe section, wherein the adjustable sleeve is arranged to be translationally extendible and / or retractable along a common axis of the lower pipe section and adjustable sleeve. According to some embodiments, said drive means comprises adjustment rods extending through an upper cap of the direct reduction shaft, wherein the adjustment rods are arranged to be able to be translationally actuated to extend and / or retract the adjustable pipe section. According to some embodiments, the adjustment rods are arranged to be able to be manually actuated. According to some embodiments, the adjustment rods are arranged to be able to be actuated by a motor. According to some embodiments, the ore charging vessel is a pressurizable charging bin arranged to operate at a pressure of greater than atmospheric pressure. According to some embodiments, the arrangement comprises a plurality of ore charging arrangements, such as at least two or at least four ore charging arrangements. According to some embodiments, each ore feed pipe arrangement comprises a single lower pipe section. According to some embodiments, the ore charging vessel is a supply hopper arranged to operate at a pressure of two Bar or less, preferably at essentially atmospheric pressure. According to some embodiments, the arrangement comprises a single ore charging arrangement. According to some embodiments, the ore feed pipe arrangement comprises a plurality of lower pipe sections, such as at least four, at least eight or at least sixteen lower pipe sections. According to some embodiments, the ore feed pipe arrangement comprises an intermediate section arranged in connection with the upper pipe section at a first end and branching to a plurality of second ends, each second end being arranged in connection with one of the plurality of lower pipe sections. The objective of the invention is also achieved by means of a process for producing direct reduced sponge iron from iron ore in a direct reduction shaft comprising: - a direct reduction shaft, - at least one ore charging arrangement, a sponge iron outlet at a bottom of the direct reduction shaft, wherein each ore charging arrangement comprises an ore charging vessel and an ore feed pipe arrangement, wherein the ore feed pipe arrangement comprises an upper pipe section and at least one lower pipe section, wherein the upper pipe section is arranged in communication with an ore outlet of the ore charging vessel, wherein the at least one lower pipe section is arranged internal to the direct reduction shaft, wherein the upper pipe section and the lower pipe section are arranged in communication such that the ore feed pipe arrangement may convey ore from the ore charging vessel to the direct reduction shaft, wherein each lower pipe section of the ore feed pipe arrangement is further equipped with a vertically adjustable pipe section, wherein each adjustable pipe section is translationally extendible and / or retractable in relation to its respective lower pipe section, and wherein the process comprises the steps of: charging iron ore into the direct reduction shaft via the at least one ore charging arrangement, thereby establishing a bed in the direct reduction shaft having an initial bed height determined by the degree of extension and / or retraction of the vertically adjustable pipe section(s), introducing a reducing gas into the direct reduction shaft in countercurrent flow to the iron ore in order to reduce the iron ore to direct reduced iron, discharging sponge iron from the sponge iron outlet, determining a discharge rate of the sponge iron through the sponge iron outlet, determining a set bed height on basis of one or more process parameters, comparing the actual bed hight with the set bed height, and, if the set bed is lower than the actual bed height, extend the adjustable pipe section downwards until the set bed height is obtained, the process being characterised in that it comprises the step of 8 determining a bed height decrease rate corresponding to the determined discharge rate, and extending the adjustable pipe section downwards with a velocity that corresponds to the determined bed height decrease rate. According to some embodiments, if the set bed height is higher than the actual bed height, the process comprises the step of retracting the adjustable pipe section(s) upwards while feeding iron ore through the vertically adjustable feed pipe section(s) until the set bed height is obtained. According to some embodiments, the process comprises the step of filling the feed pipe arrangement with iron ore pellets up to a predetermined level and maintaining a column of iron ore inside the feed pipe arrangement up to at least that level during said extension of the adjustable pipe section downwards. According to some embodiments, the process comprises the step of filling the feed pipe arrangement with iron ore pellets up to a predetermined level and maintaining a column of iron ore inside the feed pipe arrangement up to at least that level during said retraction of the adjustable pipe section upwards. According to some embodiments, said one or more process parameters comprises one or more of the following parameters: -    a composition of the reducing gas, -    a temperature of the reducing gas, - a flow rate of the reducing gas, -     a composition of the iron ore, -    a temperature of the iron ore. According to some embodiments, said one or more process parameters comprise each of the following parameters: - a composition of the reducing gas, a temperature of the reducing gas, - a flow rate of the reducing gas, -     a composition of the iron ore, -    a temperature of the iron ore. Further objects, advantages and novel features of the present invention will become apparent to one skilled in the art from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the present invention and further objects and advantages of it, the detailed description set out below should be read together with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which: Fig. la schematically illustrates a direct reduction shaft arrangement according to a first embodiment, Fig. lb schematically illustrates the direct reduction shaft arrangement according to the first embodiment, whereby the adjustable pipe section has been retracted, Fig. 2 schematically illustrates a second embodiment wherein the direct reduction shaft is arranged to be operated under elevated pressure, Fig. 3 schematically illustrates a third embodiment wherein the direct reduction shaft is arranged to be operated at essentially atmospheric pressure, and DETAILED DESCRIPTION According to a first aspect, a direct reduction shaft arrangement is provided. The direct reduction shaft arrangement comprises at least one ore charging arrangement and a direct reduction shaft. Each ore charging arrangement comprises an ore charging vessel and an ore feed pipe arrangement. The ore feed pipe arrangement comprises an upper pipe section and at least one lower pipe section. The upper pipe section is arranged in communication with an iron ore outlet of the ore charging vessel. The respective lower pipe section is arranged internal to the direct reduction shaft. The upper pipe section and the lower 10 pipe section are arranged in communication such that the ore feed pipe arrangement may convey ore from the ore charging vessel to the direct reduction shaft. Each lower pipe section of the ore feed pipe arrangement is further equipped with an adjustable pipe section. Each adjustable pipe section is translationally extendible and / or retractable in relation to its respective lower pipe section. The direct reduction shaft arrangement comprises measuring means for determining a discharge rate of sponge iron through the sponge iron outlet, and drive means for driving the respective adjustable pipe section in a vertical direction. It also comprises a control unit, which is operatively connected to said measuring means and to said drive means. The control unit is configured to determine a set bed height based on one or more process parameters. The control unit is also configured to compare the actual bed hight with the set bed height, and, if the set bed is lower than the actual bed height, controlling the drive means to extend the adjustable pipe section downwards until the set bed height is obtained. The control unit is configured to determine a bed height decrease rate corresponding to the determined discharge rate, and to control the drive means to extend the adjustable with a velocity that corresponds to the determined bed height decrease rate. By "translationally extendible and / or retractable" it is meant that that each adjustable pipe section may be adjusted to extend further into the direct reduction shaft until the outlet of the adjustable pipe section reaches its lower limit in the shaft. Likewise, each adjustable pipe section may be adjusted to retract the adjustable pipe section until the outlet of the adjustable pipe section reaches its upper limit in the shaft. Between the extremes of the upper and lower limits, the adjustable pipe section may be extended and retracted, either in a stepped or preferably in a stepless manner. The adjustable pipe section may be an adjustable sleeve arranged coaxially around the lower pipe section, wherein the adjustable sleeve is arranged to be translationally extendible and / or retractable along a common axis of the lower pipe section and adjustable sleeve. Such an arrangement is robust and readily controllable. Each adjustable pipe section may be equipped with the above-mentioned drive means formed by adjustment rods extending through an upper cap of the direct reduction shaft, wherein the adjustment rods are arranged to be able to be translationally actuated in order to extend 11 and / or retract the adjustable pipe section. Such an arrangement is robust and readily controllable. The adjustment rods may be arranged to be able to be manually actuated. Such an arrangement is robust and readily controllable. Alternatively, or in addition, the adjustment rods may be arranged to be able to be actuated by a motor. Such an arrangement permits easier variation of the bed height, during operation of the direct reduction shaft. The ore charging vessel may be a pressurizable charging bin, such as a charging bin arranged to operate at a pressure of greater than atmospheric pressure, preferably greater than two Bar, even more preferably greater than four Bar. Such pressurizable charging bins, also known as lockhoppers, are typically used in direct reduction shaft processes operating at elevated pressures, such as the HYL or Energiron processes, or variants thereof. Typically, in such a case, but not limited only to such cases, the direct reduction shaft arrangement may comprise a plurality of ore charging arrangements, such as at least two or at least four ore charging arrangements. Also typically in such a case, but not limited only to such cases, each ore feed pipe arrangement may comprise a single lower pipe section. The present disclosure is thus readily applicable to direct reduction shaft processes operating under elevated pressures. Alternatively, the ore charging vessel may be a supply hopper arranged to operate at a pressure of two Bar or less, preferably atmospheric pressure. Such supply hoppers are typically used in direct reduction processes operating at near-atmospheric pressures, such as the Midrex process and variants thereof. Typically, in such a case, but not limited only to such cases, the direct reduction shaft arrangement may comprise a single ore charging arrangement. Also, typically in such cases, but not limited only to such cases, the ore feed pipe arrangement may comprise a plurality of lower pipe sections, such as at least four, at least eight or at least 16 lower pipe sections. When the ore feed pipe arrangement comprises a plurality of lower pipe sections, the ore feed pipe arrangement may comprise an intermediate section arranged in connection with the upper pipe section at a first end and branching to a plurality of second ends, each second end being arranged in connection with one of the plurality of lower pipe sections. The present disclosure is thus readily applicable to direct reduction shaft processes operating under near-atmospheric pressures. Direct reduction process According to a second aspect there is provided a process for producing direct reduced iron from iron ore. The process comprises the following steps: - providing a direct reduction shaft arrangement as described herein, - adapting a degree of extension and / or retraction of the adjustable pipe sections, - charging iron ore into the direct reduction shaft via the at least one ore charging arrangement, thereby establishing a bed in the direct reduction shaft having a bed height determined by the degree of extension and / or retraction of the adjustable pipe section, and - introducing the reducing gas into the direct reduction shaft in countercurrent flow to the iron ore to reduce the iron ore to direct reduced iron. The degree of extension and / or retraction of the adjustable pipe sections may be adjusted based on one or more of the following parameters: a composition of the reducing gas, a temperature of the reducing gas, a flow rate of he reducing gas, a composition of the iron ore, a temperature of the iron ore, and a discharge rate of the direct reduced iron. Thus, the bed height in the direct reduction shaft may be optimized to prevailing inputs to the shaft or adapted to respond to changed inputs to the shaft. Effects and features of the second aspect are to a large extent analogous to those described above in connection with the first aspect. Embodiments mentioned in relation to the first aspect are largely compatible with the second aspect. The invention will now be described in more detail with reference to certain exemplifying embodiments and the drawings. However, the invention is not limited to the exemplifying embodiments discussed herein and / or shown in the drawings but may be varied within the scope of the appended claims. Furthermore, the drawings shall not be considered drawn to scale as some features may be exaggerated to more clearly illustrate certain features. Figure la schematically illustrates a direct reduction shaft arrangement 1 comprising: an ore charging arrangement 3 and a direct reduction shaft 5. Note that only an upper region of the direct reduction shaft 5 is shown illustrated in all figures, not the whole shaft. The ore charging arrangement comprises an ore charging vessel 7 and an ore feed pipe arrangement 9, and an sponge iron outlet 6. The ore feed pipe arrangement 9 comprises an upper pipe section 91 and a lower pipe section 93. The upper pipe section 91 is arranged in communication with an outlet 71 of the ore charging vessel 7. The lower pipe section 93 is arranged internal to the direct reduction shaft 5. The lower pipe section 93 is further equipped with an adjustable pipe section 95 that is translationally extendible and / or retractable in relation to the lower pipe section 93. In the illustrated embodiment, the adjustable pipe section 95 is shown as an adjustable sleeve arranged coaxially around the lower pipe section 93, wherein the adjustable sleeve is arranged to be translationally extendible and / or retractable along a common axis of the lower pipe section and adjustable sleeve. The adjustable pipe section 95 is equipped with drive means formed by adjustment rods 97 extending through an upper cap 51 of the direct reduction shaft 5 (i.e. the section of the direct reduction shaft comprising the top gas outlet 55). The adjustment rods 97 are arranged to be able to be translationally actuated in order to extend and / or retract the adjustable pipe section 95. For example, the adjustment rods may be threaded at an upper end to be moved into place relative to the upper cap 51 of the direct reduction shaft by rotation of a threaded nut or a rotary motor (not illustrated). If necessary, each adjustment rods 97 may be enclosed with a gas-tight cap (not illustrated) providing a gastight seal to prevent process gases from leaking from the direct reduction shaft at the aperture where the adjustment rod 97 passes through the upper cap 51. The upper pipe section 91 and the lower pipe section 93 are arranged in communication such that the ore feed pipe arrangement 9 may convey ore from the ore charging vessel 7 to the direct reduction shaft 5. That is to say that when in use, ore flows from the ore charging vessel 7 to the direct reduction shaft 5 via the upper pipe section 91, low pipe section 93 and adjustable pipe section 95. The degree of extension / retraction of the adjustable pipe section 95 determines the height of the bed 53 in the direct reduction shaft 5. Figure lb schematically illustrates the same direct reduction shaft arrangement 1 as in Figure la, wherein the adjustable pipe section 95 has been retracted compared to Figure la. Due to this, ore previously standing in the ore feed pipe arrangement 9 has flowed out of the adjustable pipe section 95, leading to the height of the bed 53 in the direct reduction shaft 5 being increased. Figure 2 schematically illustrates an embodiment wherein the direct reduction shaft is arranged to be operated under elevated pressure. In this embodiment, the direct reduction shaft arrangement 1 comprises a plurality of ore charging arrangements 3, 3', here illustrated as two charging arrangements, but more commonly four charging arrangements. Each ore charging arrangement 3, 3' comprises a pressurizable charging bin 7, 7' as the ore charging vessel. Each pressurizable charging bin may be configured to be able to supply ore under inert conditions and at an appropriately elevated pressure to the ore feed pipe arrangement 9, 9'. Each ore feed pipe arrangement 9, 9' comprises a single lower pipe section 93, 93'. Each adjustable pipe section 95, 95' may be separately adjustable, or alternatively, all adjustable pipe sections 95, 95' may be simultaneously extendible and / or retractable, e.g. by a motor drive (not illustrated). Figure 3 schematically illustrates an embodiment wherein the direct reduction shaft is arranged to be operated at essentially atmospheric pressure. In this embodiment, the direct reduction shaft arrangement 1 comprises a single ore charging arrangements 3. The ore charging arrangement comprises a single supply hopper 7 as the ore charging vessel. The outlet 71 of the supply hopper is connected to an upper pipe section 91. This upper pipe section may be equipped with a dynamic seal arrangement (not illustrated) to prevent air from being introduced to the shaft 5 together with the ore. The ore feed pipe arrangement 9 comprises an intermediate section 92 arranged in connection with the upper pipe section 91 at a first end 921 and branching to a plurality of second ends 923, 923', each second end being arranged in connection with one of a plurality of lower pipe sections 93,93'. Each lower pipe section 93, 93' is equipped with a respective adjustable pipe section 95, 95'. The present embodiment shows the intermediate section 92 having two branches, but more commonly the ore feed pipe arrangement branches to a total of eight or 16 outlets. Each adjustable pipe section 95, 95' may be separately adjustable, or alternatively, all adjustable pipe sections 95, 95' may be simultaneously extendible and / or retractable, e.g. by a motor drive (not illustrated). The arrangement, as disclosed in all embodiments presented herein, further comprises measuring means 96 for determining a discharge rate of sponge iron through the sponge iron outlet. In the disclosed exemplifying embodiments, the measuring means 96 for determining the discharge rate comprises and out-feed mechanism formed be a cell feeder for the out- 15 feed of sponge iron, whereby a measurable operation parameter of the out-feed mechanism is proportional to the sponge iron discharge rate. The arrangement, as disclosed in all embodiments presented herein, further comprises a control unit 98, which is operatively connected to said measuring means 96 and to said drive means 97. The control unit 98 is configured to determine a set bed height base on a plurality of process parameters that affect the required residence time of the iron ore in the reduction shaft. The process parameters comprise the composition of the reducing gas entering the shaft, the temperature of the reducing gas entering the shaft, the flow rate of the reducing gas entering the shaft, the composition of the iron ore entering the shaft, and the temperature of the iron ore. The control unit 98 is configured to compare the actual bed hight with the set bed height, and, if the set bed is lower than the actual bed height, controlling the drive means 97 to extend the adjustable pipe section downwards until the set bed height is obtained. Thereby, the control unit 98 is configured to determine a bed height decrease rate corresponding to the determined discharge rate, and to control the drive means 97 to extend the adjustable with a velocity that corresponds to the determined bed height decrease rate. The control unit 98 is also configured compare the actual bed hight with the set bed height, and, if the set bed is higher than the actual bed height, controlling the drive means 97 to retract the adjustable pipe section(s) upwards while feeding iron ore through the vertically adjustable feed pipe section(s) until the set bed height is obtained. The arrangement comprise a sensor 100, here a radioactive sensor, for sensing presence of iron ore at a predetermined level in the feed pipe arrangement, wherein, said sensor is connected to the control unit 98 and wherein the control unit 98 is configured to control the ore charging vessel 7 to fill the feed pipe arrangement 9 with iron ore pellets up to said predetermined level and maintain a column of iron ore inside the feed pipe arrangement 9 up to at least that level during said extension or retraction of the adjustable pipe section downwards / upwards. The operation of the arrangement accordingly comprises the steps of charging iron ore into the direct reduction shaft via the at least one ore charging arrangement 3, thereby establishing a bed in the direct reduction shaft having an initial bed height determined by the degree of extension and / or retraction of the vertically adjustable pipe section(s), introducing a reducing gas into the direct reduction shaft in counter-current flow to the iron ore to reduce the iron ore to direct reduced sponge iron, discharging sponge iron from the sponge iron outlet, determining a discharge rate of the sponge iron through the sponge iron outlet, determining a set bed height based on the above-mentioned process parameters, comparing the actual bed hight with the set bed height, and, if the set bed is lower than the actual bed height, extend the adjustable pipe section downwards until the set bed height is obtained. It also comprises the steps of determining a bed height decrease rate corresponding to the determined discharge rate and extending the adjustable pipe section with a velocity that corresponds to the determined bed height decrease rate. If the set bed height is higher than the actual bed height, the adjustable pipe section(s) is retracted upwards while feeding iron ore through the vertically adjustable feed pipe section(s) until the set bed height is obtained. The process also comprises the step of filling the feed pipe arrangement 9 with iron ore pellets up to said predetermined level and maintaining a column of iron ore inside the feed pipe arrangement 9 up to at least that level during said extension of the adjustable pipe section downwards or retraction of the adjustable pipe section 95 upwards. The person skilled in the art realizes that the present disclosure is not limited to the preferred embodiments described above. The person skilled in the art further realizes that modifications and variations are possible within the scope of the appended claims. For example, there are a variety of alternative means of actuating each adjustable pipe section that are apparent to a person skilled in the art. These include, but are not limited to: - actuating each adjustable pipe section by connection to a rod of a pneumatic or hydraulic cylinder, - actuating each adjustable pipe section using a rack and pinion system, and - incorporating a cam into the lower pipe section and / or adjustable pipe section such that rotary movement of the pipe is translated into axial movement. Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed disclosure, from a study of the drawings, the disclosure, and the appended claims.

Claims

1. A direct reduction shaft arrangement (1) for producing direct reduced sponge iron from iron ore comprising:- a direct reduction shaft (5),- at least one ore charging arrangement (3),- a sponge iron outlet (6) at a bottom of the direct reduction shaft (5),- wherein each ore charging arrangement (3) comprises an ore charging vessel (7) and an ore feed pipe arrangement (9),- wherein the ore feed pipe arrangement comprises an upper pipe section (91) and at least one lower pipe section (93),- wherein the upper pipe section (91) is arranged in communication with an ore outlet (71) of the ore charging vessel (7),- wherein the at least one lower pipe section (93) is arranged internal to the direct reduction shaft (5),- wherein the upper pipe section (91) and the lower pipe section (93) are arranged in communication such that the ore feed pipe arrangement (9) may convey ore from the ore charging vessel (7) to the direct reduction shaft (5),- wherein each lower pipe section (93) of the ore feed pipe arrangement is further equipped with a vertically adjustable pipe section (95),- wherein each adjustable pipe section (95) is translationally extendible and / or retractable in relation to its respective lower pipe section (93), wherein the direct reduction shaft arrangement further comprises- measuring means (96) for determining a discharge rate of sponge iron through the sponge iron outlet,- drive means (97) for driving the adjustable pipe section (95) in a vertical direction,- a control unit (98), which is operatively connected to said measuring means and to said drive means (97), said control unit being configured to- determine a set bed height on basis of one or more process parameters,- compare the actual bed hight with the set bed height, and, if the set bed is lower than the actual bed height, controlling the drive means (97) to extend the18 adjustable pipe section downwards until the set bed height is obtained, the arrangement (1) being characterised in thatthe control unit (98) is configured to determine a bed height decrease rate corresponding to the determined discharge rate, and to control the drive means (97) to extend the adjustable pipe section (95) downwards with a velocity that corresponds to the determined bed height decrease rate.

2. The direct reduction shaft arrangement according to claim 1, wherein the control unit (98) is configured compare the actual bed hight with the set bed height, and, if the set bed is higher than the actual bed height, controlling the drive means (97) to retract the adjustable pipe section(s) upwards while feeding iron ore through the vertically adjustable feed pipe section(s) until the set bed height is obtained.

3. The direct reduction shaft arrangement according to claim 1 or 2, comprising a sensor for sensing presence of iron ore at a predetermined level in the feed pipe arrangement, wherein, said sensor is connected to the control unit and wherein the control unit is configured to control the ore charging vessel (7) to fill the feed pipe arrangement (9) with iron ore pellets up to said predetermined level and maintain a column of iron ore inside the feed pipe arrangement (9) up to at least that level during said extension of the adjustable pipe section downwards.

4. The direct reduction shaft arrangement according to any one of claims 1-3, comprising a sensor for sensing presence of iron ore at a predetermined level in the feed pipe arrangement, wherein, said sensor is connected to the control unit (98) and wherein the control unit (98) is configured to control the ore charging vessel (7) to fill the feed pipe arrangement (9) with iron ore pellets up to said predetermined level and maintain a column of iron ore inside the feed pipe arrangement (9) up to at least that level during said retraction of the adjustable pipe section upwards.

5. The direct reduction shaft arrangement according to any one of claims 1-4, wherein said one or more process parameters comprises one or more of the following parameters:-    a composition of the reducing gas,- a flow rate of the reducing gas,-     a composition of the iron ore,-    a temperature of the iron ore.

6. The direct reduction shaft arrangement according to any one of claims 1-4, wherein said one or more process parameters comprises each of the following parameters:-    a composition of the reducing gas,-    a temperature of the reducing gas,- a flow rate of the reducing gas,-     a composition of the iron ore,-    a temperature of the iron ore.

7. The direct reduction shaft arrangement according to any one of the preceding claims,wherein the adjustable pipe section (95) is an adjustable sleeve arranged coaxially around the lower pipe section (93), wherein the adjustable sleeve is arranged to be translationally extendible and / or retractable along a common axis of the lower pipe section and adjustable sleeve.

8. The direct reduction shaft arrangement according to any one of the preceding claims, said drive means (97) comprises adjustment rods (97) extending through an upper cap (51) of the direct reduction shaft (5), wherein the adjustment rods (97) are arranged to be able to be translationally actuated in order to extend and / or retract the adjustable pipe section (95).

9. The direct reduction shaft arrangement according to claim 8, wherein the adjustment rods (97) are arranged to be able to be manually actuated.

10. The direct reduction shaft arrangement according to claim 9, wherein the adjustment rods (97) are arranged to be able to be actuated by a motor.

11. The direct reduction shaft arrangement according to any one of the claims 1-10, wherein the ore charging vessel (7) is a pressurizable charging bin arranged to operate at a pressure of greater than atmospheric pressure.

12. The direct reduction shaft arrangement according to claim 11, comprising a plurality of ore charging arrangements (3, 3'), such as at least two or at least four ore charging arrangements.

13. The direct reduction shaft arrangement according to any one of the claims 11-12, wherein each ore feed pipe arrangement (9) comprises a single lower pipe section (93).

14. The direct reduction shaft arrangement according to any one of claims 1-13, wherein the ore charging vessel (7) is a supply hopper arranged to operate at a pressure of two Bar or less, preferably at essentially atmospheric pressure.

15. The direct reduction shaft arrangement according to claim 14, comprising a single ore charging arrangement (3).

16. The direct reduction shaft arrangement according to any one of the claims 14-15, wherein the ore feed pipe arrangement (9) comprises a plurality of lower pipe sections (93, 93'), such as at least four, at least eight or at least 16 lower pipe sections.

17. The direct reduction shaft arrangement according to claim 16, wherein the ore feed pipe arrangement comprises an intermediate section (92) arranged in connection with the upper pipe section (91) at a first end (921) and branching to a plurality of second ends (923, 923'), each second end being arranged in connection with one of the plurality of lower pipe sections (93, 93').

18. A process for producing direct reduced sponge iron from iron ore in a direct reduction shaft comprising:- a direct reduction shaft (5),- at least one ore charging arrangement (3),- a sponge iron outlet at a bottom of the direct reduction shaft (5),- wherein each ore charging arrangement (3) comprises an ore charging vessel (7) and an ore feed pipe arrangement (9),wherein the ore feed pipe arrangement comprises an upper pipe section (91) and at least one lower pipe section (93),wherein the upper pipe section (91) is arranged in communication with an ore outlet (71) of the ore charging vessel (7),wherein the at least one lower pipe section (93) is arranged internal to the direct reduction shaft (5),wherein the upper pipe section (91) and the lower pipe section (93) are arranged in communication such that the ore feed pipe arrangement (9) may convey ore from the ore charging vessel (7) to the direct reduction shaft (5),wherein each lower pipe section (93) of the ore feed pipe arrangement is further equipped with a vertically adjustable pipe section (95),wherein each adjustable pipe section (95) is translationally extendible and / or retractable in relation to its respective lower pipe section (93), and wherein the process comprises the steps of:charging iron ore into the direct reduction shaft via the at least one ore charging arrangement (3), thereby establishing a bed in the direct reduction shaft having an initial bed height determined by the degree of extension and / or retraction of the vertically adjustable pipe section(s),introducing a reducing gas into the direct reduction shaft in counter-current flow to the iron ore to reduce the iron ore to direct reduced sponge iron,discharging sponge iron from the sponge iron outlet,determining a discharge rate of the sponge iron through the sponge iron outlet,determining a set bed height on basis of one or more process parameters,comparing the actual bed hight with the set bed height, and, if the set bed is lower than the actual bed height, extend the adjustable pipe section downwards until the set bed height is obtained, the process being characterised in that it comprises the step of determining a bed height decrease rate corresponding to the determined discharge rate, and extending the adjustable pipe section (95) with a velocity that corresponds to the determined bed height decrease rate.

19. The process according to claim 18, wherein, if the set bed height is higher than the actual bed height, retract the adjustable pipe section(s) upwards while feeding iron ore through the vertically adjustable feed pipe section(s) until the set bed height is obtained.

20. The process according to claim 18 or 19, comprising the step of filling the feed pipe arrangement (9) with iron ore pellets up to a predetermined level and maintaining a column of iron ore inside the feed pipe arrangement (9) up to at least that level during said extension of the adjustable pipe section downwards.

21. The process according to any one of claims 18-20, comprising the step of filling the feed pipe arrangement (9) with iron ore pellets up to a predetermined level and maintaining a column of iron ore inside the feed pipe arrangement (9) up to at least that level during said retraction of the adjustable pipe section upwards.

22. The process according to any one of claims 18-21, wherein said one or more process parameters comprises one or more of the following parameters:-    a composition of the reducing gas,-    a temperature of the reducing gas,- a flow rate of the reducing gas,-     a composition of the iron ore,-    a temperature of the iron ore.

23. The process according to any one of claims 18-21, wherein said process parameter comprises each of the following parameters:-    a composition of the reducing gas,-    a temperature of the reducing gas,- a flow rate of the reducing gas,-     a composition of the iron ore,

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