Method for producing reduced iron, and shaft furnace

Abstract

Disclosed is a new technique for improving the average reduction rate of raw material in a method for producing reduced iron using a shaft furnace. This method for producing reduced iron comprises supplying a raw material including iron oxide into a shaft furnace through an upper portion thereof, and also supplying a reducing gas including hydrogen gas into the shaft furnace through a side wall thereof, to thereby reduce the iron oxide and obtain the reduced iron from a lower portion of the shaft furnace, and is characterized by comprising performing an action for causing the flow of the reducing gas inside the shaft furnace to be changed from the side wall side of the shaft furnace toward the center of the shaft furnace.

Description

TITLE: METHOD FOR PRODUCING REDUCED IRON AND SHAFT FURNACE FIELD

[0001] The present application discloses a method for producing reduced iron and a shaft furnace. BACKGROUND

[0002] Known in the art is the use of the direct reduction method utilizing a shaft furnace to reduce iron oxide and produce reduced iron. Specifically, a feedstock containing iron oxide is supplied from a top part of the shaft furnace to the inside, a reducing gas is supplied from a side wall of the shaft furnace to the inside, iron oxide is reduced at an inside of the shaft furnace, and reduced iron is obtained from a bottom part of the shaft furnace. The reducing gas contains, for example, hydrogen gas. Here, if the reducing gas containing hydrogen gas is supplied from the side wall of the shaft furnace to the inside, much of that hydrogen gas ends up rising along the vicinity of the furnace wall. The supply of hydrogen gas to the center part (central part) of the inside of the shaft furnace easily becomes insufficient. As a result, the average reduction rate of the feedstock easily falls.

[0003] PTL 1 discloses a technique for dividing a body of a shaft furnace to improve uniformity of gas in the furnace. However, if dividing the furnace body, the capital cost increases and a rate of utilization of space in the furnace falls.

[0004] PTL 2 discloses a technique for dividing a gas exhaust system at a top part of a shaft furnace. However, with just dividing the gas exhaust system, it is difficult to improve the uniformity of the gas in the furnace. Further, if dividing the gas exhaust system, the structure of the top part of the furnace becomes complicated.

[0005] PTL 3 discloses a technique for providing piping for supplying a reducing gas to a center part of a shaft furnace. However, in this case, the structure of the shaft furnace becomes complicated and the capital cost increases. In addition, at the time of operation, excessive pressure is generated at the piping at the center part of the shaft furnace and the piping is easily damaged.

[0006] PTL 4 discloses a technique for controlling a position of supply of feedstock to an inside of a shaft furnace in a furnace radial direction in accordance with a temperature of exhaust gas at a top part of the shaft furnace. However, even if controlling the position of supply of feedstock, it is difficult to improve the uniformity of the gas in the furnace.

[0007] PTL 5 discloses a technique for arranging hollow pipes in a staggered manner at the inside of a shaft furnace and using the hollow pipes to disturb a vertically downward flow of powder material inside the furnace and make high temperature gas circulate inside the hollow pipes. However, if placing hollow pipes in the furnace, the capital cost increases and the rate of utilization of space inside the furnace falls. Further, at the time of operation, excessive pressure is generated at the hollow pipes and the hollow pipes are easily damaged. [CITATION LIST] [PATENT LITERATURE]

[0008] [PTL 1] Japanese Examined Patent Publication No. 57-019163 [PTL 2] Japanese Examined Patent Publication No. 59-034763 [PTL 3] Japanese Unexamined Patent Publication No. 62-294127 [PTL 4] Japanese Examined Patent Publication No. 6-072248 [PTL 5] Japanese Patent No. 3083810 SUMMARY [TECHNICAL PROBLEM]

[0009] A new technique is required for raising the average reduction rate of a feedstock using a shaft furnace to produce reduced iron. [SOLUTION TO PROBLEM]

[0010] The present application discloses the following aspects as solutions to the above technical problem. <Aspect 1> A method for producing reduced iron comprising: supplying a feedstock containing iron oxide from a top part of a shaft furnace to the inside, supplying a reducing gas containing hydrogen gas from a side wall of the shaft furnace to the inside, and reducing the iron oxide to obtain reduced iron from a bottom part of the shaft furnace, wherein the method includes performing an action for changing a flow of the reducing gas inside the shaft furnace from the side wall side of the shaft furnace to the center side of the shaft furnace. <Aspect 2> The method for producing reduced iron according to the aspect 1, wherein the action includes at least one of the following actions 1 to 4: Action 1: cooling at least the inside wall of the shaft furnace at least between a position of supply of the feedstock and a position of supply of the reducing gas; Action 2: mixing an inert gas with the reducing gas; Action 3: dividing the reducing gas supplied to the inside of the shaft furnace into a first gas with a relatively low reducing power and a second gas with a relatively high reducing power and supplying the first gas from above the second gas; and Action 4: making an average particle size of the feedstock supplied to the center side of the shaft furnace larger than the average particle size of the feedstock supplied to the side wall side of the shaft furnace. <Aspect 3> The method for producing reduced iron according to the aspect 2, wherein the Action 1 is the following Action 1A: Action 1A: cooling by water cooling at least the inside wall of the shaft furnace at least between the position of supply of the feedstock and the position of supply of the reducing gas. <Aspect 4> The method for producing reduced iron according to the aspect 2 or 3, wherein the Action 4 is the following Action 4A: Action 4A: supplying the feedstock to the side wall side of the shaft furnace so that the average particle size of the feedstock supplied to the center side of the shaft furnace becomes larger than the average particle size of the feedstock supplied to the side wall side of the shaft furnace. <Aspect 5> The method for producing reduced iron according to any one of the aspects 2 to 4, wherein the first gas and the second gas in the Action 3 satisfy one or both of the following conditions A and B: Condition A: the temperature of the first gas is lower than the temperature of the second gas and Condition B: the hydrogen gas concentration of the first gas is lower than the hydrogen gas concentration of the second gas. <Aspect 6> The method for producing reduced iron according to any one of the aspects 2 to 5, wherein the method comprises: estimating information relating to a reduction rate of the feedstock inside the shaft furnace; and performing the action based on the estimated information. <Aspect 7> The method for producing reduced iron according to the aspect 6, wherein the information is the reduction rate of the feedstock at the side wall side inside the shaft furnace or an indicator representing the reduction rate, and the action is performed when the estimated reduction rate or the indicator representing the reduction rate is greater than a first threshold value. <Aspect 8> The method for producing reduced iron according to the aspect 6, wherein the information is a deviation in a furnace radial direction of the reduction rate of the feedstock or the indicator representing the reduction rate inside the shaft furnace, and the action is performed when the estimated deviation is greater than a second threshold value. <Aspect 9> A shaft furnace comprising a feedstock supply opening, a gas supply opening, a reduced iron discharge opening, a gas discharge opening, and an action performing device, wherein the feedstock supply opening is provided at a top part of the shaft furnace, the gas supply opening is provided at a side wall of the shaft furnace lower than the feedstock supply opening, the reduced iron discharge opening is provided lower than the gas supply opening, the gas discharge opening is provided higher than the gas supply opening, the action performing device is configured so as to perform an action for changing a flow of the reducing gas inside the shaft furnace from the side wall side of the shaft furnace to the center side of the shaft furnace. <Aspect 10> The shaft furnace according to the aspect 9, wherein the action performing device is at least one of a cooling device, a mixing device, a gas supply device, and a feedstock supply device, the cooling device is configured to cool at least the inside wall of the shaft furnace at least between a position of supply of the feedstock and a position of supply of the reducing gas, the mixing device is configured to mix an inert gas with the reducing gas; the gas supply device is configured to supply a first gas with a relatively low reducing power and a second gas with a relatively high reducing power from the gas supply opening to the inside of the shaft furnace and make the position of supply of the first gas above the position of supply of the second gas, and the feedstock supply device is configured to supply the feedstock through the feedstock supply opening to the inside of the shaft furnace so that the average particle size of the feedstock supplied to the center side of the shaft furnace becomes larger than the average particle size of the feedstock supplied to the side wall side of the shaft furnace. <Aspect 11> The shaft furnace according to the aspect 10, wherein the cooling device is configured to cool at least the inside wall of the shaft furnace by water cooling at least between the feedstock supply opening and the gas supply opening. <Aspect 12> The shaft furnace according to the aspect 10 or 11, wherein the feedstock supply device is configured so as to supply the feedstock to the side wall side inside the shaft furnace. <Aspect 13> The shaft furnace according to any one of the aspects 10 to 12, wherein the gas supply device is configured so that the first gas and the second gas satisfy one or both of the following conditions A and B: Condition A: the temperature of the first gas is lower than the temperature of the second gas and Condition B: the hydrogen gas concentration of the first gas is lower than the hydrogen gas concentration of the second gas. <Aspect 14> The shaft furnace according to any one of the aspects 9 to 13, wherein the shaft furnace comprises an estimation device and a control device, the estimation device is configured to estimate information relating to a reduction rate of the feedstock inside the shaft furnace and the control device controls the action performing device so that the action is performed based on the estimated information. <Aspect 15> The shaft furnace according to the aspect 14, wherein the information is the reduction rate of the feedstock or an indicator representing the reduction rate at the side wall side of the inside of the shaft furnace, and the control device controls the action performing device so that the action is performed when the estimated reduction rate or the indicator representing the reduction rate is greater than a first threshold value. <Aspect 16> The shaft furnace according to the aspect 14, wherein the information is a deviation in the furnace radial direction of the reduction rate of the feedstock or the indicator representing the reduction rate inside the shaft furnace, and the control device controls the action performing device so that the action is performed when the estimated deviation is greater than a second threshold value. [ADVANTAGEOUS EFFECT OF INVENTION]

[0011] According to the art of the present disclosure, it is possible to raise the average reduction rate of feedstock when using a shaft furnace to produce reduced iron. BRIEF DESCRIPTION OF DRAWINGS

[0012] FIG. 1 schematically shows one example of a state before a predetermined action is performed in a method for producing reduced iron. FIG. 2 schematically shows one example of a state after an Action 1 is performed in a method for producing reduced iron. FIG. 3 schematically shows one example of a state after an Action 2 is performed in a method for producing reduced iron. FIG. 4 schematically shows one example of a state after an Action 3 is performed in a method for producing reduced iron. FIG. 5 schematically shows one example of a state after an Action 4 is performed in a method for producing reduced iron. FIG. 6 schematically shows one example of an Action 4. FIG. 7 schematically shows one example of an Action 4. FIG. 8 schematically shows one example of a configuration in the case of performing a predetermined estimation in a method for producing reduced iron. FIG. 9 schematically shows one example of a configuration in the case of performing a predetermined estimation in a method for producing reduced iron. FIG. 10 schematically shows a furnace body structure employed in calculations in an embodiment. DESCRIPTION OF EMBODIMENTS

[0013] Below, referring to the drawings, a method for producing reduced iron according to an embodiment and a shaft furnace according to an embodiment will be explained, but the art of the present disclosure is not limited to these.

[0014] 1.  Method for Producing Reduced Iron As shown in FIG. 1, the method for producing reduced iron of the embodiment comprises supplying a feedstock 10 containing iron oxide from a top part of a shaft furnace 100 to an inside, supplying a reducing gas containing hydrogen gas from a side wall 100a of the shaft furnace 100 to the inside, and reducing the iron oxide to obtain reduced iron 30 from a bottom part of the shaft furnace 100. Here, the method for producing reduced iron according to one embodiment includes performing an action for changing a flow of the reducing gas inside the shaft furnace 100 from the side wall side of the shaft furnace 100 to the center side of the shaft furnace 100.

[0015] 1.1. Feedstock The feedstock 10 contains at least iron oxide. The feedstock 10 may, for example, be at least one type selected from iron ore pellets, lumps of ore, and sintered ore. The feedstock 10 may also contain, in addition to the iron oxide, for example, one or both of silicon dioxide and aluminum oxide. The feedstock 10 may be one having a distribution of particle size or one having a uniform particle size. The average particle size of the feedstock 10 may, for example, be 10.0 mm or more and 15.0 mm or less. The feedstock 10 may be one formed into pellets etc., may be a powder state, may be a lump shape, or may be a shape other than these.

[0016] As the amount of supply of the feedstock 10 to the shaft furnace 100, the optimum amount may be selected in accordance with the scale, operating conditions, etc. of the shaft furnace 100. The feedstock 10 is supplied from a top part of the shaft furnace 100 to the inside. The position of supply of the feedstock 10 may be above the position of supply of the reducing gas. The feedstock 10, for example, may be supplied through a feedstock supply opening 101 provided at the top part of the shaft furnace 100 etc. The system for supplying the feedstock 10 is not particularly limited. For example, it may be supplied by a hopper, chute, etc. The feedstock 10 may also be supplied by free fall. In particular, when using a rotating chute, the later explained Action 4 can be more easily performed.

[0017] By the feedstock 10 being supplied from the top part of the shaft furnace 100 to the inside, a packed bed 20 is formed inside the shaft furnace 100. The packing rate of the packed bed 20 is not particularly limited. The packing rate of the packed bed 20 may be made similar to the packing rate in a conventional method for producing reduced iron using a shaft furnace.

[0018] The feedstock 10 moves downward inside the shaft furnace 100. That is, in the state where the feedstock 10 substantially packs the inside of the shaft furnace 100, it gradually moves downward by cascading down. If focusing on one feedstock particle in the packed bed 20, that feedstock particle may move continuously toward the bottom at a constant speed or may move intermittently repeating a falling and stopping motion. If focusing on one feedstock particle in the packed bed 20, the average speed of movement downward of that feedstock particle is not particularly limited. For example, the average speed of movement can be adjusted in accordance with the amount of supply (speed of supply) of the feedstock. When moving the packed bed 20 downward, to prevent bridging, a burden feeder etc. may be used. The configuration of the burden feeder in the shaft furnace 100 is known.

[0019] The feedstock 10 may have a distribution of particle size or a distribution of temperature at the packed bed 20 from the top part of the shaft furnace 100 toward the bottom part and / or in the radial direction of the shaft furnace 100. The distribution of the particle size of the feedstock 10, for example, may be a distribution of particle size achieved by the later explained Action 4. Alternatively, the feedstock 10 may have an irregular distribution of particle size at the packed bed 20. Further, the temperature distribution of the packed bed 20 is not particularly limited. The packed bed 20 has a temperature at which reduction by the reducing gas can proceed. The packed bed 20 may be cooled below the position of supply of the reducing gas. For example, the packed bed 20 can be cooled by supplying cooling gas to the packed bed below the position of supply of the reducing gas as well. As the cooling gas, for example, at least one type selected from an inert gas, natural gas, hydrogen gas, etc. can be employed.

[0020] 1.2. Reducing Gas The reducing gas contains at least hydrogen gas. The reducing gas may also contain a gas besides hydrogen gas in addition to the hydrogen gas. As the gas besides hydrogen gas, carbon monoxide gas, inert gas, etc. may be mentioned. The inert gas may, for example, be at least one type selected from nitrogen gas, argon gas, or other rare gases, carbon dioxide gas, steam, etc. The hydrogen gas concentration of the reducing gas (if the reducing gas contains the later explained first gas and second gas, the average hydrogen gas concentration of the same) may, for example, be 80 vol% or more and 100 vol% or less. The supply temperature of the reducing gas (temperature right before contacting packed bed) need only be a temperature at which a reduction reaction with iron oxide occurs. For example, it may be 700°C or more and 1000°C or less and may be 800°C or more and 1000°C or less.

[0021] The reducing gas is supplied from the side wall 100a of the shaft furnace 100 to the inside of the shaft furnace 100. The system for supplying the reducing gas is not particularly limited. For example, piping etc. may be connected to gas supply openings 102 provided at the side wall 100a of the shaft furnace 100 and the reducing gas supplied through that piping etc. from the outside of the shaft furnace 100 to the inside of the shaft furnace 100. Here, the front ends of the piping etc. connected to the gas supply openings 102 do not have to project from the inside wall 100ax into the interior of the shaft furnace 100.

[0022] 1.3. Reduced Iron By at least part of the iron oxide contained in the feedstock 10 being reduced by the above reduction reaction, reduced iron 30 of a solid reaction product containing at least metallic iron is obtained. The reduced iron 30 may contain, in addition to metallic iron, iron oxide remaining without being reduced, silicon dioxide, aluminum oxide, etc. The reduced iron 30 containing the metallic iron can be recovered from the bottom part of the shaft furnace 100 (below position of supply of reducing gas).

[0023] 1.4. Actions In a method for producing reduced iron according to one embodiment, an action is performed for changing a flow of reducing gas inside the shaft furnace 100 from the side wall side of the shaft furnace 100 to the center side of the shaft furnace 100. That action, for example, is performed by the action performing device 110. By the action for changing the flow of reducing gas inside the shaft furnace 100 from the side wall side of the shaft furnace 100 to the center side of the shaft furnace 100 being performed, uneven flow of reducing gas inside the shaft furnace 100 is eliminated and the average reduction rate of the feedstock 10 can be improved.

[0024] According to the findings of the inventor, when that action includes, for example, at least one of the following Actions 1 to 4, it is possible to change the flow of reducing gas inside the shaft furnace 100 from the side wall side of the shaft furnace 100 to the center side of the shaft furnace 100 without employing a complicated configuration at the shaft furnace 100.

[0025] Action 1: cooling at least the inside wall 100ax of the shaft furnace 100 at least between a position of supply of the feedstock 10 and a position of supply of the reducing gas;

[0026] Action 2: mixing an inert gas with the reducing gas;

[0027] Action 3: dividing the reducing gas supplied to the inside of the shaft furnace 100 into a first gas with a relatively low reducing power and a second gas with a relatively high reducing power and supplying the first gas from above the second gas;

[0028] Action 4: making the average particle size of the feedstock 10 supplied to the center side of the shaft furnace 100 larger than the average particle size of the feedstock 10 supplied to the side wall side of the shaft furnace 100.

[0029] According to at least one of the above Actions 1 to 3, for example, it is believed that the position where the reduction reaction by the reducing gas at the side wall side inside the shaft furnace 100 is completed moves downward and the flow of reducing gas inside the shaft furnace 100 changes from the side wall side of the shaft furnace 100 to the center side of the shaft furnace 100. Further, according to the above Action 4, it is believed that the state of the packed bed inside the shaft furnace 100 is controlled, the supply of gas to the center side inside the shaft furnace 100 is promoted, and the flow of reducing gas inside the shaft furnace 100 changes from the side wall side of the shaft furnace 100 to the center side of the shaft furnace 100.

[0030] 1.4.1. Action 1 As shown in FIG. 2, according to the Action 1, at least the inside wall 100ax of the shaft furnace 100 is cooled at least between the position of supply of the feedstock 10 and the position of supply of the reducing gas (above position of supply of reducing gas and between feedstock supply opening 101 and gas supply opening 102, for example, reduction zone 100ay where iron oxide is reduced). By cooling the inside wall 100ax between the position of supply of the feedstock 10 and the position of supply of the reducing gas, it is possible to make the position where the reduction reaction is completed closer to the position of supply of the reducing gas and possible to increase the region which a reaction gas with a viscosity and density greater than hydrogen gas (for example, steam) occupies in the vicinity of the wall. The pressure loss in the vicinity of the furnace wall rises. Due to this, it is possible to make the amount of supply of reducing gas to the inside, that is, the center part of the shaft furnace 100, increase from the vicinity of the furnace wall.

[0031] Further, to make the reduction reaction of the iron oxide by hydrogen proceed, the temperature of the reducing gas and feedstock 10 has to be a certain high temperature or more (for example, 700°C or more). On the other hand, the reduction reaction of the iron oxide by hydrogen is an endothermic reaction, therefore unless supplementing thermal energy in the system from the outside, the temperature inside the system will fall and the reduction reaction will end up harder to occur. For this reason, in conventional technical thinking, not cooling the inside wall of the shaft furnace, but rather heating the inside of the system and holding the temperature of the inside of the shaft furnace at a high temperature is usual. As opposed to this, in the Action 1, by deliberately employing an operation becoming disadvantageous to the reduction reaction of iron oxide (cooling the inside wall of the shaft furnace), it is possible to make the position where the reduction reaction is completed close to the position of supply of the reducing gas to improve the uniformity of the gas inside the shaft furnace 100 and suppress uneven reaction of the iron oxide. As a result, compared with when not cooling the inside wall of the shaft furnace 100, the ratio of the iron oxide contained in the reduced iron after the reduction reaction falls and the ratio of metallic iron can increase. That is, the average reduction rate Rave can be improved.

[0032] In the Action 1, the method of cooling the inside wall of the shaft furnace 100 is not particularly limited. For example, a known cooling device 111 can be used to cool the inside wall of the shaft furnace 100. While depending also on the type of the furnace wall, for example, it is possible to provide a mechanism for making cooling water circulate inside the furnace wall between the position of supply of the feedstock 10 and the position of supply of the reducing gas and water cool the inside wall of the shaft furnace 100. That is, in the method for producing reduced iron according to one embodiment, the above Action 1 may also be the following Action 1A.

[0033] Action 1A: cooling by water cooling at least the inside wall 100ax of the shaft furnace 100 between the position of supply of the feedstock 10 and the position of supply of the reducing gas.

[0034] In the Action 1, the height position at which the inside wall of the shaft furnace 100 is cooled is at least between the position of supply of the feedstock 10 and the position of supply of the reducing gas (above position of supply of reducing gas and between feedstock supply opening 101 and gas supply opening 102, for example, reduction zone 100ay where iron oxide is reduced). In the Action 1, the inside wall of the shaft furnace 100 may be cooled over the entire span between the position of supply of the feedstock 10 and the position of supply of the reducing gas or the inside wall of the shaft furnace 100 may be cooled at part of the span between the position of supply of the feedstock 10 and the position of supply of the reducing gas.

[0035] In the Action 1, the entire circumference of the inside wall of the shaft furnace 100 may be cooled or part of the inside circumference may be cooled. In particular, if the entire circumference of the inside wall of the shaft furnace 100 is cooled, a higher effect can be expected.

[0036] 1.4.2. Action 2 As shown in FIG. 3, according to the Action 2, an inert gas is mixed with the reducing gas supplied to the inside of the shaft furnace 100.

[0037] By inert gas being mixed with the reducing gas, in the same way as the Action 1, it is possible to make the position where the reduction reaction is completed in the vicinity of the furnace wall inside the shaft furnace 100 closer to the position of supply of the reducing gas and possible to increase the region which a reaction gas with a viscosity and density greater than hydrogen gas (for example, steam) occupies in the vicinity of the wall. The pressure loss in the vicinity of the furnace wall rises. Due to this, it is possible to make the amount of supply of reducing gas to the inside from the vicinity of the furnace wall, that is, the center part of the shaft furnace 100, increase, the uniformity of the gas inside the shaft furnace 100 is improved, and uneven reaction of iron oxide inside the shaft furnace 100 can be suppressed. As a result, compared with the case of not mixing inert gas with the reducing gas, the ratio of the iron oxide contained in the solid product after the reduction reaction falls and the ratio of the reduced iron can increase. That is, the average reduction rate Rave can be improved.

[0038] In the Action 2, for example, the reducing gas supply system may have an inert gas supply system connected to it, then inert gas may be mixed with the reducing gas through that inert gas supply system. In the Action 2, the method of mixing the reducing gas and the inert gas is not particularly limited. The reducing gas and the inert gas may, for example, be mixed by a suitable mixing device 112. The amount of the inert gas mixed with the reducing gas is not particularly limited. For example, the inert gas may be mixed with the reducing gas so that the concentration of the inert gas in the total of the reducing gas and inert gas becomes 5 vol% or more and 15 vol% or less. The inert gas may be at least one gas selected from nitrogen, argon, or other rare gas etc. In particular, nitrogen is preferable.

[0039] 1.4.3. Action 3 As shown in FIG. 4, according to the Action 3, the reducing gas supplied to the inside of the shaft furnace 100 is divided into a first gas with a relatively low reducing power and a second gas with a relatively high reducing power and the first gas is supplied from above the second gas.

[0040] By supplying the first gas with a relatively low reducing power from above the second gas with a relatively high reducing power, in the same way as the Action 1, it is possible to make the position where the reduction reaction is completed close to the position of supply of the reducing gas and possible to increase the region which a reaction gas with a viscosity and density greater than hydrogen gas (for example, steam) occupies in the vicinity of the wall. The pressure loss in the vicinity of the furnace wall rises. Due to this, it is possible to make the amount of supply of reducing gas to the inside, that is, the center part of the shaft furnace, increase from the vicinity of the furnace wall, the uniformity of the gas at the inside is improved, and uneven reaction of iron oxide at the inside can be suppressed. As a result, compared with the case of supplying only one type of reducing gas, the ratio of the iron oxide contained in the reduced iron after the reduction reaction falls and the ratio of the metallic iron can increase. That is, the average reduction rate Rave can be improved.

[0041] In the Action 3, if, for example, the temperature of the first gas is lower than the temperature of the second gas and / or if the hydrogen gas concentration of the first gas is lower than the hydrogen gas concentration of the second gas, the reducing power of the first gas becomes relatively low compared with the reducing power of the second gas. That is, the first gas and second gas in the Action 3 may be ones satisfying one or both of the following Conditions A and B.

[0042] Condition A: the temperature of the first gas is lower than the temperature of the second gas

[0043] Condition B: the hydrogen gas concentration of the first gas is lower than the hydrogen gas concentration of the second gas.

[0044] By lowering the temperature of the first gas like in the above Condition A, an effect of improvement of the reduction rate and also an effect of reduction of the energy required for heating are obtained. Regarding the Condition A, the difference of the temperature of the first gas and the temperature of the second gas is not particularly limited. The difference of the temperature of the first gas and the temperature of the second gas can be suitably adjusted in accordance with the targeted average reduction rate etc. If the Condition A is satisfied, the composition of the first gas and the composition of the second gas may be the same or may be different. The first gas may contain hydrogen gas or may not contain it. On the other hand, the second gas always contains hydrogen gas. The first gas and second gas may also contain a gas besides hydrogen gas in addition to hydrogen gas. As the gas besides hydrogen gas, carbon monoxide, an inert gas, etc. may be mentioned. As an inert gas, nitrogen, argon, carbon dioxide, steam, etc. may be mentioned.

[0045] By lowering the hydrogen gas concentration of the first gas like the above Condition B, an effect of improvement of the reduction rate and an effect of reduction of the necessary amount of hydrogen gas are obtained. In relation to the Condition B, the difference of the hydrogen gas concentration of the first gas and hydrogen gas concentration of the second gas is not particularly limited. The difference of the hydrogen gas concentration of the first gas and hydrogen gas concentration of the second gas can be suitably adjusted in accordance with the targeted average reduction rate. The method of making the hydrogen gas concentration of the first gas lower than the hydrogen concentration of the second gas is not particularly limited. For example, the method of mixing an inert gas with the first gas etc. may be mentioned. The first gas may or may not contain hydrogen gas. On the other hand, the second gas always contains hydrogen gas. The first gas and second gas may contain a gas besides hydrogen gas in addition to the hydrogen gas. As the gas besides hydrogen gas, carbon monoxide, an inert gas, etc. may be mentioned. As the inert gas, nitrogen, argon, carbon dioxide, steam, etc. may be mentioned. If the Condition B is satisfied, the temperature of the first gas and the temperature of the second gas may be the same or may be different.

[0046] In the Action 3, for example, the gas supply system at the gas supply device 113 is divided into two systems, an upper and lower one, or three systems, an upper, middle, and lower one, or more and the first gas supplied from at least one system at the upper side and the second gas supplied from at least one system at the lower side. The position of supply of the first gas may be right above the position of supply of the second gas or may be above it at a slant, but in particular a much higher effect is easily obtained if right above. Further, in the Action 3, the amount of supply or speed of supply of the first gas and the amount of supply or speed of supply of the second gas may be the same or different. For example, in the Action 3, the ratio of the first gas in the total of the first gas and second gas supplied to the inside of the shaft furnace 100 (first gas / (first gas+second gas)) may be more than 0 vol% and 10 vol% or less. Further, in the Action 3, the exhaust gas discharged from the gas discharge opening 104 of the shaft furnace 100 may be reutilized as the first gas (gas with relatively low hydrogen concentration compared with second gas and / or gas with relatively low temperature compared with second gas).

[0047] 1.4.4. Action 4 As shown in FIG. 5, in the Action 4, the average particle size of the feedstock 10 supplied to the center side of the shaft furnace 100 (center region 20a of packed bed 20) is made larger than the average particle size of the feedstock 10 supplied to the side wall side of the shaft furnace 100 (region 20b becoming outside in radial direction compared with center region 20a at packed bed 20).

[0048] Further, in the present application, the “particle size” of the feedstock means the maximum outside diameter of the particles of the feedstock. Further, the “average particle size” of the feedstock means the harmonic mean of the maximum outside diameter of the particles of the feedstock. Further, in the present application, a predetermined position between the center and inside wall of the shaft furnace is defined as a boundary, the area between the boundary and center is defined as the “center side of the shaft furnace”, and the area between the boundary and the inside wall is defined as the “side wall side of the shaft furnace”. Specifically, the range from the center of the shaft furnace to 1 / 4 of the furnace inside diameter (up to 1 / 2 of the radius) is defined as the range at the “center side of the shaft furnace” and the range at the outside from that is defined as the range at the “side wall side of the shaft furnace”.

[0049] In the Action 4, by having coarse particles arranged at the center side inside the shaft furnace 100 and having fine particles arranged at the side wall side inside the shaft furnace 100, the pressure loss of the gas rises in the vicinity of the furnace wall in the packed bed 20 and reducing gas becomes easier to supply to the center side of the furnace. That is, the uniformity of the gas inside the shaft furnace 100 is improved and uneven reaction of the iron oxide inside the shaft furnace 100 can be suppressed. As a result, compared with the case of not controlling the average particle size of the packed bed 20, sometimes the ratio of the iron oxide contained in the reduced iron after the reduction reaction falls and the ratio of metallic iron increases. That is, the average reduction rate can be improved.

[0050] In the method for producing reduced iron according to one embodiment, as the Action 4, for example, if the following Action 4A or 4B is employed, the average particle size of the feedstock 10 supplied to the center side of the shaft furnace 100 easily becomes larger than the average particle size of the feedstock 10 supplied to the side wall side of the shaft furnace 100. Action 4A: As shown in FIG. 6, utilizing the fact that coarse particles gather at the center of the shaft furnace 100 when using a rotating chute as a feedstock supply device 114 and a mound or slope are formed from the particles of the feedstock 10 at the side wall side inside the shaft furnace 100. Specifically, supplying the feedstock 10 to the inside of the shaft furnace 100 so that the top part 20x of the packed bed 20 is formed at the side wall side of the shaft furnace 100. Action 4B: As shown in FIG. 7, providing a plurality of hoppers as feedstock supply devices 114 in the radial direction of the shaft furnace 100, supplying feedstock with fine particle size through the hoppers at the side wall side of the shaft furnace 100, and supplying feedstock with coarse particle size through the hopper at the center side of the shaft furnace 100.

[0051] In particular, the Action 4A such as shown in FIG. 6 is simple. That is, in the method for producing reduced iron according to one embodiment, the above Action 4 may be the following Action 4A.

[0052] Action 4A: supplying the feedstock 10 to the side wall side of the shaft furnace 100 (inside wall 100ax side) so that the average particle size of the feedstock 10 supplied to the center side of the shaft furnace 100 becomes greater than the average particle size of the feedstock 10 supplied to the side wall side of the shaft furnace 100 (inside wall 100ax side).

[0053] At the packed bed 20 formed after the Action 4, the average particle size of the feedstock 10 may continuously fall or may intermittently fall from the center side of the shaft furnace 100 to the side wall side of the shaft furnace 100. If, at the packed bed 20 formed after the Action 4, for example, the average particle size of the feedstock 10 as a whole is 10.0 mm or more and 15.0 mm or less, the difference between the average particle size of the feedstock 10 at the side wall side and the average particle size of the feedstock 10 at the center side is preferably 1.0 mm or more.

[0054] 1.5. Timing of Performing Action In the method for producing reduced iron, the above action may be performed at any timing. It may be performed periodically and may be performed based on a criterion determined in advance.

[0055] For example, the above action may be performed at any timing by judgment of the operator based on operational experience.

[0056] Alternatively, information relating to the reduction rate of the feedstock 10 inside the shaft furnace 100 may be estimated and the above action performed based on the estimated information. That information may, for example, be the reduction rate of the feedstock at the side wall side inside the shaft furnace 100 or an indicator representing that reduction rate (following first aspect). Alternatively, that information may, for example, be deviation in the furnace radial direction of the reduction rate of the feedstock 10 inside the shaft furnace 100 or an indicator representing that reduction rate (following second aspect).

[0057] 1.5.1. First Aspect As shown in FIG. 8, in the method for producing reduced iron according to one embodiment, the above information is the reduction rate R of the feedstock 10 at the side wall side of the inside of the shaft furnace 100 or an indicator I representing the reduction rate R. The above action may be performed if the estimated reduction rate R or the indicator I representing the reduction rate R is greater than a first threshold value.

[0058] The “reduction rate of the feedstock 10 at the side wall side of the inside of the shaft furnace 100 or an indicator representing the reduction rate” means the reduction rate R of the feedstock 10 in proximity to the side wall of the inside of the shaft furnace 100 or an indicator I representing the reduction rate R. Specifically, it means the reduction rate R of the feedstock 10 at a position where a distance from a side wall of the inside of the shaft furnace 100 is within 1 / 4 of the furnace inside radius of the shaft furnace 100 or the indicator I representing the reduction rate R. The height position of the side wall inside the shaft furnace 100 at which the reduction rate R of the feedstock 10 is estimated may be, for example, a region present in a range of 0.2 or more and 0.7 or less when making the height of the gas supply opening 102 “0” and making the feedstock stock level (the upper end of the packed bed 20) “1.0”. That region can change according to the furnace shape etc. As shown in FIG. 8, the reduction rate R of the feedstock 10 or the indicator I representing the reduction rate R can be estimated by various estimation devices 105. For estimation of the reduction rate R of the feedstock 10, the feedstock 10 may be sampled and analyzed. Further, it can also be estimated based on numerical simulation regarding the operating conditions at the shaft furnace 100. Alternatively, it is possible to sample and analyze the gas and find the indicator I representing the reduction rate R. For the indicator I representing the reduction rate R, the hydrogen gas concentration etc. can be used.

[0059] In the first aspect, the above action is performed if the estimated reduction rate R or the indicator I representing the reduction rate R is larger than a first threshold value. The “threshold value” in this case, for example, can be determined by numerical simulation, operational analysis, etc. For example, the above action may be performed if it is learned that the reduction rate R of the feedstock 10 at the side wall side of the shaft furnace 100 is 33% or more (if it is found that the feedstock has been reduced to Wustite or more). Alternatively, the above action may be performed if it is estimated that the hydrogen utilization rate at the side wall side of the inside of the shaft furnace 100 is 30 mol% or more.

[0060] In the first aspect, if the estimated reduction rate R or the indicator I representing the reduction rate R is large, this indicates that the reduction reaction by the reducing gas has been completed in the vicinity of the furnace wall inside the shaft furnace 100 and top part of the shaft furnace 100 (vicinity of furnace top). At this time, this can be said to be the state of the reducing gas inside the shaft furnace 100 easily flowing in the vicinity of the furnace wall and reducing gas being hard to be sufficiently supplied up to the center part inside the shaft furnace 100. That is, the state can be said to be one where the ratio occupied by hydrogen gas at the vicinity of the furnace wall increases, the pressure loss falls, and the supply of gas to the center part is obstructed. By the above action being performed in such a case, it is possible to make the amount of supply of reducing gas to the inside from the vicinity of the furnace wall, that is, to the center part of the shaft furnace 100, increase and possible to improve the uniformity of the gas inside the shaft furnace 100 and suppress uneven reaction of the iron oxide inside the shaft furnace 100. As a result, the ratio of iron oxide contained in the reduced iron after the reduction reaction falls and the ratio of metallic iron can increase. That is, the average reduction rate R can be improved.

[0061] 1.5.2. Second Aspect As shown in FIG. 9, in the method for producing reduced iron according to one embodiment, the above information is the deviation D in the furnace radial direction of the reduction rate R of the feedstock 10 inside the shaft furnace 100 or the indicator I representing the reduction rate R. The above action may also be performed if the estimated deviation D is larger than the second threshold value.

[0062] The second aspect, compared with the first aspect, simultaneously utilizes not only the information of the side wall side of the shaft furnace 100, but also the center side of the shaft furnace 100, therefore the timing of performance of the action can be judged more accurately.

[0063] The “deviation (%) in the furnace radial direction of the reduction rate of the feedstock or the indicator representing the reduction rate” is the variation of the reduction rate R (%) of the feedstock 10 in the furnace radial direction inside the shaft furnace 100 or the indicator I representing the reduction rate R. The position in the furnace radial direction is preferably made the side wall and center because a larger deviation can be detected. The deviation D in the furnace radial direction of the reduction rate R of the feedstock 10 or the deviation D in the furnace radial direction of the indicator I representing the reduction rate R of the feedstock 10 can be estimated based on the numerical simulation for the operating conditions at the shaft furnace 100. The height position inside the furnace at which the reduction rate of the feedstock 10 in this case is estimated may be a region present in a range of 0.2 or more and 0.7 or less when, for example, making the height of the gas supply opening 102 “0” and making the feedstock stock level (the upper end of the packed bed 20) “1.0”. Alternatively, as shown in FIG. 9, by using a flow rate measuring device, gas analysis device, or other various devices 120 etc. to analyze the exhaust gas components in the furnace radial direction at the furnace top part and find the hydrogen distribution in the furnace radial direction for the exhaust gas at the furnace top part, it is possible to find the hydrogen utilization rate at the furnace wall side and the hydrogen utilization rate at the furnace center side and find the difference between that hydrogen utilization rate at the furnace wall side and the hydrogen utilization rate at the furnace center side. The information obtained from the gas information at the furnace top part represents the overall height direction of the packed bed 20. The deviation D in the furnace radial direction of the reduction rate R of the feedstock 10 may be estimated based on this information. Alternatively, as shown in FIG. 9, various devices 120 etc. may be used to measure the gas flow rate in the furnace radial direction for the exhaust gas at the furnace top part, and the deviation D in the furnace radial direction of the reduction rate R of the feedstock 10 may be estimated from the deviation of the gas flow rate in the furnace radial direction. Alternatively, as shown in FIG. 9, it is possible to directly use the hydrogen distribution or gas flow rate of the exhaust gas at the above mentioned top furnace part measured using the various devices 120 etc. as the indicator I representing the reduction rate R. The deviation D in the furnace radial direction may be estimated from this information.

[0064] In the second aspect, the above action is performed if the estimated deviation D is greater than a second threshold value. The second threshold value can, for example, be determined by numerical simulation, operational analysis, or analysis of the operational results. The second threshold value may be a coefficient of variation (2x(side wall value-center value) / (side wall value+center value)) of, for example, 0.1 or more and 0.3 or less. Alternatively, if measuring the gas flow rates at the side wall and the center and converting them to the standard states, the above action is performed if the side wall value is larger than the center value by a predetermined value or more (for example, 10% or more).

[0065] In the second aspect, if the estimated deviation D is large, this shows that the difference between the reduction rate of the feedstock 10 at the furnace wall side inside the shaft furnace 100 and the reduction rate of the feedstock 10 at the center side is large. This can be said to be a result of reflection of the state of the reducing gas easily flowing in the vicinity of the furnace wall inside the shaft furnace 100 and reducing gas being hard to be sufficiently supplied up to the center part inside the shaft furnace 100. That is, the state can be said to be one where the reduction reaction due to the reducing gas is completed in the vicinity of the furnace wall and the top part of the shaft furnace (vicinity of furnace top), the ratio occupied by hydrogen gas at the vicinity of the furnace wall increases and the pressure loss falls, and the supply of gas to the center part is obstructed. By the above action being performed in such a case, it is possible to make the amount of supply of reducing gas to the inside from the vicinity of the furnace wall, that is, to the center part of the shaft furnace 100, increase and possible to improve the uniformity of the gas inside the shaft furnace 100 and suppress uneven reaction of the iron oxide inside the shaft furnace 100. As a result, the ratio of iron oxide contained in the solid product after the reduction reaction falls and the ratio of reduced iron can be increased. That is, the average reduction rate can be improved.

[0066] 1.6. Addendum In the method for producing reduced iron according to the aspect, only one type of action may be performed or several types of action may be performed. For example, FIGS. 2 to 7 show the state where one of the above Actions 1 to 4 is performed in the method for producing reduced iron, but in the method for producing reduced iron according to one embodiment, only one among the above Actions 1 to 4 may be performed, two or more of the above Actions 1 to 4 may be performed, three or more of the above Actions 1 to 4 may be performed, or all of the above Actions 1 to 4 may be performed. Further, in the method for producing reduced iron according to one embodiment, another action may be performed after a certain action is performed. For example, in the method for producing reduced iron according to one embodiment, an action separate from the Action 1 (for example, any of the Actions 2 to 4 or the Action 1 different in conditions) may also be performed simultaneously with the Action 1 or after it. Further, in the method for producing reduced iron according to one embodiment, after performing the predetermined action, that action may be freely interrupted or suspended. In any case, in the method for producing reduced iron according to one embodiment, by the above action being performed, the average reduction rate of the feedstock can be improved. In other words, in the method for producing reduced iron according to one embodiment, rather than the reduced iron produced before performing the action, the reduced iron produced after performing the action has a high reduction rate and results in a better product reduced iron.

[0067] 2.   Shaft Furnace The art of the present disclosure also has an aspect as a shaft furnace. As shown in FIGS. 1 to 7, the shaft furnace 100 according to one embodiment is provided with a feedstock supply opening 101, gas supply openings 102, reduced iron discharge opening 103, gas discharge opening 104, and action performing device 110. The feedstock supply opening 101 is provided at the top part of the shaft furnace 100, the gas supply openings 102 are provided at a side wall of the shaft furnace 100 lower than the feedstock supply opening 101, the reduced iron discharge opening 103 is provided below the gas supply openings 102, and the gas discharge opening 104 is provided above the gas supply openings 102. The action performing device 110 is configured to perform an action changing the flow of reducing gas inside the shaft furnace 100 from the side wall side of the shaft furnace 100 to the center side of the shaft furnace 100.

[0068] 2.1. Feedstock Supply Opening, Gas Supply Openings, Reduced Iron Discharge Opening, Gas Discharge Opening At the shaft furnace 100, the feedstock supply opening 101, gas supply openings 102, reduced iron discharge opening 103, and gas discharge opening 104 are not particularly limited in type so long as the above positional relationship is satisfied. The feedstock supply opening 101, for example, may be provided at the top part of the shaft furnace 100. Further, the gas supply opening 102, for example, may be provided right under the position becoming the reduction zone 100ay of the shaft furnace 100. Further, the reduced iron discharge opening 103 may be provided at the bottom part of the shaft furnace 100. Further, the gas discharge opening 104 may be provided at the top part of the shaft furnace 100 at a portion different from the feedstock supply opening 101. By the feedstock supply opening 101, gas supply openings 102, reduced iron discharge opening 103, and gas discharge opening 104 satisfying the above positional relationship, (I) it is possible to supply the feedstock 10 containing the iron oxide from a top part of the shaft furnace 100 to the inside so as to form a packed bed 20 of the feedstock 10 inside the shaft furnace 100 (II) it is possible to supply the reducing gas containing hydrogen gas from the side wall 100a of the shaft furnace 100 to the inside, and (III) it is possible to reduce the iron oxide to obtain reduced iron 30 from the bottom part of the shaft furnace 100.

[0069] 2.2. Action Performing Device The shaft furnace 100 is provided with an action performing device 110. The action performing device 110, for example, may be at least one of a cooling device 111, mixing device 112, gas supply device 113, and feedstock supply device 114. Here, the cooling device 111 is configured to cool at least the inside wall of the shaft furnace 100 at least between the feedstock supply opening 101 and the gas supply openings 102. Further, the mixing device 112 is configured so as to mix an inert gas with the reducing gas. The gas supply device 113 supplies a first gas with a relatively low reducing power and a second gas with a relatively high reducing power from the gas supply opening 102 to the inside of the shaft furnace 100 and is configured so that the position of supply of the first gas becomes above the position of supply of the second gas. Further, the feedstock supply device 114 is configured to supply the feedstock 10 through the feedstock supply opening 101 to the inside of the shaft furnace 100 so that the average particle size of the feedstock 10 supplied to the center side of the shaft furnace 100 becomes larger than the average particle size of the feedstock 10 supplied to the side wall side of the shaft furnace 100. Details of the action by the action performing device 110 are as explained above.

[0070] 2.2.1. Addendum Regarding Cooling Device The cooling device 111, for example, may also be configured so as to cool by water cooling at least the inside wall 100ax of the shaft furnace 100 at least between the feedstock supply opening 101 and gas supply openings 102. That is, the cooling device 111 may also be a water cooling device. More specifically, the cooling device 111 may be one configured to make cooling water circulate inside the walls of the shaft furnace 100 and at least between the feedstock supply opening 101 and gas supply opening 102. The cooling device 111 may also be configured to cool the entire circumference of the inside wall of the shaft furnace 100. More specifically, the cooling device 111 may also be configured to make cooling water circulate inside the walls of the shaft furnace 100 and over the entire circumference of the walls of the shaft furnace 100 at least between the feedstock supply opening 101 and gas supply opening 102. The cooling device 111 may be one employing a configuration similar to the device for cooling the wall of a blast furnace. The cooling device 111 is one of the specific means for performing the above Action 1. The cooling conditions by the cooling device 111 may be similar to those in the above Action 1.

[0071] 2.2.2. Addendum Regarding Mixing Device The mixing device 112, for example, may be configured so as to connect an inert gas supply system to a reducing gas supply system such as shown in FIG. 3. More specifically, the mixing device 112, for example, may be configured to be connected to the reducing gas supply system from a reducing gas source and an inert gas supply system from an inert gas source and to have the reducing gas and inert gas mixed in the mixing device 112. The mixing device 112 may be provided with valves etc. for adjusting the flow rate and pressure etc. of reducing gas from the reducing gas supply system to the mixing device 112 and for adjusting the flow rate and pressure etc. of inert gas from the inert gas supply system to the mixing device 112. One example of the mixing ratio of the reducing gas and inert gas in the mixing device 112 etc. was explained above. The mixing device 112 is one of the specific means for performing the above Action 2. The mixing conditions and supply conditions of the reducing gas and inert gas by the mixing device 112 may be made similar to those in the above Action 2. 2.2.3. Addendum Regarding Gas Supply Device The gas supply device 113, for example, may have two gas supply systems, an upper and lower one, such as shown in FIG. 4, or three or more gas supply systems, an upper, middle, and lower one, and may be configured so as to supply the first gas from at least one upper system and supply the second gas from at least one lower system. More specifically, the gas supply device 113, for example, may be configured to have two or more gas supply systems, have at least a gas supply system among them as a first gas supply system from the gas source, have at least one other gas supply system separate from the first gas supply system as a second gas supply system from a second gas source, have the first gas supply system and second gas supply system connected to a side wall of the shaft furnace 100, and have a connection position of the first gas supply system and the side wall of the shaft furnace 100 become higher than a connection position of the second gas supply system and the side wall of the shaft furnace 100. The type of the first gas in the first gas supply system and the type of the second gas in the second gas supply system are as explained above. For example, the gas supply device 113 may be configured so that the first gas and second gas satisfy one or both of the following Conditions A and B. The gas supply device 113 is one of the specific means for performing the above Action 3. The gas supply conditions by the gas supply device 113 may be similar to those in the above Action 3. Condition A: the temperature of the first gas is lower than the temperature of the second gas. Condition B: the hydrogen gas concentration of the first gas is lower than the hydrogen gas concentration of the second gas.

[0073] 2.2.4. Addendum Regarding Feedstock Supply Device The feedstock supply device 114 may be configured so as to supply the feedstock 10 to a side wall side of the shaft furnace 100. The feedstock supply device 114 may, for example, be a rotating chute such as shown in FIG. 6 or may be a plurality of hoppers provided in the radial direction such as shown in FIG. 7. More specifically, the feedstock supply device 114, for example, may be a rotating chute supplying the feedstock 10 to the inside of the shaft furnace 100 so that a top part 20x of the packed bed 20 is formed at the side wall side of the shaft furnace 100. Alternatively, the feedstock supply device 114 may, for example, be provided with a plurality of first hoppers and second hoppers provided in the radial direction of the shaft furnace 100 and be configured so that feedstock with a fine particle size is supplied from the first hoppers provided at the side wall side of the shaft furnace 100 and feedstock with a coarse particle size is supplied from second hoppers provided at the center side of the shaft furnace 100. Here, it can be configured to have the first hoppers, for example, connected to a first feedstock supply source, the second hoppers, for example, connected to a second feedstock supply source different from the first feedstock supply source, feedstock with a fine particle size supplied from the first feedstock supply source to the first hoppers, and feedstock with a coarse particle size supplied from the second feedstock supply source to the second hoppers. The feedstock supply device 114 is one of the specific means for performing the above Action 4. The feedstock supply conditions by the feedstock supply device 114 may be made similar to those in the above Action 4.

[0074] 2.3. Estimation Device and Control Device The shaft furnace 100 may be provided with estimation devices 105, 107 and control devices 106, 108. For example, the estimation devices 105, 107 may be configured to estimate information relating to the reduction rate of the feedstock 10 inside the shaft furnace 100, while the control devices 106, 108 may be ones controlling the above action performing device 110 so that the above action is performed based on the estimated information. More specifically, the information estimated by the estimation device 105 may be a reduction rate R of the feedstock 10 at the side wall side inside the shaft furnace 100 or an indicator I representing the reduction rate R. In this case, the control device 106 may be one controlling the action performing device 110 so that the above action is performed if the estimated reduction rate R or the indicator I representing the reduction rate R is greater than a first threshold value. Alternatively, the information estimated by the estimation device 107 may be a deviation D in the furnace radial direction of the reduction rate R of the feedstock 10 inside the shaft furnace 100 or the indicator I representing the reduction rate R. In this case, the control device 108 may be one controlling the action performing device 110 so that the above action is performed if the estimated deviation D is greater than a second threshold value.

[0075] 2.3.1. Addendum Regarding Estimation Device (First Aspect) As explained above, the estimation device 105 may be configured to estimate a reduction rate R of the feedstock 10 at the inside wall of the furnace or an indicator I representing the reduction rate R. The method of estimating the reduction rate R or the indicator I is as explained above. As explained above, the reduction rate R and the indicator I can, for example, be estimated based on numerical simulation of the operating conditions of the shaft furnace 100. That is, the estimation device 105 may be a numerical simulation device. Alternatively, the estimation device 105 may be one which samples the feedstock from a predetermined position of the furnace inside wall of the shaft furnace 100 and estimates the reduction rate R of that feedstock based on results of analysis of that feedstock. Alternatively, the estimation device 105 may be one which estimates the indicator I representing the reduction rate R of the feedstock from the results of analysis of the sampled gas. For the indicator I representing the reduction rate R, the hydrogen gas concentration, hydrogen utilization rate, etc. can be used. The estimation device 105 is provided with the configuration required for making such estimations. For example, the estimation device 105 may be provided with a known processing device etc.

[0076] 2.3.2. Addendum Regarding Estimation Device (Second Aspect) Alternatively, the estimation device 107 may be configured to estimate the deviation D in the furnace radial direction of the reduction rate R of the feedstock 10 or the indicator I representing the reduction rate R. The method of estimation of the deviation D is as explained above. As explained above, the deviation D can, for example, be estimated based on numerical simulation of the operating conditions of the shaft furnace 100. That is, the estimation device 107 may also be a numerical simulation device. Alternatively, the estimation device 107 may find the distribution of hydrogen in the furnace radial direction in the exhaust gas at the furnace top part from the results of analysis of the exhaust gas components in the furnace radial direction at the furnace top part, find the rate of utilization of hydrogen at the furnace wall side and the rate of utilization of hydrogen at the furnace center side, and estimate the deviation D in the furnace radial direction of the reduction rate R of the feedstock 10 based on the difference between the rate of utilization of hydrogen at the furnace wall side and the rate of utilization of hydrogen at the furnace center side. Alternatively, the estimation device 107 may estimate the deviation D in the furnace radial direction of the reduction rate R of the feedstock 10 based on the deviation of the gas flow rate in the furnace radial direction from the results of measurement of the gas flow rate in the furnace radial direction for the exhaust gas at the furnace top part. Alternatively, the estimation device 107 may estimate the deviation D in the furnace radial direction of the reduction rate R of the feedstock 10 based on the reduction rates of the material reduced at the furnace wall and the material reduced at the furnace center part. The estimation device 107 is provided with a constitution required for such estimation. For example, the estimation device 107 may be provided with a known processing device etc.

[0077] 2.3.3. Addendum Regarding Control Device (First Aspect) The control device 106 may be one which controls the action performing device 110 so that the above action is performed when the reduction rate R or the indicator I representing the reduction rate R estimated by the estimation device 105 is larger than a first threshold value. The control device 106 is provided with the constitution required for controlling the performance of the action based on the result of estimation by the estimation device 105. For example, the control device 106 may be provided with a CPU, RAM, ROM, etc.

[0078] 2.3.4. Addendum Regarding Control Device (Second Aspect) The control device 108 may be one which controls the action performing device 110 so that the above action is performed when the deviation D estimated by the estimation device 107 is larger than a second threshold value. The control device 108 is provided with the constitution required for controlling the performance of the action based on the result of estimation of the deviation D by the estimation device 107. For example, the control device 108 may be provided with a CPU, RAM, ROM, etc.

[0079] 2.4. Other Constitutions The shape of the body of the shaft furnace 100 may be similar to the shape of the body of a known shaft furnace. For example, as shown in FIGS. 1 to 9, the body of the shaft furnace 100 may be a tubular part (cylindrical part) comprising a furnace top part, a furnace bottom part, and a side wall between the furnace top part and furnace bottom part. The tubular part may have a barrel part and a constricted part provided lower than the barrel part. At the constricted part, the inside diameter of the furnace may be constricted from the top toward the bottom. Further, the shaft furnace 100 may be provided with a burden feeder etc. for preventing bridging of the packed bed 20 when the packed bed 20 is made to move downward at the inside. Further, the shaft furnace 100 may also be provided below the gas supply openings 102 with a cooling gas supply opening for supplying cooling gas and a gas discharge opening for discharging the cooling gas. The cooling gas supply opening may be provided at the inside from the side wall of the furnace, while the cooling gas discharge opening may be provided at the side wall of the furnace below the gas supply opening 102. The burden feeder, cooling gas supply opening, and cooling gas discharge opening provided at the shaft furnace 100 are known.

[0080] 2.5. Addendum The shaft furnace 100 may be provided with both of a configuration according to the first aspect and a configuration according to the second aspect. In this case, the estimation device 105 and the estimation device 107 may also be the same device or may be different devices. For example, one estimation device provided at the shaft furnace 100 may also function as the estimation device 105 and the estimation device 107. Further, the control device 106 and the control device 108 may also be the same device or may be different devices. For example, one control device provided at the shaft furnace 100 may function as the control device 106 and the control device 108. Further, the estimation devices 105, 107 and the control devices 106, 108 may be the same devices and may be different devices. For example, one device provided at the shaft furnace may function as the estimation devices 105, 107 and the control devices 106, 108. Specifically, for example, in the shaft furnace 100, the estimation device may be configured to estimate at least one of the reduction rate R at the furnace inside wall of the feedstock 10 or the indicator I representing the reduction rate R and the deviation D in the furnace radial direction of the reduction rate R of the feedstock 10 or the indicator I representing the reduction rate R. Further, the control device may also control the action performing device 110 so that the above action is performed when the estimated reduction rate R, indicator I, and / or deviation D is greater than a threshold value. Further, the control device may also control the interruption or suspension of action by the action performing device 110.

[0081] 3. Advantageous Effects As explained above, according to the art of the present disclosure, when using a shaft furnace 100 to produce reduced iron, the average reduction rate of the reduced iron 30 is easily improved. EXAMPLES

[0082] Below, the inventor will present examples and explain in more detail the effects due to the art of the present disclosure, but the art of the present disclosure is not limited to the following examples.

[0083] 1. Furnace Body Structure and Boundary Conditions The inventor analyzed the behavior of the reducing gas in the furnace (distribution of hydrogen concentration, distribution of pressure, and distribution of flow rate), the distribution of reduction rate of iron oxide in the furnace, and the average reduction rate in the case of using a shaft furnace to reduce a feedstock containing iron oxide by a reducing gas (hydrogen gas) and obtain reduced iron by numerical simulation employing the following furnace body structure and boundary conditions.

[0084] For the furnace body structure, the one shown in FIG. 10 was employed. Further, the structure shown in FIG. 10 is the structure of the left half when dividing the furnace internal structure at the cross-section passing through the center axis of the furnace and running along the center axis into a right half and a left half about the center axis of the furnace. The flow rate of the reducing gas was set to 6300 (Nm3 / min), pure hydrogen was used for the type of the reducing gas, and the temperature was made 950°C. Further, the cooling gas was deemed supplied below the position of supply of the reducing gas. For the cooling gas, CH4 was used. The flow rate of the cooling gas was made 1400 (Nm3 / min) so that the product average temperature became roughly 80°C. The extraction flow rate of the cooling gas was made 1260 (Nm3 / min) so as to become 90% of the charged amount.

[0085] 2. Conditions of Calculation The inventor conducted calculations using the conditions described above as the basis and changing the reducing gas charging conditions, the feedstock conditions, the pressure conditions, and the wall surface heat boundary conditions. The average reduction rates were compared. A list of the calculation conditions is given in the following Table 1.

[0086] [Table 1] Feedstock supply temp. (°C) Furnace top gage pressure (kPa) Reducing gas (second gas) comp. (%) Furnace wall heat transfer coefficient (W / m2 / K) Upper first gas Particle size difference (mm) Ratio (%) Temp. (°C) Comp. (%) Base 25 41 H2: 100 0.60 A A A 0 Furnace wall cooling Action 1 25 41 H2: 100 55 - - - 0 N2 substitution Action 2 25 41 H2: 90 N2: 10 0.60 - - - 0 Divided charging of reducing gas Action 3 25 41 H2: 100 0.60 1 800 H2 0 Imparting particle size deviation Action 4 25 41 H2: 100 0.60 - - - 1.0

[0087] 3. Results of Calculations The results of the calculations are shown in Table 2.

[0088] [Table 2] Upper first gas Base Effect of improvement of average reduction rate of actions 1 2 3 4 No division 94.7 +1.4 +1.1 - +1.5 1% - - - +2.0 -

[0089] 3.1. Base As shown in Table 2, the average reduction rate at the base was 94.7%.

[0090] 3.2. Furnace Wall Cooling (Action 1) The inventor investigated the effect of cooling the furnace wall. Calculations were performed based on boundary conditions similar to a blast furnace (water cooling at 25°C) as the wall surface boundary conditions. As shown by the Action 1 of Table 2, the average reduction rate after performing the Action 1 was improved by 1.4% over the base. It is believed that the effect due to lowering the reduction completion point exceeds the effect of the drop in the calorific content.

[0091] 3.3. Partial N2 Substitution of Reducing Gas (Action 2) The inventor investigated the effect due to replacing part of the reducing gas with N2 . As shown by the Action 2 of Table 2, the average reduction rate after performing the Action 2 was improved by +1.1% with respect to the base. The inventor checked the distribution of hydrogen concentration whereupon the hydrogen rich region in the vicinity of the wall decreased and the pressure increased. Due to the weaker reducing power, the reduction completion point in the vicinity of the wall decreased and gas more easily flowed to the furnace center side. That effect is believed to be above the effect of the weaker reducing power of the gas.

[0092] 3.4. Divided Charging of Reducing Gas (Action 3) As means for lowering the reduction completion point, the inventor studied the method of providing several charging openings for reducing gas and charging gas with a low reducing power from above. Here, the inventor added another charging opening 1 m above the charging position of the base conditions and charged gas of the same composition but with its temperature lowered by 150°C at a flow rate corresponding to 1% of the total flow rate of 6300 (Nm3 / min). As shown by the Action 3 of Table 2, the average reduction rate after performing the Action 3 was improved by +2.0% from the base.

[0093] 3.5. Imparting Deviation in Particle Size (Action 4) In the above, as a measure for promoting introduction of gas to the center part, the inventor studied the measure of lowering the reduction completion point in the vicinity of the wall surface. Here, more directly, the inventor studied manipulating the particle size as a condition of the solid side to promote the introduction of gas to the center part. Specifically, to make the harmonic mean size become 13.5 mm, particles with large particle size were arranged at the center, particles with small particle size were arranged at the wall side, and the difference between the smallest and largest particle sizes was made to become 1 mm by imparting a deviation in particle size causing the particle size to linearly change from the center to the wall side. As a result, the region of hydrogen in the vicinity of the wall surface was shrunk and the average reduction rate was improved by +1.5% over the base.

[0094] 4. Summary From the above results, it is learned that in the method for producing reduced iron using a shaft furnace, the average reduction rate of the feedstock is improved by performing an action for making the flow of reducing gas inside the shaft furnace move from the side wall side of the shaft furnace to the center side of the shaft furnace (for example, the above Actions 1 to 4).

[0095] That is, it can be said that the average reduction rate of the feedstock can be raised in the production of reduced iron using a shaft furnace according to the following (1). In particular, it can be said that the effect of raising the average reduction rate of the feedstock becomes particularly remarkable according to the following (2).

[0096] (1) A method for producing reduced iron comprising supplying a feedstock containing iron oxide from a top part of a shaft furnace to the inside, supplying a reducing gas containing hydrogen gas from a side wall of the shaft furnace to the inside, and reducing the iron oxide to obtain reduced iron from a bottom part of the shaft furnace, the method for producing reduced iron including performing an action for changing a flow of the reducing gas inside the shaft furnace from the side wall side of the shaft furnace to the center side of the shaft furnace. (2) A method for producing reduced iron in which the action includes at least one of the following actions 1 to 4: Action 1: cooling at least the inside wall of the shaft furnace at least between a position of supply of the feedstock and a position of supply of the reducing gas; Action 2: mixing an inert gas with the reducing gas; Action 3: dividing the reducing gas supplied to the inside of the shaft furnace into a first gas with a relatively low reducing power and a second gas with a relatively high reducing power and supplying the first gas from above the second gas; and Action 4: making an average particle size of the feedstock supplied to the center side of the shaft furnace larger than the average particle size of the feedstock supplied to the side wall side of the shaft furnace. REFERENCE SIGNS LIST

[0097] 10 feedstock 20 packed bed 30 reduced iron 100 shaft furnace 100a side wall 100ax inside wall 101 feedstock supply opening 102 gas supply opening 5          103 reduced iron discharge opening 104 gas discharge opening 105, 107 estimation device 106, 108 control device 110 action performing device 10           111 cooling device 112 mixing device 113 gas supply device 114 feedstock supply device

Claims

1. A method for producing reduced iron comprising:supplying a feedstock containing iron oxide from a top part of a shaft furnace to the inside,supplying a reducing gas containing hydrogen gas from a side wall of the shaft furnace to the inside, andreducing the iron oxide to obtain reduced iron from a bottom part of the shaft furnace, whereinthe method includes performing an action for changing a flow of the reducing gas inside the shaft furnace from the side wall side of the shaft furnace to the center side of the shaft furnace.

2. The method for producing reduced iron according to claim 1, whereinthe action includes at least one of the following actions 1 to 4:Action 1: cooling at least the inside wall of the shaft furnace at least between a position of supply of the feedstock and a position of supply of the reducing gas;Action 2: mixing an inert gas with the reducing gas;Action 3: dividing the reducing gas supplied to the inside of the shaft furnace into a first gas with a relatively low reducing power and a second gas with a relatively high reducing power and supplying the first gas from above the second gas; andAction 4: making an average particle size of the feedstock supplied to the center side of the shaft furnace larger than the average particle size of the feedstock supplied to the side wall side of the shaft furnace.

3. The method for producing reduced iron according to claim 2, whereinthe Action 1 is the following Action 1A:Action 1A: cooling by water cooling at least the inside wall of the shaft furnace at least between the position of supply of the feedstock and the position of supply of the reducing gas.

4. The method for producing reduced iron according to claim 2, whereinthe Action 4 is the following Action 4A:Action 4A: supplying the feedstock to the side wall side of the shaft furnace so that the average particle size of the feedstock supplied to the center side of the shaft furnace becomeslarger than the average particle size of the feedstock supplied to the side wall side of the shaft furnace.

5. The method for producing reduced iron according to claim 2, whereinthe first gas and the second gas in the Action 3 satisfy one or both of the following conditions A and B:Condition A: the temperature of the first gas is lower than the temperature of the second gas andCondition B: the hydrogen gas concentration of the first gas is lower than the hydrogen gas concentration of the second gas.

6. The method for producing reduced iron according to any one of claims 1 to 5, wherein the method comprises:estimating information relating to a reduction rate of the feedstock inside the shaft furnace; andperforming the action based on the estimated information.

7. The method for producing reduced iron according to claim 6, whereinthe information is the reduction rate of the feedstock at the side wall side inside the shaft furnace or an indicator representing the reduction rate, andthe action is performed when the estimated reduction rate or the indicator representing the reduction rate is greater than a first threshold value.

8. The method for producing reduced iron according to claim 6, whereinthe information is a deviation in a furnace radial direction of the reduction rate of the feedstock or the indicator representing the reduction rate inside the shaft furnace, andthe action is performed when the estimated deviation is greater than a second threshold value.

9. A shaft furnace comprising a feedstock supply opening, a gas supply opening, a reduced iron discharge opening, a gas discharge opening, and an action performing device, whereinthe feedstock supply opening is provided at a top part of the shaft furnace,the gas supply opening is provided at a side wall of the shaft furnace lower than the feedstock supply opening,the reduced iron discharge opening is provided lower than the gas supply opening,the gas discharge opening is provided higher than the gas supply opening,the action performing device is configured so as to perform an action for changing a flow of the reducing gas inside the shaft furnace from the side wall side of the shaft furnace to the center side of the shaft furnace.

10. The shaft furnace according to claim 9, whereinthe action performing device is at least one of a cooling device, a mixing device, a gas supply device, and a feedstock supply device,the cooling device is configured to cool at least the inside wall of the shaft furnace at least between a position of supply of the feedstock and a position of supply of the reducing gas,the mixing device is configured to mix an inert gas with the reducing gas;the gas supply device is configured to supply a first gas with a relatively low reducing power and a second gas with a relatively high reducing power from the gas supply opening to the inside of the shaft furnace and make the position of supply of the first gas above the position of supply of the second gas, andthe feedstock supply device is configured to supply the feedstock through the feedstock supply opening to the inside of the shaft furnace so that the average particle size of the feedstock supplied to the center side of the shaft furnace becomes larger than the average particle size of the feedstock supplied to the side wall side of the shaft furnace.

11. The shaft furnace according to claim 10, whereinthe cooling device is configured to cool at least the inside wall of the shaft furnace by water cooling at least between the feedstock supply opening and the gas supply opening.

12. The shaft furnace according to claim 10, whereinthe feedstock supply device is configured so as to supply the feedstock to the side wall side inside the shaft furnace.

13. The shaft furnace according to claim 10, whereinthe gas supply device is configured so that the first gas and the second gas satisfy one or both of the following conditions A and B:Condition A: the temperature of the first gas is lower than the temperature of the second gas andCondition B: the hydrogen gas concentration of the first gas is lower than the hydrogen gas concentration of the second gas.

14. The shaft furnace according to any one of claims 9 to 13, whereinthe shaft furnace comprises an estimation device and a control device,the estimation device is configured to estimate information relating to a reduction rate of the feedstock inside the shaft furnace andthe control device controls the action performing device so that the action is performed based on the estimated information.

15. The shaft furnace according to claim 14, whereinthe information is the reduction rate of the feedstock or an indicator representing the reduction rate at the side wall side inside the shaft furnace, andthe control device controls the action performing device so that the action is performed when the estimated reduction rate or the indicator representing the reduction rate is greater than a first threshold value.

16. The shaft furnace according to claim 14, whereinthe information is a deviation in the furnace radial direction of the reduction rate of the feedstock or the indicator representing the reduction rate inside the shaft furnace, andthe control device controls the action performing device so that the action is performed when the estimated deviation is greater than a second threshold value.

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