JP5605828B2 - Iron making method and iron making system - Google Patents

Description

  The present invention relates to iron making technology, and more particularly, to an iron making method and an iron making system using a reduction reaction with ammonia.

  Conventionally, in the iron making process, a process of obtaining pig iron from iron ore using a blast furnace is mainly used. Specifically, iron ore and coke are alternately supplied from the upper part of the blast furnace, and hot hot air is blown from the lower part. As a result, iron oxide in the iron ore is reduced by carbon monoxide generated by the combustion of coke and the Budwar reaction, and iron is separated.

  Japanese Patent Application Laid-Open No. 2009-221549 also proposes a method of using hydrogen as a reducing agent instead of coke in the blast furnace method described above (Patent Document 1). In this method, in a blast furnace operation in which a reducing agent containing 10 mass% or more of hydrogen is blown from the tuyere, a preheated raw material is charged from the top of the blast furnace.

JP 2009-221549 A

  However, in the blast furnace method using the above-mentioned coke, the coke Budower reaction is rate-determined, and thus it is necessary to maintain a high temperature exceeding 1000 ° C. in order to obtain reduced iron. For this reason, there is a problem that the fuel consumption is as large as 500 kg / t-pig iron and the amount of carbon dioxide emission is extremely large. Further, since the utilization rate of the reducing agent is as low as about 50%, a process for recovering the chemical energy of the blast furnace outlet gas is also required. Note that the utilization rate of the reducing agent refers to the ratio of the reducing agent used in the reaction when a certain reducing agent is used in the reduction reaction (amount used in the reduction reaction / total amount before the reduction reaction). And

  Further, the invention described in Patent Document 1 has a problem that an infrastructure for transporting hydrogen as a reducing agent has not been prepared. For transporting hydrogen, a liquefying method, a compressing method, a method using a hydrogen storage alloy, and the like can be considered, but in order to liquefy, it is necessary to cool to about −252 ° C. or less. In addition, a high pressure compressor and a high strength pressure vessel are required for compression. Furthermore, the hydrogen storage alloy has a low storage amount of less than 10%, and there are still problems to be solved for practical use.

  The present invention has been made to solve such problems, and by using ammonia as a reducing agent for which a transportation method has been established, the reduction reaction can be performed at a low temperature, the amount of reducing agent used, fuel An object of the present invention is to provide an iron making method and an iron making system capable of reducing consumption and carbon dioxide emission.

  The iron making method according to the present invention is to produce iron by supplying a steel making raw material and ammonia into a reactor and causing a reduction reaction.

  In the present invention, the ammonia may be supplied into the reactor after being preheated to a temperature equal to or higher than the reduction reaction temperature of the ironmaking raw material.

  Furthermore, in the present invention, oxygen or air may be mixed with the ammonia and supplied into the reactor.

  In the present invention, oxygen or air may be supplied into the reactor separately from the ammonia.

  Furthermore, in the present invention, the inside of the reactor may be maintained at 450 ° C. or higher.

  An iron making system according to the present invention includes an iron making raw material and ammonia, and a reactor for producing iron by a reduction reaction, an iron making raw material supply means for supplying the iron making raw material into the reactor, and the inside of the reactor. And an ammonia supply means for supplying ammonia.

  Moreover, in this invention, you may have the ammonia preheating means which preheats the said ammonia more than the reduction reaction temperature of the said steelmaking raw material.

  Furthermore, in the present invention, the ammonia supply unit may mix oxygen or air with the ammonia and supply the mixture into the reactor.

  Moreover, in this invention, you may have an oxygen supply means which supplies oxygen or air into the said reactor separately from the said ammonia.

  Furthermore, in the present invention, the inside of the reactor may be maintained at 450 ° C. or higher.

  According to the present invention, by using ammonia for which a transportation method has been established as a reducing agent, the reduction reaction can be performed at a low temperature, and the amount of reducing agent used, the amount of fuel consumed, and the amount of carbon dioxide emitted can be reduced.

It is a flowchart figure which shows one Embodiment of the iron manufacturing method which concerns on this invention. It is a block diagram which shows one Embodiment of the iron manufacturing system which concerns on this invention. It is a general view which shows the experimental apparatus used in the present Example. In Example 1, it is a graph which shows the result of having measured the composition of the exit gas of a reaction tube with the mass spectrometer. In Example 1, it is a graph which shows the value which differentiated the time change of a density | concentration about each gas. In Example 1, it is a figure which shows the analysis result by the X-ray-diffraction apparatus of the sample after a reduction | restoration. In Example 2, it is a graph which shows the result of having measured the composition of the exit gas of a reaction tube with the mass spectrometer. In Example 2, it is a graph which shows the value which differentiated the time change of a density | concentration about each gas. In Example 2, it is a figure which shows the analysis result by the X-ray-diffraction apparatus of the sample after a reduction | restoration. It is a graph which shows the change of the Gibbs free energy with respect to a temperature change about iron, ammonia, and iron nitride. It is a graph which shows the change of the Gibbs free energy with respect to a temperature change about each reduction reaction.

In order to solve the above-mentioned problems, the inventors of the present application conducted a preliminary study with the goal of reducing the temperature of the reduction reaction. Specifically, it was first proposed to use ammonia as a reducing agent due to the following characteristics.
(1) The ammonia liquefaction temperature is −33 ° C., which is easier to liquefy than hydrogen.
(2) Ammonia has a high hydrogen storage amount of 17.6 mass% compared to other typical hydrogen storage materials.
(3) A method for producing and transporting ammonia has already been established, and the current infrastructure can be used.

  Therefore, as shown in FIG. 11, a thermodynamic equilibrium calculation was performed on the reduction reaction of hematite, which is a raw material for iron making. As a result, we focused on the fact that the reduction equilibrium of hematite by ammonia shifts to the production side at about 300 ° C. compared to carbon and hydrogen. In addition, since carbon monoxide has no industrially produced process, it was considered that carbon monoxide is not appropriate in terms of application and application to an actual steelmaking process. And as a result of earnest research, it discovered that iron could be manufactured by supplying a steelmaking raw material and ammonia in a reactor, and making it reduce-react.

  Hereinafter, embodiments of the iron making method and the iron making system according to the present invention will be described with reference to the drawings. FIG. 1 is a flowchart showing the iron making method of the present embodiment, and FIG. 2 is a block diagram showing an iron making system 1 that performs the iron making method of the present embodiment.

  As shown in FIG. 1 and FIG. 2, in this embodiment, first, the iron-making raw material is supplied to the reactor 3 by the iron-making raw material supply means 2 such as a belt conveyor (step S1). In the present invention, the reactor 3 is a concept including all containers having heat resistance and containing a predetermined substance to cause a chemical reaction. In the present invention, the iron-making raw material includes all raw materials mainly composed of iron oxide, and examples thereof include iron ores such as hematite, magnetite, and limonite.

  Next, ammonia is preheated by the ammonia preheating means 4 comprising a gas heater or the like (step S2). Here, since the reduction of the iron-making raw material with ammonia is an endothermic reaction, the temperature decreases as the reduction reaction proceeds. Therefore, when the iron making method according to the present invention is applied to an actual iron making process, it is necessary to supplement the endothermic component in some form. Therefore, in the present embodiment, sensible heat is increased by preheating ammonia to compensate for the above endothermic component. In addition, by preheating ammonia at a temperature equal to or higher than the reduction reaction temperature of the iron-making raw material, sensible heat that completely complements the endothermic component is imparted. Note that the reduction reaction temperature is the minimum temperature required to start the reduction reaction, and in this embodiment, can be said to be about 300 ° C. from FIG.

  Note that the pre-heat treatment in step S2 is one of the processes considered as a method for supplementing the endothermic component when ammonia is supplied alone. However, when oxygen or air is supplied in addition to ammonia, the ammonia partially burns in the reactor 3 and heat is supplied inside. Therefore, it is possible to supply heat by combining this partial combustion and this pre-heat treatment, or it is possible to omit this main heat treatment and supply heat only by partial combustion.

  Next, ammonia is supplied to the reactor 3 by the ammonia supply means 5 including a flow rate regulator or the like (step S3). In the present embodiment, the ammonia supply means 5 is configured to supply the ammonia gas preheated by the ammonia preheating means 4 into the reactor 3 at a constant flow rate when performing the pre-heat treatment described above. On the other hand, when the heat supply by the partial combustion described above is performed, the ammonia supply means 5 mixes oxygen or air with ammonia and supplies the mixture into the reactor 3.

  In addition, when heat supply by partial combustion is performed, oxygen or air may not be mixed with ammonia, and may be separately supplied into the reactor 3 by the oxygen supply means 6 including a flow rate regulator (step S4). ). However, it is necessary to suppress oxygen or air supplied into the reactor 3 from being selectively oxidized before the reduced iron is contacted with ammonia. Therefore, the oxygen supply means 6 has a supply method and layout that can be controlled. However, the supply layout is not a problem when the combustion reaction of ammonia is allowed to proceed sufficiently faster than the oxidation reaction of the ironmaking raw material.

Finally, the inside of the reactor 3 is heated to a predetermined temperature or higher by the heating means 7 composed of a heating furnace or the like (step S5). Thereby, the reductive reaction of the iron-making raw material by ammonia advances, and reduced iron is obtained. In this embodiment, the reaction in which iron oxide, which is the main component of the iron-making raw material, is reduced by ammonia is considered to be different depending on the heating temperature from the results of Examples described later. Specifically, after ammonia is decomposed into nitrogen and hydrogen (the following formula (1)), it is reduced by the hydrogen (the following formula (2)), and directly into iron nitride (Fe ₄ N) by ammonia. It is considered that there is a case (the following formula (4)) in which the iron nitride is decomposed after the reduction (the following formula (3)).

NH ₃ → 1 / 2N ₂ + 3 / 2H ₂ Formula (1)
Fe ₂ O ₃ + 3H ₂ → 2Fe + 3H ₂ O Formula (2)
Fe ₂ O ₃ + 6NH ₃ → 2Fe ₄ N + 3H ₂ O + 2N ₂ Formula (3)
Fe ₄ N → 4Fe + 1 / 2N ₂ Formula (4)

In the former case, ammonia generates semi-reduced iron (Fe ₃ O ₄ , FeO) in the process of reducing iron oxide (the following formulas (5) to (7)). And it has the effect | action which lowers the temperature of the hydrogen production | generation process of said Formula (1) by the catalytic action of this semi-reduced iron. Further, it is considered that the reduction reaction of the half-reduced iron is further advanced by the hydrogen generated by the above formula (1) (the following formulas (8) to (10)) and finally reduced to iron.

Fe ₂ O ₃ + 2 / 9NH ₃ → 2 / 3Fe ₃ O ₄ + 1 / 3H ₂ O + 1 / 9N ₂ Formula (5)
Fe ₂ O ₃ + 2 / 3NH ₃ → 2FeO + H ₂ O + 1 / 3N ₂ Formula (6)
Fe ₃ O ₄ + 2 / 3NH ₃ → 3FeO + H ₂ O + 1 / 3N ₂ (7)
Fe ₂ O ₃ + 1 / 3H ₂ → 2/3 Fe ₃ O ₄ + 1 / 3H ₂ O Formula (8)
Fe ₂ O ₃ + H ₂ → 2FeO + H ₂ O (9)
Fe ₃ O ₄ + H ₂ → 3FeO + H ₂ O Formula (10)

  On the other hand, in the latter case, ammonia directly reduces iron oxide to iron nitride. And it is thought that a part of produced | generated iron nitride decomposes | disassembles and changes to iron. In addition, it is thought that the iron nitride produced | generated by the said Formula (3) functions as a catalyst which decomposes | disassembles ammonia separately, and advances reaction of the said Formula (1).

  In any of the above cases, the lower the temperature in the reactor 3, the more difficult the reduction reaction proceeds. Therefore, in order to advance the reduction reaction to such an extent that it can be put into practical use, it is necessary to heat the inside of the reactor 3 to a predetermined temperature or higher. In the present embodiment, from the results of Examples described later, when the inside of the reactor 3 is heated to 450 ° C. or higher, the reduction reaction by ammonia proceeds without delay.

  In the present embodiment described above, the method of heating the inside of the reactor 3 by the heating means 7 has been described. However, when the ammonia can be sufficiently preheated, the heating means 7 may not be used. That is, when the ammonia preheated to such an extent that the inside of the reactor 3 can maintain the temperature equal to or higher than the reduction reaction temperature is supplied by sensible heat of ammonia, the heating means 7 can be omitted separately.

  As described above, in the present invention, the methods for supplying the heat necessary for the reduction reaction include the external heating method for supplying heat from the outside of the reactor 3 and the internal heating method for generating heat inside the reactor 3. Any one of them may be used alone or in combination. Moreover, as an external heating type, a method of supplying ammonia by preheating and a method of heating the inside of the reactor 3 are conceivable, and either one of them may be used alone or in combination. . Furthermore, as the internal heat type, there are a method in which oxygen or air is mixed and supplied to ammonia, and a method in which oxygen or air is supplied separately from ammonia, whichever is selected in consideration of manufacturing efficiency and cost. May be.

According to the present embodiment as described above, the following operational effects can be obtained.
1. Compared with the conventional blast furnace method, a reduction reaction at a low temperature can be realized, and the amount of fuel consumed and the amount of carbon dioxide emitted for supplying heat necessary for the reduction reaction can be reduced.
2. The process can be designed to increase the utilization rate of ammonia in the reduction reaction, and the amount of reducing agent used can be reduced.
3. Since the production method and transportation method of ammonia have been established, ammonia can be easily obtained using the existing infrastructure, and the possibility of practical use is high.
4). By using ammonia derived from biomass or high-temperature gasifier, the amount of carbon dioxide emission can be further reduced.

  Next, description will be made based on specific examples of the iron making method and the iron making system 1 according to the present invention. The technical scope of the present invention is not limited to the features shown by the following examples.

  In Example 1, an experiment was conducted to reduce hematite (hematite) as a raw material for iron making with ammonia. Specifically, first, as shown in FIG. 3, a fixed bed type reaction tube 11 (corresponding to the reactor 3: manufactured by ULVAC-RIKO) is prepared, and the quartz wool 12 provided in the reaction tube 11 is Then, about 270 mg of a hematite reagent (purity 99%, particle size <1 μm) was packed so that the layer height was 1 cm.

  Subsequently, ammonia gas (Ar balance) having a concentration of 5 vol% was circulated in the reaction tube 11 at a rate of 200 mL / min via the flow rate regulator 13 (corresponding to the ammonia supply means 5) and the stop valve 14. And after confirming that the inside of the reaction tube 11 was replaced with ammonia gas by a mass spectrometer 16 (manufactured by Pfeiffer Vacuum; Prism QMS200) connected to the computer 15, the infrared furnace 17 (the heating means 7) Equivalent: Heating was started by ULVAC-RIKO; RHL-E210).

  Under the above conditions, the infrared furnace 17 is controlled using a temperature controller 19 (manufactured by ULVAC-RIKO, Inc .; TCP-1000) connected to a thermocouple 18 that measures the temperature in the reaction tube 11, and the reaction tube 11 The inside was heated to 600 ° C. at a rate of 10 ° C./min and then held for 2 hours. The result of measuring the composition of the outlet gas of the reaction tube 11 in this case with the mass spectrometer 16 is shown in FIG. Note that the left vertical axis in FIG. 4 is a value (relative intensity) obtained by normalizing the detection intensity of each gas with the detection intensity of argon. Moreover, the value which differentiated the time change of a density | concentration about each gas is shown in FIG.

As shown in FIG. 4, when the furnace temperature reached about 500 ° C., the ammonia concentration decreased, while the hydrogen and water vapor (H ₂ O) concentrations increased. In this case, the decrease in ammonia concentration and the increase in hydrogen concentration are attributed to the decomposition of ammonia as shown in the above formula (1). The increase in water vapor concentration is due to the reduction of iron oxide (Fe ₂ O ₃ ), which is the main component of hematite, as shown in the above formula (2). In FIG. 4, the display of nitrogen is omitted, but in actuality, it increases almost simultaneously with the increase of water vapor.

  Moreover, as shown in FIG. 5, the value which differentiated the time change of each gas density | concentration recognized the sudden change about each of ammonia, nitrogen, and water vapor | steam about 2500 seconds after starting a heating. The furnace temperature at this time was about 450 ° C. Thereafter, a sudden change in the hydrogen concentration was confirmed about 3000 seconds after the start of heating. The furnace temperature at this time was about 530 ° C.

  Since the generation of water vapor at a furnace temperature of 450 ° C. is not accompanied by the generation of hydrogen, it is considered to be caused by the reduction reaction of the above formula (3). On the other hand, when the furnace temperature rises to 530 ° C., hydrogen is generated, so it is considered that the reduction reactions of the above formulas (1) and (2) also proceed simultaneously. Further, as shown in FIG. 5, after the hydrogen concentration increases, the rate of increase of the water vapor concentration decreases.

  From the above results, it was suggested that the reduction rate with hydrogen was relatively slower than the reduction of iron oxide with ammonia. In addition, it was suggested that the generation of hydrogen with a slow reaction rate reduces the overall reduction rate, including reduction with ammonia, and consequently inhibits reduction with ammonia.

  In Example 1, as described above, after holding at 600 ° C. for 2 hours, the reaction tube 11 is cooled, and at the same time, the atmospheric gas is converted into argon via the mass flow controller 20 and the stop valve 14. Switched to. Note that the outlet gas of the reaction tube 11 was released into the atmosphere after the ammonia gas was absorbed by the absorber 21. After cooling to room temperature, the weight of the reduced sample remaining in the reaction tube 11 was measured, pulverized, and the product phase was identified by an X-ray diffractometer (manufactured by Rigaku Corporation; MiniFlex). The result is shown in FIG.

  As shown in FIG. 6, it was confirmed that the product phase of the sample after reduction was all iron. Moreover, the reduction rate by weight measurement of the sample after reduction was 98.6% (error ± 5%), and it was shown that hematite was almost completely reduced to iron by ammonia. The reduction rate indicates the ratio of oxygen lost due to reduction when the oxygen in the hematite reagent used in Example 1 is 100.

  According to the present Example 1 as described above, it was shown that when the inside of the reaction tube 11 is heated to 450 ° C. or more, the reduction reaction of iron oxide by ammonia is started. Further, it was shown that when the inside of the reaction tube 11 was kept at 600 ° C., iron oxide was almost completely reduced to iron.

  In Example 2, the experiment was performed under the same experimental conditions as in Example 1 described above, changing the holding temperature and holding time in the reaction tube 11. Specifically, the inside of the reaction tube 11 was heated to 450 ° C. at a rate of 10 ° C./min and then held for 3 hours. The composition of the outlet gas of the reaction tube 11 in this case is shown in FIG. Moreover, the value which differentiated the time change of a density | concentration about each gas is shown in FIG.

As shown in FIGS. 7 and 8, in Example 2, even when the furnace temperature reached 450 ° C., generation of water vapor indicating that a reduction reaction occurred was not confirmed. However, as shown in FIG. 9, in the reduced sample, iron was generated as the main phase, and iron nitride (Fe ₄ N) was generated as the subphase.

Here, as shown in FIG. 10, at 450 ° C., the equilibrium of iron nitride, iron, and nitrogen is closer to the decomposition side. Also, the Gibbs free energy in the decomposition reaction of iron nitride is always lower than the Gibbs free energy in the nitriding reaction with iron and ammonia. Therefore, it can be said that the reaction in which iron nitride decomposes is given priority over the reaction in which iron and ammonia react and nitride. For this reason, it is considered that ammonia is directly reacting with iron oxide (Fe ₂ O ₃ ) as a route for generating iron nitride. That is, also in Example 2, a result suggesting that ammonia is directly involved in the reduction of iron oxide was obtained.

  In Example 2, as shown in FIGS. 7 and 8, the hydrogen concentration indicating that ammonia is decomposed is increased. Therefore, it is considered that the produced iron nitride also functions as a catalyst for decomposing ammonia.

In addition to the case where the iron nitride produced in Example 2 is produced by the above formula (3), the iron decomposed by the above formula (4) is replaced with ammonia as shown in the following formula (11). A case of reaction is also assumed. However, as described above, since the decomposition reaction of iron nitride is prioritized over the nitridation reaction of iron and ammonia, it is considered that the decomposition reaction hardly proceeds at a temperature of 450 ° C.
Fe + 1 / 4NH ₃ → 1 / 4Fe ₄ N + 3 / 8H ₂ Formula (11)

  According to the present Example 2 as described above, as in Example 1, it was shown that when the inside of the reaction tube 11 was heated to 450 ° C. or higher, the reduction reaction of iron oxide by ammonia was started. Moreover, it was shown that when the inside of the reaction tube 11 is held at 450 ° C., iron oxide is reduced to iron and iron nitride. Since this iron nitride has the property of being easily decomposed as shown in FIG. 10, it can be said that iron is generated.

  In addition, the iron manufacturing method and the iron manufacturing system 1 which concern on this invention are not limited to embodiment mentioned above, It can change suitably.

  For example, in the present embodiment described above, preheated ammonia or oxygen or air is supplied on the assumption that the present embodiment is applied to an actual iron making process, but the present invention is not limited to this configuration. That is, when carrying out the iron making method according to the present invention other than the actual iron making process, the endothermic component due to the reduction reaction may be supplemented separately, such as heating the inside of the reactor 3.

DESCRIPTION OF SYMBOLS 1 Iron-making system 2 Iron-making raw material supply means 3 Reactor 4 Ammonia preheating means 5 Ammonia supply means 6 Oxygen supply means 11 Reaction tube 12 Quartz wool 13 Flow controller 14 Stop valve 15 Computer 16 Mass spectrometer 17 Infrared furnace 18 Thermocouple 19 Temperature controller 20 Mass flow controller 21 Absorber

Claims (6)

An iron making raw material and ammonia are supplied into the reactor, the inside of the reactor is maintained at 450 ° C. or higher and lower than 600 ° C. , and at least a part of the iron making raw material is reduced to iron nitride by the ammonia, and then the iron nitride However, it functions as a catalyst which decomposes | disassembles the said ammonia, and manufactures iron by the said iron nitride being decomposed | disassembled. The iron making method according to claim 1 , wherein the inside of the reactor is maintained at 450 ° C or higher and lower than 530 ° C. The iron making method according to claim 1 or 2 , wherein the ammonia is preheated to a temperature equal to or higher than a reduction reaction temperature of the iron making raw material and then supplied into the reactor. The iron making method according to any one of claims 1 to 3 , wherein oxygen or air is mixed with the ammonia and fed into the reactor. The iron making method according to any one of claims 1 to 3 , wherein oxygen or air is supplied into the reactor separately from the ammonia. An iron making system used in the iron making method according to any one of claims 1 to 5 .