Method for reducing iron powder

Abstract

This ensures reliable reduction of high-temperature iron powder particles. [Solution] This is a method for reducing high-temperature iron powder particles in a mixed gas containing hydrogen, in which the relationship between the value of the volume ratio C of hydrogen to water vapor contained in the mixed gas and the value of the temperature T °C of the iron powder particles satisfies the following formula (1): 2.8 ≦ C when 765 ° C ≦ T ≦ 805 ° C, and formula (2): 3.5 ≦ C when 670 ° C ≦ T < 765 ° C. The fuel cell system 10 has an electrode composite container 12, a mixed gas composition regulator 14, an iron powder particle container 16, a pre-adjusted mixed gas supply pipe 22, a post-adjusted mixed gas supply pipe 24, and a post-reacted mixed gas supply pipe 26. The pre-adjusted mixed gas supply pipe 22 supplies the mixed gas before the composition adjustment to the mixed gas composition regulator 14. The post-adjusted mixed gas supply pipe 24 supplies the mixed gas after the composition adjustment by the method for reducing iron powder particles of the present invention to the iron powder particle container 16. The post-reacted mixed gas supply pipe 26 supplies the mixed gas after the oxidation-reduction reaction to the fuel electrode space 12c.

Description

[Technical field]

[0001] The present invention relates to a method for reducing iron granules, and more particularly to a method for reducing hot iron granules in a gas mixture containing hydrogen. [Background technology]

[0002] Next-generation secondary batteries that utilize the redox reaction of iron have been disclosed. For example, Patent Document 1 discloses a secondary battery in which, when charging power is supplied from the outside, a reduction reaction of iron occurs, discharging oxygen to the outside, and when charging power is stopped and oxygen is supplied from the outside, an oxidation reaction of iron occurs, supplying power to the outside. Meanwhile, Patent Document 2 discloses a method for reducing iron for the secondary battery in a state in which the amount of water vapor in a hydrogen gas atmosphere is reduced by a moisture absorbent. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5210450 [Patent Document 2] Patent Publication No. 2022-167164 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the reduction method of Patent Document 2 has a problem in that high-temperature conditions above 400° C. are not considered.

[0005] The present invention has been made in consideration of the above-mentioned problems in the conventional art, and an object of the present invention is to provide a method for reducing iron powder particles that can reliably reduce high-temperature iron powder particles. In addition to the above object, another object of the present invention is to provide a method for reducing iron powder particles, which is capable of reducing high-temperature iron powder particles in a short period of time. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the inventors conducted extensive research and discovered that by changing the value of the volume ratio C of hydrogen to water vapor and the value of the temperature T°C of the iron powder particles, the weight ratio to the initial weight of the iron powder particles after the same time period from the start of the reduction reaction changes.

[0007] The inventors also discovered that by varying the volume ratio C and the temperature T°C and selecting a preferred combination of these values, it is possible to reliably reduce high-temperature iron powder particles and further shorten the reduction reaction time, which led to the present invention.

[0008] In other words, the present invention provides a method for reducing iron powder particles, in which high-temperature iron powder particles are reduced in a mixed gas containing hydrogen and water vapor, in which the relationship between the volume ratio C of hydrogen to the water vapor contained in the mixed gas and the temperature T°C of the iron powder particles satisfies the following formulas (1) to (2). When 765℃≦T≦805℃, 2.8≦C≦ 3.9 (1) When 670℃≦T<765℃, 3.5≦C≦ 3.9 (2)

[0009] In the above, it is preferable that the relationship between the value of C and the value of T° C. satisfies the following formula (3). When 695℃≦T≦805℃, 3.5≦C≦ 3.9 (3) The mixed gas preferably further contains an inert gas. Effect of the Invention

[0010] According to the present invention, it is possible to reliably carry out reduction of high-temperature iron powder particles. Furthermore, according to the present invention, in addition to the above effects, the reduction of high-temperature iron powder particles can be carried out in a short period of time. [Brief description of the drawings]

[0011] [Figure 1]1 is a block diagram showing a schematic diagram of an example of a fuel cell system for carrying out a method for reducing iron powder of the present invention. [Diagram 2] FIG. 1 is a block diagram showing a schematic diagram of an example of an apparatus for measuring the reduction state of iron powder particles. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings. First, the method for reducing iron powder particles of the present invention will be described in detail. Fig. 1 is a block diagram showing a schematic diagram of an example of a fuel cell system for carrying out the method for reducing iron powder particles of the present invention.

[0013] The method for reducing iron powder of the present invention is a method for reducing high-temperature iron powder in a mixed gas containing hydrogen, in which the relationship between the volume ratio C of hydrogen to water vapor contained in the mixed gas and the temperature T°C of the iron powder satisfies the following formulas (1) to (2). For 765°C ≤ T ≤ 805°C, 2.8 ≤ C (1) For 670℃≦T<765℃, 3.5≦C (2) Here, the volume ratio C of hydrogen to water vapor is obtained by dividing the volume ratio C1 of hydrogen contained in the mixed gas by the volume ratio C2 of water vapor contained in the mixed gas. By adopting such a configuration, the method for reducing iron powder of the present invention can reliably reduce iron powder at high temperatures.

[0014] It is preferable that the relationship between the value of C and the value of T° C. satisfies the following formula (3). For 695°C ≤ T ≤ 805°C, 3.5 ≤ C (3) By adopting such a configuration, the method for reducing iron powder of the present invention can reliably reduce high-temperature iron powder in a short period of time.

[0015] The mixed gas preferably further contains an inert gas. Examples of the inert gas include argon gas, helium gas, and nitrogen gas. The volume ratio C2 of water vapor contained in the mixed gas includes an extremely small amount and zero percent. In that case, the value of C is infinite, but the value of C is preferably 999 or less, more preferably 99.9 or less, and even more preferably 9.99 or less.

[0016] The fuel cell system 10 includes an electrode composite container 12, a mixed gas component regulator 14, an iron powder container 16, an air supply pipe 18, an air discharge pipe 20, a pre-adjusted mixed gas supply pipe 22, a post-adjusted mixed gas supply pipe 24, and a post-reaction mixed gas supply pipe 26. The electrode composite container 12 includes an electrode composite 12a, an air electrode space 12b, and a fuel electrode space 12c inside. The electrode composite 12a includes an air electrode and a fuel electrode. The air electrode reduces oxygen in the air to oxygen ions during discharge, and oxidizes the oxygen ions to oxygen and releases them during charge. The fuel electrode oxidizes hydrogen gas to water vapor during discharge, and reduces water vapor to hydrogen gas during charge. The air electrode space 12b is a space that brings the air electrode into contact with oxygen in the air. The fuel electrode space 12c is a space that brings the fuel electrode into contact with the mixed gas after the component adjustment. The mixed gas component regulator 14 has the function of increasing the hydrogen gas component ratio contained in the mixed gas and increasing or decreasing the water vapor component ratio contained in the mixed gas. The hydrogen gas component ratio is increased, for example, by supplying hydrogen from a hydrogen gas cylinder. The water vapor component ratio is increased, for example, by supplying water vapor obtained by heating water, and is decreased, for example, by a cold trap.

[0017] The iron powder granule container 16 has iron powder granules 16a inside. The iron powder granules 16a react with water vapor during discharge to generate hydrogen gas and become an oxide, while reacting with hydrogen gas to generate water vapor during charge and being reduced. The air supply pipe 18 is connected to the electrode composite container 12 and supplies air to the air electrode space 12b. The air exhaust pipe 20 is connected to the electrode composite container 12 and exhausts air from the air electrode space 12b. The unadjusted mixed gas supply pipe 22 is connected between the electrode composite container 12 and the mixed gas component regulator 14 and supplies the mixed gas before the composition adjustment to the mixed gas component regulator 14. The adjusted mixed gas supply pipe 24 is connected between the mixed gas component regulator 14 and the iron powder granule container 16 and supplies the mixed gas after the composition adjustment by the method for reducing iron powder granules of the present invention to the iron powder granule container 16. The post-reaction mixed gas supply pipe 26 is connected between the iron powder container 16 and the electrode composite container 12, and supplies the post-oxidation-reduction reaction mixed gas to the fuel electrode space 12c.

[0018] By adopting such a configuration, the method for reducing iron powder of the present invention can reliably reduce iron powder at high temperatures. Furthermore, the method for reducing iron powder of the present invention can reduce iron powder at high temperatures in a short period of time. The method for reducing iron powder of the present invention is basically configured as described above. EXAMPLES

[0019] Next, the present invention will be described in more detail with reference to specific examples of the present invention. Fig. 2 is a block diagram showing a schematic diagram of an example of an apparatus for measuring the reduced state of iron powder.

[0020] The reduction state measuring device 30 has a bubbler 32, a hydrogen cylinder 34, a hydrogen mass flow controller 36, an argon cylinder 38, an argon mass flow controller 40, and a TG measuring device 42. The bubbler 32 prepares a mixed gas by adding water vapor to the gas supplied. The hydrogen cylinder 34 supplies hydrogen gas to the bubbler 32. The hydrogen mass flow controller 36 is connected between the hydrogen cylinder 34 and the bubbler 32, and adjusts the flow rate of hydrogen gas supplied from the hydrogen cylinder 34 to the bubbler 32. The argon cylinder 38 supplies argon gas to the bubbler 32. The argon mass flow controller 40 is connected between the argon cylinder 38 and the bubbler 32, and adjusts the flow rate of argon gas supplied from the argon cylinder 38 to the bubbler 32. The TG measuring device 42 measures the weight of iron powder particles which changes over time in a chamber at a predetermined temperature T° C. filled with a mixed gas of hydrogen to water vapor at a predetermined volume ratio C from the bubbler 32.

[0021] Next, the procedure for measuring the weight of the iron powder particles and the procedure for calculating the weight ratio will be described in detail. Note that the component ratio of the mixed gas in the following description means volume % rather than weight %. First, as Example 1, measurements and calculations were performed according to the following procedure. 1. (Step 1) A STA2500Regulus (registered trademark) (NETZSCH) is used as the TG measurement device 42, and triiron tetroxide powder MT-Z (Ishihara Sangyo Kaisha) is placed in the chamber as the iron powder particles 16a, and the chamber is heated to 800°C. 2. (Step 2) A humidification system HG-120 (ACE) is used as the bubbler 32, in which a mixed gas of 14.7% hydrogen gas and 85.3% argon gas is prepared, and this mixed gas is filled into the TG measurement device 42, and the weight of the iron powder particles is measured at 3 second intervals from the start of filling. Note that, although the mixed gas filled into the TG measurement device 42 in Example 1 does not contain water vapor, in other Examples and Comparative Examples, when the mixed gas contains water vapor, when preparing the mixed gas in the bubbler 32, it is first humidified to the saturated vapor pressure of the water vapor, and the flow rates of the hydrogen gas and the argon gas are adjusted so that a predetermined volume ratio C of hydrogen to water vapor becomes a predetermined value. 3. (Step 3) The weight of the iron powder particles at 3-second intervals is divided by the weight of the iron powder particles at the start of filling to calculate the weight ratio of the iron powder particles that changes over time.

[0022] Next, in Example 2, measurements and calculations were performed with the chamber temperature in step 1 set to 730° C., the mixed gas components in step 2 set to 14.7% hydrogen gas and 85.3% argon gas, and the weight measurement intervals in steps 2 and 3 set to 3 seconds. Next, in Example 3, measurements and calculations were performed with the chamber temperature in step 1 set to 700° C., the mixed gas components in step 2 set to 15.2% hydrogen gas and 84.8% argon gas, and the weight measurement intervals in steps 2 and 3 set to 15 seconds. Next, as Example 4, measurements and calculations were performed with the chamber temperature in step 1 set to 800°C, the mixed gas components in step 2 set to 14.6% hydrogen gas, 3.7% water vapor, and 81.7% argon gas, and the weight measurement intervals in steps 2 and 3 set to 30 seconds. Next, as Example 5, measurements and calculations were performed with the chamber temperature in step 1 set to 730°C, the mixed gas components in step 2 set to 14.6% hydrogen gas, 3.7% water vapor, and 81.7% argon gas, and the weight measurement intervals in steps 2 and 3 set to 3 seconds. Next, as Example 6, measurements and calculations were performed with the chamber temperature in step 1 set to 700°C, the mixed gas components in step 2 set to 14.6% hydrogen gas, 3.7% water vapor, and 81.7% argon gas, and the weight measurement intervals in steps 2 and 3 set to 1 second. Next, as Example 7, measurements and calculations were performed with the chamber temperature in step 1 set to 675°C, the mixed gas components in step 2 set to 14.6% hydrogen gas, 3.7% water vapor, and 81.7% argon gas, and the weight measurement intervals in steps 2 and 3 set to 15 seconds. Next, in Example 8, measurements and calculations were performed with the chamber temperature in step 1 set to 800°C, the mixed gas components in step 2 set to 14.4% hydrogen gas, 4.8% water vapor, and 80.8% argon gas, and the weight measurement intervals in steps 2 and 3 set to 30 seconds. Next, as Example 9, measurements and calculations were performed with the chamber temperature in step 1 set to 770°C, the mixed gas components in step 2 set to 14.4% hydrogen gas, 4.8% water vapor, and 80.8% argon gas, and the weight measurement intervals in steps 2 and 3 set to 15 seconds.

[0023] Next, as Comparative Example 1, measurements and calculations were performed with the chamber temperature in step 1 set to 650°C, the mixed gas components in step 2 set to 14.6% hydrogen gas, 3.7% water vapor, and 81.7% argon gas, and the weight measurement intervals in steps 2 and 3 set to 15 seconds. Next, as Comparative Example 2, measurements and calculations were performed with the chamber temperature in step 1 set to 600°C, the mixed gas components in step 2 set to 14.6% hydrogen gas, 3.7% water vapor, and 81.7% argon gas, and the weight measurement intervals in steps 2 and 3 set to 15 seconds. Next, as Comparative Example 3, measurements and calculations were performed with the chamber temperature in step 1 set to 750°C, the mixed gas components in step 2 set to 14.4% hydrogen gas, 4.8% water vapor, and 80.8% argon gas, and the weight measurement intervals in steps 2 and 3 set to 150 seconds. Next, as Comparative Example 4, measurements and calculations were performed with the chamber temperature in step 1 set to 730°C, the mixed gas components in step 2 set to 14.4% hydrogen gas, 4.8% water vapor, and 80.8% argon gas, and the weight measurement intervals in steps 2 and 3 set to 15 seconds. Next, as Comparative Example 5, measurements and calculations were performed with the chamber temperature in step 1 set to 700°C, the mixed gas components in step 2 set to 14.4% hydrogen gas, 4.8% water vapor, and 80.8% argon gas, and the weight measurement intervals in steps 2 and 3 set to 1 second. Next, as Comparative Example 6, measurements and calculations were performed with the chamber temperature in step 1 set to 800°C, the mixed gas components in step 2 set to 14.3% hydrogen gas, 5.7% water vapor, and 80.0% argon gas, and the weight measurement intervals in steps 2 and 3 set to 15 seconds. Next, as Comparative Example 7, measurements and calculations were performed with the chamber temperature in step 1 set to 800°C, the mixed gas components in step 2 set to 13.8% hydrogen gas, 8.9% water vapor, and 77.3% argon gas, and the weight measurement intervals in steps 2 and 3 set to 15 seconds. Next, as Comparative Example 8, measurements and calculations were performed with the chamber temperature in step 1 set to 700°C, the mixed gas components in step 2 set to 9.8% hydrogen gas, 6.3% water vapor, and 83.9% argon gas, and the weight measurement intervals in steps 2 and 3 set to 1 second.

[0024] <Reduction reaction time to reach less than the set weight ratio> Next, the procedure for determining the reduction reaction time to reach less than a set weight ratio and the results thereof will be described. The evaluation criteria for the weight ratio were set to 90% and 85%, and the first target range of 1500 minutes or less and the second target range of 600 minutes or less were set as the reduction reaction time at the time when the weight ratio fell to less than 90%, and the third target range of 6000 minutes or less and the fourth target range of 1200 minutes or less were set as the reduction reaction time at the time when the weight ratio fell to less than 85%.

[0025] 1. (Step 1) From the calculated value of the weight ratio of the iron powder particles, which changes with time, find the shortest time at which the weight ratio becomes less than 90% to obtain the reduction reaction time Ta. 2. (Step 2) From the calculated value of the weight ratio of the iron powder particles, which changes over time, find the shortest time at which the weight ratio becomes less than 85% to obtain the reduction reaction time Tb. First, for Examples 1 to 6, the reduction reaction time Ta was 17 to 293 minutes, and the reduction reaction time Tb was 29 to 642 minutes. Next, for Examples 7 to 9, the reduction reaction time Ta was 659 to 1346 minutes, and the reduction reaction time Tb was 1482 to 5623 minutes. Next, for Comparative Examples 1 to 8, the calculated value of the weight ratio of the iron powder particles was not less than 85%, nor was it less than 90%. The results are shown in Table 1.

[0026] [Table 1]

[0027] As a result, the reduction reaction times of Examples 1 to 6 were within all of the first to fourth target ranges, whereas the reduction reaction times of Examples 7 to 9 were within the first and third target ranges but outside the second and fourth target ranges, and the reduction reaction times of Comparative Examples 1 to 8 were outside the first to fourth target ranges.

[0028] <Reduction reaction time and weight ratio at the end of the reduction reaction> Next, the procedure for determining the reduction reaction time and weight ratio at the end of the reduction reaction and the results thereof will be described. Although no particular target range was set for the reduction reaction time at the end of the reduction reaction, a target range of 93% or less was set for the weight ratio.

[0029] 3. (Step 3) Subtract the weight ratio of the iron powder particles calculated from the previous measurement from the weight ratio of the iron powder particles at each point in time, and divide the result by the measurement time interval to calculate the differential value of the change in the weight ratio of the iron powder particles. 4. (Step 4) For each derivative value of the change in the weight ratio of the iron powder particles, all derivative values ​​between that time and a time 10 minutes prior to that time are averaged to calculate the average derivative value. 5. (Step 5) From the calculated average differential values ​​that change with time, the shortest time at which the average differential value is -0.002 or more is found to determine the reduction reaction time Tc, and the weight ratio at that time is calculated.

[0030] First, for Examples 1 to 6, the reduction reaction time Tc was 146 to 1089 minutes, and the weight ratio was 77 to 85%. Next, for Examples 7 to 9, the reduction reaction time Tc was 1455 to 2205 minutes, and the weight ratio was 85 to 90%. Next, for Comparative Examples 1 to 8, the reduction reaction time Tc was 28 to 226 minutes, and the weight ratio was 96 to 100%. The results are shown in Table 1 above.

[0031] As a result, the weight ratios at the end of the reduction reaction in Examples 1 to 9 were within the target range, but the weight ratios at the end of the reduction reaction in Comparative Examples 1 to 8 were outside the target range.

[0032] From these results, it is clear that by configuring a reduction method for iron powder particles in a manner similar to that of Examples 1 to 9, it is possible to reliably reduce high-temperature iron powder particles, and it is clear that by configuring a reduction method for iron powder particles in a manner similar to that of Examples 1 to 6, it is possible to reliably reduce high-temperature iron powder particles in a short period of time.

[0033] The method for reducing iron powder of the present invention has been described in detail above with reference to examples. However, the present invention is not limited to the above description, and various improvements and modifications may be made without departing from the spirit and scope of the present invention. [Industrial Applicability]

[0034] The method for reducing iron powder of the present invention has the effect of being able to reliably reduce high-temperature iron powder, as well as the effect of being able to reduce high-temperature iron powder in a short period of time, making it industrially useful. [Explanation of symbols]

[0035] 10. Fuel Cell System 12 Electrode complex container 12a Electrode complex inside 12b Air pole space 12c Fuel electrode space 14 Mixed gas component regulator 16 Iron powder container 16a Iron powder particles 18 Air supply pipe 20 Air exhaust pipe 22 Unadjusted mixed gas supply pipe 24 Adjusted mixed gas supply pipe 26 Post-reaction mixed gas supply pipe 30 Redox state measuring device 32 Bubbler 34 Hydrogen Cylinder 36 Hydrogen Mass Flow Controller 38 Argon Cylinder 40 Argon Mass Flow Controller 42 TG measuring device

Claims

1. A method for reducing iron powder particles, comprising the steps of: reducing high-temperature iron powder particles in a mixed gas containing hydrogen and water vapor, A method for reducing iron powder particles, wherein the relationship between the volume ratio C of the hydrogen to the water vapor contained in the mixed gas and the temperature T°C of the iron powder particles satisfies the following formulas (1) and (2). When 765° C.≦T≦805° C., 2.8≦C≦3.9 (1) When 670° C.≦T<765° C., 3.5≦C≦3.9 (2)

2. 2. The method for reducing iron powder granules according to claim 1, wherein the relationship between the value of C and the value of T°C satisfies the following formula (3). When 695° C.≦T≦805° C., 3.5≦C≦3.9 (3)

3. 3. The method for reducing iron powder according to claim 1, wherein the mixed gas further contains an inert gas.

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