Method for determining particle size of low-shrinkage carbon material and method for producing coke
By determining the optimal particle size of low-shrinkage carbon materials through a five-step process and compensating with a binding agent, the method enhances coke particle size while maintaining or improving DI and CSR, addressing the limitations of existing methods.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- NIPPON STEEL CORPORATION
- Filing Date
- 2022-02-15
- Publication Date
- 2026-05-27
AI Technical Summary
Existing methods for adding low-shrinkage carbon materials to coal to increase coke particle size fail to consider the impact on post-heat reaction strength (CSR) and reactivity index (CRI), leading to potential decreases in these critical quality control indicators.
A method to determine the optimal particle size of low-shrinkage carbon materials by calculating evaluation values for DI and CSR reduction relative to MS expansion, using a five-step process to identify the most suitable particle size category, and compensating with a binding agent to maintain or enhance CSR and DI.
The method allows for increased coke particle size while minimizing decreases in DI and CSR, optimizing the particle size to balance MS expansion, DI reduction, and CSR maintenance, thereby improving coke quality.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a particle size determination method for determining the particle size of a low shrinkage carbon material added to coal, which is a raw material for coke, and the like.
Background Art
[0002] Coke for blast furnaces is used as a filler for ensuring the air permeability in the furnace. Therefore, as a quality control index for coke for blast furnaces, it is required to increase the coke particle size while maintaining the coke strength (hereinafter, also referred to as "DI"). As a method for increasing the coke particle size, a method of adding a low shrinkage carbon material such as pulverized coke to the blended coal is known. Since the low shrinkage carbon material does not expand during the softening and melting of coal and has a structure that is difficult to shrink during the re-solidification of coal, it inhibits the adhesion between coal particles during coal expansion and generates cracks during coal shrinkage, thereby reducing DI.
[0003] In Patent Document 1, the influence degree of the low shrinkage carbon material on the average particle size (hereinafter, also referred to as "MS") and DI of coke is determined in advance for each particle size of the low shrinkage carbon material, and blending adjustment and the like are performed so as to satisfy the target values of MS and DI. A method has been proposed.
[0004] For coke for blast furnaces, in addition to DI, it is also required to have high post-heat reaction strength (hereinafter, also referred to as "CSR"). This is because if CSR is low, the amount of coke pulverization after the reaction in the furnace increases, and the air permeability of the blast furnace is inhibited. Also, it is required that the reactivity index (hereinafter, also referred to as "CRI") of coke is low. If CRI is high, the reactivity in the furnace becomes high, and the amount of coke pulverization increases as in the case of CSR.
Prior Art Documents
Patent Documents
[0005]
Patent Document 1
Non-Patent Documents
[0006] [Non-Patent Document 1] MacPhee et al., Fuel Processing technology, p.16 (2009) [Overview of the Initiative] [Problems that the invention aims to solve]
[0007] Patent Document 1 discloses that it is possible to achieve both an increase in coke particle size and an improvement in DI by adding low-shrinkage carbon material, but it does not consider CSR, which is a quality control indicator other than DI.
[0008] Furthermore, Non-Patent Document 1 discloses a comparison between char coal, a type of low-shrinkage carbon material crushed to 60 mesh (0.22 mm) or less (hereinafter also referred to as "small-diameter char coal"), and char coal, which is sized to 1 / 4 to 3 / 8 inch (6.4 to 9.5 mm) (hereinafter also referred to as "large-diameter char coal"), showing that small-diameter char coal has a higher CRI and a lower CSR than large-diameter char coal. Based on this finding, it is generally predicted that low-shrinkage carbon materials with larger particle sizes will have smaller CRIs and therefore larger CSRs. However, there is no disclosure regarding particle size between small-diameter and large-diameter char coal, nor is there any disclosure regarding powdered coke widely used in steel mills.
[0009] The present invention aims to suppress the decrease in DI and CSR while expanding the MS of coke by setting the particle size of the low-shrinkage carbon material to an optimal particle size. [Means for solving the problem]
[0010] To solve the above problems, the particle size determination method for low-shrinkage carbon material according to the present invention is a method for determining the particle size of low-shrinkage carbon material added to coal, which is a raw material for coke, wherein when the average particle size of coke is defined as MS, the strength of coke as DI, and the strength of coke after hot reaction as CSR, a first step is to add a plurality of low-shrinkage carbon materials with different particle size classifications to coal, carbonize them in a test coke oven, and then obtain MS, DI, and CSR, and the difference between the MS of coke obtained by carbonizing coal in a test coke oven without adding low-shrinkage carbon material (hereinafter referred to as "base coke") and the MS obtained in the first step is divided by the addition rate of low-shrinkage carbon material to determine the MS expansion amount. The method is characterized by comprising: a second step of calculating for each particle size category; a third step of calculating the DI reduction amount for each particle size category by dividing the difference between the DI of the base coke and the DI obtained in the first step by the addition rate of the low-shrinkage carbon material; a fourth step of calculating the CSR reduction amount for each particle size category by dividing the difference between the CSR of the base coke and the CSR obtained in the first step by the addition rate of the low-shrinkage carbon material; and a fifth step of calculating a first evaluation value, which is the ratio of the DI reduction amount to the MS expansion amount, and a second evaluation value, which is the ratio of the CSR reduction amount to the MS expansion amount, for each particle size category, and determining at least one optimal particle size category for the low-shrinkage carbon material based on the magnitude of these first and second evaluation values.
[0011] (2) The method for determining the particle size of a low-shrinkage carbon material according to (1) above, characterized in that, when the low-shrinkage carbon material is powdered coke, the optimal particle size category determined in step 5 above is included in the range of greater than 0.074 mm and less than or equal to 0.3 mm.
[0012] (3) The method for producing coke according to the present invention is characterized by comprising: a low-shrinkage carbon material selection step of selecting a low-shrinkage carbon material included in the optimal particle size category determined according to the low-shrinkage carbon material particle size determination method described in (1) or (2) above; a first addition rate determination step of determining the addition rate of the low-shrinkage carbon material selected in the low-shrinkage carbon material selection step to coal so as to satisfy the target value of MS; a second addition rate determination step of calculating the addition rate of a coking compensator necessary to compensate for the decrease in DI and the decrease in CSR when the low-shrinkage carbon material is added to coal according to the addition rate determined in the first addition rate determination step, and determining the higher addition rate among these calculated addition rates as the addition rate of the coking compensator; and a carbonization step of adding the low-shrinkage carbon material and the coking compensator to coal according to the addition rates determined in the first addition rate determination step and the second addition rate determination step, and carbonizing in a coke oven. [Effects of the Invention]
[0013] According to the present invention, by setting the particle size of the low-shrinkage carbon material to an optimal particle size, it is possible to increase the MS of coke while suppressing the decrease in DI and CSR. [Brief explanation of the drawing]
[0014] [Figure 1] This bar graph shows the relationship between the particle size classification of the added coke powder and the MS (Mass Factor). [Figure 2] This bar graph shows the relationship between the particle size classification of the added coke powder and the DI (Diagram Indication). [Figure 3] This bar graph shows the relationship between the particle size classification of the added coke powder and the CRI (Critical Ratio Intake). [Figure 4] This bar graph shows the relationship between the particle size classification of the added coke powder and CSR (Chemical Saturation Ratio). [Figure 5] This bar graph shows the relationship between the particle size classification of the added coke powder and the DI reduction / MS expansion. [Figure 6] This bar graph shows the relationship between the particle size classification of the added coke powder and the CSR reduction / MS expansion. [Modes for carrying out the invention]
[0015] (First Embodiment) A method for determining the particle size of a low-shrinkage carbon material, which is an embodiment of the present invention, will be described. The method for determining the particle size of the low-shrinkage carbon material in this embodiment is a method for determining the particle size of a low-shrinkage carbon material added to coal, which is a raw material for blast furnace coke, and includes the following steps 1 to 5.
[0016] (Step 1) Add a plurality of low-shrinkage carbon materials with different particle size classifications to coal respectively, carbonize them in a test coke oven, and then obtain MS, DI, and CSR. In this specification, a carbon material with a shrinkage rate of 10% or less is defined as a low-shrinkage carbon material. The shrinkage rate can be obtained by heating the low-shrinkage carbon material (sample) charged in a container from room temperature to a temperature T °C (for example, T = 1000 °C) sufficiently higher than the re-solidification temperature using an electric furnace or the like, and dividing the difference in volume or length of the sample at the re-solidification temperature and 1000 °C by the volume or length at the re-solidification temperature. It is recommended that the heating rate be 3 °C / min, which simulates the heating rate in a coke oven. Incidentally, the re-solidification temperature can be grasped from the temperature when the displacement of the sample in the heating process is observed using a piston-type shrinkage rate measuring device (see Japanese Patent Application Laid-Open No. 2005-232349) and the displacement suddenly increases. Note that since a low-shrinkage carbon material without softening and melting properties such as pulverized coke does not re-solidify, the shrinkage rate may be measured by the above method with room temperature as the re-solidification temperature. As the low-shrinkage carbon material, pulverized coke, petroleum coke, inert tissue, semi-anthracite, etc. can be used. For example, pulverized coke obtained at a steelworks can be used as the pulverized coke.
[0017] Regarding the particle size classification, in order to improve the accuracy, it is desirable to divide it into at least 3 classifications. The upper limit of the particle size classification is not particularly specified, but it is desirable to set it to about 7 classifications because the processing becomes complicated. Also, the width of each particle size classification is desirably set to an appropriate value such that a significant difference occurs in MS, DI, and CSR between the particle size classifications.
[0018] MS may also be obtained by performing a drum test in accordance with "JIS K2151". Specifically, the sample can be subjected to a drum test apparatus, and the MS of coke can be obtained from samples larger than 25 mm after 30 rotations. Furthermore, as described in Patent Document 1 above, for example, the MS can also be predicted by considering the influence of the type and length of the low-shrinkage carbon material.
[0019] The method for obtaining CSR is as follows: Coke is produced by carbonizing coal to which low-shrinkage carbon material has been added in a test coke oven. 200g of coke, adjusted to a size of 20±1mm, is reacted under specified conditions (gas composition: 100% carbon dioxide, reaction temperature: 1100℃, reaction time: 2 hours). After the reaction, the material is rotated 600 times in a Type I drum, and the percentage of the mass on a 9.56mm sieve relative to the post-reaction mass is calculated, which can then be used as the CSR.
[0020] The DI can be obtained by subjecting the coke obtained from the aforementioned test coke oven to a drum test (see JIS K2151). That is, the DI is obtained by sieving the coke up to 15 mm after 150 rotations of the drum. 150 15 ) can be used as the DI. Alternatively, as described in Patent Document 1 above, for example, the DI may be predicted by considering the influence of the type and length of the low-shrinkage carbon material.
[0021] The addition rate of low-shrinkage carbon material is preferably 3% by mass (external amount) or more. If the addition rate of low-shrinkage carbon material is excessively low, the effect on CSR in particular becomes small, and considering measurement errors, it becomes difficult to accurately grasp the change in CSR in particular.
[0022] (Step 2) The MS (Mass Strength) of coke obtained by carbonization in a test coke oven without adding low-shrinkage carbon material (hereinafter referred to as "base coke") and the MS obtained in Step 1 are used to calculate the MS expansion allowance (hereinafter also referred to as "MS expansion allowance") for each particle size category due to the addition of low-shrinkage carbon material. Specifically, the MS expansion allowance can be determined by subtracting the MS of the base coke from the MS obtained in Step 1 and dividing this by the addition rate of low-shrinkage carbon material.
[0023] (Step 3) The DI of the base coke and the DI obtained in Step 1 are used to calculate the reduction in DI due to the addition of low-shrinkage carbon material (hereinafter also referred to as "DI reduction amount") for each particle size category. Specifically, the DI reduction can be determined by subtracting the DI obtained in step 1 from the DI of the base coke and dividing this by the addition rate of the low-shrinkage carbon material.
[0024] (Step 4) The reduction in CSR due to the addition of low-shrinkage carbon material (hereinafter also referred to as "CSR reduction amount") is calculated for each particle size category from the CSR of the base coke and the CSR obtained in Step 1. Specifically, the CSR reduction can be calculated by subtracting the CSR obtained in Step 1 from the CSR of the base coke and dividing this by the addition rate of the low-shrinkage carbon material.
[0025] (Step 5) After determining a first evaluation value, which is the ratio of the DI reduction amount to the MS expansion amount, and a second evaluation value, which is the ratio of the CSR reduction amount to the MS expansion amount, for each particle size category, at least one optimal particle size category for the low-shrinkage carbon material is determined based on the magnitude of these first and second evaluation values. The ratio of the DI reduction amount to the MS expansion amount can be expressed as "DI reduction amount / MS expansion amount," which is obtained by dividing the DI reduction amount by the MS expansion amount. When the DI reduction amount / MS expansion amount is large, the decrease in DI will be greater when the MS is expanded. However, the ratio of the DI reduction amount to the MS expansion amount may also be expressed as MS expansion amount / DI reduction amount. In this case, if the MS expansion amount / DI reduction amount is small, the reduction in DI will be greater when MS is expanded. The ratio of the cost of reducing CSR to the cost of expanding MS can be expressed as "CSR cost / MS expansion cost," which is the CSR cost divided by the MS expansion cost. When the CSR cost / MS expansion cost is large, expanding MS will result in a larger decrease in CSR. However, the ratio of the CSR cost to the MS expansion cost may also be expressed as MS expansion cost / CSR cost. In this case, when the MS expansion cost / CSR cost is small, expanding MS will result in a larger decrease in CSR.
[0026] Based on the relative magnitudes of the first and second evaluation values, at least one optimal particle size classification for low-shrinkage carbon material is determined while expanding the MS to minimize the reduction in DI and CSR. Since it says "at least one," there may be more than one optimal particle size classification. For example, a particle size category where the DI reduction / MS expansion (first evaluation value) is small and the CSR reduction / MS expansion (second evaluation value) is excessively large will not be considered an optimal particle size category. Similarly, a particle size category where the CSR reduction / MS expansion (second evaluation value) is small and the DI reduction / MS expansion (first evaluation value) is excessively large will not be considered an optimal particle size category. It is desirable to evaluate a particle size category where neither the DI reduction / MS expansion (first evaluation value) nor the CSR reduction / MS expansion (second evaluation value) is excessively large as the optimal particle size category. Whether or not a value is "excessively large" can be determined by setting a threshold, or by determining it based on the experience of those skilled in the art.
[0027] Furthermore, since the relationship between MS, DI, and CSR and the addition rate of low-shrinkage carbon material is linear, the optimal particle size classification can be determined using the first and second evaluation values described above, even if the addition rate of low-shrinkage carbon material changes. For example, if the optimal particle size classification is determined by setting the addition rate of low-shrinkage carbon material in step 1 to 4 mass%, this determined optimal particle size classification will not change even if the addition rate of low-shrinkage carbon material changes to 5 mass%. However, if the addition rate of low-shrinkage carbon material increases excessively (for example, to 10 mass% or more), linearity is lost, so it is desirable to determine the optimal particle size classification again by performing the processing in steps 1 to 5.
[0028] (Second Embodiment) This embodiment relates to a method for producing blast furnace coke using low-shrinkage carbon material according to the optimal particle size classification determined in the first embodiment, and compensates for the decrease in DI and CSR due to the addition of low-shrinkage carbon material by adding a binding agent. As the binding agent, petroleum-based binding agents (ASP, etc.), coal-based binding agents (tar, pitch, SRC (Solvent Refined Coal), etc.), and other polymeric substances with high aromaticity and softening / melting properties can be used. The coke production method of this embodiment includes the following steps 10 to 13.
[0029] (Step 10) In the first embodiment, low-shrinkage carbon material included in the optimal particle size category determined is selected as low-shrinkage carbon material for charging into the coke oven (corresponding to the low-shrinkage carbon material selection step). For example, in the first embodiment, if the optimal particle size category for powdered coke is determined to be two categories, "greater than 0.074 mm and less than or equal to 0.1 mm" and "greater than 0.1 mm and less than or equal to 0.3 mm", then powdered coke included in these particle size categories (greater than 0.074 mm and less than or equal to 0.3 mm) is selected as low-shrinkage carbon material for charging into the coke oven.
[0030] (Step 11) The addition rate of low-shrinkage coal material to coal necessary to satisfy the target MS value is determined (corresponding to the first addition rate determination step). The target MS value can be predetermined. In step 2 of the first embodiment, the amount of MS expansion (i.e., MS expansion allowance) when the addition rate is increased by 1 mass% is known for each particle size category. Therefore, the addition rate of low-shrinkage coal material can be determined by dividing the difference between the MS of the base coke and the target MS value by the MS expansion allowance.
[0031] (Step 12) Determine the addition rate of the adhesive filler (corresponding to the second addition rate determination step). Specifically, the amount of decrease in DI and decrease in CSR when low-shrinkage carbon material is added is determined according to the addition rate determined in step 11. In steps 3 and 4 of the first embodiment, the amount of decrease in DI (DI decrease) and decrease in CSR (CSR decrease) when the addition rate is increased by 1% is known for each particle size category. Therefore, the amount of decrease in DI and decrease in CSR can be determined by multiplying these DI decrease and CSR decrease amounts by the addition rate of low-shrinkage carbon material determined in step 11. Next, the addition rates of the binding agent needed to compensate for the calculated decrease in DI and decrease in CSR are calculated, and the higher of the calculated addition rates is determined as the addition rate of the binding agent. For example, if the addition rate of the binding agent needed to reduce the decrease in DI to zero is 1% by mass, and the addition rate of the binding agent needed to reduce the decrease in CSR to zero is 5% by mass, the addition rate of the binding agent is set to 5% by mass. In this case, the DI will be greater than that of the base coke, and the CSR will be equal to that of the base coke. The addition rate of the binding filler can be determined, for example, based on Non-Patent Document 2 (Nishi et al., Iron and Steel 68(15), 2141-2147(1982)).
[0032] (Step 13) In steps 11 and 12, the low-shrinkage carbon material and the coking filler are added to the coal according to the addition rates determined in those steps, and the coal is carbonized in a coke oven (corresponding to the carbonization step). According to this embodiment, the MS can be increased relative to the base coke while increasing the DI and CSR to be equal to or higher than that of the base coke. Furthermore, by using low-shrinkage carbon material belonging to the optimal particle size category, the addition rate of the coking filler can be reduced compared to when using low-shrinkage carbon material belonging to other particle size categories, thus reducing costs. In step 5 of the first embodiment, if multiple optimal particle size categories are determined, it is desirable to select the particle size category with the lowest addition rate of the binding filler from among these particle size categories, and then select the low-shrinkage carbon material belonging to this selected particle size category in step 10.
[0033] (First embodiment) The first embodiment (method for determining particle size of low-shrinkage carbon material) will be described in detail with reference to an example. Various powdered cokes (low-shrinkage carbon material) with different particle size classifications were added to the blended coal, and cokes with different MS were produced by carbonization in a test coke oven. The blending conditions for the blended coal were 50, 15, and 15 mass% (total 80 mass%) of three types of coking coal and 15 and 5 mass% (total 20 mass%) of two types of non-coking coal. The properties of the coking coal were a ΣVM (volatile matter) of 22.9 mass% and a ΣTD (total expansion rate) of 172.8%, weighted by the weighted average of the blending ratios. The properties of the non-coking coal were a ΣVM (volatile matter) of 33.7 mass% and a ΣTD (total expansion rate) of 20.3%, weighted by the weighted average of the blending ratios. The particle size of the blended coal was adjusted to less than 3 mm for 85 mass%. The properties of the blended coal were ΣVM (volatile matter) of 25.0 mass% and ΣTD (total expansion coefficient) of 142.3%.
[0034] Table 1 shows the conditions for adding coke pulverizer (Conditions 1 to 7). In Condition 1, no coke pulverizer was added. In Conditions 2 to 6, coke pulverizer generated at the steel mill was classified using a sieve, separating coke pulverizer particles smaller than 1 mm into five particle size categories. The coke pulverizer addition rate was set to 4% by mass. Note that the coke pulverizer addition rate is an external value (the same applies hereafter). [Table 1]
[0035] The dimensions of the carbonization vessel for the test coke oven were: furnace width (W): 400 mm, furnace length (L): 600 mm, and furnace height (H): 420 mm. The coal charging bulk density was 850 kg / m³ on a dry basis. 3 The final temperature reached in the test coke oven was set at 1150°C, and the carbonization time was set at 18.5 hours.
[0036] Each coke sample was subjected to a drum test apparatus in accordance with "JIS K2151". The MS of the coke was determined from samples larger than 25 mm after 30 rotations, and the DI was determined from samples after 150 rotations. The CSR of the coke was measured using the method described in the embodiment. The CRI of the coke was also measured. The CRI was calculated by reacting 200 g of coke, which had been granulated to a size of 20 ± 1 mm, under predetermined conditions (gas composition: 100% carbon dioxide, reaction temperature: 1100°C, reaction time: 2 hours), measuring the mass after the reaction, and using the formula "CRI = (mass before reaction - mass after reaction) / mass before reaction × 100". The measured values of MS, DI, CRI, and CSR for each coke are shown in Figures 1 to 4.
[0037] Referring to Figure 1, under conditions 2-6, where powdered coke was added, the MS (Mass Strength Factor) was larger than under condition 1, where powdered coke was not added. Furthermore, under particle size conditions of 1 mm or less, the MS increased as the particle size of the powdered coke increased. This is thought to be because the addition of powdered coke reduces the shrinkage rate of the coke, and this shrinkage rate reduction effect is enhanced by the increase in the particle size of the powdered coke.
[0038] Referring to Figure 2, under conditions 2-6, where powdered coke was added, the DI was lower than under condition 1, where powdered coke was not added. Furthermore, under particle size conditions of 1 mm or less, the DI decreased as the particle size of the powdered coke increased. This is thought to be because the addition of powdered coke causes microcracks to form in the coke, and these microcracks expand in proportion to the increase in the particle size of the powdered coke.
[0039] Referring to Figure 3, under conditions 2-6, where powdered coke was added, the CRI was higher than under condition 1, where no powdered coke was added. Furthermore, under particle size conditions of 1 mm or less, the CRI increased as the particle size of the powdered coke decreased. This is thought to be because, when the addition rate of powdered coke is the same, the number of particles increases as the particle size of the powdered coke decreases, thus increasing the total surface area of the gasification reaction area due to the microcracks formed around the powdered coke.
[0040] Referring to Figure 4, under conditions 2-6, where powdered coke was added, the CSR was lower than under condition 1, where powdered coke was not added. This is because CSR, which is the strength after hot reaction, is influenced by DI and CRI, and the addition of powdered coke reduces coke strength (DI) and increases reactivity (CRI). Furthermore, under particle size conditions of 1 mm or less, particle size category B had the highest CSR, and CSR decreased as the particle size increased beyond particle size category B. This is presumed to be due to the influence of coke strength (DI) shown in Figure 2. Furthermore, particle size category A showed a lower CSR than particle size category B. It is presumed that the decrease in CSR was greater in particle size category A because it has a higher CRI compared to the other particle size categories.
[0041] Next, for each particle size category A to E, the MS expansion allowance, DI reduction allowance, and CSR reduction allowance were determined according to the method described in Embodiment 1, and the ratio of the MS expansion allowance to the DI reduction allowance (DI reduction allowance / MS expansion allowance) and the ratio of the MS expansion allowance to the CSR reduction allowance (CSR reduction allowance / MS expansion allowance) were also determined. The results are shown in Figures 5 and 6.
[0042] Referring to Figure 5, particle size categories D and E are not optimal because the DI reduction / MS expansion is excessively large. Referring to Figure 6, particle size category A is not optimal because the CSR reduction / MS expansion is excessively large. Taking all of these into consideration, in this embodiment, particle size categories B and C were determined to be the "optimal particle size categories". Furthermore, if the proportion of coal in the blended coal is significantly changed, if molded materials are added, or if a low-shrinkage coal material different from powdered coke is used, the above-mentioned experiments should be conducted again to determine the optimal particle size classification.
[0043] (Second example) The second embodiment will be described in detail with reference to examples. For coke without added powdered coke (hereinafter also referred to as "base coke"), powdered coke was added to increase the MS by 2 mm, and the reduced DI and CSR were compensated for with SRC (coking compound). The base coke satisfies the desired DI and CSR. Based on Non-Patent Literature 2 mentioned above, it was assumed that increasing the SRC addition rate by 1% (external) would increase DI and CSR by 0.2 points (hereinafter referred to as "pt") and 1 pt, respectively. The results are shown in Table 2. The SRC addition rate (DI compensation) was calculated by dividing the decrease in DI by 0.2 and rounding to the second decimal place. The SRC addition rate (CSR compensation) was calculated by dividing the decrease in CSR by 1 and rounding to the second decimal place. [Table 2]
[0044] When adding powdered coke of particle size category A, the addition rate of powdered coke will be 2.9% by mass. The SRC addition rates required to eliminate the decrease in DI and CSR are estimated to be 0.8% by mass and 5.6% by mass, respectively (CSR bottleneck). Therefore, the required SRC addition rate is estimated to be 5.6% by mass. When adding powdered coke of particle size category B, the powdered coke addition rate is 2.1% by mass, and the SRC addition rates required to eliminate the decrease in DI and CSR are estimated to be 2.4% by mass and 3.1% by mass, respectively (CSR neck). Therefore, the required SRC addition rate is estimated to be 3.1% by mass. When adding powdered coke of particle size category C, the powdered coke addition rate is 1.9% by mass, and the SRC addition rates required to eliminate the decrease in DI and CSR are estimated to be 2.3% by mass and 3.4% by mass, respectively (CSR neck). Therefore, the required SRC addition rate is estimated to be 3.4% by mass. When adding powdered coke of particle size category D, the powdered coke addition rate is 1.5% by mass, and the SRC addition rates required to eliminate the decrease in DI and CSR are estimated to be 6.2% by mass and 3.8% by mass, respectively (DI neck). Therefore, the required SRC addition rate is estimated to be 6.2% by mass.
[0045] From the above estimation results, it was found that particle size categories B and C allow for a lower SRC addition rate than particle size categories A and D. Therefore, by selecting powdered coke within the range of particle size categories B and C, which were determined to be the optimal particle size categories in the first example (in other words, the range from the lower limit of particle size category B to the upper limit of particle size category C), the SRC addition rate can be reduced while suppressing the expansion of MS, the decrease in DI and CSR, and thus costs can be reduced. Furthermore, by selecting particle size category B, which has a lower SRC addition rate among the optimal particle size categories B and C, costs can be reduced more effectively.
Claims
1. A method for determining the particle size of low-shrinkage carbon material added to coal, which is a raw material for coke, When the average particle size of coke is defined as MS, the strength of coke as DI, and the strength of coke after hot reaction as CSR, The first step involves adding multiple low-shrinkage carbon materials with different particle size classifications to coal, carbonizing them in a test coke oven, and then obtaining MS, DI, and CSR. The second step involves calculating the MS expansion rate for each particle size category by dividing the difference between the MS of coke obtained by carbonization in a test coke oven without adding low-shrinkage carbon material (hereinafter referred to as "base coke") and the MS obtained in the first step by the addition rate of low-shrinkage carbon material. A third step involves calculating the DI reduction amount for each particle size category by dividing the difference between the DI of the base coke and the DI obtained in the first step by the addition rate of low-shrinkage carbon material, The fourth step involves calculating the CSR reduction for each particle size category by dividing the difference between the CSR of the base coke and the CSR obtained in the first step by the addition rate of low-shrinkage carbon material, A fifth step involves calculating a first evaluation value, which is the ratio of the DI reduction amount to the MS expansion amount, and a second evaluation value, which is the ratio of the CSR reduction amount to the MS expansion amount, for each particle size category, excluding particle size categories where the first evaluation value exceeds a predetermined first threshold, and particle size categories where the second evaluation value exceeds a predetermined second threshold, from the optimal particle size categories, and determining at least one optimal particle size category for low-shrinkage carbon material from among the remaining particle size categories after exclusion. A method for determining the particle size of low-shrinkage carbon material, characterized by having the following features.
2. The method for determining the particle size of a low-shrinkage carbon material according to claim 1, characterized in that, when the low-shrinkage carbon material is powdered coke, the optimal particle size category determined in the fifth step is included in the range of more than 0.074 mm and less than or equal to 0.3 mm.
3. A low-shrinkage carbon material selection step of selecting a low-shrinkage carbon material that is included in the optimal particle size category determined according to the method for determining the particle size of low-shrinkage carbon material described in claim 1 or 2, A first addition rate determination step determines the addition rate of the low-shrinkage coal material selected in the low-shrinkage coal material selection step to the coal in order to satisfy the MS target value, A second addition rate determination step involves calculating the addition rates of the cohesive filler material necessary to compensate for the decrease in DI and CSR when low-shrinkage coal material is added to coal according to the addition rate determined in the first addition rate determination step, and determining the higher of these calculated addition rates as the addition rate of the cohesive filler material. A carbonization step in which low-shrinkage carbon material and coking filler are added to coal according to the addition rates determined in the first addition rate determination step and the second addition rate determination step, and carbonized in a coke oven, A method for producing coke, characterized by having the following features.