Method for evaluating post-reaction strength of highly reactive coke

Abstract

To provide a method for evaluating the strength of highly reactive coke after reaction.SOLUTION: A method for evaluating post-reaction strength of highly reactive coke according to the present invention includes charging a sample of highly reactive coke into a reaction vessel, heating the sample to a predetermined temperature, and then allowing the sample and carbon dioxide to react with each other for 20 minutes or more and 110 minutes or less while allowing carbon dioxide to flow through the reaction vessel; A mass A of the sample after the reaction is measured, the sample is then charged into a drum of an I-type drum tester, the drum is rotated under predetermined conditions, a mass B of the sample on a sieve having a predetermined size is then measured, and the strength of the highly reactive coke after the reaction in the blast furnace is evaluated based on a ratio of the mass B to the mass A.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the post-reaction strength of highly reactive coke. [Background technology]

[0002] To operate blast furnaces efficiently, coke, which is produced by carbonizing coal in a coke oven, is charged into the furnace. The coke charged into the furnace serves several purposes, including as a spacer to improve ventilation inside the furnace, as a reducing agent, and as a heat source.

[0003] In recent years, technologies for using highly reactive coke have been investigated from the viewpoint of improving the reactivity of coke. Highly reactive coke initiates the reaction at a lower temperature in the blast furnace, which significantly improves the reaction efficiency and is expected to reduce the reducing agent ratio. Ferro-coke, which contains metallic iron inside the coke, is known as an example of a highly reactive coke.

[0004] On the other hand, when aiming for operation at a low reducing agent ratio, the amount of reducing agent used is reduced, so ensuring ventilation within the furnace becomes extremely important. Coke breaks down due to deterioration caused by reactions in the furnace and wear when the material is lowered, but if coke with low strength after the reaction is used, the amount of powdering increases within the blast furnace, leading to reduced productivity due to poor ventilation and an increase in the reducing agent ratio.

[0005] Highly reactive coke completes the reaction in the upper part of the furnace and disappears as a gas. Therefore, it is thought that the reactivity is not as high as that of ordinary coke, which acts as a spacer in the furnace. However, considering that there is a possibility that the coke may become powdery during the reaction, it is very important to manage its strength after the reaction.

[0006] The Coke Strength after Reaction (CSR) value is commonly used as an index of coke strength after reaction (see Non-Patent Document 1). The method for measuring the CSR value is specified in ISO 18894. Specifically, the method involves measuring the mass A of a coke sample that has been reacted with carbon dioxide (CO2) for two hours at a temperature of 1100°C, and the mass B of the sample that remains on a 9.5 mm sieve after the reaction has been rotated 600 times in an I-type testing machine, and evaluating the coke strength after reaction based on the ratio of mass B to mass A. A coke with a high CSR value is considered to be suitable for blast furnaces because it has low tendency to disintegrate in the furnace.

[0007] One method proposed for estimating the CSR value is to estimate it from the amount of components in the ash of coal that contribute to the reaction (see Patent Document 1).In addition, a method has been proposed for evaluating the strength after reaction, which more closely simulates the pulverization that occurs in a blast furnace by reacting coke with CO2 while applying an impact (see Patent Document 2). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 61-213287 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-309672 [Non-patent literature]

[0009] [Non-Patent Document 1] Shozo Murakami et al., Coke Circular, Vol. 23, 1974, pp. 82-87 Summary of the Invention [Problem to be solved by the invention]

[0010] However, due to the high reactivity of high-reactivity cokes, such as ferro-coke, used to promote reduction, the conventional CSR measurement method described above results in almost all samples being pulverized during post-reaction strength measurement, making it impossible to measure the post-reaction strength and thus making it impossible to fully evaluate the post-reaction strength in the blast furnace. Furthermore, high-reactivity cokes, which undergo gasification at lower temperatures than conventional cokes, are thought to exhibit completely different pulverization behavior in the blast furnace due to their extremely fast reaction rate. Therefore, conventional CSR measurement conditions may not adequately represent the post-gasification strength of high-reactivity cokes.

[0011] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method capable of evaluating the post-reaction strength of high-reactivity coke such as ferro-coke. [Means for solving the problem]

[0012] The present invention, which solves the above problems, is as follows. [1] A method for evaluating the strength of a high-reactivity coke after reaction, comprising the steps of: loading a sample of high-reactivity coke into a reaction vessel; heating the sample to a predetermined reaction temperature; reacting the sample with carbon dioxide for 20 minutes to 110 minutes while circulating carbon dioxide through the reaction vessel; measuring a mass A of the sample after the reaction; loading the sample into the drum of an I-type drum testing machine; rotating the drum under predetermined conditions; sieving the sample through a sieve of a predetermined size; and measuring a mass B of the sample on the sieve; and evaluating the strength of the high-reactivity coke after reaction in a blast furnace based on the ratio of mass B to mass A. [2] The method for evaluating the post-reaction strength of a high-reactivity coke according to [1] above, characterized in that a sample of high-reactivity coke is placed in a reaction vessel, the sample is heated to a predetermined reaction temperature, and then the sample and carbon dioxide are reacted for 20 minutes to 110 minutes while circulating carbon dioxide through the reaction vessel, a mass A of the sample after the reaction is measured, the sample is then placed in the drum of an I-type drum testing machine, the drum is rotated 600 times at a speed of 20 rpm, and a mass B of the sample on a 9.5 mm sieve is measured, and the strength of the high-reactivity coke after the reaction in a blast furnace is evaluated based on the ratio of mass B to mass A.

[0013] [3] The method for evaluating the post-reaction strength of a high-reactivity coke according to [1] or [2], wherein the predetermined reaction temperature is 900°C or higher and 1100°C or lower.

[0014] [4] The method for evaluating the post-reaction strength of a high-reactivity coke according to any one of [1] to [3] above, wherein the high-reactivity coke is a coke having a reaction initiation temperature of less than 900°C.

[0015] [5] The method for evaluating the post-reaction strength of a high-reactivity coke according to any one of [1] to [4] above, wherein the high-reactivity coke is ferro-coke. [Effects of the Invention]

[0016] According to the present invention, the post-reaction strength of highly reactive coke can be evaluated. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a graph showing the relationship between reaction time and strength after reaction for three levels of ferro-coke used in the examples. [Figure 2] FIG. 1 is a diagram showing the relationship between reaction temperature and strength after reaction for three levels of ferro-coke used in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. A method for evaluating the post-reaction strength of high-reactivity coke according to the present invention includes charging a sample of high-reactivity coke into a reaction vessel, heating the sample to a predetermined reaction temperature, reacting the sample with carbon dioxide for 20 to 110 minutes while flowing carbon dioxide through the reaction vessel, measuring a mass A of the sample after the reaction, charging the sample into the drum of an I-drum testing machine, rotating the drum under predetermined conditions, sieving the sample through a sieve of a predetermined size, measuring a mass B of the sample on the sieve, and evaluating the strength of the high-reactivity coke after the reaction in a blast furnace based on the ratio of mass B to mass A.

[0019] To evaluate the post-reaction strength of high-reactivity coke, the inventors conducted reaction tests under various conditions using ferro-coke, a typical high-reactivity coke, based on the CSR value measurement method specified in ISO 18894. The results showed that even for samples for which the measurement results were almost the same when measured using the conventional method of reacting coke with carbon dioxide for 120 minutes, the difference could be detected by shortening the reaction time. Specifically, the inventors discovered that by setting the reaction time between 20 and 110 minutes, it was possible to detect differences between high-reactivity cokes with different properties and evaluate the post-reaction strength of high-reactivity coke, leading to the completion of the present invention.

[0020] As described above, the present invention is characterized by the reaction time between coke and carbon dioxide, and other conditions can be the same as those used to evaluate the CSR of conventional cokes that are not highly reactive, and are not limited thereto. The present invention will be specifically described below, but the present invention is not limited thereto.

[0021] First, a sample of high-reactivity coke to be evaluated is prepared. In the present invention, "high-reactivity coke" refers to coke with a reaction initiation temperature of less than 900°C. Examples of such high-reactivity coke include ferro-coke, alkali-added coke, and biomass-blended coke. The reaction initiation temperature of the coke can be measured, for example, by the method described in the reference (Yamamoto Tetsuya et al., Iron and Steel, Vol. 96, 2010, pp. 683-690).

[0022] It is preferable to prepare a sample of high-reactivity coke with a particle size of 20±1 mm, as in the conventional method for determining the post-reaction strength of non-highly reactive coke. If the produced high-reactivity coke has the above particle size, prior particle size adjustment such as crushing is not necessary.

[0023] The post-reaction strength of high-reactivity coke varies significantly depending on the type and blending conditions of the coke raw materials. In particular, increasing the blending ratio of iron ore improves the reactivity of high-reactivity coke, but it also reduces the post-reaction strength and increases the risk of poor permeability due to powdering in the blast furnace. The upper limit of the iron ore ratio that can be blended, taking the post-reaction strength into consideration, varies depending on pre-treatment conditions such as the type and particle size of the iron ore, as well as the type of coal. Therefore, by determining the lower limit of the post-reaction strength of usable high-reactivity coke in advance based on the operating conditions of the blast furnace when using ferro-coke using the method of the present invention and controlling the iron ore ratio so that it does not fall below the determined lower limit, it is possible to reduce the risk of poor permeability due to powdering of the high-reactivity coke in the blast furnace.

[0024] Next, the sample of high-reactivity coke prepared as described above is charged into a reaction vessel. A conventional reaction vessel that has been used to measure the post-reaction strength of non-highly reactive coke can be used as the reaction vessel. The reaction vessel can be configured, for example, as a reaction vessel having a gas inlet for introducing carbon dioxide and a gas outlet for discharging the post-reaction gas.

[0025] Next, the high-reactivity coke sample placed in the reactor is heated to a predetermined reaction temperature. The sample can be heated by placing a heating device, such as a heater, around the reactor. The heating temperature of the sample is set to the reaction initiation temperature of the high-reactivity coke or higher. Because the reaction does not accelerate if the reaction temperature is too low, it is preferable to perform a preliminary evaluation within a temperature range that can simulate the reaction in a blast furnace. As shown in the examples described below, the inventors conducted various studies and found that a reaction temperature of 900°C or higher is preferable because it allows for accurate detection of differences in post-reaction strength between samples. On the other hand, a reaction temperature of 1100°C or lower prevents the majority of the sample from being pulverized, allowing for accurate detection of differences in post-reaction strength between samples. A reaction temperature of 1000°C is most preferable.

[0026] After heating the sample to a predetermined temperature, carbon dioxide is circulated through the reaction vessel to react the sample with carbon dioxide. An inert gas (Ar, N2, etc.) is circulated through the reaction vessel until the sample is heated to the predetermined temperature, and then the gas is switched to carbon dioxide after heating to the predetermined temperature. While 100% carbon dioxide is preferred, a mixture of an inert gas (Ar, N2, etc.) may also be used. The reaction between the sample and carbon dioxide is preferably carried out using 100% carbon dioxide at a flow rate of 5 L / min, as in conventional CSR measurement methods.

[0027] As described above, the reaction time between the high-reactivity coke sample and carbon dioxide is set to 20 minutes or more and 110 minutes or less. Setting the reaction time to 20 minutes or more makes it possible to detect differences in post-reaction strength between multiple samples with different properties. A reaction time of 30 minutes or more is preferred. On the other hand, when the reaction time is 120 minutes, which is the reaction time used in CSR measurements of non-highly reactive coke, most of the high-reactivity coke samples are pulverized during post-reaction strength measurement, making it impossible to detect post-reaction strength, and thus post-reaction strength differences. However, it has been found that a reaction time of 110 minutes or less allows the strength of the post-reaction samples to be measured and the post-reaction strength differences between samples to be detected. Therefore, the reaction time is set to 110 minutes or less. A reaction time of 90 minutes or less is preferred. Furthermore, as shown in the examples described below, a reaction time of 60 minutes is the most preferred because it maximizes the post-reaction strength differences between samples.

[0028] After the highly reactive coke and carbon dioxide are reacted with each other, the sample is taken out of the reaction vessel and the mass A of the sample after the reaction is measured.

[0029] Next, the post-reaction sample whose mass A has been measured is placed in the drum of an I-type drum testing machine, and the drum is rotated under specified conditions to perform a strength test. The drum rotation conditions can be determined as appropriate, but the strength test can be performed by rotating the drum 600 times at a speed of 20 rpm, the same conditions as in conventional CSR measurements. The sample after the strength test is then removed from the drum and placed on a sieve of a specified size to sieve it, and the mass B, which is the mass of the sample remaining on the sieve, is measured. The sieve mesh size is not particularly limited, but a 9.5 mm mesh is suitable for evaluation, as in conventional CSR measurements.

[0030] In the present invention, the strength of the high-reactivity coke after the reaction in the blast furnace is evaluated based on the ratio of mass B to mass A measured as described above (mass B / mass A × 100 (%)). A larger value of this ratio indicates a higher post-reaction strength of the high-reactivity coke. Then, based on the post-reaction strength, the effect of ventilation when charging the high-reactivity coke into the blast furnace can be evaluated. [Example]

[0031] Example 1 In Example 1, the effect of the reaction time between ferro-coke and carbon dioxide on the strength after the reaction was evaluated. The properties of the three types of ferro-coke used in the test are shown in Table 1. In Table 1, FC represents the fixed carbon ratio of the ferro-coke, and T.Fe represents the iron content.

[0032] [Table 1]

[0033] Three types of ferro-cokes, A, B, and C, with different properties (all with reaction initiation temperatures below 900°C), were prepared, and the difference in post-reaction strength among the samples over time was investigated. Specifically, 20 ferro-coke particles were placed in a cylindrical reactor, and the samples were reacted with carbon dioxide at 1000°C for 30 minutes. The mass A of each sample after the reaction was measured. The post-reaction ferro-coke sample was then rotated 600 times at 20 rpm using an I-type testing machine, placed on a 9.5 mm mesh sieve, and the mass B of the sample remaining on the sieve was measured. The ratio of mass B to mass A was then calculated from the measured masses A and B, and the resulting ratio was used as the post-reaction strength. The same post-reaction strength measurements were also performed for reaction times of 0, 60, 90, and 120 minutes. Figure 1 shows the relationship between reaction time and post-reaction strength for ferro-cokes A to C.

[0034] Regarding the post-reaction strength of ferro-coke, the difference in post-reaction strength between samples increased up to a reaction time of 60 minutes, but conversely, the difference between samples decreased once the reaction time exceeded 60 minutes. As a result of the above, it was found that the method for evaluating post-reaction strength of the present invention can detect the difference in post-reaction strength between samples when the reaction time is between 20 and 110 minutes, that the difference in post-reaction strength between samples increases when the reaction time is between 30 and 90 minutes, and that the difference is greatest when the reaction time is 60 minutes.

[0035] Example 2 In Example 2, the effect of the reaction temperature between ferro-coke and carbon dioxide on the post-reaction strength was evaluated. The three types of ferro-coke used in the test were the same as those used in Example 1. Three types of ferro-coke A, B, and C with different properties were used to investigate the difference in post-reaction strength between samples as a function of reaction temperature. Specifically, 20 ferro-coke particles were placed in a cylindrical reaction vessel, and the samples were reacted with carbon dioxide at a temperature of 900°C for 60 minutes. The mass A of the sample after the reaction was measured. Next, the post-reaction ferro-coke sample was placed in the drum of an I-type testing machine, and the drum was rotated 600 times at 20 rpm. After that, the sample was placed on a sieve with 9.5 mm mesh and sieved. The mass B of the sample remaining on the sieve was measured. The ratio of mass B to mass A was calculated from the measured masses A and B, and the resulting ratio was used as the post-reaction strength. The above post-reaction strength measurement was also performed at reaction temperatures of 800°C, 1000°C, and 1100°C. The relationship between the reaction time and strength after reaction for ferro-cokes A to C is shown in Figure 2.

[0036] The post-reaction strength of ferro-coke showed almost no difference between samples at a reaction temperature of 700°C, but the difference increased above 800°C, reaching its widest at 1000°C. Above 1000°C, the difference in post-reaction strength decreased with increasing reaction temperature, but differences were detectable up to 1100°C. However, at a reaction temperature of 1200°C, almost no difference between samples was detectable. These results demonstrate that the post-reaction strength measurement method of the present invention can be used at reaction temperatures between 800°C and 1100°C, with the largest difference occurring at 1000°C.

[0037] Example 3 In Example 3, to evaluate the influence of post-reaction strength on permeability in a blast furnace by the evaluation method of the present invention, four types of ferro-coke with different post-reaction strengths obtained by the method of the present invention were used in a blast furnace, and the operating results under each condition were compared with those under the conditions of a reference example to evaluate reducibility and permeability. The permeability resistance index was calculated using the K value (=(P B 2 -P T 2 ) / V 1.7 )(P B : Air pressure, PT The conditions for measuring the strength after the reaction were a reaction time of 60 minutes and a reaction temperature of 1000°C. The results are shown in Table 2.

[0038] [Table 2]

[0039] When ferro-coke with post-reaction strengths of 58.6%, 49.5%, and 38.6% was used, the gas utilization rate, an index of reduction efficiency, improved and the reducing agent rate decreased. Permeability during this period was either equivalent to that of the reference example, or even if it deteriorated, it did not pose a problem for blast furnace operation. On the other hand, when ferro-coke with a low post-reaction strength of 28.7% was used, the permeability resistance index increased significantly, forcing a reduction in airflow and resulting in a decrease in productivity. These results confirmed that the post-reaction strength evaluation method of the present invention can be used to evaluate the permeability impact of ferro-coke when used in a blast furnace. [Industrial Applicability]

[0040] According to the present invention, the post-reaction strength of highly reactive coke can be evaluated.

Claims

1. A method for evaluating the post-reaction strength of a high-reactivity coke, comprising: loading a sample of high-reactivity coke into a reaction vessel; heating the sample to a predetermined reaction temperature; reacting the sample with carbon dioxide for 20 minutes to 110 minutes while circulating carbon dioxide through the reaction vessel; measuring a mass A of the sample after the reaction; loading the sample into the drum of an I-type drum testing machine; rotating the drum under predetermined conditions; sieving the sample through a sieve of a predetermined size; and measuring a mass B of the sample on the sieve; and evaluating the strength of the high-reactivity coke after reaction in a blast furnace based on the ratio of mass B to mass A.

2. 2. The method for evaluating the post-reaction strength of a high-reactivity coke according to claim 1, characterized in that a sample of high-reactivity coke is charged into a reaction vessel, the sample is heated to a predetermined reaction temperature, the sample and carbon dioxide are reacted for 20 minutes to 110 minutes while circulating carbon dioxide through the reaction vessel, a mass A of the sample after the reaction is measured, the sample is then charged into the drum of an I-type drum testing machine, the drum is rotated 600 times at a speed of 20 rpm, and a mass B of the sample on a 9.5 mm sieve is measured, and the strength of the high-reactivity coke after the reaction in a blast furnace is evaluated based on the ratio of the mass B to the mass A.

3. 3. The method for evaluating the post-reaction strength of a high-reactivity coke according to claim 1, wherein the predetermined reaction temperature is 900°C or higher and 1100°C or lower.

4. 3. The method for evaluating the post-reaction strength of a high-reactivity coke according to claim 1, wherein the high-reactivity coke has a reaction initiation temperature of less than 900°C.

5. 3. The method for evaluating the post-reaction strength of a high-reactivity coke according to claim 1, wherein the high-reactivity coke is a ferro-coke.

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