Method for producing coal cake, method for producing metallurgical coke, and strength enhancing material for coal cake

Abstract

Provided is a method which is for producing a coal cake and by which the strength of a coal cake can be improved without using a caking binder. A method for producing a coal cake according to the present invention is a method for producing a coal cake in a stamp charge-type coke oven, and is characterized in that fibers having a length of 1.0-200 mm and a length-to-diameter ratio of at least 10 are added to and mixed with a raw material of a powdery coal cake, and the obtained fiber-mixed raw material is stamped to obtain a coal cake.

Description

Manufacturing method for coal cake, manufacturing method for metallurgical coke, and strength improving material for coal cake

[0001] The present invention relates to a method for producing a coal cake, a method for producing metallurgical coke, and a method for producing a strength improver for a coal cake.

[0002] Currently, in the production of pig iron using a blast furnace, coke produced by carbonizing coal in a coke oven is used as a reducing agent for iron ore and to ensure gas permeability inside the blast furnace. It is known that high-strength coke is preferable for efficient blast furnace operation. This is because, if coke breaks down inside the blast furnace, the resulting fines will deteriorate the gas permeability of the blast furnace, making it difficult to operate efficiently.

[0003] It is known that increasing the bulk density of the coal charged into the coke oven is effective in producing high-strength coke, and for this purpose, stamp-charge coke ovens are used. In the typical coke ovens currently used in Japan (hereinafter referred to as "top-charge coke ovens"), the coal, which is the raw material for coke, is charged by gravity from the top of the coke oven carbonization chamber, and the bulk density of the gravity-charged coal is 700 to 800 kg-dry / m ３ is.

[0004] On the other hand, in a stamp-charge coke oven, coal is compacted by a stamping device located on the side of the coke oven's carbonization chamber before being charged into the coke oven, and the bulk density is 1000 kg-dry / m ３ After being processed into the above coal cakes, they are mechanically charged into the coke oven chamber from the side. By using a stamp-charge coke oven, the density of the coke raw material can be increased before carbonization, as described above, and higher strength coke can be produced compared to when it is produced in a top-charge coke oven.

[0005] As mentioned above, stamp-charge coke ovens have an advantage over top-charge coke ovens in terms of coke strength. However, if the strength of the coal cake produced by stamping is low, the coal cake may collapse while being charged into the coke oven chamber, causing operational problems. Therefore, technology to produce high-strength coal cakes is needed to ensure stable operation of stamp-charge coke ovens.

[0006] It is also known that the strength of a coal cake is significantly affected by the moisture content of the coal, and in stamp charge coke ovens, the moisture content of the coal is generally adjusted to 10 to 12 mass%. However, if the moisture content of the coal cake is high, the carbonization time increases accordingly, resulting in a decrease in productivity. Therefore, in order to improve the productivity of stamp charge coke ovens, there is a need to develop technology that can produce coal cakes with sufficient strength for operation while maintaining a low coal moisture content.

[0007] To date, the use of caking binders has been investigated for the above-mentioned purposes. For example, Patent Document 1 reports a method in which caking coal is heated to 300 to 500°C and the coal in a softened, molten state is used as a binder for the coal cake. Also, Non-Patent Document 1 reports that adding pitch with a softening point of 80°C as a binder to the raw materials increases the strength of the coal cake, making it possible to produce a coal cake with sufficient strength even under conditions where the coal moisture content is lower than usual.

[0008] Japanese Patent Application Publication No. 7-109467

[0009] SH Krishnan, et al., "Application of Binder in Stamp Charge Coke Making", ISIJ International, 44(2004), 1150.

[0010] In the methods using a caking binder described in Patent Document 1 and Non-Patent Document 1, the caking raw material adheres to the belt conveyor and stamping device during the process of transporting the coke raw material containing the caking binder and during the process of compacting the raw material with a stamping device, which requires frequent cleaning of the device and results in a problem of reduced productivity.

[0011] An object of the present invention is to provide a method for producing a coal cake that can improve the strength of the coal cake without using a caking binder.

[0012] The inventors conducted extensive research to solve the above-mentioned problems and obtained experimental results showing that mixing synthetic fibers such as polyethylene with the raw materials of the coal cake improves the strength of the coal cake. The inventors also discovered that fibers can be used as binders for stamp-charge coke ovens and that the length of the fibers significantly affects the strength of the coal cake. Furthermore, in response to the recent social demand for carbon neutrality, the inventors discovered that similar effects can be achieved using fibrous plant materials, leading to the completion of the present invention.

[0013] The present invention provides a method for producing a coal cake in a stamp charge coke oven, comprising: mixing a powdered coal cake raw material with fibers having a length of 1.0 mm or more and 200 mm or less and a length-to-diameter ratio of 10 or more; and stamping the resulting fiber-mixed raw material to obtain a coal cake.

[0014] [2] The method for producing a coal cake described in [1], wherein the blending ratio of the fibers is 2.0 mass% or less relative to 100 mass% of the raw materials of the coal cake.

[0015] [3] A method for producing metallurgical coke, characterized by carbonizing a coal cake produced by the method according to [1] or [2] in a coke oven to obtain coke.

[0016] [4] A strength improving material for coal cake used in stamp charge coke ovens, characterized by being a fiber having a length of 1.0 mm or more and 200 mm or less.

[0017] According to the present invention, it is possible to provide a method for producing a coal cake that can improve the strength of the coal cake without using a caking binder. Furthermore, according to the present invention, it is possible to produce a coal cake that has sufficient strength for operational purposes while maintaining the coal moisture at a low level.

[0018] The present invention provides a method for producing a coal cake in a stamp-charge coke oven, which includes mixing a powdered coal cake raw material with fibers having a length of 1.0 mm to 200 mm and a length-to-diameter ratio of 10 or more, and stamping the resulting fiber mixture to obtain a coal cake.

[0019] First, fibers having a length of 1.0 mm or more and 200 mm or less and a length-to-diameter ratio of 10 or more are blended and mixed with the coal cake raw material to prepare a fiber mixed raw material.

[0020] [Coal Cake Raw Materials] The coal cake raw material may be a powdered coal blend mainly composed of raw material coal generally used for coke production. In addition to raw material coal, non- or slightly caking coal, biomass, charcoal obtained by heating biomass, or other raw materials mainly composed of carbon may also be used, as long as the quality of the coke obtained by carbonizing the coal cake is not an issue.

[0021] The raw material may be crushed using a hammer crusher or the like to a particle size of −3 mm, 70 to 100 mass%, as is conventionally done in the operation of a stamp charge coke oven (crushed so that the proportion of particles having a particle diameter of 3 mm or less is 70 to 100 mass%), and used as a raw material for the coal cake.

[0022] The moisture content of the coal cake raw material can be adjusted before or after the above-mentioned crushing treatment by drying using coal moisture control equipment, spraying water from a nozzle, etc. The target value of the moisture content of the coal cake raw material is preferably 10 to 12 mass% for the purpose of increasing the strength of the coal cake, but for the purpose of improving productivity, the moisture content may be reduced to a range in which the strength of the coal cake does not become an issue.

[0023] [Fibers] Examples of fibers that can be used include synthetic fibers such as nylon and polyester, natural fibers such as silk and cotton cut to any length, and fibrous plant materials. A specific example of a fibrous plant material is Empty Fruits Bunch (EFB) fiber, which is mechanically defibrated palm bunches.

[0024] In recent years, CO ２ In response to societal demands for reducing emissions, palm oil and palm kernel shells derived from oil palms are increasingly being used as fuels for biomass power generation, replacing conventional fossil fuels. However, palm bunches, the residue left over after harvesting the fruit from oil palms, contain a lot of moisture and ash and are prone to decay, so most of them are currently discarded. Palm bunches have a fibrous shape, and by mechanically breaking them down, fibers with diameters of 0.5 to 1.0 mm and lengths of approximately 50 to 100 mm can be obtained.

[0025] In this way, if we could focus on the shapes of plants that are currently discarded and use them as binders for stamp-charge coke ovens, it would lead to more effective use of resources. Furthermore, materials other than those mentioned above could also be used as binders for stamp-charge coke ovens, as long as they are fibers primarily composed of carbon, oxygen, and hydrogen.

[0026] In the present invention, fibers having a certain length or longer are mixed and dispersed in the coal cake raw material, forming a fiber mixed raw material in which the fibers are intertwined to form a network, thereby enabling the production of a high-strength coal cake.

[0027] The longer the fibers, the more contact the fibers have with each other, forming a fiber network throughout the coal cake. To improve the strength of the coal cake, the fiber length needs to be 1.0 mm or more. Longer fibers are preferable in terms of improving the strength of the coal cake, and the length of the fibers mixed into the coal cake raw material is preferably 3.0 mm or more, and more preferably 5.0 mm or more. On the other hand, even if the fibers are longer than 200 mm, the strength of the coal cake saturates, but the problem of poor mixability with the powdered coal cake raw material arises. Therefore, the length of the fibers mixed into the coal cake raw material is set to 200 mm or less, preferably 180 mm or less, and more preferably 160 mm or less.

[0028] The fiber lengths do not need to be uniform and may be irregular. It is sufficient that a predetermined amount of fibers with lengths of 1.0 mm to 200 mm are mixed. Fibers with lengths less than 1.0 mm do not contribute to improving the strength of the coal cake, but they do not reduce the strength either, so the inclusion of fine fibers is not a problem. Small amounts of fibers with lengths of 200 mm or more hardly reduce the strength, but increasing the amount can reduce the strength. Therefore, it is desirable not to intentionally incorporate fibers with lengths of 200 mm or more. Furthermore, in terms of fiber shape, thick and short fibers, i.e., fibers closer to a spherical shape, are thought to be less likely to cause the entanglement phenomenon described above when mixed into the coal cake. As shown in the examples described below, the use of thick and short fibers does not improve the strength of the coal cake, but does not reduce it either, so the inclusion of thick and short fibers is not a problem. What is required here is to incorporate fibers with an elongated shape, and a larger ratio of the length to the diameter of the fibers is preferable. In the present invention, the ratio of length to diameter of the fibers is 10 or more, preferably 15 or more, and more preferably 30 or more.

[0029] When synthetic fibers or natural fibers are cut and used, the fiber length can be set freely within a wide range, taking into consideration the target value of the coal cake strength set by each factory and the ease of mixing the coal cake raw material with the fiber. On the other hand, when using fibrous plant materials, it is difficult to set the fiber length freely, but the use of biomass raw materials instead of fossil fuel-derived binders reduces CO emissions. ２ The type and length of the above fibers are determined based on the operational targets of each factory (coal cake strength, CO ２ This can be determined arbitrarily depending on the amount of CO2 emissions (emission reduction) and the capacity of the mixing equipment.

[0030] In the present invention, a high-strength coal cake can be produced by blending fibers into the powdered coal cake raw material and then stamping and compacting the resulting fiber-mixed raw material.

[0031] Regarding the fiber blending ratio relative to the coal cake raw materials, as shown in the examples described below, the higher the fiber blending ratio, the stronger the coal cake. Therefore, from the perspective of coal cake strength, there is no upper limit to the blending ratio. However, in the present invention, blending a small amount of fiber into the coal cake raw materials exhibits a significant strength improvement effect. Therefore, from the perspective of preventing the coal cake from collapsing and stabilizing operations, there is little benefit in increasing the coal cake strength more than necessary. Therefore, from an economical perspective, the fiber blending ratio is preferably 2.0 mass% or less relative to 100 mass% of the coal cake raw materials. Note that blending fibers at a blending ratio of 2.0 mass% or less means blending the fibers so that the dry mass of the fibers is 2.0 mass% or less when the total dry mass of the raw materials (coal, coal dry distillate, other carbonaceous materials, etc., excluding fibers) used to produce the coal cake is 100 mass%. The fiber blending ratio is more preferably 1.5 mass% or less, and even more preferably 1.0 mass% or less.

[0032] On the other hand, even when the fiber blending ratio is low, the effect of improving the coal cake strength corresponding to the blending ratio is exhibited, and therefore the lower limit of the blending ratio is not particularly limited. However, from the viewpoint of producing a coal cake with higher strength and preventing the coal cake from collapsing, the fiber blending ratio is preferably 0.01 mass% or more, more preferably 0.02 mass% or more, and even more preferably 0.05 mass% or more.

[0033] It is noted that coal cake raw materials and plant-derived fibers generally contain a certain amount of moisture. Therefore, the moisture content of the coal cake raw materials and fibers is measured in advance, and the fiber blending ratio is calculated using the dry mass (mass excluding moisture). The moisture content of the fibers is calculated from the weight loss of a sample after heating and drying at 107°C for 1 hour using the loss on drying method in air specified in JIS M 8812. It is noted that although this method is a moisture quantification method for coals, the moisture content of coal cake raw materials and fibers containing materials other than coal may also be measured using the same method.

[0034] The method for blending and mixing the fibers into the coal cake raw material is not particularly limited, and may be a method using a mixer that is generally used for mixing coal in a coke plant. Another example is a method using a mixer with chopper blades, such as a Pam Apex Mixer (manufactured by Pacific Machinery Works, Ltd.), in order to blend and mix fibers into a large amount of coal cake raw material in a shorter time and increase productivity.

[0035] When producing a coal cake from the fiber mixed raw material prepared as described above, it may be produced using a stamping device that compacts the fiber mixed raw material by impact with a falling weight. In this case, when fibers having a length of 1.0 mm to 200 mm and a length-to-diameter ratio of 10 or more are mixed, a coal cake with higher strength can be produced compared to a case where no fibers are mixed. Therefore, the coal cake is less likely to collapse, enabling stable operation of the coke oven. Furthermore, even under operating conditions where the coal moisture content is low and coal cake collapses frequently, the strength of the coal cake can be maintained within a range that does not pose operational problems when the above fibers are mixed. The effect of mixing fibers on the strength of the coal cake will be explained in more detail in the following examples.

[0036] (Method for Producing Metallurgical Coke) Next, a method for producing metallurgical coke according to the present invention will be described. The method for producing metallurgical coke according to the present invention is characterized in that the coal cake produced by the above-mentioned method for producing coal cake according to the present invention is carbonized in a coke oven.

[0037] The coal cake produced by the above-described coal cake manufacturing method according to the present invention is mechanically charged from the side of the coke oven carbonization chamber. At this time, the coal cake is subjected to the impact of its own weight and the vibration of the charging machine. If the coal cake has low strength, the coal cake may collapse during charging, which may cause operational problems. In the coal cake manufacturing method according to the present invention, fibers are used as a binder, which improves the strength of the coal cake and prevents the coal cake from collapsing.

[0038] There are no particular restrictions on the conditions for carbonizing the coal cake. The coal cake may be carbonized at a temperature of approximately 900° C. or higher using a general stamp charge coke oven.

[0039] (Strength improving material for coal cake) Next, the strength improving material for coal cake according to the present invention will be described. The strength improving material for coal cake according to the present invention is a strength improving material for coal cake used in a stamp charge coke oven, and is characterized by being composed of fibers having a length of 1.0 mm or more and 200 mm or less.

[0040] The fibers may be the same as those used in the method for producing a coal cake according to the present invention. The requirements for the fibers may also be the same as those for the fibers used in the method for producing a coal cake.

[0041] As described above, a high-strength coal cake can be manufactured by blending fibers having a length of 1.0 mm or more and 200 mm or less as a binder into the coal cake raw material and then stamping the resulting fiber-mixed raw material. As a result, when the resulting coal cake is carbonized in a coke oven to produce coke, the coal cake can be prevented from collapsing, thereby enabling stable operation of the coke oven.

[0042] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples and can be modified as desired without departing from the gist of the present invention.

[0043] (Example 1) In Example 1, polyethylene fibers and polypropylene fibers having different fiber lengths and diameters were blended with the raw materials for the coal cake and mixed, and a coal cake was manufactured using the coal cake manufacturing method according to the present invention, and its strength was evaluated.

[0044] The coal cake raw material was a blended coal prepared so that the weighted average coal rank (Ro) was 0.94, and the blend was pulverized to a particle size of -3 mm (90 mass%). Polyethylene fibers or polypropylene fibers were cut to the lengths shown in Table 1 and mixed with the coal cake raw material at the blending ratios shown in Table 1. The moisture content of the mixture was measured, and a calculated amount of water was added so that the moisture content was 10 mass%, which is a typical condition for a stamp charge coke oven.

[0045]

[0046] A coal cake was produced using the fiber mixture whose moisture content had been adjusted as described above, as follows. First, approximately 200 g of the fiber mixture was placed in a metal mold with an inner diameter of 10 cm and a height of 20 cm. A 9 kg rammer was then dropped 10 times from a height of 30 cm above the sample surface, compacting the loaded fiber mixture with the impact. The above procedure from loading the coal to dropping the rammer was repeated 10 times to produce a coal cake with a diameter of 10 cm, a height of 20 cm, and a weight of approximately 2 kg. The mold was then gently removed from the coal cake, and the strength of the coal cake was measured. The strength of the coal cake was evaluated using the uniaxial compressive strength specified in JIS A 1216. The results are shown in Table 1.

[0047] Table 1 shows the strength of coal cakes when synthetic fibers of different lengths and diameters are blended into the coal cake raw material. Coal cake strength (uniaxial compressive strength) varies significantly depending on the type and particle size of the coal cake raw material used. Therefore, when evaluating the effect of additives on coal cake strength, it is advisable to evaluate each coal cake raw material in terms of the strength ratio to the uniaxial compressive strength of a coal cake produced under typical conditions for stamp-charge coke ovens, with a moisture content of 10% by mass and no additives.

[0048] If the intensity ratio is less than 1.0, the coal cake strength is lower than under typical operating conditions, and the conditions can be considered to be conditions that are prone to problems such as coal cake collapse. On the other hand, if the intensity ratio is greater than 1.0, the coal cake strength is higher than under typical operating conditions, and the conditions can be considered to be conditions desirable for stable operation in which the coal cake is less likely to collapse. From this perspective, in the comparative example in which polypropylene fibers with a diameter of 1.2 mm were cut to lengths of 5 mm or 10 mm and mixed, the intensity ratio to the reference was less than 1.0, and it can be said that mixing the fibers reduced the coal cake strength and made the coal cake more prone to collapse. The reason for this is thought to be that under the conditions of the comparative example, the shape of the additive was nearly spherical, and a network in which the fibers were entangled was not formed, and the effect of improving the coal cake strength was not observed.

[0049] On the other hand, in other examples of the present invention, the strength of the coal cake was improved by mixing fibers, making the coal cake less likely to collapse, which is a desirable condition for stable operation.The results of this example clearly show that the strength of the coal cake can be improved by mixing fibers having a length of 1.0 mm or more and 200 mm or less and a length-to-diameter ratio of 10 or more into the coal cake raw material.

[0050] In Example 2, the influence of mixing fibers on the strength of the coal cake was investigated under conditions in which the moisture content of the coal cake raw material was 7% by mass, which is lower than the operating conditions of general stamp charging, where the moisture content was 10% by mass. To this end, coal cakes were manufactured using the manufacturing method of the coal cake according to the present invention, and their strength was evaluated.

[0051] The coal cake raw material was prepared by blending raw coal to a weighted average coalification rank (Ro) of 0.94, and pulverizing the blended coal to a particle size of -3 mm (90% by mass). Polyethylene or polypropylene fibers were cut to the lengths shown in Table 2 and mixed with the coal cake raw material at the blending ratios shown in Table 2. The moisture content of the mixture was measured, and a calculated amount of water was added to adjust the moisture value to 10% by mass, which is the typical condition for a stamp charge coke oven, or 7% by mass, which is a lower moisture content than usual. Using the coal cake raw material whose moisture content had been adjusted by blending fibers using the above procedure, a coal cake was produced in the same manner as in Example 1, and its strength was measured. The results are shown in Table 2.

[0052]

[0053] Table 2 shows the effect of blending fibers on coal cake strength when the coal moisture content is lower than that typically found in stamp charge coke ovens. As shown in Table 2 as a reference example, when the moisture content of the coal cake raw material is reduced from 10% by mass to 7% by mass, the strength ratio of the coal cake to the reference value drops to 0.46. Under these conditions, the coal cake frequently collapses, making stable coke production difficult. Also shown as a comparative example is the strength of the coal cake when polypropylene fibers with a diameter of 1.2 mm and a length of 10 mm are blended. The strength of the coal cake is lower than that of the coal cake without blending fibers. In contrast, in the inventive example, by blending fibers with a length of 1.0 mm to 200 mm and a length-to-diameter ratio of 10 or more, the strength ratio is higher than the reference value, even when the moisture content of the coal cake raw material is 7% by mass. In other words, blending fibers can reduce the moisture content of the coal cake while maintaining its strength, thereby improving coke productivity.

[0054] Example 3 In Example 3, fibers obtained from palm bunches (EFB fibers) were mixed with coal cake raw materials, and a coal cake was manufactured by the manufacturing method of the coal cake according to the present invention, and the strength was evaluated.

[0055] The raw coal cake material was prepared by blending raw coal to a weighted average coal rank (Ro) of 0.93 and pulverizing it to a particle size of -3 mm (90% by mass). EFB fiber was blended with the raw coal cake material at the blending ratios shown in Table 3. The EFB fibers used had a uniform diameter of 0.8 mm, but their lengths varied between 50 and 100 mm. Therefore, a range was allowed for the fiber length and the ratio of length to diameter. The moisture content of the mixture was measured, and a calculated amount of water was added to achieve a moisture content of 10% by mass, which is the typical condition for stamp-charge coke ovens. Using the raw coal cake material with the EFB fiber mixed and moisture adjusted as described above, a coal cake was produced in the same manner as in Example 1, and the strength of the resulting coal cake was measured. The results are shown in Table 3.

[0056]

[0057] As shown in Table 3, the strength of the coal cake is also improved by mixing fibrous plant materials such as EFB fiber, and fibrous plant materials can be used as clean binders for stamp-charge coke ovens, replacing binders derived from fossil fuels.

[0058] According to the present invention, the strength of the coal cake can be improved without using a caking binder.

Claims

1. A method for producing a coal cake in a stamp charge type coke oven, comprising the steps of: mixing a powdered coal cake raw material with fibers having a length of 1.0 mm or more and 200 mm or less and a length to diameter ratio of 10 or more; and stamping the resulting fiber mixture raw material to obtain a coal cake.

2. The method for producing a coal cake according to claim 1, wherein the blending ratio of the fiber is 2.0 mass% or less relative to 100 mass% of the raw materials of the coal cake.

3. A method for producing metallurgical coke, comprising carbonizing the coal cake produced by the method according to claim 1 or 2 in a coke oven to obtain coke.

4. A strength improving material for coal cake used in stamp charge coke ovens, characterized in that the fiber has a length of 1.0 mm or more and 200 mm or less.

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