JP7347462B2 - Method for producing molded products and method for producing molded coke - Google Patents

Description

The present invention relates to a method for manufacturing a molded product mainly consisting of coal, which is a raw material for molded coke, and a method for producing molded coke by carbonizing the manufactured molded product.

Coke for steelmaking is produced by carbonizing coal (by steaming it while blocking air) in a coke oven to a temperature of 1000°C or higher, and is used in a blast furnace, which is the main ironmaking equipment. The coke charged in the blast furnace contains a reducing agent that reduces iron ore, which is the main raw material for the ironmaking process, a heat source that supplies the heat necessary for the ironmaking reaction, and a countercurrent reaction device for solid/liquid and gas. It plays a role such as a spacer to ensure ventilation and liquid passage inside the blast furnace. Generally, in order to achieve low reducing agent ratio operation which is effective for energy saving and reduction of CO ₂ emissions in blast furnaces, it is considered necessary to increase the strength of the coke used.

In a coke manufacturing process using a chamber-type coke oven, which is the most widely used coke manufacturing process, in order to manufacture high-strength coke, it is necessary to use a large amount of highly caking coal that has high caking properties. However, since strongly coking coal is rare and expensive, there is a strong demand for producing high-strength coke while using cheaper inferior quality coal such as non-slightly coking coal.

Conventional molded coke production processes are being researched and developed as an effective process for producing high-strength coke while using a large amount of inferior quality coal. Molded coke is a carbonization product obtained by preparing coal, the main raw material, in various steps, then mechanically compacting and molding it to create a high-density molded product, and carbonizing the molded product. Molded coke is generally manufactured so that the shape of the molded product is maintained.

A number of processes related to molded coke have been studied so far. For example, regarding the molding step, there is a cold molding method in which a binder is added to coal and cold molding, and a binder-less method in which coal is heated to around 400°C, where coal has caking properties. There is a hot forming method for forming molded products. Regarding the carbonization step, in addition to the carbonization method using a chamber coke oven, carbonization methods using a moving bed carbonization furnace, a continuous vertical shaft furnace, etc. have been proposed. Among these, the process in which the molded product obtained by cold forming is charged from the upper part of a vertical shaft furnace and carbonized, and the molded coke is continuously discharged from the lower part of the shaft furnace, is produced by the Japan Iron and Steel Federation. This process has been jointly researched and developed by steel companies, and has been developed to the point where it is on the verge of practical application (commonly known as the Steel Federation-style forming coke process). This method is promising because it can increase the amount of inferior quality coal that has poor caking properties, and has characteristics such as high productivity, high production elasticity, and low environmental impact.

However, in the method of producing molded coke in a vertical shaft furnace, it is necessary to prevent molded products from fusing together during carbonization. This is because when the molded products fuse together in the shaft furnace, a huge lump is formed, and if the lump is larger than the discharge port at the bottom of the furnace, the lump cannot be discharged and the operation becomes impossible. In order to avoid this situation, a method has been reported in which the temperature is rapidly increased in the early stage of carbonization to form a hardened layer of coke on the surface of the molded product to prevent fusion. Furthermore, it has been reported that the properties of raw materials, such as caking properties such as tackiness and expandability, affect the fusion properties of molded products. Methods for controlling raw material properties include a method of blending coal with poor caking such as anthracite or semi-anthracite (Patent Document 1), a method of using coal with high ash content (Patent Document 2), A method (Patent Document 3) of controlling the blending ratio of coal that is highly fused and easily fused (hereinafter referred to as easily softenable coal) has been proposed.

Patent No. 5017969 Patent No. 6016001 International Publication 2016/125727

As mentioned above, in order to suppress the fusion of molded products during carbonization, it is effective to change the carbonization conditions or change the blending composition of raw coal to control the properties. However, the conventional technology has the following problems.

Changing the carbonization conditions is not easy to implement because it affects the production schedule and the amount of heat of carbonization. Furthermore, it is difficult to precisely control the caking properties of raw coal for molded coke. One of the reasons for this is that the coal mainly used for molded coke has poor caking properties, such as steam coal for fuel, but the caking properties of steam coal are strictly controlled at the base of the mountain. is not subject to quality control (because its properties are not particularly important for fuel use). Therefore, even if the brand of coal is the same, there are large lot differences in caking properties, and if coal with higher caking properties arrives than expected, the molded coke plant may use the coal it has in its inventory. , a situation may occur in which the caking properties of raw coal cannot be fully adjusted. In response to this, procuring new coal to adjust the caking properties of raw material coal not only takes extra time and disrupts the operating schedule, but also causes additional costs. On the other hand, in order to increase the ability to adjust the caking properties of coking coal in order to respond to lot fluctuations, it is necessary to have multiple types of coal in stock, which poses problems such as securing space and the complexity of inventory management. become. Another reason is that evaluation of low caking properties has low accuracy to begin with. There are various evaluation tests for caking property (for example, JIS M 8801 crucible swelling test and fluidity test), but detection sensitivity is low in regions of low caking property. Therefore, it may be difficult to accurately control the properties of raw coal.

An object of the present invention is to propose a method for producing molded products as a technique for suppressing fusion between molded products during carbonization, relatively simply and quickly, without limiting the carbonization conditions or the raw materials used. .

Therefore, the inventors conducted extensive research on the relationship between the manufacturing conditions of molded coke, particularly the manufacturing conditions of molded products, and the fusion rate during carbonization of molded coke. As a result, they found that increasing the raw material temperature during molding suppresses the expansion of the molded product and reduces the fusion rate during carbonization of molded coke. Based on this discovery, further studies were conducted and it was confirmed that the raw material temperature during molding to prevent fusion in a shaft furnace differs depending on the ease of fusion of the molded product. Based on these findings, the present invention has been completed.

That is, the present invention provides a method for producing a molded article, which includes the steps of preparing a raw material mainly consisting of one or more coals, heating the prepared raw material, and molding the heated raw material. And,
When the fusion rate (α) of the molded product based on the following <Definition of fusion rate (α)> is 30 mass% or more, in the molding step, the temperature (Tb) of the raw material is set at 75°C or more and 250°C or less. A method for manufacturing a molded article, characterized by:
<Definition of fusion rate (α)>
The raw material processed in the raw material preparation step is molded at a temperature of less than 75°C, and a plurality of molded products are placed adjacent to each other and heated (carbonized) in an inert gas atmosphere to a temperature equal to or higher than the resolidification temperature of the raw material. After completing the softening and fusing, the product is cooled to produce a carbonized product, and the percentage of the weight of the carbonized product in which two or more molded products are connected to the total weight of the carbonized product is determined as the fusion rate. Let (α) be.

In addition, in the method for manufacturing a molded article according to the present invention configured as described above,
(1) The temperature (Tb (°C)) of the raw material in the molding step is determined according to the fusion rate (α (mass%)) so as to satisfy the following equations (1) and (2). Characterized by:
1.25×α+32.5≦Tb≦250...(1)
75≦Tb...(2),
(2) The above <definition of fusion rate (α)> shall be as follows:
<Definition of fusion rate (α)>
The raw material processed in the raw material preparation step is molded at 70°C, and a plurality of molded products are placed adjacent to each other and heated (carbonized) in an inert gas atmosphere to a temperature higher than the re-solidification temperature of the raw material to soften and melt. After finishing the deposition, the product is cooled to produce a carbonized product, and the percentage of the weight of the carbonized product in which two or more molded products are connected to the total weight of the carbonized product is calculated as the fusion rate (α). and
(3) carbonizing the molded product manufactured according to the method for manufacturing the molded product above;
is considered to be a more preferable solution.

According to the present invention, in the molding step, the temperature (Tb) of the raw material is controlled to be 75°C or more and 250°C or less for raw materials that are determined to have properties that are likely to be fused. It is possible to prevent molded products from adhering to each other in a carbonization furnace relatively easily and quickly without being subject to restrictions on carbonization conditions or raw materials used. Therefore, stable production of molded coke is possible.

It is a graph showing the relationship between the shrinkage rate in the height direction of a molded product obtained by cold or hot molding of coal and the temperature during carbonization. It is a graph showing the relationship between the temperature of the raw material during molding and the fusion rate of molded coke. It is a graph showing the relationship between the fusion rate of a molded product at a temperature of 70° C. during molding of raw coal and the lower limit of the temperature during molding required to make the fusion rate less than 30 mass%.

The method for manufacturing a molded article of the present invention usually includes the steps of preparing a single or plural coal-based raw materials, heating the raw materials, and molding the raw materials. In the present invention, the step of preparing a raw material refers to a step of producing a raw material in a state suitable for manufacturing a molded article, mainly using a single coal or a plurality of coals. Examples include blending multiple coals, adding additives to coal, and adjusting the particle size and moisture content of raw materials for molded products containing coal. In this method, it was confirmed that the raw material temperature during molding to prevent fusion from occurring when the molded product obtained in the molding step is carbonized varies depending on the ease of fusion of the molded product, Based on this knowledge, the present invention has been completed.

First, we will show the results of a preliminary experiment that confirmed the principle of this finding. Coal A with VM=31.2 (%d.b.), logMF=1.0, and CSN=1.0 was used in the experiment. Coal A was air-dried and then pulverized so that the content of particles of 0.1 mm or less was 100 wt%. 2 g of this crushed sample was filled into a φ16 mm mold and molded at room temperature under a pressure of 100 MPa (cold molding) or heated to 200°C in an argon gas atmosphere and molded at the same pressure (hot molding). A product and a hot-molded product were obtained. When these molded products were heated to 900° C. in an electric furnace under nitrogen gas flow, the shrinkage rate of the height relative to the initial height of the molded products was investigated. The results are shown in Figure 1.

From the results shown in FIG. 1, it can be seen that the cold-formed product expands from around 400° C., where coal exhibits softening and melting properties. On the other hand, the hot molded product showed no expansion during carbonization and uniformly shrunk after 400°C. Since the higher the expansibility of raw coal, the more easily fusion occurs between molded products during carbonization, it was expected that hot forming would suppress the fusion of molded products during carbonization. The reason for the decrease in expandability due to hot forming is that a slight structural change in the coal molecules occurred during hot forming, which had some effect on the thermal decomposition reaction during carbonization. Note that the upper limit of the temperature for hot forming of the present invention is about 250°C at most, which is clearly lower than the temperature for conventional hot forming, which utilizes the caking properties of coal to achieve bonding between coals. low. Conventionally, it has been thought that thermal decomposition reactions of coal do not occur at temperatures of about 250° C., and changes in properties are limited. The novel part of the present invention is the discovery that even in this relatively mild heating temperature range (75 to 250°C), the expandability of coal and, by extension, the fusion properties of the molded product change.

Next, the fusion rate (α) was investigated by changing the blending and molding temperatures (details are shown in the examples below). Here, the fusion rate (α) is obtained by molding the raw material processed in the step of preparing the raw material at a temperature of less than 75°C to produce a molded product, and when a plurality of molded products are placed adjacent to each other. After heating (carbonization) in an inert gas atmosphere to a temperature equal to or higher than the resolidification temperature of the raw material to complete the softening and fusion, the carbonization product is produced by cooling, and 2 or more pieces are added to the total weight of the carbonization product. It can be determined as a percentage of the weight of the carbonized product in which the molded products are connected. Furthermore, the fusion rate when molding is performed at a different temperature may be estimated from the fusion rate determined through an experiment at a certain molding temperature. The fusion rate (α) is a value indicating the ease with which the carbonized product is fused, and it can be determined that the larger the fusion rate (α) is, the easier the molded product is to be fused. In addition, as a preferable example of "heating (carbonization) in an inert gas atmosphere to the softening melting temperature with a plurality of molded products adjacent to each other to complete the softening and fusion bonding," In this state, it may be heated to at least 600°C at a rate of temperature increase of 3 to 5°C/min. By heating to at least 600° C. at a temperature increase rate of 3 to 5° C./min, softening and melting of the molded product is completed. Caking coal, which is suitably used as a raw material for producing coke, softens and melts when heated, and solidifies again when the heating temperature is further increased. The temperature at which the softened and melted coal solidifies again is called the resolidification temperature, and the softening and melting ends with resolidification. That is, by heating the molded products to a temperature equal to or higher than the resolidification temperature, a fused material in which the molded products are adhered to each other is generated.

This knowledge was organized and formulated. Depending on the fusion rate (α (mass%)) of the molded product obtained by molding the raw material at a temperature of less than 75°C, the temperature of the raw material during molding (Tb (°C)) in order to make the fusion rate less than 30 mass% is It has been found that the preferred range is to satisfy the following formulas (1) and (2):
1.25×α+32.5≦Tb≦250...(1),
75≦Tb...(2).

Therefore, it is desirable to investigate the fusion rate (α) of a molded product molded at a temperature of less than 75° C. and, depending on the result, change the raw material temperature during the molding step to the above-mentioned preferred range. Note that if the temperature in the molding machine exceeds 250°C, the risk of equipment trouble or disasters such as fire or explosion increases due to the gasification of flammable volatile matter. Therefore, it is desirable that the temperature during molding be 250° C. or lower.

Temperature control during molding in the step of molding heated raw materials varies depending on the type of molding equipment, but in systems that can directly heat, such as compression presses, heat is applied during molding to bring the raw material temperature above the lower limit. This is desirable. On the other hand, in the case of equipment such as roll molding where direct heating is difficult, it is also effective to raise the temperature in a step prior to the molding step (such as a compounding step). Particularly in the molding step, since softening of the binder due to heating also affects the quality of the molded product, it is desirable to control the heating temperature here. However, in this case, it is necessary to determine the heating temperature so that the temperature of the raw material during molding is 75° C. to 250° C., taking into account the decrease in raw material temperature due to heat removal up to the molding step. Note that the temperature of the raw material during molding can be confirmed by measuring the temperature of the molded product immediately after molding. Similarly, regarding the molding temperature when determining the fusion rate (α), the temperature of the raw material during molding may be set to be less than 75°C. In addition, since the molding temperature when determining the fusion rate is lower than the temperature of the molding step in the method for manufacturing molded products of the present invention, there is little temperature drop from heating the raw material to molding, and the raw material before molding If the temperature is less than 75°C, the temperature during molding will be essentially the same as the temperature of the raw material, so molding is performed by controlling the temperature of the raw material before molding (the temperature of the raw material introduced into the molding machine). It's okay.

Furthermore, a low oxygen concentration is desirable as an atmosphere during heating and molding. When coal is heated in the presence of oxygen, the quality of the coal may deteriorate due to a so-called weathering phenomenon. Additionally, an atmosphere with low oxygen concentration is desirable from the perspective of reducing the risk of fire, explosion, etc. The oxygen concentration in the atmosphere during heating or molding is preferably 18% by volume or less, but if the quality deterioration of the coal is practically negligible or if sufficient measures are taken to prevent the risk of fire or explosion, Heating and molding may also be performed. In order to reduce the oxygen concentration, methods such as creating an atmosphere in which an inert gas such as nitrogen is added, or increasing the partial pressure of water vapor in the atmosphere to lower the oxygen concentration can be adopted.

In order to investigate the relationship between the raw material temperature during molding and the fusion rate of molded coke after carbonization, the blending ratio of various easily softenable coals (coal with a button index CSN of JIS M 8801 exceeding 2.0) was changed. The fusion rate was measured when molded products were carbonized by varying the temperature during kneading of raw materials. The molding method and carbonization method for the molded product were as follows.

First, a binder was added to a coal blend made of multiple types of coal brands, and the mixture was kneaded and molded. Regarding the softening and melting properties of the blended coal, the logarithm weighted average value (LogMF) of the maximum Gieseler fluidity should be in the range of 0.4 to 1.1, and the ash content of the blended coal should be in the range of 10.0 to 10.5 mass%. did. The total particle size of the coal was 2 mm or less. Further, as a binder, soft pitch and coal tar were added in an amount of 8.0 to 10.0 mass% based on the weight of the raw material. The mixture was kneaded at 100° C. to 200° C. using a high-speed mixer, which is a kneading machine, and the kneaded raw materials were used to produce a molded product using a double roll molding machine. The roll size was 650 mmφ x 104 mm, and the molding was performed at a rotation speed of 2 rpm and a linear pressure of 1 to 4 t/cm. The size of the molded product is 30 mm x 25 mm x 18 mm (6 cc), and the shape is oval.

The temperature of the molded product immediately after molding was measured, and this was taken as the temperature during molding. The temperature during molding was approximately 70°C to 150°C, which coincided with the temperature of the raw material immediately before entering the molding roll. That is, the temperature at the time of molding can be set as the temperature (Tb) of the raw material to be molded. Furthermore, a high degree of correlation was observed between the temperature during molding and the temperature during kneading. That is, by adjusting the temperature during kneading, the temperature during molding can be adjusted. Carbonization of the molded product was performed using the following laboratory scale carbonization method (fixed bed). A carbonization can measuring 200 mm in length, 60 mm in width, and 200 mm in height was filled with 1.8 kg of the molded product, carbonized by program heating using an electric furnace, and then cooled in a nitrogen atmosphere. Program heating increases the temperature of the gap between the molded products in the center of the molded product layer from room temperature to 500°C at a rate of 15°C/min, and from 500 to 750°C at a rate of 3°C/min until the temperature exceeds 750°C. The test was carried out under the conditions of holding for 143 minutes. After cooling, the molded coke was taken out from the container, and the weight ratio of the sample in which two or more pieces of molded coke were fused was calculated and defined as the fusion rate, and the relationship between the fusion rate and the temperature during molding was investigated. At the temperature of the void between the molded materials in the center of the molded material layer (or the internal temperature of the briquette coal near the center of the molded material layer), the heating rate is 2 to 20°C/min at 350 to 500°C. More desirably, the fusion rate will be approximately equal if the temperature is 2 to 15°C/min and the maximum temperature is 700 to 1000°C, so the fusion rate under such carbonization conditions will increase the ease of fusion of the molded product. It is possible to evaluate. Among these, when the temperature increase rate from 350 to 500° C. is faster than 20° C./min, the fusion rate increases significantly, making it difficult to detect the difference in the fusion rate due to the difference in the properties of the molded product. Therefore, it is desirable to set the temperature increase rate within the above-mentioned preferred range.

FIG. 2 shows the relationship between the fusion rate and the temperature during molding. From the results shown in FIG. 2, it was found that the fusion rate at the same molding temperature increased as the easily softened coal content increased. It was also confirmed that although the fusion rate decreased as the temperature during molding increased, the slope remained constant regardless of the formulation. In other words, it was found that as the blending ratio of easily softened coal increases, the temperature of the raw material during molding at which the fusion rate reaches a certain value increases.

When obtaining molded coke by carbonizing coal molded products using a shaft furnace, if the fusion rate exceeds a certain value, the unloading of the molded coke will be delayed, making it difficult to discharge from the furnace, which will impede the operation of the furnace. It is known that the probability increases. The inventor investigated the relationship between the fusion rate and operational troubles and found that smooth operation becomes difficult when the fusion rate exceeds 30 mass%. In FIG. 2, a line with a fusion rate of 30 mass% is shown as an example of the operational upper limit. Normally, if the fusion rate is below this line, operation is possible without major problems. However, depending on the type of furnace and operating conditions, the fusion rate may not reach 30 mass%, which makes smooth operation difficult. Even in that case, it is clear that raw materials with a fusion rate of 30 mass% or more when molded at a temperature below 75°C are easily fused raw materials, and for such raw materials, the molding temperature should be set at 75 to 250°C. By raising the molding temperature to 75°C, the fusion rate during operation can be lowered than when molding is performed at a temperature below 75°C. That is, in the present invention, raw materials that are likely to be fused are identified based on the fusion rate α of the raw material molded product obtained under predetermined conditions, and when using raw materials that are easy to fused, the molding temperature is set to 75 to 75. By increasing the temperature to 250°C, the problem of suppressing fusion during carbonization is solved. This method has the effect that if the fusion rate decreases, operational troubles can be reduced accordingly. The target value of how much the fusion rate should be reduced during operation can be appropriately set by a person skilled in the art based on operational experience. Adjusting the molding temperature based on ease of molding is one embodiment of the present invention.

Under the conditions shown in FIG. 2, when the temperature during molding is further lowered below 70° C., the fusion rate tends to increase as the temperature decreases. In the present invention, the fusion rate α is determined for a molded article molded at a temperature of less than 75°C, and when the fusion rate α is 30 mass% or more, the molding temperature in the molding step in the production of the molded article is set to 75°C. Increase the temperature to above ℃ to suppress fusion. If the molding temperature when determining α is low, the value of α will be large, so for example, when determining α by molding at a temperature below 75°C, the fusion of the raw material will be higher than when molding at 75°C. is evaluated highly (easily fused). Therefore, when the molding temperature when determining α is low, the temperature in the molding step is increased for a wider range of raw materials, and fusion can be more reliably suppressed.

However, by molding a wider range of raw materials at a higher molding temperature during the molding step in the production of molded products, it is possible to reliably prevent fusion, but at the same time the amount of raw materials molded at high temperatures increases. Therefore, there will be a disadvantage in terms of energy usage. Therefore, it may be preferable to set the molding temperature for determining the fusion rate as high as possible. Considering these advantages and disadvantages, the molding temperature when determining the fusion rate α is preferably set at 65°C or higher and lower than 75°C, and more preferably at 70°C. At this time, in the operation to determine the fusion rate α, it is not necessarily necessary to perform molding at 70°C, but based on the test results of molding at other molding temperatures, the fusion rate when molded at 70°C can be calculated. It may be estimated. As a method for estimating such a fusion rate, the fusion rate when molded at 70°C may be estimated by interpolation or extrapolation from multiple experimental results, or, for example, by using the correlation shown in Figure 2. It can be estimated from In this way, the molding temperature in the molding step in manufacturing the molded article can be determined based on the fusion rate α when molding is performed at 70°C.

Therefore, based on the relationship between raw material temperature and fusion rate for each raw material shown in Figure 2, we calculated the fusion rate at a molding temperature of 70°C for a certain raw material and the time when the raw material was molded to have a fusion rate of 30 mass%. Figure 3 shows the results of determining the temperature of the raw material. Here, the fusion rate at a molding temperature of 70°C represents the ease of fusion of the coal blend. The regression line in FIG. 3 indicates the lower limit temperature for reducing the fusion rate to 30% or less when the raw material having the fusion rate when molded at 70° C. is carbonized. Therefore, if molding is performed at a temperature higher than this regression line, the fusion rate can be reduced to less than 30%. From this result, in order to prevent the fusion of molded products from becoming a problem during carbonization, it is necessary to raise the temperature of the raw material during molding to a certain degree depending on the fusion rate of 70°C for raw coal. You can see if you can control the amount of wear. Based on this result, the preferred range of the present invention was defined.

The method for manufacturing a molded product according to the present invention is not limited to molded products that are raw materials for molded coke, but can also be applied to other molded products where fusion of molded products due to heating is a problem.

Claims (3)

A method for producing a molded article, comprising the steps of preparing a raw material mainly consisting of one or more coals, heating the prepared raw material, and molding the heated raw material,
When the fusion rate (α) of the molded product based on the following <Definition of fusion rate (α)> is 30 mass% or more, in the molding step, the temperature of the raw material (Tb (°C)) is A method for manufacturing a molded article, characterized in that it is determined according to the adhesion rate (α (mass%)) so as to satisfy the following formulas (1) and (2):
1.25×α+32.5≦Tb≦250...(1)
75≦Tb...(2 )
<Definition of fusion rate (α)>
The raw material processed in the raw material preparation step is molded at a temperature of less than 75°C, and a plurality of molded products are placed adjacent to each other and heated (carbonized) in an inert gas atmosphere to a temperature equal to or higher than the resolidification temperature of the raw material. After completing the softening and fusing, the product is cooled to produce a carbonized product, and the percentage of the weight of the carbonized product in which two or more molded products are connected to the total weight of the carbonized product is determined as the fusion rate. Let it be (α). The method for manufacturing a molded article according to claim 1 , wherein the <definition of fusion rate (α)> is as follows:
<Definition of fusion rate (α)>
The raw material processed in the raw material preparation step is molded at 70°C, and a plurality of molded products are placed adjacent to each other and heated (carbonized) in an inert gas atmosphere to a temperature higher than the re-solidification temperature of the raw material to soften and melt. After finishing the deposition, the product is cooled to produce a carbonized product, and the percentage of the weight of the carbonized product in which two or more molded products are connected to the total weight of the carbonized product is calculated as the fusion rate (α). shall be. A method for producing molded coke, comprising carbonizing a molded product produced according to the method for manufacturing a molded product according to claim 1 or 2 .

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