JP5900083B2 - Coal bond strength measurement method - Google Patents

Description

  For coal for coke production, the adhesion property between coal particles during softening and melting is a very important property. In the blast furnace coke, in order to maintain the air permeability in the blast furnace, it is required to produce a robust coke. Coal is softened and melted by dry distillation and adheres to each other to form coke. Therefore, it can be said that the difference in coal adhesive properties has a great influence on coke strength.

  As a method for evaluating the adhesive property of coal, there is a coal fluidity test method by the Gisela plastometer method defined in JIS M8801. In the Gisela plastometer method, coal pulverized to 425 μm or less is placed in a specified crucible, heated at a specified temperature rise rate, measured for the rotation speed of a stir bar applied with a specified torque, and divided every minute. This is a method for expressing the flow characteristics of a sample. When the coal particle packed bed is dry-distilled, the coal softens and melts from 350 ° C. to 500 ° C., the adjacent particles come into contact with each other, and then solidify to coke. Coal with higher fluidity is considered to have a higher adhesive strength because the contact area with adjacent particles increases. Therefore, it is considered that the adhesion properties of coal can be shown by the Gieseler plastometer method.

  Further, as another method for evaluating the adhesion property of coal, a coal expansibility test method by a dilatometer method defined in JIS M8801 can be cited. Coal exhibits expansion behavior when softened and melted. When the coal particle packed bed is dry-distilled, the coal particles come into contact with and adhere to the adjacent particles due to expansion, and therefore expansibility is regarded as important in addition to fluidity.

In addition, as a method for measuring the adhesive strength of coal, there is a method for obtaining the adhesive strength from the indirect tensile strength and the porosity (see, for example, Patent Document 1). Indirect tensile strength is a method to obtain the tensile strength indirectly from the compressive load, and is JIS standardized as a tensile strength test method for concrete. This is a method for deriving the tensile strength from the strength of the time using a mathematical formula. In the case of coke, a sample obtained by hollowing out coke into a cylindrical shape is measured as a sample (see, for example, Non-Patent Document 1). In addition, an example in which a sample obtained by filling coal in a cylindrical container and measuring it as a sample has been reported (for example, see Non-Patent Document 2). In Non-Patent Document 2, a stainless steel cylinder having a diameter of 20 mm is reported. Coal pulverized to 0.15 mm or less is charged into a container so as to have a bulk density of 0.8 g / cm ^3, and after dry distillation, cut into a thickness of 5 mm is used as a sample. In Patent Document 1, the adhesive strength is calculated from the logarithm of indirect tensile strength and the slope of the porosity graph.

JP-A-6-330048

Aya Miyagawa: Fuel Association, Vol. 54 (1975), p983 Toshimasa Takanohashi, Takahiro Shishio, and Ikuo Saito: Energy & Fuels, Vol. 22 (2008), p1799

  In order to measure the bond strength during coal softening and melting, it is important to actually measure the bond strength at the coal particle interface. In that respect, the Gieseler plastometer method and the dilatometer method merely measure the fluidity and expansibility considered to be greatly involved in adhesion, and these cannot be defined as adhesion strength.

  Regarding the method of deriving the adhesive strength from the indirect tensile strength and the porosity, the strength is actually measured, but the indirect tensile strength and the adhesive strength are not the same characteristics. That is, in the measurement of the indirect tensile strength, there is a problem that the sample does not always break on the adhesion surface. In particular, it is known that the indirect tensile strength of a porous material such as coke depends greatly on the porosity. By occurring in the thinned part. Such pores are generated by coal degassing during the carbonization process, and there is no direct relationship between coal particle interface adhesion and pore generation, and the point of failure is not limited to the adhesive surface, Indirect tensile strength is insufficient for evaluating adhesive strength. Attempts have been made to estimate the adhesive strength from the indirect tensile strength and the porosity, but it cannot be said that this method can actually avoid the problem of strength measurement. Moreover, in terms of the versatility of the evaluation method, the indirect tensile strength test also has a problem that it cannot be evaluated when the coking property is insufficient and a sample for measurement cannot be obtained. As described above, in the conventional technique, a suitable technique for evaluating the adhesive strength of coal has not been known.

The features of the present invention for solving such problems are as follows.
(1) Coal finely pulverized to a predetermined particle size or less, compression molded with a load capable of maintaining the shape after compression molding, and subjected to dry distillation in an inert atmosphere and coke as a measurement sample, A method for measuring the adhesive strength of coal for coke production, wherein the compressive strength of the measurement sample is measured, and the pressure at the time of fracture is taken as the adhesive strength.
(2) The adhesive strength measuring method according to (1), wherein the coal pulverized to 75 μm or less is compression-molded at a pressure of 20 MPa or less, and dry-distilled in an inert atmosphere to form coke.

  By using the present invention, it is possible to measure the bond strength of coal for coke production as an actual measurement value. According to the present invention, it is possible to evaluate from a new viewpoint of adhesive strength for coal mined and produced in various production areas. By using coal with high adhesive strength, high strength coke can be produced. It becomes possible.

It is a figure which shows the carbonization apparatus used in the Example. It is an arrangement plan of a molding in an example. It is a figure which shows the relationship between the adhesive strength measured in the Example, and MF. It is a figure which shows the relationship between the adhesive strength measured in the Example, and TD.

  In order to solve the above-described problems, the present invention has found a method for preparing a sample in which pore formation is suppressed and measuring the strength of the sample. By suppressing the formation of pores, it is possible to eliminate the influence of pores in the strength measurement test and to effectively evaluate the adhesive strength. The pores generated in the coal particles grow as the gas generated gradually from the coal particles continues to stay in the particles. Therefore, to stop the growth of the pores, the diameter of the coal particles is reduced and the pores are generated in the coal particles. It is important to release the gas quickly out of the particles. Further, reducing the particle diameter leads to an increase in the surface area of the coal particles present in the measurement sample per unit mass, and has the effect of increasing the influence of the adhesive strength on the measurement strength. However, if the particle diameter is reduced, the specific surface area of the particles increases, and the particles do not adhere at all unless compressed to some extent. On the other hand, when the compression is performed at a high density, the distance between particles becomes very small, and the gas stays inside the compressed product, whereby the compressed product itself expands, and a void with high porosity and extremely low strength can be formed inside the compressed product. Therefore, it is preferable to use a measurement sample formed by applying a compressive force weak enough to be bonded for strength measurement. As a result of investigating various sample preparation conditions, the present invention has been found by finding suitable conditions.

  A measurement sample used in the present invention is prepared through three processes of pulverization, molding, and dry distillation. Details of each process are described below.

  As for pulverization, it is important to make it as fine as possible in order to promote gas diffusion inside the coal particles. When the coal particles are large, they often expand during dry distillation and a uniform sample cannot be obtained. As a result of investigations by the inventors, it is desirable to pulverize the coal to 75 μm or less.

  For molding, the size of the molded product is preferably a cylindrical shape having a diameter of 10 mm or less and a thickness of 2.5 mm or less. When the diameter and thickness are large, there is a high possibility that voids are generated inside the measurement sample after dry distillation. In addition, when the sample is enlarged, the temperature gradient inside and inside the sample during dry distillation increases, and the influence of cracks cannot be ignored. As for the molding conditions, it is preferable to hold the pressure for a certain period of time by applying a pressure of 14 MPa or more and 20 MPa or less. The reason why the pressure is set to 14 MPa or more is that when the pressure is less than that, the strength of the measurement sample after molding is small, the shape cannot be maintained after compression molding, and the possibility of breakage during handling is high. The reason why the pressure is set to 20 MPa or less is that, when molding is performed at a pressure higher than this, there is a high possibility that voids are generated inside after dry-molding the molded product.

  For carbonization, it is important that the carbonization rate simulates carbonization conditions in a normal coke oven. It is desirable to dry-distill up to 1000 ° C. at 3 ° C./min in an inert gas atmosphere. Here, the inert gas includes not only a rare gas such as argon gas but also nitrogen gas, and it is practical to use nitrogen gas. In addition, it is important that the measurement sample has uniform heat transfer. A desirable form is dry distillation in an embedded state in the powder coke.

  The adhesive strength of the measurement sample is measured by compressive strength measurement. The pressure when pressure was applied in the thickness direction of the molded product to break it was used as an index of adhesive strength. The reason for measuring the strength by applying pressure in the thickness direction is that the measurement sample after compression fracture is shattered. When the sample is divided into a small number of parts due to compression (for example, when the sample is divided into two parts), stress concentration may occur at the crack generation site of the sample during compression, and crack propagation may occur. In such a case, a defect in the sample may be a starting point and breakage may occur. However, since the present invention is intended to evaluate the degree of adhesion between many coal particles, It was desirable to eliminate the influence of fracture based on the defects of this as much as possible, and it was desirable to form a fracture form in which many joint parts of coal particles were sheared and fractured by compression, and pressure application from the thickness direction was adopted. For the strength measurement of coke, indirect tensile strength with a load applied in the diameter direction of a cylindrical sample is often adopted. It is not preferable for the purpose of the invention, and the present invention is superior in that it can evaluate unprecedented physical properties by controlling the load loading direction in the compression test together with coal pulverization conditions and molding conditions.

An example of preparing a measurement sample and measuring the adhesive strength is shown below. Nine types of coal were used for the measurement. Table 1 shows the properties of the coal used. Moreover, in order to measure the adhesive strength between two types of coal, the strength of the blended coal obtained by blending two types of coal at 1: 1 was determined. Combinations and average properties of the blends are shown in Table 1. Coal is pulverized to 75 μm or less, coal is charged into a mold having a hole with a diameter of 6.6 mm, and the amount of coal is adjusted so that the dimension after molding is 6.6 mm in diameter and 2.5 mm in thickness. A molding was prepared by applying pressure for 10 seconds. Ten molded products were prepared for each type of coal and blended coal. The bulk density of the molded product was different depending on the coal brand, and those values were in the range of 860 to 920 kg / m ³ . Ten molded articles were placed in a powder coke packed bed adjusted to 1 mm or less and subjected to dry distillation. The powder coke was filled in an iron container of 200 mm × 200 mm × H 500 mm. Fig. 1 shows the dry distillation apparatus and Fig. 2 shows the arrangement of the molded product. The dry distillation conditions were dry distillation to 1000 ° C. at 3 ° C./min in a nitrogen atmosphere, and cooling in a nitrogen atmosphere after dry distillation.

  The compressive strength was measured using an autograph manufactured by Shimadzu Corporation. A load was applied in the thickness direction of the measurement sample, and the load at break was measured. The pressure obtained by dividing the load by the area of the load application surface of the measurement sample was defined as the adhesive strength. The compressive strength and the area of the load application surface of 10 measurement samples of one level were measured, and the average of the respective adhesive strengths was defined as the adhesive strength at that level. The measurement results are shown in Table 2.

  FIG. 3 shows the relationship between the adhesive strength and the maximum fluidity (MF) of the Gisela plastometer, and FIG. 4 shows the relationship between the total expansion rate (TD) measured with a dilatometer. In the figure, the legend “coal” indicates that a sample of coke from a single brand of coal is used, and “mixed coal” indicates that a sample of coke prepared by mixing multiple brands of coal is used. 3 and 4, it can be seen that although there is some correlation between the adhesive strength and MF and TD, they are not exactly the same index.

  As shown in the results, the method of the present invention is applicable not only to the adhesion of a single brand of coal but also to the evaluation of the adhesion of multiple brands. For example, in Table 2, although the bond strength of B coal is 105 MPa and the bond strength of I coal is 107 MPa, the bond strength of B coal-I coal is 35 MPa at the interface between B coal and I coal. It shows that the adhesive strength is low, and it can be seen that the adhesion between different carbon types can also be evaluated.

  In addition, coals A, B, and C in Tables 1 and 2 are coals with poor caking properties that cannot obtain good coke by dry distillation by a normal method, and are used for indirect tensile tests of conventional methods. The sample could not be prepared by cutting it from coke. The method of this invention has the outstanding point that evaluation is possible even if it is such a low caking coal.

DESCRIPTION OF SYMBOLS 1 Refractory 2 Heating body 3 Container for dry distillation 4 Powder coke 5 Measurement sample

Claims (1)

Coal that has been finely pulverized to 75 μm or less is compression-molded into a cylindrical shape at a pressure of 14 MPa or more and 20 MPa or less, subjected to dry distillation under an inert atmosphere and coked, and the pressure is applied in the thickness direction of the measurement sample. A method for measuring the adhesive strength of coal for coke production, characterized in that the adhesive pressure is the pressure at the time of destruction.