JP2003041263A - Method for estimating cold strength of metallurgical coke - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for simply estimating with high precision cold strength of coke by estimating a pore structure of coke, particularly a pore size distribution from the composition and the like of a blended coal, and by designing a formulation in consideration of this pore size distribution. SOLUTION: In the method for estimating cold strength of metallurgical coke obtained by dry distillation of a blended coal, cold strength of coke is estimated from the relations between the amount of pores of each pore size division, determined according to the estimated pore size distribution in the coke estimated by a discrete element method, and breakdown velocity of each grain size division of powders generated when coke undergoes abrasion or impact.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to the cold strength of a product coke under the composition of the coal blend when the coal blend obtained by blending a plurality of brands of raw coal is carbonized to produce a coke for metallurgy. We propose a method to estimate and use it as an effective method to feed back to the blending design of blended coal.

[0002]

2. Description of the Related Art As coke for metallurgy used in a blast furnace and the like, coke having stable quality such as strength, grain size and porosity is required from the viewpoint of stable operation of the blast furnace. Normally, blast furnace coke is produced by dry-distilling blended coal obtained by blending 10 to 20 brands of raw coal, and the coal used for the raw coal is the country of origin, coal mine,
Since the properties differ depending on the coal bed, etc., in order to produce coke of stable quality, the coke characteristics of the blended coal consisting of various raw material coals with different properties, especially the cold strength, are estimated and fed back to the raw material. It is essential to manage the mixture of charcoal.

Under such a background, conventionally, Japanese Unexamined Patent Publication No. Sho 57-57
Japanese Patent Laid-Open No. 144443 proposes a coke strength estimating method using a microstrength value representing coke porosity and pore wall strength. In addition, JP-A-4-132
In Japanese Patent Publication No. 792, a coke strength estimating method using a pore wall wear index and a porosity is proposed.

[0004]

Each of the above-mentioned prior arts is
Although each could be evaluated, there were still problems to be solved. For example, the method disclosed in JP-A-57-144443 is a technique for estimating coke strength using porosity and pore wall strength. However, the pore size of coke is not always limited to a certain size, and both large pore sizes and small pore sizes are mixed and distributed. The above method lacked consideration for this point because the estimation considering distribution was necessary. Also, in the method disclosed in Japanese Patent Laid-Open No. 4-132792, the influence of the pore size distribution is not considered at all. In other words, none of these methods could accurately estimate the coke strength because the influence of the pore size distribution was not considered at all.

Therefore, an object of the present invention is to overcome the above-mentioned problems of the prior art. In particular, the pore structure of coke, particularly the pore size distribution, is estimated from the composition of the blended coal, and this pore size is estimated. It is to propose a method for easily estimating the cold strength of coke with high accuracy by performing a mixture design considering distribution.

[0006]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the inventors have conducted extensive studies on coke pulverization characteristics, types of coking coal and their blending. as a result,
The inventors have found that there is a close relationship between the powder generated when the coke is subject to wear or impact and the pore structure of the coke, particularly the pore size distribution, and have developed the present invention.

That is, the present invention is a method for estimating the cold strength of coke produced by dry distillation of blended coal, in which the pore structure in the coke is estimated by the discrete element method and is determined according to the estimated pore structure. Coke for metallurgy characterized by estimating the cold strength of coke from the relationship between the amount of pores in each pore size category and the fracture speed in each particle size category of powder generated when the coke is subject to wear or impact. It is a method of estimating the cold strength of.

Further, the present invention is manufactured by dry distillation of blended coal.
In the method for estimating the cold strength of
By the elementary method, the coarse air holes between coal particles and the inside of each coal particle
Pore size distribution consisting of intragranular pores formed between unit particles
Pore size, which is determined for each estimated pore size distribution
Porosity Por for each category_xAnd the coke is subject to wear and impact
Rate constant k for each particle size classification_xSeki
Estimate the cold strength of coke based on the formula below
Of cold strength of metallurgical coke characterized by
Method. Record TI₆= 100exp [-(k₁+ K_Two) S_At = 100exp [-(a_l+ B_lPor_l+ A_Two+ B_Two
Por_Two) × S_A× t] k_l= A_l+ B_lPor_l k_Two= A_Two+ B_TwoPor_Two Por_l: Coarse air hole Por_Two: Intragranular pore k₁, k_Two: Fracture rate constant a_l, A_Two, B_l, B_Two:constant S_A: Sphere equivalent surface area per unit mass of lump coke A t: rotation speed

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the first place, coke has a wide pore size distribution, and the pore size distribution greatly changes depending on the properties of the coal blend and the conditions of carbonization. Since the strength of coke is strongly influenced not only by the porosity but also by the size of the pore size in the coke, it is possible to accurately estimate the cold strength of coke by simply using only the porosity as the standard as in the past. You cannot do it. Therefore, in order to estimate the cold strength of coke, it is essential to obtain the pore structure of coke, that is, the pore size distribution.

Therefore, in the present invention, in estimating the cold strength of the coke, first, the pore structure of the coke produced by carbonization of the blended coal, particularly the pore size distribution, will be explained as follows. We decided to make an estimation by calculation using the discrete element method. Such a discrete element method considers coal particles to be an aggregate of minute unit particles, calculates the force acting on each minute unit particle, and calculates the movement of the minute unit particles at each minute time step, to obtain the coke after carbonization. This is a method for obtaining the pore structure. The unit particles are particles used in the calculation of the discrete element method.

In the calculation by the discrete element method, as the effect on each unit particle, the gas generation rate was defined as a function of the property of coal and the temperature, and the particle size reduction and the weight decrease due to the gas generation were considered. As the force acting on each minute unit particle, the pressure due to gas permeation, the adhesive force between unit particles, and the repulsive force were considered. Then, assuming the viscous fluid around the particle of interest, the moving distance of each unit particle was calculated. Here, the viscous resistance was given as a function of temperature and local porosity around the particle of interest.

However, in order to model the carbonization behavior of coke with a single particle size and to obtain the pore size distribution on the order of 1 μm to several mm, it is necessary to further calculate the size of a unit particle on the order of at least 0.1 μm. Required,
It is not practical because it requires a huge amount of calculation time and calculation cost. Therefore, the inventors of the present invention, as to the pore structure in the coke, were caused by poor fusion between coal particles due to insufficient fluidity of coal, as will be described later: several hundred μm order formed between coal particles The rough atmosphere pores and voids (hereinafter, simply referred to as "coarse atmosphere pores") and those formed in coal particles during melting: fine pores of the order of 0.1 μm will be considered separately. That is, the coal particles themselves are regarded as an aggregate of unit particles as shown in FIG.
By estimating the pore structure (intragranular pores) in the coal particles, while separately estimating from the coarse air holes and the like appearing between the coal particles, and then by summing these,
We decided to accurately estimate the pore structure of the entire coke in a short time.

For that purpose, for example, as shown in FIG.
Estimating the pore size distribution by dividing the pore structure of coke obtained by the discrete element method into meshes with a size of about 1/10 of the unit particle, and obtaining the maximum diameter that does not overlap the unit particles in each mesh. Is possible. The particle size of the unit particles may be any size as long as the average particle size is the above size, and may have a particle size distribution. Further, the pore size distribution was estimated by superposing unit particles of two sizes, but it is preferable to divide the unit particles into a larger number. Here, it is considered that it affects the cold strength of the coke,
The size of the coarse air holes and voids is about several 100 μm.
On the other hand, the size of the intragranular pores in the coal particles is on the order of several μm to several 100 μm.

The tumbler strength index TI (6/40) is generally used as an index representing coke dusting resistance.
0) is used. This index is 6 after 400 rotations
It represents the mass fraction of lump coke of mm or more. In addition, as an index showing coke dust resistance,
The drum strength index DI (15/150) is also used. These tests are an index (strength index) representing the amount of powder generated when the coke is subject to external wear or impact, that is, the resistance to pulverization.

For example, FIG. 2 shows the results of measurement of the particle size distribution of coke after 400 rotations after loading a coke of 50 to 75 mm in a tumbler strength tester. As can be seen from this figure, the particle size distribution of the lump coke is about 10
It can be seen that two-component property is exhibited with the vicinity of mm as the boundary. It is considered that this is due to volume breakdown on the coarse grain side and surface breakdown on the fine grain side. The tumbler strength index T1 (6/400) can be regarded as an index representing the surface destruction. Therefore, in order to estimate the tumbler strength index TI, it is necessary to estimate the degree of surface breakage of coke. Regarding such coke surface destruction, Litster et al. (Transac
tions ISIJ, Vol.26, 1986, p704-709).
According to the explanation, when an evaluation experiment of the surface breakage rate of various cokes having different qualities was carried out using the Mycam drum tester, the surface breakage of the coke was determined by the following equation (1). It is explained that it can be expressed by a crushing rate formula. dM / dt = -kM (1) M: Weight fraction on 1 mm sieve k: Breaking rate constant

The above report by Litster et al. Referred to a method of estimating the coke strength based on the relationship between the fracture rate constant k and the pore size distribution and coal properties, rather than the method of directly estimating the coke strength. Not a thing.
And, of course, it does not disclose that these relationships can be used for coal blending design.

On the other hand, in order to clarify the relationship between the above equation (1) of the surface fracture rate of the coke and the cold strength of the coke, the inventors of the present invention distributed the pore size of the coke and the occurrence of the coke during the strength test. The relationship of the particle size distribution of the powder was investigated. as a result,
It turns out that there is a close relationship between these. The results of experiments conducted to clarify these relationships will be described below. In addition, it can be said that this experiment verifies the surface breakdown rate equation (1), which is the premise of the present invention.

In the strength test, a normal method (tumbler strength test) and a 100-rotation method were carried out using the same sample. Tumbler strength test method (JI
SK 2151) is a block coke 10 of 50 to 75 mm.
+ 6m after 400 rotations by loading kg into the tester
The mass fraction of m coke of coke was expressed as TI (6/400). Further, in the 100-rotation method, as in the case of the normal method, 10 kg of lump coke of 50 to 75 mm was loaded into the test machine, and the mass fraction of lump coke of +6 mm was measured every 100 rotations to determine the total amount of powder and lump coke. Was reloaded into the testing machine and repeated until the total number of rotations reached 400. The results of this test are shown in FIG. As is clear from this figure, it was found that the tumbler strength index and the 100-rotation strength index are represented by the first-order surface breakage rate equation (1).

Next, the findings obtained from the results of the above experiments,
That is, in view of the fact that the surface breakage rate equation (1) is well-signed to the cold strength of coke, the mechanism of surface breakage of coke was further examined under the following two cases. Destruction between coal particles caused by coarse air holes formed between coal particles caused by poor fusion between coal particles due to insufficient fluidity of coal. Destruction of coal particles caused by micropores formed in the coal particles during melting. Assuming that the surface failure of coke considered in this way is modeled as shown in FIG. 4, and assuming that the failure factors are the same, it is assumed that the same surface failure rate constant k _x results in (1 ) Is expressed by the following (2)-
It can be expressed as in equation (4). Here, as the particle size classification, for example, the lump coke A is +6 mm, the powder coke B is 0.3 to 6 mm, and the powder coke C is -0.3 mm. It should be noted that the particle size classification should be at least 3 or more, and it is preferable to divide the particle size into a larger number. _{dW A / dt = - (k} 1 + k 2) S A W A ··· (2) dW B / dt = k l S A W A -k 2 S B W B ··· (3) dW C / dt _{= k 2 (S a W a} + S B W B) ··· (4) W a, W B, W C: mass _S a of each particle size component, _{S B:} sphere equivalent surface area per unit mass of each particle size component k _x : Failure rate constant t: Tumbler rotation speed

Further, if the above equations (2) to (4) are solved with the sphere-equivalent surface area per unit weight of each particle size component being constant, the weight fraction of each particle size component A, B, C The surface breaking rate constant k _x in the particle size component is obtained.
When these surface fracture rate constants k _x are used, the cold strength TI ₆ of the lump coke (A) is described in (5) below.
It becomes possible to express it like a formula. TI ₆ = 100W _A / W ₀ = 100exp [− (k ₁ + k ₂ ) S _A t] (5)

In the above description, the tumbler strength index is used as the coke strength.
This is not limited to tumbler strength only.
Further, as a matter of course, the present invention can be applied to the drum strength index, the Mycam strength index, and the like. For example, when applied to the commonly used drum strength index DI (15/150), it is common to use the +15 mm index after 150 rotations, but by appropriately setting the sieve mesh to 6 mm or the like. Can be applied to the present invention. In addition, although the commonly used sieve mesh of 6 mm is used here, 10 mm may be set as the upper limit if necessary.

Next, in the present invention, the relationship between the surface fracture rate constant k _x and the pore structure of coke, that is, the pore size distribution, was examined. It is considered that the fracture rate constant k _x is determined according to the pore diameter of the coke, and as a result, the particle size distribution of the generated powder is regulated. Therefore, the particle size distribution of the generated powder is divided into two, for example, +300 μm and −300 μm, the fracture rate constant k _x in each grain size is obtained, and the pore size corresponding to the fracture rate constant (for example, +200 μm and − 200 μm).

As shown in FIG. 5, the relationship between the fracture rate constant k _x and the pore volume Por _{x for} each pore diameter section is obtained, which can be expressed by the following equations (6) and (7). Substituting this result into the equation (5), the cold strength estimation equation TI considering the coke pore size distribution as shown in the following equation (8)
₆ is obtained. The porosity Por _x means the pore volume contained per unit weight of coke.

The particle size components in the formula: A, B and C, and the corresponding pore size classes may be designed by appropriately changing them based on the experimental results. _{k l = a l + b l} Por l ··· (6) k 2 = a 2 + b 2 Por 2 ··· (7) Por l: coarse pores (e.g. + 200μm) Por _2: intragranular pores (e.g. -200Myuemu) _{k 1,} k _2: breaking rate constants _{a l, a 2, b l} , b 2: constant _{S a:} per unit mass equivalent sphere surface area _TI 6 = 100exp of lump coke _{a [- (k 1 + k} 2) S a _{t = 100exp [- (a l} + b l Por l + a 2 + b 2 Por 2) × S A × t] ··· (8)

In this way, the cold strength of the coke can be estimated from the pore size distribution of the coke based on the above equation (8). The contents described in the specification of Japanese Patent Application No. 2000-124549 previously proposed by the inventors are effective for helping understanding of the present invention.

[0026]

EXAMPLE In this example, 15 representative types of coal (carbonization degree R _o : 0.75 to 1.65, maximum fluidity MF: 0.8 to
This is an attempt to estimate the tumbler strength by preparing plain coke of 4.3) and measuring the pore size distribution of each of these cokes.

FIG. 6 shows the relationship between the amount of pores estimated by the discrete element method and the measured amount of pores, and both have a good correspondence. Therefore, when the estimated value of the tumbler strength was obtained by the tumbler strength estimation equation TI ₆ shown in the equation (8) using the porosity estimated by the discrete element method, as shown in FIG. It was found that they were in good agreement, and the action and effect of the present invention were confirmed.

[0028]

As described above, according to the present invention,
It is possible to estimate the coke strength with high accuracy from the blending plan of this blending coal (charging coal) with a specific blending composition, so the blending design of the raw coal is easy and the estimation accuracy of the coke strength is improved. To do. Therefore, the use of inferior coking coal can be increased as the estimation accuracy increases. As a result, the cost of manufacturing blast furnace coke can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a pore structure in a particle calculated by a discrete element method.

FIG. 2 is a graph showing the particle size distribution of coke after a strength test.

FIG. 3 is a graph showing a change in +6 mm mass fraction of coke every 100 rotations.

FIG. 4 is a schematic diagram for explaining a model of surface destruction of coke.

FIG. 5 is a graph illustrating the relationship between the amount of pores in each pore segment and the fracture rate constant.

FIG. 6 is a graph showing the relationship between the pore volume estimated by the discrete element method and the pore volume actually measured.

FIG. 7 is a graph showing the relationship between the estimated value of tumbler strength calculated from the amount of pores propelled by the discrete element method and the actual measured value of tumbler strength.

Continued front page    (72) Inventor Tetsuya Yamamoto             Mizushima Kawasaki Dori, Kurashiki City, Okayama Prefecture (no address)             Kawasaki Steel Co., Ltd. Mizushima Steel Works (72) Inventor Seiji Sakamoto             Mizushima Kawasaki Dori, Kurashiki City, Okayama Prefecture (no address)             Kawasaki Steel Co., Ltd. Mizushima Steel Works (72) Inventor Ikawa Victory             Mizushima Kawasaki Dori, Kurashiki City, Okayama Prefecture (no address)             Kawasaki Steel Co., Ltd. Mizushima Steel Works F-term (reference) 4H012 LA00

Claims (2)

[Claims] 1. A method for estimating the cold strength of coke produced by carbonization of blended coal, wherein the pore structure in coke is estimated by the discrete element method, and the pore size classification is determined according to the estimated pore structure. Cold strength of coke for metallurgy, which is characterized by estimating the cold strength of coke from the relationship between the porosity of each and the breaking speed of each particle size classification of the powder generated when the coke is subject to wear or impact. Estimation method. 2. Cold coke produced by dry distillation of blended coal
In the method of estimating the strength between
Coarse air holes between coal particles and the shape between unit particles within each coal particle
The pore size distribution consisting of intragranular pores
Pore volume for each pore size category determined for each estimated pore size distribution
Por_xAnd when the coke is subject to wear or impact
Rate constant k for each particle size classification_xThe following formula showing the relationship with
It is characterized by estimating the cold strength of coke based on
Method for estimating cold strength of metallurgical coke. Record TI₆= 100exp [-(k₁+ K_Two) S_At = 10
0exp [-(a_l+ B_lPor_l+ A_Two+ B_TwoPor
_Two) × S_A× t] k_l= A_l+ B_lPor_l k_Two= A_Two+ B_TwoPor_Two Por_l: Coarse air hole Por_Two: Intragranular pore k₁, k_Two: Fracture rate constant a_l, A_Two, B_l, B_Two:constant S_A: Sphere equivalent surface area per unit mass of lump coke A t: rotation speed