JPH07102260A - Production of formed coke - Google Patents

Abstract

PURPOSE:To make it possible to prevent the internal cracking of formed coke, by carbonizing formed lump coal at a heating rate specified for each of the temperature ranges, i.e., up to a softening or melting initiating temperature, then up to a resolidification completing temperature, and thereafter, with these temperatures being obtained from the volatile matter content of caking coal component. CONSTITUTION:A lump coal obtained by mixing coal blend comprising a noncaking coal and a caking coal with caking additives and press molding the mixture is carbonized according to a heat pattern of the following conditions. The heating rate is 5-15 deg.C/min up to the softening initiating temperature of the caking coal in the coal blend, given by formula I or II, at most 2 deg.C/min then up to the resolidification completing temperature thereof given by the formula III or IV, and at most 25 deg.C/min thereafter. In the formulas, VM is the volatile matter content (wt.%) of the caking coal in the coal blend. By providing the period during which the heating rate is maintained at most 2 deg.C/min, the occurrence of internal cracking of formed coke product is greatly reduced, the yield is improved, and a blast furnace coke with good strength and little occurrence of fine powder is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a molded coke usable in a blast furnace.

[0002]

BACKGROUND OF THE INVENTION Blast furnace coke functions as a reducing material, a heat source, and a supporting material for maintaining air permeability, and is essential in the blast furnace ironmaking method. In particular,
In order for the blast furnace coke to function as a breathable holding material, the strength to withstand the load from the furnace interior contents and
Abrasion resistance is required to minimize the amount of fine powder that causes deterioration of air permeability.

In order to produce a coke having such a high strength, it is necessary to have a strong coking coal in a certain proportion or more in the raw material coal. However, the production of strong coking coal has regional, quantitative, and price restrictions, and it is expected that resources will be exhausted in the near future. In addition, in the existing coke ovens, it has been pointed out that the environment has a bad influence due to deterioration of sealing property due to long-term use.

Against the background of such circumstances, a binder coal such as pitch, asphalt, tar, etc. is added to a blended coal which is a mixture of non-caking coal and caking coal, the mixture is pressure-molded, and the mixture is dry-distilled into coke. The so-called molded coke, which is used as a product, is being tested on a trial basis. For example, a method for producing molded coke is described in Trans ISIJ, Vol 23 (1983) P.700-709. According to it, a roll type briquette forming machine was used, coal tar pitch was used as a binder, and apparent density, 1180-1210 kg / m ³ , bulk density, 673
Molded coke of about kg / m ³ is obtained.

However, the conventional forming coke production method using the above-mentioned example as an example is as follows: (1) The original yield on the outlet side of the carbonization furnace (the forming coke can be obtained without breaking, fusing, or deforming). The problem was that the ratio was low. The cause of this is that destruction due to thermal stress during carbonization, blistering due to expansion at the time of softening and melting, and mutual fusion and formation of pseudo clusters.

In order to solve these problems, attention has been paid to changes in the physical properties of coal during carbonization, and the following improvement methods have been proposed. For example, in Japanese Patent Laid-Open No. 54-156007, as a heat pattern when carbonizing agglomerated coal, the maximum temperature gradient inside the agglomerated coal ([agglomerated coal surface temperature-agglomerated coal central temperature] / agglomerated coal) It discloses a method of preventing the original yield rate and strength of a molded coke from lowering due to thermal strain by setting the shortest distance between the center of the coal and the surface) to 15 ° C / mm or less.

However, in this method, a large number of cracks remain, and due to the volatile content of the blended coal constituting the agglomerated coal, the maximum temperature gradient value of 15 ° C./mm is obtained in a certain temperature range of the carbonization heat pattern. Even if the heat pattern including the above temperature gradient is used, a high original yield and strength may be obtained in some cases. Furthermore, various particle sizes charged into a carbonization furnace, the surface temperature and center temperature of the agglomerated coal having a forming structure of blended coal, and the shortest distance between the agglomerated coal center and the surface are measured,
It was almost impossible to operate so that most of the temperature was kept below the maximum temperature gradient value from the viewpoint of field operation management.

Further, Japanese Patent Publication No. 60-12389 discloses a heat pattern for carbonization of agglomerated coal as a heat pattern when the temperature of the agglomerated coal is 200 ° C. to 600 ° C. The upper and lower limits are set for the speed, and the core temperature of the agglomerated coal is
By using a heat pattern with a predetermined upper limit value different from the above in the range of 600 ° C or higher, it is possible to prevent blistering and cracking in the temperature range of 500 ° C or lower and to shrink the semi-coke in the temperature range of 500 ° C or higher. This is a method of preventing the generation of cracks and heat cracks associated with

However, in the present invention, the volatile content of the caking coal constituting the agglomerated coal is not taken into consideration, and even when the agglomerated coal is dry-distilled by using the heat pattern in the present invention, X-rays are emitted. As a result of observing the inside of the formed coal during carbonization using it, as a result, although the original yield can be improved, a large crack is generated inside, and these cracks are generated until the forming coke is charged into the blast furnace. In the case of handling, it was a starting point of cracking of the molding coke, which sometimes lowered the usable product yield of the molding coke before the blast furnace.

[0010]

DISCLOSURE OF THE INVENTION The present invention solves the above problems and controls the temperature rising cycle in accordance with the volatile content of the blended coal constituting the agglomerated coal, thereby providing the agglomerated coal. Blistering cracks, cracks and heat cracks that occur during carbonization of the carbon dioxide are prevented, the yield of the original shape on the outlet side of the carbonization furnace is improved, and even if the forming coke is handled until it is charged into the blast furnace, it is difficult to crack, and the yield in front of the furnace is reduced. It is an object of the present invention to propose a method for producing a molded coke that does not contain coke.

[0011]

[Means for Solving the Problems] That is, the present invention provides a method for dry-distilling agglomerated coal prepared by mixing a coal blending mixture of non-caking coal and caking coal and a binder to dry-blend the mixture. The heating rate of the agglomerated coal is 5 to 15 ° C / min until the softening and melting start temperature of the caking coal component in the coal given by the following formula (1) or (1 '), and then in the blended coal The agglomerated coal is dry-distilled according to the heat pattern of the heating temperature of 2 ° C./min or less until the re-solidification end temperature given by the following formula (2) or (2 ′) of the caking coal component of It is a method for producing a molded coke, which comprises carrying out dry distillation at a heating rate of 25 ° C./min or less.

Softening / melting start temperature: T (° C) = -8.8VM (%) + 632 (16≤VM≤32) ... (1) T (° C) = 350 (32≤VM) ... (1 ') Resolidification end temperature: T (℃) = 4.0VM (%) + 428 (16 ≦ VM ≦ 26) ・ ・ ・ ・ (2) T (℃) = -7.5VM (%) + 727 (26 ≦ VM ≦ 37) ··· (2 ′) where VM is the volatile content (weight) of the caking coal component in the blended coal.
%).

[0013]

The present inventors have agglomerated coal which is obtained by pressure-molding blended coal containing caking coal as a main component and having various volatile contents, and various volatile contents containing non-caking coal as a main component. The following findings were obtained by dry distillation of pressure-molded agglomerated coal in which blended coal and a binder were mixed while observing X-rays with various heat patterns.

(1) Generally, when coking carbon for coke production is simply carbonized (heated by shutting off air), 100 ° C.
Up to the time when water vaporizes, methane and its homologues and stored gas are released. From 100 ℃ to 300 ℃, there is almost no change except that it releases the water of crystallization contained in the minerals contained in coal and a small amount of gas stored in coal.

(2) When the temperature exceeds 300 ° C., thermal decomposition of the essence of coal begins, gas, compound water, and tar are rapidly generated, and caking coal such as bituminous coal softens and melts to exhibit an expansion phenomenon. After that, the softening / melting phenomenon accompanied by gas decomposition is greatly changed depending on the coal-containing volatiles, and almost shrinks and solidifies (called resolidification) at about 500 ° C or later.
And becomes a semi-coke having a porous mass.

(3) Further, due to the subsequent temperature rise, decomposition gas is generated, and at around 700 ° C., decomposition gas mainly containing hydrogen is generated while further solidifying and contracting. (4) When the volatile components in coal differ, the starting temperature of re-solidification temperature and the amount of shrinkage differ greatly. (5) In forming coke, the decrease in caking property due to the incorporation of non-caking coal, that is, the decrease in coke strength can be improved by increasing the density by increasing the pressure applied during agglomerated coal forming.
In other words, coke having a high strength and few cracks can be produced, which is as good as the coke of the chamber furnace because of the increase in the caking property due to the high density of the blended coal even if the caking property is small.

(6) At this time, the proportion of coking coal in the blended coal should preferably be 20% by weight or more. (7) The softening and melting start temperature of agglomerated coal is related to the amount of volatile components of the coking coal component in the blended coal, and the following (1) or (1 ')
It was confirmed to be expressed by the formula. T (℃) = -8.8VM (%) + 632 (16 ≦ VM ≦ 32) ・ ・ ・ ・ (1) T (℃) = 350 (32 ≦ VM) ・ ・ ・ ・ (1 ') where VM Is the volatile content (weight) of the caking coal component in the blended coal.
%).

(8) In the softened and melted agglomerated coal, coal particles encased in the melt are joined to each other to form a nodule, and volatile components are separated from the nodule to form semi-coke. At that time, shrinkage of the nodule occurs, and depending on the viscosity of the melt covering the nodule and the amount of volatile matter generated from the nodule, fine pores after the volatile matter has been dispersed are left in the coke after solidification. , Cracks may occur. This is called the resolidification end temperature.

(9) It is confirmed that the resolidification end temperature of the agglomerated coal is related to the amount of volatile components of the coking coal component in the blended coal and is represented by the following formula (2) or (2 '). Was done. T (℃) = 4.0VM (%) + 428 (16 ≦ VM ≦ 26) ・ ・ ・ ・ (2) T (℃) = -7.5VM (%) + 727 (26 ≦ VM ≦ 37) ・ ・ ・ ( 2 ') where VM is the volatile content (weight) of the caking coal component in the blended coal.
%). (10) When the heating rate of agglomerated coal is 2 ° C / min or less, the resolidification end temperature of the surface layer and center The resolidification end temperatures of the parts do not substantially differ from each other, and therefore the resolidification end temperature as a whole can be said to be the temperature described by the above formula (2) or (2 '). (11) Further, a decomposition gas is generated by the subsequent temperature rise, and a decomposition gas mainly containing hydrogen is generated at around 700 ° C. while further solidifying and contracting. (12) Mixing blended coal and a binder with non-caking coal and caking coal, and dry-distilling the pressure-formed agglomerated coal causes internal cracks in the mechanism described later. Since it is not possible to judge by appearance, it is brought into the subsequent process with internal defects and causes damage during handling or in the blast furnace. (13) As a result of carrying out the X-ray observation carbonization experiment described above, it was found that these fractures and internal cracks can be prevented by heating at a constant low heating rate from the beginning, but the bond strength between coal grains is low. Moreover, the dry distillation time becomes long, which is not suitable for practical use.

Further, the inventors of the present invention have clarified the mechanism of internal crack generation by observing the inside of the formed coal during carbonization using X-rays and performing thermal stress calculation simulating carbonization. We have found a heat pattern that prevents internal cracking without taking excessive carbonization time. That is, the details will be described below. (1) As shown schematically in FIG. 1, the heat pattern in the present invention has a predetermined temperature rise before and after a section in which the heating temperature is kept at 2 ° C./min or less. It has speed.

(2) First, the relationship between the rate of temperature rise from the softening and melting start temperature to the re-solidification end temperature and the rate of cracks occurring inside the briquette charcoal obtained from the X-ray observation experiment during carbonized carbon dry distillation As shown in FIG. The softening start temperature of the caking coal component in the blended coal used is about 414 ° C, and the resolidification end temperature is about 527 ° C. (3) From this, if the section where the heating temperature is kept at 2 ° C / min or less is set to the softening melting start temperature and the resolidification ending temperature of the caking coal component in the blended coal, the occurrence rate of internal cracks is greatly reduced.

(4) Further, the mechanism of this phenomenon will be explained by calculating thermal stress simulating carbonization by generating thermal cracks and strains inside the agglomerated coal with the progress of carbonization. it can. (5) That is, as shown in FIG. 3 as an example of crack generation, as the carbonization progresses, each point of the agglomerated coal shrinks toward the center with re-solidification, and the compressive stress becomes closer to the center,
The closer to the surface, the higher the tensile stress. The strain is
The amount of shrinkage strain increases at any position, but elongation strain occurs when resolidifying at each point.

(6) This elongation strain is generated because the deformation becomes non-uniform due to the increase in rigidity due to re-solidification, and the elongation extends in the direction of the smallest rigidity. When the matrix phase yields during this process, when the heating rate decreases or the heating temperature becomes constant, the plastic strain around the plastic deformation portion causes the thermal strain due to the decrease in the temperature gradient. It is interpreted that deformation that eliminates non-uniformity is hindered and tensile stress occurs inside.

(7) In brittle materials such as agglomerated coal or coke, the tensile strength is about an order of magnitude lower than the compressive strength, and the internal cracks obtained by an internal observation experiment of formed coal during carbonization by X-ray. Since the time of occurrence coincides with the time of occurrence of the internal tensile stress, the above tensile stress causes internal cracking or fracture. (8) Considering the underlying cause of this tensile stress, it is due to plastic deformation when the softening / melting phase re-solidifies,
It can be seen that this is due to the decrease in the temperature gradient after that, and further back in time there was a large temperature gradient in the resolidification temperature range. That is, the tensile stress can be prevented from occurring by setting the temperature of the entire briquette to a substantially uniform temperature before it is resolidified so that the resolidification is performed without a temperature gradient.

Based on the above findings, the present invention has been completed. That is, the heating rate in a temperature range lower than the softening and melting start temperature defined by the above formula (1) or (1 ') must be set to a certain value or more in order to obtain an appropriate binding force between the formed coal grains. However, it is necessary to make a uniform temperature distribution before the start of re-solidification, and a specific heating rate is approximately 5 to 15 ° C / min, although it depends on the shape of the forming coal.

Then, thereafter, the above (2) or (2 ')
Refrain from raising the temperature until the re-solidification end temperature specified by the formula, 2
It is effective to prevent the occurrence of cracks at a temperature of ℃ / min or less. Furthermore, after re-solidification is completed, there is no plastic strain inside, and since an excessive temperature gradient does not occur due to the rapid increase in thermal conductivity associated with coking, there is no effect on the occurrence or fracture of internal cracks. The heating rate can be increased and the dry distillation time can be shortened. However, even at that time, if the temperature exceeds 25 ° C./min, the solidification shrinkage that occurs at around 700 ° C. becomes too rapid and cracks occur.
Therefore, the rate of temperature increase after the resolidification end temperature is limited to 25 ° C./min or less.

[0027]

【Example】

(Example 1) A dry distillation experiment was carried out on the 70 × 60 × 35 mm pillow-shaped forming coal shown in FIG. The composition of coking coal is non-caking coal:
23% by weight, caking coal: 77% by weight, volatile content of caking coal: 24.8
% By weight, ash: 9.2% by weight. In this composition, the softening start temperature is 414 ° C and the resolidification end temperature is 527 ° C.
The forming coal was formed by the twin roll method, and the dry distillation was performed for each forming coal in a nitrogen gas atmosphere. The carbonized coal was irradiated with X-rays during carbonization, and the state of internal cracks was observed from the transmission image. The heat pattern is as follows: charging the forming coal at an ambient temperature of 350 ° C, and rapidly heating it up to 350 ° C at a heating rate of practically a maximum of 15 ° C / min, then increasing the temperature to 5 ° C / min up to 414 ° C. After that, the temperature was raised to 527 ° C at 1.0, 1.5, and 2 ° C / min, and further increased to more than 527 ° C and 1120 ° C at 20 ° C / min. For comparison, the heating rate from 414 ° C to 527 ° C was changed to 3.0, 4.0 and 5.0. Table 1 shows the internal crack generation state during carbonization and the fracture rate after carbonization.

[0028]

[Table 1]

(Example 2) Non-caking coal: 50% by weight, caking coal: 50% by weight, volatile content of caking coal part: 30.2% by weight, ash content: 11.0% by weight. In this composition, the softening and melting start temperature is 366 ° C, and the resolidification end temperature is 549 ° C. The forming coal was formed by the twin roll method, and the dry distillation was performed for each forming coal in a nitrogen gas atmosphere. The carbonized coal was irradiated with X-rays during carbonization, and the state of internal cracks was observed from the transmission image.
The heat pattern is as follows: charging coal with an ambient temperature of 350 ° C, rapid heating up to 350 ° C at a maximum heating rate of 15 ° C / min, and then heating up to 366 ° C at 5 ° C / min. After that, the temperature was raised to 549 ° C at a rate of 1.5 and 2 ° C / min, and further increased to more than 549 ° C to 1120 ° C at 20 ° C / min. For comparison, the heating rate from 366 ℃ to 549 ℃ was changed to 3.0 ℃ / min. Table 2 shows the internal crack generation state during carbonization and the fracture rate after carbonization.

[0030]

[Table 2]

From the above, the molded coke obtained by dry distillation using the heat pattern of the present invention has a high yield in the original shape and has a very low probability of including internal cracks. It has been found that the deterioration and the generation of powder can be prevented, and problems such as ventilation, obstruction of liquid permeability, and furnace core inactivity can be avoided.

[0032]

EFFECTS OF THE INVENTION According to the present invention, it is possible to prevent the generation of tensile stress in the inside during the carbonization of the formed coal to prevent the reduction of the original yield on the discharge side of the carbonization furnace, and also to suppress the generation of the internal cracks, thereby charging the blast furnace. It became possible to prevent the particle size reduction before and in the blast furnace.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a heat pattern of the present invention.

FIG. 2 is a diagram showing a relationship between a holding temperature and a ratio of cracks generated inside the briquette.

FIG. 3 is a schematic diagram showing a thermal stress analysis result inside a formed coal during carbonization.

FIG. 4 is a schematic diagram showing a 70 × 60 × 35 mm pillow-shaped forming coal.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Mikiharu Takeda 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Technical Research Division (72) Inventor Hiroshi Itaya, Kawasaki-cho, Chuo-ku, Chiba Kawasaki Steel Corporation Technical Research Division

Claims (1)

[Claims] 1. When carbonizing agglomerated coal, which is obtained by mixing a coal blending mixture of non-caking coal and caking coal and a binder, and subjecting the coal to pressure-molding by carbonization. (1) or (1 ')
Up to the softening melting start temperature given by the formula, the heating rate of the agglomerated coal is set to 5 to 15 ° C / min, and then, by the following formula (2) or (2 ') of the caking coal component in the blended coal. Molding characterized by dry-distilling the agglomerated coal according to a heat pattern that keeps the heating temperature at 2 ° C / min or less up to a given re-solidification end temperature, and thereafter at a heating rate of 25 ° C / min or less Coke manufacturing method. Softening start temperature: T (℃) = -8.8VM (%) + 632 (16 ≦ VM ≦ 32) ・ ・ ・ ・ (1) T (℃) = 350 (32 ≦ VM) ・ ・ ・ ・ (1 ' ) Resolidification end temperature: T (℃) = 4.0VM (%) + 428 (16 ≦ VM ≦ 26) ・ ・ ・ ・ (2) T (℃) = -7.5VM (%) + 727 (26 ≦ VM ≦) 37) ··· (2 ′) where VM is the volatile content (% by weight) of the caking coal component in the blended coal.
Is.