JP5011833B2 - Coke manufacturing method - Google Patents

Description

  The present invention relates to a method for producing high-quality coke used in a blast furnace.

  The metallurgical coke used in the blast furnace plays an important role chemically as a heat source for melting iron ore and as a reducing agent for reducing iron oxide to metallic iron. It also plays an important physical role in ensuring the liquid permeability of the melt. In particular, in order to stably carry out large-scale blast furnace pulverized coal injection operation, high brewing ratio operation or low reducing material ratio operation in blast furnace in recent years, the strength of coke is high, the particle size is difficult to decrease, so-called high quality Coke is becoming essential. Therefore, development of a technique for producing such high quality coke is strongly desired.

  To produce high-strength coke that is difficult to be pulverized in a blast furnace, the properties of the coal blended with various types of coal, such as average maximum reflectance (Ro) and maximum fluidity (MF), are charged into the coke oven. Raising is the simplest method. However, high quality coals with large Ro and MF are becoming increasingly difficult to obtain with the depletion of coal resources, and are expensive, so there are significant restrictions in terms of cost.

  Therefore, it has been considered to reduce the cost by using inexpensive non-coking coal as a part of the blended coal. However, since the non-slightly caking coal is of low quality (such as low MF), when the blending ratio of the non-slightly caking coal is increased, the coke strength is greatly lowered and cannot be practically used. Therefore, development of a technique capable of obtaining high-strength coke even when low-quality non-coking coal is used as blending coal has been performed.

  As a technique for producing high-quality coke while using inexpensive and low-quality coal for blending, a method for controlling the particle size of coal to be blended is known. For example, in Patent Document 1, a plurality of brands of coal are divided into three groups of low-reflectivity non-slightly caking coal, high-reflectivity non-slightly caking coal, and caking coal having different coking properties. A technique is disclosed in which coke oven charging coal having a predetermined particle size distribution is obtained by pulverizing into different particle size distributions according to the properties and mixing, and using this, low cost and high strength coke is obtained. Further, in Patent Document 2, when coke is produced by dry distillation of coal blended with caking coal and non-slightly caking coal, the strength of the non-slightly caking coal is set to 3 mm or less and 100%. A technique for obtaining coke having a low bulk density and excellent air permeability without lowering the temperature is disclosed.

On the other hand, in Patent Document 3, in the production of metallurgical coke, the coke strength is increased and the particle size is controlled by adding finely pulverized coke whose particle size has been adjusted in advance to the raw material coal in accordance with the target coke particle size. Technology is disclosed.
JP 2001-181650 A Japanese Patent Laid-Open No. 11-021561 Japanese Patent Application Laid-Open No. 60-069193

  Certainly, the techniques described in Patent Document 1 and Patent Document 2 enable the production of coke having the same level of strength as that of conventional coke even if low quality non-coking coal is used. Also, by using the method described in Patent Document 3, a certain degree of improvement in coke strength can be expected. However, the above-described technology alone cannot sufficiently meet the current demand for producing higher strength coke at a lower cost.

  Accordingly, an object of the present invention is to solve such a problem of the prior art and propose a coke production method capable of producing high quality, particularly high strength coke at low cost.

  In order to solve the above-mentioned problems, the inventors pay attention to the relationship between the structure of coke obtained by dry distillation of the blended coal mainly composed of conventional caking coal and the particle size of the low-quality coal to be blended. We studied earnestly. As a result, the low volatile content non-coking coal that forms a structure having a mechanical property value different from that of the coke structure obtained from the conventional blended coal is made smaller than the pore wall thickness of the coke structure. The present inventors have newly found that the strength of coke can be improved as compared with the prior art by mixing and dispersing, thereby completing the present invention.

That is, the present invention is a method for producing coke by dry distillation of blended coal. In this blended coal, the Geeseler maximum fluidity MF is 0 to 10 ddpm, the volatile content is 20 mass% or less , and the pore wall thickness of the coke structure or less. And a low volatile content non-slightly caking coal (excluding “anthracite”) obtained by pulverizing 0.15 mm or less to a particle size of 95 mass% or more .

  Moreover, the addition amount of the said low volatile matter non-slightly caking coal in this invention is 0.5-10 mass% with respect to all the coal blends, It is characterized by the above-mentioned.

  According to the present invention, low-quality and inexpensive low-volatile non-coking coal is used as a raw material for coke and a part of some blended coal, so that the quality (high strength) is higher than that of conventionally produced coke. Coke can be provided at low cost. In addition, since the coke of the present invention has higher strength than conventional coke, when it is used in a blast furnace, the air permeability in the blast furnace is sufficiently ensured and greatly contributes to stable operation of the blast furnace.

  The inventors use low-quality, low-volatile non-slightly caking coal as part of the coal blend used as a raw material for coke, rather than coke produced from conventional coal blends mainly composed of caking coal. We studied repeatedly to develop a technology to produce high strength and cheap coke. As a result, the low volatile content non-slightly caking coal that forms a structure having a mechanical property value different from that of the coke structure obtained from the conventional caking coal is dispersed to be smaller than the thickness of the pore wall of the coke structure. As a result, it was newly found that the coke strength can be greatly improved as compared with the conventional one.

  In other words, when a structure derived from low volatile content non-slightly caking coal with different physical properties is dispersed in a coke structure derived from conventional caking coal, stress concentration occurs at the interface between these structures. The stress applied to other pore wall portions is relieved. Further, when the boundary surface is small and dispersed, the pore wall is less likely to be destroyed due to stress concentration on this portion.

  In addition, a blended coal in which a low volatile non-slightly caking coal is dispersed smaller than the pore wall thickness in a blended coal consisting of a conventional caking coal has a complete slurry state during softening and melting in the dry distillation process. Since it becomes easy to form, the apparent viscosity of the softened material increases and the gas permeation resistance increases. As a result, the gas pressure of the pores formed in the softened melt is increased, the pressure between the softened melts is increased, and the coke strength is improved.

  On the other hand, when the particle size of the non-slightly caking coal to be added is relatively large with respect to the pore wall thickness, the caking coal-derived structure and the pore wall portion become the same size, A large thermal stress is generated at the interface between the structure derived from caking coal and the structure derived from non-slightly caking coal, and defects having a size that reduces the strength of the pore walls are generated.

  Further, as the particle size of the non-slightly caking coal to be added becomes relatively large with respect to the pore wall thickness, the gas-solid-liquid dispersion system at the time of softening and melting in the dry distillation process becomes a funicular state or a capillary state. The effect of increasing the gas pressure in the pores like the state cannot be expected. As a result, the coke strength decreases.

  Therefore, in order to obtain high-strength coke, it is necessary to make the particle size of the low-volatile non-slightly caking coal to be added smaller than the average pore wall thickness of the coke, and relative to the pore wall thickness. The smaller the value, the greater the effect of addition.

  Here, the average pore wall thickness of the coke is the distance between the pores formed in the coke structure. Specifically, the image when observed with a microscope of the coke structure is binarized and separated into pores (white background) and coke matrix (black background), and this binarized image is equidistantly spaced. A measurement line is drawn, and all pore-to-pore distances on the line are image-processed and measured, and the average value of these measured values is defined as the average pore wall thickness.

  In addition, the low volatile matter non-coking coal in the present invention has a Gieseller maximum fluidity MF in the range of 0 to 10 ddpm (dial division per minute) and a volatile content of 20 mass% or less on a dry (anhydrous) basis. Means things. Here, the Gieseller maximum fluidity MF is one of the indexes representing caking properties, and its measuring method is defined in JIS M8801. The measurement method of volatile content is defined in JIS M8812.

The reason why the MF is limited to the range of 0 to 10 ddpm is that, when the MF of coal including non-slightly caking coal increases, as shown in FIG. 1, the expansion of coal particles is recognized. This particle expansion is a phenomenon that occurs because the internal pores become large. As a result, the wall thickness of the pores centering on the particles becomes small, which causes a decrease in strength. Therefore, the MF range should be about 10 ddpm or less where the coal particles do not expand. On the other hand, MF is preferably as low as possible, and most preferably 0. In addition, although the coal of MF = 0 is also called non-caking coal, in this invention, the thing of the range whose MF is 0-10 ddpm is called non-caking coal.

  The reason for limiting the volatile content to 20 mass% or less on a dry (anhydrous) basis is that the amount of pores formed in the coke increases as the volatile content increases. The probability of connection increases and relatively large pores are formed, causing a decrease in strength. Therefore, 20 mass% was defined as the upper limit of the volatile content that hardly causes pores to be connected.

  In addition to the low volatile content non-slightly caking coal, the materials that can be blended in the coal blend that will be the raw material for coke are carbon materials coke, high volatile content coal, and caking coal pulverized. However, since the same effect is exhibited, it can be used. However, fine coke has little difference in mechanical properties with the surrounding tissue, so the effect of improving coke strength is small. In addition, the pulverized highly volatile coal has a high probability that the gas remains in the pore wall, and thus the effect of improving the coke strength is small. In addition, the pulverized caking coal only increases the raw material cost.

  Moreover, when aiming only at the improvement of coke strength, fine powders such as metals and oxides of inorganic materials may be added to the blended coal. However, components other than carbon become slag in the blast furnace, and increase the reducing material ratio of the blast furnace. Therefore, it is desirable to use a material having a high carbon content as a material to be blended in the blended coal, which is the reason why the present invention pays attention to low volatile content non-coking coal.

We conducted a test to produce coke by dry distillation of blended coal (base coal) that is a raw material for coke and blended with low volatile non-finely caking coal with different particle sizes in the outer frame, and the non-fine effect on coke strength The effect of caking coal particle size was investigated. In the above test, a base coal adjusted to have Ro = 1.05 and MF = 200 was used. Coal A having the properties shown in Table 1 was pulverized and sized to the base coal. The particle size is divided into five water orders of 0.075 to 0.15 mm, 0.15 to 0.30 mm, 0.30 to 0.50 mm, 0.50 to 0.71 mm and 0.71 to 1.00 mm. And what added 3% by the outer frame was used for the blended coal. In addition, the industrial analysis value (ash content, volatile content) in Table 1 is a value measured according to JIS M8812, and the Gieseler maximum fluidity MF is a value measured according to JIS M8801. The base charcoal had an average pore wall thickness of a coke structure obtained by dry distillation of 0.24 mm.
The dry distillation test was performed using an electric furnace capable of simulating an actual coke oven, and the filling conditions at this time were constant conditions of moisture: 8% and charged bulk density: 750 kg / m ³ . The quality of the obtained coke was evaluated by measuring a crushing strength 15 mm index (DI ¹⁵⁰ ₁₅ ) at 150 revolutions using a drum test method defined in JIS K2151.

  The results of the evaluation test are shown in FIG. From FIG. 2, the strength of coke decreases with the addition of non-slightly caking coal, but the amount of decrease in coke strength decreases as the particle size of non-slightly caking coal to be added decreases. It can be seen that when the thickness is 0.15 mm or less, which is smaller than the average pore wall thickness, a material having higher strength than coke obtained from base charcoal is obtained.

Ro = 1.00, MF = 631 It is adjusted to be constant, and a base charcoal having an average pore wall thickness of 0.24 mm obtained when coke is used. The base charcoal has a particle size of 0.075 mm or less. Coke is produced using coal blended with 5 mass%, 10 mass% and 20 mass% of coal A shown in Table 1 added to the outer frame, and the blending amount (addition rate) of low volatile non-coking coal is The effect on coke strength was investigated. At this time, coal was charged into the electric furnace under the same conditions as in Example 1 except that the moisture was 8% and the charging bulk density was 800 kg / m ³ .

  The results of the evaluation test are shown in FIG. From FIG. 3, the coke strength is affected by the addition rate even when the particle size of the non-slightly caking coal is adjusted to be equal to or less than the average pore wall thickness, and the coke strength increases when the addition rate is 10 mass% or less, but 10 mass%. On the other hand, it can be seen that the coke strength starts to decrease.

Coke raw coal obtained by adding 5 mass% of non-slightly caking coal obtained by pulverizing coals A and B shown in Table 1 to a particle size of 0.075 mm or less to the same base coal as used in Example 2 with an outer frame. The production of coke was carried out in the same manner as in Example 1 except that the use and the filling of the coal into the electric furnace were constant conditions of moisture: 8% and charging bulk density: 800 kg / m ^3. The effect of the type (quality) of low-volatile non-slightly caking coal on coke strength was investigated.

  The results of the evaluation test are shown in FIG. From FIG. 4, both Coal A and Coal B have the effect of improving the coke strength, that is, the type (quality) of non-slightly caking coal if it is a low volatile matter non-slightly caking coal according to the conditions of the present invention. Regardless, it was confirmed that there is an effect of improving the coke strength as compared with the base charcoal.

  The technique of the present invention is not limited to the production of high-quality (high strength) metallurgical coke, but can also be applied to the field of porous composite materials such as ceramics.

It is a graph which shows the relationship between the maximum fluidity MF and the maximum expansion coefficient TD. It is a graph which shows the influence which the particle size of the low volatile matter non-finely caking coal mix | blended with base charcoal exerts on coke crush strength. It is a graph which shows the influence which the addition rate of the low volatile matter non-slightly caking coal mix | blended with base charcoal has on coke crush strength. It is a graph which shows the influence which the kind (property) of the low volatile matter non-fine caking coal mix | blended with base charcoal has on coke crush strength.

Claims (2)

In the method of producing coke by dry distillation of blended coal, in this blended coal, the maximum Gieseller fluidity MF is 0 to 10 ddpm, the volatile content is 20 mass% or less , the pore wall thickness of the coke structure is 0.15 mm or less. A method for producing coke, characterized in that it contains low-volatile non-slightly caking coal (except “anthracite”), which is pulverized to a particle size of 95 mass% or more . The method for producing a coke according to claim 1, wherein the addition amount of the low volatile non-slightly caking coal is 0.5 to 10 mass% with respect to the total blended coal.

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