JP5590071B2 - Manufacturing method of high strength coke - Google Patents

Description

  The present invention relates to a method for producing high-strength metallurgical coke mainly used in a blast furnace or the like in the field of steel production.

  Coke charged to the blast furnace plays an important role in ensuring the air permeability in the blast furnace, in order to achieve stable operation of large quantity of pulverized coal injection, high output ratio operation or low reduction ratio ratio operation. The use of high-quality coke is considered essential. Under such circumstances, there has been a strong demand for the development of a technology for producing high-strength coke with low pulverization in a blast furnace at low cost.

  As the properties of coal that affect the quality of coke, average maximum reflectance (Ro), maximum fluidity (MF), total expansion (TD), etc. are known. Conventionally, high strength coke is produced. As a method, it is common to use coal having excellent properties. However, in recent years, high quality coals with large Ro and MF (or TD) have become increasingly difficult to obtain due to depletion of resources and rising prices. Therefore, simply increasing the blending ratio of high-quality coal is problematic because it directly leads to an increase in coke production costs. Therefore, development of a technique for producing high-strength coke at low cost is desired.

  Conventionally, as a method of reducing the production cost of coke, there has been a method of using low-quality but inexpensive non-slightly caking coal as blending coal, for example, blending with high-quality coal. However, this method is a method of simply increasing the blending ratio of low-quality non-slightly caking coal, and has a limit because it causes a reduction in coke strength.

  For this reason, techniques for producing high-quality (high-strength) coke using low-quality and inexpensive coal have been studied from various viewpoints. For example, development of coal blending technology and development of coal pretreatment technology. In particular, the latter technique has been confirmed to have great results by adjusting the moisture content of coal and controlling the grinding method. However, since this technology requires a large amount of capital investment, it is not easy to put it into practical use.

  Therefore, recently, studies from the aspect of blending technology are also being promoted. For example, Patent Document 1 focuses on the gas pressure or expansion pressure at the time of coal dry distillation, and improves the coal fusion state by setting the gas pressure or expansion pressure of the blended coal to a certain level or higher, thereby reducing the quality and cost. A method for obtaining coke having a quality equivalent to or higher than that of conventional coke while using non-slightly caking coal is disclosed.

JP 09-228771 A

  By the way, the strength of coke is determined by the strength of the structure of the coke substrate (substrate strength, adhesion strength between coal particles, etc.), the ratio of defective parts including pores, their distribution form, and the like. Therefore, as in the technique of Patent Document 1, in the method of increasing the gas pressure, although the adhesion strength between coal particles and the shape improvement of the defect portion (reduction of defects having a shape where stress concentration tends to occur) are expected, On the contrary, when the gas pressure is increased, rough atmospheric pores are formed, leading to a decrease in coke strength. However, this negative effect cannot be sufficiently eliminated simply by controlling the gas pressure of the blended coal. In order to avoid this risk, the coal quality of the blended coal must be set higher than necessary, and therefore there is a problem that the coke production cost cannot be sufficiently reduced.

  Therefore, an object of the present invention is to propose a method for producing high-strength coke that can produce high-strength coke at low cost even when low-quality coal is used.

  The inventors have made extensive studies in order to solve the above problems of the prior art. As a result, in addition to the physical property values (gas pressure, expansion pressure, etc.) indicating the pressure of the coal softening melt layer during the heating process, this parameter is set to an appropriate value using the parameters that incorporate the coal softening melt viscosity. Thus, by determining the blending conditions of coal blend, it was found that high-strength and inexpensive coke can be stably produced even when low-quality coal is used, and the present invention has been completed.

That is, the present invention is a method for producing coke by dry distillation of blended coal, and in the heating process of the blended coal, the ratio of the pressure ΔP and the viscosity η of the coal softening and melting layer is the following formula (2):
R = ΔP / η (2)
(Where R: pore growth parameter [1 / s], ΔP: pressure in the coal softened molten layer [Pa], η: viscosity of the coal softened molten layer [Pa · s])
The blending condition of the coal blend is determined so that the maximum value R _max in the temperature profile of the pore growth parameter R represented by the formula is in the range of 0.125 to 0.183 [1 / s]. This is a method for producing high-strength coke.

  ADVANTAGE OF THE INVENTION According to this invention, even if it uses low quality coal, the high quality coke which has the intensity | strength more than equivalent to the coke currently manufactured conventionally can be manufactured stably. Therefore, when this coke is used in a blast furnace, air permeability is sufficiently ensured and contributes greatly to the stable operation of the blast furnace. In addition, according to the present invention, a large amount of non-slightly caking coal that is cheaper than caking coal can be used, which contributes to the reduction of coke production costs.

It is a graph which shows the relationship between the ratio of the coarse air hole of 1 mm or more, and coke intensity | strength. It is a graph which shows the actual measurement example of the relationship between expansion pressure (DELTA) P of coal softening, and temperature. It is a graph which shows the measurement example of the relationship between viscosity (eta) of coal softening, and temperature. It is a graph which shows the temperature dependence of the pore growth parameter R calculated | required from FIG. 2 and FIG. It is a graph which shows the relationship between the pore growth parameter R and the ratio of the rough air hole of 1 mm or more. It is an example of a pore distribution image obtained by performing image processing on a tomographic photograph of a coke mass. It is a graph which shows the relationship between the pore growth parameter Rmax and coke strength in simple coal. It is a graph which shows the relationship between the pore growth parameter Rmax and coke strength in blended coal.

The inventors have studied the characteristics of the pores that lead to structural defects in coke. In the research, the inventors first investigated the relationship between the rough atmospheric pores and the coke strength. FIG. 1 shows that a coke obtained by carbonizing a simple coal or a blended coal containing a plurality of coals using an electric furnace capable of simulating the carbonization conditions of an actual coke oven is 1 mm or more existing in the coke. It shows the relationship between the proportion of the area occupied by coarse pores having a size of 5 and the coke strength (rotational strength; D ¹⁵⁰ ₁₅ ). In addition, the water | moisture content and particle size of the coal used for the said test were made constant, and the packing bulk density of coal at the time of dry distillation and heat treatment conditions were also made constant.

  From FIG. 1, as the ratio of coarse air holes of 1 mm or more existing in the coke increases, the coke strength tends to decrease and the range of variation tends to increase. Therefore, in order to stably obtain high-strength coke, it has been found that it is effective to reduce the area ratio by suppressing the growth of coarse air holes present in the coke.

Accordingly, the inventors have decided to introduce a bubble growth theory in foaming molding of a polymer with respect to a pore growth mechanism in a softening and melting state of coal that determines the structure of coke. According to this theory, the growth rate of bubbles existing in the liquid phase is expressed by the following formula (1).
dr / dt = r / 4η (ΔP-2γ / r) (1)
Here, r: bubble radius, t: time, ΔP: pressure in the bubble (difference between bubble pressure and atmospheric pressure), η: viscosity of the liquid phase, and γ: surface tension of the liquid phase.

  Here, when the above formula is applied to dry distillation of coal, the surface tension γ generally decreases as the temperature increases, but the softening and melting temperature of coal is as high as around 400 to 500 ° C. The influence of surface tension γ is considered negligible. As a result, dr / dt, which is the pore growth rate in the coke, is proportional to the pressure ΔP in the coal softening melt layer, that is, the gas pressure or expansion pressure in the pores, and inversely proportional to the viscosity η.

As a result, the above equation (1) relating to the bubble growth theory can be expressed as the following equation (2) relating to the pore growth parameter R, when this is shown as an equation representing the pore growth rate in the softened and molten layer of coal. .
R = ΔP / η (2)
Here, R: pore growth parameter [1 / s], ΔP: pressure in the coal softened molten layer [Pa], and η: viscosity of the coal softened molten layer [Pa · s].

  From the above equation (2), it is understood that when the viscosity η is constant, the pore growth parameter R increases as the pressure ΔP in the coal softening / melting layer increases, and the pores easily grow. When the pressure ΔP is assumed to be constant, the pore growth parameter R increases as the viscosity η decreases, and conversely, the pore growth parameter R decreases as the viscosity η increases. Therefore, the pore growth rate in the coal softened molten layer, that is, the pore size, is not sufficient to evaluate the gas pressure and expansion pressure of the softened molten layer, and the influence of the viscosity η needs to be considered. I understand that there is.

Note that the method of measuring the pressure of the coal softened molten layer, that is, the gas pressure in the pores or the expansion pressure, inserts a probe for pressure measurement into the coal packed bed, and the gas pressure in the packed bed in the dry distillation process is determined. There are a measuring method, a method of measuring the expansion pressure of the coal packed bed in the dry distillation process under a constant volume, and any method may be used. However, since the absolute value of the pressure of the coal softening and melting layer varies depending on the measurement conditions, it is preferable in terms of operation management that the measurement method is once determined and then unified into the method. As an example, an actual measurement example of expansion pressure under a constant volume when a coal packed bed in which coal having a particle diameter of 3 mm or less and 100% is packed to a density of 800 kg / m ³ is heated from 300 ° C. to 500 ° C. at 3 ° C./min. Is shown in FIG.

In addition, a method for measuring the viscosity of the coal softened molten layer is defined in JIS M8801, a method for obtaining a viscosity by inserting a stirring rod into a coal packed bed and rotating at a constant speed and detecting torque at this time. As in the Gieseller blast meter method, there is a method of indirectly obtaining the viscosity from the number of rotations when the torque is constant, and any method may be used. However, since the absolute value of the viscosity also varies depending on the measurement conditions, it is preferable to once unify the measurement method after it has been determined. As an example, a coal packed bed in which coal having a particle diameter of 0.5 mm or less and 100% is packed to a density of 850 kg / m ³ is heated from 350 ° C. to 500 ° C. at 3 ° C./min, and a shear rate of 0.01 [1 An example of obtaining the viscosity from / s] is shown in FIG.

Further, the pore growth parameter R can be obtained from the ratio of the pressure ΔP and the viscosity η of the coal softening / melting layer obtained as described above. As an example, the pore growth parameter R was calculated from the measurement data of FIGS. 2 and 3, and the temperature profile was obtained in FIG. 4. The pore growth parameter R shows a maximum value around 450 ° C. Recognize. In the present invention, the temperature profile and the maximum value (R _max ) of the pore growth parameter R can be effectively used as an index for determining the blending conditions.

FIG. 5 is a graph showing the relationship between the pore growth parameter R _max and the proportion of coarse atmospheric pores of 1 mm or more present in the coke. From Figure 5, the maximum value R _max of the pore growth parameters, it can be seen that there is an optimum value that minimizes the proportion of coarse pores. The reason is that when the pore growth parameter R is small (the growth rate of the pores is small), the coal particles have a low expansion rate, so that the adhesion between the coal particles is insufficient, and many coarse air holes remain. . Conversely, when the pore growth parameter R is large (the growth rate of the pores is large), it is considered that the pores in the coal particles grow too much and a large number of coarse air holes are generated.

  In addition, as a method of quantifying the ratio of the area of large pores (coarse atmospheric pores) existing in the coke, for example, a cross-sectional photograph of the coke is taken with an optical microscope or an electron microscope, and the photograph is subjected to image analysis. And a method of taking a tomographic image of a coke mass using microfocus X-ray CT and analyzing the image, but the method is not limited to these. A method may be used. The photograph in FIG. 6 is an example in which a tomographic image of a coke mass is taken using microfocus X-ray CT, the tomographic image is image-processed and binarized, and the pore portion is displayed as light gray. The ratio of pores can be quantified by image analysis.

  As described above, in order to stably produce high-quality coke having high strength, it is effective to reduce the area ratio of coarse pores formed in the coke. It is important to preliminarily adjust the blending conditions of the coal used as a raw material so that the pore growth parameter R has a minimum ratio of coarse pores.

  In the present invention, the rough pores are defined as those having a maximum pore diameter of 1 mm or more determined as described above. Note that the maximum diameter is not an equivalent diameter, but a pore diameter determined by a maximum ferret diameter, a maximum diameter, or the like, that is, a pore diameter representing an actual size of a pore. The reason is that the equivalent diameter is the same between the case where the pores approximate to a circle and the case of a flat gap, but the latter is more fragile. Therefore, it is preferable to use the maximum ferret diameter or the maximum diameter. Moreover, the reason why the size of the coarse air holes is set to 1 mm or more is that small holes less than 1 mm do not significantly affect the decrease in coke strength, and conversely, the existence ratio of holes that are too large is extremely small. For this reason, since there is no correlation with the coke strength, 1 mm is the most preferable threshold value for the pore size. Coke is impacted after dry distillation, passing through the CDQ facility, or transferring on a belt conveyor. The degree of impact history varies depending on the facility, and the rough air hole is the impact received by the sample before measurement. Since it changes also with a log | history, it is not necessary to limit the rough air hole in coke to 1 mm, It is preferable to change suitably according to conditions.

Moreover, in this invention, it is preferable to adjust the pore growth parameter R of coal (mixed coal) so that the ratio of the area of the rough atmospheric pores in the coke is 0.1 or less. The reason why the area ratio of the rough air holes is 0.1 or less is that, as shown in FIG. 1, in the case of commonly used metallurgical coke, if the ratio of the rough air holes is 0.1 or less, the coke strength ( This is because D ¹⁵⁰ ₁₅ ) ≧ 80. In addition, since the ratio of rough atmospheric pores also changes depending on required characteristics and the like, it is preferable to appropriately change the threshold value accordingly.

Table 1 shows the properties of caking coal (solid coal) and the pore growth parameter R _max of the caking coal. FIG. 7 shows the relationship between the pore growth parameter R _max and the coke strength of simple coal in Table 1, and it can be seen that the coke strength decreases regardless of whether the pore growth parameter is large or small. That is, the coke strength can be estimated by using the pore growth parameters.

Using a viscosity coals shown in Table 1, by changing the blending ratio of non- or slightly-caking coal of a low quality for coking coal as shown in Table 2, varying the maximum value R _max of the pore growth parameters R Thirteen types of blended charcoal were prepared. In addition, Ro and TI of Table 1 and Table 2 are based on JIS M8816, LogMF of Table 1 is measured based on JIS M8801, and LogMF of Table 2 is LogMF of simple coal. The weighted average was obtained according to the above.

When the relationship between the maximum value R _max of the pore growth parameter R and the ratio of the coarse pores of 1 mm or more was measured for the 13 types of blended coal in Table 2, the maximum value R _{max of} the pore growth parameter R was 0.125,0. 174, 0.183 indicating a value of 0.183. Nos. 1, 2 and 3 have the smallest ratio of coarse air holes and R _max is larger than that. 4, and _R.sub.max having a smaller R _max . In any of the blended coals of 5 to 13, there was a tendency for the ratio of the rough air holes to increase.

Next, the 13 types of blended coal were subjected to dry distillation using an electric furnace capable of simulating the dry distillation conditions of an actual coke oven, and a test for producing coke was performed. In addition, the filling of the coal into the electric furnace was performed under constant conditions such that the moisture was 8 mass% and the charging bulk density was 750 kg / m ³ . About the coke obtained as described above, the drum 150 rotation 15 mm index (D ¹⁵⁰ ₁₅ ) was measured by using the rotational strength test method defined in JIS K2151, and the coke strength was evaluated.

FIG. 8 shows the measurement result of the coke strength as a relationship with the maximum value R _max of the pore growth parameter R. From FIG. 8, the blended coal No. shown in Table 2 in which the ratio (area ratio) of the coarse air holes is minimized. The coke strength of 1, 2, 3 (R _max = 0.125, 0.174, 0.183) is as high as 81 or more (shown as an example of the invention), and the coke regardless of whether R _max is larger or smaller than that value. It can be seen that the strength has decreased. As can be seen from Table 2, the blended coal from which the maximum coke strength is obtained has a high blending ratio of non-slightly caking coal of 45 to 47 mass%. FIG. 8 also shows that coke strength of 80 or more is obtained when R _max is in the range of 0.125 to 0.183 [1 / s]. For this reason, coke having high strength even when the blending ratio of non-finely caking coal is increased by appropriately controlling the pore growth parameter R without being bound by the conventional coal properties (Ro, LogMF, TI). It can be seen that can be manufactured.

Claims (1)

In the method of producing coke by dry distillation of blended coal,
The maximum value R _max in the temperature profile of the pore growth parameter R represented by the following formula (2), which is the ratio between the pressure ΔP and the viscosity η of the coal softening molten layer in the heating process of the blended coal, is 0.125 to 0 . The method for producing high-strength coke, wherein the blending conditions of the blended coal are determined so as to be in the range of 183 [1 / s].
R = ΔP / η (2)
(Where R: pore growth parameter [1 / s], ΔP: pressure in the coal softened molten layer [Pa], η: viscosity of the coal softened molten layer [Pa · s])

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