EP2944681A1

EP2944681A1 - Coal briquette manufacturing method and coal briquette manufacturing apparatus

Info

Publication number: EP2944681A1
Application number: EP13868221.6A
Authority: EP
Inventors: Chang-Il Son; Nam-Hwan Heo; Jin Ho Ryou; Sang-Ho Yi
Original assignee: Posco Co Ltd
Current assignee: Posco Holdings Inc
Priority date: 2012-12-26
Filing date: 2013-12-12
Publication date: 2015-11-18
Also published as: EP2944681A4; US20150344800A1; CN104884587B; WO2014104624A1; KR101405478B1; CN104884587A

Abstract

A method and an apparatus for manufacturing coal briquettes capable of implementing excellent cold strength and hot strength by separating and crushing coal per each kind of coals are provided. In the manufacturing method of coal briquettes, the coal briquettes are charged into a dome part of a melter-gasifier to be rapidly heated in a manufacturing apparatus of molten iron including i) a melter-gasifier in which reduced iron is charged, and ii) a reducing furnace connected to the melter-gasifier and providing the reduced iron. The manufacturing method of coal briquettes includes: i) providing a plurality of kinds of coal; ii) storing the plurality of kinds of coal, respectively; iii) providing powdered coals by crushing the plurality of kinds of coal, respectively; iv) providing mixtures by mixing the powdered coal, a hardening agent, and a binder; and v) providing coal briquettes by molding the mixture.

Description

[Technical Field]

The present invention relates to a method and an apparatus for manufacturing coal briquettes. In more detail, the present invention relates to a method and an apparatus for manufacturing coal briquettes capable of implementing excellent cold strength and hot strength by separating and crushing coal per each kind of coals.

[Backcrushed Art]

In a smelting reduction iron-making method, a reducing furnace for reducing iron ores and a melter-gasifier for melting reduced iron ores are used. In the case of melting iron ores in the melter-gasifier, as a heat source to melt iron ores, coal briquettes are charged into the melter-gasifier. Here, reduced iron is melted in the melter-gasifier, transformed to molten iron and slag, and then discharged outside. The coal briquettes charged into the melter-gasifier form a coal-packed bed. After oxygen is injected through a tuyere installed in the melter-gasifier, the coal-packed bed is combusted to generate combustion gas. The combustion gas is transformed into reducing gas at a high temperature while increasing a temperature through the coal-packed bed. The hot reducing gas is discharged outside the melter-gasifier to be supplied to the reducing furnace as the reducing gas.
In the case of using the coal briquettes, there is a need to utilize a manufacturing process of molten iron by increasing yield of molten iron and reducing a fuel ratio. To this end, differentiation capacity in the melter-gasifier of the coal briquettes is reduced and thus the coal briquettes in the melter-gasifier need to be maintained with a large grain size. In this case, reaction efficiency and heat-transfer efficiency may be increased by ensuring permeability and flow so that gas and liquid smoothly pass through the melter-gasifier. Further, due to differentiation, a generation amount of fine powder which is not efficiently used during manufacture of molten iron may be reduced. There is a limit to reduce the generation amount of fine powder by combination of various coal kinds.

[DISCLOSURE]

[Technical Problem]

The present invention has been made in an effort to provide a manufacturing method of coal briquettes having advantage of implementing excellent cold strength and hot strength by separating and crushing coal for each of coal kinds. The present invention has been made in an effort to provide a manufacturing apparatus of coal briquettes having an advantage of implementing excellent cold strength and hot strength by separating and crushing coal per each kind of coals.

[Technical Solution]

An exemplary embodiment of the present invention provides a method for manufacturing coal briquettes charged into a dome part of the melter-gasifier to be rapidly heated in an apparatus for manufacturing molten iron including a melter-gasifier into which reduced iron is charged, and a reducing furnace connected to the melter-gasifier and providing the reduced iron. The method includes i) providing a plurality of kinds of coal; ii) storing the plurality of kinds of coal, respectively; iii) providing powdered coals by crushing the plurality of kinds of coal, respectively; iv) providing mixtures by mixing the powdered coal, a hardening agent, and a binder; and v) providing coal briquettes by molding the mixtures.
A method for manufacturing coal briquettes according to an exemplary embodiment of the present invention may include drying the plurality of kinds of powdered coals together. A water standard deviation of the plurality of kinds of powdered coals may be 0.3 or less. In the providing of the plurality of kinds of coal, among the plurality of kinds of coal, a plurality of kinds of coal having a difference between Hardgrove Crushability Indexes (HGIs) of 10 or less may be mixed and provided together. The difference between the HGIs among the plurality of kinds of coal may be 5 or less.
The providing of the mixture may include i) uniformly mixing the powdered coals, and ii) providing and mixing the binder and the hardening agent with the uniformly mixed powdered coal. In the providing of the powdered coals, a grain size of the powdered coals may be greater than 0mm and may be 5mm or less. The grain size of the powdered coals may be 1 mm to 3mm.
In the providing of the powdered coals, the plurality of kinds of coals may include first coal and second coal, and a crushing time of the first coal may be different from the crushing time of the second coal. The crushing time of the first coal may be greater than that of the second coal, and a caking property of the first coal is smaller than that of the second coal.
An apparatus for manufacturing coal briquettes according to an embodiment of the present invention includes i) a plurality of coal storage tanks storing a plurality of kinds of coal; ii) a plurality of crushers connected to the plurality of coal storage tanks to provide powdered coals by crushing the plurality of kinds of coals, respectively; iii) a binder storage tank storing a binder; iv) a hardening agent storage tank storing a hardening agent; v) a mixer providing mixtures by mixing the powdered coals provided from the plurality of crushers, the binder provided from the binder storage tank, and the hardening agent provided from the hardening agent storage tank; and vi) a molding machine molding the mixture by receiving the mixture from the mixer.

[Advantageous Effects]

Since different kinds of coal are separately crushed, and dried per each kinds of coals to manufacture the coal briquettes, cold strength and hot strength thereof may be improved. Accordingly, process efficiency and fuel ratio may be improved in a manufacturing process of molten iron by increasing the size and the strength of chars obtained by drastically pyrolyzing the coal briquettes in the melter-gasifier. Further, low-priced coal having difficulty in crushing may be used as raw materials for coal briquettes and an amount of the binder may be reduced.

[Description of the Drawings]

FIG. 1 is a schematic flowchart of a manufacturing method of coal briquettes according to an exemplary embodiment of the present invention.
FIG. 2 is a schematic diagram of a manufacturing apparatus of coal briquettes according to another exemplary embodiment of the present invention.
FIG. 3 is a schematic diagram of a manufacturing apparatus of molten iron connected to the manufacturing apparatus of coal briquettes of FIG. 2.
FIG. 4 is a schematic diagram of another manufacturing apparatus of molten iron connected to the manufacturing apparatus of coal briquettes of FIG. 2.

[Mode for Invention]

Terms used herein such as first, second, and third are used to illustrate various portions, components, regions, layers, and/or sections, but not to limit them. These terms are used to discriminate the portions, components, regions, layers, or sections from the other portions, components, regions, layers, or sections. Therefore, the first portion, component, region, layer, or section as described below may be the second portion, component, region, layer, or section within the scope of the present invention.
It is to be understood that the terminology used herein is only for the purpose of describing particular embodiments and is not intended to be limiting. It must be noted that, as used in the specification and the appended claims, the singular forms include plural references unless the context clearly dictates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated properties, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other properties, regions, integers, steps, operations, elements, and/or components thereof.
Unless it is not mentioned, all terms including technical terms and scientific terms used herein have the same meaning as the meaning generally understood by a person with ordinary skill in the art to which the present invention belongs. The terminologies that are defined previously are further understood to have the meaning that coincides with relating technical documents and the contents that are disclosed currently, but are not to be interpreted as the ideal or overly official meaning unless so defined.
The term "HGI" to be used below is used an index representing resistance of coal for crushing as a Hardgrove Crushability Index. For example, in the HGI, 50 g of a coal sample prepared with a predetermined size is put in a crushing unit, the unit is processed at a predetermined pressure by a standard rotation number, the coal sample is crushed by a steel ball in the unit, and coal particles are divided, and an amount of the coal of less than a predetermined size is recorded and converted to an HGI value.
The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are illustrated. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.
FIG. 1 schematically illustrates a flowchart of a manufacturing method of coal briquettes according to an exemplary embodiment of the present invention. The manufacturing method of coal briquettes in FIG. 1 is just to exemplify the present invention, and the present invention is not limited thereto. Accordingly, the manufacturing method of coal briquettes may be variously modified.
As illustrated in FIG. 1, the manufacturing method of coal briquettes includes providing a plurality of kinds of coal (S10), storing the plurality of kinds of coal, respectively (S20), crushing the plurality of kinds of coal, respectively (S30), providing mixtures by mixing the crushed coal, a hardening agent, and a binder (S40), and providing coal briquettes by molding the mixtures (S50). In addition, if necessary, the manufacturing method of coal briquettes may further include other processes.
First, in step S10, the plurality of kinds of coal are provided. As a coal required for manufacturing the coal briquettes, for example, anthracite coal, coking coal, semi-anthracite coal, weak coking coal, and the like may be used. The weak coking coal may include a large amount of volatile matter. Meanwhile, although not illustrated in FIG. 1, in order to improve the quality of molten iron, coal for quality control may be mixed with powdered coals. Here, as the coal for quality control, coal having reflectance of a predetermined value or more may be used.
A grain-size distribution range of the plurality of kinds of coal is very wide as being more than 0 and 50 mm or less. Meanwhile, regarding the coal, a Hardgrove Crushability Index (HGI) varies according to a carbonization degree. Brown coal or sub-bituminous coal having a low carbonization degree have a low HGI, bituminous coal have a high HGI, and anthracite coal having the highest carbonization degree have a low HGI again.
In addition, in step S20, the plurality of kinds of coal are separated to be stored, respectively. In the case of mixing and storing the plurality of kinds of coal together, due to a difference in grain size and a moisture, the quality of the coal briquettes has negatively influenced on a subsequent process for manufacturing the coal briquettes. Accordingly, the plurality of kinds of coal are separated from each other to be separately stored.
Next, in step S30, the plurality of kinds of coal is separately crushed to provide powdered coals. That is, the plurality of kinds of coal are separately divided and crushed. For example, the plurality of kinds of coal may be crushed to be controlled with average grain size to be 5 mm or less. When the average grain size of the plurality of kinds of coal is greater than 5mm, since it is difficult to uniformly mix the plurality of kinds of coal in a subsequent process, the quality of the coal briquettes may be deteriorated. Accordingly, the average grain size of the plurality of kinds of coal is controlled in the aforementioned range. Preferably, the average grain size of the coal may be controlled to 1 mm to 3 mm.
The plurality of kinds of coal may have different HGIs. For example, a difference between HGIs of the plurality of kinds of coal may be 10 or less. When the difference between HGIs is very large, it is inappropriate for use as a coal raw material for manufacturing the coal briquettes. Accordingly, the difference between HGIs is controlled in the aforementioned range. Preferably, the difference between HGIs may be 5 or less.
Meanwhile, since the plurality of kinds of coal having different HGIs are separately crushed, a crushing time of the plurality of kinds of coal may be different from each other. That is, since coal having a low HGI is not crushed well as particles, the crushing time is set to be longer. On the contrary, since coal having a high HGI is crushed well, the crushing time may be reduced. Meanwhile, since coal having a high caking property is crushed well, as the caking property is higher, the crushing time is set to be longer.
In a conventional method, various kinds of coal were dried together, and then crushed together as well. In this case, since a grain size of coal is changed according to a difference in strength between the coal kinds, a grain-size distribution of mixed coal in which coal are collected is increased too much. Accordingly, a water deviation of mixed coal is large, it is difficult to manage a grain size due to a wide grain-size distribution caused by different HGIs, and it is difficult to control a grain size when a mixing ratio of coal per each kind of coals is changed. As a result, this may have a negative influence on hot strength and cold strength of coal briquettes manufactured in a subsequent process. On the contrary, in an exemplary embodiment of the present invention, since sifferent kinds of coal are separately crushed and then mixed together, the grain-size distribution decreases. Here, the crushing of the coal is performed by changing a capacity of a crusher, a crushing condition, a crushing speed, and the like. As a result, since the water deviation of the mixed coal is small and the mixed coal has a uniform grain size, coal briquettes having an excellent characteristic may be manufactured.
Meanwhile, although not illustrated in FIG. 1, mixed coals made by mixing separately crushed coals together may be dried. In this case, since the crushed coals having a constant grain size are dried, the water deviation of the mixed coal may be minimized. Accordingly, since a water amount and a water deviation of the mixed coal may be properly controlled, the quality of coal briquettes may be further improved. For example, a water standard deviation of the mixed coals in which powdered coals are mixed may be controlled to be 0.3 or less. When the water standard deviation of the mixed coals is too large, the water amount included in the mixed coal is not constant and thus the quality of coal briquettes deteriorates.
In a conventional method, a water amount of the coal after drying the coal was automatically controlled to become a target value. In this case, for automatic control, there was a need to consider many parameters such as a dry amount of coal, a drying temperature of a coal drier, an air flow, and a water amount of coal before drying. Further, in the case of measuring the water, in order to enhance accuracy of the measurement value, a large sample for measuring water is required and the sample needs to be uniformly collected. Then, it becomes more difficult to mechanically collect and dry the sample for automatically measuring the water of the coal. Accordingly, since it is difficult to control a water variation of coal before drying the coal, the automatic water control is impossible. Unlike this, in the exemplary embodiment of the present invention, since the coal is crushed and then dried after the grain sizes are uniformalized, the drying process of the coal is simplified.
Next, in step S40, mixtures are provided by mixing the crushed coals, a hardening agent, and a binder. Here, the crushed coals, graphite, the hardening agent, and the binder may be mixed in a random order or specific raw materials may be added first. For example, after the crushed coal and the binder are first mixed, the hardening agent may be mixed therein. Alternatively, after the crushed coal and the hardening agent are mixed, the binder may be mixed therein.
As the hardening agent, quicklime, slaked lime, a metal oxide, fly ash, clay, a surface active agent, a cationic resin, an accelerator, fiber, phosphate, sludge, waste plastics, waste lubricating oil, waste toner, graphite, activated carbon, or the like may be used. Further, as the binder, molasses, starch, sugar, a polymer resin, pitch, tar, bitumen, oil, cement, asphalt, water glass, or the like may be used. For example, by using molasses as the binder and quicklime as the hardening agent, the cold strength of coal briquettes may be largely increased by a saccharate bond when the coal briquettes are manufactured.
Meanwhile, in step S40, the different kinds of powdered coals are first uniformly mixed and then the binder and the hardening agent are provided to provide the mixtures. That is, since the powdered coals include various kinds of coal, when the kinds of powdered coals are not uniformly mixed, the quality of coal briquettes may be deteriorated. Accordingly, before supplying the binder and the hardening agent to the powdered coal, powdered coals are uniformly mixed.
Finally, in step S50, the coal briquettes are provided by molding the mixture. For example, the coal briquettes may be manufactured by continuously compressing the mixture by using a molding machine including a pair of rollers.
FIG. 2 schematically illustrates an apparatus for manufacturing coal briquettes 100 according to another exemplary embodiment of the present invention. The apparatus for manufacturing coal briquettes 100 in FIG. 2 is just to exemplify the present invention, and the present invention is not limited thereto. Accordingly, a structure of the apparatus for manufacturing coal briquettes 100 may be variously modified.
As illustrated in FIG. 2, the apparatus for manufacturing coal briquettes 100 includes a coal storage tank 10, a crusher 20, a binder storage tank 40, a hardening agent storage tank 50, a mixer 60, and a molding machine 70. In addition, the apparatus for manufacturing coal briquettes 100 further includes a dryer 90, a mixed coal storage tank 92, a collected coal storage tank 94, and a separator 805. If necessary, the apparatus for manufacturing coal briquettes 100 may further include other devices. Since a detailed structure and an operation method of respective devices included in the apparatus for manufacturing coal briquettes 100 of FIG. 2 can be easily understood by those skilled in the art, the detailed description is omitted.
A plurality of coal storage tanks 10 separately store a plurality of kinds of coal, respectively. For example, in order to improve the quality of coal briquettes in addition to the coal used as a raw material of coal briquettes, coal for controlling quality may be used. Accordingly, in order to mix an appropriate amount of coal for controlling quality according to an amount of the coal used as a raw material, the plurality of coal storage tanks 10 are separately installed.
A plurality of crushers 20 are connected to the plurality of coal storage tanks 10, respectively. The plurality of crushers 20 receive different kinds of coal from the plurality of coal storage tanks 10, respectively, to crush the different kinds of coals. For example, the coal is crushed to be provided as powdered coals having a grain size of 8 mm or less. Although not illustrated in FIG. 2, the crushed powdered coals may be directly provided to the mixer 60. Further, the crushed powdered coals may be dried and then supplied to the mixer 60.
The drier 90 dries the crushed powdered coals together which are supplied from each crusher 20. Accordingly, a plurality of kinds of powdered coals are mixed together in the drier 90, dried, and then may be supplied to the mixer 60.
As illustrated in FIG. 2, the binder is stored in the binder storage tank 40. The binder binds the plurality of kinds of powdered coals with each other to make them in a state suitable for manufacturing the coal briquettes. The binder storage tank 40 is connected with the mixer 60 to provide the binder to the mixer 60.
Meanwhile, the hardening agent is stored in the hardening agent storage tank 50. The hardening agent is combined with the powdered coals to harden the coal briquettes and thus the strength of coal briquettes may be optimized. The hardening agent storage tank 50 is connected with the mixer 60 to provide the hardening agent thereto.
The mixer 60 mixes the powdered coal, the binder, the hardening agent, and the like with each other to provide the mixtures for manufacturing the coal briquettes. Before being supplied to the mixer 60, the plurality of kinds of coal are stored and pre-mixed in the mixed coal storage tank 92 together and uniformly mixed with each other in the mixer 60 again. Since the powdered coals include a plurality of kinds of coals, the powdered coals are uniformly mixed by driving the mixer 60 in advance before the binder and the hardening agent are put into the mixer 60. When the binder and the hardening agent are directly charged into the mixer 60, the plurality of kinds of powdered coals are not uniformly mixed and thus the quality of coal briquettes may be deteriorated. Accordingly, the plurality of kinds of powdered coals are first mixed in the mixer 60.
As illustrated in FIG. 2, the molding machine 70 includes a pair of rolls that rotate in an opposite direction to each other. The mixtures are compressed by the pair of rolls by supplying them between the pair of rolls to manufacture the coal briquettes. Meanwhile, the powdered coals are stored in the collected coal storage tank 94 by dividing the manufactured coal briquettes through the separator 805 again. The powdered coals stored in the collected coal storage tank 94 is re-supplied to the mixer 60 again to be used as a raw material of the coal briquettes. As a result, use efficiency of the powdered coals may be improved.
FIG. 3 schematically illustrates a apparatus for manufacturing molten iron 200 which is connected to the apparatus for manufacturing coal briquettes 100 of FIG. 2, and uses the coal briquettes manufactured by the apparatus for manufacturing coal briquettes 100. A structure of the apparatus for manufacturing molten iron 200 in FIG. 3 is just to exemplify the present invention, and the present invention is not limited thereto. Accordingly, the apparatus for manufacturing molten iron 200 in FIG. 3 may be modified in various forms.
The apparatus for manufacturing molten iron 200 of FIG. 3 includes a melter-gasifier 210 and a reducing furnace 220. In addition, if necessary, the apparatus for manufacturing molten iron 200 may include other devices. Iron ore is charged into and reduced in the reducing furnace 220. The iron ore charged into the reducing furnace 220 is dried in advance and then prepared as reduced iron while passing through the reducing furnace 220. The reducing furnace 220, as a packed-bed reducing furnace, receives the reducing gas from the melter-gasifier 210 to form a packed bed in the reducing furnace 220.
Since the coal briquettes manufactured by the apparatus for manufacturing coal briquettes 100 of FIG. 2 are charged into the melter-gasifier 210 of FIG. 3, a coal-packed bed is formed in the melter-gasifier 210. A dome part 2101 is formed at an upper portion of the melter-gasifier 210. That is, in the dome part 2101 having a wider space than another part of the melter-gasifier 210, hot reducing gas exists. The coal briquettes are charged into the dome part 2101 of the melter-gasifier 210 and then drastically heated while falling down to the lower portion of the melter-gasifier 210. Char generated by a pyrolysis reaction of the coal briquettes moves downward in the melter-gasifier 210 to exothermically react with oxygen supplied through a tuyere 230. As a result, the coal briquettes may be used as a heat source which keeps the melter-gasifier 210 at a high temperature. Meanwhile, since the char has permeability, a large amount of gas generated from the lower portion of the melter-gasifier 210 and reduced iron supplied from the reducing furnace 220 may more easily and uniformly pass through the coal-packed bed in the melter-gasifier 210.
In addition to the aforementioned coal briquettes, if necessary, lump carbonaceous materials or cokes may be charged into the melter-gasifier 210. The tuyere 230 is installed at an outer wall of the melter-gasifier 10 to inject oxygen. Oxygen is injected to the coal-packed bed to form a raceway. The coal briquettes are combusted in the raceway to generate reducing gas.
FIG. 4 schematically illustrates another apparatus for manufacturing molten iron 300 which is connected to the apparatus for manufacturing coal briquettes 100 of FIG. 2, and uses the coal briquettes manufactured by the apparatus for manufacturing coal briquettes 100. A structure of the apparatus for manufacturing molten iron 300 in FIG. 4 is just to exemplify the present invention, and the present invention is not limited thereto. Accordingly, the apparatus for manufacturing molten iron 300 in FIG. 4 may be modified in various shapes. Since the structure of the apparatus for manufacturing molten iron 300 in FIG. 4 is similar to the structure of the apparatus for manufacturing molten iron 200 in FIG. 3, like reference numerals refer to like parts, and the detailed description is omitted.
As illustrated in FIG. 4, the apparatus for manufacturing molten iron 300 includes a melter-gasifier 210, a fluidized-bed reducing furnace 310, a reduced iron compression device 320, and a compacted irons storage tank 330. The compacted irons storage tank 330 may be omitted.
The manufactured coal briquettes are charged into the melter-gasifier 210. The coal briquettes generate reducing gas in the melter-gasifier 210, and the generated reducing gas is supplied to a fluidized-bed reducing furnace 310. Fine iron ores are supplied to the fluidized-bed reducing furnace 310 and manufactured to be reduced irons while flowing by reducing gas supplied to the fluidized-bed reducing furnace 310 from the melter-gasifier 210. The reduced irons are compressed by the apparatus for manufacturing compacted irons 320 and then stored in the compacted irons storage tank 50. The compacted irons is supplied from the compacted irons storage tank 330 to the melter-gasifier 210 to be melted in the melter-gasifier 210. Since the coal briquettes are charged into the melter-gasifier 210 to be transformed to char having permeability, a large amount of gas are generated at a lower portion of the melter-gasifier 210 and the compacted irons more easily and uniformly pass through the coal-packed bed in the melter-gasifier 210 to manufacture molten iron with a good quality. Meanwhile, oxygen is supplied through the tuyere 230 to combust the coal briquettes.
Hereinafter, the present invention will be described in more detail through experimental examples. experimental examples are just to exemplify the present invention, and the present invention is not limited thereto.

Experimental Example

Experiment for evaluating grain-size distribution change after crushing according to an HGI difference per each kind of coals

Coal samples configured by coal A, coal B, and coal C having a grain size of 5 mm to 20 mm were prepared. Coal A was coking coal, coal B was weak coking coal of high volatile matter, and coal C was semi-anthracite coal. The entire amount of coal A, coal B, and coal C was crushed by using a crusher so that the grain size became 5 mm or less. In addition, a grain-size distribution was measured by dividing coal A, coal B, and coal C. The measured grain-size distribution is represented by the following Table 1. (Table 1)

NO Coal HGI

1 Coal A 80 to 90

2 Coal B 50 to 60

3 Coal C 80 to 90
As listed in Table 1, in an HGI of each coal, coal A and coal C were 80 to 90 and coal B was 50 to 60. When the HGI value is large, the crushing is performed well, and when the HGI value is small, the crushing is not performed well. Accordingly, it was well known that coal A and coal C were crushed well as compared with coal B.

Meanwhile, a grain-size distribution of each coal according to an HGI difference is listed in the following Table 2. As listed in Table 2, in coal A and coal C having a high HGI value, a coarse grain-size ratio of 1 to 5 mm was relatively low as compared with coal B having a low HGI value. On the contrary, in coal A and coal C, a fine grain-size ratio of 0.25 mm or less was relatively high as compared with coal B. Accordingly, when coal A, coal B, and coal C are mixed together and then crushed, coal A and coal C have a high possibility to be over-crushed and coal B has a high possibility to be non-crushed. Accordingly, the grain sizes of coal A and coal C are relatively decreased, while the grain size of coal B may be relatively increased. As described above, when the grain-size distribution characteristic of the crushed powdered coals is not uniform, an optimal grain-size distribution characteristic may not be implemented, and thus quality of the coal briquettes in hot and cold states is deteriorated. Further, when coal A to coal C were mixed and then crushed, it was difficult to control the overall grain size.

(Table 2)

NO	Coal	Coal grain-size distribution
		-0.25 mm	0.25 to 0.5 mm	0.5 to 1 mm	1 to 5 mm
1	Coal A	30.6 %	14.0 %	18.2 %	37.2 %
2	Coal B	12.1 %	11.6 %	22.3 %	54.0 %
3	Coal C	29.2 %	14.4 %	17.2 %	39.2 %

Evaluation experiment of quality in cold and hot states according to grain-size distribution

Coal A, coal B, and coal C were prepared. Maximum grain-size upper limits of coal per each kind of coals were divided into 5mm, 3mm, and 1 mm, respectively. Each kind of coal, a binder, and a hardening agent were mixed at an appropriate ratio and then pressed by using a roll press at room temperature to manufacture coal briquettes with a pillow shape with a diameter of 51 mm, a width of 37mm, and a thickness of 24mm. The volume of coal briquettes was 25 cm³, and a compressive strength of coal briquettes was calculated according to the following Equation 1. $Compressive strength (kgf) = compressive strength by compressive strength measurer (average value measured 10 times)$
Table 3 lists a compressive strength of coal briquettes accoridng to the aforementioned grain-size distribution. As listed in Table 3, coal A to coal C had the highest compressive strength when the maximum upper-limit grain size was 3mm. When pressure was applied to coal having a layered structure, cracks due to pressure occurred, and as a result, it is assumed that as the grain size was increased, the crack was increased and thus the compressive strength of coal briquettes was regarded to be deteriorated. (Table 3)

NO Coal Maximum upper-limit grain size of coal

-5 mm -3 mm -1 mm

1 Coal A 43.2 kgf 49.3 kgf 48.2 kgf

2 Coal B 43.0 kgf 44.2 kgf 44.1 kgf

3 Coal C 44.1 kgf 47.2 kgf 46.5 kgf
Meanwhile, since an HGI of coal B was lower than HGIs of coal A and coal C, a ratio of coarse coal was high and coarse coal had a large influence on the compressive strength. Further, an arithmetic mean grain size of coal B calculated by the following Equation 2 was significantly larger than an arithmetic mean grain size of coal A. $Arithmetic mean grain size (mm) = (weight ratio of grain size of 3 to 5 mm \times 4 mm) + (weight ratio of grain size of 1 to 3 mm \times 2 mm) + (weight ratio of grain size of 1 mm or less \times 0.5 mm)$

In addition, as listed in the following Table 4, it was shown that a weight of coal briquettes manufactured by coal B was lower than a weight of those manufactured by coal A and coal C. Accordingly, the compressive strength of coal B was shown to be little. Considering the aforementioned view point, in the case of mixing and crushing coal A to coal C, the grain size of coal B after crushing is relatively increased, and thus the compressive strength of coal briquettes is deteriorated. Accordingly, in the case of manufacturing coal briquettes by separating, crushing, and mixing coal A to coal C, it could be known that the compressive strength of coal briquettes may be improved.

(Table 4)

NO	coal	Grain-size distribution	After crushing +3mm(%)	Arithmetic mean(mm)	Specific gravity of coal briquettes (g/cm³)
1	Coal A	-5mm	2.7	0.98	1.223
2		-3mm	0.0	0.58	1.238
3		-1mm	0.0	0.31	1.224
4	Coal B	-5mm	5.3	1.36	1.211
5		-3mm	0.0	0.75	1.210
6		-1mm	0.0	0.40	1.205
7	Coal C	-5mm	4.1	1.19	1.256
8		-3mm	0.0	0.72	1.256
9		-1mm	0.0	0.37	1.257

experiment for effect influenced by a strength of char with upper-limit grain size per each kind of coals

The coal briquettes manufactured as described above were completely dried for 24 hours. The coal briquettes were put in a circular reaction furnace with an inert atmosphere at 1000 °C and rotated at 10 rpm for 60 minutes. Among chars discharged from the circular reaction furnace, char having a grain size of 10 mm or more was put in an I drum strength machine and rotated 600 times at 20 rpm for 30 minutes. In addition, a ratio of coarse chars of 10 mm or more was set as a char strength according to the following Equation 3. $Char strength (%) = ((char weight (g) having grain size of 10 mm or more after measuring l drum strength / (char weight (g) having grain size of 10 mm or more before measuring l drum strength) \times 100$
The char strength according to the upper-limit grain size difference per each kind of coals is shown in the following Table 5. As listed in Table 5, unlike the aforementioned compressive strength, the char strength in coal A and coal B was good as the maximum upper-limit grain size was increased, but the maximum upper-limit grain size of coal C was decreased, the char strength of coal C was good. (Table 5)

NO Coal Maximum upper-limit grain size of coal

-5 mm -3 mm -1 mm

1 Coal A 46.8 % 42.4 % 41.0 %

2 Coal B 65.6 % 64.7 % 59.0 %

3 Coal C 49.1 % 51.5 % 54.6 %
As the aforementioned experimental result, the compressive strength representing quality of coal briquettes in a cold state and the char stength representing quality of coal briquettes in a hot state had different characteristics per each kind of coals and each grain size. Accordingly, in order to manufacture the coal briquettes having good charateristics of the compressive strength and the char strength of the coal briquettes, it was determined to be preferred for various kinds of coal to be separated and crushed by considering unique coal characteristics such as an HGI and a grain shape. In order to support the determination, another experiment was performed as follows.

Experiment according to process division

Experimental Example 1

Coal A, coal B, and coal C were separated, crushed, and dried per each kind of coals, respectively, to manufacture coal briquettes. That is, a particle characteristic of coal was considered by separately crushing coal A, coal B, and coal C, and the crushed coal A, coal B, and coal C were mixed and dried together to manufacture the coal briquettes. Coal A, coal B, and coal C were mixed with each other at a mixing ratio of 40wt%, 30wt%, and 30wt%, respectively. In addition, the compressive strength and the char strength of the coal briquettes were measured.

Comparative Example 1

The same kinds of coal as those coal used in Experimental Example 1 were mixed, dried, and then crushed together. The rest of the experimental processes were the same as those of the aforementioned Experimental Example 1.
Table 6 exhibits a measuring result of compressive strength and char strength of the coal briquettes manufactured according to Experimental Example 1 and Comparative Example 1. As listed in Table 6, in Experimental Example 1, the compressive strength was increased by approximately 8.8 % and the char strength was increased by approximately 5.4 % as compared with Comparative Example 1. Accordingly, it could be seen that in the case of using a separating and crushing process per each kind of coals of Experimental Example 1 instead of an integral crushing process per each kind of coals of Comparative Example 1, quality of the coal briquettes may be improved in a hot and cold state. (Table 6)

NO Experimental Example Compressive strength Char strength

1 Experimental Example 1 47.1 kgf 54.6 %

2 Comparative Example 1 43.3 kgf 51.8 %

Water deviation experiment of coal briquettes

Standard deviations were calculated by measuring water amounts of mixed coal 20 times when the coal briquettes of Experimental Example 1 and Comparative Example 1 were manufactured to be compared with each other. Table 7 exhibits water standard deviations of mixed coal of Experimental Example 1 and Comparative Example 1 which are compared with each other.
As listed in Table 7, in Comparative Example 1, the water standard deviation was 0.43, but in Experimental Example 1, the water standard deviation was 0.30 which was smaller. The reason is that when the different kinds of coal are first dried before crushing like the process of Comparative Example 1, a grain-size range of the coal injected in the drier was wide as 0 to 50mm, and even in the same drying condition, there is a difference in drying according to a difference in grain size. However, like Experimental Example 1, when the coal is crushed and then dried, the grain-size range of the coal is very small as 0 to 5 mm, thereby improving the water deviation of the mixed coal. Therefore, the coal briquettes having excellent quality in hot and cold state may be manufactured by uniformly controlling the water amount included in the mixed coal. (Table 7)

NO Experimental Example Water standard deviation

1 Experimental Example 1 0.30

2 Comparative Example 1 0.43
While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

A method for manufacturing coal briquettes charged into a dome part of the melter-gasifier to be rapidly heated in an apparatus for manufacturing molten iron including a melter-gasifier into which reduced iron is charged, and a reducing furnace connected to the melter-gasifier and providing the reduced iron, the method comprising:
providing a plurality of kinds of coal;

storing the plurality of kinds of coal, respectively;

providing powdered coals by crushing the plurality of kinds of coal, respectively;

providing mixtures by mixing the powdered coal, a hardening agent, and a binder; and

providing coal briquettes by molding the mixtures.
The method of claim 1 further comprising drying the plurality of kinds of powdered coals together.
The method of claim 2, wherein a water standard deviation of the plurality of kinds of powdered coals is 0.3 or less.
The method of claim 1, wherein, in the providing of the plurality of kinds of coal, among the plurality of kinds of coal, a plurality of kinds of coal having a difference between Hardgrove Crushability Indexes (HGIs) of 10 or less are mixed and provided together.
The method of claim 4, wherein the difference between the HGIs among the plurality of kinds of coal is 5 or less.
The method of claim 1, wherein the providing of the mixture comprises:
uniformly mixing the powdered coals, and

providing and mixing the binder and the hardening agent with the uniformly mixed powdered coal.
The method of claim 1, wherein in the providing of the powdered coals, a grain size of the powdered coals is greater than 0mm and is 5mm or less.
The method of claim 7, wherein the grain size of the powdered coals is 1 mm to 3mm.
The method of claim 1, wherein in the providing of the powdered coals, the plurality of kinds of coals include first coal and second coal, and a crushing time of the first coal is different from the crushing time of the second coal.
The method of claim 9, wherein the crushing time of the first coal is greater than that of the second coal, and a caking property of the first coal is smaller than that of the second coal.
An apparatus for manufacturing coal briquettes, comprising:
a plurality of coal storage tanks storing a plurality of kinds of coal;

a plurality of crushers connected to the plurality of coal storage tanks to provide powdered coals by crushing the plurality of kinds of coals, respectively;

a binder storage tank storing a binder;

a hardening agent storage tank storing a hardening agent;

a mixer providing mixtures by mixing the powdered coals provided from the plurality of crushers, the binder provided from the binder storage tank, and the hardening agent provided from the hardening agent storage tank; and

a molding machine molding the mixture by receiving the mixture from the mixer.
The apparatus of claim 11 further comprising a drier connected directly with the plurality of crushers to dry the powdered coals together.