COAL BRIQUETTE AND PRODUCTION METHOD THEREFOR

Abstract

 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 irons are charged, and a reducing furnace connected to the melter-gasifier and providing the reduced iron. The method for manufacturing coal briquettes include i) providing fine coal; ii) preparing a mixture by mixing a hardening agent of 1 to 5 parts by weight and a binder of 5 to 15 parts by weight with respect to fine coals of 100 parts by weight; and iii) molding the mixture. In the providing of the fine coal, the fine coals include low-grade coal of more than 0 and 50wt% or less and remaining carbonaceous materials. The low-grade coal has a volatile matter (on a dry basis) of 25wt% to 40wt% and a free swelling index of more than 0 and less than 3.

Description

[Technical Field]

[0001] The present invention relates to coal briquettes and a method for manufacturing the same. More particularly, the present invention relates to coal briquettes including low-grade coal and a method for manufacturing the same.

[Background Art]

[0002] In a smelting reduction iron-making method, a reducing furnace reducing iron ore and a melter-gasifier melting reduced iron ore are used. In the case of melting iron ore in the melter-gasifier, as a heat source to melt iron ore, 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 to the outside. The coal briquettes charged into the melter-gasifier form a coal-packed bed. After oxygen is injected through a tuyere installed at the melter-gasifier, it combusted the coal-packed bed to generate a combustion gas. The combustion gas is transformed into hot reducing gas while rising 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.

[0003] The coal briquettes may be prepared by using bituminous coals. A ratio of the bituminous coals to the coal is very low, while the bituminous coal is not produced at all in Korea. Accordingly, all the bituminous coals required for preparing molten irons is imported from abroad to be used. Most of the bituminous coals are produced only in a few countries such as Australia, Canada, and the United States across the world, thereby high-quality bituminous coal used for iron making is being gradually depleted, so a supply and demand imbalance is caused and prices serioulsy fluctuate.

[DISCLOSURE]

[Technical Problem]

[0004] The present invention has been made in an effort to provide A method for manufacturing coal briquettes including low-grade coals.

[Technical Solution]

[0005] 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 i) a melter-gasifier into which reduced irons are charged, and ii) a reducing furnace connected to the melter-gasifier and providing the reduced iron. The method includes i) providing fine coal; ii) preparing a mixture by mixing a hardening agent of 1 to 5 parts by weight and a binder of 5 to 15 parts by weight with respect to fine coals of 100 parts by weight; and iii) molding the mixture. In the providing of the fine coal, the fine coals include i) low-grade coal of more than 0 and 50wt% or less and ii) remaining carbonaceous materials. The low-grade coal has a volatile matter (on a dry basis) of 25wt% to 40wt% and a free swelling index of more than 0 and less than 3.

[0006] In the providing of the fine coal, a gross calorific value on a dry basis of the fine coals may be 5500 Kcal/kg to 7000 Kcal/kg. In the providing of the fine coals, a carbon source additive of more than 0 wt% and 20 wt% or less may be added to the fine coal. The carbon source additive may include at least one carbon source selected from a group consisting of fine cokes, coke dusts, graphites, activated carbons, and carbon blacks. An amount of a first carbon included in the carbon source additive may be greater than that of a second carbon included in the carbonaceous materials.

[0007] In the providing of the fine coals, the amount of the low-grade coals may be 10wt% to 40wt%. More preferably, the amount of the low-grade coals may be 15wt% to 30wt%.

[0008] In the preparing of the mixture, the hardening agent may be at least one material selected from a group consisting of quicklime, slaked lime, limestone, calcium carbonate, cement, bentonite, clay, silica, silicate, dolomite, phosphoric acid, sulfuric acid, and an oxide. In the preparing of the mixture, the binder may be at least one material selected from a group consisting of molasses, bitumen, asphalt, coal tar, pitch, starch, water glass, plastic, a polymer resin, and oil.

[Advantageous Effects]

[0009] Since the coal briquettes are manufactured by using low-grade coal, manufacturing cost of the coal briquettes may be largely decreased. Further, a scope of resource utilization may be increased by using the low-grade coal.

[Description of the Drawings]

[0010] 

FIG. 1 is a schematic flowchart of a method for manufacturing coal briquettes according to an exemplary embodiment of the present invention.

FIG. 2 is a schematic diagram of an apparatus for manufacturing molten irons using the coal briquettes manufactured in FIG. 1.

FIG. 3 is a schematic diagram of another manufacturing apparatus of molten irons using the coal briquettes manufactured in FIG. 1.

[Mode for Invention]

[0011] Terms 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.

[0012] It is to be understood that the terminology used therein 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.

[0013] Unless it is mentioned otherwise, 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 meanings that coincide with related technical documents and the contents that are currently disclosed, but are not to be interpreted as the ideal or very official meaning unless it is defined otherwise.

[0014] It is understood that the term "hole" used below includes all of penetrating or digging shapes in dot, line, or face forms. Accordingly, the term "hole" includes all of shapes formed as a cavity or formed as a channel.

[0015] 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.

[0016] FIG. 1 is a schematic flowchart of a method for manufacturing coal briquettes according to an exemplary embodiment of the present invention. A flowchart of the manufacturing method of the coal briquettes of FIG. 1 is just to exemplify the present invention, and the present invention is not limited thereto. Accordingly, the manufacturing method of the coal briquettes may be variously modified.

[0017] As illustrated in FIG. 1, the manufacturing method of the coal briquettes includes i) providing fine coals, ii) manufacuring a mixture by mixing a hardening agent of 1 to 5 parts by weight and a binder of 5 to 15 parts by weight with respect to the fine coal of 100 parts by weight, and iii) molding the mixture. In addition, if necessary, the method for manufacturing coal briquettes may further include other processes.

[0018] First, in step S10, the fine coals are provided. The fine coals include low-grade coals and remaining carbonaceous materials. An amount of a volatile matter included in the fine coal is 20 wt% to 35 wt%. If the amount of the volatile matter is very little, a sufficient amount of reducing gas required for reducing iron ore may not be manufactured by charging the coal briquettes manufactured by the fine coals into the melter-gasifier. Further, if the amount of the volatile matter is very great, the coal briquettes charged into the melter-gasifier are easily differentiated and thus a heat source required for melting reduced iron charged into the melter-gasifier may not be sufficiently ensured. Accordingly, the amount of the volatile matter is controlled in the aforementioned range.

[0019] The coal may be classified by various types. In order to classify the coal, the degree of coalification may be used as a reference. The degree of coalification means a process in which a volatile matter of a plant is reduced and amount of fixed carbon is increased according to changes in a time, pressure, and a temperature in the underground. The coal may be classified as follows according to the degree of coalification. That is, the coal is classified into peat coal having carbon (on dry ash free basis) of about 60 % or less, brown coal having carbon of about 60% to 70%, sub-bituminous coal having carbon of about 70% to 75%, bituminous coal having carbon of about 75% to 85%, and anthracite coal having carbon of about 85% to 94%, according to the degree of coalification.

[0020] Meanwhile, the coals may be classified into coking coal and non-coking coal according to a coking property. Bituminous coal having a coking property has a characteristic in which coal particles are coupled to each other during carbonization. The coking property means that coal particles are contracted by solidification around 450°C to 500 °C while having heat softening and a flowing phenomenon around 350°C to 400°C and being coupled to each other to be swollen by generation of pyrolysis gas when the coal is heated. The coking property is evaluated as a free swelling index (FSI) by a measuring method (KS E ISO 501) for a coal-crucible swelling index in which a swelling property of the coal is measured by heating the coal up to a final temperature of 820±5 °C. Coal having an FSI of 3 or more is classified as coking coal, and coal having an FSI of less than 3 or less is classified as non-coking coal.

[0021] Bituminous coal having the coking property is mainly used for iron making for manufacturing coke. Meanwhile, since the non-coking coal has no binding capacity between coal particles, coke quality is deteriorated while the non-coking coal is used for manufacturing coke and thus the non-coking coal is not used for iron making. Thus, brown coal which is a non-coking coal and has a high volatile matter content, subbituminous coal, and bituminous coal having no coking property have been mainly used only for power generation. Meanwhile, anthracite coal which is a non-coking coal and has high fixed carbon and calorific value is mainly used in a fine coal injection (PCI) process.

[0022] The low-grade coal means inexpensive coal having a high volatile matter content, as a non-coking coal of which a free swelling index (FSI) is less than 3. The low-grade coal is mainly pulverized to fine coal to be used for power generation. In an exemplary embodiment of the present invention, inexpensive low-grade coal which is not used as coal for metallurgy is used.

[0023] The coal briquettes charged into the melter-gasifier directly contact a hot gas flow at approximately 1000 °C at a dome part of the melter-gasifier to be rapidly heated at 30°C/min or more. When a heating speed increases, a softening zone is increased to a high temperature and fluidity rapidly increases. Ultimately, non-coking coals which are not melted at a low heating speed of 3 °C/min are also melted at a rapid heating speed. When a change in viscosity for a temperature of the coals is large, tar particles are large, and the heating speed is fast, fluidity is changed according to discharge of tar, lots of oxygen exists, and cross-bonding is easily generated at a low heating speed. As a result, the fluidity of the coals is increased by rapid heating. Therefore, even when melting is not easy, soften-melting is generated by rapid heating.

[0024] Since the coke for iron making is manufactured by heating at a low speed of 3 °C/min, high-quality coke may be manufactured if the fluidity of the coal itself is high. Accordingly, if inexpensive low-grade coal having a low coking property and low fluidity is used, quality of the coke deteriorates. On the contrary, the coal briquettes are rapidly heated at 30 °C/min or more by directly contacting a hot gas flow at approximately 1000°C at the dome part of the melter-gasifier. Accordingly, the coal briquettes may be manufactured with the inexpensive low-grade coal which cannot be used when the coke for iron making is manufactured. For example, coal for power generation may be used as the low-grade coal.

[0025] The fine coal forming the coal briquettes charged into the melter-gasifier influences the behavior of the melter-gasifier. Accordingly, only the fine coal having limited characteristics may be used in the melter-gasifier. Here, the fine coal need to satisfy various conditions in terms of cold strength, hot strength, a hot differentiation rate, a coal ash content, and a fixed carbon content. Meanwhile, high-quality coal may be manufactured by mixing coal for controlling quality having a high mean reflectance with fine coal, but there is a problem in that manufacturing cost of the coal briquettes increases.

[0026] The amount of low-grade coal may be 0 to 50wt%. When the amount of low-grade coal is very large, since the quality of the manufactured coal briquettes deteriorates, the coal briquettes are differentiated well at a high temperature and the strength of char of the coal briquettes deteriorates, and thereby the operation of the melter-gasifier may be unstabilized. Accordingly, the amount of low-grade coal is controlled to the aforementione range. Preferably, the amount of low-grade coal may be 10wt% to 40wt%. More preferably, the amount of low-grade coal may be 15wt% to 30wt%.

[0027] A gross calorific value on dry basis of low-grade coals may be 5500Kcal/kg to 7000Kcal/kg. The calorific value represents a calorific value discharged by coal per unit mass during perfect combustion. The calorific value is measured by a KS E3707 standard and is represented by the gross calorific value on a dry basis. Strong coking coal having a high coking property among bituminous coal mainly used for metallurgy has a high calorific value of approximately 7500 Kcal/kg or more, and weak coking coals have a calorific value of 7000 Kcal/kg to 7500 Kcal/kg. Metallurgical coal has a high calorific value of approximately 7000 Kcal/kg or more, but the low-grade coal has volatile matter of 25wt% to 40wt%, an FSI (on a dry basis) of more than 0 and less than 3, and a low calorific value of 5500 Kcal/kg to 7000 Kcal/kg.

[0028] When the volatile matter content of low-grade coal is very high, the volatile matter component included in the coal briquettes is rapidly discharged and thus the coal briquettes are differentiated when the coal briquettes are charged into the melter-gasifier. As a result, the operation of the melter-gasifier may become unstable. Among the coal having the volatile matter content of less than 25%, the coking coal having a high FSI is expensive high-grad coal which is mainly used for manufacturing cokes in an iron making process. On the contrary, non-coking coal having a low FSI is coal having a high calorific value such as anthracite coals which is mainly used in a process of injecting pulverized fine coals. Accordingly, there is no coal having a volatile matter content of less than 25%, low FSI, and low calorific value among the low-grade coal.

[0029] Coal having the high FSI is usable for manufacturing coke and thus is traded at an expensive price. If coal having a high FSI is used for power generation, coal is swollen in a proportion to an increase of temperature to block an injection nozzle during the fine coal injection. Accordingly, only non-coking coal having an FSI of more than 0 and less than 3 enough to not block the injection nozzle while charging it may be used for power generation or in the process of charging fine coal.

[0030] When the calorific value of low-grade coal is very low, a sufficient calorific value for melting reduced iron may not be ensured while the coal briquettes are charged into the melter-gasifier. Further, low-grade coal having a high calorific value may be used, but non-coking coal having a high calorific value has a low volatile matter content such as anthracite coal which is mainly used in the process of injecting fine coal. Accordingly, there is no coal with the volatile matter content (on a dry basis) of 25% to 40% and high calorific value as non-coking coal having a low FSI, among the low-grade coal. Therefore, the calorific value of low-grade coal is maintianed in the aforementioned range.

[0031] Meanwhile, in the fine coal, a carbon source additive of more than 0 wt% and 20wt% or less may be added. As the carbon source additive, fine coke, coke dust, graphite, activated carbon, carbon black, or the like may be used. Here, an amount of a first carbon included in the carbon source additive may be greater than that of a second carbon included in carbonaceous materials. Accordingly, an amount of fixed carbon of the coal briquettes may be increased by the carbon source additive.

[0032] That is, since the low-grade coal has a high volatile matter content and a lower content of fixed carbon than that of bituminous coals, the low-grade coal may not be used for manufacturing molten iron. In the case of using coal briquettes including the low-grade coal in the melter-gasifier, the amount of reducing gas generated by coal briquettes is large, but a char production amount is relatively small. In this case, in order to supply a sufficient amount of char required in the melter-gasifier, more coal briquettes need to be charged into the melter-gasifier. Here, the reducing gas is in a redundant state, and since the amount of coal used per production ton of molten iron increases, manufacturing cost of molten iron increases. Accordingly, the carbon source additive having a high carbon content is partially mixed with fine coal to ensure the amount of fixed carbon required for coal briquettes.

[0033] Next, in step S20, a mixture is manufactured by mixing a hardening agent of 1 to 5 parts by weight and a binder of 5 to 15 parts by weight with respect to fine coal of 100 parts by weight. As the hardening agent, quicklime, slaked lime, limestone, calcium carbonate, cement, bentonite, clay, silica, silicate, dolomite, phosphoric acid, sulfuric acid, oxide, or the like may be used. When the amount of the hardening agent is very small, chemical binding between the binder and the hardening agent is not sufficiently generated, and thus the strength of coal briquettes may not be sufficiently ensured. Further, when the amount of hardening agent is very large, ash in coal briquettes increases and thus coal briquettes may not play a sufficient role as a fuel in the melter-gasifier. Accordingly, the amount of hardening agent is controlled in the aforementioned range.

[0034] As the binder, molasses, bitumen, asphalt, coal tar, pitch, starch, water glass, plastic, a polymer resin, oil, or the like may be used. Meanwhile, when the amount of binder is very small, the strength of coal briquettes may deteriorate. Further, when the amount of binder is very large, problems such as attachment during mixing of fine coal and the binder are caused. Accordingly, the amount of binder is controlled in the aforementioned range.

[0035] Meanwhile, a mixing order of the hardening agent and the binder may be randomly set. Accordingly, the hardening agent is mixed with fine coal and then the binder is mixed therein, or the binder is mixed with fine coal and then the hardening agent may be mixed therein.

[0036] Finally, in step S30, the mixture is molded. Although not illustrated in FIG. 1, the mixture is charged between a pair of rolls rotating in opposite directions to manufacture coal briquettes in a pocket or strip shape. As a result, coal briquettes having excellent hot strength and cold strength may be manufactured.

[0037] FIG. 2 illustrates a schematic diagram of an apparatus for manufacturing molten iron 100 using coal briquettes manufactured in FIG. 1. A structure of an apparatus for manufacturing molten iron 100 in FIG. 2 is just to exemplify the present invention, and the present invention is not limited thereto. Accordingly, the apparatus for manufacturing molten iron 100 in FIG. 2 may be modified in various shapes.

[0038] The apparatus for manufacturing molten iron 100 in FIG. 2 includes a melter-gasifier 10 and a reducing furnace 20. In addition, if necessary, other devices may be included. Iron ore is charged into the reducing furnace 20 and reduced. The iron ore charged into the reducing furnace 20 is dried in advance and then passed through the reducing furnace 20 to be prepared as reduced iron. The reducing furnace 20 is a packed layer type and receives reducing gas from the melter-gasifier 10 to form a packed layer therein.

[0039] Since coal briquettes manufactured by the manufacturing method of FIG. 1 are charged into the melter-gasifier 10, a coal-packed bed is formed in the melter-gasifier 10. A dome portion 101 is formed at an upper part of the melter-gasifier 10. That is, a wide space is formed as compared with another part of the melter-gasifier 10, and hot reducing gas exists therein. Accordingly, coal briquettes charged into the dome portion 101 may be easily differentiated by the hot reducing gas. However, since coal briquettes manufactured by the method of FIG. 1 have a high hot strengh, the coal briquettes are not differentiated at the dome portion of the melter-gasifier 10 and fall to the bottom of the melter-gasifier 10. Char generated by a pyrolysis reaction of coal briquettes falls to a lower portion of the melter-gasifier 10 to exothermic-react with oxygen injected via a tuyere 30. As a result, coal briquettes may be used as a heat source which keeps the melter-gasifier 10 at a high temperature. Meanwhile, since the char provides permeability, a large amount of gas generated below the melter-gasifier 10 and reduced iron supplied from the reducing furnace 20 may more easily and uniformly pass through the coal-packed bed in the melter-gasifier 10.

[0040] In addition to the aforementioned coal briquettes, if necessary, lump carbonaceous materials or coke may be charged into the melter-gasifier 10. A tuyere 30 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 combustion zone. The coal briquettes are combusted in the combustion zone to generate reducing gas.

[0041] FIG. 3 schematically illustrates an apparatus for manufacturing molten iron 200 using coal briquettes manufactured in FIG. 1. 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 shapes. Since the structure of the apparatus for manufacturing molten iron 200 in FIG. 3 is similar to the structure of the apparatus for manufacturing molten iron 100 in FIG. 2, like reference numerals are used for like parts, and the detailed description thereof is omitted.

[0042] As illustrated in FIG. 3, the apparatus for manufacturing molten iron 200 includes a melter-gasifier 10, a reducing furnace 22, a device for manufacturing compacted irons 40, and a compacted iron storage bin 50. Here, the compacted iron storage bin 50 may be omitted.

[0043] The manufactured coal briquettes are charged into the melter-gasifier 10. Here, the coal briquettes generate a reducing gas in the melter-gasifier 10 and the generated reducing gas is supplied to a fluidized-bed reducing furnace. Fine iron ore is supplied to a plurality of fluidized-bed reducing furnaces 22, and is manufactured into reduced iron while flowing by reducing gas supplied to the reducing furnaces 22 from the melter-gasifier 10. The reduced iron is compacted by the device for manufacturing compacted irons 40 and stored in the compacted iron storage bin 50. The compacted reduced iron is supplied from the compacted iron storage bin 50 to the melter-gasifier 10 to be melted in the melter-gasifier 10. Since the coal briquettes are supplied to the melter-gasifier 10 to be transformed to char having permeability, a large amount of gas generated below the melter-gasifier 10 and the compacted reduced iron more easily and uniformly pass through the coal-packed bed in the melter-gasifier 10 to manufacture high-quality molten iron.

[0044] In the following, the present invention will be described in more detail through experimental examples. The following experimental examples are just to exemplify the present invention, and the present invention is not limited thereto.

Experimental Example

[0045] Fine coal having an average shape and a mean grain size of 3.4 mm or less was prepared. The fine coal was manufactured by mixing metallurgical coal and low-grade coal. A carbon source additive was additionally mixed in the fine coal. Characteristics of the used metallurgical coal, low-grade coal, and carbon source additive are listed in the following Table 1. The volatile matter content of low-grade coal D and low-grade coal E was 30 % or more, respectively and a coking property (FSI) was 1.

(Table 1)

Coal group		Technical analysis (on dry basis)			Coking property	Calorific value
		VM	Ash	FC	FSI	Kcal/kg
Metallurgical coal	A	23.1	10.5	66.4	5.5	7530
	B	35.1	9.5	55.4	5.4	7170
	C	34.0	8.6	57.4	4.3	7220
Low-grade coal	D	31.5	15.0	53.5	1.0	6510
	E	30.8	13.4	55.8	1.0	6900
Carbon source additive	F	2.2	12.9	84.9	0.0	7070

[0046] 2.7 parts by weight of quicklime as a hardening agent based on 100 parts by weight of the manufactured fine coals was mixed, and then 10 parts by weight of molasses as a binder were uniformly mixed to manufacture a mixture. The mixture was compacted by a roll press to manufacture coal briquettes of a pillow shape and having dimensions of 64.5 mm × 25.4 mm × 19.1 mm. The hot strength of the coal briquettes was then measured.

Comparative Example

[0047] For comparison with the aforementioned experimental example, the fine coal was manufactured by using the metallurgical coal and the carbon source additive without using the low-grade coal. The rest of the manufacturing processes of the coal briquettes were the same as those in the aforementioend experimental example.

Experimental Example 1

[0048] Fine coal was manufactured by mixing metallurgical coal A of 35wt%, metallurgical coal B of 25wt%, low-grade coal E of 30wt%, and a carbon source additive of 10wt%.

Experimental Example 2

[0049] Fine coal was manufactured by mixing metallurgical coal A of 35wt%, metallurgical coal B of 20wt%, low-grade coal E of 30 wt%, and a carbon source additive of 15wt%.

Experimental Example 3

[0050] Fine coal was manufactured by mixing metallurgical coal A of 60wt%, low-grade coal D of 30wt%, and a carbon source additive of 10wt%.

Experimental Example 4

[0051] Fine coal was manufactured by mixing metallurgical coal A of 40wt%, low-grade coal D of 50wt%, and a carbon source additive of 10wt%.

Experimental Example 5

[0052] Fine coal was manufactured by mixing metallurgical coal A of 40wt%, metallurgical coal B of 30wt%, and low-grade coal D of 30wt%.

Experimental Example 6

[0053] Fine coal was manufactured by mixing metallurgical coal A of 20wt%, low-grade coal D of 70wt%, and a carbon source additive of 10wt%.

Experimental Example 7

[0054] Fine coal was manufactured by mixing metallurgical coal C of 20wt%, low-grade coal D of 70wt%, and a carbon source additive of 10wt%.

Comparative Example 1

[0055] Fine coal was manufactured by mixing metallurgical coal A of 35wt%, metallurgical coal B of 25wt%, metallurgical coal C of 30wt%, and a carbon source additive of 10wt%.

Experimental Result

[0056] The hot strength, the char strength, and the fixed carbon of the coal briquettes manufactured by Experimental Examples 1 to 7 and Comparative Example 1 were measured.

Hot strength measurement experiment

[0057] The hot strength of coal briquettes was measured in order to determine the differentiation degree of the coal briquettes generated in the melter-gasifier. To this end, under a heating condition set as 1000°C and an inert nitrogen atmosphere, coal briquettes of approximately 1 Kg were injected into a cylindrical reaction furnace with a diameter of 280mm at room temperature, and then the cylindrical reaction furnace was rotated at a rotational speed of 2rpm for 15minutes. In addition, the cylindrical reaction furnace was additionally rotated at a rotational speed of 20rpm for 30minutes to manufacture coal briquette char. As the differentiation degree of the coal briquette char was decreased, it was determined that the hot strength is excellent, and thus the hot strength was measured at a ratio of char with a grain size of 10mm or more as a contrast ratio.

Char strength measurement experiment

[0058] In order to verify whether the strength of char manufactured in a measuring apparatus of the hot strength of the coal briquettes deteriorates or not, the strength of the coal briquette char was evaluated by using an I-type drum device for measuring hot strength of coke for metallurgy. That is, 200g of coal briquette char with a grain size of 16 mm or more was put in the I-type drum device having a length of 600mm for measuring the hot strength of coke and rotated 600 at a speed of 20 rotations per minute, and then a residual ratio of 100mm or more was measured, and as a result, abrasion and impact resistance of the coal briquette char were measured. As a contrast ratio of the coal briquette char obtained by the hot strength measurement method is larger and the coal briquette char strength is higher, the differentiation of the coal briquettes in the melter-gasifier is small, thereby ensuring the char strength at a high temperature. The measurement results of the aforementioned hot strength and char strength and the measured amount of fixed carbon are listed in the following Table 2.

(Table 2)

Classification	Mixed ratio of fine coals						Quality of coal briquettes
	Metallurgical coals			Low-grade coals		Carbon source additive	Hot strength (%, contrast ratio)	Char strength (%, + 10 mm)	Fixed carbon (%, on dry basis)
	A	B	C	D	E	F
Experimental Example 1	35	25			30	10	91.6	78.3	56.2
Experimental Example 2	35	20			30	15	90.5	77.8	57.6
Experimental Example 3	60			30		10	88.5	73.7	59.6
Experimental Example 4	40			50		10	86.0	65.6	58.1
Experimental Example 5	40	30		30			90.1	70.1	54.3
Experimental Example 6	20			70		10	76.6	41.6	56.1
Experimental Example 7			20	70		10	70.4	37.9	53.9
Comparative Example 1	35	25	30			10	91.4	77.9	57.0

[0059] As listed in Table 2, the hot strength, the char strength, and fixed carbon of coal briquettes according to Experimental Example 1 to Experimental Example 5 were similar to the hot strength, the char strength, and fixed carbon of coal briquettes according to Comparative Example 1. Accordingly, even though fine coal is manufactured by mixing low-grade coal, coal briquettes having the same characteristics as the coal briquettes without the low-grade coals may be manufactured. However, like Experimental Example 6 and Experimental Example 7, when coal briquettes are manufactured by using a large amount of low-grade coals, the char stength was lower than the char stength of the coal briquettes manufactured according to Experimental Example 1 to Experimental Example 5 and the hot strength deteriorated, and as a result, it was not suitable for being used as the coal briquettes. Therefore, when a certain amount of low-grade coals was mixed, it could be seen that manufacturing costs of coal briquettes were reduced and the characteristics of coal briquettes were maintained.

Claims

1. 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 comprising:

a melter-gasifier into which reduced irons are charged, and a reducing furnace connected to the melter-gasifier and providing the reduced iron, the method comprising:

providing fine coal;

preparing a mixture by mixing a hardening agent of 1 to 5 parts by weight and a binder of 5 to 15 parts by weight with respect to fine coals of 100 parts by weight; and

molding the mixture, and

wherein in the providing of the fine coal, the fine coals comprise low-grade coal of more than 0 and 50wt% or less and remaining carbonaceous materials, and the low-grade coal has a volatile matter (on a dry basis) of 25wt% to 40wt% and a free swelling index of more than 0 and less than 3.

2. The method of claim 1, wherein in the providing of the fine coal, a gross calorific value on a dry basis of the fine coals is 5500 Kcal/kg to 7000 Kcal/kg.

3.  The method of claim 1, wherein in the providing of the fine coals, a carbon source additive of more than 0 wt% and 20 wt% or less is added to the fine coal.

4. The method of claim 3, wherein the carbon source additive comprises at least one carbon source selected from a group consisting of fine cokes, coke dusts, graphites, activated carbons, and carbon blacks, and an amount of a first carbon included in the carbon source additive is greater than that of a second carbon included in the carbonaceous materials.

5. The method of claim 1, wherein in the providing of the fine coals, the amount of the low-grade coals are 10wt% to 40wt%.

6. The method of claim 5, wherein the amount of the low-grade coals are 15wt% to 30wt%.

7. The method of claim 1, wherein in the preparing of the mixture, the hardening agent is at least one material selected from a group consisting of quicklime, slaked lime, limestone, calcium carbonate, cement, bentonite, clay, silica, silicate, dolomite, phosphoric acid, sulfuric acid, and an oxide.

8. The method of claim 1, wherein in the preparing of the mixture, the binder is at least one material selected from a group consisting of molasses, bitumen, asphalt, coal tar, pitch, starch, water glass, plastic, a polymer resin, and oil.

Drawing