AU2012210130A1

AU2012210130A1 - Method for Producing Low-Grade Coal Slurry, Apparatus for Producing Low-Grade Coal Slurry, and System for Gasifying Low-Grade Coal

Info

Publication number: AU2012210130A1
Application number: AU2012210130A
Authority: AU
Inventors: Noriyuki Kimura; Norihiko Kumada; Shoichi Mori; Motohiko Nishimura; Yoshiharu Nonaka; Shoichi Takao
Original assignee: Kawasaki Heavy Industries Ltd; Kawasaki Jukogyo KK
Current assignee: Kawasaki Motors Ltd
Priority date: 2011-01-24
Filing date: 2012-01-11
Publication date: 2013-06-27
Anticipated expiration: 2032-01-11
Also published as: JP2012153760A; WO2012101963A1; CN103282469B; JP6134087B2; CN103282469A; AU2012210130B2

Abstract

The purpose of the present invention is to provide: a production method and production device with which it is easy to produce a low-grade coal slurry having a high slurry concentration and a low viscosity, and which is appropriate for gasification using a pressurized gasification furnace; and a gasification system provided with such a production device. This low-grade coal slurry production method has: a first step for performing a modification treatment on coarsely ground low-grade coal under high-temperature and high-pressure conditions; and a second step for adding water and a dispersant to the modification-treated low-grade coal, and forming a slurry from the low-grade coal using a wet-grinding method. In addition, this low-grade coal slurry production device has: a dry-grinding device for dry-grinding the low-grade coal; a high-temperature/high-pressure kneading device for performing a modification treatment on the dry-ground low-grade coal; and a wet-grinding device for adding the dispersant, and the water discharged from the low-grade coal during the modification treatment, and forming a slurry from the modification-treated low-grade coal.

Description

[DESCRIPTION] [Title of Invention] METHOD FOR PRODUCING LOW-GRADE COAL SLURRY, APPARATUS FOR PRODUCING LOW-GRADE COAL SLURRY, AND SYSTEM FOR GASIFYING LOW-GRADE COAL [Technical Field] [0001] The present invention relates to a method and an apparatus for producing a slurry suitable as fuel for pressurized gasification furnaces from low-grade coal such as brown coal. The present invention also relates to a low-grade coal gasification system equipped with a pressurized gasification furnace using such a slurry as fuel. [Background Art] [00021 In recent years, the consumption of energy resources has been growing rapidly on a global basis and the price of oil, coal, natural gas, or the like as a main energy source has been increasing. Therefore, how to effectively utilize these energy sources has become a critical issue. [0003] From the viewpoint of not only the efficiency and cost of power generation but also the safety of physical distribution such as transportation or storage, bituminous coal with a high calorific value is usually utilized as fuel coal. However, supply and demand of bituminous coal has become tight on a global basis due to economic growth in developing countries. [00041 On the other hand, it is estimated that the reserves of low-grade coal such as brown coal, lignite, or subbituminous coal are 600 billion tons or more that exceeds the reserves of high-grade coal such as bituminous coal. However, low-grade coal has a high moisture content, and therefore the utilization thereof as fuel for power generation boilers or the like reduces thermal efficiency and increases power generation cost. Further, brown coal has high reactivity and is more likely to spontaneously ignite when dried, and is therefore hardly utilized at present due to difficulty in transportation and storage. [0005] 1 Further, carbon dioxide (C0 2 ) emissions by coal-fired power generation tend to rapidly increase on a global basis, and it is believed that this is a serious factor causing global warming. Coal has higher CO 2 emissions per unit calorific value than oil or natural gas, and therefore the utilization of coal has been reduced in developed countries such as Japan due to an increased demand for reduction in CO 2 emissions. [0006] Low-grade coal such as brown coal is very cheap and is a promising fuel resource with large reserves, but is, in fact, not effectively utilized due to the above problems. Under the circumstances, technical developments are being made to provide a method for gasifying brown coal near a coal mine to utilize obtained syngas. The term "syngas" refers to a crude gas produced using, as a raw material, hydrocarbon such as coal or natural gas and containing hydrogen (H 2 ) , carbon monoxide (CO), and carbon dioxide (C0 2 ) or methane or the like, and is a generic name for a raw-material gas used for ammonia synthesis, methanol synthesis, hydrogen production, or the like. [00071 Particularly, attention is being given to utilization of C0 2 -free syngas obtained by separating and recovering CO 2 from syngas produced by gasifying low-grade coal such as brown coal near a coal mine. For example, it is expected that a method will be established in a future hydrogen society, in which hydrogen is separated from syngas obtained by gasifying brown coal, purified, and liquefied to obtain liquid hydrogen and the liquid hydrogen is transported and used as fuel for gas turbines or gas engines. [0008] A technique for gasifying bituminous coal using a coal gasification furnace has already been applied to a commercial plant in which bituminous coal is wet-ground to prepare a water slurry and the water slurry is supplied together with oxygen to awet-type oxygen-blown gasification furnace operatedunder high temperature and pressure. Further, a method for carrying powdered coal obtained by finely grinding bituminous coal by airflow to supply the powdered coal to a gasification furnace has also already been applied to a commercial plant. [0009] 2 When bituminous coal is gasified using a pressurized gasification furnace, handling and transfer of groundbituminous coal become easy by adding water and an additive such as a dispersing agent thereto so that a slurry is prepared. Bituminous coal is lower in price per unit calorific value than heavy oil or the like, and is therefore attracting attention as a fuel alternative to oil. [0010] When coal is supplied as a slurry to a pressurized gasification furnace, a reduction in the viscosity of the slurry makes it easy to handle and transfer the slurry, but a reduction in the slurry concentration (coal concentration) of the slurry reduces energy efficiency. Particularly, in the case of low-grade coal such as brown coal, a reduction in slurry concentration causes a significant reduction in energy efficiency because of its higher moisture content than bituminous coal. Therefore, there is a demand for a method for producing a high-concentration and low-viscosity low-grade coal slurry. [0011] Patent Document 1 discloses a method in which, for the purpose of obtaining a slurry having a preferred appearance viscosity of about 1000 cP and a coal content as high as possible (about 70 wt%) with the use of low-grade coal as raw-material coal, a dehydrated cake, water, and a dispersing agent are kneaded in two steps: a first step in which a dehydrated cake and water are kneaded with no dispersing agent added or with a dispersing agent added in such a small amount that a kneaded product does not have flowability; and a second step in which the dispersing agent is added when the kneaded product is turned into a paste and the paste is further kneaded. [Citation List] [Patent Literature] [0012] PTL 1: Japanese Laid-open Patent Application Publication No. 11-335680 [Summary of Invention] [Technical Problem] [0013] The moisture content of brown coal reaches as high as 30 3 to 70%, and therefore when a water slurry is prepared by further adding water, the total moisture content of the slurry (the total amount of moisture contained in the brown coal and moisture present outside the brown coal as a dispersion medium of the slurry) becomes extremely high. In this case, a great amount of heat is consumed for moisture evaporation in a pressurized gasification furnace, and therefore energy efficiency becomes extremely low. For this reason, a method has hardly been studied in which a water slurry of low-grade coal, such as brown coal, with a high moisture content is prepared and supplied to a pressurized gasification furnace to gasify the low-grade coal. [00141 Fig. 2 shows a schematic flow chart of a slurry production method disclosed in Patent Literature 1. It is reported that the slurry production method disclosed in Patent Literature 1 is capable of producing a high-concentration slurry even when brown coal or subbituminous coal is used which is highly hygroscopic, has a high moisture content (30 to 70 wt%) , and has a hydrophilic surface. [0015] According to the slurry production method disclosed in Patent Literature 1 (Claim 3) , in a first step (grinding step) water is added to brown coal or subbituminous coal and a low-concentration slurry (10 to 40 wt%) is prepared by wet coarse grinding. However, areas near coal mines are often poor in water infrastructures, and therefore it can be imagined that it is hard to ensure a large amount of water. [0016] Then, the slurry is reformed by hot-water treatment (pressure: 12 to 15 MPa, temperature: 250 to 330 0 C) in a second step (reforming step) , and the reformed slurry is dehydrated in a third step (dehydration step) to obtain a dehydrated cake. However, the dehydrated cake has no flowability and is therefore difficult to handle and transfer. In a subsequent fourth step (first kneading step) , the dehydrated cake is kneaded to obtain a paste to again prepare a slurry, but the paste has no flowability and is therefore difficult to handle and transfer. Further, it cannot be expected that the brown coal or the like will be finely ground by kneading. [00171 4 Further, in a fifth step (second kneading step), a water slurry is prepared by adding a dispersing agent, but it is difficult to uniformly disperse the dispersing agent by kneading. [0018] An object of the present invention is to provide a method for easily producing a high-slurry concentration and low-viscosity low-grade coal slurry suitable for gasification by a pressurized gasification furnace. [Solution to Problem] [0019] The present inventor has intensively studied to solve the above problems associated with the conventional technique for producing a low-grade coal slurry. As a result, the present inventor has found that, when a low-grade coal slurry is prepared, the amount of moisture contained in low-grade coal can be reduced while increasing the amount of moisture present outside the low-grade coal as a dispersion medium not by externally adding water to the ground low-grade coal but by reforming the low-grade coal under high temperature and pressure to release water contained in the low-grade coal. Further, the present inventor has found that by doing so, it is possible, even when low-grade coal is used as raw material coal, to obtain a slurry that has a total moisture content comparable to that obtained by the conventional technique but has a low viscosity and is easy to handle and transfer. These findings have led to the completion of the present invention. [0020] Specifically, the present invention provides a method for producing a low-grade coal slurry, comprising: a first step of subjecting coarsely-ground low-grade coal to reforming treatment under high temperature and pressure; and a second step of adding water released from the low-grade coal in the first step and a dispersing agent to the low-grade coal subjected to reforming treatment and wet-grinding the low-grade coal to prepare a slurry. [0021] In the first step, water contained in the coarsely-ground low-grade coal is released so that the low-grade coal is dried. Further, a surface microstructure of the low-grade coal is filled 5 with a tar component, which makes it possible to prevent the released water from being reabsorbed by the low-grade coal. [00221 Here, the low-grade coal refers to brown coal, subbituminous coal, lignite, or a mixture of two or more of them, but the present invention is particularly preferably applied to brown coal. [00231 The water (self-release water) released from the low-grade coal in the first step is recovered and used when the low-grade coal subjected to reforming treatment is wet-ground to prepare a slurry in the second step, which makes it possible to prepare a low-grade coal slurry even in the neighborhood of a coal mine poor in water resources. [00241 It is preferred that the reforming treatment in the first step is performed at a pressure of 0.5 MPa or higher but 8 MPa or lower and a temperature of 100 0 C or higher but 400 0 C or lower. [00251 It is preferred that a moisture content of the low-grade coal after the first step is 20 wt% or lower. The term "moisture content of the low-grade coal" here refers to the percentage of the weight of moisture contained in the low-grade coal to the total weight of the low-grade coal. [00261 It is preferred that the slurry obtained in the second step has a slurry concentration of 40 wt% or higher but 65 wt% or lower. The term "slurry concentration" here refers to the percentage by weight of the low-grade coal contained in the slurry on a dry coal basis (in terms of the weight of dry coal having a moisture content of 0 wt%, that is, on a dry basis). [00271 It is preferable to further include, after the second step, a third step of subjecting the obtained slurry to high-speed stirring treatment. By subjecting the slurry to high-speed stirring treatment, the stability of the slurry can be improved and therefore the slurry can also be stored before supplied to a pressurized gasification furnace. [00281 It is preferred that the dispersing agent is a 6 polystyrene-based dispersing agent, a naphthalenesulfonic acid-based dispersing agent, a methacrylic acid-based dispersing agent, or a lignin sulfonic acid-based dispersing agent, and an amount of the dispersing agent to be added to the slurry is 0.2 wt% or higher but 2 wt% or lower with respect to a dry weight of the low-grade coal. [00291 The present invention also provides an apparatus for producing a low-grade coal slurry, comprising: a high-temperature and high-pressure kneading device that subjects dry-ground low-grade coal to reforming treatment; and a wet-type grinding device that prepares a slurry of the low-grade coal by adding water released from the low-grade coal by reforming treatment and a dispersing agent to the low-grade coal subjected to reforming treatment. [00301 It is preferred that the apparatus for producing a low-grade coal slurry according to the present invention further includes a dry-type grinding device that coarsely grinds the low-grade coal. [00311 It is preferred that the apparatus for producing a low-grade coal slurry according to the present invention further includes a stirring device that subjects the slurry obtained by the wet-type grinding device to high-speed stirring treatment. [00321 The present invention also provides a system for gasifying low-grade coal, comprising: the apparatus for producing a low-grade coal slurry; a transfer pipe through which a slurry obtained from the wet-type grinding device or the stirring device is transferred; and a pressurized gasification furnace that gasifies the slurry transferred through the transfer pipe. [0033] The foregoing objects, other objects, characteristics, and advantages of the present invention will be clear from detailed descriptions of preferred embodiments givenbelowwith reference to attached drawings. 7 [Advantageous Effects of Invention] [0033] According to the present invention, it is possible to easily produce a high-slurry concentration and low-viscosity low-grade coal slurry suitable for gasification by a pressurized gasification furnace. Further, it is also possible to efficiently gasify, using a pressurized gasification furnace, low-grade coal, such as brown coal, that has hardly been used effectively. [Brief Description of Drawings] [00341 Fig. 1 shows a schematic configuration diagram illustrating one example of an apparatus for implementing a method for producing a low-grade coal slurry according to the present invention. Fig. 2 shows a schematic flow chart of a method for producing a low-grade coal slurry disclosed in Patent Literature 1. [Description of Embodiments] [0035] Hereinbelow, the present invention will be described in detail. It should be noted that the present invention is not limited to the descriptions given below. [0036] Fig. 1 is a schematic configuration diagram illustrating one example of an apparatus for implementing a method for producing a low-grade coal slurry according to the present invention. First, low-grade coal is coarsely ground by a dry-type grinding device 1. At this time, the low-grade coal is coarsely ground so that the amount of grains with a grain size of 3 mm or less (grains that pass through a sieve with a mesh size of 3 mm) is 70 wt% or more, preferably 90 wt% or more. [0037] Then, the coarsely-ground low-grade coal is supplied to a high-temperature and high-pressure kneading device 2 and subjected to reforming treatment by the application of heat and pressure. At this time, if necessary, a small amount of water may be supplied together with the low-grade coal to the high-temperature and high-pressure kneading device. In this case, the ratio between the low-grade coal and the water in the high-temperature and high-pressure kneading device 2 is 8 preferably adjusted so that the amount of the low-grade coal is 80 wt% or more on a wet coal basis (on the basis of the weight of the coarsely-ground low-grade coal itself (moisture content: 30 to 70 wt%), that is, on a wet basis). [00381 As the high-temperature and high-pressure kneading device 2, for example, a high-temperature pressurized batch double-arm kneader or a high-temperature pressurized continuous double-arm kneader can be used. The reforming treatment is preferably performed under conditions of a pressure of 0.5 MPa or higher but 8 MPa or lower and a temperature of 100 0 C or higher but 400 0 C or lower. By kneading the low-grade coal under such pressure and temperature conditions, moisture contained in the low-grade coal is released to the outside with little change in grain size (non-evaporating dehydration). As a result, the low-grade coal is dehydrated by non-evaporation to achieve a moisture content of 20 wt% or less. Further, the surface microstructure of the low-grade coal is filled with a tar component and hydrophilic functional groups on the surface of the low-grade coal are changed to hydrophobic functional groups, and therefore the released moisture is less likely to be reabsorbed by the low-grade coal so that the surface hydrophobicity of the low-grade coal is enhanced. [0039] The low-grade coal subjected to reforming treatment in the high-temperature and high-pressure kneading device 2 is supplied to a shaking screen 4. At this time, the moisture content of the low-grade coal is preferably 20 wt% or lower. The shaking screen 4 separates the low-grade coal and part of the moisture released from the low-grade coal from each other. Part of the moisture released from the low-grade coal is usually recovered by the shaking screen 4 as hot water. However, when the temperature of the reforming treatment is high, part of the moisture released from the low-grade coal may be recovered as water vapor from the high-temperature and high-pressure kneading device 2. [00401 It should be noted that the shaking screen 4 is an optional component and may be omitted when the moisture released from the low-grade coal is taken out of the high-temperature and 9 high-pressure kneading device 2 as water vapor. In this case, the water vapor is cooled and recovered as drain water. [00411 The low-grade coal separated from the moisture is supplied to a wet-type grinding device 5 together with all or part of the water (recovered water) recovered by the shaking screen 4 and a dispersing agent. Then, the low-grade coal is finely ground by the wet-type grinding device 5 to prepare a low-grade coal slurry. As the wet-type grinding device 5, for example, a wet-type ball mill or a media agitating mill can be used. It should be noted that a surplus of the recovered water may be disposed of or used for any other purposes. [00421 The amount of water to be supplied to the wet-type grinding device 5 is preferably adjusted so that the concentration of the low-grade coal slurry is in the range of 40 to 65 wt% on a dry coal basis (on a dry basis) depending on the degree of dehydration by the shaking screen 4. When only the recovered water is not enough to meet the water requirement of the slurry, the required amount of extra water is added. Further, the low-grade coal slurry is preferably finely ground so that the amount of low-grade coal grains with a grain size of 74 ptmor less (low-grade coal grains that pass through 200 mesh) is 30 to 90% of the total amount of low-grade coal grains. [00431 As the dispersing agent, a polystyrene-based dispersing agent, a naphthalenesulfonic acid-based dispersing agent, a methacrylic acid-based dispersing agent, or a lignin sulfonic acid-based dispersing agent can be used. The dispersing agent is preferably added so that its concentration in the low-grade coal slurry is 0.2 wt% or higher but 2 wt% or lower with respect to the dry weight of the low-grade coal contained in the low-grade coal slurry. [00441 In addition to the dispersing agent, a stabilizing agent such as carboxymethyl cellulose and/or a thickening agent such as xanthan gum may be added to the low-grade coal slurry to further improve the stability of the slurry. The concentration of the stabilizing agent or the thickening agent in the low-grade coal slurry is preferably adjusted to be 0.001 to 0.05 wt%. 10 [0045] A low-grade coal slurry obtained by the present invention is smaller in the amount of moisture contained in low-grade coal but larger in the amount of water as a dispersion medium than a conventional low-grade coal slurry even when they have the same level of total moisture content. Therefore, the low-grade coal slurry obtained by the present invention has a higher concentration and a lower viscosity than the conventional low-grade coal slurry and has properties suitable for gasification by a pressurized gasification furnace. [0046] Unlike a method disclosed in Patent Literature 1, in the present invention, a dispersing agent is added at the same time as mixing coarsely-ground low-grade coal with water to prepare a slurry, and therefore the dispersing agent can be uniformly dispersed in the slurry. [00471 As in the case of Patent Literature 1, when a low-concentration slurry is wet-ground, a grain size distribution with a small amount of fine grains is obtained. On the other hand, in the present invention, a very high-concentration mixture of low-grade coal and water is wet-ground, and therefore the wet-ground low-grade coal has an ideal grain size distribution with a large amount of fine grains. [00481 The low-grade coal slurry obtained by the wet-type grinding device 5 is stored in a slurry tank 6. The low-grade coal slurry in the slurry tank 6 is preferably stirred by a stirrer 7 (low-speed stirrer). Then, the low-grade coal slurry is supplied from the slurry tank 6 to a stirring device 10 through a transfer pipe 9 equipped with a transfer pump 8. By subjecting the low-grade coal slurry to high-speed stirring treatment using the stirring device 10 (high-speed stirrer) , the stability of the low-grade coal slurry is improved and therefore the separation of the low-grade coal can be prevented. [0049] As the stirring device 10, a line mixer or a mixing tank equippedwith ahigh speed-stirrer canbe used. When alinemixer is used, the rotation speed of the line mixer is preferably set to 500 to 5000 rpm, and the retention time of the low-grade coal 11 slurry is preferably set to 10 seconds to 2 minutes. The low-grade coal slurry (product slurry) subjected to high-speed stirring treatment is supplied to a pressurized gasification furnace through a transfer pipe 13 equipped with a transfer pump 12. [0050] It should be noted that the stirring device 10 is an optional component, and may be omitted when the low-grade coal slurry contained in the slurry tank 6 is immediately supplied to the pressurized gasification furnace. In this case, the low-grade coal slurry is supplied from the slurry tank 6 to the pressurized gasification furnace through the transfer pipe 9. [00511 The low-grade coal slurry supplied to the pressurized gasification furnace (wet coal slurry feed-type coalpressurized gasification furnace) is gasified therein and converted to syngas. If necessary, the obtained syngas is purified by separating impurities such as CO or C0 2 , to obtain hydrogen gas. The separated CO 2 is preferably fixed. Further, the separated CO is preferably oxidized to CO 2 and then fixed. In this way, a system for gasifying low-grade coal as a raw material in a pressurized gasification furnace is formed. [00521 [Example] (First step) Brown coal (Loy Yang coal fromAustralia) having properties shown in Table 1 was coarsely ground using a jaw crusher so that the amount of grains having a grain size of 3 mm or less was 90 wt% or higher (so that the amount of grains that pass through a sieve with a mesh size of 3 mm was 90 wt% or higher of the total weight of the brown coal) . The coarsely-ground brown coal was mixed with water to prepare a brown coal-water mixture with a brown coal content of 95 wt%. Ten kilograms of the mixture was fed into a high-temperature and high-pressure batch-type kneader equipped with a double-arm kneading blade and having a capacity of about 20 L. 12 [00531 TABLE 1 Total moisture 59.8 wt% Ash 0.8 wt% Volatile matter 20.6 wt% Fixed carbon 18.8 wt% [00541 The brown coal-water mixture was kneaded for 1 hour under conditions of a pressure of 5.0 MPa and a temperature of 280 0 C to dehydrate the brown coal by non-evaporation to subject the brown coal to reforming treatment. After the reforming treatment, the brown coal-water mixture turned into a paste (kneaded product) was taken out of the high-temperature and high-pressure batch-type kneader. The resulting kneaded product had total moisture content of 56.0 wt% due to the loss of moisture by evaporation etc. The inherent moisture content of the dehydrated brown coal (the amount of moisture contained in the brown coal) in the kneaded product was 18 wt%. [00551 Then, 3 kg of the kneaded product was supplied to a shaking screen to separate moisture. The total moisture content of the kneaded product after moisture separation was 36.0 wt%. Recovered water and a polystyrene-based dispersing agent were further added to the kneaded product subjected to moisture separation, and then the resulting mixture was fed into a wet-type ball mill (# 300 mm x L 300 mm, capacity: about 21 L) The amount of the recovered water to be added was adjusted so that the concentration of the brown coal in the entire kneaded product was 57 wt% on a dry coal basis. Further, the polystyrene-based dispersing agent was added in an amount of 0. 6 wt% with respect to the weight of the brown coal (on a dry coal basis). [0056] (Second step) The kneaded product, the water, and the dispersing agent fed into the wet-type ball mill were subjected to batch grinding to obtain a brown coal slurry containing brown coal grains that pass through 200 mesh in an amount of 75 wt% of the total weight 13 of the brown coal. The brown coal slurry had a concentration of 57 wt% on a dry coal basis, and its appearance viscosity as measured under conditions of a share velocity of 100 sec-1 and a temperature of 25 0 C was 1.3 Pa-s (1300 cP) . The brown coal slurry was allowed to stand (room temperature) in a plastic container with an internal volume of 500 mL at room temperature for 7 days, and as a result, the amount of the brown coal settled was about 7 vol%. [00571 (Third step) The brown coal slurry with a concentration of 57 wt% obtained in the second step was further subjected to high-speed stirring treatment using a high-speed stirrer (T.K Homomixer MARK II Type 2.5 manufactured by PRIMIX Corporation) at 1000 rpm for 1 minute. The appearance viscosity of the brown coal slurry after high-speed stirring treatment, as measured under conditions of a shear velocity of 100 sec- and a temperature of 25 0 C, was 1.1 Pa-s (1100 cP) . The brown coal slurry subjected to high-speed stirring treatment was allowed to stand (room temperature) in a plastic container with an internal volume of 500 mL for 7 days, and as a result, the amount of the brown coal settled was about 2 vol%. Therefore, it was confirmed that the stability of the brown coal slurry obtained in the second step was improved by further subjecting the brown coal slurry to high-speed stirring treatment. [0059] From the foregoing explanations, many improvements on and other embodiments of the present invention are apparent to a person skilled in the art. Therefore, the explanations above should be construed as illustrative examples provided for the purpose of explaining the best mode for carrying out the present invention to a person skilled in the art. It is possible to substantially alter the details of the structure and/or functions without deviating from the spirit of the present invention. [Industrial Applicability] [00581 The method for producing a low-grade coal slurry, the apparatus for producing a low-grade coal slurry, and the system for gasifying low-grade coal according to the present invention 14 are useful in the field of fuel or energy. [Reference Signs List] [0059] 1: Dry-type grinding device 2: High-temperature and high-pressure kneading device 3,11: Motor 4: Shaking screen 5: Wet-type grinding device 6: Slurry tank 7: Stirrer (Low-speed stirrer) 8,12: Transfer pump 9,13: Transfer pipe 10: Stirring device (High-speed stirrer) 15

Claims

1. A method for producing a low-grade coal slurry comprising: a first step of subjecting coarsely-ground low-grade coal to reforming treatment under high temperature and pressure; and a second step of adding water released from the low-grade coal in the first step and a dispersing agent to the low-grade coal subjected to reforming treatment and wet-grinding the low-grade coal to prepare a slurry.

2. The method for producing a low-grade coal slurry according to claim 1, wherein the reforming treatment in the first step is performed at a pressure of 0.5 MPa or higher but 8.0 MPa or lower and a temperature of 100 0 C or higher but 400 0 C or lower.

3. The method for producing a low-grade coal slurry according to claim 1, wherein a moisture content of the low-grade coal after the first step is 20 wt% or lower.

4. The method for producing a low-grade coal slurry according to claim 1, wherein the slurry obtained in the second step has a concentration of 40 wt% or higher but 65 wt% or lower.

5. The method for producing a low-grade coal slurry according to claim 1, wherein the dispersing agent is a polystyrene-based dispersing agent, a naphthalenesulfonic acid-based dispersing agent, a methacrylic acid-based dispersing agent, or a lignin sulfonic acid-based dispersing agent, and an amount of the dispersing agent to be added to the slurry is 0.2 wt% or higher but 2 wt% or lower with respect to a dry weight of the low-grade coal.

6. The method for producing a low-grade coal slurry according to claim 1, comprising, after the second step, a third step of subjecting the obtained slurry to high-speed stirring treatment.

7. An apparatus for producing a low-grade coal slurry comprising: a high-temperature and high-pressure kneading device that subjects coarsely-ground low-grade coal to reforming treatment; 16 and a wet-type grinding device that prepares a slurry of the low-grade coal by adding water released from the low-grade coal by reforming treatment and a dispersing agent to the low-grade coal subjected to reforming treatment.

8. The apparatus for producing a low-grade coal slurry according to claim 7, further comprising a dry-type grinding device that coarsely grinds the low-grade coal.

9. The apparatus for producing a low-grade coal slurry according to claim 7, further comprising a stirring device that subjects the slurry obtained by the wet-type grinding device to high-speed stirring treatment.

10. A system for gasifying a low-grade coal comprising: the apparatus for producing a low-grade coal slurry according to claim 7; a transfer pipe through which the slurry obtained from the wet-type grinding device or the stirring device is transferred; and a pressurized gasification furnace that gasifies the slurry transferred through the transfer pipe. 17