AU2012359295B2

AU2012359295B2 - High-calorific hybrid coal coated with biomass-derived carbon source, high concentration hybrid coal slurry, and fabrication methods thereof

Info

Publication number: AU2012359295B2
Application number: AU2012359295A
Authority: AU
Inventors: Young Chan Choi; Dong Wook Lee
Original assignee: Korea Institute of Energy Research KIER
Current assignee: Korea Institute of Energy Research KIER
Priority date: 2012-02-29
Filing date: 2012-08-17
Publication date: 2015-08-20
Anticipated expiration: 2032-08-17
Also published as: AU2012359295A1; JP2015513593A; CN103429718B; CN103429718A; WO2013129744A1

Abstract

The present invention provides high-calorific hybrid coal and its fabrication method in which a coal-inherent natural carbon ingredient and an artificial carbon ingredient are combined by coating a carbon ingredient of biomass-derived material on a hydrophilic surface of low-rank coal and thus changing the hydrophilic surface into a hydrophobic surface so as to suppress re-absorption of moisture after drying. Also, the present invention provides high-calorific hybrid coal with significantly lower moisture re absorption by using a two-step drying process. And also, the present invention provides high concentration hybrid coal slurry and its fabrication method in which the above-mentioned hybrid coal is added to one dispersion medium selected from water/alcohol, water/surfactant, and water/alcohol/surfactant.

Description

SPECIFICATION Title of the Invention HIGH-CALORIFIC HYBRID COAL COATED WITH BIOMASS-DERIVED CARBON SOURCE, HIGH CONCENTRATION HYBRID COAL SLURRY, AND FABRICATION METHODS THEREOF Technical Field The present invention relates to hybrid coal having biomass-derived carbon source coated on a hydrophilic surface thereof and a method for fabricating the hybrid coal. More particularly, the present invention relates to high-calorific hybrid coal and its fabrication method in which a coal inherent natural carbon ingredient and a biomass-derived artificial carbon ingredient are combined by coating the biomass-derived carbon source ingredient on a hydrophilic surface of raw coal containing moisture or dried coal and thus changing the hydrophilic surface into a hydrophobic surface so as to suppress re-absorption of moisture after drying. Also, the present invention relates to high concentration hybrid coal slurry and its fabrication method in which the above-mentioned hybrid coal is added to one dispersion medium selected from water/alcohol, water/surfactant, and water/alcohol/surfactant. Background Art Due to increasing oil prices and a deep distrust of the stability of atomic energy, coal as energy sources is again in the spotlight. In 2007, 1 minable reserves of total fossil fuel are about 100 years in consideration of a current consumption rate, and approximately 60 percent of them are just coal. Especially, low-rank coal such as brown coal and subbituminous coal is estimated to have about 50 percent of whole coal reserves, so that development of more efficient utilization technology for low-rank coal is required [Yvonne Traa, Chem. Commun., 2010, 46, 2175]. However, there are some serious problems to be overcome for efficient use of low-rank coal. Actually, to solve difficulties of high-rank coal supply, a thermoelectric power plant has used low-rank coal for mixed firing. However, this causes a reduction in generating efficiency due to higher inherent moisture content (20-65 wt%) of low-rank coal, and thus C02 emissions increase 20 percent or more in comparison with high-rank coal [X. Li et al., Energy Fuels, 2010, 24, 160]. As one solution, several low-rank coal drying technologies such as a simple drying, a high-pressure hydrothermal drying or a drying using high temperature organic solvent have been widely studied. However, this solution has still some drawbacks such as a complicated process and a lowering of generating efficiency due to re-absorption of moisture after drying. Additionally, in this solution, spontaneous combustion often occurs, unfavorably resulting in loss of stored coal [M. Morimoto et al., Energy Fuels, 2009, 23, 4533; D.J. Allardice et al., Fuel, 2003, 82, 661]. Accordingly, one of serious problems to be solved for promoting the use and supply of low-rank coal is technique to prevent low-rank dried coal from re-absorbing moisture and thereby to keep a reliable heating value and also suppress spontaneous combustion. One of techniques currently proposed to improve this issue is to remove inherent moisture of coal by heating low-rank coal through high-temperature organic solvent in a high 2 pressure atmosphere. However, this technique needs to selectively recover organic solvent and also to incur another energy cost due to a relatively complicated process. Therefore, simpler and more effective technique to suppress moisture re-absorption of dried coal is required. Meanwhile, as alternative energy sources, renewable energy is getting the spotlight all over the world. Compared to existing fossil fuel such as oil, coal, etc., renewable energy can reduce the emission of carbon dioxide and thus positively cope with global warming and climatic change. However, the use and supply of renewable energy such as solar power or wind power are still limited due to higher generation cost than fossil fuel. Furthermore, as the issue of a reduction in greenhouse gas has come to the fore by the Climatic Change Convention, and as the Renewable Portfolio Standard (RPS) has been introduced in Korea from 2012, most of energy providers have greatly burdened themselves. Therefore, the development and use of renewable energy sources are surely necessary to promote the use and supply of new renewable energy and to meet the RPS. Recently, compared to other renewable energy sources, biomass has become an object of attention since there is no need to worry about exhaustion and since technical development as energy sources is relatively easier. Particularly, as a recently remarkable one of renewable energy sources, biomass-derived material such as wood pellet or wood chip is expected to face with increasing demand since it is available for power production by mixing with coal. However, actually, there is a difficulty in keeping a stable supply of wood pellet or wood chip. In order to secure a stable supply of biomass fuel to be used for 3 reduced C02 emissions in a thermoelectric power plant, there is a need to develop new technique to utilize various biomass-derived materials for coal fired power generation [E.D. Larson et al., Energy Environ. Sci., 2010, 3, 28]. Additionally, in recent years, various eco-friendly, high efficiency techniques such as syngas fabrication through coal gasification, power generation through IGCC (Integrated Gasification Combined Cycle), synthetic oil fabrication and chemicals production through CTL (Coal To Liquid), and the like have been proposed and developed. Such techniques require the maintenance of a high concentration coal slurry state. Meanwhile, wet type coal gasification has still had a difficulty in fabricating high concentration slurry. Normally entrained-flow gasification is classified into dry-feeding type and wet-feeding type. Compared to dry feeding type, wet-feeding entrained-flow gasification has many advantages such as low construction cost, simple system structure and operation, and easy supply of coal slurry at a high pressure. Notwithstanding these advantages, wet-feeding type has a drawback of lower gasification efficiency caused by lower heating value of coal slurry than dry-feeding type because water is further required to produce slurry used for wet type gasification. Although various studies have been carried out to produce high concentration coal slurry so as to overcome the above drawback, it has been known that a more serious problem in case of low-rank coal is low concentration of coal slurry due to higher inherent moisture content thereof. Detailed Description of the Invention Technical Problems In order to solve the above-discussed problems, the first object of the 4 present invention is to promote an effective use of low-rank coal by providing high-calorific hybrid coal and its fabrication method in which a coal-inherent natural carbon ingredient and an artificial carbon ingredient are combined by coating the artificial carbon ingredient on a hydrophilic surface of the low-rank coal and thus changing the hydrophilic surface into a hydrophobic surface so as to suppress re-absorption of moisture after drying. The second object of the present invention is to promote the use and supply of new renewable energy by employing biomass-derived material as a carbon ingredient when coating the carbon ingredient on a hydrophilic surface of high-rank coal as well as low-rank coal and thus changing the hydrophilic surface into a hydrophobic surface. The third object of the present invention is to provide high concentration hybrid coal slurry and its fabrication method in which the above-mentioned hybrid coal is added to one dispersion medium selected from water/alcohol, water/surfactant, and water/alcohol/surfactant. Technical Solutions In order to accomplish the above-mentioned objects, the present invention provides a high-calorific hybrid coal that includes a coal-inherent natural carbon ingredient and an artificial carbon ingredient of biomass derived material coated on a hydrophilic surface of coal. The hydrophilic surface may be the surface of ash of the coal. The hydrophilic surface may be the surfaces of fixed carbon and volatile matter of the coal having functional groups of -COOH (carboxyl), NH 2 (amine), and -OH (hydroxyl). 5 The coal may be one selected from peat, lignite, subbituminous coal, bituminous coal, and anthracite. The coal may be raw coal having inherent moisture content of 5-70 weight percents. The coal may be dried coal having inherent moisture content less than 5 weight percent. The biomass-derived material may be sugar cane or molasses. The biomass-derived material may be saccharide converted from ligno cellulose or saccharide obtained by enzyme decomposition of starch. The biomass-derived material may be one selected from monosaccharide, disaccharide, and polysaccharide. The monosaccharide may be one selected from glucose, pructose, and galactose. The disaccharide may be one selected from sucrose, maltose, and lactose. The polysaccharide may be one selected from starch and ligno cellulose. A higher heating value of the hybrid coal may be 4000 kcal/kg or more. Additionally, the present invention provides a method for fabricating high-calorific hybrid coal including a biomass-derived carbon ingredient coated on a hydrophilic surface of coal. This method comprises steps of: i) forming paste by mixing the coal and a solution of biomass-derived material, and ii) putting the paste into a carbonizing furnace and then simultaneously performing both drying and carbonization of the biomass-derived material. In the step i), the biomass-derived material may be added 0.1-50 weight percents with regard to coal weight. 6 In the step i), the solution of the biomass-derived material may use water or organic solvent. Water-to-coal or organic solvent-to-coal weight ratio may be 0.1-5. In the step i), the organic solvent may be one selected from methanol, ethanol, and propanol. In the step ii), the drying and carbonization of the biomass-derived material may be performed at 150-900 for 0.1-10 hours. Also, this method may further comprise step of aging the paste in an atmosphere of normal temperature and pressure before the step ii). An aging time of the aging step may be 5-240 hours. The biomass-derived material may perform a function of binder for forming the hybrid coal. Additionally, as another technical solution for controlling a moisture re absorption ratio of high-calorific hybrid coal to much lower level, the present invention provides a method for fabricating high-calorific hybrid coal including a biomass-derived carbon ingredient coated on a hydrophilic surface of coal, together with the high-calorific hybrid coal fabricated using the method. This method comprises steps of: i) forming paste by mixing the coal and a solution of biomass-derived material; ii) aging the paste in an atmosphere of normal temperature and pressure for 5-240 hours; iii) pre drying the aged paste; and iv) putting the pre-dried paste into a carbonizing furnace and then simultaneously performing both drying and carbonization of the biomass-derived material. Additionally, the present invention provides a method for fabricating high concentration hybrid coal slurry. This method comprises step of forming the hybrid coal slurry by adding hybrid coal, fabricated using the 7 above fabrication methods, to one dispersion medium selected from water/alcohol, water/surfactant, and water/alcohol/surfactant. The water/alcohol dispersion medium may have alcohol-to-water weight ratio of 0.01-0.99. The alcohol used in the water/alcohol dispersion medium may be one selected from methanol, ethanol, and propanol. The surfactant may be one selected from CWM1002 (formaldehyde condensate of sodium naphthalene sulfonate), CWM1001 (polymer sulfonate), Na-CMC (carboxymethyl cellulose), Na-DBS (alkylbenzene sulfate), Na-LS (alkylsulfate sodium salt), NP1020 (alkylphenol ethyleneoxide(1 0)), NP1060 (alkylphenol ethyleneoxide(50)), CA1 053 (casteroil ethyleneoxide(50)), ATLOX4913 (methyl methacrylate graft copolymer), cetyltrimethylammonium bromide, and cetyltrimethylammonium chloride. Additionally, the present invention provides high concentration hybrid coal slurry fabricated using the above fabrication method. Advantageous Effects According to this invention, the hybrid coal in which biomass-derived material is penetrated and carbonized into a hydrophilic surface of coal and thereby hydrophobic carbon is coated on a hydrophilic surface can strongly suppress re-absorption of moisture and thus maintain a higher heating value of dried coal. Therefore, the hybrid coal of the invention can be favorably used as pulverized fuel for a power plant, enhance generating efficiency in comparison with a typical case of using low-rank coal itself for mixed firing, and significantly reduce C02 emissions of a power plant. Furthermore, 8 biomass added for fabrication of hybrid coal allows an additional reduction in C02 emissions. Also, this invention is useful in getting rid of burden of energy providers to have to secure biomass fuel to meet the RPS. Additionally, according to this invention, the hybrid coal slurry in which the above-mentioned hybrid coal is added to one dispersion medium selected from water/alcohol, water/surfactant, and water/alcohol/surfactant has much higher coal concentration in slurry in comparison with slurry using raw coal or dried coal. Therefore, when the high concentration hybrid coal slurry of this invention is applied to wet-feeding entrained-flow gasification, it is expected that gasification performance such as coal conversion ratio or cold gas efficiency is improved and thus C02 emissions are reduced in a gasification process. Moreover, the realization of high concentration slurry using low rank coal with high moisture content can raise competitiveness of a wet feeding gasifier over a dry-feeding gasifier with a complicated structure. Besides, since biomass-derived material is added 0.1-50 weight percents with regard to coal weight in fabrication of hybrid coal used for slurry, the use of high concentration hybrid coal slurry in a wet-feeding coal gasifier can further reduce C02 emissions through the influence of biomass. Description of the Drawing FIG. 1 is a schematic view of high concentration hybrid coal slurry which is upgraded using biomass-derived material from low-rank coal in accordance with an embodiment of the present invention. FIG. 2 is a photograph showing the result of hydrophobic experiment regarding hybrid coal and simple dried coal fabricated respectively in the 9 embodiment 1 and the comparative example 1. FIG. 3 is a graph showing the result of viscosity measurement regarding hybrid coal slurry in the embodiments 1 and 2 and slurry of dried coal and raw coal in the comparative examples 1 and 2. FIG. 4 is a graph showing variations in heating values of slurry according to viscosity of hybrid coal slurry in the embodiment 1 and slurry of dried coal and raw coal in the comparative examples 1 and 2. FIG. 5 is a view showing the result of hydrophobic evaluation (contact angle measurement) regarding hybrid coal and simple dried coal fabricated respectively in the embodiment 3 and the comparative example 3. FIG. 6 is a graph showing a distribution of pore sizes of hybrid coal fabricated in the embodiment 3 and the comparative example 4. Best Mode for Carrying Out the Invention Hereinafter described in detail is technique to upgrade low-rank coal by means of fabrication of high-calorific hybrid coal in which a coal-inherent natural carbon ingredient and an artificial carbon ingredient are combined by coating a carbon ingredient of biomass-derived material on a hydrophilic surface of low-rank coal and thus changing the hydrophilic surface into a hydrophobic surface so as to suppress re-absorption of moisture after drying. Additionally, technique to fabricate high concentration hybrid coal slurry in which the aforesaid hybrid coal is added to one dispersion medium selected from water/alcohol, water/surfactant, and water/alcohol/surfactant will be described in detail with reference to the accompanying drawings. 10 FIG. 1 is a schematic view of high concentration hybrid coal slurry which is upgraded using biomass-derived material from low-rank coal in accordance with an embodiment of the present invention. As shown in FIG. 1, in one aspect of this invention, high-calorific hybrid coal including a biomass-derived carbon ingredient coated on a hydrophilic surface of coal is obtained through steps of i) forming paste by mixing the coal and a solution of biomass-derived material, and ii) putting the paste into a carbonizing furnace and then simultaneously performing both drying and carbonization of the biomass-derived material. The hydrophilic surface is the surface of ash of the coal, and surfaces of fixed carbon and volatile matter of the coal having functional groups of COOH (carboxyl), -NH 2 (amine), and -OH (hydroxyl). The coal may be one selected from peat, lignite, subbituminous coal, bituminous coal, and anthracite. Although this invention is basically to fabricate high-calorific hybrid coal from low-rank coal, the method for fabricating hybrid coal of the invention may also be applied to high-rank coal. Additionally, the coal is raw coal having inherent moisture content of 5-70 weight percents or dried coal having inherent moisture content less than 5 weight percent. Meanwhile, the biomass-derived material is sugar cane or molasses, and may be one selected from monosaccharide, disaccharide, and polysaccharide. The reason for being able to coat a carbon ingredient by using the biomass-derived material is that the biomass-derived material contains saccharide. Therefore, besides sugar cane or molasses, the biomass 11 derived material may include saccharide converted from ligno-cellulose or saccharide obtained by enzyme decomposition of starch such as corn. The monosaccharide is selected from glucose, pructose, and galactose. Also, the disaccharide is selected from sucrose, maltose, and lactose. And also, the polysaccharide is selected from starch and ligno-cellulose. A higher heating value of the hybrid coal is 4000 kcal/kg or more. Preferably, the paste is formed by adding the biomass-derived material to water or organic solvent selected from methanol, ethanol, and propanol. At this time, the biomass-derived material is added 0.1-50 weight percents with regard to coal weight. If the biomass-derived material is added less than 0.1 weight percent, it is difficult to change a hydrophilic surface of coal into a hydrophobic surface due to an insufficient coating of the biomass derived material on the hydrophilic surface of coal. If the biomass-derived material is added more than 50 weight percent, it is difficult to obtain a paste form due to poor processability. When a solution of the biomass-derived material is created using water or organic solvent, water-to-coal or organic solvent-to-coal weight ratio is maintained in the range of 0.1 to 5. If the above ratio is less than 0.1, it is difficult to change a hydrophilic surface of coal into a hydrophobic surface due to poor penetration of the biomass-derived material into the hydrophilic surface of coal. If the above ratio is more than 5, energy consumption is unfavorably increased in drying and carbonization processes. After the paste is formed, the paste put into a carbonizing furnace, and then the drying and carbonization processes are simultaneously performed, preferably, at 150-900 for 0.1-10 hours. If the drying and carbonization processes are performed at less than 150 for less than 0.1 hours, it not 12 only causes insufficient drying of water or organic solvent, but also causes incomplete carbonization of the biomass-derived material. If the drying and carbonization processes are performed at more than 900 for more than 10 hours, longer drying and carbonization processes at a higher temperature deteriorate efficiency due to increased energy cost. Additionally, the fabrication method further includes, before the step ii), step of aging the paste in an atmosphere of normal temperature and pressure so as to improve the penetration of the biomass-derived material into the hydrophilic surface of coal. An aging time of the aging step is 5-240 hours. Meanwhile, the biomass-derived material used for changing a hydrophilic surface of coal into a hydrophobic surface also performs a function of binder for forming the hybrid coal. This results in enhanced formability and processability. Additionally, in another aspect of this invention, in order to control a moisture re-absorption ratio of high-calorific hybrid coal to much lower level, high-calorific hybrid coal including a biomass-derived carbon ingredient coated on a hydrophilic surface of coal is fabricated through a two-step drying process, including steps of: i) forming paste by mixing the coal and a solution of biomass-derived material; ii) aging the paste in an atmosphere of normal temperature and pressure for 5-240 hours; iii) pre-drying the aged paste; and iv) putting the pre-dried paste into a carbonizing furnace and then simultaneously performing both drying and carbonization of the biomass-derived material. This aspect of the invention is characterized by aging the paste in an atmosphere of normal temperature and pressure for 5-240 hours so as to 13 improve the penetration of the biomass-derived material into the hydrophilic surface of coal, and then pre-drying the aged paste. In conventional technique, biomass and coal are simply and physically combined together. Unfortunately, this causes uneven combustion characteristics. However, in the present invention, the biomass-derived material is penetrated into pores of coal and physicochemically combined with coal. This causes uniform combustion characteristics, and also pore filling of coal reduces the degree of re-absorption of moisture after drying. Therefore, as the pores of coal are more effectively filled, a re-absorption ratio of moisture becomes more reduced. In this aspect of the invention, the step of pre-drying the paste of coal and biomass-derived material allows the paste to fill more effectively the pores of coal. Therefore, the volume of pores becomes much more decreased, and a re-absorption ratio of moisture is remarkably reduced in the hybrid coal passing through the succeeding drying and carbonization step. Preferably, the pre-drying step is performed at 50-150 for 0.1-24 hours. If the pre-drying step is performed at less than 50 for less than 0.1 hours, it not only causes insufficient drying of water or organic solvent, but also results in insignificant pore-filling of coal. If the pre-drying step is performed at more than 150 for more than 24 hours, longer pre-drying step at a higher temperature deteriorates efficiency due to increased energy cost. In this aspect of the invention, the method for fabricating high-calorific hybrid coal through a two-step drying process has the same conditions of process as those in the above-discussed previous aspect, except for the pre-drying step. 14 The high-calorific hybrid coal fabricated through a two-step drying process has a heating value of 4000 kcal/kg or more as received basis. Additionally, as shown in FIG. 1, this invention provides a method for fabricating high concentration hybrid coal slurry by adding the above discussed hybrid coal to one dispersion medium selected from water/alcohol, water/surfactant, and water/alcohol/surfactant. In case of using water/alcohol as dispersion medium, an alcohol-to-water weight ratio is 0.01-0.99. If the alcohol-to-water weight ratio is less than 0.01, poor dispersibility makes it difficult to form slurry. If the alcohol-to-water weight ratio is more than 0.99, a wet gasification reaction does not occur. It is therefore desirable that the alcohol-to-water weight ratio is maintained in the range of 0.01 to 0.99. Alternatively, to enhance dispersibility, water/surfactant may be used as dispersion medium by replacing alcohol with surfactant. Although any kind of surfactant used normally for enhancing dispersibility in slurry fabrication is available, it is desirable to use, as surfactant, CWM1002 (formaldehyde condensate of sodium naphthalene sulfonate), CWM1001 (polymer sulfonate), Na-CMC (carboxymethyl cellulose), Na-DBS (alkylbenzene sulfate), Na-LS (alkylsulfate sodium salt), NP1020 (alkylphenol ethyleneoxide(10)), NP1060 (alkylphenol ethyleneoxide(50)), CA1053 (casteroil ethyleneoxide(50)), ATLOX4913 (methyl methacrylate graft copolymer), cetyltrimethylammonium bromide, or cetyltrimethylammonium chloride. The amount of such surfactant added may be suitably adjusted depending on the kind of surfactant within the range allowing good formation of slurry. 15 Also, in order to much enhance dispersibility, water/alcohol/surfactant may be alternatively used as dispersion medium. In the water/alcohol dispersion medium, alcohol is selected from methanol, ethanol, and propanol. Mode for Carrying Out the Invention Now, various embodiments of the present invention will be described in detail. (Fabrication Example of Hybrid Coal) Raw coal obtained from Shivee ovoo in Mongolia was dried in the oven of 110 for 12 hours so as to prepare dried coal 100g. Also, sucrose 25g was dissolved in water 100g so as to prepare a sucrose solution. Then, by mixing the dried Shivee ovoo coal and the sucrose solution, a complex of the Shivee ovoo coal and the sucrose solution was obtained in the form of paste. The above paste was put into a reactor of 250 in a nitrogen atmosphere, and then a drying and carbonization process was performed for 5 hours. As a result, hybrid coal was fabricated. Table 1 given below shows the result of technical analysis and heating values of the Shivee ovoo raw coal and the hybrid coal in this fabrication example. [Table 1] analysis technical analysis (wt%) higher lower heating item moistur volatile ash fixed heating value value /sample e matter carbon (kcal/kg) (kcal/kg) 16 Shivee 35.10 25.23 15.78 23.89 4,420 3,990 ovoo raw coal hybrid coal 3.25 37.27 21.40 38.08 4,770 4,560 As shown in Table 1, a lower heating value (in case of considering latent heat of vaporization) of the hybrid coal was greater by 570 kcal/kg than that of the Shivee ovoo raw coal. Also, a higher heating value of the hybrid coal was greater by 350 kcal/kg than that of the Shivee ovoo raw coal. This shows that the hybrid coal has increased heating values. Additionally, compared to the Shivee ovoo raw coal, the hybrid coal contains much fixed carbon increased by about 14.2 wt% because of further having artificial carbon formed biomass-derived material. The more important point than the hybrid coal has greater heating values than the Shivee ovoo raw coal is that such heating values of the hybrid coal are maintained for a long time since moisture is not re-absorbed. Meanwhile, in the field of coal, technique to measure viscosity and concentration of slurry has been typically used for measuring moisture content absorbed in coal. It has been known that coal concentration in slurry is generally in inverse proportion to moisture absorption of coal at any viscosity. Namely, as coal concentration in slurry is lower, the amount of moisture absorption of coal is higher. With regard to hybrid coal in embodiments 1 and 2 given below and Shivee ovoo dried coal and Shivee ovoo raw coal in comparative examples 1 and 2 given below, the amount of moisture absorption was checked through viscosity measurement of slurry fabricated in the following embodiments. The result is shown in FIG. 3. [Embodiment 1] 17 Raw coal obtained from Shivee ovoo in Mongolia was prepared. Also, molasse 32g was dissolved in water 280g so as to prepare a molasse solution. Then, by mixing the Shivee ovoo raw coal and the molasse solution, a complex of the Shivee ovoo raw coal and the molasse solution was obtained in the form of paste. The above paste was put into a reactor of 250 in a nitrogen atmosphere, and then a drying and carbonization process was performed for 5 hours. As a result, hybrid coal was fabricated. By sieving the fabricated hybrid coal with 200 mesh, a sample of 75 or less was collected. Then, by adding the hybrid coal of 75 or less to a mixed solvent of ethanol/water having 0.1 weight ratio, slurry having hybrid coal concentration of 28, 30, 32, 34, 36, 38, 40 and 42 wt%, based on dried coal, was fabricated. [Embodiment 2] Slurry was fabricated by means of the same method as the above embodiment 1, except for fabricating hybrid coal by putting paste into a reactor of 350 in a nitrogen atmosphere and performing a drying and carbonization process for 5 hours. [Comparative Example 1] Raw coal obtained from Shivee ovoo in Mongolia was dried in the oven of 1100C for 12 hours so as to prepare dried coal 500g. By sieving the Shivee ovoo dried coal with 200 mesh, a sample of 75 or less was collected. Then, by adding the Shivee ovoo dried coal of 75 or less to a mixed solvent of ethanol/water having 0.1 weight ratio, slurry having hybrid coal concentration of 28, 30, 32, 34, 36, 38, 40 and 42 wt%, based on dried coal, was fabricated. 18 [Comparative Example 2] Slurry was fabricated by means of the same method as the comparative example 1, except for replacing the Shivee ovoo dried coal with Shivee ovoo raw coal. [Embodiment 3] Raw coal obtained from Shivee ovoo in Mongolia was dried in the oven of 105 for 12 hours so as to prepare dried coal 500g. Also, molasse 32g was dissolved in water 280g so as to prepare a molasse solution. Then, by mixing the dried Shivee ovoo coal and the molasse solution, a complex of the Shivee ovoo coal and the molasse solution was obtained in the form of paste. The above paste was aged in an atmosphere of normal temperature and pressure for 24 hours. The aged paste was pre-dried at 105 for 12 hours. The pre-dried paste was put into a reactor of 250 in a nitrogen atmosphere, and then a drying and carbonization process was performed for 2 hours. As a result, hybrid coal was fabricated. [Comparative Example 3] Shivee ovoo coal 500g was obtained by merely drying Shivee ovoo raw coal in the oven of 105 for 2 hours. [Comparative Example 4] The pre-drying step of the embodiment 3 was skipped. The aged paste was put into a reactor of 250 in a nitrogen atmosphere, and then a drying and carbonization process was performed for 2 hours. As a result, hybrid coal was fabricated. [Experimental Example 1] A simple experiment was performed to evaluate the hydrophobic 19 property of hybrid coal and simple dried coal, prior to slurry fabrication, in the embodiment 1 and the comparative example 1. Hybrid coal 3g was added to water 50g and mixed strongly using spatula. For comparison, Shivee ovoo dried coal 3g is added to water 50g and mixed strongly using spatula. FIG. 2 is a photograph showing each sample after mixing. As shown in FIG. 2, the Shivee ovoo dried coal easily absorbed water due to its amphiphilic property and thereby was dispersed, whereas the hybrid coal mostly floated on the surface of water due to its hydrophobic property in spite of strong mixing. This shows that hydrophilic pore surfaces of the hybrid coal were changed into hydrophobic and thereby re absorption of moisture was suppressed. The viscosity of coal slurry was measured to check coal concentration of hybrid coal slurry fabricated in the embodiments 1 and 2. Also, the viscosity was measured using slurry fabricated from Shivee ovoo dried coal and raw coal in the comparative examples 1 and 2. FIG. 3 shows the results. As shown in FIG. 3, at the same slurry viscosity, coal concentration was higher in order of hybrid coal, dried coal, and raw coal. Particularly, it was observed that coal concentration of slurry was significantly higher in case of the hybrid coal of this invention. When the viscosity of coal slurry is 3000 cP, coal concentration of slurry using hybrid coal fabricated in the embodiment 1 was higher by 9.4 wt% than in case of Shivee ovoo raw coal and was higher by 5.5 wt% than in case of Shivee ovoo dried coal. Similarly, coal concentration of slurry using hybrid coal fabricated in the embodiment 2 was higher by 8.1 wt% than in case of Shivee ovoo raw coal and was higher by 4.2 wt% than in case of Shivee ovoo dried coal. The reason is 20 that carbon coating of biomass-derived material prevents water added during slurry fabrication from permeating through hydrophilic surfaces changed into hydrophobic. Further, the reason is that an artificial carbon ingredient of biomass-derived material which fills hydrophilic ash pores reduces an effective volume for holding water. FIG. 4 shows variations in heating values of slurry according to viscosity of slurry with regard to respective samples in the embodiment 1 and the comparative examples 1 and 2. As shown, at the same viscosity conditions, hybrid coal in the embodiment 1 had a much higher heating value in comparison with Shivee ovoo dried coal in the comparative example 1 and Shivee ovoo raw coal in the comparative example 2. Therefore, the use of hybrid coal slurry for entrained-flow gasification may enhance gasification performance much more than the use of slurry of raw coal or dried coal. [Experimental Example 2] In order to evaluate a hydrophobic property of hybrid coal and simple dried coal fabricated respectively in the embodiment 3 and the comparative example 3, a disk of each coal sample was produced and then a contact angle of water drop was measured on the disk surface. Hybrid coal and dried coal were sieved respectively to obtain powder under 100 and then compressed with 50 atmospheric pressure to produce disks of 3cm in diameter. After dropping water on the disks of hybrid coal and dried coal fabricated respectively in the embodiment 3 and the comparative example 3, contact angles with disk surface were measured. FIG. 5 shows the results. As shown in FIG. 5, a contact angle of simple dried coal is 78.1 degrees, whereas a contact angle of hybrid coal is greatly increased to 21 132.3 degrees. A higher contact angle of water means a higher hydrophobic property of sample, and any contact angle more than 120 degrees is normally regarded as a high hydrophobic property. Therefore, it was verified that a hydrophobic property of hybrid coal is very high. This shows that hydrophilic pore surfaces of the hybrid coal were changed into hydrophobic and thereby re-absorption of moisture was significantly lowered. Meanwhile, Table 2 given below shows the result of technical analysis and heating values of the Shivee ovoo raw coal and the hybrid coal in the embodiment 3. [Table 2] analysis technical analysis (wt%) heating value net heating item moistur volatile ash fixed as received value /sample e matter carbon basis (kcal/kg) (kcal/kg) Shivee 34.44 25.22 18.91 21.43 2,786 2,466 ovoo raw coal hybrid coal 1.14 33.89 30.14 34.83 4,083 3,914 (embodime nt 3) As shown in Table 2, a net heating value (in case of considering latent heat of vaporization) of the hybrid coal was greater by about 1450 kcal/kg than that of the Shivee ovoo raw coal. Also, a heating value of the hybrid coal as received basis was greater by about 1300 kcal/kg than that of the Shivee ovoo raw coal. This shows that the hybrid coal has increased heating values. Additionally, compared to the Shivee ovoo raw coal, the hybrid coal 22 contains much fixed carbon increased by about 13.4 wt% because of further having artificial carbon formed biomass-derived material. The more important point than the hybrid coal has greater heating values than the Shivee ovoo raw coal is that such heating values of the hybrid coal are maintained for a long time since moisture is not re-absorbed. FIG. 6 is a graph showing a distribution of pore sizes of hybrid coal fabricated in the embodiment 3 using a two-step drying process by adopting a pre-drying step of paste and the comparative example 4 using a single drying process without a pre-drying step. As shown in FIG. 6, a pore size in the mezopore area of hybrid coal in the comparative example 4 is greater than that of hybrid coal fabricated in the embodiment 3. Namely, the hybrid coal using the pre-drying step of paste can further reduce a pore size by maximizing pore-filling effects. [Experimental Example 3] Coal fabricated in the embodiment 3 and the comparative examples 3 and 4 was immersed in water and agitation was carried out for 10 minutes such that water could be penetrated into a pore. Then percolation was performed for 20 minutes to remove external moisture and weight was measured. A moisture re-absorption ratio was calculated as below. Moisture re-absorption ratio (wt%) = (Cwet - Cdry) / Cdry * 100 [Cwet is weight of coal before moisture removal, and Cdry is weight of coal after moisture removal] Measurement results are shown in Table 3 given below. [Table 3] sample Shivee ovoo dried hybrid coal based hybrid coal based 23 coal (compar. on single-step on two-step example 3) drying (compar. drying example 4) (embodiment 3) moisture re- 44.55 34.93 30.74 absorption ratio (wt%) As shown in Table 3, the hybrid coal fabricated in the embodiment 3 using a two-step drying process has a moisture re-absorption ratio of 30.74 wt%, which is significantly lower than a moisture re-absorption ratio of 44.55 wt% in case of Shivee ovoo dried coal simply dried at 105 in the comparative example 3 and a moisture re-absorption ratio of 34.93 wt% in case of hybrid coal fabricated in the comparative example 4 using a single step drying process. Industrial Applicability The hybrid coal of this invention fabricated through a two-step drying process can be favorably used as pulverized fuel for a power plant by maintaining a higher heating value of dried coal, and also enhance generating efficiency in comparison with a typical case of using low-rank coal itself for mixed firing. 24

Claims

1. A method for fabricating high-calorific hybrid coal including a biomass-derived carbon ingredient coated on a hydrophilic surface of coal, the method comprising steps of: i) forming paste by mixing the coal and a solution of biomass-derived material; ii) aging the paste in an atmosphere of normal temperature and pressure; and iii) putting the paste into a carbonizing furnace and then simultaneously performing both drying and carbonization of the biomass-derived material.

2. The method of claim 1, wherein the biomass-derived material is added 0 1-50 weight percents with regard to coal weight.

3. The method of claim 1, wherein the solution of the biomass-derived material uses water or organic solvent.

4. The method of claim 3, wherein the organic solvent is one selected from methanol, ethanol, and propanol.

5. The method of claim 3, wherein water-to-coal or organic solvent-to coal weight ratio is 0.1-5.

6. The method of claim 1, wherein an aging time of the aging step is 5-240 hours.

7. The method of claim 1, wherein the drying and carbonization of the biomass-derived material is performed at a temperature of 150 "C-900"C for 0.1-10 hours. 25

8. The method of claim 14, wherein the biomass-derived material performs a function of binder for forming the hybrid coal.

9. A method for fabricating high-calorific hybrid coal including a biomass-derived carbon ingredient coated on a hydrophilic surface of coal, the method comprising steps of: i) forming paste by mixing the coal and a solution of biomass-derived material; ii) aging the paste in an atmosphere of normal temperature and pressure for 5-240 hours; iii) pre-drying the aged paste; and iv) putting the pre-dried paste into a carbonizing furnace and then simultaneously performing both drying and carbonization of the biomass-derived material.

10. The method of claim 9, wherein a heating value of the hybrid coal is 4000 kcal/kg or more as received basis.

11. The method of claim 9, wherein the pre-drying of the step iii) is performed at a temperature of 50 0 -150 0 C for 0.1-24 hours.

12. A method for fabricating high concentration hybrid coal slurry, the method comprising step of: forming paste by mixing a coal and a solution of biomass-derived material; aging the paste in an atmosphere of normal temperature and pressure; and putting the paste into a carbonizing furnace and then simultaneously 26 performing both drying and carbonization of the biomass-derived material to fabricate a hybrid coal; and forming the hybrid coal slurry by adding hybrid coal to one dispersion medium selected from water/alcohol, water/surfactant, and water/alcohol/surfactant.

13. The method of claim 12, wherein the water/alcohol dispersion medium has alcohol-to-water weight ratio of 0.01-0.99.

14. The method of claim 12, wherein alcohol used in the water/alcohol dispersion medium is one selected from methanol, ethanol, and propanol. 27