[DESCRIPTION] [Invention Title] Counter flow multi baffle dryer for drying of high moisture coal and method thereof [Detailed Description] [Technical Field] The present invention relates to counter flow multi baffle dryer for drying of high moisture coal and method thereof. More specifically, the present invention relates to dryer with a multi baffle formed in zigzag to increase the drying efficiency of the coal. [Background Art] The use of coal that contains high moisture (peat, lignite, sub-bituminous coal) has been increasing with the increase of the coal price. The low-rank coal such as lignite contains more than 35% of moisture and its calorific value is under 4,200kcal/kg. The moisture in coal absorbs heat of vaporization during the combustion. As a result, it consumes the energy of the fuel. If a water-free coal gets combusted, the heat value by weight of the fuel increases and the amount of coal being used decreases to earn the needed energy. Decreased use of coal results in reduced amount of the green-house gas and improved thermal - 1 efficiency of the power plant. There have been many attempts to remove the moisture before using the low-rank coal. The moisture can be removed by using the hot air and saturated steam, or by squeezing the moisture out when the coal is mixed with a liquid. Using a hot air for drying the coal has been already commercialized. The GRE (Great River Energy) used the waste heat from the power plant to heat the air in order to dry the brown coal. They were able to decrease the amount of moisture in coal from 38% to 29%, and increased the efficiency of the power plant 0.27%. The fluid bed drying technology dries the coal through the fluidization the coal and requires long contact time (30 to 90 minutes). This technology needs a lot of electric power. The white Energy Co. in Australia developed a technology that allows the coal to dry more quickly by heating the coal up to 400 degrees Celsius. However, they have not yet succeeded in the commercialization of such technology. The flash drying technology reduces the contact time (less than 3 seconds), but the air speed is so fast that in produces fine particle and results in the loss of coal. It also uses high temperature (400 degrees Celsius or higher) to reduce the contact time, and causes a problem of combustion of the coal. Also, fine dusts get produced everywhere because of the fast air speed, and the coal may - 2 ignite. [Disclosure] [Technical Problem] It is an object of the present invention to provide an equipment to effectively dry the coal with low temperature and short contact time. It is an object of the present invention to increase the contact efficiency between the coal and the air, the rate of drying coal through maintained driving force, and the drying efficiency with the pressure gradient produced by the baffle. [Technical Solution] It is a feature of an example embodiment of the present invention to provide a dryer for coal, wherein the coal falls down from the upper part and air is fed in from the bottom part of it, the dryer comprises a multi baffle having a downward inclination formed in zigzag, wherein the coal is dried by falling in zigzag along the baffle. The baffle has downward inclinations at an angle of 20 - 80 degree against inner wall of the dryer. The baffle is formed alternately with adjacent baffle at the opposite side of the inner wall. The coal falls down continuously and repeatedly from the baffle to adjacent other baffle at the opposite side. - 3 - The baffle makes the air a turbulent flow and increase contact efficiency between the coal and the air. The dryer further provides a steady temperature gradient between the top and the bottom of the dryer and allowing a driving force to be constant in the dryer. The dryer further provides a vacuum at the upper part of baffles as the air travel fast at the upper part of them, whereby the coal is dried more effectively. The baffle is made with a good heat conduction metal to facilitate drying of the coal. The temperature of the air flowing from the bottom of the dryer is in the range of 80-C and 200-C. The amount of the air flowing from the bottom of the dryer is in the range of 3 to 15Nmm3/kg. The residence time of the coal inside of the dryer is in the range of 2 to 8 seconds. The dryer further comprises a coal inlet unit feeding the coal at the top of the dryer, a coal discharge unit collecting the dried coal at the bottom of the dryer, and an air inlet unit feeding the air inside of the dryer. The dryer further comprises a recovery unit to collect the pulverized coal. [Advantageous Effects] According to the invention, the coal crashes against the baffle, and as it falls down, the contact time with the air gradually increases. The rising air produces turbulent -4 flow by the baffle and contacts the coal. As a result, the efficiency of drying the coal increases. Also, the dryer made with this invention allows the maintenance of the temperature difference between the coal and the air, and keeps the drying speed steadily. High pressure is then formed around under the baffle and lower pressure is then formed around on the baffle and because of this difference of pressure, the drying process accelerates. Therefore, this dryer with such technology is able to dry the coal effectively even with the low temperature, low amount of air, and a short contact time. Additionally, the temperature decreases with the air going upwards, and as the coal falls down, its surface moisture gets removed, because it meets the low temperature air at the top of the dryer and it meets higher air temperature at the middle and bottom part of the dryer. This allows an effective drying process. [Description of Drawings] Figure 1 shows a schematic diagram of the dryer with a multi baffle. Figure 2 shows a comparison between the flash dryer of comparative example 2 and the multi baffle dryer of the present invention according to the height of the dryer. Figure 3 shows the simulation of the pressure gradient that is inside of the multi baffle dryer. [Best Mode] -5- Next, an embodiment of the presented invention will be described in details with reference to the drawings. The present invention relates to dryer with a multi baffle formed in zigzag to increase the drying efficiency of the coal Figure 1 shows a schematic diagram of the dryer with a multi baffle. Figure 2 shows a comparison between a flash dryer and multi baffle dryer of the present invention according to the height of the dryer. Figure 3 shows the simulation of the pressure gradient that is inside of the multi baffle dryer. As shown in figure 1, the dryer with the multi baffle is a counter flow dryer where the coal and the air meet in an opposite direction. Although the presented invention can use the low-rank - coal that contains a lot of moisture, the coal is not particularly limited. In dryer (100), the coal falls down from the upper part of the dryer, and the air is poured in from the bottom part of it. To have enough time for the coal to fall down, it is preferable to have a square pillar design for the structure of the dryer. The height and the width of the dryer are adjustable depending on the size, amount, and the reaction time of the coal. -6- In dryer (100), the multi baffles (10, 1, 2) are formed in a zigzag. In this invention, the coal is dried by falling in zigzag. As shown in figure 1, the baffles are formed at the inner part of the dryer, and have a downward inclination at a certain angle against inner wall of the dryer. The angle of baffle is between 20 to 80 degrees, preferably between 30 to 60 degrees. If the baffles have a downward slope at the angle of gradient, the efficiency of the drying process is most optimized. The baffles(10) are formed in zigzag and the inner wall of the dryer. The coal falls in a zigzag form in this invention. This means that the coal does not fall in straight line, but it falls by moving from the one side to the opposite side of the inner wall repeatedly. The downward baffle(1) in the one side and the downward baffle(2) in the opposite side of the inner wall are formed in zigzag repeatedly. There are various ways the baffles can form a zigzag. For example, as shown in figure 1, a declined angle baffle(1) can be placed higher or lower than the declined baffle(2) in the opposite side of the inner wall of the dryer. As the adjacent baffles (1, 2) alternate with each other at the opposite side of the inner wall, the baffles can form a zigzag. -7- This invention is not particularly limited to the number of the baffles. The baffles can vary in number depending on the time the coal stays in the dryer, the amount of coal, and the flow of the air. The dryer can have 10 to 30 baffles. The coal falls down continuously and repeatedly from a baffle to adjacent other baffle at the opposite side. Such design of the dryer and the way the coals fall allows them to stay longer in contact with the air inside of the dryer. As shown in figure 1 and 2, the invention allows the coal to flow from the top of the dryer and the air from the bottom of the dryer. This provides a steady temperature gradient between the top and the bottom of the dryer. This also increases the effectiveness of drying, because it allows the driving force to be constant. The coal is dried by convective drying as soon as it enters from the top of the dryer, because the surface moisture gets dry by the low temperature air. When the surface moisture gets removed, the coal meets higher air temperature at the middle and bottom part of the dryer and its residual moisture gets dried. As shown in figure 1 and 3, the overall pressure of the inside of the dryer decreases as it rises from the bottom to the top. It is typical that the pressure decrease - 8 as it rises from the bottom to the top of the dryer. Figure 3 shows that the lower part(5) of the baffle(2) is located higher than the upper part(6) of the baffle(3) of the dryer. However, the lower part(5) of the baffle(2) has higher pressure than the upper part(6) of the baffle(3), because the rising air more stays in the lower part(5) of the baffle. The upper part(6) of the baffle(3) has lower pressure, because the air travels fast through the upper part(6) of baffle. Such pressure difference of the dryer allows the coals to dry more effectively, because they meet the low pressure, for example the vacuum of 0 ~ -5mmHg, as they pass the upper part of the dryer (vacuum dry effect). The baffles(10) can use a metal that is a good heat conductor. It can also be coated or made with a material that prevents oxidation with high temperature or moisture. Since the coal is falling as it contacts with the baffles, the drying process becomes more effective as the moisture dries out quicker. The temperature of the air flowing from the bottom of the dryer is between 50 and 200 degrees Celsius, preferably between 80 and 150 degrees Celsius. The amount of the air flowing from the bottom of the dryer may be 3 to 15Nmm3/kg, more preferably between 5 and 10Nm3/kg. -9- The time for the coals to stay in the dryer is around 2 to 8 seconds, preferably from 3 to 6 seconds As shown in figure 1, the dryer of the invention comprises a coal inlet unit(200), a coal discharge unit (300) and an air inlet unit(400). The coal will be entered through the coal inlet unit(200) at the top of the dryer. In addition to, the coal inlet unit(200) stores a coal and transfers and feeds it onto inner of the dryer. The coal inlet unit(200) can be used already disclosed machine or technique without any limitation. For example, as shown Fig 1, the coal inlet unit(200) locates in the top of the dryer, and the coal can be entered from the inlet unit(200) into the upper of the dryer by using a screw. In addition, the coal can be entered directly from coal store tank(not shown) into the upper of the dryer by using a conveyor. The coal discharge unit (300) is for collecting the dried coal. It can be installed at the bottom of the dryer. The air inlet unit(400) is for feeding the air inside of the dryer, and it can be used without any limitation. It is suggested to feed the air from below of the lowest baffle of the dryer. The dryer can also include a recovery unit (500) to collect the pulverized coal. This unit can use a cyclone - 10 precipitator. In another aspect, the invention relates to the method of drying with multi baffles. Such method allows the coal to fall from the top as the air gets flowed from the bottom of the dryer. Since the coals fall in zigzag, its contact time with the air is longer, therefore, the effectiveness of the drying process increases. The baffles form between 20 and 80degrees, preferably from 30 to 60 degrees against inner wall of the dryer. The baffles can also be formed alternately with the adjacent baffle in the inner wall of the dryer. This controls the size of the baffles, the amount, declining angle, and the speed of the air. Such drying method is referred from the description mentioned above. Example 1 The coal was dried under the condition described in figure 1. Amount: 100g/min of raw coal (30% moisture) Amount of the air: 0.6 Nm3/min Number of baffles: 16 Contact time : 4sec Result: the moisture of the raw coal went from 30% to 18% Comparative example 1 and 2 - 11 - Comparative example l(fluidized bed dryer), Comparative example 2(flash dryer) and the present invention(multi baffles dryer) was analyzed; the result is shown below. Test result: Evaluation Amount of Contact Degrees in Percentage subject gas/coal time Celsius of of dryness (Nm3/kg) air Comparative 8 30-90min 150 50 example 1 Comparative 20 2 sec 400 70 example 2 the present 6 4 sec 80 50 invention 6 5 sec 150 70 As shown in the table above, the original fluidized bed dryer requires 8Nm3/Kg of the air, and the flash dryer needs 20Nm3/Kg. However, the multi baffles dryer only needs 6Nm3/Kg. It also had a very similar percentage of dryness even when it used a low air temperature as compared to the Comparative example 1 and 2. Example embodiments of the present invention have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of - 12 limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims. - 13 -