WO2013089337A1

WO2013089337A1 - System for drying coal using hot superheated steam which is heated multiple times

Info

Publication number: WO2013089337A1
Application number: PCT/KR2012/006892
Authority: WO
Inventors: Sung Kon Kim
Original assignee: Hankook Technology Inc.; Korea Western Power Co., Ltd.
Priority date: 2011-12-15
Filing date: 2012-08-29
Publication date: 2013-06-20
Also published as: KR101216814B1

Abstract

A system for drying coal. A superheated steam reheating unit includes heating pipes connected in multiple stages to reheat superheated steam supplied from a superheated steam supply pipe and a connector pipe communicating between the heating pipes. Each heating pipe has therein a dry heater, which converts applied electrical energy into heat due to electrical resistance. A hot air supplier creates hot air by burning fuel. A superheated steam dry unit removes moisture from the surface of coal using the superheated steam while transporting the coal on a steam conveyor belt. A hot air dry unit removes moisture from the inside of the coal using the hot air while transporting the coal on a dry conveyor belt. A natural dry unit lowers the temperature of the coal by drying the coal at room temperature while transporting the coal on a flat conveyor belt.

Description

SYSTEM FOR DRYING COAL USING HOT SUPERHEATED STEAM WHICH IS HEATED MULTIPLE TIMES

The present invention relates, in general, to a system for drying coal using hot superheated steam which is heated multiple times and, more particularly, to a coal drying system for removing moisture contained in coal, which is used as fuel in a thermal power plant, using hot superheated steam which is heated multiple times.

Generally, a thermal power plant, which generates power using coal as fuel, burns coal of about 180 tons per hour to generate 500MW. One pulverizer supplies an amount of coal corresponding to about 37 tons to the boiler. About 6 coal storage units each of which has a capacity of about 500 tons are installed in a thermal power plant that generates 500MW of power using the coal. Coal is normally supplied to 5 of the 6 coal storage units, and the remaining 1 coal storage unit is operated as a coal depot in which a reserve of coal is stored, which can be used for a predetermined period.

In addition, a thermal power plant that generates power using coal as fuel is designed such that it uses bituminous coal that has low-moisture content of 10% or less and 6,080kcal/kg, according to the standards applied to coal. Some thermal power plants use imported coal some of which has average moisture content of 17% or greater, which decreases the combustion efficiency of a boiler. When coal that is used has low heat content owing to the limit of combustion of 5,400kcal/kg, a decrease in power generation and an increase in the fuel consumed are expected owing to a decrease in the combustion efficiency. In addition, when sub-bituminous coal, i.e. low grade coal having high moisture content and low heat content, is used, a transfer system that conveys coal does not operate efficiently, the efficiency of pulverizing coal using a crusher is lowered, the efficiency of combustion is lowered owing to partial imperfect combustion, thermal distribution occurring inside the boiler has a drift, and an abnormal operation occurs. However, the use of sub-bituminous coal in thermal power plants is on an increasing trend in order to reduce the cost of fuel.

In addition, as the preference to thermal power plants increases because a global economic recovery is expected and safety demands are increased owing to the destruction of an atomic power plant by the Japanese earthquake, it seems that the consumption and cost of coal will gradually increase. Since the global coal market is changing from a user-oriented to provider-oriented environment, it will be difficult to secure a stable supply of coal. It is prospected that the amount of coal having high heat content that is to be produced will stay at the current level. Therefore, the demand and supply of coal are not expected to be in balance.

The amount of coal having low heat content occupies a large portion of 47% of the total amount of global coal deposits. However, the coal having low heat content has a low heat content but also a high moisture content. When burned, such coal that has a low heat content has the problem of abnormal combustion, thereby making it difficult for this type of coal to be completely burned. Therefore, this type of coal is being neglected in the market. To date, global power generation has been highly dependent on the stable cost of petroleum and the low cost of atomic power generation. However, recently, plans for the construction of thermal power plants using coal are increasing because of rapid increases in the cost of petroleum and the feeling of anxiety about atomic power generation.

Conventional technologies for drying coal (thermal drying) generally include a rotary dry method, a flash pneumatic dry method, and a fluid-bed dry method. The rotary dry method dries coal particles, which are loaded into a cylindrical shell, using hot gas while rotating the shell. The flash pneumatic dry method dries coal by raising hot dry gas from bottom to top while supplying the coal from top to bottom. The fluid-bed dry method dries coal by raising hot dry gas upwards so that the hot dry gas brings fine particles.

The moisture of coal is divided into surface moisture, which is attached to pores between coal particles, and bound moisture, which is bound to pores inside the coal. The surface moisture is mostly moisture that is sprayed during a cleaning process at a place or production or during transportation and storage, and the amount thereof is determined depending on the surface area and absorptivity. The moisture content increases as the size of the particles decreases, because the surface area increases and capillary tubes between particles in which moisture can be retained are formed. The bound moisture is formed in the period when the coal was created, and the amount thereof becomes smaller in the sequence of lignite, soft coal (bituminous coal, sub-bituminous coal) and anthracitic coal. When coal has more moisture, the heat content thereof decreases, and the cost of transportation increases. It is therefore required to control the moisture in processes of, for example, mixing, pulverizing and sorting coal.

Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and a purpose of the present invention is to increase the heat content of coal by drying coal using a large quantity of superheated steam and high-temperature hot wind so that the coal can have suitable water content before the coal is supplied from a coal depot to a silo. This can consequently increase the combustion efficiency of a boiler of a thermal power plant, thereby decreasing the amount of fuel that is used.

Another purpose of the invention is to provide a drying technology that can prevent environmental problems attributable to the imperfect combustion of coal by adjusting the moisture in the coal and a technology that is applicable to thermal power plants.

In an aspect, the present invention provides a system for drying coal that includes a superheated steam boiler, which creates superheated steam by heating water supplied from a water tank by burning fuel supplied from a gas tank. The system also includes a superheated steam reheating unit, which includes heating pipes, which are connected in multiple stages to reheat the superheated steam after expanding the superheated steam which issupplied from a superheated steam supply pipe of the superheated steam boiler, and a connector pipe communicating between the heating pipes, each of the heating pipes having therein a dry heater, which converts applied electrical energy into heat due to electrical resistance. The system also includes a hot air supplier, which creates hot air by burning fuel supplied from the gas tank, and blows the hot air, and a superheated steam dry unit, which removes moisture from the surface of coal using the superheated steam supplied from the superheated steam reheating unit while transporting the coal on a steam conveyor belt, the coal having been transported on a trough conveyor belt from a coal depot and sorted by a sorter. The system also includes a hot air dry unit, which removes moisture from the inside of the coal using the hot air supplied from the hot air supplier while transporting the coal on a dry conveyor belt, the coal having passed through the superheated steam dry unit; and a natural dry unit, which lowers the temperature of the coal by drying the coal so that natural vaporization occurs at room temperature while transporting the coal on a flat conveyor belt, the coal having passed through the hot air dry unit.

In an embodiment, the superheated steam dry unit may include an electric motor, which moves the steam conveyor belt; a duct, which is disposed on the steam conveyor belt, thereby defining a drying space; and a superheated steam injection pipe, which injects the superheated steam into the duct, the superheated steam being supplied via a superheated steam supply pipe from the superheated steam boiler.

In an embodiment, the hot air dry unit may include an electric motor, which transports the dry conveyor belt; a duct, which is disposed on the dry conveyor belt, thereby defining a drying space; and a hot air injection pipe, which injects the hot air into the duct, the hot air being supplied via a hot air supply pipe from the hot air supplier. The hot air dry unit may be one or more hot air dry units, which are staked on a structure.

In an embodiment, the natural dry unit may include an electric motor, which moves the flat conveyor belt; and a duct, which is disposed on the flat conveyor, thereby defining a drying space.

In an embodiment, wherein a waste heat collecting pipe may be connected to the duct via a heat exchanger.

In an embodiment, the heat exchanger may separate a pollutant from heat that is collected from the waste heat collecting pipe, the separated heat may be supplied to the hot air supplier via a waste heat supply pipe, and the separated pollutant may be supplied to a cleaner via a pollutant supply line.

In an embodiment, the superheated steam boiler may create the superheated steam that has a pressure ranging from 0.5kg/cm² to 5kg/cm² and a temperature ranging from 400℃ to 600℃, and raise a temperature of the coal to a range from 90℃ to 110℃, the coal being transported on the steam conveyor belt of the superheated steam dry unit.

According to embodiments of the invention, it is possible to prevent the imperfect combustion of coal, which is fuel used in thermal power plants, by removing residual moisture that resides in the inner and outer portions of the coal, thereby increasing the heat content of the coal, minimizing the exhaust of pollutants, preventing the system from being corroded, and improving longevity. It is possible to decrease the ratio of spontaneous combustion attributable to the drop in moisture, improve the crushing efficiency of a coal pulverizer, improve the thermal distribution of a power generation boiler when burning coal, and overcome the phenomenon in which a transportation passage is clogged when transporting the coal. It is also possible to improve the stability of the supply of coal by increasing the usability of low-quality coal that is not frequently in demand. In addition, it is possible to use low grade coal that is cheaper than high grade coal, reduce the cost of fuel and the prime cost by decreasing the amount of coal that is imported. Since the amount of coal that is consumed can be decreased, it is possible to decrease the exhaust of waste materials and pollutants that occur from combustion gas and the exhaust of carbon dioxide. The effect of creating a substitute for foreign technology and an effect on export facilities abroad can be expected.

FIG. 1 is a block diagram showing a system for drying coal using a large quantity of superheated steam according to an embodiment of the invention;

FIG. 2 is a configuration view showing a system for drying coal using a large quantity of superheated steam according to an embodiment of the invention;

FIG. 3 is a front elevation view of a coal-drying apparatus according to an embodiment of the invention;

FIG. 4 is a side elevation view of the coal-drying apparatus according to an embodiment of the invention; and

FIG. 5 is a cross-sectional view showing a superheated steam reheating unit, which is connected to a superheated steam boiler according to an embodiment of the invention is provided.

Reference will now be made in greater detail to a system for drying coal using a large quantity of superheated steam according to the invention, embodiments of which are illustrated in the accompanying drawings.

Referring to FIG. 1, a coal depot 10 is a place in which coal which is to be used as fuel for a boiler of a thermal power plant is kept and stored. The surface and inside of the coal contain moisture. In addition, water is periodically showered to the coal in the coal depot in order to prevent coal powder from scattering. The coal stored in the coal depot 10 is carried to a system for drying the coal on a transportation means such as a conveyor system. Here, it is possible to move the coal in the coal depot 10, from which moisture is not removed, to a storage tank where the coal is then stored. The coal in the coal depot 10 is transported to a sorter 20 via a flat conveyor belt 11 and a trough conveyor belt 12.

The function of the sorter 20 is to sort the coal that is transported from the coal depot 10 by uniformly spreading it at a predetermined height on a steam conveyor belt 112, which is provided in a superheated steam dry unit 110. The sorter 20 serves to help the coal be easily dried by superheated steam in the superheated steam dry unit 110 when the coal that is transported from the coal depot 10 is supplied to the steam conveyor belt 112.

Referring to FIG. 2, in a coal-drying apparatus 100 for drying the coal, the superheated steam dry unit 110 as well as a plurality of hot air dry units 120 and a natural dry unit 140 are vertically disposed from top to bottom. The coal-drying apparatus 100 is disposed inside a structure 101, which is constituted of a plurality of frames.

Referring to FIG. 3, the superheated steam dry unit 110 serves to remove moisture from the surface of the coal c using superheated air that is supplied from a superheated steam boiler 70 while transporting the coal c that has been sorted and stacked to a predetermined height in the sorter 20. A plurality of electric motors 113 is disposed in the superheated steam dry unit 110 such that the electric motors 113 drive a steam conveyor belt 12, which is fixedly supported on the structure and transports the coal. The steam conveyor belt 112 is provided with a duct 111, which forms a space in which the coal can be dried by superheated steam. The duct 111 can be disposed above the steam conveyor belt 112 or be disposed such that the seam conveyor belt 112 extends through the duct. Inside the duct 111, a superheated steam injection pipe 72 is connected to a superheated steam supply pipe 71, which supplies superheated steam from the superheated steam boiler 70. The superheated steam injection pipe 72 is disposed such that the superheated steam that is supplied via the superheated steam supply pipe 71 can be uniformly injected onto the surface of the coal that is being transported on the steam conveyor belt 112.

When the coal c is dropped after it is dried by the superheated steam in the superheated steam dry unit 110, the hot air dry units 120 serves to remove moisture inside the coal c using hot air that is supplied from a hot air supplier 60. One or more hot air dry units 120 are disposed. The hot air dry units 120 according to an embodiment of the invention are disposed in three stages below the superheated steam dry unit 110 such that they can sufficiently evaporate and remove moisture from inside the coal that is being transported on respective

dry conveyor belts

123, 127 and 132. The hot air dry units 120 include a first hot air dry unit 121, a second hot air dry unit 125 and a third hot air dry unit 130.

The first hot air dry unit 121 is disposed such that it is fixedly supported by the structure 101 below the superheated steam dry unit 110, and is provided with a dry conveyor belt 123, which receives and transports the coal c that is dropped from the steal conveyor belt 112. A plurality of electric motors 124 is disposed such that the electric motors transport the dry conveyor belt 123. The electric motors 124 generate power that is used to rotate the dry conveyor belt 123 at a predetermined speed. The dry conveyor belt 123 is provided with a duct 122, which defines a space where the coal c can be dried by hot air. The duct 122 may be disposed above the dry conveyor belt 123 or be disposed such that the dry conveyor belt 123 extends through the duct. A hot air injection pipe 62, which is disposed inside the duct 122, is connected to a hot air supply pipe 61, which supplies the hot air from the hot air supplier 60. The hot air supply pipe 62 is disposed such that the hot air that is supplied via the hot air supplier 60 can be uniformly injected onto the coal c that is transported on the dry conveyor belt 123.

The second hot air dry unit 125 is disposed such that it is fixedly supported by the structure 101 below the first hot air dry unit 121, and is provided with a dry conveyor belt 127, which receives and transports the coal c that is dropped from the dry conveyor belt 123. A plurality of electric motors 128, which transport the dry conveyor belt 127, is disposed. The electric motors 128 generate the power that is used to rotate the dry conveyor belt 127 at a predetermined speed. The dry conveyor belt 127 is provided with a duct 126, which defines a space where the coal c can be dried by the hot air. The duct 126 may be disposed above the dry conveyor belt 127 or be disposed such that the dry conveyor belt 127 extends through the duct. A hot air injection pipe 63, which is disposed inside the duct 126, is connected to the hot air supply pipe 61, which supplies the hot air from the hot air supplier 60. The hot air supply pipe 63 is disposed such that the hot air supplied via the hot air supplier 60 is uniformly injected onto the coal c that is transported on the dry conveyor belt 127.

The third hot air dry unit 130 is disposed such that it is fixedly supported by the structure 101 below the first hot air dry unit 125, and is provided with a dry conveyor belt 132, which receives and transports the coal c that is dropped from the dry conveyor belt 127. A plurality of electric motors 133, which transport the dry conveyor belt 132, are also put in place. The electric motors 133 generate power that is used to rotate the dry conveyor belt 132 at a predetermined speed. The dry conveyor belt 132 is provided with a duct 131, which defines a space where the coal c can be dried by the hot air. The duct 131 can be disposed above the dry conveyor belt 132 or be disposed such that the dry conveyor belt 132 extends through the duct. A hot air injection pipe 64, which is disposed inside the duct 131, is connected to the hot air supply pipe 61, which supplies the hot air from the hot air supplier 60. The hot air supply pipe 64 is disposed such that the hot air that is supplied via the hot air supplier 60 is uniformly injected onto the coal c that is transported on the dry conveyor belt 132.

The natural dry unit 140 lowers the temperature of the coal c by drying the coal at room temperature so that natural vaporization occurs while transporting the coal c that is dropped on a flat conveyor belt 142 after being dried by the hot air in the multistage hot air dry units 120. The natural dry unit 140 is disposed such that it is fixedly supported by the structure 101 below the third hot air dry unit 130, and is provided with a flat conveyor belt 142, which receives and transports the coal c that is dropped from the dry conveyor belt 132. A plurality of electric motors 143, which drive the flat conveyor belt 142, is provided. The electric motors 143 generate power that is used to rotate the flat conveyor belt 142 at a predetermined sped. The flat conveyor belt 142 is provided with a duct 141, which defines a space where the coal c can be naturally dried at a temperature that does not exceed room temperature. The duct 141 can be disposed above the flat conveyor belt 141 or be disposed such that the flat conveyor belt 142 extends through the duct. Air at room temperature can be forcibly blown so that it is supplied into the duct 141. The duct 141 may be disposed such that it prevents dust from being created from the dried coal and being scattered to the outside although it may not be provided.

The coal that is dried by natural vaporization in the natural dry unit 140 is supplied to a silo 50 via a trough conveyor belt 51 and is then stored in the silo 50. The coal that is stored in the silo 50 is supplied to the boiler of the thermal power plant via a trough conveyor belt 52.

A waste heat collecting pipe 31 is connected to the

respective ducts

111, 122, 126, 131 and 141 of the superheated steam dry unit 110, the hot air dry unit 120 and the natural dry unit 140 such that hot waste heat occurring inside the ducts can be collected by a heat exchanger 30. The heat exchanger 30 separates pollutants such as dust from heat that is collected from the waste heat collecting pipe 31. The heat that is separated by the heat exchanger 30 can be supplied to the hot air supplier 60 via a waste heat supply pipe 32 and then added to the hot air that is created by the hot air supplier 60. The hot air supplier 60 can then decrease the use of fuel required to heat the hot air by using the heat that is collected in the heat exchanger 30. In addition, the pollutants separated by the heat exchanger 30 can be supplied along a pollutant supply line 33 to a cleaner 40, be water-treated in the cleaner 40, and be then discharged as waste water. The cleaner 40 serves to clean the pollutants that have been introduced from the heat exchanger 30 using water so that dust can be discharged in the waste water, and thus purified air can be exhausted to the outside.

The superheated steam boiler 70 generates superheated steam by heating water that is supplied from a water tank 3 using fuel that is supplied from a gas tank 4. The superheated steam boiler 70 generates superheated steam that has a low pressure approximately ranging from 0.5kg/cm² to 5kg/cm² and a high temperature approximately ranging from 400℃ to 600℃. As the superheated boiler 70, a boiler that generates superheated steam of 30kg per hour is applied. The superheated boiler 70 is configured such that it can raise the temperature of the coal that is transported on the steam conveyor belt 112 of the superheated steam dry unit 110 to an approximate range from 90℃ to 110℃. Although coal spontaneously burns at a temperature approximately ranging from 93℃ to 95℃, the superheated steam having a temperature approximately ranging from 400℃ to 600℃ does not burn the coal because oxygen is scarce. The superheated steam is transparent gas in which the latent heat of vaporization, which is the heat of vaporization, is mixed with condensing heat transfer, which is generated by sensible heat of heating, and also mixed with radiation-conduction heat. The superheated steam is created by heating saturated steam that is generated from the boiler using a superheater. The superheated steam that is generated from the superheated steam boiler has low pressure and high temperature although superheated steam that is generated from a boiler for power generation has high pressure and high temperature. Since the superheated steam is created by heating room-temperature water, the residual oxygen in water is several ppm. Thus it can be heat-treated in the oxygen-free state without mixing with air. The superheated steam also has very strong heat transfer power and drying ability since the heat content thereof is high. The heat treatment performance of the superheated steam is about 10 times superior to that of hot wind, i.e. hot air. Therefore, the superheated steam is effective in removing latent heat away from the coal.

The hot air supplier 60 serves to supply air to fuel that is supplied form the gas tank 4 by heating the air to a high temperature and then blowing the heated air to the fuel. The quantity of heat created by the hot air supplier 60 is about 100,000kcal per hour.

In addition, a superheated steam reheating unit 300 has

heating pipes

301, 303 and 305, which are connected in multiple stages. The

heating pipes

301, 303 and 305 serve to reheat the superheated steam after expanding the superheated steam that is supplied from the superheated steam supply pipe 71 of the superheated steam boiler 70. Each of the

heating pipes

301, 303 and 305 is internally provided with a corresponding one of

dry heaters

310, 312 and 314, which converts applied electrical energy into heat due to electrical resistance. A connector pipe 302 communicates between the

heating pipes

301 and 303 and a connector pipe 304 communicates between the

heating pipes

303 and 305 in order to deliver the superheated steam that is reheated.

Electrodes

311, 313 and 315 to which electrical energy is applied are individually connected to the

dry heaters

310, 312 and 314. Finally, a superheated steam exhaust pipe 306 is connected to the heating pipe 305. Therefore, the superheated steam that is introduced from the superheated steam supply pipe 71 is converted into hotter superheated steam while passing through a plurality of the

heating pipes

310, 303 and 305. The hot superheated steam is then supplied to the superheated steam dry unit 110 via the superheated steam exhaust pipe 306.

The purpose of the superheated steam reheating unit 300 is to reheat the superheated steam that is supplied from the superheated steam boiler 70 so that the temperature of the superheated steam can be increased. Although the

heating pipes

301, 303 and 305 of the superheated steam reheating unit 300 are connected in three stages according to the invention, the number of the heating pipes that are to be connected can be increased or decreased depending on the temperature of the superheated steam that is supplied to the superheated steam dry unit 110. In addition, the number of the heating pipes may vary depending on the volume or capacity of the heating pipes of the superheated steam reheating unit 300. The connector pipes 302 and 304 are applied such that their diameter is smaller than that of the

heating pipes

301, 303 and 305. In addition, when the superheated steam is supplied from the superheated steam boiler 70 through the superheated steam supply pipe 71 that has a smaller diameter to the heating pipe 301 that has a larger diameter, the superheated steam is subjected to the Venturi principle based on the Bernoulli’s theorem. That is, the superheated steam that has been supplied at high pressure and a high speed in the superheated steam supply pipe 71 is supplied at low pressure and a low speed in the heating pipe 301. Here, in response to heat generation of the dry heater 310 inside the heating pipe 301, the superheated steam becomes much hotter. In addition, the superheated steam that is heated in the heating pipe 301 is at high pressure and increases in speed when being supplied to the heating pipe 303 via the connector pipe 302, but is at low temperature and drops back down to a slower speed when flowing through the heating pipe 305. The superheated steam in the heating pipe 303 becomes much hotter due to heat generation of the dry heater 313. In addition, the super heated steam that is heated in the heating pipe 303 is at high pressure and increases in speed when supplied to the heating pipe 304 via the connector pipe 304, but is at low pressure and decreases in speed again when flowing through the heating pipe 305. The superheated steam in the heating pipe 305 becomes much hotter due to heat generation of the dry heater 314. The superheated steam that has passed through the

heating pipes

301, 303 and 305 and the connector pipes 302 and 304, which are provided in multiple stages, is heated to a much higher temperature and is then discharged to the superheated steam exhaust pipe 306.

According to the results of experiments which detected variations in the temperature of the superheated steam using the superheated steam reheating unit 300 of the invention, it was possible to convert superheated steam of 100℃ into superheated steam of about 600℃ or higher through the superheated steam exhaust pipe 306 after passing through the three stages of the

heating pipes

301, 303 and 305.

Consequently, it is possible to produce superheated steam at the desired temperature depending on the number of heating pipes, which are connected in multiple stages. In addition, it is possible to change the temperature of the superheated steam depending on the amount of heat that the dry heaters generate and the capacity of the heating pipes.

The hot air supplier 60 serves to supply air to fuel that is supplied form the gas tank 4 by heating the air to a high temperature and then blowing the heated air onto the fuel. The quantity of heat created by the hot air supplier 60 is about 100,000kcal per hour.

The system for drying coal using a large quantity of superheated steam that has the above-described components according to the invention transports the coal that has been stored in the coal depot 10 to an apparatus for drying coal using a conveyor belt that horizontally transports the coal or a conveyor belt that transports the coal by raising it to a predetermined height. The coal that is transported to the inlet of the apparatus for drying coal is uniformly spread while passing through the sorter 20 and is then loaded on the steam conveyor belt 112 of the superheated steam dry unit 110.

The coal that is loaded into the steam conveyor belt 112 is transported into the duct 111. Inside the duct 111, superheated steam having low pressure and high temperature is supplied through the superheated steam supply pipe 71 from the superheated steam boiler 70 and is injected from the injection pipe 72 to the coal, thereby removing moisture from the surface of the coal. Here, a large quantity of the superheated steam can be input again into the duct 111 through the superheated steam supply pipe 71 and the superheated steam injection pipe 72 while the superheated steam passes through the superheated steam enhancing unit 200 of the superheated steam boiler 70.

The coal that is transported to the terminal end of the steam conveyor belt 112 of the superheated steam dry unit 110 drops onto the dry conveyor belt 123 of the first hot air dry unit 121 under the influence of gravity. The coal that dropped onto the dry conveyor belt 123 of the first hot air dry unit 121 is transported into the duct 122. Inside the duct 122, hot wind having a high temperature is supplied through the hot air supply pipe 61 from the hot air supplier 60 and is injected from the hot air injection pipe 62 onto the coal c, thereby removing moisture from the inside of the coal. In addition, the coal that is transported to the terminal end of the steam conveyor belt 123 of the first superheated steam dry unit 121 drops onto the dry conveyor belt 127 of the second hot air dry unit 125 under gravity. Then, hot wind at a high temperature removes the moisture again from the inside of the coal while the coal passes through the duct 126 of the second hot air dry unit 125. In addition, the coal that is being transported to the terminal end of the steam conveyor belt 127 of the first superheated steam dry unit 125 drops onto the dry conveyor belt 32 of the third hot air dry unit 130 under gravity. Then, the hot wind at high temperature removes the moisture from the inside of the coal for a third time while the coal passes through the duct 131 of the second hot air dry unit 130.

In addition, the coal that is being transported to the terminal end of the steam conveyor belt 132 of the first superheated steam dry unit 130 drops onto the flat conveyor belt 142 of the natural drying unit 140 under gravity. The coal that dropped onto the flat conveyor belt 142 of the natural drying unit 140 is transported into the duct 141, inside which natural vaporization occurs at room temperature, thereby lowering the temperature of the coal.

The steam conveyor belt 112 of the superheated steam dry unit 110, the respective

dry conveyor belts

123, 127 and 132 of the hot air

dry units

121, 125 and 130, and the flat conveyor belt 142 of the natural drying unit 140 are horizontally disposed, and these conveyor belts are positioned by predetermined intervals in the vertical direction. Furthermore, the inlet of the dry conveyor belt 123 of the first hog air dry unit 121 protrudes for a longer distance than does the outlet of the dry conveyor belt 127 of the second hot air dry unit 125, the inlet of the dry conveyor belt 127 of the second hot air dry unit 125 protrudes for a longer distance than does the outlet of the dry conveyor belt 123 of the first hot air dry unit 121, and the inlet of the dry conveyor belt 132 of the third hot air dry unit 130 protrudes for a longer distance than does the outlet of the dry conveyor belt 127 of the second hot air dry unit 125. In addition, the inlet of the trough conveyor belt 51, which is connected to the silo 50, protrudes below the outlet of the flat conveyor belt 142 of the natural dry unit 140. That is, in the inlet and the outlet of the trough conveyor belt 51, which is disposed between the natural dry unit 130 and the silo 50, the inlet is positioned below the outlet of the natural dry unit 130 and the outlet is positioned in the upper portion of the silo 50. Furthermore, the trough conveyor belt 52 is connected between the outlet of the silo 50 and the boiler of the thermal power plant.

It also deserves mention that the superheated steam that is produced after the moisture has been removed from the surface of the coal inside the duct 111 of the superheated steam dry unit 110, the hot air that is produced after the moisture has been removed from the inside of the coal inside the

ducts

122, 126 and 131 of the hot air

dry units

121, 125 and 130, and the hot air that is produced owing to natural vaporization from the coal inside the duct 141 of the natural dry unit 140 are collected and sent to the heat exchanger 30 via the waste heat collecting pipe 31. The heat exchanger 30 performs heat exchange using the collected waste heat. Afterwards, the heat-exchanged waste heat is re-circulated to the hot air supplier 60 via the waste heat supply pipe 32. Pollutants such as dust that become separated from the coal using the waste heat that is heat-exchanged in the heat exchanger 30 are transported to the cleaner 40 via the pollutant supply line 33. In the cleaner 40, the pollutants can be cleaned and absorbed by water so that the pollutants can be retreated as waste water, and the air from which the pollutants are filtered is exhausted to the atmosphere.

Although the specific embodiments of the present invention have been shown and described, those skilled in the art will appreciate that various modifications and changes are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

1: water supply pipe 2: gas supply pipe

3: water tank 4: gas tank

10: coal depot 11: flat conveyor belt

12: trough conveyor belt 20: sorter

30: heat exchanger 31: waste heat collecting pipe

32: waste heat supply pipe 33: pollutant supply line

40: cleaner 50: silo

60: hot air supplier 61: hot air supply pipe

62, 63, 64: hot air injection pipe

70: superheated steam boiler

71: superheated steam supply pipe

72: superheated steam injection pipe

100: apparatus for drying coal

101: structure 110: superheated steam dry unit

111, 122, 126, 131, 141: duct

112: steam conveyor belt

113, 124, 128, 133, 143: electric motor

120, 121, 135, 130: hot air dry unit

123, 127, 132: dry conveyor belt

140: natural dry unit

300: superheated steam reheating unit

301, 303, 305: heating pipe

302, 304:

connector pipe

310, 312, 314: dry heater

311, 313, 315: electrode

306: superheated steam exhaust pipe

Claims

A system for drying coal comprising:

a superheated steam boiler, which creates superheated steam by heating water supplied from a water tank by burning fuel supplied from a gas tank;

a superheated steam reheating unit, wherein the superheated steam reheating unit comprises heating pipes, which are connected in multiple stages to reheat the superheated steam after expanding the superheated steam which is supplied from a superheated steam supply pipe of the superheated steam boiler, and a connector pipe communicating between the heating pipes, each of the heating pipes having therein a dry heater, which converts applied electrical energy into heat due to electrical resistance;

a hot air supplier, which creates hot air by burning fuel supplied from the gas tank, and blows the hot air;

a superheated steam dry unit, which removes moisture from a surface of coal using the superheated steam supplied from the superheated steam reheating unit while transporting the coal on a steam conveyor belt, the coal having been transported on a trough conveyor belt from a coal depot and sorted by a sorter;

a hot air dry unit, which removes moisture from an inside of the coal using the hot air supplied from the hot air supplier while transporting the coal on a dry conveyor belt, the coal having passed through the superheated steam dry unit; and

a natural dry unit, which lowers a temperature of the coal by drying the coal so that natural vaporization occurs at room temperature while transporting the coal on a flat conveyor belt, the coal having passed through the hot air dry unit.
The system for drying coal of claim 1, wherein the superheated steam dry unit comprises:

an electric motor, which moves the steam conveyor belt;

a duct, which is disposed on the steam conveyor belt, thereby defining a drying space; and

a superheated steam injection pipe, which injects the superheated steam into the duct, the superheated steam being supplied via a superheated steam supply pipe from the superheated steam boiler.
The system for drying coal of claim 1, wherein the hot air dry unit comprises:

an electric motor, which transports the dry conveyor belt;

a duct, which is disposed on the dry conveyor belt, thereby defining a drying space; and

a hot air injection pipe, which injects the hot air into the duct, the hot air being supplied via a hot air supply pipe from the hot air supplier,

wherein the hot air dry unit comprises one or more hot air dry units, which are staked on a structure.
The system for drying coal of claim 1, wherein the natural dry unit comprises:

an electric motor, which moves the flat conveyor belt; and

a duct, which is disposed on the flat conveyor, thereby defining a drying space.
The system for drying coal of any one of claims 2 to 4, wherein a waste heat collecting pipe is connected to the duct via a heat exchanger.
The system for drying coal of claim 5, wherein the heat exchanger separates a pollutant from heat that is collected from the waste heat collecting pipe, the separated heat is supplied to the hot air supplier via a waste heat supply pipe, and the separated pollutant is supplied to a cleaner via a pollutant supply line.
The system for drying coal of claim 1, wherein the superheated steam boiler creates the superheated steam that has a pressure ranging from 0.5kg/cm² to 5kg/cm² and a temperature ranging from 400℃ to 600℃, and raises a temperature of the coal to a range from 90℃ to 110℃, the coal being transported on the steam conveyor belt of the superheated steam dry unit.