METHOD FOR PRODUCING RESIDUE COAL

Abstract

In a method for producing residue coal according to the present invention, a solvent is separated by evaporation from a solid material concentrate, which has been separated in a gravity settling vessel (7), in a solvent separator (10), thereby producing a residue coal mixture in which the solvent is remained in the residue coal. Subsequently, the remaining solvent is separated by evaporation from the residue coal mixture in a drier (11), thereby producing the residue coal. In the drier (11), the remaining solvent is separated by evaporation from the residue coal mixture utilizing a heat the residue coal mixture itself has. In this manner, an apparatus for drying the residue coal mixture can be simplified, and the cost required for the drying can be reduced.

Description

TECHNICAL FIELD

The present invention relates to a method for producing a by-product coal which is yielded as a by-product when an ashless coal is obtained through removal of ash components from coal.

BACKGROUND ART

A method for producing an ashless coal is disclosed in Patent Document 1. In such a production method, a raw material coal as a mixture of steam coal and caking coal is mixed with a solvent to prepare a slurry, and the slurry thus prepared is heated, thereby extracting coal components soluble in the solvent, then the gravitational settling method is applied to the slurry in which the coal components has been extracted, thereby separating the slurry into a solution which contains the coal components soluble in the solvent and a solid-content concentrated liquid containing coal components insoluble in the solvent, and further the removal of the solvent from the separated solution is carried out, thereby obtaining an ashless coal.

PRIOR ART DOCUMENT

Patent Documents

Patent Document 1: JP-A-2009-227718

SUMMARY OF THE INVENTION

Problem that the Invention is to Solve

In the process for producing an ashless coal, a by-product coal is yielded as a by-product in addition to an ashless coal as the final product.

The by-product coal is obtained through the evaporative separation of a solvent from a solid-content concentrated liquid. In the process, a by-product coal mixture containing the by-product coal in which the solvent remains is obtained first through the evaporative separation of the solvent from the solid-content concentrated liquid, and then the by-product coal is obtained through the evaporative separation of the remaining solvent from the by-product coal mixture.

In the case of intending to obtain a by-product coal through the drying of a large quantity of by-product coal mixture, however, there arises a problem that there is no drying means which allows the temperature of the by-product coal mixture to be increased to temperatures equal to or higher than the boiling temperature of the solvent (about 240° C.). The steam temperature of a steam tube dryer as an example of drying means is 220° C. at the highest, and hence prolongation of a residence time becomes necessary, which results in a cost increase.

An object of the present invention is therefore to provide a method for producing a by-product coal, which allows a reduction in cost for drying a by-product coal mixture through the simplification of a device for drying the by-product coal mixture.

Means for Solving the Problem

A method for producing a by-product coal according to the present invention comprises: an extraction step of heating a slurry prepared by mixing a coal and a solvent, thereby extracting a coal component soluble in the solvent; a separation step of separating the slurry which has been obtained in the extraction step into a solution in which the coal component soluble in the solvent is dissolved and a solid-content concentrated liquid in which a coal component insoluble in the solvent is concentrated; and a by-product coal acquirement step of evaporating and separating the solvent from the solid-content concentrated liquid which has been separated in the separation step, thereby acquiring a by-product coal; wherein the by-product coal acquirement step comprises: a by-product coal mixture acquirement step of evaporating and separating the solvent from the solid-content concentrated liquid which has been separated in the separation step, thereby acquiring a by-product coal mixture containing a by-product coal in which the solvent remains; and a by-product coal drying step of evaporating and separating the remaining solvent from the by-product coal mixture, thereby acquiring the by-product coal, wherein, in the by-product coal drying step, the solvent remaining in the by-product coal mixture is evaporated and separated by exploiting heat that the by-product coal mixture itself has.

Advantageous Effects of the Invention

According to the method for producing a by-product coal in the present invention, the device for drying a by-product coal mixture is simplified, and thus, the cost for drying the by-product coal mixture can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an ashless coal production equipment.

FIG. 2 is a graph showing evaluation results based on drying time.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

In the following, an exemplary embodiment for carrying out the present invention is illustrated in detail by reference to the drawings.

(Method for Producing Ashless Coal)

The method of producing a by-product coal in accordance with an exemplary embodiment in the present invention is carried out in ashless-coal production equipment 100 to be used for a method of producing an ashless coal. As shown in FIG. 1, the ashless-coal production equipment 100 includes, in the order from the upstream side of the production process of an ashless coal (HPC), a coal hopper 1, a solvent tank 2, a slurry preparation tank 3, a transport pump 4, a preheater 5, an extraction tank 6, a gravitational settling tank 7, a filter unit 8, solvent separators 9 and 10, and a dryer 11.

The method of producing an ashless coal includes a slurry preparation step, an extraction step, a separation step, an ashless coal acquirement step and a by-product coal acquirement step. Of these steps, the slurry preparation step, the extraction step, the separation step and the by-product coal acquirement step are included in the method for producing a by-product coal in accordance with the present embodiment. Each of these steps is explained below. Additionally, a coal to be used as a raw material in the present production method has no particular restriction, and bituminous coal high in extraction rate may be used or a low rank coal low in price (such as subbituminous coal or brown coal) may be used. Herein, the term “ashless coal” refers to a coal having an ash content of 5 wt % or less, preferably 3 wt % or less.

(Slurry Preparation Step)

The slurry preparation step is a step of preparing a slurry by mixing a coal and a solvent. This slurry preparation step is performed in the slurry preparation tank 3 in FIG. 1. The coal as a raw material is added to the slurry preparation tank 3 from the coal hopper 1, and simultaneously, a solvent is added to the slurry preparation tank 3 from the solvent tank 2. The coal and solvent which are added to the slurry preparation tank 3 are mixed by the stirrer 3a, thereby forming into a slurry composed of the coal and the solvent.

The mixing proportion of the coals to the solvent is e.g. from 10 to 50 wt %, preferably from 20 to 35 wt %, on a dried coal basis.

(Extraction Step)

The extraction step is a step of extracting coal components soluble in the solvent (a step of dissolving such components in the solvent) by heating the slurry obtained in the slurry preparation step. This extraction step is performed in the preheater 5 and the extraction tank 6 in FIG. 1. The slurry which has been prepared in the slurry preparation tank 3 is fed to the preheater 5 by means of the transport pump 4, heated up to a predetermined temperature, then fed to the extraction tank 6, and further kept at a predetermined temperature while stirring by the stirrer 6a. In this way, the extraction is performed.

In a case of extracting coal components soluble in the solvent by heating the slurry prepared by mixing the coal with the solvent, a solvent in which the coal is highly soluble, more specifically an aromatic solvent (a hydrogen donative solvent or a hydrogen nondonative solvent) in many cases, is mixed with a coal, and by heating the resulting mixture, organic components in the coal are extracted.

The hydrogen nondonative solvent is a coal-derived solvent obtained mainly by refining carbonization products of coal and predominantly composed of bicyclic aromatic compounds. Because such a hydrogen nondonative solvent is stable even under conditions of heating and has a high affinity for coal, the proportion of soluble components (coal components) extracted with the solvent (hereafter referred to as the extraction rate, too) is high, and the solvent can be easily recovered by the methods such as distillation. Main ingredients in the hydrogen nondonative solvent are bicyclic aromatic compounds such as naphthalene, methylnaphthalene, dimethylnaphthalene or trimethylnaphthalene. As the other ingredients in the hydrogen nondonative solvent, examples thereof include a naphthalene, a anthracene and a fluorine, which each have aliphatic side chains, and further include biphenyl and an alkylbenzene having long-chain aliphatic side chains.

Although the case of using a hydrogen nondonative compound as the solvent is described in the above explanation, it goes without saying that any of hydrogen donative compounds (including the case of coal liquefied oil), typified by tetralin, can be used as the solvent. The use of a hydrogen donative solvent brings about enhancement of ashless coal yield.

Additionally, the solvent has no particular restriction as to its boiling temperature. From the viewpoints of pressure reductions in the extraction step and separation step, an extraction rate in the extraction step, a solvent recovery rate in the ashless coal acquirement step and the like, solvents having boiling temperatures in a range of 180° C. to 300° C., especially 240° C. to 280° C., can be used favorably. In the present embodiment, the boiling temperature of the solvent is about 240° C.

The heating temperature of the slurry in the extraction step has no particular limitations so long as dissolution of solvent-soluble components can be achieved. From the viewpoint of ensuring thorough dissolution of solvent-soluble components and improvement in extraction rate, the heating temperature is e.g. from 300° C. to 420° C., preferably 360° C. to 400° C. In the present embodiment, the slurry is heated by the preheater 5, and thereby, as mentioned later, the temperature of a solid-content concentrated liquid to be fed to a solvent separator 10 is adjusted so that a by-product coal mixture to be fed to a dryer 11 has a calorific value allowing the remaining solvent to be evaporated and separated from the by-product coal mixture.

The heating time (extraction time) also has no particular limitations, but from the viewpoint of ensuring thorough dissolution and improvement in extraction rate, the heating time is e.g. from 10 to 60 minutes. Herein, the term “heating time” refers to the sum of the heating time in the preheater 5 in FIG. 1 and the heating time in the extraction tank 6 in FIG. 1.

The extraction step is carried out in the presence of an inert gas such as nitrogen. The suitable pressure inside the extraction tank 6 is e.g. from 1.0 to 2.0 MPa, though it depends on the temperature during the extraction and the vapor pressure of a solvent to be used. When the pressure inside the extraction tank 6 is lower than the vapor pressure of the solvent, the solvent vaporizes and the solvent cannot be confined within the liquid phase, and the extraction ends in failure. In order to confine the solvent within the liquid phase, pressure higher than the vapor pressure of the solvent is therefore necessary. On the other hand, when the pressure is too high, it brings about increases in costs of equipment and operation, and it is therefore uneconomical.

(Separation Step)

The separation step is a step of separating the slurry which has been obtained in the extraction step into a solution in which coal components soluble in the solvent are dissolved and a solid-content concentrated liquid (solvent-insoluble component concentrated liquid) which contains coal components insoluble in the solvent (solvent-insoluble components such as ash components) in a concentrated state, by the gravitational settling method. This separation step is carried out in the gravitational settling tank 7 in FIG. 1. In the gravitational settling tank 7, the slurry which has been obtained in the extraction step is separated into supernatant liquor as the solution and the solid-content concentrated liquid by dint of gravity. The supernatant liquor in the upper part of the gravitational settling tank 7 is discharged into the solvent separator 9, if necessary, by way of the filter unit 8, and simultaneously, the solid-content concentrated liquid settled in the lower part of the gravitational settling tank 7 is discharged into the solvent separator 10.

The gravitational settling method is a method of holding the slurry in the tank, and settling and separating the solvent-insoluble components by exploiting gravity. The solvent-insoluble components (e.g. ash components) having a specific gravity larger than that of the solution in which coal components soluble in the solvent are dissolved, settle in the lower part of the gravitational settling tank 7 by the force of gravity. By continuously discharging the supernatant liquor from the upper part of the tank and the solid-content concentrated liquid from the lower part of the tank while continuously feeding the slurry into the tank, continuous separation treatment becomes possible.

For prevention of reprecipitation of solvent-soluble components eluted from the coal, it is appropriate that the inside of the gravitational settling tank 7 be kept warm (or in a heated state) or be left pressurized. The warming (heating) temperature is e.g. from 300° C. to 380° C., and the pressure inside the tank is e.g. from 1.0 MPa to 3.0 MPa.

In addition to the gravitational settling method, examples of methods for separating the solution which contains coal components dissolved in the solvent from the slurry which has been obtained in the extraction step include a filtration method, a centrifugal separation method and the like.

(Ashless Coal Acquirement Step)

The ashless coal acquirement step is a step of acquiring an ashless coal (HPC) through the evaporative separation of the solvent from the solution (supernatant liquor) which has been separated in the separation step. This ashless coal acquirement step is carried out in the solvent separator 9 in FIG. 1. After the filtration in the filter unit 8, the solution which has been separated in the gravitational settling tank 7 is fed to the solvent separator 9, and in the solvent separator 9, the solvent is evaporated and separated from the supernatant liquor. The evaporative separation of the solvent from the solution is preferably carried out in the presence of an inert gas such as nitrogen. In the present embodiment, the solvent is evaporated and separated from the solution in an atmosphere of nitrogen gas introduced into the solvent separator 9.

As the method for separating the solvent from the solution (supernatant liquor), a common distillation or evaporation method or the like can be used. The solvent which has been separated in the solvent separator 9 is returned to the solvent tank 2, and is used in cycles. Circulating use of the solvent is preferable, but not essential (which is also applicable to the by-product coal acquirement step mentioned later). By separating the solvent from the supernatant liquor, an ashless coal (HPC) containing substantially no ash components can be obtained.

The ashless coal contains almost no ash components, is absolutely free of moisture, and offers a calorific value higher than a raw material coal. In addition, the ashless coal has an extensive improvement in coal plastic properties (flowability) which are especially important for a raw material of steelmaking coke, and even when the raw material coal has no plastic properties, the ashless coal (HPC) obtained from it has excellent plastic properties. Accordingly, the ashless coal can be used e.g. in a coal blend as a raw material for making coke. Further, the ashless coal almost free of ash components has high combustion efficiency and can reduce the amount of ashes produced. Attention is therefore being given to the use of ashless coal as a gas turbine direct-injection fuel in a high-efficiency, combined-cycle generation system utilizing gas turbine combustion.

(By-Product Coal Acquirement Step)

The by-product coal acquirement step is a step of evaporating and separating the solvent from the solid-content concentrated liquid which has been separated in the separation step, thereby acquiring a by-product coal. This by-product coal acquirement step includes a by-product coal mixture acquirement step and a by-product coal drying step.

(By-Product Coal Mixture Acquirement Step)

The by-product coal mixture acquirement step is a step of evaporating and separating the solvent from the solid-content concentrated liquid which has been separated in the separation step, thereby acquiring a by-product coal mixture containing a by-product coal in which the solvent remains. This by-product coal mixture acquirement step is carried out in the solvent separator 10 in FIG. 1. The solid-content concentrated liquid which has been separated by the gravitational settling tank 7 is fed to the solvent separator 10, and the solvent is evaporated and separated from the solid-content concentrated liquid in the solvent separator 10. The evaporative separation of the solvent from the solid-content concentrated liquid is preferably performed in the presence of an inert gas such as nitrogen. In the present embodiment, the solvent separator 10 is a flash distillation tank to be used in a flash distillation method. The flash distillation method is a method of spraying a solid-content concentrated liquid into a tank inside of which has been in an atmosphere of nitrogen gas, thereby evaporating and separating the solvent.

The method for separating the solvent from the solid-content concentrated liquid is not limited to the flash distillation method, and a common distillation or evaporation method can be applicable thereto as in the case of the ashless coal acquirement step. The solvent which has been separated in the solvent separator 10 is returned to the solvent tank 2, and is used in cycles. By separating the solvent from the solid-content concentrated liquid, a by-product coal mixture containing the by-product coal in which the solvent remains in a proportion of 5 to 10 wt % can be obtained.

The solid-content concentrated liquid which has been separated by the gravitational settling tank 7 has been in a high-temperature high-pressure condition which does not allow the solvent to be evaporated and separated. By spraying the solid-content concentrated liquid which has been in such a condition into the solvent separator 10 the inside of which is held at normal pressure, the pressure on the solid-content concentrated liquid is released. Thus, the boiling temperature of the solvent is lowered, and the solvent is evaporated and separated at a dash from the high-temperature solid-content concentrated liquid. At this time, the temperature of the solid-content concentrated liquid to be fed to the solvent separator 10 has been adjusted so that the by-product coal mixture to be fed to the dryer 11 at a later time has a calorific value allowing the remaining solvent to be evaporated and separated from the by-product coal mixture. This temperature adjustment is carried out, as mentioned above, by means of the preheater 5 for heating the slurry which has been prepared in the slurry preparation tank 3. This temperature adjustment may be carried out by heating the solid-content concentrated liquid which has been separated by the gravitational settling tank 7 but before feeding into the solvent separator 10. Alternatively, this temperature adjustment may be carried out by heating both the slurry which has been prepared in the slurry preparation tank 3 and the solid-content concentrated liquid which has been separated by the gravitational settling tank 7.

(By-Product Coal Drying Step)

The by-product coal drying step is a step of evaporating and separating the remaining solvent from the by-product coal mixture, thereby acquiring the by-product coal. This by-product coal drying step is carried out in the dryer 11 in FIG. 1. The by-product coal mixture which has been obtained in the solvent separator 10 is fed to the dryer 11 and the remaining solvent is evaporated and separated from the by-product coal mixture in the dryer 11. The evaporative separation of the solvent from the by-product coal mixture is preferably carried out in the presence of an inert gas such as nitrogen. In the present embodiment, the dryer 11 is a rotary dryer which holds therein the by-product coal mixture and carries out stirring while circulating therein a nitrogen gas as carrier gas. By separating the remaining solvent from the by-product coal mixture, it becomes possible to obtain the by-product coal (RC, also referred to as residual coal) in which solvent-insoluble components including ash components have been concentrated.

The by-product coal contains absolutely no moisture though it contains ash components, and has a sufficient calorific value. The by-product coal shows no coal plastic properties, and when used in a coal blend, it does not impair the coal plastic properties of other kinds of coals included in the coal blend because it has been subjected to elimination of oxygen-containing functional groups. Thus, this by-product coal can be used as a portion of the coal blend for coke-making material as in the case of usual non- or slightly-caking coals, and may also be used for various kinds of fuels without being used as a coke-making material.

In the present embodiment, the remaining solvent is evaporated and separated from the by-product coal mixture in the dryer 11 by exploiting the heat that the by-product coal mixture itself, which is the mixture including the by-product coal and solvent, has. More specifically, in the dryer 11, the by-product coal mixture is only retained and stirred, and any heat is not given to the by-product coal mixture. The expression that “the heat that the by-product coal mixture itself has” means the heat borne (possessed) by the by-product coal mixture obtained through the separation of the solvent from the solid-content concentrated liquid, and does not mean the heat generated from the by-product coal mixture through chemical reaction. Since the by-product coal mixture itself has heat, the by-product coal mixture has a given calorific value. The calorific value that the by-product coal mixture has is a value allowing the remaining solvent to be evaporated and separated from the by-product coal mixture. When a main ingredient of the solvent is methylnaphthalene, the calorific value required for evaporating and separating the solvent in a unit amount is 330 kJ/kg (the calorific value required for evaporation of 1 kg of the solvent). As mentioned above, by adjusting the temperature of the solid-content concentrated liquid fed to the solvent separator 10, the by-product coal mixture fed to the dryer 11 is adjusted so as to have such a calorific value.

In order to dry powder, it generally becomes necessary to use a device for applying heat to the powder. However, the by-product coal mixture itself, which is obtained in the by-product coal mixture acquirement step (the solvent separator 10), has a considerable amount of heat. Thus, by evaporating and separating the remaining solvent from the by-product coal mixture by exploiting the heat that the by-product coal mixture itself has, necessity for applying heat to the by-product coal mixture is eliminated. With this being the situation, a device for drying the by-product coal mixture can be simplified, and costs for drying the by-product coal mixture can be reduced.

In addition, by adjusting the temperature of the solid-content concentrated liquid fed to the by-product coal mixture acquirement step (the solvent separator 10), the by-product coal mixture fed to the by-product coal drying step (the dryer 11) is adjusted so as to have a calorific value allowing the remaining solvent to be evaporated and separated from the by-product coal mixture. In general the application of heat to liquid is greater in efficiency than the case where heat is applied to solid. The temperature adjustment of the solid-content concentrated liquid in a liquid state is therefore easier than that of the by-product coal mixture in a somewhat solidified state. Thus, the temperature adjustment is not given to the by-product coal mixture fed to the by-product coal drying step (the dryer 11), but the temperature adjustment is given to the solid-content concentrated liquid fed to the by-product coal mixture acquirement step (the solvent separator 10). Thereby, it becomes possible to appropriately provide the by-product coal mixture with a calorific value allowing the remaining solvent to be evaporated and separated from the by-product coal mixture.

Further, the temperature of the solid-content concentrated liquid fed to the by-product coal mixture acquirement step (the solvent separator 10) is adjusted by heating at least one of the slurry prepared in the slurry preparation tank 3 and the solid-content concentrated liquid separated by the gravitational settling tank 7. Because the slurry and the solid-content concentrated liquid are liquids, heat can be applied to them with efficiency. Thus, by heating the slurry or the solid-content concentrated liquid, the temperature of the solid-content concentrated liquid fed to the by-product coal mixture acquirement step can be adjusted appropriately.

(Drying Time Evaluation)

Next, the time required to dry the by-product coal was evaluated at each of different drying temperatures. For making such evaluations, a tube furnace was used. In a procedure for each evaluation, first of all, the temperature was raised so that the temperature inside the furnace reached a predetermined drying temperature while circulating a nitrogen gas through the furnace. Then, a by-product coal mixture containing 28 wt % of the solvent, as a sample, was put in the furnace in a condition that the sample was placed on a porcelain dish fitted with a thermocouple. Thereafter, drying time measurement was started at the time when the temperature of the sample reached the predetermined drying temperature. The sample was taken out after the passage of a predetermined time, and examined on the solvent content therein. In accordance with this procedure, the evaluation is performed under each of different drying temperatures of 210° C., 250° C. and 270° C. Evaluation results obtained are shown in FIG. 2.

As to the times required to reduce the solvent content in the sample to 2 wt % under different drying temperatures, they were about 30 minutes under the drying temperature of 210° C., about 15 minutes under the drying temperature of 250° C. and about 10 minutes under the drying temperature of 270° C. These results show that, as compared the case of the drying temperature of 210° C. corresponding to the steam temperature of a steam tube dryer, the time required for drying under the temperature of 250° C. can be cut in about one-half. In addition, it is also shown that the time required for drying under the temperature of 270° C. can be reduced to about one-third as compared with the case under the drying temperature of 210° C.

(Effects)

As mentioned above, according to the method of producing a by-product coal according to the present embodiment, the remaining solvent is evaporated and separated from the by-product coal mixture by exploiting heat that the by-product coal mixture itself has, in the by-product coal drying step (the dryer 11). In general, a device for applying heat to powder becomes necessary for the powder to be dried. However, the by-product coal mixture itself, which is obtained in the by-product coal mixture acquirement step (the solvent separator 10), has a considerable amount of heat. Thus, by evaporating and separating the remaining solvent from the by-product coal mixture by exploiting the heat that the by-product coal mixture itself has, necessity for applying heat to the by-product coal mixture is eliminated. By doing so, a device for drying the by-product coal mixture can be simplified, and costs for drying the by-product coal mixture can be reduced.

In addition, by adjusting the temperature of the solid-content concentrated liquid fed to the by-product coal mixture acquirement step (the solvent separator 10), the by-product coal mixture fed to the by-product coal drying step (the dryer 11) is adjusted so as to have a calorific value allowing the remaining solvent to be evaporated and separated from the by-product coal mixture. In general, the application of heat to liquid is greater in efficiency the case where heat is applied to solid. Therefore, the temperature adjustment of the solid-content concentrated liquid in a liquid state is easier than that of the by-product coal mixture in a somewhat solidified state. Thus, the temperature adjustment is not given to the by-product coal mixture fed to the by-product coal drying step, but the temperature adjustment is given to the solid-content concentrated liquid fed to the by-product coal mixture acquirement step. By doing so, it becomes possible to appropriately provide the by-product coal mixture with a calorific value allowing the remaining solvent to be evaporated and separated from the by-product coal mixture.

Further, the temperature of the solid-content concentrated liquid fed to the by-product coal mixture acquirement step (the solvent separator 10) is adjusted by heating at least one of the slurry and the solid-content concentrated liquid. Because the slurry and the solid-content concentrated liquid are liquids, heat can be applied to them with efficiency. Thus, by heating the slurry or the solid-content concentrated liquid, the temperature of the solid-content concentrated liquid fed to the by-product coal mixture acquirement step can be adjusted appropriately.

Furthermore, in the by-product coal mixture acquirement step (the solvent separator 10), the solid-content concentrated liquid which has been in a high-temperature high-pressure condition, which does not allow the solvent to be evaporated and separated, is sprayed into a tank the inside of which is kept at normal pressure, and then, the pressure on the solid-content concentrated liquid is released. Thus, the boiling temperature of the solvent is lowered, and the solvent is evaporated and separated at a dash from the high-temperature solid-content concentrated liquid. With this being the situation, the solvent can be appropriately evaporated and separated from the solid-content concentrated liquid.

MODIFICATION EXAMPLES OF PRESENT EMBODIMENT

Although an exemplary embodiment in the present invention has been described in the foregoing, it merely exemplifies the concrete example and should not be construed as particularly limiting the present invention. The concrete configuration and on the like can be modified as appropriate. Further, the actions and effects described in the embodiment in the present invention are merely recited as the most appropriate actions and effects produced by the present invention, and actions and effects which can be achieved by the present invention should not be construed as being limited to those described in the exemplary embodiment in the present invention.

This application is based on Japanese Patent Application No. 2013-025509 filed on Feb. 13, 2013, the entire contents of which are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

The method for producing a by-product coal in the present invention allows simplification of a device for drying a by-product coal mixture and the reduction of costs for drying.

DESCRIPTION OF REFERENCE NUMBERS

1: Coal hopper

2: Solvent tank

3: Slurry preparation tank

3a: Stirrer

4: Transport pump

5: Preheater

6: Extraction tank

6a: Stirrer

7: Gravitational settling tank

8: Filter unit

9, 10: Solvent separator

11: Dryer

100: Ashless coal production equipment

Claims

1. A method for producing a by-product coal, comprising:

(1) heating a slurry prepared by mixing a coal and a solvent, thereby extracting a coal component soluble in the solvent;

(2) separating the slurry which has been obtained in the extraction (1) into a solution in which the coal component soluble in the solvent is dissolved and a solid-content concentrated liquid in which a coal component insoluble in the solvent is concentrated; and

(3) evaporating and separating the solvent from the solid-content concentrated liquid which has been separated in (2), thereby acquiring a by-product coal,

wherein (3) comprises:

(3a) evaporating and separating the solvent from the solid-content concentrated liquid which has been separated in (2), thereby acquiring a by-product coal mixture containing a by-product coal in which the solvent remains; and

(3b) evaporating and separating the remaining solvent from the by-product coal mixture, thereby acquiring the by-product coal,

wherein, in (3b), the remaining solvent is evaporated and separated from the by-product coal mixture by exploiting heat that the by-product coal mixture itself has.

2. The method for producing a by-product coal according to claim 1, wherein a temperature of the solid-content concentrated liquid to be fed to (3a) is adjusted so that the by-product coal mixture to be fed to (3b) has a calorific value allowing the remaining solvent to be evaporated and separated from the by-product coal mixture.

3. The method for producing a by-product coal according to claim 2, wherein the temperature of the solid-content concentrated liquid to be fed to (3a) is adjusted by heating at least one of the slurry to be fed to (2) and the solid-content concentrated liquid to be fed to (3).

4. The method for producing a by-product coal according to claim 1,

wherein (2) is performed under a pressurized condition, and

in (3a), the solvent is evaporated and separated from the solid-content concentrated liquid by spraying the solid-content concentrated liquid which has been in a high-temperature high-pressure condition, which does not allow the solvent to be evaporated and separated, into a normal-pressure tank.

5. The method for producing a by-product coal according to claim 2,

wherein (2) is performed under a pressurized condition, and

in (3a), the solvent is evaporated and separated from the solid-content concentrated liquid by spraying the solid-content concentrated liquid which has been in a high-temperature high-pressure condition, which does not allow the solvent to be evaporated and separated, into a normal-pressure tank.

6. The method for producing a by-product coal according to claim 3,

wherein (2) is performed under a pressurized condition, and

in (3a), the solvent is evaporated and separated from the solid-content concentrated liquid by spraying the solid-content concentrated liquid which has been in a high-temperature high-pressure condition, which does not allow the solvent to be evaporated and separated, into a normal-pressure tank.