CN112805356B

CN112805356B - Method for producing molded coal

Info

Publication number: CN112805356B
Application number: CN201880098424.2A
Authority: CN
Inventors: 森英一朗; 安田和真; 小菅克志; 藤吉旭; 浦田裕介; 有吉大辅
Original assignee: Nippon Steel and Sumikin Engineering Co Ltd
Current assignee: Nippon Steel Engineering Co Ltd
Priority date: 2018-10-03
Filing date: 2018-10-03
Publication date: 2023-05-09
Anticipated expiration: 2038-10-03
Also published as: CN112805356A; AU2018444217A1; WO2020070838A1; AU2018444217B2

Abstract

A method for producing a molded coal, which comprises a step of molding a molding material comprising a powdery dry distillation coal and a binder and drying the molding material at 60-100 ℃ to obtain a molded coal having a water content of 5 wt% or less. The binder contains an aqueous solution of polyvinyl alcohol having a saponification degree of more than 99.3mol% and a polymerization degree of 1700 or more. The pulverized dry distilled coal is pulverized coal obtained by drying and dry distilling coal containing at least one of lignite and subbituminous coal.

Description

Method for producing molded coal

Technical Field

The present invention relates to a method for producing molded coal.

Background

In the coal production process, pulverized coal is produced in the form of powder. Pulverized coal may become a cause of dust generation in addition to being difficult to handle. Therefore, it has been studied to effectively utilize pulverized coal by molding the pulverized coal into molded coal. For example, patent document 1 proposes a technique in which starch is added to powdered coal as a binder and mixed, and the surface of a molded product obtained by molding is covered with heavy oil such as heavy oil or tar. Patent document 2 proposes a technique of adding tar or tar residue to pulverized coal and molding the pulverized coal.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2003-64377

Patent document 2: japanese patent laid-open No. 9-3458

Disclosure of Invention

Problems to be solved by the invention

In order to realize the effective utilization of low-quality coals such as lignite and subbituminous coals, modification techniques including drying and carbonization have been studied. Pulverized coal is produced when this modification process is performed. From the viewpoints of improving safety and preventing liquefaction, it is preferable that the pulverized coal to be produced is transported not as a powder but as molded coal. Here, in transportation, the molded coal is required to have high strength so that it is not easily damaged by vibration, impact, or the like. In addition, in the case of transporting and storing coal on the sea, since the molded coal is exposed to wind and rain, it is required to maintain high strength without collapsing even if it is wetted with water.

Since pulverized coal of retorted coal is difficult to mold as compared with raw coal, a binder is required for producing molded coal. Here, when a heavy oil such as tar is used as a binder, heating is required at the time of kneading with pulverized coal. However, since pulverized coal generated during carbonization is liable to spontaneously ignite, heating is not preferable from the viewpoint of safety. In addition, since a heating device is required and it is difficult to uniformly heat the molded coal in the case of kneading in a large amount, there is a concern that kneading becomes uneven and the strength of the molded coal becomes uneven.

In addition, in the case of using starch as a binder and covering the surface with an oil-type binder, if the molded coal is broken to expose the inside, the starch is water-soluble, and therefore there is a concern that the strength when wetted with water is lowered. Under such circumstances, it is required to establish a technique for producing a molded coal having high safety and excellent water resistance.

Accordingly, an object of one aspect of the present invention is to provide a method for producing a molded coal which is excellent in safety and can maintain high strength even when wetted with water.

Solution for solving the problem

In one aspect, the present invention provides a method for producing molded coal, comprising a step of molding a molding material comprising pulverized dry distilled coal and a binder, the molding material being dried at 60 to 100 ℃ to obtain molded coal having a moisture content of 5 wt% or less, the binder comprising an aqueous solution of polyvinyl alcohol having a saponification degree of more than 99.3mol% and a polymerization degree of 1700 or more, the pulverized dry distilled coal being pulverized coal obtained by drying and dry distilling coal comprising at least one of lignite and subbituminous coal.

In this production method, a binder containing an aqueous solution of polyvinyl alcohol having a saponification degree of more than 99.3mol% is used. From this, it can be seen that since an aqueous solution is used as the binder, safety is excellent. Further, polyvinyl alcohol having a high saponification degree exhibits excellent water resistance when dried, in which hydroxyl groups in each molecule are bonded to each other by hydrogen bonding. That is, the molecules of the polyvinyl alcohol contained in the molded coal as a binder are firmly bonded to each other, and thus high strength can be maintained even when the molded coal is wetted with water.

The polymerization degree of the polyvinyl alcohol is preferably 2500 or more. This can further improve the strength of the molded coal, particularly, during drying.

In the above step, the molded product of the molding material is dried to obtain a molded coal having a moisture content of 5% by weight or less. By reducing the moisture content of the molded article in this way, the formation of hydrogen bonds is promoted, and the strength of the molded coal when wetted with water can be improved.

The content of polyvinyl alcohol in the aqueous solution of polyvinyl alcohol is preferably 1 to 10% by weight. Thus, the dispersibility of the powdery dry distilled coal and the binder is improved, and the uniformity of the molding material can be improved. Therefore, the strength unevenness of the molded coal can be reduced.

The content of polyvinyl alcohol is preferably 1 part by weight or more relative to 100 parts by weight of the dry distillation coal. Thus, the strength of the molded coal can be further improved.

The binder may contain polyvinyl alcohol together with alpha starch. Since alpha starch is inexpensive, manufacturing costs can be reduced. In addition, if alpha starch is used, the strength of the molded coal at the time of drying can be sufficiently improved. Therefore, α starch is useful in applications where the strength at the time of drying is important more than the water resistance.

The molded coal obtained by the above production method preferably has a compressive strength of 50N or more after being immersed in water at 20℃for 24 hours. This can sufficiently suppress collapse due to exposure to wind and rain during transportation and storage of coal.

Preferably, neither calcium oxide nor magnesium oxide is added to the molding material. Thus, when the molded coal is used as a solid fuel, the heat generation amount can be sufficiently increased.

The briquette preferably has a compressive strength of 50N or more after being immersed in water at 20 ℃ for 24 hours. This can sufficiently suppress collapse due to exposure to wind and rain during transportation and storage of coal. Therefore, the molded coal obtained by the above-described production method is suitable for use as a solid fuel because it can be safely transported and stored on the sea.

ADVANTAGEOUS EFFECTS OF INVENTION

In one aspect, the present invention provides a method for producing a molded coal which is excellent in safety and can maintain high strength even when wetted with water.

Drawings

FIG. 1 is a schematic view of a measuring apparatus for measuring the compressive strength of molded coal.

Fig. 2 is a semilogarithmic graph showing the relationship between the impregnation time and the compressive strength of the molded coal of examples 2, 3 and comparative examples 2, 3.

Fig. 3 is a semilogarithmic graph showing the relationship between the impregnation time and the compressive strength of the molded coal of reference examples 4 to 6.

Fig. 4 is a graph showing data of the molded coals of reference examples 4 to 6 before immersion in water (after drying) and after 24 hours (1440 minutes) immersion, wherein the vertical axis represents compressive strength, and the horizontal axis represents polymerization degree of polyvinyl alcohol.

Fig. 5 is a semilogarithmic graph showing the relationship between the impregnation time and the compressive strength of the molded coal of reference examples 6 to 10.

Fig. 6 is a semilogarithmic graph showing the relationship between the impregnation time and the compressive strength of the molded coal of reference examples 11 to 13.

FIG. 7 is a graph showing data of the molded coals of reference example 8 and reference examples 11 to 13 before immersion in water (after drying) and after immersion for 24 hours (1440 minutes), wherein the vertical axis represents compressive strength and the horizontal axis represents compounding ratio of alpha starch

Detailed Description

Embodiments of the present invention will be described below with reference to the drawings. However, the following embodiments are examples for illustrating the present invention, and are not intended to limit the present invention to the following.

The method for producing a molded coal according to the present embodiment includes a step of molding a molding material including powdery dry distillation coal and a binder, and drying the molding material to obtain a molded coal. The pulverized dry distilled coal is pulverized coal obtained by drying and dry distilling coal containing at least one of lignite and subbituminous coal. Thus, the low-quality lignite and subbituminous coal can be effectively utilized in coal. The particle size of the dry distilled coal is not particularly limited, and may be, for example, undersize pulverized coal obtained by sieving with a 1 to 10mm sieve. In the case of sieving with a 1mm sieve, the ratio of the sieve to the whole dry distillation coal may be 80% by weight or more from the viewpoint of improving the moldability.

The binder contains an aqueous solution of polyvinyl alcohol (PVA) having a saponification degree of more than 99.3mol% and a polymerization degree of 1700 or more. Pulverized coal obtained by drying and dry distilling low-quality coals such as brown coal and subbituminous coal has more pores than coke powder produced from high-quality coals. Therefore, the density of the molded product of the pulverized coal is small, and the strength tends to be low. However, in the present embodiment, strength can be improved by using the above-described binder.

The saponification degree of polyvinyl alcohol (PVA) represents the proportion of units actually saponified into vinyl alcohol units among units convertible into vinyl alcohol units by saponification. The saponification degree can be measured by a neutralization titration method according to JIS K6726-1994. Specifically, a phenolphthalein solution was added to polyvinyl alcohol, and sodium hydroxide was added dropwise until the color became pale red. The residue (residual acetate group) was obtained from the amount of the solution to be added dropwise, and the saponification degree was calculated.

That is, in the polyvinyl alcohol having the molecular structure of the following formula (1), the saponification degree is calculated by the mathematical formula of n/(m+n). Times.100. The partially saponified polyvinyl alcohol has a molecular structure of the following formula (1), whereas the completely saponified polyvinyl alcohol is represented by the following formula (2) in which the acetate group is almost substituted with a hydroxyl group.

When the polyvinyl alcohol having a saponification degree of more than 99.3mol% is dried, hydroxyl groups in each molecule are firmly bonded to each other through hydrogen bonds. Such bonds are not easily dissociated even if they are again contacted with water once formed. Therefore, the molded coal obtained by molding and drying using a binder comprising an aqueous solution of polyvinyl alcohol having a saponification degree of more than 99.3mol% is excellent in water resistance. The saponification degree of polyvinyl alcohol is preferably 99.5mol% or more from the viewpoint of further improving the strength of the molded coal at the time of drying and at the time of wetting with water.

As the polyvinyl alcohol, commercially available ones can be used. In particular, from the viewpoint of improving the strength of the molded coal at the time of drying, the polymerization degree of polyvinyl alcohol is 1700 or more, preferably 2500 or more, and more preferably 3300 or more. The polymerization degree of polyvinyl alcohol can be measured by a solution viscosity measurement method according to JIS K6726-1994.

The content of the polyvinyl alcohol in the aqueous solution of the polyvinyl alcohol is preferably 1 to 10% by weight, more preferably 2 to 10% by weight. This facilitates kneading with powdery dry distillation coal, and can improve dispersibility. Therefore, uniformity of the molding material is improved, and unevenness in strength of the molded coal can be reduced. The viscosity (20 ℃) of the aqueous solution of polyvinyl alcohol may be, for example, 20 to 500 mPas.

The binder contains an aqueous solution, and therefore is excellent in safety as compared with a binder composed of only combustible substances. Further, since the dry distillation coal and the binder can be kneaded at room temperature without heating, even the dry distillation coal having spontaneous combustibility can be kneaded very safely. However, heating is not excluded to carry out kneading.

The powdery dry distillation coal can be compounded with a binder comprising an aqueous solution of polyvinyl alcohol and kneaded to prepare a molding material. Water may be mixed together according to the viscosity of the aqueous solution of polyvinyl alcohol or the content of polyvinyl alcohol in the aqueous solution, and kneading may be performed. From the viewpoint of achieving both moldability and kneading properties at a sufficiently high level, the mixing ratio of the aqueous solution of polyvinyl alcohol may be, for example, 5 to 50 parts by weight or 5 to 30 parts by weight relative to 100 parts by weight of the powdery dry distillation coal.

From the viewpoint of sufficiently improving the strength of the molded coal, the content of polyvinyl alcohol in the molding material is preferably 0.5% by weight or more, more preferably 1.5% by weight or more. On the other hand, from the viewpoint of reducing the production cost of the molded coal, the content of polyvinyl alcohol in the molding material is preferably 10% by weight or less. From the viewpoint of achieving both moldability and kneading properties at a sufficiently high level, the water content in the molding material is preferably 20 to 40% by weight.

The binder may contain components other than polyvinyl alcohol and water. The component may be a water-soluble component. As the water-soluble component, alpha starch is preferable from the viewpoint of manufacturing cost. Alpha starch is generally cheaper than polyvinyl alcohol, so by replacing part of the polyvinyl alcohol with alpha starch, the manufacturing cost of the molded coal can be reduced. In addition, when the alpha starch is used, the strength of the molded coal at the time of drying can be sufficiently improved. In the molding material, the blending ratio of the alpha starch is preferably 1 to 9 parts by weight relative to 100 parts by weight of the dry distillation coal from the viewpoint of sufficiently improving the strength at the time of drying while maintaining the water resistance.

From the viewpoint of sufficiently increasing the heat generation amount when the molded coal is used as a solid fuel, it is preferable that neither calcium oxide nor magnesium oxide be added to the molding material.

Examples of the equipment for molding the molding material include a general twin-roll molding machine, a single-screw press molding machine, and the like. The shape of the molded article obtained by molding the molding material is not particularly limited, and may be, for example, mosaic type, spherical, cylindrical or prismatic. The density of the briquette may be, for example, 1.0 to 2.0g/ml. The molding pressure is, for example, 1 to 10 tons/cm by a line pressure gauge and 40 to 390MPa by a surface pressure gauge.

Subsequently, the obtained molded article is dried by, for example, an electric furnace or a dryer to reduce the moisture. The molded coal is obtained by drying the molded product. The drying may be carried out, for example, in air at 60 to 100℃or in an inert gas atmosphere. The drying time may be, for example, 1 to 20 hours. By drying at a relatively low temperature of 60 to 100 ℃, a molded coal which can maintain high strength even when wetted with water can be produced. Drying may also be carried out in the exhaust gas of a burner. By such drying, the moisture content of the molded coal is preferably reduced to 5% by weight or less. By setting the water content to this level, hydrogen bonding between molecules (between hydroxyl groups) of the polyvinyl alcohol is sufficiently promoted, and the strength of the molded coal can be further improved. The moisture of the molded coal can be measured by a moisture measuring machine by a heat drying method (a method of measuring the weight before and after heat drying).

The molded coal comprises dry distilled coal and a binder comprising polyvinyl alcohol having a saponification degree of more than 99.3mol% and a polymerization degree of 1700 or more. In this molded coal, the content of polyvinyl alcohol is preferably 1 part by weight or more, more preferably 2 parts by weight or more, based on 100 parts by weight of dry distillation coal, from the viewpoint of excellent water resistance and sufficiently improved strength. From the viewpoint of production cost, the content of polyvinyl alcohol in the molded coal is, for example, 10 parts by weight or less per 100 parts by weight of the dry distillation coal. From the viewpoint of improving the strength, the moisture content of the molded coal is 5% by weight or less, preferably 4% by weight or less. In the case where the binder contains polyvinyl alcohol and alpha starch, the content of alpha starch is preferably 1 to 9 parts by weight, and the total content of polyvinyl alcohol and alpha starch is preferably 2 to 10 parts by weight, relative to 100 parts by weight of dry distillation coal, in the molded coal.

The strength of the briquette can be quantified in terms of the compressive strength measured by the measuring apparatus 10 shown in fig. 1. As a sample, a cylindrical (phi 15 mm. Times.15 mm in height) briquette 16 was prepared. The molded coal 16 is disposed on a support plate 17 disposed on a bottom plate of the bracket 18 so that a peripheral surface of the molded coal 16 to be measured is in contact with an upper surface of the support plate 17. Then, the movable plate 14, which is mounted to be movable up and down on the support 18, is lowered, and the molded coal 16 is sandwiched between the movable plate 14 and the support plate 17. Then, by operating the movable plate 14, a load is applied in the radial direction of the molded coal 16. The compressive strength was finally obtained from the load at the time of fracture of the briquette 16.

The compressive strength of the molded coal is preferably 100N or more, more preferably 150N or more, when dried (moisture: 2 to 4 wt%). The compressive strength of the molded coal after immersing in water at 20 ℃ for 24 hours is preferably 40N or more, more preferably 50N or more. It can be seen that the molded coal of the present embodiment maintains high strength even when wetted with water, not only when dried.

In the above, several embodiments of the present invention have been described, but the present invention is not limited to the above embodiments.

Examples

The content of the present invention will be described in more detail with reference to examples, reference examples and comparative examples, but the present invention is not limited to the following examples.

[ investigation of the kind of Binder ]

(example 1 and comparative example 1)

< preparation of Molding Material >

The following 12 binders were prepared.

( 1) Polyvinyl alcohol (degree of polymerization: 1700. saponification degree: 99.7 mol%) of an aqueous solution (polyvinyl alcohol content: 10 wt.% )

(2) Alpha starch (from corn)

(3) Alpha starch (from cassava)

(4) Straight-run asphalt

(5) Soft asphalt (SOP)

(6) Asphalt A

(7) Asphalt B

(8) Vinyl acetate emulsion

(9) Waste molasses A (slaked lime not added)

(10) Waste molasses B (adding slaked lime)

(11) Pulp waste liquid

(12) Alkaline aqueous solutions of humic acid

(13) Bentonite clay

The undersize dry distilled coal obtained by sieving the dry distilled coal obtained by dry distillation with a 1mm sieve is kneaded with the binders (1) to (13) respectively, to obtain a molding material. The binders (1) and (8) to (13) may be kneaded at room temperature to prepare molding materials. On the other hand, since the viscosity of the binders (4) to (7) is high, it is difficult to knead them at room temperature (20 ℃). Thus, the binders (4) to (7) were kneaded with dry distilled coal while being heated to 120 to 130 ℃ to prepare molding materials.

< evaluation of the production and Forming Property of molded coal >

The molding material thus prepared was molded using a single screw press molding machine at a molding pressure of 283MPa to prepare a molded coal. For each binder, the blending amount of the binder required to set the compressive strength of the molded coal to 50N or more was examined. Further, the moldability of each binder was evaluated by the following criteria. That is, the binder content of the entire molded coal was evaluated as "a" and the binder content of the molded coal was more than 10% by weight and not more than 40% by weight as "B", and the binder content of the molded coal was not molded or the compressive strength of the molded coal was not 50N even when the binder content was 40% by weight as "C". The evaluation results are shown in Table 1.

< evaluation of Water resistance of molded coal >

For the samples evaluated as "A" or "B" for moldability, the water resistance was evaluated by the following procedure. The briquette was immersed in water for 1440 minutes. Then, the molded coal was taken out of the water, and the shape before the impregnation was evaluated as "a", and the shape before the impregnation was not maintained was evaluated as "B". The evaluation results are shown in Table 1.

TABLE 1

	Kinds of binders	Whether or not to heat	Moldability (formability)	Water resistance
					Example 1	(1)	Does not need	A	A
Comparative example 1-1	(2)	Does not need	A	B
					Comparative examples 1 to 2	(3)	Does not need	A	B
Comparative examples 1 to 3	(4)	Needs to be as follows	B	A
					Comparative examples 1 to 4	(5)	Needs to be as follows	B	A
Comparative examples 1 to 5	(6)	Needs to be as follows	C	-
					Comparative examples 1 to 6	(7)	Needs to be as follows	C	-
Comparative examples 1 to 7	(8)	Does not need	C	-
					Comparative examples 1 to 8	(9)	Does not need	C	-
Comparative examples 1 to 9	(10)	Does not need	C	-
					Comparative examples 1 to 10	(11)	Does not need	C	-
Comparative examples 1 to 11	(12)	Does not need	C	-
					Comparative examples 1 to 12	(13)	Does not need	C	-

As shown in table 1, example 1 using polyvinyl alcohol as a binder can obtain molded coal excellent in moldability as compared with comparative examples 1-3 to 1-12 using binders (4) to (13). The molded coal of example 1 was also excellent in water resistance. Comparative examples 1-1 and 1-2 using the binders (2) and (3) were excellent in moldability, but disintegrated when immersed in water, and could not maintain the original shape.

[ influence of saponification degree ]

Example 2

An aqueous solution (binder aqueous solution) containing polyvinyl alcohol (saponification degree: 99.85mol%, polymerization degree: 1700) at a concentration of 10% by weight, water and the dry distilled coal used in example 1 were mixed to obtain a mixture. The blending ratio based on the weight at this time was 30 parts by weight of the aqueous binder solution and 10 parts by weight of water based on 100 parts by weight of the dry distilled coal. The mixture was molded using a single screw press molding machine (molding pressure: 283 MPa) to prepare a plurality of molded coals (before drying). The moisture content of the molded coal was 27.6 wt%, and the compressive strength (average value of n=2) was 66N. Compressive strength was measured using the measuring apparatus of fig. 1.

The molded coal thus produced was dried in air at 80℃for 15 hours. The moisture and compressive strength of the dried briquette are shown in Table 2. The moisture of the molded coal before and after drying was measured by a heat drying method using a commercially available moisture measuring machine.

The dried molded coals were immersed in water at about 20 ℃ for a predetermined period of time. After a predetermined soaking time shown in table 2, the molded coal was taken out of the water, and the compressive strength was measured by measuring the moisture (a part of the water was not measured). The measurement results of the immersion time and moisture and the compressive strength are shown in Table 2.

The molded coal immersed in water for 1440 minutes was dried in air at 80℃for 15 hours. The moisture content of the re-dried molded coal was measured, and the compressive strength was measured. The results of moisture and compressive strength are shown in table 2.

TABLE 2

As shown in table 2, the briquette of example 2 maintained compressive strength of 90N or more even after 24 hours had elapsed.

Example 3

A molded coal was produced and measured in the same manner as in example 2, except that polyvinyl alcohol (saponification degree: 99.3mol%, polymerization degree: 1700) was used instead of the polyvinyl alcohol used in example 2. The results are shown in Table 3.

TABLE 3

As shown in table 3, the molded coal of example 3 maintained a compressive strength of 70N or more even after 24 hours had passed. Example 2, which had a high saponification degree, had higher compressive strength and also had excellent water resistance than example 3.

Comparative example 2

A molded coal was produced and measured in the same manner as in example 2, except that polyvinyl alcohol (saponification degree: 94.5 to 95.5mol%, polymerization degree: 1700) was used instead of polyvinyl alcohol used in example 2. The results are shown in Table 4.

TABLE 4

As shown in table 4, the compression strength of the molded coal of comparative example 2 after drying was significantly lower than that of examples 2 and 3. Further, since the molded coal gradually disintegrates when immersed in water, measurement of the immersion time after 30 minutes was not performed.

Comparative example 3

A molded coal was produced and measured in the same manner as in example 2, except that polyvinyl alcohol (saponification degree: 87 to 89mol%, polymerization degree: 1700) was used instead of the polyvinyl alcohol used in example 2. The results are shown in Table 5.

TABLE 5

As shown in table 5, the compression strength of the molded coal of comparative example 3 after drying was lower than that of comparative example 2. Further, since the molded coal gradually disintegrates when immersed in water, measurement of the immersion time after 1 minute was not performed.

Fig. 2 is a semilogarithmic graph showing the relationship between the impregnation time and the compressive strength of the molded coal of examples 2, 3 and comparative examples 2, 3. The compressive strength of the sample disintegrated by immersion in water is plotted as 0 in the graph.

[ influence of polymerization degree ]

Reference example 4

A molded coal was produced and measured in the same manner as in example 2, except that polyvinyl alcohol (saponification degree: 99mol%, polymerization degree: 2500) was used instead of the polyvinyl alcohol used in example 2. The results are shown in Table 6.

TABLE 6

/>

As shown in table 6, the molded coal of reference example 4 maintained a compressive strength of 100N or more even after the immersion time had elapsed for 24 hours.

Reference example 5

A molded coal was produced and measured in the same manner as in example 2, except that polyvinyl alcohol (saponification degree: 99mol%, polymerization degree: 3300) was used instead of the polyvinyl alcohol used in example 2. The results are shown in Table 7.

TABLE 7

As shown in table 7, the molded coal of reference example 5 maintained a compressive strength of 100N or more even after the immersion time had elapsed for 24 hours. Reference example 5, in which the degree of polymerization of polyvinyl alcohol was large, exhibited higher compressive strength both before and after impregnation in water, as compared with reference example 4.

Reference example 6

A molded coal was produced and measured in the same manner as in example 2, except that polyvinyl alcohol (saponification degree: 99mol%, polymerization degree: 4000) was used instead of the polyvinyl alcohol used in example 2. The results are shown in Table 8.

TABLE 8

As shown in table 8, the briquette of reference example 6 maintained a compressive strength of 100N or more even after 24 hours had elapsed. The molded coal of reference example 6, which has a large degree of polymerization of polyvinyl alcohol, has particularly high compressive strength before impregnation (before and after drying) and after re-drying, compared with reference examples 4 and 5.

Fig. 3 is a semilogarithmic graph showing the relationship between the impregnation time and the compressive strength of the molded coal of reference examples 4 to 6. Fig. 4 is a graph showing data of the molded coals of reference examples 4 to 6 before immersion in water (after drying) and after 24 hours (1440 minutes) immersion, wherein the vertical axis represents compressive strength, and the horizontal axis represents polymerization degree of polyvinyl alcohol. As shown in fig. 3 and 4, as the polymerization degree of polyvinyl alcohol increases, the compressive strength and the water resistance before immersion in water increase. In addition, the compressive strength of the dried molded coal is greatly improved by increasing the polymerization degree of the polyvinyl alcohol.

[ influence of the content of polyvinyl alcohol ]

Reference example 7

An aqueous binder solution containing polyvinyl alcohol (saponification degree: 99mol%, polymerization degree: 4000) used in reference example 6 at a concentration of 10% by weight, water and dry distilled coal used in example 1 were mixed to prepare a mixture. The blending ratio based on the weight at this time was 3 parts by weight of the binder aqueous solution and 34.3 parts by weight of water based on 100 parts by weight of the dry distillation coal. Using this mixture, a molded coal was produced in the same manner as in example 2, and measurement was performed. The results are shown in Table 9.

TABLE 9

Reference example 8

A molded coal was produced and measured in the same manner as in reference example 7, except that a mixture was prepared by setting the mixing ratio of the binder aqueous solution, water and dry distilled coal to 100 parts by weight of dry distilled coal, and setting the binder aqueous solution to 10 parts by weight and the water to 28 parts by weight. The results are shown in Table 10.

TABLE 10

Reference example 9

A molded coal was produced and measured in the same manner as in reference example 7, except that a mixture was prepared by setting the mixing ratio of the binder aqueous solution, water and dry distilled coal to 100 parts by weight of dry distilled coal, the binder aqueous solution being 15 parts by weight and the water being 23.5 parts by weight. The results are shown in Table 11.

TABLE 11

Reference example 10

A molded coal was produced and measured in the same manner as in reference example 7, except that a mixture was prepared by setting the mixing ratio of the binder aqueous solution, water and dry distilled coal based on the weight of the binder aqueous solution to 100 parts by weight of dry distilled coal, and setting the binder aqueous solution to 20 parts by weight and the water to 19 parts by weight. The results are shown in Table 12.

TABLE 12

Fig. 5 is a semilogarithmic graph showing the relationship between the impregnation time and the compressive strength of the molded coal of reference examples 6 to 10. It was confirmed that the compressive strength increased with increasing content of polyvinyl alcohol. It was confirmed that in order to achieve a compressive strength of 100N or more both before and after impregnation into water, it was necessary to set the ratio of polyvinyl alcohol to 100 parts by weight of dry distillation coal to 1.5 parts by weight or more.

[ composite addition of polyvinyl alcohol and alpha starch ]

Reference example 11

An aqueous polyvinyl alcohol solution containing polyvinyl alcohol (saponification degree: 99mol%, polymerization degree: 4000) at a concentration of 10% by weight, alpha starch used in comparative example 1-1, water and dry distilled coal used in example 1 were mixed to obtain a mixture. The blending ratio based on the weight at this time was 10 parts by weight of the polyvinyl alcohol aqueous solution, 1 part by weight of the alpha starch and 28 parts by weight of water based on 100 parts by weight of the dry distillation coal. A molded coal was produced and measured in the same manner as in example 2, except that the mixture was used. The results are shown in Table 13.

TABLE 13

Reference example 12

A molded coal was produced and measured in the same manner as in reference example 11, except that a mixture was prepared by setting 10 parts by weight of the aqueous polyvinyl alcohol solution, 3 parts by weight of the alpha starch, and 28 parts by weight of water, based on 100 parts by weight of the dry distilled coal. The results are shown in Table 14.

TABLE 14

Reference example 13

A molded coal was produced and measured in the same manner as in reference example 11, except that a mixture was prepared by setting 10 parts by weight of the aqueous polyvinyl alcohol solution, 5 parts by weight of the alpha starch, and 28 parts by weight of water, based on 100 parts by weight of the dry distilled coal. The results are shown in Table 15.

TABLE 15

Fig. 6 is a semilogarithmic graph showing the relationship between the impregnation time and the compressive strength of the molded coal of reference examples 11 to 13. Fig. 7 is a graph showing data of the molded coals of reference example 8 and reference examples 11 to 13 before immersion in water (after drying) and after 24 hours (1440 minutes) in which the vertical axis represents compressive strength and the horizontal axis represents blending ratio (parts by weight) of alpha starch. From these data, it was confirmed that the addition of alpha starch did not improve the water resistance, but the compressive strength of the molded coal before immersion in water (after drying) and after re-drying could be greatly improved.

[ influence of immersion time ]

Example 14

A molded coal was produced and measured in the same manner as in example 2, except that polyvinyl alcohol (saponification degree: 99.7mol%, polymerization degree: 1700) was used instead of the polyvinyl alcohol used in example 2. Immersion in water was performed for a maximum of 72 hours. The results are shown in Table 16.

TABLE 16

As shown in table 16, it was confirmed that the compressive strength was reduced at the start of immersion in water, but the compressive strength was hardly reduced at the time of immersion exceeding 30 minutes. Thus, the compressive strength after 24 hours of impregnation can be easily evaluated by setting the impregnation time to 30 minutes.

Comparative example 4

A molded coal was produced and measured in the same manner as in example 2, except that polyvinyl alcohol (saponification degree: 87 to 88mol%, polymerization degree: 1700) was used instead of the polyvinyl alcohol used in example 2. The results are shown in Table 17.

TABLE 17

The molded coal disintegrated after 1 minute of immersion in water. Therefore, the compressive strength after immersion in water cannot be measured.

Comparative example 4

A molded coal was produced in the same manner as in example 2, except that polyvinyl alcohol (saponification degree: 98.0 to 99.0mol%, polymerization degree: 1700) was used instead of the polyvinyl alcohol used in example 2. The compressive strength of the molded coal thus obtained (after drying and after immersing in water at 20℃for 24 hours) was measured by the same procedure as in example 2. The results are shown in Table 18. The results of comparative example 2, comparative example 3, example 2 and example 3 are shown together in table 18.

TABLE 18

As shown in table 18, the compressive strength of comparative example 4 was slightly higher than that of comparative examples 2 and 3. In contrast, examples 2 and 3 using polyvinyl alcohol having a saponification degree falling within a range of more than 99.3mol% have significantly higher compressive strength after drying and after water immersion than comparative examples 2 to 4. These examples and comparative examples are examples in which polyvinyl alcohol was blended in a proportion of 3 parts by weight based on 100 parts by weight of dry distilled coal. From this, it was confirmed that even if the blending ratio of polyvinyl alcohol is low, high compressive strength can be obtained by using polyvinyl alcohol having a high degree of saponification and a degree of polymerization of a predetermined value or more.

Industrial applicability

According to the present invention, a method for producing a molded coal which is excellent in safety and can maintain high strength even when wetted with water can be provided. In addition, a molded coal that can maintain high strength even when wetted with water can be provided.

Description of the reference numerals

10 … measuring device, 14 … movable plate, 16 … molded coal, 17 … supporting plate, 18 … bracket.

Claims

1. A method for producing a molded coal, comprising a step of molding a molding material comprising a powdery dry distillation coal and a binder and drying the molding material at 60 to 100 ℃ to obtain a molded coal having a water content of 5% by weight or less,

the binder contains an aqueous solution of polyvinyl alcohol having a saponification degree of more than 99.3mol% and a polymerization degree of 1700 or more,

the pulverized dry distilled coal is pulverized coal obtained by drying and dry distilling coal containing at least one of lignite and subbituminous coal.

2. The method for producing molded coal according to claim 1, wherein the polyvinyl alcohol has a polymerization degree of 2500 or more.

3. The method for producing a molded coal according to claim 1 or 2, wherein the polyvinyl alcohol content in the aqueous solution is 1 to 10% by weight.

4. The method for producing a molded coal according to claim 1 or 2, wherein the polyvinyl alcohol is contained in an amount of 1 part by weight or more based on 100 parts by weight of the dry distillation coal.

5. The method for producing a molded coal according to claim 1 or 2, wherein the binder contains an alpha starch.

6. The method for producing a molded coal according to claim 1 or 2, wherein the molded coal has a compressive strength of 50N or more after being immersed in water at 20 ℃ for 24 hours.

7. The method for producing a molded coal according to claim 1 or 2, wherein neither calcium oxide nor magnesium oxide is added to the molding material.

8. The method for producing a molded coal according to claim 5, wherein neither calcium oxide nor magnesium oxide is added to the molding material.