RU2847039C2 - Method of producing coal briquettes - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing coal briquettes, which can be used as fuel for burning in everyday life, boiler houses for domestic purposes, at thermal power plants, in furnaces of railway cars, as well as for coking in coke-chemical and metallurgical industry. Method of producing coal briquettes comprises mixing crushed coal with a polymer binder pre-crushed to a size of less than 2 mm, heating the mixture and obtaining briquettes at a briquetting pressure of 78 MPa, wherein polymer binder used is ethylene vinyl acetate in amount of 1.7–3.0% to coal, with size less than 3 mm, is heated to temperature of 100–120 °C without isothermal curing and performing briquetting of heated mixture, preventing its cooling below 90 °C.

EFFECT: obtaining water-resistant briquettes with sufficient mechanical strength, reduced loss of coal, as well as reduced loss of briquettes during storage and transportation.

1 cl, 1 dwg, 1 ex

Description

The invention relates to the coal processing industry, specifically to the production of fuel briquettes from coal, including high-grade coal, to produce agglomerated solid fuel. The resulting briquettes can be used as fuel for combustion in homes, municipal boiler houses, thermal power plants, railway car furnaces, and for coking in the coke and metallurgy industries. The application of the fuel briquettes will depend on the grade of coal used to produce the briquettes.

A method for producing fuel briquettes is known [1], which is a method for producing fuel briquettes and a device for its implementation, including mixing components in the following ratio, wt. %: coal fines, including anthracite fines - 80-70, wood sawdust, crushed bark, straw and other organic waste - 2-2.5, water and a binder, which is sodium carboxymethyl cellulose (CMC-N) - 0.5-2.0 and clay - 5.5-10.

The disadvantages of briquettes obtained using this technology are:

- low compressive strength (0.3-1.1 MPa);

- the presence of clay in briquettes (5.5-10%), which increases the ash content of the briquettes and, consequently, reduces the heat of combustion of the briquettes;

- the use of a highly water-soluble binding additive, such as a polymer such as sodium carboxymethyl cellulose (CMC-N), does not allow for the production of water-resistant briquettes, which, upon contact with water, lose their strength properties and crumble.

A known method for preparing coal for the formation of briquettes [2] consists of the following: after drying, the coal charge (95-97 wt.%) and powdered polypropylene (3-5 wt.%) are mixed and heated simultaneously in a twin-screw mixer at a temperature of 190°C. The products are pressed under a pressure of 250-400 kg/ ^cm2 and a temperature of 170-220°C, then cooling occurs on a conveyor at ambient temperature and atmospheric pressure.

The disadvantage of this method is the high temperature of mixing and pressing, which causes the decomposition of a polymer such as polypropylene, releasing toxic substances.

A method for producing fuel briquettes from brown coal is known [3], in which household waste polyethylene, crushed to particle sizes of less than 7 mm in an amount of 6-7% of the dry mass of coal, is used as a binder; the briquetting mixture is heated to a temperature of 90-130°C, the briquettes are pressed at a pressure of 98-99 MPa, the mechanical compressive strength of the briquettes is at least 5.5 MPa.

The disadvantage of this method is the high briquetting pressure (98-99 MPa) and low compressive strength (5.5 MPa) of the resulting briquettes when using a polymer such as polyethylene as a binder. Consumer requirements require a minimum mechanical compressive strength of 7-9 MPa for the briquettes. A decrease in mechanical strength leads to briquette breakage during transportation, an increase in the content of fines, and, consequently, fuel loss.

The closest to the invention (prototype) is a method for producing fuel briquettes from brown coal [4], the essence of which lies in mixing brown coal with a particle size of less than 6.0 mm with polyethylene (household waste) pre-crushed to particles less than 2 mm in an amount of 4.4-5.0% (based on the dry mass of coal), heating the mixture to a temperature of 120-140°C with isothermal holding for 30 minutes, obtaining briquettes at a briquetting pressure of 78 MPa. The mechanical compressive strength of the resulting briquettes is at least 7.8 MPa.

A disadvantage of this method, which uses a polymer such as polyethylene as a binder, is its high energy consumption due to the heating of the briquetted mixture to 120-140°C and isothermal holding for 30 minutes, which is due to the melting point of polyethylene. Furthermore, the prototype uses brown coal as a raw material, whereas the enrichment of valuable grades of hard coal produces a large amount of coal fines, which could be used industrially as briquettes, thereby reducing the loss of fine grades of valuable coal. Furthermore, the prototype does not contain information on the water resistance of the briquettes, which can also be considered a disadvantage. Producing water-resistant briquettes would ultimately reduce losses during storage and transportation.

The essence of the claimed method for producing coal briquettes consists of mixing coal with a particle size of less than 3 mm with a polymer binder (ethylene vinyl acetate) with a particle size of less than 2 mm in an amount of 1.7-3.0%. Heating the mixture to a temperature of 100-120°C without isothermal holding, and subsequent briquetting at a pressure of 78 MPa, without allowing the mixture to cool below 90°C. The compressive mechanical strength of the resulting briquettes (including after exposure to water) is at least 7-9 MPa.

The aim of the proposed invention is to create an efficient and cost-effective technology for producing coal briquettes, as well as to expand the range of binding additives for the production of durable and water-resistant fuel briquettes from coal.

The technical objective of the proposed invention is to find an effective binder for coal briquetting, which ensures a reduction in time and energy costs in the production of briquettes and their sufficient mechanical strength, including after the briquettes have been in water.

The technical result of the proposed method is the production of water-resistant briquettes of sufficient mechanical strength, a reduction in coal losses, and a reduction in briquettes losses during storage and transportation.

The technical result in the method for producing coal briquettes is achieved by using a polymer binder (ethylene vinyl acetate), which, with small additions to coal, allows for the production of water-resistant briquettes of sufficient mechanical strength.

Features used to characterize the method:

- coal with a size of less than 3 mm;

- polymer binder (ethylene vinyl acetate);

- the size of ethylene vinyl acetate is less than 2 mm;

- the content of ethylene vinyl acetate in the mixture is from 1.7-3.0%;

- heating temperature of the mixture up to 100-120°С;

- absence of isothermal holding;

- briquetting of the heated mixture, preventing it from cooling below 90°C.

The essence of the technical solution is explained by the drawing, where Fig. 1 shows a graph of the change in the mechanical compressive strength of briquettes depending on the addition of a binder:

1 - changes in the mechanical compressive strength of briquettes are shown when a polymeric substance (ethylene vinyl acetate) is added as a binder;

2 - a curve showing the change in mechanical compressive strength of briquettes after they have been in water with the addition of a polymeric substance (ethylene vinyl acetate) as a binder is shown;

3, 4 - the dependences of mechanical compressive strength depending on the addition of a binder (polyethylene) for the prototype are shown (3 - when heating the mixture to 120°C; 4 - when heating the mixture to 140°C);

5, 6 - the range for sufficient mechanical compressive strength from 7 to 9 MPa is indicated in accordance with the requirements for finished coal briquettes.

The coal briquettes are produced as follows. The coal is crushed to a particle size of less than 3 mm. The ethylene vinyl acetate is ground and sifted through a 2 mm mesh screen, which allows for a more uniform distribution of the binder in the mixture. The briquetting mixtures are prepared by mechanically mixing the components in a mixer. The mixture is then heated. Heating is continued until the mixture reaches 100-120°C, which is higher than the melting point of ethylene vinyl acetate, which for various grades is 70-90°C. When briquetting in a stamp press, heating can occur directly in the dies. When briquetting in a roller press, the mixture must not be allowed to cool below 90°C. The specific briquetting pressure is 78 MPa.

Briquettes undergo compression testing according to GOST 21289-2018 24 hours after production, once the structure formation and hardening process has completed. According to consumer requirements, briquettes must have a mechanical compressive strength of 7 to 9 MPa, in line with the requirements for finished coal briquettes.

Briquettes are tested for water resistance according to GOST 21290-2018. Briquettes are considered water-resistant if they retain at least 40% of their original strength after exposure to water.

The results are presented in graph form in Fig. 1. Changes in mechanical compressive strength of briquettes with the addition of a polymer binder (ethylene vinyl acetate) are shown. In the specified range of permissible mechanical compressive strength of at least 7-9 MPa, the addition of 1.7 to 2.7% of ethylene vinyl acetate is sufficient. After being in water, briquettes with the addition of a polymer binder (ethylene vinyl acetate) are characterized by an insignificant loss of strength. Fig. 1 shows changes in the mechanical compressive strength of briquettes after their stay in water: in the specified range of permissible mechanical compressive strength of at least 7-9 MPa, the addition of a polymer binder (ethylene vinyl acetate) from 2.1 to 3.0% is sufficient. The presented data also show that the briquettes have high residual compressive strength after being in water, which is 85-95% of the original.

Thus, with the addition of a polymer binder (ethylene vinyl acetate) from 1.7 to 3.0%, coal briquettes are water-resistant and have sufficient mechanical strength (at least 7-9 MPa).

Example. To prepare briquettes, coal of grade K4, class less than 3 mm (working moisture W ^r = 1.0%, ash content A ^d = 26.2%, volatile matter yield V ^daf = 25.5%) was used.

The coal was pre-crushed and screened using a 3mm mesh vibrating screen. The oversize product was returned to the crusher and further crushed to a particle size of less than 3mm. The polymer binder (ethylene vinyl acetate) was ground and screened using a 2mm mesh screen.

The briquetted mixtures were prepared by mechanically mixing the components in a mixer. Coal with a particle size of less than 3 mm was loaded into the mixer, followed by the addition of a polymer binder (ethylene vinyl acetate) with a particle size of less than 2 mm in an amount ranging from 1.7% to 3.0%. After mixing the coal and binder, the mixture was loaded into dies with an internal diameter of 40 mm and a height of 60 mm and heated to a temperature of 100-120°C.

Pressing was carried out directly in the dies using a stamp press, providing a briquetting pressure of 78 MPa. During briquetting, the mixture was not allowed to cool below 90°C. Without waiting for the dies to cool, they were filled with a new batch of the briquetting mixture. The compressive mechanical strength of the resulting briquettes is at least 7-9 MPa, including after exposure to water.

The advantages of the proposed method for producing coal briquettes are:

- increased and stable physical and mechanical characteristics of coal briquettes during operation, including after exposure to water;

- reduction of heating time of the briquetted mixture;

- reduction of energy costs for heating the briquetted mixture;

- involvement of small-grade coals, including valuable grades, in industrial use.

Sources of information selected during the patent search:

1. A.s. 2157952 USSR, MKI ⁷ F23K 1/00. Method for producing fuel briquettes and device for its implementation, published on 20.10.2000, BI No. 29.

2. Patent. 93032471 Russian Federation, IPC ⁶ C10L 5/14, 5/10 Method of preparing coal for forming briquettes, published 1996.02.27, Bulletin No. 23.

3. Patent 2296794 Russian Federation, IPC C10L5/14. Method for producing fuel briquettes from brown coal, published 10.04.07, Bulletin No. 10.

4. Patent 2373261 Russian Federation, IPC C10L 5/14. Method for producing briquettes from brown coal, published 20.11.2009, Bulletin No. 32 (prototype).

Claims (1)

A method for producing coal briquettes, which consists of mixing crushed coal with a polymer binder pre-crushed to a size of less than 2 mm, heating the mixture and producing briquettes at a briquetting pressure of 78 MPa, characterized in that ethylene vinyl acetate is used as a polymer binder in an amount of 1.7-3.0% of coal, with a size of less than 3 mm, heating to a temperature of 100-120°C without isothermal holding and briquetting the heated mixture, not allowing it to cool below 90°C.