RU2835631C1 - Method of producing fuel briquettes from coal beneficiation tailings and pulp-and-cardboard production wastes - Google Patents

Abstract

FIELD: performing operations.

SUBSTANCE: proposed invention relates to processing of coal beneficiation tailings, namely fine-dispersed wastes of coal industry and wastes of pulp-and-cardboard production in the form of hydrolytic lignin (sodium lignosulphonate) into agglomerated fuel for domestic, coal and power engineering purposes. Substance of the invention consists in a method of producing fuel briquettes, which includes operations for preparing a crude mixture in the form of coal beneficiation tails, which are not separated in heavy-medium liquids, with a predominant content of fractions from 0 to 0.5 mm and moisture in an air-dry state of 10-15 % with a liquid binder in the form of an aqueous suspension of hydrolytic lignin with a dry substance concentration of 4-6 wt. %, mixing the obtained composition in the form of a "hard" moulding mixture with moisture content of up to 20 % and briquetting the mixture with subsequent drying of briquettes. At the same time initial drying of briquettes is performed directly in process of briquetting due to heat released by interparticle friction during pressing. Then, drying of briquettes with strength gain is carried out either for first 3-5 days at room temperature of 15-20 °C, or accelerated heat treatment in range of 70-90 °C for 1.5-2 hours. Mechanical strength of the produced briquettes is not less than 3.5 MPa.

EFFECT: solving environmental problems associated with rational use of coal beneficiation wastes and recycling of pulp and cardboard production wastes.

1 cl, 1 dwg, 4 tbl

Description

The invention relates to the processing of non-marketable tailings from coal enrichment, which are finely dispersed waste from coal flotation and off-balance waste from pulp and paperboard production in the form of an aqueous suspension of hydrolytic lignin (sodium lignosulfonate) into agglomerated fuel (fuel briquettes) for municipal, coal engineering and energy purposes by briquetting with a binding additive.

In the production of fuel briquettes, briquetting methods using petroleum, bituminous binders, and coal tar pitch have become widespread. It is believed that only they most fully meet all the requirements for the process. However, the above-mentioned methods are known to have the disadvantage that when burned, they form a high content of carcinogenic substances. Therefore, many other types of binders are also used in the briquetting industry (see Krohin V.N. "Briquetting of Coals". - Moscow: Nedra, 1984; Elishevich L.T. Technology of Briquetting of Minerals. - Moscow: Nedra, 1989).

Thus, a method for producing fuel briquettes is known (Patent of the Russian Federation No. 95102684, IPC C10L 5/20, published in 1996), which consists of mixing coal fines, which are pre-dried until a moisture content of 1-1.5% is reached and briquetted with an aqueous solution of sodium lignosulfonate with a concentration of 53-55% in the following ratio, mass %: sodium lignosulfonate - 10-20, the rest is coal fines. After briquetting, the resulting briquettes are dried.

The disadvantages of this method are:

- the need for deep dehydration and thermal drying of the original coal fines to minimum moisture values, up to 1-1.5%, which significantly complicates and increases the cost of the briquetting process;

- the raw material charge contains only expensive coal screenings in the form of coal fines, which increases the cost of briquettes;

- the existing technology is not intended for use as a feedstock of finely dispersed coal sludge (size class 0-1.0 mm), formed during the extraction and enrichment of coal. At the same time, coal sludge is discharged into settling ponds and waste heaps at coal mining enterprises, which worsens the environmental situation in coal mining regions.

Also known is a method for producing fuel briquettes, which includes mixing crushed carbon-containing material consisting of coking coal, dehydrated coal sludge and peat, having the following granulometric composition: 20% of fractions +3 mm, 30-55% of fractions 0-5 mm and 50-75% of fractions 0-2 mm with the addition of dry powdered ammonium lignosulfonate as a binder, as well as petroleum and coal tar pitch in a proportion of 3-8 parts by weight per 100 parts by weight of carbon-containing material, briquetting the resulting charge having a moisture content of 5-8 parts by weight, followed by heat treatment of the briquettes at 200-600°C (UK Patent GB1321729A, IPC C 10L 5/02, published on 27.06.1973).

Disadvantages of this method:

- in addition to dehydrated coal sludge, the raw material mixture contains a combination of expensive coking coal screenings, anthracite fines and narrow fraction peat crumbs, which complicates and increases the cost of briquetting technology;

- for the production of fuel briquettes using the presented technology, in addition to lignosulfonate, local resources of oil and coal tar pitch are required;

- the use of heat treatment at the final stage of briquettes production carried out in a high temperature range of 200-600°C, which also increases the cost of briquettes.

The closest to the proposed invention is a method for briquetting coal sludge together with coal fines (Patent of the Russian Federation No. 2078794, IPC C 10L 5/20, published in 1997), which consists in the fact that 5% dry lignosulfonate powder is used as a binder and 30% of coal screenings are added to the raw material charge, with subsequent heat treatment of the briquettes, carried out in the range of 160-200°C for 1-1.5 hours.

Disadvantages of this method:

- the raw material mixture contains a binder in the form of dry powdered lignosulfonate, which requires its deep dehydration by thermal drying to a moisture content of 5% and, in addition (due to the pyrophoric properties inherent in dry lignosulfonate), proper storage, which complicates and increases the cost of the briquetting process;

- the raw material charge contains 30% of expensive coal screenings, which increases the cost of briquettes;

- the need for subsequent heat treatment during drying of briquettes, carried out in the range of 160-200°C for 1-1.5 hours, which also increases the cost of briquettes.

The proposed method for obtaining fuel briquettes, unlike the known ones, allows performing operations on obtaining the charge, its briquetting and dehydration (drying) of the finished product with a smaller number of operations than the known ones and with lower energy costs, which significantly reduces the cost of the process of processing coal enrichment tailings, allowing to achieve cost-effectiveness due to the reduction of energy costs and simplification of the technology for obtaining briquettes, due to the rational use of coal flotation waste and waste from pulp and cardboard production.

The specified technical result in the described method for producing fuel briquettes, including operations for preparing a raw mix in the form of coal enrichment tailings that are not separated in heavy-medium liquids, with a predominant content of fractions from 0 to 5 mm and a moisture content in the air-dry state of up to 10-15% with a liquid binder in the form of an aqueous suspension of hydrolytic lignin with a dry matter concentration of 4-6%, mixing the resulting composition in the form of a "rigid" mold mixture with a moisture content of up to 20% and briquetting the charge with subsequent drying of the briquettes. In this case, the initial drying of the briquettes is carried out directly in the briquetting process due to the heat released by interparticle friction during pressing. Then, drying of the briquettes with a gain of strength is carried out either during the first 3-5 days at room temperature of 15-20°C, or by accelerated heat treatment in the range of 70-90°C for 1.5-2 hours.

The advantage of this invention is that there is no need for preliminary deep drying of both coal sludge (coal enrichment tailings) and hydrolytic lignin (sodium lignosulfonate), as well as rapid drying with a set of briquettes strength and their satisfactory water resistance. The briquettes retain their shape during combustion, which prevents them from spilling under the grate and, thus, ensures more complete combustion.

The objectives of the invention are:

- to obtain mechanically strong fuel briquettes from non-marketable coal enrichment tailings (coal sludge);

- use off-balance waste from pulp and cardboard production (hydrolytic lignin) as a binder;

- reduce the cost of the resulting briquettes;

- simplify the technology of producing agglomerated fuel;

- partially solve the environmental problem of rational use of waste from coal enrichment and pulp and cardboard production.

The distinctive features of the invention are: the use of coal sludge (coal beneficiation tailings) as a carbon material, composed entirely of coal-mineral particle agglomerates (organomineral matrix) that do not separate in heavy-medium liquids, with a predominant content of fractions from 0 to 5 mm and an air-dry humidity of 10-15%; the use of an aqueous suspension of sodium lignosulfonate (a waste product of pulp and cardboard production) as a binder, which has high adhesion to coal sludge particles and is also a surfactant that helps reduce the humidity of the briquettes during the drying process; the initial drying of the briquettes is carried out directly during the briquetting process due to the heat generated by interparticle friction during pressing; Drying of briquettes with a gain in strength is carried out either during the first 3-5 days at room temperature of 15-20°C, or by accelerated heat treatment in the range of 60-90°C for 1.5-2 hours.

The drawing shows the basic scheme of the method implementation (figure). The scheme sequentially contains: a mixer-loosener (1) for mixing and preparing a charge consisting of coal sludge and a binder (hydrolysis lignin), pressing equipment (2) for forming briquettes, a drying device (3) for removing ballast moisture and gaining strength during accelerated drying of briquettes.

In the presented method, coal sludge (coal enrichment tailings) from the enrichment plant of JSC Razrez Tugnuisky of PAO SUEK, Olon-Shibirsky coal basin of the Republic of Buryatia, was used as the initial raw material for obtaining fuel briquettes.

Coal sludge was represented by grade G1 with a total ash content of up to 35%. Microlithotype-petrographic composition of the organic part, mass. %: Vt - 93.1; Sv - 3.0; F - 2.3; L - 1.6; R - 0.36; yield of volatile components V ^daf = 30.6%, sulfur content S _total = 0.29%, working heat of combustion Q _i ^r = 3031 kcal/kg. Wide fractions of 0-0.5 mm with a moisture range of 10-15% were used for briquetting. Humidity was controlled by periodic sampling. Coal sludge is characterized by an organomineral matrix, almost entirely composed of intergrowths-agglomerates of coal-mineral particles that are not separated in heavy-medium liquids (Table 1).

Table 1

Technical Analysis Indicators of Coal Sludge

"Tugnuysky open pit mine" of the Olon-Shibirsky coal basin

Carbon material Quantitative indicators, % Heat of combustion
Q ^r , kcal/kg Moisture,W ^r Ash,A ^d Volatile yield, V ^daf Carbon,
C ^daf Hydrogen,
H ^daf Sulfur,
S ^daf Nitrogen,
N ^daf Oxygen,
Oh ^daf Coal
sludge fractions 0-0.5 mm 10-15 35 30.6 42.25 2,3 0.29 0.85 23 3031

An aqueous suspension of hydrolytic lignin, which is waste from the Selenginsk Pulp and Cardboard Mill of the Republic of Buryatia, was used as a binder (Table 2).

Table 2

X-ray elemental analysis of hydrolytic lignin

C O Na Al S Summary 50.93 40.26 1.24 5.72 1.85 100.00

By using hydrolytic lignin, which is a waste product of pulp and cardboard production, as well as a local raw material, and therefore stands apart among binders, it was possible to obtain a highly plastic raw material charge that does not require the use of water for mixing. That is, all the moisture present in the lignin is spent on wetting and grinding the mold mixture during its briquetting. The lignin itself does not enter into chemical reactions of phase formation, but, having high plasticity of particles, it promotes (when the briquette dries) the interaction of surface tension forces causing the dispersed material to contract with each other, thereby forming a strong bond of adjacent particles. The charge for briquetting was prepared in a 5:1 ratio, i.e. 5 kg of coal sludge mixed with 1 kg of hydrolytic lignin of natural moisture content up to 85%. In terms of percentages, excluding moisture loss during pressing and its natural evaporation during briquettes drying, the amount of dry lignin introduced into the briquette was 5% (Table 3). When preparing briquettes, the batch was thoroughly mixed in a mixing machine until a homogeneous mass was formed, the so-called "rigid" mold mixture, which did not stain hands when squeezed into a fist. Using the presented method, a strong and dense solid fuel briquette was obtained, suitable for long-term storage and transportation. In addition, with a decrease in the size of the coal sludge fractions, a denser briquette packing was achieved due to an increase in the total surface area of the particles, and the humidity and pressing pressure increased the adhesive forces between its grains.

Table 3

Characteristics of fuel briquettes

(according to the proposed method of obtaining)

The resulting product Carbon analysis W ^r , % A ^d ,% V ^daf , % S ^daf , % Q ^r , kcal/kg Fuel briquette 4.5 35.5 32.0 0.37 3920

Table 4

Mechanical properties test results

fuel briquettes

Composition of the batch
(raw material mixture) Coal sludge + hydrolytic lignin suspension Binder consumption, % 5 Pressing pressure (average), MPa 25 Mechanical strength δ _comp. ,
MPa (kg/ ^cm2 ) (GOST 21289-2018) 3.5 (35) Impact resistance R _sbr.
(GOST 21289-2018) 76.3 Abrasion resistance R _ist. (%)
(GOST 21289-2018) 72.0 Moisture saturation, %
(GOST 21290-2018) 11-13 Resistance to combustion, min. 25 Thermal stability
(at 600-1100°C) It didn't collapse

The analysis of the data in Tables 3 and 4 confirms that in order to obtain fuel briquettes with sufficiently high characteristics - calorific value and mechanical strength, as well as satisfactory water resistance, the briquetting process can be carried out at a charge humidity of up to 20% using coal slurry of wide fractions of 0-0.5 mm with a humidity of 10-15% and an optimal amount of a binder in the form of an aqueous suspension of hydrolytic lignin with a natural humidity of up to 85% with a dry matter concentration of 4-6%. Drying of briquettes with a gain in strength is carried out either during the first 3-5 days at room temperature of 15-20 ° C, or by accelerated heat treatment in the range of 60-90 ° C for 1.5-2 hours. In this case, the mechanical strength according to GOST 21289-2018 is: for abrasion - 72%; for dropping - 76.3%; crushing strength - 3.5 MPa (35 kgf/ ^cm2 ). In addition, the resulting briquettes retain their shape when burned in a temperature range of 600-1100°C for 20-25 minutes, which prevents them from spilling under the grate and, thus, ensures more complete combustion.

The fuel briquettes obtained by the proposed method, possessing mechanical strength and satisfactory water resistance, can be used as agglomerated refined fuel both in the coal engineering and energy industries, and as municipal and household fuel for the purpose of heating premises and other objects.

Brief description of the drawings

The drawing (Fig. 1) shows the basic scheme of the method implementation. The scheme sequentially contains: a mixer-loosener (1) for mixing and preparing a charge consisting of coal sludge and a binder (hydrolysis lignin), pressing equipment (2) for forming briquettes, a drying device (3) for removing ballast moisture and gaining strength during accelerated drying of the briquettes.

Claims (1)

A method for producing fuel briquettes, which includes preparing a raw material mixture from coal enrichment tailings, with a predominant content of fractions of size from 0 to 0.5 mm and a moisture content of 10-15% and a liquid binder in the form of an aqueous suspension of hydrolytic lignin with a dry matter concentration of 4-6 wt.%; mixing the resulting mixture until a homogeneous mass is formed in the form of a charge with a moisture content of up to 20%; briquetting of the batch with subsequent drying of the briquettes, whereby the initial drying of the briquettes is carried out directly during the briquetting process due to the heat generated by interparticle friction during pressing, subsequent drying of the briquettes with a gain in strength is carried out either during the first 3-5 days at room temperature of 15-20°C, or by accelerated heat treatment in the range of 70-90°C for 1.5-2 hours, whereby the mechanical strength of the produced briquettes is not less than 3.5 MPa.

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