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44RELEVANCE OF THE CHOICE OF BINDERS FOR COAL BRIQUETTES
Akmaljon Xakimov Nasibaxon Vohidova
Ferghana Polytechnic Institute
ABSTRACT
The article analyzes the binders from local raw materials, in particular the distillery stillage of the Kokand distillery for briquetting coal fines from the Angren coal basin. An installation for pressing mixed mass into coal briquettes has been developed. An analysis is also given of other binders used for briquetting coal fines.
Key words: coal fines, distillery stillage, fine fraction briquetting, biomass, molding press, briquetting technology.
Introduction:
At present, due to high prices for oil and gas, interest in coal in the world as an alternative energy source is constantly growing. Experts (the latest forecast of the IMF World Economic Outlook) predict rather high prices for oil and gas until 2050. A number of strong national economies (primarily the United States, Russia and China, as well as India, Canada) intend to seriously increase the number of coal-fired power plants. It should be noted that one of the main tasks that must be solved when processing coal is its full use. The increase in the cost of oil and the gradual depletion of its richest sources led to an increase in the share of coal in the fuel balance and the development of work on the production of new products from coal, including fine coal. Therefore, the beginning of the XXI century should be considered a period of preparation for a significant increase in the share of coal in the fuel and energy balance, for the implementation of new technological processes of coal processing.
As the data of researchers show, approximately 25% of the mined coal of the Angren coal basin has a fine and dusty fraction. These fractions are not in demand among consumers due to the complexity of its use. Difficulties also arise for heating private houses: it wakes up through the grate and therefore has a low thermal efficiency, often a large amount of coal fines blocks the access of oxygen, which is why the furnace dies out. For these reasons, a lot of dust and coal of fine fractions (up to 6 mm in size) accumulates in warehouses, in fuel sheds in private farmsteads. The problem is solved in the production of briquetted coal. This technology makes it possible to produce fuel briquettes from coal dust at high pressure. They tolerate transportation and storage well.
For efficient briquetting of fine and pulverized coal, it is necessary to develop new technological devices, taking into account the infrastructure features of the facility. Therefore, research is needed to develop a rational technology for briquetting fine coal in the Angren (Republic of Uzbekistan) coal basin [1].
Currently, the main reasons hindering the development of briquetting of coal fines are the lack of an available and cheap binder. For this reason, the search for various options for individual or combined binders for obtaining fuel briquettes is being carried out everywhere and constantly, their range is expanding.
For example:
An undoubted environmental advantage is the involvement in the processing of waste technical stillage of the Kokand distillery, which is harmful to the environment. As briquette filler, we use solid coal fines or its mixture with carbon-containing biomass. The addition of porous carbon-containing materials (in particular, technical hydrolysis alcohol stillage) and the perforated form of the fuel briquette improve the combustion kinetics. There are additives that catalyze the briquette ignition process (inorganic oxidants, peat, and charcoal). Depending on the characteristics of the briquetted material, schemes are used with the introduction of a binder material and briquetting without it. There are binders of petroleum origin, products of thermochemical processing of coal and binders of a non-hydrocarbon nature. Carrying out post-forming heat treatment helps to reduce smoke and increase porosity, but entails additional costs. The factors influencing the briquetting process are moisture content, material size and temperature, pressure and pressing duration. These parameters are closely related to each other [2].
While various wood wastes in the form of sawdust and wood chips can be easily burned in specially adapted long-burning boilers, the situation is different with fine coal and dust. One of the ways to burn coal fines is to melt the boiler with wood, and then pour the dusty fraction of fuel on top of the burning logs. But this is too troublesome business, since coal dust must be added in small portions, which means - often. The best way is to form briquettes from the fine fraction by pressing, which then burn very well, releasing a large amount of heat. Such a solution as coal briquetting was proposed at the beginning of the nineteenth century in Russia by the inventor A.P.Veshnyakov to this day is successfully used both for industrial purposes and in everyday life. Its essence is that the compaction of fine coal using high pressure on special equipment allows you to obtain fuel, whose calorific value is not less than that of high-quality coals [3].
Coal briquettes are made from brown coal, crumbs and dust of anthracite and coal, semi-coke and coke breeze. Depending on the type of feedstock, binders are added to it or not.
The formation of brown coal briquettes occurs without the addition of binders, since the material itself contains up to 20% bitumen. During processing, raw materials are crushed, heated and dried, bringing to 18-20% moisture content. After cooling, the resulting crumb is fed to a high-pressure press, where lump fuel is formed. After cooling, they can be used or improved in quality characteristics in semi-coking plants.
Briquetting of small coal fines can also occur with or without binders. In industrial production, the following substances are added as a binder: petroleum bitumen, lignosulfonates, molasses, liquid glass and cement [4].
Coal briquettes have the following advantages over the original coal: Higher energy value (by 20-30%) Longer burning time (4 times longer) Ash powder 22% less CO2 emissions
Less sulfur emissions (less than 1% and can be controlled) Easier packing, transportation, warehousing Ready for automatic feeding into the firebox Possibility of packaging for the consumer market Export opportunities
Liquid glass and cement are used in the processing of some types of coal and fine coke. Such briquettes are used in metallurgy in those processes where the presence of such components is permissible. Coal tar and petroleum bitumen are also used to produce industrial fuels. Such briquettes are not suitable for heating houses: during combustion, unsupported and other harmful substances are released, so they are prohibited by the SES and the demand for them is very limited [5].
To make such briquettes from fine coal, you need to figure out how and with what machines they are stamped at the plant. Equipment for the production of heating briquettes is a technological line consisting of the following units: crusher; drying chamber; press for briquetting. Items of equipment are listed in the same order in which they stand according to the technology. Raw materials are fed and moved between installations by means of belt or screw conveyors [6].
The coal fuel pressing process is as follows;
1. In the crusher, small coal is crushed to particles of the same size, depending on the characteristics of the pressing equipment. The maximum permissible size of the fraction is 6 mm.
2. In the dryer, the moisture content of the raw material is reduced to 15% (maximum).
3. The last stage is pressing, carried out under a pressure of 20 to 120 MPa, depending on the technology used.
Since the technology for the production of coal briquettes without any additives for household purposes is more optimal, then it is worth considering it. So, the sequence of the process is as follows;
1.First, the coal goes through the grinding operation, while the maximum size of the fraction is 6 mm;
2.The next step is drying to achieve an optimum moisture content of 15%. For this, special equipment is used for the production of coal briquettes - steam or gas dryers;
3.After drying, the composition is cooled and fed to pressing. The operation takes place at a pressure of 100-150 MPa in a so-called stamp press;
4.Final cooling and shipping to the warehouse [7].
This is a traditional technological process, but the requirements for particle size and moisture content of raw materials may vary depending on the equipment used. For example, a modern mini-plant of the Russian company UNITEK requires a particle size of up to 0.25 mm with a moisture content of 6 to 16%. That is, in this case, the coal briquetting technology should provide for better grinding, but the pressing pressure is applied much lower. The output is a coal briquette, whose ash content does not exceed 15-20%, the maximum permissible mechanical load is 3 kg / cm2, and when falling from a height of up to 2 m, the product loses no more than 15% of its mass as a result of an impact. The heat of combustion depends on the grades of coal from which the briquette is pressed [8].
We have developed a press for molding a mixture of fine coal and alcohol stillage
(Fig. 1).
1 - electric motor; 2 - worm gear; 3 - auger; 4 - form.5 - mouthpiece; 6 -bunker; 7.9 - clutch; 8 - auger; 10 - shaft; 11 - bearing; 12 - pressing part; 13 - corpus; 14.15-flanges.
Fig.1. Press for molding.
This allows you to end up with a briquette in composition and characteristics that is not inferior to the original high-quality type of coal and to avoid the usual
disadvantages (foreign smell, high ash content, low calorific value, etc.) The main working unit of the proposed equipment is extruder presses, which are specially designed for briquetting rocks, anthracite waste, coal sludge, brown coal crumbs, peat, etc. The pressing technology is based on adhesive-chemical processes occurring in viscous-chemical systems formed by finely dispersed particles of fossil coals, which themselves act as binders. To put it simply, during the operation of the press, such physicochemical conditions are created that make the fossil organic components already included in the coal (phenols, resins, wax, etc.) with the participation of water, polarize on the surface of the particles, forcing them to bind together. When cooled and dried, the briquette hardens and becomes fixed. Briquetted fuel has high heat and power properties, in particular, sufficient mechanical strength, water resistance and heat resistance. The layer of such fuel during combustion has good gas permeability, which ensures full combustion even with a relatively high ash content. To achieve the maximum productivity of briquetting presses, our company has developed storage bins with auger pre-compactors, which ensure uninterrupted supply of the charge under the required pressure and at the design speed. In addition, the briquetting line includes box conveyors with air coolers and a thermowell. To obtain a charge of the required moisture content, mixing drums with a capacity of up to one ton of finished raw materials have been developed [9].
The recipe for fuel briquettes can be illustrated by the following examples:
1.Using the aforementioned equipment, a batch of fuel pellets forty-eight millimeters high and fifty millimeters in diameter was produced. The composition of the fuel pellets is crushed charcoal (92%), water (2%), potato starch (6%). The material is pressed and dried using the aforementioned technology. The briquettes made in this way are easily ignited by a match and burn with an almost imperceptible red glow, without forming a flame, soot, smoke, toxic substances, or odor for two hours. They generate a lot of heat, which is enough to heat a greenhouse or living room in winter.
2.Using the same equipment, a batch of fuel pellets with a height of forty-eight millimeters and a diameter of fifty millimeters was made. The composition of the released tablets: crushed charcoal 92 %, carboxyl methylcellulose 6%, water 2%. Mix, press and dry, as in example l. These fuel briquettes are not inferior in quality to the briquettes from the first example.
3.Using the same equipment, a batch of tablets of the same size is produced with the following composition: crushed charcoal 94%, sodium hydrogen silicate 4%, water 2%. Finished briquettes are characterized by increased strength, their characteristics are not inferior to the aforementioned fuel briquettes.
4.On the same equipment, a batch of tablets of similar sizes was made, having the following composition: crushed charcoal 80%, potato starch 18%, water 2%. In terms of their quality, these fuel briquettes are significantly inferior to all of the above. They are
distinguished by lower compressive strength and specific heat of combustion reduced to 6,000 kcal / kg.
5.Fuel pellets on the same equipment of similar dimensions were made with the following composition: crushed charcoal 06%, starch 2%, water 2%. Finished briquettes have a much lower mechanical strength [10].
Strength and energy parameters of fuel briquettes depend on the amount of components used for their manufacture. If the binder is used more than the norm, the energy characteristics of the produced briquettes will deteriorate, and if less than the norm, then their strength will decrease, up to destruction. With even a slight increase in the amount of water, the flammability will deteriorate, and steam will start to evolve when ignited.
Tests have shown that when a lump silicate or liquid glass is used as a binder, the crushing strength of the briquette increases by one and a half times, and the abrasion strength - two times [11]. Conclusion:
We would like to emphasize that in the absence of open fire when burning briquettes, the likelihood of ignition is excluded if a flammable liquid (acetone, alcohol, gasoline, etc.) gets on their surface. Thanks to this property, the area of use of fuel briquettes is significantly expanded. They can be used to warm up gas pipeline fittings, automobile engines in the winter season.
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