The briquetting of the lignite

BRIQUETTING (EN: briquetting; DE: Brikettierung; FR: agglomeration briquetage; ES: briqueteado; RU: брикетирование) is the process of the processing of the raw materials (mostly of the mineral raw materials) into the lumps of uniform composition and geometrically regular shape, the so-named briquettes. The briquetting of coals has been proposed within Russia during the 30-ies of the 19th century by A. P. Veshnyakov, who has developed the method for the obtainment of briquettes from the charcoal and tiny pieces of mineral coal, and was naming these briquettes as carboleine. During the 1858, there has been commissioned within Germany the first lignite briquetting plant, and after several years later, there has been commissioned the mineral coal plant, which used the black pitch from mineral coal as the raw material. The briquetting of the tiny pieces of ores has been performed for the first time within Sweden during the 80-ies of the 19th century (according to the patent by G. Grøndahl). Within the pre-revolutionary Russia, the ore briquetting plants have emerged during the start of the 20th century at many metallurgical plants (Kerch, Taganrog, Enakievo, Kuvshinovo, and others).

Briquetting increases the heat of combustion for the tiny pieces of mineral coal, for anthracite culms, for lignites, and for peat, improves the efficiency for combustion, the transportability, the conditions for the storage and usage for these types of the fuel raw materials. Besides these facts, briquetting creates the additional resources of the raw materials for the production of the low-smoke and zero-smoke fuel, and also of the ore and non-metallic raw materials, thanks to the recycling of the wastes from various productions (flue dust, metallic shavings, hot metal scale, slags, wastes from the industry of the non-metallic building materials, from the series of the chemical productions, and so on), expands the resource base for the coking process at the expense of the usage within the coke batches (mixtures) of such marks of mineral coals, which are easy to procure. The worldwide production of briquettes exceeds 200 million tonnes per year, including approximately 40% of the lignite briquettes (1980).

Depending on the properties of the raw materials, the briquetting is performed without the binding substances (for young lignites, peat) with the pressure of 100-250 megapascals, and with the binding substances (for the tiny pieces of ore and mineral coal, anthracite culm, and so on) with the pressure of 20-80 megapascals. During the briquetting without the binding substances, there proceeds the gradual filling of the voids between the particles, then later there are compacted and deformed the particles themselves, and there emerge between them the forces of the molecular cohesion. The increase of the pressure and of the duration for the being of the material under the impact of the pressure, leads to the decrease of the magnitudes of the elastic deformations, and to the transition of these deformations into the plastic deformations, as the consequence of which the structure of the briquette becomes more sturdy. The briquetting of the young lignites without the binding substances (Figure # 1) is performed for the household needs.

They crush the young lignites (the Wp water content is up to 60%) to the particle size of 0-6 millimetres, and dry them within the steam pipes-dryers, or within the gas pipes-dryers, to the optimal humidity of 15-20%. The sushonka (the dried coal) is cooled to 40-50 degrees Celsius, is pressed (see the "Briquetting press" article) under the pressure of 100-150 megapascals within the punching presses, less often under the pressure of 200-500 megapascals within the annular presses, the briquettes are cooled within the cooling troughs (drums) to 40-45 degrees Celsius, and are delivered into the warehouse for the requirements of a customer; while with the binding substances for the coals for the technological purposes (coking, semi-coking, and others) there are introduced additionally the improved crushing of the sushonka after the first stage of drying, and the repeated drying (usually within the steam pipes-dryers) for the alignment of the difference for the humidity within the coals of different classes, with the purpose of improvement their physical-mechanical properties. The mass of the lignite briquettes is 300-600 grams. The technological scheme for the production of the peat briquettes differs from the lignite scheme mostly with the usage of the other drying equipment, with the preservation of the sequence for all the operations. For the drying of the high-humidity peat (the Wp water content is 60%) to the humidity of 15-20%, there serve the pneumatic-steam-water, steam-gas, pneumatic-gas, shaft-mill (the variety of pneumatic-gas) dryers. They press the briquettes at the punching presses under the pressure of up to 100 megapascals.

The briquetting of the mineral coal

The physical-chemical parametres for the process of briquetting with the binding substances depend on the method for the briquetting, on the properties of the source raw materials, and of the binding substances, which are used, on the conditions for the strengthening of briquettes, and also on the speeds of the polymerization for the binding substances, and of the forming of various cementing substances within the structure of the briquettes. The briquetting of mineral coals in this case (black pitch, petroleum bitumina, and so on) includes the preparation of the tiny pieces of mineral coal, usually with the size of 0-6 millimetres, the drying of these pieces to the humidity of 2-4%, the dosage and mixing with the liquid or solid binding substance (the size is from 0-1 to 0-3 millimetres) (Figure # 2).

The batch (mixture) is delivered into the mechanical steam mixer, where, at the temperature of 100-150 degrees Celsius (depending on the type of the binding substance), the mixture is thoroughly steamed and mixed; the mixture is cooled (for ~ 20 degrees Celsius), and is pressed within the roller briquetting press (20-80 megapascals); the ready-to-use briquettes are cooled and stored. The mass of the mineral coal briquettes is 30-360 grams.

The briquetting for the ores and concentrates of the ferrous and non-ferrous metals is performed according to various technological schemes, depending on the properties of the source raw materials, and on the requirements of the consumer, with the binding substances (lime, sulfite-alcohol sludge waste from the production of alcohol, cements, liquid glass (sodium silicate), and others), or without the binding substances. There has got the distribution the production of the ore briquettes according to the so-named method for the hot briquetting. According to this technology, tiny pieces of the ore are heated, in most cases within various apparatuses with the fluidized bed, to 800-1100 degrees Celsius, and are briquetted within the enclosed roller presses (up to 100 megapascals); the ready-to-use briquettes are cooled and stored. This technology is used for the preparation of the raw materials for the processes of the direct obtainment of iron from the ores, and for the recycling of various metallurgical waste. There are briquetted (mostly with the binding substances) the copper, manganese, chromium, nickel, molybdenum, zinc, and other ores and concentrates.

The general requirements for the briquettes are their high physical-mechanical properties (including the heat-resistance and water-resistance). According to the chemical composition, there are presented to the household coal briquettes the requirements, which are corresponding to the quality of the source raw materials within the given coal-extracting region of the country, but their ash content must not exceed 20%. For the peat briquettes, the ash content is not more than 15%, the humidity for the working mass is not more than 16%, the heat of combustion is 15-20 megajoules per kilogram. The additional requirements for the ore briquettes cover the metallurgical and certain physical properties (recoverability, gas permeability, porosity, thermomechanical strength, and others).

The prospects for the development of briquetting are associated with the expansion of the raw materials base for the coking through the usage within the batches (mixtures) of the elevated quantities of the slightly caking, non-caking, and young lignites, with the preparation of various metallurgical raw materials within the ferrous and non-ferrous metallurgy, and primarily for the processes of the direct obtainment of iron from the ores, for the production of the series of ferroalloys (silicone-manganese, ferrosilicon, and others), with the recycling of various industrial wastes, and so on. Briquetting increases the economic effectiveness for the series of productions (for example, the intensification for the series of processes within the ferrous metallurgy is associated with the increase for the contact surface of the metal oxides with carbon, which is the reductant, which ensures the more rapid proceeding for the processes of reduction, and is achieved through the united briquetting of the ores or concentrates with the reductant). The cost for 1 tonne of the ore briquettes is approximately for 20-50% less than the cost of sinter, and for 10-30% less than the cost of the pellets with baking. They use the coal and peat briquettes as the household fuel, as the raw materials for the obtainment of the smokeless fuel, and for the expansion of the raw materials base for the coking.