Current coal-concentrating enterprises constantly face the problem of dehydration of coal slimes. (As a rule one refers to coal slimes products of less 0,5 mm size.) The decision of this problem depends on the right choice of the method of intensification of the dehydration process. The application of different reagents is one of the most convenient and effective methods. It is possible to apply surface-active agents, water-soluble polymers, oils and synthetic latexes. Each of these reagents has its own advantages and disadvantages. This or that reagent is applied versus grain-size composition and physical properties of products which dehydrate.
Aims and tasks of works.
1. To analyze the literature on this topic;
2. To single out reagents applied to the intensification process of dehydration;
3. To compare technologies of intensification of dehydration;
4. To ground the choice of technology, reagent which is recommended to apply.
1. Ways of intensification of dehydration process when filtering.
The intensification of the process assumes growth of filter capacity, reduction of sediment moisture and solids content in the filter.
1. Thermal methods: the heating of the pulp to 40-60 raises the efficiency of filter to 30-40% for poor-pressed slime products. It is more efficient to warm sludge in the zone of drying, because of decrease of water volume which is being warmed. The warming is realized with steam supply which promotes the reduction of surface tension and viscosity.
2. Improvement of the structure of sediment - the more sediment porosity is, the more reduction of moisture is. Dopant of slime to 30-40% by volume of granular product increases efficiency to 25-30% and decreases the resistance of sediment at the expense of the pore diameter extension where the water separates.
3. The mechanical influence on the sediment promotes the reduction of moisture. It is employed for the belt filters when using the sediment compactors of impact action. The application of vibrations - the structure of sediment is destroyed and new channels for moisture removal arise.
4. Addition of reagents-intensifiers.
2. Scanning of reagents-intensifiers which are applied.
Surface-active agents (SAA), polymers, various oils and synthetic latex flocculants are used at the coal-cleaning plants. SAA only change the property of the coal surface and make it more hydrophobic. Polymers flocculate the fines, but not selectively like the synthetic latexes and oils.
Surface-active agents are called such chemical compounds, which are selectively adsorbed on the surface of phase disengagement when dissolving and dispersing in liquid, which defines the set of their physicochemical or chemical properties, which have practical importance.
Molecules of polymers are series of repeated clusters of atoms which are connected with covalent bonds. If the parts are repeated the combination have the same structure, then the substance is called homopolymer. Polymer macromolecule can have either linear structure, or branched structure.
Four groups are used for selective aggregation of coal from oil reagents:
1) reagents - oil products;
2) reagents of solid fuel;
3) recyclable oils;
4) reagents - mixture.
Synthetic latexes are microheterogeneous systems, which present aqueous dispersions of colloidal rubber particles (globules), stabilized by surface-active agents-emulsifiers.
3. The “bridge” mechanism of formation of coal-latex plagettes.
The bridge flocculation is characterized by the formation of molecular links as the result of adsorption of macromolecule on several particles.
Flocculation by polymers (bridge flocculation) is used for coals. Molecules of polymers have a chain structure. The atoms of carbon are joined by covalent links on-the-miter 109o and form the zigzag chains. The chains have branches which are functional (or lateral) groups. With the help of branches macromolecules consolidate with flocculating particles joining them into the flocculus.
Summary
In order to ensure the normal work of factory it requires broadening of dehydration department and applying of new qualitative equipment. At the same time the demand of more advanced equipment leaves behind the rate of its creation, it arises necessity of searching others ways of intensification of dehydration process. Considerable prospects have physicochemical methods, they allow to increase efficiency of dehydration without considerable capital expenditure. The experience of industrial application of reagents- intensifiers at concentration plants has given positive results. Physicochemical methods of intensification of dehydration make it possible to increase efficiency of filter equipment, decrease the carry-over of solid with filter and reduce the sediment moisture. It will bring to improvement of technological performance of concentration process in the whole thanks to the reduction of the degree of dirty return water. Thus, the use of reagents-intensifiers is one of the prominent factors in solving the problem of improvement the water slime husbandry at the concentration plants.
List of references:
1. Бейлин М.И. Теоретические основы процессов обезвоживания углей.-М.: Недра, 1969.-240 с.
2. Долина Л.Ф. Интенсификация технологических процессов углеобогащения с применением поверхностно-активных веществ.- Черматинформация,1977,М., сер. 10, вып.2.
3. Batel W.Vorausberechung der Restfeuchtsgkest – Chem. ING, 1959., 28, р.343.
4. Ройтер И., Крефкльд Ф.Полимерные синтетические флокулянты и ихприменение при обогащении минерального сырья-Глюкауф,1976,№3, с. 25
5. Білецький В.С, Сергєєв П.В., Папушин Ю.Л. Теорія і практика селективної масляної агрегації вугілля. – Донецьк: Грань, 1996. –264 с
6. Елисеева В.И. Полимерные дисперсии.- М.:Химия, 1980.-296 с.
7. І.М. Нікітін, П.В. Сергеев,В.С. Білецькиц. Селективна флокуляція вугільних шламів латексами. –Донецьк . «Східний видавничий дім»,2001.-152с.
© DonNTU 2008 Umanets S.S.
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