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| 2. |
- Dwari, Ranjan, et al.
(författare)
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Characterising electron transfer mechanism in tribo-electrification of pyrite through contact angle measurements
- 2008
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Ingår i: Open Mineral Processing Journal. - : Bentham Science Publishers Ltd.. - 1874-8414. ; 1, s. 6-17
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Tidskriftsartikel (refereegranskat)abstract
- Coal beneficiation by tribo-electrostatic method depends on tribo-charging attributes of coal and ash forming minerals. The tribo-electrification behaviour of pyrite mineral contacted with different materials has been investigated through charge measurements and the charge acquisition is probed through surface energy calculations from liquid contact angle data. Liquid contact angle on pyrite powder after tribo-electrification is determined by Kruss tensiometer using Washburn's equation. The sample holder in tensiometer is specially fabricated with different materials serving the purpose of tribo-electrification and contact angle measurement. The acid and base parameters of pyrite surface determined with van Oss acid-base approach using liquid contact angle data after tribo-electrification with different materials revealed the charging phenomena and electron transfer mechanism. The results showed an explicit correlation between the charge generated by pyrite powder and surface acceptor (acid)-donor (base) electronic state underlying the work functions of contacting surfaces. Thus a method for characterising the changes in surface energetic structure of solids during contact electrification in terms of surface acid-base parameters has been illustrated for the first time.
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| 4. |
- Dwari, Ranjan
(författare)
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High ash non-coking coal preparation by tribo-electrostatic dry process
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Coal is the single largest fossil fuel used world-wide and accounts for more than 60% of the total commercial energy consumed. Between 60 to 80% of this coal is used for electric power generation and most of which through a system of pulverised coal combustion. Major portion of the coal used for such power generation is not clean enough to maintain environmental standards. This problem is attributed to high sulphur content in coal used in most of the western countries or ash as is the case in countries like India. In India at present nearly 260 million tonnes per year of coal is used for power generation and the average ash in coals used is invariably above 40%. A substantial portion of ash is liberated as it enters the boiler from the mill. It is crucial to reduce the amount of ash going from the mill to the boilers not only to improve the performance of power generation and increase the life of the boilers but also became mandatory due to environmental regulations. Thus the main objective of the work is to develop a dry tribo-electrostatic process for the separation of ash forming inorganic matter from coal material with a thorough understanding of the response and behaviour of coal and non-coal matters to contact electrification and in electric field. This work is financially supported by the Department for Research Cooperation of the Swedish International Development Cooperation Agency (SIDA/SAREC). The literature on dry coal preparation processes has been reviewed and the advantages of triboelectric process compared to other processes have been highlighted and further research needs to make it a viable industrial technology are outlined. Three Indian coal samples from three different major coal fields, i.e., Ramagundam, Ib-valley and Talcher, have been collected and characterised for macerals and mineral composition by microscopic and XRD analyses. The beneficiation potential at different size fractions of the coal samples is judged by the washability studies. The charge polarity and magnitude of pure quartz, pyrite kaolinite, illite and carbon after contact electrification with different tribo-charging media have been measured by Faraday cup method using Keithley electrometer. The predicted work functions of the tribo charging material and mineral phases agree closely with the reported values. The electron accepting and donating (acid-base) property of mineral phases determined by Kr¨¹ss Tensiometer through polar and non-polar liquid contact angles on solids also corroborated the acquired charge polarity in contact electrification with copper, aluminium and brass materials underlying their work functions. This methodology can be applied for the choice of organic acidic/basic solvents treatment of coal material to enlarge the difference in work functions between the tribo-charger and mineral phases, and to achieve greater separation efficiency of inorganic matter from coal. The process of tribo-electric coal/ash cleaning is carried out with a newly built cylindrical fluidised-bed tribo-charger with internal baffles, made up of copper metal, and the influence of equipment and process variables have been evaluated. The collecting bins of the material underneath the copper plate electrodes are designed to function as Faraday cups such that the charge polarity and magnitude of particles in each bin can be measured directly. The coal and mineral particles respectively charged with positive and negative polarities with relatively higher magnitude illustrating greater efficiency of contact electrification in the fluidised bed tribo- charger system. The separation results with minus 300 ¦Ìm size fraction of coal containing 43% ash showed that the ash content can be reduced to 18% and 33% with an yield of about 30% and 67% respectively. With a 30% ash coal, a clean coal of about 15% ash is obtained with about 70% yield. These results are comparable to the maximum separation efficiency curves of washability studies on the coal samples. Since the ash percentage of coal particles collected in the bins close to positive and negative electrodes are about 70% and 20%, a better yield with further reduced ash content can be accomplished by recycling the material. Thus, the tribo-electrostatic method observed to be a promising dry coal preparation technique, where the present laboratory size separator needs to be scaled to plant level for commercial application.
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- Dwari, Ranjan, et al.
(författare)
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Non-coking coal preparation by novel tribo-electrostatic method
- 2008
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 87:17-18, s. 3562-3571
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Tidskriftsartikel (refereegranskat)abstract
- A new laboratory fluidised bed tribo-electrostatic separator has been assembled and the beneficiation potential of thermal non-coking coal from Hingula block of Talcher coal field, India, is examined on this separator. The uniqueness of the separator originates from the efficient tribo-electrification of coal material in the cylindrical fluidised bed with internal baffle system. The collecting bins of the material underneath the copper plate electrodes are designed to function as Faraday cups such that the charge polarity and magnitude of particles in each bin can be measured directly. The liberation attributes of coal material is assessed by sink and float analysis of various size fractions. The mineral and maceral composition is determined by XRD and petrographic analysis. The separation tests were conducted at different tribo-charging and applied voltage conditions. The material collected in bins close to positive and negative electrodes show an ash content of 61% and 8% respectively, illustrating differential charge acquisition of mineral rich and coal rich particles during tribo-electrification. The charge results are in good agreement with the ash content of the coal material collected in the bins. The results showed that a clean coal of about 15% ash can be obtained from a coal containing 30% ash with about 70% yield. A better separation results can be achieved by recycling the material. The ash content in the clean coal is however limited by the liberation characteristics of the coal, which is evidenced by the SEM analysis of the particles in different bins. Thus, the tribo-electrostatic method observed to be a promising dry coal preparation technique.
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| 6. |
- Dwari, Ranjan, et al.
(författare)
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Novel fluidised-bed tribo-electrostatic separator for dry coal preparation
- 2008
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Ingår i: Conference in Minerals Engineering 2008. - Luleå : Luleå tekniska universitet. ; , s. 15-29
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Dry coal beneficiation has been examined by tribo-electrostatic method using Indian thermal coal sample from Ramagundam coal mines. The process of triboelectric coal/ash cleaning is carried out with a newly built cylindrical fluidised-bed tribocharger with internal baffles, all made up of copper metal. The charge transfer of coal maceral and mineral particles upon contacts with copper plate of tribocharger is measured. Separation of particles in an electrostatic separator according to the polarity of particle charge is discussed with respect to gas flow rate and residence time in fluidised-bed trobo-charger and the applied electric field. The coal and mineral particles charge with positive and negative polarities respectively. The magnitude of particles charge found to be relatively high illustrating greater efficiency of contact electrification in fluidised bed tribo-charger. The separation results with minus 300 μm size fraction of coal containing 43% ash showed that the ash content is reduced to 18% and 33% with an yield of about 30% and 67%, respectively. These results are comparable to the maximum separation efficiency curve of washability studies on this coal sample. Since the ash percentage of coal particles collected in the bins close to positive and negative electrodes are about 70% and 20%, a better yield with low ash content can be accomplished on recycling the material.
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