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- Dwari, Ranjan, et al.
(författare)
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Characterisation of particle tribo-charging and electron transfer with reference to electrostatic dry coal cleaning
- 2009
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Ingår i: International Journal of Mineral Processing. - : Elsevier BV. - 0301-7516 .- 1879-3525. ; 91:3-4, s. 100-110
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Tidskriftsartikel (refereegranskat)abstract
- The electrostatic beneficiation of coal is based on different tribo-charging characteristics of ash forming minerals and coal particles. In this work the tribo-charging of quartz and coal particles contacted with various metals and polymer materials have been measured and the charge acquisition was examined through surface energy calculations from liquid contact angle data. The contacts angles, before and after tribo-charging of solids, were measured with Krüss tensiometer using Washburn's equation where the sample holders in tensiometer are specially constructed with tribo-charger materials. The polarity and amount of charge acquired by quartz and carbon powders with metal tribo-chargers were found to be in good agreement with the reported work functions of the contacting surfaces. The results for the charge with polymer materials differed from the work function values, presumably due to surface contamination. The surface energy of quartz particles calculated from the measured contact angle data showed that the tribo-charging increases the surface energy. Both polar and non-polar components computed using Fowkes and Owens-Wendt approaches showed that these components increase after tribo-electrification. However, the polar component divided into acid and base parts, as in van Oss approach, manifest decreasing acid part and increasing base part. Since quartz charged negatively during tribo-charging with metal surfaces and therefore suggests acceptance of electrons, the determined acid-base surface energy components are consistent with the charge transfer process. The results also elucidate an explicit correlation between the charge generated by powders and the surface acceptor (acid) and donor (base) electronic state and thereby the work functions. Thus a method for characterising the changes in surface energetic structure of solids during tribo-electrification in terms of acid-base parameters of electron transfer between the contacting surfaces has been described for the first time.
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- 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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- Dwari, Ranjan, et al.
(författare)
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Dry beneficiation of coal : a review
- 2007
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Ingår i: Mineral Processing and Extractive Metallurgy Review. - : Informa UK Limited. - 0882-7508 .- 1547-7401. ; 28:3, s. 177-234
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Forskningsöversikt (övrigt vetenskapligt/konstnärligt)abstract
- Coal continues to play a major role in the economic development of a country, especially in metallurgical industries and conventional power generation plants. For effective utilization of high ash coals, it is necessary to beneficiate them. The wet beneficiation process for coal cleaning is currently the predominant method of purification of coal in the world. However, dry beneficiation of coal has obvious advantages over wet processes. The dry processes for coal are based on the physical properties of coal and its associated mineral matters. Different types of equipment for dry beneficiation have been developed, based on the exploitation of physical properties such as density, size, shape, magnetic susceptibility, and electrical conductivity. This article presents a summary assessment of different technologies and their performance in the beneficiation process of high ash coals with particular reference to Indian thermal coals. The literature on sorting, air jigs, magnetic separation, air-dense medium fluidized bed separation, and electrostatic separation is summarized and discussed
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- Dwari, Ranjan, et al.
(författare)
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Fine coal preparation using novel tribo-electrostatic separator
- 2009
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Ingår i: Minerals Engineering. - : Elsevier BV. - 0892-6875 .- 1872-9444. ; 22:2, s. 119-127
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Tidskriftsartikel (refereegranskat)abstract
- Dry coal beneficiation has been examined by tribo-electrostatic method using Indian thermal coal sample from Ramagundam coal mines. 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. The charge transfer in coal maceral and mineral particles after repeated contact with copper plate tribo-charger is measured. Separation of particles in an electrostatic separator according to the polarity of particle charge generated during tribo-electrification is discussed with respect to gas flow rate and residence time in fluidised bed tribo-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 -300 μm 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. 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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