A.K. Sahu

Development of Air Dense Medium Fluidized Bed Technology For Dry Beneficiation of Coal – A Review

Wet processing of coal requires a large quantity of water. Waste generated from wet process ties up a significant amount of water and land. The slurry ponds also pose serious problems in case of dam breakage. Dry beneficiation of coal offers a better alternative approach for cleaning coal. An overview on the development of separation technology for beneficiation of coal using dense medium fluidized bed system is described. A theory of the dry separation relevant to coal beneficiation by density difference has been highlighted. This paper summarizes past and present development of different designs and operational features of a counter-current cascade fluidization (CCFC) system and air dense medium fluidized bed separator (ADMFBS) based on their separation efficiency for different sizes of coal at different scales of operation. For fine coal beneficiation, magnetically stabilized bed improves the separation efficiency by preventing the back mixing of the separated solids.

Stability Study of an Air Dense Medium Fluidized Bed Separator for Beneficiation of High-Ash Indian Coal

Indian high ash noncoking coal contains a substantial quantity of near-gravity materials (NGM). The presence of NGM needs beneficiation in dense medium separation process. Air dense medium fluidized bed separator (ADMFBS) uses the magnetite medium to improve the separation efficiency of beneficiation of high NGM coal. Stability of the particulate fluidized bed in this system is the essential prerequisite for the separation of heavy and light particles. In this study, the characterization of medium and particulate fluidized bed was assessed to maintain the nonbubbling condition. Stability of the fluidized bed was characterized by different expressions like fluidization index, particulate expansion function, Froude number of particle, Reynolds number of particle, and pressure drop ratio using the minimum fluidization velocity, minimum bubbling velocity, pressure drop of distributor and bed, bed porosity, air viscosity, aspect ratio, density of air, and density of medium. It was found that the fluidization indexes of this system for different experimental runs are around 1 to 2. The system was scaled up from laboratory to pilot scale, having a feed throughput capacity of 600 kg/hr. Indian high ash noncoking coal at particular size (−25 + 6 mm) was used in continuous operation. The partition number was calculated based on washability data of product and reject. The Ep and imperfection value for the pilot-scale ADMFBS was found to be 0.12 and 0.071, respectively.

Preparation of graphene oxide by dry planetary ball milling process from natural graphite

Graphene oxides (GO) with different degrees of oxidation have been prepared by an in-house designed horizontal high energy planetary ball milling process. The prepared graphene oxides have been studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) with selected area electron diffraction (SAED), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), micro Raman spectroscopy, Fourier transform infrared (FTIR) spectra, Brunauer–Emmett–Teller (BET) test and thermogravimetric analysis (TGA). XPS study shows an increasing trend of atomic concentration ratio of O/C with increasing ball milling time duration from 2 to 24 h of high purity graphite sample (FEED). This result is attributed to the formation of more oxidation in the graphite sample, produced due to the increasing time duration of milling. From micro Raman analysis it is also noted that ID/IG ratio increases with increasing milling time of FEED, which further supported the preparation of graphene oxide. In this study the graphene oxide prepared by 16 h of milling may be considered as the optimized sample as far as the degree of oxidation, time and energy consumption factors are concerned.