Patent ID: 8647400
Filing Date: 2014-02-11
Classification: C10L

Abstract:
1. An improved beneficiation process to produce low ash clean coal from high ash coals, comprising the steps of: (a) feeding raw coal to a continuous ball mill with size reduction via a primary crusher, (b) screening the crushed coal output from the ball mill; (c) transferring the crushed and screened fine coal to a bunker having load cells for weight-monitoring of the fine coal including a vibratory device for smooth inflow, and a rotary feeder device for easy outflow from the bunker; (d) preparing a coal slurry from the fine coal received in batches from the bunker in a slurry preparation tank having means for stirring, and provided with process water controlled via a control valve, the tank being further supplied with compressed air, the prepared coal slurry being discharged from the tank to a first reactor, the first reactor being maintained at a temperature between 85° C. to 90° C.; (e) preparing an alkali solution with a predetermined concentration from NaOH and water in a first tank; and discharging the prepared alkali solution to said first reactor; (f) carrying-out a leaching reaction between the coal slurry and the aqueous alkali solution inside the first reactor for about 2 to 5 hours by varying the speed of a stirrer inside the first reactor to form a reaction mixture; (g) transferring the reaction mixture from the first reactor to a second reactor either directly or through a first rotary drum filter for filtration and washing to produce a filter cake and a filtrate, the filtrate being transferred to a separate storage tank, the filter cake being continuously washed by using sprayed water and transferred back to a coal slurry preparation tank; (h) preparing a diluted acid solution in a second tank by supplying therein concentrated acid and process water via feed lines having control valves and flow sensors, the second tank being provided with at least one level sensor, and at least one stirrer, the prepared acid solution being delivered to a second reactor, the second reactor having a stirrer; (i) preparing a diluted alkali solution in a third tank having at least one first feed line for delivery of recycled alkali, a hopper with load cells, control valves, flow sensors, level sensors, a stirrer, and at least one second feed line for a supply of process water, the produced alkali solution including recycled alkali being delivered to the second reactor; (j) preparing a slaked lime in a fourth tank for adding the slaked lime with the recycled alkali along with the fresh alkali; (k) feeding a coal slurry prepared from said filter cake into the second reactor for washing the alkali-treated coal with acid at room temperature, and transferring to a second filtration unit for filtration; (l) transferring a product after filtration to a third reactor; (m) carrying-out different leaching reaction sequences in the first, second, and third reactor; (n) transferring the treated slurry to a second filtration unit after completion of the reaction from the third reactor, producing a filter cake and a filtrate; (o) transferring to a fifth tank the finally treated coal filter cake for drying, the dried filter cake being taken up for physical, chemical, rheological, and petrographical analysis; and (p) neutralizing the filtrate discharged from the second filtration unit with lime for precipitation and transferring the rest of the filtrate to an evaporator for concentration of NaOH.