Technological Implication of Coal Quality Improvement for Power Stations by Beneficiation and Blending Kalyan Sen N. S. Das A. Choudhury S. G. Chowdhury R. Dasgupta S. Biswas Central Fuel Research Institute, Dhanbad

INDIAN RAW COAL as Feed to TPS Constraints: < Genetic : high inertinite content, high moisture < Operational : mechanized mining in large OCP < Organizational: multiple sources/ linkages

Net result igh ash content A high ash content A heterogeneity in size A deterioration in heat value Need Beneficiation to a limited extent that meets the desired qualities

Probable alternates for Improvement 1 mixing cleans of coarse fractions with untreated smalls 2 blending a part of raw coal with its cleans 3 blending low ash imported coal with high ash indigenous coal 4 mixing cleans of all fractions (whole coal beneficiation )

Alternate 1 to 3, only meet the mandate on overall ash and moisture content but, combustion qualities ?

Alternate 1: 20-40% of finer fraction (5-10% of whole coal) is obvious dirt Alternate 2: Multiple sources - variable feed Alternate 3: Blending coals of widely different ranks causes differential combustion behaviour in boilers LIMITATIONS Alternate 4: Needs finer fractions to be beneficiated

Beneficiation of Finer Fractions to be or not to be !

Case Study

Quality of Raw Coal and Screened Fine Fraction: Type Coal Overall Finer frac. Ash% Ash% 1) A ) B &C ) D 47 44

Beneficiation schemes adopted Schemes Optimization parameter I Only coarse coal overall ash 34% II Whole coal at Ep 0.12 a. overall ash 34% ( Jig) b. corresponding to  = 55% III Whole coal at Ep 0.04 a. overall ash 34% ( HM washer) b. corresponding to  = 55%

Result of the study Coal Schemes Upgradn. Yield Remarks (UHV level) (%) A I 1 >90 >15% of cleans is II(a), III(a) 1 >90 obvious dirt II(b),III(b) 2 ~ 75 < 5% “ B I % “ & II & III-a with  = 55%, <5% C II & III-b dirt D I not achievable II & III-a < 5% “ II & III-b overall ash may be >34

Ash,% Yield,% Raw coal A I (Ash34%) IIa (a34%) IIb (lambda 55%) IIIb (lambda55%) Densiometric Distribution of simulated products from coal A Amount of undesired particles having ash content >55% (above sp.gr ) A I IIa IIIb IIb

Suggestions _ Beneficiation of whole coal, particularly, where crushing to finer size does not help in liberation  washing coal at a specific gravity determined from = 50-55%. This will minimize the presence of non- combustibles