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

Constraints:

INDIAN RAW COAL as Feed to TPS



Genetic : high inertinite content, moisture high



Operational : mechanized mining in large OCP



Organizational: multiple sources/ linkages

Net result

  

h igh ash content heterogeneity in size 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 ?

LIMITATIONS 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 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: 1) 2) 3) Type Coal A Overall Ash% 37 B &C 43-38 D 47 Finer frac.

Ash% 27 34-37 44

Beneficiation schemes adopted

Schemes Optimization parameter I Only coarse coal II Whole coal at Ep 0.12

( Jig) III Whole coal at Ep 0.04

( HM washer) overall ash 34% a. overall ash 34% b. corresponding to

l

= 55% a. overall ash 34% b. corresponding to

l

= 55%

Result of the study

Coal Schemes Upgradn .

(UHV level) Yield (%) Remarks A I II(a), III(a) II(b),III(b) B I & II & III-a C II & III-b 1 1 2 1 1 1 D I II & III-a II & III-b >90 >15% of cleans is >90 obvious dirt ~ 75 < 5% “ 65-69 7-10% “ 67-85 with

l

= 55%, <5% 70-85 dirt 2 not achievable 45-57 < 5% “ 1 62-65 overall ash may be >34

10 0 20 30 40 50 60 70 80 90 100 0

Densiometric Distribution of simulated products from coal A Amount of undesired particles having ash content >55% (above sp.gr. 1.80-1.85)

10

IIa

20

A I Ash,% IIIb Raw coal A I (Ash34%) IIa (a34%) IIb (lambda 55%) IIIb (lambda55%) IIb

30 40

Suggestions



Beneficiation of whole coal, particularly, where crushing to finer size does not help in liberation



washing coal at a specific gravity determined from

l

= 50-55%. This will minimize the presence of non combustibles