Technological Implication of Coal Technological Implication of Coal Quality Improvement for Power Quality Improvement for Power Stations by Beneficiation and Stations by Beneficiation and BlendingBlending Kalyan Sen

N. S. Das

A. Choudhury

S. G. Chowdhury

R. Dasgupta

S. Biswas

Central Fuel Research Institute, Dhanbad

INDIAN RAW COALINDIAN RAW COALas Feed to TPS as Feed to TPS

Constraints:

Genetic : high inertinite content, high moisture

Operational : mechanized mining in large OCP

Organizational: multiple sources/ linkages

Net result

high ash contentigh ash content heterogeneity in sizeheterogeneity in size deterioration in heat valuedeterioration in heat value

NeedNeed

Beneficiation to a limited extent that meets the desired qualities

Probable alternates for ImprovementProbable 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

LIMITATIONSLIMITATIONS

Alternate 4:

Needs finer fractions to be beneficiated

Beneficiation of Finer Beneficiation of Finer FractionsFractions

to be or not to be !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 37 27

2) B &C 43-38 34-37

3) D 47 44

Beneficiation schemes adoptedBeneficiation 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 studyResult of the studyCoal 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 1 65-69 7-10% “& II & III-a 1 67-85 with = 55%, <5% C II & III-b 1 70-85 dirt

D I not achievable II & III-a 2 45-57 < 5% “ II & III-b 1 62-65 overall ash may be >34

Ash,%

Yie

ld,%

0

10

20

30

40

50

60

70

80

90

1000 10 20 30 40

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. 1.80-1.85)

AI

IIa

IIIb

IIb

SuggestionsSuggestions

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