Some RelevantTechnical Issues

onConsistent Coal Quality

Asim Chowdhuri &Dr Kalyan Sen, CFRI, 2003

Approach towards Quality Improvement &

Supply of Consistent Quality

Proper QMS

Technological options for Quality enhancement

Modification of Standards

Revision of Coal Categorisation

Existing Quality Monitoring System

• Manual sampling

• Wagon top sampling

• Mechanical sampling

ConstraintsHandling of large sized coal

Quality Monitoring of Coal

• Less reliable due to higher errors

• Disputes between supplier & consumer

• Nation being the ultimate looser

Problems of Wagon top sampling

Sampling sites

• Inadequate facility - sampling, preparation & analysis

• Insufficient time, manpower, etc.

• Results sampling from top only

How it affects final results

Quality Monitoring of Coal

• Higher Bias leading to disputes

• High Spillage

• Frequent Chute choking

• Rapid wear & Tear

• High Capital investment & Maintenance costs

Problems of Mechanical Sampling(200mm sized coal)

Constraints

Proposed Modification in SamplingProcedure

Benefits• More reliable quality data

• Less Capital investment

• Low maintenance cost

in case of temporary failure of AMS theadvantage would be for switching over towagon top sampling with better precisionthan that for higher sized coals

• Supply of lower size coals (50 mm or below) and inclusion of AMS

Identified Technological Optionsfor Coal Quality Upgradation

Globally accepted Options for better economicsand less environmental pollution

• Mine planning

• Dry deshaling at Pit heads

• Judicious blending

• Wet beneficiation

Identified Technological Optionsfor Coal Quality Upgradation

Proposed: The degree of washing should be limited to that density of cut at which the final product is free from any particle of ash higher than 50-55%. Of course, this often leads to overallash content level more or less 34%.

Present rider: ash level of 34%

Technology Routes for beneficiationTechnology Routes for beneficiation

Level Scheme Methodology Ash%reducn

Cleans (%)

M % over ROM coal

I Dry benefic. Separation of stone/shale based on differential breakage potentiality

3-4 >90 Nil

II Crushing, screening & coarse coal cleaning

Coarse coal (13/30mm) washed & mixed with untreated fines; dewatering screens.

<10 70-90 2-3%

III Crushing, screening and total cleaning

Coarser fraction washed at optimum efficiency levels: fine coal by Spiral: dewatering

>10 <60 3-4%

Proposed Modification of Standards

• Adoption of ISO 13909 (Mechanical Sampling)

• Adoption of ISO 9931 (for Pulverized Coal)

• Reaffirmation of IS 13810 (Code for F&S)

• Change in ISO 1213 -1 (a new term)

Characteristic Ash:

The ash of the particles in a closely spaced relative density fraction obtained from Float & Sink analysis

Revision of Coal Categorisationfor commercial purpose

Categorisation system based on GCV (as recd. Moist. basis) & weightage on the ash

A Matrix system with closely spaced GCV & ash value.

Coal quality could be assessed by maximum ash value and lowest GCV value that will

• Remove anomalies of the present system

• Provide incentive for better quality

• Ensure consistent quality of a consignment

Figure 16: Variation of GCV and UHV with Ash (Combined Data)

-2000

-1000

0

1000

2000

3000

4000

5000

6000

7000

8000

0 10 20 30 40 50 60 70 80

Ash%

GC

V (

kc

al/k

g)

GCV

UHV

. Minimum GCV of the consignment at as received Moisture Level

6000 5800 5600 5400 5200 5000 4800 4600 4400 4200 4000 3800 3600 3400 3200 3000 2800 2600 2400 220020

Max 21ash% 22

232425262728293031323334353637

. 38394041424344454647484950

Ash

GCV