upgradation of coal

UPGRADATION OF LAKHRA COAL BY HEAVY MEDIUM SEPARATION METHOD

UNDER THE KIND SUPERVISION OFASST PROF SIKANDAR CHANNA

GOALS AND OBJECTIVES

Objective was to clean the impure coal after treating it with the heavy mediums using float-&-sink techniques.

INTRODUCTION OF LAKHRA COAL

Lakhra coal resources are estimated about 1318 million tonnes.

Its rank is lignite. The mined coal mostly

consists of lumps with dumb black color.

It has high moisture, ash content, sulfur and low calorific value.

IMPACT OF ITS IMPURITES

The contents which hinder its direct application in the generation of electric power, have been its high sulfur content and huge quantity of ash. Sulfur on burning creates environmental pollution and corrodes the equipment; causing financial loss to the industry. The ash due to its very nature of fusing to slag at high temperature, thus hindering the burning process itself.

Coal Sample Preparation

The sample was collected from Habibullah Coal Mines Ltd.

For coal preparation, the sample quantity required was 1 gm for each test and in size of -250 micron. Therefore, the required size was obtained by proper:

crushing, sieving and grinding

SIZE ANALYSIS OF ROLL CRUSHER PRODUCT

Sr. No. Sample size

mm

Weight

retained

g

Cum. Wt.

retained

g

Wt.

retained

%

Cum. Wt.

retained

%

Cum. wt.

passed

%

1 40 204.90 204.90 6.03 6.03 93.97

2 30 360.60 565.50 10.62 16.65 83.35

3 20 652.40 1217.9 19.22 35.87 64.13

4 10 720.30 1938.2 21.22 57.09 42.91

5 5 720.40 2658.6 21.23 78.32 21.68

6 2.5 304.00 2962.6 8.95 87.27 12.73

7 0.00 212.00 3274.6 6.24 93.51 0.00

CUMULATIVE WEIGHT GRAPH OF SIEVE ANALYSIS

0

20

40

60

80

100

120

0 5 10 15 20 25 30 35 40 45

cummulative weight passed %

size(mm)

CURVE A

CURVE B

SPECIFIC GRAVITY

Relative density, or specific gravity is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material.

Specific gravity determination is the crucial part of the experiment on which the float-&-sink technique was based.

The specific gravity of coal is obtained as 1.47 and that of the heavy mediums are obtained by standard procedure.

SPECIFIC GRAVITY OF AIR DRIED COAL

Sr.

No.

Sample

size

mm

Bottle

No

Wt. of bottle

with stopper

Weight of

bottle+distilled

water(B+W)

=W3

Weight of sample=W1

g

Weight of

bottle+distilled

water+sample

(B+W+S)=W2

SG Average SG

1 -2.5 23 38.4562 138.2204 5.0037 139.2774 1.26

2 -5 + 2.5 1 51.3318 153.9941 5.0004 156.0350 1.68

3 -10 + 5 13 43.0362 142.4988 5.0074 144.2527 1.53 1.47

4 -20 +10 22 41.2156 140.8059 5.0050 142.8231 1.67

5 -30 +20 10 36.8973 136.5838 5.0045 137.6959 1.28

6 -40 +30 4 45.5187 144.5390 5.0000 146.0861 1.44

COAL ANALYSIS

Before proceeding for the physical cleaning of coal we determined different properties of coal samples in the laboratory by:

Proximate Analysis (Ash, Moisture, Volatile matter, and Fixed carbon)

Ultimate Analysis (Sulfur) Calorific value

Following are tables which shows the proximate and ultimate analysis as well as calorific value of different sample sizes of coal.

Ash content in the various size fractions of the air dried coal

Sr.

No.

Sample size

mm

Crucible

No

Wt. of

empty

crucible=A

g

Wt. of

sample=C

g

Wt. of

Ash+

crucible=B

g

Weight of

Ash=B-A

g

Ash content

(B-A/C)

%

Avg Ash

content

%

1 -2.5 5 34.2627 1.0056 34.4469 0.1842 18.31

2 -5 + 2.5 19 34.5765 1.0010 34.7072 0.1307 13.05

3 -10 + 5 9 34.1807 1.0153 34.3398 0.1591 15.67 14.991

4 -20 +10 24 33.9244 1.0055 34.0536 0.1292 12.84

5 -30 +20 14 34.0850 1.0002 34.2466 0.1616 16.15

6 -40 +30 9 36.8700 1.0196 37.0121 0.1421 13.93

Moisture content in the various size fractions of the air dried coal

Sr.

No.

Sample

size

mm

Dish No Wt. of

dish

g

Wt. of

sample=C

g

Wt. of

dish+sample

(before heating)

=A

g

Wt. of

dish + sample

(after heating)

=B

g

Diff: of

wt.=A-B

g

moisture

content

(A-B/C)

%

Avg

moisture

content

%

1 -2.5 3 22.6101 1.0221 23.6322 23.5220 0.1102 10.78

2 -5 + 2.5 7 21.6660 1.0133 22.6793 22.5636 0.1157 11.41

3 -10 + 5 6 23.4812 1.0064 24.4876 24.3744 0.1132 11.24 11.7

4 -20 +10 13 27.9837 1.0544 29.0381 28.8969 0.1412 13.39

5 -30 +20 11 25.7169 1.0192 26.7361 26.6170 0.1184 11.61

6 -40 +30 9 25.6295 1.0114 26.6409 26.5223 0.1186 11.72

Volatile matter in the various size fractions of the air dried coal

Sr.

No.

Sampl

e size

mm

Dish

No

Wt.

of

dish

g

Wt. of

sample=

C

g

Wt. of

crucible +

sample (before

heating) =A

g

Wt. of

crucible +

sample

(after heating)

=B

g

Diff: of

wt.=

A-B

Total

VM

(A-B/C)

%

Deduct

moist:

conten

t

%

Net

VM

%

Avg

VM

%

1 -2.5 1 13.40

0

1.0082 14.4082 13.9509 0.4573 45.35 10.78 34.57

2 -5 +

2.5

2 12.68

8

1.0112 13.6995 13.2185 0.4810 47.56 11.41 36.15

3 -10 + 5 3 12.94

3

1.0086 13.9522 13.4734 0.4788 47.47 11.24 36.23 35.93

4 -20

+10

4 13.10

3

1.0045 14.1084 13.6179 0.4905 48.83 13.39 35.44

5 -30

+20

5 13.00

9

1.0100 14.0194 13.5435 0.4759 47.11 11.61 35.50

6 -40

+30

6 14.53

7

1.0095 15.5474 15.0486 0.4988 49.41 11.72 37.69

Fixed carbon in the various size fractions of the air dried coal

Sr. No. Sample size

mm

moisture content

%

Ash

%

Volatile Matter

%

Fixed Carbon

%

Avg Fixed

Carbon

%

1 -2.5 10.78 18.31 34.57 36.34

2 -5 + 2.5 11.41 13.05 36.15 39.39

3 -10 + 5 11.24 15.67 36.23 36.86 37.386

4 -20 +10 13.39 12.84 35.44 38.33

5 -30 +20 11.61 16.15 35.50 36.74

6 -40 +30 11.72 13.93 37.69 36.66

Sulfur in the various size fractions of the air dried coal

Sr.

No.

Sample size

mm

Weight of sample

g

Sulfur

%

Average sulfur

%

1 -2.5 0.1360 9.686

2 -5 + 2.5 0.1320 6.825

3 -10 + 5 0.1370 6.732 6.71

4 -20 + 10 0.1370 6.279

5 -30 + 20 0.1350 4.379

6 -40 + 30 0.1360 6.417

Clorific value in the various size fractions of the air dried coal

Sr. No. Sample size mm Gross calorific value Btu/lb Avg gross calorific value Btu/

lb

1 -2.5 6046

2 -5 + 2.5 7473

3 -10 + 5 6052 6825.666

4 -20 + 10 7722

5 -30 + 20 6921

6 -40 + 30 6740

HEAVY MEDIUMS

Heavy mediums or gravity mediums were the solutions of the following two halides prepared with the desired specific gravities.

3. Zinc Chloride4. Calcium Chloride

PREPARATION

The preferred heavy mediums were the solutions that were prepared by adding certain amount of either zinc chloride or calcium chloride in distilled water upto the desired specific gravity that was noted at every instance using Hydrometer and was stirred continuously until the salt completely dissolves into the distilled water.

The specific gravities of the heavy mediums were achieved in the range of 1.30,1.35, 1.40 and 1.45.

FLOAT -&-SINK TECHNIQUE

The float-&-sink technique was used to get the two layers of float and sink separate on the basis of specific gravities difference after the impure untreated coal was introduced to that heavy medium of least density initially.

The presence of more impurities into coal made it denser than medium and thus it sunk.

On the contrary the float gave pure coal that had minimum impurities and was less denser.

FLOAT -&-SINK TECHNIQUE (continue)

The same step was repeated for the sink on the medium of slightly higher and finally on the higher medium that gave the recovery of pure coal at the float in varying percentage.

IMPURITIES RE-DETERMINATION

The coal recovered was re-determined in the end thus showing variation in the obtained results that were low then the untreated coal previously, thus giving us the optimum result for its applications.

Float and sink analysis and washability curves of sample No.1, 2,3,4 and 5 respectively are shown below.

FLOAT AND SINK ANALYSIS OF SAMPLE NO.1 ON ASH BASISSIZE OF SAMPLE (-5+2.5 mm)WEIGHT OF SAMPLE 10gm.

Sr.

No.

S.G. of

solution

FLOAT Wt.% of Moisture

content in cum. Wt.

of Floats

Cum wt. of

float Ash

g

Cum wt. of Float Ash in

air dried sample

%Wt.

g

Cum.

Wt.

g

Wt.

%

Cum.

wt.

%

01 1.30 3.37 3.37 33.7 33.7 10.28 0.09 9

02 1.35 1.95 5.32 19.5 53.2 10.05 0.12 12

03 1.40 0.83 6.15 8.3 61.5 9.97 0.132 13.2

04 1.45 0.31 6.46 3.1 64.6 9.65 0.139 13.9

Washability curves of sample No. 1

FLOAT AND SINK ANALYSIS OF SAMPLE NO.2 ON ASH BASISSIZE OF SAMPLE (-10+5 mm)WEIGHT OF SAMPLE 10gm.

Sr.

No.

S.G. of

solution


content in cum. Wt.

of Floats

Cum wt. of

float Ash

g


air dried sample

%Wt.

g

Cum.

Wt.

g

Wt

%

Cum. wt.

%

01 1.30 5.34 5.34 53.4 53.4 9.73 0.92 9.2

02 1.35 1.25 6.59 12.5 65.9 8.25 0.129 12.9

03 1.40 1.07 7.66 10.7 76.6 8.77 0.138 13.8

04 1.45 0.92 8.58 9.2 85.8 9.11 0.141 14.1

FLOAT AND SINK ANALYSIS OF SAMPLE NO.3 ON ASH BASISSIZE OF SAMPLE (-20+10 mm)WEIGHT OF SAMPLE 10gm.

Sr.

No.

S.G. of

solution


content in cum. Wt.

of Floats

Cum wt. of

float Ash

g


air dried sample

%Wt.

g

Cum.

Wt.

g

Wt.

%

Cum.

wt.

%

01 1.30 6.02 6.02 60.2 60.2 10.56 0.09 9

02 1.35 0.95 6.97 9.5 69.7 9.22 0.11 11

03 1.40 0.67 7.64 6.7 76.4 8.97 0.119 11.9

04 1.45 0.44 8.08 4.4 80.8 9.1 0.121 12.1

FLOAT AND SINK ANALYSIS OF SAMPLE NO.4 ON ASH BASISSIZE OF SAMPLE (-30+20 mm)

WEIGHT OF SAMPLE 10gm.

Sr.

No.

S.G. of

solution


content in cum. Wt.

of Floats

Cum wt. of

float Ash

g


air dried sample

%Wt.

g

Cum.

Wt.

g

Wt.

%

Cum.

wt.

%

01 1.30 3.72 3.72 37.2 37.2 9.22 0.11 11

02 1.35 1.12 4.84 11.2 48.4 9.98 0.13 13

03 1.40 1.0 5.84 10 58.4 9.44 0.132 13.2

04 1.45 0.71 6.55 7.1 65.5 10.22 0.139 13.9

FLOAT AND SINK ANALYSIS OF SAMPLE NO.5 ON ASH BASISSIZE OF SAMPLE (-40+30 mm)

WEIGHT OF SAMPLE 10gm.

Sr.

No.

S.G. of

solution


content in cum. Wt. of

Floats

Cum wt. of

float Ash

g

Cum wt. of Float Ash in air

dried sample

%Wt.

g

Cum.

Wt.

g

Wt.

%

Cum.

wt.

%

01 1.30 4.25 4.25 42.5 42.5 10.2 0.103 10.3

02 1.35 1.11 5.36 11.1 53.6 9.3 0.13 13

03 1.40 0.97 6.33 9.7 63.3 9.1 0.133 13.3

04 1.45 0.65 6.98 6.5 69.8 9.9 0.139 13.9

CONCLUSION

The clean coal recovery comes out to be 78%, 79%, 74%, 71% and 69% respectively.

The clean coal would be separated from its associated mineral metals, which are comparatively heavier than the pure coal, at a specific gravity of 1.47, 1.46, 1.4, 1.46 and 1.45 respectively.

Since the second laboratory test on the sub-sample, representing the fraction size(-10+5)mm of the original “Head Sample”, gave the best results, yielding 14 % of ash and the theoretical recovery of the clean coal obtained from this sample is about 79 percentage by weight at a specific gravity of 1.46.

In the case of the raw coal samples, supplied by HML, (Habibullah Coal Mines Limited), washing at a specific gravity less than 1.35, would not be of much benefit. However, the washability at this or above specific gravity may improve the possible sample separation of the near gravity material to an acceptable level.

The Lakhra coal is classified as lignite (low grade fuel) and as such can not be used as a substitute to bituminous coal due to its high moisture, volatile matter, ash and sulfur contents. But if the modern coal preparation methods are applied and research is under taken to up-grade the Lakhra Coal by reducing ash and sulfur contents, it is possible to use these lignite’s to their best.

THANKS

PREPARED BY: GROUP MEMBERS

upgradation of coal

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