1. Studies on the Effect of Coal Blend Crushing and Carbonization Time on Coke Quality
Presented by:
Praveen Kumar Jha

2. INTRODUCTION
Coke quality is one of the significant factors affecting blast furnace performance.
Coke accounts for >50% of hot metal cost,
Main coke quality parameters influencing productivity and coke rate in Blast Furnaces
M10,
M40,
CSR (Coke strength after reaction),
CRI (Coke reactivity index),
Coke Ash,
Size distribution of coke

3. INTRODUCTION Contd…
One point reduction in M10 index improves BF productivity by 2.5% and reduces coke rate by 2.0%.
Coke quality depends on following factors
Coal blend quality,
Granulometry (Crushing index) of coal blend,
Pre-carbonisation technology,
Carbonisation conditions,
Post-carbonisation treatment of coke
With a view to improve coke quality, effects of coal blend crushing index and coking time have been studied with blend of one of the SAIL plant.

4. Experimental
Around 2 ton of coal blend was collected from charging car of coke oven battery.
After proper homogenization, coal blend was divided in 6 equal parts for carbonization tests.
Tests carried out at RDCIS, Ranchi:
Coal blend properties
Pilot oven carbonization test
Coke quality

5. Experimental contd… Following coal blend properties were determined
Size analysis
Proximate analysis
Fluidity
Crucible swelling number
Petrographic analysis
Proximate analysis of different size fraction (+10 mm , + 6 mm , +3.2 mm , mm, -0.5 mm)

6. Coke mass temperature, 0C
Experimental contd…
Pilot oven test was carried out in the electrically heated
movable wall pilot coke oven.
Crushing index, carbonization condition of six different
samples were maintained as shown below:
Sample No
Crushing Index
(-3.2 fraction), %
Coking Period, hrs.
Coke mass temperature, 0C 1
71.8
23.5 2
72.1 22 3
79.2 4
79.8 20 5
80.2 6
85.5

7. Experimental contd…
Coke quality of six different coke produced from pilot oven were determined to asses the quality of coke with different level of crushing index and coking time.
Micum indices (M10 & M40)
Proximate analysis of coke
Size analysis of coke

8. Results Proximate analysis of coal blend Coking Properties Tests
Values
Proximate Analysis (IS: 1350 Part I- 1984)
Analytical Moisture % (air dried basis)
1.09
Volatile Matter, % (air dried basis)
24.9
Ash, % (air dried basis)
13.1
Coking Properties
CSN
3.5
Initial Softening Temp, 0C
406
Max. Fluidity Temp, 0C
448
Re-solidification Temp, 0C
481
Plastic Range, 0C 75
Max Fluidity, ddpm
648

9. Results A. Maceral distribution, % (ISO 7404-3: 1994) Vitrinite 51.4
Petrographic analysis of coal blend
A. Maceral distribution, % (ISO : 1994)
Vitrinite
51.4
Semi-vitrinite (Reactive semi-fusinite)
1.7
Liptinite
3.2
Inertinite
35.8
Mineral Matter
7.9
B. Reflectance , RoR,% (ISO : 1994)
1.012
C. MMR, % (ISO : 1994)
1.07

10. Results Proximate analysis of different size fraction of coal blend
(+10mm)
(+6mm)
(+3.2mm)
(+1mm)
(+0.5mm)
(-0.5mm)
VM, %
24.68
25.18
25.3
25.16
25.38
25.57
Ash, %
20.71
17.91
16.14
13.46
13.06
10.78
CSN
1.5 2 3
3.5
4.5
Ash content increases with increase in size fraction
CSN deteriorated with increase in size.

11. Results VM & Ash of Different Size fractions of Coal Blend
Due to difference in the plastic and shrinkage behavior of inert rich particles and rest of the charge, local stresses are developed and cracks form adversely affecting coke quality.

12. Results
Micum Indices of Coke Vs Crushing Index of Coal Blend

13. Results
+ 25 mm fraction of Coke Vs CI of Coal Blend

14. Results Coke quality produced from pilot oven with different CI & CT
Parameters
 Units
Sample
# 1 
# 2
# 3 
# 4 
# 5
# 6
Coking Period
Hrs.
23.5 22 20
Proximate Analysis 
Ash % 
17.5
17.6
17.4
17.3 VM
%  
0.37
0.41
0.67
0.66
0.6
0.59
Micum Indices 
M10
13.6
13.0
11.8
12.2
11.2
M40
70.4
73.6
76.4 78
78.0
80.2

15. Results
As coking period was decreased from 23.5 hrs to 22 hrs, the coke quality in terms of M10 improved for same crushing index of ~72%.
M40 index also showed an increasing trend with reduction in coking time.
As the thermal stress in coke layer increases along with increase of the heating rate and transverse temperature gradient of coal layer, the size of coke is decreased. Bigger size coke (+80 mm) is generally weak.

16. Results
Correlation developed between Micum indices and Coking time & Crushing Index
M10 = *CT – 0.05* CI * (% +6mm) R2 = 0.87
M40 = 72.1 – 0.77* CT + 0.3*CI - 0.3* (% +6mm) R2 = 0.90
CT : Coking time
CI : Crushing index

17. Conclusion
Bigger size fractions of coal blend have inferior coking properties.
For producing good quality coke, crushing index of coal charge needs to be at least >80%. +6mm fraction in coal charge should be as low as possible.
Coke quality improves with reduction in Coking time.