Studies on the Effect of Coal Blend Crushing and Carbonization Time on Coke Quality   Presented by: Praveen Kumar Jha e-mail: praveen@sail-rdcis.com

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

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.

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

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 , + 0.5 mm, -0.5 mm)

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 1000+10 2 72.1 22 3 79.2 4 79.8 20 5 80.2 6 85.5

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

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

Results A. Maceral distribution, % (ISO 7404-3: 1994) Vitrinite 51.4 Petrographic analysis of coal blend A. Maceral distribution, % (ISO 7404-3: 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 7404-5: 1994) 1.012 C. MMR, % (ISO 7404-5: 1994) 1.07

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.

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.

Results Micum Indices of Coke Vs Crushing Index of Coal Blend

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

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

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.

Results Correlation developed between Micum indices and Coking time & Crushing Index M10 = 14.5 + 0.01*CT – 0.05* CI + 0.13* (% +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

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.