CHAR REACTIVITY AND ITS IMPLICATIONS FOR BLAST FURNACE COAL INJECTION *J.M. Steer, R. Marsh, M. Greenslade Cardiff University - School of Engineering ECCRIA 2016
Content Introduction Blast furnace coal injection, burnout and unburnt char impact Char reactivity comparison Char preparation, testing and reactivity measurement Alternative reductants for BF injection Alternatives to coal and their impact on coal blends Conclusion
Introduction blast furnace coal injection 200 C 900 C Blast furnace (cross section) 1200 C 1800 C 2000 C Assessment of refractory condition in a blast furnace hearth using computational fluid dynamics, Wright et al, 3 rd international conference on CFD 2003
Blast furnace coal sample testing - Burnout (Drop tube furnace in air @ 1100 C, 100ms residence time) Significant levels of unburnt coal char
Introduction unburnt coal implications Particulate emissions (BF dust) Reduced burden permeability Thermal instability Reduced efficiency
Introduction coal sample characterisation Proximate analysis (oven dried) LV1 LV2 LV3 MV1 MV2 MV3 HV1 Ash (%) 11.2 8.1 4.9 7.7 7.7 7.8 7.0 Volatile matter (%) 91 9.1 13.33 14.7 24.6 18.88 20.3 32.5 Fixed carbon (%) 79.7 78.6 80.4 67.7 73.5 71.9 60.5 Calorific value (MJ/kg) 34.4 32.3 34.4 31.3 n/a n/a 32.3 Petrographic analysis Vitrinite (%) 83 60 78 52 69 78 71 Liptinite (exinite) (%) 1 0 1 1 0 1 10 Inertinite (%) 14 39 18 46 31 20 17 Mineral matter (%) 2 1 3 1 0 1 2 Coal sample sieve classifications 100% <1mm 50%<250µm 100% < 500µm 100% <106µm
Char reactivity preparation and testing Drop tube furnace Thermogravimetric/DSC analyser Coal burnout / Char preparation Char testing 900 C i th lt t 1100 C for 35ms in air 900 C isothermal test with CO 2 flow at 100ml/min
Char reactivity gasification of different coal chars Gasification reactivity t 0.5 = time to reach 50% conversion
Char reactivity gasification of different size classifications Gasification reactivity t 0.5 = time to reach 50% conversion
Alternative reductants for the Iron and Steel industry 6.7% of total world CO 2 emissions Steel use set to increase 1.5 times by 2050 Coal and coke make up 40-50% of total energy requirement Coke making and sintering account for 70% total energy Reductant Volatile matter (%) Ash (%) Fixed Carbon (%) MV2 - Bituminous coal 18.8 7.7 73.5 MV3 - Bituminous coal 20.3 7.8 71.9 AR1 - Carbon black 12.7 18.3 69.0 AR2 - Tyre char 3.4 16.6 80.0 AR3 - Torrified biomass 70.4 5.9 23.7 AR4 - Ground kernel biomass 82.3 4.4 13.3 AR5 - Tyre derived fuel 65.0 7.8 27.2 AR6 - Biochar 6.2 18.7 75.1
Alternative reductants for BF injection Coal char gasification Significantly ifi better gasification reactivity it Some blends improved MV3 gasification reactivity it
Alternative reductants Coal char gasification for different particle size classifications Small differences in the gasification reactivity relative to coke
Alternative reductants Coal char gasification biochar blends Improvements in the gasification reactivity by blending biochar
Alternative reductants - burnout Drop tube furnace 1100 C 35ms Coal particle size classification particularly important on coal burnout at low residence times
Alternative reductants biochar blend burnouts Drop tube furnace 1100 C 35ms Biochar blending improved burnouts for larger particle sizes but a reduced burnout was observed in smaller particle size
Dv90 particle size change MV3 Fragmentation Agglomeration
Porosity measurements - MV3 coal and coal char (Brunauer Emmett Teller Tll method) thd) Biochar has limited it effect on porosity post DTF
Carbon Sp 2 /Sp 3 character (X-ray Photoelectron Spectroscopy carbon auger analysis) Biochar blending showed some increase in the graphitic nature (sp 2 bonding) in the smaller coal particle size
Inductively Coupled Plasma ash analysis (absolute mass % in coal / coal char sample) Increased absolute quantities of Ca, Na, K, Si, Mg & Ti
X-ray Photoelectron Spectroscopy survey scan Atomic concentration (%) C 1s N 1s S 2p O 1s Ca 2p Si 2p Al 2p MV3 106 micron 35ms +20% biochar 90.7 08 0.8 00 0.0 63 6.3 03 0.3 10 1.0 10 1.0 88.3 0.9 0.0 8.1 0.9 1.2 0.7 MV3 1000micron 35ms +20% biochar 87.2 1.2 0.0 8.5 0.0 1.8 1.3 86.2 1.4 0.1 9.0 0.6 1.8 0.9 Increased quantities of Calcium on the particle surface
SEM surface images 1000 micron 35ms Including 20% biochar 35ms Including 20% biochar 35ms 106 micron 35ms Including 20% biochar 35ms Including 20% biochar 35ms
Conclusions High levels of unburnt coal char Unburnt coal chars had better gasification reactivity than coke Bio-based reductants potentially suitable for blast furnace injection reducing CO 2 emissions per tonne of steel Blending biochar improved both burnout and gasification reactivity significantly Milling coals had more impact on combustion burnout compared to gasification Biochar blends had higher levels of calcium on char surface