Co-pyrolysis of coal with biomass residues and coke breeze for superior quality coke via hot pressing technology

Abstract

Superior quality coke is essential in the metallurgical industry. However, the coking coal source is limited. The biomass or breeze could be blended into the coking coal to produce high-standard cokes by hot pressing technology. High-standard cokes should have low reactivity (chemical reaction intensity of coke and CO2 at high temperature) and high strength. The influences of biomass category and blending ratio on pore structure, reactivity and crushing strength of cokes were explored. Pore evolution during the coking process was studied by experiments and simulations to reveal the mechanism of producing high-quality cokes with biomass and breeze blended into coking coal via hot pressing technology. Results show that hot pressing technology can make high-quality cokes when the blending ratio of biomass or breeze is appropriate. When 5% bamboo, wood or straw is blended to produce hot-pressed coke, the coke reactivity decreases by 6.58%, 7.66% and 6.41% and the crushing strength increases to 1.15, 1.19 and 1.12 times when compared with coke in case of no blending and no pressing, respectively. The proper blending ratio of the three biomasses should be less than 15% because the coke quality deteriorates greatly when the blending ratio increases to 15%. If the breeze is mixed with coal to produce high-standard cokes under hot pressing conditions, the blending ratio should not exceed 30%. Hot pressing technology can reduce the coke pores when the biomass or breeze is blended into the coal with a low ratio. When 5% bamboo or 10% breeze is blended, the porosity of hot-pressed coke in the center region decreases by 5.69% and 4.02% than coke with no blending and no pressing, respectively. The low porosity contributes to the reduction of coke reactivity. The fewer pores, thicker pore walls and higher carbon matrix strength impede the growth of cracks, resulting in a higher coke crushing strength. Therefore, hot pressing technology can effectively enhance coke quality if the biomass or breeze is mixed with the coking coal with an appropriate blending ratio.