Preparation of high-strength biochar composite briquette for blast furnace iron making

In this research, using iron-oxide fines (average size: 2.5 mm) and biochar fines (average size: 50.0 mm), the biochar composite briquette (BCB) for blast furnace (BF) application was prepared by cold briquetting followed by heat treatment. The preparing conditions were optimized regarding its cold crushing strength. Anti-pulverization capability, reaction development, and structure evolution of the optimally designed BCB under simulated BF conditions were then examined. Results of optimizing BCB preparation conditions showed that a heating temperature of 1073 K was optimal for preparing the BCB. The optimally designed BCB contained 11.10 wt.% carbon, 72.21 wt.% Fe₃O₄, 11.25 wt.% FeO, and 0.77 wt.% Fe, 6.44 wt.% gangue, and had a cold crushing strength of 1800 N/briquette. Results of BCB behavior under simulated BF conditions showed that the cold crushing strength after partial reaction of the BCB ranged from 1500 N/briquette to 5500 N/briquette and its maximum volume shrinkage degree was 0.45. The high anti-pulverization capability of the BCB was supported by the slag matrix or the iron network. Under the simulated BF conditions, the BCB underwent five stages of reduction by atmosphere, partial self-reduction and reduction by atmosphere, full self-reduction, partial self-reduction and gasification by atmosphere, and gasification by atmosphere. It is inferred from the experimental findings that, by charging the BCB in BF, an increase of top gas utilization efficiency could be realized, and a favorable influence on lowering the temperature level of the thermal reserve zone could be obtained. (authors)