Production of coke from lignites was studied in continuation of a previous study that demonstrated effectiveness of a sequence of hot briquetting and carbonization on preparation of high strength coke from a lignite. Cokes were prepared from four Indonesian lignites with or without pretreatments such as hydrothermal treatment (HT) at 200−300 °C, acid washing (AW), and a combination of them (HT−AW). The hot briquetting of the raw lignites at temperature and mechanical pressure of 200 °C and 128 MPa, respectively, enabled cokes to be produced with a tensile strength (TS) of 7−22 MPa. The pretreatments, AW and HT at 200 °C (HT200), increased TSs of resulting cokes to 18−24 and 13−36 MPa, respectively. A sequence of HT200 and AW further increased TSs of cokes to 27−40 MPa. AW and HT200 modified the macromolecular structure of the lignites by different mechanisms. AW removed alkali and alkaline earth metallic species that played roles of cross-links in the macromolecular network, while HT200 rearranged macromolecules physically. Both HT and AW enhanced plasticization and then deformation/coalescence of lignite particles during the briquetting, which formed high strength briquettes. There were strong correlations between TS of coke and that of briquette and also between TS and bulk density of coke from the individual lignites.
The steelmaking industry requires coke as a reducing agent, as an energy source, and for its ability to hold slag in a blast furnace. Coking coal as raw coke material is very limited. Studying the use of biomass as a mixture of coking coal in the synthesis of biocoke is necessary to reduce greenhouse gas coal emissions. This research focuses on biomass and heating temperature through the coal blending method to produce biocoke with optimal mechanical properties for the blast-furnace standard. The heating temperature of biomass to biochar was evaluated at 400, 500, and 600 °C. The blending of coking coal with biochar was in the compositions of 95:5, 85:15, and 75:25 wt.%. A compacting force of 20 MPa was employed to produce biocoke that was 50 mm in diameter and 27 mm thick using a hot cylinder dye. The green sample was heated at 1100 °C for 4 h, followed by quenching with a water medium, resulting in dense samples. Increasing heating temperature is generally directly proportional to an increase in fixed carbon and calorific value. Biocoke that meets several blast-furnace criteria is a coal mixture with coconut-shell charcoal of 85:15 wt.%. Carbonization at 500 °C, yielding fixed carbon, calorific value, and compressive strength, was achieved at 89.02 ± 0.11%; 29.681 ± 0.46 MJ/kg, and 6.53 ± 0.4 MPa, respectively. This product meets several criteria for blast-furnace applications, with CRI 29.8 and CSR 55.1.
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