Multi-stage coking for increased tar yield and formed coke of high strength. 2. Rapid heating carbonization in the multi-stage coking of weathered coal blends

Two stage coking was applied to a blend of coking coals which had been stored in air for a long time. Although the blend provided a little less tetrahydrofuran-soluble (THFS) residue (13%) after the preheat treatment at 450 °C than the unoxidized coals, the formed coke of tetrahydrofuran-insoluble (THFI) residue failed to provide enough mechanical strength for blast furnace application after calcination at 1000 °C when the heating rate at the carbonization stage was 10 °C min^-1. More rapid heating at 50 °C min^-1 gave a high mechanical strength of 6 MPa by calcination at 700 °C, yielding 5% additional tar. The coke prepared from the extracted residue, through the controlled THF extraction yield of 10%, exhibited a high strength of 10 MPa after calcination at 800 °C when the carbonization heating rate was 10 °C min^-1. Favourable influences of rapid heating against less fusible residue are discussed.