Utilization of coal tar residue as a binder for coal slime in the preparation of high-strength formed char: The functional mechanism during the carbonization process

Abstract

For the purpose of efficiently recycling two types of carbon-containing solid wastes, namely coal slime (CS) and coal tar residue (CTR), high-strength formed char was prepared through cold pressing and carbonization methods, and interaction during carbonization process of CS and CTR was investigated. Results demonstrated that higher temperature led to lower calorific value of formed char, with lowest calorific value achieved when CTR addition amount was 10 %. As CTR addition amount increased, strength of formed char was significantly enhanced, indicating that CTR addition amount and carbonization temperature are main factors influencing strength and calorific value of formed char. Further research revealed that due to volatile content of CTR being higher than that of CS, when CTR addition amount ranged from 0 to 10 %, CTR would promote release of volatile components, resulting in decrease in calorific value, C and H contents. As CTR addition amount increased from 10 % to 20 %, generated heavy oil would deposit acicular crystals and flocculent gels in cracks, strengthening internal crack structure of formed char and enhancing its strength. A large amount of heavy oil condensed in cracks, blocking cracks, suppressing decomposition of unsaturated hydrocarbons, and increasing calorific value of formed char. In conclusion, when CTR addition amount and temperature were 20 % and 600 °C respectively, formed char exhibited maximum calorific value and strength.