Distribution Characteristics of Coking Products and Mechanism of Tar Lightening in Preparation of High-Strength Gasification-Coke with Low-Rank Coal Blending

Abstract

During the preparation of high-strength gasification-coke with low-rank coal blending, evolution of pyrolysis tar and gas is still unclear for situations where large amounts of low-rank coal are blended. Herein, the effect of low-rank coal blending on the distribution of coking products was thoroughly investigated and the mechanism of tar lightening was studied by simulating the coking process with 1 kg laboratory-scale coke oven. The results showed that more liquids but less gases were formed compared to the theoretically calculated values due to a stronger cohesive interaction in the coal blending system. Moreover, the gas yield and volatile matters in dry ash-free basis (Vdaf) showed an opposite linear correlation for single coal and blended coal, probably due to this strong cohesive interaction. The facileness of long-chain aliphatic hydrocarbons to crack into low-molecular-weight hydrocarbons is attributed to their weaker interactions with more low-rank coal blends. The low-rank coal blending significantly promoted the release of phenols due to the presence of hydrogen-donor groups. In addition, more fractured branched alkanes inhibited the deep condensation of free radicals (cohesive compounds), which led to tar lightening in the low-rank coal blending system. In contrast, in the caking coal blending system (without the addition of low-rank coal), aromatization of fractured olefin terminals promoted deep condensation of cohesive free radicals, resulting in the formation of more heavy tar. The current study also demonstrated that the conversion of heavy tar into light products could be promoted by adjusting the input of low-rank coal during the caking coal upgrading process, thereby increasing the profitability of the coking process.