Semicoke is usually a solid carbonaceous product obtained from low - and medium-temperature retorting and pyrolysis of low - rank coal as raw material. It also produces coal tar, gas and so on. It is a traditional form of coal qualitative utilization.
From the chemical point of view, low rank coal is a macromolecular aggregate formed by condensation of aromatic ring, aliphatic chain and other functional groups. It contains not only 60% ~ 80% (mass fraction) of solid components represented by amorphous carbon and ash, but also up to 10% ~ 40% (mass fraction) of volatile components of inherent oil and gas represented by paraffins, aromatic hydrocarbons and carbon and oxygen branch chains . The oil and gas volatiles of coal are first extracted by pyrolysis, which can not only realize high value-added utilization of high-quality components, but also the quality of pyrolyzed blue carbon is far better than that of raw coal.
Table 1 shows the energy conversion efficiency, coal consumption per unit product, fresh water consumption, CO2 emission and investment intensity of coal gasification, liquefaction and pyrolysis. Among them, the system parameters of coal pyrolysis to produce blue carbon are the best, which is significantly higher than other coal conversion processes.