Product distribution and reactivity of coal pyrolysis at high temperature and in atmospheres containing O₂/steam

The product distribution and reactivity of coal pyrolysis at temperatures up to 850 ℃ and in atmospheres containing O₂ and steam were studied. The effects of reaction temperature, equivalent air ratio (ER) and the mass ratio of steam to coal (S/C) were examined. The gas yield increased with the increases of the temperature, ER and S/C, whereas the yields of char and tar correspondingly decreased. When O₂ was present in the atmosphere, the CO₂ and CO productions obviously increased, while that of H₂ decreased. The simultaneous presence of O₂ and steam in the atmosphere improved the specific surface area and reactivity of the resultant char. However, the gasification reactivity of char produced at 900 ℃ in N₂ and/or in an atmosphere with an ER 0.22 at 850 ℃ was low because of occurrence of carbon graphitization. The inclusion of O₂ and steam into the atmosphere had a great effect on the tar properties. Compared with pyrolysis in pure N₂, the tar produced in O₂ and steam contained fewer single-ring aromatics and phenolic, ketonic and aliphatic hydrocarbons, which made the tar more reactive for cracking and reforming.