Rapid pyrolysis of brown coal in a drop-tube reactor with co-feeding of char as a promoter of in situ tar reforming

A Victorian brown coal (Loy Yang, LY) was co-fed with char prepared from the same coal in an atmospheric drop-tube reactor (DTR) at 900 and 950 °C in the presence of 50% steam to study in situ reforming of tar derived from rapid pyrolysis of brown coal over a char surface. Two different chars were prepared, including devolatilised LY at 800 °C under nitrogen flow (LYC, surface area 524 m²/g) and LYC gasified with steam at 900 °C (GLYC, surface area 734 m²/g). The concentrations of chars in the blended samples varied from 50% to 85% on a carbon basis. The yield of tar derived from LY (no char was blended) was 4.2 wt.% at 900 °C and particle residence time around 3-4 s. The yield decreased with increasing char concentration, and was 0.5 wt.% at a GLYC concentration of 85% at 900 °C. Tar conversion over GLYC was more extensive than that over LYC and occurred more significantly at a higher temperature. Increasing the feeding rate of sample particles enhanced tar reforming, suggesting that solid hold-up was an important factor determining tar conversion characteristics. Liquid chromatography (LC) showed that the major components of heavy tar included typical polycyclic aromatic hydrocarbons (PAHs) ranging from three-membered rings (acenaphthylene) to seven-membered rings (coronene).