Experimental study on pyrolysis tar removal over rice straw char and inner pore structure evolution of char

A lab scale two staged hot rod reactor was constructed to stimulate the two staged downdraft biomass gasifier. The present study focused on the heterogeneous conversion of the pyrolysis tars over biomass char. A typical Chinese agricultural waste, the rice straw, was chosen for the raw material and the source of the biomass char. Effects of the temperature, the presence of the char and pretreatments of the char, including the water washed char and the char added with K2CO3 powder, on the pyrolysis tar removal were investigated. The products of tars were qualitatively and quantitatively analyzed. The evolution of the inner pore structure of chars with different temperatures and residence times was also investigated. The char bed condition exhibited higher tar conversion efficiency than the thermal cracking condition. The results indicated that the presence of the char could catalytically promote the formation of alkyl monoaromatics and meanwhile inhibit the formation of PAHs (polycyclic aromatic hydrocarbons) from the primary tars. The alkali metal elements might play a key role for the catalytic effect of the char. The appropriate increases in the temperature and the residence time for the char production could promote the development of the micro pores in chars.