Analysis of product distribution and quality for continuous pyrolysis of coal in different atomspheres

The continuous coal pyrolysis at 850 ℃ in a fluidized bed reactor under atmospheres containing O₂, H₂, CO, CH₄, N₂ and CO₂ were carried out. The char product was characterized using Raman, BET and TGA (for evaluating reactivity). The results show that without O₂ in the atmosphere, adding H₂ and CO₂ lowers the pyrolysis tar yield which is conversely higher with raising the CO and CH₄ contents in the atmosphere. The introduction of O₂ promotes the formation of CO and CO₂, and thus the yields of tar and char decrease. The char yield increases with the addition of CH₄ into the pure N₂ atmosphere, which is ascribed to the cracking of CH₄. PAHs content decreases with the addition of O₂ into N₂ atmosphere. CH₄ promotes the production of alkyl-substituted naphthalenes and benzenes. CO inhibits the cracking of phenols to form benzenes. CO₂ facilitates the formation of new micropores or opening of the closed pores, producing the chars with high surface area and the corresponding highest oxidation reactivity. The carbon deposition via CO disproportionation and CH₄ cracking in the presence of CO/CH₄ blocks some pores and thus lowers the surface area and reactivity of the char. The char produced with the inclusion of H₂ and CH₄ results in a more condensed crystallite structure via hydrogen radicals penetration and thus lowers the oxidation reactivity.