Polycyclic aromatic hydrocarbons formation in coal direct chemical-looping combustion of CaSO4 / bentonite oxygen carrier

To control the formation of polycyclic aromatic hydrocarbons ( PAHs) and reduce the carbon deposition phenomenon on the surface of oxygen carrier,the mechanical mixing method to prepare CaSO4 / bentonite oxygen carri- er was adopted to react with coal in a simulated chemical-looping combustion (CLC) fuel reactor. Gas chromatography was employed for qualitative and quantitative analysis on PAHs. The emission characteristics of PAHs were discussed at different coal types,temperatures and oxygen carriers / coal ratios. The results show that with the volatile increasing, the total amount of PAHs formation at different coal types is in the order as anthracite< bituminous coal 1< bituminous coal 2< bituminous coal 3. PAHs formation is also influenced by carbon content,n(H) / n(C) and n(O) / n(C) ratio. In the CLC process,2-ring and 3-ring PAHs are predominant as 4-ring and 5-ring PAHs are relatively small,while 6- ring PAHs is not produced. When the temperature is 900 ℃ and oxygen carrier / coal ratio is 2. 4,the total amount of PAHs formation is the least in the reaction of CaSO4 / bentonite oxygen carrier and bituminous coal 3.