Analysis on the chemical compositions of the tar from sewage sludge gasification in a fluidized bed reactor

The influence of the gasification temperature(650, 750 and 850℃)and sludge types on the yield and chemical compositions of tar produced by the air gasification of sewage sludge in a fluidized bed gasifier was studied by GC-MS analysis. The results show that the yields of tar decrease with gasification temperature increasing, and the yields of tar from anaerobic digestion sludge gasification are lower than that from indigested sludge gasification. The chemical compositions of tar can be divided into five categories:aliphatic compounds, alicyclic compounds, aromatic hydrocarbons, aromatic hydrocarbon derivatives and heterocyclic compounds. When the gasification temperature increases, the yields of aliphatic and alicyclic compounds in the tar from the gasification of indigestion sludge produced by Anaerobic-Anoxic-Oxic (A²/O) process decrease; the yields of aromatic hydrocarbon derivatives in the tar increase; and the yields of aromatic hydrocarbons and heterocyclic compounds firstly increase and then decrease. At 650℃, the yields of all the organic compounds in the tar from the gasification of digestion sludge produced by activated sludge process are lower than that from the indigestion sludge gasification; the yields of aromatic hydrocarbons in the tar from the gasification of the digestion sludge produced by A²/O process are higher than that from the indigestion sludge gasification; and the yields of the other organic compounds are lower than that for the indigestion sludge gasification.