Experimental Study On The Pyrolysis Mechanism Of Sewage Sludge

The pyrolysis of sewage sludges was conducted in a slowly heating and gas sweeping fixed-bed reactor.The yields of the four major gases produced?H₂,CO,CH₄ and CO₂?were quantitatively analyzed on a gas chromatograph.The concentrations of the compounds in the pyrolysis liquids were semiquantitatively examined using GC×GC-TOFMS.The pyrolysis mechanism of the sewage sludge was analyzed online using in situ FTIR from ambient temperature to 600°C.The important role played by the mineral matters in the process of sewage sludge pyrolysis was studied by adding alkali or alkaline earth metals.The catalytic effect of sewage sludge char on the pyrolysis volatiles was studied to optimize the compositions of the gas and liquid products.The main conclusions are included as follows:The liquid products derived from the pyrolysis of sludge were fully examined using GC×GC-TOFMS,and more than 5100 compounds were detected.The main compounds in the liquid products were classified based on their functional groups into five chemical groups:?1?monoaromatics,?2?PAHs,?3?nitrogen-containing compounds,?4?oxygen-containing compounds and?5?cyclosiloxanes.The mechanism of the pyrolysis of the sewage sludge was analyzed online using in situ FTIR,and the trend of the functional groups in the sewage sludge was consistent with the variation of the chemical composition of the pyrolysis gas and liquid.The addition of alkali or alkaline earth metals accelerated the reduction of the relative yield of most compounds in sewage sludge pyrolysis liquids.The trend of the functional groups in the sewage sludge was consistent with the variation of the chemical composition of the pyrolysis liquids.The increasing secondary reaction temperatures or the catalytic effect of sewage sludge char led to a release of H₂ and CO at a lower pyrolysis temperature?325??.Normally,with the catalytic effect of char,aliphatic compounds in the sewage sludge pyrolysis liquids decomposed into gas.With the increasing char,aromatic compounds in the liquids will decompose,as well.