Research On The Thermochemical Conversion Mechanism And Gasification Characteristics Of Sludge

Thermal conversion technology is considered as an attractive approach to realize the capacity reduction,reduction and resource recycling of sludge.Two sludge samples,which were generated from municipal and chemical industry sewage treatment plants,were taken as the research object in this work.Based on its physical-chemical analysis,the mechanisms of different thermal conversion process of sludge were studied using Thermo-gravimetric analysis coupled with Fourier Transform Infrared Spectroscopy technology?TG-FTIR?.Furthermore,the characteristics of sludge gasification under CO₂ atmosphere were conducted with a bench scale gasifier.The thermo-chemical conversion mechanism of sludge under different atmosphere and different heating rate was studied with TG-FTIR method.Different atmosphere of air,CO₂ or N₂ is related to different thermal conversion process,i.e.incineration,gasification and pyrolysis,respectively.Thermal analysis method was used to analyze the behavior of weight loss and kinetic characteristics of sludge.In different thermal conversion process,the first two reaction stages were similar and considered as the water evaporation and volatile release.The heating rate was observed to be related with the maximum weight loss rate of sludge.At the same time,the kinetic parameters such as activation energy and frequency factor of sludge also changed accordingly.The activation energy,maximum weight loss rate and heating rate have a positive correlation.The temperature of main reaction zone also moved to high temperature area.The properties of products in different thermal conversion process were analyzed with FTIR spectrum.It shown that the intensity and width of the absorption peaks of C-O,C-C,C=O,O-H and C-H in reaction products were all negatively correlated with the reaction temperature.The absorption peak of H2 O,CH4,CO₂,CO and NH3 in syngas reached the maximum absorption value with the increasing temperature,and then declined.CH4 and CO increased obviously with the increase of temperature.CH4 mostly came from the secondary reaction of sludge.In low temperature stage,CH4 mainly came from the poly-condensation of free hydrogen ions.In high temperature stage,CH4 was related to decomposition and recombination of functional groups?-CH2-,-CH3-?.The products also contained NH3 and carbonyl compounds.In order to further study the gasification mechanism of sludge,a small bench scalevertical gasifier was used to carry out the gasification experiments under CO₂ atmosphere with the final gasification temperature of 800 ?,900 ? and 1000 ?.The formation regularity and distribution of the major products of syngas were analyzed by Micro GC.The results showed that the sysgas mainly contained CO,CH4,H2,etc.The amount of CO was higher than CH4 and H2.CO was generated and released in the temperature range of400-830?.CH4 and H2 were produced after 400 ?.H2 reached the maximum generation peak firstly with the increasing temperature,while CH4 generation obviously increased above800?.