Research On CO₂ Gasification Characteristics Of Industrial Sludge And Its Experiment Of Co-gasification With Coal And Waste Activated Carbon

With the rapid development of industrialization,the production of industrial sludge has been increasing year by year,which has brought a great threat to the environment.Gasification method has been paid much attention with its advantage of low secondary pollution and high energy utilization rate.Based on the preliminary study on the preparation of sludge derived fuel（SDF）and the pilot experiment of gasification and melting of SDF,the hazardous industrial sludge was selected as the research object in this work to furtherly investigate the gasification mechanism of industrial sludge and the co-gasification characteristics of mixture of sludge with coal or waste activated carbon.CO₂was applied as the gasification agent.The gasification characteristics of pure sludge were investigated firstly.On this basis,the co-gasification of sludge with coal or waste activated carbon at different mixing ratios were studied.Firstly,TG-FTIR combined technology was used to study the thermo-chemical conversion characteristics of sludge under CO₂ and N₂ atmospheres.The influence of atmosphere on the pyrolysis or gasification process of industrial sludge was investigated.The weight loss,product releasing and reaction kinetic parameters at different reaction stages under N₂/CO₂ atmosphere were mainly analyzed.The influence of CO₂ on sludge weight loss and conversion mainly showed in temperature range above 700℃.In this stage CO₂ participated in gasification reaction and the weight loss rate greatly increased.This promoted the generation of CO,CH₄ and NH₃at high temperature.FTIR analysis showed a large number of methyl compounds released at around 1000℃,and the releasing strength was much higher in CO₂atmosphere.The activation energy of each reaction stage gradually increased with the increase of temperature.The activation energy of CO₂ gasification was slightly lower than that in the same reaction stage under N₂ atmosphere.The influence of temperature（800℃,900℃,1000℃）and CO₂ flow rate on industrial sludge gasification characteristics was studied with a horizontal fixed bed gasifier.The composition of syngas generated during gasification process was analyzed with Gas Chromatograph（GC）.It was shown that the CO,H₂ and CH₄were the main combustible component in syngas.The gasification of this sludge could be well performed under low CO₂ flow rate due to its low carbon content.With the increasing CO₂ flow rate,the proportion and the maximum releasing rate of CO,H₂and CH₄ decreased due to the dilution effect.Gasification temperature showed the significant influence on gasification reaction rate.The maximum gas production rate increased with the increasing temperature,and the time required to reach the maximum releasing rate decreased.The proportion of CO in syngas gradually increased with the increase of temperature,but the increment decreased.H₂ and CH₄showed a downward trend with the increase of temperature.Coal and waste activated carbon were mixed with sludge at the mass ratios of 40%and 80%,respectively,to investigate the influence of different materials and their mixing ratios on the thermo-gravity transformation properties and the co-gasification characteristics in fixed bed gasifier.The synergistic effect during co-gasification were observed in the stage of coke gasification.When the mixing ratio was 40%,the synergy effect was more significant and the activation energy was also lower.The addition of coal and waste activated carbon increased the volume proportion of H₂ and CH₄ in syngas.The volume fraction of CO gradually increased with the increase of CO₂ flow rate.The addition of waste activated carbon showed similar effect on the promotion of CO,H₂ and CH₄ production compared with coal.It is considered that the waste activated carbon can be used to replace coal for collaborative waste disposal with industrial sludge.