| The combustion characteristics of municipal sludge and coal gangue and the migration and transformation law of heavy metals determine the possible direction of their resource utilization.Based on the data of industrial analysis,calorific value of bomb,mercury and occurrence form content,combined with thermogravimetric experiment and temperature-programmed experiment,the combustion characteristics of municipal sludge and coal gangue samples were studied in this paper.Meanwhile,the release rule of mercury occurrence form in the samples was discussed,aiming to provide data reference for mercury pollution control process of low calorific value fuel resource utilization.The research content and main conclusions of this thesis are as follows:The combustion performance of municipal sludge and coal gangue was analyzed by thermogravimetry.The weight loss curve of 1#sludge/2#sludge combustion was divided into four weight loss stages.The weight loss curve of coal gangue combustion is divided into three weight loss stages.Mixing sludge in coal gangue will reduce the ignition temperature and burnout temperature of the mixture,accelerate the combustion reaction and shorten the combustion cycle.The results of combustion kinetics show that the maximum weight loss rate increases with the increase of sludge blending ratio of coal gangue,and the internal mechanism of this phenomenon is that the activation energy of the reaction decreases within the range,which promotes the combustion reaction.The decrease of O2 concentration in the combustion atmosphere will increase the weight loss temperature range of the mixture,reduce the comprehensive combustion characteristic index Dc,and deteriorate the combustion performance of the sample.With the increase of heating rate,the weight loss region of G1/G2 mixture moves to the high temperature region,and the sample ignition temperature and burnout temperature increase.The sequential chemical extraction was used to find that there were differences in the forms of mercury in sludge and gangue.The 1#sludge mainly existed in sulfate,carbonate and oxide combined state and residue state,accounting for more than 80%of the total mercury.The mercury form in 2#sludge is mainly carbonate,oxide combined state and residue state,accounting for about 70%of the total mercury content.The main forms of mercury in coal gangue are sulfide binding state and residual state,accounting for more than 85%of the total mercury content.Combined with the temperature-programmed combustion experiment,it is concluded that the mercury released in the low temperature zone of 200℃ to 390℃is mainly organic bonded mercury and carbonate bonded mercury,while the mercury released in the high temperature zone of 390℃ to 450℃ is mainly sulfide bonded mercury.In the low temperature area of 300℃ to 400℃,the mercury released from coal gangue is mainly organic bonded mercury,carbonate bonded mercury and oxide bonded mercury,while in the high temperature area of 400℃ to 600℃,the mercury released is mainly sulfide bonded mercury and some oxide bonded mercury.Sludge mixing promoted the mercury in the mixture to release in the low temperature area in advance,and the promotion effect became stronger with the increase of sludge mixing rate.With the increase of oxygen content in the atmosphere,CO2 produced in the combustion process will be adsorbed on the surface of the particles and increase the heat transfer resistance,thus inhibiting the release of organic-bound mercury and some carbonate-bound mercury in the mixture.Meanwhile,it was found that the effect of atmosphere on the release behavior of mercury in the high proportion of sludge mixture was reduced. |
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