Investigation On Characteristic Of Sludge Drying & Co-combustion And Its Harmless Disposal In MSW Incinerator

With the continuous development of national economy and the acceleration of urbanization process,the production of municipal sludge and industrial sludge sharply increases.However,the proportion of sludge with harmless disposal was relatively low,thus it is imminent to promote the sludge treatment of harmlessness,minimization and recovery.In this paper,the experimental investigations about sludge drying and combustion characteristics were conducted to analyze the factors that affected its drying and combustion performance.Also,CFD(Computational Fluid Dynamics)method was adopted to research the harmless disposal of sludge in MSW incinerators through numerical study.The results of this study are as follows:1.The drying profiles of municipal sludge with additives(including straw and Ca O)were investigated through isothermal drying experiments in online weighting,and its effect mechanism was analyzed.The results show that temperature was the main factor that influenced the drying period and drying rate.As the increase of temperature,the acceleration of sludge drying increased,but the decrease range of drying period declined.With the addition of 1%,2% and 3% straw,the drying rates of sludge obviously improved,but it would reduce as the addition ratio increased to 5%.Therefore,appropriate addition of straw played a role of framework for sludge drying.The sludge would adhere to the straw to form three-dimensional network structure,which sharply increased the surface area of sludge,so the drying rates significantly improved.The addition of Ca O raised the PH value of sludge,and broke its granular cell structure,making the intracellular water into surface absorbedwater.Calcium ion could be absorbed by humus acid in sludge,forming porous grid framework.The framework restrained the shrink of sludge and weakened the crusting phenomenon,so themoisturediffusion resistance decreased,and the surface area of sludge was efficiently increased.2.The drying kinetics of sludge was investigated by drying sludge at different conditions,and a novel drying kinetics model was proposed.Based on the online weighting drying experiments,the existing several drying kinetics models were applied for theoretical calculation and analysis of experimental data.Through the fitting of sludge drying experiments,a novel drying kinetics model(exp(())nMR =a-kt +b)was proposed.For pure sludge,sludge/straw mixtures and Ca O/sludge mixtures,the determination coefficient(R2)of the novel model was the highest value among all of the coefficient values(0.99913-0.99992),and root-mean-square error(RMSE)was the lowest(0.00295-0.00920),so did the variance(?2)0.00001-0.00008).It indicated that the new model could better describe the drying process of these three materials.3.The combustion characteristics of paper mill sludge,paper sludge/biomass mixtures and paper sludge/coal mixtures were investigated through thermogravimetric analysis.The kinetics parameters of combustion were obtained,and the interaction in the mixing combustion was analyzed.The results show that among straw,eucalypt and bagasse,eucalypt had best combustion performance and bagasse was the worst when mixed with paper sludge.When the weighting ratio of straw in mixture was 30%,there was the minimum average activation energy of 139.01 k J/mol(Friedman)and 143.39 k J/mol(FWO).When the weighting ratio of eucalypt was 10%,there was the minimum average activation energy of 162.74 k J/mol(FR)and 167.03 k J/mol(FWO).When the weighting ratio of eucalypt was 10%,there was the minimum average activation energy of 173.69 k J/mol(FR)and 171.78 k J/mol(FWO).From the experiment results of paper sludge combustion mixing with different coal,the combustibility performance was the best while mixing with lignite,and was the worst while mixing with bituminite.The performance of ignition,burnout and combustion was improved with the increase of coal/sludge ratio.When the weighting ratio of lignite was 10%,the average activation energy in minimum was 65.19 k J/mol(FR)and 70.11 k J/mol(FWO).When the weighting ratio of lignite was 30%,the average activation energy in minimum was 49.58 k J/mol(FR)and 59.90 k J/mol(FWO).4.The numerical model of MSW grate furnace combustion was built adopting CFD technology,and the reliability of this model was verified by the actual operation data.Using this model,the combustibility performance and pollutants emission characteristics of sludge with different moisture content and sludge/MSW with different ratio were analyzed,then the feasibility of harmless co-treatment of sludge and MSW was verified.The results show that the errors between measurement values and prediction values were lower than 5.68% at different positions.As the sludge mixing ratio increased,the weight loss ratio declined from 80.2% to 72.4%.CO content at the first vertical flue outlet was lower than 5×10-4mg/Nm3,and NO content at the same position was 104.8 mg/Nm3.The average velocity of flue gas in vertical direction was 2.6 m/s,ensuring the residence time of flue gas at the first flue over 850°C was more than 2 s.At last,the feature of this paper was evaluated,and the key conclusion and innovation points were summarized.In addition,the expectation and the further research targets were proposed.