The Study On Kinetics Of Sludge-Mixing Pyrolysis/Combustion Based On Distributed Threshold Energy Model(DTEM)

Sewage sludge,which is a complicated by-products of municipal wastewater disposal process,contains a large amount of toxic substances.Themochemical conversion is one of effective technologies for sludge's reduction,innocuity and resource utilization.However,the direct use of sludge is limited becasue of its intrinsically physicochemical property,and co-utilization is more appropriate.After blending with sewage sludge,a complex reaction system formates inside the feedstock,leading to the variation on reaction characteristics and kinetic behavior.The reactor should be rectified and optimized for the new status of feedstock.The blends are more complex than the original feedstock,and the conventional kinetics methods are no longer practical and efficient for modeling such reaction.In recent years,DAEM,distributed activation energy model,shows great advantages on the application of modeling complex reaction system.Equipping with global optimization algorithm,DAEM could reach at a tremendous level of fitness,and the operation is convenient.In this study,we deduced a specific DAEM which was called DTEM(distributed threshold energy model)through a combination of the DAEM,TAK(thermal analysis kinetics)and collision theory.The molecule group collision model could interpret the compensation effect of DTEM qualitatively.Three situations of co-utilization were used to test DTEM for its possibility of wide application.We also compared the DTEM with single/mutiple-heating-rate models to see the difference between them.Three situations were: co-pyrolysis of sewage sludge and oil shale,co-combustion of sewage sludge and oil shale,co-pyrolysis of bagasse and sewage sludge.And every single situation's heating rates were set as: 10~50°C/min(interval = 10°C/min)?10~30°C/min(interval = 10°C/min)?10~25°C/min(interval = 5°C/min).The relevant kinetic models included four-pseudocomponents DTEM,single-pseudocomponent DTEM,FWO-first-oder model,FWO-n-order model,Coats-Redfern-evaluation-function model,Coats-Redfern-direct-linearization model.Based on the total fitness on experimental data,these models were put in descending order: 4-pseudocomponents DTEM >single-pseudocomponent DTEM > FWO-n-order model > FWO-first-oder model >Coats-Redfern-evaluation-function model > FWO-first-oder model ?Coats-Redfern-direct-linearization model.Among these models,DTEM has the best fitness.Most of sample's fitnesses,which is modeled by the single-pseudocomponents DTEM,reached at over 0.99 which is even over 0.999 when they are modeled by four-pseudocomponents DTEM.Besieds,DTEM also keeps the highest level among other models.In DTEM,the global threshold energy of blending sample has a good linear relation with the mass proportion of sewage sludge.In single-pseudocomponents DTEM,the global threshold energies were 195.8~234.8kJ/mol,197.16~221.41kJ/mol,187.57~196.19kJ/mol for sludge-shale pyrolysis,sludge-shale combustion,sludge-bagasse pyrolysis respectively.All of three situations have approximately equal global threshold energy to that of single-pseudocomponent DTEM,and acoording to the result of this study,this phenomenon could be generalized as a three-points guesses of global threshold energy:This research performed preliminary discusstion of DTEM theory based on collision theory,and the experimetal verification on DTEM was valid.Comparing with the regular single/multiple heating rate methods,DTEM has many advantages for modeling experimental data,and this method provides a unique route for the modeling theory of apparent kinetic analysis.