Characterization Of Sewage Sludge And Municipal Solid Waste Incineration Fly Ash Co-processes In Cement Kilns

Sewage sludge and municipal solid waste incineration fly ash have the characteristics of high yield,scattered distribution and high hazard,and separate disposal is restricted by technology,equipment and other conditions,and new disposal technologies are being studied to achieve better resource utilization while reducing the impact on the environment.Existing cement industry rotary kiln has a high temperature thermal environment of 800～2000℃and a complete pollutant emission removal system,with direct conditions and inherent advantages for solid waste disposal,which can realize the harmless disposal of solid waste while producing cement clinker.In terms of basic characteristics,cement rotary kilns have direct conditions for co-disposal of these two types of solid wastes.Meanwhile,the high moisture content of municipal sludge can effectively reduce the release of soluble salt ions in waste incineration fly ash,while the high calcium,p H and salinity characteristics of waste incineration fly ash can also significantly improve the conditioning and dewatering properties of municipal sludge,and the co-disposal of the two is theoretically feasible.Therefore,co-disposal of sewage sludge and municipal solid waste incineration fly ash in cement kilns is a potential way to treat these two types of solid wastes.In this paper,the feasibility of co-disposal of sewage sludge and municipal solid waste incineration fly ash in rotary kilns is investigated and analyzed through a combination of experiments and simulations,with municipal sludge,waste incineration fly ash and their mixed raw materials as the main research objects,and theoretical support is provided for industrial practical co-disposal.The specific research contents of this paper are as follows:（1）The thermal weight loss,kinetics,co-disposal characteristics,and their synergistic effects of sewage sludge,municipal solid waste incineration fly ash,and their mixed raw materials are studied through thermogravimetric experimental analysis under different atmospheric conditions.The results show that the synergistic effect of sewage sludge and municipal solid waste incineration fly ash mainly occurs in the two stages of devolatilization and volatile fraction combustion,and the most significant mutual promotion effect occurs when the mass proportion of sewage sludge is 60%,in which the maximum heat loss rate difference between the actual DTG curve and the theoretical weighted DTG curve occurs at460℃is 0.78%.According to the experimental results of thermal weight at different ramp rates,it was shown that when the ramp rate was at 25°C/min,the amount of mixed feedstock residue was less and the feedstock disposal was better.When the mass of sewage sludge was in the range of 60～100%,the difference between the integrated combustion characteristics indexes of mixed samples at the same heating rate was in the range of 4.3x10^-8～5.7x10^-7,at which time the mass share of municipal solid waste incineration fly ash had little effect on the integrated combustion characteristics indexes of mixed raw materials.The results of the kinetic parameters of mixed raw materials analyzed by four models of FWO,Starink,and CR show that in the process of co-disposal of sewage sludge and municipal solid waste incineration fly ash,the activation energy changes show a trend of first increasing and then decreasing with the increase of the mass proportion of municipal solid waste incineration fly ash,which indicates that there is an inflection point in the process of increasing the mass proportion of municipal solid waste incineration fly ash,and after this inflection point,the activation energy of mixed samples increases again when the mass proportion of municipal solid waste incineration fly ash is increased.After this inflection point,the activation energy of the mixed sample will show a decreasing trend,thus making the reaction easier.（2）The existing one-dimensional non-stationary combustion model BASIC was used to simulate the combustion process of mixed feedstock fixed bed accumulation at 80%and 60%of sewage sludge mass ratio,and according to the simulation results,it can be seen that the first 70 seconds of the mixed feedstock combustion process is mainly the water evaporation stage,and then enters the stable combustion stage in the time interval of 100～200 seconds,during which the combustible material in the mixed feedstock reaches the ignition point When the mass of municipal solid waste incineration fly ash accounts for a larger proportion,the transformation layer of the volatile fraction of mixed raw materials decomposed into gaseous products has a tendency to grow,corresponding to the existence of a more violent reaction in the volatile phase.When the mass share of sewage sludge is at 60%,the mixed feedstock has a better overall heat transfer effect,with internal temperature convergence up to 350°C.（3）Based on the rapid combustion experimental platform of the tube furnace built in the laboratory,the combustion characteristics of the mixed feedstock of pulverized coal-sewage sludge-municipal solid waste incineration fly ash were analyzed at different blending ratios and temperatures,and the results showed that the residue yield of the mixed feedstock and the peak concentration and generation of SO₂ precipitation during the combustion process tended to decrease with the increase in temperature during the co-combustion of the mixed feedstock.At 1300°C,the mixed feedstock had the smallest residue yield at 20%of sewage sludge and the smaller SO₂ generation at 20%and 40%of sewage sludge mass.The actual generation of NO is mostly smaller than the theoretical value in terms of NOx release,thus indicating that NOx emission can be effectively reduced when sewage sludge is mixed with municipal solid waste incineration fly ash,where NO generation reaches the minimum value when the sewage sludge mass ratio is at 30%.（4）Numerical simulation of rotary kiln co-disposal process based on Ansys Fluent was carried out,and material heating,volatilization analysis out and coke combustion models in porous media area were established by UDF（User-defined functions）programming.The temperature distribution,oxygen distribution and NO distribution in the rotary kiln under different blast conditions were obtained.