Study On A Coupled System Of Sludge Drying With Sludge Pyrolysis

In order to realize the high-value utilization of sewage sludge,this paper introduced a coupled system of sludge drying with sludge pyrolysis.On the one hand,the technology of dried sludge returning to feedstocks was adopted in sludge drying unit,which controlled the moisture content of mixed sludge below 40%,improving the heat efficiency.On the other hand,the combustible gas produced by sludge pyrolysis unit was burned directly without condensation,which supplies heat for sludge drying and pyrolysis unit,achieving the self-sufficiency of the system.Simulation results of coupled system of sludge drying with sludge pyrolysis on Aspen Plus software showed that the model proved applicable and reliable under the setting parameters,and the technology could be used to deal with excess sludge without external energy input,while the energy utilization ratio of system accounted for 60.1%.The process system could operate normally at the poplar sawdust addition ratio of more than 43.5wt.%.Furthermore,the production of bio-oil could be further enhanced at 550 °C.This study indicates that sludge treatment without external heat supply is practically feasible.In this paper,the drying unit was taken as an example to design and manufacture the sludge indirect drying device,and the optimal process conditions of the device were determined.It was found that the sludge dryer could operate normally for more than 25 min preheated before the test In addition,the dried sludge could meet the predetermined drying requirements at residence time of 18 min and initial moisture content below 35%when sludge flow reached 6 kg/.Further,in order to expand the utilization of sludge,chars from the co-pyrolysis of sewage sludge and poplar sawdust were activated using KOH for the production of activated carbons(AC)via chemical activation method.The obtained activated carbons were characterized for their physical properties.It was found that the surface area of activated carbon reached 551.0 m2/g and the total pore volume 0.29 cm3/g,and most of pores are microporous.The phenol-adsorption experiments indicated that the activated carbon was very effective in removing phenols when phenol solution was used as a model compound for phenol-containing wastewater.It was also found that a phenol removal rate of 80.6%was achieved at the AC addition ratio of 0.175 g/100 mL when the concentration of phenol solution is 50 mg/L.Furthermore,the adsorption of phenols could be enhanced at a weakly acidic condition of pH=5.Finally,the fitting of experimental data showed that the adsorption of phenols with the AC prepared could be described by a pseudo-second order kinetic model while its adsorption isotherm could be simulated with the Langmuir model.Thermodynamic results showed that the adsorption of phenol is a spontaneous and exothermic process,basing on physical adsorption.