Drying kinetics of sewage sludge and simulation of its co-generation system with biomass co-gasification
The efficient drying pre-treatment and gasification resource utilization of sewage sludge is one of the important ways to realize green and sustainable city development.Firstly,the thermogravimetric reactor was used to study the drying kinetics of sludge.Then,the influence of high temperature-low speed flue gas and low temperature-high speed flue gas on the sludge drying process was clarified based on Fluent numerical simulation.Finally,a new type of sludge and biomass co-gasification co-generation system was established by Aspen Plus,and the thermodynamic performance of the system was discussed.The results show that,the drying process of sludge in thermogravimetric reactor can be divided into the ascending stage,the first decreasing stage and the second decreasing stage,and the decreasing stage is the main stage.The water diffusion coefficients of SW-60 and SW-80 ranged from 6.34×10-6 to 3.72×10-5 m2/s and 3.69×10-5 to 2.60×10-4 m2/s,respectively.The drying activation energy of SW-60 and SW-80 was 9.55 kJ/mol and 28.25 kJ/mol,respectively,with the increase of initial moisture content.In the drying bed,the drying efficiency of high temperature-low speed flue gas is about 2.67 times that of low temperature-high speed flue gas.In the co-generation system,as the biomass blending ratio increases,the input heat,air flow,low heating value of syngas,yield of syngas and potential of co-generation all increase.However,the electrical efficiency,thermal efficiency and system efficiency will decrease slowly.When the biomass blending ratio is 20%,the blend of 30%moisture dry sludge and biomass can produce electrical energy potential and thermal energy potential of 0.61 kW·h and 4.212 MJ per kg,respectively.