Research On The Heat And Mass Transfer Mechanism Of The Spiral Sludge Dryer

With the development of China's economic reconstruction,the production of municipal sludge has increased rapidly.Sludge seriously pollutes the environment and pollution threatens health of urban residents.However,treatment technology of sludge in China started relatively late,and because of the limitations of technology,the treatment rate is low.Currently,problems of low heat utilization rate and secondary pollution in direct drying equipment.On the basis of a company's indirect drying process system,an indirect sludge drying system with multiple levels of heat recycling and tail gas utilization was designed.The heat transfer of the wall dryer was analyzed,and the actual production was based on analysis.First,the paper investigates indirect drying process and equipment of sludge,and summarizes the theories,methods and models of existing indirect sludge drying research.In view of the shortcomings of the original drying system,a sludge drying system with multiple levels of heat,recycling,preheating and recycling,and utilization of exhaust gas separation were designed.Remove the system's material balance and heat balance flow chart,calculate the system process parameters,and experience the design of the new partition wall sludge dryer.Secondly,binding abilities and drying capacity of moisture and sludge particles are studied according to the distribution of sludge moisture,water-sorption isotherms of sludge and sludge drying characteristics.Establishing the sludge atmospheric penetration model,studying the transfer of heat from the sludge wall,on the basis of the basic thermal conduction and heat convection calculation,establishing the whole dryer heat utilization calculation diagram,and the theoretical calculation value is calculated with the instance.Build on previous experiments,to determine the relationship between the physical parameters of sludge density,specific heat,effective thermal conductivity,effective diffusion coefficient and the change of moisture content of the drying process.According to the parameter expression to build the model,using COMSOL to simulate the process of heat and mass transfer of sludge,comparing the simulation results and experimental data.It can be calculated that when the drying temperature is in the range of 180-220? and the thickness of the thin layer is in the range of 15-18mm,the conclusion can meet the sludge drying optimization demand and the sludge drying heat demand can be calculated accordingly.In order to meet the demand for sludge drying heat,through research,it has been observed that increasing the spoiler structure on the outside of the heat transfer wall can increase the heat transfer efficiency.After analysis of different built-in items,it can be concluded that the built-in spiral piece has a better reinforcing effect.After the enhanced heat transfer mechanism,the annulus heat transfer model was established and CFD simulation was performed.After verifying the accuracy of the model,the heat transfer and flow characteristics of the inner wall spiral structure are described,and the influence of different structural parameters of the spiral internal structure on the heat transfer enhancement is analyzed.Finally,on the basis of the nondimensionalization of the structural parameters,the RSM was utilized to design the annular spiral pipe.On the basis of experimental design,analysis of variance and regression analysis,the law of impact was revealed by response surface methodology,at the same time,optimal constraint conditions of Pareto are used to design.It can be seen that when Nu/Nu0=3.18,f/f0=5.12,and PEC=4.5,the corresponding built-in organizational parameters are optimal,and the effect of heat transfer enhancement is illustrated through comparison.Statistics of the above data,the thermal utilization rate of the whole machine is finally obtained.According to the sludge drying thermal analysis and the spiral heat transfer analysis,the structural parameters of the inter-deck sludge dryer conforming to its demand parameters were obtained,and the parameters of the pre-experience designed drying were corrected based on the parameters.After research and design,a complete set of indirect drying system design was scheduled to end.Heat utilization analysis of the wall-type dryer was completed through the combination of simulation and theory.With the heat demand as the core,the design parameters are shifted.The design of the inner wall sludge dryer meets the need of the company.