Experimental And Numerical Study On The Gas-Solid Flow Characteristics Of Solid Waste Pyrolysis In A Dual-Fluidized Bed

The disposal of municipal solid waste(MSW)has become an important issue with the rapid development of our country.Pyrolysis under middle-low temperature,as an effective method for harmless,reducible and recyclable treatment of solid waste,has been an important research on solid waste disposal in China.However,at present,the domestic and abroad pyrolysis equipment generally has disadvantages such as slow heat transfer rate,low energy utilization degree and poor equipment integration,which is difficult to realize large-scale application.Therefore,a novel dual fluidized bed unit for solid waste pyrolysis is proposed in this paper.The circulating fluidized bed plus bubbling fluidized bed was selected as the main structure and the pattern of mechanical return with non-mechanical return was adopted between the two beds.The pilot setup of dual fluidized bed with a capacity of 50kg/h was designed and constructed.Based on the above equipment,the experimental and numerical study on gas-solid flow characteristics was carried out.By monitoring the pressure,the whole field pressure distribution of the dual bed and the gas-solid flow characteristics of combustion furnace were studied through experiment.The results show that the whole field pressure matches stably and the mechanical returner functions satisfactorily,which can generate stable return under various working pressure difference.The fluidized air flow rate and working pressure of pyrolysis furnace have little effect on the pressure distribution of combustion furnace.The particle concentration change mainly occurs in the bottom region of the furnace when using different operating parameters.The particle concentration at the bottom is positively correlated with the particle circulation flux,the initial pile height of the combustion furnace as well as the height of the secondary air inlet.Besides,it is negatively correlated with the primary and secondary air flow rate of the combustion furnace.Insufficient particle circulation flux,small initial pile height or large primary air flow rate will lead to the unstable dense phase area at the bottom,which further influences the stable flow state in the combustion furnace.Under the condition of stable function of the dual bed,the operation characteristics of the non-mechanical return device were tested.The results show that the loose air and fluidizing air can be used together to control the U type valve.When the basic operating conditions remains the identical,a variety of proportions between loose air and fluidized air can produce the same running material height in the descending pipe.When it is merely controlled by loose air,the dual bed only relies on self-balance to return the material.Moreover,there is one-to-one correspondence between the running material height and the loose air volume.Under the same operating condition,the ratio of loose air and fluidizing air has almost no effect on the pressure gradient and gas channeling in the downpipe.The pressure gradient and gas channeling in the downpipe decrease with the running material height and increase with the inverse pressure difference.The dual fluidized bed’s gas-solid flow and two-component particle mixing in lateral flash pyrolysis furnace for numerical simulation research are based on EulerianEulerian model and select EMMS drag model.The results show that the combustion furnace upper part of the particle radial distribution center sparse,side wall is thicker and under the influence of lateral feeding,no obvious radial distribution law at the bottom of the particles;Increasing the particle diameter of the material into the pyrolysis furnace is easy to cause its deposition at the bottom of the pyrolysis furnace,thus prolonging its average residence time in the furnace.