Experiment And Numerical Simulation On Gasification Behavior Of Biomass In Quadruple Fluidized Bed

Based on the traditional dual fluidized bed biomass gasification device,a new quadruple fluidized bed(QFB)biomass gasification device was designed in this study,which combined biomass gasification,carbon dioxide capture and chemical looping oxygen production,effectively improving the efficiency of biomass gasification and greatly reducing carbon dioxide emissions.In order to study the operating parameters and overall efficiency of the device,a quadruple fluidized bed biomass gasification cold test bench was built,and on this basis,the cold and hot state numerical simulation was carried out.In the cold-state experiment of biomass gasification in the QFB,the pressure distribution was obtained through the pressure sensors arranged in several positions of the test bench.It was found that the maximum value of the pressure inside the QFB appeared at the inlet of two fast beds,and the minimum value appeared at the upper part of two bubbling beds.The pressure difference is formed on both sides of the upper return device to drive the bed material through the upper return device.The particle concentration distribution in the bubbling bed was obtained by means of a concentration measuring probe.The results show that the concentration of particles near the wall of bubbling bed is greater than the inside,while the particle concentration in the lower part is greater than in the upper part.On the basis of the cold-state experiment,the open source software Open FOAM is used to carry out the cold-state numerical simulation.A Multi-phase Particle-in-cell(MPPIC)method was used and a custom solver was developed for numerical simulation.The results show that the movement of particles in the QFB,the pressure and concentration values at each measuring point are in good agreement with the experimental values,which proves the accuracy of the cold-state model and the applicability of MPPIC method in fluidized bed simulation.Subsequently,a thermodynamic model of the QFB was established using Aspen Plus software.The processes of biomass gasification,carbon dioxide capture and chemical looping oxygen production were simulated using Gibbs reactor.The results show that the volume fraction of hydrogen and methane in the generated gas increases,the volume fraction of carbon monoxide and carbon dioxide decreases and cold gas efficiency decreases with the increase of Ca O /Fuel ratio.By increasing the make-up/Fuel ratio,the carbon dioxide capture rate increases significantly,up to about 70%.Finally,based on the cold-state model,a QFB biomass gasification hot-state model was established.The simulation results show that hydrogen,carbon monoxide,methane and carbon dioxide account for about 60%,20%,8% and 12% of the generated gases,which basically do not change with time.By comparing the above results with the experimental results,the errors were concentrated in the volume fraction of hydrogen and carbon monoxide,which were 3% and 2%,respectively.Therefore,the hot-state model could be considered accurate and reliable.In this study,the hydrodynamic and thermodynamic properties of the QFB were fully studied by cold-state experiment,cold-state model,thermodynamic model and hotstate model,which provided a certain reference for the practical application in the next step of engineering.