Experimental And Numerical Study On The Influence Of Internals On Hydrodynamics In Chemical Looping Reactor

The huge energy consumption has contributed to the large emission of greenhouse gas such as CO₂.It is widely acknowledged that the emission of CO₂ should be effectively controlled and reduced Chemical-Looping Combustion?CLC?with inherent CO₂ separation during combustion process has become one of the most promising technologies.The design and optimization of the reactor of CLC has a significant impact on fuel conversion efficiency and carbon capture efficiency.At present,most of the fuel reactors are bubbling fluidized beds,where large bubbles decrease the gas-solid contact efficiency.Besides,it leads to the decrease of fuel conversion efficiency and carbon capture efficiency.In this study,the internals were added to the fuel reactor to strengthen the gas-solid contact and improve the fuel conversion efficiency.,Numerical study Based on the computational particle fluid dynamics?CPFD?method was conducted to study the influence of internals on hydrodynamics in fuel reactor.Additionally,hot state experiments were carried out to study the performance of the reactor with internals based on the numerical results.The gas-solid flow in the fuel reactor was simulated based on the CPFD method.Simulation results were in a good agreement with the previous experiment data.The influence of internals with different structures?number,opening ratio and opening type?on hydrodynamics in chemical looping reactor was also discussed.The results showed that internals could reduce the fluctuation of pressure drop in fuel reactor and downcomer,indicating the fluidized bed un more stably.After adding internals,the fuel reactor was divided into several chambers which was composed of dense phase zone and dilute phase zone.In addition,the distribution of solid volume fraction and axial velocity in each chamber were similar.Increasing the opening ratio can effectively reduce the phenomenon where particles pack near the lateral wall above the internals.Moreover,it reduced the pressure drop at the internals,suggesting the wear of the internals were lower.However,too large opening ratio?13.6%?could lead to non-uniform distribution of solid volume fraction in the upper chamber.Concerning the type of internals,the radial mixing of gas and solid near the internals and the efficiency of gas-solid contact were promoted because of the pressure difference between holes with different diametersThe pretreatment process of bubble image was designed based on Matlab.After pretreatment,the instantaneous solid volume fraction distribution image obtained from CPFD simulation results was processed to obtain accurate bubble parameters.Statistical analysis were conducted to explore the influence of internals with different structures including number,opening ratio and opening type)on bubble behaviors in fuel reactor.With more internals,the frequency of small bubbles in the reactor became higher and the frequency of the circular bubbles was higher,which increased the gas-solid contact dramatically.The internals with smaller opening ratio led to effective inhibition of bubble aggregation in the bed.Therefore,the frequency of large-diameter bubbles decreased.However,smaller opening ratio was able to decrease the aspect ratio,resulting in the non-uniformity of the shape of the bubbles,which could weaken the gas-solid contact.Regarding the type of internals,adding internals with mixed opening type could make the distribution of bubble diameter more uniform,which could increase the efficiency of gas-solid contact.To sum up,adding four internals with the opening ratio 9.4%,and the opening type 2?+2?was the best choice to improve the efficiency of gas-solid contact.Moreover,the hot state experiments were conducted on the new CLC facility with internals based on the results of the numerical simulation.The performance of the new CLC unit was tested using CO and biomass as fuel and hematite as oxygen carrier.The results showed that the multi-chambers fluidized bed could effectively improve gas-solid contact and break the large bubbles.CO can be converted into CO₂ efficiently in the temperature and the conversion efficiency of CO was above 90%between 840?and 900?.the fuel reactor temperature exerted a positive effect on the fuel conversion and carbon capture efficiency when the biomass was adopted as fuel.The carbon conversion and carbon capture efficiency reached 92.5%and98.5%at 900?,respectively.