Study On Solid Circulation System Of A Dual Fluidized Bed

Tri-generation technology based on dual fluidized bed for coal pyrolysis and combustion,which successfully couples circulating fluidized bed combustion and coal fluidized bed pyrolysis technology,is one of main ways to realize clean and efficient coal utilization.The solid circulating performance is the key issues in the design,development and operation of dual fluidized bed reactors.Based on these issues,there are two parts to be studied for the reactor in this paper,one is the experiment study on the solid circulation system conducted on the cold-model dual fluidized bed,another is the dynamic model developed for this cold-model dual fluidized bed.In the experimental part,with glass beads being used as the experiment bed solid,the relationship between different parameters and solid circulation rate(Gs)was investigated on the self-built cold-model dual fluidized bed using self-made solid circulation rate measuring device.The experimental results show that:(1)The solid circulation rate(Gs)increase with the air velocity in the furnace(Uc),the static bed heitht(Hb)or fluidization number of pyrolysis furnace(ubn)increasing,while the increase of particle size(dp)will make the Gs decrease significantly;(2)The relationship between operating parameters and loop-seal performance was analyzed,and it is found that the variation trend of loop-seal pressure drop is similar to that of Gs.Based on the analysis of the pressure balance of the solid circulation system,a dynamic model of the solid circulation system on cold-model dual fluidized beds,which adoptes the“Section”modeling method and takes the effect of the combustion furnace outlet on Gs into account by applying the particle back-mixing rate at the exit of the furnace,was developed and established.The simulation results are in good agreement with the experimental results.By adjusting some parameters of the model,the solid circulation system using mixture of ash and glass beads with different density and particle size distribution was simulated.The result show that the Gs increases with the mass ratio of ash(wa)in the circulating solid.After that,sensitivity analysis of the parameters involved in the model such as model parameters,operation parameters and structural parameters was carried out.The results show that:(1)Compared with the model parameters and structure parameters,the operation parameters of double fluidized bed have the greatest influence on the solid circulation system,especially the sensitivity of Uc,Hb and particle density(?_p)to Gs;(2)Among the model parameters,the axial particle back-mixing rate(?)and bed expansion rate(R)have greater influence on the model results;(3)In the structure parameters of the dual fluidized bed reactor,the total height of the furnace(Hf)has a great influence on the Gs.Finally,based on the understanding of solid circulation system and the result of Gs sensitivity analysis,the possible control methods or measures are proposed for how to deal with the problems of adjusting Gs,solid distribution in the system and loop-seal gas reversal.These results can deepen the understanding of the solid circulation system of the dual fluidized bed reactor,and also provide some consultative advice for the design,development and operation of the system.