Numerical simulation progress of flow characteristics in a CFB boiler

Circulating fluidized bed boiler (CFBB) combustion technology is currently one of the best clean coal combustion technologies.The flow characteristics in the CFBB determine the combustion and heat transfer in the furnace,which is the most valuable content of CFBB.The traditional experimental method has the limitations of high research cost and low accuracy,for this reason,the numerical simulation method has become the choice of more researchers.CFBB simulation must start with gas solid multiphase flow model.First of all,the research progress of furnace flow regime simulation in the past decade is reviewed.Numerical simulation can provide more flow details and visualization results,which helps to deepen the understanding of the macro and micro flow characteristics of the gas solid two phase in the furnace.It can even improve the definition of furnace flow patterns.Secondly,the drag model,which is the key factor that determines the success or failure of the simulation,is reviewed.The drag model can be divided into three types:homogeneous model,correlation model and EMMS model.Then the application scope,advantages and disadvantages of the drag models are discussed.EMMS model,which has the ability to describe the meso scale structure,is considered to be the best drag model at present.Finally,the coupling method of multiphase flow model and drag model is summarized and analysed.Among them,the coupling of TFM multiphase flow model and EMMS drag model has obtained the most applications and best results,but it has the disadvantages of inability to achieve particle size distribution and lack of scale separation.The coupling of CPFD multiphase flow model and EMMS drag model has the ability to consider the influence of particle size distribution and meso scale structure inhomogeneity on the flow characteristics of CFBB,it has more development potential in the simulation of CFBB.