第十一屆國際流化床技術會議論文集（簡體書）

Abstract Oxy-fuel fluidized bed combustion technology is considered to be one of the most promising technologies to reduce the CO2 emissions from power plants. In this paper, regarding a 6 kWth bubbling fluidized bed, numerical simulation method for coal combustion process in fiuidized bed under O2/CO2 atmospheres was discussed, and char combustion models were modified by adding calculation model of char gasification reactions. Simulations results of flow field, temperature field, species concentrations, combustion characteristics in fluidized bed and the influence of gasification reactions were analyzed. The accuracy of numerical simulation results were validated by comparing with experimental data. The results reveal that the flow and combustion in the furnace were in good condition, conforming to typical rules of bubbling fluidized bed. The process of char consumption was significantly influenced by char gasification reactions. The prediction error of the CO concentration at outlet was reduced by 30% under the O2/CO2 atmosphere when adding the char gasification reactions into the model.The experimental results agreed with simulations well, proving that the coal combustion calculating model was reliable.
INTRODUCTION
Oxy-fuel fluidized bed combustion technology is considered to be one of the most promising technologies to reduce the CO2 emissions from power plants (Damen K, et al. 2006). At present, the technology still has a lot of basic uncertainties required in-depth studies, such as pollutant emission control and selections of optimal operating conditions, et al (Chen L, et al. 2012). Numerical simulation is an effective tool to study on combustion characteristic and the optimization design of demonstration projects, for its visualization to describe flow and combustion processes. Thus, it has important theoretical and application significance to study suitable numerical simulation methods for coal combustion processes.
At present, there are several difficulties and points required improvement for numerical simulation studies in fluidized bed under O2/CO2 atmospheres. On the one hand, the flow and combustion in fluidized bed are typical unsteady state, and the coupling calculation of violent reactions such as combustion of volatiles and char, and the fluid flow with heat transfer are somewhat difficult. It is found that it is not easy to make the calculation convergence and the convergence requires a lot of time. These have been important obstruction for CFD to apply in numerical simulation of combustion in fluidized bed. On the other hand, when air is replaced by O2 and CO2 in combustion system, because CO2 is not inert gas and there are physical and chemical properties differences compared with N2, the numerical simulation is different from that in air atmosphere (Wang XF et al., 2009). Thus, further study of suitable numerical simulation method for coal combustion in fluidized bed under O2/CO2 atmospheres is required in order to better description and analysis of combustion characteristics of in furnace.
In this paper, regarding a 6 kWth bubbling fluidized bed, numerical simulation method for coal combustion in fluidized bed under O2/CO2 atmospheres was discussed, and char combustion models were modified by adding calculation model of char gasification reactions. Simulations results of flow field, temperature field,species concentrations, combustion characteristics in fluidized bed and the influence of gasification reactions were analyzed. The accuracy of numerical simulation results were validated by comparing with experimental data.