Research On The Hvdrodynamics And Heat Transfer In A600Mw CFB Boiler Furnace

As a high effitient and clear coal combustion technology, circulating fluidiszed bed boiler has developed rapidly in recent years with towards the direction of larger capacity and higher steam parameters. The background of this paper is the development of600MW supercritical circulating fluidized bed boiler in China. Sponsored by the National Key Technologies R&D Program of China and the Cooperation Project of Dongfang Boiler Company, in this paper, experimental research and numerical simulation are carried out on the in-furnace gas-solid hy drodynamics and heat transfer characteristics in the600MW supercritical CFB boiler.A CFB cold model with a pant-leg structure and six cyclones is built according to the CFB scaling method. It is scaled down from the DBC600MW supercritical CFB boiler. Experimental study and numerical simulation are carried out in this paper which can be divided into five parts. Experimental study includes:①solids overturn features of the pant-leg furnace;②effect of extended top on the gas-solid flow structure:③solids circulation rate distribution among the six cyclones. A heat transfer coefficient calculation method is established based on the numerical simulation of gas-solid flow. Numerical simulation includes:④hydrodynamic and heat transfer characteristics in the CFB model with a pant-leg structure and six cyclones;⑤hydrodynamic and heat transfer characteristics in the600M W supercritical CFB boiler furnace.The experimental results verified the gas transportation mechanism for the lateral particle migration during the solid overturn process in the pant-leg CFB. Balance control strategy was discussed based on the analysis of theoretical critical status between the self-balancing and the solid overturn. The experimental results also showed that two core-annulus flow structures are formed independently in the two individual pant-leg zones and these two cores are merged into one core at up-section of the pant-leg. It is found that the distribution of solids circulation rate on the two side are similar. The solids circulation rate of the middle circulation loop is about6.3～9.0%lower than the other two loops on each side of the furnace.In terms of numerical simulation, A heat transfer coefficient calculation method is established based on the numerical simulation of gas-solid flow. With the Fluent commercial software, the gas-solid flow in the furnace is numerical simulated using two-fluid Model combined with the EMMS drag coefficient computational method. With the hydrodynamic results from the simulation, the heat transfer coefficient distributions of the in-furnace heating surfaces are calculated with the cluster renewal model which is base on the "core-annulus" gas-solid flow structure. The calculation method is achieved by a computer code in Fortran language.This method was verified in the simulation of hydrodynamic and heat transfer characteristics in the CFB cold model and the parameters of the model are optimized with the experimental results. Then this method was applied in the simulation of600MW supercritical CFB boiler. The numerical results showed that two core-annulus flow structures exist in the furnace. Clusters with downward particle velocities exist in the surfaces of both the enclosure walls and the partition walls. The particle velocities on the surfaces of wing walls are mainly positive. The wing walls near the furnace outlets have higher solid concentration and particle velocity.3-D distributions of heat transfer coefficient and heat flux on the in-fuenace heating surfaces of the600MW supercritical CFB boiler are obtained from the simulation.The research in this paper provides a theoretical and technical basis for the development of600MW supercritical CFB boiler.