Numerical Simulation Of Combustion And Alkali Metal Distribution In High Alkali Coal Fired Boiler Based On The EDC Model

Zhundong coal has abundant reserves,but its sodium content is high.It is easy to cause serious slagging and contamination in the process of burning Zhundong coal in existing boilers,and it is impossible to burn Zhundong coal at full load.For this reason,the Ministry of Science and Technology of China has set up a project to jointly develop a furnace type capable of fully burning high alkali coal in Zhundong by means of production,teaching and research,which will be a practical,effective and rational way to utilize Zhundong coal.As one of the important research contents of this subject,the combustion characteristics and distribution of alkali metals in a newly designed fully-fired high-alkali coal boiler are simulated numerically in this paper.In order to grasp the transformation and distribution law of alkali metals in the furnace,this paper provides theoretical support for the development of key prevention and control technologies for slagging and contamination of high alkali coal boilers.The key factors affecting slagging and contamination of Zhundong coal-fired boilers are analyzed.The main technical concepts of the design of Zhundong coal-fired boilers and the key prevention and control technologies to be adopted are discussed in view of these factors.In order to predict the chemical reactions of sodium-containing substances and coal components in the furnace during the numerical calculation of combustion in the furnace,the eddy dissipation concept(EDC)model is applied to the gas-phase reaction process in this paper.The chemical reaction mechanism of combustion in furnace and conversion of alkali metals was analyzed and simplified.The chemical reaction mechanism package consisting of 7 elements,29 components and 51 steps of elementary reaction was obtained.The different design schemes and operating conditions of the counter-impingement combustion boiler for 660 MW full-fired high-alkali coal demonstration project unit are simulated numerically.The aerodynamic field,combustion characteristics and heat flow distribution in the furnace under full load are analyzed.The simulation results show that the flue gas temperature at the outlet of the furnace is 926.67 C,and the flue gas temperature near the wall is lower,which is helpful to the combustion.The problem of slagging and contamination in the furnace can be alleviated.The alignment under the seven-layer burner helps to reduce slagging contamination.24m/s is recommended for simulating different primary wind speeds.The transformation and concentration distribution of alkali metals in full-fired high-alkali coal boilers are predicted.NaCl is the representative material for the precipitation of alkali metals in the boilers.NaCl is transformed into Na2SO4 through two paths in the high temperature zone.The simulation results show that the main transformation path is the path from NaCl to Na first and then to other intermediate products.The concentration of Na2SO4 increased with the decrease of smoke temperature.The variation of load has a great influence on the distribution of alkali metals.