Numerical Simulation Study Of CFB Boiler Slime Coupled Biomass Combustion

In order to realize the comprehensive green transformation of economic and social development,the Chinese government has made remarkable achievements in optimizing the energy structure and vigorously developing a series of new energy power generation technologies such as photovoltaic,wind energy and biomass energy in the past two decades,The traditional fossil fuel based thermal power generation units will still play a major role in the contribution of electric energy,and coal-fired power will still occupy the main part of the power production market.Coal is the main consumption of traditional energy for thermal power generation.With the rapid development of domestic economy,China's demand for electricity has increased sharply,resulting in huge consumption of coal resources and serious environmental pollution.Therefore,the key to solve this problem is to improve the fuel flexibility of thermal power units.Slime is a by-product produced in wet coal washing process of raw coal.Due to its high water holding capacity,high ash content,low calorific value,fine particle size and other characteristics,its large-scale utilization in industry is limited.Biomass(wheat straw)has the advantages of high volatile,low pollutant elements,abundant reserves and affordable price.The coupling combustion of coal slime and biomass(wheat straw)can not only fully save resources,but also effectively control the generation of pollutants(NOx).It is also the transition and guarantee of coal power generation to new energy power generation,and is an effective measure to solve the current problems of thermal power enterprises.In this paper,a 75t/h CFB boiler of a self provided power plant in a mining area of Western Guizhou Province is taken as the research object,and the fluent simulation software is used to simulate the velocity field,temperature field,component field and NOx concentration distribution in the furnace under seven groups of different mixing ratio of coal slime and wheat straw,different excess air coefficient and different wheat straw particle size under three loads of 100%,80% and 60%.The results show that: the addition of biomass(wheat straw)has a combustion supporting effect on the combustion in the furnace,with the increase of the proportion of wheat straw,the temperature in the furnace gradually increases;CO mainly distributes in the dense phase area,and its mass fraction gradually decreases with the increase of the proportion of wheat straw;the concentration of NOx gradually decreases with the increase of the proportion of wheat straw.After comprehensive analysis,the following suggestions were made on the proportion of wheat straw under three kinds of load: the best proportion of 100% load was 15%,the proportion of 80% load should not exceed 15%,when the load was 60%,the proportion of 20% was the best.The excess air coefficient has a deep influence on the velocity field distribution in the furnace.With the increase of the excess air coefficient,the overall temperature and NOx concentration in the furnace increase.When the excess air coefficient ? = 1.2,? =1.3,? = 1.4,the furnace outlet temperature is relatively high,and the furnace outlet NOx is relatively high.When the excess air coefficient is 1.1,the furnace temperature increases with the increase of particle size When the particle size is 12 mm,the maximum section temperature in the furnace decreases by 119 K compared with that when the particle size is 2 mm,and the section temperature at the outlet decreases by106 K,by 9.16% and 8.26% respectively.The NOx concentration in the furnace increases with the increase of grain size.When the grain size of wheat straw is 12 mm,the NOx concentration in the outlet section increases by 32 ppm compared with 2mm,and the increase rate reaches 41.03%.It is suggested that the best grain size of wheat straw is 5-8mm.Through the research,the optimal adding proportion of three groups of load is obtained,and the influence of excess air coefficient and straw particle size on Combustion Characteristics and NOx generation is studied for condition 4 under 80%load,in order to have a certain reference value for the actual operation of the power plant.