Numerical Simulation Of Blended Coal Combustion For 1076t/h Subcritical Circulating Fluidized Bed Boiler

With the rapid development of the national economy and the increasing improvement of people's living standards,China's demand for electricity has increased dramatically,coal,as the main traditional energy source for thermal power generation,is often in short supply.The soaring price of coal also makes it impossible for power plants to burn a single coal for a long time.Blended combustion of multiple coals is a feasible policy.Circulating fluidized bed(CFB)technology has been developed rapidly due to its strong adaptability to coal combustion,high combustion efficiency and low emission pollution.On the premise of guaranteeing the stable operation of the boiler,proper adjustment of coal blending ratio and change of combustion structure are helpful to improve combustion efficiency,stability and economy,therefore,it is of great significance to study the optimization of blended coal combustion in Circulating Fluidized Bed boilers.In this paper,a 1076t/h MW Circulating Fluidized Bed boiler in a power plant is taken as the research object to simulate the combustion in the furnace,and the simulation results are compared and analyzed,which provides a theoretical basis for the efficient and stable economic operation of the power plant in the future.The specific research contents are as follows:Firstly,the research object is analyzed theoretically,according to the actual size of the boiler,the physical model is established,carry out mesh generation and ensure good mesh quality.The ANSYS FLUENT is used to simulate the furnace combustion.The Realizable k-? is chosen as turbulence model,which makes up for the shortcoming of standard k-? in calculating negative stress in strong swirling mixing;Using Euler-Euler Model to Describe Multiphase Flow;Using Component Transportation Model to simulate the combustible gas combustion;UDF is written to control the reaction rate of volatilization analysis and coke combustion as isophase reaction;Gidaspow gas-solid drag model is used to describe the momentum exchange relationship and interaction between two phases;The P1 radiation model is used to describe the radiation heat transfer in the furnace.Secondly,the industrial analysis of the actual coal samples burned in the target power plant is carried out to lay the foundation for the optimum coal blending ratio.Taking the thermogravimetric analysis test of the coal samples by using HS-TGA-101 thermogravimetric analysis,statistical ignition point of each coal and calculation of general ignition coefficient.The coal purchase price,general ignition coefficient and calorific value are taken as the objective function of multi-objective fuzzy decision-making model,and the weights of several different target factors are determined artificially,six final coal blending schemes are obtained.Among them,Case2 working condition is close to the composition of designed coal,and the combustion conditions and economy of other schemes are analyzed on the basis of Case2 working condition.Finally,six kinds of coal blending schemes including power plant boiler combustion design conditions are calculated and analyzed.The combustion velocity field,two-phase component distribution field,temperature field,heat exchange situation and material burnout are obtained.The emission of nitrogen oxides is briefly analyzed.The numerical simulation results are basically consistent with the actual operation status of the power plant.Compared with other coal blending schemes,it can be concluded that with the gradual improvement of coal combustion economy,the gas-solid mixing ability in dense phase zone decreases,the temperature distribution in dilute phase zone tends to be uniform,the proportion of heat transfer in furnace increases relative to that in tail flue,the burnout degree decreases,and the emission of NOx decreases.After a rough calculation,the Case3 and Case4 programs can save 1.254 million yuan and 2.394 million yuan per year for the power plant.Compared with the design conditions of utility boilers,Case3 and Case4 can improve the economy of coal-fired power plants,and the combustion in the furnace is in good condition.In view of the actual operation of the boilers,Case3 and Case4 can be used as alternatives.In addition,the influence of the change of the proportion of coal blends on the combustion state in Circulating fluidized bed boilers can play a guiding role in the selection of boiler operation schemes.