Numerical Simulation Of Limestone Injection In Tangentially Fired Furnace Of Pulverized Coal Boiler

Atmosphere is a basic environmental factor of human living, however, with the rapid development of economy in recent .decades. massive combustion of fossil fuel has been making the atmospheric environment get worse and worse. This is not only harmful to the sustainable development of economy, but also endangering human health.Controlling SO₂ emission has become an urgent task in coal-fired power plants in China. Limestone injection desulfurization is the cheapest method in desulfurization processes, however, its efficiency should be improved greatly.CFD is developing with the development of computer in 1970s. It is a scientific knowledge which includes the graphics of fluid mechanics, numerical computation and computer, and it uses numerical computational method to solve and forecast delivery of momentum, heat, and mass as physical phenomenon. With nearly a half century's development, CFD has become mature and powerful, at the same time , many kinds of universal commercial software, which can solve idiographic problems in different field and are used widely in many areas, have been developed. FLUENT is one of the CFD software that is over-all in function, intensive in applicability and wide in use.Mixing limestone powders with gas in the process of limestone injection desulfurization is the key factor to affect desulfurization efficiency. According to the process of limestone injection desulfurization, this simulation study on the flow-field distribution in the furnace of the CG-670/13.7-M boiler is carried out using the commercial CFD software FLUENT. The velocity-field and the traces of limestone particles have been simulated, and the characteristic of flow-field and distribution of limestone particles in such boiler have been analyzed.In this thesis, the coal-fines airflow is looked upon as continuous phase, limestone particles are looked upon as discrete phases, the transition of mass and momentum are employed, and cold-state numerical simulation with SIMPLE algorithm is applied. The well-known standardκ-εturbulence model is used to quantify turbulent transfer in the furnace. The representative limestone particles are tracked in furnace by using stochastic trajectory model. The continuous-phase flow field is simulated first, and then the particle phase is simulated by using DPM (Discrete Phase Model) model. By the means of changing the injecting position (26m and 28m) , injecting angle (0°, 20°, 30°, 40°and 45°) and injecting velocity (60m/s,70m/s, 80m/s and 90m/s) , this study simulates the mixing of limestone and gas and their influence on the fluid field. The best injecting seting of the limestone nozzle are pointed out resulting from comparison of the above conditions.The simulation results in this thesis reflect the flow condition in the process of limestone injection, which would provide with a good reference for the efficiency improvement, engineering design and operation prectice.