Experimental Research On The Influence Of Desulfurization In Coal-fired Furnace On Mercury Transformation

Coal-fired power plants hold a significant fraction of the anthropogenic emissions of mercury into the atmosphere. The mercury emission is accelerating, and people are getting to know more about its threat. So mercury emission caused by coal conbustion and its control have attrcted more and more attention and become a concern in this world.In this thesis, the emissions, hazards, generation and control technologies of SO₂ and Hg are summarized separately, and experiments on the mercury speciation in coal combustion products are conducted. The influence of excessive air coefficient, the process of desulfurizaton based on limestone, flue gas temperature and natural gas reburning during desulfurization on mercury speciation and transformation are studied.Experimental results indicate that gas phase mercury is the major state of emission, oxidized mercury is the main speciation in flue gas, and mercury concentration in the fly ash is higher than that incorporated into the slag. The decrease of excessive air coefficient reduced the oxidized and elemental mercury, while increased the concentration of mercury contained in fly ash and slag. The process of desulfurization based on limestone in the furnace not only removes SO₂ in flue gas, but also affects the mercury status of emission. It can transform gas phase mercury into solid-combined state, which improves the emission control of mercury. Flue gas temperature plays an important role in mercury speciation and transformation. When the flue gas temperature becomes lower, more gas phase mercury incorporated into solid will be obtained, and less amount of element mercury will emit into the atmosphere. Natural gas reburning companied with desulfurization can remove NO_x as well as transform elemental mercury into oxidized mercury dispersing in gas and solid phases, which is beneficial to mercury capture and immobilization; however more experiments are needed to certify this phenomenon.Numerical simulation results of coal combustion in the furnace show that a...