Investigation of the Relationship between Particulate-Bound Mercury and Properties of Fly Ash in a Full-Scale 100 MWe Pulverized Coal Combustion Boiler

摘要

There is an increasing concern over mercury emissions from coal-fired boilers. Coal-fired power generation accounts for approximately 33% of total mercury emission in the United States. Once it is emitted into the atmosphere and deposited on land or water, mercury can transform into methylmercury, an organic form. Mercury can then enter the food chain, which poses a potential threat to human health and the environment. To study the relationship between particulate bound mercury and fly ash properties, fly ash samples were collected from the mechanical hopper (MHP) and the electrostatic precipitator (ESP) of a 100 MWe pulverized coal-fired boiler and analyzed for particulate mercury concentration (Hgp), unburned carbon, loss on ignition (LOI), elemental content and specific surface area (SSA). Different types of software, such as Microsoft Excel, Minitab and Origin, were applied to build the regression models to evaluate the relationship between Hgp and fly ash properties. The results of the analysis indicate that the amount of mercury emissions is dependent on the properties of the fly ash at the MHP and ESP as well as the amount of fly ash removed by air pollution control devices (APCD). Their relationship can be described as: Hgp (MHP), ppm = 0.0230 + 0.00838 Carbon (MHP), % + 0.00385 LOI (MHP), % Hgp (ESP), ppm = -0.0180 + 0.0670 Carbon (ESP), % + 0.0448 LOI (ESP), % The SSA of ESP ash is larger than MHP ash, which can help explain why Hgp at the ESP is higher than at the MHP. For the multiple metal oxides in fly ash, all the regression results indicate the trace elements have a very weak relationship with Hgp. There is no significant effect from trace elements on mercury absorption. Further study of Hgp catalyst mechanism and absorption phenomenon is ongoing. The function of various emission control technologies such as SCR and hot-side ESP in some coal-fired power plants are being evaluated.