Evaluation Study on New Sorbents for Mercury in Coal-Fired Flue Gas

More and more concern has been put on the mercury emitted from power stations burning coal because of its harm to human health. Both of the US EPA and European Commission have set regulations on the mercury emission from the electric utilities. China also pays more and more attention to the mercury emission and starts to sponsor the projects relative to the mercury emission and its control. Mercury emission control technologies may be divided into three classes, i.e., pre-combustion control, combustion control and flue gas control, among which the flue gas mercury removal technology is most widely used. The existed flue gas pollution control devices such as bag filter, electrostatic precipitator and wet FGD may remove the oxidized mercury from the flue gas. However, they have no obvious removal efficiency on the elemental mercury. The main direction in the development of new mercury removal technology is to transform the element of mercury into oxidized mercury and particulate-bounded mercury, which may be effectively removed. Before the sorbent is used to remove mercury from the flue gas, it needs to be evaluated on a lab-scale device, pilot-scale and full scale reactor or power station. The simulated flue gas composed of mercury vapors from the vapor generator and compressed air was used to conduct the experiment on removal of Hg in the sorbent evaluation test-bed in order to research different sorbents for the mercury removal efficiency. The experimental results indicate that the mercury removal efficiency of activated carbon is 60%; while fly ash is of low cost and its efficiency is limited. Unmodified fly ash adsorption efficiency is from 10% to 20%, and the specific surface area of modified fly ash has been increased a lot, and its adsorption efficiency can reach up to 25%, but it is far from the adsorption efficiency of activated carbon. The activated carbon is with higher mercury removal efficiency than fly ash, but its cost is very high. It is one of the studying directions to find high effective cheap sorbents.