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 st- - udying directions to find high effective cheap sorbents.

A typical coal used widely in the power stations in Shanghai area is adopted as the experimental coal type. A pilot-scale coal-combustion furnace was designed and constructed to study the mercury speciation and transformations in the flue gas under different conditions. The results showed that gaseous mercury in the tested coal products accounted for two thirds of total mercury and solid-state mercury accounted for one third of total mercury. It indicates that gaseous mercury is the main form of mercury emission from the tested coal-fired flue gas. The bivalent mercury accounted for about three fifth of the total gaseous mercury and the elementary mercury accounted for about two fifth of the total gaseous mercury. Of the solid-state mercury, mercury in the fly ash was around thirty one percent and mercury in the slag was about three percent of the total mercury. It shows that bivalent mercury is the main form of gaseous mercury, the mercury content in the fly ash compared to the end of the mercury is higher. The addition of chloride additive makes the percentage of both gaseous bivalent and gaseous elemental mercury in the total mercury decline at some degree, and percentage of particle mercury increase correspondingly. However, with the increasing of additive, the increasing trend of particle mercury became flat gradually and the decreasing of elemental mercury becomes gentle gradually.

A simultaneous test between a dry and wet based SCEM system was conducted at ESP outlet of a power station. The data by the dry and wet based methods showed a similar changing trend, and the difference between the two is within an acceptable range. According to the analysis of the relative standard difference (RSD), it was found that the dry based method could provide higher quality data than the wet based method. The practical experimental process shows that the dry based method can work well for more time than the wet based method under unattended condition. The dry based mercury SCEM is expected to be a trend of the mercury SCEM and it is more possible for the dry based SCEM than the wet based SCEM to become a compact model and enter the control room in the power station to provide mercury concentration in the flue gas. At the other hand, as a new developing technology, the dry based SCEM needs more practical tests.

Mercury speciation distribution features in flue gas were studied on an self-designed one-dimensional pulverized coal combustion test rig.And the influence of NaCl,being used as an additive into the coal combustion,on the mercury speciation distribution was analyzed.Results show that the gaseous state of mercury is of the overwhelming content in the emitted mercury for the test coal,and the bivalent mercury is of the major part in the gaseous mercury.In addition,the mercury content in fly ash is higher than that in slag.Adding NaCl causes a certain reduction of percentage of both gaseous bivalent and elemental mercury in the total content,but an increment of ratio of particle mercury.However,with increased addition of NaCl,the particle mercury increases smoothly and the elemental mercury reduces also slowly.

Mercury is harmful to our health and environment, so research on mercury emission from coal-fired power station, the main source of anthropogenic mercury emission, is very important. In this paper, mercury emission and speciation in the flue gas from a coal-fired power station was measured by three methods, i.e., OHM (Ontario Hydro method), Hg SCEM (semi-continuous emission monitors), and EPA Appendix K (carbon trap method). The effects of boiler load, flue gas characteristics on mercury emission and its speciation were analyzed. Mercury mass balance was calculated based on the analyses of mercury contents in coal, pyrite, bottom ash, fly ash, FGD (flue gas desulphurization) slurry, and flue gas at FGD inlet and stack. The results indicate that data by the three methods have good consistency within acceptable range. The total mercury emission increases with the increasing of mercury content in fuel and boiler load. The percentages of elemental mercury in the flue gas at FGD inlet and stack are around 26%-48% and 70%-85% respectively. Wet FGD would capture more than 80% of oxidized mercury.