Study on Mercury Speciation and Transformations of Coal-Combustion Flue Gases on Pilot-Scale Furnace

摘要

A pilot-scale coal-combustion furnace was designed and constructed to study the mercury speciation and transformations in the flue gas under different conditions. A typical coal used widely in the power stations in Shanghai area is adopted as the experimental coal type. The designed pilot-scale one-dimensional pulverized coal combustion system had reliable performance to study mercury speciation distribution characteristics in the flue gas. The results showed that gaseous mercury in the tested coal products accounted for 66% of total mercury and solid-state mercury accounted for 34% 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 60% of the total gaseous mercury and the elementary mercury accounted for about 40% of the total gaseous mercury. Of the solid-state mercury, mercury in the fly ash was around 31% and mercury in the slag was about 3% 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 NaCl 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 NaCl additive, the increasing trend of particle mercury became flat gradually and the decreasing of elemental mercury become gentle gradually. The addition of NaCl additive obviously helped mercury removal, but large quantity of NaCl addition into the pulverized coal may cause metal corrosion, so the negative effects of NaCl addition needs further consideration before NaCl is taken as an additive to remove mercury.