Research on the Effect of Chloride Additive on Mercury Speciation in Coal-Fired Derived Flue Gases

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.