(364b) Direct Measurements Of Oxidized Mercury From Simulated Combustion Flue Gas

Padak, B., Stanford University

Coal-fired power plants are the greatest anthropogenic source of mercury emissions in the United States. Mercury exists in coal combustion flue gas in a variety of forms depending on the coal type and combustion conditions, i.e. elemental (Hg0), oxidized (HgCl2 or HgO), and particulate (Hgp). Understanding mercury speciation during combustion and how the transformations occur between different forms of mercury is essential to develop an effective control mechanism for removing mercury from flue gas.

Mercury is in its elemental form at boiler temperatures and it is oxidized as the gases cool down after the boiler. Therefore, the rate of quenching is one of the key factors affecting mercury speciation. Thermodynamic calculations show that mercury oxidation reactions are kinetically controlled. Rate parameters for the mercury oxidation reactions are calculated in our group using quantum mechanical methods. This 10-reaction mechanism will be combined with other reactions occurring during combustion and incorporated into a global combustion model using CHEMKIN. Modeling results will be compared to the experiment and the effects of flue gas composition and quench rate will be investigated.

Experiments will be performed through generating flue gas by combusting natural gas. Mercury and chlorine will be introduced into a laminar premixed methane-air flame. Cooled flue gas will be sampled and sent to the mass spectrometer specially designed for mercury observation. The use of mass spectrometer allows for distinguishing between the different forms of oxidized mercury (Hg+, Hg+2), which has not been achieved before. The direct measurement of mercury will aid in the understanding of mercury speciation in flue gas, thus allowing for the development of novel control technologies for mercury removal.