Recent work at Ohio University has led to development of membrane collection “plates” forapplication in electrostatic precipitators. These membranes generally are made of woven, fibrous,corrosion resistant materials that permit a small degree of gas penetration between flow channelsthrough the fibers. Following work done by other researchers using TiO_2 particles activated withuv radiation to oxidize and capture elemental mercury (Hg~0), an investigation was launched intoapplication of a TiO_2 coated membranes as a potential Hg~0 collection agent in an electrostaticprecipitator. A lab scale electrostatic precipitator was constructed to perform Hg~0 collectionexperiments using simulated coal flue gas conditions with three coated Omnisil substratemembranes coated with an average of 1-2 μm (thickness) of TiO_2. Temperatures weremaintained at 110-150 °C with an average delivery rate of 20-30 μg/m~3 of Hg~0. Various levels ofuv radiation were used to activate the TiO_2, as generated by combinations of uv lamps and fromthe corona produced by the discharge electrodes. Both gas phase measurements taken using theOntario Hydro protocol and solid (captured) phase measurements indicated that 9-18% ofelemental mercury was oxidized and captured on TiO_2 coated membrane collection electrodes.Further, it was found that 97% of all Hg was Hg~0 in the gas stream, both up- and downstream ofthe collectors, while 94% of Hg was found to be in the oxidized form on the membranes. Thisindicated that Hg oxidation occurred on the surface of TiO_2 and the mercury compound wasstable on the collection surface. Results also indicated that the reaction rate was enhanced byincreasing uv intensity and temperature. Finally, it is speculated that a beneficial transportphenomena was generated inside the precipitator because electrostatic forces should notsignificantly affect the transport of gas phase Hg~0. In order for Hg~0 to be collected on surfacesparallel to the bulk gas flow, the gas must be “pushed” towards the collectors. Preliminarymodeling indicates that turbulent transport would not have been sufficient to produce 9-18%capture. Corona wind transport could have played a role and will be examined in future work.
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