Yongxin Zhao

Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Chemical Engineering


This research is particularly related to mercury control technologies. The state of the art in mercury emission control is generally classified into two categories: Mercury Transformation and Mercury Capture. In this research, two chapters (3 & 4) are specifically related to mercury transformation and another two (5 & 6) are related to mercury capture.

Chapter 3 investigates the capabilities of HCI and CU on Hg° oxidation. The resulting data indicated that both were effective in the combustor. However, HCI was less effective in a quartz reactor. Subsequently, the inhibitory effects of NO and S02 were identified in the quartz reactor. The result and mechanism showed that the presence of HiO was necessary for NO and S02 to have an inhibitory effect probably by scavenging Cl and CI2 in the flue gas.

Chapter 4 studies the capability of gold catalyst in catalytically promoting Hg° oxidation by chlorine. Gold was selected as catalyst because of its inertial property in adsorbing ITO, S02 and NO. This property was demonstrated critical to avoid the inhibitory effects of NO and SOi on Hg° oxidation.

Chapter 5 presents recent insights, theoretically and experimentally, into the effects of aqueous S(IV) species (sulfite or bisulfite) on llg11 reemissions. Evidence indicated that bisulfite, rather than sulfite, was the primary species in the wet flue gas desulfurization (FGD) scrubber that caused llg" to be reemitted. The llg" reemission in S(1V) solution was also simulated by fitting experimental data, showing that the llg" reemission was proportional to HSOf concentration, but inversely proportional to total S(IV) concentration. When industrial limestone was used to validate the gained mechanism, it appeared that limestone was also capable of suppressing Hg° reemission by adsorbing I lgCE onto its alkaline surfaces.

Chapter 6 particularly relates to mercury control in wet flue gas desulfurization systems. The effects of such scrubber operating parameters as liquid/gas (L/G), S02 concentration, and slurry pH on mercury capture and reemission were investigated. The result indicated that the capture of oxidized mercury across the scrubber was strongly dependent upon the water solubility of HgCI2, and insensitive to slurry pH and S02 concentration. Increasing the L/G increased the reemission source by delivering more Hg2' back to the spray tower and enhanced the contact surfaces.