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The catalytic oxidation on elemental mercury (Hg0) to water-soluble oxidized mercury (Hg2+) is a good mercury (Hg) control approach for coal-fired power plants, and Hg2+ can be removed by the existing wet flue gas desulfurization (FGD) device. Oxygen-enriched combustion (OEC) is considered as an optimal option for the post CO2 capture among the clean coal combustion technologies. On the basis of the established bench-scale experimental apparatus, this paper studied the influence mechanism of a high H2O concentration on Hg0 oxidation in the simulated flue gas in OEC. The results showed that both the high HCl concentration and the high temperature could improve the Hg0 oxidation in the simulated flue gas above 500 °C and with as high as 30% of H2O content in OEC. A key intermediate reaction step was needed to complete the reaction between Hg0 and HCl. HCl was first oxidized to oxidative Cl by O2. Then, Hg0 was further oxidized by oxidative Cl. The high H2O concentration could inhibit this process of Hg0 oxi...

The change of mercury speciation was measured by a continuous emission monitor when elemental mercury (Hg°) was adsorbed by activated carbon (AC-CS, made from coconut shell) in simulated coal-fired flue gas on a bench-scale adsorption experiment. Results showed that Hg° was oxidized to divalent mercury (Hg2+) and escaped as Hg2+ completely during the adsorption process in simulated flue gas. The components, such as NO, NO2, etc., had double influences on the Hg° adsorption on AC-CS. The positive way was that they could oxidize Hg° to Hg2+ with the catalysis of AC-CS surface, which promotes the Hg° adsorption, and the negative way was that they had competitive adsorption with Hg2+ on the AC-CS surface to inhibit the adsorption to a certain degree. It is economical to use the original AC to capture Hg in a complete flue gas with oxidization components and to use chemically treated AC in a clean flue gas.

Bench-scale adsorption experiments were conducted to explore and verify the change of mercury speciation during elemental mercury (Hg0) adsorption by activated carbon (AC) impregnated with chlorine...

Hg 0 adsorption experiments with different kinds of activated carbons (ACs) were conducted in nitrogen environment to study the effects of ACs with different surface characteristics on adsorption. Three kinds of ACs prepared by steam activation did not adsorb elemental mercury (Hg 0 ) in nitrogen environment, while another kind of AC prepared by chemical activation using zinc chloride (ZnCl 2 ) showed significant Hg 0 adsorption capability in the same experimental conditions because Hg 0 was oxidized by the oxidative elements on the surface of AC. ACs without oxidative elements did not adsorb Hg 0 through physical adsorption in nitrogen environment. It was therefore concluded that Hg 0 adsorption by AC was a chemical adsorption process.

In the bench scale, gaseous mercury oxidization was investigated in postcombustion conditions with the experimental flue gas. The baseline experimental flue gas consisted of CO 2 and N 2 . Other flue-gas constituents varied with O 2 , SO 2 , HCl, and NO. The measurement of mercury speciation was carried out at the downstream of the reaction tube using the Ontario Hydro method. Results showed that the possible intermediates Cl and Cl 2 from HCl are the most important factors in mercury oxidization in the experimental flue gases. More mercury oxidization occurs with a higher reaction temperature and higher HCl concentration in most of experimental flue gases with HCl addition. O 2 and NO also enhance mercury oxidization in the experimental flue gases with or without HCl and SO 2 . However, the effect of SO 2 on mercury oxidization depends upon the presence of HCl.

The stability of adsorbed mercury on activated carbon (AC) is very important for avoiding reemission. Based on research concerning the stability of mercury on the AC relative to leaching and thermal desorption, our conclusions are as follows. Leaching tests show that mercury appears to be very stable on the AC. The Hg concentration in the leachate is much lower than the TCLP safety limit of 0.025 mg/l. Leaching time and liquid to solid (L/S) have some influence on the leaching results, but the influence is far less than which leads the Hg concentrate to exceed the safety limit. Leaching tests for mercury at lower and higher pH are aggressive compared with the neutral pH test. There is much more mercury released from the AC at longer heating time for mercury. At the same time, it seems that the stability of adsorbed original Hg0 on the AC is stronger than that of adsorbed original Hg2+.