Effect of flue gas components on Hg⁰ oxidation and adsorption by modified walnut shell coke in O₂/CO₂ atmosphere

Abstract

Walnut shell was pyrolyzed and then impregnated with NH4Br to make sorbent for Hg0 removal. The effect of flue gas components on Hg0 removal performance was studied in O2/CO2 atmosphere, and the results were compared with those in O2/N2 atmosphere. The mercury valence distribution during adsorption was obtained. NH4Br‐modified walnut shell coke promoted Hg0 removal, the Br‐containing chemisorption site was a crucial factor. Although addition of CO2 did not introduce new oxygen‐containing functional groups or change the mercury species, Hg0 removal efficiency increased significantly. This may be because CO2 can increase the active sites on the carbon surface. In O2/N2 atmosphere, O2 promoted formation of active center on the sorbent surface, which made Hg0 more easily adsorbed and then reacted with Br‐functional group to form more HgBr2. In O2/CO2 atmosphere, O2 promoted formation of some reactive carbon–oxygen complexes which acted as catalyst to facilitate Hg0 oxidation and formation of HgO. NO improved removal of Hg0, because the C─O functional group on the sorbent surface could catalyze the conversion of NO to NO2 in the adsorbed state and then formed Hg2(NO3)2. SO2 consumed oxygen on the sorbent surface and inhibited the Hg0 removal.

Experimental study Char‐NO reduction characteristics at elevated pressure

“…The N‐5 and N‐6 structures were gradually transformed into more stable N‐Q structures that had more aromatic ring. Wang 19 also obtained the experimental conclusions that the N‐5 and N‐6 structures on the surface of char samples decreased and the N‐Q increased as the reaction temperature increased during the temperature‐programmed reduction of NO experiments. Zhang 30 also conducted XPS analysis on char samples with two different pyrolysis temperatures and found that the relative contents of N‐5 and N‐6 on the surface of the pyrolysis char that prepared at 1000°C are lower than that at 800°C under high pressure (0.8–1.2 MPa) conditions, while the evolution trends of N‐Q of those were opposite.…”

“…Its main components were NO, N 2 O, and NO 2 , of which NO accounted for more than 90%. At present, many researchers have carried out some studies on the NO x emission characteristics during the combustion process of pulverized coal/char samples under pressurized oxy‐fuel combustion conditions 8–19 …”

Decomposition kinetics of sodium amalgam in fixed bed of WC‐coated tubular SS‐304 packing: Modelling and validation

“…Recently, however, significantly novel materials and processes have been developed to efficiently accomplish mercury removal from air and water at plant scale 9–13 . Furthermore, much research has been done to oxidize the mercury vapour from Hg 0 to Hg 2+ to blunt its detrimental consequences on lungs and brain after inhalation 14–16 …”

“…[9][10][11][12][13] Furthermore, much research has been done to oxidize the mercury vapour from Hg 0 to Hg 2+ to blunt its detrimental consequences on lungs and brain after inhalation. [14][15][16] To overcome the drawback of graphite erosion, the present work employs tubular packing of stainless steel SS-304 with tungsten carbide (WC) coated on its outer surface using indigenously developed laser-directed energy deposition (LDED) technique for application as a plausible alternative to conventional graphite packing. Meneghini and Bertin observed that the coating on outer surface of amalgam wettable material (here, SS-304) should be pure or compound carbide of electrically conducting transition metals such as titanium, zirconium, niobium, tantalum or tungsten.…”