Mercury transformations in coal combustion flue gas

• Published in: Fuel processing technology 2000-06, Vol.65, p.289-310
• Main Authors: Galbreath, Kevin C., Zygarlicke, Christopher J.
• Format: Article
• Language: English
• Subjects: Air toxics; Coal; Combustion; Hazardous air pollutants; Mercury; Speciation; Transformations
• ISSN: 0378-3820; 1873-7188
• DOI: 10.1016/S0378-3820(99)00102-2

Mercury chlorination [i.e., formation of HgCl 2(g)] is generally assumed to be the dominant mercury-transformation mechanism in coal combustion flue gas. Other potential mechanisms involve mercury interactions with ash particle surfaces where reactive chemical species, oxidation catalysts, and active sorption sites are available to transform Hg 0(g) to Hg 2+X(g) (e.g., where X is Cl 2 or O) as well as Hg 0(g) and HgCl 2(g) to particulate mercury, Hg(p). Results from an investigation of Hg 0(g)–O 2(g)–HCl(g) and Hg 0,2+(g)–HCl(g)–CaO(s)-fly ash interactions in a 42-MJ/h combustion system are consistent with the following mechanisms: mercury chlorination, catalysis of mercury oxidation by Al 2O 3(s) and/or TiO 2(s), and mercury sorption on a calcium-rich (25.0 wt.% CaO) subbituminous coal fly ash. Additions of 50 and 100 ppmv of HCl(g) and ≈12.6 wt.% of CaO(s) to the subbituminous coal combustion environment inhibited Hg(p) formation, primarily via a change in ash surface chemistry and a decrease in particle surface area, respectively.