The impact of wet flue gas desulfurization scrubbing on mercury emissions from coal-fired power stations

Journal Article · Fri Jul 01 00:00:00 EDT 2005 · Journal of the Air and Waste Management Association

DOI:https://doi.org/10.1080/10473289.2005.10464689· OSTI ID:20638631

Niksa, Stephen; Fujiwara, Naoki ^[1]

---

1. Niksa Energy Associates, Belmont, CA (US)

The article introduces a predictive capability for mercury (Hg) retention in any Ca-based wet flue gas desulfurization (FGD) scrubber, given Hg speciation at the FGD inlet, the flue gas composition, and the sulphur dioxide (SO{sub 2}) capture efficiency. A preliminary statistical analysis of data from 17 full-scale wet FGDs connects flue gas compositions, the extents of Hg oxidation at FGD inlets, and Hg retention efficiencies. These connections show that solution chemistry within the FGD determines Hg retention. A more thorough analysis based on thermochemical equilibrium yields highly accurate predictions for total Hg retention with no parameter adjustments. For the most reliable data, the predictions were within measurement uncertainties for both limestone and Mg/lime systems operating in both forced and natural oxidation mode. With the U.S. Environmental Protection Agency's (EPA) Information Collection Request (ICR) database, the quantitative performance was almost as good for the most modern FGDs, which probably conform to the very high SO{sub 2} absorption efficiencies assumed in the calculations. The large discrepancies for older FGDs are tentatively attributed to the unspecified SO{sub 2} capture efficiencies and operating temperatures and to the possible elimination of HCl in prescrubbers. The equilibrium calculations suggest that Hg retention is most sensitive to inlet HCl and O{sub 2} levels and the FGD temperature; weakly dependent on SO{sub 2} capture efficiency; and insensitive to HgCl{sub 2}, NO, CA:S ratio, slurry dilution level in limestone FGDs, and MgSO{sub 3} levels in Mg/lime systems. Consequently, systems with prescrubbers to eliminate HCl probably retain less Hg than fully integrated FGDs. The analysis also predicts re-emission of Hg{sub 0} but only for inlet O{sub 2} levels that are much lower than those in full-scale FGDs. 12 refs., 5 figs., 3 tabs.

• OSTI ID: 20638631
• Journal Information: Journal of the Air and Waste Management Association, Vol. 55, Issue 7; Other Information: [e-mail]; ISSN 1047-3289
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
20 FOSSIL-FUELED POWER PLANTS
FLUE GAS
DESULFURIZATION
MERCURY
EMISSION
COAL
RETENTION
FOSSIL-FUEL POWER PLANTS
SCRUBBERS
CHEMICAL COMPOSITION
OXIDATION
EFFICIENCY
REGRESSION ANALYSIS
PREDICTION EQUATIONS
LIMESTONE
LIME-LIMESTONE WET SCRUBBING PROCESSES
PARAMETRIC ANALYSIS
MERCURY CHLORIDES
HYDROCHLORIC ACID