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S22 Mercury control at coal-fired power plants

Friday, 29 July, 2011

FS22-O1 — 11:00-11:15
CONSIDERATIONS IN MATCHING MERCURY CONTROL TECHNOLOGIES TO POWER PLANT CONDITIONS
Author: NELSON, Sid1
(1)Albemarle Corporation, Sid.Nelson.Jr@Albemarle.com

The United Nations is in the process of formulating a global instrument for environmental mercury reductions which includes an examination of the possibility of emission reductions from coal-fired power plants. In recent years, a variety of mercury control technologies have been developed for such plants and an understanding has emerged of their relative strengths and weaknesses.

In applying these technologies, however, different countries are in different situations. Each nation has its own coal supplies with their particular chemical characteristics, its own existing fleet of plant configurations, its own coal residue disposal practices, and its own capability to pay for power plant emission reductions. This presentation will explore each of these considerations – coal characteristics, fleet configurations, and disposal practices – in relation to the various technology options that are available in order to assist in the minimization of costs and maximization of emission reductions.

FS22-O2 — 11:15-11:30
SORBENT-BASED MERCURY CONTROL STRATEGIES AT A PLANT COMBUSTING SUBBITUMINOUS COAL
Authors: PAVLISH, John H.1, LENTZ, Nicholas B.1, KAY, John P.1, HAMRE, Lucinda L.1
(1) University of North Dakota Energy & Environmental Research Center, jpavlish@undeerc.org

The Energy & Environmental Research Center (EERC) has been evaluating and developing sorbent-based strategies for mercury control that are both effective and cost-efficient for well over a decade. Mercury control strategies that can concurrently capture other trace metals are very valuable. The EERC conducted such an evaluation of two sorbent-based strategies at a 400-MW subbituminous power plant that included baseline, parametric, and long-term measurements. Testing included commercial sorbent-based strategies—commercial carbons and a suite of proprietary sorbent enhancement additives and sorbents (carbon and noncarbon based)—with special emphasis on evaluating balance-of-plant impacts. Trace metal measurements were obtained by coal analysis, continuous mercury monitors, and sorbent traps. Fly ash was analyzed for halogens, mercury, and loss-on-ignition changes as a result of using the technologies. This project showed the benefit of coupling proprietary sorbent enhancement additives with sorbents to achieve high levels of mercury removal with concurrent removal of other trace metals.

FS22-O3 — 11:30-11:45
GEOCHEMISTRY AND FATE OF MERCURY IN COAL FIRED POWER PLANT FLUE GAS DESULFURIZATION (FGD) SCRUBBER SYSTEMS
Authors: BLOOM, Nicolas S1, CHU, Paul2
(1)URS Corp. R&D, nbloom@ymail.com; (2) Electric Power Research Institute.

Recent investigations regarding the behaviour of mercury in coal-fired power plant FGD scrubbers and subsequent wastewater treatment systems have revealed some surprising results. In some FGD systems, Hg is found to be largely in the labile Hg(ll) form, while at the other extreme, virtually all of the inorganic Hg is so strongly complexed that it is not even extractable by ammonium pyrrolidine dithiocarbamate (APDC). These observations are strongly correlated with the degree of successful Hg removal by the waste water treatment systems downstream of the FGD scrubbers. Breaking down the chemical composition of the aqueous matrices revealed two likely variables most strongly affecting the complexation of Hg in solution—Total iodine and dissolved organic carbon (DOC), most likely in the form of humic acids. While the source of iodine is likely due to the combustion of the coal, the presence of humic-like substances is more of a mystery. However, after careful consideration, it seems likely that humic substances derive from the dissolution of massive amounts of limestone used in the FGD scrubbers. We provide current evidence for these conclusions, together with a plan for future lab and modeling studies which will further clarify the very complex set of parameters and reactions controlling the geochemistry and fate of Hg in FGD systems. In addition to iodine and humic acids, another key control on the fate of Hg may be the mineralogy of the solid phase, which includes gypsum (CaSO4.2H2O), anhydrite (CaSO4), calcite (CaCO3), aragonite (CaCO3), hematite (Fe2O3), goethite (am-FeOOH), and pyrolusite (MnO2), all of which differ in their adsorption characteristics with respect to Hg(ll). The FGD aqueous phase is also awash with strongly complexing ligands such as thiosulfate (S2O3=), dithionite (S2O2=), meta-bisulfite (S2O5=), polycarboxylic acids, and amidosulfonic acids (e.g. amido-disulfonic acid (ADS or HN(HSO3)2), and hydroxylamine monosulfonic acid (HAMS or HOHNHSO3). Finally, in some FGD systems, the ORP-pH boundaries are consistent with the production of reduced elemental mercury (Hgo), as well as Seo, So, and Ago, all of which bind strongly with Hgo, and so affect which phase Hg will report to. We will present data collected from six (unidentified) real world sites, as well as preliminary modeling efforts using Rockware’s Geochemist’s Workbench™.

FS22-O4 — 11:45-12:00
DEACTIVATION PERFORMANCE AND MECHANISM OF ALKALI (EARTH) METALS ON V2O5-WO3/TIO2 CATALYST FOR OXIDATION OF GASEOUS ELEMENTAL MERCURY IN SIMULATED COAL-FIRED FLUE GAS
Authors: WAN, Qi1, DUAN, Lei1
(1)Tsinghua university, wanq07@mails.tsinghua.edu.cn

Catalysis deactivation caused by alkali (earth) metals (Na, K, Mg and Ca) over V2O5-WO3/TiO2 catalyst for oxidation of Hg0 by hydrogen chloride was investigated in the presence of O2. Deactivation effects caused by alkali (earth) metals were well associated with alkalinity value and shown in sequence as: K > Na ~ Ca > Mg. Results also indicated that the deactivation increased proportionately with alkali (earth) metal doping amounts. Further investigations on BET surface area, XRD, Hg-TPD, XPS and H2-TPR demonstrated that surface characteristics were not the dominant factor for the deactivation. However, surface coverage by alkali (earth) metals might cause surface area and total pore volume decreases. Hg-TPD results indicated that the doping of alkali (earth) metals would decrease surface Hg0 adsorption amount associated with alkalinity value. More decrease of surface adsorption and redox ability (Oα) in doped catalysts than the fresh one could lead to less active performance according to the H2-TPR and XPS of O1s results. Consequently, the decrease of Hg0 adsorption and surface redox ability (Oα), and the formation of inactive metavanadate species such as KVO3 could be responsible for the deactivation performance caused by alkali (earth) metals over vanadium-based catalyst for oxidation of gaseous elemental mercury.

Friday, 29 July, 2011