Assessing Sorbents for Mercury Control in Coal-Combustion Flue Gas

Abstract

Sorbent injection for Hg control is one of the most promising technologies for reducing Hg emissions from powergeneration facilities, particularly units that do not require wet scrubbers for SO 2 control. Since 1992, EPRI has been assessing the performance of Hg sorbents in pilot-scale systems installed at full-scale facilities. The initial tests were conducted on a 5000-acfm (142-m 3 /min) pilot baghouse. Screening potential sorbents at this scale required substantial resources for installation and operation and did not provide an opportunity to characterize sorbents over a wide temperature range.Data collected in the laboratory and in field tests indicate that sorbents are affected by flue gas composition and temperature. Tests carried out in actual flue gas at a number of power plants also have shown that sorbent performance can be site-specific. In addition, data collected at a field site often are different from data collected in the laboratory, with simulated flue gas mixed to match the major components in the site's gas. To effectively estimate the costs of Hg sorbent systems at different plants, a measure of sorbent performance in the respective flue gases must be obtained. However, injection testing at multiple facilities with large pilot systems is not practical.Over the past five years, fixed-bed characterization testing, modeling studies, and bench-scale injection testing have been undertaken to develop a low-cost technique to characterize sorbent performance in actual flue gas and subsequently to project normalized costs for Hg removal prior to full-scale demonstration. This article describes the techniques used and summarizes field-testing results from two plants burning Powder River Basin (PRB) coal for commercial activated carbon and several other sorbent types. Full-scale projections based on the results and data collected on larger-scale systems also are included.

Pyrrolidinium Imides: Promising Ionic Liquids for Direct Capture of Elemental Mercury from Flue Gas

“…Many research efforts have focused on the modification of activated carbon by, for example, impregnation with sulfur or halogens to improve mercury capture efficiency (Krishnan et al 1994;Vidic and Chang 1998;Huggins et al 1999;Sjostrom et al 2002). However, these modifications have not been shown to increase elemental mercury capacity significantly (O'Dowd et al 2004).…”

The Homogeneus Forcing of Mercury Oxidation to provide Low-Cost Capture

“…These SCR and SNCR processes utilize urea or ammonia in a reduction reaction with NO X to form water and elemental nitrogen. The titanium and vanadium oxides used as catalysts in SCR promote mercury oxidation (Richardson et al, 2002;Lee et al, 2004;Richardson et al, 2003). Mercury is found to oxidize across these systems with the presence of HCl (Lee et al, 2003;.…”

Field Test Program to Develop Comprehensive Design, Operating, and Cost Data for Mercury Control Systems

“…Near real-time, vapor-phase mercury measurements were made using semi-continuous emissions monitors (S-CEM) designed and operated by Apogee Scientific, Inc. This instrument was developed with EPRI funding to facilitate EPRI research and development efforts 5 . Multiple S-CEMs were used throughout the system.…”