Full-Scale Testing of a Mercury Oxidation Catalyst Upstream of a Wet FGD System

Abstract

This document presents and discusses results from Cooperative Agreement DE-FC26-06NT42778, "Full-scale Testing of a Mercury Oxidation Catalyst Upstream of a Wet FGD System," which was conducted over the time-period July 24, 2006 through June 30, 2010. The objective of the project was to demonstrate at full scale the use of solid honeycomb catalysts to promote the oxidation of elemental mercury in pulverized-coal-fired flue gas. Oxidized mercury is removed downstream in wet flue gas desulfurization (FGD) absorbers and collected with the byproducts from the FGD system. The project was co-funded by EPRI, the Lower Colorado River Authority (LCRA), who also provided the host site, Great River Energy, Johnson Matthey, Southern Company, Salt River Project (SRP), the Tennessee Valley Authority (TVA), NRG Energy, Ontario Power and Westar. URS Group was the prime contractor and also provided cofunding.The scope of this project included installing and testing a gold-based catalyst upstream of one full-scale wet FGD absorber module (about 200-MW scale) at LCRA's Fayette Power Project (FPP) Unit 3, which fires Powder River Basin coal. Installation of the catalyst involved modifying the ductwork upstream of one of three wet FGD absorbers on Unit 3, Absorber C. The FGD system uses limestone reagent, operates with forced sulfite oxidation, and normally runs with two FGD modules in service and one spare. The full-scale catalyst test was planned for 24 months to provide catalyst life data. Over the test period, data were collected on catalyst pressure drop, elemental mercury oxidation across the catalyst module, and mercury capture by the downstream wet FGD absorber.The demonstration period began on May 6, 2008 with plans for the catalyst to remain in service until May 5, 2010. However, because of continual increases in pressure drop across the catalyst and concerns that further increases would adversely affect Unit 3 operations, LCRA decided to end the demonstration early, during a planned unit outage. On October 2, 2009, Unit 3 was taken out of service for a fall outage and the catalyst upstream of Absorber C was removed. This ended the demonstration after approximately 17 months of the planned 24 months of operation. This report discusses reasons for the pressure drop increase and potential measures to mitigate such problems in any future application of this technology.Mercury oxidation and capture measurements were made on Unit 3 four times during the 17-month demonstration. Measurements were performed across the catalyst and Absorber C and "baseline" measurements were performed across Absorber A or B, which did not have a catalyst upstream. Results are presented in the report from all four sets of measurements during the demonstration period. These results include elemental mercury oxidation across the catalyst, mercury capture across Absorber C downstream of the catalyst, baseline mercury capture across Absorber A or B, and mercury re-emissions across both absorbers in service. Also presented in the report are estim...

Oxidation Catalysts for Elemental Mercury in Flue Gases—A Review

“…Recently, the potential use of gold-based catalysts in mercury pollution control applications has attracted much interest from academia as well as industry [29,30,37,40,46,47]. The studies have concentrated on the temperature range between 140 and 225 °C with, in most cases, 1 wt.-% gold on alumina and in one case with Au on a Teflon-coated quartz filter.…”

“…Pilot [39,46] and full scale [40,47] investigations were conducted with the main objective to demonstrate the effectiveness and deactivation properties of a commercial gold catalyst wash coated on γ-alumina honeycomb substrate in promoting Hg el oxidation in flue gases from coal combustion. The catalyst modules were located downstream of a particulate control device [47] and in the flue gas scrubber inlet duct [40].…”

“…The catalyst modules were located downstream of a particulate control device [47] and in the flue gas scrubber inlet duct [40]. The flue gas contained only about 2 ppm HCl and 500 pm SO 2 .…”

“…It is believed that some of this activity loss was real, but that a substantial portion was "artificial" in that it resulted from build-up of fly ash in the catalyst, which blocked the otherwise active surface area of the catalyst. Gas flow to parts of the second and third layers was blocked by fly ash buildup in the first layer [40]. An uneven distribution of the gas flow and the small channel width of 3.2 mm of the honeycomb catalyst contributed to the blocking.…”

Pilot Testing of Mercury Oxidation Catalysts for Upstream of Wet FGD Systems

“…A later full-scale demonstration of oxidation catalyst technology was also limited by fly ash buildup and pressure drop increases across 64 cpsi (9.9 cells/cm 2 ) catalysts 7 . However, in this case it was theorized that the problems were related to process scale-up issues (e.g., poor flue gas velocity distribution and non-ideal sonic horn placement) rather than clearly representing a limitation on the technology.…”