URS Group, Inc., Austin, TX, will demonstrate at the pilot scale the use of solid honeycomb catalysts to promote the oxidation of elemental mercury in the flue gas from coal combustion, and the use of a wet flue gas desulfurization (FGD) system downstream to remove the oxidized mercury at high efficiency. The project's pilot tests, conducted at electric generating plants using wet flue gas desulfurization systems and particulate collection systems, will be conducted for periods up to 14 months to provide data for future, full-scale designs. Mercury-oxidation potential will be measured periodically to provide long-term catalyst life data. The project is applicable to about 90,000 megawatts of generation capacity. Project partners are the Electric Power Research Institute, Palo Alto, CA, which will co-manage and co-fund the pilot tests, and five utilities.

Process Concept

Project Abstract: The proposed project will develop a process that uses honeycomb catalysts to promote the oxidation of elemental mercury in the flue gas from coal-fired power plants to enhance removal in downstream wet lime or limestone flue gas desulfurization (FGD) systems. The oxidants are already present in the flue gas, and may include chlorine, hydrochloric acid, oxygen and/or other species. Oxidized mercury is removed in the wet FGD absorbers, and co-precipitates in a stable form with the byproducts from the FGD system. The co-precipitated mercury does not appear to adversely affect the disposal or reuse properties of the FGD byproduct.

The project will test catalysts previously identified as being effective in small-scale research funded by the DOE, but in a commercial form, at larger scale and for longer periods. The proposed testing will provide engineering data for future, full-scale designs. The pilot-scale catalyst tests will continue for approximately 14 months at each site. Over that period, mercury oxidation percentages across each catalyst will be measured on approximately a monthly basis using a mercury semi-continuous emission monitor, to provide longer-term catalyst life data. The mercury monitor data will be verified by triplicate runs with the Ontario Hydro method on three occasions over the 14 months at each site. Other measurements will be made, including characterizing the host site’s flue gas and closing mercury mass balances around a pilot wet FGD system.

Oxidation Catalyst Pilot Unit

Besides providing performance data for the mercury oxidation catalysts, the testing will provide an opportunity to integrate the oxidation catalyst technology with a pilot-scale wet FGD absorber. The addition of a pilot-scale absorber will allow determination of the removal efficiency across a wet FGD system of mercury oxidized by up to four different catalysts. The FGD absorber will be operated intermittently under lime/natural oxidation and limestone/forced oxidation conditions.

Based on information collected in the U.S. EPA's Mercury Information Collection Request (ICR), this technology is probably best suited for plants with a high-efficiency particulate control device upstream of the FGD system, rather than systems that use high-energy scrubbers to achieve combined particulate and SO₂ control. The former represents the majority of FGD systems in the U.S., about 90,000 MW of generating capacity. The ICR results also suggest that catalytic oxidation of elemental mercury would be most effective on flue gases from lignite and subbituminous coal, where most of the mercury is present in the elemental form. There are approximately 28,000 MW of scrubbed capacity firing these fuels, with more systems planned.

This project is supported by a team consisting of URS Group, Inc., EPRI, and four electric utilities. URS will be the prime contractor, and will design and construct the pilot units, conduct all catalyst testing and prepare project reports. EPRI will co-manage and co-fund the effort. EPRI also holds the intellectual property rights to the catalytic oxidation process being proposed. The four utilities will provide co-funding, technical guidance, and host sites for testing. The utilities are Great River Energy, which fires a North Dakota lignite at their Coal Creek Station, City Public Service of San Antonio, which fires a Powder River Basin subbituminous coal at their J.K. Spruce Plant, TXU which fires a blend of 80% Texas lignite and 20% PRB at the Monticello Steam Electric Station Unit 3, Duke Energy’s Marshall Station which fires Eastern bituminous low sulfur coal, and Southern Company Services, which fires an Eastern low-sulfur bituminous coal at their Plant Yates. All host sites have existing wet FGD systems downstream of high-efficiency particulate control devices.

The proposed project represents a success for the DOE National Energy Technology Laboratory's mercury research program. The catalytic oxidation process was developed in a DOE sponsored Mega-PRDA project that began in 1995. Pilot-scale testing in the proposed project would represent a logical progression towards commercialization of the mercury catalytic oxidation process.