It somewhat resembles a honeycomb: row upon row of sturdy fabric bags, each 26 feet long and stretched over a steel frame that preserves its conical shape. For high-tech gadgetry, it s short on bells and whistles. Yet this mechanism inside a cavernous building at the Presque Isle Power Plant may help achieve one of the nation s top environmental goals: slashing mercury emissions from incineration of coal to generate electricity.

Its part of a new system called Toxecon. Designed by industry researchers, it prevents gaseous mercury from escaping into the atmosphere by mixing it with carbon, creating ash that is collected in the fabric bags and trucked to landfills. Power companies are rushing to develop such technology as pressure mounts from government regulators and environmental activists to reduce emissions of mercury and other harmful pollutants. Presque Isle was chosen in 2003 to host the first demonstration of Toxecon under real-world operating conditions.

After initial testing this year, project manager Steven Derenne says theres reason for optimism that Toxecon can filter out 90 percent of the mercury from low-sulfur, subbituminous coal burned at many U.S. electric plants. The state Department of Environmental Quality will impose that standard by 2015 for Michigan, while the Bush administration is requiring a more gradual 70 percent nationwide reduction.

"Im confident that we can make this work," says Derenne, an engineer with We Energies, the Milwaukee-based company that owns Presque Isle. The 625-mewagatt plant on the Lake Superior shore produces half the electricity generated in the Upper Peninsula -- and is the region s leading generator of atmospheric mercury pollution. But problems remain, Derenne said, from operational glitches to major hurdles such as figuring out how to calibrate instruments so they can measure the tiny bits of mercury captured in the gas.

The Toxecon experiment comes amid debate over whether power companies have the ability -- and the money -- to hit the 90 percent mercury reduction target set by Gov. Jennifer Granholm in April. A number of other states, including Illinois, Pennsylvania and Minnesota, are adopting the same requirement. Vince Hellwig, chief of the state DEQs air quality division, says technology is available that can enable companies to meet the 2015 deadline. If they implement a strategy in good faith and it flops, theyll get more time, he says. Industry leaders say the job is harder than it sounds.

Mercury is a trace element in coal and forms roughly 1 part per billion of the gas created by incineration. Capturing 90 percent of it is like dumping 30 billion white pingpong balls and 30 black ones into a football stadium, then tracking down 27 of the black balls, says Lou Pocalujka, senior environmental planner for Consumers Energy. "It really relies on the technology being able to deliver," he says. Companies also say a mandatory 90 percent reduction will make them pour money into research and equipment yielding relatively little benefit.

"It s really not going to gain very much in terms of public health," says Leonard Levin, principal technical manager with the Electric Power Research Institute (EPRI) in Palo Alto, Calif., the industry s research arm. Most of the mercury that can become methylmercury, the form that accumulates in fish and can cause neurological damage in humans, would be captured under the Environmental Protection Agencys plan for a 70 percent rollback, Levin says. That could be achieved mostly with existing technology, such as smokestack scrubbers, used for reducing other pollutants, he says. Detroit Edison is spending more than $1 billion on such equipment for its Monroe Power Plant, the biggest mercury emissions source in Michigan, says Skiles Boyd, vice president for environmental management.

The remaining 30 percent of mercury would be mostly a different variety that doesn t settle in nearby waters, but tends to circulate globally in the atmosphere with mercury generated elsewhere, Levin says. Costly new technologies such as carbon injection are needed to capture it. But Derenne says it s not certain that existing technology can achieve the 70 percent reduction. It depends on the type of coal used and other factors, he says.

Either way, EPRI is pushing ahead with technology aimed at reaching the 90 percent goal -- including Toxecon, which the institute patented. The U.S. Department of Energy considered its prospects solid enough to pay half the $53 million cost of installing and testing the system on three of the Presque Isle plant s nine generating units. Toxecon injects activated, powdery carbon into the superheated gas from coal incineration. The carbon absorbs the mercury and flows into a newly constructed building called a "bag house," where its trapped inside the network of fabric bags.

As a bonus, designers hope the process also will remove up to 70 percent of the sulfur dioxide and 30 percent of the nitrogen oxide from the gas, along with the 1 percent of fly ash from coal combustion that isnt captured earlier. The system has reached the 90 percent threshold for mercury removal during testing this year, although not continuously. Once perfected, it should be able to average 90 percent if the correct amount of carbon is injected, Derenne says. The three Presque Isle units emit a combined 90 pounds of mercury in a typical year. If Toxecon succeeds, it will prevent about 82 pounds from slipping into the air.

But nagging problems have surfaced, such as overheated gas burning the bags and water collecting in ash hoppers for no apparent reason. Those issues were resolved, but the latest struggle involves how to make the captured mercury less dusty so it doesn t blow away. "We re plowing new ground and theres always these setbacks," Derenne says while conducting a tour of the baghouse. But the industry can benefit from them, he adds. "Theyre going to build on the lessons learned at Presque Isle -- probably not just in the U.S., but the world."

Regardless of how the experiment turns out, Toxecon is not "a uniform magic potion" for all mercury emissions, Levin says. Power plants have varying configurations and use different types of coal, so a mechanism that succeeds one place might not somewhere else.
(Por John Flesher, Environmental News Network, 29/08/2006)