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Low-VOC coatings cut air pollution

Low-VOC coatings cut air pollution

According to the Environmental Protection Agency (EPA), air quality in the U.S. has steadily improved since 1970. Professionals working in industry agree that air pollution in this country has become less serious.

"Certain cities still have air pollution problems," says John Burke, manager of corporate environmental engineering for Eaton Corp., Cleveland, OH. "Generally things are getting slightly better, not slightly worse." And Robert Lapp, director, governmental and public affairs at Timken Corp., Canton, OH, insists that air quality has improved. "Air pollution in the U.S. is substantially less than it was 20 years ago. Investment made and compliance established over the last ten years has been substantial."

As data have accumulated, EPA has changed its focus somewhat. "The current agency emphasis is on tropospheric ozone--urban smog--and on fine particulate matter," says Blair Martin, associate division director at EPA's National Risk Management Research Laboratory, Research Triangle Park, NC.

Reflecting that emphasis, last November the EPA proposed revisions to primary and secondary National Ambient Air Quality Standards (NAAQS) for particulate matter (PM) and ozone. The EPA proposes to set an annual standard for particles 2.5 mum in diameter (PM2.5) of 15 mugm/cu-meter and a set new 24-hour standard at 50 mugm/cu-meter. Present standards apply to particles 10 mum in diameter (PM10). As for ozone, the EPA proposes to set a standard of 0.08 ppm as an eight-hour average exposure. Final rules for PM2.5 and ozone will be issued by EPA by July 19.

Attacking ozone.For a large part of the country, reducing ozone emissions involves cutting nitrogen oxides rather than Volatile Organic Compounds (VOCs). A number of technologies have the potential for control levels beyond current low-NOx burners. One, selective non-catalytic reduction, involves injecting compounds to create NH radicals in the upper regions of a furnace, under conditions where the NH reacts selectively with the NO to form N2 and water. "This approach achieves 50 to 60% NOx control on top of the control achieved with low-NOx burners," says Martin.

A selective catalytic reduction (SCR) system places a catalyst into the hot flue gas stream, and injects ammonia upstream of the catalyst. "You have a catalytic selective reaction of the ammonia with the NO. And that technology gives you 80% to 90% NOx control," Martin explains. One such SCR system, made by ARI Technologies, a subsidiary of U.S. Filter/Engineered Systems located in Schaumburg, IL, uses a fluidized bed of transition metal oxide catalyst. In one application, ARI designed an Econ-NoxTM SCR system and retrofitted it into a wastewater treatment plant in 25 weeks. The equipment handles VOCs and NOx, achieving better than 90% NOx control and removing 98% or more of VOCs and hydrocarbons.

Natural gas reburning, a technology widely used overseas, adds a stream of natural gas to NOx formed under normal combustion conditions in the primary burner zone. Doing so helps consume excess air and create a reducing condition. This condition generates NH radicals and other compounds that reduce NOx to N2. Adding air completes secondary fuel burnout. This approach controls 50% to 60% of NOx.

Meeting the PM2.5 standard. EPA's Martin says there are a number of interesting technologies for control of fine PM. One is super ESP, a technology related to conventional electrostatic precipitator technology. Another is the electrostatic fabric filter. A marriage of the two involves removing the ESP plates from the precipitator's last field and installing an electrostatic fabric filter.

"There's a lot of emphasis on low-VOC or no-VOC coatings," says Martin, "both in terms of the nature of the coatings themselves and in the application equipment. And there are a horde of innovative technologies for VOCs being developed."

The new standards will certainly impose new costs on industry. For some companies, those costs could become a significant problem. If the proposed PM2.5 standard becomes law, "We would find it extremely difficult to be globally competitive," says Timken's Bob Lapp. "Some of our biggest competitors are Japanese, Chinese, Korean. They do not have these standards, but they do have other costs that are substantially lower than ours."

Eaton's John Burke has a different view: The PM2.5 standard "is going to affect every industry that has an exhaust stack." But are environmental controls threatening the viability of businesses like Eaton? Burke doesn't think so. "We're concerned about new regulations, and we don't like to be picked on. We may reach a breaking point, but I don't think we're there yet."

How to live without VOCs

Truck transmissions made by Eaton Corporation are protected by a coating of paint that must survive a 480-hour salt-spray test. Meeting this requirement, as well as the EPA's regulations governing VOCs, called for something new. "The way we did it was to research various paint systems, explains Eaton's John Burke. "After about 1 1/2 years of looking, we found a water-reducible paint that had roughly 98% less VOC content in the as-mixed formula."

Its VOC content gives a paint the ability to wet into a surface and penetrate into pores. That penetration ensures adhesion. "We're painting over some surfaces that are bare steel, some that have been primed by casting supply houses, and different substrates--including aluminum, steel, cast iron, and hoses," says Burke. "And all these have to be coated with one paint, one color."

In addition, speed to cure was extremely important. "Our painting process is the final operation on a transmission; the parts go on a skid, four transmissions to a skid, and then are shrink-wrapped together. Well, if the paint is still tacky," says Burke, "you could shrink-wrap them, but when the guy takes the shrink-wrap off, the paint comes with it." Eaton's paint cures in roughly 15 minutes.

The solution required not only water-based paint but an entirely new painting system, which cost Eaton more than $500,000. "Everything was new. We had all new paint guns," Burke explains. "We couldn't use any of the old components, nor could we use the original paint booth." The residual VOC level generated by the new painting system is so low that standards do not require it be captured. "We couldn't have painted ten transmissions with the high-VOC paint and met the regulations," says Burke. With the new system Eaton meets all the regulations that affect the Kings Mountain plant.

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