Chromium and the New MACT Requirements

Article From: Products Finishing,

Posted on: 8/1/1998

Meeting the new chromium MACT requirements can be done without spending a fortune...

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TWIN fume control scrubbers

TWIN fume control scrubbers

DUAL mist eliminators

DUAL mist eliminators

For electroplaters and finishers,the implementation of 1997's stricter MACT standards made costly capital investments in emissions equipment and controls seem inevitable. This sweeping two-tier regulation limits emissions on a long list of common industrial chemicals. For companies such as Ductile Chrome Process Co. (DCP), Livonia, Michigan, the stiffer regulations meant total chromium emissions were restricted to 0.03mg/dscm.

Fortunately, the company helped create a viable alternative. "The solution brought emissions into compliance immediately and at far less cost than new equipment would have cost," stated Jim Nicolai, president DCP. "And, as a bonus, we did it all in a week during a planned holiday shutdown."

DCP is a 54-year-old second-generation plating company supplying precision plating for automotive, aerospace and military manufacturers. Heavy-build plating for tool repair, where immersion times of 24 to 36 hours to achieve applications of 0.02 to 0.3 inch are common, is another specialty. The majority of the work is hard chromium and cadmium plating. The company also performs sulfamate and electroless nickel plating and blackening services.

Mr. Nicolai was instrumental in buying and starting up an existing air pollution control system late in 1986. Seeking the best long-term solution and trying to anticipate what EPA would do a decade later, he spent time during 1986 consulting with colleagues and contacts on the West Coast, where regulations at the time were most stringent. "The idea," Mr. Nicolai said, "was to find the most cost-effective, long-term solution. This was not an issue I wanted to solve over and over."

Ironically, the supplier most often recommended was a Michigan neighbor. Tri-Mer Corp., Owosso, Michigan, had built its business supplying large manufacturers such as Boeing Corp., Seattle, Washington, and Sundstrand Aerospace, Denver, Colorado, as well as high-volume job shops with emissions control technologies that operated predictably, particularly under high and variable loadings. Collection efficiencies on these systems were consistently 99.2 pct and higher.

"These facts were particularly important to us," stated Mr. Nicolai, "because we run stronger than most. Our baths are 32 oz/gal for hard chromium, compared to the standard 20 oz/gal. Also, some of our customers are just-in-time manufacturers, so we do not have the luxury of long lead times."

The system installed at DCP in 1986 consisted of twin Fan/Separator® fume control scrubbers, each dedicated to one processing tank and configured in a closed loop. These units are horizontal-format scrubbers that use one-tenth the water of conventional wet scrubbers and 20 pct less brake horsepower. These efficiencies are possible due to the system's use of the fan as a centrifuge during scrubbing operations. Fan velocity is precisely controlled so that air crossing the rigid packed media stays within design parameters. The system is positively pressured, working in reverse of conventional negative-air scrubbers pushing air rather than pulling it through the system.

Fifty pct of system performance results come from contact between the contaminant-laden air and the rigid tube packing, and another 50 pct is from the centrifugal action of the fan wheel. The unit is extremely effective in eliminating corrosive contaminants, with a resulting low-humidity stack. Total energy consumption is generally 15 to 20 pct less than comparable wet scrubbers with a negative pressure design.

The scrubbers produced instant compliance with emissions regulations in effect at that time. They also eliminated indoor fumes, improved the housekeeping and ergonomics of the work area and reduced DCP's total costs for plating chemicals by 75 pct.

Facing new requirements in 1997, Mr. Nicolai contacted his original supplier and other vendors to discuss alternatives. The most cost-effective idea emerged from a series of discussions between Mr. Nicolai and Greg Worthington, a technical representative of the original supplier. The idea called for a series of modifications to the original equipment, which would bring the operation well within compliance maximums.

Central to the DCP upgrade is "tri-phase" mesh-pad technology, which replaces the rigid packing tubes that had been used originally. With an appearance that brings to mind thousands of tiny pyramids, these sealed pads significantly improve chromium collection efficiencies, allowing higher recovery and keeping both stack and ductwork free of chromic acid.

The DCP system includes a mist eliminator, installed at the intake of the TWIN fume control scrubbers ductwork of the tank, which removes 99 pct of chromium mist droplets 10 microns and larger at the source. Within the scrubber units, a specially designed mesh pad was introduced into the secondary (there are two) pack, which captures chromic acid droplets of five microns and larger with greater than 99 pct efficiency and returns it to the tanks.

Specially designed PVC duct work prevents any acid from settling. Wash-down nozzles in the exhaust stream allow DCP to wash down both the duct work and mesh pads in a two to three minute cycle, daily or weekly on demand.

Instrumentation was moved inside the building, and the original flexible tubing was replaced by copper. Airflow exhaust at the tanks was not changed. Air make-up, to counteract the negative pull of the exhaust, is supplied by a forced-air furnace.

DCP's total investment for the upgrade package was $24,900, including installation. Stack tests performed on scrubber No. 1 six weeks after installation read 0.006 mg/dscm, comfortably below the 0.03 mg/dscm limit. Tests on scrubber No.2 read of 0.004 mg/dscm. DCP had achieved compliance.

"Other than buying new equipment, there were other avenues open to us," said Mr. Nicolai. Chemical foam blankets, which work by increasing the elasticity of water vapor in order to reduce mists, were one early idea.

"During plating, hydrogen bubbling causes lots of misting," explained Mr. Nicolai. "The high-current electroplating we do can be especially problematic. So, foam blankets originally sounded good, but when we talked to users we heard that maintenance and analysis could be high. More importantly, we use some proprietary chemicals, and adding wetting agents to our baths was not an idea we were comfortable with.

"With this all-mechanical system, our major maintenance task is simple record keeping and cleaning. If pressure between the packs moves more than one inch in either direction of the baseline, we know to start the cleaning cycle or change the filter packs.

The modifications package has since been adapted for use by other platers and has been engineered for compatibility with virtually all existing scrubbers, regardless of the manufacturer.

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