The Problem -

Our client re-cycles scrap metal into new steel products.  One component of the scrap metal feedstock is junked or end-of-life automobiles.  Until 2002, mercury was used by vehicle manufacturers in switches for automotive hood- and trunk-lighting, as well as anti-lock braking systems.  The presence of very small quantities of mercury in this component of the scrap metal received by the steel mill posed a significant challenge.  It was possible for the mercury in these switches to be released to the environment during the recycling process, including when the vehicle scrap was melted to manufacture new steel products.  Because it is impossible to identify and remove mercury-containing switches after a vehicle has been dismantled, shredded or crushed, our client retained Roux Associates to investigate this matter and to attempt to reduce its mercury emissions.

Our Solution

Roux Associates, working with our client, developed a multi-faceted program that evaluated the feasibility of pollution prevention measures, as well as add-on controls for mercury emission reduction. Pollution prevention involves removal of mercury switches from vehicles before they are shredded or crushed.  If successful, this would be the most effective solution, because the mercury switches would be isolated from further environmental impact, and re-cycled or disposed of in an environmentally friendly manner. 

In an effort to demonstrate the viability of such an approach, a pilot test program was conducted in association with scrap metal suppliers, shredders, the State environmental protection agency, and our client.  Numerous scrap yards volunteered to participate in the program, and information was shared with them on where switches were located, and how they might easily be removed.
Roux Associates staff provided quality assurance oversight for the program, and used stack testing to evaluate the extent to which mercury emissions were lowered.  This pilot test generated approximately 300 tons of scrap metal (with mercury switches removed), and demonstrated the viability of the switch removal program.  Our client committed to participating in the National Vehicle Mercury Switch Removal Program, partly as a result of this successful pilot test program. Since it may not be possible to remove a sufficient percentage of mercury switches on an ongoing basis, add-on controls were also evaluated by Roux Associates as an alternative method of mercury emission reduction. Add-on controls for mercury are not commercially available or a proven technology in the steel manufacturing industry.    
To investigate the potential for technology transfer, a mercury control technology that had demonstrated some success when applied to coal fired power plants was pilot tested at our client’s facility.  The test program involved the temporary installation of a skid mounted system to inject specially treated powdered activated carbon (PAC) into the flue gas stream collected as a result of scrap metal melting operations.  The test program investigated mercury control effectiveness based upon different rates of injection.  The program also examined the effect of the PAC on various system and process components.  A continuous emissions monitoring system (CEMs) for mercury was also installed at the same time that the PAC injection system was being tested.

To our knowledge, this was the first time that operation of such sophisticated equipment had been attempted in the steel manufacturing industry.  The high variability in mercury emissions posed a particular challenge to continuous measurement of this contaminant.  Nonetheless, the real time mercury emissions data were used to make real time adjustments to PAC injection rates.  This feedback loop concept was implemented to optimize this mercury control technology application, which shows the potential for successful application of this technology in this sector.  At the same time, the benefit of an expanding nationwide program of pollution prevention through switch removal of the scrap feedstock is also being evaluated.