Choosing the clean path

11/12/2014

It behooves manufacturers to address their hazardous waste byproducts in a way that enhances productivity while still complying with environmental regulation. Finding this balance is a challenge with multiple solutions, as showcased in each of Interlake Mecalux’s U.S.manufacturing plants. Each facility, as is the case with most facilities, employs different production methods that engender potentially hazardous byproducts, amplifying the need for solutions that maximize the performance efficiency in each facility. This prompts the need for companies to align themselves with likeminded allies equally supportive of enacting environmentally efficient, cost-saving measures. Through each of these allies’ unique waste-reducing initiatives,InterlakeMecalux is not only keeping its facilities clean, but also its environmental conscience.

Clean, coat, rinse, repeat
At the Sumter and Pontiac facilities in the South Carolina and Illinois respectively, an “all-in-one” and “worry-free” pretreatment solution was put into practice to reduce, not only the amount of effluent and environmental hazards, but also the number of stages required in a pretreatment process. Since 2007, the process has allowed the Interlake Mecalux facilities to accomplish its 24 steel beams-per-minute pretreatment operation while still maintaining the highest environmental standards. Both production centers employ powder coating, which allows the zirconium phosphate and iron-rich cleaner coater to be effective in the pretreatment process, providing greater paint adhesion to the steel beams and protecting the metal against corrosion. This cleaner coater is composed of a 1 percent mixture (1 percent nitric acid and less than 1 percent phosphoric acid) that phosphatizes all metal parts, displacing surface oils and etching the steel with an amorphous layer. The layer not only provides a greater adhesion for the powder coating, but it is also vastly effective in improving the durability against corrosion of the painted surface.

Perhaps the biggest benefit of the cleaner coater is that it does not accrue any phosphoric sludge (a highly volatile chemical waste). The only byproduct remaining is the dirt residue entering the rinse tanks when the beams are cleaned. The beams go through a tunnel washer that sprays the cleaner coater onto the steel beams, and tanks underneath collect the excess liquid and reuse it to further apply the cleaner coater of incoming beams. Considering the low percentage of the chemical in the cleaner coater, the tanks have a longer bath life and require minimal overflow to replenish them.

Initially, the washer was a five-stage process, first going through a caustic cleaner, followed by a pre-wash, onto a rinse stage, passed through a phosphoric acid to etch the steel, and finally rinsing off the metal pieces. Currently, the facilities’ processes have been reduced to three stages: pretreatment, cleaning, and rinsing. Downsizing process stages has meant a substantial reduction of both previously used water resources, and effluent levels discharged into the city water system. Furthermore, considering that the cleaner coater is an ambient temperature agent, it does away with the boilers that previously were used to bring the solution to a temperature that would activate the bonding properties. The elimination of these boilers meant that emissions standards were removed and heating costs were drastically reduced.

Ultimately, with the advancement of metal treatment processes, the aim is to obtain a cleaner coater that would act as a wetting agent and render rinse tanks unnecessary. If rinse tanks were removed from the process, the result would be the reduction of water consumption and treatment costs, since the water source used for this stage comes from the city waterworks. Since water also acts as a minor surfactant and it also enables the cleaner coater to adhere to the metallic surface, the rinse stage is still required.

Full steam ahead
The challenge to reduce hazardous waste is different at the Illinois facility in Melrose Park. Unlike the other plants, this facility coats its metal pieces cataphoretically. Metal pieces are pretreated in microcrystalline zinc phosphate, an organic solvent that renders negatively charged cathodes to the metallic surface and provides greater adhesion to the paint. Once the metal has been pretreated, it is immersed in epoxy-type paint tanks that possess positive-charged electrodes applied by a continuous current voltage. The attraction between the metal surface and the paint solution allows for a widespread adhesion to occur. The coated pieces undergo a drying process in ovens. Although paint by cataphoresis will produce low amounts of volatile organic compounds (VOC), emissions consisting of butyl cellosolve, n-butyl alcohol and dimethylethanolamine will still be released. To prevent this volatile organic material from entering the atmosphere, the Melrose Park facility requires a fully automated system that both filters and captures the hazardous air pollutants at a continuous rate,. Fortunately, a device that combats VOCs while achieving energy efficiency exists: the regenerative thermal oxidizer (RTO), a behemoth presence that makes the everyday fight against pollution a low-cost campaign.

The exhaust fumes heat up as they travel through the MLM, which can maintain a temperature of up to 2,200 degrees Fahrenheit. Once the exhaust fumes have been heated, the pneumatic poppet valves push it into a combustion chamber where the air will be oxidized at 1,600 degrees Fahrenheit. During the process, 98 percent of the VOCs present in the air will be converted to carbon dioxide and water vapor. The final stage of the process involves the combusted VOCs moving into the second regenerator tower chamber where the cleaned exhaust will be released into the atmosphere, while the residual heat will be used to treat air entering the first chamber.

An automatic Temperature Safety System (TSS) will monitor and provide status reports on all operations, including the temperature regulation to decrease thermal stress on the unit caused by possible temperature fluctuations. The TSS is responsible for cycling the valves and bringing the combustion chamber to the correct operating temperature, as well as programming the different temperature settings for each phase and monitoring the adequate temperature to ensure that the greatest energy efficiency rate is reached.

Despite the size of the RTO unit, its contribution to theMelrose Parkfacility is invaluable. Since 2007, the unit’s presence has enacted a substantial reduction of hazardous air pollutants being released, allowing the facility to continue its production output unencumbered by environmental safeguarding restrictions.

Leading by example
Enacting an environmentally sound process is a daunting task. Each innovative measure is a contributing factor mitigating the waste byproducts of a manufacturing plants’ output. Despite reaching these environmental milestones, there is still a great distance to be traversed by the industrial sector in making them a ubiquitous presence at their production sites. The hope is that effective environmental actions resulting from accelerated technological progress will usher in a singular era of a sustainable industrial habitat: where industry and environment coexist in persistent mutualism. Example begets action, andInterlakeMecaluxis aware of the footprints it leaves behind as it clears a path toward a green future, hoping others will follow as well.