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Many Products Finishing readers know that I personally am skeptical of the idea of anthropogenic global warming, and have expressed this skepticism quite a few times in the magazine and its electronic counterpart. So information about a way for finishers and other manufacturers to reduce emissions of so-called greenhouse gases, including carbon dioxide, presented a dilemma.
One of our PF columnists, a consultant with years of finishing industry experience, helped put things in perspective. "It's always a good idea to focus on the areas traditionally looked at for efficiency improvements," he said in response to an e-mail query. "Better transfer efficiency, longer filter life, reducing air leaks, better insulation, etc., all save money and reduce carbon footprint.
"But this is low hanging fruit. We should be going through the next industrial revolution right now, while we have the motivation, the technology and the incentive. Reduction in GHG can put us on a road to a new manufacturing future that would be very good for our country and far more sustainable than current methods. The same old economics apply in terms of cost-benefit analysis and ROI. But we have to get past the desire for quick growth and focus on long-term benefits."
Put in those terms, the need for technology to reduce carbon footprint makes some sense. And, such systems are available.
Consider, for example, an upgrade to finishing ovens and pollution control systems installed at Corus Shotton Works, a steel finishing facility in Deeside, North Wales. The company, a subsidiary of Tata Steel, manufactures pre-finished steel sheet and strip products for the architectural and appliance markets, among others.
Paint is applied via roll coating of continuous galvanized steel strips, then cured at temperature. The company's No. 1 Colorcoat line can coat strip up to 1,400 mm wide and 1.6 mm thick, producing up to 4,000 metric tons/week of precoated steel.
The process requires large amounts of natural gas to ensure proper application and fast curing time in the ovens. Combustion generates carbon dioxide (CO2) and nitrogen oxides (NOX), and the solvent-based coatings used release HAPs and VOCs that require scrubbing before release into the atmosphere. Shotton Works destroys VOCs and HAPs using a thermal oxidizer—yet another source of greenhouse gases. In light of tightening environmental regulations, increasing energy prices increase and the emergence of new technologies, the company decided to reevaluate its system with the objectives of reducing natural gas consumption by at least 45% and increasing processing speeds on certain products. But managers quickly realized another benefit to their sustainable energy plans: a much smaller carbon footprint.
Shotton Works worked with Spooner Industries, a UK-based supplier of pollution control technology, to complete several upgrades that not only brought the system up to speed with current technology standards but also increased its flexibility. In the curing ovens, each zone was retrofitted with a special low-NOX burner to reduce emissions. Variable-frequency drives or inverters on oven fans were incorporated into the control system to make each section more efficient and reduce electrical consumption. Changes to ductwork assured that hot air was brought into the system quickly, while new thermocouples, pressure transmitters, pressure switches and flow measurement systems allowed for remote monitoring and fine-tuning.
The company also implemented a new PLC-based control system that allows the central Corus production management system to communicate with ovens. This allows ovens to be set up for different production runs, eliminating errors and decreasing setup time.
Thermal oxidizers also came in for an update. Two existing RTOs controlled VOC and HAP emissions but required large amounts of natural gas to do so. Breakdowns and maintenance problems were also costing the company money in repairs and lost production.
After consulting with the engineers at both Spooner Industries and its U.S. partner Anguil Environmental Systems Inc. (Milwaukee), Corus managers decided to replace their multiple air pollution control systems with a single regenerative thermal oxidizer from Spooner Anguil. The three-chamber design processes 55,000 scfm of air, achieving 99%+ destruction efficiency without visible emissions and 85%+ heat recovery for energy-efficient operation.
The RTO self-sustains at low solvent-loading conditions, meaning that once the oxidizer is at operating temperature and receiving process airflow it requires no additional fuel for emission destruction. A secondary heat exchanger sends waste heat directly back to the ovens, reducing the amount of natural gas required for product curing.
As a result of the upgrades, carbon emissions and energy consumption are both substantially reduced. Gas usage has dropped by more than 60%, saving over £1 million/yr. At 181 g of CO2 produced per kWh used, Corus is preventing 1 metric ton of carbon from reaching the atmosphere each hour—a total of nearly 8,000 metric tons per year.