In case you haven’t heard, our planet is getting warmer. At what rate it is occurring, or how much human activity has to do with the increasing temperatures, is a heated debate (pardon the pun). One thing is known: carbon dioxide (CO₂) is a contributing factor in global warming, and humans are responsible for a large portion of these emissions.

If you had asked someone five years ago what their carbon footprint was, most people would have likely responded by looking towards their feet, thinking they stepped in something. Indeed, things are much different today than they were five years ago. Individuals and businesses alike are trying to reduce their environmental impact and greenhouse gas (GHG) emissions. What many people do not realize is that they have two carbon footprints: primary and secondary. The primary footprint is a measure of each person’s direct emissions of CO₂ from the burning of fossil fuels, including domestic energy consumption and transportation (e.g., car and plane). The secondary footprint is a measure of indirect CO₂ emissions from the complete lifecycle of products used — those associated with their manufacturing and eventual breakdown.

That is why companies like Corus, a subsidiary of Tata Steel, work to reduce the world’s secondary footprint by improving the energy efficiency of their manufacturing processes. Corus is Europe’s second largest steel producer and has operating divisions focused on strip products, long products, and distribution and building systems. Corus Colors, a part of the Strip Products Division, is an international manufacturer of pre-finished steel for the building envelope, domestic appliances and manufactured goods markets.

Corus Colors-Shotton Works, located at Deeside, North Wales, produces organic paint coated, prefinished steel principally for cladding, composite walling and roofing applications within the building and construction sector, both in the United Kingdom and overseas.

Two manufacturing processes are used at Shotton Works for coating steel strip with paint. They use a series of driven-roller coaters and industrial curing ovens, controlled within a continuous process line, that are capable of applying protective and decorative, high quality finishes to the galvanized flat steel strip substrate. The No. 1 Colorcoat Line process is capable of coating strip widths up to ~55" (1,400 mm)  with a thickness up to ~0.063" (1.6 mm), giving a weekly throughput capability of up to 4,000 tonnes, subject to product type and dimensions.

This manufacturing process requires large amounts of natural gas to ensure proper application and fast curing time in the ovens, which, in turn generates a substantial amount of CO₂ and NO_X (nitrous oxides). In addition to these emissions, the solvent-based coatings release hazardous air pollutants (HAPs) and volatile organic compounds (VOCs) during the drying process that need to be treated by an air pollution control device such as an oxidizer. New oxidizer systems are capable of destroying more than 99 percent of the HAPs and VOCs through the process of high temperature destruction with little fuel consumption. However, older technologies can be a source of CO₂ and NO_X as well as require a lot of maintenance and large operating expenditures.

Pollution control initiatives are nothing new to Corus — the company has been monitoring and controlling the oven emissions at the Shotton Works, North Wales, facility, since the 1970s. The first oxidizer/incinerator was installed on the paint coating processes for abating exhaust gases and solvents. Even then, the company was thinking “green” by utilizing waste heat from these oxidizers/incinerators to preheat the ovens and to supply the manufacturing facility with additional process steam.

As environmental regulations tightened, however, energy prices increased and new technologies emerged. The company decided to re-evaluate the entire system as part of manufacturing efficiency improvements as well as the wider corporate responsibility program for energy usage reduction. The objective was to reduce the gas consumption by at least 45 percent and increase processing speeds on certain products. The company but they quickly realized another benefit to their sustainable energy plans: a much smaller carbon footprint.

Looking for a sustainable energy solution, the company worked with Spooner Industries in the United Kingdom, a supplier the company had collaborated with closely on a number of projects over the past 30 years. Oven technology and safety regulations had changed dramatically since the line was first installed, but Spooner was able to successfully complete several upgrades that brought the system up to current standards and increase its flexibility.

• Each zone was retrofitted with a low NO_X burner to reduce emissions.
  
• Variable-frequency drives or inverters on every oven fan were incorporated into the control system to make each section more efficient and reduce electrical consumption.
  
• The ductwork was changed to bring hot air into the system quickly, reducing maintenance issues.
  
• New thermocouples, pressure transmitters, pressure switches and flow measurement systems were installed in the ovens to bring the equipment up to current technology standards, allowing for remote monitoring and fine-tuning.
  
• A computer-controlled system was integrated with the SCADA program. The proper PLC allows the central Corus system to communicate with the ovens so they can be setup for different production runs, eliminating errors and decreasing setup time.

The oven alterations brought this production line from the least efficient in the Corus group to the most, meeting one of the two objectives set by the company. While some of the improvements reduced the company’s primary environmental footprint and gas consumption, the increased throughput would further complicate their environmental responsibilities.

Two existing, inefficient oxidizers were used to control VOC and HAP emissions for the prime and finish ovens at the North Wales facility. To achieve proper destruction, the systems required large amounts of natural gas, which affected operating expenses and contributed to CO₂ and NO_X emissions. Furthermore, breakdowns and maintenance problems were costing the company money to repair but and also causing revenue losses due to lost production. Because the oven and oxidizer are so vital to each other, Corus wanted a solution provider with experience and knowledge with both when they looked at their options. In addition, they were looking for a system with low operating costs and heat-recovery capabilities that could achieve 99.5 percent destruction removal efficiency (DRE), which was well above their permit requirements.

Spooner, having recently partnered with Anguil Environmental Systems in the United States to fabricate and install their oxidizer designs on applications throughout Europe, was confident that it could be done. After consulting with the engineers at both Spooner Industries and Anguil Environmental Systems, Corus opted to replace the multiple air pollution control systems with one regenerative thermal oxidizer (RTO) from Spooner Anguil. It would give Corus the desired efficiency and single-source solution they were looking for. The system has the following features and benefits:

• The oxidizer is a three-chamber design that processes 55,000 scfm (83,000 NM³/hr) of air, achieving more than 99 percent DRE without visible emissions and greater than 85 percent 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. Therefore, it releases very little CO₂ and NOX.
  
• A secondary heat exchanger sends waste heat directly back to the ovens, reducing the amount of natural gas required for product curing.
  
• Stainless-steel components throughout the system prevent corrosion and allow for high temperature process streams.
  
• A hot-gas bypass on the RTO is used during high loading situations to avoid overheating the oxidizer.
  
• An intelligent bake-out feature cleans the RTO of condensable organics without internal fires or safety concerns.
  
• The control panel has a large operator screen with a built-in maintenance manual and troubleshooting guide for ease of use.

Corus has made a significant investment for the new equipment, upgrades and implementation of this energy reduction project. The changes have dropped their cost per ton of steel produced considerably, and the company estimates the payback will be less than one year.

The reduction in carbon emissions and energy consumption from this facility is dramatic. Their gas usage has dropped by more than 60 percent — an average reduction of or 5,742 kW/hr (522 m³/hr), saving more than £1 million a year. At 181 grams of CO₂ produced per KWH used, Corus is preventing 1 tonne of carbon from reaching our atmosphere each hour — nearly 8,000 tonnes per year.

The company is already planning for similar modifications at other Corus plants.

For more information, contact Spooner Industries Ltd at www.spooner.co.uk or +44 (0) 1943 609505. Contact Anguil Environmental Systems Inc. at www.anguil.com or (800) 488-0230 or (414) 365-6400.