The Challenge: Reduce gas use and speed processing
The objective was to reduce natural gas consumption by at least 45 percent and increase processing speeds on certain products. Another benefit was realized – a smaller carbon footprint.
Corus is Europe’s second largest steel producer and comprises three operating divisions: Strip Products, Long Products, and Distribution and Building Systems. As part of the Strip Products Division, Corus Colors is an international business that manufactures pre-finished steel for the building envelope, domestic appliances and manufactured goods markets.
Corus Colors – Shotton Works is located in North Wales and produces organic paint coated, prefinished steel, principally for cladding, composite walling and roofing applications within the building and construction sector both in the UK and overseas.
There are two manufacturing processes 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 1,400 mm with a thickness up to 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 NOx (Nitrous Oxides). In addition to these emissions, the solvent-based coatings release HAPs (Hazardous Air Pollutants) and VOCs (Volatile Organic Compounds) 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 over 99 percent of the HAPs and VOCs through the process of high temperature destruction with very little fuel consumption. However older technologies can be a source of CO2 and NOx as well as the requirement for high maintenance and large operating expenditures.
Pollution control initiatives are nothing new to Corus, the company has been monitoring and controlling their oven emissions at the Shotton Works, North Wales facility, since the 1970’s. Their 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 older oxidizers/incinerators to pre-heat the ovens and to supply their manufacturing facility with additional process steam. However, as environmental regulations tightened, energy prices increased and new technologies emerged, the company decided to re-evaluate their entire system as part of their 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 but they quickly realized another benefit to their sustainable energy plans… a much smaller carbon footprint.
Looking for a sustainable energy solution, they turned to Spooner Industries in the United Kingdom who have worked closely with Corus 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 special low NOx 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 (temperature measurement), pressure transmitters, pressure switches and flow measurement systems were installed in the ovens to bring the equipment up to today’s technology standards, allowing for remote monitoring and fine-tuning.
A new computer controlled system was integrated with the SCADA (System Control and Data Acquisition) program. The proper PLC (Programmable Logic Controller) 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 for the company. While some of these improvements reduced the company’s environmental footprint and gas consumption, the increased throughput would further complicate their environmental responsibilities.
Two existing, inefficient oxidizers for the Prime and Finish Ovens were being used to control VOC and HAP emissions 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 NOx emissions. Furthermore, breakdowns and maintenance problems were not only costing the company money to repair but also revenue in lost production. Because the oven and oxidizer are so vital to each other, Corus wanted a solution provider with experience and knowledge on both. In addition, they were looking for a system with low operating costs and heat recovery capabilities that could achieve 99.5 percent DRE (Destruction Removal Efficiency) 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 made the decision to replace their multiple air pollution control systems with one, RTO (Regenerative Thermal Oxidizer) from Spooner Anguil. It would give them 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 83,000 nm3/hr (55,000 scfm) of air, achieving 99 percent+ DRE without visible emissions and 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, releasing 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 over heating 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 trouble shooting guide which makes for ease of use.
Corus has made a significant investment for the new equipment, upgrades and implementation of this energy reduction project. It has dropped their cost, per ton of steel produced, considerably and they estimate 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 522 m³/hr (or 5742 kW) per hour – saving over £1million a year. At 181 grams of CO2 produced per KWH used, Corus is preventing one tonne of carbon from reaching our atmosphere each hour, nearly 8,000 tonnes per year.
With innovation and continuous improvement at the heart of its business, the company is already planning for similar modifications at other Corus plants.
A spokesperson form Corus commented: “We are committed to minimizing the environmental impact of our operations and our products through the adoption of sustainable practices and continuous improvement in environmental performance.”