Metal Coil Coating Line with Oven and Oxidizer System, Heat Recovery and Advanced Air Handling Controls
The Challenge
A pioneer in the pre-painted metal coil market in Brazil, need to replace their 20+ year old coil coating line. To successfully transition from their dated energy hungry oven and air pollution control units to a state-of-the-art integrated high performance Oven and Oxidizer solution, the team identified a number of key criteria which would guide the system design. Topping that list was; realization of best in class quality, increased line capacity within the available process envelope and reduced energy consumption. Accomplishing all of these goals while at the same time meeting environmental compliance regulations and keeping within the project budget were absolute requirements.
The Solution
The overall scope of the final design included a three-zone prime oven, a four zone finish oven, integrated thermal oxidizer air pollution control and heat recovery system with primary and secondary heat exchange, complete air handling ductwork, an advanced PLC control system with quality and performance monitoring sensors and a user friendly HMI interface.
Uniformity of applied coating cure is key to product quality. To achieve uniform and consistent cure, Epcon employed their proprietary integrated internal exhaust plenums within both the 3 zone prime and 4 zone finish coat ovens. These plenums which extend through the length of the oven allow for precise tuning of the oven balance insuring uniform and consistent coating cure.
Complementing the integrated internal exhaust plenums are Epcon’s proprietary “EEZ” Energy Efficient Zone Control temperature control modules. Each of these modules incorporates tandem recirculation fans and direct fired trim burners for each of the oven zones. Each of the recirculation fans are individually VFD controlled and tied to their own recirculation supply plenum at the top and bottom of each oven zone. Together with Epcon’s proven proprietary adjustable nozzles we are able to fine tune oven balance to achieve exceptional and proven edge to edge temperature uniformity within +/-3F.
The large quantity of fuel necessary to run most thermal oxidizers for VOC control can be exorbitant, driving high operating cost. To increase efficiency and minimize operating cost, heat exchangers can be used to recover and transfer thermal energy, which would otherwise be wasted. Heat exchange methods can be the defining feature of a thermal oxidizer, as they ultimately control the desired level of efficiency and VOC destruction. In addition our proprietary large diameter Tube and Shell Heat Exchangers are a key feature of the Epcon Recuperative Thermal Oxidizer integrated into the system. Their low pressure drop design and ease of access for inspection and service provides the most robust solution insuring an exceptionally long service life.
Epcon’s proprietary integrated Thermal Oxidizer system utilizes primary and secondary heat exchangers to extract energy from the heat release from oxidizing the volatile solvents evaporated during the curing process. This approach provides most of the heat required to run the ovens while concurrently meeting air emissions compliance regulations. Energy from the Thermal Oxidizer is directed to each of the Prime and Finish Coat “EEZ” Energy Efficient Zone Temperature Control Modules.
Regulatory compliance includes meeting requirements for process exhaust as well as the ambient air quality within the coating processes. Properly managing the air flow throughout the process affects compliance as well as both cure and energy consumption performance. Employing a cascading air management strategy, drawing air from the coater rooms, through the oven and oxidizer systems minimizes fresh air make-up reducing overall system energy consumption. All of the ductwork, from coater room exhausts through the ovens, oxidizer and energy recovery was designed, fabricated and supplied by Epcon.
Each component of the system was designed for optimal efficiency and performance for it’s individual tasks as well as its role in the overall system. The advanced PLC controls monitor operating parameters, such as temperatures and pressures, throughout the system to achieve targeted zone control set-points and monitor Peak Metal Temperatures to insure the process is meeting performance goals. Pre-programmed set-points are saved as recipes for each material type and size to simplify system operation. The control system from concept through panel build, programming and custom HMI screen development was completed in-house at Epcon’s UL Certified shop.
The Results
The utlimate success of the line was the ability to achieve edge to edge temperature uniformities within such tight 3+/- margins. Equally as important, the oven’s improved zone efficiency facilitates increased strip speeds, proven to be as much as 20% higher within a given oven size, allowing the manufactuer to meet their goal of increased throughput in the production space available.
Optimizing throughput means maximizing energy transfer efficiency. The unique air handling configuration found in Epcon’s proprietary designs provides higher velocity strip impingement, resulting in increased coefficient of heat transfer allowing the oven to be operated at lower zone temperature setpoints while still achieving targeted Peak Metal Temperature. Lower zone temperatures translates to reduced energy costs as well as longer life expectancy of the system due to reduced thermal loads.
Together the design of the air managements system, PLC controls, remote sensors and associated programming results in an integrated solution that delivers an easy to manage and control balanced system.