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Coated Coil
Friday | 28 June, 2019 | 10:04 am

Thermal technology

Written by By Tasha Jamaluddin, Managing Director, Epcon Industrial Systems LP

Above: A coil coating line installed at a large aluminum parts producer is equipped with six Epcon Industrial EEZ modules for thermal uniformity and control of volatile organic compounds (VOCs).

Industrial ovens for curing coatings can be designed to reduce energy usage while providing uniform, quality finishes

July 2019 - When supplying air pollution control and process heating equipment to the metals industry, beyond meeting the stringent regulations and best manufacturing practices, equipment suppliers must develop new system designs that can keep pace with technological advancements and changing demands. As these industrial systems can have an operating lifespan of 30-plus years, it is critical to think far into the future when designing and engineering anything meant to meet tomorrow’s requirements.

Ultimately, environmental impacts and long-term operating costs will be the key drivers when creating any successful systems for a metals industry application.

Epcon embedded these principles into patented designs and systems engineering for two projects designed for coil coating operations so that the coil coaters would benefit from optimal process solutions.

The first project was a Continuous Cure Oven System for a new laminated aluminum sheet line to be operated by a manufacturer of specialty laminated metal products. Increased demand for affordable, lightweight stamped metal parts has also driven up demand for engineered equipment that can produce the highest quality and lowest reject rates for these parts. Such stampings, in this case, start with large-scale coil laminating production lines, and ensuring a consistent and uniform cure of the polymer mastic that becomes part of the laminate is critical to product performance.

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This high-velocity convection oven, which cures painted metal parts, features primary and secondary heat recovery systems that achieve a defect removal efficiency above 98 percent.

Controlling the environment

The three-zone Continuous Cure Oven System recovers heat from the custom integrated air pollution control system by directing hot, clean air from the oxidizer exhaust to the energy efficient zone (EEZ) controllers. This approach facilitates the highest energy recovery with the smallest overall package footprint, delivering a solution that achieves peak metal temperature (PMT) uniformity within +/-0.5 percent of thermal targets across a 5-foot-wide multilayered laminated sheet traveling at speeds of up to 270 feet per minute.

For this coil coater, Epcon’s proprietary EEZ temperature control modules helped to deliver the high-velocity, high-flow heat required to achieve the necessary PMT uniformity seen in production.

Each zone’s EEZ module includes tandem variable frequency drive-controlled recirculation fans directed to dedicated top and bottom recirculation plenums that incorporate Epcon’s proprietary nozzle design.

Due to the performance and affordability of Epcon’s proprietary design—and due to market demand for the specialty laminated metal product—the customer returned to Epcon to order multiple ovens in order to meet its order backlog and forecast order rates.

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A custom 35,000-cubic-feet-per-minute recuperative thermal oxidizer.

Curing quality

The second custom-designed system was developed for a large supplier of pre-painted metal coil in Brazil. The customer-defined criteria for the replacement coil coating system was best-in-class quality and increased line capacity within the available process envelope and reduced energy consumption. Accomplishing these goals, while simultaneously meeting environmental compliance regulations and keeping within the project budget, was quite a challenge.

The 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 exchanger, complete air handling ductwork, an advanced PLC control system with quality and performance monitoring sensors, and a user-friendly HMI interface.

Here again, the customer deemed that the uniformity of the applied coating cure was key to the final quality of its products. To achieve a uniform and consistent cure, Epcon employed its proprietary integrated internal exhaust plenums within both the three-zone prime and four-zone finish coat ovens. These plenums, which extend through the length of the continuous oven, allow for precise tuning of the oven balance, ensuring uniform and consistent coating cure.

Here, too, Epcon’s EEZ temperature control modules complement the integrated internal exhaust plenums. Each module incorporates tandem recirculation fans with dedicated supply plenums and direct-fired trim burners for each of the oven zones, with controls that can fine-tune oven operations to achieve edge-to-edge temperature uniformity within +/-3 degrees Fahrenheit.

Optimizing throughput means maximizing energy transfer efficiency. The unique air-handling engineering provides higher velocity strip impingement, resulting in increased coefficient of heat transfer. This allows the customer to operate the oven at lower zone temperature set points while still achieving targeted PMT.

Lower zone temperatures translate to reduced energy costs as well as longer life expectancy of the system due to reduced thermal loads. Equally as important, this improved zone efficiency facilitates increased strip speeds, proven to be as much as 20 percent higher within a given oven size.

In addition, Epcon’s integrated thermal oxidizer system uses 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.

To increase efficiency and minimize operating cost, heat exchangers can be used to recover and transfer thermal energy that would otherwise be wasted. Energy from the thermal oxidizer is directed to each of the prime and finish coat EEZ temperature control modules.

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A multi-line oven features an integrated 45,000-cubic-feet-per- minute, 2-CAN regenerative thermal oxidizer unit and heat exchange system.

Aiding compliance

Regulatory compliance includes meeting requirements for process exhaust as well as the ambient air quality within numerous coating processes, such as lamination and pre-painting. 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, which reduces energy consumption overall.

Together, Epcon’s designs for the air management system, PLC controls, remote sensors and associated programming result in an integrated solution that delivers an easy-to-manage and balanced thermal control system.

The oven/oxidizer combination system featured in both of the aforementioned projects is one of Epcon’s early patented systems proven across a number of industries, including multiple installations at metal coil coating facilities. Customers found the systems to be both efficient and cost effective.

The design process for each of these systems showcases how innovative engineering for maximum efficiency and multiple levels of thermal recycling can provide a lasting system that will meet environmental regulations and energy consumption demands for decades to come. MM

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