Coil Coating System for Metal Processing Featuring Oxidizer, Ovens and Multistage Heat Recovery ​

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Project No 3196

Coil Coating System for Metal Processing Featuring Oxidizer, Ovens and Multistage Heat Recovery

The Challenge

The Metal Processing plant approached Epcon, to replace a coating line Ovens & standalone Thermal Oxidizer system. Not only did the facility want to increase throughput capacity while remaining code compliant on emissions, but increasing operating efficiency was another request.

The Solution

After extensive evaluation and consideration of the existing system operation, it was determined that the optimal solution for this application is the use of a combination system layout, consisting of a 3-Zone Prime Oven & 4-Zone Finish Oven with a single standalone Thermal Oxidizer system, along with the secondary heat recovery system. The combination system works to capitalize on every part of the process, ensuring no heat nor material go to waste.

With Coil Coating Ovens, it is common to design the Oven with multiple zones, depending on the process. The different zones within the Oven allow for a gradual heating process, which can be a vital component when dealing with certain materials, such as paint or metal. In this particular system, the 3-Zone Prime Oven cures the primer onto the metal as the metal is processed through the Oven, reaching temperatures between 500-600°F. The 4-Zone Finish Oven continues to cure the paint onto the metal as the metal passes through each zone, gradually achieving the desired, peak metal temperature.

As the painted metal strips are being cured through the Prime & Finish ovens, the paint solvents evaporate into the Oven’s work chamber. The air laden with VOCs, is extracted from the Oven’s work chamber and routed through the Primary Heat Exchanger of the Thermal Oxidizer. The Primary Heat Exchanger pre-heats the Oven exhaust in excess of 1100 °F temperature to minimize the Oxidizer’s burner fuel consumption. The VOC exothermic reaction contributes in making the Oxidizer’s retention chamber act as a self-sustaining agent without any additional burner heat input.

The use of a Secondary Heat Exchanger further establishes an efficient, economic solution. Once the contaminated air in the Prime & Finish Coater room is effectively captured by the Thermal Oxidizer, it is routed through the Secondary Heat Exchanger. The Secondary Heat Exchanger continues to supply the pre-heated air back to both the Prime & Finish Ovens, thus increasing sustainability.

As demonstrated by this metal coating operation, by continuously recycling the heat between the Oxidizer and Ovens via two Heat Exchangers, the combination system creates optimal operational efficiency and allows the facility to capitalize on the thermal energy across the entire process.

The Results

In the Primary Heat Exchanger, when the solvent vapors oxidize and the exothermic reactions take place, the solvent acts as fuel to the oxidizer; thus further reducing the primary fuel cost of operating the Oxidizer to an absolute minimum. This optimized and efficient design of using the Primary Heat Exchanger will ultimately result in savings of approximately 8.0 MMBTU per hour for the facility.

The Secondary Heat Exchanger fully utilizes the waste heat from the Thermal Oxidizer before discharging the waste through exhaust stack. Re-circulating the air from the contaminated coater room as the source of heated air supply not only helps to reduce the Thermal Oxidizer’s required capacity, but also results in reducing the Oven burners fuel consumption by approximately 6.0 MMBTU per hour.

Beyond the combination system, additional methods can be engineered, depending on the production process and operational demands, to recycle the thermal energy to supplement the process even more. For example, to increase energy savings, we proposed the installation of a waste heat hot water Heater to capture available waste heat from flue gases. This generates hot water needed for cleaning the metal strips. By not having to use a burner and additional fuel to heat the water up to the desired temperature, the installation of the waste heat hot water, saves the facility an additional 3.0 MMBTU per hour.

In summation, the optimized system layout for this particular job resulted in a fuel savings of over 17.0 MMBTU per hour. That equaled a total savings of $320,000 per year on fuel cost alone.  This allowed the facility to pay off their investment in less than a 5-year period, thus earning an even higher ROI on their combination system than anticipated. This patented method of coupling the Heat Processing systems and Air Pollution Control systems, paired with seeking additional opportunities to capture and recycle heat, is a prime example of how thermal engineering can create value through efficiency.

Combination systems can be implemented in essentially any manufacturing facility that requires both process heating and air pollution control systems.

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