A customer approached Tempco in need of a high wattage heating solution for a battery electrode manufacturing application. In addition to the high wattage, the customer’s request included additional specialty requirements. Tempco designed multiple iterations of heaters to implement at different zones of the customer’s manufacturing process. One of the larger designs consisted of a 53” housing length operating at 400KW with a 4” custom insulation box.

Due to the heating requirement, initial designs were developed with over 100 tubular elements. However, these designs required too much welding for assembly in the standard hairpin bend formation. Through an innovative design process, Tempco was able to utilize a more specialized bend formation. Therefore we reduced the total amount of elements by over 30%. Because less tubular heating elements were needed, there was a decrease in possible failure points, overall cost and assembly complexity creating a more effective and cost-saving design.

One of the other major challenges in designing these tubular duct heaters was meeting the requirement that absolutely no free iron can enter the application airstream. Special care was taken when filling the insulation box to guarantee no additional foreign matter would come in contact with the flow stream. Additionally, in order to achieve keep iron out of the air stream, the tubular heating elements in these designs needed to be passivated. Passivation is the process of treating or coating a metal in order to reduce the chemical reactivity of its surface. In stainless steel, passivation means removing the free iron from the surface of the metal using an acid solution to prevent rust. As the air from these duct heaters will be coming in contact with lithium used for batteries, any free iron on the elements would mix with the lithium and cause failures.

Most companies can’t do passivation of such a long heater due to their tank immersion depth limitations (generally 40” to 45”). Due to the large nature of these designs, Tempco developed a custom passivation tank for proper immersion length of the elements. This acidic reservoir was able to fit each design and treat the free iron on the surface of the elements. The custom-built passivation tank effectively fit the largest design, which consisted of a 60” direct immersion length. After immersion the heaters were allowed to dry. Then they were rinsed and tested per ASTM standard. The elements were then protected to avoid further contamination.

The final heaters proved to work well for this heating application. They were able to heat a fast moving flow rate of air (around 6000cubic feet/minute) by 100˚F as it passed over the elements. Several custom thermocouples were also attached to tubular elements and placed near the outflow of air to allow for a more precise control while preventing overheating.