A window-film manufacturer using an old recuperative thermal oxidizer to destroy solvents from its drying ovens got tired of “burning” money on its coating lines.

Madico, headquartered in Woburn, Mass., produces thin solar-control laminated films for windows to screen ultraviolet rays, block heat and reduce glare. The company also makes multi-ply safety and security films that reduce hazards when glass shatters.

Madico had been relying on a recuperative thermal oxidizer to destroy solvents from drying ovens on its three process lines. Thermal energy from the oxidizer exhaust was recovered by heat exchangers and used to operate the process ovens and other in-plant systems. However, the oxidizer's operating efficiency and capacity limitations created problems.

The 20-year-old oxidizer burned more than 100,000 therms of gas monthly -- an annual bill that was upwards of a million dollars. The 20,000 scfm oxidizer used a single two-speed exhaust fan to serve three processes. The fan caused capacity and continuity conflicts between lines, demanding continuous monitoring and adjustments by operators. At times, the system ran at 25 percent lower line speeds, hurting productivity. Air temperatures from the heat exchangers exceeded 800oF (427oC), which was much hotter than the dryers needed. The oxidizer yielded more heat than the plant could use, so valuable energy had to be vented to the atmosphere.

The company sought a solution from Megtec Systems, DePere, Wis., a manufacturer of regenerative thermal oxidizers (RTOs), hoping the technology could reduce fuel usage.

Megtec supplied a 40,000-scfm CleanSwitch RTO offering high volatile organic compound destruction without a flush system, and upgraded Madico's equipment including T-dampers, exhaust fans and the required hot-and-cold fans for the heat recovery system.

The CleanSwitch RTO achieved VOC destruction efficiencies above 99 percent. The fan design allows the three lines to run independently with no operator involvement. The larger capacity eliminated the need to cut line speeds, so the plant sees higher production. The RTO provides process air at a more useful 400oF (204oC).

According to Medico, when all processes are online, the oxidizer “self-sustains” approximately 40 percent of the time, not using any gas at all. Typical monthly gas use now is less than 7,000 therms, mostly due to the building's heating load. Overall, Medico reports a 93 percent drop in gas usage. Within 18 months, energy savings provided the company with a full return on its investment.