Regenerative Thermal Oxidizer (RTO) – Case Study
A pioneering leader in the window-film industry was literally burning money to operate its coating lines. The company produces thin solar-control laminated films used to screen UV rays, block heat, reduce glare, increase occupant comfort, and enhance aesthetics. The company also produces multi-ply safety and security films that reduce hazards when glass shatters. The products are used in vehicles, homes, and buildings worldwide.
The company was using a decades-old recuperative thermal oxidizer to destroy solvents from the 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. Unfortunately, the operating efficiency and capacity limitations of the oxidizer created problems.
The plant was using more than 100,000 therms of gas monthly. 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. This demanded continuous monitoring and adjustment by operators, and caused 25 percent lower line speeds at times.
In addition to productivity issues, air temperatures from the exchangers exceeded 800°F, which was much hotter than the dryers needed. The oxidizer yielded more heat than the plant could use and valuable energy had to be vented to the atmosphere.
Dürr Megtec proposed a 40,000-scfm CleanSwitch® regenerative thermal oxidizer (RTO). This unit has a proprietary switch valve that delivers high VOC destruction without a flush system. The Dürr Megtec engineering study determined the RTO exhaust could be safely used in the drying ovens. Also proposed was a new heat recovery system and operating sequence that would run more efficiently without wasting energy. Upgraded equipment was also supplied, including T-dampers, exhaust fans, and the hot and cold fans for the heat recovery system.
The customer agreed with the recommendations and based its decision on the benefits of the CleanSwitch® design, combined with the extensive process coating and drying knowledge of Dürr Megtec and its willingness to take on non-routine problems.
The CleanSwitch® RTO achieved VOC destruction efficiencies above 99 percent. The fan design enabled the three production lines to run independently with no operator involvement. And the RTO capacity eliminated the need to reduce line speeds, which helped the plant see higher production.
The RTO provides process air at a more useful 400°F. And when all processes are on line, the CleanSwitch® RTO spends approximately 40 percent of the time in self-sustain, which does not use any gas at all. The RTO and heat recovery system reduced typical monthly gas by 93 percent. The energy savings provided full return on investment in only 18 months.