Upgrading VOC Control

Article From: Products Finishing, , from Products Finishing

Posted on: 8/1/1999

First one VOC-control method, then another...

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Regenerative thermal oxidation unit

Regenerative thermal oxidation unit destroys VOCs

Whether it is printing shops in Maine or traffic jams in California, VOC control has been a problem throughout the country. One metropolitan area in the Midwest needed assistance with VOC control. A major company manufactured steel tubes in sizes from 2 × 2 to 16 × 16 feet. The tubes were used in building steel support structures.

Usually the steel structures would be visible after the building project was completed. This was acceptable, except that steel tubes tend to rust quickly unless they are coated before they are shipped to the jobsite. Oil applied to the steel prevents rusting, but it also prevents paint from adhering to the structure after it is erected.

The steel tubing company concluded that the best way to resolve the problem was to paint the steel tubes before they left the facility. To make this affordable, the coating needed to dry to the touch quickly rather than needing to cure in an oven because of the speed at which the tubes were produced. The coating that met these requirements contained volatile solvents that flashed off quickly. Each gallon of coating contained in excess of 90% VOCs.

Because the company was in a metropolitan area of EPA Region 5, and it produced more than 100 tons of VOCs per year, a control system had to be installed that would reduce the emissions by at least 81% overall. The affordable technology was a thermal recuperative oxidizer that would incinerate the VOCs emitted from the paint booth exhaust as well as the dryer section.

As production increased and additional lines were added, another thermal recuperative oxidizer was needed. However, production was reaching levels that produced VOCs in excess of the manufacturer's EPA permit even though the process exhaust was incinerated through the oxidizers. This is when a 100% capture (a permanent total enclosure) was introduced that by definition would collect all of the VOCs produced and direct them to the oxidizers for incineration. The enclosures for the three coating lines captured 100% of VOCs. Now the overall capture and destruction efficiency achieved 99%. This allowed production to increase and still remain less than the EPA permit requirements.

However, a new problem developed: operating costs were affecting overall profits. Since production had reached three shifts, seven days per week, the electrical power and natural gas consumed by the oxidizer exceeded $500,000 per year. The company looked at changing to waterborne solvents so the oxidizers could be eliminated. However, heat would need to be introduced to dry the waterborne coating. The company worried that this could affect the coating and subsequently the quality of the final product could not be maintained.

Next, the company installed a new incinerator technology, regenerative thermal oxidation. The thermal efficiency of this type of system is 95%, and the pressure drop through the unit is about half that of the existing units. When it originally purchased the existing thermal recuperative oxidizing systems, the regenerative thermal oxidizers were not an affordable technology. Several years later, regenerative thermal oxidation became affordable.

The older units needed some repairs, so a cost comparison was made that indicated that it would be less costly to replace the existing units with regenerative thermal oxidation units. Operating cost savings for a 35,000-scfm system would be $400,000. When combined with the savings realized by not doing the repairs, the company achieved a one-year payback. Every year thereafter it saved $400,000.

Because of the regenerative thermal oxidation technology, it was able to continue using the solvent-borne coating and maintain product quality.

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