Regenerative thermal oxidizers allow one company to replace outdated pollution control equipment with systems that have exceeded expectations for reliability and efficiency.

The rotary concentrator system achieved a 10-to-1 concentration ratio, which meant a much smaller oxidizer could handle the concentrated process stream.

Emission control and the operating costs associated with meeting environmental regulations were nothing new for the Coated Products Division of Brady Corp., Milwaukee. The company has been manufacturing coated films for nearly 60 years, demonstrating during that time a commitment to pollution prevention and emission reduction programs. But these considerations were magnified when its coating plant implemented a new energy-efficient emission control system.

The coating division maintains 200 coating formulas on three continuously operating main process lines. Two of the company’s three coaters operate as so-called white rooms to allow the manufacturing of exceptionally clean products. Applying adhesives, top coats, cast films and other coatings onto a range of substrates requires solvent-based coatings with mixtures of chemicals. The dynamic process stream poses multiple challenges, particularly in that it eliminates the option of solvent recovery.

The capital cost of emission control equipment can be negligible compared to the operating costs if careful consideration is not given to proper equipment selection. With natural gas prices rising, Brady focused on getting the most efficiency from its incineration equipment.

Since the early 1990s, the facility has spent millions of dollars on air pollution control equipment to meet Environmental Protection Agency regulations imposed on coating companies. For the Milwaukee location alone, the company has purchased a total of 12 oxidizers, including thermal recuperative and regenerative thermal oxidizers, as well as concentrator systems, with a 13th oxidizer on order.

The oxidizers have been used to treat everything from coating emissions to low-point floor sweeps throughout the facility. As natural gas prices started rising in the late 1990s, and with associated costs for emission control equipment steadily increasing, Brady looked for ways to reduce its yearly operating and maintenance costs, which were overwhelming.

When one of the old electric oxidizers would fail, it generally took more than a week to replace the cold-face support grid and electric heating elements, and then bring the unit back up to temperature. Failure occurred so frequently that the maintenance department constructed a special tent so the repairs could be done in the rain or snow. The thermal recuperative oxidizers on site had many problems with internal heat exchanger failure, so a roller system was installed to move the large duct transition, allowing access to weld the tubesheet without bringing in a crane.

To solve the ongoing problem, Brady began replacing the oldest and least efficient oxidizers. The first phase of what plant personnel started referring to as its “efficient emission control plan” replaced one of the thermal recuperative oxidizers with a 35,000 scfm regenerative thermal oxidizer (RTO) from Milwaukee’s Anguil Environmental Systems Inc.

The first regenerative thermal oxidizer from Anguil replaced recuperative thermal oxidizers to give Brady a destruction efficiency rate of 99.2 percent.

High Capacity Shifts Load

The new system tested out at a destruction efficiency rate of 99.2 percent and was equipped with a hot-gas bypass, allowing it to process volatile organic compounds (VOCs) at rates up to 850 lb/hr. This high capacity VOC processing allowed some of the other less efficient oxidizers to shift their load over to the new regenerative thermal oxidizer through a common manifold collection system. With the concentration of hydrocarbons in the process airstream, the heat energy content of the VOCs was self-sustained and the oxidation process did not require additional fuel for destruction.

Brady’s maintenance team investigated several types of regenerative thermal oxidizing systems, and the team chose Anguil’s poppet valve design because its maintenance levels best-satisfied the company’s needs. The coater also liked the fact that Anguil was willing to share its complete computer operating program, something the company said other vendors were not willing to do.

The second stage of the plan proved to be more challenging but even more effective in reducing Brady’s operating costs. EPA requirements call for a permanent, total enclosure, so the coaters must create a negative pressure in all areas of the facility that process any volume of solvents. Due to the coaters layout, this became a large volume of exhaust air with very low VOC levels.

Two of the old electric oxidizers were treating the high volume, low concentration stream from the pump rooms, washup areas, compounding areas and floor sweeps throughout the facility. Large volumes of natural gas were consumed to burn a very small amount of pollutants. In addition, the units could not be turned off during plant shutdowns because of the time-consuming reheat procedure, which could take up to four days.

After evaluating the solvent vapors and various concentrations, Brady chose an Anguil Model 350 (35,000 scfm) rotor concentrator, and Model 50 (5,000 scfm) regenerative thermal oxidizer was selected to handle this portion of the process. By absorbing and concentrating the VOCs, the system achieved a 10-to-1 concentration ratio, requiring an oxidizer only a tenth the size of what would be needed with an unconcentrated stream. The energy contained in the concentrated stream entering the regenerative thermal oxidizer proved sufficient to allow self-sustaining operation, requiring little to no auxiliary fuel.

Most recently, Brady has purchased another 35,000 scfm regenerative oxidizer that replaced the last thermal recuperative system on site. Heat from the new oxidizer preheats the facility’s ovens, further reducing energy consumption. The system has enough capacity to eliminate the final thermal recuperative unit and another aging electric oxidizer.

In addition to replacing old oxidation technologies at the facility, careful consideration has been given to all the oxidizers as a single system. Brady has implemented a dual collection and distribution manifold that allows operators to divert process streams from one oxidizer to another for maintenance or equipment shutdowns.

According to Brady, the impact of these efforts has exceeded expectations for reliability and efficiency. Gas usage on the company’s three coating lines has continued to drop at a steady rate. At a time when gas prices continue to trend high, coupled with increases in production, the reduction in energy consumption drops straight to the bottom line.

The company now is investigating the option of placing secondary heat exchangers on all its oxidizers. The process would return waste heat to preheat the airstreams on all of its other coating lines.

Anguil Environmental Systems, Milwaukee, Wis., manufactures regenerative, recuperative and catalytic oxidizers as well as other VOC abatement systems and equipment. For more information, call (414) 365-6400 or visit