Commercial Technologies for Maintenance Activities

Air Pollution Control System Improvements

For many facilities, military and commercial alike, painting operations present the toughest environmental challenges. Many facilities have manually-operated spray booths, and providing a safe work area means moving large volumes of air through the booths. This sweeps droplets and solvent vapors away from workers very effecttively, but makes the job of taking toxic materials out of the air stream before they are released into the atmosphere that much harder.

Air pollution control technology for painting operations has not been standing still. Pollution control equipment for paint lines can be a manufacturing facility’s costliest environmental item, and coating facility operators are always interested in better and cheaper ways to achieve environmental compliance. New approaches to meeting this potential market, and new refinements to old approaches, appear every few years. As new manufacturing lines are built, and as old lines are upgraded, the technology must be periodically reviewed to be sure a facility is making the most sensible decision in selecting its pollution control equipment.

The Marine Corps Multi-Commodity Maintenance Center in Barstow, California operates a facility for vehicle painting and undercoating, including three spray booths with a design air flow capacity in excess of 40,000 CFM. An even larger facility will be constructed within the next few years. The existing paint line is equipped with an air pollution control system (APCS), installed in 1996. The APCS incorporates several different technologies, including ultraviolet (UV) lights to break down solvent vapors in the air stream, a wet scrubber section to absorb material into water, and a final section using activated carbon to capture any material not destroyed in the first stages. An investigation in 1999, conducted by the Applied Research Laboratory at Pennsylvania State University, under the Navy RepTech Program, concluded that the first stages of the APCS are essentially non-functional, and that all of the material is being removed by the carbon stage. This results in the need to replace the carbon bed frequently (at about six to nine month intervals), at a cost exceeding $50,000, and operational disruption.

The National Center for Manufacturing Sciences (NCMS), under the Commercial Technologies for Maintenance Activities (CTMA) program, undertook a project in 2000 to review advances in air pollution control technology, and to develop recommendations for systems appropriate for both the existing paint line at Barstow, and for the new facility. The project was completed in the summer of 2001. The attached report summarizes the results of the study.

The fundamental challenge is to remove solvent vapor from a large quantity of fast moving air. It comes down to a few choices, with associated trade-offs. Basically, you can burn it, zap it, or trap it.

· Burn it: Thermal oxidation (incineration) is undoubtedly effective. But the necessary fuel is costly, leading to high operating expenses. The more dilute the air stream, the more fuel is wasted heating air. And the long-term prospects are worrisome. Fuel prices could increase. And the fact that burning contributes to global warming could become a political liability.

· Zap it: Ultraviolet light can break down solvent vapor. But since the air stream is moving rapidly, residence times are very short. An impractical number of lamps are needed for a system to be effective.

· Trap it: Various media, such as water, activated carbon, or zeolites, can trap solvent vapor. However, since the material is not destroyed, there remains the problem of what to do with it. Once trapped, destruction becomes easier, since the material can be recovered in more concentrated form.

One additional possibility is the use of biological action to act either on the air stream itself, or on the material after it has been removed from the air. This possibility has many potential advantages, but is in a much earlier stage of commercial development.

The report examines several variations of each of these options in detail, looking not only at the technology itself, but also at factors that would affect its suitability for the practical operation at the Barstow facility. The final recommendation comprises two options.

The first option might be called “trap and burn”. It calls for a first stage, using a carbon or zeolite bed to trap and concentrate the vapor, followed by a second stage for releasing vapor from the trap and destroying it. The advantage is that the vapors are released in a much more concentrated air stream, allowing the use of a much smaller thermal oxidizer, burning much less fuel, than would have been necessary without the trapping stage. This technology is available off-the-shelf, and is a low-risk option for immediate implementation.

The second option recognizes that even the most efficient of the currently available options might not look nearly as good in a few years’ time, and that having a fallback plan ready to go would be a prudent course of action. The use of water as the trapping medium would allow subsequent destruction of the material by either chemical or biological means. The report concludes that such an alternative, particularly with the biological destruction approach, deserves additional study. One major advantage is that it would be relatively easy to use the existing system for actual in-process pilot testing. Since the first stages of the existing APCS are non-functional, and the final stage is doing all the work, a biological test system can be installed prior to the final stage. The addition of the test stage can only improve the performance of the final stage – in fact, if a pilot system is found which accomplishes significant pollutant destruction, the final stage will last longer between carbon bed changes, with resulting savings in operating costs. At the same time, the feasibility of operating a biological control system with actual Barstow operating conditions and on-site staff will be conclusively demonstrated. This information will be particularly valuable in the event that the advantages of the first option become superseded by events, and an alternative APCS becomes necessary.

Although this project was focused specifically on the system installed at Barstow, the results can be applied to a wide variety of military and commercial facilities. NCMS will be communicating the results of this project, plus the conclusions of the follow-up investigation of the biological option, to interested facility personnel to aid in evaluating their current air pollution control systems, and to help plan for the changes to come.

Program Manager: Paul Chalmer, (734) 995-4911, paulc@ncms.org


	Copyright 2008 National Center for Manufacturing Sciences