The development of new vapor recovery technologies can allow for continued use of higher-performance chemicals, reuse of those chemicals, and lower overall emissions of hazardous air pollutants/volatile organic compounds (HAPs/VOCs). The Vapor Phase Removal and Recovery System (VaPRRS™) was developed cooperatively by the University of Illinois, Engineer Research and Development Center (ERDC)-Construction Engineering Research Laboratory (CERL), and Air Force Research Laboratory (AFRL) as an economical adsorption technology to control emissions from Department of Defense (DoD) HAP/VOC emissions sources such as painting operations. During a prior pilot field study at a paint booth at Fort Hood, Texas, the VaPRRS system achieved greater than 99% control efficiency.

The objective of this ESTCP project was to demonstrate that the VaPRRS technology could efficiently and economically control VOCs from a dedicated DoD waste stream. At Hill Air Force Base (AFB), the VaPRRS technology was implemented within a compact and portable emission treatment cart. The demonstration was designed to remove VOCs from gas streams generated while painting C-130 aircraft wheel wells. The portable paint cart encloses the painting operation so that evacuation of the hangar is not necessary during painting; thus, control efficiency is important. The existing system’s cart contains granular activated carbon (GAC) beds. When the bed becomes saturated, it is sent offsite for disposal or regeneration, and a new bed is installed. VaPRRS will allow for regeneration of the adsorbent and recovery of the adsorbate. This demonstration replaces the GAC beds with a VaPRRS unit in a new treatment cart prototype.

Technology Description

VaPRRS is a new type of regenerative filter system that works by using a high-performance activated carbon fiber cloth (ACFC) contained within a vessel. Applying an electrical current regenerates the ACFC by rapidly heating it, and this initial action causes efficient desorption of the contaminant with only minimal heating of the vessel. The adsorbate is released and condensed onto the inner surface of the vessel where it is collected as a liquid. After cooling, the filter is capable of reuse. A major advantage of VaPRRS technology over conventional systems is that the entire adsorption, desorption, and recovery process occurs inside the same vessel. This advantage ultimately reduces the size, complexity, and cost of the system.

The design of the VaPRRS demonstration prototype proved to be a large challenge. The first filter design was a pleated filter that performed unsatisfactorily. This led to in-house development of filters utilizing skeletal structures. The final design resulted in cylindrical-shaped filters that were organized in arrays to be inserted into a modified version of the current emission treatment cart at Hill AFB. The prototype VaPRRS loaded treatment cart was built by Global Finishing Systems, Inc. – makers of the existing treatment cart. The VaPRRS treatment cart was tested during two troubleshooting efforts at Global Finishing’s facility in Osseo, Wisconsin.

Demonstration Results

Performance testing of the VaPRRS treatment cart occurred October 31 - November 2, 2011 at Hill AFB. Treatment of VOCs being emitted from wheel-well coating was performed by coating one C-130 aircraft during the testing period. Approximately 5.8 gal of solvents were used. Other than the regeneration phase, the new system operated similarly to the paint booth emission control cart that exists at Hill AFB, so the testing did not impact the base’s ongoing operations. 

Data from the first two days of testing showed the control efficiency during adsorption was 81.1%–84.6%. That efficiency was lower than the expected value of 98%, so the cart was modified to reduce leaks that were allowing some of the incoming coating-laden air to bypass the ACFC filters. Tests from the third day showed that the repairs were successful with an average control efficiency of 98% achieved. The ACFC did not reach breakthrough after adsorbing VOCs and water during the complete coating of the wheel wells for the C-130 aircraft.

Desorption of the cart was conducted after the wheel-well coating activity was complete on the C-130. It was evident during desorption that there was a problem because high VOC concentrations were detected near the inlet of the cart where they were not expected. There was no liquid in the liquid recovery vessel after regeneration of the primary or secondary filters. This finding suggests there were leaks or open valves that allowed the regeneration gas to escape through the adsorption inlet into the hanger. The liquid recovery efficiency was 0%, and this leak or valve sequence problem needs to be addressed before the ACFC cart can function properly.

Implementation Issues

The treatment cart with VaPRRS loaded did not pass all of the primary performance criteria because the regeneration cycle did not function properly. After sealing leaks in the initial tests, the average control efficiency was 98.0%. The cart was considered to be fully functional for each adsorption test during the field campaign, resulting in a reliability of 100%. There was 0% hazardous waste recovery, while 95% recovery was required. It was inconclusive whether the cart passed the ease-of-use criterion because the regeneration process did not function properly. The cart performed similarly to the pilot-scale unit during adsorption but did not function properly during regeneration, so the scale-up criterion was not met. The cart performed consistently for adsorption during the field campaign for the different wheel wells, coatings, and ambient weather conditions. The system required minimal operator training and did not require additional training after the first use. However, the system did not successfully operate during desorption to recover solvent, so it was inconclusive whether operators could successfully maintain the system during regeneration. The cart was not successfully utilized at Hill AFB due to the regeneration issue and thus failed the versatility criterion.

Due to the unsatisfactory performance of the VaPRRS treatment cart during the field test, a complete cost assessment was not conducted. However, a capital cost estimation suggests that the VaPRRS cart would cost 120% more than the current treatment cart ($143,000 versus $65,000). The difference in operating costs indicates that payback would occur in 6.2 years with a $48,000 savings over the 10-year life expectancy.

With the current regeneration malfunction, the cart is not recommended for further implementation. However, it is believed the problems are related to construction issues with the prototype and not with the VaPRRS technology; thus, a subsequent evaluation would be more successful if the current prototype is refurbished.