This objective of this project was to demonstrate a new cost- and process-efficient method to thermally decontaminate material potentially presenting an explosive hazard (MPPEH) with lower emissions of air pollutants compared to a legacy wood-fired unit.

An MPPEH processing propane-fueled unit was designed and built by engineers at Naval Air Warfare Center Weapons Division (NAWCWD) China Lake. The burner design is modular to customize for different sizes and consists of up to four modules of closely spaced, parallelaligned pipes for propane delivery.

Researchers at the U.S. Environmental Protection Agency (EPA) Office of Research and Development (ORD) used their in-house developed sampling equipment attached to an unmanned aerial system, which was owned and operated by pilots from the University of Maryland unmanned aerial system Test Site, to sample emissions from the wood-fired and propane-fueled units. Researchers from EPA ORD and the University of Dayton Research Institute analyzed the emissions samples for carbon monoxide, carbon dioxide, particulate matter with a diameter of 2.5 µm or less (PM2.5), total carbon (TC)/organic carbon/elemental carbon, black carbon (BC), and volatile organic compound (VOCs).

The successful functioning of the propane unit was first demonstrated by engineers at NAWCWD China Lake with a follow-on successful demonstration by Naval Surface Warfare Center (NSWC) Indian Head Division. Surrogate MPPEH materials were instrumented with thermocouples to demonstrate the effectiveness of the decontamination based on known temperatures for the thermal degradation of energetic materials. Attributes demonstrated for the propane unit included (1) met Department of Defense (DoD) Explosives Safety Board standards for thermally processing MPPEH; (2) reductions in emissions of PM2.5, TC, BC and benzene compared to the woodfueled method; (3) reductions in overall costs compared to the wood-fueled method; and (4) achievement of time-temperature decontamination requirements in much less time than wood-fueled fires. Conservative estimates indicate that the burner will pay for itself in under four years, with better returns for more frequent use.

The emission samples were limited in numbers, and the testing conditions differed from normal operations. Additional samples would be required to establish reliable emissions factors. One finding that warrants further investigation is that the propane burner emitted surprisingly high emissions of methylene chloride and of other chlorinated VOCs not found from previous similar measurements. This is related to the fuel composition rather than the performance of the propane burner. These chlorinated VOC emissions may be a byproduct of the natural gas and crude oil refining where chlorides occur naturally or due to trace chemicals from fracking processes.

There are no known implementation issues with this technology. The system has been installed for use by NSWC Indian Head Division, and can be easily replicated to benefit any DoD installation requiring the capability to thermally process MPPEH.