Hot Gas Decontamination
Hot gas decontamination is used to decontaminate equipment and structures that have been contaminated by explosive residues. It also may be used on masonry or metallic structures contaminated with explosive materials. The process raises the temperature of the contaminated equipment or material for a specified period of time by exposing it to hot gases (i.e., heated air). The U.S. Army Environmental Center (USAEC) designed a hot-gas system that includes a hot-gas furnace, ducts and fans, a control system, and a thermal oxidizer (i.e., afterburner). The furnace can accept a maximum of 3,000 pounds of contaminated materials. Treatment of contaminated off-gases occurs in a thermal oxidizer, which has a continuous emission monitoring system to measure compliance with air quality requirements.
Operating conditions (e.g., temperature and exposure time) are site-specific. Typically, the decontamination process holds a steady temperature of 500¡ to 600¡ Fahrenheit for one hour. The method involves sealing and insulating the structures, heating them with a hot gas stream at 500¡ to 600¡ Fahrenheit for a prescribed period of time, volatilizing the contaminants, and destroying them in an afterburner.
Limitations and Concerns
The largest concern is atmospheric emissions from the thermal oxidizer. If chlorinated compounds are present, formation of dioxins and furans may occur. Because there are a variety of materials being volatized, thorough analysis and continuous monitoring of emissions are recommended.
The furnace design must take into consideration possible explosions from improperly demilitarized mines or shells.
Hot gas decontamination is applicable for equipment requiring decontamination for reuse. It is also applicable for explosive items, such as mines and shells, being demilitarized (after removal of explosives) or scrap material contaminated with explosives. The method can also be used for buildings or structures associated with ammunition plants, arsenals, and depots involved in the manufacture and processing of explosives and propellants.
Other methods of decontaminating explosives-contaminated materials, such as pressure washing or stream cleaning, often surpass 99.9% destruction levels, but they frequently leave residual contamination in pores or hard-to-reach internal areas. Incineration and open burning may achieve the desired removal efficiencies, but the treated materials are generally not suitable for reuse or salvage. Uncontrolled emissions from open burning and incineration are a growing environmental concern.
Technology Development Status
This process is between the pilot test and field demonstration stage. The United States Army Environmental Center sponsored several demonstrations showing that 99.9999% decontamination of structural components is possible. The Tennessee Valley Authority (TVA) modified the system by moving the burner flame outside the decontamination furnace and adding a continuous emission monitoring system.
Other Resources and Demonstrations
See http://www.serdp-estcp.org/Program-Areas/Munitions-Response/Land/Enabling-Technologies/MR-200032/MR-200032 for a description of a demonstration at the Aberdeen Proving Ground.