The ELI Eco Logic International Inc. (Eco Logic), thermal desorption unit (TDU) is specially designed for use with Eco Logic's gas-phase chemical reduction process. The TDU, shown in the figure below, consists of an externally heated bath of molten tin metal (heated with propane) in a hydrogen gas atmosphere. Tin is used for several reasons: tin and hydrogen are nonreactive; tin's density allows soils to float on the molten bath; molten tin is a good fluid for heat transfer; tin is nontoxic in soil; and tin is used as a bath medium in the manufacture of plate glass.
Contaminated soil is conveyed into the TDU feed hopper, where an auger feeds the soil into the TDU. A screw feeder provides a gas seal between the outside air and the hydrogen atmosphere inside the TDU. The auger's variable speed drive provides feed rate control. Soil inside the TDU floats on top of the molten tin and is heated to 600 °C vaporizing the water and organic material. Decontaminated soil is removed from the tin bath into a water-filled quench tank. The water in the quench tank provides a gas seal between the TDU's hydrogen atmosphere and the outside air. A scraper mechanism removes decontaminated soil from the quench tank into drums.
After desorption from the soil, the organic contaminants are carried from the TDU to Eco Logic's proprietary gas-phase reduction reactor. In the reactor, the organic contaminants undergo gas-phase chemical reduction reactions with hydrogen at elevated temperatures and ambient pressure. This reaction converts organic and chlorinated organic contaminants into a hydrocarbon-rich gas product. After passing through a scrubber, the gas product's primary components are hydrogen, nitrogen, methane, carbon monoxide, water vapor, and other lighter hydrocarbons. Most of this gas product recirculates into the process, while excess gas can be compressed for later analysis and reuse as supplemental fuel. For further information on the Eco Logic gas-phase chemical reduction process, see the profile in the Demonstration Program section (completed projects).
The Eco Logic TDU, when used with the gas-phase chemical reduction reactor, is designed to desorb soils and sludges contaminated with hazardous organic contaminants such as polychlorinated biphenyls (PCB), polynuclear aromatic hydrocarbons, chlorinated dioxins and dibenzofurans, chlorinated solvents, chlorobenzenes, and chlorophenols. The combined technologies are suited for wastes with high water content since water is a good source of hydrogen.
In October and November 1992, the Eco Logic process, including the TDU, was demonstrated at the Middleground Landfill in Bay City, Michigan, under a Toxic Substances Control Act research and development permit. The Demonstration Bulletin (EPA/540/MR-94/504) and the Applications Analysis Report (EPA/540/AR-94/504) are available from EPA.
Further research and development since the demonstration has focused on optimizing the process for commercial operations and improving the design of the soil and sediment processing unit. According to Eco Logic, the TDU design currently in commercial operation has achieved excellent results, with contaminants in soils and sediments desorbed from high parts per million (ppm) levels to low parts per billion levels.
Two commercial-scale SE25 treatment units are currently in operation; one in Perth, Western Australia, and the other at a General Motors of Canada Ltd (GMCL) facility in Ontario. Both are currently treating a variety of waste matrices including DDT residues and PCBs in soils, oils, electrical equipment, concrete, and other solids. Following the GMCL project, the unit will be relocated to Toronto, Ontario where General Electric (GE) and Eco Logic have a contract to destroy PCB-impacted materials stored aboveground at GE's Lansdowne and Davenport facility.
Also, Eco Logic has teamed with Westinghouse Electric to treat chemical warfare agents using the process. Eco Logic has been awarded a contract through the Department of Energy's Morgantown Energy Technology Center for treatment of hazardous wastes, radioactive mixed low-level wastes, and energetics-explosives.
During the demonstration in Bay City, Michigan, the Eco Logic TDU achieved
the following:
EPA PROJECT MANAGER:
Gordon Evans
U.S. EPA
National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7684
Fax: 513-569-7787
TECHNOLOGY DEVELOPER CONTACT:
Jim Nash
ELI Eco Logic International Inc.
143 Dennis Street
Rockwood, Ontario, Canada
N0B 2K0
519-856-9591
Fax: 519-856-9235