(Hybrid Fluidized Bed System)
The Hybrid Fluidized Bed (HFB) system treats contaminated solids and sludges by incinerating organic compounds and extracting and detoxifying volatile metals. The system consists of three stages: a spouted bed, a fluidized afterburner, and a high-temperature particulate soil extraction system.
First, the spouted bed rapidly heats solids and sludges to allow extraction of volatile organic and inorganic compounds. The spouted bed retains larger soil clumps until they are reduced in size but allows fine material to quickly pass through. This segregation process is beneficial because organic contaminants in fine particles vaporize rapidly. The decontamination time for large particles is longer due to heat and mass transfer limitations.
The central spouting region is operated with an inlet gas velocity of greater than 150 feet per second. This velocity creates an abrasion and grinding action, rapidly reducing the size of the feed materials through attrition. The spouted bed operates between 1,500 and 1,700 F under oxidizing conditions.
Organic vapors, volatile metals, and fine soil particles are carried from the spouted bed through an open-hole type distributor, which forms the bottom of the second stage, the fluidized bed afterburner. The afterburner provides sufficient retention time and mixing to incinerate the organic compounds that escape the spouted bed, resulting in a destruction and removal efficiency of greater than 99.99 percent. In addition, the afterburner contains bed materials that absorb metal vapors, capture fine particles, and promote formation of insoluble metal silicates. The bed materials are typically made of silica-supported bauxite, kaolinite, or lime.
In the third stage, the high-temperature particulate soil extraction system removes clean processed soil from the effluent gas stream with one or two hot cyclones. The clean soil is extracted hot to prevent unreacted volatile metal species from condensing in the soil. Off-gases are then quenched and passed through a conventional baghouse to capture the condensed metal vapors.
Generally, material handling problems create major operational difficulties for soil cleanup devices. The HFB system uses a specially designed auger feed system. Solids and sludges are dropped through a lock hopper system into an auger shredder, which is a rugged, low-revolutions-per-minute, feeding-grinding device. Standard augers are simple and reliable, but are susceptible to clogging from feed compression in the auger. In the HFB system, the auger shredder is closecoupled to the spouted bed to reduce compression and clump formation during feeding. The close-couple arrangement locates the tip of the auger screw several inches from the internal surface of the spouted bed, preventing soil plug formation.
This technology is applicable to soils and sludges contaminated with organic and volatile inorganic contaminants. Nonvolatile inorganics are not affected.
This technology was accepted into the SITE Emerging Technology Program in January 1990. Design and construction of the commercial prototype HFB system and a limited shakedown are complete. The Emerging Technology Bulletin (EPA/540/F-93/508) is available from EPA.
EPA PROJECT MANAGER:
Teri Richardson
U.S. EPA
National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7949
Fax: 513-569-7105
TECHNOLOGY DEVELOPER CONTACT:
Richard Koppang
Energy and Environmental Research Corporation
18 Mason Street
Irvine, CA 92718
714-859-8851
Fax: 714-859-3194