&EPA
United States
Environmental Protection
Agency
EPA/540/MR-92/019
September 1992
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Demonstration Bulletin
Low Temperature Thermal Treatment (LT3®)System
Roy F. Weston, Inc.
Technology Description: The Roy F. Weston, Inc. (Weston) low
temperature thermal treatment (LT3®) system thermally desorbs
organic compounds from contaminated soil without heating the
soil to combustion temperatures. The transportable system is
comprised of equipment assembled on three flat-bed trailers.
With ancillary and support equipment, the system requires an
area of about 5,000 sq ft. It was demonstrated under the SITE
program at the Anderson Development Company (ADC) site in
Adrian, Ml, which was contaminated with volatile and semivolatile
organic compounds (VOC and SVOC), and 4,4'-methylenebis (2-
chloroaniline) (MBOCA). The LT3® system is divided into three
main areas of treatment: soil treatment, emissions control, and
water treatment. The system is shown in Figure 1 and described
below.
The LT3® thermal processor consists of two jacketed troughs,
one above the other. Each trough houses four intermeshed
screw conveyors. A front-end loader transports feed soil (or
sludge) to a weigh scale and deposits the material onto a con-
veyor that discharges into a surge feed hopper located above the
thermal processor. The surge hopper is equipped with level
sensors and provides a seal over the thermal processor to mini-
mize air infiltration and contaminant loss. Soil moves across the
upper trough, drops to the second trough, and exits the proces-
sor at the same end that it entered. Heat transfer fluid (or hot oil)
circulates through the hollow screws and trough jackets. Thus,
each screw conveyor mixes, conveys, and heats the contami-
nated soil during treatment. Soil is discharged from the thermal
processor into a conditioner, where water is sprayed onto it for
cooling and to minimize fugitive dust emissions. An inclined belt
conveys the treated soil to a truck or pile.
A burner heats the oil to an operating temperature of 400 to 650
°F (about 100°F higher than desired soil temperature). Combus-
tion gases released from the burner are used as sweep gas in
the thermal processor. A fan draws sweep gas and desorbed
organics from the thermal processor through a fabric filter bag-
house. Depending on contaminant characteristics, dust collected
on the fabric filter may be retreated, combined with treated
material, or drummed separately for offsite disposaL Exhaust gas
Oversized
material or
wastewater
Feed
conveyor
Dust
Aqueous Flow
— Vapor Flow
Figure 1. Diagram of LT3® system.
Sweep_gas_ f Hot oj, bumer off.gases
Fuel/combustion air
Surge
hopper
I *
t*.
'o
•5
<§
Thermal
processo
-h
Hot oil
system
Conditioner
conveyor
Fabric filter
baghouse
To atmosphere
Off-gases
Air-cooled
condenser
Oil/water
separator
| Organics
To offsite
disposal
To discharge or
offsite disposal
-------
from the fabric filter is drawn into an air-cooled condenser to
remove most of the water vapor and organics, and then through a
second, refrigerated condenser to further lower the temperature
and reduce the moisture and organic content of the off-gases.
Electric resistance heaters then increase the off-gas temperature
back to 70°F to optimize the performance of the vapor-phase
activated carbon column which removes any remaining organics.
While this is a typical operation, caustic scrubbers and afterburn-
ers have been employed as part of the air pollution control system
at some sites.
Condensate streams are typically treated in a three-phase oil-
water separator to remove light and heavy organic phases from
the water phase that is then treated in the carbon adsorption
system to remove residual organic contaminants. Treated con-
densate is often used for soil conditioning, and only the organic
phases are disposed offsite. However, the separation step may
not be appropriate when processing extremely wet materials like
sludge, due to the high volume of condensate generated. In such
cases, aqueous streams from both condensers may be pumped
through a disposable filter to remove particulate matter prior to the
carbon adsorption treatment and offsite disposal.
Waste Applicability: Weston reports that the LP® system can
process a wide variety of soils with differing moisture and con-
taminant concentrations, and that the technology is best suited for
soils with a moisture content of less than 20% and VOC contami-
nant concentration of up to 1%. Wastes with moisture content
greater than 50% need to be dewatered prior to treatment in the
UP® system. Screening or crushing of oversized material (greater
than 2 in.), or clay shredding may be required for some applica-
tions.
Bench-, pilot-, or full-scale LP® systems have been used to treat
soil contaminated with the following wastes: coal tar, drill cuttings
(oil-based mud), No. 2 diesel fuel, JP4 jet fuel, leaded and
unleaded gasoline, petroleum hydrocarbons, halogenated and
nonhatogenated solvents, VOCs, SVOCs, and polynuclear aromatic
hydrocarbons.
Demonstration Results: The LP® SITE demonstration was
conducted in November and December 1991, as part of a proof-
of-process test for full-scale remediation of the ADC lagoon sludge.
Feed preparation for the sludge at the ADC site included lime and
ferric chloride addition followed by filter press dewatering to a
moisture content of 14% to 44%. During the demonstration, con-
taminated sludge was heated to above 500°F for a residence
time of 90 min; the system throughput was approximately 2.1
tons/hr.
Six replicate tests were conducted, each lasting approximately 6
hr. Solid and liquid sampling locations for each test included
contaminated feed sludge, treated sludge, fabric filter dust, and
condensate liquid. Off-gases were also sampled before and after
carbon treatment during each run. Solid, liquid, and gas samples
were analyzed for MBOCA, VOCs, SVOCs, dioxins, and furans.
Samples were also analyzed for chloride and total organic halides,
to trace the fate of chloride through the system, and a variety of
other parameters were analyzed to characterize the feed and
treated sludge. Continuous emissions monitoring (GEM) of off-
gases included total hydrocarbons (THC), carbon monoxide,
carbon dioxide, and oxygen. Key findings from the SITE demon-
stration are summarized below:
• The LP® system removed VOCs to below method detection
limits (less than 0.060 milligrams per kilogram [mg/kg] for
most compounds).
• The LP® system achieved MBOCA removal efficiencies
greater than 88%; concentrations in the treated sludge ranged
from 3.0 to 9.6 mg/kg.
• The LP® system decreased the concentrations of all SVOCs
in the sludge, with two exceptions. The increase in phenol
concentration is most likely due to chemical transformations
during heating. A minor leak of heat transfer fluid, which
contains triphenylene, probably caused the apparent increase
in chrysene concentration.
• Dioxins and furans were formed in the system, but the
2,3,7,8-TCDD isomer was not detected in treated sludge.
• Stack emissions of non-methane THC increased from 6.7 to
11 parts per million by volume (ppmv) during the demonstra-
tion; the maximum emission rate was 0.2 pounds per day
(ppd). The maximum particulates emission rate was 0.02
ppd, and no chlorides were measured in stack gases.
For Further Information:
EPA Project Manager:
Paul R. dePercin
U.S. EPA Risk Reduction Engineering Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
(513) 569-7797; FAX (513) 569-7620
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/540/MR-92/019
------- |