United States
Environmental Protection
Agency
EPA/540/MR-93/524
September 1993
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Demonstration Bulletin
IN-SITU Thermal Oxidative Process
HRUBETZ Environmental Service
Technology Description: The HRUBOUT® system is an in
situ thermal oxidative process that removes hydrocarbons from
contaminated soil. In the HRUBOUT® process, heated, com-
pressed air is injected into the soil below the zone of contamina-
tion. As the heated air rises, it transfers heat to the soil and
evaporates soil moisture. Most of the volatile organic compounds
are removed with the water vapor by steam distillation effect.
The vapor is collected as it rises to the surface and is directed to
a thermal oxidizer unit that operates at temperatures of up to
1,500°F.
The HRUBOUT® system is designed to treat soil contaminated
with nonhalogenated organic compounds in any concentration
range and can be designed to treat an area of up to 3,600 square
feet at a time. The system consists of two air blowers, a burner,
and a thermal oxidizer. Injection wells of 6 to Sin. in diameter with
perforated casing at the base are drilled to a depth below the
contamination. The number of injection wells depends on the soil
permeability and the area of contamination.
Heated, compressed air is delivered by an air blower at a rate of
8,500 pounds per hour (Ib/hr) at pressures of up to 12 pounds
per sqare inch-gauge (psig), or 5,000 Ib/hr at pressures of up to
24 psig. The air is heated up to 1,200°F using a 2.9 million British
thermal units per hour (Btu/hr) adiabatic burner, fueled by either
natural gas or propane. The heated air is distributed to the
individually flow-controlled injection wells through a stainless steel
manifold. The objective of the system is to maintain a horizontally
uniform rising flow of air across the treatment area. Well spacing
is generally the same as the well depths. Initially, low-tempera-
ture air is pumped into the soil until a steady state flow rate is
achieved; and then the temperature of the injected air is gradu-
ally ipcreased. As the heated air progresses upward throughout
the sioil, the moisture is evaporated, removing the volatile con-
taminants. The temperature of the soil is recorded using 8-point
thermocouple probes placed in several wells. The thermocouple
probes provide a secondary check on the uniformity of gas flow
within the soil.
As the soil temperature gradually increases, the semivolatile and
nonvolatile constituents are volatilized or thermally oxidized. Die-
sel fuel will oxidize or vaporize and will be removed from the soil
at approximately 500°F. Heavier hydrocarbons, such as crude
petroleum, heavy heating oil, and lubricating oil, will be removed
Hot Compressed Air
(25ff>-1200°F
Aluminum Foil
Impermeable
Layer
Vent Gas
Collection
Channels
Burner/Blower
or
To Atmosphere
Incinerator
Central
Collection
Point
T=72°F
A A A Q A A = psig = 0
Thermo
Couple
Cluster
VadoseZone
Hot AT Injection
~ =250M20
ps;gr = 5-22
Water Table
Figure 1. HRUBOUT® Process Simplified Diagram
Printed on Recycled Paper
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from the soil at approximately 800°F when treated for a suffi-
ciently fong parted of time.
The soil vapor Is collected at the surface and fed to the thermal
oxidizer. The thermal oxidizer has a rating of 3.1 million Btu/hr
and operates at 1,500°F, with a 0.6-second retention time. Ac-
cording to the developer, the unit will destroy at least 99.5
percent of the hydrocarbon contaminants, and is fueled by either
natural gas or propane.
A large capacity vacuum blower dilutes the collected soil gas with
ambient air before incineration if they approach the lower explo-
sive level of concentration. Automatic system safety shutdown
features are Included for flame failure, high temperature, high
and tow gas pressure, and tow air flow. A tocal flame arrester is
also incorporated into the system.
The blower, thermal oxidizer, and the control systems are mounted
on a trailer for easy transport of the system. The system operates
from a central control panel. The unit operates 24 hours a day
while on site, and can operate largely unmanned.
Low permeability and high soil moisture significantly reduce the
effectiveness of more traditional soil vapor extraction systems.
According to the developer, HRUBOUT® technology's use of
heated air instead of unheated air or even steam enables the
system to effectively treat low permeability, high moisture soils by
(1) removing the moisture from the soil mass and increasing air
flow and (2) by creating micro and macro fissures in low perme-
ability soils such as days through shrinkage of soils after mois-
ture toss.
RELD DEMONSTRATION: The HRUBOUT® technology
was demonstrated in January and February of 1993 at Kelly Air
Fore© Base in San Antonio, Texas. On June 14,1988, approximately
80,000 gals of jet fuel (JP-4) spilled from a ruptured high-pressure
fuel pipeline in the 1100 Area of the base. The fuel was spilled into
the shallow alluvial sediments at the site, and a portion of this fuel
flowed onto the surface, where evaporation, runoff, and infiltration
occurred.
The surftcial geologic deposits at the site consist of unconsoli-
dated fluvtetile alluvium and terrace deposits, consisting of clay
and sift, and to a lesser degree, sand and gravel. Groundwater is
found at a depth of approximately 20-25 feet below ground
surface in the 1100 Area.
Characterization of the JP-4 contamination at the 1100 Area
following the spill indicated that benzene, toluene, ethylbenzene,
and xylenes (BTEX) concentrations in soil were generally less
than 130 parts per million (ppm). Likewise, total recoverable
petroleum hydrocarbon (TRPH) concentrations in soil were gen-
erally less than 1,000 ppm. Pretreatment samples collected as
part of the SITE demonstration revealed average soil TRPH
concentrations of approximately 2,700 ppm in the 20-foot-deep
treatment area. Within the treatment area, the highest concentra-
tions were observed in the top 10 feet of the soil mass.
Six hot air injection wells were installed in a rectangular 10-by 20-
foot grid spaced 10 feet apart from each other. The system was
operated 24 hours a day for approximately 3 weeks.
Computer data acquisition systems were used throughout the
demonstration to continuously monitor various system param-
eters. These parameters included the temperature and pressure
of injected air; incinerator inlet temperature, pressure, and flow
rate; and incinerator outlet temperature. In addition, the pressure,
flow rate, and moisture content of the incinerator outlet stream,
the moisture content of the incinerator inlet stream, and vertical
soil temperature profiles were measured and recorded periodi-
cally throughout the demonstration. Analysis of the extensive soil
sampling performed before and after the treatment process will
be used to analyze the effectiveness of the HRUBOUT® system.
The soil samples were analyzed for TRPH, total organic content
(TOC), permeability, and moisture content.
Description of all field activities, as well as, a thorough analysis
and interpretation of the results will be presented in the Technol-
ogy Evaluation Report. The Technology Evaluation Report will be
available in the Winter of 1993.
FOR FURTHER INFORMATION:
EPA Project Officer:
Gordon M. Evans
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
(513) 569-7684 -u.S. Government Printing Office: 1993 — 750-071/80099
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
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EPA&40/MR-93/524
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