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ENHANCED REMOVAL OF SEPARATE PHASE VISCOUS FUEL BY SIX PHASE HEATING


ENHANCED REMOVAL OF SEPARATE PHASE
VISCOUS FUEL BY ELECTRICAL RESISTANCE
HEATING AND MULTI-PHASE EXTRACTION


Gregory Beyke, P.E., Vice President of Engineering, Thermal Remediation Services, Inc., Marietta, GA
David Fleming, Vice President of Marketing and Sales, Thermal Remediation Services, Inc., Snoqualmie, WA



ABSTRACT

A floating hydrocarbon plume at a manufacturing facility in a metropolitan area located
in the southeastern part of the U.S. was remediated using Electrical Resistance Heating (ERH)
and Multi-Phase Extraction (MPE). The hydrocarbon was a specialty fuel similar to kerosene or
diesel fuel. Initially, hydrocarbon covered an area of 4900 ft
2
(500 m
2
) and was up to l0 ft (3 m)
thick, with most wells containing 1-3 ft (0.5-1 m) of hydrocarbon. Most of the floating
hydrocarbon was beneath the manufacturing building. The soil from the floor to a depth of about
50 ft (15 m) is composed of sandy clay saprolite with moderately low permeability and high
heterogeneity. The static water table is about 24 ft (7 m) below grade. Remediation began on 27
May 1999. Remediation to less than 1/8-inch (4 mm) hydrocarbon was completed on 10
December 1999. The ERH and MPE system relied on several mechanisms to remove
hydrocarbon: 1) heating to reduce hydrocarbon viscosity, 2) hydrocarbon floatation/agitation by
rising steam bubbles, 3) thermally enhanced vaporization (fuel boiling), and 4) vacuum-
enhanced pumping. ENHANCED REMOVAL OF SEPARATE PHASE
VISCOUS FUEL BY ELECTRICAL RESISTANCE
HEATING AND MULTI-PHASE EXTRACTION


Background

The site was a former manufacturing facility. A large release of a specialty fuel occurred
from a hydrocarbon pipeline where it passed beneath the exterior facility wall. The plume was
composed of a specialty fuel with boiling point (228
°C) and viscosity (2 mm
2
/s St) between
those of jet fuel and diesel fuel.
Most of the floating hydrocarbon was beneath the manufacturing facility. The soil from
the floor to a depth of about 50 ft (15 m) is composed of sandy clay saprolite with moderately
low permeability and high heterogeneity. The static water table is about 24 ft (7 m) below grade.
Initially, hydrocarbon covered an area of 4900 ft
2
(500 m
2
) and was up to 10 ft (3 m)
thick, with most wells containing 1-3 ft (0.5-1 m) of hydrocarbon. Due to site heterogeneity,
wells separated by only a few feet varied in hydrocarbon thickness by several feet.
Technology Selection

Conventional product pumping or MPE can be used to remove such fuels; however, these
processes are impeded by soil heterogeneity, hydrocarbon interfacial tension, and low fuel vapor
pressure. Thus, conventional in-situ techniques would typically require in excess of one year of
operation and have a greater chance of later hydrocarbon rebound. ERH is an electrical heating
technology that uses in situ resistance heating and steam stripping to accomplish subsurface
remediation.
ERH was originally developed by the oil industry to enhance the production of viscous
crude oil from pumping wells. ERH uses electrodes that are installed like wells to direct the flow
of electrical current through the subsurface soil and rock. The flow of electrical current through
the subsurface heats the soil and groundwater directly and uniformly. In the 1990s, ERH was
adapted for environmental purposes. The technology has now proven capable of remediating
both dense and light non-aqueous phase liquids (DNAPL and LNAPL) from both the vadose and
saturated zones, regardless of permeability or heterogeneity.
The ERH Power
Control Unit (see Figure 1)
adjusts conventional 60-
hertz three-phase electricity
from standard utility
power lines to the proper
voltage for subsurface
heating (typically 150-450
volts). The electrical
current is then delivered
throughout the
subsurface treatment volume
by vertical, angled, or
horizontal electrodes installed
using standard drilling
techniques.
Figure 1. 500 kW PCU

2 NAPLs adsorb onto
crack borders in
bedrock or low
permeability soils
Clay or
Bedrock
ERH is used for in situ steam generation
and causes faster boiling in NAPL regions
A standard computer controls the operational status of the ERH PCU and monitors the
temperature conditions in the subsurface. Operations personnel can access these computers and
control the PCUs either directly or
remotely by phone line.
ERH increases subsurface
temperatures to the boiling point of
water. The technology is equally
effective in the vadose and
saturated zones. Because the ERH
electrodes are electrically out of
phase with each other, electrical
current flows from each electrode
to all of the other out of phase
electrodes adjacent to it. In this
manner, a volume of subsurface
surrounded by ERH electrodes is
saturated by the electrical current
moving between the electrodes. It
is the resistance of the subsurface
to this current movement that
causes heating.
All soils in the treatment
region are heated; however,
electricity prefers to take pathways
of lower resistance when moving
between electrodes, and these
pathways are heated slightly faster.
Examples of low resistance
pathways in the subsurface include
silt or clay lenses and areas of
higher ion content. As dense
compounds sink through the
lithology, they tend to become
trapped on these same silt and clay
lenses (see Figure 2). Over time,
trapped solvents undergo biological
dehalogenation producing daughter
compounds and free chloride ions.
Thus, at chlorinated hydrocarbon
sites, the most impacted portions of
the subsurface are also the low resistance electrical pathways that are preferentially treated by
ERH. In a similar fashion, rock fractures and weathered rock are more electrically conductive,
and heat faster, than competent rock. Thus, low permeability soils, bedrock fractures, and solvent
hot spots heat, and clean up, slightly faster than other soils.
Steam vents quickly through contaminated
fractures and slowly migrates upward
through bulk soils and porous rock
Figure 2.
Insitu
Steam
Generation

3 Steam
Condenser
Skid
500 kW
PCU
Air Cooling
Tower
Operating
Electrode
Emergency
Shutoff
By increasing subsurface temperatures to the boiling point of water, ERH speeds the
removal of contaminants by two primary mechanisms: increased volatilization and steam
stripping. As subsurface temperatures begin to climb, contaminant vapor pressure, and the
corresponding rate of contaminant extraction, increases by a factor of about 25. However, it is
the ability to produce steam in situ that represents a significant advantage of ERH. Through
preferential heating, ERH creates steam from within silt and clay stringers and lenses. The
physical action of steam escaping these tight soil lenses drives contaminants out of those portions
of the soil matrix that tend to lock in
contamination via low permeability or
capillary forces. Released steam then acts
as a carrier gas, sweeping contaminants to
the MPE wells (Figure 4, below).
At the surface, a condenser separates
the mixture of soil vapors, steam, and
contaminant liquids which is extracted from
the subsurface into condensate and
contaminant laden vapor. If these waste
streams require pre-treatment before
discharge, standard air abatement and water
treatment technologies are used (Figure 3).

Figure 3. Equipment Staging and Voltage Checks
ERH and MPE System Installation

The impacted region inside the facility had low ceilings, 11 ft (3.3 m) high. The low
ceilings required the use of special limited-access drilling equipment that could not turn large
diameter augers. For this reason, smaller, but more numerous electrode/wells were installed than
is most commonly used for ERH.
Electrodes & MPE
Wells
The electrode/wells were
installed in 8-inch (200 mm) boreholes.
A 2-inch (50 mm) steel casing and
screen were inserted; this casing served
as both as an electrical conductor and as
a conduit for hydrocarbon extraction. A
backfill of steel shot was used as the
well gravel pack and electrode
conductive region. The borehole above
22 ft (6.5 m) was backfilled with neat
cement grout (Figure 4).


Figure 4. Electrodes & MPE Wells Inside Building

4 A total of 50 combination extraction/monitoring wells and ERH electrodes were installed.
The electrodes directed electrical heating into the region from 20 to 30 ft (6 to 9 m) below grade.
The wells extracted hydrocarbon and vapor from 22 to 2