Note: Descriptions are shown in the official language in which they were submitted.
CA 02704832 2010-11-17
CONTINUOUS SOIL REMEDIATION
BACKGROUND
This Application is a division of CA 2,565,594, filed May 17, 2004.
1. Field of the Invention
The present invention generally relates to soil remediation systems and
methods. Some embodiments of
the invention relate to systems and methods of treating soil at a plurality of
sites substantially continuously using
equipment in a central treatment facility. Certain embodiments of the
invention relate to systems and methods of
using heated, substantially uncontaminated soil at a first site to destroy
contaminants within a portion of vapors
produced from contaminated soil at a second site.
2. Description of Related Art
Soil contamination is a matter of concern in many locations. "Soil" refers to
unconsolidated and
consolidated material in the ground. Soil may include natural formation
material such as dirt, sand, and rock, as
well as fill material. Soil may be contaminated with chemical, biological,
and/or radioactive compounds.
Contamination of soil may occur in a variety of ways, such as material
spillage, leakage from storage vessels, and
landfill seepage. Public health concerns may arise if contaminants migrate
into aquifers or into air. Soil
contaminants may also migrate into the food supply through bioaccumulation in
various species in a food chain.
There are many ways to remediate contaminated soil. "Remediating soil" means
treating the soil to reduce
contaminant levels within the soil or to remove contaminants from the soil. An
ex situ method of remediating
contaminated soil is to excavate the soil and then process the soil in a
separate treatment facility to reduce
contaminant levels within the soil or to remove contaminants from the soil.
Alternatively, contaminated soil may be
remediated in situ.
Thermal desorption is a soil remediation process that may involve in situ or
ex situ heating of contaminated
soil. Heating the soil may reduce soil contamination by processes including,
but not limited to, vaporization and
vapor transport of contaminants from the soil, entrainment and removal of
contaminants in water vapor and/or an
air stream, thermal degradation (e.g., pyrolysis), and/or conversion of
contaminants into non-contaminant
compounds by oxidation or other chemical reactions within the soil. During
thermal remediation, a vacuum may be
applied to the soil to remove off-gas from the soil. Vacuum may be applied at
a soil/air interface or through
collection ports (e.g., vacuum or vapor extraction wells) placed within the
soil. The vapors may entrain volatile
contaminants and carry these contaminants toward the vacuum source. Vapors
removed from the soil by the
vacuum may include contaminants from the soil. The vapors may be transported
to a treatment facility. The vapors
removed from the soil may be processed in the treatment facility to remove
contaminants from the vapors or to
reduce contaminant levels within the vapors.
Soil may be heated by methods including, but not limited to, radiative
heating, conductive heating, radio
frequency heating, and/or electrical resistivity heating. For shallow
contaminated soil, a thermal blanket placed on
top of the soil or heaters placed horizontally in trenches within the
contaminated soil may be used to apply heat to
the soil. Shallow contaminated soil includes soil contamination that does not
extend below a depth of about I in to
about 2 m. For deeper contaminated soil, heater wells or heater/vapor
extraction wells may be used to apply heat to
the soil.
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A vacuum may be applied to remove vapors from contaminated soil. U.S. Pat. No.
4,984,594 issued to
Vinegar et al. describes an in situ thermal desorption (ISTD) process for soil
remediation of low depth soil
contamination. U.S. Pat. No. 5,318,116 issued to Vinegar et al. describes an
ISTD process for treating
contaminated subsurface soil with conductive heating.
Heat added to contaminated soil may raise a temperature of the soil above
vaporization temperatures of
soil contaminants. If soil temperature exceeds a vaporization temperature of a
soil contaminant, the contaminant
may vaporize. A vacuum may be used to draw the vaporized contaminant out of
the soil. The presence of water
vapor may result in vaporization of less volatile contaminants at or near the
boiling point of water. Heating the soil
to a temperature below vaporization temperatures of contaminants may also have
beneficial effects. Increasing soil
temperature may increase a vapor pressure of contaminants in the soil and
allow a vacuum system to remove a
greater portion of contaminants from the soil than possible at lower soil
temperatures. Evaporation of contaminants
into air or water vapor streams may be enhanced by heating. Heat applied to
the soil may also result in the
destruction of contaminants in situ.
U.S. Pat. No. 5,190,405 issued to Vinegar et al. describes an in situ method
for removing soil contaminants
using thermal conduction heating and application of a vacuum.
U.S. Pat. No. 5,229,583 issued to van Egmond et al., U.S. Pat. No. 5,233,164
issued to Dicks et al., and
U.S. Pat. No. 5,221,827 issued to Marsden et al. describe surface heating soil
remediation systems.
U.S. Pat. No. 6,632,047 issued to Vinegar et al., and U.S. Pat. No. 6,824,328
of Vinegar et al.
describe heater elements placed horizontally within trenches in the soil for
remediation.
U.S. Pat. No. 5,553,189 issued to Stegemeier et al. describes a shallow pit
for remediating near surface soil
contamination.
U.S. Pat. No. 5,249,368 issued to Bertino et al. describes a sealed roll-off
container for contaminated soil.
A soil remediation system may include four major systems. The systems may be a
heating and vapor
extraction system, an off-gas collection piping system, an off-gas treatment
system, and instrumentation and power
control systems.
A heating and vapor extraction system may be formed of wells inserted into the
soil for deep soil
contamination or of thermal blankets for shallow soil contamination. A
combination of wells and thermal blankets
may also be used. For example, thermal blankets may be placed at centroids of
groups of wells. The thermal
blankets may inhibit condensation of contaminants near the soil surface. Soil
may be heated by a variety of
methods. Methods for heating soil include, but are not limited to, heating
substantially by thermal conduction,
heating by radio frequency heating, or heating by electrical soil resistivity
heating. Thermal conductive heating
may be advantageous because temperature obtainable by thermal conductive
heating is not dependent on an amount
of water or other polar substance in the soil. Soil temperatures substantially
above the boiling point of water may
be obtained using thermal conductive heating. Soil temperatures of about 100
C, 200 C, 300 C, 400 C, 500 C
or greater may be obtained using thermal conductive heating.
Wells may be used to supply heat to the soil and to remove vapor from the
soil. The term "wells" refers to
heater wells, vapor extraction wells, and/or combination heater/vapor
extraction wells. Heater wells supply thermal
energy to the soil. Vapor extraction wells may be used to remove off-gas from
the soil. Vapor extraction wells may
be connected to an off-gas collection piping system. A vapor extraction well
may be coupled to a heater well to
form a heater/vapor extraction well. In a region adjacent to a heater/vapor
extraction well, air and vapor flow
within the soil may be counter-current to heat flow through the soil. The heat
flow may produce a temperature
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gradient within the soil. The counter-current heat transfer relative to mass
transfer may expose air and vapor that is
drawn to a vacuum source to high temperatures as the air and vapor approaches
and enters the heater/vapor
extraction well. A significant portion of contaminants within the air and
vapor may be destroyed by pyrolysis
and/or oxidation when the air and vapor passes through high temperature zones
surrounding and in heater/vapor
extraction wells. In some soil remediation systems, only selected wells may be
heater/vapor extraction wells. In
some soil remediation systems, heater wells may be separate from the vapor
extraction wells. In some
embodiments, heaters within heater wells and within heater/vapor extraction
wells may operate in a range from
about 650 C to about 870 C.
Thermal conductive heating of soil may include radiatively heating a well
casing, which conductively
heats the surrounding soil. Coincident or separate source vacuum may be
applied to remove vapors from the soil.
Vapor may be removed from the soil through extraction wells. U.S. Pat. No.
5,318,116 issued to Vinegar et al.
describe ISTD processes for treating contaminated subsurface soil with thermal
conductive heating applied to soil
from a radiantly heated casing. The heater elements are commercial
nichrome/magnesium oxide tubular heaters
with Inconel 601 sheaths operated at temperatures up to about 1250 C.
Alternatively, silicon carbide or lanthanum
chromate "glow-bar" heater elements, carbon electrodes, or tungsten/quartz
heaters could be used for still higher
temperatures. The heater elements may be tied to a support member by banding
straps.
Wells may be arranged in a number of rows and columns. Wells may be staggered
so that the wells are in
a triangular pattern. Alternatively, the wells may be aligned in a rectangular
pattern, pentagonal pattern, hexagonal
pattern or higher order polygonal pattern. In certain well pattern
embodiments, a length between adjacent wells is a
fixed distance so that a polygonal well pattern is a regular well pattern,
such as an equilateral triangle well pattern or
a square well pattern. In other well pattern embodiments, spacing of the wells
may result in non-regular polygonal
well patterns. A spacing distance between two adjacent wells may range from
about 1 in to about 13 in or more. A
typical spacing distance may be from about 2 m to about 4 m.
Wells inserted into soil may be extraction wells, injection wells and/or test
wells. An extraction well may
be used to remove off-gas from the soil. The extraction well may include a
perforated casing that allows off-gas to
pass from the soil into the extraction well. The perforations in the casing
may be, but are not limited to, holes
and/or slots. The perforations may be screened. The casing may have several
perforated zones at different
positions along a length of the casing. When the casing is inserted into the
soil, the perforated zones may be located
adjacent to contaminated layers of soil. The areas adjacent to perforated
sections of a casing may be packed with
gravel or sand. The casing may be sealed to the soil adjacent to non-producing
layers to inhibit migration of
contaminants into uncontaminated soil. An extraction well may include a
heating element that allows heat to be
transferred to soil adjacent to the well.
In some soil remediation processes, a fluid may be introduced into the soil.
The fluid may be, but is not
limited to, a heat source such as steam, a solvent, a chemical reactant such
as an oxidant, or a biological treatment
carrier. A fluid, which may be a liquid or gas, may be introduced into the
soil through an injection well. The
injection well may include a perforated casing. The injection well may be
similar to an extraction well except that
fluid is inserted into the soil through perforations in the well casing
instead of being removed from the soil through
perforations in the well casing.
A well may also be a test well. A test well may be used as a gas sampling well
to determine location and
concentration of contaminants within the soil. A test well may be used as a
logging observation well. A test well
may be an uncased opening, a cased opening, a perforated casing, or
combination cased and uncased opening.
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A wellbore for an extraction well, injection well, or test well may be formed
by augering a hole into the
soil. Cuttings made during the formation of the augered hole may have to be
treated separately from the remaining
soil. Alternatively, a wellbore for an extraction well, injection well, or
test well may be formed by driving and/or
vibrating a casing or insertion conduit into the soil. U.S. Pat. No. 3,684,037
issued to Bodine and U.S. Pat. No.
6,039,508 issued to White describe devices for sonically drilling wells.
A covering may be placed over a treatment area. The covering may inhibit fluid
loss from the soil to the
atmosphere, heat loss to the atmosphere, and fluid entry into the soil. Heat
and vacuum may be applied to the
cover. The heat may inhibit condensation of contaminants on the covering and
in soil adjacent to the covering. The
vacuum may remove vaporized contaminants from the soil adjacent to a soil/air
interface to an off-gas treatment
system.
An off-gas collection piping system may be connected to vapor extraction wells
of a heating and vapor
extraction system. The off-gas collection piping system may also be connected
to an off-gas treatment system so
that off-gas removed from the soil may be transported to the treatment system.
Typical off-gas collection piping
systems are made of metal pipe. The off-gas collection piping may be un-heated
piping that conducts off-gas and
condensate to the treatment facility. Alternatively, the off-gas collection
piping may be heated piping that inhibits
condensation of off-gas within the collection piping. The use of metal pipe
may make a cost of a collection system
expensive. Installation of a metal pipe collection system may be labor and
time intensive. In some embodiments,
off-gas collection piping may be or may include polymer piping and/or flexible
hose.
Off-gas within a collection piping system may be transported to an off-gas
treatment system. The
treatment system may include a vacuum system that draws off-gas from the soil.
The treatment system may also
remove contamination within the off-gas to acceptable levels. The treatment
facility may include a reactor system,
such as a thermal oxidizer, to eliminate contaminants or to reduce
contaminants within the off-gas to acceptable
levels. Alternatively, the treatment system may use a mass transfer system,
such as passing the off-gas through
activated carbon beds, to eliminate contaminants or to reduce contaminants
within the off-gas to acceptable levels.
A combination of a reactor system and a mass transfer system may also be used
to eliminate contaminants or to
reduce contaminants within the off-gas to acceptable levels.
Instrumentation and power control systems may be used to monitor and control
the heating rate of a soil
remediation system. The instrumentation and power control system may also be
used to monitor the vacuum
applied to the soil and to control of the operation of the off-gas treatment
system. Electrical heaters may require
controllers that inhibit the heaters from overheating. The type of controller
may be dependent on the type of
electricity used to power the heaters. For example, a silicon controlled
rectifier may be used to control power
applied to a heater that uses a direct current power source, and a zero
crossover electrical heater firing controller
may be used to control power applied to a heater that uses an alternating
current power source. In some
embodiments, the use of controllers may not be necessary.
A barrier may be placed around a region of soil that is to be treated. The
barrier may include metal plates
that are driven into the soil around a perimeter of a contaminated soil
region. A top cover for the soil remediation
system may be sealed to the barrier. The barrier may limit the amount of air
and water drawn into the treatment
area from the surroundings. The barrier may also inhibit potential spreading
of contamination from the
contaminated region to adjacent areas and/or the atmosphere.
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SUMMARY
In a soil remediation embodiment, a heated first site may be used to at least
partially destroy contaminants in vapors generated from contaminated soil at a
second
site. Vapors from the contaminated soil at the second site may be allowed to
enter the
heated first site. Contaminants in the vapors from the second site transferred
to the
first site may be at least partially destroyed by heat at the first site. In
an embodiment,
vapors from more than one site may be transferred to a site of heated,
substantially
uncontaminated soil. At least partially destroying contaminants from a second
site at a
heated first site may make efficient use of the energy needed to heat the
first site.
Destroying contaminants in a site may reduce or eliminate equipment needed to
process vapors removed from soil during remediation. For example, destroying
contaminants in a heated site may eliminate a need for a thermal oxidizer.
Eliminating
the need for a thermal oxidizer may advantageously remove the most expensive,
or
one of the most expensive, pieces of equipment to obtain, transport, and/or
operate.
In a soil remediation embodiment, contaminated soil may be transported to a
location for remediation. Two or more treatment sites may be proximate each
other at
the location. One or more barriers may form at least a partial border for
containing
soil within the treatment sites. In an embodiment, a barrier forming a border
for a
treatment site may include connectors for coupling heater elements to shared
equipment. Shared equipment at the location may be used at more than one
treatment
site. Shared equipment may include, for example, a power source and/or a
vacuum
source. In an embodiment, shared equipment may be used concurrently or
successively at two or more treatment sites at the location. Remediation at
the
treatment sites may be coordinated such that shared equipment in a central
treatment
facility operates substantially continuously.
In an embodiment, a first portion of contaminated soil may be transported to a
first treatment site. The first portion of contaminated soil at the first
treatment site
may be remediated with equipment including shared equipment. During treatment
of
the first portion of contaminated soil at the first treatment site, a second
portion of
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contaminated soil may be transported to a second treatment site. After
remediation of
soil at the first treatment site, equipment including shared equipment may be
used to
treat the second portion of contaminated soil at the second treatment site.
During
remediation of the second portion of contaminated soil at the second treatment
site,
the treated first portion of contaminated soil may be removed from the first
treatment
site. Following removal of the treated first portion of contaminated soil from
the first
treatment site, a third portion of contaminated soil may be transported to the
first
treatment site. After remediation at the second treatment site, equipment
including
shared equipment may be used to treat the third portion of contaminated soil
at the
first treatment site. During remediation of the third portion of contaminated
soil at the
first treatment site, the treated second portion of contaminated soil at the
second
treatment site may be moved to the holding area. The third portion of
contaminated
soil may be treated at the first treatment site. The process of successively
treating soil
at the first treatment site and the second treatment site may be repeated.
Thus, in accordance with one aspect of the invention, there is provided a
method, comprising: placing soil in a plurality of treatment sites; treating
soil in the
plurality of treatment sites wherein said treating comprises allowing
contaminants
within the soil to undergo pyrolysis, using equipment in a central treatment
facility;
removing soil from the plurality of treatment sites; and wherein placing soil
in each of
the plurality of treatment sites, treating soil in each of the plurality of
treatment sites,
and removing soil from each of the plurality of treatment sites is coordinated
such that
equipment in the central treatment facility operates substantially
continuously.
In another aspect of the invention there is provided a method, comprising:
placing soil
in a plurality of treatment sites, wherein placing soil comprises placing soil
at least
partially in a reusable retaining structure comprising at least one retaining
wall;
treating soil in the plurality of treatment sites using equipment in a central
treatment
facility, wherein treating the soil comprises heating the soil; removing soil
from the
plurality of treatment sites; and wherein placing soil in each of the
plurality of
treatment sites, treating soil in each of the plurality of treatment sites,
and removing
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soil from each of the plurality of treatment sites is coordinated such that
equipment in
the central treatment facility operates substantially continuously.
In still another aspect of the inventio, there is provided a method,
comprising:
placing soil in a plurality of treatment sites; treating soil in the plurality
of treatment
sites using equipment in a central treatment facility, wherein treating soil
in the
plurality of treatment sites comprises heating the soil using heat transferred
directly to
the soil from one or more wells in the soil; removing soil from the plurality
of
treatment sites; wherein placing soil in each of the plurality of treatment
sites and
removing soil from each of the plurality of treatment sites is coordinated
such that soil
in each of the plurality of treatment sites is treated sequentially; and
wherein
sequentially treating soil in the plurality of treatment sites allows
substantially
continuous operation of some equipment in the central treatment facility.
BRIEF DESCRIPTION OF THE DRAWINGS
Advantages of the invention will become apparent upon reading the following
detailed description and upon reference to the accompanying drawings in which:
Figure 1 shows a schematic plan view representation of an embodiment of a soil
remediation system.
Figure 2 shows a schematic plan view representation of an embodiment of a
soil remediation system.
Figure 3 shows a schematic view of an embodiment of a treatment system for
processing off-gas removed from soil.
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Figure 4 depicts a side representation of an embodiment of an extraction well
inserted into soil.
Figure 5 depicts a front representation of an embodiment of an extraction well
inserted into soil.
Figure 6 depicts a representation of an embodiment of an extraction well with
a radiant heater element.
Figure 7 depicts a representation of an embodiment of a heat injection well
that conductively heats soil.
Figure 8 depicts a representation of an embodiment of a heat injection well
positioned within a casing.
Figure 9 depicts a representation of an embodiment of a heat injection well
that radiatively heats soil.
Figure 10 depicts a representation of an embodiment of a heater element
positioned within a trench.
Figure 11 is a perspective view of a portion of a heater element that has a
varying cross-sectional area.
Figure 12 is a perspective view of an embodiment of a heater element.
Figure 13 depicts a schematic representation of a layout plan for heater
elements placed in trenches.
Figure 14 depicts a vertical cross-sectional representation along a width of a
pile of soil at a remediation
site.
Figure 15 depicts a vertical cross-sectional representation along a width of a
pile of soil contained by a
retaining structure.
Figure 16 depicts contaminated soil in a remediation pit.
Figure 17 depicts contaminated soil in a tank.
Figure 18 depicts a heated riser for removing contaminants from contaminated
soil.
Figure 19 depicts an embodiment of a remediation site including two treatment
sites.
Figure 20 depicts an embodiment of simultaneous remediation of contaminated
soil from more than one
location.
While the invention is susceptible to various modifications and alternative
forms, specific embodiments
thereof are shown by way of example in the drawings and will herein be
described in detail. The drawings may not
be to scale. It should be understood, however, that the drawings and detailed
description thereto are not intended to
limit the invention to the particular form disclosed, but on the contrary, the
intention is to cover all modifications,
equivalents, and alternatives falling within the spirit and scope of the
present invention as defined by the appended
claims.
DETAILED DESCRIPTION
A soil remediation system may remove or reduce contaminants within a selected
soil region. Figures 1 and
2 show schematic representations of embodiments of soil remediation systems
30. Soil remediation system 30
depicted in Figure 1 may include one or more extraction wells 32 within soil
34. Soil remediation system 30 may
optionally include one or more heat injection wells 36, one or more fluid
injection wells 38, and one or more test
wells 40. Fluid injection wells 38 and/or test wells 40 may be located inside
or outside of a pattern of extraction
wells 32 and heat injection wells 36. Extraction wells 32, heat injection
wells 36, fluid injection wells 38, and/or
test wells 40 may include well casings. Portions of the well casings may be
perforated to allow fluid to pass into or
out of the well casings. Alternatively, extraction wells 32, heat injection
wells 36, fluid injection wells 38, and/or
test wells 40 may include a cased portion and an uncased portion. The uncased
portion may be adjacent to
contaminated soil.
In some embodiments, soil remediation system 30 may be used for in situ soil
remediation. In other
embodiments, soil remediation system 30 may be used for ex situ soil
remediation. In some soil remediation
systems, extraction wells 32, heat injection wells 36, fluid injection wells
38, and/or test wells 40 may be placed
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substantially vertically in soil 34. In some soil remediation system
embodiments, extraction wells 32, heat injection
wells 36, fluid injection wells 38, and/or test wells 40 may be place
substantially horizontally in soil 40.
In addition to extraction wells 32, heat injection wells 36, fluid injection
wells 38, and/or test wells 40, soil
remediation system 30 may include ground cover 42, treatment facility 44,
vapor collection system 46, control
system 48, and/or pumping units 50. Ground cover 42 may be placed over
extraction wells 32, heat injection wells
36, fluid injection wells 38, and/or test wells 40 to inhibit heat loss and
contaminant vapor loss to the atmosphere.
Ground cover 42 may also inhibit excess air from being drawn into soil 34.
Ground cover 42 may include a layer of
thermal insulation. Ground cover 42 may include a layer that is impermeable to
contaminant vapor and/or air. The
impermeable layer may include, but is not limited to, metal sheeting and/or
concrete. Wells positioned substantially
vertically in the soil may be welded or otherwise sealed to the metal sheet.
Wells positioned substantially
horizontally in the soil may be positioned beneath the metal sheet. Vertical
barriers may be inserted into the soil
around a perimeter of the metal sheet to form an end barrier. Thermal
insulation may typically be placed above the
impermeable barrier. The thermal insulation may include, but is not limited
to, mineral or cotton wool, glass wool
or fiberglass, polystyrene foam, or aluminized mylar.
Optional surface heaters may be placed on or below ground cover 42. The
surface heaters may inhibit
contamination from condensing on ground cover 42 and flowing back into soil
34. The surface heaters are typically
electrically powered heaters.
A gas and water barrier of ground cover 42 may be placed over the remediation
site. The gas and water
barrier may be plastic sheeting. Any openings or connections to equipment may
be sealed with a silicone or other
type of sealant.
Ground cover 42 may not be needed if the contamination is so deep within soil
34 that heating the soil and
removing off-gas from the soil will have negligible effect at ground surface
52 of the soil. If a cover is not utilized,
a vacuum source may be needed to draw a vacuum around wellheads 54 of heat
injection wells and/or extraction
wells to inhibit release of vapor to the atmosphere from the wells. Wellhead
54 is equipment and/or structure
attached to an opening of a well.
Treatment facility 44 may include vacuum system 56 that draws an off-gas
stream from soil 34 through
extraction wells 32. If the soil remediation system includes surface heaters,
vacuum system 56 may be configured
to draw vacuum at ground surface 52 as well as in extraction wells 32. The
vacuum drawn in extraction wells 32
may be stronger than the vacuum drawn at surface 52. Treatment facility 44 may
also include contaminant
treatment system 58 for treating contaminants within the off-gas. Contaminant
treatment system 58 may eliminate
contaminants from the off-gas stream, reduce contaminants to acceptable
levels, and/or concentrate contaminants
for off-site transport. Contaminant treatment system 58 may include, but is
not limited to, separators, condensers,
reactor systems, mass transfer systems, and chemical storage vessels.
Figure 3 shows an embodiment of treatment system 58. Off-gas from vapor
collection system 46 may pass
into separator 60. Separator 60 may separate the off-gas into a liquid stream
and a vapor stream. Vacuum system
56 that is in-line with the vapor stream may provide the vacuum to soil 34 to
remove off-gas from the soil. Vacuum
system 56should be-capable of pulling a vacuum appropriate for the particular
combination of soil permeability and
extraction wells within a treatment system. Vacuum system 56 may be able to
pull a vacuum in the range of 0.01
atmospheres to slightly less than 1 atmosphere. The vacuum system may be a
water sealed pump.
Liquid and vapor streams may be processed by treatment system 58 to reduce
contaminants within the
streams to acceptable levels. Monitoring equipment may determine the quantity
of contaminants in processed
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streams. The monitoring equipment may sound an alarm and/or begin
recirculation of output streams from
treatment system 58 back to the beginning of the treatment system if too much
contamination is detected in the
output streams.
A liquid stream may be separated by second separator 62 into a non-aqueous
stream and an aqueous
stream. In an embodiment, second separator 62 and separator 60 may be a single
unit. The non-aqueous stream
may include oils and other non-aqueous material. The non-aqueous stream may be
very small compared to the
aqueous stream. The non-aqueous stream may be sent to treatment unit 64.
Treatment unit 64 may place the non-
aqueous stream in storage containers, such as waste barrels. The containers
may be transported off-site for disposal.
Alternatively, treatment unit 64 may be an oxidization system, thermal system,
or other reaction system that
eliminates or reduces to acceptable levels contaminants within the non-aqueous
stream.
Pump 66 may be used to move the aqueous stream. Pump 66 may transport the
aqueous stream through
activated carbon bed 68. Activated carbon bed 68 removes contaminants from the
aqueous stream. The remaining
aqueous stream may then be discharged. For example, after the aqueous stream
has passed through activated
carbon bed 68, the aqueous stream may be sent to sanitary sewer 70.
The vapor stream from separator 60 may pass through treatment unit 72.
Treatment unit 72 may be a mass
transfer system such as activated carbon bed, a reactor system such as a
thermal oxidizer, or a combination thereof.
Blower 74 may draw the vapor stream through treatment unit 72 and vent the
remaining vapor to the atmosphere.
In some embodiments of treatment systems 58, the treatment systems may not
include thermal oxidizers to
eliminate or reduce contaminants within off-gas to acceptable levels. Carbon
beds, concentrators, or non-thermal
reactor systems may be used instead of thermal oxidizers. Replacement of
thermal oxidizers with other equipment
that eliminates or reduces contaminants may lower capital costs,
transportation costs, and/or operation costs of a
soil remediation system. A thermal oxidizer may be very expensive to obtain
and to transport to treatment
locations. Also, thermal oxidizers may require on-site monitoring by
operational personnel to ensure that the
thermal oxidizer is functioning properly. Removing a thermal oxidizer from a
soil remediation process may
significantly improve economics of the process.
As shown in Figure 1, vapor collection system 46 may include a piping system
that transports off-gas
removed from soil 34 to treatment facility 44. The piping system may be
coupled to vacuum system 56 and to
extraction wells 32. In an embodiment, the piping may be un-heated piping
and/or un-insulated piping. Off-gas
produced from the soil may initially rise vertically and then travel downward
to the treatment facility. The initial
rise and subsequent downward travel may allow any condensed off-gas to pass to
a liquid trap or to a separator of
the treatment system without blocking lines of the collection system. In
alternative embodiments, the piping may
be thermally insulated and/or heated. Insulated and heated piping inhibits
condensation of off-gas within the
piping. Having a non-insulated and non-heated collection system may greatly
reduce cost, installation time, and
complexity of a soil remediation system.
Control system 48 may be a computer control system. Control system 48 may
monitor and control the
operation of treatment facility 44. If vapor collection system 46 includes
heated piping, control system 48 may
control power applied to line tracers that heat the piping. If extraction
wells 32 or heat injection wells 36 include
non-self regulating heater elements, the control system may control power
applied to heater elements of the
extraction wells.
Heat may be applied to soil 34 during a soil remediation process. Heat may be
applied to soil from heat
injection wells 36, from extraction wells 32, and/or from other heat sources.
Heat may be applied to soil 34 from
8
CA 02704832 2010-05-26
electrical resistance heater elements positioned within the extraction wells.
Power may be supplied from power
source 76 to extraction wells 32 and heat injection wells 36 through cables
78. Power source 76 may be a
transformer or transformers that are coupled to high voltage power lines. In
some embodiments of soil remediation
systems, heat may be applied to the soil by other heat sources in addition to
or in lieu of heat being applied from
electrical resistance heater elements. Heat may be applied to soil, but is not
limited to being applied to soil, by
combustors, by transfer of heat with a heat transfer fluid, by radio frequency
or microwave heating, and/or by soil
resistivity heating.
Extraction wells 32 depicted in Figure 1 are heaterlvapor extraction wells.
Heat generated by electrical
resistance heaters within extraction wells 32 apply heat to soil and to fluids
being produced. Heat generated by
heater elements within extraction wells 32 flows countercurrent to mass flow
of off-gas within soil 34. The
countercurrent flow of heat and mass may allow the off-gas to be exposed to
high temperatures adjacent to and in
extraction wells 32. The high temperatures may destroy a significant portion
of contaminants within the off-gas. In
other embodiments of soil remediation systems, some of the extraction wells,
or all of the extraction wells, may not
include heater elements that heat the soil.
In some soil remediation system embodiments, heat may be applied to the soil
only from heater/vapor
extraction wells. In other embodiments, such as the embodiment depicted in
Figure 1, only selected wells within
the soil are heater/vapor extraction wells. Using only some heater/vapor
extraction wells may significantly reduce
cost of the soil remediation system. Heater/vapor extraction wells are
typically more expensive than heater wells.
Installation and connection time for heater/vapor extraction wells is
typically more expensive and longer for
heater/vapor extraction wells than for heater wells. A vapor collection system
may need to be much more
extensive, and thus more expensive, for a soil remediation system that uses
exclusively heater/vapor extraction
wells.
In some embodiments of soil remediation systems, heat may be provided to soil
34 from heat injection
wells 36 and/or from extraction wells 32. Heat injection wells 36 are not
coupled to vacuum system 56.
Superposition of heat from heater elements of heat injection wells 36 and/or
extraction wells 32 may allow a
temperature of soil 34 within a treatment area to rise to a desired
temperature that will result in remediation of the
soil. Extraction wells 32 may remove off-gas from soil 34. The off-gas may
include contaminants and/or reaction
products of contaminants that were within soil 34.
Extraction wells 32 and heat injection wells 36 may be placed in desired
patterns within soil 34 that is to
be remediated. The patterns of extraction wells 32 and heat injection wells 36
may be, but are not limited to,
triangular patterns (as shown for extraction wells 32), rectangular patterns,
pentagonal patterns, hexagonal patterns
(as shown for beat injection wells 36), or higher order polygon patterns. An
actual soil remediation system will
typically have many more wells within a treatment area than depicted in the
schematic representation of Figure 1.
The well patterns may be regular patterns to promote uniform heating and off-
gas removal throughout a treatment
area. For example, well patterns may be equilateral-triangle patterns or
square-well patterns. Extraction wells 32
and heat injection wells 36 of the patterns may be substantially uniformly
placed throughout a treatment area. Some
of extraction wells 32 and/or heat injection wells 36 may be offset from the
regular patterns to avoid obstacles in or
on the soil. Obstacles may include, but are not limited to, structures;
impermeable, uncontaminated regions amid
contaminated soil; property lines; and underground or above ground pipes or
electrical lines. Spacing between
centers of wells may range from about I m to 13 m or more. Spacing may be
determined based on time allowable
for remediation, soil properties, type of soil contamination and other
factors. A close well spacing may require less
9
CA 02704832 2010-05-26
heating time to raise soil temperature to a desired temperature, but close
well spacings require many more
additional wells to heat the soil than would be required with a larger well
spacing.
Some soil remediation systems may include fluid injection wells 38. Fluid
injection wells 38 may be used
to introduce a fluid into soil 34. The fluid may be, but is not limited to, a
reactant, a biological agent, and/or a
flooding agent. The fluid may be injected into soil 34 by pumping units 50.
Alternatively, vacuum applied to
extraction wells 32 may draw fluid into soil 34 from fluid injection wells 38.
Some soil remediation systems may include test wells 40. Fluid samples may be
withdrawn from test
wells 40 to allow determination of the progress of soil remediation at
selected locations and at selected times.
Monitoring equipment may be positioned in test wells 40 to monitor
temperature, pressure, chemical concentration,
or other properties during a soil remediation process.
Figure 2 depicts a representation of soil remediation system 30 that uses only
heater/vapor extraction wells
as extraction wells 32. Power source 76 that heats the heater elements within
extraction wells 32 may be a three
phase transformer. For example, power source 76 may be a 112.5 kVA transformer
that has a 480 VAC 3-phase
primary and a 3-phase secondary. Each phase may be used to power a group of
extraction wells 32 that are
electrically connected in series. If more than three groups of extraction
wells 32 are needed to process a treatment
area, sections of the area may be sequentially treated, or additional power
sources may be used so that the entire
treatment area is processed at one time. Extraction wells 32 may be directly
coupled to power source 76 without the
use of well controllers if the heater elements are made of metals having self-
regulating temperature properties. The
heater elements of extraction wells 32 and power source 76 are designed to
reach a desired temperature when
connected to the power source. Heater elements may be designed to heat to a
maximum temperature of about 1250
C. Heater elements may be designed to have a steady state operating
temperature of about 900 C. An operating
range of heater elements may extend from ambient soil temperature to about
1250 C.
Off-gas drawn from soil 34 by vacuum may pass through hoses 80 and vacuum
manifold 82 to a treatment
facility44. Hoses 80 and vacuum manifold 82 may be components of vapor
collection system 46. Hoses 80 may
attach to vacuum casings of extraction well 32 and to vacuum manifold 82. The
vacuum casing may extend
through covering 42 and may rise to a height sufficient to allow the remainder
of the vapor collection system46 to
slope downwards to treatment facility44. Sealant such as welds, silicone
rubber sealant, or other types of sealant
may be used to seal casings of extraction wells 32 and other structures that
pass through covering 42 to the casing.
Seals may inhibit vapor and/or liquid from passing into or out of covering 42.
Hose 80 may be attached to each extraction well casing and to vacuum manifold
82 by solvent glue and/or
clamps, or by other attachment methods including, but not limited to,
threading or flanges. Hoses 80 may be
formed of high temperature rubber that has an upper working temperature limit
of about 230 C. Hoses 80 are
conduits for transporting off-gas from extraction wells 32 to vacuum manifold
82. Off-gas passing through hose 80
has a residence time within the hose. Hose 80 may have a sufficient length so
that the residence time of off-gas
within the hose is sufficiently long to allow the off-gas to cool. The off-gas
may cool within hoses 80 to a
temperature that is at or below an upper working temperature limit of the
material that forms vacuum manifold 82.
Vacuum manifold 82 may be formed of plastic piping. The plastic piping may be
chlorinated polyvinyl
chloride (CPVC) piping or other plastic piping that has a high upper working
temperature limit. The upper working
temperature limit of CPVC piping is approximately 90 C. Off-gas may cool as
it flows through vacuum manifold
82. Portions of vacuum manifold 82 located away from extraction wells 32 may
be formed of plastic piping, such
as PVC piping, that has a lower working temperature limit than CPVC piping.
CA 02704832 2010-05-26
The use of a collection system including hoses 80 and plastic piping vacuum
manifold 82 may result in
lower costs, simplified on-site construction, and lower mobilization costs as
compared to a metal piping collection
system. A collection system including hoses and plastic piping may not be
insulated and/or heated, thus greatly
reducing the cost, installation time, and operating cost of the collection
system. Hose 80 may be rolled into coils for
transportation. Plastic piping may be purchased locally near the site. Hose 80
and plastic piping are easily cut to
size on-site and are connectable by solvent gluing or other techniques. Also,
hose 80 and plastic piping are
lightweight and do not require machinery to lift and position during
installation. Unlike some metal piping, hose 80
and the plastic piping may be highly resistant to corrosion caused by the off-
gas. For example, off-gas may include
hydrogen chloride, especially if the soil contamination includes chlorinated
hydrocarbons. If the hydrogen chloride
forms hydrochloric acid with condensed water, the acid may rapidly corrode
metal vapor collection piping. Hose
80 and plastic piping may be highly resistant to HCl corrosion.
Figures 4, 5, and 6 depict embodiments of extraction wells 32 that include
heater elements 84. Heater
elements 84 may be bare metal without an insulation coating such as mineral
insulation. Using uninsulated, bare
metal heater elements may significantly reduce heater cost as compared to
conventional heater elements, such as
mineral insulated cables. Heater elements 84 may be placed in soil 34 without
being tied to a support member such
as a conduit or a support cable. Eliminating a support cable or conduit
reduces cost, installation time, and labor
associated installing the heater element. An electrical current may be passed
through heater elements 84 to
resistively heat the heater elements.
A vacuum system may remove off-gas from soil 34 through openings 86 in vacuum
casing 88. Figures 4
and 5 depict embodiments of extraction wells that conductively heat soil 34.
Heater elements 84 shown in Figures
4 and 5 heat packing material 90 that conducts heat to adjacent soil. Packing
material 90 may be sand, gravel, or
other fill material that may be subjected to high temperatures. The fill
material may include catalyst 92. Catalyst
92 may be a metal, metal oxide, or other type of catalyst that enhances
pyrolysis and/or oxidation of contaminants
that pass through the packing material. In an embodiment, the catalyst is
alumina. Heater elements that are packed
with fill material in the soil may thermally expand towards the surface when
heated. Allowance needs to be made
at wellheads to allow for expansion of the heater elements.
Figure 6 depicts an embodiment of extraction well 32 that includes heater
elements that radiatively heats
heater well casing 94. The inner surface of heater casing 94 may be blackened,
textured, oxidized, or otherwise
treated to increase radiative heat transfer between heater element 84 and the
heater casing. Heater well casing 94
may radiatively heat vacuum casing 88. The inner surface of the vacuum casing
may be blackened, textured,
oxidized, coated, or otherwise treated to increase radiative heat transfer
between the heater casing and the vacuum
casing. Alternatively, annular space between the heater casing and the vacuum
casing may be filled with packing
material. The packing material may include a catalyst that enhances pyrolysis
or oxidation of contaminants that
pass through the packing material.
Heater well casing 94 may prevent current leakage into soil 34 as may occur
with heater elements that do
not have casings. Some current leakage may be acceptable because the current
leakage may heat water or soil that
is drawing current from the heater elements. If excessive current leak is
possible, an external casing may be used to
surround the heater element. Heater well casing 94 may be used when the well
is to be positioned in a water
saturated zone or in soil that has a high salt content or contains brackish
water.
11
CA 02704832 2010-05-26
Heater elements 84 that radiatively heat heater well casing 94 or soil 34 may
expand downwards when
heated. Heater well casing 94 or the opening in the soil defined by opening
wall 96 that the heater element is placed
in should be sufficiently long to accommodate thermal expansion of heater
element 84 and heater well casing 94.
As depicted in Figure 6, spacers 98 may be placed along a length of heater
element 84 to prevent the heater
element from contacting, or electrically arcing, to an adjacent conduit such
as heater well casing 94. Spacers 98
may also prevent leg 100 of heater element 84 that is bent into "U" shapes
from contacting, or electrically arcing, to
an adjacent leg of the heater element. Spacers 98 may be made of ceramic
insulators. For example, spacers may be
made of high alumina ceramic insulation material. Spacers 98 may be obtained
from Cooper Industries (Houston,
Texas). Spacers 98 may slide onto heater elements 84. A weld bead may be
formed beneath a place where spacer
98 is to be located so that the spacer cannot pass the weld bead. In an
embodiment of a heater element that is
vertically positioned in a well, as depicted in Figure 6, spacers 98 may be
positioned about every 1/3 m to about
every 1/2 m along a length of the heater element. Shorter or longer spacings
may be used to accommodate
particular heater elements and system requirements. Horizontally oriented
heater elements placed within heater
well casings may require closer spacings to inhibit sagging of the heater
element when the heater element is heated.
Spacers 98 may also be positioned between vacuum casing 88 and/or soil and
heater element 84 that conductively
heats fill material 90, as depicted in Figure 5.
Figures 7, 8, and 9 depict embodiments of heat injection wells 36. Heat
injection wells 36 include heater
elements 84. An electrical current may be passed through the heater elements
84 to resistively heat the heater
elements. Figure 7 depicts an embodiment of a heat injection well 36 having
heater element 84 that conductively
heats soil 34. Figure 8 depicts a heat injection well embodiment having heater
element 84 that is enclosed in heater
casing 94. In certain embodiments, heater casing 94 may be packed with fill
material. In other embodiments, the
heater casing may radiatively heat the heater casing. Figure 9 depicts a heat
injection well embodiment having
heater element 84 that radiatively heats adjacent soil 34.
Figure 10 depicts a representation of an embodiment of heater element 84
positioned within a trench near
to ground surface 52. Heater element 84 is shown below contamination interface
102 in uncontaminated soil 104.
In other embodiments, heater element 84 may be positioned within contaminated
soil 106, or at or near
contamination interface 102. Heater element 84 is shown as having 90 angles
to the surface. In practice, ends of
the trench may taper towards the surface, and ends of heater element 84 may be
positioned on the tapering ends of
the trench.
Vacuum drawn by a treatment facility may be applied near soil surface 52.
Permeable mat 108 may be
placed on top of soil surface 52. Impermeable barrier 110 and thermal barrier
112 may be placed on top of mat 108.
Mat 108 may serve as a conduit for flow beneath impermeable barrier 110. In an
embodiment, mat 108 may be a
thin layer of high permeability sand or other granular material. Mat 108 may
include catalyst material that enhances
thermal degradation of contaminants that pass through the mat. Mat 108 may
allow off-gas to flow out of soil 34 to
vacuum manifold 82 positioned above the mat. The off-gas may flow even when
the vacuum draws impermeable
barrier 110 against mat 108 and compresses the mat. Thermal barrier 112 may
inhibit heat transfer. Alternatively,
vapor extraction wells may be inserted into the soil throughout the treatment
site to draw off-gas from the soil.
As shown in Figures 4-10, heater elements 84 may include heater sections 114,
transition sections 116, and
pins 118. Some heater elements 84 may not include transition sections between
heater sections 114 and pins 118.
All or substantially all of heater section 114 of heater element 84 may be
bare metal. "Bare metal" as used herein
refers to a metal that does not include a layer of electrical insulation, such
as mineral insulation, that is designed to
12
CA 02704832 2010-05-26
provide electrical insulation for heater section 114 during use. Bare metal
may encompass a metal that includes a
corrosion inhibiter such as a naturally occurring oxidation layer, an applied
oxidation layer, and/or a film. Bare
metal includes metal with polymeric or other types of electrical insulation
that cannot retain electrical insulating
properties at typical operating temperatures of heater section 114 of heater
element 84. Such material may be
placed on the metal and may be designed to be destroyed during a soil
remediation process. Weld material and/or
connector sections of heater sections 114 may include electrical insulation
material without changing the nature of
the heater element into an insulated heater element. Insulated sections of
heater section 114 of heater element 84
may be less than 5%, 1%, 0.5%, or 0.1% of a length of the heater section. Bare
metal heater elements 84
significantly reduce production cost and increase availability of heater
elements as compared to heater elements that
include insulated heater sections 114.
In certain embodiments of heater elements 84, portions of transition sections
116 and/or portions of pins
118 may be electrically insulated. In other embodiments of heater elements 84,
all of the heater element may be
bare metal.
Heater elements 84 depicted in Figures 4-10 are positioned substantially
vertically or horizontally. Heater
elements may be positioned at any desired orientation from 0 (horizontal) to
90 (vertical) relative to ground
surface. For example, in a soil remediation system embodiment, heater elements
may be oriented at about 45 to
remediated soil adjacent to a geological layer that slopes at about 45 . The
orientation may be chosen to result in
relatively low cost, quick, and efficient soil remediation.
Heater sections 114 of heater elements 84 may be formed of metals that are
capable of sustained use at
high operating temperatures. Portions of heater element 84 may operate from
ambient soil temperatures to
sustained temperatures of over 1000 C. In certain heater element embodiments,
such as the heater elements
depicted in Figures 4, 5, 7, 9, and 10, portions, or all, of heater elements
84 may be exposed to off-gas during soil
remediation. Such heater elements 84 may need to be made of corrosion
resistant metal. The resistance of heater
sections 114 to corrosion may be very important. High temperature and high
amperage at which heater sections 114
operate may promote corrosion of heater sections 114. Corrosion may decrease
cross-sectional areas of heater
sections 114 at certain locations along lengths of the heater sections.
Decreased cross-sectional areas of heater
sections 114 may cause the heater sections to overheat and fail.
Heater sections 114 may be formed of stainless steel. The stainless steel may
be, but is not limited to, type
304 stainless steel, type 309 stainless steel, type 310 stainless steel, or
type 316 stainless steel. Heater sections 114
may also be formed of other metals including, but not limited to, Nichrome ,
Incoloy , Hastelloy , or Monel .
For example, heater section 114 may be made of Nichrome 80 or Incoloy 800.
A specific metal used to form heater section 114 of heater element 84 may be
chosen based on cost,
temperature of the soil remediation process, electrical properties of the
metal, physical properties of the metal, and
chemical resistance properties of the metal. For example, 310 stainless steel
is a high temperature stainless steel
that may dissipate about 20% more power than 304 stainless steel of equivalent
dimensions. The corrosion
resistance of 310 stainless steel is better than the corrosion resistance of
304 stainless steel. The upper working
temperature limit of 310 stainless steel is about 160 C higher than the upper
working temperature limit of 304
stainless steel.
The extra temperature range of 310 stainless steel may be used to dissipate
extra heat into soil and shorten
remediation time. The extra temperature range may be used as a safety margin
to insure against overheating the
heater element. A cost of 310 stainless steel maybe about 25% more than a cost
of 304 stainless steel. At a design
13
CA 02704832 2010-05-26
stage of a soil remediation process, a determination may be made of whether
the better characteristics of 310
stainless steel justify the extra cost of the 310 stainless steel above the
cost of 304 stainless steel. Similar
comparisons may be made for other metals as well.
Heater sections 114 of heater elements 84 may be formed to have selected
sections that heat to higher or
lower temperatures than adjacent sections of heater elements. Portions of
heater element 84 that are configured to
heat to higher temperatures than adjacent portions may be positioned adjacent
to interfaces 102 between
contaminated soil 106 and uncontaminated soil 104. The extra temperature
produced in the high temperature
portions may help to counter heat loss due to end effects of heater section
114. High temperature portions may
dissipate greater than 5%, 15%, 25%, or 30% more heat than adjacent portions
of the heater section. Figure 11
shows a portion of heater element 84 having a high temperature portion that is
reduced cross-sectional area portion
120 positioned adjacent to larger cross-sectional area portions 122. Metal may
be removed from a portion of heater
section 114 to form a high temperature portion of heater section 114.
Alternatively, the portions of a heater section
that are to be heated to higher temperatures than adjacent areas may be
portions of a different metal that is more
electrically resistive than the metal of the adjacent sections. The more
resistive metal may have a larger, same, or
smaller cross-sectional area than adjacent portions of the heater section.
Thermally and electrically conductive
weld material may be used to couple portions 120, 122 together. Care may be
taken to ensure that ends of the
different metals abut and that a large amount of weld material couples the
different metal portions together.
Abutting metal portions and a large amount of weld material may ensure that
failure due to arcing and/or corrosion
does not occur at junctions between the metals during use.
Portions of heater sections 114 may heat to lower temperatures than
surrounding portions. Such portions
may be positioned adjacent to soil layers or obstacles that do not need to be
heated to high temperatures. For
example, a reduced heating section may be designed to reside adjacent to an
impermeable, uncontaminated soil
layer that is between two contaminated soil layers. A low heating section may
be formed of a heating section
having increased cross-sectional area as compared to adjacent areas.
Alternatively, a low heating section may be
formed of a less electrically resistive metal welded between two adjacent
portions of heater section. Care may be
taken to ensure that ends of the different metals abut and that a large amount
of weld material couples the different
metal portions together. Thermally and electrically conductive weld material
may be used to couple the portions
together. Abutting metal portions and a large amount of weld material may
ensure that failure due to arcing and/or
corrosion does not occur at junctions between the portions during use.
As shown in Figure 10, transition sections 116 of heater element 84 may be
welded to each end of heater
section 114 of the heater element. Pins 118 may be welded to transition
sections 116. Transition section 116 may
reduce a temperature of heater element 84 so that the temperature at and
adjacent to pin 118 is sufficiently cool to
allow use of insulated connector cable 78 (depicted in Figure 4) to couple pin
1.18 to power source 76. Transition
section 116 may be made of the same material as heater section 114, but the
transition section may have greater
cross-sectional area. Alternatively, the transition section may be made of a
material having less electrical resistance
than the heater section. The two sections may be welded together.
Figure 12 depicts an embodiment of heater element 84 that may be used to
radiatively heat soil. Heater
element 84 includes welds 124 between transition section 116 and heater
section 114. Thermally and electrically
conductive weld material may be used to couple sections 114, 116 together.
Abutting metal sections and a large
amount of weld material may ensure that failure due to arcing and/or corrosion
does not occur at a junction between
the sections during use.
14
CA 02704832 2010-05-26
Pins 118 may be nickel pins. In an embodiment, such as the embodiment depicted
in Figure 4, pins 118
extend through ground cover 42 when heater element 84 is inserted into the
soil 34. Connection 126 may
electrically couple the pin to cable 78. Connection 126 may be a mechanical
Kerney lug, epoxy canister, or other
type of electrical connector. Cable 78 may be electrically coupled to power
source 76. Cable 78 may be an
electrically insulated cable. Transition section 116 and cold pin 118 may
allow heater element 84, soil 34, and/or
cover 42 to be cool enough to inhibit thermal degradation of the cable
insulation during use.
In certain embodiments of heater elements, long sections of relatively low
resistance metal may be
attached to heater sections to form long heated sections that generate
temperatures sufficient to inhibit condensation
of vapor on or adjacent to the heater element. The low resistance metal may
be, but is not limited to, nickel or
alloys of nickel and copper such as Alloy 30. The long heated sections may be
needed for deep soil contamination
that does not come close to the ground surface.
Power source 76 (depicted in Figure 1) for a soil remediation system may
provide a substantially constant
voltage to heater elements of the soil remediation system. Power source 76 may
be electrical power from a power
line that passes through a transformer. Output from the transformer may be
coupled to a number of heater wells by
parallel and/or series connections to provide an appropriate electrical
circuit that will heat soil to a desired
temperature.
Heater section 114 of heater element 84 may have a large cross-sectional area
as compared to conventional
radiant heater elements. The large cross-sectional area may allow heater
element 84 to have a small electrical
resistance as compared to a conventional heater of equivalent length. The
small electrical resistance may allow
heater element 84 to be long. A heater element may be over 10 m, 50 in, or 100
in long, 300 m, 500 in or 600 m
long. The small electrical resistance may also allow several heater elements
to be electrically connected in series.
The ability to connect several heater elements 84 in series may greatly
simplify wiring requirements of a soil
remediation system. For heater elements that conductively heat adjacent
material, the large cross-sectional area of
the heater section may mean that there will be a large contact area between
the heater section and adjacent material.
For heater elements that radiatively heat adjacent material, the large cross-
sectional area of the heater may mean
that the heater section has a large surface area that will radiate heat to a
casing wall or to soil. Also, the large cross-
sectional areas of heater elements may allow the heater elements to be placed
in the soil without being attached to a
support structure. In an embodiment of a radiative heater element, the heater
element is made of 304 stainless steel
rod stock having a diameter of about 1 cm.
Radiative heater elements that are suspended within a well casing may have
telescoping sections of
different alloys and/or different cross-sectional areas to produce long heater
elements. A first section may be made
of a material that has a high creep resistance at operating temperatures of
the heater element. The first section may
be relatively thick or have a relatively large effective diameter. Many high
strength, high creep resistance materials,
such as Inconel 617 and HR 120, have higher electrical resistances than
stainless steels that may be used to form
primary heater sections of the heater element. Higher resistance material
allows the high strength and creep
resistant sections (one on each leg of a "U" shaped heater element) to heat to
high temperatures even though the
sections have large cross-sectional areas. A second section may be made of a
less expensive metal that is welded to
the first metal. The second section may have a smaller thickness or effective
diameter than the first section.
Additional sections may be welded to the strip to form a heater element having
a desired length. The diameters of
the various metals, taking into consideration the resistivity of the metals,
may be adjusted to produce a long heater
element that dissipates substantially the same amount of energy per unit
length along substantially the entire length
CA 02704832 2010-05-26
of the heater. Metals used to form the sections may include, but are not
limited to Inconel 617, HR 120, 316
stainless steel, 310 stainless steel, and 304 stainless steel. In an
embodiment of a long, radiative, suspended heater
element, a lead in section of about 30 m is made of 316 stainless steel and is
used to suspend the heater element
from a wellhead. The lead in section functions as a heater section of the
heating element. A second heater section
may be formed of a narrower cross-sectional area of 304 stainless steel (up to
about 25% less cross-sectional area to
dissipate the same amount of heat as the lead in section). The second heater
section in the particular embodiment is
160 m in length, resulting in a "U" shaped heater element having a 110 m (30 m
+ 80 m) long heating section with a
total heater section length of 220 m. A portion of the second heater section
near a 180 bend (or hairpin turn) in the
heater element may have a further reduced cross-sectional area or a different
alloy metal to dissipate more heat than
adjacent heater element sections.
In certain embodiments of radiative heater elements, a support section of a
radiative heater element may
have a cross-sectional area that tapers to a substantially constant cross-
sectional area. A support section may be
made of the same material or a different material than other portions of a
heater element. The support section may
be a transition section of a heater element that does not need to rise to high
operating temperatures. The support
section may be a portion of heater section that will rise to high operating
temperatures during use.
For a heater element that conductively heats adjacent material, a heater
section may have a substantially
rectangular cross-sectional area. For example, an embodiment of a heater
section 26 has a 25 millimeter (mm) by 3
mm rectangular cross section and a length of about 6 m. The dimensions of a
heater section may be chosen so that
the heater section produces and dissipates a desired amount of heat when
inserted into soil and when coupled to a
power source. Cross-sectional shapes other than rectangular shapes may also be
used. The cross-sectional shapes
may be,.but are not limited to, ellipsoidal, circular, arcuate, triangular,
rectangular, pentagonal, hexagonal, or higher
order polygon shaped. Heater elements that transfer heat by radiation may
typically have a substantially circular
cross-sectional area, but other cross-sectional areas, such as the cross-
sectional areas referred to above, may also be
used.
Heater elements may be positioned within the soil in a variety of ways. Some
heater elements 84 may be
directly placed within the soil, such as the embodiment of a heater element
depicted in Figure 7. Other heater
element embodiments may be separated from the soil by packing material 90,
such as is depicted in the embodiment
of Figure 4. Other heater elements may be placed in heater element casings 94,
such as the heater element depicted
in Figure 6. Heater element casing 94 may be placed or packed in the soil, or
the heater casing may be placed in
vacuum casing 88 that is placed or packed in the soil. Placing heater element
84 in heater element casing 94 may
allow the heater element to be made of a relatively inexpensive, non-corrosion
resistant material, because off-gas
will not come into direct contact with the heater element. Heater element
casing 94 may be made of a material that
has sufficient corrosion resistance to resist breakthrough corrosion during
the estimated time needed to complete
soil remediation.
Heater element 84 in Figure 4 may be driven directly into the soil. A drive
rod may be positioned at the
center of heater element 84. The drive rod may then be pounded into soil 34.
When heater element 84 is inserted to
a desired depth, the drive rod may be withdrawn. The drive rod does not need
to be a continuous rod. The drive
rod may be made of threaded sections that are assembled together as the drive
rod is pounded deeper into soil 34. A
geoprobe or a cone penetrometer rig may be used to drive heater element 84
into soil 34. Also, a sonic rig may be
used to vibrate heater element 84 to a desired depth. The sonic rig may
include an eccentric cam that vibrates
heater element 84 and a drive rod to a desired soil depth. Driving or
vibrating heater element 84 into soil 34 may
16
CA 02704832 2010-05-26
not produce cuttings as are produced when an augered opening is formed in the
soil. Driving or vibrating heater
element 84 may eliminate problems associated with disposing of cuttings
produced during the formation of an
angered hole. Avoidance of the production of cuttings may be particularly
advantageous at extremely toxic or
radioactive sites. Also, driving or vibrating heater element 84 into soil 34
may advantageously place a portion of
heater element 84 in direct contact with the soil to be heated.
For heater elements placed in openings or well casings, heater elements 84 may
be formed in "U" shapes
so that ends of both legs 100 of the heater element are accessible at ground
surface 52. Accessibility of both legs
100 allows many heater elements 84 to be easily and efficiently coupled
together electrically. Spacers may be
positioned at desired locations along a length of the heater element. The
heater element may be lowered into the
opening or casing. If fill material is to be used to pack the casing, as
depicted in Figure 4, fill material 90 may be
placed adjacent to heater element 84. To place the fill material 90, a fill
pipe, such as a polyvinyl chloride pipe,
may be inserted between legs 100 of "U"-shaped heater element 84. If fill
material is to be placed between legs 100
of the heater element and soil 34, tubes suspended by wire may be lowered down
the legs of the heater element.
The tubes may be raised as fill material 90 is placed in the opening. The
tubes may properly position each leg of
heater element 84. In certain embodiments, the fill pipe may press the heater
element against the soil. Fill material
90 may be inserted through the fill pipe while raising the fill pipe out of
soil 34. Fill material 90 may plug spaces
between heater element 84 and soil 34. Fill material 90 may include sand
and/or gravel. Fill material 90 may also
include catalyst 92, such as aluminum oxide. Catalyst 92 may be a component of
fill material for both extraction
wells 32 and heat injection wells 36. Fill material 90 may be heated to remove
moisture before being inserted
through the fill pipe. Fill material 90 may be built up in a mound at soil
surface 52 to promote water runoff away
from heater element 84.
Thermocouple well 128 may be positioned in fill material 90 between legs 100
of U-shaped heater element
84. A thermocouple placed in thermocouple well 128 may be used to measure the
temperature between legs 100 of
heater element 84 during soil remediation. The thermocouple may be lowered or
raised to determine temperatures
at selected depths. Alternatively, the thermocouple may be fixed within the
thermocouple well. In an embodiment
depicted in Figure 4, thermocouple well 128 is 0.64 cm diameter stainless
steel tubing that is inserted into the center
of a 4 cm diameter stainless steel vacuum casing 88. A thermocouple positioned
within thermocouple well 128 may
be used to monitor the temperature of heater element 84 adjacent to casing 88.
Dry fill material may need to be packed within a well in a substantially
uniform manner. Dry fill material
may need to be used to avoid formation of gaps and/or settling of the fill
material when water within the fill
material evaporates. If a gap exists within the fill material, a leg of the
heater element may expand into the gap
when the heater element expands. If a leg of a heater element expands into a
gap, the leg may contact or approach
the opposite leg of the heater element. If the leg contacts the opposite leg,
the heater element may short and fail. If
the leg approaches the opposite leg, electricity may are to the opposite leg
and cause the heater element to fail.
If heater element 84 is a radiant heating element, the heater element may
include top 130 as depicted in
Figure 12. Top 130 may thread onto heater casing 94 near ground surface 52, as
shown in Figures 6, 8, and 9, or
the top may be welded to the heater casing, to form a wellhead for the heater
element. If the casing is an enclosed
heater casing 94, as shown in Figure 6, the casing may be filled with a gas.
In some embodiments, the gas may
enhance thermal conduction between heating element 84 and casing 94 to improve
heating response time during
initial heating. In some embodiments, the gas may be a corrosion inhibiter. As
shown in Figure 12, top 130 may
17
CA 02704832 2010-05-26
include openings 132. A fill tube may be placed in a first opening and the gas
may be flowed into casing 94. Gas
originally in casing 94 may flow out of the second opening. When the desired
gas fills casing 94, the second
opening may be plugged, the tube may be removed, and the first opening may be
plugged.
If heating element 84 is to be placed in an open wellbore, as depicted in
Figure 9, cement 134 or another
type of securing method or device may fix casing 94 to soil 34. Top 130 may be
threaded or welded to casing 94.
Figure 13 shows a plan view of an embodiment of a layout for heater elements
84 positioned within
trenches. Heater elements 84 placed in trenches may be placed in long rows.
For heater elements 84 that
conductively heat adjacent material, more than one heater element may be
placed in a single trench as long as a
distance between heater elements, fill material, or spacers ensures that the
heater elements will not touch or be close
enough to each other to arc. For heater elements that radiatively heat a
heater casing, more than one heater element
may be placed within a single heater casing. Heater elements 84 may be placed
in trenches that were formed by a
trenching machine. After heater elements 84 are positioned within trenches and
electrically coupled to a power
source, cuttings formed when making the trench may be used to fill the
trenches. A vacuum system may be
installed, a cover may be placed over the treatment area, and the system may
be energized. Heater elements placed
in trenches may be used in ex situ applications or to treat low depth soil
contamination in situ that is within about 2
in of a soil surface. Heater elements positioned in trenches may have long
lengths that span across contaminated
soil 106. In certain embodiments, rows of heater elements 84 may be separated
by distances equal to about twice
the insertion depth of the heater element into soil 34. Heater elements may be
placed in casing laid in trenches and
exiting at the surface, thereby allowing replacement of heater elements.
As shown in Figure 10, heater element 84 may be placed in soil 34 so that a
portion of heater section 114 is
below contaminated soil 106, and a portion of the heater section is above the
contaminated soil. The portion of
heater section 114 below contaminated soil 106 may be 1 in or more in depth.
Heating a section of uncontaminated
soil 104 below contaminated soil 106 may prevent a falloff in temperature at
interface 102. The cross-sectional area
of heater element 84 adjacent to contamination interface 102 may be small, or
may be made of a different material,
so that more heat is diffused into the soil adjacent to the interface.
Diffusing more heat adjacent to the interface
may promote a more uniform temperature distribution throughout contaminated
soil 106.
To implement a soil remediation process, such as the process depicted in
Figure 1, wells may be positioned
in the soil. The wells may be installed by placing wells within drilled
openings, by driving and/or vacuuming wells
into the ground, or by any other method of installing wells into the soil. The
wells may be extraction wells 32, heat
injection wells 36, fluid injection wells 38, and/or test wells 40. A ring or
rings of dewatering wells may be
installed around a perimeter of the area to be treated. The dewatering wells
may be operated to remove water from
the treatment area and to inhibit water inflow into the treatment area. In
some embodiments, extraction wells,
and/or fluid injection wells (and possibly other types of wells) may be
connected to dewatering pumps so that the
treatment area is rapidly and efficiently dewatered.
Heat injection wells 36 and extraction wells 32 that include heater elements
may be coupled to controllers
(if necessary) and to power source 76 or power sources. Extraction wells 32
may be coupled to vapor collection
system 46. The vapor collection system 46 may be connected to treatment
facility 44. Other wells, such as fluid
injection wells 38 and test wells 40, may be coupled to appropriate equipment.
In some embodiments, treatment
facility 44 may be engaged to begin removing off-gas from soil 34. Heat
injection wells 36 and extraction wells 32
that include heater elements may be energized to begin heating soil 34. The
heating may be continued until the soil
reaches a desired average temperature for a desired amount of time. The
desired average temperature may be
18
CA 02704832 2010-05-26
slightly higher that the boiling point of a high boiling point contaminant
within soil 34. A desired average
temperature may be over 100 C, 400 C, 600 C, or higher. A desired amount of
time may be days, weeks, months
or longer. The desired amount of time should be sufficient to allow for
contaminant removal from soil 34.
A remediation site may be an area at or near an original location of the
contaminated soil. For ex situ
applications, contaminated soil may be collected from one or more locations
and transported to one or more
remediation sites. Collection may include excavation and transportation using
conventional earth moving
equipment.
In some embodiments, contaminated soil may be arranged in long, substantially
rectangular piles. A
remediation site may include more than one pile of soil. For example, a
remediation site may include two to four
piles of contaminated soil. A pile may have a volume of about 2,000 to about
5,000 m3. In an embodiment, a pile
may have a height of about 3 in, a width of about 8 in, and a length of about
35 in. Alternatively, a pile may have a
height of about 3 in, a width of about 25 in, and a length of about 100 in. In
an embodiment, a vertical cross-
sectional shape along a width of a soil pile may be substantially trapezoidal.
Heaters may be placed horizontally in a pile of contaminated soil by embedding
the heaters in a portion of
soil, placing the heaters in trenches formed in the soil, and/or forming
layers of heaters between layers of
contaminated soil. Alternatively, a heater elements may be placed in casing or
tubing, at least one end of which
extends to the surface to allow replacement of the heater element. In an
embodiment, a first layer of soil may be
placed in a pile and leveled using equipment including, but not limited to,
small earthmovers, bulldozers, and front
end loaders. Heaters may be placed on the soil. The heaters may be long strips
of a stainless steel. Ends of the
heaters may be coupled to a power source that supplies electricity to the
heaters to resistively heat the heaters when
initiated. Additional soil may be placed on top of the heaters and leveled.
Additional heaters and soil may be
installed to complete the pile. The heaters may be spaced relatively close
together (e.g., about 1 in apart) to allow
for rapid heating of soil in the pile. Vapor extraction wells may be placed in
desired locations in the pile, and/or a
vapor extraction system may be formed adjacent to the pile.
A cover may be placed over the pile, vacuum may be initiated, and heating of
the soil may be initiated.
The cover may be flexible to accommodate subsidence of the soil level in the
pile due to vacuum and removal of
material from the soil (e.g., water and contaminants).
In addition to allowing removal of contaminants from the soil, heating the
soil may result in the destruction
of contaminants in situ. Superposition of heat from a plurality of heaters
used to radiatively and/or conductively
heat soil at a treatment site may raise the temperature of the soil throughout
the treatment site above temperatures
that will allow for reaction of contaminants. The presence of an oxidizing
agent, such as air, may result in the
oxidation of contaminants that pass through the heated soil. In the absence of
oxidizing agents, contaminants within
the soil may be altered by pyrolysis. Vacuum applied to the soil may remove
some reaction products from the soil.
Many soil formations are characterized by a relatively large weight ratio of
water to contaminants within
the soil. Raising the temperature of the soil to a vaporization temperature of
water or above may result in
vaporization of water in the soil. The water vapor may vaporize and/or entrain
contaminants within the soil.
Vacuum applied to the soil may remove water vapor and contaminants entrained
within the water vapor from the
soil. Vaporization and entrainment of contaminants in water vapor may result
in the removal of medium and high
boiling point contaminants from the soil.
For deep contamination, heater wells may be arranged vertically within a pile
of contaminated soil to
supply heat to the soil. Some heater wells may include perforated casings that
allow fluid to be removed from the
19
CA 02704832 2010-05-26
soil. A heater well with a perforated casing may also allow fluid to be
injected into the soil. Vacuum may be
applied to the soil to draw fluid from the soil. The vacuum may be applied at
the surface and/or through vapor
extraction wells placed within the soil.
Figure 14 depicts a vertical cross section along a substantially trapezoidal
width of pile 136 of
contaminated soil 106. Sloping surfaces of pile 136 may promote stability of
the pile. A long axis of cased heaters
138 and/or heater/vapor extraction wells 140 may be substantially parallel to
a length of pile 136. In an
embodiment in which a length of pile 136 substantially exceeds a width and a
height of the pile, placing cased
heaters 138 and/or heater/vapor extraction wells 140 lengthwise within the
pile may reduce a number of wells
required to remediate a given volume of soil. One or more injection wells 142
may also be placed lengthwise
within pile 136.
A liner may be placed or assembled on a ground surface at a remediation site
before a pile of contaminated
soil is formed. The liner may inhibit fluid (e.g., air and/or water) from
entering the pile during remediation. The
liner may inhibit fluid (e.g., off-gas) from escaping to the environment from
the pile. In an embodiment, a bottom
portion of the liner may be high temperature resistant plastic and/or metal.
The sheeting may be sealed together. A
bed of gravel or sand may be placed on top of the sheeting to provide a level
surface and to insulate the sheeting
from heat applied to soil in the pile during remediation.
As shown in Figure 14, liner 144 may be placed on ground surface 52 of
uncontaminated soil 104 before
pile 136 of contaminated soil 106 is formed. Alternatively, porous layer 146
may be placed between liner 144 and
contaminated soil 106. Porous layer 146 may include a freely draining material
such as sand or gravel. Collection
conduit 148 may be placed in porous layer 146 to collect drainage from
contaminated soil 106 of pile 136.
Collection conduit 148 may be connected to a contaminant treatment system.
Sealing sheet 150 may be placed on or above contaminated soil 106 of pile 136.
Sealing sheet 150 may be
substantially impermeable to air and/or liquid. Sealing sheet 150 may be
flexible. In some embodiments, sealing
sheet 150 may be a carbon steel plate or sheet that is welded together. If the
soil to be remediated will generate
corrosive chemicals, a sealing sheet may be made of a more chemically
resistant metal than carbon steel. For
example, sealing sheet 150 may be made of 316 stainless steel that is more
resistant to hydrochloric acid corrosion
and other corrosive chemicals than carbon steel if the contaminated soil
contains chlorinated compounds that will
decompose to form hydrogen chloride and/or other corrosive compounds. In some
embodiments, corrosive
chemicals may react with clay or other components of the soil to effectively
destroy the corrosive chemicals.
Corrosive chemical generation may not be a problem in such embodiments.
A soil remediation site may include insulation 152 and/or cover 154.
Insulation 152 may inhibit heat loss
to the environment. In an embodiment, insulation 152 may be mineral wool.
Alternatively, a layer of sand or
gravel or lower conductivity cement may be used to space sealing sheet 150
away from high temperatures. Cover
154 may inhibit water from entering into pile 136. In some embodiments, cover
154 may serve as a barrier to
inhibit vapor loss from the remediation site. Cover 154 may be, but is not
limited to, a rain tarp made of waterproof
lightweight fabric, plastic sheeting, and/or sheet metal. Cover 154 may be
positioned over pile 136. In some
embodiments, cover 154 may be sealed to the ground and/or to remediation
equipment or structures. In an
embodiment, cover 154 may be positioned over contaminated soil 106 and fixed
to ground surface 52. In other
embodiments, cover 154 may be positioned on top of insulation 152 over
contaminated soil 106 and fixed to ground
surface 52.
CA 02704832 2010-05-26
Contaminated soil in a pile may be at least partially contained with barriers
along at least a portion of a
perimeter of the contaminated soil. The barriers may form a retaining
structure. Retaining structures may include,
but are not limited to, natural soil layers that are substantially
impermeable, walls of a tank, and/or walls of a man-
made remediation pit. Retaining structures may be used advantageously for
remediation of soil that contains
potentially explosive contaminants. In some embodiments, retaining structures
and materials may be reused for
subsequent treatment of contaminated soil.
Figure 15 depicts pile 136 of contaminated soil at least partially surrounded
by retaining structure 156. In
an embodiment, retaining structure 156 may include concrete retaining walls.
In some embodiments, one or more
retaining walls may be formed of assembled sections. Sections may be
disassembled and moved to facilitate
insertion and removal of soil and connection of central remediation system
equipment (e.g., power and vacuum
sources). Retaining structure 156 may include a base, such as a concrete slab.
Retaining structure 156 may be at
least partially surrounded by insulation 152. In an embodiment, insulation 152
may be styrofoam insulation. In
some embodiments, an inner surface of the side walls may be insulated with
materials such as firebrick to inhibit
thermal degradation of the side walls during remediation of contaminated soil.
In an embodiment, one or more of side walls of retaining structure 156 may
include openings that allow for
passage of monitoring equipment and heaters and/or vacuum system equipment
into soil 106. Soil 106 in retaining
structure 156 may be leveled before introduction of heaters and/or vacuum
system equipment. In an embodiment,
soil 106 may be leveled by earthmoving equipment lowered into in retaining
structure 156 by a crane. In some
embodiments, bare heaters 158, cased heaters 138, heater/vapor extraction
wells 140, and injection well 142 may be
placed as shown in Figure 15. A horizontal spacing between heaters and wells
may be about 1 in to about 2 m. A
vertical spacing between heaters and wells may be about 1 m. Collection
conduit 148 may be placed in porous
layer 146. A bottom row of heaters and wells may be spaced about 1/3 m above a
top of porous layer 146. Sealing
sheet 150, insulation 152, and cover 154 may be placed on top of contaminated
soil 106 and/or coupled to retaining
structure 156. A top row of heaters and wells may be spaced about 1/3 m below
sealing sheet 150.
Other types of barriers may be placed around a contamination site to provide
at least partial containment of
contaminated soil. U.S. Patent No. 6,419,423 of Vinegar et al. describes a
barrier for an in situ soil remediation
system. A barrier may be metal plates driven into the soil around a perimeter
of a contaminated soil region. In
other embodiments a barrier may be, but is not limited to, a grout wall formed
in the soil, and/or a frozen barrier
formed by freeze wells spaced around a treatment area.
A remediation site, such as pile 136 shown in Figures 14 and 15, may include
one or more vacuum ports.
A vacuum port may extend through and be sealed to sealing sheet 150. The
vacuum port may be coupled with
contaminated soil 106. Air and vapors may be removed from soil 106 through the
vacuum port. Air and vapors
from soil 106 may be conducted from the vacuum port to a treatment system or
treatment facility. Vapors may also
be removed from contaminated soil 106 through a conduit. In some embodiments,
a conduit may be coupled to a
lower portion of pile 136. A ventilating layer below contaminated soil 106 in
pile 136 may allow vapors to be
drawn from contaminated soil 106 into the conduit. The ventilating layer may
be a perforated plate. Vapors from
contaminated soil 106 may be transported through the conduit to a treatment
facility.
In some soil remediation system embodiments, a treatment system for processing
off-gas from
contaminated soil may include a thermal oxidizer or reaction system for
destroying contaminants in an off-gas
stream from soil remediation. The thermal oxidizer may heat the off-gas to a
high temperature to destroy some
contaminants within the off-gas. The use of thermal oxidizers may be minimized
and/or eliminated due to the large
21
CA 02704832 2010-05-26
costs associated with purchase, transportation, and operation of thermal
oxidizers. At some soil remediation sites,
the use of thermal oxidizers or other types of reactors may not be as
practical as, for example, absorbent carbon
beds.
Processing of a pile of soil at a remediation site may be achieved using a
central power supply, a central
off-gas treatment system, and central instrumentation and power control
systems. As a pile of soil is formed, wells
(e.g., heater wells and vapor extraction wells) and conduit may be placed in
the soil and coupled to central
equipment for remediation. After remediation, central equipment may be
uncoupled from wells and conduit in the
pile before removal of the treated soil. In an embodiment in which a pile of
contaminated soil is partially contained
by end walls, such as buttressed concrete end walls, central equipment may be
coupled to wells and conduit in the
soil through an end wall. In some embodiments, all or part of a horizontal
layer of wells may be structurally
coupled together. The wells may be moved as a unit using moving equipment
(e.g., a crane).
Several piles of contaminated soil may be formed at a remediation site to
process contaminated soil. In
some embodiments, piles may be treated sequentially for efficient use of
available power and central equipment.
For example, a first pile of contaminated soil may be prepared. A vacuum may
be drawn on the first pile and
heating of the first pile may be initiated. While the first pile is heating, a
second pile may be formed. When
processing of the first pile is complete, a central power supply may be
decoupled from heaters in the first pile, and
the power supply may be coupled to heaters in the second pile. Heating of the
second pile may be initiated. In
some embodiments, heat of the first pile may be transferred to the second pile
to facilitate heating of the second
pile. A third pile of contaminated soil may be formed for processing when
remediation of soil in the second pile is
completed. When soil in the third pile is processed, processed soil in the
first pile may be removed and replaced by
a new batch of contaminated soil. A cycle of use of the first pile, the second
pile, and the third pile may be repeated
to complete remediation of all contaminated soil. In an embodiment, the number
of piles used at a remediation site
may range from two to six.
In certain embodiments, placement of heaters and vapor extraction wells may
result in partial removal of
contamination from bottom edge portions ("fringe area") of the pile. After
treatment of a pile of soil, soil from a
fringe area of the pile may be treated as part of another contaminated pile
formed subsequently.
In some embodiments, a first heated soil pile may be used to destroy
contaminants in an off-gas stream
from soil in a second pile undergoing remediation. In some embodiments, a
thermal oxidizer or other reactor may
be used to process contaminants removed during remediation of soil in a first
pile. In other embodiments, soil in a
first pile may be substantially uncontaminated so that a treatment facility
without a thermal oxidizer or other reactor
is able to handle contaminants in an off-gas stream removed during
remediation. For example, soil in a first pile
may originate from a fringe area of soil contamination.
Soil in a first pile may be heated and remediated. After remediation, heaters
may maintain a high
temperature within the first pile, and a vacuum may be maintained on the first
pile. Remediation of soil in the first
pile may result in soil that is permeable and at a high temperature. In some
embodiments, a soil-filled roll off
container may be used instead of a first pile of soil. A second pile of
contaminated soil may be formed. The second
pile of contaminated soil may be formed during remediation of the first pile.
Vapor extraction wells of the second
pile may be coupled to injection wells of the first pile. In some embodiments,
a blower or other drive system may
be coupled between extraction wells of the second pile and injection wells of
the first pile to facilitate movement of
off-gas from the second pile to the first pile. The second pile may be heated
and remediated. Off-gas from the
second pile may be directed through injection wells into the heated first
pile. A portion of contaminants from the
22
CA 02704832 2010-05-26
second pile may be destroyed by pyrolysis reactions or oxidation reactions in
the first pile. Some of the pyrolysis
reactions and/or oxidation reactions may be exothermic reactions that
facilitate maintenance of a high temperature
in the first pile. Vacuum drawn on the first pile may draw off-gas from the
first pile to a treatment facility.
In some soil remediation system embodiments, a soil treatment site may be a
long, substantially
rectangular remediation pit. For example, a soil remediation pit may be a
concrete lined pit that is about 100 m
long, about 30 m wide and about 2 in deep. Remediation pits having longer or
shorter lengths, widths, and/or
depths may also be used. Several soil remediation pits may be in use at a
remediation site.
Figure 16 depicts an embodiment of soil remediation pit 160. Contaminated soil
106 may be at least be
partially contained in remediation pit 160. Remediation pit 160 may be
prepared such that leaching of contaminants
from soil 106 into surrounding soil and/or migration of contaminants from the
soil is minimized or prevented.
Remediation pit 160 may be an excavated area. Sides of a remediation pit may
be lined with thermal insulation
162. Thermal insulation 162 may minimize heat loss to surrounding soil 34
during treatment of contaminated soil
106. Thermal insulation 162 may reduce heat loss from contaminated soil 106,
thereby effectively increasing a
heating rate of the soil. Thermal insulation 162 may include, but is not
limited to, cement, sand, and/or firebrick.
Remediation pit 160 may also include vapor seal 164 at least partially
surrounding thermal insulation 162.
Lower sealing sheet 166 may be placed on surface 52 of soil 106. Lower sealing
sheet 166 may be flexible to
accommodate settling of the soil due to compaction and/or material removal
(e.g., water and/or contaminants)
during a remediation procedure. Lower sealing sheet 166 may be substantially
impervious to air and/or liquid.
In some embodiments, heaters 168 may be placed on top of lower sealing sheet
166. Heaters 168 may heat
soil 106. Seal 170 may be positioned around a perimeter of remediation pit
160. Seal 170 may be positioned on a
surface of vapor seal 164 to provide an edge seal for heaters 168 and/or lower
sealing sheet 166. Seal 170 may be
inflatable rubber tubing to allow sealing of irregular surfaces. Seal 170 may
be positioned far enough away from
heaters 168 to avoid heating of the seal. Remediation pit 160 may be covered
at least partially with insulation 152
to inhibit heat loss to the environment. In an embodiment, insulation 152 may
be mineral wool. Upper sealing
sheet 172 may be placed between heaters 168 and insulation 152.
Cover 154 may be positioned over insulation 152. Cover 154 may inhibit water
from entering into
remediation pit 160. In some embodiments, cover 154 may serve as a barrier to
inhibit vapor loss from the
remediation site. Cover 154 may be, but is not limited to, a rain tarp made of
waterproof lightweight fabric, plastic
sheeting, and/or sheet metal. Cover 154 may be positioned over remediation pit
160. In some embodiments, cover
154 may be sealed to the ground and/or to remediation equipment or structures.
In an embodiment, cover 154 may
be positioned over contaminated soil 106 and fixed to ground surface 52. In
other embodiments, cover 154 may be
positioned on top of insulation 152 over contaminated soil 106 and fixed to
ground surface 52.
A remediation site may include one or more vacuum ports 174. Vacuum port 174
may extend through and
be sealed to sealing sheets 166, 172. Air and vapors may be removed from soil
106 through vacuum port 174. Air
and vapors from soil 106 may be conducted from vacuum port 174 to a treatment
system or treatment facility.
Vapors may also be removed from contaminated soil 106 through conduit 176. In
some embodiments, conduit 176
may be coupled to a lower portion of remediation pit 160. Ventilating layer
178 below soil 106 in remediation pit
160 may allow vapors to be drawn from contaminated soil 106 into conduit 176.
Ventilating layer 178 may be a
perforated plate. Vapors from soil 106 may be transported through conduit 176
to a treatment facility.
In an embodiment of a remediation system, conduit 176 may be attached to a
fluid supply. Fluid may be
introduced into contaminated soil 106 through conduit 176. The fluid may be,
but is not limited to, steam or liquid
23
CA 02704832 2010-05-26
water, a solvent, a surfactant, a chemical reactant such as an oxidant, a
biological treatment carrier, a drive fluid,
and/or a heat transfer fluid. A solvent or surfactant may be used to increase
fluid flow through contaminated soil
106 toward vacuum port 174. A reactant may react with contaminants to destroy
contaminants and/or convert
contaminants into volatile reaction products. The reaction products may be
removed from the soil through vacuum
port 174. A drive fluid may be used to move contaminants entrained in vapors
toward vacuum port 174. A heat
transfer fluid may be used to promote convective transfer of heat through the
soil.
In some embodiments, a first conduit or conduits may allow a vacuum to be
drawn on soil in a remediation
pit from below the remediation pit. A second conduit or conduits may allow for
fluid insertion into the remediation
pit from below the soil in the remediation pit. A remediation system with a
first conduit or conduits for drawing a
vacuum and a second conduit or conduits for inserting fluids may allow for
drawing a vacuum on a remediation pit
and for inserting fluid into a remediation pit without the need to change
equipment during a remediation process.
Contaminated soil may be placed into tanks. Figure 17 depicts an embodiment of
contaminated soil 106 in
tank 180 for ex situ remediation of the soil. Tank 180 may be formed on base
182. In an embodiment, base 182
maybe made of a rigid, substantially impermeable substance such as concrete.
Base 182 may serve as a lower
insulation layer for tank 180. Tank 180 may include an outer lining or shell
184. The annular space formed
between inner lining 186 and shell 184 may be filled with thermal insulation
162. Thermal insulation 162 may be,
but is not limited to, cement, sand, firebrick, and/or mineral wool.
In some embodiments, ventilating layer 178 may be located on or adjacent to a
surface of soil 106. Vapor
extraction well 188 may be coupled to the space above ventilating layer 178 so
that the vapor extraction well is able
to draw vacuum on soil 106 below the ventilating layer. In an embodiment,
vapor extraction well 188 may be a
heater/vapor extraction well. Vapors may be conducted through ventilating
layer 178 toward vapor extraction well
188. In an embodiment, a vacuum source may draw vapors through ventilating
layer 178 toward vapor extraction
well 188. Ventilating layer 178 may be, but is not limited to, a grating,
perforated sheet metal, and/or chain-link
fence. An outer casing of vapor extraction well 188 may be perforated to allow
vapors to enter the well and be
removed by the vacuum source. The vapors may be conducted from vapor
extraction well 188 to a treatment
facility. Sealing sheet 150 may be placed between ventilating layer 178 and
insulation 152 above soil 106 to serve
as a vacuum seal.
In some embodiments, heater wells may be arranged substantially vertically
within soil 106 in a regular or
substantially regular pattern. For example, heater wells may be arranged in a
hexagonal pattern around vapor
extraction well 188 within contaminated soil 106 in tank 180. In some
embodiments, heater wells and/or vapor
extraction wells may be slanted or placed substantially horizontally in the
soil. Heater wells 190 and vapor
extraction well 188 may extend through precut holes in ventilating layer 178,
sealing sheet 150, and insulation 152
above soil 106. Sealing sheet 150 may be sealed to top hats of heater wells
190 and vapor extraction wells 188.
Allowances in heater wells, vapor extraction wells, and seals of the wells to
sealing sheet may allow for thermal
expansion and for shrinkage of soil due to material loss (e.g., water loss).
Sealing sheet 150 may be sealed to tank
180. Depending on the temperature to which the seals will be subjected, the
seals maybe formed of rubber,
silicone, and/or metal welds.
Clean soil may be used as insulation around retaining structures. For example,
a clean soil berm may be
formed around tank 180. In an embodiment, a clean soil berm may surround shell
184. A clean soil berm may also
be used as thermal insulation 162 between lining 186 and shell 184. When soil
106 is heated, a portion of the berm
24
CA 02704832 2010-05-26
adjacent to tank 180 may dry out. The dry soil may act as insulation for tank
180. In some embodiments, insulation
may be coupled to outer surface of shell 184.
Figure 18 depicts an embodiment of a portion of a remediation system that
includes risers 192. Risers 192
may be used to remediate soil that contains dense non-aqueous phase liquids
that have medium to high boiling
points and do not significantly thermally degrade at temperatures used during
remediation. For example, risers may
be used in a soil remediation system for remediating soil contaminated with
mercury. In an embodiment, riser 192
is a heated riser. Riser 192 may be coupled to sealing sheet 150 above
ventilating layer 178. A portion of vapor
extraction well 188 that extends above soil 106 may be a riser. Insulation 194
may cover a portion of riser 192. In
an embodiment, insulation 194 may cover ascending portion 196 of riser 192.
Ascending portion 196 may be
heated with heater 198 to a temperature greater than a boiling point of a
contaminant to be removed from the soil.
Heat supplied by heater 198 may inhibit condensation of the contaminant in
riser 192.
Conduit 176 exiting riser 192 may conduct vapor removed from soil to a
treatment facility. Conduit 176
may be coupled to a vacuum system. In some embodiments, all or portions of
conduit 176 may not be insulated.
Vapor may be allowed to condense within conduit 176. Conduit 176 may be
maintained at a temperature sufficient
to inhibit formation of solids in the conduit. Riser 192 may have sufficient
height so that a slope of conduit 176
towards a treatment facility will facilitate flow of any condensed liquids in
the conduit to the treatment facility.
A soil remediation site may include at least two treatment sites. In a soil
remediation embodiment, at least
a portion of the vapors produced by heating soil at a first treatment site may
be used to provide heat to contaminated
soil at a second treatment site. Figure 19 depicts an embodiment of a soil
remediation site including two treatment
sites. Remediation site 200 may contain soil 106 and remediation site 200' may
contain soil 106'. In an
embodiment, site 200 and/or site 200' may be, for example, a remediation pit
or a pile of soil. When soil 106, 106'
is initially placed in sites 200, 200; soil 106 may contain substantially the
same contaminants or different
contaminants than soil 106'. Sites 200, 200' may be coupled together by
conduits. Valve system 202 may be used
to control flow of fluids between sites 200 and 200'through conduits 176, 176,
and 204. Valve system 202 may
include a valve in conduit 176 from site 200, a valve in conduit 176' from
site 200', and a valve in other conduits
204 at the remediation site. Valve system 202 may be located in a readily
accessible portion of the remediation site.
Conduits 176, 176' are shown schematically in Figure 19 as single pipes
entering/leaving sites 200, 200'.
In a remediation system, conduits 176, 176' may be a plurality of conduits
that enter/leave sites 200, 200' at several
locations. In an embodiment, conduits 176, 176' may enter/leave a manifold
adjacent to valve system 202.
Soil 106 in site 200 may be heated with heaters 168. Heaters 168 may be
located in soil 106, above the
soil, and/or below the soil. Valve system 202 may be set to inhibit fluid
transfer from site 200 to site 200' during
heating of soil 106 in site 200. A vacuum source may be used to apply a vacuum
through vacuum port 174 during
heating and remediation of soil 106. In some embodiments, vacuum may also be
drawn through conduits 176, 204
to remove vapor from site 200. After contaminated soil 106 in site 200 is
treated, heaters 168 may be turned off.
After heaters 168 are turned off, application of the vacuum may be
discontinued. Subsequently, valve system 202
may be set to connect sites 200 and 200'. A vacuum source may be coupled to
vacuum port 174' in treatment site
200'. Air may be introduced at vacuum port 174 and allowed to flow down
through soil 106 and through conduits
176, 176'to site 200'. Air moving through site 200 may be heated by soil 106.
The heat of the air may transfer to
soil 106' in treatment site 200'. Heat transfer to air passing through soil
106 in treatment site 200 may cool soil 106.
Heaters 168' may be used to supply additional heat to soil 106' in site 200'.
Transferring heat from site 200 to site
200' may substantially reduce the amount of energy needed to be supplied to
soil 106' from heaters 168'.
CA 02704832 2010-05-26
Transferring heat from site 200 to site 200' may substantially reduce the
amount of time needed to cool soil 106 so
that the soil is cool enough to process (e.g., move to a new location).
In some process embodiments, conduit 204 may be attached to a fluid supply to
introduce fluid into soil
106 in site 200 or soil 106' in site 200'. In some process embodiments,
conduit 204 may be connected to a vacuum
system to draw fluid out of soil 106 and/or soil 106'. Fluid introduced into
soil 106 and/or soil 106' may be used to
treat the soil in site 200 and/or site 200'. The fluid may be used to move
contaminants within soil 106 and/or soil
106'to facilitate remediation. Additionally, the fluid may be used to assist
the transfer of vapors between site 200
and site 200'. Valve system 202 may be set to direct fluid to site 200 and/or
site 200'. For example, valve system
202 may allow fluids to enter site 200 through conduits 204 and 176 during
heating and remediation of soil 106.
Vacuum applied through vacuum port 174 may draw fluid into soil 106. Valve
system 202 may be set to prevent
fluid from entering site 200 after soil 106 is fully treated. If required,
additional "block and blend" valve
arrangements may be installed to positively inhibit back flow of fluids into
previously cleaned soil. After treatment
of site 200, valve system 202 may be adjusted to allow fluid to flow from site
200 to site 200'. During remediation
of contaminated soil 106' in site 200', valve system 202 may be positioned to
allow fluid to enter site 200'. In some
embodiments, a pump may be coupled to conduit 204 to force fluid into soil 106
and/or soil 106'.
In an embodiment, heated soil at one site may be used to at least partially
destroy contaminants in vapors
produced from soil at another site. Soil 106 in site 200 may be thermally
remediated to remove or reduce
contamination within the soil. Soil in site 200 may be heated to a high
temperature. The temperature may be
sufficient to allow for pyrolysis, oxidation, or other chemical reaction of
contaminants within vapor that are drawn
through the soil. In some embodiments, an average temperature of soil in site
200 may be less than about 200 C,
less than about 300 C, less than about 400 C, less than about 500 C, or
less than about 600 C.
After soil 106 in site 200 is raised to a desired temperature, heating of soil
106' in site 200' may be
initiated. Vapors removed from site 200' may be drawn by a vacuum through site
200. For example, in Figure 19,
valve system 202 may be set to allow a vacuum pulled through vacuum port 174
to draw vapor from soil 106'
through conduits 176, 176 and into soil 106. If desired, a reactant such as an
oxidant (e.g., air, oxygen, and/or
hydrogen peroxide), or other chemical may be introduced into the vapor by
setting valve system 202 to allow the
reactant to be drawn toward soil 106.
In other embodiments, soil 106 initially heated at site 200 may be
contaminated soil. Contaminants
removed from the soil during heating may be directed to a treatment facility.
The treatment facility may include a
transportable thermal oxidizer that destroys the contaminants. When the soil
is heated to the desired temperature,
the thermal oxidizer may no longer be needed to treat contaminants from soil
being remediated. The thermal
oxidizer may be removed. In some embodiments, soil 106 in site 200 may
initially be uncontaminated or
substantially uncontaminated soil that is heated to a high temperature.
Uncontaminated or substantially
uncontaminated heated soil 106 in site 200 may be used treat contaminants from
soil 106, thus reducing equipment
requirements of a coupled treatment facility.
Contaminants in the vapor from soil 106may be destroyed within heated soil 106
in site 200. In some
embodiments, an oxidant or other reactant may be drawn into site 200 to
facilitate destruction of contaminants in
heated soil. Reactions of contaminants from soil 106may be exothermic
reactions that contribute to maintenance
of high soil temperature in site 200. Soil 106 site 200 may be maintained at a
high temperature. Heating soil 106
site 200 may result in the soil having a high permeability and a large surface
area. The heat and large surface area
may advantageously be used to destroy contaminants produced from a second
site, such as site 200'.
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CA 02704832 2010-05-26
In certain embodiments, including the embodiment shown in Figure 19, a conduit
may be used to introduce
a fluid (e.g., air) to a site to accelerate heat transfer through contaminated
soil at the site. For example,
contaminated soil 106 in site 200 of Figure 19 may be heated from the top with
heaters 168 and heated from the
bottom with heaters 206, until a desired temperature is established in the
soil. Heaters 168 may be turned off and
air may be introduced to a lower portion of contaminated soil 106 through
conduit 176. The air may draw heat
from heaters 206. As heat is transferred to the air, an injection rate of heat
from heaters 206 may be increased. The
heated air may transfer the heat upward through contaminated soil 106. A
vacuum source may be coupled to
vacuum port 174. Air may be drawn through contaminated soil 106 toward vacuum
port 174. The vacuum may be
used to control airflow through (i.e., the heating rate of) the soil. Use of a
fluid (e.g., air) to transfer heat through
contaminated soil 106 may reduce the energy requirements for remediation of
contaminated soil 106 in site 200.
In an embodiment, ex situ remediation may be used in conjunction with in situ
soil remediation to
remediate soil. For example, a heated zone of subsurface soil may be used as a
site to at least partially destroy
contaminants in vapors from another site. In other embodiments, soil from more
than one location may be
remediated at one treatment site.
Figure 20 depicts an embodiment that may be used to remediate contaminated
soil from more than one
location simultaneously. Lower portion 208 of contaminated soil may be
collected in remediation pit 160 for ex
situ remediation. Alternatively, lower portion 208 of contaminated soil may be
a location of subsurface
contamination contained by barriers. Heaters 210 may be placed above lower
portion 208 of contaminated soil.
Upper portion 208' of contaminated soil maybe placed above heaters 210.
Heaters 210' may be placed within upper
portion 208' of contaminated soil. Heaters 210,210' may include, but are not
limited to, heater blankets, strip
heaters, and/or bare wires. Alternatively, heaters 210, 210' may be a
horizontal arrangement of heater wells and/or
heater/vapor extraction wells. Lower portion 208 and upper portion 208' of
contaminated soil at the site may be
collected from more than one location and may contain substantially the same
or substantially different
contaminants. Sealing sheet 150, insulation 152 over soil, and cover 154 may
be placed above upper portion 208' of
contaminated soil. Upper portion 208' and lower portion 208 of contaminated
soil, which may originate from more
than one location, may be heated with heaters 210, 210' at substantially the
same time within remediation pit 160.
For deeper sites of contaminated soil, trenches may be formed in lower portion
208 of contaminated soil,
and heaters 210" may be placed in the trenches. Alternatively, remediation pit
160 may be partially filled with
contaminated soil. Heaters 210" maybe placed on the soil, and more
contaminated soil placed over the heaters.
Alternatively, heater wells and/or heater/vapor'extraction wells may be
arranged vertically within lower portion 208
of contaminated soil and/or upper portion 208' of contaminated soil.
A layered arrangement of heaters, as shown in Figure 20, may be used to
provide relatively rapid and
substantially even heating at a remediation site. In an embodiment, two or
more coupled remediation sites (e.g.,
sites 200 and 200'shown in Figure 19) may be heated simultaneously with
layered arrangements of heaters.
Embodiments described herein may be used for high temperature removal of
contaminants from
contaminated soil at one or more sites. High temperature materials for heating
and containing the contaminated soil
may be incorporated depending on the expected temperature requirements and
properties of the contaminants and
vapors produced. Embodiments may also be used for low temperature dewatering
of contaminated sludge. Steel
tanks may be used for containing the contaminated sludge. Dewatering sludge
may substantially reduce a volume
of wet soil to facilitate handling of the soil and contaminants within the
soil.
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CA 02704832 2010-05-26
Further modifications and alternative embodiments of various aspects of the
invention will be apparent to
those skilled in the art in view of this description. Accordingly, this
description is to be construed as illustrative
only and is for the purpose of teaching those skilled in the art the general
manner of carrying out the invention. It is
to be understood that the forms of the invention shown and described herein
are to be taken as examples of
embodiments. Elements and materials may be substituted for those illustrated
and described herein, parts and
processes may be reversed, and certain features of the invention may be
utilized independently, all as would be
apparent to one skilled in the art after having the benefit of this
description of the invention. Changes may be made
in the elements described herein without departing from the spirit and scope
of the invention as described in the
following claims.
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