xvEPA
United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-214 Oct. 1981
Project Summary
Modification of Spill Factors
Affecting Air Pollution:
Volume I. An Evaluation of
Cooling as a Vapor Mitigation
Procedure for Spilled Volatile
Chemicals
J. S. Greer, S. S. Gross, R. H. Hiltz, and M. J. McGoff
Spilled chemicals that pose a hazard
to the land and water ecosystem can
also provide a significant vapor hazard.
Although the vapors released by such
chemicals may ultimately be dispersed
in the environment with few long-
term effects, they do pose a hazard to
life and property downwind of the
spill.
Among the vapor amelioration tech-
niques that have been considered is
the use of a coolant to lower the
temperature of a spill and reduce its
equilibrium vapor pressure. This pro-
gram was conducted as a feasibility
study of that mechanism.
Four potential coolants were exam-
ined: water ice, dry ice, liquid carbon
dioxide, and liquid nitrogen. Further
evaluation based on laboratory studies
and limited scaled-up tests established
dry ice as the most versatile coolant
choice. Water ice does not cool suf-
ficiently. Liquid nitrogen and carbon
dioxide require large quantities of
material and produce a dense obscur-
ing cloud that has some adverse impli-
cations. Dry ice avoids these problems
and is readily available at a reasonable
cost, but some method is required for
crushing and distributing the dry ice
on the spill. A prototype unit was thus
developed consisting of a crusher and
a pneumatic conveyor to perform
these functions.
A pool of diethyl ether with 2.23 m2
(250 ft2) of surface was cooled to
-60°C (-76°F) using 408 kg (900 Ib) of
dry ice fed at a rate of 13.6 kg/min (30
Ib/min). A measurable reduction in
downwind vapor concentration was
realized. Pool temperature was still
below -10°C (14°F) 2 hr after dry ice
discharge was terminated.
This program has established the
feasibility of the mechanism, but
additional work is necessary to estab-
lish practicality, define materials to
which cooling is applicable, and opti-
mize the dispensing equipment.
This Project Summary was devel-
oped by EPA's Municipal Environmen-
tal Research Laboratory, Cincinnati,
OH, to announce key findings of the
research project that is fully docu-
mented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Many of the chemicals that pose a
hazard to the land and water ecosystem
when spilled can also provide a signifi-
cant vapor hazard. Although the vapors
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released by such chemicals may ulti-
mately disperse into the environment
with little long term effect, they do pose
an immediate hazard to life and property
downwind of the spill. In addition, a
hazard exists to those responding to the
spill who must remain in the area for the
duration of the incident.
The vapor hazard from spilled chemi-
cals takes two forms: the release of toxic
fumes that pose a life hazard even at low
concentrations (parts per million), and
the release of flammable vapors where
minimum dangerous concentrations
are usually above 1%. Some chemicals
may exhibit both hazards, but toxicity,
with its lower allowable concentration,
will be the controlling feature.
The great difference in minimum
hazard levels creates two distinct prob-
lems. In the case of flammable vapors,
small increments of reduction can be
meaningful. For toxic materials, the
ability to provide meaningful mitigation
of the hazard may lie only with reduction
of the equilibrium vapor pressure.
A number of vapor amelioration tech-
niques have received consideration. A
review of the techniques conducted
under U.S. Coast Guard sponsorship
shows that most are ineffective. The
techniques of mechanical covers, in-
duced air movement, vapor scrubbing,
and vapor phase reaction are in this
category. The techniques of foam blan-
keting and liquid phase modification are
the only ones that in their present state
of development have had any practical
demonstration and can pass the criteria
of cost, availability, deployment, and
application. The degree of vapor control
that can be achieved with these two
techniques is beneficial where flam-
mable vapors are the hazard. But where
the vapor hazard is one of toxicity and
hazardous vapor concentrations are in
the parts per million range, such tech-
niques are not adequate.
Maintenance of vapor levels in the
parts-per-million range appears to
require a mechanism to reduce the
equilibrium vapor pressure. One poten-
tial mechanism of vapor control may
achieve that end: the use of a coolant.
Reducing the temperature of the spill
reduces the equilibrium vapor pressure
and the rate of vapor release per unit of
time.
This technique has been addressed in
two programs, but no systematic inves-
tigation has been conducted. Based on
these studies, EPA inaugurated a de-
tailed program to evaluate the potential
of cooling and, if warranted, to conduct
a simulated spill scenario to define
feasibility.
Discussion of Results
This study establishes the basic
feasibility of the cooling concept. A
literature search and data evaluation
delineated an extensive list of potential
coolants. Practical considerations of
cost, availability, safety, and field
handling reduced the candidate list to
four materials: wet ice (solid water), dry
ice (solid CO2), liquid C02, and liquid
nitrogen.
All four materials are readily available
from many sources on short notice and
at a reasonable cost. The liquefied
gases, N2 and C02, can achieve signifi-
cant reductions in the temperature of
the spill, but they are attended by
certain disadvantages. These gases
require continuous application, and the
effect does not persist if application is
discontinued. The boiling of the liquid
exaggerates the vapor release from the
spilled material, negating some of the
benefits of cooling. Both materials
produce a dense obscuring cloud above
the spill surface. This cloud provides a
nonflammable atmosphere, but it is also
nonbreathable.
Liquid CO2 can be released to form
solid C02, identified as COa snow. But
conversion is only 15 percent with
current technology, an obscuring cloud
is still generated.
Wet ice has certain advantages, but
its capability is limited to 0°C (32°F). Ice
can react with some materials and will
cause a volume increase because of its
nonvolatility.
Dry ice, crushed and applied as a
particulate, initially showed the best
potential for effective, persistent cooling
with small material losses and minimal
cloud formation. Further evaluation
supported by laboratory studies and
limited scaled-up tests were able to
establish dry ice as the best coolant
choice. The bases for this selection are
detailed in Table 1. The main comparison
was the difference of the temperatures
achieved and the rate of rise after
coolant application was stopped. A
comparison using ethyl ether is shown
in Figure 1.
Results
The laboratory results were encour-
aging, but they were not sophisticated
enough to establish the feasibility for
field use. Field application necessitated
a mechanism to convert the standard
form of dry ice blocks (10x10x1 in.; 25
x 25 x 2.5 cm) to a particulate form and a
means for dispensing the particulates to
the spill surface. A review of commer-
cial equipment revealed several types ol
applicable equipment. After a limited
testing program, a commercial shredder/
crusher was selected. The shredder
operation was modified in terms of the
speed of rotation and the configuration
of the tines to achieve a reasonable yield
of particles within an acceptable size
range. The distribution covered fine
particulates to coarse material of 0.635
to 1.27 cm (1 /4 to 1 /2 in.). Because of
the problem of sublimation, a true size
range could not be measured. Efficiency
in terms of material out versus material
in was in the range of 75%.
Several concepts were evaluated for
dispensing the crushed dry ice. A snow
blower was originally selected, but its
operation reduced the effective discharge
to 65%. The combination of snow
blower/crusher was a poor selection in
real time. The discharge distance was
not sufficient to allow operation from a
restricted location, and the machine
was difficult to manipulate around the
spill. A change was made to a pneumatic
conveyor, which was made up of an
auger feeding the particulate into an air
stream with forced discharge through a
hose. *
The combination unit was mounted
on a wheeled frame to provide mobility,
but the hose discharge allowed an
extended discharge pattern from a
single location. Some additional mate-
rial losses were encountered, reducing
efficiency to about 50%.
Field tests were conducted using
diethyl ether as a spill simulant: 757 L
(200 gal) was spilled into a 7.62- by 6.1 -
m (25- by 20-ft) impoundment. Dry ice
was charged at a rate of 13.61 kg/min
(30 Ib/min) for 30 min with an effective
application of 6.80 kg/min (15 Ib/min).
The spill temperature was reduced in
that time to an averge of -60°C (-76°F),
which resulted in a decrease of the
equilibrium vapor pressure from 440 to
4.0 mm of Hg. An absolute measure of
vapor reduction could not be obtained
because of wind effects. The available
data show the effective reduction in the
vicinity of the spill to be at least 75% of
the free spill value. Typical values show
a free spill vapor concentration of
10,000 ppm, which was reduced to 180
ppm by the dry ice application.
Conclusions
The results of this program show that
dry ice can significantly reduce th
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fable 1. Cryogen Comparisons
Cryogen
Advantages
Disadvantages
Liquefied
Nitrogen
Liquefied
Carbon
Dioxide
Solid Carbon
Dioxide
Ice
1. Cheaper than COz on a per-pound basis
2. Extremely low temperatures possible
1. No storage losses
2. Reasonable temperature reduction of spill
1. Better cost advantage than liquid COz
or liquefied Nz
2. Less application loss than with LNZ or liquid
COz
3. Rapid cooling of spill
4. No problems with COz cloud
5. Can be projected over distances
6. Readily available
7. Safer than liquefied /V2 or liquefied COz to handle
1. Safest to use
2. Most readily available
3. Can be projected
1. Vapor losses occur on storage
2. Nz cloud significantly reduces visibility
and oxygen levels in vicinity of spill
3. Larger quantities needed to cool spill than
with solid COz
4. Not as cost effective as solid COz
5. Hazardous liquid may be entrained by Nz vapors
1. Higher liquid COz losses occur upon
application to the spill
2. COz cloud significantly reduces visibility and
oxygen levels in vicinity of spill
3. More expensive than solid COz based on the
amount actually applied to the spill
1. Storage losses occur
2. Grinding necessary before application
1. Temperature of the spill is not reduced
sufficiently
2. Increases the liquid volume of the spill when
the ice melts
Liquefied
Nitrogen
1. Cheaper than COz on per pound basis
2. Extremely low temperatures possible
Liquefied
Carbon
Dioxide
Solid Carbon
Dioxide
Ice
1. No storage losses
2. Reasonable temperature reduction of spill
1. Better cost advantage than liquid COz
or liquefied Nz
2. Less application losses than with LNz or
liquid COz
3. Rapid cooling of spill
4. No problems with COz cloud
5. Can be projected over distances
6. Readily available
7. Safer than liquefied NZ or liquefied C02 to handle
1, Safest to use
2. Most readily available
3. Can be projected
1. Vapor losses on storage
2. Nz cloud significantly reduces visibility
and oxygen levels in vicinity of spill
3. Larger quantities needed to cool spill than
solid COz
4. Not as cost effective as solid COz
5. Possible entrainment of hazardous liquid by
Nz vapors
1. Higher liquid COz losses upon application
to the spill
2. COz cloud significantly reduces visibility and
oxygen levels in vicinity of spill
3. More expensive than solid COz on the basis of
amount actually applied to the spill
1. Storage losses
2. Grinding necessary before application
1. Temperature of the spill is not reduced
sufficiently
2. Increases the liquid volume of spill when the
ice melts
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20
-20
-40
2
Cb
| -60
-80
-100
-120
9.3 m2 (100 ft2) pond
208 I (55 gal) diethyl ether
-40
-20
20 40 60
Time, min.
80
WO
120
Figure 1. Subscale field test results with ethyl ether—temperature versus time
(9.3 m2(100-ft2) pond, 208 L (55 gal) diethyl ether).
temperature of a spilled liquid with a
concomitant reduction in the vapor
release rate. Crushing the dry ice to an
acceptable particulate level and dis-
tributing it over the spill surface can be
achieved by state-of-the-art techniques.
The equipment evolved in this pro-
gram required further optimization.
Further study must be done on opera-
tion, configuration, and materials of
construction. The tests that have been
conducted are not sufficiently extensive
to show clearly a practical, efficient
operation in a real-time spill scenario.
But they do support continued investi-
gation and evaluation of the cooling
concept.
The cooling concept is primarily suited
for use with materials that pose a toxic
vapor hazard rather than a flammable or
explosive vapor hazard. In most cases,
aqueous foams provide effective mitiga-
tion for such materials.
Foams are a well developed technol-
ogy in common use by emergency
organizations, but they cannot provide
the degree of vapor control necessary
where toxic levels are in the parts per
million range. This study provides a
basic guideline for further evaluation of
coolants.
The full report was submitted in
partial fulfillment of Contract No. 68-
03-2648, Task 9A. by MSA Research
Corporation under subcontract to Rock-
well International under sponsorship of
the U.S. Environmental Protection
Agency.
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J. S. Greer. S. S. Gross, P. H. Hiltz, and M. J. McGoff are with MSA Research
Corporation, Evans City, PA 16033.
John E. Brugger is the EPA Project Officer (see below).
The complete report, entitled "Modification of Spill Factors Affecting Air
Pollution: Volume I. An Evaluation of Cooling as a Vapor Mitigation Procedure
for Spilled Volatile Chemicals," (Order No. PB 82-108 382; Cost: $9.50,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Oil and Hazardous Materials Spills Branch
Municipal Environmental Research Laboratory—Cincinnati
U.S. Environmental Protection Agency
Edison, NJ 08837
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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