Solvent Emissions
Ultrasonic Cleaning
Solvent Emissions Control:
A Technical Guide
Branson Ultrasonics Corporation
recognizes the need for environmental
responsibility in manufacturing today.
As an international corporation whose
cleaning equipment is used widely in
industry, Branson holds an obligation to
address environmental concerns.
Branson is committed to fulfilling this
obligation by designing solvent and
aqueous cleaning equipment with
environmental safeties as integral
elements, by sharing our research into
emissions control with industry, and by
participating actively with government
and corporate groups to find ways to
protect earth’s environment.
Branson therefore calls for responsibility
in chemical handling and conservation
and offers methodology for
substantially decreasing emissions
in the cleaning process.
Our Commitment
As a manufacturer of aqueous as well as
solvent equipment, Branson is bias-free
in its recommendations.
Our commitment becomes action as
we at Branson:
• Work with environmental &
legislative groups.
• Test solvent alternatives in our
Cleaning Applications Laboratory.
• Incorporate emission control design
into product concepts.
• Promulgate solvent emission control
information & techniques.
Solvent Emissions
Scientific evidence indicates the global
ozone layer is being depleted or thinned
by chloroflurocarbons (CFCs) released
into the atmosphere. Holes in the layer
allow the penetration in large doses of
ultraviolet radiation which can be harmful to human health and environmental
balance. Automation of a cleaning process is the optimal way to substantially
reduce solvent emissions.
Whose Problem Is It?
Although solvent alternatives have been
developed and some with less CFCs
already are available, the issue of
environmental responsibility will
remain. Never again can we consider any chemical completely
‘safe’ for the environment or
human health. Therefore we
must institute good work practices now to decrease emissions
of any chemical as much as
possible.
How Solvent Vapors Escape
Solvents loss in the cleaning process can be attributed to three
areas:
• Operation
• Equipment Design
• Maintenance
Operation
Our research has shown that
improper operation of the
cleaning process is the primary
source of solvent emissions
from open-top degreasers.
Operation is the leading cause
because human physiology
makes exact process control
nearly impossible.
For example, lowering part fixtures into a degreaser faster than
10 feet per minute will forcefully
displace solvent vapors above the
cooling coil and out of the tank.
Yet data collected by industry
shows that the ‘typical’ operator
lowers the parts between 30 and
100 feet per minute. Even the
most conscientious operator will
tend to violate this parameter
and contribute to unnecessary
emissions. With part loads ranging from a few pounds to tens of
pounds, precise and slow speeds
are very difficult to perform. Even
if a mechanical hoist is used,
proper vertical speeds often are
exceeded in the interest of
increased production.
Our test measurements of emissions show that a vertical speed
of 20 feet per minute in the
cleaning process can consume
from 30 to 50 percent more solvent than a vertical speed of 10
feet per minute. Branson recom-
mends a controlled vertical
speed of no more than 10 feet
a minute when parts enter or
exit a solvent cleaner.
Correct residence time within
the vapor zone is another
aspect of solvent cleaning that
often falls short. Proper proce-
dure calls for holding the parts in
the vapor zone for a final vapor
dry until condensation on the
part ceases. Condensation will
cease when the temperature of
the part is in equilibrium with the
temperature of the vapors. It is
critical that the time required for
this step be carefully observed
since it is difficult for the human
eye to determine where condensation ceases. If the part is pulled
out too soon, liquid solvent will
vaporize and escape from the
equipment. Depending on the
mass and complexity of the part,
the vapor dry time could range
from 30 seconds to several minutes. If this is done manually,
extended vapor dry times can be
physically demanding and, therefore, often shortened
Correct freeboard residence
time also is important. As the
parts are removed from the
vapor zone to the freeboard area,
the remaining solvent condensation will vaporize and, being
heavier than air, will fall back into
the vapor zone. If the parts are
held in the area of the cooling
coils in the freeboard area while
still above the vapor zone, more
vapors are returned. But, as with
the vapor zone, it is physically
demanding to suspend the parts
in the freeboard area manually.
Operation - Solution
Branson recommends automating for precise control of the
correct process speeds and residence times. Our research shows
that solvent emissions can be
decreased 70% by automating
the process.
In a test conducted to measure
the effect of certain working
conditions on solvent emissions,
our base data was generated with
a covered, idling, Branson BSD
Model 1216 solvent cleaner The
base measurement was assigned
a value of one.
A representational workpiece
load was processed under
optimal conditions, that is following all of the recommended
procedures to minimize solvent
emissions.
Processing was controlled
through use of a Branson TDR
automated transport system
Production parameters were a
slow vertical transport speed,
30-second vapor zone time above
the boiling sump, 30 seconds of
ultrasonic immersion, 60 seconds
in the vapor zone for drying
and 30 seconds in the freeboard
zone Good processing achieved
a value of two.
Industry norm, however, of the
actual solvent cleaning process
generates an emission value of
eight. Typical operations include
practices such as fast vertical
speed of the parts into the equipment, reduced residence times,
liquid drag-out, and uncontrolled
spraying.
Solvent emissions can be reduced
from eight to two on
the value scale by automating
for precise process control.
Summary: Regardless of how
efficient the design of a cleaning
system, improperly operated
equipment is the biggest source
of emission. Through proper
operator training and awareness
programs, the industry norm of
“eight” can be reduced. But to
get dramatic results of a reduction from “eight” to “two”, a
programmable transport is nec-
SOLVENT EMISSIONS
EMISSION FACTOR
8
7
6
5
4
3
2
1
0
TYPICAL GOOD BASE
essary to control residence times
and proper processing speeds. In
addition, production benefits are
realized — an automated system
can increase throughput by running unattended and it minimizes health concerns for
operator safety near solvents.
Equipment Design
Many features in properly
designed cleaning equipment
will work toward decreasing
solvent emissions. Some aspects
to look for are:
• Attached sliding cover.
Actual measurements of operating equipment show that an
idling covered machine will
have 15-20 percent less emissions than a machine left
uncovered. Attached sliding
covers are best, not only for
convenience, but also because
by moving horizontally, it does
not create disturbance of the
vapor/air interface and thereby
reduces emissions. Vertical liftoff and hinged covers, when
opened cause disturbances in
the interface by creating turbulence within the machine and
increasing solvent emissions.
• 100% freeboard. The greater
the distance between the top
of a stable vapor/air interface
and the top of the unit, the
greater the diffusion distance
that solvent vapors must travel
to escape the machine. Measurement has shown that the
diffusion losses from a 75-80
percent freeboard unit are
15-20 percent higher
than 100 percent freeboard.
• Coolant flow meter/tempera-
ture sensor. Solvent emissions
can occur through failure of the
cooling coils, which would be
caused by either insufficient
coolant flow or inappropriate
coolant temperature. A coolant
flow meter and a temperature
sensor should be designed into
the equipment to shut down
the heaters immediately if
either condition should occur.
Such safety devices prevent
emissions.
• Low liquid level float. Once
the liquid level in the boiling
sump of a solvent cleaner falls
low enough to expose the
heating elements, the temperature of the elements could
rise to the point where solvent
decomposition could take
place causing an acid condition. That contaminates the
remaining solvent, which
requires disposal as hazardous
waste. A liquid level float would
guarantee a minimum level
of solvent above the heating
elements.
Some cautions
• Lip vent exhausts actually
create drafts over the top of
the machine. This device draws
air across the top of the solvent
cleaner, which acts as a
vacuum to draw additional
solvent vapor out. As much as
20 percent more solvent will
be consumed by a system with
a lip vent exhaust.
• Carbon adsorption systems,
fed by the lip vent exhaust,
collect solvent escaping the
machine. Since the lip vent
increases emission by 20
percent, the carbon adsorption
system must be efficient
enough to recover this additional solvent if it is to be
advantageous. However, a
major weakness of the lip
vent carbon adsorption systems is that they are effective
only on the solvent they see.
If liquid solvent is being
dragged out of the machine,
then the lip vent exhaust
and carbon adsorption would
provide limited benefit.
• Sprays are a commonly
accepted part of the cleaning
process, but they aggravate solvent emissions and should be
avoided when possible. If sprays
are required, they should be
used under the vapor blanket
with fixed spray manifolds
angled downward. An uncontrolled hand-held spray will
increase emissions significantly
above the manifold spray.
Equipment Maintenance
Where solvent cleaning equipment is placed and how it is
maintained are important factors
in solvent emission control.
• Leaks. All joints should be
checked for tightness routinely
to ensure no solvent is leaking.
Because the solvent will vaporize, visual inspection often
is not enough to detect leaks.
Proper gasketing material
should be used for the same
reason.
• Location. Avoid placing equip-
ment near drafts, such as from
fans or air conditioners, which
cause disturbances in the
vapor/air interface. Direct
expansion refrigeration systems on cleaners can contribute to emissions through air
movement from the fans used
to cool the compressor. These
drafts can be eliminated with
a remotely-located chiller.
• Maintenance. Solvent loss can
occur from spills when the
degreasing system is cleaned
during routine maintenance.
Avoid this possibility by selecting equipment that includes
features to simplify maintenance, such as clean-out doors
that are easy to use, easily
accessible sump drains, and
pump-out kits.
A Systems Approach
An important step towards solvent emissions management is
treating the solvent cleaning
process as an integrated system
rather than a piece of equipment
operating independently.
A well-designed emission efficient system is comprised of an
environmentally-sound solvent
cleaner and solvent recovery
still, a remotely-located chiller,
and an automated material
handling system, with all pieces
integrated to communicate
with each other for safety and
production efficiency.
Ultrasonic Cleaning
Ultrasonic Cleaning
An automated transport system
is the most effective means of
achieving exact control of the
process speeds and times. That
control reduces solvent emissions dramatically. The proper
process speed attainable only
through automation prevents
the piston effect of displacing
solvent and eliminates drag-out
losses from vapor/air interface
disturbances when workloads
enter or exit the solvent cleaner.
Correct residence time within
the vapor zone and the freeboard
area is achieved with an automated transport system. An
efficient system is easily programmed with exact parameters
for repeatability in the cleaning
process.
A solvent recovery still concentrates contaminants from the
workpiece cleaning in the still
boil sump. This reduces the
need of frequent solvent cleaner
maintenance, which reduces the
chances of spills or leaks. A still
can be hard-plumbed to the
solvent system and waste
disposal drums through the use
of pumps, so all solvent can
be transferred mechanically,
eliminating the need for manual
handling, reducing spillage
opportunity and worker expo-
sure. By concentrating the contaminants in the still, the solvent
cleaner works more effectively.
A remotely located chiller avoids
drafts created by direct expansion systems.
With this system you can minimize solvent emissions while
gaining predictable, consistent
cleaning.
Branson Ultrasonics can help you
with emission control techniques. We are prepared to work
with you to reduce solvent emissions through operation awareness, process control, system
automation, or equipment specifications. We can supply you with
a self-audit to check operations
in your own plant for solvent
emissions Information on the
effectiveness of solvent alternatives on specific applications also
is available from our Cleaning
Applications Laboratory.
For the self-audit Emissions
Checklist, a Solvent Efficiency
Package of equipment literature,
or for a Cleaning Applications
Laboratory form, call us at
203-796-0349 or write to
Branson Ultrasonics Corporation,
Solvent Efficiency Information,
41 Eagle Road, Danbury, CT.
06813-1961.
Solvent Emissions
Ultrasonic Cleaning
Sources of Emissions in the Cleaning Process
Improper Operation Primary cause — Proper operation is inconsistent with human physiology.
Carefully calibrated entrance & exit speeds of parts cannot be achieved by hand.
Solution — Automation provides consistency, proper speed.
Dragout Primary cause — Liquid on parts, inadequate vapor dry phase.
Solution — Automation for reliable timing.
Drafts Primary cause — Disturbances in vapor/air interface caused by currents from heating,
air conditioning, fans from refrigeration units or lip vent exhausts.
Solution — Equipment covers, draft-free environment.
Piston Effect Primary cause — Displacement of vapor/air interface by too rapid movement of parts.
Solution — Slower or regulated entrance/exit speed.
Accidental Emission Primary cause — Failure of cooling coils, vapors escape before heat is shutdown.
Solution — Redundant cooling coil temperature/flow measurement in equipment.
Liquid Waste Primary cause — Acid breakdown contaminates entire sump volume producing
hazardous waste.
Solution — Backup safety features to reduce chance of acid formation, periodic check
of stabilizers in chemistry.
Leaks Primary cause — Routine maintenance cycles.
Solution — Check all joints for tightness, use appropriate gasket material, look for easily
accessible maintenance features in equipment.
Americas
Branson Ultrasonics Corp.
41 Eagle Road
Danbury, CT 06813-1961
T: 800-732-9262
F: 203- 796-2250
www.bransonultrasonics.com
Europe
Branson Ultraschall
Niederlassung der Emerson
Technologies GmbH & Co. OHG
Waldstrasse 53-55
63128 Dietzenbach, Germany
T: +49-6074-497-0
F: +49-6074-497-199
www.branson.eu
Asia
Branson Ultrasonics (Shanghai) Co., Ltd.
758 Rong Le Dong Road
Song Jiang, Shanghai, PRC, 201613
T: 86-21-3781-0588
F: 86-21-5774-5100
www.branson-china.com
Solvent Emissions Control © Branson Ultrasonics Corporation 2013
The Emerson logo is a trademark and service mark of Emerson
Electric Co. Revised and printed in the U.S.A. 5/13
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