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Using Cryogenic
Condensation
to Control Organic
Solvent Vapor Emissions
Source: U.S. Environmental Protection Agency’s 2008 National Emissions Inventory Report
Figure 1. This is a simplified diagram for the various types of air pollution emission sources.
Cryogenic condensation is an established technology for controlling
emissions of organic solvent vapors classified as HAPs and VOCs. This
pollution control technology can help companies meet emission standards
while also bringing operational advantages to a production process.
By Jon Trembley and Oscar Beteta, Air Products
O
rganic solvents are
used in so many ways,
in so many industries
and in so many
applications that it is difficult
to imagine a future without
them. Organic solvents are used
commercially and industrially
as cleaning, degreasing and
sterilizing agents; in chemical
synthesis; and in the production
of surface coatings, inks and
adhesives.
Although organic solvents
have played an essential role
in economic growth since the
industrial revolution, exposure to
a number of these solvents poses
considerations to human health
and environmental sustainability.
According to the U.S.
Environmental Protection Agency
(EPA), organic solvent vapors that
are known or suspected to be
human carcinogens are classified
as hazardous air pollutants
(HAPs), and organic solvent vapors
that are known or suspected to be
highly photochemically reactive
to form ground-level ozone are
classified as volatile organic
compounds (VOCs).
Organic solvents classified as
VOCs and HAPs are regulated
by the EPA through national air
quality standards as part of the
federal Clean Air Act. The EPA
categorizes sources of air pollution
(VOCs, HAPs, etc.) as:
or more than 25 tons of a mixture of
air pollutants a year. State and local
air agencies regulate these point
sources through construction and
Title V operating air permits.
Specific emission requirements
such as how much is allowed to be
emitted per year or what pollution
control technology needs to be
implemented vary considerably
depending upon the air quality of
each area.
Areas classified as non-attainment
zones, which have air quality that
falls below the national standards,
issue more stringent regulations to
control air pollution than attainment
zones, which are areas that are in
compliance with the national air
quality standards.
The federal criterion for point
VOC emissions from all source
sources is the potential to emit more
types across the United States,
than 10 tons of a single air pollutant
as reported by the 2008
National Emissions
Inventory, are illustrated in
figure 2. Figure 3 shows a
model of estimated lifetime
cancer risks reported by the
2005 National-Scale Air Toxic
Assessment based on HAP
emissions from all sources.
Figures 2 and 3 depict the
general location of most nonattainment zones, which are
found along the northeastern
coast, the Gulf coast and the
coast of southern California,
Figure 2. This illustration shows a U.S. density
map of VOC emissions. Legend units are tons per all well-known heavy
square mile per year.
industry areas.
Source: U.S. Environmental Protection Agency’s 2008 National Emissions Inventory Report.
Several technologies
have been implemented,
and more continue to
be developed, to reduce
sources of air pollution and
control the amount of air
pollutants that are released
into the environment. The
latter are commonly known
as air pollution control
technologies and include
flares, thermal or catalytic
incineration, adsorption
and volume concentrators,
Figure 3. A U.S. model shows the estimated
absorption,
biofiltration,
lifetime cancer risk.
membrane
technology,
Source: U.S. Environmental Protection Agency’s 2005 National-Scale Air Toxic Assessment.
• Mobile On-Road Sources.
Cars and trucks.
• Mobile Nonroad Sources.
Aircraft and agricultural
field equipment.
• Nonpoint Sources.
Stationary sources such
as field burning, residential
wood burning and small
commercial sources such as
local dry-cleaners.
• Point Sources. Large
stationary sources of
emissions like those
of power plants, chemical
plants, refineries and other
heavy industrial
facilities.
ultraviolet oxidation, plasma
technology, and mechanical and
cryogenic condensation.
Why Use Cryogenic
Condensation?
Cryogenic condensation is an
effective technology for controlling
emissions of organic solvent vapors
classified as HAPs and VOCs. This
pollution control technology can
help meet emission standards while
also bringing operational advantages
to a production process.
Developed in the 1980s and
well-established across the European
Union, cryogenic condensation is
receiving considerable attention in
the U.S. as a safe, clean and economic
technology for controlling emissions
of regulated organic solvents in
the chemical, pharmaceutical and
biotechnology industries.
Principles of Cryogenic
Condensation
Cryogenic condensation uses liquid
nitrogen to control the emissions of
solvent vapors by taking advantage of
the vapor-liquid equilibrium principle
of multi-component mixtures. That
is, as the temperature of a mixture
is lowered, the saturation capacity
of the carrier gas decreases, causing
the concentration of components in
the carrier gas to decrease as they
condense into liquid droplets.
The refrigeration capacity and
low boiling temperature (-320°F or
-195°C) of liquid nitrogen gives these
systems the flexibility to cool down
gas streams from ambient to cryogenic
temperatures, resulting in a wide
range of control of the vapor-liquid
equilibrium of any combination of
solvent mixtures. Thus, it is possible to
condense and recover practically every
known organic solvent or mixture of
solvents from gas streams at levels in
excess of 99 percent.
Figure 4 shows the equilibrium
gas-phase concentration of common
solvents in gaseous nitrogen, the
carrier gas, at various cryogenic
temperatures. As an example, Figure
4 shows that a gas stream of nitrogen
and dimethylformamide must be
cooled down to -90°F (-68°C) to
achieve an emission concentration
of 10 parts per million by volume
(PPMV) of dimethylformamide. The
graph in figure 4 was generated using
one company’s thermodynamic
modeling software, which
incorporates a proprietary chemical
property database of components
used in the chemical industry.
Although the principle of
condensation is simple, the design
and implementation of cryogenic
condensation systems, with
countless combinations of chemical
components, concentrations and other
process parameters, is not.
Careful design of heat exchangers
is necessary to efficiently control the
refrigeration value of liquid nitrogen,
achieve the levels of emission control
mandated by local air pollution
agencies, and build the flexibility
for systems to adjust to changes in
regulation requirements or process
conditions in the future.
Advantages of Cryogenic
Condensation
When evaluating cryogenic
condensation systems for emission
control of regulated solvent vapors
(VOCs or HAPs), decision makers
should consider the following.
Flexibility. Emission concentration
of solvent vapors can be readily
maintained and controlled by
adjusting the flow rate of liquid
nitrogen into the system.
Nitrogen Recycling Opportunity.
Figure 4. The vapor equilibrium concentration of common organic solvents in
gaseous nitrogen is shown.
Liquid nitrogen used in indirect
contact heat exchangers is
uncontaminated and can be reused
for applications such as blanketing,
purging and pneumatic control.
Additionally, existing liquid nitrogen
storage, if normally vaporized before
use, can be tied-in to the cryogenic
condensation system to make use of
its refrigeration value.
Solvent Recycling Opportunity.
Depending on the composition and
emission requirements of the solvent
gas stream, the system can produce
pure or nearly pure condensate
streams, creating a recycle stream for
improving process economics or a
revenue stream that can be sold.
Compliance. Cryogenic
condensation systems have achieved
the lowest emissions limits mandated
by the European Union. These
A low-temperature heat exchanger with intermediate fluid is shown. Careful design
of heat exchangers is necessary to efficiently control the refrigeration value of
liquid nitrogen and achieve the levels of emission control mandated by local air
pollution agencies.
emission limits are generally more
stringent than those mandated by
the EPA, though it is expected that
U.S. environmental regulations will
become tighter in the future.
Reliability. Systems are built
with few moving parts, the bulk of
which are the automated control
valves. If correctly designed and built,
these systems are known for low
maintenance costs and high reliability.
Low Power Consumption. The
majority of the power is consumed
by the control system (control panel,
instrumentation, etc.).
Although, in principle, nearly all
organic solvents can be recovered
via cryogenic condensation,
implementation of systems worldwide
suggests that the technology is most
economic when gas stream flow rates
are below 1,000 standard cubic feet
per minute (SCFM), solvent vapor
concentrations are above 1,000 PPMV,
and the required temperature to meet
the emission limit is below -40°F
(-40°C). However, each individual case
should be reviewed for technical and
economic feasibility.
While, at times, purity
requirements hinder the opportunity
to do so, solvent recovery and reuse
by means of cryogenic condensation
systems remains a significant area of
opportunity for many users of organic
solvents today.
The application of liquid nitrogen in
the world of cryogenics is far reaching.
Cryogenic condensation technology
for controlling emissions of regulated
organic solvent vapors (VOCs or HAPs)
is not confined to special applications.
It is an established technology that
can meet emission standards while
bringing operational advantages to a
production process.
It is certainly true that some
companies have achieved significant
commercial benefits by substituting
heavily regulated substances, such
as organic solvents, with alternatives,
such as water-based solvents, freeing
themselves from strict regulatory
pressures. Clearly this practice should
be encouraged; however, organic
solvents continue to be an integral
part both directly and indirectly
of the manufacturing process that
produces the wealth of consumer
products and services we enjoy today.
As such, innovative technologies
such as cryogenic condensation for
pollution control are paramount to
continue promoting economic growth
while maintaining environmental
sustainability. PC
Jon Trembley is a technology manager
for global cryogenic applications at Air
Products, Basingstoke, United Kingdom.
Oscar Beteta is an industrial cryogenic
applications engineer at Air Products,
Allentown, Pa. The company can be
reached at 610-481-4911 or visit
www.airproducts.com.
Air Products and Chemicals, Inc.
7201 Hamilton Boulevard
Allentown, PA 18195
T 800-654-4567 or 610-706-4730
gigmrktg@airproducts.com
airproducts.com
312-14-007-US
Cryogenic Condensation In Practice
Cryo-Condap® technology employs a cryogenic condensation system developed
by Air Products in collaboration with Herco Kühltechnik, an innovative German
cryogenic equipment supplier. The core of the system is a heat exchanger design
that uses an intermediate fluid to enhance heat transfer control between liquid
nitrogen and the solvent gas stream (see Figure 5). In many cases, the cryogenic
temperature of liquid nitrogen is so close to the freezing point of the solvent
mixture that, in conventional indirect heat exchangers without intermediate heat
transfer fluids, components do not condense, but rather freeze, fouling the heat
exchanger and causing loss of control and performance.
However, the heat exchanger design of the Cryo-Condap system is such
that liquid nitrogen does not directly transfer heat with the solvent gas stream.
Instead, liquid nitrogen transfers heat directly with an intermediate fluid,
typically R507, which then transfers heat directly with the solvent gas stream.
The temperature of the heat transfer fluid can be easily adjusted by controlling
the flow rate of liquid nitrogen to achieve emission limits without fouling
the heat exchanger. Additionally, the heat transfer fluid acts as a buffer to
maintain consistent solvent emission concentrations when production process
conditions fluctuate, a common occurrence in most pharmaceutical and chemical
manufacturing processes.
Air Products and Herco have worked to develop sizing and modeling software
for the complex process analysis needed to design Cryo-Condap systems. One
of the main objectives in the design is to minimize nitrogen consumption and
maximize energy efficiency. As a norm, the heat exchangers are designed to use up
to 95 percent of the available enthalpy of liquid nitrogen.
The Cryo-Condap technology has been applied across a diverse range of
industries. Since the late 1980s, Air Products has installed over 150 Cryo-Condap
systems worldwide.
The first application was in the production of magnetic tapes by a major
German chemical company. Since then, systems have been sold into a variety
of industry sectors including ethylene oxide for sterilization, solvent coating,
fine chemical and pharmaceutical manufacturing, and freon recovery from
refrigerator recycling.
The technology has also found diverse applications in the chemical industry,
where low investment costs and the opportunity to reuse the nitrogen create
significant opportunities.
Solvent-using pharmaceutical and fine chemical businesses have also begun
to appreciate the benefits of cryogenic condensation above other means of air
pollution control, particularly where they have reduced operating costs by
reusing the nitrogen on-site. Relatively few, however, have yet capitalized on the
opportunity to reuse or resell the recovered solvents.
Looking ahead
Air Products is at the forefront of innovative solutions to the ever-changing
emission control requirements faced by industry. For example, a new patented
heat exchanger has been designed where liquid nitrogen is directly injected and
mixed with the solvent gas stream to form solvent ice particles, as opposed to
condensate, which are recovered using a filtration technology especially adapted
for cryogenic use.
The system was developed to meet and exceed the most stringent air emission
standards, and several units have already been installed in Europe. The system is
best suited for low solvent gas flow rates up to 190 SCFM.
Reprinted with permission from Process Cooling, January 2014 © 2014, BNP Media.