Has a regulatory agency announced regulations in your industry
or declared your workplace unhealthy? Do your neighbors complain
about odors? Do you face the dilemma of balancing company
profitability with the demand to meet environmental
requirements?
This quick guide will explain all the basics of pollution
control. It will help you understand the technologies and prepare
you to make informed, knowledgeable decisions. All defined terms
will be highlighted in blue and can be found in the Definitions
section.
The first concept to recognize is that many distinctly different
industries have similar pollution problems and solutions. Once you
understand the basics, then we can help you begin to decide which
is the best for you. Always contact an Anguil representative to
discuss particular applications and solutions. For now, all that
you need to know is that hazardous air pollutants (HAPs) and
Volatile Organic Compounds (VOCs) are, in fact, harmful to you and
the environment. There are hundreds of science journals and EPA
documents that can explain why toluene, ethanol, and other organic
compounds are bad for your health, but for our purposes, we just
need to know that they are.
The lessons are broken down into manageable sections. You can
jump ahead at any point, but each section is fairly brief.
- What are Volatile Organic Compounds (VOCs)?
- What are Hazardous Air Pollutants (HAPs)?
- What is oxidation?
- How do I decide which technology to use?
- Basic definitions
- All you wanted to know about Emission Control Technology
What are VOCs?
First of all, let's define the organic compound part of Volatile
Organic Compounds (VOCs). Organic compounds are compounds that
contain carbon and hydrogen. They occur naturally and can be found
in all living things, but the majority of the organic compounds
that we use are man-made.
Some organic compounds are liquids that require an additional
process like heating or cooling to create vapor, these are
considered stable compounds. An organic compound is considered
volatile if it vaporizes (a gas) at room temperature and normal
atmospheric pressure. (Think of the fumes you see on gas pumps
without vapor recovery nozzles.) Some of these vapors are dangerous
to humans when inhaled in great quantities or over a long period of
time. Some volatile organic compounds interrupt and destroy natural
plant processes. But many of the volatile compounds have a much
more complicated effect: they lead to the formation of ozone and
smog.
Ozone is three oxygen atoms bonded together to form O3. Ozone
occurs naturally, but the introduction of large amounts of VOCs
into our lower atmosphere (the air closest to us) has caused an
unhealthy amount of ozone to be created. Oxygen + VOCs + Sunlight +
Combination of complex reactions lead to the formation of
ozone.
In the earth's upper atmosphere, ozone is an important layer that
protects the earth from the sun's ultraviolet rays. But closer to
the earth, ozone is a dangerous compound. It mixes with other
compounds in the air and becomes the main component of smog.
Smog is more than an ugly brown cloud hovering over the cities
of the world. Smog causes respiratory ailments and heart
conditions; it destroys agriculture and forests. In short, smog
damages our entire environment.
The best way to prevent the increase in ozone and smog is to
eliminate these harmful VOCs from being released. Anguil's
oxidation technology is designed to do just that.
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What are HAPs?
A Hazardous Air Pollutant (HAP) is a Volatile Organic Compound
that has additional harmful properties. The effects of HAPs are
even more severe than VOCs. According to the U.S. Environmental
Protection Agency, HAPs cause 1,000 to 3,000 cancer deaths a year
in the U.S. They can cause birth defects, nervous system damage
and, during massive accidental releases, death.
HAPs also cause serious environmental damage. Fortunately,
pollution control technologies can capture and destroy HAPs before
they are released into the atmosphere. Again, the most effective
destruction of HAPs and VOCs is accomplished by oxidation.
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What is oxidation?
At the heart of most pollution control technologies is a concept
we all learned in our early chemistry classes. That concept is
oxidation; it causes compounds (in this case, contaminated air
pollutants) to be broken up and reformed into new (in this case,
safe) compounds. Add the right amount of heat and oxygen to
hydrocarbons and you create oxidation. (To be scientific, the
process is:
Cn H2m + (n + m/2) O2 → n CO2 + mH2O + Heat )
In the thermal oxidation process, the contaminated air is
heated, breaking apart the bonds of the contaminated compounds. The
molecules will reform naturally, bonding into carbon dioxide and
water vapor and releasing energy, the basic premise to all forms of
oxidation. However, during catalytic oxidation the contaminated
compounds in the air react with a catalyst material (platinum,
palladium, rhodium, etc.) which breaks apart the contaminated
compounds at a lower temperature.
Thermal oxidation requires high temperatures to break apart the
compounds. The large amounts of fuel needed to maintain high
temperatures can be expensive. Different pollution control
technologies help reduce the operating costs of the equipment.
Catalysts, for example, react and oxidize the VOCs at a lower
temperature, meaning less fuel and lower costs.
No matter which oxidation technology is best suited for your
application, the "three T's" of oxidation always apply:
Temperature, Time and Turbulence.
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Temperature:
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Based on the VOCs that need to be destroyed there is a
temperature at which the compounds can be oxidized.
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Time:
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Time relates to how long a compound needs to be at a certain
temperature in order for it to be oxidized. For example, benzene
requires a temperature of 440ºF and a residence time of 0.24
seconds for 99% destruction in a catalytic oxidizer. In a thermal
oxidizer, benzene needs 1460ºF and a residence time of 1.0 seconds
for 99% destruction.
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Turbulence:
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Turbulence is a fixed condition built into the equipment design.
It ensures a proper mixture of VOCs and oxygen for combustion.
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A successful technology achieves full oxidation of VOCs by
maintaining the proper mixture of oxygen and contaminants at the
required temperature for a sufficient amount of time.
Recuperative heat exchangers can also be added to thermal and
catalytic oxidizers to recover between 50% and 75% of the heat
required for oxidation. Another system advance is the Regenerative
oxidizer, which uses multiple ceramic chambers to recover as much
as 95% to 97%+ of the heat from oxidation. The Rotor Concentrator
is another unique approach to reducing long-term costs. By
absorbing and then desorbing or concentrating the VOCs into a
smaller airflow, the Rotor Concentrator allows for the smallest
oxidizer possible.
The secret is to determine which technology works best and most
cost effectively in each application.
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How do I decide which technology to use?
Don't be too overwhelmed, here are the basics.
In general, the selection process is dependent on these three
criteria:
- Airflow (SCFM or Nm3/hr)
- Contaminants (VOCs) in the airflow
- Concentration of contaminants in the airflow (Also called the
percent Lower Explosive Limit / %LEL)
After the rate and content of your exhaust airflow are analyzed,
the proper technology selection can be made. Hopefully the
explanations above and definitions below will help you to better
understand your application. If we can answer any questions
about this material or your application, please contact Anguil
Environmental Systems
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Basic Definitions
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Catalyst:
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Substance that increases the rate of a chemical reaction without
itself being consumed in the reaction.
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HAP:
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Hazardous Air Pollutants, cancer-causing compounds.
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Hydrocarbon:
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Compound found in all organic compounds. It is the bond that is
broken during oxidation.
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Incineration:
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Also known as oxidation.
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LEL:
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Lower Explosive Limit. The VOCs in your airstream have a known
explosive limit. The explosive limit is the lowest organic
concentration in a stream that would yield a combustible mixture in
the presence of an ignition source. It is an essential factor in
characterizing your process stream.
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Recuperative:
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An oxidation technology (thermal or catalytic) that uses a
plate, shell and tube, or other conventional type of heat exchanger
to heat incoming air with air from the oxidation process.
Recuperative systems can often recover 50% to 75% of the heat
generated by oxidation.
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Regenerative:
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An oxidation technology that uses two or more ceramic heat
transfer beds that act as smaller heat exchangers and a retention
chamber where the organics are oxidized. It can often recover
90%-95% of the heat generated by oxidation.
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Rotor Concentrator:
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An oxidation technology add-on that reduces air volume and
increases VOC concentration. The process stream flows through a
continuously rotating wheel impregnated with adsorbent. Here the
VOCs are adsorbed and the clean air is exhausted into the
atmosphere. The wheel is then regenerated by passing through a
stream of warm, low volume desorption gas that produces a
concentrated stream that can be more efficiently destroyed by an
oxidizer.
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SCFM:
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Standard Cubic Feet per Minute. Flow conditions at standard
conditions; usually defined at 70º F, sea level and one
atmosphere.
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VOCs:
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Volatile Organic Compounds: Organic chemicals that exist as
vapor in air and that react in the atmosphere with nitrogen oxides
in the presence of sunlight to form ozone (O3).
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Emission Control Technologies
A VOC Handbook.
By Gene Anguil / Founder & CEO of Anguil Environmental
Systems, Inc.
This handbook was originally written by Gene Anguil as a chapter in
the Odor and VOC Control Handbook by Harold J. Rafson
(Editor). It has recently been updated for publication on our
website to reflect technology advances and terminology changes.