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
This guide will provide a general overview of air pollution
control. It will also help you understand the various pollution
control technologies and prepare you to make informed,
knowledgeable decisions. All defined terms can be found in the
Definitions section. Be sure to visit the Overview of
Emission Control Technologies page once you are comfortable
with the concepts discussed here.
Before we begin, it is important to point out that many
distinctly different industries have very similar pollution control
challenges and also solutions. It is our goal at Anguil to utilize
our experiences in every industry to help customers apply the
proper technology on their specific application. Always feel free
to contact an Anguil Representative near you to
discuss your unique destruction requirements, efficiency demands
and process parameters.
Answers to the questions below are broken down into manageable
sections. You can jump ahead at any point, but each section is
- What is the difference between Actual Cubic Feet per Minute
(ACFM) and Standard Cubic Feet per Minute (SCFM)? How are they
- What are Volatile Organic Compounds (VOCs)?
- What are Hazardous Air Pollutants (HAPs)?
- What is thermal oxidation and how is it different from
- How do I decide which technology to use?
- Basic definitions
What is the difference between Actual Cubic Feet per Minute
(ACFM) and Standard Cubic Feet per Minute (SCFM)? How are they
ACFM and SCFM are units for volumetric airflow rates often used
in determining size of an air pollution control device or energy
ACFM is a measure of the actual volumetric air flow rate at the
conditions of the air stream. The density of air varies with
temperature and pressure. SCFM is a measure of the volumetric flow
rate if the air stream were at standard conditions. Standard
conditions are defined as 70°F and 1 atmosphere pressure. For
metric users, ACFM is the equivilant of m3/hr (cubic
meters per hour) and SCFM correlates to Nm3/hr (normal
cubic meters per hour). Nm3 equals SCFM divided by
1.71928, dividing that number by 60 will then give you per minute
comparison of feet and meters.
Here is how you would convert 5,000 ACFM of air at 230°F and 1
atmoshperic pressure to SCFM. The ideal gas law tells us
the relationship between air temperature and air density is
directly proportional. Therefore we can convert ACFM to SCFM using
the temperature ratio (absolute temperature).
SCFM = ACFM * (standard condition absolute temperature) /
(actual absolute temperature)
SCFM = 5,000 * (70 + 460) / (230 + 460)
Therefore 5,000 ACFM of air at 230°F and 1 atm = 3,841
SCFM. The equation can be rearranged to convert SCFM to ACFM.
The ideal gas law also tells us that pressure and temperature
are directly proportional. A similar conversion is used to adjust
to standard pressure.
What are Volatile Organic Compounds (VOCs)?
Let's begin by defining the organic compound part of Volatile
Organic Compounds (VOCs). Organic compounds 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
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 (forms a gas) at room temperature and
normal atmospheric pressure. An example of this would be the fumes
you see on gas pumps without a vapor recovery nozzle. 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; however, many of the
volatile compounds play a significant role in the formation of
ozone and smog.
Ozone is three oxygen atoms bonded together to form O3. It does
occur naturally in our environment 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
The best way to prevent the increase in ozone and smog is to
eliminate these harmful VOCs from being released. Anguil's oxidation
technologies are designed to do just that.
What are Hazardous Air Pollutants (HAPs)?
A Hazardous Air Pollutant (HAP) is a VOC 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 thousands of cancer deaths each 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.
What is thermal oxidation and how is it different from
At the heart of most emission destruction technologies is a
concept called 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. In scientific
terms, the process is:
Cn H2m + (n + m/2) O2 → n CO2 + mH2O
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, which is 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.
Destruction temperature is determined by the the VOCs in the
airstream. Each compound has a different temperature at which the
molecules are broken apart and oxidized.
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.
Turbulence is a fixed condition built into the equipment design.
It ensures a proper mixture of VOCs and oxygen for combustion.
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.
Metal heat exchangers can also be added to thermal and catalytic
oxidizers to recover or recup between 50% and 75% of the heat
required for oxidation. Another system advance is the Regenerative
oxidizer, which uses ceramic heat recovery media to capture and
reuse 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.
How do I decide which technology to use?
In general, the selection process is dependent on these three
- 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
Actual Cubic Feet per Minute. Flow conditions with temperature
and atmospheric conditions accounted for.
||Substance that increases the rate of a chemical reaction
without itself being consumed in the reaction.
Hazardous Air Pollutants are VOC emissions with additional
Compound found in all organic compounds. It is the bond that is
broken during oxidation.
Also known as oxidation but generally refers to solid waste
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.
An oxidation technology (thermal recuperative or catalytic
recuperative) that uses a plate, shell and tube, or other
conventional type of metal 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.
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%-97%+ of the heat generated by oxidation.
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
Standard Cubic Feet per Minute. Flow conditions at standard
conditions; usually defined at 70º F, sea level and one
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).
Emission Control Technologies
A VOC Handbook.
By Gene Anguil / Founder & CEO of Anguil Environmental
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.