Introduction to Pollution Control

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 can be found in the Definitions section.  Be sure to visit the Overview of Emission Control Technologies page once you are comfortable with the introdution found here.

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.

Answers to the questions below are broken down into manageable sections. You can jump ahead at any point, but each section is fairly brief.

• What is the difference between ACFM and SCFM? How are they calculated?
• 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

What is the difference between ACFM and SCFM? How are they calculated?

ACFM and SCFM are units for volumetric airflow rates.
ACFM = Actual Cubic Foot per Minute
SCFM = Standard Cubic Foot per Minute
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 70F and 1 atmosphere pressure.

For example: Convert ACFM to SCFM

5,000 ACFM of air at 230F and 1 atm 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) 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 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.

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.

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.

Temperature:	Based on the VOCs that need to be destroyed there is a temperature at which the compounds can be oxidized.
Time:	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:	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.

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.

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

Basic Definitions

Catalyst:	Substance that increases the rate of a chemical reaction without itself being consumed in the reaction.
HAP:	Hazardous Air Pollutants, cancer-causing compounds.
Hydrocarbon:	Compound found in all organic compounds. It is the bond that is broken during oxidation.
Incineration:	Also known as oxidation.
LEL:	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.
Recuperative:	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.
Regenerative:	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.
Rotor Concentrator:	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.
SCFM:	Standard Cubic Feet per Minute. Flow conditions at standard conditions; usually defined at 70º F, sea level and one atmosphere.
VOCs:	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 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.