Purchasing the Correct Air Pollution Control Technology
VOC Concentrators - Thermal Swing Regeneration Adsorption

Concentrators are used as an emission control device to allow higher volumes of waste gas to be collected on an adsorbent for future destruction.
Concentrators allow the lower concentrated VOC's to be collected and then exhausted at smaller volumes at higher concentration levels. Generally,
concentration levels are operated around ten times the waste gas concentration, but this value may be increased depending on the application.
Therefore by using a concentrator many thermal oxidizer systems are allowed to operate without or with minimal amounts of auxiliary fuel. Concentrators
reduce the operating cost by loading the VOC's at a higher concentration. The concentrated volume from the
VOC Concentrator reduces the size of the
oxidation equipment.

VOC's in the waste gas stream are first processed into one of the adsorption units (two are usually used, but any number above two may be used), while
one of the adsorption beds is being thermally regenerated. Hot air flows into the adsorption unit; this process heats the captured VOC's and thus
desorption or boiling off the VOC's occurs. The condensed VOC vapor may now be processed to the thermal oxidizer for thermal destruction at a higher
concentration rate, lower flow rate and higher inlet temperatures. This process reduces the amount of auxiliary fuel required to sustain the set point
destruction temperature of the system.

After the VOC are released, cooling air from a blower is admitted in place of the heated air. When the adsorbent has cooled to ambient conditions, the
“conditioned” adsorption capacity has been restored, and the adsorption bed is now considered regenerated. Regeneration equipment may be designed
to occur between one and eight hours depending on the size of adsorption equipment.

Granulated Activated Carbon Systems

Granulated Activated Carbon Systems or  vapor phase voc canisters are designed for a economical cost effective approach to air or vapor
treatment
for short or long term emission applications. Systems generally contain all of the necessary requirements for use as an effective VOC
emissions control system for air or
vapor phase process treatment applications.

All
GAC Systems include a secure carbon bed support across the entire canister lower sectional area which creates a plenum region below the support
area for proper inlet distribution across the carbon bed. These carbon canisters are generally constructed of
unlined carbon steel or T304 stainless
steel
, angle iron supports are used to support the perforated screens used with activated carbon during air treatment. Most GAC vapor phase carbon
adsorption canisters are designed for
treatment up from 10 to 2000 cfm. The vapor phase GAC adsorption units provided a wide variety of vapor
phase activated carbon products that can be specific for your air or vapor treatment application. These systems provide a very low cost, effective method
of  treating small quantities of vapor phase VOC's.

VOC Air Stripping - Tray Aeration Treatment

Contaminated VOC water is generally pumped into an inlet chamber where it flows over distribution weirs and along the aeration trays located inside the
air stripper unit. The filtered ambient air from outside the stripper unit is blown into the fluid process with sufficient pressure to push the filtered air up
through the aeration holes located on the aeration trays. As the air flows upward through the water, bubbles are created which forms froth. This
froth
increases the surface area of the treatment water which allows mass transfer of the VOC contaminates from the water to the exhaust
stream
. The stripped off gas and air continues upward and is blown out the top of the air stripper unit for discharge to an additional post treatment
device the finished water flows down to the bottom of the air stripper unit where it is
collected and pumped to the waste water distribution system.

Operation of the aeration tray system also may cause oxidation of metals and formation of scaling from the water hardness. The concentration of
this depends on the water supplied to the air treatment system. Once formed, the metals formation and scaling eventually cause fouling of the trays and
require periodic cleaning.
Periodic cleaning of the trays is accomplished by accessing ports on the system with a washing wand or high-
pressure washer
. More thorough cleaning requires that the trays be removed completely. Spare trays can be provided to allow continued operation
during cleaning.

Solvent Recovery Systems

Adsorption technology is the physical attachment of VOC ions and molecules onto the surface of another. The essential principle of adsorption
when pertaining to plant waste gas emission control is when the volatile organic compound within the process air stream passes through a bed of very
high surface area solid which usually consist of the following materials; activated carbon, silica gel, or molecular sieve material.

Once the empty spaces within the adsorption material are filled with VOC's to capacity, the waste gas process stream is then diverted to a second
adsorption container while the original container removes the VOC bonding by passing high pressure stream or by raising the temperature within the
adsorption container by thermal induction releasing highly concentrated VOC's. The highly concentrated volatile organic compounds within the air stream
passes through a condenser and a distillation column whereby it is separated and recovered from the VOC laden process stream condensate.

Alternative solutions to applying use of a condenser and distillation column is to exhaust the saturated VOC's to a thermal oxidizer during
non-peak times, when the thermal oxidizer is not heavily used and can operate with higher VOC levels
.

Higher investment capital is required with moderate energy cost. Destruction efficiencies range from 95-98% with higher maintenance
costs from replacement or regeneration of adsorption material. Additional distillation is necessary to separate several solvents with the
potential to reuse or sell the solvent.

Right Technology For The Operation

Which one of the listed technologies may best be applied for your application?  Your answer can be difficult depending on the method you take in the
evaluation process. The
best approach is to find a vendor that offers an evaluation of your waste gas process stream and production
requirements and to make recommendations for the best technology.
Most vendors will offer a free evaluation to assist you. Some of the
information is required to make the right decision are listed below:

A.        Total number of emitting sources
B.        Annual hours for each of the emitting sources
C.        Form each source the flow rate, SCFM or M3
D.        Total (lb/hr or kg/hr) of VOC material from each listed source
E.        Composition of the process stream (VOC's, particulates, silicon)
F.        Energy costs
G.        Regulatory requirements for your facility

After collection of the data, a request for quotation (RFQ) can be sent to selected vendors. A vendor should have the appropriate technologies in its
product mix and is willing to stand behind their equipment.

Guidelines For A Correct Equipment Purchase

When evaluating the options, include operating, installation, training, plant control, and equipment capital costs. Capital and operating costs
should be based on the actual utility costs, operational times and annual operating schedules of the plant.

Ask for a document presenting
all the features for the proposed equipment to ensure you are making a correct comparison. Request a
production schedule for the system to ensure that the facility can meet any of your regulatory requirements.

Working with proper data, applying utility costs, facility limitations, regulatory requirements and plant operating schedules all comprise important roles in
determining the correct abatement equipment.
Working with a vendor can greatly assist in making the right product choice.
There are many various types of VOC control technologies in today’s market, but most of them are not right
for your application. Knowing the various principals behind each of the technologies will help you choose the
technology that’s right for your waste-gas application. As Global concerns are increasing at a rapid pace,
and with
more pressure being placed on governmental authorities to create and enforce
regulations that require often higher destruction rates and improved capture procedures of air
pollutants
. Many industries around the world and air pollution control equipment manufacturers are
developing better technologies to meet these growing domestic and international regulations while providing
improvements in air pollution control investment and the associated operating costs.

A diversity of pollution control equipment is currently available, but many manufactures fail at many
technologies and have themselves trapped into splitting technologies into separate equipment.
Pioneering
technologies and system controls are now available to modify the basic emission equipment
arrangement and create many distinct types of air pollution control technologies.

Equipment modifications to your existing equipment should be simple, inexpensive and should be able
to be completed in the field within a few days.
It is significant to understand the options, benefits, and
potential shortcoming of the different air pollution control equipment types.

Biofiltration

Bio Filtration is a method of destroying unwanted hydrocarbons with the use of microbes which are
specifically designed to digest the unwanted hydrocarbon structures emitted in the off-gas process. These
microbes may be designed to work in conjunction with a granulated carbon system to produce a very high
destruction efficiency. These efficiencies commonly reach 99
+%. The major benefit of a Bio- filtration
system
is the reduction in operating costs such as fuel and electricity. The maintenance on this type of
equipment is reduced due to fewer operating parts. Insurance is also reduced over normal thermal oxidation
equipment due to the inability of the equipment to generate a fire. Although, this technology
is not a
panacea to all off-gas emission control it has a very high value to VOC and Sulfur compound remediation.  

Thermal Oxidation

These applications are most often used to convert organic hydrocarbons into carbon dioxide (CO2)
and water (H2O)
. By increasing the thermal temperature of the waste-gas process stream breaking of the
hydrogen-carbon bonds occurs, this process allows new bonds to be created such as CO2 and H2O.
Closed Thermal oxidizers characteristically are designed with a 1 sec or greater total residence time.
Residence chamber time is the time the waste process stream is contained within the heated area and is
critical for proper mixing.
Often oxidizer designs fail to complete the proper mixing in the retention
time frame and additional fuel must be burned to meet the permitted values
.

Regenerative Thermal Oxidizer

Regenerative systems are thermal oxidizers operate at high temperatures, between 1400°F to 2,300°F.
These systems use structured
ceramic stoneware or other heat exchange media to retain the
generated thermal energy. In most designs, the media is mounted in vertical or horizontal columns. The
process air stream is passed through a column of ceramic media as it enters the regenerative thermal
oxidizer.

The waste-stream is heated to the oxidation temperature within the combustion chamber and if the process
stream doesn't have ample VOC's a burner assists in bringing sufficient temperature to the combustion
chamber.

Typical temperatures of VOC waste streams of hydrocarbons range from 1400°F to 1600°F,
however higher temperatures and retention times are required for halogenated hydrocarbons 1800°F to
2200°F. The waste air stream then exits the oxidizer through a second media column. The second column
maintains or stores energy from the hot air stream.
By continued valve cycling the waste-gas air
stream switches between the heat sink columns or heat recovery beds
, by this process the
incoming air stream is heated by the heat sink media, which in the previous cycle accepted the heat from the
waste-gas air stream exiting the combustion chamber.

When the heat recovery bed starts to lose radiant heat to the incoming air stream, the valves
cycle and becomes the other heat recovery bed becomes the acceptor of energy or heat
,
continued repeating of the valve cycle assures minimum heat lose. For greater heat retention within the heat
recovery chambers the valve cycle rate is increased. The principle is simple and proven.

Regenerative Thermal Oxidizers can be designed with more than two heat recovery beds or columns.
Some of the regenerative equipment characteristics are
moderate capital equipment costs with high
thermal efficiency
. Destruction is high typically 98%-99% with lower energy costs. Loss through
radiation is slightly higher due to the large surface area, however radiant heat loss can be controlled by the
use of high density 12lb. or higher ceramic fiber insulation. Most applications include lower VOC levels with
higher waste-gas flows.
Systems can be skid mounted for quick and effective installation, start-up
and training times
.

RTO systems have materialized as the leading air pollution control technology because of their
very high heat recovery, which produces an outstanding operating cost advantage
in comparison
to other technologies while
maintaining high flexibility for many types of waste gas processes. Typically
these systems are larger, requiring greater installation work, unless the system is skid mounted.

Development efforts have focused on compact, modular and cost-effective Regenerative
Thermal Oxidizers for the VOC market
. These systems can be modular skid mounted and designed to
ship as completed assemblies with width dimensions that will comply with commercial trucking laws
without
special shipping considerations or wide-load road permits
.

Regenerative Thermal Oxidizers
can be completely assembled, including all control systems, piping,
conduit and electrical wiring
. This assembly minimizes the installation costs and efforts while maximizing
quality control over the product. Oxidizers that are assembled may undergo
simulated run conditions,
control systems check out and calibration prior to shipment, diminishing equipment operation
and control failures at the plant site
. This allows for a shorter installation, startup and training times
without the risk of equipment failure.

Regenerative Thermal Oxidizers are currently designed with minimal captured volume for design destruction
efficiency 98% without the capturing of the VOC's being exhausted during any valve switch period.
Most
regenerative systems are constructed to accept optional VOC capture vessels called puff
chambers when destruction efficiency requirements exceed 98%
. The equipment design will permit
regenerative oxidizers to be upgraded in the field with insignificant costs and time.

Regenerative Catalytic Oxidizers

Regenerative catalytic oxidizers are similar in design to the regenerative thermal oxidizer. The addition of
catalyst media to either the center of the media or the top of the media beds allows lower
operating temperatures 400F to 800F
. Depending on component design, Regenerative Catalytic
Systems may also can be operated as a Regenerative Thermal Oxidizer after catalyst degradation.

Systems have
small or no NOx formation, low levels of CO emission, very low operating costs with
high thermal efficiency
. Caution must be used not to foul or plug the catalyst heat bed and more stringent
PLC control must be used. These systems have
higher capital costs due to the metallic catalytic
media but reduce the energy consumption up to 50%.

Catalytic Oxidizers

Catalytic oxidizers are alternatives to other high temperature thermal oxidizers. These systems oxidize waste
gas streams into carbon dioxide and water. Their successful operation is
limited to a more controlled
range of applications
than other thermal oxidizers. But, catalytic oxidizing systems offer considerably
lower fuel consumption
, operating costs and lower CO and NOx emissions. The two essential parts of the
equipment are; pre-heat section which is designed to achieve a temperature uniformity of the preheated
waste stream, and the catalyst bed, where the greater part of the oxidation reaction takes place. The
oxidation of most hydrocarbons with the catalysts occurs very quickly in the range of 400-900F.

Catalytic oxidizers are
restricted to applications in which the waste stream has lower particulate
loading or “media poisons”
which can cause reductions in the effectiveness of the catalyst. Typical
poisons are principally
silicon and phosphorus, which cover the catalyst; halogens harm the active
metal coating; and sulfur, may reduce the activity of some catalysts.
Attrition, deposition, coking can
cause the media surface to become damaged and replacement is necessary.
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Buying a Regenerative Thermal Oxidizer
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Activated Carbon Absorption Treating VOC's
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Reducing Costs of VOC Abatement
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Different Types of Thermal Oxidizers
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The Correct Air Pollution Control Product

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Regenerative Thermal Oxidizer 80,000 cfm
Filtercrobe Granulated Activated Carbon System
ReGen Series Regenerative Thermal Oxidizer 25,000 cfm
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Thermal Swing Adsoprtion System