Download the complete ICAC Publications List and Order Form (pdf) (last updated November 2012)
- HCl CEMS Measurement Whitepaper
- Mercury Assessment Whitepaper
The ICAC Publications List is divided up into the following sections:
Return and Shipping Policy
2011 ICAC Air Pollution Control Equipment Market Forecast Released
ICAC has released its 2011 U.S. Market Forecast which analyzes market trends for stationary air pollution control equipment. The forecast summarizes the technological, regulatory, and general market influences driving the procurement of ESPs, fabric filters, NOx controls, VOC controls, FGD systems, CEMS and utility reagent (ammonia, urea, lime, limestone, activated carbon) usage annually through 2014. This forecast is free to ICAC regular members, $950 for ICAC associate members, and available for $2,300 to the public. To order, please contact the ICAC office at (202) 367-1114.
Mercury, Multi-Emissions & CO2 Management Workshop: Policies, Technologies & Marketplace Implications Workshop
ICAC co-hosted the "Mercury, Multi-Emissions & CO2 Management” conference featuring a panel discussion entitled "Innovative Air Pollution Control Technologies for Challenging Applications”. The presentations included:
- SO2 Emission Controls for Small Boilers; Jim Dickerman, Chemical Lime Company
- Sulfur Trioxide Plume Abatement for Coal-Fired Boilers; Vince Albanese, Fuel Tech
- Differences in Specifying Dry ESP and Wet ESP for New Coal-Fired Power Plants; Buzz Reynolds, Wheelabrator Air Pollution Control
- SCR on Lignite Plants, SCR’s Last Hurdle; Jeff van Aaken, Argillon
Please contact ICAC for a copy of the presentations.
ICAC Coal-Gen Pre-conference Workshop Proceedings Now Available:
ICAC is making available 11 presentations from its recent air pollution control workshop in Cincinnati, OH on August 15, 2006. A list of presentations given during the workshop is available at ICAC Coal-Gen Pre-conference Workshop. Workshop sessions included: Mercury Co-Benefit Control, Mercury Specific Control, Mercury Compliance Monitoring, and Preventative Measures for SO3 and Condensible Emissions and Investigating Measurement Issues. The proceedings are available on a compact disc for $50.00. Contact ICAC to place your order. (August 2006)
Forum 05’ Clean Air Technical Strategies Conference & Workshop: Responding to Regulations
ICAC CATS '05: Responding to Regulation provided practical approaches to meeting upcoming requirements to reduce SO2, NOx, SO3, PM and HAPs (mercury, VOCs, etc.). CATS ’05 featured papers providing compliance solutions for multipollutant legislation, CAIR, industrials affected by NOx SIP Call, Hg MACT, and Industrial Boiler MACT. Keynote addresses by high-level policy leaders will address upcoming challenges and opportunities. Over 40 papers and presentations available. To see conference program click here. The proceedings are available on a compact disc. The cost is $105. Click here to order (March 2005)
ICAC Forum '03 Proceedings Available: Multi-Pollutant Emission Controls & Strategies
ICAC is making available 26 papers and 9 presentations from its recent air pollution control conference in Nashville, TN on October 14-15, 2003. For list of the papers and presentations given at the conference, go to ICAC Forum '03. Conference sessions included: Regulatory Overview, Tools for Optimizing Emission Reductions, SCR Operating Experience, PM and Acid Gas Control Approaches, Multi- Pollutant Control Experience, Mercury Control Options and PM Monitoring. The proceedings are available on a compact disc. The cost is $85. To order, click here (November 2003)
Forum 02’: Cutting NOx Forum Proceedings Available
ICAC is making available 31 papers and presentations (mostly papers) from its recent technical conference, Forum '02: Cutting NOx, in Houston, Texas on February 12-13, 2002. The proceedings are on a compact disc. The cost is $85. To order, click here (February 2002)
Bid Specification and Information Requirements and Bid Evaluation Form for Activated Carbon Injection Systems (2010)
The document will assist purchasers of activated carbon injection systems compile information necessary to procure meaningful bids from suppliers of activated carbon injection systems. The document includes bid specification information requirements, a bid evaluation and a sample bid specification. Contact ICAC at 703.812.4811 or Email firstname.lastname@example.org to request a copy of the document. The document is available at no charge to ICAC members and government officials and for $30 to others.
ICAC Updates SCR White Paper (2009)
ICAC has updated its whitepaper, Selective Catalytic Reduction (SCR) for Controlling NOx Emissions from Fossil Fuel Fired Electric Power Plants. The revised whitepaper updates and informs regulators, affected industries and other stakeholders on the advances in SCR technology, management practices and applications in the power sectors. The whitepaper retains its questions and answers format and includes an SCR experience list. Contact ICAC at 703.812.4811 or email@example.com to request a copy of the document. The document is available at no charge to ICAC members and government officials and for $50 to others.
ICAC Updates SNCR White Paper (2008)
ICAC has updated its white paper, Selective Non-Catalytic Reduction (SNCR) for Controlling NOx Emissions. The document provides answers to commonly asked questions such as how to limit ammonia slip, what are the advantages and disadvantages of the technology, what are the reagent quality considerations, and what range of NOx removal is expected. The document not only answers these questions and more, but also includes a partial experience list of SNCR installations by industry category. Contact ICAC at 703.812.4811 or firstname.lastname@example.org to request a copy of the document. The document is available at no charge to ICAC members and government officials and for $30 to others.
Design and Operation of Fabric Filter and Electrostatic Precipitator Hoppers with High Carbon Ash (2007)
This White Paper summarizes the experience of members of the Institute of Clean Air Companies (ICAC) and also provides guidelines for users that are considering process changes that may increase the carbon content of the fly ash. (October 2007) Contact ICAC at 703.812.4811 or email@example.com to request a copy of the document. The document is available at no charge to ICAC members and government officials and for $30 to others.
ICAC NOX Control Installation Timing for Industrial Sources
ICAC has prepared a whitepaper for release that provides information concerning the time needed for the installation of emissions control technologies for industrial sources. The document was developed to provide information to end users and regulators concerning the deployment time of NOx controls that are applied to various industrial categories. The information in the whitepaper can be used as a general guide for the typical time required to complete a typical NOx control project from the initial bidding period through the start-up of the installed control technology. The level of retrofit difficulty and site specific conditions may increase or decrease the time required for the deployment of the control technology. To download a copy of the whitepaper click here (December 2006)
Mercury Control Technologies for the Electric Power Sector are Commercially Available
Despite the lack of any current regulatory drivers for the control of mercury from the electric power sector, technologies are commercially available. SO2 and NOx controls are able to achieve significant reductions in mercury emissions without optimizing them for mercury removal. Other commercially available technologies such as activated carbon injection have emerged even without any regulatory driver. For more information click on, Mercury Control Technology Information (July 2003)
ICAC Releases Case Studies on Rebuild/Replacement Options for VOC Oxidation Equipment
Traditionally, environmental regulations have been the primary driver for the purchase of volatile organic compound (VOC) oxidation equipment. However, new technologies and energy concerns are leading many companies to rebuild or replace existing oxidizers for economic reasons as well. The advantages of rebuilding or replacing older equipment include: lowering energy costs, improving VOC destruction efficiencies, and reducing emissions of other pollutants. For more, click here Options and Incentives to Rebuild/Replace VOC Oxidation Equipment (June 2006)
ICAC Issues Document Summarizing Requirements for Protocol Gases
ICAC has issued a document summarizing the minimum data and information that should be included in a certificate of analysis to ensure meeting requirements of a protocol gas as defined by the U.S. EPA. Ensuring the quality of protocol gases is important in the quantification of emissions, particularly at low emissions levels achieved by today's air pollution control systems and as authenticated by monitoring and measurement systems. To dowanload , click here (February 2003) (pdf)
ICAC Issues Guidance for Estimating Gas Consumption in a Regenerative Thermal Oxidizer (RTO)
Supplemental fuel consumption, typically natural gas, can be a significant consideration for the installation and operation of an RTO. To aid RTO users and others, ICAC has developed a procedure for estimating an RTO's gas consumption. ICAC's guidance contains an overview of gas consumption in an RTO, the energy consumption estimation method, a calculation of thermal efficiency, examples for estimating fuel requirements and costs, and typical information required from RTO suppliers. Click here (.pdf - 203 KB) for the ICAC guidance. Contact ICAC, with questions or comments. (July 2002)
ICAC Drafts Periodic Monitoring Test Method Using Multi- Gas Portable Optical Bench Instruments
ICAC's Emissions Measuring Division has drafted a periodic monitoring test method for determining concentrations of NOx, CO, and O2 in controlled and uncontrolled emissions from combustion sources using fuels such as coal, natural gas, propane, butane, and distillate fuel oils. This test method is for users of a portable instrument which uses optical benches such as non-dispersive infrared and chemiluminescence for CO and NOx measurements, respectively. Oxygen measurements use paramagnetic, zirconium oxide, or galvanic detectors. ICAC is recommending the method for use where an EPA reference test method is not required. The procedure is easy-to-use and may be attractive to smaller sources. The CTM can be viewed on EPA's CTM web site under (see 10/12/99 entry) or Click here to download. (ICAC previously drafted a test method for portable electrochemical analyzers which the U.S. EPA has proposed as a conditional test method, CTM-034. The Multi-Gas Portable Optical Bench Instrument is a companion document to CTM-034) (February 2001)
ICAC Recommends Guidelines for SCR Sampling Systems on Gas-Fired Boilers
ICAC is recommending guidelines for the design and operation of NOx sampling systems used for process control in conjunction with SCR systems on gas-fired boilers. We expect that following these guidelines will help avoid problems such as over-injection of ammonia and poor control. For a copy, click here (.pdf - 95 KB). (October 2000)
Payback Time for CEMS?
EPA's "any credible evidence rule" allows the agency to use any evidence to show that a source is violating applicable emission limits. Find out how using continuous emission monitors (CEMS) can lessen a company's exposure to frivolous assertions of non-compliance. See ICAC's statement (.pdf - 14 KB) for more. (March 1999)
ICAC Issues Recommendations for Monitoring Medical Waste Incinerator Emissions
ICAC's Emissions Measuring Division has prepared monitoring recommendations to assist State implementation of the recently released medical waste incinerator (MWI) emissions guidelines (Subpart Ce of 40 CFR 60). In a white paper entitled Air Emissions Monitoring for Safe and Efficient Medical Waste Incinerator Operation, the Division sets forth these recommendations, and summarizes the need for, and the availability and benefits of, cost-effective continuous emissions monitoring systems for these sources. The ICAC recommendations will help to ensure good combustion at incinerators. Good combustion is key to minimizing dioxin and furan emissions, as well as emissions of carbon monoxide and other (often toxic) incomplete combustion products. By ensuring good combustion, these requirements also will help to reduce supplemental fuel use, and so will lower operating costs and carbon dioxide emissions.
How VOC Controls Can Help Your Bottom Line
Read the ICAC VOC Control Division's thoughts on how you can use add-on VOC controls to comply with clean air rules, and help your bottom-line at the same time. For more information, contact ICAC's Executive Director, David Foerter.
ICAC Releases PM CEMS Bid Specification and Bid Evaluation Guidance Document (2008)
ICAC's PM CEMS guidance doucument is designed to help end users of Particulate Matter Continuous Emission Monitoring Systems to prepare a specification for the solicitation of bids from particulate monitor suppliers. The intent is to provide a foundation for development of a purchase specification that can be prepared directly by the buyer, if desired, to reduce acquisition costs by minimizing or eliminating the need for third party consultants. Contact ICAC at 703-812-4811 or Email: firstname.lastname@example.org to request a copy of the GUIDELINES FOR PREPARATION OF BID SPECIFICATIONS AND BID EVALUATIONS FOR PARTICULATE MATTER CONTINUOUS EMISSIONS MONITORING
SYSTEMS (PMCEMS), which is available at no charge to ICAC members and regulators, for all others $25.
ICAC Releases Guidelines for Evaluating WESP Bid Specifications (2008)
The guidance document discusses how to purchase and compare bids of wet electrostatic precipitator (WESP) equipment for electric power and industrial applications. This guidance will improve the industry-accepted understanding of engineering principles and options for WESP designs, and support technology considerations in the bid-purchase process. Contact ICAC at 703-812-4811 or Email: email@example.com to request a copy of the Bid Specification Information Requirements and Bid Evaluation Form for Wet Electrostatic Precipitators, which is available at no charge to ICAC members and regulators, for all others $25.
ICAC Release PACE-1 Guidelines For Evaluating and Selecting Portable Analyzers for Combustion Emissions Measurement (2007)
The guidance document provides guidelines for purchasing a portable emission analyzer, and help end users specify and obtain analyzers, which best meet their needs. Portable analyzers extract stack gases and measure discrete gas constituents. The guidelines were developed to ease the process of purchasing a portable emissions analyzers and to help customers specify and obtain analyzers to that best meet their needs. The document includes example bid evaluation forms with supporting discussion. Contact ICAC at 703-812-4811 or Email firstname.lastname@example.org to request a copy of the Guidelines for Evaluating and Selecting Portable Analyzers for Combustion Emission Measurement, which is available at no charge to ICAC members and regulators, for all others $25.
ICAC Releases DAHS Specification Guideline for CEMS (2007)
Continuous emissions monitoring systems (CEMS) are widely used to measure emissions of air pollutants. CEMS use data acquisition and handling systems (DAHS). ICAC has released a guideline (ICAC-EM-3) that provides CEMS users with an understanding of the scope of supply DAHS vendors provide, and also gives CEMS users a road map for satisfactory procurement of a DAHS. The 16-page document is available for $25. To order, click here.
ICAC Issues Guidance for ESP Gas Flow Model Studies and Bid Specifications for Opacity Monitors (2004)
The updated Electrostatic Precipitator Gas Flow Model Studies (EP- 7) document provides information on and establishes design criteria for modeling gas flow in ESPs using both physical flow modeling and computational fluid dynamic modeling. The Guidelines for Preparing Bid Specifications and Bid Evaluations for Continuous Opacity Monitoring Systems (COMS) provides guidelines for specifying and collecting information necessary to solicit bids from suppliers of opacity monitoring systems. Copies are available for $20. To order, click here (July 2004)
ICAC Issues Fabric Filter O&M Guidance
ICAC has issued F-3, Operation and Maintenance of Fabric Filters. It provides guidance on proper operation and maintenance of fabric collectors across a wide range of industries. Copies are available ($20). To order, click here. (January 2003)
ICAC Issues Design Guidance for SCR Reactor Structures
ICAC has issued minimum criteria for structurally-sound SCR reactor structures. The cost is $15 each. To order, click here (October 2002)
ICAC Issues New Technical Guideline for Baghouses
ICAC has issued a new technical standard, F-8 Structural Design Criteria for Fabric Filter Casings (11/01). This publication sets minimum criteria for the design of fabric filter casings so that 1) they will be functional and structurally sound under all applicable loads and 2) the basis for the design is uniform industry-wide. The standard is $15. To order, click here (January 2002)
ICAC Updates Terminology for ESPs
ICAC has updated its technical publication ICAC-EP-1, Terminology for Electrostatic Precipitators. ICAC-EP-1 includes common terms related to ESPs and their operation in the U.S. The 20-page document is available for $15. To order, click here (December 2000)
ICAC Releases Calibration Gas Guidelines
ICAC has released technical publication ICAC-EM-2, Guidelines for Specification of Calibration Gases for CEMS and Portable Stack Gas Measurement Instruments. ICAC-EM-2 is designed to assist users of CEMS and portable stack gas measurement instruments in determining, specifying, and collecting information necessary to solicit and analyze bids from suppliers of calibration gases and related gas handling equipment. Copies of ICAC-EM-2 (16 pages) are available from ICAC for $15 (or $10 in quantities of 5 or more). To order, click here (August 2000)
Return and Shipping Policy
All ICAC Publications sales are final. Claims for incorrect or damaged shipments must be made within 30 days from invoice date, or such claims are invalid. All publication request will be shipped within 7 business day using the US Postal Service unless other wise specified by the requester. If alternate means are requested requester is responsible for additional shipping charges.
Other ICAC technical standards and publications provide information and voluntary standards covering various aspects of air pollution control technologies. To order any of ICAC's publication send a check or Credit Card number (AMX, VISA, Master Card) to ICAC, 1220 N. Fillmore Street, Suite 410, Arlington, VA 22201; or fax your request to ICAC at (703)248.0682.
Using VOC Control Technologies to Go Beyond MACT Requirements . . . and Help Your Bottom- Line!
EPA is developing maximum available control technology (MACT) standards for over 100 industries, and many of these will require reductions of volatile organic compounds (VOCs). Add-on VOC control technologies offer cost-effective means of complying with these rules. These technologies also offer the possibility of going beyond compliance with existing rules to lessen future compliance burdens, to ease permitting requirements, and even to make a profit.
Going Beyond Compliance
Besides federal air toxics (MACT) regulations, existing facilities must comply with state Reasonably Available Control Technology (RACT) and post-RACT rules. New and modified facilities must comply with new source review (NSR) or prevention of significant deterioration (PSD) requirements.
Given all of these compliance obligations, why should an industry consider installing VOC control equipment for anything beyond minimal compliance? After all, purchasing and operating control equipment costs money; delaying purchases to the last minute and buying the least expensive systems would seem best for the bottom line.
This sort of thinking, while common, ignores opportunities to lower long-term costs. At a minimum, reacting to each compliance obligation individually, without considering related obligations, can be expensive. Such an approach will not be the best route to compliance if it will force you to revisit your compliance situation next year, leading to multiple equipment purchases and multiple shutdowns to install controls.
What other advantages are there to installing VOC controls above those necessary for meeting routine compliance obligations?
First, under the MACT program, those expecting upcoming regulations to be particularly onerous for their facilities may obtain compliance extensions by achieving early emissions reductions. (Section 112(i)(5) of the Clean Air Act gives sources showing 90% emissions reductions before proposal six year extensions for compliance with MACT rules.) Spending a small amount of money now may help to avoid spending much more money later.
VOC controls can also be used to create "synthetic" minor sources by keeping emissions below major source thresholds. Minor sources face simpler permitting requirements, and more important, avoid NSR/PSD. Related to this is the use of controls for "netting" purposes: if modification of a source increases emissions, decreasing emissions elsewhere at the same site by a comparable or greater amount (i.e., no net increase in emissions) allows the source to avoid NSR/PSD. NSR/PSD is expensive, with money going toward dispersion modeling and other studies not contributing directly either to increased production or environmental protection, and can lead to long permitting delays. (Even when NSR/PSD is unavoidable, agreeing to the use of controls early in the process can reduce permitting delays.)
Under the Clean Air Act, sources constructing or modifying plants in non-attainment areas must offset any emissions increases with emissions reductions elsewhere. This requirement leads to a third reason to install VOC controls beyond compliance: to generate offsets or emissions reduction credits (ERCs) for sale or for use in other facilities of your own.
Selling ERCs can be profitable. In the summer of 1998, for example, brokers were quoting VOC ERC trades in the San Diego area at $15,833, in the Houston/Galveston area of Texas at $4,500, in the San Francisco area at $5,500, in Maryland at $2,250, in Massachusetts at $2,000, and in New York/Pennsylvania at $2,300. These prices are for streams of tons: each ERC confers the right to emit one ton of VOC every year. To convert ERC prices to a single-ton basis, i.e., to the cost of the right to emit a single ton of VOC, you need to discount the stream. At a 10% discount, an ERC price of $15,863 means that a single ton of VOC emissions is worth $1,583. At a 20% discount, it is worth $3,166. In other words, if you can control emissions to below your permit limit for less than $1,000-2,000/ton, you may be able to sell ERCs profitably in many locales.
Opportunities to profit through VOC emissions trading are arising as the U.S. moves toward market-based compliance systems. Examples of such systems include open market trading, as proposed by the U.S. EPA, and local schemes, such as that being set up in Chicago and the RECLAIM VOC scheme in Los Angeles. Where trading is possible, it becomes very easy to place a value on each ton of emissions or avoided emissions. This price information shows you when installing controls might allow you to profit.
VOC Control Technology Choices
The first thought of source owners faced with requirements to lower VOC emissions is likely to be (and should be) pollution prevention. In fact, pollution prevention, e.g., reformulation of inks and coatings and modification of equipment and work practices, can provide low-cost emissions reductions. On the other hand, reformulated materials often have very different properties from their conventional parents, leading to changes in product quality, compounded by the effects of different work practices and equipment configurations. Further, pollution prevention may not be able to provide the necessary emissions reductions at an acceptable cost.
Particularly where time is limited, such as for compliance with the printing and publishing MACT rule, implementing pollution prevention approaches may be difficult. In light of these concerns, add-on VOC controls offer an excellent alternative or adjunct to pollution prevention.
Add-on controls include all technologies which remove VOCs from exhaust gas streams. Add-on controls either collect the VOCs for recovery and reuse, or destroy the VOCs.
If the VOCs have recovery value, which typically implies single-VOC exhaust streams, and if the cost of recovery is less than the cost of purchasing new material, which typically implies concentrated exhaust streams, then recovery makes sense. Carbon or zeolite adsorption, scrubbing, and condensation are typical recovery techniques. Note that the installation and operation of a recovery technology may more than pay for itself if the recovery value of the VOC is high enough.
If the VOC has no recovery value, as, for example, when it is a mixture, or if it poses disposal concerns, such as for toxic compounds, then destruction probably makes the most sense. Thermal and catalytic oxidation and biofiltration would be useful in this case.
Regardless of what control technology you use, if you have a high volume, dilute exhaust stream you probably want to consider using a concentration system upstream of the control device to reduce gas volume to process.
In the brief discussion of control technologies which follows, the focus is on technologies which are fully commercial and in wide use. Each technology will be best (i.e., least expensive for a given removal efficiency) in certain applications. However, the wide variety of VOC control technologies assures the availability of a cost-effective solution to (almost) every air pollution control problem.
Thermal oxidizers burn VOCs by heating them in enclosed combustion chambers in the presence of excess oxygen. The precise temperature and residence time needed for effective reduction of VOC emissions varies with the nature of the VOC. However, temperatures of 1400-2000 F and residence times of 0.5-2 seconds typically provide emissions reductions of 98% or greater.
Since auxiliary fuel is necessary to maintain combustion temperatures, most thermal oxidizers incorporate some form of heat recovery to lower auxiliary fuel costs. When minimizing capital cost is most important, recuperative shell-and-tube or plate heat exchangers may be acceptable. These provide 40-70% thermal efficiencies; higher efficiencies are avoided because of diminishing returns and the higher costs of the additional passes.
Because regenerative thermal oxidizers (RTOs) have up to 95% thermal efficiency, they minimize use of auxiliary fuel, using auxiliary fuel only during start-up. In an RTO, an incoming gas stream passes through a hot bed of ceramic heat transfer media. Conventional media is random-packed ceramic material or shapes, while newer designs use structured block monolith. The ceramic media heats the incoming gas to within 75 F of the retention chamber operation temperature (1500 F). After passing through a combustion chamber which provides enough residence time for completion of the oxidation, the clean gas stream is cooled by passage through a second ceramic heat exchanger. In this process, the first ceramic bed is cooled, and the second is heated. Periodically, the flow is reversed.
Thermal oxidation is an appropriate choice when the VOCs have no recovery value and you need high-efficiency destruction. Thermal oxidizers can destroy all organics, although units destroying chlorinated organics are typically followed by scrubbers to control hydrochloric acid emissions and many need to operate at higher temperatures and require a lower retention time.
Catalytic oxidizers use catalysts to lower the oxidation temperatures of VOCs. By lowering the oxidation temperature, less supplementary fuel will be needed. Further, as the reaction takes place in the catalyst layer itself, no residence time is required. Catalytic oxidizers can give 99% emission reductions, and outlet VOC levels below 1 ppm in most cases.
Most oxidation catalysts are precious metal-based, often platinum supported on alumina. Some manufacturers provide base metal catalysts. Catalysts typically are in the form of ceramic honeycomb monoliths or metal monoliths, or of fixed beds of pelleted or saddle catalysts, with fluidized bed systems used occasionally.
While catalysts originally were relatively susceptible to poisoning, for example by sulfur, newer generations of catalysts are poison-resistant, and may have effective lifetimes as long as 10 years. Catalyst washing and regeneration techniques have been developed which can restore activity. Catalyst activity has increased over the years, so that lower oxidizer temperatures are needed.
Catalytic oxidizers were initially designed with recuperative heat exchangers. However, improvements in catalyst technology have led to development and application of regenerative catalytic oxidizers which use catalyzed ceramic beds.
Like thermal oxidizers, catalytic oxidizers are suitable for destroying waste streams with no recovery value and where high removal efficiencies are necessary. Catalytic systems will be smaller and lighter than thermal regenerative systems, but must be used with care when catalyst poisons may be in the waste stream.
Adsorption on activated carbon or zeolite is useful for recovery of VOCs with intermediate molecular weights (typically about 45-130): smaller compounds do not adsorb well, and larger compounds cannot be removed during regeneration, which typically is by steam or hot air stripping. Adsorption is most effective at lower temperatures, so that cooling of hot exhaust gas streams may be necessary. Further, dehumidification of very humid streams may be necessary for the carbon to have the greatest capacity.
Activated carbon can also be used to remove compounds in a once-through process with off-site regeneration. Concentration systems are useful in front of control devices for treating very high volumes of very dilute exhaust gas. Concentration is typically based on adsorption of the VOC on carbon or zeolite, followed by desorption with a much lower volume of hot gas. Commonly, concentrators are wheels containing activated carbon or zeolite. Most of the space on the wheel functions in adsorption mode, with one small sector being regenerated at any given time. An alternative concentrator uses synthetic carbon beads as the adsorbent media in a fluidized bed system.
Rotary wheel concentrators can reduce the volume of solvent-laden air to be processed by a factor of 10 to 20, while fluidized bed concentrators can reduce the volume by factors greater than 1000:1. This allows the use of smaller control devices. As a result, operating costs tend to be much lower.
Finally, biofiltration is an oxidation process which is in common use abroad and which is beginning to find use in the U.S. There are hundreds of biofilters installed abroad, and dozens in the U.S.
In biofiltration, a VOC-containing air stream is passed through a biofilter, a filter bed on which bacteria or other microorganisms are supported. Biofilters have been as simple as beds of earth, peat, or sewage sludge. More recently used biofilters have been bacteria supported on manufactured supports such as activated carbon.
Biofiltration may provide very high VOC removal efficiencies, but works best for very low VOC concentrations, including odors. Very hot exhaust streams will require cooling upstream of the biofilter.
While the focus above has been on selecting the right technology to lessen or eliminate future compliance costs, it also is possible to lower VOC control capital and operating costs by the creative application of technology. For example, it sometimes is possible to find a way to reduce the size of the stream which must be treated, so that a smaller (and less expensive) control system is required. One way to do this is to install ductwork connecting emission points to a single control device, rather than merely controlling the exhaust from an entire building; such an approach may decrease the required control device size by 90%.
(For more on VOC control technology and its suppliers, contact the ICAC office).