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INTRODUCTIONPolychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are listed among the “Dirty Dozen” persistent organic pol-lutants. Collectively known as dioxin, these compounds typi-cally have a toxicity 10,000 times greater than that of cyanide,and are one of the most toxic chemical families known toman. The U.S. Environmental Protection Agency (EPA) hasidentified dioxin as a known human carcinogen and has linkedexposure to these compounds to birth defects, immune sys-tem damage, reproductive problems, and developmentalissues. PCDD/Fs are unintentionally produced as byproductsduring a variety of industrial applications involving the ther-mal processing of chlorine-based feedstocks.

To help meet the need to control dioxin, W.L. Gore &Associates developed a unique filtration system, called theREMEDIA catalytic filter. Designed for use in industrialapplications, this patented filter technology not only con-trols particulate matter (PM) emissions, but also destroysharmful dioxin via catalysis before being released into theenvironment. In industrial flue gas streams, dioxin canexist either in a gaseous form (“gas phase”) or bound tosolid PM (“solid phase”). The total amount of dioxin inthe gas stream is the sum of the solid and gas phase di-oxin. In waste incinerators, baghouses can remove solid

The J. Deane Sensenbaugh Award is presented annually to companies or individuals in recognition of outstandingachievement in the fields of air pollution control or waste management. This year’s award goes to W.L. Gore & AssociatesInc. for its REMEDIA catalytic filter system. The Sensenbaugh Award was presented to W.L. Gore & Associates atA&WMA’s 95th Annual Conference & Exhibition in Baltimore, MD, in June. Following is a brief description by the awardrecipients of their catalytic filter technology and its application to industry.

The REMEDIA Catalytic Filter Systemby Keith J. Fritsky and Richard A. Bucher, W.L. Gore & Associates Inc.

phase PCDD/F, usually at high efficiency. However, gasphase PCDD/F can be emitted from the stack by passingthrough a baghouse and all other flue gas cleaning equip-ment. The gas phase PCDD/F must therefore be removedby other means, including adsorption on carbon-basedadditives, or catalytic destruction.

Using W.L. Gore & Associates’ technology, catalytic destruc-tion of PCDD/F takes place within the baghouse. The catalystis incorporated into the filters housed inside the baghouse.The use of catalytic filters has advantages over other PCDD/Fremoval technologies, such as activated carbon injection. Forexample, catalytic filters

• destroy dioxins and furans instead of adsorbing them;• do not add dioxin-contaminated solids to residue

requiring disposal;• do not require additional operation and maintenance

procedures, or new equipment; and• do not pose a fire hazard.

TECHNOLOGY OVERVIEWThe structure of the REMEDIA catalytic filter is illustrated inFigure 1. In a typical application, the filter is challenged witha process stream composed of both particulate and gaseousemissions. The multilaminar structure allows for efficient removal

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Figure 1. Cross-section of the catalytic filter.

Figure 2. Installation of catalytic filter bags into an existing baghouse.

of both pollutants via the concepts of surface filtration andcatalytic filtration. As depicted in Figure 1, the gas stream firstcomes into contact with a micro-porous expanded poly-tetrafluoroethylene (ePTFE) membrane. The micro-porousstructure of this membrane allows for high-efficiency filtra-tion of PM in the gas stream. As the gas passes through thestructure, the PM is trapped on the surface of the membrane,where it can easily be cleaned. The filter media is composed ofePTFE membrane laminated to a needle-punched felt. The feltis made up of microporous ePTFE fibers with catalyst particlesbuilt into the fiber structure. This filter media is then sewninto filter bags, which can be installed in an existing baghouse(see Figure 2). In the baghouse, the raw gas from the upstreamprocess comes in from the lower left. The gas stream then flowsthrough the filter bags, where PM is trapped on the surface,

and PCDD/Fs are destroyed in the felt, before the gas exits thebaghouse and is emitted into the environment. Baghouses arewidely used in industrial applications, and conversion fromconventional particulate filtration to particulate/catalytic fil-tration is as easy as removing the conventional filter bags andinstalling the catalytic filter bags. Since no additional capitalor infrastructure is required, adoption of this technology canbe cost-effective.

APPLICATIONSIn the past five years, REMEDIA filters have been installed inmore than 30 applications worldwide, including municipalwaste incinerators, hazardous waste incinerators, medicalwaste incinerators, crematories, and secondary metals pro-cessing plants. In each application, PCDD/F emissions havebeen reduced to a level well below regulatory limits. Figure 3shows the impact of REMEDIA filters at 12 different locations(note: the white bars represent the PCDD/Fs, and the blackbars represent the resulting emissions after reaction with thefilters). In each case, the results show significant dioxin re-moval, which, in turn, leads to dramatically reduced emis-sions that are well below the most stringent regulatorystandards. For most applications, the minimum life expectancy

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Figure 3. Impact of the catalytic filter system at 12 different applications around the world.

of the system is five years. The following case histories showthe performance of the REMEDIA catalytic filter technologyat three full-scale plants.

Case History 1: IVROThe IVRO municipal waste incinerator is located in Roeselare,Belgium (see Figure 4). The plant was built in 1976 and con-sists of two incinerator lines, each with its own air pollutioncontrol train consisting of an electrostatic precipitator, dry limescrubber, and pulsejet fabric filter. Each incinerator and fluegas cleaning line feed into one common stack. Over the years,the capacity of each incinerator line has increased from 3.2tons of waste per hour to 4 tons of waste per hour. In 1996,new PCDD/F regulations were enacted in Belgium, prompt-ing IVRO to install a powdered activated carbon (PAC) injec-tion system. The PAC system was used at temperatures of200–230 °C. At these high temperatures, however, there is anincreased risk of a fire in the fabric filter. To avoid the risk offires and plant shutdowns, IVRO began to look for alterna-tives to PAC. In 1997, REMEDIA catalytic filters were installedin three compartments in the plant’s existing Line 2 fabricfilter. Simultaneous measurements were conducted at thefabric filter inlet and compartment outlets to verify that thefilters could destroy PCDD/Fs below the regulatory limit of

0.1 ng I-TEQ/Nm3. IVRO equipped the remaining 17 fabricfilter compartments of both lines with catalytic filters in 1998.Since then, PCDD/F testing has continued on both lines withmeasurements conducted at the fabric filter inlet, fabric filteroutlet, and stack. All measurements were conducted in accor-dance with EN 1948, the European standard for sampling andanalysis of PCDD/Fs.

In the Flanders region of Belgium where IVRO is located,municipal waste incinerators are not allowed to operate un-less the PCDD/F regulatory limit of 0.1 ng I-TEQ/Nm3 is met.Continuous sampling and bi-weekly analysis for PCDD/Fs areperformed to ensure compliance with the regulation duringall stages of operation, including startup and shutdown. If anincinerator is found to be out of compliance, immediate meas-ures to solve the problem must be enacted. An incinerator canbe closed down if satisfactory progress toward compliance isnot demonstrated. The catalytic filters installed at IVRO haveoperated at an air-to-cloth ratio of 1.45 m/min since May 1999.Prior to this date, the filters operated at an air-to-cloth ratio of1.1–1.2 m/min. The increase is due to furnace modificationsthat allow greater incineration capacity. With the catalytic fil-ter system installed, the maximum pressure drop across eachfabric filter is 20 mbar, and the maximum cleaning frequencyis 30 cycles per 24 operating hours.

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Figure 5 shows PCDD/F inlet (“raw gas”) concentrationsand outlet (“clean gas”) emissions at IVRO since installationof the catalytic filters. Dioxin emissions have been well belowthe regulatory limit over a period of 48 months, and thedestruction efficiency is greater than 99%. Clean gas valuesrepresent total (solid plus gas phase) PCDD/F. Raw gas valuesrepresent gas phase PCDD/F only (note: N.D. indicates valuesbelow the detection limit of 0.004 ng I-TEQ/Nm3 for the totalTEQ concentration).

From August 1997 to September 1997, particulate con-centration measurements were conducted at the outlet ofa compartment in the Line 2 fabric filter. This compart-ment was the first in which catalytic filter media was in-stalled. The PM emissions ranged from below the detectionlimit (0.2 mg/Nm3) to 0.4 mg/Nm3 at 11% O2. Since 1997,PM emissions have remained below 1 mg/Nm3, as mea-sured by a particulate monitor inthe stack. In January 1999, theconcentration in the raw gas wasmeasured as 2100 mg/Nm3 at11% O2.1 A simultaneous cleangas particulate measurement wasnot performed. However, givenevidence that PM emissions areconsistently below 1 mg/Nm3,the particulate removal efficiencyat IVRO has been demonstratedto be >99.95%.

Bonte el al.2 performed a dioxinmass balance around the baghouseand found that the amount ofgaseous dioxin adsorbed in thebaghouse (on the filters and par-ticulate) was negligible when com-pared to the amount destroyed bythe catalyst. More than 99.5% ofthe dioxin was destroyed versus0.01% being adsorbed.

Case History 2: Phoenix ServicesThe Baltimore Regional Medical Waste Incinerator, which be-gan commercial operation in January 1991, is the largest dedi-cated medical waste incinerator in the world (see Figure 6).Owned and operated by Phoenix Services Inc., the plant con-sists of two identical controlled air-type incineration lines, eachwith a nominal-processing rate of 77 metric tons of waste perday. The entire facility is permitted to process up to 136.4 metrictons per day. Each incineration line comprises primary, sec-ondary, and tertiary combustion chambers, a heat recoverysteam generator, and an air pollution control system (APCS).Flue gases enter the APCS and first go through a dry scrubberusing sodium sesquicarbonate (Na2CO3 • NaHCO3 • 2H2O), or

Figure 4. IVRO municipal waste incinerator in Roeselare, Belgium.

Figure 5. Dioxin/furan results from IVRO.

Figure 6. Phoenix Services medical waste incinerator facility.

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trona, as the sorbent. After passing through the scrubber, thedust-laden flue gas enters a pulsejet baghouse. Combustiongases are drawn through the baghouse by an induced draftfan, after which they pass up a single stack, common to bothincineration trains.

Because of its large scale and public visibility, the State ofMaryland imposed stringent emissions standards on the facil-ity for both criteria and hazardous air pollutants. A new di-oxin limit of 2.3 ng TEQ/dscm @ 7% O2 (1.76 ng TEQ/Nm3 @11% O2) was found to be considerably lower than historicaldioxin emissions at the facility. Anticipating the need to re-duce PCDD/F emissions from the plant, Phoenix Services hadperformed trials in late 1995, with both standard PAC and aproprietary activated carbon product. The results were accept-able for both materials and enabled a target injection rate tobe established for future reference.

The REMEDIA system offered the following advantages toPhoenix Services:

• gas phase PCDD/Fs are destroyed, rather than simplybeing adsorbed on a solid;

• the system is a passive solution, without the need fora new chemical feed system;

• potential future liabilities associated with dioxin-contaminated residue are reduced; and

• the system provides the particulate capture, filterpressure drop, and mechanical life advantages of anePTFE membrane filter.

In early 1998, test filters were installed in one of thebaghouses at the facility. After 10 months of operation, Phoe-nix Services decided to replace all of its woven fiberglass filterbags with the catalytic filters. Beginning in May 1999, bothbaghouses were completely refitted with the REMEDIA cata-lytic filter system. Dioxin measurements have been performedfor 30 months since the installation. Over this time, dioxinemissions have been below 0.1 ng TEQ/Nm3. For one suchmeasurement, Figure 7 shows non-TEQ (or “non-toxic equiva-lent”) concentrations of all toxic PCDD/F isomers in the rawand clean gas, as detected on the XAD sorbent trap of thesampling train. These isomer concentrations represent gaseousPCDD/Fs that react on the catalyst. The figure shows that forall toxic isomers, there is a true reduction in the mass concen-tration from the raw gas to the clean gas (note: the reductionin overall TEQ concentration was 98.4%). This indicates thatthe catalyst is destroying PCDD/F rather than chemically con-verting (or “shifting”) isomers with higher toxicity in the rawgas to lower toxicity isomers in the clean gas. With regard toPM emissions, the average removal efficiency was 99.95%. ThePM concentrations in the clean gas were 12–17 times lowerthan the emission guideline of 34 mg/dscm @ 7% O2 (26 mg/Nm3 @ 11% O2).

Case History 3: Ashibe Clean CenterNew limits for PCDD/Fs in Japan will become effective inDecember 2002. This case history presents the experience ofcatalytic filtration in a batch-type municipal incinerator

Figure 7. Non-TEQ concentrations in raw and clean gas for all toxic isomers (log scale).

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Figure 9. PCDD/F measurements from Ashibe Clean Center during startup, steady-state operation,and shutdown at the baghouse inlet and outlet (log scale).

in Japan. The Ashibe Clean Center is located in Nagasaki pre-fecture (see Figure 8). It has two stoker furnaces, two heatexchangers, and one baghouse. Each furnace has a capacityof 8.5 tons per 8-hour day and a flow rate of 20,000 Nm3/hr. The baghouse is operated with lime injection at 200 °C.Catalytic filter bags were installed in May 2000, replacingconventional filter bags. The total filter area is 500 m2. Op-eration starts at 8:30 a.m. each day, with municipal wasteinput stopping at 2:00 p.m. Operation ends each day at ap-proximately 5:00 p.m., when the furnace is allowed to cool.The flue gases pass through the catalytic filters during thefull day of operation.

Testing was performed to investi-gate PCDD/F emission levels duringsteady-state operation, as well asstartup and shutdown. Dioxin meas-urements for the Ashibe plant were con-ducted according to EN 1948, withsampling times of 1.5 hr for startup,3.5 hr for steady-state operation, and1.8 hr for shutdown. Figure 9 showsthe PCDD/F concentrations at thebaghouse inlet and outlet over theentire operation cycle. As shown by thedata, in all cases PCDD/F emissionswere significantly below 0.1 ng TEQ/Nm3. Total dioxin at the baghouseinlet showed great variability withthe stage of operation. During facilitystartup, unstable conditions produceda PCDD/F challenge over twice that ofsteady-state operation. However,even at high-inlet values (more than11 ng TEQ/Nm3) dioxins were re-moved by 99.50–99.80%. Considering only the gas phasePCDD/F, the destruction efficiency was 99.31–99.73%, asa result of the catalytic reaction. During all stages of op-eration, total PCDD/F emissions were reduced to below0.025 ng TEQ/Nm3.

CONCLUSIONThe REMEDIA catalytic filter system not only controls par-ticulate emissions via a micro-porous ePTFE membrane, butalso destroys dioxins and furans via an ePTFE/catalyst-felt sub-strate. A variety of industrial applications have chosen to re-place conventional filter bags with REMEDIA filters. In sodoing, they have demonstrated dioxin emission reductionsup to and, in some cases, greater than 99%. REMEDIA effec-tively combines the proven technologies of catalysis and sur-face filtration to produce a novel result: the destruction ofcarcinogenic dioxin and the capture of fine particulate in abaghouse in one step.

About the AuthorsKeith J. Fritsky, P.E., is global applications specialist for theCatalytic Filtration Group at W.L. Gore & Associates Inc., Elkton,MD; e-mail: kfritsky@wlgore.com; phone: (410) 506-3201. Priorto joining W.L. Gore, Fritsky worked in the U.S. Environmental Pro-tection Agency’s Office of Research & Development in ResearchTriangle Park, NC. Richard A. Bucher, Ph.D., is the global businessleader for the Catalytic Filtration Group at W.L. Gore & AssociatesInc.; e-mail: rbucher@wlgore.com; phone: (410) 506-3468.

Figure 8. Ashibe Clean Center located in Ashibe-cho, Nagasaki.

REMEDIA and GORE-TEX are trademarks of W.L. Gore &Associates Inc. More information on the REMEDIA system canbe found at www.gore.com/remedia.

REFERENCES1. Bonte, J.L. et al. Catalytic Filtration: Dioxin/Furan Destruction in the

Baghouse—Experiences at the IVRO Municipal Waste Incinerator inRoeselare, Belgium; Organohalogen Compounds 1999, 40.

2. Bonte, J.L. et al. Catalytic Destruction of PCDD/F in a Fabric Filter: Expe-rience at a Municipal Waste Incinerator in Belgium. In Proceedings of theInternational Conference on Incineration and Thermal Treatment Technolo-gies; Philadelphia, PA, 2001.

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