EMFeature. The REMEDIA Catalytic Filter System. Feature

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1 EM EMFeature Feature The J. Deane Sensenbaugh Award is presented annually to companies or individuals in recognition of outstanding achievement in the fields of air pollution control or waste management. This year s award goes to W.L. Gore & Associates Inc. for its REMEDIA catalytic filter system. The Sensenbaugh Award was presented to W.L. Gore & Associates at A&WMA s 95th Annual Conference & Exhibition in Baltimore, MD, in June. Following is a brief description by the award recipients of their catalytic filter technology and its application to industry. The REMEDIA Catalytic Filter System by Keith J. Fritsky and Richard A. Bucher, W.L. Gore & Associates Inc. INTRODUCTION Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/ Fs) are listed among the Dirty Dozen persistent organic pollutants. Collectively known as dioxin, these compounds typically have a toxicity 10,000 times greater than that of cyanide, and are one of the most toxic chemical families known to man. The U.S. Environmental Protection Agency (EPA) has identified dioxin as a known human carcinogen and has linked exposure to these compounds to birth defects, immune system damage, reproductive problems, and developmental issues. PCDD/Fs are unintentionally produced as byproducts during a variety of industrial applications involving the thermal processing of chlorine-based feedstocks. To help meet the need to control dioxin, W.L. Gore & Associates developed a unique filtration system, called the REMEDIA catalytic filter. Designed for use in industrial applications, this patented filter technology not only controls particulate matter (PM) emissions, but also destroys harmful dioxin via catalysis before being released into the environment. In industrial flue gas streams, dioxin can exist either in a gaseous form ( gas phase ) or bound to solid PM ( solid phase ). The total amount of dioxin in the gas stream is the sum of the solid and gas phase dioxin. In waste incinerators, baghouses can remove solid 32 EM July 2002 phase PCDD/F, usually at high efficiency. However, gas phase PCDD/F can be emitted from the stack by passing through a baghouse and all other flue gas cleaning equipment. The gas phase PCDD/F must therefore be removed by other means, including adsorption on carbon-based additives, or catalytic destruction. Using W.L. Gore & Associates technology, catalytic destruction of PCDD/F takes place within the baghouse. The catalyst is incorporated into the filters housed inside the baghouse. The use of catalytic filters has advantages over other PCDD/F removal technologies, such as activated carbon injection. For example, 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 OVERVIEW The structure of the REMEDIA catalytic filter is illustrated in Figure 1. In a typical application, the filter is challenged with a process stream composed of both particulate and gaseous emissions. The multilaminar structure allows for efficient removal

2 and PCDD/Fs are destroyed in the felt, before the gas exits the baghouse and is emitted into the environment. s are widely used in industrial applications, and conversion from conventional particulate filtration to particulate/catalytic filtration is as easy as removing the conventional filter bags and installing the catalytic filter bags. Since no additional capital or infrastructure is required, adoption of this technology can be cost-effective. Figure 1. Cross-section of the catalytic filter. APPLICATIONS In the past five years, REMEDIA filters have been installed in more than 30 applications worldwide, including municipal waste incinerators, hazardous waste incinerators, medical waste incinerators, crematories, and secondary metals processing plants. In each application, PCDD/F emissions have been reduced to a level well below regulatory limits. Figure 3 shows the impact of REMEDIA filters at 12 different locations (note: the white bars represent the PCDD/Fs, and the black bars represent the resulting emissions after reaction with the filters). In each case, the results show significant dioxin removal, which, in turn, leads to dramatically reduced emissions that are well below the most stringent regulatory standards. For most applications, the minimum life expectancy Figure 2. Installation of catalytic filter bags into an existing baghouse. of both pollutants via the concepts of surface filtration and catalytic filtration. As depicted in Figure 1, the gas stream first comes into contact with a micro-porous expanded polytetrafluoroethylene (eptfe) membrane. The micro-porous structure of this membrane allows for high-efficiency filtration of PM in the gas stream. As the gas passes through the structure, the PM is trapped on the surface of the membrane, where it can easily be cleaned. The filter media is composed of eptfe membrane laminated to a needle-punched felt. The felt is made up of microporous eptfe fibers with catalyst particles built into the fiber structure. This filter media is then sewn into filter bags, which can be installed in an existing baghouse (see Figure 2). In the baghouse, the raw gas from the upstream process comes in from the lower left. The gas stream then flows through the filter bags, where PM is trapped on the surface, July 2002 EM 33

3 EM Feature of the system is five years. The following case histories show the performance of the REMEDIA catalytic filter technology at three full-scale plants. Case History 1: IVRO The IVRO municipal waste incinerator is located in Roeselare, Belgium (see Figure 4). The plant was built in 1976 and consists of two incinerator lines, each with its own air pollution control train consisting of an electrostatic precipitator, dry lime scrubber, and pulsejet fabric filter. Each incinerator and flue gas cleaning line feed into one common stack. Over the years, the capacity of each incinerator line has increased from 3.2 tons of waste per hour to 4 tons of waste per hour. In 1996, new PCDD/F regulations were enacted in Belgium, prompting IVRO to install a powdered activated carbon (PAC) injection system. The PAC system was used at temperatures of C. At these high temperatures, however, there is an increased risk of a fire in the fabric filter. To avoid the risk of fires and plant shutdowns, IVRO began to look for alternatives to PAC. In 1997, REMEDIA catalytic filters were installed in three compartments in the plant s existing Line 2 fabric filter. Simultaneous measurements were conducted at the fabric filter inlet and compartment outlets to verify that the filters could destroy PCDD/Fs below the regulatory limit of 0.1 ng I-TEQ/Nm 3. IVRO equipped the remaining 17 fabric filter compartments of both lines with catalytic filters in Since then, PCDD/F testing has continued on both lines with measurements conducted at the fabric filter inlet, fabric filter outlet, and stack. All measurements were conducted in accordance with EN 1948, the European standard for sampling and analysis of PCDD/Fs. In the Flanders region of Belgium where IVRO is located, municipal waste incinerators are not allowed to operate unless the PCDD/F regulatory limit of 0.1 ng I-TEQ/Nm 3 is met. Continuous sampling and bi-weekly analysis for PCDD/Fs are performed to ensure compliance with the regulation during all stages of operation, including startup and shutdown. If an incinerator is found to be out of compliance, immediate measures to solve the problem must be enacted. An incinerator can be closed down if satisfactory progress toward compliance is not demonstrated. The catalytic filters installed at IVRO have operated at an air-to-cloth ratio of 1.45 m/min since May Prior to this date, the filters operated at an air-to-cloth ratio of m/min. The increase is due to furnace modifications that allow greater incineration capacity. With the catalytic filter system installed, the maximum pressure drop across each fabric filter is 20 mbar, and the maximum cleaning frequency is 30 cycles per 24 operating hours. PCDD/F Concentration (ng I-TEQ/Nm 11% O 2 ) Figure 3. Impact of the catalytic filter system at 12 different applications around the world. 34 EM July 2002

4 Clean Gas PCDD/F Concentration (ng 11% O2) Raw Gas PCDD/F Concentration (ng 11% O2) Figure 5 shows PCDD/F inlet ( raw gas ) concentrations and outlet ( clean gas ) emissions at IVRO since installation of the catalytic filters. Dioxin emissions have been well below the regulatory limit over a period of 48 months, and the destruction efficiency is greater than 99%. Clean gas values represent total (solid plus gas phase) PCDD/F. Raw gas values represent gas phase PCDD/F only (note: N.D. indicates values below the detection limit of ng I-TEQ/Nm3 for the total TEQ concentration). From August 1997 to September 1997, particulate concentration measurements were conducted at the outlet of a compartment in the Line 2 fabric filter. This compartment was the first in which catalytic filter media was installed. The PM emissions ranged from below the detection limit (0.2 mg/nm3) to 0.4 mg/nm3 at 11% O2. Since 1997, Figure 4. IVRO municipal waste incinerator in Roeselare, Belgium. PM emissions have remained below 1 mg/nm3, as measured by a particulate monitor in the stack. In January 1999, the concentration in the raw gas was measured as 2100 mg/nm 3 at 11% O2.1 A simultaneous clean gas particulate measurement was not performed. However, given evidence that PM emissions are consistently below 1 mg/nm3, the particulate removal efficiency at IVRO has been demonstrated to be >99.95%. Bonte el al.2 performed a dioxin mass balance around the baghouse and found that the amount of gaseous dioxin adsorbed in the baghouse (on the filters and particulate) was negligible when compared to the amount destroyed by the catalyst. More than 99.5% of the dioxin was destroyed versus 0.01% being adsorbed. Figure 5. Dioxin/furan results from IVRO. Case History 2: Phoenix Services The Baltimore Regional Medical Waste Incinerator, which began commercial operation in January 1991, is the largest dedicated medical waste incinerator in the world (see Figure 6). Owned and operated by Phoenix Services Inc., the plant consists of two identical controlled air-type incineration lines, each with a nominal-processing rate of 77 metric tons of waste per day. The entire facility is permitted to process up to metric tons per day. Each incineration line comprises primary, secondary, and tertiary combustion chambers, a heat recovery steam generator, and an air pollution control system (APCS). Flue gases enter the APCS and first go through a dry scrubber using sodium sesquicarbonate (Na2CO3 NaHCO3 2H2O), or Figure 6. Phoenix Services medical waste incinerator facility. July 2002 EM 35

5 EM Feature (Concentration (ng/nm 11% O 2 ) Figure 7. Non-TEQ concentrations in raw and clean gas for all toxic isomers (log scale). trona, as the sorbent. After passing through the scrubber, the dust-laden flue gas enters a pulsejet baghouse. Combustion gases are drawn through the baghouse by an induced draft fan, after which they pass up a single stack, common to both incineration trains. Because of its large scale and public visibility, the State of Maryland imposed stringent emissions standards on the facility for both criteria and hazardous air pollutants. A new dioxin limit of 2.3 ng 7% O 2 (1.76 ng TEQ/Nm 11% O 2 ) was found to be considerably lower than historical dioxin emissions at the facility. Anticipating the need to reduce PCDD/F emissions from the plant, Phoenix Services had performed trials in late 1995, with both standard PAC and a proprietary activated carbon product. The results were acceptable for both materials and enabled a target injection rate to be established for future reference. The REMEDIA system offered the following advantages to Phoenix Services: gas phase PCDD/Fs are destroyed, rather than simply being adsorbed on a solid; the system is a passive solution, without the need for a new chemical feed system; potential future liabilities associated with dioxincontaminated residue are reduced; and the system provides the particulate capture, filter pressure drop, and mechanical life advantages of an eptfe membrane filter. In early 1998, test filters were installed in one of the baghouses at the facility. After 10 months of operation, Phoenix Services decided to replace all of its woven fiberglass filter bags with the catalytic filters. Beginning in May 1999, both baghouses were completely refitted with the REMEDIA catalytic filter system. Dioxin measurements have been performed for 30 months since the installation. Over this time, dioxin emissions have been below 0.1 ng TEQ/Nm 3. For one such measurement, Figure 7 shows non-teq (or non-toxic equivalent ) concentrations of all toxic PCDD/F isomers in the raw and clean gas, as detected on the XAD sorbent trap of the sampling train. These isomer concentrations represent gaseous PCDD/Fs that react on the catalyst. The figure shows that for all toxic isomers, there is a true reduction in the mass concentration from the raw gas to the clean gas (note: the reduction in overall TEQ concentration was 98.4%). This indicates that the catalyst is destroying PCDD/F rather than chemically converting (or shifting ) isomers with higher toxicity in the raw gas to lower toxicity isomers in the clean gas. With regard to PM emissions, the average removal efficiency was 99.95%. The PM concentrations in the clean gas were times lower than the emission guideline of 34 7% O 2 (26 mg/ Nm 11% O 2 ). Case History 3: Ashibe Clean Center New limits for PCDD/Fs in Japan will become effective in December This case history presents the experience of catalytic filtration in a batch-type municipal incinerator 36 EM July 2002

6 in Japan. The Ashibe Clean Center is located in Nagasaki prefecture (see Figure 8). It has two stoker furnaces, two heat exchangers, and one baghouse. Each furnace has a capacity of 8.5 tons per 8-hour day and a flow rate of 20,000 Nm 3 / hr. The baghouse is operated with lime injection at 200 C. Catalytic filter bags were installed in May 2000, replacing conventional filter bags. The total filter area is 500 m 2. Operation starts at 8:30 a.m. each day, with municipal waste input stopping at 2:00 p.m. Operation ends each day at approximately 5:00 p.m., when the furnace is allowed to cool. The flue gases pass through the catalytic filters during the full day of operation. Testing was performed to investigate PCDD/F emission levels during steady-state operation, as well as startup and shutdown. Dioxin measurements for the Ashibe plant were conducted according to EN 1948, with sampling times of 1.5 hr for startup, 3.5 hr for steady-state operation, and 1.8 hr for shutdown. Figure 9 shows the PCDD/F concentrations at the baghouse inlet and outlet over the entire operation cycle. As shown by the data, in all cases PCDD/F emissions were significantly below 0.1 ng TEQ/ Nm 3. Total dioxin at the baghouse inlet showed great variability with the stage of operation. During facility startup, unstable conditions produced a PCDD/F challenge over twice that of steady-state operation. However, even at high-inlet values (more than 11 ng TEQ/Nm 3 ) dioxins were removed by %. Considering only the gas phase PCDD/F, the destruction efficiency was %, as a result of the catalytic reaction. During all stages of operation, total PCDD/F emissions were reduced to below ng TEQ/Nm 3. CONCLUSION The REMEDIA catalytic filter system not only controls particulate emissions via a micro-porous eptfe membrane, but also destroys dioxins and furans via an eptfe/catalyst-felt substrate. A variety of industrial applications have chosen to replace conventional filter bags with REMEDIA filters. In so doing, they have demonstrated dioxin emission reductions up to and, in some cases, greater than 99%. REMEDIA effectively combines the proven technologies of catalysis and surface filtration to produce a novel result: the destruction of carcinogenic dioxin and the capture of fine particulate in a baghouse in one step. Inlet Figure 8. Ashibe Clean Center located in Ashibe-cho, Nagasaki. Outlet Inlet Outlet Inlet Outlet Solid Phase Gas Phase Figure 9. PCDD/F measurements from Ashibe Clean Center during startup, steady-state operation, and shutdown at the baghouse inlet and outlet (log scale). REMEDIA and GORE-TEX are trademarks of W.L. Gore & Associates Inc. More information on the REMEDIA system can be found at REFERENCES 1. Bonte, J.L. et al. Catalytic Filtration: Dioxin/Furan Destruction in the Experiences at the IVRO Municipal Waste Incinerator in Roeselare, Belgium; Organohalogen Compounds 1999, Bonte, J.L. et al. Catalytic Destruction of PCDD/F in a Fabric Filter: Experience at a Municipal Waste Incinerator in Belgium. In Proceedings of the International Conference on Incineration and Thermal Treatment Technologies; Philadelphia, PA, About the Authors Keith J. Fritsky, P.E., is global applications specialist for the Catalytic Filtration Group at W.L. Gore & Associates Inc., Elkton, MD; kfritsky@wlgore.com; phone: (410) Prior to joining W.L. Gore, Fritsky worked in the U.S. Environmental Protection Agency s Office of Research & Development in Research Triangle Park, NC. Richard A. Bucher, Ph.D., is the global business leader for the Catalytic Filtration Group at W.L. Gore & Associates Inc.; rbucher@wlgore.com; phone: (410) July 2002 EM 37