Hybrid Filter Technology Weds ESPs with Bag Filters

Issue 2 and Volume 106.

By Steve Blankinship,
Associate Editor

DOE’s National Energy Technology Laboratories has awarded funding to support the first full-scale demonstration of W. L. Gore & Associates’ advanced hybrid filtration technology in a coal-fired utility application. The advanced hybrid particulate collection (AHPC) system is an air pollution control device that combines electrostatic precipitation and membrane filter bag technologies into a compact collection system able to capture 99.99 percent of fine particulate matter.

Gore’s integrated ESP fabric filter design is intended to capture 99.9% of emission dust as it passes through the advanced hybrid system. Illustration courtesy of W.L. Gore and Associates.
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The demonstration unit, funded under DOE’s Power Plant Initiative program, will be located at Otter Tail Power Company’s Big Stone generating site in South Dakota and is scheduled to begin operation in October. The hybrid particulate collection technology allows filter bags to operate at high air-to-cloth ratios and be cleaned without the normal concerns about dust reentrainment.

According to the developers, the technology can meet most or all present or proposed industry standards on particulate matter at lower capital and operating costs than conventional air pollution control devices. The geometry consists of alternating rows of ESP components and filter bags within the collector. The inlet dust is directed into the ESP zone, where the particles are charged and a majority is captured on grounded perforated collecting plates. The membrane filter bags capture particles that pass beyond the collecting plate.

When the filter bags are pulse cleaned, the dust is propelled back into the ESP zone, a feature unique to the system. Much of the dust is captured by the perforated collecting plate and not redeposited on the filter bag as occurs in pulse jet fabric filters. This allows the system to run at higher air-to-cloth ratios and leads to a system that is very reliable and cost effective.

The Energy & Environmental Research Center (EERC) in North Dakota first patented the concept of combining filter bags with electrostatic precipitators (ESPs) in 1999. Combining the two processes enhances overall performance. While ESPs and baghouses have been used in tandem for more than 10 years, this is the first time that the filter bags have been integrated directly into the ESP chamber. Gore has been working with EERC to develop the concept to its present form and has exclusive global rights to practice and sub-license the technology to original equipment manufacturers worldwide. ELEX AG of Switzerland owns a sublicense to sell AHPC into industrial mineral and power markets.

The system has less than half the normal number of ESP components and 65 to 75 percent fewer bags than a conventional fabric filter, thereby allowing the overall size of the system to be smaller. Capital cost is also reduced. The new system is easily adapted to new installations as well as retrofits of existing ESPs.