The Dry Scrubber Cartridge System

In recent years, technological developments have increased the use of cartridge-collectors in difficult incineration applications. These units are much smaller than conventional baghouses and their bag access method eliminates the need for high overhead clearance required by conventional top bag access pulsejets. This makes the units much easier to fit where there are space constraints.

The major components of a dry scrubbing system are a gas cooler, reagent storage and delivery system, the dry injection chamber, and a fabric-filter collector. Air-moving , ash-removal, and compressed-air systems are typical additions.

A primary concern involving use of a cartridge collector for medical incinerator scrubbing systems is the potential for caking of the highly hygroscopic hydrated lime scrubbing material in the pleated filter elements. This would hamper the lime's removal by the filter cleaning system.*

This study, involving a pilot program,**had three primary objectives:

• To determine whether a cartridge-collector-type fabric filter can effectively function as a dry scrubber component on medical-waste incinerators;
• To evaluate the environmental performance of the system; and
• To compare dry and wet systems, since there has been little direct comparison between their performance.

The principal component of the pilot system was its collector, which comprised pleated, horizontally installed cartridges and a top inlet and a side outlet plenum. The reagent, a blend of hydrated lime and activated carbon, was injected into a proprietary injection chamber located upstream of the cartridge collector.

Results

Permit limitations constrained system-operation duration. However, stable operation of the system during its limited test period gave strong indications that a full-scale system would operate successfully at 4:l, and as high as 6:1, air-to-cloth ratios with acceptable pressure drop. The system also proved highly resistant to intentional attempts to filter blinding--including running the system to convert all the lime to calcium chloride and exposing the system overnight to ambient conditions after shutdown.

The wet scrubber, with its oversized packed tower did have a somewhat higher HCl scrubbing efficiency than the dry scrubber with cartridge, but the latter's performance was well more than an order of magnitude greater than required performance level. In addition, the pilot unit's performance compared well with a typical conventional baghouse/dry scrubber.

The use of activated carbon in addition to hydrated lime aided in the removal of heavy metals. Mercury removal rate, in at least one case, exceeded 90 percent Other heavy-metal removal efficiencies, although not quantified, seemed excellent.

The success of the pilot installation on a medical waste incinerator is positive indication that many other applications may benefit from air-pollution-control systems that use dry scrubbers with cartridge units.

*To minimize this possibility, filter elements of Gore-Tex(r) membrane/Teflon(r) B fiberglass fabric were selected. Also, Gore-tex is able to handle the extremely corrosive conditions posed by medical waste incinerators.
** The pilot program made use of a side stream from a medical-waste incinerator.
Adapted from the paper, "Air Pollution for the Year 2000 (the New Dry Scrubber Cartridge Collector Control System)." Frank L. Cross, Jr. was with Harding LawsonAssociates-Cross/Tessitore & Associates at the time he prepared the paper.

Edited by Paul Hersch