The process for forming intricate three dimensional ceramic and metal shapes in a scaleable cost effective manner was developed by a team of researchers at the Massachusetts Institute of Technology. Specific Surface modified and scaled MIT's three-dimensional printing process to produce advanced ceramic and metal filter elements. One of these, the CleanStac™ compact ceramic filter, was developed for application to pulse-jet baghouses and is suitable for conventional baghouses where operating temperatures up to 600°C occur.

At Power-Gen 98 Andrew B. Jeffery of Specific Surface Corp. discussed operations of CleanStac filter on a COHPAC I pilot plant downstream of a utility coal-fired boiler. Previous experience at COHPAC I unit at Texas Utilities showed that many factors, including high flue gas temperature, high pressure drop, frequent start up and shut downs, resulted in bag lives of less than two years. COHPAC systems provide an ideal application for a high surface area filter that can operate at high filtration velocities and varying operating temperatures above the maximum for typical synthetic filter bags. Specific Surface's CeraPrint™  technology allowed high surface area designs to be considered for ceramic filter elements that would directly replace filter bags in baghouses.

A number of designs were considered for testing at EPRI's COHPAC I pilot plant at Alabama Power Company's Miller Station. The CleanStac filters comprise ceramic filter elements that are stacked together in a frame that make up a single filter module. The ceramic elements are then held in compression in the frame using spring loaded threaded rods. Two of these assemblies were placed into a test module containing ten other bags made of Ryton. The effective air-to-cloth ratio for each filter element type was measured and compared. The test program ran for 20 test periods and a total of 1660 hours. While the overall air-to-cloth ratio for the compartment ranged from 7.1 to 10.8 ft/min during the 20 test periods, the effective air-to-cloth for the CleanStac filter ranged from 5.1 to 7.4 ft/min, while the effective air-to-cloth ratio for the Ryton/P84 composite bag ranged from 10.1 to 15.1 ft/min. It was observed on many occasions that the air-to-cloth ratio through the CleanStac would rise and the air-to-cloth ratio through the filter bag would fall during a filtering period. The CleanStac filters were able to accommodate additional flow while maintaining the same average tubesheet pressure drop as the filter bags. This indicated that the CleanStac filter should be able to maintain good performance during operation under conditions of high particulate loading.

Although filter life of the CleanStac filter has not been evaluated, results indicated that further investigation of the filter was worthwhile. An ongoing program will more fully evaluate CleanStac filters as the stand alone filter medium in a COHPAC II installation at Plant Miller.

FF 00 04 05 "Evaluation of Advanced Filters for Compact Baghouse Applications" by Kenneth M. Cushing, Southern Research Institute, Birmingham, AL, Wallis A. Harrison and Mark S. Berry, Southern Company Services, Inc. and Ramsay L. Chang, Electric Power Research Institute, Palo Alto, CA. 20 p.

Two COHPAC  pilot baghouse systems have been installed at Alabama Power Co.'s Plant Miller to evaluate this technology prior to its use at full-scale in the Southern Company system. Besides proving the overall COHPAC concept, several advanced filters are being tested as potential candidates for COHPAC and other compact baghouse applications. Four types of filters have been or are being tested at the present time. These include Albarrie Environmental Services, Inc.'s P84/Ryton composite felt, Albany International's high surface area Star Bag™, Specific Surface Corp.'s ceramic Clean-Stac™ filter, and BHA Group's Pulse-Pleat™ pleated cartridge filter. Data is presented regarding the performance of these filtration products and assessment of how well these filters should perform in a full-scale COHPAC environment.

C SOUTHERN COMPANY, C ALABAMA POWER, IF 416 COHPAC, IF 630 P84, IF 334 RYTON, IF 439 CERAMIC FILTER, IF 440 CARTRIDGE FILTER