Kenneth M. Cushing

The potential of pulse-jet baghouses for utility boilers. Part 2: Performance of pulse-jet fabric filter pilot plants

Pulse-jet fabric filters (PJFFs) are widely used in U.S. industrial boiler applications and in utility and industrial boilers abroad. Their small size and reduced cost relative to more conventional reverse-gas baghouses makes the use of PJFFs appear to be an attractive particulate control option for utility boilers. This paper (Part 2 of a three-part series) summarizes the results of pilot PJFF studies sponsored by the Electric Power Research Institute at different utility sites in the United States. The purpose of these tests is to evaluate PJFF performance for U.S. fossil-fuel-fired applications. These data are also used to corroborate the results of a recent worldwide survey of PJFF user experience, as described in Part 1 of this series. Part 3 will provide a cost comparison of PJFFs to other particulate control options such as electrostatic precipitators and reverse-gas baghouses.

Survey on the use of pulse-jet fabric filters

Pulse-jet fabric filters rely on the filtration of dirty flue gas by the outside surface of the bags, which are then cleaned by a shock wave generated by an air pulse entering each bag from the top. As it travels down the length of the bag, the shock wave flexes the fabric and dislodges the dust cake. Enhancement of the pulse may be achieved by using a venturi, and cleaning may be on-line or off-line. This paper summarizes the results of an exhaustive study conducted for the Electric Power Research Institute to provide a convenient and versatile information base about the use of pulse-jet fabric filters on coal-fired boilers. Predominant features of the many pulse-jet installations identified by vendor survey and literature survey are shown in graphical and tabular form.

Operating History and Current Status of Fabric Filters in the Utility Industry

Electric utilities have made significant progress in recent years in designing and operating baghouses for collection of coal fly ash. As a result, early concerns with high operating and maintenance requirements and short bag lives are no longer an issue. With increasingly stringent air emissions regulations and imminent revision of the Clean Air Act, baghouses have become an attractive particulate collection option for utilities. In order to keep its member utilities apprised of the latest design and operation and maintenance experience with baghouses, the Electric Power Research Institute has been conducting surveys of utility baghouse user experience. This paper presents results from the latest survey, conducted in 1989. A previous survey was conducted in 1985. The 1989 survey was conducted using questionnaires mailed to the utilities, telephone inquiries, and plant visits. This paper discusses the general trends observed in baghouse design, performance, operation and maintenance.

Selenium Partitioning and Removal Across a Wet FGD Scrubber at a Coal-Fired Power Plant.

Selenium has unique fate and transport through a coal-fired power plant because of high vapor pressures of oxide (SeO2) in flue gas. This study was done at full-scale on a 900 MW coal-fired power plant with electrostatic precipitator (ESP) and wet flue gas desulfurization (FGD) scrubber. The first objective was to quantify the partitioning of selenium between gas and condensed phases at the scrubber inlet and outlet. The second objective was to determine the effect of scrubber operation conditions (pH, mass transfer, SO2 removal) on Se removal in both particulate and vapor phases. During part of the testing, hydrated lime (calcium hydroxide) was injected upstream of the scrubber. Gas-phase selenium and particulate-bound selenium were measured as a function of particle size at the inlet and outlet of the scrubber. The total (both phases) removal of Se across the scrubber averaged 61%, and was enhanced when hydrated lime sorbent was injected. There was evidence of gas-to-particle conversion of selenium across the scrubber, based on the dependence of selenium concentration on particle diameter downstream of the scrubber and on thermodynamic calculations.

METHODS FOR DETERMINING PARTICULATE MASS AND SIZE PROPERTIES: LABORATORY AND FIELD MEASUREMENTS

No single particle size measuring device was found suitable in both the fine and ultrafine particle size regimes, however, combinations of devices have been used successfully. Methods of measurement and applications in the laboratory and field are discussed.

Long-Term COHPAC Baghouse Performance at Alabama Power Company’s E. C. Gaston Units 2 & 3

Following a successful pilot-scale baghouse testing program and after reviewing the performance of Luminant’s COHPAC (EPRI’s patented Compact Hybrid Particulate Collector technology) baghouse installation at its Big Brown Station, Alabama Power Company (APCO) decided to install a COHPAC baghous on Unit 3 at its E. C. Gaston Steam Plant located near Wilsonville, Alabama in late 1996. A second COHPAC baghouse was installed at Gaston Unit 2 in 1999. These baghouse systems were designed with the low pressure/high volume pulse-jet cleaning technology (Hamon Research-Cottrell) that orients the bags in concentric rings and uses rotating pulse manifold arms. Performance of these systems at Plant Gaston Unit 3 and Unit 2 has been excellent during the past eleven and a half and nine years, respectively, Original 3.0 and 2.7 denier Ryton felted fabries have given way to higher permeability 7.0 denier PPS felt bags in both units. Overall flange-to-flange and tubesheet pressure drop performance has improved without compromising particulate collection efficiency. Recent filter drag values of 0.5 in. H2O/ft/min on Unit 3 and 0.3 in. H2O/ft/min on Unit 2 have been experienced at air-to-cloth values of 8.0 ft/min. Average pulsing frequencies have ranged from 0.2 pulses per bag per hour for recently installed 7.0 denier PPS felted bags up to 0.7 pulses per bag per hour for older 2.7 denier Ryton felt bags. COHPAC baghouse installation has successfully reduced stack opacity. Comparing the average of the last eleven years of operation (1997–2007) to the average of the two years prior to COHPAC baghouse installation on Unit 3 (1995–1996), the average opacity has been reduced 50% and the number of hours per month that the average opacity has exceeded 20% has been reduced 95%. Similar results have been experienced on Unit 2. Except for early bag failure episodes on each unit caused by bag-to-bag abrasion, bag life has been very good. The original 3.0 denier Ryton felted bags in the rear modules of the Unit 3 baghouse remained in service for five years accumulating over 39,500 hours of exposure to flue gas with few bag failures. Front module bags in Unit 3, however, had much shorter bag lives because of a higher incidence of bag failures. Average service lives for the 3.0 and 2.7 denier filter bags were similar to those of the follow-on 7.0 denier PPS felted fabrics, typically two to three years, 19,000 to 27,000 hours of exposure to flue gas. Evaluation of the performance of various test bags has been ongoing for several years. Early tests compared the performance of 6.0 denier and 7.0 denier PPS felts with traditional 2.7 denier felts. 7.0 denier felted fabries performed very well. More recently, various dual-density felts have been tested. Results after 20,000 hours of flue gas exposure indicate that the Dual Density Torcon- 9058 felt is the best of the four test fabries. The test program is continuing. COHPAC baghouse performance for Alabama Power Company has exceeded expectations and continues to provide an excellent air pollution control benefit.