April 26, 2007
High Sulfur Coal Baghouse Success is tied to Additives in Hot Topic Hour on April 26
There are not many high sulfur coal baghouses operating on utility boilers. Vectren, with a baghouse which has been in operation at Brown 1 since 2005 and one at Culley 3 that has been in operation a few months, are among the few with coal sulfur content in excess of 2.5% and with SCR for NOx control.
The first discussion in the Hot Topic Hour yesterday was whether Vectren is the first or whether there are others. John McKenna of ETSI-Inc. observed that there is some experience on industrial boilers. In fact Carmeuse contributed to the first high sulfur coal baghouse Hot Topic Hour with the ways that they extend bag life on their industrial boiler installation.
Fabric selection is important. If the temperature is not too high, PPS can be used. Terry McKenna (Filtex) pointed out that one additional advantage of PPS is that it does not absorb moisture, so you can actually wash bags as an emergency solution. Terry advised the participants that PTFE can withstand temperatures of 240°C or more than 60°C more than the PPS. But a less expensive alternative (TEFAIRE) with 50% PTFE and 50% glass can also operate at 240°C. TEFAIRE has increased mechanical strength at high temperatures, increased felt density and because of the triboelectric effect, improved filtering efficiency.
Dennis Glancy of Vectren believes that to extend the bag life beyond one year, additives will be necessary. He expressed this in terms of offsetting the acid mist with sufficient basic particulate
Rich Staehle of Marsulex stated that the work at Dominion showed it was the quantity and not the pH which was most important. Ground limestone was used in the demonstration and worked well, but additional flyash of the same particle size would also do the job.
Eric Van Rens of Mississippi Lime pointed out that there is a cost associated with creating particles 2 to 3 microns in diameter. Hydrated lime may be cost competitive with limestone due to the grinding cost.
Rich (Marsulex) pointed out that for the demonstration a waste limestone material was utilized. But, as Eric (Mississippi Lime) replied, this material is not likely to always be available in the quantities required. The Marsulex approach involves the re-design of the air heater and other initiatives and is not solely dependent on particle injection.
John McKenna (ETSI-Inc.) has evaluated baghouses vs. dry electrostatic precipitators for high sulfur coal applications. The capital cost of a pulse jet unit and a four field electrostatic precipitator are similar. The ability of the fabric filter to remove very small particles is important due to the stringent limits on specific metals which are finding their way into most permits.
For more information on previous and future Hot Topic Hours see below or click on:
http://www.mcilvainecompany.com/brochures/FGDnetoppbroch/Default1.htm