Subject: Decision on Bags for FGD Spray Driers
ePTFE Membrane Laminate Should be Considered for Spray Drier Bags
This is one of the recommendations provided by Brian Vancrum in his speech at Electric Power 2005. He covered the gamut of baghouse applications for coal-fired boilers. McIlvaine has a new service which allows the purchaser to logically select bags for FGD spray driers with a rational basis and with all the needed background data. The new service has already incorporated elements of this speech. Here is how this material has been incorporated into the decision tree.
The first major decision is reverse air or pulse jet. Brian indicates that the trend is toward pulse jets. But our question is how is the choice shaped by previous decisions? Is there a case to be made for using reverse air filters for spray drier fabric filters? There are some installations where a spray drier was coupled with an existing reverse air filter, but cost dictates the choice of pulse jets. What about the CFB dry scrubber fabric filters? They operate at slightly higher temperature and can more easily avoid reaching the acid dew point. How does this change the decision between reverse air and pulse jet? Is there any difference in bag selection based on whether rotary atomizers or dual fluid nozzles are used? Probably not, but we would be interested in reader comments.
Brian indicates that pleated filters are now available with Aramid, PPS media, and fiberglass, so this is another option. But its role is really as a way to increase air flow through an existing system. For a new installation, why spend $150 for pleated elements when the tubular is only $50? The choice of fabric is a function of cost and conditions. Spray driers operate close to the acid dew point. Brian presented a chart comparing properties of the various fabrics. Fiberglass has a "poor rating" for acid conditions. Aramid’s are only fair, whereas PPS is excellent. PPS has captured a good share of the spray drier applications. Brian estimates that PPS and woven fiberglass account for 85 percent of the total utility market. However, the fiberglass is primarily in the "particulate only" applications and not typically used for spray driers.
Brian says that decreased temperature and increased moisture have been one reason that customers have opted to select an ePTFE membrane laminate to the base media which could be PPS. The benefits are not only ease in filter cleaning, but enhanced fine particulate collection, longer bag life, and lower differential pressure. For more information on FGD Decisions, click on: http://www.mcilvainecompany.com/FGDdecbroch/Default.htm .
FGD Decisions is now also included in Power Plant Knowledge System which in turn includes the complete Fabric Filter Knowledge System. Check this out at: http://www.mcilvainecompany.com/energy.html#44I .
Bob McIlvaine
847-784-0012
rmcilvaine@mcilvainecompany.com