Multiple Spreader Stoker Boilers Provide Steam For Two 55 MW Generators
Application
Six spreader stoker boilers provide steam for two 55 MW generators. Each boiler exhausts into a 6 compartment pulse jet baghouse using Tri-Loft® fiberglass fabric filter bags at a 4.35 net A/C ratio.
Optimization Potential
Bag life of only 5-11 months caused 20-30 K lbs steam deration during on-line maintenance. A minimum of one maintenance person was required for bag change out for each shift. The baghouse was in a continuous cleaning mode (15 min.) with 95 psi pulse pressure.
Solution
Installed a full baghouse (1,008) of GORE® membrane/Teflon® B fiberglass fabric filter bags in June 1992. Conventional Ryton® felt was installed in the remaining five baghouses from May - June, 1992. In addition, the mechanical collector was refurbished and tubing added to the economizer which decreased the loading to the baghouse. Despite these upgrades, Tri-Loft was no longer considered an effective filter media.
Results
At full load, the GORE® membrane filter bags provide a baghouse pressure drop of 6.0" before cleaning and 4.0 - 5.0" after cleaning. This is maintained with a 50 psi pulse pressure and a 45-90 minute cleaning cycle. The low baghouse pressure drop allows boiler draft to be maintained at -0.10" with a 66% open I.D. fan damper setting. The conventional Ryton® felt filter bags require 95-100 psi pulse pressure, and operate at 6.0" pressure drop before cleaning, 5.5 - 6.0" DP after cleaning and a 25-35 minute cleaning cycle. Since the higher pressure drop requires a 95-100% open I.D. fan damper setting, the boiler draft can only be maintained at -0.10 to +0.10". The lower pulse pressure and infrequent bag cleaning of the GORE® membrane filter bags will allow for the potential of significantly longer bag life, without deration of the boiler. During periods of wet coal or fines from the bottom of the coal silo, the boilers with Ryton® felt has been derated by up to 10,000 lbs. steam/hr each or 1.5 MW, due to a 9.0" DP. At 5 cents/KW, this equates to $75/hr or $1,800/day in lost revenues. There has been no deration on the boiler line that uses GORE® membrane filter bags.
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