This document discusses various topics related to fabric filter design and operation including: 1) Fabric selection factors such as packing density and fiber type. 2) Common cleaning methods like shaker, reverse-air, and pulse-jet cleaning and their pros and cons. 3) Key filtration mechanisms like diffusion, impaction, and interception and how efficiency is affected by particle size. 4) Parameters that influence pressure drop over time like dust loading and filter drag coefficients. 5) Design considerations for factors like compartmentalization and cleaning cycle timing.

1. Fabric Filters Filtration Fabric Selection Fabric Cleaning Air/Cloth Ratio, Filtration Velocity Filtration Mechanisms Pressure Drop and Design Consideration Reading: Chap. 6

2. Filtration Packing density/solidity Fiber filter For fiber filter,  < 0.1 For woven filter,  ~ 0.3 Q: Do filters function simply as sieves (to collect particles larger than the sieve spacing)?

3. Theodore & Buonicore, Air Pollution Control Equipment, CRC Press , 1988.

4. Shaker Baghouse Theodore & Buonicore, Air Pollution Control Equipment, CRC Press , 1988. Shaker Cleaning Parameters Q: What are the common problems encountered?

5. Reverse-Air Q: Pros and Cons? Cleaning dust on baghouse walls by traditional sledge-hammering

6. Reverse-Air Cleaning Parameters Reverse-Jet

7. Pulse-Jet Q: How can the blown-away particles by the on-line cleaning process be collected? Q: Felted fabric or woven fabric?

8. Air/Cloth Ratio Filtration velocity (average velocity) Q: If thicker fabric is needed to sustain the high force, is its operating cost higher?

9. Filtration Mechanisms Diffusion (Lee & Liu, 1982) Lee, K.W. & Liu, B.Y.H., Aerosol Sci. Technol. , 1 :47-61, 1982 Q: How does efficiency change wrt d p ? Q: How to increase efficiency by diffusion? http://aerosol.ees.ufl.edu/respiratory/section04.html

10. Impaction (Yeh & Liu, 1974) Yeh. H.C. & Liu, B.Y.H., J. Aerosol Sci. , 5: 191-217, 1974 Q: How to increase impaction efficiency? Q: How does efficiency change wrt dp ? ( J = 2 for R > 0.4)

11. Interception (Krish & Stechkina, 1978) Krish, A. A. & Stechkina, I. B., “The theory of Aerosol Filtration with Fibrous Filters”, in Fundamentals of Aerosol Science , Ed. Shaw, D. T., Wiley, 1978. Q: How to increase interception efficiency? Fat Man’s Misery, Mammoth Cave NP

12. Gravitational Settling Total Single Fiber Efficiency Total Filter Efficiency S f : Solidarity factor Q: How does the filter efficiency change wrt particle size?

13. H = 1mm = 0.05 d f = 2  m U 0 =10 cm/s Q: Should we increase or decrease flow velocity in order to increase collection efficiency for (a) tobacco smoke, (b) cement dust?

14. Parallel Flow Operation Q: How do you determine when to clean?

15. Pressure Drop (Filter Drag Model) Areal Dust Density Filter drag K 1 & K 2 to be determined empirically (resistance factor)  P f : fabric pressure drop  P f : particle layer pressure drop  P s : structure pressure drop Q: What is the pressure drop after 100 minutes of operation? L = 5 g/m 3 and V = 0.9 m/min. K 2 K 1 990 60 690 30 610 20 505 10 380 5 150 0  P, Pa Time (min)

16. Time to clean Flow rate Filtering velocity Q: What are the parameters that affect our decision on the number of compartments to be used?

17. Areal dust density Filter drag Actual filtering velocity Pressure drop

18. Ex. Calculate the max pressure drop that must be supplied for the following baghouse for a filtration time of 60 minutes: K 1 = 1 inch H 2 O-min/ft, K 2 = 0.003 inch H 2 O-min-ft/grain, t c = 4 min, 5 compartments, L = 10 grain/ft 3 , Q = 40000 ft 3 /min, A c = 4000 ft 2 /compartment.

19. Quick Reflection