Fabric Filters • Filtration • Fabric Selection • Fabric Cleaning • Air/Cloth Ratio, Filtration Velocity • Pressure Drop and Design Consideration • NanofiberFilter • Filtration Mechanisms Reading: Chap. 6 http://exportdeck.com
Types of Filter Fibrous filter Felted filter
Types of Filter Do filters function simply as sieves (to collect particles larger than the sieve spacing)? Packing density/solidity For fiber filter, a < 0.1 For woven filter, a ~ 0.3
Theodore & Buonicore, Air Pollution Control Equipment, CRC Press, 1988.
Shaker Cleaning Parameters Shaker Baghouse What are the common problems encountered? Theodore & Buonicore, Air Pollution Control Equipment, CRC Press, 1988.
Reverse-Air Cleaning Parameters Cleaning dust on baghouse walls by traditional sledge-hammering Pros and Cons?
Pulse-Jet How can the blown-away particles by the on-line cleaning process be collected? Felted fabric or woven fabric?
Air/Cloth Ratio Filtration velocity (average velocity) If thicker fabric is needed to sustain the high force, is its operating cost higher?
Parallel Flow Operation How do you determine when to clean?
K2 K1 Pressure Drop (Filter Drag Model) Areal Dust Density Filter drag K1 & K2 to be determined empirically (resistance factor) DPf: fabric pressure drop DPf: particle layer pressure drop DPs: structure pressure drop What is the pressure drop after 100 minutes of operation? L = 5 g/m3 and V = 0.9 m/min.
Time to clean Filtering velocity Flow rate Dpm Pressure tc tj tr tf What are the parameters that affect our decision on the number of compartments to be used? Time
Filter drag Areal dust density Pressure drop Actual filtering velocity
Nanofiber Filter Ex. Calculate the max pressure drop that must be supplied for the following baghouse for a filtration time of 60 minutes: K1 = 1 inch H2O-min/ft, K2 = 0.003 inch H2O-min-ft/grain, tc = 4 min, 5 compartments, L = 10 grain/ft3, Q = 40000 ft3/min, Ac = 4000 ft2/compartment. Nano-alumina on microglass E-spun PAN nanofiber Dr. Wolfgang Sigmund, MSE. UF Argonide
Filtration Mechanisms http://aerosol.ees.ufl.edu/respiratory/section04.html • Diffusion(Lee & Liu, 1982) How does efficiency change wrtdp? How to increase efficiency by diffusion? Lee, K.W. & Liu, B.Y.H., Aerosol Sci. Technol., 1:47-61, 1982
How to increase impaction efficiency? How does efficiency change wrtdp? • Impaction (Yeh & Liu, 1974) (J = 2 for R > 0.4) Yeh. H.C. & Liu, B.Y.H., J. Aerosol Sci., 5:191-217, 1974
Interception(Krish & Stechkina, 1978) Fat Man’s Misery, Mammoth Cave NP How to increase interception efficiency? 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.
Gravitational Settling • Total Single Fiber Efficiency • Total Filter Efficiency Sf: Solidarity factor How does the filter efficiency change wrt particle size?
H = 1mm • = 0.05 df = 2mm U0=10 cm/s Should we increase or decrease flow velocity in order to increase collection efficiency for (a) tobacco smoke, (b) cement dust?
Minimum Efficiency Reporting Value (MERV) for HVAC (Heating, Ventilating and Air Conditioning) Filters http://www.mechreps.com/PDF/Merv_Rating_Chart.pdf