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Baghouse Filters & Scrubbers
Module 3b Baghouse Filters & Scrubbers
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What are we doing in class today?
MCEN 4131/5131 What are we doing in class today? How was working on the project in class? Davis readings Exam next week - closed book and notes
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Module 3a Educational Objectives
MCEN 4131/5131 Review Module 3a Educational Objectives Estimating cyclone collection efficiency (equation 4.7, 4.8 p ) 50% cut diameter dpc (equation 4.6 p. 129) Designing a cyclone from start to finish (Example 4.5 p ) Estimating ESP collection efficiency using Deutsch equation (equation 5.7 p. 152) Plate size and number, duct number, section number Designing an ESP from start to finish (p )
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Module 3b Educational Objectives
MCEN 4131/5131 Learning Objectives for Today Module 3b Educational Objectives Filtration mechanisms What is the filter drag model for (p. 181) Types of baghouses - Shaker, reverse air pulse jet (P. 184, 194) Number of compartments (p.186) Designing a baghouse accounting for superficial velocity, area per bag, cleaning methods How scrubbers work (p. 209) Venturi scrubbers (p. 212) Designing a scrubber
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Filtration Mechanisms
MCEN 4131/5131 Learning Objectives Filtration Mechanisms Diffusion Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design Q: How does efficiency change with respect to dp? a. Efficiency goes up as dp decreases b. Efficiency goes down as dp decreases
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Filtration Mechanisms
MCEN 4131/5131 Learning Objectives Filtration Mechanisms Impaction Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design Q: How does efficiency change with respect to dp? a. Efficiency goes up as dp decreases b. Efficiency goes down as dp decreases
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Filtration Mechanisms
MCEN 4131/5131 Learning Objectives Filtration Mechanisms Interception Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design Fat Man’s Misery, Mammoth Cave NP
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Learning Objectives MCEN 4131/5131 Filtration mechanisms
Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design
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FILTRATION Q: Do filters function just as a strainer,
MCEN 4131/5131 Learning Objectives FILTRATION Q: Do filters function just as a strainer, collecting particles larger than the strainer spacing? a: yes b: no Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design Fiber filter
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Filter Drag Model Areal Dust Density Filter drag
MCEN 4131/5131 Learning Objectives Filter Drag Model Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design Ks Areal Dust Density Ke Filter drag e s Time (min) DP, Pa 150 5 380 10 505 20 610 30 690 60 990 Ke & Ks to be determined empirically DPf: fabric pressure drop DPf: particle layer pressure drop DPs: structure pressure drop Q: What is the pressure drop after 100 minutes of operation? L = 5 g/m3 and V = 0.9 m/min.
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MCEN 4131/5131 Learning Objectives Types of Baghouses Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design The three common types of baghouses based on cleaning methods Clicker question: In which type is the dusty air flow blocked from the compartment to be cleaned, and the bags are then shaken to knock off the dust? Reverse-air Shaker Pulse-jet
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MCEN 4131/5131 Learning Objectives Note about pulse-jets Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design blast of compressed clean air flows briefly into the bags, while they are still filtering dusty air, knocking off some dust bottom of the bag is closed and filtration can occur on this surface - need to account for in area calculations
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Number of Compartments
MCEN 4131/5131 Learning Objectives Number of Compartments Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design Q: What is one of the parameters that affect our decision on the number of compartments to be used? a. fabric type b. time required to clean a compartment c. temperature and RH
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Parallel Flow Operation
MCEN 4131/5131 Learning Objectives Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design Parallel Flow Operation How do you determine when to clean?
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Design procedure for baghouses
MCEN 4131/5131 Learning Objectives Design procedure for baghouses Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design Identify filter velocity (V) for dust that your are trying to treat (table 6.1) Estimate net cloth area A = Q/V Remember to add area at bottom of filter if you are using pulse-jet Estimate number of compartments using table 6.3 Not needed for pulse-jet May need to develop filter-drag model to understand relationship between pressure drop DP, filtering velocity V For estimating how long you can run
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Its Raining in Boulder Liken particle scrubbers to a good rain storm
MCEN 4131/5131 Learning Objectives Its Raining in Boulder Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design Liken particle scrubbers to a good rain storm Some particles in air are removed because they are collected on or in raindrops and deposited on ground
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Its Raining in Boulder Liken particle scrubbers to a good rain storm
MCEN 4131/5131 Learning Objectives Its Raining in Boulder Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design Liken particle scrubbers to a good rain storm Some particles in air are removed because they are collected on or in raindrops and deposited on ground
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Its Raining in Boulder Liken particle scrubbers to a good rain storm
MCEN 4131/5131 Learning Objectives Its Raining in Boulder Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design Liken particle scrubbers to a good rain storm Some particles in air are removed because they are collected on or in raindrops and deposited on ground
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Its Raining in Boulder Liken particle scrubbers to a good rain storm
MCEN 4131/5131 Learning Objectives Its Raining in Boulder Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design Liken particle scrubbers to a good rain storm Some particles in air are removed because they are collected on or in raindrops and deposited on ground
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MCEN 4131/5131 Learning Objectives Question Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design The efficiency of a wet scrubber can be simply related to the energy expended in producing the actual gas-liquid contact. The (more/less) energy that is expended, the more turbulent the contacting process and the (higher/lower) the efficiency More, higher more, lower less, higher less, lower
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MCEN 4131/5131 Learning Objectives Venturi Scrubbers Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design Q: venturi scrubbers require which of the following to work efficiently? elevated temperatures within the scrubber High velocities at the point of initial gas-liquid contact Very small (what’s very small?) droplet sizes within scrubber
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Design procedure for Scrubbers
MCEN 4131/5131 Learning Objectives Design procedure for Scrubbers Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design Identify type of scrubber Counter current Cross flow Venturi Calculate Kp, impaction parameter Calculate single droplet target efficiency, hd Calculate Penetration, Ptd Collection efficiency is 1 - Ptd
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MCEN 4131/5131 Baghouse Filters Particulate control by impaction, interception, diffusion on fabric & dust layer
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Advantages/Disadvantages
MCEN 4131/5131 Advantages/Disadvantages Very high collection efficiencies Pressure drop reasonably low (at beginning of operation, must be cleaned periodically to reduce) Can’t handle high T flows or moist environments
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Wet Particle Scrubbers
MCEN 4131/5131 Wet Particle Scrubbers Particulate control by impaction, interception with water droplets Can clean both gas and particle phases High operating costs, high corrosion potential
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Other Technologies High-temp ceramic filter
MCEN 4131/5131 Other Technologies High-temp ceramic filter Operates at T > 500 F (limit for baghouses)
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