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Module 3b

Module 3b. Baghouse Filters & Scrubbers. What are we doing in class today?. How was working on the project in class? Davis readings Exam next week - closed book and notes. Review. Module 3a Educational Objectives. Estimating cyclone collection efficiency (equation 4.7, 4.8 p. 129-130)

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Module 3b

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  1. Module 3b Baghouse Filters&Scrubbers

  2. 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

  3. MCEN 4131/5131 Review Module 3a Educational Objectives • Estimating cyclone collection efficiency (equation 4.7, 4.8 p. 129-130) • 50% cut diameter dpc (equation 4.6 p. 129) • Designing a cyclone from start to finish (Example 4.5 p. 138-139) • 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. 160-161)

  4. MCEN 4131/5131 LearningObjectivesfor 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

  5. MCEN 4131/5131 LearningObjectives Filtration Mechanisms 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 • Diffusion

  6. MCEN 4131/5131 LearningObjectives Filtration Mechanisms 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 • Impaction

  7. MCEN 4131/5131 LearningObjectives Filtration Mechanisms Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design • Interception Fat Man’s Misery, Mammoth Cave NP

  8. MCEN 4131/5131 LearningObjectives Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design

  9. MCEN 4131/5131 LearningObjectives 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

  10. MCEN 4131/5131 LearningObjectives 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 s e 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.

  11. MCEN 4131/5131 LearningObjectives 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

  12. MCEN 4131/5131 LearningObjectives 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

  13. MCEN 4131/5131 LearningObjectives 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

  14. MCEN 4131/5131 LearningObjectives Parallel Flow Operation Filtration mechanisms Filter drag model Types of baghouses Number of compartments Baghouse design How scrubbers work Venturi scrubber Scrubber design How do you determine when to clean?

  15. MCEN 4131/5131 LearningObjectives 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

  16. MCEN 4131/5131 LearningObjectives 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

  17. MCEN 4131/5131 LearningObjectives 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

  18. MCEN 4131/5131 LearningObjectives 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

  19. MCEN 4131/5131 LearningObjectives 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

  20. MCEN 4131/5131 LearningObjectives 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

  21. MCEN 4131/5131 LearningObjectives 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

  22. MCEN 4131/5131 LearningObjectives 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

  23. MCEN 4131/5131 Baghouse Filters • Particulate control by impaction, interception, diffusion on fabric & dust layer

  24. 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

  25. MCEN 4131/5131 Wet Particle Scrubbers • Particulate control by impaction, interception with water droplets • Can clean both gas and particlephases • High operating costs, highcorrosion potential

  26. MCEN 4131/5131 Other Technologies • High-temp ceramic filter • Operates at T > 500 F (limit for baghouses)

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