52nd North Carolina Industrial Ventilation Conference

Transcription

1 System Components Air Cleaner Air Control Module 1 2 Types of Dry Contaminants Aerosols & Dust Particulates: Solid particulate - dust particles Liquid Particulate - Droplets Gas: substance in gaseous state Atmospheric Dust Pollen Road Dust Hair Etc Industrial/Commercial Dust Grinding Dust Fly Ash Cigarette Smoke Auto Exhaust 3 4 Dust Quality Particle Size Size Concentration Micron (Unit of length) Micron = 1meter/1,000,000 = mm/1,000 Micron = 1 / 25,400 Measure of the mean aerodynamic diameter 5 6 Module 1

2 Examples Particle Size Chart Human Hair = 50 Pollen = 10 Fly ash = 5 Metal fumes = <1 (Combustion and condensates) Microns (µ) (Log Scale) Technical Definitions Atmospheric Conditions Relative Size of Typical Airborne Particulates Scanning Electron Microscope Virus Carbon Black Fume Mist Optical Microscope Dust Spray Clay Silt Fine Sand Smog Tobacco Smoke Visible to Naked Eye Clouds/Fog Mist/Drizzle/Rain Mold Spores Human Hair Cement Dust Bacteria Fertilizer Pollen Lint Coal Dust Beach Sand Colloidal Silica Milled Flour 7 8 Dust Concentration (Dust Loading) Example # 1 Mass / Volume Grains per Cubic Foot or Milligrams per Cubic Meter 100 lb/hr of dust, 10,000 ft 3 /min air flow What is the grain loading? C = (100 lb/hr) (hr/60 min) (7000 gr/lb)/(10,000 ft 3 /min) C = 1.2 gr/ft grains = 1 pound 1 milligram/m 3 = grains/ ft Dust Loading Examples Air Cleaners Filtration Mechanism Abrasive blast room and tablet coating (20) Sand shake out and grain handling (5) Metal Furnaces (3) Visible effluent (0.05) Haze (0.005) Industrial workroom (0.0005) Straining or Sieving Inertia or Impaction Interception Diffusion Electrostatic Atmospheric dust ( ) Concentration (gr/ft 3 ) Module 2

3 Straining Impingement Interception Diffusion Mechanism Contribution Air Cleaning Devices ncy % Efficien Total Diffusion Impaction Interception Sieving Air Filters General ventilation Light dust loadings 0.1 grains/1000 ft 3 Dust Collectors Industrial ventilation Heavy dust loadings 0.1 to 20+ grains/ft Particle Size (Micron) Module 3

4 Air Filter Types Air Filter Test Methods Panel ASHRAE HEPA ULPA ASHRAE 52.1 Arrestance Efficiency DOP ASHRAE 52.2 MERV Minimum Efficiency Reporting Value MERV Measured in a test stand MERV Efficiency Table Standard 52.2 Minimum Efficiency Reporting Value (MERV) Composite Average Particle Size Efficiency, Minimum Final % in Size Range, nm Resistance Average ASHRAE Arrestance, %, by Range 1 Range 2 Range 3 Standard 52.1 Inches of ( ) ( ) ( ) Method PA Water 1 n/a n/a E3 < 20 A avg < n/a n/a E3 < A avg < n/a n/a E3 < A avg < n/a n/a E3 < A avg n/a n/a 20 E3 < 35 n/a n/a n/a 35 E3 < 50 n/a n/a n/a 50 E3 < 70 n/a n/a n/a 70 E3 n/a n/a E2 < E3 n/a n/a 50 E2 < E3 n/a n/a 65 E2 < E3 n/a n/a 80 E2 90 E3 n/a E1 < E2 90 E3 n/a E1 < E2 90 E3 n/a E1 < E2 90 E3 n/a E1 95 E2 95 E3 n/a ASHRAE 52.2 Test Results Compared to ASHRAE 51.1 & DOP Air Cleaning Devices Cellulose and MERV /20 Blends 95% ASHRAE MERV 10 MERV DOP MERV 13 Air Filters General ventilation Light dust loadings 0.1 grains/1000 ft 3 Dust Collectors Industrial ventilation Heavy dust loadings 0.1 to 20+ grains/ft 3 95% DOP MERV 17 HEPA MERV 17, 18 Source: ACGIH Industrial Ventilation Manual (American Conference of Governmental Industrial Hygienists) ULPA MERV 19, Module 4

5 Dust Collectors Collector Selection Objectives Highest feasible efficiency Economical initial installation and maintenance costs Complies with all air pollution regulations Energy Efficient Collector Selection Factors Properties of the Gas Stream Gas stream characteristics Contaminant characteristics Efficiency requirements Energy considerations Dust disposal method Temperature Water Mists/Condensation Sticky Particles Condensed Hydrocarbons (Oils) Acid Mist Condensation Dust Characteristics Dust Shape Chemical Composition Type Hygroscopicity Size Shape Dust generating process Spherical, fibrous, or flaky Fibrous Bulk Density Agglomerativeness Abrasiveness Module 5

6 Abrasiveness Agglomerativeness Tendency to rub or wear away the media or the collector Detergents, Rice hulls, or steel shot Maintain velocity <2,000 fpm Tendency to gather into a ball, mass, or cluster Paper, cellulose, cotton Special cartridge or bag Controlled airstream conditions Hygroscopicity Chemical Composition Readily taking up and retaining moisture Acids, starches, or cement Relates to release ability of dust cake MSDS information Corrosiveness Toxicity Explosiveness Basic Air Cleaning Devices Dry Mechanical Collectors Dry Mechanical Collectors Settling and Impact Chambers Cyclones Wet Collectors Electrostatic Precipitators Fabric / Media Collectors Baghouses Cartridge Collectors Others Gravity Separators Inertial Separators Centrifugal Collectors Module 6

7 Settling Chamber A long chamber allowing time for particles to settle by gravity forces Large cross section to reduce gas velocity to 200 to 350 fpm Low Efficiency 50% at 50 to 80 µm < 10% at 20 µm or less Low static pressure drop < 0.5 Inlet VP (well designed inlet and outlet) Inertial Separator Baffle(s) are added to improve collection efficiency by impaction forces Chief advantage requires less space than settling chamber Collection efficiency is 50% for dusts 20- to-40 µm Static Pressure Loss: 1.25-to-1.5 Inlet VP Uses centrifugal forces to separate particulate from gas stream Dust > 10 micron Pre-cleaner to more efficient devices Concentration is > 10 gr/dscf Product separator for kilns and dryers Advantages Low cost Low maintenance Not suitable for control of fine particulates < 5 µm Cyclones/Centrifugal Separation Conventional Cyclone High Efficiency Cyclones High Efficiency Cyclone Fractional Efficiency Curve 41 Entrance Velocity = 60 fps (50 to 65 most common) Particulate SG = Module 7

8 Multiple Cyclones Cyclone Pressure Drop Pressure Drop = (K) (VP inlet ) (K) depends on the body proportions Delta P follows the system laws DP 2 = DP 1 x (Q 2 / Q 1 ) 2 Typical Pressure Drop 0.75 to 2 wg = Conventional cyclone 3 to 6 wg = High efficiency cyclone Dry Collector Pressure Drops Mechanical Separators Settling Chambers Conventional Cyclones High Efficiency Cyclones Multi-clones in wc in wc in wc in wc Advantages Low initial cost Low maintenance Handle heavy load Disadvantages Lower efficiency on small particulate Short life on abrasive dusts High energy/efficiency Wet Collectors Wet Collectors Contact Power Theory For a well designed wet collector, the efficiency i is a function of energy utilized in the contact zone where the dirty air contacts the water droplet Module 8

9 Wet Scrubber Principles of Operation Wet Collector Classification Low pressure drop Medium pressure drop High pressure drop Can be as high as 100 P up to 5 wg 6 to 15 wg 16 wg & up Types of Wet Collectors Spray Tower Spray Tower or Chamber Packed Towers Wet Centrifugal Orifice Type Venturi Low Pressure drop 0.5 to 1.5 wg 5 to 10 gpm / 1,000 cfm psig % on 2μ Packed Tower Wet Centrifugal Contact beds for gases and liquids. Solids plug the packing. DP = 1.5 to 3 wg 5 10 gpm / 1,000 Moderate dust loads Multiple stages Variable efficiency Variable DP 2 to 6 wg 2 to 5 gpm / 1,000 cfm % on 2μ Module 9

10 Wet Centrifugal Orifice Type Inefficient fan = 4 wg Low dust loading 0.5 to 1 gpm / 1000 cfm 90% on 2μ Very compact size Moderate dust loads DP = 5 to 12 wg 0.5 to 1 gpm/1,000 cfm % on 2 2μ Venturi Scrubber Wet Collector Pressure Drops Heavy dust burdens DP 6 to >100 wg 5 to 15 gpm/1,000 cfm 99+% on 2μ Spray Tower in wc Packed Tower in wc Wet Centrifugal inwc 6.0 Orifice Type in wc Venturi Type in wc Advantages High Temperature Air Moisture Laden Air Explosive Dust Sticky Dust No Secondary Dust Problem Can Use smaller fan Wet Collectors Disadvantages Water Pollution Problem High Energy/Efficiency y Humidify the Air Corrosion Freezing Fractional Efficiency 59 Fractional Efficiency by Particle Size Particle Size Efficiency > < < < < < < < < < Module 10

11 Electrostatic Precipitators Electrostatic Process Ionizer Collection Plates Ionize the gas Charge of the particles Transport the particles to the collection plates Neutralize the charge Remove the dust from the collection plate Electrostatic Precipitators High Voltage ESP 1. High Voltage (40,000-70,000 Volt) Single-Stage-COTTRELL TYPE 2. Low Voltage (11,000-14,000 Volt) Two-Stage-PENNY TYPE High voltage ionizing electrodes between grounded collection plates Dust removal is via hammers, sonic horns or water wash Low Voltage ESP Electrostatic Precipitators Applications Hydrocarbons Plastisol l curing Quenching Forge Presses Oily Welding Advantages Low differential pressure Oils and hydrocarbons Disadvantages Maintenance intensive Medium efficiency Low loading Module 11

12 Fabric or Media Collectors Fabric Collectors Variable Design Features Type of fabric Fabric Configuration Intermittent t or Continuous Service Type of Reconditioning Housing Configuration Continuous or Intermittent Duty Fabric Types Filter Configurations Woven Non-woven Other Cylindrical bags Envelopes Pleated cartridges Corrugated medias Others Typical Media Materials Fabric Collectors Acrylic Cellulose Cotton Glass Orlon Polyester Polypropylene Nomex P84 Teflon Intermittent Duty Shaker Module 12

13 Intermittent Duty Filter Characteristics Woven Fabric Woven bags Surface filter Low energy cleaning Dust cake is filter Shaker Type Collector Continuous Automatic Arrangement Module 13

14 Fabric Collectors Reverse Air Collapse (Baghouse) Normal Operation Reverse Air Collapse Cleaning Cleaning Cycle Motion: Gentle Collapse of Bag Mode: Offstream Duration: Reverse Air 10- to-30 seconds, Total Duration 2 Minutes Bags 8-to-12 inch diameters 20-to-40 foot lengths Reverse Flow Collector Module 14

15 Advantages High Efficiency Low maintenance Ability to handle hot applications Long filter life Low cost filter media Low Energy Clean Collectors Disadvantages Variations in pressure drop Large equipment size Filter change-out is dirty Mechanical components subject to wear. Fabric Collector Continuous Duty Type Pulse Jet Continuous Duty Fabric Characteristics Dust Cake Felt bag Depth loading High energy cleaning Bag is filter 87 Bag filter with scrim 88 Filter Media Comparison of Filter Media Table 8-1 Max. Temp. Moist Heat Alkaline Acid What to Avoid Polypropylene 190 F Excellent Excellent Excellent High Heat Polyester 275 F Poor Good Fair Moist Heat High Acids Acrylic 275 F Excellent Poor Good High Heat, Alkalines Nomex 375 F Good Good Poor SO x & Moisture Ryton 375 F Excellent Excellent Excellent Teflon (PTFE) 450 F Excellent Excellent Excellent Fiberglass 500 F Excellent Fair Poor High Heat, O 2 (>9%) Oils, Tarry, Abrasion Flexing, Rubbing, Acids (HF, H 2 SO 4 ) Plain Singed Media Surface Finishes Glazed or Eggshell Silicone Oleophobic, Hydrophobic, UCF Membrane Module 15

16 Continuous Duty Pulse Jet Collector Pulse-Jet Cleaning System Pulse Jet Fabric Collector Diaphragm and Solenoid Valves Compressed Air: 80-to-100 psig Mode: Online and Offstream Pulse Duration: 0.1 sec pulse, shock wave travel time 0.5 sec Bags 4-to-6 inch diameter 8-to-14 foot lengths supported by a wire cage Tubesheet and Blowpipes Bag Removal Clean Side Module 16

17 97 98 Fabric Dust Collectors Upflow Design Downflow Design Pulse Jet Collector Envelope type Clean Side Removal Pulse-Jet Collector This shows an envelope filter element being inserted into the tube sheet. Advantages Disadvantages Stable filter differential Requires compressed pressure air Continuous duty High energy cleaning Low maintenance High Efficiency Broad applications Large equipment size Time consuming filter change out Module 17

18 Reverse Air Baghouse Reverse Air Collector Oval Bags and Cages PD Blower Air Accumulator Tank Cleaning Manifold Arm Module 18

19 Low Pressure Pulse Baghouse Fabric Filter Collectors Advantages No compressed air Long filter life High loading Ease of installation Disadvantages Large equipment size Filter cleaning system maintenance Time consuming filter changeout Pulse Jet Cartridge Type Filter Area Comparison Dust Cake Bag filter with scrim Cartridge filter with fine fiber Cartridge Options Fiber Diameter Media Cellulose Cellulose / polyester blend Spun Bond polyester Glass w/ resin Finish options PTFE membrane Nano-fibers Carbon impregnated Fluorocarbons Singed surface Module 19

20 Cartridge Variations First Cartridge Dust Collector Pulse Jet Cleaning More media in less space High efficiency Easier maintenance Decreased headroom Downflow Cartridge Collector Normal Operation Module 20

21 Filter Element Purge Cartridge Collector Applications Fine particulate Nuisance dust, loading <2 grains/ft 3 Abrasive blasting Bakeries Grinding Pharmaceuticals Pulse-Jet Cartridge Collectors Unit Collectors Advantages Higher collection efficiency Small overall size Safer, easier filter change out Low maintenance Disadvantages Lower loadings More application sensitive Requires compressed air Sensitive to sticky & agglomerative dust Unit Collectors Can be either Medium or High Energy (shaker or pulse jet) Incorporates a dust receiver, hopper, filter, filter cleaning mechanism, and fan in one common, integral unit Typically used for small, remote, or dissimilar applications Pressure drop is usually 1 to 4 in wg Module 21

22 Intermittent Applications Intermittent-Duty Collectors Grinding Abrasive blasting Batch mixing Bag dumping Advantages High efficiency Can be seasoned Low initial i i cost No compressed air Disadvantages Varying filter pressure drop Must be shut down to clean Low initial efficiency A:C AMR V f Sizing Fabric Filters Air to Cloth Ratios Air to cloth ratio Air to media ratios Filtration Velocity V f = Q/Filter Area Based on Experience Test Dust test Trial units Selecting Filtration Velocities Typical Filtration Velocities Factors Affecting Filtration Velocity Round Tube Shaker Reverse Air Collapse Pulse Jet Fabric Pulse Jet Cartridge Low Pressure Pulse Fabric 1-3 fpm 1-4 fpm 4-10 fpm fpm 4-8 fpm Operating time schedule Emission Requirements Air Density y( (DF) Temperature Elevation/Pressure Humidity Dust Concentration Inlet loading Allowable outlet emissions i Interstitial Velocities Unknowns Module 22

23 Interstitial Velocity Sometimes referred to as Tank or Can velocity Upward velocity between the filter bags Concern in Up flow pulse jet collectors Low density dust paper, fibers, etc Velocity = Q / ( A H A B ) A H = Cross sectional area of housing A B = Cross sectional area of bags Homework 1: Collector Efficiency A EPA compliance test on a dust collector resulted in 160 lb/hr inlet dust and 0.35 lb per hour outlet dust. The measured airflow was 10,000 dscfm. The permit limit is gr/dscf. Did the company pass the compliance test? What is the efficiency of the dust collector? Homework 1: Answers Basic Air Cleaning Devices Outlet Concentration = Mass Flow/Airflow = (0.35 lb/hr hr/60 min 7000 gr/dscf)/10,000 dscfm = gr/dscf Inlet Concentration = (160 lb/hr hr/60 min 7000 gr/dscf)/10,000 dscfm = 1.9 gr/dscf Collector Efficiency = [1 (Outlet/Inlet)] 100 = [1 (0.004/1.9)] 100 = 99.8% Dry Mechanical Collectors Settling and Impact Chambers Cyclones Wet Collectors Electrostatic Precipitators Fabric / Media Collectors Baghouses Cartridge Collectors Others Others Mist Collectors Mist Collectors Gaseous Contaminant Collectors Absorbers Adsorbers Oxidizeres Wet Collectors Fixed media collectors Module 23

24 Absorbers Packed Tower Absorbers remove soluble or chemically reactive gases One or more of the gas stream components dissolve in the liquid or dry reactant Adsorbers Incineration / Oxidizers Use oxygen to convert contaminants to carbon dioxide and water No chemical reaction Adhesion of molecules to a surface Activated carbon Activated alumina Fuller s earth What VOCs Organic aerosols Odorous gases How Direct Combustors Thermal Oxidizers Catalytic Oxidizers Regenerative Thermal Oxidizers Concentrators Collector Selection Objectives Highest feasible efficiency Economical initial installation and maintenance costs Complies with all air pollution regulations Minimum energy cost Thank You Module 24