Glossary
Dantherm
Dust Collection Terms
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Abrasion:
Wear on the dirty side of the cloth.
Abrasion, flex: Wear on cloth in a creased area due to flexing, normally associated with cage contact.
Abrasion Resistance: The ability of a fiber or fabric (media) to withstand surface wear.
ACFM: Actual cubic feet of gas per minute. The volume of the gas flowing per minute at the operating temperature, pressure, elevation and composition.
Acrylic: Synthetic polymerized fiber with approximately 85% acrylonitrile.
Air Horsepower: The theoretical horsepower required to drive a fan if there were no losses in the fan, that is, it its efficiency were 100%
Air, Standard: Dry air at 70 F and 29.92 in (Hg) barometer. This is substantially equivalent to 0.075 lb/cu ft. Specific heat of dry air = 0.24 BTU/lb/F.
Air-to-cloth ratio: The amount of air or process gas entering the baghouse divided by the sq. ft of cloth in the baghouse.
example:(bag diameter in inches x pi x bag length in inches)
Bag Diameter (D) = 4.875in. (0.41ft.)
Bag Length (L) = 96in. (8.00ft.)
Area / Bag (A) = (Pi x D x L) = 10.2ft2
# of Bags in Baghouse = 200
Total Filter Area Baghouse = 2042ft2
Assume the Baghouse is Handling = 10000ACFM
Air to Cloth Ratio = (ACFM / Total Filter Area) = 4.90ft/min = 4.9:1
Aspect Ratio: The ratio of the width to the length. AR = W/L
Aspect Ratio of an Elbow: The width (W) along the axis of the bend divided by depth (D) in plane of bend. AR = W/D
Baghouse: An air filtration device utilizing fabric filter bags for removing solid particulate from a gas stream (dust collector).
Blast Gate: Sliding damper
Blinding: Blockage in a fabric or media by dust that cannot be discharged by the cleaning mechanism, resulting in a reduced gas flow and an increased pressure drop across the media. Once enough material has built up, airflow is severely restricted and the bags have to be cleaned or replaced.
Brake Horsepower: The horsepower actually required to drive a fan. This includes the energy losses in the fan and can be determined only by actual test of the fan. (This does not include the drive losses between motor and fan).
Bridge: Material blockage across an opening such as a hopper outlet or between bags.
Bridging: Blockage of dust across an opening such as a hopper outlet or between bags.
Can Velocity: The theoretical speed of dust laden air as it passes upward between the filter bags. The formula for calculating can velocity is as follows: The square area of the baghouse (length times width) minus the area occupied by the bags (the sum of the areas of the number of bags) divided into the volume. This formula yields a velocity in FPM. (feet per minute), Ideally, can velocity should be less than 200 FPM, between the bags.
example:
ACFM = 10000
Tubesheet Area (AT) = 90ft2
# of Bags in Baghouse = 200
Cross Sectional Area of Bag (AC) = (Pi * D2 / 4) = 0.130ft2
Can Area = (AT - (# of Bags * AC)) = 64.08ft2
Can Velocity = (ACFM / Can Area) = 156.1ft/min
Capture Velocity: The air velocity at any point in front of the hood or at the hood opening necessary to overcome opposing air currents and to capture the contaminated air at that point by causing it to flow into the hood.
Clean Air Plenum: The baghouse area through which gases are directed, located on the clean side of the filter bags.
Cloth weight: Usually expressed in oz./sq. yard.
Coating: Immersing the filter medium in a solution to provide the fibers with a coating that will lubricate and thereby reduce self-abrasion; in the case of woven-glass bags, the most common coatings have been Teflon and Siliconegraphite.
Cold Spot: The spot on an insulated baghouse where a continuous metallic heat transfer circuit through the insulation creates an uninsulated area.
Collection Efficiency: The measure of a dust collector's ability to remove particulate from the inlet gas, typically expressed in percent or emission rate (grains per cubic foot).
Concentration: Amount of dust in the gas. Usually expressed in terms of grains/cu ft., pounds/hour.
Density: The ratio of the mass of a specimen of a substance to the volume of the specimen. The mass of a unit volume of a substance. When weight can be used without confusion, as synonymous with mass, density is the weight of a unit volume of a substance.
Density Factor:The ratio of actual air density to density of standard air. The product of the density factor and the density of standard air (0.075 lb/cu ft) will give the actual air density in lbs per cu ft. d x 0.075 = actual density of air, lbs per cu ft.
Dewpoint: The temperature at which condensation begins to form as the gas is cooled.
Diaphragm Valve: A compressed air valve operated by a solenoid valve that opens to allow a pulse to a row of bags.
Dirty Air Plenum: The baghouse area through which gases are directed, located on the dirty side of the filter bags.
Differential Pressure: The change in pressure or the pressure drop across a device (baghouse) located within an airstream. The difference between static pressures measured at the inlet and outlet of a device. (See Pressure Drop)
Dust: Small solid particles created by the breaking up of larger particles by processes such as crushing, grinding, drilling, explosions, etc. Dust particles already in existence in a mixture of materials may escape into the air through such operations as shoveling, conveying, screening, sweeping, etc.
Dust Cake: A dust buildup on the filter bags that increases the efficiency of the filter media.
Dust Collector: An air cleaning device to remove heavy dust particles from exhaust systems before discharge to outdoors. Usually in the range of 0.003 grains per cubic foot and above.
Dust Loading:The weight of solid particulate suspended in an air stream, usually expressed in grains per cubic foot (or grams per cubic meter).
Emissions: Particulate that escapes through or around a baghouse into the atmosphere.
Entry Loss: Loss of pressure caused by air flowing into a duct or hood (inches H20).
Fabric: A term applied to cloth irrespective of construction and kind of fiber used. In common parlance, it refers to a woven cloth.
Fan: A device for moving air and dust through a ventilation system. If the fan is on the dirty air side of the baghouse, it is called a positive system. If the fan is on the clean air side of a baghouse, it is called a negative system.
Felt: Fabric structures constructed by the interlocking action of the fibers themselves, without spinning, weaving, or knitting.
Felted Bag: Type of bag frequently used on pulse-jet dust collectors. Features a thick mat of fibers supported by woven backing or scrim.
Filter Cake: The dust accumulation on a bag. Often assists in the filtration process. (also see dust cake)
Filter Media: The permeable membrane employed in the filtration process to separate the particles from the fluid stream.
Filtration: A process by which particles are separated from a fluid stream by use of a permeable membrane.
Flange-to-Flange: The baghouse equipment from inlet flange to outlet flange.
Fumes: Small solid particles formed by the condensation of vapors of solid materials.
Gas-to-Cloth-Ratio: The amount of process gas entering the fabric filter dust collector divided by the amount of cloth area filtering the dust from the air. Normally the gas flow is given in CFM and the cloth in square feet. (also see air-to-cloth ratio)
Gases: Formless fluids which tend to occupy an entire space uniformly at ordinary temperatures and pressures.
Glazing: High-pressure pressing of the filter medium at elevated temperatures; fuses surface fibers to the body of the filter medium.
Grain: A dust-weight unit commonly used in air pollution control. Equal to 1/7000 lb.
Grain Loading: Grains of dust per CFM.
Gravity, Specific: The ratio of the mass of a unit volume of a substance to the mass of the same volume of a standard substance at a standard temperature. Water at 39.2° F is the standard substance usually referred to. For gases, dry air, at the same temperature and pressure as the gas, is often taken as the standard substance.
Header: A pressurized pipe that contains the compressed air supply for a pulse type baghouse.
Hood: A shaped inlet designed to capture contaminated air and conduct it into the exhaust dust system
Hopper The section of a dust collector located below the filter bag housing utilized for the accumulation and discharge of the collected dust.
Humidity, Absolute: The weight of water vapor per unit volume, pounds per cubic foot or grams per cubic centimeter.
Humidity, Relative: The ratio of the actual partial pressure of the water vapor in a space to the saturation pressure of pure water at the same temperature.
Hydrophobic Fibers: Fibers that do not absorb water easily.
Hydrophilic Fibers: Fibers that easily absorb water.
Impingement: The physical contact of a dust laden gas flow against a filter media. Typically referred to the abrasive wear caused by this impact.
Inches of Water: A unit of pressure equal to the pressure exerted by a column of water one inch high at standard conditions (70°F @ sea level), usually expressed as inches water gauge ("w.g.) or inches water column ("w.c.).
Interstices: Openings between the fibers in a woven or felted filter bag.
Interstertial Velocity: Velocity of a gas as it passes between a compartment of filter bags calculated at its highest value. (See "Can Velocity" for formula)
Leakthrough: Dust or fume that leaks through a bad bag seal or a hole or crack in the tubesheet.
Magnehelic® Gauge: An instrument used to measure the differential pressure drop in a baghouse.
Manometer: An instrument for measuring pressure.
Micron: A unit of length, the thousandth part of I mm or the millionth of a meter (approximately 1/25,000 of an inch).
Minimum Design Duct Velocity: Minimum air velocity required to move the particulates in the air stream, fpm.
Mists: Small droplets of materials that are ordinarily liquid at normal temperature and pressure.
Needled Felt: A felt constructed by the use of barbed needles moving up and down, pushing and pulling the fibers to form an interlocking of adjacent fibers.
Negative Pressure Baghouse: A system where the fan is located after the baghouse on the clean air side, pulling air through the system.
OEM: Original Equipment Manufacturer.
Particulate: Any airborne solid material.
Permeability: A measure of fabric porosity of openness, expressed in cubic feet of air per minute per square foot of fabric at a 0.5" w.c. pressure differential.
Photohelic® Gauge An instrument used to measure the differential pressure drop in a baghouse and to initiate the cleaning system by means of adjustable "high" and "low" set points for automatic actuation of a sequential timer.
Plenum: Pressure equalizing chamber.
Porosity: Sometimes erroneously used as a synonym for permeability. Originally a designation for the amount of air in a fabric, i.e., blankets.
Positive Pressure Baghouse: A system with a fan located prior to a baghouse on the dirty side, pushing air through the system.
Precoat: Material added to the air stream at start-up to aid in establishing the initial dust cake on the filter bags.
Pressure Drop: A measure of the resistance the gas stream encounters as it flows through the baghouse. It may refer to pressure differential across the media, across the baghouse, or the pressure drop across the entire system, depending upon the points of measurement.
Pressure, Static: The potential pressure exerted in all directions by a fluid at rest. For a fluid in motion it is measured in a direction normal to the direction of flow. Usually expressed in inches water gauge when dealing with air. (The tendency to either burst or collapse the pipe).
Pressure, Total: The algebraic sum of the velocity pressure and the static pressure.
Pressure, Velocity: The kinetic pressure in the direction of flow necessary to cause a fluid at rest to flow at a given velocity. Usually expressed in inches water gauge.
Pulse Clean Baghouse: A baghouse using short intermittent pulses of compressed dry air to clean dust from the filter bags.
Pulse Cycle: The interval of time between pulsing one row of bags and pulsing that same row again.
Pulse Interval: Time between pulsing one row of bags and pulsing the next row.
Pulse Duration (On-Time): The length of time a pulse lasts, generally described as the length of time the electrical signal holds the solenoid pilot valve open.
Pulse Delay (Off-Time): Elapsed time between pulses in a dust collector cleaning system.
Pulse Jet: Generic name given to all pulsing collectors.
Replacement Air: A ventilation term used to indicate the volume of controlled outdoor air supplied to a building to replace air being exhausted.
Reverse-Air Baghouse: A unit employing reverse flow flushing air to clean the dust from the bags.
Rotary Airlock Valve: Device having a star wheel (rotor) designed to provide an air tight seal between the negative or positive pressures of the collector and the outside atmosphere.
SCFM: Standard cubic feet per minute. The volume of gas flow per minute at standard temperature and pressure conditions (70°F @ sea level).
Screw Conveyor: A revolving screw operating in a fixed trough for conveying material from one point to another. Note: Should a screw conveyor be used in a dust collector system, an airlock is still required to ensure ventilation air does not bypass through the conveyor.
Scrim: A very loosely woven fabric onto which felt is needled.
Seeding: The application of a relatively coarse, dry dust to a bag before startup to provide an initial filter cake for immediate high efficiency and to protect bags from blinding. (see Pre-coat)
Shaker Baghouse: A dust collector where cleaning is accomplished by manually or automatically shaking the bags to dislodge the accumulated dust cake. Typically, the airstream within the baghouse is in a static condition during the shaker cleaning cycle.
Singeing: Passing of the filter medium over an open flame, thereby removing the protruding surface fibers.
Slot Velocity: Linear flow rate of contaminated air through cloth, fpm.
Solenoid Valve: An electromechanical plunger device that is either "normally open" or "normally closed". In use with a baghouse, it is for the relief of air pressure to activate a compressed air device such as a diaphragm valve.
Smoke: An air suspension (aerosol) of particles, usually but not necessarily solid, often originating in a solid nucleus, formed from combustion or sublimation.
Temperature, Effective: An index which combines into a single value the effect of temperature, humidity and air movement on the sensation of warmth or cold felt by the human body. The numerical value is that of the temperature of still, saturated air that would induce an identical sensation.
Temperature, Wet-Bulb: Thermodynamic wet-bulb temperature is the temperature at which liquid or solid water, by evaporating into air, can bring the air to saturation adiabatically at the same temperature. Wet-bulb temperature (without qualification) is the temperature indicated by a wet-bulb psychrometer constructed and used according to specifications.
Timer, Sequential: An electrical mechanism that activates a dust collector's cleaning system.
Transport-Conveying Velocity: See Minumum Design Duct Velocity.
Tubesheet (Dust Wall): A steel plate to which the open end of the filter bags are connected. This wall separates the clean air and dirty air plenums of the baghouse.
Turnkey: Complete baghouse System including all dust pickups, ducting, dust discharge auxiliaries and all equipment which is part of the dust collection system.
Vapor: The gaseous form of substances which are normally in the solids or liquid state and which can be changed to these states either by increasing the pressure or decreasing the temperature.
Venturi: A cone-shaped device located at the top of a tubular filter bag in a pulse-jet dust collector which creates a negative pressure at the top of the venturi for pulling additional air down into the filter elements during pulsing.
Weight (Media): The average weight per square yard of fabric.
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