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Glossary
Scroll down for definitions of commonly used terms in the industry,
or select a letter to go to that section.
A - B - C - D - E - F - G - H - I - L - M
N - O - P - R - S - T - V
-A-
Absorption |
Process where one material
consumes another
as a homogeneous mixture in solution form
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ACFM |
Acronym for Ambient Cubic Feet per Minute
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Acid
dewpoint |
The temperature at which
acidic liquid droplets condense from the vapor
phase.
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Acrylic |
Synthetic polymer fiber
that goes by trade names Orlon, Draylon, and is composed of
at least 86% acrylonitrile. There are two groups; Modacrylics
and Homopolymers.
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Activated Carbon |
Carbon with a highly
porous structure to provide filtration of odors and extremely
fine particulates.
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Agglomeration |
The
action where small particles group together to form larger
particles or nodes of a scale anywhere from pea to golf ball
size usually due to moisture or surface tension.
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Air-to-cloth
Ratio |
The ratio of the amount
of air entering the baghouse to the amount of surface area
available for filtration. Optimal air to cloth ratios vary
for different industry segments and types of dust collectors.
Example: If the fan on a baghouse is capable of 100,000 CFM
and the baghouse has 1000 bags of 6" diameter x 12' long (for
a total filtration area of 18,850 sq. ft.), the A/C ratio would
be 100,000/18,850 or 5.3:1
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Air,
Standard |
A specific value of
dry air at 65oF and 29.92" Hg pressure (Density 13.595 gm/cm3). Equivalent
to 0.075-lbs/cu. ft.
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Adsorption |
A weak surface bonding
of molecules in a fluid phase (gas) through physical or weak
chemical attraction. A good adsorbents is characterized by
a high surface-to-volume ratio (e.g. activated carbon).
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-B-
BACT |
Acronym for Best Available Control Technology. A standard for
permitting of baghouse and dust collectors that takes into
account the impact of energy and equipment costs in balance
with environmental needs in new or retrofit applications
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Baffle |
A plate, grating,
or refractory wall used especially to block, hinder, or
divert a flow. The baghouse inlet typically has the highest
velocity. Particulate will sandblast the lower portion
of the bags in the baghouse in the absence of a baffle.
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Batch
cleaning |
As a textile term
refers to the process used in heat-cleaning glass filter
cloth prior to converting into a filter by exposing it
to 500-600oF temperatures for prolonged periods to burn
off the starches and other lubricants used to assist in
the weaving process.
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Bleed |
When particulates
are so fine that they pass through the cross- section of
the filter media and exit the baghouse. If the dust cake
is poorly managed or there is little dust loading bleeding
is likely to occur.
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Bleed-through |
Particulate that
migrate through the filter media are discharged up
the stack.
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Blinding |
Particulate that accumulates
within and/or on the surface of the media such that the flow
passages for the gas are blocked restricting the flow and
resulting in high pressure drop.
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-C-
CAA |
Acronym for Clean Air Act
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Can
Velocity |
Velocity of the baghouse
process air as it flows upward through the rows of bags.
Formula: Area of the Baghouse in square feet minus the
area of the diameter of the filter bags divided by the
ACFM of the process air. Excessive Can Velocity can
cause premature bag wear due to abrasion and can cause
more dust to be carried upward to the bags overloading
the bags and the cleaning system. Conversely a Low Can
Velocity can cause segregation of the incoming dust carrying
only the finest of particles which may prevent the formation
of a good Dust Cake.
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Capture
Velocity |
The air velocity at
any point in front of the hood or at the hood opening necessary
to prevent particulate material and contaminant gases from
escaping into the working area.
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CEM |
Acronym for Continuous Emissions Monitoring.
The measurement and reporting of specific pollutant levels
at a facility.
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CFM |
Acronym for Cubic Feet
per Minute. A unit of measure
for volumetric flow of a gas.
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CFR |
Acronym for Code
of Federal Regulations. The Clean Air
Act is located in 40
CFR For a layman's look
at the Clean Air Act click here.
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Clean
Air Act |
Originally passed
in 1955 and since amended in 1970, 1977 and 1990, the Clean
Air Act sets controls at the federal and state levels for
air pollutants a.k.a. "the
800-pound gorilla."
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Concentration |
Amount of dust in
the gas. Usually expressed in terms of grains/ cu ft, Ib/l000
Ib. of gas, ppm, mg/cu mt. or Ib/million Btu.
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Criteria pollutant |
An air pollutant for
which a national ambient air quality standard has been promulgated.
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Cyclone |
A conical-shaped vessel
for separating mixed sized particulates from the gas stream.
The vessel has a tangential entry at the largest diameter
allowing larger particles to drop out and be removed
from the bottom of the cone while smaller particulate exits
overhead with the majority of the gas stream.
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-D-
Damper |
An adjustable gate installed
in a duct for the purpose of regulating airflow or introducing
outside air to the ducting system.
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Denier |
The weight, in grams,
of 9000 meters of a single fiber strand.
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Dew point |
The temperature where
water molecules in a gas will begin to condense and form a
liquid.
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Diaphragm
Valve |
A compressed air operated
valve used to deliver air in short bursts to pulse
clean bags.
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Differential
Pressure |
In a Dust Collection
System, the Differential Pressure usually refers to the difference
in pressure (typically measured in inches of water column
W.G.) between the dirty side of the baghouse and the clean
side of the baghouse. Essentially this yields the pressure
drop or resistance to the air-flow through the filter bag.
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Dispersion
model |
A computerized set of
mathematical equations that use emissions and meteorological
information to simulate the behavior and movement of air
pollutants in the atmosphere. The results of a dispersion
model are estimated outdoor concentrations of individual
air pollutants at specified locations.
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Dry
scrubber |
A chemical reaction
chamber that neutralizes acids in a gas stream. There are
two common system types: the spray dryer system
that injects a slurry; and a dry sorbent injection
system that uses a dry powder.
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Dust Cake |
Essential buildup of porous
dust layer on the surface of a filter, which significantly
increases the efficiency of the filter. Proper management of
the dust cake also effects useful life of the filter.
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Dust Loading |
The amount of particulate
(by weight) that is suspended in a gas stream at the baghouse
inlet usually expressed in grains per
cubic foot. See also Grain Loading.
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-E-
EPA |
Acronym for Environmental Protection Agency.
The federal agency responsible for developing and enforcing
environmental policy in the United States and its territories.
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Epitropic
Fiber |
Fiber whose surface
contains embedded particles to modify one or more properties
of the fiber, typically electrical conductivity.
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ESP |
Acronym for Electrostatic Precipitator.
A device that collects particulates by placing an electrical
charge on the particulate and attracting them onto a collecting
electrode.
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-F-
Felled
Seam |
Vertical seam in a
filter bag, typically a nonwoven, which requires an overlap
of the material. See also French seam.
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Felt |
Fabric structures
constructed by the interlocking action of the fibers them-
selves, without spinning, weaving, or knitting.
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Filter
Cake |
The accumulation of
dust on a bag. Often assists in the filtration process.
Also see Dust Cake.
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Filter
Media |
The permeable barrier
employed in the filtration process to separate the particles
from the fluid stream.
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Flue gas |
The gases emitted
into the atmosphere from a production or combustion process
through the flue or "smoke stack."
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Fly ash |
Gas-borne particulate
resulting from the combustion of fuels, typically fossil
fuels such as coal and lignite. The ash is composed of a
variety of oxides and silicates depending on the fuel and
efficiency of the combustion process.
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Fly
Ash |
Finely divided particles
of ash entrained in flue gases resulting from the combustion
of fuel. The ash particles consist of incompletely burned
fuel and a variety of mineral constituents.
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French
seam |
Vertical seam in a
filter bag, typically a woven, which requires a doubling
over of the material. See also felled seam.
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Fugitive dust |
Emissions from a process
or control that occurs at points other than stacks or vents.
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-G-
Glazing |
High pressure pressing of the filter
medium at elevated temperatures; fuses surface fibers to
the body of the filter medium.
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Grain |
Weight unit of measure
where one pound equals 7000 grains.
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Grain Loading |
The amount of particulate
(by weight) that is suspended in a gas stream at the baghouse
inlet. See also Dust Loading.
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Ground
Wire |
Braided metal strip,
usually copper or stainless steel, placed on or in the seam
and grounded to the collector to assist in dissipating static
build-up caused by the gas flow.
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-H-
HAP |
Acronym for Hazardous Air Pollutant.
A list of nearly 200 pollutants has been classified under
this heading by the Clean Air Act Amendments of 1990. Standards
were to have been adopted no later than November 15, 2000. Click
here for the list of the Top 33 that they will
be focusing their efforts on.
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Hydrocarbon |
A chemical compound
containing only molecules of carbon and hydrogen.
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Hydrolysis |
A chemical reaction
in which water reacts with another substance, either dust
or the filter media, breaking the chemical links and creating
two or more substances. The presence of water in a baghouse
is a significant detriment to the filter media. See also Dew point.
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Hydrophilic
Fiber |
Fiber that readily
absorbs water.
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Hydrophobic
Fiber |
Fiber that does not
readily absorb water.
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-I-
Inversion |
The occurrence of
a layer of cool air trapped beneath a warmer layer and
the cooler layer not warming and dispersing upward. The
emissions at ground level are trapped and remain concentrated
creating high concentrations of pollutants.
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-L-
LAER |
Acronym for Lowest Achievable Emission Rate
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Lime |
Common name for calcium
carbonate as it is found in the ground. When heated in a
kiln, it yields "burnt" or "quick" lime (calcium oxide).
When lime is hydrated or "slacked"
it becomes calcium hydroxide.
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-M-
MACT |
Acronym for Maximum Achievable
Control Technology
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Magnehelic
Gauge |
Instrument to measure
the differential
pressure between the dirty (inlet) and clean (outlet)
sides of a baghouse. As a general
rule differential pressures greater than 7in. W.G. indicate
serious performance problems with the unit and require investigation
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Major source |
As defined by The
Clean Air Act Amendment of 1990: "any stationary source
or group of stationary sources located within a contiguous
area and under common control that emits or has the potential
to emit considering controls, in the aggregate, 10 tons
per year or more of any hazardous air pollutant or 25 tons
per year or more of any combination of hazardous air pollutants."
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Manometer |
An instrument for
measuring pressure; a U-tube partially filled with liquid,
usually water, mercury or a light oil, so constructed that
the amount of displacement of the liquid indicates the
pressure being exerted on the instrument
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Micron |
A unit of measure equal
to 1/1,000,000 of a meter
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MIT Flex |
A test whereby a filter
media specimen is rapidly flexed in an arc under a specified
load until fabric rupture occurs. Test conditions are usually:
270° arc, 180 cycles/minute, 4-pound load, 1/2-inch width
specimen.
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Mullen
Burst Test |
Standardized ASTM
test method to measure the strength of a filter
material under multidirectional pressure expressed in pounds
per square inch.
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-N-
NAAQS |
Acronym for National Ambient Air Quality Standards
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NESHAPS |
Acronym for National Emissions Standards
for Hazardous Air Pollutants. A federal
requirement setting standards and limitations for monitoring
and reporting of carcinogenic discharges into the atmosphere.
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Non-Attainment |
When pollution criteria
being monitored exceeds the national or regional
level set for that particular pollutant.
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NSPS |
Acronym for New Source Performance Standards
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-O-
Opacity |
A measurement of the
density of emissions in the plume of a stack.
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Osmosis |
The diffusion of a
solvent through a semi-permeable membrane into a more concentrated
solution.
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-P-
PEL |
Acronym for Permissible Exposure Limit.
The allowable exposure level in the workplace for a particular
pollutant over an 8-hour shift. See also TWA.
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Permeability |
A measurement of the
ability of air to flow through a filter at a given differential
pressure. The value is expressed as (U.S.) cubic feet per
minute at .5" water gauge differential or (Metric) liter/min
at 20mm water gauge differential.
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pH |
The measure in units
from 0-14 of the acidity or alkalinity of a stream of gas
or liquid. A pH of 7 is neutral. Values below 7 tend towards
acidic; values above 7 tend toward alkaline.
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Pitot tube |
A sensing unit inserted
into the gas stream to measure gas velocity based on a differential
between the total pressure and the static pressure.
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Plenum
Chamber |
An air compartment
maintained under pressure, and connected to one or more
ducts. A pressure-equalizing chamber.
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PM10 |
A USEPA standard that
includes additional controls on particulates sized 10 micron
and smaller
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PM2.5 |
A USEPA standard that
includes additional controls on particulates sized 2.5 micron
and smaller
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Pre-coat |
Material added
to the air stream in the initial process startup to aid
in establishing a filter cake on the bags. Pre-coat is
good insurance for an operation that may introduce harmful
by products if the initial start up does not go as planned.
(e.g. incomplete combustion from a failed burner start
up sending unspent hydrocarbons to the baghouse, latent
moisture upstream of baghouse, etc. ) or to get immediate
high filtration efficiencies with a pre-built dust cake.
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Pressure
Drop |
Resistance to gas
flow; may refer to apressure differential across the cloth,
across the baghouse, or across the entire system. Units
are usually inches of water.
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Pulse-jet |
Type of baghouse design
where dust is collected on the exterior of a filter tube,
supported by a cage, and cleaned with a rapid pulse of compressed
air driven down the interior of the filter tube.
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-R-
Reagent |
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Reverse-air |
Type of baghouse design
where cleaning is accomplished by reversing the flow to a
portion of filters and dislodging the dust.
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-S-
Scrim |
A very loosely woven
fabric onto which felt is needled to add dimensional stability
and strength. Use of scrims is declining as high performance
textile equipment is allowing for the creation of 100% fiber
media with the same or superior strength characteristics.
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Self-supported |
A nonwoven fabric
that has been processed to interlock the fibers such
that a scrim is not required. Self-supported filter materials
have established themselves as the most popular choice
for low temperature applications. However, high temperature
applications of self supported fabrics, especially in long
bag configurations, should be approached with caution and
on a case by case basis.
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Shaker |
Type of baghouse design
where the filter bag is agitated by mechanical means to dislodge
the dust.
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Singeing |
Passing of the filter
medium over an open flame, thereby removing the protruding
surface fibers. Singeing the collection side of the filter
allows for easier dust cake removal.
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Sonic Cleaning |
Sonic energy from
air-powered horns produces shock waves, which enhance dust
removal from fabrics. Sonic cleaning is typically used
in reverse-air application involving a fiberglass bag.
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Specific gravity |
The ratio of a mass of
a unit volume of a substance to the mass of the same volume
of a standard substance at a standard temperature. For gases,
dry air at the same temperature and pressure as the gas is
often taken as the standard substance.
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Spunbonded |
A non-woven fabric
formed by producing, laying and self-bonding a web of filament
material in one continuous set of processing steps. Usually
made of polyester, polyamides or olefins.
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Staple
Fiber |
Short fiber cut to
specific length in synthetics to either form yarns or non-woven
felts. The size, distribution and type of fibers used in
the filtration vary to suit process needs. Selecting the
right combination is essential for maximum performance.
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-T-
Tensile
Strength |
A measure of the ability
of yarn or fabric to resist breaking by direct tension.
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Teratogen |
Substances that affect
the genetic coding of an organism such that birth defects
occur in subsequent offspring.
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Thread
count |
The number of warp and
filling yams in a fabric.
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Title V (CAA) |
The portion of the
Clean Air Act that deals with permitting of pollution sources.
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Tube Sheet |
The steel plate used
to suspended bags from in a baghouse. Both the diameter
and thickness are crucial data to ensure a dust tight seal.
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Tubing |
Sewing of fabric in
the form of a tube when making a filter bag. Standard Filter
is a world leader in this technology.
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TWA |
Acronym for Time Weighted Average.
The allowable exposure level for a pollutant over a given
time period (8-hour day or 40-hour workweek, etc.).
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-V-
Venturi |
An air affect passage
that gradually contracts to a smaller opening and expands
again at a different rate thus causing acceleration of flow
and gradient pressure change. Venturi's are typically used
in pulse-jet cages to enhance the pulse clean cycle. However
they also restrict normal flow as well and add to system
delta P. See Sonitec
Nozzle for a different approach
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VOC |
Acronym for Volatile Organic Compound
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-W-
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The yarn running lengthwise
(machine direction) in a woven fabric.
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