The acronym for actual cubic feet per minute, which is the actual gas flow rate expressed in the American Engineering system of units. ACFM is a measure of the volume of gas that passes a given point during a one-minute period.
The process whereby vapor phase compounds in the gas stream pass through a bed or layer of highly porous material (adsorbent). The vapor phase compounds diffuse to the surface of the adsorbent and are retained due to weak attractive forces.
The diameter of a spherical particle having a density of 1 gm/cm3 that has the same inertial properties (i.e. settling velocity) in the gas as the particle of interest.
A liquid whose main component is water but which can also contain significant concentrations of other dissolved solids and liquids (usually < 15% by weight) and/or low-to-moderate levels of suspended solids (usually < 2% by weight).
This term is often used interchangeably with the term "filtration systems." However, it is applicable only to pulse jet, cartridge, reverse air, and shaker-type filtration systems. The term "baghouse" does not have any clear meaning for HEPA filtration systems.
An emission limitation based on using the most up-to-date methods, systems, techniques, and production processes available to achieve the greatest feasible reductions with the consideration of energy, environmental, and economic impacts. These limitations are determined on a case-by-case basis as part of the PSD program.
An off-stoichiometric combustion modification for control of NOx performed by operating alternate burners in the combustion zone as either fuel rich, air rich, or air only.
An air pollution control device that uses a catalyst to accelerate the oxidation reaction at lower temperatures than possible in gas phase thermal oxidation.
A sampling device used to determine the particle size distribution. Particles are separated and deposited on a series of stages that correspond to different aerodynamic diameters.
A substance, usually present in small amounts compared to the reactants, that speeds up the chemical reaction rate without being consumed in the process.
A set volume of catalyst-containing material designed to facilitate contact between the gas stream and the catalyst materials. The bed is usually either in the form of a layer of beads or as a series of passages through a honeycomb structure.
Class I areas are protected by the PSD program and include national parks, national wilderness areas, national monuments, national seashores, and other areas of special national or regional natural, recreational, scenic, or historic value.
Attainment areas that are neither industrialized nor meet the specific requirements for classification as Class I areas. They are protected by the PSD program.
The production of heat and light energy through a chemical process, usually oxidation. Products of complete combustion include water and carbon dioxide; while, incomplete combustion can yield partially oxidized organic compounds and carbon monoxide. Factors that promote complete combustion include the proper fuel-air ratio, temperature range, and adequate amount of time for the fuel and its by-products to complete the combustion reactions.
Particulate matter, contained almost entirely within the PM2.5 classification, that forms from condensing gases or vapors. It forms by chemical reactions as well as by physical phenomena.
The group of common air pollutants defined by EPA whose concentrations in the ambient air must be maintained at low levels to protect public health. EPA has promulgated a National Ambient Air Quality Standard (NAAQS) for each of the criteria pollutants.
A type of mechanical collector, usually ranging in size from one to six feet in diameter, that uses a spinning movement of the gas stream to collect particles ranging in size from one-sixteenth to more than 6 inches in diameter.
The temperature at which the partial pressure of a substance (in vapor form) equals the equilibrium vapor pressure of the substance. At this temperature, a vapor begins to condense at a constant pressure.
Measure of the extent to which very small particles are influenced by molecular collisions which cause the particles to move in a random manner across the direction of gas flow.
An air pollution control device used to remove an acid gas pollutant from a gas stream. The pollutant is collected on or in a solid or liquid material, which is injected into the gas stream. A dry scrubber produces a dry product that must be collected downstream from this control device.
A substance that produces either (1) a conducting ionic melt when fused, or (2) a conducting ionic solution when dissolved in certain solvents (most often water). All acids, bases and salts are electrolytes.
A type of air pollution control system that uses high voltage fields to electrically charge and collect particulate matter. The charged particles approach an electrically grounded collection plate and accumulate as a dust layer, which is partially removed by mechanical rapping (hammers) on a routine basis.
Equipment usually consisting of (1) a sampling nozzle and probe, (2) filter and impingers for collection of gaseous and/or particulate components, (3) flow meter and flow regulation devices, and (4) a vacuum pump for collecting a representative sample of a gas stream.
Phenomenon associated with heterogeneous nucleation where partitioning of vapor phase compounds, such as metals, nucleate as particles or on very small particles.
A steady state condition. The amount of mass transferred in one direction is exactly balanced by the amount of mass transferred in the reverse direction.
The amount of substance (in grams) that supplies one gram mole of reacting units. The equivalent weight is calculated by dividing the molecular weight of a compound by the change in the oxidation number it experiences during a chemical reaction.
Equipment used to reduce the temperature of a gas stream. Fine droplets, injected into a vessel, are evaporated as they absorb heat from the gas stream.
A small, hand-held wet chemical analyzer for measuring the oxygen and carbon dioxide concentrations. A small sample is pumped into the dumbbell-shaped instruments. After absorption of oxygen or carbon dioxide into the chemicals, the pressure is reduced, which causes the diaphragm on the bottom of the instrument to move. The change in chemical height due to this movement of the diaphragm is related to the concentration of oxygen or carbon dioxide. This instrument is less accurate than an ORSAT analyzer but considerably easier to use.
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 pulling it into the hood.
A device for temporarily storing dust collected by an air pollution control device. Hoppers funnel solids into the solids handling system. There are two main types used on filtration systems: pyramidal and trough-type.
The process whereby a particle moving in a gas stream strikes slowly moving or stationary obstacles or targets (e.g. liquid droplets) directly in its path. Compare with Interception.
The process whereby a particle moving in a gas stream is offset slightly from directly impacting a moving or stationary obstacle or target. As the particle tries to move past the obstacle, the obstacle intercepts (and collects) the particle. Compare with Inertial Impaction.
A compound having the same percentage composition and molecular weight as another compound but differing in chemical or physical properties. Isomers may differ in the manner in which constituent atoms are linked or are arranged in space.
An off-stoichiometric combustion modification for control of NOx where the mixing of fuel and air is controlled in a pattern that keeps the flame temperature low and dissipates the heat quickly.
This represents the most stringent control technology achieved in practice regardless of cost. LAER is used to determine emission limits for the NSR program.
An instrument used for measuring the pressure of liquids and gases. An open-tube manometer consists of a U-shaped tube that usually contains a liquid such as mercury or water. One end of the tube is open to the atmosphere and the other end of the tube is connected to the container where the pressure is to be measured.
The particle diameter at which half the particulate mass is composed of particles larger than this diameter and half the mass is composed of particles smaller than this diameter.
A natural phenomenon in which a component travels from a region of high concentration to one of low concentration in order to minimize concentration differences in a mixture.
The minimum gas velocity that must be maintained to keep the contaminant from settling out of the gas flow stream and building up deposits in the ductwork.
The concentration of a solution given in gram moles of solute per liter of solution. A solution containing exactly one-gram mole of solute per liter of solution is referred to as "molar."
The exponent applied to the base number of 2.718 to equal a given value. For example, 2 is the natural logarithm that is equal to a value of 7.389. (2.718)2 = 7.389
The concentration of a solution expressed as the number of gram equivalent weights of solute per liter of solution. A solution containing one gram equivalent weight of solute per liter of solution is referred to as "normal."
Document required by EPA under Title V for any major stationary source. Potential-to-emit limits defining a major source are determined by the air quality of the geographical region where the facility is located. A permit contains specific information about how the facility will comply with established emission standards and guidelines set forth by EPA.
An off-stoichiometric combustion modification for control of NOx where the lower burners operate under fuel rich conditions and air injection nozzles located above these burners complete the combustion process.
A common type of gas absorber in which scrubbing liquid is dispersed over packed columns containing packing material. This design provides a large surface area for gas-liquid contact.
EPA defines PM2.5 as particulate matter with a diameter of 2.5 micrometers collected with 50% efficiency by a PM2.5 sampling collection device. However, for convenience in this reference material, the term PM2.5 includes all particles having an aerodynamic diameter of less than or equal to 2.5 micrometers.
The U.S. EPA defines PM10 as particulate matter with a diameter of 10 micrometers collected with 50% efficiency by a PM10 sampling collection device. However, for convenience in this reference material, the term PM10 includes all particles having an aerodynamic diameter of less than or equal to 10 micrometers.
The part per million concentration that is determined by comparing the volume of one constituent with the total volume of the substance. Gas concentrations are always expressed in a ppm(v/v) format as opposed to the ppm(w/w) format often used for liquids. Throughout APTI courses, the term ppm when applied to gases means ppm(v/v).
The part per million concentration that is determined by comparing the volume of one constituent with the volume of the other constituents with the exception of moisture.
The part per million concentration that is determined by comparing the mass of one constituent with the total mass of the sample. Liquid concentrations are often expressed in a ppm(w/w) format as opposed to the ppm(v/v) format used for gases. Throughout APTI courses, the term ppm when applied to liquids means ppm(w/w). Note that the abbreviation "w/w" is used despite the fact that the ppm concentration is based on a ratio of masses.
A type of filtration system that uses a short duration pulse of compressed air injected on the "clean side" of the filter media to routinely clean the filter media. Pulse jets are one of the most common types of filtration systems. They are sometimes termed reverse jets (not to be confused with reverse air filtration systems).
Rankine is an absolute temperature scale often used in engineering. Using this scale, the freezing point of water is 492°R and the boiling point of water is 672°R.
Radioactive isotopes resulting from (1) the fission of heavy nuclei of elements such as uranium and plutonium, or (2) the reaction of neutrons with stable nuclei.
A tank used in a scrubbing system to (1) provide sufficient time for reagents to dissolve into the liquid, and (2) provide sufficient pressure for the pump.
A measure of a particle's ability to conduct electricity (expressed in units of ohm-cm). Resistivity is very important in the efficient operation of electrostatic precipitators.
A dimensionless number corresponding to the ratio of the fluid inertial force to the fluid viscous force in a flow system. It is used as an index for turbulence.
A dimensionless number corresponding to the ratio of the inertial force of a particle to the viscous force of the surrounding fluid in a flow system. It is used as an index for turbulence.
The acronym for standard cubic feet per minute, which is the gas flow rate at standard conditions expressed in the American Engineering system of units.
The value equivalent to the number of times that the control device will be filled with untreated gas in a given period of time. The space velocity is the reciprocal of the treatment time (residence time). Space velocity has units of 1/seconds or 1/minutes.
An air pollution control device for removing acid gases where an alkaline slurry is introduced into the gas stream and the pollutants absorb into the droplets and react. The droplets dry in the gas stream leaving particulate matter, which is collected by a downstream particulate control device.
A complex and voluminous document that contains comprehensive emission inventories, proposed control strategies, demonstration of modeling/calculation results, summaries of regulatory authority, description of monitoring programs, and enforcement procedures.
The atmospheric layer just above the troposphere, which starts at approximately 7.5 miles (12 km) above the Earth and rises to approximately 31.1 miles (50 km). The beneficial ozone layer resides in the stratosphere.
Particulate matter of all sizes is regulated as total filterable particulate matter. This category of air pollutants was the first one that was subject to air pollution control regulations.
The length of time that pollutants reside in the air pollution control system. The treatment time is calculated by dividing the volume of the air pollution control device by the gas flow rate.
The lowest layer of the Earth's atmosphere, which rises to a height of approximately 7.5 miles (12 km). Air masses, fronts and storms reside in this layer.
The degree of clearness of a liquid or the lack of visual clarity of a liquid. It is defined by the measure of light scattering due to the presence of particles suspended in the liquid. Turbidity is similar to opacity for particles suspended in the gas phase.
In a closed system at a constant temperature the pressure exerted by gaseous molecules that are in equilibrium with molecules of the same kind in the liquid or solid state.
A type of wet scrubber that is usually highly efficient but requires a large amount of energy to operate. (Wet scrubbers are air pollution control devices.) In venturi scrubbers, a scrubbing liquid is introduced into the gas stream, which then passes through a contracted area of the scrubber at a high velocity creating a high dispersion of fine droplets. These fine droplets capture the gaseous and particulate pollutants.
1023 atoms or molecules of the material.
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