Glossary of Industry Terms

Glossary of Industry Terms

Spark - A small, burning, airborne ember or particle
 
Spark Arrester - A device intended to prevent combustible materials, usually sparks or other tiny flaming debris, from reaching a specific downstream exhaust location (i.e. dust collection system, filters, etc.)
 
Spark Arrestor - A device intended to prevent combustible materials, usually sparks or other tiny flaming debris, from reaching a specific downstream exhaust location (i.e. dust collection system, filters, etc.)
 
Spark Suppression - A means of preventing combustible materials, usually sparks or other tiny flaming debris, from reaching a specific downstream exhaust location (i.e. dust collection system, filters, etc.)
 
Spark Trap - A device intended to prevent combustible materials, usually sparks or other tiny flaming debris, from reaching a specific downstream exhaust location (i.e. dust collection system, filters, etc.)
 
Dust Collector - Designed to handle heavy dust loads, a dust collector consists of a blower, dust filter, a filter-cleaning system, and a dust receptacle or dust removal system (distinguished from air cleaners which utilize disposable filters to remove the dust).
 
Fabric Dust Collection System - Commonly known as baghouses, fabric collectors use filtration to separate dust particulates from dusty gases. They are one of the most efficient and cost effective types of dust collectors available and can achieve a collection efficiency of more than 99% for very fine particulates.
Dust-laden gases enter the baghouse and pass through fabric bags that act as filters. The bags can be of woven or felted cotton, synthetic, or glass-fiber material in either a tube or envelope shape.
The high efficiency of these collectors is due to the dust cake formed on the surfaces of the bags. The fabric primarily provides a surface on which dust particulates collect through the following four mechanisms:
  • Inertial Collection - Dust particles strike the fibers placed perpendicular to the gas-flow direction instead of changing direction with the gas stream.
  • Interception - Particles that do not cross the fluid streamlines come in contact with fibers because of the fiber size.
  • Brownian Movement - Submicrometre particles are diffused, increasing the probability of contact between the particles and collecting surfaces.
  • Electrostatic Forces - The presence of an electrostatic charge on the particles and the filter can increase dust capture.
A combination of these mechanisms results in formation of the dust cake on the filter, which eventually increases the resistance to gas flow. The filter must be cleaned periodically.
 
Baghouse Filters -
As classified by cleaning method, three common types of baghouses are -
In mechanical-shaker baghouses, tubular filter bags are fastened onto a cell plate at the bottom of the baghouse and suspended from horizontal beams at the top. Dirty gas enters the bottom of the baghouse and passes through the filter, and the dust collects on the inside surface of the bags.Mechanical Shaker
Cleaning a mechanical-shaker baghouse is accomplished by shaking the top horizontal bar from which the bags are suspended. Vibration produced by a motor-driven shaft and cam creates waves in the bags to shake off the dust cake.
Shaker baghouses range in size from small, handshaker devices to large, compartmentalized units. They can operate intermittently or continuously. Intermittent units can be used when processes operate on a batch basis-when a batch is completed, the baghouse can be cleaned. Continuous processes use compartmentalized baghouses; when one compartment is being cleaned, the airflow can be diverted to other compartments.
In shaker baghouses, there must be no positive pressure inside the bags during the shake cycle. Pressures as low as 0.02 in. wg can interfere with cleaning.
The air to cloth ratio for shaker baghouses is relatively low, hence the space requirements are quite high. However, because of the simplicity of design, they are popular in the minerals processing industry.
Reverse Air
In reverse-air baghouses, the bags are fastened onto a cell plate at the bottom of the baghouse and suspended from an adjustable hanger frame at the top. Dirty gas flow normally enters the baghouse and passes through the bag from the inside, and the dust collects on the inside of the bags.
Reverse-air baghouses are compartmentalized to allow continuous operation. Before a cleaning cycle begins, filtration is stopped in the compartment to be cleaned. Bags are cleaned by injecting clean air into the dust collector in a reverse direction, which pressurizes the compartment. The pressure makes the bags collapse partially, causing the dust cake to crack and fall into the hopper below. At the end of the cleaning cycle, reverse airflow is discontinued, and the compartment is returned to the main stream.
The flow of the dirty gas helps maintain the shape of the bag. However, to prevent total collapse and fabric chafing during the cleaning cycle, rigid rings are sewn into the bags at intervals.
Space requirements for a reverse-air baghouse are comparable to those of a shaker baghouse; however, maintenance needs are somewhat greater.
Reverse Jet
In reverse-jet baghouses, individual bags are supported by a metal cage, which is fastened onto a cell plate at the top of the baghouse. Dirty gas enters from the bottom of the baghouse and flows from outside to inside the bags. The metal cage prevents collapse of the bag.
Bags are cleaned by a short burst of compressed air injected through a common manifold over a row of bags. The compressed air is accelerated by a venturi nozzle mounted at the Reverse-Jet Baghouse top of the bag. Since the duration of the compressed-air burst is short (0.1s), it acts as a rapidly moving air bubble, traveling through the entire length of the bag and causing the bag surfaces to flex. This flexing of the bags breaks the dust cake, and the dislodged dust falls into a storage hopper below.
Reverse-jet dust collectors can be operated continuously and cleaned without interruption of flow because the burst of compressed air is very small compared with the total volume of dusty air through the collector. Because of this continuous-cleaning feature, reverse-jet dust collectors are usually not compartmentalized.
The short cleaning cycle of reverse-jet collectors reduces recirculation and redeposit of dust. These collectors provide more complete cleaning and reconditioning of bags than shaker or reverse-air cleaning methods. Also, the continuous-cleaning feature allows them to operate at higher air-to-cloth ratios, so the space requirements are lower.
Cartridge Collectors
Cartridge collectors are another commonly used type of dust collector. Unlike baghouse collectors, in which the filtering media is woven or felt bags, this type of collector employs perforated metal cartridges that contain a pleated, nonwoven filtering media. Due to its pleated design, the total filtering surface area is greater than in a conventional bag of the same diameter, resulting in reduced air to media ratio, pressure drop, and overall collector size.
Cartridge collectors are available in single use or continuous duty designs. In single-use collectors, the dirty cartridges are changed while the collector is off. In the continuous duty design, the cartridges are cleaned by the conventional pulse-jet cleaning system.
Almost always includes a steel enclosure containing porous filter media that separate fine dust particles from a flowing stream of dirty air. The most common filter media used in collectors are filter bags and cartridges. Dust particles build up on the outside of the media and form a coating called "dust cake." It is this layer that does the actual job of filtering fine particles. As the cake builds up, the pressure drop across the filter bag rises.
 
Flue Gas - Flue gas is gas that exits to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator. Quite often, it refers to the combustion exhaust gas produced at power plants. Its composition depends on what is being burned, but it will usually consist of mostly nitrogen (typically more than two-thirds) derived from the combustion air, carbon dioxide (CO2) and water vapor as well as excess oxygen (also derived from the combustion air). It further contains a small percentage of pollutants such as particulate matter, carbon monoxide, nitrogen oxides and sulfur oxides.
 
Fire Protection - Means or minimizing or eliminating risks assocciated with fire
 
In-Line Mixer - A device in a pipe or duct, "in-line" with the fluid flow, that provides for two or more fluids to become one consistent fluid
 
Welding Fumes - Exhaust smoke and material, including sparks, from a welding process.
 
Plasma Cutting Table - Plasma cutting is a process that is used to cut steel and other metals (or sometimes other materials) using a plasma torch. In this process, an inert gas (in some units, compressed air) is blown at high speed out of a nozzle; at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut, turning some of that gas to plasma. The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut.
 
Laser Cutting Table - Laser cutting is a technology that uses a laser to cut materials, and is usually used in industrial manufacturing. Laser cutting works by directing the output high power laser, by computer, at the material to be cut. The material then either melts, burns or vaporizes away leaving an edge with a high quality surface finish. Industrial laser cutters are used to cut flat-sheet material as well as structural and piping materials.
 
 Static Mixer - A device for blending (mixing) two fluids. The device consists of mixer elements contained in a cylindrical (tube) or squared housing. The static mixer elements consist of a series of baffles that are made from metal or plastic. Similarly, the mixer housing can be made from metal or plastic.
 
The overall system design incorporates a method for delivering two streams of air/gas into the static mixer. As the streams move through the mixer, the "non-moving" elements continuously blend the materials. Complete mixing is dependent on many variables including mixer length, tube inner diameter, number of elements and the design of the elements.
 
Mixing Box - A factory-made section that includes control dampers and may include one or more static air mixers.
 
Mixing Section - A factory-made enclosure, which includes one or more static mixers, that is designed to be mounted between sections of an air handling unit and is supplied separately from the mixing box.
 
Temperature Averaging Bulb -  A control sensor designed to read the average temperature across a plenum by using a capillary tube or a special averaging wire approximately 15 to 24 feet long.
 
HVAC - HVAC (pronounced either "H-V-A-C" or, occasionally, "H-VAK") is an initialism/acronym that stands for "heating, ventilation, and air conditioning". HVAC is sometimes referred to as "climate control" and is particularly important in the design of medium to large industrial and office buildings such as sky scrapers and in marine environments such as aquariums, where humidity and temperature must all be closely regulated whilst maintaining safe and healthy conditions within.
 
Blow Through System - Usually refers to a system where the filter or coil is installed downstream of the fan supply fan.  Therefore, the fan is "blowing" through the coil or filter.
 
Air Mixer - A device for eliminating air stratification in air ventilation systems.
 
Air Stratification - Stratification is normally thought of in terms of vertical temperature gradients.  However, stratification within an air handling unit is different.  Momentum in the entering air streams as well as the combined flow serves to hold the uneven profile of temperatures or constituents as they are introduced into the combined flow.
 
Destratification - Destratification is a process in which the air or water is mixed in order to eliminate stratified layers of temperature
 
Air Handling Unit - An air handler, or air handling unit and often abbreviated to AHU, is a device used as part of a heating, ventilating, and air-conditioning (HVAC) system. Usually, an air handler is a large metal box containing a blower, heating and/or cooling elements, filter racks or chambers, sound attenuators, and dampers. Air handlers usually connect to ductwork that distributes the conditioned air through the building, and returns it to the AHU. Sometimes AHUs discharge (supply) and admit (return) air directly to and from the space served, without ductwork.
 
Freeze-Stat - A low-limit thermostat used to protect hydronic coils from freezing by activating freeze protection sequences, such as air-handler shut down, in the air-handler control system.
 
Mixing Effectiveness - A means of quantifying mixing in terms of "Range" or "Standard Deviation" reduction across a static mixing device or other mixing system.
 
Frozen Coils - The result of sub-freezing temperatures coming into prolonged contact with hydronic coils in air handling units and industrial ventilation systems.
 
Hydronic Coils - Water based heating and/or coiling system for air handling units and industrial ventilation systems.
 
Glycol - A diol or glycol is a chemical compound containing two hydroxyl groups (-OH groups). Vicinal diols have hydroxyl groups attached to adjacent atoms. Examples of vicinal diol compounds are ethylene glycol and propylene glycol
 
Economizer Operation - The air-side economizer uses cool outside air to either assist mechanical cooling or, if the outside air is cool enough, provide total cooling.
 
Sensor Error - The inability of temperature sensors to get an accurate reading of the mass energy within and air stream.
 
Pressure Drop - Pressure drop is a term used to describe the change in pressure across a system.
 
Gas Mixer -  A device that eliminates stratification of gas streams
 
Industrial Mixer - Broad category of mixing devices (includes:  static mixer, in-line mixer, continuous mixer, batch mixer, etc.)
 
Ammonia Injection Grid (AIG) - A system for introducing ammonia into an exhaust air stream.  Typically used on Selective Catalytic Reduction (SCR) systems to eliminate NOx.
 
Urea - Urea is an organic compound with the chemical formula (NH2)2CO.
 
Landfill Gas - Biogas typically refers to a (biofuel) gas produced by the anaerobic digestion or fermentation of organic matter including manure, sewage sludge, municipal solid waste, biodegradable waste or any other biodegradable feedstock, under anaerobic conditions. Biogas is comprised primarily of methane and carbon dioxide.  Depending on where it is produced, biogas is also called:
Biogas can be used as a vehicle fuel or for generating electricity. It can also be burned directly for cooking, heating, lighting, process heat and absorption refrigeration.
 
Velocity Maldistribution - Variations in flow speed within a single air stream.