Absolute rating:  Refers to the largest particle that will pass through a filter with a fixed pore size as tested with round glass beads under laboratory conditions with 100% retention of any particles larger than the rating.  As the testing may be done on a one pass, low pressure, and non-pulsating condition the results may not always replicate in actual operating conditions. 

Absorption:  Assimilate into the inner structure, or taken inside of the attractant.

ACFM:  Actual Cubic Feet Per Minute.  A unit of volumetric flow dependent upon operating pressure and temperature.

Activated carbon:  Activated carbon has been processed typically by exposure to high temperature steam, or by chemical treatment and heat, to open pores in each carbon granule creating many times the original surface area. (See mesh, molasses, iodine, ash)

Adsorption:  Accumulation of matter on the surface of an attractant, such as the adherence of molecular impurities on available surfaces of activated carbon.

Aerosol:  Fine liquid or solid particles suspended in an air or gas flow.  Synonyms in coalescence are mist and fog.

Ambient:  The environmental conditions of the surrounding area, such as ambient temperature.

Annular flow:  Pertains to a 2-phase gas-liquid flow inside a vertical pipe or round vessel.  Liquid which forms and flows on the interior wall of the pipe or vessel is annulus shaped, or ring shaped.  The gas and possible entrained liquid flows in the center.

Annulus:  Pertaining to the circular area between the exterior of a coalescing cartridge and the interior vessel wall.

API:  American Petroleum Institute.  From API’s website: “API is the only national trade association representing all facets of the natural gas and oil industry.”…  “API’s mission is to promote safety across the industry globally and to influence public policy in support of a strong, viable U.S. oil and natural gas industry.”…. “We speak for the oil and natural gas industry to the public, Congress and the Executive Branch, state governments and the media. We negotiate with regulatory agencies, represent the industry in legal proceedings, participate in coalitions and work in partnership with other associations to achieve our members’ public policy goals.”

Aqueous:  Refers to a solution in which water is the solvent.  (See non aqueous)

Ash:  Activated carbon ash is the measurement of oxides in the activated carbon granule expressed as a percentage. The lower the percentage, the higher the carbon portion of the granule and its activity.  (See mesh, molasses, and iodine)

ASME:  American Society of Mechanical Engineers.   A not-for-profit with widely accepted standards which govern pressure vessel design.  The stated mission of ASME is “To serve diverse global communities by advancing, disseminating and applying engineering knowledge for improving the quality of life; and communicating the excitement of engineering.”

Atmospheric Pressure:  The environmental pressure at a given elevation above sea level.  The atmospheric pressure at sea level is 14.7 pounds per square inch.

Backflush:  Cleaning a filter or strainer by briefly reversing the flow of the fluid process to remove built up solid particulates contained in the media such that it can be drained from the housing.  This allows the media to be cleaned without opening the housing.

Bar:  A unit of pressure equal to 100,000 Pa (Pascals).  The atmospheric pressure at sea level is 1.013 bar (prox.).

Bernoulli’s Principle:  When the speed of a moving fluid such as steam, air or gas increases, the pressure within the fluid decreases and vice-versa. An example is in a pipe or steam pump; if the static pressure increases in the flowing fluid, the speed of the moving fluid will decrease. 

Beta Rating:  A method of measuring the efficiency of a filter by dividing the number of particles of a specific micron size entering a filter under multi-pass test conditions by the number of particles which pass through the filter; thus establishing the beta ratio.  A beta rating of 5000 indicates that for every 5000 particles entering a filter only 1 particle of a stated size will pass through (99.98% efficiency).  The higher the rating, the more efficient the filter.  Filter beta ratings as applied to filter and coalescing cartridges:

  • Beta 20        (95% efficiency)
  • Beta 50        (98% efficiency)
  • Beta 75        (98.7% efficiency)
  • Beta 100      (99% efficiency)
  • Beta 200      (99.5% efficiency)
  • Beta 1000    (99.9% efficiency)
  • Beta 5000    (99.98% efficiency)
  • Beta 10000  (99.99% efficiency)

Brownian motion:  Random and erratic movement of molecule-sized particles caused by collisions with molecules from the flowing media.  Vessels without separation internals, called knock-out pots, utilize Brownian Motion to assist in basic gravity settling of particulates.

Buna-N:  Nitrile rubber.  A synthetic elastomer material commonly used in industrial applications, such as for gaskets and seals, due to its resistance to degradation from oil and other fuels.

Burst Pressure:  The amount of internal pressure at which a vessel may rupture.

Caustic:  Chemicals which burn or corrode organic substances by chemical action.

Cellulose:  A polysaccharide which is the main constituent of plant cell walls.  Used in the filtration industry due to its excellent strength when wet and for its solid particulate retention capacity.  When treated with chemicals to produce hydrophobic properties it can be used to repel water as the second stage of a liquid-liquid coalescer separator. 

Centrifugal element (as used in separation of liquids from a gas stream):  A fixed element inside of a separator vessel and designed to remove liquids and solids from a gas stream.  The centrifugal element imparts a spin to the gas, forcing any liquids or solids to the vessel wall through the process of centrifugal force and with eventual draining.  

Coalescer:  A medium which removes liquids from a gas or liquid stream through the process of coalescence, or merging of liquid droplets together until large enough to drop out of the stream.  The term may be applied to a vessel for this purpose or to the internal component.

Continuous Phase:  The primary liquid in a liquid emulsion as compared with its lessor discontinuous, dispersed phase (typically the undesirable component).  (See Discontinuous phase)

Density (ρ):  Mass per unit volume of a substance.  The more matter in a given volume, the higher the density.  The less matter, the lower the density.

Depth Filter:  A filtration medium comprised of fibers compressed to a desired thickness to form a tortuous path through which solids are captured as the medium flowing passes through the filter.  Also used to coalesce liquid droplets in mechanical separation devices such as gas coalescers, liquid-liquid coalescers and filter separators.  

Desiccant:  A substance which absorbs moisture in gas or air.  Silica gel is an example. 

Differential Pressure:  Difference in pressure measurements between two points (in a vessel for example).  In mechanical filtration devices a differential pressure gauge is used to determine buildup of solid particulates in a filter cartridge to determine replacement or cleaning schedules.

Discontinuous Phase:  Undesired fluid which is to be removed from the primary fluid by means of a separation device such as a liquid-liquid coalescer or separator.

Dispersed Phase:  Particles in suspension which, in a liquid-liquid coalescer or oil-water separator are typically removed through mechanical means such as coalescing, hydrophobic filters, settling by gravity or other methods of separation.

Down-comer:  As used in a vertical vane gas separator, the down-comer is a length of small diameter pipe which provides a drainage connection between the vane element and the sump (liquid holding) area in the lower portion of the vessel. 

Effluent:  Refers to the stream of liquid exiting a vessel such as a liquid-liquid coalescer separator or a filter.

Emulsion:  A mixture of two or more immiscible liquids (liquids which will not dissolve together such as oil and water).

Entrainment:  Liquids or solids carried along with the medium flowing in a process stream.

Filter cake:  A thick buildup of particulate matter on a filter cartridge.

Filter:  A device for retaining solids typically smaller than 70 microns through the use of disposable or cleanable filtration media which may be woven, melt-blown, membrane, canisters, bulk containers, plate type, flat, pleated, or depth type. Filters are used in many industrial processes for removing contaminants such as fines, iron oxides, dust, algae, colors, and odors.

Filter-Separator (as used in the natural gas industry):  A three-stage vessel used to remove entrained liquids and solids from gas using a combination of filter cartridges and separator element.  Initial impingement on the filter pedestals and gravitational fallout of the heavier liquid occurs upon entering the vessel.   Aerosol mist droplets are enlarged in the coalescing filters and are then removed from the process by a separator element.  Solid contaminants are removed by the coalescing filters.

Gas Scrubber:  A mechanical device used to separate entrained liquids from natural gas through impingement, coalescing, centrifugal force, or other separation methods.

Gas-Liquid Coalescer:  A mechanical device using coalescing cartridges to remove Liquid aerosols and extremely fine solid particulates from natural gas.  The liquid particles are coalesced until they are large enough to break free from the cartridge fibers and fall out of the flow through gravitational forces.

GPD:  Gallons per day.

GPH:  Gallons per Hour.

GPM:  Gallons per minute.

Hydrophilic molecules are capable of hydrogen bonding and readily mix with, or dissolve in water and other polar solvents.  (See Hydrophobic)

Hydrophobic (fear of water) surfaces and molecules repel water.  Water and oil will separate from one another as oil is nonpolar.  The molecules of a hydrophobic liquid are “nonpolar” (not producing a static electric field) and will not bond with water molecules.  Liquid-liquid coalescers may contain a separator cartridge as the second stage to the coalescing cartridge.  This separator cartridge has a hydrophobic coating allowing liquid hydrocarbons to pass through while repelling water.  (See Hydrophilic)

Immiscible:  Refers to liquids that will not dissolve together (e.g., oil and water).

Influent:  Refers to the stream of liquid entering a vessel such as a liquid-liquid coalescer separator or a filter.

Insoluble:  Not capable of being dissolved, such as oil in water.

Interfacial Tension (IFT):  Interfacial tension occurs at the interface of two immiscible liquids caused by the imbalance of molecular forces and the excess energy present. The interfacial tension SI units are dynes/cm (dynes per centimeter) or mN/m (milli-Newtons per meter).

Iodine:  Activated carbon iodine number is based on the amount of iodine adsorbed in testing, and is an indicator as to the porosity, or the content of micropores (pores having diameters ≤ 2 nm) in the carbon granule after it has been activated. The higher the number, the more activation in the carbon particle. (See mesh, molasses, and ash)

Laminar Flow:  Smooth, non-turbulent flow with minimal or no mixing.  Normally occurs at lower velocities.

Liquid-Liquid Coalescers are mechanical devices designed to enhance gravity separation of a mixture of two liquids that are immiscible, or non-soluble in one another. This is accomplished by increasing the size of the dispersed phase droplets using a media such as knitted wire mesh, which causes small dispersed droplets of a lesser liquid to merge, or coalesce, into larger droplets and thereby increasing the settling rate.

Mesh, wire (see wire mesh)

Mesh:  Activated carbon mesh size refers to a measurement of the activated carbon granule. For example, if carbon is rated at an 8 × 30 mesh size, 85% of the granules will fall through an 8 × 8 US wire mesh sieve and 95% will be retained on a 30 × 30 US wire mesh sieve placed below. (See molasses, iodine, and ash)

Micron (μm):   A unit of measurement commonly used in the filtration and separation industries equal to 0.001 millimeter or 0.00003937 inch.

Miscible:  Refers to a liquid solute that will dissolve in a liquid solvent to form a homogenous solution. 

Mist Eliminator Mesh Pad (as used in separation of liquids from a gas stream):  An assembly of knitted wire mesh with a thickness of several inches or more installed in an enclosed vessel designed for the coalescence and removal of an undesirable entrained liquid in a gas flow.

MMSCFD:  Million standard cubic feet per day.

MMSCFH:  Million standard cubic feet per hour.

MMSCFM:  Million standard cubic feet per minute.

Molasses:  Activated carbon molasses number is derived from the decolorization from molasses in solution, and refers to the measure of the content of mesopores (pores having diameters 2–50 nm) in the carbon granule after it has been activated compared to a standard carbon granule. The higher the number, the larger the molecule captured. (See mesh, iodine, and ash)

MSCFD:  Thousand standard cubic feet per day.   

MSCFH:  Thousand standard cubic feet per hour.

MSCFM:  Standard cubic feet per minute. 

Nominal rating:  Refers to a degree of filtration – the removal of a minimum percentage of particles larger than the rated micron size that will pass through a filter and typically less than complete removal of the contamination content. Testing methods may vary between filter manufacturers.     

Non Aqueous:  Refers to a solution in which the liquid is not water. (See aqueous)

Open area (strainers):  A ratio of the total flow area in a strainer’s media, expressed as a percentage, to the cross sectional flow area of a pipe in which the strainer is installed.  Increasing the percentage of the strainer’s flow area serves to enlarge the contaminant holding capacity, increase flow, and reduce the pressure drop across the strainer.

PPM:  Parts per million.

Pressure Drop:  Pressure difference measured in PSID (pounds per square inch difference) between two locations, such as upstream and downstream of a filter. 

PSI:  Pounds per square inch.

PSIA:  Pounds per square inch absolute.

PSID:  Pounds per square inch differential.

PSIG:  Pounds per square inch gauge.

Radial Flow:  Flow moving at right angles, perpendicular, or sideways to the primary flow direction.  The flow into and through the carbon bed in a carbon canister is typically considered radial.

Reynolds Number (Re):  A dimensionless number used to predict the transition of laminar flow to turbulent flow in fluids in varying situations and is used in the scaling of different size flows.

RFSO:  Raised face slip-on flange.  Raised face refers to the portion of the flange which has a serrated finish for a gasket to fit against and is slightly raised above the rest of the flange face. Slip-on flanges slip over a section of pipe for installation.

RFWN:  Raised face weld-neck.  Raised face refers to the portion of the flange which has a serrated finish for a gasket to fit against and is slightly raised above the rest of the flange face.  Weld-neck flanges are welded to the end of a pipe.

RTJ:  Ring Type Joint.  A flange facing which has either 1) a deep groove for installation of a thick soft-metal gasket (female RTJ flange), or 2) an extended ring-shaped projection on the flange facing (male RTJ flange) which fits into the groove of an opposing RTJ female flange with a matching groove.  Female RTJ flanges are not as subject to damage in shipment or storage compared with male RTJ flanges.

SCFD:  Standard cubic feet per day.

SCFH:  Standard cubic feet per hour.  

SCFM:  Standard cubic feet per minute.

Separator, two phase:  A mechanical device which removes entrained liquids from natural gas, process gas, air, or steam by means of coalescing, impingement, centrifugal action, or a combination of these.  A three phase separator is a mechanical device for separating oil, water, and gas.

Slug:  A large amount of liquid flowing intermittently or occasionally through a natural gas or steam pipe.  In a natural gas pipeline liquids will accumulate at a low spot, such as when a pipeline is routed underneath a stream bed.  These liquids will collect until they fill up the low section of pipe, at which time the pressure of the gas will build up quickly and shove the liquid slug downstream, causing damage to compressors and other equipment.  A slug-catcher is often installed upstream of a filter-separator or gas-liquid coalescer to catch anticipated slugs in a gas gathering system or gas pipeline.

Soluble liquids:  Although a more general term than miscible, refers to a liquid solute that will dissolve in a liquid solvent to form a homogeneous solution.

Soluble:  Able to be dissolved in a liquid solvent, such as sugar in water.

Specific gravity (SG):   The ratio of a substance’s density to the density of water.  Substances that are heavier than water have a specific gravity greater than 1, and substances that are lighter than water have a specific gravity of less than 1.

Specific Heat:  The amount of heat in BTUs needed to raise one pound of a substance one degree Fahrenheit, or the SI system, the amount of heat in kilocalories (kcal) needed to raise one kilogram of a substance one degree Celsius.

Steam Separator:  A mechanical device which removes moisture from steam. 

Steam Trap:  Used to drain condensate from a separator. The three types of traps used in steam applications are (a) Float Trap, a steam trap using a float, which drains water when the float rises, (b) Bucket Trap, which has an open-bottom bucket which sinks with the increase in water, and (c) a trap which opens when the temperature drops.  The float trap is generally used to drain steam separators.

Steam, Dry:  Steam which has liquids which are vaporized and therefore are in a single-phase state.

Steam, Saturated:  Steam formed by boiling water or evaporation and is in the gas phase; saturated steam is in equilibrium with the heated water.

Steam, Superheated:  Steam having no saturated liquids due to the temperature at which it is heated at a constant pressure.

Steam, Wet:  Steam which has water droplets which are not vaporized and are in a two-phase state, therefore can be separated by mechanical means.

Stokes’ Law:  A law in physics which estimates the velocity of particles settling by gravity in a fluid.  Acceleration of particles will occur until resisting forces balance with gravitational force and settle at a constant speed, known as “terminal velocity.”  Application of Stokes law can be seen in the separation of two immiscible liquids such as oil and water.

Strainer, basket type:  1) a strainer shaped like a basket as used in a simplex or duplex strainer housing; 2) a start-up strainer with a flat end instead of a conical shape in order to provide more surface area without the extra length.  Also known as a truncated cone.

Strainer:  A device for retaining visible-size and larger solid particulates through the use of perforated metal, wedge wire, or woven wire mesh.  Industrial strainers typically are designed for permanent or temporary use in oil & gas, power, food and beverage, chemical, pulp & paper, water treatment and other processes requiring the retention of solid contaminants in order to protect downstream equipment. Variations include basket-type simplex, duplex, wye, tee and start-up strainers.

Surface filter:  A filter medium which is effective for entrapment of particulate only on its surface.  Surface filters are generally pleated in order to offer more filtration area.

Surfactant:  A compound which lowers the interfacial tension between two liquids.  In liquid-liquid separation processes lower interfacial tension makes the separation of the two liquids more difficult.  They do however play an important role in many applications including wetting, emulsifying, foaming, etc.  Products include Soaps, shampoos, paints, liquid drag reduction agents, etc.  

Suspension:  Solid or liquid particles which are not heavier than the medium they are in and therefore are not affected by gravity.

Terminal velocity:  A constant speed produced from the effect of the balancing of gravitational force and the frictional drag produced by the fluid viscosity.

Tortuous Path:  An erratic path which separates liquid or solid entrainment from a gas with the use of a mechanical device such as a vane or mist eliminator through which solids or liquids are separated from the flowing medium.

Turndown:  The range specified as a ratio of highest measured value to lowest measured value.  Vane separators and mist eliminators (mesh pad separators) typically are able to perform efficiently at 10:1 turndown, or maximum flow down to one-tenth of that flow.

Vane element (as used in separation of liquids from a gas stream):  A fixed assembly of corrugated plates inside of a separator or scrubber and designed for removing liquids from a gas stream.  The vane plates provide a torturous path through which all of the gas must flow.  Here, mist and entrained liquid particles are initially separated from the gas due to inertial impaction with changes in flow direction.  Pockets, or hooks, may be provided at multiple locations inside the vane assembly to catch the liquid and provide a channel for drainage.

Wire Mesh (strainers):  Wire mesh is also referred to as wire cloth.  With industrial metal strainers there are many different materials and styles for the woven wire weave.  The most common is the square wire mesh weave which has as many wires per inch in both directions in the flat sheet.  Counting the number of wires per inch, or the spaces between the wires will give the mesh size; 40 spaces in one inch equals 40 mesh, or 40 x 40 mesh.