A B C D E F G H I J K L M N O P Q R S T U V W X Y Z #

Select the first letter of the word from the list above to jump to appropriate section of the glossary. If the term you are looking for starts with a digit or symbol, choose the ‘#’ link.

– A –

ABSOLUTE PRESSURE: Actual pressure above zero, which is the atmospheric pressure added to the gauge pressure. It is expressed as a unit of pressure such as lbs. per sq. in. absolute (psia).

ACCUMULATOR – STEAM: A pressure vessel containing water and/or steam, which is used to store the heat of steam for use at a late period and at some lower pressure.

ACIDITY: Represents the amount of free carbon dioxide, mineral acids and salts (especially sulphates of iron and aluminum) which hydrolyze to give hydrogen ions in water and is reported as milliequivalents per liter of acid, or ppm acidity as calcium carbonate, or pH the measure of hydrogen ions concentration.
AIR DEFICIENCY: Insufficient air, in an air-fuel mixture, to supply the oxygen required for complete oxidation of the fuel.

AIR-FUEL RATIO: The ratio of the weight, or volume, of air to fuel.

AIR VENT: A valved opening in the top of the highest drum of a boiler or pressure vessel for venting air.

AMBIENT AIR: The air that surrounds the equipment. The standard ambient air for performance calculations is air at 80 °F, 60% relative humidity, and a barometric pressure of 29.921 in. Hg, giving a specific humidity of 0.013 LB of water vapor per LB of dry air.

ATMOSPHERIC PRESSURE: The weight of a column of air, one square inch in cross section and extending from the earth to the upper level of the blanket of air surrounding the earth. This air exerts a pressure of 14.7 pounds per square inch at sea level, where water will boil at 212°F. High altitudes have lower atmospheric pressure with correspondingly lower boiling point temperatures.

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– B –

BAROMETRIC PRESSURE: Atmospheric pressure as determined by a barometer usually expressed in inches of mercury.

BLOWDOWN: Boiler water that is removed from the boiler in order to maintain the desired concentration levels of suspended and dissolved solids in the boiler and removal of sludge.

BLOWDOWN VALVE: Also referred to as a blowoff valve. A valve which permits a boiler control to be flushed out, and the function of same to be checked.

BLOW-OFF VALVE: A specially designed, manually operated, valve that connects to the boiler for the purpose of reducing the concentration of solids in the boiler or for draining purposes. (Often called bottom blowdown.)

BOILER: A closed vessel in which steam is generated, or in which water is heated by fire or electricity.

BOILER CROWN: The part of a boiler which forms the top of the furnace in a fire box boiler, or the equivalent surface in other types of boilers.

BOILER EFFICIENCY: The term Òboiler efficiency” is often substituted for combustion or thermal efficiency. True boiler efficiency is the measure of fuel-to-steam efficiency.

BOILER FEED PUMP: A pump that is governed by a control that monitors the actual boiler water level; and only adds water to the boiler when the boiler needs it. The pump controller is mounted on the boiler.

BOILER HEATING SURFACE: The area of the heat transmitting surfaces in contact with the water (or steam) in the boiler on one side and the fire or hot gases on the other.

BOILER HORSE POWER: The equivalent evaporation of 34.5 pounds of water per hour at 212°F to steam at 212°F. This is equal to a heat output of 33,475 BTU per hour, which is equal to approximately 140 sq. ft. of steam radiation (EDR).

BOILER RATING: The heating capacity of a boiler expressed in boiler horsepower, Btu/hour, or pounds of steam/hour.

BOILER WATER: A term construed to mean a representative sample of the circulating boiler water, after the generated steam has been separated and before the incoming feed water or added chemical becomes mixed with it so that its composition is affected.

BOILING OUT: The boiling of highly alkaline water in boiler pressure parts for the removal of oils, greases, etc.
BRITISH THERMAL UNIT (BTU): The quantity of heat required to raise the temperature of 1 pound of water 1°F.

BURNER: A device for the introduction of fuel and air into a furnace at the desired velocities, turbulence and concentration.

BURNER WINDBOX: A plenum chamber around a burner that maintains an air pressure sufficient for proper distribution and discharge of secondary air.

BURNER WINDBOX PRESSURE: The air pressure maintained in the windbox or plenum chamber measured above atmospheric pressure.

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– C –

CO: Carbon monoxide.

CO²: Carbon dioxide.

COMBUSTIBLES: The heat producing constituents of a fuel.

COMBUSTION: The rapid chemical combination of oxygen with the combustible elements of a fuel resulting in the release of heat.

COMBUSTION AIR: Air used in the combustion process. Air contains oxygen which is required to combust fuel.

COMBUSTION CHAMBER: See Furnace.

COMBUSTION EFFICIENCY: The effectiveness of the burner to completely burn the fuel. A well designed burner will operate with as little as 10 to 20% excess air, while converting all combustibles in the fuel to useful energy.

CONDENSATE: In steam heating, the water formed by cooling steam as in a radiator. The capacity of traps, pumps, etc., is sometimes expressed in pounds of condensate they will handle per hour. One pound of condensate per hour is equal to approximately 4 sq. ft. of steam heating surface (240 BTU per hour per sq. ft.)

CONDENSATE PUMP: A pump that is controlled by a switch mounted on the condensate tank. It adds water to the boiler when the condensate tank becomes full, whether the boiler needs water or not.

CONDUCTIVITY: (1) A material property relating heat flux (heat transferred per unit area per unit time) to a temperature difference. In American units, it is typically defined as the amount of heat (Btu) transmitted in one hour through one square foot of material 1 inch thick, with a temperature difference of 1°F between the two surfaces of the material. (2) The property of a water sample to transmit electric current under a set of standard conditions. Usually expressed as microhms conductance.

CONTINUOUS BLOWDOWN: The uninterrupted removal of concentrated boiler water from a boiler to control total solids concentration in the remaining water.

CSD-1: Abbreviation for the ASME standard for Controls and Safety Devices.

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– D –

DEAERATION: Removal of air and gases from boiler feed water prior to its introduction to a boiler.

DEW POINT: The temperature at which condensation starts.

DISSOLVED SOLID: Those solids in water which are in solution.
DISTILLATION: Vaporization of a substance with subsequent recovery of the vapor by condensation. Often used in less precise sense to refer to vaporization of volatile constituents of a fuel without subsequent condensation.

DISTILLED WATER: Water produced by vaporization and condensation with a resulting higher purity.

DRAFT: The difference between atmospheric pressure and some lower pressure existing in the furnace stack or gas passages of a steam generating unit.

DRAFT DIFFERENTIAL: The difference in static pressure between two points in a system.

DRAFT GAUGE: A device for measuring draft, usually in inches of water.

DRY FIRE

Insufficient water in a boiler to carry off the heat of combustion. It causes dry fire which results in cracked cast iron sections, and melted fire tubes.

DRY SATURATED STEAM: Saturated steam containing no water in suspension.

DRY STEAM: Steam containing no moisture. Commercially dry steam containing not more than one half of one percent moisture.

DYNAMIC SUCTION HEAD: Includes static suction lift, friction head loss, and velocity head.

DYNAMIC SUCTION LIFT: Includes static suction head minus friction head minus velocity head.

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– E –

ECONOMIZER: Utilizes waste heat by transferring heat from flue gases to warm incoming feedwater.

EDR: Equivalent direct radiation is the rate of heat transfer from a radiator or convector. It is equivalent to the square feet of surface area necessary to transfer heat at the same rate at which it is produced by a generator. A single boiler horsepower equals 140 ft2 EDR.

EFFICIENCY: The ratio of output to input. See also Combustion, Fuel-to-Steam and Thermal Efficiency.

ENTRAINMENT: The conveying of particles of water or solids from the boiler water by the steam.
EVAPORATION: The change of state from a liquid to a vapor.

EVAPORATION RATE: The number of pounds of water that is evaporated in a unit of time.

EXCESS AIR: Air supplied for combustion in excess of that theoretically required for complete oxidation.

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– F –

FAHRENHEIT: A thermometer scale at which the freezing point of water is 32°F and its boiling point is 212°F above zero. It is generally used in the United States for expressing temperature.

FEEDWATER: Water introduced into a boiler during operation. It includes make-up and return condensate.

FEEDWATER TREATMENT: The treatment of boiler feed water by the addition of chemicals to prevent the formation of scale or to eliminate other objectionable characteristics.

FIRE TUBE BOILER: This type of boiler has the water on the external side of the tube and the heat (fire) on the internal side of the tube.

FIRING RATE CONTROL: A pressure temperature or flow controller which controls the firing rate of a burner according to the deviation from pressure or temperature set point. The system may be arranged to operate the burner on-off, high-low or in proportion to load demand.

FLAME DETECTOR: A device which indicates if a fuel (liquid, gaseous, or pulverized) is burning, or if ignition has been lost. The indication may be transmitted to a signal or to a control system.

FLAME PROPAGATION RATE: Speed of travel of ignition through a combustible mixture.

FLAME SAFEGUARD: A control that sequences the burner through several stages of operation to provide proper air purge, ignition, normal operation, and shutdown for safe operation.

FLASH (STEAM): The rapid passing into steam of water at a high temperature when the pressure it is under is reduced so that its temperature is above that of its boiling point for the reduced pressure. For example: if hot condensate is discharged by a trap into a low pressure return or into the atmosphere, a certain percentage of the water will be immediately transformed into steam. It is also called re-evaporation.

FLUE: A passage for products of combustion.

FLUE GAS: The gaseous product of combustion in the flue to the stack.

FM: Factory Mutual.

FOAMING: A condition that occurs when an organic substance, usually oil, is floating on the surface of the water in a boiler. When the boiler is fired, a layer of foam develops on the surface of the water. This generally is indicated in the gauge glass by large swings in water level.

FREEZE UP: This refers to a structure that has lost its heating system, and the water in the piping freezes.

FRICTION HEAD: The pressure expressed in lbs./sq.in. or feet of liquid needed to overcome the resistance to the flow in the pipe and fittings.

FUEL: A substance containing combustible used for generating heat.

FUEL-AIR MIXTURE: Mixture of fuel and air.

FUEL-AIR RATIO: The ratio of the weight, or volume, of fuel to air.

FURNACE: An enclosed space provided for the combustion of fuel.

FURNACE PRESSURE: Pressure occurring inside the combustion chamber; positive if greater than atmospheric, negative if less than atmospheric, and neutral if equal to atmospheric.

FURNACE VOLUME: The cubic contents of the furnace or combustion chamber.

FUSIBLE PLUG: A hollowed threaded plug having the hollowed portion filled with a low melting point material.

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– G –

GAS ANALYSIS: The determination of the constituents of a gaseous mixture.

GAS BURNER: A burner that uses gas or fuel.

GAS PRESSURE REGULATOR: A spring loaded, dead weighted or pressure balanced device which will maintain the gas pressure to the burner supply line.

GAUGE COCK: A valve attached to a water column or drum for checking water level.

GAUGE GLASS: The transparent part of a water gauge assembly connected directly or through a water column to the boiler, below and above the water line, to indicate the water level in a boiler.

GAUGE PRESSURE: The pressure above atmospheric pressure.

GRADE: Oil classification according to quality, generally based on ASTM specifications.

GRAINS PER CU-FT: The term for expressing dust loading in weight per unit of gas volume (7000 grains equals one pound).
GRAINS (WATER): A unit of measure commonly used in water analysis for the measurement of impurities in water (17.1 grains = 1 part per million – ppm).

GRAVITY: Weight index of fuels: liquid, petroleum products expressed either as specific, Baume or A.P.I. (American Petroleum Institute) gravity; weight index of gaseous fuels as specific gravity related to air under specified conditions; or weight index of solid fuels as specific gravity related to water under specified conditions.

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– H –

HEAD: Unit pressure usually expressed in ft. of water, inches of water, or pounds per sq. in.

HEAT EXCHANGER: A vessel in which heat is transferred from one medium to another.

HEAT OF THE LIQUID: The heat (BTU) contained in a liquid due to its temperature. The heat of the liquid for water is zero at 32°F, and increases 1 BTU, approximately, for every degree rise in temperature.

HEAT UNIT: In the foot-pound-second system, the British Thermal Unit (BTU).

HEATING MEDIUM: A substance such as water, steam, or air used to convey heat from the boiler, furnace, or other source of heat to the heating units from which the heat is dissipated.

HEATING SURFACE: Those surfaces which are exposed to products of combustion on one side and water on the other. This surface is measured on the side receiving the heat.

HOT WATER SYSTEM: A heating system in which water is used as the medium by which heat is carried through pipes from the boiler to the heating units.

HYDROCARBON: A chemical compound of hydrogen and carbon.

HYDROSTATIC TEST: A strength and tightness test of a closed pressure vessel by water pressure.

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– I –

IGNITION: The initiation of combustion.

IGNITION TEMPERATURE: Lowest temperature of a fuel at which combustion becomes self-sustaining.

ILLUMINANTS: Light oil or coal compounds that readily burn with a luminous flame, such as ethylene, propylene and benzene.

INCOMPLETE COMBUSTION: The partial oxidation of the combustible constituents of a fuel.

INDUCED DRAFT FAN: A fan exhausting hot gases from the heat absorbing equipment.

INERT GASEOUS CONSTITUENTS: Incombustible gases such as nitrogen which may be present in a fuel.

INHIBITOR: A substance which selectively retards a chemical action. An example in boiler work is the use of an inhibitor, when using acid to remove scale, to prevent the acid from attacking the boiler metal.

INJECTOR: A device utilizing a steam jet to entrain and deliver feed water into a boiler.

INSULATION: A material of low thermal conductivity used to reduce heat losses.

INTERLOCK: A device to prove the physical state of a required condition, and to furnish that proof to the primary safety control circuit.

INTERMITTENT BLOWDOWN: The blowing down of boiler water at intervals.

IRI: Industrial Risk Insurers.

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– J –

(empty)

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– K –

(empty)

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– L –

LAGGING: A light gauge steel covering used over a boiler, usually combined with insulation, to provide a low temperature outer surface.

LATENT HEAT OF EVAPORATION: The heat (BTU of pound) necessary to change 1 pound of liquid into vapor without raising its temperature. I round numbers, this is equal to 960 BTU per pound of water.

LOW PRESSURE STEAM: As defined by ASME, low pressure steam is 15 PSIG or less.

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– M –

MAKE-UP WATER: Fresh water added to the system, by various means, to replace normal and abnormal water losses.

MANUAL RESET: A control that has to have human input before returning to normal operation.

MAXIMUM ALLOWABLE WORKING PRESSURE: The maximum gauge pressure permissible in a completed boiler. The MAWP of the completed boiler shall be less than or equal to the lowest design pressure determined for any of its parts. This pressure is based upon either proof tests or calculations for every pressure part of the boiler using nominal thickness exclusive of allowances for corrosion and thickness required for loadings other than pressure. It is the basis for the pressure setting of the pressure relieving devices protecting the boiler.

MAXIMUM DIFFERENTIAL (MD): A control with this designation has a greater spread between on/off cycles.

MICRON: One millionth of a meter, or 0.000039 in. or 1/25400 in. The diameter of dust particles is often expressed in microns.

MINIMUM SAFE WATER LEVEL: Also know as safe operating level. The minimum level of water in a boiler where the burner will still operate. Below this level, the burner should be off due to low water.

MOISTURE LOSS: The boiler flue gas loss representing the difference in the heat content of the moisture in the exit gases and that at the temperature of the ambient air.

MULTI-FUEL BURNER: A burner by means of which more than one fuel can be burned.

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– N –

NATURAL CIRCULATION: The circulation of water in a boiler caused by differences in density.

NATURAL GAS: Gaseous fuel occurring in nature.

NET POSITIVE SUCTION HEAT (NPSH): The liquid pressure that exists at the suction end of a pump. If the NPSH is insufficient, the pump can cavitate.

NOx: Abbreviation for all of the family of oxides of nitrogen.

NOZZLE: A short flanged or welded neck connection on a drum or shell for the outlet or inlet of fluids; also a projecting spout through which a fluid flows.

NPT: National Pipe Thread

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– O –

OIL BURNER: A burner for firing oil.

OPERATING CONTROL: A control to start and stop the burner – must be in addition to the high limit control.

OPERATING PRESSURE: The pressure at which a boiler is operated.

ORGANIC MATTER: Compounds containing carbon often derived from living organisms.

ORIFICE: (1) The opening from the whirling chamber of a mechanical atomizer or the mixing chamber of a steam atomizer through which the liquid fuel is discharged. (2) A calibrated opening in a plate, inserted in a gas stream for measure velocity of flow.

OVERFIRING: A situation where the burner does not turn off, for a number of reasons. The pressure of the system rises and the safety relief valve should open.

OVERPRESSURE: Minimum operating pressure of a hot water boiler sufficient to prevent the water from steaming.

OXIDATION: Chemical combination with oxygen.

OXIDIZING ATMOSPHERE: An atmosphere which tends to promote the oxidation of immersed materials.

OXYGEN ATTACK: Corrosion or pitting in a boiler caused by oxygen.

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– P –

PACKAGED BOILER: A boiler supplied with all of its components – burner, controls and auxiliary equipment, designed as a single engineered package, and ready for on-site installation.

PACKAGED STEAM GENERATOR: See Packaged Boiler.
PARTICLE SIZE: A measure of dust size, expressed in microns or per cent passing through a standard mesh screen. PASS – A confined passageway, containing heating surface, through which a fluid flows in essentially one direction.

PETROLEUM: Naturally occurring mineral oil consisting predominately of hydrocarbons.

pH: The hydrogen ion concentration of a water to denote Acidity or Alkalinity. A pH of 7 is neutral. A pH above 7 denotes alkalinity while one below 7 denotes acidity. This pH number is the negative exponent of 10 representing hydrogen ion concentration in grams per liter. For instance a pH of 7 represent 10-7 grams per liter.

PILOT: A flame which is utilized to ignite the fuel at the main burner or burners.

PILOT VALVE: A valve that uses a small valve to operate a large valve.

PITOT TUBE: An instrument which will register total pressure and static pressure in a gas stream, used to determine its velocity.

PITTING: A concentrated attack by oxygen or other corrosive chemicals in a boiler, producing a localized depression in the metal surface.

PORT: An opening through which fluid passes.

POST PURGE: A method of scavenging the furnace and boiler passes to remove all combustible gases after flame failure controls have sensed pilot and main burner shutdown and safety shut-off valves are closed.

ppm: Abbreviation for parts per million. Used in chemical determinations as one part per million parts by weight.

PRECIPITATE: To separate materials from a solution by the formation of insoluble matter by chemical reaction. The material which is removed.

PRECIPITATION: The removal of solid or liquid particles from a fluid.

PREHEATED AIR: Air at a temperature exceeding that of the ambient air. PRESSURE – Force per unit of area.

PRESSURE: Force per unit area such as pounds per square inch.

PRESSURE DROP: The difference in pressure between two points in a system, caused by resistance to flow.

PRESSURE REDUCING VALVE: A piece of equipment for changing the pressure of a gas or liquid from a higher pressure to a lower one.

PRESSURE VESSEL: A closed vessel or container designed to confine a fluid at a pressure above atmospheric.

PRIMARY AIR: Air introduced with the fuel at the burner.

PRIMING: When the steam leaving the boiler carries large amounts of water with it, this is called priming. Insufficient heat, water hammer, and a flooded boiler, if the system has an automatic water feeder are some of the symptoms. It is generally caused by a high water level in the boiler, and near boiler piping.

PROCESS STEAM: Steam used for industrial purposes other than for producing power.

PRODUCTS OF COMBUSTION: The gases, vapors, and solids resulting form the combustion of fuel.

PULSATION: Rapid fluctuations in pressure.

PURGE: To introduce air into the furnace and the boiler flue passages in such volume and manner as to completely replace the air or gas-air mixture contained therein.

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– Q –

(empty)

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– R –

RADIATION LOSS: A comprehensive term used in a boiler-unit heat balance to account for the conduction, radiation, and convection heat losses from the boiler to the ambient air.

RADIATOR: A heating unit located within the room to be heated and exposed to view. A radiator transfers heat by radiation to objects “it can see” and by conduction to the surrounding air which in turn is circulated by natural convection.

RATED CAPACITY: The manufacturer’s stated capacity rating for mechanical equipment; for instance, the maximum continuous capacity in pounds of steam per hour for which a boiler is designed.

RATE OF BLOWDOWN: A rate normally expressed as a percentage of the water fed.

RATING: See “Load.”

RAW WATER: Water supplied to the plant before any treatment.

REACTION: A chemical transformation or change brought about by the interaction of two substances.

REASSOCIATION: The recombination of the products of dissociation.

RECIRCULATION: The reintroduction of part of the flowing fluid to repeat the cycle of circulation.

REDUCING ATMOSPHERE: An atmosphere which tends to 1) promote the removal of oxygen from a chemical compound; 2) promote the reduction of immersed materials.

REDUCTION: Removal of oxygen from a chemical compound.

REFRACTORY: Brickwork or castable used in boilers to protect metal surfaces and for boiler baffles.

RELATIVE HUMIDITY: The ratio of the mass of water vapor present in a unit volume of gas to the maximum possible mass of water vapor in unit volume of the same gas at the same temperature and pressure.

RELIEF VALVE (Safety Relief Valve): An automatic pressure relieving device actuated by the pressure upstream of the valve and characterized by opening pop action with further increase in lift with an increase in pressure over popping pressure.

RESIDUAL FUELS: Products remaining from crude petroleum by removal of some of the water and an appreciable percentage of the more volatile hydrocarbons.

RESIN: A bead-like material used in chemical exchange for softeners and dealkalizers.

RESISTANCE: Impediment to gas flow, such as pressure drop or draft loss through a dust collector. Usually measured in inches water column (“wc).

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– S –

SAFE WORKING PRESSURE: See “Design Pressure.”

SAFETY VALVE: A spring loaded valve that automatically opens when pressure attains the valve setting. Used to prevent excessive pressure from building up in a boiler.

SAFETY SHUT-OFF VALVE: A manually opened, electrically latched, electrically operated safety shut-off valve designed to automatically shut off fuel when de-energized.

SAMPLING: The removal of a portion of a material for examination or analysis.

SATURATED AIR: Air which contains the maximum amount of water vapor that it can hold at its temperature and pressure.

SATURATED STEAM: Steam at the temperature and pressure at which evaporation occurs.

SATURATED TEMPERATURE: The temperature at which evaporation occurs at a particular pressure.

SATURATED WATER: Water at its boiling point.

SCALE: A hard coating or layer of materials on surfaces of boiler pressure parts.

SECONDARY AIR: Air for combustion supplied to the furnace to supplement the primary air.

SECONDARY TREATMENT: Treatment of boiler feed water or internal treatment of boiler-water after primary treatment.

SEDIMENT: (1) Matter in water which can be removed from suspension by gravity or mechanical means. (2) A non-combustible solid matter which settles out at bottom of a liquid; a small percentage is present in residual fuel oils. SEGREGATION – The tendency of refuse of varying compositions to deposit selectively in difference parts of the unit. <

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