Thermal Power Plant Dictionary

8/13/2019 Thermal Power Plant Dictionary

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Boiler Dictionary

Absolute pressure - The pressure above zero pressure, equal; to gauge pressure plusatmospheric pressure.

Acid cleaning -The process of cleaning the interior surfaces of steam-generating units byfilling the unit with a dilute acid accompanied by an inhibitor to prevent corrosion and bysubsequently draining, washing, and neutralizing the acid by a further wash of alkaline water.

Acidity -Represents the amount of free carbon dioide, mineral acids, and salts !especiallysulfates or iron and aluminum" which hydrolyze to give hydrogen ions in water; is reported asmill equivalents per liter of acid, or ppm acidity as calcium carbonate, or p#, the measure ofhydrogen ion concentration.

Agglomeration -$roups of fine dust particles clinging together to form a larger particle.

Air-atomizing oil burner -% burner for firing oil in which the oil is atomized by compressed airwhich is forced into and through one or more streams of oil, breaking the oil into a fine spray.

Air-fuel ratio -The ratio weight, or volume, of air to fuel.

Air heater or air preheater -#eat-transfer apparatus through which air is passed and heated

by a medium of higher temperature, such as the products of combustion or steam.

Air purge -The removal of undesired matter by replacement with air.

Air vent -% valved opening in the top of the highest drum of a boiler or pressure vessel forventing air.

Alkalinity -The amount of carbonates, bicarbonates, hydroides, and silicates or phosphatesin the water; reported as grains per gallon, or parts per million as calcium carbonate.

Allowable working pressure -The maimum pressure for which the boiler was designed andconstructed; the maimum gauge pressure on a complete boiler; and the basis for the settingon the pressure relieving devices protecting the boiler.

Amplitude - &n ultrasonic testing, the vertical pulse height of a signal, usually base to peak,when indicated by an %-scan presentation.

A - scan - &n ultrasonic testing, a method of data presentation on a 'RT with the horizontalbaseline indicating distance or time and the vertical deflections from the baseline indicatingamplitude of the ultrasonic reflection.

Atomization -The process whereby a volume of liquid is converted into a multiplicity of smalldrops. The principal goal is to produce a high surface area to mass ratio so that the liquid willvaporize quickly and thus be susceptible to combustion.

Atomizer -part of an oil gun which breaks up the fuel oil flow into tiny particles by both

mechanical means the use of an atomizing medium. The oil and atomizing medium mitogether in the atomizer and then flow to the oil tip to be discharged into the furnace.

Attemperator -%pparatus for reducing and controlling the temperature of a superheater vaporor of a fluid.

Audible sound -(ibrations in a gas, liquid, or solid with components falling in the frequencyrange of )*#z to +#z.

Automatic lighter or igniter- % means for starting ignition of fuel without manual intervention.sually applied to liquid, gaseous, or pulverized fuel.

Available draft -The draft which may be utilized to cause the flow of air for combustion or the

flow of products for combustion.Backing ring -% strip of thin plate used on the inner surfaces of the abutting ends of pipe,tubes, or plates which are butt-welded. &ts purpose is to prevent irregularities at the base weldand to permit penetration at its root.


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Baffle -% plate or wall for deflecting gases or liquids.

Bag -% deep bulge in the bottom of the shell or furnace of a boiler.

Bag filter -% device containing one or more cloth bags for recovering particles from dust ladengas or air which is blown through it.

Balanced draft -The maintenance of a fied value of draft in a furnace at all combustion rates

by control of incoming air and outgoing products of combustion.

Barometric pressure - %tmospheric pressure as determined by a barometer usuallyepressed in inches of mercury.

Barrel -The cylindrical portion of a fire tube boiler shell that surrounds the tubes.

Base load -The term applied to that portion of a station or boiler load that is practicallyconstant for long periods.

Beta Ratio -or a single orifice the beta ratio is the ratio of the orifice bore diameter to that ofthe upstream pipe diameter. #owever, since in burner designs typically there is more than oneorifice at a riser pipe eit, the beta ratio is equal to the square root of the ratio between total

areas of the fuel ports to that of the upstream pipe area.

Bias -The output plus !or minus" some arbitrary value.

Black light -&n magnetic particle inspection, light in the near ultraviolet range of wavelengths,/ust shorter than visible light.

Blast furnace gas -0ean combustible by-product gas resulting from burning coke with adeficiency of air in a blast furnace.

Blowback -The number of pounds per square inch of pressure drop in a boiler from the pointwhere the safety valve pops to the point where the safety valve reseats.

Blowback ring -%n ad/ustable ring in a safety valve, used to control the amount of blowback.

Blowdown -The drain connection including the pipe and the valve at the lowest practical partof a boiler, or at the normal water level in the case of a surface blowdown. The amount of waterblown down.

Blowdown valve -% valve generally used to continuously regulate concentration of solids inthe boiler, not the drain valve.

Blower -% fan used to force air under pressure.

Boiler -% closed vessel in which water is heated, steam is generated, steam is superheated, orany combination thereof, under pressure or vacuum by the application of heat from combustible

fuels, electricity, or nuclear energy. The term dose not include such facilities of an integral partof a continuous processing unit but does include fired units of heating or vaporizing liquidsother than water where these units are separate from processing systems and are completewithin themselves.

Boiler header (box -% pressure part of the boiler consisting of a flat tube sheet into which theends of the water tubes are rolled. &n a parallel plane is a tube cap or handhole sheet. The twosheets are spaced about 1 to 2 in. or more apart. The top and bottom and both ends areflanged together and riveted or may be closed by a narrow flanged strip of plate riveted to eachsheet. 'irculating nipples connect the top of the header and drum, or the header may beflanged and riveted directly to the drum. 3elding would be used today instead of rivets.

Boiler! high-pressure! steam or vapor -% boiler in which steam or vapor is generated at a

pressure eceeding )4 psig.

Boiler! hot-water-heating -% boiler in which no steam is generated and from which hot wateris circulated for heating purposes and then returned to the boiler.


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Boiler! hot-water-supply -% boiler functioning as a water heater.

Boiler! low-pressure-steam or vapor -% boiler in which steam or vapor is generated at apressure not eceeding )4 psig.

Boiler horsepower -The evaporation of 51 6 lbs. of water per hour from a temperature of+)+o into dry saturated steam at the same temperature. 7quivalent to 55,184 9tu.

Boiler water -% term construed to mean a representative sample of the circulating boiler

water, after generated steam has been separated and before the incoming feed water or addedchemical becomes mied with it so that its composition is affected. !%:T -


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Burner windbox -% plenum chamber around a burner in which an air pressure is maintainedto ensure proper distribution and discharge of secondary air.

Bypass temperature control -'ontrol of vapor or air temperature by diverting part of or all theheating medium from passing over the heat-absorbing surfaces, usually by means of a bypassdamper.

$alorie -The amount of energy required to raise the temperature of ) gram of water by )

degree '. The kilocalorie !kcal" is a typical unit of measure in the process industry, ) kcal ?) calories.

$arryover -The moisture and entrained solids forming the film of steam bubbles; a result offoaming in the boiler. 'arryover is caused by a poor water condition within the boiler.

$asing -% covering of sheets of metal or other material such as fire resistant compositionboard used to enclose all or a portion of a steam-generating unit.

$austic cracking -%lso called caustic embitterment cracking, usually occurring in carbonsteels or iron-chromium nickel alloys that are eposed to concentrated hydroide solutions attemperatures of 1 to 12 deg. .

$heck valve -% valve designed to prevent reversal of flow. low in one direction only ispermitted.

$irculating tube -% boiler tube used to connect the water spaces of two drums or thepressure parts of a boiler.

$losed feed water heater -%n indirect -contact feed water heater; that is, one in which thesteam and water are separated by tubes or coils.

$losing-in-line -The sealing by plastic refractory between a boiler shell or head and thefirebrick wall; used to prevent hot gases from contacting the boiler above the lowest waterline.

$olloid -% finely divided organic substance which tends to inhibit the formation of dense scale

and results in the deposition of sludge, or causes it to remain in suspension, so that it may beblown from the boiler.

$ombined feeder cutoff -% device that regulates makeup water to a boiler in combinationwith a low water fuel cut off.

$ombustible -The heat-producing constituents of a fuel.

$ombustible loss -The loss representing the unelaborated thermal energy occasioned byfailure to oide completely some of the combustible matter in the fuel.

$ombustion -The rapid reaction of fuel and oidant !usually oygen in air" to produce light,heat and noise. a/or products of combustion for hydrocarbon fuels !e.g., natural gas, refinery

gas, fuel oils" are carbon dioide and water vapor. Trace products include carbon monoideand nitrogen oides, which are pollutants.

$ombustion chamber -:ee furnace

$ombustion efficiency -The fraction of carbon in the fuel that is converted into '@+ in theflue gas, customarily epressed as a percent.

$ombustion rate -The quantity of fuel fired per unit of time, as pounds of coal; per hour orcubic feet of gas per hour.

$ombustion (flame safeguard -% system for sensing the pressure or absence of flame andindicating, alarming or initiating control action.

$ondensate -'ondensed water resulting from the removal of latent heat from steam.

$onduction -The transfer of heat by molecular collision. This process is more efficient inmetals and other thermal conductors and poorer in fluids and insulators such as refractory.


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$onductivity - The amount of heat !9tu" transmitted in ) hour through ) sq. ft. of ahomogenous material ) in. thick for a difference in temperature of )o . between two surfacesof the material.

$ontinuous blowdown -The uninterrupted removal of concentrated boiler water from a boilerto control total solids concentration in the remaining water.

$ontrol -% device designed to regulate the fuel, air, water, steam, or electrical supply to the

controlled equipment. &t may be automatic, semi-automatic or manual.

$ontrol! limit -%n automatic safety control responsive to changes in liquid level, pressure, ortemperature; normally set beyond the operating range for limiting the operation of controlledequipment.

$ontrol! operating -% control, other than s safety control or interlock, to start or regulate inputaccording to demand and to stop or regulate input on satisfaction of demand. @peratingcontrols may also actuate auiliary equipment.

$ontrol! primary safety - % control responsive directly to flame properties, sensing thepresence of flame and, in the event of ignition failure or unintentional flame etinguishments,causing safety shutdown.

$ontrol! safety - %utomatic controls and interlocks !including relays, switches, and otherauiliary equipment used in con/unction to form a safety control system" which are intended toprevent unsafe operation of the controlled equipment.

$onvection -The transfer of heat or mass by large-scale fluid movements. 3hen the processoccurs, due to density and temperature differences, it is termed natural convection. 3hen theprocess occurs due to eternal devices !such as fans", it is termed forced convection.

$onvection section -The part of a furnace between the radiant section and the stack. Thearea is filled with tubes or pipes which carry process steam and which absorb heat viaconvection heat transfer from the hot gases passing through the area on their way out of thestack. The convection section forms an obstacle to the combustion gas flow and can greatly

affect furnace draft in the radiant section of the furnace.

$orrosion -The wasting away of metals as a result of chemical action. &n a boiler, usuallycaused by the presence of @+, '@+, or an acid.

$orrosion fatigue -'racks produced by the combined action of repeated or fluctuating stressand a corrosive environment, which produces the cracking at lower stress levels or fewercycles of stress than would be the case if no corrosive environment were present.

$ourse -% circumferential section of a boiler shell or drum. 3ith usual diameters, the numberof courses will equal the number of plates forming the shell or drum.

$reep - The time-dependent stretching or strain, heavily influenced by temperature, of a

material under stress.

$rimping tool -% tool used to reduce the diameter of the end of a boiler tube preparatory to itsremoval from a boiler.

$ritical pressure and critical temperature -That point at which the difference between theliquid and vapor states for water completely disappears.

$ross-box - % bolike structure to the longitudinal drum of a sectional header boiler forconnecting circulating tubes.

$rown sheet - The plate forming the roof of an internally fired furnace or a combustionchamber.

$-scan -&n ultrasonic testing a means of data presentation to show a plan view of the material,and of any discontinuities therein.


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Dba - =%= weighted average of the sound pressure levels over the entire frequency band.&ntended to be a more accurate representation of how a human hears sound.

Damper -% device for introducing a variable resistance of regulating the volumetric flow of gasor air.

Decibel -nit of sound pressure or power. %bbreviation is =d9=. ) 3att of sound power isequal to )+ d9.

Deaerator -% type of feed water heater operating with water and steam in direct contact. &t isdesigned to heat the water and drive off oygen.

Deflector - % device used to change the direction of a stream of air or of a miture ofpulverized fuel and air.

Design pressure -The pressure used in the design of a boiler for the purpose of determiningthe minimum permissible thickness or physical characteristics of the different parts of a boiler.

Differential -!of a control" the difference between cut in and cut out points.

Diffusion (raw gas flame -'ombustion state controlled by miing phenomena. uel and airdiffuse into one another until a flammable miture ratio is achieved.

Downcomer -% tube or pipe in a boiler or waterwall circulating system through which fluidflows downward between headers.

Draft -The difference between atmospheric pressure and some lower pressure eisting in thefurnace or gas passages of the steam-generating unit.

Draft control! barometric -% device that controls draft by means of a balanced damper whichbleeds air into the breeching on changes of pressure to maintain steady draft.

Draft differential -The difference in static pressure between two points in a system.

Drip leg -The container placed at a low point in a system of piping to collect condensate and

from which it may be removed.

Drum -% cylindrical shell closed at both ends, designed to withstand internal pressure.

Dry back -The baffle provided in a fire tube boiler /oining the furnace to the second pass todirect the products of combustion, that is so constructed to be separate from the pressurevessel and constructed of heat resistant material. !$enerally refractory and insulating material"

Dry steam -:team containing no moisture. 'ommercially dry steam containing not more than.4 percent moisture.

Duct -% passage for air or gas flow.

%conomizer -% series of tubes located in the path of flue gases. eed water is pumpedthrough these tubes on its way to the boiler in order to absorb waste heat from the flue gas.

%fficiency -@f boiler operationA @utput in heat units divided by input in heat units. The numberof 9tus contained in all steam evaporated is useful output. The number of 9tus contained in allfuel supplied to the boiler is input.

%&ector -% device which utilizes the kinetic energy in a /et of water or other fluid to remove afluid or fluent material from tanks or hoppers.

%lectric boiler -% boiler in which electric heating means serve as the source of energy.

%mbrittlement -%n intercrystalline corrosion of boilerplate occurring in highly stressed zones.

'racking may result.

%missivity -The efficiency with which a material radiates thermal energy, epressed as afraction between and ).


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%nthalpy -% thermal property of a fluid which is a function of state and is defined as the sum ofstored mechanical potential energy and internal energy. &t is generally epressed in 9tu perpound of fluid !/oules per kilogram".

%ntrainment -The conveying of particles of water or solids from the boiler water by the steam.

%vaporation rate -The number of pounds of water evaporated in a unit of time.

%vaporator -% pressure vessel used to evaporate raw water by means of a steam coil. The

steam is condensed by means of cooling water coils, and this distilled water is used as make-up for boiler feed.

%xcess air -The amount of air needed by a burner which is in ecess of the amount requiredfor perfect or stoichiometric combustion. :ome amount of ecess air, depending on theavailable fuelBair miing energy, is required to assure through miing of the fuel and air forcomplete combustion.

7plosion door - % door in a furnace or boiler setting designed to be opened by apredetermined gas pressure.

'an -% machine consisting of a rotor and housing for moving air or gases at relatively low-pressure differentials.

'an performance -% measure of fan operation in terms of volume, total pressures, staticpressures, speed, power input, and mechanical and static efficiency, at a stated air density.

'an performance curves -The graphical presentation of total pressure, static pressure, powerinput, and mechanical and static efficiency as ordinates and the range of volumes asabsciassas, all at constant speed and air density.

'eedwater regulator -% device for admitting feedwater to a boiler automatically on demand.Cractically a constant water level should result.

'irebox -The equivalent of a furnace. % term usually used for furnaces of locomotive boilersand similar types of boilers.

'iretube - % tube in a boiler having water on the outside and carrying the products ofcombustion on the inside.

'iring rate control -% pressure temperature or flow controller which controls the firing rate of aburner according to the deviation from pressure or temperature set point. The system may bearranged to operate the burner on-off, high-low or in proportion to load demand.

'lame -% luminous body of burning gas or vapor.

'lame detector -% device which indicates if fuel, such as liquid, gaseous, or pulverized, isburning or if ignition has been lost. The indication may be transmitted to a signal or to a controlsystem.

'lame propagation rate -:peed of travel of ignition through a combustible miture. !:eeflame speed"

'lame speed -The rate at which a flame can propagate in a combustion miture. &f the flame islower than the speed of the reacting flow, the flame may lift off the burner. &f the flame speed ishigher than the speed of the reacting flow the flame may flash back into the burner.

'lammability limits -The upper and lower bounds of the fuelBair miture which will supportcombustion. The upper flammability limit indicates the maimum fuel concentration in air thatwill support combustion. The lower flammability limit indicates the minimum fuel concentrationin the air that will support combustion. @utside of these bounds the miture does not burn.

'lareback -% burst of flame from a furnace in a direction opposed to the normal flow, usuallycaused by the ignition of an accumulation of combustible gases.

'lashback -% phenomenon occurring only in pre-mi gas burners when the flame speedovercomes the gas-air miture flow velocity eiting the gas tip. The flame rushes back to the


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gas orifice and can make an eplosive sound when flashback occurs. lashback is mostcommon when hydrogen is present in fuel gas.

'lashing - The process whereby a drop in pressure or increase in temperature causevaporization.

'lue -% passage for products of combustion.

'lue gas -The gaseous products of combustion in the flue to the stack.

'oaming -ormation of steam bubbles on the surface of boiler water due to high surfacetension of the water. :ee carryover.

'orced circulation -The circulation of water in a boiler by mechanical means eternal to theboiler.

'orced-draft fan -% fan supplying air under pressure to the fuel burning equipment.

'ouling -The accumulation of refuse in gas passages or on heat absorbing surfaces whichresults in undesirable restrictions to the flow of gas or heat.

'uel )x -D@ that is formed from nitrogen that is organically bound to the fuel molecule.

uel D@ is most often a problem with liquid fuel or coal burning. @nce the nitrogen has beencracked from the fuel molecule, the mechanism follows basically the same path as the promptD@ mechanism.

'urnace -%n enclosed space provided for the combustion of fuel.

'urnace arch -ppermost part of a radiant furnace !also called the =bridgewall=, a term whichcame from the original furnace designs and has remained in use". The last area in an upflowfurnace before the convection section.

'urnace Draft -The negative air pressure generated by buoyancy of hot gases inside afurnace. The temperature difference between gases within the furnace and in the atmospherealong with furnace and stack height basically determine the amount of draft generated by the

furnace.


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*ate valve -% stop valve using the wedge-and-double-seat principle. &t may be used to controlfluids containing some solids, for when wide open, it operates on a straight-through flow. Thereis little likelihood of its becoming obstructed.

*auge glass -% glass-enclosed visible indicator of the water level in a boiler. any gaugeglasses are tubular, but modern high-pressure practice and railroad locomotives use two thick,flat strips of glass bolted between flanged plates, with the water and steam between the glassstrips.

*auge pressure -The pressure above that of atmospheric, )1.8 psi at sea level; absolutepressure minus )1.8 at sea level.

*lobe valve -% stop valve using the round-disk-and-seat principle. sed where the fluidcontrolled is comparatively clean.

*rain -% unit of measure commonly used in water analysis for the measurement of impuritiesin water. !)8.) grains ? ) part per million - ppm"

+andhole -%n inspection, a sight, or a cleanout opening in a boiler; often elliptical and closedby a handhole plate.

+andhole cover -% handhole enclosure.

+ardness -% measure of the amount of calcium and magnesium salts in boiler water . suallyepressed as grains per gallon or parts per million as 'a'@+

+ard water -3ater which contains calcium or magnesium in an amount which requires anecessive amount of soap to form a lather.

+eader - % distribution pipe supplying a number of smaller lines tapped off of it. % mainreceiving pipe supplying one or more main pipe lines and receiving a number of supply linestapped into it.

+eat liberation -%mount of heat released during combustion of fuels. @ne of the criteria fordetermining what burner to use in an application.

+eating surface -That surface which is eposed to the heating medium for absorption andtransfer of heat to the heat medium per %merican 9oiler anufacturers %ssociation !%9%"

+eat release -The total quantity of thermal energy above a fied datum introduced into afurnace by the fuel, considered to be the product of the hourly fuel rate and its high heatingvalue, epressed in 9tu per hour per cubic foot of furnace volume or square foot of heatingsurface.

+igh fire -The input rate of a burner at or near maimum.

+igh gas pressure switch -% switch to stop the burner if gas pressure is too high.

+igher heating value -##(, the theoretical heat the combustion process can release if thefuel and oidant are converted with )E efficiency to '@+ and liquid #+.

+ot well -% tank used to receive condensate from various sources on its passage back to aboiler through the feedwater system. &t usually is vented to atmosphere.

+ydrostatic test - % pressure test by water at room temperature applied to a boiler todetermine its safety, as a check on repairs or to trace suspected leakage.

,gniter - % burner smaller than the main burner, which is ignited by a spark or otherindependent and stable ignition source and which provides proven ignition energy required toimmediately light off the main burner.

,gnition temperature -the temperature required to initiate combustion.

,mpeller -The rotating wheel of a centrifugal pump.

,mpingement -The striking of moving flame against boiler parts, causing local overheating.


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,ncomplete combustion -The partial oidation of the combustible constituents of a fuel.

,nduced draftfan -% fan ehausting hot gases from heat absorbing equipment.

,nput rating -The fuel burning capacity of a burner at sea level in 9tu per hour as specified bythe manufacturer.

,nsulation -% material of low thermal conductivity used to reduce heat loss.

,nterlock -% device to prove the physical state of a required condition and to furnish that proofto the primary safety control circuit.

,ntermittent firing -% method of firing by which fuel and air are introduced and burned in afurnace for a short period after which flow is stopped, this succession occurring in a sequenceof frequent cycles.

,ntermittent ignition -%n igniter which burns during light off and while the main burner is firingand which is shut off with the main burner.

,nternally fired boiler - % firetube boiler having an internal furnace such as a scotch,locomotive firebo, vertical tubular, or other type having a water-cooled plate type furnace.

,on -% charge atom or radical which may be positive or negative.

,on exchange -% reversible process by which ions are interchanged between solids and aliquid. These ions eist throughout the solution and act almost independently.

agging -% covering, usually of insulating material, on pipe or ducts.

aminar flow -(ery smooth flow in which all the molecules are traveling in generally the samedirection. or internal flows, it occurs at Reynolds numbers less than +.

ift-off - This condition occurs when the fuel or fuelBair miture velocity is too high, thusallowing the fuel to eit the stabilizing zone before it has achieved its ignition temperature.

ining -The material used on the furnace side of a furnace wall. &t is usually high-graderefractory tile or brick or plastic refractory material.

ive steam -:team which has not performed any of the work for which it was generated.

ow draft switch -% control to prevent the burner operation if the draft is too low. sedprimarily with mechanical draft.

ow fire start - The firing of a burner with controls in a low-fire position to provide safeoperating condition during light off.

ow gas pressure switch -% control to stop the burner if gas pressure is too low.

ower heating value -0#(, The theoretical heat the combustion process can release if thefuel and oidant are converted to )E efficiency to '@+ and #+@ vapor.

ow-oil-temperature switch -% cold-oil switch; a control to prevent burner operation if thetemperature of the oil is too low.

ow-water cutoff -% device to stop the burner on unsafe water conditions in the boiler.

ug -%s applied to boiler suspension, a steel eyepiece fitted and riveted or welded to thecurvature of a boiler shell or drum and connected by a steel -bolt or sling rod to overheadsteel structure; used to support the weight of a boiler.

.akeup water - The amount of raw water necessary to compensate for the amount ofcondensate that is not returned in the feedwater supply to the boiler.

.anhole -%n access opening to the interior of a boiler, elliptical and )) in. by )4 in. or larger orcircular )4-in. diameter or larger.


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.anifold -% pipe or header for collecting a fluid from, or the distributing of a fluid to a numberof pipes or tubes.

.anual reset device -% component of a control which requires resetting by hand to restart theburner after safe operating conditions have been restored.

.echanical draft -The negative pressure created by mechanical means.

.icron -@ne millionth of a meter, or .5F in. or )B+41 in The diameter of dust particlesis often epressed in microns.

.ixer -The part of a pre-mi burner !also gas-air mier" which uses the kinetic energy of thehigh velocity fuel gas stream to draw in part or all of the air required by the burner forcombustion.

.ud or lower drum -% pressure chamber of a drum or header type located at the loweretremity of a water-tube boiler convection bank which is normally provided with a blowoff valvefor periodic blowing off of sediment collecting in the bottom of the drum.

.ultifuel burner -% burner by means of which more than one fuel can be burned eitherseparately or simultaneously, such as pulverized fuel, oil and gas.

atural circulation -The circulation of water in a boiler caused by differences in density; alsoreferred to as thermal or thermally induced circulation.

atural gas -$aseous fuel occurring in nature.

et fan re/uirements -The calculated operating conditions for a fan ecluding tolerances.

oise -%n undesirable sound.

ormal cubic meter - !Dm5" The quantity of a gas that is present in ) m5 at thethermodynamic conditions of ) atm and o '. or an ideal gas there are ++.1) Dm5 in ) kmol.

ozzle -% short flanged or welded neck connection on a drum or shell for the outlet or inlet offluids; also a protecting spout for the outlet or inlet of fluids; also a pro/ecting spout throughwhich fluid flows.

)x -%ny combination of nitrogen and oygen in a compound form. The most common interms of environmental considerations is D@, which constitutes FE of combustion D@emissions, and D@+. %ll D@ is eventually converted to D@+ in the atmosphere. #ence, mostregulations are written to assume that the D@ which is emitted is in the form of D@+. Doemissions are influenced by many factors, including furnace temperature, flame temperature,burner design, combustion air temperature, nitrogen content of liquid fuels, ammonia content ofgas fuels, and other factors.

)il block -sually a monolithic block located at the center of a burner assembly. The oil block

acts to stabilize the oil flame.

)il burner -% burner that atomizes fuel oil and blows it into the combustion chamber in theform of a fine mist or vapor. :team or mechanical motion plus air may be used as the operatingmedium.

)il gun -The assembly of parts in a burner which provides atomized fuel oil miture to thefurnace for burning.

)il tip -Cart of the oil gun which discharges the atomized fuel oil miture into the furnacethrough multiple openings. The hole pattern in the tip has a great effect on flame size andshape.

)perating control -% control to start and stop the burner; it must be set below the high limitcontrol.


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)rifice -!)" The opening from the whirling chamber of a mechanical atomizer or the miingchamber of a steam atomizer thru which the liquid fuel is discharged. !+" % calibrated openingin a plate, inserted in a gas stream for measuring the velocity of flow.

)rifice discharge coefficient ($d -The ratio of the actual flow through an orifice to that of thetheoretical or isentropic flow through an orifice. 9asically this parameter is a measure of theorifice efficiency. (alves are dimensionless and range from .*) for a thin-plate orifice to .24for thick plate square-edged orifices, and up top .F - .F4for tapered orifices.

)rsat-%n instrument for determining the chemical analysis of flue gas.

)xidation -'hemical combination with oygen.

)xygen attack -'orrosion or pitting in a boiler caused by oygen.

0A+ (polycyclic aromatic hydrocarbons -The carcinogenic byproducts of some very sub-stoichiometric combustion processes. sually absent in process burners.

0ackaged boiler - % boiler equipped and shipped complete with fuel-burning equipment,mechanical draft equipment, automatic controls and accessories; usually shipped in one ormore ma/or sections.

0articulates -The residue left over from coal and fuel oil combustion.

0ascals -% unit of pressure. @ne Cascal !Ca" is equal to a force of one Dewton per squaremeter.

0ass - % confined passageway, containing heating surface, through which fluid flowsessentially one direction.

0erfect or 1toichiometric combustion - The complete oidation of all the combustibleconstitutes of a fuel, utilizing all the oygen supplied.

p+ -The hydrogen ion concentration of a water to denote acidity or alkalinity. % p# of 8 isneutral. % p# above 8 denotes alkalinity while one below 8 denotes acidity.

0ilot -% small burner which is used to light the main burner.

0ilot! constant -% pilot that burns without turndown throughout the entire time the boiler is inservice.

0ilot flame establishing period -The length of time fuel is permitted to be delivered to aproved pilot before the flame-sensing device is required to detect pilot flame.

0ilot! proved -% pilot flame which has been proved by flame-failure controls.

0it -'orrosion localized in a small spot.

0lenum -%n enclosure through which gas or air passes at relatively low velocities.

0ostpurge -% period after the fuel valves close during which the burner motor or fan continuesto run, to supply air to the combustion chamber.

0repurge period -% period on each start-up during which air is introduced into the combustionchamber and associated flue passages in volume and manner as to completely replace the airor fuel air-miture contained therein prior to an attempt to initiate combustion.

0re-mixed flame -9efore ignition, the fuel and air are intimately mied. The combustionprocess is controlled by heat conduction and diffusion of radicals.

0ressure -%s applied to boilers, the force eerted by a liquid or gas on a unit area. Three

pressures may be involvedA gauge pressure, the unit pressure above atmospheric pressure;absolute pressure, gauge pressure plus the atmospheric pressure; vacuum pressure; thepressure below atmospheric pressure usually epressed in inches of #g.


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0ressure! gas -The force eerted per unit area on a surface created by the collision of gasmolecules with the surface.

0ressure! static -The pressure of a gas measured at a point where the gas velocity is zero.

0ressure! total -The sum of the static pressure and the velocity pressure of the gas.

0ressure! velocity or dynamic -The pressure of flowing gas attributed to the impact of gasmolecules resulting from the velocity of the gas flow.

0rimary air -%ir introduced with fuel at the burners.

0riming -%n induction of boiler water caused by the steam flow into the steam line. The watermay be in the form of a spray or a solid body.

0rocess steam -:team used for industrial purposes other than for producing power.

0rompt )x -D@ formed at the initial stages of combustion that cannot be eplained byeither the thermal mechanism or the fuel D@ mechanism. The prompt D@ mechanismrequires the '# radical as an intermediate, so the fuel must have carbon present to createprompt D@.

0roportional control -% mode of control in which there is a continuous linear relation betweenvalue of the controller variable and position of the final control element !modulating control".

0uff -% minor combustion eplosion within the boiler furnace or setting.

0ulsation -Rapid fluctuations in furnace pressure.

0urge interlock -% device so arranged that an air flow to the furnace above a minimum musteist for a definite time interval before the interlocking system will permit an automatic ignitiontorch to be placed in operation.

Radiant -%s applied to heat, having the property that permits heat to be transmitted by rayssimilar to those of light. To absorb radiant heat, an ob/ect must be in the =light= of the fire.

Radiant section -The part of a process heater into which the burners fire. Tubes mounted inthis area of the furnace receive heat principally via direct radiation from both burner flames andfurnace refractory. Chysical volume arrangement of the radiant section has a great effect onburner choice and required flame patterns.

Radiation -%ll warm bodies emit light !electromagnetic radiation - mostly infrared". 3hen thisradiation is absorbed or emitted by a body, heat is transferred and termed =heat transfer byradiation=. :uch heat transfer requires a line of sight !view factor" and is proportional to thefourth power of the absolute temperature difference between bodies and the emissivity of thebodies.

Rated capacity -The manufacturer>s stated capacity rating for mechanical equipment, for

instance, the maimum continuous capacity in pounds of steam per hour for which a boiler isdesigned.

Ratio of specific heats (k -%lso known as isentropic coefficient. &s equal to the quotient of theheat capacity at constant pressure and the heat capacity at constant volume. !'pB'v". Thisparameter is tabulated for many pure components at standard conditions, but is technicallydependent on the gas composition and temperature. The values are dimensionless and rangefrom ). to ).*.

Rawwater -ntreated feedwater.

Recycle -The process of sequencing a normal burner start-up following shutdown.

Refractory -% heat-insulating material, such as firebrick or plastic fire clay, used for purposesas lining combustion chambers.


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Reheater -% device using highly superheated steam or high-temperature flue gases as amedium serving to restore superheat to partly epanded steam; used often between high - andlow-pressure turbines.

Relay -% device that is operative by a variation in the conditions of one electric circuit to startthe operation of other devices in the same or another electric circuit !such as pressure ortemperature relay".

Return trap -% trap designed to discharge its condensate against boiler pressure and feed to

the boiler without additional mechanical equipment.

Ringlemann chart -% series of four rectangular grids of black lines of varying widths printedon white background, used in criterion of blackness for determining smoke density fromchimneys.

Riser tube -% tube through which steam and water pass from an upper waterwall header to adrum.

Regulator! gas pressure -% spring loaded, dead weighted or pressure balanced device whichwill maintain the gas pressure to the burner supply line.

1afety shut down -The action of shutting off all fuel and ignition energy to the burner by

means of safety control or controls such that restart cannot be accomplished without operatoraction.

1afety valve -% valve that automatically opens when pressure attains the valve setting whichis ad/ustable; used to prevent ecessive pressure from building up in a boiler.

1afety valve drain -% hole of at least 5B2 in diameter required through the body below thevalve-seat level in safety valves larger than +-in diameter; used to prevent condensate fromcollecting at this point.

1afety valve escape - % pipe conducting steam discharged from a safety valve to a safelocation.

1afety-valve lifting lever -% lever by which safety valve may be lifted from its seat.

1afety-valve muffler -% silencer designed so that it will not cause appreciable restriction tosteam flow.

1afety-valve nozzle -% flanged nozzle by which a safety valve is connected to a boiler shell ordrum.

1cale -% deposit of medium to etreme hardness occurring on water heating surfaces of aboiler because of an undesirable condition of boiler water.

1crubber -%n apparatus for the removal of solids from gases by entrainment in water.

1eal weld -% weld used primarily to obtain tightness and prevent leakage.

1econdary combustion -'ombustion which occurs as a result of ignition at a point beyondthe furnace.

1econdary treatment- Treatment of boiler feedwater or internal treatment of boiler water afterprimary treatment.

1eparator- % tank-type pressure vessel installed in a steam pipe to collect condensate to betrapped off and thus providing comparatively dry steam to connect machinery.

1hell- The cylindrical portion of a pressure vessel.

1ilica -% scale-forming element found in some boiler feedwaters.

1inous header -% header of a sectional header-type boiler in which the sides are curved backand forth to suit the stagger of the boiler tubes connected to the header faces.


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1iphon -% pigtail-shaped pipe or a drop leg in the pipe leading to a steam pressure gauge,serving to trap water in the gauge and prevent overheating from direct contact with steam.

1lug -% solid body of boiler water passed into the steam flow by priming or picked up from apocket of condensate in the steam line.

1oftening -The act of reducing scale-forming calcium and magnesium impurities from water.

1oot blower -% tube from which /ets of steam or compressed air are blown for cleaning the

fireside of tubes or other parts of the boiler.

1onic flow -3hen the flow velocity is equal to the speed of sound. The point at which the flowturns sonic is called critical pressure. This transition occurs at about )+.+ psig for natural gas at*o .

1palling- The breaking off of the surface refractory material as a result of internal stresses.

1pecific gravity -The ratio of the weight of a unit volume of a material to the weight of thesame unit volume of water.

1pecific heat- The quantity of heat, epressed in 9tu !/oule" required to raise the temperatureof ) lb. !kilogram" of a substance )o !o'"

1pontaneous combustion -&gnition of combustible material following slow oidation withoutthe application of high temperature from an eternal source.

1pray nozzle -% nozzle from which a liquid fuel is discharged in the form of a spray.

11# -!seconds, :aybolt niversal" units of kinematic viscosity.

1tack -% vertical conduit, which due to the difference in density between internal and eternalgases creates a draft at its base.

1tack draft- The magnitude of the draft measured at inlet to the stack.

1tack effluent -$as and solid products discharged from the stack.

1tack loss -The fraction of total heat which eits with the flue gas through the stack. Thequantity is customarily epressed as a percent of the total heat input. The stack loss is directlyproportional to the stack eit temperature; the higher the temperature, the greater the stackloss.

1taged air- D@ reduction technique predominantly used for fuel oil firing. The fuel is in/ectedinto a fuel-rich primary zone. This stoichiometry helps to control the fuel Do mechanism. 3henfiring gas, staged air produces higher D@ emissions than staged fuel.

1taged fuel -D@ reduction technique whereby a small portion of the fuel is in/ected in a leanprimary combustion zone. The flue products from this region flow to the secondary combustion

zone where the remainder of the fuel is burned out. The lengthening of the flame creates coolerflame temperatures, thus lowering thermal D@.

1tatic pressure -The measure of potential energy of a fluid.

1taybolt- % bolt threaded through or welded at each end, into two spaced sheets of a fireboor bo header to support flat surfaces against internal pressure.

1team -The vapor phase of water substantially unmied with other gases.

1team atomizing oil burner -% burner for firing oil which is atomized by steam. &t may be ofthe inside or outside miing type.

1team binding -% restriction in circulation due to a steam pocket or rapid steam formation.

1team *age- % gage for indicating the pressure of steam.


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1team generating unit- % unit to which water, fuel, and air are supplied and in which steam isgenerated. &t consists of a boiler furnace, and fuel burning equipment, and may include ascomponent parts water walls, superheater, reheater, economizer, air heater, or anycombination thereof.

1team purity- The degree of contamination. 'ontamination usually epressed in ppm.

1team /uality- The percent by weight of a vapor in a steam and water miture.

1team scrubber -% series of screens, wires, or plates through which steam is passed toremove entrained moisture.

1team separator - % device for removing entrained water from steam.

1trainer -% device, such as a filter, to retain solid particles allowing the liquid to pass.

1ulphate - carbonate ratio - The proportion of sulphates to carbonates, or alkalinity epressedas carbonates, in boiler water. The proper maintenance of this ratio has been advocated as ameans of inhibiting caustic embrittlement.

1uperheat - To raise the temperature of steam above its saturation temperature. Thetemperature in ecess of its saturation temperature.

1uperheated steam - :team at higher temperature than its saturation temperature.

1urface blowoff - Removal of water, foam, etc. from the surface at the water level in a boiler.The equipment for such removal.

1urge- The sudden displacement or movement of water in a closed vessel or drum.

1uspended solids- ndissolved solids in boiler water.

1well -The sudden increase in the volume of steam in the water steam miture below the waterlevel.

1winging load -% load that changes at relatively short intervals.

"empering air -%ir at a lower temperature added to a stream of pre-heated air to modify itstemperature.

"ertiary air - %ir for combustion supplied to the furnace to supplement the primary andsecondary air.

"heoretical air -The quantity of air required for perfect combustion.

"heoretical draft -The draft which would be available at the base of a stack if there were nofriction or acceleration losses from the stack.

"heoretical flame temperature -:ame as =adiabatic temperature=.

"herm- % unit of heat applied especially to gas. @ne therm ? ), 9tu.

"hermal conductivity -The ability of a material to conduct heat, epressed as thermal powerconducted per unit temperature and thickness. etals and other thermal =conductors= have alarge thermal conductivity. Refractories and other thermal =insulators= have a low thermalconductivity.

"hermal )x - D@ formed via the Geldovich mechanism. The rate-limiting step in thismechanism is the formation of the @ radical. This occurs only at high temperatures !aboveabout +1o .". #ence the term thermal D@, since it is D@H produced in the highesttemperature regions of the flame.

"hermo acoustical efficiency -7qual to the sound power levelBheat release. % value used tocharacterize the amount of combustion noise emitted from a flame.


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equal to ) H )-* for premied and turbulent flames and equal to ) H )-F for diffusion andlaminar flames.

"hermocouple- % temperature measuring instrument.

"hroat -The neck portion of a passageway.

"hrough stay -% brace used in fire-tube boilers between the heads or tube sheets.

"ie plate- % plate, through which a bolt or tie rod is passed to hold brick in place.

"ie rod -% tension member between buckstays or tie plates.

"ile -% preformed, burned refractory, usually applied to shapes other than standard brick.

"ime delay- % deliberate delay of a predetermined time in the action of a safety device orcontrol.

"otal air- The total quantity of air supplied to the fuel and products of combustion. Cercenttotal air is the ratio of total air to theoretical air epressed as per cent.

"otal pressure -The sum of the static and velocity pressures.

"otal solids concentration - The weight of dissolved and suspended impurities in a unitweight of boiler water, usually epressed as ppm.

"ramp air -%ny air that enters !infiltrates" the furnace through leaks. This air may be measuredby the @+ analyzer and often contributes to the burning of the fuel.

"rap -% receptacle for the collection of undesirable material.

"reated water -3ater which has been chemically treated to make suitable for boiler feed.

"rail-for-ignition- That period of time during which the programming flame failure controlspermit the burner fuel valves to be open before the flame sensing device is required to detect

the flame.

"rail for main flame ignition -% timed interval when with the ignition means proved, the mainvalve is permitted to remain open. &f the main burner is not ignited during this period, the mainvalve and ignition means are cut off. % safety switch lockout follows.

"rail for pilot ignition -% timed interval when the pilot valve is held open and an attempt madeto ignite and prove it. &f the presence of the pilot is proved at the termination of the interval, themain valve is energized; if not the pilot and ignition are cut off followed by a safety lockout.

"ry cock -@ne of three valves mounted on a boiler or water column within the visible range ofthe gauge glass and used to check the water level.

"ube -% hollow cylinder for conveying fluids.

"ube cleaner -% device for cleaning tubes by brushing, hammering, or by rotating cutters.

"ube plug -% solid plug driven into the end of a tube.

"urbulent burner -% burner in which fuel and air are mied and discharged into the furnace insuch a manner as to produce turbulent flow from the burner.

"urbulent flow- 'haracteristically random flow patterns that form eddies from large to smallscales. or internal flows, it occurs at Reynolds numbers greater than 1. Turbulence isintegral to the miing process between the fuel and air for combustion.

#+$ -%ny unburned hydrocarbon that is emitted in a combustion process. %lso termed (@'!volatile organic compound".


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#naccounted for loss -That portion of a boiler heat balance, which represents the differencebetween ) per cent and the sum of the heat absorbed by the unit and all the classified lossesepressed as per cent.

#nburned combustible- The combustible portion of the fuel, which is not completely oidized.

#nfired pressure vessel -% vessel designed to withstand internal pressure, neither sub/ectedto heat from products of combustion nor an integral part of a fired pressure vessel system.

#se factor- The ratio of hours in operation to the total hours in that period.

2ane- % fied or ad/ustable plate inserted in a gas or air stream used to change the direction offlow.

2ane control -% set of movable vanes in the inlet of a fan to provide regulation of airflow.

2ane guide -% set of stationary vanes to govern direction, velocity and distribution of air or gasflow.

2alve! manual gas shutoff -% manually operated valve in a gas line for the purpose ofcompletely turning on or shutting off the gas supply.

2alve! manual oil shutoff -% manually operated valve in the oil line for the purpose ofcompletely turning on or shutting off the oil supply to the burner.

2alve! manual reset safety shutoff- % manually opened, electronically latched, electricallyoperated safety shut-off valve designed to automatically shut off fuel when de-energized.

2alve! motor driven reset safety shutoff -%n electrically operated safety shut-off valvedesigned to automatically shut off fuel flow upon being de-energized. The valve is opened andreset automatically by integral motor device only.

2alve! fuel control -%n automatically or manually operated device consisting essentially of aregulating valve and an operating mechanism. &t is used to regulate fuel flow and is usually inaddition to the safety shut-off valve. :uch valve may be of the automatic or manually opened

type.

2apor -The gaseous product of evaporation.

2apor generator -% container of liquid, other than water, which is vaporized by the absorptionof heat.

2aporization- The change from liquid or solid phase to the vapor phase.

2elocity pressure- The measure of kinetic energy of a fluid.

2elocity thermocouple -!suction pyrometer" a device for measuring furnace gas temperature.&t is comprised of a thermocouple, which has been recessed into an insulating shroud, and a

suction device such as an eductor, which aspirates large volumes of furnace gas through theshroud and past the thermocouple. The high velocity of a gas ensures good convective heattransfer to the thermocouple and surrounding furnace. The velocity thermocouple representsthe most accurate means to measure flue gas temperature. 9are thermocouples areunacceptable for this purpose, being in error often by more than )o due to radiation losses.

2ent -%n opening in a vessel or other enclosed space for the removal of gas or vapor.

2ertical firing -%n arrangement of a burner such that air and fuel are discharged into thefurnace, in practically a vertical direction.

2iscosity- easure of the internal friction of a fluid or its resistance to flow.

2olatile matter -Those products given off by a material as gas or vapor, determined bydefinite prescribed methods.

2olume of air -The number of cubic feet of air per minute epressed at fan outlet conditions.


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2ortex -!)" The swirling motion of a liquid in a vessel at the entrance to a discharge nozzle. !+"The point in a cyclonic gas path where the two spirals change general direction by )2o.

3aste fuel- %ny by-product fuel that is waste from a manufacturing process.

3aste heat -:ensible heat in non-combustible gases.

3ater column -% vertical tubular member connected at its top and bottom to the steam andwater space respectively to a boiler, to which the water gage, gage cocks, high and low water

alarms and fuel cutoff may be connected.

3ater gage -The gage glass and its fittings for attachment.

3ater hammer -% sudden increase in pressure of water due to an instantaneous conversionor momentum to pressure.

3ater level -The elevation of the surface of the water in a boiler.

3ater tube -% tube in a boiler having the water and steam on the inside and heat applied tothe outside.

3ater vapor -% synonym for steam, usually used to denote steam of absolute low pressure.

3eep- % term usually applied to a minute leak in a boiler /oint which forms droplets !or tears"of water very slowly.

3et back- 9affle provided in a firetube boiler /oining the furnace to the second pass to directthe products of combustion that is completely water-cooled.

3et steam -:team containing moisture.

3indbox -% chamber below the grate or surrounding a burner, thru which air under pressureis supplied for combustion of the fuel.

3indbox pressure -The static pressure in the windbo of a burner or stoker.

4ero governor -% regulating device that is normally ad/usted to deliver gas at atmosphericpressure within its flow rating.

Thermal Power Plant Dictionary

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