Terms related to Steam and Boiler

Terms related to Steam and Boiler

Different terms used in the process of steam production which describe the steam, water used for steam production, the boiler equipment, and the process parameters are given below.

Absolute pressure – It is the pressure above zero pressure, i.e., the sum of the gauge and atmospheric pressures.

Accumulator (steam) – It is a pressure vessel containing water and / or steam, which is used to store the heat of steam for use at a later period and at some lower pressure.

Acid cleaning – It is the process of cleaning the interior surfaces of steam generating units by filling the unit with dilute acid accompanied by an inhibitor to prevent corrosion, and subsequently draining, washing, and neutralizing the acid by a further wash of alkaline water.

Acidity – It represents the quantity of free carbon di-oxide, mineral acids and salts (especially sulphates of iron and aluminum) which hydrolyze to give hydrogen ions in water and is reported as milli-equivalents per litre of acid, or ppm (parts per million) acidity as calcium carbonate, or pH the measure of hydrogen ions concentration.

Adiabatic flame temperature – It is the theoretical temperature which is attained by the products of combustion provided the entire chemical energy of the fuel, the sensible heat content of the fuel, and combustion above the datum temperature are transferred to the products of combustion. This assumes no heat loss to the surroundings and no dissociation.

Air – It is the mixture of oxygen, nitrogen, and other gases, which with varying quantities of water vapour, forms the atmosphere of the earth.

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

Air deficiency – It is the condition of insufficient air, in an air-fuel mixture, for supplying the oxygen needed for complete combustion (oxidation) of the fuel.

Air-free – It is the descriptive characteristic of a substance from which air has been removed.

Air-fuel ratio – It is the ratio of the weight, or volume, of air to fuel.

Air-infiltration – It is the leakage of air into a setting or duct.

Air, saturated – It is the air which contains the maximum quantity of water vapour which it can hold at its temperature and pressure.

Air vent – It is a valved opening in the top of the highest drum of a boiler or pressure vessel for venting air.

Alarm – It is a suitable horn, bell, light, or other device which when operated indicates of the malfunctioning or off normal condition.

Alkalinity – It represents the quantities of carbonates, bi-carbonates, hydroxides, and silicates, or phosphates in the water and is reported as ppm as calcium carbonate.

Allowable working pressure – It is the pressure used in the design of a boiler for the purpose of calculating the minimum permissible thickness or physical characteristics of the different parts of the boiler.

Ambient air – It is the air which surrounds the equipment. The standard ambient air for performance calculations is air at 25 deg C, 60 % relative humidity, and a barometric pressure of 101 kilo pascals, giving a specific humidity of 0.013 kg (kilogram) of water vapour per kg of dry air.

Ambient temperature – It is the temperature of the air surrounding the equipment.

Analysis – It is the quantitative determination of the constituent parts.

Analysis, ultimate – It is the chemical analysis of solid, liquid, or gaseous fuels. In the case of coal or coke, it is the determination of carbon, hydrogen, sulphur, nitrogen, oxygen, and ash.

Aquastat – It is a water limit temperature control. It is a safety device frequently used for boilers.

Arrestor – It is a device to impede the flow of large dust particles or sparks from a stack, normally by screening at the top.

As-fired fuel – It is the fuel in the condition as fed to the fuel burning equipment.

Ash – It is the incombustible inorganic matter in the fuel.

Ash free basis – It is the method of reporting fuel analysis, whereby ash is deducted and other constituents are recalculated to total 100 %.

Ash pit – It is a pit or hopper located below a furnace where refuse is accumulated and from which refuse is removed at regular intervals.

Aspirating burner – It is a burner in which the fuel in a gaseous or finely divided form is burned in suspension, the air for combustion being supplied by bringing into contact with the fuel, air drawn through one or more openings by the lower static pressure created by the velocity of the fuel stream. As-received fuel – It is the fuel in the condition as received at the plant.

Atmospheric air – It is the air under the prevailing atmospheric conditions.

Atmospheric pressure – It is the barometric reading of pressure exerted by the atmosphere. It is the normal pressure of the atmosphere (101 kilo pascals) on the sea level at 0 deg C.

Atomizer – It is a device by means of which a liquid is reduced to a very fine spray.

Available draft – It is the draft which can be utilized to cause the flow of air for combustion or the flow of products of combustion.

Availability factor – It is the fraction of time during which the unit is in operable condition.

Axial fan – It consists of a propeller or disc type of wheel within a cylinder which discharges air parallel to the axis of the wheel.

Baffle – It is a plate or wall for deflecting gases or liquids.

Baffle tile– It is a tile for deflecting gases.

Baffle type collector – It is a device in gas paths utilizing baffles so arranged as to deflect dust particles out of the gas stream.

Bag filter – It is a device containing one or more cloth bags for recovering particles from the dust laden gas or air which is blown through it.

Bag type collector – It is a filter in which the cloth filtering medium is made in the form of cylindrical bags.

Barometric pressure – It is the atmospheric pressure as determined by a barometer normally expressed in millimeter of mercury.

Base load – Base load is the term applied to that portion of a station or boiler load which is practically constant for long periods.

Beaded tube end – It is the rounded exposed end of a rolled tube when the tube metal is formed over against the sheet in which the tube is rolled.

Blind nipple – It is a nipple, or a short piece of pipe or tube, closed at one end.

Blow down – It is the boiler water which 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.

Blow-down safety valve – It is the difference between the pressures at which a safety valve opens and at which it closes.

Blow-down valve – It is a valve normally used to continuously regulate concentration of solids in the boiler. It is not a drain valve. (It is frequently called continuous blow-down).

Blow-off valve – It is a specially designed, manually operated, valve which connects to the boiler for the purpose of reducing the concentration of solids in the boiler or for draining purposes. (It is frequently called bottom blow-down).

Blower – It is a fan used to force air under pressure.

Boiler – It is a closed vessel in which water is heated, steam is generated, steam is superheated, or any combination thereof, under pressure or vacuum by the application of heat from combustible fuels, electricity, or nuclear energy. Fig 1 shows types of steam boilers.

Fig 1 Types of steam boilers

Boiler efficiency – The term boiler efficiency is frequently substituted for combustion or thermal efficiency. True boiler efficiency is the measure of fuel-to-steam efficiency.

Boiler failure – Boiler failure is a term normally applied to the pressurized parts of the boiler. A ruptured tube or a crack which allows high-pressure steam or water to escape to the point of the boiler needing a shut-down is considered a boiler failure.

Boiler horse-power – Boiler horse-power is the capacity of a boiler to deliver steam. One boiler horse-power is equal to the thermal energy rate needed to evaporate 15.6 kg of fresh water at 100 deg C in one hour into dry saturated steam at the same temperature.

Boiler shell – It is the outer cylindrical portion of a pressure vessel.

Boiler water – It is 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 – It is the conversion of a liquid into vapour with the formation of bubbles.

Boiling out – It is the boiling of highly alkaline water in boiler pressure parts for the removal of oils, and greases etc.

Boiling point – It is the temperature (100 deg C) at which water boils. Water boils when its absolute pressure reaches the vapour pressure.

Booster fan – It is a device for increasing the pressure or flow of a gas.

Breeching – It is a duct which transports the products of combustion between parts of a steam generating unit or to the stack.

Bridge wall – It is a wall in a furnace over which the products of combustion pass.

Buckstay – It is a structural member placed against a furnace or boiler wall to restrain the motion of the wall.

Burner – It is a device for the introduction of fuel and air into a furnace at the desired velocities, turbulence, and concentration.

Burner wind-box – It is a plenum chamber around a burner which maintains an air pressure sufficient for proper distribution and discharge of secondary air.

Burner wind-box pressure – It is the air pressure maintained in the wind-box or plenum chamber measured above atmospheric pressure.

By-pass – It is a passage for a fluid, permitting a portion of the fluid to flow around its normal pass flow channel.

Calorie – It is a unit for measuring a quantity of heat and is the quantity of heat needed to increase the temperature of a gram of water by one deg C. The mean calorie is 1/100 of the heat needed to raise the temperature of 1 gram of water from 0 deg C to 100 deg C at a constant atmospheric pressure. A calorie is 4.184 joules.

Calorimeter – It is the apparatus for determining the calorific value of a fuel.

Capacity factor – It is the ratio of the average load carried to the maximum design capacity.

Carryover – It is the chemical solids and liquid entrained with the steam from a boiler.

Casing – It is a covering of sheets of metal or other material such as fire-resistant composition board used to enclose all or a portion of a steam generating unit.

Centrifugal fan – It consists of a fan rotor or wheel within a housing which discharges air at a right angle to the axis of the wheel.

Check valve – Check valve is a valve which has a hinged valve disk free to swing back and forth when pushed. If fluid passes in the flow direction, the disk is pushed open and flow is not hindered. If the flow tries to reverse, the disk is pressed against the valve seat and flow is not allowed to reverse. In other words, it is a one-way valve.

Chemical analysis – It is the determination of the principal chemical constituents.

Chemical feed pipe – It is a pipe inside a boiler drum through which chemicals for treating the boiler water are introduced.

Circulation – It is the movement of water and steam within a steam generating unit.

Circulation ratio – It is the ratio of water entering a circuit to the steam generated by the water which passes that circuit in a unit of time.

Circulator – It is a pipe or tube to pass steam or water between upper boiler drums normally located where the heat absorption is low. It is also used to apply to tubes connecting headers of horizontal water tube boilers with drums.

Clean-out door – It is a door placed so that accumulated refuse can be removed from the room in a boiler setting.

Collector – It is a device used for removing gas borne solids from flue gas.

Colloid – It is a 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 can be blown from the boiler.

Combustible loss – It is the loss representing the unliberated thermal energy occasioned by failure to oxidize completely some of the combustible matter in the fuel.

Combustibles – It is the heat producing constituents of a fuel.

Combustion – It is the rapid chemical combination of oxygen with the combustible elements of a fuel resulting in the release of heat.

Combustion air – It is the air used in the combustion process. Air contains oxygen which is needed to combust fuel.

Combustion chamber – A combustion chamber is the area within where the fuel / air mix is ignited.

Combustion efficiency – It is the effectiveness of the burner to completely burn the fuel. A well-designed burner operates with as little as 10 % to 20 % excess air, while converting all combustibles in the fuel to useful energy.

Combustion gases – Combustion gases are the hot gaseous products from the fire. These are also called ‘flue gases’ or ‘exhaust-gases’.

Combustion gas pass – One pass is the travel of the combustion gases once along the length of the boiler. If the gases are reversed and passed through another source of the boiler, this is a second pass.

Complete combustion – It is the complete oxidation of all the combustible constituents of a fuel. Concentration – It is the weight of solids contained in a unit weight of boiler or feed water. It is also the number of times which the dissolved solids have increased from the original quantity in the feed-water to that in the boiler water because of evaporation in generating steam.

Condensation – It is defined as the change in the physical state of water vapour to liquid water. It is reverse of vapourization.

Condensate – It is the liquid phase produced by the condensation of steam. It is the condensed water resulting from the removal of latent heat from steam.

Conduction – It is the transmission of heat through and by means of matter unaccompanied by any obvious motion of the matter.

Conductivity – It is the property of a water sample to transmit electric current under a set of standard conditions. It is normally expressed as micro-ohms conductance. It is a measure of the ability of water to pass an electrical current. Since dissolved salts and other inorganic chemicals conduct electrical current, conductivity increases as salinity increases. Conductivity is a material property relating heat flux (heat transferred per unit area per unit time) to a temperature difference.

Continuous blow-down – It is the uninterrupted removal of concentrated boiler water from a boiler to control total solids concentration in the remaining water.

Control – It is any manual or automatic device for the regulation of a machine to keep it at normal operation. If automatic, the device is motivated by variations in temperature, pressure, water level, time, light, or other influences.

Control valve – It is a valve used to control the flow of air, gas, water, steam, or other substance. Convection – It is the transmission of heat by the circulation of a liquid or gas. It can be natural, with the circulation caused by buoyancy affects because of temperature differences, or forced with circulation caused by a mechanical device such as a fan or pump.

Corrosion – It is the wasting away of metal because of chemical action. In a boiler, it is normally caused by the presence of oxygen, carbon di-oxide, or an acid.

Crown sheet – In a fire-box boiler, it is the plate forming the top of the furnace.

Damper – It is a device for introducing a variable pressure drop in a system, used for regulating the volumetric flow of a gas, such as air.

Davit – It is the structure on large fire-tube boilers from which the front and rear doors are suspended when opened.

Deaeration – It is the removal of air and gases from boiler feed water prior to its introduction to a boiler.

Degasification – It is the removal of gases from samples of steam taken for purity test. It is the removal of carbon di-oxide from water as in the ion exchange method of softening.

Delayed combustion – It is a continuation of combustion beyond the furnace.

Demineralized water – Demineralized water is that water in which all the mineral impurities have been removed. Demineralized water is free from all soluble mineral salts. It does not contain any anions or cations.

Density of steam – It is the mass of steam per unit of volume of steam at the given pressure and temperature. It is the reciprocal of the specific volume.

Design load – It is the load for which a steam generating unit is designed, considered the maximum load to be carried.

Design pressure – It is the pressure used in the design of a boiler for the purpose of calculating the minimum permissible thickness or physical characteristics of the different parts of the boiler.

Design steam temperature – It is the temperature of steam for which a boiler is designed.

Dew point – It is the temperature at which condensation starts.

Disengaging surface – It is the surface of the boiler water from which steam is released.

Dissociation – It is the process by which a chemical compound breaks down into simpler constituents, as do carbon di-oxide (CO2) and H2O at high temperature.

Dissolved solids – These are those solids in water which are in solution.

Distillate fuels – These are liquid fuels distilled normally from crude petroleum.

Distillation – It is the vapourization of a substance with subsequent recovery of the vapour by condensation. It is frequently used in less precise sense to refer to vapourization of volatile constituents of a fuel without subsequent condensation.

Distilled water – It is the water produced by vapourization and condensation with a resulting higher purity.

Down-comer – It is a tube or pipe in a boiler or water-wall circulating system through which fluid flows downward.

Down-time – It is the quantity of time a piece of equipment is not operational.

Draft – It is the difference between atmospheric pressure and some lower pressure existing in the furnace stack or gas passages of a steam generating unit.

Draft differential – It is the difference in static pressure between two points in a system.

Draft gauge – It is a device for measuring draft, normally in millimeter of water.

Drain – It is a valved connection at the lowest point for the removal of all water from the pressure parts. Drum – It is a cylindrical shell closed at both ends designed to withstand internal pressure.

Dry air – It is the air with which no water vapour is mixed. This term is used comparatively, since in nature there is always some water vapour included in air, and such water vapour, being a gas, is dry. Dry-back boiler – It is a fire-tube boiler with a refractory lined back door. Door opens to allow maintenance and / or inspection.

Dry gas – It is the gas containing no water vapour.

Dry-gas loss – It is the loss representing the difference between the heat content of the dry exhaust gases and their heat content at the temperature of ambient air.

Dry saturated steam – On heating the wet steam, the water particles, which are in suspension, starts evaporating gradually and at a particular moment the final particles just evaporate. The steam at that moment is called dry steam or dry saturated steam. The resulting volume is known as specific volume of dry steam. This steam does not obey the gas laws.

Dry steam – It is the steam containing no moisture. Commercially dry steam contains not more than 0.5 % moisture

Dryness fraction of saturated steam – It is a measure of quality of wet steam. It is the ratio of the mass of dry steam to the mass of total wet steam.

Duct – It is a passage for air or gas to flow.

Economizer – It utilizes waste heat by transferring heat from flue gases to warm incoming feed-water.

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 square feet EDR.

Efficiency – It is the ratio of output to input.

Ejector – It is a device which utilizes the kinetic energy in a jet of water or other fluid to remove a fluid or fluent material from tanks or hoppers.

Electric boiler – It is a boiler in which electric energy is used as the source of heat.

Electrostatic precipitator – It is a device for collecting dust, mist, or fume from a gas stream, by placing an electrical charge on the particle and removing that particle onto a collecting electrode.

Enthalpy – Enthalpy of a system is defined as the mass of the system (m) multiplied by the specific enthalpy (h) of the system and can be expressed as H = m x h, where ‘H’ is enthalpy in kilo joule (kJ), ‘m’ is mass in kilogram (kg), and ‘h’ is specific enthalpy in kJ/kg. Enthalpy is the total quantity of heat received by 1 kg of water from 0 deg C at constant pressure to convert it to desired form of steam. It is the sum of the internal energy and work done at constant pressure process, which is equal to change in enthalpy.

Enthalpy of evaporation (vapourization) – The enthalpy of vapourization is the energy needed to turn water into the gaseous form when it increases in volume by 1,600 times at standard temperature and pressure. It is same as latent heat of vapourization.

Entrainment – it is the conveying of particles of water or solids from the boiler water by the steam. Equalizer – It is the connections between parts of a boiler to equalize pressures

Equivalent evaporation – It is the evaporation expressed in kilograms of water evaporated from a temperature of 100 deg C to dry saturated steam at 100 deg C.

Externally-fired boiler – It is a boiler with the combustion chamber outside the boiler drum. This type of furnace is not surrounded by water but is surrounded by brickwork.

Evaporation – It is the change of state from a liquid to a vapour.

Evaporation rate – It is the number of kilograms of water which is evaporated in a unit of time.

Excess air – It is the air supplied for combustion in excess of that theoretically needed for complete oxidation.

Expansion joint – It is the joint to permit movement because of expansion without undue stress. Explosion door – It is a door in a furnace or boiler setting which is designed to be opened by a pre-determined gas pressure.

External treatment – It is the treatment of boiler feed water prior to its introduction into the boiler.

External work of evaporation – It is the fraction of the latent heat of vapourization which does an external work in moving the piston at constant pressure because of increase in volume. Its unit is kj/kg.

Evaporation – It is vapourization of water which occurs from the surface of water. Water is converted into water vapour which is not saturated with water.

Fan – It is a machine consisting of a rotor and housing for moving air or gases at relatively low-pressure differentials.

Fan performance – It is a measure of fan operation in terms of volume, total pressures, static pressures, speed, power input, and mechanical and static efficiency at a stated air density.

Fan performance curves – These are the graphical presentation of total pressure, static pressure, power input, mechanical and static efficiency as ordinates and the range of volumes as abscissa, all at constant speed and air density.

Feed pump – It is a pump which supplies water to a boiler.

Feed-water – It is the water introduced into a boiler during operation. It includes make-up and return condensate.

Feed-water treatment – It is the treatment of boiler feed water by the addition of chemicals to prevent the formation of scale or to eliminate other objectionable characteristics.

FGR – It is the flue gas recirculation or the recirculation of flue gas with combustion air to reduce NOx (oxides of nitrogen) emissions.

Filter – It is the porous material through which fluids or fluid and solid mixtures are passed to separate matter held in suspension.

Fin – A fin is an extended surface, a solid, experiencing energy transfer by conduction within its boundaries, as well as energy transfer with its surroundings by convection and / or radiation, used to improve heat transfer by increasing the surface area.

Fin tube – It is a tube with one or more fins.

Fired pressure water – It is a vessel containing a fluid under pressure exposed to heat from the combustion of fuel.

Fire-tube – It is a type of boiler design in which combustion gases flow inside the tubes and water flows outside the tubes.

Fire-tube boiler – It is a boiler consisting of a drum containing straight tubes through which the hot combustion gases from the fire travel. Water in the drum surrounds the tubes and the heat from the hot gases passes through the tube walls to the water.

Firing rate control – It is a pressure, temperature, or flow controller which controls the firing rate of a burner as per the deviation from pressure or temperature set point. The system can be arranged to operate the burner on-off, high-low, or in proportion to load demand.

Fitting – Fitting on a boiler means any valve, gauge, regulating or controlling device, flange, pipe fitting or other attachment on the boiler.

Fixed carbon – It is the carbonaceous residue less the ash remaining in the test container after the volatile matter has been driven off in making the proximate analysis of a solid fuel.

Flame – It is a luminous body of burning gas or vapour.

Flame detector – It is a device which indicates if a fuel (liquid, gaseous, or pulverized) is burning, or if ignition has been lost. The indication can be transmitted to a signal or to a control system.

Flame propagation rate – It is the speed of travel of ignition through a combustible mixture.

Flame safeguard – It is a control which sequences the burner through several stages of operation to provide proper air purge, ignition, normal operation, and shutdown for safe operation.

Flame scanner – Flame scanner is a device used to observe the flame in a boiler. If the flame is extinguished for any reason, the flame scanner sends a signal to close the fuel supply valve to prevent a possible explosion.

Flammability – It is susceptibility to combustion.

Flashing – It is the process of producing steam by discharging water into a region of pressure lower than the saturation pressure which corresponds to the water temperature.

Flash point – It is the lowest temperature at which, under specified conditions, fuel oil gives off enough vapour to flash into a momentary flame when ignited.

Flash steam – When hot condensate under pressure is released to lower pressure, part of it is re-evaporated, becoming what is known as flash steam. The term is traditionally used to describe steam issuing from condensate receiver vents and open-ended condensate discharge lines from steam traps.

Flue – It is a passage for products of combustion.

Flue gas – It is the gaseous product of combustion in the flue to the stack.

Fly ash – It is a by-product which is generated during the burning of pulverized coal in a boiler. Specifically, it is the unburned residue which is carried away from the burning zone in the boiler by the flue gases and then collected by electrostatic separators or by any other means.

Foaming – It is the continuous formation of bubbles which have sufficiently high surface tension to remain as bubbles beyond the disengaging surface.

Forced circulation – It is the circulation of water in a boiler by mechanical means external to the boiler. Forced draft fan – It is a fan supplying air under pressure to the fuel burning equipment.

Fouling – It is the accumulation of refuse in gas passages or on heat absorbing surfaces which results in undesirable restriction to the flow of gas or heat.

Free ash – It is the ash which is not included in the fixed ash.

Fuel – It is a substance containing combustible used for generating heat.

Fuel-air mixture – It is a mixture of fuel and air.

Fuel-air ratio – It is the ratio of the weight, or volume, of fuel to air.

Fuel oil – It is a liquid fuel derived from petroleum or coal.

Fuel-to-steam efficiency – It is the ratio of heat added to boiler feed-water to produce the output steam to the quantity of energy inputted with fuel.

Furnace – It is an enclosed space provided for the combustion of fuel.

Furnace pressure – It is the pressure occurring inside the combustion chamber. It is positive if higher than atmospheric pressure, and negative if lower than atmospheric pressure, and neutral if equal to atmospheric pressure.

Furnace volume – It is the cubic contents of the furnace or combustion chamber.

Fusible plug – It is a hollowed threaded plug having the hollowed portion filled with a low melting point material.

Gas analysis – It is the determination of the constituents of a gaseous mixture.

Gas burner – It is a burner which uses gas or fuel.

Gas pressure regulator – It is a spring loaded, dead weighted or pressure balanced device which maintains the gas pressure to the burner supply line.

Gauge cock – It is a valve attached to a water column or drum for checking water level.

Gauge glass – It is 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 – It is the pressure above atmospheric pressure.

Grade – It is the oil classification according to quality, based on standard specifications.

Handhole – It is an access opening in a pressure part normally not exceeding 150 mm in its longest dimension.

Handhole cover – It is for the closure of a handhole.

Hardness – It is a measure of the quantity of calcium and magnesium salts in water. It is normally expressed as ppm as CaCO3.

Hard water – It is the water which contains calcium or magnesium in a quantity which need an excessive amount of soap to form a lather.

Header – A header is a larger pipe which supplies to or collects from a series of smaller pipes or tubes. It is also called a manifold.

Heads – Heads are the steel plates which close off the ends of the boiler drum. They are also referred to as end plates. If the shell contains tubes which are held in position by the heads, then they are normally called tube sheets.

Heat available – It is the thermal energy above a fixed datum which is capable of being absorbed for useful work.

Heat balance – It is an accounting of the distribution of the heat input, output, and losses.

Heat exchanger – it is a vessel in which heat is transferred from one medium to another.

Heat release rate – It is the rate which describes the heat available per square metre of heat-absorbing surface in the furnace or per cubic metre of volume.

Heating surface – It is that surfaces which is exposed to products of combustion on one side and water on the other. This surface is measured on the side receiving the heat.

Heating value – It is the quantity of heat released by a fuel through complete combustion. It is normally expressed in kilocalories per cubic metre (kcal/cum).

High gas pressure control – It is a control to stop the burner if the gas pressure is very high.

High oil temperature control – It is a control to stop the burner if the oil temperature is very high.

High-pressure steam boiler – A high-pressure steam boiler is a steam boiler which operates at pressures above 103 kPa. These are also called power boilers.

Horizontal return tubular (HRT) boiler – A horizontal return tubular boiler is a fire-tube boiler normally supported in a brick combustion chamber. The hot gases from combustion sweep along the underside of the shell then return through the fire tubes to the chimney connection.

Hydro-carbon – It is a chemical compound of hydrogen and carbon.

Hydrostatic test – It is a strength and tightness test of a closed pressure vessel by water pressure.

Ignition – It is the initiation of combustion.

Ignition temperature – It is the lowest temperature of a fuel at which combustion becomes self-sustaining.

Illuminants – It is the light oil or coal compounds which readily burn with a luminous flame, such as ethylene, propylene, and benzene.

Incomplete combustion – It is the partial oxidation of the combustible constituents of a fuel.

Induced draft fan – It is a fan exhausting hot gases from the heat absorbing equipment.

Inert gaseous constituent – It is the incombustible gases such as nitrogen which can be present in a fuel. Inhibitor – It is 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 – It is a device utilizing a steam jet to entrain and deliver feed water into a boiler.

Insulation – It is a material of low thermal conductivity used to reduce heat losses.

Integral blower – It is a blower built as an integral part of a device to supply air thereto.

Integral blower burner – It is a burner of which the blower is an integral part.

Inter-lock – It is a device to prove the physical state of a needed condition, and to furnish that proof to the primary safety control circuit.

Intermittent blow-down – It is the blowing down of boiler water at intervals.

Internal (True) latent heat (internal energy of steam) – It is the energy needed to change the phase. Hence, it is the actual heat energy stored in the steam above 0 deg C. It can be calculated by subtracting the external work of evaporation from the enthalpy. Its unit is kj/kg.

Internal treatment – It is the treatment of boiler water by introducing chemicals directly into the boiler.

Internally-fired boiler – Internally-fired boiler has the combustion chamber located within the shell of the boiler, or the furnace is surrounded by water-tubes.

Ion – It is a charged atom or radical which can be positive or negative.

Lagging – It is a light gauge steel covering used over a boiler, normally combined with insulation, to provide a low temperature outer surface.

Latent heat of vapourization – It is the heat which causes a phase / state change of water without raising its temperature. 2,257 kJ of energy is needed to evaporate 1 kg of water at 100 deg C into 1 kg of steam at 100 deg C.

Leakage – It is the uncontrolled quantity of fluid which enters or leaves through the enclosure of air or gas passages.

Limit control – It is a switching device which completes or breaks an electrical circuit at pre-determined pressures or temperatures. It is also known as an interlock.

Lining – It is the material used on the furnace side of a furnace wall. It is normally of high-grade refractory tile, or brick, or plastic refractory material.

Load – It is the rate of output needed. It is also the weight carried.

Load factor – It is the ratio of the average load in a given period to the maximum load carried during that period.

Low gas pressure control – It is a control to stop the burner if gas pressure is too low.

Low oil temperature control (cold oil switch) – It is a control to prevent burner operation if the temperature of the oil is too low.

Low-pressure steam boiler – Low-pressure steam boiler is a boiler which operates at a pressure not above 103 kilo pascals.

Low water cut-off – It is a safety device which shuts off the boiler / burner in the event of low water, preventing pressure vessel failure.

Lowest permissible water level – The lowest permissible water level is the lowest water level at which the boiler can be safely operated without damaging or overheating any part of the boiler.

Lug – It consists of any projection, like an ear, used for supporting or grasping.

Make-up water – It is the water added to boiler feed to compensate for that lost through exhaust, blowdown, and leakage etc.

Manhole – It is the opening in a pressure vessel of sufficient size to permit a man to enter.

Manifold – It is a pipe or header for collection of a fluid from, or the distribution of a fluid to a number of pipes or tubes.

Manual gas shut-off valve – It is a manually operated valve in a gas line for the purpose of completely turning on or shutting off the gas supply.

Mass density (or density) of the steam – It is the specific mass of the steam in a volume of 1 cubic metre.

Maximum allowable working pressure (MAWP) – It is the maximum gauge pressure permissible in a completed boiler. The MAWP of the completed boiler is to 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 needed for loadings other than pressure. It is the basis for the pressure setting of the pressure relieving devices protecting the boiler.

Maximum continuous load – It is the maximum load which can be maintained for a specified period. Maximum instantaneous demand – It is the sudden load demand on a boiler beyond which an unbalanced condition can be established in the boiler’s internal flow pattern and / or surface release conditions.

Mechanical atomizing oil burner – It is a burner which uses the pressure of the oil for atomization. Mechanical draft – It is the negative pressure created by mechanical means.

Miniature boiler – It is a fire pressure vessel which do not exceed these limits, (i) inside diameter of shell – 400 mm, (ii) overall length to outside of heads at centre – 1,050 mm, (iii) water heating surface – 1.85 square metre, or (iv) 690 kilo pascal (kPa) maximum allowable working pressure.

Mollier diagram – It is the thermodynamic phase diagram for water / steam. The Mollier diagram is a small portion of data from the steam tables graphed onto enthalpy-entropy coordinates.  Fig 2 shows a Mollier diagram.

Fig 2 Mollier diagram

Moisture – It is the water in the liquid or vapour phase.

Moisture in steam – It consists of particles of water carried in steam, expressed as the percentage by weight.

Moisture loss – It is 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.

Multifuel burner – It is a burner by means of which more than one fuel can be burned.

Multiport burner – It is a burner having a number of nozzles from which fuel and air are discharged.

Natural circulation – It is the circulation of water in a boiler caused by differences in density.

Net positive suction heat (NPSH) – It is the liquid pressure which exists at the suction end of a pump. If the NPSH is insufficient, the pump can cavitate.

Nozzle – It is a short flanged or welded neck connection on a drum or shell for the outlet or inlet of fluids. It is also a projecting spout through which a fluid flow.

Oil burner – It is a burner for firing oil.

Oil heating and pumping set – It is a group of apparatus consisting of a heater for raising the temperature of the oil to produce the desired viscosity, and a pump for delivering the oil at the desired pressure.

Operating control – It is a control to start and stop the burner. It is in addition to the high limit control. Operating pressure – It is the pressure at which a boiler is operated.

Organic matter -It is the compounds containing carbon frequently derived from living organisms.

Orifice – It is 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. It is also a calibrated opening in a plate, inserted in a gas stream for measure velocity of flow.

Orsat – It is a gas-analysis apparatus in which certain gaseous constituents are measured by absorption in separate chemical solution.

Over-pressure – It is the minimum operating pressure of a hot water boiler sufficient to prevent the water from steaming.

Oxidation – It is the chemical combination with oxygen.

Oxidizing atmosphere – It is an atmosphere which tends to promote the oxidation of immersed materials.

Oxygen attack – It is the corrosion or pitting in a boiler caused by oxygen.

Packaged boiler – It is a boiler supplied with all of its components i.e., burner, controls and auxiliary equipment, designed as a single engineered package, and ready for on-site installation.

Particle size – It is a measure of dust size, expressed in micro-meters or per cent passing through a standard mesh screen.

Pass – It is a confined passage-way, containing heating surface, through which a fluid flows in essentially one direction.

Perfect combustion– It is the complete oxidation of all the combustible constituents of a fuel, utilizing all the oxygen supplied.

pH – It is 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 litre. For example, a pH of 7 represent (10)-7 grams per litre.

Pilot – It is a flame which is utilized to ignite the fuel at the main burner or burners.

Pitot tube– It is an instrument which registers total pressure and static pressure in a gas stream. It is used to determine its velocity.

Pitting – It is a concentrated attack by oxygen or other corrosive chemicals in a boiler, producing a localized depression in the metal surface.

Port – It is an opening through which fluid passes.

Post purge – It is a method of scavenging the furnace and boiler passes to remove all combustible gases after flame failure controls have sensed pilot and main burner shut-down and safety shut-off valves are closed.

ppm – It is the abbreviation for parts per million. It is used in chemical determinations as one part per million parts by weight.

Precipitate – It is to separate materials from a solution by the formation of insoluble matter by chemical reaction. It is also the material which is removed.

Precipitation – It is the removal of solid or liquid particles from a fluid.

Preheated air – It is the air at a temperature exceeding that of the ambient air.

Pressure – It is the force per unit of area.

Pressure-drop – It is the difference in pressure between two points in a system, caused by resistance to flow.

Pressure vessel – It is a closed vessel or container designed to confine a fluid at a pressure above atmospheric pressure.

Primary air – It is the air introduced with the fuel at the burner.

Priming – It is the discharge of steam containing excessive quantities of water in suspension from a boiler, because of violent effusion. It is the representation of wetness fraction in percentage.

Process steam – It is the steam used for industrial purposes other than for producing power. It is the steam used in various industrial processes mainly to utilize its heat and moisture. The most common operational end uses employed for process steam include stripping, fractionation, process heating and cooling, quenching, dilution, vacuum draw, pressure regulation, injection and source of process water etc.

Products of combustion – These are the gases, vapours, and solids resulting from the combustion of fuel.

Pulsation – It is the rapid fluctuations in pressure.

Purge – It is 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.

Quality of steam – It is the representation of dryness fraction in percentage.

Radiation loss – It is 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.

Rated capacity – It is the manufacturers stated capacity rating for mechanical equipment. For example, the maximum continuous capacity in kilograms of steam per hour for which a boiler is designed.

Rate of blow-down – It is a rate normally expressed as a percentage of the water fed.

Raw water – It is the water supplied to the plant before any treatment.

Reaction – It is a chemical transformation or change brought about by the interaction of two substances.

Re-association – it is the recombination of the products of dissociation.

Recirculation – It is the reintroduction of part of the flowing fluid to repeat the cycle of circulation. Reducing atmosphere – It is an atmosphere which tends to (i) promote the removal of oxygen from a chemical compound, and (ii) promote the reduction of immersed materials.

Reduction – It is the removal of oxygen from a chemical compound.

Refractory – It is the brickwork or castable used in boilers to protect metal surfaces and for boiler baffles.

Relative humidity – It is the ratio of the mass of water vapour present in a unit volume of gas to the maximum possible mass of water vapour in unit volume of the same gas at the same temperature and pressure.

Relief valve (safety relief valve) – It is 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 – These are the products remaining from crude petroleum by removal of some of the water and an appreciable percentage of the more volatile hydro-carbons.

Resin – It is a bead-like material used in chemical exchange for softeners and de-alkalizers.

Resistance – It is the impediment to gas flow, such as pressure drop or draft loss through a dust collector. It is normally measured in millimeter water column.

Return flow oil burner – It is a mechanical atomizing oil burner in which part of the oil supplied to the atomizer is withdrawn and returned to storage or to the oil line supplying the atomizer.

Ringelmann chart – It is a series of four rectangular grids of black lines of varying widths printed on a white background, and used as a criterion of blackness for determining smoke density in stack gas streams. Fig 3 shows Ringelmann chart.

Fig 3 Ringelmann chart

Rotary oil burner – It is a burner in which atomization is accomplished by feeding oil to the inside of a rapidly rotating cup.

Rupture disk – A rupture disk is a safety device which acts like a safety valve to protect against excessive pressure buildup in a system. However, the disk shatters when its maximum pressure is reached and is to be replaced each time it activates.

Saddle – It is a casting, fabricated chair, or member used for the purpose of support.

Safe working pressure – It is the maximum permissible pressure at which a steam boiler can be operated.

Safety valve – It is a spring-loaded valve which automatically opens when pressure attains the valve setting. It is used to prevent excessive pressure from building up in a boiler.

Safety shut-off valve – It is a manually opened, electrically latched, electrically operated safety shut-off valve designed to automatically shut off fuel when de-energized.

Sampling – It is the removal of a portion of a material for examination or analysis.

Saturated air – It is the air which contains the maximum quantity of water vapour which it can hold at its temperature and pressure.

Saturated steam – It is the steam at the temperature and pressure at which evaporation occurs. Once the boiling point is reached, the water temperature ceases to rise and stays the same until all the water is vapourized. The water goes from a liquid state to a vapour state by receiving energy in the form of latent heat of vapourization. As long as there is some liquid water left, the steam temperature is the same as the temperature of liquid water. This steam is then called saturated steam.

Saturated temperature – It is the temperature at which evaporation occurs at a particular pressure.

Saturated water – It is the water at its boiling point.

Scale – It is a hard coating or layer of materials on surfaces of boiler pressure parts.

Secondary air – It is the air for combustion supplied to the furnace to supplement the primary air. Secondary treatment – It is the treatment of boiler feed water or internal treatment of boiler-water after primary treatment.

Sediment – It is (i) a matter in water which can be removed from suspension by gravity or mechanical means, or (ii) a non-combustible solid matter which settles out at bottom of a liquid e.g., a small percentage is present in residual fuel oils.

Segregation – It is the tendency of refuse of varying compositions to deposit selectively in difference parts of the unit.

Self-supporting steel stack – It is a steel stack of sufficient strength which needs no lateral support.

Sensible heat – It is the heat which increases the temperature of water but does not change its phase / state.

Service water – It is the general-purpose water which has been or has not been treated for a special purpose.

Shell – It is the cylindrical portion of a pressure vessel.

Sludge – It is a soft water-formed sedimentary deposit which normally can be removed by blowing down.

Slug – It is a large ‘dose’ of chemical treatment applied internally to a steam boiler intermittently. It is also used sometimes instead of ‘priming’ to denote a discharge of water out through a boiler steam outlet in relatively large intermittent quantities.

Smoke – It consists of small gas borne particles of carbon or soot, less than 1 micro-meter in size, resulting from incomplete combustion of carbonaceous materials and of sufficient number to be observable.

Softening – It is the act of reducing scale forming calcium and magnesium impurities from water.

Soft water – It is the water which contains little or no calcium or magnesium salts, or water from which scale forming impurities have been removed or reduced.

Solution – It is a liquid, such as boiler water, containing dissolved substances.

Soot – It is unburned particles of carbon derived from hydrocarbons.

Soot blower – It is a mechanical device for discharging steam or air to clean heat absorbing surfaces.

Spalling – It is the breaking off of the surface of refractory material as a result of internal stresses.

Specific enthalpy – Specific enthalpy is a property of the fluid and can be expressed as h = u + p x v where ‘u’ is internal energy in kilojoule per kilogram, ‘p’ is absolute pressure in newton per square metre, and ‘v’ is specific volume in cubic metre per kilogram.

Specific enthalpy of steam – It is the total heat contained in 1 kilogram of steam. It is the sum of enthalpy of the various states, liquid (water) and gas (vapour).

Specific heat – It is the quantity of heat, expressed in kilocalories, needed to raise the temperature of 1 kilogram of a substance by 1 deg C.

Specific heat of steam – It is the quantity of heat necessary to increase the temperature of 1 deg C degree on a unit of mass of 1 kilogram of steam.

Specific humidity – It is the weight of water vapour in a gas water-vapour mixture per unit weight of dry gas.

Specific volume of steam – It is the volume occupied in cubic metre by 1 kilogram of steam.

Spray angle – It is the angle included between the sides of the cone formed by liquid fuel discharged from mechanical, rotary atomizers and by some forms of steam or air atomizers.

Spray nozzle – It is a nozzle from which a liquid fuel is discharged in the form of a spray.

Stack – It is a vertical conduit, which because of the difference in density between internal and external gases, creates a draft at its base.

Stack draft – It is the magnitude of the draft measured at the inlet to the stack.

Stack effect – It is that portion of a pressure differential which results from difference in elevation of the points of measurement.

Stack effluent – It is the gas and solid products discharged from stacks.

Stagnation – It is the condition of being free from movement or lacking circulation.

Standard air – it is the dry air weighing 1.25 kilogram per cubic metre at sea level (101 kilopascals pressure) and 20 deg C.

Standard flue gas – It is the gas weighing 1.25 kilogram per cubic metre at sea level (101 kilopascals pressure) and 20 deg C.

Static pressure – It is the measure of potential energy of a fluid.

Steam – It is the vapour phase of water, unmixed with other gases. It is the technical term used for water vapour, the gaseous phase of water, which is formed when water boils. Technically speaking water boils at a temperature of 100 deg C and at atmospheric pressure.

Steam atomizing oil burner – It is a burner for firing oil which is atomized by steam. It can be of the inside or outside mixing type.

Steam binding – It is a restriction in circulation because of a steam pocket or a rapid steam formation.

Steam boiler – A steam boiler is an enclosed container where water is heated under controlled conditions to convert it into steam. Boiler is basically a heat exchanger where heat is transferred to water. It is also sometimes referred to as steam generator.

Steam drum – A steam drum is a standard feature of a water tube boiler. It is a reservoir of water / steam at the top end of the water tubes. The drum stores the steam generated in the water tubes and acts as a phase separator for the steam / water mixture.

Steam engine – It is a heat engine which performs mechanical work using steam as its working fluid.

Steam gauge – It is a gauge for indicating the pressure of steam.

Steam generating unit – It is a unit to which water, fuel, and air are supplied and in which steam is generated. It consists of a boiler furnace, and fuel burning equipment, and can include as component parts water walls, superheater, reheater, economizer, air heater, or any combination thereof.

Steam generator – It is another name of steam boiler.

Steam phase diagram – It is the data provided in the steam tables which is expressed in the graphical form.

Steam pressure – The conventions of low, medium, and high-pressure steam vary as defined by the various steam users around the country.  Typically, steam below 350 kilo-pascals is termed as low-pressure steam. Steam above 350 kilo-pascals but below 1,750 kilo-pascals is termed as medium pressure steam. Steam above 1,750 kilo-pascals is termed as high-pressure steam. Some users define their steam above 4,000 kilo-pascals as ultra-high-pressure steam.

Steam purity – It is the degree of contamination. Contamination is expressed in ppm.

Steam quality – It is the percent by weight of vapour in a steam and water mixture.

Steam separator – It is a device for removing the entrained water from steam.

Steam space – Steam space is the space above the water line in a steam boiler where the boiling water and steam can separate from each other. The space also acts as a pressure reservoir to accommodate small load fluctuations.

Steam stop valve – Steam stop valve is the main valve on the steam line leaving the boiler. It is to be able to positively halt the flow of steam from a boiler.

Steam tables – Steam tables are the compilation of experimental results of the thermodynamic properties (namely specific volume, internal energy, sensible heat, latent heat, and saturation temperature etc.) of 1 kilogram of steam in a tabular column. These are available either on pressure basis or on temperature basis. These tables are useful for steam engineering calculations, as vapours do not obey gas laws. The pressures in the steam tables are in bar (absolute). In case of gauge pressures, they are to be converted in to absolute pressure by adding atmospheric pressure to them. All the values given in the steam tables are reckoned above 0 deg C. If the initial temperature of water is other than 0 deg C, the enthalpy of steam is to be calculated from the steam tables by deducting the quantity of heat contained initially by the water.

Steam trap – It is a device used to discharge condensate and non-condensable gases with a negligible consumption or loss of live steam. Most steam traps are nothing more than automatic valves. They open, close, or modulate automatically.

Steam turbine – It is a device which extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Since the turbine generates rotary motion, it is particularly suited to be used to drive an electrical generator.

Strainer – It is a device, such as a filter, to retain solid particles allowing a liquid to pass.

Stratification – It is the non-homogeneity existing transversely in a gas stream.

Stud – It is a projecting pin serving as a support or means of attachment.

Super-heated steam – It is the steam with its temperature raised above that of saturation. The temperature in excess of its saturation temperature is referred to as super-heat. When all the water is vapourized, any subsequent addition of heat raises the temperature of steam. Steam heated beyond the saturated steam level is called super-heated steam. Super-heated steam obeys gas laws.

Super saturated steam – The steam having lesser temperature and greater density with respect to the steam table values for a particular saturation pressure is called super saturated steam. This condition is obtained when it is cooled by its own expansion in a nozzle. It is very unstable and the steam soon resumes the saturated condition.

Surface blow-off – It is the removal of water, foam, etc. from the surface at the water level in a boiler.

Surge – It is the sudden displacement or movement of water in a closed vessel or drum.

Suspended solids – These are undissolved solids in boiler water.

Swinging load – It is a load which changes at relatively short intervals.

Syphon – Syphon is a protective device used to prevent steam from entering the internal works of a steam gauge. Frequently a syphon only consists of a single coil of high-pressure pipe with threaded ends.

Tertiary air – It is the air for combustion supplied to the furnace to supplement the primary and secondary air.

Theoretical air – It is the quantity of air needed for perfect combustion.

Theoretical draft – It is the draft which is available at the base of a stack if there is no friction or acceleration losses in the stack.

Theoretical flame temperature – It is the temperature which is attained by the products of combustion provided the entire chemical energy of the fuel, the sensible heat content of the fuel, and combustion above the datum temperature are transferred to the products of combustion. This assumes no heat loss to the surroundings and no dissociation.

Therm – It is a unit of heat applied especially to gas. One therm is equal to 25,210 kilocalories.

Thermal efficiency – It is the efficiency of a boiler, based on the ratio of heat absorbed to total heat input. This does not include heat loss from the boiler shell.

Thermal shock – It is a cycle of temperature swings which result in failure of metal because of the expansion and contraction.

Thermo-couple – It is a temperature measuring instrument.

Tile – It is a preformed refractory, normally applied to shapes other than standard brick.

Total air – it is the total quantity of air supplied to the fuel and products of combustion. Percent total air is the ratio of total air to theoretical air, expressed as percent.

Total pressure – It is the sum of the static and velocity pressures.

Total solids concentration – It is the weight of dissolved and suspended impurities in a unit weight of boiler water, normally expressed in ppm.

Trap – It is a receptacle for the collection of undesirable material.

Treated water – It is the water which has been chemically treated to make it suitable for boiler feed.

Trim – It is the ancillary boiler components, like water level controls, pressure controls, and temperature controls.

Tube – It is a hollow cylinder for conveying fluids.

Tube hole – It is a hole in a drum, heater, or tube sheet to accommodate a tube.

Turbulent burner – it is a burner in which fuel and air are mixed and discharged into the furnace in such a manner as to produce turbulent flow from the burner.

Turn-down ratio – It is the ratio of maximum to minimum fuel or steam input or boiler output.

UL listed – It is product certification which indicates the product meets safety standards determined by ‘underwriters-laboratories’.

Ultimate analysis – It is the chemical analysis of solid, liquid, or gaseous fuels. In the case of coal or coke, it is the determination of carbon, hydrogen, sulphur, nitrogen, oxygen, and ash.

Unaccounted for loss – It is that portion of a boiler heat balance which represents the difference between 100 % and the sum of the heat absorbed by the unit and all the classified losses expressed as percent.

Unburned combustibles – It is the combustible portion of the fuel which is not completely oxidized.

Unfired pressure vessel – It is a vessel designed to withstand internal pressure, neither subjected to heat from products of combustion nor an integral part of a fired pressure vessel system.

Unsaturated steam – It is the most common form of steam. It normally contains wetness from non-vapourized water molecules which are carried over into the distributed steam. It is also known as wet steam.

Uptake – It is the duct used to convey the spent combustion gases from the boiler to the stack or chimney. It is also known as the flue vent and breeching.

Use factor – It is the ratio of hours in operation to the total hours in that period.

Vapour – It is the gaseous product of evaporation.

Vapourization – It is the change from liquid or solid phase to the vapour phase.

Velocity pressure – It is the measure of the kinetic energy of a fluid.

Vent – It is an opening in a vessel or other enclosed space for the removal of gas or vapour.

Vertical firing – It is an arrangement of a burner such that air and fuel are discharged into the furnace in practically a vertical direction.

Vertical tubular boiler – Vertical tubular boiler is normally a smaller sized fire-tube boiler with vertical fire-tubes. Some hot water supply boilers are of the vertical tubular type.

Viscosity – It is a measure of the internal friction of a fluid or its resistance to flow.

Volatile matter – It consists of those products which are given off by a material as gas or vapour. It is determined by definite prescribed methods.

Volume of air – It is the number of cubic metres of air per minute expressed the outlet conditions of a fan.

Waste heat – It is the sensible heat in non-combustible gases discharged to the environment.

Water – It is a liquid composed of two parts of hydrogen and sixteen parts oxygen by weight.

Water column – It is a vertical tubular member connected at its top and bottom to the steam and water space respectively of a boiler, to which the water gauge, water level controls, and fuel cut-off can be connected.

Water gauge – It is the gauge glass and its fittings for attachment.

Water hammer – It is a sudden increase in pressure of water because of an instantaneous conversion of momentum to pressure.

Water level – It is the elevation of the surface of the water in a boiler.

Water line – Water line is the actual level of water in a boiler. It is the point at which water and steam separate.

Water-leg – Water-leg refers to a water-filled section extending from the shell, which surrounds the firebox of some types of boilers.

Water space – Water space is the portion of the boiler which is normally filled with water.

Water softener – It removes hardness (CaCO3) from water through an ion exchange of sodium with calcium and magnesium.

Water tube – It is a tube in a boiler having the water and steam on the inside and heat applied to the outside.

Water-tube boiler – Water-tube boiler is a boiler consisting of drums and headers which circulate water through tubes which are heated by fire and the products of combustion. The heat from the fire is transmitted through the tubes to the water.

Water vapour – It is a synonym for steam, normally used to denote steam of low absolute pressure. It is the gaseous phase of water. Water vapour can be produced by the evaporation or by boiling of liquid water. Water vapour is invisible. Under typical atmospheric conditions, water vapour is continuously generated by evaporation and removed by condensation. It is lighter than air.

Weep – It is a term normally applied to a minute leak in a boiler joint which forms droplets (or tears) of water very slowly.

Weight of steam – It is the weight of steam in kilogram per cubic metres.

Wet steam – It is the mixture of water and steam in which both are at saturation temperature. If additional heat is added to the wet steam at constant pressure, the temperature remains constant until all water is evaporated.

Wet-back boiler – It is a fire-tube boiler design wherein the back portion of the boiler has a water jacket.

Wet-bulb temperature – It is the lowest temperature which a water wetted body attains when exposed to an air current. This is the temperature of adiabatic saturation, and can be used to measure humidity. Wetness – It is a term used to designate the percentage of water in steam. It is also used to describe the presence of a water film on heating surface interiors.

Wetness fraction – It is a measure of quality of wet steam. It is the ratio of the mass of water vapour to the mass of total wet steam.

Wet steam – It is the steam containing moisture.

Wind-box – It is a chamber below the grate or surrounding a burner, through which air under pressure is supplied for combustion of the fuel.

Wind-box pressure – It is the static pressure in the wind-box of a burner or a stoker.

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