D
DAMPER – A device for introducing a variable pressure drop in a system used for regulating the volumetric flow of a gas, such as air.
DAVIT – The structure on large firetube boilers from which the front and rear doors are suspended when opened.
DEAERATION – Removal of air and gases from boiler feed water prior to its introduction to a boiler.
DEGASIFICATION – Removal of gases from samples of steam taken for purity test. Removal of CO2 from water as in the ion exchange method of softening.
DELAYED COMBUSTION – A continuation of combustion beyond the furnace. (See also Secondary Combustion.)
DESIGN LOAD – The load for which a steam generating unit is designed, considered the maximum load to be carried.
DESIGN PRESSURE – 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 – The temperature of steam for which a boiler is designed.
DEW POINT – The temperature at which condensation starts.
DISENGAGING SURFACE – The surface of the boiler water from which steam is released.
DISSOCIATION – The process by which a chemical compound breaks down into simpler constituents, as do CO2 and H2O at high temperature.
DISSOLVED SOLID – Those solids in water which are in solution.
DISTILLATE FUELS – Liquid fuels distilled usually from crude petroleum.
DISTILLATION – Vaporization of a substance with subsequent recovery of the vapor by condensation. Often used in less precise sense to refer to vaporization of volatile constituents of a fuel without subsequent condensation.
DISTILLED WATER – Water produced by vaporization and condensation with a resulting higher purity.
DOWNCOMER – A tube or pipe in a boiler or waterwall circulating system through which fluid flows downward.
DOWNTIME – Amount of time a piece of equipment is not operational.
DRAFT – The difference between atmospheric pressure and some lower pressure existing in the furnace stack or gas passages of a steam generating unit.
DRAFT DIFFERENTIAL – The difference in static pressure between two points in a system.
DRAFT GAUGE -A device for measuring draft, usually in inches of water.
DRAIN – A valved connection at the lowest point for the removal of all water from the pressure parts.
DRUM – A cylindrical shell closed at both ends designed to withstand internal pressure.
DRY AIR – Air with which no water vapor is mixed. This term is used comparatively, since in nature there is always some water vapor included in air, and such water vapor, being a gas, is dry.
DRYBACK BOILER – Firetube boiler with a refractory lined back door. Door opens to allow maintenance and/or inspection.
DRY GAS – Gas containing no water vapor.
DRY-GAS LOSS – 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 STEAM – Steam containing no moisture. Commercially dry steam containing not more than one half of one percent moisture.
DUCT – A passage for air or gas flow.
E
ECONOMIZER – Utilizes waste heat by transferring heat from flue gases to warm incoming feedwater.
EDR – Equivalent direct radiation is the rate of heat transfer from a radiator or convector. It is equivalent to the square feet of surface area necessary to transfer heat at the same rate at which it is produced by a generator. A single boiler horsepower equals 140 ft2 EDR.
EFFICIENCY – The ratio of output to input. See also Combustion, Fuel-to-Steam and Thermal Efficiency.
EJECTOR – 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 – A boiler in which electric energy is used as the source of heat.
ELECTROSTATIC PRECIPITATOR – 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.
ENTRAINMENT – The conveying of particles of water or solids from the boiler water by the steam.
EQUALIZER – Connections between parts of a boiler to equalize pressures.
EQUIVALENT EVAPORATION – Evaporation expressed in pounds of water evaporated from a temperature of 212 °F to dry saturated steam at 212 °F.
EVAPORATION – The change of state from a liquid to a vapor.
EVAPORATION RATE – The number of pounds of water that is evaporated in a unit of time.
EXCESS AIR – Air supplied for combustion in excess of that theoretically required for complete oxidation.
EXPANSION JOINT – The joint to permit movement due to expansion without undue stress.
EXPLOSION DOOR – A door in a furnace or boiler setting that is designed to be opened by a pre-determined gas pressure.
EXTERNAL TREATMENT – Treatment of boiler feed water prior to its introduction into the boiler.
BOILER GLOSSARY – F-Q
F
FAN – A machine consisting of a rotor and housing for moving air or gases at relatively low pressure differentials.
FAN PERFORMANCE – A measure of fan operation in terms of volume, total pressures, static pressures, speed, power input, mechanical and static efficiency, at a stated air density.
FAN PERFORMANCE CURVES – 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 – A pump that supplies water to a boiler.
FEEDWATER – Water introduced into a boiler during operation. It includes make-up and return condensate.
FEEDWATER TREATMENT – The treatment of boiler feed water by the addition of chemicals to prevent the formation of scale or to eliminate other objectionable characteristics.
FGR – Flue Gas Recirculation or the recirculation of flue gas with combustion air to reduce NOx emissions.
FILTER – 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 enhance heat transfer by increasing surface area.
FIN TUBE – A tube with one or more fins.
FIRED PRESSURE VESSEL – A vessel containing a fluid under pressure exposed to heat from the combustion of fuel.
FIRETUBE – A type of boiler design in which combustion gases flow inside the tubes and water flows outside the tubes.
FIRING RATE CONTROL – A pressure temperature or flow controller which controls the firing rate of a burner according to the deviation from pressure or temperature set point. The system may be arranged to operate the burner on-off, high-low or in proportion to load demand.
FIXED CARBON – 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 – A luminous body of burning gas or vapor.
FLAME DETECTOR – A device which indicates if a fuel (liquid, gaseous, or pulverized) is burning, or if ignition has been lost. The indication may be transmitted to a signal or to a control system.
FLAME PROPAGATION RATE – Speed of travel of ignition through a combustible mixture.
FLAME SAFEGUARD – A control that sequences the burner through several stages of operation to provide proper air purge, ignition, normal operation, and shutdown for safe operation.
FLAMMABILITY – Susceptibility to combustion.
FLASHING – The process of producing steam by discharging water into a region of pressure lower than the saturation pressure that corresponds to the water temperature
FLASH POINT – The lowest temperature at which, under specified conditions, fuel oil gives off enough vapor to flash into a momentary flame when ignited.
FLUE – A passage for products of combustion.
FLUE GAS – The gaseous product of combustion in the flue to the stack.
FOAMING – The continuous formation of bubbles which have sufficiently high surface tension to remain as bubbles beyond the disengaging surface.
FORCED CIRCULATION – The circulation of water in a boiler by mechanical means external to the boiler.
FORCED-DRAFT FAN – A fan supplying air under pressure to the fuel burning equipment.
FOULING – The accumulation of refuse in gas passages or on heat absorbing surfaces which results in undesirable restriction to the flow of gas or heat.
FM – Factory Mutual.
FREE ASH – Ash which is not included in the fixed ash.
FUEL – A substance containing combustible used for generating heat.
FUEL-AIR MIXTURE – Mixture of fuel and air.
FUEL-AIR RATIO – The ratio of the weight, or volume, of fuel to air.
FUEL OIL – A liquid fuel derived from petroleum or coal.
FUEL-TO-STEAM EFFICIENCY – The ratio of heat added to boiler feedwater to produce the output steam to the amount of energy inputted with fuel.
FURNACE – An enclosed space provided for the combustion of fuel.
FURNACE PRESSURE – Pressure occurring inside the combustion chamber; positive if greater than atmospheric, negative if less than atmospheric, and neutral if equal to atmospheric.
FURNACE VOLUME – The cubic contents of the furnace or combustion chamber.
FUSIBLE PLUG – A hollowed threaded plug having the hollowed portion filled with a low melting point material.