Article Index

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

Damper- Device controlling the amount of air entering a system used to regulate the volume flow of a gas, such as air.

Davit- The structure or hinges on a firetube boiler which the front and rear doors are suspended when opened.

Deaerator- A device in which oxygen, carbon dioxide, or other noncondensable gases are removed from boiler feedwater, steam condensate, or a process stream. It heats the water to drive off oxygen.

Deaeration- Removing air and gases from boiler feedwater before putting into a boiler.

Delayed combustion- A continuation of combustion beyond the furnace.

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 intendment of calculating minimum passable thickness or natural characteristics of the different parts of the boiler.

Dew point- The temperature at which condensation starts.

Disengaging surface- The surface of the boiler water from which steam is released.

Disassociation- The process by which a chemical compound breaks down into simpler constituents, as do CO2 and H2O at high temperature.

Dissolved solids- Those solids in water which are in solution.

Distillation- The evaporation and consequent collection of a liquid as a means of purification.

Distilled water- Water produced by vaporization and condensation with a resulting higher purity.

Dome- A raised location on the top of the main boiler drum, providing a high point from which to collect dry steam, reduces the risk of priming.

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 in pressure which will produce a flow of air. Drafts in boilers are used to supply combustion air to the boiler furnace.

Draft pressure differential- The difference in static pressure between two locations of gas flow in a system.

Draft gauge- A device for measuring draft air flow.

Drip leg- A bin used for removing condensate collected from steam transmission and distribution lines which it may be removed.

Drowned tube- Either a firetube or watertube that is entirely below the water-level of the operating boiler.

Drum- Cylindrical shell closed at both ends that is designed to withstand internal pressure.

Dryback boiler- Firetube boiler with a refractory lined back 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 that is at the temperature of saturation, but does not contain any moisture. Commercially dry steam containing not more than one half of one percent moisture.

Duct- Passage for air or gas to flow.

Economizer- Utilizes waste heat by transferring heat from flue gases to warm incoming feedwater.

EDR- Equivalent Direct Radiation is the standard comparison method of heat transfer from a radiator or convector. It is equivalent to the square feet of a 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.

Ejector- A device which utilizes the kinetic energy in a jet of water or other fluid.

Entrainment- The movement of sediment in a stream from the boiler water by the steam.

Equalizer- Creates equal pressure on the supply and return of the boiler.

Equivalent evaporation- Evaporation expressed in pounds per hour at which water would be vaporized in a given steam boiler if supplied and evaporated at the normal boiling point and normal atmospheric pressure.