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| Term | Definition |
|---|---|
| Absolute Pressure | Pressure above zero pressure; the sum of the gauge and atmospheric pressures. |
| Accumulator - (steam) | A pressure vessel containing water and/or steam, which is used to store the heat of steam for use at a late period and at some lower pressure. |
| Acid Cleaning | 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 | Represents the amount of free carbon dioxide, mineral acids and salts (especially sulphates of iron and aluminum) which hydrolyze to give hydrogen ions in water and is reported as milliequivalents per liter of acid, or ppm acidity as calcium carbonate, or pH the measure of hydrogen ions concentration. |
| Adiabatic Flame Temperature | The theoretical temperature that would be 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 were transferred to the products of combustion. This assumes: No heat loss to surroundings and no dissociation. |
| Air | The mixture of oxygen, nitrogen, and other gases, which with varying amounts of water vapor, forms the atmosphere of the earth. |
| Air Atomizing Oil Burner | 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 | Insufficient air, in an air-fuel mixture, to supply the oxygen required for complete oxidation of the fuel. |
| Air Infiltration | The leakage of air into a setting or duct. |
| Air Vent | A valved opening in the top of the highest drum of a boiler or pressure vessel for venting air. |
| Air, Saturated | Air which contains the maximum amount of water vapor that it can hold at its temperature and pressure. |
| Air-Free | The descriptive characteristic of a substance from which air has been removed. |
| Air-Fuel Ratio | The ratio of the weight, or volume, of air to fuel. |
| Alarm | A suitable horn, bell, light or other device which when operated will give notice of malfunction or off normal condition. |
| Alkalinity | Represents the amount of carbonates, bicarbonates, hydroxides and silicates or phosphates in the water and is reported as grains per gallon, or ppm as calcium carbonate. |
| Allowable Working Pressure | See design pressure. |
| Ambient Air | The air that surrounds the equipment. The standard ambient air for performance calculations is air at 80 °F, 60% relative humidity, and a barometric pressure of 29.921 in. Hg, giving a specific humidity of 0.013 lb of water vapor per lb of dry air. |
| Ambient Temperature | The temperature of the air surrounding the equipment. |
| Analysis | Quantitative determination of the constituent parts. |
| Analysis, Ultimate | Chemical analysis of solid, liquid or gaseous fuels. In the case of coal or coke, determination of carbon, hydrogen, sulfur, nitrogen, oxygen, and ash. |
| Aquastat | Water limit temperature control, a safety device often used on boilers. |
| Arrester | A device to impede the flow of large dust particles or sparks from a stack, usually screening at the top. |
| As-Fired Fuel | Fuel in the condition as fed to the fuel burning equipment. |
| As-Received Fuel | Fuel in the condition as received at the plant. |
| Ash | The incombustible inorganic matter in the fuel. |
| Ash Pit | A pit or hopper located below a furnace where refuse is accumulated and from which refuse is removed at intervals. |
| Ash-Free Basis | The method of reporting fuel analysis, whereby ash is deducted and other constituents are recalculated to total 100%. |
| ASME | The American Society of Mechanical Engineers. |
| Aspirating Burner | 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. |
| Atmospheric Air | Air under the prevailing atmospheric conditions. |
| Atmospheric Pressure | The barometric reading of pressure exerted by the atmosphere. At sea level 14.7 lb per sq in. or 29.92 in. of mercury. |
| Atomizer | A device by means of which a liquid is reduced to a very fine spray. |
| Availability Factor | The fraction of time during which the unit is in operable condition. |
| Available Draft | The draft which may be utilized to cause the flow of air for combustion or the flow of products of combustion. |
| Axial Fan | Consists of a propeller or disc type of wheel within a cylinder that discharges air parallel to the axis of the wheel. |
