IA Boiler Operator key terms

The horizontal cylindrical pressure vessel at the top of a watertube boiler that separates steam from water, holds a water reserve, and houses internal devices that reduce carryover and control chemical concentration.

A row of tubes lining the furnace walls, welded together with membrane bars or closely spaced, that absorbs radiant heat and protects the casing from high flame temperatures.

A heat exchanger in the flue gas path that preheats boiler feedwater before it enters the drum, recovering sensible heat and lowering stack temperature.

Equipment that transfers heat from exiting flue gas to incoming combustion air, improving combustion efficiency and reducing the heat lost up the stack.

Heat added to or removed from a substance that changes its temperature without changing its phase, as when feedwater warms from room temperature toward saturation.

The heat energy absorbed when a liquid changes to vapor at constant temperature and pressure, and released on condensation; for water at atmospheric pressure it is roughly 2257 kJ/kg.

The boiling point of water at a given pressure; it rises as pressure rises, so a boiler at higher pressure produces steam at a correspondingly higher temperature.

Steam heated above its saturation temperature at the same pressure, containing no moisture; it improves turbine efficiency and protects downstream equipment from erosion.

A bank of tubes in the hot gas path that raises saturated steam above its saturation temperature, often with attemperation to control final steam temperature over the load range.

A device that sprays high-purity water into superheated steam, or passes it through a heat exchanger, to hold final steam temperature at its design value during load changes.

A boiler in which hot combustion gases pass through tubes surrounded by water; simple and compact, it is common for low-to-medium pressure heating and process steam.

A boiler in which water circulates inside tubes heated externally by combustion gases; it can be built for high pressure and large capacity and responds quickly to load changes.

Water flow driven by the density difference between the water-and-steam mixture in heated tubes and the denser water in unheated downcomers, requiring no circulating pump.

A design in which feedwater passes through the evaporator once and leaves as steam, with no recirculating drum; flow and firing rate must be tightly matched.

The combustion chamber where fuel and air burn and radiant heat is transferred to the waterwalls; its volume and shape govern residence time and complete combustion.

The heat released by complete combustion of a fuel when the water vapor in the products is condensed, so it includes the latent heat of that moisture.

The exact quantity of air theoretically needed to burn a fuel completely, with no oxygen left over and no unburned fuel remaining.

Air supplied above the stoichiometric amount to ensure complete combustion; too little causes smoke and carbon monoxide, too much wastes heat up the stack.

Measurement of oxygen, carbon monoxide, and carbon dioxide in the exhaust to verify air-to-fuel ratio and combustion quality, usually with a portable analyzer or in-situ probes.

The fraction of fuel heat released that is usefully transferred to steam, reduced by unburned fuel, excess air, and heat carried away in the flue gas.

A sensor, often ultraviolet or infrared, that confirms a stable flame is present; loss of its signal triggers a burner trip to prevent fuel accumulation and explosion.

The interlocked control package that sequences purge, pilot light-off, main flame establishment, and shutdown, and that trips fuel on loss of flame or other unsafe conditions.

A forced flow of air through the furnace and gas passages before ignition to clear any accumulated combustible gases, typically several volume changes at rated airflow.

Water supplied to the boiler to replace steam generated; it is treated to limit scale, corrosion, and carryover, and is usually preheated in the economizer.

Raw or pretreated water added to the cycle to replace steam and condensate lost through leaks, blowdown, and process use.

Deliberate discharge of boiler water to control dissolved solids and sludge; continuous blowdown removes concentrated surface water while bottom blowdown removes settled sludge.

Hard mineral deposit, chiefly calcium and magnesium salts, that forms on heated tube surfaces, impeding heat transfer and risking overheating and tube failure.

Localized corrosion caused by dissolved oxygen attacking steel, producing small deep pits; controlled by deaeration and chemical oxygen scavengers.

A vessel that heats feedwater with steam under pressure to drive off dissolved oxygen and carbon dioxide, usually combined with a storage section and chemical scavenging.

The degree to which steam is free of dissolved solids, silica, and moisture droplets; poor purity causes deposits and erosion in superheaters and turbines.

A safety device that senses water level and shuts off fuel when the level falls below a safe limit, preventing overheating and catastrophic tube failure.

A spring-loaded valve that opens automatically at a set pressure to release steam and protect the boiler shell and piping from overpressure; it must be tested and set by qualified personnel.

A transparent sight glass connected to the drum that shows the actual water level, used to verify level indication and confirm the low-water cutoff is functioning.

A rapid change in steam demand that forces firing rate, feedwater flow, and drum level to adjust; poor control can cause carryover, pressure excursions, or flame instability.

Drum level control that positions the feedwater valve using steam flow, feedwater flow, and drum level signals, correcting for shrink and swell during load changes.

A pressure test in which the boiler is filled with water and pressurized above its normal operating pressure to reveal leaks and weak points before return to service.

Cracking that results from repeated stress cycles acting on metal already weakened by corrosive attack, often seen at tube-to-drum connections and in economizer tubes.

An instrument that displays boiler or steam-header pressure; it must be calibrated, marked with the maximum allowable working pressure, and fitted with a siphon and isolating valve.

The temperature of flue gas leaving the boiler; an abnormally high reading signals fouled heat-transfer surfaces or excessive excess air and wasted fuel.