Power Eng 3rd Class key terms

The total heat energy contained in a unit mass of a substance, combining its internal energy with the flow work needed to push it through a system. It is the property used to track energy across boilers, turbines, and heat exchangers.

The amount by which steam temperature exceeds the saturation temperature for its pressure. Superheated steam contains no entrained moisture and yields more work per kilogram in a turbine than saturated steam.

The heat absorbed or released when a substance changes phase without changing temperature, such as water boiling to steam or steam condensing. It is much larger than sensible heat for water at boiler pressures.

The boiling point of a liquid at a given pressure, at which liquid and vapour coexist in equilibrium. In a boiler it rises as pressure rises, which is why high-pressure drums require heavier construction.

A material property describing how readily heat passes through it by conduction, expressed in watts per metre-kelvin. Low-conductivity materials serve as insulation, while high-conductivity metals are used for heat transfer surfaces.

A device that transfers heat between two fluids that are physically separated by a wall, such as tubes or plates. Feedwater heaters, condensers, and air preheaters are common examples in a power plant.

A pressure surge caused when moving liquid is suddenly stopped or redirected, producing a bang and potentially damaging piping and fittings. It is prevented by slow valve operation, proper drainage, and steam trap maintenance.

A spring-loaded valve that opens automatically at a set pressure to release steam or fluid and protect equipment from overpressure. It reseats itself once pressure falls below the setpoint and must be tested and set by qualified personnel.

A vertical chamber connected to a boiler drum that dampens water-level fluctuations so the gauge glass shows a steady level. Its connections must be kept clear because blockage can give a false level reading.

A safety control that shuts off fuel to a boiler when the water level drops below a safe minimum. It is a required protective device and must be tested regularly to confirm it functions.

An automatic valve that discharges condensate and non-condensable gases from steam lines while retaining live steam. Common types include thermostatic, float-and-thermostatic, and inverted bucket designs.

Steam that has given up its latent heat and returned to liquid form. It is collected and pumped back to the boiler as feedwater because it is hot and nearly free of dissolved solids.

Water supplied to a boiler to replace steam that has been generated and sent to the plant. It is a mixture of returned condensate and treated makeup water, conditioned to prevent scale and corrosion.

The controlled draining of water from a boiler to remove dissolved solids and sludge that would otherwise concentrate and cause carryover or scaling. It may be continuous from the drum or intermittent from the bottom.

A hard deposit of mineral salts, mainly calcium and magnesium compounds, that forms on heated boiler surfaces. It insulates the metal, raises fuel consumption, and can cause overheating and tube failure.

A treatment process that removes hardness minerals, usually by ion exchange with resin that swaps calcium and magnesium for sodium. It prevents scale formation but does not reduce total dissolved solids.

A measure of a water sample's ability to carry electric current, used as an indicator of dissolved solids concentration. Boiler and condensate conductivity readings guide blowdown rate and detect contamination.

A vessel that heats feedwater and strips out dissolved oxygen and other gases to prevent corrosion in the boiler and piping. It usually operates under slight steam pressure and serves as the feedwater storage tank.

Localised corrosion in the form of small deep pits caused by dissolved oxygen attacking boiler or condensate piping metal. It is controlled by deaeration and chemical oxygen scavengers.

The gradual chemical attack and deterioration of metal by water, oxygen, acids, or other agents. In power plants it is managed through water chemistry control, coatings, and cathodic protection.

A pump that uses a rotating impeller to impart velocity and pressure to a liquid, moving it outward into a volute casing. It is the most common boiler feed and circulating pump type.

The formation and collapse of vapour bubbles in a pump when local pressure falls below the liquid's vapour pressure. It causes noise, vibration, and erosion damage and is avoided by adequate suction pressure.

The absolute pressure above a liquid's vapour pressure available at a pump suction, expressed in metres of head. Insufficient NPSH causes cavitation, so it must exceed the pump manufacturer's required value.

A valve that permits flow in only one direction and closes automatically to prevent backflow. It protects pumps from reverse rotation and isolates equipment from reverse flow in steam and water lines.

A valve with a sliding gate that is opened or closed by turning a handwheel, used mainly for isolation rather than throttling. It offers low resistance when fully open but should not be partly open for control.

A valve with a plug-and-seat arrangement that gives good throttling control of flow, at the cost of higher pressure drop. It is used where flow regulation is needed rather than simple isolation.

The air supplied to a burner to provide the oxygen needed to burn fuel completely. Its quantity is set by excess-air targets and monitored so that fuel-rich or air-rich conditions are avoided.

Air supplied beyond the theoretical amount needed for complete combustion, expressed as a percentage. Too little causes smoke and carbon monoxide; too much wastes heat by carrying it up the stack.

The measurement of oxygen, carbon dioxide, carbon monoxide, and temperature in exhaust gas to assess combustion efficiency. It is used to tune burner air-to-fuel ratios and reduce stack losses.

A heat exchanger that removes heat from exhaust steam so it condenses back to water, creating a low pressure at the turbine exhaust. This low back pressure increases the work the turbine can extract.

A separation process in which a liquid mixture is boiled and the vapour condensed to purify one component. In a power plant it is used to produce high-purity make-up water for boilers.

A fluid used in a refrigeration cycle that absorbs heat by evaporating at low pressure and releases it by condensing at high pressure. Its selection considers safety, efficiency, and environmental impact.

A machine that raises the pressure of a gas by reducing its volume, used in refrigeration cycles and instrument air systems. Common types include reciprocating, rotary screw, and centrifugal.

A temperature sensor made of two dissimilar metals joined at a point, which generates a small voltage proportional to temperature difference. It is rugged and widely used for high-temperature measurement in boilers.

An instrument that displays the pressure of a fluid, commonly using a Bourdon tube that straightens under pressure to move a pointer. Gauges must be calibrated and fitted with siphons or snubbers on steam service.

A safety procedure in which energy sources are isolated, locked, and tagged before maintenance so equipment cannot be started unexpectedly. Only the person who applied a lock may remove it.

Entering an enclosed area such as a boiler drum or tank that has limited access and may contain hazardous atmosphere. It requires a permit, atmospheric testing, ventilation, an attendant, and rescue arrangements.