Article Index

Preheated air- Air at a temperature exceeding that of the ambient air, increases efficiency.

Pressure- Is the force applied by a liquid or gas on the surface of an object per unit area over which that force is distributed.

Pressure drop- The difference in pressure between two points in a system, caused by resistance to flow.

Pressure vessel- Pressure vessel is a closed container designed to confine a fluid at a pressure substantially different from the atmospheric pressure.

Primary air- The portion of the combustion air introduced with the fuel at the burner.

Primary safety control- Safety switch to provide safety shutdown, directly controlling the response to flame properties, sensing the presence of flame and in the event of ignition failure or unintentional flame extinguishments will cause a safety shutdown.

Priming- Is a condition in the boiler of which water is carried over into the steam delivery containing high concentrations of any solids.

Process steam- Steam used for heat and industrial processes other than producing power.

Products of combustion- Gases, vapors, and solids resulting from the combustion of fuel.

Pulsation- Recurring alternate increase and decrease of pressure.

Purge- To introduce air into the furnace and the boiler flue passages in such volume and manner as to completely replace the air or gas-air mixture contained therein.

Radiant- Emitting heat or having the property transfer heat by rays similar to rays of light.

Radiation– A form of heat transfer. Radiation is the process of continuous interchange of energy by means of electromagnetic waves without a change in the temperature of the medium between two bodies involved.

Radiation loss- A term used in boiler heat balance accounting for the conduction, radiation, and convection heat losses to the ambient air.

Rated capacity- The manufacturers stated intended full-load sustained capacity rating for boiler.

Rate of blowdown- A rate normally expressed as a percentage of the water fed.

Raw water- Water that is taken directly from its source without treatment.

Reaction- Chemical transformation or change, often accompanied by a release of energy, that occurs naturally over time, or is purposefully induced by the interaction of two substances.

Recirculation- Re-adding part of the flowing fluid to repeat the cycle of circulation.

Recycle- The operation of normal burner start up after a shutdown.

Reducing atmosphere- An atmospheric condition in which oxidation is prevented by removal of oxygen and other oxidizing gases or vapors, and which may contain actively reducing gases such as hydrogen, carbon monoxide and gases that would oxidize in the presence of oxygen, such as hydrogen sulfide.        

Refractory- Material that retains its strength at high temperatures and is used in boilers to protect metal surfaces and for boiler baffles.

Reheater- Steam boiler component in which heat is added to intermediate-pressure steam, which has given up some of its energy in expansion through the exhaust. Reheaters and superheaters are one of the most important accessories of boiler that improves the thermal efficiency.

Relay- An electrical device, typically incorporating an electromagnet, that is activated by a current or signal in one circuit to open or close another circuit

Relative humidity- he amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature.