Glossary on Boilers

Flash Point is defined as the temperature at which a liquid fuel begins to generate vapours just enough to form an explosive or a mixture that is inflammable. Larger a fuel is volatile, lesser will be the flash point. This property, important for gasolines whose flash point is lower than ambient temperature, is termed Volatility.

Pour Point is defined as the lowest temperature at which a liquid will just flow or pour from a vessel.

Ignition Temperature is the lowest temperature at which combustion occurs with the mixing of the fuel in vapour form with oxygen in the surrounding air.

Flame Temperature is defined as the temperature attained by products of combustion when all the heat generated by the fuel is allowed to heat it at the original volume of the fuel, and no heat is allowed to be lost to the surroundings.

Flame Speed is the speed at which the flame will travel in a mixture of gaseous fuel and air.

Stoichiometric Combustion of a fuel is defined as the process of complete combustion of its constituents to the products of combustion with evolution of heat. The pre-requisite of any such phenomenon is the availability of the fuel in a gaseous state (when it can mix with the oxygen in the surrounding air) and the prevailing temperatures to be high enough so that the combustion reaction can take place leading to the release of heat energy.

Excess Air Factor is defined as the fraction of air required in excess of the theoretical amount.
Excess Air Factor= (actual air requirement – theoretical air requirement) / theoretical air requirement

Combustion Efficiency measures the effectiveness of the combustion reaction and is defined as
Combustion Efficiency = heat released during combustion / heat contained in the fuel

Effective Calorific Value is the effective heating value obtainable from a sample fuel which is much less than the net heating value. This is due to the partial oxidation of C to CO and some hydrogen remaining unoxidised.

Dryness Fraction of a gaseous mixture is the ratio of the mass of the steam in the mixture to the mass of the entire mixture.
Dryness fraction = mass of steam in mixture / mass of the mixture

Boiler Efficiency is the percentage of heat given out by the boiler to the heat supplied to the boiler.
Boiler Efficiency = ( heat given out by the boiler / heat supplied to the boiler ) * 100 %
= ( evaporation ratio * heat content of steam) / ( fuel rate * calorific value)

Maximum Continuous Rating is the design rating of working for which the efficiency of the boiler is maximum.

Heat Utilization Efficiency (HUE) Factor or Fuel Utilization Efficiency (FUE) Factor
= target fuel consumption / actual fuel consumption
where target fuel consumption = standard steam consumption / standard steam to fuel ratio

Weighted Average Combustion Efficiency
= ( Sum of the combustion efficiencies * average steam load ) / Sum of the average steam load

Absolute Pressure is the common gauge pressure plus the atmospheric pressure.

Caustic Embrittlement refers to the cracking of boiler steel occuring while the boiler is in service but not subjected to excessive pressure or temperature due to the boiler’s water being too caustic.