The fuel can be defined technically as any material that can burn. While commercially, the fuel can be called as any material that has specific calorific value and is able to react with oxygen in air to produce heat. Generally, fuel can be classified into three main types, namely:
- Boiler fuel solid
- Boiler fuel liquid
- Boiler fuel gas
Based on the occurrence, fuel can be differentiated into natural fuels and artificial fuels. The following below is the differences of boiler fuel based on natural fuel and artificial fuel:
Boiler fuel solid
Natural: Wood, peat, lignite, bituminous, anthracite
Artificial: wood charcoal, coke, briquettes, bagasse, palm oil waste, coconut shell
Boiler fuel liquid
Nature: Crude Oil
Artificial: Gasoline, kerosene, fuel oils
Boiler fuel gas
Nature: The gas methane (CH4), Ethane gas (C2H6), carbon monoxide (CO), LNG, LPG
Artificial: Coal gas, water gas, Raymond gas, high gas furnace, coke oven gas, producer gas.
A steam boiler requires heat source at high enough temperatures to produce steam. Fossil fuels used for generating steam are usually burned directly in the furnace boiler, although the heat for the steam boiler may also be in the form of residual heat from another process.
Combustion can be defined as rapid chemical combination of oxygen with combustible elements of fuel. There are only three important chemical elements which can be burned, namely: carbon (C), hydrogen (H) and sulfur (S). Sulfur usually have little meaning as a source of heat but can be an essential element in terms of problems of corrosion and pollution.
Any fuels which contain hydrogen will produce water (H2O) as one of product results. The water produced can be a liquid, gas or mixture of two phases. If the water formed during combustion of hydrogen in the boiler fuel can be condensed, the amount of heat that can be obtained will be greater than if the water formed in gaseous form.
Therefore, there are two kinds of combustion value or calorific value:
- Higher Heating Value (HHV)
When water vapor of combustion is condensed that must take into account of latent heat of evaporation. The value of the boiler fuel liquid combustion is useful for the calculation of heat loss which can be calculated by using the equation:
HHV = 14500 C + 62000(H2 – (O/8) + 4000 S
HHV = Higher Heating Value
C =% carbon in boiler fuel
H =% hydrogen in boiler fuel
O =% oxygen in boiler fuel
S =% of sulfur in boiler fuel
- Lower Heating Value (LHV)
When water vapor of combustion is condensed and appears entirely in the form of gas so it does not take into account of latent heat evaporation. Lower Heating Value of boiler fuel liquid is useful for the calculation of heat loss which can be calculated by using the equation:
LHV = HHV - 9720 H2 - 1110W
LHV = Lower Heating Value
H2 = percentage of hydrogen in the boiler fuel
W = content of water steam contained in air