This is the theoretical total of the energy in the fuel. However, all common fuels contain hydrogen, which burns with oxygen to form water, which passes up the stack as steam.
The gross calorific value of the fuel includes the energy used in evaporating this water. Flue gases on steam boiler plant are not condensed, therefore the actual amount of heat available to the boiler plant is reduced.
Accurate control of the amount of air is essential to boiler efficiency:
Too much air will cool the furnace, and carry away useful heat.
Too little air and combustion will be incomplete, unburned fuel will be carried over and smokemay be produced.
Presently, there is a global commitment to a Climate Change Programme, and 160 countries have signed the Kyoto Agreement of 1997. These countries agreed to take positive and individual actions to:
Reduce the emission of harmful gases to the atmosphere –
Although carbon dioxide (CO2) is the least potent of the gases covered by the agreement, it is by far the most common, and accounts for approximately 80% of the total gas emissions to be reduced.
Make quantifiable annual reductions in fuel used –
This may take the form of using either alternative, non-polluting energy sources, or using the same fuels more efficiently.
In the UK, the commitment is referred to as ‘The UK National Air Quality Strategy’, and this is having an effect via a number of laws and regulations. Other countries will have similar strategies.