The term “boiler efficiency” is often substituted for thermal efficiency or fuel-to-steam efficiency. When the term “boiler efficiency” is used, it is important to know which type of efficiency is being represented. Why? Because thermal efficiency, which does not account for radiation and convection losses, is not an indication of the true boiler efficiency. Fuelto-steam efficiency, which does account for radiation and convection losses, is a true indication of overall boiler efficiency. The term “boiler efficiency” should be defined by the boiler manufacturer before it is used in any economic evaluation.
Combustion efficiency is an indication of the burner’s ability to burn fuel. The amount of unburned fuel and excess air in the exhaust are used to assess a burner’s combustion efficiency. Burners resulting in low levels of unburned fuel while operating at low excess air levels are considered efficient. Well designed conventional burners firing gaseous and liquid fuels operate at excess air levels of 15% and result in negligible unburned fuel. Well designed ultra low emissions burners operate at a higher excess air level of 25% in order to reduce emissions to very low levels. By operating at the minimum excess air requirement, less heat from the combustion process is being used to heat excess combustion air, which increases the energy available for the load. Combustion efficiency is not the same for all fuels and, generally, gaseous and liquid fuels burn more efficiently than solid fuels.
In theory, to have the most efficient combustion in any combustion process, the quantity of fuel and air would be in a perfect ratio to provide perfect combustion with no unused fuel or air. This type of theoretical perfect combustion is called stoichiometric combustion. In practice, however, for safety and maintenance needs, additional air beyond the theoretical "perfect ratio" needs to be added to the combustion process - this is referred to as "excess air".
Circulating fluidized bed boiler is a specific type of boilers, and compared with the other boilers, it has certain advantages, which are: it has great improvement in combustion technology, which can improve the boiler combustion quality and combustion effect, and in turn, to improve the boiler effect. This is achieved because two return feeders are used in this type of boiler to allow the fuel to form a circulation loop between the furnace and the return feeder.
We would recommend your biomass boiler has at least an annual maintenance service. Like anything if you maintain your boiler correctly it will last longer and perform better. Biomass boilers burning even the most difficult of materials can operate unattended, but weekly inspection visits are required to carry out a visual inspection of the boiler and fuel feed system, to check the lubrication of bearings and to empty the ashbin.
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