A well designed and operated biomass boiler burning fuel within the specification of the boiler should not produce any smoke, but black smoke may be produced if the fuel is too wet for the boiler. All biomass boilers produce some oxides of nitrogen (NOx), particularly nitrogen dioxide (NO2). While NOx emissions from gas boilers have been reduced significantly in recent years through the use of low NOx burners which burn at a temperature slightly below that at which NOx forms, the nature of biomass combustion, and the need to ensure the complete combustion of wood gases, means that combustion takes place at a temperature where atmospheric oxygen and nitrogen can chemically combine. The better the quality of the combustion control system on a biomass boiler, the lower the NOx emissions will be. In general, biomass boilers produce less NOx than oil boilers. Biomass boilers do not produce any oxides of sulphur (SOx).
The slag produced by a biomass-fired boiler can be reused to avoid energy waste and environmental pollution. There are many ways to reuse the slag. For example, the slag can be used to improve soil and improve soil performance. If it contains potassium carbonate and organic matter, it can also be used to produce compound fertilizers. In addition, the slag is a kind of plant ash, it is also a good thermal insulation material for steelmaking.
Combustion Efficiency
Combustion efficiency is the effectiveness of the burner only and relates to its ability to completely burn the fuel. The boiler has little bearing on combustion efficiency. A well-designed burner will operate with as little as 15% to 20% excess air, while converting all combustibles in the fuel to thermal energy.
Thermal Efficiency
Thermal efficiency is the effectiveness of the heat transfer in a boiler. It does not take into account boiler radiation and convection losses - for example, from the boiler shell, water column piping, etc.
Fuel-to-Steam Efficiency
After combustion, biomass-fired boiler fuel will generate energy and also produce some combustible matter in fly ash which will have bad influence on the surrounding environment. Therefore, in order to realize the goal of environmental protection, we should reduce the generation of combustible matter in fly ash in biomass-fired boiler fuel.
In the whole drying process, we should pay attention to gradually increasing the temperature instead of burning by raging fire; regularly checking boiler's water level and keeping it within the normal range; keeping the flame balanced in the furnace. In addition, we also should properly open the drainage valve and maintain the water level, regularly record the flue gas temperature to control the rise of temperature and high temperature and keep the temperature within the normal range. In general, under these conditions, boiler’s drying quality can be ensured.
The pollution discharge of the biomass-fired boiler is less than the coal-fired boiler. It is also necessary to deal with the exhaust gas of the biomass-fired boiler to meet the national standards before boiler ignition and operation.
The air oxygen content's effect on the boiler is mainly reflected by the effect on the blowing rate. Boiler will have typical phenomena if the blowing rate is high or low.
The load control is quite significant in boiler’s operation. Both overloaded and ultra-low loaded operations have negative effects on boiler. Different types of boiler have different rated load ranges, but ultra-low loaded operation’s harm to different types of boiler is similar.
