Low emission biomass combustion in automated boilers for heat and power
Bioenergy is the main renewable energy contributing around 10% to the global energy demand. Most bioenergy is still produced through the combustion of solid biomass. While various technologies are available, mainly residential biomass contributes to local air pollution by organic compounds and particulate matter (PM). Therefore, future applications need to reduce the impact on ambient air. Automated boilers offer important options to achieve low emissions from various types of solid biomass. To maximize the contribution of biomass to a sustainable energy supply, high temperature industrial process heat and combined heat and power (potentially in combination with district heating) should be prioritized over residential heating. In addition, primary measures (in the combustion process) should be applied to achieve low emissions and supplemented with secondary measures (in emission after treatment) where needed.
In recent years we have seen important developments in the design of biomass fueled heating plants. Both innovative designs of the primary combustion technology and innovative application of advanced secondary emission abatement technology have paved the way for plants with very low levels of emission of particles and NOx – even with low grade biomass fuels.
Some countries have seen a tremendous increase in efficiency levels of especially combustion plants utilising moist fuels. The combination of decreasing temperature levels in district heating systems and application of flue gas condensation and heat pumps in the system has paved the way for increasing the capacity without additional fuel demand.
IEA Bioenergy Task 32 (biomass combustion) has reviewed these means with focus on concepts and technical consequences and highlights these developments and approaches to the benefit of potential new plant owners. The report provides an introduction to fundamentals and history of research and development over the past 30 years of primary measures and concepts as well as secondary abatement measures such as de-NOx systems. It contains examples/cases of innovative developments in the recent years from several countries such as Austria, Denmark, Netherlands and Switzerland as well as a summary and conclusion.
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Main highlights:
- Automated biomass boilers enable an efficient use of solid biomass for the provision of heat and electricity. To exploit the value of the biomass resource, high temperature process heat and cogeneration of power and heat are the most favourable applications with use of waste heat to supply buildings and thermal networks.
- The impact on ambient air can be kept on a very low level. High priority is given to primary measures based on the principle of staged combustion. In addition, the use of a suitable biomass fuel for a specific combustion system and a well-controlled operation of the combustion plant must be ensured.
- To limit the impact of biomass combustion on particulate matter in the ambient air, particle precipitators are widely applied. In large boilers, additional gas cleaning systems are applied to reduce specific pollutants depending on the fuel type and the plant size.
