Combustion requirements for conversion of ash-rich novel energy crops in a 250 kWth multifuel grate fired system

Dedicated energy crop production is seen as a path to develop local biomass sources for consumer heating needs. Nevertheless, one drawback of the novel energy crops is a more complex composition than stemwood sources been generally described as “problematic” fuels. Consequently, conversion technology should be adapted to manage their combustion characteristics. The main objective of this work was to assess the suitability of 250 kWth multifuel grate fired system technology with respect to the novel fuel properties. The thermal conversion of two pelletized novel energy crops, currently of interest in Spain, a herbaceous biomass, brassica, and a short rotation coppice, poplar were assessed in terms of the required adjustments on four combustion parameters, i.e., load input, total lambda factor, primary/secondary air distribution and residence time on the grate, leading to the best combustion performance of the system. CO (carbon monoxide) emissions and efficiency were within the European requirements established for high quality wood combustion. Nevertheless, brassica presented the worst results. This was mainly attributed to the ash composition and higher ash content of this fuel. Results have also highlighted that further improvements to and optimization of the current conversion unit are still possible in order to manage the energy crops' requirements.

► Comparison between combustion behavior of two pelletized energy crops in a 250 kWth grate firing conversion technology.
► Ash content and complexity in fuels had a significant influence on the conversion.
► The higher the ash content the higher primary air requirements.
► Sintering and slag occurrence in bottom ashes influenced the results of the air requirements.