Lignocellulosic residues for bioenergy : effects of storage, fuel design, and combustion characteristicsBozaghian Bäckman, Marjan
Utilization of lignocellulosic residues for bioenergy raises storage, handling, and combustion challenges. The ash-forming elements in biomass may cause ash-related problems during combustion, such as slagging, fouling, corrosion, or bed agglomeration. Most of these problems are linked to ash-chemical reactions involving alkali. The overall objective of this thesis was to evaluate the impact of storage, fuel design measures, and process adaptation for improving combustion characteristics of lignocellulosic residues to mitigate ash-related operational problems. This was done by monitoring storage-induced changes in bark influencing final material characteristics. Mechanical screening and Ca-additivation on forest and agricultural residues were done as a fuel design measure. In addition, the performance of different bed materials was evaluated in bubbling fluidized bed combustion. Significant changes in the lignocellulosic matrix near pile surfaces were observed during storage of bark, and these changes will not affect the combustion characteristics. Screening efficiently reduced the amount of ash but was associated with significant fuel mass losses and did not change the ash chemistry; thus, combustion characteristics and ash melting behavior can be expected to remain unchanged. The Ca-addition significantly increased the total defluidization temperatures but implied an elevated risk for forming corrosive species and high CO (g) concentrations. High interactions between fuel ash and quartz bed particles and low interactions between fuel ash, olivine, and feldspar bed particles were observed. The feldspar bed material reduced defluidization temperature due to the increased amount of alkali in the bed by diffusion of alkali from feldspar grains. Overall, a good understanding of the ash transformation reactions is needed to mitigate ashrelated problems. In addition, fuel design measures must affect the ash chemistry in the fuel to be worthwhile.
Keywordslignocellulosic residues; bark storage; combustion; ash-related operational problems; ash-transformation reactions
Published inActa Universitatis Agriculturae Sueciae
2022, number: 2022:40
ISBN: 978-91-7760-955-1, eISBN: 978-91-7760-956-8
Publisher: Swedish University of Agricultural Sciences