Powder Feeding of Biomass : Particle Shape and Feed Rate Stability

Directive 2009/28/EC from the European parliament and council of the European Union has contributed to an increased interest in production of fuels and chemicals from renewable sources. Gasification of biomass is a method for production of fuels and chemicals from renewable resources. Since the 1950s coal has been used as feedstock to gasification at full plat scale and today biomass is gasified at pilot and demonstration scale. The gasification process involves milling a fuel into a powder of small particles which then is fed into a gasifier. One issue with gasification of biomass powders is low flowability. The flowability of a powder is strongly related to physical properties like frictional forces and cohesive forces. One property of biomass powder is needle shaped particles. Needle shaped particles contributes to a larger contact area. Larger contact area contributes to higher aggregation forces between the particles which in turn could affect the flowability of a powder. The poor flow properties of biomass contributes to challenges of both design and operating of biomass plants. Many incidents to shout downs in a biomass plant can be traced to failure of some part of the biomass-handling system.The aim of this thesis was to develop a method to measure feed rate stability of three different types of biomass, Pine, Aspen and Reed canary grass. An optical analysis with focus on particle size and shape together with feed rate stability experiments was performed on these powders. The optical analysis was performed in order to investigate the possible correlation between particle, size and shape, and feed rate stability. This master’s thesis was carried out at SP Energy Technology Center in Piteå during the spring of 2015. SP ETC is a research institute focusing on thermo-chemical conversion of biomass providing services related to gasification, combustion and bio-refining processes. Biomass preparation, data handing and writing was performed at SP ETC and optical analysis and feed rate stability experiments were performed at Luleå University of Technology.The results from the feed rate stability experiment showed the highest feed rate stability for Reed canary grass, then Aspen and lowest for Pine. Between a fine and coarse powder of Pine, the fine powder had higher feed rate stability.The particle size distributions for the powders were similar. Aspect ratio was highest for Reed canary grass, then Pine and lowest for Aspen. The results showed no correlation between aspect ratio and feed rate stability.Validerat; 20150815 (global_studentproject_submitter