Abstract
Slag property management is of utmost importance for successful operation of entrained flow gasifiers. The present study investigates the influence of potassium introduced as KHCO3 on the ash and slag formation of softwood bark, a calcium-rich fuel, during entrained flow gasification. The bark contained only minor mineral inclusions causing the ash composition to be dominated by calcium and potassium. Wood bark with and without KHCO3 additive was gasified between 850 and 1400 °C at O2 stoichiometric ratio (λ) 0.6. The ash particles collided with a flat impact probe inside the hot reactor at particle impact angles set to 90°, 60°, and 30°. The reactor and probe allowed long-distance microscope data collection close to the probe surface. Particle deposition was optically monitored and resulting deposits were analyzed by SEM-EDS and XRD. Thermodynamic equilibrium and viscosity calculations were used to assist interpretation of experimental results. The predicted temperature window for liquid carbonate formation was experimentally verified, but the melt fraction of the deposit was too low to cause efficient flow and removal of ash from the probe under the prevailing experimental conditions. At higher temperatures, spherical particles indicated lower ash melting temperatures than expected from the bulk ash composition, and a detailed mechanism was proposed.
Highlights
Sustainable and economically viable entrained-flow gasification of woody biomass is a promising route for production of fossil free fuel and chemicals.[1]
The present study aimed at experimentally determining the influence of increased potassium content on ash properties during entrained flow gasification of calcium rich spruce bark
Significant amounts of liquid carbonates were formed between 900 and 950 °C using the KHCO3 additive, but due to inclusions of solid ash particles the desired flowing assisted by the presence of carbonate melt was not achieved
Summary
Sustainable and economically viable entrained-flow gasification of woody biomass is a promising route for production of fossil free fuel and chemicals.[1]. The wall deposits were found to be depleted in potassium compared to the overall ash composition of the bark fuel This directly affects slag properties and may possibly explain the poor slag flowability in bark gasification. Entrained flow gasification using bark with minute mineral content are not well studied but could be of future relevance.[6] For such barks, or commonly energy crops such as willow, calcium is the dominating ashforming element together with potassium It is well-known that such fuels typically form carbonates or oxides during thermal conversion.[7] Formation of carbonate-melts may be facilitated by the addition of potassium, a strategy employed to improve syngas yields in gasification.[8]. Thermodynamic equilibrium and viscosity calculations were used to assist interpretation of experimental results
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