Abstract
Formation and release of potassium chloride (KCl) during biomass combustion cause ash sintering and deposition during combustion of biomass fuels. In the present work, two mineral additives, zeolite 24A and kaolin, were tested in terms of their capacity for capturing KCl. This was done experimentally using a thermogravimetric method. The effects of zeolite 24A and kaolin on sintering behaviours of barley straw ash were also studied by a combination of laboratory sintering test, SEM-EDX and X-ray diffraction analyses. It was found that both zeolite 24A and kaolin have high capacities to capture KCl at elevated temperatures. Instead of evaporating into gas phase more than 50 wt% and 40 wt% of the tested KCl were retained in zeolite 24A and kaolin at 1,000 °C, respectively. The amount of KCl captured by zeolite 24A and kaolin decreased with increasing temperatures. Compared to kaolin, zeolite 24A was more effective for capturing KCl at the tested conditions. Both zeolite 24A and kaolin can react with KCl to form different potassium aluminium silicates. It indicates that chemical reactions play an important role in the overall capturing process. The barley straw ash melted severely at 1,000 °C due to formation and melting of potassium silicates. Addition of kaolin and zeolite 24A significantly reduced the sintering tendency of the barley straw ash. Together with SEM-EDX analysis, identification of high temperature melting potassium aluminium silicates by XRD partly explains the improved sintering behaviours of the ash-additive mixtures.
