Combustion of Miscanthus: Composition of the Ash by Particle Size

Miscanthus is an energy crop considered to show potential for a substantial contribution to sustainable energy production. In miscanthus combustion, 2.0% to 3.5% of the mass of the fuel remains as ash. This ash is less contaminated by heavy metals than ash from wood combustion. The concentrations are well below the typical limit concentrations for use as a soil conditioner on agricultural land and forests. The potassium concentration in the investigated miscanthus ash of 14.1% K 2 O was significantly higher than the typical concentration of potassium in ashes from wood combustion (3% to 7% K 2 O). However, in comparison to wood ashes, only very little enrichment of potassium in the fine size fractions of miscanthus ash was found. For most of the other elements, the enrichment in the fine size fractions was also low. Therefore, the production of a potassium-rich material by classification for the production of potassium fertilizer is not feasible. The absence of such an enrichment can be explained on the one hand by the significantly lower combustion temperature in the miscanthus combustion plant and, on the other hand, by the higher molar ratio of K to Cl and the low ratio of K to Si. Thus, the most sensible utilization of miscanthus ash is its direct recycling to the soil such as where the miscanthus plants are grown.