Tonn, B: Suitability of semi-natural grassland biomass for b

mid June to mid October. Chemical composition of the biomass was analyzed separately for the two species groups ¿grasses' and ¿forbs'. Ash, N, K and Cl partly reached contents problematic for the combustion process. Ash and N are responsible for dust and nitrogen oxide emissions, for which legal emission limits exist. K and Cl play a key role in ash high-temperature behaviour. They are the cause of slagging, fouling and corrosion, which may severely impair the functioning of combustion systems. Variability of biomass chemical composition was largely influenced by differences between grasses and forbs and by nutrient availability at the experimental sites. Grasses had lower ash and N contents than forbs and were less strongly influenced by site effects. However, they had higher K/Ca ratios, leading to more problematic ash melting behaviour. Harvest date had a small effect on fuel quality. The K/Ca ratio, decreasing between June and October, was the only parameter showed a relevant change over time. These results point to a low potential for conflict between nature conservation targets and fuel production from semi-natural grassland biomass.
An experiment using biomass from two grassland sites of contrasting management intensity showed that leaching by rain during the field period can lead to strong reductions of K and Cl and to smaller reductions of ash contents. These leaching effects only occurred in dry but not in freshly cut biomass. There were also differences in leachability between biomass from the two grassland sites. For this reason, a laboratory method was calibrated against the leaching effect of simulated rain in a follow-up experiment. This method was used to assess the effects of different biomass characteristics and harvest dates on leachability. Differences in leachability between biomass from five grassland sites harvested on two different dates were found to be small and were not related to initial elemental contents. The results can therefore be considered to be representative for the primary growth of semi-natural grasslands. An analysis of long-term weather data showed that the option of using on-field leaching will not exist every year, so that technical leaching processes are of interest as well. A method adapted from combustion technology was used to investigate ash high-temperature behaviour of leached and unleached biomass. It could be established that leaching improved ash melting behaviour and reduced the release of volatile elements.
Knowledge about the factors influencing semi-natural grassland biomass chemical composition allows match biomass from specific grassland sites with the most suitable combustion technology and to identify grassland biomass of high fuel quality. For biomass of a less favourable chemical composition, on-field leaching is an option for fuel quality optimization. Semi-natural grassland biomass combustion therefore has the potential to combine biodiversity conservation with the production of bioenergy.