Effects of hydrothermal conditioning and mechanical dewatering on ash melting behaviour of solid fuel produced from European semi-natural grasslands

Biomass from high nature value grasslands is a potential resource for renewable energy production, since its use as forage is declining due to decreasing livestock levels in many European regions. This study investigated silages and the derived press cakes after hydrothermal conditioning and mechanical dewatering from 18 European grassland sites on fuel relevant parameters. Through silage treatment high reductions of the concentration in the fuel of more than 73% of Cl, K and Na were obtained. Experimental investigation of the ash melting behaviour showed an increase of the ash softening temperature (AST) from approximately 1000 °C for the ash from the silage to 1050 °C for the press cake ashes. At the spherical, hemisphere and flow temperature differences between silage and press cake ashes were even bigger and ranged from 63 to 67 K. Linear regression models, which were based on the fuel content of K, Ca, Si, Al and Na, were able to predict the AST with high accuracy (R2 = 0.88-0.89). Models showed that an increasing content of K led to decreasing AST. By contrast, AST was positively influenced by increasing contents of Ca. The effect of Si depended on the content of alkalis and earth alkalis.