Full assessment of Sida (Sida hermaphrodita) biomass as a solid fuel

Due to an increased awareness of climate change and limited fossil resources, the demand of alternative energy carriers such as biomass has risen significantly during the past years. This development is supported by the idea of a transition to a bio-based economy reducing fossil based carbon dioxide emissions. Based on this trend, biomass for energy is expected to be used in the EU mainly for heating until the end of the decade. The perennial herbaceous mallow plant Sida hermaphrodita (L.) Rusby (""Sida"") has high potential as an alternative biomass plant for energy purposes. Different density cultivation scenarios of Sida accounting for 1, 2, or 4plants m-2 resulted in a total biomass yield of 21, 28, and 34 tons dry matter ha-1, respectively, over a three-year period at agricultural conditions, while the overall investment costs almost doubled from 2 to 4 plants m-2. Subsequently, Sida biomass was used as SI) chips, SII) pellets, and SIII) briquettes for combustion studies at pilot plant scale. Pellets outcompeted chips and briquettes by showing low CO emission of 40 mg Nm-3, good burnout and low slagging behavior, however with elevated NOx and SO2 levels. In contrast, combustion of chips and briquettes displayed high CO emissions of >1300 mg Nm-3, while SO2 values were below 100mg Nm-3. Contents of HCl in the flue gas ranged between 32 and 52 mg Nm-3 for all Sida fuels tested. High contents of alkaline earth metals such as CaO resulted in high ash melting points of up to 1450 °C. Life Cycle Assessment results showed the lowest ecological impact for Sida pellets taking all production parameters and environmental categories into consideration, showing further advantages of Sida over other alternative biomasses. Overall, the results indicate the improved applicability of pelletized Sida biomass as a renewable biogenic energy carrier for combustion.