Evaluation of bagasse from grape seed oil extraction as a sustainable fuel for domestic boilers

• Suitable combustion behavior was observed, although NOx and PM emissions exceeded the standard limit. • Homogeneous nucleation of alkali vapors is the main PM formation mechanism at nominal load. • Heterogeneous condensation of alkali chlorides and sulphates is the dominated PM formation mechanism al partial load. • Low deposition rate and no problems related to fouling are expected. This work evaluates the suitability of bagasse from grape seed oil extraction as a fuel for domestic boilers. Results showed an acceptable combustion efficiency (higher than 90 %) at both partial (24 kW) and nominal (55 kW) load. CO emissions (150 and 1200 mg/Nm 3 at nominal and partial load, respectively) fulfill the UN-EN 303-5 for class 3 boilers. However, although PM emissions were lower than expected (due to the high ash content of the residue, ∼4 % d.b), only PM at partial load fulfill the cited standard. In general, PM agglomerates with different sizes (depending on the load) but comparable shape and composition (mainly K, S, Cl and Na) were observed. The effect of the load was not significant for the smallest particles (PM 0.1 ), homogeneous nucleation of alkali vapors appearing as the main formation mechanism at both conditions. However, while bigger particles were formed through heterogeneous condensation of alkali chlorides and sulphates followed by agglomeration and coalescence at partial load, unburnt fuel together with fly ash dominated at nominal load. Finally, condensation of alkaline salts in the flue gas and their transport to the heat exchanger surface by diffusion or thermophoresis has been elucidated as the main route leading to fouling.