Bioslurry as a Fuel. 7: Spray Characteristics of Bio-Oil and Bioslurry via Impact and Twin-Fluid Atomizers

Abstract

This study reports the spray characteristics of two fast pyrolysis bio-oils with different viscosities (0.0753 and 0.1522 Pa·s at 21 °C) and a set of bioslurry samples prepared from the bio-oils at various biochar loading levels (5, 10, 15, and 20 wt %). Two types of atomizers (impact atomizer and two-fluid atomizer) were used. Experiments for the impact atomizers of various sizes were carried out at injection pressures of 2.07–4.96 MPa and feeding rates of 108–490 mL/min. At a constant pressure, the Sauter mean diameter (SMD) of bio-oil and bioslurry increases as the flow number increases, while at a constant flow number, the SMD decreases rapidly with increasing pressure. The biochar loading level has a significant impact on the bioslurry atomization characteristics. An increase in biochar leading level results in a substantial increase in the spray SMD. Experiments using the twin-fluid atomizer (N2 as the atomization gas) were carried out at flow rates of 2–6 mL/min. A twin-fluid atomizer is more applicable at considerably lower liquid flow rates than an impact atomizer. The spray SMD of the twin-fluid atomizer is mainly influenced by the liquid viscosity, gas/liquid ratio (GLR), and biochar loading level. An increase in viscosity and biochar loading level leads to an increase in the spray SMD, while an increase in GLR leads to a reduction in the SMD. Correlations have also been developed to predict spray SMD of bio-oil and bioslurry using both atomizers.