Frictional behaviour of wheat straw-water suspensions in vertical upward flows

The use of biofuels helps mitigate greenhouse gas emissions. Earlier studies have shown that transporting biomass in horizontal pipelines in the form of water-based slurries significantly reduces transportation costs. The frictional behaviour of water-based chopped wheat straw slurry in a vertical pipeline has not been studied and this is the focus of this study. In situ concentrations of water-based conventional solids of medium sand, glass beads, and fine sand and straw slurry flows were determined by measuring their delivered concentrations in pseudo-homogeneous regimes for prepared concentrations of 1–6% (dry volume of conventional solids) and 5–25% (saturated mass of straw), respectively. Two grades of sand and glass beads with mean particle diameters of 0.103, 0.447, and 0.5 mm, respectively, and straw with a nominal particle length of 19.2 mm were utilised. The delivered concentrations for the straw slurries and fine sand were close to their corresponding prepared concentrations and were homogeneous. There was a large discrepancy between prepared and delivered concentrations for the medium-sized sand and glass beads slurries. The pressure drop of straw slurries over the range of velocities of 0.5–4.2 m s−1 and mass concentrations of 5–25% through the vertical pipe showed a maximum drag reduction of 19% at a concentration of 25% (mass) and at a 3.5 m s−1 velocity. For concentrations of 5–20% (mass), the straw slurries showed drag-reducing capabilities in the mixed and turbulent flow regions for various velocities that were different from horizontal flows.