(379d) Rheology of Biomass Slurries to Determine Pumpability for Hydrothermal Liquefaction

The pursuit of renewable fuels and chemicals has led to the development of many different biomass conversion processes. One of these processes, hydrothermal liquefaction (HTL), has the advantage of high energy recovery, no drying step, and utilization of a green aqueous reaction media.¹ However, transport of biomass and water slurries during HTL has proven to be a challenge.^2,3 Typical reactors can only process biomass between 10 and 15 wt% solids because higher solids loadings plug reactor systems. To improve the efficiency of HTL, and other processes reliant on pumping biomass slurries, it is essential to increase solids loading. Increasing solids loading reduces the volume of waste streams and increases process throughput. In an effort to increase biomass solids loadings many people have studied the rheological properties of biomass slurries to improve pumpability.⁴ Despite these efforts there has yet to be a strong correlation developed between typical rheological properties, like viscosity, and biomass pumpability.

This work takes a unique approach to studying biomass slurry rheology by combining traditional rheometric measurements, such as viscosity and storage/loss moduli, with a novel flow characterization system. Traditional rheometric measurements are made on a rheometer capable of analysis at temperatures up to 300 °C and 2000 psi, which mimics conditions found in some traditional HTL systems. Novel flow studies performed at Idaho National Laboratory are made on an in-house designed syringe attached to an Instron load frame. This system measures the force required to push biomass through a reducing orifice and can study plugging phenomena in biomass slurry transport systems. These studies have shown how plugging can be related to biomass dewatering, followed by bridging across the flow channel. Pumpability studies have been performed on a wide variety of materials from herbaceous to woody crops and residues. In addition to characterizing pumpability in biomass slurries this work has also focused on improving the pumpability of such slurries through preprocessing techniques including: size reduction, blending, and torrefaction. This work will ultimately lead to improvements in feed handling related to hydrothermal liquefaction and other biomass slurry transport systems.

1 Toor, S. S., Rosendahl, L. & Rudolf, A. Hydrothermal liquefaction of biomass: A review of subcritical water technologies. Energy 36, 2328-2342, doi:10.1016/j.energy.2011.03.013 (2011).

2 Elliott, D. C., Biller, P., Ross, A. B., Schmidt, A. J. & Jones, S. B. Hydrothermal liquefaction of biomass: Developments from batch to continuous process. Bioresource technology 178C, 147-156, doi:10.1016/j.biortech.2014.09.132 (2015).

3 Berglin, E. J., Enderlin, C. W. & Schmidt, A. J. Review and Assessment of Commercial Vendors/Options for Feeding and Pumping Biomass Slurries for Hydrothermal Liquefaction. (Pacific Northwest National Laboratory, 2012).

4 Stickel, J. J. et al. Rheology measurements of a biomass slurry: an inter-laboratory study. Rheologica Acta 48, 1005-1015, doi:10.1007/s00397-009-0382-8 (2009).