Introduction High concentration biomass slurries are being used to improve the production of renewable fuels. Challenges to effective mixing increase as the solid concentration increases.

Impeller Power Draw in High Concentration Biomass Slurry Jian Deng, Kevin J. Myers, and Eric E. Janz Mixing XXIV Lake George, New York June 22-27, 2014

Motivation and Objective •  Develop improved understanding for

design of biomass slurry agitators •  Cavern models for agitation of yield

stress fluids often assume turbulent power number

•  Is this assumption valid when designing for high concentration biomass slurries?

•  Measure yield stress and power number in seventeen mass percent sawdust in water slurry

Yield Stress Measurement

•  Vane method using maximum torque

•  Yield Stress = 300 Pascal •  Coefficient of Variation = 7 to 50%

Power Number - Reynolds Number •  Power Number

•  Modified Reynolds number

• Typical Newtonian fluid Power number – Reynolds number data

Experimental Data

Conclusions • Metzner-Otto k=11 underestimates the Reynolds number. A k-value of 100 appears to be best. • Mixing high concentration biomass slurry occurred in the transitional regime in the laboratory. • The assumption of turbulent power number made in past cavern model studies (e.g. - Elson, 1990) and in pulp and paper mixing (Yackel, 1990) may not be suitable, particularly when mixing high yield stress fluids at the lab scale. • Uncertainty in the yield stress leads to the same uncertainty in Reynolds number and Metzner-Otto k parameter. • Most data was obtained without baffles, and the addition of standard baffling did not have a significant effect on the power number data. • In transitional operation, radial-flow impellers exhibited lower power numbers in yield stress fluid than in Newtonian fluid.

D-6 impeller, radial flow discharge

S-4 impeller, radial flow discharge

P-4 impeller, mixed flow discharge

HE-3 impeller, axial flow discharge

Acknowledgement Zheng Ma provided Newtonian fluid data

Herschel-Bulkley Fluid

Metzner-Otto Approach

Torque and Rotational Speed

Indicator Impeller