Horizontal rotating reactors offer many advantages for enzymatic hydrolysis of viscous biomass slurries; however, they do not provide homogenous mixtures since motion is only in the angular direction. Multi-directional mixing is important for dispersing enzymes and carrying products away from reaction sites. The objective here was to experimentally quantify mixing times and axial dispersion coefficients in a horizontal rotating bioreactor. Mixing times were of the same order as reaction times, indicating that enzymatic hydrolysis could be as much controlled by diffusion and mixing effects as by the complex reaction mechanism. The dispersion coefficient for the highest solids slurry was 20× less than the lowest solids slurry, which is indicative of the difference in free water and the magnitude change of viscosity with relatively small addition of solids. The slow mixing times and low dispersion may be an acceptable tradeoff with significantly lower power requirements compared to a conventional vertical reactor.
Mean age theory was applied towards predicting just suspended speed in mixing tanks by evaluating multiphase mean age near the bottom surface through strategic zone selection. Multiphase mean age equations were solved only in a thin section along the bottom of the vessel (~1% of the vessel height), allowing the mean age in proximity to the bottom to be computed. A rigorously defined method for open systems and a modified method for closed systems using modified boundaries provided equivalent results. The technique was accurate within 1-3% of experimental values across a range of solid densities, solid fractions, and particle sizes while using multiple impeller types and vessel geometries.
High-solids biomass slurries exhibit non-Newtonian behavior with a yield stress and require high power input for mixing. The goals were to determine the effect of scale and geometry on power number P 0 , and estimate the power for mixing a pretreated biomass slurry in a 3.8 million L hydrolysis reactor of conventional design. A lab-scale computational fluid dynamics model was validated against experimental data and then scaled up. A pitched-blade turbine and A310 hydrofoil were tested for various geometric arrangements. Flow was transitional; laminar and turbulence models resulted in equivalent P 0 which increased with scale. The ratio of impeller diameter to tank diameter affected P 0 for both impellers, but impeller clearance to tank diameter affected P 0 only for the A310. At least 2 MW is required to operate at this scale.
Current wind power technology is not economically feasible throughout most of the United States due to low average wind speeds. A design for a small-scale wind concentrator device suitable for use in areas of low wind velocity was tested using computational fluid dynamics (CFD). Using a novel approach, the device seeks to accelerate incoming air above minimum velocities required for economical power generation. The novel approach employs a funnel shaped inlet with relief vents along the circumference, so as to alleviate backpressure. Both inlet and outlet sections utilize funnel shapes with both parabolic and hyperbolic regions. All geometry and mesh models were created using ICEM 12.1. Simulations were performed using Fluent 12.1.2.Turbulence was modeled using the standard k-epsilon model. All mesh models contained roughly 500,000 unstructured computational cells. CFD simulations predict a 2.53X acceleration of incoming air through the throat of the device (based upon a 2 m/s ambient wind speed). Similar performance was seen across the range of 1-12 m/s. Analysis focused on testing various designs to reduce losses due to turbulent energy and backpressure, with a focus on maximizing the throat velocity where a turbine can be located. Tested variables include funnel shape, lengths of both inlet and outlet funnels, and curvature of the inlet rim. In addition to design of the device, the effect on airflow through the relief vents by a surrounding casing was also analyzed.
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