(490l) Fluid Mechanics of Pretreated Corn Stover Slurries in Process Equipment

The conversion of biomass, specifically ligno-cellulosic biomass, into fuels and chemicals has recently gained national attention as an alternative to the use of fossil fuels. Current biochemical conversion processes in research and development typically use high concentrations of water and hence low concentrations of biomass solids. Increasing the concentration of the biomass solids has a large potential to reduce the cost of conversion. The detailed rheological behavior of dilute-acid pretreated corn stover slurries was previously investigated for a range of concentrations and extents of enzymatic hydrolysis, where it was found that the slurries have a significant yield stress and are shear thinning. Data from these rheology experiments were used to select an appropriate generalized Newtonian constitutive model and to determine model coefficients. The selected model included the concentration of solids as an independent variable so that a single set of coefficients could be used for a range of slurry concentrations. Using computational fluid dynamics with the selected constitutive model, simulations of the slurry flow were made for relevant process geometries, specifically a straight pipe, a horizontal reaction vessel, and a vertical reaction vessel. The simulations show that the yielding behavior results in plug flow in the pipe and dead zones in the vertical mixer that depend on the concentration of the slurry. Power requirements for mixing and pumping were calculated from the simulations. The pipe flow simulations were verified by measuring the flow rate and pressure drop of pretreated corn stover slurries flowing in a straight pipe.