Base Case Configuration Research Articles

Energy considerations for a SSF-based softwood ethanol plant

Ethanol can be produced from softwood by steam pretreatment followed by simultaneous saccharification and fermentation (SSF). However, the final ethanol concentration in the SSF step is usually rather low (around 4 wt%) and as a result the energy demand in the downstream processing will be high. In an effort to reduce the energy consumption various alternatives for the downstream processing part of the process were evaluated from a technical-economic standpoint. With experimental data as a basis, the whole process was modelled using the commercial flowsheeting program Aspen Plus. The results were used in the subsequent economic evaluation, which was performed using Icarus process evaluator. A base case configuration, consisting of three thermally coupled distillation columns and multiple-effect evaporation was established. For a feed containing 3.5% ethanol (w/w) to the distillation step, the overall process demand for steam was estimated to be 19.0 MJ/L ethanol and the ethanol production cost 4.14 SEK/L (0.591 USD/L). Different alternatives were considered, such as integration of a stripper with the evaporation step, increasing the number of evaporation effects and the application of mechanical vapour recompression to the evaporation step. Replacement of evaporation with anaerobic digestion was also considered. Among these alternatives, evaporation using mechanical vapour recompression and the anaerobic digester alternative both resulted in significantly lower energy demand than the base case, 10.2 and 9.8 MJ/L, respectively, and productions costs of 3.82 (0.546 USD/L) and 3.84 SEK/L (0.549 USD/L).

Computational haemodynamics analysis and comparison study of arterio-venous grafts

Haemodialysis arterio-venous graft failure is related to the development of stenotic lesions most commonly located near the venous anastomosis, especially in the toe region. 'Disturbed flow' interaction with the vessel wall surface, characterized by haemodynamic parameters based on the local wall shear stress or the radial pressure gradient, have been widely recognized as the trigger mechanism of a cascade of abnormal biological events leading to occlusive developments. Assuming incompressible laminar flow and rigid, in-plane vessel walls, validated haemodynamics are numerically simulated for a constant-diameter end-to-side base case, the VenafloTM graft, and an improved graft-end configuration. The geometric design of the new graft-end was based on the reduction of three time- and area-averaged haemodynamic parameters, i.e. the wall shear stress gradient, wall shear stress angle gradient, and radial pressuregradient. Considering the critical toeregion, the VenafloTM graft has demonstrated measurable improvements over the base case configuration in predictive computer simulations as well as in clinical trials. The performance improvement should be further enhanced with the modifications illustrated by the new design.

The effect of active material loading on the performance of a cylindrical alkaline cell

Abstract The effects of varying the active material loading on the discharge performance of an AA-size Zn/MnO2 alkaline cell are studied. The active material loading is characterized by two parameters that reflect the weight fraction of solid material removed from the anode and cathode, respectively, in relation to a chosen base case configuration. The anode and cathode loadings are allowed to vary independently of each other. A variety of different capacity ratios are used. Results indicate that the best design is achieved by a specified reduction in the cathode loading, with a balanced amount of the cathode and anode active materials.