Improved prediction of shell side heat transfer in horizontal evaporative shell and tube heat exchangers

This paper presents an improved prediction method for the heat transfer and pressure drop in the shell side of a horizontal shell and tube evaporator. The results from an experimental test program are used in which a wide range of evaporating two-phase shell side flow data was collected from a TEMA E-shell evaporator. The data are compared with shell side heat transfer coefficient and pressure drop models for homogeneous and stratified flow. The comparison suggests a deterioration in the heat transfer data at low mass fluxes consistent with a transition from homogeneous to stratified flow. The pressure drop data suggest a stratified flow across the full test range. A new model is presented that suggests the transition in the heat transfer data may be due to the extent of tube wetting in the upper tube bundle. The new model, which also takes into account the orientation of the shell side baffles, provides a vast improvement on the predictions of a homogenous type model. The new model would enable designers of shell side evaporators/reboilers to avoid operating conditions where poor heat transfer could be expected, and it would also enable changes in process conditions to be assessed for their implications on likely heat transfer performance. (Abstract from WOK

Интеллектуальные информационные системы

Applying life cycle thinking at an early design stage can help engineers to deliver sustainable systems by design. To demonstrate how this can be carried out at a practical level, this paper proposes a simplified methodology for integrating life cycle considerations into process design. Combining flowsheeting and life cycle assessment, it shows how environmental 'hotspots' can be identified and translated into key design targets to improve the sustainability of a system from 'cradle to grave'. The method is applied to a carbon capture and utilisation system using waste CO2 to produce synthetic diesel in a Fischer-Tropsch process. Although the system is energy intensive, applying life cycle thinking helps to make synthetic diesel competitive not only with fossil but also with biodiesel in terms of the climate change impact

Reducing the energy demand of corn based fuel ethanol through salt extractive distillation enabled by electrodialysis

The thermal energy demand for producing fuel ethanol from the fermentation broth of a contemporary corn-to-fuel ethanol plant in the U.S. is largely satisfied by combustion of fossil fuels, which impacts the possible economical and environmental advantages of bio-ethanol over fossil fuels. To reduce the thermal energy demand for producing fuel ethanol, a process integrating salt extractive distillation – enabled by a new scheme of electrodialysis and spray drying for salt recovery – in the water-ethanol separation train of a contemporary corn-to-fuel ethanol plant is investigated. Process simulation using Aspen Plus® 2006.5, with the ENRTL-RK property method to model the vapor liquid equilibrium of the water-ethanol-salt system, was carried out. The integrated salt extractive distillation process may provide a thermal energy savings of about 30%, when compared with the contemporary process for separating fuel ethanol from the beer column distillate