Non-pinched, minimum energy distillation designs

Non-pinched, minimum energy solutions are important class of distillation designs that offer the potential advantage of a better trade-off between capital investment and operating costs. In this paper, two important tasks associated with non-pinched distillation designs are studied. Thus the novel contributions of this work to the literature are

(1) A comprehensive methodology for finding non-pinched minimum energy designs.

(2) Understanding of the reasons for the existence of non-pinched distillation designs.

It is shown that the recent shortest stripping line distance approach of Lucia et al. [Lucia, A., Amale, A. and Taylor, R., 2007, Distillation pinch points and more. Comput Chem Eng, available on-line] is capable of systematically and reliably finding non-pinched, minimum energy distillation designs. In addition, we provide an understanding of the reasons behind the existence of non-pinched designs, which include trajectories that follow unstable branches of a pinch point curve in azeotropic systems, the inherent looping structure of trajectories in hydrocarbon separations, and the presence of ancillary constraints in multi-unit processes like extraction/distillation. Several distillation examples are studied and many numerical results and geometric illustrations are presented that show the shortest stripping line distance methodology is indeed a powerful and systematic tool for computing non-pinched, minimum energy designs and that support the underlying reason we provide for the existence of non-pinched designs.     

Effect of initial dextrose concentration,seeding and cooling profile on the crystallization of dextrose monohydrate

A batch seeded cooling crystallizer was used to study dextrose monohydrate crystallization. Experiments were conducted to investigate how a 2% increase in the initial dextrose concentration (from 65.5 to 67.5%) would influence final crystal yield and size. The crystallizations were performed for three different seed masses and cooling profiles, consequently the influence of these parameters was also investigated. The parameters were varied in accordance with an industrial scale process. An in-line focused beam reflectance measurement probe and an in-line process refractometer were used to continuously monitor the crystallizations. The experimental results showed that the 2% increase in initial dextrose concentration had a major influence on the rate of crystallization and yield over a 24 h crystallization period, and only a minor influence on the median crystal size.     

Tertiary treatment of a secondary effluent by the coupling of coagulation-adsorption-ultrafiltration for reuse

We considered the treatment of secondary effluent by coagulation-adsorption coupled with ultrafiltration. Tests were performed on the secondary effluent of the wastewater treatment plant at Staoueli (Algeria) where the average chemical oxygen demand (COD) was 46 (mg O₂/L) and turbidity, 16 NTU. The ultrafiltration tests were made with mineral tubular CARBOSEP membranes — M5 (10 kg/ mol), M2 (15 kg/mol) — in the dynamic mode with a transmembrane pressure ΔP = 1 bar and cross flow velocity = 3 m/s. The reagents were calcium chloride (as coagulant agent) and powder activated carbon. Coagulation improved the ultrafiltration performances significantly. In the first step, the optimal conditions for coagulation were determined considering the best elimination of turbidity as well as organic matter. In the second step, the efficiency of different processes (coagulation, adsorption, ultrafiltration) was compared when used alone or in combination. The coagulation test showed a COD elimination equal to 12 mg/L at pH = 6.5 for a concentration of CaCl₂ = 50 mg/L and a turbidity equal to 3 NTU.     

Effect of Silicon Wafer Resistivity on Morphology and Wettability of Silicon Nanowires Arrays

Silicon - Herein, we prepare vertical and single crystalline silicon nanowires (SiNWs) via a one-step metal-assisted chemical etching method in aqueous NH4HF2/AgNO3 solution. The effects of silicon...     

Application of in-line monitoring for aiding interpretation and control of dextrose monohydrate crystallization

Two in-line monitoring probes were inserted into a 3.2 L batch cooling crystallizer to monitor the progression of a dextrose monohydrate crystallization and how it was influenced by process variables including impurities, seed size and initial dextrose concentration. The probes used were a K-patents refractometer and a Lasentec FBRM probe. These probes were applied to continuously monitor dextrose concentration in solution and crystal chord length distribution throughout the duration of the crystallization. The influence of process variables on crystallizer performance, as determined by final crystal yield and chord size, may not be intuitive and some unexpected results occurred. The continuous in-line measurement data proved very useful for interpreting how variations in the process variables influenced the crystallizer performance. Supersaturation is a key variable in the control of the crystallization process as it influences both nucleation and crystal growth. In-line monitoring of solution dextrose concentration can be applied to continuously evaluate supersaturation and this can then be applied to control supersaturation so as to achieve a desired crystallizer performance.     

Electrocoagulation of cutting oil emulsions using aluminium plate electrodes

The treatment of very concentrated oil-water emulsions by electrocoagulation (EC) was experimentally investigated as a pre-treatment step prior to a membrane process. The oil-water emulsion was prepared from a cutting mineral oil B22 currently used for drilling and machining operations. The electrocoagulation progress was followed by the measurement of COD, turbidity and pH in a batch process with recirculation of the liquid. This study is mainly focused on the effects of operating parameters such as initial pH, current density, oil concentration and recirculation rate, on the de-emulsification efficiency. Kinetic curves showed that the EC process exhibits two phases: a "reactive phase" during which the COD and the turbidity removals increase with electrolysis, and a stationary phase for which further aluminium dissolution is useless in the pollution abatement. The results showed that the treatment efficiency increases with increasing current density, but decreases with oil concentration. It appears that treatment of the considered cutting oil is completed through dissolution of around 10mgAl/g oil, with a slight positive effect of the liquid flow rate. Best results are also obtained with initial pH near 7.