Separation Duties Research Articles

Applicability of a cryogenic distillation system for D-T isotope rebalancing and protium removal in a DEMO power plant

The tritium plant at the future European DEMOnstration (DEMO) fusion power plant will require isotope separation systems for protium removal and isotopic rebalancing of the torus exhaust stream. Protium removal and isotopic rebalancing can occur within a single separation technology which is based upon the exploitation of isotopic effects; the minimum amount of exhaust gas processing can be calculated using a heuristic developed for this purpose. A model has been developed to quantify the size and separation ability of a cryogenic distillation system to perform the required separation duties. Comparison of a reference scenario and six alternative scenarios shows that the isotope imbalance ratio between deuterium and tritium has the largest effect on the size and separation ability of a cryogenic distillation system; provided that a trace amount of protium is acceptable within the gas introduction system into the torus. A cryogenic distillation system is found to be a suitable technology in terms of energy usage and isotope separation, but a single system size is not suitable to process a range of different compositions. This evaluation of the applicability of cryodistillation to isotope rebalancing and protium removal for a DEMO reactor, form a base case against which other hydrogen isotope separation technologies can be investigated and compared in terms of size, power requirements and safety.

Positron emission particle tracking and CFD investigation of hydrocyclones acting on liquids of varying viscosity

Cyclone separators are widely used for separation of solids or droplets from gases or liquid fluids. They represent an elegant and robust separation technology involving low capital and maintenance costs. It is therefore interesting, to extend cyclone technology to new applications, particularly in the oil and gas industry where separation duties are becoming ever more demanding and diverse, and separation processes are moving to more remote installations, such as sub-sea or even down-hole installations. The objective of this paper is to elucidate the working of hydrocyclones including ones acting on liquids of elevated viscosity using state-of-the-art experimental and analysis techniques, namely positron emission particle tracking (PEPT) and computational fluid dynamics (CFD) with large-eddy simulation of turbulence effects. The results show a number of interesting and anomalous features of the liquid and particle flow, such as unexpected excursions of particles to the inner vortex and the effect of the vortex end on the particle flow. It is shown that it is possible to determine the axis of the hydrocyclone very precisely by a minimization technique and thus convert the output from the tracking algorithm in Cartesian coordinates to cylindrical coordinates with the cyclone as axis. This throws additional light on the results. Tracks of different particles, some of which are eventually captured and some which are lost, are shown both in 3-D Cartesian and 2-D cylindrical coordinates and the effects of the fluid and particle properties are discussed.

Use of multiple inter-reboilers to achieve energy savings and improve thermodynamic efficiency of the distillation of N,N-dimethylformamide wastewater

The purification of N,N-dimethylformamide wastewater involves an energy intensive distillation process. We propose a novel energy-saving process scheme involving multiple inter-reboilers sed. In this scheme, ideal thermodynamic model non-random two liquid (NRTL) model was used to calculate the phase equilibrium using Aspen Plus platform. While the relationship between important process parameters and energy consumption by the distillation process was studied, several parameters such as the most suitable positions for the inter-reboilers and the most reasonable steam extraction rates were obtained. The feasibility was detected under the same separation duties and main technological structure. For 10wt% DMF wastewater, the inter-reboilers were installed on the 37th, 38th and 39th plates, while the corresponding heat transferred values were 3,038 kW, 91 kW and 179kW, respectively. In comparison to the conventional distillation process, an energy consumption of 77.43% and thermodynamic efficiency of 65.69% were obtained. For 20 wt% DMF wastewater, the inter-reboilers were installed on the 21st and 25th plate, while the corresponding values for the heat transferred were 1,632kW, and 1,450kW, respectively. In comparison to the conventional distillation process, the energy consumption can be reduced by 71.31%, while the thermodynamic efficiency can be improved by 47.10%.

Advances in post-fermented wine clarification by centrifugal technology

Wine clarification processes are deeply determined by complex interaction of wine constituents and application of available technologies as well as use of fining agents. Among others, centrifuge is a consolidated technique applied for many separation duties in the winery. Important advances on improvement of the performance of centrifugal technology have beeen focused on gentle wine treatment, minimal dissolved oxygen and significant reduction of energy consumption helping to dispel old beliefs on a technique considered to be traditional. This paper reviews the development of technology and recent advances on centrifuge improvement and aims to show, through field experimental observation, the importance of removing a portion of particles responsible of haze in the light of very low level of dissolved oxygen and complementarity of alternative recent techniques of wine filtration like cross-flow microfiltration.

Advances in post-fermented wine clarification by centrifugal technology

Wine clarification processes are deeply determined by complex interaction of wine constituents and application of available technologies as well as use of fining agents. Among others, centrifuge is a consolidated technique applied for many separation duties in the winery. Important advances on improvement of the performance of centrifugal technology have beeen focused on gentle wine treatment, minimal dissolved oxygen and significant reduction of energy consumption helping to dispel old beliefs on a technique considered to be traditional. This paper reviews the development of technology and recent advances on centrifuge improvement and aims to show, through field experimental observation, the importance of removing a portion of particles responsible of haze in the light of very low level of dissolved oxygen and complementarity of alternative recent techniques of wine filtration like cross-flow microfiltration.

Removal of particles from highly viscous liquids with hydrocyclones

In this paper the performance characteristics, expressed as cut-size, grade-efficiency curve and pressure drop, have been determined for a hydrocyclone acting on highly viscous liquids. These results are of high quality and can serve as a benchmark for simulations and model predictions. To understand the results, CFD, large-eddy simulations of the flowpattern and pressure drop have been carried out, among other things to determine the vortex intensity as a function of liquid viscosity. A version of a main-stream cyclone model has been identified that predicts the trend in hydrocyclone performance with liquid viscosity well, both in terms of separation efficiency and pressure drop. This model is given in full, providing a valuable tool in evaluating the potential of hydrocyclone technology for new and unconventional separation duties.

Advanced fractionation technology for the oleochemical industry

AbstractSteadily increasing requirements on fractionation demands in the oleochemical industry require advanced separation technology. Today, often a distillation column has not only to process several different feeds, but also be able to produce two different products simultaneously. Divided wall columns have been proposed and used in the chemical industry, but there are, presently, few applications of divided wall columns in the oleochemical sector. The main reason prohibiting their use might be in the limited familiarity, higher requirements on operation, potential corrosion problems and last but not least, limited flexibility.Fractionation columns with added side stripper are a well‐proven way to satisfy increased demand of separation duties. The availability of second‐generation structured packing increases the efficiency and reduces pressure drops while making it possible to increase capacity and/or product purities. A lower pressure drop has a positive impact on the separation itself. Combining these effects with an increase in capacity will result in a synergy effect on the separation performance.The newly developed BXPlus structured packing is a powerful tool for advanced Glycerin separation, combining good wettability resulting in high efficiency with low‐pressure drop. New columns can be designed much more compactly. Revamps will improve both capacity and/or purity. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.

Optimal operation of extractive distillation in different batch configurations

AbstractOptimal operations of extractive distillation for regular and middle‐vase1 batch columns are presented based on a profit function. Detailed models are used for the rigorous dynamic optimization considering all operational decision variables, including reflux ratio, solvent feed rate, heat duties, and possible product withdrawals during the process. Optimal feed distribution and stream configuration at the middle section of the middle‐vessel column are investigated. Separation of a minimum boiling azeotropic binary mixture (acetone and methanol using water as solvent) involving different separation duties and feed compositions is presented as a case study. The pereformanance of the middle‐vessel column is signicantly influenced by the middle‐section stream configuration, with the best profit when the stream configuration is allowed to vary during the operation. The optimal operating policy for the middle‐vessel column involved the feed being charged mainly to the reboiler still with low holdup in the middle vessel during the operation.

Process Intensification for Responsive Processing

The era of responsive processing is upon us. It has emerged from the concepts of process intensiŽ cation (PI) and is aimed towards the development of processes which are more responsive to market needs whilst responding to changes in process parameters in seconds or milliseconds rather than several minutes or hours, as is typiŽ ed in a conventional process plant using traditional batch reactors with large inventory. In order to evaluate the degree of responsiveness of a process it is essential that intensiŽ ed modules are coupled with real time performance monitoring techniques with very fast response times. Advances in reactor and unit operation technology should go hand in hand with research and development in the analytical instruments and techniques. Non-evasive techniques for characterizing monitoring the speed of reaction should be used where ever possible. The perceived beneŽ ts of this technology are many and are appropriate for the processing industry, which is currently braced with extreme challenges and is striving for a competitive edge. Process  exibility, improved product quality, speed to market, just in time manufacturing, reduced foot print, improved inherent safety and energy efŽ ciency, distributed manufacturing capability and ability to use reactants at higher concentrations are some of the beneŽ ts of the proposed technology. In order to realize the beneŽ ts of responsive processing, intensiŽ ed heat and mass transfer modules, together with novel processing routes, will be required. Research and development work in this area has been going on for over ten years and in recent times industrial interest has gathered signiŽ cant momentum. Process intensiŽ cation was pioneered by Ramshaw in the 1980s and may be deŽ ned as a strategy which aims to achieve process miniaturization, reduction in capital cost, improved inherent safety and energy efŽ ciency and often improved product quality. In order to develop an intensiŽ ed process plant, it is essential that all the unit operation systems be intensiŽ ed i.e. reactors, heat exchangers, distillation columns, separators etc. Wherever possible the aim should be to develop and use multi-functional modules for performing heat transfer, mass transfer, and separation duties. PI encompasses not only the development of novel, more compact equipment but also the development of intensiŽ ed methods of processing such as the use of ultrasonic and radiation as energy sources. Additional beneŽ ts of PI are improved intrinsic safety, easier scale up, and increased energy efŽ ciency. Adopting the PI approach can substantially improve the intrinsic safety of a process by having a signiŽ cantly reduced volume of potentially hazardous chemical at any time in a smaller intensiŽ ed unit. In addition, one of the objectives of PI is to move away from batch processing to small continuous reactors, the latter giving more efŽ cient overall operation especially in the case of hugely exothermic reactions whereby the heat can be removed continuously as it is being released. The inherent safety aspect of PI based technologies and its role in minimizing hazards in the Chemical and Process Industries has been discussed in a recent article. Design considerations which may be taken into account for intensifying a process are presented in Table 1.

Use of Continuous Distillation Columns for Batch Separation

Over the last few decades many alternative column configurations and modes of operation have been suggested for batch distillation. This paper addresses the potential use of continuous distillation columns for the batch separation task. It is shown that under certain circumstances the conventional dynamic batch operation (inherent with a batch distillation column) can be replaced by the steady state operation of a continuous column without significant compromise of the recovery and energy consumption. This allows steady state modelling and optimization as opposed to dynamic modelling and optimization. Multi-Pass Sequential Steady State (MPSSS) operation is suggested to achieve high recovery of species in short operation time and low energy cost (meaning high productivity). Multi-pass operation achieves better recovery compared to conventional operation for the same energy consumption and operation time. The performance of a continuous column un dergoing multiple separation duties is also addressed in this work. It is shown that by choosing an optimal feed rate, an existing continuous column can be used effectively for separating multiple binary mixtures with different ‘degrees of difficulty’ of separation.

Simultaneous optimization of design and operation of multicomponent batch distillation column—single and multiple separation duties

A method is presented for the simultaneous optimization of a batch distillation column design and its operation, for single and multiple separation duties, each involving different multicomponent mixtures and complex operations with intermediate cuts. For operation structures selected a priori, the formulation presented permits the use of general distillation design and cost models. The objective function and constraints include capital and operating cost. In particular, the number of internal plates is optimized along with the most significant operating variables (recoveries in various cuts and reflux ratio profiles and times). The multiple duty formulation presented accounts for the different importance of each duty and setup time between batches. Application of the method to single duty multicomponent separation from the literature shows that significant profit improvements can be achieved within acceptable computing times. For multiple separation duties (two binary mixtures), the method clearly shows the importance of including allocation time to each duty and setup time for each batch in the objective function.

Production of oxy-rich air by RPSA for combustion use

The capital and energy costs of production of oxygen enriched air by a rapid pressure swing adsorption (RPSA) process can be reduced by decoupling the air drying and the air separation duties of the process. Integration of the oxygen-RPSA process with an enhanced combustion application system allows thermal swing adsorption drying of air feed to the RPSA process. The air separation process then can be run using an ad(de)sorption pressure envelope of 2:1 atmospheres, which significantly reduces the cost and energy of operation of the air compressor.