•Arbitrarily fixing distillation column pressure at 1atm does not give the optimum design in many systems, particularly in azeotropic separations.•Optimum pressures in the extractive and solvent ...recovery column are often different.•Quantitative determination of the optimum column pressure requires consideration of both energy costs and capital investment.
Selection of the operating pressure of a distillation column is one of the most important design decisions. Pressure has a major impact on phase equilibrium in terms of relative volatilities, column temperatures and the existence of azeotropes, which affect energy requirements, utility costs and process configurations. Since many separations are favored by low temperatures, pressures in most columns are established by the desire to use inexpensive cooling water as the heat sink in the condenser. For components with low vapor pressures, this criterion results in pressures below atmospheric. However, there appears to be some hesitancy to use vacuum distillation columns, particularly in azeotropic separations. Numerous papers simply fix the pressure arbitrarily at 1atm despite the fact that lower pressure could be achieved and still use cooling water.
This paper illustrates the significant economic advantages, both in capital investment and utility costs, of using vacuum distillation in some systems. The numerical example is taken from a recent paper in which an extractive distillation system to separate n-heptane from isobutanol is designed with column pressures fixed at 1atm. Our results show that vacuum operation can reduce total annual cost by 27%, despite an 8% increase in capital investment, because of a 37% decrease in reboiler steam costs.
Both accuracy and efficiency are of equal importance to the human pose estimation. Most of the existing methods simply pursue excellent performance, sacrificing massive computing resources and ...memory. Out of this consideration, we present a novel compact and lightweight framework to train more efficient estimators using knowledge distillation. Three distillation mechanisms are proposed in our method from different perspectives, including logit distillation, feature distillation and structure distillation. Concretely, the logit distillation regards the output of teacher model as soft target to stimulate the student model. The feature distillation distills the high-level features of the teacher model to assist the student. Unlike the above strategies, the structure distillation considers the problem in a global view, aiming at ensuring the student prediction contains quite abundant structure knowledge like the teacher. We empirically demonstrate the effectiveness and efficiency of our methods on two multi-person pose estimation datasets (COCO and MPII). Specifically, our model can achieve competitive performance with the most state-of-the-art methods and consume only 35% model parameters and GFLOPs of our baseline (SimpleBaseline-ResNet-50) on the COCO dataset.
A number of seawater desalination technologies have been developed during the last several decades to augment the supply of water in arid regions of the world. Due to the constraints of high ...desalination costs, many countries are unable to afford these technologies as a fresh water resource. However, the steady increasing usage of seawater desalination has demonstrated that seawater desalination is a feasible water resource free from the variations in rainfall. A seawater desalination process separates saline seawater into two streams: a fresh water stream containing a low concentration of dissolved salts and a concentrated brine stream. The process requires some form of energy to desalinate, and utilizes several different technologies for separation. Two of the most commercially important technologies are based on the multi-stage flash (MSF) distillation and reverse osmosis (RO) processes. Although the desalination technologies are mature enough to be a reliable source for fresh water from the sea, a significant amount of research and development (R&D) has been carried out in order to constantly improve the technologies and reduce the cost of desalination. This paper reviews the current status, practices, and advances that have been made in the realm of seawater desalination technologies. Additionally, this paper provides an overview of R&D activities and outlines future prospects for the state-of-the-art seawater desalination technologies. Overall, the present review is made with special emphasis on the MSF and RO desalination technologies because they are the most successful processes for the commercial production of large quantities of fresh water from seawater.
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•Several operation policies in batch distillation are evaluated.•The total reflux start-up is found to be an unnecessary step in most cases.•An efficient decanter is essential for a ...single-batch approach.•A moderate decanter performance is adequate for a sequential-batch approach.•Distillation with no reflux is preferred over 70% aqueous phase return fraction.
Heteroazeotropic batch distillation of methyl isobutyl ketone-water binary mixture is investigated, seeking a reliable operation for dehydration of methyl isobutyl ketone (MIBK). The dynamic batch distillation module (BatchSep) of the commercial package Aspen Plus V.12.1® is applied for simulations. An initially fed unit at atmospheric pressure is simulated from the heating-up step until it reaches the desired MIBK purity of 99.8 wt%. Three configurations, namely conventional batch distillation unit (Mode I), batch distillation unit with decanter (Mode II), and a simple distillation unit (Mode III), are compared in a wide range of operating conditions. The effects of condenser temperature and the number of theoretical stages are also examined. According to the results, applying a decanter (Mode II) with a return fraction of over 0.75 for the MIBK-rich phase and below 0.4 for the aqueous phase provides higher MIBK recovery than the maximum achievable value in a conventional unit (Mode I), with almost no increase in process time. A perfect decanter offers an almost complete MIBK recovery, which is about 5% over the maximum value by conventional units (Mode I). Moreover, cutting the reflux (Mode III) offers the fastest way to the desired product but provides the lowest MIBK recovery value. The aqueous phase return fraction does not significantly impact MIBK recovery, but if it exceeds 0.5, it remarkably affects the process time/energy cost. When maximum MIBK recovery rate/minimum energy cost is desired, applying a decanter (Mode II) with a return fraction above 0.5 for the MIBK-rich phase and below 0.55 for the aqueous phase yields a higher production rate and a lower energy cost per unit quantity of product compared to the best achievable values for a conventional unit (Mode I). A perfect decanter improvesproductionrateandenergyefficiencyby8 %overthe best case in a conventionalunit (ModeI). Also, operation without reflux (Mode III) is preferred over a conventional operation (Mode I) with a total return fraction over 0.7 due to its superior energy efficiency and production rate.
This study demonstrated a forward osmosis-membrane distillation (FO-MD) hybrid system for real human urine treatment. A series of NaCl solutions at different concentrations were adopted for draw ...solutions in FO process, which were also the feed solutions of MD process. To establish a stable and continuous integrated FO-MD system, individual FO process with different NaCl concentrations and individual direct contact membrane distillation (DCMD) process with different feed temperatures were firstly investigated separately. Four stable equilibrium conditions were obtained from matching the water transfer rates of individual FO and MD processes. It was found that the integrated system is stable and sustainable when the water transfer rate of FO subsystem is equal to that of MD subsystem. The rejections to main contaminants in human urine were also investigated. Although individual FO process had relatively high rejection to Total Organic Carbon (TOC), Total Nitrogen (TN) and Ammonium Nitrogen (NH4+-N) in human urine, these contaminants could also accumulate in draw solution after long term performance. The MD process provided an effective rejection to contaminants in draw solution after FO process and the integrated system revealed nearly complete rejection to TOC, TN and NH4+-N. This work provided a potential treatment process for human urine in some fields such as water regeneration in space station and water or nutrient recovery from source-separated urine.
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•An integrated FO-MD system for real human urine treatment was established.•Four equilibrium conditions were established for stable and continuous operation.•We revealed the trend of contaminants accumulation in draw solution.•FO-MD hybrid system had nearly completely rejection to contaminants in urine.•The product water of FO-MD had much higher quality than that of MD alone.
•Daily freshwater yield of cases 1, 2, 3, and 4 are 3.26, 3.572, 3.81, and 3.685 kg/m2, respectively.•Using PCM in cases 2, 3 and 4 extended the time of freshwater yield by about 5 h, 7 h, and 4 h, ...respectively.•Daily evaporative exergy of case 4 is greater than that of cases 1, 2, and 3 by 13%, 8%, and 2%, respectively.•Cases 2, 3, and 4 exhibit an increment of exergy efficiency 5%, 12%, and 16%, respectively compared to case 1.
In this experimental work, the energetic and exergetic performance enhancement of solar distillation system (solar still incorporated with PCM storage unit) is performed by using two techniques. First, pin fins heat sink (PF) is embedded inside the PCM to act as a thermal conductivity enhancer. Second, black steel mesh fibers (SWF) are employed in the solar still basin with PCM. In this regard, four cases of the solar stills are studied and compared conventional still: conventional solar still (without PCM), still with PCM (With PCM), still with PCM and pin fins heat sink embedded in the PCM (With PCM-PF) and still with PCM and SWF in the basin (With PCM-SWF). The energetic and exergetic performance of the four cases is evaluated and compared under the meteorological conditions of New Borg El-Arab City, Egypt. The results show that the total daily cumulative yield of distilled water of still with PCM, still with PCM-PF, and still with PCM-SWF are greater than of conventional still by 9.5%, 16.8%, and 13%, respectively. Additionally, the inclusion of the fins heat sink in the PCM increases the average daily energy and exergy efficiencies by 17.9, and 13.2%, respectively compared to conventional one. Likewise, the energy and exergy efficiencies of still with PCM-PF are higher than those of solar still with PCM by 7.7 and, 6.8%, respectively. Furthermore, placing SWF in the basin of still with PCM significantly enhances the daytime energy and exergy efficiencies with a considerable reduction of these values in the nighttime. The total daily evaporative exergy for still with PCM-SWF is greater than those of conventional still, still with PCM, and still with PCM-PF by 13, 8, and 2%, respectively. Also, still with PCM, still with PCM-PF, and still with PCM-SWF exhibit an increment of the daily exergy efficiency 5.9, 13.2, and 17.3%, respectively compared to still without PCM. Still with PCM-PF achieved the highest accumulated daily water productivity and energy efficiency but still with PCM-SWF attained the highest daily exergy efficiency with nearly no additional cost.
•Nanofluids benefits in heat engineering applications.•Improving the main mechanisms in solar distillation by means of nanofluids.•Identification of nanofluids key parameters in solar ...distillation.•Perspectives with nanofluids: challenge in direct desalination systems.
The current paper reviews a comprehensive outlook about the role of nanofluids in many fields especially in solar energy desalination technologies. Benefits of using nanofluids were highlighted from the angle of their positive effects on the solar stills (direct solar distillation) thermal performances improvement with acceptable consequences. Undoubtedly, nanofluids showed relevant characteristics and a promising large applicability, based on enhancement of thermal conductivity in comparison to basefluids free from additional metal or metal oxide nanoscaled particles. The behaviors of nanofluids in such configurations were deeply weighed up mainly by means of the experimental investigations issued from the open literature. An attempt based on critical analysis has been carried out to confront the different results. The plan of this review consists of exhibiting the performed researches through several facets, mainly objectivity of the studies and the results, mathematical models and data measurements. It was observed within the foregoing contributions many stagnant issues that should be taken into account, namely few works have analyzed nanofluids in solar still active configurations. Moreover, further investigations are required to examine the effects of nanoparticle size, shape of the nano grain, amount of the nanoparticles, stability of the nanofluids and the dispersion procedure.
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•A novel submerged vacuum membrane distillation module that utilizes solar energy is developed.•Solar evacuated tube collectors are used as the feed container.•The system achieved a ...stable water production under different scenarios (weather profiles).•Feed agitation enhanced the water production rate by 22%.
Submerged membrane distillation (S-MD) has been proposed as an alternative to conventional cross-flow MD systems to desalinate hypersaline water. In conventional S-MD systems, the hydrophobic membrane is submerged in the feed water tank that is directly heated by an electric heating element, eliminating the need for feed pumping. In this study, a solar-heated submerged vacuum membrane distillation (S-VMD) system that uses an evacuated tube collector as the feed container is proposed. Indoor tests under steady-state operating conditions and daily outdoor tests under ambient weather conditions were conducted to investigate the system’s functionality. The effect of two agitation techniques (aeration and internal circulation) to reduce temperature and concentration polarizations were studied. The daily performance tests revealed that the solar-heated S-VMD system can achieve a permeate flux of 5.9–11.1 kg·m−2·h−1 depending on solar intensity. The permeate flux was enhanced by 9% under aeration and by 22% under circulation in the outdoor tests. The water production per solar absorbing area can be as high as 0.96 kg·m−2·h−1. The system maintained a stable permeate flux and excellent water quality over a long-term operation. The small-scale system can provide fresh water in remote areas with limited natural resources.
Controllability features of the extractive distillation process and the pressure‐swing distillation process were studied with dynamic tools and compared in the case study of separation of a mixture ...of 50 mol % tetrahydrofuran and 50 mol % water. Process simulations with Aspen Plus and Aspen Plus Dynamics were carried out to obtain 99.9 mol % product purity. Control structures for the two distillation techniques were determined. Load rejection studies were completed for ±10 % feed throughput and ±10 % feed composition disturbances, for both processes. The comparison of the dynamic responses, integral absolute errors, and integral square errors shows that the pressure‐swing distillation process has better controllability features than extractive distillation.
The dynamic controllability, in the time domain, of extractive and pressure‐swing distillation in tetrahydrofuran dehydration is investigated while the systems are subjected to feed rate and feed composition disturbances. The results indicate that the pressure‐swing distillation has better controllability features.
