•Cryogenic distillation process of CO2/CH4 separation is adopted to upgrade biogas.•New technique is developed to mitigate CO2 freeze-out in the distillation column.•With avoiding freezing, CH4 ...purity is enhanced from 60 to 97.2% by only one column.•High-purity liquid CO2 (>99%) is also generated on merit as a valuable by-product.•The system showed promising energy and cost efficiency against traditional methods.
In this paper, ideas for improving the cryogenic separation of CO2/CH4 mixture are drawn in order to upgrade biogas to biomethane, matching natural gas standards. On this basis, a novel technique is developed to mitigate CO2 freeze-out, which was a crucial obstacle upon implementing cryogenic approaches. In the proposed process, four-stage compression, one distillation column combined with flash separator, and sufficient heat recovery are adopted. The process is simulated in ASPEN HYSYS. The thermodynamic framework is validated against experimental data. Additionally, to reveal the efficacy of the added modifications, different configurations are modeled, starting from the simple system to the proposed one. The operating conditions – distillation pressure, reflux ratio, feed tray location, and inlet composition – are optimized towards minimizing energy demand and diminishing frosting danger. With avoiding frosting presence, the suggested process can boost CH4 purity from 60% up to 97.2% (mol), which has not been reached before in any previous studies using only one column, suitable for commercial uses. Also, a valuable by-product of high-purity liquid CO2 (above 99%) can be generated rather than being emitted into air. Compared to former cryogenic systems, the present process achieves not only the highest CH4 purity (97.2%) – even higher than previous study utilized two columns – but also the least energy penalty (0.38 kWh/Nm3cleaned_gas). Another comparison held against conventional approaches, the proposed process stands among the highest in CH4 and CO2 purities generated, witnesses the lowest in methane loss, is among the least in energy consumption, and shows high competitiveness in investment cost.
The extraction of essential oils is generally carried out by two main techniques: azeotropic distillation (hydrodistillation, hydrodiffusion, and steam distillation) and extraction with solvents. ...However, these traditional methods are a bit expensive, especially since they are extremely energy and solvent consuming. This work consists in studying two methods of extraction of the essential oils of Rosmarinus officinalis L.: microwave assisted hydrodistillation (MAH) and Clevenger hydrodistillation (CH). Several parameters have been studied: the extraction time, the yield, and the chemical composition of the essential oils as well as the efficiency and cost of each procedure. The results obtained revealed that microwave-assisted hydrodistillation makes it possible to minimize the extraction time of the essential oils in comparison with conventional hydrodistillation. Thus, the same yield of essential oils is obtained for 20 minutes only with MAH while it takes 180 minutes with CH. In addition, the quality of the essential oil is improved thanks to a 1.14% increase in oxygenates. In conclusion, the MAH method offers significant advantages over conventional hydrodistillation and can therefore replace it on a pilot and industrial scale.
As an essential transportation system in modern society, the significance of railway track safety cannot be overlooked. In recent years, computer vision systems and deep learning have been ...increasingly applied to unserved track defect detection. Although several algorithms have been proposed to address safety concerns, there is a need to enhance their efficiency and accuracy. This study introduces an efficient progressive enhancement network via knowledge distillation (PENet-KD) for detecting defects on the rail surface. In PENet-KD, we utilize knowledge distillation to transfer the expertise of the teacher network to the student network, resulting in a lightweight model with high speed and accuracy. Additionally, two modules were developed to gradually refine features. Initially, cross-modal information is dynamically fused using a regenerative high-level attention module based on a graphical convolutional network, which corrects the features derived from the encoder. Subsequently, in the decoding stage, significant semantic guidance information is obtained by applying 3-D attentional optimization to the highest layer features, thereby guiding the progressive distillation module to produce precise outcomes. Extensive experiments conducted on an industrial RGB-D NEU detection of rail surface defect (RSDDS)-AUG benchmark dataset demonstrate that the proposed PENet-KD outperforms the existing state-of-the-art (SOTA) methods, thus showcasing its generality and effectiveness. Notably, on the RSDDS-AUG dataset, PENet-KD achieved a maximum <inline-formula> <tex-math notation="LaTeX">E </tex-math></inline-formula>-measure gain of 1.4% and an <inline-formula> <tex-math notation="LaTeX">S </tex-math></inline-formula>-measure gain of 1.2% compared to the best current method. The code and models utilized in this research are publicly available at https://github.com/Wang-5ying/PENet-KD .
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•A ZIF-CoZn@PVDF-HFP nanofiber membrane for MD were fabricated via coaxial electrospinning technology.•The composite nanofiber membrane possessed prominent heat insulation and ...hydrophobicity.•The composite nanofiber membrane presented better anti-wetting capabilities.•The composite nanofiber membrane showed high permeate flux (21.8 L m−2 h−1) and salt rejection (99.99 %).
Membrane Distillation (MD) technology stands out for its cost-effectiveness and sustainability in diverse applications, such as high-salinity wastewater treatment and seawater desalination. However, conventional MD membranes frequently encounter challenges associated with inadequate permeate flux and insufficient anti-wetting performance. In the present study, we fabricated a series of ZIF-CoZn@PVDF-HFP composite nanofiber membranes with a core–shell structure via coaxial electrospinning. Here, PVDF-HFP functions as the core, while a blend of bimetallic Zeolitic imidazolate framework ZIF-CoZn nanoparticles and PVDF-HFP constitutes the shell. Through the utilization of the coaxial technology, functional nanoparticles achieve uniform and stably dispersed on the nanofiber surface, leading to the creation of a secondary rough structure in addition to the inherent roughness of single-nozzle electrospinning. This results in a surface with a 3D-hierarchical structure. The significantly amplifies the evaporation area on the surface of the composite nanofiber membrane, thereby bolstering the permeate flux in the MD process. Additionally, the incorporation of bimetallic ZIF-CoZn nanoparticles, recognized for their superior hydrophobicity and low thermal conductivity, improves the anti-wetting and heat-insulating properties of the composite nanofiber membrane, further advancing permeate flux performance. Using a 35 g L−1 NaCl as the feed solution, the optimal 1 % ZIF-CoZn@PVDF-HFP composite nanofiber membrane demonstrated a permeate flux of 21.8 L m−2 h−1, coupled with a salt rejection rate exceeding 99.9 %. Even during long-term MD testing, it maintained excellent insulation and anti-wetting capabilities. Our research offers a convenient and effective approach for fabricating anti-wetting composite nanofiber membranes.
An energy-efficient crude distillation unit (CDU) with a divided wall column was introduced to evaluate its performance compared to the conventional CDU. The large energy demand of the CDU in the ...United States-equivalent to more than a half of biofuel produced-was reduced by applying a divided wall column to the unit also known as the energy-efficient distillation column. The divided wall column lowers mixing at feed tray and raises the thermodynamic efficiency of the CDU. The performance evaluation of the proposed unit indicates that the unit saves 37% of heat supply over the conventional unit and cooling by 17%. The economic analysis shows a 9% of investment saving and a 26% decrease in the utility cost from the proposed unit. The thermodynamic efficiency of the proposed CDU is improved by 8%. The modification of conventional CDU was minimal, suggesting an easy revamping of the current conventional CDUs.
•Optimization framework for integrated ORC, RO and MD system.•A new index considering brine wastewater disposal mixing potential.•To assess the effect of the MD system in an integrated ORC-RO-MD ...configuration.
Supplying water for the growing population of the world has become an important issue, therefore, desalination industries are being developed to produce fresh water especially from seawater. Owing to the large energy consumption, the focus is finding alternative solutions to supply energy demand in desalination plants.
This work presents a model for the optimal integration of reverse osmosis and membrane distillation systems for seawater desalination through waste heat exploitation from an industrial process plant. In this regard, heat is exploited through organic Rankine cycle (ORC) and the generated power in this cycle is delivered to a reverse osmosis (RO) plant. The brine of the reverse osmosis plant is preheated utilizing the excess heat from the process plant and then is sent to the membrane distillation (MD) plant for further treatment. A multi-objective optimization approach is implemented in this work to take economic and environmental issues into accounts. The first objective function is to maximize the annual profit of the system. Additionally, an environmental measure has been defined in order to ensure that the maximum amount of fresh water production is obtained while the mixing of the brine disposal from this system with seawater is well done.
The results show that applying the membrane distillation in ORC-RO-MD integrated system, despite from the working fluid used in the organic Rankine cycle, considerably improves both economic and environmental aspects of the system when compared with ORC-RO system.
This work investigated the influence of dye class on permeate flux and color rejection by comparing direct contact membrane distillation (DCMD) and vacuum membrane distillation (VMD) applied to ...remediation of dyeing wastewater. The same operating system at the feed side was used and the driving force of each configuration was determined. Reactive and disperse dye solutions were considered, and a commercial membrane was employed. Final color rejection > 90.79% was obtained, and water was recovered at the permeate side (final normalized permeate flux up to 38.92 kg m
−2
day
−1
kPa
−1
). VMD showed higher normalized permeate flux when compared to DCMD. However, the performance according to dye class depended on MD configuration. Reactive dye resulted in higher permeate flux than the disperse dye solution in DCMD. Contrarily, disperse dye solution showed higher permeate flux in VMD. The formation of a concentration boundary layer at the permeate membrane interface was suggested with disperse dye solution in DCMD, decreasing thus the driving force. In VMD, the boundary effect is negligible with disperse dye solution. This result implies that the VMD performance in the textile industry may depend more on driving force rather than the dye class of the dyeing bath.
Knowledge distillation is a widely-used and effective technique to boost the performance of a lightweight student network, by having it mimic the behavior of a more powerful teacher network. This ...paper presents an end-to-end online knowledge distillation strategy, in which several peer students are trained together and their predictions are aggregated into a powerful teacher ensemble via an effective ensembling technique that uses an online supervisor network to determine the optimal way of combining the student logits. Intuitively, this supervisor network learns the area of expertise of each student and assigns a weight to each student accordingly►it has knowledge of the input image, the ground truth data, and the predictions of each individual student, and tries to answer the following question: “how much can we rely on each student’s prediction, given the current input image with this ground truth class?”. The proposed technique can be thought of as an inference optimization mechanism as it improves the overall accuracy over the same number of parameters. The experiments we performed show that the proposed knowledge distillation consistently improves the performance of the knowledge-distilled students vs. the independently trained students.
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•Online elitist multiple students ensembling distillation framework with a supervisor.•Supervisor learns student expertise using: input, ground truth, student predictions.•Supervisor - discarded at test time. Only the best student is extracted and used.•Extensive experiments show consistent improvements over vanilla trained students.
Abstract
Based on the solution of the mathematical description of the static mode operation in the distillation column, the concentration and temperature profiles along the height of the column were ...obtained, and the positions of the control plates were determined by calculating their gradients. The sequence of solving the material balance equations is determined under the assumption of the ideal mixing of the liquid on the control plate in the dynamic mode by the method of piecewise linear approximation. A reflux consuming control scheme has been developed according to the condition of minimum deviation time on the control plate of the current concentration value (x
t
) at each time interval t from its set value. This in turn makes it possible to anticipate changes in the concentration in the distillation for the time of a transport disturbance in the interval “control plate-top of the column” to provide the required quality of the top product.
Membrane distillation (MD) technology has been mainly used as a treatment method for saline or contaminated wastewater. Despite the rapid progress in material engineering and design of novel MD ...systems, principal challenges as temperature polarization (TP) and high-energy consumption per unit of produced water still restrict its commercialization. Recently, TP mitigation has been addressed by modification and configuration of MD systems or by using advanced materials for membrane fabrication. These include coating thermally conductive or photonic nanomaterials on the membrane's surface or using thermally conductive metallic based membranes that impact heat dispersion along the membrane. In addition, frame-like turbulence promoters and modified feed channels were shown to lower TP by enhancing the characteristics of the feed flow. Finally, systems able to directly heat the membrane's surface without preheating the feed solution, including solar, Joule, and induction heating, were shown effective in eliminating TP due to the higher temperature at the membrane-water interface in comparison to the temperature of the bulk feed solution. The review aims to summarize recent advances made in TP mitigation for MD systems and assess their influence on distillation efficiency. We include a brief description of the TP phenomenon and its observed effects on MD and describe advanced MD processes from the aspects of low or negligible TP, high distillate flux, and improved energy efficiency.
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•Temperature polarization (TP) impacts the performance of membrane distillation (MD).•The review aims to summarize recent advances made in TP mitigation for MD systems.•The ability to mitigate TP by surface modification is discussed in details.•The impact of flow promotors on TP mitigation was evaluated.•TP mitigation by self-heating MD (solar, Joule and induction heating) is presented.
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