查看更多>>摘要： A series of Ag2CO3 doping g-C3N4 composites labeled as AgCN_x-T (x represented the weight content of g-C3N4 and T referred to the hydrothermal temperature) were synthesized by a simple precipitation method. Various techniques such as BET, XRD, FTIR, SEM, and XPS were employed to explore the morphology structure and physicochemical properties of catalysts ascribed to the decoration of Ag2CO3 onto g-C3N4 and the results revealed that the hydrothermal temperature played an important role in the size dimension and crystallinity of Ag2CO3. It was worthy noted, the decorating of Ag2CO3 would provide more active sites on the catalyst surface, strengthen the regeneration and transmission of electrons, improve the utilization of 03, and promote the generation of reactive oxygen species, thus improving the catalytic ozonation performance. Amongst, the AgCN_(0.4)-100 composite had the optimal performance with 99.99% of OA degradation efficiency and 93.19% of OA mineralization. Moreover, the AgCN_(0.4)-100 exhibited satisfactory reusability for multiple consecutive cycles (=5) with low Ag ion release (< 0.3 mg L~(-1)). The reactive species (O_2~(·-) and ~1O2) were verified to take predominant roles in the reaction through the radical scavenger experiments and ESR spectra. Accordingly, an empirical kinetic model was established to predict OA concentration with the given operational parameters. Finally, the synergistic mechanism of OA degradation in catalytic ozonation system was also proposed, which possessed promising prospect in practical water treatment for environmental applications.
查看更多>>摘要： This study applied two advanced oxidation processes dominated by different reactive oxygen species (ROS), microwave-iron-hydrogen peroxide (Microwave/ZVI/H2O2) and microwave-iron-peroxydisulfate (MW Microwave/ZVI/PDS), to the degradation of refractory organic matter in the membrane bioreactor (MBR) effluent from landfill leachate treatment. The two processes were systematically compared according to their degradation efficiencies and transformation mechanisms toward refractory organic matter in MBR effluent. Controlled experiments and an influential factor analysis showed that the total organic carbon (TOC) removal efficiencies of the Microwave/ZVI/H2O2 and Microwave/ZVI/PDS processes were 74.48% and 64.40%, respectively. After treatment by the two processes, fulvic-like substances with a low molecular weight and high fluorescence frequency, and humic-Iike substances with a large molecular weight, stable chemical structure, and high aromaticity were substantially degraded. In addition, the Microwave/ZVI/H2O2 process had a better TOC removal efficiency than the Microwave/ZVI/PDS process over a wider pH range (3-11), which was mainly attributed to the different dominant ROS in the two processes. Both Fe3O4 and FeOOH were found in the reacted ZVI of the two processes, and the reaction mechanisms included Fenton-like reactions and adsorption-precipitation by iron (hydro)oxides, which were promoted by microwave irradiation. This study provided a theoretical reference for the efficient treatment of MBR effluent.
查看更多>>摘要： This paper proposes a risk informed decision-making framework for siting Major Accident Hazard Installations in Sri Lanka. It is named the 'Upper Bound FN curve' method. Generic failure rate data are utilized as country specific data are not available. FN Curves are derived for each process node of a Major Accident Hazard Installation using different failure rate data sets available in literature. The data sets giving the 'worst case' FN Curve for each process node is identified. These FN Curves are called the Upper Bound FN Curves. Using these curves, a composite FN Curve is developed which is compared against the country specific risk acceptance criterion line. If the risk is not acceptable, further safety barriers are introduced. Safety distances are then determined using a scaling factor developed in this study called the relative risk reduction factor (RRRF). The RRRF is determined based on the comparative position of the composite FN curve with respect to the criterion line. The proposed methodology was applied in a case study of liquefied propane storage tank. Guidelines for application of the proposed framework, interpretation of the 'Upper Bound FN Curve' method and estimation of safety distances are presented.
查看更多>>摘要： A series of vented hydrogen-air explosion experiments were carried out in an end-vented rectangular tube, and the effect of hydrogen concentrations varying from 10% to 50% on the flame evolution and the maximum overpressure inside and outside the duct were investigated. Experimental results reveal that the flame behavior was strongly affected by hydrogen concentration: the flame speed at the vent exit first increased and then decreased as hydrogen concentration was increased; a tulip flame and two bright fireballs were respectively observed within and outside the duct in some tests. Two dominant pressure peaks and two types of oscillations could be distinguished in the internal pressure curves, corresponding to the rupture of the membrane, venting of the burned gas, Helmholtz, and acoustic oscillations, respectively. Under the current experimental conditions, the pressure peak with a low amplitude owing to the rupture of membrane dominated the external pressure-time histories for hydrogen concentrations less than 25%. However, when the hydrogen concentration ranged from 30% to 50%, the pressure peak caused by the second external explosion become dominant. Besides, the influence of the external explosions on the internal pressure peak structures was discussed. As hydrogen concentration was increased, the maximum internal overpressure first increased and then decreased, whereas the maximum external overpressure increased monotonically. In this study, the maximum reduced overpressures calculated by Molkov's best-fit model agreed well with the experimental data for near-stoichiometric and rich hydrogen-air mixtures.
查看更多>>摘要： Reliability-based and risk-based methods for directing maintenance activities play a critical role in ensuring system safety and reducing unnecessary downtime. Those methods focus on preventive maintenance to avoid component failures and are applicable before unexpected disruptions occur. However, when disruptions are unavoidable, more attention should be paid to systems' recovery from unwanted changes. As a remedy of preventive maintenance, improving system restoration capacity of resilience through optimizing the system's maintenance asset and operational cost is an efficient way to help system restore from disruption conditions within an optimal cost. In this paper, a resilience-based approach is proposed to optimize maintenance asset and operational cost. A novel resilience metric is developed and utilized to quantify system resilience under various restoration capacities. The minimal acceptable resilience level (MARL) and maximal acceptable restoration time (MART) are proposed to determine the optimal maintenance cost. The proposed approach is applied to the Chevron Richmond refinery crude unit and its upstream process. The results show that it can help practitioners identify the optimal cost to ensure a system is resilient to respond to uncertain disruptions and provide a dynamic resilience profile to support decision-making.
查看更多>>摘要： The outstanding properties of metal-organic frameworks (MOFs) have proven that this type of crystalline adsorbent has great potential in CO2 capture applications. Most of the MOF research studies on new functional MOFs are conducted to improve the performance of CO2 gas adsorption. Combined studies of material evaluation and process design on engineering issues in CO2 capture applications in industry are rarely carried out. In this study, the authors attempted to address engineering issues by developing a biometal-organic framework with the bioligand L-glutamic acid that has more practical fabrication cost than petrochemical MOFs. Herein, the demonstration of the prediction and optimization of CO2 adsorption capacity, selectivity, and heat of adsorption using a multiobjective genetic algorithm (MOGA) combined with an artificial neural network (ANN). The success of the Bio-MOF fabrication was evaluated by scanning electron microscopy, N2 adsorption-desorption isotherm analysis, thermal gravimetric analysis, X-ray diffraction, and Fourier transform infrared spectroscopy techniques. Furthermore, volumetric measurements were performed at several temperatures (27, 35 and, 50 °C). The isosteric heat of adsorption was then evaluated by an indirect method with the Clausius-Clapeyron (C-C) and Chakraborty, Saha, and Koyama (CSK) equations. Then, CO2/N2 selectivity was analysed by IAST techniques by regressing the experimental data with the Langmuir-Freundlich isothermal equation. The computational study by ANN and MOGA also gives satisfying results in balancing three requirements criteria. Thus, this study paved the way for the development of low-cost scalable MOF fabrication in industry by applying the optimization and balancing principles of the three objective functions.
查看更多>>摘要： Nitrous oxide (N2O) is a key parameter for evaluating the greenhouse gas emissions from wastewater treatment plants. In this study, a new method for predicting liquid N2O production during nitrification was developed based on a mechanistic model and machine learning (ML) algorithm. The mechanistic model was first used for simulation of two 15-day experimental trials in a nitrifying sequencing batch reactor. Then, model predictions (NH4-N, NO2-N, NO3-N, MLSS, MLVSS) along with the recorded online measurements (DO, pH, temperature) were used as input data for the ML models. The data from the experiments at 20 °C and 12 °C, respectively, were used for training and testing of three ML algorithms, including artificial neural network (ANN), gradient boosting machine (GBM), and support vector machine (SVM). The best predictive model was the ANN algorithm and that model was further subjected to the 95% confidence interval analysis for calculation of the true data probability and estimating an error range of the data population. Moreover, Feature Selection (FS) techniques, such as Pearson correlation and Random Forest, were used to identify the most relevant parameters influencing liquid N2O predictions. The results of FS analysis showed that NH4-N, followed by NO2-N had the highest correlation with the liquid N2O production. With the proposed approach, a prompt method was obtained for enhancing prediction of the liquid N2O concentrations for short-term studies with the limited availability of measured data.
查看更多>>摘要： Metals in waste printed circuit boards (WPCBs) are usually recovered by hydrometallurgical processes. The reuse of leached residues, i.e. non-metallic components, has become a new challenge. In this study, the calorific value properties of leached residues with various particle sizes were studied to explore their potential utilization value. In order to realize the clean recovery of calorific value, bromine in resin was debrominated by pyrolysis. The morphology and phase of the leaching residue were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD), the results show that the residue is mainly composed of irregular resin particles. Subsequently, thermogravimetric analyzer was adopted to determine the pyrolysis characteristics, the resin particles were debrominated and pyrolyzed in a tubular furnace, the composition and functional groups of the pyrolysis products were analyzed by gas chromatography mass spectrometer (GC-MS) and fourier transform infrared spectroscopy (FT-1R). The results show that the optimal pyrolysis temperature of the residue is 300-400 °C. Both calcium carbonate and calcium hydroxide can achieve effective debromination. Pyrolytic oil, as the main pyrolysis product, is mainly composed of phenols. Finally, the calorific value of pyrolysis products was measured by calorimeter, and the calorific value of pyrolysis oil and pyrolysis residue reached 31.72 MJ/kg and 8.54 MJ/kg. Therefore, leached residues have the potential as a secondary fuel. The ultimate goal is realize the clean and harmless treatment, a comprehensive utilization method of the leach residue of metal components in WPCBs was proposed.
查看更多>>摘要： Alarm deadbands and delay timers are widely used in practice to remove false alarms. This paper proposes a method to design serial alarm systems that are composed of alarm deadbands serially followed by delay timers. Serial alarm systems are effective for removing false alarms with different types of alarm deviations and alarm durations, while alarm deadbands or delay timers alone are suitable only for one type of false alarms. A minimization problem is formulated to simultaneously design optimal values of the alarm deadband width and delay timer factor, for achieving a desired ratio of false alarms to be remove. Bayesian estimation approach is exploited to resolve a main technical challenge in achieving reliable estimates of joint probabilities of alarm deviations and alarm durations. Existing methods are confined to the isolated design of alarm deadbands or delay timers based on probability density functions of process variables, and are subject to a restrictive assumption that process variables are independent and identically distributed. By contrast, the proposed method is for the joint design of serially-connected alarm deadbands and delay timers; it is based on joint probabilities of alarm deviations and alarm durations, and does not require the restrictive assumption. Numerical and industrial examples are provided to illustrate the proposed method and compare with existing ones.
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