Abstract: Technologies for the emission and control of pollutants have been widely applied in coal-fired power plants in China to control the emissions of SO2, NOx, and particulate matter (PM). SO2 and NOx belong to the pollutants of major elements, with PM pertaining to the solid products. Control technologies for the above three pollutants, such as flue gas desulfurization, selective catalytic reduction, and electrostatic precipitators, have been proven to be highly efficient at removing the abovementioned pollutants in practical settings. The emission and control of Hg pollutants have also been extensively studied. However, control technologies for pollutants from trace elements, including Cd, Cr, Pb, Se, and As, which are also hazardous to long-term human health and the ecosystem, must be further developed both experimentally and theoretically. As a first step in future studies and analyses, the development of accurate and reliable methods for generating trace element pollutants is extremely important for the development of their future control technologies. In this paper, different ways of generating trace elements pollutants in simulated flue gas have been summarized and compared, including solution evaporation, combustion, sublimation, and hydride oxidization methods. The detailed procedures of these methods have been presented, and the advantages and disadvantages of each method have been discussed in detail. The findings indicate that the solution evaporation method is simple and feasible, but includes water vapor and other possible gaseous by-products that will have a negative effect on the results of subsequent experiments. The combustion method offers a realistic simulated flue gas, although factors related to the fuel or combustion conditions might influence the results and the product constituents are somewhat complex. The sublimation and hydride oxidation methods provide the most accurate trace element pollutants, but they are only suitable for the generation of certain types of gaseous trace pollutants and the installation of the hydride oxide apparatus is complicated. The applicability of these methods has also been discussed carefully in this study. A joint method for generating trace element pollutants has been proposed to obtain results that are closer to the actual situation and more precise than those obtained using any single method.
Abstract: The study of multi-field coupling of rocks has been carried out for decades, including the effects of single physical field, two-field coupling, and three-field coupling of rocks. However, the occurrence environment of rock mass in deep mining of mineral resources and underground space development is very complex. Thermal–hydrological–mechanical–chemical (THMC) multi-field coupling effect will occur in rock mass under high temperature, high osmotic pressure, high stress, and complex hydrochemical environment. The multi-field coupling of rocks is not the simple superposition of multiple physical fields, but the mutual influence and action of each physical field. The research on fracture evolution, deformation mechanics mechanism, mechanical constitutive and coupling model construction was comprehensively analyzed. Based on the analysis of rock strength theory, the development of a rock multi-field coupling constitutive model and a rock creep constitutive model were obtained. There are some differences in the research focus of multi-field coupling of rocks for different industries. The multi-field coupling of rocks not only involves the development of mineral resources, oil and gas fields, geothermal resources and other resources and energy fields, but also water conservancy and hydropower engineering, alpine engineering, underground engineering, underground nuclear waste disposal, and deep buried energy storage. Under the action of high stress, seepage, high temperature and chemical action, not only will the coupling effect occur, but the physical and mechanical properties of rock itself will be affected. It is of great practical significance to analyze and study the mechanical properties of rocks under the action of multi-field coupling for preventing accidents and ensuring engineering safety. Finally, the key and difficult points of rock multi field coupling research and the direction of future research were discussed, which provides a reference for engineering practice and related problems.
Abstract: China has maintained the world’s highest zinc production for many years, which has generated a tremendous amount of zinc slag, and 60% of which has not been effectively treated. Most of this slag is zinc leaching residue produced by the hydrometallurgical processing of zinc. The accumulation and storage of zinc leaching residue requires large tracts of land and harmful elements like arsenic and cadmium in the residue contaminate the surrounding soil and groundwater. From another perspective, zinc leaching residue represents a solid waste resource with a very high comprehensive utilization value. For example, many valuable metals are present in zinc leaching residue, including zinc, lead, and silver, which have high recovery values. In addition, zinc leaching residue can be fully utilized to produce cement, glass, ceramics, and a range of chemical materials. The comprehensive recovery and total material utilization of zinc leaching residue would help to significantly reduce the burden of its storage. This paper summarized research progress on the recovery of valuable metals from and the total material utilization of zinc leaching residue. Two main methods were used to recover valuable metals from this residue: pyrometallurgical and hydrometallurgical processes. Based on a detailed comparative analysis of the advantages, disadvantages, and feasibility of various typical recovery processes, this paper proposed a combined method of bioleaching and chloride leaching for the efficient extraction of zinc, lead, and silver from zinc leaching residue. This combined method has good applicability to different types of zinc leaching residue and good prospects for industrial application. In addition, this paper introduced the progress achieved in the total material utilization of zinc leaching residue and the future development prospects for utilization technologies. The total material utilization of zinc leach residue should be developed to product high-performance, sophisticated, environment-friendly and energy-efficient materials. Greater economic benefit can be gained while realizing clean production in the zinc industry.
Abstract: Currently, energy demand and consumption problems have become a focus issue due to rapid economic growth, environmental pollution, and energy shortages. Hence, new technologies must be explored and developed for the recovery of wasted energy or to harness solar energy. Thermal energy storage will not only improve energy utilization efficiency and store wasted heat; it will also ease the problem of energy supply and demand. Thermal energy storage is considered to be one of the most efficient approaches for the sustainable control and utilization of energy. Organic phase-change energy storage as a strategy for thermal energy storage has attracted widespread attention in recent years by virtues of its high latent storage capacity, suitable phase-change temperature, chemical and thermal stability, non-toxicity, and nearly absent supercooling properties. However, the leakage problem and low conductivity of organic phase-change materials during the phase-change process hinder their practical application. Leakage can cause serious environmental damage and reduce thermal energy storage. Low thermal conductivity can result in a large temperature gradient and insensitivity to temperature changes, thereby reducing the heat transfer efficiency of phase-change materials. To solve the above issues, various encapsulation techniques have been developed and substances with high thermal conductivity have become a research hotspot. In this work, we summarized three main approaches—porous absorption, microencapsulation, and electrospinning—to prepare shape-stabilized phase-change materials. For porous absorption, we identified some widely available, low-cost renewable materials that can be used as support material for fabricating composite phase-change materials, such as biomass-derived wood, winter melon, potatoes, and cotton. In addition, the energy conversion mechanism of composite phase-change materials was discussed. The applications of phase-change materials in solar absorption refrigeration systems, solar energy systems, energy storage systems for buildings, passive thermal management of batteries, cold storage, and photovoltaic electricity generation were summarized. Lastly, future research directions on composite phase-change energy storage materials were also proposed.
Abstract: Text detection is widely applied in the automatic driving and cross-modal image retrieval fields. This technique is also an important pre-procedure in optical character-based text recognition tasks. At present, text detection in complex natural scenes remains a challenging topic. Because text distribution and orientation are varied in different scenes and domains, there is still room for improvement in existing computer vision-based text detection methods. To complicate matters, natural scene texts, such as those in guideposts and shop signs, always contain words in different languages. Even characters are missing from some natural scene texts. These circumstances present more difficulties for feature extraction and feature description, thereby weakening the detectability of existing computer vision and image processing methods. In this context, text detection applications in natural scenes were summarized in this paper, the classical and newly presented techniques were reviewed, and the research progress and status were analyzed. First, the definitions of natural scene text detection and associated concepts were provided based on an analysis of the main characteristics of this problem. In addition, the classic natural scene text detection technologies, such as connected component analysis-based methods and sliding detection window-based methods, were introduced comprehensively. These methods were also compared and discussed. Furthermore, common deep learning models for scene text detection of the past decade were also reviewed. We divided these models into two main categories: region proposal-based models and segmentation-based models. Accordingly, the typical detection and semantic segmentation frameworks, including Faster R-CNN, SSD, Mask R-CNN, FCN, and FCIS, were integrated in the deep learning methods reviewed in this section. Moreover, hybrid algorithms that use region proposal ideas and segmentation strategies were also analyzed. As a supplement, several end-to-end text recognition strategies that can automatically identify characters in natural scenes were elucidated. Finally, possible research directions and prospects in this field were analyzed and discussed.
Abstract: There are many practical engineering problems in the hydraulic fracturing of crack reservoirs, such as the maintenance of wall rock, the efficiency of reservoir's permeability and the prevention of groundwater hazard. In this paper, the control mechanism of fracture pressure under multi-field and multi-phase coupling in horizontal wells and the fracturing evaluation of crack reservoirs were studied deeply to address these issues. Firstly, the transformation effect of the perforation concentration on the original stress field was analyzed. Secondly, the permeability of fracturing fluid in the primary fractures was considered. Finally, based on the strength principle of fracture mechanics, the calculation model of fracture pressure for horizontal wells in the reservoir was established. Furthermore, the influence of the spatial geometric parameters of the fracture field on the initiation pressure was analyzed, and the concept of the characteristic parameters of the fracture field was proposed. The results indicate that the coupling of fluid-solid multiphase in the fields of perforation stress, fracturing fluid permeation and original fracture leads to horizontal well hydraulic fracturing, and the characteristic parameter of fracture field plays a leading role in controlling the initiation pressure. Among them, the biggest controlling factor on initiation pressure is crack width. When the crack width of reservoir is within 200–700 μm, hydraulic fracturing has practical significance for improving reservoir permeability, which solves the problem about the quantification of initiation pressure and the fracturing evaluation in crack reservoirs. By calculating initiation pressure and contrasting to engineering example, it is found that the productivity of the sandstone reservoir is very ideal in the H8 section of the eastern Sulige gas field after hydraulic fracturing, and the theoretical value of fracture initiation pressure is in good agreement with the measured value, which verifies the correctness of the model. These can provide theoretical basis for fracturing construction of horizontal wells.
Abstract: Red mud is a solid waste produced in the process of bauxite refining alumina, with high alkali content, and its treatment methods are mainly stacking and ocean dumping, which not only occupy a large amount of cultivated land and pollute land and water sources, but also have high safety risk. The preparation of red mud-based filling materials to fill the underground goaf can improve the utilization rate of mineral resources and reduce the harm of red mud to the environment, which has the effect of killing two birds with one stone. In view of the problems of low utilization rate of bayer red mud in mine filling system, low strength, bleeding and shrinkage in filling materials slurry with low concentration, the effects of the addition ratio of fly ash, desulfurization gypsum, lime and initiator on the early strength and volume stability were studied in this paper. Scanning electron microscope- energy dispersive spectroscope (SEM-EDS) and X-ray diffraction (XRD) were used to analyze the hydration mechanism of the filling materials. The results show that when the ratio of red mud to fly ash is 4∶6, the mechanical properties of the filling material are the best. Desulfurized gypsum promotes the formation of ettringite. Lime promotes the pozzolanic effect of fly ash. The composite activator can accelerate the hydration process of red mud and fly ash. All of this enhance the red mud backfill strength. The filling materials 28 d compressive strength is 3.35 MPa, and the initial and 60 min fluidity are above 200 mm. Microscopic test results show that the hydration products of hardened paste are ettringite, lawsonite, silica aluminate gel, which fill the pores and improve the strength of slurry. Through adding activator, activating red mud activity and designing low concentration filling material, it is the direction of mass and green utilization of red mud, desulfurization gypsum and other solid wastes. The utilization ratio of solid waste of red mud filling materials reaches 92%, no bleeding, no shrinkage, and has high economic value and environmental value.
Abstract: Aluminum alloys are widely used in cutting-edge technologies and emerging strategic industries, namely aerospace, high-speed rail transportation, electric vehicles, advanced functional materials, new energy storage, and conversion devices. The processability as well as the mechanical properties of aluminum alloys can be improved via the addition of trace scandium. The ultrasonically assisted molten salt electrolysis is a promising, short technical route for large-scale preparation of low-cost, Al–Sc-based alloys characterized by uniform and fine strengthening phases. At present, it is still unclear if that is the case for the ultrasonic refining mechanism of the Sc-bearing ternary phase. This study aims at clarifying the ultrasonic refining mechanism on the strengthening phase containing scandium. Two Al–Sc based alloys were prepared using ultrasonically assisted molten salt electrolysis while the effect of ultrasound on the morphology and size of the Sc-bearing ternary phase was studied using optical microscope, scanning electron microscope, and X-ray diffraction meter. The results show that the synergetic ultrasound facilitates the transformation of the ternary AlSiSc phase from the coarse rhombic tubes (~205 μm) to the short rod (40 μm). The cluster size of ternary AlCuSc phase is also greatly reduced from ~100 μm to ~30 μm. The ultrasonic refining mechanism is mainly related to the increase of the nucleation rate of the primary Al3Sc particles which are greatly refined and dispersed in the alloy melt before the solidification stage. The refinement of the Sc-bearing ternary phase is considered to be caused by the fine and disperse Al3Sc particles serving as nuclei. Furthermore, ultrasound can also aid the uniform distribution of solute field and prevent the precipitation of coarse Al3Sc phase. The effect of ultrasonic refinement of the ternary rhenium-containing phase is mainly present at the solidification stage after electrolysis.
Abstract: Extensive efforts have been made to remove “harmful” inclusions during the steelmaking process. However, the concept of “oxide metallurgy” was proposed, where fine inclusions are used to induce the formation of acicular ferrite and pin the grain boundary, thus enhancing the low temperature toughness of the heat-affected zone (HAZ). The technology of improving the toughness of HAZ by forming TiOx?MgO?CaO fine particles (ITFFP) in steel has been successfully applied to the trial production of 30 mm (H30) and 60 mm (H60) thick high heat input welding EH420 offshore steel. The mechanical testing results show that the yield strength, tensile strength, and elongation of H30 steel are 461 MPa, 579 MPa, and 26%, respectively. In addition, the yield strength, tensile strength, and elongation of H60 steel are 534 MPa, 628 MPa, and 24.5%, respectively. The tested H30 and H60 steels achieved the national standard of EH420 offshore steel. The effect of ITFFP technology on the microstructure and impact toughness in the HAZ of H30 and H60 steels subjected to a 200 kJ·cm?1 heat input were investigated using a Gleeble-3800 welding simulation machine and Charpy impact tests. The results indicate that the CaO(?MgO)?Al2O3?TiOx?MnS formed in the tested steels induces the formation of acicular ferrite, and thus significantly improves the impact toughness. Additionally, electrode-gas welding with heat inputs of 247 kJ·cm?1 and 224 kJ·cm?1 was applied to H30 and H60 steels. The experimental results show that the impact absorbed energy of the weld in H30 tested steel is larger than 74 J at ?40 ℃, and the HAZ exhibits an absorbed energy larger than 115 J at ?40 ℃. In addition, the impact absorbed energy of the weld in H60 tested steel is larger than 91 J at ?40 ℃, and the HAZ exhibits an absorbed energy larger than 75 J at ?40 ℃. The impact absorbed energy of welded joints is much higher than the requirement of the national standard (42 J).
Abstract: As the use of high-strength thick plates is increasing in marine engineering, bridge engineering, petroleum pipelines, and other fields, the required performance level of thick welded plates is also increasing. Oxide metallurgy technology, which is used to improve the toughness of heat-affected zones by controlling the formation and dispersion of high-melting-temperature oxide particles in steel, has attracted increasing attention by researchers in recent years. The effect of cerium on the welding performance of industrial quenched and tempered high-strength steel was investigated. Using a Gleeble 3500 thermal simulator, the coarse-grained heat-affected zones of high-strength steel were simulated with different cerium contents. The microstructures, austenite grains, and mechanical properties of the heat-affected zone were investigated by using optical microscopy, scanning electron microscopy equipped with energy dispersive spectrometry, and hardness testing. The results show that when the heat inputs are 25 kJ·cm?1 and 50 kJ·cm?1, the impact energies of the heat-affected zone of Ce-undoped steel are 84.8 J and 24.5 J, respectively. When the mass fraction of Ce is 0.0018%, the impact energies of the heat-affected zone are 110.0 J and 112.0 J, respectively. The different degrees of toughness of the two experimental steels indicate that the appropriate content of rare earth element can effectively improve welding performance. By comparing and analyzing the microstructures and prior-austenite grain sizes of the two experimental steels, it can be seen that with increases in the welding heat input, the microstructure of the heat-affected zone of the high-strength steel gradually transforms from martensite and lower bainite to upper bainite and granular bainite, and the average size of the prior-austenite grains in the heat-affected zone obviously increases. However, at the same welding heat input, the size of the prior-austenite grains in the heat-affected zone of Ce-doped high-strength steel is significantly smaller. The observed microstructure of Ce-doped steel is finer with a reduced content of brittle upper bainite, which significantly improves the welding performance of 700 MPa high-strength steel.
Abstract: The lead-cooled fast reactor (LFR) is one of six reactor concepts selected in the Generation IV Technology Roadmap and is perhaps the first to be applied commercially. Because the heavy liquid metal coolant has a severe corrosion effect on the core structure, the compatibility of the heavy liquid metal coolant and structural materials is recognized as a key limitation in the design and application of the LFR. Corrosion by heavy liquid metals such as liquid lead or lead–bismuth eutectic (LBE) is a physical or physical–chemical process involving surface oxidation, dissolution of material constituents, erosion corrosion, and fretting corrosion. Corrosion by heavy liquid metal can change the microstructure, composition, and surface morphology of structural materials, which will affect their mechanical and physical properties and lead to system failure. Currently, LFR research institutes are devoting great effort to the research and development of structural materials with good high-temperature mechanical properties and excellent corrosion and irradiation resistances. In this study, a series of experiments and analyses were performed on self-developed 11Cr?1Si ferritic/martensitic (F/M) steel, including heat treatment tests, mechanical tests, corrosion tests in static lead-bismuth eutectic (LBE), and slow strain-rate tests (SSRT) in LBE. The heat treatment results show that 11Cr?1Si steel obtains a good combination of high strength and toughness after quenching at 950 ℃ and tempering at 750 ℃. 11Cr?1Si steel was found to have good LBE corrosion resistance after exposure in static LBE for 3368 h, with a sufficiently low oxidation rate and a continuous and compact surface oxide layer, which protect the base metal of 11Cr?1Si from LBE penetration. The SSRT results show that the ductility of 11Cr?1Si in contact with LBE is sensitive to temperature, with loss of ductility observed at 350 ℃ and 400 ℃, but not at 450 ℃.
Abstract: Single crystal germanium is an important infrared optical material, which is widely used in defense industry, microelectronics, and other fields. It is extremely difficult to achieve the required surface quality by conventional processing methods due to its hardness and brittleness. Practically, single-point diamond tool is used for micro-cutting. During the micro-cutting process of single crystal germanium, the change of cutting temperature leads to increased tool wear and material surface hardening, which results in poor surface quality and also reduces processing accuracy. Therefore, analyzing the micro-cutting temperature distribution of single crystal germanium has become the key to better understanding its heat transfer mechanism and for improving product quality and efficiency. Aiming to analyze heat transfer mechanism of single crystal germanium micro-cutting, the moving heat source method was used. It establishes the theoretical model with temperature rise during micro-cutting of single crystal germanium under the action of the heat source of the shear slip surface and the friction heat source of the rake face and the chip, respectively. The maximum cutting temperature of germanium at three cutting speeds, and the model was verified with the cutting temperature of homogeneous hard and brittle material single crystal silicon. Through a single-point diamond turning experiment, an infrared thermal imager was used to measure the temperature of the single crystal germanium micro-cutting process online. When experimental measurement results and the model calculation results are compared, it revealed that the maximum cutting temperature of single crystal germanium has displayed same trend under different cutting speeds, which is that the cutting temperature is directly proportional to the cutting speed. The relative error is found to be between 2.56% and 6.64%. The relative error of the maximum cutting temperature is 3.84%. The model can accurately predict the temperature field of single crystal germanium and also for similar hard and brittle materials, providing further theoretical support for analyzing its thermal effects.
Abstract: In recent decades, the small-scale pressure swing adsorption (PSA) oxygen generator has been widely used in the fields of home medical and hospital oxygen supply, anoxic environments, and plateau environments due to its cost effectiveness, operational flexibility, and adequate O2 volume fraction. The flexible optimization of PSA oxygen generation in response to changes in product demand is an important factor in its practical performance. To study the influence of a variable product flow rate on O2 volume fraction in the small-scale PSA oxygen generator, experimental equipment was set up, which consisted of a modified Skarstrom-cycle two-bed PSA system. The research results show that variations in the parameters at the lower product flow rate (≤10.37 L·min?1) may have a negative effect on oxygen countercurrent mixing, which can impair oxygen generation, and at higher product flow rates (≥13.57 L·min?1) may cause the negative effect of nitrogen breakthrough, which decreases the working capacity of the adsorbents in the bed. The O2 volume fraction at the lower product flow rate was improved by increasing the ratio of total oxygen in the purge gas to the total oxygen in the feed gas (P/F) and by decreasing the ratio of the highest adsorption pressure to the lowest desorption pressure (θ) during a cycle to suppress oxygen countercurrent mixing. The O2 volume fraction at the higher product flow rate was improved by increasing the P/F and θ values to improve the working capacity of the adsorbents in the bed. Accordingly, adjustments are made in the P/F and θ values at the lower and higher product flow rates to achieve optimal oxygen generation performances, enhancing the O2 volume fraction from 92.4% and 74.0% to 95.7% and 74.9% at the respective product flow rates of 3.55 L·min?1 and 19.88 L·min?1. This work is meaningful for the optimization of the parameters of the PSA oxygen production process at variable product flow rates.
Abstract: With the rapid growth of the UAV market, UAVs have been widely used in aerial photography, agricultural plant protection, power inspection, forest fire prevention, high-altitude fire fighting, emergency communication, and UAV logistics. However, “black flight” incidents of unlicensed flights and random flights frequently occur, which results in severe security risks to civil aviation airports, sensitive targets, and major activities. Moreover, owing to their characteristics of maneuverability, intelligent control, and low cost, UAVs can be easily used for criminal activities, which threatens public and national security. How to effectively detect UAVs and implement effective measures for UAVs, especially “black-flying” UAVs, is an active and difficult problem that needs to be urgently solved, and it is also an important research area in the field of anti-UAV systems. The research and development of anti-UAV systems is an important focus in national public security, and UAV identification is one of the key technologies in anti-UAV systems. Aiming at the problem of how to recognize UAVs, a sound-recognition method based on a convolutional neural network (CNN) was proposed. The UAV anti-jamming technology based on acoustic signals is not easily affected by an UAV size, shelter, ambient light, and ground clutter, and sound is an inherent attribute of UAVs, which is also applicable to UAVs in a radio-silence state. In this study, UAV sounds, bird sounds, and human voice within 100 m were collected and preprocessed; then the mel frequency cepstral coefficient and gammatone frequency cepstral coefficient eigenvalues were extracted. Support vector machine (SVM) and CNN models were designed to recognize UAV sounds and other sounds. The experimental results show that the SVM and CNN accuracies are 93.3% and 96.7%, respectively. To further verify the recognition ability of the designed CNN, it was tested on some Urbansound8K datasets, and its accuracy reached 90%. The experimental results show that a CNN is feasible for UAV recognition, and it has a better recognition performance than a SVM.
Abstract: The automatic recognition of a wagon number plays an important role in railroad transportation systems. However, the wagon number character only occupies a very small area of the entire wagon image, and it is often accompanied by uneven illumination, a complex background, image contamination, and character stroke breakage, which makes the high-precision automatic recognition difficult. In recent years, object detection algorithm based on deep learning has made great progress, and it provides a solid technical basis for us to improve the performance of the train number recognition algorithm. This paper proposes a two-phase efficient wagon number recognition algorithm based on the high-performance YOLOv3 object detection algorithm. The entire recognition process is divided into two phases. In the first phase, the region of the wagon number in an image is detected from a low-resolution global image; in the second stage, the characters are detected in a high-resolution local image, formed into the wagon number according to their spatial position, and the final wagon number is obtained after verification based on the recognition confidence of each character and international wagon number coding rules. In addition, we proposed a new deep learning network-pruning algorithm based on the batch normalize scale factor and filter correlation. The importance of every filter was computed by considering the correlation between filter weights and the scale factor generated via batch normalization. By pruning and retraining the region detection model and character detection model, the storage space occupation and computational complexity were reduced without sacrificing recognition accuracy (which is even slightly improved in our experiment). Finally, we tested the proposed two-phase wagon number recognition algorithm on 1072 images from practical engineering application scenarios, and the results show that the proposed algorithm achieves 96.9% of the overall correct ratio (here, “correct” means all 12 characters are detected and recognized correctly), and the average recognition time is only 191 ms.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
