Abstract: Currently, fossil fuels such as oil, coal, and natural gas are the world's primary energy sources. However, it is anticipated that these energy sources will be depleted in less than 100 years. As such, the development of new energy technologies is urgently needed. Biomass is one of the earliest sources of energy, and is used especially in rural areas where it is often the only one that is accessible and affordable. With the depletion of fossil fuels and increasing environmental degradation, biomass energy is attracting increasing attention around the world. Compared with fossil fuel, biomass is carbon neutral and sustainable, and has a smaller greenhouse gas footprint and lower SO2 emission levels. In addition, biomass energy remains the only renewable green energy that can be stored and transported. A number of countries have developed mature and proven combustion technologies, but these technologies are mainly based on wood biomass fuels. Unlike these developed countries, China is a large agricultural country with a limited amount of available firewood. As such, foreign experience cannot be fully applied in China. Although biomass fuels typically have relatively low fuel-N contents, this fuel-N between 70%-100% mass fraction is converted to NOx during combustion. In addition, the combustion of straw and other biomass fuels emits more NOx than wood fuels. In recent years, the air quality in China has become a serious public health concern, and NOx is a widespread atmospheric pollutant with significant impacts on human health and the economy. In this paper, an overview of biomass combustion technologies and NOx control systems in China and around the world was presented, and their advantages and disadvantages were summarized. The main bottleneck was identified in NOx control technologies with respect to biomass boilers in China and the development of new technologies in this field was predicted.
Abstract: Mold flux, which plays an important role in continuous casting, occurs when liquid slag on top of the molten steel infiltrates the gap between the shell and mold. During this process, a liquid slag film forms on the shell side, whereas a solid slag film forms on the mold side. The behavior of the slag film between the shell and mold has a significant effect on the sequence casting and quality of the slab surface. To investigate the in-mold behavior and heat transfer of slag film, researchers have simulated the formation of slag film in the laboratory. Measurements and theoretical calculations have been performed to study the heat transfer of slag film. In this paper, the experimental methods used to simulate the formation of slag film were described and the research related to heat transfer in slag film was summarized, including the interfacial thermal resistance, the thermal conductivity of the mold flux, radiative heat transfer, and optical properties of the slag film. The issues related to the formation and heat transfer of slag film were also identified, that require further investigation. The results of recent studies indicate that the hot thermocouple technique could be applied to observe the formation of slag film, and the copper-finger dig test could be used to obtain samples for investigations related to the microstructure of solid slag film. The interfacial heat resistance is reported to be between 0.0002 and 0.002 m2·K·W-1. The thermal conductivity of mold flux at 800℃ ranges from 1.0-2.0 m2·K·W-1, and increases with increased temperature. Crystals in the solid slag film not only increase the interfacial heat resistance, but also decrease the radiative heat flux by reducing the reflectivity of slag film. Furthermore, due to the resulting change in optical properties, the addition of transition metal oxides and fine particles dispersed in slag film may also influence the radiative heat transfer through slag film.
Abstract: Compared to the traditional electrochemical power source, lithium ion batteries (LIBs) have the advantages of higher energy density, longer life, and absence of any memory effect, and thus have attracted widespread research interest around the world. After Sony Inc. invented and produced the first commercial 18650 cell, many domestic and international research centers and companies have promoted the industrialization of LIBs. With the development of LIB technology, its application scope has extended from traditional consumer electronics to the new energy vehicles (NEVs) and energy storage fields. NEVs include pure electric vehicles (PEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). LIBs have been the main driving force for PEVs to date, and their cathode technology development process has had three generations, i.e., the first using LiCoO2, the second using LiMn2O4 and LiFePO4, and the third generation using Li(NixCoyMn1-x-y)O2. With the development of cathode and anode materials with higher capacities and the increased reliability of LIB safety technology (including separators with higher temperature resistance, electrolytes with higher voltage resistance, and other protection methods), cells with higher energy densities and longer lives can be developed and applied in the future. These improvements will enable PEVs to travel longer distances, which is the most critical issue to customers. This paper provides a review of the development status of the power battery industry and an analysis of the direction of LIB technology with respect to the following: (1) the cathode/anode materials used, including the higher Ni content in Li(NixCoyMn1-x-y)O2, along with its structural modification, and the stability of silicon and improvements in its efficiency and cycle life; (2) the design technology, including the electrode and structure designs developed using simulation technology, theoretical modeling, and experimental methods based on Taguchi design; and (3) advances in process technology, including mixing and coating processes. Based on the above information, a clear picture of the technical direction was provided for LIBs in the PEV field.
Abstract: Rock masses are typically anisotropic discontinuous materials composed of joints, fractures, and interlayers. Many instability and failure cases in geotechnical engineering have been induced by the expansion and transfixion of cracks in the rock masses. The mechanical properties and fracture characteristics of joints usually determine the bearing capacities and fracture modes of rocks. As such, the investigation of the crack initiation and expansion law, strength, and deformation characteristics of fractured rock masses has great significance. In this study, the rock samples investigated were taken from deep zones in the Sanshandao gold mine, where the surrounding rock masses are fractured and the maintenance costs of deep tunnels are very high. To investigate the mechanical behaviors of fractured rock masses, uniaxial compression experiments were conducted on granite samples with pre-existing cracks. First, cracks were generated in cylindrical rock samples by a water-jet cutter. Then, the rock samples with cracks and intact samples were compressively tested using a rigid testing machine (GAW2000) to determine their strength characteristics, crack initiation rules, and failure modes. The experimental results show that the uniaxial compressive strength (UCS) values of granite samples with pre-existing cracks are lower than those of intact samples, and the extent of the UCS reduction is closely related to β, i.e., the angle between the pre-existing crack and the direction of the external load. When β is 75°, the UCS values of the samples are at their minimum, and the reduction rate reaches 84.5%. These experimental results are in good agreement with the numerical solution of the maximum distortion energy criterion. Pre-existing cracks change the failure modes of rocks. With an increase in the dip angle of a pre-existing crack, the crack initiation angle increases monotonically, and the failure mode of the rock sample changes from shear failure to tensile failure. The mechanical properties and crack initiation characteristics of real-fracture rock samples can more accurately reveal the strength characteristics and failure modes of fissured granite, and thereby provide a scientific basis for the support of fractured rock masses and geotechnical engineering design.
Abstract: The purpose of this study was to reduce the loss of raw material calcium in the preparation of calcium silicate board and improve the synergistic utilization efficiency of solid waste. This test used a carbide slag-coal-based solid waste gelling system as the raw material to develop high-strength pure solid waste calcium silicate board. The main mineral components produced in the calcium silicate board and the variation in calcium silicate board strength with different proportioning were analyzed using thermogravimetry-differential scanning calorimetry (TG-DSC) and X-ray diffraction (XRD) test. The results show that the use of carbide slag completely substitutes cement. Fly ash and silica fume were mixed in mass ratio of 1:1 to prepare a mixed gelling system. Finally, the tobago mullite pure solid-waste calcium silicate template could be made with a water-cement ratio of 0.3. When silica fume was added in the mass percent of 0-10%, the bending strength of the template strengthened. Flexural strength of the calcium silicate board reached maximum when the amount of silica fume was 10%. Here, raw material particles composed of various dimensions were fully mixed. Also, crystals and hydrated gels closely interacted. Thus, the mechanical properties of the calcium silicate board significantly improved. The bending strength of the calcium silicate board tends to increase first, and then decrease with increasing NaOH dosage. The surface of the calcium silicate board was smooth when the mass percent of NaOH was 4% and mechanical strength reached a maximum of 11.8 MPa. This proved to be the optimum amount of added NaOH. The hydration reaction of the gelling system can achieve the best stimulating effect when 4% NaOH is added using scanning electron microscopy analysis. Moreover, the microstructure of material billets has an important impact on the final mechanical properties. However, the mechanical strength of the pre-cured calcium silicate board is not decisive of the final mechanical properties. The internal hydration gel number, shape, and connection are linked to each other inside the calcium silicate board; this is the key factor in determining the final mechanical properties of the calcium silicate board.
Abstract: Typical tailings discharge at low solids concentrations can cause serious environmental pollution and disasters, including tailings dam failures and the collapse of underground voids. High-density cemented backfill, which consists of unclassified mine tailings, binders, additive agents, and water, are increasingly being considered as simple and effective means for reducing the hazards of conventional slurry deposition and recovering water for recycling. Gravity thickening has been widely used in the minerals industry to increase solids concentrations of tailings. The prediction of gravity thickener performance by characterizing relevant material properties is of great importance, and batch settling and pressure filtration have proven to be the most useful methods for characterizing the dewaterability of tailings for gravity thickener performance predictions. In this research, batch settling and pressure filtration experiments were conducted to obtain dewatering data with respect to gel point, compressive yield stress, and hindered settling function by curve fitting. A predictive algorithm of steady-state thickening, proposed by Usher, was introduced and a rakeless deep cone thickener model was constructed to analyze the effect of flocculant dosage, underflow concentration, and mud height on solid flux and solid throughput. The results indicate that flocculant dosage has a greater impact on the settling zone than on the compaction zone, optimum thickening performance is obtained at a dosage of 20 g·t-1, and as underflow concentration increases, solid flux decreases. Solid flux was determined to be related to the concentration, and not influenced by mud height in the settling zone, whereas, in the compaction zone, solid flux is a function of concentration and mud height. In the range of the model's parameters, solid throughput is a function of concentration and mud height at heights less than 3.5 m, and the change law of solid throughput is similar to that of solid flux.
Abstract: As a key production quality index of grinding process, particle size is of great importance to closed-loop optimization and control. This is because controlling particle within a proper range can improve the concentrate grade, enhance the recovery rate of useful minerals, and reduce the loss of metal in the sorting operation; thus, the particle size determines the overall performance of the grinding process. In fact, it is not easy to optimize or control the practical industrial process because the optimal operation largely depends on a good measurement of particle size of grinding process; however, it is difficult to realize the real-time measurement of particle size because of limitations of economy or technique. Employing soft sensor techniques is necessary to solve the problem of particle size estimation, which is particularly important for the actual grinding processes. Considering that soft sensors are applicable in many fields, the data-driven soft sensor will be a useful tool for achieving particle size estimation. However, most of the iron ores processed in China are characterized by hematite with unstable properties, and the slurry particles exhibit magnetic agglomeration, giving rise to a large number of outliers in the collected data. In this case, there are gross errors in the particle size estimation model constructed based on the data and thus unreliable measurements. Meanwhile, the traditional feedforward neural networks have the disadvantages of slow convergence speed and easily fall into local minimum during the prediction process. A single model tends to lack superiority in sound generalization, and the performance of existing ensemble learning methods will be worse under outlier interference. Therefore, in this study, based on the improved random vector functional link networks (RVFLN), the Bagging algorithm is incorporated into an adaptive weighted data fusion technique to develop an ensemble learning method for particle size estimation of grinding processes. Experimental studies were first conducted through benchmark regression issues and then validated by the samples collected from an actual grinding process, indicating the effectiveness of the proposed method.
Abstract: A large number of tunnel projects are being constructed or will be constructed in the mountainous areas of western China. However, they are several safety challenges in the construction of deep hard rock tunnels because of the complex topographic and geological conditions, strong geological tectonic activities, large burial depth, and high in situ stress level. Uncertainty of tunnel wall parameters is one of main factors that contribute to tunnel construction risk. The traditional deterministic back analysis method cannot reflect the uncertainty characteristics of tunnel wall parameters; therefore, within the framework of Bayesian theory, a probabilistic back analysis method based on integrating multi-source monitoring information was proposed for determining the surrounding rock parameters of deep hard rock tunnel. First, the uncertainty sources of three parameters——uniaxial compressive strength (UCS), crack initiation stress to UCS ratio, and tensile strength for the widely used damage initiation and spalling limit approach——were analyzed, and their probabilistic statistical characteristics were determined. Second, a multi-output support vector machine (MSVM) was optimized by particle swarm optimization (PSO) algorithm, and an intelligent response surface model was established to reflect the nonlinear mapping relationship between back-analyzed parameters and field monitoring data. Last, by combination with the Bayesian (B) analysis method, the B-PSO-MSVM model was established, and surrounding rock parameters were dynamically updated by applying the Markov Chain Monte Carlo simulation algorithm. The method was applied to a deep hard rock tunnel, and parameters from probabilistic back analysis were utilized to calculate the point change of the tunnel vault settlement and peripheral displacement convergence as well as the depth of excavation damage zones, and the results agreed well with the actual monitoring data. It is shown that this method can be used to back analyze multi parameters of surrounding rock quickly and probabilistically, and parameters updated can be applied for risk assessment in construction safety and structural reliability design for the hard rock tunnel.
Abstract: High value-added utilization of solid wastes, such as the development of an inexpensive inorganic rubber filler, is one of the important approaches of sustainable development. Phosphoric acid, silane KH550, and steel slag were innovatively used to prepare modified porous steel slag, which partially replaced carbon black in this study. Modified porous steel slag was combined with carbon black, rubber, accelerator, sulfur, stearic acid, and zinc oxide to prepare a series of modified porous steel slag/rubber composite materials. This study investigated the mass ratios of phosphoric acid/steel slag, silane KH550/porous steel slag, accelerator/sulfur, and stearic acid/zinc oxide and the effect of the mass ratio of modified porous steel slag/carbon black on the mechanical properties of the prepared modified porous steel slag/rubber composite materials. At the same time, the influence mechanism was analyzed. The results indicate that the modified porous steel slag/rubber composites (the amounts of phosphoric acid, steel slag, silane KH550, carbon black, accelerator, sulfur, stearic acid, zinc oxide, and rubber are 1.2, 30, 0.3, 20, 0.8, 1.2, 0.8, 2.2, and 100 g, respectively) have good mechanical properties, with the tensile strength of 18.4 MPa, Shore A hardness of 68.8, and tearing strength of 44.6 kN·m-1. Phosphoric acid and silane KH550 can improve the pore and surface structures of steel slag. Appropriate ratios of accelerator/sulfur and stearic acid/zinc oxide can destroy the internal sulfur ring, which stabilizes the cross bond of rubber. Thus, a desirable package structure can be obtained by physically combining modified porous steel slag with rubber.
Abstract: With the development of the aerospace industry and the need for industrialized production, the casting processes of large diameter aluminum alloy ingot have come into focus in the industry. Among them, ultrasonic-assisted casting technology is widely used. Ultrasonic-assisted casting technology has the advantages of improving solute segregation of ingot and refining solidification organization. Other advantages have been widely reported. At present, most of the aluminum ingots used in the non-hot top ultrasonic casting process with very shallow liquid cavities, while the casting process does not involve the issue of ultrasonic vibration depth. With the use of a hot-top mold for ultrasound in the casting and casting process of large diameter ingot, the liquid level of aluminum melt is very high. The ultrasonic vibration depth will affect the cavitation range and finally affect the fine grain effect of the ingot. In the present study, a double source ultrasonic vibration system was applied in the process of semi-continuous casting of aluminum alloy with a diameter of 650 mm, and the influence of ultrasonic immersion depth on the macroscopic solidification structure of ingot was studied. Based on the test results of the solidified microstructure of aluminum alloy ingot and the simulation results of the sound field of the finite element software such as ANSYS, the mechanism of the microstructure refinement of the aluminum alloy ingot under different vibration depths was discussed at length. Study results show that, with increasing vibrational depth of the supersonic radiation rod, the whole cross section of the ingot is further refined, and grain shape changs from developed dendrites to equiaxed dendrites. Because of the end faces of the ultrasonic radiation rod, there is a vibrational peak at the fixed position, which leads to different ultrasonic cavities under different ultrasonic vibrational depths in the aluminum melt. This leads to different refinement mechanisms of the solidified structure.
Abstract: Obtaining a near-γ texture that parallels that of a rolling plane enhances the r value of steel, thereby improving its formability. A high-angle grain boundary with a misorientation greater than 45 degrees is another crucial factor contributing to the formability of steel. Steel's crack arrest capability is dramatically improved by increasing the density of the high-angle grain boundary. The primary factors associated with texture evolution include chemical composition, finishing delivery temperature (FDT), rolling speed, and cooling rate after final rolling, of which the FDT is the most critical. Previous studies, which emphasized only pipelines and interstitial-free steels, have suggested that there is a discrepancy in the relationship between FDT and texture, and this relationship remains unclear with respect to high-titanium high-formability ferrite-pearlite steel. In this study, the microstructure and crystallographic texture of a 600 MPa grade high-titanium high-formability ferrite-pearlite steel with differential FDT were investigated by scanning electron microscopy and electron backscatter diffraction techniques. The results reveal that its microstructure comprises ferrite and pearlite irrespective of FDT, but increases in the FTD cause an increase in the high-angle grain-boundary density. The primary microstructure is ferrite in both these samples, with a small amount of pearlite dispersed between the ferrite grains. The texture dramatically changes with elevated FDT. The intensity of all the textures significantly increases as the FDT increases from 850℃ to 875℃, with the transformation of a large amount of apparent near-γ textures, which is beneficial to formability. The intensities of near-α texture and γ texture are low in the sample with an FDT of 850℃, wherein the primary textures include {001}[110], {113}[471], {114}[110], and {223}[110]. The intensity of the textures disadvantageous for formability is stronger than that of the advantageous textures in the sample with a lower FDT, which constrains formability and should be avoided. A positive change was observed in the textures as the FDT increased to 875℃. A strong near-γ texture was transformed in the steel that was finally rolled at 875℃, and its fraction increased to 41% from 19.9% at 850℃. A strong {001}[110] rotated cubic texture also occurred in the 875℃ finally rolled steel, which is bad for formability. However, superior formability can be guaranteed in general as the transformation of more advantageous textures than disadvantageous textures was observed.
Abstract: Lithium titanate (Li4Ti5O12, LTO) is an important material to be used as an anode for LIBs (Li+ ion battery). LTO is a zero-strain material (i.e., no structural change occurs during Li insertion/extraction). Although LTO is a very safe material that can be used as an anode material in high and low temperature environment, its rate capability is compromised by its low electronic conductivity and poor Li+ diffusion coefficient. In the recent years, considerable research around the world has focused on improving LTO rate performance. Efforts to achieve better electrical conduction between LTO particles have included LTO particle size control, conductive-material surface coatings, and alien ion doping. However, in this study electrochemical properties were improved by changing the morphology of LTO. Based on traditional electrospinning technology, LTO fibers with a hollow structure were produced using a nested coaxial nozzle modified from the conventional spinning nozzle and coaxial cospinning with two different solutions. A comparison of this results with those of solid LTO prepared by traditional electrospinning technology demonstrates that hollow LTO is characterized by uniform particle size and no agglomeration, along with an obvious hollow structure, clear crystal lattice stripes, and good crystallization property. The specific surface of this hollow LTO is 1.3 times than its solid counterpart. This morphological change greatly improves the electrochemical performance of the material. Although the discharge specific capacities of both the solid and hollow LTO are close to the theoretical value for small ratios, the hollow LTO is superior to its solid counterpart at 20C. The discharge specific capacity of the hollow LTO can reach 130 mA·h·g-1 at 20C, and after 200 cycles, its capacity retention ratio remains at 98%, which suggests good stability. Cyclic voltammetry and AC impedance curves also show that the hollow structure reduces the degree of polarization and the electrochemical reaction impedance of LTO, which makes LTO more conducive to electrochemical reaction.
Abstract: The Ni3Al intermetallic compound is considered an excellent wear-resistant material. The addition of Cr3C2 particles can further improve the wear resistance of Ni3Al-based alloys. In order to elucidate the wear mechanism of Cr3C2/Ni3Al composites improved by the Cr3C2 strengthening phase, Ni3Al-alloy and Cr3C2/Ni3Al composites were prepared by the hot isostatic pressing process in this study. The mechanical properties and wear resistance of each phase in the Ni3Al-alloy and Cr3C2/Ni3Al composites were investigated using a nano-indentation instrument and a pin-on-disk friction and wear tester, respectively. The worn surface morphologies and the hardness of the subsurface layer under the worn surfaces of the Ni3Al-alloy and Cr3C2/Ni3Al composites were determined by a scanning electron microscopy (SEM) and a nano-indentation instrument. The results indicate that the hardness of the matrix phase in the Cr3C2/Ni3Al composites is significantly improved by the addition of Cr3C2 particles. The nano-hardness and the elastic modulus of each phase in the Cr3C2/Ni3Al composites gradually increase from matrix phase through diffusion phase to hard core phase. The mechanical properties between the matrix, diffusion, and hard core phases in the Cr3C2/Ni3Al composites present a gradient transition. This kind of structure distribution is good for enhancing the wear resistance of Cr3C2/Ni3Al composite materials. As for friction and wear conditions in this study, abrasive wear was the dominant wear mechanism, which occurred on the surfaces of the Ni3Al-alloy and Cr3C2/Ni3Al composites. The Cr3C2/Ni3Al composites showed a good wear resistant property. The carbide-strengthening phase can block up the cutting action of the wear debris, reduce the interaction between the wear materials, and decrease the thickness of the subsurface layer and the size of the wear debris, resulting in improved wear resistance of Cr3C2/Ni3Al composites.
Abstract: The primary pipe is a critical equipment that ensures the safe operation in a nuclear island, therefore; the primary pipe must have extremely high service performance in complex environments characterized by high pressure, temperature, and/or radiation. In addition, generation Ⅲ AP1000 nuclear power plants require a service life of 60 years, which pose great challenges to traditional manufacturing processes, such as casting and section-forging methods with partial welding. The currently popular free-forging method can enhance the resulting properties, but the repeated heating during multiple passes induce coarse grains, and these coarse grains are difficult to refine at key positions. With the rapid development of extrusion devices and optimized extrusion processes, the hot extrusion approach promises to produce primary pipes using a near-net shaping method. However, the huge size and complex shape of the two asymmetrical branches of the primary pipe brings enormous difficulties to the ordinary extrusion process. In this study, a novel simultaneous extrusion process was proposed, wherein a primary pipe with two asymmetrical branches is produced on a uniaxial extrusion press platform with the additional effect of a moving elevating ram. In this study, the principle underlying the simultaneous formation process was first analyzed with respect to the material flow during the extrusion process. The relations between the top-mandrel speed, lift cylinder speed, and branch size were derived to ensure the conditions necessary for the simultaneous formation of the two branches. Next, a finite element model of the proposed primary pipe extrusion process was constructed and the results verified its feasibility. The superiority of this process in preventing shear fracture at the branch root was evaluated by comparing its formation quality with that of traditional unidirectional extrusion. Finally, the influences of billet temperature, extrusion speed, and friction condition on the formation quality were studied to minimize the deformation load, refine the grain, and improve the homogeneity of the microstructure. The results of this research provide a method for reference and an analytical foundation for further development of practical approaches to the formation of primary pipes.
Abstract: Expressway hedgerow pruning robots need be able to recognize hedgerow and position themselves real-time, to plan an obstacle avoidance trajectory from the starting point to target point based on the position relationship between hedgerows and obstacles. Compared with the traditional industry manipulator, the expressway hedgerow pruning robot manipulator frequently works in unstructured environments with unknown obstacles and irregular scales. It is difficult to establish a mathematical model of obstacles precisely and comprehensively. The problem of real-time obstacle avoidance can be solved by path planning. Thus, aiming at the problem of real-time obstacle avoidance for expressway hedgerows pruning robot manipulator in an unstructured environment, a novel path planning method to avoid obstacle based on perturbed artificial potential field (PAPF) was proposed. According to the distribution of hedgerows and obstacles, simplified models of intelligent pruning robot and sphere enveloping obstacle were established. By considering the geometric relationship between manipulator and obstacle, the collision conditions of manipulator and obstacles were analyzed, and then, the collision avoidance space of manipulator was solved. The traditional artificial potential field method was associated with some problems such as local minimum point (LMP) and goals nonreachable with obstacles nearby(GNRON). In this study, a repulsion field adjustment strategy was presented to optimize the function model of potential field, and a repulsion field perturbation mechanism was introduced to adjust the effect of repulsion in order to flexibly avoid obstacles and successfully reach the target point. The path planning simulation of the designed manipulator was carried out in the collision avoidance space using PAPF. The simulation result shows that the manipulator smoothly jumps out of the LMP and reaches the target point successfully by accurately avoiding obstacles in real time, which verifies the effectiveness and feasibility of the proposed method.
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
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