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Due to the strengths on compact structure and continuously operating ability, a rotary wheel device in rotating packed-bed configuration for adsorption process based on temperature swing has been proposed to achieve CO2 capture in engineering application. The 3D simulations of the rotary adsorption wheel for post-combustion CO2 capture based on non-equilibrium model have not been reported. In this study, considering the non-equilibrium of heat and mass transfer, the mathematical modeling was performed for temperature swing adsorption process in the rotary bisectional adsorption wheel for the cooling-and-feeding process and rinsing-and-heating process. Comparison with the experimental breakthrough data on the fixed packed-bed was performed to validate the model. Distributions of temperature and mass fraction in the rotary adsorption wheel were obtained in three dimensions, based on which a reasonable arrangement of fluid ducting should be set to meet the different concentration requirement of CO2 capture. There is an optimal rotating speed to make the adsorption-outlet N-2 concentration as high as possible and the desorption-outlet N-2 concentration as low as possible. Whether considering the adsorption enthalpy or not in the model can greatly impact the heat and mass transfer characteristics of rotary adsorption wheel. The effects of other parameters including particle size, porosity and adsorbent materials will be further analyzed in the future study.

Existing approaches for the 3D modeling of tunnels suffer from several problems, such as highly difficult data acquisition, redundancy of model data, large computational burden, and the inability of the resulting models to be monolithic. Therefore, solutions to the tunnel network modeling problem for complex structures need to be proposed and elaborated in detail. In this paper, a construction method for a three-dimensional tunnel general monomer model based on parallel pathfinding is proposed. Widely used tunnel CAD drawings are analyzed and read, a disordered arc ensemble intersection trend decision method is developed, and an automatic path extraction solution algorithm for unidirectional modeling of tunnel centerlines is constructed. By constructing and splicing the surface elements of the 3D model, a monomeric 3D tunnel model representing the complex network structure is finally obtained. Moreover, the modeling of shafts is realized based on the monomer model, allowing for the three-dimensional topological relationships between different sub-levels of the tunnel and the ground to be established. The automatic modeling method proposed in this paper is applied to the digital twin platform of a filling project in a mining area in Gansu province, China. The experimental results demonstrate that the 3D tunnel models constructed in this way have a smaller data volume, higher modeling accuracy, and more stable growth of modeling speed.

The Hapke two-layer medium model is an efficient way of simulating the spectra of dusty leaves. However, the simulation accuracy is low when the amount of dustfall is small. To solve this problem, we introduced the dust coverage factor and the linear spectral mixing model, to improve the accuracy of the Hapke two-layer medium model. Firstly, based on the assumption of spherical dust particles, the arrangement and accumulation mode of the particles were set, and the coverage factor and accumulation thickness of particles in the leaf area were calculated. Then, the coverage factor was used as an abundance. Endmembers were the spectra of dust-free leaves (measured) and dust-covered leaves (simulated by model), and the final simulated spectra were calculated using linear spectral mixing theory. This study presents the following findings: (1) When the coverage factor was calculated using the exponential model, the maximum difference between the corrected simulated spectra and the measured spectra was 3.4%, and the maximum difference between the original simulated spectra and the measured spectra was 15.2%. The accuracy of the corrected spectra is much higher than that of the original simulated spectra. (2) In this study, the physical thickness and optical thickness calculated by the Hapke two-layer medium model are equivalent, which is quite different from the actual dust accumulation. When the linear spectral mixing model is introduced, to modify the simulation value when the number of dust particles accumulated is less than one layer, the spectral endmember value of the simulated dust leaf is replaced by the simulation spectrum when the number of dust particles accumulated is exactly one layer. The calculated cor-rection spectrum has high rationality and credibility. This finding may be beneficial for monitoring amounts of dustfall accurately using remote sensing in mining areas.

Path planning is widely used in many domains, and it is crucial for the advancement of map navigation, autonomous driving, and robot path planning. However, existing path planning methods have certain limitations for complex field scenes with undulating terrain and diverse landcover types. This paper presents an energy-efficient 3D path planning algorithm based on an improved A* algorithm and the particle swarm algorithm in complex field scenes. The evaluation function of the A* algorithm was improved to be suitable for complex field scenes. The slope parameter and friction coefficient were respectively used in the evaluation function to represent different terrain features and landcover types. The selection of expanding nodes in the algorithm depends not only on the minimum distance but also on the minimum consumption cost. Furthermore, the turning radius factor and slope threshold factor of vehicles were added to the definition of impassable points in the improved A* algorithm, so that the accessibility of path planning could be guaranteed by excluding some bends and steep slopes. To meet the requirements for multi-target path planning, the improved A* algorithm was used as the fitness function of the particle swarm algorithm to solve the traveling salesman problem. The experimental results showed that the proposed algorithm is capable of multi-target path planning in complex field scenes. Furthermore, the path planned by this algorithm is more passable and more energy efficient. In this experimental environment model, the average energy-saving efficiency of the path planned by the improved algorithm is 14.7% compared to the traditional A* algorithm. This would be beneficial to the development of ecotourism and geological exploration.

When planning the development of the energy sector, significant attention is given to the energy from the renewable sources, amongst which the biomass has an important role. Computational fluid mechanics and machine learning models are the powerful and efficient tools which allow the analysis of various heat and mass transfer phenomena in energy facilities. In this study, the in-house developed CFD code and machine learning models (Random Forest, Gradient Boosting and Artificial Neural Network) for predicting the biomass trajectories, particle mass burnout and residence time in a swirl burner reactor are presented. Pulverized biomass combustion cases (fine straw, pinewood and switch grass) with various mean diameters (ranging between 60 and 650 μm) and different shape factors (within the range 0–1) are considered. The results of numerical simulations revealed a noticeably nonlinear dependence between the input values (particle types, sizes and shapes) and the output values (particle trajectories, mass burnout and residence time), mostly due to the complex swirling flow in the reactor. For particles with the mean diameters within the ranges considered, the mass burnout of particles generally decreases as the biomass particle shape factor increases. The residence time of pulverized biomass in the reactor shows in most cases a decreasing trend as the particle shape factor increases. Artificial Neural Network showed the best predictions for both particle mass burnout (RMSE = 0.083 and R2 = 0.937) and particle residence time (RMSE = 1.145 s and R2 = 0.900), providing the reliable assessment of these important indicators in the combustion process.

Semi-coke is a low-volatile solid carbonaceous fuel, which is quite difficult to combustion individually. Co-processing semi-coke with bituminous coal has the potential for efficient and clean utilization of powdery semi-coke, while the co-pyrolysis is an important step and the physical-chemical properties of residual solid products yield great influences on subsequent combustion characteristics and NOx formation. However, less work, if any, has aimed at the co-pyrolysis of bituminous coal and semi-coke, and the synergistic mechanisms on physical and chemical properties of solid products have yet to be fully understood. Even limited oxygen may generate remarkable influences on co-pyrolysis behaviors. In addition, limited oxygen is possibly present during pyrolysis process, which has been rarely paid attention to. In this work, the physicochemical properties of solid co-pyrolysis products of bituminous coal and semi-coke were investigated experiment, while the effects of multiple atmosphere composition were also emphasized, including CO2/N2 atmosphere, N2 atmosphere with limited O2, and CO2/N2 atmosphere with a little O2. The results indicate that the dehydrogenation and polycondensation of bituminous aromatics are observed over 700 °C. The semi-coke and bituminous coal have the synergistic effect in the co-pyrolysis process. In N2 atmosphere with little oxygen, the pore development mainly occurs as the O2 concentration is below 3%. The residual char is over-ablated with the further increasing oxygen content. When the atmosphere contains O2, a small number of nitrogen oxides are formed. The present work can provide a scientific guidance for the utilization of semi-coke in large-scale and the design of power plant co-fired with semi-coke. This work is also beneficial to improve combustion reactivity of blended fuel, determine the optimal blending ratio and control NOx emissions.

Unmanned aerial vehicle (UAV) oblique photography technology is widely used in a variety of fields because of its excellent efficiency, realism, and low cost of manufacturing. However, due to the influence of lighting, occlusion, weak textures, and other factors in aerial images, the modeling results can have the problem of an incorrect structure that is inconsistent with the real scene. The edge line of a building is the main external expression of its structure. Whether the edge line is straight or not will directly affect the realism of the building, so the restoration of the edge line can improve the realism of the building. In this study, we proposed and developed a method for the restoration of the edge line of a 3D building model based on triangular mesh cutting. Firstly, the feature line of the edge line was drawn using human–computer interaction, and axis-aligned bounding box (AABB) collision detection was carried out around the feature line to determine the triangular patches to be cut. Then, the triangular cutting algorithm was used to cut the triangular patches projected onto the plane. Finally, the structure and texture of the 3D building model were reconstructed. This method allowed us to actualize the physical separation of continuous triangulation; the triangulation around the edge line was cut, and the plane was fitted. This method was able to improve cutting accuracy and edge flatness and enhance the edge features of buildings and the rendering quality of models. The experimental results showed that the edge restoration method proposed in this paper is reliable and that it can effectively improve the building rendering effect of a 3D building model based on UAV oblique photography and can also enhance the realism of the model.

This article investigates the performance of a novel hybrid heat pump system, which is developed to recover the waste heat from the flue gas of domestic heating boiler. The purpose of proposed system is: to increase the return water temperature, to heat the boiler supply air, and to provide the hot air for indoor heating. The developed system consists of an air heater (acts as a dedicated mechanical sub-cooler), a multistage condensing economizer and a vapor compression heat pump. A test case of common building is considered for the performance assessment of system, which is based on the 4E analysis. For this purpose, ten refrigerants are selected. The results show that about 25.58% increase in the coefficient of performance can be obtained for the proposed model as compared to simple vapor compression cycle if operated with R245fa, which also have a lowest exergy destruction rate (38.27%) as compared to other studied refrigerants. From the perspective of improvement in boiler’s energy and exergy efficiency, R114 is used to be the most effective among other refrigerant (10.33% increase in energy efficiency and 4.74% increase in exergy efficiency). Parametric study results have shown that the variation in ambient conditions should be considered carefully while selecting a refrigerant to significantly improve the system performance, exergy efficiency, and relevant economics on regional basis. From the obtained results, a novel yet simple refrigerant selection approach is proposed which can also be adopted for other thermodynamic cycles.

In order to obtain the mechanism of the effect of CO2 on the NO heterogeneous reduction, density functional theory (DFT) was adopted to investigate the interactions between char and NO with the participation of CO2. The armchair configuration composed with several aromatic ring clusters was selected as the carbonaceous surfaces. Geometric optimizations were carried out at the B3LYP-D3/6-31G(d) level. Energies of optimized geometries were calculated at the B3LYP-D3/def2-TZVP level. The results show that, the surface carbonyl groups produced by the adsorption of CO2 combine with the adsorbed NO to desorb CO2, thereby providing adjacent carbon active sites for subsequent NO adsorption and N2 desorption. Thermodynamic studies show that the exothermic heat of this reaction is 853.9 kJ/mol, and the highest energy barrier is 297.0 kJ/mol without the participation of CO2, but the exothermic heat of this reaction is 593.7 kJ/mol, and the highest energy barrier is 214.1 kJ/mol with the participation of CO2. Kinetic studies show that over the temperature range of 298.15–1800 K, the reaction rate constants of rate-limiting steps are calculated with conventional transition state theory. The rate constant with the participation of CO2 is higher than that without the participation of CO2. In summary, CO2 plays a promoting role in interacting with NO and char and reducing energy barrier to form N2 directly.

Oxygen-enriched and deep-staging (OE and DS) combustion has drawn increasing attention due to its superior nitrogen oxide reduction efficiency and combustion efficiency. To clarify the NOx generati...

Self-excited thermoacoustic oscillations seriously threaten the operation of combustion equipment. Various active and passive control methods for self-excited thermoacoustic oscillations have been ...

A printed circuit heat exchanger (PCHE) is utilized to cool the compressor inlet air to increase the compression efficiency in a liquid air energy storage and liquid natural gas (LNG) coupled system, which can offer large-scale energy storage with significantly improved exergy efficiency and round-trip efficiency. In this work, the effect of pressure of air, incline angle, and hydraulic diameter on the performance of a compressed air–water PCHE with a semicircle cross-section was studied. The results show that PCHE can realize the intermediate cooling of air compression in the liquid air energy storage system, and the pressure variation of air shows a limited effect on the heat transfer of PCHE; however, the hydraulic diameter and the incline angle both affect the heat transfer and the flow resistance of PCHE, and the best incline angle is 15°.

Tar-rich coal has the potential to substitute the supply of oil-gas resources, which is abundant in China. The effective conversion of tar-rich coal into oil-gas products can promote coal utilization, reduce resource wastage, alleviate environmental pollution, and benefit carbon neutrality. Nevertheless, less work, if any, has been performed on the pyrolysis and mild oxidation behaviors of tar-rich coal in Northwestern China. The influences of limited oxygen addition and an extremely low heating rate on the micromorphology of the residual semi-coke are yet to be fully understood. Here, an experimental study on the pyrolysis and mild oxidation characteristics of tar-rich coal was conducted by the thermogravimetric analysis method, with further elucidation of the physical-chemical properties of the residual semi-coke. Experimental results show that an increase in the ultimate temperature of pyrolysis leads to a decline in the residue mass, while the mass loss from 500 to 550 °C presents the maximum elevation. Volatile matter is inclined to discharge from a certain direction, and the pores formed in various directions hold different possibilities. The organic components undergo both pyrolysis and slow oxidation with limited oxygen in the heating medium. Compared with an inert atmosphere, the mass loss under conditions of a small amount of O

Cofiring biomass syngas (BS) with pulverized coal under the oxy-fuel condition is a promising technology, which could encourage the utilization of biomass energy and reduce the emission of greenhouse gases. To investigate cofiring characteristics of biomass syngas and coal, a numerical study was conducted. The influences of oxy-fuel condition, syngas quality, and injection position on temperature distributions and flue gas components in boiler furnace were analyzed. To predict cofiring characteristics accurately under oxy-fuel conditions, a new refined weighted-sum-of-gray-gases model, HCN oxidation model, and NO-char reaction model were used. The simulation results show that syngas reburning and oxy-fuel conditions could reduce NO emission. The NO emission in O2/CO2O2/CO2O2/CO2 conditions is higher than that in air. Biomass syngas with higher calorific values contributes to higher furnace temperatures. Besides, biomass syngas with higher hydrocarbon components is beneficial to lower NO emission. Compared to pure coal combustion, NO concentration at the furnace outlet reduces by 40.2%, 69.0%, and 35.2% in the cases of cofiring with Type A, B, and C biomass syngas at a cofiring ratio of 10%, respectively. The injection position of biomass syngas also has crucial impacts on cofiring characteristics and NO emissions. NO emission has the lowest value when the biomass syngas is injected at the bottom level of the reburn zone. This study could provide a reference for optimization of boiler design and operation when cofiring biomass syngas with pulverized coal under the oxy-fuel condition.

The utilization of powdery semi-coke as a power fuel in pulverized coal-fired power plants has become a new and potential technique to consume the excess powdery semi-coke. The characteristic of low volatile results in poor combustion performance and high NOx emission, and to co-fire with bituminous coal is a practical strategy to address this problem. However, the co-combustion characteristics and the inherent interaction between semi-coke and coal remain insufficiently understood. In addition, the influences of secondary air arrangement, the boiler operation load, and the fuel type on co-combustion process are still unclear, which is urgent to be further explored. In the present study, experiments and numerical simulations were jointly utilized to inquire into the co-combustion behaviors and NOx emission features of semi-coke and coal. The results demonstrated that the “out-furnace method” was a suitable choice for small-capacity boiler when the proportion of semi-coke was 33%, due to the limited combinations of the semi-coke injection position. It was recommended that semi-coke was preferred to be injected from the middle layers of the furnace under the “in-furnace method” to improve the overall co-combustion performance. The critical value of the separated over fire air ratio in this study was 27.5%, over which a slight drop of carbon content in fly ash could come about. Moreover, the elevation in the proportion of separated over fire air gave rise to the significant decline of NOx concentration. The constricted secondary air arrangement was preferred to be employed due to the high boiler efficiency. The separated over fire air and the surrounding air needed to maintain a wide-open degree to prevent the increase of NOx emissions and the coking of nozzles. For the load reduction regulation method adopted in this study, the NOx concentration first rose and then dropped, while the burnout ratio decreased obviously as the operation load was reduced. Different combinations of coal and semi-coke generated significant influences on co-combustion behaviors within the furnace. The NOx generated by high-volatile fuel (bituminous coal) combustion was mainly affected by volatile-N, while the NOx generated by low-volatile fuel (semi-coke) was mainly impacted by char-N. This study is of guiding significance for the efficient and clean utilization and beneficial to the large-scale application of powder semi-coke in power plants.

Low calorific gas (LCG) is largely produced in industries and agricultures, but its utilization is difficult due to the poor combustibility and high NO x emission. The pilot ignition combustion has the potential to improve LCG’s combustibility and also reduce NO production with combining air stage approach. However, the complex atmosphere created under pilot ignition condition could complicate the NO reduction (by CH4) behavior and should be clarified. This paper is aimed at gain a deep insight on this issue by exploring the interaction between temperature and atmosphere, the individual role of α and CH4 concentration (or its ratio to NO), and the influence of CO and CO2 presence. The results show that with dropping α, the maximum NO reduction ratio increases, but a higher temperature is needed to achieve this value. Under fuel rich condition, NO reduction was accompanied with HCN formation, which must be considered to analyze the effective reduction. The CO2 generated from pilot flame or originally contained in LCG could inhibit the NO reduction, with this effect being more pronounced at a fuel rich atmosphere. For a CO/CH4 duel reactive LCGs, CO reduces the NO reduction ratio at lower temperature, but improves at higher temperature.

The electrolytic aluminum waste contains harmful components, such as fluorides. Sending it to coal-fired boilers seems to be a prospective scheme to achieve the harmless treatment of waste. However...

Zhundong high-alkali coal has been studied a lot owing to its abundant reserve but serious ash-related issues. Oxy-fuel combustion profits the reduction of pollutant emissions and coal blending alleviates the ash-related problems practically. Nevertheless, little work if any has been carried out on oxy-fuel co-combustion of Zhundong coal, while the influences of blending on the migration of iron and alkali alkaline-earth metals have yet to be adequately understood. This study aims to illuminate the release and migration behaviors of alkali alkaline-earth metals, iron and aluminum in oxy-fuel co-combustion via a lab-scale experimental system. Experimental results showed that the yield, color, bulk, and composition of ash were greatly temperature-dependent and significantly affected by the blending ratio in oxy-fuel co-combustion. As the blending ratio was 50%, the transformation and release features of iron, sodium and calcium in the blend with combustion temperature were close to those of non-Zhundong coal. The blending of Lingxin coal into Zhundong coal could benefit the transformation from NH4Ac-soluble calcium to H2O-soluble form, and facilitate the transformation of HCl-soluble aluminum and iron to insoluble form. The occurrence modes of elements and the ash yield of individual coal both exerted profound impacts on the element release ratio and chemical forms within ash of the blends. The present research has potential to offer an improved knowledge on the functional mechanisms of alkali alkaline-earth metals, aluminum, and iron on ash-related issues during high-alkali coal oxy-fuel co-combustion.