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China has abundant resources of tar-rich coal, and the in-situ pyrolysis extraction of oil and gas can not only achieve efficient, clean, and low-carbon utilization of tar-rich coal, but also alleviate the external dependence of oil and gas, which is one of the important development directions of tar-rich coal exploitation and utilization in the future. In this paper, the thermal and physical properties and distribution characteristics of tar-rich coal, the technological characteristics of surface pyrolysis and in-situ pyrolysis are described briefly. It focuses on the research status and progress of in-situ pyrolysis of tar-rich coal (including well layout, heating method, integration of in-situ gasification and pyrolysis, waste heat utilization, reservoir fracturing, and underground sealing technology). Also, the future development direction of tar-rich coal in-situ pyrolysis technology is prospected. The findings are summarized as follows: ① the cascade utilization is an important way for the surface pyrolysis of tar-rich coal. Well drilling in-situ pyrolysis can achieve underground oil recovery, but it is necessary to solve the insulation problem of long-distance transportation pipelines. Drilling in-situ pyrolysis is carried out through high-temperature medium or electric heating, and can use distributed energy from the mining area to heat the heat carrier fluid. ② It is recommended to use a composite heating technology with convection heating as the main method and others as auxiliary heating methods, which can use the residual heat from in-situ pyrolysis to preheat the heat carrier fluid, and the heat from the local oxidation reaction of coal seam can also be used in the in-situ pyrolysis process of oil-rich coal to reduce the heat injection energy consumption of heat carrier fluid. ③ The integrated technology of in-situ gasification and pyrolysis can effectively improve the utilization rate of thermal energy, but the gasification cavity needs to be filled. ④ In order to enhance the heat conduction efficiency of coal seam and reduce the migration difficulty of oil and gas products in coal seam, the porosity change law of reservoir fracturing and in-situ pyrolysis of oil-rich coal is comprehensively considered to control the fracture formation path and form the fracture network. ⑤ Based on the characteristics of the pyrolysis process of tar-rich coal, selecting suitable underground system closure technology can promote efficient energy utilization and ecological environment protection during the in-situ pyrolysis process of tar-rich coal, among them, the CO2 gas drive water sealing technology can not only realize the closure of the underground system, but also carry out oil and gas displacement and realize the geological storage of CO2.

Air staged combustion reduces NOx emissions, but increases the H2S concentration in primary combustion zone. The excessive H2S concentration near the furnace wall is an important factor that aggravates the high-temperature corrosion of the water-cooled wall. With large-scale renewable power integrated into the grid, the demand for flexible peak-shaving operation of traditional thermal power units has increased. The H2S concentration distribution near the furnace wall under different boiler loads deserves attention. Hence, the influence of different operating parameters of tangentially coal-fired boiler on H2S concentration distribution near the furnace wall was investigated by orthogonal test. A supercritical 600 MW tangentially coal-fired boiler was selected to establish a numerical model. The L16(45) orthogonal numerical conditions was designed to cover four boiler loads, including 100% BMCR, 75% THA, 50% THA and 35% BMCR. A user-defined SOx generation model was employed to calculate the H2S concentration distribution inside the furnace. The release of fuel sulfur and mutual transformation of sulfur components were considered. At the same time, the model included a multiple surface reaction model for describing the heterogeneous reaction between coke and O2/CO2/H2O, and the ratio of the gasification rate to the consumption rate for char particle was calculated. The results show that the high H2S concentration areas are mainly located below the bottom burner that on operation and between the top burner and SOFA nozzle. The main reason for the high H2S concentration in the latter area is that the tangential circle of flue gas increases gradually along the furnace height. The orthogonal analysis indicates that the average H2S concentration in the key area of the furnace wall under 35% BMCR load is 364 μL/L, which is significantly lower than that under the other loads. In addition, the impact of operating parameters on the H2S concentration in key areas follows the order of boiler load > primary air rate > excess air coefficient of main combustion zone > imaginary tangent circle diameter > vertical swing angle of burner.

The special geography of the plateau area leads to a series of problems in boiler operation. In this study, the absorption coefficients and total emissivity of flue gas were determined under different air pressures during air combustion using the Line-By-Line (LBL) method based on the HITEMP2010 database (High-temperature molecular spectroscopic database). The effects of pressure, temperature, and molar fraction (H2O and CO2) on the radiative properties of flue gas were analyzed. An improved Weighted-Sum-of-Gray-Gases (WSGG) correlation, which relates the absorption coefficients to temperature and total pressure, was proposed. The results show that the reduced total pressure diminishes the total emissivity of flue gas. The maximum differences in total emissivity along the path lengths for the four working conditions with a pressure drop from 0.101 325 to 0.061 655 are 0.093 4, 0.084 5, 0.091 1, and 0.084 3, respectively. For a larger molar fraction, the effect of pressure on the total emissivity is greater for shorter path lengths but not for longer ones. Similarly, the higher temperature would reduce the total emissivity of flue gas. The maximum differences in total emissivity along the path lengths for the four working conditions with a temperature increase from 1 000 K to 2 500 K are 0.273 6, 0.270 5, 0.251 5, and 0.250 5, respectively. For a larger molar fraction, temperature has a greater effect on the total emissivity for shorter path lengths but not for longer ones. Furthermore, increasing the molar fraction enhances the total emissivity of flue gas. The maximum differences in total emissivity along the path lengths for the four working conditions with a molar fraction increase from 1 to 2 are 0.088 1, 0.100 4, 0.088 9, and 0.100 6, respectively. For a higher temperature or lower pressure, the effect of molar fraction on the total emissivity is smaller for shorter path lengths but greater for longer ones. The maximum relative error of the improved WSGG model for the total emissivity of flue gas under different working conditions is 3.67%. It is a significant reduction in the error compared to that of the existing WSGG model. Therefore, the improved WSGG model is more accurate for air combustion atmosphere and sub-atmospheric pressure.

To accommodate the integration of renewable energy, coal-fired power plants must take on the task of peak regulation, making the low-load operation of boilers increasingly routine. Under low-load conditions, the phase transition point (PTP) of the working fluid fluctuates, leading to potential flow instability, which can compromise boiler safety. In this paper, a one-dimensional coupled dynamic model of the combustion and hydrodynamics of a supercritical boiler is developed on the Modelica/Dymola 2022 platform. The spatial distribution of key thermal parameters in the furnace and the PTP position in the water-cooled wall (WCW) are analyzed in a 660 MW supercritical boiler when parameters on the combustion side change under full-load and low-load conditions. The dynamic response characteristics of the temperature, mass flow rate, and the PTP position are investigated. The results show that the over-fire air (OFA) ratio significantly influences the flue gas temperature distribution. A lower OFA ratio increases the flue gas temperature in the burner zone but reduces it at the furnace exit. The lower OFA ratio leads to a higher fluid temperature and shortens the length of the evaporation section. The temperature difference in the WCW outlet fluid between the 20% and 60% OFA ratios is 11.7 °C under BMCR conditions and 7.4 °C under 50% THA conditions. Under the BMCR and 50% THA conditions, a 5% increase in the coal caloric value raises the flue gas outlet temperature by 32.7 °C and 35.4 °C and the fluid outlet temperature by 6.5 °C and 9.9 °C, respectively. An increase in the coal calorific value reduces the length of the evaporation section. The changes in the length of the evaporation section are −2.95 m, 2.95 m, −2.62 m, and 0.54 m when the coal feeding rate, feedwater flow rate, feedwater temperature, and air supply rate are increased by 5%, respectively.

The control of carbon emissions has already become a great social strategic problem in China which must be solved at present and in the future. It is imperative to carry out safe, efficient, and low-carbon utilizations in the coal industry under the target of achieving carbon emission peak. Tar-rich coal is abundant in western China. It is mostly combusted for power generation, which results in the wastage of valuable resources and serious environmental pollution. The in-situ pyrolysis process of tar-rich coal provides a new method for generating oil from coal. This method is to produce oil without mining coal while alleviating damage and pollution to geological formations. Compared with traditional coal mining methods, it can reduce the size of goaf section and minimize the damage to rock structure. As a new coal-to-oil route, the in-situ pyrolysis of oil-rich coal is still at an initial stage for research, for which there are still few carbon emission evaluations from the perspective of the full life cycle analysis. Based on the carbon emission accounting method widely adopted, the life cycle analysis (LCA) is employed to analyze the carbon dioxide emission in the whole process of an in-situ tar-rich coal pyrolysis project, including coal seam modification, in-situ heating, product processing, product transportation and terminal consumption. A lateral comparison of greenhouse gas inventory with indirect coal liquefaction and direct coal liquefaction is also carried out. At the same time, the greenhouse gas emission from the in-situ pyrolysis of tar-rich coal is analyzed systematically. The results show that it is necessary to adopt low-carbon energy in the development of in-situ pyrolysis of oil-rich coal. With power grid as the energy source, the LCA carbon emission of in-situ pyrolysis is about 2.234 5 t CO2 for each tonne of coal treated, while with wind power as the energy source, merely 0.608 6 t CO2. The in-situ pyrolysis of tar-rich coal has an obvious advantage in carbon emission reduction over indirect or direct coal liquefaction process. To reduce carbon emissions effectively, several mitigation measures need to be combined, including promoting energy efficiency, optimizing heat sources, and increasing the proportion of clean energy.

The opposed wall-fired boiler is widely used in Chinese power plants due to its adaptability. However, deviations from design conditions can cause the reduction of combustion efficiency and combustion stability, and the overheating of heating surfaces. This study conducted numerical simulations on a 600 MW supercritical opposed wall-fired boiler at 75%, 50%, and 30% Turbine Heat Acceptance (THA) load conditions. The variation of temperature field and heat flux in the furnace under different loads, and parameters such as distributions of heat flux, temperature, and the stress of the high-temperature heating surface are analyzed. Results indicate that reducing the load from 75% to 30% THA lowers the furnace outlet temperature from 1158 to 1009 K and reduces the average gas temperature of the high-temperature heating surface from 1800 to 1570 K. Under a high load, the maximum heat flux concentrates on the side water-cooled wall of the combustion zone. However, when the load decreases, the heat absorption shifts towards the main combustion zone. Furthermore, under a high load, the average wall temperature of the high-temperature heating surface remains at 1600 K with a uniform temperature distribution. In contrast, when the load drops to 30% THA, significant temperature differences appear on the heating surface, with a maximum difference of 400 K. This leads to excessive expansion and slagging on the high-temperature heating surface, particularly in the middle and lower sections, due to the increased stress. These findings offer valuable insights for optimizing the combustion characteristics of opposed wall-fired boilers and preventing overtemperature explosions on the platen heating surface.

The octagonal tangentially fired boiler can be utilized for burning lignite with high moisture. Co-firing biomass in an octagonal tangential boiler is considered a promising approach. A numerical simulation is carried out in this study to analyze the impact of flue gas recirculation (FGR) and the biomass blending ratio on heat and mass transfer in an octagonal tangentially fired boiler. When the FGR rate increases from 0 to 30%, the maximum temperature in the boiler decreases from 2162.8 to 2106.5 K. Simultaneously, the average temperature of the center longitudinal section decreases from 1589.0 to 1531.9 K. The maximum fluctuation of the outlet flue gas temperature remains within 10.9 K for the four calculated working conditions. Consequently, the efficiency of the boiler is basically unchanged. However, the flue gas temperature at the furnace outlet decreases significantly from 1605.9 to 1491.9 K. When the biomass blending ratio increases from 0 to 20%, the mean temperature of the primary combustion zone decreases from 1600.5 to 1571.2 K.

Ammonia is an ideal renewable, carbon-free fuel and hydrogen carrier, which produces nitrogen and water after complete combustion in the presence of oxygen. However, ammonia has low reactivity, slow flame-propagation speed, and carries risks of high nitrogen oxide (NOx) emissions. Co-firing ammonia with an industrial by-product gas (with CH4 and CO being the main combustible materials) is a cost-effective and convenient method of improving the combustion characteristics of ammonia, but attention still needs to be paid to the NOx generation. Currently, the research on NOx formation during co-firing of ammonia with other fuel gases is still insufficient. In this study, a high-temperature furnace reaction system was used to investigate the NOx formation and inhibition mechanisms during the combustion of NH3/CH4 and NH3/CO mixtures. By varying the ammonia blending ratio, excess air coefficient (α), temperature, residence time, and fuel concentration, the key factors influencing NOx generation and inhibition were further analyzed. The results showed that when α was no less than 1, the production of NOx initially increased and then decreased with an increasing proportion of ammonia in the fuel gas. Within the temperature range of 900 °C to 1500 °C, the amount of NOx generated during the combustion of the mixed gas gradually decreased with the increase in temperature. Under the conditions of NH3/CH4 and NH3/CO, the emissions of NOx were higher than those during pure ammonia combustion.

Self-excited thermoacoustic instability (SETAI) is an undesirable and dangerous phenomenon in combustion systems. However, its control is difficult, thus greatly limiting the development of combustion technology. Our previous works clarified how the premixed chamber length (LP) and equivalence ratio (φ) influence SETAI behavior in a symmetrical hedge premixed combustion system. On real-world sites, however, the supply structure or combustion condition in a multi-flame system could be asymmetric due to space limitations or combustion adjustment needs. This paper aims to clarify the SETAI behavior of a combustion system with an asymmetric supply structure or an asymmetric combustion condition. The results indicate that the sound pressure amplitude under strong oscillation can reach 160 dB, which is about 5% of the total pressure. The SETAI state under the asymmetric condition is determined by the coupling between the heat release oscillation and sound pressure oscillation on each side and their cooperation. The asymmetric supply structure leads to asynchronous heat release oscillations between the two sides; it may be that one promotes oscillation and that the other suppresses it, or that both have a promotion effect but with asynchronous action, thus partly canceling each other out to lower the system’s oscillation intensity. This brings an advantage for controlling SETAI, which can be achieved by only changing one side of the structure. The oscillation amplitude can be reduced by 80–90% by appropriately changing one LP only by ~20%. Under an asymmetric combustion condition with φ differing between the two sides, the heat release oscillation on each side is dependent on the local φ but not the global φ. Consequently, SETAI can also be controlled by changing the distribution but maintaining a constant fuel feeding rate and φ. The concepts identified in this paper demonstrate that SETAI can be effectively controlled by adopting an asymmetric φ distribution or an asymmetric structure of the supply system. This provides a convenient SETAI control approach without affecting the equipment’s thermal performance.

Oblique photography 3D models are increasingly used in 3D modeling and visualization, urban planning and design, smart cities, smart mines, and other fields. To ensure that 3D models can be replaced and updated, it is necessary to deal with the model holes and incomplete areas caused by the incorrect matching of feature points in the modeling process. Moreover, in 3D models of the planning and management of certain mining areas or urban areas to be developed, regions can also be delineated for replacements and updates. Due to the unsatisfactory display effect of the manually modeled models used to replace and update, the authenticity of the model texture and the detail characteristics of the model triangle meshes cannot be guaranteed during integration. Therefore, this paper proposes a 3D model triangle mesh integration method for oblique photography data which integrates the real and complete 3D models used for replacement with the incomplete part or the part of the original model that needs to be replaced. The experimental results show that this method can integrate the original terrain model and the replacement model efficiently and quickly, the integrated model has no gap, and the display effect is good, effectively achieving model repair or model update and replacement.

Gas-fired boilers, gas stoves, and wall-mounted gas boilers are the main consumers of gas fuel, but they generally encounter problems when operating at high altitudes, such as reduced thermal efficiency and increased pollutant emissions. Previous studies on gas combustion characteristics under sub-atmospheric pressure were mostly carried out in a large space, which is quite different from chamber combustion equipment. Therefore, it is insufficient to guide the design and operation optimization of plateau gas equipment. In this paper, experimentations were carried out to explore the characteristics of a methane diffusion flame under sub-atmospheric pressures. The mass flow rates of methane and air remain consistent under different pressure conditions. The centerline temperature (Tc) distribution, flame appearance, smoke point, CO emission, and NOx emission under different pressures (ranging from 61.66 to 97.75 kPa) were examined under both fuel rich and lean conditions. The results show that Tc at the rear and front of furnace variation with pressure is opposite under fuel-lean and -rich combustion. The Tc at the front of furnace decreases with decreasing pressure, whereas Tc at the rear of furnace increases with decreasing pressure. With decreasing pressure, flame length decreases under lean combustion, but increases under rich combustion. The smoke point fuel flow rate, flame length, and residence time increases with decreasing pressure, following the law of negative exponent. The CO emission decreases with decreasing pressure, which indicates that the reduced pressure makes methane combustion more complete. For NO emission, the reduced pressure results in an opposite tendency under fuel-lean and -rich combustion. With decreasing pressure, the NO emission decreases under fuel-lean combustion but increases under fuel-rich combustion.

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.

Three-dimensional (3D) modeling of geological surfaces, such as coal seams and strata horizons, from sparsely sampled data collected in the field, is a crucial task in geological modeling. Interpolation is a common approach for this task to construct continuous geological surface models. However, this problem becomes challenging considering the impact of the faults on geological surfaces. Existing methods tend to solve this problem through three steps, including interpolating stratum and fault surface, applying a fault modeling method to modify the geological surface, and optimizing the modified surface to pass sample points fallen into the fault displacement zone. This paper presents a more concise method to generate a faulted geological surface, in which 1) a constrained Delaunay triangulated irregular network (CD-TIN) is constructed to facilitate the neighborhood search process of the ordinary kriging (OK) interpolation, 2) the CD-TIN is also directly constrained by horizon cut-off lines formed from theoretical fault displacement profiles, and 3) subsequently, neighbors of the location to be estimated are selected effectively in the CD-TIN considering the fault topology. The proposed method significantly improves the time efficiency of the OK interpolation by utilizing the CD-TIN and incorporates fault effects directly into the interpolation process by inserting fault horizontal cut-off lines into CD-TIN. Moreover, by integrating the fault effects directly into the interpolation process, the surface modeling process is accomplished in a single stage instead of two separate stages of interpolation first and then modifying the surface in the fault area. By this strategy, the proposed method significantly improves the time efficiency of the OK interpolation algorithm and achieves more accurate modeling of the faulted geological surface. Experiments were designed to compare the performance of our method with several commonly used approaches, and the results indicate that the proposed TIN-constrained OK method achieves better accuracy and efficiency in modeling faulted geological surfaces than other methods. This method could also be used in geospatial interpolation studies, such as meteorological data interpolation.

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.

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.

Metallic aluminum is widely used in propellants, energy-containing materials, and batteries due to its high energy density. In addition to burning in the air, aluminum can react with water to generate hydrogen. Aluminum is carbon-free and the solid-phase products can be recycled easily after the reaction. Micron aluminum powder is stable in the air and enables global trade. Aluminum metal is considered to be a viable recyclable carrier for clean energy. Based on the reaction characteristics of aluminum fuel in air and water, this work summarizes the energy conversion system of aluminum fuel, the combustion characteristics of aluminum, and the recycling of aluminum. The conversion path and application direction of electric energy and chemistry in the aluminum energy conversion system are described. The reaction properties of aluminum in the air are described, as well as the mode of activation and the effects of the aluminum-water reaction. In situ hydrogen production is achievable through the aluminum-water reaction. The development of low-carbon and energy-saving electrolytic aluminum technology is introduced. The work also analyzes the current difficulties and development directions for the large-scale application of aluminum fuel energy storage technology. The development of energy storage technology based on aluminum is conducive to transforming the energy structure.

Global navigation satellite system (GNSS) signals are affected by refraction when traveling through the troposphere, which result in tropospheric delay. Generally, the tropospheric delay is estimated as an unknown parameter in GNSS data processing. With the increasing demand for GNSS real-time applications, high-precision tropospheric delay augmentation information is vital to speed up the convergence of PPP. In this research, we estimate the zenith tropospheric delay (ZTD) from 2018 to 2019 by static precise point positioning (PPP) using the fixed position mode; GNSS observations were obtained from the National Geomatics Center of China (NGCC). Firstly, ZTD outliers were detected, and data gaps were interpolated using the K-nearest neighbor algorithm (KNN). Secondly, The ZTD differences between the KNN and periodic model were employed as input datasets to train the long short-term memory (LSTM) neural network. Finally, LSTM forecasted ZTD differences and the ZTD periodic signals were combined to recover the final forecasted ZTD results. In addition, the forecasted ZTD results were applied in static PPP as a prior constraint to reduce PPP convergence time. Numerical results show that the average root-mean-square error (RMSE) of predicting ZTD is about 1 cm. The convergence time of the PPP which was corrected by the LSTM-ZTD predictions is reduced by 13.9, 22.6, and 30.7% in the summer, autumn, and winter, respectively, over GPT2-ZTD corrected PPP and unconstrained conventional PPP for different seasons.

Constructing high quality three-dimensional (3D) geological models of coal seams from multi-source data, such as boreholes and geological maps, is a crucial task in seam distribution analysis and production planning of coal mine. However, widely used interpolation methods in geology, such as inverse distance weighting (IDW) and ordinary kriging (OK), ignore the variety of uncertainties in multi-source data. In this paper, sample points extracted from the archival data of a coal mine were classified into two categories, the hard data and the soft data, according to their sources. Field boundaries and fault observations were also obtained from data processing. A 3D geological modeling workflow was developed to integrate these data, in which (1) the weighted kriging (WK) method was used to interpolate both hard data and soft data, and (2) a fault modeling method was proposed to build faults' geometry as well as their impact on coal seam surface model. The WK method improves the accuracy of interpolation compared with the OK and IDW methods, and the proposed fault modeling method can integrate expert interpretations into the final 3D geological model of the coal seams.

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°.

The Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) satellite uses a synchronized multi-beam photon-counting method to collect data from three pairs of synchronous ground tracks. The sampling rate along the ground tracks is designed to be ∼0.7 m, much smaller than that used in conventional radar altimeters. Hence, it is reasonable to expect an improvement in marine gravity recovery over coastal zones using ICESat-2 data. ICESat-2 provides valid sea surface height (SSH) measurements and a standard data product (ATL12) over ocean areas. This led us to consider the possibility of investigating its ability to calculate the deflection of vertical (DOV) and marine gravity anomalies. We processed ATL12 data about 22 months over the South China Sea (0°–23°N, 103°–120°E) and verified the ability of ICESat-2 SSH measurements to be used in calculating directional components of DOV. The results show that the ICESat-2 SSH data have a similar centimeter-magnitude accuracy level as data from the Jason-2 satellite. Furthermore, the accuracy of cross-track deflection of vertical (CTDOV) calculations between non-identical side beams is lower. For along-track points, the difference in accuracy between the solution of the prime component and the meridional component is significantly reduced, the prime component accuracy is significantly better than the directional components of the gridded deflection of vertical (GDOV), although the enhancement is weak for the meridional component. We also implemented the inversion of the ICESat-2 single mission based on the inverse Vening Meinesz formula, and verified the capability of ICESat-2 gravity field detection using shipborne gravity measurements and XGM2019 gravity field model, and found that the accuracy is 1.35 mGal and 2.47 mGal, respectively. ICESat-2 deserves the attention of the altimetry community, and its advantages are expected to make it an alternative data source for multi-mission fusion inversion of the ocean gravity field in the future.

The homogeneous oxidation of elemental mercury (Hg0) can promote Hg pollution control in coal-fired power plants, while the mechanisms and quantitative contributions of homogeneous reactions in Hg0 oxidation, especially the reactions between Hg and chlorine (Cl), are still unclear. Here, a numerical study on the homogeneous reactions of Hg was conducted within a 600 MW tangentially fired boiler for the first time. A novel Hg sub-model was established by coupling the thermodynamics, reaction kinetics and fluid dynamics. The results showed that the higher Cl content in coal was beneficial to the oxidation of Hg0. The homogeneous reactions of Hg mainly occurred in the vertical flue pass at low temperature. Hg0 was still the dominant Hg-containing species at the boiler exit, and the concentration of mercury chloride (HgCl2) was the highest among the oxidized mercury. When low-Cl coal was fired, the addition of a small amount of chlorine species into the boiler at the burnout area increased the ratio of HgCl2 by over 16 times without causing serious chlorine corrosion problems.

Mining can provide necessary mineral resources for humans. However, mining activities may cause damage to the surrounding ecology and environment. Vegetation change analysis is a key tool for evaluating damage to ecology and the environment. Liaoning is one of the major mining provinces in China, with rich mineral resources and long-term, high-intensity mining activities. Taking Liaoning Province as an example, vegetation change in six mining areas was investigated using multisource remote sensing data to evaluate ecological and environmental changes. Based on MODIS NDVI series data from 2000 to 2019, change trends of vegetation were evaluated using linear regression. According to the results, there are large highly degraded vegetation areas in the Anshan, Benxi, and Yingkou mining areas, which indicates that mining activities have seriously damaged the vegetation in these areas. In contrast, there are considerable areas with improved vegetation in the Anshan, Fushun, and Fuxin mining areas, which indicates that ecological reclamation has played a positive role in these areas. Based on Sentinel-2A data, leaf chlorophyll content was inferred by using the vegetation index MERIS Terrestrial Chlorophyll Index (MTCI) after measurement of leaf spectra and chlorophyll content were carried out on the ground to validate the performance of MTCI. According to the results, the leaf chlorophyll content in the mines is generally lower than in adjacent areas in these mining areas with individual differences. In the Yingkou mining area, the chlorophyll content in adjacent areas is close to the magnesite mines, which means the spillover effect of environmental pollution in mines should be considerable. In the Anshan, Benxi, and Diaobingshan mining areas, the environmental stress on adjacent areas is slight. All in all, iron and magnesite open-pit mines should be monitored closely for vegetation destruction and stress due to the high intensity of mining activities and serious pollution. In contrast, the disturbance to vegetation is limited in resource-exhausted open-pit coal mines and underground coal mines. It is suggested that land reclamation should be enhanced to improve the vegetation in active open-pit mining areas, such as the Anshan, Benxi, and Yingkou mining areas. Additionally, environmental protection measures should be enhanced to relieve vegetation stress in the Yingkou mining area.

Dust pollution is severe in some mining areas in China due to rapid industrial development. Dust deposited on the vegetation canopy may change its spectra. However, a relationship between canopy spectra and dust amount has not been quantitatively studied, and a pixel-scale condition for remote sensing application has not been considered yet. In this study, the dust dispersion characteristics in an iron mining area were investigated using the American Meteorological Society (AMS) and the U.S. Environmental Protection Agency (EPA) regulatory model (AERMOD). Further, based on the three-dimensional discrete anisotropic radiative transfer (DART) model, the spectral characteristics of vegetation canopy under the dusty condition were simulated, and the influence of dustfall on vegetation canopy spectra was studied. Finally, the dust effect on vegetation spectra at the canopy scale was extended to a pixel scale, and the response of dust effect on vegetation spectra at the pixel scale was determined under different fractional vegetation covers (FVCs). The experimental results show that the dust pollution along a haul road was more severe and extensive than that in a stope. Taking dust dispersion along the road as an example, the variation of vegetation canopy spectra increased with the height of dust deposited on the vegetation canopy. At the pixel scale, a lower vegetation FVC would weaken the influence of dust on the spectra. The results derived from simulation spectral data were tested using satellite remote sensing images. The tested result indicates that the influence of dust retention on the pixel spectra with different FVCs was consistent with that created with the simulated data. The finding could be beneficial for those making decisions on monitoring vegetation under dusty conditions and reducing dust pollution in mining areas using remote sensing technology.

In this paper, coal gasification characteristics in the reductor were investigated in a full-scale two-stage pressurized entrained-flow gasifier, which has been seldom conducted previously. The present study aimed at elucidating the effects of gasifying agent concentration, coal input rate, and operation period under full reductor load on the performance of a utility two-stage pressurized entrained-flow gasifier for the first time. When the steam input in the combustor was raised from 3318 kg/h to 5722 kg/h, the total outputs of H2, CO, and CO2 were increased by 1765 Nm3/h and 2063 Nm3/h, respectively, while the CH4 output was decreased by 49 Nm3/h. The coal conversion rate was minimal at low steam input. In addition, more coal gasified in the reductor could increase the output of CH4, while CH4 could reach 1.24% with the coal input in the range of 8000–10,000 kg/h. The present work can offer a further understanding of the gasification performance in the reductor of the full-scale two-stage pressurized entrained-flow gasifier, and motivates the potential for clean utilization of coal resource.

Staged combustion is an effective technology to control NOx emissions for coal-fired boilers. In this paper, the characteristics of NOx emissions under a high temperature and strong reducing atmosphere conditions in staged air and O2/CO2 combustion were investigated by CHEMKIN. A methane flame doped with ammonia and hydrogen cyanide in a tandem-type tube furnace was simulated to detect the effects of combustion temperature and stoichiometric ratio on NOx emissions. Mechanism analysis was performed to identify the elementary steps for NOx formation and reduction at high temperatures. The results indicate that in both air and O2/CO2 staged combustion, the conversion ratios of fuel-N to NOx at the main combustion zone exit increase as the stoichiometric ratio rises, and they are slightly affected by the combustion temperature. The conversion ratios at the burnout zone exit decrease with the increasing stoichiometric ratio at low temperatures, and they are much higher than those at the main combustion zone exit. A lot of nitrogen compounds remain in the exhaust of the main combustion zone and are oxidized to NOx after the injection of a secondary gas. Staged combustion can lower NOx emissions remarkably, especially under a high temperature (≥1600 °C) and strong reducing atmosphere (SR ≤ 0.8) conditions. Increasing the combustion temperature under strong reducing atmosphere conditions can raise the H atom concentration and change the radical pool composition and size, which facilitate the reduction of NO to N2. Ultimately, the increased OH/H ratio in staged O2/CO2 combustion offsets part of the reducibility, resulting in the final NOx emissions being higher than those in air combustion under the same conditions.

Elemental mercury (Hg0) emitted from a coal-fired boiler is a serious menace and challenge to humans. Using high-efficiency CeO2/TiO2 catalysts to enhance the conversion from elemental mercury to oxidized mercury is a promising approach to reducing Hg0 emission. However, most of the CeO2/TiO2 catalysts were prepared by impregnation method or coprecipitation method while little attention has been paid to sol–gel method, which has many advantages in material production. In this study, a series of catalysts were synthesized through the sol–gel method to remove the gaseous Hg0 from simulated flue gas. The effect of vanadium (V) on Hg0 removal efficiency and the simultaneous removal of Hg0 and NO were also investigated. The results showed the optimal temperature for Hg0 removal over the CeO2/TiO2 catalysts was 350 °C. The oxidation of Hg0 could be promoted by O2, HCl, and NO, but inhibited by NH3 and SO2. The addition of vanadium could enhance the Hg0 removal performance and the resistance to NH3 and SO2. A synergetic effect was found during the simultaneous removal of Hg0 and NO. The high redox reaction reactivity of Ce4+/Ce3+ and V5+/V4+ should take the credit for the oxidation of Hg0 and the removal of NO. Based upon the performance tests and the characterization experiments of the samples, the detailed mechanisms of the Hg0 and NO removal over the catalysts were proposed.

An inherent defect of the operating rotary air preheaters (RAPH) is known as leakage, which seriously hinders the efficient and safe operation of RAPH. It is significant for the estimation of the direct leakage to determine the effects of different structure parameters of sealing sheets and different operation parameters of a RAPH. A direct leakage set-up was built and a three-dimensional numerical model was established to explore the local direct air leaking process of rotary regenerative air preheater and study the effects of geometrical and operational parameters on the leakage. The numerical simulation using the transition k-kl-ω turbulence model was verified by the experimental results. The results show that the local direct air leakage mainly depends on the total pressure difference between the two sides of the seal instead of the one-side pressure. The air leakage can be significantly reduced by narrowing the leakage gap. The increase in the number of sealing sheets can reduce the air leakage own to the increase in the leakage resistance. The increase in the spacing between the adjacent sealing sheets can enlarge the recirculation zone and increase the energy loss of mainstream, greatly reducing the local direct air leakage. Due to the different size recirculation zone formation and streamline curvature induced by sealing sheet, the effect of bending angle on the direct air leakage varies. To obtain lower leakage rate, it is recommended for the rotor of tri-sectional air preheater to pass through flue gas section, secondary-air section, and primary-air section in sequence.

Carbide slag is a waste residue during the production of acetylene. Due to its high content of Ca(OH)2, carbide slag becomes a potential alternative to limestone as the in-bed desulfurizer of circulating fluidized bed (CFB) boilers. In this study, the calcination and sulfation characteristics of carbide slag were investigated by three different facilities, thermogravimetric analyzer (TGA), 1 MWth pilot CFB boiler, and 690 t·h−1 CFB boiler. Pore structures and sulfation behaviors of carbide slag and limestone were investigated for the sake of comparison. The results showed that carbide slag has a lower calcination temperature than limestone. Its calcined product has a better pore structure and desulfurization activity. The carbide slag exhibited a higher desulfurization efficiency than the limestone in the pilot tests. The SO2 emission concentration showed a downward trend with the increase of molar fraction of carbide slag in the desulfurizer. Meanwhile, carbide slag had a better sintering-resistance property, which makes it possible to effectively reduce SO2 emissions even at high combustion temperatures (>910 °C). While the field test results were similar to that of the pilot tests, the desulfurization efficiency of carbide slag with the same Ca/S mole ratio was higher than that of limestone. The fine size of carbide slag particles and the lower separation efficiency of the cyclone on the 690 t·h−1 boiler left the carbide slag with insufficient residence time in the furnace. Therefore, it is necessary to ensure a high separation efficiency of the cyclone if the carbide slag is used as an alternative desulfurizer in furnace.

In this paper, a new bell-type air nozzle, which overcomes the structural defects of traditional bell-type air nozzles, is proposed and validated by cold test and numerical simulation. The pressure drop characteristic of the new bell-type air nozzle is measured. Furthermore, the causes of cover outlet abrasion and blockage, inner tube fracture, and irregular resistance change in traditional bell-type air nozzles applied in circulating fluidized bed (CFB) boilers are analyzed. Then, the performance of the new bell-type air nozzle is evaluated in a real CFB boiler, which is operated under regular working conditions. The results show that the new bell-type air nozzle has stronger anti-wear ability, excellent resistance characteristics, longer service life, and easier maintenance.

Semi-coke is one of the principal by-products of coal pyrolysis and gasification, which features the disadvantages of ignition difficulty, low burnout rate, and high nitrogen oxides (NOx) emission during combustion process. Co-firing semi-coke with coal is a potential approach to achieve clean and efficient utilization of such low-volatile fuel. In this paper, the co-firing performance of semi-coke and lean coal in a 600 MW supercritical wall-fired boiler was numerically investigated which has been seldom done previously. The influences of semi-coke blending ratio, injection position of semi-coke, excess air ratio in the main combustion zone, the co-firing method, and over fire air (OFA) arrangement on the combustion efficiency and NOx generation characteristics of the utility boiler were extensively analyzed. The simulation results indicated that as the blending ratio of semi-coke increased, the NOx emission at furnace outlet decreased. The blending methods (in-furnace versus out-furnace) had certain impacts on the NOx emission and carbon content in fly ash, while the in-furnace blending method showed more flexibility in co-firing adjustment. The injection of semi-coke from the upper burners could significantly abate NOx emission at the furnace outlet, but also brought about the rise of carbon content in fly ash and the increase of outlet temperature. Compared with the condition that semi-coke and lean coal were injected from different burners, the burnout ratio of the blend premixed outside the furnace was higher at the same blending ratio of semi-coke. With the excess air ratio in the main combustion zone increased, NOx concentration at the furnace outlet was increased. The excess air ratio of 0.75 in the main combustion zone was recommended for co-firing 45% semi-coke with lean coal. The operational performance of the boiler co-firing semi-coke was greatly affected by the arrangement of OFA as well. The amount of NOx generated from the supercritical wall-fired boiler could be reduced with an increase of the OFA height.

Oxy-fuel combustion technology can capture carbon dioxide (CO2) in the large-scale and greatly lower nitrogen oxides (NOx) emission in coal-fired power plants. However, the influence of inherent minerals on NOx reduction still remains unclear and the impact of oxy-fuel combustion on the transformation of different nitrogen functional groups has yet to be fully understood. The present work aims to obtain a further understanding of the NOx reduction during oxy-fuel combustion using synthetic coals with pyrrolic or pyridinic nitrogen. Compared to pyridinic nitrogen, more of the pyrrolic nitrogen in synthetic coal was converted to NOx. The conversion ratio of nitric oxide (NO) first increased significantly with the rising oxygen content and then trended to an asymptotically constant as the oxygen (O2) content varied between 10⁻50%. The nitrogen dioxide (NO2) formation was roughly proportional to the oxygen content. The NO2 conversion was increased with particle size but the case of NO showed a non-monotonic variation. The catalytic effects of sodium carbonate (Na2CO3), calcium carbonate (CaCO3), and ferric oxide (Fe2O3) on the transformation of pyridinic nitrogen to NO were independent of the combustion atmosphere, while the alteration from air to the oxy-fuel combustion led to a change of mineral catalytic effect on the oxidation of pyrrolic nitrogen within the coal matrix.

Iron tailings ponds are engineered dam and dyke systems used to capture iron tailings. They are high-risk hazards with high potential energy. If the tailings dam broke, it would pose a serious threat to the surrounding ecological environment, residents’ lives, and property. Rainfall is one of the most important influencing factors causing the tailings dam break. This paper took Chengde Area, a typical iron-producing area, as the study area, and proposed a remote sensing method to evaluate the safety risk of tailings ponds under rainfall condition by using runoff coefficient and catchment area. Firstly, the vegetation coverage in the study area was estimated using the pixel dichotomy model, and the vegetation type was classified by the support vector machine (SVM) method from Landsat 8 OLI image. Based on DEM, the slope of the study area was extracted, and the catchment area of the tailings pond was plotted. Then, taking slope, vegetation coverage, and vegetation type as three influencing factors, the runoff coefficient was constructed by weight assignment of each factor using analytic hierarchy process (AHP) model in both quantitative and qualitative way. Finally, the safety risk of tailings ponds was assessed according to average runoff coefficient and catchment area in the study area. The results showed that there were 124 low-risk tailings ponds, 16 moderate-risk tailings ponds, and 4 high-risk tailings ponds in the study area. This method could be useful for selecting targeted tailings ponds for focused safety monitoring. Necessary monitoring measurements should be carried out for the high-risk and moderate-risk tailings ponds in rainy season.