Abstract

Micro-cracks in coal play an important role in the safe mining and coalbed methane extraction processes. The propagation and nucleation of micro-cracks during coal mining are key factors that cause the damage of the coal formation and the overlaying rocks. They are also the main transport ways for the coalbed methane. Therefore, accurate characterization of the micro-cracks in coal is crucial in uncovering the coal failure and the gas transports mechanisms. Imaging methods, such as X-ray CT scan provides an effective way in obtaining the 3D fracture distribution in a coal rock. However, accurate extraction of the fractures in the greyscale CT images remains to be improved, especially for those faint micro-cracks. The difficulties are mainly caused by the limited CT image resolution and the precise segmentation of the micro-cracks influenced by surrounding noises. In this paper, we first used super-resolution and greyscale enhancement techniques to improve the 3D image resolution and quality obtained through the industrial CT scanning. With these applied preprocessing steps, more details of the CT image could be identified. Then multi-scale Hessian filtering techniques was employed to enhance the identification and segmentation of the fractures. Through Hessian filtering, the faint micro-cracks were accurately recognized. Moreover, a connectivity check postprocessing eliminated the noises in the segmented image. The successful recognition of micro-cracks enabled the further studies on the mechanical and transport properties of coal through image-based calculation methods.

Abstract

The in-situ pyrolysis conversion of coal for extracting the tar is carried out to decrease the solid waste, reduce environmental pollution, and ensure energy safety. However, thermal conductivity, the most key thermal parameter, is quite indistinct for underground tar-rich coal seam under actual conditions. To obtain the thermal conductivity of underground tar-rich coal seam under actual conditions, the non-linear regression algorithm model of support vector machine was constructed. The results show that the training model demonstrates favorable generalization ability for predicting in-situ thermal conductivity of tar-rich coal seam. Moreover, the trained model subsequently predicts thermal conductivity of underground tar-rich coal seam with positive matching and reliability in the testing sets. The predicted study may promote further elucidation of the thermal conductivity evolution during the in-situ pyrolysis of tar-rich coal seam.

Abstract

Achieving the Paris Agreement’s goal of limiting global temperature rise to 1.5°C or 2°C above pre-industrial levels requires global greenhouse gas emission reductions. Currently, most of the global greenhouse gas emission reductions are focused on the energy sector, such as reducing fossil fuel combustion, improving utilization efficiency, and using clean energy. However, studies have shown that decarbonization in the energy sector alone may not be sufficient to meet the goals of the Paris Agreement. Because the global food system accounts for about one-third of global greenhouse gas emissions, reducing emissions from the global food system is also key to reaching this goal. By dividing the world into two camps according to economic levels and using population projection data, individual diet structure data, and food carbon footprint data in each segment, this paper projects human GHG emissions from 2020-2060 due to the consumption of major foods such as grains, meat, dairy products, vegetables, fruits, legumes, and aquatic food groups. The LMDI analysis of GHG emissions due to food production in different regions was also conducted to analyse the magnitude of the driving forces of three factors: population, food structure, and carbon footprint on emissions.

Abstract

Enhanced geothermal system can efficiently extract heat, while Organic Rankine Cycle system can generate electricity with heat extracted by Enhanced geothermal system. A combination of underground heat extraction and ground power generation systems is proposed in present work. The underground heat extraction system consists of an enhanced geothermal system coupled with hydraulic-thermal horizontal wells with five disc-shaped fractures. The ground power generation system is comprised of the basic Organic Rankine Cycle system, and R245FA is used as the working fluid. The performance of combined system is numerically investigated. The results show that with the increase of geothermal fluid flow rate, the geothermal fluid outlet temperature decreases more rapidly and the reservoir life is exhausted earlier. Case 7 (geothermal fluid flow rate of 50kg/s and injection temperature of 40℃) can obtain the maximum power generation performance, with net output work and heat absorption of 13.3 MW and 13.4%, respectively. It’s also found that the geothermal fluid flow rate has a greater impact on the power generation performance compared that on the geothermal fluid injection temperature.

Abstract

In power stations, adjusting operating parameters to control NOx emissions has attracted more and more attention. In this study, a three-dimensional CFD model was established to simulate a 600 MW tangentially coal-fired boiler. The orthogonal tests were employed to analyze the effect of operating load, primary air rate, air staging, burner swing, and SOFA air swing on NOx emissions. Results show that at 35% BMCR, primary air ratio of 0.24, air staging of 0.75, burner swing of 15°, and SOFA air swing of 0°, the NOx emission is 208.8 mg/Nm3, which is 27.8% lower than the basic case. Increasing the operating load has the opposite effect to the primary air ratio, so does the burner swing and SOFA air swing. Orthogonal analysis shows that the air staging is the most significant factor in NOx emissions. Appropriate reduction of air staging is beneficial to reduce NOx emissions.

Abstract

The integral spiral finned tube has significant advantages compared with the conventional finned tube, which makes it have broad application prospects in boiler economizers. In this study, numerical simulation methods were applied to investigate the effects of base tube diameter, fin height, fin pitch, fin tip width, fin root width, transverse tube pitch and longitudinal tube pitch on the heat transfer and flow characteristics of the integral spiral fin tube. The optimal structural parameters were analyzed through multi-objective optimization. The total heat transfer coefficient is not greatly affected by the fin pitch. With the increase of the longitudinal pitch, the total heat transfer coefficient first increases and then decreases, and the optimum is around 90mm. The optimal structural parameters were obtained while considering the flow and heat transfer characteristics that: the base tube diameter is 32 mm, the fin height is 13 mm, the fin pitch is 7 mm, the fin tip width is 2.4 mm, the fin root width is 4.2 mm, the transverse pitch is 80 mm, the longitudinal pitch is 90 mm, and the inlet flow velocity is 12 m/s.

Abstract

Steam-assisted gravity drainage is one of the most efficient thermal methods to develop heavy oil and bitumen accumulations. However, SAGD requires a large amount of steam injection especially in long production time, which may make the process uneconomical. As an improvement of SAGD technology, steam and gas push (SAGP) has attracted more attention due to its better performance. This method involves the addition of a non-condensable gas such as carbon dioxide co-injected with steam, which reduces the total amount of steam needed and improves energy efficiency. Due to the geological tectonic movement, heavy oil reservoirs with dip angles are widely distributed around the world. The influence of reservoir dip angle on SAGP method must be seriously considered. In this paper, the development effects of SAGP and SAGD methods for heavy oil reservoir with dip angle are compared based on the basic production parameter SOR and cumulative oil production by CMG-STARS. Secondly, the steam chamber evolution of dip angle reservoir with time is analyzed. Finally, we improve the low production caused by reservoir dip angle by optimizing well pair location. The well pair should be placed close to the side boundary in downdip zone, not in the center of the reservoir by numerical simulation. The results show that SAGP process is more suitable for dip Angle reservoir development than SAGD process. In addition, carbon dioxide injection in SAGP process is also conducive to reducing greenhouse effect and contributing to environmental protection This paper has a certain guiding significance for the development of widely distributed dip angle heavy oil reservoir.

Abstract

Proton exchange membrane fuel cells(PEMFCs) have the advantages of clean efficiency, long range and fast recharging, with a short life span and harsh operating conditions. To ensure their safe operation, extend the life of PEMFCs and improve the dynamic characteristics of the power system. This paper uses a combination of PEMFC, battery and supercapacitor (SC) to form a PEMFC hybrid power system. A comprehensive dynamic model is developed for the non-linearity and time-varying nature of the system.
Based on this, Adaptive Model Predictive Control
(AMPC) is used to allocate power to the system.
Minimized hydrogen consumption is considered in the rolling optimization function in AMPC. The simulation is validated by two different types of operating conditions and the experimental results show the effectiveness of the system’s model and power allocation strategy. The proposed energy management strategy can improve the stability of the PEMFC output and guarantee that the fuel cell, battery and SC work in a safe interval.

Abstract

In recent years, due to its excellent performance in adsorbing heavy metals in sewage, biochar has attracted more and more attention. This paper studied the adsorption properties and mechanism of pine wood and soybean straw, which were produced under different pyrolysis temperature of 400, 600, and 800 °C. The biochar was characterized by scanning electron microscopy, elemental composition analysis and BET surface analyzer. Six types of biochar were used for adsorption experiments with solutions containing Pb2+, respectively. The influences of pyrolysis temperature, solution pH on the adsorption performance of biochar Pb2+ were discussed. The results show that, the specific surface area of pine wood biochar is significantly higher than that of soybean straw biochar. The internal functional groups of soybean straw biochar are abundant. With the increase of pyrolysis temperature, the C content, specific surface area, and the amount of alkali metal all rise. Meanwhile, the adsorption capacity of biochar to Pb2+ in the solution all increase. Under the same pyrolysis temperature, the adsorption capacity of soybean straw biochar is stronger than that of pine biochar. As pH increases, the adsorption capacity of pine wood and soybean straw biochar would be stronger, especially for pine wood biochar.

Abstract

The stability dispatch of the microgrid has an important impact on the safety of the power system, so the research on the stability dispatch of the microgrid is necessary. We have established a microgrid model with diesel engines, microturbines, fuel cells, wind turbines and photovoltaic arrays targeting the system load variance. The scheduling algorithm uses an improved particle swarm optimization algorithm based on dimensional learning. The global extremum in the algorithm is derived from the individual extremum of dimensional learning. Firstly, 13 standard test functions are applied to test the performance of the improved dimensional learning algorithm. The simulation results show the effectiveness of the improved algorithm. Then the algorithm and model are combined, and as a result the safety of the system with distributed power generation is better than the system without distributed power generation by comparing the two strategies with or without distributed power generation strategies.