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Dynamic Characteristic Analysis of Sco2 Brayton Cycle Under Different Turbine Back Pressure Modes

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SSRN 2023年

作者： Zhao, Quanbin Xu, Jia yuan Hou, Min Zhang, Dalin Chong, Daotong Wang, Jinshi Chen, Weixiong State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Closed supercritical carbon dioxide Brayton cycle has the advantages of high efficiency and high compactness. The compact structure and completely closed loop with supercritical state makes the dynamic characteristic different from that of steam Rankin cycle. This paper mainly focuses on the dynamic character of SCO2 cycle with different disturbance. Firstly, the dynamic characteristic of isolated heat exchangers is investigated under different disturbances. The response time of HTR and LTR is about 70 seconds, which is much longer than others. Then dynamic characteristics of SCO2 cycle are investigated with different turbine back pressure modes. Under cooled water flow rate disturbance, the operation parameter fluctuation amplitude and the response time with normal back pressure mode are slightly larger than those under fixed back pressure modes, and the effect of pressure iteration is not remarkable when cold water disturbance amplitude is small. But when water flow rate decreases 30%, the discrepancy becomes large and the tendency becomes opposite. Under heat fluoride flow rate disturbance conditions, the parameters iteration in closed loop restrain the non-coordinative of SCO2 pressure and temperatures. © 2023, The Authors. All rights reserved.

关键词： Brayton cycle

Molecular dynamics revealing the non-monotonic variation of oil–water interfacial tension under the effect of cations and asphaltenes

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Journal of Molecular Liquids 2025年 431卷

作者： Zhang, Faxue Wen, Boyao Lu, Xi Wang, Haibo Luo, Zhengyuan Bai, Bofeng State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Shaanxi Xi'an710049 China Petroleum Exploration and Production Research Institute of Sinopec Beijing China

The cations can significantly affect the interfacial dynamics of asphaltene molecules, which greatly change the mechanics of oil–water interfaces and thus have a remarkable impact on the chemical flooding process of heavy oil. However, Due to the weak amphiphilic property of asphaltene, the effects of cations on the interfacial behaviors of asphaltene as well as the interfacial mechanics are still unclear. Here, we study the effects of different types and concentrations of cations (Na+, Ca2+ and Mg2+) on the interfacial tension of oil–water systems with different asphaltenes (C5Pe) concentrations by using molecular dynamics simulations. As asphaltene concentration rises, the stronger interactions between cation and asphaltene induce an interfacial enrichment of asphaltenes, resulting in a decrease of interfacial tension. The cations have a more prominent impact on the interfacial tension when the oil–water interfaces reach supersaturated adsorption state of asphaltene molecules. The interfacial tension shows a non-monotonic variation with cation concentration increasing, which has a minimum at intermediate cation concentrations in our simulations. We explain this non-monotonic dependence of interfacial tension on cation concentration by a coupling effect of cations and asphaltene molecules. Under low cation concentrations, the interaction between cations and asphaltenes gradually enhances with cation concentration increasing, leading to a weaker π–π interaction between asphaltenes. Consequently, the asphaltene aggregates disperse and individual asphaltene molecules can easily migrate to the interface. The surface density of asphaltene thus increases, causing a reduction in interfacial tension. At high cation concentrations, cations strongly shield the electrostatic attraction between asphaltene and water molecules, so that the adsorption ability of asphaltenes at interface will weaken or even desorb, thus the interfacial tension elevate. Our results reveal the under

关键词： Adsorption Aggregation Asphaltenes Cations Interfacial tension Molecular dynamics

An Investigation on Characteristics of Severe Slugging in an Offshore S-Shaped Riser with a Long Pipeline

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SSRN 2023年

作者： Yu, Haiyang Xu, Qiang Huang, Bo Cao, Yeqi Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering Xi 'an Jiaotong University Xi’an710049 China

Long pipelines and risers are essential for transporting oil and gas from the seabed to offshore processing facilities. However, most research focuses on riser systems with short pipelines (≤ 400 m). A 29.1 m high S-shaped riser connecting a 1657 m horizontal pipe, which is comparable to the scale of industrial fields, is utilized for investigating the characteristics of severe slugging. Based on the visual data of gas-liquid interface evolution and the fluctuation of the riser's pressure, the flow pattern map is drawn. Long pipelines delay the liquid accumulation and prolong the severe slugging period. A new correlation for predicting the slugging period is proposed with a deviation of ±15%. The long pipeline provides sufficient compression space and aggravates the blowouts of liquid slugs. The maximum blowout velocity reaches 23 times the mixing velocity. The gas accumulated in the pipeline expands sharply, which causes the instability of the gas-liquid interface in the horizontal pipe and induces a large number of liquid slugs to flow into the riser, where the continuity blowdown of slugs appears. A slug-tracking model considering pressure and liquid holdup is established to precisely forecast the fluctuation of riser pressure during the slug continuity blowdown. © 2023, The Authors. All rights reserved.

关键词： flow patterns

Enhancement of Scr Denitrification Control Strategy Considering Fluegas Temperature Fluctuation: Fundamental Principle and Performance Evaluation

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SSRN 2023年

作者： Gao, Wei Yin, Junjie Liu, Ming Zhao, Yongliang Wang, Chaoyang Yan, Junjie State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Nitrogen oxides (NOx) is one of the main pollutants in coal-fired power plants, and selective catalytic reduction (SCR) is widely applied to reduce NOx emissions. Coal-fired power plants should frequently change their output power to help the power grid to accommodate high penetration of intermittent renewable power. However, NOx emission transient overshoot often occurs in coal-fired power plants when coal-fired power plants dynamically change their output power. In this study, the dynamic models for a coal-fired power plant and SCR denitrification are developed. The fluegas temperature fluctuation is revealed as a key cause for the NOx emission transient overshoot. The change law of SCR reaction temperature during load cycling processes is obtained, and its prediction model based on neural network algorithm is developed. Then, an enhanced control strategy considering temperature fluctuation of SCR inlet fluegas is proposed, and denitrification performance with the original and enhanced control strategies during load cycling processes are compared. The results show that the transient overshoot of NOx outlet concentration is avoided during load cycling processes, and the maximum value of NOx emissions during loading down and loading up processes with the enhanced control strategy are 48.62 and 49.44 mg m−3, which decreases by 7.36 and 4.63 mg m−3 compared with the original control strategy, respectively. Moreover, when the enhanced control strategy is adopted, the cumulative NH3 consumption decreases by 0.48 and 11.84 g m−3 during loading down and loading up processes, respectively. © 2023, The Authors. All rights reserved.

关键词： Coal fired power plant

Experimental and Kinetic Study of Methanol Reforming and Methanol-Syngas Co-Oxidation at High Pressure

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SSRN 2023年

作者： Zhan, Haochen Li, Shuming Yin, Geyuan Gao, Yibo Hu, Erjiang Huang, Zuohua State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Using engine exhaust heat to improve efficiency by performing co-combustion after partial reforming of methanol to syngas is a favored strategy to address the challenges associated with methanol engine applications. In the present work, experiments of methanol pyrolysis and methanol-syngas oxidation were conducted using high-pressure flow reactors at 1.0-5.0 MPa. The ratio of syngas to methanol varied from 0–50%. Mech15.34 was selected as the most reliable kinetic model to further kinetic analysis, which revealed that pressure decreases the decomposition of CH3OH to CH3, enhances the H-abstraction of CH3OH to CH2OH and CH3O, and increases the yield of H2 and CO. Furthermore, high pressure inhibits CH2OH = CH2O + H, thus reducing CH2O. The effects of blending syngas can be divided into dilution and chemical effects. The dilution effect refers to the reduction of CH3OH, which directly decreases the CH2O formation. The chemical effect refers to the competition of H2 and CO for OH radicals, which decelerates the CH3OH oxidation, decreasing the CH2O generation. Meanwhile, the reaction H2O2 + H = H2 + HO2 proceeds in reverse direction with H2 blending, generating more H radicals, which enhances the CH2O consumption through the reaction CH2O + H = HCO + H2. © 2023, The Authors. All rights reserved.

关键词： Oxidation

Experimental Investigation on Heat Transfer of Supercritical Water flowing in a Horizontal Tube with Axially Non-Uniform Heating

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SSRN 2023年

作者： Hou, Zhenghui Huang, Xin Gao, Yu Zhang, Shengjie Wang, Haijun State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

For a heat exchanger, the heat flux is usually non-uniform in the axial direction, and the knowledge about heat transfer of supercritical water with axially non-uniform heating is scarce. To fill the gap, experiments were conducted in a horizontal tube to study the heat transfer characteristics of supercritical water with axially sinusoidal heating. The pressures varied from 23.5 to 26.5 MPa, mass fluxes 200 to 400 kg·m-2·s-1 and average heat fluxes 50 to 150 kW·m-2. Compared with uniform heat flux, the temperature difference between the top and bottom wall is larger than that of the axially sinusoidal heat flux. The inner-wall heat flux is non-uniform along the circumference due to the temperature difference, being higher at the side wall and lower at the top wall. A relative heat flux parameter is defined to describe the relative magnitude of the local heat flux. The relative heat flux parameter of the top generatrix, which is inversely proportional to the average heat flux, decreases linearly with the increase of the temperature difference between the top and side generatrix. The non-uniform degree of heat flux along the circumference is positively correlated with the average heat flux. Additionally, the local heat transfer characteristics should be considered in horizontal tubes. On the one hand, the heat transfer deterioration may occur when the fluid temperature near the top wall is higher than the pseudo-critical temperature and it can be suppressed with increasing Reynolds number. On the other hand, the local heat transfer can be enhanced if the side and bottom wall temperatures exceed the pseudo-critical temperature. © 2023, The Authors. All rights reserved.

关键词： Heat flux

Exergy-Based Control Strategy Design and Dynamic Performance Enhancement for Parabolic Trough Solar Receiver-Reactor of Methanol Decomposition Reaction

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SSRN 2023年

作者： Zhang, Peiye Liu, Ming Mu, Ruiqi Yan, Junjie State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

The parabolic trough solar receiver-reactors of methanol decomposition reaction (PTSRR-MDR) enable efficient hydrogen production with solar energy at users' end. Solar fluctuations affect the solar-to-chemical efficiency, hydrogen yield and system stability, indicating the necessity for an appropriate control strategy. In this study, dynamic and thermodynamic models of PTSRR-MDR with Cu/ZnO/Al2O3 as catalyst were developed. Results of thermodynamic analysis show that an optimal flow rate exists for methanol to achieve the maximum solar-to-chemical exergy efficiency of the PTSRR-MDR. The temperature increases sharply and exceeds the catalyst sintering temperature when the methanol flow rate decreases under its optimal value. Then, control objectives to achieve the maximum efficiency were obtained with a temperature of 3 °C to guarantee the PTSRR-MDR safety. Control strategies based on Dynamic Matrix Control (DMC), Forward-Feedback Control (FFC) and Ramp Control (RC) were evaluated under cloud shading/recovering and real radiation processes. Results show that strategies based on DMC, FFC, and RC increase the solar-to-chemical exergy efficiency from 14.76% to 16.31%, 16.28% and 15.65%, respectively. The Integral Squared Error (ISE) for methanol conversion rate under three methods are 1.46, 0.32 and 5.28, respectively, indicating that strategy based on FFC is considered most suitable for PTSRR-MDR operation control. © 2023, The Authors. All rights reserved.

关键词： Methanol

Numerical Simulation of Fluid-Particle flow of Jet in Supercritical Water Environment

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SSRN 2023年

作者： Zhang, Chuan Shang, Yuqi Su, Haozhe Ge, Zhiwei Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Supercritical water gasification provides a new approach to the green transformation of coal. Nevertheless, the flow behaviour of the fluid and particles inject into the reactor through the nozzle still warrant further research. In this paper, a three-dimensional numerical simulation of the particle jet in supercritical water environment is carried out using LES-DPM. The simulations focus on the effects of particle size, Stokes number, mass flux ratio and fluid initial velocity on the flow characteristics of the fluid-solid flow. The findings were that as the particle size decreases and the initial fluid velocity increases, the evolution of vortex structures became increasingly fierce, such as the destruction of large-scale coherent structures, the disappearance of vortex ribs, and the lateral expansion of vortices in the development section. Particle distribution exhibited characteristics similar to the vortex structure due to particles stuck closely with the carrier fluid when Stokes number is small (St1), the particles were freer from fluid interference and kept their original motion state moving forward. The fluid velocity at the center of the transverse interface jet decreased with increased mass flow ratio. © 2023, The Authors. All rights reserved.

关键词： Vortex flow

Experimental Investigation of the Photovoltaic Thermal (Pvt) Integrated with Ground Heat Exchanger (Ghe) Using Volcanic Tuff Stones

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SSRN 2024年

作者： Alqatamin, Ahmad Jinzhan, S.U. International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi’an Jiaotong University Xi’an710049 China

This study investigates the combination of photovoltaic thermal (PVT) and ground heat exchanger (GHE) using volcanic tuff stones as a heat storage material if the combination of PVT and GHE technologies provides the potential for energy generation increased efficiency and performance. Volcanic tuff stones known for their high thermal conductivity and heat retention, act as an effective means of heat exchange in the system. The objective of the study is to investigate the electrical, thermal performance and efficiency of this integrated system. Where the ground heat exchanger comprises a single hole filled with volcanic tuff stones arranged strategically, featuring gaps between them to facilitate heat exchange. The hole dimensions are specified as 2.5 meters in length, 2 meters in width, and 3 meters in depth. A fan is situated at the exit square duct (400*400 mm) to extract ambient air. Experimental data was collected from the PVT-GHE system to evaluate its efficiency in harnessing solar energy and providing space heating or other heating applications and compared it with a traditional PVT system. The results show that integrating GHE into PVT systems dramatically decreases solar cell temperature and improves electrical efficiency. A PVT system with GHE had the maximum electrical efficiency at 17.99%, compared to 17.52% in a PVT system without GHE. In addition, the greatest possible electrical power in a PVT system with GHE was 65 W, but in a PVT system without GHE, it was 61W. Also, the outlet air temperature from GHE was consistently higher than the ambient temperature throughout the days of the experiment, with an average difference of about 10 ºC. © 2024, The Authors. All rights reserved.

关键词： Solar energy