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CO2 Emission Characteristics Modeling and Low-Carbon Scheduling of Coal-Fired power Units Under Peak Shaving Conditions

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SSRN 2023年

作者： Yuan, Rongsheng Liu, Ming Chen, Weixiong Yan, Junjie State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

To accommodate the high penetration of renewable power, the operational flexibility of coal-fired power units is highly required by the power system, so coal-fired power units frequently operate under peak shaving conditions. The CO2 emission characteristics of a coal-fired power unit are significantly influenced by the load factor, and also by unit capacity and many other design parameters. Therefore, detailed CO2 emission characteristics of a coal-fired power unit should be modeled and considered in the low-carbon scheduling of coal-fired power units under peak shaving conditions. In this study, coal-fired power units are classified by live steam parameters, unit capacity, reheat stages, cooling mode, and operation mode, and the models of detailed CO2 emission characteristics are developed and validated. An indicator is defined and modeled to evaluate the CO2 emission reduction rate of a coal-fired power unit considering the renewable power accommodation, and an optimization method for low-carbon scheduling is proposed. The proposed optimization method reduces the computational time by ~80%. Finally, a reference case study, including zero, current, and 2030 renewable power accommodation scenarios, is conducted. Results show that the marginal carbon emission of the power system decreases by 123.33 g/kWh in the 2030 renewable power accommodation scenario. © 2023, The Authors. All rights reserved.

关键词： Carbon

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

State-of-the-art progress in overall water splitting of carbon nitride based photocatalysts

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Frontiers in Energy 2021年第3期15卷 600-620页

作者： Bing LUO Yuxin ZHAO Dengwei JING School of Chemical Engineering and Technology Xi’an Jiaotong UniversityXi’an 710049China International Research Center for Renewable Energy and State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an 710049China

Converting solar energy into hydrogen(H_(2))by photocatalytic water splitting is a promising approach to simultaneously address the increasing energy demand and environmental *** decade has passed since the discovery of photo-induced water splitting phenomenon on TiO_(2)photoanode,while the solar to H_(2) efficiency is still around 1%,far below the least industrial ***,developing efficient photocatalyst with a high energy conversion efficiency is still one of the main tasks to be *** carbon nitride(g-C_(3)N_(4))is just such an emerging and potential ***,in this review,the state-of-the-art advances in g-C_(3)N_(4)based photocatalysts for overall water splitting were summarized in three sections according to the strategies used,and future challenges and new directions were discussed.

关键词： photocatalysis overall water splitting carbon nitride hydrogen

Simulation Study on Hydrogen-Heating-power Poly-Generation System based on Solar Driven Supercritical Water Biomass Gasification with Compressed Gas Products as an Energy Storage System

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Journal of Thermal Science 2020年第2期29卷 365-377页

作者： JIN Hui WANG Cui FAN Chao State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an 710049China

Supercritical water gasification driven by solar energy is a promising way for clean utilization of biomass with high moisture content, but direct discharge of liquid residual causes energy waste and decreases energy efficiency. To reduce energy waste, a poly-generation system for hydrogen-rich gas production coupling heat supply and power generation based on supercritical water gasification of biomass driven by concentrated solar energy was established in this paper, which also provided a novel energy storage method to overcome the shortcomings of solar discontinuity. Thermodynamic model of the system was proposed and life cycle assessment(LCA) of the system was conducted. Influence of different parameters(temperature of 600℃ to 800℃, outlet temperature of heat exchanger of 42℃ to 56℃, biomass slurry concentration of 5% to 6.5%) on the gasification performance, energy and exergy efficiency, energy distribution and global warming potential(GWP) was discussed. The results indicated that hydrogen yield increased as gasification temperature increased since free radical reaction was enhanced which gas production reaction was classified into. Molar fraction of hydrogen increased as gasification temperature increased and reached 65.6% at 750℃. Energy and exergy efficiency of the system reached 74.84% and 34.87% at 700℃ and 600℃ respectively and that of gas production was 18.15% at 650℃, which was the highest. Increasing reaction temperature and decreasing biomass slurry concentration were effective ways to decrease GWP. Optimal operating parameter was reaction temperature of 650℃, outlet temperature of heat exchanger of 50℃ and biomass concentration of 5%.

关键词： biomass supercritical water gasification poly-generation system thermodynamics analysis energy storage life cycle assessment

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

Hydrodynamic Interaction of Two Droplets Covered with Insoluble Surfactant in Shear flow

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SSRN 2023年

作者： Wei, Wei Luo, Zhengyuan Bai, Bofeng State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Despite its significance in various applications, e.g., droplet microfluidics and enhancing oil recovery, the effects of surfactants on the hydrodynamic interactions of droplets in shear flow still need to be clarified. This paper presents a systematic investigation on the hydrodynamic interaction of two droplets covered with the insoluble surfactant in a simple shear flow, which is realized by using our own three-dimensional front-tracking code. Our results indicate that surfactants significantly affect the hydrodynamic interactions of droplets, characterized by the maximum deviation in the z-direction and the shear-induced self-diffusion. Then we examine the effects of surfactant-relevant parameters, i.e., the surface Peclet number and the elasticity number. Both the maximum deviation in the z-direction and the shear-induced self-diffusion increase with the elasticity number and the surface Peclet number. Specifically, we find two mechanisms underlying the effects of surfactant on the hydrodynamic interaction of two droplets. First, Marangoni stress induced by surfactant sharply increases the maximum deviation in the z-direction when the surface Peclet number is large. It is because that Marangoni stress hinders liquid drainage from the near-contact region and thickens the liquid film between the droplets. Second, hydrodynamic interactions during crossing lead to considerable alterations of the shape and local surfactant concentration, resulting in an irreversible trajectory shift of the droplets. So, the shear-induced self-diffusion sharply rises at the high surface Peclet number. © 2023, The Authors. All rights reserved.

关键词： Surface active agents

Experimental Study on Boiling Heat Transfer Characteristics in Helical Coils with Large Coiled Diameters

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SSRN 2024年

作者： Shi, Yanggen Wu, Zhiyuan Li, Kepiao Zhang, Kui Tian, Wenxi Qiu, Suizheng State Key Laboratory of Multiphase Flow in Power Engineering Department of Nuclear Science and Technology Xi’an Jiaotong University Xi’an710049 China

The boiling heat transfer characteristics in helical coils were investigated by experimental study. Experimental results indicated that the distribution of wall temperature trended to be more uniform due to weakened influence of centrifugal force and gravity force when the bulk fluid is closed to saturation temperature. Increase in heat flux decreases the quality of ONB (onset of nucleate boiling) while increase in mass flux delay ONB. The heat transfer was dominated by nucleate boiling with quality range of 00.6 in saturated boiling region. The quality of dryou decreases with the increase of pressure and it’s scarcely affected by heat flux. Dryout rends to occur at lower quality with the increase of heat flux at high pressure since redeposition rate decreases at higher pressure and entrainment rate increases due to higher heat flux © 2024, The Authors. All rights reserved.

关键词： Heat flux

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 Study on the Plate-Type Fuel Melting Behaviors Based on Alternative Materials

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SSRN 2024年

作者： Wu, Zhiyuan Li, Kepiao Zhang, Kui Chen, Ronghua Tian, Wenxi Qiu, Suizheng State Key Laboratory of Multiphase Flow in Power Engineering Department of Nuclear Science and Technology Xi’an Jiaotong University Xi’an710049 China

In this paper, low-temperature experiments are carried out on the visualized experimental device to study the melting behavior of plate-type fuel in severe accidents of the reactor. In the experiments, the plate-type fuel with different sizes made of nickel-chromium alloy, zinc and aluminum was used to carry out the visualized experiments in air, argon, and vacuum environment. It was found that both the size of the plate and the experimental environment have a significant influence on the melting behavior in this study. And the temperature distribution, melting behavior characteristic, the key parameters such as foaming position, foaming size, breaking position and breaking size were also obtained. Based on the experimental data, the physical phenomena and processes related to the blistering and melting of the fuel plates are analyzed in this paper, which provides experimental data support for the development of analysis model and formulating perfect mitigation strategies for severe accidents. © 2024, The Authors. All rights reserved.

关键词： Melting