Springer Link: https://link.springer.com/journal/11630/28/3
Special Issue dedicated to the 1st International Conference on Supercritical CO2 Power System (ICSCPS 2018)
This Special Issue of Journal of Thermal Science (JTS) contains a selection of peer-reviewed papers from the ICSCPS 2018, held in Beijing, China during June 29th to July 1st, 2018. The conference was chaired by Professor Jinliang Xu from the North China Electric Power University and sponsored by the Ministry of Science and Technology of China based on the National Key Research & Development Project "Fundamental studies and key technology development of high-efficiency carbon dioxide coal-fired power system".
The conference aimed to bring together leading academic scientists and researchers worldwide to share their outcomes and experiences on supercritical CO2 (S-CO2) power systems and to discuss the practical challenges. A wide range of topics were covered by the conference including coal-fired power generation, clean energy utilization, thermodynamic cycles, system optimization as well as life cycle and economic analysis of the power system.
Fourteen papers collected in this Special Issue have passed the conference review process and been presented at ICSCPS 2018. To make sure that these papers are eligible for publication in JTS, a further peer review process by qualified international reviewers was also carried out by JTS after the conference, which finally resulted in the selections of this Special Issue, which is a valuable presentation of the state-of-the-art advances in S-CO2 Power systems.
Research papers cover the subjects of combination of CO2 cycle with pulverized or fluidized bed coal-fired boiler, solar energy, solid oxide fuel cell (SOFC) and diesel engine. Especially, Professor Ilmutdin Abdulagatov from the Russian Academy of Sciences has contributed a critical review on the S-CO2 properties and technological applications; Prof. Jinliang Xu and coauthors have investigated the reheat arrangements in application of S-CO2 cycle in coal-fired power generation systems. Topics also include the proper selection of the material dispersion using supercritical fluid media, the heat transfer characteristics of S-CO2 in heat transfer tubes in a pulverized coal-fired furnace, the S-CO2 cycle applied in a fluidized bed boiler, the performance of S-CO2 cycle and ORC combined system considering the diurnal distribution of solar radiation, the S-CO2 cycle and a radial turbine for SOFC vehicle waste-heat recovery, the transcritical Rankine cycle for multiple waste heat recovery of a diesel engine using CO2 as the working medium.
It is therefore with pleasure that we were given the opportunity to edit this Special Issue. We would like to thank all the contributors of this Special Issue for their support and cooperation. We also thank all the reviewers for their critical comments to ensure the academic quality of this Special Issue.
Leading Guest Editor:
Prof. JinliangXu, E-mail: xjl@ncepu.edu.cn
North China Electric Power University, Beijing,China
Guest Editors:
Prof. Yinshi Li, E-mail: ysli@mail.xjtu.edu.cn
Xi’an Jiaotong University, Xi’an, China
Dr. Jian Xie, E-mail: xiejian90@ncepu.edu.cn
North China Electric Power University, Beijing,China
Prof. Gongnan Xie, E-mail:xgn@nwpu.edu.cn
Northwestern Polytechnical University, Xi’an, China
CONTENS
1. Supercritical CO2: Properties and Technological Applications - A Review
NIKOLAI Polikhronidi, RABIYAT Batyrova, ASLAN Aliev, ILMUTDIN Abdulagatov
Journal of Thermal Science, 2019, 28(3): 394-430
DOI: https://doi.org/10.1007/s11630-019-1118-4
Keywords: carbon dioxide, critical point, equation of state, supercritical fluid, thermodynamic properties, transport properties
Abstract: The main goal of the present paper is to assess the available information so as to obtain a general procedure for dealing with the critical enhancement of the thermodynamic and transport properties of supercritical CO2 and CO2 containing binary mixtures for practical and scientific applications. The present review provides comprehensive analysis of the thermodynamic and transport properties of supercritical carbon dioxide and CO2 containing binary mixtures (experiment and theory) and their various technological and scientific applications in different natural and industrial processes. The available information for the thermodynamic and transport properties (experiment and theory) enhancement (anomaly) of supercritical carbon dioxide and SC CO2 + solute mixtures is comprehensively reviewed. The effect of long-range order parameter fluctuations on the thermodynamic and transport properties of supercritical fluids (SC CO2) will be discussed. Simplified scaling type equation based on mode-coupling theory of critical dynamics with two critical amplitudes and one cutoff wave number as fluid-specific parameters was used to accurately predict of the transport properties of supercritical carbon dioxide. The recommended values of the specific parameters (asymptotic critical amplitudes) of the carbon dioxide for practical (prediction of the thermodynamic and transport properties of the supercritical CO2 for technological applications) and scientific use were provided. The role of the critical line shapes of the carbon dioxide containing binary mixture (SC CO2+solvent) in determination of the critical behavior of the mixture near the critical point of pure supercritical solvent (CO2) is discussed. Krichevskii parameter concept for a description of thermodynamic behavior of dilute near-critical SC CO2+solute mixtures is also discussed. The structural and thermodynamic properties of the carbon dioxide containing binary mixtures near the critical point of pure solvent (CO2) are discussed.
2. Single-Reheatingor Double-Reheating, Which is Better for S-CO2 Coal Fired Power GenerationSystem?
SUN Enhui, XU Jinliang, HU Han, YAN Chenshuai, LIU Chao
Journal of Thermal Science, 2019, 28(3): 431-441
DOI: https://doi.org/10.1007/s11630-019-1130-8
Keywords: S-CO2 coal fired power system, thermodynamics, heat transfer, reheating, residual flue gas heat
Abstract: The objective of this paper is to provide the optimal choice of single-reheating or double-reheating when considering residual flue gas heat in S-CO2 coal fired power system. The cascade utilization of flue gas energy includes three temperature levels, with high and low temperature ranges of flue gas heat extracted by S-CO2 cycle and air preheater, respectively. Two methods are proposed to absorb residual flue gas heat Qre in middle temperature range. Both methods shall decrease CO2 temperature entering the boiler T4 and increase secondary air temperature Tsec air, whose maximum value is deduced based on energy conservation in air preheater. The system is analyzed incorporating thermodynamics, boiler pressure drop and energy distribution. It is shown that at a given main vapor temperature T5, the main vapor pressure P5 can be adjusted to a value so that Qre is completely eliminated, which is called the main vapor pressure adjustment method. For this method, single-reheating is only available for higher main vapor temperatures. The power generation efficiency for single-reheating is obviously higher than double-reheating. If residual flue gas heat does exist, a flue gas heater FGC is integrated with S-CO2 cycle, which is called the FGC method. Both single-reheating and double-reheating share similar power generation efficiency, but single-reheating creates less residual flue gas heat. We conclude that single-reheating is preferable, and the pressure adjustment method achieves obviously higher power generation efficiency than the FGC method.
3. Numerical Investigationof Heat Transfer Characteristics of Supercritical CO2 Tube in Combustion Chamberof Coal-Fired Boiler
WANG Jimin, CHEN Xue, ZHANG Chao, GU Mingyan, CHU Huaqiang
Journal of Thermal Science, 2019, 28(3): 442-453
DOI: https://doi.org/10.1007/s11630-019-1106-8
Keywords: supercritical CO2, numerical simulation, combustion chamber, heat transfer characteristics, inclined angle
Abstract: To achieve compact structure, light weight, and high thermal efficiency for the coal-fired boiler, the supercritical CO2 power cycle has been considered as one of the promising alternatives in the coal-fired power conversion system. One of the major problems concerning fossil fuel powered plants is the safety of the water wall in boiler design. In this work, the heat transfer characteristics of the supercritical CO2 tube in the combustion chamber were determined through the low Reynolds number k-εmodel, the gas real model and the P-1 radiation model. The study covered the supercritical CO2 tube and the fins, and the annulus flue gas passage was also included. The wall temperature and the heat transfer coefficient were compared against those obtained from the experiments. Based on the examinations of the calculated flow and turbulence fields, the distributions of the velocity and the temperature inside the supercritical CO2 tube in the combustion chamber were resolved numerically. Moreover, the effects of the heat transfer coefficient on the heat transfer characteristics were also discussed. And it was numerically focused on the influence of the inclined angle on the flow and the heat transfer of the supercritical CO2 tube. The results show that the heat transfer coefficient keeps namely constant as the increasing inclined angle. It would help to better understand the heat transfer mechanism of unique characteristics of supercritical CO2 above the pseudo-critical temperature, which may provide the corresponding theoretical basis on the optimization design of the coal-fired boiler.
4. Effect of Operating Condition and Structural Parameter in the Hydrostatic Thrust CO2 Bearing
LI Liangliang, XIE Yonghui
Journal of Thermal Science, 2019, 28(3): 454-462
DOI: https://doi.org/10.1007/s11630-019-1113-9
Keywords: slit-restricted, supercritical carbon dioxide, hydrostatic thrusting bearing, slit arrangement, film thickness, rotating speed
Abstract: Hydrostatic thrust bearings are widely applied inrotating machinery field. Its comprehensive performance and safe operation is of great significance for ensuring equipment efficiency. In this paper, the numerical method is adopted to investigate the slit-restricted hydrostatic thrust CO2 bearing with a small film thickness. The research is carried out from two aspects, which mainly consider the operating conditions and structural parameters. Firstly, the influence of different working fluid types including real air and CO2 (include subcritical and supercritical state) on the static characteristics of bearing is studied, and the results indicate that the bearing with CO2 as working fluid has a better static performance. Secondly, the influence of rotor rotating speed is studied and the conclusion shows that the rotating speed has a significant effect on bearing static characteristics. Thirdly, the influence of different slit arrangement forms is investigated, and the consequence indicates that the circumferential slits show a better load capacity than that of radial slits, while the flow rate difference is small. Finally, the effect of film thickness on bearing static performance is investigated and the research shows that this factor affects static performance in a dramatical way. When the clearance tends to be smaller, the load capacity increases sharply, while the massflow rate of working fluid decreases.
5. Performance of S-CO2 Brayton Cycle and Organic Rankine Cycle (ORC) Combined System Considering the Diurnal Distribution of Solar Radiation
GAO Wei, YAO Mingyu*, CHEN Yong, LI Hongzhi*, ZHANG Yifan, ZHANG Lei
Journal of Thermal Science, 2019, 28(3): 463-471
DOI: https://doi.org/10.1007/s11630-019-1114-8
Keywords: solar power generation, S-CO2 brayton cycle, ORC, thermal storage temperature, combined cycle
Abstract: This paper researches the performance of a novel supercritical carbon dioxide (S-CO2) Brayton cycle and organic Rankine cycle (ORC) combined system with a theoretical solar radiation diurnal distribution. The new system supplies all solar energy to a S-CO2 Brayton cycle heater, where heat releasing from the S-CO2 cooler is stored in the thermal storage system which is supplied to the ORC. Therefore, solar energy is kept at a high temperature, while at the same time the thermal storage system temperature is low. This paper builds a simple solar radiation diurnal distribution model. The maximum continuous working time, mass of thermal storage material, and parameter variations of the two cycles are simulated with the solar radiation diurnal distribution model. 10 organic fluids and 5 representative thermal storage materials are compared in this paper, with the mass and volume of these materials being shown. The longer the continuous working time is, the lower the system thermal efficiency is. The maximum continuous working time can reach 19.1 hours if the system provides a constant power output. At the same time, the system efficiency can be kept above 38% for most fluids.
6. Research on the Influence of Guide Blade Trailing Edge Structure on Turbine Performance
GAO Wenjing, LI Lei, YUE Zhufeng, LI Honglin, XIE Gongnan, TONG Fujuan
Journal of Thermal Science, 2019, 28(3): 472-483
DOI: https://doi.org/10.1007/s11630-019-1091-y
Keywords: high pressure turbine, trailing edge structure, turbine performance
Abstract: The complex structure at trailing edge reduces the manufacturing precision, which results in an error in the size of the trailing edge structure. In this study, the performance of a stage high-pressure turbine (HP turbine) is calculated out in three dimensions. In the HP turbine guide vane, the trailing edge cutback configuration is adopted. Through three-dimensional simulation,the complex flow around the trailing edge with cutback cooling configuration is presented in this study, and the manufacturing precision reduction due to the complex structure at trailing edge is considered. Furthermore, the effect of trailing edge lip thickness and deflection of the stator on the turbine performance is discussed. Overall, as the press-side lip thickness increasing, the turbine efficiency and turbine inlet flow are reduced. However, the changes in the turbine work output are relatively complex. On the other hand, as the spacing between suction-side lip and press-side lip increases, turbine performance becomes worse. Both of the turbine efficiency and the turbine work output become smaller, while the turbine inlet flow becomes bigger. The effect of the spacing between suction-side lip and press-side lip is obviously greater than that of the press-side lip thickness. The change of the press-side lip thickness has little effect on the relation between the turbine performance and the spacing between suction-side lip and press-side lip. However, when the spacing between suction-side lip and press-side lip deviates from the baseline value, the effect law of the press-side lip thickness on the turbine performance will be affected. As the press-side lip thickness increases, it leads to an increase in the low-velocity zone at both of the pressure-side and suction-side trailing edge. And more mainstream is affected or mixed into the wake flow. When the spacing between suction-side lip and press-side lip becomes smaller, the low-velocity zone at the trailing edge is smaller, and the change of vortex with the press-side lip thickness is affected. With a bigger spacing between suction-side lip and press-side lip, the variation iscontrary.
7. Phase Prediction of Supercritical Carbon Dioxide and its Application in Fracturing Oil Wellbores
GONG Liang, CHEN Shichao, ZUO Jiaqiang, BAI Bin, BAI Zhang
Journal of Thermal Science, 2019, 28(3): 484-493
DOI: https://doi.org/10.1007/s11630-019-1092-x
Keywords: supercritical carbon dioxide, unsteady-state heat transfer, phase prediction, wellbore
Abstract: In recent oil and gas exploration, the most reservoirs are low permeability with abundant reserves. Conventional mining of low permeability reservoir is commonly utilizing the hydraulic fracturing technology, whereas, it encounters various technical issues, such as clay expansion and water lock damage. Using the fluid of supercritical carbon dioxide (S-CO2) to exploit the low permeability oil and gas reservoirs is attracting more attention. The implementation of S-CO2, without liquid phase, can help avoid the aforementioned problems. Nevertheless, the phase change of CO2 during fracturing is complicate, and it is difficult to accurately predict the CO2 phase transition. In this work, first, the physical properties of S-CO2 were analyzed by the Span-Wagner model and Vesovic model. Next, S-CO2 was applied to atypical oilfield, and an unsteady coupling model of heat transfer and pressure drop was developed. Then the staggered grid method and iteration procedures were used for numerical solutions, and the temperature and pressure distributions of wellbores were investigated. The results indicate that the temperature control of a wellbore is the key to the phase prediction of S-CO2; CO2 within the single-diameter pipeline below 2300m can maintain the supercritical state, while CO2 within the stepped pipeline can maintain the supercritical state at the depth of 2280 m. Moreover, compared with the single-diameter pipeline, the bottom pressure of the stepped pipelineis lower and the bottom temperature is higher. By analyzing the flow and heat transfer of S-CO2 in the wellbores, the phase state of S-CO2 was well predicted, which is helpful to improve the exploring performance oflow permeability oil and gas reservoirs.
8. Carbon Dioxideas Working Fluids in Transcritical Rankine Cycle for Diesel Engine Multiple Waste Heat Recoveryin Comparison to Hydrocarbons
LIU Peng, SHU Gequn, TIAN Hua
Journal of Thermal Science, 2019, 28(3): 494-504
DOI: https://doi.org/10.1007/s11630-019-1090-z
Keywords: transcritical Rankine cycle, natural working fluid, multiple waste heat, performance comparison
Abstract: In consideration of the high-temperature characteristic of engine’s waste heat and stricter environmental regulations, natural substance, including CO2 and hydrocarbons, have been treated as promising working fluid for diesel engine waste heat recovery due to its environment friendly and excellent physical and chemical properties. This paper presented a comprehensive performance analysis on transcritical Rankine cycles for diesel engine multiple waste heat recovery using hydrocarbons and CO2 as working fluid. The optimal turbine inlet pressures corresponding to maximum net power output, maximum exergy efficiency and minimum electricity production cost (EPC) were obtained. The effect of working fluid on these optimal pressures has been discussed. For fluids with low critical temperature, the optimal pressure corresponding to maximum net power output is lower than the one for maximum exergy efficiency, while the opposite results can be found for fluid with high critical temperature. Then, the effect of various working fluid properties in transcritical cycle performance is discussed. Comparison results show that CO2 obtains only more power output than Ethane, Propane and Propene, but CO2 is capable of absorbing more energy from engine coolant and regeneration heat with comparable total heat transfer areas and has an advantage in turbine size, particularly for hydrocarbons with high critical temperature.
9. System Analysis on Supercritical CO2 Power Cycle with Circulating Fluidized Bed Oxy-Coal Combustion
SHI Yan, ZHONG Wenqi, SHAO Yingjuan, XIANG Jun
Journal of Thermal Science, 2019, 28(3): 505-518
DOI: https://doi.org/10.1007/s11630-019-1094-8
Keywords: S-CO2, oxy-coal combustion, CO2capture, CFB boiler, process simulation
Abstract: Supercritical carbon dioxide (S-CO2) Brayton power cycle is a competitive technology to achieve high efficiency in a variety of applications. However, in coal power applications, the CO2 generated from coal combustion still discharges into the atmosphere causing a series of environment problems. In this work, an 300 MWe S-CO2 power cycle with circulating fluidized bed (CFB) oxy-coal combustion was established including air separation unit (ASU), CFB boiler, recuperator system and carbon dioxide compression and purification unit (CPU). Based on the material and energy conservation, the cycle efficiency of S-CO2 (620°C, 25 MPa) Brayton power cycle with CFB oxy-coal combustion is evaluated compared to the oxy-coal combustion steam Rankine cycle and S-CO2 Brayton power cycle with the 31.65 kg/s coal supply. After that, the influence of several factors, e.g., exhaust flue gas temperature, split ratio in recuperator system and the oxygen supply on the cycle efficiency was investigated and analyzed. The results show that the net efficiency of S-CO2 power cycle with CFB oxy-coal combustion (32.67%) is much higher than the steam Rankine cycle utilizing CFB with 17.5 Mpa, 540°C steam (27.3%), and 25 Mpa, 620°C steam (30.15%) under the same exhaust flue gas temperature. In addition, lower exhaust flue gas temperature and higher split ratio are preferred to achieve higher cycle efficiency. Lower oxygen supply can reduce the energy consumption of ASU and CPU, further increasing the system net efficiency. However, the energy losses of ASU and CPU are still very large in oxy-coal combustion and need to be improved in further work.
10. Supercritical Fluid Media in Challenges of Substance and Material Dispersion
KHAIRUTDINOV Vener, GUMEROV Farid, KHABRIEV Ilnar
Journal of Thermal Science, 2019, 28(3): 519-546
DOI: https://doi.org/10.1007/s11630-019-1098-4
Keywords: supercritical fluid media, supercritical fluid anti-solvent method, dispersion, polycarbonate, paracetamol, ethylene-vinyl acetate copolymers
Abstract: The paper deals with the problem of material dispersion using supercritical fluid media. At the same time, emphasis is made on modifications (SAS, GAS, SEDS and ASES) of the supercritical fluid anti-solvent method of dispersion. The results of SAS method implementation for dispersion of pure polycarbonate and polycarbonate doped with “CdSe/CdS - core/shell” quantum dots (carried out in the pressure range of 8.0-25.0 MPa at temperatures of 313.15 K and 358.15 K) are submitted. The range of the operating parameters has been established through the example of pure polycarbonate dispersion, which provides the production of nanoparticles with the size range of 10-100 nm. Encapsulation of CdSe/CdS quantum dots into polycarbonate using the SAS method has no effect on optical properties of the encapsulated quantum dots. The results of paracetamol dispersion using the SEDS method are presented. The effect of operating conditions of the paracetamol dispersion process on morphology of the obtained product is described. Co-dispersion of ethylene–vinyl acetate copolymers and low-density polyethylene mixtures by SEDS method has been carried out under pressures of 8.0-25.0 MPa at temperatures of 313 K, 323 K, and 333 K. The comparison of melting and crystallization between the resulting copolymer mixtures and mixtures with the same composition obtained by mixing in the liquid melt, has shown that implementation of SEDS results in an increase of crystallinity degree of the polymer mixtures.
11. Research on the Performance of Supercritical CO2 Dry Gas Seal with Different Deep Spiral Groove
DU Qiuwan, ZHANG Di
Journal of Thermal Science, 2019, 28(3): 547-558
DOI: https://doi.org/10.1007/s11630-019-1139-z
Keywords: supercritical carbon dioxide, different deep spiral groove, dry gas seal, thermal-fluid-solid coupling method
Abstract: The performance of supercritical CO2 (SCO2) dry gas seal (DGS) with different deep spiral groove is investigated with the thermal-fluid-solid coupling method. The performance parameters of DGSs with five different kinds of grooves are obtained. The influence of inlet temperature, inlet pressure, velocity and film thickness on performance is analyzed compared with air DGS. The average film pressure, open force and leakage decrease while the average face temperature and flow velocity increase as the spiral groove number increases. The average film pressure, average face temperature, open force and leakage of DGS with radial different deep groove are higher than those of DGS with circumferential different deep groove respectively under the same spiral groove number while the average flow velocity is the opposite. SCO2 DGS can generate larger average film pressure, open force and leakage with lower average face temperature than air DGS. SCO2 DGS could maintain better sealing performance despite larger leakage with the variations of inlet temperature, inlet pressure, velocity and film thickness. The variables hold a more remarkable influence on SCO2 DGS compared with air DGS.
12. Design and Analysis of S-CO2 Cycle and Radial Turbine for SOFC Vehicle Waste-Heat Recovery
XIA Liu, LI Xuesong, SONG Jian, REN Xiaodong, GU Chunwei
Journal of Thermal Science, 2019, 28(3): 559-570
DOI: https://doi.org/10.1007/s11630-019-1105-9
Keywords: SOFC, waste-heat recovery, supercritical carbon dioxide, radial turbine
Abstract: Solid oxide fuel cell (SOFC) vehicles are considered to have broad prospects for development, and the high operating temperature of SOFC results in great potential for waste-heat recovery. Many concepts for utilizing waste heat of SOFC have been suggested and studied, and most of them directly couple an SOFC to a gas turbine, which require the SOFC to operate at an elevated pressure and make the system less flexible and thus harder to operate. In recent years, with the development of turbine and heat exchanger technology, the supercritical carbon dioxide (S-CO2) power cycle has raised widespread attractions for the waste recovery. This study explores the potential of S-CO2 Brayton cycle to realize waste-heat recovery for an SOFC vehicle. The SOFC can operate at atmospheric pressure, and the hybrid system is easier to operate than the directly coupled systems. In this paper, a simple recuperated S-CO2 Brayton cycle is proposed and the key component, radial inflow turbine is designed and focused. The flow state of the designed turbine is analyzed in detail based on computational fluid dynamics (CFD) numerical simulation. Five cases with different impeller tip clearances are numerically simulated to study its influence on the turbine performance. In addition, off-design performance analysis of the radial inflow turbine is conducted considering the temperature fluctuation of SOFC in practical applications.
13. Study on Flow Characteristics of a Turbulent Boundary Layer and Vortex Structure of High Pressure Guide Vanesin SCO2 Turbines
HAN Wanlong, WANG Yueming, FENG Zhenping, LI Hongzhi, YAO Mingyu, ZHANG Yifan
Journal of Thermal Science, 2019, 28(3): 571-584
DOI: https://doi.org/10.1007/s11630-019-1110-z
Keywords: SCO2 turbine, vortex structure, dimensionless vorticity, logarithmic layer, viscous sublayer, secondary flow
Abstract: In order to further understand the aerothermodynamic performance and flow loss mechanism of SCO2 turbines, RANS equations and an SST Turbulence Model were chosen for a numerical study on the secondary flow and vortex structure of cascades using the commercial software CFX. The dimensionless vorticity analysis method was used to study the flow characteristics of the logarithmic layer and viscous sublayer in high pressure guide vane cascades. The new vortex structure and formation mechanism of the vortices were given and analyzed. Simulation results indicated that during the motion of the boundary layer in the cascades, the logarithmic layer and viscous sublayer obtain the different rotational direction vorticity, respectively. The endwall logarithmic layer and pressure side leg of the horseshoe votex gradually develop into the passage vortex, with the endwall viscous sublayer gradually developing into the corner viscous sublayer vortex II and the endwall viscous sublayer vortex I. The endwall viscous sublayer that rolled by the passage vortex is encountered with the upstream-side and radial boundary layer of the vane at the suction separation line, forming the suction separation line vortex beside the passage vortex. A pair of radial transition vortices are formed between the wake and the main stream.
14. Design and Performance Simulation of a Novel Liquid CO2 Cycle Refrigeration System for Heat Hazard Controlin Coal Mines
ZHAI Xiaowei, XU Yu, YU Zhijin
Journal of Thermal Science, 2019, 28(3): 585-595
DOI: https://doi.org/10.1007/s11630-019-1111-y
Keywords: LCO2 refrigeration, working face cooling, numerical simulation, heat exchange
Abstract: LCO2 (liquid CO2) can absorb heat and release latent heat via phase transition, which can provide considerable cooling energy and effectively solve the problem of thermal damage in deep coal mining processes. A LCO2 cycle refrigeration system is designed to continuously cool down the working face in a mine, and CO2 is cyclically utilized. Additionally, LCO2 is used not only as a cold source but also to prevent spontaneous combustion of coal in the gob. COMSOL Multiphysics simulation software is used to characterize the thermal performance of the heat exchange system, where the heat transfers between the CO2 and the airflow. For a LCO2 consumption of 13.54 m3/h, the temperature of the airflow in the tunnel decreases by 7.72°C, and the cooling volume of the system reaches 142.99 kW/h; the cooling volume provides a latent heat release of 46.68 kW/h. The main influencing factors of the refrigeration system, such as ventilation flux, LCO2 flow, LCO2 temperature and initial tunnel temperature, are also analyzed quantitatively through the software. The temperature of the steady airflow in the tunnel is proportional to the square of the local fan ventilation flux, and it decreases linearly with an increase in the LCO2 flow but increases with both the temperature of the LCO2 and the initial temperature in the tunnel. When the temperature difference between the LCO2 and wind increases, the heat exchange between the CO2 and wind intensifies, and the cooling volume increases.
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