CGN Delingha 50MW parabolic trough solar power plant is China's first commercial trough solar power station. There are 190 heat collecting loops in the solar field of the power plant. Due to the mutual coupling of heat collecting loops layout location, environmental conditions, medium flow, working medium physical property changes and other factors, the hydrodynamic characteristics of the solar field are complex. In practical operation, balancing the flow of the heat absorbing medium in each loop of the large-scale trough solar thermal power plant and stabilizing the outlet medium temperature are difficult problems. Taking CGN Delingha 50MW parabolic trough solar power plant as the research object, this paper adopts the idea of modular modeling to establish the mathematical model of the main equipment in different systems of the power plant, to build the dynamic model of its solar field, steam generation system, heat storage system and steam turbine system. Based on the parallel computing function of the real-time dynamic simulation platform STAR-90, the real-time coupling calculation between different systems is realized. The error of the built model in steady-state is less than 2%, and the dynamic results of the model are in good agreement with the actual operation data. The modeling method in this paper is universal and can be a reference for dynamic modeling of other large-scale trough solar thermal power plants.

先进绝热压缩空气储能是一种储能规模大、对环境无污染的储能方式.为了提高储能系统效率,本工作提出了一种耦合光热发电储热-有机朗肯循环的先进绝热压缩空气储能系统(AA-CAES+CSP+ORC).该系统中光热发电储热用来解决先进绝热压缩空气储能系统压缩热有限的问题,而有机朗肯循环发电系统中的中低温余热发电来进一步提升储能效率.本工作首先在Aspen Plus软件上搭建了该耦合系统的热力学仿真模型,随后本工作研究并对比两种聚光太阳能储热介质对系统性能的影响,研究结果表明,导热油和太阳盐相比,使用太阳盐为聚光太阳能储热介质的系统性能更好,储能效率达到了115.9％,往返效率达到了68.2％,?效率达到了76.8％,储电折合转化系数达到了92.8％,储能密度达到了5.53 kWh/m3.此外,本研究还发现低环境温度、高空气汽轮机入口温度及高空气汽轮机入口压力有利于系统储能性能的提高.

A dynamic simulation model of a heliostat field and molten salt receiver system are developed on the STAR-90 simulation platform. In addition, a real-time simulation model coupling the above two models is built to study the photothermal conversion process of Delingha’s 50 MW solar power tower plant. The nonuniform and time-varying characteristics of the energy flux density on the receiver surface and the dynamic characteristics under different operating conditions are studied. The operational process of the receiver of a typical day is simulated. It was found that there was a strong positive correlation between the energy flux and DNI, and the maximum energy flux density on the surface of the heat absorbing tube panel moved from the first tube panel to the fourth in sequence from 12:00 to 18:00. At the same time, the energy flux density of the last four panels decreased gradually along the arrangement order of the panels. DNI, molten salt mass flow rate and inlet temperature step disturbance simulations are carried out, and the response curves of the molten salt outlet temperature and tube wall temperature are obtained. The conclusion of this paper has important guiding significance for the establishment of an operational strategy for photothermal coupling in a molten salt solar power tower plant.

槽式太阳能光热电站运行过程中,集热回路的导热工质出口温度稳定是电站安全可靠运行的重要控制目标.由于集热管的结构特点,槽式集热器出口温度具有大惯性、大延迟、出口温度控制问题复杂等特性.为此,构建了兆瓦级槽式太阳能集热回路的动态数学模型,并在集热器出口构建了温度控制系统,提出一种槽式太阳能发电集热回路出口温度的阶梯式预测控制器,并基于 MATLAB/Simulink 平台进行了仿真.仿真结果表明,对于槽式集热回路,在辐照、导热油入口温度和环境温度扰动情况下,相较于传统PID控制系统,阶梯式预测控制器调节时间更短,超调量更小,鲁棒性更好,控制效果提升明显.所提出预测控制器能很好地应对集热场出口导热油超温及导热油流量波动频繁的情况,有利于槽式集热场的安全稳定运行.

In China, most pumped-storages power plant employ design scheme of one water conveyance system with several units, especially one water conveyance system with two units. Therefore, phenomenon of hydraulic disturbance often occurs. In this paper, focusing on two units in one conveyance system of Xianju pump-storage station, i.e. Unit 1 and Unit 2, disturbed powerhouse vibration was investigated for the other unit 100% load rejected. Time-domain and frequency domain characteristics were obtained by techniques of time-domain and frequency-domain analysis. The research indicates that for the disturbed powerhouse section, the permutation entropy of vibration signals have the same trend of active power, the disturbed powerhouse section is much more affected by disturbed unit (Unit 1) than the load rejection unit (Unit 2), the maximum root-mean-square value of vibrations in the powerhouse section of the disturbed unit occurs during the active power regulation of unit 1, and the vibration signals contain rich rotor-stator interference frequency components caused by load rejection unit. The observation results provide a useful basis for the optimization analysis of powerhouse structure in the subsequent construction of pumped-storage power station.

China General Nuclear Power Group (CGNPC) Delingha 50 MW parabolic trough solar thermal power plant is the first commercial trough solar plant in China, and its solar field consists of 190 parallel heat collecting loops. For large-scale trough solar plant, balancing the flow rate of heat absorbing medium in each loop and stabilizing the outlet temperature are the key technologies and difficult problems. Regarding the Delingha 50 MW solar field as the research object, this paper mainly focusing on the dynamic characteristics of flow and heat transfer in the solar field. The hydrodynamic calculation model and the heat transfer dynamic model are established on the real-time dynamic simulation platform STAR-90. With the actual operation data, the built solar field model is vali-dated by comparing the simulation results. On this basis, the disturbance simulations of direct normal irradiance (DNI), heat transfer oil's mass flow and heat transfer oil's inlet temperature are carried out. The dynamic response curves of disturbance and the thermal inertia time constant of the loops are obtained. The conclusions lay a theoretical foundation for the formulation of outlet medium's temperature control strategy in the solar field of large-scale trough solar thermal power generation system.

储热系统的热功转换使得太阳能热发电技术与其他可再生能源发电技术相比具有独特的优势.在太阳能热发电领域,槽式聚光集热发电技术与双罐熔盐间接储热系统应用最为广泛,并已成功商业化.以德令哈50 MW槽式太阳能光热电站为研究对象,基于集总参数法建立了其双罐熔盐间接储热系统的动态仿真模型,在iSimu仿真平台上对模型进行了验证.在此基础上,在充热、放热过程中进行了导热油质量流量阶跃扰动模拟仿真,研究了导热油/盐管壳式换热器中导热油出口温度、熔盐出口温度和熔盐储罐内熔盐高度的变化.仿真结果表明,所建立的模型能很好地模拟双罐熔盐间接热能储存系统的充放热动态特性,对系统设计、调峰控制和安全运行策略制订具有指导意义.

In spite of the discontinuous nature of solar energy, concentrated solar power (CSP) plant with thermal energy can not only stabilize output but also be operated as a peak load regulation plant in a multi-energy system. This work demonstrates the dynamic characteristics of the key heat transfer components and thermal transport processes of a solar power tower (SPT) plant with thermal energy storage, which is operated under the disturbances of external environment and electricity demand. A 50MW commercial power tower plant is chosen as the study object. Detailed systematic dynamic models based on two modelling method of essential sub-systems are developed, implemented, and integrated into TRNSYS to improve the reliability of simulation as well as the prevision accuracy. The model is completed with a control strategy that regulates the water level in the evaporator efficiently. System-level simulation is conducted by two time scales, during a couple of minutes, and on a couple of hours. It is shown that the model can provide theoretical reference data for the unit operating characteristic analysis, predict the trend of the plant thermal characteristics. The thermal transport characteristics in the steam generation system and steam turbine have been revealed, which is useful for the study of regulatory mechanisms for a peak-shaving plant.

The spherical capsule is one of the most common geometrical configurations for latent heat thermal energy storage. This study develops a modified heat capacity method coupling with the volume of fluid model to calculate the unconstrained melting inside the spherical capsule. Based on the force balance of the sinking solid body PCM, the solid velocity is implicitly introduced and incorporated in the extended Darcy term. The forces exerted on the solid PCM are calculated through the volume integral. Then, the proposed model is used to simulate the reported unconstrained melting experiments inside a spherical capsule filled with n-octadecane. The influence of the mushy zone constant on the melting processes is discussed, and the natural convection, solid moving, heat transfer, and melting behaviors are analyzed. It is found that the melting rate decreases with the increase of the mushy zone constant. The present model with a suitable mushy zone constant can reasonably predict the unconstrained melting. Besides, the appropriate mushy zone constant tends to increase with a higher Ste number. The total charging heat transfer rate linearly decreases during the melting process after the melt layer shapes. The heat transfer rate of the contact melting below the solid PCM is about 60 %-80 % of the total heat transfer rate and is much higher than that of the natural convection above the solid PCM. The thickness of the melt layer between the bottom solid PCM and the capsule shell increases after the lifting phenomenon, and it is less than 1 % of the capsule diameter.

Operation control of parabolic trough solar thermal power generation system is a difficult issue in the operation of the system. The solar field of the first 50 MW trough solar thermal demonstration power plant in China is taken as the research object. Based on the topological structure and working principle of the solar field and the basic laws of optics and thermodynamics, the hydrodynamic calculation model and the heat transfer dynamic model of the multiple parallel heat collecting loops are developed on the real-time dynamic simulation platform iSimu. Using the parallel computing capabilities of the platform iSimu, the full working condition simulation of the solar field is realized. On this basis, the step disturbance experiments of direct normal irradiance (DNI), heat transfer oil’s flow and heat transfer oil’s temperature at the inlet of the solar field are carried out. In addition, the dynamic response curves of step disturbance and the inertia time constant of the heat collecting loops are obtained. The conclusions of this paper have important guiding significance for the operation control strategy formulation and system optimization design of trough solar thermal power generation system.

太阳能热发电发电量计算的准确性,直接影响太阳能热发电项目技术经济性评价结果.当前太阳能热发电性能评估软件采用以1 h为计算步长的静态发电量计算模型,不能准确计算太阳辐照波动引起的槽式太阳能热发电系统工况变化过程发电量.在中广核德令哈50 MW槽式太阳能热发电示范项目实践的基础上,根据槽式太阳能热发电系统组成和工作原理,开发了集热场、储能系统、蒸汽发生器和汽轮发电机组的动态数学模型,能够准确计算因气象条件变化引起槽式太阳能热发电系统变工况过程的发电量.在此基础上,根据项目现金流和财务计算方法建立了槽式太阳能热发电项目的技术经济模型,开发了适合我国国情的槽式太阳能热发电性能评估软件,为我国槽式太阳能热发电项目技术经济性评价和项目投资决策提供技术支撑.

对塔式太阳能热电站进行能量分析,可有效地提升系统性能.传统的(火用)分析可从本质上揭示热力系统中能量损失发生的部位及原因,而先进(火用)分析通过将部件的(火用)拆分量化计算,可进一步提示部件与系统间的耦合关系.本文以某太阳能塔式热发电站的能量系统为研究对象,在给定的镜场布置与太阳辐射模型条件下,计算出各子系统的(火用)损与(火用)效率,定位能耗较高的部件.在此基础上,开展先进(火用)分析的计算,得到各部件的内部/外部(火用)损的结果,对各部件的不可逆性与系统耦合影响进行了量化分析.文中所用方法可为塔式光热系统的优化设计提供参考.

In order to control the outlet temperature of the heat transfer fluid within reasonable range, it is necessary to develop a fast-response and effective control system for the outlet temperature in the parabolic trough solar plants. In this paper, a dynamic mathematical model of parabolic trough collector loop was established first, which took the solar field of a 1 MW solar parabolic trough power plant as the research object. And then an internal model controller (IMC) for the outlet temperature of the heat transfer fluid was proposed based on the developed mathematical model. Afterwards the IMC control system and PID control system were built respectively on the Simulink platform such that. the control effects under multiple disturbances were compared and analyzed accordingly. The results show that: under the disturbances of solar radiation, inlet temperature and ambient temperature, the IMC controller demonstrates better control effect with less time duration for control setting and less overshoot in contrast with the PID controller.

To better understand the characteristics of a large-scaled parabolic trough solar field (PTSF) under cloud passages, a novel method which combines a closed-loop thermal hydraulic model (CLTHM) and cloud vector (CV) is developed. Besides, the CLTHM is established and validated based on a pilot plant. Moreover, some key parameters which are used to characterize a typical PTSF and CV are presented for further simulation. Furthermore, two sets of results simulated by the CLTHM are compared and discussed. One set deals with cloud passages by the CV, while the other by the traditionally distributed weather stations (DWSs). Because of considering the solar irradiance distribution in a more detailed and realistically way, compared with the distributed weather station (DWS) simulation, all essential parameters, such as the total flowrate, flow distribution, outlet temperature, thermal and exergetic efficiency, and exergetic destruction tend to be more precise and smoother in the CV simulation. For example, for the runner outlet temperature, which is the most crucial parameter for a running PTSF, the maximum relative error reaches −15% in the comparison. In addition, the mechanism of thermal and hydraulic unbalance caused by cloud passages are explained based on the simulation.

The study investigates the heat transport characteristics of the solar power tower station with thermal energy storage, which serves as a peak regulation source in the grid. A 50 MW power tower plant is chosen as object. The systematic dynamic models of essential sub-systems are developed. The model is matched with control strategy that regulates the water level in the evaporator efficiently. System-level simulation is conducted under different disturbances. For a short period disturbance, the thermal transport characteristics of system parameters during the heat transport process under four-step disturbances have been analyzed. Variation of heat distribution among different heat exchangers and instability of water level are discovered. The steam generating system has significant thermal inertia compared with that of steam turbine. For a long period of disturbance, the peak shaving characteristic curve of the plant operated under peak regulation mode is presented. It takes 1 h to load-up and 2 h to off-load between the basic load and designed load. Dangerous working condition is found during offload. The impact of different ramp rates is revealed. PID control strategy is more sensitive to an 8% ramp rate. The results could provide references for peak regulation capacity of a solar power tower station. (C) 2020 Elsevier Ltd. All rights reserved.

Solar resources are inherently unsteady and their energy density on the earth is low. Thereby, when the solar energy is converted into thermal energy through concentrating the sunlight, how to predict the transient performance of parabolic trough solar collectors under the operating conditions is necessary for the steady useful output and the efficient use of the energy. So this paper describes a mathematical model of the transient thermal behaviors of parabolic trough solar collectors. Then, to validate this transient model, its numerical results are compared with the experimental data. These data were collected from a utility-scale loop of parabolic trough solar collectors. The comparison between the model predictions and the experimental data shows a consistent and reasonable agreement. Furthermore, the primary interest of this study is to determine how the temperature distributions of the absorber, the glass envelope and the heat transfer fluid evolve from initial conditions with specified optical and thermal parameters. Thus, this model is used to carry out parametric studies to make analyses of essential impact factors on transient behaviors of parabolic trough solar collectors. These factors include the temperature of the heat transfer fluid at the inlet, the initial conditions, and the optical efficiency. Moreover, this model has the function of continuous adjustment of the flow rate to satisfy the requirement of the temperature of the heat transfer fluid at the outlet according to varying boundary conditions. Hence, another analysis is performed to investigate transient processes when the flow rate is continuously adjusted at various DNI ramp rates.

A thermal energy storage system is a critical component in concentrating solar power plants (CSPP), owing to which concentrating solar power (CSP) has superiorities over photovoltaic and wind power. Currently, the sole thermal energy storage (TES) system which is commercially applied to parabolic trough solar power (PTSP) plants worldwide is the two-tank indirect TES. In this study, the dynamic models of a solar field (SF), a two-tank indirect TES system, and a steam generation system (SGS) in a PTSP plant were developed and validated. Control and operation strategies on a clear day and a cloudy day were provided, and the dynamic simulations of the coupled operation using actual meteorological data were conducted. The influence of the two-tank indirect TES system on the dynamic characteristics of SGS on a system level was analyzed. Other key parameter variations were also presented. The results show that during the transition from the charge to the discharge process, the steam parameters slowly decrease. The variation of the molten salt height is further affected by the molten salt mass flow rate at the inlet and outlet of the molten salt tank. We adopted the PI control to adjust the thermal oil mass flow rate, thermal oil temperature, and water height. The developed dynamic models are useful in guiding system operation and control.

For parabolic trough solar collectors, several factors (such as the amount of the gas in the evacuated annulus, the absorber emissivity, the wind speed and temperature distributions of the absorber, the glass envelope and the heat transfer fluid) are critical to influence their heat losses and consequently their overall performance. Therefore, this study develops a mathematical model for thermal behaviors of parabolic trough solar collectors in consideration of these impact factors. Additionally, to validate this model, experimental data were measured for a test facility. This facility includes a utility-scale loop of parabolic trough solar collectors which can be applicable to solar thermal power plants. The comparison indicates a good agreement between predicted and measured temperatures of the heat transfer fluid at the outlet of the collectors. Using this model, parametric studies were conducted for impact factors. These factors are the pressure of the H-2 or air from 0.01 to 1E5 Pa, the absorber emissivity from a measured basis to its four times, the wind speed from 2 to 12 m/s, and temperature distributions with and without the concentrated solar flux. Consequently, several conclusions were drawn by analyzing how they influence heat losses and further overall performance under specified boundary conditions. (C) 2018 Elsevier Ltd. All rights reserved.

In a parabolic trough solar power plant, the steam generation system is the junction of the heat transfer fluid circuit and the water/steam circuit. Due to the discontinuous nature of solar radiation, the dynamic characteristics of working fluid physical parameters, such as mass flow rate, temperature, and pressure, are more evident in the steam generation system in this kind of plant, increasing the complexity of system operation. In this paper, a zero-dimension dynamic model of an oil/water steam generation system was developed based on the lumped parameter method. Based on the developed model, four typical single-parameter disturbance processes were simulated, and then the control strategy was obtained. System-level simulations on different days (clear and cloudy) and in different seasons (spring, summer, autumn, and winter) were also conducted on a STAR-90 simulation platform using real meteorological data. The simulation results show that PI control can be used to adjust the water level, that system operation on cloudy days should be avoided, and that the system can continue to generate steam after the sun sets. The simulation results can provide a useful reference for plant operators.

In this paper, a thermal hydraulic dynamic model (THDM) is developed to improve the efficiency and controllability of a parabolic trough solar field (SF). The THDM is divided into a hydraulic submodel and a thermal submodel; these two submodels interact via flowrate and temperature of the heat transfer fluid. Three experimental cases are then used to validate the THDM based on the Badaling 1 MW parabolic trough solar thermal power pilot plant. In Case 1, the compared results show good agreement between the simulated and measured values without the effect of the control valve, the root mean square errors (RMSEs) for the flowrate and the outlet temperature are less than 0.3 m(3)/h and 8 degrees C, respectively. In Case 2, the compared results maintain good agreement under the influence of the control valve, the RMSEs for the flowrate and the outlet temperature are less than 1m(3)/h and 10 degrees C, respectively. In Case 3, a method for balancing the flow distribution is tested using the pilot plant. The results indicate that this method enables the standard variance of the flow distribution to approach zero by changing the valve position to the calculated values. (C) 2018 Elsevier Ltd. All rights reserved.