Table of Content

25 May 2020, Volume 42 Issue 5

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Performance study on two-axis tracking method of parabolic trough collectors

ZHANG Zhi，SUN Jie*，QI Haojun

2020, 42(5):  1-7. 

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The performance affecting factors of two-axis tracking method taking by parabolic trough collectors were analyzed，and various tracking methods under different geometrically constrained conditions were compared. A time-intime heat collection simulation program for parabolic trough collectors was developed based on Matlab and validated. According to the analysis results，the solar radiation per unit area received annually shows an increase trend followed by a slight decline as the altitude rises，and its uneven distribution is more prominent as the latitude increases. Under geometrically constrained conditions，when the ratio of side length is greater than 1，the solar radiation per unit area received annually（Q）of a one-axis tracking device displayed in north-south direction is higher than that of the device displayed in east-west direction.As the row number of one-axis tracking devices increases，the Q gradually increases and is generally higher than that of two-axis tracking devices. Under the selected geographic conditions，the annual emission reduction is proportional to Q，and the cost of solar radiation per unit area received annually by two-axis tracking method is the lowest among various methods，and the cost of the devices displayed in north-south direction is lower than that displayed in east-west direction.

  Research on thermal stratification and control process in molten salt storage tanks

CUI Kaiping，HAN Wei，NI Yu，HAN Zhenxing，Francisco MANGAS

2020, 42(5):  8-13. 

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Heat storage system is one of the core systems in a CSP plant. During the commissioning，overhaul or under continuous poor weather conditions，storage tanks will encounter long-period shutdowns，resulting in thermal stratification which will affect the storage tank security. Intensifying the disturbance in storage tanks is the most effective means to eliminating the thermal stratification phenomenon，but there is little research on this method in storage tank design.The thermal stratification elimination realized by recirculation disturbance after the formation of thermal stratification in molten salt storage tanks was analyzed by CFD simulation. The results show that the molten salt recirculating inside the tanks can be fully mixed in 2.8 h when it is disturbed by a 100 kg/s flow. In a cold tank with a circulation pipe，it takes 3.1 h for mixing，and the maximum temperature difference of the molten salt in the storage tank drops to 14.5 ℃.Therefore，this flow can be regarded as the recirculating disturbance flow after thermal stratification in the operation phase of the project.

Modeling and optimization research on cascade heating of solar mirror fields

YU Xiucheng，ZHANG Zhi

2020, 42(5):  14-19. 

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Under such a background that China's electricity power is mainly generated by coal，solar energy，who has shown great potential in power generation coordinated with coal-fired power plants，is of high cost，large energy losses and other drawbacks. Taking the concept of cascade heating，a coordinated power generating model integrating solar mirror fields who combined evacuated tube heat collectors and parabolic trough collectors with traditional coal-fired units was presented， which can reduce the cost and energy losses efficiently. Besides，a parameter optimization study on the evacuated tube heat collector added in the model was carried out. The following conclusions were drawn based on a N600-24.2/566/566 supercritical intermediate reheat condensing coal-fired unit.The annual collected heat increased first and then decreased with the enlarging of tilt angle，and the optimal tilt angle was around 40° to 50°. The annual collected heat dropped gradually with the widening of plate spacing. Replacing the first stage extraction steam completely by the hybrid cascade heating system，the optimal temperature at the evacuated tube heat collector outlet was at 160 ℃ when the lowest Levelized Cost of Energy（LCOE）bottomed at 0.734 Yuan/（kW∙h）.

Finite element analysis on special pipe fittings of air cooling pipelines for solar thermal power plants

LIU Xue，LI Guodong，LIN Weining，CHE Chi

2020, 42(5):  20-23. 

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In order to ensure the secure and reliable operation of key pipe fittings in air cooling large exhaust pipelines of solar thermal power plants，ANSYS software is used to analyze a special reducing cross in the direct air cooling largediameter exhaust pipeline of 1×50 MW Xinjiang Hami Tower Solar Thermal Project. The stress state of the special reducing cross under the vacuum external pressure and self weight load is calculated，and its overall stability is analyzed. The stress calculation results are checked and verified according to the standard JB/T 4732—2005，which witness the necessity of improvement on the original pipe structure. The improved special reducing cross meets the requirements of the standard. The improvement can provide theoretical reference for the secure and reliable operation of a whole direct air cooling exhaust system.

  Preliminary design of combustion chambers of micro gas turbines

WANG Qingwu，WEI Mingxiang，ZHANG Junwei，WANG Jinqin

2020, 42(5):  24-30. 

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The combustion chamber is one of the core components in a gas turbine，whose performance is an important index for evaluating the performance of the gas turbine. According to the structural characteristics of the combustion chamber，a comprehensive design method for it is given. Firstly，functional zoning was made on the combustion chamber. Then，the temperature of the main combustion zone was selected based on the emissions of CO and NOx ，and the diameter of the outer cylinder was set in light of empirical values.Assuming that the air flow and the air temperature were linearly distributed along the axis，the length of combustion chamber could be chosen based on air residence time .To settle the vents down on the wall of the combustion chamber properly，the general distribution of the three combustion areas should be primarily set from experience and be specified by equivalent area method. Proven by several ignition tests，the combustion chamber designed by the method above has neither flameout nor flame ejection，which shows that the design method is feasible and realizes the rapid and accurate design of the micro gas turbine combustion chamber.

 Numerical analysis on 9E gas turbine DLN1.0 combustion system

DING Yang，HAO Jiangang，XIE Daxing

2020, 42(5):  31-36. 

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 To understand the design features of current low-pollution combustion chambers，numerical simulation was used

to simulate all combustion states in a DLN1.0 combustion chamber，and the actual NOx emission under combustion

adjustment state was compared with the simulation results. The results show that there are three recirculation zones

available for combustion in the DLN1.0 combustion chamber.The primary and lean-lean modes are of a higher flow velocity

in the Venturi tube. The conversion mode is of the highest heat load，and the premixed mode is of the lowest. The high

temperature zone is around the Venturi tube and the secondary nozzles.During the combustion adjusting process，the NOx

generated locally in the central combustion zone and in the outer combustion zone show an opposite variation trend.As the

fuel flow in the first-stage combustion zone increases，the mass concentration of NOx discharges from the combustion

chamber outlet drop to the bottom and increase slowly afterwards.

  Energy efficiency indicator modification and benchmarking management for gas turbine units

ZHU Yadi，LI Chen，XIE Daxing，XU Tingting

2020, 42(5):  37-42. 

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In order to develop the benchmarking management system for energy efficiency indicators，and improve the energy efficiency indicator management level for domestic gas turbine units，a three-level energy efficiency indicator benchmarking system was established based on the benchmarking experiences in traditional coal-fired units and characteristics of gas turbine units. Data statistical analysis，mechanism analysis，simulation calculation and other methods were used to establish the calculation model for the correction coefficients of power supply gas consumption affected by various boundary factors. According to the calculation model，a plant-level energy efficiency indicator benchmarking management system was established on a digital integrated platform of an E-level gas power generation enterprise，which achieved online benchmarking and analysis of energy efficiency indicators. This system makes it easy for operators to find the energy consumption gap from horizontal and vertical dimensions，and make diagnostic analysis on the location and causes of energy efficiency deviations，which provides guidance for unit operation optimization adjustment.

Early warning method for wind turbine generator temperature based on HK-SVM

CAO Li，PAN Qiaobo，WANG Mingyu，MA Dong

2020, 42(5):  43-49. 

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The operation state of a wind turbine will be affected by its generator，a key component of a wind turbine.The hybrid kernel-support vector machine（HK-SVM）was used to train the temperature model of a generator under normal working condition to make prediction.Firstly，appropriate sample data were screened，and the parameters with the highest correlationship with the generator bearing temperature at driving end were selected from them by using correlation calculation.Then，temperature range for a generator at normal working condition was established.When the generator ran abnormally，its dynamic characteristics deviated from that under normal working state，resulting in residual difference between the actual temperature and the predicted temperature obtained by HK-SVM. The residual distribution characteristics in the sliding window were calculated dynamically，and a reasonable alarm logic and a threshold were set to realize the early warning for the abnormal state of generators. The results show that this method is of great guiding significance for fault early warning and remote diagnosis of wind turbine.

 Research on wind turbine power curve based on Nacelle Transfer Function

YANG Mingming

2020, 42(5):  50-54. 

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Power curve is an important index to evaluate the performance of wind turbines. The power curve calculated by Nacelle Transfer Function is efficient，fast and comprehensive.A comprehensive analysis on three main Nacelle Transfer Functions was made. Among them，the momentum theory correction method based on momentum theory stream tube model is used to calculate the free flow wind speed according to the nacelle wind speed and power .The Binned-NTF correction method and the high-order polynomial partition fitting correction method use the nacelle wind speed and the wind speed measured by LiDAR to correct the wind speed based on the least square method. The engineering example of a plain wind farm shows that the fitting accuracy of wind speed and the error rate of power generation obtained by fitting methods are better than that made by momentum theory correction method. In the fitting methods，the high-order polynomial partition fitting method is better than the binned NTF method. The power generation error of the three methods is between -2.33% and 5.23%. The momentum theory correction method is affected by the approximation of lower section wind speed and the measurement accuracy of the nacelle anemometer，therefore the power generation error rate is slightly larger. In conclusion，the measurement accuracy of nacelle anemometer will affect the accuracy of NTF methods，and the high-order polynomial partition fitting correction method is better than the other two NTF methods.

Self-detecting method for faults in wind turbine controller I/O hardware based on BP neural network algorithm

JIANG Yin，REN Hongwei，CHEN Kai，ZHU Changjiang

2020, 42(5):  55-60. 

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With the fierce competition in wind power industry，market's requirements for the product delivery，operation and maintenance service provided by machine manufacturers are increasingly demanding.A low-cost fault self-detecting method suitable for controller Input and Output（I/O）hardware was proposed based on BP neural network algorithm，in order to mitigate the negative impacts of certain defective I/O hardware of controllers′batch inventory on the operation and maintenance service of the project.The neural network model was trained with the random sequence of fault sample data set. The self-detecting circuit constructed with I/O hardware and relays is designed for collecting sampling signals which are processed into a characteristic matrix of normalized data.Putting the data into the self-detecting model，reference results will be output after fault identification and classification. The experiment preliminarily verified that the method can effectively identify the I/O hardware fault without specified equipment，which is of practical application values.

Research and prospects of 66 kV offshore wind power AC collection scheme

WANG Feng，RUI Shoujuan，WANG Xiaohe，WANG Huaiming，WANG Yiwei

2020, 42(5):  61-65. 

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  With the continuous increase in the capacity and scale of offshore wind power units，the limitations of

conventional 35kVAC power collection schemes emerge，which are fewer interconnection wind turbines，longer submarine

cables and increasing costs per unit. A 66 kV AC power collection scheme with a high voltage level is proposed. Compared

with the 35 kV AC power collection scheme，it has more technical and economic advantages. It can not only transmit large

capacity power，but can also save investment and operating costs. The equipment for 66 kV AC power collection scheme is

investigated and its prospect is discussed in combination with the development trend of offshore wind power.

Research on multiple energy flow co-simulation technology applied in integrated energy system

SUN Hao，CHEN Yonghua

2020, 42(5):  66-72. 

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In order to realize the co-simulation of regional integrated energy，an integrated energy system with unified modeling and simulation platform is established，and a technical solution for cross-platform digital simulation technology is proposed.For its abundant thermodynamic component library，open source TRNSYS system is selected to build a integrated energy co-simulation platform with MATLAB/Simulink.The communication between TRNSYS and MATLAB is based on FMI technology，which integrates models established by different software at different levels of specification.It can meet the deeper simulation requirements of integrated energy.Taking a university in South China as the simulation scenario，a digital co-simulation model is built on the targeted platform to analysis the diversified energy demand including cooling，heating， powering and steam.Proven by the research，the muti-energy flow co-simulation technical route based on FMI technology is feasible，and the digital co-simulation of multiple energy can be realized by associating MATLAB with TRNSYS. The research achievement can be applied in more scenarios，and realize the digital co-simulation of software platform.It provides technical support for the hardware in the loop simulation，physical model simulation in the future.

Status and prospect of virtual power plant technology

YANG Xiaosi，TAO Xinlei，HAN Li

2020, 42(5):  73-78. 

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Intensive integration of information technology and energy technology is the development direction of energy industry at home and abroad. Based on modern communication technology and Internet technology，virtual power plants have broken through the geographical limitation through networks.The virtual plant integrates distributed renewable energy generation，energy storage，controllable load and other subsystems into a virtual entity to participate in transactions of the power market.And it provides capacity services and auxiliary services for the power grid，so as to improve the economy and reliability of the power system and facilitate the consumption and efficient utilization of renewable energy as well. The demonstration power plants in developed European countries and China were studied and compared from their key points， the core technologies and the practice effect.Consideration of the current situation and prospect of the energy industry in China，it is concluded that the technical route of European virtual power plants is more suitable for domestic power plants in the future，and reasonable suggestions for the key technologies and development direction of domestic virtual power plants are put forward .

  Application of a multi-pass circulating fluidized bed biomass boiler in a central heating project

CHU Leizhe，ZHANG Yanguo，YAN Jiaoping

2020, 42(5):  79-82. 

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工业园区的节能减排工作是区域经济发展中的重要内容。以某工业园区集中供热项目改造为例，分析了该项目供热锅炉的燃烧方法及燃料特性，介绍了多流程循环流化床技术的原理及其锅炉结构，重点阐述了针对生物质燃料所做的燃烧技术改进以及污染物排放控制措施。运行情况显示，项目改造后的多流程循环流化床生物质锅炉效率高、污染物排放低，在生物质资源丰富的工业园区采用集中供热可以取得很好的运行效果。

Treatment on excessive vibration of the main feedwater booster pump in a nuclear power plant

CHENG Xueqing，SHI Jiayun

2020, 42(5):  83-88. 

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Three constant speed pumps with 33.3% rated capacity are used in the main water supply system of a nuclear power project. During the commissioning，drive shaft end bearings of all the main feedwater booster pumps were of excessive vibrations，which grew slowly with the increase of running time. To solve the problem，we took a series of measures，such as re-alignment of the coupling，fastening inlet and outlet pipe supports，readjusting the parallelism and concentricity of pipes and adjusting the bearing interfaces，but none of them can effectively alleviate the vibration.Through analysis on the vibration spectrum ，as well as the manufacturing and installation features of the pumps，we have formulated and implemented a bearing box transformation scheme for the main feedwater booster pumps，which has greatly reduced the vibration value，effectively solved the problem of excessive vibration，and improved the stiffness of pump body and bearing case.