Table of Content

05 July 2020, Volume 53 Issue 7

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Relationship between Electricity Elasticity Coefficient and Industrialization Stage in China

SHAN Baoguo, ZHANG Chenglong, WANG Xiang, YAO Li, LIU Qing, TAN Xiandong

2020, 53(7):  1-6.  DOI: 10.11930/j.issn.1004-9649.202004057

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The electricity elasticity coefficient is an index used to express the relationship between electricity consumption and economic growth. This paper studies the relationship between the electricity elasticity coefficient and industrialization process, which will have practical significance. The main conclusions of this study are that in the middle stage of industrialization, the electricity elasticity coefficient in various regions is generally high, and then it decreases obviously; the electricity elasticity coefficient in the provinces where the industry ratio is significant is relatively high. During the Fourteenth Five-Year Plan period (2021~2025), China will achieve high-quality economic development, and the electricity demand will maintain a moderate speed of growth with the national electricity elasticity coefficient of about 0.8, which is consistent with the later stage of China's industrialization.

Key Issues of China's Offshore Wind Power Development in the “14th Five-Year Plan”

SHI Zhiyong, WANG Caixia, LI Qionghui

2020, 53(7):  8-17.  DOI: 10.11930/j.issn.1004-9649.202004096

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Since 2016, China's offshore wind power has developed rapidly, completing the "13th Five-Year Plan" target one year ahead of schedule. In light of the "13th Five-Year Plan" and the development and operation experience of European offshore wind power, the paper discusses several issues concerning the technical equipment capacity, economy and development layout of China's offshore wind power during the "14th Five-Year Plan". The research results show that by the end of the "14th Five-Year Plan", China's cumulative installed capacity of offshore wind power will reach 25 to 35 million kilowatts; its equipment manufacturing capacity can meet the needs of offshore wind power development of 3 to 5 million kilowatts per year; except for a few provinces and sea areas, where parity can be achieved, it's difficult to reach overall parity for the whole grid. Carrying out offshore wind power survey and resource reassessment, selecting unit capacity to meet China's wind resource conditions, improving the safety and stability of large-scale centralized offshore wind power operation, and improving related policies for offshore wind power development are important measures to promote development of offshore wind power.

Output and Fluctuation Characteristics of Off-shore, Coastal and Inland Wind Farms in Jiangsu Province

ZHANG Ningyu, ZHOU Qian, LIU Jiankun

2020, 53(7):  18-23.  DOI: 10.11930/j.issn.1004-9649.201908005

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Wind power in Jiangsu are not only large in installed capacities but also varied in wind farm types, which include off-shore, coastal and inland wind farms. It is of significance to the planning, dispatching and operation of power grids to obtain the active output and fluctuation characteristics of different wind farms. According to the actual operation data of inland, coastal and off shore wind farms in Jiangsu province, several probability models are used to simulate the active output of wind farms and the fluctuation characteristics. The maximum likelihood estimation method is adopted to estimate the model parameters, and multiple indexes are used to assess the fitting accuracy. The result shows that the offshore wind power output follows Gamma distribution in probability density function, while the inland and coastal wind power output follows the Weibull distribution. The optimal fitness of output fluctuation of the three types of wind farms follows t distribution of the Location-Scale function.

Research on Optimal Site Selection for Offshore Wind Farms Substation

YANG Yuan, Tang Xiang, XIN Yanli

2020, 53(7):  24-28,71.  DOI: 10.11930/j.issn.1004-9649.201912152

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Site selection of offshore substation plays a vital role for wind farm investment cost. This paper presents a method for optimal substation site selection for offshore wind farms substation. Firstly, the nearest offshore point of an offshore wind farms substations is determined by the shortest distance between the offshore wind farm and the onshore centralized control center. Then according to the position coordinates of each wind turbine, the gravity point of the offshore wind farm is obtained by the gravity method. Subsequently, a straight line is obtained by connecting the nearest offshore point of the offshore substation to the gravity point of the offshore wind farm. Next the substation site is moved along the straight line, and the layout of the current collection system the offshore wind farm is determined by improved Prim algorithm. Then the increased distance of the medium voltage submarine cable and the decreased distance of the high voltage submarine cable are calculated, and the voltage drop of medium voltage submarine cable is checked. Finally, combining the cost of submarine cables and the requirements of construction conditions, the optimal site of the offshore substation is obtained. The results show that the proposed method of this paper is simple, feasible and economically reasonable.

Research and Development of 66 kV Water Tree Retardant XLPE Light Insulated Submarine Cable

CHEN Guo, CAI Jian, XIE Shuhong, HU Ming, LIU Ligang, JING Yang, LING Zhiwei

2020, 53(7):  29-35,43.  DOI: 10.11930/j.issn.1004-9649.202003097

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This paper introduces the development method of a light submarine cable with rated voltage of 66 kV and water tree retardant cross linked polyethylene insulation(XLPE). Through testing the breakdown performance of power frequency voltage and lightning impulse voltage on the model cable, the developed samples were tested for wet insulation quality of 500 Hz/3000 h, 50 Hz/8750 h and 50 Hz/17500 h according to CIGRE TB 722:2018. The developed products were tested for type test according to CIGRE TB 490:2012 and CIGRE TB 623:2015, and the test results fully met the requirements of the design specification. In the future, the deep sea and high-power offshore wind power interconnection array submarine cable selection, 66 kV water-tree retardant XLPE light insulated submarine cable can perfectly replace 35 kV XLPE insulated submarine cable.

Technical and Economical Performance Comparison of Copper and Aluminum Conductor Submarine Cables with Equal Transmission Capacity

LI Lei, XIE Shuhong, HU Ming, ZHAO Youlin, XU Yongjun, WANG Haiyang

2020, 53(7):  36-43.  DOI: 10.11930/j.issn.1004-9649.202003096

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In view of the increasing shortage of copper resources, which causes the high cost of raw materials in wire and cable industry, this paper analyzes the performance differences of copper and aluminum materials, and calculates the cross-section conversion of copper and aluminum conductors under equal transmission capacity. According to the existing production process, adopting the analytical method, this paper completes the parameter calculation of copper and aluminum conductors for submarine cables, and the economic applicability and electrical characteristics of copper and aluminum conductor submarine cables are compared, including the further study on the connection performance of aluminum conductor. The statistics show that the unit mass of copper and aluminum conductor submarine cables is approximately equal under the condition of equal transmission capacity. The loss and short circuit current characteristics of the two conductors are similar. However, the cost of copper conductor submarine cables is 110% ~180% of that of aluminum conductor submarine cables. Good electrical and mechanical properties of aluminum conductor joints can be achieved by AC argon arc welding. Therefore, the economic performance of aluminum conductor submarine cable is comparatively better.

Diode Rectifier Unit Based LFAC Transmission for Offshore Wind Farm Integration

TANG Yingjie, ZHANG Zheren, XU Zheng

2020, 53(7):  44-54,168.  DOI: 10.11930/j.issn.1004-9649.202005071

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The offshore wind power, which is high in density and small in fluctuation, will be the focus for wind power development in the future. Up to now, the offshore wind power transmission projects in operation have mostly adopted VSC-HVDC technology, whereas their capital cost is relatively high. So, this paper proposes a diode uncontrolled unit (DRU) based low frequency alternative current (LFAC) transmission scheme for the offshore wind farms, in which the offshore platform of the rectifier is cancelled and the rectifier in the traditional AC-DC-AC frequency converter is substituted by the DRU, thus significantly reducing the project investment and operating cost. Since the DRU is uncontrolled, a corresponding control strategy of the offshore wind turbines is proposed for LFAC transmission system, in which the machine side converter (MSC) controls the DC voltage and the grid side converter (GSC) implements the maximum power point tracking (MPPT) and AC voltage control together in the global unified reference coordinate system. Case simulations in PSCAD/EMTDC were carried out in the end to study the system response to typical operating conditions including wind power fluctuation and three-phase faults in the onshore grid and offshore grid, and the feasibility of the proposed scheme is verified.

Application Status and Prospect of VSC-HVDC Technology for Large-Scale Offshore Wind Farms

LIU Weidong, LI Qinan, WANG Xuan, ZHANG Fan, LI Lanfang, YAN Hui

2020, 53(7):  55-71.  DOI: 10.11930/j.issn.1004-9649.202002108

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Due to the strong wind resource stability and high annual utilization hours of offshore wind power, with the increasing capacities of offshore wind turbines, the expansion of investment scale and the reduction of construction costs, VSC-HVDC based large-scale offshore wind power transmission technology has become a popular topic for offshore wind power development and research. Based on typical offshore wind power VSC-HVDC transmission projects, application status of key electrical equipment including converter valves, interface transformers, energy-dissipating devices, HVDC breaker, submarine DC cables have been analyzed and summarized in this paper. In addition, control system structure and hardware configuration as well as control algorithm are introduced. Considering the salt mist corrosion environment where offshore platforms are located, both the anticorrosion design and seawater cooling system design of the interface transformers, converter valves are introduced. The current research status of large-scale offshore wind power grid integration solutions have also been analyzed and summarized. The prospect of offshore converter stations and offshore wind farms has been forecasted.

Techno-economic of 66 kV AC Connection Solution for Offshore Wind Power

LYU Jie, YANG Weijia, HUANG Wei, PANG Hui, KONG Ming, YANG Yunxia, ZHANG Wenwen

2020, 53(7):  72-79.  DOI: 10.11930/j.issn.1004-9649.202002025

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For techno-economic comparison between the scheme of 66 kV AC collection system of offshore wind power connected directly to converter station and the traditional scheme of 35 kV collection system connected to converter station through a 220 kV booster station and 220 kV cables, an offshore wind farm in South China Sea is chosen for a case study. The two connection schemes of the wind farm are compared in terms of power loss, primary electrical equipment investment, and others. It is concluded that the 66 kV AC connection scheme is better in economic benefit. Along with the development of offshore wind farms in China, the 66 kV AC connection scheme has very good technical advantages in reducing the construction cost of VSC-HVDC system for offshore wind power and promoting innovation of technologies.

Medium Frequency Diode Rectifier Unit Based HVDC Transmission for Offshore Wind Farm Integration

ZHANG Zheren, TANG Yingjie, XU Zheng

2020, 53(7):  80-91.  DOI: 10.11930/j.issn.1004-9649.202005085

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The offshore wind farms are the main trend of the wind power development in the future. Till now, the commissioned far offshore wind farms are always connected to the onshore AC system by VSC-HVDC systems. The hybrid HVDC topology with uncontrolled diode rectifier unit (DRU) has drawn attentions from both the academia and the industry, due to its economic benefits. In order to further improve the economic efficiency of far offshore wind power transmission systems, this paper proposed the medium frequency uncontrolled rectifier offshore wind power transmission system based on the DRU at the rectifier side. The offshore ac system rated frequency of the proposed system is set as 100~400 Hz, which could significantly decrease the weight and the volume of the transformer and the AC filters at the offshore platform. The corresponding control scheme of the wind turbine are also proposed, where the machine side converter controls the DC voltage and the grid side converter controls the machine power and the AC side voltage together in the global unified reference coordinate system. Based on time domain simulations in PSCAD/EMTDC, the feasibility of the proposed schemes is verified.

Non-uniform Transmission Line Model of Offshore Wind Turbine Tower

SONG Yuanjian, XU Zheng, YU Jingqiu, ZHANG Zheren

2020, 53(7):  92-99,216.  DOI: 10.11930/j.issn.1004-9649.202001065

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The modeling of wind turbine tower is an important part of the research on lightning protection of offshore wind turbines. The establishment of its model has an important impact on the analysis results. This paper first analyzes the inapplicability of the tower multi-surge impedance model in the research of lightning protection for offshore wind turbines, and then establishes a non-uniform transmission line model of tower. Secondly, the influence of the spatial structure change of the tower on its own electromagnetic transient characteristics was studied by using the multi-surge impedance model. The results show that the more the tower is divided into sections, the more accurate its electromagnetic transient response is. Finally, a comparative analysis of the lightning transient response of the tower using the non-uniform transmission line model and the multi-surge impedance model is performed, which proves that the non-uniform transmission line model is more in line with actual conditions.

Review on Floating Foundation Structures for Offshore Wind Turbines

ZHOU Xuhong, WANG Yuhang, DENG Ran

2020, 53(7):  100-105,112.  DOI: 10.11930/j.issn.1004-9649.202004140

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With the gradual increase of renewable and clean energy demand in China, the development of onshore wind energy tends to be saturated. It is an inevitable trend for wind power to be applied in offshore and deep-sea areas. The development and engineering application of floating foundation structures are the key technical measures to promote this trend. This paper comprehensively reviews the applicable depth range, basic types, mooring system, fabrication and installation of floating foundation structure for offshore wind turbines, which aims to provide technical references for the development of wind power in offshore and deep-sea areas.

Electromagnetic Transient Modelling and Verifying of Wind Turbine Generator

ZHANG Xing, SUN Yanxia, LI Lina, GAO Caiyun, MA Junhua, GAO Liping, LIU Keke, HE Guoqing, LI Guanghui

2020, 53(7):  106-112.  DOI: 10.11930/j.issn.1004-9649.202001088

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The transient characteristics of wind turbine generator have great influence on the stable operation of renewable energy base and the power grid in the near region, therefore it is of great significance to build accurate wind turbine generator model for large scale renewable energy integration. However, current wind turbine generator model mostly adopt typical model, some differences exist between the model and the real wind turbine generator, dissatisfying the demand of power system simulation. This paper presents a new EMT modeling method of "filed test - control hardware in the loop(CHIL) - dynamic link library(DLL)" for wind turbine generator. CHIL simulation platform based on FPGA is built and the accuracy of CHIL modeling is verified by filed test. Furthermore, a controller-less digital modeling method based on dynamic link library is proposed with the controller code packaged in the digital model, thus, the EMT model of wind turbine generator is realized and the two level time domain consistency verification proves the feasibility and accuracy of this modelling method.

Optimization Strategy for Black-Start Partitioning of Active Distribution Network to Minimize Customer Outage Cost

ZHAO Jinquan, ZHANG Qiang, FANG Song, PENG Song

2020, 53(7):  114-121.  DOI: 10.11930/j.issn.1004-9649.202001032

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When power system blackout occurs, the active distribution network with high penetration of distributed generations can realize fast parallel restoration through zone partitioning. An optimization strategy for black-start partitioning of active distribution network is proposed. With the minimum customer outage cost as objective, a mixed integer linear programming model is established for black-start partitioning of active distribution network, and the restoration operation sequences inside each partition are integrated into the partition model through the restoration constraints of distributed generations, lines, buses and loads. The linear programming solver ILOG CPLEX is adopted to solve the model, and then the partition restoration scheme of distribution network is obtained. The effectiveness of the proposed model and strategy is verified by the modified IEEE 69-bus distribution system.

An Assistant Decision-making System for Black-Start Path Generation and System Restoration

XIANG Yinxing, TANG Xiaojian, LIN Jikeng

2020, 53(7):  122-131.  DOI: 10.11930/j.issn.1004-9649.202001089

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How to quickly generate a black-start path and system restoration scheme has always been one of the urgent problems needing to be solved in emergency response of power system. This paper develops an assistant decision-making system for black-start path generation and system restoration scheme based on 3D visualization technology. Firstly, The overall framework architecture of the system is introduced; And then, the module functions and its implementation methods of the system are further described in detail, including data base, graph platform, and algorithm library that is composed of initial path generation, path check and assessment, and system restoration; Finally, an actual power system is used to verify the effectiveness and correctness of the designed system. The results show that the designed system has a perfect integrated graph-model system formed by graphical interface, database system and algorithm library, which has the advantages of reasonable configuration, complete functions and convenient for use.

Implementation Method for Fast State Estimation of Super-large Power Grid

LUO Yuchun, WANG Yi, SHAN Xin, DAI Zemei, ZHANG Lei

2020, 53(7):  132-140.  DOI: 10.11930/j.issn.1004-9649.202002062

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With the construction of global analysis and decision-making center for integrated interconnected large power grid, higher speed is needed for the calculation of real-time state estimation. The multi-thread parallel computing technology is used to realize the fast calculation of the gain matrix of the fast decoupled state estimation, and the STL associated container storage format is used in the process of sparse matrix bus optimal ordering and its triangular factorization. Based on the verification environment of the new generation control system and the actual grid connection models, case calculations are carried out. The results show that the multi-threaded parallel calculation of the gain matrix and its factorization have a higher speedup ratio when used for state estimation of super large power grids, and can effectively improve the programming efficiency and quality and the computation efficiency of the state estimation when combined with the STL associated container based sparse matrix storage format.

Parameter Identification of Short Parallel Double-Circuit Lines Based on PMU Measurements

HUANG Xiaoxiao, YANG Tao, ZHENG Xiaolin, GUO Lingxu, LIN Jikeng

2020, 53(7):  141-148.  DOI: 10.11930/j.issn.1004-9649.202001047

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With the continuous increasing of short parallel double-circuit lines, it is an urgent problem to obtain their accurate parameters. In this paper, a new PMU-based method is proposed to estimate the parameters of short parallel double-circuit lines. Firstly, based on the coupling between conductors, the impedance model of short parallel double-circuit lines is deduced. And then, the corresponding short line phase angle correction method and the parameter estimation algorithm of short parallel double-circuit lines based on least square method are presented using the online PMU measurement data. The proposed model is complete, and the algorithm is simple and straightforward, which can accurately and quickly calculate all the parameters of short parallel double-lines. Case study has validated the effectiveness and correctness of the proposed method.

Performance Analysis of Generator Dynamic State Estimation under Uncertain Measurement

ZHAO Jingbo, WEI Zhinong, WANG Hanwen, XIE Bing, HUANG Mei, MENG Xia

2020, 53(7):  149-159.  DOI: 10.11930/j.issn.1004-9649.201909119

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Random errors are unavoidable in phasor measurement unit (PMU), and the PMU measurement data may be uncertain in actual power system, such as delay, reordering or even missing. In order to accurately estimate the state information in the electromechanical transient process of power system, a generator dynamic state estimation model is firstly established under the missing measurement; And then, the model is simulated in an actual power system using the unscented mixture filter (UMF), particle filtering (PF) and the improved particle filtering (IPF) proposed in this paper respectively. The results show that, under uncertain measurement, the proposed IPF is superior to UMF and PF in filtering performance and robust performance, and more applicable to generator dynamic state estimation.

New Partition Model and Algorithm of System Restoration

XIANG Yinxing, LI Qi, LIN Jiken

2020, 53(7):  160-168.  DOI: 10.11930/j.issn.1004-9649.202001023

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Establishing a reasonable grid partition scheme for parallel restoration can effectively shorten the system restoration time, while how to build a more effective partition model and algorithm is the key to this issue. This paper proposes a new partition model and fast algorithm for parallel restoration of power grids. Firstly, based on the actual process of system restoration, a new model is constructed for optimal partitioning of system parallel restoration; And then, in order to overcome the difficulty for solving the large mixed integer nonlinear programming, a step-by-step solution strategy is proposed: First, the start-up units are divided and adjusted according to the electrical distance; Second, the loads are divided and adjusted based on electrical distance and power flow tracking algorithms. The model constructed in this paper is relatively complete, and the proposed algorithm has good computing performance and is easy to implement, which is expected to be used in engineering practice. Examples of different scales have verified the effectiveness and correctness of the model and algorithm proposed.

Design and Application of State Estimation Research Mode

PENG Long, NING Jian, WANG Yi, LU Juanjuan, ZHANG Yong, LUO Yuchun

2020, 53(7):  169-175.  DOI: 10.11930/j.issn.1004-9649.201809119

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Because of the complexity of actual operation conditions of power systems, non-convergence is hard to be avoided in state estimation and section results are difficult to be reproduced in inversion, and the adjustment of measurement and parameters will lead to the fluctuation of the eligibility rate and affect the stable operation of the real-time network analysis application system. Based on an analysis of the existing problems and application requirements in operation of state estimation, a research mode analysis platform for state estimation is designed and implemented. Firstly, all the information needed for state estimation is saved through section management and reading function; secondly, section reading, analysis and debugging calculation are realized through researching mode inversion; finally, the indicator reference is provided for parameters and measurement adjustment through comparison function. The results of state estimation are completely reproduced, and the analysis process is independent of the real-time state estimation and thus does not affect the real-time eligibility rate. The automation professionals can analyze the measurement and parameter problems purposefully according to the indicators provided by the comparison function. Through the actual application in North China Branch Center of SGCC, it is proved that the platform's functions can meet the needs of professionals for analysis and debugging of state estimation. The analysis basis is provided through index comparison. Through the actual use of North China Branch Center, it is proved that the platform function can meet the needs of professional personnel for analysis and debugging of state estimation.

Mechanism Study on Heat and Mass Transfer Process of Conductive Gap Membrane Distillation Module with Condensation Microstructure

MA Tao, DU Xiaoze, WU Jiangbo, LIU Shujun

2020, 53(7):  176-183.  DOI: 10.11930/j.issn.1004-9649.201909123

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Membrane distillation technology has exhibited great application prospects in the recovery and treatment of desulfurization wastewater from coal-fired power plants because of its applicability under low temperature conditions and high recycling water quality. In this paper, the heat and mass transfer of a new conductive gap membrane distillation (CGMD) with condensing microstructure is theoretically analyzed. Based on the present theories, the heat and mass transfer on the hot side of the membrane and the heat transfer after the condensing microstructure added into the gap are taken into consideration. Then the selection of mass transfer models with different pore sizes and temperatures for the mechanism of mass transfer across the membrane in microporous membranes has been emphatically analyzed. Finally, the influence of temperature and pore size on the selection of transmembrane mass transfer model is illustrated by corresponding experiments such that the experimental results are obtained and then verified to be mostly consistent with the theoretical analysis results.

Thermal Cost Analysis on Thermal Zero Discharge Technology for Flue Gas Desulfurization (FGD) Wastewater of Coal-Fired Units

ZHAO Shuran, HAN Xiaoqu, ZHANG Dan, LIU Jiping

2020, 53(7):  184-188,196.  DOI: 10.11930/j.issn.1004-9649.201910135

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It is expected to achieve low-cost zero discharge of FGD wastewater by using MED or MSF technology driven by different heat sources of the power plant. In this paper, five different combinations of schemes are proposed for the desulfurization wastewater pretreated in the “pretreatment-concentration-evaporation desalination” process to achieve the target of "concentration-deep desalination". The thermal economic analysis model of each scheme was established respectively, and the change rules of gained output ratio (GOR) and heat cost was also quantitatively studied. The results show that as far as the heat source is concerned, the cost of auxiliary steam is higher, while the cost using the waste heat of the flue gas is cheaper with the pumping power becoming the major cost contributor. With the TVC device installed, the GOR of MED can be improved by 10%~100%, and the heat cost can be reduced by about 10%~50%. However, in addition to its high sensitivity to fluctuations in wastewater salt concentration, the structure of the MED structure is not suitable for treating high salt concentration wastewater. In contrast, the MSF structure demonstrates high adaptability to salt concentration. The heating cost of using flue gas heating is about 0.3~1.2 yuan/t.

System Characteristic Analysis of Waste Heat Recovery and Cascade Utilization of Tail Flue Gas of Power Boiler

TENG Da, LI Tielin, LI Ang, AN Liansuo, CHEN Haiping, SHEN Guoqing

2020, 53(7):  189-196.  DOI: 10.11930/j.issn.1004-9649.201909089

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The exhaust gas temperature of the power station boiler is generally 130~150 ℃. Further recovery of flue gas waste heat is beneficial for the reduction of coal consumption and pollutant emissions. Regarding the different flue gas parameters at various parts of the tail of the power station boiler, the waste heat recovery system is formulated with two-stage heat exchangers installed, i.e., one after the air preheater and the other after the wet desulfurization device. In consideration of the operation of the 330 MW coal-fired power station boiler, the effects of heat transfer, condensate and static pressure difference on both sides of the two-stage heat exchangers and the reduction of coal consumption for power generation were analyzed under different load conditions. Change of solid particulate matter in flue gas before and after heat exchanger was also monitored. The results show that the heat exchange capacity of the primary heat exchanger is significantly higher than that of the secondary heat exchanger, and the condensed water mainly occurs in the secondary heat exchanger. The standard coal consumption reduction value can reach up to 3.09 g/(kW·h). Besides, the content of solid particles in the flue gas after the heat exchanger is significantly reduced. This paper provides certain reference value for the waste heat recovery of flue gas from power station boilers.

Precipitation Characteristics of Chlorine in the Process of Desulfurization Wastewater Spray Before and After Treatment

ZHANG Qian, NI Li, DOU Chaozong, XIAO Haiping

2020, 53(7):  197-202.  DOI: 10.11930/j.issn.1004-9649.201910029

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Desulfurization wastewater contains high concentrations of chloride salts, which affects the safe operation of the desulfurization system. The Factsage thermodynamic calculation software was used to simulate the precipitation characteristics of chlorine in a single chloride solution and the desulfurization wastewater before and after treatment through the tail flue spray. The results showed that the precipitates were observed in the form of chlorine-contained gas if CaCl₂, MgCl₂ and NH₄Cl solutions were sprayed. While if NaCl solution was sprayed, all of the chlorine content were precipitated as NaCl(s) without any gas evolution. In the process of spray evaporation with untreated desulfurization wastewater, more than 75% of chlorine were precipitated as NaCl(s). After the removal of Ca²⁺, Mg²⁺, NH₄⁺, etc., no HCl gas was formed in the flue gas spray evaporation process of the desulfurization wastewater, and the product NaCl(s) would be removed by electric dust removal device. Therefore, the pretreatment of the desulfurization wastewater has effectively reduced the precipitation of chlorine-contained gas and therefore the corrosion of the tail flue is mitigated.

Safety Evaluation and Control Optimization Technology for in-Depth Peak-Shaving of Subcritical Drum Boiler

ZHANG Shun, YAN Peifei, YAO Hongyu, LI Shengpeng, CAO Shibao, GAO Yazhou

2020, 53(7):  203-210.  DOI: 10.11930/j.issn.1004-9649.201907042

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In order to address the difficulties of power system frequency regulation and peak shaving stemming from fast-growing new energy absorption capacity, as a type of conventional power sources, coal-fired units have to implement deep, rapid and frequent load adjustment, which is anticipated to reduce or eliminate the impact of intermittency and randomness of wind and photovoltaic power on the security of power grid operations. Taking a 330 MW subcritical drum furnace unit as the study object, this paper explores the boundary conditions and assesses the reasonable lower limit of peak shaving in deep load variation process. Then by virtue of the optimization design of advanced control strategy, the quality and reliability of the control over each system have been improved. The study results show that the unit is capable of performing peak shaving at 27% of rated load without any engagement of system or equipment transformation.

Analysis and Test on the Effect of Bearing Vibration on Oil Film Whirl

HE Guoan, HU Xiangyu, YANG Cheng, AN Shijiang, ZHANG Xueyan

2020, 53(7):  211-216.  DOI: 10.11930/j.issn.1004-9649.201912079

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In order to study the coupling effect of bearing vibration on oil whirl, the motion mechanism of bearing vibration is analyzed, and the dynamic equation representing the effect of bearing vibration on oil whirl is established. It is pointed out that bearing vibration will change the boundary conditions of lubricating oil film and hence disturb the lubricating flow field, which may aggravate oil film whirl and produce significant half-frequency vibration fluctuation. On the other hand, it may also change the thickness of the oil film such that the oil film stiffness also changes, causing the fundamental frequency vibration fluctuation. Subsequently, a verification test was performed on the actual units on site. The results show that the vibration of small or light load bearings has remarkable effect on the oil whirl, which will cause severe fundamental and half-frequency vibration fluctuation, while the vibration of large or heavy load bearings does not affect the oil whirl very much, which will only trigger some fundamental frequency vibration fluctuation at certain level.