Table of Content

05 March 2018, Volume 51 Issue 3

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Analysis on IGCC Unit Trip Caused by Low Temperature at Gas Turbine Inlet and Its Solutions

DING Jianbo, ZHAO Yanpeng, WANG Jian

2018, 51(3):  1-6.  DOI: 10.11930/j.issn.1004-9649.20160466

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The gas turbine in Tianjin IGCC demonstration power plant is fueled with light diesel oil and the synthesis gas with low calorific value. After desulfurization, the synthesis gas produced in the gasifier enters the gas turbine through the gas hybrid humidification system. In the synthesis gas exchange process, problems such as the temperature fluctuation in the entrance, the instability of combustion condition occur frequently, resulting in the chain tripping under some severe circumstances. The entrance temperature is a major factor that affects the stable operation of the gas turbine. In this article, the factors that influence the entrance temperature change are analyzed. It is concluded that water accumulated inside the turbine is the main cause of the entrance temperature decrease and direct tripping. Based on the analysis, the technological conditions, the pipeline drainage equipments and the system control logic are improved to prevent such problems from occurring again.

Experimental Study on Reducing Thermal Stress of Steam-Side Oxide Scales by Vacuum Method

HE Wenbo

2018, 51(3):  7-12.  DOI: 10.11930/j.issn.1004-9649.201609039

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Generally, the generation unit is started from cold state by means of pressure method. However, when this method is applied in supercritical boiler, it is inevitable that convective heating surface will be heated dry without steam and, then cooled down with steam. As a result the oxide scales will have to withstand the thermal stress from about 100℃ cooling temperature difference, which can cause the oxide scales flaking. In this paper, the vacuum method is adopted to start the unit. The low temperature saturated steam flows the heated surface of the boiler before ignition, which can effectively avoid the peeling off of the oxide scales during the startup process. corresponding experimental study is carried out in No. 2 boiler in Changsha Power Station Co., Ltd of Hunan CHD and satisfactory results are obtained. The temperature difference of the heating surface is significantly reduced before and after the ignition of the boiler, which effectively diminishes the risk of oxide scales flaking. The method is simple and reliable with no equipment modification needed.

Prediction of Superheater Tube Wall Temperature in Supercritical/Ultra-Supercritical Boilers for Different Loading

DENG Bo, XU Hong, GUO Peng, ZHANG Naiqiang, NI Yongzhong

2018, 51(3):  13-20.  DOI: 10.11930/j.issn.1004-9649.201711189

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In this paper, the influencing factors of the superheater wall temperature in supercritical/ultra-supercritical boilers are analyzed. By using the real-time operation data acquired from the DCS system in a power plant,the grey relational analysis on the measured temperature of the superheater tubes is conducted to determine the input variables of the prediction model. The results show that the influencing factors, such as the outlet steam temperature of both the primary and secondary superheaters, the main steam temperature,the layer E opening of secondary air throttles and the active power are vital to the tube wall temperature. Then by using the BP neural network algorithm, 14 main influencing factors with the threshold of more than 0.70 are used to predict the tube wall temperature at the scenario of up loading, steady loading and down loading,which concludes that the development trend of the prediction results is consistent with that of the measured results, and the largest relative error is about 1.42%. The prediction results can provide good guideline to avoid overheating.

Optimization on Valve Flow Characteristics of Steam Turbine Based on Model Self-Adaptation and Its Application

LEI Zhiwei, ZHANG Xing, CHEN Tao, CHEN Shengli, WU Haicheng, ZHANG Jian

2018, 51(3):  21-28.  DOI: 10.11930/j.issn.1004-9649.201707172

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The valve flow characteristics of steam turbines have significant impacts on the system security and operation stability as well as load regulation performance of the units. In this paper, regarding the valve structure in nozzle governing, the non-linear valve flow characteristic model is first built for sequence valve control by taking advantage of model adaptive algorithm to conduct flow characteristic linearization based on optimization arithmetic. Second, the simulation study is carried out on this model. The results indicate that the single flow characteristic simulation model adopting RBF network has high model precision. By virtue of the model adaptive optimization algorithm approximate ideal linearity and optimum valve overlap can be obtained. Finally, the simulation result is applied to a 660-MW unit. The test result shows that the method can not only improve the linearity of the valve flow characteristics, but also lower the valve overlap, improve the AGC load response performance and alleviate the valve shaking issue and reduce the throttling losses of the unit.

Control Strategy and RB Logic of the Feed-Water System with Steam-Driven and Motor-Driven Pumps in Parallel for 660-MW Units

XING Zhiwei, YUE Tao, LIU Lei

2018, 51(3):  29-34.  DOI: 10.11930/j.issn.1004-9649.201711004

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Regarding the feed-water system with steam-driven and motor-driven pumps in parallel in the 660 MW once-through unit of Tashan Power Generation Co Ltd, the “water following coal” method and the intermediate steam temperature modification are used for the control of the feed-water system. The demand of the water system is transformed to the control signals fed into the motor-driven pump in terms of polyline function. Therefore, the steam-driven and motor-driven pumps can operate simultaneously and contribute to the control of the feed-water system. During the runback (RB) of the steam-driven water pump, by interlocking the start of motor-driven pump and increasing the opening percentage of the scoop tube, the supply water flow is reduced smoothly such that the steam temperature can be kept steady. The operation and test results show that the control strategy for the feed-water system can ensure the safety and stability of the unit in operation. In addition, in the feed-water pump runback process, the unit can shed the load promptly and steadily while the transition of major parameters still remains smooth.

Vibration Frequency Identification and Analysis for UHV Line Shield Ring

ZHANG Yujiao, YANG Qi, JIANG Lan, XU Tianyong, DONG Xiaohu

2018, 51(3):  35-41.  DOI: 10.11930/j.issn.1004-9649.201703070

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In order to monitor the vibration frequency of shielding ring of transmission lines, a non-contact vibration frequency identification method is proposed. Taking a shield ring of an ultra-high voltage (UHV) transmission line as an example, the method of image recognition is used to recognize the vibration frequency, and the finite element method is used to verify the feasibility of the proposed method. The analyzing results show that the frequency obtained by two different methods are close, and the image recognition method can be used to identify the vibration frequency of shielding ring of transmission lines.

Optimal Design of Grounding Grid for 110 kV Whole-Indoor Intelligent Substation

WANG Ping, JIA Lili, LI Shouxue, LI Kang, LV Fangcheng

2018, 51(3):  42-48.  DOI: 10.11930/j.issn.1004-9649.201612032

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Because of the small area and high level of ground fault current in today's whole-indoor urban intelligent substation, it is difficult to decrease the grounding resistance and the grounding potential rise, even with the low soil resistivity. Based on a soil model of a 110kV whole-indoor substation, the optimal grounding grid of a whole-indoor intelligent substation 110-A2-X1 is designed. In the process of optimal design, the threshold for grounding potential rise was relaxed appropriately by analyzing the requirements for grounding parameters in design code. The resistance reduction effects of two-layer grounding grid and deep-well grounding electrodes of different numbers and length were investigated with CDEGS software, and the safety and economy of the two resistance reduction measures were compared. The results show that the grounding deep-well has high cost but good resistance reduction effects compared with the two-layer grounding grid. And for unattended 110kV whole-indoor intelligent substation, it is suggested to use six grounding wells each with a depth of 55m for grounding grid o reduce the resistance.

Influence of Wire Tension Insulator String's Load to Conductor Sag and Tension in ±800 kV Transmission Line

ZHOU He, HUANG Jian, NIU Linhua

2018, 51(3):  49-53,61.  DOI: 10.11930/j.issn.1004-9649.201606202

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In ±800 kV DC overhead transmission line project, the effect of wire tension insulator string's load to wire sag and tension cannot be ignored in the continuous span because the string is longer and heavier than those of low voltage level. The stringing methods of ±800 kV DC transmission line are described briefly. By using moment balance principle, the relationship among conductor load, conductor sag and tension in the continuous span is analyzed. In both long continuous span strain section and Tension-Tangent-Tension strain section, analysis results prove effectiveness of proposed calculation method and treatment measures of tension tower adjacent span's conductor sag. The result is also verified in engineering practice.

Simulation Analysis of Voltage Support to Binjin HVDC Provided by Pumped Storage Unit's Synchronous Condenser Operation

WU Kuayu, LU Cencen, YUAN Yazhou

2018, 51(3):  54-61.  DOI: 10.11930/j.issn.1004-9649.201607095

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Voltage support provided by infeed ultra HVDC transmission system is of great significance for reducing the probability of HVDC's blocking or commutation failure and improving operation stability and reliability. This paper demonstrates key technologies and feasibility of pumped storage unit's (PSU's) synchronous condenser operation (SCO) mode. Moreover, a new operation mode which utilizes nearby PSU's SCO to provide voltage support to infeed ultra HVDC transmission system is proposed. The Binjin HVDC in Zhejiang grid and nearby abuilding PSU are considered in simulation analysis, which analyze impact of voltage support provided by PSU in SCO mode on Binjin HVDC system under some typical fault including AC system short circuit. Simulating result verifies that under specific conditions, the PSU's SCO can be utilized to improve HVDC operation reliability, which further improves security and reliability of HVDC multi-infeed Zhejiang power grid.

Development and Application of GIS Integrated Real Type Partial Discharge Defect Simulation Device

LIU Yan, LI Qiong, ZHOU Youwu, SHI Zhiming

2018, 51(3):  62-68,162.  DOI: 10.11930/j.issn.1004-9649.201611120

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Real GIS device has poor repeatability, stability and controllability when used in field testing. Four typical insulation defects are studied and an integrated GIS simulation device is designed. The device has ability to simulate different kinds of partial discharge defects during online and offline operation and detection. Then a simulation test platform is set up to study four typical insulation defects. Testing data and graphs are studied to reflect GIS operation status. The proposed device provides important basis for GIS equipment maintenance, overcomes field environment constraints, improves efficiency and saves maintenance costs.

Characteristics of Surface Discharge on the Interface of Solid Insulation and Liquid Nitrogen in Superconducting Applications

ZHENG Zhong, YU Zhicheng, DU He, HUANG Xiaohua

2018, 51(3):  69-73.  DOI: 10.11930/j.issn.1004-9649.201604094

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Advances in superconducting transmission technology require better insulation materials. The breakdown in composite insulation system mostly occurs on the interface between solid insulation material and liquid nitrogen. Under liquid nitrogen temperature, insulation material discharge behaviors differ a lot from those in room temperature. An electrode system is designed to generate severe non-uniform electric field on surface of solid dielectrics and liquid Nitrogen. The discharge behavior of three different solid dielectrics are tested and analyzed. The results can be used in real engineering applications.

A Novel Method for Double Terminal Traveling Wave Fault Location Based on Simple Communication

LI Zhenxing, WU Liqun, TAN Hong, CHENG Yixing, LI Zhenhua

2018, 51(3):  74-79.  DOI: 10.11930/j.issn.1004-9649.201605051

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Improving the reliability and precision is of vital importance for traveling wave fault location. After a brief comparison of the pros and cons of single terminal method and double terminal method, it comes to the conclusion that even though the traditional double terminal method have higher precision, its reliability is highly dependent on the time dissemination system. Therefore, by taking advantage of the connection channel at the ends of the lines where simple communication can be performed, a pulse signal is sent immediately to the other terminal as soon as the initial wave-front is detected. Then using high precision timer together with wave velocity, the fault location can be calculated without time synchronization at both ends. Finally through the analysis of the existing hardware manufacturing technology, it is believed that this method will have higher accuracy.

Economic Mapping of Core Physical Architecture of Power Projects

WU Hongliang, YOU Weiyang, DONG Nan

2018, 51(3):  80-87.  DOI: 10.11930/j.issn.1004-9649.201606187

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With gradually deepen of electric power system reform and harsh situation of power grid business in China, importance of grid investment economic benefit evaluation is constantly improving in grid business. Due to unclear benefit issues derived from three fundamental characteristics, namely power grid network characteristics, continuous yearly investment and semi non-profit requirement, economic analysis and evaluation of complex system of main network projects in network structure have not been solved well. Based on physical characteristics of regional power transmission project, impacts of new construction on power grid safety, reliability and economy are analyzed. Set of physical indexes is built first. Then deep, direct and indirect physical benefit indicators are extracted based on intuitionistic fuzzy sets method and interpretive structure model. Economic mapping of core physical architecture is proposed according to grid investment significance. Through economic mapping of core physical architecture, definition of economic benefits of regional power transmission projects area can be further clarified.

Analysis on Grid-Connected Benefit of Distributed Photovoltaic Power Generation Based on LCOE Model

SUN Jianmei, CHEN Lu

2018, 51(3):  88-93.  DOI: 10.11930/j.issn.1004-9649.201702106

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In order to provide reliable, low-carbon power, the development of distributed photovoltaic power generation is of great significance. This paper firstly improves the cost-of-use model by combining the factors of certificated emission reductions (CERs), and then analyzes the sensitivity of influencing factors of electricity cost and the impact of incentives such as loan methods on the economic efficiency of the project. Finally, through a case study, a comprehensive analysis is made on the economic benefits of grid-connected power generation under the typical operating modes based on the independent power producers and distribution companies. The results show that the distributed PV power generation brings both negative and positive returns to the distribution companies, while the spontaneous self-use model can bring more benefits to the independent investors. The change of the generating capacity has the biggest impact on the electricity cost. After considering the income of CERs, the effect of effective light hours and the decay rate of PV modules on the levelized cost of energy (LCOE) increases. The carbon emission benefit has certain influence on the project economic benefit. The improvement of carbon trading market and effective incentive mechanism will promote the development of photovoltaic industry.

Development and Technology Roadmap of Marine Power Generation System

ZHANG Yajie, ZHAO Qiang, CHU Wenjia

2018, 51(3):  94-99.  DOI: 10.11930/j.issn.1004-9649.20150260

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Marine power generation technology is conducive to meet electricity demand in a clean and green way. According to study on distribution and development of tidal, wave, tidal current, thermal and osmotic energy, key technologies of marine power generation are discussed in detail. Development obstacles of research, policy and environment are listed. Based on introduction of marine power development pathway in United States, development models and marine energy utilization methods in China are discussed. Finally, key technology road maps are proposed in different time periods.

Research on Development Prospect of Wind Power in Eastern and Central China

XIE Guohui, HE Yongsheng, WANG Qingran

2018, 51(3):  100-104.  DOI: 10.11930/j.issn.1004-9649.201704045

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Wind power development in Eastern and Central Region became new hot spots with layout optimization in order to reduce curtailment during the Thirteen five period. Current status of wind power deployment in 12 provinces are described. Main impact factors on wind power development are analyzed from aspects of wind resources distribution, low-speed wind turbine application and developing cost. Wind power development prospects are discussed. During the Thirteen five period, wind power in Eastern and Central Region will accelerate rapidly driven by polices. After that, wind power deploying scale limit will be reached due to resource constrain. Further supporting tariff policy are needed to compensate development cost.

Improved Energy Storage Smoothing Control Strategy Based on Geometric Weighted Moving Average Filter Algorithm

LI Hui, GUO Zhonghan, LI Zhaohan, QIU Shoudong

2018, 51(3):  105-112.  DOI: 10.11930/j.issn.1004-9649.201706191

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For the current use of energy storage in the PV output smoothing, this paper introduces a geometric weighted moving average filtering algorithm to obtain the reference value of the energy output battery in the PV system so as to reduce the impact of PV power on the power grid. By improving the moving average filtering algorithm, the proposed algorithm not only improves the delay of the filter, but also has the ability of adaptive stabilization. On the basis of energy storage output reference value, a new method of modifying the reference value by fuzzy control is proposed, which maintains the state of charge (SOC) of the energy storage battery in a reasonable range to ensure that the energy storage battery has the best running condition and the minimum capacity configuration.

Energy Internet Oriented Evaluation of Distributed Energy Storage Utility in User-Side

HONG Bowen, HU Jing, WANG Jianguo, HUANG Bibin, LIU Jianing, ZHOU Jingjing

2018, 51(3):  113-120,130.  DOI: 10.11930/j.issn.1004-9649.201704014

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With the development of China's energy internet, the distributed energy storage system will surely have a great new development opportunity for its excellent flexibility and power consistency, which is of great strategic significance in promoting electricity production and utility pattern change. In view of the user-side distributed energy storage which takes the grid-connected "distributed photovoltaic+energy storage" as the main application mode, a distributed energy storage evaluation model based on double-granularity optimal operation strategy is proposed, which is built on life-cycle cost-benefit analysis model for user-side distributed energy storage considering its operation optimization in advance. Taking the large industrial and business consumers in a China's province as an example, a sensitivity analysis is made of the user-side distributed energy storage value under the effects of the load characteristics, electricity price policy, energy storage costs and technology characteristics, and the future development potential and trend of the user-side distributed energy storage is predicted.

Harmonic Resonance Mechanism Study of Large-Scale Photovoltaic Power Plants

ZHU Wu, LIU Yajuan

2018, 51(3):  121-130.  DOI: 10.11930/j.issn.1004-9649.201702058

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Grid impedance that cannot be ignored between Large-Scale Photovoltaic Plants(LSPV) and the grid makes interaction among LSPV, grid and parallel inverters in LSPV. The interaction leads to system harmonic resonance. In order to study the LSPV resonance mechanism, a decoupling model that transforms multi-inverters parallel system into equivalent single inverter system is established. Then functions related to grid impedance, parallel inverters number, resonant frequency, damping ratio, stability margin are derived based on proposed decoupled model. A deep analysis on impact for system stability caused by grid impedance and the number of parallel inverters is also given. The harmonic resonance mechanism of LSPV is revealed from the point of closed-loop gain. Grid impedance will not disable active damping and resonance is caused by stability margin reduction related to grid impedance. The study is validated through simulations and experiment.

Discussion on Smart Grid Information &Communication Architecture Evolution

ZHOU Jing, SUN Yuanyuan, HU Ziwei, LU Lifeng, LIU Guojun

2018, 51(3):  131-135.  DOI: 10.11930/j.issn.1004-9649.201606082

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Based on future requirements and vision, smart grid architectural goals and principles are proposed. The architect takes into consideration of effective utilization of existing resources. Service reusability, system manageability and open standards are also the focus of architecture evolution. The smart grid evolution route is designed to transform system architecture from business silo mode to system integration mode. A future architecture vision based on open standards and layered services, which is the essence of “system of systems” is also proposed. The vision supports proposed evolution route and has high service oriented integration. Services and interfaces are reusable and loosely coupled due to compliance with open standard. Hence the proposed architecture is flexible, strong and adaptive with future requirement.

A Unified Data Reading and Communication Method of Independent Transformer Monitoring Devices

ZHANG Qi, XIONG Haijun

2018, 51(3):  136-143.  DOI: 10.11930/j.issn.1004-9649.201612065

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The existing transformer monitoring and testing devices operate independently without uniform standards, which makes it impossible to share data and to conduct comprehensive diagnosis of transformers based on multiple parameters within the same system. To solve this problem, a unified data reading and communication method is proposed in this paper. A unified communication framework is designed for on-line monitoring device, and the transformation method of private protocol and I0 protocol in smart substation condition monitoring system is proposed. The method of mapping big data and MODBUS register address is proposed, and the method of transforming the data of partial discharge monitoring device from unified XML file format and private file format to this format is put up. The practicability of our method is verified by the experimental results of the on-line and off-line monitoring devices. This method can advance the share application of isolated data of independent monitoring devices, and provide communication and data solution for integrated diagnosis of transformers.

Study on Carbon Emission Characteristics and Suggestions on Carbon Emission Management of Coal-fired Power Plant

SUN Youyuan, ZHENG Zhang, QIN Yaqi, GUO Zhen, REN Jian

2018, 51(3):  144-149,169.  DOI: 10.11930/j.issn.1004-9649.201702079

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To analyze the carbon emissions characteristics of coal-fired power plant accurately, a simplified calculation model and a detailed calculation model of power supply carbon emission intensity are established based on the China national standard GB/T 32151.1, and the reliability of the established models is verified using the measured carbon content of unit calorific value and carbon oxidation rate data, which shows that the proposed model can accurately and quickly obtain the carbon emission intensity of the power plant. Taking an ultra-high pressure CFB (circulating fluidized bed) unit as an example, the influences of net coal consumption and coal type characteristics on carbon emissions are analyzed according to the detailed calculation model, which shows that the decrease of net coal consumption and carbon emission coefficient of standard coal can reduce the carbon emission intensity, then some suggestions on carbon emission management are given, which provides a reference for the management of carbon emissions in the other power plants.

Analysis and Design of Insulator on Low-low Temperature Electrostatic Precipitator

SHEN Jiadong, ZHAO Haibao

2018, 51(3):  150-154.  DOI: 10.11930/j.issn.1004-9649.201609026

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Due to the low temperature flue gas in low-low temperature electrostatic precipitator (LLT-ESP) technology, certain measures should be taken to prevent the accumulation of dewing and knot ashes on the surface of high voltage ceramic insulator in order to ensure high operation stability. The paper designed three new insulator device structures of LLT-ESP, i.e., insulator within small chamber, insulator under wide beam and insulator within big incubator. Then the structural advantages and characteristics are analyzed respectively. At last, the applications of such technologies in Wenzhou and Huaiyin LLT-ESP devices are elaborated, where the insulator failure problem has been successfully solved.

The Characteristics of Limestone Dissolution under Oxy-firing Combustion Surroundings

SHI Xiaohong, LIU Yi, ZHONG Zhaoping, ZHANG Kai, ZHAO Kai

2018, 51(3):  155-162.  DOI: 10.11930/j.issn.1004-9649.201608011

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Under the oxy-firing combustion surroundings, the characteristics of limestone dissolution used for WFGD were researched on a small-scale test rig. The results indicate that higher CO₂ concentration can enhance the dissolution of limestone. Especially at 80% CO₂ concentration the rate of limestone dissolution increases significantly. The higher CO₂ concentration, the faster rate of dissolution under the same pH value. When pH is equal to 4.5, it takes 70 more minutes under low CO₂ concentration surroundings than with the high CO₂ concentration surroundings. Apparently, the CO₂ concentration has significant impact on the limestone dissolution.

Study on Life Management of the SCR Denitrification Catalyst

FU Yu, LU Qiang, TANG Shijie, ZHUANG Ke, HU Xiaoying, DONG Changqing

2018, 51(3):  163-169.  DOI: 10.11930/j.issn.1004-9649.201701125

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The catalyst is the key element of the SCR denitrification system in the coal-fired power plant. It deactivates gradually during the running process. In-time replacement or supplement of the catalyst not only guarantees the denitrification efficiency, but also reduces the system reaction costs. In this work, with the ammonia slip amount as the evaluation indicator, the catalyst life management model in line with the actual conditions of the denitrification is established based on the basic model of the SCR reactor and the deactivation model of the catalyst. The actual conditions of the ammonia-nitrogen ratio less than 1 are adopted as the modeling conditions, with the changes of the ammonia-nitrogen ratios at the reactor inlet and each catalyst layer in the reactor in consideration. Through comparing with the actual catalyst deactivation time, it is concluded that the model is proved to be accurate and the catalyst operating conditions are assumed properly. On this basis, combining with the catalyst replacement or supplement situation, 12 feasible catalyst management schemes are proposed. The optimal scheme is obtained when the service life of the catalyst is set as the evaluation indicator.

Review on Theoretical Research of the Catalytic Oxidation of Hg⁰ in Coal-Fired Flue Gas

ZHAO Li, LIU Yu, WU Yangwen, ZHUANG Ke, LU Qiang

2018, 51(3):  170-176.  DOI: 10.11930/j.issn.1004-9649.201611113

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Mercury is one of the heavy metal element pollution in the flue gas of coal-fired power generation, with elemental mercury (Hg⁰), oxidized mercury (Hg²⁺) and particulate mercury (Hg^P) as its main existing forms. Since Hg⁰ is difficult to be removed, it is usually oxidized to Hg²⁺, which can be removed easily with the help of catalysts. Hg⁰ oxidation catalyst can be divided into three major types according to their different sources and functions, i.e., coal-fired fly ash, conventional Hg⁰ oxidation catalyst, and cooperative de-NO_X and Hg-removal catalyst. In this paper, the present status of the density functional theory (DFT) study of oxidation reaction of Hg⁰ under different catalysts is reviewed. Then the mechanisms of adsorption and oxidation reaction of Hg⁰ on various catalysts are summarized and the contents and results of some similar studies are compared. In addition, the deficiency of the current research is pointed out and the future development trend of DFT calculation study of Hg⁰ oxidation catalyst is put forward.

Analysis on Coordinated Reduction of SO₃ in Whole Process of Ultra-low Emission in Coal-Fired Flue Gas

TAO Leixing, WENG Jie, LI Xiaofeng, YUE Chunmei, WANG Jian, AI Chunmei, DONG Feiying

2018, 51(3):  177-184.  DOI: 10.11930/j.issn.1004-9649.201704063

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It is necessary to study the formation, concentration, emission level and influencing factors of the sulfur trioxide in the control process of flue gas pollutants in thermal power plants because the sulfur trioxide in the flue gas is one of the precursors of smog. Based on the onsite measurements of ultra-low emission facilities of 300~1 000 MW coal-fired units and the whole process test of a 1 000 MW unit, the comparison with the conventional pollutant control process shows that the ultra-low emission facilities have a better control effect on SO₃ with SO₃ comprehensive removal efficiency reaching 90%. The SO₃ removal mechanism and effect of each equipment in flue gas flow process were also analyzed. The results show that: (1) SCR denitrification device has a catalytic oxidation effect on SO₂ converted to SO₃. (2) The air preheater consumes SO₃ indirectly during the process of the flue gas temperature drop. The low-low temperature electrostatic precipitator, the wet desulfurization absorber and the wet electrostatic precipitator all contribute to the SO₃ reduction, accounting for 30%, 40%, 15% and 5% of total reduction respectively. (3) The air preheater, electrostatic precipitator operating temperature has great impacts on SO₃ removal rate. (4) The high-efficiency desulfurization synergistic dust removing integrated absorption tower has a better effect of SO₃ removal.