- HU Nan;XU Meng;ZHANG Man;YANG Hairui;ZHANG Shouyu;ZHAO Bing;GONG Taiyi;WANG Jialin;Jilin Province S&T Innovation Center for Physical Simulation and Security of Water Resources and Electric Power Engineering,Changchun Institute of Technology;Key Laboratory for Thermal Science and Power Engineering of Ministry of Education,Tsinghua University;School of Energy and Power Engineering,University of Shanghai for Science and Technology;Huadian Power International Co.,Ltd.TEDA Branch;
The inevitable result of circulating fluidized bed( CFB) boilers scale-up is the increasing of furnace cross-sectional size and the parallel circuit. The coal combustion and heat transfer in a fluidized bed boiler are determined by the characteristics of gas-solid flow in the furnace. The uniformity of gas-solid flow has an important impact on the safe operation of CFB boiler. In this paper,the static and dynamic lateral non-uniformity of gas-solid flow in large CFB boilers were analyzed. The static non-uniformity problems include the air distribution uniformity,the gas-solid flow deviation along the section caused by the parallel circuit and the flow distribution deviation of each circuit,which does not change with time under the stable operation condition. The resistance characteristic of separator is an important characteristic parameter of cyclone. Under the same gas phase flow rate,the effect of solid concentration on the pressure drop of cyclone is non-monotonic. The cyclone pressure drop decreases first and then slowly increases as the concentration of solid particles increasing. The solutions of the governing equation of multi-cyclone system are multi-velued. Therefore,the solid circulating rate of each cyclone has deviation under the condition of multi loop parallel. The hanging platen superheater in CFB boiler affects the local concentration distribution of particles and then affects the distribution of solid particle circulation flow rate of each separator. In the aspect of air distribution uniformity,the way of air inlet from both sides and the back wall will lead to uneven air distribution in different degrees. The outlet duct of the cyclones has a significant influence on gas-solid flow distribution of the cyclones. The large margin and long-term pressure fluctuation in CFB furnace is discovered during lower load operation,which is the dynamic lateral non-uniformity. The large cross-section air distribution,reduction of the primary air and the multi-circuit parallel are main reasons for this problem. The mathematical model of lateral fluctuation is based on the assumption of natural frequency of lateral fluctuation of gas-solid two-phase flow system. When the disturbance frequency is close to natural frequency,lateral wave will be generated. The dynamic non-uniformity problem is lack of in-depth and systematic research on the laboratory scale,and the mechanism is still relatively vague,which is the main research direction of the gas-solid flow non-uniformity problem. At the same time,the coupling effect of uneven wind distribution and dense phase gas-solid flow needs further study.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 740K] - LIU Xiandong;WU Yuxin;ZHANG Yang;ZHOU Shuai;YANG Hairui;ZHANG Hai;LYU Junfu;ZHANG Kai;Key Laboratory for Thermal Science and Power Engineering of Ministry of Education,Department of Energy and Power Engineering,Tsinghua University;Taiyuan Boiler Group Co.,Ltd.;
The ash circulating rate of high-temperature bed material is a crucial parameter for circulating fluidized bed( CFB) boilers,while there is no measurement technology that can be applied to the industrial boiler at present. Therefore,an in-situ impact measurement method for solid particle circulation rate of CFB boilers was proposed in this paper,and its prototype equipment was built. The theoretical model of the measurement process was established and the cold state test was carried out in the laboratory. The proposed measurement method of circulating flow rate measurement was also applied to a 116 MWthCFB boiler for a hot state test. The prototype equipment had the geometry structure of cantilever,which was arranged at the bottom of standpipe in circulating fluidized bed. One end of the prototype was fixed with the outer wall surface of the boiler and the other end carrying a target piece was inserted into the dense phase area of standpipe. The device calculated the impact force of particles and reversed the impact velocity of particles by measuring the deformation caused by the impact on the target plate when the materials in the riser fell,so as to obtain the circulating flow rate. Meanwhile,instrument air is supplied to cool equipment and prevents it from blocking. This measurement method has the advantages of high-temperature resistance,the ability of in-situ measurements and no disturbances to the boiler operation. The results indicate that the resistance and resistance coefficient of gas-solid flow at different impacting velocity are measured in cold state experiment. As the increase of impact velocity,the gas-solid flow resistance increases and the resistance coefficient decreases and the phenomenon of shear shinning appears. In hot state test in real boiler,the measuring method is capable of capturing the variation of the ash circulating rate when the boiler starts,shuts-down and the load changes. Based on the magnitude analysis and the checking calculation with the product of pressure drop of dilute phase area in furnace and average velocity in furnace,the feasibility of the in-situ utilization of the proposed method in CFB boilers is verified.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 6660K] - ZHANG Yangxin;WANG Zhining;ZHANG Yang;CHENG Lu;FAN Baoguo;ZHANG Hai;LYU Junfu;College of Electrical and Power Engineering,Taiyuan University of Technology;Shanxi Research Institute for Clean Energy Tsinghua University;Key Laboratory for Thermal Science and Power Engineering of Ministry Education,Department of Energy and Power Engineering,Tsinghua University;
Circulating material flow rate is an important parameter for the design and operation of circulating fluidized bed( CFB) boilers,but the hot-state in-situ measurements of it is still difficult. In the present study,the measurement method of circulating flow rate based on the heat transfer process was further improved. The effects on heat transfer coefficient between the high temperature solids and the tube surface were studied in hot state tests. The high temperature test data and the prediction model of the convective heat transfer coefficient proposed by Borodulya et al were used to establish the correlation between heat transfer coefficient and solid circulation rate. The results show that the influencing factors of the heat transfer coefficient include the solid circulation rate,particle temperature and the particle size. The error between the measured material flow rate and the preset value is within ±25%. The method can match the circulating material flow rate and heat transfer coefficient in pairs,and has good prediction in a wide range of flow rate. According to the research results,once the heat transfer coefficient is determined in the measurement,the solid circulation rate can be obtained by using the proposed model,and thereby the measurement of high temperature solid circulation rate is achieved. The heat transfer method is simple and has the advantages of low manufacturing cost. Based on the research,it has further improved practicability. It is a promising method of the measurement of circulating flow rate in CFB boilers.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 5777K] - XU Zhaofeng;XUE Yali;LI Zheng;State Key Lab of Power Systems,Department of Energy and Power Engineering,Tsinghua University;
In general,ultra-supercritical circulating fluidized bed( CFB) boilers are equipped with external heat exchangers( EHE) to increase the heat transfer area and heat transfer. In order to study the startup process characteristics of the external heat exchanger of CFB boiler,so as to provide the basis for wide load operation and flexible peak regulation of CFB,The dynamic characteristics of startup process of EHEs of a 660 MW ultra-supercritical CFB boiler were studied,by establishing the dynamic mathematical models of CFB boiler with EHEs and simulating and analyzing the cold startup process and the hot startup process of EHEs. Before the cold startup and the hot startup,the furnace temperature is 776 ℃,while the temperature of EHEs is 50 ℃ and 660 ℃ respectively. At the 30 th minute,the conical valve is opened and EHEs start to work. Due to the low temperature of EHEs in the cold startup,the conical valve is only 5% open in order to avoid overheating of the EHE pipe. Such limitation does not exist in the hot startup,and the conical valve can be open up to 30%. In order to show the change caused by one variable,only the opening degree of the conical valve is different in the cold startup process and the hot startup process,and the slag discharge quantity is automatically controlled in other active control quantities to maintain the stable furnace pressure. In the cold startup process,heat released from EHEs changes from negative value to positive value: EHEs absorb heat from the working medium( medium temperature superheated steam) first because the initial temperature of EHEs is lower than that of the working medium; when the temperature of EHEs is higher than that of the working medium,EHEs release heat to the working medium. In the hot startup process,EHEs always release heat to the working medium all the time,because the initial temperature of EHEs is much higher than that of the working medium. Therefore,the flow rate of working medium should be maintained at the set value and above before cold startup or hot startup,otherwise the condensation or sudden temperature rise of working medium at the startup moment will lead to the drastic temperature change of pipe,resulting in pipe burst and other accidents. When EHEs reach energy balance after cold or hot startup,the furnace temperature decreases in varying degrees,because the furnace releases less heat and EHEs release more heat accordingly,under the condition that the input energy of CFB boiler remains unchanged. In the hot startup process,the circulating ash flowrate and heat discharge of EHEs are large,because the opening degree of the conical valve is 30%,resulting that the furnace releases less heat than that of the cold startup and the furnace balance temperature is lower than that of the cold startup. In the cold startup process,the temperature rise of the external heat exchanger is higher. The conical valve is only 5% open in order to avoid the high rate of temperature rise on the wall of the heat exchange surface,resulting that the characteristic time of the temperature rise curve of EHEs is obviously larger than that in the hot startup process.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 1790K] - LI Juan;LI Yinlong;NIU Tiantian;XIN Yafei;YANG Dong;State Key Laboatory of Multiphase flow in Power Engineering,Xi'an Jiaotong University;
Circulating fluidized bed( CFB) power generation technology has been rapidly developed and widely used due to its unique advantages. In recent years,in order to achieve the goals of ultra-low emission and ultra-low energy consumption,the design and research of large-scale and high-parameter ultra-supercritical CFB boiler) has become the main development direction of clean coal power generation technology in China. At present,the basic theory and design calculations of ultra-supercritical generating units are not perfect,so it is particularly important for the simulation of its operation and the prediction of the main parameters of the boiler when the operating conditions change. Aspen Plus can perform sophisticated steady-state simulation and process design of complex chemical processes. Based on the built-in modules provided by the Aspen Plus software and the external subroutines of the FORTRAN compiler,the simulation model of coal decoupled combustion process in combustion chamber of a 660 MW ultra-supercritical CFB boiler was established. The process simulation model mainly includes the equivalent pyrolysis model of coal,simplified decoupled combustion model,separator,external bed and tail flue low temperature superheater and low temperature reheater model. Based on the established steady-state model,the performance of the 660 MW ultra-supercritical circulating fluidized bed boiler under full-load operating conditions( B-MCR) was simulated and calculated. The calculation results of its main temperature can be obtained,the gas component concentrations in the dense phase zone can be analyzed and the sparse phase zone in the combustion chamber,and the influence of the primary air ratio of the CFB combustion chamber operating parameters on the concentration of CO2,CO and SO2 in the dense phase zone and the influence of excess air coefficient on the concentration of the exhaust gas components SO2,SO3,NO and N2 O can be successfully predicted. At the same time,the model was used to calculate the effect of excess air coefficient and changing the ratio of primary return material on the outlet steam temperature of medium temperature superheater,low temperature superheater,and the temperature of flue gas at low temperature reheater and economizer. The design and research of the 660 MW ultra-supercritical circulating fluidized bed boiler provides a reference basis for reducing pollutant emissions,reducing boiler heat loss and improving boiler efficiency.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 1877K] - MING Xiangdong;DUAN Yufeng;LIU Shuai;HU Peng;Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education,School of Energy and Environment,Southeast University;
Circulating fluidized bed( CFB) boiler has the advantages of wide adaptability of coal type,strong load regulation ability,ultralow emission of pollutants,etc,which is widely used in clean combustion of coal. In order to explore the generation and emission of pollutants in CFB,a systematical modelling and prediction of a 0. 3 MWthCFB coal-fired pilot facility based on the Aspen Plus scheme were conducted,including the sub-models of coal combustion and pollutant control devices. The Gibbs minimum free energy thermodynamic analysis method was used to analyze and calculate the coal combustion products,and the sensitivity analysis tool included in the software was used to analyze the sensitivity of different operating parameters. The effects of operational parameters of the combustion system on flue gas components,denitrition of selective catalytic reduction( SCR) and desulfurization of limestone-gypsum wet flue gas were predicted. The variable process of NOx,SOxremoval efficiency and generation of SO3 versus the excess air coefficient,flue gas temperature,ammonium to nitrogen ratio and calcium to sulfure ratio was simulated. The results show that under the conditions of circulating fluidized bed coal combustion,the changes of temperature have a significant effect on the formation of NOxand SOx. The increase of temperature will promote the conversion of NH3,HCN and other precursors,and promote the production of fuel nitrogen to NOx; under high temperature conditions,the chemical equilibrium of the SO2 formation reaction moves to the positive direction,but the reaction rate decreases with the increasing of temperature and concentration,while SO3 is the opposite. During the SCR denitration process,the denitration rate increases with the increase of temperature at lower temperatures,and the optimal active temperature is around 360 ℃ . Before the reaction temperature of SCR is 380 ℃,the content of SO3 increases significantly,and there is a maximum value point at 380 ℃,and then tends to be gentle and slightly decreases. When the ammonia-nitrogen ratio is less than 1,the denitration rate promotes with the increase of the ratio of ammonia to nitrogen,and the best ratio is 1.05. During the WFGD desulfurization process,increasing of the calcium-sulfur ratio can significantly enhance desulfurization efficiency and reduce the emission of SO3,and the best ratio of calcium to sulfur is about 1.05. The elevation of WFGD inlet temperature results in less desulfurization efficiency but promotes the formation of SO3.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 1971K] - GAO Mingming;YU Haoyang;LYU Junfu;YU Xiaohong;LI Wenrui;LI Cunhuai;WEI Guang;State Key Lab of Alternate Electric Power System With Renewable Energy Sources (North China Electric Power University);State Key Laboratory of Power Systems,Tsinghua University;Tianjin Branch,China Huadian Group Go.,Ltd.;Tianjin Development Area Branch,Huadian Power International Co.,Ltd.;
With the increasingly strict requirements of environmental protection,in order to reduce the NOxemission of CFB units,it is necessary to accurately estimate the NOxconcentration generated in the furnace and apply it to the control. For this,it is necessary to establish an accurate and practical mechanism control model. At the same time,it is necessary to comprehensively consider the optimization control to reduce nitrogen oxide and SNCR generated in the furnace combustion,and the comprehensive control of nitrogen oxide inside and outside the furnace should be optimized by using this model.Based on the analysis of the formation mechanism of nitrogen oxides,the CO concentration prediction model at the furnace outlet was established with fuel NOxproduced by CFB boiler combustion as the main body,the method of mathematical modeling and simulation,and coal feed,air flow,etc. used as model inputs. Based on this model,the prediction model of the NOxconcentration at the furnace outlet could be established by using the model as the input of the burning coal model.The above method was used to establish a prediction model of CO concentration at furnace outlet,and the parameters of the model were obtained and simulated based on the actual operating data,and the furnace combustion control was not well coordinated with SNCR denitration,which led to the problem of high levels of nitrogen oxide emissions. Based on the established prediction model of NOxconcentration at furnace outlet,a comprehensive control technology route for nitrogen oxides inside and outside the furnace was proposed,and a primary and secondary air volume optimization and SNCR optimization control ideas were designed based on the NOxconcentration prediction model.The simulation proves that the established model has good accuracy,meets the accuracy requirements of the actual control system,and has a certain predictive effect. The design of the integrated nitrogen oxide control technology route and optimized control ideas inside and outside the furnace can provide a reference for the low-emission control of nitrogen oxides in circulating fluidized bed units.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 2948K] - CHEN Baoming;DUAN Yufeng;GENG Xinze;XU Yifan;ZHAO Shilin;HUANG Tianfang;Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education,School of Energy and Environment,Southeast University;
In order to find out the causes of heat loss of circulating fluidized bed( CFB) boiler unit,the thermal performance of CFB coalfired boiler with rated load of 75 t/h was tested. In order to compare with the measured method,a new idea of obtaining the thermal efficiency of CFB boiler based on Aspen Plus model method was proposed,that is,by using Aspen Plus process simulation software to model and calculate CFB boiler. In the experiment,three operating conditions of low load,full load and high load were selected,and the heat losses was calculated by the anti-balance method,and then the effects of different operating conditions on the thermal efficiency of the CFB boiler were explored,the distribution of unburned carbon( UBC) in fly ash and slag under different operating conditions was analyzed.By modeling the four sub-processes of coal pyrolysis,coal combustion,flue gas-fly ash separation and heat exchange of CFB boiler,and based on the data of inlet and outlet flow unit temperature,pressure,flow rate,etc. in heat exchange equipment at all levels of the boiler,the heat loss,the heat efficiency and the concentration of flue gas at the outlet of the boiler were calculated under the condition of full load( working condition 2). The accuracy and reliability of the model were verified by comparing the measured data with the simulation results.The results show that the model method is in good agreement with the measured data and can accurately predict the composition of flue gas at furnace outlet. Through the comparison of the heat loss and thermal efficiency of boiler,it is found that the measured result of exhaust heat loss q2 is 7.75%,and the model result is 6.48%.The measured result of solid incomplete combustion q4 is 3.72% and the model result is 3.17%.The relative error between two methods is small,indicating that Aspen Plus modeling can be used to accurately predict the heat loss of smoke exhaust and the heat loss of incomplete solid combustion. The thermal efficiency of the boiler calculated by the model is88.66%,the measured thermal efficiency of boiler is 87.426%,and the relative error is only 1.41%,the calculation results of thermal efficiency and heat loss is extremely close between the measured method and the model method,which can verify the veracity and reliability of the modeling idea and method,and the feasibility of CFB boiler thermal efficiency calculation based on Aspen Plus model is also verified.There are some problems in the operation of the boiler under the three operating conditions,such as high flue gas temperature,high carbon content of fly ash,and low actual thermal efficiency that does not reach the boiler design value. The content of UBC in fly ash after coal combustion is relatively high,ranging from 13.28% to 16.40%,while the content of UBC in slag is low,ranging from 2.92% to3.39% under three operating conditions,the heat loss of boiler exhaust flue gas between 7. 64%-7. 93%,the heat loss of solid incomplete combustion between 3.72%-4.69%,the boiler thermal efficiency is between 86.14%-87.43%,in which η2>η3>η1.It shows that it is feasible and reliable to use Aspen Plus to model CFB boiler for thermal calculation.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 1442K] - HUANG Peng;ZHAO Bing;WANG Jialin;GONG Taiyi;WANG Yong;WANG Dongzhen;State Key Lab of Alternate Electric Power System With Renewable Energy Sources(North China Electric Power University);Tianjin Development Branch,Huadian International Power Co.,Ltd.;China Huadian Group Tianjin Company;
With the country's increasingly strict requirements for the emission of air pollutants from coal-fired power plants,circulating fluidized bed boiler has attracted more and more attention because of its good adaptability to coal and low emission of air pollutants. In order to study the emission law of air pollutants in CFB and provide a scientific basis for the actual operation,and based on the combustion mechanism of CFB boiler,the coal in the boiler was divided into volatile and burning carbon. The formation of sulfur dioxide and nitrogen oxide was also divided into two parts,one was generated immediately with the combustion of volatile matter,the other was generated with the combustion of burning carbon. The amount of sulfur dioxide removal in the furnace mainly focused on the calcium sulfur ratio,while the amount of nitrogen oxide self reduction in the furnace was mainly related to the amount of burning carbon and carbon monoxide concentration in the furnace. On this basis,the models of SO2 concentration and NOxconcentration at the inlet of desulfurization tower were derived. The model has been verified on the operation data of a 330 MW subcritical circulating fluidized bed. The calculated value of the model is in good agreement with the actual value,and it is about 2-4 minutes ahead of the actual value,which eliminates the measurement delay caused by the location of the measurement points of air pollutants,and has a good prediction effect. The relationship between the amount of burning carbon in the furnace and the sulfur dioxide concentration at the inlet of the desulfurization tower and the nitrogen oxide concentration at the inlet of SNCR was studied. The calculation results show that the change trend of the amount of burning carbon is the same as that of the sulfur dioxide concentration at the inlet of the desulfurization tower and is the opposite with that of the nitrogen oxide concentration at the inlet of SNCR when the desulfurizer does not change much. At last,the model was used to calculate after changing the air volume and coal volume on the original operation data. The results show that the increase of air volume will reduce the sulfur dioxide concentration at the inlet of desulfurization tower under the condition of constant coal quantity,but increase the nitrogen oxide concentration at the inlet of SNCR. However,the effect of coal volume increase on the concentration of air pollutants emission is opposite to that of air volume increase. The calculation results have a certain guiding effect on the actual operation.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 4633K] - ZHANG Yao;LIN Chen;YU Juan;FENG Fan;ZHANG Zhongxiao;School of Mechanical and Power Engineering,Shanghai Jiao Tong University;
The formation control of NOxis related to fluidized bed fluidization characteristics and gas-solid flow,and the cold state test can more directly reflect the gas-solid flow state and fluidization effect,so the results of the cold state test can provide reference for the parameter selection of the reaction thermal experiment of fluidized bed denitration. Previous researches mostly used narrow screening bed material particles,and mostly focused on the traditional wall type secondary air arrangement. Few scholars comprehensively studied the penetration performance of secondary air arrangement in the center and its influence on the fluidization characteristics of the furnace.Therefore,the influence of central secondary air distribution and bed material with wide and narrow screening on fluidization characteristics was studied on the cold experimental bench of circulating fluidized bed. The dimensionless residual temperature,material circulation rate and apparent particle volume fraction were used to quantitatively describe the secondary air penetration,material circulation efficiency and particle concentration distribution. The experimental results show that the particle concentration near the jet height increases with the increase of the secondary air jet. When the secondary air injection height is 15 cm,in the dense phase area below 35 cm,the larger the proportion of secondary air is,the more obvious the increase of particle concentration is. The penetration performance of the secondary air jet can be effectively improved by increasing the proportion of secondary air jet,increasing the velocity of the secondary air jet and improving the jet position of the secondary air jet. When the injection height of secondary air is 5 cm from the bottom of the furnace,the jet penetration rate is 0.4; When the injection height is 15 cm,the jet penetration rate is 0. 84. When the injection height continues to rise by10 cm,the jet penetration rate reaches 1.0. The reason for this phenomenon is that the closer to the bottom of the furnace is,the greater the concentration of the bed material particles is,and the secondary wind resistance increases sharply. With the decrease of the average particle size of the narrow screening bed material,the overall pressure drop in the furnace increases,and the pressure drop tends to be stable at a higher position in the furnace,and the circulation flow rate of the material also increases. This indicates that more particles can be carried out of the furnace along with the uplift of fluidized wind and enter the separator to participate in the circulation outside the furnace. Different from the narrow sieve bed material,the proportion of fine particles in the bed material determines the furnace pressure drop,particle concentration distribution and material circulation rate of the wide sieve bed material. The higher the proportion of fine particles is,the greater the pressure drop in furnace and the circulating flow rate of materials are. In wide screening,the particle concentration distribution and material circulating flow rate of bed materials with large average particle size are not necessarily small,because under the experimental wind speed,particles with particle size less than 300 μm are more likely to be carried to the furnace outlet along with the elutriation action of fluidized wind. The higher the proportion of these fine particles is,the greater the particle concentration distribution and the material circulation rateare. Coarse particles tend to concentrate at the bottom of the furnace.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 5084K] - YU Bin;WANG Ai;SUN Hongbin;WA Qier;CHEN Yu'an;ZHENG Yan;YAO Xuan;Salaqi Power Plant,Beijing Guodian Dianli Co.,Ltd.;Beijing Guodian Longyuan Environmental Engineering Co.,Ltd.;
Flow field characters have influential impacts on the improvement of desulfurization efficiency and system stability in the circulating fluidized bed semi dry desulfurization system,among whichthe uniformity and stability of the flow field are two key points of the whole system. Only when the design of fluidized bed and conveying equipment are reasonable,the stable and efficient operation of the desulfurization system can be guaranteed. Using CFD method and taking a semi-dry desulfurization plant of 300 MW coal-fired unit as the research objectives,and based on the calculation of the flue gas field in the desulfurization tower area and flue behind the dust collector,the non-uniformity of the flue gas flow field in the semi dry desulfurization system and improvement methods were investigated. Two models were established in the experiment. Model A is from the header of the 4 trumpet outlets of the pre-dust collector to the entrance of the bag dust collector,which is the main desulfurization reaction area. Model B is from the outlet of the bag filter to the inlet header of the induced draft fan and the main purpose of this area optimization is to reduce system resistance. Computational fluid dynamics simulation has been taken for analyzing placement and the number of guide vane as factors affecting flue flow field,velocity vector and pressure field. The result of optimization showed that the uniformity of the flow field can be improved by the application of the expansion header at the outlet of the pre-dust collector in model A. However,it is necessary to consider the ash accumulation caused by the reduction of the expansion flow rate,adjust the design of the ash accumulation load of the flue and steel structure and improve safety margin. A deflector blade is installed at the bottom of the desulfurization tower,which can effectively solve the bias problem and ensure the uniformity of the flue gas velocity entering the venturi,and the system resistance is also well controlled. The total resistance is around 2 200 Pa. The main optimization element of the bag flue outlet flue( model B) is to reduce the system resistance. The guide vane at the elbow 1 can effectively improve the speed distribution and reduce the resistance of the flue. When the number of guide vanes is 1-2,the effect is poor. When the number of guide vanes exceeds 3,the resistance basically reaches the optimal value and the air flow distribution is apparently improved. The guide vanes at the elbow 2 have little effect on reducing the resistance and improving the uniformity of flue gas flow field.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 15315K] - LI Lulu;YAO Xuan;ZHANG Man;JIN Yan;YANG Hairui;College of Electrical and Power Engineering,Taiyuan University of Technology;Department of Energy and Power Engineering,Tsinghua University;Beijing Guodian Longyuan Environmental Engineering Co.,Ltd.;
Wet desulfurization technology is mostly adopted in large and medium-sized coal-fired power plants,which results in a large amount of water evaporation in the desulfurization process. For 600 MW units,the flue gas discharged after wet desulfurization carries more than 200 t/h of water vapor. Water vapor and low-temperature waste heat in desulfurization wet flue gas are important parts of water resources and energy loss in coal-fired power plants. In order to reduce the moisture content in flue gas,effectively recover the moisture and waste heat in flue gas,and solve the problems such as chimney corrosion, " gypsum rain" and " white smoke" caused by condensation of water vapor in wet flue gas,a three-dimensional steady-state CFD model was built based on fluent software to simulate the condensation process of flue gas after wet desulfurization. Taking the optimized condensation chamber as the calculation object,the energy,mass and momentum exchange between gas-liquid two-phase flows were fully considered. The influence of the structure of the condensation chamber itself and the gas-liquid two-phase parameters on heat and mass transfer was comprehensively discussed. The results show that there is an optimal spacing between the two spray layers,and the optimal spacing in the simulation is 1 m. This spacing can make the residence time of liquid droplets in the condensation chamber and the gas-liquid contact uniformity reach a higher level at the same time. Within a certain range of flue gas velocity,the flue gas velocity is high,the residence time of flue gas in the condensation chamber is short,the contact time between gas and liquid is short,and the degree of heat exchange is poor. The flue gas flow rate is low,the flue gas Reynolds number is small,the turbulent flow is weak,and the amount of air treated per unit area per unit time is small,therefore,there is an optimal flue gas flow rate. The research shows that the optimal flue gas flow rate is 3.5 m/s. Proper increase of liquid-gas ratio,reasonable reduction of droplet diameter,reduction of spray liquid temperature and increase of nozzle angle can effectively ensure the uniformity of flow field,improve the gas-liquid contact strength and enhance the heat and mass transfer effect between gas and liquid. However,increasing the liquid-gas ratio requires a larger amount of water,which is not conducive to saving water and energy. Reducing the temperature of spray liquid can increase the temperature difference of heat exchange,but a lower cooling water source is required. Increasing the nozzle angle has limited effect on improving condensation. Among them,the most effective method is to reduce the droplet diameter. Using a nozzle with good atomization degree,the droplet diameter is less than 210 μm,which can condense wet flue gas from 323 K to 311. 75 K. For600 MW units,at least 80 t of water resources and 6.59 MW of energy can be recovered per hour,so as to achieve the goal of water saving and energy saving, " white elimination" and dust removal integration.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 11761K] - CAI Jin;ZHANG Man;WANG Zhongwei;RONG Haojie;YAO Xuan;WU Yuxin;Key Laboratory of Thermal Science and Power Engineeringof the Ministry of Education,Department of Energy and Power Engineering,Tsinghua University;Shanxi Research Institute for Clean Energy Tsinghua University;China Special Equipment Inspection And Research Institute;Shanxi Hepo Power Plant Co.,Ltd.;
When the desulfurization in circulating luidized bed( CFB) boiler can not meet the discharge requirements,further purification of exhaust gas is needed. There are two options for the exhaust flue gas desulphurization( FGD) in the circulating fluidized bed boiler,such as limestone-gypsum wet FGD and CFB semi-dry FGD. In order to identify the most economical and suitable FGD technology for circulating fluidized bed combustion conditions,the techno-economic analysis model was suggested and the techno-economic index for two processes was predicted under the condition of full load and 70% desulphurization efficiency in the CFB combustion by limestone injection. The model results indicate that the operating cost and total cost of CFB semi-dry FGD technology are relatively low,require sulfur contents is required below 1.1% and 2.1%. The cost proportion of the desulfurizing agent for( CFB) semi-dry FGD is significantly large,while the electricity cost proportion of limestone-gypsum wet FGD is slightly large. Limestone price,on-grid power tariff and annual operation time are the main factors affecting desulfurization cost. The sensitivity of limestone to desulfurization cost is greater than that of on-grid power tariff.On the basis of the furnace desulfurization efficiency of 70%,the operating cost of limestone-gypsum wet FGD is higher than that of CFB semi-dry FGD when the price of limestone is less than 112 yuan per ton. When the on-grid power tariff is lower than 0.43 yuan per kilowatt hour,the operating cost of limestone-gypsum wet FGD is relatively low. The total cost of CFB semi-dry FGD is lower than that of limestone-gypsum wet FGD within the fluctuation range of limestone price,electricity price,and annual operating time. Compared with the conventional furnace desulfurization technology,the desulfurization cost of the ultra-fine limestone furnace desulfurization technology is lower,and the comprehensive advantages combined with the CFB semi-dry FGD technology are more prominent.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 5499K] - MA Tao;RU Yu;LI Kezhang;HUI Jianfei;ZHU Hai;LI Meng;Qinhuangdao Qinre Power Generation Co.,Ltd.;China Huaneng Clean Energy Research Institute;
With the continuous improvement of environmental protection pressure,in-depth denitrification retrofit for many fluidized circulating bed( CFB) boilers needs to be carried out to achieve ultra-low emissions,while there is little research on the application of SCR retrofit in CFB boilers at present. SCR denitrification system has been added to a 320 MW fluidized bed unit. Based on this project,the grid method was used to measure the parameters of flue gas temperature,flue gas composition,etc.,the boiler performance test before and after the retrofit was carried out,and the denitrification performance and its influencing factors after SCR retrofit were studied. Besides,the boiler efficiency was measured. The results show that the average temperature at SCR inlet is 268.11-309.53 ℃ under different loads,which basically meets the extended temperature window for SCR reaction( 260-420 ℃) . With 320 MW load,the measured denitrification efficiency is 72.48%,and the corresponding ammonia escape concentration is 0.7 mg/Nm3. Under 40%-100% load,the NOxemission is lower than 25 mg/Nm3,and the ammonia escape concentration is lower than 1 mg/Nm3. Because the flue gas temperature is lower than that of pulverized coal boiler,the denitrification efficiency of SCR reactor in this test is lower than that used in pulverized coal boiler. The urea consumption under 40%-100% load is lower than that of pulverized boiler with the same grade,and the urea consumption under full load is 279.09 kg/h. Under the same emission value,the urea consumption is reduced by more than 50%,and the effect of energy saving is significant. The results of emission and urea consumption show that SNCR are well coupled with SCR,and this technology has a great advantage in CFB boiler. The NOxdistribution at the SCR outlet is not uniform,showing a trend of high NOxconcentration on the right side and low NOxconcentration on the left side on the horizontal section of flue,which is consistent with the temperature distribution at the SCR inlet. Temperature is the main factor affecting the denitrification efficiency and NOxdistribution. The average boiler efficiency after retrofit is 90.07%,which is basically equal to that before retrofit,indicating that SCR retrofit has little effect on boiler efficiency. More than 90%of the heat loss of the boiler is caused by the heat loss of exhaust gas and incomplete combustion. The key to improve the boiler thermal efficiency is to reduce q2( heat loss of exhaust gas) and q4( incomplete combustion of solid).
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 2980K] - ZHANG Jiajia;GE Ming;HU Jun;WANG Shengjia;GUO Kang;HUO Hongbin;HE Lucan;DAI Weibao;CHE Guoqing;Guodian Science and Technology Research Institute Co.,Ltd.;Guodian Bengbu Power Generation Co.,Ltd.;
Considering the problem that the dust collector could not be put into operation due to the large amount of ammonia escaping from the denitrification system,the optimization adjustment of ammonia injection in vortex mixer SCR denitrification system was carried out. It is found that the NOxconcentration in the denitration outlet is unevenly distributed in the width direction. By adjusting the manual butterfly valve of the ammonia injection branch pipe,the non-uniformity of NOxconcentration in the denitration outlet is reduced. At full capacity,the inhomogeneity of A side of the flue decreases from 48.3% to 19.4%,the inhomogeneity of B side decreases from 62.7% to 21.8%. After adjustment,the NOxdistribution inhomogeneity decreases significantly. There is no obvious deviation of flue flow on both sides under high and low load. The distribution of flow field is relatively uniform. A new type of eddy current static mixer was adopted whcih was helpful to solve the problem of uneven distribution of NOxconcentration in the outlet of denitration along the depth direction. It is found from the SIS data that the CEMS measuring point of NOxconcentration at denitrification outlet is inaccurate,which leads to the excessive amount of ammonia spray and the large amount of ammonia escape during automatic operation of ammonia injection. The measuring point of CEMS is not representative,which is recommended to use grid sampling method. A regular calibration of CEMS measuring points is recommended.The poor following performance of ammonia spray causes a certain delay between the ammonia spray and the NOxconcentration at the denitrification inlet in control strategy of ammonia injection. The ammonia spray control logic should be optimized. The NOxemission concentration of net flue gas should not be set too low. The lower the setting value is,the greater the ammonia escape amount is. Considering the environmental requirements and economy,it is recommended that the net flue gas NOxemission concentration is controlled within 25-35 mg/m3. After the ammonia injection optimization,the overall ammonia escape is controlled below 3×10-6.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 7179K] - LIN Chen;ZHANG Yao;YU Juan;FENG Fan;ZHANG Zhongxiao;School of Mechanical Engineering,Shanghai Jiao Tong University;
With the increasingly severe situation of air pollution,the relevant environmental protection standards for controlling NOxemissions have become increasingly strict. Selective non-catalytic reduction( SNCR) can effectively reduce NOxemissions,but the denitration efficiency in fluidized bed is limited due to the narrow reaction temperature window. Previous studies have proved that when H2,hydrocarbon and CO are used as additives,the reaction temperature window of SNCR can be can widened and the denitration reaction at low temperature can be carried out. However,in the thermal test system of circulating fluidized bed,few studies have been carried out to analyze the effect of coexisting H2,hydrocarbon and CO on SNCR by using industrial by-products such as coal gasification syngas as additives. In order to study the influence of the mixture reducing agent composed of syngas and ammonia on the denitrification reaction,the denitrification effects of ammonia water and the mixed reductant composed of syngas and ammonia water were compared in a combustion experimental system of circulating fluidized bed. At the same time,the factors such as reaction temperature,molar ratio of ammonia to NOx( NSR),additive concentration and injection location were considered. The experimental results show that at low temperature of 840 ℃,the SNCR reaction using ammonia reducing agent not only fails,but also the NOxemission increases. The denitrification efficiency in the low temperature zone can be greatly improved by mixing reductants,and the addition of syngas can promote the SNCR reaction to be carried out at a lower temperature. At 840 ℃,the denitration efficiency increases from 0 to 44%-62%. When the NSR is relatively low,such as NSR = 0.5 or1.0,and the syngas is 120×10-6,the different syngas injection positions have little impact on NOxemissions. However,when ammonia is in excess( NSR>1.0),the syngas is injected into the flue gas pipe with a low temperature in front of the separator to enhance ammonia selectivity and further reduce NOxemissions. When NSR = 1. 5,NOxemissions reaches a minimum of 101-110 mg/m3,which is about60 mg/m3 lower than injection at the outlet of the furnace. The way of injecting ammonia water and syngas to independently mix in the furnace has a better denitration effect than the way of injecting premixed ammonia and syngas. NOxemissions are about 60 mg/m3 lower than that of premixed injection. Syngas additive and ammonia have a strong synergistic and promoting effect on each other. Synthesis gas can improve the selectivity of ammonia reducing agent.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 4027K] - XIN Shengwei;ZHANG Man;WANG Junfeng;HE Feng;CAO Peiqing;CAI Runxia;ZHANG Peng;WANG Hu;CHEN Jianbin;YANG Hairui;Shenhua Guoneng Energy Group;Department of Energy and Power Engineering,Tsinghua University;Harbin Boiler Co.,Ltd.;
The external heat exchanger( EHE) is of great significance for the high-efficient operation of large circulating fluidized bed( CFB) boilers. In order to fully master the operation characteristics of external heat exchanger( EHE) in CFB boiler and eliminate the temperature deviation of EHE tube wall in ultra-supercritical CFB boiler at this stage,in this paper,the research status and key technology of the EHE were systematically summarized,and the design scheme of the EHE for ultra-supercritical CFB boiler was introduced. The results show that the wall temperature deviation of the EHE of 600 MW supercritical CFB boiler is very obvious,and the wall temperature distribution is saddle-shaped( the wall temperature of the tube panel in the center area is high and the wall temperature of the tube panel in the side wall area is low),which is determined by the uneven distribution of bubbles. The heat transfer coefficient of the EHE is closely related to the spatial position of the heating surface arrangement. When the speed of fluidization wind( Ug) of the EHE is 0.4 m/s,the heat transfer coefficient from the center of the bed to x/Xw≈0.6 is basically the same,while near the wall area,the heat transfer coefficient decreases significantly,and the side wall flow area accounts for about 25%-30% of the bed width. The arrangement of the tube bundle away from the side wall area can improve the inhomogeneity of the spatial distribution of the heat transfer coefficient,and the extreme deviation of the heat transfer coefficient is reduced from 15% to 6%. The design and calculation of the EHE of the 660 MW ultra-supercritical CFB boiler show that when the EHE is arranged with high reheating surface,the temperature difference between the middle diameter wall temperature of the high temperature reheater tube and the steam temperature can reach 58 ℃,which significantly restricts the safe operation of the EHE. Therefore,in the EHE of ultra-supercritical CFB boiler,all medium-temperature superheaters with relatively low steam temperature will be arranged. and TP347 H and TP347 HFG materials are used for the heating surface,which can meet the requirements and still ensure a certain margin. The arrangement of EHE tube is chosen to be parallel to the direction of ash flow in order to eliminate the local heat transfer unevenness caused by the side wall flow. In the design,it is considered to avoid the arrangement of the tube screen in the side wall area,and the distance between the tube screen and the side wall should be increased from 250 mm to more than 500 mm,which can improve the gas-solid flow and heat transfer behavior in the EHE to reduce the heat transfer deviation of the particle side. The design can control the furnace temperature and steam temperature effectively while ensuring the safe operation of the EHE.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 5257K] - ZHANG Peng;HE Jianping;WANG Hu;GU Wei;XIN Shengwei;XU Huaide;CAO Peiqing;HU Changhua;DU Jiajun;GU Congyang;CHN Energy CFB Technology R&D Center;Shenhua Shendong Electric Power Shanxi Hequ Power Generation Co.,Ltd.;
With the boiler capacity and steam parameters of circulating fluidized bed( CFB) greatly improved,material of high-temperature heating surface of the boiler has reached the highest level. In the actual operation,the steam temperature deviation characteristics of the high temperature heating surface tube panel are directly related to the safety and reliability of the unit. To accurately obtain steam temperature deviation characteristics of platen heating surface in a supercritical or ultra-supercritical CFB boiler,real furnace experiments were carried out on a 350 MW supercritical CFB boiler. By installing wall temperature monitoring points on all panels of two types of hightemperature platen heating surface of the boiler,steam temperature deviation and its distribution uniformity among tube panels in the same high-temperature platen heating surface were obtained under full boiler load condition,then the corresponding equipment transformation was carried out on the basis of the field test. The results show that there is an objective deviation of steam temperature among tube panels in the same high-temperature platen heating surface inside the furnace,and maximum deviation of steam temperature can reach above 60℃ . Wall temperature of tube panels laid with resistant refractory at wall side and facing fire side are obviously lower than that in central area,and maximum wall temperature deviation of high-temperature platen reheater is about 40 ℃ higher than that of high-temperature platen superheater. Maximum wall temperature deviation can not be monitored accurately by the traditional wall temperature monitoring points arranged alternately on the platen heating surface,and issue of relative inadequacy of wall temperature monitoring points arranged on tube panels of high-temperature platen reheater is more prominent. It is necessary to optimize the layout position according to platen width and height,especially more wall temperature monitoring points are arranged on tube panel facing the fire side( number from 4 th to 17 th inward to the outermost tube at fire side). The steam temperature deviation and its distribution uniformity of the platen type high temperature heating surface can be effectively controlled by the measures of split platen design and the optimization of the laying height of resistant refractory material. After optimization,the maximum steam temperature deviation of high-temperature platen superheater is 24 ℃( the maximum value of split platen superheater at water wall side is 16 ℃),and the steam temperature standard deviation is 6.2 ℃ . While steam temperature deviation of high-temperature platen reheater is 50 ℃,( that of split platen reheater at water wall side is 21 ℃),and the steam temperature standard deviation is 14.5 ℃ .
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 3192K] - JIA Xiaotao;ZHU Shahong;WANG Ke;WANG Pengcheng;ZHANG Man;YANG Hairui;Shanxi Hepo Power Plant Co.,Ltd.;State Key Laboratory of Power Systems,Department of Energy and Power Engineering,Tsinghua University;
In recent years,the development of new energy has put forward higher requirements for the flexible operation of thermal power units. Therefore,it is imminent to thoroughly study the operation mode of the deep peak shaving of the thermal power unit and solve the related technical problems. CFB boiler can realize stable combustion at low load and has the natural advantage of deep peak regulation. Due to the characteristics of small investment,short modification period and good thermo economy,the flexible low pressure( LP) cylinder cutting technology based on steam process reconstruction is an efficient way to achieve deep peak shaving of cogeneration units and realize thermoelectric decoupling. Based on the practical experience of a 350 MWe supercritical CFB boiler cogeneration unit,the follow-up operating problems of LP cylinder cutting technology in CFB boiler unit were analyzed and the corresponding solutions were proposed. During reconstruction,the wide-range control technology to avoid flutter was used for the first time in China. The online monitoring flutter equipment was developed and installed for the first time in the same type of domestic units. Also,the technology of extracting five-stage extraction steam to six-stage extraction steam was used for the first time. Through technical transformation,the key follow-up problems like low pressure cylinder blast under the condition of cylinder cutting,blade erosion and flutter,safe operation of the turbine,air cooled antifreeze,low temperature corrosion of air preheater,fuel system fluctuation and interlock protection fitment were solved by a series of technologies.Compared with the conventional LP cylinder cutting reconstruction,the wide-range cylinder cutting control technology adopted is more flexible and smoother,which eliminates some hazards of the previous rapid cylinder cutting technology. Among them,the reconstruction of the supporting system of CFB boiler provides guarantee for its high fuel flexibility. Based on the low load stable combustion characteristics of CFB boiler,the unit operates safely after the low pressure cylinder cut-off transformation and reaches the NOxultra-low emission standard. Not only is the thermoelectric decoupling achieved,the load regulation range is widened from 60%-94% to 30%-94%,and the heating capacity is increased by 50%,but also the purpose of energy saving and consumption reduction in heating period is achieved and the the ratio of district heating and electricity generation is enhanced especially under low load,which improves the resource utilization and unit thermal economy. Under 40% load conditions,the the ratio of district heating and electricity generation increases from 0.97 to 2.11 and the coal consumption in generation is reduced by 70.49 g/k Wh. Above all,the new flexible LP cutting reconstruction technology proposed in this paper has solved a series of technical problems,achieved a number of technological breakthroughs,accumulated operating experience and made contributions to tapping the great potential of the peak shaving of the cogeneration unit,improving the operational flexibility of thermal power in China and the capacity of the new energy consumption.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 750K] - LI Jun;ZHANG Man;LIU Qing;GUO Xuemao;ZHANG Jianchun;Taiyuan Boiler Group Co.,Ltd.;Key Laboratory for Thermal Science and Power Engineering of Ministry of Education,Department of Thermal Engineering,Tsinghua University;
Circulating Fluidized Bed( CFB) boiler,featured by the low quality coal as the fuel,is widely used in China. One of the CFB combustion advantage is its lower NOxemission without cost due to its lower and uniform combustion temperature of the alone circulating loop as well as its unique characteristics that the combustion atmosphere is reduced. With the increasingly strict emission requirements for coal fired power plant in China,the original NOxemission of CFB combustion exceeds the emission limit of the updated National Emission Regulation. Therefore,the CFB combustion processing was theoretically analyzed,according to the NOxgeneration and reduction paths under the condition of CFB combustion. It is believed that it is possible to decrease the NOxoriginal emission in advance by controling NOxgeneration and reduction and using the optimized gas-solid two-phase flow pattern. Furthermore,the engineering method to optimize the gas-solid two-phase flow pattern was suggested,which was to improve the bed quality,decrease the course bed inventory and increase the circulating flow rate. The principle of this technology was discussed,including the improvement of bed quality,the decreasing of the course bed inventory and the increasing of the circulating flow rate. It can significantly enhance the reduced atmosphere to decrease NOxgeneration in both dense zone and dilute phase area and promote the reduction of NOxin freeboard even in cyclone. Besides,the reasonable bed temperature and air supply should be considered. The NOxemission of this technology was expected less than 50 mg/m3 without flue gas denitrification. After the key points were confirmed in laboratory one by one,this technique was proved to be effective in CFB boilers with capacity of 150,260 and 560 t/h. The operation results show that the gas-solid two-phase flow pattern optimization decreases the NOxemission obviously and achieves ultra lower NOxemission. In the same time,no obvious decrease of combustion efficiency is found.These engineering cases of original ultra-low emission include bituminous coal,lean coal and anthracite coal. This technical method of reducing NOxemission concentration through flow design optimization provides a new approach to control the NOxemission in CFB boilers.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 3622K] - MIAO Miao;DENG Boyu;KONG Hao;ZHANG Man;YANG Hairui;State key Laboratory of power systems,Department of Energy and Power Engineering,Tsinghua University;
In order to study the SO2 emission characteristics of coal combustion in a fluidized bed under oxygen-enriched combustion atmosphere,combustion experiments were carried out in a small fluidized bed reactor with lignite and anthracite as raw materials under 21%,29%,42% and 56% O2/CO2 atmosphere,respectively. The influence of combustion atmosphere on SO2 emission from fluidized bed coal combustion was investigated. The results show that with the increase of oxygen concentration,the SO2 emission of two different types of coal tends to increase gradually after combustion at 770 ℃ under the atmosphere of O2/CO2. The SO2 emission of lignite can increase from 925×10-6 to 6 526×10-6 by volume and that of anthracite can increase from 1 310 ×10-6 to 5 357×10-6 by volume. Compared with anthracite,the increasing trend of lignite is more obvious. The effect of oxygen concentration on SO2 precipitation rate is also obvious. SO2 precipitation reaches a higher peak value in 15 s or even shorter time. When the oxygen concentration increases from 21% to 29%,the transformation S increases significantly,and then with the increase of oxygen concentration,the transformstion S increases slowly. It is explained from the mechanism that the high oxygen concentration provides more oxygen for sulfide precipitation and promotes the formation of SO2. At the same time,the high oxygen concentration accelerates the combustion speed of volatile matter and char and improves the combustion and burnout characteristics of coal. By enhancing the self-heating effect of coal itself,the combustion process of coal is accelerated. Therefore,the release of sulfur element in coal is promoted and the emission of SO2 is correspondingly increased. With the increase of oxygen concentration,the CO of lignite remains at a relatively stable level,indicating that the change of oxygen concentration has little effect on it. Lignite has a high volatile content,so it is easy to be short of residence time,which leads to inadequate combustion and a certain amount of CO in the flue gas. The emission of SO2 is not only related to the concentration of oxygen,but also related to the sulfur content in coal. Generally,the higher the sulfur content is,the more SO2 produced by coal combustion is. The sulfur content of the coal involved in this paper is high,so the SO2 emission is at a high level. In the process of oxygen-enriched combustion,the SO2 emission control should be fully considered for the coal with high sulfur content. The ash also affects SO2 emission,Si O2 and Al2 O3 have little effect on SO2 to SO3,while Ca O and MgO have obvious effect. The content of Fe2 O3 and K2 O in coal ash also has influence on the transformation process.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 1371K] - TAO Jun;GU Xiaobing;ZHANG Fan;DUAN Yufeng;Datang Environment Industry Group Co.,Ltd.;School of Energy and Environment,Southeast University;
Heavy metal mercury is a toxic trace element in coal-fired flue gas. Due to the atmospheric mobility and bioaccumulation,it is very easy to cause harm to ecosystems and human health. So heavy metal mercury has become one of the four major pollutants from coalfired flue gas. The synergistic mercury removal techniques by utilizing the conventional air pollution control devices( APCDs) has been increasingly studied in coal-fired power plants. The wet flue gas desulfurization( WFGD) device has become an important equipment for the removal of divalent mercury in flue gas with higher efficiency. However,the Hg2+absorbed by the WFGD device is released into the flue gas in the form of Hg0 under the action of reducing ions in the desulfurization slurry,which reduces the overall synergistic mercury removal efficiency of the APCDs. In this paper,the mechanism of mercury re-release in wet desulfurization slurry,the influencing factors,the principle of inhibiting mercury re-release and the research progress of mercury stabilizing additives were summarized. The effect of the desulfurization system operating parameters such as flue gas oxygen content,desulfurization slurry temperature,slurry p H,liquid-gas ratio,etc.,and coexisting ions such as SO23-,Cl-and Ca2+etc. on the mercury re-release behavior was elaborated; the classification and characteristics of additives that inhibit mercury re-release in the desulfurization slurry,as well as the chemical reaction mechanism and influencing factors of the interaction between the common additives and Hg2+was discussed; the latest research results of the mercury stabilizing additives by domestic and foreign scholars in recent years were summarized,such as the typical ones like H2 S,inorganic sulfides,halides,Fenton reagents and organic sulfur chelating agents DTC,TMT and STC etc. At the same time,The features of different additives,utilization condition,effects of mercury stabilization,and merits and drawbacks of them were analyzed. Some questions in the ongoing experimental research were surveyed and the directions for future improvement were proposed. It provides a reference for research and development on mercury re-release inhibition and mercury stabilizing additives in WFGD slurry.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 1657K] - MA Dafu;ZHOU Wentai;ZHANG Shouyu;HE Xiang;TAO Li;Shanghai Power Equipment Research Institute Co.,Ltd.;School of Energy and Power Engineering,Shanghai University of Science and Technology;
In view of the cracking phenomenon of front water wall of a 600 MW supercritical W-flame boiler,the thermocouples on the fireside and backfiring surface of the water wall were installed. The influence of different location of the temperature and thermal load of water wall characteristics under the influence of the typical operating conditions,the oxygen concentration,the pulverized coal fineness and Fdampers opening under the process of boiler start-up and 600 MW load conditions was investigated. The test results show that due to the existence of the the angle of flame break,the flue gas flow is close to the front wall,the thermal load on the front wall is higher than that on the back wall under high load,and the thermal load on the front wall is the highest at 36.8 m,and the furnace width is up to 32 meters,which increases the possibility of water wall tearing. The F damper scale of rear wall pressing front wall can reduce the thermal load of front wall water wall as well as the possibility of water wall tearing. The thermal load decreases rapidly along with the furnace height. For the former wall,the average dimensionless thermal load at 36.8,44.0 and 48.5 m elevation of the former wall is 0.75,0.50 and 0.19 respectively.In the process of boiler start-up,the temperature difference between the the fireside and backfiring surface gradually increases,and the thermal load on the wall gradually increases after the pulverized coal is put into operation. Although the wall temperature of backfired surface has transient overtemperature when startingmill,the overall thermal load is low and the water wall is relatively safe. Oxygen concentration has little effect on the overall thermal load in the furnace. Under the condition of full load,the oxygen content is recommended to maintain at 2% under the premise of low CO concentration in the rear region. The thermal load decreases slightly after the pulverized coal become smaller. It is suggested that the scale of the folding dampers in condition 8 should be adopted without considering the coal mill output.
2020 03 v.26;No.127 [Abstract][OnlineView][HTML全文][Download 4155K] 下载本期数据