- DUAN Yufeng;ZHU Chun;SHE Min;YAO Ting;ZHAO Shilin;TANG Hongjian;HUANG Tianfang;LIU Meng;Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education,School of Energy and Environment,Southeast University;
Mercury emissions from coal-fired boilers have been the largest anthropogenic source of mercury pollution in China.With the characteristics of neurotoxicity,atmospheric mobility and bioaccumulation,mercury brings a serious harm to the natural environment and human health,which has aroused a worldwide concern.At present,mercury control is mainly based on the synergistic removal techniques by utilizing the conventional air pollution control devices( APCDs) in China’s coal-fired power plants( CFPPs).Along with accomplishment of the " near-zero emissions" target,mercury emission limits for the flue gas,fly ash and waste water in power plant will be further tightened.This paper firstly summarizes the current status of rapid update of atmospheric emission standards for mercury pollutants from CFPPs in China,and points out that it is necessary to carry out the deeper mercury removal for coal-fired boiler systems in response to increasingly stringent mercury emission limits.Secondly,the technologies progress in the flue gas mercury measurement is introduced to meet the requirement of atmospheric mercury monitoring and regulation. Thirdly,the removal technologies for mercury from coal combustion are reviewed,especially the research progress in techniques regarding mercury removal by APCDs and flue gas sorbent injection. The development trend of new mercury removal adsorbents is proposed.Fourthly,the removal effect of ultra-low emission retrofit implemented in CFPPs in China on mercury emission reduction has been discussed.Finally,a prospective mercury removal research topic is proposed considering the problems existed in current mercury removal techniques,which aims to provide a scientific reference for the realization of "near-zero mercury emission"and the stabilization of mercury in coal combustion by-products in CFPPs.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 2962K] - ZHOU Huaichun;FAN Haihong;ZHAO Jun;LIU Yaoping;CHENG Chao;ZENG Xiongwei;TANG Wen;LIU Xing;TAN Houzhang;Key Laboratory of Condition Monitoring and Control for Power Plant Equipment,Ministry of Education ( North China Electric Power University);School of Energy and Power Engineering,Northeast Electric Power University;Suzhou Jijie Power Technology Co.,Ltd.;Hubei Huadian Xiangyang Power Generation Co.,Ltd.;Jiangsu Xinao Clean Energy Developments Ltd.;School of Energy and Power Engineering,Xi’an Jia
The traditional boiler combustion air flowrate control is based on the concept of air to coal ratio,and the feedforward roughly adjustment is made according to the fuel flowrate,and the fine adjustment is made according to the deviation of the oxygen content in the flue gas.The adjustment of fuel flowrate will affect the control of air flowrate.The development of smart power generation technology needs to innovate the existing basic methods of existing combustion control.The essence of coal-fired generation unit control is load control,that is,the energy conversion stages should be adjusted according to the load demand from the release of chemical energy in fuel combustion to the power generation of turbo-generator. The theoretical air volume required for different kinds of coal in combustion to produce the same amount of heat( corresponding to roughly the same energy level and power output of the unit) was basically unchanged,which was consistent with the conclusions in the relevant authoritative technical works.Therefore,the concept of " air-carbon ratio" was proposed to replace " air-coal ratio",that is,the ratio of a certain mass of air to a certain mass of carbon in complete combustion,which is about 11.5( mass ratio),being roughly constant for different types of coal. The concept of air-heat equivalent is further put forward,which means that the heat released by any kind of coal burning steadily and continuously per kilogram of air in a confined space( furnace) is approximately equal to a constant value of 3.01 MJ/kg air.On this basis,it is proposed that the total air flowrate rate into a boiler should be controlled mainly according to the change of load demand,and the influence of fuel kind changes can be neglected in the total air flowrate control under the same load level.If the efficiency of boiler decreased as the change of coal kind burned in the boiler,more heat would be generated by the fuel in the furnace,and the air flowrate of the boiler should be increased,and vice versa.The new concept of air flowrate control in this paper has been successfully applied into a 300 MW tangentially coal-fired power generation unit from August 2017.The input rate has exceeded 80%,which laid a foundation for the implementation of a new strategy of air-coal decoupling and independent control for boiler combustion.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 1678K] - CHAI Jin;WAN Zhongcheng;WU Kai;ZHANG Jingrui;CHEN Jianing;LIU Qibin;MA Shuangchen;School of Environmental Science and Engineering,North China Electric Power University ( Baoding);Sheng Fa Environment Protection and Technology Co.,Ltd.;
Since the "Action Plan for Prevention and Control of Water Pollution" was promulgated,the zero-liquid discharge of desulfurization wastewater from coal-fired power plants has become an inevitable requirement for the deep wastewater treatment in power plants.Due to it simple process,higher safety &reliability and low investment and cost,evaporation technology using flue gas has become a main one in this field.Investigating the existing technologies,the flue gas evaporation technolog can be divided into three types: low-temperature flue evaporation,bypass high-temperature flue gas evaporation,and concentration and decrement using flue gas waste heat.The evaporation capacity of flue gas was calculated,the research progress of desulfurization wastewater evaporation technology was reviewed,and the process characteristics,advantages and disadvantages of each evaporation technology were analyzed deeply.It can be seen that flue gas evaporation capacity of coal-fired power plants is extremely strong and can be used as heat source for zero discharge of desulfurization wastewater.What’s more,low temperature flue evaporation is not suitable due to its vulnerability of boiler load,the combination of concentration and decrement using flue gas waste heat with high temperature evaporation or solidification is one of research directions in future.This paper responds to the national policy actively,provides a reference for selection of zero-liquid discharge technologies in coal-fired power plants and has important practical significance and application value.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 2123K] - LIU Xing;HE Yu;LU Xuchao;XIONG Xiaohe;TAN Houzhang;HUI Shien;MOE Key Laboratory of Thermo-Fluid Science and Engineering,Xi’an Jiaotong University;Xi’an Special Equipment Inspection Institute;
With the environmental policies being strict,the NO_x of conventional thermal power units can reach the level of less than 50 mg/m3 after combustion denitrification in furnace and post-combustion denitrification in flue through the transformation of ultra-low nitrogen emission.With the continuous development of low NO_x combustion technology,the ultra-low NO_x combustion technology of pulverized coal pyrolysis and gasification coupled with combustion has attracted more attention in the industry.The main idea of this technology is to introduce hot thermal source to heat up the pulverized coal air/fuel stream with ultra-low stoichiometric ratio in the pre-combustion chamber.The pulverized coal first fast releases volatile matter and partly combusts in the pre-combustion chamber.The gas phase products and high temperature semi-coke leave pre-combustion chamber and are transferred to the furnace through the burner for low NO_x combustion. Compared with traditional post-combustion denitrification method such as SCR and SNCR,this technology directly reduces nitrogen in the furnace combustion process by burning high-temperature semi-coke,which has greater technical advantages and economic potential. The pre-combustion source is the key step to produce gas phase products and high temperature semi-coke.According to different pre-combustion sources,this paper introduced these pulverized coal pre-combustion technologies,the natural gas heating pulverized coal pre-combustion,circulating fluidized bed heating pulverized coal pre-combustion,plasma ignition pre-combustion chamber,induction-heating ignition pre-combustion chamber and traditional pre-combustion chamber burners,etc.The progress and application of those technologies were analyzed to provide references for relevant technical staff.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 2161K] - TAN Houzhang;LIU Xing;WANG Wenhui;LIU Hexin;Institute of Zhejiang Xi’an Jiaotong University;School of Energy and Power Engineering,Xi’an Jiaotong University;
Wet desulphurization device is widely applied in coal fired power plant in the context of ultra low emission.The saturated wet flue gas emitted from the device outlet usually form wet plume at the chimney outlet,resulting in adverse effects on ecological environment and human health.In this paper,the state of flue gas and ambient air were calculated to determine the critical temperature of wet plume removal and the equivalent ratio of mixed air,and the applicable environmental conditions and technical parameters of different flue gas blanking technology routes were compared based on the tangential method.The result shows that the wet plume is more difficult to be eliminated with lower environment temperature and higher relative humidity.If the relative humidity is 60% and the flue gas temperature at the outlet of the wet desulphurization tower is 50 ℃,the critical temperature of 37.3 ℃ for wet plume elimination can be realized without any measures.So the flue gas parameters of the wet desulfurization unit should be adjusted for wet plume elimination under ordinary environment conditions.Assuming that the maximum cooling amplitude of applicable flue gas is 30 ℃ and the maximum warming amplitude is 30 ℃,the critical environment temperature of smoke plume elimination is 12.9 ℃ only by flue gas heating technology,while the critical environment temperature of smoke plume elimination is 8. 7 ℃ only by flue gas condensation technology and the critical environment temperature of smoke plume elimination is -12.9 ℃ by both flue gas condensation and heating technology.For air heating mixing technology,the heat balance of the air and flue gas mixing process was calculated to determine the critical air equivalent ratio of wet plume elimination based on the tangent method.The combination of flue gas heating,flue gas condensation and air heating technology can enlarge the applicable environmental conditions of wet flue gas plume elimination.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 4107K] - ZHANG Wei;LU Cheng;CHEN Donglin;DENG Weili;SONG Quanbin;FENG Yanlin;GONG Weicheng;SONG Jian;School of Energy and Power Engineering,Changsha University of Science & Technology;Key Laboratory of Renewable Energy Electric-Technology of Hunan Province;Hunan Province 2011 Collarative Innovation Center of Clean Energy and Smart Grid;Hunan Datang Energy-saving Technology Co.,Ltd.;Yonker Environmental Protection Co.,Ltd.;
The fly ash in the flue gas of coal-fired power station deposits a strong scale on the surface of the SCR catalyst,which is an important reason of catalyst deactivation. The ultrasonic resonance combined with steam purging method is usually used to clean the strong scale layer on the catalyst surface in time,However,due to the deposition of coal-fired fly ash on the surface of the catalyst,the formation of the strong scale layer is relatively stable,which results in the effect of ash removal under high-energy operation in the field not obvious.To better study the influence of fly ash deposition and agglomeration on the surface of the catalyst on the formation of strong scale,the stainless steel sampling tray was placed on the windward side of the three-layer catalyst layer for sampling by means of the field minor repair period and the thermal performance test of the SCR retrofit project.The samples of the three-layer SCR catalyst scale were characterized by atomic force microscopy( AFM).The black and white binary images were obtained by Matlab pattern processing by setting appropriate threshold values,and the box size was obtained by information entropy method to analyze the influence of multi-fractal scale interval.The results show that as the elevation zone of the stratification layer of the flue gas gradually becomes fragmented,the granularity of the deposited fly ash gradually becomes uniform,and the multi-fractal parameters have scale invariance with the increase of the flue gas flow.Meanwhile,the associated fractal dimension D_2 gradually closes to the Hausdorff fractal dimension D_0 with the increase of the flue gas flow.According to the variation property of weighted moment,it is found that the microscopic particles of the slab layer gradually change from loose non-uniformity to density uniformity with the increase of the flue gas flow.According to the multi-fractal spectrum symmetry of the three-layer slab layer,it is found that with the extension of the flue gas flow,the multi-fractal spectrum width Δα of the catalyst scale layer increases obviously,the surface roughness of the corresponding scale layer increases gradually,and the distribution of singular peaks on the surface of the scale layer is more obvious.The dominant factors of scale layer formation by fly ash deposition on the surface of the catalyst is mainly due to the probability distribution point of small particles and small elevation.The research shows that with the increase of flue gas flow,the multi-fractal characteristics of the scale layer on the catalyst surface become obvious,the particle size of the deposited fly ash becomes smaller,and the uniformity of the harden layer increases,and the elevation clustering feature of the micro-topological surface disappears,which provide a theoretical basis for on-site ash removal operations such as ultrasonic resonance and steam purge.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 3760K] - DUAN Xiaoli;ZHANG YANDi;ZHU Chenzhao;YANG Hao;ZHANG Xu;WANG Chang’an;ZHAO Lei;HAN Tao;LIU Yinhe;State Key Laboratory of Multiphase Flow in Power Engineering,Xi’an Jiaotong University;
The boiler burning with Zhundong coal is prone to deposition and slagging problems on heat-exchanger surfaces,which severely restricts the wide utilization of coal resources in the Zhundong area of Xinjiang province.In this paper,the ash deposition characteristics of Wucaiwan coal were studied on the one-dimensional settling furnace combustion and ash accumulation test system,and the effects of dilution gas type and oxygen concentration of O_2/CO_2 combustion on fly ash deposition were analyzed.The results show that at the concentration of 21% oxygen,compared with N_2,when the diluent gas is CO_2,the adhesion phenomenon of the ash deposition is not obvious,and the tendency of ash accumulation is weak.Under combustion condition of O_2/CO_2,with the rise of oxygen concentration,the ash deposition of Wucaiwan coal tends to increase and the fine ash particles gradually decrease,the proportion of spherical ash particles gradually increases,and the adhesion phenomenon of ash particles gradually increases.The results of SEM-EDS analysis illustrate that with the increase of oxygen concentration in O_2/CO_2 combustion,the surface shrinkage and pits of the ash particles in the deposited ash gradually increase,the white fine floc ash adheres to the surface of the ash particles,and the enrichment of Na and Cl is gradually aggravated,which is an important reason for the intensification of ash deposition on the heating surface in the combustion with high oxygen concentration.In the influence research of dilution gas species on the ash deposition tendency of Wucaiwan coal,the element contents of Na and Cl are obviously higher when the diluent gas is N_2( air combustion) than when the diluent gas is CO_2( O_2/CO_2 combustion).In addition,the enrichment of Ca and S elements also occurs in the deposited ash when the combustion diluent gas is N_2.At high temperature condition,Ca O reacts with the aluminosilicate to form low-temperature eutectics,which is also an important reason why the ash deposition in air combustion is more serious than that in O_2/CO_2 combustion.The results of XRD analysis confirm the conclusion of EDS to some extent.The enrichment of low-melting substances such as CaSO_4 and NaCl in ash leads to the intensification of ash deposition in air combustion conditions and high oxygen concentration O_2/CO_2 combustion conditions.The difference in particle temperature of combustion is the main reason for the difference of ash deposition characteristics between O_2/CO_2 combustion and air combustion,and also is the main reason for the difference of ash deposition characteristics in O_2/CO_2 combustion under different oxygen concentrations.When the combustion temperature of coal particles is higher,the pulverized coal ignition and combustion performance are improved.The higher particle temperature causes more molten ash particles to appear in the flue gas,and the molten phase on the surface of ash particles will increase the viscidity of ash surface and aggravate the phenomenon of ash accumulation.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 5963K] - LI Huijun;XIE Xingyun;ZHAO Jing;ZHANG Yufeng;WEI Xiaolin;School of Energy Power and Mechanical Engineering,North China Electric Power University;College of Engineering Science,University of Chinese Academy of Sciences;State Key Laboratory of High Temperature Gas Dynamics,Institute of Mechanics,Chinese Academy of Sciences;
As a renewable and clean energy,biomass will play an increasingly important role in Chinese energy structure.The content of alkali metal elements( mainly K) in biomass is usually relatively rich,and it is the main component of biomass ash.Alkali metals in biomass are easily released in combustion due to the low melting point of alkali metal inorganic salts( for example,KCl),which brings serious technical safety problems to the development and utilization of biomass energy. In the biomass combustion process,partial alkali metal ash is easy to condense,adsorb and deposit on the heated surface of the boiler chamber after the gaseous release,which causes problems such as pollution,scale formation and ash accumulation and seriously affects the heat transfer of the boiler and even causes corrosion.Therefore,the release law and mechanism of alkali metal elements in the process of biomass combustion research will provide strong theoretical support for the clean and efficient utilization of biomass in China,which has good socio-economic and academic significance.In this paper,the release characteristics of alkali metals in the biomass combustion process of wheat straw were studied. The release characteristics of alkali metals at the combustion temperature of 400-900 ℃ were researched through the horizontal tube furnace and XRD,SEM-EDS and other test means.The results show that alkali metal K mainly exists in the form of water soluble,while alkali earth metals Ca and Mg mainly exists in the form of ammonium acetate soluble and water soluble.Water-soluble K mainly exists in hydrated ions or crystals of KCl,KNO_3,K_2SO_4 and K_3PO_4.In the combustion process,the main organic K and a small amount of inorganic K release within 400 ℃,inorganic potassium in the form of KNO_3 is mainly released within 400-600 ℃,KCl and KNO_3 are mainly released above 600 ℃.Alkaline earth metals Ca and Mg form relatively stable compounds which are not easy to release.K and Cl contents change synchronously according to the analysis of element enrichment on the ash surface,.K and Cl contents grow simultaneously below 600 ℃ mainly because there are more alkali metal compounds in the form of KCl.K and Cl contents on the surface of ash surface reduce over 600 ℃ mainly because KCl reacts with SiO_2,or directly release in the form of KCl.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 3574K] - HU Qingwei;WANG Weishu;Datang Sanmenxia Power Generation Co.,Ltd.;Thermal Engineering Research Center,North China University of Water Resources and Electric Power;
In order to study the combustion characteristics of the supercritical coal-fired boilers,the velocity,trajectory of pulverized coal particles,temperature and composition distribution characteristics and NO_x release features during coal combustion in the 600 MW counter-rotating swirling boiler were numerically studied using CFD( Computational Fluid Dynamics) numerical simulation software.The standard k-ε model and lagrangian random orbit model were explored to simulate gas-phase turbulent flow and gas-solid two-phase flow.The solid fuel was simulated by the discrete phase model,besisdes,the pulverized coal combusted in the furnace was simulated by the non-premixed combustion model.The convection term adopted the second order upwind to obtain a more accurate understanding of the matter.Considering the high temperature of the boiler furnace and the large amount of radiation heat transfer,the P1 radiation model was used to calculate the radiation heat transfer between the gas-gas and the gas-solid.The standard wall function method was used to calculated flow heat transfer,which could save the space and calculation time. The results show that the cross-section velocity of the staged combustion boiler is symmetric,the gas flow is full and the combustion is stable.Besides,the symmetrical reflux caused by swirling combustion in the furnace could enhance the disturbance between the gas flow in the furnace and the pulverized coal particles,and then strengthen the heat and mass transfer and increase the residence time of the pulverized coal particles in the furnace.The particle size of pulverized coal in the furnace could affect the combustion process.Specifically,the smaller the particle size the shorter the residence time of pulverized coal particles is in the furnace,which will influence the combustion and burnout of the fuel and the efficiency of the boiler.On the contrary,if the particle size is too large,the pulverized coal particles fall into the ash hopper slagging by their own gravity,and impacts the normal safe operation of the boiler.Therefore,the proper particle size is significantly important for the combustion process in the furnace.The average temperature of the flue gas in the furnace rises and then decreases along the height of the furnace and then reach to about 1 100 K in the cross section of the furnace exit.The temperature in the burnout zone is slightly reduced due to the supplemented over-fire-air.The distribution of various components in the furnace are X = 11.093 5 m section,along the height of the furnace,the volume fraction of O_2 first rises and then decreases,the volume fraction of CO_2 increases gradually,the volume fraction of CO first rises and then decreases,the staged combustion reduces the overall NO_x production,and the concentration of NO_x at the furnace outlet is about 385.14 mg/m~3.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 2958K] - ZHANG Hongxia;WANG Yuzhao;ZHANG Hai;Chengde Petroleum College;Key Laboratory for Thermal Science and Power Engineering of Ministry of Education,Tsinghua University;
The flow field in the separation area of the dynamic separator with static guide cascade was measured by angular displacement sensor and endoscope head based on PIV technology.The airflow shows a strong turbulent rotational flow in the annular region outside static cascade,and the impellerspeed has little effect on the flow field in this area.The airflow presents a vortex flow in the stator blade,the vortex center position moves backward gradually with the increase of impeller rotate speed.The lower the regional position is,the closer the vortex center is to the leeward of the blade,and the longer the vortex is.In the region between the static cascade and the impeller,the airflow rotates with the impeller,and the higher the impeller speed of impeller,the stronger the airflow rotates.In the rotor blade,the airflow flows evenly along the runner,and the angle between the flow direction of the airflow and the blade increases with the increase of impeller speed.The gas-solid separation in the dynamic separator is divided into three stages,the first stage is the centrifugal separation in the annular region outside the static cascade,the separation effect of this stage is hardly affected by the impeller speed,the second stage is the vortex separation and impact separation in the static blade,and the third stage separation occurs in the impeller inlet area,which includes centrifugal separation and impact separation.The impeller speed has a great influence on the separation of the latter two stages.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 9136K] - DU Jie;DAI Gaofeng;LI Shuaishuai;WANG Xuebin;SUN Xiaowei;TAN Houzhang;Shaanxi Yanchang Coal Yulin Energy and Chemical Co.,Ltd.;School of Energy and Power Engineering,Xi’an Jiaotong Unviersity;
In the process of coal gasification,a large amount of fine gasification slag( HC-ash) with high carbon content is produced.The ash-waste landfilling occupies a lot of land,causes the pollution of soil and water,and also wastes the energy.How to utilize the coal-gasification ash( HC-ash) is attracting more and more attentions recently.Based on the proximate and ultimate analysis,particle size distribution,ash compositions,and micro-morphologies of HC-ash,the characteristics of HC-ash combustion alone and combustion with raw coal were studied by thermos gravimetric analysis( TGA).The difference of combustion characteristics between HC-ash and typical coal was compared.The influence of mixing ratio on mixture combustion was also considered.The results show that the moisture of HC-ash( as received basis) reaches 69.7%,the ash of dried HC-ash is 54.5%,the carbon content in dried HC-ash is 43.4% with a heating value of 16.14 MJ/kg.The carbon content and calorific value of dried HC-ash are equivalent to that of inferior bituminous coal.The particle size of dried HC-ash is generally smaller than 200 μm,but with a very developed porous structure.The results of SEM show that the microstructure of HC-ash is composed of sphere and porous irregular shapes.HC-ash compared with other types of combustion characteristics show that the ignition temperature and burnout temperature of HC-ash is 601.6 ℃ and 680.8 ℃,respectively,which are slightly worse than those of contrastive coal samples.The TGA results with different mixing ratio of HC-ash and raw coal show that a significant synergistic effect is observed during the co-combustion of HC-ash and raw coal,which can significantly improve the combustion property of HC-ash.When mixing ratio is 25%,the combustion property of HC-ash is significantly improved and the combustion characteristics of mixed coal with HC-ash decreases slightly compared with pure raw coal.This study indicates that the dried HC-ash is of great application value,its co-firing with raw coal has little influence on the combustion characteristics of mixed coal and is able to improve the overall combustion properties.The overall results suggest that combustion of dried HC-ash with raw coal is a feasible technical scheme to utilize the calorific value of HC-ash.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 3264K] - YANG Fan;ZHENG Xiong;LI Jianbo;WANG Quanhai;XUE Jingwen;LU Kai;LU Xiaofeng;Key Laboratory of Low-Grade Energy Utilization Technology & System,Chongqing University;
In terms of the problems that exsit in the waste heat recovery of bulk solid particles,such as insufficient heat transfer,high gassolid flow resistance and low quality of the waste heat recovery,a cooling technology for high temperature particle using gas-solid crossflow moving bed was proposed in this study.The experimental study on particle flow characteristics under cold operating conditions was carried out with CFB boiler ash via a self-designed industrial experimental apparatus.Particle flow characteristics were measured by sampling and high-speed photography.The effects of the cross-sectional size of the particle flow on particle flow characteristics and cross-sectional gas speed on particle flow stability were analyzed and discussed.The results show that the downward velocity of particles in the central part of the straight flow section is basically constant. Neglecting the influence of the side walls,the calculated flow index M_(F1) of the front and side section of straight flow section exceed 0.3,which show that the particle flow was considered as a bulk flow under the experimental conditions.By sampling the particles at different locations,it is found that the maximum difference of particle mass ratio is about 14.4%,which could be considered that the particle flow in the enlarged section was uniform in practical engineering,while the particle size distribution at different locations is different.With increasing the transverse air velocity,the particle carrying rate increases.The air velocity in the downward moving bed can not exceed 1.45 m/s.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 3895K] - ZHAO Jing;WEI Xiaolin;ZHANG Yufeng;LI Teng;State Key Laboratory of High-Temperature Gas Dynamics,Institute of Mechanics,Chinese Academy of Sciences;School of Engineering Science,University of Chinese Academy of Sciences;
Zhundong coal,which is produced in Zhundong district,Xinjiang,is a kind of coal featured low ash and sulfur contents,and high reactivity.However,the alkali metals tend to release into the flue gas in the form of gas phase during combustion,which leads to changes in physicochemical properties of the fly ash particles,such as reducing their ash melting point and enhancing their cohesiveness and corrosivity.Furthermore,it will cause serious problems such as fouling,slagging,and corrosion on the surface of the boilers and heat exchange equipments.The occurrence modes of alkali metals determine the release behavior,thus in-depth study of occurrence forms and contents of alkali metals would be beneficial to accurately predict their release form and content,and it would be meaningful for clean and efficient use of Zhundong coal.Zhundong coal with high Na content was employed in this paper.The surface distribution characteristics of different elements were analyzed by scanning electron microscopy-energy dispersive spectrometry( SEM-EDS).Simultaneously,the occurrence modes and contents were investigated by inductively coupled plasma optical emission spectrometer( ICP-OES).X-ray photoelectron spectroscopy( XPS) and X-ray diffraction( XRD) were employed for calculating surface elemental content and crystalline structure of alkali metals,respectively.The SEM-EDS results show that Ca and S are obviously enriched in same regions,indicating that CaSO_4 is presented in these regions; no highlight region for Cl was observed during the scanning process,suggesting that Cl is evenly distributed in Zhundong coal; In addition,a small number of highlight regions in Na co-exist with S,implying that the Na_2SO_4 crystal is also presented in Zhundong coal.The XRD results illuminate that Na exists in the form of crystalline structure of Na Cl and Na_2SO_4 after drying at 105 ℃.The corresponding peak intensity decreases or even disappears after extraction via deionized water.The ICP-OES results show that Na in Zhundong coal is mainly presented in the form of water-soluble,ammonium acetate and acid-soluble Na. with mass fraction of 78.42%,11.57%,and 6. 44%,respectively.And the remaining 3.57% is the insoluble-Na in the form of aluminosilicate; the cations in the extract liquid are mainly sodium,calcium,and magnesium ions,and the anions are mainly chloride,sulfate,and hydrogencarbonate ions.The total charge numbers of cations and anions were calculated to be 5.369 mmol/L and 5.385 mmol/L,respecctively.This indicates that the charge numbers of anions and cations are basically conserved in the solution.The water-soluble Na is considered to exist mainly in the form of crystals or hydrated ions of Na Cl,Na_2SO_4,and NaHCO_3,with mass fraction of 5.32%,85.7% and 8.98%,respectively( uniformly distributed).Besides,XPS was used to analyze samples dried at different temperatures,and the results indicate that the water-soluble Na can migrate to the surface with the water during drying process and then release with the evaporating water when temperature reached to 100 ℃.The Na/C ratio on the surface of the sample increases first and then decreases with the migration of moisture.The released Na through this process can be defined as water-volatile Na.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 2754K] - HU Nan;XU Meng;YANG Hairui;LYU Junfu;ZHANG Ji;Changchun Institute of Technology;Key Laboratory for Thermal Science and Power Engineering of Ministry of Education,Tsinghua University;Electric Power Research Institute of State Grid Liaoning Electric Power Co.,Ltd.;
With the large-scale development of CFB boilers,the furnace cross-section has far exceeded the CFB reactor in the chemical industry.The lateral non-uniformity of boiler operating parameters,especially temperature,seriously affects the safety and efficient operation of boilers.Accordingly,a two-dimensional cell model is established for the combustion system of a 300 MW CFB boiler.The model divides the cross-section into three parallel cells.The model includes gas-solid fluidization model,lateral dispersion model,combustion model and heat transfer model.The calculation and test results show that the temperature distribution in the width direction is obvious non-uniform.The temperature of the intermediate circuit is higher than that of the sides.The dispersion coefficient of dilute region has a significant influence on the lateral temperature distribution. According to the model calculation and test data,the dispersion coefficient of dilute region should be in the range of 0.006-0.010 m~2/s.In the dense bed,the lateral dispersion of particles is severe.When the coal flowrate of each coal feeding point is changed,the local concentration of coal is quickly eliminated by lateral mixing and dispersion. Therefore,the lateral temperature distribution of the furnace is less affected by the change of coal feeding distribution.The key point for the temperature deviation is that the water wall area of each cell on sides is larger than that of the middle one.By adjusting the arrangement of the screen heating surface in the furnace,the problem of uneven temperature distribution can be effectively improved.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 2030K] - DENG Yusheng;CUI Jian;HUANG Zhengxian;WANG Pei;DUAN Yuanqiang;DUAN Lunbo;Thermal Power Branch,SINOPEC Maoming Petrochemical Company;Key Laboratory of Energy Thermal Conversion and Control,Ministry of Education,School of Energy and Environment,Southeast University;Jiangsu Design and Research Institute of Energy Conservation Engineering;
Pb released from coal-fired power plants is characterized by long-distance migration,bioaccumulation and persistent hazards.Although the content of Pb in coal is quite low,the amount of released Pb from the coal-fired power plant could cause serious environmental pollution due to the tremendous coal consumption.Due to the complexity of on-site sampling,the studies on the migration and emission characteristics of Pb in coal-fired power plants are very scarce. In this study,a 410 t/h circulating fluidized bed( CFB) boiler burning mixed fuel of coal and petroleum was selected as the research object,and the EPA Method 29 was used to simultaneously sample flue gas before and after fabric filter( FF) and wet flue gas desulfurization( WFGD).Meanwhile,the flue gas sampling,feed fuel,limestone,bottom ash,fly ash,gypsum,effluent water,limestone slurry and flush water were also sampled and analyzed.The distribution of Pb in combustion byproducts and the migration and emission characteristic of Pb were obtained based on Pb balance calculation. The results show that the mass balance ratio of Pb is in the range of 105.1%-106.4%,which indicates the high accuracy and reliability of the test.During the combustion process,the Pb released into the gas phase is mainly in the gaseous forms,such as Pb~0 and PbO,only a small part remains in the bottom ash.In this study,Pb in bottom ash accounts for 13.7% of the total Pb in the whole system.With the flue gas flow and temperature decrease,most of the Pb compounds in the flue gas will undergo the processes of homogeneous nucleation,heterogeneous condensation,deposition and adsorption on the particle surface to form particulate Pb.Therefore,at the outlet of air-preheater,particulate-bound Pb is the dominant species in the flue gas,accounting for over 99%; while the content of Pb released into the atmosphere is only 0.4%.The removal efficiency of Pb in the flue gas by the fabric filter is as high as 99%,which is mainly reflected in the removal of particulate Pb.The wet desulfurization tower has a certain removal effect on the water-soluble gaseous Pb and particulate Pb,and the removal efficiency can reach to 67%.After the removal by these pollutant control devices,the final concentration of Pb emitted into the atmosphere is extremely low( about 2.99 μg/m~3); and the emission factor of Pb is 0.90×10~(-12) g/J.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 1502K] - GAO Yi;YAO Kai;ZHANG Haidan;LIU Dan;YANG Dong;Zhejiang Zheneng Taizhou Second Electric Power Generation Co.,Ltd.;Zhejiang Energy Group R&D Institute Co.,Ltd.;State Key Laboratory of Multiphase flow in Power Engineering,Xi’an Jiaotong University;
Ultra-supercritical coal-fired power generation technology is an important way of coal clean utilization.Among the ultra-supercritical boilers,the furnace arch at the joint between the furnace outlet of the П type boiler and the horizontal flue is easy to form ash deposition due to the existence of the recirculation zone,which seriously affects the safe operation of the boiler.Through the mechanism analysis of the ash deposition of the furnace arch in the ultra-supercritical coal-fired boiler,including the adhesion force between the ash particle and the sediment and the force of destructing ash deposition the mathematical model of ash deposition of the furnace arch and the pre-judging model of ash collapse were established to give a prediction result of whether the ash collapse would occur,which could provide a guidance plan for the safe operation and maintenance of the power station.The ash deposition and ash collapse pre-judging model obtained the moving speed of the coal ash particles in the flue gas,the depth of the sediment layer and the surface tension based on adopting the coal quality parameters,boiler design parameters and operating data,so as to quantitatively calculate the adhesion force of ash particles in the per unit area of inclined plane of the furnace arch and the impact of the ash particles on sediments.The theoretical maximum ash deposition height and the actual maximum ash deposition height at the furnace arch position were obtained according to the equilibrium relationship among the adhesion force,gravity and frictional force in per unit area.When the theoretical maximum ash deposition height is greater than the actual maximum ash deposition height,the friction and adhesion force of the sediment layer are greater than the component force of gravity along the inclined plane of the furnace arch,and the ash deposition of the furnace arch does not collapse,otherwise,when the maximum ash deposition height is less than the actual maximum ash deposition height,ash collapse will occur.For the 1 000 MW ultra-supercritical П-type coal-fired boiler of Second Electric Power Generation Co.,Ltd. Taizhou Zhejiang province,the characteristics of the ash deposition and ash collapse at the furnace arch were calculated and analyzed.The results show that,the when the furnace outlet temperature is 1 035 ℃ and the design coal is burned,the actual ash height at furnace arch is 2.48 m,which is less than the gravity balance height of 6.69 m.The furnace arch of the boiler does not occur ash collapse,and the design and operation of the furnace arch is reasonable and feasible.The pre-judgment model of ash deposition and ash collapse at the furnace arch of the ultra-supercritical boiler has certain reference value for boiler design and optimization operation.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 1259K] - GU Xiaobing;TAO Jun;GENG Xinze;LIU Shuai;HU Peng;LU Jincheng;LIU Meng;DUAN Yufeng;Datang Environment Industry Group Co.,Ltd.;Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education,School of Energy and Environment,Southeast University;
In order to study the effect of flue gas injection temperature and adsorbent injection amount on mercury removal efficiency in coal-fired flue gas,1% NH_4Br solution was used to impregnate and modify rice husk coke to prepare mercury removal adsorbent NH_4Br modified rice husk coke( Br-RHC).The pore structure of the adsorbent before and after modification was characterized by specific surface area and porosity analyzer,and the experiment of adsorbent injection removing mercury in the flue was carried out in a 0.3 MW coal-fired circulating fluidized bed combustor of pilot scale.The results show that the specific surface area,micropore volume and total pore volume of the adsorbent after modification increase to some extent.The efficiency of injection mercury removal increases with the increase of injection amount and tends to be stable.The mercury removal efficiency increases from 69.36% to 79.44% when the injection amount increases from 0.3 kg/h to 0.5 kg/h.The mercury removal efficiency of the injection process increases with the increase of flue gas temperature,it rose from 57.74% at 142 ℃ to 79.48% at 200 ℃.It is verified that the chemical modified biomass rice husk char is a suitable alternative for activated carbon to be applied into the flue gas injection demercuration technology in coal-fired boilers.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 1318K] - XU Ji;WANG Ben;YU Jie;SUN Lushi;YANG Wu;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;
In order to get scientific evaluation result of coal-fired power denitrification technologies,deviation degree theory was applied to construct subordinate function of interval index,besides,the game theory weighting method was used in index weight calculation and optimizing evaluation model of denitrification technologies.The model was applied to the pulverized coal fired boiler and fluidized bed boiler with low NOxburner of 660 MW coal-fired plant in China.Three kinds of denitration technology,i.e.,selective catalyst reduction( SCR),selective non-catalyst reduction( SNCR) and hybrid SNCR-SCR,were comprehensively evaluated. Results show that SCR technology should be preferred for denitration of 660 MW thermal power pulverized coal furnace with stable rated load under the condition of low nitrogen reformation in the furnace,SNCR should be preferentially selected for the fluidized bed boiler,SNCR-SCR technology can be used to realize ultra low emission.More importantly,the evaluation results are consistent with the feasible technical guide for prevention and control of pollution in thermal power plants,which verifies the rationality of the evaluation model.The evaluation results under 75% and 50% load show that SNCR-SCR technology should be preferentially selected for the pulverized coal fired boiler under 50% load.The evaluation results of the remaining low-load working conditions are consistent with the rated load working conditions,which provides a reference and theoretical basis for the evaluation and technical selection of denitrification technologies.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 1430K] - WANG Jianjiang;WEI Bo;ZHANG Xuehui;LI Xian;TAN Houzhang;Key Laboratory of Coal Cleaning Conversion & Chemical Engineering Process,Xinjiang University;MOE Key Laboratory of Thermo-Fluid Science and Engineering,Xi’an Jiaotong University;
The high content of alkali metals in Zhundong coal induces serious slagging and fouling problems during combustion,however,the migration and transformation rules of alkali metals under pressurized condition in Zhundong coal gasification are still ambiguous.In order to obtain the migration and transformation mechanism of Na Cl in Zhundong coal under pressurized condition,according to the thermodynamic calculation method of Gibbs free energy minimum principle of the system,the thermodynamic equilibrium calculation module of HSC Chemistry was adopted to calculate the molar mass of sodium-based compounds in the pressurized gasification process of pure Na Cl and Zhundong coal.The results show that pressure impacts the gasification temperature of pure Na Cl significantly.At ordinary pressure,the start and finish temperatures of gasification are 800 ℃ and 1 400 ℃ respectively.When the reaction pressure up to 4 MPa,the start and finish temperatures of gasification increase to 1 500 ℃ and 2 200 ℃ respectively.When the Si,Al,H,O of Zhundong coal participate in the reaction under the condition of 0.1 MPa,300 ℃,the Na Cl will react with SiO_2,Al_2O_3 and H_2O in the coal ash to form a large number of sodium-based compounds,such as NaAlSi_3O_8,NaAlSiO_4,etc.In 1 500 ℃,the generated gaseous Na Cl accounts for only about 25% of the molar mass of Na.The higher the reaction pressure of the system is,the more NaAlSi_3O_8,NaAlSiO_4 and Na_2SiO_3 with low melting point and fluxing action will be generated,and the higher risk of slagging in the furnace will be.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 1952K] - LIU Dingpo;YANG Peijun;FENG Kuolei;LIU Yang;YUN Panfeng;China Xi’an Thermal Power Research Institute Co.,Ltd.;School of Energy and Power Engineering,Xi’an Jiaotong University;
In recent years,the installed capacity of wind power generation and solar power generation is growing rapidly.In order to improve the absorption capacity of new energy,the flexible operation of coal-fired units is the general trend.At present,large-capacity power station boilers are generally equipped with direct-blowing pulverizing system,and the large deviation of pulverized coal and air distribution in the outlet air pipe of coal mill is a common problem.With the development of flexible operation of the unit,large deviation of pulverized coal and air distribution directly limits the flexible operation of the unit.In this paper,the reasons for the large deviation of pulverized coal and air distribution of the coal mill outlet parallel primary air duct were analyzed from the point of view of the pulverizing system equipment.Various problems in the boiler operation process caused by the large deviation of pulverized coal and air distribution,such as flame deflection,coking,high temperature corrosion,high NO_x emission,high fly ash fuel and low boiler efficiency,were described.The problem is especially serious in the process of unit flexibility transformation.During low-load operation,the deviation of pulverized coal and air distribution will increase ignition distance of the boiler,resulting in unstable combustion and even extinguishing the fire. Uneven heat load in the furnace will aggravate the deviation of the steam in the boiler,worsen heat transfer,and overheat the heating surface,which will directly affect the operation safety of the unit.In order to improve the deviation of pulverized coal and air distribution.the performance advantages and disadvantages of pulverized coal distributors were analyzed,and the application and effect of pulverized coal distributor in power station boiler in recent years were introduced.Therefore,with the development of flexible operation,it is necessary to reform the pulverizing system of flexible operation units,install the matching coal powder distributor,improve the pulverized coal and air distribution characteristics,and improve the operation stability and safety of units.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 1192K] - XU Hong;XIONG Xiaohe;LIU Xing;TAN Houzhang;DENG Shuanghui;WANG Meng;Jiangsu Fangtian Electric Power Technology Co.,Ltd.;MOE Key Laboratory of Thermo-Fluid Science and Engineering,Xi’an Jiaotong University;
The water wall temperature of large utility boilers with sub-critical and above parameters is generally high.The application of low NO_x staged combustion technology leads to the oxygen deficiency in the primary combustion zone,which often causes serious high temperature corrosion.The sample of the water wall tube after high temperature corrosion was cut off from a 300 MW utility boiler for characterization analysis.The cause and the classification of high temperature corrosion were discussed. The results show that the corrosion products contain a large amount of FeS,which belongs to typical sulfide corrosion.Blue and yellow-green products are covered on the tube surface,whose main composition are iron oxides and sulfides.The iron sulphides in the blue products are FeS while in yellow-green products are ZnS.The FeS presents a hexagonal crystal and with a size of 10-20 μm.Meanwhile,large amount of unburned fly ash particles were found at the surface of the sample tube,indicating that the air distribution in the furnace were irrational and the flame brushing walls phenomenon was existent.After the reconstruction of the burners,the cold aerodynamic field using fireworks in furnace was conducted.It is found that the whole tangential circle is in good condition and does not deviate from the geometric center of the furnace,which meets the design requirements.The diameter of imaginary primary air tangential circle is 790 mm,which basically coincides with the design value.The air flow in each layer is relatively stretched,and no obvious brushing walls phenomenon is observed.The imaged flame is full of the furnace and the condition of the aerodynamic field is obviously improved.The hot state operating results show that the adaptability to coal change is greatly improved,the combustion stability and anti-slagging ability are greatly improved.The boiler can be continuous operated above 800 t/h load under 50% blending ratio of lean coal.The flame colour is uniform and no large continuous coking phenomenon was found.The high temperature corrosion was obviously relieved.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 4922K] - HUANG Jian;WANG Hao;ZHANG Feng;LIU Yuqiang;ZHANG Kai;Huadian Qudong Power Generation Ltd.;
With the increasing requirements of environmental protection,nitrogen oxides( NO_x) have become the focus of gas pollutant emission control after dust removal and desulfurization in thermal power plants.The corresponding boiler combustion system should also be changed when the existing units are reformed for ultra-low emission.The change of combustion system has a direct impact on the temperature field in the furnace.The formation and shedding of oxide scales in furnace tubes has been the main treatment problem of ultra-supercritical units,while the oxide scales of sub-critical units have not been effectively concerned.The reformation of low nitrogen burner of boiler mainly uses four-zone theory,namely pyrolysis zone,main combustion zone,reduction zone and burnout zone,to delay combustion by reducing excess air coefficient in the initial stage,which has a certain impact on the temperature field in the furnace.At this time,the change of burner will aggravate the change of temperature field in the furnace and stimulate the sensitivity of tubes with lower oxidation margin in the furnace.In this paper,several tube bursts occurred continuously after the retrofit of 330 MW subcritical unit with ultra-low emission in a power plant.By comparing the causes of tube bursts,the aging of tubes and the changes of temperature field in the furnace before and after the retrofitting,it is confirmed that the main cause of tube burst caused by the change of temperature field in the furnace is the low oxidation margin.In view of the secondary problems that may arise from the retrofitting of subcritical boilers,it is proposed that attention should be paid to the change of temperature field in the furnace after the retrofitting of the burner during the retrofitting of ultra-low emission boilers.When the temperature field of SA213-T23 in the subcritical unit rises by about 20 ℃,the acceleration of oxide scale production and the acceleration of aging of metal structure are prone to occur.The subcritical unit should strengthen the detection of oxide scale,grasp the aging degree of pipes,and expand the antioxidant margin of pipes appropriately in material selection.
2019 02 v.25;No.120 [Abstract][OnlineView][HTML全文][Download 3875K] 下载本期数据