2022年12期目次

  • Basic characteristics of fast-reaction thermogravimetric analysis for kinetic studies of Ca(OH)2/CaO fluidized thermochemical heat storage

    FENG Yupeng;DENG Boyu;ZHANG Shuangming;DING Yi;YANG Xinhua;ZHANG Man;YANG Hairui;State Key Laboratory of Power System and Generation Equipment,Department of Energy and Power Engineering,Tsinghua University;SDIC Power Holding Co.,Ltd.;

    Thermal energy storage is necessary for improving energy utilization efficiency. Using Ca(OH)_2/CaO in fluidized bed reactorscan realize rapid storage and release large-scale thermal energy, and hence, research on the reaction kinetics of Ca(OH)_2/CaO underfluidization is important. However, the thermogravimetric analysis(TGA) technique cannot provide the constant temperature reaction con-ditions required for Ca(OH)_2, and its mass transfer inhibition phenomenon is significant. Hence, a fast-reaction TGA technique was pro-posed that can provide reaction conditions closer to those of fluidization for Ca(OH)_2/CaO, when compared with the conventional TGAtechnique. The fast-reaction TGA technique could provide a higher heating rate and better mass transfer conditions for heat storage materi-al by rapidly moving the high-temperature reactor and introducing a high-speed purge gas. The influence of the reactor temperature, mov-ing speed and airflow on the fast-reaction TGA performance was clarified by decoupling experiment. When tested with Ca(OH)_2, the de-viation in the material conversion obtained with the fast-reaction TGA technique from that obtained with the conventional TGA technique isonly 0.81%, which demonstrates the accuracy of the fast-reaction TGA.

    2022 12 v.28;No.148 [Abstract][OnlineView][HTML全文][Download 15316K]

  • Research and application of depth peak regulation technology for supercritical circulating fluidized bed boiler

    WANG Hu;FAN Haodong;XIN Shengwei;ZHANG Man;WANG Junfeng;WU Wanzhu;YANG Hairui;ZHANG Peng;CHN Energy CFB Technology R&D Center;Department of Energy and Power Engineering,Tsinghua University;College of Electrical and Power Engineering,Taiyuan University of Technology;Harbin Boiler Co.,Ltd.;

    In the process of deep peak regulation of supercritical circulating fluidized bed units, in addition to the problems of stable fluidization of air distribution plate and nitrogen oxide control under low load conditions faced by subcritical units, the safety of hydrodynamics is also involved. In view of the technical problems of deep peak regulation of supercritical circulating fluidized bed boiler, through the reconstruction of flow pattern, the critical fluidization air velocity was reduced, the air volume needed to ensure stable fluidization was reduced, and the combustion share in the lower part of the furnace was reduced. Furthermore, the area of air distribution plate was reduced to ensure the stability of ultra-low load fluidization, and the working fluid flow of secondary rising water wall with vertical tube ring was developed to ensure the hydrodynamic safety of low load. Reduce the particle size of bed material and circulating material, on the premise of ensuring fluidization and combustion, reduce the proportion of primary air, strengthen the local reducing atmosphere on the surface of coke particles, optimize the arrangement of coal feeding, slag discharge and air supply, ensure the uniformity of oxygen and temperature distribution in the furnace, provide a guarantee for the control of nitrogen oxides, and finally realize the stable operation of 350 MW supercritical circulating fluidized bed boiler under 20% BMCR conditions. The maximum wall temperature deviation is 17 ℃,and the temperature deviation of the same layer in the furnace is less than 30 ℃. In addition, in the process of boiler operation from start-up to full load and variable load, the temperature deviation of the inlet flue gas temperature of the three cyclone separators is always within 10 ℃,and the NO_x emission is ultra-low at full load.

    2022 12 v.28;No.148 [Abstract][OnlineView][HTML全文][Download 23379K]

  • Recent research and application on anti-wear technology of furnace water-wall in circulating fluidized bed boiler

    CHEN Han;YAO Yuge;ZHANG Guoqing;ZHANG Daixin;MA Youfu;HUANG Zhong;Department of Energy and power Engineering,Tsinghua Unversity;Department of Energy and Power Engineering,University of Shanghai for Science and Technology;School of Chemistry and Environmental Engineering,China University of Mining and Technology-Beijing;College of Electrical and Power Engineering,Taiyuan University of Technology;

    The wear of the heating surfaces is a key parameter on the long-term safe and stable operation for a circulating fluidized bed(CFB) boiler, and the wear is affected by many factors, such as the structure of the furnace, coal characteristics, operation method, and maintenance. Abrasion is always concentrated on areas with high solid volume fraction, high flow rate of flue gas and abrupt changes in flow field, such as dense zone, transition zone, connection area of platen heating surface, irregular parts in dilute region, the roof and outlet of furnace, and so on. Therefore, lower velocity of flue gas, the design of kick-out tube, and positive or passive anti-wearing methods are widely adopted to protect heating surfaces for purpose of attenuating adverse effects of the wear on the operation. As for the anti-wear effectiveness, anti-wear beam, metal grid, metal spraying, and laser cladding can all reduce the wear in the furnace to a certain extent, the influence on heat transfer and the convenience of inspection and maintenance need to be taken into consideration before selection of anti-wear technology.In general, the combination of metal grid and metal spraying or laser cladding has achieved the best use effect. At present, the wear problem in the furnace of the CFB boiler has been under effective control. The CFB boilers can continuously operate for longer hours and the operation safety has been significantly improved.

    2022 12 v.28;No.148 [Abstract][OnlineView][HTML全文][Download 27496K]

  • Recent advances of calcium-based oxygen carriers for the chemical looping combustion process

    DI Zichen;GONG Pan;YANG Fengling;SONG Huiping;CHENG Fangqin;Institute of Resources and Environmental Engineering,Shanxi University;Shanxi Laboratory for Yellow River,Shanxi University;

    Fossil fuel combustion emits large amounts of CO_2,and carbon capture, utilization and storage(CCUS) is currently the only emission reduction technology that can realize large-scale low-carbon utilization of fossil energy. Chemical looping combustion(CLC) is a recently developed decoupled combustion technology, which can realize in situ carbon capture during combustion. Oxygen carrier is one of key component for developing and optimizing of the CLC technology. Calcium-based oxygen carriers have potential applications due to their unique characteristics of high oxygen loading capacity, low cost, wide availability and environment benign. The principles and development of chemical looping combustion technology, as well as six common types of oxygen carriers, were summarized. The bottleneck problem of calcium-based oxygen carriers, which are difficult to match the appropriate thermodynamic and kinetic temperature and partial pressure zones, were emphatically introduced. In this paper, the relevant researches on the regulation of reaction process by controlling reaction conditions and additives at home and abroad were summarized, and the strengthening effect and influence mechanism of inert carriers, metal oxides and other additives on the performance of calcium based oxygen carriers were analyzed. It has been demonstrated that inert carriers can be effective in improving the dispersion characteristics of the oxygen carriers, thereby increasing reactivity, and contributing to mechanical strength. In comparison to inert carriers, the addition of metal oxides is likely to be more effective. However, in terms of current research progress, traditional functional strengthening methods can improve the performance of oxygen carriers to a degree, but it is difficult to fundamentally breaking the bottleneck of poor regenerative properties. Future research can focus on two aspects to address this issue: utilizing artificial intelligence in materials science, targeted screening and optimization of inexpensive calcium-based natural ores/industrial solid waste materials as oxygen carriers, reconstructing the morphological structure and crystal structure of oxygen carriers to regulate the migration and transformation behavior of oxygen and sulphur atoms, so as to reduce the carrying effect of oxygen transfer on sulfur atoms and achieve regeneration performance enhancement.

    2022 12 v.28;No.148 [Abstract][OnlineView][HTML全文][Download 12127K]

  • Research progress on carbon materials in CH4-CO2 reforming

    GUO Shuowen;SUN Yinghui;LI Ying;XU Tong;ZHANG Guojie;ZHANG Yongfa;BAI Jie;College of Chemical Engineering,Inner Mongolia University of Technology;State Key Laboratory of Clean and Efficient Utilization of Coal Energy,Taiyuan University of Technology;

    In dual carbon era, carbon dioxide emission reduction and conversion projects have been a current research hotspot. Methane carbon dioxide reforming is a catalytically induced syngas production process that utilizes both greenhouse gases simultaneously and converts them into syngas(carbon monoxide and hydrogen). The syngas produced by this reaction can be synthesized by Fischer-Tropsch to solve the inherent storage and transportation problems of gaseous fuels. Among the raw materials for the methane-carbon dioxide reforming reaction, the methane molecule has a regular tetrahedral configuration, which is not easy to decompose. Carbon dioxide is the smallest non-polar molecule, and high energy is required for ■ bond cleavage. Therefore, the methane carbon dioxide reforming reaction requires catalyst, and the use of inexpensive catalysts for reforming reactions that maximize synthesis gas production has been a focus of research. Non-precious metals are the best choices in current catalytic materials, but they cannot combine the activity and stability of catalysts. Different from metal catalysts, carbon materials have well-developed pore structures and some biomass materials contain rich functional groups, which can improve the adsorption and activation of reactive gases, and can also disperse and fix active metals, thereby improving the stability and anti-cokingability of catalysts. The application of carbon materials in CH_4-CO_2 reforming reaction was summarized, and the mechanism of different carbon materials in improving the anti-sintering and anti-coking properties of catalysts was analyzed. The activity of carbon material alone as a catalyst is not ideal, and the use of carbon material as a carrier or modification of carbon material can improve the catalytic performance of carbon material catalyst. When the carbon material is used as a carrier, the structural properties of the carbon material can be combined with the high activity of the metal by loading active metals and additives, and the activity and stability of the catalyst can be improved at the same time. Carbon material modification is to enrich the surface structure of carbon materials and optimize the physical properties of carbon materials through different chemical reagents and methods. Heteroatom doping modification can improve the catalytic performance of carbonaceous catalysts by expanding the pore advantage of carbon materials and increasing the content of functional groups on the surface of carbon materials. Combining these two methods to obtain a modified carbon material carrier is the latest research stage of carbon material catalyst, which is not only conducive to metal dispersion and anchoring, but also improves the adsorption and activation rate of the carrier and the reaction gases. The review can provide a reference for the research direction of catalytic methane dry reforming and the use of carbon catalysts.

    2022 12 v.28;No.148 [Abstract][OnlineView][HTML全文][Download 17715K]

  • Effect of n-heptane on the evaporation characteristics of methanol droplets

    ZHANG Meijuan;WEI Yanju;ZHANG Qixia;CHEN Shengmin;School of Automotive and Traffic,Wuxi Institute of Technology;School of Automobile & Traffic Engineering,Jiangsu University;School of Energy and Power Engineering,Xi′an Jiaotong University;

    Methanol fueling can make diesel engine achieve efficient and clean combustion. The evaporative properties of the fuel have a significant effect on the mixing, ignition and combustion process. Methanol has a low cetane number, which makes ignition difficult. The cetane number of methanol fuel can be increased by the addition of n-heptane. the droplet evaporation process of n-heptane methanol droplet was studied based on image processing technology by using the single droplet hanging measurement method and high-speed camera to capture the droplet evaporation image. The effects of different n-heptane blending volume ratios(0, 5%, 10%, 15%) and ambient temperatures(100-500 ℃) on the evaporation characteristics of droplets were analyzed. The results show that the evaporation characteristics of n-heptane-methanol droplet followed the D~2 law, which means that the square of the ratio of the droplet diameter D to the initial droplet diameter D_0((D/D_0)~2) is linearly related to the evaporation time. The trend of the relative area of the droplets with time is approximated as a straight line with a negative slope. The evaporation rate of droplets increases with the increase of temperature when the mixing ratio is fixed. The evaporation rates per unit area of droplets is increased by 543%, 639%, 896%, and 556% for 0, 5%, 10%, and 15% n-heptane blending ratios, respectively, when the temperature is increased from 100 ℃ to 500 ℃. The evaporation trends of methanol droplets with different n-heptane additive blending ratios are basically the same when the temperature is certain. Compared with pure methanol, 5% volume ratio of n-heptane prolongs the evaporation time of droplets except at 200 and 300 ℃. At 100 ℃, the droplet evaporation time is shortened with the increase of n-heptane blending ratio, while prolonged at 200 ℃. At the rest of the test temperatures, the droplet evaporation time is prolonged and then decreased with the increase of n-heptane blending ratio. At 200, 300, 400 and 500 ℃, the droplet evaporation time is prolonged by 53.9%, 17.1%, 47.5% and 53.1% when the n-heptane blending volume ratio increases from 5% to 15%, respectively.

    2022 12 v.28;No.148 [Abstract][OnlineView][HTML全文][Download 23161K]

  • Analysis and prospect of coke combustion model for coal fired power plant boiler unit

    LIU Pengyu;LI Debo;LIU Yanfeng;LIAO Hongkai;FENG Yongxin;Department of Power Engineering,North China Electric Power University;China Southern Grid Power Technology Co.,Ltd.;

    Coke combustion is the main process of pulverized coal combustion in coal-fired power plant boilers, and its combustion process consists of power combustion zone, diffusion/dynamic zone and diffusion control zone, among which the combustion process and mechanism in the diffusion/dynamic zone are the most complicated and often affect the accuracy of numerical simulation of coke combustion. To further improve the accuracy of the numerical simulation on the boiler side of coal-fired power plants, the FLUENT self-contained model, the improved random hole model and the existing improved model for coke combustion were reviewed and compared. The results show that the self-contained model of FLUENT does not consider the influence of ash on oxygen diffusion during actual combustion, resulting in large differences between numerical simulation and engineering practice.Based on the improved random pore model, it is considered that temperature is the reason for the difficulty of oxygen contact with coke in the diffusion zone, but it is not the fundamental factor.The existing models generally do not consider the influence of internal surface area on the reaction rate when burning poor quality coal in engineering practice, resulting in large differences between predicted and actual values at the stage of low conversion rate.In the application of nucleation model considering the diffusion resistance of ash layer, the softening temperature of combustion coal with the combustion temperature should be compared first, and the consideration of thermal deactivation and the internal surface area of porous carbon spheres should be considered.The thermal deactivation and ash suppression model should adopt a more suitable ash suppression model to improve the accuracy of model prediction.At present, in the numerical simulation of other problems of coal-fired boiler based on FLUENT, the diffusion/dynamic models with large errors are used, and the adoption of improved coke combustion models in subsequent studies is an important research direction.

    2022 12 v.28;No.148 [Abstract][OnlineView][HTML全文][Download 15025K]

  • Numerical simulation on the influence of secondary air ratio and swirling intensity on the performance of a pre-combustion low nitrogen swirl burner

    FAN Yongcheng;ZHANG Feilong;WANG Yongdong;WANG Li;LIU Junjie;TAN Houzhang;XU Xinwei;WANG Xuebin;CHN Energy Shendong Coal Group Co.,Ltd.;School of Energy and Power Engineering,Xi′an Jiaotong University;

    At present, the total number of industrial boilers in China exceeds 600 000, among which the coal-fired indus trial boilers account for more than 80% of the total number of active industrial boilers, and are widely used in various fields of production and life as the main heat supply equipment. As the second largest coal-fired pollution source in China, coal-fired industrial boilers are an inevitable way to achieve win-win economic, environmental and social benefits by promoting their clean and efficient operation, effective energy conservation and emission reduction. A low-nitrogen swirl burner capable of preheating was designed. On the basis of the low-nitrogen swirl burner, a precombustion chamber was added to achieve stable combustion, and the products of pulverized coal after preheating solutionwere sent into the furnace for combustion. By controlling the pyrolysis atmosphere, NO generated in the pyrolysis gas can be reduced to N_2 to further control the emission of NO_x. In this paper, CFD simulation method was used to study the influence of internal and external secondary air ratio and secondary air swirl intensity on combustion performance and pollutant emission characteristics of preheating solution low-nitrogen swirl burner. Through the comparative analysis of multi-working conditions of velocity field, temperature field and component distribution, suggestions were put forward for the optimization of burner operation parameters. The simulation results show that when the internal secondary air rate increases to 54%, the internal secondary air destroys the backflow zone in the precombustion chamber, making the burner unable to achieve stable combustion. The maximum internal secondary air rate of the preheating solution low-nitrogen swirl burner is about 50%. In the range of ensur-ing combustion stability, the secondary air rate is increased, the area of low oxygen area in the precombustion chamber is increased, the mixing of secondary air and primary air is delayed, NO_x emission is reduced, but the residence time of coal powder is reduced by high wind speed, and the burnout rate of exit section coke is slightly reduced. When the internal secondary air swirl blade angle decreases to 30°, the annular combustion zone in the precombustion chamber disappears, making the burner unable to achieve stable ignition. There is a minimum internal secondary air swirl blade angle for stable combustion of the burner between 30° and 45°. The angle of the internal secondary wind cyclone blade increases, the flame rigidity of the burner outlet decreases and is compressed in the axial direction, the temperature in the front part of the furnace increases, and the high temperature zone is concentrated, so that the coke is fully burned, but the NO_x concentration in the cross-section of the furnace outlet increases slightly.

    2022 12 v.28;No.148 [Abstract][OnlineView][HTML全文][Download 22375K]

  • CFD optimization of flow field in denitrification system of W flame boiler

    GENG Xuan;WANG Yang;WANG Kailiang;China Huadian Engineering Co.,Ltd.;

    Because of higher thermal load and flame center temperature of the flame center, the generation of thermal NO_x is increased. The down-fired boiler has higher NO_x mass concentration than other coal boilers, and the selective catalytic reduction(SCR) denitrification device at the rear of the boiler has high requirements. To investigate the influences of flow field and species concentration profile on deNO_x efficiency and ammonia slip in an industrial SCR reactor, a 3 D computational fluid dynamics(CFD) model of SCR device was established based on ANSYS FLUENT software, so as to improve the denitrification performance of device, and numerical simulation was carried out.In order to make the calculation results closer to the actual conditions, the actual NO_x concentration of the boiler under full load was used as the SCR inlet boundary conditions in the numerical simulation. Through detailed analysis of flow characteristics of SCR system such as flue gas velocity distribution, component concentration distribution, ammonia escape, etc.,simulation and optimization were carried out for the influence of flow field optimization, zoned ammonia injection and new static mixer on denitration performance, so as to improve the flow field and concentration field uniformity of SCR system. The simulation results show that by increasing the number of deflectors in the top chimney flue, the uniformity of catalyst inlet velocity distribution is improved, and the strip area with high velocity can be eliminated. After optimization, the relative standard deviation of catalyst inlet velocity distribution is reduced from 20.86% to 3.80%. The influence of uneven NO_x concentration distribution at the inlet can be eliminated by adding a static mixer with triangular airfoil, and SCR uniformity of the concentration field can be improved. The relative standard deviation of the maximum ammonia nitrogen molar ratio is reduced from 10.72% to 1.78%.The reconstruction scheme is obviously superior to the original design, which has important guiding significance for engineering design.

    2022 12 v.28;No.148 [Abstract][OnlineView][HTML全文][Download 13998K]

  • Operation and optimization technology of deep peak for 330 MW CFB boiler units

    LIU Xuankun;DENG Boyu;ZHANG Sihai;ZHANG Shuangming;YANG Xinhua;ZHANG Man;YANG Hairui;Shanxi Research Institute for Clean Energy,Tsinghua University;Department of Energy and Power Engineering,Tsinghua University;Ningxia Guo Hua Ningdong Power Generation Co.,Ltd.;

    In order to further improve the capacity of thermal power units to absorb new energy, the demand for peak load regulation of thermal power units becomes higher and higher. Taking a 330 MW subcritical circulating fluidized bed unit of a power plant as an example, the corresponding operation strategies and technical measures were put forward to solve the problems of fluidization safety, high pollutant emission concentration and working medium deviation that restricted the realization of deep peak shaving. By changing the spacing of screen plate spacer bars to 8 mm, the coal particle size entering the furnace can be reduced.A throttle ring of "return" shape was installed on the wind cap, which improved the fluidization state of the unit under deep peak shaving. By adjusting the area of the air distributor and the ratio of primary air to secondary air, the minimum fluidizing air volume during deep peak shaving can be effectively reduced. After adjustment, when the fluidizing air volume is 380 km~3/h and the air temperature is 245 ℃,the resistance of the air distributor is increased by 2 231 Pa. Under 50% load, the average temperature difference before and after the fluidized bed decreases from 126.8 ℃ to 27.2 ℃. The flue gas recirculation system was introduced, which was retrofitted with multi fluid multi particle furnace desulfurization technology and denitration lance. 300-500 μm limestone was sent into the furnace by secondary air, and 1-2 mm limestone was sent into the furnace by coal feeding. The multiple groups of denitration nozzles were installed in the direction tangential to the middle and lower part of the furnace and the slope of the secondary air outlet, and the switches of the denitration nozzle were adjusted according to different peak loads. When 20% of the units are operating at the depth of peak shaving, SO_2 emission can be stably controlled within 5 mg/m~3,NO_x emission can be reduced to below 30 mg/m~3,and the original water cooling shield is transformed into a small area parallel type to reduce the flow deviation and temperature deviation of the working medium. The boiler unit shall be subject to pressure fire protection test to maximize peak load regulation. The research results can provide reference for the deep peak shaving operation of coal-fired boilers at the same level.

    2022 12 v.28;No.148 [Abstract][OnlineView][HTML全文][Download 9224K]

  • NO removal in coal-fired flue gas by activated carbon assisted nonthermal plasma

    FAN Jinhang;LI Ye;WANG Shiqing;WANG Huanjun;LIU Lianbo;NIU Hongwei;GUO Dongfang;State Key Laboratory of Coal Based Clean Energy,China Huaneng Group Clean Energy Research Institute Co.,Ltd.;

    NO is the nitrogen oxide in coal-fired flue gas, of which the tremendous emission generates great damage on natural environment as well as human health. To overcome the problems of low efficiency and high energy consumption of NO removal by Nonthermal plasma(NTP) technology, the influences of different gas flow rate, O_2 content, and initial NO concentration on the NO removal in the low-temperature plasma process were systematically investigated. The results show that the highest NO treatment capacity of per unit energy consumption is 4.17 g/kWh, corresponding to the NO removal rate of 90% and the gas flow rate of 5 L/min under the N_2/NO gas mixture. The presence of O_2 has an inhibitory effect on the conversion of NO. Moreover, improving the output power is disadvantageous to NO removal conversely at high O_2 concentration. It is found that under the 6% O_(2 )concentration condition, the NO removal rate is less than 46%,the corresponding treatment capacity of NO per unit energy consumption is only 2.29 g/kWh. To achieve high efficiency and low energy consume of NO removal at oxygen atmosphere, the activated carbon adsorption and oxidation process was added before the NTP process. Firstly, activated carbon was used to adsorb and oxidize NO,reducing the high NO concentration entering into the NTP reactor. Then, the residual NO was deeply oxidized by low-temperature plasma technology to achieve the efficient removal of NO with low energy consumption. The results show that the removal rate of NO by activated carbon adsorption and oxidation is more than 55% using coupled process. Controlling the NTP output power to be 9.66 W,the overall removal rate and treatment capacity of NO for coupled technique can be reached as high as 90.5% and 13.58 g/kWh, respectively. Compared with individual NTP process, the treatment capacity of NO per unit energy consumption corresponding to this coupling process has been increased by nearly five times, which has a good application prospects and socio-economic value.

    2022 12 v.28;No.148 [Abstract][OnlineView][HTML全文][Download 9669K]

  • Simulation analysis of flue evaporation characteristics of desulfurization wastewater with multiple nozzles

    JIAO Shiquan;LI Yulong;LI Hengfan;HAN Zhonghe;Hebei Key Laboratory of Low Carbon and High Efficiency Power Generation Technology,North China Electric Power University;HCIG Energy Science and Technology Research Institute Co.,Ltd.;

    The desulfurization wastewater produced by wet desulfurization in thermal power plants is difficult to treat, and the flue evaporation technology of desulfurization wastewater can effectively reduce the discharge of desulfurization wastewater and even achieve zero emission of desulfurization wastewater, thereby reducing the operation cost of power plants. In order to guide the practical application of flue evaporation technology of desulfurization wastewater, the heat and mass transfer model of atomized droplets in the flue gas was established to reveal the process of spray evaporation of desulfurized wastewater in the tail flue of the boiler. Taking the tail flue of a 330 MW boiler as the research object, the effects of flue gas and atomized droplet properties on the evaporation process of wastewater were studied with multiple nozzles by CFD simulation. The results show that when the number of nozzles is properly increased at a certain flow rate, the less the wastewater flow of a single nozzle, the more uniform the distribution of wastewater droplets in the flue, and the area of the low-temperature area above the nozzle gradually increases along the flow direction, the average temperature and minimum temperature increase.With different flue gas and droplet properties, the increase of the number of nozzles will make the evaporation speed of droplets faster, and the evaporation time and moving distance will be shortened, but the shortening range will gradually decrease, and the evaporation distance of droplets is positively related to the evaporation time. The number of nozzles has little effect on the droplet velocity, and the droplet velocity is hardly affected by the change of the number of nozzles, but the droplet velocity is mainly affected by the flue gas velocity. With different nozzle numbers, droplet evaporation time and distance decrease with rising of flue gas temperature, droplet jet velocity, droplet initial temperature and reducing of water vapor content, droplet initial diameter. The increase of the flue gas flow rate reduces the evaporation time. In the case of single nozzle, the evaporation distance first decreases and then increases. When the flue gas flow rate is 10 m/s, the minimum evaporation distance is 9.85 m. In the case of multiple nozzles, the evaporation distance is always reduced.

    2022 12 v.28;No.148 [Abstract][OnlineView][HTML全文][Download 28474K]

  • Long term operation strategy of tubular air preheater based on environmental protection and ultra low emission

    WANG Pengcheng;LIU Xuankun;CAI Jin;YANG Hairui;Shanxi Hepo Power Plant Co.,Ltd.;Shanxi Research Institute for Clean Energy,Tsinghua University;State Key Laboratory of Power Systems,Department of Energy and Power Engineering,Tsinghua University;

    In view of problems such as abrasion, corrosion and blockage of tubular air preheater, and taking Hepo 350 MW supercritical circulating fluidized bed boiler unit as an example, the pipe wall temperature of air preheater is determined according to the prediction results of acid dew point through the intelligent temperature control strategy of air preheater inlet air temperature, so as to adjust the output of air heater, ensure that the inlet air temperature of air preheater is always above the acid dew point, so as to reduce the low-temperature corrosion at the end of air preheater. Combined with low oxygen combustion technology, the oxygen content of the boiler under different loads is finally determined through operation tests: 2.7%-3.0% under 350 MW load, 3.0%-3.2% under 310 MW load, and 3.2%-3.5% under 230 MW load, which effectively reduces the corrosion of the low temperature section of the air preheater. The secondary air inlet is used to inject limestone into the furnace to quickly respond to the desulfurization technology in the furnace, so that limestone can be directly injected into the micro oxidation dilute phase area in the furnace, shortening the desulfurization response time, reducing the amount of limestone used as the desulfurization agent in the furnace, avoiding the sharp fluctuation of SO_2 content in the flue gas, and effectively improving the desulfurization efficiency in the furnace. By comparing the efficiency of each denitration spray gun and the position of the denitration spray gun, determining the high and low order of the spray gun efficiency, optimizing the spray gun of the SNCR system, increasing the setting of denitration spray gun in the inclined section of the secondary air duct, the average denitration efficiency under full load is improved, the amount of ammonia escape can be reduced, the consumption of denitration reducing agent of the unit is effectively reduced, and the risk of ammonia escape hydrogen sulfate ammonia corrosion and blockage of the air preheater are greatly reduced. Through the above technical means, the air preheater has been operating for 6 years, working in good condition and stable operation, which can provide reference for the operation and maintenance of air preheaters of similar units.

    2022 12 v.28;No.148 [Abstract][OnlineView][HTML全文][Download 6673K]

  • Numerical simulation on burner burnout characteristics and optimization in a 600 MW swirling opposed boiler

    MAO Rui;LI Yuan;REN Liming;ZHANG Ping′an;MA Lun;CHEN Xinke;ZHANG Gengfan;FANG Qingyan;ZHANG Cheng;Rundian Energy Science and Technology Co.,Ltd.;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;

    In actual operation, the flow rate into the same-layer burners from the large air box is uneven for the swirl opposed-firing boiler, which will significantly affect the burnout characteristics of pulverized-coal. However, there are the research on the burn-out characteristics of single burner in the furnace. Taking a 600 MW front and rear wall swirl opposed boiler as the object, the numerical study and optimization on the burnout characteristics were carried out, and the effects of the air distribution, the swirl intensity and the burner output on burnout characteristics of pulverized coal were also studied. The simulated results show that the carbon content in the fly ash of the lower burner is higher than that of the upper and middle burners, and the carbon content(about 0.1%) in the fly ash of the middle burner is lower than that of the side burners(about 3%), which is consistent with the field measurement results. The incomplete combustion of pulverized-coal from the burner near the side walls is the main source of the carbon content in the fly ash. There is a relatively small impact on the burnout characteristics of the middle burner by appropriately reducing the air ratio of the middle burner and increasing the air ratio of the burners near the side wall, which can effectively improve the burnout characteristics of the burners near the side wall(the carbon content in fly ash reduces from 3% to less than 1.6%). Appropriately increasing the swirling intensity of the burner near the side wall, or properly increasing the output of the middle burner and reducing the combustion output of the burners near the side wall, can significantly reduce the carbon content(less than 2%) in the fly ash of the burners near the side wall and improve the pulverized coal burnout characteristics.

    2022 12 v.28;No.148 [Abstract][OnlineView][HTML全文][Download 24683K]

  • Recent advances on transcritical power cycles based on organic fluids and CO2

    CHEN Chonghui;OU Shaoduan;SU Wen;LI Xiaoya;LIN Xinxing;ZHOU Naijun;School of Energy Science and Engineering,Central South University;School of Electrical and Electronic Engineering,Nanyang Technological University;Institute of Science and Technology,China Three Gorges Corporation;

    Transcritical power cycle is a thermodynamic system that converts thermal energy into mechanical work, which has received much attention from both academia and industry, owing to its high thermal efficiency and good economic performance in energy conversion from low-to medium-temperature heat sources. At present, most of the existing literature is reviewed for specific applications of transcritical power cycles, and there is few general discussions of cycle construction, simulation models and working fluids. Firstly, taking the transcritical power cycle as the main line, the existing structures of the transcritical power cycle were reviewed. Thereafter, the thermodynamic models(steady-state and dynamic), the economic models(exergy economic model and the system cost model) for cycle simulation were introduced. Recent advances on transcritical power cycles were presented in terms of the working fluids(organic fluids, CO_2 and CO_2 mixture) at home and abroad. Lastly, the relevant experimental researches on transcritical cycles in recent years were illustrated. Based on the above reviews, it′s pointed out that the cycle construction will be developed towards artificial intelligence-based methods, and CO_2-based mixture may become a hot research spot in the future. Meanwhile, it′s urgent to vigorously develop system components and conduct more experimental researches on transcritical system.

    2022 12 v.28;No.148 [Abstract][OnlineView][HTML全文][Download 23475K]

  • Treatment of coal washing waste water by aluminum dross-based poly aluminum chloride

    LI Zhanbing;LI Huiquan;LIU Qingqing;ZHANG Jianbo;HUANG Xingzhong;WU Xiuwen;LI Shaopeng;School of Materials Science and Technology,China University of Gensciences,Beijing;CAS Key Laboratory of Green Process and Engineering,National Engineering Research Center of Strategic Metal Resources Green Recycling and Utilization,Institute of Process Engineering,Chinese Academy of Sciences;School of Chemical Engineering,University of Chinese Academy of Sciences;

    Aluminum dross is a kind of hazardous wastes produced from aluminum electrolysis, processing and regeneration industry. Direct stacking is easy to cause serious environmental pollution and waste of resource. Nevertheless, aluminum dross containing alumina more than 70% can be used to produce poly aluminum chloride. In order to realize the utilization of aluminum dross and solve the pollution problem of coal washing waste water, the coal washing waste water was treated with aluminum dross based poly aluminum chloride(AD-PAC). And the effects of AD-PAC addition amount, temperature, pH, mixing speed for stirring, mixing time for stirring, reaction speed for stirring, reaction time and sedimentation time for stirring on removing the turbidity of coal washing waste water were systematically investigated. The binding mechanism between AD-PAC and particle in coal washing wastewater was discussed by the change of flocculating constituent particle size. And the flocculating mechanism of AD-PAC for coal washing waste water was expounded. The results show that the turbidity removal ratios reach maximum values 99.08%, and the turbidity of coal washing waste water decreases from 54.63 NTU to 0.50 NTU with the conditions of AD-PAC addition 100 mg/L, temperature 40 ℃, pH=10, mixing speed for stirring 300 r/min, mixing time for stirring 30 s, reaction speed for stirring 100 r/min, reaction time for stirring 45 min and sedimentation time 20 min. The average particle sizes of flocs increase from 59.67 μm to 145.90 μm. The AD-PAC make the particles unstable by electric neutralization/adsorption and net capture respectively, and make the particle transmit to large particle flocculates to purify coal washing waste water. The research in this paper will provide a strong support for the application of AD-PAC in wastewater treatment industry.

    2022 12 v.28;No.148 [Abstract][OnlineView][HTML全文][Download 11362K]



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