• Research progress of nickel-based catalysts for carbon dioxide methanation

    ZHANG Xiaoli;GU Fangna;SU Fangbing;XU Guangwen;Key Laboratory on Resources Chemicals and Materials of Ministry Education,Shenyang University of Chemical Technology;State Key Laboratory of Multiphase Complex Systems,Institute of process Engineering,Chinese Academy of Sciences;Institute of Industrial Chemistry and Energy Technology,Shenyang University of Chemical Technology;

    Carbon dioxide methanation is a promising technology for realizing the recycling of CO_2 and solving the environmental problems caused by CO_2 emissions. Ni-based catalysts have been widely used in CO_2 methanation in recent years because of their good catalytic activity, high CH_4 selectivity, and low price. The effects of Ni particle size effect, surface microstructure, support type and physicochemical properties(alkaline site, oxygen vacancy, specific surface area, pore structure and metal support interaction) on the catalytic performance of CO_2 methanation catalyst were emphatically described. The effects of Ni-based bimetallic alloy, structure and electronic additives on its catalytic performance were introduced, the CO_2 methanation mechanism on different catalysts were summarized, the reasons for the deactivation of Ni based catalysts were analyzed, and the application of Ni-based catalysts in photothermal catalytic CO_2 methanation was discussed. Finally, the future research direction of CO_2 methanation catalyst has been prospected. By comparing the results of different systems, it reveals that the CO_2 methanation is a structure-sensitive reaction, in which Ni particle size has significant effect on the activity of the catalysts. However, the optimum Ni particle sizes obtained by different studies are various, which may be related to the difference of the surface microstructure(such as different crystal planes, defect sites, etc.) of Ni particles caused by the different interaction between metals and carriers or preparation methods. Thus, the size effect of Ni particles remains to be further studied. Moreover, the activity and stability of the Ni catalysts can also be improved by adding the second metal or promoters, or tuning the interaction between Ni particles and carriers. The abundant alkaline sites and oxygen vacancies on the surface of the support are conducive to CO_2 adsorption and activation, so as to improve the activity of the catalyst. At present, the proposed mechanisms of CO_2 methanation over Ni-based catalysts are mainly classified into CO pathway and formate pathway, which pathway followed may relate to the surface properties of the catalysts(such as the concentration of hydroxyl or O~(2-)adsorption site, etc.) and reaction conditions(such as temperature, pressure, etc.). However, there is a lack of in-depth cognition about the nano-interface structure between promoters or carriers and Ni species, and the influence mechanism of different promoters and carriers on the catalytic active sites and the pathway of CO_2 methanation. Therefore, it is necessary to make a fine and dynamic structural analysis of the surface interface geometry and electronic structure of the Ni-based catalyst using a series of in-situ imaging and spectroscopy techniques, and establish a dynamic structure activity relationship between structure and performance, which is conducive to the understanding of the above problems, and can also guide the design and synthesis of highly efficient Ni-based catalysts with specific structures.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 25037K]

  • Analysis of migration characteristics of C/O/N elements in coal under preheated combustion reducing atmosphere

    ZHANG Yi;ZHU Jianguo;LYU Qinggang;ZHANG Xiaoyu;ZHANG Jiahang;PAN Fei;Institute of Engineering Thermophysics,Chinese Academy of Sciences;University of Chinese Academy of Sciences;

    The deep control of the coal combustion process is the ultimate goal pursued by coal combustion researchers. Based on the gas conversion and the solid functional group conversion, the C/O/N element migration discipline of the fuel in the four reducing atmosphere regions was mainly analyzed and elaborated during the pulverized coal preheating combustion process. From the gas transformation analysis, it can be obtained that the carbon element in the whole process is mainly released in the form of CO and CO_2,the oxygen element is mainly released with gaseous carbon oxide and nitrogen oxide, and the nitrogen element is mainly released in the form of N_2 during the preheating stage. It is mainly released in the form of NO_2 and NO during combustion stage, its nitrogen-containing form is related to the distance from the top of the combustion chamber. From the analysis of solid functional group transformation, it can be seen that the types of carbon-containing double bonds and nitrogen-containing functional groups on the surface of raw coal increase after preheating. In the three reducing regions of the combustion chamber, the carbon-containing double bonds on the fuel surface are consumed and generated for many times, the adsorbed oxygen on the surface is released and adsorbed for many times, and the types of nitrogen-containing functional groups also change. The preheated char and the solid sample at 400 mm generate the most carbon-containing double bonds and there is the regeneration of adsorbed oxygen, thus the samples generated at these two positions are the most active. The samples at 100 mm and 900 mm contain the most types of unstable N-containing functional groups, which makes the nitrogen in the sample easier to be released in the form of gas at these two locations. The experimental results can provide basic experimental data support for the depth control of NO_x during coal combustion.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 4766K]

  • Numerical analysis of CH_4/air porous media combustion characteristics based on GRI-Mech 3.0 mechanism

    WANG Pengtao;JIA Nan;LIU Pengzhong;CUI Yuhong;NIU Fang;China Coal Research Institute Company of Energy Conservation;State Key Laboratory of High Efficient Mining and Clean Utilization of Coal Resources;National Energy Technology & Equipment Laboratory of Coal Utilization and Emission Control;

    Compared with conventional free flame, porous medium combustion flame has higher power density, wider flammability limit, higher combustion rate and lower pollutant emission. In order to investigate the combustion flame and pollutant emission characteristics of methane porous medium, the combustion characteristics of premixed gas in three-dimensional alumina pellet porous medium burner were numerically simulated by using computational fluid dynamics(CFD) method and GRI-Mech 3.0 mechanism. The effects of equivalence ratio on flame surface, combustion reaction rate and emission characteristics of CO and NO_x were analyzed. The results show that the CH_4/air combustion goes through three stages: preheating-combustion-burnout, and reaches the peak of temperature and combustion reaction rate in the main combustion zone. In the second half of the main combustion zone and the burn out zone, the combustion temperature tends to be uniform, which is an important difference between porous medium combustion and traditional combustion. There is no linear relationship between the effect of chemical equivalence ratio on the overall combustion characteristics of methane/air porous media, when the stoichiometric ratio is 1.0,the overall combustion characteristics are better. The NO concentration in porous media combustion field first increases rapidly due to the influence of thermal NO generation mechanism, and then a certain concentration of NO is consumed by the reduction reaction involving NO in GRI-Mech 3.0 mechanism due to the enhancement of reducing atmosphere.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 13790K]

  • A review of preheating-low NO_x combustion coupling technology of pulverized coal

    WANG Shuai;LIU Yang;LIU Yuanwu;NIU Yanqing;ZHU Guangqing;XUE Xufeng;HUI Shien;State Key Laboratory of Multiphase Flow in Power Engineering,School of Energy and Power Engineering,Xi′an Jiaotong University;Xi′an Thermal Power Research Institute Co.,Ltd.;Xi′an Jiaoda Siyuan Technology Co.,Ltd.;

    Reducing NO_x formation during pulverized coal(PC) combustion process is the simplest and most efficient way to minimize NO_x pollution. PC preheating and combustion technology has been paid more and more attention because of its great potential in low NO_x combustion. The key idea of preheating-low NO_x combustion is that before pulverized coal enters the furnace for combustion, the pulverized coal is preheated by setting an independent physical space with high temperature, low oxygen and strong reducibility, and the volatile is rapidly precipitated and transformed in the preheating area, so as to promote the release of volatile N and increase the proportion of volatile N reduced to N_2,so as to reduce the probability of N in coal being oxidized to NO_x. Meanwhile, by integrating low-NO_x technology, such as air staging and MILD combustion, the formation of NO_x is further reduced. So far, according to different preheating heat sources and preheating devices, PC preheating technology can be divided into gas-fired preheating, fluidized bed preheating and self-preheating burners. Among them, self-preheating burner organically combines the pulverized coal self-preheating technology with the radial and axial multistage step-by-step air distribution technology, fuel concentration and dilution separation and graded powder feeding technology through optimal design, which has the advantages of low cost and transformation flexibility while ensuring high efficiency and low NO_x. The self-preheating burner shows excellent operation stability, load adaptability and low NO_x production by integrating self-preheating, multi air staging, fuel-rich/lean separation and fuel staging technology.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 10168K]

  • Effects of staged oxygen on NO_x formation and ash deposition characteristics during oxy-fuel combustion of high-alkali coal

    SUN Ruijin;WANG Chang′an;ZHAO Lin;WANG Chaowei;MA Chengguo;CHE Defu;State Key Laboratory of Multiphase Flow in Power Engineering,Xi′an Jiaotong University;Black Dragon New Double Stock Co.,Ltd.;

    Zhundong coal is rich in reserves, but its high contents of alkali and alkaline earth metals can result in serious fouling on the heat exchange surface, influencing the boiler efficiency and the safe operation. Oxy-fuel combustion is promising to realize the clean utilization of Zhundong coal, and the oxy-fuel combustion under staged condition can further decrease NO_x emission, while it affects the evolution of mineral in coal as well. There is little research on the effect of staged oxygen on ash deposition caused by high-alkali coal, and the possible relationship between NO_x formation and ash deposition remains unclear. The characteristics of NO_x formation and ash deposition under oxy-fuel combustion with staged oxygen were studied via a two-stage furnace. The experimental results show that the NO concentration in flue gas under oxy-fuel condition is much lower than that in air. The NO concentration in oxy-fuel atmosphere is about 80×10~(-6),while the NO concentration in air exceeds 170×10~(-6). Under the same O_2 volume fraction(21%),the ash deposition propensity under oxy-fuel condition is also weaker than that in air, which is 26.20 mg/g and 16.45 mg/g, respectively. The results indicate the superiority of oxy-fuel combustion. With the increase of oxygen content in the main combustion zone(25%-60%),the conversion ratio of fuel nitrogen and ash deposition propensity of Wucaiwan coal both gradually increases. The overall structure of ash deposit is more compact, the agglomeration and adhesion between the accumulated ash particles are serious, the number of independent ash particles is significantly reduced. In addition, the pits on the particles surfaces develope, with more pore structures and more serious sintering observed. This reseach helps to better understand the ash deposition and NO_x formation characteristics during the oxy-fuel combustion with oxygen staged, which is also conducive to accelerating the safe and clean utilization of high-alkali coal.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 51793K]

  • Experimental study on oxidation removal of elemental mercury from flue gas by chloridesalts modified cordierite adsorbents

    XING Xiangwen;FANG Beibei;ZHANG Xiaoyang;CUI Lin;DONG Yong;School of Energy and Power Engineering,Shandong University;National Engineering Laboratory for Reducing Emissions from Coal Combustion,Shandong University;

    Mercury is one of the harmful trace heavy metal elements in coal with strong volatility and toxicity. During coal combustion, mercury is mainly released into the flue gas in the form of Hg~0. The element Cl in flue gas can efficiently oxidize Hg~0 to Hg~(2+),and then Hg~(2+) can be removed in downstream dust removal and wet desulfurization facilities. However, most of the coal in China belongs to low-chlorine coal, resulting in a high proportion of Hg~0 in flue gas, and the low mercury removal efficiency of existing flue gas pollutant control units in power plants. In order to solve the problems of low chlorine content, poor oxidation effect and high content of Hg~0 in flue, it was proposed to impregnate cordierite with four kinds of chlorine salts to prepare MCl_x/Cord adsorbent. The Hg~0 oxidation experiment of the adsorbent with a wide temperature window was carried out to explore the oxidation performance of cordierite modified by chlorine salts to Hg~0. The results show that in the range of 0-8% O_2 content and 150-350 ℃,the highest Hg~0 removal efficiency of cordierite is only 8%,while that of cordierite sorbents modified with CaCl_2,MgCl_2,FeCl_3 and CuCl_2 reach 30,95,97 and 98%,respectively. It can be seen that the chlorine salts greatly improve the performance of cordierite sorbents for removal of Hg~0. The temperature and oxygen content have great influence on the Hg~0 removal performance of MgCl_2/Cord, CaCl_2/Cord and FeCl_3/Cord. The temperature and O_2 content have little influence on the Hg~0 removal efficiency of CuCl_2/Cord, which is always more than 93%. CuCl_2/Cord shows a stable performance on mercury oxidation removal, so it is suitable to be used as a potential oxidation sorbent for oxidation and adsorption removal of Hg~0 from flue gas. Chlorine salt impregnation modification can improve the oxidation performance of cordierite to Hg~0. Cordierite modified by CuCl_2 impregnation has the best Hg~0 oxidation effect, and it is almost not affected by the change of temperature and O_2 content.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 29618K]

  • Real time monitoring of accumulated pulverized coal temperature field based on acoustic method

    YANG Geng;YAN Jidong;SHEN Guoqing;AN Liansuo;LI Zongjin;School of Energy,Power and Mechanical Engineering,North China Electric Power University;

    In the process of preparation, transportation and storage of pulverized coal, the accumulated pulverized coal is usually exposed to oxidation environment. When the external temperature is too high, it is very easy to spontaneous combustion. The low frequency sound wave has the characteristics of low attenuation and long propagation distance. The acoustic temperature measurement method using low frequency sound wave as sound source can effectively make up for the lag warning of conventional thermocouple and realize real-time measurement, and significantly improve the intelligent level of power generation process. The sound absorption characteristics of the accumulated pulverized coal and the propagation characteristics of low-frequency sound waves(frequency in 200-2 000 Hz) in the accumulated pulverized coal were mainly explored. Four kinds of coal samples with different particle sizes were prepared from the bituminous coal produced by Fuquan coal mine. The sound absorption characteristics of pulverized coal were mainly studied from two aspects of different particle sizes and stacking height. The results show that the sound absorption curve of stacked pulverized coal has multi-peak phenomenon; experiments on the propagation characteristics of low-frequency sound waves in accumulated pulverized coal at different frequencies were carried out. The results show that the acoustic attenuation coefficient has an obvious downward trend in the range of 1 000-2 000 Hz. The velocity measurement results show that the range of sound velocity is 142.261-142.851 m/s, and the standard deviation is about 0.1%. The results are more stable. The feasibility of acoustic measurement of temperature distribution of accumulated pulverized coal is verified.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 8533K]

  • Numerical investigation on the flow field and performance optimization of the direct air-cooled condenser

    WANG Miao;HUANG Qian;CAO Wenguang;LI Shuiqing;Department of Energy and Power Engineering,Tsinghua University;Key Laboratory for Thermal Science and Power Engineering of Ministry of Education,Tsinghua University;

    In coal-fired power plants, the ambience wind speed and ambient temperature play an important role in determining the convective heat transfer between the cooling air and hot steam in the triangular cavity of the direct air-cooled condenser. Thus affecting the operational stability of the unit. In this paper, taking 600 MW unit single row/single air-cooled unit as an example, the performance of the direct air-cooled condenser was investigated by means of three-dimensional CFD under varied ambience conditions. Moreover, a novel "wing-type" solid/porous deflect plate with the adjustable angle in the triangular cavity to optimize the flow field of the condenser was proposed. The simulated results indicate that: the single row condenser is affected by the ambient wind effect, and the average air flow rate of the air condenser at the first position in the air inlet direction is most affected by the environmental wind speed. When the environmental wind speed increases from 3 m/s to 9 m/s, the average air flow rate of single column(consisting of 8 air cooling units) air condenser decreases by about 590 kg/s, indicating that the air disturbance increase and the heat transfer is unfavorable in the triangular cavity with high wind speed. The method of adding solid plate/porous plate in the condenser triangle cavity has obvious rectifying effect on the flow vortex generated in adverse environment. Besides, by adjusting the angle of the two plates to 240°,the static pressure in the triangular cavity has increased by 153 Pa on average, which can effectively alleviate the freezing phenomenon at the bottom of heat exchange tubes in the winter. This kind of direct air condenser with diversion device is suitable for a wide range of environmental conditions, which is beneficial to realize the functions of high temperature resistance prevention, low temperature anti-freezing and stable operation in practical engineering.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 13717K]

  • Research status of SCR ammonia conversion, adsorption and ammonia removal technology from fly ash

    TANG Xiao;XU Renbo;ZHANG Fajie;MA Yunlong;ZHAO Hong;WANG Lele;SUN Lushi;YU Jie;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;Huaneng Dalian Power Plant;Suzhou Branch of Xi′an Thermal Power Research Institute Co.,Ltd.;

    Due to the stricter regulations on the emission of pollutants from coal-fired power plants, all coal-fired power plants have installed denitrification devices(SCR) to remove NO_x from flue gas in China. Normally, the denitrification efficiency of SCR facility can be 80%-90%. Under the ultra-low emission restriction, the actual denitrification efficiency of SCR operation of some coal-fired boiler is as high as 95%,which will lead to a sharp increase in the difficulty of ammonia escape control. The formation and removal of ammonia hydrogen sulfate in fly ash after SCR denitration of coal-fired power station boilers at home and abroad were reviewed, its formation mechanism and removal methods were analyzed, and its industrial application was prospected. But it is found that the presence of SO_3 and H_2O in flue gas can promote the adsorption of ammonia in fly ash. The concentration of NH_3 and SO_3 and coal grade are the main factors affecting the ammonia adsorption on fly ash. The existing fly ash deamination technologies include heating method, oxidation method, water washing method and alkali addition method. At 204 ℃,the removal of ammonia in fly ash is very slow. After treatment for 80 minutes, the ammonia removal rate is less than 50%. The heating method needs to be carried out at 260 ℃,and the energy consumption is high. When the water content in the ash is higher than 3%,the ammonia removal rate is fast, but in the subsequent drying stage, when the water content in the ash drops below 2%,the ammonia removal rate decreases rapidly, and the water washing method will produce additional wastewater; the oxidation method is to select a suitable catalyst and install it behind the SCR Flue gas denitration device and in front of the air preheater to selectively catalyze and oxidize NH_3 in the flue gas into N_2,so as to effectively remove the escaping NH_3 in the flue gas, reduce the generation of NH_4HSO_4 and reduce the ammonia content of fly ash, but it can not ensure that the oxidant reacts completely with ammonia, resulting in the escape of residual oxidant. Adding calcium base alkali and water to fly ash and stirring can obtain excellent ammonia removal effect. Adding a small amount of water(~2%) and a small amount of alkali(≤2%) to fly ash can reduce the mass fraction of ammonia in fly ash to less than 100 mg/kg. Due to the small amount of water added, the flue gas can be dried after desulfurization of the subsequent unit, and the NH_3 generated in the treatment process can be re injected into the SCR Flue gas denitration device or ammonia water. Alkali addition method has low cost and high efficiency. It is an excellent method to remove ammonia from ash. At present, industry standard regarding the ammonia content in fly ash is not issused. Meanwhile, the effect of ammonia in fly ash on environment and its utilization as construction materials still lacks engineering verification testing. At present, the removal of ammonia in fly ash is still in the stage of laboratory research and industrial pilot test. In the future, the detailed economic analysis is also needed to realize its utilization.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 6353K]

  • Key technologies for treatment of wastewater from coal-to-ethylene glycol

    YANG Qian;WEI Jiangbo;SUN Qi;LIU Zhixue;TENG Wei;TAO Zhida;China Coal Processing and Utilization Association;Shenhua Engineering Technology Co.,Ltd.;College of Environmental and Energy Engineering,Beijing University of Technology;Appraisal Center for Environment and Engineering,Ministry of Ecology and Environment;

    Ethylene glycol is a pivotal fundamental organic chemical product and raw material. There are three preparation routes of ethylene glycol: petrochemical, biomass and coal gasification syngas. In recent years, the technology of coal gasification syngas to produce ethylene glycol has developed rapidly in China. However, ethylene glycol wastewater which comes from gasification and DMO synthesis stage has the characteristics of high organic matter, high nitrate, toxic substances and refractory substances, so the standard discharge of wastewater has become one of the main constraints for the application of coal to ethylene glycol technology. The key technologies for the treatment of coal-to-ethylene glycol wastewater, including extraction and stripping pretreatment of coal gasification wastewater for ammonia removal, phenol removal and cyanide destruction, esterification and nitric acid removal of wastewater, composite membrane denitrification, biochemical degradation of organic matter, concentration and crystallization of high-salt wastewater were reviewed and the application scenarios and characteristics of each process were summarized. The results show that the oil, phenol, ammonia, suspended solids and other toxic substances in the wastewater can be removed by the pretreatment unit. The COD,ammonia and organic matters can be reduced by the biological stage. "Wastewater near-zero discharge" can be realized by the evaporation and crystallization. It is suitable to treat coal-to-ethylene glycol from syngas wastewater with the pretreatment-biochemical-salt separation crystallization technology. Finally, in the view of resource, the future research trend and suggestions of wastewater treatment from coal-to-ethylene glycol are proposed to strengthen the source pollution control, implement clean production, and develop "near-zero discharge" technology on high salt wastewater.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 3799K]

  • Synthesis of Ni_2P/Al_2O_3-TiO_2 catalyst and its phenanthrene hydrogenation saturation performance

    CHEN Yu;WANG Jiuzhan;LI Ze;JING Jieying;LI Wenying;State Key Laboratory of Clean and Efficient Coal Utilization,Taiyuan University of Technology;

    The characteristics of coal tar rich in aromatic hydrocarbons give it the feasibility of preparing high-performance jet fuels, and the hydrogenation saturated products of fused-ring aromatic compounds(such as perhydrophenanthrene) can significantly enhance the thermal stability of jet fuels. The key point to realize this process is to prepare high performance hydrogenation saturation catalyst. In view of the adsorption problems in the saturation reaction of phenanthrene hydrogenation, based on the special electronic structure of Ni_2P,in order to strengthen aromatics adsorption as the goal, the composite oxide carrier Al_2O_3-TiO_2 was prepared by sol-gel method, and a series of Ni_2P/Al_2O_3-TiO_2-phenanthrene hydrogenation saturation catalyst were prepared by the hypophosphite decomposition method. The effects of different content of TiO_2 on the geometrical structure, electronic structure and phenanthrene hydrogenation saturation of Ni_2P catalyst were investigated. The results show that when the reaction temperature is 320 ℃,the reaction pressure is 5 MPa, and the WHSV is 52 h~(-1)),contrast with Ni_2P/Al_2O_3 catalyst, the conversion of phenanthrene do not changed(95%),while the selectivity of perhydrophenanthrene over Ni_2P/Al_2O_3-TiO_2(15% TiO_2))is increased from 49% to 68%. Meanwhile, the turnover frequency was also improved from 0.3 s~(-1) to 0.7 s~(-1). The geometric structure and electronic structure of the catalysts were analyzed, and it is found that TiO_2 can deliver the appropriate amount of electrons to the Ni in Ni_2P catalyst, and so that Ni in Ni_2P is in a suitable electron deficient state, which will enhance the adsorption capacity of Ni_2P/Al_2O_3-TiO_2 catalyst for phenanthrene and intermediate products. Moreover, the doping of TiO_2 is beneficial to the formation of Ni_2P with smaller particle size. When TiO_2 doping amount is 15%,Ni_2P has the smallest particle size(4.3 nm) in the catalyst, which can provide more active sites for hydrogenation reaction and make the catalyst have strong phenanthrene hydrogenation saturation capacity.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 38646K]

  • Pyrolysis experiment and product analysis of Shendong coal in 40 kg experimental oven

    PENG Dejun;DI Chuangeng;ZHANG Fei;CHN Energy Shendong Coal Group Co.,Ltd.;

    Shendong coal is a typical Jurassic non stick coal, which has the advantages of low ash, low sulfur, low phosphorus, low potassium and sodium content, high tar yield, high volatile yield, medium grindability index and thermal stability. It is more suitable for medium and low temperature pyrolysis processing. In order to study the pyrolysis characteristics of Shendong coal comprehensively, thermogravimetric analyzer and 40 kg pyrolysis unit were used to study the formation and properties of tar, pyrolysis gas and char of Shendong coal. The results show that excellent coal qualities with high tar yield are found of Shendong coal, which makes it suitable for upgrading in medium-low temperature pyrolysis. With the increasing of pyrolysis temperature, the yield of pyrolysis gas increases significantly while the yield of char decreases gradually. The content of volatile matter in char decreases rapidly, while the content of carbon increases gradually. The mechanical strength of char degrades gradually. The reactivity and grindability of char decrease while the specific resistance decreases rapidly. The specific surface and the phenol adsorption capacity of char are relatively low. Excellent properties are found of pyrolysis tar, which makes it suitable for hydrogenation to prepare clean fuel.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 5756K]

  • Fragmentation characteristics of Shendong coal during pyrolysis in rotary kiln

    CHANG Liang;National Institute of Clean-and-Low Carbon Energy;

    In order to study the fragmentation characteristics of Shendong coal during pyrolysis process in the rotary kiln, the pyrolysis and crushing experimental of Shendong coal with a particle size of 25-13 mm were studied in a 100 kg rotary kiln. The effects of temperature, residence time and rotary speed on the degree of fragmentation and pulverization of Shendong coal were investigated. The results show that with the increase of temperature(120-700 ℃),the total fragmentation rate α of Shendong coal products increases from 20.48% to 68.74%,and the pulverization rate β increases from 1.70% to 16.55%;with the residence time increasing, the α increases from 15.66% to 68.22%,and the β increases from 1.32% to 15.71%;with the rotation speed of the rotary kiln increasing, the α increases from 17.54% to 71.43%,the β increases from 1.26% to 15.08%.Through the grey correlation analysis of the factors affecting the crushing of Shendong coal rotary kiln pyrolysis process, it is found that the three reaction conditions(final reaction temperature, residence time, rotary kiln speed) have the same order of impact on the fragmentation and pulverization rate of the product. The temperature has the largest impact, followed by the residence time, and the rotary kiln speed has the least impact. The particle size correlation function model of Shendong coal pyrolysis and fragmentation process was established, the model reflected the relationship between coal pyrolysis temperature, residence time and rotational speed on particle size distribution, and it is verified that the relative error between the calculated value and the experimental value of the average particle size after crushing is less than 5%,which can better predict the change of the particle size of Shendong coal during the pyrolysis process of the rotary kiln.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 7565K]

  • Generation characteristics of tar in fluidized bed coal gasification

    DENG Shangzhi;JIANG Huawei;LI Weiqiang;YUAN Ye;GUO Qingjie;WANG Cuiping;College of Mechanical and Electrical Engineering,Qingdao University;State Key Laboratory of High-efficiency Utilization of Coal and Green Chemical Engineering,Ningxia University;College of Civil Engineering and Architecture,Shandong University of Science and Technology;

    Tar generated during the coal gasification may condense at low temperature, thus blocking the process equipment, leading to the pollution of the equipment, and increasing operating costs. The adjustment of operation parameters based on the tar generation characteristics would be conducive to reduce the original tar emission from a gasifier and reduce the cost of tar removal. In order to obtain the generation characteristics of tar in fluidized bed coal gasification, the effects of parameters such as bed temperature, air equivalent ratio, superficial gas velocity, coal particle size and water content, upon the generation amount of tar in the product gas were studied by fluidized bed reactor. The results show that increasing temperature or air equivalent ratio is beneficial to the decrease of tar mass concentration, but the effects are both limited. When the apparent gas velocity u_g in the furnace increases from 0.19 to 0.33 m/s, more intensified contact and mixing between gas and solids improve the effects of heat transfer and mass transfer in the gasifier and promote the thermal decomposition of tar produced. However, as the bubbling fluidization transits to turbulent fluidization, the contact and mixing between gas and solids are no longer significantly enhanced, and the tar mass concentration thus changes little. The small diameters of coal particles can improve the chemical reaction rate and promote the thermal decomposition of tar. However, at a certain fluidization gas velocity, the smaller the gasification feedstocks is, the more it is easily distributed on the bed, which weakens the heat transfer between coals and bed materials, and shortens the residence time of tar in the furnace, leading to the rise of tar mass concentration. The tar mass concentrations in the product gas of coal gasification under different moisture contents have obvious difference. Neither too high nor too low for water content are beneficial to the reduction of tar generation.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 9421K]

  • Effect of modification on structure and electrochemical properties of coal based activated carbon

    ZHANG Zhaohua;WANG Qian;ZHANG Buqin;ZHANG Fengmei;ZHANG Chuanxiang;HUANG Guangxu;XING Baolin;College of Chemistry and Chemical Engineering,Henan Polytechnic University;Jizhong Energy Fengfeng Group Co.,Ltd.;

    Supercapacitor is a new type of energy storage device, and electrode material as its key component has been attracting much attention, among which the modification treatment of electrode material is crucial for the research of high-performance supercapacitor.Coal-based capacitive carbon with high specific surface area(2 586 m~2/g) was prepared with using Hebei anthracite coal as the precursor, KOH as the activator, alkali to coal mass ratio of 2∶1 and activation temperature of 800 ℃. The evolution of microstructure and surface chemistry of the capacitance carbon during hydrothermal reduction at different temperatures(600-1 000 ℃) and their effects on electrochemical properties were investigated by using coal-based capacitance carbon as raw material. The results show that with the increase of hydrothermal reduction temperature, the specific surface area of the samples first slightly increases and then gradually decreases, and the mesoporosity increases to different degrees compared with the original coal-based capacitive carbon. Among them, the samples obtained by hydrothermal reduction treatment at 700 ℃ have lower oxygen content(0.35%),stronger electrical conductivity, better wettability with organic electrolyte and higher degree of defects, and the electrochemical properties has been significantly improved: higher specific capacitance(179 F/g at 0.5 A/g current density),energy density(33.36 Wh/kg),power density(1 014.75 W/kg),multiplicative performance(58.7% capacitance retention at 5 A/g current density),and cycling stability(82% capacitance retention at 5 000 cycles). For coal-based capacitive carbon, hydrothermal reduction is a good modification treatment.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 25167K]

  • Influence of the cellulosehe, micellulose and lignin on the combustion behavior of biomass

    LIU Yang;JIANG Tong;ZOU Chun;ZHANG Haisheng;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;School of Energy and Power Engineering,Huazhong University of Science and Technology;Foshan Public Utilities Holdings Co.,Ltd .;Foran Energy Group Co.,Ltd.;

    Biomass energy has become a hot topic of energy field research due to its advantage of zero carbon dioxide emission and renewable energy. How to utilize biomass energy rationally and fully has been concerned by governments and scientific research institutions at home and abroad. The study on the influence mechanism of the three components of biomass(cellulosehe, micellulose and lignin) on the ignition and combustion behavior of biomass can be used for the selection of biomass species and evaluation of biomass and coal co-combustion in biomass power plants. Hencken flat flame burner and a high-speed camera were used to record the ignition delay time of three components of biomass, three types of biomass, and simulated biomass. Combined with the radiation energy temperature measurement technology, the combustion characteristics of three components of biomass, three types of biomass and simulated biomass were discussed, and the effects of biomass structure characteristics on the combustion characteristics were analyzed. The results show that the ignition delay time of lignin among the three components of biomass is the shortest, followed by hemicellulose, and cellulose has the longest ignition delay time, which are 2.08,4.16 and 7.52 s respectively. The ignition behavior of three kinds of biomass and the corresponding simulated biomass are obviously different, and this difference increases with the increase of lignin content in biomass. After the ignition of cellulose and hemicellulose coke, the combustion temperature increases sharply to more than 1 000 K,while the particle temperature increases relatively gently after the ignition of lignin coke. In addition, the ignition delay time of real biomass is longer than that of simulated biomass, and the ignition delay time of simulated biomass decreases with the increase of lignin content. For the real biomass, the trend of peak temperature curves of rice stalk and chestnut shell are close to each other, and the temperature of chestnut shell is higher at the beginning of combustion, while the temperature curve of bamboo is special.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 10957K]

  • Experimental study on deep peak regulation operation of coal-fired thermal power unit

    ZHANG Xuhui;YANG Xingsen;XIN Gang;LIU Ke;CUI Fuxing;ZHAO Zhonghua;State Grid Shandong Electric Power Research Institute;State Grid Shandong Electric Power Company;

    The scale of new energy power generation such as wind power and photovoltaics continues to grow rapidly, and the peak-to-valley difference of grid load continues to increase, as a result, the peak shaving operation of coal-fired thermal power units has become more frequent. In order to study the key influencing factors in the actual peak-shaving operation of coal-fired units, the peak-shaving test of 8 coal-fired units with different types was carried out. In the test, the stable combustion ability of the boiler under the deep peak regulation operation state was analyzed by measuring the negative pressure of the boiler furnace, the fire detection signal and the state of the combustion-supporting measures. The pollutant emission concentration of the coal-fired unit under the low-load operation state, and the variation law of the temperature of the SCR flue gas denitrification device under different loads was also analyzed. In addition, the relationship between the heat supply of the extraction steam heating unit and the peak regulation capacity was studied, and the effect of unit heat supply on peak shaving performance was analyzed. The results show that when the coal quality is close to the design coal quality, most units can achieve stable operation below 40% of the rated capacity under pure condensing conditions, which is close to the unit′s design minimum stable combustion load; NO_x emission has become an important limiting factor during the deep peak-shaving operation of coal-fired power units. The operating temperature of the SCR denitrification device may drop below 300 ℃ under low load, which will seriously affect the normal operation of the SCR device and restrict the deep peak shaving operation of the unit.The small heat supply of the unit will help to improve the low-load operation of the boiler.However, when the heat supply is large, it will seriously affect the deep peak shaving of the unit, which may reduce the peak shaving capacity of the unit by more than 20%.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 14958K]

  • Combustion and NO_x formation characteristics of a central fuel-rich direct current pulverized coal burner

    SHEN Tao;SONG Minhang;XIA Liangwei;HUANG Ying;LU Pisi;Harbin Boiler Co., Ltd.;State Key Laboratory of Efficient and Clean Coal-fired Utility Boilers,Harbin Boiler Co.,Ltd.;Institute of Process Engineering,Chinese Academy of Sciences;

    In order to improve the performance of direct-flow pulverized coal burner in promoting the coal ignition and stable combustion, and simultaneously reducing the NO_x generation, Harbin Boiler Co.,Ltd. developed a central fuel-rich direct-current pulverized coal burner. In this burner, a combination of two stages of pulverized coal concentration, a blunt body and combustion stabilization teeth were used to enhance fuel rich/lean organization, stabilize combustion and reduce NO_x generation. The overall combustion performance of this type of burner was obtained by using ANSYS fluent numerical calculation method, and the gas/solid flow, combustion and NO_x generation characteristics of the burner were studied by adjusting the air distribution. The research results show that after the primary coal/air flow is concentrated in two stages, most of the coal particles(about 80%-90% of the total coal particles) can be concentrated in the middle fuel-rich flow channel, and the corresponding flow velocity is between 12 and 16 m/s. Therefore, a low-velocity and fuel-rich zone can be formed near the burner nozzle, which is beneficial to promote the timely ignition of the coal/air flow, and the ignition location is about 300 mm away from the burner nozzles. At the same time, the setting of the combustion stabilizing plate can form two symmetrical high-temperature recirculation zones at the burner outlet, and the corresponding recirculation zone length is around 160 mm. by decreasing the primary air flux and increasing the secondary air flux, the volatile reaction rate is reduced, the reaction time of CO and fixed carbon is prolonged, and the flame length area is simultaneously increased, which is not conducive to suppressing NO_x generation. When the secondary air flux increases and the overfire air flux reduces, the entrainment effect of the high-velocity secondary air on the coal/air flow is enhanced, so as to continuously provide oxygen for the subsequent coal combustion and promote the further heat release. At the same time, due to the further weakening of the effect of air staged combustion, the reducing effect of the main combustion area is weakened, and the NO_x emission concentration is maintained at a high level of 237.3 mg/m~3 at 6% O_2. According to the NO_x generation characteristics of the burner under the reference working condition, under the benchmark conditions, due to the combined effect of the high-temperature recirculation zone and the low-velocity fuel-rich zone, an oxygen-lean and fuel-rich strong reducing atmosphere is formed near the burner nozzles, which obviously inhibits the NO_x production, and a low NO_x emission concentration of 162.34 mg/m~3 at 6% O_2 is achieved.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 23675K]

  • Research and application of low nitrogen combustion adjustment technology based on reaction temperature control

    SHI Bin;DAN Zhenyu;MOU Kehui;LI Nan;ZHAO Pengbo;SUN Xianbin;Fenyi Power Plant,SPIC Jiangxi Electric Power Co.,Ltd.;Huaneng Clean Energy Research Institute Co.,Ltd.;

    In order to improve the efficiency of SNCR denitrification and realize SNCR denitrification with wide load, a low nitrogen combustion adjustment test was carried out on a 130 t/h CFB boiler. Through the research on the temperature control mechanism of the separator, the influencing factors affecting the temperature of the separator were explored, and the control method of separator outlet temperature(T_(sep))were studied. The results show that, there is a most efficient reaction temperature point T_(opt),in the SNCR temperature window. Higher SNCR denitration efficiency can be obtained by precisely controlling the T_(sep) around T_(opt). Flue gas recirculation(FGR) can adjust T_(sep). FGR is put into operation at 130,90 and 70 t/h respectively, and the separator temperature is increased by 30,40 and 70 ℃. With the decrease of boiler load, the control ability of FGR to T_(sep) is enhanced. The ratio of upper and lower secondary air also also can adjust T_(sep). By switching the upper and lower secondary air, The change range of T_(sep) is about 30 ℃. T_(sep) decreases with the increase of primary air rate, the adjustment range of T_(sep) is 18 ℃ at 4.5% oxygen content and the adjustment range of T_(sep) is 35 ℃ at 3.5% oxygen content, and the regulation range of primary air rate on T_(sep) is larger under low oxygen content. During the boiler load of 110-130 t/h, after the separator temperature is accurately controlled at(850±5) ℃,the 20% mass concentration of ammonia is reduced from 350 kg/h to 200 kg/h. The practical application shows that the separator temperature control technology can optimize the SNCR reaction efficiency at high load, and reduce the operation cost of denitration, restart the SNCR reaction at low load to achieve NO_x emission standard, save 2.8 million yuan of ammonia cost.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 4116K]

  • Occurrence and leaching characteristics of fluorine in coal and combustion products of coal fired power plant

    HAO Qiankun;FANG Quanguo;CHEN Yafei;PI Zhongyuan;CHEN Sihan;China Coal Research Institute;Test Branch of China Coal Research Institute Co.,Ltd.;Coal Chemistry Branch of Beijing Research of Coal Chemistry China Coal Research Institute Co.;

    As one of the harmful elements in coal, it is essential to investigate the migration, occurrence and leaching characteristics of fluorine in power plant coal and combustion products to control the migration behavior of fluorine during coal combustion and the potential risk of solid waste. This paper took the coal and combustion products of coal-fired power plant as the research object, the distribution of fluorine in coal-fired power plants was studied through the mass balance of fluorine, the occurrence of fluorine in coal and combustion products of coal-fired power plant was analyzed by scanning electron microscope-energy spectrum(SEM-EDS) and step-by-step chemical extraction test. On this basis, the leaching characteristics of fluorine were studied by standard toxicity leaching method TCLP and HJ/T 300—2007 "Solid waste-Extraction procedure for leaching toxicity-Acetic acid buffer solution method" leaching test. The results show that fluorine is a volatile element. After combustion, fluorine in coal is mainly distributed in flue gas and captured by desulphurization gypsum, followed by fly ash, and only a small part of fluoride with good high temperature stability remains in slag. Fluorine in coal and slag is dominated by residual fluorine existing in aluminosilicate minerals. The transformation of residual fluorine during combustion and the adsorption of fluorine in flue gas by fly ash increase the proportion of active fluorine in fly ash, and the proportion of active fluorine in fly ash is 63%-68%. Desulphurization gypsum is mainly residual fluorine, and the proportion of active fluorine is 38%-50%. The leaching test results show that the leaching amounts of different samples in coal-fired power plant is between 0.12-27.31 μg/mL,which is lower than the limit of fluorine concentration in hazardous waste leaching solution. The leaching of fluorine is mainly related to the occurrence state and environment of fluorine. In the mild environment, the ion exchangeable fluorine in the solid sample will affect the environment, and in the acidic environment, ion exchangeable fluorine and carbonate bound fluorine are the main reasons that affect the fluorine pollution in the environment.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 19166K]

  • Slagging characteristics of coal fired boiler furnace based on fuzzy neural network

    ZHU Chao;YU Xiang;LI Feng;ZHOU Xihong;BI Lingfeng;YANG Dong;Electric Power Research Institute of State Grid Shaanxi Electric Power Company;State Key Laboatory of Multiphase Flow in Power Engineering,Xi′an Jiaotong University;

    At present, coal is still the main energy consumption in the power industry. In addition, the sulfur content and ash content in the commonly used coal for power station boilers is high, which is easy to cause ash and slagging on the heated surface. The serious slagging in the furnace will limit the output of the boiler and threaten the economy and safety of the unit operation, therefore, the development of a comprehensive and comprehensive slagging prediction model will be the focus of further research, which is very important to effectively monitor the degree of slagging in boiler furnace and its development trend. Combining fuzzy mathematics theory with BP neural network, a fuzzy neural network suitable for judging characteristics of slagging in the furnace of coal-fired power plant was constructed. When selecting the input evaluation index, not only its slagging characteristics from the coal ash itself were considered, but also the dimensionless furnace maximum temperature, which reflects the slagging judgment index of unit operation, was incorporated into the model. Taking the operating conditions of the boiler into account, the judgment basis is more comprehensive. A total of 6 factors with higher resolution and the most representative were selected as the input discriminant indicators of this model. Four different types of membership functions were used to fuzz the discriminative index as the input of the fuzzy neural network model, and the neural network without fuzzification was used as the comparison. According to the principles of statistics, the result with the highest occurrence probability was selected as the final evaluation index to increase the accuracy of the prediction result. The results show that when the unit burns Huating coal, the furnace slagging discrimination indexes softening temperature, silicon ratio, silicon aluminum ratio, alkali acid ratio, comprehensive index and the dimensionless maximum temperature of the furnace are 1 220 ℃,58.71,1.63,0.48,2.55 and 0.982 respectively, which are severe slagging. When Huangling No. 1 coal is properly mixed, it is 1 255 ℃,71.02,2.04,0.31,2.15 and 0.958 respectively, which is medium slagging. Therefore, proper blending of high-quality coal can be used to improve the slagging condition of the furnace. The prediction result of this model is accurate, which can provides a new way to comprehensively evaluate the slagging characteristics of the boiler furnace.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 8174K]

  • Performance of cyclone separator replacing vortex finder with air curtain

    SUN Shichao;ZHOU Zhengang;YUAN Donghui;ZHENG Xiuping;DUAN Lunbo;Key Laboratory of Energy Thermal Conversion and Control,Ministry of Education,Southeast University;Inner Mongolia Electric Power Research Institute Branch,Inner Monglia Electric Power (Group) Co.,Ltd.;Inner Mongolia Jingtai Power Generation Co., Ltd.;

    Cyclone separator is one of the important equipment in circulating fluidized bed boiler, which has the advantages of simple structure and low cost. However, many accidents such as deformation, crack, downward movement and even falling off of the vortex finder of the cyclone separator are easy to occur during the operation of the circulating fluidized bed boiler, resulting in serious economic losses.A cyclone separator without vortex finder was presented, and the dust free fresh air was introduced into the original vortex finder to form an air curtain to adjust the separation efficiency of cyclone separator, which could avoid the failure accident of vortex finder and flexibly adjust the separation efficiency of cyclone separator. The separation performance of the cyclone separator was studied by cold state experiment and numerical simulation. The results show that the separation efficiency of the cyclone separator decreases after the vortex finder falls off. Then the separation efficiency of the wind behind 3,6,9 and 12 m/s respectively increases first and then decreases. When the air curtain velocity is 9 m/s, the separation efficiency is the highest, which is 3.17% higher than that of the cyclone separator without air curtain. After the shedding of the vortex finder, the fractional separation efficiency of particles with particle size less than 6 μm shows little change compared with that in the presence of the vortex finder. However, the fractional separation efficiency of particles with particle size greater than 6 μm is significantly lower than that in the presence of the vortex finder. The separation efficiency of cyclone separator for particles with particle size less than 6 μm can be greatly improved behind the wind. After the vortex finder of cyclone separator falls off, the pressure drop will decrease slightly. When the fresh air is introduced into the original vortex finder, the pressure drop behind the wind will increase, and the pressure drop will increase with the increase of the wind curtain speed.

    2022 04 v.28;No.140 [PaperDigest][OnlineView][HTML全文][Download 11740K]
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