- ZHOU Huaichun;LI Kuangyu;AN Yuan;LOU Chun;Jiangsu Smart Energy Technology and Equipment Engineering Research Center,School of Low-carbon Energy and Power Engineering,China University of Mining and Technology;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;
Under the background of carbon neutrality, the deep peak shaving and flexible operation of coal-fired generating units put forward urgent requirements for real-time monitoring of the three-dimensional combustion conditions in the furnace. This paper summarized the research progress of three-dimensional combustion temperature distribution monitoring of coal-fired power plant boilers and industrial furnaces. As for the radiation imaging model of combustion flame, the DRESOR method for directional radiation intensity calculation based on Monte Carlo method and the recent optimization of DRESOR method were mainly introduced, which laid a good foundation for improving the inversion accuracy of combustion temperature and inversion of the distribution of radiation characteristic parameters of combustion medium. The basic method to solve the simultaneous inversion problem of three-dimensional temperature field and radiation parameters is to reconstruct the temperature distribution in the furnace from the monochromatic radiative intensity images by Tikhonov regularization method. Then the radiative properties of the particle medium are updated with optimization method and solved iteratively. Recently, there have been new developments in the inversion algorithm. The new algorithm can be divided into three stages. Firstly, assuming uniform distribution of absorption coefficient, scattering coefficient and reflectivity of the furnace wall, the optimal radiation parameters and temperature distribution inside the furnace are obtained by the optimization solution. Secondly, on the basis of stage 1, the absorption and scattering coefficients in the furnace are set as second-order polynomial fitting distributions in spatial coordinates, and the walls are still set with uniform reflectivity to further optimize the iterative calculation. Finally, on the basis of the convergence of the calculation in stage 2, the second-order polynomial distribution of the reflectivity of the furnace wall in wall coordinates is further assumed, and then the calculation is optimized iteratively. The latest development of the inversion algorithm has obtained the reconstruction result of the combustion temperature with reconstruction error within 1%, and realizes the reconstruction of the relative distribution of pulverized coal concentration in the furnace based on the radiative properties. The monitoring systems of three-dimensional temperature field in the furnace has been industrially applied in the combustion monitoring of 200, 300 and 600 MW coal-fired power plant boilers and further expanded to oil-fired or gas-fired industrial kilns such as walking furnace in rolling mill, tubular furnace in petrochemical plant, single burner combustion furnace and cracking furnace in chemical plant, showing a good application prospect. In the future, machine learning and artificial intelligence theory need to be adopted to further improve the efficiency of solution of the coupled reconstruction problem, combined with three-dimensional real-time and dynamic modeling of furnace conditions and thermal system, to realize real-time monitoring and diagnosis of the parameters of the three-dimensional furnace conditions distribution(furnace atmosphere, particulate matter, pollutants, furnace heat load, furnace wall heat load distribution, etc.) and modeling and prediction of the parameters of the distribution of hydrodynamic and thermal systems in the boiler water wall, to further build a multi-timescale big data-driven digital twin system for coal-fired generating units, contributing to the development of the smart boiler and furnace optimization control system.
2022 10 v.28;No.146 [Abstract][OnlineView][HTML全文][Download 49416K]
2022 10 v.28;No.146 [Abstract][OnlineView][Download 4389K] - QUE Zhengbin;LI Debo;XIAO Xianbin;MIAO Jianjie;LIU Pengyu;CHEN Zhaoli;CHEN Zhihao;FENG Yongxin;National Engineering Laboratory of Biomass Power Generation Equipment,North China Electric Power University;China Southern Grid Power Technology Co.,Ltd.;Energy Power and Mechanical Engineering Department,North China Electric Power University;
Incineration power generation is the main way to deal with domestic waste in China. The industry market is huge and the future development prospects are broad. For grate furnaces widely used in waste incineration power plants, there are problems such as high cost, long period, and non-detailed data results in model experiments and engineering experiments. Numerical simulation technology is usually considered for research work. Based on the combustion process and specific structure of waste in the grate furnace, the mathematical models of the gas-solid combustion process on the grate and the gas-phase combustion process in the furnace were described, respectively, and the existing modeling process of the grate furnace was summarized. The method of coupling calculations with different models to simulate the entire incineration process was highlighted. On the basis of expounding the modeling process of grate furnace, it focused on the content of numerical simulation research using Fluent software, and introduced the research and application of numerical simulation technology in grate furnace. At present, the relevant research mainly adopts the method of controlling variables to study the influence of a single parameter on the operation process of the grate furnace. Therefore, various parameters were classified according to fuel characteristics, operating parameters, structure of the grate furnace, and air and smoke system, and the progress and results of the research were analyzed and summarized. Based on the above analysis and research, the technical route of using numerical simulation technology to carry out design, construction and transformation and optimization of waste incineration power plants was proposed. Finally, the numerical simulation research of grate furnace was prospected to provide reference for further research work and practical engineering applications.
2022 10 v.28;No.146 [Abstract][OnlineView][HTML全文][Download 28607K] - LI Weijie;XIE Mengqian;TU Yaojie;WISfur Thermal Technology Co., Ltd.;School of Materials and Metellugy,Wuhan University of Science and Technology;School of Energy and Power Engineering,Huazhong University of Science and Technology;
To understand the heat transfer behavior and mechanisms inside furnaces under MILD combustion, the conjugate heat transfer(CHT) model was established for a 20 kW MILD combustion furnace firing methane, and CFD modeling by integrating combustion, fluid and heat transfer was conducted. By comparing the predicting results against experimental measurement in terms of temperature and gas species, the reliability of the numerical models was verified. The results show that the original Okafor chemical reaction mechanism can accurately predict the temperature, O_2 and CO distributions inside the MILD combustion furnace, but overestimate the NO emission. However, the NO prediction can be improved by optimize the N-related elementary reactions in the original Okafor mechanism. By comparing the temperature and heat flux density distribution on different wall regions before and after coupling with CHT model, it is found that the flue gas absorbs heat from the furnace front wall, which disagrees with the actual condition, demonstrating the higher prediction accuracy of CHT model on describing the heat transfer behavior inside furnaces. Based on the coupled CHT model, the difference of heat transfer mechanisms between MILD combustion and traditional combustion was compared. It is found that the wall temperature is generally higher for traditional combustion than MILD combustion by 20-40 ℃ regardless of regions, resulting in a higher heat transfer amount of 0.018, 0.622 and 0.028 percentage points on front wall, side wall and back wall, respectively, in traditional combustion, together with 0.67% reduction of stack loss. By further examining the convection and radiation heat transfer on furnace walls, it is found that MILD combustion produces a higher radiation by 2.21 W and 24.62 W, but a reduction of convection by 3.93 W and 27.27 W on front wall and back wall, respectively. On furnace side wall, MILD combustion reduces the radiation heat transfer by 290.71 W and increases convection heat transfer by 231.63 W compared to conventional combustion. Overall, radiation accounts for 70.72% and 81.92% for MILD combustion and traditional combustion, respectively, while convection accounts for 29.28% and 18.08%, respectively. The reduction of radiation on side wall is the main reason for the decreased overall heat flux for MILD combustion, and the deeper reason comes from the lower combustion temperature under MILD combustion mode.
2022 10 v.28;No.146 [Abstract][OnlineView][HTML全文][Download 40928K] - LI Debo;QUE Zhengbin;MIAO Jianjie;CHEN Tuo;CHEN Zhihao;CHEN Zhaoli;FENG Yongxin;China Southern Grid Power Technology Co.,Ltd.;National Engineering Laboratory of Biomass Power Generation Equipment,North China Electric Power University;College of Power Engineering,North China Electric Power University;
Incineration treatment is the main disposal method of domestic sludge in my country. Mixing combustion with coal is one of the research hotspots, but it is less researched and applied in small-scale coal-fired units. Based on the 210 MW four-corner tangential-circle coal-fired unit of a domestic power plant, field tests of mixing domestic sludge for 8 working conditions were carried out, respectively, and the monitoring data and test results were compared and analyzed. The results show that ash content and the sulfur content increase gradually with the increase of sludge blending ratio, the calorific value of the fuel decreases gradually. For solid products, since the content of heavy metals in sludge is higher than that of coal, the content of heavy metals in fly ash, slag and desulfurized gypsum increase after mixed sludge combustion, and there is a risk of secondary pollution. The emission of conventional flue gas pollutants NO_x,SO_2 and dust is less affected by the mixed burning of sludge, and the existing flue gas purification process can meet the ultra-low emission requirements of coal-fired flue gas.After mixed burning of sludge, the concentration of heavy metals and their compounds and other pollutants increase by about 3.6 times at most. Under full load condition, when 10% sludge is mixed burning, the average mass concentration of dioxin is 0.021 ng/m~3(calculated by toxic equivalent concentration TEQ), but it still meets the relevant emission requirements. When 10% domestic sludge is mixed, the average temperature in the furnace only decrease by 15 ℃, and the decrease in thermal efficiency is less than 0.5%, the effect is not significant.
2022 10 v.28;No.146 [Abstract][OnlineView][HTML全文][Download 5040K] - XIE Bin;YANG Jianping;LENG Lijian;LI Hailong;School of Energy Science and Engineering,Central South University;
In order to clarify the causes and caking characteristics of steel rolling oil sludge in the rotary kiln, an evaluation method of ring formation characteristics in the rotary kiln of oxidation pellets was used to study the cohering behavior of steel rolling oil sludge under different working conditions.The physical composition and morphology of the crystalline ring products were characterized and tested by ash melting point, powder X-ray fluorescence spectroscopy XRF, powder X-ray diffraction spectroscopy(XRD), bulk scanning electron microscopy(SEM) and energy spectrum analyzer(EDS). The effects of roasting temperature and roasting time on the cohering properties of the rolled oil steel sludge on the refractory brick surface were investigated by using ring index and adhesion index as evaluation indexes. The results show that the ringing index and adhesion index of steel rolling oil sludge increase with the increase of roasting time and roasting temperature.The fastest growth rate is in the range of 1 150 ℃ to 1 250 ℃, which coincides with the dense distribution of the main ringing materials in the kiln, indirectly confirming the applicability of the method for evaluating the ringing behavior. The characterization results show that the mineral phase of the crystalline material has coarse grains, the uneven structure, more voids, the obvious distribution of individual grain crystals and the fused surface, and the low degree of crystallization of the whole.The ring-forming process of steel rolling oil sludge rotary kiln are mainly due to the solid-phase solidification reaction of Fe_2O_3, and the remaining small amount of impurities generate low melting point substances, which to a certain extent promote the migration of iron grains and intensify the ring-forming behavior.That is consistent with the XRD detection that the physical phase of the rings is mainly hematite, followed by iron oxides such as magnetite and low melting point substances.The deformation temperature and softening temperature of the rings in the gray melting point test are generally increasing, which further proves that the recrystallization of secondary Fe_2O_3 and generated Fe_3O_4 in the oxidizing environment makes the rings stronger and less fragile, thus causing the evolution of the ring to deteriorate.
2022 10 v.28;No.146 [Abstract][OnlineView][HTML全文][Download 19279K] - CHEN Yumin;LU Qiancheng;LEI Wentao;YUE Wenjing;ZHANG Bing;HUANG Wenjie;ZHAO Yongchun;ZHANG Junying;School of Low-Carbon Energy and Power Engineering,China University of Mining and Technology;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;
CO_2-CH_4 reforming by non-equilibrium plasma to syngas is an important emerging technology pathway to realize the resource utilization for the two greenhouse gases. The reaction pathway of CO_2-CH_4 reforming by non-thermal plasma in a dielectric barrier discharge(DBD) reactor at ambient temperature and pressure was thoroughly investigated by combing emission spectrometry analysis, reaction kinetics simulation and continuous mass spectrometry measurements. A maximum conversion of CH_4 and CO_2 of 25.8% and 9.6% respectively, can be achieved under a specific energy input(S_(EI)) of 52 J/cm~3. The continuous mass spectrometry online analysis of the stable gaseous products shows that C_2H_4 acts as a key intermediate in the formation of C_(2 )hydrocarbons. The higher the proportion of CH_4, the greater the generation of C_2 hydrocarbons, and it increases in the order of C_2H_6<C_2H_4<C_2H_2.·CH, ·C_2 radicals and characteristic spectral lines of CO and CO■ are detected in the emission spectrum. The relative intensity of ·CH decreases significantly with theincrease of specific power, and the relative intensity of CO■ changes little. The generation and consumption pathways of C_2 and C_3 products are analyzed by kinetic calculation, and it is found that 89.2% of C_2H_6 comes from the combination reactionCH_3+CH_3(+M) C_2H_6(+M), 78.9% of C_2H_4 is mainly formed byCH_4+CH C_2H_4+H and C_2H_3+H(+M) C_2H_4(+M) reaction, 61.1% of C_2H_2 is formed by electron collision reaction, and the formation of C_2 product follows the path: CH_4→C_2H_6→C_2H_4→C_2H_2. The reaction of electron collision dissociation ■ CO_2 is an important formation pathway of CO, while the reactionCH_3+CH_4 C_2H~+_5+H_2 and electron collision dissociation of CH_4 are the key generation pathway of H_2. Integration of emission spectroscopy and kinetic calculation provides a useful tool to uncover the reaction mechanism of plasma-enhanced CO_2-CH_4 reforming process.
2022 10 v.28;No.146 [Abstract][OnlineView][HTML全文][Download 48642K] - ZOU Renjie;LUO Guangqian;LYU Min;FANG Can;WANG Li;FU Biao;LI Zehua;LI Xian;YAO Hong;School of Energy and Power Engineering,Huazhong University of Science and Technology;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;
The clean and efficient utilization of coal is an important way to promote the low-carbon and green transformation of the energy structure of China. As one of the main pollutants duning coal combustion, heavy metals are harmful to human beings and the ecological environment. At present, the United States has begun to implement heavy metal emission standards for coal-fired power plants, and the emission compliance is realized mainly by coal washing to reduce the heavy metal inputs. The coal consumption amount of China is huge, with the high heavy metal content in some types of coal, and regional differences are large. It is urgent to develop heavy metal control technologies which meet China′s national conditions. Three typical heavy metals(arsenic, selenium and lead), which were highly volatile and highly toxic, were selected to summarize the current emission status and control technologies of heavy metal in coal-fired power plants at home and abroad. The ultra-low emission technology route of China has a synergistic control effect on heavy metals. Among them, selenium mostly exists in the gaseous form, and is mainly washed out in the wet flue gas desulfurization system. Arsenic and lead are mainly attached to the particulate matter, and the dust collector has synergistic capture effects for them. However there are still some bottlenecks such as poor mass transfer driving force for trace gaseous selenium and penetration of fine-particulate arsenic and lead, making it difficult to achieve stable and efficient capture of heavy metals. "Transformation and fixation" is the general idea of heavy metal control, that is, by chemical composition regulation and physical flow field optimization, to promote the transformation of heavy metals in flue gas from fine-particulate and gaseous form to coarse-particulate form, and from high toxicity form to low toxicity form, so as to realize the harmless treatment of heavy metals. Based on this idea, a series of whole-process control technologies for heavy metals in coal-fired power plants have been formed, which can be divided into three categories: pre-furnace, in-furnace, and post-furnace according to the action stage. The specific technologies include coal washing, coal blending, in-furnace adsorbents, agglomeration, internal component optimization, etc. The stabilization of heavy metals in coal-fired by-products(such as desulfurization gypsum and wastewater) requires additional attention. The release risk of heavy metals in by-products can be reduced by in-situ solidification of slurry or advanced wastewater treatment technologies. Some of the above heavy metal control technologies have been verified through pilot tests or the full-scaled unit experiments, which have a good application prospect. In order to further develop the coal-fired heavy metal control technologies and improve the level of heavy metal pollution governance, some prospects about the development of heavy metals control technologies were put forward: developing the online continuous detection technology of trace heavy metals in the actual coal-fired flue gas to realize the real-time acquisition of heavy metal concentrations in flue gas, analyzing the transformation behavior and kinetic characteristics of heavy metals under the multiple mechanisms, to clarify the detailed migration mechanism of heavy metals under complex flue gas conditions, establishing an evaluation system for coal-fired heavy metal control technologies, and providing targeted heavy metal solutions according to power plant characteristics, target, technology maturity, economy, environmental risks, etc.
2022 10 v.28;No.146 [Abstract][OnlineView][HTML全文][Download 10272K] - NI Peng;LIU Ting;MA Xiaotong;FENG Tai;LI Zishun;LI Yincui;DENG Shengnan;ZHANG Huawei;College of Mechanical and Electrical Engineering,Shandong University of Science and Technology;School of Environmental and Municipal Engineering,Qingdao University of Technology;
Trace elemental mercury in flue gas of coal burning is one of the main atmospheric mercury emission sources in China. How to achieve efficient removal of elemental mercury in flue gas of coal burning is the focus of attention and research in China. Previously, scholars have conducted in-depth studies on the effectiveness and reaction mechanism of existing devices for co-dehumidification, catalyst oxidation, plasma oxidation, photocatalytic oxidation, free radical oxidation and adsorbent in terms of different reaction components, reaction concentrations, reaction temperatures and reaction air velocities. However, the practical application of elemental mercury still faces many bottlenecks due to the obstacles of competition caused by the competition of flue gas components of SO_2 and H_2O for active sites, low adsorption capacity and secondary waste pollution. This study systematically introduced the different ways and characteristics of elemental mercury capture at present and focused on analyzing the influence of different experimental conditions on the application of catalysts and adsorbents in mercury removal. The progress of the present stage of mercury removal was summarized, including how to overcome the mercury removal toxicity of H_2O and SO_2, select the appropriate reaction temperature, obtain stable mercury removal compounds, explore safe and simple sample preparation methods, and realize the directional loading of functional groups at active sites. The results show that the loading of sulfur active sites can effectively resist the influence of SO_2 in flue gas. Methyl groups and specific structures can make the adsorbent have high hydrophobic characteristics. Suitable pore structure and adsorbents with certain layer spacing can improve the performance of mercury removal by overcoming the limitation of the mass transfer diffusion step. The actual conditions in flue gas, such as flow field and physical-chemical reactions, affect the time evolution and internal evolution of fluid mass transfer to deviate from the standard, and influence the practical application of the adsorbent. The experimental effect analysis, kinetic analysis model and density functional theory reflect the influence of the limiting factors of elemental mercury removal, migration path and the influence of external reaction parameters and internal structure. The analysis of the adsorption configuration and migration paths of gaseous singlet mercury on defective and intact surfaces, for example, can reveal the adsorption process of singlet mercury. In terms of separation and regeneration, the actual spray application of the existing adsorbents, the influencing factors and the regeneration mode of the adsorbents were compared. It is found that the introduction of metals or metal-like oxides can improve the separation problem of adsorbents and the regeneration effect and the high regeneration temperature are the problems faced in the regeneration process. The adsorbent is generally regenerated by heat treatment. The regeneration temperature of heat treatment is 300-500 ℃, and the regeneration time is generally 30-180 min, which can achieve high mercury removal efficiency. The regeneration is realized by supplementing the corresponding active sites and functional groups. Finally, the bottleneck, challenge and optimization direction of catalysts and adsorbents were prospected, which can provide reference for the industrial application of elemental mercury control.
2022 10 v.28;No.146 [Abstract][OnlineView][HTML全文][Download 27747K] - ZHU Xiaolei;YANG Jianping;LI Hailong;ZHAO Yongchun;ZHANG Junying;School of Energy Science and Engineering,Central South University;School of Energy and Power Engineering,Huazhong University of Science and Technology;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;
Coal combustion is one of the most significant anthropogenetic mercury emission sources. The massive discharge of mercury-containing desulfurization wastewater from coal-fired power plants poses a serious threat to human health and the ecological environment. It is urgent to develop efficient and economical mercury ion removal technology from desulfurization wastewater. The magnetic zeolite mercury adsorbent was prepared by extracting aluminum silicon minerals from fly ash, a byproduct of coal combustion. The magnetic zeolite mercury adsorbent was prepared by using the iron minerals in fly ash, in order to solve the problem that the adsorbent was difficult to separate from the waste water after mercury adsorption, resulting in the secondary release of mercury. The synthesized magnetic zeolite was characterized and analyzed by BET, XRD, TEM and other characterization methods. The effects of parameters such as solid-liquid ratio, initial pH of solution, and oscillation time on the adsorption of magnetic zeolite for mercury ions were systematically studied. The kinetics of adsorption of mercury ions on magnetic zeolites was studied. The results show that the synthesized magnetic zeolite has a spherical core-shell structure, and the magnetic core is evenly wrapped by the zeolite. The specific surface area of the magnetic zeolite is 4.46 m~2/g, the most probable pore size is 18.25 nm, which belongs to the mesoporous range. The magnetic zeolite exhibits magnetization hysteresis, its coercivity is about 10 000 A/m, and it can be separated from desulfurization wastewater by external magnetic field. The optimum adsorption con-ditions are as follows: the solid-liquid ratio is 5 g/L, the optimum initial pH is 5, and the shaking time is 90 min. Under these conditions, the removal rate of Hg~(2+) reaches 92%. The kinetic study results show that the pseudo-first-order kinetic model can more accurately describe the variation of Hg~(2+) adsorption capacity with time, and the fitted equilibrium adsorption capacity is 23.24 mg/g, which is better than that of commercial activated carbon mercury adsorbents. Magnetic zeolite has good removal for mercury ions in desulfurization wastewater, which provides a new idea for the refined utilization of coal-fired fly ash.
2022 10 v.28;No.146 [Abstract][OnlineView][HTML全文][Download 14347K] - ZHANG Cheng;LI Junchen;FANG Dingli;TAN Peng;MA Lun;FANG Qingyan;CHEN Gang;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;
Selective catalytic reduction technology is a mature and reliable denitrification technology, which is widely used in the removal of fixed source nitrogen oxides. The temperature window of commercial vanadium-titanium catalysts is narrow and high. In order to meet the denitration requirements of lower temperature windows in the non-power industries, low-temperature NH_3-SCR has received extensive attention. In recent years, manganese-based catalysts have been regarded as the most promising low-temperature SCR catalysts due to their good low-temperature activity. The performance research of different kinds of manganese-based catalysts and the mechanism of anti-sulfur, water-resistance, alkali/alkaline-earth metal(K, Na, Ca, Mg) and heavy metal poisoning(As, Zn, Pb) on manganese-based catalysts was discussed in detail. Different anti-poisoning studies and modification methods were analyzed and summarized. The conclusions are listed as follows:(1) The best preparation method of traditional unsupported Mn-based catalysts is co-precipitation method, and the denitration efficiency is up to 100%. Microbial treatment method is a new green synthesis method, with high economic and environmental protection, which provides a feasible way for green synthesis of Mn-based catalysts.(2) Doping elements such as Ce, Fe, Cu, Ni, Ho, Nd, Zr, Co, and Eu can effectively improve the denitration activity and anti-poisoning performance of Mn-based catalysts. They can be considered as "shell" materials of "core-shell" structure to improve the anti-poisoning performance of Mn-based catalysts.(3) Molecular sieve with specific pore size is an ideal material to solve the catalyst sulfur poisoning, but the problem of mass transfer resistance has not yet been solved, and the preparation method and process of molecular sieve need to be further optimized.(4) The anti-alkali metal poisoning of Mn-based catalysts is focused on doping modification. The modification strategies are divided into two categories: one is to increase the acid sites of alkali resistance on the surface of catalysts, the other is to directly inhibit the influence of alkali metals on the active components of Mn. At present, the defects of the above two modification strategies are that the modified catalyst is not economical in long-term operation of denitrification, so it is necessary to fundamentally eliminate the contact between the catalyst and alkali metals.(5) There are few studies on Mn-based catalysts′resistance to heavy metal poisoning. It is suggested to carry out research on the migration and transformation of heavy metals in low-temperature section and the mechanism of resistance to heavy metal poisoning by modification of Mn-based catalysts.(6) The poisoned catalyst is harmful to the environment, and the research on the environmental hazard assessment and renewable utilization of the poisoned catalyst also needs to be further promoted.(7) The synergistic effects between different types of poisoning of Mn catalysts remains to be studied tomeet the practical application requirements of Mn based catalysts.
2022 10 v.28;No.146 [Abstract][OnlineView][HTML全文][Download 96520K] - ZHONG Yuxiu;YIN Zijun;SU Sheng;QING Mengxia;XIE Yuxian;LIU Tao;SONG Yawei;XU Kai;WANG Yi;HU Song;XIANG Jun;State Key Laboratory of Coal Combustion,Huazhong University of Science & Technology;School of Energy and Power Engineering,Changsha University of Science & Technology;
A series of WO_3/TiO_2 catalysts with different W loading were prepared by impregnation method, and the effects of W loading, temperature and SO_2 concentration on the SO_2 oxidation process on the catalysts were investigated. The results show that the SO_2 oxidation rate on the catalyst surface increases with the increase of W loading and temperature. The SO_2 oxidation rate increases from 0.034% to 0.210% when the W loading is increased from 1% to 7%, and the SO_2 oxidation rate increases from 0.043% to 0.240% when the temperature is increased from 280 ℃ to 400 ℃. N_2 adsorption, X-ray diffraction(XRD), Raman analysis(Raman), NH_3 programmed temperature(NH_3-TPD), H_2 programmed temperature(H_2-TPD), X-ray photoelectron spectroscopy(XPS) were used to characterize catalyst properties. The results illustrate that the increase of W leads to the increase of WO_x, which can weaken the strength of Br?nsted acid site and enhance the adsorption of SO_2. The oxygen(O_α) adsorbed on the catalyst increases considerably upon the content of W loading, which is not beneficial to reducing the oxidation of SO_2. The in-situ FTIR results of 5% W loading show that SO_2 will react with the W—O—W structure and be oxidized to HSO~-_4, and W~(6+) will be reduced to W~(5+) after the introduction of SO_2. During the reaction, O_2 does not directly oxidize SO_2, but reacts with intermediate products to regenerate W—O—W, which makes W~(5+) oxidized to W~(6+) again.In addition, O_2 promotes the conversion of HSO~-_4 to adsorbed SO_3, while promoting the desorption of SO_3 on the catalyst surface.
2022 10 v.28;No.146 [Abstract][OnlineView][HTML全文][Download 23708K] - FU Biao;YAO Hong;LUO Guangqian;LI Xian;ZOU Renjie;HOWER James C;ZHANG Wencai;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;University of Kentucky Center for Applied Energy Research;Department of Mining and Minerals Engineering,Virginia Polytechnic Institute and State University;
Coal and coal ash have been regarded as important alternative sources for REEs(Rare earth elements). Compared with coal, the combustion of coal can enrich REEs in coal ash and thus the recovery of REEs from coal ash is a hot issue in both domestic and foreign research institutes. Efficient extraction of REEs from coal ash must understand the speciation of REEs in coal ash, the distribution and enrichment trends in coal ash, and develop novel technologies for REEs extraction and separation from coal ash. Accordingly, to provide knowledge base and insights into these issues, this review summarized the speciation of REEs in coal and coal ash. REEs in coal mainly exists as inorganic mineral forms, including but not limited to REEs phosphates, REEs carbonates, silicates, adsorbed to clay minerals. Detailed REEs speciation in coal relied on the sediments sources of the coal basin, sedimentary environment, epigenetic igneous activities, and the circulating of hydrothermal solutions in the coal seams. Compared with coal, REEs in coal ash is different with regard to their different chemical states and structure and physical associations such as particle size and encapsulation in aluminosilicate glass. Then, the combustion behavior of REEs including thermal composition, fragmentation, oxidation, sintering, and mineral-mineral chemical reactions were discussed. After coal combustion, REEs in the flue gas may react with acid gas to form REEs sulfates or chlorides. The distribution and enrichment of REEs in coal-fired power plants were summarized. REEs mainly transported to coal fly ash during coal combustion, where no significant variations can be observed among different hopper ashes. Based on these results, two mechanisms were proposed to elucidate the capture processes of REEs in coal fly ash in the high-temperature combustion process and flue gas cooling process. Current REEs recovery methods from coal ash were reviewed and they can be classified as physical beneficiation and hydrometallurgical extraction. Future work should focus on developing new methods for measuring the micro-structure of REEs and quantifying the REEs species in coal ash, understanding the relationship of coal combustion conditions-REEs speciation in ash-REEs extractability from coal ash, designing high-efficient leaching methods and green reagents for extraction and separation of REEs from coal ash, co-extraction of other critical metals from coal ash, and comprehensive disposal and utilization of the extraction ash residue.
2022 10 v.28;No.146 [Abstract][OnlineView][HTML全文][Download 17976K] - ZHANG Yili;GAO Tian;XIAO Rihong;XIONG Zhuo;ZHAO Yongchun;ZHANG Junying;School of Energy and Power Engineering,Xi′an Jiaotong University;State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology;
Photocatalytic oxidation technology, as a green and environment-friendly new mercury removal technology, has broad application prospects. At present, most of the photocatalysis reactor systems use powdered catalyst, which has poor utilization of light source in the photocatalysis process, is not easy to recover, and has limited prospects for industrial application. Therefore, a new type of slot plate photocatalytic reactor was designed, which had the advantages of good light reception, wear resistance, long service life, small size. The mercury oxidation experiment was carried out with plate catalyst, and the catalyst was characterized in detail. Compared with the conventional fixed bed reactor system, the mercury oxidation efficiency of the slotted plate TiO_2(VTi_B) is increased from 64.8% to 86.0% under the UV light intensity of 80 mW/cm~2. The mercury oxidation efficiency of the catalyst decreases with the increase of reaction temperature and increases with the increase of UV light intensity. In the plate catalytic system, the photocatalytic mercury oxidation performance of the Ce doped TiO_2(Ce-VTi_B) catalyst increases significantly, and the efficiency of 1.0% Ce-VTi_B is the highest, reaching 92.4%. There are two main reasons. On the one hand, Ce doping can effectively reduce the band gap energy of the catalyst. Compared with VTi_B catalyst, the band gap energy of 1.0% Ce-VTi_B catalyst decreases by 0.68 eV, so that the absorption ability of the catalyst to ultraviolet light is enhanced. Under ultraviolet irradiation, the surface of Ce-VTi_B catalyst particles is excited to generate ·OH active radicals, which oxidize Hg~0 to Hg~(2+). On the other hand, some Ce atoms can combine with electrons to reduce the recombination of e~-/h~+.
2022 10 v.28;No.146 [Abstract][OnlineView][HTML全文][Download 30286K] - WANG Pingping;ZHAO Yongchun;ZHANG Junying;XIONG Zhuo;State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology;
Carbon measurement is the cornerstone of the stable development of the carbon trading market and the data basis for the country to formulate carbon emission reduction policies. Coal fired power plants are one of the largest sources of carbon emissions in China. It is of great significance for the achievement of China′s dual carbon goal to accurately quantify the carbon emissions of coal-fired power plants. Firstly, carbon accounting standards and policies at home and abroad were introduced. Developed countries have initially formed carbon emission measurement system. Thermal power in the United States mainly uses the measure method to calculate carbon emissions. The United States has written technical standards and specifications into regulations. Coal fired units above 25 MW must use the measure method and submit a mandatory greenhouse gas report. The current carbon measurement in EU adopts both accounting method and measure method. Power plants are divided into different tiers according to carbon emissions, and different tiers have different uncertainty requirements. At the same time, the EU carbon trading market has developed rapidly, which providing a reference for the construction of carbon trading markets in other countries. Compared with developed countries, our country still lacks the complete carbon accounting system. The measure method is in the initial stage of development. At present, China lacks carbon emission database and carbon measurement standards need to be improved. Secondly, The development status of emission factor method, material balance algorithm, measure method, life cycle method and model method for carbon measurement in coal-fired power plants were introduced respectively. The advantages, disadvantages and scope of application were summarized. The calculation process of emission factor method is simple and has the widest application range. However, the calculation error of carbon emissions in China is large, if the default values of emission factors in IPCC guidelines are used. The material balance algorithm uses carbon balance to calculate the carbon emissions of coal-fired power plants. It has many intermediate processes and requires complete data to obtain accurate carbon emissions. The measure method is different from other calculation methods, which can directly measure the flue gas flow and CO_2 concentration in the flue gas. It is developing rapidly under the promotion of China′s policies. The life cycle method can add carbon emissions in the upstream and downstream of the power production stage, so it can expand the accounting boundary. The model method can directly predict carbon emissions or element carbon content, which makes up for the lack of key accounting data. The research status of accounting method and measure method was compared. The error source of the accounting method is mainly the selection and measurement of emission factors and net calorific value. The error source of the measure method is mainly the measurement of flue gas flow and CO_2 concentration. The latter generally has higher accuracy. Finally, the future research directions such as the development of carbon trading market, the exploration of uncertain sources, and the formulation of carbon emission policies and regulations were prospected, with a view to providing reference for the formulation of carbon emission measurement method system of coal-fired power plants with Chinese characteristics.
2022 10 v.28;No.146 [Abstract][OnlineView][HTML全文][Download 14525K] - YAN Xianyao;YU Shuihua;CHU Huaqiang;School of Energy and Environment,Anhui University of Technology;
The CO_2 produced by the large-scale combustion of coal aggravates the global warming and greenhouse effect. The sorption-enhanced steam gasification of coal using CaO-based materials could realize CO_2 capture and H_2 production simultaneously, which has a good industrial application prospect. On the basis of recent advances of sorption-enhanced steam gasification of coal using CaO-based materials, the system procedure of this technology was described. The reaction characteristics and activity reduction mechanism of calcium based materials for CO_2 capture and enhanced hydrogen production in the system were reviewed. The methods to improve the cycling stability, CO_2 capture and catalytic hydrogen production of calcium based materials were summarized. Migration pathways of alkali metal and other trace elements during steam gasification of coal using CaO-based materials were analyzed. The effects of trace elements on CO_2 capture and enhanced H_2 production of CaO-based materials were reviewed. The energy and economic analysis of this system based on kinetic calculations were described. The coupling of calcium based materials enhanced coal gasification hydrogen production system and other renewable energy systems and its influence on hydrogen production characteristics were summarized. In view of the research progress and potential challenge of sorption-enhanced steam gasification of coal using Ca-based materials, the possible research directions in the future were prospected. It is believed that screening additives can improve the reaction of calcium based materials in many aspects, and adopting decoupling gasification and coal/biomass co-gasification technology can achieve higher hydrogen production and gasification conversion. It is of great significance to study the migration of trace elements in coal and the coupling with other renewable energy systems for the development of this technology.
2022 10 v.28;No.146 [Abstract][OnlineView][HTML全文][Download 11450K] - KUANG Shengduo;CHEN Wei;LIN Wensheng;WANG Ao;LIU Shengyan;TIAN Chong;School of Power and Mechanical Engineering,Wuhan University;
Under the background of carbon neutral, the development and application of CO_2 capture and storage technology is urgent. Ca-based adsorbents are good carbon capture adsorbents with strong CO_2 capture ability and high adsorption capacity, however, their recycling performance needs to be improved. In order to improve the cycling performance of Ca-based adsorbents, magnesium/yttrium(Mg/Y) modified Ca-based adsorbents were prepared by sol-gel self-propagating combustion method, characterized by XRD and SEM characterization, investigated the thermogravimetric analyzer and fixed bed cycle adsorption experiment under the high temperature of 700 ℃. The adsorption performance and cycle stability of modified Ca-based sorbents were researched. The results show that among the Mg-doped Ca-based adsorbents, when the mass ratio of Ca to Mg is 8∶2, the adsorbent has the best performance, and the adsorption capacity of CO_2 in the first cycle is up to 0.60 g/g(based on adsorbent). It decays to 0.49 g/g after 15 cycles, which is better than that of the undoped Ca-based adsorbents. Studies on Mg and Y-doped Ca-based sorbents show that the initial adsorption capacity of Ca/Mg sorbents is higher than that of Ca/Y sorbents, but the cycling performance of Ca/Y sorbents is significantly improved. The adsorption and cycling properties of Ca-based adsorbents modified by double doping(Ca/Mg/Y) and single doping(Ca/Mg, Ca/Y) were compared while the mass fraction of CaO in the adsorbent was maintained at 80%. The results show that Ca/Mg adsorbent has the highest initial adsorption capacity of 0.60 g/g, which decays to about 0.54 g/g after 5 cycles and 0.49 g/g after 15 cycles. The adsorption capacity of Ca/Y adsorbent maintains at about 0.52-0.58 g/g within 15 cycles. The adsorption capacity of Ca/Mg/Y adsorbent increases from 0.50 g/g to about 0.56 g/g for 5 cycles, and the adsorption capacity increases significantly with the increase of cycles. The cycling performance of Ca-based adsorbent is improved after doping, and the effect of Y is better than Mg.
2022 10 v.28;No.146 [Abstract][OnlineView][HTML全文][Download 18625K] - YU Zetao;ZENG Guanghua;ZHOU Yabin;TAN Peng;ZHANG Cheng;School of Energy and Power Engineering,Huazhong University of Science and Technology;State Key laboratory of Coal Combustion,Huazhong University of Science and Technology;
Porous carbon has shown excellent performance in CO_2 adsorption which is one of the important methods for CO_2 capture and storage. It is important to achieve the goal of "peak carbon dioxide emissions" and "carbon neutrality". Taking three typical traditional Chinese medicine solid wastes that isatis root residue, licorice residue and Caulis Spatholobi residue as examples, the preparation of porous carbon from traditional Chinese medicine solid waste by nitrogen doped hydrothermal carbonization chemical activation two-step method was explored, as well as its CO_2 adsorption performance. Hydrothermal method eliminates the pre drying of traditional Chinese medicine solid waste and adapts to the characteristics of high moisture content of traditional Chinese medicine solid waste. KOH was used as activator in chemical activation method, and it was activated under high temperature environment(experimental temperature is 600, 700 and 800 ℃). Urea was used as surface modifier in the preparation process, and N was doped on the surface of porous carbon to improve the adsorption performance. In order to explore whether N is doped on the surface of porous carbon, hydrothermal carbon and porous carbon were tested by elemental analysis and XPS. The results show that N has been successfully doped on the surface of porous carbon. Through the analysis of the experimental results, nitrogen doped porous carbon shows richer pore structure and better adsorption performance under the same preparation conditions, which means that nitrogen-containing functional groups have a positive effect on the adsorption performance of porous carbon. In order to compare the adsorption properties of porous carbon prepared at different activation temperatures, its CO_2 adsorption capacity was studied. Langmuir and Freundlich models were used to fit the CO_2 adsorption isotherm. The results show that compared with 700 and 800 ℃, the porous carbon activated at 600 ℃ has better CO_2 adsorption performance due to the loss of N caused by high temperature activation, which has an adverse effect on the adsorption performance. In general, the porous carbon obtained has rich pore structure, and the specific surface areas of the porous carbon prepared from the three raw materials are 2 516, 2 518 and 1 996 m~2/g, respectively. At the activation temperature of 600 ℃, the porous carbon prepared from the three raw materials shows good CO_2 adsorption capacity, which are 6.70, 6.52 and 6.43 mmol/g, respectively. It means that the effect of hydrothermal simultaneous nitrogen doping and chemical activation on the CO_2 adsorption capacity of the prepared porous carbon can be reduced, but the raw materials still have a great impact on the CO_2/N_2 selectivity.
2022 10 v.28;No.146 [Abstract][OnlineView][HTML全文][Download 19431K] 下载本期数据