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Study on the separation characteristics of MgO-based selective adsorbents for Hg0 and HgCl_2
SHANG Yu;LI Haiyang;CHEN Yingying;WAN Zhaoxin;TONG Jiangyi;DUAN Yufeng;[Objective] Selective adsorption of elemental mercury(Hg0) and oxidized mercury(Hg2+) is one of the key technologies in continuous mercury emission monitoring systems(Hg-CEMS). Magnesium oxide(MgO) is a commonly used adsorbent; however, its application is limited due to its relatively low surface area, short service life, and unclear interaction mechanisms with flue gas components. In order to solve the limitations of adsorbents in application and improve the removal efficiency of Hg0, it is necessary to conduct in-depth research on MgO-based adsorbents.[Methods] In this study, MgO was supported on porous γ-Al_2O3 via a sol-gel method to enhance its adsorption performance for HgCl2. Experimental investigations and various characterization techniques were employed to elucidate the competitive reaction mechanisms between flue gas components and HgCl2 on the surface of Mg-based adsorbents. [Results] The results show that the best precursor is magnesium oxalate, and the optimal loading ratio is achieved when the molar ratio of MgO to carrier is 1.5∶1.0. Compared with the original MgO, the specific surface area of the loaded adsorbent increased from 14.54 m2/g to 143.15 m2/g, and the penetration rate of HgCl2 decreased from 36.2% to 2.78%. After adding 500 μL/L NO and 12% O2 separately, the corresponding penetration rates of HgCl2 were 4.20% and 2.77%, respectively.These non-acid gases will not interfere with the selective adsorption performance of the adsorbent for Hg0 and HgCl2. However, when 50 μL/L HCl, 200 μL/L SO2 and 16% CO2 were added separately, the corresponding penetration rates of HgCl2 decreased to 13.50%, 26.07% and 6.56%, respectively. This is due to the competitive adsorption of acidic gases and HgCl2 on the surface of the adsorbent, which consumes alkaline active sites, blocks the pores of the adsorbent, and inhibits the capture of HgCl2 by the adsorbent. [Conclusion] These findings provide theoretical guidance for the industrial application of MgO-based selective adsorbents.
Optimization design of spray humidification system for indirect air cooling tower based on multi-objective genetic algorithm
CHEN Yang;WANG Lei;ZHANG Xin;SHI Pengfei;ZHANG Huafeng;ZHANG Li;HU Yahui;YOU Qin;[Objective] In order to enhance the heat transfer effect of indirect cooling tower in high temperature environment in summer and reduce the consumption of water resources, the optimization design of spray humidification system was carried out. [Methods] In this paper, the cooling tower is taken as the research object, and the fan-shaped calculation area of the cooling tower is established. The standard response surface method of the full second-order polynomial is used to create the response surface model. The influence of nozzle single factor(flow rate, pressure and opening angle) on heat transfer and residual water flow is analyzed. The multi-objective genetic algorithm(MOGA) is used to optimize the multi-parameter of the nozzle at different ambient temperatures with the maximum heat transfer and residual water flow as the target. [Results] The results show that the nozzle flow rate is the most important factor affecting the heat transfer, and increasing the nozzle flow rate can significantly improve the heat transfer effect. When the nozzle flow rate increased from 1 g/s to 15 g/s, the heat transfer increased from 1 607.49 kW to 1 742.53 kW, an increase of 8.4%. The influence of nozzle opening angle and nozzle pressure on the residual water flow is much greater than that on the heat transfer. When the nozzle opening angle increases from 15° to 67.5°, the residual water flow decreases from 2.3 g/s to 1.2 g/s, with a decrease of 46%. When the nozzle pressure increases from 0.5 MPa to 15 MPa, the residual water flow increases from 0.19 g/s to 2.5 g/s, with an increase of 1 175.6%. After MOGA optimization, when the ambient temperature is 20, 25, 30, 35 ℃, the heat transfer per unit nozzle flow at the optimal operating point is 2 053.83, 1 856.55, 1 605.38 and 1 499.94 kJ/kg, respectively, and decreases with the increase of temperature. [Conclusion] This study provides theoretical support and engineering optimization scheme for the efficient operation of indirect air cooling system under high temperature environment in summer.
Research on the preparation of porous carbon by pyrolysis of biomass molten salt and its application in mercury removal from flue gas
TONG Haoyu;LIU Jun;ZHANG Bingduo;LIU Hangyu;LIU Bingxu;YANG Jianping;[Objective] Coal-fired power plants are one of the largest mercury emission sources. The development of carbon-based mercury adsorbents by using low-cost biomass materials with high carbon content has become a research hotspot. [Methods] This study utilizes molten salt pyrolysis to realize one-step carbonization and activation of wood chips to produce porous carbon materials. Scanning electron microscopy, Bruneian-EmmettTeller and X-ray photoelectron spectroscopy(XPS) was adopted to determine the microstructure and surface chemistry of as-prepared porous carbon. Programmed temperature desorption experiment was conducted to identify the mercury adsorption products, and the involved mechanism for Hg0 adsorption on porous carbon was excluded. The pyrolysis process was simulated by Aspen Plus to provide basis results for building molten salten pyrolysis technology.[Results] Molten salt porous carbon has a macroporous-mesoporous-microporous skeleton, and its surface has abundant oxygen-containing functional groups, showing good mercury removal performance in the temperature range of 50-150 ℃. The addition of Fe(NO3)3 in LiCl-KCl molten salt system can significantly improve the mercury removal performance of porous carbon, and the mercury removal efficiency is more than 90%. The abundant C== O groups on the surface of porous carbon oxidize gaseous Hg0 and further convert it into organically bound mercury(Hg-OM), while C== O is reduced to C—O. The molten salt can be recycled more than three times, and the porous carbon prepared after the cycle still maintains high mercury removal performance. Aspen Plus simulation shows that the carbon yield of sawdust pyrolysis at 700 ℃ is about 31%, which is consistent with the experimental results. [Conclusion] An one-step pyrolysis and activation strategy within molten salt system was developed to prepare porous carbon, which exhibited superior mercury adsorption performance from coal-fired flue gases. This work provided a new idea for mercury abatement from coal-fired power plants.
Study on transport mechanisms of heavy metal lead in silica nanopores
WANG Mingjun;SHEN Ao;HU Haitao;[Objective]A thorough understanding of the diffusion and adsorption behaviors of lead(Pb) in nanopores is crucial for elucidating the transport mechanisms of gaseous lead in complex porous structures and developing efficient lead adsorbents. [Methods]In this study, an amorphous silica-based nanopore model was constructed, and the LennardJones(LJ) force field parameters for PbO were fitted using first-principles calculations. A self-developed Monte Carlo algorithm was employed to establish the radial force field of gaseous lead molecules within silica nanopores. Furthermore, Oscillator diffusion theory and adsorption equilibrium models were applied to investigate the effects of temperature, pore size, and molecular properties on fluid diffusivity and adsorption equilibrium constants. [Results]The results indicate that the diffusion coefficient of gaseous lead increases significantly with pore size, with molecule Pb exhibiting higher diffusivity than PbO due to its lower molecular mass and weaker fluid-solid interaction potential. The adsorption equilibrium constant decreases with increasing pore size, showing pronounced adsorption effects in sub-1 nm pores but rapidly approaching unity in larger pores. Elevated temperatures enhance lead diffusion but suppress adsorption. The transport coefficient of gaseous lead increases with both pore size and temperature, exhibiting a quadratic dependence on pore size, leading to a more pronounced enhancement in larger pores. However, under lowtemperature and small-pore conditions, adsorption dominates, causing the transport coefficient to decrease with increasing pore size and temperature. [Conclusion]This study quantitatively elucidates the transport mechanisms of gaseous lead in complex nanoporous structures, providing a theoretical foundation for controlling heavy metal emissions in coal-fired flue gas and designing high-performance adsorbents.
Numerical simulation study on the synergistic control of steam temperature increasement and NOx emissions in a 600 MW pulverized coal boiler
YAN Jin;WU Xuyang;XU Yiming;WANG Shuyuan;XIANG Xin;MAO Xucheng;WANG Yuchong;WANG Ziyuan;[Objective]To address the issues of low main/reheat steam temperatures at high load and excessive NOx emissions at low load in a 600 MW pulverized coal boiler,a comprehensive retrofit solution is proposed.[Methods]The solution includes staged coal feeding,burner modifications,combustion air optimization,and additional reburn air.A 3D numerical model was developed using Fluent,and simulations were conducted to evaluate the effectiveness in improving steam temperature,combustion stability,and pollutant control.[Results]After retrofit,steam temperatures increased by 10-15℃，stabilizing at 540±10°C under full load.The NOx emission was reduced by 30%to 200±20 mg/m3，and CO concentration decreased by 40%-50%.Additionally,NOx concentration dropped to 154 mg/m~3during loadfollowing,and combustion stability extended to 260 MW.[Conclusion]The proposed solution improves load-following flexibility and environmental performance without modifying heating surfaces,providing technical support for efficient,low-carbon operation of coal-fired boilers.
Effects and reaction mechanism study of element doping on the wide-temperature denitrification performance and sulfur resistance of VW/Ti-based catalysts
DU Changfei;ZHANG Boya;CHENG Jiebing;LIU Yuan;WU Lingzhi;SHEN Kai;ZHANG Yaping;[Objective]Under the increasing demand for deep peak regulation and flexible operation of coal-fired units, to address the decline in catalyst activity of conventional V_2O5-WO3/TiO2(VW/Ti)-based selective catalytic reduction(SCR) catalysts caused by reduced flue gas temperature at low loads. [Methods]In this study, efforts were devoted to improving the wide-temperature denitrification performance and sulfur resistance of SCR catalysts. Different transition metal elements were introduced via an impregnation method to modify the catalysts, and the effects of dopant species and doping ratios on catalytic performance were systematically investigated. Structural properties, surface acidity, redox behavior, and reaction mechanisms were comprehensively analyzed using multiple characterization techniques. [Results]The results showed that Nb, Sb, Ce and Nd doped catalysts exhibit significantly enhanced low-temperature DeNOx activity in the range of 160-240 ℃, with Ce doping showing the most pronounced improvement,while doping with Ho and Sm leads to a decline in performance. The effective denitrification temperature window of the V2 O5-WO3-5 CeO2/TiO2(VW5 Ce/Ti) catalyst was broadened to 220-400 ℃, indicating improved adaptability to deep peak shaving operation conditions. Under simulated flue gas conditions containing H_2O and SO2, the VW5 Ce/Ti catalyst exhibited a markedly lower activity decay than the undoped VW/Ti catalyst, demonstrating superior resistance to water vapor and sulfur poisoning. Characterization results obtained from X-ray diffraction, brunauer-emmett-teller, hydrogen temperatureprogrammed reduction, ammonia temperature-programmed desorption, and in situ diffuse reflectance infrared fourier transform spectroscopy(DRIFTS) indicate that Ce doping does not significantly alter the crystalline structure of the TiO2 support but increases the number of surface acidic sites and enhances the redox capability of the catalyst, thereby facilitating the adsorption and reaction of NH3 and NOx species. Furthermore, in situ DRIFTS analysis confirmed that both Lewis and Brønsted acid sites coexist on the surface of the VW5 Ce/Ti catalyst, and the SCR reaction follows a combination of Langmuir-Hinshelwood and Eley-Rideal mechanisms. [Conclusion]Ce doping is demonstrated to be an effective approach for enhancing the wide-temperature denitrification performance and sulfur resistance of VW/Ti based SCR catalysts. The study provide theoretical support for catalyst design and engineering applications under deep peak shaving and ultra-low emission conditions.
Effect of different preparation methods on the performance of manganese-based catalysts for NO and toluene removal
HUANG Shuo;CHU Xinyue;ZHANG Yaoyu;SHENG Zhongyi;YANG Liu;[Objective]To achieve the synergistic control of nitrogen oxides(NOx) and volatile organic compounds(VOCs) in flue gas from the thermal power industry, screen high-performance catalysts, and investigate the influence of different preparation methods on their performance. [Methods]Here, Ce-and Mn-loaded TiO2 catalysts for concurrent NO and toluene(PhCH3) removal were prepared by sol-gel, hydrothermal, co-precipitation and impregnation routes, and their performance was evaluated between 200 ℃ and 450 ℃. The effects of different preparation methods on the physicochemical properties of the catalysts were analyzed using characterization techniques such as scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, ammonia temperature-programmed desorption, and hydrogen temperature-programmed reduction.[Results] The results indicate that the standalone DeNOx activity of the four catalysts follows the order: MnCe/Ti(S) > MnCe/Ti(H) > MnCe/Ti(I) > MnCe/Ti(C),the NO conversion rates of both MnCe/Ti(S) and MnCe/Ti(H) catalysts remained above 90% within the test range, whereas MnCe/Ti(I) and MnCe/Ti(C) catalysts failed to reach 90% even at 300 ℃. At a reaction temperature of 200 ℃, the MnCe/Ti(S) catalyst achieved a 97.6% removal rate for NO. At 250 ℃, the catalyst demonstrated an 80% removal rate for toluene. When the temperature is between 250 and 350 ℃, Mn Ce/Ti(S) exhibited the most effective removal performance for both pollutants. Compared to MnCe/Ti catalysts prepared by the other three methods, the Mn Ce/Ti(S) catalyst exhibited more uniform surface particles and superior elemental dispersion. Furthermore, the Mn3+ concentration in MnCe/Ti(S) catalysts, which is beneficial for NO oxidation, accounted for 83.98%, significantly higher than that in MnCe/Ti(H) and other catalysts. Additionally, MnCe/Ti(S) catalysts exhibited markedly higher acid content and acid strength, along with superior low-temperature De NOx performance. [Conclusion]The work provides an efficient catalyst option for simultaneous NOx and VOCs abatement in power-plant and steel-industry flue gases and offers theoretical guidance for optimising Mn-based catalyst synthesis.
Study on the heavy metal poisoning characteristics of VWTi catalyst
LI Kunpeng;YAO Zhanpeng;HUANG Hexiao;ZHANG Yaoyu;SHENG Zhongyi;YANG Liu;HUANG Shuo;CHENG Fangmei;[Objective] To address the heavy metal poisoning issue of the vanadium-tungsten-titanium denitration catalyst V_2O5-WO3/TiO2(VWTi) in the flue gas from co-combustion of sewage sludge in coal-fired power plants, thereby improving the denitration efficiency during sludge co-combustion. [Methods] This study systematically evaluates the individual poisoning effects of six typical heavy metals—Pb, Cr, Hg, Cd, As, and Zn—present in flue gas on commercial VWTi denitration catalysts. Using Pb, the most toxic among them, as a representative, the influence of poisoning severity on catalyst activity, operating temperature window, and byproduct N_2O selectivity was elucidated. Poisoned samples with varying Pb/V molar ratios(0～2.0) were prepared via impregnation-calcination. Multi-scale characterization techniques, including brunauer-emmett-teller, X-ray diffraction, X-ray photoelectron spectroscopy, hydrogen temperatureprogrammed reduction and ammonia temperature-programmed desorption. [Results] The results indicated that in terms of NOx conversion rate,the toxicity ranking of heavy metals was Pb>Zn>As>Hg>Cd>Cr; among them, Pb poisoning has a significant effect on the NOx conversion rate of the catalyst, although Cr had a minimal impact on NOx conversion, it significantly increased N_2O emissions. Performance assessment demonstrated that at Pb/V=1.5, NOx conversion dropped from >90%(fresh catalyst) to <50%, the active temperature shifts from 240 ℃ to 120 ℃, narrowing by 120 ℃. At Pb/V=2.0, the catalyst was nearly deactivated at high temperatures, yet N_2O generation decreased by 40%, enhancing N2 selectivity. The characterization analysis results showed that Pb is highly dispersed on the TiO2 surface in the form of PbO revealed that PbO species are highly dispersed on the TiO2 surface, preferentially reacting with VOx active sites to form V4+-O-Pb. This reaction reduced the V5+ proportion from 66.1% to 25.1% and decreased chemisorbed oxygen(O_α) proportion from 27.3% to 18.6%, accompanied by a significant loss of both Brønsted and Lewis acid sites,the reduction peak temperature shifting toward higher temperature by more than 50 ℃, this may lead to a sharp decrease in NOx conversion activity. [Conclusion]This study provides quantitative support for the synergistic control of heavy metals and NOx in the co-combustion of sludge.
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Introduction
Electric Power Technology and Environmental Protection
Bimonthly issued
CN 32-1808/X
ISSN 1674-8069
Governed by:
China Energy Investment Group Co., Ltd.
Sponsored by:
China Energy Group Science and Technology Research Institute Co., Ltd.
Academic support：
State Key Laboratory of Low-carbon Smart Coal-fired PowerGeneration and Ultra-clean Emission
Columns:
Thermal Energy Engineering, Clean Power Generation, New Energy Generation, Integrated Power Generation.
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