NH3对SCR催化剂Hg0催化氧化性能的影响

作为我国主要的汞污染源之一,燃煤电厂汞污染物排放控制是我国环保标准的要求。通过改性SCR催化剂和卤化物添加等方法将Hg⁰氧化为Hg²⁺,进而通过后续设备进行脱除,是提高汞脱除率的有效方法。但对我国而言,这类结合现有环保设备的联合脱除方法都面临着SCR入口高浓度NH₃的抑制作用。为此,基于文献调研,总结了NH₃对SCR催化剂Hg⁰氧化性能的影响,以及卤素存在条件下NH₃对Hg⁰氧化性能的影响,分析了改性催化剂及卤化物添加对Hg⁰氧化率的提高机理,进而对应地分析了NH₃对Hg⁰氧化的抑制机理。研究结果为实际燃煤电厂提高SCR设备Hg⁰氧化率提供了参考。     

NH3选择性催化还原NOx催化剂及其中毒研究进展

选择性催化还原(SCR)技术广泛应用于燃煤电厂锅炉的烟气脱硝过程中,SCR工艺中的核心是高效稳定的催化剂.如何提高SCR催化剂的脱硝效率、稳定性和抗中毒能力,一直是国内外科研人员的研究重点之一.目前钒基催化剂广泛应用于工业生产中,但钒基催化剂具有生物毒性,操作温度高且N2选择性低,因此对环境友好且稳定高效的新型催化剂成...     

燃煤烟气中Hg迁移转化特性研究

研究了300 MW煤粉锅炉系统选择性催化还原（selective catalytic reduction,SCR）、低低温电除尘器、海水脱硫、湿式电除尘器等超低排放设施在不同工况、不同煤种情况下的Hg迁移特性和脱除能力。结果表明：各工况下总汞排放浓度为1.16~2.90 μg/m³。最终排入大气中的汞主要以单质汞存在,还有少量氧化态汞,颗粒态汞被全部脱除;汞主要是在海水法烟气脱硫中被去除的,低低温电除尘器、海水脱硫、湿式电除尘器对总汞平均脱除率分别为25%、62%、37%;Hg²⁺占比是影响烟气中汞脱除效率的关键,气相中较高的Hg²⁺份额有利于在电除尘器和海水脱硫装置中获得较高的脱除效率;在该配备SCR脱硝、低低温电除尘器、海水脱硫、湿式电除尘器等超低排放设施的300 MW煤粉锅炉电厂中,总汞平均脱除率约为83%,能够实现较大程度的汞脱除。     

茶梗基生物炭吸附气态单质汞的热力学分析

燃煤电厂作为单质汞最大的排放源,其排放标准也日趋严格。新的火电厂排放标准已于2012年1月1日起正式实施,其中规定汞及其化合物的排放限值为0.03mg/m~3。以云南废弃普洱茶梗为碳源,利用超声等体积浸渍法制备了质量分数分别为4%CeO_2-4%CuO(CC)和4%CeO_2-4%MnO_2(CM)生物炭。在100～300℃范围内,模拟固定床选择性催化还原法(SCR)条件下进行单质汞和NO的联合去除实验。为了探究改性茶梗生物炭吸附气态单质汞的热力学特征和吸附机理,利用热力学方程对数据进行拟合,结果表明随着温度的逐步升高,化学反应发生机率降低,化学吸附随之减少。     

燃煤电厂汞排放控制技术分析

燃煤烟气中的汞以最基本的三种形式存在:元素汞,氧化态汞和颗粒态汞.在此介绍了燃煤电厂汞排放及其迁移转化规律、燃煤过程中汞的存在形态及影响汞去除率的主要因素;分析了燃烧前脱汞、燃烧中脱汞、燃烧后脱汞等方面的技术;较为详细地论述了汞排放控制技术现状及研究进展.     

脱硝用还原剂经济技术分析

选择性催化还原（SCR）烟气脱硝技术,是20世纪80年代初开始逐渐应用于燃煤锅炉烟气脱除NOx,目前已在日本、德国、美国等发达国家的燃煤电厂广泛应用,在我国新建的大型火力发电厂也开始了应用。     

Mn-HAP基低温SCR催化剂的制备及抗硫中毒性能

低温选择性催化还原(SCR)脱硝是工业烟气末端治理的重要技术, 强化催化剂硫抗性是低温SCR领域内亟待解决的问题。本研究以羟基磷灰石(HAP)为载体、Mn为活性组分通过共沉淀法成功合成了Mn-HAP低温(100~200℃)脱硝催化剂, 探究了其脱硝性能及金属硫酸盐和硫酸铵的中毒特性。结果表明: 以HAP作为活性组分Mn的载体能一定程度上提高催化剂的抗硫性。当反应温度为140 ℃时, SCR催化剂脱硝效率达到100%, 金属硫酸盐相较硫酸铵对催化剂低温脱硝活性的影响更显著, 120 ℃时脱硝效率分别降低37.40%和8.83%。不同手段分析表明, 不同表面硫物种均会不同程度地降低催化剂比表面积并改变活性Mn氧化态。金属硫酸盐显著降低Mn⁴⁺/Mn比例是造成催化剂失活的主要原因。     

燃煤电厂烟气汞的监测方法

燃煤电厂汞污染已经成为继S02污染之后的又一重大污染问题。燃煤烟气中汞的迁移转化规律及污染控制技术的研究是目前重要的环保课题之一，但是对烟气汞的准确监测是各项研究的前提和关键。本文综述了国内外燃煤电厂烟气中汞的监测方法，并做了简要的分析与总结，对未来我国燃煤烟气汞监测方法的发展进行了展望。     

V_2O_5-WO_3/TiO_2基SCR催化剂的研究进展

SCR是一种新型的脱硝催化技术.概述了选择性催化还原法的反应机理、载体掺杂V2O5-WO3对催化性能的影响,介绍了各种因素对催化剂成型性能的影响,提出了催化剂需要满足的一些条件,分析了技术方面需要解决的一些问题,总结了国内外SCR催化剂的研究现状和发展前景.     

CO催化氧化催化剂活性成分研究进展

CO催化氧化消除在环保、氢燃料电池等许多领域具有重要应用,其催化剂活性成分可以使用单组分及多组分的贵金属、非贵金属、金属氧化物、复合氧化物等。非贵金属活性成分的使用对降低催化剂的成本具有重要意义。从催化剂活性成分的角度来审视不同催化剂的催化性能和构效关系,综述了CO催化氧化催化剂的研究现状。     

Mechanism of Hg<Superscript>0</Superscript> oxidation in the presence of HCl over a CuCl<Subscript>2</Subscript>-modified SCR catalyst

CuCl₂-SCR catalysts prepared by an improved impregnation method were examined to evaluate the catalytic activity for gaseous elemental mercury (Hg⁰) oxidation in the presence of HCl at the typical SCR reaction temperature of 350 °C. It was found that Hg⁰ oxidation activity of commercial SCR catalyst was significantly improved by the introduction of CuCl₂. The X-ray fluorescence and Hg⁰ temperature-programmed desorption (Hg⁰-TPD) methods were employed to characterize the catalysts. The results indicated that CuCl₂ on CuCl₂-SCR catalyst could release active Cl species in the presence of O₂ at 350 °C, and the released active Cl species could be replenished in the presence of gas-phase HCl. CuCl₂-SCR catalyst possessed the appropriate active sites for the adsorption of NH₃ and HCl, which could scavenge the inhibiting effect of NH₃ on Hg⁰ oxidation. Hg⁰-TPD results suggested that the oxidized mercury compounds mainly exited as HgCl₂ once HCl was present. The Hg⁰ oxidation mechanism over CuCl₂-SCR catalyst in the presence of HCl could be explained as follows: The adsorbed Hg⁰ reacted with active Cl species released by CuCl₂ to form HgCl₂. The reduced CuCl was re-chlorinated to CuCl₂ via the intermediate copper oxychloride (Cu₂OCl₂) formation by being exposed to the gas-phase HCl.     

Synthesis,characterization and evaluation of resin-based carbon spheres modified by oxygen functional groups for gaseous elemental mercury capture

A novel resin-based spherical carbon material was successfully prepared by suspension polymerization of alkyl phenol and formaldehyde and steam activation in combination with surface modification by heat treatment with dry air for enhancing Hg⁰ adsorption. The analysis results demonstrate that the oxidation-modified activated carbon spheres possess better mercury removal performance than untreated sorbents, and the ACS-O300 obtained by oxidation modified at 300 °C is the optimal sorbent at the adsorption temperature range from 25 to 150 °C. The main reason is assigned to the increase of the oxygen functional groups of C=O and C(O)–O–C that play an important role as effective active sites for binding the Hg⁰, even though the C(O)–O–C predominates in mercury removal performance under higher adsorption temperature. The optimum O₂ concentration is 4 vol% at the O₂ concentration range from 0 to 8 vol%. SO₂ and NO are favorable to the mercury adsorption under 4 vol% O₂, while H₂O leads to the inhibition of the mercury adsorption. The TPD results suggest that a strong desorption peak at temperature around 235 °C and a weak peak at 324 °C should generate from mercury desorption of C?=?O and C(O)–O–C, correspondingly. Moreover, the XPS analysis results of the fresh and used sorbent indicates that the C=O and C(O)–O–C serve as strong oxidizer and facilitate electron transfer for converting Hg⁰ to Hg²⁺ in the chemisorption process. These results suggest that the obtained resin-based spherical porous carbon (ACS-O300) is promising for Hg⁰ capture.     

Near-Zero Air Pollutant Emission Technologies and Applications for Clean Coal-Fired Power

Coal is the dominant energy source in China, and coal-fired power accounts for about half of coal consumption. However, air pollutant emissions from coal-fired power plants cause severe ecological and environmental problems. This paper focuses on near-zero emission technologies and applications for clean coal-fired power. The long-term operation states of near-zero emission units were evaluated, and synergistic and special mercury (Hg) control technologies were researched. The results show that the principle technical route of near-zero emission, which was applied to 101 of China’s coal-fired units, has good adaptability to coal properties. The emission concentrations of particulate matter (PM), SO₂, and NO_x were below the emission limits of gas-fired power plants and the compliance rates of the hourly average emission concentrations reaching near-zero emission in long-term operation exceeded 99%. With the application of near-zero emission technologies, the generating costs increased by about 0.01 CNY∙(kW∙h)^–1. However, the total emissions of air pollutants decreased by about 90%, resulting in effective improvement of the ambient air quality. Furthermore, while the Hg emission concentrations of the near-zero emission units ranged from 0.51 to 2.89 μg∙m⁻³, after the modified fly ash (MFA) special Hg removal system was applied, Hg emission concentration reached as low as 0.29 μg∙m⁻³. The operating cost of this system was only 10%–15% of the cost of mainstream Hg removal technology using activated carbon injection. Based on experimental studies carried out in a 50 000 m³∙h⁻¹ coal-fired flue gas pollutant control pilot platform, the interaction relationships of multi-pollutant removal were obtained and solutions were developed for emissions reaching different limits. A combined demonstration application for clean coal-fired power, with the new “1123” eco-friendly emission limits of 1, 10, 20 mg∙m⁻³, and 3 μg∙m⁻³, respectively, for PM, SO₂, NO_x, and Hg from near-zero emission coal-fired power were put forward and realized, providing engineering and technical support for the national enhanced pollution emission standards.     

Oxide Catalysts with Ultrastrong Resistance to SO2 Deactivation for Removing Nitric Oxide at Low Temperature

Nitrogen oxides are one of the major sources of air pollution. To remove these pollutants originating from combustion of fossil fuels remains challenging in steel, cement, and glass industries as the catalysts are severely deactivated by SO₂ during the low‐temperature selective catalytic reduction (SCR) process. Here, a MnO_X/CeO₂ nanorod catalyst with outstanding resistance to SO₂ deactivation is reported, which is designed based on critical information obtained from in situ transmission electron microscopy (TEM) experiments under reaction conditions and theoretical calculations. The catalysts show almost no activity loss (apparent NO_X reaction rate kept unchanged at 1800 µmol g^?1 h^?1) for 1000 h test at 523 K in the presence of 200 ppm SO₂. This unprecedented performance is achieved by establishing a dynamic equilibrium between sulfates formation and decomposition over the CeO₂ surface during the reactions and preventing the MnO_X cluster from the steric hindrance induced by SO₂, which minimized the deactivation of the active sites of MnO_X/CeO₂. This work presents the ultralong lifetime of catalysts in the presence of SO₂, along with decent activity, marking a milestone in practical applications in low‐temperature selective catalytic reduction (SCR) of NO_X.     

基于遗传算法优化BP神经网络的SCR脱硝系统催化剂体积设计

火电厂SCR脱硝系统的设计需要在满足脱硝效率的同时,尽可能节约成本,因此需要准确预测SCR脱硝所需的催化剂体积。火电厂的烟气条件复杂多变,烟气温度、烟气流量、出入口NO_x浓度等参数都会影响SCR催化剂的体积设计,因此催化剂体积预测是一个多因素耦合的问题。针对这一特点,使用BP神经网络对催化剂体积设计进行了预测,并针对该模型结构上的缺陷,进行基于遗传算法优化的神经网络建模研究。结果表明,遗传算法优化后的BP神经网络模型预测精度和数据拟合能力均有提高,为脱硝系统的催化剂体积设计提供了新思路。     

Aqueous and vapor phase mercury sorption by inorganic oxide materials functionalized with thiols and poly-thiols

The objective of the study is the development of sorbents where the sorption sites are highly accessible for the capture of mercury from aqueous and vapor streams. Only a small fraction of the equilibrium capacity is utilized for a sorbent in applications involving short residence times (e.g., vapor phase capture of mercury from coal-fired power plant flue gases). So, dynamic capacity rather than equilibrium capacity is more relevant for these kinds of situations. Rapid sorption rates and higher dynamic capacity can be achieved by increasing the accessibility of active sites and decreasing the diffusional resistance to mass transport for the adsorbing species. This requires the use of open structured sorbent materials and attachment of functional groups on the external surface area of supports. The strong interaction of sulfur containing ligands (e.g., thiol) with mercury makes them suitable candidates for immobilization on these types of materials. In this study, inorganic oxide supports like alumina and silica are functionalized with thiol moieties like mercapto silane, cysteine and poly-cysteine for capturing mercury from aqueous and vapor phase. Aqueous phase Hg (II) sorption studies with cysteine/poly-cysteine functionalized silica showed that high dynamic capacity can be achieved by attaching active sites (thiol) on the external area of supports. Vapor phase Hg capture studies with thiol-functionalized mesoporous silica (Hg⁰ concentration = 3.37 mg/m³ with N₂ as the carrier, gas temperature = 70 ^°C) yielded a capacity of 143 g Hg/g for the sorbent. Although the sulfur content for the sorbent was low (0.80 wt. %) the molar ratio of Hg captured to sulfur was comparatively high (2.86×10^–3) pointing to the high accessibility of sulfur sites.     

锰基催化剂低温选择催化还原处理NOx的研究现状与展望

锰基催化剂具有较高的催化活性,且成本低,在选择性催化还原(SCR)尾气中的NO_x领域具有广阔应用前景。介绍了锰基低温SCR催化剂处理NO_x的最新进展。锰基催化剂可分为两类:锰氧化物催化剂和锰基掺杂过渡金属氧化物催化剂。针对锰氧化物催化剂,主要分析了锰的氧化价态、结晶形态、比表面积以及形态学对催化效果的影响;对于锰基掺杂过渡金属氧化物催化剂,重点分析了掺杂物对催化剂的催化能力、催化温度范围、N_2的选择性和抗SO_2、H_2O毒化能力的影响。最后在总结全文的基础上,展望了锰基催化剂的应用前景。     

Industrial Application of a Deep Purification Technology for Flue Gas Involving Phase-Transition Agglomeration and Dehumidification

A moist plume forms when the flue gas emitted from wet desulfurization equipment exits into the ambient air, resulting in a waste of water resources and visual pollution. In addition, sulfur trioxide (SO₃), water with dissolved salts, and particles in the wet flue gas form secondary pollution in the surrounding atmosphere. In this study, a deep purification technology for flue gas involving phase-transition agglomeration and dehumidification (PAD) is proposed. This deep purification technology includes two technical routes: the integrated technology of phase-transition agglomeration and a wet electrostatic precipitator (PAW); and the integrated technology of phase-transition agglomeration and a mist eliminator (PAM). Industrial applications of PAW and PAM were carried out on 630 and 1000 MW coal-fired units, respectively. The results show that the average amount of recycled water obtained from wet flue gas by means of PAD is more than 4 g·(kg·°C)⁻¹. Decreasing the wet flue gas temperature by 1.5–5.3 °C allows 5%–20% of the moisture in the flue gas to be recycled; therefore, this process could effectively save water resources and significantly reduce water vapor emissions. In addition, the moist plume is effectively eliminated. With the use of this process, the ion concentration in droplets of flue gas is decreased by more than 65%, the SO₃ removal efficiency from flue gas is greater than 75%, and the removal efficiency of particulate matter is 92.53%.