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环境污染治理包括防治在生产建设或其他活动中产生的废气、废水、废渣、医疗废物、粉尘、恶臭气体、放射性物质等污染物,以及降低噪声、振动、光辐射、电磁辐射等对人体与环境的危害。其中,工业污染治理是环境污染治理的重点内容。燃油燃气锅炉、焦化、玻璃、陶瓷、水泥、垃圾焚烧、危废、酸洗、燃气发电等行业会排放大量气态硫化物、氮化物和汞,造成生态环境持久破坏,并危害人体健康,引起急、慢性中毒和致癌、致畸等远期危害[1]。现有的气体污染物净化方法包括:催化氧化还原、催化燃烧、利用吸收和吸附等[2]。然而,由于环境污染的复杂性,这些技术都不同程度地存在净化不彻底、投资成本高、操作复杂、回收率低、能耗高等缺点[2],也可能产生二次污染,所以需要探索和开发新技术、新方法,解决现有技术的问题。除反应机理和条件外,引入外加场也是提高反应效率和改善性能的方法,如引入磁场、电场等外加场会影响反应过程,并提高去除效率。
磁场是一种特殊物质,也是一种能量场,已被化学家和物理学家广泛应用于化学和物理控制过程。永磁铁或电磁铁在空间上产生磁场强度较为均匀的磁场。电子的运动伴生着磁场,磁性来自电子的运动,物质中带电粒子的运动形成物质的元磁矩。当这些元磁矩取向有序时,便形成了物质的磁性。通常物质的磁性分为顺磁性、抗磁性以及铁磁性[3]。顺磁性物质具有固定磁矩,在外加磁场中呈现微弱磁性,并产生与外加磁场同方向的附加磁场,能被磁体轻微吸引。抗磁性物质在外加磁场中呈现微弱磁性,并产生与外加磁场反方向的附加磁场,能被磁体轻微排斥。抗磁性在所有物质中都存在,由于抗磁性极其微弱,故常常被掩盖。铁磁性物质在外加磁场中呈现很强的磁性,并产生与外加磁场同方向的附加磁场,能被磁体强烈吸引,具有磁矩的分子表现为顺磁性,外磁场会影响磁性分子的取向,亦即影响反应体系的熵[4-5]。磁场能有效控制某些反应的速率,影响反应历程[6]。由经典电磁理论,磁场会对运动的化学粒子产生洛仑兹力。仅从能量看,磁场提供的能量较热运动的能量,不足以影响化学反应。但量子力学认为,化学反应还取决于化学粒子的电子自旋,磁场会影响化学反应粒子未成对电子的自旋状态,改变反应体系的熵,从而影响化学反应的进程和结果。磁场对化学反应影响是量子力学效应和磁流体力学效应之一或共同作用的结果[7]。有关磁场效应(磁场效应主要来自量子效应、磁热力学效应、磁矩、洛伦兹力、法拉第力、涡流和能量输入)的研究也是一个重要领域[8-9]。磁场的这些特性逐渐被研究开发,因提升了污染物处理效果和去除效率,而被运用于工业废气和废水处理、分选、高分子聚合以及催化剂制备等领域,成为一种新型污染控制技术。
近年来,利用磁场对磁性物质力的作用、对水中污染物的高能破坏作用和对微生物生长和酶活性的正向刺激作用,实现工业废水中污染物的去除已有一些研究进展[10]。在分选中利用其本身作用力,与磁场相互作用,受到转磁力矩和平动磁力而产生粒子聚集现象(粒子间磁偶极子力、拖曳力、布朗力、引力和范德华力),可实现杂质颗粒快速便捷分离和废物循环利用[11-13]。磁场在以自由基反应占主导地位的高分子聚合领域获得了一定成果,获得了产率高、分子量高且分布较窄的高聚物,且聚合物结晶度、大分子链的规整性、热性等都因磁场得到有效控制[14-16]。然而,磁场对工业废气污染的治理还未得到总结,目前磁场在废气治理研究方面,更多集中在废气脱硫脱硝和脱汞。
磁场应用于水处理的研究早已兴起,而利用磁场处理工业废气的研究发展缓慢。最开始,陈凡植等[17]使用高梯度磁分离器处理氧气顶吹转炉和电弧炼钢炉产生的烟尘,取得较好的粉尘去除效果。俞明等[18]研究发现磁场运用于汽车尾气中能够对HC及CO排放量和燃油经济性有一定改善。朱传征等[19]发现,常压下磁场能够提高合成氨反应的反应速率和转化率。随着研究人员对磁场去除污染物影响规律和作用机理的研究深入,磁场应用于工业废气处理有了一定的发展。本文介绍磁场对二氧化硫、氮氧化物和汞这3种气体污染物去除的影响效果和作用机理,为实际利用磁场治理工业废气提供理论和技术参考,为工业废气净化应用研究提供新思路与方向。
磁场应用于工业废气脱硫、脱硝和脱汞的研究进展
Research status of magnetic field in flue gas desulfurization, denitrification and mercury removal
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摘要: 随着磁场技术不断发展以及对其研究的深入,磁场已被越来越多应用于环境污染治理领域。总结磁场在废气脱硫脱硝和脱汞方面的研究进展,着重叙述和探讨了磁场对催化氧化二氧化硫、氮氧化物和汞这3种气体污染物的影响机制与去除机理。现有研究表明,外加磁场受顺磁逆磁材料、磁场种类、强度和气体组分的影响。一方面,磁场能够改善吸附剂传质性能、促进自由基和中间产物生成速率、控制自由基对的系间跃迁、抑制单重态自由基对的重结合、提高催化活性,而使有效反应温度降低;另一方面,磁化力增强了运输效应和化学吸附,且磁场与磁性催化剂具有协同作用,可造成局部磁场叠加,形成微小磁场源,从而促进顺磁性组分氧化,还可将逆磁性反应物转化为顺磁性产物,加速反应中的电子传递、增强反应物质在磁性位点的上活化,最终促进反应进行:磁场技术可为工业废气中气体污染物的去除提供新思路。Abstract: With the continuous development of magnetic field technology and the deepening of its research, magnetic field has been more and more applied in the field of environmental pollution control. In this paper, it summarizes the research progress of magnetic field in gas desulfurization, denitrification and mercury removal, especially the properties of magnetic field affects the removal mechanism of sulfur dioxide, nitrogen oxide and mercury. Affected by paramagnetic and diamagnetic materials, magnetic field types, intensities and gas components, the results show that the applied magnetic field can improve the mass transfer performance of adsorbent, promote the formation rate of free radicals and intermediates, control the transition between free radicals, inhibit the recombination of singlet free radicals, improve the catalytic activity, and reduce the effective reaction temperature. Magnetizing force on the other hand enhances transport effect and chemical adsorption, thereby the magnetic field and magnetic catalysts have synergy, it can cause local magnetic field superposition and form small magnetic field source. Not only promote the oxidation of paramagnetic component, but also convert diamagnetism reactant to paramagnetic products, accelerate the electron transfer reactions, enhance reaction material on the site of magnetic activated, thus promote the reaction. The magnetic field technique introduced in this paper provides a new idea for the removal of gaseous pollutants from industrial waste gas.
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Key words:
- magnetic field /
- desulfurization /
- denitrification /
- mercury removal /
- catalysis /
- reaction mechanism
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表 1 负载磁性Ag、Co、Cu、Fe对去除Hg0的影响
Table 1. Effect of Hg0 removal using load magnetic Ag,Co,Cu,Fe
载体 负载物质 制备方法 反应温度/℃ 负载量/% 去除率/% 反应式 沸石 Ag 离子交换法 250 — 80 2Ag++Hg0→2Ag+Hg2+ 粉煤灰 Co 浸渍和热分解法 150 5.8 95 Hg0+CoxOy→HgO+CoxOy-1
HgO+CoxOy-1→HgO+CoxOy粉煤灰 Cu 浸渍法 150 6 90.6 Cu2++ Hg0→Cu+Hg2+
CuO+ Hg0→Cu+HgOMBC Fe 浸渍法 200 1.5 90 Hg0→2e−+Hg2+
C=O+e− →C—O
O2−+Hg2+ →HgO表 2 不同气体对Co-MF催化剂去除Hg0的影响
Table 2. Effect of different gases for Hg0 removal in Co-MF catalyst
气体组分 作用 添加气体浓度/
(mg·m−3)Hg0去除率的
变化情况作用机理 反应式 SO2 抑制 1 047
3 141降低3%
降低13.4%SO2与Hg0在催化剂表面的竞争性吸附,
与催化剂表面氧反应生成SO32SO2+O2→2SO3 H2O 抑制 2 208
5 889下降7%
下降14.9%H2O与Hg0的竞争性吸附,导致Hg0去除
能力失活无 O2 促进 — — 可再生所消耗的表面氧 CoxOy-1+1/2O2→CoxOy HCl 促进 15 上升5% 表面氧在纯N2气氛下作为氧化剂,HCl
氧化成Cl2,可以显著促进Hg0氧化和化
学吸附,HCl吸附在催化剂表面,形成
表面活性氯种,发生了不均匀氧化4HCl+O2→2Cl2+2H2O NO 双面效应 61
368上升8%
降低,轻微抑制少量NO提高Hg0去除效率,过量NO提高Hg0去除效率,晶格氧和化学吸附氧可以
氧化NO,形成新的物种,如NO2、NO+
等,Hg0与NO2相互作用Hg0+NO2→HgO+NO
Hg0+2NO2+O2→Hg(NO3)2
HgO+2NO+3/2O2→Hg(NO3)2 -
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