燃煤烟气汞污染控制技术

燃煤烟气汞污染控制技术

3

田立辉　李彩亭　曾光明　高　招　罗　瑶

(湖南大学环境科学与工程学院,湖南长沙410082)

摘要　介绍了燃煤电站汞的排放状况,论述烟气中汞的存在形式以及影响其存在形式的因素。介绍当前燃煤电站汞排放控制技术的研究进展,并对各种烟气脱汞技术的特点和净化效率进行对比。最后对烟气脱汞技术的研究趋势进行了展望,提出了适合于我国国情的研究方向。

关键词　燃煤烟气　汞的存在形式　影响因素　烟气脱汞技术

3教育部科学技术研究重点项目(105126);湖南省自然科学基金项目(03JJ Y 2002);新世纪人才支持计划项目(NECT 20420769)。

0　引言

煤作为一次性能源的主要利用方式是燃烧,其燃烧产物会对环境造成严重的破坏。煤燃烧过程中生成的污染物除S O 2、NO x 和C O 2以外,还有各种形态的汞。汞及其化合物可通过呼吸道、皮肤和消化道等不同途径侵入人体,造成神经性中毒和深部组织病变,而且汞毒性具有积累性,往往需几年或十几年才有表现,所以燃煤过程中的汞污染控制问题越来越受到重视

[122]

。在我国煤炭是主要燃料能源,据统计2003年

我国燃煤电站汞排放量达到8618t ,废渣汞排放量为28194t

[3]

。可以预见,防止燃煤汞污染是21世纪电

力工业最重要的环保课题之一。1　烟气中汞的存在形式及其影响因素111　汞的存在形式

烟气中汞的存在形式主要包括3种[4]

:单质汞

(Hg 0),化合态汞(Hg +和Hg 2+)和颗粒态汞。通常而言,化合态汞易溶于水可被湿法洗涤系统所捕获而脱除

[5]

,颗粒态汞可以通过除尘器除去,所以这2种形

态的汞相对比较容易除去。而单质汞容易在大气中通过长距离的大气运输,其在大气中的平均停留时间可达半年至两年,是最难控制的形态之一。因此,对单质汞污染的控制成了当前研究的重点和难点。112　影响烟气中汞存在形式的因素

烟气中汞的存在形式对汞的脱除效率有重要影响。影响烟气中汞存在状态的主要因素包括烟气温度、烟气气氛和烟气成分等。

(1)烟气温度及烟气气氛的影响。刘迎晖[6]等人研究发现汞在氧化性气氛下,当温度>800K 时单

质汞是主要存在形式;温度<600K 时氯化汞是主要形态;在600～1000K 有少量的氧化汞生成;在温度>400K 的还原性气氛中99%的汞以单质汞的形式存在。

(2)烟气成分的影响。燃烧后烟气中含有的微

量成分对元素汞的氧化有重要影响,Laudal D L [7]

等人对不同气体组分存在条件下汞的氧化进行了研究,给出了不同气体存在时氧化态汞与元素汞的比例,见表1。

表1　不同气体组分存在条件下汞的形态分布[7]

气体组分

氧化态汞Π%

元素汞Π%

Cl 2

84181512飞灰

1109910HCl 0139917S O 2

0179913飞灰、Cl 2、S O 228157115飞灰、HCl 、S O 2

1139817NO ΠNO 2

2119719飞灰、NO ΠNO 2、Cl 278152115飞灰、NO ΠNO 2、S O 2

37116219S O 2、NO ΠNO 2、HCl

0119917飞灰、HCl 、S O 2、NO ΠNO 2、Cl 2

4617

5317

2　烟气脱汞技术

汞排放控制技术的研究目前主要集中在3个方面:燃烧前脱汞、燃烧中脱汞和燃烧后脱汞,其中燃烧后脱汞即烟气脱汞是目前研究的重点。烟气脱汞的方法主要有吸附剂法和化学氧化法。211　吸附剂法21111　活性炭法

在烟气中喷入活性炭是研究最为集中且最为成

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2008年10月第26卷第5期

熟的一种除汞方法。但是该技术运行成本相当高[8]。

目前,针对活性炭喷射技术的改进,主要是提高活性炭的吸附能力,降低活性炭用量,节省成本。经研究表明,相同条件下,注碘或注硫活性炭的吸附性能好于一般的活性炭[9]。Radisav D V[10]通过实验指出经硫氯化物浸渍后活性炭对汞的吸附能力大大提高,最高效率可达95%～98%,但是同时也增加了成本。

高洪亮[11]等研究证明,对活性炭进行FeCl

3

处理后吸附效果得到了很大的提高,有效吸附时间从65min延长到180min,改性的活性炭在经过100min 的吸附后吸附效率仍可达到75%。

21112　飞灰注入法

燃煤过程中产生的飞灰可吸附一部分气态汞[12],飞灰对汞的吸附主要通过物理吸附、化学吸附、化学反应以及三者结合的方式。将飞灰重新注入烟气中可进一步捕集汞。尽管目前学术界一致认为飞灰颗粒能捕获气相汞,但对其机理还没有很好的认识。美国Radian实验室[13]认为飞灰先吸附元素态

汞,当达到动态平衡时和烟气中的HCl、S O

2和NO x等气体之间发生复杂反应,部分元素汞被氧化,氧化态的汞可以在接下来的脱硫装置中去除,吸附元素汞的飞灰可经过除尘器除去。中试实验表明[14],在135～160℃附近,汞去除率在13%～80%。目前认为飞灰吸附主要受到温度、飞灰粒径、碳含量、烟气成分以及飞灰中无机成分对汞的催化作用等因素影响。江贻满[15]等研究证明:颗粒粒径越小,比表面越大,飞灰吸附汞的能力越强;飞灰含碳量与汞含量呈正相关关系;亚微米级颗粒物对汞的吸附不仅与其比表面积有关,而且与其比表面积的利用率有关。

21113　钙基吸附剂

钙基吸附剂如CaO、Ca(OH)

2、CaC O

3、CaS O4?2H2O等价格低廉,且已广泛用于烟气中S O2的脱除。如果钙基物质能够在烟气汞排放的控制方面也有所突破,则可作为脱除烟气中多种污染物的有效物质。研究表明[16],钙基物质如Ca(OH)2对HgCl2的吸附效

率可达到85%,CaO同样也可以很好的吸附HgCl

2

,但

是Ca(OH)

2和CaO对于单质汞的吸附效率却很低,因此需要加强钙基类物质对单质汞吸附的研究。目前主要从两方面进行尝试,一方面是增加钙类物质捕捉单质汞的活性区域,另一方面是把氧化性物质加到钙基吸附剂中。G horishi等人[17]采用第2种方法改善石灰和硅酸钙的吸附性能,结果发现改性后吸附效率

有所增加。

21114　高分子壳聚糖吸附法

壳聚糖(Chitosan,CS)又称脱乙酰几丁质、聚氨基葡萄糖、可溶性甲壳素,是一种储量极为丰富的天然碱性高分子多糖,多为虾、蟹甲壳提取物,是由甲壳素(Chitin)部分脱乙酰化衍生物[18]。它具有耐热、耐腐蚀和兼容性宽的优点,其分子中含有大量的NH

2和?OH,是重金属离子的良好吸附剂,被广泛应用[19220]。高鹏[21]研究发现壳聚糖除汞效率很高,在80℃吸附

效率达96143%,同时对S O

x和NO x有一定的脱除效果,壳聚糖吸附剂脱除汞的反应是化学反应占主导,它可以高效的脱除Hg2+和Hg单质,理论上最佳吸附反应温度为80～120℃。

212　化学氧化法

21211　光催化氧化法

光催化氧化技术,是针对现有湿法烟气脱硫(WFG D)设备中Hg2+的脱除效率较高而Hg0脱除效率甚低的现象而开发的,将Hg0氧化处理的新技术,

处理效果可达到99%[22]。其机理是:T iO

2

经过紫外

线照射后,在其表面会产生?OH,当烟气通过T iO

2的

表面时,Hg0被?OH氧化成HgO,进而被吸附在T iO

2颗粒的表面。

在模拟燃煤烟气成分的状态下,Y ing Li[23]等研

究了T iO

22SiO2在紫外线照射下对汞的去除效果,研

究表明:HCl和S O

2的存在提高了T iO22SiO2对汞的氧

化和捕集能力,H

2

O和NO的存在降低T iO22SiO2对汞

的氧化和捕集能力,NO

2的影响效果不明显。

21212　选择性催化还原法(SCR)

选择性催化还原法就是在将氮氧化物催化还原为氮气的同时,可将Hg0氧化成Hg2+,Hg2+相对更易被湿式喷淋装置脱除。Hg0被SCR装置催化氧化的效率可达80%～90%,氧化效率的高低受气体空间流速、氨的浓度和气流中氯的浓度等[24]因素影响。Machalek T[25]研究发现汞的氧化效率随气体空间流速的增大而减少,当气体空间流速由3000kmΠh增加到7800kmΠh时,汞的氧化效率从40%降低到5%。同时还有研究表明[26],汞的氧化效率随着氨浓度的增加而减小,随着气流中氯浓度的增加而增大。21213　臭氧法

利用臭氧的强氧化性将Hg0氧化成Hg2+,然后

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通过脱硫装置和除尘装置除去。

该方法的突出优点是在氧化汞的同时可以氧化烟气中的S O

2和NO x,而且汞的氧化效率比较高。Zhihua Wang[27]研究发现,当臭氧的体积分数达到250×10-6时,模拟烟气中汞的氧化效率可达89%。在洗涤塔存在的条件下,当臭氧的体积分数达到360×10-6时,NO和S O2的去除效率可分别达到97%和100%。

综上所述,烟气脱汞技术对比见表2。

表2　烟气脱汞技术对比

方法特点

净化效率

Hg0Hg2+活性炭法汞的脱除效率高,而且能够同时脱除多种污染物,但费用高高高飞灰注入法费用低,Hg2+的脱除效率高,变废为宝,但是对Hg0脱出效果一般一般较高钙基吸收剂Hg2+的脱除效率高,费用低,可同时脱除S O2,对Hg0脱除效果不明显低较高高分子壳聚糖吸附法费用低,汞的脱除效率高,对S O2和NO有一定的去除效果,具有很好的应用前景高高光催化氧化法对汞的脱除效率高,但是现在处于初步研究阶段,如果效果好可实现脱硫、脱硝和脱汞一体化,

应用前景较好

高高

SCR法对汞的脱除效率较高,实现脱硝和脱汞一体化,是今后研究的重点较高较高臭氧法对汞的脱除效率高,可以同时脱除S O2和NO高高

3　研究展望

综上所述,活性炭吸附法对汞的去除效率最高,但是该技术运行成本高,并不适合我国国情。根据我国的经济现状,烟气脱汞技术的进一步研究可集中在:

(1)开发新型廉价高效的吸附剂取代价格昂贵的活性炭;

(2)寻找一种优良的氧化剂,提高元素汞的氧化效率;

(3)研究开发高效的催化剂,实现SCR同时脱硝脱汞。

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(下转第53页)

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图3　加热器控温电路

　

系统控制程序如图4所示

。

图4　控制系统运行程序

3　结论

EPS 再生装置经安装调试和实际生产,其运行稳

定,温度控制符合工艺要求,所生产的产品质量良好,

颗粒大小为<3mm ×6mm 左右,可以根据实际要求调节颗粒大小,经实际检测生产效率达50～80kg Πh ,由于生产过程采用循环冷却水,因此生产过程中无水耗,大大节约生产成本。

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作者通信处　殷苏民　212013　江苏镇江　江苏大学机械工程学院

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tion safety.

K eyw ords tipper mechanisms of dust production numerical simulation collecting and cleaning dust dust cleaning effect

EXPERI MENT A L RESEARCH ON HIGH TEMPERATURE GRANULAR BED FI LTER

Hao Jingzhang He Peng (28)…………………………………………………………………………………………………………………Abstract The g oal of this study was to evaluate the per formance of granular filter designed for hot gas cleaning.The effect of tem perature on the characteristic of granular bed filter for high tem perature dust rem oval was studied ,and a formula of tem perature versus dust rem oval efficiency and pressure drop was obtained.M oreover ,the experimental results were similar with those of the formula.With the increase of tem perature ,the dust 2rem oving efficiency and pressure drop w ould become higher during the process of dust 2cleaning.

K eyw ords dust 2rem oving granular bed high tem perature I NVESTIG ATION ON ENVIRONMENT A L PROTECTION OF BUI LDI N G CONSTRUCTION

Tian Jing (31)………………………………………………………………………………………………………………………………Abstract I t is done an investigation on the attitude of managing pers onnel of construction enterprise and that of residents around w orksites to environmental protection.The results show that in treatment of pollution ,building refuses are mainly incinerated or transported to a land fill site ;for construction noises ,there are no constructions at night ,anti noise walls are set up.Insu fficient supervision of environment.less input in environ 2mental protection and lack of scientific management are the main factors to pollute environment by building constructions.The relevant s olutions are proposed based on per fection of specifications and laws ,enhancement of construction management ,and im provement on construction techniques etc.

K eyw ords building construction attitude to environmental protection questionnaire

THE SI MULATION OF MASS BA LANCE AND AI DED DESIG N I N SCR FUME DENITRATION SYSTEM Du Yungui Wu Qirong Yu Yu (35)

………………………………………………………………………………Abstract SCR (selective catalyst reduction )denitration technology is one of the main fume denitration technology in thermal power plants ,whose mass balance calculation is an im portant means of guiding practice and technological design.Based on technical principle of SCR fume denitration and the experience of engineering practice ,it was explored the program for mass balance of SCR and simulated the main technological parameters of SCR system ,as well as developed the auxiliary design function of each device.

K eyw ords flue gas denitration (SCR )　mass balance program design aided design

SMO KE PURIFICATION AND ENER GY 2SAVI N G TECHNOLO GICA L TRANSFORMATION FOR CHAR GI N G CAR OF CO KE 2OVEN Chen Yingying Wang Haitao (38)

……………………………………………Abstract Sm oke purification of charging car of coke 2oven is one of the key points in coking plant sm oke purification.This paper introduces how to trans form sm oke wet purification of the charging car of coke 2oven to dry purification ,including the effects of saving energy ,water and re 2ducing noise.

K eyw ords charging car sm oke purification energy 2saving technology

COUNTERMEASURES FOR CONTROLLI N G NO X POLLUTION OF CENTRA L HEATI N G BOI L 2ERS Li Wei Ding Xiaowen Ma Wenjing et al (41)

…………………………………………………………………………Abstract The boilers with low excess air coefficient were chosen in the environmental im pact assessment of a central heating project ,mean 2while the scheme of enhancing management of boiler operation was used to control NO X emission.The low excess air coefficient of the selected boil 2

ers was lower than 1143,by which NO X emission concentration in fume could be reduced to 143mg Πm 3

.The index of NO x can meet the emission standard.

K eyw ords central heating environmental im pact assessment control of NO X pollution

THE DEVE LO PMENT OF POWER SUPPLY FOR E LECTRO ST ATIC PRECIPIT ATOR

Liu Jun Shi Jianjiang (44)…………………………………………………………………………………………………………………Abstract The power supply for an electrostatic precipitator is the key part in the electrostatic precipitator system ,and its per formance is the key factor to im prove the efficiency of the dust rem oval.The development of power supply for electrostatic precipitators is reviewed based on energy 2saving and im provement of dust rem oval efficiency.I t has three development trends ,which is from single 2phase power supply to three 2phase power supply ,from v oltage regulation under line frequency to high frequency inverting and from one power m ode to hybrid power m ode.The high frequen 2cy power supply for electrostatic precipitators is the developing trends and has the advantages of flexible control ,controlled waveform of output high v oltage and fast reaction under flashover and restart.

K eyw ords electrostatic precipitation dedust efficiency three phase high frequency high v oltage pulse

MERCURY CONTROL TECHNOLO GIES FOR COA L 2FIRED F LUE G AS

Tian Lihui Li Caiting Zeng Guangming et al (48)

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Abstract I t is introduced status of mercury emissions from coal 2fired power plants ,discussed the mercury speciation in flue gas and the main im pact factors in fluencing its speciation.I t is als o presented progress in mercury control technologies for coal 2fired power plants.The characteris 2tics and purification efficiency of all the technologies for mercury rem oval are com pared.Finally ,it is discussed the tendency of mercury control technologies and proposed the research direction that suits the situation of our country.

K eyw ords coal 2fired flue gas mercury speciation in fluential factors mercury control technologies of the flue gas

THE DESIG N OF FULL 2AUTOMATIC REGENERATI VE DEVICE OF EXPANDED POLYSTYRENE (EPS )　AND ITS CONTROL Lin Weijian Yin Sumin Chen Bin (51)

……………………………………………Abstract According to the characteristics of EPS and the requirements of regeneration technique ,a full 2automatic regenerator was de 2signed ,by which the foamed refuses could be converted to polystyrene granulas with a small v olume and high density.The process flow of crush 2ing ,thawing ,cooling and granula 2cutting was used for the device.According to automatic demands ,a self 2controlling system was als o developed using P LC and touchable technology.I ts automation was realize after actual debugging ,whose productivity was up to 50～80kg Πh with product meeting requirements.

K eyw ords EPS regnerative device P LC

THE STUDY ON SI MULATION MATHEMATICA L MODE L OF E LECTRO ST ATIC PRECIPIT ATOR 2BAG DUST REMOVER I N POWER PLANT Hu Manyin Zhang Ruiying (54)

…………………………………Abstract T aking a 300MW electric precipitator and the cloth sack dust rem over system as the object of study ,through researching mecha 2nism of system ,a series of corresponding mathematic simulation m odels were established ,including flue 2gas parameter m ode ,the electric precipi 2tator local design parameter m odel ,electric precipitator per formance parameter m odel ,the bag dust rem over local design parameter m odel ,the bag dust rem over per formance parameter m odel and that of total dedusting efficiency of the precipitator 2bag dust rem over etc.Based on the simulation m odels ,the simulation s oftware was designed and developed.The references for the system running ,system maintenance and pers onnel training can be provided.

K eyw ords electrostatic precipitator 2bag dust rem over mathematical m odel simulation

THE NUMERICA L STUDY ON THE CHARACTERISTICS OF I NSI DE F LOW FIE LD OF A DOWN AIR I NLET BAG FI LTER Gao Guangde Zhang Yanting (58)

……………………………………………………………Abstract The F LUE NT 613s oftware is used to simulate the inside flow field of the tw o down air inlets bag filters ,i.e.straight tube inlet and quadrangular inlet.I t is analyzed the characteristics of the inside field of tw o kinds of bag filters based on the result of numerical simulation.On the basis of which ,it is com pared the field property of the tw o kinds of bag filters ,and the simulation result may be a reference for the design of a bag 2type collector.

K eyw ords bag filter numerical simulation flow field

A NEW DUST REMOVA L METHOD TO REMOVE DUST FROM SU

B 2PACK AGI N G AND PA

C 2K AGI N G OF DRU GS Chai Yusheng Zhang Qi Zhang Heng et al (60)

……………………………………………Abstract In order to rem ove dust contamination during pharmaceutical production ,sub 2packaging and packaging ,a set of automatic de 2dusters were developed.I t could control com pletely the direction of dust flow and collect them in the fixed places.By which a separation of dust from people was realized.

K eyw ords automatic cabinet of dust rem oval purification of air circulation gravimetric method determination of inhalable particulate concentration

DESIG N OF WATER SYSTEM BA LANCE OF IRON AND STEE L I NDUSTRY

Hui K egang Wang Ling Meng Yanxiao (62)…………………………

………………………………………………………………………………Abstract I t is described that the center ,em phasis and core problems of water 2saving and pollutant reduction of iron and steel industry at present ,as well as major contents and requirements of the design of water system balance of iron and steel enterprises.I t is pointed out that mak 2ing a g ood job in quantity balance of water ,tem perature balance and suspended s olid balance is the best choice to realize water 2saving and pollut 2ant reduction of iron and steel enterprises.

K eyw ords iron and steel industry balance of water system design and research

DISCUSSION ON APERTURE 2VARIED O PENI N G METHOD OF PERFORATED DISTRI BUTI N G WATER PIPE Yang Haitao Wan Yanhua Wang Zhif ang et al (65)

……………………………………………………Abstract Aiming at the problem of the uneven distributing water and the higher energy consum ption on the per forated pipe distributing water at present ,it is analysed the feasibility of aperture 2varied opening method of per forated distributing water pipe on the basis of sharp 2edge orifice outflow principle ,and deduced the formula of hydraulic calculation of aperture 2varied opening orifice.C onsidering the actual problems in engi 2neering application ,it is als o put forward the calculation method of segment 2equidistant aperture 2varied opening on per forated pipe.A set of new schemes for the application of per forated pipe in practical project are proposed.

K eyw ords aperture 2varied per forated pipe hydraulic calculation segmental opening

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E NVIRONME NT A L E NGINEERING V ol 126,N o 15,October ,2008