换热器腐蚀污垢的形成机理及其防治措施.pdf

有取暖系统,夏季制冷,冬季取暖。不使用氟里昂工作,无毒无害。制冷量大,可供利用余热资源大。7结论(1)吸附制冷作为一种直接利用热能的制冷技术,较适合于余热的回收利用。(2)将吸附制冷技术应用于余热的回收利用,可有效降低能耗,提高整个国家的能源利用效率。(3)吸附制冷的有关研究人员除了继续关注基础理论的研究外,应将研究重点放在应用研究上,着重于吸附制冷技术在各种余热资源的利用和相关产品的开发上。(4)吸附制冷技术应用于余热的回收利用存在巨大的市场潜力,将形成一个庞大的产业,应引起政府有关部门和企业界的关注。参考文献1姜周曙,王如竹,卢允庄,等.内燃机车司机室吸附式空调器的实验研究J.工程热物理学报,2002,23(3):280-282.2郭晓平,颜富纯,王占杰.内燃机排气 固体吸附制冷系统研究J.现代节能,1995,(4):10-11.3韩宝琦,朱瑞琪.利用余热的沸石分子筛吸附制冷的实验研究J.低温工程,1991,59:71-76.4孙永明.固体吸附式制冷在船舶上的应用研究J.上海海运学院学报.2000,21(2):52-56.5Zhu Ruiqi,Han Baoqi,Lin Meizhen,et al.Experimerltal in2vestigation on an adsorption system forproducing chilled wa2terJ.International Journal of Refrigeration,1992,15(1):31-34.(收稿日期:2003-11-24)换热器腐蚀污垢的形成机理及其防治措施衡世权1,姜 莉2(11 东北电力学院,吉林132012;21 佳木斯热力公司,黑龙江 佳木斯154002)摘要:换热器表面形成的腐蚀污垢使换热器面的传热热阻增加、传热系数降低,从而增加了换热器的总费用。本文主要对腐蚀污垢的定义、形成机理、数学预测模型及其防治措施作了详细介绍。在防治措施中,特别介绍了涂层和非金属材料的防治效果。关键词:换热器;腐蚀污垢;防治措施;涂层;缓蚀剂中图分类号:TK172 文献标识码:A 文章编号:10047948(2004)04-0028-03 据调查表明,90%以上的换热器都存在不同程度的污垢问题,污垢就是指在与不洁净流体相接触的固体表面上逐渐积聚起来的那层固态物质。本文主要讨论液侧污垢中腐蚀污垢的形成机理及其防治措施。1腐蚀污垢的定义腐蚀污垢是指换热面材料本身参与化学反应所产生的腐蚀物的积聚。这类污垢不仅本身污染了换热面,而且还可能促使其他潜在的污秽物质附着于换热面而形成垢层。2腐蚀污垢的形成机理腐蚀污垢的形成是由换热面上腐蚀产生的污秽物质(沉积过程)和污秽物质被流体冲击而剥离(去除过程)两种现象叠加的结果。211腐蚀污垢的电化学机理腐蚀分为化学腐蚀和电化学腐蚀两大类,而换热器表面的腐蚀就属于电化学腐蚀。腐蚀在阳极和阴极上涉及了两个同时的电化学反应。本文假设阳极和阴极都处于溶解氧饱和的流动溶液中,且pH值在410(典型的天然水)。在阳极,假设有化合价为z的金属M,电化学反应方程式为:MMz+ze-(1)在阴极,涉及到溶液中溶解氧降低的电化学反应方程式为:z4O2+z2H2O+ze-z(OH-)(2)溶液和外部金属导电体把阳极和阴极连接在一起,电荷通过电子e-在外部金属导电体和溶液中进82节 能ENERGY CONSERVATION2004年第4期(总第261期)行特殊的离子传输(对于均匀腐蚀来说,发生在阳极或阴极区的物理和化学过程控制腐蚀速率)。除了上述(1)、(2)两个反应之外,当腐蚀介质是水时,表面的阴极区还发生次级反应。其反应方程式为:Mz+z(OH-)M(OH)z(3)综合(1)、(2)、(3)三个反应方程,可得总的反应方程为:O2+2H2O+4zM4zM(OH)z(4)如果金属从水中取出、干燥,金属氢氧化物失去组成水,变成了金属氧化物。这些金属氧化物和氢氧化物就组成腐蚀沉积。如图1所示。图1 换热器表面腐蚀污垢的形成图212腐蚀污垢沉积过程的数学模型显然,从上述各反应方程来看,腐蚀热阻的变化率主要取决于溶液中溶解氧到换热器表面的输送率和腐蚀反应对氧的消耗率。因此,在换热器表面腐蚀沉积率的数学模型为:dmgd=K1dm1d(5)式中 K1常数,无量纲K1=4MgzM1(6)Mg,M1分别为污垢和氧的摩尔质量,kg/kmol;m1单位换热面上氧质量,kg/m2。如果将氧到换热面的输运看作是先由主流至污垢流体界面的对流输运,再通过腐蚀产物的扩散所组成的,则有dm1d=Cb1-Cs11km1+D1(7)Mahato等假定Cs1为已知,研究了式(7)分母中传质项的特征后,通过计算和测量将式(7)改写作dm1d=kmo(Cb1-Cs1)(8)式中,kmo综合(对流输运和扩散)传质系数,m/s,它可表示为1kmo=Do+k1m7/21D1+D+k2m1exp(k3m1)D1(9)这里,Do清洁换热面上被抑制的湍流边界层厚度,m。显然,为了利用式(9)确定kmo,需要知道Do、k1、k2、k3和D。这些通常是由实验测定的。通过等温条件下的管内腐蚀的实验研究,得出的上述式中的各常数值为:k1=3151710-4dRe-01371dm3/mg7/2(10)k2=2183410-4Re-01785dm/mg(11)k3=1118910-3Re-01256dm3/mg(12)而D则需给定。213腐蚀污垢剥离过程的数学模型腐蚀污垢的剥离过程就是指沉积在换热面上的污垢重新脱离换热面或污垢层被流动流体带走的过程。按其脱离表面的基本形态相应地提出了三种剥离机制:溶解、磨蚀和剥落。溶解就是腐蚀污垢物质以离子形态脱离固体表面的过程;磨蚀就是腐蚀污垢物质以微粒形式脱离固体表面的过程;剥落就是腐蚀污垢物质以大片或成片形式脱离固体表面的过程。目前,比较认可的是Dillon提出的数学模型为:dmrd=fC1(13)式中,C1经验常数;f腐蚀沉积密度,kg/m3。所以,腐蚀污垢整体的数学模型为dmfd=dmgd-dmrd1=K1(Cb1-Cs1)1km1+D1-fC1(14)3腐蚀污垢的防治措施腐蚀污垢的形成主要是由于材料的腐蚀引起的,只要能控制材料表面的腐蚀,就能抑制腐蚀污垢的增长,就是说防腐的过程就是阻垢的过程。下面从防治材料表面腐蚀来控制腐蚀污垢的形成。(1)采用耐腐蚀的金属和合金材料。(2)提 高 循 环 水 的pH。提 高 循 环 水 中 的922004年第4期(总第261期)节 能ENERGY CONSERVATIONOH-浓度,可以抑制阴极溶解氧的反应过程。从而使金属腐蚀速率大大降低。但pH值不可无限制地提高,因为碱性太强时,某些两性金属能与碱反应生成盐,特别是采暖系统,由于温度较高,当pH很高时,除了锌、铝等两性金属,铁也能溶解生成铁酸盐。(3)添加缓蚀剂。这是一种行之有效的方法,只要缓蚀剂选用得当,一般都能把腐蚀率控制在允许的范围内,并且还能与阻垢结合起来选用药剂,既达到缓蚀的目的,又达到阻垢的目的。常见的缓蚀剂有:聚磷酸盐、有机多元膦酸、磷酸盐、水玻璃等。(4)用耐腐蚀的材料涂敷在系统内与水接触的一侧。在换热器表面涂上一层阻止氧渗透的材料来防止腐蚀污垢的产生,但是换热面上的涂层又引入在设计阶段都必须考虑的换热器损失。Daly J F等使用蒸汽凝汽器对大量的涂层进行了实验,其结果如表1。根据阻抗Birc数不超过015的标准,从热交换器角度来看,除环氧树脂和硅碳耐火材料外,其他均可用作换热器表面的涂层。表1 冷凝器管涂层材料的阻抗Birc数涂 层涂层热阻Rc/m2kW-1阻抗Birc数聚氨酯底层+硅树脂涂层410510-501173聚氨酯底层+环氧树脂511610-501220环氧树脂811010-501345改良硅碳耐火材料814610-501360改良环氧树脂117610-401735硅碳耐火材料117610-401735 注:Rc=cA0Ac,Birc=U0Rc,其中U0=4260W/(m2k)(5)用非金属材料如石墨、聚四氟乙烯(PTFE)等代替金属材料制造换热面。此种材料的优点是质轻、费用低和几乎不产生腐蚀,但是非金属材料的热导率非常低。我们使用由PTFE和石墨制造成外径为31175cm、壁厚为01476cm的非金属管做了实验,其结果如表2。根据阻抗Birc数不超过015的标准,从热交换器角度来看,PTFE是不可取的,而石墨还是比较适合用来制作换热器的材料。表2 非金属材料管的阻抗Birc数氛 围U0/W(m2k)-1BircPTFE石墨汽-汽57117010026液-汽170511010077水冷式蒸汽凝汽器426012701194 注:11 对于PTFE来说=01190W/(mk);21 对于石墨来说=125W/(mk);31D0=31175cm,Di=212225cm主要符号Cb1 氧气的平均浓度,kg/m3Cs1氧气的Cs值,kg/m3D1沉积层中氧气的质量扩散率,m2/sD1 水中氧气的质量扩散率,m2/skm传质系数,m/sm 质量,kg 沉积层厚度,mD 湍流质量扩散系数,m2/s 时间,h或s 热导率,W/(mk)U0换热器的整体系数,W/(m2k)Rc涂层热阻,(m2k)/WA0管外表面面积,m2Ac涂层的对数平均面积,m2 污垢层氧的质量扩散,m2/s参考文献1Scully JC,李启中译.腐蚀原理M.北京:水利电力出版社,1984.2杨善让,徐志明.换热设备的污垢与对策M.北京:科学出版社,1995.3Rosner D E.Transport processes in chemically reacting flowsystemM.Butterworths,New York,1986.4Dillon R L.Corrosion of aluminum oxide as a regulating fac2tor in aqueous of reactor materials,brussels belgium,October14-17,1959,U.S R.Atomic Energy commission ReportTID-7587,July 1960.5DalyJ F,Norman G,Padilla A,et al.Condenser tube coatingas an alternative to retubing:in Condenser Technology Con2ferenceJ.Electric Power Research Institute,Palo Alto,CA(1993).作者简介:衡世权(1978-),男,硕士学位,从事腐蚀污垢与节能、在线腐蚀速度监测仪的研究。(收稿日期:2004-01-16;修回日期:2004-02-19)03节 能ENERGY CONSERVATION2004年第4期(总第261期)Energy Conservation(Monthly)Sponsor:Liaoning Provincial Institute of Science andTechnology InformationPublisher:Energy ConservationMagazine PublishingHouseChief Editor:ZHANG Wei2huaAddress:No.274 Qingnian Boulevard Shenyang CityLiaoning Province ChinaPost Code:110016ABSTRACTSApril 2004 No.4 Total Issue No.261Reviewand prospect of research on latentthermal energy storage in the domain of HVACFU Ying2hui,FENG Guo2hui,LShi2lei,et alThe researches of phase change heat transfer are reviewed in thispaper from the following four aspects.(1)The characteristics and solvingmethods of phase change heat transfer;(2)The developing and effect ofPCM wallboards;(3)The applying of phase-change in heating and air-conditioning systems;(4)The benefitsof latent thermal energy storageused in HVAC.At last,directions and contents of research on latentthermal energy storage in the domain of HVAC are put forward.Key words:phase change heat transfer;PCM wallboard;phasechange thermal and cool storage6Analysis on temperature field arounddirectly2buried pipes with multi2layer insulationCHENG Yan,SHEN Sheng2qiang,YUAN Yong2boThe temperature field induced by directly-buried pipes was ana2lyzed by boundary element method.The imagined adiabatic boundarywas introduced into the remote area around buried pipes.Therefore thediscretization elements are reduced since they are mainly on ground sur2face.With the method the temperature distributions in multi-layer in2sulation were computed for both single pipe and double pies under2ground.The results show the influence of multi-pipes.Key words:BEM;multi-layer insultion;directly-buried pipe9The discussions of the methods ofevaluating vibration stress relief effectGONG Yue2xia,FU Jian2ke,YOU MinAccording to the latest research results of the present VSR technol2ogy,the methods,principles and application charactersof the VSR evalu2ationsof presently used and still under research approaches were analysedin this article,and give the main directions of its development.Key words:vibratory stress relief;residual stress;examination;dynamic stress;evaluation14The selection of optimal load range for theparallelly running transformers in substationsCHEN Hai2han,GUO Xiao2long,LIU Ming2boBasing on the theory of economical running of power transformer,series of formulae about the scope are introduced and a practical algo2lithm is proposed in the paper.These can be used to improve the ar2rangement of transformersparallel running for the purpose of reducingthe energy loss.Key words:transformer;parallel running;optimation21The application of adsorption refrigerationin using remaining energyDU Wei2ming,XU Ming2fang YAN Gang,et alIn this paper existing remaining heat was introduced briefly andenumerated some adsorption refrigeration applications in using remainingheat,pointed out the adsorption refrigeration considerable market valueand enormous development potentiality in using remaining heat.Key words:adsorption refrigeration;using remaining heat;energysaving25Fundamental mechanism and preventivemeasures of heat transfer corrosion foulingHENG Shi2quan,JIANG LiThe corrosion fouling that is formed on heat transfer surface in2creases heat transfer thermal resistance and decreases heat transfer coef2ficient,so that the total expenses of heat transfer increase.This papermainly introduces definition、fundamentalmechanism、mathematicalmodel for predicting and preventive measures of corrosion fouling.Inpreventive measures of corrosion fouling,it especially presents the pre2ventive result of coating and non-metal materials.Key words:corrosion fouling;preventive measures;corrosion in2hibitor;coating28Several method of running of secondary pressurepump station save energy in residential quarterLI Jing2yao,ZHANG Yan,LI Ya2feng,et alSecondary water-supply technological equipment at secondarypressure pump station in a residential quarter can run through variableflow and variable pressure according to the water flow and pressure ofinternal network in the residential quarter.That has always been a diffi2cult problem in secondary pressure microcomputer water-supply equip2ment at secondary pressure pump station for many years,exploring an e2conomical,practical,stable and reliable method of variable flow and pres2sure has become a common target of domestic water-supply anddrainage industry and water-supply electromechanical equipment facto2ries in the recent years.”Model XBT microcomputer intelligent water-supply cabinet”series products not only successfully solves the difficultproblem of“variable flow and pressure”running of water-supply equip2ment at secondary pressure pump station,but also solves the problem ofautomatic remote control and monitor to secondary pressure pump sta2tion.Key words:pump station;save energy;variable frequency watersupply;variable flow and variable pressure31The analyses of the problem about normal air supplyopening used in cryogenic air supply systemWANG YongThis article uses the method of numerical calculation to study theproblem resulted from that normal air supply opening are used in thecryogenic system by a calculation example.And it explains why the cryo2genic system isnt used so well in our country.Key words:cryogenic air supply;normal air supply opening;in2duction42The application in the power plant watertreatment of two rooms double-deck floats bedZHAO Zhen2shengPass the adoption with two rooms double-deck floats bed for theequipments of system water,can not only improves the supply abilitythat divided by the brine system,but also be excellent to turn the pro2duction craft,increase the utilization of the reborn liquid to attain thepurpose of save energy and increases performance.Key words:floats beds;fixed bed;except salt solution;technigue;save energy49Analysis and countermeasure for the troubleduring discharging boiler wastewaterLU Zu2liang,GU Wen2zhongIt was analyzed that the reason of vibration noise and pipe jam dur2ing the steam vessel V-521 discharging boiler wastewater,and im2proved on the process of discharging boiler wastewater,which effectiveresolved the troubles.Key words:V-521 discharging boiler wastewater;noise;produceblock;chemical reaction522节 能ENERGY CONSERVATION2004年第4期(总第261期)