我国火电厂循环冷却水处理技术的发展

收稿日期:　20030611作者简介:　罗奖合,男,教授级高级工程师,现任国电热工研究院科研业务部副主任兼国电水处理公司总经理。

主要从事电厂化学水处理技术及药剂的研究开发。

我国火电厂循环冷却水处理技术的发展罗奖合1,李营根1,郭怀保2(1.国电热工研究院,陕西西安　710032;2.苇湖梁发电有限责任公司,新疆乌鲁木齐　830002)[摘　要]　介绍电力体制改革后我国火电厂循环冷却水处理技术面临的主要问题和今后的发展方向。

根据目前的实际需要和可能,认为近期内各火电厂循环水的浓缩倍率应以大于3为控制目标,为此提出了8点建议:(1)完善循环水的外部处理方法;(2)开发新型水质稳定剂和高效复合配方;(3)加强凝汽器管防腐技术研究;(4)对城市污水用于循环水技术进行研究;(5)探索其它杀菌剂的应用;(6)加强自动控制技术的应用;(7)对运行中除垢技术进行研究;(8)循环水处理药剂应定点生产。

[关键词]　火电厂;循环水;浓缩倍率;药剂;配方;凝汽器;结垢;腐蚀[中图分类号]TM621.8 [文献标识码]A [文章编号]10023364(2003)08000903 五大发电集团公司成立后将实行“厂网分开、竟价上网”的方针。

发电企业的生产要以节能降耗来降低发电成本,增强上网电价的竞争力。

做好火电厂循环水处理工作,对于降低发电成本有着重要的作用。

1　火电厂循环冷却水处理技术面临的主要问题1.1　水资源日益紧张我国水资源人均拥有量为2200m 3,只有世界平均水平的1/4,属缺水国家。

且有限的水资源分配很不均匀,81%分布在长江流域及其以南地区。

目前我国一方面水资源紧张,另一方面却又存在大量浪费水资源的情况。

火电厂是工业用水大户,其耗水量约占工业用水量的20%左右。

在缺水的北方地区,水资源严重不足,使火电厂的建设规划和运行受到限制,因此节约用水已成为当务之急。

据有关资料统计,我国凝汽式火电厂(采用冷却塔和水力输灰)的耗水率为1.64m 3/(s ・GW ),与国外水平(0.7～0.9)m 3/(s ・GW )差距较大,说明我国火电厂节水潜力很大。

目前经原国家经贸委批准的单位发电量取水量标准已正式实施,其目的在于限制火力发电厂的取水量,具体规定如下:采用循环冷却供水系统时单位发电量取水量定额,在单机容量<300MW 时为4.80m 3/(MW ・h );在单机容量≥300MW 时为3.84m 3/(MW ・h )。

当前全国达到这一标准的火电厂还不到30%,因此节水空间巨大。

火电厂全厂用水的比例:循环冷却水系统补给水50%～80%,水力输灰用水20%～40%,锅炉补给水2%～4%。

因此,火电厂节水工作的重点应在优化冷却水和冲灰水系统的设计和运行方面,尽可能减少循环冷却系统的排污,提高循环冷却水的浓缩倍率,可取得良好的经济效益。

但浓缩倍率的提高,会使结垢和腐蚀等问题更加突出,同时对循环水处理技术也提出了更高的要求。

1.2　环境保护的要求更为严格进入21世纪以来,以环保为主题的绿色能源声势日高,为了保护水资源水质,减少工业排放废水及污水对水体造成的危害,环保部门对火力发电厂排放水量和水质提出了严格要求。

就排放水量而言,将对火力技术经济综述热力发电・2003(8)9发电厂这类排水大户超标排放施以巨额罚款,因此火电厂必须大幅度提高循环冷却水的浓缩倍率,以减少冷却系统的排污水量。

这无疑增加了循环水处理的难度。

就排放水质而言,对涉及循环水药剂处理的一些关键指标提出了新的要求,如排放水中P的含量应小于0.5mg/L。

这必将限制某些循环水处理药剂的使用,如目前广泛使用的有机磷系药剂,迫使火电厂寻求高效环保型循环水处理药剂及其处理技术。

1.3　源水水质不断恶化由于干旱、开采过量、不断污染使得水资源水质不断恶化,给循环水处理带来了许多难题,并由此增加了处理费用。

更有甚者,由于水体严重污染,个别电厂已出现所采用的地表水水质劣于一般二级城市污水水质的状况,无法以常规循环水处理技术解决系统出现的问题。

循环水补水水质逐年恶化和缺水地区越来越多采用城市污水等其它再生水源,加之浓缩倍率的提高,使凝汽器管的腐蚀问题变得突出起来。

由此,提出其在生产、运输、储存、安装、发展期及正常运行时应采用何种科学合理的保护方式和技术措施的问题。

1.4　仪表装备落后我国火电厂循环水处理系统所用计量仪表不全,自动化水平落后,与发达国家相比差距很大。

如美国NALCO、B ETZ公司和日本栗田公司都开发了在线监测的自动加药系统,能将循环水系统的药剂浓度控制在目标管理范围内,从而达到平稳操作,使药剂发挥最大作用和节约用药的目的。

1.5　缺乏既先进又经济的外部处理技术按照目前采用循环水补水水质特点和趋势,石灰处理系统的有关问题还未完全解决,弱酸处理的初投资和运行成本还比较高。

面对复杂多变的补水水质,先进和经济的外部处理技术尚待开发。

2　火电厂循环冷却水处理技术的研究方向根据循环水补水水质的变化特点,依照循环水系统节水幅度和处理成本的关系,综合分析认为,将浓缩倍率提高到5(多数工业发达国家的火电厂,浓缩倍率约为4～6)左右是适宜的;但按照目前实际的需要和可能,近期内各火电厂应以大于3为控制目标。

要达此目标,必须解决上述问题,因此提出如下建议。

2.1　完善外部处理方法根据我国天然水碳酸盐硬度高的特点和国外的先进经验,应开发技术先进、投资和运行成本较低的外部处理方式。

(1)重点在于逐步完善和解决国外(如德国)已使用成熟的石灰处理系统的有关问题,如高纯度石灰粉的供应和系统设备磨损。

回收冲灰水作为循环水补充水。

利用粉煤灰中游离CaO来处理循环水补充水的设想也值得研究和探讨。

(2)进一步研究降低弱酸处理的初投资和废液排放量较大及铜管腐蚀较严重等问题。

如采用部分弱酸处理,应用双流床,以移动床代替固定床,添加合适的缓蚀剂等。

(3)采用旁流过滤(以大理石为滤料)与稳定剂联合处理,可除去碳酸钙的过饱和微晶粒,从而降低循环水的碱度、p H值和碳酸钙的过饱和度,这是一个提高浓缩倍率较有希望的方法。

2.2　开发新型水质稳定剂和高效复合配方对于已投产的电厂,为了达到浓缩倍率大于3的目标,建设完善的外部处理系统,目前难以做到。

鉴于加药处理的优点,开发新型水质稳定剂和高效复合配方,完善和深化循环水的药剂处理是今后努力的方向。

近年来,国外开发的新型水质稳定剂以多元共聚物为主,如美国CAL GON、NALCO、B ETZ和ROHM&HASS等公司在开发有机磺酸/不饱和羧酸二元共聚物的基础上,又向含磺酸、羧酸和膦酸基等官能团的三元或多元共聚物发展,这些药剂都有极强的分散作用,其复合配方更加适合苛刻条件下的水质处理,可使水的钙硬度达2000mg/L,浓缩倍率在6～8间。

此外具有特种结构和特种性能的阻垢分散剂开始出现,如二乙烯三胺五甲叉膦酸(PAPEMP),更适合超高硬度和碱度的水质处理。

这些新型药剂应用于水质较差的循环水时,不辅加硫酸,单加稳定剂就可达到防垢目的。

此外,在药剂研究方面,还应开发和推广符合环保要求的无P、N高效水稳剂;在控制铜管腐蚀速率方面,还要研究几乎无侵蚀的复合配方。

2.3　加强凝汽器管防腐技术的研究铜管目前仍是普遍使用的管材,循环水补水水质的逐渐恶化和浓缩倍率的提高,使铜管防腐技术的研究更加迫切,具体考虑如下。

技术经济综述　λυ　热力发电・2003(8)(1)除严格控制铜管的出厂质量外,尚需加强对运输、储存、安装、发展期过程的管理和监督,如安装前进行电化学检测评定等,采用的保护方式和技术措施应规范化、导则化。

(2)研究新的FeSO4成膜工艺和技术,保证运行和停机时的成膜质量。

特别是状态检修技术的应用,运行中成膜工艺及质量将变得尤为重要。

(3)复合配方中添加的缓蚀剂,要既能在洁净的铜管上起到防腐作用又能在有脏物的铜管上对膜进行保护和修补。

(4)在运行中对铜管的腐蚀类型和状况进行准确的在线检测,如采用凝汽器铜管腐蚀在线检测仪,这对于及时掌握腐蚀变化,采取有效措施,保护铜管和延长其平均寿命(我国为10年,某些发达国家可达40年)有实际意义。

(5)机组停运期间,铜管内的湿气和积水易造成铜管斑蚀、点蚀,要研究和重视可靠的防腐措施。

(6)还应积极研究不锈钢管(包括价格低廉的低合金钢)的应用问题。

2.4　三级处理后的城市污水作为循环水补水的研究由于淡水资源日益紧张,将经处理的城市污水回用于火电厂循环冷却系统的情况会不断增加,但城市污水中含有氨氮和硝酸盐及细菌、微生物等,加之受其它因素的影响,会带来以下问题:(1)循环水铜离子含量明显上升,使得腐蚀速率严重超标;(2)细菌总数大大增加,粘泥生成量增加;(3)硝化反应的良好进行,造成循环水的p H值异常降低;(4)氯的杀菌效果降低。

要解决这些问题应该研究:(1)是否要在电厂中增加某些处理设施,如曝气吹脱装置、氧化沟、旁流过滤等设备;(2)选择何种材质的凝汽器管。

2.5　探索其它杀菌剂的应用我国火电厂主要采用氯作为杀菌剂。

随着城市污水回用的增加,源水呈有机物强烈污染的情况增加,循环水采用稳定处理时,水的p H较高,这些都要求探索其它杀菌剂的应用。

如臭氧,它具有以下优点:杀菌效果良好;不受p H值的影响;是一种好的粘泥剥离剂;不与氨反应,因而在有机物污染严重、含氨高的水中也可很好地发挥杀菌作用;杀菌时形成的副产物危害小,有利于环境保护。

2.6　加强自动控制技术的应用在研究开发、数据处理、现场监测、在线分析和配方选择等方面,应广泛应用自动控制技术。

加药处理具有投资少、操作简便的优点,目前大都采用人工配制、投加的方式。

实现与循环水相关水质指标和腐蚀状况建立内在关系的闭环控制自动加药,消除人工加药的误差,提高药剂处理的控制水平,将会对冷却系统防垢防腐起到积极作用。

2.7　运行中除垢技术的研究目前由于发电机组单机容量较大,停机除垢会影响整个地区的供电,并给电厂带来很大的经济损失,因此应研究运行中除垢和除粘泥等附着物技术。

2.8　循环水处理药剂的定点生产目前我国电力系统所用的循环水处理药剂,80%以上是小型乡镇企业和个体企业生产,这些企业由于技术力量薄弱,管理水平低,致使产品质量不稳定,合格率低(9种常用的182个样品,合格率为67%)。

实际使用情况表明,对循环水处理药剂实施定点和集中生产很有必要。

[参　考　文　献][1]　高秀山,杨东方.火电厂循环冷却水处理[M].中国电力出版社,2001.[2]　周国定,吴一平.凝汽器铜管表面状态的电化学评定[J].中国电力,2001,(1).欢迎订阅欢迎投稿欢迎刊登广告技术经济综述热力发电・2003(8)λϖ　THERMAL POWER GENERATIONV ol.32　No.8　Aug.2003Contents&AbstractsRETR OFITTING FOR OPTIMIING EQUIPMENT AN D SYSTEM FOR H OME-MADE300MW TURBINE UNIT OF IMPORTE D ………………………………………………………………………………………………………………………T YPE W ang X u et al(2) The operational situ ation and troublesome problems existing in equipment and system for home-m ade300MW turbine unit N o.3of imported type after putting into operation at Shihong Pow er Plant have been briefly described,and the retrof itting measures for perfection of said unit and practical results after implementation of technical retroff itting be2 ing expounded.Through said retroff itting,the specif ic heat consumption has been relatively reduced by333.45kJ/(kWh),specif ic coal consumption for electric energy genera2 tion by12.5g/(kWh),having obvious retrof itting effectiveness.PRESENT SITUATION OF STU DYING THE TECHNIQUE T O BURN FUE L IN STEPS AN D APPL ICATION PR OSPECTS THERE OF …………………………………………………………………………………………………………………………Ling R onghu a et al(6) The situ ation of stud ying the technique to burn fuel in steps at home and abroad has been presented,and the application prospects of said technique in our country being analysed from view points of natural resources,technical econom y,and environmental protection policy of the state.It is considered from analysis that the said technique can effectively control N O x emission,and is m aturity in application,at the same time has rem arkable com petitive force in economic aspect.Along with the requirements of environmental pro2 tection are becoming increasingly higher,the application of said technique in our countory will certainly be widened.DEVE LOPMENT OF RECIRCU LATING COOL ING WATER TREATMENT TECHNI QUES IN THERMA L POWER PLANTS OF OUR ………………………………………………………………………………………………………………COUNTR Y Luo Jianghe et al(9) The m ain problems lying ahead of recirulating cooling w ater treatment techniques in therm al pow er plants of our country after reform of the pow er system and the development direction of said techniques in the future have been presented.B ased on the practical dem and and possibility at present,it is considered that the enrichment factor of circulator y w ater at each therm al pow er plant in the near future should be greater than three,and taking this factor as a control target.For this reason,eight points of recommend ation have been put forw ard as follows:(1)perfection of external treatment method for circulator y w ater;(2)development of new stabilizing agents and high-effective complex prescrip2 tion;(3)strengthening the research of anticorrosion technolo gy for condenser tubes;(4)carrying out the study on technique of using urb an sew as recirculating w ater;(5) exploring application of other pestisides;(6)strengthening application of autom atic control techni ques;(7)carrying out the study of descaling technique during the time of oper2 ation;(8)assigning f ixed points to produce agents used for circulatory w ater treatment.………………………STU DY ON ADAPTABI L IT Y OF LOW N O x BURNERS T O VARIOUS COA L QUA L IT Y H uo X uezhi et al(12) Analysis and discussion have been m ade in the followin g aspects,namely the w orking principle of low N O x burners,the relationship betw een qu antity of N O x form ation during initial stage of combustion and the volatile of coal qu ality,the effect of technology to burn air in steps on coal of different qu ality,the situ ation of utilizing low N O x burners in our country,as w ell as the ad aptability of low N O x burners to coal of various qu ality etc.H ence,some recommend ations for develo ping and spreading low N O x burners have been put forw ard.STU DY ON USING SUPERSONIC SPEE D B OOSTING HEATER WITH STEAM-L IQUID TWO-PHASE F LOW IN DESA L INATE D ……………………………………………………………………………………WATER HEATING SYSTEM W ang Xiaofeng et al(16) The method of regulating the outlet flow rate of the boosting heater with supersonic speed steam-liquid tw o-phase flow has theoritically been studied,and a desalinated w ater heating system composed of four boosting heaters and a recirculating pipeline has been designed and built b ased on the said stud y.The said system can heat up the desalinated w a2 ter to a given temperature while the outlet flow rate changing from60t/h to360t/h,and having boosting capability.practical operation test shows that the operation of the said system is stable and reliable,satisfying completely the requirements of production process in therm al pow er plants.DESIGN AN D REA L IZATION OF CONSUMPTION DIFFERENCE ANA LYSING SYSTEM FOR THERMA L POWER UNITS BASE D ………………………………………………………………………………………ON WEB H YBRID MODE Cheng hongw ei et al(20) On the b asis of inform ation resources existin g in the therm al pow er plants,a consumption difference analysing system for therm al pow er units has been developed b ased on the de2 sign idea of modularized structure b y using computer technique.The C/S mode and the B/S mode have been anal ysed and compared,obtaining a realizing scheme of system b ased on a hybrid mode both of them.Directing against key problems such as d ata aquisition and d ata storage etc.in the system,OPC technical specif ications and design idea of sharing the internal storage has been used,enhancing safety real-time nature of the said system.Application in the f ields shows that the said s ystem can effectively improve the opera2 tion level of operators and operation m anagement level of the entire pow er plant.DESIGN OF ADAPTIVE CONTR OLLER IN CONTR OLL ING SUPERHEATE D STEAM TEMPERATURE AN D REA L IZATION OF ITS ……………………………………………………………………………………………………CONFIGURATION Zhang Xilin et al(23) I n view of defects existing in conventinal superheated steam temperature control,such as slow response speed,long transient time,and large overshoot m agnitude etc.,a design method of the controller b ased on ad aptive regulations has been put forw ard,m aking parameters of the PI D controller can autom aticall y suit to the variation of ob ject,achieving the purpose of optim al controlling.At the same time,the conf i guration of ad aptive controller and the w orking principle of its every part have been given.The result of simulation shows that the qu ality of ad aptive PI D controller is much better than that of the conventional PI D controllin g.STU DY ON FAI L URE MODE OF WE LDE D JOINTS FOR AUSTENITE STEE L WITH DISSIMI LAR META LS ON HIGH-TEMPER2…………………………………………………………………………ATURE B OI LER TUBES IN POWER PLANTS R en Ai et al(27) The aging features,as w ell as creep rupture strength limit and persistent strength limit of w elded joints for austenite steel(such as304Hand347H stainless steel)with dissimilar metals(such2.25C r-1Mo ferrite heatresisting steel etc.)after long-term service have been tested and studied.The said heat-resisting steel has comparatively extensive uti2 lization in our country.The causes leading to aging and failure of the said joints have been comprehensively analysed from several aspects,namely structure aging,peform ance variation,features of joint’s conf iguration,carbon migration,and therm al expansion coeff icient of m aterials etc.TESTING OF COA L PU L VERIZING SYSTEM AS WE LL AS ENERG Y-SAVING AN D CONSUMPTION-RE DUCING THERE OF ……………………………………………………………………………………………………………………W ang H ongyu et al(32) Combined with optimizition of adjusting and testing for the coal pulverizing system with intermediate storage bunker of a410t/h boiler’s b all mills in a pow er plant.the influence of various factors upon operating condition of the coal pulverizing system has been analysed.Through optimization of adjusting,the operating condition of said system becomes more resonable,enhancing economic aspect,reducing the specif ic consumption of electricity for coal pulverizing more than2.51kWh/t.CAUSE ANA LYSIS OF FAU LTS OCCURRE D ON HIGH-PRESSURE FEE D-WATER PUMPS AN D IMPR OVEMENTS OF REPAIR ………………………………………………………………………………………………………………TECHNIQUES Su Shaolin(35) D G270-140B type high-pressure feed-w ater pumps are early typical products of Shenyang W ater Pumps’F actory,being widely used in m any pow er plants.Due to special oparating conditions and insuff iciency existing in the design,such faults as seal packing leakage,vibration,and burn-melting of thrust bearing shoe etc.have frequently oc2 curred.For this reason,several effective repair techniques are recommented.CAUSE ANA LYSIS OF RADIAT OR TUBE BUN DLES’FR OST-CRACK FOR IN DIRECT AIR-COOLE D SYSTEM WITH SURFACE …………………………………………………………………………………………………………CON DENSER Wen Xingu et al(38) Frost-crack of the radiator tube bundles during the period of winter in frigid area is a comparatively prominent problem for indirect air-cooled system with suface condenser, a cause analysis for the said problem has been carried out,taking emphatically the freeze-up mechanism as the point of departure.It is considered from said analysis that the short-circuit of intermediate partition plate is the m ain cause resulting in frost-crack of the said tube bundles,and corres ponding technical measures for improvements have。