自然通风逆流湿式冷却塔蒸发水损失研究
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摘要
循环水在冷却塔内的冷却过程是电力生产中一个十分重要的过程,循环水的冷却是靠冷却塔内接触散热和蒸发散热实现的。冷却过程中通过蒸发散热损失掉的水量是冷却塔水损失的重要组成部分,也是火电厂最大的耗水项目。蒸发水损失的产生不仅会给火电厂造成很大的经济损失,同时由于蒸发水损失会在塔顶形成“白烟”而污染周围环境。因此对冷却塔蒸发水损失进行研究具有很重要的现实意义。
本文以自然通风逆流湿式冷却塔为研究对象,在分析冷却塔传热传质的基础上,建立了冷却塔蒸发水损失计算模型,并编制了此模型的求解程序。分别以某300MW和600MW机组对应的实型塔为例,计算了不同工况下冷却塔的出塔水温和蒸发水损失,并分别对比了计算出塔水温与实测出塔水温、模型计算蒸发水损失与近似公式计算蒸发水损失,对比表明两参数的相对误差均在允许误差范围内,验证了此模型用以研究冷却塔蒸发水损失的可行性。
本文以某300MW机组对应的实型塔为例,先从冷却塔单独运行的角度出发,研究了进塔水温、循环水量以及环境参数对冷却塔蒸发水损失产生的影响规律。计算结果表明:其他参数不变,冷却塔进塔水温升高,蒸发水损失增加,但单位温差引起的蒸发水损失率降低;进塔水温不变,进塔水量减少,冷却塔蒸发水损失减少,但单位温差引起的蒸发水损失率升高;进塔水温不变,环境干球温度升高,冷却塔蒸发水损失减少,但单位温差引起的蒸发水损失率升高;进塔水温不变,环境相对湿度增加,冷却塔蒸发水损失减少,单位温差引起的蒸发水损失率减少。
火电厂中,冷却塔和凝汽器作为冷端系统的重要组成部分,两者相互影响,相互制约。循环水量以及环境气象参数发生变化不仅会直接影响冷却塔蒸发水损失,而且还会通过影响凝汽器侧的换热性能来间接影响冷却塔的蒸发水损失。因此,为全面分析和评价冷却塔蒸发水损失,本文还以整体运行的冷端系统为研究对象,在凝汽器总换热量保持不变的前提下,研究了循环水量和环境参数变化对冷却塔蒸发水损失产生的整体影响。计算结果表明:在凝汽器换热量保持不变的前提下,环境干球温度升高,冷却塔蒸发水损失以及单位温差引起的蒸发水损失率也都升高;环境相对湿度增加,蒸发水损失减少,单位温差引起的蒸发水损失率降低;循环水量减少,冷却塔蒸发水损失以及单位温差引起的蒸发水损失率均是降低的。
蒸发水损失与冷端系统节水存在极大的关系,分析蒸发水损失的最终目的在于节水。本课题的研究成果,为冷却塔节水奠定了理论基础。
The cooling process of circulating water is very important in power generation industry. Circulating water can be cooled not only by heat transfer through contaction but also by heat transfer through evaporation mainly.The evaporation loss induced by heat transfer through evaporation is a very important part of water loss in cooling tower, and also is the maximum water-consumption project in thermal power plant. Not only evaporation loss will bring great economic loss to thermal power plants, but it also will pollute the environment by forming white fog on the top of cooling tower. Therefore research on evaporation loss of cooling tower is of much practical significance.
In this paper, with the research object of natural draft counter-flow wet cooling tower, calculation model of evaporation loss was established and solving program was composed based on analyzing heat and mass transfer in cooling tower. Taking a certain 300MW and a certain 600MW generating unit for example respectively, outlet water temperature and evaporation loss of cooling tower under different working conditions were calculated, and comparisons were done between calculated and measured outlet water temperature, between evaporation losses calculated through calculation model and approximate formulas respectively. The results show that relative errors of the two parameters are both in the allowable error range, and verifies the feasibility of studying evaporation loss through this model.
This paper takes a certain 300MW generating unit for example, and studies the influence law of inlet water temperature, circulating water flow and environmental parameters on evaporation loss, from the perspective of independent operation of cooling tower. Following laws are concluded from the calculation results. Firstly, when inlet water temperature increases and the other parameters keep constant, the evaporation loss increases while evaporation loss rate per unit temperature difference decreases. Secondly, when inlet water flow decreases and inlet water temperature keeps constant, the evaporation loss decreases while evaporation loss rate per unit temperature difference increases. Thirdly, when the dry bulb temperature increases and inlet water temperature keeps constant, the evaporation loss decreases while evaporation loss rate per unit temperature difference increases. Fourthly, when the ambient relative humidity increases and inlet water temperature keeps constant, the evaporation loss and evaporation loss rate per unit temperature difference both decrease.
In thermal power plant, cooling tower and condenser are both important parts of cold end system, and they are interdependent and interactive. Not only circulating water flow and ambient parameters will influence the evaporation loss directly, but they will also influence the evaporation loss through influencing heat transfer performance of the condenser indirectly. Therefore, in order to analyze and evaluate the evaporation loss completely, this paper also takes the whole cold end system as research object, and studies the overall influence of circulating water flow and ambient parameters on evaporation loss, under the premise of total heat transfer of condenser keeping constant. The following conclusions are drawn from the calculation results. Firstly, when the dry bulb temperature increases, the evaporation loss increases and evaporation loss rate per unit temperature difference also increases. Secondly, when the ambient relative humidity increases, the evaporation loss decreases and evaporation loss rate per unit temperature difference also decreases. Thirdly, when circulating water flow decreases and total heat transfer of condenser keeps constant, the evaporation loss has little decrease and evaporation loss rate per unit temperature difference decreases slowly.
There is very great relationship between evaporation loss and water saving of cold end system, and the final purpose of analyzing evaporation loss is to save water. Research results of this subject lay a theoretical foundation for water-saving of cooling tower.
本文以自然通风逆流湿式冷却塔为研究对象,在分析冷却塔传热传质的基础上,建立了冷却塔蒸发水损失计算模型,并编制了此模型的求解程序。分别以某300MW和600MW机组对应的实型塔为例,计算了不同工况下冷却塔的出塔水温和蒸发水损失,并分别对比了计算出塔水温与实测出塔水温、模型计算蒸发水损失与近似公式计算蒸发水损失,对比表明两参数的相对误差均在允许误差范围内,验证了此模型用以研究冷却塔蒸发水损失的可行性。
本文以某300MW机组对应的实型塔为例,先从冷却塔单独运行的角度出发,研究了进塔水温、循环水量以及环境参数对冷却塔蒸发水损失产生的影响规律。计算结果表明:其他参数不变,冷却塔进塔水温升高,蒸发水损失增加,但单位温差引起的蒸发水损失率降低;进塔水温不变,进塔水量减少,冷却塔蒸发水损失减少,但单位温差引起的蒸发水损失率升高;进塔水温不变,环境干球温度升高,冷却塔蒸发水损失减少,但单位温差引起的蒸发水损失率升高;进塔水温不变,环境相对湿度增加,冷却塔蒸发水损失减少,单位温差引起的蒸发水损失率减少。
火电厂中,冷却塔和凝汽器作为冷端系统的重要组成部分,两者相互影响,相互制约。循环水量以及环境气象参数发生变化不仅会直接影响冷却塔蒸发水损失,而且还会通过影响凝汽器侧的换热性能来间接影响冷却塔的蒸发水损失。因此,为全面分析和评价冷却塔蒸发水损失,本文还以整体运行的冷端系统为研究对象,在凝汽器总换热量保持不变的前提下,研究了循环水量和环境参数变化对冷却塔蒸发水损失产生的整体影响。计算结果表明:在凝汽器换热量保持不变的前提下,环境干球温度升高,冷却塔蒸发水损失以及单位温差引起的蒸发水损失率也都升高;环境相对湿度增加,蒸发水损失减少,单位温差引起的蒸发水损失率降低;循环水量减少,冷却塔蒸发水损失以及单位温差引起的蒸发水损失率均是降低的。
蒸发水损失与冷端系统节水存在极大的关系,分析蒸发水损失的最终目的在于节水。本课题的研究成果,为冷却塔节水奠定了理论基础。
The cooling process of circulating water is very important in power generation industry. Circulating water can be cooled not only by heat transfer through contaction but also by heat transfer through evaporation mainly.The evaporation loss induced by heat transfer through evaporation is a very important part of water loss in cooling tower, and also is the maximum water-consumption project in thermal power plant. Not only evaporation loss will bring great economic loss to thermal power plants, but it also will pollute the environment by forming white fog on the top of cooling tower. Therefore research on evaporation loss of cooling tower is of much practical significance.
In this paper, with the research object of natural draft counter-flow wet cooling tower, calculation model of evaporation loss was established and solving program was composed based on analyzing heat and mass transfer in cooling tower. Taking a certain 300MW and a certain 600MW generating unit for example respectively, outlet water temperature and evaporation loss of cooling tower under different working conditions were calculated, and comparisons were done between calculated and measured outlet water temperature, between evaporation losses calculated through calculation model and approximate formulas respectively. The results show that relative errors of the two parameters are both in the allowable error range, and verifies the feasibility of studying evaporation loss through this model.
This paper takes a certain 300MW generating unit for example, and studies the influence law of inlet water temperature, circulating water flow and environmental parameters on evaporation loss, from the perspective of independent operation of cooling tower. Following laws are concluded from the calculation results. Firstly, when inlet water temperature increases and the other parameters keep constant, the evaporation loss increases while evaporation loss rate per unit temperature difference decreases. Secondly, when inlet water flow decreases and inlet water temperature keeps constant, the evaporation loss decreases while evaporation loss rate per unit temperature difference increases. Thirdly, when the dry bulb temperature increases and inlet water temperature keeps constant, the evaporation loss decreases while evaporation loss rate per unit temperature difference increases. Fourthly, when the ambient relative humidity increases and inlet water temperature keeps constant, the evaporation loss and evaporation loss rate per unit temperature difference both decrease.
In thermal power plant, cooling tower and condenser are both important parts of cold end system, and they are interdependent and interactive. Not only circulating water flow and ambient parameters will influence the evaporation loss directly, but they will also influence the evaporation loss through influencing heat transfer performance of the condenser indirectly. Therefore, in order to analyze and evaluate the evaporation loss completely, this paper also takes the whole cold end system as research object, and studies the overall influence of circulating water flow and ambient parameters on evaporation loss, under the premise of total heat transfer of condenser keeping constant. The following conclusions are drawn from the calculation results. Firstly, when the dry bulb temperature increases, the evaporation loss increases and evaporation loss rate per unit temperature difference also increases. Secondly, when the ambient relative humidity increases, the evaporation loss decreases and evaporation loss rate per unit temperature difference also decreases. Thirdly, when circulating water flow decreases and total heat transfer of condenser keeps constant, the evaporation loss has little decrease and evaporation loss rate per unit temperature difference decreases slowly.
There is very great relationship between evaporation loss and water saving of cold end system, and the final purpose of analyzing evaporation loss is to save water. Research results of this subject lay a theoretical foundation for water-saving of cooling tower.
引文
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[4]周彤.污水同用:解决城市缺水的有效途径[J].建设科技,2002,1:43-45.
[5]王佩璋.研究各种节水技术大幅度降低火力发电取水量[J].电站辅机,2004,91(4):30-34.
[6]刘存波.火电厂水务管理[M].北京:中国电力出版社,1998.
[7]A.Pasricha,S.K.Jain.Zero discharge water management sustem.Proceedings of american power conference[J].1981(43):1153-1154.
[8]王芳.我国火电厂耗水水平分析与节水措施[J].河北电力技术,2001,20:6-9.
[9]Roger Jorden and John Maulbetsch.Zero-discharge concept grapples with reality[J].Power,1982(6):107-111.
[10]L.C.Webb,K.R.Weiss.True Zero Discharge:Water and Wastewater Design Considerations[J].Power Engineering.1989,93(7):36-39.
[11]张晓燕,张新海,薛渌.空冷技术热点问题探讨.电力设备,2006,3:107-110.
[12]R.Benedeto,A.J.Freedman,D.Boschetti,GF.Hays.Cooling Towers& Secondary Waste Makeup:Four Years' Operating Experience[J].IWC-99-42:331-343.
[13]A.C.Rogers,J.W.Kluesener,C.V.Jensen.Management of Power Plant Water and Wastewater in Water-Short Regions[J].Proceeding of the American Power Conference.1980(42):1040-1047.
[14]H.J.Martin,GR.Miller.A Zero Discharge Steam Electric Power Generating Station[J].Journal AWWA.1986(5):57-58.
[15]Joel.M.Davie,K.Yegerlehner,T.Scheurman.Design,Start-up,and Initial Operation of The Zero Discharge System at Indiantown Generating Plant[J].IWC-98-27:199-201.
[16]A.L.Farber,E.E.Harniman,R.Mital.Complete Reuse of Wastewater from a Refinery/Petrochemical Plant[J].IWC-98-53:32-37.
[17]曾德勇,李建玺,王蓉蓉,陈浩.二级污水在火电厂循环冷却系统中的应用[J],热力发电,2004,3:55-57.
[18]黄德勇,杨宝红,王璟,许臻.废水在电厂循环水系统中的应用[J],热力发电,2003.5:58-60.
[19]许臻,李秀娟,杨宝红等.生活污水在菏泽发电厂的应用[J],热力发电,2004.6:68-70.
[20]王天正,王佩璋.高压静电收水技术在冷却塔上的应用:——火电厂节水技术的最新发展[J].静电,1995,10(3):9-13.
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