侧风环境下自然通风逆流湿式冷却塔的配水系统研究
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摘要
自然通风逆流湿式冷却塔是电站冷端系统的重要设备,其冷却效率的高低影响凝汽器内的真空,进而影响整个热力系统的循环热效率。冷却塔配水的好坏与冷却效率的高低密切相关,因此研究侧风环境中冷却塔的配水方式并对其进行优化,具有十分重要的工程意义。
本文总结了冷却塔尤其是配水系统的发展过程,介绍了国内外关于配水的研究现状,然后从配水系统的作用、型式、实际运行中存在的问题及原因对冷却塔的配水系统进行了全面阐述。虹吸式配水方式由于只采用一个中央竖井,解决了多竖井配水不均的问题,并且能够实现分区配水,使得冷却塔的运行更加经济,近年来在不少冷却塔中得到应用。
在冷却塔的热力计算中,不少方法都假定出塔空气处于饱和状态。因为出塔空气可能达到过饱和状态,所以这些方法对分析冷却塔内的传热传质是片面的。本文引入了能准确求解出塔空气状态的Poppe方法,分别针对出塔空气未饱和或饱和、出塔空气过饱和建立了控制方程。作者通过编写Matlab程序完成了对该模型的求解,从而为冷却塔传热传质参数的计算奠定了基础。冷却塔内气水之间的总换热量包括接触换热量和蒸发换热量,蒸发换热是气水换热的主要方式。
试验研究是科学研究的重要方法之一,本文主要依靠热态试验研究冷却塔的配水系统,介绍了试验步骤、测量参数及所用仪表。模型试验应满足几何相似、动力相似、气流流动相似的原则,根据动力相似的原则可以确定热态试验中风速应为实际风速的1/10,试验中设定的侧风风速为0、0.2、0.4、0.6、0.8m/s,用于模拟大气环境中常出现的一级到五级风。
在冷却塔的运行中会出现喷溅装置堵塞或损坏从而造成相应的区域出现局部配水障碍,通过试验对其如何影响冷却塔的冷却性能进行了研究。研究发现,随着局部配水障碍面积的增大,冷却性能逐渐降低,本文给出了若干工况下冷却塔的传热量、蒸发水量随局部配水障碍面积的变化曲线,从而对冷却性能受影响的程度有一个量的认识。
本文在对空气动力场分析的基础上,分析了配水方向对冷却塔冷却性能的影响,并且考虑环境侧风的影响,提出了配水方向由外向内的一个方案,即环形中空管式配水,介绍了它的特点。通过热态试验与全塔均匀配水在不同侧风影响下的冷却性能对比,表明配水方向由外向内能使得配水更好的和空气动力场相协调,冷却塔的冷却效率提高。
Natural draft counter-flow wet cooling tower (NDWCT) is the main equipment of the cold end system in power plants. Its cooling efficiency influences the vacuum of condenser. Furthermore, it also has effects on the cycle thermal efficiency of the thermal power system. Because the effect of water distribution has something to do with the cooling efficiency, it is of great important engineering implication to study on the water distribution mode and make optimization under cross wind conditions.
This paper summarizes the development process of the NDWCT as well as its distribution system especially. It introduces the present condition of domestic and international research. Then the function and pattern of water distribution system are introduced. It points out the current problems and its cause in the engineering practice. Recently, suction type shaft water distribution mode is used in many cooling towers, which only have one vertical well for each one. Compared with the cooling tower which has several vertical wells, water distribution is more uniform. It can divide the water distribution zone and make the operation of cooling towers more economic.
In the thermal power calculation of cooling tower, many methods assume that the outlet air is saturated. It is unilateral to analyse the heat and mass transfer in the cooling tower because the outlet air may reach to the supersaturated status. In order to ascertain the outlet air status exactly, the Poppe method is cited in this paper, which sets up the governing equations for unsaturated or saturated and supersaturated air respectively. A Matlab program has been written by the author to solve the model and it is good for the calculation of the parameters concerning about the heat and mass transfer in cooling towers. The total heat transfer between water and air includes the convective and the evaporative heat transfer and the latter is the main mode.
Experimental study is one of the important way of scientific research. This paper mainly depends on the thermal status experiment to study the water distribution system of NDWCT. It introduces the experimental procedure and measurement parameters with corresponding instruments. Especially, the simulation experiment should satisfy the principle of geometry similarity, dynamical and air flow analogue. According to the dynamical analogue, the velocity in the experiment should correspond to 10% of the actual value. The cross wind velocity is set respectively to be 0, 0.2, 0.4, 0.6 and 0.8m/s, which is used to simulate the wind from band 1 to band 5 in the atmosphere.
Due to the blockage or damage of the spray equipment, local anomalies of water distribution appear in the corresponding zone during the operation process of cooling tower. Experimental study has been carried out to learn how to influence the cooling performance. The result in the form of photographs shows that with the increasing area of local anomalies, the cooling performance decreases gradually. Therefore, the influence of local anomalies on the cooling performance can be learned deeply on the level of quantity.
Influence of water distribution direction on the cooling tower performance is analyzed on the basis of analysis of air dynamical field. Considering about the influence of the cross wind, one project whose water distribution direction is from exterior to interior is proposed, i.e. the circular piping distribution mode without water in the central zone. Also, its characteristics are introduced in this paper. Compared to the uniform water distribution with the aid of thermal status experiment, the result has shown that water distribution can harmonize with the air dynamical field all the better while the water flow direction is from exterior to interior. Thus the cooling efficiency is improved.
本文总结了冷却塔尤其是配水系统的发展过程,介绍了国内外关于配水的研究现状,然后从配水系统的作用、型式、实际运行中存在的问题及原因对冷却塔的配水系统进行了全面阐述。虹吸式配水方式由于只采用一个中央竖井,解决了多竖井配水不均的问题,并且能够实现分区配水,使得冷却塔的运行更加经济,近年来在不少冷却塔中得到应用。
在冷却塔的热力计算中,不少方法都假定出塔空气处于饱和状态。因为出塔空气可能达到过饱和状态,所以这些方法对分析冷却塔内的传热传质是片面的。本文引入了能准确求解出塔空气状态的Poppe方法,分别针对出塔空气未饱和或饱和、出塔空气过饱和建立了控制方程。作者通过编写Matlab程序完成了对该模型的求解,从而为冷却塔传热传质参数的计算奠定了基础。冷却塔内气水之间的总换热量包括接触换热量和蒸发换热量,蒸发换热是气水换热的主要方式。
试验研究是科学研究的重要方法之一,本文主要依靠热态试验研究冷却塔的配水系统,介绍了试验步骤、测量参数及所用仪表。模型试验应满足几何相似、动力相似、气流流动相似的原则,根据动力相似的原则可以确定热态试验中风速应为实际风速的1/10,试验中设定的侧风风速为0、0.2、0.4、0.6、0.8m/s,用于模拟大气环境中常出现的一级到五级风。
在冷却塔的运行中会出现喷溅装置堵塞或损坏从而造成相应的区域出现局部配水障碍,通过试验对其如何影响冷却塔的冷却性能进行了研究。研究发现,随着局部配水障碍面积的增大,冷却性能逐渐降低,本文给出了若干工况下冷却塔的传热量、蒸发水量随局部配水障碍面积的变化曲线,从而对冷却性能受影响的程度有一个量的认识。
本文在对空气动力场分析的基础上,分析了配水方向对冷却塔冷却性能的影响,并且考虑环境侧风的影响,提出了配水方向由外向内的一个方案,即环形中空管式配水,介绍了它的特点。通过热态试验与全塔均匀配水在不同侧风影响下的冷却性能对比,表明配水方向由外向内能使得配水更好的和空气动力场相协调,冷却塔的冷却效率提高。
Natural draft counter-flow wet cooling tower (NDWCT) is the main equipment of the cold end system in power plants. Its cooling efficiency influences the vacuum of condenser. Furthermore, it also has effects on the cycle thermal efficiency of the thermal power system. Because the effect of water distribution has something to do with the cooling efficiency, it is of great important engineering implication to study on the water distribution mode and make optimization under cross wind conditions.
This paper summarizes the development process of the NDWCT as well as its distribution system especially. It introduces the present condition of domestic and international research. Then the function and pattern of water distribution system are introduced. It points out the current problems and its cause in the engineering practice. Recently, suction type shaft water distribution mode is used in many cooling towers, which only have one vertical well for each one. Compared with the cooling tower which has several vertical wells, water distribution is more uniform. It can divide the water distribution zone and make the operation of cooling towers more economic.
In the thermal power calculation of cooling tower, many methods assume that the outlet air is saturated. It is unilateral to analyse the heat and mass transfer in the cooling tower because the outlet air may reach to the supersaturated status. In order to ascertain the outlet air status exactly, the Poppe method is cited in this paper, which sets up the governing equations for unsaturated or saturated and supersaturated air respectively. A Matlab program has been written by the author to solve the model and it is good for the calculation of the parameters concerning about the heat and mass transfer in cooling towers. The total heat transfer between water and air includes the convective and the evaporative heat transfer and the latter is the main mode.
Experimental study is one of the important way of scientific research. This paper mainly depends on the thermal status experiment to study the water distribution system of NDWCT. It introduces the experimental procedure and measurement parameters with corresponding instruments. Especially, the simulation experiment should satisfy the principle of geometry similarity, dynamical and air flow analogue. According to the dynamical analogue, the velocity in the experiment should correspond to 10% of the actual value. The cross wind velocity is set respectively to be 0, 0.2, 0.4, 0.6 and 0.8m/s, which is used to simulate the wind from band 1 to band 5 in the atmosphere.
Due to the blockage or damage of the spray equipment, local anomalies of water distribution appear in the corresponding zone during the operation process of cooling tower. Experimental study has been carried out to learn how to influence the cooling performance. The result in the form of photographs shows that with the increasing area of local anomalies, the cooling performance decreases gradually. Therefore, the influence of local anomalies on the cooling performance can be learned deeply on the level of quantity.
Influence of water distribution direction on the cooling tower performance is analyzed on the basis of analysis of air dynamical field. Considering about the influence of the cross wind, one project whose water distribution direction is from exterior to interior is proposed, i.e. the circular piping distribution mode without water in the central zone. Also, its characteristics are introduced in this paper. Compared to the uniform water distribution with the aid of thermal status experiment, the result has shown that water distribution can harmonize with the air dynamical field all the better while the water flow direction is from exterior to interior. Thus the cooling efficiency is improved.
引文
[1]Baker,Donald.Cooling tower performance[M].New York:Chemical Pub.Co.,1984.
[2]Cooper,John H.The Worthington cooling tower for the continuous use of condensing water[J].Journal of the Franklin Institute,June,1896.
[3]赵振国.冷却塔[M].北京:中国水利水电出版社,2001.
[4]史佑吉.冷却塔运行与试验[M].北京:水利电力出版社,1990.
[5]胡三季,陈玉玲.自然通风冷却塔的节能改造[J].热力发电,2004(12).
[6]J.Smrekar,J.Oman and B.Sirok.Improving the efficiency of natural draft cooling towers[J].Energy Conversion and Management,2006(47):1086-1100.
[7]曾建柱.自然通风逆流式冷却塔配水型式比较[J].电力建设,2002年4月第23卷第4期.
[8]翁迅干,陆振铎.自然通风逆流式冷却塔虹吸式竖井配水的探讨[J].电力建设,2001年5月第22卷第5期.
[9]高坤华,李恒远.冷却塔虹吸式配水系统简介[J].山东电力技术,2001年第3期.
[10]杨世斌,张小东,刘卫东.自然通风逆流冷却塔的治理改造[N].电力学报,2005年第20卷第1期.
[11]徐跃芹,屠珊,黄文江,李慧君.火电厂自然通风冷却塔性能研究[J].汽轮机技术,2005年10月第47卷第5期.
[12]赵海廷.大型冷却塔出水温度异常的原因及处理[J].发电设备,2007 No.4.
[13]曾建柱.虹吸式竖井配水冷却塔设计、施工、运行中的问题与对策[J].电力建设,2007年1月第28卷第1期.
[14]J.C.Kloppers,D.G.Kroger,A critical investigation into the heat and mass transfer analysis of counterflow wet-cooling towers,Int.J.Heat Mass Transfer 48(2005)765-777.
[15]Walker WH,Lewis WK,McAdams WH,Gilliland ER,Principles of chemical engineering,3rd ed,New York,McGraw-Hill Inc,1923.
[16]Merkel F.Verdunstungshuhlung,Zeitschrift des Vereines Deutscher Ingenieure(VDI)1925;70:123-8.
[17]Nenad Milosavljevic,Pertti Heikkila,A comprehensive approach to cooling tower design,Applied Thermal Engineering 21(2001)899-915.
[18]M.N.A.Hawlader,B.M.Liu,Numerical study of the thermal-hydraulic performance of evaporative natural draft cooling towers,Applied Thermal Engineering 22(2002)41-59.
[19]S.P.Fisenko,A.I.Petruchik,A.D.Solodukhin,Evaporative cooling of water in a natural draft cooling tower,Int.J.Heat Mass Transfer 45(2002)4683-4694.
[20]J.R.Khan,M.Yaqub,Syed M.Zubair,Performance characteristics of counter flow wet cooling towers,Energy Conversion and Management 44(2003)2073-2091.
[21]Paisarn Naphon,Study on the heat transfer characteristics of an evaporative cooling tower,International Communications in Heat and Mass Transfer 32(2005)1066-1074.
[22]V.D.Papaefthimiou,T.C.Zannis,E.D.Rogdakis,Thermodynamic study of wet cooling tower performance,Int.J.Energy Res.30(2006)411-426.
[23]Thirapong Muangnoi,Wanchai Asvapoositkul,Somchai Wongwises,An exergy analysis on the performance of a counterflow wet cooling tower,Applied Thermal Engineering 27(2007)910-917.
[24]F.Bosnjakovic,Technische Thermodinamik;Theodor Steinkopf,Dresden,1965.
[25]W.M.Simpson,T.K.Sherwood,Performance of small mechanical draft cooling towers,Refrigerating Engineering 52(6)(1946)525-543,574-576.
[26]J.C.Kloppers,D.G.Kroger,The Lewis factor and its influence on the performance prediction of wet-cooling towers,International Journal of Thermal Sciences 44(2005)879-884.
[27]李浪艇.贵阳电厂#2冷却塔效率的提高[J].贵州电力技术,2005年第4期.
[28]贺平,孙刚.供热工程(第三版)[M].北京:中国建筑工业出版社,2000.
[29]王凯.自然通风冷却塔进风口空气动力场的数值模拟与阻力研究[D].山东大学硕士学位论文,2006.
[30]章熙民,任泽霈.传热学(第四版)[M].北京:中国建筑工业出版社,2001.
[31]高明.侧风环境下自然通风逆流湿式冷却塔传热传质特性的研究[D].山东大学博士学位论文,2007.
[32]程艳花.自然通风逆流湿式冷却塔基础性能及环境侧风影响的研究[D].山东大学硕士学位论文,2007.
[2]Cooper,John H.The Worthington cooling tower for the continuous use of condensing water[J].Journal of the Franklin Institute,June,1896.
[3]赵振国.冷却塔[M].北京:中国水利水电出版社,2001.
[4]史佑吉.冷却塔运行与试验[M].北京:水利电力出版社,1990.
[5]胡三季,陈玉玲.自然通风冷却塔的节能改造[J].热力发电,2004(12).
[6]J.Smrekar,J.Oman and B.Sirok.Improving the efficiency of natural draft cooling towers[J].Energy Conversion and Management,2006(47):1086-1100.
[7]曾建柱.自然通风逆流式冷却塔配水型式比较[J].电力建设,2002年4月第23卷第4期.
[8]翁迅干,陆振铎.自然通风逆流式冷却塔虹吸式竖井配水的探讨[J].电力建设,2001年5月第22卷第5期.
[9]高坤华,李恒远.冷却塔虹吸式配水系统简介[J].山东电力技术,2001年第3期.
[10]杨世斌,张小东,刘卫东.自然通风逆流冷却塔的治理改造[N].电力学报,2005年第20卷第1期.
[11]徐跃芹,屠珊,黄文江,李慧君.火电厂自然通风冷却塔性能研究[J].汽轮机技术,2005年10月第47卷第5期.
[12]赵海廷.大型冷却塔出水温度异常的原因及处理[J].发电设备,2007 No.4.
[13]曾建柱.虹吸式竖井配水冷却塔设计、施工、运行中的问题与对策[J].电力建设,2007年1月第28卷第1期.
[14]J.C.Kloppers,D.G.Kroger,A critical investigation into the heat and mass transfer analysis of counterflow wet-cooling towers,Int.J.Heat Mass Transfer 48(2005)765-777.
[15]Walker WH,Lewis WK,McAdams WH,Gilliland ER,Principles of chemical engineering,3rd ed,New York,McGraw-Hill Inc,1923.
[16]Merkel F.Verdunstungshuhlung,Zeitschrift des Vereines Deutscher Ingenieure(VDI)1925;70:123-8.
[17]Nenad Milosavljevic,Pertti Heikkila,A comprehensive approach to cooling tower design,Applied Thermal Engineering 21(2001)899-915.
[18]M.N.A.Hawlader,B.M.Liu,Numerical study of the thermal-hydraulic performance of evaporative natural draft cooling towers,Applied Thermal Engineering 22(2002)41-59.
[19]S.P.Fisenko,A.I.Petruchik,A.D.Solodukhin,Evaporative cooling of water in a natural draft cooling tower,Int.J.Heat Mass Transfer 45(2002)4683-4694.
[20]J.R.Khan,M.Yaqub,Syed M.Zubair,Performance characteristics of counter flow wet cooling towers,Energy Conversion and Management 44(2003)2073-2091.
[21]Paisarn Naphon,Study on the heat transfer characteristics of an evaporative cooling tower,International Communications in Heat and Mass Transfer 32(2005)1066-1074.
[22]V.D.Papaefthimiou,T.C.Zannis,E.D.Rogdakis,Thermodynamic study of wet cooling tower performance,Int.J.Energy Res.30(2006)411-426.
[23]Thirapong Muangnoi,Wanchai Asvapoositkul,Somchai Wongwises,An exergy analysis on the performance of a counterflow wet cooling tower,Applied Thermal Engineering 27(2007)910-917.
[24]F.Bosnjakovic,Technische Thermodinamik;Theodor Steinkopf,Dresden,1965.
[25]W.M.Simpson,T.K.Sherwood,Performance of small mechanical draft cooling towers,Refrigerating Engineering 52(6)(1946)525-543,574-576.
[26]J.C.Kloppers,D.G.Kroger,The Lewis factor and its influence on the performance prediction of wet-cooling towers,International Journal of Thermal Sciences 44(2005)879-884.
[27]李浪艇.贵阳电厂#2冷却塔效率的提高[J].贵州电力技术,2005年第4期.
[28]贺平,孙刚.供热工程(第三版)[M].北京:中国建筑工业出版社,2000.
[29]王凯.自然通风冷却塔进风口空气动力场的数值模拟与阻力研究[D].山东大学硕士学位论文,2006.
[30]章熙民,任泽霈.传热学(第四版)[M].北京:中国建筑工业出版社,2001.
[31]高明.侧风环境下自然通风逆流湿式冷却塔传热传质特性的研究[D].山东大学博士学位论文,2007.
[32]程艳花.自然通风逆流湿式冷却塔基础性能及环境侧风影响的研究[D].山东大学硕士学位论文,2007.