600 MW机组冷却塔优化改造后热力性能分析

冷却塔作为火电厂热力循环中最主要的冷端设备之一,与电厂经济运行有着密切的关系,但其节能问题往往被忽视。以某600 MW机组双曲线逆流式自然通风冷却塔为研究对象,对冷却塔的淋水填料和喷溅装置优化改造后进行了热力性能试验,并对其冷却能力进行计算,同时,将改造后的淋水填料特性和喷头优化性能进行分析,指出冷却塔冷却能力得到提升的原因,为电厂在今后的冷却塔运行优化和节能改造提供了依据。     

600MW机组冷却塔风水匹配强化换热改造研究

根据冷却塔内吸热侧湿空气和放热侧循环水的温度场、速度场、湿度场的分布情况,重新设计冷却塔配水系统及其填料的布置方式,并对其实施改造达到风水匹配最佳效果。改造后实测冷却能力值达到115.0%,超过了设计冷却能力,对大型及超大型自然通风逆流式冷却塔相应的后续研究与改造有示范意义。     

逆流湿式冷却塔内不锈钢填料热力性能的试验研究

逆流湿式冷却塔是工业生产中普遍使用的换热设备,填料热力性能优劣直接影响到冷却塔热力性能优劣。为研究不锈钢填料的热力性能,搭建了逆流湿式冷却塔实验台,对比分析了S波、人字波和V波三种不锈钢填料与S波PVC填料随进塔水温的热力性能变化规律,以及研究了S波不锈钢填料随淋水密度的热力性能,结果表明:不锈钢填料的热力性能比常用PVC填料好,S波、人字波和V波不锈钢填料与S波PVC填料的冷却塔进出水温差和总换热量均随进塔水温的增大而增大,而冷却塔的冷却效率随进塔水温的升高先增大后减小,进塔水温在37.5～38.5℃时,冷却塔的冷却效率达到最大;且S波不锈钢填料冷却塔进出水温差、冷却塔的冷却效率及总换热量随淋水密度的增大而减小。优化填料波纹形状以及材料均有助于提高冷却塔的热力性能。     

火电厂自然通风冷却塔性能研究

冷却塔是汽轮发电机组重要的冷端设备之一,其冷却性能对电站的经济和安全运行有重要的影响。以双曲线型自然通风冷却塔为研究对象,根据实际运行参数,通过对冷却塔热力性能的计算,得到了冷却水出塔水温及其主要影响因素——填料层淋水密度不均对出塔水温的影响。计算结果与实测值相符。同时,对冷却塔内气体流场建立热态模型并进行了空气动力性能的数值计算。冷却塔热力和空气动力性能的变化规律为冷却塔的运行、检修和改造提供了依据。     

湿式冷却塔配水系统分区配水的数值模拟研究

为分析配水系统分区配水在不同流量下对自然循环通风逆流湿式冷却塔冷却性能的影响,基于计算流体力学软件ANSYS FLUENT对冷却塔配水系统进行了研究。详细模拟了冷却塔分区配水在不同配水流量下对出塔水温的影响,给出了冷却塔最大冷却能力所对应的配水流量,并对冷却塔塔内的速度及温度参数进行了详细分析。结果表明,分区配水方式结合适当的配水流量可以有效地降低出塔水温,提高冷却塔的效率与经济性。     

300MW机组冷却塔进风优化改造前后的性能评价

搜集分析了某300MW自然通风逆流湿式冷却塔采用进风口进风优化技术改造前后的实际运行数据,时间跨度大约3年,分别采用了传统的冷却塔评价指标:冷却温差、冷却幅高、冷却效率以及特性系数评价指标,对冷却塔的冷却性能进行了分析比较,结果表明改造后冷却塔的冷却性能优于改造前冷却塔的冷却性能,四周进风均匀化,循环水温度可以降低0.5℃～1.5℃.     

某百万级核电站冷却塔配置研究与优化

基于某百万级核电站冷却塔配置比较及优化分析,高位收水塔方案年运行费用优于常规塔方案,冷却塔采用高位收水装置后,能有效降低水泵几何扬程,节省运行费用。淋水面积越大,采用高位收水装置的经济优势越大。根据数模试验结论,高位收水塔应进行塔内填料布置深度优化,即减小外围填料厚度、增大内围填料厚度,最终实现冷却塔整体热力性能的最大化。     

热电厂自然通风冷却塔的提效改造

分析仪征化纤公司热电中心2~#循环水冷却塔冷却效率下降的原因,阐述通过更新冷却塔填料、喷溅装置等一系列方法和措施来提升该冷却塔进、出水温差,达到提升其冷却效率的改造情况。最后,分析此次2~#冷却塔提效改造后对热电厂提高发电经济效益影响。     

考虑冷却塔淋水密度影响的循环水泵运行优化分析

传统循环水泵运行优化方法未考虑冷却水流量变化、冷却塔淋水密度变化对冷却塔出塔水温的影响。随着循环水泵运行方式变化,冷却水流量变化、冷却塔淋水密度变化,直接影响冷却塔出塔水温变化,而且随着冷却塔淋水密度增大,冷却塔出塔水温提高幅度逐渐加大。结合机组实际运行情况,研究了考虑冷却塔淋水密度影响的循环水泵运行优化方法,通过试验调整的方式分析确定冷却塔淋水密度变化对冷却塔出塔水温的影响,完善了循环水泵运行优化方法,使运行优化结果更结合实际生产情况,提高机组运行经济性。     

高层建筑冷却塔选型校核及气流组织模拟

本文对某高层建筑屋面冷却塔在节能改造后所出现的夏季极端天气无法达到设计冷却能力的状况通过改造工程进行分析,并采用Airpak软件对夏季工况进行了CFD模拟。模拟结果所显示的逆流式冷却塔四周的梁、柱、擦窗机轨道、和核心筒外墙等建筑遮挡物并未对冷却塔散热效果造成影响。夏季屋面风速的变化,未影响冷却塔进风与排风,未出现热湿空气回流现象,间接反映了设备布置合理。此项目对同类型的建筑物屋面放置冷却塔有一定的参考意义。     

自然通风湿式冷却塔加装挡风板优化设计

以湿冷机组自然通风冷却塔相关理论为基础,借助于CFD模拟软件,建立了火电机组湿式冷却塔的传热传质模型,主要的换热区域如填料、雨区和喷淋区采用离散相模型。由于冬季气温较低和塔内的换热不均,在冷却塔的填料下面、进风口处、基环面容易结冰,提出了在进风口处加装挡风板的方案,数值模拟分析结果显示,该方案改善了塔内温度场,有效的防止了塔内结冰。     

Numerical simulation of a closed wet cooling tower with novel design

A closed wet cooling tower with novel design was proposed and numerically investigated. The studied cooling tower consists of two main parts: one heat and mass transfer unit (HMTU) and one heat transfer unit (HTU). In the HMTU, copper tubes are arranged as heat transfer tubes while plastic tubes are collocated to enlarge the mass transfer area between the spray water and the airflow. In the HTU, only copper tubes are adopted as heat transfer tubes. Heat and mass transfer process takes place among the process water, airflow and spray water in the HMTU, while in the HTU only heat transfer between the process water and the spray water is observed. A transient one dimensional distributed-parameter model was adopted to evaluate the cooling tower performance under different operating conditions. Determination of heat and mass transfer coefficients, as well as the influence of Lewis number on the cooling tower performance, was presented.     

基于焓差理论的带填料逆流闭塔热力性能分析

为了分析不同风量和喷淋水量对填料逆流闭式冷却塔热力性能的影响,建立和验证了带填料逆流闭式冷却塔热质交换的数学模型,基于焓差理论对模型计算的结果进行分析。结果表明：加入填料相当于对盘管区进口的喷淋水进行预冷,降低了喷淋水的平均温度,使带填料闭式冷却塔的冷却性能优于纯盘管闭式冷却塔;风量的增加可以提高带填料逆流闭式冷却塔和纯盘管逆流闭式冷却塔的热力性能,两种塔的冷却性能随风量增加的提升速率相同;喷淋水量的增加对纯盘管逆流闭式冷却塔的热力性能的影响较小,却可以较大幅度提高带填料逆流闭式冷却塔的热力性能。     

Energy and Mass Transfer Phenomena in Natural Draft Cooling Towers

In this paper, the development of natural draft cooling towers diagnostics is presented. Diagnostic method is based on measurements of velocity and temperature fields of the airflow in the entire surface area of cooling tower and the raised phenomenological model of heat and mass transfer in a selected reference vertical segment of cooling tower. Velocity and temperature fields of the airflow were measured with the aid of a remote control mobile robot unit that was developed to enable measurements in an arbitrary measurement point above the spray zones over the entire cooling tower area. Topological structures of the humid air velocity profiles and temperature profiles above the spray zones were obtained at constant integral parameters of a power plant. Measurement results of temperature and mass flow characteristics of the air and water flows in a selected reference vertical segment of cooling tower are presented in the form of phenomenological dependence. Phenomenological dependence links local cooling tower efficiency, geometrical characteristics of spray elements, and air and water flow rates. In the concluding part, both methods are applied together on a selected segment of cooling tower, and local and integral cooling tower efficiency can be determined.     

Simplification of analytical models and incorporation with CFD for the performance predication of closed‐wet cooling towers

Simplified analytical models are developed for evaluating the thermal performance of closed‐wet cooling towers (CWCTs) for use with chilled ceilings in cooling of buildings. Two methods of simplification are used with regard to the temperature of spray water inside the tower. The results obtained from these models for a prototype cooling tower are very close to experimental measurements. The thermal performance of the cooling tower is evaluated under nominal conditions. The results show that the maximum difference in the calculated cooling water heat or air sensible heat between the two simplified methods and a general computational model is less than 3%. The analytical model distribution of the sensible heat along the tower is then incorporated with computational fluid dynamics (CFD) to assess the thermal performance of the tower. It is found that CFD results agree well with the analytical results when the air flow is simulated with air supply from the bottom of the tower, which represents a uniform air flow. CFD shows the importance of the uniform distribution of air and spray water to achieve optimum design. Copyright © 2002 John Wiley & Sons, Ltd.     

Three-dimensional numerical study on thermal performance of a super large natural draft cooling tower of 220m height

Based on the heat and mass transfer theory and the characteristics of general-purpose software FLUENT, a three-dimensional numerical simulation platform, composed of lots of user defined functions（UDF）, has been developed to simulate the thermal performance of natural draft wet cooling towers（NDWCTs）. After validation, this platform is used to analyse thermal performances of a 220m high super large cooling tower designed for inland nuclear plant under different operational conditions. Variations of outlet temperature of the cooling tower caused by changes of water flow rates, inlet water temperatures are investigated. Effects of optimization through non-uniform water distributions on outlet water temperature are discussed, and the influences on the flow field inside the cooling tower are analyzed in detail. It is found that the outlet water temperature will increase as the water flow rate increases, but the air flow rate will decrease. The outlet water temperature will decrease 0.095K and 0.205K, respectively, if two non-uniform water distribution approaches are applied.     

自然通风湿式冷却塔防冻数值研究

由于我国北方地区冬季气温较低,冷却塔普遍存在结冰问题,必须采取一定的防冻措施。通过FLUENT软件模拟分析得出进塔水温对塔内不同特征面水温的影响规律,并进一步模拟加装不同层数挡风板后冷却塔内流场的变化。计算结果表明:①当运行工况其它条件不变时,随着进塔水温的升高,塔内不同特征面最低水温升高;②加装一定层数挡风板能使填料下面空气温度场和进风口上沿面空气速度场分布逐渐趋于均匀,有利于防止塔内结冰;③选取进塔水温分别为17.80℃、21.95℃、26.77℃、30.04℃时,分别加装4、3、2、1层挡风板可有效防止塔内结冰。     

A comprehensive approach to cooling tower design

In this paper, a mathematical model for a counterflow wet cooling tower is derived, which is based on one-dimensional heat and mass balance equations using the measured heat transfer coefficient. The balance equations are solved numerically to predict the temperature change of air and water, as well as the humidity as a function of the cooling tower high. Experimental measurements on two pilot-scale cooling towers were carried out in order to analyze the performance of different cooling tower filling materials. Also, the performance of other cooling tower elements, such as droplet separators and water spray nozzles, was investigated in the pilot experiments. The flow distribution, i.e. the velocity field, upstream to the filling material was predicted using the three-dimensional version of the computational fluid dynamics (CFD) code Fluent/uns, version 4.2. The calculated flow fields are presented for different distances between the inlet of the air and the filling material. In addition, the two-dimensional version of the CFD code Fluent/uns, version 4.2, was applied to predict the external airflow around the cooling tower and the backflow in different weather conditions in summer and winter. The research project was carried out in connection to an industrial cooling tower installation.     

利用冷却塔节能的途径与方法

通过分析不同因素对冷却塔冷却能力的影响，从运行过程中节约风机、水泵等能耗的观点出发，总结了利用冷却塔节能的各种实施方法。