Full scale experimental study of a small natural draft dry cooling tower for concentrating solar thermal power plant

Concentrating solar thermal power system can provide low carbon,renewable energy resources in countries or regions with strong solar irradiation.For this kind of power plant which is likely to be located in the arid area,natural draft dry cooling tower is a promising choice.To develop the experimental studies on small cooling tower,a 20 m high natural draft dry cooling tower with fully instrumented measurement system was established by the Queensland Geothermal Energy Centre of Excellence.The performance of this cooling tower was measured with the constant heat input of 600 kW and 840 kW and with ambient temperature ranging from 20 ℃ to 32 ℃.The cooling tower numerical model was refined and validated with the experimental data.The model of 1 MW concentrating solar thermal supercritical CO2 power cycle was developed and integrated with the cooling tower model.The influences of changing ambient temperature and the performance of the cooling tower on efficiency of the power system were simulated.The differences of the mechanism of the ambient temperature effect on Rankine cycle and supercritical CO2 Brayton cycle were analysed and discussed.

NUMERICAL INVESTIGATION OF THE ADVERSE EFFECT OF WIND ON THE HEAT TRANSFER PERFORMANCE OF TWO NATURAL DRAFT COOLING TOWERS IN TANDEM ARRANGEMENT

This article reports the findings on the adverse effect of the crosswind on the performance of natural draft cooling towers through numerical computation with the k-epsilon eddy-viscosity turbulence model. It is observed here that the cause of the adverse effect of the crosswind on the cooling towers call be attributed to the around flow effect which destroys the radial inflow into the cooling towers when the wind is absent. Hence, a significant deterioration in the heat transfer from the heat exchangers at lateral sides occurs.

Spray Effect on the Thermal Performances of a Dry Cooling Tower

Pre-cooling the inlet air of a dry cooling tower by means of a spray can improve the tower performance during periods of high temperature.To study the spray effect on the thermal performance of natural draft dry cooling towers(NDDCTs),in this study 3-D numerical simulations of such a process have been conducted using Fluent 16.2(a two-way coupled Eulerian-Lagrangian approach).The considered NDDCT is 120 m high and only half system is simulated due to its structural symmetry.Three different spray strategies have been investigated at a typical crosswind speed of 4 m/s,which is the most frequent wind speed.The results have shown that:(1)The three implemented spray strategies can improve the thermal performance of the studied NDDCT with a vary-ing degree of success.In one case,the heat rejection rate can be increased by 35.2%,and the tower outlet water temperature can be decreased by 2.1℃ when compared with the no spray case;(2)To improve the thermal per-formance of the NDDCT using a small amount of water,the design of the spray pre-cooling system must include more nozzles on the windward and fewer or even no nozzles on the leeward sides of the NDDCT.

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.

低风阻流线型导风板对自然通风湿式冷却塔的性能影响

为改善冷却塔雨区流场结构,进一步增大通风量,在已有平板型导风板基础上,提出一种布置在雨区的低风阻流线型导风板。设计工况下,以常规冷却塔和在各高度布置平板型导风板的改造塔为参考对象,分析5种不同布置高度(1/6、1/3、1/2、2/3、5/6进风高度)下低风阻流线型导风板对整塔通风量、塔内流场结构和温度分布等参数的影响。结果表明:随着导风板布置高度的升高,塔内各区域的空气分配发生了变化,对内区填料换热产生了明显影响,使整塔冷却性能呈现出先提升后下降的趋势;在进风口高度2/3处布置流线型导风板时,通风量增量与填料区底部平均温度减量达到最优值,冷却塔性能改善效果最佳,此时相较于常规冷却塔,循环水温降相对增长2.65%,通风量相对增长2.78%。此外,相较于最佳布置高度的平板型导风板,采用低风阻流线型导风板改造后循环水温降相对增长1.2%。

冷却塔定向拆除时剩余支柱的轴力计算方法

为了使冷却塔的定向拆除更加安全可控,对冷却塔保留柱轴向力的计算方法展开研究。根据力的相似关系给出支柱轴向力与其Z向力之间的关系式,基于平截面假定推导保留柱Z向力的计算公式;利用有限元研究环梁和支柱的弹性模量、支柱高度、保留柱数量以及相邻柱柱顶所对应的圆心角5种参数对保留柱Z向力的影响;根据有限元的结果对保留柱Z向力的计算公式进行修正,并研究修正后公式的适用性。结果表明:爆破后的冷却塔在所有保留柱上并不满足平截面假定;在实际工程范围内,上述5种参数不影响保留柱Z向力的分布规律为Z向力沿着y轴方向上的分布形态始终“两端受压,中间受拉”,且保留柱中的最大压力始终出现在第n排保留柱上,最大拉力始终出现在第(n-4)排保留柱上;当爆破圆心角为200°~240°时,修正后计算值的相对误差在21%以内,且该公式在不同冷却塔上具有良好的适用性。保留柱轴向力的计算公式从力学角度为冷却塔的拆除提供了理论支撑,增加了拆除工作的安全性。

某大型石化项目海水冷却系统设计

通过国外某大型石化项目海水冷却系统设计,对海水直流冷却及海水循环冷却2种设计方案进行比较,从工艺流程、平面布置、构筑物设置、设备选型及投资估算等方面进行探讨,分析了设计中注意事项,以及设计中遇到的重难点问题,总结出相关思路及经验,以供类似项目参考。

高位收水冷却塔噪声预测方法优化及噪声治理措施探讨

对湖北省某660 MW燃煤发电厂高位收水冷却塔进行了现场测试,根据测试结果对高位收水冷却塔噪声预测模型进行了优化和验证,并对高位收水冷却塔的噪声治理措施进行了探讨。结果表明,采用发声部位水平面声源优化模型计算得到的高位收水冷却塔噪声衰减规律与实测结果更加接近;虽然高位收水冷却塔附近地面噪声源强实测声级较常规冷却塔低约8 dB(A),但总体声功率级的改善效果并不能达到8 dB(A)的水平;同时,由于高位收水冷却塔声源位置较高,对围墙外某些特殊点位,高位收水冷却塔的噪声影响可能反而会略高于常规冷却塔;消声导流片及吸隔声屏障在应用于高位收水冷却塔降噪时需根据声源实际情况进行模型验证优化,而声源降噪措施可从改善水滴对收水斜板的冲击以及收水斜板本身振动噪声方面进一步研究。

A decoupled method to identify affecting mechanism of crosswind on performance of a natural draft dry cooling tower

The natural draft dry cooling tower(NDDCT)has been increasingly used for cooling in power generation in arid area.As crosswind affects the performance of a NDDCT in a complicated way,and the basic affecting mechanism is unclear,attempts have been made to improve the performance of a NDDCT based on limited experiences.This paper introduces a decoupled method to study the complicated crosswind effects on the inlet and outlet of a NDDCT separately by computational fluid dynamics(CFD)modeling and hot state experiments.Accordingly,the basic affecting mechanism of crosswind on the NDDCT performance is identified.Crosswind changes the inlet flow field of a NDDCT and induces mainstream vortices inside the tower,so as to degrade the ventilation.Besides,low crosswind deflects the upward plume at the outlet to further degrade the ventilation,while high crosswind induces the low pressure area at the outlet to reduce the ventilation degradation.

Experimental Study of Effects of Cross Wind on Flow in Natural-draft Dry-cooling Towers

The effects of cross wind on the flow field in natural draft dry cooling towers are studied experimentally in a wind tunnel using similarity principles. Particular attention is focused on the flow fields inside the tower. The study illustrates the influence of wind on the cooling tower performance and proposes a number of techniques for improving tower performance with a cross wind

STUDY ON THE AIRFLOW RESISTANCE IN NATURAL DRAFT COOLING TOWERS

A new approach for improving the calculation of the airflow resistance coefficient of natural draft cooling towers from the inlet to throat (4) has been presented in this paper. The suggested equations areWhere. ζ1 is the coefficient of the airflow resistance with no consideration of waterdrop in rain zone, ζ2 is the coefficient of the airflow resistance due to falling of waterdrop in rain zone, s is the rate of the inlet area to the area at elevation of the packing, q is the water loading, V0 air velocity at the packing section.

A Novel Approach for Energy Efficiency Prediction of Various Natural Draft Wet Cooling Towers Using ANN

Cooling tower is crucial equipment in the cool-end system of power plant and the natural draft counter-flow wet cooling tower(NDWCT)gets wide application.The artificial neural network(ANN)technique is becoming an effective method for the thermal performance investigation of cooling towers.However,the neural network research on the energy efficiency performance of NDWCTs is not sufficient.In this paper,a novel approach was proposed to predict energy efficiency of various NDWCTs by using Back Propagation(BP)neural network:Firstly,based on 638 sets of field test data within 36 diverse NDWCTs in power plant,a three-layer BP neural network model with structure of 8-14-2 was developed.Then the cooling number and evaporation loss of water of different NDWCTs were predicted adopting the BP model.The results show that the established BP neural network has preferable prediction accuracy for the heat and mass transfer performance of NDWCT with various scales.The predicted cooling number and evaporative loss proportion of the testing cooling towers are in good agreement with experimental values with the mean relative error in the range of 2.11%–4.45%and 1.04%–4.52%,respectively.Furthermore,the energy efficiency of different NDWCTs can also be predicted by the proposed BP model with consideration of evaporation loss of water in cooling tower.At last,a novel method for energy efficiency prediction of various NDWCTs using the developed ANN model was proposed.The energy efficiency index(EEI)of different NDWCTs can be achieved readily without measuring the temperature as well as velocity of the outlet air.

双层布置间冷散热器数值试验研究

利用ANSYSFluent软件,在自然通风状态下,对我国首创并实施的双层布置间冷散热器的流动和换热性能进行了数值模拟、分析和研究。环境风速不大于4.5m/s时,下层各冷却柱的通风量和换热量均高于相应上层冷却柱。当环境风速为10m/s~20m/s时,间冷塔迎风面,下层冷却柱的通风量和换热量均低于上层;在间冷塔两侧及下风侧,下层冷却柱的通风量和换热量则高于上层。随着环境风速的增大,上层冷却柱将首先出现热空气流出间冷塔和“穿堂风”的现象。不同环境风速下,下层冷却柱的总通风量和总换热量均高于上层,二者总通风量相差1.29%~10.18%,总换热量相差1.11%~9.23%。

环境风向对自然通风直接空冷塔散热影响

自然通风直接空冷系统既不需要机械通风风机,也不需要间接空冷系统的循环水泵,大幅度降低了噪声、厂用电率和供电煤耗,符合“低碳”时代发展要求。自然通风直接空冷系统在大容量机组尚未应用,需掌握环境风向对自然通风直接空冷塔散热的影响规律。利用流体力学模型仿真FLUENT软件,对2×660 MW机组的直接空冷塔不同风向进行数值模拟,得到不同风向下各散热三角的通风量和散热量分布特点、直接空冷塔总体散热性能以及风向对直接空冷塔和主厂房总体布置的影响。结果表明,2台机组的自然通风直接空冷塔的中心连线优先与主导风向平行。

塔壁导热对钢结构间接空冷系统流动换热性能的影响

文章探究塔壁导热对钢结构空冷塔浮升力和流动换热性能的影响,建立塔壁导热对钢塔输运性能影响的理论模型;以2×350 MW热电联产机组配置一座钢塔为工程实例,开展数值模拟计算并与混凝土塔进行对比分析。结果表明:塔外蒙皮条件下的钢塔导热性能,远高于塔内外均置蒙皮下的钢塔和混凝土塔;塔外蒙皮条件下的钢塔导热对空冷系统浮升力将产生小幅度影响;任意塔壁导热条件下,可以忽略塔壁导热对系统整体换热性能的影响,然而环境风效应下,背风区域局部换热性能将受到一定的影响。

典型侧风下喷嘴十字布置的喷淋方案对空冷塔冷却性能的影响

针对侧风会改变空冷塔内部及其周围的空气动力场,为了研究侧风下喷淋预冷对空冷塔换热性能的影响,建立了空冷塔的半塔数值仿真模型,研究了典型侧风风速4 m/s下120 m高的自然通风空冷塔在喷嘴十字布置下换热性能的变化规律。结果表明:侧风与喷嘴十字布置的夹角(即侧风风向)对喷淋冷却效果影响较大,在夹角为45°时喷淋液滴有效蒸发比和半塔的换热量都达到最大值分别为69.7%和58.8 MW,此时单位质量喷淋水量对空冷塔的换热性能提升最好,空冷塔单位换热量的最大值为2.3 MJ/kg;通过喷淋适应环境侧风的调控,与未喷淋时相比,空冷塔的全塔换热量提高了8.6%(由108.4 MW提高到了117.7 MW),出水温度降低了0.8℃,为侧风下空冷塔预喷淋系统的全塔喷嘴布置优化提供指导。

燃气-蒸汽联合电厂冷却塔选型配置研究

冷却塔塔型的合理选择是电厂安全可靠、经济高效运行的重要保证。以某1×470 MW级燃气—蒸汽联合电厂为例,首先针对带机械通风冷却塔的二次循环供水系统进行优化分析计算,然后采用“冷效相同”原则,对本工程循环水系统采用不同塔型的方案进行技术经济比较。

多功能一体化布置高位收水冷却塔

以安全可靠、高效环保、节能降耗、配置优化、经济合理为基础,对某项目机械通风冷却塔型式进行研究,选取常规机械通风冷却塔和机械通风高位收水冷却塔两种选型方案,并在高位收水塔的方案上进行创新,将循环水泵站、综合水池、综合水泵站与高位收水冷却塔进行一体化布置,得到了年费用更低、节能环保的冷却塔布置方案。

大型冷却塔表面脉动风压原型实测与分布准则

我国冷却塔规范风荷载条款仍源自20世纪80年代原型冷却塔(约90m高)实测资料,且仅规定了塔筒表面静态风压分布。事实上,超大型冷却塔(高度≥165m)风振问题与风荷载脉动作用关系更加密切,由此导致了冷却塔数学和物理试验模型雷诺数效应模拟准则的不完整性,难于准确再现冷却塔表面动态风荷载与来流条件、塔群组合状况等参数间的合理关系,已成为制约大型冷却塔抗风性能研究和结构设计的瓶颈。为此,采用全天候动态风压采集设备,对某电厂冷却塔(约166m高)进行通风筒表面动、静态风压长期现场观测,量化表面脉动压力与来流紊流度之间的影响关系,提出具有原创性的冷却塔超高雷诺数条件(Re≥6E7)脉动风压雷诺数效应模拟准则。

采用数值风洞模型对热电厂烟塔合一大气污染扩散的研究

随着城市的快速建设,城市建筑的高度和体量不断增加,同时大气污染源的排放方式和排放状态也与从前发生了很大的变化,特别是热电厂采用烟塔合一排放方式的出现,对常规应用的稳态远距离以统计学为基础理论的高斯大气预测方法提出了挑战。目前国内外广泛使用的大气污染物预测模式——德国模式在烟塔合一排放方式的预测上存在着许多关键性问题,如大风下洗条件下,冷却塔附近空腔区的大小和范围、空腔区污染物最高地面浓度等无法给出准确的预测结果。为准确预测烟塔合一排放方式的大气污染物扩散情况,采用一种新的大气污染物扩散的预测模式——数值风洞模型进行模拟预测研究,预测结果表明,在烟塔合一排放方式下,大气污染物最高地面浓度随风速增加而增加,同时在冷却塔下风向存在负压区,污染物在该区域高浓度聚集。且在夏季6.0m/s风速下,冷却塔下风向最高地面浓度出现峰值,属于最不利的气象条件。数值风洞模型可利用图形化手段实现对空腔区产生、变化、破碎至再生成的全过程描述,从而建立了一种大气污染预测的重要手段。