Air interaction around outdoor air-cooled condensers

In order to increase cooling or heating efficiency,a porous computational fluid dynamics（CFD）model is employed to predict the thermo-fluid status and optimize the placement of outdoor units.A full scale model is established to validate the accuracy of CFD simulation in terms of velocity and temperature distributions.The comparison between the measurement and the simulation shows a good agreement.By evaluating the condensers＇ sucked air temperature with CFD for three units installed in a row,it is found that the minimum separation distance among neighboring units is 0.2 m;a vertical wall should be apart from the unit line by at least 0.8 m;and large different operating pressures among units do not impact the flow rate and the heat transfer of the other units meaningfully.

Thermodynamic Simulation of CCP in Air-Cooled Heat Pump Unit with HFCs and CO₂Trans-Critical

The exergy analysis and finite time thermodynamic methods had been employed to analyze the compound condensation process (CCP). It was based on the air-cooling heat pump unit. The cooling capacity of the chiller unit is about 1 kW, and the work refrigerant is R22/R407C/R410A/CO2. The MATLAB/SIMULINK software was employed to build the simulation model. The thermodynamic simulation model is significant for the optimization of parameters of the unit, such as condensation and evaporation temperature and mass flow of the sanitary hot water and size of hot water storage tank. The COP of the CCP of R410A system is about 3% - 5% higher than the CCP of the R22 system, while CCP of the R407C system is a little lower than the CCP of R22 system. And the CCP of CO2 trans-critical system has advantage in the hot supply mode. The simulation method provided a theoretical reference for developing the production of CCP with substitute refrigerant R407C/R410A/CO2.

The Experimental Investigation of Recirculation of Air-Cooled System for a Large Power Plant

The paper introduces thermal buoyancy effects to experimental investigation of wind tunnel simulation on direct air-cooled condenser for a large power plant. In order to get thermal flow field of air-cooled tower, PIV experiments are carried out and recirculation ratio of each condition is calculated. Results show that the thermal flow field of the cooling tower has great influence on the recirculation under the cooling tower. Ameliorating the thermal flow field of the cooling tower can reduce the recirculation under the cooling tower and improve the efficiency of air-cooled condenser also.

Influence of thermal flow field of cooling tower on recirculation ratio of a direct air-cooled system for a power plant

In order to get thermal flow field of direct air-cooled system,the hot water was supplied to the model of direct air-cooled condenser(ACC). The particle image velocimetery (PIV) experiments were carried out to get thermal flow field of a ACC under different conditions in low velocity wind tunnel,at the same time,the recirculation ratio at cooling tower was measured,so the relationship between flow field characteristics and recirculation ratio of cooling tower can be discussed. From the results we can see that the flow field configuration around cooling tower has great effects on average recirculation ratio under cooling tower. The eddy formed around cooling tower is a key reason that recirculation produces. The eddy intensity relates to velocity magnitude and direction angle,and the configuration of eddy lies on the geometry size of cooling tower. So changing the flow field configuration around cooling tower reasonably can decrease recirculation ratio under cooling tower,and heat dispel effect of ACC can also be improved.

Measures against the adverse impact of natural wind on air-cooled condensers in power plant

The natural wind plays disadvantageous roles in the operation of air-cooled steam condensers in power plant.It is of use to take various measures against the adverse effect of wind for the performance improvement of air-cooled condensers.Based on representative 2×600 MW direct air-cooled power plant,three ways that can arrange and optimize the flow field of cooling air thus enhance the heat transfer of air-cooled condensers were proposed.The physical and mathematical models of air-cooled condensers with various flow leading measures were presented and the flow and temperature fields of cooling air were obtained by CFD simulation.The back pressures of turbine were calculated for different measures on the basis of the heat transfer model of air-cooled condensers.The results show that the performance of air-cooled condensers is improved thus the back pressure of turbine is lowered to some extent by taking measures against the adverse impact of natural wind.

Thermo-flow characteristics and air flow field leading of the air-cooled condenser cell in a power plant

Special A-frame geometry of the air-cooled condenser cell and the complicated flow field at the exit of the axial flow fan bring on the air mal-distribution on the surface of the finned tube bundles and the deteriorated thermo-flow performances of a condenser cell. It is of benefit to the design and operation optimization of the direct dry cooling system in a power plant to investigate the thermo-flow characteristics of the condenser cell and propose the flow leading measures of cooling air. On the basis of the representative configuration of the air-cooled condenser cell in a 600 MW direct dry cooling power plant, the computa- tional models of the air side fluid and heat flows are built, in which the actual fan blade geometric details are considered. Various flow field leading ways of cooling air are presented and the thermo-flow characteristics in the A-frame condenser cell and through the finned tube bundles are compared. Results show that the flow field leading measures can result in the increased volumetric flow rate and heat rejection, thus bringing on the improved performance of the condenser cell. The improvement of thermo-flow oerformances depends upon the geometric details of the flow guiding device.

Influences of Lateral Double-Layered Deflectors on Cooling Performance of Air-Cooled Condenser

The cooling performance of air-cooled condenser(ACC)is susceptible to adverse impacts of ambient winds.In this work,three kinds of lateral double-layered deflectors installed under the ACC platform are proposed to weaken the unfavorable effects of cross winds.Through CFD simulation methods,the main parameters of thermo-flow performances of a 2×660 MW direct dry cooling system are obtained,by which it can be concluded that the deflectors can effectively reduce the inlet air temperatures while enhance the mass flow rates of upwind fans due to the guiding effect,especially at high wind speeds,while the improvement of cooling capacity of ACCs in the 0°wind direction is weak.The inclined-vertical deflectors are superior to others in performance improvement of ACCs for all cases,which can reduce the turbine back pressure by 12.15%when the wind speed is 12 m/s,so they can be applied to the performance enhancement of ACCs under windy conditions in practical engineering.

Performance Assessment of Air-Cooled Steam Condenser with Guide Vane Cascade

Ambient wind has an unfavourable impact on air-cooled steam condenser(ACSC) performance. A new measure to improve ACSC performance is proposed by setting a diffusion type guide vane cascade beneath the ACSC platform. The numerical models are developed to illustrate the effects of diffusion type guide vane cascade on ACSC performance. The simulation results show that this vane cascade can cause the increases in coolant flows across almost all fans due to its diffusion function and lower flow resistance. Meanwhile, the guide vane cascade also decreases the fan inlet temperatures because of the uniform flow field around the condenser cells. Comparing with the case without guide device, the overall heat transfer efficiency is increased by 11.2% for guide vane cascade case under the condition of 9 m/s. The heat transfer efficiency firstly enhances and then decreases with decreasing stagger angle of guide vane under a certain wind speed. The optimum stagger angle corresponding to the maximum heat transfer efficiency is about 65.5°. The heat transfer efficiency always enhances as increasing vane cascade height, and a vane cascade with 20 m to 30 m height may be suitable to the ACSC as considering the cost.

Application of machine learning to develop a real-time air-cooled condenser monitoring platform using thermofluid simulation data

A data-driven surrogate model is proposed for a 64-cell air-cooled condenser system at a power plant.The surro-gate model was developed using thermofluid simulation data from an existing detailed 1-D thermofluid network simulation model.The thermofluid network model requires a minimum of 20 min to solve for a single set of in-puts.With operating conditions fluctuating constantly,performance predictions are required in shorter intervals,leading to the development of a surrogate model.Simulation data covered three operating scopes across a range of ambient air temperatures,inlet steam mass flow rates,number of operating cells,and wind speeds.The surrogate model uses multi-layer perceptron deep neural networks in the form of a binary classifier network to avoid ex-trapolation from the simulation dataset,and a regression network to provide performance predictions,including the steady-state backpressure,heat rejections,air mass flowrates,and fan motor powers on a system level.The integrated surrogate model had an average relative error of 0.3%on the test set,while the binary classifier had a 99.85%classification accuracy,indicating sufficient generalisation.The surrogate model was validated using site-data covering 10 days of operation for the case-study ACC system,providing backpressure predictions for all 1967 input samples within a few seconds of compute time.Approximately 93.5%of backpressure predictions were within±6%of the recorded backpressures,indicating sufficient accuracy of the surrogate model with a significant decrease in compute time.

An Influencing Factor - Water-Filter Ratio on Heat Resistance of Condensate Polishing Filter Material in Water

In air-cooled condenser, high temperature condensing water m summer which approaching and exceed 60＊ C, which may result in filter materials degradation and release impurities. This paper discusses an influencing factor, water-filter ratio （soaking solution and filter quality ratio）, on leachable dissolution rate and filter material degradation rate m high temperature water. The UV absorption at 254nm （A254） and the exchange capacity ware measured after heat test as composite indicators. In addition, the Wends of A254 variation with heating time were measured in different water-filter ratio. The stability is probably due to the effect of water-filter ratio. This has been further borne out that, water-filter ratio increases, leachable concentration decreases exponentially and tends to a fLxed value.

ACC凝结水精处理系统的选择

论述了ACC凝结水精处理系统配备的必要性，分析了2种配备的优缺点。

ACC凝结水溶氧不合格的治理

以云冈热电厂为例，叙述了ACC凝结水溶氧不合格的原因，提出了治理方案。

用扩散层模型与多相流方法对空冷凝汽器逆流管内凝结与流动的数值模拟

针对空冷凝汽器上的逆流凝结管,用扩散层模型模拟管内空气–蒸汽的组分输运,用多相流理论中的VOF方法建立管内两相流的控制方程,分别用Lee模型与CSF模型计算方程中的质量与动量源项。在一根仿真样管(长宽高尺寸:1000mm?5mm?50mm,倾斜角:60?)上,运行9个算例,对管内两相流的凝结换热与流动进行数值模拟。数值结果表明,在样管出口管段,管壁上的热流密度波动较大;当样管入口的空气含量超过1.0%时,不可凝气体对管内蒸汽凝结的影响不可忽略。获得了管内气相组分浓度的标量场,发现,扩散层内存在的空气浓度梯度是管内蒸汽凝结性能恶化的原因。利用瞬态计算,捕捉到管内复杂的动力学特性,包括液膜悬空、液膜爬坡与液滴夹带,发现这些特性会破坏管内扩散层的稳定与完整,增强蒸汽凝结;用可视化的两相流体积分数云图,表现液膜悬空、爬坡溢出以及液滴从形成到抛起的连续过程,并分析这些现象发生时,两相流的速度特征;数值计算还得到了管壁上液膜的流型,将其定性为溪状流。

基于SVM的电站空冷凝汽器积灰特性建模

电站空冷凝汽器(ACC)积灰严重降低了换热性能,建立有效的积灰特性模型是ACC换热性能在线监测与优化清洗的基础.以600MW机组参数为例,通过ACC传热过程理论计算模型,提取ACC积灰特征参数,使用支持向量机算法,利用现场实验获取的检测数据,建立ACC换热面积灰状态下换热系数预测模型,进而推导ACC清洁系数,从而实时监测积灰清洗状况.结果表明:所建模型可实现换热性能的快速监测,有效降低换热系数的计算复杂度;模型验证样本均方根误差、绝对百分比误差和决定系数分别为0.60、2.13%和0.9838,预测性能良好.该模型可为开发大型空冷机组ACC积灰监测与智能清洗系统提供依据.

大型直接空冷电站的设计和运行情况

针对大同第二发电厂二期工程2×600MW直接空冷电站设计经验,对空冷汽轮机技术条件、空冷系统容量、风机群噪声、大风对空冷系统的影响等问题提出意见。如:留出足够的安全运行背压余量,尽量避免机组跳闸现象的发生;对汽轮机汽封设计及汽封加热器容量应给以足够的重视;空冷机组负荷调度应符合空冷系统运行的特点。文章最后分析了汽轮发电机基座和空冷平台支撑结构安装的技术问题,目前,已开展小柱距全钢结构空冷平台的研究和应用,以降低造价,减轻施工难度。

9F级燃气—蒸汽联合循环电厂空冷凝汽器与水冷凝汽器对全厂效率的技术及经济性影响对比分析

为分析空冷凝汽器（ACC）与水冷凝汽器对于9F级燃气—蒸汽联合循环电站全厂经济性指标的影响,通过引用9F级燃气—蒸汽联合循环电站方案的相关参数,建立ACC与水冷凝汽器方案对比分析模型.通过理论分析,并与实际项目方案和运行电站的经济性指标对比,验证了理论分析模型的可靠性.理论分析结果表明,ISO环境条件、纯凝无抽汽的工况下,采用ACC的9F燃气-蒸汽联合循环的全厂毛效率约为57.3482％～57.7869％,而采用水冷凝汽器的9F燃气-蒸汽联合循环的全厂毛效率约为58.4662％.ACC方案相对水冷凝汽器方案全厂效率降低约为0.6793％～1.1180％.

火电厂300MW机组直接空冷系统的控制与运行

在分析了火电厂直接空冷系统的工艺过程和功能特点的基础上,介绍了基于DCS控制的300MW机组直接空冷控制系统的组成、测点布置及控制功能,并对系统的启动准备、启动运行、正常运行、低负荷运行、关闭运行、非正常运行、紧急运行等工况进行了详细分析,实际运行结果表明直接空冷冬季防冻措施灵活可靠,直接空冷可通过改变风机转速或停运风机或使风机反转来调节空冷凝汽器的进风量或直至吸热风来防止空冷凝汽器冻结,调节相对灵活,效果良好。

国产660MW超临界直接空冷机组甩负荷试验分析

分析某电厂660MW超临界直接空冷机组甩负荷试验实例,介绍试验前的必备条件和必要操作,甩负荷试验过程中的具体时间控制和各参数变化情况,提出保证甩负荷试验成功的操作要点,供同类型机组甩负荷试验借鉴和参考。

冷凝器空气泄漏标准的探讨

电站汽轮机凝汽器真空的维持对于机组运行的经济性和安全性的影响重大,目前的真空泄漏标准一直沿用《电力建设施工验收技术规范》的相关规定,现场反映这个标准太松。结合制造厂及现场泄漏率的计算,期望能得到一个更合理的泄漏标准,对今后标准的制订有一定的参考价值。

1 000 MW直接空冷发电机组凝汽器传热性能试验研究

不同工况下空冷凝汽器的换热性能,是火电直接空冷机组设计、优化和运行的主要依据。针对实际运行的1 000 MW超超临界直接空冷机组,对其凝汽器进行了夏季、冬季和秋季工况的试验研究。试验获得了夏季和冬季工况下凝汽器翅片管束迎面风速的分布和壁面温度的分布,发现翅片管束迎面风速分布从上至下逐渐增高,而管束壁面温度分布对于顺流单元从上至下逐渐降低,对于逆流单元从上至下逐渐增高;获得了顺流翅片管束的易结冻区域;获得了秋季工况下1 000 MW空冷机组空冷凝汽器空气侧努赛尔数和雷诺数之间的无量纲关联式。