直接空冷风机的选型原则和步骤

介绍空冷电站的直接空冷风机的选型原则和步骤,并分析与直接空冷风机的选型有关的影响因素。     

基于正交试验方法的直接空冷风机耗电影响因素分析

直接空冷机组的空冷风机耗电量大,优化其运行方式可以提高全厂经济性.从直接空冷凝汽器的换热过程和风机耗电量的理论分析,找出了影响空冷风机电耗大小的主要因素.以某300MW直接空冷机组为例,利用其大量的历史运行数据,采用正交试验方法,分析了影响其空冷风机耗电的主要因素,得到环境温度、背压、负荷等因素对空冷风机电耗的影响规律.结果表明,环境温度对空冷风机的电耗影响最为显著.     

锅炉侧面来风对空冷机组换热效率的影响

环境风特别是横向环境风会引起热风回流,造成空气凝汽器换热恶化,影响直接空冷机组的安全、经济性运行。以国内某电厂300MW直接空冷系统为例,利用Fluent软件,针对锅炉侧面风给直接空冷机组带来的不利影响,对空冷岛外部流场进行了数值模拟研究。主要分析了锅炉侧面来风的不同风速下空冷平台流场情况,研究了锅炉侧面风在对空冷风机冷空气吸入量和空冷凝汽器换热性能的影响。     

环境因素对直接空冷机组的影响

直接空冷机组的运行状况受周围环境的影响很大,不同的风速、风向不仅会影响到机组运行的经济性,甚至还会造成掉闸停机事故。本文在总结火力发电厂空冷系统特点的基础上,对现场环境及所采集数据进行了系统分析,重点研究了环境作用对直接空冷机组空冷风机吸入风量和入口温度以及空冷机组背压影响,同时分析了环境温度的变化对空冷机组供电煤耗的影响。     

某660MW超临界机组空冷系统运行优化研究

为了对某660MW超临界空冷机组空冷系统进行优化,建立了该机组空冷凝汽器变工况计算模型,并对影响排汽压力的主要因素进行分析。研究结果表明:随着风机运行台数的增加、风机运行频率的升高,机组排汽压力均降低;随着风机运行台数或频率的逐渐降低,排汽压力升高愈发剧烈,此时要注意安全运行;最佳频率所对应的排汽压力随着负荷增加而升高,低负荷低环境温度时,排汽压力维持在阻塞背压附近,高负荷高环境温度时,排汽压力增加逐渐加剧。最终提出优先降低空冷风机运行频率,当空冷风机运行频率低于规定最低频率时,再减少空冷风机运行台数的策略,得到该机组运行最佳排汽压力所对应的最佳空冷风机运行频率曲线,为同类型机组空冷风机优化运行提供参考。     

某300MW直接空冷机组风机运行调整研究

以某300MW直接空冷机组为研究对象,进行春秋季节风机调整实验研究。通过对空冷风机转速的调节,由DPM读取风机转速的调整值、机组背压值和环境温度等,来观察机组各参数的变化及对机组的影响情况。通过对结果进行分析,得到风机转速的变化对机组背压的影响规律,并指导机组的运行。     

直接空冷机组最佳背压计算方法及应用

分析了直接空冷机组运行中背压的主要影响因素,基于机组运行数据,采用支持向量机和粒子群算法建立了一个最佳背压计算模型,分析了背压与发电机功率和空冷风机耗功功率的关系.以某300 MW直接空冷机组为研究对象,利用所建模型计算得出不同负荷段内不同环境温度所对应的最佳背压;在DCS里设计背压优化调节方案,将最佳背压送入背压调节逻辑中参与控制.结果表明:直接空冷机组最佳背压随负荷和环境温度的升高而升高;最佳背压实际应用后,能够在保证机组安全平稳运行的前提下提高经济效益.     

防风网在直接空冷系统中防风效应的分析

讨论了自然风对空冷风机入口的影响情况,阐述了防风网的防风机理,并分析了防风网在空冷系统中的防风效果,其可以有效降低风机入口横向风速,增加空冷凝汽器换热效率进而提高机组的经济性和安全性。     

某600MW直接空冷系统运行优化研究

旨在科学指导空冷系统优化运行,实现节能减排,以某600MW直接空冷系统为技术依托,通过机组背压对机组出力影响试验和机组空冷风机耗功试验,以净出力法为指导,进行空冷系统运行优化试验研究,得到了机组不同负荷、不同环境气温下的最佳风机运行方式,以风机同操模式下的频率、机组负荷和环境温度的函数关联式编入机组控制系统中,并实现了空冷系统优化运行的自动控制。在年平均气温和平均负荷下,空冷系统运行优化使得机组供电煤耗下降0.6g/(kW·h)。     

冷媒除霜系统应用于冻结库时除霜性能研究

基于优化冷风机结构为目的的冷媒除霜系统应用于冻结库中,通过采用6mm翅片间距的冷风机进行冻结过程中除霜与不除霜的对比实验。并且研究除霜过程对库温波动、冻结物温度波动、冻结时间等参数的影响,以及系统运行的特性。研究表明:应用冷媒除霜系统,每次除霜对库内造成的温度波动都在5℃以内、除霜过程对冻结物温度不产生波动、除霜情况的冻结时间较不除霜缩短了一小时,并且选择除霜对系统更节能。因此,在冷媒除霜系统中采用适时除霜的方式不仅可以避免翅片间隙被冰霜封堵,还可以缩小冷风机翅片间距。在相同换热面积下,缩小冷风机翅片间距还可以达到减小冷风机体积和占地面积的效果。     

超临界补气增焓高温CO2热泵热风机实验研究

针对工业上循环加热工况下,CO₂热泵气体冷却器出口温度过高、能效显著降低的问题,文章提出了带有超临界补气的高温CO₂热泵循环,并对系统进行了实验研究。主要分析了主路膨胀阀开度、压缩机频率、气体冷却器的风机频率对出风温度、性能系数COP等参数的影响。实验结果表明:出风温度随着主路膨胀阀开度的增大呈现降低趋势而COP呈升高趋势;降低气体冷却器的风机频率对出风温度的提升效果最为明显,风机频率每调低1%,出风温度最大提升5.07%。以得到最高出风温度为目标的实验数据表明,该系统在气体冷却器出口温度为75℃以上时,出风温度可达130℃以上,对应COP为1.40~1.50。     

空冷器风机变频器的DCS状态显示控制系统改造

空冷器风机在DCS系统中的状态只有正常运行显示，没有停机或者故障显示，变频器保护停机后的再启动的时间间隔将会引起系统操作参数波动，影响产品质量和正常生产。针对这种情况将变频参数优化与控制线路改进，使空冷器风机变频器保护停运时，DCS系统能显示空冷器风机停运并发出报警信号，重新启动时间由原来3min少到5s以内，大大缩短了空冷器风机启动时间，解决了空冷器风机停运对装置造成的影响，确保了生产的连续平稳运行。     

Thermal comfort enhancement by using a ceiling fan

A parametric analysis on the effect of using a ceiling fan in an air-conditioned room is performed by two-dimensional (2D) numerical simulation of steady state airflow and heat transfer. Thermal comfort analysis is done for a person standing in a room with an inlet and an outlet for air conditioning and a ceiling fan. Representative three-dimensional (3D) simulation is also performed for the comparison of results obtained by using 2D and 3D models. Distributions of velocity, temperature, and relative humidity are presented. Different cases in which the ceilings fan may be not in use or in use with different air speed normal to the plane of fan blades due to different rotational speeds are considered. Predicted mean vote is computed and used to assess the thermal comfort characteristics. It is found that as the normal air speed from the fan increases, thermal comfort significantly shifts toward the cooler scale to allow higher supply air temperature or higher heat load in the room while maintaining the same comfort level.     

Theoretical analysis on heat and mass transfer in a direct evaporative cooler

The heat and mass transfer between air and water film in the direct evaporative cooler is theoretically analyzed in present paper. A simplified cooling efficiency correlation is proposed based on the energy balance analysis of air. The correlation may be applied to the water-drip cross-flow direct evaporative cooler, in which the wet special durable papers with different wave angles form the air channel. The Influences of the air frontal velocity and the thickness of pad module on the cooling efficiency of a direct evaporative cooler are discussed. An optimum frontal velocity of 2.5 m/s is recommended to decide the frontal area of pad module in the given air flow. The simplified correlation of cooling efficiency is validated by the test results of a direct evaporative cooler.     

拖拉机空冷系统流场的数值模拟研究

拖拉机在农田作业时行驶速度慢，作业环境差，经常大负荷甚至超负荷工作，容易造成散热不足。本文利用UG建立包括风扇、水箱、空调散热器、机油散热器、空气中间冷却器和拖拉机罩的模型，利用CFD计算流体方法对风扇转速为200r／min、800r／min、1400r／min的空气流动特性分析，结果表明风扇转速为800—1000r／min时，对拖拉机散热比较有利。     

循环流化床锅炉对排渣和供风系统的要求

从循环流化床锅炉的工作原理出发,结合百余台实际运行的循环流化床锅炉的实践,分析了锅炉性能对排渣、配风以及燃料、石灰石系统的要求.提出了有效床存量的概念、床压控制的原则、一次风机压头选择的依据.认为风帽阻力是漏渣的根本原因;在排渣粒度可以保证的条件下,且物料平衡系统对选择性排渣有要求时,尽量采用床下连续排渣、流化床冷渣器;考虑燃料的适应性和运行灵活性,建议送风机流量储备系数宜为1.25,压力储备系数1.3,而引风机的流量储备系数为1.25,压力储备系数1.20;若是燃用生物质等易燃燃料,储备系数还应更大一些.     

Numerical investigation on the heat and mass transfer in a direct evaporative cooler

A simplified mathematical model is developed to describe the heat and moisture transfer between water and air in a direct evaporative cooler. The mass of evaporated water is treated as a mass source of air flow, and the related latent heat of water evaporation is taken as a heat source in the energy equation. The momentum caused by water evaporation is taken into account in the momentum equations. The effective air viscosity and diffusion coefficient are decided experimentally. The models and methods are validated by comparing the numerical results with those of experiment for the same evaporative cooler. The influences of the inlet frontal air velocity, pad thickness, inlet air dry-bulb and wet-bulb temperatures on the cooling efficiency of the evaporative cooler are calculated and analyzed.The cooling effects of the direct evaporative cooler are predicted for use in four different regions in northwest China using the present numerical method and local weather data for air conditioning design. The predicted results show the direct evaporative cooler with high performance pad material may be well applied for air conditioning with reasonable choices for the inlet frontal velocity and pad thickness.     

双回路中冷的柴油机冷却水系统

将用于机车柴油机的双冷却水回路增压空气中间冷却器（中冷器）和常用的单水回路中冷器冷却方式进行了对比,介绍双回路中冷的柴油机冷却水系统对机车、陆用发电机组等利用风扇来冷却柴油机和水的机组的好处,并分析其相应的系统原理。     

Modelling of a direct evaporative air cooler using artificial neural network

This paper proposes the use of artificial neural networks (ANNs) to predict various performance parameters of a direct evaporative air cooler. For this aim, an experimental evaporative cooler was operated at steady‐state conditions, while varying the dry bulb temperature and relative humidity of the entering air along with the flow rates of air and water streams. Using some of the experimental data for training, a three‐layer feed‐forward ANN model based on back propagation algorithm was developed. This model was used for predicting various performance parameters of the cooler, namely the dry bulb temperature and relative humidity of the leaving air, mass flow rate of the water evaporated into the air stream, sensible cooling rate, and effectiveness of the cooler. Then, the performance of the ANN predictions was tested by applying a set of new experimental data. The predictions usually agreed well with the experimental values with correlation coefficients in the range of 0.969–0.993, mean relative errors in the range of 0.66–4.04%, and very low root mean square errors. This study reveals that, as an alternative to classical modelling techniques, the ANN approach can be used successfully for predicting the performance of direct evaporative air coolers. Copyright © 2007 John Wiley & Sons, Ltd.