【作者】 石维柱；

【导师】 安连锁； 陈海平；

【作者基本信息】 华北电力大学（河北） ， 热能工程， 2010， 博士

【摘要】 直接空冷机组在我国富煤贫水地区得到了快速的发展,但其在运行过程中存在着背压高、真空严密性差、热风回流、受热面污染、易发生冻结等诸多问题,严重影响了机组的安全和经济运行。以某国产300MW直接空冷机组为例,对其运行特性进行了分析,研究了度夏和防冻的关键技术问题,给出了相应的解决方案。提出了空冷凝汽器变工况特性的简洁计算方法,得到了排汽压力的目标值和凝汽器变工况特性曲线,所得结果能够满足工程需要;基于排汽压力的实测值和目标值建立了管外壁污垢热阻和清洁系数的数学模型,并计算了管外壁清洁系数随时间的变化趋势,得到了空冷岛的最佳清洗周期;推导了排汽压力与其影响因素之间的微分关系式,得到了影响排汽压力的主要因素;计算得到了任意工况下风机的最佳运行转速;基于VB 6.0软件,开发了空冷岛性能计算软件。设计了七种不同型式的喷淋冷却系统,建立了空冷单元加装喷淋冷却系统的数值分析模型;对比了喷淋冷却系统结构、喷嘴型式、冷却方式对空冷单元换热效果的影响,得到了影响喷淋冷却系统换热效果的主要因素。结果表明:喷嘴个数和喷嘴距散热面的垂直距离是影响换热效果的主要因素;直接蒸发冷却方式优于绝热增湿冷却方式;使用螺旋喷嘴的系统D是最佳设计方案。建立了环境风对空冷岛换热性能影响的数值分析模型,得到了空冷岛换热效率与不同风向、风速之间的关系;数值模拟了挡风墙下沿安装防风网对空冷岛换热性能的影响,对比了有防风网和无防风网时的温度场和速度场,研究了开孔率和防风网高度对空冷岛换热效率的影响。结果表明:加装防风网后,空冷单元的空气流量和换热量明显增加,随着环境风速的增大,防风网的防风效果越明显;对于6m/s的侧向横风,防风网最优开孔率和高度分别为15%和12m;对于6m/s的炉后来风,防风网最优开孔率和高度分别为28%和7m。提出了基于空冷凝汽器基管管壁温度实现监测管束冻结状态的方法,建立了最小防冻蒸汽流量的计算模型,得到了最小防冻蒸汽流量与环境温度之间的关系,计算了不同工况下的管束结冰系数和防冻经济背压;提出了基于模糊神经网络对空冷凝汽器结冰故障进行诊断的方法,并开发了空冷凝汽器结冰故障诊断软件,实例验证了该方法的可行性。以国产某300MW直接空冷机组为例,基于MS Dotnet 2.0 + Fortran V4.0 + J2EE 2.0软件平台,开发了运行优化分析与指导系统。运行实践验证了软件的可靠性。更多还原

【Abstract】 In China, direct air cooling (DAC) unit develops rapidly in the region of coal-rich and water-poor. But in operation, there are many problems such as higher back pressure, poor vacuum leakage performance, hot air recirculation, radiator fouling and freeze, which influence seriously safe and economic operation of DAC unit. Take domestic 300MW DAC unit as an example, the operation performance was analyzed, and the key technologies and solution scheme of summer operation and anti-freeze were approached.The simple calculation method of air cooling condenser (ACC) off-design performance was brought forward, and condenser pressure target value and off-design performance curves were obtained, which was satisfied with the data provided by manufacturer. Fouling thermoresistance and cleaning coefficient of tube outside were calculated, and the tendency of cleaning coefficient with time and optimum cleaning period were obtained. Differential relationship equation between condenser pressure and its influencing factors were derived, and the main factor influencing condenser pressure was found. The optimal rotate speed of fan was calculated also. Based on VB 6.0 software, performance calculation program of ACC is written.Seven different types of spray cooling systems were designed, and numerical analysis model of spray cooling system was established. The influence of system structure, nozzle type, cooling mode on the performance of spray cooling system was analyzed, and the results show that the important factors of influencing heat exchange are nozzle number and vertical dimension from radiator. The cooling performance of direct evaporation mode is better than that of adiabatic humidification mode, and spray system D with spiral nozzle is the best option.Numerical analysis model of environmental wind influence was built, and the relationship between heat exchange efficiency of ACC and wind direction & speed was obtained. The influence of installing windbreak net down along windbreak wall was simulated, and the temperature and speed field with or without windbreak net were compared. The influence of opening ratio and net height were approached. The results show that air flow and heat transfer rate of air cooling unit with windbreak net are both increased, and the higher wind speed is, the more increment is. For 6m/s crosswind, the optimal opening ratio and height of windbreak net are 15% and 12m. For 6m/s wind from boiler side, the optimal opening ratio and height of windbreak net are 28% and 7m.The method of monitoring radiator freeze status was brought forward based on finned tube wall temperature. The acceptable minimum limit of steam flow (AMLSF) is calculated, and the relation between AMLSF and environment temperature was obtained. Tube frozen coefficient and economic back pressure of anti-freeze were calculated also. The model of diagnosing ACC freeze was built based on fuzzy neural network, and the diagnose software was developed, which was proven to be feasible.Take domestic 300MW DAC unit as an example, the optimal operation and guide system was exploited based on MS Dotnet 2.0 + Fortran V4.0 + J2EE 2.0. The system was proven to be reliable by operation practice.更多还原