凝汽器抽真空系统研究与性能优化

发布时间：2018-01-28 07:07

本文关键词： 凝汽器抽真空系统水环真空泵工作水温　出处：《山东大学》2017年硕士论文　论文类型：学位论文

【摘要】：随着经济发展,能源利用增加,一次能源逐渐减少,环保问题加重。在我国火力发电比重较大,节能减排的提出,使电力行业开始转需其他可再生能源,短时期内进行节能改造。冷端系统的改造已经引起了越来越高的重视。作为冷端系统之一的凝汽器抽真空系统,在外界环境温度较高时,抽气器性能显著降低,导致汽轮机的排汽压力升高,煤耗增大。电厂辅机中的凝汽器抽真空系统优化就是为了解决这一问题,达到节约煤耗,增大发电功率目的。本文分别对凝汽器和抽气器的分类、结构、工作原理进行了介绍,分析了影响水冷凝汽器压力的几个因素:冷却水进口温度、温升、凝汽器端差以及抽真空系统的性能。当抽气器性能处于良好情况时,凝汽器进口水温越低,温升越小,端差小,则凝汽器真空较高。但考虑到循环水泵耗功问题,因此凝汽器的真空并不是越高越好,它存在一个最佳真空值。三种常用的抽气器:射汽、射水抽气器与水环真空泵,其中以水环真空泵的抽气性能最佳。但水环泵因其工作液是水,当泵内压力低于其极限压力时,就会产生汽蚀现象,本文就此现象提出防止措施。空气的存在会阻碍凝汽器内部蒸汽的换热,使得传热端差增大,凝汽器真空降低,还会增大凝结水过冷度,降低机组热经济性。需要抽气器及时将空气抽取出来,以免空气积聚,文中对漏入空气量进行了计算。运用EES模拟了水环泵抽真空系统,对变工况的水环真空泵进行分析,研究了对水环泵的性能影响特性和规律。结论如下:真空泵的吸气性能随工作液温度的升高而降低,但是工作水温对水环泵的这种影响会随着抽气压力的增大而逐渐减弱。当吸气压力在某一范围内逐渐增大时,吸气流量也会增大;超过临界压力后,吸气流量反而随压力降低减小。吸气温度越高,真空泵的抽气性能越差。经比较,对水环泵性能影响最大的因素就是工作液温度,因此在夏季高温下,泵内工作液温度会明显升高,真空泵的出力会显著下降,凝汽器真空度降低,进而会影响整个机组的安全经济性。本文分析了机组不同负荷下不同工作液温度分别对应的凝汽器压力,并制作相关用户界面,分别介绍了评价汽轮机背压变化对功率影响的两种方法。为有效改善夏季工况下抽真空系统性能,维持凝汽器正常运行,提高整个发电机组的安全经济性,可通过在该系统中增加空调冷冻水的方法提高凝汽器的真空。本文对山东电厂某60万机组进行了数据采集,建立了收益与投资关系,发现凝汽器抽真空系统增加冷冻水这一方案可以提高真空约0.6kpa,产生的总效益达185万元,一年内即能收回成本。本文还提出了一种新型抽真空方案,冷冻水直接通入水环泵作密封液,较之前的改造系统减少了管程损失,真空可增大约0.8kpa,产生的经济效益可观。
[Abstract]:With the development of economy, the increase of energy utilization, the decrease of primary energy and the aggravation of environmental protection problems. The retrofit of the cold end system has attracted more and more attention. As one of the cold end systems, the performance of the condenser vacuum pumping system is significantly reduced when the external environment temperature is high. The optimization of condenser vacuum pumping system in auxiliary unit of power plant is to solve this problem and save coal consumption. In this paper, the classification, structure and working principle of condenser and air extractor are introduced, and several factors affecting the pressure of water-cooled condenser are analyzed: the inlet temperature of cooling water, the temperature rise. The end difference of condenser and the performance of vacuum pumping system. The lower the inlet water temperature, the smaller the temperature rise and the smaller the end difference when the performance of the condenser is in good condition. But considering the power consumption of circulating water pump, the vacuum of condenser is not as high as possible, it has an optimum vacuum value. The pumping performance of water ring vacuum pump is the best, but the water ring pump has cavitation phenomenon when the pressure inside the pump is lower than its limit pressure because its working fluid is water. The existence of air will hinder the heat transfer of steam in the condenser, increase the end difference of heat transfer, reduce the vacuum of condenser and increase the supercooling degree of condensate. In order to reduce the thermal economy of the unit, it is necessary for the air to be extracted by the air extractor in time to avoid the accumulation of air. The leakage air volume is calculated. The vacuum system of the water loop pump is simulated by EES. The influence characteristics and rules of water ring vacuum pump on the performance of water ring vacuum pump are analyzed. The conclusion is as follows: the suction performance of vacuum pump decreases with the increase of working fluid temperature. However, the effect of working water temperature on the water loop pump will be weakened with the increase of the pumping pressure. When the suction pressure increases gradually in a certain range, the suction flow rate will also increase. The higher the suction temperature, the worse the suction performance of the vacuum pump. By comparison, the working fluid temperature is the most important factor affecting the performance of the water ring pump. Therefore, under the high temperature in summer, the temperature of the working fluid in the pump will increase obviously, the output of the vacuum pump will decrease significantly, and the vacuum degree of the condenser will decrease. Then it will affect the safety and economy of the whole unit. This paper analyzes the condenser pressure corresponding to different working fluid temperature under different load and makes the relevant user interface. Two methods to evaluate the influence of steam turbine back pressure on power are introduced in this paper. In order to improve the performance of vacuum pumping system under summer working conditions, to maintain the normal operation of condenser and to improve the safety and economy of the whole generator set. The vacuum of condenser can be improved by adding air conditioning chilled water in the system. The data collection of a 600,000 unit in Shandong Power Plant has been carried out and the relationship between income and investment has been established. It is found that the vacuum of condenser vacuum pumping system can be increased by about 0.6 KPA, and the total benefit can reach 1.85 million yuan. The cost can be recovered within one year. A new vacuum pumping scheme is proposed in this paper, in which the refrigerated water is directly pumped into the water ring pump as the sealing fluid, which reduces the loss of the pipe path and increases the vacuum by about 0.8 kpa compared with the previous revamping system. The economic benefits generated are considerable.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM621

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