内螺纹管低温段空气预热器设计及优化

【作者】 张斌；

【导师】 吴存真； 孙志坚；

【作者基本信息】 浙江大学 ， 工程热物理， 2003， 硕士

【摘要】 锅炉设备中的低温段管式空气预热器位于锅炉烟气温度比较低的区域，它的管子通常采用光管构成。由于烟气温度低而产生了两个问题：一个是传热温压小，管子所用金属的消耗量相对比较多；另一个是受热面的管内侧金属壁面容易出现低温腐蚀。前一个问题和受热面的造价紧密相关，从节能和余热回收利用的角度出发，应当强化传热过程。后一个问题和受热面的安全运行和寿命有关，最好的改善方法是提高管壁的温度。通过分析，认为采取提高管内烟气侧换热系数的措施将有助于同时解决两个问题。空预器烟气侧的换热类型是管内单相强迫紊流换热，论文在查阅了相关文献的基础上，比较了几种不同的管内强化换热措施，在其中选择内螺纹管代替光管，来改造管式空气预热器。 内螺纹管是一种异形管，和光管相比，管内侧的换热系数大大增强了，应用于空气预热器可以起到提高总传热系数、节约受热面金属消耗量的目的；同时提高了管壁温度，能够减轻低温腐蚀的程度和速度；不足之处是带来了更大的阻力损失。所以，在用内螺纹管代替光管进行管式空预器的设计时，需要进行全面的核算。相关文献都认为选取小螺距、浅槽深的螺纹结构是合适的，在强化了管内烟气侧换热的同时，不至于过多的增加阻力。结合一些电厂中用内螺纹管改造空预器的实例，可以认为内螺纹管适合于代替光管改造和设计管式空预器。 设计管式空气预热器时的计算任务比较繁重，为了减轻设计时的工作量，论文采用了面向对象和可视化的编程技术，编制了内螺纹管空气预热器的设计计算程序。在程序中处理了设计过程中与热力计算、结构计算和阻力计算相关的公式、图表和曲线，使之可以在计算机上使用。对大部分的热工、阻力方面的参数，如烟气和空气的焓值、热物性参数和阻力系数等的计算，采用了类描述即面向对象的方法，使得无论是调用还是修改这些参数的计算方法，都显得十分方便。可视化的编程使得人机之间的交互方便，可以根据需要改动设计时的结构限制条件，也能很快的获得设计结果。 应用编制的内螺纹管空气预热器计算程序，以某130t／h燃煤锅炉的管式空气预热器为例，用内螺纹管进行设计。比较了几个重要的设计变量，如外管径、烟气流速等参数变化时，总传热系数和空预器本体管子总重量，阻力损失以及最低管壁温度等几个重要设计结果的变化趋势，对内螺纹管空气预热器的设计具有借鉴意义；其间还分析了内螺纹管与光管在设计时的不同之处；最后，初步分析了内螺纹管的优化设计问题，提出了一些建议。更多还原

【Abstract】 Lower temperature tubular air pre-heater is one components of boiler that applied in power plant. It works in the field where the temperature of gas is lowest of all components that be heated in the boiler. In general, air pre-heater is made of smooth pipes. There come two questions when the temperature of gas is low. One is that metal consumed in air pre-heater is relatively more, due to lower temperature press and heat transfer coefficient. The other is that corrosion of pipe result from SO2, which exists in gas. It is considered that enhancing heat transfer coefficient between gas and pipe is helpful for the solution of these two questions. The type of heat transfer inside the pipes belongs to single-phase compulsive turbulent flow of inner pipe.Inner trachea is a kind of special pipe compared by smooth pipe, which can strengthen heat transfer inside pipe. There are a lot of advantages when inner trachea applied in air pre-heater, such as the improvement of the temperature of pipe, the low consumption of metal, except for the increment of flow resistance. According to many related papers, it is more proper inner trachea with the structure of short distant between two whorls and shallow depth of whorl. It can enhance heat transfer with smaller flow loss. Refer to some application examples of inner trachea tubular air pre-heater in power plants it is a good replacement pipe of the old smooth pipe.To reduce the hardness of the work when designing tubular air pre-heater, it is needed to work out program by computer to realize the process of the design. Object Oriented Programming and visualization technologies are adopted in the program of this paper. In designing program, many formulas, curves and charts used in calculations have been completed. The great part of parameters, such as the enthalpy of gas and air, are described by the Class method. The utilization of visualization makes it easy for people to communicate with computer program. Even if some restrictive conditions of structure are changed, the results of the design can be gotten rapidly.Taking some tubular air pre-heater used in one boiler whose capacity is 130 t/h as an example, new blue print with inner trachea is completed by means of computer program. Several key design variables may be changed, such as diameter of pipe and velocity of flow of gas. These cases have been considered, and their results have also been compared with each other. The difference between smooth pipe and inner trachea in the design process is analyzed. At last, optimization of design with inner trachea is studied.更多还原