Analytical Research And Improvement Of Sealing Structure In The Tube Channel End Of Breech Lock Closure Type U-Tube Heat Exchanger

As the petroleum resources scarce increasingly and constant increasing environmental protection efforts be made, hydrogenation in oil refinery has become more and more in demand. Breech lock closure type U-tube heat exchanger is one of the important high temperature and high pressure heat exchangers.Its operating pressure is usually 9.0～20.0MPa in the tube side and 2.5～20.0MPa in the shell side, and its operating temperature is 200～440℃ in both tube side and shell side.The nominal diameter range of this type heat exchanger is Φ500mm～Φ1900mm,and the media in it aways contain hydrogen and hydrogen sulfide. Breech lock closure type U-tube heat exchanger has some exceeding advantages over general shell and tube bolt flanged U-tube type heat exchanger, such as more reliability and online controllability of sealing, more compact structure and higher ratio of effective heat exchange area. Aside from its excellent features, it still owns a few disadvantages to be overcome, such as machining and assembly and disassembly difficulties of threaded lock ring, relatively heavy tube channel and high cost. Therefore, research, analyses and improvements of the tube channel end structure have been conducted in this thesis, that is using a new type D-section bolt to replace the original connection in the tube channel end with large stub ACME screw threads, and elastic-plastic mechanical analyses, comparison and optimization of this new type D-section bolt U-tube heat exchanger before and after improvement have also been performed. Details are as follows:First, the structure and its features, the principle of sealing, the process of assembly and disassembly and some existing problems were studied and analyzed. And the design method of breech lock closure type U-tube heat exchanger was also presented. The stress distribution in the root of the stub ACME screw threads was obtained through the elastic analysis on the channel end. The influence of thread number, thread pitch, thread angle and threads root radius on the carrying capacity was obtained by simulating the stub ACME screw threads with different geometry parameters. The thermal stress analysis and the elastic-plastic analysis on the tube channel end were carried out to help understand the influence of temperature and material model on the stress distribution. In addition, structural optimization was applied to reduce the consumption of material and the cost.Secondly, the structure and its features, the manufacturing, the process of assembly and disassembly and the design method of new type D-section bolt U-tube heat exchanger were described. Compared to the original one, the new structure has improved performance in manufacturing, assembly and disassembly and material consumption.The elastic analysis on the two type tube channel ends with different D-section bolt arrangement of new structures was carried out to get their stress distributions, especially in the root of the threads. Furthermore, thermal stress analysis and elastic-plastic analysis were carried out to help understand the influence of temperature and material model on the stress distribution. Comparisons show that the stress distribution of the new type D-section bolt U-tube heat exchanger with its D-section bolt axis located in the cover is better than the other one.Finally, a designing software that can be applied to the design of breech lock closure type U-tube heat exchangers and new type D-section bolt U-tube heat exchanger was developed by Visual Basic.NET, which can improve the efficiency of development and design.