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Bonnet Neck Temperature Field Analysis and Structural Design of Cryogenic Valve

Author: JinWeiZeng
Tutor: YuShuRong
School: Lanzhou University of Technology
Course: Safety Technology and Engineering
Keywords: cryogenic valves long-neck bonnet seal temperature field stuffing finite element analysis
CLC: TH134
Type: Master's thesis
Year: 2012
Downloads: 128
Quote: 0
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Abstract

With the vigorous development of industry in China, the scales of production in petrochemical engineering, air separation, natural gas, refrigeration and cryogenic engineering continue to grow and develop higher and higher demands on the cryogenic valves. The practice of cryogenic engineering tells us that the good and bad of the quality of cryogenic valves have a direct impact on the progress of the entire cryogenic engineering in the practice of which there are many lessons. A valve is not sealed,shut lax or open, often leading to a failure of large-scale test or an accident, resulting in a waste of a lot of manpower, material and financial resources,and therefore affect the development of our comtry’s cryogenic engineering.The cryogenic valves the same as industrial pipeline valves is also used to cut or adjust the cryogenic liquid. The low temperature valves work in a media whose temperature is equal to or less than120K, and the influence of the working medium with this temperature on the valve components may be sustained, or a short time. In addition to working in low-temperature media, the ambient temperature shall be taken into account meanwhile, that is, working in temperatures of about295K. The low-temperature medium temperature and ambient temperature must be considered in the design of valve components together.In the low-temperature device, the working conditions of valves are much worse than the common industrial valves. The valve seal is verv difficult in a wide temperature range, and therefore we must improve the valve seal to prevent leaks. The tightness of stuffing boxes is the key to the design of cryogenic valves, and long-neck bonnets are used to serve to protect the stuffing, where leakage will reduce the cold effect, resulting in vaporization of liquid and the elasticity of the filler is gradually disappearing as the temperature decreases at low temperatures with the following result that the leak-proof performance drops. The freezing ice between filler and stem caused by medium leakage affects the normal operation of the valve stem and also cause filler scratches in the process of stem’s moving up and down and a serious leakage. Therefore, cryogenic valves must take the structure of long-neck bonnet.In addition, the long-neck bonnet is easy to wind materials of cold insulation preventing the loss of cold energy.In this paper, a mathematical model of relation between the neck length and temperature field was established by simplifying physical model of long-necked bonnet of low-temperature valves reasonably with an example of low-temperature socket welded globe valve. A relation between the neck length and temperature field was deduced on a basis of the temperature field distribution of the long-necked bonnet with the method of separation of variable on another theoretical basis of heat transmission science. The minimum length of the valve cover was obtained meeting the designing standard of valves. The length of the valve cover will be tested right or not by taking an thermal analysis of low-temperature socket welded globe valve with a diameter of DN25on the modeling and analyzing platform of a software of finite element analysis, ANSYS. Also, the influence of structural factors on the stuffing box was studied providing a theoretical reference for the engineering design.

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