Optimization Analysis Of Large Cryogenic System Process Using Pinch Technology

With the construction of large scientific systems,such as large particle accelerators,positive and negative ion colliders,and cryogenic superconducting systems,as well as the continued development of Aerospace Technology,the application of large-scale cryogenic system is more and more widespread and important.Helium liquefaction system can provide a 4 ～ 5K ultra-low temperature environment,which is very important to aerospace industry,scientific research,medical treatment and so on.Because of the 4.2K low temperature,the systems’ energy consumption and leakage heat is quite serious.Therefore,it is important to optimize the large helium cryogenic system,increase the energy efficiency of the system,in order to save energy.But because of the variable key parameters and structural processes,the current optimization results are lack of comprehensive,complex,and not easy to understand that the researches are under certain fixed conditions,based on first law of thermodynamics or based on the second law of thermodynamics,or based on some algorithms.Pinch-point technology was developed by Prof.Linnhof at the Federal Institute of Technology in Switzerland and the University of Leeds in the 1970 s,and then discussed and researched by multiple parties.Eventually,it became a methodological method of process optimization.It can consider the three-dimensional balance of energy saving,investment and operability at the same time.Because of unique ideas,simple methods and remarkable results,it has been appraised as one of the most significant breakthroughs in the field of energy synthesis in today’s world.To address the above issues in this paper,the main research work is as follows:Firsr,several typical helium liquefaction cycle systems were selected to study the distribution of energy flow with temperature.And then the cold / hot combination curves on the thermo-enthalpy graph are plotted using the pinch technique to determine the pinch position and temperature difference of the system.This process is the key to the application of pinch technology,can be simple and intuitive to show the different systems of energy distribution,bottlenecks and optimization goals.Second,According to the temperature-enthalpy graph,the energy utilization of the selected cycles are compared with each other,and the comparative results and theoretical analysis are given qualitatively and explained by the theory of "entransy theory".The efficiency of the entire system is sorted from highest to lowest: Multi-level modified Brayton cycle>Collins cycle>Two-level modified Brayton cycle;final revision of the Collins cycle>Collins cycle>Two-level modified Brayton cycle。Third,some simulation calculations of the selected cycles are been done based on pinch technology using Fortran and Aspen HYSYS.According to the key performance parameters such as compressor outlet pressure,expander splitter ratio and intermediate pressure,that the efficiency of the system and the cold box under different conditions and the liquefaction rate of the system are obtained.And the conclusions are compared with the theoretical analysis result of the temperature-enthalpy diagram based on the pinch technique.In addition,on the basis of the above analysis,the key problems of different system efficiency and cold box efficiency are summarized-the optimal inlet pressure of the throttle valve liquefaction rate is 640KPa;In order to solve this problem,an improved new helium liquefaction process is proposed..Fourth,the theoretical analysis and numeral Calculations of a multi-stage helium liquefaction / refrigeration cycle in series are been done based on pinch technology,and optimized performance indicators are obtained to compare with the actual data,which can describe the advantages of pinch technology applied to large cryogenic systems.