Simulation And Performance Analysis Of Multi-stream Heat Exchangers Of Air Separation Units

Multi-stream heat exchanger(MHEX)is an important equipment to recover cold energy in air separation units(ASU).Working at the best operating point of MHEX is a vital measure of energy-saving,so it is necessary to establish a robust and efficient MHEX model under various operation points.However,the first principle model of an industrial MHEX is difficult to be established due to the complex structure of the proprietary.In this thesis,modeling and heat transfer efficiency of the MHEX are studied as follows,1)An data regression model operating model for MHEX is established to balance model convergence and accuracy.It is developed on the base of mechanistic comprehension to correlate the outlet temperatures with the inlet temperatures and flowrates.Data preprocessing takes up a lot of workload and largely improves the accuracy of the models.Relative predicted Errors of model are within 1%.2)Exergy analysis is used to determine representation mode of heat transfer performance of MHEX,and reheating cold loss is chosen.One-dimensional scaling analysis is used to show the sensitivity of recovery rate and reheating cold loss concerning total air flowrate and reheating cold loss is obviously more sensitive.Principal component analysis(PCA)reduces the dimension of variables of MHEX by feature extraction and building new irrelevant variable ‘principal component'.The first and second principal components contain 94% information of originalvariables.MHEX model and PCA predict that optimal operational areas should be controlled minimum of first principle component under variable-loading operation of ASU.3)An MHEX model built on the framework of Aspen custom modular is developed.This operational modular can replace the design modular,MHeatX,to fulfill simulation of MHEX in the flowsheeting.Inaccurate measured data reconciliation is critical step of simulation and simulation error of main parameters within 5%.4)An equation oriented(EO)modelling method is proposed for complex MHEX.MHEX is decomposed to multi-Bundles because parts of streams are designed to enter or leave from the middle layer of MHEX.A multiple Bundle structure model is developed instead of treating the regression as a pure black-box model and each Bundle is a regression model.Relative predicted Error of EO model of complex MHEX within2%.