Steady-state thermodynamic simulation and structural design of the dephlegmator used in mixed-refrigerant Joule-Thomson refrigerators

Abstract Dephlegmators can be used to reduce the energy consumption and simplify the layout of the mixed-refrigerant Joule–Thomson (MRJT) cycle. Heat-exchange characteristics and refrigeration design are currently based on highly simplified assumptions. Synthesis methods to efficiently solve all design issues of dephlegmators in MRJT cycle are insufficient. No suitable separation module is available for the simultaneous heat and mass transfer processes in Aspen Plus because the module should be programmed and incorporated into Aspen Plus as a user-defined unit. In this paper, a systematic steady-state method was proposed for the detailed design of dephlegmators for gas mixture separation, considering the simulation and heat exchanger design simultaneously. The material balance, vapor–liquid equilibrium, mole fraction summation and heat balance (MESH) model was programmed in FORTRAN language. Good agreements and the feasibility of the MESH model were found. Deviations between the simulation results and patent data were all within 5%. The errors in the predicted temperatures of vapor and liquid products were less than 2% and 10%, respectively. Fine applicability and low energy consumption of the dephlegmator were addressed. The mole fraction of n-butane in the liquid phase had high recovery ratio of 90%. The dephlegmator decreased more than 30% of energy consumption compared with the traditional distillation tower under similar separation effects. In the structural design process, the dephlegmator was divided into certain segments by baffle plates on the basis of segmented calculation. The heat transfer coefficient, heat transfer area, pressure drop, and structural parameters of the dephlegmator were evaluated. A clear and comprehensive three-dimensional dephlegmator model was shown.

[1]  M. Gong,et al.  A new type mixture refrigeration auto-cascade cycle with partial condensation and separation reflux exchanger and its preliminary experimental test , 2002 .

[2]  N. L. Franklin,et al.  The interpretation of minimum reflux conditions in multi-component distillation , 1997 .

[3]  Lin Chun-mian.  Inhibiting Effect of DMF Hydrolysis in DMF Recycling System , 2010 .

[4]  T. B. Drew,et al.  The condensation of mixed vapors , 1965 .

[5]  Syed A.M. Said,et al.  Analysis of a solar powered absorption system , 2015 .

[6]  Wenming Yang,et al.  Fundamental formulation of a modified LMTD method to study indirect evaporative heat exchangers , 2014 .

[7]  Ronaldo Hoffmann,et al.  Operation parameters of a small scale batch distillation column for hydrous ethanol fuel (HEF) production , 2015 .

[8]  Ercang Luo,et al.  Further Development of the Mixture Refrigeration Cycle with a Dephlegmation Separator , 2003 .

[9]  Christy V. Vazhappilly,et al.  Modeling And Experimental Analysis Of Generator In Vapour Absorption Refrigeration System , 2013 .

[11]  G. Grossman,et al.  Analysis of an activated-carbon sorption compressor operating with gas mixtures , 2012 .

[12]  Robin Smith,et al.  Dephlegmator Design in Low Temperature Gas Separation , 2005 .

[13]  B. S. Petukhov.  Heat Transfer and Friction in Turbulent Pipe Flow with Variable Physical Properties , 1970 .

[14]  Leland M. Vane,et al.  Hybrid vapor stripping–vapor permeation process for recovery and dehydration of 1‐butanol and acetone/butanol/ethanol from dilute aqueous solutions. Part 2. Experimental validation with simple mixtures and actual fermentation broth , 2013 .

[15]  R. Baker,et al.  Separation of Vapor-Phase Alcohol/Water Mixtures via Fractional Condensation Using a Pilot-Scale Dephlegmator: Enhancement of the Pervaporation Process Separation Factor , 2004 .

[16]  N. Tzabar,et al.  Binary mixed-refrigerants for steady cooling temperatures between 80 K and 150 K with Joule–Thomson cryocoolers , 2014 .

[17]  Ignacio E. Grossmann,et al.  A disjunctive programming approach for the optimal design of reactive distillation columns , 2001 .

[18]  R. Baker,et al.  Experimental validation of hybrid distillation‐vapor permeation process for energy efficient ethanol–water separation , 2009 .

[19]  H. Röhm.  The simulation of steady state behaviour of the dephlegmation of multi-component mixed vapours , 1980 .

[20]  Wen-De Xiao,et al.  A reactive distillation process for a cascade and azeotropic reaction system: Carbonylation of ethanol with dimethyl carbonate , 2001 .

[21]  Gregory Nellis,et al.  Thermodynamic optimization of mixed refrigerant Joule- Thomson systems constrained by heat transfer considerations , 2015 .

[22]  Rajamani Krishna,et al.  A multicomponent film model incorporating a general matrix method of solution to the Maxwell-Stefan equations , 1976 .

[23]  Robin Smith,et al.  Synthesis and Optimization of Low-Temperature Gas Separation Processes , 2005 .

[24]  R. Baker,et al.  Low-Energy Distillation-Membrane Separation Process , 2010 .

[25]  Ruzhu Wang,et al.  Forced flow and convective melting heat transfer of clathrate hydrate slurry in tubes , 2010 .

[26]  Jules Thibault,et al.  Membrane Dephlegmation: A hybrid membrane separation process for efficient ethanol recovery , 2011 .