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Thermodynamic Analysis of Ethylene Plant Distillation Columns

IP.com Disclosure Number: IPCOM000218582D
Publication Date: 2012-Jun-05

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Thermodynamic Analysis

of

Ethylene Plant Distillation Columns

      David B. Manley
The University of Missouri-Rolla and
Paul S. Chan and Duffer B. Crawford

The M. W. Kellogg Company

 Preparedforpresentation at the 1992AIChESpringNationalMeeting Session #85 - Expansion and Life Extension Techniquesin Ethylene Plants

New Orleans, Louisiana 31 March 1992


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   ThermodynamicAnalysis
of
Ethylene Plant Distillation Columns

Introduction

From a thermodynamic point of view, conventional fractionation processes are relative1

Consequently, as part of a corporate initiative to better develop and execute new chemical process technology,The M.W. Kellogg Company has made a major effort to understand the fundamental reasons for distillation inefficiencies and to create appropriate procedures for designing better fractionation processses. This has led to a new method of analyzing the distillation process which graphically identifies fractionation inefficiences relating to heating and cooling effects, momentum, and heat and mass transfer lost work for multicomponent distillation columns. This graphical analysis helps in understanding the concepts of distillation as a heat exchange process, parallel distillation and heat transfer, and distributed distillation.

inefficient1. However, much higher efficiencies can theoretically be achieved3.

vintage ethylene recovery process with the objective of achieving a 20 percent capacity increase without moddying the existing distillation columns or refrigeration compressors. These constraintsmay not be appropriatefor all plant expansions; however, they are chosen to highlight the effects of process thermodynamic efficiency improvements as opposed to hardware improvements in column internals and feed locations. Also, if compressor and column modifications can be minimized, then the process down time required for incorporating an expansion can be minimized. An additional objective is to maximize reuse of existing equipment and minimizethe capitalcost of the expansion.

Modifications in the ethylene plant Demethanizer system are presented below to illustrate distributed distillation concepts and the effects on equipment loadings. Every plant is unique, and the optimum expansion strategy canonly be established after an economic evaluationof capital costs,operatingcosts,and turnaround duration of each revamp option.

Original Flowscheme

Figure 1shows the Demethanizer and Demethanizer feed system of the plant chosen for study. This plant was built by The M. W. Kellogg Company in the late 1970's to produce

@'

@

r3



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The separated vapor stream is split el streams and cooled to -1400F. One is cooled by reheating cold methane

                              The other is cooled by three levels of ethylene refrigeration. The con s are again separated and are used as the middle feed to the demethanizer remaining vapor stream is then cooled to -2050F to recover essentially all o ne asliquid condensate which is separated, reheated to -1500F again...