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Advanced Computer Control of an Ethylene/Ethane Splitter Column

IP.com Disclosure Number: IPCOM000218712D
Publication Date: 2012-Jun-06

Publishing Venue

The IP.com Prior Art Database

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ADVANCED COMPUTER CONTROL OF AN E m N E / E T H A N E

SPLITTER COLUKN

William B. Stewart, Jr.

The M. W. Kellogg Company
Three Greenway
Plaza

Houston, TX 77046-0395


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ABSTRACT

Advanced computer control has been applied to the ethylene/ethanesplitter column at Yukong Ltd'sNaphtha Cracking Center inUlsan,Korea. The ethane concentration inthe ethylene product isbeing controlledby the manipulation of the internal reflux rate. The ethylenein the ethane recycle isinferentially controlledby controlling the temperature on one of the lower trays. The propylene vapor flow to the reboilerisadjustedto control this tray temperature. Both top and bottom controls employ Kellogg'sLinear Model Based Control (LMBC) algorithmand account for measured disturbances ina feedforward manner. An interreboiler installed as part of an energy conservation revamp isalso included inthe control scheme. Disturbances introduced intothe ethylenejethane splitteras a consequence of this process interconnection are taken into account. State-of-the-art process identification techniques were used to determine the dynamic process models used in the control algorithms. The controls have markedly decreased the variation of product compositions and have greatly increased the stability af Q p e r a W n n f the splitter.

INTRODUCTION

The ethylene/ethane ((22) splitteristhe major user of the

plant. The C2 splitter isa superfractionatorwith rigid

consequences if these specifications are violated. These characteristics,coupled with the fact that the C2splitter is often a capa-cityconstraint,canmake it the most profitable advanced control applicationinthe ethylene plant cold side.

U L A n an eclnyiene

Typical control objectives are to maintain ethane and methane and lighter inthe ethyleneproduct below the specification maximums and to keepethylene concentrations inthe bottoms product at acceptable levels. This control isusually accomplished by manual operator manipulation of reflux,reboil,vent flow,and product draw. The C2 splitter isdifficult t o operate because it has significant deadtimes and very long response times to controller changes.
critical nature of the product specifications causes the operator to runwith a substantial safety cushion between the specificationconstraints. This results inover specificationproduct and increased refrigeration usage.

The difficulty of operation coupled with the

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Once online analyzershave been installed,an advanced control scheme canbe implemented to strive for the same objectives as the operator controlby moving the same controllers. The difference isthat the effects of feed disturbances and the highly interactiveand sluggish nature of the column are taken into account. These features coupled with the continuous monitoring of the computer allow the ethylene product specificationto be approachedmore closely and to be maintained at high throughputs.
results in substantialrefrigeration savingsand improved ethyle...