binary distillation column

8/19/2019 Binary Distillation Column

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Control Techniques“Application on a binary distillation column” Oliver González Hernández

Noelia Rodríguez Hernández


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Table of contents

1. Introduction

2. asic control

2.1 Control o! a single co"#osition

2.2 Control o! t$o co"#ositions

%. #lication o! !eed!o$ard

'. (ressure and te"#erature control

). *ultivaria+le control overvie$

,. -u""ar


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1.Introduction

• /istillation is an unit o#eration

• It is used !or se#aratingdi0erent co"#onents o! a +lend

• It is +ased on the di0erentvolatilit o! each co"#onent

Overhead #roduct otto" #roduct

• hen $e o+tain ust t$o#roducts3 the "ost volatile 4o$su# to the to# o! the colu"n andthe less volatile !alls do$n to the+otto" o! the colu"n

inar distillation The si"#lest case


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1.Introduction

• The #roduct in the +otto" is heated3 "a5ing the "ost volatile#roduct +eco"es gas

• These gases ascend into the colu"ns through several tras• This ascend causes a te"#erature gradient the !eed co"es

#re6heated into the colu"n at the level $here the te"#eratureis si"ilar

CON/7N-7R

R789:; /R:*

Oee#ing thesevalues at the

required level


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2. Basiccontrol

• The +asic control is #er!or"ed onl + using !eed+ac5 inthe control loo#s

• This control ai"s to 5ee# the controlled varia+les in theirre!erence value

877/

• It is nor"all used as controlled varia+les the level o!#roduct in the +otto" o! the colu"n and the level inside

the re4u? dru"


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2.1. Control of a singlecomposition

• The control varia+les are nor"all the re4u? 4o$ @9A andthe 4o$ o! ther"al 4uid @


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2.2. Control of twocompositions

• I! the t$o co"#ositions Boverhead #roduct and +otto"#roduct are going to +e controlled it is necessar to

avoid cou#ling.• The +etter o#tion is to control the re4u? 4o$ @9A and 4o$

@A as $e see in the ne?t Dgure

9

• Cou#ling +et$een head and +otto" is al$as #resent$hen $e atte"#t to control t$o co"#ositions $hen there4u? is increased to i"#rove the qualit o! the overhead

#roduct3 the colu"n tends to get cold3 $orsening thequalit o! the +otto" #roduct.


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3. Presure and temperature control

It is necessar tocontrol the #ressureo! the #rocess3since it strongla0ects the +oilingte"#erature o! theco"#onents and3consequentl3 thequalit o! the#roducts.

The control o! the!eed te"#eratureis ver si"#le.

It is onlnecessar that thiste"#eraturere"ains si"ilar tothe te"#erature o!the level $herethe !eed is

inected.

PressureControl

Feed TemperatureControl

Ga

s

9iquid

Te"#erature control

8eed


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4. Application of te feedforwardtecni!ue

• Technique that consists in antici#ate events that coulda0ect the #lant3 act +e!ore these events a0ect the

out#ut.• *athe"atic "odel allo$s !orecast.

• *odel $ill never +e #er!ect the !eed!or$ard is al$asco"#le"ented $ith a traditional !eed+ac5 control.

• :se!ul to antici#ate changes o! the te"#erature and"ass 4o$ in !eed and ther"al 4uid3 $ith a t#ical controlsche"e as !ollo$sE

F""# C$%T&$''"#(A&IAB'"

)A%IP*'AT"#(A&IAB'"

B$TT$)T")P"&AT*&"

F""#BAC+C$%T&$'

F""#F$,A&#"-TI)AT"-

#%A)ICC$)P"%-ATI$%

#%A)IC

C$)P"%-ATI$%

P&$C"--

T/"&)A' F'*I#

-P


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0. )ultiariable controloeriew• Huge a"ount o! varia+les "ultivaria+le control a##ears.

• The techniques used in #ractice are oriented to decou#ling3

e.g. Inverse "odel decou#ling

$e need lo$ de#endenc+et$een varia+les

• One o! the "ain "ethods used !or this #ur#ose is the@relative gains "ethodsA $hich consist in calculate theinteraction +et$een controlled varia+les and "ani#ulatedvaria+les3 using a relative gain "atri?

)A%IP*'AT"# (A&IAB'"-

C $ % T & $ ' " # (

A &

I A B ' " -

hen thesecoeFcients arecloser to the unit3 thesta+ilit o! thesste" is +etter3although the

dna"ic res#onse is!aster i! thecoeFcients arehigher than the unit.

Thus3 this "atri?allo$s avoiding using$rong co"+inationso! control varia+les.


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. -ummar

• Control o! distillation colu"ns is a ver usual #ro+le"

in the industr• inar colu"n is the si"#lest case3 $here onl t$o

#roducts are e?tracted

• asic control techniques B!eed+ac5 allo$s controllinga single co"#osition3 +ut has #ro+le"s controlling

+oth co"#ositions due to cou#ling• 8eed!or$ard control can +e a##lied to avoid that the

4uctuations in te"#erature and "ass 4o$ o! the !eed+e!ore the a0ect the out#ut

• hen a "ultivaria+le control atte"#ts to +e

i"#le"ented3 it "ust +e avoided cou#ling3 usingtechniques as the @relative gains "atri? A


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Than5s !or our attention

binary distillation column

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