Reboiler Calculations Design Guide

8/13/2019 Reboiler Calculations Design Guide

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PROCESS TECHNOLOGY PROCEDURES

PREPARED BY

Edited from existindo! "# $ Andr%&is

DATE

A'ri( )*+ 2***

DEPART,ENT PROCESS ENGNEERNG

APPRO/ED BY

0RB

SUB0ECT REBOER CACUATONS DESGN GUDE RE/SON DATE

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TABLE OF CONTENTS

Section

1.0 SCOPE.............................................................................................................

2.0 RESPONSIBILITIES........................................................................................

3.0 DESIGN CRITERIA..........................................................................................

3.1 Cold Side.................................................................................................3.2 Hot Side...................................................................................................

4.0 CALCULATIONS.............................................................................................

4.1 Horizontal Thermosyphon Reboiler Calculations...................................4.2 Kettle Reboiler Calculations....................................................................4.3 Vertical Thermosyphon Reboiler Calculations........................................

.0 PROCESS SPECIFICATION...........................................................................

LIST OF ILLUSTRATIONS

Fi!"#e

1 Horizontal Thermosyphon Reboiler Side !ra"o##.........................................2 Horizontal Thermosyphon Reboiler $ottom !ra"o##.....................................3 Kettle Reboiler %ressured Type....................................................................4 Kettle Reboiler &ra'ity (lo" Type..............................................................) Vertical Thermosyphon Reboiler $ottom !ra"o##.........................................* Vertical Thermosyphon Reboiler Side !ra"o##.............................................


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1.0 SCOPE

This desi+n +uide1 co'ers the calculation o# 'essel s,irt hei+hts- pressure drops- linesizes- and calculation o# dri'in+ head to determine reuired dra"o## nozzle ele'ations #orreboiler circuits.

2.0 RESPONSIBILITIES

The process en+ineer is responsible #or determinin+ 'essel s,irt hei+hts- pressure drops-line sizes- and dri'in+ heads #or reboiler circuits.

3.0 DESIGN CRITERIA

3.1 Co$% Si%e

/ines carryin+ liuid to the reboiler shall be sized usin+ a ma0imum liuid 'elocity o# 4 to

) #eet per second. (or lines dra"in+ liuid #rom the side o# a column- a 'elocity o# 2 #eetper second shall be used #or a minimum len+th o# ) #eet.

3.2 Hot Si%e

(or a reboiler 'apor outlet- V2 should +enerally not e0ceed ). The mi0edphasereboiler return line shall be sized usin+ a minimum 'apor 'elocity o# 1) #eet per second-e'en i# this produces unstable #lo" in the 'ertical up. n cases "here the density is lo"-hi+her 'elocities "ill occur- but these should not e0ceed 1 #eet per second.

The horizontal portion o# the mi0edphase line may be lar+er 'apor 'elocity may be

lo"er than the 'ertical up portion o# the line- i# necessary to maintain stable #lo" in boththe horizontal and 'ertical run o# lines.

4.0 CALCULATIONS

The reboiler calculations are se+re+ated on the #ollo"in+ arran+ements5

1. Horizontal Thermosyphon Reboiler Calculations

a. Side dra"o## (i+ure 1

b. $ottom dra"o## (i+ure 2

2. Kettle Reboiler Calculationsa. %ressured type (i+ure 3

b. &ra'ity #lo" type (i+ure 4

1Re4. * of t5e Desin G6ide &%s %d%'ted &it5 minim%( !5%nes from % P%s%den% do!6ment+ DSG-,P7+ 18)


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3. Vertical Thermosyphon Reboiler Calculations

a. $ottom dra"o## (i+ure )

b. Side dra"o## (i+ure *

4.1 Ho#i&ont'$ T(e#)o*+,(on Re-oi$e# C'$c"$'tion*

Horizontal reboilers- "ith natural circulation- ha'e a simple circulation system. /iuid#lo"s #rom a to"er sidedra"o## nozzle- to"er bottom- or an ele'ated drum throu+h ado"ncomer pipe to the bottom o# the reboiler shell. The liuid is heated- partially'aporized- and lea'es the reboiler in the return pipin+ as 'aporliuid mi0ture- then#lo"in+ bac, to the to"er or drum. The circulation is #orced by the static head di##erencebet"een the t"o #luid columns.

6se the e0chan+er centerline as a re#erence line.

1 1 17144P H= 8. 41

2 2 27144P H= 8. 42

( ) ( )1 2 1 1 2 217144P P P H H = = 8. 43

"here5

H19 hei+ht o# do"ncomer- in #t

H29 hei+ht o# riser- in #t

%19 do"ncomer static pressure at reboiler center line- in pounds per suare inch

atmosphere psia

%29 riser static pressure at reboiler center line- in psia

% 9 pressure drop- in pounds per suare inch psi

19 hot liuid density- in lb7cu #t

29 liuid7'apor density- in lb7cu #t

This % is the dri'in+ #orce necessary #or natural circulation. This is also the pressurea'ailable to o'ercome e0chan+er and pipin+ #riction losses.

% %reboiler: %do"ncomer: %riser: %sa#ety#actor 8. 44

%reboiler+enerally ran+es #rom .2) to .) psi.


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"here5

% 9 %reboiler: %do"ncomer: %riser: .1 sa#ety #actor

The 'alue o# H1is use#ul "hen ele'ation ad=ustments are made to 'essel hei+hts durin+

plant layout or "hen the 'essel can be located at a minimum ele'ation.

>any to"ers ha'e a bottom dra"o## pump. %ump net positi'e suction head


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(or the minimum do"ncomer len+th H1- the return line nozzle ele'ation H3 must be

,no"n. nsert H29 H1: H3into !% 8uation 43 and sol'e #or H1- as sho"n in 8uation

4B5

2 3

1

1 2

144 P HH

+=

8. 4B

4.2 ett$e Re-oi$e# C'$c"$'tion*

There are t"o +eneral types o# ,ettle reboilers5 the pressured #lo" and the +ra'ity #lo".

(i+ure 3 Kettle Reboiler %ressured Type

4.2.1 Kettle Reboilers %ressured (lo"

n this type o# ,ettle reboiler- the liuid le'el in the reboiler is +enerally controlled by ale'el controller. 80cess liuid #lo"s #rom the reboiler to a lo"er pressure destinationthrou+h a le'el control 'al'e. These reboilers are +enerally mounted at +rade- and thehydraulics in'ol'ed is the same as #or any pressured #lo" #rom a 'essel.


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HoH" speci#ic +ra'ity 0 .4331 psi %reboiler: %do"ncomer: %riser 8. 4

D

"here5

Ho9 ele'ation o# to"er do"ncomer outlet nozzle- in #tH"9 ele'ation o# top o# reboiler "eir- in #t

%reboiler+enerally ran+es #rom .2) to .) psi.

%do"ncomer and %riser should be calculated usin+ the %arsons /ine Sizin+ and

;ptimization pro+ram and the desi+n criteria in Section 3.. These %s should includepipe inlet and outlet losses.

A ,ettletype reboiler produces hi+h e'aporation rates and a lar+e diameter return line

mi+ht be necessary. The process #lo" dia+ram- o# course- should indicate #lo"rates andthe physical properties o# the #lo"in+ #luid.

The static head bet"een the top o# the "eir in the reboiler and the to"er hi+h liuid le'elmust be +reat enou+h to o'ercome the liuid return line pressure drops- includin+ the pipeinlet and outlet losses.

H" HH// 0 speci#ic +ra'ity 0 .433 psi % liuid return line 8. 4E

"here5

H"9 ele'ation o# top o# the "eir in the reboilerHH//9 ele'ation o# hi+h liuid le'el in the to"er

4.3 /e#tic'$ T(e#)o*+,(on Re-oi$e# C'$c"$'tion*

/iuid #lo"s #rom a to"er side dra"o## nozzle- to"er bottom- or an ele'ated drum throu+ha do"ncomer to the bottom o# the 'ertical reboiler shell. The liuid is heated and lea'esthe reboiler in the return pipin+ as 'apor or 'aporliuid mi0ture. t then #lo"s bac, to theto"er or drum. A simpli#ied- conser'ati'e- and con'enient assumption is made thatdensity 'aries alon+ the 'ertical reboiler len+th in a strai+htline proportion.


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(i+ure ) Vertical Thermosyphon Reboiler $ottom !ra"o##

4.3.1 Vertical Thermosyphon Reboiler $ottom !ra"o##

Assumin+ that the #luid density in the reboiler "ill be an a'era+e o# the liuid do"ncomer

and return line densities "e ha'e

1 2

32

+= 8. 41

The sum o# the static heads +i'es the #ollo"in+ euation5

( ) ( )1 1 2 2 3 417144 ?P H H H = 8. 411

"here5

H?19 relati'e ele'ation bet"een the to"er bottom tan+ent and bottom o# the reboiler

H29 hei+ht o# riser- in #t

H39 ele'ation bet"een the to"er bottom tan+ent and 'apor return nozzles- in #t

H49 hei+ht o# the 'ertical reboiler- in #t

19 density o# the liuid- in lb7cu #t


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29 density o# the 'apor7liuid mi0ture- in lb7cu #t

3 9 a'era+e density o# #luid in the reboiler- in lb7cu #t

This % is the dri'in+ #orce #or 'ertical reboilers. (riction losses should be smaller thanthis.

The relati'e position bet"een the to"er bottom tan+ent and the bottom o# the reboilermust be a minimum o# H?1#eet. 80pressin+ H?1#rom the abo'e euation and insertin+

2 1 3 4 1 3 2 4? ?H H H H or H H H H = + + = +

The relati'e ele'ation di##erence as sho"n in 8uation 4125

( )

( )2 3 4 3 4

1

1 2

144?

P H H H H

+ +=

8. 412

Assumin+ that the to"er bottom tan+ent line and the top tubesheet are on the sameele'ation- the abo'e 8uations 411 and 412 can be simpli#ied- because H?19 H4and

H39 H2. Conseuently5

( ) ( )1 1 3 3 317144 ?P H H = 8. 413

and

( )2 3

1

1 3

144?

P HH

+=

- no sa#ety #actor has been included 8. 414

The H2dimension can be +reater than H3. The minimum liuid le'el static head abo'e

the bottom tan+ent line can also be ta,en into account as an additional dri'in+ #orce.


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(i+ure * Vertical Thermosyphon Reboiler Side !ra"o##

4.3.2 Vertical Thermosyphon Reboiler Side !ra"o##

(or a 'ertical reboiler "ith a hi+h dra"o## nozzle- the dri'in+ #orce is5

( ) ( )2 1 2 2 3 417144 FP H H H = 8. 41)

"here5

HF1 9 relati'e ele'ation bet"een the to"er dra"o## nozzle and the bottom o# the

reboiler- in #t

This % is the dri'in+ #orce #or 'ertical reboilers. (riction losses should be smaller thanthis.

The minimum hei+ht bet"een the liuid dra"o## nozzle and the 'apor return nozzle is 3

#eet. There#ore- the minimum dra"o## nozzle ele'ation "ill be as sho"n in 8uation 41*5

2 4 3 4

1

1 2

144 3F

P H HH

+ +=

- no sa#ety #actor has been included 8. 41*

;nce more the total system loss %- ,no"n densities- and e0chan+er len+th H4 "ill

+i'e the distance bet"een the dra"o## nozzle and the reboiler bottom tubesheet HF1.

.0 PROCESS SPECIFICATION


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The process en+ineer is responsible #or selectin+ the type o# Reboiler reuired #or theser'ice. The process speci#ication shall include the type- either by indication the type onthe data sheet or better include a s,etch- e0amples #i+ure 1 throu+h * - depictin+ the typeo# boiler speci#ied.

Reboiler Calculations Design Guide

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