Jacketed Vessel Design Nov 08 2010 01:20 PM | Guest Guest in in Heat Transfer
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|More Jacketing a process vesse provi!e! e"ceent heat transfer in ter#s of efficienc$% contro an! pro!uct &uait$' ( i&ui!s can )e use! as *e as stea# an! other high te#perature vapor circuation' The te#perature an! veocit$ of the heat transfer #e!ia can )e accurate$ controe!' The various t$pes of +ackets use! in process in!ustr$ are : 1' 2' .' '
Spira$ )affe! +ackets, conventiona +ackets -i#pe +ackets Partia/pipe coi ,i#pet +acket Pane t$pe, pate t$pe coi +ackets o##on$ use! heat transfer #e!ias incu!e *ater% stea# various pressures3% hot oi such as Ther#ino43% an! -o*ther#4 vapor'
Matching Jacket Types to Heat Transfer Media Water : -epen!ing on the process te#perature% stress corrosion cracking can so#eti#es )e a concern !ue to the chori!es usua$ foun! in *ater' 5n so#e cases% !i#pe +ackets #a$ re&uires the use of high/nicke ao$s *hich are ver$ e"pensive' The haf/pipe coi can use 1,66 thick car)on stee for the +acketing )ut their econo#$ versus conventiona +ackets #ust to )e consi!ere!' 7ith services invoving arge vou#es of *ater use! to #aintain a high te#perature !ifference3 !ifference3 the conventiona +acket usua$ offers the )est soution' Steam: oth !i#pe an! haf coi +ackets are *e suite! use *ith high pressure stea#' The !i#pe +ackets are genera$ i#ite! to .00 psig !esign Steam: pressure *hie haf/coi +ackets can )e use! up to a !esign pressure of 90 psig' ;or haf/pipe coi +acket% the higher heat fu" rate #a$ re&uire #utipe sections of +ackets to avoi! having con!ensate covering too #uch of the heat transfer area' ;or o* pressure stea# services convention +ackets are a #uch #ore econo#ica econo#ica choice' Hot Oils and Heat Transfer Fluids : (though pressures are usua$ o* *hen using ois or heat transfer fui!s% the te#peratures are usua$ high' The resut is o* ao*a)e stress vaues for the inner/vesse #ateria' Therefore )oth haf/pipe +ackets +ackets an! !i#pe +ackets can provi!e goo! soutions' onventiona +ackets re&uire a greater she thickness aong *ith e"pansion +oints to ei#inate stresses in!uce! )$ the !ifference in ther#a e"pansion *hen the +acket is not #anufacturere! fro# the sa#e #ateria as that of she' Dowtherm™ Vapors:The Vapors :The a)iit$ to var$ the !istance )et*een the outer an! innver vesse *as #akes conventiona +ackets i!ea$ suite! to han!e -o*ther#4 vapors' (so since -o*ther# vapor has a o* enthap$ 1,10 that of stea#3 a arge +acket space is nee!e! for given heat fu"' The +acket #ust )e !esigne! in accor!ance *ith (SM< o!e specifications' The #a"i#u# ao*a)e space is i#ite! )$ section =(/10 Paragraph c an! s'
Conventional Jackets "Conventional jackets" can be divided into two (2) main categories: baffled and non-baffled. Baffled jackets Figure 1: Conventional often utilize a!"et wat is known as a s!irall wound baffle. #e baffle consist of a metal stri! wound around te inner vessel wall from te jacket utilit inlet to te utilit outlet. #e baffle directs te flow in a s!iral !at wit a fluid velocit of $-% ft&s. #e fabrication metods does allow for small internal leakage or b!ass around te baffle. 'enerall b!ass flows can eceed $&* to $&2 of te total circulating flow. Conventional baffled jackets are usuall a!!lied wit small vessels using ig tem!eratures were te internal !ressure in more tan twice te jacket !ressure. +!irall baffled jackets are limited to a !ressure of $,, !sig because vessel wall tickness becomes large and te eat transfer is greatl reduced. n te case of an allo reactor a ver costl vessel can result. or ig tem!erature a!!lications te termal e!ansion differential must be considered wen coosing materials for te vessel and jacket. /esign and
construction details are given in /ivision $ of te 0+1 Code +ection 3 0!!endi 4 "5acketed 3essel". Heat Transfer Coefficients: Conventional Jackets without Baffles h + -e , k3 > 1'02 N ?e3
0'
NPr 3
0'..
-e, @3
0'
- +o, - +i3
0'8
NGr 3 0'0
Figure #: S!hemati! of Conventional a!"et
Eq. !"
6ere: j 7 8ocal eat transfer coefficient on te jacket side /e 7 9uivalent draulic diameter ;e 7 ;enolds umber
&? 6ere / is te e9uivalent diameter 3 is te fluid velocit > is te fluid densit ? and is te fluid viscosit. #e
or conventional jackets wit baffles te following can be used to calculate te eat transfer coefficient: h + -e,k> 0'029N ?e30'8 NPr 30'.. A,A *30'1 1B.' - e,-c3 3 ;or N ?e C 10%0003
Eq. #"
h + -e,k > 1'8D E N ?e3 NPr 3 -c,-e3 F 0'.. A,A *30'1 ;or N ?e 2100 3
Eq. $"
#wo new variables are introduced. /c is defined as te centerline diameter of te jacket !assage. t is calculated as / ji @ ((/ jo/ ji)&2). #e viscosit at te jacket wall is now defined as Aw. 6en calculating te eat transfer cofficients an effective mass flow rate sould be Figure $: S!hemati! of Conventional a!"et with %affle
taken as ,., feed mass flow rate to account for te substantial b!assing tat will be e!ected. /e is defined at % jacket s!acing. #e flow cross sectional area is defined as te baffle !itc jacket s!acing.
Half %ipe Coil Jackets Haf pipe cois provi!e high veocit$ an!
Figure &: Half 'ipe
tur)uence' The veocit$ can )e cose$ controe! to achieve a goo! fi# coefficient' The goo! heat transfer rates% co#)ine! *ith the structura rigi!it$ of the !esign% #ake haf/pipe cois a goo! choice for a *i!e range of appications' ( goo! !esign veocit$ for i&ui! utiities is 2' to ft,s' The #a"i#u#spacing )et*een cois shou! )e i#ite! to .,' Haf/pipe cois are i!ea$ suite! for high te#perature appications *here the utiit$ fui! is a i&ui!' There are no i#itations of the nu#)er of inet an! outet noIIes% so the +acket can )e !ivi!e! in #utipass Iones for # a"i#u# fe"i)iit$' The rigi!it$ of the haf/pipe coi !esign can aso #ini#iIe the thickness of the inner vesse *a *hich can )e especia$ attractive *hen utiiIing ao$s' Haf/pipe coi +ackets are not covere! in Section 555% -ivision 5 of the (SM< co!e' Genera$% the$ are i#ite! to D00 psig !esign pressure an! a !esign te#perature up to 920 K;' ( car)on stee haf/pipe +acket can )e appie! to a stainess stee vesse up to .00 K;' Lver .00 K;% the +acket shou! )e stainess stee as *e'
Heat Transfer Coefficients: Half&%ipe Coil Jackets Haf/pipe coi +ackets are genera$ #anufacture! *ith either 180K or 120K centra anges -
3:
ci
Figure (: Depi!tion of Center )ngles ;or a 180K centra ange:
Figure *: Half+'ipe Coil to Tan" Details
<&uivaent Heat Transfer -ia#eter% -e > , - ci3 ross Section (rea of
;o*% (" > , 8 - ci233 ;or a 120K centra ange: <&uivaent Heat Transfer -ia#eter% -e > 0'908 - ci ross Section (rea of ;o*% (" > 0'1 - ci23 =sing the sa#e no#encature as previous% the heat transfer coefficients are cacuate! as foo*s: h + -e, k> 0'029N ?e30'8 NPr 30'.. A,A 730'1 1B.' - c,-e3 3 ;or N ?eC10%0003
Eq. '"
h + -e, k > 1'8D E N ?e3 NPr 3 -c,-e3 F 0'.. A,A 730'1 ;or N ?e2%1003
Eq. ("
Do not confuse D ci with Dc .
-c is !efine! as - +i B - +o/- +i3,23'
Hydraulic )adius: Half&%ipe Coil Jackets ?eferring to ;igure9:
Figure ,: H-drauli! .adius Dimensions
The !esign of !i#pe +ackets per#its construction fro# ight gauge #etas *ithout sacrificing the strength re&uire! to *ithstan! the specifie! pressure' This resuts in consi!era)e cost saving as co#pare! to convention +ackets' -esign cacuation )egin *ith an assu#e! fo* veocit$ )et*een 2 an! ft,s' (s a rue of thu#) the +acket pressure *i )e governing *hen interna pressure of vesse is ess than 1'D9 ti#es the +acket pressure' (t such con!itions% !i#pe +ackets are t$pica$ #ore econo#ica than other choices' Ho*ever in s#a vesses ess than 10 gaons3 it is not practica to app$ !i#pe +ackets' The !esign of !i#pe +ackets is governe! )$ the Nationa oar! of oier an! P ressure esse 5nspectors an! can )e sta#pe! in accor!ance *ith (SM< =nfire! Pressure esse o!e' -i#pe +ackets are i#ite! to a pressure of .00 psi )$ Section 555% -iv'5 of the (SM< o!e' The !esign te#perature is i#ite! to 900 K;' (t high te#peratures% it is #an!ator$ that +acket )e fa)ricate! fro# a #eta having sa#e ther#a coefficient of e"pansion as that use! in inner vesse'
Figure /: Vessel with Dimple a!"et 0nstalled
Figure : Dimple a!"et Details
Heat Transfer Coefficients: *i+ple Jackets h + -o,k> + N?e3 NPr 30'.. ;or 1000 N ?e 0%0003
Eq. !,"
7here: + > 0'08 *,"3 0'.D8 (#in,(#a"3/0'.8. N?e/0'.0 * > center/to/center !istance )et*een !i#pes " > center/to/center !istance )et*een !i#pes parae to fo* Note: (w/x) is equal to one for square spacings as is often the case -o > !1 B !23,2 (#in > I */- o3 (#a" > I* ( other varia)es are as previous$ !efine!' Garvin CEP Magazine, April !!") reports an average error of '8O *ith #anufacturers !ata for the a)ove correation an! a #a"i#u# error of .0O over 11D !ata points' This resuts in average !eviations in the heat transfer coefficient of 1/20O #ost of *hich *as at veocities )eo* 2 ft,s' Goo! agree#ent *ith #anufacturers !ata *as foun! )et*een . an! D ft,s' ( reco##en!e! e"cess area of 1O shou! )e use! in this veocit$ range' The correation a)ove is for integra$ *e!e! +ackets ie' +ackets *e!e! !irect$ to the vesse3' 5f a !i#pe +acket is ca#pe! onto an e"isting vesse an! a!here! *ith heat transfer #astic% the overa heat transfer coefficient of the s$ste# *i )e ver$ o*' Mastic is use! to tr$ to #ini#iIe air pocket resistances )et*een the vesse *a an! the +acket' Historica$% this arrange#ent resuts in poor heat transfer' ( reco##en!e! overa heat transfer coefficient of 10/1 tu,h ft 2 K; shou! )e use! for such s$ste#s regar!ess of the utiit$ use!'
%ressure *rop: *i+ple Jackets The pressure oss in a !i#pe +acket can )e esti#ate! fro# the foo*ing for *ater or *ater/ike fui!s: Pressure @oss in Jacket > Tota @enght of ;o*% ft3 " 0'0 " eocit$% ft,s3 / 0'.3 Pressure @oss (cross Pressure @oss in Jacket B 0'103Pressure @oss in Jacket3 The a)ove esti#ates shou! )e use! for veocities ranging fro# 1' to D ft,s' This #etho! is )ase! on a graph foun! on page 219 of the Enc#clope$ia of Phar%aceutical &echnolog# )$ Ja#es S*ar)rick' ;or !etaie! !esign% it is a!visa)e to re$ on #anufacturer6s !ata for pressure !rop cacuations'
Heat Transfer Coefficients -nside gitated /essels 5n or!er to co#pete the overa heat transfer coefficient cacuation% an esti#ate #ust aso )e #a!e insi!e the process vesse' The foo*ing esti#ate shou! $ie! reasona)e resuts:
Eq. !!"
7here: (! > agitator !ia#eter N > agitator spee!% rev,s ( other varia)es as previous$ !efine! a is !efine! )$ the ta)e )eo*:
Ta0le !: *i+ension 1a1 for 2se with Equation !! )gitator
Surfa!e
2a2
Tur)ine
Jacket
0'D2
Tur)ine
oi
1'0
Pa!!e
Jacket
0'.D
Pa!!e
oi
0'89
(nchor
Jacket
0'D
Propeer
Jacket
0'
Propeer
oi
0'8.
Calculating the 3verall Heat Transfer Coefficient 7hen cacuating the overa heat transfer coefficient for a s$ste#% the vesse *a resistance an! an$ +acket fouing #ust )e taken into account:
Eq. !#"
Notice that the ther#a con!ucitivit$ of the vesse *a an! the *a thickness are incu!e! in the cacuation' ( t$pica +acket fouing factor is aroun! 0'001 h ft 2 K;,tu' 7hen cacuating the overa heat transfer coefficient% use a co##on sense ana$sis of the fina vaue' The ta)es )eo* *i give so#e gui!ance to reasona)e fina vaues: Ta3le #: 4stimated Overall Heat Transfer Coeffi!ients for a!"eted Tan" S-stems 50mperial 6nits7
Ta3le $: 4stimated Overall Heat Transfer Coeffi!ients for a!"eted Tan" S-stems 58etri! 6nits7
)eferences 1' 2' .' ' ' D' 9'
Heat Transfer -esign Metho!s )$ 6John J' Mcetta6 Han! ook of che#ica
