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GAS TANKER OPERATION
Sequence of Cargo Operation On Board Liquefied Gas Tanker.
1 Drying Tanks.
2 Inerting Cargo Tanks / Cargo Syste.
! Loading Deck Tank
! Gassing "p
# Coo$ing Do%n Cargo Tanks.
& Inerting 'o$d space
( )repairing Tanks for Loading.
* Loading
+ Loaded ,oyage- "n$oading Of Cargo
-.1 "n$oading %it Deep%e$$ )up at Cargo Tep.
-.2 "n$oading %it Deep%e$$ )up t Terina$ required Tep
-.! Booster )up Discarge
10 Ba$$ast ,oyage
11 Canging Of Cargo
12 )reparation for dry Dock.
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1. Lining "pTe Cargo Tanks to e gas freed are connected to te for%ard ent stacks if possi$e.
1.1 Connecting te Inert Gas Line
2. ,enting off ,apour
In port
3n routeto a$ter te course steered if te re$atie %ind direction is unfaoura$e4 at ancor
to eae up te ancor and stea to find ost faoura$e re$atie %ind direction.
!. 5ecircu$ating ir6conditioningTe air6conditioning p$ant sou$d e canged to recircu$ating during te initia$ ours of enting off apour.
#. ,enting aonia using f$e7i$e oses
s a eans to preent dangerous reactions te fo$$o%ing precautions sou$d e osered.
Te Inert Gas Line sa$$ on$y e connected to te Cargo Tanks %en te tanks are ready for inerting and te InertGas )$ant is ready to produce inert gas of te requested qua$ity.
Te tie for connecting and disconnecting te Inert Gas Line to te Cargo Tanks sa$$ e noted in te esse$8sofficia$ $og ook.
Te gas concentration in te cargo tanks is igest during te initia$ ours of enting off and %i$$ gradua$$ydecrease as te atospere in te cargo tanks is di$uted y inert gas 9or air if c$eaning after aonia.:
To ensure tat te apour ented off during te initia$ ours is not drifting to%ards te accoodation and airintakes to te engine roo it ay e necessary;
Terina$ or port regu$ations regarding enting or purging of cargo apour ust e osered. Suc regu$ationsay require tat ented cargo apours sou$d e $ed to a f$are4 or ent stack or for use in te sore p$ant.
If te cargo apour is not $ed asore adance notification sou$d e gien to te port autorities and perissionotained efore starting te operation.
If it is required to reduce te nitrogen pressure of a cargo tank containing cargo suc nitrogen sou$d e regardedas cargo apour and port regu$ations regarding enting cargo apour ust e osered.
If apour in arfu$ concentrations cannot e aoided at te accoodation and engine roo air intakes4 it ay e necessary to postpone te tank c$eaning in %ic case te )rofit Centre sa$$ e adised iediate$y.
)ersonne$ %orking in te engine roo sa$$ e infored %en enting off apour is coenced. s te airintakes to te engine roo cannot e cop$ete$y c$osed during tank c$eaning4 te engineers %i$$ often e te firstto notice any detecta$e gas.
onia %i$$ %en in contact %it %ater generate a intense eat %ic is a$e to e$t te ose and ignite anyreains of preious cargoes c$inging to te inside of te oses. Tis as een e7perienced in a gas carrier %enenting after te carriage of aonia. Te generated eat e$ted te ose connected to te anifo$diediate$y after opening te anifo$d a$e and ignited te po$yerised utadiene residues.
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Before eing used te oses sou$d e cecked for c$ean$iness fro reains of oter cargoes fro preious tankc$eaning operations. It ay e necessary to p$ace te oses on deck and $eae te e7panded for a fe% ours inorder to a$$o% te oses to attain aient teperature and to ensure te oses are dry.
fter eing used te oses sou$d e c$eaned. )rior eing co$$apsed and stored te oses sou$d e $eft on tedeck in e7panded condition for soe tie in order to ena$ing te to e toroug$y dry.
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1. DRYING TANKSTe Tanks of Liquefied Gas Tanker out of Sipyard 9 o$$o%ing Sou$d e done prior c$osing Do%n Tanks.
1 Inspection of Tanks ust e carried out.
2 C$ean tanks. Dry any %et surface in tanks.
! ny Loose o?ect sou$d e reoed and a$$ fitting ust e proper$y secured.
# Trun )up y and and Ceck Loca$$y for any un%anted sound / noise. Ceck tat )up turns easi$y.
& Ceck a$$ spray no@@$es are free.
( Ceck tat te Sap$ing points are C$ear.
* Drain out a$$ ,ent asts.
+ Operate Bu$kead a$e and ark proper$y for Open / Sut )osition.
-
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To
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Inerting o# Air $ille% &ol% / Tanks / Cargo System 'it( Inert Gas.
Inerting Cargo Tanks.
or Inerting Tanks ; Disp$aceent of ir tospere By Inert Gas. In Series.
1 Inerting tanks.
2 Inerting Deck tank Std.
! Inerting Liquid Line.
# Inerting ,apour Line.
& Inerting Condensate Line.
( Inerting Booster )up Line.
* Inerting 5e$iquification units / Lines in copressor roos.
Te air atospere is canged %it Inert gast to reduce O7ygen. Te Concentration of 2 O7ygen or e$o%
is sufficient in Cargo tanks.
IGG Ca"aity )
De' Point )
S!""ly O*ygen Contant ) +., -
Cecks to e done prior Starting Of Inert gas On Deck.
1 Ca$irate O7ygen i$$ing Side: nd te Out Let fro te Tank is Connected ack to IG Line.
! Ceck $$ sa$ing points are C$ear.
# I.G. O7ygen eter is Ca$irated and recorded.
& Line up for te >or%ard ,ent ast.( Drain out any %ater fro ,ent asts.
* Inspect te ,ent ast >$ae arrestor screen is c$ean.
+ Operate a$$ a$es on te cargo syste. $$ to e %orking satisfactory.
- $$ anifo$ds are B$anked 9Liquid and ,apour: . 5eoe $ank of Cargo anifo$d drain a$es and eep te
dain a$aes sut.
10
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Eo ! Tk Capacity ; 11(!+
Eo 2 Tk Capacity; 1&&!(
Eo 1 Tk Capacity; 11&2+
Deck Tk 9): Capacity ; 1#(
Deck Tk 9S: Capacity ; 2-!
Tota$ Cuic capacity
of tanks for Inerting. !-1#1
!!.& 'rs
2.& 'rs
Inerting to e carried out in series. s so%n in Line "p diagra.
eep cecking O7ygen reading for eac tanks eery our.
In series Inerting4 Eo. ! Tank %i$$ e Inerted >irst. Once te Tank O2 reading at ! different $ee$s is 2 or
e$o%4 Eo ! Tank is Inerted.
5ine 6" Diagram Atta(e%.
Open te IG Line Iso$ation / at Eo! F sut te anua$ ent / at Eo ! tank doe.4 $so sut te Eo !
as slo'ly as "ossi3le so as not to im"e%e t(e "iston e##et / strati#iation in tanks.
5ine 6" Diagram Atta(e%.
On cop$etion of Inerting of Eo 2 tank co8d Inerting Deck tank 1 F 2 in para$$e$ %it Eo 1 cargo tank Te $ine up diagra is attaced. On cop$etion of Inerting of Cargo and deck tanks4 Line up for inerting
Cargo pipe $ine syste.
5ine !" Diagram #or Inerting Pi"elines on argo system is atta(e%.
Inerting 5i7!i% 5ine.
Inerting 8a"o!r 5ines 9 Connet R!33er (ose at 8a"o!r (ea%er / 5i7!i% (ea%er 9At 5i7!i% mani#ol%
Connet 10:;ooster P!m"4 Cargo (eater/8a"oriser.
Inerting Reli7!i#iation Plant.
5ine !" %iagram is atta(e%.
Eote on 'o% to Do
Open "p Liquid Line aster / at Eo ! Tank doe4 Liquid eader Eo 1FEo2 at Eo ! Tk. Open Liquid
anifo$d a$e port 9ot
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See Atta(e% 5ine !" Diagram.
Inerting of 5e$iquefication units and associated cargo )iping.
Eote tat efore starting Inerting of re$iquefication units and associated cargo pipe $ines a$$ tanks are
cop$ete$y Inerted.
See atta(e% %iagram.
Te 5e$iquefication syste can e Inerted y Eitrogen a$so Te Line up diagra is attaced. Tis %ay
inerting of Cargo tks / )ipe $ine and 5e$iquefied syste can e done siu$taneous$y.
>or Inerting copressor Eo !.
,112 666H ,5 !02666H B>2&01 666H 1st Satge 666H Intercoo$er 666H 2nd Stage 666H B>2&0& 666H !rd stage 666H
B>2&0# 666H B>2&11 666H '5!01 666H '5!01 666H 002 666HEO2,5/B>2&0# 666H COED3ESO5 666H 5C,5
B2&12 666H B2&1& 666H B2&1( 666H 3) ,/, 666H C5!01 666H C001 666HL00# 666H 2,5
C5!02 ia C002 666H L(22 666H L(!2 666H L(!1 666HL00# 666H ,3ET
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Instr!tions #or 5oa%ing Coolant
>u$$y refrigerated L)G8s are equipped %it t%o deck tanks for $oading and/or storing purge parce$s.
Tis akes it possi$e to aoid ca$$ing at an additiona$ port for $oading a purge parce$ .
te aonia trade4 te tank ay e used for storing additiona$ L)G for coo$ing purposes.
Pre"arationsBefore purging is coenced a nuer of conditions ae to e taken into consideration4 suc as;
Euer of tanks to e $oaded %it te product in question.
3stiated product $oss.
Do te deck tanks contain sufficient product to accop$is requireents.
P!rging 'it( 5PG
a= P!rge Parel
In order tat tere is sufficient product to perfor a fu$$ conditioning of te cargo tanks4 as uc cargo as
possi$e sou$d e transferred to te deck tank9s: during nora$ operation in te L)G trade 9%en
canging grades etc.:. If possi$e te $arge deck tank sou$d a$%ays contain )ropane.
3= 5oa%ing P!rge Parel
If te deck tank9s: does not contain sufficient product to perfor a fu$$ purging of te cargo tanks4
additiona$ product sa$$ e $oaded eiter in te deck tank9s: or in a cargo tank if a$ready conditioned.
= P!rging
See attaced Line "p Diagra
%= Trans#erring 5i7!i% to t(e 8a"oriser
Deck tank pup sou$d e used to transfer te $iquid if te deck tank pressure is e$o% * ar.
e= 8a"oriser
Starting procedure for te aporiser is descried in te L)G operation anua$.
#= $lo' Diretion o# 8a"o!r
Te cargo tanks sa$$ e purged in para$$e$ as tis %i$$ iniise te f$o% troug eac cargo tank and tus
increase te stai$ity of te stratification. Te additiona$ product used for purging in para$$e$ copared to
purging in series is argina$.
,apour is directed fro te aporiser to te cargo tanks troug te $iquid fi$$ing $ine.
Eitrogen or inert gas is reoed fro te cargo tanks troug te apour $ines %ic sa$$ e connected
to te ent stacks %it e$o%s.
g= Press!re
In order to aintain te est possi$e stratification te cargo tank pressure sa$$ e kept to a iniu.
(= ?onitoring an% Reor%ing
It is essentia$ to onitor te progress c$ose$y during te entire purging operation %it regu$ar
easureents taken to ensure unifor distriution of apour in a$$ tanks.
>ro tese easureents4 graps sa$$ e dra%n. Te graps %i$$ c$ear$y indicate te progress of te
purging4 terey ena$ing ear$y interention4 sou$d te purging not proceed as p$anned. >urterore4
tese graps %i$$ indicate4 at %ic tie te purging can e7pect to e cop$eted.
i= Starting Com"ressors
Before starting te copressors4 it is good practice to continue te purging for 1& inutes after 100 .
reading is reaced
Te $arger deck tank of !00 ! is nora$$y used for storing L)G.
Te sa$$er deck tank of 1&0 ! is nora$$y used for storing aonia4 o%eer4 if esse$ is not $ike$y to e in
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@= >lo' o##
Sou$d te atospere in te cargo tanks not e 100 pure gas4 te inert gas/nitrogen ay e ented off
ia te condensers unti$ te top of te cargo tank is 100 gas.
k= Cooling
On cop$etion of purging4 te $iquid reaining sou$d e transferred to te $iquid $ine. It is ten used to
coo$ te cargo tanks ia te upper spray $ine.
l= Press!re
If te tank pressure fa$$s too quick$y during coo$ing tere ay e insufficient pressure to cop$ete te
operation. )roided tere is sufficient $iquid in te cargo tanks and te pressure is not aoe 0.2& ar4 te
cargo pups sou$d ten e started and $iquid circu$ated troug te upper spray $ine.
m= Tem"erat!re
Te cange in teperature sa$$ a$%ays e %itin te recoended $iits. Tis %i$$ e cop$ied %it y
unifor$y coo$ing te tank troug te upper spray $ine.
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2. P!rging 'it( ammoniaa= P!rge Parel
If te purge parce$ is $oaded in one of te cargo tanks4 ten te cargo tank sa$$ a$%ays e purged to 100
aonia prior to starting $oading $iquid.
3= P!rging
onia reacts %it arious coponents in te inert gas foring sa$ine products. It is terefore not
a$$o%ed to purge %it aonia in tanks containing inert gas.
Due to aonia8s narro% range of f$aai$ity and ig ignition teperature it does not genera$$y
constitute a fire a@ard. Terefore it is considered safe to purge aonia into tanks containing fres air.
'o%eer4 soe terina$s do require tat te cargo tanks are inerted to a $o% o7ygen $ee$ efore $oading.
Inerting sa$$ in tese circustances e conducted %it nitrogen.
= Trans#erring li7!i% to t(e 8a"oriser.
s te sa$$ deck tank does not ae a transfer pup4 any cargo sto%ed in tis tank sou$d e as %ar as
possi$e. Cargo sou$d ten e transferred to te cargo tank ia te aporiser to preent any fu$$y
refrigerated product entering te tank.
d: ,aporiser.
)$ease refer to section 2.2.2.
e= $lo' Diretion o# 8a"o!r
Te apour is directed fro te aporiser into te cargo tanks ia te apour $ine and te upper spray $ine.
Te anua$ a$e et%een te $iquid $ine and te condensate $ine sa$$ e c$osed and prior to initiating
purging it sa$$ e ensured tat tis a$e is c$osed secure$y.
ir or nitrogen is disp$aced fro te tanks troug te $iquid fi$$ing $ine4 %ic sa$$ e connected to te
ent stacks %it e$o%s.
#= ?onitoring an% Reor%ing
)$ease a$so refer to section 2.2.&.
=en purging %it aonia4 arrett6testers are used to easure te aonia concentration. Tese testers
use fres %ater and do not require te use of any specia$ ceica$s.
g= Stress Corrosion Craks
Tere is a possii$ity on te fu$$y ref. esse$s of stress corrosion cracks %en carrying aonia is present.
ccording to e7perience stress corrosion cracking ay occur in cargo tanks containing aonia4
depending on type and treatent of stee$.
To iniise te risk of stress corrosion cracking4 te fo$$o%ing guide$ines issued y SIGTTO sa$$
e fo$$o%ed;
(= Tem"erat!re
i= ater ontent.
=ater %i$$ act as an iniitor against stress corrosion and it is recoended y sore insta$$ations tat teaonia sou$d contain a iniu 0.2 y %eigt of %ater.
Te carriage teperature sa$$ e kept e$o% 6!0oC.
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@= O*ygen ontent.
onia does not cause stress corrosion cracking un$ess it is containated y o7ygen. =en
anufactured aonia as an e7tree$y $o% o7ygen content4 $ess tan 1 pp y %eigt.
During coo$ do%n an o7ygen content of 0.& y o$ue is genera$$y considered safe.
'o%eer4 te o7ygen content sou$d e $ess tan 0.02& y o$ue prior to introducing $iquid to te cargo
tanks.
k= Starting Com"ressors
s easureents are not a$%ays aso$ute$y accurate4 it is a good practice to continue te purging for 1& to
!0 inutes after 100 aonia concentration in te otto of te cargo tanks as een easured efore
starting te copressors.
l= >lo'o##
During te first fe% days of operation of te re$iquefaction p$ant4 te incondensi$e gases %ic accuu$ate
in te condensers4 i.e. te air reaining in te cargo tanks4 sa$$ e ented off.
m= Cooling)$ease refer to section 2.!.
0. Cal!lation o# t(e Time Re7!ire% #or Preooling
Te stee$ ass of te cargo tanks on a !&4000 J fu$$y ref. gas carrier is estiated to e 24(-+ etric tons.
Te stee$ as to e coo$ed fro 2&KC to 6 #0KC. Te cargo tanks are purged %it (0 t of propane apour
at 2&KC.
Te fo$$o%ing quantity of eat ust e sustracted;
>ro te stee$ ass;
24(-+4000 kg 7 0.12 7 92& #0: 2140##4#00 ca$ 9%ere 0.12 is te specific eat of te stee$:.
>ro te propane apour; 1004000 7 91-&.- 6 1*+.-: 14*004000 ca$ 1-&.- and 1*+.- are te enta$py of te
propane apour at 2&KC and 6 #0KC.
Tota$ capacity of re$iquefaction p$ant; 140!&4000 ca$.
Tie required; aout 22 ours.
Te aoe ca$cu$ation does not take into consideration te eat f$o% troug te tanks and sou$d e
regarded as guidance
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>e#ore 5oa%ing or Dis(arging
>e#ore loa%ing or %is(arging is ommene% t(e #ollo'ing ations s(all 3e taken)
2. 3ergency to% off %ires sa$$ e rigged and e ready for use on ot te poop and te forecast$e.
!. >ire figting equipent sa$$ e in order and e ready for use.
-. ny notices fro sore aout safety requireents sa$$ e posted.
12. Te a$es on deck sa$$ e set according to te pre6p$anned $oading or discarging procedure.
If te cargo eat e7canger is to e used during $oading or discarging4 it sou$d e pressure tested %e$$ inadance of arria$.
Te pressure test is conducted y fi$$ing te eat e7canger8s sea %ater section %it fres%ater and tence
pressurising it y eans of a and pup to aout & ars oerpressure.If te eat e7canger is capa$e of aintaining tis oer pressure for aout t%o ours %itout a noticea$e dropregistered on te pressure gauge4 it can e considered tigt.
If tis is not te case4 it ust e opened up and te $eaking pipes identified and sea$ed off. ne% pressure testust ten e perfored.
1. Te MSip/Sore Ceck ListM sa$$ a$%ays e cop$eted in co6operation %it a representatie fro te soreinsta$$ation. If te sore does not present a ceck $ist for cop$etion4 te . ).
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D!ring 5oa%ing an% Dis(arging)Trougout $oading and discarging te fo$$o%ing instructions sa$$ app$y;
!. To ensure free operation of te u$kead a$es a$$ a$es sa$$ e oed prior to $oading.
Te a$es sa$$ a$so e oed frequent$y during $oading.
fter cop$etion of $oading te u$kead a$es sa$$ e c$osed4 and reain c$osed during te oyage.
If any a$es do not oe free$y tis is to e reported iediate$y.
Detai$s of te oeent of te a$es sa$$ e recorded in te Deck Logook.
Te cargo and$ing p$an sou$d inc$ude ut not $iited to te fo$$o%ing inforation;
. . Ba$$ast inforation.
G. ccess to te sip and soking restrictions.
'. diagra so%ing te $ining up of te cargo $ines in use.
1!. 5e$ief a$es for te cargo tanks sa$$ e ad?usted to te correct $ifting pressure efore $oading iscoenced. Te pneuatic a$es at te anifo$ds ust not e operated fro te cargo contro$ roo efore teoses are connected and te $oading or discarging are to coence.
1#. =en oses are connected and notice of readiness is gien to or receied fro sore4 $oading or discargingay coence. Loading sa$$ egin at a $o% rate4 and te $oading rate ay on$y e increased %en it is positie$y erified tat $iquid is entering te cargo tanks as p$anned4 and te cargo pipes are not $eaking.Discarging sa$$ egin %it a s$o% puping rate and te pup pressure gauges sa$$ e constant$y onitored.
1&. )acking g$ands at te discarge a$e sa$$ a$%ays e kept tigt and te doe sa$$ not e $eft unattendedunti$ g$ands are ensured tigt %itout any $eakage to te atospere.
1. Te %atckeeping officer8s station is on deck or in te deck6office4 and it is is duty to ensure tat te pups
and ose coup$ings are kept under oseration.
2. Soundings4 tank pressures and teperatures4 and anifo$d pressure and teperatures4 sa$$ e cecked atfrequent intera$s.
#. Te sip8s oorings sa$$ e cecked at regu$ar intera$s to ensure tat tey do not ecoe too tigt or toos$ack.
&. )ersons not assigned duties regarding cargo operation4 %atc keeping4 or oter tasks on deck sa$$ e refusedaccess to te tank deck.
(. Leakage8s fro f$anges4 g$ands and coup$ings sa$$ e stopped iediate$y. If $eakage8s are too $arge to eand$ed iediate$y4 te cargo operation sa$$ e stopped and te syste de6pressurised.
Te Cief Officer sa$$ not $eae te deck/deck6office unti$ e as anded oer %ritten instructions aout tecargo operation arrangeents inc$uding a$$ast to te Officer of te =atc 9OO=:4 and as satisfied ise$f tatte OO= as understood te instructions.
I. ny oter inforation %ic sou$d e aai$a2$e to te OO= in order to ensure a soot and safe cargooperation.
If on$y a part cargo as een $oaded or discarged4 soundings4 pressures and teperatures sa$$ again eeasured under te superision of te cief officer and te receier8s representatie in a$$ te sip8s tanks4
inc$uding te tanks fro %ic no cargo as een $oaded or discarged in te
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1. 8a"orising li7!i% (eelCopressors %it apour $o%ers are used to eat up te reaining $iquid 9%ic ten eaporates:4 te
aonia apours4 and tank stee$. It is ery iportant to distriute eat een$y trougout te tank
a$toug te pup sup sou$d e eated coparatie$y ore. Te pup sup sou$d genera$$y e
eated for an additiona$ 1 to 2 ours4 after a$$ $iquid as een aporised4 in order to preent recondensing
of apour against co$d stee$.
2. S!3oolingIt is an inaria$e ru$e tat tanks 6 inc$uding tank stee$ 6 are eated to a teperature aoe de%point of te
air used for enti$ating. Teoretica$$y4 it sou$d e sufficient to eat to a teperature of e.g. 62&KC %en
enti$ating %it te IG6$o%er4 as tis supp$ies air %it a de%point of aout 6#&KC.
'o%eer4 tis does not app$y in practise as oter conditions ae to e considered.
It sou$d e a genera$ ru$e to eat te tanks to not $ess tan 20KC4 and specia$ care sou$d e taken to
ensure tat te pup sup is eated toroug$y.
. Remoal o# oer"ress!re
0. 8entilating
,. 8enting o## ammonia 'it( IG3lo'er
It ay a$so e necessary to ad?ust te course so tat apour c$ears te accoodation.
If %arer and especia$$y ore uid air is added to te tanks8 atospere4 tis air %i$$ asor te aoniaapour aking te aonia $iquid4 try to fi$$ te tank space %it apour y eaporation. Te eat required fortis process is taken fro te nearest surroundings4 e.g. te tank stee$4 and a drastic drop in teperature can e
osered. Teperatures far e$o% te stee$8s design teperature and a rate of decrease u$tip$e e7ceeding tat%ic te tanks are designed for can e osered and terey possi$y daage te tanks. Te uidity in te air%i$$ a$so re$iquify against te stee$4 te %ater %i$$ disso$e te aonia and sustantia$ pro$ongation of teduration of te tank c$eaning ust e faced4 as tis aonia and %ater so$ution is ery difficu$t to reoe.
In order to e a$e to eat up te tanks to required teperatures4 te esse$s ae een furnised %it 2 DeckB$o%er units %it a tota$ of 2 7 22000 ! capacity4 %it stea eating of te air. "sing tese $o%ers it is possi$e to eat up te tanks to at $east #0KC. t tis teperature it is not difficu$t to $o%er te aoniaconcentration.
Oerpressure is reoed gradua$$y fro te tanks troug te ent asts in te usua$ %ay c$ose$y onitoring teteroeters.
=it aonia it is a specia$ requireent not to use inert gas for di$uting te gas as certain coponents in teinert gas react %it aonia to for sa$ine products %ic $ock up a$es4 pipes etc.
s aonia8s e7p$osion $iits are fro 1( to 2& percent and it is difficu$t to ignite and a$so %it a $o% ca$orifica$ue4 it can under nora$ circustances e regarded as non f$aa$e. Tus4 tanks can e enti$ated %itoutfirst eing inerted.
Te porta$e $o%ers are not a$e to %ork against ack pressure of any significant si@e. It is terefore necessaryto enti$ate aonia y using te inert gas $o%er %i$e te concentration is sti$$ too ig for it to e ented offtroug open tank atces4 i.e. %i$e te concentration of aonia is too ig for personne$ contact. ir frote inert gas $o%er is supp$ied to te tanks troug $iquid $ines oer te anifo$d to te tanks8 $iquid fi$$ing$ines. By reason of aonia8s apour density copared to tat of air4 tanks sou$d e connected in para$$e$.Tanks are ented off at te top4 and te ented off apour is $ed to te for%ard gas ast in order to iniiseinconeniences fro te aonia.
Te process of di$ution can e onitored c$ose$y using Barrett testers. ery c$ear stratification can e e7pected."sua$$y one cange of atospere can e e7pected to e sufficient to ring te concentration e$o% easura$e$iits using Barrett6testers.
,enti$ating using te inert gas $o%er ust e continued for appro7iate$y anoter 1& ours as te porta$e $o%ers cannot %ork against ack pressure.
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B. 6sing (ot air 3lo'ers
t a concentration of aout *00 pp4 2 ot air $o%ers can e put to %ork.
. $inal entilation
12. Drying tanks
During tis pase4 Drger test tues can e used to indicate4 %en te porta$e ot air $o%ers sou$d e rougtinto use. t a reading of &006*00 pp4 te concentration %i$$ no $onger dec$ine gradua$$y ut instead rise andfa$$. Tis is an indication tat te tank stee$ is eginning to free trapped aonia.
It is necessary to open te tank atces to ake it possi$e for te ot air $o%ers to supp$y air at a ratesustantia$$y iger tan tat of te Inert gas $o%er.
To iniise te ack pressure4 it is necessary to open te atces y reoing a$$ ut 2 o$ts4 %ic are on$y$oosened. By squee@ing one o$t under te atc coers4 sufficient c$earance is otained to aoid too ig a ack pressure. t a concentration of aout *00 pp4 %ork can e carried out on te atces %itout any inconenienceand %itout using gas asks.
Te $o%ers are started and stea eating app$ied. arked increase in efficiency can e seen after initiating teot air $o%ers. fter appro7iate$y & ours4 te concentration %i$$ ae een reduced enoug to ake it possi$e to reoe te atces and rig oses in te tanks.
noter 2062# ours8 enti$ation %i$$ e required. fter tis4 concentration can e e7pected to e %e$$ e$o% & pp.
Tus4 an aonia concentration %ic is detecta$e ut uneasura$e4 can e acieed y enti$ating %it otair.
=en ot air enti$ation as een cop$eted4 te tanks ust ten e dried toroug$y %ic is done y using teinert gas $o%er. ,enti$ation is continued unti$ te required de%point as een reaced. It is not anticipated tatte aonia concentration %i$$ increase again.
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5oa%ing O# Coolant in No 1 Tank
1 P!rging No 1 Cargo Tank.
2 5oa% In Cargo Tank No 1
Loading 2&0o$$o%ing is to e prepared prior )urging / Loading of Coo$ant.
1 Ceck O7ygen reading for Eo 1 Tank. It sou$d e 2 o7ygen or e$o%.
2 )ressuri@e te Tank %it IG and ceck no $eaks on tank doe.
! 5e$ease te IG pressure troug ,ent ast Eo 1.
# Cargo sea%ater pup to e running sea%ater f$o%ing troug cargo eater / aporiser.
& Ca$irate fi7ed gas detectot syste.
( Ca$irate Gas easuring porta$e equipent.
* 'ydrau$ic p/p 4 anti$ation fan for copressor r 4 3$ otor r air $ock antia$tion fans running.
+ /C on partia$ recircu$ation. ire figting equipant stand y at anifo$d4 in ready to use state.10 Te
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,112 /,111 666H ,5101/,5102 666H B>2&01 666H 1ST STG3 666H IET35COOL35S 666H2ED STG3
!rd stage 666H B>2&0# 666H B>2&11 666H'5102 666H '5102666H'5101666H'00!666H ,00& 9 ,apour return:
Pls see 5ine 6" Diagram
Cooling %o'n 'it( a"o!r ret!rn to s(ore.
=en te gassing up procedure is cop$eted4 coo$ do%n of Eo 1 Cargo tank c$d e started prior to Loading
cargo into te tank.
Coence $oading $iquid $ine at a s$o% rate into Eo 1 cargo tk. Initia$$y to $oad troug condensate return
$ine into te top spray no@@$es. On coenceent of te coo$ing do%n operation te tank pressure s$d e
as $o% as possi$e.
s $ong as te teperature of te tank atospere is igter ten te saturated tep of te propane In?ect
troug te spray no@@$es4 Te tank atospere teperature and cosequent$y te stee$ teperature %i$$
decrease.
3aporation of te Liquid to $o%er tep %i$$ cange te cargo apour ,o$ F )ressure. t te eginning of
spraying4 te apour o$ue %i$$ decrease due to reduced tep and te pressure in te tank %i$$ reduce.
fter a %i$e te added spray quantity %i$$ e doinant and te tanks pressure %i$$ start to increase.
Due to te eaiour of te process4 te tanks pressure s$d e onitored carefu$$y.Once te tank tep as reaced to 62& Deg C coence introducing $iquid into te otto sup tru te
codensate otto $ine.
=en te sup is fu$$ of $iquid coence $oading y te ain Liquid $ine into te tank. Loading rate to e
Increased gradua$$y.
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P!rging / Gassing 6"
>o$$o%ing to e cecked
1 Ceck 'C reading for eac tank / at eac sap$ing point.
2 Connect f$e7i$e oses on tank doe to ent to respectie tank ent ast Line.
!
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COO5ING TANKS
Once te reading so%s 100 'C. Continue gassing up for at $east 10 !tane )T%o Stage copression %itout Intercoo$er.
!antity o# &eat to 3e remoe% #rom tanks
Te stee$ ass of te cargo tanks on a !&4000 J fu$$y ref. gas carrier is estiated to e 24(-+ etric tons.
Te stee$ as to e coo$ed fro 2&KC to 6 #0KC. Te cargo tanks are purged %it (0 t of propane apour
at 2&KC.
Te fo$$o%ing quantity of eat ust e sustracted;
>ro te stee$ ass;
24(-+4000 kg 7 0.12 7 92& #0: 2140##4#00 ca$ 9%ere 0.12 is te specific eat of te stee$:.
>ro te propane apour; 1004000 7 91-&.- 6 1*+.-: 14*004000 ca$ 1-&.- and 1*+.- are te enta$py of te
propane apour at 2&KC and 6 #0KC.
Tota$ capacity of re$iquefaction p$ant; 140!&4000 ca$. < Q 9 1610:
Tie required; aout 22 ours.
Te aoe ca$cu$ation does not take into consideration te eat f$o% troug te tanks and sou$d e
regarded as guidance
T(e Cargo (an%ling man!al gies gra"( #rom '(ere t(e Time taken #or ooling an 3e al!late% straig(t
$or N&
T%o stage copression %it Intercoo$ing 9 S= Tep R 20 O C :
Tree stage copression %it Intercoo$ing 9 S= Tep H 20 O C :
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C(anging Cargo #rom Pro"ane to >!tane
If ne7t cargo is Butane after )ropane4 ten te cargo tank conditioning is to e done.
1 t te Discarge port as far as possi$e strip out a7iu cargo.
2 Te tank is to ade $iquid free.
Start copressors on ot gas ode and start putting ot gas in Sup of te tanks. It Liquid in sup %i$$
get eaporated and If %e ae tie One copressor can e run to take apour fro te tank and re6$iquify
and dup te $iquid into te Deck tank %it )ropane. =ic can e used in future for coo$ing tanks for
prepairing for )ropane fro Butane.
If deck tank is fu$$ or tie is $iited. Te propane apour is to e re$ised to atospere.
Te Tank is ot gassed and te ,apour fored due to eaporation od Liquid %i$$ pressurise te tanks.
Te pressure can e re$ised to atospere fro ent asts.
=en te pressure is re$ised te Tank %i$$ coo$ do%n. It is good practice to re$ease tank pressure in contro$
%ay. $%ays ake sure tat te Tank pressure is igt ten te tosperic pressure. So no ack f$o% of
air can take p$ace in any case.
! Once te Sup teperature is aout 6+ to 610 Deg C te 'ot gassing can e stopped. nd tank isConditioned to Load Butane.
3nta$py of )ropane at 6#0 dec C #00 /g
3nta$py of )ropane at 610 Deg C +00 /g
Cange in 3nta$py #00 /g
)ropane in Tank !0
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Density of Gas at 20 deg C and Atm Pressure
Air 1.024
Ammonia 0.714
Butane 2.484
Propane 1.866
Loer !"p#osi$e Limit
Butane 1.%0&
Propane 2.00&
Ammonia 1%&