TRANSPORTATION AND STORAGE OF BULK, LOW-PRESSURE LIQUID CARBON DIOXIDE ARBON dioxide hss hecome C an important industrial chemical. It is being used ex-
thermore, dry ice is not a convenient source of carbon dioxide liquid or vapor ns needed by industry. It is necesssry to crush the solid carbon dioxide, place it in high-pressure cylinders, and allow it to liquefy to obtain commercially usable liquid or vapor. The handling of liquid carbon dioxide in the 50-poundcapacity cylinders is entirely satisfactory except for the excessive oost and inconvenience involved in handling the many heavy cylinders to obtain appreciable qusntitiw-of the gas. The bulk, low-prewure method of handling liquid wbon dioxide makes it poesible to eliminate the majority of the objeotions to the high-pmmre liquid method 88 well aa to the dry ice method. This new method takes advantage of the fad that a reduotion in the temparstura of liquid carbon dioxide renulta in a raduction in the vapor pressure. By maintaining a constant low temperatura, a constant low preeawe is main. hind. At m temperatureof 0' F. it is pactid to nae large presmm vessels instead of small Bteel cylinders. At this loa tempersture only 290 pounds presstve per quare inah ir exerted, so that relatively thin-walled pressure vessels om br used. Each pressure 1is thermally insulated to p m t rapid heat entrance from the surrounding atmosphere. The storage
Transpobtion and storage of bulk, low-pressure liquid carbon dioxide are discussed and compared with conventional high-pressure methods of handling. Over PO per cent of United States production of liquid carbon dioxide is being handled by the bulk, low-pressure method. General engineering featurn are discussed and data presented to show practicability of bulk, lowpressure liquid carbon dioxide handling at hot weather conditions. Data on the efficiency of various thermal insulating materials are presented.
tensively in dislodging coal in mines, in carbonation of soft drinks, for refrigeration purposes, in various chemical manufaatwing pmceaeea, and in lire extiiguiahing systems. The bulk, low-prwnreliquid method of handling carbon dioxide is playing an important role in expanding t h w uses. Carbon dioxide hss been tranawrkd and stored in the liquici state since 1&23 (1). Cylinders of 60-pound c s e t y have been the common size unit wed. Becsuse of the hgb vapor preglure of liquid carbon dioxide at temperatures encountered in the temperatesone, it is neoe8881y to make thew 50-pound-capacity steel cylinders of heavy wall construction. The tare weight ranges from 90 to 135 pounds per cylinder. These cylinders must be tested periodidy at a pressure of 3OOO pounds per square inch. The pressure which develops in a normally filled cylinder at 68"F. is 8M) pounds per quare inch, at 77' F. it is 1136 pounds, and at 86' F. it is 1436 pounds (8). Carbon dioxide is ala0 handled in ita solid (dry ioe) form at approximately - 1 l O O F . Dryhe CUI he hsndled witbout pressure equipment, but because of ita extremely low temperature, mmiduable loss m l t a from ex&hest input. Fur-
1124
t
sw4anJ=,
1941
i
I N D U S T B I A L A N D E N Q I N E E R I N Q CHEMISTBY
tanka am equipped with meahaniost rrbri((Snt0rs to maintain a ralatively constant temperaTraMprt tru& and tsnL cars are not equipped with nmhand * redrigantorsbe caw it is seldom that the pressure risea to the point where vapor must be relieved by the eafety valvw to maintain normal workiq preaeure. The cold liquid is transferredfrom dto v d by mesns of 1.5-i hose h e and a centrifugal, or rotm and ststor pump, at the rate of about 10 tons per hour. Storage tanke ranging in aspacity from 0.26 to 126 torrs of low-preesure liquid carbon dioxide are being used. Figurea 1 and 2 show the general construction of a typid popular sine storage tank. Construction of %rag.
Tank
wE8sm VrnSsnL (TANK WOPEB). Each storage tsnL pressure vessel is m a n u f & d acmrding to psrsgraph UB8 ofthe b 8.M.E. wdefm un6red pleswnewacls. The &ton tank, Af (Figure l),hscaworkingprassure of326pounds per quare inch and is testedat 650 pounaspersquveinoh. It has8 &inch internal dimebrwith a La/L,-inchwaU. Amanway, 88, is supplied on eroh Vessa to slimmtetnalinopwtion or m p k . At the bottom of the t.nL is welded e l.6inoh extra heavy pipe, AS. This pipem wed in -or removing liquid carbon &wide. It is dp Md in cmmeahm In with the liquid level indiastar. This pipe is dmigned with a liquid trap immediately outside the prmnllm VraSeL Fxaept when withdrawing or supplying liquid, the pipe Contrins only
1115
--
only about onseemath of the tenk's internal diameter. Thia pipe is used to equaliw the Vepor pr0sure between vassels when liquid is being tranelsrredfrom one to the other. It further is used to that tile vesselism with liquid to only six seventh of ita depth w h at the n o d storage p m . It is also used to supply carbon divapor for utility purmch water carbonatim A fourth pipe, 46, welded to tile top dthe vessel, is used in a h d i n g the various d e t y devioss and preeaum contrul equipment. T w o other pipes, A7 and AS,are welded to the dto allow entrance and exit of the ref-tor mil which rsats in the vapor spaoe of the vessel. REPF~IQ~TOR COIL.A hard copper coil, Bf,is placed in the vapor spnse of the stOrsge ten!& Either end of the coil is led to the outaide of the pressure vessel where it is attached tothe meahanidrefrigemtor. This coil is placed in the vessel lmfm the 5 d elliptid head, AB, is welded to the struight aeo(i0n.
MOUNPIXQBASE. A c h m e l iron baea or frame. Cf.is
used in mounting the pnrasure VeaSeL Three W (3,RIpport the veSel.3 i n&
d e n
d&,
h t h e channel icau bssa to
whi& it is murely bolted. IUBUIATXON. &dl plpaure d is insulated with an Sinoh lam of &&ant thermal inarlati material (DI). Vuiou indating nmtmida wem &died and data will be given l a k i n the p 6 p . REISWEBASOR. Eeoh storage tank is equipped with a meohniaa refrigemtor. In mod ca+mthin refrigerator is mounted with the v e d on the channel iron bsse vapor. Cf. The refrigemtor is mountad hehind the grill panel, E l . An extra heavy pipe, 4, is welded into the preanue vessel In SLSS of 2 b o ~ ~ p o w and e r lower, the refrigerator is an airat the top and extends nesrly to the bottom of the d. wold type. Thia is used in withdrawing liquid aarbon dioxide for utility Tam Houmo. It has hwu found neoedasly to seal herpurposebmI&~6reextinguishing and dry iae manuf&w. d d y the prpsnve d iosubtion. A housing, Pf,is Another pipe, Ab, is welded into the top of the p w m d , pmvidednot odytossslthe insulstion but also to house the It is also a diptube type; however, it dips into t h e d f q d r i p a h and imlnag the appesrance of the stom@ tank an a unit (Fisure 2). Hotrolled &et metal is welded to~ l o m e l c e t h i s ~ u. m s t r i p s o a n b e u s e d to trim the unit. Ramotnble doom give to the rn frigamtmunitand fillinglinemlve. h m m m ' P m . A front view of the end of the storsgetankisgiveninFigure2. Theinstrument panel, 01 (F%ure l),is looated hehinda gbssdwr, (38. The &a makeg it pasible to ohserve the prea~oegage, the liquid level &age, and the pressure control awitch but preventa tampering with the valve& homo LEVRLGAQU. Various typea of liquid level gages havebeen tented. The typnsholminFigUres1(HI) and2 ia eatiefaotory. It is a mercury msnometer whioh measures the dilTmuae between the pmmue exerted at the top and at the bottom of the vessel; it is &hated a i f d o n of f d . The higher bottom pressure is due to the hydrmtetic head of liquid carbon dioxide added to the normal vmpor premue. Pmmm GAQZ. A 6OO-paundrange, heavyduty p r e m m e , If, haa been found eatiebaatory. ELedriosl contaota on the &age can . , . be used to indicate preu3w vsriI .a ation beyond the normal range of 276 to 825 pound8 per squara inah. P~WWJZB CONTROL SWITCH. Esch storage tank refrigerator is mhhdby a pressureswitch, JI . It hss been found eatisfaotory to uw a memury mit& operated by a Bourdon tube. Usually the
-
.
1126
NDUSTRIAL A N D ENGINEERING CHEMISTRY
FIQW 4 (Righi). 3.5TONTBUCK, SHOWINQ PIPINQAND CYLINDmR FILLING SIDE VIEW OF
r
Vol 33 N- Q
'\-
..
sesbmb=, 1041
I N D U S T R I A L A N D E N Q~ I N E E R I N QCHEMISTRY
Figures 1 and 2, which is 10 pounds above the diaphragm valve relieving pressure
TIME
hQWI6.
IN
MINUTES
h B n Q m TANS h W S r r r O e DUEINQ FBIQWTION &-
ONE Rk
In addition to the pressure relief valves the tank is provided with a frangible diaphragm assembly, K4. The diaphragm b ~ a t a p r e s s u r e o f 6 o o p o ~ p e r s q n a r e i n c hThisis50 . pounde below the presrntra at which the vessel is teated when manufactured. Valve K6 is placed in the Line leading to the frangible diaphragm EO that it is possible to change the diaphragm if corrosive atmcspherea should be present. This valve is designed EO that it @an be looked in only the open poeition. Tms S m m VALVES. Where it is required to have no loss of gas, the shut& valvea have either special Babbitt or syntheticrubber seating disks.
lla?
Some of the tru& have n power tske-off to drive t r a d e r pump for Elling high-pnssura carbon dioxide cylinders (Figure 4); .others have low-pressure M e r pump driven by power take-oE. Figure 5 is a rear view of a semitrsiler showing the instrument panel and safety valve assembly. In the foregroundis a rotor and stator (electriemotordriven) bulktransfer pump.
Operating Data DIMENSIONS AND DPBIQN. Table I gives dimeneiom and information concerning the variona sire &rage tanks. PimaVARIATION DURING Noauar. OPXS~ATION. Figure 6 shm the pressure data obtained during one complete refrigeration cycle. A onehomepower Freon refrigerator wae used. The &ton storage tank, including the refrigerator, was placed in a constant-hperature mom maintained at 100' F. The refrigerator was shut oi? at zero time by the preeanre control switch nt 294.7 pounds gage pressure. As soon M the refrigerator stopped, the preeaure me a h p l y , then the rate of rise gradually decressed. This type curve is a result of the fact that the surface of the liquid in the tank is colder tban the body of the liquid during the refrigemtor running Mod. The convection owrente, set up because of the formation of cold denser liquid on the surface, are not able to maintain a uniform hperatm in the liquid. The vapor p m m is governed by the temperature of the surface layer. Thus when the refrigerator is stopped, tbe wanner liquid helow the surface c o r n to the snrface, and we find an initial rapid rate of preeanre rise.
Pottable Unit,
SMALL CAEWET UNIT. Fignre 3 ahows a 5oo-pound urpscity storage tank. This unit is mounted on wheeh and can be easily moved. The refrigeratm unit is mounted in the upper motion nbove thevertically mounted pressure VeeSeL TBANWOI~TATION Eampyw~. The transportstion equipment is similar to the storage tanks. The maindiiTemnoeaare bridy as follows: The pressure veada aru attgched as an integral part of the truck, semitrailer, or rdwny tank ear. They do not have meohsnid refrigeratom attachd. The preeaure veaeels are made of lighter weight ateel and for slightly lower m r h g pressures in eome rase. The welded sesms are x-rayed to prove perfection, and in eome CBBBB the v e d s are streas-relieveed.
After 108 minutes, nt 305 pounds per square inch, the pressure BIRitch tnrned on the refrigerator which begsn to condense carbon dioxide vapor on the mfrigerator coil. Condensation of this vapor c a d evuporation fmm the surface of the liquid carbon dioxide. This evaporation, combmed with the dripping of cold liquid from the refrigeratorcoil,prod u d rapid oooling of the surface layer of the carbon dioxide liquid and hence the initial rapid preeawe drop. As contion currentsbegan to developin the liquid carbon dioxide, the rate of preeanre declina heaame lasa. After 57 minutes of running, the preeanre was reduced to 294.7 pounds per square inch and the refrigerator wan stopped by the presswe control saitch.
R ~ B I ~ ~ A TCon. O E TIO ON m D~SIQN.The re frigmatm coil was placed at variona locatiom in the storage veawb,and it wae f m d that the greateat transfer per square foot of coil surfme was obtained when the coil was in the vapor apace of the pressure 4.Muoh leae coil surface per B. t. n. trader is required when condensing pun volatile liquid vapom than when cooling gam sueh as air. This is due to the fact that, as the earbon dioxide is m n d e d to
vapor was bled manually to maintain a cor&& p m . The amount of carbon dioxide r e l e a d hourly waa determined by weight. A typiaal set of data is shown in Figure 7. The rate of carbon dioxide release is very small at the heginning of the
;
t
\ ALARY RANQ
300,
RELIEF VALVE ON
REfRlOERATlON ON
\
PI5
librium inside-the preanve veaael. The resulta obtained with variow insulathg material are given in Table 11. The valueu for rate of gss ralesse per hour are those obtained after the rate of vapor releaee became constant. An ainch layer of insulation waa uaed in all c.wa except those using the vacuum space insulation. Of those studied, vegetable oork is the beat insulathg material aa a p plied to t h w tanks. By multiplying the pow& of carbon dioxide releesed per hour by the heat of vaporization a t that temperature, we find the total heat input per hour (Table II). The K factor is the average heat trader per square foot of tank sUrtace per F. temperature difference for one inch of ineulation thickness. It is found by sulmtituthg in the equation:
VARIATIONIN BTOUAQE TANKF’RESSORBAND REUEF VAL^ OPZBATION.In thin particular study the storage tank was insulated with 8 inches of kapok-bound batting and placed in the 1 0 0 O F. conhnt-temperatm m m . The re frigeratorwas shut off manually at the end of ita running cycle, And the inarew in pressure waa observed against time. The test simulateswhat would happen on a hot summer day if the refrigerator failed. TIM tank wan on the d e s , which made it possible to determine the rate of carbon dioxide release when the relief valve c ~ m into e day. The data are aven in graphio form in Figure 8. K x sq. It. of tank a w f m x O F . tamp. ~ ~ r highdde n The p m alarm rang a few hours after the B. t. u./hr. thiaknem of innulation in i n c h refrigerator had teen shut ofl. About 8 hours after the alarm beto ring (warning that the p m had risen In this K factor we have a standard value which allows aomabove n o d ) , the &iliary refrigerstion valve began to re psrison of different methods of insulation, regardleas of sire leaee carbon dioxide vapor from the tank. The valve in d e d of tank, temperature difference, or insulation thicknees. It “auxiliary refrigeration valve” becaw it functions to refrimshould be undsrstood that K includes heat t r a d e r through ate the l o w - v u r e liquid carbon dioxide 4 by bleeding piping aa well as insulating material. off carbon dioxide vapor at a slow rate. An average of 3 RATEOF ~ B B O R Itrm. B While these storage tsnlrs were pounds of vapor releam per hour maintained a constsnt presin the constant temperature room,the rate of preasun, riae was sure over the 15-how bleeding period. determined. Temperature conditions were 100’ F. ambient Nearly 24 hours were allowed to elapse from the time the and 2’ F. liquid carbon dioxide at the start. The values in alarm began to sound, indiating refrigeration failure, until Table I1 are those obtained after the rate of rim became the refrigamtor was turned on m a n d y . This would comenearly oonstsnt. wond to a full day for refrigerator repair. Forty-five pounaS 2 carbondioxide were lost becaw of this Bimulated refrigera% tor failure. Thin shown what may happen on the transport Taem 11. INSULATION Emclarcr DATA trucks, etc., which w no meahanid ref-br if the haul COI Bled is a long one. They U S ~ arrive Y a t their destination and fa H-t unload hefore the pressure has risen to the relief valve settimg. Ins”. anM b m .t.m It should he noted that all of the data given in this paper Thick- R, hnL RB.T.6.1 m. h m 4 . w m ohtained at 100’ F. room temperature, equivalent to a Er. BU(0r I n./&: % 12&z!lI I d Lt%. hot aummer day. VWbl m k 8 8.9 10W 0.410 1.91 P.8 10.5 IPW 0.404 1.8d.O BMk Literatun Cited 886 SS.5 14.0 x.10 o m 3.06 45.8 Kspok ... a(hn.Hgrmu 060 l.M ... (1) Quinn and J“Cubon Dioxide”. A. C. 8. Monoprbph ?a. ... IWL. ~~~m~~s m a 8m 1.10 ... Drddr8Ds 80.8 om a.s ... ... ch.p.I, New York, W d PublLhing Corn.. 1936.
_ _
-
-
=e’
-
y&-
(a)
ma..p. 180.
End of Sympodun
