March 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
267
Close-up of Cells in Operation Showing Electric Leads, Insulators, Gas Lines, and \ a l \ e Board, with Sheet 3Ietal Co\er oter Pop Yal\e on Cell i to Preieiit Splashing
co-t for replacement anti removed t h e difficulty due t o accumulat ion of fluoride sludge froin tlie consumption of nickel anodes.
.\I1 of thebe considerations resulted in t h e choice of the high temImxture cell; despite .ignificant developments in the lower temI)er;ltui,e tyl:ey, t h e authors lielieve t h a t tlie high temperature niodific:\tion still poses-ea a uuniher of adxmtage5. 600-800 A3IPERE CELL
.\s :L r e . d t of experience with several designs of intermediate
iinit h o w electrical and piping connections ; I S u-cll as t h e g n : burners miti heat insulation, angle iron support, : i i i d contien.er. I n this unit direct gas heating ivas selected as s t)eing more economical, but a thermostatic liquid ~ m interposed Iletneen t h e gas flame and the electrolyte box t o avoid local overlieating and corro.sion of the electrolyte container. Diphenyl oxide vas selected as a thermostatic liquid since it boils a t 259 o C., \\-liicli is above t h e melting point of the e l e c t r o l ~ t eand a t t h e Ion-er end of the operating range of such a cell. F h e n t h e cell \vas not in operation, heat ~v upplied t o maintain the electro-
lyte i n a liquid condition. During operation, however, the cell did not require auxiliary heat, and the liquid w w e d t o keep t h e temperature within t h e desired range. T h e diphenyl oxide vapor n-as liquefied in vater-cooled condenser.3 anti returned to t h e cell. In the follon-ing description of t h e cell construction the numbers refer to Figure 1. T h e outermost or coolant liox 1 and 18 \vas of ~ e l d e dsteel construction a n d contsined approsinlately 6 gallons of liquid. I t ivas provided with suit'aI,le drain and filling pipes 17 and 71 and with elbow and flanges 33 and 34 for at'tacliing the reflux condensers. The condensers c'on-isted of six 3/r-inc.11 copper tubes in a 5-foot long \rater jacket and m r e constructed entirely of copper and brass. Electrolyte container and cell cathode, 11, v a s :Liiarrmv Monel box, 4 X 16 x 31 inches provided with Moncbl flange 5 n r n r t,he top. All seams n e r e electrically n-elded and tested for gas leaks. T h e flange on t h e ?*Ionel box rested on the similar flange, 21, of the iron box beloit-, and thereby sealed t h e diphenyl oxide compartment. A clamp flange, 4,of steel rested on the blonel flange and vas provided with clamp studs, 25, near the inside periphery, n-hich served t o bolt don-n the cell head when iri place. The term ,.head" IT-as a convenient defigiiation for the assembly xhich con..isted of the anode, skirt, diaphragm cage, and all auxil-
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268
INDUSTRIAL AND ENGINEERING CHEMISTRY
iary equipment i n one integral unit. I t could be lifted out of t h e electrolyte container in one piece and normally was t h e only p a r t of t h e cell to require maintenance or repair n-ork. All parts above and n-ithin t h e electrolyte box were, when assembled, attached t o a single plate of copper called t h e headplate, 2. When ion-ered into place, this rested on t h e machined t o p edge of t h e Monel box using gasket 3 and was held securely in place by the headplate clamps, 24. Symmetrically arranged on t h e headplate were three cathode tubes, 41, of 3-inch i.d. copper tubing; these supported t h e skirt, diaphragm cage, and anode assembly by means of clamp rings 36, 37, and 39. Tetrafluoroethylene polymer (Teflon), 38, 40, was used as packing and for electrical insulation between the cathode and skirt assembly. On early models t h e cathode tubes were shorter and reduced the over-all height of t h e head proportionately. It !vas found, however, t h a t t h e packing could not withstand the higher temperatures near t h e headplate; in later models, consequently, it n-as raised t o take advantage of air cooling. In addition, the annular space between t h e cathode tube and the skirt tube ivas continuously snlept with anhydrous hydrogen fluoride t o provide a protective blanket below t h e packing and insulation. The unsymmetrically locat'ed fourth tube, 63, on the headplate served as an outlet, 54, for t h e gases from t h e cathode (hydrogen and entrained hydrogen fluoride) and carried a pressure release valve, 55-62. The skirt, 8, which projected about 1 inch belov t h e surface of t'he electrolyte during operation, served t o divide the anode gas compartment from t h e cathode gas space and, in addition, supported the diaphragm cage. A41thought h e cell did not require a wire screen diaphragm below t h e ekirt t o separate t h e gases athey n-ere generated a t t h e anode and cathode, the cage assembly, 14, 15, and 20, was provided t o confine fragments from broken anodes and prevent them from short-circuiting between anode and cathode. This could result in an arc which ~vouldpuncture t h e cathode box and require a major repair. The hottom plate, 14, IT-as the same width as the skirt and served t o prevent any hydrogen liberated a t the bottom of the cathode box from riiing into t h e fluorine compartment and reducing the cell efficiency. The skirt and cage assenihly were 3/iB-inchcheet hloriel elertrically welded, and the anode tuhes, 42, n-ere of 2-inch Alone1 tubing. T h e end tubes were provided n-itli specially insulated packing glands, 43-46, through n-hirh the anode liw riGers passed and n-hicli served t o .;upport the anode assembly. The central tube, 53, eerx-ed as outlet for fluorine and entr:iined hydrogen fluoride. In this case also provision v a s made for R 1)rotectivr. hydrogen fluoride sn-eep in t h e annular ring
Construction Details of 600-800 h i p e r e Cell
37. Lock ring 38. Packing
3 5 . Yalrc 5eat Illate
39. Cathode riser ring 40. Packing 41. Cathode tuhe 42. .%node tiibe (diaphragm riser) 43. h o c k packing gland 44. Packing 4 5 , Insulation sleeve 48. .Inode Ilacking n u t 47. Spacer 48. C l a n i p block bolt a n d n i i t 49. Claing block 30. .Inode bus b a r 51. .\node bus har bolt a n d niit 52, Anode bar riqer 33. Fluorine outlet fitting 34. I I y d r o g e n outlet
57. Spacer 58. Spacer ni:t 59. Bushing 60. Guide plate 61. Valve 8teiii 62. T a l r e s p r i n g 03. Hydrogen o:itlet t:ibe 64. Elboir 85. S i p p l e 66. Tee G 7 . Inspection port bolt 08. Inspection p o r t C O I E ~ 69. Inspection Ijort ea-Let 7 0 . Inspection port riun 7 1 . Coolant overiion
5 6 . Valve p l u n u c ~
s
270
E F
I i
/
/
',
I;,,
I
Figure 2. A.
Vol. 39, No. 3
INDUSTRIAL AND ENGINEERING CHEMISTRY
Piping .%rrangementson 600-800 inipere Cell
T u b u l a r condenser for refluxing coolant
B. All t u b e insulators (designated b y I) are flanged, uiinv Teflon insi;lntion between flanges; bolts a r e insulated with fiber bushings; only Trflon can c o m e in contact nitli t h e gaSes
C. H? a n d HI: out
D . Fluorine a n d H F
oiit
E. F.
Fluorine side: IIF gas s\I-r-cei, to protect pncLing ir2 ride Regeneration line: supplies IIF under 5-10 lb. gaze p r e - i i i i ~ ; provided vent t o prevent sucking back G. Coolant drain H. Electrically insulated mount for burners I . Siipporting frame J. Gas burner: four No. G O - G Johnson Lonen-ass b u r n e r s a n d lI,'?-inch John-on air-gas mi.;er a n d ra13-e. Gas supply: 3ia-inch ljiile size required K . Outer steel box insulated o n sides a n d end- only u i t h 1 1 >-inch .-hret niagne.ia. silpported b y * , ' B X 1 inch steel s t r a p s L. Coolant fill and 01-erflow M . Source of 800-ampere 30-volt ( i n n s i n ~ t i r i ~dircrt ) current: one side xroiinded; norrnal voltage, 8-10 volts
t o polniization, which tiecnnie incre:a~hg.lytroutileiome a': the anode aged, and partly t o nn uritleterrniiiecl plienonienon, protiahly at the anode, ~ l i i c l reduced i the output ~ v i t l i i i u taffectiiig the current density. k o u t : A i s s m f B I d i -LIFE. The liniit!rig f:trtoi, i i i t l i ~oprt,atinq life of it unit \vas almost aln-ays deteiiotution of thc roiit:ict l ~ e txeen tlie carbons and c o p ~ i e m r o d r Ixw. Despite the pi~ei~aution.; taken t o provide a sound meclianicxl :ind rlectric*:il runtart, the resistance a t this point increased with ne. tvitli :iii :wcom~~:iriyiiio; y, to decrease in out,put and eficienc>-. It n-nsn c c e ~ s a i ~thereforc, renew t h e anode bars periodically by rciiioving the car lion^, remachining the socket., and i n ~ e r t i n gnen- c.ariions. A nunitier of efforts v e r e made t o overcome ttii. troul,lr t u t were n o t conipletely successful. Using nii anode ~ ~ s . - r n i l ~ofl ytlli- type, tlie following data were typical of experiencr over a pwiod of ahout six months: The average life of aii nnode asqeml)ly v-as187,000 ampere-hours, and t h e life of the oltle rsposed to the electrolytc wei'c r i o t sati.i'artot,y i n this rr\prc,t. TIli, :Llld
p w t < :ri,o\.r 111(:1n but g : i w littlv
. copper
evidence of m r r w i o i i ; Moncl J ~ : L >tl1ca only w t i ~ f u c t o i ~ in:itrri:il y for tlica skirt anti t,iqrr tuties i n cont:Lrt \vi1 li fluorine. The eitini:itei of tlic, lil'c of the c~ini~ionentp:trth \\-ere :Ifollon-.: c*:ithocle bow-, skirts, : i i i i I cage-, 18 month:; coppel' tiriul 1x11t;, 1 year; and skirt ii-lindersare stored for a week to detect leaks
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