Application of the Electric Furnace to the Melting of Cathode Copper at the Tacoma Smelter Alvin H
Montana Tech Library Digital Commons @ Montana Tech
Bachelors Theses and Reports, 1928 - 1970 Student Scholarship
5-17-1949 Application of the Electric Furnace to the Melting of Cathode Copper at the Tacoma Smelter Alvin H. Nelson
Follow this and additional works at: http://digitalcommons.mtech.edu/bach_theses Part of the Ceramic Materials Commons, Environmental Engineering Commons, Geology Commons, Geophysics and Seismology Commons, Metallurgy Commons, Other Engineering Commons, and the Other Materials Science and Engineering Commons
Recommended Citation Nelson, Alvin H., "Application of the Electric Furnace to the Melting of Cathode Copper at the Tacoma Smelter" (1949). Bachelors Theses and Reports, 1928 - 1970. 284. http://digitalcommons.mtech.edu/bach_theses/284
This Bachelors Thesis is brought to you for free and open access by the Student Scholarship at Digital Commons @ Montana Tech. It has been accepted for inclusion in Bachelors Theses and Reports, 1928 - 1970 by an authorized administrator of Digital Commons @ Montana Tech. For more information, please contact [email protected]. .APFJ,I CNL' I eN OF Th,lJl FIEC'l'.Rl C :FUhl'iAOj1
TO '.lEE hili'I.'l'ING J£ C.Nl'IIvDE CO.2l~EH ..',.. " J,T TEE 'tACOM.A 5,IFL'l'n~
. ,
'by
Alvin H. Nelson . ·;H H . · 0'., . r
A Thesis
~ubni tted to the Depe.rtmen t of Metallu.rgy
in P.."rtia.l :b'ulfillment of the P..equire::L1ents for the Degl'ee of ., Bachelor of t.;)cience in l!etallu!'cicl3.l Engineel'ing
Montana School of ~ines
Butte. Mont8na
May 17 J 1949 APPLICATION OF THE ELECTRIC FURNACE
TO THE MEL'l'ING or CATHODE COPPER
AT THE TACOMA Slv'lELTER
by
Alvin H. Nelson
A Thesis
Submi tted to the Department of Metallurg-y
in Partial Fulfillment of the Requirements for the Degree of
Bachelor of Science in Metallurgical Engineering
20255
Montana Scr.ool ~f Mines
Butte, Montana
May 17, 1949 • TABLE OF CONTENTS Page
Introduction 1 Present Operations 6
Proposed Operations 9
Comparison 20
Conclusion 22
Acknowledgement 23 Bibliography 24
Appendix 26 INTRODUCTION
The fundamental principle of the mineral industry has been, and at the present time is, the ,profitable production of useful metal from metalliferous ores. Hence the growth of the industry is dependent upon the development of processes to achieve this end. Since the world economy is never completely stable, this presents a challenge to the industry. The varying costs of labor, equipment, and supplies, as well as the changing price of the products, must be compensated fOI' by technolog- ical changes in production. In the field of copper metallurgy, the major chang- es effected in the original metallurgical scheme have been based largely upon the lowering in grade of copper
ores, and the more particular demands of the fabricators
of the metal. The former trend fostered the development
of mineral beneficiation, which in turn caused the con- version from blast furnace to reverberatory furnace
smel,t.i ng , This change to much finer raw rnateria1s made
dust collection imperative, and increased the need for
smoke control. Thus through the adoption of more elab-
orate reduction pract i ces, the percentage of metal re-
covery has been greatly enhanced. Hand in hand wi th the growth of more complex smeLt-
ing came the development of the copper pefining process.
In the early days of the industry, an d in rare cases
today, marketable copper was produced by fire refining blister copper in a reverberatory furnace. The efficien- cy of metal separation in this operation is limited and cannot alone meet the present day demands of the f abr i ca-, ting industry. In most of the world's copper plants, therefore, fire refining has been replaced by the elec- trolytic process of copper purification. Two reverber- atory steps, which are modifications of the original fire refining operation, have, however, been retained, anode and cathode refining.
It has been found through experience that converter copper does not make desirable anodes, due largely to the comparatively high content of soluble gases. Anode refining, used as a step previous to electrolytic refin- ing is therefore invaluable. Through this relatively simple, but exacting pro c ea s , a large part of the harm- ful impuri ties a.re removed from the copper. It is then possi ble to produce anodes of uniform size and composi- tion, which re required in the electrolytic process to obtain increased efficiency through uniformity of oper- ating conditions.
-2- Further elimination of impurities, both harmful and valuable, is effected through electrolysis. This pro- cess produces cathode copper of very high puri ty but in a shape not acceptable to the majori ty of the ue ers of the metal. The cathodes are thin and flat, bri ttle, non- uniform in internal structure, a.nd contain occluded sul- fates. Commercial shapes required by the fabricating in- dustry are ingots and ingotbars for re-mel ting or alloy- ing, and w i r ebaz-e for rod end wire manufacture. The requirements for wirebars are that the metal be dense. and homogeneous, and possess sufficient ductility, high electrical conducti vi ty, and physical soundness. For ingots the latter two characteristics are not so essen- tial. In the present day metallurgical scheme these com-
./ mercial shapes wi th standard chemical and phy s i cal p rop-- erties are produced by the cathode refining proc ess.
This is essentially the same operation as anode refining, but applied to a more pure metal. Since the major por- tion of the impurity content of the cathode exists as mechanical contamination, the conversion from cathode to commercial copper should be merely melting followed by casting. During the melting, however, a certain
-3- portion of the con taminants will be incorporated chemi ....
cally. -along with a considerable amoupt from the fuel.
Utilization of the conventional oil- or coal-fIred rever-
beratory furnace, then, complicates the process by intro-
ducing the necessity of effecting a partial refinement
of the metal previous to casting. The physical proper-
ties of cathode copper are bettered through fixe refin-
ing, but at a sacrifice of purity. It would seem that here is an excellent application of the electric t'urnac e,
When the electrothermal mel ting process is ana-
lyzed, the results seem to indi~ate that this innovation
is of far reaching importa.nce an d long overdue in the
copper industry. The -electric furnace offers a means
of simplifying the present method of converting cathode
copper into finished shapes, with a sUbstantial saving
in time, labor, and inventory. These factors, as proved by the operations of the International Nickel Company of
Canada, Ltd. at Copper Cliff, Ontario, outweigh the ma- jor disa~vantages of high power costs.
In thi s paper an at t emp t will be made to determine the practicability of replacing the oil-fired reverbera- tory melting furnace at the Tacoma Smelter, American
Smelting and Refining Company, Tacoma, Washington, with
-4- an electrothermal scheme, ba.sed on an 8-hour cycle of operations.· This investiga.tion constitutes an analysis and compariaon of present and proposed methods of cath- ode melting an d is illustI'ated wi th drawings of an elec- tric furnace designed for continuous operation.
-5- PRESENT OPERATIONS
The process of fire refining copper has fundamen- tally not changed since its origination in'the early
Welsh smelters. Modification has taken place in the size of furnace, improvements in design and construc- tion, and better charging and casting methods to pro- duce purer copper, but the principle remains the same.
The operations are generally considered as being five in number, namely, charging, melting, oxidizing, poling, and casting. The methods employed by the Tacoma Smel- tel':formelting cathode copper are, in general, typical of the industry.
Furnace Construction
Two reverberatory furnaces are available for the refining operation, similar in construction to smelting reverberatories, but considerably smaller in size. One furnace is undergoing repairs or stands rea.dyto be fir- ed, while the other is in operation. The outside dimen- sions are: length, 40 feet 8 inches; height, 9 feet 7~ inches; and width, 20 feet. The daily charge is 240 tons of cathode copper. When casting ingots, No. 1
Copper scrap is also added, if available.
-6- The crucible is laid up with burned magnesite brick and flanked in the lower sidewalls by silica brick. flRitex" is used in the upper sidewalls~ which are 20 inches thick. The roof is a sprung arch of 15- inch silica brick. The furnace life is approximately
140 charges.
One pair of metal-backed refractory doors , is 10-
cated in the west side of the furnace to provide an 0- pening for charging. The tap-hole is in the opposite
side. Poling is effected through an opening in the north end of the furna.ce between the two burner ports.
The stack rises from the south end. No attempt is made to recover waste heat or metalliferous particles
leaving with the gases. Oil, averaging 18,200 Btu per pound, is used for
fuel. It is pre-heated with stea.m and burned at the rate of 0.55 barrels per ton of copper melted.
Daily production is based upon a.24-hour cycle of
op erat i on , The f'urnac e is charged through the side
bay by means of an electric charging-crane. The oper-
a.tion takes about two hours. Melting is then started
and continues for ten hours after which any slag form-
ed is skimmed. The oxidizing p erLo d la.sts about four
-7 .. hours, and is followed by another skim. The slag, aft- er solidification is sent to the converters. Poling is
I effected in the conventional manner, using green fir poles. A normal charge can be cast in five hours, us- ing a Walker wheel. The commercial shapes produced con- tain 99.96% copper.
-8- . . PROPOSED OPERATIONS
The United States Metals Refining Company is the I real pioneer in the large-scale application of the elec- tric furnace for melting copper. started the commercial production of oxygen-free-high- conductivity copper using an induction furnace. The op- eration is economically and technologically successful and produces copper of a superior grade.
In 1936, the International Nickel Company of Canada,
Ltd., began operation of a circular three-phase direct- arc furnace for the continuous melting of cathode cop- per. This application was so great a success that an- other unit was installed in 1938. At this time use of the coal-fired reverberatory furnaces was permanently discontinued. These operations seem to have the same goal, which is typical of the apparent trend in the copper industry; that is, the maximum production of higher grade metal at a lower cost. While the merits of the two processes have not, as yet, been decided, the method employed by the International Nickel Company seems to be more ad- vantageous for large tonnage operations. Even this pro- cess, of course, leaves much to be desired.
-9- The plan develop ed in this thesis is based upon the adoption of the Heroul t-type or elliptical furnace rath- er than circular furnace. The former seems more the I practical for handling large tonnages because of its greater simplici ty in construction, dual feeding, shape of refractories, and placement of electrodes. The same electrical balance is obtained in both types.
Furnace Construction
The furnace diagrammed ·in Figures 1, 2, and :3 is of the direct-series-arc type utilizing three-phase 25- cycle cur ren t , and is rated at 12,000 kv.a;. The outside dimensions are: length, 20 feet :3 inches; height, 9-feet
4 inches; width, 11 feet :3 inches. It has a holding ca- pacity of 65 tons of molten metal.
The bottom of the furnace is a It-inch steel plate resting longitudinally on three 24-inch wide-flange beams.
The shell is also of It-inch steel plate with welded joints, and topped with a 9-inch structural-tee, into one side of which fits the removable roof. Four openings are provided: two rectangular slots, one at each end, through which cathodes are charged; one tap-hole in the front; and a working-door opening above the tap-hole.
In addition to the structural-tee on top and three elec-
-10- trode supports on the back of the furnace, the necessary rigidi ty and strength are provided by vertical ribs of 6- inch "I" beams welded on ei the!' si de of the charge slots and working-door. Water-jackets are fastened to the fur- nace sides below the metal line. The first refractory course in the furnace bottom is of 3-inch insulating bri ck . Overlying thi s are three courses of 2~-inch dead-burned magnesi te brick. This re- fractory is also used in the lower sidewalls up to the second course above the charge slots; thi s course being laid up of chrome brick. The upper sidewalls are built of high-heat duty fireclay brick and are 13-inches thick. The framework around the furnace openings is constructed of unburned magnesite brick with the exception of the sills, which are carbofrax shapes. The latter r ef r ac t ory is relatively immune from attRck by molten copper and is also highly resistant to mechanical wear.
The working bottom of the furnace consists of a mon- olithic hearth of dead-burned grain magnesi te rammed into place to a depth of one foot. This type of hearth is more advantageous than brick because it is more easily repaired, has a lack of seams or joints which eliminates difficulties due to expansion, and allows no metal pene- tration if properly rammed. This requires skill to ob-
-11- tain a high density evenly throughout. In comparison wi th a burned-in bottom, it should be cheaper and more rapid to insta.lland at least as easily repaired. It I also seems logical that it would have nearly as long a life, since the material fuses during furnace opera- tion. To yield a high refractory life, it is impera- tive that the hearth material contain a high percent- age of coarse particles. These have less expansion than the fines and so cushion and bind the mixture yielding fusion to greater depth. Grain magnesite is prepared especially for use in rammed bottoms.
The furnace roof consists of a bonded arch of 9- inch high-heat-duty fireclay brick springing from a specially fabricated steel channel which rests inside the upper part of the structural-tee on top of the sidewalls. The skewbacks are placed inside the chan- nel ring which is stiffened by crossbars extending over the arch. The roof is therefore so constructed as to be easily removable with a crane. This is desir- able because the inside of the furnace is then more readil~ accessible for periodic cleaning and repairs.
Water-cooled steel rings are built around each e- lectrode port to provide against excessive burning of the electrodes. A stuffing box is also provided for
-12- each electrode to effect a seal and thus retard the destructive action of hot gases.
A gas vent is installed in the furnace ,roof in front of the working door and connects to a steel duct leading from a hood placed over the working door.
This duct is joined to an exhaust fan and wet scrubber for the collection of metal particles lost during op- eration.
The tap-hole block is of solid carbon l?t-inches high by 18 inches wide with a 3-inch inside diameter horizon tal carbofrax tube cemented in tel'nally for a tap-hole. The block is designed to fit between the
courses of brick so that replacement can be readily made.
Current is supplied to the furnace through three
standard carbon electrodes 30 inches in diameter by
110 inches in length set in a row on 4-foot lO-inch
centers. In order to decrease the chances of pitting
and necking, the electrodes are sheathed with l4-gauge
sheet-iron. Each is supported in two water-cooled
cast copper holders bolted together in front by one
large bolt. In back, each casting is fastened to a 12-
inch steel channel by means of one large bolt and lugs
to which the flexible copper cables carrying the cur-
-13- rent are attached. The cooling pipes and cables extend along these supports. Each pad r of arms is attached to a l4-inch wide-flange column on which they are moved up or down by automatic electrode controls. These masts are welded to the side of the furnace and are of suffi- cient height to allow the electrodes to clear the top of the roof.
Furnace Operation
The schedule of operation as proposed herein and for which this furnace was designed is based upon one
8 hour shift per day and five days per week. The fur- nace is shut down completely over the week-end. Tal::lle
I shows the program of operations for a daily produc- tion of 240 tons of wirebars.
For the initial charge about 20 tons of cathodes and copper scrap are piled in the furnace before put-
ting the roof and electrodes in place. The electrodes are lowered, an arc struck, and mel ting proceeds wi th low power. In the initial stages, heat must be applied gradua.lly in order to mi nimize thermal shock to the re-
fractories. After the furnace has been brought up to
temperature, 2200 F, the power input is increased and
cha..rging is started. When the bath has been buiJ.t up
-14- to capacity of 65 tons, cast i ng begins and is continued until nearly the end of the shift. Charging is stopped about a half hour before the termination of casting to ensure ccmpLet e melting. Operations are curtailed from
11:00 A.M. to 12 M in order to allow each worker a rest period of a half-hour.
Subsequent daily operation differs from the first start-up only in the method of initial charge. A pool of about ten tons of metal is left in the furnace from the previous day, and upon this an arc is struck. As soon as the working temperature is reached, cathodes and copp er scrap are charged to the furnace. The lat- tel'material is supplied at intervals through the work- ing door by means of the charging crane.
Casting is effected on two standard Walker wheels.
The tapped metal flows from the furnace through enclo- sed refractory-lined launders to two pour hearths, one for each wheel. Heat is f'urni shed to the pour hearths by a low-frequency induction unit. Through this sys- tem the desired casting temperature of about 2170 F can be maintained. Besides speeding up production, a major advantage of two-wheel casting is that two shapes can be cast simultaneously.
-15. TABLE I
FURNACE OPERA'rnW SCHEDULE
Day Shift ~ 7:00 A.M. to 3:30 P.M.
Daily Production (wirebars) ~ 240 tons
Mel ting rate per hour :;:: 41 tons
Melting time ~ 6 hr s ,
Casting rate per hour ::: 50 tons (2 wheels) 1 Casting time ~ 52'h rs ,
Hours Operation Tons Chg. Tons Cast
7:00-9:00 Charging & Melting 65 0
9:00-11:00 Charging & Mel ting 78 90
11:00-12:00 Charging & Melting 22 25
12:00-2:30 Charging & Melting 85 100
2:30-3:00 Casting 0 25
3:00-3:30 Clean-Up 0 0
Total 250 240
-16- -- z ~l ..:t.
, I "i ...J ~, UJ I. .~!.~ . t 1\ . I I I I~ I,.
.It) .-1.
_j .Q) ~ ;3 bO ~I ori Iii I I I. t 1 r j I ! «J -..,. -- _._-. ..._ ...... _-.,.._ ---- , -- .. I -17- z· cr % I lJJ ~ Q. ) I W 0.. u 0 <( o t Z '0 0: ~I -~ I ::> a f ~ 0 -" I a:: I i U0l- .. -lL~ .-~ It u o l- V) o (U o . ...J :2 W i= ~ .J I I.u .. 2: " I
I
:I , I I ._.U·-~--rrr-----J I I i I I ,I 1 I• j I l) / . I 1 ~ f ! / j ..__------.,~----..:. ..--,-.- .. ------.---,- .~..--- ...... -. - __J -18- ...... 1".,_ .._ ... , ...... " .....,._ ..._ ...... ~__ ,...... _. .01_ .....· ...."'''._~ ... _.'\. ~_ ~ .. '~ ...... h'...... __ .~.._...__.....:.., ~ __ ~ _ n I .j! I II. II I II I I I I I I @II . •II I ~ ,. H i~ ______..l. l f' ·t i -~_,.I:!oio=. ~~ II' ..~r~ ~ 'I H 'I I; ! I I I -~.. ..~ _.J __ ....L ---'~---- " '\ " _.- .-----. --- _. -..~--- - _" _.._....,. ------._-_.--~-- ,'. •• ._ ...... --.iI! ••• _, ...... __ ... , ~...... -_ ... -_. _""., - Recorded in Table II is a summary of the op era- ting data and furnace construction of the present and proposed operations. The calculations by which the figures were derived are appended to this report. Data from the International Tickel Company's op- erations at Copper Cliff, Ontario are included in or- del' to offer a comparison to a successful electrother- mal scheme. The cost of power is based upon the Ta- coma area, so that a consistent economic comparison of melting is obtained. -20- MONTANA SCHOOL OF MINES LlBBAR) B1lUI I 1 _ I 1 (1)0::, m 1 r(j ...-t C\2 00t:O j".-1 I I 0.-1~ til - .. .-1 1 H • ).:! (I).p I ...-t (D m...-t til 0)' 0) IH ...-t I •.-1 .c: .j..J .p .j..J.j..J .j..J .,-l .,-l o ~ til til I! .-... 0) '" o (I) (I) al HH~ E ~ ~ •.-1 al ~ C\2><;j-1...-t 00 OD 'dri CIS al ;::lO til I, co '"' ...-t E E ...00 ;::l .'" 0') .~ Ie OHt0 o til ...-t (I) r(j ro •.-1 •.-1 to ;::l bO...-t ...-t 0) (I) (I) H 0 C ~c.ci ..0 ~ ~ 'd= 0 .j..J 'Ii ~ ."'.,-1 H H ·,-l0 ...-t o ... I:; C(I) til H (I) ;::l .j..J I~~~I~ .,-l •.-1 I I I o rtJ .. - - ~"' ...c: til C~ r:--,~ H (I) Ht0 ...-t o • "'l'i til ~ .j..J ~ N (I) io en r(j H ...... eo C\l kO)C\l H E (I) _ (I) H ~ r.t1 ..0 -.-1 0 'd 0.1 '"(j:: ,-lIN:: .j..J§I ~ .c: H til (I) m til •.-1 ...-t...-t H ...-t...-t o 0) r.t1 r.1l (I) .j..J...-t ~ ~ o 0.0 r.1l r.1l -,-l H H C H 0 0) (I) H "-;;::l ~ P-l (I) H ~ p::;o 38' -21- 20255 CONCLUSIONS The conclusions derived from this investigation are: 1. The electrothermal scheme for melting cathode copper, as proposed in this paper, may be practical from a technical standpoint, but is impractical from an econ- omic standpoint. 2. A smaller electric furnace operating on a 24- hour cycle could successfully replace the present oil- fired reverberatory furnace. The pecularities of power contracts place limita- tions on size and mode of operation of electric furnaces. As shown in the calculations appended hereto, the maj or electrical cost is derived from the demand charge when the furnace ra't i ng is high. This ch a rge is computed from the peak load drawn during the month. Therefore, a furnace of low rating operating on a long cycle is far more economical than a furnace of high rating operating on a short cycle. When expanding to a long cycle, the energy charge increases very Ii ttle as compared to the large decrease in demand charge wi th a drop in rating. The physical size of an electric furnace, then, is re- stricted by the cost of the electrical energy for its successful operation rather than technical considerations. -22- ACKNOWLEDGElvlli~T The author is indebted to Prof. J. P. Spielman for his guidance and suggestions given during the writing of this thesis. Thanks are also due to Mr. B. E. Ander- son and Mr. Clyde Leonard of the Tacoma Smelter for fur- nishing much of the data concerning present operations. A number of my classmates were very helpful by listening an d offering arguments to a number of the ideas fostered by thi s subj ect. -23- BIBLIOGHA1?HY A. Books 1. Addicks, L. Conner Refining. New York: MacMillan, 1921 2. Butts, Allison. Metallurgical Problems. New York: McGraw-Hill Book Co., 1943 3. Creighton, H. J. and Koehler, W. A. Principles and Ap- plications of Electrochemistr::!. 2 vols. New York: John Wiley and Sons, Inc., 1947 4. Harbison-Walker Refractories Company. Modern Refrac- tory Practice. Cleveland:: Caxton Company, 1937 5. Mineral Industr:y:During 1937,. v oL, 46:196. New York: McGraw-Hill Book Co., 1943 6. Newton, J. and Wilson, C. L. Metallurgy of Copper. New York: John Wiley and Sons, Inc., 1942 7. Paschkis, V. Industrial Electric Fur'riaces . 2 vols. New York: Interscience Publishers, In~., 1945 8. Peters, E. C. Practice of Copper Smel~ing. New York: McGraw-Hill Book Co., 1911 9. Stansfield, A. The Electric Furnace. New York: McGraw-Hill Book Co., 1914 10. Stoughton, B. Metallurg:y: of Iron and Steel. New York: McGraw-Hill Book Co., 1934 11. Trinks, W. Industrial Furnaces. 2 vols. New York: John Wiley and Sons, Inc., 1942 B. Periodicals 1. Byrk, P. etal. "Out okumpu" s Copper Smelter Doubles Output During War." Engineering; and Mining Journal, 148:68, January, 1947 -24- 2. Curtis, Harry A. and Heaton, Roy C. "Design fOI' a Phosphate :F'urnace. II Chemical and Metallurgi cal Ene&:i.- neering, 45: 536-540, October, 1938 . 3. Ford, C. E. "Ca.rbcn and Graphite. II Industrial and Engineering Chemistr;y, 39: 1202, October, 1941( . 4. Sem, M. and Collin, F. C. "Electric Smelting Points Way to Lower Cost. II Enginee:t'ing and Mining Journal, 148: 86-90, August, 1947 5. Waddington, R. H. an d Bischoff, J. C. "Electric Fur- nace Melting of Copp e r, II The Canadi n Insti tute of Mining and Me.tall.Bl'El: Transactions, 49:. 199-226 6. Zoller, • H. "Rammed Ref'r-ac t.c r Le e in ElectI'ic J?ur-' naces." Brick and Clay: ]\e.c.9l'2t, 110: 72-76, March, 19:47 -25- APP]:NDIX 1. Data: (Butt's Metallurgical Problems) 1. Melting point of copper ~-1983 F 2. Mean specific heat of copper ~ 0.112 lb-cal!lb. 3. Latent heat of fusion of copper ~ 57.6 gr. cal/gr. 4. Room temp era ture ~ 68 F 5. Weight copper per cu. ft. ~ 556 Lbs . 6. Conversions: Btu x 0.2928 x 10 ~ 1 kilowatt-hour gram-cal./gram x 1.8 - Btu/lb. 2. Theoretical power required to melt 1 ton copper (2000, lbs.) Temp era ture change: 1983 - 68 ~ -1915 degrees Btu required for temp. change: 2000 x 0.112 x 1915 ~ 428,960 Btu required for fusion: 2000 x 57.6 x 1.8 ~-207,360 Total Btu required to melt 1 ton copper ~ 636,320 Kw-hrs. required to melt 1 ton copper ~ 186 Theoretical power required: 186 • 80% P.F. ~~234 3. Power used in Copper Cliff operations to melt one ton of copp er: Feed ~-15 tons cathodes/hour. to produce wirebars -26- Power::;:4000 kva at 82.5 P.P. =: 3300 kw. 3300 ~ 15 ::;:220kW-hr./ton coppers. 4. Cap aci ty of 12,000 kw -hr , furnac e wi th 80% power fac to r: a) Theoretical: 12,000 kw-hr. x 0.80 P.P. ~ 234 ~ 41.0 tons/hr. b) Based on Copper Cliff operations: 12,000 kw-hr. x 0.80 P.F. ~ 220 =:·43.6 tons/hr. 5. Volume required for h oLdd ng c ap ac i ty of 65 tons: 1 ton copper: 2000 ~ 556 ::;:-3.6cu. ft. 65 ton copper' :::;65 x 3.6 ::;:-= 234 cu. ft. Dimensions of bath: (approximate) length ::;:13 ft. width ::;:-9 ft. depth ::;:·1.5ft. 6. Current density: Assume 22,000 amp s , for op era"tion. area of 30-inch electrode: 708 sq. in. C.D. ::;:-22,000~ 708 ::;:··31.28mps/sq. in. 7. Arch Oaf cuf.et t cn e: (Modern Hefractory Practice) Arch Dimensions -27- Span (S) "=-9 ft. =: 108 in. 19 Hise/ft of S :::: -132 in.::::1.608 in. Thickness(T) ==9 in. 19 11 Total rise (h) :::: 9 ft. x 132 in. ==-14 32 in. ]'rom tabl e: Inside radius (r) ::::1.000 S ::::9 ft. - 0 in. Central angle (Q) ==60 . - .§.Q_ 1 Part of clrcle ::::360 "=6 ::::0.16667 Inside arc (Ai) :::: 1.04720 S ::::-1.0472 x 108 ==_ 113.0976 ==-9 ft. - 5~ in. Difference between outside and inside arcs:- 1.04720 T ==,1.04720 x 9 :::: 9.4248 ::::gll 64 in. Outside arc A2: Ai + (A2 Ai) ==113.0976 + 9.0248 :::: 122.5224 in. ::::10 ft - 23212 in. 8. Cost of p r-oposed operation: 1. Monthly kw-hr. consumption: Production:::: 240 T/day at 20 day s > 4800 T/mo. Con sump tion ==234 ~w-hr?T copp eX' ::::~234x 4800 ::::1,123,200 kW-hr/mo. 2. Power demand: 1 kw-hr =: 1.341 hp-hr. 9600 kw-hr. x 1.341 =: 12,873 hp-hr. 3. Demand charge: $1.00/mo./hp. -28- 12,873 x $1.00 ~ $12,873 4. Energy charge: ~~O.0040/kw-hr. ~ 0.004 x 1,123,200 ~ $4,493 5. Cost per ton copper: $12,873 + $4,493 + 4800 ::::$3.61 9. Cost of Copper Cliff operation 1. Monthly kw-hr consumption: Production ~ 360 T/day at 20 days::::7200 T/mo. Consumption ~ 220 kw-hr/T copper ~ 220 x 7200 ::::1,584,000 kw-hr/mo. 2. Power demand: 1 kw-hr ~ 1.341 hp-hr. 3300 kw-hr x 1.341 ~ 4,425 hp-hr 3. Demand charge: $1.00/mo./hp. 4,425 x $1.00 ~ $4,425 4. Energy charge: $0. 0040/kw-hr" ::::0.0040 x 1,584,000 ::::$6,336 5. Cost per ton copper: $4,425 + $6,336 + 7200 ::::~~1.49 -29- .