I
1
A Staff-Industry Collaborative Report RODNEY N. HADE Aswcbk MHor
;i
m
a
ourJ;r, .
aE
produchou of “synthetic” graphite by the electric fumaee method LB . among ‘ the oldest of the chemical proceed rndustries ,-ni k i n g beea foanded jwt ehartiy b e h e the ~m d the -buy And while it in notamatohinsge for the manuf.stpn,d adfuric raid (perhap our oldest wmmercial chemical endeavor .nd long mnidered 80 accurate bammeter of o v e r 4 buehtaa setivie), tba indtwiry-ud am@&Uy th.t m a t devoted ta‘the produation of graphite electrodethan beeome w infused in chemical and metallurgical proeeas industries that one familisrwithelsotrodsmiukebcanasetbemlikeduricacid d 8 3 ,to gr@ 8 e x d kdwtrid setivitp. Sptheiio graphite’s wnductivity, wmbined with excellent Rdraotarinesland rrsiabnes to thermal &mk, makw it an eltrade materhl without peer. The mntinned eqmfidrl of elt?ic
furnaae oparabiw and the trend toward
larger f
m
s
and M e r inout. of w w e r bave lea’ ta the omduction of the
a d an-a p&t mold material in tbe casting of metals. V i inactive chemically, it 6wb application fia an anode materid in the electrolytic production of chlorine, sodium, mda, and chlorates, an well an in the m a n u f e ture&eipisc~dBtmcturalmembern for heat exchangers, rem tion tawem, and acid sdsorbers. &&itsand amorphowcarbon 8bapes, becsllse of the me& *that must bbprrsaio theirlosnufeokus, av3mae a0 ta 30% pee. applications where this porosity in unclenimble, sadsl treatxaenta csn be employed to render the materials impaiouS to Ler Q licaids. ir not norm& a db .bRU.rqiqmaallurgical applications, Sinae most liquid m h l n Q not wet graphite at temperaturesordinarily encountered.
a
i
Graphite occurs in n a b in fair abundauce. Depsita 818 known all over the world, and the natural product han been used for agca m vr+w applications. However, the natursl pmduct is usually quiWimpUre, and heneficiation often makee it expensive. In nddithn, tbe B t r f q G l of w e e formed fmaatunl graphite is oftan rather poor. When the eleotzio poner induatry wan in its h y , ths meed for fa& pisser of graphite not readily p r e p m a fmm tbe naturd proauot Dm0 appred, with the reault t h a t w q w i m e n t d work aimed a t graphite synwan beyn. %!he esprhentation wan demnitely suawnfd, leading to the #evebpmenb of a sy.thetic m a t e d ooataining amall c i y h l n in a random arrangement tbat +des strength in all directions. In !JO Yaws, E l c k i c Furnoem CapaciH.. Have I n c M @ dh q 1 ta 1SO TONS pIBatch
carbon ateel. Tbe m&Jhrgical prooeeaae for produokg the alloys that wem developed required close wntrol, k t acmm
pliahed by the aae of the electric furnace. Early furnaoes prcduced ab per batoh end wad electden, perhaps in& in with a cllmlcapacity of aim
I
1a)Oamperea. Tcdnythelargeatfurnaoeshold150tonsormow0 aUoy per batch, ptoduciug thia amount in an little 88 4 hours. Power inputs have been increased to the vicinity of 35,OOO kva through the uw of synthetic &te electrodes a0 to 24 inch indheter, up to BB rnchen long, and weighing over a ton each. The ourrent-canyiag capscities of Bome of t6eae electrodes range from 35,OOO to 45,oOO amperes
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 46, No.
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PLANT PROCESSES-Graphite Production of new structural materials such as magnesium and titanium is heavily dependent on high quality synthetic graphite electrodes. Amorphous carbon electrodes offer similar advantages in the electric furnace methods used to produce calcium carbide, elemental phosphorus, and ferroalloys. For these applications, electrodes up to 48 inches in diameter and weighing as much as 4 tons each are available. The curve in Figure 1, in which estimated values of annual synthetic graphite production are plotted for the past half century, indicates the rapid rate of growth the industry has experienced in recent years. Similar growth has occurred in other industrial nations ( 7 ) . The history of commercial production of synthetic graphite electrodes dates from June 1897, when the first furnace load, consisting of 2905 small electrodes (7/8 X l l / n X 15 inches) totaling 2300 pounds in weight, was graphitized in a Carborundum Co. furnace under the supervision of E. G. Acheson, to whom a patent had been issued in 1896 ( 1 ) . That first commercial operation was sufficiently successful that during the remainder of 1897 a total of 142,000 pounds of electrodes was graphitized (6). The discovery that graphite can be produced in an electric furnace resulted from an earlier discovery of a method for manufacturing silicon carbide. I n studying the effects of high temperatures on this compound, it had been observed that a t high temperatures it was decomposed; silicon was vaporized, and the carbon remained behind not in an amorphous but in a graphitic form. Acheson pursued this lead to develop a commercial process for graphite production based upon anthracite coal. The graphitizing process itself has not been changed in essence since it was first discovered; rather, improved techniques in various manufacturing steps have permitted the production of superior products in ever-increasing size and variety. From a
350
1
3001 ,
!q 150
100
-
50
1910
...' ...-,
,
I
1920 I930 YEAR
,
, 1940
,
, 1950
Figure 1. Estimated Production of Synthetic Graphite in the United States-1 899 to date January 1954
very limited market for a few products such as small electrodes, crucibles, arc rod carbons, and specialty items, the industry has branched out to produce a range of useful materials that have actually led in some cases to the founding of new key industries. -4n example is the electric furnace steel industry, already responsible for the major portion of high alloy steel production, and now promising keen competition for the open hearth process in the large scale manufacture of ordinary steel @).
Table I. Properties of Typical Raw Materials for Graphite Electrode Manufacture Calcined Petroleum Coke 2.00-2.10 0.5-4.0 0.3-1.5
Coal T a r Pitch
Impregnrtting Pitch
Extrusion Lubricant
0.2-0.5 0.2-0.5 99-101 29-32
0,2-0.5 0.2-0.5 90-95 12-15
.. .. ..
.. ..
1.29-1.32
1.25-1.29
0.85-0.95
450
150
, .
60
40
.. ..
Viscosity, cp. A t 160° C. At 1000 c. Coking valuea, % a
..
..
..
I
.
9-37
..
I n electrode manufacture
While basic processes have not changed radically over the years, there has been a major evolution in raw materials sourcea and production technology. The industry in its early days operated with anthracite coal, wood charcoal, or coal beneficiated to lower its ash content; little attention was given to the uniformity of the carbon used or the pitch employed as binder. With the development of applications technology, however, sources of carbon of controlled purity became increasingly important, until finally the industry standardized on petroleum coke-the purest form of industrial carbon available in large quantities. Petroleum coke has been the chief source of electrode carbon since about 1918, and both coke and binder pitch are now required to meet rigid specifications in chemical and physical properties, Typical properties of raw materials currently in use are given in Table I. The growth of the electrode industry, especially in the size of products made, has necessitated a continuous development of its manufacturing techniques. Major improvements have been made in extrusion press design, baking furnaces, and graphitizing units. The successful operation of large graphitizers has occurred with the cooperation of the electrical equipment producers since new designs in transformer size and bus-bar systems were requited. These equipment developments have also extended to machining operations. Chemically, Electrodes Are Essentially Pure Carbon
&.--a
1900
Electrodes
The conversion of amorphous carbon to graphite was first believed to involve the formation of intermediate carbides, generated through the reaction of the carbon with minerals and metallic oxides present as impurities. The graphite crystallites were believed to be formed through decomposition of the carbides a t high temperatures. While it is recognized that graphite can be formed by the thermal decomposition of carbides, current theories regarding the conversion of amorphous carbons to graphite do not acknowledge intermediate carbide formation as an essential element in the mechanism (3). Such carbonaceous materials as calcined petroleum coke are believed to contain groups of small, graphitelike crystallites with a proportion of unorganized carbon, presumably attached to the edge atoms of the graphitelike layers and linking the crystallites one to another, On further heating, thermal recrystallization causes the graphitelike crystallites to grow a t the
INDUSTRIAL AND ENGINEERING CHEMISTRY
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ENGINEERING AND PROCESS DEVELOPMENT angle scattering. As the temperature of the heat treatment increases within the graphitizing range (beginning a t about 1600" C.) a further sharpening of previously visible reflections as well as the appearance of additional higher order reflections is observed. These transformations in the x-ray patterns attend the growth HEATED TO 90O0 C. and mutual orientation of the graphite crystallitee. The impurities that occur in the raw materials for synthetic graphite production are eventually almost entirely removed by distillation. For the most part these impurities, present in the form of minerals and HEATED T O 1500° C. metallic oxides, are converted to carbides and subsequently decomposed as furnace temperatures reach high enough levels to distill the elements from the system. Tables I1 and I11 show thermodynamic relationships for typical impurities found in the raw materials for elecGREEN ELECTRODE WITH BINDER PITCH AND COKE,' CALCINED TO trode manufacture, or formed during 1 3 0 0 O C. the baking or graphitizing cycles. Since virtually all such impurities are vaporized during processing, it might appear that the presence of relatively large amounts of impurities is unobjectionable; however, the amount of ash in a given coke may ELECTRODE HEATED T O POOOo C. strongly influence the physical properties of the finished graphite made from it. Table IV presents typical physical properties for a graphite mold stock, 20-inch diameter electrode, graphite electrolytic anode, porous carbon, and porous graphite, ELECTRODE HEATED T O 9500' C. all based on petroleum coke. Chemically, all are essentially pure carbon, analyzing 99 to 100% carbon. Virtually all synthetic graphite production in this country is a t present divided amdng three major producers, Great Lakes Carbon Corp., ELECTRODE HEATED T O P800° C. International Graphite & Electrode Corp., and National Carbon Co., Inc.' 'Of these, Great Lakes is the Figure 2. Growth of Crystallites in Graphite Synthesis as Indicated by X-Ray the most recent entry into the Diffraction Patterns field. Prior t o 1940, the principal business of Great Lakes Carbon Corp. (then known as Great Lakes expense of the unorganized carbon. Once the unorganized carbon has been consumed, further growth occurs by gradual Coal and Coke) was calcining refinery coke. As a natural movement of whole layers or even groups of layers, and not by step toward integration, Great Lakes entered the electrode addition of isolated atoms or small groups of atoms. This profield, establishing its electrode division to handle production gression in the growth of graphitelike crystallites is vividly and sales of graphite and amorphous carbon electrodes and redemonstrated by the series of x-ray diffraction patterns shown in lated carbon products. Figure 2. The division's first plant, established a t Niagara Falls, N. Y., The top pattern of "raw coke" contains only two visible reflecis still in operation both as a producing unit and as a center for tions-both are diffuse, and one is very weak. The small angle technical development and service activities. Specialized prodscattering around the central spot is pronounced. With increasucts such as amorphous carbon cement for use as cathodic lining ing temperature of heat treatment the appearance of higher in aluminum pots are also produced a t Niagara Falls. Most order reflections with a progressive sharpening of the lines is obbasic research for the division is conducted at the company's served. The pattern for the green electrode resembles that of the laboratories at Morton Grove, Ill., where research for all Great petroleum coke from which it was prepared, except that t8hepresLakes divisions is centered. ence of the binder has given rise to a greater amount of small R A W PETROLEUM COKE PREPARED IN DELAYED COKING UNIT A T 9P5' F.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, No. 1
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PLANT PROCESSES-Graphite
Electrodes
Morganton, N. C., Plant of Great lakes Carbon Co. Produces Electrodes from Petroleum Coke and Coal Tar Pitch Binder
The Illorganton, N. C., plant of Great Lakes electrode division is one of the most modern integrated electrode plants in the world; it produces a complete line of synthetic graphite products. When current expansions are completed, this plant will turn out over 60,000,000 pounds of synthetic graphite products per year. Built for the Federal Government in 1943 as a war plant, the installation was purchased in 1947 by Great Lakes, and reactivated in the first quarter of 1949. AS shown in Figure 3, the principal steps in the manufacture of graphite electrodes a r e t h e p r e p a r a t i o n , weighing, and mixing of raw materials, extrusion of the heated mixture in desired shapes and cross sections, baking in gas-fired furnaces, and graphitizing in electric Operator Samples Air-Cooled Mixture as It Pours from Cooler to Extrusion Press furnaces. The final product is a high purity, electrically conductive material, relatively soft and readily machinable. Most graphite elecV shows the relative proportions of various sizes of coke particle trodes are produced as round cylinders, bored and threaded fractions and pitch binder content for typical formulations of a t each end to permit the successive addition of new lengths, mold stocks, anodes, and electrodes in various sizes. forming essentially continuous electrodes. Calcined petroleum coke from any of several silos, each of Principal raw materials are a high purity carbon, primarily 450 tons capacity, is passed through a hammer mill ( I E ) , and petroleum coke, and a highly aromatic binder, usually coal tar the particles are sized by means of vibrating screens (4E). Each pitch. A typical mixture consists of about 40 parts of one or size is discharged to an individual bin above the weighing floor, more Bizes of screened petroleum coke particles, about 60 parts permitting gravity flow into weighing hoppers. Fines produced of fine petroleum coke'flour, and about 30 parts of coal tar pitch in the crushing and screening operation are passed through a ringaa binder. The larger electrodes contain coke particle fractions roller suction mill (6E)which further comminutes the particles as large as one half inch on three mesh, while the smaller electrodes until 52 to 55% will pass through a 200-mesh screen. Since the may contain particles as small as through 20 on 35 mesh. Table fines fraction is generally too small to provide enough flour, some crushed coke is added to provide the desired proportion of flour. The mill's built-in air classifiers automatically return oversized particles for further grinding. Material of suitable size is colTable II. Thermodynamic Properties of Impurities in lected in the unit's bag filters and transferred to flour bins above Synthetic Graphite Manufacture the weighing floor. P.n.3 Energy of Heat of Heat of The coal tar pitch used as binder is received in solid form and Formation Formation Melting Boiling Vaporiinch or smaller. Graphite is crushed (6%) to a particle size of Element or Point, P:int, zation (AHrsa) (AFnda, Compound C C. Kcal./Mble Kcal./hlhe Kcal /Mole electrodes and amorphous carbon electrodes are made with the 15RO 2760) 84.2b c d _F*same kind of pitch. The crushed material is stored in bins 38.6 0 d Ca c d --"Ti above the weighing floor; only small quantities are crushed and I 2-u
~IOU
ii FeO CaO TiOz
Ah08 V206
Si02 (tridymite)
17506 1440 1371 2500b 1850 2020
..
1713
2600 3000b 2630
69.'6
e
d
c
7i.'6b
c
d d
-64.5 -151.9 -219 400 -382
-
-144.4 - 206 -378 -350
-206.5
-193.6
. I
3k00b 3000b 3260
..
33006
,
.
..
.. . ,
- 59
Table 111.
-28
-27 -22.9 -23.5 .. -114 -113 * AFnos is calculated from the expression AF = AH TAS, where T = 298. values of A H and A S from Kubaschewski and Evans (6). b'Estimated. Heat of formation of the elements is zero. d Free energy of formation of the elements is zero.
FeS Cas
1190
..
..
-
January 1954
Reaction 4C = FesC
+ 3CO FeaC(or) = 3Fe(a) + C 2AlzOs + 9C = AlaCa + 6CO AlaCs = 481(s) + 3C Ti02 - 3C = TiC + 2CO TiC = Ti + C CaO + 3C = CaCn(@) + CO CaCz(B) = Ca(1) + 2C SiOn + 3C = S i c + 3CO S i c = Si(d + C
3Fe0
+
Free Energy Changes for Reactions of Impurities in Synthetic Graphite Manufacture
Sources:
A F , Free Energy of Reaction, Koal./Mole
Temp. Range,
K.
-
110,300 - 14.95 T log T 300-1640 69.9 T -4,265 1 4 . 9 5 T log T 300-1640 37.8 T 3.36 X 10-8 TP 566,300 257 T 300-2300 43 300 -E 1 8 T 300-930 109:OOO 3.k6 Tlog T 9 3 . 3 T 400-2000 57,000 2.75 T 300-2000 112 000 63 T 300-2500 1123-1963 14:600 5.88 T 300-1700 126,900 83.8 T 28,000 1.9 T 300-1700 Kelley ( 4 ) and Kubaschewski and Evana (6).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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++--
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-
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ENGINEERING AND PROCESS DEVELOPMENT
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I N D U S T R I A L A N'D E N G I N E E R I N G C H E M I S T R Y
Vel. 46, No.
PLANT PROCESSES-Graphite
Apparent density, ../FC.
,
Rerl density, s.loo.
R-tivity ohm-inch Lowitudind TnUB"*rJa Mod"lW Of l"Pt"lD, Ih.Jsa. inch
1.70
1.60 2.09
..
0.0020
.. ..
..
1.70 2.24 0.00088
1.57
1.65
..
2.08
..
0.0023
1.54 2.24
1.56-1.66
0.00035
..
Electrod..
1.05
1.06
2.24
2.08
2.24
0.00035
0.M
..
0.001
.. ..
.. ..
O.OW45
..
2200 (appmx.j
2600 2200
.. ..
..
..
1500 appro= 1 8 L~p p m J
Iwo 1300
.. ..
575 (wpror.)
..
575
..
7W-1MO
..
180
..
1IO
.. ..
8ooo (appmx.)
Bwo (appro=.)
.. ..
4c€nl 24.5
3000
31.2
4wo 30
S O
wo
.. ..
.. ..
100% Flour
..
.03(-20mah)
O.OO30
m
(appro..
22
0.08 (-!!.Omah)
24
0.08(-20mcah)
..
..
..
.. ..
21
14 18
..
..
.. Thermal conductivity. B.t.u./aq. ft./ft./ b./F.
5
1.2
x
..
..
10'
85
Stored in w m weather, since the pitch tend# to resolidify at
elevated temperatures. To facilitate extrusion, amall quantitien of a petroleum-base oil are added to the raw mixture for both graphite and amorphous electrodes. A primary requirement for the oil is that it have a low miacibility with pitch, in order that i t may remain on particle surfaces ahere lubrication is moat important. "OM" Eledrodes A n Exlruded In Num.rcur Sizes ond Cress %lions
Electrode production is eaeentially a batch procbas, although eome steps are handled on an essentially continuous basis. Each batoh of wkepitch-oil mixtnre is weighed separately into a moucrail CSI that holdn about 600 pounds. The properly proportioned batch is dum+ through a bole in the Eoor into a horirontal steam-jaoketed mixer (3.87 on the Eoor below. Paddletype agibtors keep the batch thoroughly mixed during a % minute heating cycle. At the end of the cycle the batch temperature is about 150' C. Fifteen horizontal mixera in parallel are required to maintain an adequate rate of feed to the plant's single extrusion preaa. At the end of the mixing and heating cycle, the mixer door is o p e d , permitting the mix to be discharged onto a conveyor belt that leads to a cooler. Normdly about four mixers are d i s chsrged 6imulte.neody to provide a full charge for one of the coolers. Two coolers are ueed in parallel. The cooler (t.87 is a rotating tumbler, somewhat similsr to a concrete mixer in design. An the amler rotatee, ah is drawn thmugb it by a suction fan; the mix is tumbled in the mler until ita tempruture is lowered to about lDoo C. When the proper temperature is reached, the cooler batch is dkharged into a chute that l e d a to the extrusion
..
..
..
..
27
..
15 20
..
1.5 X
..
0
..
10
11 16
15
1V
60
700.000
1.1-1.3
15-85
65
..
6a
..
5500
Sdw
27
21
..
x
..
4w.m
1 0 (Wpmr)
1.4
..
300,wo (*WX.)
45
A hydraulic ram tben enters the cylinder forcing the mixture, under a pressure of 500 to 2500 pounds per aquare inch (depnding upon die size) through the extrusion die. The entire p m , including the die, is steam-jacketed. The extruded stock, still at approximately 100' C., is cut to length by meane of a knffe or taut wire, and discharged on a Eat table. Smsll electrodca are set a i d e at this point for air coolin& while larger sizes are rolled down a slight incline into a water bath. After su hour or more in the bath, with water at 25' C., the electrodes are removed for inspection of quality. After inspection, the satisfactory pieces, now known aa "geen" electrodes, are either stored or sent immediately to the bakin# furnace. Care is exercised to prevent exposure of the Stored
w.
The press (7m, with interchangeable dien for the production of electrodes in all L ~ Z M and cm88 sectione, contains an extrusion cylinder or "mud chamber" about 3 feet in diameter. Mounted on heavy trunione, the cylinder can be rotated through an angle of go'. It is turned to the vertical position to receive the cooled mix from the cooler's chute. A vertical tamping ram wmpaota the mix in the cylinder, after which the tamp is withdrawn and the cylinder is rotated to the horisontal position for operation.
ImUary 1954
TINE-DAYS
Figure 4.
Typical Temperature Cycles for Baking a n d Graphitizing Furnaces
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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ENGINEERING AND PROCESS DEVELOPMENT
Giant Electrode Rolls into Cooling Trough as Another Issues from Extrusion Press
Table V.
Proportions of Dry Ingredients for Preparation of Typical Graphite Products Parts Screened Petroleum Coke Particles Through 1 / ~inch Through Through on 3 mesh 10 on 20 20 on 35
Graphite mold stock Intermediate eleotrode, 1020 inches diameter Large electrode 20-24 inohe; diameter Anode or small electrode
Parts petroleum Coke Flour, 55% through 200 Mesh
Parts Coal Tar Pitch
.,
,.
50
50
34
..
25
15
GO
32
20
10
10
GO
30
..
*.
..
100
36
electrodes to high temperatures, since the pitoh binder tends to soften a t elevated temperatures, causing distortion and rejection by the inspection department. They Are Baked at Internal Temperature of 950’ C.
The gas-fired baking furnaces are brick-lined chambers 10 X
30 x 111/2feet deep, For the baking operation, iarge electrodes
gas, manufactured in an adjacent building on the plant site. After a maximum temperature of about 950’ C. (within the electrodes) has been reached, firing is discontinued. When the furnace has cooled sufficiently, the top layer of packing is removed and the electrodes are pulled from the furnace for further cooling in air. Loose packing material is brushed from the electrodes, and each piece is visually inspected for cracks, chipping, severe bowing, or cross-sectional distortion. After culling out defective pieces, normally amounting to 1 to 2%, samples are selected for measurement of diameter, length, weight, roundness, apparent density, and electrical resistivity. Acceptable baked electrodes are then either stored in piles or transferred directly to the graphitizing furnaces,
Electric Furnaces (at 2800’ C.) Convert Coke into Graphite
In the graphitizing furnaces, electric current is used to heat the electrodes to a temperature of about 2800’ C., a treatment that converts the relatively hard coke structure into soft, unctuous graphite. The electrodes themselves form the central part of the graphitizing furnace, with current flowing through as well as around them. The furnace loading is built up on a semipermanent brick bed 12 feet wide, 30 feet long, and 2 feet deep. A layer of fine carbon is spread over the bed as a base for the electrodes, which are then placed horizontally on the bed. The electrodes are separated by to 6 or 7 inches of “resistor” material. Spacing is adjusted according to the size of the electrodes under treatment. The resistor material consists of a mixture of graphitized and ungraphitized coke particles. With the tiers of electrodes in place and surrounded by resistor material, concrete blocks are used to build up the outside walls of the furnace. These are placed about 2 feet away from the electrode ends, and the intervening space is filled with insulating material consisting essentially of sand and coke in the proportions required for the formation of silicon carbide. The insulation is recycled many times in the furnace, gradually building up a substantial silicon carbide content. The furnace loading step is completed by placing a layer of insulation about 2 feet thick over the electrode load.
are stationed vertically in the furnace, and smaller ones are placed in horizontal layers. In the furnace, electrodes are separated from one another by a packing material which consists of a mixture of sized petroleum coke and river sand. The furnace is loaded to a depth of several inches with packing material, upon which the electrodes are carefully spaced. Depending on size, the electrodes are placed from inch to 2 Inches apart, with additional packing material in the interstices; electrodes are stacked layer upon layer until the furnace is nearly filled. A fairly thick layer of packing material is placed over the top. Thermocouples are inserted at several critical spots between electrodes, and the furnace is ready for operation. Partially Dismantled Furnace Prior to Unloading Graphitized Electrodes The furnaces are fired with producer
a
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 46, No. 1
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A
I o 0 Le$ P (20 LEJ)
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SHWPIHO
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,.'
...,
".
c
ENGINEERING AND PROCESS DEVELOPMENT
Miniature Chlorine Cell Tests Operating Characteristics
of 300 pounds of finished electrodes, ready for shipping, requires 165 pounds of the principal direct raw materials. In addition, relatively large amounts of auxiliary materials must be handled during the manufacturing process. In the baking furnaces, for example, one pound of packing material is used for each pound of electrode in process. In the graphitizing furnace, about three times the weight of the electrode charge is added as insulation and resistor material, or about 2.6 pounds of insulation and 0.4 pound of resistor material per pound of electrodes. The total weight of the furnace load for a 50,000-pound charge of electrodes is thus approximately 200,000 pounds. Electric power consumption for all processing needs varies from 2.5 kw.-hr. per pound of finished product for anodes and small electrodes to 3 kw.-hr. per pound for mold stock and intermediate (10- to 20-inch diameter) electrodes. Consumption of coal for producer gas, used in the baking furnaces, varies from 0.3 to 1.0 pound per pound of finished electrode, depending upon whether the sensible heat in furnace flue gases is used for preheating other furnace charges. About 6 gallons of water is required for each pound of graphite. Of this amount, 45% is used in the graphitizing department, 30% in extrusion, 20% in baking,and 5%for miscellaneous plant uses. Water is used only once a t the Morganton plant; there is no cooling pond. The total number of hourly employees a t the hforganton plant averages 350, including operating and control personnel. In addition, there are about 65 salaried employees a t the plant.
of Experimental Graphite Anodes
process, physical and chemical determinations are employed to eliminate faulty materials or specimens. Through frequent sampling the coke milling machines are carefully controlled in order that the proper proportions of closely sized coke particles and flour fractions can be maintained. The particle size range of each coke fraction obtained from the screening operation is carefully checked by frequent sampling and screm analysis. In the steam-jacketed mixers, cycles are controlled by automatic timers. In the coolers, temperature measurements determine when batches are ready for extrusion, and the temperature of the mix is recorded a t the beginning and end of every extruder charge. The proportion of green electrodes selected for physical testing varies from 100% on large sizes (12-inch diameter or larger) to about 5% on small sizes. On all sizes, however, each piece is inspected after each processing step. Green electrode samples, after cooling, are measured for length, diameter, roundness, and apparent density. After baking, all pieces are inspected, and selected samples are checked for length, diameter, roundness, density, and electrical resistivity. These same tests are performed on samples after the graphitizing step, and further determinations are made for coefficient of thermal expansion and for the moduli of rupture, elasticity, and shear.
lest Checks Control Size, Shape, Density, and Resistivity of Product
Metallurgical Operations Demand larger and larger Electrodes for Increased Production and New Applications
Great Lakes maintains an exhaustive system of inspection and testing checks, beginning with raw materials and extending even into the purchaser’s plant. To make certain that flaws will be discovered a t the earliest possible point in the sequence of production steps, every shipment of rawmaterials-coke, pitch, andoil-entering the Morganton plant is sampled and analyzed for conformance to specifications. At every stage thereafter in the manufacturing
With the growing need throughout the world for special alloys, and the increasing tendency toward the production of even ordinary metals by electric furnace methods, a solid future is assured for synthetic graphite and amorphous carbon electrodes. Great Lakes Carbon Corp. has steadily pursued a policy of expansion and diversification which will enable it to keep up with developments in the graphite market, including electrolytic anodes.
10
INDUSTRIAL AND ENGINEERING CHEMISTRY
VoI. 46, No. 1
PLANT PROCESSES-Graphite
Electrodes
A major expansion of facilities is currently nearing completion a t the Morganton plant. When finished, the installation will have been increased by 4070 in over-all capacity. One building in the section now under construction will hold new graphitizing furnaces of a larger size. Each of these furnaces will hold more than four times as large a load of electrodes as will the furnaces now in use. Transformer capacity will be four times that now available, and current capacity will be doubled. I n addition, there will be a decided increase in the efficiency of utilization of the power. The new furnaces are intended t o satisfy the growing demand for larger diameter and longer electrodes. They will handle electrodes up t o 110 inches long and 30 inches in diameter, as well as the smaller sizes now being made. The principle of operation will remain unchanged. An interesting feature in the construction of the new power system Giant Electric Furnace Competes with Open Hearth in Steel Production is the aluminum bus line, which will Note three cylindrical graphite electrodes extending through furnace cover be of welded construction rather than bolted. Each bus bar in the system will thus be a single piece, 240 The past decade has witnessed widespread diversification of feet long; all downcomers and angles are being welded Copsynthetic graphite products and has demonstrated the firm per bus bars are used in the original plant. When the infoundation upon which this industry fits into our over-all econstallation was built during World War 11, copper was scarce omy. It is reasonable to expect that this industry will show and bus bars were made of solid silver. When copper in the next decade a t least a similar, and in all probability a again became available, the silver was returned to the Governgreater, growth in diversity of application and improvement in ment. process technology. Future outlets that now appear to offer great promise for synthetic graphite manufacturers are in the production of zirconium, titanium, special alloys, and the fluorocarbons. Jet literature Cited aircraft applications and atomic energy uses may also require (1) Acheson, E. G., U. 8. Patent 568,323 (Sept. 28, 1896). sizable quantities of graphite as a material of construction. I n (2) Case, S. L., Moore, D. D., Sims, C. E., and Lund, R. J., “Comconnection with proposals for generdion of electric power from parative Economics of Open-Hearth and Electric Furnaces for nuclear energy, graphite is specified in several of the suggested Production of Low Carbon Steel,” Pittsburgh, Pa., Bituminous designs, since it provides a desirable combination of nuclear and Coal Research, Inc., 1953. mechanical properties, and is available in the quantities required. (3) Franklin, R. E., Proc. Roy. S ~ C(London), . A209, 1097, 196-218 In this application, graphite of high purity and high density is (1951). (4) Kelley, K. K., U . S. Bur. Mines BUZZ.406 and 407 (1937). required, in order t o assure maximum neutron utilization. One (5) Kubaschewski, O., and Evans, E. Ll., “Metallurgical Thermoestimate for the construction of a 350-megawatt (heat) level chemistry,” pp. 217-309, New Ycrk, Academic Press, 1951. power reactor, helium-cooled and graphite-moderated, indicates (6) Mantell, C. L., “Industrial Carbon,” 2nd ed., New York, D. Van that nearly 1500 tons of graphite would be required for the reNostrand Co., Inc., 1947. actor core assembly and reflector. Of this amount, approximately (7) Ueda, Yuji, “Carbon Products,” Tokyo, 1950. 1000 tons of high-grade graphite would be used in the reactor core, and another 500 tons of a perhaps slightly lower grade carbon in Processing Equipment the surrounding reflector section. In the metallurgical field, the output of ordinary steel by elec(1E) Jeffery Mfg. Go., Columbus, Ohio, swing hammer pulverizers, tric furnace methods is increasing a t a rate twice that of the pro20-50 hp., adjustable grate bar spacings, l / g to 1 inch. duction of all steel. Here again, the trend is toward the use of (2E) Koehring Co., Milwaukee, Wis., rotary mix coolers, 28 cu. ft. capacity, 7.5 hp., 7.5 r.p.m., 10,300 cu. ft./min. air volume. larger diameter and longer electrodes, which will require further (3E) Ohio Machine & Boiler Co., Cleveland, Ohio, horizontal mixers, development to ensure the retention of maximum strength and 3 f t . inside diam., rotating paddles, 16 hp., 68.5 r.p.m. proper physical characteristics as size is increased. (4E) Orville Simpson Co., Cincinnati, Ohio, five-deck gyratory Research in the synthetic graphite industry is currently aimed “Rotex” screens, screen size, 40 X 120 inches, 5 hp. drive. in three directions: improvement of raw materials, improvement (5E) Raymond Div., Combustion Engineering, Inc., Chicago, Ill., of basic production techniques, and development of basically difring-roller suction mill with bag filter, 75 hp. drive, 1160 ferent forms of graphite as well as new and different articles prer.p.m., 60 hp. fan. (6E) Sturtevant Mill Co., Boston, Mass., vertical rotor crushers, pared from graphite. A typical product of this attempt t o extend 20 hp. the diversity of the material’s application is a new graphite that (7E) Watson-Stillman Co., Roselle, N. J., horizontal hydraulic ex. resists oxidation a t temperatures up to 800” C. The exceptrusion press, tilting type, with steam-heated cylinder, ram tional oxidation resistance is achieved through the addition of diam. 36 inches, stroke 98 inches, ram speed 27 inches/min. various phosphate materials. a t full load. January 1954
INDUSTRIAL AND ENGINEERING CHEMISTRY
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