The values in ‘Table IV represent the temperature drop of 330,000 pounds of steel if that quantity were instantaneously placed in a ladle and then permitted to remain there for 15, 30, or 60 minutes. Such is not the case in actual practice. Actually, it requires approximately 60 minutes’ total time to tap, hold, and completely teem 330,000 pounds of steel; and during this time, two variables, the weight of steel in the ladle and the exposed brick area, are constantly changing. These variables were treated as constant for this computation. Consequently, Table I V is presented not as the expected temperature drop of the steel during tapping and teeming, but as a qualitative illustration of the relationship between steel-temperature drop and ladle preheating. For example, preheating a ladle to 150’ F. does not retard steel heat loss; preheating to over 1000” F. retards it significantly. Table IV also shows that the rate of temperature drop is greatest during the first minutes of holding time. Conclusions
Preheating large ladles does not affect steel temperature drop during teeming unless the preheating is of considerable magnitude (over 1000 O F.). The rate of conductive heat loss from steel is greatest during the first minutes of steel-brick contact. General conduction equations and relationships can be applied to the ladle problem, even though the physical and thermal properties of the brick change with temperature, if the proper k value is used. The thermal conductivity value, k , which gave the best heat-loss estimation, was not estimated at an average tempera(that tcold faee)//2. Instead it w-as evaluated ture-i.e., near the hot-face temperature.
+
Table IV.
Relationship between Steel Tempercrture Drop and ladle Preheating
Initial Ladle Tcmp., ’F .
Temp. Drop, F., in Steel after 75 min. 30 min. 60 min.
50 100
55
150 1000
53 35
54
77 75 74 49
107 104 102 68
Acknowledgment
The authors express appreciation to the Crucible Steel Co. of America for permission to publish this paper. literature Cited (1) Adams, C. M., Jr., Taylor, H. F., Trans. A m . Foundrymen’s Sod. 65, 170-6 (1957). ( 2 ) Dusinberre, G. M., “Numerical Analysis of Heat Flow,”
pp. 186-97, McGraw-Hill, New York, 1949. ( 3 ) Henzel, J. G.. Jr.. Keverian. J., “Ladle Temperature Loss.” Electric Furnace Conference, Pittsburgh, Pa.?Dec. 6-8, 1961. ’ (4) Paschkis, V., Tranr. Am. Foundrymen’s SOP,64, 565-76 (1956). (5) Samways, N. L., Dancy, T. E., Li, K., Halapatz. J., “.4nalysis of Factors Affecting Temperature Drop between Tapping and Teeming in Steelmaking,” International Symposium on the Physical Chemistry of Process Metallurgy, Pittsburgh, Pa.. April 27 to May 1, 1959. \
,
RECEIVED for review May 22, 1961 ACCEPTED May 14, 1962 Division of Industrial and Engineering Chemistry, 141st Meeting, ACS, Washington, D. C., March 1962.
THE SIGNIFICANCE OF FLUID DYNAMICS IN THE BLAST FURNACE STACK J. C. A G A R W A L A N D W . L. D A V I S , J R . Applied Research Laboratory, United States Steel Gorp., Monroeuille, Pa.
To improve the productivity and thermal and chemical efficiency of the blast furnace process, it is important to establish favorable fluid-flow characteristics in the blast furnace stack. These characteristics are related to the permeability of the burden m a t e r i a l s q r e , coke, and limestone-within the stack, the particle size and distribution of solids, and gas velocity, density, viscosity, pressure, and temperature. The application of chemical engineering techniques and process engineering analysis indicated that considerable improvement in blast furnace operation would result from various procedures for beneficiating the burden materials. The chemical engineering aspects of beneficiation processes such as sintering, pelletizing, and briquetting are discussed, together with the resulting improvements in fluid-flow characteristics and blast furnace performance.
HE BLAST FURNACE
is a countercurrent, packed-bed reactor
Tin which the burden materials are heated, dried, calcined, reduced, smelted, and partly refined by the hot ascending gases generated by the combustion of coke with preheated air. There has recently been a great leap forward in blast-furnace technology, which is evidenced by an approximately twofold increase in production rate for some furnaces and a one-third decrease in coke consumption per ton of molten pig iron or hot metal. These spectacular improvements could not have 14
I & E C PROCESS D E S I G N AND D E V E L O P M E N T
been achieved without more uniform gas flow and gas-solids contact in the stack. The efficient utilization of the reducing gases and heat generated in the furnace depends upon the intimacy and uniformity of gas-solid contact. The amount of reducing gases and heat depends upon the moles of oxygen (contained in the air blast) blown into the furnace in a unit of time, usually referred to as the wind rate. The two factors, gas-solid contact and wind rate, determine the productivity and efficiency of the furnace. .4ccordingly. attempts to apply
some of the principles of the packing behavior of solids and the flow characteristics of gases through these solids should lead to a better understanding of the blast furnace process. I n charging a blast furnace, ore, coke, and limestone are placed in the hopper formed between two or more bells that seal the top of the furnace. When the bell is lowered, the charge in the hopper slides down its surface and falls a few feet to the stockline. I n falling from the bell, the burden strikes near the walls of the furnace and slides or rolls toward the center of the furnace. Because of the greater inertia of the larger particles, they tend to segregate in the center, and the finer particles tend to remain near the walls of the furnace. Figure 1 diagrammatically illustrates the effect on fluid flow of using a raw ore burden that contains a wide particle-size spectrum. Such a burden inherently packs more densely and unevenly. Therefore, the gases will channel in the stack without efficient contact with the solids. As a result, a large portion of the fine material will be elutriated, and an appreciable percentage of the burden will reach the !“yere zone inadequately preheated and reduced. The thermal and chemical efficiency of the process will suffer, resulting in low production rates and high coke consumption per ton of product. Figure 2 shows the desirable condition of uniform fluid flow through a burden.
Fig, of gases rnrougn a row ore burden
gases burden OT
form flow rnrough a
Theoretical Considerations Consider now a moving packed bed of uniformly sized particles through which gases are flowing uniformly across the cross-sectional area. The maximum gas flow rate is that a t which the solids cease to move downward and “hang.” A further increase in the gas flow rate will fluidize the solids. The pressure drop per unit area for gas flow under these circumstances is approximately equal to the force per unit area exerted by !he weight of the bed of the solids. For the solids to move smoothly in a moving packed-bed reactor, the pressure drop must be sufficiently less than the fluidization pressure drop to provide enough residual downward force to overcome the inherent cohesive tendency of the solids caused by the interlocking and frictional forces between particles. Although most present-day blast furnaces are charged with burdens having wide-sized spectrums, these furnaces still operate a t pressure drops approximating 50 to 70% of the theoretical maximum pressure drop based upon incipient fluidization. The equation below shows the conventional pressure-drop relationship for padied beds as given by Erguu ( 3 ) .
k
dP =
E ’ S URE 0 5
INlTlUL
MINIMUM
E
OCCURS WHCN VOLUME Yo
OF LURGER COMPONENT I S 55 TO 65 02
0
01
dp
03
0 2
04
%
05
/ Dp , OIAMEIER OF SMALL TO LARGE PARTICLES
06
Figure 3. Effect of size distribution on void volume for two-corn ponent mixtures
1-
& (Tf) w2
where P = pressure, L = length, k = constant, D, = diameter of particle, B = void fraction, p = gas density, and u = gas velocity. Several other forms of this relationship have been proposed ( 6 ) in which the void fraction appears in different functional forms. However, for the authors’ purpose this is merely a detail because all modifications of this equation state that an increase in void fraction decreases the pressure drop. The relationships also state that larger particle diameters decrease the pressure drop. Accordingly, increasing the size of particles or the void fraction should allow more gas to pass through the bed with no increase in pressure drop. Also, since higher elutriatian velocities are required for larger diameter particles, the implication far blast furnace operation is that a larger particle size in the stack should permit more wind to be blown without inmeasins !he dust carried over. Unfortunately, blast furnace burdens have many constituenrs-namely, coke.
Ll-L.LL!
020
02
04
06
d, /Elp , OIAMETER
08
10
12
OF SMULL TO LARGE PURTICLES
Figure 4. Effect of size distribution on void volume for multicomponent mixtures A. 4 companenlr.
8. 3 components.
VOL.
2
NO,
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C. 2 components JANUARY 1963
IS
t
STRi
I
NODULES
Figure 8. Figure 5.
Figure 6.
16
Typical products
. from agglomerating processes
Diagram of sintering strand
Per cent 3/s-inch sinter vs. production rate
70 - l/B Figure 7.
-.
IN MATiRIAL IN PRODUCT
Effect of fines on sinter recycle rotio
l & E C P R O C E S S DESIGN AND DEVELOPMENT
ore, and stone-and all have different densities and size spectrums. Therefore, only a qualitative statement can be made-that blast furnace operation would benefit by the use of burden materials having an optimum particle diameter, particularly because other process requirements are involved, such as rates of heat transfer and rates of reduction. T h e determination of maximum and minimum voidages can easily he described for packed beds of spheres. For example, when a bed of uniform-sized spheres is arranged in a square array with each layer directly over the other, a maximum voidage of about 48% occurs. A minimum voidage of about 26y0occurs far the rhombohedral arrangement, in which each sphere rests in a pocket formed by three other spheres. Randomly packed beds of uniform spheres would be expected to fall within the extremes of 26 and 48% voidage. Although the analogy with spheres indicates that fluid flow within the blast furnace stack can be improved and made more uniform by causing the burden to become more uniform in size and shape, this ideal is difficult to practice. I t is, however, possible to make appreciable improvements by practical expedients such as limiting the size distribution of the burden materials. The next two figures are based upon data developed by Furnas (4) over 30 years ago. Figure 3 applies to binary mixtures and illustrates the fact that particlesize distribution alone can lead to wide variations in packing density. Note that even though the fractional void volume for each component is initially 0.5, and that the volume percentage of each component in the mixture remains essentially constant, the fractional void volume can be cut in half merely by decreasing the ratio of particle diameters. Decreasing the ratio of the particle-size diameter of the small size to that of the large size is simply a method of stating quantitatively that the size distribution is becoming wider. Figure 4 illustrates in an idealized manner the effect of particle-size distribution on minimum fractional void volume when several size components are present in a bed of solids. The presence of more components tends to minimize the decrease in minimum fractional void volume over a wider spectrum of size ranges. However, note that even for the four-component system the fractional void volume rapidly falls as the ratio of the diameter of the smallest particles to the diameter of the largest particles goes below 0.2. Considering
l
2800
2
0 \
~
-
i
~
l
~ 0 5/60
~
'
l
~
i
~
l
-
ARMCO- 3,
z 2600-
-
0 t-
$ LT
11/60 0
-
z n 3 V
1
2400-
2200
0
O 3/60
$ 1
HOD M :{3-::
s
2 m
9oc
I:
60
60
70
80
90
100
II 0
HOMESTEAD-3 A
11/60 I
!
70
,
I
eo
'
1 90
'
I
IOC
1 IO
I I I20
I20
WIND RATE, 1000 S C F M
'CIIND RATE,
I000 S C F M
Figure 9. Production rate vs. wind rate for sinter and pellet burdens
Figure 10. Carbon rate vs. wind rate for sinter and pellet burdens
that the usual blast furnace charge materials contain several size components, it is reasonable to assume that the fractional void volume for the blast furnace stack would approximate the behavior of the four-component system shown in Figure 4. The obvious conclusion is that the fractional void volume and the permeability of the blast-furnace burden should increase, and it should be possible to blow more wind if the ratio of the diameters of the smallest to the largest particles is as high as possible. ,4 practical way to accomplish this would be to screen out all -33/E-inch material from the blast furnace burden materials before charging them to the blast furnace, and also to limit the top size. I n addition, by removing the -33/E-inch material, the average particle size of the burden increases, which also causes the pressure drop to decrease according to the pressure-drop equation.
total ore burden on .4merican blast furnaces was sinter, but in 1960, the average had increased to 40y0. Several blast furnaces are presently operating with favorable results on 100% sinter burdens. Sinter, though a vast improvement over crude-ore burdens, has inherent disadvantages. I t is produced in large chunks that must be crushed, screened, and sized. This leads to a large quantity of --3/8-inch material that must be recycled at the sinter plant. However, even though the sinter product is all +3/E-inch material as it leaves th: sinter plant, it undergoes considerable degradation during shipment. I t is not unusual to find that as much as 35% of the sinter leaving the agglomeration plant has degraded into --3j8-inch material by the time it is actually charged into the blast furnace. Figures 3 and 4 have shown that fine material produced by degradation during shipment and handling, or more broadly by any source, is harmful to blast furnace operation; it causes a decrease in fractional void volume and results in excessive pressure drops and channeling of gases. Furthermore, much is elutriated by the off-gases and must in any case be recycled to the sinter plant. I t therefore appears expedient to screen 3/E-inch masinter at the blast furnace to produce 100yc terial. Impressive results have been obtained by instituting this practice. Figure 6 shows: for example, that the United Steel Companies, Ltd. ( 7 ) > Appleby-Frodingham, England, obtained a 30% production-rate increase in the blast furnace by this practice. U. S. Steel's newest furnace, the Duquesne No. 6, will be equipped to screen sinter at the furnace. However, it is costly to screen and recycle an appreciable percentage of the total sinter production from the blast furnace to the sinter plant. Because sinter plants are often located far from the blast furnace, it may be more economical to increase moderately the unit cost of sinter in order to increase product quality. I n this manner, the recycle material caused by crushing and sizing at the sinter plant and by degradation in transit can be minimized. Figure 7 shoivs the amount of material recycled per ton of +3/,-inch product as the percentage of --iE-inch material in the product increases. Please note that this relationship is exponential. Accordingly, an increase in the amount of fines in sinter product lvhich appears to be small, from 35 to 45'3,, in reality causes the recycle ratio, or ratio of the amount of material recyclrd to the amount of +3/E-inch product, to increase drastically from 0.54 t? 0.82. This is a 50Yc increase in the material to be reprocessed. I n addition to sintering, there are alternative agglomeration
Improvements in Ore Physical Properties
About 10 years ago, it was recognized within the steel industry-more by intuition than by a theoretical analysis of fluid dynamics-that appreciable advantages M-ould accrue by limiting the size range and increasing the particle size of burden materials. Accordingly, large sintering facilities were installed to agglomerate the -l/*-inch fraction of iron ores. I n the sintering process (Figure 5 ) , ore fines are mixed with finely divided coke and recycle sinter fines in pug mills? balling drums, or disk pelletizers. Water is added to promote the balling tendency of the fine particles and thereby to increase the permeability and reduce the pressure drop through this packed bed of solids. The mixture is ignited and sintered to form large c inkers. The heat for sintering is supplied by combustion within the bed and is maintained by imposing a suction at the bottom of a traveling grate that supports a 14- to 18-inch bed of material. A high-temperature combustion zone sloivly moves from the top of the bed downward by heat transfer from hot air and combustion products passing through the bed. The bed of material on the grates moves slo~vlyat a controlled speed so that combustion and sintering. are complete at the discharge end. The sinter is then cooled, crushed, and screened. Although a detailed discussion of the unit operations involved in the sintering process is not lvithin the scope of this paper, the major operations in sintering, as \vel1 as in other ore-agglomerating processes, and in the blast furnace stack itself, are fluid floxv and heat transfer in packed beds of solids. The importance of sintering to the steel industry can be appreciated by considering that in 1950 only about 5yc of the
+
VOL. 2
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JANUARY
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17
TO STACK
HOT AIR AND FINES F R O M
CONVEYOR
-+=Figure 1 1 .
PRODUCT C O N V E Y O R
Diagram of hot-ore-briqueting pilot plant
processes, the main ones being nodulizing, pelietizing, and hat-ore briquetting. Figure 8 shows typical products from these processes. The nodulizing process employs a rotary kiln to heat ironore fines to about 2400' F., a t which temperature the fine particles agglomerate. This process is used commercially but not to the general extent of sintering. One large plant (2) presently in operation a t Virginia, Minn., adjacent to the Mesabi iron-ore range, produces ahout 1500 net tons per day of nodules from taconite concentrate. Because, as Figure 8 indicates, nodules are physically quite similar to sinter, the conclusions on the use of sinter in blast furnaces also apply to the use of nodules. At ahout the time that the value of sinter was being recognized, pellets made from -200-mesh taconite concentrate appeared. I n this process, weak or "green" pellets are first formed by mixing ore concentrate with a binder such as bentonite and with the proper amount of water, and rolling it in a drum or disk. The green pellets are then heat-hardened a t over 2000" F. Figure 8 shows that pellets closely approach the condition of uniform-sized spheres, and obviously have a much narrower size spectrum than sinter. This is quantitatively shown in the table below. Note that pellets have only about 5% of -3-mesh material, whereas sinter often contains up to 50% -3-mesh material.
Average Sire Consist of Raw Materials Curnulotiuaper Cant ?;-*"-
U'lfibll
+1 inch
inch +3 mesh +10 mesh
+L/2
SUPERFICIAL VELOCITY, F T / S E C
Figure 13. Pressure drop vs. superficial velocity for briquets and pellets 2600
I
I
I COKE SIZE.
18
+
%t3,-2
I
I
IN
i
I 1
Effect of coke and ore size on blast-furnoce
Figure 14. production A.
I
3/.
-
2-inch.
B.
+ - 3-inch.
C.
f a/84nch
l&EC P R O C E S S D E S I G N A N D D E V E L O P M E N T
ll.ll,
D",7",~
2.6 13.1 50.7 91.7
A pellet burden should give a larger and more uniform voidvolume within the blast furnace stack. As previously diss cussed, this should result in a lower pressure drop, and allow a higher wind or blast air rate and a corresponding increase in production rate. Confirmation was obtained on the 28-foothearth-diameter furnace of Armco Steel Co., Middleton, Ohio (5). Figure 9 shows that when this furnace used a 100% pellet burden, up to 2820 tons per day of hot metal were produced a t a wind rate of approximately 114,000 standard cubic feet per minute. By comparison, the other furnaces indicated in this figure used a 100% sinter burden and produced only 2000 to 2250 tons per day because the maximum wind rate varied between 70,000 and 87,000 standard cubic feet per minute (7). These other furnaces were not equipped to screen sinter a t the blast furnace. Figure 10 shows that a t the same carbon rate per ton of hot metal, more wind could be blown into the furnace having the pellet burden. Thus, a higher wind rate and a corresponding production rate were not accompanied by a n increase in carbon usage per tan of hot metal produced. Therefore, the efficiency of utilization of heat and reducing gases in the blast furnace stack did not decrease even though the residence time of gases in transit through the stack was diminished. U. S. Steel has developed a hot-ore-briquetting process for producing uniform-sized agglomerates by compacting iron ore a t high temperatures and pressures. Figure 11 shows the main features of the process which include facilities for heating the ore to 1500' to 1800' F., for compacting the ore into
I
12 I
011 INJECTION
5 P
f
: 4. a
I/, goo
Figure 15.
Lu
E
, IO
,
20
30 TOP PRESSURE, P S l G
n I
40
Effect of top pressure vs. wind rate
briquets, and for cooling the product. Figure 12 shous a sample of briquets together \vith the hematite ore fines from which they were made. These ore fines were screened at 3’5 inch and therefore contain a fairly large percentage of coarse particles as compared Lvith the very fine -200-mesh ores needed to make green spherical balls for the pelletizing process. This illustrates one advantage of hot-ore briquetting over pelletizing-namely. that grinding is not required and natural ore fines can be used. T M O additional advantayes are that no material binder such as bentonite is needed, and that the maximum operating temperature, depending upon the particular ore. is 500’ to 800’ F. lower than is needed for heathardening green pellets. Because sufficient quantities of briquets have not been produced, a direct comparison between briquets and pellets in a full-sized blast furnace has not been accomplished. However, several thousand tons of briquets made from \’enemelan ore fines produced in U. S. Steel’s 50-ton-per-day hot-orebriquetting pilot plant have been tested in the U. S. Bureau of Mines’ 4-foot-hearth-diameter experimental blast furnace. Although these tests Lvere of short duration, the results indicated that blast-furnace operation with a briquet burden should be practically identical with operation ivith a pellet burden. I n fact, a study of the pressure drop in a 3-foot diameter packed column for briquets and for pellets both made from Venezuelan ore fines indicates that briquets should give a slightly smaller pressure drop than pellets (Figure 13). The pellets were sized at 3/8 to 5/s inch in diameter and the briquets measured X ll/r X ‘/2 inch. Improvements in Coke Physical Characteristics
The necessity for improving the size spectrum of the other major burden component, coke, has not been overlooked. Screening of coke at the blast furnace prior to charging is now a general practice. The available data indicate that the top size of coke should be limited and that its size spectrum should be made approximately the same as that of the iron-ore aqglomerate. Fiqure 14 (8)shoxs that as the amount of -2-inch +3j4-inch coke increases from an average of 54%, an appreciable increase in iron production is obtained if the ore also has a similarly narroir size spectrum, such as 60% -2-inch and
0
4
‘h Figure 16. density
H2
8 IN BOSH GAS
12
Effect of hydrogen on bosh gas
+3js-inch. ,4 slightly \vider size spectrum for the iron ore (- 3-inch +3/’s-inch) decreases the production-rate advantage obtained by narrowing the coke size spectrum. If: however, the size spectrum of the coke is narrokved Lvithout concurrently narroit-ing the spectrum of the ore to similar top and bottom sizes, the production rate decreases instead of increasing. The conclusion reached is that often no improvement in performance occurs when only one constituent of the burden is improved, and a detrimental result may occur. .411 burden constituents should simultaneously be improved. Operation at High Top Pressure
There is a practical limit to the pressure drop and the gas velocity that can be imposed on a moving packed bed of solids such as exists xvithin a blast furnace shaft. Hoivever, the productivity of a blast furnace is dependent upon the moles of blast air that can be blown per minute. Therefore, productivity can be increased if the moles of air per minute can be increased without appreciably increasing the pressure drop and gas velocity. This can be done by increasing the top or back pressure on the furnace. Figure 1 5 shows the effect of an increasing top pressure on the \vind rate. .At 1.5 p.s.i.g., approximately 95,000 standard cubic feet per minute of air can be blown into a 28-foot-diameter furnace \\.hen a 100% sinter burden is used. By an increase of the top pressure to 30 p.s.i.g., 140,000 standard cubic feet per minute of \vind could be blown, an increase of nearly 45yC, The production rate ivould increase correspondingly. U.S. Steel‘s new 28foot-hearth-diameter furnace at Duquesne LVorks has been designed for a top pressure of 30 p.s.i.g. The U.S.Steel 4foot-hearth-diameter experimental furnace at Universal, Pa.: has been designed for a top pressure of 50 p.s.i.q. Operation with Tuyere Fuel Injection
An examination of the pressure-drop equation indicates that the pressure drop and hence the amount of Lvind that can be blown in The furnace should also be affected by the density of the gas. A lower gas density will result in a smaller pressure drop and hence smoother burden movement; or: at the same pressure drop, an increase in gas velocity could be tolerated. Hydrogen, besides being a better reducing agent than carbon monoxide, is approximately 1/14 as heavy as the other gases VOL. 2
NO.
1
JANUARY 1963
19
present in the blast furnace. Therefore, even a small amount of hydrogen in the blast furnace gas tends to improve the flow characteristics and the burden movement in the stack. Until recently, this hydrogen has come mainly from the blast humidity (moisture injected into the blast air). However, with the recent use of various fuels injected into the blast furnace tuyeres, large quantities of hydrogen are now produced in the high temperature tuyere zone. Figure 16 shows the hydrogen content of the gases produced in the tuyere zone (bosh gas) that is caused by various injectants, and its effect on the boshgas density. All of these injectants decrease gas density, but natural-gas injection produces the largest decrease. It is therefore not surprising that, almost without exception. blast furnace operators have reported smoother burden movement when natural gas is injected.
multiconstituent problems, the application of proper process engineering analysis has resulted in impressive results. A great deal more work needs to be done. literature Cited (1) Ararwal. J. C.. Davis. W. L.. “Recent Advances in Blast\
Fugace Technofogy,” AIChE Annual Meeting, New York, N. Y., December 1961. (2) Bennett, R. L., Hagan, R. E., Mielke, M. V., Mining Eng. 6, 73 -- 11054\ \-’” ‘I’
( 3 ) Ergun, Sabri, IND.ENG.CHEM.45, 477 (1953). (4) Furnas, C. C., Zbid., 23, 1052 (1931).
(5) Haley, K. R., “Operational Results Using Taconite Pellets in Armco’s Middleton Blast Furnace,” Blast Furnace, Coke Oven, and Raw Materials Conference, AIME, Philadelphia, Pa., April 1961. (6) Happel, J., IND.ENG.CHEM.41, 1161 (1949). (7) MacDonald. N. D.. “The Effect of Screened Sinter in Furnace Productivity,’; Blast ’Furnace, Coke Oven, and Raw Materials Conference, AIME, Philadelphia, Pa., April 1961. (8) White, R. H., “Recent Advances in Iron Production Techniques,” Minnesota Section AIME, Annual Meeting, Duluth, Minn., January 1962. \
Conclusions
There is presently very limited knowledge on fluid flow and packing behavior in moving packed beds containing multicomponent particle sizes. I n addition, very limited information is available on moving packed beds containing multiconstituents having varying solid densities. I n spite of these limitations, and the fact that fluid flow and burden movement in the blast furnace stack involve both multicomponent and
,
I
RECEIVED for review April 5, 1962 ACCEPTED November 1, 1962 Division of Industrial and Engineering Chemistry, 141st Meeting, ACS, LYashington, D. C., March 1962.
PLUTONIUM ELECTROREFINING L A W R E N C E J. M U L L I N S , J O S E P H A . L E A R Y , A R T H U R N. M O R G A N , A N D W I L L I A M J. M A R A M A N
Los Alamos ScientiJc Laboratory, University of California, Los Alamos, N . M . The production of large amounts of high purity plutonium metal b y bomb reduction techniques i s a difficult and time-consuming task. Electrorefining processes have been developed that provide good yields of the pure metal in a compact form of high density on either the 500-gram or 3.5-kg. scale. Because of the operational simplicity, the method i s also ideally suited to the economical processing of plutonium metal scrap.
preparation of milligram quantities plutonium metal was first reported in 1944 by Kolodney of this laboratory (6). Kolodney obtained the metal by the electrolytic reduction of PuC13 in a fused solvent of BaC12KC1-XaCl. The method was never applied to large scale operation because of the success of the bomb reduction method developed at about the same time at Los Alamos ( 7 ) . More recently, plutonium electrorefining on a large scale has been considered for application to the following important problems : HE ELECTROCHEMICAL
Preparation of high purity metal for chemical and metallurgical studies Recycle of impure plutonium metal scrap (at present done by rather expensive methods) Recycle of impure plutonium compounds by converting these to impure metal for subsequent electrorefining Reprocessing of plutonium from plutonium-fueled nuclear reactors I n 1958, the purification of plutonium nuclear fuel by electrorefining was reported by Leary et al. (7). These ex20
l & E C PROCESS D E S I G N A N D DEVELOPMENT
periments indicated that excellent purification of plutonium was possible, as anticipated from thermodynamic estimates. Small scale preparation of pure plutonium metal by electrorefining was reported by Blumenthal and Brodsky of the Argonne National Laboratory in 1960 ( 2 ) . They collected the electrorefined product below the melting point of plutonium, then melted it into a button in a second container. Plutonium electrorefining rates of about 6 grams per hour were achieved, resulting in buttons weighing u p to 55 grams. Large scale preparation of pure plutonium at the Los Alamos Scientific Laboratory vias reported in 1960 by Mullins, Leary, and Bjorklund ( 8 ) . The plutonium product was deposited as a liquid a t the cathode by operating the cell above the melting point of plutonium. The liquid metal could be either cast into the desired shape in situ or removed from the cell continuously. A maximum of 278 grams of metals as electrorefined in a single run. The batch process was extended to the 500-gram and 3.5-kg. scales and was reported in 1362 (70).
