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Патент USA US3076258

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‘Feb. 5, 1963-
Filed Nov. 17, 1960
2 Sheets-Sheet 1
1% Q, 2,
WE/VDEZL A.mmvrozzs
DAR/F0” 4%
By Jam/,4 144 mass
im’ M»a
FeB. 5, 1963
w, L, DARRow ETAL.
Filed Nov. 17. 1960
2 Sheets-Sheet 2
l/m mgm
Widow; WW3”
United States Patent C?ice
Patented Feb. 5, ‘1,9613
?nes, which do not require screening prior to their in
troduction into the phosphorus furnace. I
Wendell L. Darrow, Alameda, Idaho, and Joseph W. Kass,
Kemmerer,. Wyo., assignors to FMC Corporation, a
corporation of Delaware
It is an additional object to produce a calcined phos:
phate agglomerate by a process which minimizes dust
It is a further object to produce a calcined phosphate
agglomerate by a process which eliminates theneed for
Filed Nov. 17, 1960, Ser. No. 69,933
6 Claims. (Cl. 25-4156)
low-temperature drying of the briquette feed to the cal
This invention relates to the production of calcined
It has now been determined, quite unexpectedly, that
phosphate agglomerates, and‘ particularly to the produc
tion of agglomerates which are especially suitable for
phosphate agglomerates having high tumbling strengths
furnace feedin the mahufac'ture of phosphorus.
The phosphate ores obtainable in ‘the western part of
phorus can be produced by crushing phosphate shale
containing minor ‘amounts of shale oil (generally on
and suitable for furnace feeds in the production of phos-'
the United States are composed of large deposits of phos 15 the order of about 2 to 4%), screening the shale into a
phate shale containing up to about 32% P205 in the form
?nes fraction which passes ‘through a 6 mm. screen, and
of calcium phosphate. These ores also contain silica,
into a coarse lump fraction having a particle size of about
iron oxide, organic matter, clay, small quantities of’
1A to 3 inches in diameter, treating the ?nes by briquetting
chromium oxide ‘and vanadium oxide, and from). to 4%
or pelletizing them in 1a wet agglomeration step, placing
shale oil. These ores are converted to phosphoriis by 20 a portion of the coarse lump fraction on a nonéagitated
reduction in an electric arc furnace.
perforate carrier as an underhearth layer, placing an
Heretofore, ealcinedphosphate ag‘glorner‘at'e‘s, deriifed
overlay layer of agglomerated ?nes and remaining lump
from phosphate shale and suitable for furnacefeed, have
been produced by crushing the aboveédescribed ‘shale in a
fractions on the underhearth layer, and calcining the
resultant bed ?or about 15 to 25 minutes. The calcinai
hammer mill into particulate form to pass a 4-inch screen, 25 vtion is performed by heating, the agglomerates to tem-'
screening the shale ‘into ?ne ‘(~6 mm.) and coarse (1A
peratures between about 2250° to 2500° F. on the non;
to 3") fractions, treating the ?nes fraction by either
briquetting or pelletizing using wet agglomenation, cal:
agitated, perforate carrier. The under-hearth layer should
comprise at least about 16% of the total bed depth.
cinirlg the agglomerates and the previously ‘separated
It has further been determined that if the phosphate
coarse fraction in a rotary kiln, and screening‘hbjection 30 feed to be calcined consists only of briquettes or pellets,
able ?nes out of the calcined product to yield a coarse
oalcination may be performed using an underhearth layer
nodule or calcined phosphate. The calcined ?nes, which
of calcined product in lieu of the phosphate lump.
are smaller‘than 6 mesh, ‘are returnedto the a'ggiemera:
The exact reason for this increased tumbling strength
tion‘step for further br‘iquetting or pelletizing.
, ‘
over the phosphate vagglomerates produced in a rotary
The operation‘ of a rotary kiln “in this process gives 35 kiln is not known, but it is probably due to the surface,
rise to serious dil?culties, One of the principal di?iculties
encountered‘ is the relatively low mechanical strength of
fusion of ?ne particles of oily shale whichact as a natural
binder to hold the individual feed particles together.
the calcined phosphate product. As a‘ result, the calcined
This fusion can take place in the present process because
the calcination is carried out upon anon-agitated carrier
be screened out at the termination of the ‘ealcinatioii 40 which gives the ?ne oily shale particles an opportunity
process. These calcined ?nes are recycled ‘to "the ag-_
to consolidate in place; the rotating kiln doesnot allow
glomeration step, and‘represent a recycle load of at
such undisturbed consolidatioh because of iits‘tumbling
phosphate aggiomerates disintegrate into?neswh'ich: must
least 13% on the agglomeration equipment,‘ and a ,re- ’
cycle load of 10%‘ on the rotary kilns. As a‘ further
‘ result of the low mechanical strength of the ealcined
operation. However, regardless of the ‘reasomit has been
determined that the non-agitated perforate carrielgtypev
calciner ‘produces phosphate agglomerates of signi?cantly,
higher resistance to disintegration than does the tumbled
15% are formed
?nes‘ ininitial
the amount
of abdut
of the10‘
bed of the rotated kiln. ,
product. These unscreened ?nes enter the phosphorus
furnaces along with the calcined phosphate nodules, and’
their presence in the furnace burdens‘ creates a serious‘ 50 a signi?cant correlation between the tumbling strengths
problem since ‘they cause erratic furnace‘ operation.
and the maximum temperature of the bed layer. A‘
‘Rotary kilns‘ are also objectionable’ because they‘ re;
graphic computation of this data is ‘shown in FIGURE 1,
quire a low-temperature drying step to prevent green
wherein tumbling strengths are employed as ordinates, and
briquettes from spalling or breaking into pieces when‘
maximum bed temperatures as a‘rscissas. ‘If we adopt as
exposed to the heating shock of the calcining tempera} 55 a satisfactory tumbling strength that which was obtained
tures employed. Additionally; under kiln conditions,
in the rotary kiln, i.e. greater than 83%, it is found that
?nes which are released during calci-na‘tion undergo rapid
temperatures between about 2250° F. and 25000 F. pro~~
heating, partially melt, and adhere to the kiln surfaces.
duced calcined phosphate agglomeratesk having satisfac—
These agglomerates change the internal shape of the‘
tory tumbling strengths for use as furnace feeds. Tem
kiln, and ?nally formpinto balls which block .th‘efpass'a'g'e' 60 peratures above 2560° F. are not desirable because of
of air through the kiln.’ When this occurs, a shutdown
for clean-out is required.
_ v
excessive fusion of the product, rendering it dif?cult to
work with. Additionally, heating costs become unduly
It is an object of the present invention to‘ produce cal
high at temperatures above 2500° F. I
oinecl phosphate agglomerates suitable for furnace feeds,
having high strengths and containing reduced-amounts of
‘It is‘ a" further
object‘ to_ produce calcined._ phosphate
p I
agglomerates having high strength and freedoni from‘
The tumbling tests are made by tumbling SOC-gram
samplesof the calcined product for ten minutes in a‘ 14
inch diameter can, equipped with one 21/2-in'ch radial,
lifter. The tumbler is rotated on a central axis, at a speed
of 45 Loss on tumbling is de?ned as the percent
is made up of an underhearth layer, which rests directly
of the sample passing through a 6-mesh screen after
tumbling; the percent remaining on the screen is the
tumbling strength of the sample. This test is designed
to show the physical strength of the calcined materials.
on the continuous grate, and an overlay of phosphate
The depth of this underhearth layer is
generally maintained at about 3 to 12 inches, which con
stitutes at least 16% of the bed, and is made up of
A speci?c non-agitated perforate carrier which may be
employed in the practice of the invention is illustrated by
way of example in the attached drawings. In the draw
screened phosphate lump having a particle size of about
1A to 3 inches in diameter.
Calcined product may be
employed as the underhearth layer in lieu of phosphate
lump when the feed comprises only phosphate agglomer
FIGURE 1 is the graph referred to above.
FIGURE 2 is a schematic representation of an appa 10 ates. However, the use of phosphate lump is preferable
in that maximum production per unit of grate area is
ratus having a non-agitated grate-type carrier with a cal
The agglomerated feed which is to be calcined is carried
on top of the underhearth layer. This feed consists of a
paratus along line 3—3 of the calcining section.
In these drawings a continuous grate is made up of 15 mixture of briquettes, obtained from the agglomeration
step, and- a previously separated coarse fraction of phos
a plurality of pallets, 4, forming an endless train and
phate shale. The endless grate carrying the underhearth
supported on rails, 2. Lump phosphate which forms the
cining zone and a cooling zone.
FIGURE 3 represents a cross-sectional view of the ap
layer and the overlay thereupon slowly move these layers
underhearth layer is added through hopper 36, while phos
into the drying and calcining section, and then ?nally into
phate feed is placed on top of the underhearth layer us
ing hopper 34. The pallets may range in size from 20 the cooling section. The speed of the grate is regulated
so that the retention time during the calcining operation
about 15 x 24 inches to about 3 x 8 feet. Metal side
is maintained between about 15 to about 25 minutes.
plates, 6, bolted to the pallets, 4, permit the grate to
During this step, hot gas at a temperature of about 2100°
carry a phosphate bed of about 18 to 24 inches deep.
F. to 2300° F. is passed downwardly through the layers
The cast grate bars, 8, are held in the bottom of the pal
lets by single pins, 9, while the slots for the passage of 25 in the drying and calcining zone at a rate of about 0.43
to about 0.53 pound mol/min./ft.2 of grate.
gas between the grate bars, 8, are about 1A of an inch
It is preferred that the heating gas contain oxygen in
wide. Each of the pallets is supported by four casters,
order to burn the shale oil contained in the feed and
10, two on each side. The casters, 10, are attached to
thereby reduce the heating requirements of the calciner.
pickup rods 12. A tooth sprocket, 38, connected to a
varidrive, engages the pickup rods, 12, and lifts the
pallets to the top or forward track. The sprocket, 38,
imparts a pushing action on the pallet as it disengages
from the sprocket, and this pallet in turn pushes the rest
of the train. Normally, they will not be connected or
hinged to each other. While the pallets are passing 35
Non-oxygen containing gases may be employed for
heating but are not as desirable since these merely vapor
ize the shale oil without burning it. These hot gases
raise the temperature of the material being calcined to
at least about 2250° F. The temperature of the material
will exceed slightly the temperature of the gas, because
combustion of the shale oil within the bed contributes
through the drying»calcining zone, 40, and the cooling
its heat to the calciner.
zone, 42, a required gas seal is provided over the wind
The calcined phosphate is cooled in the cooling zone
boxes, 20 and 26, as illustrated in section 3-3. The seal
by means of ambient air so that the average temperature
is provided by a ‘Te?on strip, 16, in contact with pallet
seal plate, 14. The Te?on strip, 16, is held in place by a 40 of the product is low enough to permit it to be handled
on rubber conveyors. Generally this temperature is
seal support plate, 18, and by a wall of windbox 20.
about 250 to 450" F. After passing through the cool
Heat is supplied by passing a hot gas downward through
ing section, the calcined particles are spilled and re
opening 32 of the drying-calcining zone, 40, and through
the layer of briquettes on the grate bars, 8. The gas then
The resultant calcined phosphate product comprises
?ows between the space of the grate bars, 8, and into 45
a feed which has been freed of volatiles such as shale
windboxes 20. The main current of hot air is removed
through duct 24 for reheating, while ?nes are removed ‘ oil, CO2, H20, and the like. This calcination results in
lowering the original weight of the ore by about 5 to 10%,
through lower vents 22.
and leaves the other ingredients substantially unchanged.
When the heated briquettes pass into the cooling sec
tion, ambient air is forced downwardly through the phos
. ,In the operation of the continuous grate calciner, an
underhearth layer is required in order to obtain a prod
phate bed and through grate bars 8 into windboxes 26.
uct which has more uniform tumbling strength, for any
The main current of cooling air is expelled through duct
particular calcining time employed. This is necessary
28 for recycle to the calcining hood, while ?nes are re
because calcination through the bed is not entirely uni
moved, through lower vents 30.
The phosphate shale treated by the present method 55 form. At the top of the bed, where the hot gases ini
tially impinge and penetrate to heat the bed, excellent
contains about 22% to 32% P205 in the form of calcium
calcination takes place and results in calcined products
phosphate along with silica, iron oxide, and 2 to 4% of
having high tumbling strengths. In contrast, calcination
shale oil. Additionally, other organic matter and clay are
takes place under less favorable conditions at the bottom
present with small quantities of chromium oxide and
of the bed and results in products having tumbling
vanadium oxide. This phosphate shale is crushed in a
strengths which are below those obtained at the top of
hammer mill into particulate form, and these particles are
the bed. As a result, a random mixture of phosphate
screened into ?nes and coarse fractions. The ?nes frac
lump and briquettes cannot be calcined to give a product
tion of the shale, which passes through a 6 mm. mesh
having a high, uniform tumbling strength.
sieve, is sent to an agglomeration step. In this operation
For this reason, an underhearth layer of phosphate
the ?nes fraction is subject to either briquetting or pelletiz
lump is employed, since its calcined product inherently
ing by compressing it in the presence of water. How
yields higher tumbling strength than corresponding cal
ever, any conventional briquetting or pelletizing process
cined briquettes. The feed briquettes which are used in
may be employed to agglomerate the shale ?nes.
The coarse shale fraction previously separated, rang 70 the upper layer, above the underhearth layer, therefore
are calcined under conditions which yield high tumbling
ing in size from 1A to 3 inches, is termed phosphate lump
and is employed in the formation of an underhearth layer
strengths. This is further demonstrated in Example 2,
hereinafter described. In this regard, the following com
on the calciner; excess phosphate lump can also be used
as part of the green phosphate feed which is placed on
parative data illustrate the effect of an underhearth layer
top of the underhearth layer. The bed which is calcined 75 on product quality.
cleaner ‘and safer working conditions are obtained in the
Calcining Time, Minutes ___________________ __
kiln area.
Loss on
Loss on
Tumbling Tumbling
With N o Underhearth ______________________ -_
' With 4%” of Underhearth l _________________ __
The present process has. a‘material et?ciency which is
much higher, being about 93%, than that of the rotary
kilns, which is about 83%. Accordingly, the present
calcining operation reduces the ore requirements by about
11%. Furthermore, due to the lack of recycle of cal
cined ?nes, the instant process will convert over 90% of
the dry feed to furnaceable phosphate, whereas the‘ rotary
kilns will only convert about 72% of the dry feed to
lOalculated on the assumption that the tumbling strength of the
underhearth layer is 85%.
furnaceable phosphate. A
Another advantage of the present process is ‘the more
The underhearth layer also reduces maintenance costs
on the grate bars by keeping them at a cooler tempera
ture than would be obtained without the underhearth
e?icient utilization of heat derived from the ctifnbnstion
of the shale oil which is present in the phosphate shale
feed. In rotary kiln calcin‘ation, this shale oil does not
contribute a signi?cant amount of heat because it burns
in the gas stream above the bed of calcining material._ In
the present process, the heat from the combustibles is
liberated progressively from tne'rop'to the bottom of the 7
The employment of a non-agitated perforate carrier for
‘calcination of the phosphate briquettes in the present
process has resulted in obtaining a calcined phosphate
furnace feed having an unexpected increase in strength,‘ 20 bed and thereby is e?ectively used for'heating the lower
coupled with extremely small amounts of ?nes in the
‘portion ofthe bed. Because‘thé combustion heat is re
leased in intimate contact within the bed, the heat can
cined phosphate for use in a phosphate furnace, when
be effectively absorbed in the lower section of the bed,
compared with calcined phosphate produced in a rotary
and temperature penetration downward into the bed is
kiln, is shown by the following typical comparative data: 25 faster than if ‘all the heat is supplied‘ by the inlet calcin
calcined product. The superiority of the resulting cal
Property, Percent
ing gas. As a result, a lower inlet gas heat input and
temperature are required which reduce fuel cost for op
erating the calciner.
Another advantage which is obtained by using the pres
Product Product
30 ent calcining process is the elimination of a low-tempera
ture drying period for the green briquett'e feed. In the
normal rotating kiln process,‘ a drying period of ap
proximately 6 minutes is required to dry out the green
briquettes before tumbling. This is necessarylrto pre
These results clearly show an improvement in the 35 vent the green agglomerates from spalling or degrading
Loss on Tumbling _____________________ __; _______ __
17. 0
Fines (-6 m.) Content __________________________ __
Ignition Loss
0. 45
tumbling strength of the calcined particles produced'by
into ?nes upon shock heating at calcining temperatures.
the present process as compared with the rotary kiln prod
uct. However, in addition to this unexpected increase in
strength, it is noted that the ?nes content of the product
period doesvnot seriously‘ reduce the average tumbling‘
of the non-agitated calciner is only 2.6% compared with
calcining time of about 15 to 25 minutes is used in the
It has been determined that the elimination of the drying
strength .of the calcined agglomerate product when a
the 12 to 15% ?nes present in the product from the
non-agitated perforate carrier-type calciner.
rotating kiln.
Another unexpected advantage is that briquettes con
taining shale concentrates can be calcined by the present
process but cannot be ef?ciently calcined in rotary kilns.
Shale concentrates are formed by crushing a low grade
ore containing small amounts of phosphate embedded
in the shale. The crushed product is then treated to a
The low ?nes content obtained by the instant process
makes it unnecessary to screen the calcined product
before it is proportioned to the furnace. As a result,
substantially no part of the calcined product of the present
process need be recycled to the briquetting or pelletizing
operation for additional agglomeration, thereby eliminat
?otation step‘ and the phosphate nodules separated from"
the residual shale. These phosphate concentrates are
then treated to a pellet‘izing or briquettin‘g operation using
ing a recycle load on both the briquetting step and on'
the calcining operation.
‘The unscreened nodule produced on a continuous non
water as the‘ binder". These briquettes, containing phos
phate concentrates, are then calcined and used as phos
perforated carrier also contains a higher percentage of
the larger screen fractions than does the screened nodule
from the rotary kiln. This latter product contains about
30% plus one inch (+1") material compared to about
phate furnace feeds.
The use of shale-concentrates is necessary in the fore‘
seeable future‘ in order to bene?ciate the phosphate ores,
to reduce mining cost, and to extend phosphate reserves.
79% plus one inch (+1") material produced by’ the
instant calcining operation.
‘In the pilot tests that were ‘conducted in the ?eld, it Was
found that- briquettes containing concentrates cannot be
The immediate result of obtaining a- large nodule plus a
drastic reduction in the ?nes content of the present prod
e?iciently calcined in rotary kilns even if the briquettes
are partially dried before calcination. The present proc
uct is improved phosphorus ‘furnace operation when
using this calcined phosphate as the furnace burden.
More speci?cally, the improvement in furnace operation
involves less severe and less frequent load ?uctuations
tial drying operation. Furthermore, the use of concen
trates in the briquettes does not change the requirements
65 of the gnate area of the calciner.
and smoother'all-arou‘nd furnace operation. In addition,
P4 loss in the slag when employing the large nodule
feed is about 52% lower than experienced with the
rotary kiln nodule. A similar reduction of P205 in the
slag is obtained with the large nodule as compared with
the nodule produced by the rotary kiln process.
és’s, in contrast, successfully calcines these shale concen
trate-‘containing' briquettes, Without‘even requiring a par
A continuous grate calciner of the type illustrated in
1, and having pallets 15 inches wide and 2
Other bene?ts also derived from using a calciner 70 FIGURE
feet long, was employed to calcine a bed of phosphate bri
having a non-agitated, non-perforated carrier are obtained
quettes 18 inches deep. An underhearth layer of lump
because of the diminished dust loss. The dust loss is
phosphate, having a depth of 4.5 inches, was used as the
reduced from about 10% of the dry feed in the rotary
lower section of the bed. The bed was calcined for 21.3
kiln, to well below 1% of the dry feed in the present
minutes at a temperature of 2235 ° F. with the gas ‘ve
process. In addition, an improved plant appearance and 75 locity in the calcining zone at 0.47 pound mol/rnin./ft.2
,of- grate. The calcined phosphate-briquettes 'were found
‘to have a tumbling strength of 85.4% and an ignition
loss of 0.31% -(dry~basis). Tumbling strength of the
Pursuant to the requirements of the patent statutes, the
principle of this invention has been explained and ex
‘underhearth layer was 88.8% and the ignition loss was
1.18%. .A material balance of the system is given in
Table I.
Table I
by those skilled in the art, such exempli?cation includ
[Phosphate material balance-B asis, dry feed]
empli?ed in a manner so that it can be readily practiced
ing what is considered to represent the best embodiment
of the invention. However, it should be clearly under‘
stood that, within the scope of the appended claims, the
invention may be practiced by those skilled in the art, and
having the bene?t of this disclosure, otherwise than as
10 speci?cally described and exempli?ed herein.
What is claimed is:
1. The method of producing a phosphate agglomerate
of Input
2, 249
24. 0
having a high structural strength which comprises placing
Briquette ________ __
7, 108
76. 0
9, 357
100 0
8, 427
90. 1
a crushed phosphate lump having a particle size of about 1A
15 to about 3 inches in diameter on a non-agitated perforate
carrier to form an underhearth layer, placing an overlay
of agglomerate phosphate feed on said underhearth layer
Total Input _______________________________ __
ll ________________________________________ __
Windbor Fines.
1. 1
Stack Fines. _ __
0. 1
Ignition Loss 1. -
6. 2
9, 113
07. 5
Unaceounted for __________________________ __
2. 5
9, 357
100. 0
Total Aeeounted f0r____
Material Et?eieuey (Spill and Wlndbox Fines). ________ __
to ‘form a feed bed, said agglomerate phosphate feed being
formed by the agglomeration of crushed phosphate ore
containing minor amounts of shale oil and capable of
passing through a 6 mm. screen, maintaining said under
hearth layer in proportions of at least about 16% of the
total feed bed depth, passing said feed bed through a
calcining zone, passing a heated gas through said feed
bed in said calcining zone and heating said agglonierates
to temperatures between about 2250 to 2500“ F., main
taining said feed bed in the calcining zone for from about
15 to 25 minutes, passing the resulting calcining phos
phate into a cooling zone and recovering the calcined
91. 2
1 Calculated from ignition loss content in feed and spill.
Other runs which were similarly conducted on a non
agitated grate at varying temperatures and calcining
times are listed in Table II. The conditions of operations
and the calcining strength of the resultant products also 30 product.
are listed in Table II.
2. Process of claim 1 wherein said heating gas con
tains oxygen.
3. Process of claim 1 wherein said heating gas is inert
to the phosphate feed material.
4. Process of claim 1 wherein said heating gas is passed
through the calcining zone between about 0.43 to 0.53
Table II
Test run
Brlquette Calcining
2, 230
2, 350
2, 400
2, 330
2, 380
Caleining Time, Minutes.
Total Bed Depth, Inches.
emp., ° F ___________ __ 2, 270
Calcined Briquettes-_-.
Gas Velocity in Calcining
0. 5
0. 5
0. 5
0. 5
Tumbling Strength of
Zone, Lb. mol/min/ft.2
of Grate ______________ __
pound mol/minJft.2 of carrier.
5. Process of claim 1 wherein said underhearth layer
comprises previously calcined phosphate agglomerate.
6. The method of producing a phosphate agglomerate
having a high structural strength which comprises crush
ing a phosphate ore containing 2 to 4% shale oil, screen
ing the crushed ore into 'a'?nes fraction which passes
through a 6 mm. screen, and into a coarse fraction hav
Phosphate briquettes were calcined on a non-agitated 45 ing a particle size of about 1A to about 3 inches in di
grate calciner in a bed 18 inches deep. The bed was
ameter, treating said ?nes fraction to an agglomeration
heated for 25 minutes at a calcining temperature of 2260°
step to form agglomerates, placing a portion of said coarse
F. The bed was heated by gas passed through the bed
traction on a non-agitated perforate carrier to form an
at 0.50 pound mol/min./ft.2 of grate. The temperatures
reached by the phosphate briquettes at various depths in
underhearth layer, placing an overlay of said agglomerates
the bed were determined using thermocouples. After the
calcination time elapsed, the calcined briquettes were
cooled and tested for tumbling strength. The tempera
tures which were reached at the various depths of the
ing said underhearth layer in proportions of at least about
16% of the total feed bed depth, passing said feed bed
through a calcining zone, passing a heating gas through
on said underhearth layer to form a feed bed, maintain
said feed bed in said calcining zone and heating said ag
glomerates to temperatures between about 2250 to 2500’
F., maintaining said feed bed in the calcining zone for
from about 15 to 25 minutes, passing the resulting cal;
cined phosphate into a cooling zone, and recovering the
bed and the tumbling strengths of the briquettes calcined
at those depths are given in Table III.
Table III
Top M 01 Bed
2nd 34 of Bed
3rd % of Bed
vB0tt%3néd% of
TgmF?" Pzigé'rlt T811113" Pg‘r'cseht T21?" Prerr'cséht T§l§?"1>gi§éi1t
2, 400
1 Tumbling strength.
2,150 l
calcined product.
References Cited in the ?le of this patent
Ahlmann ____________ __ Sept. 26, 1939
Marcellus ______________ __ Jan. 8, 1957
Kaufmann ____________ __ Aug. 18, 1959
Pajenkamp et al _______ __'__ July 19, 1960
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