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THESIS FOR DEGREE OF M. E.
19d@.
AN ANALYSIS OF

CRITICAL ECONOMIES
IN

PORTLAND CEMENT PRODUCTION,

BY ,
EARNEST A..RICHMOND.

 

Grand Raepide, Ntich.
THESIS
| AN  AMALYSIS | —
OF CRITIOAL ECONOMIES IN PORTLAND CEMENT PRODUCTION

   

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The manufacture of portland cezent has become a very
important industry in the United. States, in fact is next to
that of fron and steel in the oapi tal invested and value of
yearly produot. "Tn consideration of. this importance it is
remarkable that so very little information regarding the
process is available. Especially is this true of the
data bearing on operating costs. §$ Nearly ell of the plants
heve accurate systems of cost keeping and any change in the.
cost of an item in immediately noted and tts Cn u 8@. sought
out. Very . little attention is paid however to the.
relative cost of the various operations and as these costs
are carefully guarded it is difficult to tabulate enything
like average costs and results.

Port land coment is very exact ly defined by the German
Cement Manufacturers’. Association as follows:-.
Port lend cenent is a hydraulic cesenting saterial with not
less than 1:7 parts by weight of lime to 1 part by weight
of soluvlée silice, plus alumina, plus iron oxide; prepared
by fine erinding. To this oenent shall not be added nore

than 3% of other material for partioular purposes. The
maximun magnesia content shall not exceed 4% and the
sulfuric anhydride shall Rot exceed 2 1/2%.

108435

 
The elements that enter into. the composition of .
portiand cement are the most comaon found. on earth, viz,
calcium, silicon, aluainua, iron. In the United States
limestone, marl, olay, and shale are used and in the middle.
West a species of ohalk rook, and in the Bast a "cement Roo:
having nearly correct proportions. of the elenents.

In the manufacture.of the product there:are | four
important operations :-

(aj Proportioning the raw materials.

(bo) Mixing and grinding the raw materials.
(o) Burning mixture.to a clinker.

(a) Grinding clinxers to cenent.

The physical properties of the raw materials are so
varied that the necessary machinery for grinding can
hardly be reduced to a standard, as some of them are very
soft, sone of them are already finely divided, and again
the limestone and cement rocx my be very hard and refractoy
requiring. very different treatment.

In proportioning tne raw naterials tne formula in
post common use is: = > i.

Maxi aye. Calotum = 2.8. Line: de 1 caluah ae + tron. Oxide,

Pree lime in very injurious to cement as it causes it
to swell and cheox, therefore the proportion of line.
approaches this maximum as closely as experience snows
to be possible , the nearer the better. the cement as long
as there is no free. lime present.

Tne burning was formeriy done witn a vertioal kiln
similar to those in wnioh lise is burned. These nowever nave
nearly all been replaced in the United States by the.
rotary Kiln whion is inolined a few degrees out of tne
horizontal. The vertical xiln requried consideravle lavor
 

 

 

 

 

 

 

 

 

 

 

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Page 3.

ana did. not.deliver:a usiform product. The rotary «xiln dos
deliver a uniform product ana requires very little labor, —
it is not as economical in fuel. The aesign of tnese kilns

nave undergone rapia transformation, especialy Since Edison

- Obtained good results witn a.very long kiln. Up to the.

present time there nas veen no puvlished comparison of the
efficienoy of the various designs. .

BEST LENGTH AND DIAMETER FOR KILNS,

Edison's kiln was 150 feet long and had a diameter of
9 feet. It devoloped a capacity of 750 Barrels in 24 hours
with a fuel consumption of 85 pounds of coal per barrel.
The 6° x 60' kiln has a capacity of 240 barrels per day
and a fuel consuaption of 110 pounds of coal per barrel.

The following table -ives the lenght, diazeter, fuel

consusption, and heat units per oarrel ou various «ilns:-

Size. __ -Papact ty . _. Fuel Sigg. eds Te.USe 2 ow.

govezaxz00l8s_24.br8s consumption. per bbl... ___eeeees
-150x9 750 85lbs. coal 1240000

1254,8 | 751 9.25 gal. o11 1280000

100x 7 | 400 87,5 lbs. coal 1280000.

80 x 7 | 300 - .92,.5 ™ 1350000

60x 6 | 240 1190. «~~: 161.0000

 

 

Diagram "A" is a ourve plotted from the heat units per
barrel-and the len.,th of the kilns. The first isorease in
length gave very marked decrease in fuel consumption but
the amount drops off very rapidly after we pass the 100’
mark.
 

 
 

 
 

 

 

Page 4.

The heat lost by radiation is so very great tnat tne.
diameter of the <iln is also very. important. Diagraa "Bb"
isa ourve of the heat units and the ratio of.the length
to the diameter of the «iln.

The fuel used was coal pulverized to 92% through a
;00 mesh sieve. with the exception of the .25' x 8’ kiln
which used residuur oil from a refinery in the Miaale West.
This o11 contains many impurities ana does not burn quite
as efficiently as pulverized coal. Allowing, for this we:
have very smooth ourves for "A" and "B",

A very important element in tne study of tne rotary
xiln is its capacity. Diagram "OC" has been prepared to snow
tnat the capacity inoreased with tne lengtn up to a certain
point. The 125 foot xiln has the sane capacity as tne.
150 foot although the fuei consumption in tne latter is
slightly lower. As the ourve nas a very great slope as it
approaches 125' and comes bac« to the same capacity at 150'
it must fallow a path something lixe that snown oy tne.
dotted portion. Tne 225’ siln- 751 barrels as an average
and has a maximum record. of 1100 varrels per 24 hours.

This would indicate that tne »reatest capacity woulu ve
Odtaineu ve a xiln naving a length somewnere vetween 125'
and 150' lofige —

Diagram "D" is.the same capacity. records plotted .
acoording to. the. ratio. of .the length. to. the aiameter und
determines. that. a. ratio petween 15.6 and 16./7.should.ve:
correct for maxibus capacity. |

‘In consideration of . these diagrams. the. ideal <iln

geems. to ve.one.that has a length of .130' ~ 140' and a

Giameter of 8' 4". . Touis xiln -shoulu have a capacity of
about 1000 varrels and «a fuei consumption. of 86 lvs.. of.

coal per varrel.
 

 

 

   

 

 

 

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Page 5.

THE EFSECTS OF FINE GRINDING.

In an analysis of the effects of fine grinding of
raw material in preparation for burning. there are many
things to ve taxen into consideration am some of them nave
a very critical bearing on operation. fre nearer. the
raw material in its natural state satisfies the formula for
correct proportions the ooarser it may be fed into the «xiln.
In the process of burning.it is first necessary to drive.
off the volitile carbon, oxigen, sulfur, eto. Next each
group Of elements that form a molecule of ceaynt compound
shoula be associateu to,ether anda ‘fused into a oinder.

In a perrect cegent roc..this zrouping 1s already in
existence but in an artifioial mixture this grouping has to
ve performed meohanioally vy fine yrinding and tnorough
mixing. It is obvious. that much uepends upon the position
of the elements when they shoulda unite and the closer they
are orought tozgetner the less work (heat) is necessary to
perfeot the process.

| COST OF FINE GRINDING.

To establish the exact amount of grinding to reaon a
desired finesess will require a definite materiai to work
upone Inan effort to determine the amount of wora
necessary to reduct nard limestone to various aeyrees of
fineness a quantity of it was placed in a test tube will
ana at tne enu of 19 hours 75% would pass 200 mesh sieve,
at 21 hours 80%, at 23 hours 85%, and at 26 hours 90%.

Dia,ram "5" is a curve illustratin, these results and
Show that the time will vary nearly witn tne fineness

witnin the linits Ziven.
 

 

 

 

 

 

 

 

 

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Pare 66

A tube mill veing delivereu a harn iimestone mixture of
.tne same class, ail of wo icon passeq a 20mesh sieve and 45%
through a 100 mesd sieve, ,ave. the fellowing capacities:-
87% througn 100 meSh, 30 barrels per hour: 92% fine, 16.
oarrels; 99% fine, 5 varrels. .The avera,e for a Urirfin
mill on the same material was 87% fine, 9 barrels; 92% fine,
4 oarrels; 94% fine, 2 barrels. These capacities are shown
by diagrams "F" and "u".

All of these diagrams indicate tnat for eaon aezgree of
fineness obtaineu a definite amount. of grinaing must oe.
done. The tuce mill reqireu avout 80 HP. to operate. it
and tne urlifin mill avout 30 horsepower. From "F" ana "u"
the following tavle nas veen preparea which shows. the.

horsepower nours per varrel for.each and tne average.

Fine Capaoity Horsepower hours Average HP.Hours.

_ wie uriffi ait | uri ft fan . oe .
Mil MATE asa -

99 5 "16 26.3

,9816. 13. 21.0

,971 7.6 10.5 17.0

.95110,3 7,8 | 10,6

-93114,.0 | 3 5.7 10 7.8

92/16.0 | 4 5.0 7.5 6.2

91118.3 5 4.4 6.0 5.2

90 | 21.6 6 3.7 5.0 4.3

89124,4 7 3.3 4.3 3.8

88 |27.2 8. 2.9 3.475 3.3

87/30.0 | 9 2.7 3.3 3.0

 

 

 

 

 

Diagrams "H" and "I" are plotted from the horsepower
hours for tne tuve mill anu for tne criffin mill.

"UO" is an averace curve and shows tnat the horsepower nours
will increase very fast for reductions finer than 92%.
 

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Page 7.

FUBL SAVED BY FINE GRINDING.

IT has already Veen shown that less fuel will be.
required for burning fine particles. than for coarse ones.
This fact is well «known but. there is no published record
of just what saving ia effected. The remarxable fuel
consurmption of tnree «<ilns operating on a mixture of dry
warl and clay iS very ~,ood proof of this. The marl when
Separated frow the insoluble matter, mostly silica, will
all pass 200 mesh sieve. The yearly average of tnese kilns
(60' x 6") was 65 pounds of coal per barrel. The alupina-
iron ratio was very nigh ana does influence this low record
very materially but does not account for the faot that this
fuel consumption is at least 35% lower tnan it woula be on
the average Milieu raw rock. |

Again, a raw matorial avera,ing /2% on 200 mesh sieve
and 85% on 100 mesh required a temperature ot 2936 de,rees
Fahrenheit to properly burn. Tne same material wnen °
reyround would avera,e. 98% on 200 mesh sieve and required
a temperature of but 2687 de-rees, or 246 lower to do the
Same WOrke

Taxing 400 pounds of oclinxer.to the varrel ana its
Specific heat to ve .25 it woula represent a saving of
100,000 B. T. Ue. per varrel in the heat supplied tne olinxes
The efficiency of tne rotary xiln 1s avout 27.5% henoe the
actuai saving in heat units is about 364,000 3b. T. U.

A general average of the heat units required per barrel is
about 1,360,000 B. T. U., nenoce a saving of 26.8% in fuel
can be made by regrinding. this material.

Observations of the fuel oonsumption of 125° x 8'
kiln gave for 95.5.% through a 100 mesh sieve 1280000 3. T.U
while 1390000 B. T. UJ. were required for 93 1/3% fine, and
2420000 B. T. U. for 87% fine.
 

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Page 8.

- The material and. other conditions were. tne same. throughout.
The figures were taken from tne daily recora of tne mill ana
each 13 an averaze value,.tne waole extending over a period

of several montns. .

Diagram "K" is plotted from these records.
airect from the diazram we can ,et the neat units saveu for
each increaseu per cent of fineness and yy using the value
of 14,6000 5. T. J. per pound of coal, its coal value can
This value diviaed by tne efficiency of the

Reading

be obtained.
<iln gives the actual savin; of coal effected.

Pulverized coal costs delivered to the kiln avout
$7.00 per ton and on tois basis tne money value of the
Saving for eacn degree of fimeness can be odtained.

Fine 3s. FT. U. Difference Coal Actual Saving. ©
a sso9snceecerscesseeeesee=== fee -G0alde-------=-=2
87 | 2420000 | | |

88 | 2130000 290000 | 19.9 72.5 $252
89 | 1930000 200000 | 13.7 50.0 0175
90 | 1770000 160000 | 10.9 40.0 140
91 | 1630000 140000 | 9.6 35,0 122
92 | 1820000 110000 | 7.5 27,4 .096
93 | 1420000 100000 | 6.8 24.7 . 086
94 | 1350000 70000 | 4.8 17.4 2061 |
95 | 1290000 60000 | 4.1 14,9 052
96 | 1260000 30000 | 2.1 7.7 027
97 | 1230000 ,

 

 

 

 

The cost per horsepower hour will average about $.015
and this figure can be used in computing tne cost per

barrel for each increased percent of fineness. The cost of
maintanence will also increase pei barrel as tne output is
restricted ana snould be considered. In the case of the
tube mill this cnarge will be about °1155 per year or $.13

per mill hour. Prom "F" oan be obtained the oapacities
 

 

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_ SS SECTION PAPER. 10X 10-1 INCH.
 

Page 9.

per hour for each peroent.of fineness. Dividing the
maintenance charz,e per hour oy tne capacity, tne maintenance
charge per barrel for tne various fineness of product is
ootained from wnich. the charge for each percent of inoreased
fineness can. be determined. All.of these steps nave veen

combined in the following table:-.

 

 

 

 

 

 

 
 

 

A - % Fineness tnrough 100 mesh sieve.

B ~ Horsepower hours per barrel.

C —- Power cost per barrel.

2 - Maintenance and depreciation cost per pvarrel.
B - Total cost of yzrinuing per parrel.

F - Increase cost of grinding per %@ Fineness.
G - Saving in fuel per each increasea % Fineness.
A BC. _D E Fr G

87| 3.0 £045; .0040 | ,0490

88| 3.3 [2050] 2.0055 | .0555},0065 | .252

9| 3,8 |.058| .0065 | ,0645|,0090| .175

90| 4,3 |.064| .0070 | ,0710/.0065 | .140

91] 5.2 |.078| .0075 | .0855].0135 0122

92| 6.2 |.093] .0081 | ,1011].0156 | .096.

93] 7.8 £117] 20108 | .12785.0267 | 086

941 8.7|.130] .0130 | .1430f.0162 | .061

95] 10.6.159| .c151 | .174160311 | %052

96} 13.3,.200|] .0180 | .2180F.0439 | .027

97) 17.90.255 | .0226 | .2776) .0596

98 ]-24.0,315 | 0240 | .3390].,0614 |

-99126.3 |,3941 .0260 | .4200|;c910 |

Diagrams "L" and "M" show the relative increased cost
of each percent of fine griniaing and the corresponding

aecrease in the

cost in fuel.

They meet at a point of

fineness of about 96% and as tne curves meet at a very wide
angle it iS apparent tnat for tne conaitions considered this
is the most economicai point to wnich fine grinding can 0e

carried.
Curves "A" and "Bb" show tnat very little saving in fuel
consumption nged be looked for by increasing the length of
_tne kilns more. than 150 foet or by a length to diameter
ratio of more than 17. Mechanical difficulties also vecome
very nard to overcome. Increasiny the length and also the.
len.th to diameter ratio increases the capacity very rapidly
up to a length of 125" and a ratio of 15.7; but vetween this
a point where length is 15C' and ratio is 17 there seeas to.
be no increase in capacity and very little r:1eduction in fuel
consumpti on. - Should the 125" kiln record ve an exceeding
good one and the 150' a poor one the ourves might pass
between them and still have ,reatly inoreased values for

zreater ratios and longer kilns. By special appliances it
is possible to xeep tne f. 25" «silns open and free from rings

-of material but it more than provavle that these diffiacultie
<eep down the capacities of the longer <ilns. Hence a xiln
135! long and 8' 4" shoula neet all conditions imposed on

it petter than any other and shoulu have a capacity of about
1000 barrels per day and a fuel consumption of less than

86 pounds of coal per barrel.

Tne data on fine grinding are avera,es of long perioas
on haru limestone, olay, or shale anu snould be conclusive
for this natevial. For otner raw material it may ve
necessary to mace Slixht Onanges wnich can ve determined oy
Observation of tne sp@cial case and corrections made by
Similar process of calculation. the first cost of fuel
will vary between very wiae limits as will its heating value
and will effect the cost of burning and power cost vut
increasing or decreasing to,ether as they will, the results
will be compensating to a dezree. Tne curves for fine
xyrinding all snow that the ,reatest reduction of particles
for power applied ta«xe place between certain limits anu |
woula inuicate that much can be expected by grinding in rely
Pare 11.

where a tineness of 92% or finer is desired.

Another very important consideration of fine zrinuing
it .that tne finer. the material is ,round the more perfeotly
the correot formula is set up in each molecule, maxing tne
cement more uniform, of much zreater stren,thn, and its
Soundness is assured to a much ,reater ue, ree.
eT ES eS

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