US1985868A - Manufacture of cement - Google Patents

Description

Dec. 25, 1934. v E, J MAUs-r 1,985,868

' MANUFACTURE OF CEMENT Filed Oct. 21, 1931 3 Sheets-Sheet 1 WA TE}? WA 75/? MA TE R/A LS M/XERS 43 EQUA LIZ/N6 STORA GE INVENTOR (ERNEST J. MAUST- ATTORNEY E. J. MAUST I 1,985,868

MANUFACTURE OF CEMENT- Fil ed Oct. 21. 1951 3 Sheets-Sheet 2 SHALE LIME STONE FIG. 2.

LOW LIME HIGH LIME TH/CKENER TH/CKENER a 99 M00 10/ r402 SMALL FILL AND DRAW CORRECT/ON TANKS EQUAL/Z/NG T //09 STORAGE TANK/ INVENTOR, ERNEST J. MAUST'.

De1:.25,1934. y MAU T 1,985,868

MANUFACTURE OF CEMENT- Filed Oct. 21, 1931 1 3 SheetsSheet 3 LOW LIME a HIGH LIME THICKENER 75 TH/CKENER OVERFLOW FROM BOWL CLASS/PIER MED/UML/ME HIGH um: TH/CKLNER TH/CKENER TH/C/(ENER INVVENTOR RNST J. MAusr. BY

ATTORNEY PatentedDec. 25, 1934 I w;

. i Ac'rUREoF CEMENT i Ernest J. Maust, NewYork,.N. Y., assignorto V l, .Dorr c pany, Inc.,' New ration "of Delaware Application ctober 121; 1531, Serial No I s-cl ims; (o l f dPzsi The present inventionrelates to the manufac tureof Portland cement, with special reference to a method ofzand apparatus for controlling the composition of the mixture of raw constituents '5 as prepared by what is knownkas'the wet process;

I Since the raw materials used in the manufacture of cement, such "as limestone and shale, are obtained from quarriesornatural deposits, there is usually a considerable variation in :chemical composition of materials .robtained from different areas or'differentstrata of: the quarry, and whilepreliminary chemical control may therefore be efiected in a general waybyselective quarrying, such controlis at most a very rough approximation and must .be followed by suitable correction at another step or steps in the process. 1Heretofore thefnecessary correction has been made by running the ground 7 mixture from{ the mills into batch slurry mixers or correctiontanks from which catch samplesare taken and analyzed' Two or more such tanks thusvfilled and tested, are maintained with high lime and low lime mixtures which are drawn. oiiinsuitable proportions into .kiln feedbasins to'iform theproperi mix for burning. Such correction tanks' require fromrsix to eight hours filling time; which together with thetime required ,for sampling and: analyzing results in a lapse of ten or 'twelve' hours from the time the raw materials for that batch'entered the mills, with the disadvantage that such analysis lags much too farbehindthe mill feed topermit of any but a very general, control by variation ofjthecomposition of; mill feed; 7 I I 1 I i The chief object :of the present invention is to obviate this ,disadvantage'an'd provide a substantially continuous and more accurate .contr'olof the composition of the mixture-throughout the process. 'I'his object is accomplished through the uti-i lization of closed circuit grinding with repeated analysis of the mill; output at relativelyshort pe-,

riods, two hours orleSSf, While repeatedly correct" ing the milli feed toi compensate for, variations from the desired" mixture as indicated by such analyses and thus cause the composition of the mill output toaverage that desired together with the use of a thickener in a mannerto receive and continuously blend the 1 fluctuations I in composi-; tion of the milloutput wherebyeven relatively wide fluctuations if of :suflicientlyj short duration and properly average or "compensated, I will be smoothedout in thegthickener underflowp Further correction of the thickener underflow is ob tained through the practice of what may be termed closed circuit thickening, which comprises recirculating a portion of the underfiow through the ;thickener,advantage being taken of the variation 0f mixt'ure within dififerent' parts of the thickener by recirculating a'porti'on of the underflow via a zone in the'thickener containing a mixturerich in-the constituent needed forl correctfion. The amount of variation necessary for correction is slight because variationsin the thickener underfiow take the form of a relatively slow trend in which the timerequired fora variation sufficient to necessitate correction is inclusive of a period I sufiicient :for the 1 making of several analyses'of the underfiow.

-A' modification of the invention accomplishes this object of continuous and accurate control, through the use of closedcircuit grinding in combinationwith a plurality of 'thic'keners arrangedv to-coofier'ate with each other in the correction of fluctuations in" compositiorf-oi: the 1 mill 1 output. To this end variations of mixtures discharged from the grinding circuit'rich in lim'eare blended or averaged separatelyfrom the variations of mixtures deficient in'lime,*in high and low lime thickeners, respectively,and final adjustment effectedby proportionate blending of the underflow from the difierent thickeners according to the analyses ofsuchun'derfiows; There may be several high-lime and several low-lime thickeners toiprovide a number of grades of each of thetwo kinds of mixtures for final adjustment. There may also be one forrniore medium 'thickeners for receiving substantially correct: or medium mixture, or for receivingmutually compensating fluc- V tuations in Imixture of'such'short duration: as to readily blend into an average which will equalorsapproximate the desired composition.

"In distributing the mill output to the difierent thickeners itmay bediverte'd substantially all to one thickener :at a. time, I or split among two or more thickeners in portions difiering according to the kind of mixture being delivered at the time and the difference in kind of average mixture to be stored in each of such thickeners. I

i For final correction of the slurry to bring it to the'proper complex ratios'and fine adjustment of lime ratio before going to the filter or kiln, it is passed through a plurality of correction tanks connected in series and supplied with t the slurry and the necessary correction materials in a manner' enabling the: slurry to be detained and sampled, and'further corrected if necessary, at successive points en route to the filter or kiln without interruption to continuity of supply to the filter or kiln. I I I i Other objects and advantages of the invention will be apparent froma perusal of the following lime and low lime thickeners.

Fig. 4 is a fiow sheet showingthe'method of proportioning the thickenerfeed amdng'high lime, low lime and medium mixture thickeners.

Referring to the drawings in detail, and first to Fig. 1, bins 1 and 2 are for storing the main raw material such as crushed cement rock or limestoneior. ready, supply toa primary or coarse grindingball mill 3; as indicated by the flow line 4:2. The rock; roughly classified, is stored, inthe binsl and-=21 as highlime; and low lime rock, re: spectively, suitable feedcontrol means -such as the.- usual variable speed feeders, indicated at 5 and; 6, being. operatively connected; between each biniand. the: mill. for. proportioning the materials fed to the mill. @The primary {mill 3 is arranged, inplosed circuit 'with.-a=.Dorr classifier 7, from which theoverflow is :fed intothe bowl 8 of a Dorr bowl classifier 9 as indicatedbytheflow line 10. Suitable means are provided for adding water to th'e mill and cIaSsifier asindicated at 11 and 12. to maintain optimum= working dilutions. Where the-raw material taken from the. bins, 1 and 2 contains. a' considerable quantityzof natural fines, it may be. introduced directly into the primary classifier 7, the raw materialjbeing supplied in;a size sufficiently small-for :such method of .feed; The bowkclassifier 9. is-arrangedin closed circuit with a. secondary, orrfine grinding milll3, means being provided. forjadding. water to the bowl, 8

of; the classifier and to mill 13.asindicatedat' Hand 15, and ior adding clay or clay slipto the secondary. mill Bras. indicatedrat; 16. r

est dilution and. in a turbulent and well dispersed;

condition; :w I

The. thickener-.17 is. a Dorr. type' traction thickener of relatively large capacity in proportion to the. grinding apparatusitoj aiiorlda wide margin. of storage capacity. .It hasthe usual slopingbottom 22 along :whichthe thickened. slurryis raked by the usual rotating rake arms231and' 24' toward the :central 1 discharge. point. 25 to; the: underflow line 26.: It is also provided with the *usual central, annular, feed trough-27: which receives the feed from the-bowl 8 .as indicated bythe flow line'18.

and delivers it'intd. the thickener'below'theliquid level 128,)all as' is-Jwell understood in' the' art. The thickener overflow 29 may lead te -waste or be pas'sed' back into circuit in the usual manner asiwater supply tothe grinders' or classifiers. "A

-,-, Underfiow from the thickener is conducted by way of pump 37 to a surge tank 38 as indicated by flow line 39, the surge tank 38 discharging through flow line 40 and valves 41 and 42 into two or more slurry mixers 43 and 44, the slurry mixers in turn being arranged to discharge through regulating valves 45 and 46 into an equalizing storage tank 47. From the storage tank the slurry passes on to the usual kilns or other suitable burning means as indicated at 48, either directly or through filters. The surge tank .38

is arranged to discharge also into the returnv feed launder 30 as indicated by flow line 49. Suit.- able valve means 50 and 51 are provided in the flow lines 40 and 49, respectively. A sampler 52, preferably of the automatic type, is arrangedto take samples of the flow through flow line 40;

The apparatus is also arranged to facilitate the taking of samples, such as the usual catch-sample from the surge tank 38 asindicated diagrammati cally at 53.; Means are also provided for adding suitable correction materials to the contents of the slurry mixers 43 and 44 as, indicated at 54 and 55,-to effect any final correction necessary.

a In the operation of the system and apparatus,

shown in diagram in Fig. 1 to carry out the method of the invention, the raw materials, classified into two portions, one of high lime and one of low lime content, for'example, the limestone and shale, or limestone withlittle or no clay and limestone with more clay than that required for 'a proper mix, and properly crushed for grinding, say about three-fourths inch, are stored in the high lime and low lime supply bins 1 and 2 respectively, ac=

cording to their lime content, and fed therefrom 1 through the feed regulating means 5 and 6 into swThe hOwl classifier 9 isarranged to discharge,

the primary mill 3 along with the necessary amount of water supplied through conduit 11 to bring the contents of the mill to the optimum dilution or viscosity for grinding to the size de sired. The mill 3 being arranged in closed cir-' cuit with the classifier 7, discharges the ground materials thereinto, water being added from the source 12 to bring-the dilution from that of the optimum grinding dilution to the further dilution desired for classification. The classifier operates to remove the oversize and return it to the mill 3 asindicated by fiow' line 57. From the classifier 7, the fines with the bulk of the water,- overflow into the bowl classifier 9, from which theintermediate oversize is fed into a secondary or fine grinding mill 13 as indicated by flow line 58, which secondary mill, being in closed circuit with the bowl classifier 9, delivers its discharge into the bowl 8 of the classifier as indicated by flow line 59. Where 'there'is insufiicient clay or its equivalent in the raw material supplied from bins 1 and 2,

the required amount of clay may be added to the contents of the mill 13 as indicated at 16. Water is supplied by 15 to the mill 13 to bring its contents to the proper viscosity for efiic'ient grinding at the size determined upon. Where the ma'-' terial supplied from the bins 1 and 2 containsa considerable amount of natural fines, the feed therefrom may be run directly into the classifier noes-gees than" three-fourths 'inch and more; suitable for skilled in the art;..; 1'

proper dilution 'for final classification water added'as indicated at 1'4. At't his final and high est dilution the finished fines" overfiowing"thebdwl 8jarepassed into the annular feed-launder 2150f the thickener 17,flthe" mixture bei'ng maintained in sufiicient turbulence and dispersio'non its way past the sampler 20- to-the' thickener to 5 enable a substantially 'pe'rfect sample to be taken. Samples are thus' repeatedly taken and analyzed to ascertain thecoinposition of the thickener feed. The thickener feed passing"int o" thelaund'er 27 is distributed thereby' into the thickener-17in the usual manner. a i 3 The rake arms 23-24r'otate at the proper speed-to rake the settled material into the cen-" tral discharge point 25 and produce a slight-dis t'u'rbance as hereinafter described,butirisufiicient to preventthe desired decantation; The thick-""- aneu- (lisch'arge or underfiow passes onthrough the ii'nderflow line 26 to pump sv-rrom whence it is passed on through flow line 39 to thesurge tank 38;; rram" the surge tank the slurry is conducted on through flow line 40 to one of the-batchslu'r'ry mixers; sayil a sample of the slurry being taken: at52.'"From the slurry mixers 41'-and"42"'the slurryisdrawn into the equalizing storage tank 47', the batchmixers being alternately filled and drawn, one drawri while the other is being filled and its contents tested-and corrected to bring it to thefinal desired adjustment of complex ratios, such as ratiosof iron, silica, alumina and soluble salts From the equalizing'tank 47 the" slurry is ruiieither directly to a kiln for burning or-"first througha filter and then to the kiln.

the'dilution of the discharge from the =secondarymill 13 is only that necessary ;for optimumgrind-ing, viscosity is relatively low and maybe as owasthat at which the final raw product is passed' to" the kilnfor'burning; jIt istherefOre necessary to further dilute the discharge of mill- 13 for hydraulic classification in the bowl classie fler9;which dilution is effected as it isfed into thebowl 8 along with the overflow fromclassifier 'l w'ith additional water supplied 'at jl l'. Asthe an analysis of the composition of a sample, which time for exainple, may be in theneighborhoodof two to'four hours, and is sufficient to give the operator a definite accounting of the average bee irig carriedin the thickener. This timeghowever,"

is srfian compared with the time 1 r detention in:

thethickener, whose equalizing effect-on anyva riati'on in composition of feed is brought to a highgdegree of' perfection by rotatihgtherake;

armsat a speed sufficient to "properljrakejthe' thickened underflow to the point of'discharge with slight stirring, insufiicientlto prevent the I desired decantation or settling, and by having the capacity or "the thickener so large in propo'r' tion tof -the; rate of feed and intervalsofanalysisand eorrectiong-that the quantities of mixture'fed into" the thickener during suchsuccessive-periods aresprea'din-"stratasuflicien'tlythintobe inter-- arms-v This coordination of magnitudesof time; capacity of settlingz'one and rate of stirring 'an important feature ofthe' invention whichmakesfor-the attainment of my objectofimproved con trol'of'thecomposition o'f-the product? P Tl1e?underfiow from the thickener thus of a composition wh-ich is an "average of the total volume of mixture t ed into the thickener {foraim-1g period of-timerelative tothe time between corrections of such mixture, with the result thatany changein the composition of the uriderflow' takes the IOrmfof a gradual "trend requiring along-time; in the neighborhood of several days,- to? exceed-a permissiblemarginf which makes the taking of ordinary catchQsamples at 52* suflic'ient tof indi cate changes 2 in the trend in-timegtomake 'suit--' able correctionin thickener-feed to offs'et a-trend toward excess. Such offset'may be"accomplishedl by making a correction over-compensating ifor the reduirementf indica'tedby the a'na'lysis of the catch sample w'hich accelerates the trend 1 anopposite direction sufiiciently to prevent the trend;

rr m exceeding th permissiblevariationg A5 a specific; practical example' offeed control; and thickener underfio'w response, an analysis {at intervalsoftwo to four hours gives the operator? definite knowledge or what he is grinding and'a definiteaccounting of the average being" carried in the thickener. The raw mill leed for one pe==- riod is roughly adjusted tocompens'ate'fo'r dis-= crepancies of I the preceding period and the variations between 'the different periods are per mittedto average outin the thickeneri Sh'ort ire-- riod variations in the {mix going to' the 'thicken'er except they affectthe' averag'eof about 36 hours operation. Even when a distinct'and -per manent change is" suddenly made in the" nix' 'to the thiCkenelfl-the swing towardit th thickerler discharg isglfadfial. 1J1

In addition to the tendency to variation in dir ferent thin" strata; due' to slight variations 'i-n c'oinposition of feed for brief intervals oftimeffor: making -correctionsaccording' to the requirements indicated by analysis of f the samples of feed; which variations are substantially 'ofiset by the= slight disturbin'g effect of the -rakei mechanism on the relatively thin strata,=there is aslight varration *incomposition at-fdifferent intermediate zones in the thickener due to difference Eh'IIQSBlT-i' tling rate of the different-main constituents sot that even though -the' composition of the 'solidconstituents of feed, and consequently the com-J position of the solid constituents: of i the undemflow are uniform; there will: be a 3 zone near .1 the top ofthe. thickener where the composition will; be low in lime, aniintermediate zoneiwherethe;

composition ;will be higherin lime. and -a zone near the discharge Where the compositionofthe thickened mixture will be that of the .feed.

n; be clear whenit is recalled that with an ev -Y n ior liquids only all the solids in tile feed ill: pass out withthe underflow so that the co 1% tion of the mixture of solids in theundeifiowwfll beident icalgwith that ofvthemixtu'fe 6r solids in theifee d regardless of intermediate stra fication due to difie'renjc'e in settling" ate of differ n Stituent Solids,"

f This intermediate segregation page of to bring" about a nner and relativuy'more rapidly responsive control vofg-tlie composition ofv the underflow without having to wait for a. change inthe trend iii-response to anadjustment in feed;

by the practice of what'may be termed closed circult. thickening which; is. accomplished-through,

the. use of the, arrangement for recirculati'ng the underfiom; To this-end, aportion of the1-.under-- closed andathe valve 36, opened so as to direct.

the return from. surge tank.38 through flow line 49, valve-36 and pipe, 3ltoa-zone in the thickener near the central pointI of :thickener discharge, whereby the-vcha-racteruof the discharge is un--. changeddue tothe fact that in thiszone the, composition of. thematerialis the same as that being returned.

. r If the under iiowiislow lime," then. valves 34, and 36 are maintained closed andtvalveopened to; feed the return from feedqwellfillthrough valve- 35 and pipe 33' 1303.11 intermediate zoneqof relative: 1y high lime; constituenhthus displacing the highlimemixture withlow-limemixture with the result that .the movement of,the, displaced high lime mixture toward the discharge is hastened, while, at the same time? the returned low-limemixture. is: placed a little nearer to'the incoming high-limecorrective feed. I 7 0n theotherha nd, if :the underfiow is too. rich in lime, valves 35 and 36 are maintained closed. and valve 34 opened'to direct the return through Valve34 and pipe 3 2'to an upper zoneof low-lime mixture, thus displacing the lovv-limev mixture,

with a. high-lime mixture, with theresult that;

the movement of the displaced low lime mixturetoward the discharge i s-hastened, and at the same timethe returned high-lime -mixture is; placedv H. near the incoming low-lime corrective feed, thus.

fastening, equalization. v

The numberof; return; feed; pipes; such as 31,, wand, 33, and-the location of the zones in the. thickener towhich-they distribute thereturnfeed, may be ,variedaccording to the location of the;

different; zones of variation in. mixture, the shapeand proportions, of;the thickener, andthe: characteroi rawmaterialsgused.

From the surgetank 38, the; uncle is passed.

via flow lineg iogto. one of the batchslurrymixers, say 43, the.;valve 41 .being opened and the valve 42.closed for this purpose. When desired, the slurry passingintotheslurry mixersmay besam pled'at some point; in-theflow line .as at. 52 instead of'or-in addition tothe catch samples takenat'the'surgettank 38-: Final; correction for obtainingihe-final desired complex ratios,- iff necessary-{is accomplished in the slurry mixer byad'ditlon ot th'efproper amount and kinds of correc tion 'materlals', as'indicated at '55'jin a man ner well understood by those skilled 'in-the art. After theslurry 'mixer 43 is' filled, the-valve 41 is cioseaana" t e "valve 515 opene to reed the con-- tents of the mixer to the fequalizing storage tank 47, while the supply of slurry from the surge tank is diverted to,th e nextislurry mixerffiji'andso on according to the number of 'slurry'ffniixers. used.

From the storage tank 47 the mixture 'i'sflfed" ihi l -fi9 l i afii i tin ?ihew directly-or} first through; a: suitablefilter brother" suitable further dewatering-device.;-. M

The-long. period of settling in the thickener: the: substantial storage of settled slurrythat is carried above the discharge point; in'the thickener gives a discharge moisture that is substantially free from variation as long as the averagesettling: character of. the raw materials remains oonstant..-; Where the settling character of, the raw materials changes, the swing of moisture in. the thickener; discharge is very gradual .per mitting reliable readjustment of slurry-feeders or filters aheadof the kiln-so that constant,ton-- nage rates through the kiln can be maintained. Evenii the feeders or nlters'are notreadiusted. the; change: is 0 gradual that conditions of ir.-. regular depth of charge different parts of thekiln atthe same time are avoided and a uniformly burned clinker can. be obtained..-

It will be understood that the system-or plant and its operation as above described is not-dependent on the; specific elementary components: falling strictly within the definitions used,i n-., thedescription forthe sake of disclosure,;-f0r example, the term flow line is .,used to indicate any known or other suitable form of means or; arrangement for conducting, guiding or convey-5 ing material from one point to another,, such as a pipe, trough, conveyor, et c according to the, nature of; the material conveyed andother ex igencies of the particular phasein the process. Also the term valve is used to indicate any known or other suitable means for controlling the. flow of material such as any known form of valve,

. stopper, gate or the equivalent selected according to the kind of conductor or conveyer-in which it; is. used and the nature of the material whose flow is to be controlled. 3

The above described system of composition control is in practice substantially a one pointcontrol system, because the sampling and control of the thickener feed. islthe. only oneeessential outside of the occasional.checkingotthe trend of underflowcomposition and its. correc tion locally by, manipulation oithe recirculation through the thickener pending response to control of thethickener f eed. I Referring .now to Fig. 2, this shows a modifi cation using two relatively small equalizingstorage thickeners'lqand 'Zl instead of a single relatively large thickener- The grinding is here shown, as of the single stage type; but itis to be understood that it may alsobe of the double: stagetypeas shown in Fig l, Here the raw materials are stored in high-lime and low-lime bins 72 and. 73 respectively, according to their. composition, which bins are arranged to supply the. materialsv in proper controlled ratio, over-Qflow line '74 to the mill .75., A Dorr bowl-classifier 76 is. arranged. in closed circuit with the mill 75- through iiow lines 77 and78, withits overflow discharging through flow line 79 to the equalize ing storage. thickeners '70- 7l, ,an automatic sampler 80 of anyknown or other suitable type; being operatively associated ,with the .ifiow line 79 for taking composite samples therefrom. The; flow line 79 feeds the thickeners through branch.- lines- 31 and 82 provided with suitable valve eIements 83 and 84. Overflow from the thickeners is eturned to the bowl classifier overflow line 85.. Underflowfromthickeners 70 and 71 is conduct ed over suitable flow lines 86and 87. respectively, to. several (small, preferably 8-hour correction, tanks 88,. 89- and'90, selective distribution to the tanks being effected through branch conduits 91,,

92,%."8t0.;f controlledby valve elements .97, 98,1etc.

1 Go'nduitsw 103 a I etc., provided with: suitable "valve i ur Intcarrying out' the method with the system just described" above, thebowl classifier overflow is'divert'ed from fiowlline '79 overflow limellthickenerwl, respectively, according asto whether the analyses oftthe samples taken at80 indicate the overflow to 'be of -high lime I content on low lime' -content- The thickened slurry is drawn: from both thickeners '70 and '71 intoxthe correction tanks 88"etcJ, to fill them with mixture of the desired composition, which composition-is controlled by proper 'propo'rtioning of the mixturesf furnished by the difierent' ,thickeners' in accordance=with'thef lime content of suchmixtures shown 1 -by analyses of l the samples" taken at 11 1 and 1 12 1 Advantage is" taken of the in'-- herent i equalizing efie'ct of the; thickeners" to insure" against substantial change in composttion of thioken'er' under-flow in the time interval between the samplinghand analyzingy with the result that a very fine control of the-composition of the Inixturein the correction tanks is accomplished.

From the correction tanks the slurry is passed to the usual equalizing storage 109 from whence it is fed as required over fiow line 110 to suitable kilns not shown. To enhance the equalizing effect of the thickeners they may be operated periodically as slurry mixers by driving the rakes at relatively higher speed, preferably so operating one when the other is receiving all or substantially all of the feed. I

Where the high-lime and low-lime thickeners are of a size suificient only to handle a portion of total feed from the bowl classifier overflow,

for example 75 per cent, the arrangement of Fig.

3 is used, wherein the overflow, after passing thesampler is caused to flow through a suitable splitter 125 to split the feed to the thickeners in the ratio of 25 per cent to the low-lime thickener '71 and '75 per cent to the high-lime thickener 70, when the analyses of the samples indicates a high lime content, and in the opposite ratio when the analysis indicates a low lime content.

Where it is desired to use a still larger number of smaller thickeners, say three, each of a capacity sufficient only to handle say 50 per cent of the total overflow from the bowl classifier, the

' arrangement shown in Fig. 4 is used wherein the the high-lime thickener '70 and a tertiary or.

medium-mixture thickener 132, the splitter being arranged to dividethe feed equally between the two thickeners. The fiow line 127 is similarly arranged to conduct the feed through a suitable splitter I31 intet1ual sproportions r to the low lime valve element129 is closedlandthelvalve element a 128 opened to divert; the feed overflow: line .126 and through splitter 130. inaequakproportions to the thickeners and .132. .1 Likewise, when the analyses indicate: a 10w: lime content 1 valve ele'-" mew-.2128 is 1 closed? and: 129 opened to divert the feed through: flow line? 127 and splitter 131,. in equal proportions tothickenerss'fll:andxl32. '1aThe three thickeners will thus serve'as -equaliz-' ing storage zones for the :mixtures of three different characters,=' highivlinie, :1 low "lime! and medium; lfrom l which the 'f-underfiow may be drawn sin'properiiproportions for mixtures in the usual suitable tcorrecticn:,;=tanks,- in a mannerwhich will be well understood in the light ofthe description of Figa 23 2: J It willfbeclear fromther above that-thisphaSe of the invention involvingthe' splitting" ofthe feeduinl different prop'ortionsto different thickeners will be waried in its application according to the capacity of the 11 thick'eriers' in relation to the .volume of =feedsupply. For example; where three thickenersare used each of 'a capacity less than 50 per centof -the total supply,- a threeway splitter would be used, arranged'to divide as much of the feed as can be handled. by two thickeners; equally between one i of 1 the extreme thickeners and the tertiary-thickener;diverting the small remainder t'os the" other extreme thickenen the distribution bein'g alternated in relation to the extreme thickeners according to variations in the lime content ofthe feedl A -modification of this latter system of feed is to feed one of the extreme ,thickeners at full capacity (less than half the total supply) and distribute the remainder of the supply equally between the two remaining thickeners.

While certain specific modifications, embodiments and. applications of the invention have been herein shown and described for the purpose of disclosure, it is to be understood that the invention is not limited to such specific embodiments and applications, but contemplates all such modifications and variants thereof as fall fairly within the scope of the appended claims.

Having thus described the invention what is claimed and desired to be secured by Letters Patent is:

1. In the process of manufacturing cement by wet grinding, the method of controlling the composition of the finished ground mixture to be burned, which comprises passing the finished groundmaterial into a settling zone, withdrawing a portion of the settled mixture for said burning, analyzing a sample of the portion withdrawn for burning, and returning to the settling zone a portion of the mixture withdrawn, to displace a portion of the mixture in the settling zone having an excess of the element needed in the sample tested.

2. In the process of manufacturing cement by wet grinding, the method oi controlling the composition of the finished ground mixture to be burned, which comprises passing the finished ground mixture into a settling zone, withdrawing a portion of the settled mixture for saidburning, analyzing a sample of the portion withdrawn for burning, and using a portion of the mixture withdrawn to displace portions of those strata in the settling zone containing a corrective mixture and thereby accelerating-Lthei movement the displaced portion towardthe pointof-discharge.z 7 i 1 35: In a process; of; manufacturing cement includingasteprat which theiground raw mixture offlgive'n desired composition is detained in relativelylarge :volume, and portions thereof with-.

drawn:- from the zone "of? detention; the method of; varying the composition of the mixture withdrawnf-rom: the zone of 1- detention which comprises displacing portions." of v the .mixture in the zone of :detentiomhavingan excess; of .the element .wanting in: i the -mixture withdrawn with pontion-of'theemixture Withdrawn to disturbthe stratification of portions ofdifierent composition int-the zone .of.:detention.; 1 y :-iEn.,:a process of manufacturing, cement including a stepiati whichithe' ground raw mixture of given desired icomposition is:;detainecl in relatively; large volume, rand portions, thereof with? drawn from the zone of detention; the method of :control ling theqcomposition withdrawn from the zone;;of detention which comprises using a portion of-;:the;- mixture withdrawn tofldisplace portions of those-strata containing a corrective vmixture-and thereby accelerate the movement of such portions-toward .the'point of discharge. 115, -';I'he.process,of;makingcement which comprises segregating- .thelraw material into highlime-randlow limezsupplies, proportioning a mixtureof the said supplies to form a grinding mill feed;= r.injding thermill feed, hydraulically classitying the; mill discharge-passing the classifier v overflovw; to,; ai thickener, sampling 1 and analyzing the classifier,overfiow sampling: the thickener discharge, varying the said mixture of, raw materials tovary the composition of the classifier overflow as indicated by the hanalysis-of such overflow to compensate. for variation 'inathe thickener discharge as indicated by the analysis thereof, and accelerating the movement of oer-1 tain high-lime or low-lime portions of the thickener contents toward the discharge: to correct composition of discharge during time required to effect correction of thickener contents by variation of raw material composition, byvretumingor recirculating thickener underfiow to ,certain sludge zones in the thickener in a manner Sub-Q stantially as described. 1'

6. In the manufacture of cement by wet grinding, the method of controlling the composition'of theJfinished ground mixture to be burned, whichcomprises passing the finished ground mixture into a 'settling zone at a dilution greater-than that of the mill discharge, repeatedly diverting :a' portion of the feed in its passage to the settling zone and analyzing said sample, varying the composition of the feed to compensate foreany variation from the desired composition as indi cated'bysuch analyses, withdrawing the settled mixture; from the settling zone for burning, sampling and analyzing the mixture withdrawn, and controlling the composition of the mixture withdrawn to compensate for fluctuationsin the. composition of the feed by'returning to they sets tling zone a portion of the'mixture withdrawn to displace other portions of the mixture in the settling zone such as are rich in the element wanting in, the mixture withdrawn to accelerate the movement of such displaced portions tothe point of discharge.

' ERNEST l. MAUsTQ L

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