US2287437A - Low temperature carbonization of coal - Google Patents

Description

`llne 23, 1942. c, E, LESHER f- TAL 2,287,437

LOW TEMPERATURE CARBONIZATION OF COAL Filed Jan. 26, 1940 INVENTORS Carl El 65h61 john E.Go0de Peieoie'd June 23,1942 y y y 2,287,437

a UNITED STATES PATENT-OFFICE y ,Y .2,227,431V f un y Low- TEMPERATURE cARBoNTzA'rIoN oF CarlE.kLesher, Ben` von Heights, .and John v Goode, McDonald, Pa., assignors toPitvtsburxh n Coal Carboniz'ation Company, Pittsburgh, a corporation of Delaware Application Januaryzs, 1940, seal No. 315,118 i 1o crains; (ciauz-fs) This inve tion relates to the low temperature for commercial use-or in finely divided' particles 'carbonization of coal and particularly to certain which have nocommercial value. This., as we l temperature carbonization processyabove 1re 15 ytion has I existed over a considerable period the coal is plastic at a temperature not higher yi118 ilQthe interiorf the Steel yShell aS Well as -"One of "the prin vhas been of r undesirablypoorquality Iand has." -frial meets the steel shell of the retort the .teniimprovements in the manufacture of coal balls believehas been dueto improper control of by the low temperature vcarbo'nization process. the movement of thecoalthrough the carbone This process is the subject of Wisner Patents 5 iz'erand-:lackof proper heat treatment thereof Nos. 1,490,357, 1,748,815 r and 1,756,896 and in the preheating,.p1astic and` ball-conditioning Lesher Patent-No.2,080,946. Whilethe process zones. y 4 disclosed in osaid patents has proved commer` `It isvdifiicult for us to assign denite reacially satisfactory it-has been'found to vhave cer.- sons for the unsatisfactory results obtained by tain operating disadvantages which havegreat-l 1o the prior process and. we do not assume to 1y reduced the leconomy ofthe processandhave understand or state `fully all of such reasons. in some instances adversely aiiected-thequality It is, however, the fact that such process has of the product. 1 not given .uniform resultsand hasnot at yall In the manufacture ofv coal balls ,by the low times-been `fully ysatisfactory and, this condiferred to'iinelydivided coal is ordinarily Yiirst prior to the present.y invention. `The following thermodized or roasted infcontact with air, y explanation represents our present belief as to which results in partially oxidizing the coal, the reasons for the shortcomings of the prior andthe roasted partial1yoxidizedjcoal is then process. z t preferably maintained ina heated recirculating Certain observable` facts in .the prior process storage streamffrom which it iswithdrawn, are that iine. coal is heated to 600F..in the mixed with coke breeze and fed tothe carbon',- presence oi air ,and mixed withI fine coke, also, izer; With certain coals the roasting step: is preheated tol about. the same temperature; the omitted.' The carbonizer may assume various mixture ischarged into the upper end oany informs and invone embodiment constitutes an inclined` .revolving steel retort, externally heated clinedrotary retort.r The coal heated to about by, gases rangingdn temperatureffrom 1050" F. 600 F. is introduced into the,upper'e n'd `of gthe at the lower end of the rertto 850 cr 950 F. retort and'as-the Vretort rotates thevcoall works at the llppel'nd; the S1096 0f 'the :retort and its way downwardly therein. In the retortv the ,itsr revolving action convey this mixture of hot coal is first preheated-or raised kto a tempera- 30 coal` and cokebreeze along its length; hydro,- ture approaching its softening temperaturel ors carbon gas is discharged at either the upper that at which it :becomes plastic. vUpon further end or ,the-1 lowerA end 0f the retort and 10W heating :the coal becomes plastic, after which temperaturel colte in ball form is `discharged it breaks up andformsv'into lballsvas described at the lower end. ,I y, y, y ,A in the patents abovementioned. :Such balls Wlltakesl P1306 inthe revlvng'tlt in will'be referred to herein :as coal lballsT,- al; *,operationis, of course,impossibleofl direct'obthough they are of course; constituted by parservation. Wehave made observations of. the tiallycarboni'zed coal orseini-coke. 3 i interiors of retortswhich havev cooled voff subvThe temperatureat which-the coal becomes sequent toy operation over verving periods. v plastic vvaries withdifferentwcoalsbut is ordi- 40 From Athe character of the material "found nai-ily' between 700 and 800' E. 51.1111- any event, throughout thelength 0f .the reifill'` and adherthan-about v850" 11K-and upon further heat treate Athe lrielkirlse on theshell we .are able to reconment inthe inclinedrotary retorttne ooaibaus struct to some extentfthey reactions bv 'which are formed. The retort. is externally heated, coal balls `are made. The conclusions reached the. heating gases ranging in temperat'ur'el from from theseobservations have been. checked and about. io5o F. at Ione lower efndoi the retort to confirmed by tests mede in revolving retorts with 850 vto 950 F. at the vupper end, such gases `intermittent operation. s traversing the 'retort' from the lower 't'o rthe -Themxture 0fvr nely divided Coal and breeze upper endth'ereof. '1 50]'v charged into the Vretort at about, 600 lli. is, .as f

cipal disadvantages ofthe above mentioned, conveyed bythe revolving acprocess as carried' out heretofore 'has been the r tionof the inclinedretort` toward the dischargel non-uniformity of the product, which attimes end. Atl'the pointvwiiere the incoming matetaken form 'either in balls..whichare too large" 55 perature of the shell is about 800 F. The ternperature of the coal mixture is increased as it progresses until it attains the temperature at which it becomes soft or plastic. Yellow tar vapor is first given of! as it approaches the softening temperature. In the dry' state' the feed of coal and breeze does not stick to\l the steel shell of the retort. 'I'he hot, dry, nne coal and breeze flows almost as freely as a fluid. Its rate of ilow is rapid and the cross section of material is thin and its arc of contact with the steel shell is small. Because there is thus little tendency'for the material tov be carried up by the revolving action of the retort, mixing and turning is at a minimum vand segregation is promoted.

At a temperature above 700"v F. the coal softens and gives olf hydrocarbon vapors and distillation has begun. The exact temperature at which the coal softens is different for different coals, but the range is between 700- and 800 l". Distillation Vreally begins at lower temperatures. Some hydrocarbon vapors are given offat temperatures below 600 F. These vapors are condensable light oils and the vapors are white, whereas the vapors given olf at or about the softening point of the coal are yellow and condense to tar.

As the coal softens it becomes sticlLv. The whole mass does not melt into a fluid state, but some constituents of the coal soften, wet the surfaces of adjacent unsoftened or inert particles and bind the whole into a loosely coherent mass. In this condition its coeillcient oi' friction on steel is greatly increased. Insteadof a thin layer, loosely flowing, there is a thickening of the bed, because the increase in friction not only retards its ow down the retort but increases the length of climb up the arc of the revolving shell. The charge has changed from dry to wet. It is now in the plastic stage. The transition takes place quickly, probably in two or three-minutes.

Revolving action of the retort raises the mass and as it falls over it is kneaded and disintegrated into smaller masses, quite irregular in shape and size. The segregationinto small masses; that later become hardened as coal balls is not dependent on snow balling action; that is, the larger masses are not the result of small pieces rolling down a surface of material and increasingv in size as a snow ball gains in size as it rolls down a slope. The size of 'the masses that finally emerge as balls is determined by the agglutinating property of the coal at the time it reaches its softening temperature in the retort.

Transition from the dry state of the incoming feed, through the plastic stage, to the dry stage of senil-coke is rapid, of the order of 5 to` l0 minutes, perhaps for some `coals even less. The semi-Huid mixture is torn apart lby the revolving action of the retort into soft masses that quickly attain suilicient consistency to be individual pieces. Only under most unusual conditions do two such pieces coalesce or do'we flnd one ball rolled within another. Free to move along and out of the way of oncoming coal, these smaller masses of soft material soon become dry Vand solid with roughly spherical shape.

Size and structure of the coal balls are the most important objectivesin control of the process.

a prod uct with satisfactory structure will have a volatile matter content of between 14 and18%. Experience has shown that for any given coal (l) 'nie size of the pieces that emerge as low temperature coke balls is determined by the agglutinating .property of the coal at the time it reaches its softening temperature in'the retort, and

(2) The structure of the low temperature coke is determined v(a) by the character and proportion-of inerts mixed with the coal and (b) by the rate and maximum temperature of heating and the effective control of the rates and temperatures in preplastic, plastic and post-plastic ranges.

Proper application of heat to the coal is one ofthe problems encountered. Coal and low temperature coke are fair insulating materials. Haat transfer is slow under low temperature potential.

In this process the heat forprocessing is applied both'indirectly and directly. Indirect application is'through the'steel ducts of the roaster and the shell of the carbonizer. Heat transfer here is ef flcientbecause the coal is kept inV motion over the steel and because by mixing fresh surfaces are constantlytouching the metal. Thatiathe transfer of heat is emcientso long as the metal is clean. There is nodimculty in keeping the metal clean in roaster and storage apparatus but in the carbonizer, where the atmosphere contains condensable tar vapors, scale` accumulates on the steel and retards heat transfer.

One-factor determining the structureof the coal Iballs is the rate oi' application of heat and the maximum temperature in the carbonizing retort. Sufficient heat must be supplied to the coal f and breeze mixture in the carbonizer to raise its temperature to 'about 850 F. Higherv temperatures than this ordinarily simply serve to harden the surfaces of the balls and ldevelop shrinkage cracks. Unless the material in process is heated to about 850 F. theproduct will be too high ln volatile matter content and. too soft to handle .and its shatter index will be too low.

It is found that in the prior process coal fed into the upper end of the inclined rotary retort willtraverse the length of theiretort-some 100 feet-and be discharged at the lower end in l0 minutes. 'This movement is undesirably fast.

' The coal isnot carbonized to the proper extent.

The desired size of product is a range between one and six to eight'inches in diameter.` The structure should be dense, homogeneous and resistant to shatter. Ash, sulphur -and fusion point of ash are determined by the coal used.- The content of volatile matter will depend on the treatment in the retort. .It has been found that While hot it is soft and can be pressed or changed in shape. 'Ihe pieces do not assume the desired roughly spherical shape." I'he surfaces rof the masses are wrinkled vancl folded. f

The conical outlet of the retort retains a bed of material'the' length of whichdepends on the shape and slopefof the retort'. The bed consists of coke balls'at thelower and deeper end and coal at 4the Vupper end where it thins out to the minimum depth. Coal flows down the shell from the charging end in a thin stream until it meets vthe tail of the bed. The bed may.' be too long and deep at the lower end and theballs destroy themselves byvlong continual grinding and in fact cut the steel ,of the retort. y u We have discovered that by properly controlling the movement of the coal through the carbonizer the disadvantagesof the prior process maybe eliminated. The movement of the coal through thecarbonizer may bey regulated so that the coal is properlyvpreheated and vdoes not pile up against the coal in the plastic zone. Moreover, the vdepth of the coal in the ball-conditioning zone may be deslrably reduced and the ballsl ejected at the proper time. 'I'he quality'of the product is superior and the production of the carof the coal in the plastic nnulal passageway bonizing unit is increased.

We restrain the movement of the coal along the retort. While this is particularly'important in thepreheating zone we flnd that advantages are also obtained by restraining the movement and .ball-conditioning zones. We also find that it is of .advantageto at least partially temporarily 'segregate the coal which has not yet reached plastic state from that which has reachedplastic state. Preferably the coal in each of the three zones-the first or .pre-

heating zone, the'second or plastic zoney and the third or ball-conditioningv zone--is at least'partially temporarily segregated during the process.v

This segregation may be eife'cted by dams in the. i

carbonizer. Such dams, in addition to perform-J ing'theirsegregating function. also perform a re-v straining function to prevent the coal from piling up undesirably. The restraining function may also be performed by other meanssuch as baflies or, as we have termed it, rifling, arranged in various ways in the carbonizer.' At the lower or discharge end of the carbonizer the balls are preferably discharged throughan opening at a higher level than the position of the balls in theI carbonizer adjacent such opening and are ele` 29.' means (not shown) a stationary conduit I8. In-

ing the shell form -no part of the present invention such means are not shown, but it will be understood that the shell is' suitably supported to permit rotation therewithin of the retort 2. At its opposite ends the shell 8 has seals III which substantially seal the passageway 9.

There is provided-a furnace gases are recirculated through a conduit I5 to a fan I8 which discharges the same through a.v conduct Il back into the furnace II. The .fan I6 `also creates the draft for forcing 'the heating gases from the furnace II into yand through the passageway l9.

i At the upper end of the retortl2 there is positioned and maintained by suitable 1 supporting .tegral with the retort 2 is an internal skirt porueny is which at its' left hand end, viewing vated from such position to the level of the opening. This is preferably done by dischargelifters in the carbonizer. The combined result of the dams,v baiiies .and discharge lifters is to bring Figure 1, is of the same diameter as the interior of the retort and welded thereto and atA its right handend is reduced to substantially eifecta seal with the left hand end of theV stationary conduit I8, such seal being designated 20. The stavtionary-.clmduit I8 is perforated to admit va about a, nicety of control n the apparatus and y thermal and economic advantages.

f Other details, objects and advantages of the invention will become apparent as the following description `of a present preferred embodiment thereof and a present preferred'method of practicingthe same proceeds. i

vIn the accompanying drawing vWe have shown a present preferred embodiment of the invention and a present preferredmethod of practicing the y same, in which Figure 1 is a diagrammatic central longitudinalY cross-sectional viewthrough an inclined rotary carbonizing retort; and I Figure 2 is a transverse cross-sectional view taken on the line II-II of Figure .1.

Referring now more particularly to the drawing,4 reference numeral 2 designates an inclined rotary carbonizing retort which in its general shape andy structuremay be of standard design. The retort is designed for rotation in the direction of the arrow vA in Figure 2, being Asupported for rotation upon'rollers (cooperating with tires l carried by the retort. The retort is rotated by a gear 5 carried by a driving shaft 8 and meshing with-a ring-gear 1 carriedby the retort adjacent its upper vend. The means for supporting and rotating' they retort are shown purely diagrammatically and without a showing-of detail because the invention ydoes not reside therein. Suitable thrust means are provided to prevent the retort from moving longitudinally during rotation.

'I'he retort 2 is inclined as shown so that upon rotation the material therein will feed generally downwardly from right to left viewing Figure 1 due to gravity. The 'retort is surrounded throughoutthe major portion of its length by a stationaryshell 8 the body of which is of generally cylindrical shape. as is the retort', spaced from the retort suflivciently to provide an 9 between the retort and the shell. Both the retort and the shell are preferably made of steel.

and isk vcylindrical casing 2I containing a feed screw 22 through which the charge ofecoal and breeze is fed into the retort. vThe charge passes into the n I casing 2| through a conduit 23.v The screw 221s "rotated by a motor 2l.v

The lower or left hand end of the retort 2 may be either sealed or open to the atmosphere. The conduit I8 discharges the hydrocarbon gas issu- 'ing from the upper end of the retord through a water chamber 25 and a conduit 26to a suitable gasreservoir. The movement of gas throughthe conduits I8' and 26 maybe and preferably is facilitated by an exhaust fan (not shown).

Most of what has ybeen described above is of more or less standard construction. The present invention has to of the charge within Within the retort is aplurality of dams 21, 28, 29,

three dams being shown. lalthough the number' thereof may be increased or decreased. The particular arrangement shown, however, affords particular operating advantages. Each of the dams is of generally frusta-conical shape and is welded at its periphery to the interior of the retort 2. The dams are inclined generally. downwardlyof the retort as shown. They serve to retard or restrain the movement of thecharge along the retortwhereby to insure proper carbonizatlon thereof as above explained. The preheating zone As the means for support- 76 lof above referred to extends substantially from the point at which the charge enters the retort to the dam 21. The plastic zoneextends substantially from the dam 21 to the dam 28. The ballconditioning zone extends substantially from the dam.28 to the dam 29.. The portion of the retort to the left of the dam 28 may be considered as a of the ball-conditioning zone as the balls pass from the dam 29'and lthrough the zone to before they are discharged. The retort is also provided with bailles lor rifling 38. Each of such baffles may conveniently comprise a metal angle having the ends of its legs.

welded to the interior of the retort as shown in Figure 2. The baffles SI1-are disposed at an angle to the length of the retort so that upon rotation the'retort they exert a restraining force on the Il equipped withl one or more gasburners I2 for supplying heat do primarily with the control. the inclined rotary retort 2.v

charge tending to retard its downward movement in the retort. The bailles also serve to promote better mixing of the charge in the retort and to eliminate segregation, as upon rotation of the retort portions of the charge are carried up by the baiiles and ultimately fall back into otherportions thereof. The baflles also serve an important function in the portion of the retort to the left of the dam 28 in relieving the interior of the retort of the severe abrasive action of the balls. It has been found that without the protection of the baiiles the retort adjacent itsloweriend has become worn substantially time.

Discharge lifters 3| are provided at the discharge end of the retort 2, such liftels being in the form of hanged metal plates having the edges of their webs welded to the interior of the inclined nose 32 of the retort as shown. The flanges 33 cooperate with the webs of the plates so that upon rotation of the retort the lifters in effect scoop up balls which rise above a predetermined level at the lower end of the retort and raise the same to discharge them through an outlet 3l. The thickness of the bed of balls in the lower end of the retort may be controlled by the lifters 3|, as those balls which lie below the lowest point which the lifters assume during rotation of the retort will not be lifted and ejected thereby. The lifters serve an important function in controlling the discharge of the balls and the depth of the bed at the lower end of the retort.

The dams, bailles and lifters cooperate to bring about controlled movement of the charge through the retort. The depth of the bed is maintained as desired at all points along the retort and proper carbonization of the charge is insured. Although ballles 30 are shown only in the zones before and after the plastic zone and not in the plastic zone, bailles may in some instances be provided in that zone or bailies 'may be omitted elsewhere in the carbonizer as the particular conditions may dictate. y The character of the coal used is perhaps the major factor determining the particular arrangement of dams, bailles and liftthrough in a short ranged. -Also the baflles may assume various other forms while still accomplishing the desired functions.

While we have shown and described alpresent.

preferred, embodiment of the invention and a present preferred method of practicing the same,

tating said heated mixture of coal and breeze in an inclined rotary retort to form it intoballs and retarding the movement of said mixture along" the retort sufliciently to cause said mixture to move through the retort at an average speed substantially less than 10 feet per minute so that it forms into balls of reasonably uniform size for fuel by exerting at successive points along the retort extraneous pressure on surfaces of said mixture other than those surfaces which facer radially outwardly from the axis of the retort.

2. A process. of low temperature carbonization ol''coklng` coal toA form ballsl of f semicoke comprising heating to a temperature not substantially lo'wervthan about 600 F. and not substantially higher than about 800 F. a mixture of coking coal and breeze and tumbling said heated mixture and advancing the same at an average speed of less than 10 feet per minute to reduce the coal tor plastic state and continuing said heating, 'tumblingV and advancin to form said mixture into balls and retarding the advancing movement of said mixture suillciently to cause said mixture to advance at an average speed substantially *less than 10 feet per Aminute so that it forms into balls of reasonably uniform size for fuel by exerting at successive points along the advance Aof said mixture extraneous ,pressure on surfaces of said mixture facing genof said mixture in said chamber and retarding` the advancing movement of Isaid mixture before it becomes plastic sufficiently to cause said mixture to move through the retort at an average speed substantially less than 10 feet per minute so that it forms -into balls of reasonably uniform "size yfor fuel by exerting at successive points along the retort extraneous pressure on surfaces of said mixture facing generally in the direction of advance of said mixture.

4. A process of low temperature carbonization Aof coking coal to fonn balls of semi-coke comprising heating to avtemperature not substantially lower than about 600 F. and not substantially higher than about 800 F. a mixture of coking coal and breeze and tumbling said heated ,mixture and vadvancing the same at an average speed of less than 10 feet per minute to reduce the coal to plastic state and continuing said` tumbling andvheatingv to lonn the mixture into` balls and atleast partially temporarily segregating in the direction of movement 'the tumbling mixture which has not yet lreached plastic state. from that which hasreached plastic state.

5. A process o1'v lowtemperature carboniza'tion of coking coal to form balls of semi-coke comprising heating to a temperature not ysubstantially lower than about 600 F'. and not substantially higherthan about 800 F. a mixture of coking coal and breeze and tumbling said heated mixture and advancing the same at an average speed of less than 10 feet per minute to preheat said mixture in a first zone and reduce the coal to'plastic stateand continuingl said tumbling and heating to form the coal into balls in a second zone and at least partially temporarily segregating in the Adirection of movement the tumblin mixture in said respective zones. Y

6. A process of low temperature carbonization of coking coal to form balls of semi-coke comprising heating to a temperature not substantially lower than about 600 F. and notjsubstantially higher than about 800 F. a mixture of of coking coal 7. A process of low temperature carbonization of coking coal to form ballsof semi-coke comprising simultaneously advancing, heating to a temperature not substantially lower than about 600 F. and not substantially higher than about 800 F. and tumbling a body of coking coal mixed with breeze to reduce the mixture of coking coal and breeze to plastic state and thereafter continuing the heating of'said mixture and advancing and tumbling the same and exerting extraneous pressure at successive points along the retort on surfaces of said'mixturefacing generally in the direction of advance oi said mixture sutliciently to Vcause said mixture to advancev at `an average speed substantially less than 10 feet per minute 'so' that said mixture forms into balls-of reasonably uniform size for fuel.

8. A process `of low temperature carbonization to form balls of semi-coke comprising heating the coking coal mixed with breeze to a temperature not substantially lower than about 600 F. and not substantially higher than about 800 F.r to plastic state and thereafter forming it into balls by continuing the heating advancing the through the retort at an average speed maintaining a layer of substantial depth or balls at the lower end of the retort, elevating the balls inclined rotary retort whilel opening at a A of less than 10 of thev material in the retort to discharge the upper portion only of said layer through an higher level than the position of the balls in the retort adj acent such opening..

at the lower end of 9. A process of low temperature carbonizaticn` of coking coal to form balls of, semi-coke com.- prising heating the coking coal mixed with breeze to .a temperature not substantially lower'than about 600 F. and notsubstantially higherthan about 800 F. to plastic state and forming it into balls bycontinuing the heating and tumbling in an inclined Arotary retort while advancing the charge through the retort' at an average speed layer of substantial depth of balls at the lower end of the retort, elevating the balls at the lower end of the retort to discharge the upper portion only of said layer through an opening at a. higher level than the position of the balls in the retort adjacent such opening and regulating the depth the retort adjacent the discharge opening by said elevation and discharge. Y10. A process of low temperature carbonization of coking coal to form balls of semi-coke Vcomprising heating to a temperature not substantially lower than about 600 F. andv not substantially higher than'about 800 F. a mixture of coking coal and breeze to bring the coal to plastic state and tumbling the mixture in a retort while advancing the same at an tially less than l0 feet ,per minute so that it forms into balls, maintaining a layer of substantial depth of balls at the lower end of the retort and regulating the depthof the charge at the portion thereof where balls are formed by elevating and discharging only balls rising above the desired level. f

CARL E. LESI-IER. JOHN B. GOODE.

feet per minute', maintaining aV average speed substan-

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