US1716572A - Process and apparatus for burning lime - Google Patents

Description

June 11, 1929. c. J. WRIGHT PROCESS AND APPARATUS FOR-BURNING LIME 3 Sheets-Sheet Filed Aug. l5 1923 s sheets-sheet 2 c. J. WRIGHT PROCESS AND APPARATUS FOR BURNING LIME Filed Aug. l5

June H, 1929.

June ll, 1929. C, 1 WRIGHT L'ZG'Z PROCESS AND APPARATUS FOR BURNING LIME Filed Aug. 15, 1925 3 SheetSv-Sheel', 5

Patented June" Il, 1929.

UNITED STATES cARL J. WRIGHT, O E WEsT NEW BRIGHTON, NEW YORK, AssIGNoR, :BY IIEsNE AssIGNMENTs, To cOMBUsTION UTILITIES CORPORATION, OE NEW YORK, N. Y.,A

CORPORATION OE MAINE.

PROcEss AND ArRARATUs EOR BURNING LIME.

Apucation med August 1 5, 1923. serial No. 657,492.

-Thisfinvention relates to the manufacture of lime and carbonio acid gas from carbonates in a continuous manner.

A large part of the lime made' in this coun- 5 try is calcined in a kiln either in direct contact with the fuel or with the fuel gases,

. so that. the ultimate products are moreor less impure. In such a process the gaseous products of combustion ofthe fuel. such as nitrogen of the air used for combustion, sulphur dioxide 'and ammonia become mixed with the carbonicacid'gas, giving a gaseous product With a low carbonio acid content, which is not eflicient for use in soda ash manufac- 15Ature, and is too `impure for other purposes. In addition to giving impure carbonio acid gas, this method of burning lime is expensive Y and inetlicient, and is diiicult to-control, often 'resulting in underburning or overburning a -part of the lime. Moreover, the solid and liquid products of decomposition of the fuel,

such as ash, tar and clinkers arewithdrawn in considerable-amount mixed With the lime,

i) r resulting in an unclean lime 'with 4poor slacking qualities. Various attempts have been made to :overcome these diiliculties by employing other heating means, 'in particular icurrents of lsuperheated air or superheated steam, but' it isnot known that anyof these ao. attemptshave resultedin aprocess -Which 'could be adopted in .general commercial practice.

The'primary object of tlie present inven.

tion iis to provide a process for burning lime by which lime may be eici'ently and economi# cally produced and comparatively pure carbonio acid gas may be obtained While burning lime.'

'Another object ofthe present invention isl l r 40 `to provide a' process for burning lime by which a minimum 'amount of heat is lost due to the removal of highly heated products from theapparatus in which the process is carried out. v-

Another object of the present invention is to provide a process for burning. lime by which the temperature'will be accurately controlled so that the lime will :not be under or over burned.

' Another object ofthe present invention is to provide acommercially practicable -process for burning. lime by Which the decompositionl temperature of the lime is obtained solely by heat transfer from a chemically inert gaseous mixture.

A further'object of the invention is to provide an apparatus in which lime may be eificiently burned and the above process carr1ed out. With these and other objects in viewthe invention consists in the improved process and apparatus for burning lime hereinafter described and claimed.

The various features of the invention are illustrated in the accompanying drawings,

in which s Fig. 1 is a more or' less diagrammaticalliliv view in side elevation with parts in-section'.

of a lime burning kiln .and 'the auxiliary gas treating apparatus embodying the preferred form ofthe invention.

Fig. 2 is a view in plan partly in section of the apparatus shown in Fig. 1. Fig. 3 is an enlarged horizontal cross `sectional view of the lower portion of the kiln showing in plan the mechanism for supf porting a charge column of limestone in the kiln and for removing charge the foot of the column.

Fig. 4c is an enlarged 'view in Kvertical section of the charge supporting and discharge mechanism' shown in plan in Fig. 3, taken on theline 1 -4 of Fig. 3.

The process and apparatus ofthe present invention is so designed that lime may be economically vand continuously4 burned and substantially pure lime and carbonio acidgas apparatus any gaseous medium preferred may be superh'eated to the temperature desired vfor carrying on a chemical reaction. According to the preferred form of this invention a mix-v ture of carbonio acid gas and steam is superheated to :1t-temperature of about 1900o F. tov

material rom 'may be obtained. By the use of an improved that the lime will not be under or over burned,-

and the resulting' gaseous mixture composed through a condenser to removethe. steam, v

leaving substantially pure carbon dioxidev of carbon dioxide and' steam can run- Y ratus.

' production of lime and carbonio acid gas at a considerably lower cost than has heretofore been realized in commercial practice. n w

To carry out the improved process inthe apparatus illustrated in the .drawings,lime stone is passed in -a column downwardly through a shaft kiln 10, Fig. 1. The limestone is dropped from a bin 12 into a charging hopper 14 located at the top of the kiln, by opening a gate 16 on the bottom of the bin. The gate 16 is then closed and a gate 18 at the bottom of the charging hopper is opened, permitting the limestone in the charging hopper to flow into the top of the kiln. The charging operation is an intermittent one, and the gates 16 and 18 are so operated that while one is open the other will always be closed,

in order to prevent the escape of gases `from the kiln into the bin. The limestone is sup#A ported in the furnace in a '.ertical column, and is continuously advanced downwardly through the column, In its passage through the furnace the column of lime is passed through three distinct zones,namely, a heating zone 20, in the upper part of the shaft, a hot mid zone 22, and a lime cooling zone 24 in the lower part of the shaft. The limestone is decomposed in the mid zone 22 of the kiln, at a temperature of from 1400o to 2000o F., into lime and carbonio acid gas, according to the following reaction:

' The gate 26 is shown as a revolving trunl Y has been previously heated by the heat of combustion of producer gases whichl have been generated in some form of Stoker.

The Stoker indicated as 28 in Fig. 2 may he yan ordinary coal furnace, a gas producer, a

. gas burnerfor an oil burner.

' hot conduits In this Stoker'Y the cheapest type of fuelcan be burned, and the products of combustion are sentthrough 0 or 32, to one of a pair of regenerators or' reheaters 34 or 36, as shown. The circulati ,n of the hot gases is controlled by hot valves x38 and 40 which are especially designed to withstand high temperatures,

and exhaus'ters 62 or 64.

and preferably, arrangement made so that ,the pressure on the opposite sides of the valves issubstantially the same, so that there is a mmlmum leakage. When one regenerator 1s `being heated by the hot gases, the other regenerator which has previously been heated.

is used vfor preheating carbonio vacid as and steam. The hot, furnace gases a ter passing through either of the regenerators.

are drawn through conduits 42 or 44, provided with hot valves 46 or 48, into feed water heaters, 50 and 52, and from the feed water heaters they are 'exhausted to the atmosphere throughstack pipes 54, 56 or 58, 60, The feed water heaters have water pipeconnectionsl v66 and 68 with a steam boiler 7 0, and a part of the hot gases from the stoker are drawn through a conduit 72 to be utilized in generating steam in the boiler, at substantially 212o F. and atmospheric pressure. The only pressure built up in the boiler is that required for positively controlling the circulation 'of steam. v

Steam from the boiler is admitted into the lower endof the kiln byl means of pipes 74 connected to ahorizontal coil 76 placed a short distance above the discharge gate., said coil being perforated'in such a way that the steam will be evenlydistributed throughout the body of lime in the-lower part of the kiln.

To support the column of lime and to insure an equalized downward movement of the charge throughout the kiln, as well as to aid in evenly distributing steam throughout the body of the charge, a grate is set in the lower part of the shaft just above the steam -coil 7 6j ln its preferred form this grate may consist of a` series of hoppers 78, that is six peripheral hoppers andra central hopper, formed respectively by the opposed sloping sides of six uniformly spaced and peripherally disposed, stationary tent shaped supporting members 79 and a centrally disposed ring shaped member 81 of conical cross section, connected therewith, with discharge openings80 in the bottom of each peripheral hopper through which the lime passes from the bottom of the column onto aseries of movable platforms 82. The platforms 82 are given a reciprocating motion by means of water operated engines 84, to discharge the lime from the platforms into a hopper 86, forming the` bottom of theshell. A more complete description of this discharge mechanism will be found in the British patent to Henry O. Loebell, N o. 216,488,6May 23, 1923. The amount of steam admitted into the bottom of the charge through the perforated coill 76 is controlled so as to cool the lime at the discharge gate to a comparatively low temperature, that is, to as low a temperature as is consistent with' the production of quick lime as distinguished from slack lime at the base of the column, or in pther words to a temperature above the dissociation temperature of calcium hydrate. 'In burning lime'-a stone to recover lime and carbonio acid gas, the reaction which takes place is reversible in cases where an excess of carbonio acidgas may come in contact with the lime. The introduction of steam into the bottom of the charge 0drives out any carbonio acid gas which might be carried down with the lime,.pre vents any reversal of the, primary reaction and insures the complete burning of the lime. As the steam rises toward the high tempera- 'ture zone it takes up heat from the descendused in the present process for heating the mid zone of the descending body of limestone to a temperature such that complete decomposition takes place, consists of inert gases, and is preferably composed of about CO2 and 30% steam by Weight. The mixture of carbonio acid gas and steam is forced by a blower through the hot brick .Work 88 of one of .the pair of regenerators or preheaters shown, while the otherregeneratoris being heated by recovering. the heat of combustion of furnace gas therein. When one regenerator has been cooled to the minimum Working temperature which' is desirable, by passing carbonio acid gas and steam through it, the

balance. .After passing through the oftake the mixture of gases is divided at the T 104, a partbeing reoirculated through the blowere102 and pipes 106 or 108 through the regenerators and kiln to maintain the high tem era- 70,

ture in the mid portion of the body of ime, While the remainder of the gas mixture is run through a tubular condenser 110, in which the steam is condensed and from which the practically pure carbonio acid gas may be passed throughs a fan .116 and discharge pipe 117 to soda ash absorption towers or to other use in the arts. water from the tubular condenser may be led )to the feed water heaters by pipes 112 and .80

114, and from there to the boiler, vif desired. The amount of gas passingthe otake which is recirculated, and the amount which is Withdrawn through the condenser, is gov-v erned by the speed of the exhauster 102,*and

the speed of the fan 1,16 in the condenser circuit. Y

JThe shaft furnace 10 is arranged vto support the fuel in a vertical column in suc a manner that the limestone may be1 continuouslyad- 90 having a top cover. consisting of the charging 'hopper 14 and the bin 12,.With'theintermit. ltently operating charging valves 16 and 18, and a Alime discharging hopper 86 at its circulation of the steam and CO2' mixture is lower end in which the discharge gate 26 is stopped andthen started in the other regen.

erator, which was being heated during the time when the first regenerator was used for heating the mixture `of steam and CO2. In-

- into a, passage 98 surrounding the fuel column, by means of which it is evenly distributed throughout the cross-section of the column. `Here the mixture 'of blast gases is joined by the steam which was introduced at the bottom of thecolumn of lime, and by the carbonio acid gas produced in the decomposition of the limestone. As this body of mixed gases asoends toward the top ofthe kiln it is cooled by a heat transfer with the Vbody ofl descending limestone in the heating zone 20 so that the limestone is gradually heated as it approaches the high temperature zone 22 of the kiln, and the mixed gases as lthey approachv an offta'ke pipe 100 at the top v of the kiln are gradually cooled to a located; The refractory lining 120 is pref- 100 erably positioned in all the inner. surface-of the shell which comes into contact with the heated limestone. The shell and lining are both so' constructed as to graduallyinorease the cross-sectional area of -the column of lime- 195 stone as itadvancesto the mid zone of the furnace, in order that it may expand into a larger spaceto be in an openv condition to assist the cross blast inI penetrating through the column.`

'.l`he.rei.ractoryl lining is constructed so as to 110 form a flat fire arch 122 immediately above the blast necks 90 and 92thus forning the. passage 98 between the descending body of the( charge and the lining immediately beneath the iat arches around the whole circumference of the shaft, through which the hot gases f will distribute themselves equallythroughout the central section of the descending charge.

theqross sectional area-of the column of lime 125 as it descends from the hot mid zone toward the discharge, so that the calcined lime, which has lost in volume during thel burning process, is compressed gradually' as vit cools, bythe weight of the descending'column, and'this 130 The condensed steamand the These Hat arches confine the cross blast of superheated gases to the zone 2.2 and prevent a direct application of the hot'blast compression of the burnt lime assists the cooling and cleansing action of the steam ris ing from the coil 76.

The regenerators or preheaters 34 and 86 for preheating'the inert blast gases and for absorbing the heat of the stoker lgases preferably consist of cylindrical gas-tight shells which have refractory linings 124 covering their innersurface. The heat recuperation of the gases in the i'egenerators is'efl'ected mainly by means of a series of checker bricks 88 which are supported on grates positioned near the bottom of the shells and extend to the level of the iiues 30, 32, 90 and 92,. Hot valves are positioned in the Stoker conduit, the blast neck, the gas circuit line fromithe blower, and the combustion gas conduit between the-regenerator and feed water heater,

fractory material, which is connected to a head, and is moved through slots in the conduit in which the valveA is located, by hydraulic power.

Incase no supply ofcarbonic acid gas or of mixed carbonic acid gas and steam is readily available at the time the present lime burning process isfirst put into operation after a shutdown, the heat required forputtiug the process into the continuous normal operation above described is'supplied in the following` manner: After introducing a charge of limestone into the kiln a high degree of preheat is first imparted to the refractory linings of preheaters 34 and 35, preferably by the combustion ofgas'eousfuel from Stoker 28 in heat transferring Y relationship therewith, and steam is then conducted from boiler -70 through branch pipe connections 126 and conduits 108 preferably into the base of both preheaters.' In passing through the heated linings of the preheaters a hivh degree of superheat, about 1900o to 2000o is ini-parted to .the steam and this superheated steam is then sent through the charge of limestone to raise the temperature off the charge` to thatpoint at whichdecomposition into calcium 'oxideland ocarbonic acid gas begins in the blast zone. After thus initiating the lime burning operation this initial 'supply 0f superheatcd steam is preferably .cut pli' by closing valves 128 in the pipesi126 and thereafter the heat supply :for maintainingAthe hme burnmg operation. iS carried to "the .charge by the circuitof mixed Steam and 'carbonic acid gas withdrawn from the top of `the kiln, as already described.

y.YF-rom the foregoing description it is evident that a very eiicient recover 'of heat is obtained from the combustion o the cheapest type of fuel in the Stoker, and also from the solid and gaseous productsof the decomposition of limestone in the furnace. This efficient heat recovery and the fact that a cheap fuel may beutil'ized, cuts the cost of fuel to less than a half of that necessary in present day lime burning operations. At the same time practically pure products are produced; and the control of 'the operation is so closely governed as to insure that the lime will always be buried to just the degree desired. p

By using a mixture of steam with carbonic acid gas, or other chemical] y inert gases Such as air or nitrogen the tension of the expelled carbonic acid gases is reduced, due to partial pressures, and this fact permits the liberation of the carbonic acid gas at somewhat lower temperatures and in a shorter period of time than is obtained by using a single gas as heating medium.

The preferred form of the invention having been thus described what is claimed as new is:

1. A process of burning limestone comprising, continuously passing limestone downwardly\in a column through a shaft kiln, effecting continuous thermal 'decomposition .of the limestone in the mid-portion of the column by contactingit`with a stream of preheated inert Ygas, coolin r the lime product of said decomposition in the lower portion of the column by contacting it with a counter-flow stream of saturated steam., and continuously withdrawing cool lime from the foot of said column and a cool mixture of steam and carbon dioxide from the'top of said column.

ion

2. A process of burning limestone comi prising, continuously passing limestone downwardly in ,a column through a shaft f kiln, effecting continuous thermal decomposition of the limestonein the mid-portion of the column by contactingit with a stream l of preheated insert gas, cooling the lime product of said decomposition in the lower portion of the column by contacting it with a counter-How stream of saturated steam, continuously' withdrawing lime from the foot of said column and a cool mixt-ure of steam and carbon dioxide 'formed' from the top of saidcolumn, and controlling the temperature and volume of Said inert gas stream and the volume of said saturated steam cooling medium to prevent under or over burn-- ing of lune 1n said decomposition zone.

. 3. `A`process of burning.. limestone com- 4,25.

prising, continuously advancing limestone downwardly in a column'through a shaft kiln, eiiecting'pcontintious thermal decomposition of said limestone by contacting it with a superheated mixture of steam and carbon\dioxide introduced circumferentially into' the mid-portion of said column and passed upwardly therethrough,'cooling the lime product of said decomposltion by contacting it with steam introduced at the base of. said column and passed upwardly therethrough, and controlling the volume of saturated steam thus introduced to maintain the temperature of the lime at the foot of said column only slightly above the dissociation temperature of calcium hydrate.

4. A process `of burning limestone comprising, continuously advancing limestonev downwardly in a ,column through a shaft kiln, effecting continuous thermal decomposition of the limestone in the mid-portion of said column by direct heat transfer with a` .superheated mixture of steam and carbon wardly in a column through .a shaft kiln,

effecting continuous thermal decomposition of the limestone in the mid-portion of said column by direct heat transfer with a superheated mixture of steam and carbon dioxide, regenerating a substantial part of. the sensible heat of the lime formed by heat transfer with saturated steam introduced at the foot of the' column and passed upwardly therethrough, regenerating a substantial part of the sensible heat of the carbon dioxide formed bycontacting it with the limestone in the up.- per part of the column, withdrawing cooled lime from the foot of the column and a cool carbon dioxide-steam mixture from the top of n the column, and superheating part of the car-` bon dioxide-steam mixturethus withdrawn and reintroducing it into the mid-portionof said column. j

6. A process of burninglimestone comprising, continuously advancing limestone downwardly in a column through a shaft kiln, effecting continuous thermal degomposition of the limestone in the mid-portn of said column by direct'heat transfer with a superheated mixture of steam and carbon dioxide passedupwardly therethrough, regenerating a substantialpart of the sensible heat of the lime formed by heat transfer with steam introduced at the foot of the column and passed. upwardly therethrough, regenerating a substantial part of the sensible heat of the cary bon dioxide'formed by contacting it with the limestone in the upper part ot the column,

continuously withdrawing cool lime at a con- `fecting continuous thermal decomposition of 190 trolled rate from the foot of the column and a cooly carbon dioxide-steam mixture from the top .of the column, and continuously superheating a part of the carbon dioxide-steam mixture thus withdrawn and recycling it `through the upper half only qfsaid column.

7. A process ofvburning limestone comprising,- continuously passing limestone. downwardly in a column through a 4shaft kiln, effecting continuous thermal decomposition of the limestone in the mid-portion of the column by contacting it with a counter-How mixture of super-heated steam and-carbon dioxide, preheating thejlimestone in the upper part of the column prior to such decomposition by contacting it with the carbon dioxide product of said decomposition, su-

perheating steam used in eectlngv such decomposition by contacting it with the lime product ofsaid decomposition in the lower part of the column, continuously withdrawing cool lime at a controlled rate from the foot of the column and a cool steam-carbon dioxide mixture from the top of the column, superheatinga part of the steam-carbon dioxide mixture thus withdrawn and recycling it through the upper half of the column, and supplementing the volume of said recycled mixture with -the steam superheated' in the lower part of ,the column and with .the

carbon dioxide product of said decomposition.

8. A process of burning limestone comprising, continuously Apassing `limestone downwardly in a column through a shaft kiln, ef-

fecting continuous thermal decomposition of the limestone in the mid-portion of the column by contacting it with a counterow mix-- ture of superheated steam and carbony dioxlde, preheating the limestone in the upper "part of the column prior to such decomposition by contacting it with the carbon dioxide product ofsaid decomposition, superheating steam used in effecting-such decomposition by contacting it with the limeproduct; of

ics

said decompositin in the lower part 'of the' column, continuously, Awithdrawing l' e at a controlled rate from thefoot of .thecolumn and a steam-carbon dioxide mixture from the top of `thecolumn, superheating part of the steam-carbon dioxide mixture thu s withdraw-n and recycling it ythrough the'upper half ofthe column, supplementing the Volume .of said rec cled mixture' with the steam superheated in the lower part of the column and with the. carbon dioxide product of said decomposition, and se arating steam from the `part of the car on dioxide-steam' mixture not thusmecycled and.

collectingethe carbon dioxide resulting' from said separation.

y9. Aproce'ss of burning'limestone compris-i ing, continuously passing limestone down-z wardly-in a coluinn through a shaft kiln, ef-

iccvv v ltheflimesftonein the mid-portion of the column by contacting it with a counter-How mixture o superheated steam and carbon diox- 1de, preheatmg the limestone in the upper part of the columnprior to such decomposi-V tion by contacting it with a counter-current stream of carbon dioxide product of said decomposition, 'superheating steam used inv effecting such decomposition by contacting it with the lime product of said decomposition in the lower-part of the column, continuously withdrawing lime 'at a controlled rate from the foot of the column and a steam-carbon dioxide mixture from the top of the column, superheating part of the steam-carbon dioxide mixture thus withdrawn and recycling it through the upper half of the column, supplementing the volumeoi saidrecycled mixture with the steam superheated in the lower part of the column and with the carbon dioxide roduct of said decomposition, and control ing the volume of saturated steam introduced into the foot of the column to maintain the composition of the steam-carbon dioxide mixture removed from the top of the column substantially constant.

l0. A process of burning limestone comprising, continuously advancing limestone downwardly in a column through a shaft kiln, heating the limestone in the mid-portion of the column to a temperature sufliciently high to decomposeI it by contacting it with a superheated mixture of steam and carbon dioxide gas, vcooling the lime formed as it advances toward the foot of the column by contacting withy steam, gradually expanding the limestone as it advances toward the mid-portion of the column, gradually compressing the lime formed as it advances toward the foot of the column, and withdrawing comparatively cool lime from the foot of the column and comparatively cool carbonic acid gas and steam from the top of the column.

, foot of the column, withdrawing comparatively cool lime' from the foot of the column and comparatively cool carbonic acid' gas and steam from the top of the column, and controlling the volume of steam intrcfduced. at the foot of the column andthe 'temperature and volume of said superheated carbon dioxide-steam mixture to prevent underor overburning'of the lime and to maintain the comf position of the carbon dioxide-steam mixture removed from the top of the column substantially constant.I y

12. A process of burninglimestone comprising, continuously advancing limestonev downwardly in a column through a shaft kiln, superheating a mixture of carbonic l acid gas and steam, decomposing said limestone by introducing said'superheated carbonic acid gas-steam mixtureinto the midportion of the column and passingit upwardly in contact with the limestone in the upper half ofdthe column, supplementing the heating eiect of said superheated carbonicacidsteam mixture with an additional supply of superheated steam developed inthe lower portion of the column atthe expense of heat regenerated from the lime product of said decomposition, withdrawing lime from the. foot of said column and a carbonic acidgassteam mixture from the top of said column, maintaining the composition of the carbonic acid gas-steammixture thus withdrawn sub-4 stantially constant at about 30% steam and carbonic acid gas by weight, and superheating and recycling a portion said carbonic acid gas-steam mixture tlrough 4the upper half of said limestone column.

13.`A process of burning limestone comprising, continuously passing limestone downwardly in a column through'a shaft kiln, effecting continuous thermal decomposition of the limestone in the mid-portion ot the column by contacting it with a super'- -heatedfmixture of steam and carbonic acid (gas, continuously circulating superheated steam and carbonic Iacid gas ,through the upper half of said column, regenerating the sensible heat of the carbonic acid gas formed by heat transfer with limestone in the upper portion of the column, regenerating the sensible heat ofthe burnt lime by heat transfer with steam in the lower portion of the column, returning the heat thus regenerated' to the mid-portion of the columnin the form of preheated limestone and superheated steam, respectively,v and continuously with-l drawing the lime from the foot of the column;

and a carbonic acid gas-steam mixture from" p the top of the column; I,

v14. lA process for burning limestone com-i prising passing a column of limestone through a shaft kiln, decomposing said limestone by introducing a superheated gaseous mixture comprising carbonic acid gas and steam into the mid portion of said column, introducing saturated steam into the bottom ofthe column in an amount such that the gas mixture. leaving the top of the column will contain approximately 30% steam and 70% CO2 by weight, superheating a part of the gas mixture drawn from the top of the shaft by'passing it-through a hot preheater, and returning said superheated gas mixture to the shaft. L

15.4 A process for :burning limestone comprisin passing acolumn of limestone through a sha t kiln, decomposing the limestone into lime and carbonio acid gas by direct contact with a counter-current circuit of superheated steam and carbonio acid gas during its p assage through the kiln, withdrawing carbonio acld gas and 4steam from the top of the column, and regulating the rate at which limestone is passed through the kiln and the volume and composition'of the gas circuit passed countercurrently therethrough to maintain the temperature of the mixture of carbonio acid gas and steam leaving the top of the column in the neighborhood of 500 F.

16. In lime burning apparatus, an upright shaft kiln, a gas sealed charging device 'at the top of the shaft, a gas sealed discharging device at the foot of the shaft, means mounted in the lower portion of the shaft for supporting a charge column therein, said means having combined therewith mechanism for 'rc- Amoving charge material at a controlled rate from the foot of the column, a gas oftake at the top 0f the-shaft, a gas intake in themidportion of the shaft, means for introducing steam at a controlled rate into the lower portion of the shaft, a gas preheater, a blower, a gas -connection between said offtake anc the intake sideof said blower, a valved connection between the discharge side of said blower and said preheater, and avalved gas connection between said preheater and the gas intake in said shaft.

17. An apparatus for burning lime comprising anupright shaft, a discharging device at` the top of the shaft, a discharging',J device at the bottom of the shaft, a circumferential enlargement and a gas inlet in the mid portion of the shaft, agas outlet in the top portion of the shaft, a preheater, means for circulating gas from the gas outlet through the preheater and gas inlet back into the midportion of the shaft, and means for introducing aheating gas into the preheater.

18. An apparatus for burning lime comprising a shaft kiln, a charging device for charging limestone into the top of the shaft, a discharging device for discharging lime from the bottom of the shaft, means for controlling the movement of lime through the shaft, a gas oftake at the top of the shaft, atpair of preheaters connected to gas inlets inthe mid portion ofthe shaft, means forI heating said preheaters, a blower, a gas con- .nectionbetween the intake of said blower lpreheater gas connections.

@fill-9. An appparatus forburning lime com-f prising an upright shaftkiln, means for introducing limestone into the upper portion of the shaft, means for removing lime from the bottom oT the shaft, a gas oiftakeponnected with e top of the shaft, a pa1r of gas inlets connected with the central portion of the shaft, a preheaterconnected with each A inlet and with the gas otake, means to introduce a heating gas into the preheaters, means for introducing amixture ofinert gases into the preheaters to be heated, means 'for circulating inert gases from-preheaters through the gas inlets and upper portion of thel shaft, and meansv for cutting of'one preheater from the shaft when the other preheateris used to superheat the mixture of v .the bottom of the shaft, a gas oftake at the top of the shaft, a pair of preheaters 0011-' nected to gas inlets in the mid portion ofthe shaft, means forcirculating gas from the Oiftake through the preheaters, gas inlets and upper portion of the shaft, a boiler foi` generating steam, feed water heaters, means for supplying heat to the preheaters, boilerand feed water heaters, water connections between said vboiler and heaters, and steam lcg'imections between said boiler and shaft 2'1. An apparatus for burning lime'comprising an upright shaft kiln, means for charging limestone into the top of the shaft, means for discharging lime from the bottom of the shaft, means connected to a gas inlet in the mideportion of the shaft for preheating a mixture of gases before its introduction into `the mid portion of the shaft, means for introducing steam linto the bottom of the shaft, a gas offtake at the top of thecshaft, a

blower, a condenser, and connectionsl for ref.'

circulating a portion of the gases drawn from .blower and condenser.

22. An apparatus forburning lime com ,95 mel les` the top ofthe shaft through the blower and prising an upright shaft, a charging device" at the top of the shaflt,`a gasoftake at 'the top of the shaft, preheaters connected to the gasvofftake and to'blast inlets in the central portionof the shaft, Aa steam distributing coil? in the bottom of the shaft, a steam boiler, a condenser connected with the gas oiftake, feed water heaters connected to the preheaters,

and connections for leading' water from the. condenser through the' feed water heatersfto the boiler, and connections for leading steam from the boiler to the coil in the bottom of the shaft and to the preheaters.

23. In an apparatus fonburninglime, an" 4 upright shaftkiln, a charging devicel at the" top of the shaft, a discharging device at the foot of the shaft, means mounted in the lower portion of the shaft for supporting a charge' column in the sha-ft and for controlling the through said hot gas introducing means and movement of charge material through the /the upperpart of the shaft, said shaft having 10 shaft, a gasofl'talre at the top of the shaft, its largest interior crossl sectional dimensions means for introducing hot gas into thek midf at its midzone andgraduallydecreased cross '5 portion-ofi the shaft, 1neans for introducing sectional dimensions toward its top and botsteamfat' a controlled rate into the lower portom extremities. v tion the shaft, and means for circulating In testimony vwhereof I aiix my signature. gas removed through said offtake hack CARL J. WRIGHT.

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