US2653809A

US2653809A - Kiln

Info

Publication number: US2653809A
Application number: US106376A
Authority: US
Inventors: Victor J Azbe
Original assignee: Azbe Corp
Current assignee: Azbe Corp
Priority date: 1949-07-23
Filing date: 1949-07-23
Publication date: 1953-09-29
Anticipated expiration: 1970-09-29

Description

V. J. AZBE Sept. 29, 1953 KILN 4 Sheets-Sheet l Filed July 25, 1949 Sept. 29, 1953 v, J, AZBE 2,653,809

KILN

Filed July 23 1949 irv Sheets-Sheet 2 4 Sheets-Sheet 3 V. J. AZBE KILN Sept. 29, 1953 Filed July 25, 1949 l V. J. AZBE sept. 29, 1953 KILN . n J l a J O1' 000 l 4. Sheets-Sheet 4 Filed July 23 1949 Patented Sept. 29, 1953 KILN Victor J. Azbe, Webster Groves, Mo., assigner to Azbe Corporation, Clayton, Mo., a corporation of Missouri Application July 23, 1949, Serial No. 106,376

7 Claims. l

This invention relates to kilns, and more particularly to rotary kilns for burning lime, cement, magnesite, et cetera.

Brieiiy, the invention comprises the combination of -a rotary kiln element (including endwise circular sections and a longitudinally sectored part extending into the calcining zone) with a combination stone preheater and dust collector at the inlet; a stationary shaft at the outlet comprising a finishing and -a cooling zone; and ring means at the outlet of the rotary element which includes recirculating heat recuperator means supplied both from the inlet and from the stationary shaft. The invention also includes iinprovements per se in the constituent elements of the stated. combination. By means of the invention, a smaller-sized kiln of lower iirst cost and upkeep may be employed for a given capacity operating at a much higher thermal eiciency and at a considerably lower temperature peak than heretofore. The lower temperature peak allows for more effective heat insulation without in-` curring refractory failure, scale adhesions and ring problems in the rotary elements. The in- Vention also provides a kiln of the rotary type which is more easily controlled andy less critical in its stone size acceptance than was the case with prior rotary kilns and one in which the dust hazard usually associated with rotary kilns is reduced. Moreover, a superior but more economical product is obtained. Other features will be in part obvious and in part pointed out hereinafter. f f

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of the application oi which will be indicated in the following claims.

Fig. 1 is a diagrammatic side elevation on a reduced scale, showing the invention in gross;

Fig. 2 is a chart of gas temperatures (upper curve) and per cent of heat transferred from gas to charge (lower curve), being longitudinally related to Fig. l so as to indicate kconditions throughout the kiln;

Fig. 3 is a detailed axial section of the left end inlet portions of Fig. 1, showing a stone Contact preheater and dust collector;

Fig. 4 is a detailed axial section (parts being broken away) illustrating the intermediate ro'- tary portion of the kiln;

Fig. k5 is a detailed axial section of the righthand portion of Fig. l, showing certain firing, finishing and recuperating cooling apparatus;

Figs. 11 and 12 are views similar to Fig. l0 eX-` cept that they illustrate corresponding conditions at successive angles of operation in the rotary kiln elements employed in the invention, being taken on line I-II of Fig. 4; and,

Fig. 13 is a detailed section taken on line I3-I 3 of Fig. 5.

Similar reference characters indicate corresponding parts throughout the several views of the drawings.

Referring now more particularly to Fig. 1, the board outlines of the apparatus will iirst be described. These comprise a sloping rotary drum section I, consisting of a steel tube 3 lined withY refractory and heat insulating material 5. This tube 3 is carried by rings 'I riding on supporting rollers 9. This drum also carries a ring gear H driven by a pinion I3, the latter being driven from a motor I5 through a speed-reduction gear box At the upper open inlet end I9 of the drum l is located a heat economizer and dust chamber 2I. In the dust chamber is a stone preheater cone 23rwhich receives stone or like material to be burned from a bunker 25. The Stone finds its way from the bunker 25 through the preheater 23 to the open end I9 of the drum I, in a manner to be detailed below.

At its opposite or lower end, the drum I has an outlet 2l leading into a ring hood 29, surrounding ya burner assembly 3|. The firing hood forms the top of a vertical shaft 33 constituting (Fig. 5) an upper finishing zone 2 and a lower cooling zone 4 through which passes the not quite finished discharge from the drum I. The finally finished and cooled product is finally discharged through a` Variable capacity feeder 35 to a pressurized outlet chamber 3l from which it escapes through an air lock 39 to an outside conveyor 4I Recirculating heat economizer means in two parts are employed. One of these is the firing khood 29 which, as will be shown below, receives air that has been warmed in the cooling zone l of the shaft 33 but which by-passes the finishing zone 2. The hood also receives gases from the zone 2. The hood delivers its warm gases to the outlet 21 of the drum I, these being injected into the drum by the discharge from the burner assembly 3|. The second part of the recirculating system comprises a. recirculating pipe 43 leading from the chamber 2| and to the burner assembly through a recirculating fan 45.

Details of the elements broadly outlined above are as follows, startingwith the drum This drum has an open section 41 near its upper outlet I9 wherein preheating takes place. The pre-- heating zone is indicated at 53. At the other end of this open section are spiral fins 49 (see also Figs. 4 and 8). At the lower: endof the drum is a second open sectionv5|,.wherein fuel. carburetion takes place. Between the fins 49 and the section 5| is a divided or-quadrated. section which includes a part of the preheating zone 53 and a calcining zone 55. The quadrating construction is indicated generally by the numeral 51 and is shown in particular in Figs. ll and 12. It is constituted by cruciform refrac-v tory walls 59, which divide the section 51 into four axial sectors into which under rotation: of the drum the charge is distributed by the' spiral fins 49. The effect of these sectors upon the charge may be noted bycomparing Fig. l with Figs. 11 and 12. Fig. 10 shows how a charge acts in an ordinary non-quadrated rotary kiln. As rotation takes place (anticlockwise) there is an anticlockwise rolling action applied to thel charge. This causes the formation of' an outer stratification of coarse particles 6|, which in turn surround a stratification of mixed particles B3, which in turn surround a central stratication of fine particles 65. Thus the ner the particles are, the more they are blocked off from the reception of heat. Heretofore, high temperatures were required in rotary kilns applied for long periods in order to penetrate the stratifications in order to complete theY calcining of the fine particles. The increased time needed required an increase in theV length of the drum and the high temperatures precluded carrying any quadrating structure into the calcining zone. As demonstrated in Figs. 11 and 12, all of the categories of coarse particles 6|, mixed particles 83 and fine particles 65 are tumbled, sol that at some time or times during the rotary process they become exposedto radiant heat.

At its left end the drum I carries an annular end seal 61 with the dust chamber 2|, the seal being provided with a negative internal pressure by bleeding to the recirculating duct 43 via a connection 69 wherein there is a control valve 1|. At this end the drum also carries an inwardly directed stone spill dam |09. Atits other (lower) end, there is also arranged a seal 13 between the drum I and the firing hood 29. At this point the refractory is stepped inwardly to form a dam 15 beyond which is a nose ring 11. This ring is interiorly channel-shaped and may include openings or foraminations 19, to act as a classifier. However, this classifier function is not always necessary, in which event the nose ring is made without openings through its channel section.

Referring to further details of the dust chamber 2|, it will be seen to include a dust hopper 3| at the bottom of which is a gate 33; also a stone-spill hopper 85 at the bottom of which is a gate 81. The preheater 23 is in the upper part of the dust chamber 2| and includes an i-nternal spreader hood 89, which causes the rock entering from the rock supply bunker 25 to assume a surface of repose such as indicated at 9|. This surface is within a conical portion 93, wherein are louvers through which hot gases may enter the interior mass of stone. This spreads the rock over the louvers. These gases traverse the stone, which acts as a filter to settle much of the entrained dust. Heat is also transferred from the gases to the stone for initial preheating. The filtered gases are drawn off through an exhaust duct 91 which is connected to the spreader hood B9, being pulled off by an exhaust fan 99. A by-pass duct |9| connects the chamber 2| with the duct 91. Contml' dampers |031and1|05 are used in the ducts 91 and. IUI.. It willlbe noted that not all of the gases leavethe chamber 2| via pipes 91 and |0|, but that some of them are drawn off over the hot gas recirculating duct 43. The function of this will appear.

At the lower end of the cone 93 is an outlet pipe |01- to which is pivoted a feed spoutA controlled in position by adjustable suspension means I3. The spout may take a lowered position shown in solid lines, or a raised position Shown in dotted lines. In the lower position, the level of the stone in the open section 41 will be less than it is in the raised position, since when the level of the stone reaches the outlet of the feed spout, no more stone will flow until this levelis reduced by the .stone` proceeding down the section 41.

Referring now to the details of the stationary shaft 33 at the lower opening outlet end ofthe drum I, it comprises the ring hood 29 around the nose ring 11. Below the outlet of the drum I the shaft is constructed as shown in Fig. 6, wherein it is divided into six downwardly extending chambers |I5 having tapered lower outlets I |1. The exact number of these is optional. They are viewed from the bottom in Fig. 7. They carry airinlet louvres 6 and are surrounded by an air plenum chamber 8. Under the outlets ||1 are doorsk |I9 carried adjustably upon reciprocating bars |2I, the latter being carried in bearings |23 and being joined by a crosshead |25. The crosshead |25, and consequently the rods I2| and doors ||9, are reciprocated by connectionsA |21 with cranks |29 driven from a suitable actuator |3|. Thus through adjustment of the doors II9 on the rods |2| and the reciprocation of the rods, the finished material may be drawn from the respective chambers I|5, thereby providing a variable capacity output for each of these. Below the outlets ||1 is a conveyor belt |33 which delivers all of the material withdrawn from the chambers ||5 to the outlet 39 from whence it is delivered to the belt 4| for delivery to storage. In the outlet 39 is an air lock as illustrated in Fig. 13, which consists of a rotary vane member |35 in a. cylindric passage |31. This member upon rotation passes solid material out without permitting continuous ow of air. The reason for this air lock is that the outlets I|1 are surrounded by an air-pressure plenum chamber |39 from which it is desired to allow air to escape only by passage through the openings |I1 to the chambers ||5 as the finished material shakes therefrom. This air is obtained through an air pressure connection |4| (in which is a control valve |42) with an air mani fold |43 supplied by a cooling fan |45. The manifold |43 also has connections |41 (in which are control valves |48) which supply cooling air individually to the lower ends of the plenum chamber 8. This air enters the louvers 6 and cools the charges as they approach their outlet gates. As will be shown, it is desired to have a heat-soaking finishing operation occur at the upper ends of the chambers I I5 and to have a portion of the cooling air by-pass the resulting finishing zone. This is accomplished by means of horizontal offtake pipes |49 across the pas-y sages H5 at an intermediate point thereof, each having lower openings |5I and a control valve |53. These pipes include risers |55 which are reconnected at points near the firing hood, as shown at |51. Thus the region below the pipes |49 constitutes a cooling zone and a substantial portion (but not all) of the air used in that zone by-passes the finishing zone above the pipes |49. The remainder passes through the finishing zone. All of the air finally enters the firing hood 29 and most of it is directly injected as secondary air along with fuel into the carbureting section 5I of the drum I. Some is drawn off through the recirculation duct 43 via offtake |61, to be used as primary air in the burner 3|.

The burner assembly 3| includes a fiaring fuel nozzle |59 appropriate to the fuel being used, such as natural or artificial gas, oil, powdered coal, etc. This nozzle is surrounded by a fiaring manifold jacket ISI supplied with hot recirculating gas over line |63. In line |63 is a recirculating fan 45 drawing hot gases from the recirculating duct 43. Thus both spent gases (from the dust chamber) and some air (from the firing hood) are delivered to the manifold IBI by the fan |65. Additional air for temperature control may be obtained from bleeders |69 controlled by valves |1I. The flare of the burner provides a wide-angle entry of combustible into the drum I, wherein it spirals to aid carburetion. If spirallingr is not inherent suitable spiral baffles may be incorporated between the nozzle |59 and the manifold jacket I6I. While the walls 59 stop spiralling action of the gases, it is reinstated the section 41 by the spiral fins 49. The flaring dam coopcrates with the flaring burner to carburet,` and with the adjustable feed spout III maintains a desired level of material passing out of the drum I.

Since some scale is encountered in the material leaving the drum I, agitator grates |13 are provided, which screen out scalematerial and send it toward a clean-out door |15 for delivery to a suitable hopper |11 via chute |19.

Operation is as follows:

The drum I is rotated and the feed spout III adjusted to the depth of charge to be carried in the inlet section 41. Stone (or any similar material to be burned or calcined) leaves the supply by gravity and is spread into the shape 9| (within the cone 93) by the spreader hood 89. Here it is preliminarily preheated by hot gases traversing it, while it acts as a dust filter for the gases. From here it descends the spout III and rotation of the drum I carries it down the slope of the open section 41 at the end of which it is picked up by the spirals 49 and distributed amongst the sector-shaped passages determined by the quadrating walls 59. During this stage the material is further preheated. It then proceeds down the walls, being tumbled and adequately brought to the surface at intervals, passing through the hot calcining zone (into which the walls 59 extend) and finally entering the open carbureting section 5|. Its level is maintained by the eleva-*l tion of spout |I| and the dam 15, over which it finally spills through the nose ring 11 and enters the finishing and cooling chambers II5. The finer portions may pass the openings of the nose ring and fall into the closest set of passages II5. Most of the remainder passes mostly to the remaining passages I|5 and spalls are deflected by the grates |13.

In the above it has been assumed that the burner assembly 3| has been lighted. This injects fuel, air and recirculating gas into the carbureting section 5I also entraining air which has risen into the firing hood from the operations in the stationary shaft 33. Thus preheated secondary air, as Well as preheated primary air, is obtained, along with injection of hot recirculating gases, the latter having the desirable effect of properly modulating combustion to avoid producing hot spots.

Referring to Fig. 2, it will be seen that the spent but hot gases passing through the entering rock in the cone 43 cause this cone to act as a preliminary contact preheater, the temperatures being of the order of 600 to 900 F. These spent gases have also had their preheating effect in the open section 41 as indicated by the chart. As the stone reaches the quadrated section of the drum I, it enters a zone of higher preheat preliminary to calcining, in which the temperature rises until the caleining zone is reached. A large segment of this calcining zone is constituted by the quadrated section, the remainder being rin the carburetting open section 5|. The maximum temperature of 2500 F. or so is reached at the lower region of the quadrated section. In the open section 5I the temperature is high at the upper end but drops off rapidly toward the dam 15 due to the time required for the gases properly to mix and ignite in passing through the section 5I. Since in a rotary kiln it is difficult to reach the ideal condition wherein all material is completely calcined before leaving the drum, I cause the material to be sent to the stationary shaft 33 for final finishing by a self soaking action supported by the heat carried in the material itself. Any unfinished nodules have their calcining finished by this soaking action. As indicated in the temperature chart, the final finishing is done With a high, but not the highest, temperature used in the process. Then as the finished material descends through the chambers I I5, it encounters the cooling zone 4 below the pipes |49, wherein finishing action ceases, and heat is abstracted by the cooling air, the latter returning to the drum. This air by-passes the finishing zone 2 above the pipes |49 so as not to interfere with the heat-soaking action required in the finishing zone. However, some air is permitted to pass through the fiinishing zone to carry on the finishing process. Finally, the material reaches a position at the gates IIS where it is controllably shaken out into the pressure chamber |39, from whence it escapes through the air lock 39 to the conveyor 4|. In order to maintain the temperature required in the chambers I I5, these are properly heat-insulated.

The chart of Fig, 2 shows the percentage of heat transferred to finished material as progress is made through the apparatus. The largest gain in heat transfer occurs in the calcininf,r zone into which the quadration of the drum I enters. Heretofore it has not been feasible to enter a calcining zone of a rotary kiln with any similar quadrating structure because of the destructive higlitemperatures used v(about'3000 FJ. In the present apparatus, the highest- 'temperature is 2500 F., which is considerably below the usual practice in rotary kilns, and safe for available refractory and insulating materials. This reduction in temperature 'is made possible by the fact that the rotary drumelement is not used entirely to complete the calcining operation, this being done in the stationary vertical shaft 33, wherein, as the chart discloses, a substantial additional heatntransfer is effected. The result is that the drum I may -be :made much shorter since retention timeV is shorter, which tin turn reduces the rather large heat losses associated with long drums. Moreover, the temperature being lower since cacining is not driven to the limit in the drum, the hea-t radiating losses are much lower. The size of the apparatus `for a given capacity is also reduced.

The ordinary rotary kiln requires in excess of 50 cubic feet of clear kiln volume per ton of capacity, and at times as much as 100 cubic feet. The present kiln requires only about 20-30 cubic feet of corresponding kiln space per ton of capacity. This considerably reduces the first cost, operating and maintenance cost, and radiation heat losses. In addition, the thermal 'efficiency is about doubled from about 30% to 60%.

Another advantage of carrying the quadrating section into the calcining zone within the drum is that during calcination a thorough tumbling action is obtained without stratification thus exposing all material to radiant heat. This permits the drum to accept a wider range of stone sizes than heretofore. Hence lthere 'is eliminated ail the apparatus usually required for close sizing of stone heretofore required for rotary kilns.

Another advantage of the invention is that a substantial amount of preheating is done outside of the drum i, although some preheating is accomplished in the open section 4l and the upper part of the quadrated section. Preheating accomplished in the dust chamber by passage of the spent gases through the rock in the cone 93 is more eiiicient and, moreover, has the stated effect of reducing the escaping dust. It is to be noted in this connection that the spent gases pass through a limited and uniform stone-bed -thickness, assuring proper gas distribution. It is to be noted in this connection that Athe by-pass pipe 10| is to take care'of the condition encountered during shut-down, when stone flow is interrupted. During such period the bed in the'cone 93 may become choked with dust and the by-pass pipe IDI allows operation until vactive stone flow is again established.

One of the advantages of Ythe use of the stationary shaft 33, which acts as a secondary calciner, is the utilization of the sensible heat of lime which is discharged by the rotary drum to do additional calcination work outside of the drum. By means of the present invention, as much as 10% of the total calcination work can be accomplished in this secondary calciner, which 10% in the ordinary rotary kiln requires about 30% of the energy besides requiring large highcost apparatus.

The purpose of the multiple chambers H5 in the shaft 33 is to prevent gaseous ilow stratifications. By means of the separate chambers H5, discharge, as well as air admission, can be inde'- pendently controlled to avoid this diiculty.

Over all control is simple, both as to air supply and material withdrawal. Control of initial combustion temperatures is obtained either by controlling the mixture of 'air and combustibles, or controlling the amount of spent gas (CO2) iobtained from the recirculating duct 43. Control over the luminosity of the flame is obtained by creating conditions conducive to cracking of hydrocarbon, that is, creation of stratified flow and retarded access of air to the combustible gases. However, the present kiln is less dependent on high luminosity of ame, since it contains an abundance of heat-absorbing surfaces.

In view of the high `temperatures encountered in an ordinary rotary kiln, it is not feasible to insulate them; whereas with the relatively low temperatures used in the rotary drum herein, insulating material may Ibe Acombined with the refractory lining of the -drum I without danger of excessive deterioration due to high temperatures.

Air to the cooling zone 4 is regulated in accordance with Vthe lime drawn, and air by-pass of the finishing zone above pipe |49 is regulated in accordance with the temperature of lime 4leaving the finishing zone. If additional air is needed for combustion in the drum l, this enters through the burner assembly 3| or leakage air at the kiln front induced by vthe general kiln draft created by the exhaust fan 99. This draft is regulated by the thermal orifice established by the dam |09, this being the choke, besides preventing rock spillage in the dust chamber.

In view of the above, it will :be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a. limiting sense.

I claim:

1. In a kiln, the combination -of a rotary primary ca'lcining drum sloping from a combination material inlet and gas 'outlet to a combination material 'outlet and fuel inlet, means at the lower end of the drum adapted to drop calcined material into several different streams of partially calcined material, a stationary vertical shaft located at the lower end of the drum having means to determine said Vstreams and having 'an upper hood enveloping the material outlet and the fuel inlet, said shaft having separate lower compartments adapted respectively to receive the different streams of material for further and individual 'secondary calcining and cooling, means for withdrawing individual streams of material from the individual compartments, means for introducing cooling air Lto the lower ends of said compart' ments, and means for extracting air from intermediate points of said compartments to establish a cooling zone and reintroducing said air into said hood whereby self-'calcination may continue in the upper portions of said compartments, the gaseous product of calcination in said upper portions of the compartments and by-passed air and also fuel from said fuel inlet passing through the hood into said drum for primary tempered calcination in the drum in the presence of combustion of fuel.

2. A kiln made according to claim l including means for individually controlling said selfcalcination in said compartments.

3. A kiln comprising a sloping rotary drum of constant diameter `throughout for down-flowing material from an upper open end to a lower open end and 'for up-'flowing gases from the lower to the upper end, means dividing only a mid- 9 portion of the drum into radially disposed sectors, the ends of which sectors are substantially spaced from the respective ends of the drum to provide unobstructed endwise drum lengths, a burner nozzle adjacent the lower end of the drum adapted to inject a combustible mixture into said lower end, the distance from said lower end of the drum to one end of the dividing means being substantial and sufficient to allow thorough mixing of said combustible mixture without interference from any sectors, in order to provide for efficient carburetion, the lengths of said sectors being sufficient to effect substantial calcination, the unobstructed drum length from the other ends of said sectors to the upper open end of the drum being suicient to effect a substantial perheating of material approaching the sectors.

4. A kiln comprising a rotary drum having an upper combined material inlet and gas outlet, a dust 4chamber enclosing said outlet, a rock container in the dust chamber having a rock inlet from the outside and a rock outlet pipe leading into said drum, gas passages in the wall of the rock container for admitting gas from the dust chamber into the rock container independently of said rock outlet to the drum, whereby a substantial amount of gas may enter the rock container to pass through the rock to settle dust from the entering gas and to preheat the rock, said rock container having an outlet for said gas.

5. A kiln made according to claim 4, wherein said rock outlet pipe leading to the drum is movable in a manner to adjust the position of its outlet relative to the inside bottom of the drum.

6. A kiln made according to Claim 4, wherein said gas passages consist of louvers in the rock container and wherein said rock container is of downwardly tapered form containing the louvers, and a spreader in the container adapted to spread rock over the louvers in its passage to said outlet pipe.

7. In a kiln, a dust chamber having an opening, a rotary calcining drum having an end rotary in said opening and introducing hot gases into the dust chamber, a peripheral enclosure around said opening, circular running sealing means between said peripheral enclosure and the drum and axially spaced from said opening, and means other than said opening for drawing and leading 01T hot gases from said peripheral enclosure, hot gases being supplied to the enclosure by outward flow through said opening, whereby infiltration of cold outside air to the dust chamber is positively prevented.

VICTOR J. AZBE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 928,512 Eldred July 20, 1909 1,011,804 Jones Dec. 12, 1911 1,332,138 Newhouse Feb. 24, 1920 1,510,140 Fasting Sept. 30, 1924 1,581,522 Stehrnann Apr. 20, 1926 1,605,279 Pike Nov. 2, 1926 1,684,006 Bent et al. Sept. l1, 1928 1,754,854 Gelstharp Apr. 15, 1930 1,788,839 Luther Jan. 13, 1931 1,789,895 Fassotte Jan. 20, 1931 1,912,810 Wechter June 6, 1933 1,955,914 Holzapfel Apr. 24, 1934 2,007,121 Johannsen July 2, 1935 2,012,881 Lee Aug. 27, 1935 2,095,446 Lee Oct. 12, 1937 2,451,024 Ellerbeck Oct. 12, 1948 2,520,384 Davis Aug. 29, 1950 2,522,639 Royster Sept. 19, 1950