US2314836A - Rotary kiln - Google Patents

Description

March 23, 1943. I G. E. SEIL 2,314,836

ROTARY KILN FiledMay 12 1942 2 Sh ets-Sheet 1 FIGJ. /B/- I w 24 f o IIT 4 INVENTOR GILBERT E. SEIL BY WM ATTORNEY Patented Mar. 23, 1943 UNITED STATES PATENT OFFICE- ROTARY KILN Gilbert E. Seil, Cynwytl, Pa. Application May 12, 1942, Serial No. 442,600

2 Claims.

Thisinvention relates to rotary kilns for heattreating operations wherein the material being heat-treated, and a gaseous heat carrying medium, move in counter-current flow through the drum. The material to be heat-treated is in the form of a slurry of finely ground particles, and is fed to one end of the kiln drum, to be (1) dried; (2) heated to cause physical changes and/or chemical reactions to take place; (3) to be solidified, nodulized or sintered as the material continues through the drum, and, finally, (4) to be discharged from the other end of the kiln. Examples of such operations are the burning of cement slurry, or the firing of refractory mixes, or the nodulizing of ore slurries.

More particularly, the invention relates to the practice of providing in the kiln drum means for increasing the efiiciency thereof comprising an arrangement of loosely disposed chains which by reason of their suspension from th interior periphery of the drum, move alternatively into and out of contact with the mass or body of material being treated in the drum.

Such chains are provided in the kiln near the end at which the wet charge enters and increase the eiiiciency of the kiln, by slowing up the rate of travel of the wet slurry to provide a longer treatment time, by increasing the transfer of heat from the hot kiln gases to the material being treated due to the fact of the chains alternately absorbing heat from the gases and transferring such heat to th material being treated. Also, thewet chains constantly moving through a section of the kiln serve to catch the fine particles of dust, thus serving as a means of preventing loss of such material through the stack.

The usual arrangements of chains as now used, impede the fiow of raw material to such an ex tent that the output of the kiln is seriously affected. This is especially true if the material has a tendency to become sticky at some definite point, or to solidify into hard rigid lumps which cling or stick to the shell, the chains, and other lumps. In such cases, the material will form constrictions that are ring-like either in whole or in part, at that section of the kiln where transformation from a smooth flowing slurry to a sticky mass occurs, and this constriction increases insize until it impedes progressive flow of materials through the kiln.

However, I have observed that the anchoring points of the chains, thatis to say, the points of attachment of the chains to the interior wall surface or periphery of the drum, tend to become the nuclei of umps of material adhering to and building up to various sizes and hardening around these anchoring points, thus promoting th formation of free passage area of the drum. I have observed that as the drum rotates, the weight of the chain undesirable constrictions in the exerts a certain leverage upon the hardened lump of material encasing the anchoring points,

' which leverage depends upon the size of that accumulation. Thus the greatest leverage is liable to break up first, and the others offering smaller leverage follow.

It is among the objects of the invention to discourage the growth of such constrictions by effectively breaking up the lumps of material formed around the anchoring points of the chains, and to provide simple and effective means for that purpose.

This end is attained, according to this invention, by providing chain assemblies in each of which a plurality of chains are interconnected by a common weight member. The dropping of that weight as the drum rotates will break up the accumulated lumps at the anchoring points of the chains in quick succession or simultaneously. By the law of averages and because of the difierence in sizes of the various lumps, it can be visualized that approximately the fullweight is supported by only one anchoring point at a time, so that in efiect the common weight is concentrated substantially upon one chain at a time, and upon breakage of the lump around the anchoring point of that chain the others follow suit in such quick order that indeed the efiect appears to be almost simultaneous. I have found that such a common weight member acting on a plurality of chains of the assembly is much more eifective than indiiidual weights represented by each chain, even though their aggregate weight were equal to the weights of the common weight member of this invention.

According to one feature, I provide an assembly or series of chains with their anchoring points spaced a suitable distance apart from one another, with one end of the chains being attached to the interior surface of the drum at points along a line substantially longitudinal of the drum, the other end of the chains being attached to a rail or beam constituting the common weight member for the chains of that assembly unit, the length of the rail consequently being substantially not less than the length of the assembly.

There are provided a suitable number of such chain assemblies of a length and a weight such that they will dislodge and disintegrate any accumulations of material in the kiln drum which tend to form constrictions. This arrangement and'action of the chain assemblies precludes inlump presenting the -terference with the steady fiow of material through the kiln, and any lumps thatform around the anchoring points are broken with but a minimum of total weighting needed.

According to another feature, such weighted chain assemblies are used in combination with annular flow retarding dams or baflles provided in the drum, to help break up and dislodge acupon the dams.

cumulations of material tending to form at and The provision of these chain assemblies makes possible the use of the dams in spite of their tendency to promote the flow of mud rings which are liable to impede normal and uniform operation.

As illustrative of a form of construction by which the invention hereof may be realized, reference is made to the accompanying drawings constituting a part of this specification, and in which drawings:

Fig. 1 shows a longitudinal section through a rotary kiln provided with weighted chain assemblies according to this invention.

Fig. 2 is a greatly enlarged detail view of a weighted chain assembly.

Fig. 3 is a cross-section along the line 3--3 upon Fig. 2. 1

Figs. 4, 5, 6 are cross-sections on the line 4-4 of the kiln drum in various phases of rotation, to illustrate the breaking up of the lumps of accumulated material at the anchoringpoints of the chains.

Fig. 7 is a feed end or drier portion of the rotary kiln, provided with annular fiow retarding dams in combination with the weighted chain assemblies.

Fig.8 is a cross-section of the kiln drum taken along the line 8-8 in Fig. 'I.

The rotary kiln construction embodying this invention is shown somewhat diagrammatically in Fig. 1, in which a rotary drum Ii! is disposed at a slight downward slope, the upper end of the drum being rotatable in a stationary structure or housing portion ll serving as a flue and provided with or intersected by a feed hopper l2 for supplying material to be treated to the interior of the drum by way of the upper end thereof. The .lower end of the drum I is rotatable in a stationary structure or housing portion l3 which serves on the one hand to receive the treated material from the drum and on the other hand is provided with means in the form of fuel injection nozzles or burners 14 for supplying a heat carrying gaseous medium or hot combustion gases indicated at Hi to the interior of the drum to pass therethrough in counter-current to the movement of the material being treated by contact with the heating gases. The drive of the drum is indicated by a pair of bull gears 11 surrounding the drum and fixed thereto with a corresponding pair of gear-driving pinions i8 and I9 rotatably supported by means of a shaft in journals 2| and 22.

The drum in is shown to be refractory lining 23, except for a portion of drum that is closest to the feed end thereof. The proportions of the refractory lined and the unlined parts of the drum will hereinafter be referred to more in detail, but their respective lengths are herein designated by the letters A and B respectively.

The unlined portion of the drum is shown to be equipped with a plurality of chain assemblies constructed according to this invention. Each of these chain assemblies is herein referred to by the numeral C.

One such chain assembly as shown more clearly in the enlarged detailed Fig. 2, is shown, by way of example, to comprise a base or anchoring member in the form of an angle-iron 24 extending interioriy longitudinally of the drum and provided with a fastened to the wall of the'drum as by means of bolts 25. A suitable number of chains 26 of substantially equal length have their one end atlongitudinal section of a modified l6 and the tached to the anchoring member or angle-iron 24. the anchoring points of the chains being substantially equi-distantly spaced from one another. The opposite free ends of the chains are similarly attached to a rail member 21 which represents the common weight member herein referred to of this chain assembly C. There are shown to be provided (see Figs. 4, 5 and 6), a plurality of such chain assemblies substantially evenly spaced from one another along the circumference of the interior of the drum. Figures 4, 5 and 6 representing cross-sections of the drum sion A. The remaining 30 feet representing the in various phases of clockwise rotation thereof illustrate the function and novel effect of the rail members 21 in the respective chain assembly units C, especially with respect to the breaking up of the objectionable lump formation around the anchoring points of the chains 26 at the wall of the drum.

Operation According to a practical example a kiln drum' v for the present purpose is feet long and 8 feet in diameter, to be used for the manufacture of sodium ferrite. Refractory lining 23 extends from the discharge end of the kiln drum for a distance of about '70 feet representing the dimendimensionB of the drum length are unlined and provided with the arrangement of the chain assembly units according to this invention. The chains of each assembly unit are spaced from one another about 12 inches, and consequently there are thirty chains to one assembly unit, the length of each chain being preferablyfive-eighths of the diameter of the drum H), which makes them about five feet long. in each chain assembly C is a single length of heavy iron or rail. In the section B of the drum there is provided a pluralityof such chain assembly units, for instance, four, six or eight, as desired, equally spaced around the circumference and so arranged that the angle-irons or anchoring members 24 to which the chains are attached are substantially equally other. The angle-irons spaced from one anmembers 21.

The raw material charged to the kiln is a slurry consisting of iron oxide and soda ashsuspended in a solution of sodium carbonate and sodium hydroxide.

through the kiln, it reaches a stage at which it becomes sticky and then rapidly hardens into a l i Unless some means other than the normal chain arrangement is provided concrete-like mass.

in the portion of the kiln where this transformation occurs, the material and build a ring or constriction which grows in cleaned.

material around the anchoring points of the chains. If

the weight of the individual chain is not sufll j cient to break up these accumulations or lumps, the build-up gradually tates shutting down the kiln.

consolidated and their individual effect with respect to breaking up the lumps or accumulations is multiplied, by rality of assembly units- The common weight 24 are consequently A about thirty feet in length, and so are the rail As the charge dries in its passage i will stick to the shell grows until a ring is I formed representing a constriction that necessi- According to this J invention, the action of the individual chainsis forming the chains intoa plu- [I The common weight -chainthus in each assembly unit multiplies the effect of each chain with respect to the breaking up of the lumps of material that have caked around the anchoring point of the chain.

As the kiln rotates the angle-iron or anchoring member 24 of each chain assembly unit passes through the charge or burden in the bottom of the kiln. As the angle-iron 24 approaches the top of the kiln, the weight or rail member 21 drops and the weight of the entire assembly, that is the. weight of the rail and the chains, will break loose any accumulation of material that may be sticking to the wall at that point. -In particular, it will break up the lumps that have built up around the anchoring points of the chains and that keep encased the initial portion of the chain. Because of the difference in size of the various lumps around the anchoring points of the chains in any one particular chain assembly unit, a greater weight due to the rail member 21 will be concentrated upon that chain, the anchoring portion of which is encased by the largest, that is to say, the relatively highest lump. Therefore, that chain will be more taut than the others with the result that the lump of that chain breaks up first. The very removal of thislump causes concentrated weight from the rail 21 to shift itself to the next smaller lump with the same result that the same is broken up, and so on until all lumps around the chains of that particular assembly unit have been broken up. The net result is that the lumps around the base ends of the chains are thus effectively broken up in contrast to chains that have no such longitudinal interconnecting member as the rail 21. w

The breaking up of the lumps is illustrated in reater deiailin-Figs. 4, 5 and 6. As the kiln rotates in the clock-wise direction shown, the weight of the chain assembly begins to act upon the solidified lmnps of material surrounding the anchoring points and base portions of the chains. and ii. the weight of the assembly, inclusive of the rail member 21, is great enough to break the hnnpsh'om the drum shell, the formation of a ring or constriction can be prevented. In Fig. 4 a chain assembly 0 has reached a position where the weight of the assembly is about to make itself felt upon the lumps P surrounding the anchoring points of the chains. Fig.5 shows more specifically the condition or the chain assembly unit due to the formation of the lumps P. That is to say. the hnnp P surrounds an initial portion of the maintaining that portion at; an angle to the vertical, while the balance b of the chain hangs perpendicular from the point ,0 downward, which point 0 designatesthe tip of the lump P. As soon as th full weight of the assembly makes itself suificiently felt with respect to the anchoring point of the chain and with respect to the lumps, the lumps will break up and the chain will straighten out perpendicularly as shown in Fig. 6. It will be noted (see Fig. 5), that due to the size of the lump P the chain portion 11 and the rail acting perpendicularly will establish a leverage L upon the lump P and with respect to the anchoring point X, which leverage is eifective in the breaking up of the lumps P. It will be noted that there is no entangling of the chains with one another in the lower portion of the drmn, nor an imdue interference of the chains with the progress of the material being treated, beyond that desired to retard the flow oi. material in that particular treatment phase. It will also be the drum will not interfere to any objectionable degree with the progress of the material through the drum or with the passage of the gases therethrough. However, the chains as well as the weights will absorb heat by contact with the gases in the upper portion of the drum and that absorbed heat will in turn be transferred to the material as-the chains and the rail come again into contact with th material in the lower portion of the drum; 7 i

annular baflles or flow retarding dams provided permit the slurryzto instead of causing it to 'back up towards the feed inlet end. For example, in Fig. 7 there are shown to be provided iive such dams 28, each dam containing a slurry level 28 slightly lower than the one preceding. The dams 28 while desirable as flow retarding elements also tend to act as a base upon which objectionable and undesirable mud rings or accumulations of material tend to build up. A slightmud ring formed for instance on the first or uppermost dam 28 would change the 'efiect thereof with respect to the operation to such an extent as to cause" the'ma'terial or slurry fed to the ldln to back up and out otthe feed end of the kiln. Likewise, ainud ring or constriction formed on any of the other dams would cause the material similarly to backj iipfand to interfere with the desired normal functioning To! the kiln.

However, the provision of assemblies as conceived according to this intention make feasible the use of the flow retar ing da s 28, because the chain assemblies break up and tend to prevent the formation of mudrings or constrictions, so

the dams can be used and the time available for evaporation of the water in the slurry can b cor-.

respondingly and greatly increased by their use.

aim:

I cl 1. A rotary kiln construction having one end of the kiln drum adapted 'to havefed thereto material to be treated, and th opposite end ofthe drum adapted for the entry into the interioroi' the drum of gases to pass through the drum in counter-current to the material being treated therein, said kiln construction being characterized by a plurality of weighted chain assembly units provided in that portion of th'edrum' that is closest to the material feed end thereof,'eaeh of which assembly units comprises a series ofchains fastened to the drum,,at points along a'line substantially longitudinally oi. the drum, and a common weight member attached to the free ends of the chains of that assembly unit for weighting the noted that the rails extending longitudinally of 1s chains, which common weight member comprises a rail member extending substantially the length of said chain assembly longitudinally of the drum. 2. A rotary kiln construction according to claim 1, with the addition that a series of annular flow retarding elements is provided inside the feed end portion or the drum, said annular elements exin respective planes transversely of the longitudinal axis of the drum.

GILBERT SEIL.

determined by th slope of the kiln so thatit will be lower than the dam which precedes it and flow forward through the

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