US3709474A - Rotary kiln for the production of a granular, bloated product - Google Patents

Abstract

This invention relates to a rotary kiln for the production of a granular bloated clay product, the kiln comprising a drying-kiln section and a burning-kiln section. In the heating zone in which the temperature of the clay granules increases from 300*-400*C to 800*-900*C the kiln is provided with a centrally located gas-flow tube which serves to protect the granules from the oxygen in the flue gas in the heating zone so that the bloating will be very effective. When passing the heating zone the granules pass the annular cavity between the outer surface of the gas-flow tube and the inner surface of the kiln lining. The outer surface of the gas-flow tube is provided with blades extending along the tube so that improved heat transfer from tube to granules is obtained.

Description

United States Patent 91 Kamstrup-Larsen 1 Jan. 9, 1973 [54] ROTARY KILN FOR THE PRODUCTION OF A GRANULAR, BLOATED PRODUCT [75] Inventor: nan-y Kamstrup Larsen, Copenhagan Valby, Denmark [73] Assignee: A/S Dnnsk Leca, Glostrup, Denmark '22 Filed: Jan. 18, 1971 [21] Appl. No.: 106,994

[30] Foreign Application Priority Data Jan. 27, 1970 Denmark ..373/70 May 5, 1970 Denmark ..2279/70 52 us. Cl "263/3211, 263/21 B [51] Inn-Cl ..F27b 7/02 [58] Field of Search ..263/21 B, 32 R [56] References Cited UNITED STATES PATENTS 3,454,357 7/1969 Rhees et al ..263/2i B 3,312,455 4/i967 Chassevent et al. ..263/32 R Primary Examiner-John J. Camby AttorneyCushman, Darby & Cushman [57] ABSTRACT This invention relates to a rotary kiln for the production of a granular bloated clay product, the kiln comprising a drying-kiln section and a burning-kiln section, In the heating zone in which the temperature of ;the clagrariuleincreases from 300-400 C to 00%999? C ist c i m d- 2 with r fsm s located gas-flow tube which serves to protect the granules from the oxygen in the flue gas in the heating,

zone so that the bloating will be very effective. When passing the heating zone the granules pass the annular cavity between the outer surface of the gas-flow tube and the inner surface of the kiln lining. The outer surface of the gas-flow tube is provided with blades extending along the tube so that improved heat transfer from tube to granules is obtained.

16 Claims, 17 Drawing Figures PATENTEU JAN 9 I975 SHEET 1 [1F 5 Fig. 7

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LL] lI II/I/ Ill PATENTED JAN 9 I975 sum 3 0F 5 PATENTEDJAN 9 ms SHEET 5 [IF 5 ROTARY KILN FOR THE PRODUCTION OF A GRANULARJ'SLOATED PRODUCT The present invention relates to a rotary kiln for the production of a granular, bloated clay product, comprising a drying-kiln section and a burning-kiln section which are either fastened rigidly together or capable of rotating independently of each other.

it is gradually forced away from the wall of the kiln toward the longitudinal axis so that the flue gas is The belief has hitherto been held that a completely I as long as condition (b) is observed faithfully in the socalled heating zone of the kiln, it is not so vital to fulfil condition (a), since experiment has revealed that an acceptable degree of bloating can be achieved provided that the oxygen content of the atmosphere in the heating zone in which the temperature increases from 300400C to 800-900C is kept low, and the heating process of the clay'is primarily rectilinear. It has moreover been discovered that the flue gas in the kiln does not affect the bloating properties while the granules of clay are still moist, which is no doubt connected with the fact that the moisture released by the granules during heating completely eliminates the effect of the oxygen in the flue gas. It is not therefore necessary to protect the moist granules. Finally it has been noted that the oxygen content of the flue gas in the region of the kiln in whichthe temperature of the granules is approx. 800900C is of little significance to bloating. This is presumably due to the factthat the radiant heat from the kiln flameis more effective here, and that this is therefore the point at which it is possible to apply the rapid heat increase mentioned above.

The purpose of the invention is to indicate a method of construction of a rotary kiln of the type mentioned above, permitting flue gas with an oxygen content to be kept completely or partially separate from the clay granules in'the heating zone of the kiln in which the protect the granules from the oxygen in the flue gas, the

granules passing through an annular cavity surrounding the gas-flow tube. The effect of this arrangement is that when the clay granules move into the aforesaid zone they pass into the bottom of the aforesaid cavity and are covered by the gas-flow tube; as-the flue gas with its oxygen content flows through the gas flow tube, the latter will protect the clay granules againstthe undesirable effects of the flue gas in the critical zone of temperature increases from 300--400C to 800-900 the kiln. Bloating does not occur until the heating zone rangement is that as the flue gas passes through the kiln drawn from the clay granules.

Moreover, according to the invention, the part of the gas-flow tube that projects into the drying-kiln section can have a smaller diameter than the part projecting into the burning-kiln section. This design has been 7 proved in practice to be particularly suitable.

According to the invention, the part of the gas-flow tube pointing in the direction of flow of the flue gas can have a funnel which expands in this direction, and the funnel can be sufficiently far from the wall of the kiln to permit all the granules to pass on the outside of the gasflow tube while the latter takes in the major portion of flue gas. The effect of this arrangement is that there is a high degree of certainty that no flue gas will pass .through the annular cavity. The flue gas will pass only through the gas-flow tube.

Moreover, according to the invention, the part of the gas-flow tube that projects into the drying-kiln section can be unsupported in this section and can have a length which is less than or equal to the length of that partof the tube located in the burning-kiln section. The effect of this arrangement is a particularly simple design of gas-flow tube.

Another embodiment of the rotary kiln according to the invention is peculiar in thatthe part of the gas-flow tube located in the burning-kiln section is rigidly secured to the inside of this section of the kiln and that the part of the tube located in the drying-kiln section is rigidly secured to this section, and that the two portions of tube are linked in such a manner that they can rotate in relation to each other, and the joint between the two portions is smooth. This design is particularly suitable when the two sections of kiln can be rotated in relation to each other. i

It is further possible that the two portions of the gasflow tube can be linked by means of labyrinthal connecting devices. This arrangement produces a durable and simple connection between the portion of the gasflow tube.

Moreover, according to the invention, the outside of the gas-flow tube can be equipped with blades of a heat-conducting material, which blades extend along the length of the outer jacket and whose height equals something between one-tenth and nine-tenths ofthe gap between the outside of the tube and the inside of the lining of the kiln. The effect of this arrangement is that, as v the kiln rotates, the clay granules flowing through the annular cavity will be heated suitably rapidly since they touch and are conveyed by the blades. The blades are warm because theyare heatconducting and in contact with the tube, and the tube itself is hot because of the hot flue gas flowing inside it. As the kiln rotates, the blades convey some of the clay granules, which prolongs the period during which the granules are in contact with the hot blades and improves the conditions of heat transfer.

According tothe invention, the blades can comprise plate components bolted together with plate .segments, the plate segments forming the gas-flow tube. This arrangement ensures the possibility of simplified as-- sembly of the gas-flow tube and blades even when the kiln is closed.

Furthermore, according to the invention, part of the blades can project into the cavity bounded by the. gasflow tube. The effect of this arrangement is that the area enveloped by the hot flue gas is increased, which ensures that greater quantities of heat can be transferred to the blades.

According to the invention, the blades can be secured to the gas-flow tube by welding. This form of gas-flow tube is particularly suitable for fitting in a kiln whose ends can be made accessible.

Moreover, according to the invention, each blade can be located on a helix with a very steep angle in relation to the diameter of the gas-flow tube. This arrangement ensures that the forward movement of clay granules during rotation of the kiln is impeded with the result that the heat given off by the blades is sufficiently great.

Furthermore, according to the invention, each blade can be built up of two plates which together form a blade with a Y cross-section. This arrangement ensures that a wide area of contact is provided between the blade and the clay granules, which promotes the transfer of heat.

According to the invention, it is also possible to design each blade in the form of a rail with an L, T or hook" section. This arrangement ensures the simple design of a blade with great strength and large area.

Finally, according to the invention, the segments of the gas-flow tube can be designed as rails primarily with a U section in which the perpendicular webs of the U converge very slightly. This arrangement ensures a gas-flow tube with excellent wearing properties.

The invention is explained below with reference to the drawings, in which FIG. 1 shows an embodiment of the rotary kiln according to the invention in which the kiln is in two parts and the gas-flow tube is designed as a single unit;

FIG. 2 shows a cross-section of the same kiln through line lI in FIG. 1;

FIG. 3 shows a cross-section of the kiln through line II-Il in FIG. 1;

FIG. 4 shows a cross-section of the kiln through line III-Ill in FIG. 1;

FIG. 5 shows a second embodiment of the rotary kiln according to the invention in which the kiln is in two parts and the gas-flow tube is designed as a two-part unit;

FIG. 6 shows a third embodiment of the rotary kiln according to the invention in which the kiln is designed as one long tube inside which the gas-flow tube is designed as a single unit;

FIG 7 shows a larger scale section of a two-part gasflow tube forming part of the rotary kiln according to the invention; v

FIG. 8 shows a perspective view of a gas-flow tube;

FIG. 9 shows a cross-section of part of the kiln accordingto the invention in which the gas-flow tube with related blades are shown in the assembled position;

FIG. 10 shows a side view of part of the gas-flow tube with related blades, the blades extending parallel to the axis of the kiln;

FIG. 11 shows another design for the gas-flow tube with the blades located on helices;

FIG, 12 shows part of a rotary kiln inside which L- FIG. 13 shows aperspective view of part of the blades shown in FIG. 9;

FIG. 14 shows a perspective view of part of the blades shown in FIG. 12;

FIG. 15 shows a perspective view of part of a blade with a T cross-section;

FIG. 16 shows a perspective view of part of a blade whose edge is turned in; and

FIG. 17 shows a perspective view of part of one of the segments of which the gas-flow tube in FIG. 9 is built up.

The rotary kiln 1 shown in FIG. 1 consists of a drying-kiln section 2 and a burning-kiln section 3, the latter section being of slightly greater diameter than secton 2. The two sections can rotate at different speeds, and in a heating zone a between the two sections in which the moving granules are heated from approx. 300-400C to approx. 800-900C the kiln is fitted with a gas-flow tube 4 formed as a solid of revolution with an axis coinciding with the axis of the kiln. The gas-flow tube consists of a funnel portion 4a, a cylindrical portion 4b with a relatively large diameter, another funnel portion 40, and finally a cylindrical portion 4d whose length is less than the length of portion 4b. The tube is secured to the wall of the kiln by staybolts 7 with the result that an annular cavity 5 is formed between the tube and the inside of the kiln wall; This cavity extends the full length of the tube. The bottom of the cavity can hold clay granules 10 as these gradually move forward along the bottom of the kiln. When the clay granules arrive at cross-section IIIIII, all water will have evaporated and the temperature will be approximately 300400C, and in section a the granules will now be protected against the effects of the oxygen in the flue gas which flows through the center of the kiln from left to right in the direction of arrow A. When the granules reach cross-section II-II, they will have a temperature of approx. 800-900C. This increase in temperature is produced with the aid of heattransfer elements 6 located opposite parts 40, 4b and 4c the burning-kiln section 3 but the cylindrical part called 4 d is not connected with the wall of the kiln in the drying-kiln section. The tube is built of refractory steel and can therefore stand the high temperature of the flue gas.

FIG. 5 shows a rotary kiln in two sections, witha drying-kiln section 2 and a burning-kiln section 3, containgas-flow tube;

ing a gas-flow tube having two parts, 4e and 4f. The two parts are secured inside each section with the result that the desired cavity 5 is formed. As can be seen, part 4f is fitted inside part 4e, providing a firm guide between the two parts and an unbroken transfer from one part to the other. I

FIG. 6 shows another embodiment of the rotary kiln according to the invention, in which the kiln consists of a long tube in which is fitted a gas-flow tube made as a single unit. The temperature of the clay granules as they move forward and as the time passes does not require to increase very rapidly in the heating zone a but a relatively good bloating effect can be achieved if the temperature increases more or less uniformly through the kiln. 1

FIG. 7 shows in large scale the longitudinal section of a twopart gas-flow tube. The two parts are controlled in the axial direction.

FIG. 8 shows a projected view of a one-part gas-flow tube. As can be seen, the tube incorporates holes 9 to accommodate the stay-bolts 7.

The gas-flow tube can be designed in the form of one long cylinder or can be slightly tapered. The shape of the tube must depend on the design of the kiln. The important factor is that a suitable cavity must be formed between the outside of the tube and the inside of the kiln wall.

FIG. 9 shows a rotary kiln with a kiln wall 11 and a gas-flow tube 12. This tube can, for-example, consist of two parts in the shape of a truncated cone and two cylindrical parts but for the sake of clarity has been il-" lustrated with a cylindrical shape. Blades 13 project from the outside of the tube 12 with a length great enough topermit them to penetrate relatively deeply into the volume of clay granules 14 which roll forward along the bottom of the kiln. In FIG. 9 the blades 13 have been given a Y section, being built up of two angle-plates l3 and 13" fitted closely together. The gas-flow tube comprises rails 15 which are primarily channel-shape and whose perpendicular webs 15' and 15" converge slightly (see FIG. 17). Plates 13' and 13" and webs 15' and 15 are supplied with holes 24 in order that the parts can be bolted together by means of bolts 16. The blades in FIG. 9 extend parallel with the axis of the kiln, which axis rungs through point C. For the sake of clarity the section in the gas-flow tube and blades in FIG. 9 has not been shaded. When the hot flue gas passes along the interior of the gas-flow tube, it will contact the inside of the tube and transfer heat both to the tube and to the blades, and this heat will then be conveyed through the blades to the clay granules.

FIG. 10 illustrates part of the gas-flow tube viewed from one side (seen from outside the tube), the tube being fitted with the Y shape blades illustrated in FIG. 9. In FIG. 10 only one half is seen of the lower blade 13. The other blades are indicated by the brackets on the left of the figure. The blades opposite the two lower brackets are shown in full while the blade opposite the top bracket is partly concealed by the next lower blade, which itself is partly concealed by its neighbor. The axis of the kiln is indicated at 17. As the figure shows, the blades run parallel to the axis.

Instead of locating the blades parallel to the axis, they can be located on helices 18, 19, 20, 21 and 22 as indicated'in FIG. 11. The broken lines indicate the lines at which the blades are secured to the surface of the gas-flow tube 12.

Instead of building the gas-flow tube of plate segments bolted together, one may make'the tube of a homogeneous pipe 23 (FIG. 12). L-shaped blades 30 are welded on the outside of the tube either on straight lines extending parallel to the axis of the kiln or helices as shown in FIG. 11. The helices have however a fairly steep angle in relation to the diameter of the tube. As FIG. 12 illustrates, the outer portion of the blades project into the volume 14 of forward-moving clay granules. The blades with a Y section shown in FIGS. 9 and '10 are illustrated in a perspective view in more detail in FIG. 13. Instead of making the blade of two plates 13' and 13" fitted together, one may make it with a perpendicular web on whose upper edge an equal legged angle-iron is welded.

Part of the blades 30 in FIG. 12 is shown in more detail in FIG. 14, which is also a perspective view.

FIGS. 15 and 16 show two other forms of blade 25 and 26 with T section and hook section respectively. The characteristic of these blade designs is that they each have a very large surface, which promotes the transfer of heat between blade and clay granules.

The height of the blades can vary between one-tenth and nine-tenths of the gap between the outside 23 of the gas-flow tube 12 and the inside of the kiln wall 11, while their length can correspond to the length of the tube but there is no objection to their being discontinued at intervals along the tube. In the accompanying illustrations the blades are shown fitted on a cylindrical gas-flow device. There is nothing to prevent them also being fitted on the truncated-cone portions of the tube.

Many modifications of the invention are possible without deviating from its basic idea.

What we claim is:

j 1. In a rotary kiln for the production of a granular, bloated clay product, said kiln being of the type using a hotgas and including a drying zone for heating material to a predetermined temperature, a transition zone in flow communication with said drying zone for heating said material to a temperature higher than said predetermined temperature, a burning zone in flow communication with said transition zone, the improvement comprising tubular means disposed in said transition zone for substantially separating the hot gas from said material while said material is located in said transition zone.

2. The invention as claimed in claim 1 wherein said kiln is of the type in which the hot gas flows from said burning zone to said transition zone and then through said drying zone and said tubular means has a funnel shaped portion defining the boundary between said burning zone and said transition zone, said funnel shaped portion having one wide end which faces in the direction of said'burning zone and an end that is narrower than said wide end and spaced therefrom.

3. The invention as claimed in claim 2 wherein said tubular means further includes a hollow tube'having one end connected to said narrower end of said funnel shaped portion.

4. The invention as claimed in claim 3 wherein said hollow tube has a portion spaced from said one end thereof and which extends into said drying zone.

5. The invention as claimed in claim 4 wherein said kiln comprises a first elongated hollow member having an axis rotation and a generally cylindrically shaped interior surface of a selected diameter and an outlet end, a second elongated hollow member having an axis of rotation and a generally cylindrically shaped interior surface of a diameter greater than said selected diameter andan inlet end surrounding said outlet end of said first member, said funnel shaped portion being disposed in said second member and having a conical exterior surface that tapers in an axial direction radially inwardly from said interior surface of said second member.

6. The invention as claimed in claim 5 wherein said hollow tube with said funnel shaped portion connected as aforesaid is rigidly supported in said second hollow member and the exterior surfaces of said tube and funnel shaped portion are spaced radially inwardly from the interior surface of said second member to define a cavity for reception of material. 7

7. The invention as claimed in claim 6 where the said portion of said hollow tube which extends into said drying zone is rigidly supported in said first hollow member and is rotatable therewith independent of the rotation of said hollow tube.

8. The invention as claimed in claim 3 wherein said zones of said kiln have interior walls and the exterior of said hollow tube is spaced radially inwardly from said walls to define a cavity and the exterior of said hollow tube is provided with a plurality of blades of heat-conducting material, said blades extending into said cavity.

9. The invention as claimed in claim 8 wherein said hollow tube is constructed from a plurality of plate segments which are bolted together to form said tube with a said blade being bolted between adjoining plate segments. 10. The invention as claimed in claim 8 wherein said blades are welded to the exterior of said hollow tube.

11. The invention as claimed in claim 8 wherein said blades are mounted on the exterior of said hollow tube along the line of a helix. 12. The invention as claimed in claim 8 wherein eac of said blades has an end spaced from said hollow tube, said end having diverging portions in the form of a Y.

13. The invention as claimed in claim 8 wherein said blades are T-shaped in cross-section.

14. The invention as claimed in claim 8 wherein said blades are L-shaped in cross-section. I 15. The invention as claimed in claim 8 wherein said blades are provided withends that are hook-shaped.

16. The invention as claimed in claim 9 wherein said plate segments are U-shaped in cross-section with the legs of the U converging towards each other.

a: a a a:

Claims (16)

1. In a rotary kiln for the production of a granular, bloated clay product, said kiln being of the type using a hot gas and including a drying zone for heating material to a predetermined temperature, a transition zone in flow communication with said drying zone for heating said material to a temperature higher than said predetermined temperature, a burning zone in flow communication with said transition zone, the improvement comprising tubular means disposed in said transition zone for substantially separating the hot gas from said material while said material is located in said traNsition zone.

2. The invention as claimed in claim 1 wherein said kiln is of the type in which the hot gas flows from said burning zone to said transition zone and then through said drying zone and said tubular means has a funnel shaped portion defining the boundary between said burning zone and said transition zone, said funnel shaped portion having one wide end which faces in the direction of said burning zone and an end that is narrower than said wide end and spaced therefrom.

3. The invention as claimed in claim 2 wherein said tubular means further includes a hollow tube having one end connected to said narrower end of said funnel shaped portion.

4. The invention as claimed in claim 3 wherein said hollow tube has a portion spaced from said one end thereof and which extends into said drying zone.

5. The invention as claimed in claim 4 wherein said kiln comprises a first elongated hollow member having an axis rotation and a generally cylindrically shaped interior surface of a selected diameter and an outlet end, a second elongated hollow member having an axis of rotation and a generally cylindrically shaped interior surface of a diameter greater than said selected diameter and an inlet end surrounding said outlet end of said first member, said funnel shaped portion being disposed in said second member and having a conical exterior surface that tapers in an axial direction radially inwardly from said interior surface of said second member.

6. The invention as claimed in claim 5 wherein said hollow tube with said funnel shaped portion connected as aforesaid is rigidly supported in said second hollow member and the exterior surfaces of said tube and funnel shaped portion are spaced radially inwardly from the interior surface of said second member to define a cavity for reception of material.

7. The invention as claimed in claim 6 where the said portion of said hollow tube which extends into said drying zone is rigidly supported in said first hollow member and is rotatable therewith independent of the rotation of said hollow tube.

8. The invention as claimed in claim 3 wherein said zones of said kiln have interior walls and the exterior of said hollow tube is spaced radially inwardly from said walls to define a cavity and the exterior of said hollow tube is provided with a plurality of blades of heat-conducting material, said blades extending into said cavity.

9. The invention as claimed in claim 8 wherein said hollow tube is constructed from a plurality of plate segments which are bolted together to form said tube with a said blade being bolted between adjoining plate segments.

10. The invention as claimed in claim 8 wherein said blades are welded to the exterior of said hollow tube.

11. The invention as claimed in claim 8 wherein said blades are mounted on the exterior of said hollow tube along the line of a helix.

12. The invention as claimed in claim 8 wherein each of said blades has an end spaced from said hollow tube, said end having diverging portions in the form of a Y.

13. The invention as claimed in claim 8 wherein said blades are T-shaped in cross-section.

14. The invention as claimed in claim 8 wherein said blades are L-shaped in cross-section.

15. The invention as claimed in claim 8 wherein said blades are provided with ends that are hook-shaped.

16. The invention as claimed in claim 9 wherein said plate segments are U-shaped in cross-section with the legs of the U converging towards each other.

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