US3717938A

US3717938A - Apparatus and method for drying or pre-heating pulverulent material

Info

Publication number: US3717938A
Application number: US00068050A
Authority: US
Inventors: K Sylvest
Original assignee: FLSmidth and Co AS
Current assignee: FLSmidth and Co AS
Priority date: 1969-09-02
Filing date: 1970-09-28
Publication date: 1973-02-27
Anticipated expiration: 1990-02-27
Also published as: SE365042B; DE2043534A1; GB1251572A; FR2060811A5; ES383273A1

Abstract

An apparatus and method for drying or preheating granular or pulverulent material. The apparatus is in the form of an upright stack or tubular conduit within which a continuous helical surface extends sloping in a downward manner. Heated gas flows from the bottom of the stack along at least one vertical channel within the stack to heat the material descending down the stack. Specific means are provided within the stack to prevent the gas from flowing continuously over the helical surface.

Description

United States Patent [191 Sylvest 11 Feb. 27,1973

[ APPARATUS AND METHOD FOR DRYING OR PRE-HEATING PULVERULENT MATERIAL [75] Inventor: Karl Jens Sylvest, Copenhagen-Valby, Denmark [73] Assignce: F. L. Smidth & Co., Cresskill, NJ.

[22] Filed: Sept. 28, 1970 [211 Appl. No: 68,050

[30] Foreign Application Priority Data Sept. 2, 1969 Great Britain ..43,349/69 52'] U.S.Cl ..34/168, 34/171 51 Int. Cl ..F26b 17/12 [58] Field otSearch....34/64, 65, 168, 171, 164, 169;

[56] References Cited UNITED STATES PATENTS 1,920,107 7/1933 Richardson ..34/1 74 X 5/1961 Zimmermann et al. ..34/l7l X 4/1963 Hansen ..34/l64 Primary Examiner-Kenneth W. Sprague Assistant Examiner-James C. Yeung AttorneyPennie, Edmonds, Morton, Taylor & Adams [57] ABSTRACT An apparatus and method for drying or preheating granular or pulverulent material. The apparatus is in the form of an upright stack or tubular conduit within which a continuous helical surface extends sloping in a downward manner. Heated gas flows from the bottom of the stack along at least one vertical channel within the stack to heat the material descending down the stack. Specific means are provided within the stack to prevent the gas from flowing continuously over the helical surface.

10 Claims, 7 Drawing Figures PATENTEH f 3.717, 938

INVENTOR. KARL J'ENS SYLVEST BY M M,%m,'12 26* K04 ATTORNEYS PATENTEDFEBZ? 191s SHEET 3 BF 3 INVENTOR. KARL J'ENS SYLVEST ATTO R NEYS APPARATUS AND METHOD FOR DRYING OR PRE-I-IEATING PULVERULENT MATERIAL BACKGROUND OF THE INVENTION Preheaters of the stack type are provided with staggered, built-in guide surfaces, often projecting from the walls of the stack. The material supplied to the stack at its upper end and passing downby gravity slides from one guide surface to the next. The guide surfaces may be inclined or horizontal and served to retard the passage of the material so as to bring about contact between the material and the hot gas flowing countercurrently up through the stack. Heat exchangers of this kind are used for drying or cooling as well as preheating granular or pulverulent material. These heat exchangers or stack preheaters are extensively used in com-- bination with a rotary kiln for burning cement. The raw material fed to the upper end of the stack is preheated by means of the waste gases from the rotary kiln, the gas outlet of which is connected to the lower end of the shaft, and the raw material preheated in the shaft passes from the bottom of it into the rotary kiln.

As the material falls down through the stack from one guiding surface to the next it is subjected to a certain intended whirling movement by the flow of the gas which is caused to form eddies by passing between the guide surfaces. Thus a more intimate contact between the material and the gas is provided by which the heat exchange is improved. In the known heat exchangers of this type the formation of eddies is not very effective, and the heat exchangers have to be provided with many stages and therefore become very tall if a reasonable and effective heat exchange is to be obtained.

The flow of material and gas in the space above the restricted cross-sections of ordinary stack pre-heaters are of essential importance to the operation of the shaft. Ordinary stack pre-heaters contain restrictions which extend along separate closed horizontal paths. In the non-flow space above these cross-sections there is formed a saturated suspension of material in smoke gas called aggregates, which makes it possible for the material to move in stages down through the stack countercurrently to the gas. Eddies are formed, and

, these stationary eddies will tumble over theedge formed by the restricted cross-section as they pass from one chamber to the next lower chamber. The length of therestriction measured along a line, i.e., the length of the perimeter of the circle bounding the restricted cross-section, is an indication of the extent of the spaces of non-flow.

It appears that the dispersion of the aggregates in th space below a restricted cross-section is necessary so that the heat may be transmitted from the gas to the material during the time available. Thus greater effi- .ciency of heat transmission within the stack is obtained the more frequently the formation and subsequent dispersion of the aggregates takes place in the stack during the passage of the gas. This frequency is dependent on the frequency at which the gas passes a restricted section while flowing up the stack. Thus, the effectiveness of heat transmission within the stack depends upon the total length of the restrictions and the number of times this length extends around the axis of the shaft.

SUMMARY OF THE INVENTION The present invention provides an improved apparatus and method for drying or preheating materials, such as cement, in granular or powder form. It is the object of the present invention to increase both the length of the restrictions and the number of times this length passes around the stack axis so as to obtain an improved effectiveness of the heat transmission in the stack without increasing the height of the stack.

According to the present invention the apparatus for drying or preheating pulverulent material comprises an upright stack or tubular conduit. Means are provided for feeding the material into the upper end of the stack and means are provided for supplying gas to the lower end of the stack to flow counter-currently to the material descending through the stack. There is provided at least one vertical channel extending along the stack to allow for the free passage of the gas. A continuous helical guide means extends throughout the stack and slopes downwards from the top to the bottom of the stack. Means are provided for preventing the gas from flowing continuously over the helical guide means as the gas flows up the stack.

In performing the method of the present invention for drying or preheating pulverulent material, the material is introduced into the upper end of an upright stack and is directed in a continuous helical path in a downward direction through the stack. Gas is introduced at the lower end of the stack to flow countercurrently to the material descending through the stack. The gas is allowed to flow through at least one vertical channel extending along the stack while the gas is controlled in a manner which prevents the gas from flowing continuously over the helical path.

In the present invention specific means are provided for preventing the gas from moving continuously over the helical surface or surfaces in a helical path as the gas flows upwards. These means in the form of baffles may, for example, be vertical ribs positioned between the turns of the helix, but so constructed as not to interfere with the free downward passage of the material on the helical surface.

According to the present invention, the restrictions do not extend along separate closed circular horizontal circular paths as in the prior art devices, but extend obliquely, e.g., along an uninterrupted helix. Vertical ribs or the like extend parallel to the axis of the stack and prevent the gases from rotating or moving along a spiral formed path in the stack.

Furthermore, in accordance with the present invention, it is possible to form the obliquely extending restriction and the vertical ribs, which prevent rotation, in such a manner that there will not be any passage of saturated material (aggregates) in the form of stationary eddies through restricted cross-sections of the stack, but that such material willflow continuously along the obliquely extending restriction from the inlet to the outlet of the stack. During this continous flow, the material is constantly subjected to the action of eddies of passing gases. Thus, there will be a more pronounced countercurrent preheating in the moving eddies.

The gas flow up the shaft is essentially turbulent. At each point in the entire length of the helical surface, part of the stream is passing a protrusion constituted by the edge of the sloping surface. This results in a change in the velocity of this part of the stream and of course the circumferential position of this part is continually changing. Eddies with axis substantially perpendicular to the plane of the stack are formed immediately above the sloping surface as a result of the velocity changes. Moreover, the gas tends to flow in a helical path, and is consistently prevented from so doing by the baffles or their equivalent. Under these conditions, and provided that the relative quantities of material and gas are appropriate, the descending material forms the eddying aggregates or dense clouds, which move down the sloping surface towards its edge. On leaving this and entering gas of lower velocity, the eddies break up. In addition when any eddy collects more particles of material than it can carry, it breaks and new eddies are formed. Extremely effective heat exchange takes place during the repeated agitated movement of the material and gas in these eddies. Furthermore, when the gas velocity changes, particles of material entrained in the gas are deposited from it into the aggregates. This is a process which is continuously repeated .and which also increases the exchange of heat.

Two general features of the present invention are the provision of means for preventing the gases from passing helically up through the stack and the provision of an oblique edge encircling the center part of the stack for bounding the openings between consecutive chambers. Both of these features are characteristic of the two possible modes of operation in the stack, i.e., the operation involving stationary" eddies and the operation involving travelling eddies. The variables which determine the particular type of eddie in the operation are the inclination of the oblique edge and whether the baffles used for preventing a circulatory movement of the gases extend close to the edges. If the inclination of the edge is substantially small, and if the baffles extend close to the edge, the eddies will be stationary, whereas if the inclination of the edge is large enough and if the baffles leave free space just above the edge to enable the eddies to pass, then travelling eddies will be produced.

The tendency of the gas to flow at uniform velocity helically upwards may be still further reduced by providing vertical ribs extending into the free space of the upward passage of gas and thus'dividing that space into individual vertical channels. These channels need not be closed in relation to each other, as the ribs may be interrupted and not continuous.

The helical guide surface may be in the form of a continuous helical rib on the inner wall of the shaft. The gas would then flow centrally up through the stack with constant changes in direction as explained above. In this particular embodiment a central core in the form of a pipe or a solid core can be provided in the stack so that the free space through which the gas flows upwards is annular about the core. This is desirable in order to ensure that no gas flows upwards along the axis of the stack without taking part in the process of heat exchange with the material. Baffles, e.g., vertical ribs, to divide the free space into individual channels may project inwards from the central core. Alternately, the helical surface may be in the form of a continuous helical guide surface on a central core in the shaft. The free space for the passage of the gas would then be outside this core. Baffles, e.g., vertical ribs, to divide the free space into individual channels may project inwards from the inner wall of the stack.

Embodiments of stack preheaters constructed in accordance with the present invention are illustrated in the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical section through a stack preheater in a cement manufacturing plant, a part of which is also shown;

FIG. 2 is an enlarged cross section on the line 2-2 of FIG. 1;

FIG. 3 is a vertical section through a modified form of a stack pre-heater similar to FIG. 1;

FIG. 4 is a cross section on the line 4-4 of FIG. 3;

FIG. 5 is a vertical section through a second modified form of a stack pre-heater similar to FIG. 1;

FIG. 6 is a cross section on the line 66 of FIG. 5; and

FIG. 7 is a cross section through another modified form of a stack pre-heater.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show a preheater with a tubular stack 1 which at its lower end communicates directly with a rotary kiln 2 through a pipe 3 through which waste gas from the kiln flows. Also, through pipe 3, the material is introduced into the kiln. At its upper end the stack 1 has an inlet opening 4 for the introduction of raw material. The stack also has outlet openings 5 for the passage of gas through pipes 6 to cyclones 7. The gas The top of the stack has an opening 11 closed by a plate 12 which can be raised when desired. The stack has a refractory lining l3 and is supported on pillars 14.

The essential feature of the stack 1 as shown in FIG. 1, is the incorporation of a continuous helical guide 15 on the inner surface of the stack, the helical guide forming a downwardly sloping surface. Another essential feature of the stack are the triangular plates which project inwardly from the wall of the stack to prevent the gas from the kiln from flowing upwards in a helical path.

The stack is formed within a steel casing, but the parts inside of the stack that come into contact with the hot gases are made of a refractory material. The helical guide 15 is reinforced by metal reinforcement 16. Naturally the dimensions of the helical guide and the proportion of the height of the stack that it occupies may vary. The space available for the upflow of the gases must, of course, be adequate and may amount, for example, to 25 percent or more of the cross-sectional area of the stack.

When the raw material is introduced through the inlet opening 4, it is brought into contact with the gases coming from the kiln 2.and flowing upwards through the stack. The inlet opening 4 lies in a part of the stack of relatively small diameter and the velocity of the gases is therefore so high that most of the material is carried out of the stack by the gases. However, when the gases pass through the cyclones 7 the raw material is separated from the gases and passes to the interior of the stack just above the cylindrical part of the wall. The material is entrained in the gas when the velocity of the gas is steady and is separated from the gas when the velocity changes.

In FIGS. 3 and 4 a column 19 shaped similar to a drill bit with a helical thread, is built centrally into a tubular stack 1, the thread forming a downwardly sloping surface 18. A free space 21 forming a vertical channel for the upward passage of the gases is formed around this central column. To prevent helical flow of the gas, baffles in the form of triangular plates 22 may be fixed between the turns of the thread, or vertical partitions 23 may be provided in the free space between the stack wall and the edges of the thread and extend substantially from the bottom to the top of the stack. As shown in FIG. 3, the plates or partitions, as the case may be, extend over the whole length of the helix. Although not shown, it is possible in accordance with the present invention to use a combination of plates 22 and partitions 23.

The stack pro-heater shown in FIGS. 5 and 6 is similar to that shown in FIG. 1 except that a central pipe 24 is built into the preheater, so that the free space for the upward flow of gas is annular and outside this pipe. Vertical ribs 17 extend between the wall of the shaft and the wall of the pipe. The pipe 24 may be used to bring the gases from cyclones, such as those shown at 7, to a fan at ground level.

The shaft need not be circular in cross-section, but may for example be elliptical as shown at 25 in FIG. 7. A continuous essentially helical rib 26 is provided inside the shaft to present the sloping surface. A core 27 with ribs 28 is built into the shaft, and the free space for the upward passage of gas is that between the core 27 and the inner edge of the rib 26.

The capacity of any of the shafts shown may be increased by providing a multiple rather than a single helix within it.

Furthermore the apparatus according to the present invention may also be used for cooling hot material by introducing air or some other cold gas at the lower part of the stack.

Iclaim:

1. An apparatus for drying or pre-heating pulverulent material comprising an upright stack, means for feeding the material into the upper end of the stack, means for supplying gas to the lower end of the stack to flow counter-currently to the material descending through the stack, a continuous helical material guide means extending throughout the stack encompassing and defining at least one vertical open space extending along the stack to allow for the free passage of gas therethrough, the guide means sloping downwards from the top to the bottom of the stack, and means for preventing the gas from flowing continuously over the the downward passage of the material.

3. An apparatus according to 01mm 2 wherein the vertical ribs extend into the channel for the upward passage of the gas dividing the channel into individual vertical channels.

4. An apparatus according to claim 1 wherein the stack includes a central core extending vertically through the stack forming an annular channel between the external wall of the core and the internal wall of the stack for the free passage of gas, and the continuous helical guide means comprises a continuous helical rib on the inner wall of the stack.

5. An apparatus according to claim 4 wherein vertical ribs project outwardly from the central core dividing the annular channel into individual channels.

6. An apparatus according to claim 1 wherein the stack includes a central core extending vertically through the stack, the continuous helical guide means comprising a continuous helical rilb on the central core, whereby a channel for the upward passage of the gas is outside of the core.

7. An apparatus according to claim 6 wherein vertical ribs project inward from the inner wall of the stack dividing the channel into individual channels.

8. A method for drying or preheating pulverulent material comprising introducing the material into the upper end of an upright stack, directing the material in a continuous helical path in a downward direction through the stack along a guide means extending throughout the stack, introducing gas at the lower end of the stack to flow counter-currentlyto the material descending through the stack, allowing the gas to flow through at least one 'vertical channel extending along the stack the channel being defined by the guide means, and controlling the gas in a manner which prevents the gas from flowing continuously over the helical path.

9. A method according to claim 8 wherein the gas is controlled by vertical ribs without interfering with the downward passage of the material.

10. An apparatus for drying or pre-heating pulverulent material comprising an upright stack, means for feeding the material into the upper end of the stack, means for supplying gas to the lower end of the stack to flow counter-currently to the material descending through the stack, at least one inclined material guide means extending downward in the stack encompassing and defining at least one vertical open space extending along the stack to allow for the free passage of gas therethrough, and means for preventing the gas from flowing continuously over the guide means along a helical path as the gas flows up the stack.

i t III I II

Claims

1. An apparatus for drying or pre-heating pulverulent material comprising an upright stack, means for feeding the material into the upper end of the stack, means for supplying gas to the lower end of the stack to flow counter-currently to the material descending through the stack, a continuous helical material guide means extending throughout the stack encompassing and defining at least one vertical open space extending along the stack to allow for the free passage of gas therethrough, the guide means sloping downwards from the top to the bottom of the stack, and means for preventing the gas from flowing continuously over the helical guide means along a helical path as the gas flows up the stack.

2. An apparatus according to claim 1 wherein said means for preventing the gas from flowing continuously over the helical guide comprises vertical ribs mounted above the helical guide means without interfering with the downward passage of the material.

3. An apparatus according to claim 2 wherein the vertical ribs extend into the channel for the upward passage of the gas dividing the channel into individual vertical channels.

6. An apparatus according to claim 1 wherein the stack includes a central core extending vertically through the stack, the continuous helical guide means comprising a continuous helical rib on the central core, whereby a channel for the upward passage of the gas is outside of the core.

8. A method for drying or preheating pulverulent material comprising introducing the material into the upper end of an upright stack, directing the material in a continuous helical path in a downward direction through the stack along a guide means extending throughout the stack, introducing gas at the lower end of the stack to flow counter-currently to the material descending through the stack, allowing the gas to flow through at least one vertical channel extending along the stack the channel being defined by the guide means, and controlling the gas in a manner which prevents the gas from flowing continuously over the helical path.