EP0044476B1 - Tube for the indirect heating of easy flowing material and heat exchanger composed of such tubes - Google Patents

Description

The invention relates to the use of a tube which can be rotated parallel to the tube about an axis which can be inside or outside the tube, the tube shell of which is composed of flat surfaces for indirect heat treatment of powdery to granular, free-flowing material and the use of a Heat exchanger that is constructed from such tubes.

It is known to heat-treat powdery to granular, free-flowing material in a rotary kiln, the axis of which can run horizontally or obliquely. This can lead to direct or indirect heat transfer. Indirect heat transfer occurs when the transition from the solid to be treated to a liquid or gaseous medium or another solid takes place via a partition, ie direct contact with the substance to be treated by the heat transfer medium is avoided.

The rotary kiln can be divided into chambers connected in parallel to increase the surface. A continuous process is preferred; Therefore, conveying elements for the product to be treated are present in known rotary kilns; Usually, these are the helix in the (cylindrical) tube on the inside. It is known that it is very important that the material to be treated is thoroughly mixed in the tube in order to achieve uniform treatment and good heat transfer and to avoid damage to the material. Therefore, in known heat exchangers to improve the mixing effect, in addition to the helical conveying elements, baffles or rods or other baffles are also provided parallel to the tube jacket, as a result of which better mixing is achieved when the tube is turned.

It is also known that the heat exchange area of an apparatus is increased in that several smaller tubes are connected in parallel to form a bundle instead of a single tube with a large cross section; Such a rotating bundle is also referred to as a rotary kiln.

US-A-2 899 176 describes round tubes with conveying elements in which the main amount of heat is transferred through the conveying elements. The stakes are quite complex.

Flat surfaces in heat exchangers for the treatment of gases and liquids are known according to FR-A-489 266 or AU-B-481 237. There are considerable differences between the heat transfer from solid to pipe and liquid or gas to pipe in rotary kilns.

The heat transfer coefficients in fixed horizontal pipes through which gases or liquids are passed are easily comparable with those in rotating pipes, while with solids in pipes the rotary movement is always necessary to determine the heat transfer coefficients.

The cooler, as described in US-A-1 769412, shows round tubes with spirals which give no suggestion to make the tubes square and to provide the flat surfaces with baffles.

It has now been found that a pipe or a heat exchanger which consists of a plurality of pipes connected in parallel has advantageous properties if the pipe jacket is composed of flat surfaces and baffles are present at least on an inner pipe jacket surface at an angle to the pipe axis. The invention therefore relates to a tube for indirect heat treatment of powdery to granular, free-flowing material which runs parallel to the tube, can be rotated about an axis which can be inside or outside the tube, and whose tube jacket is composed of flat surfaces and inclined baffles are provided on the pipe axis at least on an inner pipe surface. Pipes whose cross sections are square or equilateral triangular are very particularly preferred. A heat exchanger constructed from the pipes according to the invention is particularly suitable for heat exchange with another solid medium if equilateral triangles or squares are interconnected in the densest packing, which are flowed through in such a way that two pipes through which the same medium does not abut on one side. In the case of heat transfer to a liquid or gaseous medium, a line-shaped arrangement of the tubes according to the invention can be useful. The distance between two such tube surface bundles can be chosen freely according to the heat transfer conditions.

The tube according to the invention with flat surfaces has several advantages over the known cylindrical tube, which are particularly useful when several such tubes are connected in parallel. With the same cross-section, the heat exchange surface is larger. With less effort than with cylindrical pipes, the conveying and mixing performance can be improved by simple installations. While a circular tube running around the entire inner wall is practically always required for a circular tube for manufacturing reasons and baffles on the wall are required to increase the mixing effect, it is sufficient for a triangular or square tube if a tube inner wall extends obliquely to the axis Sheets are attached. The dwell time spectrum is not significantly broadened by the omission of conveyor elements on some inner sides.

Because of the conveying elements, the rotary kiln according to the invention is generally operated horizontally. Solid material can also flow through it in cocurrent or countercurrent without difficulty. In terms of production technology, it is considerably less complex if rectangular guide plates only have to be attached to a flat inner wall than if a continuous helix are attached to the inner tube got to. Such tubes can also be produced with a very small cross section without difficulty. The heat exchange surface can be increased considerably for a given cross section of the furnace; In addition, the mixing compared to round tubes is increased. The edges where the flat outer surfaces meet look like chicanes. It has been shown that in the tubes according to the invention it is usually possible to dispense with rods or further guide plates. Despite the unusual tube shape, a reactor can be produced more economically from the tubes according to the invention than with round tubes of the same output.

There are no problems with the dimensioning of the heat exchanger; however, some conditions for optimal heat transfer are particularly adaptable. Such a heat exchanger can be adapted particularly well both for indirect heat exchange with a gas or a liquid or with another solid substance. The triangular and rectangular cross section of the tubes is preferred. The obvious hexagonal honeycomb arrangement in a heat exchanger is less suitable. Even pipes with a side length of a few centimeters can be realized.

To produce the tube bundles in a reactor, it is usually sufficient if correspondingly folded sheets are welded or screwed on the outside. It can then occur that good passes from one tube into the adjacent tube via the abutting edges; the rotation changes little in the degree of filling of the individual tubes. The skilled worker is aware that it is important to dose the material to be treated onto the individual pipes and not to overfill the pipes. It is irrelevant in the heat exchanger according to the invention whether the two product flows flow in the same direction or counter to one another. Both options can be implemented in a simple manner.

In the case of indirect heat transfer to a gaseous medium, it may be necessary to make the gaps through which the gas flows relatively narrow in order to achieve a high flow rate of the gaseous medium. Because of the flat boundary surfaces of the pipes, it is easy to make the distances between the pipes very even, which is never possible with round pipes (in special cases, double-walled pipes are even required there).

The shape of the tubes according to the invention allows the heat exchanger inserts to be produced in a particularly simple manner.

• Fig. 1: Vierkantrohr mit Förderrippen;
• Fig. 2a, 2b: Vierkantrohr mit Förder- und Staurippen;
• Fig. 3: Dreieckrohr mit Förderrippen;
• Fig. 4a, 4b, 4c: Dreieckrohr mit Förder- und Staurippen;
• Fig. 5: Längsschnitt durch einen Feststoff-Feststoffwärmetauscher (Schnitt 5-5 nach Fig. 7);
• Fig. 6: Querschnitt durch einen Feststoff-Feststoffwärmetauscher mit Dreieckrohren;
• Fig. 7: Querschnitt durch einen Feststoff-Feststoffwärmetauscher mit Viereckrohren (Schnitt 7-7 nach Fig. 5);
• Fig. 8: Querschnitt durch einen Feststoff Gas-oder Flüssigkeitswärmetauscher;
• Fig. 9: Viereckigen Rohreinsatz für Wärmetauscher;
• Fig. 10: Viereckigen Rohreinsatz für Wärmetauscher;
• Fig. 11: Dreieckiger Rohreinsatz für Wärmetauscher.

The invention is further described below by way of example and illustrated in the drawing. Show it:

• Fig. 1: Square tube with ribs;
• Fig. 2a, 2b: square tube with conveying and storage ribs;
• Fig. 3: triangular tube with ribs;
• 4a, 4b, 4c: triangular tube with conveying and retaining ribs;
• 5 shows a longitudinal section through a solid-to-solid heat exchanger (section 5-5 according to FIG. 7);
• Fig. 6: cross section through a solid-solid heat exchanger with triangular tubes;
• Fig. 7: cross section through a solid-solid heat exchanger with square tubes (section 7-7 according to Fig. 5);
• 8: cross section through a solid gas or liquid heat exchanger;
• Fig. 9: Square tube insert for heat exchangers;
• Fig. 10: Square tube insert for heat exchangers;
• Fig. 11: Triangular tube insert for heat exchangers.

In Fig. 1, a tube 1 according to the invention is shown schematically with a square cross section. When the pipe is horizontal, it is sufficient to transport the solids if rectangular conveyor ribs 2 are welded onto an inside. In particular, baffles parallel to the pipe axis can normally be dispensed with.

In Fig. 2, a square tube 1 with conveyor 2 and baffle ribs 3 is shown in cross and longitudinal section.

Even with a triangular tube 4, in FIG. 3 here with an equilateral cross section, it is normally sufficient if there are conveying ribs 5 on the inside.

4 shows a triangular tube 4 with conveyor ribs 5 and retaining ribs 6.

The length of the flat surfaces in cross section is particularly preferably 80 to 200 mm.

In many cases, the tubes according to the invention are connected in parallel to enlarge the heat exchange surface. A longitudinal section through such a heat exchanger is shown in Fig. 5. The interconnected pipes 10 are normally surrounded by a cylindrical sleeve 11. The reactor is operated horizontally. In this example, a heat exchange is to take place between two solid products. In this example, the heat-emitting product is fed in via the hopper 12 and passes through the reactor from left to right. In mirror image, there is an analog feed device for the cold product on the right side (not shown here); during the passage through the tubes 10 from right to left, it absorbs heat and exits the heat exchanger via the outlet opening 13. The product feed device 14 effects a uniform metering. Matched to the conveying devices 15 in the pipes, the metering 14 always ensures that the filling height in the pipes 10 always remains constant over the entire length, and that all pipes which are flowed through by the same product are also filled to the same extent, if at all A correction of the quantity may be necessary for the outer tubes of the insert, since these tubes do not heat in the same way on all sides transition are involved. A section 7-7 through the heat exchanger in Fig. 5 with triangular tubes is shown in Fig. 6, with square tubes in Fig. 7. The product to be heated flows through the tubes 10a, and the product to be cooled flows through the tubes 10b in the opposite direction.

While in solid / solid heat exchangers the pipes through which the two media flow are of the same magnitude and have the same cross-section, the cross-sectional areas can also be different in a reactor with heat transfer between a solid and a liquid or gaseous medium (FIG. 8). In this case, the tubes 12a are combined in a band-like manner; the solid medium is guided through them. The heating or cooling gas or the liquid flows around them on all sides. The densest packing was dispensed with here in order to reduce the flow rate z. B. to reduce the gas.

In the heat exchangers according to the invention, it is possible to construct the inserts in disks from the same elements. In pipes with a square cross section as in FIG. 9 or 10, two sheets 10, 21 are folded at right angles and welded 22 or screwed 22a at their ends.

Even if there is a small gap in some areas where two edges meet, the functionality of the heat exchange tubes is hardly disturbed, since the same product flow goes through all the tubes formed by the plates 20, 21 and there is no excess between the two due to the rotation Can form tubes. If a heat exchanger is built up from inserts according to FIG. 9, the cross-sectional areas for the two media are the same. Such a heat exchanger can also be achieved with inserts according to FIG. 10 if the inserts collide at their tips and are welded or screwed together on the outside. Inserts according to FIG. 10 can, however, also be interconnected in such a way that the tips of the upper insert fall into the “valleys” of the lower insert and thus an arbitrarily adjustable gap is created between the two inserts. This structure is particularly preferred when the solid substance flowing through an insert according to FIG. 10 is to give off or absorb its heat to a liquid or a gas, for which of course no tubular guide is necessary. In the case of a liquid medium, the gap between two inserts according to FIG. 10 can be small. If the second medium is a gas, it can be useful if there are ribs on the outside of the plate inserts according to FIG. 10 in order to enlarge the heat exchange surface.

The same variety as for plates made of square tubes according to FIG. 10 can also be achieved for plates with triangular tubes according to FIG. 11. Again, it is usually sufficient if the two plates 23, 24 are welded at their ends 25 or 25 a) screwed. If these plates are stacked tightly on one another and laterally welded or screwed together, a heat exchanger is obtained, the cross-sectional area of which is relatively the same for both media and which is particularly suitable for a solid / solid heat exchanger. If, on the other hand, there is heat transfer to a liquid or gaseous medium, the individual distances can also be arranged at a greater distance from one another, as is also indicated in FIG. 8, for example, or the inserts according to FIG. 11 can also be composed in this way ensure that the tips interlock or that the flat bases face each other, which means that very small distances can be maintained. When repairing the heat exchanger bundle, the ease of maintenance of the inserts according to the invention is particularly noticeable.

In general, it can be said that these pipes can achieve heat transfer coefficients of over 100 W - m - ^{1 -} K- ^{1 in} relation to the entire pipe area.

Claims (5)

1. Use of a tube which is rotatable about an axis which runs parallel to the tube and may be located inside or outside the tube, the jacket (1, 4, 20, 23) of which tube is composed of flat surfaces, and guide plates (2, 5) are present at an angle to the tube axis and on at least one interior surface of the tube jacket, for the indirect heat-treatment of pulverulent to granular, flowable material.

2. Use of a heat exchanger, consisting of a tube bundle which is rotatable about a common axis running parallel to the tubes, which tube bundle has a feeding device (14) for the individual tubes, the tube jackets (1, 4, 20, 23) of each tube in the bundle are composed of flat surfaces, guide plates (2, 5) are present at an angle to the tube axis and on at least one interior tube jacket surface, for the indirect heat treatment of pulverulent to granular, flowable material.

3. A tube bundle layer to be fitted into rotating tube heat exchanges characterised in that the tubes of the tube bundle layer are identical and are composed of flat surfaces (20, 21, 23, 24), the tubes are arranged next to each other in lines, only the adges of the tubes touching each other, and another medium flows around all the sides of the tubes, and in that the flat surfaces are composed of preformed sheets (20, 21, 23, 24) which are joined to each other in a gastight manner only at their two outer edges (22, 25, 22a, 25a).

4. Tube bundle layer according to Claim 3, characterised in that the shape of the cross- section of the tubes is rectangular, preferably square, or triangular, preferably equilateral.

5. Use according to Claim 2, characterised in that the material to be indirectly heat-treated is transported cocurrently or countercurrently in relation to neighbouring tube bundles.

Images