EP0029194A1 - Rotatable heat exchanging tube to be heated or cooled from the outside for the heat treatment of pulverulent to granular flotational, possibly sludged material - Google Patents

Abstract

In order to improve heat transfer in rotatable heat exchange tubes which can be heated or cooled from the outside, use is made of inserts consisting of a structural unit (12) and made from longitudinal strips (13) and coils (14), this unit (12) preferably being exchangeable. <IMAGE>

Description

The invention is directed to an externally heatable or coolable, rotatable heat exchanger tube for the heat treatment of powdery to granular, free-flowing, optionally slurried material, which has internals.

Such tubes are either individual tubes that can be rotated about their own axis or are arranged in parallel in a rotor rotating about a central axis. The rotary tube or the rotor are surrounded by a housing which is covered by a heat exchange medium, e.g. tempered gas or liquid is flowed through. The heat is exchanged between the temperature control medium and the material passing through the pipe via the pipe wall. Heat transfer by radiation (e.g. heating elements) is also possible.

For example, cooling and heating drums, the pipes of which have internals, such as lifting blades and / or screw spirals, are sufficiently known. With direct heating, the material to be treated is in the pipes in the Co-current or counter-current conveyed with the heating medium with an inclined or horizontal drum. The aim of these embodiments is to mix the heating gas and the material intimately in order to achieve the best possible heat transfer. This type of direct heat transfer from the heating or cooling medium to the goods is simple and very effective. However, many goods must not come into contact with the heating medium. In addition, the cleaning of the heating and cooling gases from entrained particles is very complex. Therefore, indirectly tempered cooling or heating drums are increasingly being used.

Various embodiments of tube dryers for indirect heat treatment are known, in which helices are built in for the uniform transport of the material. In the case of drying drums, which generally have pipes of larger diameter, strips are often attached to the inner wall, which are intended to prevent slipping, sliding or rolling on the drum wall. If one were to install the lifting blades or strips known from the directly heatable tubes in indirectly heated tubes, then this would be disadvantageous. The dust discharge would increase considerably, so that filters would have to be used; undesirable recondensation would occur and the undesirable cross-mixing with the product separation in the case of different grain sizes could occur in the case of indirect heating.

With direct heat treatment, it can be disadvantageous when all particles experience a precisely defined, even transport, that there is good contact with the pipe wall and that there is little gas inclusion between the particles. Indirect heat treatment, on the other hand, strives for exactly the opposite effects. The mechanisms of heat transfer in indirect heat treatment depend to a much greater extent on the properties of the material to be treated, the pipe dimensions and the layer heights than in direct heat transfer. With indirect heat transfer, the measures for good heat transfer at low temperatures (transfer through contact) can also be different than at high temperatures (transfer through radiation).

However, each type of indirect heat transfer has the following requirements in common: As far as possible no sliding, rolling or sliding of the goods on the pipe wall, but a defined dwell time on the wall; Throwing or sliding of the goods conveyed up during the rotary movement directly above the surface of the goods, so that the dropped goods can slide down, slide or roll on the sloping surface formed. The slope of the coils arranged in the pipes for transport should only be so steep that no union takes place.

The arrangement, shape and height of the strips (in extreme cases there may be bars against the wall), which should prevent the material from slipping on the inside of the pipe, are the decisive factors for good heat transfer in addition to the speed of the pipe and the spiral pitch. It is particularly advantageous to position the strips at such an angle that the strip is oriented approximately parallel to the surface of the material when the tube rotates when it slides out of the material. The shape of the strips, which is ideal for good heat transfer, is difficult to achieve, since the uniform transport of the goods is disturbed by these internals. In all solutions, however, the tube should only be filled with material to such an extent that the material does not flow over the spiral webs in order to avoid undesired cross-mixing.

The demands for the uniform transport of all particles, the adherence of the goods to the pipe wall, dropping of the highly conveyed goods directly above the surface of the goods and the avoidance of throws during the conveyance is achieved according to the invention in that the internals from near the Pipe inner wall arranged longitudinal strips and at least one coil coinciding with its axis with the pipe axis, the longitudinal strips together with the coil forming a structural unit which is attached to the pipe ends.

The result of this is that, if the speed is appropriately matched to the flowability and thermal conductivity of the material and the degree of filling of the pipe, a defined contact is obtained with the indirectly heated or cooled pipe wall, so that the circulation of the material takes place in defined, essentially vortex-free layers, and that through the Avoiding throws, a retention time defined for all particles is maintained with low cross-mixing.

The structural units are preferably interchangeably attached to the pipe ends. This embodiment is particularly favorable since the pipes are usually too narrow for a man to crawl in to fix the internals. The design allows the internals for each tube to be pushed into or pulled out of the tube as a unit. The attachment to the pipe ends is easily accessible. This constructive design is not only advantageous for the initial assembly; it is also particularly economical when replacing worn-out installation units and, by replacing the entire installation set, allows installations which are particularly adapted to the goods to be treated to be used without great effort, in order to optimize the heat transfer during the successive treatment of different goods. The tubes themselves are preferably on the outside with ribs, for. B. longitudinal or transverse ribs, or other area-enlarging elements to improve the heat transfer.

• Fig. 1 Das Drehrohr im Längsschnitt und
• Fig. 2 das Rohr im Schnitt gemäß Linie A-B in Figur 1.

In a drawing, the heat exchanger tube according to the invention is shown purely schematically in one embodiment and explained in more detail below. Show it:

• Fig. 1 The rotary tube in longitudinal section and
• 2 shows the tube in section along line AB in FIG. 1.

A rotary tube 2 is rotatably held in bearings 3 in a housing 1 and can be driven by means of a drive 4. Via a material feed pipe 5 and a chute 6, the feed is carried out on the front side 7 of the housing 1. A hot gas supply nozzle 8 opens out into the interior of the housing 1 through the front side 7. In the rotary tube 2, a unit 12 of internals, which consists of longitudinal strips 13 and a helix 14, is arranged and fastened to the tube ends by means of screw connections 15. The longitudinal strips 13 have such an inclination that when they emerge from the material they are parallel to the surface thereof. They are lower than the web height of the helix 14. Of course, the influence of the speed of the rotary tube 2 is important here. The helix 14 has such a slope that there is no throw during the conveyance.

Claims (2)

1. From the outside heatable or coolable, rotatable heat exchanger tube for the heat treatment of powdery to granular, free-flowing, optionally slurried material, which has internals, characterized in that the internals from in the vicinity of the inner wall of the tube (2) arranged longitudinal strips (13) and at least one helix (14) coinciding with its axis with the tube axis, the longitudinal strips (13) together with the helix (14) forming a structural unit (12) which is fastened to the tube ends. 2. Heat exchanger tube according to claim 1, characterized in that the structural unit (12) is interchangeable.

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