The invention in question concerns the manufacture of a tubular heat exchanger specially suited to conditions where there are major requirements for a high level of heat recovery, and for problem-free operation in connection with large variations in the relative amounts of the substances in the heat exchanger, as, for example, the percentage proportion of solid material in a slurry, where the substances are corrosive, and where the process is automatic for problem-free operation in connection with starting and stopping.

It is normal that, where cooling or heating is concerned, the substances in the cooling tube must move themselves with a high linear speed relative to the exchanger ^' s surface, This means that the exchanger should be long, but this is impractical. The exchanger is thus, in many cases, twisted into a spiral so that one achieves the criteria mentioned above, but within a smaller area. Such a spiral is, then, normally inside a tank, and the exchange of heat takes place between the substance in the tank and the spiral. However, the linear speed of the substance in the tank, relative to the outer surface of the spiral, is considerably less, and an agitator is fitted to increase this. This renders such a construction both expensive and complicated.

Of course, the agitator tank can also take the form of a smaller tube, through which the substance is pumped so quickly that an effective heat exchange is created, but e.g. at the cost of large quantities of coolant. The ideal solution would be for the diameter of the tube for a substance to be in accordance with its relative need for heat transfer to another substance.

This can be achieved by making a spiral-formed tubular heat exchanger with one or more spiral-formed exchangers contained within this first spiral-formed exchanger. In this way one achieves high linear speeds for effective heat exchange, the possibilities of optimal heat exchange between corrosive substances and relative inert substances through the choice of the spiral material, and, by no means least, the fact that the pitch on the spiral can be made less than the slip angle of possible solid material in a slurry or gas, so that, should operation be interrupted or brought to a halt, this solid material

will not slide down and block the heat exchanger, but will quite simply remain at the base of the tube. Upon starting up, the slurry/gas will be able to pass freely through the upper part of the tube, gradually taking the slurry with it in order thus to be able to restart without problems.

The Fl explanatory document no. 74,805, the DE official documents nos. 30 27 070, 31 14 297 and 32 27 119, detail known tubular heat exchangers which are manufactured by means of one or more tubes with a smaller diameter being housed within an outer tube, whereupon the tube combination is coiled or structured to the required spiral shape.

The method in question involves, briefly, the separate forming to a spiral the tube which is to be outermost, together with the separate forming to a spiral or spirals of the thinner tube or tubes, which are to be found within this outer tube, in order thereafter to screw the thinner tube spiral or spirals into the outer spiral. Thereafter the necessary supports/outer spacers and necessary flanges are mounted in the known manner.

The manufacture of the new tubular heat exchangers is illustrated by reference to the attached figures.

Fig. 1 shows an inner tube (1 ) which is partially screwed into the outer tube (2).

Fig. 2 shows a typical, ready mounted tubular heat exchanger, where (1) is the inner tube and (2) is the outer tube and (3) is a flange.

Fig. 3 shows a cross-section of a multi-tube where (2) is the outer tube and (1 ) is the inner tube and (4) is an extra inner tube. The inner tubes (1) and (4) are fitted with spacers which separate the tubes from one another.

The principle involved in screwing two spirals with approximately the same diameter and the spiral pitch of tubes of different diameters, and thereafter screwing the individual spiral-formed tubes together in order thus to achieve a multi-

tubular heat exchanger, is itself the essence of the invention in question.

The choice of tube materials is, of course, dependent upon the substance which is to be heat exchanged (cooled/heated). Here, for example, a titanium spiral for a corrosive slurry may be screwed into a plastic spiral for cooling water.

If one of these spirals gets damaged, it is a simple matter to unscrew the damaged spiral and replace it with a new one (or, possibly, repair the old one). This makes assembly and dismantling simple.

In order to avoid possible solid matter in a substance (slurry), which is to be heat-exchanged in the tubular heat exchanger, causing a blockage, it is preferable for the pitch on the spiral rings to be less than the slip angle for this solid matter in the substance, so that in the event of a halt to the operation, the solid matter does not slip down through the spiral and block it, but just remains at the bottom of the tube without blocking it.

The invention in question is, naturally, not limited by this since spirals with a very large pitch can also be constructed by means of the method under discussion.

The method in question thus represents a simple and cheap method in respect of the manufacture of the tubular heat exchanger concerned, and the repair of a damaged spiral can be effected quickly and simply, which is why tubular heat exchangers manufactured in accordance with the invention in question represent a cheaper and simpler alternative compared to known tubular heat exchangers and will, as a consequence of its mechanical construction, also display greater heat recovery, greater flexibility in respect of slurry or corrosive substances, and display a less problematical start/stop function for automatic processes.