Rotary heat exchanger

Heat exchanger for the heating or cooling of a liquid, in particular of a suspension, comprises of a container provided with an inlet and an outlet and wherein there is disposed at least one rotatably mounted, substantially horizontal heat exchange unit having two end pieces between which heat transfer pipes have been fitted, and a conduit for conducting a heat-accepting or heat-releasing fluid through the end pieces and the heat transfer pipes of said heat exchange unit, a central tube concentrically disposed in relation to the rotational axis of the heat exchange unit between the end pieces among the heat transfer pipes, the diameter of the central tube being not less than 40% of the greatest distance between any two heat transfer pipes, measured at right angles to the rotational axis and that at least the lower edge of the outlet from the container in which the heat exchanger unit has been disposed being located at a level lower than the topmost part of the central tube so that the latter can be held above the free liquid level in the container.

FIELD OF THE INVENTION 
The present invention ralates to a heat exchanger wherein a liquid, in 
particular a suspension, is heated or cooled by causing the suspension to 
flow through a container in which a substantially horizontal heat exchange 
unit consisting of a pipe set has been rotatably mounted. 
Heat exchange between two fluids, one of them being heated or vapourised 
and the other being cooled or condensed, usually takes place in surface 
heat exchangers in which both fluids are caused to flow past a heat 
transfer wall, through which heat is transferred as a consequence of 
temperature differences between the fluids, and which prevent mixing of 
the fluids. In view of obtaining efficient heat transfer between a fluid 
in a surface heat exchanger and its heat transfer wall, a relative 
velocity between wall and fluid is required. This is normally accomplished 
by allowing the fluid to flow through sufficiently narrow closed flow 
ducts which are confined by the heat transfer wall in part at least. If 
the fluid is a suspension with a relatively high content of solid 
particles, it will be viscid whereby a high inlet pressure has to be 
generated by means of a pump in order to transport the suspension through 
the flow passages of the heat exchanger. There is even a high risk that 
the flow passages are blocked by the solid material present in the 
suspension, and likewise the risk that this material within a short time 
may form a coat on the heat transfer wall detrimental to heat flow. 
It is well known that a relative velocity of the suspension with respect to 
the heat transfer wall may also be produced in that with the aid of a 
drive the heat transfer wall is set in motion within a stationary or 
slowly flowing suspension. In such case a pump is not absolutely necessary 
to transport the suspension through the heat exchange apparatus. 
The Swedish Pat. No. 384,569 discloses a heat exchanger featuring a 
rotating heating loop. This loop then rotates in a container totally 
filled with the heat-receiving fluid. In case this fluid is viscid and 
there are several layers of tubes in radial direction in the rotating tube 
set, the tube set will also tend to impart a rotation to the contents of 
the container, whereby the relative velocity of contents and tube set with 
reference to each other, which is necessary for heat transfer, will be 
low. 
The object of the present invention is to provide a heat exchanger fitted 
with a rotating tube set wherein the rotation of the container's contents 
is prevented, and wherein a high relative velocity is obtained even 
between a viscid suspension and the heat transfer wall and, moreover, in 
such a manner that it is easy to clean the heat transfer wall of deposits. 
SUMMARY OF THE INVENTION 
According to the invention a central tube has been concentrically disposed 
in relation to the rotational axis of the heat exchange unit between the 
end pieces among the heat transfer tubes, the diameter of the central tube 
being not less than 40% of the largest distance between any two heat 
transfer tubes, measured at right angles to the rotational axis, at least 
the lower edge of the outlet from the container being located at a level 
lower than the topmost part of the central tube, so that the latter can be 
kept above the free liquid level in the container.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In these Figures, 1 is the container through which the suspension is caused 
to flow with inflow through the inlet 2 and withdrawal by the outlet 30. 
The container may be opened the top or provided with cover 4. Within the 
container the rotating heat exchange unit has been accommodated, its shaft 
5 on the drive side being carried in the bearing 6 and sealed against the 
container within the seal 7. On the opposite side, the heat exchange unit 
has a double jacketed hollow shaft 8, which is carried on the outside of 
the container in the bearing 9 and has been sealed against the container 
within the seal 10. The hollow shaft terminates in a double packing box 
11, which has been connected to the inlet 12 and outlet 13 of the heat 
exchange fluid. This fluid may be, for instance, cooling water, hot water 
or condensing steam. 
The inlet 12 and outlet 13 communicate by the hollow shaft 8 in open 
connection each with one of the mutually separated compartments 14 and 15 
in an end piece 16. On the driven side of the apparatus an equivalent end 
piece 17 is found. These end pieces are connected to an air-filled central 
tube 18 disposed concentrically around the rotational axis. On the outside 
of the central tube between the end pieces 16 and 17 are a plurality of 
pipe lines 19, which constitute open connections between the end pieces 
and the compartments 14, 15 and 20 separated by means of partitions, and 
which arrangement compels any liquid introduced into the end piece to flow 
through series-connected pipe bundles of pipe lines 19 connected in 
parallel. In an apparatus such as is shown in FIG. 2, one has four such 
pipe bundles with about 40 pipe lines each. Other numbers of pipe lines 
and of pipe bundles may naturally also be contemplated. In view of bracing 
the pipe lines 19 which constitute the heat transfer wall, and also in 
order to guide the flow course within the apparatus, the apparatus 
comprises supporting plates 21 affixed to the central tube 18, these 
plates having cut-outs so as to cause each plate to brace or support part 
of the pipes 19 and at the same time to leave open another part 22, 
through which the suspension may flow in axial direction. By arranging the 
cut-outs 22 of different supporting plates to be continuous with different 
pipes 19, all these pipes can be braced. In one of the embodiments, the 
cut-outs 22 may be totally omitted. 
The container 1 is cylindrical in its lower part with merely a narrow gap 
between the outermost of pipes 19 and the container wall. Upwardly from 
the plane of the rotational axis the walls of the container are preferably 
vertical, so that the rotating part may be lifted out of the container if 
required. 
The structure supporting the apparatus has not been depicted in FIGS. 1-6. 
It is of a conventional kind and it is so constructed that the axis of the 
heat exchange unit is horizontal or has an inclination so that the end of 
the apparatus where the inlet of the suspension is located has a higher 
elevation than the outlet end. The apparatus operates in a continuous 
steady state in one of two alternative ways. According to one of these 
ways, the heat exchange unit rotates within the container in a direction 
such that the pipe lines move upwardly on that side where the inlet 2 of 
the suspension is located. This is illustrated by FIG. 4. Since the outlet 
3 of the suspension is located at an elevation lower than the inlet 2, 
partly due to its placement in the container 1 and partly owing to the 
potential inclination of the apparatus with reference to the horizontal 
plane, the suspension will only partially fill the container 1 and there 
will be a free suspension surface in the apparatus. This free suspension 
level will, as a result of the heat exchange unit's rotation, adjust 
itself at a higher level 23 on the suspension inlet side from the central 
tube 18 compared with the level 24 on the opposite side. This difference 
in level produces a flow of suspension at right angles to the pipes 19 and 
to their direction of motion. The flow in axial direction is adjusted by 
means of the cut-outs 22 in the supporting plates 21 and the suspension is 
withdrawn, for instance, by free overflow through the outlet 3 at the 
other end of the apparatus. 
By appropriate choice of the distances between pipes 19 and of the heat 
exchanger unit's peripheral velocity, the pressure drop encountered as the 
suspension flows at right angles to the pipes 19 may be balanced by the 
static differential pressure which arises from the difference in level 
between surfaces 23 and 24, in such manner that the surface 23 will not 
rise past the highest point 25 of the central tube 18. The suspension is 
hereby prevented from rotating along with the heat transfer pipes 19, and 
one achieves the relative velocity which is necessary for efficient heat 
transfer, between the heat transfer pipes 19 and the suspension. In 
addition to this function, the central tube affords requisite rigidity to 
the rotating part of the apparatus. 
The second mode of use is illustrated by FIG. 5. According to this mode of 
use, the heat exchange unit rotates in such direction within the container 
that the pipe lines 19 move downwardly on the side where the inlet 2 of 
the suspension is located. By effect of the rotation, the free surface of 
the suspension 23 on the suspension outlet side from the central tube 18 
will be at an elevation higher than the free surface 24 on the opposite 
side. In this case too, it is possible by appropriate selection of 
peripheral velocity of the heat exchanger, to make the surface 23 adjust 
itself to remain below the highest point 25 of the central tube, whence 
follows that the suspension cannot rotate in the apparatus with a velocity 
identical to that of the heat exchange unit. In this applicacation, too, 
the supporting plates 21 prevent free axial flow of the suspension from 
inlet to outlet. In an apparatus with this particular direction of 
rotation the outlet may be located on the same elevational level as the 
inlet. 
It has been assumed in the preceding functional descriptions that the inlet 
2 and outlet 3 of the suspension are chutes with a free surface. However, 
the inlet and outlet may equally be closed pipelines, in which connection 
modified places of connection and which permit the maintaining of a free 
liquid level in the container are possible without diversion from the 
scope of the invention. 
The apparatus may also be used to warm and cool liquids containing no solid 
particles. The heat transfer pipes are easy to clean on the side which is 
in contact with the suspension, even without any need to empty the 
apparatus, since all heat transfer pipes can be brought into a position in 
which they are above the suspension surface.