Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~.o404~9
rrhis invention relates to an apparatus in the shape
of a heat exchanger for indirect heating, drying or
cooliny o moist taclcy material, said apparatus being
of the kind having a stationary drum with a revolving
hollow shaft or rotor with an inlet for a drying medium
and an outlet for the same or a condensate thereof, the
rotor carrying annular bodies with cavities connected
to the hollow space of the rotor.
An apparatus of the said kind will speciPically
lo be use~ul in the drying o~` ~ishmeal, offal ~rom slaught-
erhouses, mash ~rom breweries, and the like tacky ma-
terial o~ animal or vegetable originO
Formerly, materials of the said kind were dried by
means of direct fired air driers, but since the mate-
SCnS; f;vC
~ ~ 15 rials are often heat sensi~le and in1ammable when dried,
`:~
;~ driers of this kind have been abandoned in favour o~
¦ driers with indirect heating.
Thus, drum driers with longitudinal pipes have
been used, wherein the drum and the pipes rotate to-
~¦ 20 gether or, as according to the Norwegian Patent No.
.... ,;
, 62.174, the drums are stationary being fitted with also
~.1
stationary heating pipes coiled in planes perpendicular
to the drum axis, and with rotating stirring members
~;~ mounted upon a central shaft, and moving between the
1 25 coils. In another embodiment according to the same
Sp;~a //y
patent, the heating pipes are hclically coiled and mount-
¦ ed upon a rotating hollow shaft.
These apparatus types are not suited for drying of
~ ., ;. ~
~-` tacky materials, because their ef~ectivity is rapidly
decreased owing to the material forming deposits on the
~'
,.
.
104~419
pipes, which are removed only with difficulty, and be-
~c n ~ v c
cause the materials, if heat ~en3iblc, will be damaged,
unless the temperature of the heating medium is limited
to values below the scorching temperature of the mate-
rial in question. The deposits will also often be of poor
heat conductivity.
In the Norwegian Patent No. 95.490, therefore, a
dryer has been proposed, having a stationary drum en-
closing a hollow rotor encircled by hollow annular bo-
lo dies of triangular cross section, so that only smooth
surfaces come into contact with the material to be dried.
Possible deposits on such smooth surfàces are relatively
easily detached during the movement of the surfaces in
the material to be dried, even as the possibility exists
l 15 of providing stationary reamers.
;~ The said design has various disadvantages. Thus,
I smooth surfaces as those of the said annular bodies are
not very resistant to pressure, and because pressurized
steam is yenerally used as a heating medium, the bodies
have either to be made from heavy sheet material, which
involves weight problems, or, as is usual in the appa-
ratuses used in practise, stays have to be welded in
between the two frustoconical sheets making up one such
annular body. This welding of stays is dif~icult to me-
~j 25 chanize and since as many as 90 stays are used in each
¦ body, this contrivance is very costly.
;l Further, the cross-sectionally triangular design of
the annular bodies makes them bulky so that only a limit-
ed number of bodies can find room on the hollow rotor,
and the effective space for reception of the material to
be dried is reduced.
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1040419
~he object of the invention is to provide a dryer sub-
s-tantially relieving the said disadvantayes, being con-
structionally so designed that the manufacture thereof can
be largely mechanized and automatically carried through.
With this object in view, the characteristic feature
of the drier of the invention is that the annular bodies
S~o;ra t
A encircling the rotor are designed as ribs with a hclical
hollow space, the inner end of which is in connection
with the interior of the rotor, the outer end near the
lo circumference of the rib being closed.
This design is based upon the recognition that the
heat transmission number between heating surface and
drying goods for the materials dealt with here is so low,
20 - 60 kcal/m2hC, that a fin or rib design as stated
hereinbefore, where only part of the surface is directly
heated, is effective. Owing to the small cross-sectional
area of the heating coil and its confinement within curved
surfaces, it will endure a relatively high pressure of
the heating medium without any need for additional bracing.
Since the heating coil is preferably of lenticular cross-
section, the thickness of the individual annular body is
small, and this, and the reduced weight on account of the
reduced consumption of rib material, has the effect that
additional annular bodies can find room upon the hollow
, .j
rotor without overloading the latter and without reduc~ing
the available space for material to be dried too much.
At the same time, the advantage of having smooth surfaces
in contact with the material to be dried, and the possi-
bility of using stationary reamers as in the hereinbefore
described known design, is retained.
lQ4Q419
In an embodiment of the drying apparatus
according to the invention the individual ribs have
been manufactured from plane sheets, and the helical
hollow space has been formed by attachment to the sheet of
Sp ;~ a lly
a hclically cut strip of arcuate cross-section, possibly
a strip made from a coiled tube being cut into halves
along an axial plane. Besides, the space between indi-
vidual turns of the coil can be reduced to a minimum by
s,~;ral
forming the strip used for making the h~lic~l hollow
lo space from a sheet, in which only a single helical cut
is made. The distance between the individual turns will
then correspond to the reduction in width resulting from
the curving of the strip plus the width oP the coil, and
you get the largest possible area o~ the rib, which is in
direct contact with the heating medium.
To increase the heat transmission, the above described
embodiment may be changed so that the outer end of the
helical hollow space according to the invention is con-
nected with a radially extending return passage to the
, :
~ 20 hollow space of the rotor through an opening in the plane
`I rib sheet. In this way, the flow rate of the heat medium
can be increased, resulting in a larger heat transmis-
sion.
I The heat transmission can be further increased in
another embodiment according to the invention, by a hc~
lical strip of curved cross-section being mounted on
each side of the plane sheet from which the rib is made.
In the latter embodiment according to the invention
Sp~ ral
the outer ends of the hclical, hollow spaces can overlap
one another and be mutually connected through an opening
in the rib sheet.
,r~,
` i04~)419
The stiffness of the rib sheet, and the capacity of
withstanding internal pressure can be increased in a further
embodiment according to the invention, by embossing or calander-
ing a helical bulb in the sheet, from which the rib is made, said
bulb being covered by a spirall~ cut, and also embossed strip to
form the spiral hollow space.
In cases, where no direct flow of the heating medium
through the spiral hollow spaces is possible, and when the heat
medium is a vapour which is condensed, a problem may arise in
getting the condensate and possible air contained in the vapour
returned to the hollow rotor in counter-current to the vapour flow.
In an embodiment of the drier according to the invention, this
problem is solved by the provision in the helical hollow space of
a more or less tight-fitting guide plate consisting of a corres-
pondingly spiral strip terminating shortly before the closed
outer end of the hollow space.
This strip is only tightly fastened in part to allow
the condensate to pass between the strip and the inner side of
the heating coil. The condensate will mainly be collected in the
outer hollow space, where it is concurrent to the vapour. In
this manner, the condensate and the air is more easily chased out
of the heating coil. The direction of rotation is preferably
chosen so that the condensate is screwed towards the shaft.
Instead of a strip, a tube may be used, which is
inserted in the hollow space of the heating coil. By means of
this tube, the heating medium may be led forward to the outer end
of the heating spiral.
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Finally, an embodiment of the dryer may advantageously
be designed so that the distance between the turns of the spiral
hollow space is adjusted so that helically cut strips can be used
for forming the hollow spaces, said strips being substantially
of a width corresponding to the distance between the turns of
these spiral strips. Thus, a saving of material is gained,
since two interlocking spiral strips may be cut from one and the
same sheet.
Common to all of the above embodiments is that the
construction work, consisting mainly in sheet cutting and welding,
is well suited for automation owing to the long cuts and con-
tinuous welding seams. Further, the design of the fins or ribs
results in a good utilization of the construction material,
allowing for use of a more costly material, e.g. rustproof steel.
Some embodiments of the drier according to the
invention will be described more detailed in the following having
reference to the accompanying drawings, in which:
Fig. 1 schematically shows a longitudinal section of
the drier,
Fig. 2 on a larger scale an elevation of a rib on the
hollow rotor of the apparatus, said rotor being seen in cross-
section,
Fig. 3 a radial section through a rib,
Fig. 4 a radial section through another embodiment of
a rib,
Fig. 5 an elevation of part of a rib as shown in Fig.
4, and
Fig. 6 a section along the line A-A in Fig. 5.
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i~40419
The drier schematically shown in Fig. 1 consists of a
stationary drum 10, having a heating jacket 11 around its
cylindrical part, an inlet 12 for the material to be dried, and
an outlet 13, which is here placed at the bottom, but may also
be placed some way up the side of the drum.
Within the drum 10 and coaxially with it is pivotally
mounted a rotor 14 having hollow axle-necks 15 and 16.
Through the axle-neck 15 passes a supply pipe 17 for
.
the heating medium, here supposed to be steam, and through the
,~ 10 axle-neck 16 a siphon pipe 18 is inserted for draining off
condensate, respectively heating medium, if the latter does not
condense.
The rotor 14 is fitted with ribs 19 having a smooth,
: :'
but not plane exterior.
. ~, .
The said ribs may be of the design shown in elevation
in Fig. 2 and in cross-section in Fig. 3 as having a spiral duct
20 for the heating medium, said duct being connected at its
inner end with the hollow space of the rotor 14 through a length
of pipe 21.
Preferably, the duct 20 is of lenticular or spindle-
shaped cross-section in the outer turns, see Fig. 3, whereas the
turn adjacent the rotor is of substantially triangular cross-
section with a generatrix for the rotor wall as base.
In this case, the rib 19 has been cut from a plane
metal sheet, after which a substantially spiral bulb has been
embossed or calendered into~the sheet, and the resulting depression
:~ .
is covered wi~h a strip 22, which has been spirally cut out and
embossed to an arcuate
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lQ4~419
cross-section, said strip being welded on to ~orm the duct
200
As suggested by the broken line, the duct 20 may be longi-
tudinally divided almost onto the closed end by means of a
coiled strip 28 being part-welded alony one or both borders
to the middle of the passage 20. As appears from Fig. 2,
the strip 23 extends to contact with, and is possibly
fixed onto the exterior of the rotor 14 behind the supply
pipe 21 for the heating medium. Thus, the medium is forced
lo to first flow on to the extreme end of the duct 20 through
that part of the said duct being closer to the rotor.
It can then pass around the end of the partition formed
by the strip 23 and return through the other part
of the duct 20. Possibly formed condensate will thus be
driven forward by the heating medium and more easily re-
turns to the hollow space of the rotor, from where it can
be removed through the siphon pipe 18. More important
is, however, that possibly separated air is also carried along
and does not become stationary to form air pockets
inhibiting or stopping the heating medium from enteriny
the duct 20 .
Condensate and air are returned to the rotor through
a pipe 24. Just behind said pipe, a closed partition 25
is provided.
At the circumference of some or all of the ribs 1~,
shovels 26 ( Fig. ~ may be mounted crosswise to aid in
moving the material to be dried forward towards the outlet
13.
If the partition 23 is omitted, the rotation of the
rotor should be in such direction that the closed end of
the duct 20 iS in front so that the movement of the conden-
- ~4C~419
sate back to the hollow space o~ the rotor is aided by
the rotor movement.
This is not unconditionally necessary when the par-
tition 23 is built into the duct 20, even i~ also in this
case the movement o~ the condensate is aided.
~;l The supply pipe 21 projects some way into the hollow
space of the rotor so that its inner end will always be
above the condensate level in the rotor space, said level
beiny controlled by the siphon pipe 18.
lo In the ernbodiment as shown in Figs. ~-6, each oP the
.l ribs 19 consists oP a plane sheet to which has been weld-
Sp ~ r a //y
-1 ~ ed the helicill~f cut, and to an arcuate form embossed
stri.p 22 to Porm the hclical duct 20. Adjacent the closed
outer end oP the said duct, an opening 27 leads to a ra-
; 15 dial passage 28 on the backside oP the rib 19, so that the
, condensate may be returned through this passage to the in-
terior o~ the rotor 14.
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