Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to an apparatus for fer-
mentation of organic material, which is transported sub-
stan-tiall~ horizontally through a fermentor.
~n apparatus of this type is disclosed, for example
in French Patent Specification No. 732738, according to which
the material is pushed through t:he fermentor by gaseous
pressure and is heated during its passage through the vessel
by an internally heated, rotatable pipe coil, which is
lQ provided peripherally with blades for stirring the material.
This invention relates to an improvement of said
device to increase the heati.ng efficiency and has a rotatable
screw, provided with blades, which screw carries out the
horizontal transport, and a device for the internal heating
of the screw blades, at least along a part of the screw
elongation.
According to the present invention therefore there
is provided an apparatus for anaerobic digestion of organic
material to produce methane gas and including a substantially
rigid, horlzontal cylindrical tank having a symmetrical
axis, a horizontal transport screw, and means for heating
said screw internall~v for heat transfer, the combination of
means mounting said screw for rotation about an axis
located below said symmetxical axis of the tank, said tank
having an inlet end portion provided with an inlet opening
for organic material located below said rotation axis and
at the lower portion of the tank, said tank also having an
3~ ~utlet end portion provided with an outlet opening at the
lower portion of the tank, said screw having an outer
per~pheral portion ad~acent the tank's bottom and operable
t~ transport sludge along said bottom toward said outlet
Qpenin~ said peri.pheral portion of the screw forming with
3S at least one side of the tank an open space for recirculation
~f fermented material to said inlet end portion, said
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peripheral portion also formi.ng with the upper part of the
tank an accumulation space for evolved gas, said upper paxt
of the tank having an outlet from said accumulation space.
The advantages with sald screw are that its blades
pxovide a large heat transfer area and this area moves in
relationship to the material, which is transported and mixed
by the screw~ These advantages provide the desired improve-
ment in heat transfer efficiency.
~ further advantage wit:h the invention is that,
for instance, when fermenting manure anaerobically, gas
bubbles con-
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taining methane develop. These lift solid particles to the
manure surface to form a solid ma-t. The good mixing, -that the
screw carries ou-t, prevents the formation of -this ma-t and
forces the gas bubbles from -the particles which collec-t in
the upper part of the fermentor~ From -there the gas can be
discharged.
A further advantage of the -transpor-t screw is
that it will efficiently prevent solid material from being
accumula-ted and plugging in the fermentor over -time. The
design of -the screw prevents the forma-tion of short circuit
flows, which could mean lower efficien-ty in -the fermenta-
tion process. As -the heat requiremen-t of the fermentation
process norrnally prevails in the star-ting end of -the fermen-tor,
where the organic. material is fed, it can be sufficient -to
heat the transpor-t screw blades subs-tan-tially at the inlet of
the fermen-tor. Set-ting of the desired -temperature, for in-
stance 35C for anaerobic fermentation, can be effec-ted by
regulating the -tempera-ture and/or the flow of the medium,
that is used for heating, such as warm water.
A further improvement in the heating of the con-
tents of the fermentor can be obtained by one or a plurality
of pipes, oriented in the axial direction of the screw and pre-
ferably rotatable with the screw, provided for internal heat-
ing. These pipes can be fastened to the screw at the peri-
phery, serving to carry the screw.
It may be desirable to inocula-te the material,
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enke,ring the fermentor~ with microorganisms to accelerate
the start of the fermenting process, ~ccordin~ to a furthex
feature of the invention this can be achieved by providing
the fermentor with a space, located outside the periphery
of the screw, which stretches along the screw, which space
allows recirculation of fermented material to the material
inlet to the fermentor. The recirculation is carried
out automatically by returning part of the material, that
has reached the gable of the fermentor at the outlet end
lQ for the material, moving it outside the screw periphery back
towards the inle-t side.
The invention will be further illustrated ~ore in
detail by way of the accompanying drawings, in which:
Figure 1 is a longitudinal sectional view of the
fermentor in accordance with one embodiment of the present
invention, and
2Q Figure 2 is a cross sectional view of the apparatus
of ~igure 1 seen from the left.
Methane gas is produced by natural anaerobic
fermentation.
Figure 1 shows the both ends of an elongated closed
fer~entor 1 which is provided with external heat insulation
(not shown). Manure is fed through a pipe 2 to an inlet
chamber 3, provided with a cap 4, in order that the inner
3Q parts of the chamber may be accessible. From a bottom space
5 in the chamber 3 manure flows into the fermentor 1, and
~nto ~ bottom space 6 in an outlet chamber 7. Fermented
~anUxe then leaves chamber 3, through a weir outlet 8. In
the fermentor methane
gas fumes, which fi:L:ls a space 9 above the manure surface 10
in -the fermentor 1. In -the chambers 3 and 7 a rnanure level
will be es-tablished, which is higher than -the level 10 and
which is determined by the gas pressure in -the space 9. The
me-thane gas is discharged under overpressure through a pipe
11. A -transpor-t screw 12 is suppor-ted by a rectangular frame
13 of pipes, which is welded to -the periphery of -the screw.
The frame 13 is supported at the gables of -the fermentor by
bearings 14 and 15. Bearing 15 is firmly connected to shaft
tap 16, which, by means of a motor, rotates the frame 13 and
thus also the screw 12. Ho-t water is fed through a channel
17, which passes through the shaft ~ap and the bearing 15.
In the frame 13 there is provided a blocking wall 18, which in
the posi-ton of the frame shown directs water upwardly -through
the frame. As indicated in the Figure the left part 19 of
the blade of the screw 12 is hollow, and water can - via a
connection - reach this hollow blade part from the frame 13.
A blocking wall 20a prevents water from flowing further to
the left in the upper par-t of the frame.
~ ccording to the Figure the cavity of the screw
blade ceases after one blade turn and -the water flows -through
a new connection once more into the frame 13 and continues
in the frame to -the blocking wall 18. Here -the water reaches
an outlet channel 20 and leaves the apparatus. The frame 13
is provided, a-t -the outlet end, wi-th baffles 21, which help
to keep -the ou-tlet free and discharge -the fermented manure
into the space 6. Also the chamber 7 has a cap 22, which
again makes the inner parts of the chamber accessible. The
chamber 7 and -the left gable of the fermentor are also for
similar reasons de-tachable from the rest of the fermen-tor by
a screw joint 23.
In Figure 2 corresponding parts have -the same re-
ference numbers as in Figure 1. Furthermore, there are shown
in Figure 2 two rods 24 which suppor-t the chamber 7. Further-
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more -there is a space 25 between the periphery of the screw
12 and the inner side of the fermentor 1. Through -this space
25 part of -the fermen-ted manure is recirculated from the lef-t
gable of the fermentor -to -the right one, thus innoculating
-the fresh en-tering manure wi-th microorganisms.
Further the screw 12 and the frame 13 by rota-tion
break the mat., that would o-therwise be formed below the sur-
face 10, especially through -the flo-tation ac-tion, that -the
ascending gas bubbles per:Eorm on the sol.id particles oE the
manure.
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