Note: Descriptions are shown in the official language in which they were submitted.
2~80~7
A ~ethod ~nd ~ Mixer ~or ~ixing peat and sludge
The object of the invention is a method for mixing peat and
sludge as a homogenous mass, in which the peat and sludge are
mixed mechanically. The invention is also concerned with a
device for realizing the method. Here peat also means any other
substance, by means of which it is desired to bind the sludge,
that has a great surface tension. Here sludge also means liquid
manure.
Various kinds of sludges form a waste problem, because they
cannot be put directly into the natural environment. In nature
the eludges threaten surface and ground waters. Sludges can
cause smell, taste, hygienic and eutrophy problems in the
environment. The most usual sludges are waste water and septic
tank sludges, as well as the liquid manure produced in
agriculture.
Attempts have been made to mix sludge with various kinds of dry
masses, especially with peat. A homogenous mixture of peat and
sludge has shown itself to be very advantageous on account of
the fact that the sludge liquids and nutrients bind themselves
to peat very effectively. In practice, however, the mixing of
peat and especially liquid manure has been very difficult.
The~e do not mix naturally, the peat tending, even after
mechanical treatment, to rise to the surface, nor does it, due
to its great surface tension, suck the sludge into itself. Up
until now mixing has taken place for example in such a way that
the peat and liquid manure have been spread in layers as a
mattress about 50 cm thick in a shallow pond. After this a
tractor i8 driven several times on top of the mixture, when the
final mixing and the sucking of the liguid manure into the cell
structure of the peat has taken place. In practice this kind of
method is laborious and slow, as well as expensive.
The purpose of the invention is to find a new mixing and a
mixer, by means of which peat and sludge can be mixed as a
homogenous mass as a continual process. The characteristic
features of the method in accordance with the invention are
presented in the accompanying Patent Claim 1 and the
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characteristic features of a corresponding mixer are presented
in Patent Claim 3. The invention is based to a great extent on
the realization that mixing takes place by raising the pressure
of the mass to be mixed for a sufficiently long time, when the
counter force caused by surface tension is overcome.
Patent Claim 4 presents an especially advantageous mixer
solution, which to some extent overcomes even an uneven feed of
peat and sludge.
In what follows the invention is illustrated with the aid of
the accompanying illustrations, which show various mixers in
accordance with invention.
5 Figure 1 shows a mixer seen from the side in partial
cross-section
Figure 2 shows a mixer seen from above, in cross-section
at point II-II in Figure 1
Figure 3 shows a cross-section of Figure 1 at point III-
III
Figure 4 shows another kind of mixer
Figure 5 shows the mixer in Figure 4 seen from the side
The principal component~ of the mixer in Figure 1 are the ~ilo
1 and the double screw 4 at the foot of it, continuations ofthe screws 5 being located in pipe 12. The pipe feeding sludge
is joined to connection 15 and the sludge is sprayed
longitudinally on top of screws 5 by means of a nozzle 2. Peat
is loaded into the silo 1 by some suitable method. In practice
the peat need not bee fed into the silo absolutely evenly,
rather it can be fed in suitable batches.
The silo includes two auxilliary mixerR 3, by means of which
the arching of peat in the silo 1 is prevented. The screws 5
located on the foot of the silo 1 continue inside pipe 12 up to
a distance of about 30 cm of the end of the pipe. The free
initial parts of the screws 5 here form the mixer 8 proper. A
nozzle component 10 is attached the the end of pipe 12, this
including a nozzle opening adjustable with bolts 11. The final
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section of pipe 12 and the nozzle component 10 form a
pressurization chamber 9, through which the peat-sludge mass
must travel before bursting out of nozzle 10. During the delay
caused by this the sludge is able to be well absorbed by the
peat mass.
The auxilliary mixers 3 and the screws 5 are here equipped with
their own electric motor transmission units 6 and 7, but their
operation can also be combined in a single motor. In practice
it has been shown that a suitable rotational speed for the
double screws 5 (diameter D = 240 mm) is about 120 rpm and
correspondingly a suitable speed for the mixer axle would be 30
- 50 rpm. The pitch of the screws is about the same as the
diameter. The mixer will tolerate a certain degree of
unevennes~ in the feed of sludge and peat, but the feeding of
too much s~udge alone must be avoided, because then the sludge
begins to circulate in the screw conveyor, nor does the mass
move forward any longer. Generally the problem disappear~ when
balancing peat is fed to the silo. The best results are
achieved by feeding peat and sludge to the mixer in an even
flow.
Here the double screw 4 forms both a screw conveyor and a
pre~surization unit.
According to the latest research the best form of application
i~ regarded as being a mixer in accordance with Figures 4 and
5. In Figures 4 and 5 the same reference numbers are used for
components that are operationally the same as those in Figures
1 - 3. These are a silo 1, the sludge feed connection 15, the
double ~crew conveyor 4, its screws 5, the mixer 8 formed by
their initial section, a pressurization chamber 9 formed by
pipe 12, and nozzle component 10. The end of pipe 12 includes
an end plate 17, on which the bearings 18 carrying screws 5 can
easily be installed.
From the point of view of loading and in order to prevent
arching one side of the silo 1 is vertical. The double-screw
conveyor 4 is in a position that rises. In addition the
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reducing the height of the device, this assists the feed of the
sludge. Here the sludge is introduced simply by joining its
connection 15 to the start of the pipe 12, in which case the
real mixing of the sludge takes place in the first part of pipe
12. By means of this arrangement a continual flow of peat into
the pressurization chamber 9 is ensured. The length of the
closed section of the pipe 12 is about 3 m. In mixers in
accordance with Figures 1 - 3 a phenomenon was observed, in
which the sludge alone began to circulate in the screws 5, this
being due to the effect of an uneven feed.
A separate pressurization section is not required in pipe 12,
because the pitch of the end 14 of the screws 5 is less than
that of the beginning 13. There is an opening 16 formed by
nozzle 10 at the end of pipe 12, which can be adjusted by
means of plate 19 moving in guides. The reduction in pitch
(20%) at the end creates the required increase pressure here
and the nozzle component 10 is formed simply by the discharge
opening formed in the end of pipe 12.
The rotation of the screws 5 takes place by means of a tractor.
A cardan shaft in connected between its power-take-off and the
continuation gear of the screws 5. Naturally the mixer can also
be equipped with its own motor.
In this mixer a pre-mixing screw 20 i8 used, which returns the
mass to the beginning of the screw conveyor 4. Thus effective
pre-mixing is achieved.
By using the mixer of Figures 4 and 5 25 m3/h of very wet
sludge can be mixed in a ratio 1:1 by volume with peat, when
the motor output iB 40 kW. The mixing ratio of the mass can be
varied within broad limits. The maximum pressure appears to be
15 - 20 bar. The pressure remains at more than 10 bar for even
more than 10 ~econds. In order for the mixing to succeed a
guide value can be given, according to which the pressure
should remain at at least 8 bar (abs) for at least 3 seconds,
preferably more than 5 seconds.
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The pressurization device can also be formed in a manner
differing from the abovementioned form of application. Even
though a double screw has its own mixing effect, it is also
pos~ible to use a single screw. The movement and pressurization
can also be created by means of a piston device. Here the
technique that is as such known from sod peat machines can be
exploited. What is essential in the device is principally the
fact that a considerable pressure arises at the end of the
screw, by means of which the sludge is forced into the peat.
