Note: Descriptions are shown in the official language in which they were submitted.
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, METHOD FOR THE SEPARATION OF SLURRY INTO A SOLID FRACTION AND A
LIQUID FRACTION, AND THE ASSOCIATED INSTALLATION
The invention relates to a method and installation for the
separation of slurry into a solid fraction and a liquid fraction.
A similar method is known and is applied to separate slurry,
in the form of the excreta of pigs and similar animals from the
animal husbandry sector, into a solid fraction and a liquid
fraction, following which further processing can take place to
provide for example compost and potable water respectively. This
processing makes it possible to reduce the burden on the
environment in comparison to processing of the slurry by
spreading it over open land. Such separation is applied on a
large scale as a consequence of increasingly stringent
environmental legislation.
The method described has the disadvantage that the
separation is slow and insufficiently thorough.
The invention has the objective of providing an installation
and a method whereby the faster and yet at least as effective
separation takes place between the solid and the liquid
components is possible in a way which imposes a lower burden on
the environment.
This objective is achieved by a method in accordance with
the introduction, with characteristics in accordance with claim
1.
Using the method in accordance with the invention it is
unnecessary to create air bubbles in the flotation tank. Further,
it appears that the addition of rising air bubbles there has a
retardant effect on the separation there of the floating fraction
and the sinking/falling fraction.
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. With the application of the method in accordance with the
invention, when the slurry to be separated is led into the
flotation tank the air bubbles are already within that slurry and
the flocculating agent, so that they do not disturb the
separation of the slurry in the flotation tank.
A further advantage of the method in accordance with the
invention is that the air in the flotation tank is located
immediately in the place where it is used, namely with the
flocculating agent to which it attaches. Also no thinning occurs.
The eventual consequence is that less air bubbles are necessary
to achieve the same result.
Since the liquid medium is at least to some extent formed by
the sinking fraction, there is the advantage that no process
water from outside is needed, whereby there is also less burden
on the environment.
In the variant in claim 2, where both mixtures are already
added together before they are brought together into the
flotation tank, the foam from the second mixture already has the
opportunity to attach itself to the floccules from the first
mixture as it passes through the supply line to the flotation
tank. In other words the air bubbles are then already present
with the flocculating agent in the slurry to be separated, before
this arrives in the flotation tank. This also appears to have a
positive effect on the separation process.
In an advantageous embodiment, the addition of the first
and/or second mixture to the flotation tank takes place in or
just below the fraction floating on the liquid surface. In this
way the mixture is immediately in almost the correct position and
no time therefore needs to be lost in getting it to the correct
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, position in the flotation tank by means of convection. Also in
this manner it minimally disturbs the motion of the sinking
fraction. This supply may take place at a location at a fixed
height, this being particularly suitable for a continuous and
stable process, and may alternatively take place at a location at
a variable height, this being particularly suitable for a non-
continuous process and for continuous processes with variations
in throughput.
In another embodiment the addition of the first and/or
second mixture to the flotation tank takes place in the vertical
direction, raised to a height. In this manner the floating
fraction already has the correct direction of movement, and the
separation will take place more quickly, in particular where the
supply takes place into or just below the separation area. The
vertical supply rate is then also advantageously lower than 30
cm/minute.
In another embodiment the supply of the second mixture takes
place via a vertical riser pipe, widening as it approaches the
discharge end. In this manner the outflow from the riser pipe is
delayed with respect to the inflow into the riser pipe,
preventing turbulence at the outflow to a large extent, with the
consequence that the flows in the separation area are disturbed
still less.
In a further embodiment the step of removing the floating
fraction is carried out by an endless conveyor belt provided with
transverse partitions attached to the belt, whereby the scooping
or pushing transverse partitions are active at the level of the
floating fraction and the conveyor belt moves upwards with
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respect to the horizontal over a first processing section in the
direction of the motion of these partitions, with a gradient of
less than 1:20 and preferably 1:25. In this way the floating
fraction is made to move vertically to only a small degree and
the flow in the separation area below it is hardly disturbed,
again resulting in a faster separation. The conveyor belt may
also preferably have a running speed of less than 25 cm/minute,
so as to disturb the flow particularly in the horizontal
direction still less than in known installations, where the speed
is higher.
In a particular embodiment the conveyor belt runs upwards
with respect to the horizontal in the direction of motion of
these partitions over a second processing section which lies
downstream of the first processing section, and a guide partition
sloping upwards lies below and close to the first section. This
measure also has the consequence that the flow in the flotation
tank, in particular in the separation area, remains to a large
extent undisturbed.
In a further embodiment the stage of adding the air bubbles
to the first mixture is preceded by the preparation of the air
bubbles by mixing the air bubbles with the sinking fraction from
the flotation tank or located downstream of it. Using no water
but instead tapping off the sinking fraction and returning it
again to the flotation tank together with air, flocculating agent
and slurry saves on the consumption of water. This reduces costs
and less water needs to be removed from the floating fraction
downstream of the flotation tank and/or less sinking fraction
needs to be purified, which again reduces the costs of the
method.
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The method is preferably carried out as a continuous
process, as in this way the highest speed of separation is
achieved in the flotation tank, as the flows can be near enough
unvarying or laminar.
The invention further relates to an installation in
accordance with claim 10. Such an installation offers similar
advantages to those described above.
Other advantageous embodiments are defined in the sub-
claims.
The invention will now be further explained on the basis of
the figures below, in which similar elements have been provided
with the same reference numbers. In this:
Figures lA and 1B show schematic partial representations of
an installation in accordance with a first embodiment of the
invention.
Figure 2A shows a schematic representation of an embodiment
of the method in accordance with the invention, as can be
embodied in the installation in Figure 1.
Figure 23 shows a schematic representation of a stage from
Figure 2A broken down into several sub-stages.
Figure 3A shows a schematic representation of a cleaning
installation for the installation from Figures 1A and 13, and
Figure 38 shows a detail of the transverse section through
3B-3B.
Figure lA shows the pre-processing section of an
installation 1 for the separation of slurry into a solid fraction
and a liquid fraction in accordance with the invention. The
installation 1 includes a storage tank 2 for a mixture of the
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= solid and liquid fractions of slurry. Storage tank 2 has a supply
line 3 and a drain line 4 which leads to a mixing unit 5. A
polymer production station 6 has a supply line 7 for a standard
solution and a supply line for water 8, and an outlet line 9 and
which runs to the mixing unit 5. From the mixing unit 5 a line 10
runs via an aeration station 10a and via A to a flotation tank 11
shown in Figure 1A. Also visible in Figure lA is a pressure
vessel 12, in which are located a large number of PVC rings 13.
The pressure vessel 12 has a drain line 14 which leads to line 10
and two supply lines, namely a supply line 15 for compressed air
and a supply line 16 for the liquid fraction of slurry, arriving
- via C - from flotation tank 11 via inter alia a filter 17
installed in the supply line 16, which filter has a tap-off line
18 for flushing purposes.
In Figure 1B the flotation tank 11 has side and bottom walls
112, an open upper face 113 and riser pipe 114, into which A
emerges. A drain line 115 for the liquid fraction is provided
close to the floor of flotation tank 11 and emerges at overflow
tank 116 which itself has a drain line 117 leading to a water
production unit 118, using reverse osmosis. This water production
unit 118 has two outlets, one outlet 19 for pure water, and
another outlet 20 for filtered out residual matter.
In a variant of the flotation tank in Figure 1B which is not
shown, the riser pipe 114 has a variable length, being fabricated
in the cylindrical section at the lower end in the form of two
cylinders, sliding one within the other. This variable length can
if necessary be continually adjusted to the current level of the
underside of the floating fraction, so that the end of the riser
pipe 114 is always just below this underside.
A scraper unit 21 is provided at the upper surface of
flotation tank 11, having an endless conveyor belt 22 with
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. rollers 23 which guide the belt 24, and there are transverse
partitions fitted to the belt 24, transverse to the surface of
the belt 24 and serving to scrape solid constituents above the
flotation tank 11, as will be described in further detail below.
At the end of conveyor belt 22 the side wall 112 of the flotation
tank 11 is formed with a rising inclination, approximately
parallel to the belt 24 immediately above it. While this is not
shown in the Figure, the lower surface of the conveyor belt can
also be installed with an inclination to the left of the bend in
the belt at the middle guide roller 23 (viewed horizontally),
rising from left to right in Figure 1B.
The dimensions of the flotation tank are approximately: a
height of 3.5 metres, a length of 6 metres and a width of 3.5
metres, with a normal water level of 3.3 metres and the end of
the riser pipe 14 at a height of around 3.25 metres.
A conveyor belt 26 runs from the output end of the conveyor
belt 22 to a belt press 27 of a known type, in this case the BPF
1200 WR 11 Greenland supplied by Sernagiotto (a subsidiary of
Siemens). The latter has two endless mesh screen belts 28 which
run between rollers in a filtering section of the belt press 27
and between rollers in a press section of belt press 27. A
flushing and brushing unit 29 designed by the applicant for
screening belts 28 has been provided in the press section of the
belt press, which is shown in Figure 3A with detail 3B.
The operation of the installation shown in Figure lA and
Figure 1B is described below, by means of reference to Figures 2A
and 2B.
The stages in the process are represented in Figure 2A, with
the component from the installation shown in Figures lA and 1B in
which the stage in question takes place specified in brackets.
Slurry consisting of a solid fraction and a liquid fraction
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is preferably continuously or virtually continuously fed in and
stored in storage tank 2 which serves as a buffer, and a
flocculating agent is added in mixing unit 5, in this case a
polymer with a positive charge of the brand Breustedt Chemie type
BC FLOC EM 1750 or Brenntag type Sedipur CL 343, but some other
agent is also possible. In some cases it will also be necessary
to add a coagulating agent, such as for example Digi-Floc by
Breustedt Chemie, in order to obtain stable floccules. However
the addition of a coagulating agent leads to an elevated salt
content in the fractions, which may be undesirable as requiring
further processing.
The working solution of the polymer is prepared in the
polymer production station 6, as for example supplied by
Melspring, Axflow or ProMinent, by means of mixing of a so-called
standard solution with liquid, in this case water, although if
desired the liquid fraction from the flotation tank 11 may be
used.
In order to obtain a sufficiently homogeneous first mixture
Ml, mixing unit 5 includes a pump with an eccentric worm, after
which is installed a constricted polymer injector. This sequence
has the advantage that the slurry is first brought into a rotary
motion by the worm pump, before the polymer is injected into the
slurry, so that good mixing occurs, better than if no worm pump
were used. The constriction amplifies this effect.
The result of the aforementioned mixing is a first mixture
Ml, which is subsequently mixed in air mixing station 10a with
air bubbles dissolved in the liquid fraction arriving from
pressure vessel 12 where air is mixed with the liquid fraction
under elevated pressure, in this case around 6 Bar. The mixing of
the air bubbles in the liquid fraction in the pressure vessel 12
is improved by the presence of the PVC rings 13 in the in the
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pressure vessel 12 which come into motion and break up the air
bubbles entering pressure vessel 12 to create smaller air bubbles
and sometimes foam. The first mixture M1 mixed with air bubbles
and liquid fraction forms a second mixture M2 which is led via A
to flotation tank 12 where it is separated. This separation takes
place in sub-stages shown in Figure 2B, namely inflow (Si), in
this example via riser pipe 114, followed by the separation
proper (S2), whereby the liquid fraction sinks under the
influence of gravity and the solid fraction with air attached to
it rises, that is to say it commences to float.
The inflow is of importance since in this example and in
accordance with a preference for the invention this takes place
just below the region where the floating fraction consolidates
and comes to a standstill, at least in the vertical direction,
close to the surface of flotation tank 11 or a little further
from it, depending on the quantity of floating fraction present,
before being led off by conveyor belt 21.
In this way the
floating fraction fed in only has to cover a small distance and
therefore disturbs the natural convectional flow of the sinking
fraction little or not at all. The fact that the outflow orifice
of riser pipe 114 is large so that there is only a minor vertical
speed component from the slurry fed in with its solid and liquid
fraction contributes to this, as does the vertical position of
riser pipe 14.
The de facto separation is followed by the draining of the
sinking, predominantly liquid fraction via the drain line 15 (S3)
and the skimming off of the floating fraction from the liquid
surface (S4), which is largely solid, by scraper unit 21 and
specifically by its transverse partitions 25, which as they move
to the right in Figure 1B very gradually and falling with an
inclination of 1:25 (20 cm in 5 metres) in the flotation tank 11,
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= and moreover with a very low speed of around 0.25 m/minute or 15
m/hr, take the floating solid fraction to the right where it is
gradually moved upwards due to the inclined rising side wall 112
of the flotation tank 11 and so led off, subsequently falling
onto conveyor belt 26, which leads on to the belt press 27 for
further separation, where it first drains and is then pressed,
and the residual component is led off in the form of compost.
Stage S5 achieves level control for the material in flotation
tank 11, obtained through overflow tank 116.
Because of the careful manner of taking off the floating
fraction described above, the actual separation resulting from
gravity is so little negatively affected that it can take place
quickly.
The sinking fraction led off from flotation tank 11 consists
of a liquid fraction and possibly a very small quantity of small
solid elements, and this is separated in the water production
unit 118 by means of reverse osmosis into water, via 18 and
residual matter, in particular salts, via 20.
In Figure 3A the flushing and brushing unit 29 lies against
and here below the belt 28, and consists of a tube 30 which is
oriented transversely to the belt 28 and runs parallel to it,
horizontally in this example, and is provided on its upper
surface with a number of spray orifices 31 as well as a feed
orifice 32 and a rotating rod 33 lying along the longitudinal
axis of the tube 30 which is connected to an electric or other
motor 34 and which carries brushes 35 (see Figure 3B) which lie
against the interior surface of the tube 30. A flushing valve 36
is connected to a drain line 37 and offers the possibility to
flush the tube 39 by allowing the liquid fed in via the feed
orifice 32, including the soiling brushed loose by the brushes
35, to flow away when flushing valve 36 is opened.
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= The flushing and brushing unit 29 of belt press 27 serves to
spray the belt clean with sinking fraction from the flotation
tank 11, through the openings 31 which are formed to act as
sprayers. Experience has shown that the orifices 31 block up from
time to time as a result of the presence of an extremely small
quantity of solid components which have remained present in the
sinking fraction. In order to prevent such blockages the flushing
valve 36 is opened after a preset time (typically 15 minutes) and
the electric motor 34 is activated for some time, and
subsequently in the reverse direction of rotation, so that the
brushes 35 clean the interior of the tube 30 and in particular
unblock the orifices 31. Soiling is thereby led off via flushing
valve 36. Following this process the flushing valve is closed
again and orifices 31 again spray the belt 28 clean.
Because the cleaning of the belt 28 takes place using the
sinking fraction from flotation tank 11, and not with water, no
water is introduced to the process and there is eventually less
moisture to be purified in unit 118.
Because the moisture from belt press 27 is fed back to the
storage tank, whereupon it passes once again through the
separation process, a more complete separation of the solid and
liquid fraction of the slurry is achieved, and also an element of
the added flocculant, in this case polymer, is reused, so that
less polymer is required, which is advantageous from the cost and
environmental perspectives.
While the method in accordance with the invention is
illustrated using the installation 1 in Figures 1A and 1B, the
method can also be implemented in other separation installations.
