Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PLANT AND METHOD FOR GENERATING BIOGAS FROM BIOLOGICALLY
DEGRADABLE MATERIAL CONTAINING LIQUID AND SOLID COMPONENTS, IN
PARTICULAR WASTE PRODUCTS, AND A BIOGAS GENERATION CONTAINER
FOR USE IN THE PLANT
The invention relates to a plant and a method for generating biogas from
organic
biologically degradable material containing liquid and solid components, in
particular
waste products such as liquid manure from agricultural facilities, and further
to a biogas
generation container or tank for use in the plant.
The invention relates in particular to a process of concentrating anaerobic
biomass in fermenters for the purpose of generating biogas.
A conventional plant (US 5 015 384 A) comprises a biogas generating tank from
the upper part thereof the extracted biogas can be removed, and a floatation-
type
separating device located outside the tank. Liquid biomass derived from the
tank can
be introduced into the device together with a gas for forming micro-bubbles in
order to
separate solids from the biomass. These are re-introduced into the tank,
whereas the
purified liquid can be fed out for further use. The flotation-type separation
operation
thus takes place outside the biogas generating tank in a separate flotation
separator.
An object of the invention is to provide a biogas generating plant adapted to
be
designed in compact manner, and a corresponding method having increased
effectiveness in regard to the yield of biogas per unit time whereby lower
operating and
capital costs can be achieved.
Reference is made to claims 1 and 8 for achieving this object.
A feature of the invention is a flotation-type separation operation into
liquid and
solid constituents within the biogas generating tank by means of a chamber
zone
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confined therein. Clarified liquid is produced in the chamber zone and can be
withdrawn from the lower part thereof. At the same time, there is a continuous
exchange of separated solid biomass from the chamber zone for mixing with the
waste
products present in the tank and of waste products into the chamber zone
without the
need to use separate feed and discharge line systems for this purpose. A
continuous
build-up in the concentration of the anaerobic biomass for the purposes of
generating
biogas is thereby obtained, whereby the effectiveness of the plant is
substantially
increased. In accordance with an embodiment of the invention, the production
of micro-
bubbles in the chamber zone can be effected in that a branched partial stream
of the
clarified liquid is supplied from the chamber zone to a gasification means and
gasified
liquid is then fed back into the chamber zone where the gas is set free in the
form of
micro-bubbles due to expansion effects. In accordance with another embodiment,
a
gas can be introduced into a porous substrate in the chamber zone, whereby gas
bubbling out from the substrate in the form of micro-bubbles. The micro-
bubbles
produced should be as fine as possible in order to capture a large amount of
the solid
biomass by the effects of surface tension and force it upwards in the chamber
zone.
The confined chamber zone ends at an adequate distance below the level of the
liquid
in the biogas tank. Consequently, the waste products supplied to the chamber
zone
flow through the confined zone from the top in a direction opposite to that of
the
ascending stream of micro-bubbles.
The biologically degradable material is preferably submitted to an additional
mechanical separating stage for separating it into its liquid and solid
constituents,
preferably by means of a press screw separator, before or after being
introduced into
the biogas generating tank. In accordance with a further embodiment of the
invention,
the liquid constituents obtained from the mechanical separation stage can be
sub-
divided into different partial amounts and fed back into the chamber zone. A
certain
advantageous split into streams of liquid having different rates of flow and
directed
towards the bottom and the open end of the chamber zone in a direction
opposite to
that of the ascending stream of micro-bubbles is thereby obtained in the
chamber zone,
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whereby the effectiveness of the plant can be raised still more. In accordance
with a
further aspect of the invention, a biogas generating tank is provided.
The invention is described in more detail hereinafter with reference to
embodiments thereof and the drawing. In the drawings:
Fig. 1 is a schematic, partially sectional view of a biogas plant in
accordance with a first embodiment of the invention, integrated into a plant
for
separating liquid manure obtained from agricultural facilities into liquid and
solid
constituents,
Fig. 2 is a view similar to Fig. 1 of a biogas plant and its surroundings in
accordance with a second embodiment of the invention,
Fig. 3 is an enlarged fragmentary view of a confined chamber zone of a
biogas tank in the biogas plant of Fig. 2,
Fig. 4 is a cross sectional plan view of the confined chamber zone of the
biogas tank shown in Fig. 3,
Fig. 5 is a view similar to Fig. 1 of a biogas plant in accordance with a
third embodiment of the invention,
Fig. 6 is a sectional view similar to Fig. 4 of the confined chamber zone of
the biogas tank shown in Fig. 5, and
Fig. 7 is a cross sectional plan view of the confined chamber zone of the
biogas tank shown in Fig. 5.
Although the invention is described hereinafter and is illustrated in the
drawing in
connection with the generation of biogas from liquid manure resulting from
agricultural
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facilities, it is to be understood that the protection of the invention is not
to be
considered as being restricted to this application. Rathermore, it can also be
advantageously used for obtaining biogas from materials and wastes from other
sources, and in particular communal or industrial facilities.
In the first embodiment of the invention shown in Fig. 1, the liquid manure
containing liquid and solid constituents and emanating from a stable area 1 is
passed
through a line 2 into a collecting tank 3; it can be homogenized therein by
means of an
agitator 4. A pump 5 is provided in order to supply the homogenized liquid
manure from
the collecting tank 3 to a solid/liquid separator 6. The solid/liquid
separator 6 is
preferably a press screw separator such as is described e.g. in EU-6-0367037
so that
reference can be made thereto for further details. Other types of solid/liquid
separators
could likewise be employed if so desired.
The solid phase separated in the solid/liquid separator 6 can be formed into a
pile, as indicated at 7, and can be spread over fields as a fertilizer,
possibly in
composted form, or it can be used as bedding in stables after being subjected
to a
suitable aerobic treatment.
The liquid phase of the liquid manure that has been freed to a large extent
from
the solid constituents is fed through a line 8 into a biogas generating tank
or biogas
fermenter 9 in a biogas plant constructed in accordance with the present
invention. An
agitator 10 is provided in the tank 9 in order to constantly mix and stir the
liquid
contained therein which is indicated by dash-dotted lines in the drawing.
In place of or in addition to an agitator 10, provision could also be made for
a
circulating pump system (not shown) wherein a circulating pump sucks the
liquid from
the tank and then feeds it back in tangentially.
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The formation of the biogas is effected by fermenting the biomass in the
presence of anaerobic bacteria as is in principle known to the skilled person
so that a
more detailed explanation of this process is unnecessary.
Although this is not illustrated in the drawing, provision could also be made
for a
further separation step for separating out fine solid materials in the form of
e.g. fine
sand-like constituents that might stiil remain in the liquid output of the
solid/liquid
separator 6. Preferably, this separation operation can be effected by means of
a
centrifugal separator integrated into the line 8. The additional separation
operation
ensures that muddy deposits consisting of fine particles that are not
biologically
degradable will not be formed in the biogas generating tank 9.
As is indicated by dotted lines in the drawing, the resulting biogas collects
in the
upper portion 11 of the tank 9 which serves as a biogas reservoir and is
covered by a
foil or the like_ From there, the biogas can be fed off through a(ine 12 for
further use,
e.g. for generating electricity by means of a micro gas turbine.
In accordance with the invention, in the interior of the tank 9 there is
provided a
partition 13 projecting upwardly from the bottom of the tank and creating an
upwardly
open confined zone 14 in the tank 9, c.f. also Fig. 4. The partition 13 ends
at a suitable
distance of e.g. about 0.5 to 1.0 m, below the fluid level in the tank 9, as
is indicated by
dashed lines in the drawing.
A further separation of liquid and any solid biomass still present therein
takes
place in the confined zone 14 in accord with a flotation-type separation
principle. To
this end, purified liquid is fed off outwardly through a line 16 near the
bottom of the
confined zone 14 and supplied to a means 15 for generating micro-bubbles. Such
micro-bubble generating means are known to the skilled person. They serve to
create
micro gas bubbles suitable for a flotation-type separation process by means of
charging
or loading liquid with gas at high pressure and then causing the liquid to
expand in flow-
intensive manner in a field of cavitation. In the plant according to the
invention, the gas
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is a portion of the biogas which is branched off from the line 12 and
introduced through
the line 17 into the micro-bubble generating means 15. In particular, biogas
can be
sucked out by restricting the flow of the stream of liquid before a
centrifugal pump (not
shown) and it is then introduced under pressure into the purified liquid so as
to be
dissolved therein. Dissolved components of the gas are then wrenched from the
liquid
in the cavitation field by means of a flow-intensive expansion process. Micro-
bubbles in
a pm-range are thereby formed. The construction of one type of micro-bubble
means is
described e.g. in DE 3733583 A.
The clarified liquid charged with gas is fed back through a line 18 into the
confined zone 14 close to the bottom thereof. The gas bubbles bubbling out of
the
liquid rise upwardly in the confined zone 14, whereas the liquid biomass
introduced into
the tank 9 through the line 8 flows into the confined zone 14 from the top in
a direction
opposed to that of the stream of ascending micro-bubbles. Whilst floating
upwardly, the
micro-bubbles carry any particles in the liquid biomass upwardly therewith so
that
clarified and, to a large extent, now odouriess liquid remains near the bottom
of the
confined zone 14. Due to the effects of surface tension, very fine particles
in the
biomass also attach themselves to the micro-bubbles and are carried upwardly
therewith.
The clarified liquid can be fed out externally through a line 20 branching off
from
the line 16. A venting means 21 can be provided in order to ensure that there
is always
a constant suction-free flow in the line 20. The reference 19 indicates the
overflow
height which is defined by the line 20; this height determining the maximum
level for the
liquid biomass in the tank 9.
The agitator 10 keeps the liquid biomass in motion throughout the entire tank
9
and at the same time guides the solid biomass that is ascending as a result of
the
flotation process away from the confined zone 14 and mixes it with the
remaining
contents of the tank 9.
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For the purposes of assisting the mixing of the separated solid biomass with
the
remaining contents of the tank 9, the suction side of the agitator 10 can be
provided with
a guide tube (not shown) led from a possibly forming floating layer of biomass
near the
confined zone 14 to the rear of the agitator 10.
A second embodiment of the invention is shown in Figs. 2 to 4.
In this embodiment in like manner to the previously described first
embodiment,
liquid manure 100 incorporating liquid and solid constituents and emanating
from a
stable area (not shown) is fed at a certain rate into a collecting tank 102
and can be
homogenized therein by means of an agitator 103. A pump 104 supplies the
liquid from
the collecting tank 102 to a biogas tank 105. The biogas 106 formed therein
collects
under a collecting foil 107 which can be strengthened by an e.g. PVC coated
polyester
cloth 108. The biogas can be fed off from there for further use.
A pair of agitators 109 at diametrically opposite positions in the biogas tank
105
can be provided in order to constantly mix the contents of the tank.
As was the case in the first embodiment of the invention, a partition 113
projecting upwardly from the bottom of the tank is provided in the interior of
the tank
105, said partition creating an upwardly open confined zone 114 within the
tank 105,
see also Fig. 4. The partition 113 ends at a suitable distance of e.g. about
0.5 to 1.0 m
below the fluid level in the tank 105 which is indicated by dashed lines in
the drawing.
Liquid manure can be withdrawn from the bottom of the biogas tank 105 through
an extraction pipe 110 to a location outside the confined zone 114 by means of
a pump
111 and supplied to a solid/liquid separator 112. The solid/liquid separator
112 is
preferably a press screw separator in like manner to the first embodiment.
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In accordance with the invention, the amount per unit time at which liquid
manure
is withdrawn from the biogas tank 105 is approximately 10 to 20 % greater than
the
throughput through the plant.
The solid constituents in the liquid manure are separated in the separator
112.
The separated solid can be piled up, as is indicated by 130, for further use
e.g. for
transportation by means of a trailer.
A larger part of the entire amount of liquid running out of the separator 112
is
supplied through a line 122 to the confined zone 114 of the biogas tank 105 at
a
suitable point near the open upper end thereof, preferably e.g. within the
upper third
thereof. As in the previously described first embodiment of the invention, a
centrifugal
separator or another suitable separation means for separating fine, e.g. sandy
non
bacterially degradable constituents in the liquid can be provided in the line
122.
A smaller partial stream of the quantity of liquid running from the separator
112 is
supplied to a means 115 for forming micro-bubbles and leaves the means in the
form of
a liquid packed with micro-bubbles which is fed through a line 123 into the
confined
zone 114 at a suitable position close to its bottom, preferably within the
lower third
thereof.
The micro-bubble means 115 may be of similar construction to that of the first
embodiment of the invention. Again, a portion of the resultant biogas is
preferably used
as the gas, as is indicated in Fig. 2 by the branch line 127' shown in dashed-
lines.
The liquid now reduced of its solid components can be fed out from the
confined
zone 114 of the biogas plant through a drain line 121 provided near the botfom
of the
confined zone 114 and collected in a temporary storage facility 117 for
further use. For
example, the liquid collected in the temporary storage facility 117 can be
made available
as a liquid fertilizer for agricultural purposes through a run-off 118.
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The biogas that has been produced can be supplied through a line 127 to a
block
heating station 119 for further use, e.g. for generating electricity or heat.
The resultant
heat can be used for heating up the contents of the biogas tank 105 by means
of a heat
exchanger provided therein, as is indicated by 120, for the purposes of
assisting the
biological decomposition process.
The flow patterns resulting from the aforementioned supply of liquid to the
confined zone 114 are explained hereinafter with reference to Fig. 3.
The smaller partial stream enters the confined zone 114 through the line 122,
whilst the main stream is introduced through the line 123 so that, in toto,
the sum of
both these partial amounts arrives in the confined zone 114. A certain
quantity of liquid
that has been reduced of its solid components is withdrawn through the line
121
arranged near the bottom of the separated zone 114. Hereby, the liquid
originating from
the line 122 divides into a partial stream 124 having a smaller rate of flow
which flows
back into the biogas tank 105, whilst a partial stream 125 having a greater
rate of flow
flows to the bottom of the confined zone 114 and is fed outwardly through the
drain line
121.
The micro-bubbles 126 from the quantity of gasified liquid supplied through
the
line 123 float upwardly against the partial stream 125 due to their buoyancy
and thereby
unite with the solid biomass in the partial stream 125 by virtue of their
surface tension,
thereby solid biomass is returned to the biogas tank 105 together with the
partial stream
124.
Fig. 4 shows the confined zone 114 in the form of a plan view. As can be
perceived, the partition 113 extends in the shape of an arc from an attachment
point on
one side wall of the biogas tank 105 to a peripherally spaced attachment point
so that
the confined zone 114 can have a cross section which is substantially in the
form of a
segment of a circle. The invention is not however limited to such a
configuration of the
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confined zone 114 and in consequence, it could also be formed in some other
suitable
manner.
Example 1:
10 m3/h of separated liquid reaches the solid/liquid separator 112. This is
divided
into a larger partial amount of 9 m3/h and a smaller partial amount of 1 m3/h.
The larger
partial amount is introduced through the line 122 into an upper third of the
chamber
zone 114, the smaller partial amount being introduced into the lower third
through the
line 123 after a gasification process. 8 m3/h of clarified liquid is withdrawn
from the
chamber zone through the line 121. The quantity per unit time of the upwardly
directed
stream of fluid 124 within the chamber zone amounts to 2 m3/h, and that of the
downwardly directed stream 125 amounts to 7 m3/h. The downwardly directed
stream
125 and the partial amount at 123 thus correspond in sum to the 8 m3/h of the
withdrawn stream 121.
A third embodiment of the invention is shown in Figs. 5 to 7. This
distinguishes
essentially from the second embodiment by virtue of a modified arrangement for
forming
the micro-bubbles in the confined chamber zone so that reference can be made
to the
description of the second embodiment in regard to the remaining components.
Equivalent or similar components thus bear the same reference symbols, but the
first
digit of the number is changed to "2 -".
In contrast to the previously described embodiments, the micro-bubbles are not
formed by means of a micro-bubble means located externally of the biogas tank,
but
rather, they are formed in the interior thereof by means of a disk-shaped
substrate 229
made of micro-pored ceramic provided at a position in the confined chamber
zone 214
close to the bottom thereof. A pressurised gas can be introduced into the disk-
shaped
substrate 229 through a line 228, whereby the gas can bubble out of the micro-
pored
ceramic substrate 229 in the form of micro-bubbles. A suitable micro-pored
ceramic
substrate material can be obtained under the trade name "Kerafoi" from
Keramische
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Folien GmbH, Stegenthumbach 4 - 6, D-92676 Eschenbach/Germany. Again, the gas
is preferably the biogas which is extracted from the biogas tank 205 and is
subjected to
a suitable pressure by means of a compressor 231 integrated in the line 228
before it
enters the micro-pored ceramic substrate 229.
Example 2:
m3lh of the separated liquid reaches the solid/liquid separator 212. This is
introduced through the line 222 into an upper third of the chamber zone 214. 8
m3/h of
clarified liquid is withdrawn from the chamber zone through the line 221.
Biogas is fed
into the micro-pored ceramic substrate 229 at a pressure of 2.2 bar through
the line
228. The amount per unit time of the upwardly directed stream of fluid 224
within the
chamber zone amounts to 2 m3/h and that of the downwardly directed stream 125
amounts to 8 m3/h.
Although gasification in the micro-bubble generating means by using the
derived
biogas was described hereinabove as being advantageous, it is to be understood
that, if
so desired, suitable foreign gases from a source of foreign gas can be used
instead.
