Note: Descriptions are shown in the official language in which they were submitted.
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A METHOD AND AN ARRANGEMENT FOR EXTRACTING CARBON DIOXIDE
FROM AIR
FIELD OF THE INVENTION
The present invention relates to a method and an arrangement for extracting
carbon
dioxide from air.
BACKGROUND OF THE INVENTION
Carbon dioxide (C02) is a compound that is often regarded as undesirable. For
example,
carbon dioxide is generally regarded as a pollutant of the earth's atmosphere.
In many
technical or industrial processes, carbon dioxide is generated as a by-
product, for
example during combustion of oil or gasoline. Various proposals have been
presented
for removing carbon dioxide from air. For example, it has been suggested in US
patent
No. 6946288 that a ventilation system for a building can be provided with
catalysing
means for catalysing hydration of carbon dioxide contained in air into a
solution of
carbonate ions and hydrogen ions, and thereby remove carbon dioxide from the
air.
Carbon dioxide is not always just an undesirable pollutant, it can also be
used for
different purposes. For example, it has been suggested in DE 196 44 684 Al
that carbon
dioxide can be used as a raw material in a process where methanol is
manufactured. It is
known that methanol can be used as a source of energy. For example, methanol
can be
used in a fuel cell in a process where electricity is generated. Methanol can
also be used
to produce energy by combustion.
Another possible use for carbon dioxide is disclosed in for example US patent
No.
7008985 where it is suggested that carbon dioxide can be used as a propellant
in aerosol
spray containers.
It is an object of the present invention to provide a method and an
arrangement for
removing carbon dioxide from air, either to obtain carbon dioxide that will
subsequently
be put to use for other purposes or simply for reducing the content of carbon
dioxide in
the air.
DISCLOSURE OF THE INVENTION
The inventive method comprises the steps of providing a wall having a surface
on
which a carbonic anhydrase is arranged, exposing the wall to a stream of air,
and using
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the carbonic anhydrase to remove carbon dioxide from the stream of air.
Optionally, the
carbon dioxide so obtained may subsequently be used for some other purpose,
for
example to produce methanol. The carbonic anhydrase may be immobilized on the
surface of the wall.
If the carbon dioxide is used to manufacture methanol, this can be done by a
chemical
reaction where electrical energy is used to transform water and carbon dioxide
to
methanol.
According to the invention, the wall is formed by a rotor blade, in particular
a rotor
blade of a wind power plant. Electrical energy from the wind power plant may
optionally be used to transform water and carbon dioxide into methanol. Of
course,
even if the wall is formed by a rotor blade of a wind power plant, electrical
energy used
to produce methanol may also come from another source than the wind power
plant.
The rotor blade may be divided into a plurality of cells separated from each
other in the
radial direction of the rotor blade. Each cell may then have a wall on which
carbonic
anhydrase is arranged, e.g. immobilized, such that each cell can extract
carbon dioxide.
In case the carbon dioxide is used to produce methanol, the methanol so
obtained may
subsequently be used to produce electrical energy in for example a fuel cell.
The invention also relates to an arrangement for extracting/removing carbon
dioxide
from air. The arrangement comprises a wall having a surface upon which
carbonic
anhydrase is arranged/immobilized such that carbon dioxide can be extracted
from a
gas, in particular air. The wall is formed by a rotor blade, in particular the
rotor blade of
a wind power plant.
The arrangement may optionally also comprise a fuel cell connected to the wall
and a
source of electrical energy connected to the fuel cell.
In some embodiments, the rotor blade can be divided into a plurality of cells
separated
from each other in the radial direction of the rotor blade. At least some of
the cells and
possibly each cell has a wall on which carbonic anhydrase is placed, e.g.
immobilized,
such that some cells (or each cell) can extract carbon dioxide.
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DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic representation of how carbon dioxide may be extracted
in a cell
designed for that purpose.
Figure 2 shows an embodiment of the invention where cells like the cell shown
in Fig. 1
are placed in a rotor blade.
Figure 3 shows schematically how the invention may be applied to a wind power
plant.
Figure 4 is a cross-sectional schematic representation similar to Fig. 1 but
showing
more clearly the path of evacuation of carbon dioxide.
Figure 5 is a side view of the cell shown in Fig. 4.
Figure 6 shows schematically a process in a fuel cell.
Figure 7 is a schematic representation of a process run in reverse in relation
to the
process of Fig. 6.
DETAILED DESCRIPTION OF THE INVENTION
With reference to Fig. 1, the inventive method for extracting carbon dioxide
from air
comprises providing a wall 1 having a surface 2 on which a carbonic anhydrase
3 is
immobilized. Carbonic anhydrase is an enzyme that has the capacity to remove
carbon
dioxide from a stream of gas (for example a stream of air). A process where
carbon
dioxide is removed from air is disclosed in, for example, US patent No.
6143556 and
reference is made to that document for further detail about carbonic anhydrase
and the
process by which carbonic anhydrase removes carbon dioxide from air. In the
method
according to the present invention, the surface 2 of the wall 1 is exposed to
a stream of
gas such as air. The carbonic anhydrase 3 is thereby put to use to remove
carbon dioxide
from the stream of gas. Optionally, the carbon dioxide so obtained may
subsequently be
used for some other purpose, for example as a propellant in aerosol spray
containers or
to manufacture methanol.
As indicated in Fig. 1, the wall 1 on the surface of which the carbonic
anhydrase 3 is
placed constitutes an outer surface of a ce118 having an extraction chamber 19
for
extraction of carbon dioxide. The chamber 19 may be divided into a front
compartment
20 and a rear compartment 21 and where the front compartment 20 serves as an
extraction compartment. The chamber 19 is filled with liquid. The liquid in
the chamber
19 can be pumped around by a pump 22 that keeps the liquid circulating between
the
front compartment 20 and the rear compartment 21. The liquid pressure in the
rear
compartment should preferably be higher than the pressure in the front
compartment 20.
For this purpose, a flow restriction 23 may be formed between the rear and
front
compartment 20, 21. To enter the front compartment, the liquid must pass the
flow
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restriction 23. The liquid in the chamber 19 is an aqueous phosphate buffer
system, i.e.
it is based on water. The liquid may contain an anti-freezing agent. A rear
wa114 of the
ce118 is in contact with a primary evacuation conduit 24.
With reference to Fig. 2, the wall 1 is formed by a rotor blade 5 and is a
part of the rotor
blade 5. The rotor blade 5 is rotatably j ournalled such that the rotor blade
may rotate. As
indicated schematically in Fig. 3, the rotor blade 5 may in particular be the
rotor blade 5
of a wind power plant 6.
The function of the arrangement is as follows. The rotor blade 5 rotates in
the air. As the
rotor blade 5 rotates in the air, it will contact large quantities of air that
moves relative
to the surface of the rotor blade 5. This is especially the case if the rotor
blade 5 is the
rotor blade 5 of a wind power plant and the rotation of the rotor blade 5 is
caused by the
wind. As a consequence, the carbonic anhydrase on the rotor blade 5 will
contact much
more air than if the carbonic anhydrase had been placed on a stationary wall.
Carbon
dioxide is absorbed by the carbonic anhydrase and passes through the wall 1
into the
liquid in the front compartment 20 of the ce118. The part of the wall 1 where
the
carbonic anhydrase 3 is placed is formed by a permeable or semipermeable
membrane,
for example a semipermeable plastic membrane or a lipid membrane. The membrane
may be doped with ionophores to provide ion conducting channels. The liquid is
circulated by pump 22 into the rear compartment 21. From the rear compartment
21,
carbon dioxide passes through the rear wa114 into the primary evacuation
conduit 24.
The rear wa114 is also formed by a permeable or semipermeable membrane, for
example a lipid membrane. During this process, the atmospheric pressure Pi is
larger
than the pressure P2 in the front compartment 20, i.e. Pi > P2. The pressure
P3 in the
rear compartment 21 is also higher than the pressure P2 in the front
compartment 20, i.e.
P3 > P2. The pressure P3 in the rear compartment 21 is also higher than the
pressure P4 in
the primary evacuation conduit 24.
Per second, 1 gram carbonic anhydrase can process 10 moles of carbon dioxide
which
equals 440 grams of carbon dioxide. In normal air, there is about 340 ml
carbon dioxide
per m3 which equals 0.61 grams of carbon dioxide per m3. Consequently, 1 gram
of
carbonic anhydrase can process the carbon dioxide in 70 m3 air per second.
The pH in the front compartment 20 should preferably exceed 7Ø A suitable pH
level
for the front compartment 20 may be, for example, 7.4. When pH is above 7, the
carbon
dioxide is more easily solved in the water phase in the front compartment 20
(the
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extraction compartment). The carbonic anhydrase here works to transform the
carbon
dioxide into hydrocarbonate that is immediately solved in the liquid.
With reference to Fig. 2, the rotor blade 5 is preferably divided into a
plurality of cells 8
separated from each other in the radial direction of the rotor blade 5, each
ce118 has a
wall 1 on which carbonic anhydrase is arranged, e.g. immobilized, such that
each cell 8
can extract carbon dioxide. If necessary, steps may be taken to reduce
pressure in the
cells.
In Fig, 3, the rotor blade is shown as being part of a wind power plant 6 and
mounted on
a hub 27. The hub is rotatably journalled in a housing 30 that is supported by
a pillar 29.
As indicated in Fig. 4 and Fig. 5, the primary evacuation conduit 24 leads to
a main
evacuation conduit 25 that may be common to several cells 8 for extraction of
carbon
dioxide. With reference once again to Fig. 2, the main evacuation conduit 25
extends
along the rotor blade 5 from an outer part of the blade 5 and up through the
hub 27 of
the rotor blade 5. The main evacuation conduit 25 can be connected to a source
26 of
underpressure/vacuum that can be located inside the structure of the wind
power plant 6.
The source 26 of underpressure may be, for example, a pump or a fan. From the
source
26 of underpressure, the carbon dioxide may optionally be sent through a
further
conduit 28 (see Fig. 3) to a further destination, for example to a storage
tank for carbon
dioxide or to a unit 9 where the carbon dioxide is used in a process for
producing a
further product. The unit 9 may be, for example, a fuel cell where carbon
dioxide is
used in a process to manufacture methanol. The unit 9 (for example a fuel
ce119) is thus
connected to the wall 1 of the rotor blade 5 in such a way that carbon dioxide
extracted
from the air through the wall 1 can be transported from the wall 1 to the unit
9. In the
above disclosed embodiment, the wall 1 is connected to the unit 9 through the
conduits
24, 25 and 28 and the source of underpressure 26. However, it should be
understood
that the connection or communication line from the wall 1 to the unit 9 could
be
designed in other ways than that which has been disclosed above. For example,
if a
source of underpressure 26 is used, the source of underpressure 26 does not
necessarily
have to be located inside the structure of the wind power plant 6.
As mentioned above, the carbon dioxide extracted from air may optionally be
used to
produce methanol in a chemical reaction where electrical energy is used to
transform
water and carbon dioxide to methanol, i.e. electrical current + C02+H20 --*
CH3OH
(the process is here indicated in a simplified form, in practice the process
may include
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the formation of intermediate compounds such as Oz). When the rotor blade 5 is
the
rotor blade 5 of a wind power plant 6, electrical energy obtained from the
wind power
plant 6 can be used in a process where water and carbon dioxide is transformed
into
methanol. Alternatively, electrical energy for such a process may come from
another
source than the wind power plant 6. For example, it could come from the power-
mains.
In order to produce methanol, a fuel ce119 may be used. In a process to
produce
methanol, the fuel ce119 will be run in reverse compared to its normal mode of
operation where methanol would be used as fuel in a process where electricity
is
generated.
A possible process for producing methanol will now be explained with reference
to Fig.
6. In Fig.6, it can be seen that the fuel ce119 is shown as has an anode 15
and a cathode
16. The anode 15 and the cathode 16 are separated by a membrane 17. An
electric
circuit is indicated by the numeral 18. To produce methanol, carbon dioxide
and water
are fed into a fuel ce119 through the opening 11 in the fuel ce119. An
electric current is
added at the electric circuit 18. On the cathode side, water is added through
opening 13
while Oz exits through opening 14 (it should be understood that Fig. 6 is a
schematic
representation). In Fig. 5, methanol (CH3OH) leaves the fuel cell through
opening 12.
It should be understood that the process can also be run in the opposite
direction as
indicated in Fig. 7. In Fig. 7, it is indicated how methanol is supplied to
the fuel ce119
through opening 12. In the resulting reaction, an electrical current is
generated in the
circuit 18.
It should be understood that the invention can also be described in terms of
an
arrangement for removing carbon dioxide from air. The arrangement comprises a
wall 1
having a surface 2 upon which carbonic anhydrase 3 is immobilized such that
carbon
dioxide can be extracted from the air.
The function of the arrangement is as follows. When the wind is blowing, the
rotor 5 of
a wind power plant 6 is exposed to a stream of air. At the same time as
electrical energy
is generated by the wind power plant, carbon dioxide is extracted along the
rotor blade
5.
From the rotor blade 5, a conduit may lead to a fuel ce119 where the carbon
dioxide can
be transformed into methanol. A part of the electricity generated by the wind
power
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plant 6 is used for a reaction where the extracted carbon dioxide is used to
produce
methanol which can then be stored.
In some embodiments of the invention, the need for electrical energy may be
monitored.
For example, one or several indicators may be monitored in order to determine
whether
electrical energy is needed somewhere else. One such indicator may be, for
example,
the price of electricity. An increase in the price of electricity may indicate
that the need
for electricity has increased. At times when a high need for electricity is
indicated,
stored methanol may be used to produce electricity such that electricity can
be produced
when the need for electricity is large.
Instead of being a part of a wind power plant 6, the rotor blade 5 with
carbonic
anhydrase could be placed in an exhaust chimney where large amounts of gas
containing carbon dioxide are discharged and it is desirable to reduce the
level of carbon
dioxide before the gas is discharged into the atmosphere. A rotor blade with
carbonic
anhydrase could also be used in a building to reduce the level of carbon
dioxide.
With reference to Fig. 2, an embodiment is indicated where the rotor blade 5
is divided
into a plurality of cells 8 that are separated from each other in the radial
direction of the
rotor blade 5. Each ce118 has a wall 1 on which carbonic anhydrase 3 is
immobilized
such that each ce118 can extract carbon dioxide. Since the cells 8 contain
liquid, the
liquid pressure could become undesirably high if one single cell extended
along the
entire rotor blade - the column of liquid would be high and the centrifugal
forces would
make the problem even more serious. If a plurality of cells 8 is used, the
liquid in each
cell can be separated from the liquid in the other cells. In this way, liquid
pressure can
be kept lower. Preferably, each cell should have an extension along the rotor
blade
(height) of no more than 20 mm even though dimensions larger than 20 mm could
be
considered. If the height of a cell is no more than 20 mm, this reduces the
risk of
excessively high pressure in the cell.
One aspect of the invention shall now be explained with reference to Fig. 4.
In Fig. 4,
the circulation of the liquid in chamber 19 is indicated as going in an anti-
clockwise
direction. In the front chamber adjacent the atmosphere, the liquid will then
move in the
direction of arrow C. The rotor blade 5 is preferably arranged such that, as
the rotor
blade 5 moves through the air, the air moves relative to the rotor blade in
the direction
of arrow A such that the wind assists in pressing the fluid in chamber 19 in
the correct
direction. In, for example, a wind power plant, the relative direction of
movement of the
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wind in relation to the rotor blade can be determined in advance and the cells
8 oriented
such that the wind will assist in the circulation of liquid inside each ce118.
With reference to Fig. 1, the arrangement according to the invention may
optionally also
include a fuel ce119 where methanol can be may be manufactured. The fuel ce119
is in
communication with the wall 1 that is provided with carbonic anhydrase. A tank
10 may
be connected to the fuel ce119 such that methanol produced in the fuel ce119
can be
subsequently stored in the storage tank 10.
By placing the carbonic anhydrase 3 on a rotor blade 5 that rotates in the
air, large
amounts of air can come into contact with the carbonic anhydrase which means
that
larger quantities of carbon dioxide can be extracted. The invention can be
used purely to
reduce the content of carbon dioxide in air, for example in a building where
humans live
or work. For such purposes, the rotor blade could be a component of, for
example, a fan
and driven by a motor, for example an electric motor. The invention could also
be put to
use for such purposes where the objective is to obtain carbon dioxide. For
such
purposes, the rotor blade could be the rotor blade 5 of a wind power plant or
some other
device where a blowing wind causes the rotor blade to rotate.
The rotor blade provided with carbonic anhydrase could also be placed in an
exhaust
conduit where there is a flow of gas containing carbon dioxide. The rotatably
joumalled
rotor blade 5 could then remove carbon dioxide from the gas and at the same
time
generate electrical energy.
While the invention has been described in terms of a method and an
arrangement, it
should be understood that these categories only reflect different aspects of
one and the
same invention. The method may thus comprise such steps that would be the
inevitable
result of using the inventive arrangement, regardless of whether such steps
have been
explicitly mentioned or not. In the same way, features of the arrangement have
been
explained with reference to the inventive method.
