SYSTEM FOR SUPPORTING ALGAE GROWTH
WITH ADSORBED CARBON DIOXIDE
FIELD OF THE INVENTION
The present invention pertains generally to methods for growing algae.
More particularly, the present invention pertains to the use of a medium for
growing algae that is comprised of a solution of sodium bicarbonate. The
present invention is particularly, but not exclusively, useful as a system for
supporting growth of algae with bicarbonate solution, and with charging used
solution with adsorbed carbon dioxide at a liquid-gas contact medium for
further support of algae growth.
BACKGROUND OF THE INVENTION
As worldwide petroleum deposits decrease, there is rising concern over
petroleum shortages and the costs that are associated with the production of
hydrocarbon products. As a result, alternatives to products that are currently
processed from petroleum are being investigated. In this effort, biofuel such
as biodiesel has been identified as a possible alternative to petroleum-based
transportation fuels. In general, a biodiesel is a fuel comprised of mono-alkyl
esters of long chain fatty acids derived from plant oils or animal fats. In
industrial practice, biodiesel is created when plant oils or animal fats react
with an alcohol, such as methanol.
For plant-derived biofuel, solar energy is first transformed into chemical
energy through photosynthesis. The chemical energy is then refined into a
usable fuel. Currently, the process involved in creating biofuel from plant oils
is expensive relative to the process of extracting and refining petroleum. It is
possible, however, that the cost of processing a plant-derived biofuel could be
reduced by maximizing the rate of growth of the plant source. Because algae
is known to be one of the most efficient plants for converting solar energy into
cell growth, it is of particular interest as a biofuel source. Importantly, the use
of algae as a biofuel source presents no exceptional problems, i.e., biofuel
can be processed from oil in algae as easily as from oils in land-based plants.
While algae can efficiently transform solar energy into chemical energy
via a high rate of cell growth, it has been difficult to create environments in
which algae cell growth rates are optimized. Specifically, the conditions
necessary to facilitate a fast growth rate for algae cells in large-scale
operations have been found to be expensive to create. While sunlight can be
cheaply and easily fed to algae, the other sources of growth may require
expensive distribution systems. For instance, it may be difficult to provide
carbon dioxide at the appropriate levels throughout a system. For commercial
purposes, reliance on normal absorption of CO2 from the atmosphere, such as
at a pond-air interface, is too slow. On the other hand, conventional pumping
techniques with extensive piping networks are too costly. Thus, an alternate
source of C0 2 is required. One possible source of carbon dioxide is found in
flue gases from power plants or other combustion sources. Further, the
carbon dioxide in flue gases is generally treated as pollution. Therefore, using
carbon dioxide from flue gases will help abate pollution.
A commercially viable source of CO2 for algae photosynthesis is a
bicarbonate solution. During this photosynthesis, it happens that a carbonate
solution is generated. Further, it is known that such a carbonate solution will
adsorb C0 2 from air (albeit somewhat inefficiently) for conversion back to a
bicarbonate solution. Within this cycle, in a microalgae bioreactor system, the
conversion from a bicarbonate solution to a carbonate solution is a
consequence of algae growth. On the other hand, as mentioned above, the
conversion from a carbonate solution (medium) to a bicarbonate solution can
be accomplished merely by exposure to air. Also, in a situation where algae
are being grown in a bioreactor system for the purpose of manufacturing a
biodiesel fuel, C0 2 can be recovered from the power plant effluent to create a
bicarbonate solution.
In light of the above, it is an object of the present invention to provide a
system for supporting the growth of algae which also reduces fossil fuel
pollution. Another object of the present invention is to provide a system for
growing algae which reduces input costs. Another object of the present
invention is to adsorb carbon dioxide at a liquid-gas contact medium into a
solution for feeding algae. Another object of the present invention is to
provide a system for growing algae that utilizes a bicarbonate solution to
deliver carbon to the algae. Another object of the present invention is to
replenish spent medium with carbon dioxide in order to support further growth
of algae in the medium. Still another object of the present invention is to
introduce a bicarbonate solution into an algae growth medium to establish
elevated CO2 levels in a bioreactor system for algae growth. Another object
of the present invention is to recycle a carbonate solution from a bioreactor
system for conversion to a bicarbonate solution for subsequent use in growing
algae in the bioreactor system. Yet another object of the present invention is
to provide a system and method for growing algae that is simple to implement,
easy to use, and comparatively cost effective.
SUMMARY OF THE INVENTION
In accordance with the present invention, a system and method are
provided for growing algae. Importantly, the system and method provide for
the adsorption of carbon dioxide into the medium for supporting algae growth.
Further, the system is able to use the carbon dioxide from flue gases or other
pollution.
In the system, a channel holds bicarbonate solution to support algae
growth. During growth, the algae uses carbon dioxide and converts the
bicarbonate solution into carbonate solution. In order to reuse the solution,
the system provides a high surface area gas-liquid contact medium.
Specifically, the carbonate solution is delivered to and moves through the gasliquid
contact medium. At the same time, air including the carbon dioxide is
moved across the contact medium. During contact between the gas and
liquid, the carbonate solution adsorbs carbon dioxide from the air and is
converted into bicarbonate solution. After this process is completed, the
bicarbonate solution is returned to the channel to support further algae
growth.
When used with a power plant, the system can be optimized by using
steam power from the power plant for operation. Specifically, a fan using the
steam power can direct the air across the contact medium. Further, the
steam power can be used to move the solution to, from, and within the
channel.
BRIEF DESCRIPTION OF THE DRAWINGS
The novel features of this invention, as well as the invention itself, both
as to its structure and its operation, will be best understood from the
accompanying drawings, taken in conjunction with the accompanying
description, in which similar reference characters refer to similar parts, and in
which:
Fig. 1 is a schematic view of an algae growing system in accordance
with the present invention; and
Fig. 2 is a schematic view of the conversion between carbonate and
bicarbonate for the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Fig. 1, a system for producing biofuel from pollutant-fed
algae is shown and generally designated 10. As shown, the system 10
includes a scrubber 12 for scrubbing a pollutant-contaminated fluid stream.
Specifically, the scrubber 12 includes a chamber 14 and an input port 16a for
receiving flue gas from a combustion source such as a power plant 18 and a
scrubber solution 20. Typically, the flue gas includes pollutants such as
carbon dioxide, sulfur oxides, and/or nitrogen oxides. Also, the scrubber
solution 20 typically comprises sodium bicarbonate. As further shown, the
scrubber 12 includes a solution outlet 22 and a gas outlet 24. Also, the
system 10 includes an oxidation stage 26 for oxidizing pollutants in the flue
gas to facilitate their removal from the flue gas. As shown, the oxidation stage
26 is interconnected between the power plant 18 and the scrubber 12.
As further shown, the system 10 includes a bioreactor 28 comprised of
at least one chemostat 30 for growing algae cells (exemplary cells depicted at
32) and a plug flow reactor 34 for treating the algae cells 32 to trigger cell
production of triglycerides. Preferably, and as shown, both the chemostat 30
and the plug flow reactor 34 are open raceways, though closed systems are
also contemplated. Further, such open systems 10 can cover several acres
of land to optimize economies of scale. For purposes of the present
invention, the system 10 includes an algae separator 36 for removing the
algae cells 32 from the plug flow reactor 34. As shown in Fig. 1, the
chemostat 30 includes a channel 38. As further shown, the channel 38 is
provided with an input port 40 that is in fluid communication with the solution
outlet 22 of the scrubber chamber 14. For purposes of the present invention,
the input port 40 is also in communication with a reservoir (not illustrated)
holding a nutrient mix (indicated by arrow 42). Preferably, the nutrient mix 42
includes phosphorous, nitrogen, sulfur and numerous trace elements
necessary to support algae growth that are not provided to the bioreactor 28
by the scrubber solution 20. Further, the chemostat 30 is provided with a
paddlewheel 44 for causing the medium 46 formed by the scrubber solution
20 and the nutrient mix 42 to continuously circulate around the channel 38 at
a predetermined fluid flow velocity. Also, each channel 38 is provided with an
output port 48 in communication with the plug flow reactor 34.
As shown, the plug flow reactor 34 includes an input port 50a for
receiving overflow medium (indicated by arrow 46') with algae cells 32 from
the output port 48 of the chemostat 30. As further shown, the plug flow
reactor 34 includes a channel 52 for passing the medium 46" with algae cells
32 downstream. The flow rate of the medium 46" is due solely to gravity and
the force of the incoming overflow medium 46' from the chemostat 30.
Preferably, the plug flow reactor 34 has a substantially fixed residence time of
about one to four days. For purposes of the present invention, the system 0
is provided with a reservoir (not shown) that holds a modified nutrient mix
(indicated by arrow 54). Further, the channel 52 is provided with an input port
50b for receiving the modified nutrient mix 54. In order to manipulate the
cellular behavior of algae cells 32 within the plug flow reactor 34, the modified
nutrient mix 54 may contain a limited amount of a selected constituent, such
as nitrogen or phosphorous. For instance, the nutrient mix 54 may contain no
nitrogen. Alternatively, the algae cells 32 may exhaust nutrients such as
nitrogen or phosphorous in the nutrient mix 42 at a predetermined point in the
plug flow reactor 34. By allowing such nutrients to be exhausted, desired
behavior in the algae cells 32 can be caused without adding a specific
modified nutrient mix 54. Further, simply water can be added through the
modified nutrient mix 54 to compensate for evaporation. In addition to input
ports 50a and 50b, the channel 52 is further provided with an input port 50c to
receive other matter.
In Fig. 1, the algae separator 36 is shown in fluid communication with
the channel 52 of the plug flow reactor 34. For purposes of the present
invention, the algae separator 36 separates the algae cells 32 from the
medium 46" and the remaining nutrients therein through flocculation and/or
filtration. As further shown, the algae separator 36 includes an effluence
outlet 56 and an algae cell outlet 60. For purposes of the present invention,
the system 10 includes a channel 58 providing fluid communication between
the effluence outlet 56 and the scrubber 12 through a solution input port 16b
in the scrubber chamber 14.
Also, the system 10 includes a cell lysis apparatus 62 that receives
algae cells 32 from the algae outlet 60 of the algae separator 36. As shown,
the cell lysis apparatus 62 is in fluid communication with an oil separator 64.
For purposes of the present invention, the oil separator 64 is provided with
two outlets 66, 68. As shown, the outlet 66 is connected to a hydrolysis
apparatus 70. Further, the hydrolysis apparatus 70 is connected to the input
port 40 in the channel 38 of the chemostat 30.
Referring back to the oil separator 64, it can be seen that the outlet 68
is connected to a biofuel reactor 72. It is further shown that the biofuel reactor
72 includes two exits 74, 76. For purposes of the present invention, the exit
74 is connected to the input port 50c in the channel 52 of the plug flow reactor
34. Additionally or alternatively, the exit 74 may be connected to the input
port 40 in the chemostat 30. Further, the exit 76 may be connected to a tank
or reservoir (not shown) for purposes of the present invention.
In operation of the present invention, pollutant-contaminated flue gas
(indicated by arrow 78) is directed from the power plant 18 to the oxidation
stage 26. At the oxidation stage 26, nitrogen monoxide in the flue gas 78 is
oxidized by nitric acid or by other catalytic or non-catalytic technologies to
improve the efficiency of its subsequent removal. Specifically, nitrogen
monoxide is oxidized to nitrogen dioxide. Thereafter, the oxidized flue gas
(indicated by arrow 80) is delivered from the oxidation stage 26 to the
scrubber 12. Specifically, the oxidized flue gas 80 enters the chamber 14 of
the scrubber 12 through the input port 16a. Upon the entrance of the flue gas
80 into the chamber 14, the scrubber solution 20 is sprayed within the
chamber 14 to absorb, adsorb or otherwise trap the pollutants in the flue gas
80 as is known in the field of scrubbing. With its pollutants removed, the
clean flue gas (indicated by arrow 82) exits the scrubber 12 through the gas
outlet 24. At the same time, the scrubber solution 20 and the pollutants exit
the scrubber 12 through the solution outlet 22.
After exiting the scrubber 12, the scrubber solution 20 and pollutants
(indicated by arrow 84) enter the chemostat 30 through the input port 40.
Further, the nutrient mix 42 is fed to the chemostat 30 through the input port
40. In the channel 38 of the chemostat 30, the nutrient mix 42, scrubber
solution 20 and pollutants (arrow 84) form the medium 46 for growing the
algae cells 32. This medium 46 is circulated around the channel 38 by the
paddlewheel 44. Further, the conditions in the channel 38 are maintained for
maximum algal growth. For instance, in order to maintain the desired
conditions, the medium 46 and the algae cells 32 are moved around the
channel 38 at a preferred fluid flow velocity of approximately fifty centimeters
per second. Further, the amount of algae cells 32 in the channel 38 is kept
substantially constant. Specifically, the nutrient mix 42 and the scrubber
solution 20 with pollutants (arrow 84) are continuously fed at selected rates
into the channel 38 through the input port 40, and an overflow medium 46'
containing algae cells 32 is continuously removed through the output port 48
of the channel 38.
After entering the input port 50a of the plug flow reactor 34, the
medium 46" containing algae cells 32 moves downstream through the channel
52 in a plug flow regime. Further, as the medium 46" moves downstream, the
modified nutrient mix 54 may be added to the channel 52 through the input
port 50b. This modified nutrient mix 54 may contain a limited amount of a
selected constituent, such as nitrogen or phosphorous. The absence or small
amount of the selected constituent causes the algae cells 32 to focus on
energy storage rather than growth. As a result, the algae cells 32 form
triglycerides.
At the end of the channel 52, the algae separator 36 removes the algae
cells 32 from the remaining effluence (indicated by arrow 86). Thereafter, the
effluence 86 is discharged from the algae separator 36 through the effluence
outlet 56. In order to recycle the effluence 86, it is delivered through channel
58 to the input port 16b of the scrubber 12 for reuse as the scrubber solution
20. Further, the removed algae cells (indicated by arrow 88) are delivered to
the cell lysis apparatus 62. Specifically, the removed algae cells 88 pass out
of the algae cell outlet 60 to the cell lysis apparatus 62. For purposes of the
present invention, the cell lysis apparatus 62 lyses the removed algae cells 88
to unbind the oil therein from the remaining cell matter. After the lysing
process occurs, the unbound oil and remaining cell matter, collectively
identified by arrow 90, are transmitted to the oil separator 64. Thereafter, the
oil separator 64 withdraws the oil from the remaining cell matter as is known
in the art. After this separation is performed, the oil separator 64 discharges
the remaining cell matter (identified by arrow 92) out of the outlet 66 of the oil
separator 64 to the input port 40 of the chemostat 30.
In the chemostat 30, the remaining cell matter 92 is utilized as a source
of nutrients and energy for the growth of algae cells 32. Because small units
of the remaining cell matter 92 are more easily absorbed or otherwise
processed by the growing algae cells 32, the remaining cell matter 92 may
first be broken down before being fed into the input port 40 of the chemostat
30. To this end, the hydrolysis apparatus 70 is interconnected between the oil
separator 64 and the chemostat 30. Accordingly, the hydrolysis apparatus 70
receives the remaining cell matter 92 from the oil separator 64, hydrolyzes the
received cell matter 92, and then passes hydrolyzed cell matter (identified by
arrow 94) to the chemostat 30.
Referring back to the oil separator 64, it is recalled that the remaining
cell matter 92 was discharged through the outlet 66. At the same time, the oil
withdrawn by the oil separator 64 is discharged through the outlet 68.
Specifically, the oil (identified by arrow 96) is delivered to the biofuei reactor
72. In the biofuei reactor 72, the oil 96 is reacted with alcohol, such as
methanol, to create mono-alkyl esters, i.e., biofuei fuel. This biofuei fuel
(identified by arrow 98) is released from the exit 76 of the biofuei reactor 72 to
a tank, reservoir, or pipeline (not shown) for use as fuel. In addition to the
biofuei fuel 98, the reaction between the oil 96 and the alcohol produces
glycerin as a byproduct. For purposes of the present invention, the glycerin
(identified by arrow 100) is pumped out of the exit 74 of the biofuei reactor 72
to the input port 50c of the plug flow reactor 34.
In the plug flow reactor 34, the glycerin 100 is utilized as a source of
carbon by the algae cells 32. Importantly, the glycerin 100 does not provide
any nutrients that may be limited to induce oil production by the algae cells 32
or to trigger flocculation. The glycerin 100 may be added to the plug flow
reactor 34 at night to aid in night-time oil production. Further, because
glycerin 100 would otherwise provide bacteria and/or other nonphotosynthetic
organisms with an energy source, limiting the addition of
glycerin 100 to the plug flow reactor 34 only at night allows the algae cells 32
to utilize the glycerin 100 without facilitating the growth of foreign organisms.
As shown in Fig. 1, the exit 74 of the biofuel reactor 72 may also be in fluid
communication with the input port 40 of the chemostat 30 (connection shown
in phantom). This arrangement allows the glycerin 100 to be provided to the
chemostat 30 as a carbon source. While Fig. 1 illustrates that a paddlewheel
44 or gravity for moving the medium 46 through the channels 38 and 52,
steam power 102 from the power plant 18 may be used to power such
movement.
In Fig. 2, a system for supporting algae growth with adsorbed carbon
dioxide is illustrated and generally designated 103. In Fig. 2, the channels 38
and 52 are represented collectively by reference number 104. These
channels 104 hold the medium 46 that includes bicarbonate solution. As
algae 32 grows in the channels 104 it depletes the medium 46 of carbon and
the medium 46 becomes principally carbonate solution. In order to replenish
the carbonate solution, the system 103 provides for removal of the carbonate
solution 106 from the channels 104. As shown, the carbonate solution 106 is
delivered to a high surface area liquid-gas contact medium 108. As shown, a
fan 110, powered by steam power 102, moves air 112 including carbon
dioxide across the contact medium 108. As a result, when the carbonate
solution 106 moves slowly across or drips through the contact medium 108, it
adsorbs carbon dioxide and is converted back into bicarbonate solution.
Thereafter, the bicarbonate solution 114 is returned from the contact medium
108 to the channels 104 to support further growth of the algae 32 therein.
While the particular System for Supporting Algae Growth with
Adsorbed Carbon Dioxide as herein shown and disclosed in detail is fully
capable of obtaining the objects and providing the advantages herein before
stated, it is to be understood that it is merely illustrative of the presently
preferred embodiments of the invention and that no limitations are intended to
the details of construction or design herein shown other than as described in
the appended claims.
What is claimed is:
1. A system for supporting algae growth with adsorbed carbon
dioxide comprising:
a high surface area liquid-gas contact medium;
a carbonate solution passing through the contact medium to
adsorb carbon dioxide and convert into bicarbonate solution;
a channel for holding the bicarbonate solution to support algae
growth, wherein the algae converts the bicarbonate solution into
carbonate solution; and
a means for delivering the carbonate solution from the channel
to the contact medium.
2. A system as recited in claim 1 further comprising a fan to move
air across the contact medium.
3. A system as recited in claim 2 wherein the carbon dioxide is
recovered from air including effluent from a power plant, and wherein low
pressure steam from the power plant is used to drive the fan.
4. A system as recited in claim 3 wherein low pressure steam from
the power plant is used to move the bicarbonate solution through the channel.
5. A system as recited in claim 4 further comprising an algae
separator for removing algae from the channel.
6. A system as recited in claim 5 further comprising a cell lysis
device for freeing oil within the algae.
7. A system as recited in claim 6 further comprising an oil
separator for removing the oil from other cell material.
8. A system as recited in claim 7 further comprising a biofuels
reactor for creating biofuel from the oil.
9. A system for producing biofuel which comprises:
a channel for growing algae therein;
an algae separator in fluid communication with the channel for
removing algae therefrom;
a cell lysis device for freeing oil from within the algae;
an oil separator for isolating the oil from remaining algae matter;
a biofuels reactor for converting the oil into biofuel;
a bicarbonate solution flowing through the channel to support
algae growth, wherein the algae converts the bicarbonate solution into
carbonate solution; and
a high surface area liquid-gas contact medium for adsorbing
carbon dioxide into the carbonate solution for conversion into
bicarbonate solution.
10. A system as recited in claim 9 further comprising a fan to move
air across the contact medium.
11. A system as recited in claim 10 wherein the carbon dioxide is
adsorbed from air including effluent from a power plant, and wherein low
pressure steam from the power plant is used to drive the fan.
12. A system as recited in claim 11 wherein low pressure steam
from the power plant is used to move the bicarbonate solution through the
channel.
13. A method for supporting algae growth with adsorbed carbon
dioxide comprising the steps of:
providing a high surface area liquid-gas contact medium;
passing a carbonate solution through the contact medium to
adsorb carbon dioxide and convert into bicarbonate solution;
moving the bicarbonate solution through a channel to support
algae growth, wherein the algae converts the bicarbonate solution into
carbonate solution; and
delivering the carbonate solution from the channel to the contact
medium.
14. A method as recited in claim 13 further comprising the step of
moving air across the contact medium.
5. A method as recited in claim 14 wherein the carbon dioxide is
recovered from air including effluent from a power plant, and wherein low
pressure steam from the power plant is used to move air across the contact
medium.
16. A method as recited in claim 15 wherein low pressure steam
from the power plant is used to move the bicarbonate solution through the
channel.
17. A method as recited in claim 16 further comprising the step of
removing the algae from the channel with an algae separator.
18. A method as recited in claim 17 further comprising the step of
freeing oil within the algae with a cell lysis device.
19. A method as recited in claim 18 further comprising the step of
removing the oil from other cell material with an oil separator.
20. A method as recited in claim 19 further comprising the step of
creating biofuel from the oil with a biofuels reactor.
21. A system for establishing elevated carbon dioxide levels in an
algae growth medium of a bioreactor which comprises:
a first subsystem having a contact medium for receiving a
carbonate solution from the bioreactor, wherein the contact medium
includes a plurality of panels with each panel having an extended
surface to maximize a surface interface between air and the carbonate
solution to convert the carbonate solution into a bicarbonate solution;
and
a second subsystem for including the bicarbonate solution in the
algae growth medium, and for then feeding the algae growth medium
to the bioreactor for consumption of carbon dioxide in the bicarbonate
solution by algae for growth of the algae and for conversion of the
bicarbonate solution to a carbonate solution for return to the first
subsystem.