Patent Publication Number: US-11661572-B2

Title: Photobioreactors, gas concentrators, and periodic surfaces

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 62/904,065 filed Sep. 23, 2019, which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Concerns about climate change, carbon dioxide (CO 2 ) emissions, and depletion of subterranean oil and gas resources have led to widespread interest in the production of biofuels from algae and microalgae. As used herein, the term “biofuel” refers to any type of fuel produced from algae, and the term “algae” will include microalgae, unless explicitly distinguished. 
     As compared to some other plant-based biofuel feedstocks, algae have higher CO 2  fixation efficiencies and growth rates, and growing algae can efficiently utilize wastewater and industrial gases as nutrient sources. The biomass of algae stores increasing quantities of lipids as it grows. Methods for harvesting and utilizing algae involve extracting and converting their stored lipids and carbohydrates into renewable biofuels, such as diesel and jet fuel, or into other hydrocarbons, as examples. 
     Algae biomass is generally grown in a water slurry contained in a bioreactor system. Algae bioreactors are sometimes referred to as “photobioreactors” since they utilize a light source to cultivate algae, which are photoautotrophic organisms or organisms that can survive, grow, and reproduce with energy derived entirely from the sun through the process of photosynthesis. Photosynthesis, aided by other cellular biochemical processes, is essentially a carbon recycling process through which inorganic CO 2  is absorbed and combined with solar energy, nutrients, and water to synthesize carbohydrates, lipids, and other compounds necessary to algae life. In addition to production of lipids and carbohydrates for biofuel production, the benefits of growing and harvesting algae includes utilization of CO 2  and production of oxygen. 
     The CO 2  used for algae growth may come from any suitable source, including atmospheric air, flue gas/exhaust streams from a combustion process, or a storage location including tanks or geological formations, as examples. In some locations, options are limited primarily or exclusively to atmospheric air or another relatively low-concentration source of CO 2 . In these locations and others, equipment and methods that provide improvements to the delivery of CO 2  for algae growth would be desirable. 
     SUMMARY OF THE INVENTION 
     The present disclosure is related to growing algae for biofuel production and, more particularly, to delivering concentrated gas for algae growth and to structures to enhance gas concentrators or photobioreactors. 
     In some embodiments, a system for growing algae is disclosed herein and includes a photobioreactor comprising a tubular structure having inner and outer surfaces, an annular space defined between the inner and outer surfaces, an inlet to allow an algae slurry to enter the annular space, and a mechanism configured to produce radially-directed contractions and expansions in the tubular structure. At least one of the inner and outer surfaces is transparent to at least some wavelengths of light useful for growing algae within the algae slurry. 
     In some embodiments, a method for growing algae is disclosed herein and includes providing an algae slurry to an annular space located between an inner surface and an outer surface of a tubular structure, and inducing contractions and expansions in the tubular structure. 
     In one or more additional embodiments, a photobioreactor is disclosed and includes a tubular structure having inner and outer surfaces and an annular space defined between the inner and outer surfaces, an inlet to allow an algae slurry to enter the annular space, an inner passageway defined by the inner surface, and one or more apertures defined in the inner surface to allow a gas to flow from the inner passageway into the annular space. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following figures are included to illustrate certain aspects of the embodiments, and should not be viewed as exclusive embodiments. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to those skilled in the art and having the benefit of this disclosure. 
         FIG.  1    is a schematic diagram of an example system for growing algae, according to one or more embodiments of the present disclosure. 
         FIG.  2    illustrates another example system for growing algae, according to one or more embodiments of the present disclosure. 
         FIG.  3    illustrates still another example system for growing algae, according to one or more embodiments of the present disclosure. 
         FIG.  4    illustrates an example system for growing algae in a pond, according to one or more embodiments of the present disclosure. 
         FIG.  5    illustrates an example gas concentrator, according to one or more embodiments of the present disclosure. 
         FIGS.  6 A- 6 C  depict examples of singly periodic structures of which the gas concentrator of  FIG.  5    may be formed or may include. 
         FIGS.  7 A- 7 E  depict examples of doubly periodic structures of which the gas concentrator of  FIG.  5    may be formed or may include. 
         FIGS.  8 A- 8 E  depict examples of triply periodic structures of which the gas concentrator of  FIG.  5    may be formed or may include. 
         FIG.  9    illustrates another example gas concentrator, according to one or more embodiments of the present disclosure. 
         FIG.  10    illustrates a system for growing algae, according to one or more embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is related to growing algae for biofuel production and, more particularly, to delivering concentrated gas for algae growth and to structures configured to enhance operation of gas concentrators or photobioreactors. 
       FIG.  1    is a schematic diagram of an example system  100  for growing algae, according to one or more embodiments of the present disclosure. As illustrated, the system  100  includes a photobioreactor (PBR)  104  and a gas concentrator  106  fluidically coupled by a transfer line  108 . The PBR  104  may be any type of bioreactor configured for the cultivation, growth, and harvesting of algae from an algae slurry contained within the PBR  104 . Examples of the PBR  104  include, but are not limited to, an open pond, a closed pond, an open reactor vessel, and a closed reactor vessel. Though not shown, the system  100  may also include any of the following: suitable valving, a water supply, and other equipment to support algae growth and harvesting. 
     As used herein, the term “algae slurry,” and grammatical variants thereof, refers to a flowable liquid mixture comprising water, algae cells, and nutrients. The algae cells may alternately referred to as “algae” or “algae biomass.” As used herein, the term “gas” refers to a single gas or a mixture of gases. 
     As illustrated, the system  100  may further include a recycling line  110  and a gas storage tank  112 . The recycling line  110  fluidically couples a gas port  122  on the PBR  104  to an inlet  124  of the gas concentrator  106  or to the transfer line  108 . In some embodiments, the recycling line  110  may include a check valve to ensure fluid may exit gas port  122  but may not enter it. Some embodiments of the system  100  include multiple gas concentrators  106  fluidically coupled to one or more photobioreactors  104 . Some of the gas concentrators  106  may be disposed adjacent the one or more PBRs  104  to reduce piping or pressure drop or to improve utilization of available space, as examples. 
     The storage tank  112  is in fluid communication with the gas concentrator  106  and the PBR  104  to collect, hold, and release a gas, such as one or more gases containing carbon dioxide (CO 2 ). In this example, the recycling line  110  provides fluid communication between the storage tank  112  and the gas concentrator  106  and the PBR  104 . In some embodiments, the storage tank  112  may receive gas discharged from the gas concentrator  106 . In other embodiments, or in addition thereto, the storage tank  112  may receive gas discharged from the PBR  104 . The recycling line  110  may be configured to selectively feed discharged gases back to either the gas concentrator  106  or the PBR  104 , and the storage tank  112  may be tapped as needed. Thus, at various stages of operation, the storage tank  112  may receive and discharge one or more gases containing carbon dioxide (CO 2 ), which may be ultimately fed back into the PBR  104 . In some embodiments, the storage tank  112  may be located adjacent the gas concentrator  106  or the PBR  104  to reduce piping, which may reduce pressure drop (operational costs) and capital costs, or to improve utilization of available space (e.g., land, plant floor area), as examples. 
     As illustrated in  FIG.  1   , the PBR  104  includes an inlet  130  fluidically coupled to transfer line  108  to receive a gas containing CO 2 , an inlet  132  to receive water, nutrients, or algae seed material to make the algae slurry, the gas port  122  coupled to recycling line  110 , an outlet  134  to discharge a byproduct gas including oxygen ( 02 ) produced and released by algae, and a product outlet  136  to discharge algae biomass, which may be in a slurry. Other equipment downstream of the product outlet  136  may separate, filter, or otherwise process the discharged algae. 
     The gas concentrator  106  includes the inlet  124  to receive a first gas, an outlet  142  to discharge unwanted a gas, and an outlet  144  fluidically coupled to the transfer line  108  to discharge a second gas containing CO 2  at a higher concentration than is present in the first gas. The first gas may come from any suitable source, including atmospheric air, flue gas/exhaust streams from a combustion process, or a storage location including tanks or geological formations, as examples. The gas concentrator  106  may operate using a process selected from a group that includes pressure swing adsorption, vacuum swing adsorption, voltage swing adsorption, temperature swing adsorption, displacement desorption, and any combination thereof, as examples. 
     The system  100  may further include a control system  114  used to operate the system  100 . The control system  114  may include a controller, instrumentation, and machine-readable code that causes operation of the controller. In example operation, the control system  114  may be configured or otherwise programmed to monitor or control the flow of fluids through the various inlets, outlets, and lines of the system  100 , and to maintain and adjust fluid levels within the PBR  104 , as examples. 
     During an example first stage of operation, the PBR  104  contains an algae slurry for the growth and cultivation of algae. The gas concentrator  106  receives through the inlet  124  a first gas containing CO 2  at a first concentration, discharges through the outlet  142  unwanted gas, and discharges to the transfer line  108  the second gas, which contains CO 2  at a second concentration higher than the first concentration. The transfer line  108  transfers the second gas containing CO 2  to the PBR  104 . During a growth period, the algae in the PBR  104  absorbs CO 2  from the second gas, which may be bubbled or sparged through the algae slurry, and the algae produces and releases oxygen. A third gas (e.g., a mixture of gases) may accumulate in the PBR  104 . During the first stage of operation, the third gas includes the produced oxygen and, potentially, a residual portion of the second gas that entered the PBR  104 , which may include nitrogen, oxygen, or CO 2 , as examples. During the first stage, the third gas may be discharged from the PBR  104  though outlet  134  as a byproduct gas. 
     During a second stage of operation for the system  100 , the third gas include CO 2  is taken from the PBR  104  and is directed through the recycling line  110 . The third gas that enters the recycling line  110  from the PBR  104  may be sent to the gas concentrator  106 , the gas storage tank  112 , the transfer line  108 , or any combination of these destinations. Ultimately, the third gas or some of its CO 2 , may be returned to the PBR  104 . For example, the third gas may be combined into the second gas at the transfer line  108  and delivered to the PBR  104  during a subsequent occurrence of the first stage of operation. Some embodiments or operational modes of the system  100  may exclude the second stage of operation. 
     During the second stage, a flow of gas from the transfer line  108  to the PBR  104  may be shut-off. The execution of the various stages of operation of the system  100  may be governed by the control system  114 , which may allow or disallow fluid communication between the transfer line  108  and the PBR  104  or between the PBR  104  and recycling line  110 . The control system  114  may be configured to direct the third gas coming from the PBR  104  to the recycling line  110 , the transfer line  108 , the gas concentrator  106 , the gas storage tank  112 , or any combination of these destinations. In some cases, the control system  114  may be configured to direct the third gas back to the PBR  104 . This recycling of the third gas may occur during the current second stage of operation, during a future first stage, or during a future second stage. In this manner, the third gas may be recycled through the system  100 . In some embodiments, the operational stages (e.g. time periods) of PBR  104 , including the recycling of gas through line  110 , may be, alternatively, controlled manually. 
     The algae in the PBR  104  may release CO 2  during a portion of its life cycle, such as when photosynthesis in the algae ceases. The released CO 2  may have been produced by the algae or may have been temporarily held by the algae. The released CO 2 , becomes a portion or constituent of the third gas within the PBR  104 . During this time frame, the third gas is anticipated to include a residual portion of the second gas that entered the PBR  104  through the transfer line  108 , in addition to the newly generated/released CO 2 . Some released O 2  may also be present. Thus, the third gas is anticipated to have a composition that varies through the different stages of operation of the system  100 ; likewise, the composition of the second gas that enters PBR  104  is anticipated to vary due to recycling of the third gas into gas concentrator  106  or transfer line  108 . The algae may release CO 2  periodically, such as during a night or during other periods of low light or when photosynthesis ceases. The control system  114  may include sensors to monitor, detect, or estimate time periods during which the algae is or may be releasing CO 2 . Control system  114  may implement the second stage of operation during or subsequent to a period when it is determined or estimated that the algae is releasing CO 2 . 
       FIG.  2    presents another example system  200  for growing algae, according to one or more additional embodiments of the present disclosure. System  200  includes the PBR  104  and a plurality of gas concentrators  106  located (i.e., disposed) in close proximity to the PBR  104 . In this example, the PBR  104  and the gas concentrators, shown as gas concentrators  106 A- 106 F. The six gas concentrators  106 A-F are shown with cylindrical bodies having circular foot prints and arranged around PBR  104  and adjacent to it. Other embodiments of the system  200  may include more or fewer gas concentrators located around or adjacent the PBR  104 , based on the shapes and the relative sizes of these different components or based on another design criterion, such as the efficiency of the selected type of gas concentrator(s). The tight arrangement of the system  200 , as shown, may result in reduced piping or pressure drop or improved utilization of available space, or another benefit. 
     The system  200  is an example embodiment of the system  100  of  FIG.  1   . In general, unless specifically described as being different, the configurations and operations, including the potential variations described for the system  100  of  FIG.  1    and its various components, are applicable to the system  200  and its corresponding components, respectively. For example, some or all of the fluidic couplings shown if  FIG.  1    are applicable to one or more portions of the system  200  of  FIG.  2   . The gas concentrators  106 A-F may be selected so that they all use the same process, or one or more may use a different process than one or more of the other gas concentrators. Examples of processes for gas concentrator were described above with reference to  FIG.  1   . 
     In some embodiments, the system  200  may include one or more storage tanks (not shown) coupled to or adjacent to one or more of the gas concentrators  106 A-G or the PBR  104 . The storage tank(s) may be similar to the storage tank  112  of  FIG.  1   , and may be used to store CO2 for recycling back through the system  200  at predetermined intervals or otherwise as needed. In some embodiments, alternating gas concentrators, for example gas concentrators  106 B, D, F, may be replaced by a storage tank to achieve the tight arrangement shown in  FIG.  2   , while having both gas concentrator and storage tank immediately adjacent the PBR  104 . Alternatively, or in addition thereto, the storage tanks and gas concentrators may be stacked. In some embodiments, the system  200  may include multiple systems  200  arranged in series or parallel. Moreover, in some embodiments based on the system  200 , multiple photobioreactors  104  may share one or more gas concentrators, or one or more storage tanks in a tight arrangement. 
       FIG.  3    presents still another example system  300  for growing algae, according to one or more additional embodiments of the present disclosure. System  300  includes the PBR  104  and a plurality of gas concentrators, shown as gas concentrators  106 H- 106 K, arranged in close proximity to the PBR  104 . In this example, the PBR  104  and the gas concentrators are shown with rectangular bodies having rectangular foot prints, and the system  300  is shown with four gas concentrators  106 H-K located around PBR  104  and extending lengthwise away from the PBR  104 . Other orientations of one or more of the concentrators  106 H-K with respect to the PBR  104  are possible, without departing from the scope of the disclosure. Other embodiments of the system  300  may include more or fewer gas concentrators  106 H-K located around or adjacent the PBR  104 , based on the shapes and the relative sizes of these different components or based on another design criterion, such as the efficiency of the selected type of gas concentrator(s). The tight arrangement of the system  300 , as shown, may result in reduced piping or pressure drop or improved utilization of available space, or another benefit. 
     The system  300  is an example embodiment of the system  100  of  FIG.  1   . In general, unless specifically described as being different, the configurations and operations, including the potential variations, described for the system  100  of  FIG.  1    and its various components, are applicable to the system  300  and its corresponding components, respectively. For example, some or all of the fluidic couplings shown if  FIG.  1    are applicable to one or more portions of the system  300  of  FIG.  3   . The gas concentrators  106 H-K may be selected so that they all use the same process, or one or more may use a different process than one or more of the other gas concentrators. Examples of processes for gas concentrators were described above with reference to  FIG.  1   . 
     In some embodiments, the system  300  may include one or more storage tanks (not shown) coupled to or adjacent to one or more of the gas concentrators  106 H-K or the PBR  104 . In some embodiments, alternating gas concentrators, for example the gas concentrators  106 I, K, may be each replaced by a storage tank (e.g., the storage tank  112  of  FIG.  1   ) to achieve the tight arrangement shown in  FIG.  3   , while having both gas concentrator and storage tank immediately adjacent the PBR  104 , or the storage tanks and the gas concentrators  106 H-K may be stacked. In some embodiments, the system  300  may include two or more systems  300  arranged in series or parallel. In some embodiments based on the system  300 , multiple photobioreactors  104  share one or more gas concentrators  106 H-K or one or more storage tanks in a tight arrangement. 
       FIG.  4    illustrates another example system  400  for growing algae in a pond  404 , according to one or more embodiments of the present disclosure. The pond  404  may be an open pond or a closed pond and may include a covering in various embodiments. Although the pond  404  is represented as being rectangular as viewed from above, in other embodiments, the pond  404  may include any suitable shape. As illustrated, the pond  404  may include a plurality of gas concentrators  106  paired with a plurality of storage tanks  112  and spaced apart on one or more support structures or islands  405  extending over a portion of the pond  404  or otherwise located in the pond  404 . This distributed arrangement of the system  400  may result in reduced piping or pressure drop for fluid flows between pond  404 , the gas concentrators  106 , and the adjacent storage tanks  112 , and may also improve utilization of available space. 
     The system  400  is an example embodiment of the system  100  of  FIG.  1   . In general, unless specifically described as being different, the configurations and operations, including the potential variations, described for the system  100  of  FIG.  1    and its various components, are applicable to the system  400  and its corresponding components, respectively. For example, some or all of the fluidic couplings shown in  FIG.  1    are applicable to one or more portions of the system  400  of  FIG.  4   . As another example, in some embodiments of the system  400 , the gas concentrators  106  or storage tanks  112  may collect CO 2  released by algae in pond  404  during a portion of its life cycle and may recycle it back to pond  404  during another time period. In some embodiments, for example, this can be done with a collection system configured to outgas the CO 2  (e.g., reduce its solubility) by mild changes in temperature of the fluid (water). This can be performed, for instance, by passing the water thru a collection pipe that is suitably heated and has provisions to allow the gas collected to be conveyed outside the pond  404 . The water can be moved using an impeller or similar device. 
     The gas concentrators  106  of  FIG.  4    may be selected so that they all use the same process, or one or more may use a different process than one or more of the other gas concentrators. Examples of processes for gas concentrators were described above with reference to  FIG.  1   . Some pairs that include a gas concentrator  106  fluidically coupled to an adjacent storage tank  112  may be fluidically coupled other pairs to share supply lines or transfer lines. 
       FIG.  5    illustrates an example gas concentrator  500 , according to one or more embodiments of the present disclosure. The gas concentrator  500  may be the same as or similar to any of the gas concentrators  106  used in the systems  100 ,  200 ,  300 ,  400  described herein. As illustrated, the gas concentrator  500  includes a body or shell  502  that contains one or more periodic structures  505 , which includes a first periodic surface  506  and a second periodic surface  508  generally facing opposite the first periodic surface  506 . An adsorbent material  510  may be disposed adjacent or on the periodic surfaces  506 , and one or more mechanisms  511  may be included on the periodic structure  505  to cause movement of the periodic structure  505 . 
     In this example, the first periodic surface  506  is an outer surface for the periodic structure  505 , and the second periodic surface  508  is an inner surface for the periodic structure  505  and is also periodic. The outer, periodic surface  506  and the inner, periodic, second surface  508  define the thin-wall shell  502  of the periodic structure  505 . In various embodiments, the adsorbent material is attached to the periodic surface  506 , coats the periodic surface  506 , or is incorporated into pellets or monoliths, equivalently, granules located in an inner volume  512  of the shell  502 , potentially contacting the periodic surface  506 . The adsorbent material  510  is capable of preferentially absorbing CO 2  from a mixture of gases. The adsorbent material  510  may include a metal organic framework (MOF), amine-appended MOF with a Type V isotherm for CO 2 , an amine appended MOF with a Type 1 isotherm for CO 2 , a metal impregnated microporous silicate, metal impregnated alkalized alumina, mixed-metal oxides, hydrotalcites, treated activated carbons including metal doped carbons, and any combination thereof, as examples. The gas concentrator  500  may operate using a process selected from a group that includes pressure swing adsorption, vacuum swing adsorption, voltage swing adsorption, temperature swing adsorption, displacement desorption, and any combination thereof, as examples. 
     In  FIG.  5   , the shell  502  is depicted with a bottom wall  503  and side walls  504 . An upper wall or surface is removed to expose the inner volume  512  of the shell  502 . A first flow path  514  through gas concentrator  500  includes an inlet  516 , the inner volume  512  of shell  502 , an outlet  518  to discharge unwanted a gas, and an outlet  520  to release a product gas that may contain CO 2  at an increased concentration as compared to a gas that entered at inlet  516 . The inner volume  512  of the shell  502  is defined in part by the periodic surface  506  and the adsorbent material  510 . Some embodiments may include multiple inlets  516  or multiple outlets  520 . 
     A second flow path  530  through the gas concentrator  500  includes the second surface  508  of periodic structure  505 , one or more inlets  532 , and one or more outlets  534  fluidically coupled to second surface  508 . In various embodiments, multiple inlets  532  may be merged or routed to fewer inlets, perhaps a single inlet, by a manifold located within or outside shell  520 , and the multiple outlets  534  may be similarly merged or routed. Other quantities, relative quantities, or arrangements of the inlets  532  and outlets  534  are possible. Due to the multiple inlets  532  and outlets  534  and due to the multiple, intersecting passageways defined by the second surface  508 , the second flow path  530  includes multiple intersecting routes for a fluid to travel inside periodic structure  505 . The second flow path  530  may be fluidically separated from the first flow path  514 . The thin-wall, shell-like configuration of the periodic structure  505  may augment efficient heat transfer between a fluid in the first flow path  514  and another fluid in the second flow path  530 . 
     The periodic structure  505  includes multiple, repeating patterns or smaller periodic structures  542 , which are incremental portions, possibly “building blocks,” of the larger periodic structure  505 . Each periodic structure  542  defines a portion of periodic surface  506  and a portion of a second surface  508 .  FIG.  5    shows four of the periodic structures  542  forming a single layer that extends generally parallel to the bottom  503  of the shell  502 . Various embodiments may include more or fewer of the periodic structures  542  in a layer. The periodic structure  505  is depicted with the apertures  540  that are open in directions generally perpendicular to bottom  503 . Although  FIG.  5    shows a single layer of the periodic structure  505 , apertures  540  accommodate additional layers of periodic structure  505  that may be placed generally parallel to the depicted layer and may be fluidically coupled through apertures  540 . Alternatively, some embodiments may include only one layer of the periodic structure  505 , and the apertures  540  are either closed or non-existent. Thus, the gas concentrator  500  includes a plurality of periodic structures (e.g., the structures  542  or the layers of adjoined structures  542 ), and the first flow path  514  includes the periodic surfaces of the plurality of periodic structures, and the second flow path  530  includes the second surfaces of the plurality of periodic structures. 
     In the example of  FIG.  5   , the plurality of the mechanisms  511  are selected and positioned to cause movement of periodic structure  505 . The mechanisms  511  may be coupled to or integrated into the outer, periodic surface  506 , the inner, second surface  508  or may be embedded in the structure of periodic structure  505  in any combination. In  FIG.  5   , the mechanisms  511  are located at regions of minimal diameter on periodic structure  505  and extend circumferentially around, but other positions and other arrangements may be utilized in some embodiments. The movement of periodic structure  505  caused by mechanism  511  may be vibration, expansion, contraction, or a combination of these modes of movement, as examples. The contractions and expansions may be radially-directed, axially-directed, or a combination of these movements in some embodiments. The mechanisms  511  may induce peristaltic motion in the periodic structure  505  and its periodic surface  506 ,  508 . The movement of periodic structure  505  may promote the movement of the heat transfer fluid through flow path  530  of the gas concentrator. The operation of mechanisms  511  may be governed by a controller, such as the control system  114  of  FIG.  1   . 
     In some embodiments, a first, second, and third mechanism  511  are spaced apart from each other and are configured to produce a first, second, and third periodic cycles of contractions and expansions, respectively. In some examples, the second periodic cycle of the contractions and expansions is out-of-phase with the first periodic cycle of the contractions and expansions. Also, the third periodic cycle of the contractions and expansions is out-of-phase with the second periodic cycle of the contractions and expansions. In some examples, the out-of-phase cycles of the contractions and expansions (e.g., any two of the mentioned periodic cycles or the first, second, and third periodic cycles working together) cause the peristaltic motion in the periodic structure  505  and its periodic surface  506 ,  508 . 
     Example operation of gas concentrator  500  may include receiving a first gas into the first flow path  514 , obtaining a second gas from the first flow path  514  via the outlet  520 , and passing a heat transfer fluid through the second flow path  530  to provide cooling to the periodic structure  505  and the adsorbent material  510 . The heat transfer fluid may be a liquid or a gas. The first gas may come from any suitable source, including atmospheric air, flue gas/exhaust streams from a combustion process, or a storage location including tanks or geological formations, as examples. The second gas contains CO 2  at a higher concentration than was present in the first gas. Obtaining the second gas from the first flow path  514  may include one or more of the following steps: absorbing CO 2  into the adsorbent  510 , opening the outlet  518  to release non-absorbed portions of the first gas, closing the outlet  518 , and opening outlet  520  to release the second gas to a downstream storage location or process, a process such as a PBR  104  of  FIG.  1   . When activated, the mechanisms  511  may cause beneficial agitation in the fluid in the first flow path  514 , the fluid in the second flow path  530 , or in both fluids. The motions of the mechanisms  511  may be synchronized to produce the first, second, and third, periodic cycles of the contractions and expansions in the periodic structure  505  to induce movement in one or more of those fluids. In some embodiments, the motions of the mechanisms  511  may be synchronized to induce a peristaltic movement in the periodic structure  505  to induce movement in the fluid in the first flow path  514 , the fluid in the second flow path  530 , or in both fluids. Other operations of the apparatus  500  may pass the heat transfer fluid through the second flow path  530  to provide heating to the periodic structure  505  and to the fluid in first flow path  514 . 
       FIGS.  6 A- 6 C  depict examples of singly periodic structures of which the gas concentrator  500  of  FIG.  5    may be formed or may include. As illustrated, the singly periodic structures can periodically transition between a sphere or bulbous section and a cylinder. Typically, a singly periodic structure exhibits a periodicity along a single axis. This periodicity in the surface can be, for example, a regular undulation or curvature that repeats exactly. For the purposes of gas concentrators, the singly periodic surface is a surface that includes curvature in addition to the curvature of a cylindrical surface.  
       FIGS.  7 A- 7 E  depict examples of doubly periodic structures of which the gas concentrator  500  of  FIG.  5    may be formed or may include, and  FIGS.  8 A- 8 E  depict examples of triply periodic structures of which the gas concentrator  500  of  FIG.  5    may be formed or may include. Doubly periodic structures approach two families of orthogonal planes, and triply periodic structures are minimal structures in three dimensions in R 3  that is invariant under a rank-3 lattice of translations. Triply periodic structures have the symmetries of a crystallographic group, such as cubic, tetragonal, rhombohedral, and orthorhombic symmetries. Doubly and triply periodic surfaces possess additional axes of periodicity (i.e., in the Y and Z directions), which are therefore capable of introducing additional surface features. In addition, all such periodic surfaces can be mass-produced efficiently with modern 3D printing techniques. One advantage of triply periodic surfaces is their ability to provide minimal surfaces, which minimize the volume of material for the surface provided. This occurs in a variety of examples in nature, including butterfly wings, which have remarkable resilience yet are extremely lightweight. This feature is advantageous for increasing photobioreactor wall strength while using only minimal amount of material, which latter also maintains light absorption and control.  
       FIG.  9    illustrates another example gas concentrator  900 , according to one or more additional embodiments of the present disclosure. The gas concentrator  900  may be the same as or similar to any of the gas concentrators  106  used in the systems  100 ,  200 ,  300 ,  400  described herein. As illustrated, the gas concentrator  900  includes a body or shell  902  that contains one or more periodic structures  905 , an adsorbent material  910  disposed adjacent or on the periodic structures  905  within an inner volume  912  of the shell  902 , and one or more mechanisms  911  (shown as dashed boxes) to cause movement of the periodic structures  905 . In some illustrative examples, actuation of the mechanisms  911  can consist of mechanical perturbations delivered from the boundaries of the periodic structures  905 . In one such case, the outer edges of the surfaces of the periodic structures  905  can be wrapped around a mandrel, which can be wound or unwound to generate motion throughout the corresponding surface. Similar mandrels can be used at the other boundaries. In other embodiments, however, perturbations can alternatively be possible and generated using ultrasonic means. 
     The present embodiment includes a plurality of periodic structures  905 , each formed as a smoothly curved sheet that includes a first, periodic surface  906  and a second, periodic surface  908  generally facing opposite the first surface  906 . The adsorbent material  910  may be configured as pellets or, equivalently, granules distributed among the periodic structures  905  and associated surfaces  906 ,  908 . Considering any of the various periodic structures  905 , a portion of the granules is located adjacent the first periodic surface  906  and another portion of the granules located adjacent the second periodic surface  908 . In various embodiments, the adsorbent material is attached to or coats the periodic surface  906  or the second surface  908  in place of or in addition to the granules. The adsorbent material  910  is capable of preferentially absorbing CO 2  from a mixture of gases. The adsorbent material  910  may include a metal organic framework (MOF), amine-appended MOF with a Type V isotherm for CO 2 , an amine appended MOF with a Type 1 isotherm for CO 2 , a metal impregnated microporous silicate, metal impregnated alkalized alumina, mixed-metal oxides, hydrotalcites, treated activated carbons including metal doped carbons, and any combination thereof, as examples. The gas concentrator  900  may operate using a process selected from a group that includes pressure swing adsorption, vacuum swing adsorption, voltage swing adsorption, temperature swing adsorption, displacement desorption, and any combination thereof, as examples. 
     The shell  902  is depicted with an inlet  916 , a first outlet  918 , and a second outlet  920 . A flow path  914  through the gas concentrator  900  is defined by the inlet  916 , the inner volume  912 , the periodic surfaces  906 , the second surfaces  908 , the outlet  918 , and the second outlet  920 . The granular adsorbent material  910  is contained in flow path  914 . Shell  902  and the configuration of periodic structures  905  perform as a manifold to allow a fluid entering inlet  916  to be distributed among the various passageways between the several periodic structures  905  and surfaces  906 ,  908 . The arrangements or orientations of the inlet  916  and the outlets  918 ,  920  may be different than are shown, and some embodiments, may include additional inlets or outlets. Some other embodiments based on gas concentrator  900  include multiple, fluidically separated flow paths in place of the combined flow path  914  and a separate inlet and outlet are provided for each flow path, similar to the configuration of  FIG.  5   , to keep a first or supply gas and a concentrated second gas separate from a heat transfer fluid. 
     The example of  FIG.  9    includes a plurality of the mechanisms  911  that are selected and positioned to cause movement of periodic structure  905 . The mechanisms  911  may be coupled or integrated into one or more of the periodic surfaces  906 , one or more of the second surfaces  908 , may be imbedded in the structure of the periodic structure  905 , or may be attached to or integrated with shell  902 , alone or in any feasible combination. In  FIG.  9   , the mechanisms  911  are located at various boundaries of the surfaces  906 ,  908  and, as briefly mentioned above, can consist of mechanically operated or motorized mandrels on which edges of the periodic surfaces  906 ,  908  are wrapped. The mandrels at one boundary can then be mechanically wound or unwound to generate the motion, operating desirably in unison with corresponding mandrels on the adjacent boundary  906 ,  908 . In some cases, the mandrels can also be embedded at regular intervals inside the reactor  900  but accessible from the boundaries for the purposes of motorized winding or unwinding. As will be appreciated, however, other positions and other arrangements may be utilized for the mechanisms  911 , without departing from the scope of the disclosure. 
     The movement of the periodic structure  905  caused by one or more of the mechanisms  911  may be vibration, expansion, contraction, or a combination of these modes of movement, as examples. The contractions and expansions may be radially-directed, axially-directed, or a combination of these movements in some embodiments. The operation of the mechanisms  911  may be governed by a controller, such as the control system  114  of  FIG.  1   . 
     In some embodiments, a first, second, and third mechanism  911  are spaced apart from each other and are configured to produce a first, second, and third periodic cycles of contractions and expansions, respectively. In some examples, the second periodic cycle of the contractions and expansions is out-of-phase with the first periodic cycle of the contractions and expansions. Also, the third periodic cycle of the contractions and expansions is out-of-phase with the second periodic cycle of the contractions and expansions. In some examples, the out-of-phase cycles of the contractions and expansions (e.g., any two of the mentioned periodic cycles or the first, second, and third periodic cycles working together) cause the peristaltic motion in the periodic structure  905  and its periodic surfaces  906 ,  908 . 
     Example operation of the gas concentrator  900  may include receiving the first gas into the flow path  914 , obtaining the second gas from the flow path  914  via the second outlet  920 , and may also include passing a heat transfer fluid through the same flow path  914  to provide cooling to the periodic structure  905  and the adsorbent material  910 . Both fluids would contact the absorbent material  910 . The heat transfer fluid may be a liquid or a gas and the operation of the concentrator  900  may involve two-phase flow. Thus, as configured, the gas concentrator  900  provides direct contact heat transfer between a cooling fluid and the absorbent material  910  and may provide direct contact heat transfer between the cooling fluid and the first and second gases. The flow of the first gas and the flow of heat transfer fluid may be alternated or pulsed, and the outlet  918  may be closed when heat transfer fluid passes through the gas concentrator  900 . The first gas may come from any suitable source, including atmospheric air, flue gas/exhaust streams from a combustion process, or a storage location including tanks or geological formations, as examples. 
     The second gas includes CO 2  at a higher concentration than was present in the first gas. Obtaining the second gas from the flow path  914  may include one or more of the following steps: absorbing CO 2  into the adsorbent  910 , opening the outlet  918  to release non-absorbed portions of the first gas, closing the outlet  918 , and opening second outlet  920  to release the second gas to a downstream storage location or a process, such as the PBR  104  of  FIG.  1   . 
     When activated, the mechanisms  911  may cause beneficial agitation or movement in one or both of the fluids in the flow path  914 . For example, the motions of the mechanisms  911  may be synchronized to produce the first, second, and third, periodic cycles of the contractions and expansions in the periodic structure  905  to induce movement in one or more of those fluids. The motions of the mechanisms  911  may be synchronized to induce a peristaltic movement in the periodic structure  905  to induce movement in one or both of the fluids in the flow path  914 . Other operations of the apparatus  900  may pass a heat transfer fluid through the flow path  914  to provide heating to the periodic structure  905  and the gas. The gas concentrator  900  may be configured as a trickle-bed reactor designed for co-current or counter current flow of the first gas and the heat transfer fluid simultaneously. Although depicted as being horizontal, the flow path  914  may be vertical. Some embodiments may include separate inlets or separate outlets for the gas and the heat transfer fluid. 
       FIG.  10    illustrates an example system  1000  for growing algae, according to one or more to additional embodiments of the present disclosure. The system  1000  may be characterized as a photobioreactor system operable for the cultivation and growth of algae. In at least one embodiment, the system  1000  may be used as the PBR  104  in the system  100  of  FIG.  1   . 
     The system  1000  includes one or more photobioreactors (PBR)  1004 . Each PBR  1004  includes a tubular structure  1006  extending along a longitudinal axis  1008  and having an inner sleeve  1010  defining an inner surface  1012  and an outer sleeve  1014  defining an outer surface  1016 . Each PBR  1004  further includes an annular space  1018  defined between the inner and outer surfaces  1012 ,  1016 , and an inlet  1020  to allow an algae slurry to enter the annular space  1018  and an exit  1022  to allow the algae slurry to be removed. The outer surface  1016  is transparent to at least some wavelengths of light useful for growing algae within the algae slurry, which may include water, algae, nutrients, and dissolved gases. The PBR  1004  further includes one or more mechanisms  1026  to produce movement of the outer surface  1016  and the outer sleeve  1014 . In some embodiments, operation of the mechanisms  1026  may produce peristaltic motion in the tubular structures  1006  to promote the axial movement of the algae slurry through annular space  1018 . 
     The system  1000  is shown with three PBRs  1004  positioned adjacent and aligned generally parallel to each other. Other embodiments may include more or fewer PBRs  1004 . As illustrated, the PBRs  1004  may be supported by and may hang vertically from a support structure  1030  that may define or otherwise operate as an inlet manifold fluidically coupled to each inlet  1020  for the annular spaces  1018 . The PBRs  1004  are arranged to allow ambient light to penetrate portions of the outer surface  1016  of each PBR  1004  to provide energy for the algae to grow. Other arrangements and various light sources are possible, without departing from the scope of the disclosure. 
     The outer surface  1016  and the inner surface  1012  may be periodic, as is depicted in  FIG.  10   . Alternatively, the outer sleeve  1014  and its outer surface  1016  or the inner sleeve  1010  and its inner surface  1012  may be cylindrical in shape and exhibit a constant diameter between the inlet  1020  and the outlet  1022 . In such embodiments, the mechanisms  1026  may induce a temporary periodic shape to the outer sleeve  1014  and its outer surface  1016 . 
     The inner sleeve  1010  defines an inner passageway  1040  and one or more apertures  1042  are provided in the inner sleeve to facilitate fluid communication between the inner passageway  1040  and the annular space  1018 . The inner passageway  1040  includes an inlet  1044  to receive the gas, which, preferably includes CO 2 . The gas provided to the inner passageway  1040  may come from any suitable source, including atmospheric air, flue gas/exhaust streams from a combustion process, or a storage location including tanks or geological formations, as examples. The system  1000  includes a gas manifold  1046  fluidically coupled to each of the inner passageways  1040 . In some embodiments, the gas manifold  1046  may be integrated with the support structure  1030 . In some embodiments, a gas concentrator (not shown) may be fluidly coupled to the gas manifold  1046  to provide the gas to the inner passageway  1040  and ultimately to the annular space  1018 . The gas concentrator may be of a conventional design or may be any of the gas concentrators disclosed herein. 
       FIG.  10    shows a plurality of mechanisms  1026 , axially spaced apart along the outer surface  1016  of each PBR  1004 . In some embodiments, the mechanisms  1026  may extend circumferentially around the outer sleeve  1014  or its outer surface  1016  and constrict radially or circumferentially. In some embodiments, one or more of the mechanisms  1026  may include opposing plates that move linearly to compress or to relax a tubular structure  1006 . 
     The individual mechanisms  1026  of the far-left PBR  1004  are distinguished by a letter designator, e.g., A, B, C, etc. In this example, a first mechanism  1026 A is positioned at a first axial location along the tubular structure  1006  and configured to produce a first periodic cycle of contractions and expansions. A second mechanism  1026 B is positioned at a second axial location along the tubular structure  1006  and configured to produce a second periodic cycle of contractions and expansions. A third mechanism  1026 C is positioned at a third axial location along the tubular structure  1006  and configured to produce a third periodic cycle of contractions and expansions. Fourth and fifth mechanisms  1026 D,E are similarly positioned and configured for operation. Some embodiments may have more or fewer than five mechanisms to induce motion in the tubular structure  1006 . In some examples, the second periodic cycle of the contractions and expansions is out-of-phase with the first periodic cycle of the contractions and expansions. Also, the third periodic cycle of the contractions and expansions is out-of-phase with the second periodic cycle of the contractions and expansions. In some examples, the out-of-phase cycles of the contractions and expansions (e.g., any two of the mentioned periodic cycles or the first, second, and third periodic cycles working together) cause peristaltic motion in the outer sleeve  1014  of the tubular structure  1006 . 
     Applicable to any of the PBRs  1004 , algae may grow in the slurry within the annular space  1018 , on the inner surface  1012 , on the outer sleeve  1014 , or in a combination of these locations. The motion of the outer sleeve  1014  induced by the mechanisms  1026 , e.g., peristaltic motion, may cause or aid axial movement of the algae slurry through the annular space  1018  from the inlet  1020  to the exit  1022  or may act to loosen or remove algae that may be growing on the inner surface  1012  or on the outer sleeve  1014  to allow algae to be harvested.  FIG.  10    includes arrows indicating radially-directed contractions and expansions of the mechanisms  1026  and the outer sleeve  1014  during a moment in time. In some embodiments, the mechanisms  1026  are configured to produce axially-directed movements in addition to or in placed of the radially-directed contractions and expansions. The operation of any PBR  1004  or the system  1000 , including the movements of mechanisms  1026 , may be governed by a controller, such as the control system  114  of  FIG.  1   . 
     Embodiments Listing: 
     The present disclosure provides, among others, the following embodiments, each of which may be considered as alternatively including any alternate embodiments. 
     Clause 1. A system for growing algae includes a photobioreactor comprising a tubular structure having inner and outer surfaces, an annular space defined between the inner and outer surfaces, an inlet to allow an algae slurry to enter the annular space, and a mechanism configured to produce radially-directed contractions and expansions in the tubular structure, wherein at least one of the inner and outer surfaces is transparent to at least some wavelengths of light useful for growing algae within the algae slurry. 
     Clause 2. The system of Clause 1, wherein the mechanism comprises a plurality of mechanisms configured to produce radially-directed contractions and expansions and thereby cause peristaltic motion in the tubular structure. 
     Clause 3. The system of Clause 1 or Clause 2, wherein the mechanism is a first mechanism disposed at a first axial location along the tubular structure and configured to produce a first periodic cycle of contractions and expansions, the system further comprising a second mechanism disposed at a second axial location along the tubular structure and configured to produce a second periodic cycle of contractions and expansions that is out-of-phase with the first periodic cycle of the contractions and expansions. 
     Clause 4. The system of any of Clauses 1 to 3, wherein the inner surface comprises a periodic structure. 
     Clause 5. The system of any of Clauses 1 to 5, wherein the outer surface comprises a periodic structure. 
     Clause 6. The system of any of Clauses 1 to 6, wherein the photobioreactor further comprises an inner passageway defined by the inner surface, and one or more apertures defined in the inner surface to allow a gas to flow into the annular space from the inner passageway. 
     Clause 7. The system of Clause 6, further comprising a gas concentrator coupled to the photobioreactor to provide the gas to the inner passageway. 
     Clause 8. The system of any of Clauses 1 to 7, wherein the photobioreactor is a first photobioreactor, the system further comprising a plurality of photobioreactors, including the first photobioreactor, positioned adjacent each other and arranged to allow light to penetrate portions of the outer surface of each photobioreactor. 
     Clause 9. The system of Clause 8, further comprising an inlet manifold fluidically coupled to the inlet of each photobioreactor, wherein the plurality of photobioreactors extend downward from the inlet manifold. 
     Clause 10. A method for growing algae includes providing an algae slurry to an annular space located between an inner surface and an outer surface of a tubular structure, and inducing contractions and expansions in the tubular structure. 
     Clause 11. The method of Clause 10, wherein inducing contractions and expansions includes inducing a first periodic cycle of contractions and expansions in a first portion of the tubular structure, and inducing a second periodic cycle of contractions and expansions in a second portion of the tubular structure, wherein the second portion is axially displaced from the first portion, and the second periodic cycle is out-of-phase with the first periodic cycle. 
     Clause 12. The method of Clause 11, wherein inducing the first periodic cycle and inducing the second periodic cycle participate in causing algae to flow axially through the annular space. 
     Clause 13. The method of Clause 11, wherein the first and second periodic cycles participate in causing peristaltic motion in the tubular structure. 
     Clause 14. The method of any of Clauses 10 to 13, wherein the outer surface comprises a periodic structure. 
     Clause 15. The method of any of Clauses 10 to 14, further comprising introducing a gas containing CO2 into a passageway defined by the inner surface of the tubular structure, and flowing the gas into the annular space from the passageway via one or more apertures defined in the inner surface of the tubular structure. 
     Clause 16. A photobioreactor includes a tubular structure having inner and outer surfaces and an annular space defined between the inner and outer surfaces, an inlet to allow an algae slurry to enter the annular space, an inner passageway defined by the inner surface, and one or more apertures defined in the inner surface to allow a gas to flow from the inner passageway into the annular space. 
     Clause 17. The system of Clause 16, wherein the outer surface is transparent to at least some wavelengths of light useful for growing algae within the algae slurry. 
     Clause 18. The system of Clause 16 or Clause 17, further comprising a mechanism configured to produce radially-directed contractions and expansions in the tubular structure. 
     Clause 19. The system of any of Clauses 16 to 18, wherein the inner surface comprises a periodic structure. 
     Clause 20. The system of any of Clauses 16 to 19, wherein the outer surface comprises a periodic structure. 
     Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms used herein, including the claims, have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used herein, including the claims, are defined herein to mean one or more than one of the element that it introduces. 
     The term “or” as used in a phrase such as “A or B” herein is intended to include alternatively of any of the following: “A” alone, “B” alone, and, where feasible, “A and B.” Ordinal numbers such as first, second, third, etc. do not indicate a quantity but are used for naming and reference purposes. In addition, ordinal numbers used in the claims in reference to a component or feature may differ from the ordinal numbers used in the written description for the corresponding component or feature. For example, a “second object” in a claim might be described as a “third object” or may be described without an ordinal number in the written description. 
     As used herein, including the claims, the term “line” for fluid communication may include any of the following pipe, piping, tubing, hose, fittings, valves, gauges, check valves, flow meters, filters, and the like. 
     Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as length, volume, mass, molecular weight, operating conditions, and so forth used in the present specification and associated claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the embodiments of the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claim, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. 
     For the sake of clarity, not all features of a physical embodiment are described or shown in this application. It is understood that in the development of a physical embodiment incorporating the embodiments of the present disclosure, numerous implementation-specific decisions must be made to achieve the developer&#39;s goals, such as compliance with system-related, business-related, government-related, and other constraints, which vary by implementation and from time to time. While a developer&#39;s efforts might be time-consuming, such efforts would be, nevertheless, a routine undertaking for those of ordinary skill in the art and having benefit of this disclosure. 
     Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined, or modified and all such variations are considered within the scope and spirit of the present invention. The illustrative embodiments disclosed herein suitably may be implemented in the absence of any element that is not specifically disclosed herein and/or any alternative element disclosed herein. While components, compositions, and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the components, compositions, and methods can also “consist essentially of” or “consist of” the various components and steps. For the methods herein, the order of various process steps may be rearranged in some embodiments and yet remain within the scope of the disclosure, including the claims.