Patent Publication Number: US-2021179986-A1

Title: System and method of growing algae using geothermal gas

Description:
TECHNICAL FIELD OF THE INVENTION 
     The invention generally relates to the field of algae cultivation in artificial conditions and more precisely using geothermal gas a source for CO 2  in algae cultivation. 
     BACKGROUND OF THE INVENTION 
     Bio-reactors for algae cultivation in artificial conditions has become increasingly common for producing biomass. Algae (or microalgae)-water culture is introduced into a container comprising water and supplied (e.g., fed) with small bubbles of gas that includes CO 2  and air. The algae in the container is further exposed to illumination (either artificial illumination, or from sunlight). For the algae biomass to perform photosynthesize and grow, the CO 2  needs to be dissolved into the water surrounding the algae culture. In phototropic algae cultivation systems the major inputs (or macro-nutrients) for growth are light, CO 2 , nutrients (such as Nitrogen, Phosphorus, etc.), and water with turbulent mixing in order to distribute those resources to individual algae cultivation cells. 
     Microalgae can be grown in many types of systems, such as flat panel photo-bio-reactors having efficient light capture and utilization, and high surface area-to-volume ratio. Light sources for algae growth can be any type of visible light in the range of about 400-700 nm wavelengths. Light emitting diodes (LEDs) have the capability of providing light of specific wavelengths, for example in the visible light (e.g., blue and/or red) wavelength range. 
     The CO 2 /air mixture is form by mixing CO 2  reach gas (e.g., above 50 weight percent (wt. %) CO 2 ) and air. The mixture usually includes 10-30 wt. % CO 2 . The gas mixture is introduced as small bubbles into the algae-water culture in the reactor. The portion of the gas not dissolved or consumed by the algae is released into the outside atmosphere. Only a very small portion of the CO 2  is consumed by the algae, therefore the majority of CO 2  is being released and wasted. 
     There are several resources for CO 2 . CO 2  reach gas can be obtained by distillation from air or combustion of carbon based fuels such as methane. CO 2  reach gas may include gas that have more than 50 wt. % CO 2 , for example, more than 80 wt. %, more than 85 wt. % and above. Another source for CO 2  may be partially purified geothermal gas. Geothermal gas contains, for example, about 74 wt. % CO 2  but is also highly contaminated with toxic gasses such as 23.32 wt. % H 2 S and explosive gasses such as 0.81 wt. % hydrogen, and 0.34 wt. % methane. Therefore, geothermal gas cannot be mixed with air to avoid explosion. Furthermore, due to the toxicity of some of the gasses in the geothermal gas, introducing such toxic gasses into an algae culture may have undesired effect on the growth of algae. Even relatively purified geothermal gas still contains 0.79 wt. % H 2 S and 2.16 wt. % hydrogen, which makes it problematic to be used as a provider of CO 2  for algae cultivation. 
     Accordingly, in order to use geothermal gas in algae cultivation a special system and method is required. 
     SUMMARY OF THE INVENTION 
     Some aspects of the invention may be related to a method of growing algae in a cultivation container. In some embodiments, the method may include: circulating, via the cultivation container, in a closed loop, a first predetermined amount of gas mixture comprising a first type of gas and at least one second type of gas, the gas mixture enters the container via one or more entrance spargers and exit via at least one exit pipe, wherein the first type of gas contains CO 2  at a known first amount; receiving signal indicative of the amount of CO 2 , in the gas mixture; when the signal indicates that the amount of CO 2  drops below a first predetermined level, extracting a second predetermined amount of the gas mixture from the cultivation container: and adding an amount of the first type of gas to the gas mixture, equal to the second predetermined amount. 
     In some embodiments, the first type of gas may further include a toxic gas at a known second amount. In some embodiments, the first type of gas may be a geothermal gas. In some embodiments, the first known amount may be at least 9 weight % CO 2 . In some embodiments, the second type of gas may include N 2 . In some embodiments, the method may further include receiving signal indicative of the amount of O 2  in the circulating gas mixture; and replacing the circulating gas mixture with a new first predetermined amount of the gas mixture when the amount of O 2  raised above a second predetermined level. 
     Some aspects of the invention may be related to an algae cultivation system, the system may include: a cultivation container having one or more entrance spargers for introducing a gas mixture into the cultivation container and an exit pipe for releasing the gas mixture from cultivation container; a circulating system for circulating the gas mixture in closed loop form the exit pipe back to the one or more entrance spargers; at least one sensor for detecting changes in an amount of CO 2  in the gas mixture and a first gas supply system for supplying a first type of gas. In some embodiments, the first type of gas may include CO 2  at a known first amount. In some embodiments, the system may further include: a second gas supply system for supplying a second type of gas; and a controller configured to: control the first gas supply system and the second gas supply system to supply to the circulating system a first predetermined amount of gas mixture comprising the first type of gas and second type of gas; receive from the sensor a signal indicative of the amount of CO 2  in the gas mixture; and when the signal indicates that the amount of CO 2  drops below a first predetermined level, open a valve to extract a second predetermined amount of the gas mixture from the cultivation container; and control the first gas supply system to supply to the circulating system the first type of gas in an amount equal to the second predetermined amount. 
     In some embodiments, each of the first and the second gas supply systems may include a valve controlled by the controller. In some embodiments, the system may further include a third gas supply system for providing substantially pure CO 2 . In some embodiments, the at least one sensor is one of: pH sensor located at the cultivation container and CO 2  sensor located in a circulation pipe included in the circulation system. 
     In some embodiments, the algae cultivation system may further include an O 2  sensor for detecting changes in an amount of O 2  in the circulating gas mixture. In some embodiments, the controller may further be configured to: receive a signal indicative of the amount of O 2  in the circulating gas mixture; when the amount of O 2  raised above a second predetermined level, control a relive valve included in the circulation system to release the circulating gas mixture; and control the first gas supply system and the second gas supply system to supply to the circulating system the first predetermined amount of gas mixture comprising the first type of gas and second type of gas. 
     In some embodiments, the first type of gas further may include a toxic gas at a known second amount. In some embodiments, the first type of gas may be a geothermal gas. In some embodiments, the first known amount may be at least 9 weight % of CO 2 . In some embodiments, the second type of gas contains N 2 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which: 
         FIG. 1  is an illustration of an algae cultivation system according to some embodiments of the invention; and 
         FIG. 2  is a flowchart of a method of growing algae in a cultivation container according to some embodiments of the invention. 
     
    
    
     It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. 
     DETAILED DESCRIPTION OF THE PRESENT INVENTION 
     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention. 
     Reference is now made to  FIG. 1 , which schematically illustrates an algae cultivation system  100 , according to some embodiments of the invention. System  100  may include a cultivation container  110  having one or more entrance spargers  112  for introducing gas into an algae culture and water located inside cultivation container  110  and an exit pipe  114  for releasing gas from cultivation container  110 . System  100  may further include a circulating system  120  that includes a pipe  122  and a pump  125  for circulating gas in closed loop form the exit pipe  114  back to the one or more entrance spargers  112 . System  100  may further include, at least one sensor  130  or  135  for detecting signals indicative of the amount of a first type of gas (e.g., CO 2 ), and two or more gas supply systems  141 ,  143  and  145  for providing a first type of gas, a second type of gas and/or a third type of gas to circulation system  120 . In some embodiments, the system may include a relief valve  148  for relieving gas from circulation system  120 . In some embodiments, system  100  may further include one or more O 2  sensors  136  and  138  for detecting changes in an amount of O 2  in the circulating gas mixture. 
     In some embodiments, system  100  may further include a controller  150  configured to receive signals from sensor  130  and/or sensor  135  and control valves  142 - 146  to open and allow gas supply systems  141 ,  143  and  145  to supply one or more of the first, second and third types of gasses to circulation system  120 . 
     In some embodiments, container  110  may be any algae cultivation container known in the art. For example, container  10  may include at least two panels (not illustrated) within a water filled cultivation container  110 , the panels positioned along a first plane the first plane is perpendicular to the gravitational force. In some embodiments, a cultivation volume may be created between each pair of panels, whereby the cultivation volumes may be fluidly coupled to allow horizontal flow therebetween along the first plane. 
     In some embodiments, one or more entrance spargers  112  may each include a plurality of nozzles, to distribute gas (e.g., CO 2 , geothermal gas and/or air mixture) into cultivation container  110 . In some embodiments, the gas bubbles may have a diameter of no more than 5 mm, for example, 2 mm or 1 mm. One or more entrance spargers  112  may supply the gas mixture to the container at 0.5-3 litter/minute for every liter of algae culture. In some embodiments, the bubbles may be introduced at a flow capacity sufficient for cleaning the walls of container  110  from biofilm covering the walls. In some embodiments, exit pipe  114  may include any device for collecting or extracting gasses from containers. Circulating system  120  may include one or more pipes  122  and any number of required connectors, valves, faucets and the like that may be required to allow forming a closed structure (a loop) for circulating gas form exit pipe  114  back to one or more entrance spargers  112 . Circulating system  120  may include a pump  125  or a compressor or blower for evacuating the gas from the upper portion of container  110 . 
     CO 2  sensor  130  may be any sensor configured to detect CO 2 . For example, sensor  130  may be an infrared gas sensor (NDIR), a chemical gas sensor and the like. Sensor  135  may be any sensor that may provide indication to the amount of CO 2  in the algae culture, for example, sensor  135  may include a pH sensor. As the amount of CO 2  dissolve in the algae culture decrease below a required level the pH level may raise above a harmful level, which depends from the type of algae grow in cultivation container  110  (e.g., pH 7.5). Therefore, the pH may serve as an indicator to the amount of CO 2  in the gas mixture. 
     O 2  sensors  136  and  138  may be any sensors that may provide indication to the amount of O 2  in the gas mixture. Sensor  136  may be located at circulating container  110  configured to measure the amount of O 2  dissolved in the algae culture. Sensor  138  may be any chemical sensor configured to measure the amount of O 2  in the circulating gas mixture and may be located in pipe  122 . 
     First gas supply system  141  may be configured to supply a first type of gas, containing CO 2  at a known first amount, for example, a geothermal gas or a partially purified geothermal gas. First gas supply system  141  may be in fluid communication with a reservoir (e.g., a tank, a pipe, etc.) that includes the first type of gas. In some embodiments, first gas supply system  141  may include valve  142 , controlled by controller  150  and configured to supply the first type of gas to pipe  122  at a predetermined amount. In some embodiments, the known first amount may be at least 9 wt. % or more of CO 2 . In some embodiments, the first type of gas may further include a toxic gas at a known second amount. For example, a partially purified geothermal gas may include up to 0.79 wt. % H 2 S and 2.16 wt. % hydrogen. H 2 S and/or hydrogen may be toxic to the algae and a system and method according to embodiments of the invention may be configured to control the amount of provided toxic gases to be below the toxicity level, for example, by continuous circulating the partially purified geothermal gas to cause maximum consumption of CO 2  by the algae without providing additional toxic gases, thus increase the level of toxicity to above a harming level. 
     Second gas supply system  143  may be configured to supply a second type of gas, for example, a gas containing nitrogen, such as air, nitrogen and the like. In some embodiments, second gas supply system  143  may include valve  144 , controlled by controller  150  and configured to supply the second type of gas, for example, at a predetermined amount. 
     Third gas supply system  145  may be configured to supply a third type of gas, for example, a substantially pure CO 2  (e.g., a gas containing at least 90% CO 2 ). In some embodiments, third gas supply system  144  may include valve  146 , controlled by controller  150  and configured to supply the third type of gas, for example, at a predetermined amount. 
     In some embodiments, only one or two types of gasses may be supplied via the one or more gas supply systems  141 ,  143  and  145 . In such embodiments, some of gas supply systems may not be active, or may be operated to provide the same gas or gasses as another supply system. For example, gas supply systems  141  and  143  may supply a first type of gas and system  145  may supply a second type of gas. In another example, supply system  145  may not be operated, while each of supply systems  141  and  143  may supply a different type of gas. 
     Controller  150  may be any computation platform that is configured to perform instructions to control various components in system  100 . Controller  150  may include a processor and a memory to store thereon instructions according to embodiments of the invention. Controller  150  may be configured to: control the first gas supply system to supply to the circulating pipe a first type of gas at a predetermined amount. For example, the controller may be configured to control supply system  141  to supply partially purified geothermal to pipe  120 . and control second gas supply system  143  to supply to circulating pipe  120  the second type of gas for example, air or nitrogen. The first type of gas and the second type of gas may be supplied, to pipe  120 , to form a first predetermined amount of gas mixture containing the first type of gas and second type of gas. The relative amounts of the first type of gas and the second type of gas, in the gas mixture, may also be predetermined, for example, based on the type of the algae growing in cultivation container  110 . In some embodiments, the gas mixture may include (after mixing) at least 5 wt. % CO 2  The gas mixture may continually be circulated via container  110 , by pump  125 . During the circulation at least a portion of the small gas bubbles may dissolve into the water in container  110  and the CO 2  may be consumed by the algae. Therefore, in time the amount of the CO 2  may be reduced. 
     Controller  150  may further receive from sensor  130  and/or sensor  135  signal indicative to the amount of the CO 2  in the gas mixture. Controller  150  may continuously monitor the level of the CO 2  as the gas mixture being circulated via container  110 . In some embodiments, when the amount of the CO 2  drops below a first predetermined level, controller  150  may open valve  148  to extract a second predetermined amount of the gas mixture from the cultivation container. Controller  150  may than control first gas system  141  to supply the first type of gas in an amount equal to the second predetermined amount. For example, when the a pH signal raised above 7.5, indicating that the amount of CO 2  is too low, controller  150  may control first gas system  141  to supply geothermal gas having 50% CO 2  to pipe  122 . Alternatively, controller  150  may control third gas supply system  145  to supply CO 2  instead of geothermal gas. 
     In some embodiments, supplying controlled amounts of geothermal gas, may not harm the algae culture inside container  110  and may eliminate the risk of explosion. 
     Reference is now made to  FIG. 2  which is a flowchart of a method of growing algae in a cultivation container using, for example, geothermic gas, according to some embodiments of the invention. In box  210 , a first predetermined amount of gas mixture comprising a first type of gas and at least one second type of gas, may be circulated, via a container (e.g., container  110 ), in a closed loop. In some embodiments, the gas mixture may enter the container via one or more entrance spargers (e.g., spargers  112 ) and exit via at least one exit pipe (e.g., exit pipe  114 ). For example, a mixture including a first type of gas containing known amount of CO 2  (e.g., geothermal gas containing at least 9 wt. % CO 2 ) and air may be circulated via a container (e.g., a bio-reactor) holding algae (e.g., micro-algae) and water. The entrance spargers may spray the gas mixture to form small bubbles having a diameter of no more than 5 mm, for example, 1 mm. In some embodiments, the first predetermined amount of gas mixture may be circulated continuously to allow consumption of the CO 2  from at least the first type of gas. In some embodiments, the first type of gas may include a toxic gas at a known second amount, for example, H 2 S or hydrogen included in the geothermal gas. In some embodiments, the continuous circulation may allow the algae to consume the CO 2  from the geothermal gas before an additional amount of geothermal gas containing toxic gas(es) has to be added. 
     In some embodiments, the second type of gas may include gas containing N 2 , such as, air. The second type of gas may provide the required bubbling and circulation for the algae culture, while the first type of gas may provide the nutrition, in the form of CO 2 . In some embodiments, the ratio between the first type of gas and second type of gas in the gas mixture may be predetermined, for example, based on the type of algae. For example, the gas mixture may include at least 5% CO 2 . The first predetermined amount may be determined to provide sufficient CO 2  and sufficient mixing and turbulence of the algae culture in container  110 . 
     In box  220 , signal indicative of the amount of CO 2 , in the gas mixture may be received. For example, sensor  130  may continually measure the amount of CO 2  in pipe  122  and a controller such as controller  150  may monitor the measured amount. Additionally or alternatively, sensor  135  may monitor the pH level in container  110 , the pH level may be indicative to the amount of CO 2  in the algae culture and the gas mixture. 
     If the signal indicative of the amount of CO 2  shows that the amount dropped below a predetermined level (box  225 —YES), then in box  230 , a second predetermined amount of the gas mixture from the cultivation container may be extracted. In some embodiments, controller  150  may control valve  148  to open and extract from circulation system  120 , the second predetermined amount of gas mixture. The extracted gas mixture may have less relative amount of CO 2  than the gas mixture initially supplied in box  210 . For example, 0.5 litters of circulated gas mixture per liter culture may be extracted when the pH of the algae culture reaches 7.5. 
     Following the extraction (e.g., after controller  150  closed valve  148 ) an amount of the first type of gas may be added to the gas mixture, in box  240 . The added amount may be equal to the second predetermined amount. For example, controller  150  may control first gas system  141  to add 0.5 liters of geothermal gas per liter culture to circulation system  120 . 
     In some embodiments, the process may continue until the amount of O 2  in the gas mixture and/or the algae capture reached a second predetermined level, for example, 35 wt. %. During the photosynthesis process the algae consumes the CO 2  and produces O 2  which above a certain amount prevents further grow of the algae. In some embodiments, the method may include replacing the circulating gas mixture with a new first predetermined amount of the gas mixture when the amount of O 2  raised above a second predetermined level. For example, controller  150  may control relive valve  148  to release the circulating gas mixture entirely. In this release all toxic gases accumulated in the circulating gas mixture are released as well. Following the release controller  150  may control first gas supply system  141  and the second gas supply system  143  to supply to the circulating system the first predetermined amount of gas mixture comprising the first type of gas and second type of gas, thus repeating the step in box  210 . 
     While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.