Systems and methods for off-shore energy production

Abstract

The invention is directed to aquatic systems and methods for off-shore energy production, particularly to systems and methods for generating large amounts of methane via anaerobic digestion, purifying the methane produced, and sequestering environmentally deleterious by-products such as carbon dioxide. The energy production systems contain one or more flexible, inflatable containers supported by water, at least one of which is an anaerobic digester containing bacteria which can produce energy sources such as methane or hydrogen from aquatic plants or animals. Off-shore energy production facilities supported by water bodies offer many advantages over land-based digesters, including the use of large, available open water bodies as an alternative means of support and the potential for locating the facilities at sites that already contain, or can be easily modified to generate, sufficient amounts of feedstock onsite. In addition, the containers of the invention can be large enough to provide adequate amounts of energy to support off-shore activities and relatively easy to manufacture and ship to remote production sites. The systems can also be readily adapted to sequester carbon dioxide or replenish feedstocks growing nutrients on site.

We claim: 
     
         1 . An aquatic method for producing methane, carbon dioxide, and plant nutrients comprising microbial anaerobic digestion of a feedstock by at least one bacterium wherein:
 the feedstock comprises water and at least one plant or animal material;   the feedstock is digested within at least one first, flexible container wherein the at least one first container is supported by and submerged in a water body, thereby producing a methane gas and a carbon dioxide gas wherein a first concentration of the methane gas dissolved in the at least one first container is in excess of its equilibrium concentration and a second concentration of the carbon dioxide gas dissolved in the at least one first container is below its equilibrium concentration;   the gases generated in excess of their equilibrium concentration collect at the top of the at least one first container and pass upwards through at least one second container;   the water in the at least one first container passes downward through at least one third container;   the water exiting the at least one third container contains at least one respective third, equilibrium concentration of dissolved methane and a fourth concentration of dissolved carbon dioxide, wherein the third and fourth concentrations of methane and carbon dioxide, respectively are lower than the first and second concentrations of methane and carbon dioxide, respectively; and   the carbon dioxide dissolved in the water exiting the at least one third container is captured.   
     
     
         2 . The method of  claim 1 , wherein the feedstock comprises at least one plant material comprising plant tissue. 
     
     
         3 . The method of  claim 1 , wherein the feedstock comprises at least one animal material comprising animal tissue. 
     
     
         4 . The method of  claim 1 , wherein the method is performed off-shore. 
     
     
         5 . The method of  claim 1 , wherein the method is automated. 
     
     
         6 . A quantity of methane produced according to the method of  claim 1 . 
     
     
         7 . The methane of  claim 6 , wherein the purity of the methane is at least 70%. 
     
     
         8 . The methane of  claim 7 , wherein the purity of the methane is in the range of about 87% to about 100%. 
     
     
         9 . An aquatic method for producing methane, carbon dioxide, and plant nutrients comprising microbial anaerobic digestion of a feedstock by at least one bacterium wherein:
 the feedstock comprises water and at least one plant or animal material;   the feedstock is digested within at least one first, flexible container wherein the at least one first container is supported by and submerged in a water body, thereby producing a methane gas and a carbon dioxide gas wherein a first concentration of the methane gas dissolved in the at least one first container is in excess of its equilibrium concentration and a second concentration of the carbon dioxide gas dissolved in the at least one first container is below its equilibrium concentration;   the gases generated in excess of their equilibrium concentration collect at the top of the at least one first container and pass upwards through a second container;   the water in the at least one first container passes downward through a third container;   the water exiting the third container contains a third, equilibrium concentration of dissolved methane and a fourth concentration of dissolved carbon dioxide, wherein the third and fourth concentrations of methane and carbon dioxide, respectively are lower than the first and second concentrations of methane and carbon dioxide, respectively; and   the carbon dioxide dissolved in the water exiting the third container is captured.   
     
     
         10 . An aquatic method for producing methane, the method comprising anaerobic digestion of at least one feedstock material by at least one bacterium, wherein:
 the feedstock material comprises at least one of a plant material and an animal material;   the feedstock material is digested within at least one flexible container supported by and submerged in a first water body, thereby producing a gas comprising methane and a liquid comprising liquid phase carbon dioxide, wherein the gas and liquid are formed at a pressure of at least two atmospheres in a first location of the first water body;   collecting the gas in at least one first storage container;   collecting the liquid in at least one second storage container;   purifying the methane in the gas by lowering the depth of the at least one first storage container or the gas, thereby liquefying a quantity of gas phase carbon dioxide in the at least one first storage container;   purifying the carbon dioxide in the liquid by separating the liquid phase carbon dioxide from at least one other liquid in the at least one second storage container;   reacting the liquid in the at least one second storage container to form a composition comprising carbon dioxide, wherein the composition is a solid; and   sequestering the carbon dioxide by transporting the at least one second storage container to a second location in the first water body or a second water body, or transporting the liquid phase carbon dioxide or the solid from the at least one second storage container to at least one third storage container located in the second location in the first or a second water body, wherein the density of the liquid phase carbon dioxide or solid in the at least one third storage container is greater than the density of the first or second water body at the second location.   
     
     
         11 . The method of  claim 10 , wherein the at least one feedstock material comprises at least one plant material comprising plant tissue. 
     
     
         12 . The method of  claim 10 , wherein the at least one feedstock material comprises at least one animal material comprising animal tissue. 
     
     
         13 . The method of  claim 10 , wherein the method is performed off-shore. 
     
     
         14 . The method of  claim 10 , wherein the method is automated. 
     
     
         15 . A quantity of methane produced according to the method of  claim 10 . 
     
     
         16 . The methane of  claim 15 , wherein the purity of the methane is at least 70%. 
     
     
         17 . The methane of  claim 16 , wherein the purity of the methane is in a range of about 87% to about 100%.