Abstract:
A methanogenic reactor for the production of methane, cellular biomass and other useful products for use in the manufacturing of specialty chemicals. The methanogenic reactor includes a bottom wall, perimeter wall, and top wall defining an interior space environmentally separable from an exterior space outside of the reactor vessel for holding a methanogenic culture and growth media. The reactor also includes at least one sparger positioned substantially within the interior space for facilitating the direction of an input gas stream into the reactor to be brought into contact with the methanogenic culture. The reactor also includes an output material stream port for releasing an output material stream created at least in part by the methanogenic culture.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This application is related to application serial number TBD, entitled System For The Production Of Methane And Other Useful Products And Method Of Use filed Mar. 13, 2009. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to the generation of green natural gas through methanogenic conversion and more particularly pertains to a new methanogenic reactor for generating natural gas and cellular biomass from a variety of input material including syngas, mixed gas, or combined individual gas streams. 
         [0004]    2. Description of the Prior Art 
         [0005]    The use of methanogens and methanogenic processes is known in the prior art. More specifically, the systems utilizing methanogens to generate natural gas heretofore devised and utilized have generally been either capturing the gaseous output of naturally occurring systems, such as the Volta Experiment on Lake Como in 1778 or anaerobic digestion systems which consist basically of familiar, expected and obvious biological, chemical, and structural configurations, notwithstanding the myriad of designs encompassed by the crowded prior art which have been developed for the fulfillment of countless objectives and requirements. 
         [0006]    The process of Methanogenesis is fairly well known. The following references provide a good working overview of the methanogenic process and are hereby incorporated by reference for all purposes: Archea: Molecular and Cellular Biology—Chapter 13 Methanogenesis, James G. Ferry and Kyle A. Kastead, Department of Biochemestry and Molecular Biology, The Pennsylvania State University, University Park, Pa., edited by Ricardo Cavicchiolo, ©2007 ASM Press, Washington, DC; and Continuous Cultures Limited by a Gaseous Substrate: Development of a Simple, unstructured Mathematical Model and Experimental Verification with Methanobacterium thermoautotrophicum, N. Schill; W. M. van Gulik, D. Voisard, and U. von Stockar, Institute of Chemical Engineering, Swiss Federal Institute of Technology, Lausanne (EPFL), CH-1015 Lausanne, Switzerland, Biotechnology and Bioengineering, Vol. 51, P6450658 (1996) John Wiley &amp; Sons, Inc. 
         [0007]    Illustrative examples of the types of systems known in the prior art include anaerobic digestion systems and U.S. Pat. Nos. 1,940,944; 2,097,454; 3,640,846; 4,722,741; 5,821,111 and application no. PCT/US07/71138. 
         [0008]    In these respects, the methanogenic reactor according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in so doing provides an apparatus primarily developed for the purpose of generating green natural gas and cellular biomass from a variety of source materials. 
       SUMMARY OF THE INVENTION 
       [0009]    To promote the development of renewable energy sources, the United States government has identified a “billion ton” goal of biomass production per year. At present the largest single component of that supply is corn stover. It is widely accepted that adverse ecological effects of corn production such as the anoxic zone in the Caribbean will encourage biomass production from other sources. Chief among these alternatives will be perennial grasses such as switchgrass and native prairie grasses. Testing currently underway on novel, high yield grasses such as miscanthus points to the prospect of biomass production in lieu of conventional crops on marginal lands. 
         [0010]    Despite these developments on the production side there remain critical issues on the conversion of these biomass sources to useable forms as substitutes for fossil fuels. 
         [0011]    Pelletizing improves the handling characteristics of biomass, but adds enough cost to the resulting fuel cost to largely eliminate any fuel cost advantage. In addition, biomass fuels burn dirty, producing sulfur and nitrogen oxides and hydrogen chloride. Equipment to burn these fuels is expensive and air permitting remains problematic. A clean solution to these limitations would be to convert biomass into pipeline quality biomethane near the point of origin for transmission to existing natural gas customers via existing natural gas pipelines. This same process can also supply biomethane to specialty chemical facilities for the production of green specialty chemicals, including but not limited to “green plastics”. Further, the present invention also generates cellular biomass, which may be utilized as a food or nutrient for livestock and humans 
         [0012]    The two primary routes to biomethane currently recognized are anaerobic digestion and thermochemical conversion. A third process for the conversion of biomass to liquid fuels is being pursued which involves enzymatic breakdown of cellulose and hemicelluloses into fermentable sugars. While these processes are effective on some feedstocks and at some capacities, none of them provide a fully satisfactory route to biomass use. 
         [0013]    To understand why this is so, it is helpful to understand the progression of plant composition during the growing season. The three primary structures in a plant are cellulose, hemicelluloses, and lignin. These compounds are in turn polymers of 6-carbon sugars, 5-carbon sugars, and phenolics respectively. As the plant matures, there is a progressive conversion of cellulose and hemicelluloses to lignin. This is reflected in the decrease of total digestable nutrients and the increase of acid detergent fiber content. 
         [0014]    Anaerobic digestion uses mixed cultures of microbes to break down biomass into fermentable sugars, amino acids, and organic acids. This process is multi-step and is subject to upset by over-production of organic acids which kill the methanogenic organisims. The great benefit of anaerobic digestion is that it is generally recognized as specific, producing methane and carbon dioxide in a readily recoverable form. 
         [0015]    Anaerobic digestion of grasses and corn stover has been extensively studied. Mahert (Mahert, Pia, et al, “Batch and Semi-continuous Biogas Production from Different Grass Species”. December 2005) and others have studied the potential for biomethane production from various grasses. The chief finding of this work is that while biomethane can be produced by this route, the required digester volume per unit of energy produced is uneconomical. In addition, the grasses must be harvested at or before full bloom. Corn stover is substantially limited and in some instances near impervious to anaerobic digestion. 
         [0016]    A further disadvantage of anaerobic digestion of grasses is that when native or prairie grass is cut before October, the yield the following year is half or less of what is expected. This appears to be related to the manner in which nutrients are returned to the root structure after frost. 
         [0017]    Thermochemcial conversion of biomass to biomethane and liquid fuels is a proven technology base on some old coal chemistry. A large scale coal to natural gas plant at Beulah, N.D. has been in operation since the late 1980&#39;s. The chief limitation of this technology is that it strongly favors large scale operations, generally over 400 tons per day. 
         [0018]    Enzymatic processes to break down biomass to fermentable sugars remain an elusive and expensive undertaking. Even if successful, however, enzymatic processes are likely to be highly specific to certain species and perhaps even varieties within species due to their high specificity. One of the objectives associated with biomass production is promotion of multiple species cultivation. Highly specific enzyme processes will tend to promote monocultures and leave the ecosystem no richer than a corn/soybean mix. 
         [0019]    As the foregoing shows, there is room for development of a novel process which will address the limitations of all the current options. Such a process will have at least some of the following characteristics:
       1) It will produce a fuel which is directly compatible with existing energy distribution and use equipment;   2) It will use a variety of feed stocks ranging from corn stover to perennial grasses to wood without loss of yield per ton of saleable energy;   3) It will utilize feedstock harvested late in season and preferable after frost;   4) It will be economical at a scale of 200 ton per day or less;   5) It will be modular to allow initial construction and expansion as the biomass supply chain becomes established and more efficient and   6) It will produce cellular biomass that can have useful and economic value.       
 
         [0026]    The present invention provides each of these advantages by using a hybrid process which combines the flexibility and power of gasification with the specificity of anaerobic digestion, and with improved efficiency and higher production rates than anaerobic digestion. The gasification step overcomes biomass species and variety variations producing uniform, readily fermentable feedstock to the methanogenic reactor. The culture in the methanogenic reactor is efficient and specific producing only methane, cellular biomass, and water as its co-products. 
         [0027]    The present invention utilizes gases which maybe derived from a wide variety of feedstocks ranging from crop residues, low value co-products from agriculture processing and energy crops such as switchgrass and corn stover, waste wood products, and other similar biomass sources. The raw materials may be processed such as being reduced to a uniform size and moisture content (preferably very low) prior to gasification. The gassification process converts the biomass into an intermediate gas stream known as syngas or synthesis gas. The syngas, after going through a heat recovery process, may be directed through a filtering system and or a water gas shift prior to being directed into the methanogenic reactor vessel for conversion by the methanogenic culture into methane. 
         [0028]    It is important to note that while the present invention is directed towards providing green natural gas from biomass, the same process can be done with municipal or landfill wastes or nonconventional carbon and hydrogen sources (collectively “landfill waste”). The use of the present invention with landfill wastes as the feed stock would allow the reclamation of hundreds of thousands of acres currently used as landfills. If landfill wastes are utilized as a feedstock, the filtering and cleanup process after gasification can be much more complex than that required for biomass feedstock. 
         [0029]    Further, it should be noted that the present invention can be utilized for the generation of cellular biomass. Typical algae systems used for biomass generation produce between 0.2 and 4.0 grams per liter of reactor volume per day. Other methanogenic systems have been reported to produce up to 2.88 grams per liter of reactor volume per day. The present methanogenic reactor, when properly operated in a biomass production mode, can produce 12 grams per liter of reactor volume per hour. This present approximately a 1000× improvement over algae generation systems currently in use. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    The invention will be better understood and objects of the invention will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein: 
           [0031]      FIG. 1  is a schematic functional block diagram of a new Methanogenic Reactor in use according to the present invention. 
           [0032]      FIG. 2  is a schematic functional block diagram of an embodiment of the present invention. 
           [0033]      FIG. 3  is a schematic functional block diagram of another embodiment of the present invention. 
           [0034]      FIG. 4  is a schematic functional block diagram of a further embodiment of the present invention. 
           [0035]      FIG. 5  is a schematic functional block diagram of still a further embodiment of the present invention. 
           [0036]      FIG. 6  is a schematic flow diagram of the present invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0037]    With reference now to the drawings, and in particular to  FIGS. 1 through 6  thereof, a new Methanogenic Reactor embodying the principles and concepts of the present invention and generally designated by the reference numeral  10  will be described. 
         [0038]    As best illustrated in  FIGS. 1 through 6 , the methanogenic reactor  10  generally comprises a reactor vessel  11  for the methanogenic conversion of an input material stream to an output materials stream, including a bottom wall  21 , perimeter wall  22 , and top wall  23 . Preferably, the perimeter wall  22  is operationally coupled to the bottom wall  21  and extends upwardly from the bottom wall  21 . Similarly, the top wall  23  is operationally coupled to the perimeter wall  22 . Thus, the bottom wall  21 , perimeter wall  22 , and top wall  23  define an interior space  27  which is environmentally separable from an exterior space outside of the reactor vessel  11 . 
         [0039]    The bottom wall  21  and the perimeter wall  22  may be made out of any suitable material such as stainless steel, fiberglass, or concrete. Additionally, the bottom and perimeter walls  22  may have an interior surface lining  24  of epoxy, a polymeric material, or fiberglass. Preferably, the bottom wall  21  and the perimeter wall  22  are constructed out of the same material for ease of production. However at least one embodiment of the present invention contemplates the bottom wall  21  and the perimeter wall  22  being made out of different materials. 
         [0040]    Similarly, the top wall  23  may also made out of any suitable material such as stainless steel, fiberglass, or concrete; and may have an interior surface lines with epoxy, a polymeric material, or fiberglass. However, it should be noted that the top wall  23  may be made out of a different material that the bottom wall  21  or the perimeter wall  22 . The top wall  23  may be configured as a floating roof. 
         [0041]    At least one embodiment of the reactor vessel  11  is formed substantially in the shape of a sphere, which has a bottom portion, a perimeter portion, and a top portion each corresponding to a bottom wall, perimeter wall and top wall respectively. 
         [0042]    In an embodiment the bottom wall  21  has a slope from a back side downwardly to a front side. Preferably, the slope is between 0.075 and 1.5 inches per linear foot. 
         [0043]    In another embodiment the bottom wall  21  has a slope from a perimeter downwardly towards a central portion. Preferably, the slope is between 0.75 and 1.5 inches per linear foot. 
         [0044]    The present invention contemplates at least one embodiment, in which at least a portion of the reactor vessel  11  abuts an earthen wall  2 , such as when at least a portion of the reactor vessel  11  is buried. In such an embodiment, the reactor vessel  11  may also include an insulating layer  25  which abuts the earthen wall  2  and provides a thermal insulation between the reactor vessel  11  and the earthen wall  2 . 
         [0045]    The reactor vessel  11  may also include an access port  26  for facilitating the clean-out and/or repair of the reactor vessel  11 . The access port  26  may be located in the top wall  23 , but more preferably is located in the bottom wall  21  or perimeter wall  22 . 
         [0046]    In a further embodiment, the reactor vessel  11  also includes a thermal conditioning unit  34 , which has a thermal transfer portion  35  operationally coupled to the perimeter wall  22 . The thermal transfer portion may include either a fluid jacket or an electrical heating coil, which encompasses at least a portion of the perimeter wall  22 . 
         [0047]    In still a further embodiment, the reactor vessel  11  also includes a culture conditioning chamber  37 . The culture conditioning chamber  37  is environmentally coupleable with the interior space  27  and is operationally coupled to the thermal transfer portion  35 . The culture conditioning chamber  37  may be used for thermally preconditioning a quantity of culture and media prior to introducing the culture and media into the interior space  27  of the reactor vessel  11 . 
         [0048]    The reactor vessel  11  may also include at least one sparger  40 , positioned substantially within the interior space  27 . The sparger  40  is operationally coupled to an input gas stream. When a single sparger  40  is utilized, either a mixed gas must be used as the input gas stream or a mixing assembly may be used to mix various gases from various prior to being introduced into the interior space  27 . 
         [0049]    In an embodiment, an array of spargers  41  is used. Each one of the array of spargers  41  is operationally coupled to an associated input gas stream. The array of spargers  41  may include at least one of each of the following: a Carbon Dioxide (CO2) sparger  42 , a Hydrogen (H2) sparger  43 , a Hydrogen Sulfide (H2S) sparger  44 , a Carbon Monoxide (CO) sparger  45 , and/or a Nitrogen (N) Sparger  46 . 
         [0050]    In at least one embodiment at least one H2 sparger  43  is positioned vertically above at least one CO2 sparger  42 , and at least one H2S sparger  44  is positioned vertically above at least one H2 sparger  43  and at least one CO sparger  45  is positioned vertically above at least one H2S sparger  44 . 
         [0051]    The Nitrogen sparger  45  can be particularly useful when the reactor is used at least partially for the creation of biomass. The biomass created in the reactor vessel  11  during normal operation may range of approximately  12  grams per liter of effective reactor volume per hour. 
         [0052]    Any one of the spargers may be a ring-type sparger, a bayonet type sparger, or any other appropriate configuration. Preferably the spargers create bubbles approximately  1  to  10  microns in diameter. 
         [0053]    In at least one embodiment, the reactor vessel  11  also includes an oxidation reduction potential (ORP) control system  50 . 
         [0054]    In a further embodiment, the oxidation reduction potential control system  50  further includes an oxidation reduction potential probe  51 , oxidation reduction potential measurement unit  52 , and an oxidation reduction potential adjustment unit  53 . Preferably the oxidation reduction potential probe  51  is positioned at least partially within the interior space  27  or a culture/media recycling tube. The oxidation reduction potential probe  51  measures an oxidation reduction potential of a culture/media solution positioned in the interior portion. The oxidation reduction potential measurement unit  52  is operationally coupled to the oxidation reduction potential probe  51  and compares an output of the oxidation reduction potential probe  51  to a predetermined ORP upper value and/or a predetermined ORP lower value. The oxidation reduction potential adjustment unit  53  injects a first oxidation reduction buffer agent  54  into the interior space  27  when the oxidation reduction potential measurement unit  52  determines the output of the oxidation reduction potential probe  51  is at least trending towards the predetermined ORP upper value. Similarly, the oxidation reduction potential adjustment unit  53  injects a second oxidation reduction buffer agent  55  into the interior space  27  when the oxidation reduction potential measurement unit  52  determines the output of the oxidation reduction potential probe  51  is at least trending towards the predetermined ORP lower value. 
         [0055]    In a further embodiment the first oxidation reduction buffer agent  54  is either H2S or H2. The ORP upper value is between −400 and −600 mV and more preferably, is approximately −500 mV. 
         [0056]    In still a further embodiment the second oxidation reduction buffer agent  55  is CO. The ORP lower value is between −600 and −800 mV and more preferably is approximately −700 mV. 
         [0057]    In at least one embodiment the reactor vessel  11  also includes a pH control system  60 . 
         [0058]    In a further embodiment the pH control system  60  further includes a pH probe  61 , a pH measurement unit  62 , and a pH adjustment unit  63 . Preferably, the pH probe  61  is positioned at least partially within the interior space  27  or a culture/media recycling tube  73 , and measures a pH of a culture/media solution positioned in the interior portion. The pH measurement unit  62  is operationally coupled to the pH probe  61  and compares an output of the pH probe  61  to a predetermined pH upper value and/or a predetermined pH lower value. The pH adjustment unit  63  injects a pH buffer agent  64  into the interior space  27  when the pH measurement unit  62  determines the output of the pH probe  61  is at least trending towards the predetermined pH upper value. Similarly, the pH adjustment unit  63  injects a second pH buffer agent  65  into the interior space  27  when the pH measurement unit  62  determines the output of the pH probe  61  is at least trending towards the predetermined pH lower value. 
         [0059]    In still a further embodiment the first pH buffer agent  64  includes CO2, and the pH upper value is between 7.5 and 9, and more preferably the pH upper value is approximately 8. 
         [0060]    In even still a further embodiment the second pH buffer agent  65  is selected from a group of agents including sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium bicarbonate, ammonia, ammonium and ammonium nitrate. Preferably, the pH lower value is between 6 and 8, and more preferably is approximately 7.6. 
         [0061]    In yet a further embodiment, the second buffer agent  65  is selected at least in part based upon the rate of change of the pH of the culture/media in the interior space  27  of the reactor vessel  11 . 
         [0062]    In at least one embodiment, the reactor vessel  11  also includes an agitation system  76 . 
         [0063]    In an embodiment, the agitation system  76  further includes an agitation drive means and an impeller  77 . The impeller  77  operationally coupled to the agitation drive means, the impeller  77  positioned within the reactor vessel  11 . As an illustrative example of an agitation drive means as contemplated by the present invention, a motor electrically coupled to a variable frequency drive to control the speed of the motor may be magnetically coupled to an agitation shaft positioned within the reactor. The impeller  77  is thus operationally coupled to the motor. 
         [0064]    In a further embodiment the impeller  77  rotates at between 1100 and 2100 rpm. 
         [0065]    In still a further embodiment the impeller  77  rotates at between 1500 and 1800 rpm. 
         [0066]    In still yet a further embodiment the impeller  77  rotates at greater than 110% of the resonance of the reactor vessel  11 . Resonance being defined as the sympathetic frequency of vibration for the reactor vessel  11 . 
         [0067]    The impeller  77  may be any physical configuration appropriate for the form factor of the interior space  27  of the reactor vessel  11 . Preferably the impeller  77  is a rushton impeller. 
         [0068]    The magnetic coupling unit  78  may be operationally coupled to the top wall  23  or the perimeter wall  22 . 
         [0069]    In at least one embodiment the interior space  27  further includes a culture/media holding space  28  and a head space  29 . 
         [0070]    In a further embodiment a volume of the culture/media holding space  28  to a volume of the head space  29  has a ratio between 1.5:1 to 5:1. 
         [0071]    In a more preferred embodiment a volume of the culture/media holding space  28  to a volume of the head space  29  has a ratio of approximately 2.57:1. 
         [0072]    In an embodiment the reactor vessel  11  has an overall interior height between 10 and 220 feet. 
         [0073]    In another embodiment the reactor vessel  11  has an overall interior height between 60 and 150 feet. 
         [0074]    In a preferred embodiment the reactor vessel  11  has an overall interior height of approximately 140 feet. 
         [0075]    In an embodiment the reactor vessel  11  has an overall interior volume between 75000 and 300000 gallons. 
         [0076]    In a preferred embodiment the reactor vessel  11  has an overall interior volume of 250000 gallons, with an overall interior height of approximately 140 feet, and a volume of the culture/media holding space  28  to a volume of the head space  29  has a ratio of approximately between 2.3:1 and 2.8:1. 
         [0077]    In at least one embodiment, the reactor vessel  11  further includes a culture/media recirculating system  70 . 
         [0078]    In a further embodiment the culture/media recirculating system  70  further comprising a recirculation output port  71 , a recirculation pump  72 , a recirculation tube  73 , and a recirculation input port  74 . The recirculation output port  71  is environmentally coupled to the interior space  27 . The recirculation pump  72  operationally coupled to the recirculation output port  71 . The recirculation input port  74  is environmentally coupled to the interior space  27  and operationally coupled to the recirculation pump  72 . 
         [0079]    The reactor vessel  11  may include a plurality of ports for facilitating routing of materials into and out of the interior space  27  of the reactor vessel  11 . This plurality of ports may include an input material stream port  12 , an output material stream port  13 , biomass removal port  15 , culture/media input port  16 , and/or a culture sampling port  17 . Some of these ports may be environmentally coupled to the interior space  27  through a recycling tube  73  or other intermediate structure. 
         [0080]    The reactor vessel  11  may also include a secondary vessel  57  environmentally coupled to the output material stream port  13 . 
         [0081]    In an embodiment, the secondary vessel  57  is a condenser. Preferably the condenser has a cooling jacket  58  to facilitate the removal of moisture and/or foam from the output material stream. Such moisture and/or foam may be returned into the interior space  27  of the reactor vessel  11  or disposed of through a drain port  59  in the secondary vessel  57 . 
         [0082]    Alternatively, the secondary vessel  57  may be a non-thermal separation system, such as a reverse osmosis system. 
         [0083]    In an embodiment the reactor vessel  11  further includes a data system  67  operationally coupled to at least one of the culture media recirculation system  70 , oxidation reduction potential control system  50 , pH control system  60 , agitation system  76 , thermal conditioning unit  34 , or at least one sparger  40 . 
         [0084]    In an embodiment the reactor vessel  11  further includes a hydrogen diffuser  48  system positioned substantially within the interior space  27  for releasing hydrogen from a mixed gas stream flowing through the hydrogen diffuser  48  system into the interior space  27 . 
         [0085]    In a further embodiment the hydrogen diffuser  48  system is operationally coupled between an input material stream port  12  and a first output material stream port  13 . 
         [0086]    In an alternate embodiment the first output material stream port  13  is operationally coupled to an input of an intermediate processing unit  49  providing a filtering function. The intermediate processing unit preferably includes an output operationally coupled to a second input material stream port  12  environmentally coupled to the interior space  27 . Illustrative examples of intermediate processing include filtering means such as PSA and water-gas shift. 
         [0087]    In still another alternate embodiment the hydrogen diffuser  48  system is operationally coupled between a first output material stream port  13  and a second output material stream port  14 . 
         [0088]    In a further embodiment the hydrogen diffuser  48  system further includes a length of tubing having a perimeter wall  22  permeable by hydrogen and substantially impermeable to other components in the mixed gas stream. 
         [0089]    The present invention also contemplates the interior space  27  of the reactor vessel  11  having a plurality of zones. 
         [0090]    In an embodiment the plurality of zones includes a tank pressure zone  30  having a greater pressure due to the column of culture/media within and above the tank pressure zone  30 . 
         [0091]    In a further embodiment the plurality of zones includes a diffuser zone  31 , and the hydrogen diffuser  48  system is positioned substantially within the diffuser zone  31 . 
         [0092]    In still a further embodiment the plurality of zones includes an agitation and defoaming zone  32 . 
         [0093]    Preferably, the diffuser zone  31  is positioned vertically above the tank pressure zone  30  and the agitation and defoaming zone  32  is positioned vertically above the diffuser zone  31 . 
         [0094]    In an embodiment the interior space  27  is designed for holding a vertical column of media/culture of at least 50 feet. 
         [0095]    In more preferred embodiment the interior space  27  is designed for holding a vertical column of media/culture of at least 100 feet. 
         [0096]    The reactor vessel  11  may include a defoaming bar  79  positioned substantially within the agitation and defoaming zone  32 . Additionally, a defoaming agent input port  18  may be environmentally coupled with the interior space  27  for the selective introduction of a defoaming agent into the interior space  27 .