Patent Application
20100233775
This application is related to application serial number TBD, entitled Methanogenic Reactor filed TBD.
1. Field of the Invention
The present invention relates to the generation of green natural gas through methanogenic conversion and more particularly pertains to a new system for the production of methane and other useful product and method of use for generating natural gas and cellular biomass from a variety of input material including biomass.
2. Description of the Prior Art
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.
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, Universtiy Park, P A, 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 & Sons, Inc.
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.
In these respects, the system for the production of methane and other useful product and method of use 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 including biomass.
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.
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.
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
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.
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.
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.
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.
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.
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. Dak. has been in operation since the late 1980's. The chief limitation of this technology is that it strongly favors large scale operations, generally over 400 tons per day.
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.
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:
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 reactor. The culture in the reactor is efficient and specific producing only methane, cellular biomass, and water as its co-products.
The present invention utilizes 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 reactor vessel for conversion by the methanogenic culture into methane.
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.
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:
With reference now to the drawings, and in particular to
As best illustrated in
In at least one embodiment, the present invention includes at least one culture of methanogenic archea 26 (“methanogens”), at least one reactor vessel 30, at least one input material stream 24, and at least one output material stream 72.
The methanogens convert an input material 20into an output material, including methane and cellular biomass. Typically, the present invention uses primarily a gas mixture for the input stream and generates at least a gas and excess biological material as the output materials.
At least one reactor vessel 30 is used for housing at least a portion of the culture of methanogenic archea 26. The present invention also has at least one embodiment in which multiple reactor vessels 30 are used in parallel. This type of parallel arrangement has the benefits of scaling the total reactor volume as desired by adding additional reactor vessels 30, providing the ability to continue operations during maintenance procedures, and advantageous vessel sizing.
The input material stream 24 is directed into the reactor vessel 30 to facilitate contact between the input material stream 24 and the methanogenic archea 26. While conceptualized as an input material stream 24 the present invention also has at least one embodiment wherein multiple input streams are utilized. As an illustrative example only, one such embodiment may occur when sequestered CO2 is used along with other input materials. In this example, the sequestered CO2 could be directed into the reactor vessel 30 separate from the other input materials. Further, the present invention also includes at least one embodiment wherein H2, CO, CO2, and/or H2S are directed into the reactor vessel 30 as separate input streams.
The output material stream 72 is created at least in part by bringing the methanogens into contact with the input material stream 24. Preferably, this contact occurs at a molecular scale. The output material stream 72 may also include multiple output material streams 72 such as a gas stream, a solids stream, and a liquids stream. The liquids stream may include particulate matter and dissolved gases.
In an embodiment each one of the reactor vessels 30 includes at least one input material stream port 31 for operationally coupling the reactor vessel 30 to a source of the input material stream 24, at least one output material stream port 32 for facilitating removal of the output material stream 72.
Preferably each one of the reactor vessel 30s also may include an agitation system 40, a recirculation system, a pH adjustment system 60, a condenser 54, an input material stream flow control 34, atmoshpheric pressure control system 36, and an Oxidation Reduction Potential control system 38. The agitation system 40 is at least partially positioned within the reactor vessel 30 and is used for enhancing contact between the input material stream 24 and the culture of methanogenic archea 26 and for reducing foaming within the reactor vessel 30. In some cases an anti-foaming agent may be added into the reactor to further reduce foaming. The recirculation system 50 is also used to enhance contact between the input material stream 24 and the culture of methanogenic archea 26. The pH adjustment system 60 facilitates the maintenance of a pH of the methanogenic archea 26 combined with a mixture of the input material stream 24 and the output material stream 72. Typically if the pH falls below a predetermined level, a buffer solution is added into the reactor vessel 30, and if the pH increases above a second predetermined level, additional CO2 is introduced into the reactor vessel 30. The condenser 54 is preferably environmentally coupled to the output material stream 72 port 32, and allows a gaseous portion of the output material stream 72 to be separated from a non-gaseous portion of the output material stream 72. In at least one embodiment the condenser 54 is sixed such that the volume of the condenser 54 to the volume of the reactor is between 1:20 and 1:160. The input material stream flow control 34 is used to control the type and rate of material in the input material stream 24 being directed into the reactor vessel 30. The atmospheric pressure adjustment system facilitates the control and maintenance of atmospheric pressure within the reactor vessel 30. Typically the pressure utilized within the reactor vessel 30 is between 0.5 and 7 atmospheres. In at least one embodiment at “normal” atmospheric pressure the reactor in operation may maintain between 2 and 7 PSI of back pressure. The oxidation reduction potential adjustment system facilitates the maintenance of an oxidation reduction potential (“ORP”) of the methanogenic archea 26 combined with a mixture of the input material stream 24 and the output material stream 72. Typically if the ORP falls outside of a desired range a predetermined quantity of H2 or H2S is introduced into the reactor vessel 30.
In at least one embodiment, at least a portion of the input material stream 24 is the output of a gasifier 22. The gasifier 22 type may include steam reforming, air swept, or oxygen swept dependent at least in part on the type of materials to be gasified. The present invention accommodates a wide range of gasifier 22 input materials including corn stover, switch grass, wood waste products, municipal or landfill wastes, and other similar materials.
The input material stream 24 or streams directed into the reactor vessel 30 may include any of the following combinations:
As may be readily appreciated from reviewing the above listing, the present invention has significant tolerance to variations in the input material stream 24, and as such gas cleanup prior to introduction into the reactor vessel 30 may be significantly reduced or potentially eliminated. Further, for each of the combinations listed above, the input material stream 24 may be directed into the reactor vessel 30 as a single mixed stream, or as a combination of multiple streams each directed into the reactor vessel 30.
For sustained operation, the present invention may also include a growth media solution 65 for promoting the ongoing growth of the culture of methanogenic archea 26, as well as enhancing the production of methane by the methanogenic archea 26.
In an embodiment the growth media solution 65 includes both a macro ingredient solution 66 and a micro ingredient solution 67. Preferably, the macro ingredient solution 66 comprises KH2PO4, NH4CL, and NaCl. More preferably, the macro ingredient solution 66 comprises 75 to 300 grams of KH2PO4, 350 to 1600 grams of NH4CL, and 30 to 130 grams of NaCl dissolved in 20 to 40 gallons of deionized water. In at least one embodiment, the macro ingredient solution 66 comprises approximately 153.8 grams of KH2PO4, approximately 725.3 grams of NH4CL, and approximately 66.0 grams of NaCl dissolved in approximately 30 gallons of water.
In a preferred embodiment the micro ingredient solution 67 comprises Na2 nitrilotriacetates, MgCl2-6H2O, FeSO4-7H2O, CoCl2-6H2o, Na2MoO4-2H2O, NiCl2-6H2o, Na2SeO3, Na2WO4-2H2O. More preferably the micro ingredient solution 67 comprises 35 to 150 grams per liter of Na2 nitrilotriacetates, 25 to 100 grams per liter of MgCl2-6H2O, 6 to 30 grams per liter of FeSO4-7H2O, 0.07 to 0.30 grams per liter of CoCl2-6H2O, 0.07 to 0.30 grams per liter of Na2MoO4-2H2O, 0.15 to 0.60 grams per liter of NiCl2-6H2O, 0.01 to 0.1 grams per liter of Na2SeO3, 0.40 to 1.7 grams per liter Na2WO4-2H2O. In at least one embodiment, the micro ingredient solution 67 comprises approximately 70.5 grams per liter of Na2 nitrilotriacetates, approximately 50.8 grams per liter of MgCl2-6H2O, approximately 13.9 grams per liter of FeSO4-7H2O, approximately 0.15 grams per liter of CoCl2-6H2O, approximately 0.15 grams per liter of Na2MoO4-2H2O, approximately 0.30 grams per liter of NiCl2-6H2O, approximately 0.04 grams per liter of Na2SeO3, approximately 0.82 grams per liter Na2WO4-2H2O.
In an embodiment the micro ingredient solution 67 is prepared using deaerated water and maintained in anoxic condition in order to maintain iron ions as iron+3.
In at least one embodiment, the growth media solution 65 is prepared by first preparing the macro ingredient solution 66 under normal atmospheric conditions and then deaerating the macro ingredient solution 66. Concurrently, the micro ingredient solution 67 is prepared under anoxic condition. The micro ingredient solution 67 is added to the deaerated macro ingredient solution 66.
In a further embodiment the micro ingredient solution 67 is added to the deaerated macro ingredient solution 66 at a ratio between 1 part micro ingredient solution 67 to 100 to 400 parts macro ingredient solution 66.
In still a further embodiment the micro ingredient solution 67 is added to the deaerated macro ingredient solution 66 at a ratio of 1 part micro ingredient solution 67 to 250 parts macro ingredient solution 66.
In an embodiment the media growth solution is directed into the reactor vessel 30 through at least one media input port.
Preferably, the media growth solution is maintained under a nitrogen blanket.
In an embodiment the input material stream 24 comprises at least in part carbon dioxide and a percentage of carbon dioxide is converted into cellular biomass during exposure to the culture of methanogenic archea 26 is less than 20 percent.
In an embodiment the input material stream 24 comprises at least in part carbon dioxide and a percentage of carbon dioxide is converted into biomass during exposure to the culture of methanogenic archea 26 is between approximately 5 and 15 percent inclusive.
In an embodiment excess or dead biomass is selectively removed from the reactor through at least one biomass elimination port positioned on a lower portion of the reactor vessel 30.
In an embodiment the pH adjustment system 60 further comprises a pH buffer agent 61. The buffer agent 61 may be sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium bicarbonate, ammonia, ammonium, or ammonia nitrate. Preferably the buffer solution is prepared using deaerated water and maintained under nitrogen until introduction into the reactor vessel 30.
In at least one embodiment the buffer agent 61 is prepared as approximately a 1.0 Normal solution.
In another embodiment the pH buffer agent 61 is prepared as less than a 1.0 Normal solution.
In still a further embodiment, multiple buffer solutions, selected from the list of buffer solutions provided above are available, and a specific buffer solution or combination of buffer solutions are used based at least in part upon the rate of change of the pH within the reactor vessel 30. If the pH falls out of a predetermined desirable range, typically 7.6 to 8.6, then buffer solution is added to the reactor vessel 30.
In an embodiment the input material stream 24 is routed into the reactor vessel 30 at a rate of 0.5 to 4.0 scfm per 5 cubic feet of reactor vessel 30 volume.
In an embodiment the input material stream 24 is routed into the reactor vessel 30 at a rate of 1.0 to 2.6 scfm per 5 cubic feet of reactor vessel 30 volume.
In an embodiment the input material stream 24 is routed into the reactor vessel 30 at a rate of approximately 1.9 to 2.6 scfm per 5 cubic feet of reactor vessel 30 volume.
In an embodiment the input material stream 24 is routed into the reactor vessel 30 and through a sparger 56 positioned within the reactor vessel 30.
In an embodiment the sparger 56 creates bubbles approximately 1 micron to 10 microns in diameter.
In an embodiment the output material stream 72 is generated at a rate of between 10 and 150 volumes per effective reactor volume per day (“VVD”). As an illustrative example only, let us assume that a 1000 cubic foot reactor is used. Further let us assume that there is a headspace within the reactor that occupies approximately 200 cubic feet. Thus the effective reactor volume is 800 cubic feet. If the output material stream 72 for this illustrative example is produced at 100 VVD, then the resulting output would be 80,000 cubic feet, per day.
In another embodiment the output material stream 72 is generated at a rate of between 35 and 100 VVD.
In still another embodiment the output material stream 72 is generated at a rate of between 45 and 70 VVD.
In at least one embodiment, the input material stream 24, whether directed into the reactor as a blended gas or as individual gas streams, may include approximately four parts hydrogen to one part carbon dioxide. In the methanogenic reaction which follows, approximately 5 to 15% of the carbon dioxide is converted to cellular biomass through contact with the culture of methanogenic archea and the output material stream 72 comprises approximately 60 to 85% CH4. The output material stream 72 may also include hydrogen.
In another embodiment, the input material stream 24, whether directed into the reactor as a blended gas stream or as individual gas streams, may include approximately two parts hydrogen to one part carbon dioxide. In the methanogenic reactor which follows, approximately 5 to 15% of the carbon dioxide is converted to cellular biomass through contact with the culture of methanogenic archea 26, and the output material stream 72 comprises approximately 50 to 85% CH4. The output material stream 72 may also include carbon dioxide.
In yet another embodiment, the input material stream 24 whether directed into the reactor as a blended gas or as individual gas streams, or as multiple streams at least one of which comprises a combination of gases, may include between approximately two parts hydrogen, approximately five parts hydrogen and approximately one part carbon dioxide. In the methanogenic reaction which follows, approximately 5 to 15% of the carbon dioxide is converted to cellular biomass through contact with the culture of methanogenic archea 26. And the output material stream 72 comprises approximately 50 to 85% CH4. The output material stream 72 may also include carbon dioxide and/or hydrogen.
Depending upon the composition of the input material stream 24 provided, it may be desirous to direct the input material stream 24 through a gas filtering means 58 prior to directing the input material stream 24 into the reactor vessel 30. Several types of gas filtering means 58 are known, and may be selected at least in part based upon the composition of the input material stream 24. Examples of such gas filtering means 58 include, but are not limited to: Water Gas Shift Reactors, Pressure Swing Adsorption Reactors, Vacuum Swing Adsorption Reactor, and Membrane Filters.
Similarly, the output material stream 72 may be directed through a gas filtering means 58, prior to being stored, compressed, or otherwise utilized. The gas filtering means 58 for the output material stream 72 may be any one of a number of gas filtering means 58, including but not limited to: Water Gas Shift Reactors, Pressure Swing Adsorption Reactors, Vacuum Swing Adsorption Reactors, and Membrane Filters.
In at least one embodiment the output stream filtering means includes a methane output and a recycling output. The recycling output may be directed back into the reactor vessel 30.
The system may also include a thermal conditioning assembly operationally coupled to the reactor vessel 30, for helping to maintain an internal temperature for the reactor vessel 30 between 55 and 70 degrees Celsius, and more preferably, between 60 and 65 degrees Celsius.
The system may also include a second culture of methanogenic archea 28 for converting an input material 20into an output material. This second culture may be inoculated into the reactor vessel 30, or may be generated within the reactor vessel 30 during a prolonged operational phase for the system.
The system may also make use of multiple reactor vessels 30, with the reactor vessels 30 being connected in parallel between the input material stream 24 and output material stream 72. Each one of the multiple reactor vessels 30 may enclose an associated culture of methanogenic archea 26. The cultures of the multiple reactors need not necessarily be the same strain or type of methanogenic archea 26.
In at least one embodiment the input material stream 24 is directed into the reactor vessel 30 and the output material stream 72 is released from the reactor vessel 30 in a continuous manner.
In another embodiment the input material stream 24 is directed into the reactor vessel 30 periodically.
In still another embodiment the output material stream 72 is released from the reactor vessel 30 periodically.
The agitation system 40 may include an agitation drive means 41, and an impeller 44 operationally coupled to the agitation drive means 41. As an illustrative example of an agitation drive means 41 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 43 positioned within the reactor. The impeller 44 is thus operationally coupled to the motor.
In an embodiment the impeller 44 rotates at between 1100 and 2100 rpm during normal operation of the reactor. More preferable the impeller 44 rotates at between 1500 and 1800 rpm during normal operation.
In another embodiment the impeller 44 rotates at greater than 110% of the resonance of the reactor vessel 30.
It is important to note that the tip speed of the impeller 44 is critical and thus proper sizing is important. In at least one embodiment the tip speed of the impeller 44 is between 5 and 45 mph.
The recirculation system 50 selectively removes a portion of a combination of the culture of methanogenic archea 26 and the growth media through at least one recirculation outlet port 51 of the reactor vessel 30. The recirculation system 50 returns the portion of the combination into the reactor through at least one recirculation inlet port 52 of the reactor vessel 30.
In an embodiment the selective removal and returning of the portion of the combination is done at a rate of between 5 and 50 percent of the reactor volume per hour.
In another embodiment the selective removal and returning of the portion of the combination is done at a rate of between 10 and 20 percent of the reactor volume per hour.
In an embodiment the culture of methanogenic archea 26 comprises methanobacterim thermoautotrophicum or methanothermobacter thermautotrophicus.
With respect to the above description then, it is to be realized that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention.
Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.
