Patent Application
20060213370
This patent document pertains generally to biogas processing systems and methods, and more particularly, but not by way of limitation, to mobile biogas processing systems and methods.
Biogas is produced, for example, by anaerobic fermentation of animal wastes or other waste products. Raw biogas is typically primarily a mixture of carbon dioxide and methane with trace levels of hydrogen sulfide and water vapor. Raw biogas is combustible, and has been used to generate electricity.
Biogas can also be processed to produce a cleaned or enriched product that can be used, for example, as a substitute for natural gas. The primary constituent of natural gas is methane, the same primary constituent as biogas. Biogas with enriched methane content can be used to power a vehicle, for example.
Many sources of biogas are located at remote locations, such as rural farms. Construction of permanent biogas processing systems at farms can prohibitively expensive or inefficient. Transport of methane-producing waste products to processing facilities can also be impractical and inefficient due to transport and storage concerns. Improved biogas processing systems and methods are needed.
An example mobile biogas processing system includes a mobile platform; a first compressor physically coupled to the mobile platform and having a biogas input and a compressed biogas output, a first pump physically coupled to the mobile platform and having a water input and a water output, and a first scrubber tower physically coupled to the mobile platform. The first scrubber tower includes a mixing chamber, a compressed gas input, a water input coupleable to the water output of the first pump, a water output, and a processed gas output. The mixing chamber is in communication with the compressed gas input, the compressed gas output, the water input and the water output. In an example, the mobile biogas processing system also includes a second scrubber tower physically coupled to the mobile platform, the second scrubber tower having a mixing chamber, a compressed gas input in communication with the output of the first scrubber tower, a water input, a water output, and a processed gas output. In an example, the mobile biogas processing system also includes a flash tank physically coupled to the mobile platform, the flash tank having a water input coupled to the water output of the first scrubber, a water output, and a gas recirculation output.
In an example, the mobile biogas processing system also includes a means for removing water and/or hydrogen sulphide from biogas before the biogas enters the first compressor.
In an example, the mobile platform includes one or more skids, a plurality of skids, a truck bed, a trailer, and/or a container.
In an example, the mobile biogas processing system also includes at least one engine operable on methane or biogas, and a hydraulic system coupled to the gas-powered engine
Another example mobile biogas processing system includes a compression system, a scrubbing system, a flash system. The compression system has an input in communication with a biogas source, a compressed biogas output. The scrubbing system has a biogas input in communication with the compressed biogas output of the compression system, a water input, a processed gas output, and a water output. The flash system has a water input in communication with the water output of the scrubbing system, a water output, and a gas output in communication with a gas recirculation line coupled to the compression system. At least the scrubbing system is physically coupled to the mobile platform. In an example, the system also includes a biogas storage system that is physically coupled to the mobile platform. In an example, the scrubbing system includes a plurality of scrubber towers physically coupled to the mobile platform
An example method includes coupling a first biogas compressor to a mobile platform, and coupling a first scrubber tower to the mobile platform. The mobile platform, biogas compressor, and first scrubber tower are deliverable to a location having a biogas source. In an example, the method further includes coupling an output of the biogas compressor to a biogas input on the first scrubber tower, and/or coupling a flash tank to the mobile platform and coupling a scrubber tower water outlet to the flash tank. In an example, the method also includes supplying a biogas to the compressor, delivering compressed biogas from the compressor to the scrubber tower, delivering water to the scrubber tower, and exposing the compressed biogas to the water in the scrubber tower, and outputting a processed gas from the scrubber tower.
In an example, the method further includes supplying air to the scrubber tower and bleeding biogas or methane from the scrubber tower to prepare the scrubber tower for transport.
In an example, the method further includes remotely monitoring the processing of biogas, and sending a command from a remote location to adjust at least one processing parameter and electrically executing the command. In an example, the method includes operating the mobile biogas processing system of claim so as to produce a processed gas that includes about 90% to about 100% methane.
In the drawings, which are not necessarily drawn to scale, like numerals describe substantially similar components throughout the several views. Like numerals having different letter suffixes represent different instances of substantially similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.
The following detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments, which are also referred to herein as “examples,” are described in enough detail to enable those skilled in the art to practice the invention. The embodiments may be combined, other embodiments may be utilized, or structural, logical and electrical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.
In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one. In this document, the term “or” is used to refer to a nonexclusive or, unless otherwise indicated. Furthermore, all publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference.
An example mobile biogas processing system includes a mobile platform and biogas processing components mounted on the platform. The mobile platform includes one or more skids, a trailer, a truck, and/or a container, for example. The mobile platform is transportable to a remote site such as a farm where biogas is available for processing. In some examples, the components of the processing system are designed for road and/or rail transport and are sized to process farm-scale quantities of biogas. In an example, the biogas processing system includes sensing and communication systems that allow for remote monitoring and remote control of the processing system, which can be advantageous because staffing is not necessarily available at all times at remote processing locations. In some examples, the system requires little or no on-site assembly.
Biogas processing has been conducted at large fixed processing plants. Processing plants typically remove carbon dioxide from biogas through water absorption, polyethylene glycol absorption, carbon molecular sieves, or membrane separation. Hydrogen sulphide is removed by air/oxygen dosing to digester biogas, iron chloride dosing to digester slurry, or other processes. In some instances, siloxane, halogenated hydrocarbons, oxygen or nitrogen are also removed from biogas. The present mobile systems and methods include some or all of the capability of plant-based systems, and make this capability available at remote biogas sites, such as farms. Biogas sites include farms, landfills, wastewater treatment plants, and other locations where organic material is generated or gathered. Biogas is generated from a variety of sources, such as waste from cattle, hogs, chickens, turkeys and other animals, as well as human waste and plant products.
Water absorption or “water scrubbing” techniques are predicated on the relative solubility of methane and carbon dioxide in water. Carbon dioxide is more soluble in water under pressure than at atmospheric pressure. Methane is mostly insoluble even at elevated pressures. Pressurizing a methane/carbon dioxide biogas mixture in the presence of water drives carbon dioxide into solution in the water but drives little methane into solution. The resulting processed biogas has an enriched methane content because some or all of the carbon dioxide has been processed out of the gas and into solution in the water. The optimum relative solubility difference for methane and carbon dioxide is in the range from 150 to 200 pounds per square inch gauge (psig). In some systems, the carbon dioxide-laden water generated in the water scrubbing process is passed to a flash vessel operated at a lower pressure than the water absorption system. A portion of the methane absorbed in the water during the scrubbing process can be recaptured in the flash vessel, because methane desorbs from water more easily than carbon dioxide.
Raw biogas is supplied to a biogas compression system 300. In some embodiments of the invention, the raw biogas is produced at a biogas site utilizing anaerobic digestion of organic materials, e.g., manure, e.g., human, hog, turkey, chicken and/or cattle manure. The organic materials may be located at a biogas site, e.g., a landfill or a farm. Raw biogas typically includes a mixture of carbon dioxide and methane with trace levels of hydrogen sulfide and water vapor.
In an example, the compression system 300 first removes at least some of the hydrogen sulfide and water vapor and then compresses the biogas. In one example, the moisture content is reduced to less than about 1.4%, and the biogas is compressed to an operating pressure of about 150 to about 200 psig. The compressed operating pressure is a function of the temperature, carbon dioxide mole fraction in the gas, and the desired methane purity
The compressed biogas is supplied to the biogas scrubber system 400. The scrubber system 400 is also connected to a water supply system 500 that pumps water into the scrubber system. The gas flows in counter-flow or cross-flow with the water. As the gas flows past the water, carbon dioxide is absorbed into the water. Some methane is typically also absorbed into the water. However, substantially less methane is absorbed into the water than carbon dioxide because of the difference in relative water solubility between methane and carbon dioxide. In an example, at about 200 psig, nearly all of the carbon dioxide in biogas is absorbed into water and about 5% of methane is absorbed, even though methane is the more prevalent component in biogas.
In one example, the scrubber system 400 includes two or more sequential scrubber towers that move biogas and water in counter-flow. In an example, the scrubber system includes one or more vertical columns that contain Rashig rings, sieve plates, bubble cap or disk and donut gas/liquid contact devices. In another example, the scrubber system 400 includes one or more cross-flow chambers in which water is passed in cross-flow over the biogas.
In an example, water output from the scrubber returns to the water supply system 500. In an example, methane is reclaimed from the water output of the scrubber system 400. In an example, the reclaimed methane is recirculated into the biogas compression system 300.
The scrubber system 400 outputs a processed gas. In an example, the processed or “cleaned” gas is crude methane. The processed gas is delivered to an analysis and final processing system 600. In an example, the analysis and final processing system 600 samples the processed gas to determine its makeup. The processed gas is burnable for energy. In an example, water vapor and trace contaminants are removed from the processed gas. In an example, the analysis and final processing system also further compresses the gas to prepare it for transport via truck, pipeline or other transport as compressed natural gas (CNG) or liquefied natural gas (LNG). In an example, the gas is fully processed by the mobile biogas processing system 100. In another example, the processed gas is post-processed on site or off site.
In some embodiments of the invention, the processed gas contains from about 90% to about 100% (e.g., at least about 95%; at least about 98%; about 90%; about 91%; about 92%; about 93%; about 94%; about 95%; about 96%; about 97%; about 98%; about 99%; or about 100%) methane gas.
In an example, the systems 300, 400, 500, 600 are mounted on a single unitary platform, such as a truck bed or a shipping container.
As water moves down the tower, biogas flows up the tower and exits near the top 421 of the tower 411. At least some of the carbon dioxide in the gas absorbs into the water. The gas exiting the top of the tower has a higher concentration of methane than the gas entering the bottom of the tower because some of the carbon dioxide is removed from the gas.
In the example shown in
Water output from the scrubbers is directed to an optional flash tank 413. The flash tank 413 subjects the water to a pressure decrease, which pulls at least some of the methane out of the water. In an example the water output from the scrubbers is at about 150 to about 200 psig, and the flash tank is at about 25-50 psig. Because of the difference in solubility between methane and carbon dioxide, methane desorbs out of the water more quickly than carbon dioxide. In the example shown in
Water output from the CO2 stripper 516 has reduced CO2/H2S or no CO2/H2S. In an example, a pH monitor 540 detects the pH of water before and after passing through the CO2 stripper 516. The water output from the CO2 stripper 516 is supplied to the pumps 517, 518, which recirculate the water through the stripper system. In an example, a water makeup valve 535 is provided to replace water that is lost through evaporation in the CO2 stripper or elsewhere in the system. In an example, the water makeup valve 535 is coupled to a water tank or other reservoir that is part of the mobile biogas processing system. This allows the water supply system to be self contained and operable with no external supply of water. A self-contained system is advantageous, because it enables the gas processing system to operate regardless of the on-site water situation. In another example, makeup water is provided externally, but the majority of the scrubbing system water requirement is met by recirculated water. In other examples, external water supplies or containment areas are used. For example, desorbtion can be handled by a pond or reservoir. In other examples, desorbtion is accomplished using a cooling tower or an open vertical pipe.
In an example, a valve draws off a portion of the dried and purified gas to be burned by a combustion engine that powers some or all of the various motors in the biogas processing system through hydraulic or mechanical connections.
Returning to
The tower 700 includes a demist pad 750 near the top 720 of the tower. The demist pad 750 removes water from the upwardly-flowing gas stream.
The systems 811, 812, 813, 814 are separable for transport. In an example, the systems 811, 812, 813, 814 are modular, so that one of the systems can be replaced or upgraded and integrated with the other systems to process biogas. For example, scrubbing capacity can be upgraded by replacing the scrubbing system 812 with a larger system.
In an example, the processing of biogas is monitored remotely, at step 1135. A computer coupled to sensors and a communications link detects processes characteristics such as methane quality, flow rates, pressures, and/or temperatures, and relays such information through the communication link. Remote monitoring allows a system to be run without personnel on site. At 1140, a command can be issued from a remote location to adjust at least one processing parameter. In an example a processing parameter is adjusted through the computer. In another example, a person is directed to the site to tend to the system.
At 1145, processed biogas is output from the second scrubber. The processed gas exiting the second scrubber has a lower carbon dioxide content and higher methane concentration than the raw biogas. In an example, crude methane is output from the second scrubber.
At 1150, biogas is burned to generate power for compressors or pumps in the biogas processing system. In another example, processed gas or methane is burned to generate power.
The system is prepared for transit by supplying air to the system at 1155 and bleeding biogas from the system at 1160.
Gas processing techniques are described in U.S. Pat. Nos. 3,981,800 and 4,409,102 and in Perry's Chemical Engineer Handbook, pp. 14-28 to 14-30 (4th Ed. 1963).
It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.
The Abstract of the Disclosure is provided to comply with 37 C.F.R. §1.72(b), requiring an abstract that will allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, various features may be grouped together to streamline the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter may lie in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment.
This application claims the benefit of priority, under 35 U.S.C. 119(e), to U.S. Provisional Application Ser. No. 60/660,890, filed on Mar. 11, 2005, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60660890 | Mar 2005 | US |
