Patent Application
20230250374
This disclosure relates generally to anaerobic digestion and related processing of gaseous materials, and in particular, a covered anaerobic digest system and the installation or operation thereof.
Anaerobic digestion is a process that can be used to convert a wide range of biomass materials into useable gas, such as a gas comprising mostly methane and carbon dioxide (CO2). Carbon dioxide can be used for a variety of purposes such as food and industrial processing. Methane, which may be more valuable than carbon dioxide, can be used as a direct replacement for fossil fuels such as oil and natural gas. When methane is generated from anaerobic digestion from organic matter (i.e., biomass), it is often referred to as biomethane.
Biomethane can be used as a fuel (e.g., for combustion engines or fuel cells) to provide power and heat. When biomethane is burnt, the exhaust typically comprises only carbon dioxide and water. In principle, the quantity of carbon dioxide released equals the amount that would have been released had the biomass had been allowed to aerobically decompose naturally; therefore, methane produced in this way is effectively considered a zero-carbon fuel. The use of anaerobic digestion of biomass to produce methane is therefore seen as an effective way to reduce the level of carbon dioxide in the atmosphere and help to mitigate climate change. Patent Application PCT/IB2020/054392, titled “Anaerobic Digester and Mobile Biogas Processing Plant,” describes an anaerobic digester and certain gas processing devices and methods.
Because anaerobic digestion systems are often outdoors or otherwise exposed to natural elements (e.g., rain and snow), operation and monitoring of such systems may be difficult. Accordingly, there is a need for improved anaerobic digestion systems and methods, as well as associated gas processing.
According to embodiments, devices and systems are provided, such as a digester. The digester may be, for example, an anaerobic digester used to process biomass. In certain aspects, the digester comprises a biomass storage container, a cover positioned over the biomass storage container, and one or more weights positioned on a top surface of the cover. The cover and at least one of the weights can form a pleated feature (e.g., a corner or other edge). At least one of the weights may be positioned at the center of the cover, with one or more of the other weights arranged in each corner of the cover. In some embodiments, the cover (and/or the storage container) is rectangular or square and the weights form a pleated corner in each of the corners. Other shapes having corners may be used. The digester may comprise one or more subsystems, including thermal management systems, gas processing systems, status monitoring systems, a plant for mixing/thermal control of a slurry, water collection and management systems, and/or energy recovery and storage systems. While described with one or more pleated corners in this example, some embodiments may be implemented without pleated corners. This could include, for instance, pleats in other locations (e.g., centrally) or no pleats at all. In some embodiments, the cover is configured to expand from a first position to a second position upon an increase in gas generated in the biomass storage container.
According to embodiments, an anaerobic digester is provided, which comprises a biomass storage container (e.g., a slurry lagoon with one or more tapered sidewalls) and a cover positioned over the biomass storage container. In certain aspects, the cover is sealed at an outer edge of the anaerobic digester to form a water collection region. The water may be, for instance, rainwater and the cover may be a gas membrane. Where the water covers one or more gas seals, it may be monitored to indicate a leak. In certain aspects, the cover can be held in place, for example, by weighted tubes that form pleated corners on the cover. In some embodiments, an angled bracket (e.g., formed by a portion of a gutter ring beam) can be used, such that the bracket is configured to confine the water in the water collection region. The anaerobic digester may also comprises one or more liners, such as a lagoon liner membrane or a slurry cover membrane. In some embodiments, at least one of the membranes, such as an additional intermediate membrane, is selectively permeable between methane and CO2. However, in some instances, at least one of the membranes is non-permeable to biogas and its constituent materials (e.g., both the lagoon liner and slurry cover can be non-permeable). In certain aspects, the cover, bracket, slurry cover membrane, and lagoon liner membrane are all attached to an installation post, for instance, with one or more clamps. In some embodiments, an outer membrane clamp and inner membrane clamp are used. This can prevent biogas from coming into contact with portions of the digester that are susceptible to corrosion. The anaerobic digester may further comprise one or more sub-systems, such as a gas filtrations system, a thermal management system, a monitoring system, a water re-use system, an energy recovery system, and a plant for mixing/thermal control of a slurry.
In some embodiments, at least one weight is positioned on a top surface of the cover. The weights may be, for example, tubes or pipes. The weights can be arranged to create tension on the cover and prevent flapping of the cover in the wind. In some embodiments, where the cover is rectangular or square, at least one of the weights forms a pleated corner of the cover. Additionally, a weight can be arranged in each corner of the cover. However, other weights can be used, for instance, in a center region of the cover or on a slurry membrane of the biomass storage container. In some embodiments, a weight tube is connected to a water collection region of the anaerobic digester and configured to move water from the cover to the collection region (or vice-versa).
According to some embodiments, a method of assembling an anaerobic digester may comprise, for instance, the steps of placing a cover over a storage container, placing one or more weights (e.g., to form pleated corners), and assembling/attaching any thermal or water management system, or other system described herein. In some aspects, the method may also include optionally filling the weights. Other steps in the method could include: (i) digging or otherwise preparing a slurry lagoon with tapered sidewalls and/or a liner membrane; (ii) installing one or more gas membranes, including one or more semi-permeable membranes; (iii) sealing the digester; and (iv) filling the digester with biomass or otherwise operating the digester, including operating any of the associated systems. This could include, for example, extracting and processing gas generated in the digester after installation.
According to embodiments, a thermal management system is provided for an anaerobic digester. The system may comprise, for example, a circulation device (e.g., comprising one or more pumps) and plurality of tubes connected to the circulation device. In this example, the plurality of tubes could comprise: (1) one or more tubes on a surface of an anaerobic digester cover; and/or (2) or one or more tubes on a surface of (e.g., on a surface of a liner of) or within a biomass storage container of the anaerobic digester. Other tubes may be used. In some embodiments, the plurality of tubes are water-filled. The circulation device can be configured to flow warm water from the surface of the anaerobic digester cover to the biomass storage container. This could improve an anaerobic digestion process in the container. Similarly, the system can be configured to flow warm water from the biomass storage container surface to the cover. This could be used, for instance, to melt snow on the cover, which can cause damage to the digester and/or its components.
According to embodiments, a status sensing and monitoring system is provided. For instance, an anaerobic digester or similar system is can be equipped with such a system. This may comprise, for example, a biomass storage container (e.g., a slurry lagoon); a cover (e.g., a gas membrane) positioned over the biomass storage container; and one or more sensors configured to indicate a gas or slurry state (e.g., level) of the anaerobic digester. In some embodiments, the anaerobic digester comprises a cover weight and at least one of the sensors is a pressure sensor attached to (e.g., within) the weight. In some embodiments, at least one of the sensors is a line-of-sight sensor (e.g., a camera or other optics-based device) configured to monitor a top level of the cover or a slurry membrane. In some embodiments, at least one of the sensors is an angular sensor array on the cover or slurry membrane (e.g., a festoon string of gyroscopic sensors). Additionally, the system may also include a processing circuit (e.g., a processor, memory, and transmitter) configured to determine and report the gas or slurry state based on measurements form the one or more sensors. The reporting may be locally, over a wireless channel, using the Internet, etc. In certain aspects, the one or more sensors of the system may be arranged on a top-most membrane/cover, an intermediate membrane, a slurry-level membrane, or any other membrane of a digester. Additionally, one or more sensors may be mounted on other components, including the storage container itself.
According to embodiments, an energy storage and recovery system is provided. The system may comprise one more storage containers of gaseous or liquid materials; a gas pressure driven generator (e.g., generating mechanical and/or electrical energy) coupled to the one or more storage containers and configured to generate power using exhaust gas vented from the one or more storage containers; and a gas buffer configured to store at least a portion of the exhaust gas after it is used by (e.g., passes through) the generator. The materials may include compressed gas or cryogenic liquids in some embodiments, and the generator may be a turbine. In certain aspects, the gas buffer is a part of an anaerobic digester, such as any of the digesters described herein. For example, the buffer may be a region located between a slurry region and a cover of the anaerobic digester. Other buffers may be used in some embodiments. The system may further comprise a gas processing system configured to extract the gas from the gas buffer and store it in the one or more storage containers. Processing stages could include, for example, a compressor, dryer, cooler, liquid storage vessel, etc. In some embodiments, the system is part of a mixed electricity generating system comprising one or more of photovoltaics and wind energy devices (e.g., a windmill). The gaseous or liquid materials may be, for instance methane or CO2 from biogas in some embodiments.
According to embodiments, a method for energy recovery and/or storage is provided. The method can include, for instance, the following steps: (1) venting gas from one more storage containers of gaseous or liquid materials (e.g., compressed gas or cryogenic liquid); (2) generating electricity using the vented gas (e.g., operating a turbine using the vented gas); and (3) passing remaining vented gas to a gas buffer. In some embodiments, the method further comprise storing gas from the gas buffer in the one or more storage containers, which can include compressing the gas from the gas buffer, and in some cases, the gas from the buffer was previously used to generate electricity in the generating step. That is, the cycle may be repeated. In certain aspects, at least one of the venting gas and storing gas steps is based at least in part on the supply of electricity from a photovoltaic, wind energy device, and/or battery. Additionally, energy used for the storing step can be provided by a photovoltaic, wind energy device, and/or battery. In some embodiments, before the venting step, the method includes generating gas in an anaerobic digester and storing it in the one or more storage containers, wherein the step of passing the remaining vented gas to a gas buffer comprises passing the remaining vented gas to the anaerobic digester used to generate the gas.
A covered slurry lagoon according to embodiments, and methods of operating and covering such a slurry lagoon, can have certain benefits. One benefit may be controlling the amount of rainwater that enters the lagoon, thereby minimizing the necessary size of the lagoon for an application. Another benefit may be an edge sealing system that, when filled with water, permits the monitoring/detection of leaks in one or more seals. Another benefit may be an edge sealing system that directs rainwater into a storage system such that the collected rainwater can be used for a variety of farmyard tasks. Another benefit may be an edge sealing system that minimizes contact between the metallic parts of the covered lagoon and the biogas generated or stored therein, thus reducing the possibility of corrosion.
According to embodiments, methods and devices are provided for monitoring the amount of methane or slurry in an anaerobic digester (e.g., in one or more gas or slurry storage regions of the digester), which may be required for remote control and monitoring of the lagoon and any associated gas recovery plant.
According to embodiments, methods and devices are provided for using water-filled weight tubes in the pleats of an outer cover to reduce movement of the cover due to buffeting by winds, and reduce fatigue in the outer cover.
According to embodiments, methods and devices are provided for pumping heated water through one or more weight tubes to remove ice or snow. Similarly, methods and devices are provided for recovering heat from the outer cover and pumping this heat into the slurry. This can increase the digestion rate.
According to some embodiments, methods and devices are provided for using a gas buffer store (e.g., of an anaerobic digester) as part of an energy storage and recovery system.
Other features and characteristics of the subject matter of this disclosure, as well as the methods of operation, functions of related elements of structure and the combination of parts, and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures.
The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments of the subject matter of this disclosure. In the drawings, like reference numbers indicate identical or functionally similar elements.
While aspects of the subject matter of the present disclosure may be embodied in a variety of forms, the following description and accompanying drawings are merely intended to disclose some of these forms as specific examples of the subject matter. Accordingly, the subject matter of this disclosure is not intended to be limited to the forms or embodiments so described and illustrated.
Unless defined otherwise, all terms of art, notations and other technical terms or terminology used herein have the same meaning as is commonly understood by persons of ordinary skill in the art to which this disclosure belongs. All patents, applications, published applications and other publications referred to herein are incorporated by reference in their entirety. If a definition set forth in this section is contrary to or otherwise inconsistent with a definition set forth in the patents, applications, published applications, and other publications that are herein incorporated by reference, the definition set forth in this section prevails over the definition that is incorporated herein by reference.
Unless otherwise indicated or the context suggests otherwise, as used herein, “a” or “an” means “at least one” or “one or more.”
This description may use relative spatial and/or orientation terms in describing the position and/or orientation of a component, apparatus, location, feature, or a portion thereof. Unless specifically stated, or otherwise dictated by the context of the description, such terms, including, without limitation, top, bottom, above, below, under, on top of, upper, lower, left of, right of, in front of, behind, next to, adjacent, between, horizontal, vertical, diagonal, longitudinal, transverse, radial, axial, etc., are used for convenience in referring to such component, apparatus, location, feature, or a portion thereof in the drawings and are not intended to be limiting.
Furthermore, unless otherwise stated, any specific dimensions mentioned in this description are merely representative of an exemplary implementation of a device embodying aspects of the disclosure and are not intended to be limiting.
As used herein, the term “adjacent” refers to being near or adjoining. Adjacent objects can be spaced apart from one another or can be in actual or direct contact with one another. In some instances, adjacent objects can be coupled to one another or can be formed integrally with one another.
As used herein, the terms “substantially” and “substantial” refer to a considerable degree or extent. When used in conjunction with, for example, an event, circumstance, characteristic, or property, the terms can refer to instances in which the event, circumstance, characteristic, or property occurs precisely as well as instances in which the event, circumstance, characteristic, or property occurs to a close approximation, such as accounting for typical tolerance levels or variability of the embodiments described herein.
According to embodiments, many types of materials may be digested, including the anaerobic digestion of biomass. To achieve the most beneficial impact with respect to climate change, using anaerobic digestion to limit or eradicate “fugitive” emissions of methane (such as those that are currently created by the poor management of animal manures such as cow and pig slurry in open lagoons) may be most effective. Specifically, the use of open-slurry lagoons in the agriculture sector can result in very high levels of fugitive methane emissions. By sealing the slurry lagoon to prevent aerobic digestion, the methane can be contained. This practice can be advantageous for the purposes of limiting or eradicating “fugitive” emissions of methane, and in embodiments disclosed herein can also provide for considerable operational benefits. Such benefits may include reduced nitrogen loss where nitrogen is contained in the digestate (i.e., the material remaining after the anaerobic digestion of the biomass), which can in turn reduce the need for fertilizer when the digestate is spread back onto the land. Another benefit may include reduced handling and management of slurry. This is because rain water is prevented from entering the covered lagoon, meaning that the digestate is more concentrated and there is less to spread. Another benefit may be reduced risk of overspill because rain water is prevented from entering the covered lagoon, and in turn minimizes the possibility of leakage of raw slurry into waterways. Another benefit could include reduced greenhouse gases. Where biomass (such as waste or spoiled animal feed) is managed by composting aerobically and in an uncontrolled manner, the energy held in it is lost as heat during this process, and may result in large quantities of methane and nitrous oxides, both powerful greenhouse gases. Such greenhouse gases are reduced, however, with the use of a sealed slurry lagoon, such as provided by embodiments disclosed herein. Another benefit may be reduced energy demands This is because anaerobically generated methane may be used as fuel for a generator, for instance to generate electricity and heat that can be used on the farm, thereby offsetting its electricity and energy usage. Where the installation cost of a covered slurry lagoon is kept low, for instance, the above benefits can provide a reasonable return on investment for small- to mid-sized farms as compared to an open slurry lagoon.
Excess methane derived from one or more embodiments can be used to generate power that is then injected into the electricity grid, or alternatively processed and upgraded for injection into the mains gas grid.
An abundant source of biomass is grass cuttings, such as on managed land including gardens, sports fields, roadside verges, and golf courses. Currently, either the grass cuttings are left where they fall or are collected and composted. Either way, this is carried out aerobically, thereby losing the methane generation potential as wasted heat. In addition, much of the northern hemisphere is covered in vast areas of unmanaged or under-utilized grassland that could be used to generate biomethane. As is the case with small, remote farms, however, it is difficult to realize the true value of methane producible through this process, due to, for instance, the remote location of manage or unmanaged grasslands, or the lack of electricity or gas-grid infrastructure. The financial and environmental value of this abundant form of renewable and zero carbon energy cannot be economically realized, leaving it effectively land-locked. Embodiments can address one or more of these issues.
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In certain aspects, the digester is a biogas storage container with a semi-permeable membrane separating the biogas storage region into a first space and a second space, such that the first space is configured to be methane enriched and the second space is configured to be CO2 enriched. The first and second space may be, for instance, on either side of membrane 138 in some embodiments. In some embodiments, the semi-permeable membrane comprises a stretched polytetrafluoroethylene-based material or silicone. In some embodiments, the cover positioned over the container is transparent, and is configured to provide passive solar heating (e.g., to the slurry). The cover can be made of numerous materials. In an example, the material is strong, chemically inert and immune to damage from ultraviolet light, such as Ethylene Tera Fluoro Ethylene (ETFE), though other materials may be suitable. While illustrated with a single semi-permeable membrane 138, multiple membranes may be used (e.g., 2, 3, 4, 5, etc.) in some embodiments, thereby creating more than two gas spaces. For example, there may be an additional membrane, and the first and second membranes would then separate the container into three spaces—a first space, second space, and third space that would contain more pure methane than the first space. One or more of the spaces formed by membranes (e.g., membrane 138) in the digester 100 can serve as a receiving or extracting spaces, for instance, when used as a buffer for an energy recovery and storage system. In some embodiments, it is the uppermost space (or whichever space comprises the cleanest biogas). In some embodiments, a gas processing (e.g., cleaning) system may draw from one or more of the spaces.
In certain aspects, the digestion system 100 may also include an input for receiving biomass (such as slurry) into the biomass storage container. Additionally, anaerobic digester 100 may include output valves coupled respectively to the second space and first space. That is, the biogas located within the biogas storage regions (e.g., in buffer 116) of digester 100 may be removed by pipes or hoses connecting to one or more of output valves. Such pipes and hoses may connect to one or more other systems described herein, including for gas processing, energy storage, and energy recovery. In embodiments, the second space and the remainder of the biomass storage container may be coextensive. That is, in some embodiments, there may be no physical separation between the biomass storage and the various gas regions.
According to some embodiments, one or more of the gas cover 104, separation liner 106, any membranes 138, and lagoon liner 114 are held in place by a bracket element 118. Bracket 118 may be mounted, for instance, to an installation post 120 in ground 112b. The bracket 118 may be a portion of a beam. In certain aspects, the bracket 118 shown in
In certain aspects, the lagoon cover 104 eliminates the extra capacity needed to cope with and store rainfall on the lagoon. The rainfall on an open lagoon has the effect of diluting the contents—the extra volume has to be accommodated in a larger sized lagoon.
According to embodiments, the system 100 can include one or more additional sub-systems. This could include, for instance, thermal management 124, energy storage and recovery 126, gas processing 128, and slurry mixing 130. Gas processing 128 may include, for instance, the extraction of gas from the biomass storage region 102 to the gas buffer 116 under cover 104. This is further illustrated, for instance, in
With respect to slurry mixing plant 130, embodiments may include an in/out pipe 132a; one or more mixing pipes 132b and 132c; and one or more angled mixing elements 134. According to embodiments, the mixing elements 134 are angled relative to the base of the lagoon, and can have an angle that matches the angle of the sides of the lagoon in the slurry region 102. In certain aspects, the mixing plant 130 may perform, or otherwise be part of, a thermal management system. In some embodiments, the mixing plant 130 contains one or more sensors for monitoring the temperature or PH of the slurry. For instance, the slurry may flow past one or more of such sensors, for instance, mounted within the plant 130 housing or the mixing pipes. Such information can be used for control of the overall system 100.
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According to embodiments, a membrane clip strip 210 may be used to connect edge portions of liner 114 (or any other membrane) to an upper edge of the bracket 118. Additionally, an outer membrane clamp 202 and an inner membrane clamp 204 may be used to secure one or more of the gas cover 104, separation liner 106, and lagoon liner 104 to the installation post 120. The clamps may have, for instance, an “L” shape. In some embodiments, the shape of the clamps (alone or taken together) match the shape of a water collection region. In some embodiments, the seal can be improved with one or more gaskets 208 (e.g., PVC closed cell foam gaskets). The arrangement 200 of
According to embodiments, sour gas can be extracted 231 (e.g., from a slurry region), processed by system 128, and returned to a gas storage region as refined gas 232.
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In embodiments, system 124 may function as a heating system (e.g., a closed loop heating system), in which solar-heated water from gas cover 104 (e.g., through weight tubes, such as weights 108) can be circulated to or through to slurry, such as slurry membrane 106 (e.g., through weight tubes, such as weights 110) to heat the biomass storage 102 of a lagoon. Similarly, hot water from a system process (e.g., anaerobic digestion in the lagoon) can be circulated to/or through the gas cover (e.g., through weight tubes) to prevent build-up of snow or ice, which can damage the system 100. In this respect, system 124 may include one or more ice/snow defrosting circuits 302, and a slurry heating circuit 304. These circuits may be internal or external to a housing of system 124, for instance integrated into one or more tubes/piping or not, and may be co-located or separately located from each other. According to embodiments, one or more of the circuits comprises a loop of tubing together with a pump and a heating element. The heating element may be fed, for instance, from either waste electricity or waste heat from another process, either directly or indirectly via a heat exchanger. In this example, hot water may be circulated (e.g., using a pump) to or from the cover 104 via tube or pipe/tube 306a, while tube or pipe 306b is used for cold water. Similarly, hot water may be circulated to or from the slurry membrane 106 via tube or pipe 308a, while tube or pipe 308b is used for cold water. While illustrated with different pipes/tubes, a single pipe/tube may be used in some embodiments. Additionally, where different pipes/tubes are used, such piping may be dedicated based on direction as opposed to temperature. For both 306 and 308, the water may be moved through a weighted tube as described elsewhere in this disclosure. That is, a weighted tube may be used for multiple purposes, including stabilizing a cover (e.g., 104 or 106) while also moving water for thermal management of the system 100. In some embodiments, rainwater management 310 can be used to move water from cover 104. This could be, for instance, flowed through a weight, the collection or runoff, or utilize a pump. In some embodiments, excess rainwater is pumped off from a top of gas cover 104 to collection region 122, or vice-versa.
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According to embodiments, system 400 may include a covered slurry lagoon 401 comprising a slurry stored 402 therein and a gas buffer region 404, for example, as described with respect to
System 400 may further include one or more elements for cleaning or liquefaction of gas (e.g., methane) for cryogenic storage. This may include, for instance, the use of a cold store 438 or other cooler 436. A liquefier element 428 can convert gas from the gas buffer or bottle storage to liquid form (e.g., convert methane gas to liquid methane) using one or more cooling/refrigeration components, such as a Joule Thompson unit, other cryocoolers (e.g., a Sterling cooler), a sacrificial liquid (e.g., liquid nitrogen), or Brayton cycle device. Additionally, one or more cooling stages may be cascaded. An additional cooling element (e.g., a Sterling cooler 430) can be used to reduce the overall temperature of a liquid storage vessel 434. In the example of
According to embodiments, system 400 may further include one or more processing and control components, such as apparatus 500. Such processing and control components can be used to monitor the availability of energy from other sources (e.g., photovoltaic or wind), receive communications for on-demand processing, open or close one or more connected valves (e.g., to vent gas from storage) of the system 400, monitor storage levels, and activate elements (e.g., a generator or compressor). In embodiments, one or more steps of process 450 may be responsive to or otherwise based on such monitoring and/or communications. For example, the system may be configured to store energy (e.g., in bottle storage) when energy is available from other sources, and generate energy (e.g., with a generator) when energy from other sources is not available. Such actions may be taken by activating one or more components of system 400, for instance, in response to an indication by apparatus 500.
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In some embodiments, the process may optionally begin with step 452, in which gas is generated in an anaerobic digester (e.g., system 100) and then stored in one or more storage containers. Such storage containers may include, for instance, high pressure gas storage and/or cryogenic liquid storage. The storage step may include cleaning, compression, and/or liquefaction of biogas. While anaerobic digestion is used as an example, the energy recovery process 450 may be used with stored gaseous or liquid materials derived from other sources. That is, system 400 and process 450 are not limited to biogas in all embodiments. According to embodiments, one or more aspects of step 452 may be based on and/or responsive to the availability or price of energy from other sources (e.g., photovoltaic, wind, mains electric).
Step 454 comprises venting gas from one more storage containers of gaseous or liquid materials (e.g., compressed gas or cryogenic liquid such as methane). In some embodiments, the gas is biogas.
Step 456 comprises generating electricity using the vented gas. This may include, for instance, passing the vented gas through a turbine. According to embodiments, one or more of the venting (454) and generating (456) can be based on the availability of energy from another source, such as a battery, photovoltaic, and/or wind-driven device. In certain aspects, gas venting can be used to generate electricity when other sources are unavailable or inefficient. Conversely, gas may be stored (e.g., step 452 or 460) when power from such other sources is readily available. In this respect, power generation, storage, and recovery may be optimized as needed.
Step 458 comprises passing the remaining vented gas to a gas buffer. This may include, for instance, passing the gas back to a buffer storage associated with an anaerobic digestion system 100, or otherwise coupled to storage (e.g., bottle storage as shown in
In step 460, which may be optional in some embodiments, gas from the gas buffer is stored in the one or more storage containers. According to embodiments, the process 450 may be repeated as needed. That is, gas may be compressed and stored, used to generate electricity, then re-compressed and re-stored as needed.
According to embodiments, a system or method for taking a cryogenic liquid and converting it to a gas at, or around, room temperature allows energy recovery on three levels. Firstly, the expansion of the gas (from the conversion of the liquid to the gaseous phase) is fed through a pneumatic generator for the generation of power. Secondly waste heat can be used to augment that process and increase the volumetric expansion ratio. Thirdly the methane gas can be used in an internal combustion (IC) engine to create additional power. In some embodiments, the third aspect can be omitted, and the gas returned to storage where it can either stay until required and used in an IC engine or used for other purposes. According to embodiments, this may be accomplished with the system 400, which can include an IC engine.
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A water head—an end (e.g., the bottom) of one or more water filled weight tubes on a gas cover (e.g., cover 104 or slurry membrane 106) can be fitted with pressure sensors to measure the water head pressure. As the gas store fills, the center of the gas membrane is lifted and the water head increases. Similarly, as a slurry level decreases, the slurry membrane drops and the water head decreases. The system can be calibrated to calculate the amount of gas building up in the store or slurry available or digestion, e.g., using apparatus 500 of
Line of sight device(s)—a camera can be mounted and calibrated to monitor the top level of the gas or slurry membrane. Such monitoring can use multiple cameras at different levels and locations. Again, the results may be processed by apparatus 500, for instance, using computer vision techniques of filtering by colour hue and/or shape detection to map image pixel key-points to geometric feature points. In certain aspects, prominent shapes of conspicuous colour can be adhered to the cover or coloured objects placed behind to enable key-points of height and angle to be determined due to their presence, invisibility, or perspective in the images captured. That is, a cover or other membrane may comprise a prominent geometric shape or pattern or shapes, including at least one shape of a different color than the cover or membrane.
A sensor array—a festoon string array of sensors (e.g., gyroscopic accelerometers or angular sensors) can be used on the surface of a membrane (e.g., gas cover 104 or slurry membrane 106). Such an array may run, for instance, from a gutter (e.g., water confinement region) to the center of a gas membrane. A cross section of the inflation profile may be determined from modelling the cover shape by interpolating the inflation angle between known points where angular measurements exist. As the membrane moves (e.g., rises or falls), the string or sensors will similarly move. The movement can be calibrated such that it is associated with a particular level, and processed by apparatus 500.
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The biogas mixture (e.g. the methane enriched biogas, such as from one or more of the methane-enriched spaces of the anaerobic digester 100) is optionally first compressed by a compressor (not shown) to a processing pressure (e.g. between 100 bar and 300 bar), filtered by one or more filters (not shown), and then fed to the gas inlet 902. As a general matter, the lower the processing pressure, the less energy is required for liquefaction, while the higher the processing pressure, the easier it is to separate the carbon dioxide and methane (e.g. because there is more separation in phase diagrams for allowing the carbon dioxide to become a liquid while the methane remains a gas). In embodiments, the processing pressure could be as low as 30 bar, and may be higher than 300 bar. Also, the size of components may generally be made smaller as the pressure increases, e.g. due to the volume of gas decreasing at higher pressure. As noted, in exemplary embodiments, the processing pressure is around 100 bar to 300 bar. The biogas entering at inlet 902 will be, in some embodiments, approximately 85% methane and approximately 15% carbon dioxide, from about 100 bar to 300 bar, and about 20° C. (or whatever temperature the biogas is at after exiting the anaerobic digester 100). In embodiments, the biogas may be pre-processed, such that one or more of compression and/or filtering are not required.
From gas inlet 902, the biogas mixture passes through piping 921 to a heat exchanger 904 and then through piping 923 to a CO2 removal unit (e.g., cold box) 906. Heat exchanger 904 may, in some embodiments, be cooled by CO2 (e.g. at around −60° C.) before the biogas flows through piping 923 to enter the cold box 906. The CO2 (e.g., in liquid form) that cools the heat exchanger 904 may be supplied by the removal unit 906 by piping 933 (in which case it will be at approximately the temperature of the cold box), prior to the liquid CO2 exiting the system by piping 925 to the CO2 outlet 910. Such CO2 can also be provided to the liquefaction unit 912 in some instances, as a source of cold.
Inside the removal unit 906, there may be a second heat exchanger 914 (see, e.g.,
According to embodiments, the methane is cooled but remains a gas as it passes over the heat exchanger 914, whereas the CO2 condenses to a liquid (or, in some embodiments, a solid) and falls to the bottom 906a of the cold box 906. The extracted CO2 may then exit cold box 906 by piping 933. In some embodiments, solid CO2 may be retained in solid form until a batch of biomethane has been refined or the box is full, when the system may be shut down, the equipment warmed, and the CO2 may be removed in either gaseous or liquid form. As noted above, it may in some embodiments first pass through the heat exchanger 904 in order to take advantage of the fact that liquid CO2 is cooled by the cold box (e.g., to approximately −60° C.). Doing this can save considerable energy requirements, because the cascade refrigerator 908 will not need to cool the gas entering the cold box as much in such a case. When the CO2 leaves the heat exchanger 904 by piping 925 and reaches the outlet 910, it may have an approximate temperature of around 20° C. (or approximately whatever temperature the biogas entering the heat exchanger 904 has), and be at about 100 bar-300 bar. The cold box 906 is insulated (insulation shown by dashed lines around cold box 906) to conserve cold and reduce the cooling power requirement.
The now cold, but still pressurized methane, passes by piping 931 to the liquefaction unit (e.g., Joule-Thompson unit) 912. The liquefaction unit may also serve as a storage unit. However, the system 900 may include additional methane storage units (not illustrated), which can be removable as needed. When passing through piping 931, the gas is approximately 99% pure methane, with around 1% carbon dioxide, is still at around 100 bar-300 bar, and is cooled due to the cold box 906 (e.g. to approximately −60° C.). In the examples of
The Joule-Thompson unit 912 just described is an exemplary mechanism for liquefying methane gas. In some embodiments, a cryocooler, Brayton cycle device, or other device for liquefying methane may be used. Further, while the description above noted that the cold box is configured to liquefy CO2 gas but not methane gas, in embodiments the cold box may be configured to liquefy and/or solidify CO2 gas but not methane gas.
For high levels of methane refinement where the CO2 makes up a small fraction of the total volume (such as approximately 1-10%), the CO2 can conveniently be removed as a solid without requiring equipment (such as a cold box or heat exchanger) that is bulky or too large for being used as part of a mobile biogas processing plant. The methane can then be simultaneously removed as a liquid at low pressure. By sizing the heat exchanger appropriately, this can occur within a common liquefaction and low-pressure CO2 removal unit (e.g., cold box enclosure), such as shown in
As well as the source of cold being a sacrificial cryogenic liquid, where convenient it could also be a mechanical cooler used to liquefy air at the site or alternatively a close cycle refrigeration circuit. Whichever source is used, it should provide sufficient cooling for both phase changes in the CO2 gas to solid and the methane gas to liquid in embodiments. Where the refrigerant is a sacrificial cryogenic liquid such as liquid nitrogen or liquid argon that has a boiling point lower than the freezing point of methane care must be taken to ensure that the methane liquefaction process temperature is maintained above the freezing point of methane at the process operating pressure otherwise solid methane will form causing blockages in the heat exchanger path. At atmospheric pressure methane freezes at approximately −182° C. which is above both the boiling point of liquid nitrogen and liquid argon. A safe liquefaction operation temperature can conveniently be achieved by holding the sacrificial cryogenic liquid at a higher than atmospheric pressure via a pressure release valve. This also has the advantage of providing a failsafe system ensuring that its boiling point is maintained above that of the freezing point of methane without the need for active control. For liquid nitrogen for example a pressure of 5 bar would maintain a boiling point of approximately 172° C. ensuring that the methane gas stream never freezes.
According to embodiments, solid CO2 may be used to improve the liquefaction process in stage 912. For instance, a refrigerant liquid can be introduced to cause solid-form CO2 buildup in stage 912, which can in turn provide a source of cold for liquefaction of the methane. As such, a liquefaction stage 912 may comprise a refrigerant liquid input and output, as shown in
One or more embodiments are further described below.
In a first example, an anaerobic digester (or anaerobic digestion system) is provided that comprises: a biomass storage container (e.g., a slurry lagoon with one or more tapered sidewall); and a cover (e.g., a gas membrane) positioned over the biomass storage container, wherein the cover is sealed at an outer edge of the anaerobic digester to form a water (e.g., rainwater) collection region. The digester may further comprise an angled bracket (e.g., a gutter ring beam), wherein the bracket is configured to confine the water in the water collection region. The digester may further comprise an installation post (e.g., comprising a post, insulation, and cladding). In certain aspect, the biomass storage container comprises a lagoon liner membrane. The digester of this example may further comprise one or more membranes (e.g., a slurry cover membrane) between the biomass storage container and the cover. At least one of the membranes is selectively permeable between methane and CO2, or at least one of the membranes is non-permeable to biogas and its constituent materials. In this example, the cover, bracket, slurry cover membrane, and lagoon liner membrane may all be attached to the installation post. Additionally, at least one of the cover, bracket, slurry cover membrane, and lagoon liner membrane is attached to the installation post with one or more clamps (e.g., an outer membrane clamp and inner membrane clamp). This assembly may further comprise a gasket (e.g., a PVC closed cell foam gasket) on a top surface of the installation post and below one or more of the cover, bracket, slurry cover membrane, and lagoon liner membrane. In certain aspects, the cover is configured for protecting the biomass storage container and its contents against rain and wind. In certain aspects of the example, the cover is transparent and is configured to provide solar heating for the anaerobic digester. The cover may be made of a fabric reinforced polymer material (e.g., comprising a plurality of sheets). A gas filtrations system may also be included, wherein the gas filtration system is configured to process sour gas extracted from the biomass storage container and provide refined biogas to a region between the one or more membranes (e.g., slurry cover membrane) and the cover. In certain aspects, the processing of sour gas comprises removal of one or more of hydrogen sulfide and CO2. Other systems and features may be included, such as: a thermal management system (e.g., as described with respect to Example 2); a gas or slurry state monitoring system (e.g., as described with respect to Example 3); an energy recovery system (e.g., as described with respect to Example 4); and/or one or more cover weights (e.g., as described with respect to Example 5). In some embodiments, the cover has a rectangular or square shape and comprises one or more pleated corners. Another system that may be used in Example 1 is a water recovery and re-use system, wherein the water recovery and re-use system is configured to divert water from the water collection region to a second system (e.g., a water storage tank, washing station, livestock watering system, irrigation system). The water recovery and re-use system may comprise a water cleaning stage interposed between the collection region and the second system. In some instance, the digester may also comprise a mixer for circulating slurry within the biomass storage container, for instance, using an input/output pipe and one or more angled mixing outlets (e.g., angled to match the angel of one or more of biomass storage container sidewalls). The digester may also have a pump, wherein the pump is configured to move water from the cover to the water collection region (or vice-versa). In some embodiments, the cover, bracket, slurry cover membrane, and lagoon liner membrane are arranged such that biogas generated in the anaerobic digester does not come in contact with metallic components (e.g., to prevent corrosion). Additionally, the water collection region can cover all gas seals at the installation post, such that a gas leak would be identifiable by monitoring the water collection region.
According to embodiments, a method is provided for operating a digester according to Example 1. The method may comprise one or more of the following steps: (i) providing a slurry or other bio-materials to the container, such as pumping slurry to a covered lagoon; (ii) operating or otherwise controlling the anaerobic digestion process within the digester (e.g., temperature control, mixing, venting); (iii) extracting and/or processing gas from the digester; (iii) monitoring a water collection region for gas leaks; (iv) operating an associated thermal management system (e.g., flowing warm water between the cover and the slurry region to either provide heat to the digestion process or melty ice/snow on the cover), for instance, based on feedback from one or more level or temperature sensors (e.g., as described in Example 3); (v) operating a water management system; and (vi) performing energy storage or recovery.
In a second example, a thermal management system for an anaerobic digester is provided. The system comprises: a circulation device (e.g., comprising one or more pumps); and a plurality of tubes (or pipes) connected to the circulation device, wherein the plurality of tubes comprise: (1) one or more tubes on a surface of an anaerobic digester cover; and/or (2) or one or more tubes on a surface of (e.g., on a surface of a liner of) or within a biomass storage container of the anaerobic digester. The plurality of tubes may be water-filled. In this example, the circulation device is configured to flow warm water from the surface of the anaerobic digester cover to the biomass storage container (e.g., to improve an anaerobic digestion process in the container), and/or flow warm water from the biomass storage container surface of the anaerobic digester to the cover (e.g., to melt snow on the cover, which can cause damage to the digester and/or its components). In certain aspects, at least one of the tubes on the surface of digester cover is a weighted tube arranged to keep the cover in place (e.g., as described with respect to Examples 1,3, and 5). In this example, the biomass storage container may comprise a thermal storage region (e.g., filled with pea gravel), where the system is configured to flow warm water to the thermal storage region.
According to embodiments, a method of operating the thermal management system of Example 2 is provided. The method may comprise the steps of pumping heated water through the weight tubes to remove ice on the over and/or recovering heat from the outer cover and pumping this heat into the slurry, thereby increasing the digestion rate. One or more thermal management operations may be based on a determination of a status of the digester (e.g., based on a sensor output as described in Example 3).
In a third example, an anaerobic digester (or anaerobic digestion system) is provided that comprises: a biomass storage container (e.g., a slurry lagoon); a cover (e.g., a gas or slurry membrane) positioned over the biomass storage container; and one or more sensors configured to indicate a gas or slurry state (e.g., level) of the anaerobic digester. The anaerobic digester may further comprise a cover weight, where at least one of the sensors is a pressure sensor attached to (e.g., within) the weight. In some embodiments, at least one of the sensors is a line-of-sight sensor (e.g., a camera) configured to monitor a top level of the cover. In some embodiments, at least one of the sensors is an angular sensor array on the cover (e.g., a festoon string of gyroscopic sensors). In this example, the digester may also include a processing circuit (e.g., a processor, memory, and transmitter) configured to determine and report (e.g., locally, over a wireless channel, using the Internet, etc.) the gas or slurry state based on measurements form the one or more sensors.
According to embodiments, a method of operating the anaerobic digester of Example 3 is provided. The method may include, for instance, monitoring the amount of fugitive methane in the bag, which is required for remote control of monitoring of the lagoon and associated gas recovery plant. Additionally, one or more systems may be operated responsive to the sensing. This could include, for instance, activation of a thermal system, starting/stopping a slurry mixing process (e.g., to adjust the level of the gas up or down or otherwise affect digestion rate); venting (e.g., if the gas level or pressure is too high); or initiating gas processing (e.g., if the level reaches a predetermined volume or pressure threshold).
In a fourth example, an energy storage system is provided. The system comprises: one more storage containers of gaseous or liquid materials (e.g., compressed gas or cryogenic liquid); a gas pressure driven electrical generator (e.g., a turbine) coupled to the one or more storage containers and configured to generate power (e.g., electricity) using gas generated (e.g., vented) from the one or more storage containers; and a gas buffer configured to store at least a portion of an exhaust gas after it is used by (e.g., passes through) the generator. The gas or liquid could be, for instance, methane, CO2, hydrogen, or a mixture thereof. In certain aspects, the gas buffer is a part of an anaerobic digester (e.g., as described with respect to Examples 1, 3, and 5). For instance, the gas buffer can be the region located between a slurry region and a cover of the anaerobic digester. In certain aspects, a gas processing system (e.g., comprising a compressor, dryer, cooler, liquefaction stage, liquid storage vessel) can be included and configured to extract the gas from the gas buffer and store it in the one or more storage containers. In some embodiments, wherein the energy storage system is part of a mixed electricity generating system comprising one or more of photovoltaics and wind energy devices (e.g., a windmill), and/or an internal combustion (IC) engine is configured to operate using the gas (e.g., after expansion). While an internal combustion engine is used as an example, other engines (such as other combustion engines, or non-combustion engines) may be used as well in this Example and other embodiments.
According to embodiments, a method of operating an energy storage system according to Example 4 is provided. For instance, an energy recovery process may be performed that comprises: venting gas from one more storage containers of gaseous or liquid materials (e.g., compressed gas or cryogenic liquid); generating electricity using the vented gas; and passing remaining vented gas to a gas buffer. Generating electricity may comprise operating a turbine using the vented gas. Other types of power or mechanical energy may be generated according to embodiments. In certain aspects, the method may also comprise storing gas from the gas buffer in the one or more storage containers, for instance, by compressing the gas from the gas buffer, wherein the gas from the buffer was previously used to generate electricity in the generating step. In embodiments, at least one of the venting gas and storing gas is based at least in part on the supply of electricity from a photovoltaic, wind energy device, or battery, and/or energy used for the storing step is provided by a photovoltaic, wind energy device, or battery. In embodiments, passing the remaining vented gas to a gas buffer comprises passing the remaining vented gas to an anaerobic digester (e.g., as described with respect to Example 1). The method of this example may also comprise passing the generated electricity to a mains electricity system. The method of this example may also comprise passing the vented gas through a heating element before the electricity generation step. In some embodiments, the method comprises: before the venting step, generating gas in an anaerobic digester; and storing it in the one or more storage containers, wherein the step of passing the remaining vented gas to a gas buffer comprises passing the remaining vented gas to the anaerobic digester used to generate the gas. Embodiments may comprise using the vented gas to power an engine (e.g., after an expansion of the gas that utilizes waste heat).
In a fifth example, an anaerobic digester is provided that comprises: a biomass storage container; a cover positioned over the biomass storage container; and one or more weights, wherein at least one of the weights is positioned on a top surface of the cover. In some embodiments, the cover is rectangular or square and at least one of the weights forms a pleated corner of the cover. In some embodiments, a weight is arranged in each corner of the cover. A weight may also be arranged in a center region of the cover or on a slurry membrane of the biomass storage container. In certain aspects, at least one of the weights comprises a pressure sensor. In certain aspects, at least one of the weights is a tube (or pipe). In embodiments, at least one of the weights is a hollow tube, a solid tube, a rock-filled tube, or a water-filled tube. In certain aspects, the weight tube is connected to a water collection region of the anaerobic digester and configured to move water from the cover to the collection region (or vice-versa). In certain aspects, the weight tube is connected to a water circulation device. In certain aspects, the weight tube is filled with gravel or heated water. In certain aspects, the one or more weights are arranged to create tension on cover and prevent flapping of the cover in the wind. The cover may be expandable upon an increase in gas generated in the biomass storage container (e.g., expansion via one or more pleats).
According to embodiments, a method of assembling the anaerobic digester of Example 5 is provided. The method may comprise, for instance, the steps of placing the cover, placing the weights to form pleated corners, assembling/attaching any thermal management system, and optionally filling one or more weights. A similar method may be used to assemble the digester of Example 1, for instance.
While one or more of the examples provided herein are described with respect to an anaerobic digester, according to embodiments, the individual components and systems may be implemented separately from the digesters described in the embodiments of this disclosure.
While various embodiments of the present disclosure are described herein, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.
Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.
The present application claims priority to U.S. provisional Application No. 63/052,190 filed on Jul. 15, 2020, the disclosure of which is incorporated here in it its entirety by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2021/056375 | 7/15/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63052190 | Jul 2020 | US |
