Sorbent emitter for direct air capture of carbon dioxide

An emitter apparatus is mounted on a marine structure powered by wind or marine hydrokinetic energy to disperse a carbon dioxide sorbent such as sodium hydroxide. The sorbent can be generated by reverse osmosis of seawater with electrolysis of the brine, or delivered from an external supply. Suitable marine structures include offshore wind turbines, marine hydrokinetic generators, offshore oil platforms, merchant vessels, and other fixed and mobile structures. Effective capture is made by dispersing a fine mist or fog of aqueous sorbent from nozzles with a particle size from a nozzle of less than 100 microns. The sorbent reacts with atmospheric carbon dioxide forming carbonates and bicarbonates, which drift and fall to the ocean surface, reducing surface acidity and capturing additional atmospheric carbon dioxide via absorption at the local ocean surface. The resulting carbonates sink to the ocean floor and are there sequestered.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to the sequestration of atmospheric carbon dioxide.

2. Description of Related Art

Deep reductions in carbon dioxide (CO2) emissions are required to reduce atmospheric CO2concentration, mitigating global heating. Carbon dioxide is a greenhouse gas that absorbs and radiates heat from the sun. CO2concentrations are rising primarily because fossil fuels are burned for power production, the CO2trapping additional heat and raising Earth's average temperature. The scale needed to transform the world's primary energy sources from carbon-emitting fossil fuels to renewable energy is vast. It requires an impractical transition rate, indicating that carbon dioxide capture and storage are imperative to achieving the level of future CO2reduction needed to combat global warming and climate change.

Current techniques for carbon capture are directed at capturing CO2from large stationary sources, such as power plants. Typically, CO2is separated from flue gas, compressed, and transported to be sequestered underground.

Direct ambient air capture (DAC) of CO2occurs when ambient air passes across an alkaline solution, such as sodium hydroxide. However, various DAC methods have proved costly due to the energy needed to process sufficient amounts of air to capture dilute (˜419 ppm) atmospheric CO2, the cost and delivery of the alkaline feedstock, the recovery of the feedstock, the transfer and containment of the CO2to be sequestered, and the large land area and structures needed for the air processing system.

Water loss may be substantial in an air capture system as the relatively low concentration of CO2in the atmosphere requires a large amount of interaction between the gaseous and the liquid phases. Freshwater availability is a significant problem in many parts of the world. As rising atmospheric temperatures drive changes in the hydrological cycle, water availability for DAC is often limited. In a typical DAC system, water loss is about 20 moles for every mole of CO2absorbed (at 15 degrees C. and 65% RH). However, it can be lowered significantly by appropriate design and operating parameters.

It is compelling to look beyond land-based CO2sequestration to the oceans for both process water availability and the sequestration of CO2, mimicking parts of the natural cycle of ocean CO2absorption and helping to reduce the acidification of the oceans. Rising atmospheric CO2has led to more CO2dissolving into the sea and a drop in average pH (now about 8.1).

SUMMARY OF THE INVENTION

The present invention overcomes these and other deficiencies of the prior art by capturing atmospheric CO2by dispersing, via a sorbent emitter placed on a wind or marine current turbine platform, a sorbent such as aqueous sodium hydroxide (NaOH) into the wind above an ocean surface. Effective capture of CO2is achieved by dispersing a fine mist or fog of the aqueous sorbent with a particle size from a nozzle of less than 100 microns. The sorbent reacts with atmospheric CO2forming carbonates and bicarbonates, which drift and fall to the ocean surface, reducing ocean acidity and capturing additional atmospheric CO2via absorption at the local ocean surface. The resulting carbonates sink to the ocean floor and are there sequestered.

In an embodiment where the sorbent emitter is fitted to an offshore turbine, the turbine powers onboard desalination to deliver fresh water to shore and processes the residual brine into the CO2sorbent. The sorbent can be diluted with water and pumped to nozzles on the tower head. Sorbent may also be delivered to the offshore wind turbine via a pipeline or by a merchant vessel, thereby allowing the power generated by the turbine to produce more desalinated water or shore power rather than onboard production of the sorbent.

In an embodiment of the invention, a carbon dioxide sorbent emitter system comprises: a sorbent emitter apparatus comprising a hub; and a plurality of spokes, wherein each one of the plurality of spokes is paired with an aerodynamic foil, each aerodynamic foil comprising a plurality of carbon dioxide sorbent emitting nozzles; and an offshore platform supporting the sorbent emitter apparatus above a marine surface. The sorbent emitter apparatus further comprises a rim coupled to the plurality of spokes. The offshore platform comprises a wind turbine generator or marine hydrokinetic energy generator and a desalination system, wherein the wind turbine generator or marine hydrokinetic energy generator powers the desalination system, and the desalination system produces brine for processing into carbon dioxide sorbent on the offshore platform. The carbon dioxide sorbent is sodium hydroxide emitted from the plurality of sorbent emitting nozzles. The sorbent emitter apparatus is mounted to the wind turbine generator. The hub and the plurality of spokes rotate about a horizontal axis. The plurality of spokes rotate about a vertical axis. A pitch of each aerodynamic foil is adjustable. Each aerodynamic foil comprises a carbon dioxide sorbent feeder tube and an air feeder tube, and the hub comprises a swivel tube connector connected to the carbon dioxide sorbent feeder tube of each aerodynamic foil. A size of the plurality of the carbon dioxide sorbent emitting nozzles is adjustable. The offshore platform is a ship or oil drilling platform.

In another embodiment of the invention, a method of dispersing carbon dioxide sorbent in a marine environment to sequester atmospheric carbon dioxide, the method comprising the steps of: coupling a carbon dioxide sorbent emitter apparatus to an offshore platform, wherein the carbon dioxide sorbent emitter apparatus comprises a hub, a plurality of spokes, wherein each one of the plurality of spokes includes an aerodynamic foil, each aerodynamic foil comprising a plurality of carbon dioxide sorbent emitting nozzles, and the offshore platform supports the sorbent emitter apparatus above a marine surface, and dispersing carbon dioxide sorbent through the plurality of carbon dioxide sorbent emitting nozzles.

The offshore platform comprises a wind turbine generator or marine hydrokinetic energy generator and a desalination system, and the method further comprises processing brine from the desalination system into carbon dioxide sorbent. The method further comprises the step of rotating the hub and the plurality of spokes about a horizontal axis. The method further comprises the step of rotating the plurality of spokes about a vertical axis. The method further comprises the step of adjusting a pitch of each aerodynamic foil. The method further comprises the step of adjusting a size of the plurality of the carbon dioxide sorbent emitting nozzles. The offshore platform may also be a ship or oil drilling platform.

The foregoing and other features and advantages of the invention will be apparent from the following, a more detailed description of the invention's preferred embodiments, as shown in the accompanying drawings and the claims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention and their advantages may be understood by referring toFIGS.1-7, wherein like reference numerals refer to like elements. The present invention may be deployed in any water environment, preferably where renewable energy is available. It can also be configured to use a range of alkaline CO2absorbents apart from sodium hydroxide (NaOH).

The present invention is a continuation of U.S. patent application Ser. No. 17/391,884, entitled “Wind-Powered Direct Air Carbon Dioxide Capture for Ocean Sequestration,” which teaches locating sorbent emitter nozzles on the blades or structure of an offshore wind turbine. Blade rotation enhances sorbent dispersion, and the turbine's height above the ocean allows sufficient air retention time for the sorbent mist particles to mix in the atmosphere and react with CO2. The air running through the rotor can travel for tens of kilometers downwind in an hour. Shifting wind direction creates an expansive ocean area where the carbonates are deposited. However, locating the emitter nozzles on the turbine blades requires the onshore manufacturing and offshore installation of new turbines and platforms. There is a need to adapt existing offshore turbines and platforms to utilize aftermarket sorbent emitters to accelerate sorbent emission and capture CO2.

FIGS.1A and1Billustrate front and side views of an offshore wind turbine system100according to an embodiment of the invention. The system100comprises a wind turbine generator (WTG)110with rotor blades112, a tower (mast)120, and a platform130fixed or floating with anchoring to a seafloor. The platform130can be a spar buoy, as disclosed in U.S. patent application Ser. No. 17/391,884, which houses reverse osmosis components to generate NaOH solution as a by-product of desalinating seawater into freshwater.

As an alternative to the turbine blade-mounted nozzles as disclosed in the above-noted application, a sorbent emitter apparatus140is mounted or retrofitted to a bedplate114of the WTG110as shown or fixed to the turbine tower120or the platform130. In a preferred embodiment of the invention, the sorbent emitter apparatus140is located at a height at least 30 m above the ocean surface for optimal NaOH/CO2absorption. Moving the sorbent emitter apparatus140away from the blades112of the WTG110allows it to be deployed rapidly in practice by retrofitting already operating offshore turbines, eliminating the deployment delay associated with newly built wind turbines. Due to the urgency of carbon dioxide removal from the atmosphere, adapting existing offshore turbines is critical to gaining sufficient carbon capture to help mitigate rising global temperatures.

The NaOH solution is internally piped to the sorbent emitter apparatus140and emitted as a fine mist142into the atmosphere. Atmospheric CO2is absorbed by the NaOH mist142, forming sodium carbonate and sodium hydrogen carbonate (“sodium bicarbonate”). The carbonate droplets are drawn by gravity to the surface layer of the ocean, where mixing by the orbital action of waves leads to increased levels of dissolved carbonates and gradual capture by marine organisms and incorporation into the natural carbon cycle. The reaction solution drops landing on the ocean are mildly alkaline, comprising a mixture of carbonate, bicarbonate, and unreacted hydroxide ions. Therefore, the present invention has the potential to locally reduce ocean acidity with the associated benefits to marine ecosystems.

Referring toFIGS.2A-2C, which show side and front views of the sorbent emitter apparatus140atop the WTG110. The sorbent emitter apparatus140is a fixed or rotating wheel-type structure, with a hub242and multiple spokes244. On each spoke244is an aerodynamic foil245. As shown inFIGS.2A and2B, the sorbent emitter apparatus140may include a circular rim246coupled to the spokes244. As shown inFIG.2C, the spokes244are rigid and supported only by the hub connection242without the rim246. The spoke structure offers high nozzle density along the length of each spoke244while having a narrow foil245profile area (low solidity) to help minimize the drag/resistance to the air flowing through the blades112and the sorbent emitter apparatus140.

The foils245house internal sorbent plumbing and exterior surface sorbent nozzles248and optional internal air plumbing to the nozzles245. In an exemplary embodiment of the invention, the aqueous sodium hydroxide sorbent flows through a hollow axle of the hub242to tubing within each foil245. Misting nozzles248may require an air supply, which can be plumbed through the hub axel or by having electric power delivered to the hub242to drive a compressor(s) for the air supply to the air plumbing.

FIGS.3A and3Billustrate a cross-sectional view of a spoke244and a foil245along the cut-axis A-A (as marked inFIG.2). Each foil245houses an air feeder tube342, a sorbent solution feeder tube344, and a plurality of external nozzles248. The air feeder tube342is coupled to nozzles248via a tube343. Each foil245is pitchable by rotating a respective spoke244.FIG.3Aillustrates the foil245in a feathered position with no rotation.FIG.3Billustrates the foil245in a rotated position. The nozzles248are placed near or at the foil trailing edge to cause minimal disturbance of the airflow over the foil245, help disperse the sorbent mist142from nozzles248, and reduce drag.

FIG.4illustrates the inner air and sorbent plumbing of the sorbent emitter apparatus140according to an embodiment of the invention. A spoke244connects to the hub242and the rim246, if needed, for example, in a large-scale structure (10 m or more diameter). The hub242contains swivel tube connectors (not shown) in the hub's axel442. From these axel tubes, flexible tubing444and445connect to the spoke-mounted feeder tubes342and344, which convey the air and sorbent solution, respectively, to nozzles248. The flexible tubing444and445allows for the foil245pitching movement.

The aerodynamic foil245containing feeder tubes and nozzles can be either fixed or actively rotated/pitched around the axis of the spoke on which the assembly of feeder tubes342and344and nozzles248is mounted. Collective pitch control for all the aerodynamic foils245is actuated by a motor (not shown) in the rim246, the hub242, or spokes244. By pitching each foil245, an aerodynamic lift is created to provide torque at the hub242to drive a generator to pump air and the sorbent fluid to the nozzles248.

Nozzles that move across the wind gain more exposure to the air passing around each nozzle248than nozzles stationary in the wind. Thus, rotation of the emitter140on its axle provides greater dispersion of the emitted sorbent mist142and exposure to more of the sparse atmospheric CO2(417 ppm) closer to the emitter140. This increases sorbent droplet dispersion by more air volume exposure closer to the emission point. This also reduces the needed dwell time in the atmosphere for optimal CO2absorption, making it possible to have effective capture at lower heights above the ocean. Variations in the diameter of the emitter wheel246, the number of spokes244, the nozzle spacing on the spokes, and the structural requirements of the emitter140change the rate of sorbent misting.

While certain ocean regions may not have an adequately energetic wind resource for wind turbines, these regions may have sufficient marine currents to generate power.FIG.5illustrates a marine hydrokinetic energy (MHK) mounted sorbent emitter500according to an embodiment of the invention. Here, a surface piercing marine current power generator510serves as an effective structure for capturing CO2by mounting on the surface structure530, a mast520with a sorbent emitter apparatus140at the masthead, where the sorbent emitter140is configured to yaw about the mast, either by aerodynamic drag positioning (weather vanning) with the wind or by motorized yawing. Wave energy and marine current platforms are permanently moored and positionally stable and thus provide a suitable base for a mast520with a radial emitter device140. Power generated is applied onboard to desalinate water, process the brine, and produce and disperse the sorbent.

In poor wind resource regions, MHK generators with a sorbent emitter apparatus140can provide wide dispersion of carbonates on the ocean by slowly motoring the radial emitter while also yawing the emitter over a 360-degree dispersion zone around the platform for the carbonates to spread across the ocean surface and sink to the seabed. The sorbent emitter apparatus140is fitted with a motor-generator, whereby motoring the spoke foils245produces fan-like air movement, increasing the dispersion area of the sorbent emitted.

FIG.6illustrates a side view, a top view, and a time-lapse view of a sorbent dispersion pattern according to an embodiment of the invention. As shown in the top drawing, rotation of the sorbent emitter apparatus140over time provides greater dispersion of the sorbent mist and more exposure to the sparse atmospheric CO2(417 ppm). By motoring the emitter apparatus140, air movement is driven by the foiled spokes244. During times with little wind, the radial emitter140is motored and slowly yawed, creating a longer, moving sorbent dispersal zone610around the platform and avoiding excess carbonates reaching the ocean surface in a narrow directional area.

FIG.7illustrates sorbent emitters140mounted on a ship710according to an embodiment of the invention. A ship710, such as a merchant vessel, provides a means for direct air capture of CO2when the ship is underway in the open ocean. Such vessels would load the sorbent onboard at portside and use onboard desalination to dilute the sorbent for emitter dispersal.

Offshore oil platforms located in windy regions are also candidate structures for sorbent emitters140because they usually have elevated platforms on which an emitter mast can be mounted. On the platform, the wind causes the emitter to freewheel, increasing the air passing the radial emitter nozzles for a greater rate of dispersal in air and sorbent-CO2reaction than by a fixed (non-rotating) structure.

The carbon capture capacity needed to stem global temperature rise using offshore wind turbines, marine hydrokinetic energy generators, and other offshore platforms to desalinate water and produce the sorbent onboard, offers a scale that can contribute a substantial part of the ten gigatons of CO2capture needed per year by 2050, as estimated by the Intergovernmental Panel on Climate Change (IPCC). There is a dire need for far more atmospheric dispersal of CO2sorbent in a tight time frame. A sorbent volume many times greater is required than can be available by onboard sorbent production, which is dependent on the power generated by an offshore wind turbine, marine current turbine, or wave generator.

The capacity for CO2capture is proportional to the volume of sorbent emitted. A much greater volume of sorbent delivered to an emitter will boost the capacity for CO2capture. The diameter of the radial emitter140can be adjusted to accommodate a far greater number of nozzles and sorbent dispersion capacity than is available by the sorbent produced with renewable energy onboard generators.

The many-fold increase (10 to 30 times greater) in sorbent mist dispersal is accomplished by importing dry sorbent or sorbent as a concentrated solution to the offshore platform, diluted with water for emission from the nozzles. An external, ample tonnage supply of dry or a concentrated sorbent solution to the offshore platform can be provided by an ocean floor pipeline connected to a shoreside sorbent source or tanker delivery to storage tanks of the dispersal platform.

In an embodiment of the invention, a system controller commands nozzle sorbent dispersion volume, and particle size is varied to optimize sorbent droplet size for air retention time when carried downwind depending on atmospheric conditions, including wind speed, temperature, and humidity. The controller commands nozzle dispersion characteristics and selects among groups of nozzles with the specific volume and particle size best suited to the prevailing atmospheric conditions. For example, with little or no wind, nozzles producing tiny sorbent particle size (˜5-micron) make a very fine mist in the air that will drift for longer distances than larger droplets. However, larger droplets (30 to 50 microns) can be emitted in higher winds and drift long distances for more CO2exposure. Diffusing sorbent in a greater air volume creates more significant exposure to CO2molecules and enables more direct air capture of CO2as the drops coalesce and fall to the ocean. Nozzle operation by the controller is integrated with emitter yawing, airfoil pitch control depending on capturing energy for generating, powering to induce air movement and sorbent dispersion, or freewheeling with the wind.

The invention has been described herein using specific embodiments for illustration only. However, it will be readily apparent to one of ordinary skill in the art that the invention's principles can be embodied in other ways. Therefore, the invention should not be regarded as limited in scope to the specific embodiments disclosed herein; it should be fully commensurate in scope with the following claims.