NO20230416A1

NO20230416A1 - Systems and methods relating to direct air capture of co2

Info

Publication number: NO20230416A1
Application number: NO20230416A
Authority: NO
Inventors: Per Lothe; Tor Christensen
Original assignee: Knutsen Tech As
Priority date: 2023-04-17
Filing date: 2023-04-17
Publication date: 2024-10-18
Also published as: WO2024219979A1

Description

SYSTEMS AND METHODS RELATING TO DIRECT AIR CAPTURE OF CO2

FIELD

The present invention relates to powering of a Direct Air Capture (DAC) system. More specifically, the present invention relates to providing a reliable and flexible power source for a DAC system, whilst optimising the CO2 capture capabilities of the DAC system.

BACKGROUND

Direct Air Capture of CO2 has recently gained interest as a means to offset CO2 emissions and thereby combat climate change. DAC systems utilise either chemical process for the capture of CO2, or less energy intensive physical methods.

The most common capture method is by chemical means such as fibers impregnated with a suitable amine. The amine and the CO2 react to form fairly strong chemical bonds. This reaction releases large amounts of energy. In order to recover the captured CO2 as a CO2 product, at least the same amount of energy must be supplied by external means. Therefore the CO2 capture energy increases significantly if the air is slightly enriched in CO2.

Physical methods, which are the focus of the present disclosure, include the use of a physical sorbent, such as a highly porous solid where the CO2 may diffuse into the pores. The CO2 may attach to sites within the pores using weak intermolecular forces. The amount of heat released in this process is low, typically around four times lower than heat evolved in chemical reactions.

However, this number may vary significantly depending on the system in question. Recovery of the CO2 may be accomplished by heating the sorbent and subsequently supplying an amount of heat that is similar to the amount of heat released in the capture process.

DAC systems require a power source. While one of the major advantages with DAC is flexibility with respect to location, the supply of power may put severe limitation on the number of suitable locations. If power is supplied from a local power grid there may be competition for the available power and long waiting lists before the access power is granted. Furthermore, the amount of power available may be very limited and much less than planned for the DAC project. If located in remote areas, power supply from a power grid may require new high voltage power lines which may delay the DAC project and incur new power losses.

It will be apparent that power supplied to DAC systems should not result new CO2 emissions to the atmosphere, thereby countering the very purpose of the DAC system itself. In this connection, renewable sources have been contemplated. Photovoltaic, wind or wave energy or combinations of such sources have been suggested. These are attractive alternatives in many locations. However, the power supply will be semi-continuous and guaranteeing an annual capture rate will be more challenging. For economic feasibility of a DAC system, it is highly desirable to be able to guarantee a minimum annual capture rate.

It is an aim of the present disclosure to provide a system and method for power supply to a DAC system based on a hydrocarbon fuelled power unit, where the DAC system captures CO2 both from the air and from the power unit, with minimal negative effect on the capability to capture CO2 from air.

The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art. The object is achieved through features, which are specified in the description below and in the claims that follow.

SUMMARY

According to a first aspect of the invention, there is provided a CO2 capture system comprising: a hydrocarbon fuelled power unit; a scrubbing and cooling system; a pressure control system; a mixing system; and direct air capture (DAC) system comprising a physical sorbent; wherein the hydrocarbon fuelled power unit is configured to provide electrical power and flue gas; the scrubbing and cooling system is connected to the hydrocarbon fuelled power unit to receive electrical power and the flue gas and is configured to clean and cool the flue gas to provide a cleaned and cooled flue gas; the pressure control system is connected to the scrubbing and cooling system to receive the cleaned and cooled flue gas and is configured to: vent cleaned and cooled flue gas to the atmosphere if the pressure of the cleaned and cooled flue gas flow is above atmospheric pressure and to mix atmospheric air into the cleaned and cooled flue gas flow if the pressure of the cleaned and cooled flue gas is below atmospheric pressure; thereby in use ensuring a constant back pressure equal to atmospheric pressure; the mixing system is connected to the hydrocarbon fuelled power unit to receive electrical power and is further connected to the pressure control system to receive the cleaned and cooled flue gas flow at atmospheric pressure and to mix atmospheric air with the cleaned and cooled flue gas flow at a ratio of between 10:1 and 200:1, thereby providing a DAC system intake gas stream; and the DAC system is connected to the hydrocarbon fuelled power unit to receive electrical power and is further connected to the mixing system to receive the DAC system intake gas stream, wherein the DAC system is configured to capture CO2 from the DAC system intake gas stream.

The hydrocarbon fuelled power unit may be a methane power unit.

The hydrocarbon fuelled power unit may be configured to provide auxiliary electrical power to power auxiliary equipment.

The hydrocarbon fuelled power unit may comprise a gas turbine or a piston engine.

The CO2 capture system may further comprise a renewable energy electrical power source configured to supplement the power delivered by the hydrocarbon fuelled power unit in use.

The scrubbing and cooling system may comprise: a structure packing; a pump; and a cooler; wherein the scrubbing and cooling system is configured in use to allow flue gas to flow upwards countercurrent to circulating water pumped by the pump and cooled by the cooler, such that the circulating water can absorb sour components from the flue gas and cool the flue gas to not more than 15°C above the ambient temperature.

The scrubbing and cooling system may further comprise a connection for connecting to a supply of clean water in use and a conduit for the disposal of contaminated water.

The pressure control system may comprise a flue stack.

The pressure control system may be a passive pressure control system.

The CO2 capture system may further comprise a booster fan located between the pressure control system and the mixing system, wherein the booster fan is configured to boost the cleaned and cooled flue gas.

The mixing system may be configured to mix atmospheric air with the cleaned and cooled flue gas flow at a ratio of between 50:1 and 200:1 or a ratio of between 100:1 and 200:1 or a ratio of between 160:1 and 200:1.

The physical sorbent may be zeolite.

The mixing system may comprise a manifold distributed across the mixing system and configured to deliver the atmospheric air substantially evenly across the cleaned and cooled flue gas stream in use.

According to a second aspect of the invention, there is provided an intermediate system for locating between a hydrocarbon fuelled power unit and a direct air capture system comprising a physical sorbent in a CO2 capture system, the intermediate system comprising: a scrubbing and cooling system; a pressure control system; and a mixing system; wherein the scrubbing and cooling system is configured to be connectable in use to the hydrocarbon fuelled power unit to receive electrical power and the flue gas and to clean and cool the flue gas to provide a cleaned and cooled flue gas; the pressure control system is configured to be connectable in use to the scrubbing and cooling system to receive the cleaned and cooled flue gas and to: vent cleaned and cooled flue gas to the atmosphere if the pressure of the cleaned and cooled flue gas flow is above atmospheric pressure and to mix atmospheric air into the cleaned and cooled flue gas flow if the pressure of the cleaned and cooled flue gas is below atmospheric pressure; thereby in use ensuring a constant back pressure equal to atmospheric pressure; the mixing system is configured to be connectable in use to: the hydrocarbon fuelled power unit to receive electrical power; the pressure control system to receive the cleaned and cooled flue gas flow at atmospheric pressure and to mix atmospheric air with the cleaned and cooled flue gas flow at a ratio of between 10:1 and 200:1, thereby providing a DAC system intake gas stream; and the DAC system to deliver the DAC system intake gas stream thereto.

The scrubbing and cooling system may further comprise a connection for connecting to a supply of clean water and a conduit for the disposal of contaminated water.

The pressure control system may comprise a flue stack.

The pressure control system may comprise a passive pressure control system.

The intermediate system may further comprise a booster fan configured to be located between the pressure control system and the mixing system in use, wherein the booster fan is configured in use to boost the cleaned and cooled flue gas.

According to a third aspect of the invention, there is provided a CO2 capture kit comprising: a hydrocarbon fuelled power unit; a scrubbing and cooling system; a pressure control system; a mixing system; and direct air capture (DAC) system comprising a physical sorbent; wherein the hydrocarbon fuelled power unit is configured to provide electrical power and flue gas; the scrubbing and cooling system is configured to be connectable in use to the hydrocarbon fuelled power unit to receive electrical power and the flue gas and to clean and cool the flue gas to provide a cleaned and cooled flue gas; the pressure control system is configured to be connectable in use to the scrubbing and cooling system to receive the cleaned and cooled flue gas and to: vent cleaned and cooled flue gas to the atmosphere if the pressure of the cleaned and cooled flue gas flow is above atmospheric pressure and to mix atmospheric air into the cleaned and cooled flue gas flow if the pressure of the cleaned and cooled flue gas is below atmospheric pressure; thereby in use ensuring a constant back pressure equal to atmospheric pressure; the mixing system is configured to be connectable in use to the hydrocarbon fuelled power unit to receive electrical power and to be further connectable in use to pressure control system to receive the cleaned and cooled flue gas flow at atmospheric pressure and to mix atmospheric air with the cleaned and cooled flue gas flow at a ratio of between 10:1 and 200:1, thereby providing a DAC system intake gas stream; the DAC system is configured to be connectable in use to the mixing system to receive the DAC system intake gas stream and to capture CO2 from the DAC system intake gas stream.

According to a fourth aspect of the invention, there is provided a method of CO2 capture from the atmosphere, comprising the steps of: providing a CO2 capture system according to the first aspect of the invention; running the hydrocarbon fuelled power unit to provide electrical power to the scrubbing and cooling system, the mixing system and the DAC system and to provide flue gas to the scrubbing and cooling system; cleaning and cooling the flue gas in the scrubbing and cooling system to provide cleaned and cooled flue gas to the pressure control system; providing a constant back pressure equal to atmospheric pressure by: venting cleaned and cooled flue gas to the atmosphere in the pressure control system if the pressure of the cleaned and cooled flue gas flow into the pressure control system is above atmospheric pressure; or mixing atmospheric air into the cleaned and cooled flue gas flow in the pressure control system if the pressure of the cleaned and cooled flue gas into the pressure control system is below atmospheric pressure; mixing atmospheric air with the cleaned and cooled flue gas flow at a ratio of between 10:1 and 200:1 in the mixing system to provide a DAC system intake gas stream; operating the DAC system to capture CO2 from the DAC system intake gas stream.

The step of mixing atmospheric air with cleaned and cooled flue gas may be at a ratio of between 50:1 and 200:1 or a ratio of between 100:1 and 200:1 or a ratio of between 160:1 and 200:1.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to the following drawings, in which:

Figure 1 shows an overview of an example of a power and CO2 capture system in accordance with the present invention;

Figure 2 shows further details of the power and CO2 capture system of Figure 1 in use;

Figure 3 shows a detailed view of the power unit, scrubbing and cooling system, pressure control system and mixing system of the power and CO2 capture system of Figure 1;

Figure 4 shows a detailed view of the DAC system of the power and CO2 capture system of Figure 1;

Figure 5 shows a detailed view of the pressure control system of the power and CO2 capture system of Figure 1;

Figure 6a shows a perspective view the mixing system of the power and CO2 capture system Figure 1;

Figure 6b shows a cross-sectional view of the mixing system shown in perspective view in Figure 6a;

Figure 7 shows an example of a system in accordance with the present invention utilising a combined cycle gas turbine unit;

Figure 8 shows an example of a DAC system powered by renewable energy;

Figure 9 shows the amount of CO2 captured vs auxiliary electrical power from the power unit in the system of Figure 7;

Figure 10 shows the ratio of air flow to flue gas flow vs auxiliary power for the system of Figure 7;

Figure 11 shows the number of separate but similar power units that can be annulled in terms of CO2 emissions from those power units because of CO2 capture from air vs amount of auxiliary power provided by the power unit in the system of Figure 7;

Figure 12 shows the specific energy consumption of the DAC system vs the amount of auxiliary power provided by the power unit in the system of Figure 7; and

Figure 13 shows the concentration of CO2 entering the DAC system vs the amount of auxiliary power provided.

For clarity reasons, some elements may in some of the figures be without reference numerals. A person skilled in the art will understand that the figures are just principal drawings. The relative proportions of individual elements may also be distorted.

DETAILED DESCRIPTION OF THE DRAWINGS

Unless otherwise defined, all terms of art, notations and other scientific terms or terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this disclosure pertains. Certain terms of art, notations, and other scientific terms or terminology may, however, be defined specifically as indicated below.

The term “CO2 concentration” in ppm represents the number of molecules of CO2 in the gas relative to the total number of gas molecules in a given volume. The unit of standard volume, Sm<3>, refers to the volume of the same moles of gas standard conditions with temperature 15°C and atmospheric pressure 1.013 bar.

For the sake of clarity and brevity, flow lines and conduits have been omitted from the description and are discussed only with reference to the fluid therein. It will be within the capabilities of a person skilled in the art to provide appropriate flow lines or conduits. The flow lines or conduits may include insulation. The insulation may have a thickness of 5 – 30 cm, preferably 10 – 20 cm. The insulation may comprise polymer foam, an aerogel, a rubber, a fiber material, a composite material, or any other suitable form of insulation.

In Figure 1 there is provided an overview of the main components of a power and CO2 capture system 1 which will each be described in more detail with reference to subsequent figures. The major components of the power and CO2 capture system 100 are a hydrocarbon power unit 100, a scrubbing and cooling system 200, a pressure control system 300, a mixing system 400 and a DAC system 500.

The hydrocarbon power unit 100 may be a gas turbine, gas engine or another hydrocarbon fuelled power unit. That is to say, the power unit 100 utilises hydrocarbon fuel to produce power and flue gas as a biproduct of the power production. The power produced is delivered to the scrubbing and cooling system 200, mixing system 400 and DAC system 500 for operation of these systems. The pressure control system 300 is a passive system requiring no power input. As will be explained in more detail later, the power delivered to these systems may be supplemented by additional energy sources, preferably renewable or clean energy sources. In some examples, as will also be described further in due course, some of the energy produced by the power unit 100 may be used to power other systems (not shown in Figure 1) in the proximity of the power unit 100 or alternatively be provided back to an electrical power grid or an electrical storage system.

The flue gas produced by the power unit 100 is processed by the scrubbing and cooling system 200, pressure control system 300 and mixing system 400 before reaching the DAC system 500, as will be explained.

The pressure control system 300 provides back pressure control such that the flue gas back pressure is substantially constant. The mixing system 400 mixes the flue gas with air before delivering the mixture to the DAC system 500 where the CO2 is separated from the flue gas and air mixture by use of a physical sorbent within the DAC system 500. The mixing system 400 is further configured to provide venting of excess flue gas, when required. Both of these operations will be explained in more detail later.

Referring now to Figure 2, further details of the power and CO2 capture system 1 are now described with reference to an exemplary arrangement of the power and CO2 capture system 1 such that CO2 can be captured, liquified, stored and transported.

The power unit 100 is provided with fuel (not shown) and provides main electrical power 110 and power unit flue gas 120. The main electrical power 110 is used to power the scrubbing and cooling system 200, mixing system 400 and DAC system 500.

In some examples, as in the presently described example, the power unit 100 may also provide auxiliary electrical power 130 to power auxiliary equipment connected thereto. The distribution of power between the main electrical power 110 supply and the auxiliary electrical power 130 supply in use will be described later.

Still referring to Figure 2, it can be seen that the main electrical power 110 may be supplemented by additional electrical power 140 in some examples. As will be explained in more detail, the additional electrical power 140 may preferably be from renewable power sources such as, but not limited to, solar, wind etc.

Still referring to Figure 2, it can be seen that the power unit flue gas 120 passes through the scrubbing and cooling system 200 and pressure control system 300 before being mixed with atmospheric air 150 in the mixing system 400. Mixed flue gas and air 410 is then delivered to the DAC system 500, as shown in Figure 2, where CO2 is captured from the mixture.

The DAC system 500 is connected, in the presently described example, to a liquefaction system 600. The liquified CO2 may then be stored in a CO2 intermediate storage system 700 and/or shipped in a CO2 shipping system 800. It will be understood that these additional steps are optional in the presently described invention. From the DAC system 500, some air 510 is vented to the atmosphere 900. Further details of each of the major components of the system, i.e. the power unit 100, scrubbing and cooling system 200, pressure control system 300, mixing system 400 and DAC system 500 are now explained.

Firstly, Figure 3 shows further details of the power unit 100, scrubbing and cooling system 200, pressure control system 300 and mixing system 400.

In the power unit 100, ambient air 101 enters a compressor 102 and is compressed therein producing compressed air 103 which is delivered to a combustor 104 where the air is mixed with fuel 105 and heated. The resulting compressed air and fuel mixture 106 is then expanded in an expander 107 that drives the compressor 102 and a first generator 108 via a first shaft 109. Hot flue gas 101’ from the expander 107 is directed to a combined cycle heat recovery unit 102’ comprised of a boiler and steam turbine (not shown). The steam turbine drives a second generator 103’ via a second shaft 104’. The skilled person will understand that this is a general process for the production of power from a hydrocarbon fuel. The skilled person will understand that in different examples, different specific ways of generating electrical power from a hydrocarbon fuel may be utilised in the presently described invention. A non-limiting example of such a method includes the use of a piston engine for example, instead of the presently described gas turbine.

Exiting the power unit 100 there is cooled power unit flue gas 120 which is delivered to the scrubbing and cooling unit 200. Within the scrubbing the cooling unit 200, the power unit flue gas 120 flows upwards over a structured packing 201. Structured packings are well known in the art. The term “structured packing” generally refers to a range of specifically designed materials typically consisting of thin corrugated metal plates or gauzes arranged in a way that forces fluids to take complicated paths therethrough. This creates a large surface area for contact between different phases. It is not critical the type or particular arrangement of the structured packing, and it will be well within the capabilities of a person skilled in the art to provide a suitable packing arrangement with the other components of the system.

Circulating water 202 is pumped from below the structured packing 201 to the top of the structured packing 201 by a pump 203 through a cooler 204. The power unit flue gas 120 flows upwards countercurrent to the circulating water 202 flowing downwards. The circulating water 202 absorbs sour components from the flue gas, such as SOx and NOx. The circulating water 202 also cools the flue gas to a temperature of not more than 15°C above the ambient temperature. The circulating water 202 shown in Figure 3 does not show a supply of clean water or withdrawal of a corresponding amount of contaminated water, which have been omitted for the sake of clarity and brevity.

Cleaned and cooled flue gas 205 is delivered from the scrubbing and cooling system 200 to the pressure control system 300. A desired amount of flue gas 301 is withdrawn from the pressure control system 300. A connection 302 to the atmosphere allows any excess flue gas (not shown) to flow out of the pressure control system 300. If the flow of flue gas 301 out of the pressure control system 300 exceeds the flue gas flow 205 into the pressure control system 300 then air will flow (not shown) from the atmosphere via the connection 302 into the pressure control system 300. In this way the back pressure of the flue gas flow 205 can be maintained substantially at atmospheric pressure at all times, thereby ensuring optimum operation of the power unit 100.

The flue gas 301 flow is then directed to a booster fan 302, the suction pressure of which is ensured to be maintained substantially constant by the pressure control system 300. Constant suction pressure may ensure there is no free spin of the booster fan 302 due to excess suction pressure produced by the power unit 100, which may damage the booster fan 302. Flue gas 303 boosted by the booster fan 302 is then directed to the mixing system 400 where it is mixed with air 401 from the atmosphere.

The ratio of air 401 to flue gas 303 must be at least 10:1. Preferably, the ratio of air 401 to flue gas 303 is less than 200:1. Preferably, the ratio of air 401 to flue gas 303 is greater than 50:1. More preferably, the ratio of air 401 to flue gas 303 is greater than 100:1. Most preferably the ratio of air 401 to glue gas is greater than 160:1. The mixing system 400 produces a DAC system intake gas stream 402 which is then processed by the DAC system 500 to capture CO2 from the DAC system intake gas stream 402, as is now briefly described.

Figure 4 shows an example of a suitable DAC system 500. The DAC system intake gas stream 402 is provided to the DAC system 500 by the mixing system 400 as detailed above. The DAC system 500 then processes the DAC system intake gas stream 402 to captured CO2 within the DAC system 500.

The DAC system 500 employs a physical and solid CO2 sorbent in the present invention. In the presently described example, the physical and solid CO2 sorbent is zeolite. However, it will be understood that in alternative examples other physical and solid CO2 sorbents may be used. Zeolite is a particularly suitable CO2 sorbent due to its low heat of CO2 adsorption and desorption, which is around 40kJ/kg CO2 or about 0.25 kWh/kg CO2.

In an example system which will be described later, the total energy required to capture CO2 from the DAC system intake gas stream in the DAC system is about 1.5 kWh/kg CO2.1.25 kWh/kg CO2 is therefore used for DAC system intake gas stream and water handling.

Therefore, a DAC system intake gas stream 402 with high CO2 content, such as 4 volume% CO2, supplies much more CO2 which does not affect the energy requirement significantly because the adsorption and desorption energy is low.

Furthermore, such a high CO2 content intake gas stream 402 does not affect the energy needed for intake gas stream 402 and H2O handling because with flue gas, this volume is low compared to the amount of CO2.

Referring still to Figure 4, the DAC system 500 in the presently described example is comprised of two sections: a gas pre-treatment section 510 and a sorbent section 520.

The DAC system intake gas stream 402 is temporarily dehydrated to dew-point -20 to -40°C soon after the DAC system intake gas stream 402 enters the DAC system 500, thereby producing a dehydrated gas stream 502. Temporary dehydration is performed by H2O selective adsorbent coated heat exchanger wheels 511, represented schematically simply by a rectangular item in Figure 4. The pressure of the dehydrated gas stream 502 is boosted by a fan 512 thereby producing a fan boosted gas stream 503. The dehydrated gas stream 502 may be boosted by 1000 to 2000 Pa, in some examples. The fan boosted gas stream 503 then passes through a heat exchanger 513 such that heat is exchanged with return gas 504 from the sorbent section 520, thereby producing a heat exchanged gas stream 505. In some examples, the heat exchanged gas stream 505 has a temperature of between -30 and 0°C. The temperature of the heat exchanged gas stream 505 may vary in other examples. The heat exchanged gas stream 505 is then trim cooled in a cooler 514 to produce a trim cooled gas stream 506 which then flows into the sorbent section 520 and flows alternately to a first sorbent bed 521 and a second sorbent bed 522.

Referring to Figure 4, the trim cooled gas stream 506 can be seen to flow to the second sorbent bed 522 where CO2 is captured by the second sorbent bed 522 from the trim cooled gas stream 506. Depleted and deep dehydrated gas 507 is then delivered to the heat exchanger 513 as return gas 504 where the gas is re-heated to near ambient temperature, producing ambient returned gas 508.

The ambient returned gas 508 is then directed to the H2O selective adsorbent coated heat exchanger wheels 511, where the ambient returned gas 508 is rehydrated, thus regenerating the H2O sorbent coated heat exchange wheels 511 and producing rehydrated ambient returned gas 509. The rehydrated ambient returned gas 509 is then delivered to the atmosphere as can be seen in Figure 4.

While the second sorbent bed 522 is in adsorption mode, the first sorbent bed 521 is regenerated by circulating gas 501’ over the first sorbent bed 521, in a direction opposite to the direction used for adsorption, with use of a (not shown) fan and gas heater. The temperature of the circulating gas 501’ entering the first sorbent bed 521 is typically in the range 200 to 300°C. CO2 gas released from the first sorbent bed 521 is directed to post-treatment or sequestration 501.

Similarly, after CO2 saturation of the second sorbent bed 522 and completed regeneration of the first sorbent bed 521, the first sorbent bed 521 is switched to adsorption mode while the second sorbent bed 522 is regenerated by circulating gas over the second sorbent bed 521 in a direction opposite to the direction used for adsorption, with use of a (not shown) fan and gas heater.

Referring now to Figure 5, further details of the pressure control system 300 are now described. The pressure control system 300 is a passive pressure control system 300, which is to say that it automatically regulates, as required, discharge or intake into the pressure control system 300 to ensure a substantially constant back pressure at all times. In operation, cleaned and cooled flue gas 205 is delivered from the scrubbing and cooling system 200 to the pressure control system 300 as previously described, and as can be seen in Figure 5. The cleaned and cooled flue gas 205 flows upwards within the pressure control system 300, and out to the atmosphere as discharged cleaned and cooled flue gas 205A if the flue gas 301 directed to the booster fan 302 is less than is supplied to the pressure control system 300, i.e. the cleaned and cooled flue gas 205.

On the other hand, if the flue gas 301 directed to the booster fan 302 is greater than the cleaned and cooled flue gas 205 supplied to the pressure control system 300, some atmospheric air 205B will be drawn into the pressure control system 300 mixed with the cleaned and cooled flue gas 205 before exiting the pressure control system 300 as flue gas 301 towards the booster fan 302. The pressure control system 300 in the presently described example is a flue gas stack, however it will be understood that the pressure control system 300 in other examples not shown may be in an alternative form. The pressure control system 300 provides passive control of back pressure to the power unit 100. The pressure control system 300 is provided with a cover 310 to prevent rain from entering, as can be seen in Figure 5.

Referring now to Figures 6a and 6b, further details of the mixing system 400 are now provided. Figure 6a shows a perspective view of the mixing system 400 and Figure 6b shows a cross-sectional view through the mixing system 400.

As can be seen in Figure 6a, the mixing system 400 is provided with weather hoods 420, 421, 422, 423, 424, 425, 426, 427 and vertical shields 428, 429 which protect air intakes 430, 431, 432, 433, 434, 435, 436, 437 from wind and rain. In use, air is drawn under the weather hoods 420, 421, 422, 423, 424, 425, 426, 427 by the fan 512 of the DAC system 500.

A vertical manifold 440 is located near the weather hoods 420, 421, 422, 423, 424, 425, 426, 427 inside the volume defined by the weather hoods 420, 421, 422, 423, 424, 425, 426, 427 and the vertical shields 428, 429.

As can be seen in the cross-sectional view shown in Figure 6b, flue gas 303 (boosted by the booster fan 302) is connected to the manifold 440.

In the manifold 440 the flue gas 303 is distributed to nozzles 450, 451, 452, 453, 454, 455, 456. Upon exiting these nozzles 450, 451, 452, 453, 454, 455, 456 the flue gas 303 is mixed with incoming air 460, 461, 462, 463, 464, 465, 466, 467 to form the DAC system intake gas stream 402.

The number of nozzles and weather hoods may vary in alternative examples. It will be understood that the specific number of nozzles and weather hoods provided in the presently described example may easily be changed.

It will now be understood that the power unit 100 provides power which is utilised to operate the remainder of the system 1. The main CO2 source to the system 1 is from atmospheric air, however this is supplemented by CO2 in the flue gas 120 from the power unit 100.

Examples

In the following first example CO2 is captured from air with a system and method according to the present invention. The first example system is shown in Figure 7. For comparison, in a second example, CO2 is captured from air with the system and method powered only by a non-CO2 producing energy source. The second example system is shown in Figure 8.

First example – CO2 capture from air using a methane fuelled power unit Referring firstly to Figure 7, the system 1A comprises a power unit 100A in the form of a combined cycle gas turbine unit with 100MW power and high efficiency of 60%. The power unit 100A is provided with fuel (not shown) in the form of methane. The power unit 100A provides main electrical power 110A (which is not supplemented with any renewable or other additional electrical power (140 in Figure 2). The power unit 100A also produces power unit flue gas 120A with CO2 present in the flue gas 120A. In this way the power unit 100A emits 33 tons of CO2 per hour during operation.

As can be seen in Figure 7, the main electrical power 110A is used to power the scrubbing and cooling system 200A, mixing system 400A and DAC system 500A. The power unit 100A may also provide auxiliary electrical power 130A to power auxiliary equipment connected thereto.

Still referring to Figure 7, it can be seen that the power unit flue gas 120A passes through the scrubbing and cooling system 200A and pressure control system 300A before being mixed with atmospheric air 150A in the mixing system 400A.

Mixed flue gas and air 410A is then delivered to the DAC system 500A, where CO2 is captured from the mixture.

In the presently described example, the DAC system 500A is not connected to a liquefaction, storage or transportation system. These optional components are not critical to the invention. From the DAC system 500A, some air 510A is vented to the atmosphere 900A.

In use the capacity of the fan (not shown in Figure 7) within the DAC system 500A can be controlled such that the power requirement for the scrubbing and cooling system 200A, the mixing system 400A and the DAC system 500A is the same as the power output from the power unit 100A. The pressure control system 300A is a passive system requiring no energy input. In the present example, when no auxiliary electrical power 130A is required, the power output from the power unit 100A is 100MW.

In the presently described example, the power unit flue gas 120A flow rate is 4.5e5 Sm3/h. The power unit flue gas has a CO2 mole% of 4. The power unit flue gas 120A flow passes through the scrubbing and cooling system 200A, pressure control system 300A and is mixed with atmospheric air 150A in the mixing system 400A at a flow rate of 7.8e7 Sm3/h, producing mixed flue gas and air 410A. The atmospheric air 150A has a CO2 content of 420ppm. The mixed flue gas and air 410A has a CO2 content of 648ppm and is delivered to the DAC system 500A for capture of CO2 at a rate of 94 tons per hour.33 tons of CO2 originates from the power unit 100A and 61 tons originates from the atmospheric air 150A. Said another way, all CO2 emissions from the power unit 100A are captured in the DAC system 500A and 61 tons per hour is captured from the atmospheric air.

Second example – CO2 capture from air using a non-CO2 producing energy source

Referring now to Figure 8, the system 1B is modified to be powered solely by a non-CO2 producing energy source. This is provided for comparison with the first example which is in accordance with the present invention. For the avoidance of doubt, the solely renewable energy powered system is not the subject of the invention.

As can be seen in Figure 8, only electrical power 140B is provided to the system 1B, with no flue gas generation from the non-CO2 producing energy source. The hydrocarbon fuelled power unit has been omitted from Figure 8, although it may be present and not running. Although shown in Figure 8, the scrubbing and cooling system 200B and pressure control system 300B are not operating since there is no flue gas generation from the hydrocarbon fuelled power unit, therefore there is no flue gas to be scrubbed and cooled by the scrubbing and cooling system 200B and no back pressure control required by the pressure control system 300B.

In the first example system 1A, the flue gas and air mixture 410A is delivered to the DAC system 500A. In the presently described second example, only atmospheric air 410B is delivered to the DAC system 500B since there is no flue gas. The DAC system 500B processes the air 410B such that CO2 is captured from the air 410B.

In the present example, a 100MW electrical power 140B is provided (as was provided in the first example from the power unit 100A), which results in CO2 capture of 67 tons per hour.

Overview of data from examples

In the above examples, the air composition was as given below in Table 1.

Table 1 - Air composition

The full data from the first and second examples above is now provided in Table 2.

Table 2 - Full data relates to examples 1 and 2 above

The above data and examples show that there is only a small drop in overall CO2 capture from the air when the system and method are powered by a hydrocarbon power unit 100. The examples also show that all of the excess CO2 produced by the hydrocarbon power unit 100 is captured by the system, therefore the system and method may provide the advantage of CO2 capture independent of grid power or renewable power with greater flexibility of site location, while providing only a minor drop in CO2 capture rate. The system and method may also be used to annul CO2 emissions from power plants in locations unsuitable for local CO2 capture.

Referring now to Figures 9 to 13, further data relating to the above described first example is now provided.

In the first example system, the power unit 100A operates at 60% efficiency and 100MW of power is used. The fuel used, methane, has a lower heating value of 50,000 kJ/kg or about 13.9 kWh per kg. The fuel consumption is 12 tons per hour which produces 33 tons per hour CO2 that is mixed with air and captured. The total energy required to capture CO2 is about 1.5 kWh/kg CO2.1.25 kWh/kg CO2 is therefore used for DAC system intake gas stream and water handling.

An atmospheric air CO2 content of 420 ppm or about 0.79 g per Sm3 is assumed. To produce 1 kg CO2 it is necessary to treat 1272 Sm3 air. This is the basis for the data provided in Figures 9 to 13.

Figure 9 shows the amount of CO2 captured in tons per hour (y-axis) vs auxiliary electrical power 130A from the power unit 100A in MW (x-axis). With zero auxiliary electrical power 130A, 100 MW is used for CO2 capture. With 60 MW auxiliary electrical power 130A, 40 MW is used for CO2 capture. All CO2 from the flue gas 120A is captured in every case, with amount of air 150A mixed with the flue gas 120A adjusted to utilise all available power or the power that is not provided as auxiliary power 130A, i.e. exported.

The total amount of CO2 captured is shown in the solid line, starting at about 93 tons per hour when all 100 MW is used for CO2 capture. This drops to about 55 tons per hour if 60% of the power produced is provided as auxiliary electrical power 130A, i.e. exported, and 40% is used for CO2 capture. The dashed line shows net CO2 captured from air 150A. This is 33 tons per hour lower than the total amount of CO2 captured, starting at 60 tons per hour and dropping to about 32 tons per hour if 60% of the power is provided as auxiliary electrical power 130A, i.e. exported.

Figure 10 shows the ratio of air flow 150A to flue gas 120A volume flow (y-axis) vs auxiliary power 130A in MW (x-axis). The ratio is about 165 for maximum CO2 capture, when all energy from the power unit 100 is utilised (i.e. no auxiliary electrical power 130 is provided). This ratio drops to about 60 when 60% of the energy is provided for auxiliary power 130A, or 40 MW is used for CO2 capture.

Figure 11 shows the number of separate but similar power units that can be annulled (y-axis) in terms of CO2 emissions from those power units because of CO2 capture from air 150A vs amount of auxiliary power 130A provided in MW (x-axis). When all power is used for the CO2 capture process, emissions from about 1.82 power units of similar type can be annulled. When 40% of the power is provided as auxiliary power 130A, i.e. exported, CO2 emissions from one power unit of similar type can be annulled.

Figure 12 shows the specific energy consumption of the DAC system 500A in kWh/kg (y-axis) as function of the amount of auxiliary power 130A provided in MW (x-axis). It starts at about 1.07 kWh/kg CO2 when no auxiliary power 130A is provided, or the maximum amount of air 150A is mixed with the flue gas 120A to capture maximum amount of CO2. The specific power drops as more auxiliary power 130A is provided and less air 150A is mixed with the flue gas 120A.

Figure 13 shows the concentration in ppm of CO2 entering the DAC system 500A vs the amount of auxiliary power 130A provided in MW. The concentration is lowest when no auxiliary power 130A is provided and maximum amount of air 150A is mixed with the flue gas 120A. The concentration increases when some auxiliary power 130A is provided and therefore less air 150A can be mixed with the flue gas 120A in order to utilise the power available for CO2 capture.

As shown above, a very attractive energy source for DAC is a hydrocarbon power unit. This preserves one of the main advantages with DAC, namely the possibility to freely choose location for the DAC system.

The invention may find particular utility in oil and gas operations where there is an urgent need to reduce CO2 emissions. Furthermore, in oil and gas operations there is already existing hydrocarbon fuelled power units which may be easily connected to the other components of the system described herein.

It has been shown that CO2 from the power unit may be captured by the DAC system, with only minimal effect on the amount of CO2 captured from the air. This solution may be more attractive than employing a dedicated, traditional capture unit for the power plant flue gas. This would require a DAC technology that is only marginally affected by the extra gas volume and CO2 originating from the power plant.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims

1. A CO2 capture system comprising:

a hydrocarbon fuelled power unit;

a scrubbing and cooling system;

a pressure control system;

a mixing system; and

direct air capture (DAC) system comprising a physical sorbent; wherein the hydrocarbon fuelled power unit is configured to provide electrical power and flue gas;

the scrubbing and cooling system is connected to the hydrocarbon fuelled power unit to receive electrical power and the flue gas and is configured to clean and cool the flue gas to provide a cleaned and cooled flue gas;

the pressure control system is connected to the scrubbing and cooling system to receive the cleaned and cooled flue gas and is configured to:

vent cleaned and cooled flue gas to the atmosphere if the pressure of the cleaned and cooled flue gas flow is above atmospheric pressure and to

mix atmospheric air into the cleaned and cooled flue gas flow if the pressure of the cleaned and cooled flue gas is below atmospheric pressure;

thereby in use ensuring a constant back pressure equal to atmospheric pressure;

the mixing system is connected to the hydrocarbon fuelled power unit to receive electrical power and is further connected to the pressure control system to receive the cleaned and cooled flue gas flow at atmospheric pressure and to mix atmospheric air with the cleaned and cooled flue gas flow at a ratio of between 10:1 and 200:1, thereby providing a DAC system intake gas stream; and

the DAC system is connected to the hydrocarbon fuelled power unit to receive electrical power and is further connected to the mixing system to receive the DAC system intake gas stream, wherein the DAC system is configured to capture CO2 from the DAC system intake gas stream.

2. The CO2 capture system according to claim 1, wherein the hydrocarbon fuelled power unit is a methane power unit.

3. The CO2 capture system according to claim 1 or 2, wherein the hydrocarbon fuelled power unit is configured to provide auxiliary electrical power to power auxiliary equipment.

4. The CO2 capture system according to any preceding claim, wherein the hydrocarbon fuelled power unit comprises a gas turbine or a piston engine.

5. The CO2 capture system according to any preceding claim, further comprising a renewable energy electrical power source configured to supplement the power delivered by the hydrocarbon fuelled power unit in use.

6. The CO2 capture system according to any preceding claim, wherein the scrubbing and cooling system comprises:

a structure packing;

a pump; and

a cooler;

wherein the scrubbing and cooling system is configured in use to allow flue gas to flow upwards countercurrent to circulating water pumped by the pump and cooled by the cooler, such that the circulating water can absorb sour components from the flue gas and cool the flue gas to not more than 15°C above the ambient temperature.

7. The CO2 capture system according to claim 6, wherein scrubbing and cooling system further comprises a connection for connecting to a supply of clean water in use and a conduit for the disposal of contaminated water.

8. The CO2 capture system according to any preceding claim, wherein the pressure control system comprises a flue stack.

9. The CO2 capture system according to any preceding claim, wherein the pressure control system is a passive pressure control system.

10. The CO2 capture system according to any preceding claim, further comprising a booster fan located between the pressure control system and the mixing system, wherein the booster fan is configured to boost the cleaned and cooled flue gas.

11. The CO2 capture system according to any preceding claim, wherein the mixing system is configured to mix atmospheric air with the cleaned and cooled flue gas flow at a ratio of between 50:1 and 200:1 or a ratio of between 100:1 and 200:1 or a ratio of between 160:1 and 200:1.

12. The CO2 capture system according to any preceding claim, wherein the physical sorbent is zeolite.

13. The CO2 capture system according to any preceding claim, wherein the mixing system comprises a manifold distributed across the mixing system and configured to deliver the atmospheric air substantially evenly across the cleaned and cooled flue gas stream in use.

14. An intermediate system for locating between a hydrocarbon fuelled power unit and a direct air capture system comprising a physical sorbent in a CO2 capture system, the intermediate system comprising:

a scrubbing and cooling system;

a pressure control system; and

a mixing system;

wherein the scrubbing and cooling system is configured to be connectable in use to the hydrocarbon fuelled power unit to receive electrical power and the flue gas and to clean and cool the flue gas to provide a cleaned and cooled flue gas;

the pressure control system is configured to be connectable in use to the scrubbing and cooling system to receive the cleaned and cooled flue gas and to:

thereby in use ensuring a constant back pressure equal to atmospheric pressure;

the mixing system is configured to be connectable in use to:

the hydrocarbon fuelled power unit to receive electrical power; the pressure control system to receive the cleaned and cooled flue gas flow at atmospheric pressure and to mix atmospheric air with the cleaned and cooled flue gas flow at a ratio of between 10:1 and 200:1, thereby providing a DAC system intake gas stream; and

the DAC system to deliver the DAC system intake gas stream thereto.

15. The intermediate system according to claim 14, wherein the scrubbing and cooling system comprises:

a structure packing;

a pump; and

a cooler;

16. The intermediate system according to claim 14 or 15, wherein scrubbing and cooling system further comprises a connection for connecting to a supply of clean water and a conduit for the disposal of contaminated water.

17. The intermediate system according to any of claims 14 to 16, wherein the pressure control system comprises a flue stack.

18. The intermediate system according to any of claims 14 to 17, wherein the pressure control system is a passive pressure control system.

19. The intermediate system according to any of claims 14 to 18, further comprising a booster fan configured to be located between the pressure control system and the mixing system in use, wherein the booster fan is configured in use to boost the cleaned and cooled flue gas.

20. The intermediate system according to any of claims 14 to 19, wherein the mixing system is configured to mix atmospheric air with the cleaned and cooled flue gas flow at a ratio of between 50:1 and 200:1 or a ratio of between 100:1 and 200:1 or a ratio of between 160:1 and 200:1.

21. The intermediate system according to any of claims 14 to 20, wherein the mixing system comprises a manifold distributed across the mixing system and configured to deliver the atmospheric air substantially evenly across the cleaned and cooled flue gas stream in use.

22. A CO2 capture kit comprising:

a hydrocarbon fuelled power unit;

a scrubbing and cooling system;

a pressure control system;

a mixing system; and

the scrubbing and cooling system is configured to be connectable in use to the hydrocarbon fuelled power unit to receive electrical power and the flue gas and to clean and cool the flue gas to provide a cleaned and cooled flue gas;

thereby in use ensuring a constant back pressure equal to atmospheric pressure;

the mixing system is configured to be connectable in use to the hydrocarbon fuelled power unit to receive electrical power and to be further connectable in use to pressure control system to receive the cleaned and cooled flue gas flow at atmospheric pressure and to mix atmospheric air with the cleaned and cooled flue gas flow at a ratio of between 10:1 and 200:1, thereby providing a DAC system intake gas stream;

the DAC system is configured to be connectable in use to the mixing system to receive the DAC system intake gas stream and to capture CO2 from the DAC system intake gas stream.

23. A method of CO2 capture from the atmosphere, comprising the steps of:

providing a CO2 capture system according to any of claims 1 to 13;

running the hydrocarbon fuelled power unit to provide electrical power to the scrubbing and cooling system, the mixing system and the DAC system and to provide flue gas to the scrubbing and cooling system;

cleaning and cooling the flue gas in the scrubbing and cooling system to provide cleaned and cooled flue gas to the pressure control system;

providing a constant back pressure equal to atmospheric pressure by:

venting cleaned and cooled flue gas to the atmosphere in the pressure control system if the pressure of the cleaned and cooled flue gas flow into the pressure control system is above atmospheric pressure; or

mixing atmospheric air into the cleaned and cooled flue gas flow in the pressure control system if the pressure of the cleaned and cooled flue gas into the pressure control system is below atmospheric pressure;

mixing atmospheric air with the cleaned and cooled flue gas flow at a ratio of between 10:1 and 200:1 in the mixing system to provide a DAC system intake gas stream;

operating the DAC system to capture CO2 from the DAC system intake gas stream.

24. The method of CO2 capture according to claim 23, wherein the step of mixing atmospheric air with cleaned and cooled flue gas is at a ratio of between 50:1 and 200:1 or a ratio of between 100:1 and 200:1 or a ratio of between 160:1 and 200:1.