WO2022112366A1

WO2022112366A1 - Providing heat energy to direct air carbon dioxide capture processes using waste heat from data centre

Info

Publication number: WO2022112366A1
Application number: PCT/EP2021/082890
Authority: WO
Inventors: Don MACELROY; Wolfgang Schmitt; Sebastien VAESEN
Original assignee: The Provost, Fellows, Foundation Scholars, And The Other Members Of Board, Of The College Of The Holy And Undivided Trinity Of Queen Elizabeth, Near Dublin
Priority date: 2020-11-26
Filing date: 2021-11-24
Publication date: 2022-06-02
Also published as: GB2592707A; GB202018646D0; GB2592707B

Abstract

A system for providing heat energy to a direct air carbon dioxide capture process. The system comprises a heat source, coupled via a first thermal transfer circuit to an input of a heat pump, said system further comprising a direct air carbon dioxide capture process apparatus for performing a direct air carbon dioxide capture process coupled to an output of the heat pump via a second thermal transfer circuit. The heat source is a computing data centre, and in use, low grade waste heat energy from the computing data centre is transferred via the first thermal transfer circuit to the heat pump which generates higher grade heat energy which is then transferred from the heat pump to the direct air carbon dioxide capture process apparatus via the second thermal transfer circuit for performing the direct air carbon dioxide capture process. The direct air carbon dioxide capture process is one of a temperature swing adsorption carbon dioxide capture process or a vacuum temperature swing adsorption carbon dioxide capture process.

Description

Providing Heat Energy to Direct Air Carbon Dioxide Capture Processes Using

Waste Heat from Data Centre Technical Field

The present invention relates to techniques for providing heat energy to direct air carbon dioxide capture processes.

Background Carbon dioxide is a greenhouse gas, and the role of increasing atmospheric carbon dioxide concentration on global warming is generally well accepted.

Widespread combustion of fossil fuels and other industrial activity has raised levels of carbon dioxide in the atmosphere from 280 ppmV in preindustrial times to the present excess of 410 ppmV.

It is predicted that fossil fuels will remain a global energy source for the next 25 years at least, and modest reductions of carbon dioxide emissions will only delay the increase of carbon dioxide levels in the atmosphere.

According to the Intergovernmental Panel on Climate Change (IPCC), a four-fold decrease in carbon dioxide emissions is required in the coming decades to successfully stabilise carbon dioxide concentrations by the year 2100 to reach a stabilising benchmark concentration of 550 ppmV.

Carbon dioxide capture directly from air, that is, direct air carbon dioxide capture is a potentially promising technological approach to reduce the carbon dioxide quantity in the atmosphere. Its viability relies on the development of cost-effective materials and low-cost processes.

Working prototypes have been deployed but none are considered commercially viable due to a number of factors including the high energy required for the processes to be performed. Also, IT technologies (such as data storage, clouding, streaming, etc.) require a worldwide ever-increasing number of data centres which use electricity and turn it into low grade heat implying the cooling of these data centres.

It is an aim of certain embodiments of the invention to provide more commercially viable techniques for providing heat energy to direct air carbon dioxide capture processes by using heat produced by data centres.

Summary of the Invention

In accordance with a first aspect of the invention, there is provided a system for providing heat energy to a direct air carbon dioxide capture process. The system comprises a heat source, coupled via a first thermal transfer circuit to an input of a heat pump, said system further comprising a direct air carbon dioxide capture process apparatus for performing a direct air carbon dioxide capture process coupled to an output of the heat pump via a second thermal transfer circuit. The heat source is a computing data centre, and in use, low grade waste heat energy from the computing data centre is transferred via the first thermal transfer circuit to the heat pump which generates higher grade heat energy which is then transferred from the heat pump to the direct air carbon dioxide capture process apparatus via the second thermal transfer circuit for performing the direct air carbon dioxide capture process. The direct air carbon dioxide capture process is one of a temperature swing adsorption carbon dioxide capture process or a vacuum temperature swing adsorption carbon dioxide capture process.

Optionally, the first thermal transfer circuit forms at least part of a computing data centre cooling system.

Optionally, the heat pump is one of a single-stage heat pump, a-double stage heat pump or a multi-stage heat pump.

Optionally, a refrigerant used in the heat pump comprises one of water (R718), ammonia (R717) or a hydrofluoroolefin.

Optionally, wherein the coefficient of performance of the heat pump is greater than 3, preferentially greater than 4, and optimally greater than 5.

Optionally, wherein output carbon dioxide from the direct air carbon dioxide capture process is used in a subsequent process.

Optionally, output carbon dioxide from the direct air carbon dioxide capture process is stored. Optionally, the input of the heat pump is an evaporator and the output of the heat pump is a condenser.

In accordance with a second aspect of the invention, there is provided a method of providing heat energy to a direct air carbon dioxide capture process. The method comprises: transferring low grade waste heat energy from a computing data centre to the input of a heat pump via a first thermal transfer circuit; converting, using the heat pump, the low-grade waste heat energy to higher grade heat energy; transferring the higher-grade heat energy from an output of the heat pump to a direct air carbon dioxide capture process apparatus via a second thermal transfer circuit, and using the higher- grade heat energy to provide heat energy to the direct air carbon dioxide capture process apparatus to perform a direct air carbon dioxide capture process. The direct air carbon dioxide capture process performed by the direct air carbon dioxide capture process apparatus is one of a temperature swing adsorption carbon dioxide capture process or a vacuum temperature swing adsorption carbon dioxide capture process.

Optionally, the heat pump in one of a single-stage heat pump, a double-stage heat pump or a multi-stage heat pump.

Optionally, the coefficient of performance of the heat pump is greater than 3, preferentially greater than 4, and optimally greater than 5.

Optionally, the method further comprises using output carbon dioxide from the direct air carbon dioxide capture process in a subsequent process. Optionally, the method further comprises storing output carbon dioxide from the direct air carbon dioxide capture process.

Optionally, the input of the heat pump is an evaporator, and the output of the heat pump is a condenser.

In accordance with embodiments of the invention it has been recognised that by providing a suitable heat pump system, waste heat, which is an inevitable by-product of the operation of computing data centres, can usefully provide a source of energy for systems performing carbon dioxide capture processes, in particular DAC carbon dioxide capture processes. Typically, such direct air carbon dioxide capture processes need input heat to operate and using conventional techniques, this heat would be provided by a heating system that uses the Joule effect (heating by passing a current through a heating element) or by a system that provides a hot fluid, heated, for example by a gas burner or electric heater.

Advantageously, integrating an otherwise conventional heat pump system with, for example, a cooling system of a data centre, provides a means by which the low-grade waste heat from a computing data centre can be converted to useful high-grade heat for providing energy for a carbon dioxide capture process.

The amount of energy necessary to power the heat pump to convert the low-grade waste heat from the computing data centre to high-grade heat suitable for use in the direct air carbon dioxide capture process, is less than the amount of energy that would otherwise be required to perform the direct air carbon dioxide capture process. Techniques in accordance with embodiments of the invention reduce the amount of energy that would otherwise be required to perform a direct air carbon dioxide capture process therefore making the use of direct air carbon dioxide capture processes for removing carbon dioxide from atmospheric air more economically viable.

Further, systems in accordance with certain embodiments of the invention can either supplement or replace normal data centre cooling systems, offsetting the energy that would otherwise be used to power such cooling systems. Various further features and aspects of the invention are defined in the claims.

Brief Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings where like parts are provided with corresponding reference numerals and in which:

Figure 1 provides a simplified schematic diagram of a system for providing heat energy from a computing data centre to a direct air carbon dioxide capture process in accordance with certain examples of the invention; Figure 2 provides a schematic diagram providing an overview of the thermodynamic operation of a heat pump in accordance with embodiments of the invention;

Figure 3 provides a simplified schematic diagram providing a detailed depiction of a system arranged in accordance with certain embodiments of the invention;

Figure 4 provides a detailed view of a heat transfer component of a direct air carbon dioxide capture apparatus in accordance with certain embodiments of the invention;

Figure 5 provides a schematic diagram depicting a direct air carbon dioxide capture process apparatus suitable for use in certain embodiments of the invention;

Figure 6a provides a schematic diagram depicting a system comprising a double-stage heat pump in accordance with certain embodiments of the invention; Figure 6b provides a schematic diagram depicting a system comprising a multi-stage heat pump in accordance with certain embodiments of the invention, and

Figure 7 provides a diagram depicting a graph showing a first, second and third curve depicting the change in the required coefficient of performance for a system arranged in accordance with examples of the invention. Detailed Description

Figure 1 provides a simplified schematic diagram of a system 101 for providing heat energy to a direct air carbon dioxide capture process in accordance with certain examples of the invention.

A computing data centre 102 comprising computing devices is powered by a first power source 103. During operation of the computing devices, they generate heat. This heat is “low-grade” heat, i.e. heat in a temperature range that cannot readily be used to do useful work. The heat output by computing devices is typically below 50 °C.

Heat in this temperature range is often considered “waste” heat because it is not of a high enough temperature to be easily used in another process requiring heat energy.

The low-grade heat generated by the computing data centre 102 is transferred to a heat pump 104. The heat pump 104 is powered by a second power source 105. The amount of energy transferred from the second power source 105 to the heat pump 104 over a given period of time is lower, typically substantially lower, than the total amount of energy transferred from the first power source 103 to the computing data centre 102 over the same period of time.

Using energy from the low-grade heat from the computing data centre 102 and the second electrical power source 105, the heat pump outputs high-grade heat, i.e., heat in a temperature range of above 50°C. Energy from the output high-grade heat is used to provide heat for a system 106 performing a direct air carbon dioxide capture process.

Advantageously, by using a system as depicted in Figure 1 , low-grade heat, that would normally be treated as waste heat, can instead be used to power a direct air carbon dioxide capture process.

By virtue of the provision of a relatively low amount of input energy from the second power source 105, the low-grade heat that is a by-product of computing data centre operation and that would not normally be used, is used to provide input heat to a direct air carbon dioxide capture process.

Figure 2 provides a schematic diagram providing an overview of the thermodynamic operation of a heat pump 201 in accordance with embodiments of the invention. The heat pump includes an evaporator 202, compressor 203, condenser 204 and expansion valve 205. A refrigerant circulates around the heat exchanger in the direction indicated by the arrows. Energy from the low-grade heat energy Q_e output from the computing data centre is input to the evaporator 202. This causes the refrigerant to undergo a phase change transition from a liquid/vapour mixture to a pure vapour phase. The refrigerant then enters the compressor 203. The compressor 203, using the energy W, compresses the refrigerant (isentropic compression) which increases both pressure and temperature at the same time. The compressed refrigerant exits the compressor 203 and enters the condenser 204 as super-heated vapour from which high-grade heat energy Q_c is output to power the direct air carbon dioxide capture process. As this energy is extracted, the refrigerant undergoes condensation (isobaric condensation). The condensed refrigerant then enters the expansion valve 205 to undergo an isenthalpic expansion. This reduces the pressure and the temperature of the refrigerant which becomes a liquid/vapour mixture. The cooled refrigerant then exits the expansion valve and enters the evaporator 202 as a liquid/vapour mixture. The refrigerant then undergoes evaporation due to the low-grade heat energy Q_e output from the computing data centre (isobaric evaporation), and the cycle repeats.

The Coefficient of Performance (COP) of a heat pump is calculated as:

The heat demand, Eheat, of a typical carbon capture process such as a vacuum temperature swing adsorption (VTSA) process is determined by the following four energy requirements: 1) E_ads , the energy requirement to heat the adsorbent:

2) E_dev, the energy requirement to heat the vessel:

3) the energy requirement to heat the CO₂:

4)

the energy requirement to desorb the CO₂:

In the equations above, m_ads and m_ves represent the masses of the adsorbent and the vessel (kg), c_p,ads and c_p,ves are the specific heat capacities of the adsorbent and the vessel (J kg^-1 K^_1), ΔT is the differential temperature between the capture and the release of the process, is the mass of adsorbed CO₂ at the end of the

capture process, Rec is the relative recovery, and is the CO₂ adsorption

enthalpy (J kg^·1).

Thus

Thus, electricity requirement, W, required to generate heat for a typical direct air carbon dioxide capture process is given by:

where E_heat is the requirement energy requirement to heat the direct air carbon dioxide process.

Figure 3 provides a simplified schematic diagram providing a more detailed depiction of a system 301 arranged in accordance with certain embodiments of the invention. The system 301 includes a computing data centre 302, a heat pump system 303 and an apparatus for performing a direct air carbon dioxide capture process 304.

The computing data centre includes computing equipment 302a such as data processing servers; telecommunications equipment, such as data routers, data storing severs and so on. The computing equipment 302a is provided with a plurality of thermal heatsinks 305 via which waste heat generated as a result of the computing processes undertaken by the computing equipment 302a is transferred from the computing equipment 302a. The heatsinks 305 are thermally coupled to a first side 306a of a first thermal transfer circuit 306. The first thermal transfer circuit 306 is provided by a liquid cooling circuit comprising tubes through which a liquid coolant, for example water, is circulated by a pump 307. The direction of flow of coolant is indicated by the arrows.

A second side 306b of the first thermal transfer circuit 306 is thermally coupled to an evaporator 308 of the heat pump system 303. The evaporator 308 is provided by a series of tubes through which a liquid refrigerant is circulated.

In use, driven by the pump, liquid coolant circulates through the first side 306a of the first thermal transfer circuit 306 thermally coupled to the heatsinks 305 and heat energy is transferred from the heatsinks 305 to the liquid coolant. Advantageously, this process also cools the computing equipment 302a.

The heated coolant circulates through the first thermal transfer circuit 306 and circulates through the second side 306b of the first thermal transfer circuit 306 thermally coupled to the evaporator 308 of the heat pump system 303. Heat energy is transferred from the liquid coolant to the refrigerant in the evaporator 308.

The evaporator 308 is coupled to a compressor 309. The compressor 309, powered by an external power source 310, compresses the refrigerant which heats the refrigerant. The refrigerant, heated and compressed, is then directed into a condenser 311 which is provided by a further series of tubes through which the vapour refrigerant is circulated.

Thermally coupled to the condenser 311 is a second thermal transfer circuit 312.

The second thermal transfer circuit 312 is provided by a liquid coolant circuit comprising tubes through which a liquid coolant, for example water, is circulated by a pump 313. The condenser 311 is thermally coupled to a first side 312a of the second thermal transfer circuit 312. A second side 312b of the second thermal transfer circuit

312 is thermally coupled to a heat transfer component 314 of the direct air carbon dioxide capture apparatus 304.

In use, driven by the pump 313, liquid coolant circulates through the first side 312a of the second thermal transfer circuit 312 thermally coupled to the condenser 311 and heat energy is transferred from the refrigerant in the condenser 311 to the liquid coolant in the second thermal transfer circuit 312. The heated coolant circulates through the second side 312b of the second thermal transfer circuit 312 and heat energy is transferred from the liquid coolant to the heat transfer component 314 of the direct air carbon dioxide capture apparatus 304.

In the condenser 311 , the vapour refrigerant is first cooled down and then undergoes a phase transition from the vapour to the liquid phase. In the condenser 311 , most of the energy is due to latent heat. The heat pump system 303 further includes an expansion valve 315. The condenser 311 is coupled to an input of the expansion valve 315 and the evaporator 308 is coupled to an output of the expansion valve 315. Refrigerant, partially cooled and turned into pure liquid after thermal energy has been extracted by the second thermal transfer circuit 312, is directed through the expansion valve 315 which reduces the pressure, cools it further and partially turns it into vapor. Cooled refrigerant is then pumped back into the evaporator 308 to be heated again by thermal energy extracted from the computing data centre 302 by the first thermal transfer circuit 306. The apparatus for performing a direct air carbon dioxide capture process 304 is configured to receive atmospheric air (containing carbon dioxide) via an inlet 316, perform a carbon dioxide capture process on this air to extract carbon dioxide, and exhaust treated air via an outlet 317.

The carbon dioxide extracted during this process is output via a second outlet 318. In certain embodiments, the carbon dioxide can be stored for example in the form of liquid. More specifically, in certain examples, the carbon dioxide output via the second outlet is at 100 kPa (1 bar) pressure and is sent to a series of compressors. At 20 °C, the CO₂ becomes liquid at 5270 kPa (52.7 bar). The liquid carbon dioxide can then be easily transported and handled in cylinders or tanks.

Alternatively, the carbon dioxide can be used in other processes. For example, carbon dioxide can be used directly (e.g. sent into greenhouses, sent to beverage industries (for the production of sparkling drinks)) or it can be used as a feedstock for chemical synthesis (e.g. urea, methane, hydrocarbons, methanol, formic acid etc...). Using the extracted carbon dioxide in this way is advantageous because, conventionally, CO₂ used in the chemical industries mainly comes from fossil sources. The output carbon dioxide will be compressed first, and then can be sent by pipes (if, for example a recipient is close enough) or sent by trucks.

Figure 4 provides a more detailed view of the heat transfer component 314 of the direct air carbon dioxide capture apparatus 304 transferring heat energy from the second side 312b of the second thermal transfer circuit to the direct air carbon dioxide capture process. As can be seen, the heat transfer component comprises a conduit through which the heated refrigerant passes, the conduit being disposed within the direct air carbon dioxide capture process apparatus.

The direct air carbon dioxide capture process performed by the direct air carbon dioxide capture apparatus 304 can be any suitable direct air carbon dioxide capture process that can be powered from high-grade heat out from the heat pump system 303, for example a temperature swing adsorption process or a vacuum temperature swing adsorption process. Figure 5 provides a simplified schematic diagram depicting an example of direct air carbon dioxide capture apparatus 500 which implements a vacuum temperature swing adsorption (VTSA) carbon dioxide capture process that can be used in certain embodiments of the invention. The apparatus includes an adsorbent bed 501 , an air blower 502, a vacuum pump 503, a first valve 504, a second valve 505 and a third valve 506. Only one adsorbent bed 501 is shown, but typically in an industrial application, multiple adsorbent beds would be employed ensuring a continuous capturing of carbon dioxide and, consequently, generating a constant demand for heat.

The apparatus implements a three-stage process.

During a first stage, the first valve 504 and second valve 505 are open and the third valve 506 is closed. The blower 502 pushes air from the inlet 316 through the adsorbent bed 501.

Carbon dioxide is captured by the adsorbent bed and the treated air, from which carbon dioxide has been removed, is exhausted through the outlet 317. The capture continues until the adsorbent is saturated with carbon dioxide.

During a second stage of the process the first valve 504, second valve 505 and third valve 506 are closed and there is no air flowing through the system.

The heated liquid coolant circulates through the second side 312b of the second thermal transfer circuit 312 and heat energy is delivered to the adsorbent bed 501 . It increases the temperature of the adsorbent bed 501 and partially releases the adsorbed carbon dioxide.

During a third stage of the process, the third valve 506 is opened and the first valve 504 and the second valve 505 close. The carbon dioxide is pumped by the vacuum pump 503 and sent to the outlet 318. During this step, as the release of the carbon dioxide from the adsorbent of the adsorbent bed 501 is an endothermic process, the heated liquid coolant continues to circulate through the second sid2e 312b of the second thermal transfer circuit 312 to maintain the temperature of the adsorbent bed 501 . When the carbon dioxide is released, the process begins again.

The refrigerant used in the heat pump system 303 can be any suitable refrigerant, for example water (R718) or ammonia (R717), or a hydrofluoroolefin (HFO) refrigerant such as R-1233zd (CF₃-CH=CCIH); R-1234yf (CF₃-CF=CH₂); R-1234ze (CF₃- CH=CFH) or R-1336mzz (CF₃-CH=CH-CF₃).

In certain embodiments, the heat transfer circuit used to transfer heat energy from computing equipment of the computing data centre can supplement or replace the conventional cooling system that would otherwise be used to cool the computing equipment of the computing data centre.

In the system depicted in Figure 3, the first and second heat transfer circuits are thermally coupled to the other components of the system by heat exchanger coil arrangements. However, it will be understood that this is only one example of how the heat transfer circuits may be connected. In other embodiments, alternative suitable thermal coupling arrangements could be used, for example “shell and tube” thermal couplings and “plate exchanger” thermal couplings, as is well-known in the art.

Shell and tube configurations tend to be low-cost and can handle high pressures and high temperatures. Such configurations tend to exhibit a low pressure drop and tube leaks can be easily found.

Plate exchanger configurations tend to be simple and compact and exhibit improved heat transfer. They are also readily cleaned, tend not to require extra space needed for dismantling, their capacity can be readily increased, and maintenance is simple.

The heat pump system configuration depicted in Figure 3 is one example of heat pump system configuration that can be used in embodiments of the invention. In other embodiments, alternative heat pump configurations could be used, for example the heat exchanger could be a double-stage heat pump or a multi-stage heat pump.

Double and multi-stage heat pumps provide higher COP values (so lower energy requirements) but require higher investments costs. Therefore, the use of such designs has to be determined by a precise costs study in order to determine the optimum configuration.

Figure 6a provides a schematic diagram depicting a double stage heat pump 601 in which heat energy is transferred from a data centre via a heat transfer circuit to the refrigerant in the evaporator of a first heat pump stage which is then pumped via a compressor to a condenser stage heating the refrigerant further. Heat energy from the heated refrigerant in the condenser of the first heat pump stage is transferred via a second heat transfer circuit to the refrigerant in the evaporator of a second heat pump stage. This refrigerant is then pumped via a compressor of the second heat pump stage to a condenser of the second heat pump stage heating the refrigerant further. Heat energy from the heated refrigerant in the condenser of the of the second heat pump stage of the first heat pump stage is transferred via a third heat transfer circuit to a direct air carbon dioxide capture process.

As will be understood, a multi-heat pump stage can be used, using the same principle with “N” intermediate stages between a heat pump stage connected to the data centre via a first heat transfer circuit and a final heat pump stage connected to the direct air carbon dioxide capture process via a final heat transfer circuit. Figure 6b provides a schematic diagram depicting such a multi-stage heat pump 602.

Further, as will be understood by the skilled person, more complex heat pump systems can be used implementing more complex thermodynamic cycles using for example, multiple interconnected loops. Further components can be integrated to the heat pump for example flash separators.

The performance of systems arranged in accordance with embodiments of the invention, that is, the amount of energy saved by using waste heat from a computing data centre to provide heat energy to a direct air carbon dioxide capture process, will depend on several factors. These factors include: the temperature of the waste heat extracted from the computing data centre; the temperature of the heat required to undertake the direct air carbon dioxide capture process (which will depend on the direct air carbon dioxide capture process used); the total energy required to perform the direct air carbon dioxide capture process; the refrigerant used in the heat pump; the COP of the heat pump (which will depend on the heat pump configuration) and the energy requirement to operate the heat pump. The following table provides some indicative values for these factors and the corresponding energy savings that have been calculated to be achieved for running a direct air carbon dioxide capture process in accordance with examples of the invention, in particular using a single stage heat pump.

For the examples in the table above, the following system parameters are assumed: mass of adsorbent ( m_ads): 224 kg specific heat capacity of the adsorbent ( c_p,ads): 1000 J/kg/K - mass of the vessel ( m_ves ): 300 kg

- specific heat capacity of the vessel ( c_p,ves): 500 J/kg/K

- temperature of the capture process: 20°C

- mass of CO₂ captured at saturation

2.4 kg

- specific heat capacity of the carbon dioxide

1040 J/kg/K

- carbon dioxide heat of desorption

1 ,818,181 J/kg

- recovery of the carbon dioxide ( Rec): 80%

More generally, it has been determined that for systems arranged in accordance with embodiments of the invention, the COP value of the heat pump is ideally, at a minimum greater than 3, preferentially greater than 4 and optimally greater than 5.

This can be appreciated further with reference to Figure 7. Figure 7 depicts a graph showing a first, second and third curve depicting the change in the required coefficient of performance for a system arranged in accordance with examples of the invention (for example of the type depicted in Figure 3) as the regeneration temperature (T_reg) (corresponding to the temperature of the input heat to the direct air carbon capture process) increases.

The first curve 701 corresponds to a temperature of the input heat to the heat exchanger (corresponding to the temperature of the waste heat) of 20°C, the second curve 702 corresponds to a temperature of the input heat to the heat exchanger of 40°C, and the third curve 703 corresponds to a temperature of the input heat to the heat exchanger of 60°C.

The graph shown in Figure 7 is based on values for a single stage heat pump. The values for the coefficient of performance are determined by plotting, on an appropriate thermodynamic cycle on a pressure-enthalpy diagram, the temperature of the available waste heat (T_DC) and the temperature required by the direct air carbon dioxide capture process (T_reg).

The graph shown in Figure 7 is based on a water-based (R718) heat pump. The graph depicted in Figure 7 is based on assumptions including that the compressor isentropic efficiency is 0.7 and the temperature of the condenser of the system is 5 degrees higher than the temperature required by the direct air carbon dioxide capture process (T_reg). These assumptions are made to consider non-ideal behaviours of the heat pumps, such as pressure drops and heat losses.

Compared to a conventional process for producing heat (for example, gas burning processes) the capital costs of heat pump systems are substantially higher. Moreover, typically, the cost of the source of energy is up to 3 times more expensive (for example the average electricity price compared to the average price of gas on a kWh basis).

It has been determined that to be economically optimal for use in industrial settings, the COP value of heat pumps used in systems according to embodiments of the invention must typically be greater than 3, preferentially greater than 4 and optimally greater than 5.

The selection of direct air carbon capture processes in embodiments of the invention provides a particular advantage when considered with respect to other carbon capture techniques. For example, flue gas absorption processes which use liquid media typically require higher regeneration temperatures than direct air carbon capture processes to operate efficiently. This is exemplified in the following table:

Given the comparatively low waste heat output temperatures of data centres, the requirement for higher regeneration temperatures would establish a substantial difference between the heat pump input temperature (TDC) and the heat pump output temperature (T_reg). As the efficiency of a heat pump decreases as this temperature difference increases, the requirement for a higher regeneration temperature (T_reg) in a system with a comparatively lower input temperature (TDC) results in a reduction in efficiency of the heat pump and therefore an increase in operational costs. Accordingly, in the setting of using waste heat from a data centre to provide heat for a carbon capture process, the use of direct air carbon capture processes, increases efficiency and decreases cost.

By using direct air carbon capture processes, a further cost saving is achieved. Higher regeneration temperatures (as required by flue gas absorption processes), typically result in higher temperatures at the compressor outlet (upwards of 500°C in certain examples). Constructing equipment capable of withstanding such temperatures increases the overall cost of the system. Conversely, using direct air carbon capture processes, which require a lower regeneration temperature, have lower temperatures at the compressor outlet and can therefore be constructed at a lower cost.

The system depicted in Figure 3 is one example of a system of implementing a technique for providing heat energy to a carbon dioxide capture process in accordance with the invention.

Alternative arrangements will be apparent to the skilled person. The process of providing heat energy to a direct air carbon dioxide capture process performed by systems arranged in accordance with the invention include the steps of: transferring low grade waste heat energy from a computing data centre to the input of a heat pump via a first thermal transfer circuit; converting, using the heat pump, the low-grade waste heat energy to higher grade heat energy; transferring the higher-grade heat energy from an output of the heat pump to a direct air carbon dioxide capture process apparatus via a second thermal transfer circuit, and using the higher-grade heat energy to provide heat energy to the direct air carbon dioxide capture process apparatus to perform a direct air carbon dioxide capture process.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., “a” and/or “an” should be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, means at least two recitations, or two or more recitations).

It will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope being indicated by the following claims.

Claims

1. A system for providing heat energy to a direct air carbon dioxide capture process, said system comprising: a heat source, coupled via a first thermal transfer circuit to an input of a heat pump, said system further comprising a direct air carbon dioxide capture process apparatus for performing a direct air carbon dioxide capture process coupled to an output of the heat pump via a second thermal transfer circuit, wherein said heat source is a computing data centre, and in use, low grade waste heat energy from the computing data centre is transferred via the first thermal transfer circuit to the heat pump which generates higher grade heat energy which is then transferred from the heat pump to the direct air carbon dioxide capture process apparatus via the second thermal transfer circuit for performing the direct air carbon dioxide capture process, wherein said direct air carbon dioxide capture process is one of a temperature swing adsorption carbon dioxide capture process or a vacuum temperature swing adsorption carbon dioxide capture process.

2. A system according to claim 1 , wherein the first thermal transfer circuit forms at least part of a computing data centre cooling system.

3. A system according to any previous claim, wherein the heat pump is one of a single-stage heat pump, a-double stage heat pump or a multi-stage heat pump.

4. A system according to any previous claim, wherein a refrigerant used in the heat pump comprises one of water (R718), ammonia (R717) or a hydrofluoroolefin.

5. A system according to any previous claim, wherein the coefficient of performance of the heat pump is greater than 3, preferentially greater than 4, and optimally greater than 5.

6. A system according to any previous claim, wherein output carbon dioxide from the direct air carbon dioxide capture process is used in a subsequent process.

7. A system according to any of claims 1 to 5, wherein output carbon dioxide from the direct air carbon dioxide capture process is stored.

8. A system according to any preceding claim, wherein the input of the heat pump is an evaporator and the output of the heat pump is a condenser.

9. A method of providing heat energy to a direct air carbon dioxide capture process, said method comprising: transferring low grade waste heat energy from a computing data centre to the input of a heat pump via a first thermal transfer circuit; converting, using the heat pump, the low-grade waste heat energy to higher grade heat energy; transferring the higher-grade heat energy from an output of the heat pump to a direct air carbon dioxide capture process apparatus via a second thermal transfer circuit, and using the higher-grade heat energy to provide heat energy to the direct air carbon dioxide capture process apparatus to perform a direct air carbon dioxide capture process, wherein the direct air carbon dioxide capture process performed by the direct air carbon dioxide capture process apparatus is one of a temperature swing adsorption carbon dioxide capture process or a vacuum temperature swing adsorption carbon dioxide capture process.

10. A method according to claim 9, wherein the first thermal transfer circuit forms at least part of a computing data centre cooling system.

11. A method according to any of claims 9 to 10, wherein the heat pump in one of a single-stage heat pump, a double-stage heat pump or a multi-stage heat pump.

12. A method according to any of claims 9 to 11 , wherein a refrigerant used in the heat pump comprises one of water (R718), ammonia (R717) or a hydrofluoroolefin.

13. A method according to any of claims 9 to 12, wherein the coefficient of performance of the heat pump is greater than 3, preferentially greater than 4, and optimally greater than 5.

14. A method according to any of claims 9 to 13, said method further comprising using output carbon dioxide from the direct air carbon dioxide capture process in a subsequent process.

15. A method according to any of claims 9 to 13, further comprising storing output carbon dioxide from the direct air carbon dioxide capture process.

16. A method according to any of claims 9 to 15, wherein the input of the heat pump is an evaporator, and the output of the heat pump is a condenser.