Plant and process for capturing carbon dioxide directly from a gaseous mixture

Abstract

A plant and process for capturing carbon dioxide directly from a gaseous mixture is provided, wherein the movement of air in the plant and the desorbing step to capture carbon dioxide are supported by renewable sources, preferably solar thermal energy.

Description

[0001] PLANT AND PROCESS FOR CAPTURING CARBON DIOXIDE DIRECTLY FROM A

[0002] GASEOUS MIXTURE

[0003] Cross-Reference to Related Applications

[0004] This Patent Application claims priority from Italian Patent Application No . 102024000019012 filed on August 14 , 2024 , the entire disclosure of which is incorporated herein by reference .

[0005] Background of the Invention

[0006] The present invention relates to a plant for capturing carbon dioxide directly from a gaseous mixture , in particular from the atmospheric air .

[0007] The present invention also relates to a process for capturing carbon dioxide directly from a gaseous mixture , in particular from the atmospheric air .

[0008] Prior Art

[0009] Over recent years , the climate change caused by the continual increase in climate-altering gases emitted into the atmosphere , particularly carbon dioxide ( CO2 ) , is becoming increasingly evident . High concentrations of climate-altering gases in the atmosphere cause a rise in the average temperatures of the planet , with a consequent increase in the surface of deserti fied areas , an increase in melting of glaciers and an increase in the frequency of extreme weather events , which produce huge damage every year, in addition to losses of human li fe .

[0010] Governments throughout the world are becoming increasingly aware of the problem and are working on long-term solutions to try and fight the current climate change . For example , at the Paris Climate Conference ( COP21 ) in 2015 , the long-term goal set was to keep the increase in the global average temperature to below 2 ° C above pre-industrial levels , thanks to a cut in carbon dioxide emissions between 40% and 70% by 2050 . Furthermore , more recently, the European Union launched the "Green New Deal" plan, with the objective of making the European continent "carbon neutral" by 2050.

[0011] In order to achieve these objectives, it is essential to identify appropriate technological solutions that allow both a reduction in carbon dioxide emissions into the atmosphere and the carbon dioxide emitted into the atmosphere to be captured.

[0012] In parallel with the development of alternative energies to reduce emissions, capturing carbon dioxide forms part of a particularly interesting area of research, which ranges from capture and storage of carbon dioxide (Carbon Capture and Storage, or CCS) to reforestation.

[0013] The various CCS methods include the traditional ones, in which exploitation is localised at the points of maximum carbon dioxide emission, for example close to the chimneys of a steelworks, and those that capture the carbon dioxide directly from the atmosphere (Direct Air Capture, or DAC) . The latter methods are one of the most promising options for solutions to remove carbon dioxide.

[0014] DAC technology does, in fact, offer the following advantages:

[0015] 1) its implementation is not necessarily associated with the source of carbon dioxide emission, with a reduction in the costs of transporting it from the place of capture to the place of storage. In other words, DAC technology can be implemented in any place, which encourages its widespread use;

[0016] 2) the captured carbon dioxide can be easily quantified, which facilitates the activity of certifying agencies for the production of carbon credits.

[0017] However, compared to traditional CCS technologies, the DAC method operates on gaseous mixtures in which the carbon dioxide is highly diluted. For example, the concentration of carbon dioxide is around 400 ppm (around 0.04%) in the atmospheric air. Therefore , in order to obtain quantities of captured carbon dioxide comparable to those obtained using traditional CCS technologies , the DAC method must act on large volumes of gaseous mixture , for example of the atmospheric air .

[0018] In the existing DAC technologies , the atmospheric air is moved by electric fans , in a controlled environment where the carbon dioxide is adsorbed by special filters . The carbon dioxide- free air is then reintroduced into the atmosphere , whereas the carbon dioxide is desorbed by the filter and stored for subsequent uses .

[0019] Therefore , the need to operate on large quantities of atmospheric air leads , inevitably, to a considerable consumption of electricity to operate the fans , with an associated financial expenditure and environmental disadvantages .

[0020] Consequently, despite the maj or capacity and potential of DAC technology, its widespread use is prevented primarily by financial and environmental limitations .

[0021] In addition to movement of the air, the phase of desorption of the carbon dioxide from the filter is energy-intensive . The carbon dioxide desorption reaction is , in fact , highly endothermic, requiring around double the amount of electricity delivered to the fans . Consequently, in order to achieve an optimal yield of desorbed carbon dioxide , it is necessary to achieve speci fic reaction conditions , such as low pressure ( typically below to 5 - I O4Pa) and / or high temperatures ( typically comprised between 70 and 110 ° C ) . Obviously, the material comprising the filter influences the ef ficiency of the desorption reaction .

[0022] In order to mitigate the energy dependency of the solutions based on DAC technology, patent CN115318061B describes a method and the relative system, in which the DAC technology is implemented in Solar Updraft Towers ( SUTs ) .

[0023] It is common knowledge that the purpose of a solar updraft tower is production of electricity using solar energy and it comprises a tower, a collector at the base of the tower and turbines positioned between the tower and the collector . The air that enters the solar updraft tower is heated by the solar energy collected by the collectors and the natural convective motion of the hot air, induced by the air density gradient , is used to create an air current in the plant that causes the turbines to rotate and produce electricity .

[0024] In patent CN115318061B, the solar updraft tower does not have turbines and its sole purpose is movement of the air in the system to capture carbon dioxide . Circulation of the air produced in this manner makes the fans traditionally present in DAC technologies superfluous , reducing the energy dependency of DAC technology .

[0025] However, the invention described in patent CN115318061B is not free of further drawbacks .

[0026] In the first place , the invention described in patent CN115318061B does not allow the desorption phase to be optimised .

[0027] In fact , the hot air moved in the solar updraft tower exchanges a quantity of heat with the desorption fluid, involved in the carbon dioxide desorption phase , such as not to allow reaching of the necessary temperatures in the desorption chamber to trigger the desorption reaction . The desorption reaction therefore does not reach optimal thermodynamic conditions such as to maximise desorption of the carbon dioxide from the filters .

[0028] In the second place , the system described in CN115318061B is not suf ficiently flexible to be adapted to changing environmental conditions ( for example , the levels of daily solar radiation) , j ust as the geometric constraints of the system and the process conditions are not suf ficiently optimised .

[0029] There is therefore the need to provide a plant and a process for capturing carbon dioxide that are free of the drawbacks of the prior art , so as to enhance and spread DAC technology .

[0030] Object and Summary of the Invention

[0031] Consequently, an obj ect of the present invention is to provide a process and a plant for capturing carbon dioxide that is capable of combining inexpensiveness and environmental benefits with ef ficient capture of carbon dioxide with respect to the prior art .

[0032] In particular, the present invention allows carbon dioxide to be captured ef ficiently in quantities that are comparable to , or even higher than, those of the known technologies , even when powered primarily by renewable sources .

[0033] More in particular, an obj ect of the present invention consists of providing a process and a plant for capturing carbon dioxide in which the renewable sources guarantee both movement of the air inside the plant and optimisation of the desorption phase .

[0034] A further obj ect of the present inventions consists of providing a process and a plant for capturing carbon dioxide that can be constructed in any place , is flexible to changes in the control conditions ( for example , based on fluctuations in solar radiation) and scalable ( for example , based on the productivity required) .

[0035] Consequently, the present invention relates to a plant and a process for capturing carbon dioxide , as defined in independent claims 1 and 10 . Preferred and advantageous features of the invention form the obj ect of the dependent claims .

[0036] Briefly, the present invention exploits renewable sources , preferably the principles of a solar updraft tower, in DAC technology . However, in contrast with the known processes and plants , the renewable sources provide the heat needed not only to support movement of the gaseous mixture inside the plant , but also to optimise the carbon dioxide desorption phase .

[0037] In fact , it has been found that trans ferring heat from the renewable source directly to the desorption phase allows the optimal temperature to be reached ef ficiently, so as to move the reaction equilibrium of carbon dioxide desorption towards the products , thus facilitating the release of carbon dioxide from the filter on which it has been previously adsorbed .

[0038] In addition to providing heat to facilitate both movement of the air and the desorption phase , the present invention also allows action in a controlled manner on the quantity of heat to be used in the two activities .

[0039] Advantageously, the present invention is , in fact : easily controllable not only in terms of splitting of the heat , but also in terms of movement of the air based on the geometry of the ducts ; flexible in terms of storage of heat or trans fer of heat based on the daily fluctuations of solar radiation; of reduced dimensions and scalable based on the productivity required; ef ficient : capture of carbon dioxide is very high, even starting with low concentrations of carbon dioxide in the gaseous mixture adsorbed; constructable in any place and not necessarily close to points of high carbon dioxide emission; and sustainable in terms of reuse of the carbon dioxide desorbed in a further phase of desorption as a source of heat and in terms of use of the heat released by the exergonic reaction of adsorption in the simultaneous phase of movement of the gaseous mixture .

[0040] These results cannot be envisaged in consideration of the teachings of the prior art .

[0041] Brief Description of the Drawings

[0042] Further features , obj ects and advantages of the invention will emerge from the description that follows , which is purely illustrative and non-limiting and is supported by the appended drawings , in which :

[0043] - Figure 1 is a block diagram of a first embodiment of a plant for capturing carbon dioxide directly from a gaseous mixture in accordance with the invention;

[0044] - Figure 2 is a block diagram of a plant for capturing carbon dioxide in accordance with a second embodiment of the invention, and

[0045] - Figure 3 is a block diagram of a plant for capturing carbon dioxide in accordance with a further embodiment of the invention .

[0046] Preferred Embodiments of the Invention

[0047] In Figure 1 , the number 1 indicates a first embodiment of a plant for capturing carbon dioxide from a gaseous mixture . In detail , the plant 1 is the Direct Air Capture (DAC ) type ; therefore , the gaseous mixture is preferably atmospheric air in which the quantity of carbon dioxide is around 0 . 04 % in volume with respect to the air .

[0048] The plant 1 is suited to capturing carbon dioxide present in a gaseous mixture F subj ected to natural atmospheric convective flows and / or a gaseous mixture F subj ected to a forced flow .

[0049] The plant 1 comprises : - an air circulation circuit 2 comprising, in turn, a system of ducts from 4a to 4c ( for simplicity, only one duct 4a-4c belonging to the system of ducts 4a-4c is shown in Figure 1 ) adapted to be crossed by the gaseous mixture of di f ferent composition depending on the process step, and an exhaust tower 5,

[0050] - a solar thermal system 6 ,

[0051] - a heating circuit 7 , and

[0052] - one or more systems 12 for the capture of carbon dioxide ( for simplicity, only one system 12 is shown in the figure ) .

[0053] The air circulation circuit 2 is communicating with the environment outside the plant 1 by means of an opening 3 , through which the gaseous mixture F enters .

[0054] The air circulation circuit 2 is configured to be connected to the system 12 by means of the duct system 4a, in which the gaseous mixture F circulates . In detail , the duct system 4a is configured to feed the gaseous mixture F to be treated to the system 12 . The circulation circuit 2 also includes a duct system 4b configured to be crossed by a clean gaseous mixture , i . e . without carbon dioxide , exiting from the system 12 .

[0055] Compared to the traditional plants based on DAC technology, in which the gaseous mixture F to be treated, and also the clean mixture downstream of the adsorption filters , are not confined in a duct system, introduction of the system of ducts 4a, 4b into the present plant advantageously allows the quantity of heat trans ferred through the ducts to be modulated ( an aspect that will be detailed below) , selecting the suitable shape and dimensions of the ducts .

[0056] The system 12 for the capture of carbon dioxide comprises : one or more adsorption filters 15a, 15b, adapted to adsorb carbon dioxide from said gaseous mixture F; and

[0057] - at least one desorber module 16 adapted to desorb carbon dioxide previously adsorbed from the adsorption filters 15a, 15b .

[0058] In detail , the desorber module 16 comprises thermal means 17 placed in contact with said adsorption filters 15a, 15b .

[0059] In turn, the thermal means 17 comprise a circulation system 18 for a desorption fluid 19 and, optionally, a circulation system 18a for a cooling fluid 59 . Such thermal means 17 are therefore configured to heat and, optionally, to cool the adsorption filter 15a, 15b coupled to the desorber module 16 .

[0060] Each adsorption filter 15a, 15b is characterised by its own capture capacity, i . e . a quantity of carbon dioxide adsorbed from it per unit of gaseous mixture treated . Such capture capacity depends , in a known way, on the geometry of the adsorption filters 15a, 15b, on the type and on the quantity of adsorbing material dispersed on the filter . By way of nonlimiting example , the capture capacity of the adsorption filters 15a, 15b is comprised between 0 . 5 and 5 mmol of carbon dioxide per gram of adsorbing material .

[0061] The adsorption filters 15a, 15b are formed, for example , of a support of monolithic ceramics coated with aluminium or silica and impregnated with polyethylenimine ( PEI ) or a corrugated support comprising V-shaped cells incorporating polymer pellets functionalised with amino groups . Alternatively, the adsorption filters 15a, 15b can comprise particles with a Metal Organic Framework (MOE) incorporated and / or dispersed in a polymeric matrix .

[0062] Preferably, the area of the adsorption filter 15a, 15b is comprised between 1 and 4 m2, more preferably between 1 . 5 and 2 . 5 m2, while the length is comprised between 0 . 1 and 0 . 8 m, more preferably between 0 . 2 and 0 . 5 m . These dimensions of the adsorption filter 15a, 15b have preferably been selected in a manner to minimise the drop in pressure at the outlet from the filter 15a, 15b and to maximise the flow rate of gaseous mixture , with the same solar energy and the same quantity of adsorbing material .

[0063] Preferably, the system 12 comprises a number of adsorption filters 15a, 15b up to 10 units , more preferably the number of adsorption filters 15 is lower than or equal to 4 units , even more preferably the number of adsorption filters 15 is equal to 2 units .

[0064] In the simplest embodiments (not shown in the figure ) , the system 12 comprises only the adsorption f ilter 15a . The plant operates in batch mode (not continuous ) . During the adsorption step, the adsorption filter 15a adsorbs the CO2 from the gaseous mixture F . Subsequently, when the filter is saturated, the adsorption filter 15a is coupled to the desorber module 16 , entering into contact with the thermal means 17 . In particular, the desorber module 16 moves from a first position of inactivity to a second position of activity, placing the adsorption filter 15a in contact with the thermal means 17 .

[0065] Alternatively, as shown in Figures 1 and 2 , when the number of adsorption filters 15 is equal to 2 ( 15a and 15b) , the system 12 operates in continuous mode : the filter 15a is in adsorption configuration, whereas , simultaneously, the filter 15b, comprised in / coupled to the desorber module 16 , is in desorption configuration .

[0066] The dashed line used to illustrate the desorber module 16 is intended precisely to indicate the movable pos ition of the desorber module 16 in the system 12 for the capture of carbon dioxide .

[0067] In the description that follows , it will be said that the adsorption filter 15a, 15b is in a desorption configuration when it is comprised in the desorber module 16 , and is therefore placed in contact with the thermal means 17 .

[0068] In an embodiment of the plant 1 , the system 12 for the capture of carbon dioxide corresponds with the system for the capture of carbon dioxide described in patent application IT102024000016588 .

[0069] Briefly, the system for the capture of carbon dioxide described in patent application IT102024000016588 comprises , in addition to two adsorption filters ( i . e . a first or a second filter, corresponding with the filters 15a and 15b ) and a desorber module ( corresponding with the desorber module 16 ) , also a frame , connected to the two filters , and a mechanism adapted to move the desorber module , with respect to the frame , between the first and the second adsorption filter, and a control unit operatively connected to the desorber module and configured to control the movement of said desorber module between the first filter and the second filter, based on one or more operating parameters ( for example , temperature , pressure and adsorption time ) .

[0070] The plant 1 of the present invention can comprise a single system 12 for the capture of carbon dioxide , as shown in Figure 1 , or a number of systems 12 higher than one . Preferably, the number of systems 12 for the capture of carbon dioxide is higher than 20 , more preferably higher than 40 . According to this configuration, the plant 1 advantageously assumes a modular configuration .

[0071] In this configuration, each system 12 is connected to the air circulation circuit 2 by means of a duct system 4a, 4b .

[0072] The gaseous mixture exiting from the duct system 4b is then directed towards the exhaust tower 5 through the duct system 4c, as will be detailed below . When the plant 1 is in modular configuration, the systems 12 are , for example , arranged in a circle around the base of the exhaust tower 5 . Preferably, the systems 12 are equally spaced from one another .

[0073] As introduced above , the plant 1 further comprises a solar thermal system 6 adapted to trans form the solar energy into thermal energy . The solar thermal system 6 comprises , in turn, at least one solar collector 20 and one storage tank 22 .

[0074] The collector 20 can be a thermal panel or a parabolic collector or an evacuated tube solar thermal panel .

[0075] In one embodiment of the invention, the collector 20 is arranged above the duct system 4a-4c of the air circulation circuit 2 by means of metallic supports .

[0076] According to known technologies , the collector 20 absorbs solar radiation and, by heating a heat trans fer fluid 25 that circulates inside it , therefore converts the solar energy into heat . Part of the heat trans fer fluid 25 is stored in the tank 22 , which therefore acts as a thermal energy reserve , and part is introduced into the heating circuit 7 , introduced above .

[0077] The heat trans fer fluid 25 can be selected in the group formed of water, glycated water, pressurised water, oil and molten salts .

[0078] When the plant 1 is in modular configuration, the si ze of the solar thermal system 6 is preferably proportionate to the number of systems 12 for the capture of carbon dioxide , so as to produce a power rating comprised between 10 and 100 kW per system 12 , preferably between 20 kW and 40 kW per system 12 .

[0079] The heating circuit 7 comprises at least one line 9 , in which the heat transfer fluid 25 exiting from the solar thermal system 6 circulates.

[0080] In other words, the heating circuit 7 is connected to the connector 20 and / or the tank 22 by means of the line 9.

[0081] The heat transfer fluid 25, exiting from the solar thermal system 6 and circulating in the line 9 of the heating circuit 7, preferably has a temperature comprised between 100 and 200°C, more preferably between 120 and 160°C, even more preferably between 130 and 150°C.

[0082] Thanks to the connection between the tank 22 and the heating circuit 7, the plant 1 can advantageously operate even when the solar energy, absorbed by the collector 20, does not sufficiently heat the heat transfer fluid 25, for example during the night-time hours.

[0083] The plant 1 further comprises a valve 27 positioned in the heating circuit 7 and configured to split the heat transfer fluid 25, circulating in the line 9, into a first fraction 25a and into a second fraction 25b, circulating in two lines 9a and 9b, respectively, of the heating circuit 7.

[0084] The purpose of said valve 27 is therefore to make the thermal energy, stored by the heat transfer fluid 25, usable by at least two components of the plant 1.

[0085] The first fraction of the heat transfer fluid 25a, circulating in the line 9a, is directed towards an exchanger 30.

[0086] The exchanger 30 allows thermal exchange between the line 9a and the duct system 4b, exiting from the system 12, which carries the clean gaseous mixture, i.e. without CO2.

[0087] In one embodiment of the invention, the line 9a can be located inside the system of ducts 4b to optimise the exchange of heat between the fluids that cross them . Preferably, the line 9a is in the form of a tube . In one embodiment , the line 9a comprises a number of tubes comprised between 2 and 16 , more preferably between 4 and 8 , arranged inside each duct of the duct system 4b .

[0088] Therefore , the heat exchanger 30 serves to trans fer heat from the first fraction 25a of heat trans fer fluid to the clean gaseous mixture , producing a clean and hot gaseous mixture , which is introduced into the duct system 4c .

[0089] Advantageously, the clean and hot gaseous mixture 4c is sent to the exhaust tower 5 . In this manner, thanks to the trans fer of heat that occurs in the exchanger 30 , the movement of the gaseous mixture in the plant 1 is facilitated, exploiting the natural convective motion of the hot air, induced by the air density gradient , in accordance with the principles of solar updraft towers .

[0090] Therefore , circulation of the gaseous mixture of various composition ( from the gaseous mixture to be treated to the clean gaseous mixture , to the clean and hot gaseous mixture ) in the plant 1 does not require the assistance of fans or other electric means , but rather is created by the solar energy, converted into thermal energy .

[0091] Supported by the movement of the air, the clean and hot gaseous mixture , transported by the duct system 4c, reaches the base of the exhaust tower 5 , in order then to be reintroduced into the atmosphere from the top of the exhaust tower 5 .

[0092] After the trans fer of heat has occurred, i . e . downstream of the exchanger 30 , the first fraction 25a of heat trans fer fluid, now cooled down, is directed once again towards the heating circuit 7 , by means of a first return line 9c, where it comes into contact with the heat trans fer fluid 25 , exiting from the solar thermal system 6 and circulating in the line 9 .

[0093] The second fraction 25b of heat trans fer fluid, exiting from the valve 27 and transported by the line 9b, is directed towards the desorber module 16. More precisely, the second fraction 25b of heat trans fer fluid is configured to be introduced into the circulation system 18 for the desorption fluid 19 , comprised in the thermal means 17 of the desorber module 16 .

[0094] According to an embodiment of the plant 1 , the second fraction 25b of the heat trans fer fluid also acts as desorption fluid 19 , circulating in the circulation system 18 .

[0095] Therefore , the desorption fluid 19 , and thus also the heat trans fer fluid 25 , is selected in the group formed of water, glycated water, pressurised water, oil and molten salts .

[0096] In other words , the second fraction 25b of heat trans fer fluid provides the heat necessary to support the endothermic reaction of desorption of the carbon dioxide , adsorbed previously by the adsorption filter 15b .

[0097] Therefore , advantageously, the thermal load required by the desorption reaction is directly provided by the solar thermal system, minimising losses of heat due to intermediate trans fers of heat ( for example , when the air, heated by the thermal panels , in turn trans fers the heat to the desorption fluid) and therefore maximising the capture of carbon dioxide .

[0098] After the desorption reaction has occurred, the second fraction 25b of heat trans fer fluid, now cooled down, is directed once again towards the heating circuit 7 , by means of a second return line 9d, where it comes into contact with the heat trans fer fluid 25 , exiting from the solar thermal system 6 and circulating in the line 9 . Furthermore, when the desorption reaction is complete, the carbon dioxide stream 33 extracted from the system 12 is directed towards a tank 35 by means of a line 37 that fluidly connects the system 12 and the tank 35.

[0099] The carbon dioxide thus stored in the tank 35 can be compressed in order to be used in various commercial areas (for example, in the chemicals industry) and / or permanently stored, for example for mineralisation in rocks.

[0100] Preferably, the desorber module 16 is fluidly connected to a vacuum source 40 via a line 41. Such line 41 has a valve 43 adapted to selectively prevent fluid communication between the desorber module 16 and the vacuum source 40. Specifically, when the adsorption filter 15b is in a desorption configuration (i.e. the adsorption filter 15b is coupled to the desorber module 16 and is in contact with the desorption fluid 19, circulating in the system 18 of the thermal means 17) , a control unit 50 allows communication between the desorber module 16 and the vacuum source 40, acting on the valve 43. In fact, the desorption reaction is facilitated not only thermodynamically (i.e. by the heat provided via the desorption fluid 19) , but also by acting on the pressure of the adsorption filter 15b in desorption configuration. Preferably, the pressure of the adsorption filter 15b in desorption configuration is in the range comprised between 1 -104and 6 -IO4Pa, more preferably between 2 -IO4and 5 -IO4Pa.

[0101] Figure 2 shows a second embodiment of the plant lb according to the present invention, in which details similar or identical to the ones already described are indicated, for simplicity, with the same reference numbers as Figure 1.

[0102] The main difference between the plant 1 of Figure 1 and the plant lb of Figure 2 is the different type of desorption fluid 19 of the system 12 for capture of carbon dioxide, which requires further components of the plant lb compared to the plant 1. In fact, in plant lb, the desorption fluid 19 derives from the flow of carbon dioxide 33, exiting from the system 12.

[0103] In accordance with this second embodiment, the plant lb further comprises a recirculation circuit 65, exiting from the tank 35, in which at least a fraction 33a of the carbon dioxide stream 33 circulates. The recirculation circuit 65 exchanges heat with the line 9b, in which the second fraction 25b of the heat transfer fluid flows, by means of a heat exchanger 67. Such heat exchanger 67 is configured precisely to transfer the heat from the second fraction 25b of the heat transfer fluid to the fraction 33a of the carbon dioxide stream 33. Thanks to the heat received, the fraction 33a of the hot carbon dioxide stream reaches, via a line 69, the desorber module 16 and, in particular, the circulation system 18 for the desorption fluid 19, comprised in the thermal means 17, at the temperature suited to facilitating the desorption reaction.

[0104] The presence of the exchanger 67 leads to a reduction in the temperature of the desorption fluid 19 (i.e. the fraction 33a of the hot carbon dioxide stream) with respect to the characteristic temperature of the heat transfer fluid 25a (comprised between 100 and 200°C, preferably between 120 and 160°C and even more preferably between 130 and 150°C) . According to this second embodiment of the invention, the desorption fluid 19 has, in fact, a temperature comprised between 60 and 140°C, preferably between 80 and 120°C, more preferably between 90 and 110°C. Such temperature of the desorption fluid 19 is nonetheless sufficient to optimise the desorption reaction.

[0105] The exchanger 67 can, for example, be integrated into the desorber module 16.

[0106] After the heat exchange has occurred, the second fraction 25b of heat trans fer fluid, now cooled down, returns to the cooling circuit 7 by means of the second return line 9d, which converges into the line 9 in which the heat trans fer fluid 25 exiting from the solar thermal system 6 flows . At the same time , the fraction 33a of carbon dioxide , together with a further carbon dioxide stream 33 extracted from the system 12 , returns to the tank 35 via a fluid line 37 .

[0107] Compared to a desorption fluid in liquid form ( for example , when it coincides with the heat trans fer fluid selected in the group formed of water, glycated water, pressurised water, oil and molten salts according to the first embodiment of the plant 1 of Figure 1 ) , using the carbon dioxide stream as the desorption fluid, thanks to the type of plant associated with it ( see Figure 2 ) , allows the losses of heat during the desorption reaction to be reduced . Therefore , the desorption reaction in accordance with the second embodiment of the present plant is more ef ficient in terms of yield and reaction times .

[0108] In a third embodiment , the desorption fluid can be both the second fraction 25b of the heat trans fer fluid and a fraction of the carbon dioxide stream 33a . According to this configuration, part of the second fraction 25b of the heat trans fer fluid is directed to the circulation system 18 of the desorption fluid in the desorber module 16 and part comes into contact with the fraction 33a of the carbon dioxide stream by means of the exchanger 67 .

[0109] Figure 3 shows a further embodiment of the plant 1c according to the present invention, in which details similar or identical to the ones already described are indicated, for simplicity, with the same reference numbers as Figure 1 .

[0110] In accordance with the further embodiment of the present invention, the valve 27 is configured to split the heat trans fer fluid 25 into three fractions : into a first fraction 25a and into a second fraction 25b, as already described, and also into a third fraction 25c of the heat trans fer fluid .

[0111] Independently of the use of the second fraction 25b of heat trans fer fluid, whether it trans fers heat directly to the desorption fluid ( see Figure 1 ) or to the fraction 33a of the carbon dioxide stream ( see Figure 2 ) , the third fraction 25c of the heat trans fer fluid is directed to an adsorption cooling system 55 via a line 9e .

[0112] The adsorption cooling system 55 further comprises a heat exchanger 57 , a cooling tower 56 (not shown in Figure 1 ) and a circulation circuit 58 of a cooling fluid 59 . The heat trans ferred from the third fraction 25c of the heat trans fer fluid to the cooling system 55 , by means of the heat exchanger 57 , provides the energy necessary to support the conventional refrigerating cycle that takes part in the cooling system 55 , maintaining the cooling fluid 59 at a temperature lower than ambient temperature .

[0113] In an alternative embodiment of the plant 1c, the cooling system 55 can also be electrically powered by sources external to the plant 1c .

[0114] Preferably, the cooling fluid 59 is an aqueous solution of lithium bromide , for example , at concentrations higher than 50% by weight .

[0115] The adsorption cooling system 55 is connected to the thermal means 17 of the desorber module 16 by means of a line 60 , in which the cooling fluid 59 circulates . Speci fically, the cooling fluid is introduced into the circulation system 18a for the cooling fluid 59 comprised, optionally, in the thermal means 17 . The cooling fluid 59 then returns into the cooling system 55 via a return line 63 , in order to undergo a new cooling cycle . Such line 60 is provided with a valve 62 adapted to selectively prevent passage of the cooling fluid 59 towards the thermal means 17 . Specifically, after the desorption reaction is concluded, the control unit 50 allows communication between the cooling system 55 and the desorber module 16 , acting on the valve 62 . In this manner, the adsorption filter 15b in desorption configuration ( i . e . when the adsorption filter 15b is coupled to the desorber module 16 and therefore in contact with the thermal means 17 ) can be cooled with respect to the temperature at which the desorption reaction occurs . Taking the adsorption filter 15a, 15b to ambient temperature , through contact with the cooling fluid 59, allows damage to the adsorption filter 15a, 15b to be avoided . In fact , the adsorbent material of which the adsorption filter 15a, 15b is formed can be easily degraded by the combined action of oxygen in the gaseous mixture and high temperatures . Use of the cooling f luid 59 therefore allows this drawback to be avoided and the adsorption filter 15a, 15b to be made available to assume once again the adsorption conformation in a reduced time . Compared to the known DAC technologies , in which the cooling times of the filters are lengthy, because they are linked to their natural cooling, the present invention, on the other hand, allows the cooling times of the filters 15a, 15b to be modulated, thanks to the cooling system, selectively activated by the control unit 50 . In other words , actively controlling the cooling times of the filters 15a, 15b is reflected in the possibility of advantageously controlling the desorption / adsorption times .

[0116] It is worth emphasising that the adsorption cooling system 55 can also be easily integrated into the plant lb of Figure 2 , as in the third embodiment of the plant ( described previously) , resulting from combination of the plant 1 and lb, in which the desorption fluid is both the second fraction 25b of the heat trans fer fluid and the fraction 33a of the carbon dioxide stream .

[0117] Preferably, the plant 1 , lb, 1c also comprises photovoltaic panels configured to convert solar energy into electric energy, which can be used in the switch-on phase of the plant 1, lb, 1c and / or through electrically-powered auxiliary and / or support means, such as pumps used, for example, in the solar thermal system and / or in the cooling system 55.

[0118] In a further embodiment of the plant 1, lb, 1c and combinations thereof, a heat exchanger 70 (not shown in the drawings) is arranged upstream of the valve 27 and along the line 9. According to this embodiment, the heat transfer fluid 25, circulating in the line 9, exchanges heat with the heat exchanger 70. Therefore, the heat transfer fluid 25, exiting from the heat exchanger 70, has a lower temperature than the temperature of the heat transfer fluid 25, directly exiting from the solar thermal system 6 (i.e. between 100 and 200°C, preferably between 120 and 160°C and even more preferably between 130 and 150°C) . Introduction of the heat exchanger 70 advantageously allows control of the temperature of the heat transfer fluid 25 and therefore of the successive fractions 25a, 25b and, optionally, 25c, and thus also of the activities associated with them (i.e. movement of the air, desorption phase and, optionally, cooling phase) .

[0119] The control unit 50 is configured, as already mentioned, to control the valve 27, the valve 62 and the valve 43 based on detection of operating parameters (for example, temperature and / or pressure) with sensors preferably comprised in the plant 1, lb, 1c.

[0120] Preferably, the control unit 50 is also configured to control the movement of the desorber module 16, as described in patent application IT102024000016588.

[0121] Operation of the plant 1, lb, 1c in implementation of the process for capture of carbon dioxide comprises a series of steps: a. circulating the gaseous mixture in a duct system 4a of the air circulation circuit 2; b. feeding the gaseous mixture to one or more adsorption filters 15a, 15b, comprised in the system 12 for the capture of carbon dioxide, obtaining a clean gaseous mixture (i.e. one without carbon dioxide) .

[0122] In other words, the step of absorption of carbon dioxide in the filter 15a, 15b takes place during step b. (see Figures 1 and 2) .

[0123] In addition to step b . , the present process comprises step c. of transferring heat from at least one collector 20 of the solar thermal system 6 to the heat transfer fluid 25.

[0124] Preferably, the heat transfer fluid 25 has a temperature comprised between 100 and 200°C, more preferably between 120 and 160°C and even more preferably between 130 and 150°C.

[0125] The process according to the invention comprises the further steps of: d. circulating the heat transfer fluid 25 in at least one line 9 of the heating circuit 7 downstream of the solar thermal system 6; e. splitting the heat transfer fluid 25 into a first fraction 25a and a second fraction 25b of the heat transfer fluid by means of the valve 27 placed in the air circulation circuit 7.

[0126] Preferably, in addition to the valve 27, splitting of the heat transfer fluid 25 can also take place by selecting the number of active tubes of the line 9a in which the first fraction 25a of heat transfer fluid flows. This selection reflects on the quantity of heat transferred to the clean gaseous mixture: the greater the number of active tubes, the greater will be the heat used in movement of the air and the lower will be the one used in the desorption phase.

[0127] Following step e., the process comprises step f. of transferring heat from the first fraction 25a of heat transfer fluid to the clean gaseous mixture, exiting from the system 12, by means of the heat exchanger 30, obtaining the clean and hot gaseous mixture .

[0128] In other words, the transfer of heat that occurs in step f. is adapted to stabilise the movement of the air during the present process, thanks precisely to the natural convective motions of the hot air.

[0129] Preferably, the heat transferred in step f. from the first fraction 25a of the heat transfer fluid to the clean gaseous mixture corresponds with a range comprised between 1:5 and 1:2 of the solar energy absorbed by the solar thermal system 6.

[0130] It should be noted that the heat released by the exothermic adsorption reaction that occurs in step b. is also used in step f., contributing to the movement of the air during the steps of the present process.

[0131] Preferably, the process also comprises a step, subsequent to step f., of recirculating the first fraction 25a of the heat transfer fluid in the heating circuit 7 via the first return line 9c.

[0132] Step f. of the process is followed by step g. of conveying the clean and hot gaseous mixture through the exhaust tower 5, where it will be reintroduced into the atmosphere from the top of the tower 5.

[0133] The present process further comprises step h. of exchanging heat from the second fraction 25b of heat transfer fluid to the desorption fluid 19 in at least one desorber module 16 of the system 12, capturing a carbon dioxide stream resulting from the desorption reaction. In other words, during step h., the desorption phase occurs, at the end of which carbon dioxide previously adsorbed by the adsorption filter 15b is captured. The desorption reaction is therefore thermodynamically facilitated by the solar energy, converted into heat.

[0134] Preferably, the heat transferred in step h. from the second fraction 25b of the heat transfer fluid 25 to the desorption fluid 19 corresponds to a range between 4:5 and 1:2 of the solar thermal energy absorbed by the solar thermal system 6.

[0135] In an embodiment of the process, the carbon dioxide adsorption step (step b.) and the desorption step (step h.) occur cyclically and in a coordinated manner, so as to maintain a fixed ratio between the adsorption time and the desorption time, corresponding with a number of adsorption filters 15a in adsorption configuration equal to the number of adsorption filters 15b in desorption configuration, as illustrated in Figures 1-3.

[0136] With reference to Figure 1, the desorption fluid 19 used in step h. coincides with the second fraction 25b of the desorption fluid .

[0137] In a second embodiment of the present process (with reference to Figure 2) , this also comprises the steps of recirculating at least one fraction 33a of the carbon dioxide stream 33, captured during step h., in the desorber module 16 and transferring heat from the second fraction 25b of the heat transfer fluid to the fraction 33a of the carbon dioxide stream, by means of the heat exchanger 67, obtaining a fraction of the hot carbon dioxide stream. According to this embodiment of the process, the desorption fluid 19, involved in step h., can also be the fraction 33a of hot carbon dioxide.

[0138] According to a third embodiment of the present process, the desorption fluid 19 can be both the second fraction 25b of the heat trans fer fluid and the fraction 33a of the hot carbon dioxide stream .

[0139] Independently of the type of desorption fluid 19, the process preferably also comprises a step, subsequent to step h . , of recirculating the second fraction 25b of the heat trans fer fluid in the heating circuit 7 via the second return line 9c .

[0140] In an embodiment of the present process , the process also comprises a step parallel to step h . of placing the vacuum source 40 in communication with the desorber module 16 , so that the desorption reaction is optimised not only thermodynamically . This step does , in fact , allow an optimal pressure to be reached on the adsorption filter 15b in desorption configuration, preferably comprised between 1 - 104and 6 - I O4Pa, more preferably between 2 - I O4and 5 - I O4Pa .

[0141] With reference to Figure 3 , the present process can further comprise a step, subsequent to step h . , of cooling the desorption filter 15b in desorption configuration, connecting the desorber module 16 with the absorption cooling system 57 , so that the adsorption filter 15b is once again available to assume the adsorption configuration, without comprising the characteristics of the adsorbent material of which the filter is formed . In fact , when the adsorption step is alternated cyclically with the desorption step, the adsorption filter 15b in desorption configuration is at a temperature higher than ambient temperature , but in the absence of oxygen, in view of activation of the vacuum source . This condition does not cause deterioration of the adsorbent material . However, when the adsorption filter 15a is in adsorption configuration, and therefore fed by the gaseous mixture F ( step b . ) , the combination of oxygen ( the vacuum source is not active ) and the other temperatures could cause deterioration of the adsorbent material . Therefore , at the end of step h . , the adsorption filter 15a, 15b is cooled to avoid damage thereof when it assumes the adsorption configuration .

[0142] In accordance with this embodiment of the process (with reference to Figure 3 ) , the valve 27 splits the heat trans fer fluid 25 into three fractions 25a, 25b and 25c, circulating in lines 9a, 9b and 9e , respectively .

[0143] According to this embodiment , the cooling system 55 is fed by the heat trans ferred to it by the third fraction 9e of the heat trans fer fluid via the exchanger 57 .

[0144] It is clear that further changes and variants may be made to the process and the plant described without deviating from the scope of the appended claims .

Claims

CLAIMS1. A plant (1, lb, 1c) for capturing carbon dioxide directly from a gaseous mixture F comprising:- an air circulation circuit (2) comprising an exhaust tower (5) and a duct system (4a, 4b, 4c) adapted to be crossed by said gaseous mixture F;- a solar thermal system (6) comprising at least one collector (20) adapted to release heat to a heat transfer fluid (25) ;- a heating circuit (7) comprising at least one line (9, 9a-9e) for said heat transfer fluid (25) circulation exiting from said solar thermal system (6) ;- one or more systems (12) for the capture of carbon dioxide comprising : one or more adsorption filters (15a, 15b) adapted to adsorb carbon dioxide from said gaseous mixture F; and at least one desorber module (16) adapted to desorb carbon dioxide previously adsorbed from said adsorption filter (15a, 15b) , said desorber module (16) comprising thermal means (17) placed in contact with said adsorption filter (15a, 15b) and comprising a circulation system (18) for a desorption fluid (19) ; wherein said air circulation circuit (2) is configured to be connected to said one or more systems (12) for the capture of carbon dioxide for feeding said gaseous mixture F to said one or more adsorption filters (15a, 15b) , for obtaining a clean gaseous mixture; said plant (1, lb, 1c) further comprising: a valve (27) , placed in said heating circuit (7) , configured to split said heat transfer fluid (25) into a first fraction (25a) , directed to a heat exchanger (30) , and a second fraction (25b) , directed to said desorber module (16) , from which a carbon dioxide stream (33) is extracted; and wherein said heat exchanger (30) is configured to transfer heat from said first fraction (25a) of heat transfer fluid (25) , circulating in said line (9a) of said heating circuit (7) , to said clean gaseous mixture, circulating in said duct system (4b)of said air circulation circuit (2) , for obtaining a clean and hot gaseous mixture, said clean and hot gaseous mixture being conveyed, by means of said duct system (4c) , in the exhaust tower (5) .

2. The plant (1, lb, 1c) as claimed in claim 1, further comprising a recirculation circuit (65) adapted to recirculate at least a fraction (33a) of said carbon dioxide stream (33) and exchanging heat with the line (9b) of said heating circuit (7) , in which flows said second fraction (25b) of the heat transfer fluid (25) by means of a heat exchanger (67) adapted to transfer heat from said second fraction (25b) of the heat transfer fluid (25) to said fraction (33a) of the carbon dioxide stream (33) , for obtaining a hot fraction of the carbon dioxide stream.

3. The plant (1, lb, 1c) as claimed in claim 2, wherein the desorption fluid (19) is selected from the group consisting of said second fraction (25b) of the heat transfer fluid (25) , said fraction (33a) of the carbon dioxide stream (33) and their combinations .

4. The plant (1, lb, 1c) as claimed in one of the previous claims, wherein the solar thermal system (6) further comprises a tank ( 22 ) .

5. The plant (1, lb, 1c) as claimed in one of the previous claims, further comprising a control unit (50) adapted to control at least said valve (27) .

6. The plant (1, lb, 1c) as claimed in one of the previous claims, wherein the valve (27) is adapted to split the heat transfer fluid (25) into a third fraction (25c) adapted to feed an absorption cooling system (55) by means of a heat exchanger (57) comprised in the absorption cooling system (55) .

7. The plant ( 1 , lb, 1c) as claimed in claim 6, wherein theabsorption cooling system (59) is connected to thermal means(17) of the desorber module (16) .

8. The plant (1, lb, 1c) as claimed in one of the previous claims, further comprising a vacuum source (40) , fluidly connected to the desorber module (16) via a line (41) .

9. The plant (1, lb, 1c) as claimed in one of the previous claims, wherein a heat exchanger (70) is placed upstream of the valve (27) and configured to exchange heat with the heat transfer fluid (25) , circulating in the line (9) .

10. A process for capturing carbon dioxide directly from a gaseous mixture F comprising the following steps of: a. circulating said gaseous mixture F in a duct system (4a, 4b, 4c) of an air circulation circuit (2) ; b. feeding said gaseous mixture F to one or more adsorption filters (15a, 15b) , comprised in one or more systems (12) for the capture of carbon dioxide, for obtaining a clean gaseous mixture ; c. transferring heat from at least one collector (20) of a solar thermal system (6) to a heat transfer fluid (25) ; d. circulating said heat transfer fluid (25) in at least one line (9, 9a-9e) of a heating circuit (7) ; e. splitting said heat transfer fluid (25) into a first fraction (25a) and a second fraction (25b) of said heat transfer fluid (25) by means of a valve (27) placed in the heating circuit (7) ; f. transferring heat from said first fraction (25a) of heat transfer fluid (25) to said clean gaseous mixture by means of a heat exchanger (30) , for obtaining a clean and hot gaseous mixture ; g. conveying said clean and hot gaseous mixture through an exhaust tower (5) of said air circulation circuit (2) ; and h. exchanging heat from said second fraction (25b) of the heat transfer fluid (25) to a desorption fluid (19) , circulating inat least one desorber module (16) , comprised in the system (12) for the capture of carbon dioxide, for extracting a carbon dioxide stream (33) .

11. The process as claimed in claim 10, wherein the heat transferred from said first fraction (25a) of the heat transfer fluid (25) to said clean gaseous mixture during step f. corresponds to a range between 1:5 and 1:2 of the solar thermal energy absorbed by said solar thermal system (6) .

12. The process as claimed in claim 10 or 11, wherein the heat exchanged from said second fraction (25b) of the heat transfer fluid (25) to the desorption fluid (19) during step h. corresponds to a range between 4:5 and 1:2 of the solar thermal energy absorbed by said solar thermal system (6) .

13. The process as claimed in one of the claims 10-12, wherein the heat transfer fluid (25) has a temperature ranging between 100 and 200 °C, preferably between 120 and 160 °C, more preferably between 130 and 150 °C.

14. The process as claimed in one of the claims 10-13, further comprising the steps of recirculating at least one fraction (33a) of said carbon dioxide stream (33) , extracted during step h., into said desorber module (16) and of exchanging heat from said second fraction (25b) of heat transfer fluid (25) to said fraction (33a) of carbon dioxide stream, for obtaining a hot fraction of the carbon dioxide stream.

15. The process as claimed in claim 14, wherein the desorption fluid (19) is selected from the group consisting of said second fraction (25b) of the heat transfer fluid (25) , said fraction (33a) of the carbon dioxide stream (33) and their combinations.

16. The process as claimed in one of the claims 10-15, further comprising a step, following step h., of cooling the desorber module (16) by means of an adsorption cooling system (55) .

Images