Einige Inhalte dieser Anwendung sind momentan nicht verfügbar.
Wenn diese Situation weiterhin besteht, kontaktieren Sie uns bitte unterFeedback&Kontakt
1. (WO2016088002) PLANT FOR SEQUESTRATION OF CARBON DIOXIDE
Anmerkung: Text basiert auf automatischer optischer Zeichenerkennung (OCR). Verwenden Sie bitte aus rechtlichen Gründen die PDF-Version.

Plant for sequestration of carbon dioxide

[1] The present invention relates to an apparatus for sequestration of C02 in a low-cost and environmentally sustainable manner.

[2] For some time the effects of so-called "greenhouse gases" on the climate, and in particular the link between the concentration of C02 (carbon dioxide) in the atmosphere and global warming, have been known.

[3] In recent years the efforts of the scientific community and world politics have been directed towards trying to counteract the increase in the emissions of greenhouse gases into the atmosphere, with a view to preventing global warming, i.e. the increase in the average temperature worldwide.

[4] In a manner known per se, various international projects have been launched with the aim of limiting the emission of C02 into the atmosphere. Among others the Kyoto Protocol, which was signed by more than 180 countries in 1997, is worthy of mention.

[5] The methods identified by the scientific community for preventing global warming are many and involve essentially a reduction in the use of fossil fuels such as coal, petroleum and natural gas, while promoting the development of renewable energies, such as water energy, wind energy, solar energy and biomass exploitation.

[6] Moreover, many of the efforts of the international community are focused on the more efficient use of energy, as in the case of lighting using low-power lamps, transportation using the latest generation of high-efficiency engines and, with regard to electric power generation, the replacement of old and inefficient coal and oil-fired power stations with new combined-cycle plants which use gas turbines and steam turbines, having an energy efficiency of nearly 60%.

[7] Despite the technological efforts of the more advanced countries, the forecasts made by known international and national bodies as to the global energy requirement in coming years indicate that there will be a major increase in the demand for electric power, thermal power for industry and fuels for transportation.

[8] Consequently, these forecasts indicate a major increase on the use of fossil fuels such as petroleum, coal and natural gas, in particular by recently

industrialized developing countries. This increased use is in fact favored by the huge availability of such resources and the discovery of new reservoirs and methods for the extraction thereof, these factors overall resulting in these energy sources being advantageous from a cost point of view.

[9] Based on the data forecast by these reliable studies, not only is a reduction in worldwide C02 emissions in order to counteract global warming not expected, but on the contrary a substantial doubling of the emissions is forecast over the next 50 years, due mainly to the increase in the world population and the new industrialization of entire countries.

[10] The catastrophic effects of this situation on the climate may be easily imagined and are difficult to prevent in particular because the developing countries consider that the renewable energy option is too sophisticated and costly and they are therefore more oriented towards promoting short-term economic growth programs rather than limiting C02 emissions and solving environmental issues.

[11] Different technologies have been proposed for capturing and sequestering the C02 produced by industrial plants and electric power generating stations in which fossil fuels are used. In general all these technologies separate the C02 from the other gases using chemical/physical means.

[12] The problem of separation of the C02 from combustion gases or synthesis gases ("syngas"), cost-related factors aside, has been completely solved and does not represent a technological obstacle to the efforts to reduce the C02 emissions into the atmosphere.

[13] The most complex problem to be solved is instead that of finding a way of sequestering, in a permanent manner which is also sustainable from an environmental and economic point of view, the C02 captured from the fumes of industrial and energy-related activities.

[14] In a manner known per se, different technologies have been proposed for sequestering definitively the C02, some of these having been adopted and promoted by the legislation in different countries.

[15] The main CCS (Carbon Capture and Sequestration) technologies proposed and known are:

- Sequestration of the C02 in deep saline aquifers, said method having been recognized and promoted by the European Union with its special directive dated 2009.

- Sequestration of the C02 directly at the bottom of the ocean, in liquid form.

- Sequestration of the C02 in calcium carbonates or calcium silicates, directly or with the use of peptoids, known as Mineral Carbonation.

- Sequestration of the C02 in oil wells where it is injected in order to increase the oil production of said well using a technology called EOR (Enhanced Oil Recovery).

[16] As can be readily understood, none of the technologies proposed hitherto is satisfactory either from the technical point of view or from the economic point of view. This is particularly evident since, despite the fact that the need to reduce C02 emission levels is now urgent, none of the aforementioned technologies has progressed further than the experimental stage or is without problems from an environmental point of view.

[17] The sequestration of C02 in deep saline aquifers would appear to be the most promising solution, but it has not yet been fully tested and is encountering strong opposition from various environmental lobbies.

[18] The criticism expressed is motivated in particular by three main considerations. The first is that there is no certainty where the saline water displaced by the high-pressure injection of C02 will end up. The second consideration relates to the possible problems associated with the loss of C02 from existing wells or from irregularities in the aquifer. Finally, the third consideration is the possibility that the high-pressure injection of large quantities of C02 may cause earthquakes.

[19] The injection, in various forms, of liquid C02 directly into the deep waters of the ocean is greatly opposed because of the danger of acidification of the ocean waters, with catastrophic consequences for the ecosystem.

[20] The mineralization of the C02 implies both an enormous mining activity and possible acidification of the waters with consequent damage for the ecosystem.

[21] The use of C02 in depleted oil wells in order to increase the production of oil by means of EOR technology, a method much used commercially in some countries, does not ensure stable confinement of the C02 and therefore does not provide the necessary guarantees for long-term sequestration.

[22] A task of the present invention is to overcome the drawbacks mentioned above with reference to the prior art.

[23] In particular, a task of the present invention is to provide an apparatus for the permanent sequestration of the C02, in an environmentally friendly and economically sustainable manner.

[24] Another task of the present invention is to provide an apparatus for the permanent sequestration of the C02 which can be used in vast areas all over the world and with relative ease.

[25] Another task of the present invention is that it may be easily used in projects where it is possible to produce C02 from a renewable source, such as the production of hydrogen from biomass. In this case the overall benefit for the environment consists not only in the sequestered C02 , but also in elimination of the emissions due to the use of renewable fuels rather than fossil fuels. Some of the projects envisage the use of land which is not suitable for agriculture, for example owing to the presence of brackish water. This land, which allows the production of huge quantities of biomass, is situated in general in coastal areas with easy access to the sea.

[26] This object and these tasks are achieved by means of an apparatus for sequestration of C02 according to claim 1.

[27] In order to better understand the invention and appreciate its advantages, a number of non-limiting examples of embodiment are described below with reference to the attached drawings in which:

[28] Figure l.a is a simplified schematic view of a plant for the permanent sequestration of C02 according to the invention;

[29] Figure l.b is a simplified schematic view of a plant for the permanent sequestration of C02 according to the invention;

[30] Figure 2 is a simplified schematic view of a detail of the plant according to the invention;

[31] Figure 3. a is a schematic view of a possible container designed to contain the C02 to be sequestered;

[32] Figure 3.b is a schematic view of the container according to Figure 3. a partially filled with C02;

[33] Figure 4 is a schematic view of the action of the pressures which are exerted on the surface of the container according to Figure 3. a filled with C02 once immersed in the deep waters of the sea;

[34] Figures 5 are schematic views, in sequence, of a possible method for sealing a container once filled;

[35] Figures 6. a and 6.b are schematic views of two possible configurations of the loading device and the associated pneumatic plant according to the invention;

[36] Figures 7. a to 7.f are schematic views, in sequence, of the working steps of a loading device according to the invention;

[37] Figure 8 is a schematic view of a possible configuration of a loading device according to the invention;

[38] Figure 9 shows the step of loading a container into the loading device according to Figure 8;

[39] Figure 10 shows the step of pressurization of the loading device according to Figure 8;

[40] Figure 11 shows the step of partial (hydraulic) opening of the vertical tube in the loading device according to Figure 8;

[41] Figure 12 shows the step of filling with C02 a container in the loading device according to Figure 8;

[42] Figure 13 shows a first step of displacement of a container in the loading device according to Figure 8;

[43] Figure 14 shows the step of sealing a container in the loading device according to Figure 8;

[44] Figure 15 shows a second step of displacement of a container in the loading device according to Figure 8;

[45] Figure 16 shows the step of actuating the vertical sucker on a container in the loading device according to Figure 8;

[46] Figure 17 shows the step of total (mechanical) opening of the vertical duct in the loading device according to Figure 8;

[47] Figure 18 shows the step of positioning a container for descent inside the tube in the loading device according to Figure 8;

[48] Figure 19 shows the step of initial descent of a container inside the tube in the loading device according to Figure 8;

[49] Figure 20 shows the step of descent of a container inside the tube in the loading device according to Figure 8;

[50] Figures 21. a and 21. b are schematic views of a solution for slowing down the descent of a container according to the invention;

[51] Figures 22. a and 22.b are schematic views of another solution for slowing down the descent of a container according to the invention;

[52] Figures 23. a and 23.b are schematic views of a further solution for slowing down the descent of a container according to the invention;

[53] Figure 24 is a phase diagram of the C02 obtained from data available in literature;

[54] Figure 25 is a graph which shows the correlation between the pressure and the temperature of the C02, along the boiling-point curve obtained from data available in the literature;

[55] Figure 26 is a graph which shows the correlation between the density and the temperature of the C02 along the boiling-point curve, obtained from data available in the literature;

[56] Figure 27 is a graph indicating the temperature of the sea water as a function of the depth, obtained from data available in the literature;

[57] Figure 28 is a diagram which illustrates operation of a detail of the embodiment shown in Figure l.b; and

[58] Figure 29 is a schematic view of a possible container designed to contain the C02 to be sequestered.

[59] In the continuation of the description often reference will be made to the concepts "top", "upper" and the like and, respectively, the concepts "bottom" "lower" and the like. These concepts are to be understood uniquely with reference to the apparatus correctly arranged in operating terms and therefore subject to the force of gravity.

[60] In the description reference more will be made to "C02", this being understood as meaning a mixture of gas containing mainly carbon dioxide, in the solid, liquid, gaseous or supercritical state, and other substances including H2S, S02, NOx. C02 is in the supercritical state when the pressure and the temperature are higher than those of the critical point, i.e. when the pressure is higher than 73.8 bar and the temperature is higher than 31.1°C (see in this connection also the graph in Figure 24).

[61] In the description reference will also be made to the "air", this being understood as meaning the atmospheric air or a gas mixture containing different gases in any proportion.

[62] In the description reference will also be made to the "sea", this being understood as meaning not only the actual sea, but also an ocean, a lake or any body of salty, brackish or freshwater having the desired depth, typically greater than 350 m.

[63] In the description reference will be made also to "low pressure" and "high pressure", this being understood as meaning respectively a pressure close to atmospheric pressure (1 bar) and a substantially higher pressure, for example a pressure higher than 35 bar.

[64] In the description reference will be made to an off-shore platform, this being understood as meaning any platform or vessel which is fixed or mobile, floating or supported by special pylons anchored to the seabed and is provided with its own propulsive means or is drawn along by tug-boats.

[65] In the attached figures, the reference number 100 denotes overall a plant for the permanent sequestration of C02. The plant 100 comprises firstly a logistics base 200, an optional store 40 for the C02, an optional store for containers 30, and an apparatus 10 for loading and arranging containers 30 on the sea bottom, according to the invention. The logistics base 200 may comprise an off-shore platform 20.

[66] The plant 10 also comprises means 42 for supplying the C02. For example, the logistics base 200 may be connected to a suitable gas pipeline for transporting the C02. More particularly, the off-shore platform 20 may be connected to the coast by means of a suitable gas pipeline for transportation of the C02. Alternatively, it is possible to use other methods known per se for transportation of the C02, for example by means of pressurized freight containers loaded on special transportation means and/or on special boats.

[67] The apparatus 10 for the sequestration of carbon dioxide C02 in containers 30 comprises a loading device 12 and a pressurized tube 14 which connects the loading device to the depth of the sea.

[68] The loading device 12 according to the invention comprises a chamber 123, pressurization means 16, filling means 126 and sealing means 127, wherein:

- the loading device 12 is immersed, during use, in an external low-pressure environment;

- the chamber 123 is designed to be opened towards the external low-pressure environment so as to receive at its inlet at least one container 30;

- the chamber 123 is designed to be hermetically sealed from the low-pressure external environment;

- the pressurization means 16 are designed to increase the pressure inside the chamber 123 until a predefined high pressure level, called working pressure, is reached;

- the chamber 123 is designed to withstand the difference between the external low pressure and the working pressure which is established internally;

- the filling means 126 are designed to fill the container with C02;

- the sealing means 127 are designed to hermetically seal the container 30 full of C02;

- the chamber 123 is designed to be opened towards an external environment at the working pressure so as to output the container 30 full of C02.

[69] With particular reference to the embodiment schematically shown in Figure 2, it is possible to identify a number of components, the presence of which is preferable for the loading device 12 according to the invention;

- a loading valve 122 which allows the containers 30 to pass from an external environment inside the chamber 123 of the loading device 12 and which

hydraulically seals off the environment outside the low-pressure loading device, which is generally at sea-level, from the chamber 123 of said loading device 12;

- an actuator 121 for operating the loading valve 122;

- the chamber 123 of the loading device 12 which has a suitable, generally cylindrical shape, is designed to contain inside it one or more containers 30 and is designed to withstand the difference between the external atmospheric pressure and the working pressure which is established internally;

- an unloading valve 124 which allows the containers 30 to pass from inside the chamber 123 of the loading device 12 to the tube 14 and which hydraulically seals off the chamber of the loading device 12 from the tube 14 at the working pressure (high pressure);

- an actuator 124 for operating the unloading valve 125.

[70] Still with reference to Figure 2, the following may also be identified:

- the pressurized tube 14 for descent of the containers 30 from the level 50 to the level 60;

- the sea water 52;

- the surface level of the sea 50;

- the level 51 of the water inside the tube 14 during normal operation of the apparatus, i.e. when the tube 14 is kept at the design pressure;

- the minimum depth 60 which the sea bottom must have in order for the invention to be able to function, i.e. the depth at which the design pressure is established.

[71] The design pressure Pp, to which reference has been and will be frequently made, is the minimum pressure at which the containers 30 may be deposited and kept for an indefinite period of time, once filled with C02. It corresponds to the pressure of the depth 60. The working pressure Pi is instead the maximum pressure which is established inside the chamber 123 during the various steps of the method according to the invention. The working pressure Pi is equal to or greater than the design pressure Pp.

[72] In the description below, the information necessary for defining the design pressure will be provided. As the person skilled in the art may well understand, said design pressure depends generally on the conditions (in particular the

temperature and depth) of the seabed where the containers 30 are to be deposited. Moreover the design pressure also depends on the mechanical characteristics of the container 30 itself.

[73] It should be noted that the level 51 of the sea water 52 inside the tube 14 will not coincide in general with the depth 60. Along the tube 14, in fact, the pressure varies from that which is present close to the loading device 12. Variations in pressure are for example due to the air column and the presence of containers 30 falling inside the tube 14.

[74] The tube 14, which is shown schematically in Figures 1, 2 and 6 to 23, is a duct which may be vertical or differently inclined, with a preferably circular cross-section, which is straight or curved, suitable for allowing the passage of the containers 30 filled with C02, and which connects the loading device 12 situated at the level 50, generally the surface of the sea, to the desired depth 60.

[75] With reference to Figures 6, the apparatus 10 according to the invention may comprise means 16 for compressing fluids in order to generate the working pressure (high pressure) in the loading device 12 and in the tube 14. The compressed fluids may be liquids, such as water, or gases, such as air or a mixture of other gases containing generally nitrogen, oxygen or C02. The following may be identified:

- An optional compressor or pump 1631 complete with intake duct 1632 and discharge duct 1633.

- An optional compressor or pump 1651 complete with intake duct 1652 and discharge duct 1653.

[76] With reference again to Figures 6, the apparatus 10 according to the invention may comprise different types and configurations of valves 122 and 125.

[77] With reference to Figures 7, the different operating steps of a simplified embodiment of the loading device 12 may be defined:

- Figure 7. a: step for loading a container 30 inside the chamber 123 of the loading device 12;

- Figure 7.b: step for closing the loading valve 122 and pressurization of the chamber 123 of the loading device 12;

- Figure 7.c: step for filling the container with C02, sealing it and subsequent opening of the unloading valve 125 when the pressure inside the chamber 123 of the loading device 12 is the same as the pressure inside the tube 14 (working pressure);

- Figure 7.d: step for positioning the container 30 at the inlet mouth of the tube 14;

- Figure 7.e: step for inserting the container 30 inside the tube 14 and starting the descent towards the depth 60;

- Figure 7.f: step for closing the unloading valve 125 and opening the loading valve 122 for starting a new cycle.

[78] In accordance with some embodiments of the invention and with particular reference to Figure 3, the containers 30 used may have a spherical shape and be made of glass and/or ceramic material.

[79] The containers 30 have the function of containing the C02 and isolating it completely from the external environment. The containers 30 in particular have as first function that of retaining the C02 inside them so that it cannot be released and cannot reach the atmosphere. The containers 30 have moreover as second function that of forming an impermeable physical barrier which keeps the C02 separated from the surrounding environment, in particular from the sea water 52.

[80] The containers 30 must be preferably made of materials which may have a practically infinite duration in the environment and in any case a duration of thousands of years

[81] The containers 30 must be made preferably with a shape which minimizes the quantity of material used per unit of volume of C02 stored.

[82] The containers 30 must preferably be able to withstand external pressures without breaking or cracking.

[83] The containers 30 must be preferably made using non-toxic materials which are not harmful for the environment.

[84] The containers 30 must be preferably made of materials which are easily found and low-cost.

[85] Among the materials suitable for the manufacture of containers 30 used in the plant 100 there are glass or ceramic or glass-ceramic materials.

[86] Glass, ceramic or glass-ceramic materials are characterized by the following main chemical elements which are present in different proportions: Si02, A1203; Fe203; CaO; MgO; Na20; K20; S03; B203, and may have an amorphous, crystalline or intermediate structure depending on the production process by means of which they are obtained.

[87] Glass, ceramic or glass-ceramic materials are characterized by good mechanical strength values with a Young's modulus generally of between 50 Gpa and 500 Gpa.

[88] Glass, ceramic or glass-ceramic materials, as well as in their ordinary single-phase homogeneous form, may also be used in a composite form, where a fiber reinforcement is embedded in a matrix which maintains the cohesion of the reinforcement. For example it is possible to use glass fibers in a glass matrix.

[89] Among the materials suitable for the manufacture of the containers used in the plant 100 there are also cements, with or without a reinforcement, for example artificial fibers or glass fibers.

[90] Cements are characterized by the following main chemical elements which are present in different proportions: Si02, A1203; Fe203; CaO; MgO; Na20; K20; and S03.

[91] In accordance with certain embodiments of the invention and with particular reference to Figure 3, the containers 30 are hollow spheres provided with at least one opening 32 for allowing filling with C02.

[92] The spherical shape is one which, in the manufacture of the container 30, minimizes the quantity of material per unit of storable volume.

[93] The spherical shape is one which optimizes the mechanical strength of the container 30 when it is subject to external pressures as can be seen in the diagram of Figure 4.

[94] The spherical shape is one which optimizes the mechanical strength of the container 30 also when it is subject to internal pressures, i.e. when the internal pressure of the C02 is greater than the external pressure.

[95] In accordance with other embodiments of the invention and with particular reference to Figure 29, the containers 30 have a capsule-like shape, i.e. formed by a central cylindrical section which is closed at the ends by two semi-spherical caps.

[96] Owing to the capsule-like shape the quantity of C02 contained in a single container 30 for the same diameter of the tube 14 may be increased.

[97] Owing to the capsule-like, albeit elongate shape, the container 30 may travel along the tube 14 also where there are bends, provided that these have a radius which is greater than a threshold value which may be easily determined during design of the plant.

[98] Owing to the capsule-like shape, the container 30, in addition obviously to displacement along the axis of the tube 14, may only perform rotation about the same axis. This allows any forms to be adopted for the opening 32 and for the closing plug 33 of the container 30. In fact, the constrained position of the container 30 with respect to the tube 14 prevents the volume of these elements from causing problems along the tube 14.

[99] Other embodiments of the containers 30 are possible, in order to meet specific requirements. Obviously in this case a greater amount of material will be used per unit of stored volume and there will be a lower mechanical strength for the same thickness of the wall 31 of the said container 30.

[100] Other possible shapes of the containers 30 include for example a cylindrical shape, conical shape, oval shape, toroidal shape, parallelepiped shape and pyramid shape.

[101] The container 30 must be preferably able to sequester the greatest possible quantity of C02 per quantity of material used for its manufacture. The C02 may be present in any form: gas and/or liquid and/or solid and/or supercritical.

[102] With reference to Figure 24, it is possible to see the state diagram of the C02 where its different phases can be identified. For the purposes of sequestration of the C02 it will be clear to a person skilled in the art that it is preferable for the C02 stored in the containers 30 to have a sufficiently high density.

[103] The density of the C02 in the liquid phase is optimal at the normal temperatures at the depth of the sea, i.e. between 5°C and 20°C (see in this connection Figure 27). The density of the liquid C02 38, along the saturation curve at such temperatures, varies between about 750 kg/m 3 and about 900 kg/m 3.

At these temperatures and density the pressures of the C02 vary from about 40 bar to about 57 bar. Higher densities may be obtained at these temperatures by increasing the pressures with respect to those of the saturation curve.

[104] For example, in order to obtain a density of the liquid C02 equal to about 1000 kg/m at the temperature of 5°C, the container must be filled to the pressure of 200 bar, while at the temperature of 20°C a pressure of 350 bar is required. Based on the above considerations it is possible to define the design pressure, i.e. the pressure at which filling of the containers 30 is performed.

[105] By way of a simple comparison, for example the density of the C02 in the vapor phase at the same temperatures (between 5°C and 20°C) lies between 2 and 200 kg/m depending on the pressure. Sequestration in the vapor phase would therefore be decidedly less efficient at these temperatures, since it would require a greater volume of the containers for the same stored mass.

[106] Figure 25 shows a graph in which the temperature of the liquid C02 is shown in relation to its boiling pressure. A skilled person may easily understand that the minimum pressure necessary for keeping the C02 in liquid form is 39.7 bar at 5°C and 57.29 bar at 20°C. This means that the pressure inside the container in order to obtain liquid C02 38 at a temperature of 5°C is equal to or greater than 39.7 bar.

[107] Figure 26 is a graph showing the temperature of the C02 in relation to its density along the boiling-point curve thereof. A person skilled in the art may easily understand that the density of the liquid C02 38 is 895.9 kg/m at a temperature of 5°C and 773,4 kg/m at a temperature of 20°C. This means that the density of the liquid C02 38 inside the container at a temperature of 5°C is equal to or greater than 895,9 kg/m .

[108] The invention preferably envisages that the containers 30 are constructed making optimum use of structural material such as glass or ceramics.

[109] It is known that materials such as glass, cement or ceramics have an optimum mechanical behavior and an optimum strength under compression, while they have a poor tensile strength. It is therefore preferable that the container 30, once filled with C02, should always be subject to compressive forces rather than tensile forces in order to minimize the use of material for construction thereof. [110] In order to achieve this goal, it is preferable that the container 30, once filled with C02, should always be subject, after sealing, during all the stages of descent (both inside the tube 14 and in the water 52) as far as the final destination on the bottom, to an external pressure equal to or greater than the design pressure exerted internally by the C02. This is achieved by pressurizing the loading device 12 and immersing the container 30 to a suitable depth in the sea.

[Ill] In particular, let us consider the example where the temperature of the sea is 5°C and it is decided to fill the container with C02 to a design pressure corresponding to the saturation pressure. In this case the depth at which the pressure of the C02 inside the container is completely balanced by the external pressure exerted by the water 52 is approximately 400 m. It should be noted that the depth defined in this way is also the minimum depth 60 which the sea-bottom must have in order for it to be possible to implement the invention. In this equilibrium condition at the design pressure, the wall 31 of the container 30 is not subject either to tractional forces (which would occur if the external pressure were less than the internal pressure) nor to compressive forces (which would occur if the external pressure were greater than the internal pressure). Based on these values, containers 30 with extremely thin walls 31 may be made and simple and inexpensive materials used.

[112] If the seabed is at a depth greater than that which results in balancing of the design pressure, the wall of the container must be designed with dimensions for withstanding implosion. The greater the depth of the seabed, the greater the thickness 31 of the container 30 must be for the same material, or, for the same thickness, the better its mechanical characteristics must be.

[113] In the particular case where the containers 30 are spherical, there exist different mathematical models for calculating the minimum thickness of the wall 31 of the sphere in order to withstand the external hydrostatic pressures and avoid the danger of implosion.

[114] In accordance with a particular embodiment of the invention, if the hydrostatic pressure outside the spherical container 30 is 100 bar more than the internal pressure, i.e. if the seabed is located at 1000 m below the level 60, the result is that the weight of the container 30 made of glass with a Young's modulus of 50 Gpa represents about 11% of the weight of the C02 stored in the said container.

[115] In accordance with a particular example, if the volume of the spherical container is 167 liters, with the aforementioned conditions, the thickness 31 is equal to about 5 mm and the total weight of the material to about 18 kg.

[116] It can be noted that a priori there are no particular limitations for definition of the volume of the containers 30. With reference merely to considerations of a technological nature, associated therefore with the production of the containers 30, and of a logistical nature, associated therefore with the movement of the containers 30 when both empty and full of C02, it is possible to define as a preferable range of values the range of between 0.1 liters and 1000 liters, with a particular preference for volumes of between 5 liters and 200 liters.

[117] In a form known per se, the manufacture of a glass material implies in the worst case (using therefore virgin raw materials) C02 emissions calculated by known international bodies at about 850 kg/ton.

[118] In a form known per se, the production of electric energy in European and American electrical systems generates average C02 emissions of 400 kg/MWh.

[119] In a form known per se, the pressurization with air of 1 m of space from atmospheric pressure to the pressure of 100 bar with air requires a quantity of electric energy equal to about 25 kWh and therefore, as regards the above, implies 10 kg of C02 emission for the use of electric energy. The loading device 12 according to the invention may require the pressurization of about 2 m of air for 1000 kg of stored C02.

[120] From the above information a person skilled in the art may therefore deduce that, in the case where conventional technologies are used, the C02 emissions generated by the manufacture of the containers and the pressurization of the loading device 12 in order to sequester 1000 kg of C02 are equal to about 105 kg, namely about 11% by weight of the stored C02.

[121] In a manner known per se, the pressurization of 1000 kg of C02 at atmospheric pressure to the pressure of 100 bar for filling the containers requires about 110 kWh which involve about 44 kg of C02 emissions for the electric power consumption.

[122] The plant 100 according to the invention also envisages accessory energy applications for transportation of the containers 30, for management of the logistics base 200, for movement of the platform 20, for transportation of the C02 via a gas pipeline or via ship from the coast to the platform. This further energy may be calculated on average as 10 kWh per ton of stored C02 and therefore adds about 4 kg of C02 emissions for the electric power consumption.

[123] A person skilled in the art may therefore easily calculate that the C02 sequestration efficiency according to the invention, i.e. the difference between the C02 stored and the C02 emitted by the same process in relation to the stored C02, is equal to about 84%.

[124] As mentioned, the situation considered above envisages the use of conventional technologies. However, as the person skilled in the art may readily understand, it is possible to use dedicated technologies which allow a reduction in the C02 emissions. For example, it is possible to sequester immediately at the source the C02 produced in the furnaces for the production of the glass used for the containers 30 and in the electric energy power plant for powering of the plant. This result is facilitated in particular by using oxygen combustion technology, i.e. a technology where the fuel is combined with pure oxygen instead of with air. In this way it is possible to obtain an exhaust gas which consists substantially of water and C02 and which therefore allows sequestration of the latter in an easy and immediate manner. In this way it is possible to achieve a C02 sequestration efficiency greater than 97%.

[125] With reference to Figures 1 and 2, a person skilled in the art may understand that a container 30 filled with liquid C02 38 will receive, based on Archimedes' principle, a thrust from the bottom upwards equal to the weight of the displaced water volume.

[126] In order to allow the containers 30 to descend to the bottom of the sea and rest there stably on the seabed, it is necessary that the weight of the C02 inside the container 30 added to the weight of the material used for manufacture of the container 30 should be greater than the weight of the volume of water displaced by said container 30. In order to achieve this result it has been proposed increasing the density of the C02 inside the container 30 and/or increasing the

weight of the said container 30, for example by increasing the thicknesses of the material used for its construction or using suitable ballast weights which may be placed both inside and outside the container 30.

[127] A particularly advantageous configuration of the invention envisages using a design pressure inside the containers 30 which allows C02 with a minimum density close to that of water to be obtained, namely about 950 kg/m at the temperatures typically associated with the seabed. This design pressure will therefore be comprised between about 100 bar for a seabed at 5°C and about 250 bar for a seabed at 20°C.

[128] A particularly advantageous configuration of the invention envisages using the seabeds at depths of between 1000 m and 8000 m, where the pressure varies between about 100 bar and 800 bar. A person skilled in the art will certainly agree that the average depth of the oceans is located at about 4000 m and that there exists a practically infinite space for application of the invention.

[129] In accordance with a particular embodiment of the invention, the containers 30 may be filled with dry ice, i.e. C02 in solid form rather than liquid C02. At atmospheric pressure the C02 is in its solid state when the temperature falls to about -78°C. The density of the dry ice is equal to about 1500 kg/m .

[130] Since the density of dry ice is greater than that of liquid C02, the container 30 must be filled only partially with dry ice in order to prevent, with raising of the temperature, the internal pressure of the C02 from increasing to the point of causing the container 30 to explode. On the other hand, it is necessary to calculate the mass of dry ice by ensuring that, when the temperature rises from -78°C to the equilibrium temperature of the water on the seabed, the pressure and the density of the C02 inside the container are exactly those which are envisaged for the conditions of the seabed.

[131] It should be noted that, while filling of the containers 39 with C02 in the liquid or gaseous state must be performed at design pressure (high pressure), filling with C02 in the solid state may also be performed in low pressure conditions. For this reason, in the particular case where dry ice is used, the step of filling the container 30 may precede the step of pressurization of the chamber 123.

Moreover, in this particular case, the filling means 126 may be optionally outside the chamber 123.

[132] In accordance with a particular embodiment of the invention, the containers 30 must be completely and permanently sealed off from the external environment.

[133] With reference to Figure 3 this shows a particular application of the invention where the containers 30 have a spherical shape. These containers 30 comprise a wall 31 and an opening 32 for allowing filling thereof with liquid C02 38. A special plug 33 is necessary for closing the container.

[134] With reference to Figure 5, this shows a particular embodiment of the invention where the containers 30 are hermetically sealed by means of a welding process. In this embodiment, the container 30 and the plug 33 are both made of glass. The particular process schematically shown in Figures 5 uses an induction welding technique which is described below.

[135] With reference to Figure 5. a, it can be seen that the plug 33 has mounted on it a suitable ring 34 made of ferromagnetic material. Once the plug 33 has been positioned inside the opening 32 of the container 30, the ring 34 completely covers the gap between the plug 33 and the wall 31 of the containers 30. When a suitable electromagnetic field generator 35 is moved towards the ring 34, the latter is heated to temperatures higher than 1000°C due to the effect of the magnetic induction. The ring 34 transmits by means of contact and by means of radiation heat to the underlying glass of the plug 33 and the wall 31 of the container 30, causing localized melting thereof and consequent sealing of the container 30.

[136] In order to fix the plug 33 inside the opening 32 of the container 30 it is possible obviously to use for this purpose other methods, in addition to or instead of induction welding. Some methods suitable for this purpose are, for example, laser welding, plasma welding, oxyacetylene torch welding or bonding using suitable adhesives. In particular, suitable adhesives must have the characteristic feature of not dissolving in water, good mechanical and sealing properties, a potential duration of thousands of years and must be non-toxic for the environment. Some adhesives of this type are for example special types of ionomer cements or ceramic adhesives.

[137] As mentioned, above the containers 30, once deposited on the seabed, are preferably subject to an external pressure greater than the internal design pressure. For this reason, in some embodiments, the opening 32 and respective plug 33 have a frustoconical form. This form prevents the plug from being pushed inside the container 30 and, at the same time, produces the effect that it is the difference in pressure which keeps the plug 33 in position.

[138] Figure 8 shows, again in schematic form, an apparatus 10 according to the invention which comprises advantageously a number of secondary systems, such as for example the means 16 for pressurization of the loading device 12 and the tube 14, the filling means 126, the sealing means 127, the means 128 for displacement of the containers 30 and the means for closing the tube 14.

[139] More particularly, the pressurization means 16 may comprise a compressor 1631 which is designed to generate the pressures necessary for pressurizing the loading device 12 at least up to the design pressure, i.e. the pressure at which filling of the C02 inside the containers 30 takes place. The compressor 1631 comprises an intake 1632 for a suitable liquid and/or gas, typically air or a gas mixture containing different gases in any proportion.

[140] A duct 1633, provided with suitable process and safety valves, connects the compressor 1631 to the chamber 123 of the loading device 12. A duct 1634, provided with suitable process and safety valves, connects the chamber 123 of the loading device 12 to a low-pressure environment, typically at atmospheric pressure. Alternatively, the duct 1634 may connect the chamber 123 of the loading device 12 to a confined environment which allows recovery at least partially of the air pressure at the moment of release with a view to opening the loading valve 122.

[141] Furthermore, a turbine which is able to make use of expansion of the compressed air output from the chamber 123 in order to generate energy is advantageously mounted on the duct 1634.

[142] The means 126 for filling the containers 30 with C02 comprise a nozzle 1261 for conveying the C02 inside the container 30.

[143] The means 127 for sealing the containers 30 comprises a welding head 1271 which may for example be an inductive electrode similar to that indicated by 35 in Figures 5.c and 5.d.

[144] The means 128 for displacement of the containers 30 comprise a sucker 1281 which is designed to grip the container 30 and retain it in a sufficiently firm manner so as to be able to move inside the chamber 123 of the loading device 12.

[145] There are also two different systems for closing the tube 14. The first means 129 for partial (or mechanical) closing of the tube 14 comprise a stop member 1291 designed to prevent the uncontrolled falling of the container 30 inside the tube 14 and ensure at the same time hydraulic communication, and therefore a pressure equilibrium, between the tube 14 and the body 134 of the loading device 12.

[146] The second means 124 for total (or hydraulic) closing of the tube 14 comprise an unloading valve 125 designed to close hermetically the tube 14 with respect to the body 134 of the loading device 12, thus ensuring the possibility of establishing different pressures in the two environments. The unloading valve 125 may advantageously comprise a sucker 1251 designed to grip the container 30 and retain it in a sufficiently firm manner to prevent it from falling in an uncontrolled manner inside the tube 14.

[147] The operating principle of one of the possible embodiments of the apparatus 10 is described below, with specific reference to Figures 9 to 20.

[148] With reference to Figure 9:

the loading valve 122 is in the open position;

the container 30 is empty and is introduced into the chamber 123 of the loading device 12;

the chamber 123 of the loading device 12 is at atmospheric pressure; and the tube 14 is closed by the unloading valve 125 and is at the working pressure.

[149] With reference to Figure 10:

the loading valve 122 is closed so as to seal hermetically the chamber 123 of the loading device 12;

the container 30 is in the position where it will be filled with C02;

the loading valve 125 is in the closed position, hermetically sealing the chamber 123 of the loading device 12 from the tube 14; and

the compressor 1631 introduces into the chamber 123 of the loading device a quantity of air sufficient to increase the pressure inside the chamber 123 until it is equal to the working pressure and equal to the pressure present inside the tube 14.

[150] With reference to Figure 11 :

the loading valve 122 is in the closed position, hermetically sealing the chamber 123 of the loading device 12;

the unloading valve 125 is opened when the pressure inside the chamber 123 of the loading device 12 is equal to the pressure inside the tube 14;

the chamber 123 of the loading device 12 is kept at the working pressure by the compressor 1631;

the filling means 126 fill the container 30 with the liquid C02 38;

the partial closing means 129 close partially the inlet mouth of the tube 14; and

the displacement means 128 move towards the container 30 and grip it with the special sucker 1281.

[151] With reference to Figure 12:

the loading valve 122 is in the closed position;

the unloading valve 125 is in the open position;

the chamber 123 of the loading device 12 is kept at the working pressure; and the filling means 126 fill the container 30 with liquid C02 38.

[152] With reference to Figure 13:

the loading valve 122 is in the closed position;

the unloading valve 125 is in the open position;

the chamber 123 of the loading device 12 is kept at the working pressure; and the displacement means 128 move the container 30 with its load of liquid C02 38 into the sealing position.

[153] With reference to Figure 14:

the loading valve 122 is in the closed position;

the unloading valve 125 is in the open position;

the chamber 123 of the loading device 12 is kept at the working pressure; and the sealing means 127 hermetically seal the container 30 by means of the welding of the plug 33.

[154] With reference to Figure 15:

the loading valve 122 is in the closed position;

the unloading valve 125 is in the open position;

the displacement means 129 move the container 30 into the position for entry into the tube; and

the means 129 for partially closing the inlet mouth of the tube 14 prevent the container 30 from falling in an uncontrolled manner inside the tube 14.

[155] With reference to Figure 16:

the loading valve 122 is in the closed position;

the unloading valve 125 is in the open position; and

the sucker 1251 grips the container 30.

[156] With reference to Figure 17:

the loading valve 122 is in the closed position;

the unloading valve 125 is in the open position;

the sucker 1251 keeps the container 30 firmly connected to the body of the unloading valve 125;

the displacement means 128 are retracted into a rest position, leaving the container 30 free;

the means 129 for partially closing the inlet mouth of the tube 14 are retracted into the rest position, leaving the inlet mouth of the tube 14 completely free; and

the container 30 is supported by the sucker 1251 and may not accidentally fall into the tube 14.

[157] With reference to Figure 18:

the loading valve 122 is in the closed position;

the unloading valve 125 starts the closing step;

the sucker 1251 keeps the container 30 firmly connected to the body of the unloading valve 125; and

the container 30 supported by the sucker 1251 starts to enter in a controlled manner the tube 14;

[158] With reference to Figure 19:

the loading valve 122 is in the closed position;

the unloading valve 125 continues the closing step;

the sucker 1251 keeps the container 30 integrally connected to the body of the unloading valve 125; and

the container 30 supported by the sucker 1251 enters the tube 14 completely and in a controlled manner.

[159] With reference to Figure 20:

the loading valve 122 is in the closed position;

the unloading valve 125 closes completely sealing off the chamber 123 of the loading device from tube 14; and

the sucker 1251 releases the container 30 which is free to descend inside the tube 14.

[160] After discharging from the chamber 123 the air stored in order to cause lowering of the pressure inside the loading device 12 to the pressure outside of the loading device, generally atmospheric pressure, it is possible finally to open again the loading valve 122 and set the apparatus 10 to the initial condition, similar to that shown in Figure 9. It is then possible to repeat the cycle described above, an indefinite number of times.

[161] As the person skilled in the art may well understand, the solution described above and schematically shown in Figures 8 to 20 is only one possible embodiment of the loading device 12, which embodiment highlights particularly well the different steps in the process. Obviously, other embodiments may be defined, for example, in order to reduce the internal volume of the chamber 123 of the loading device, so as to reduce the volume of fluid to be brought to the working pressure at each cycle. In order to reduce the volume inside the chamber it is for example possible to reduce the number of positions which the container 30 assumes inside the chamber 123, for example providing a multi-function head which may perform in succession more than one task from among filling and/or sealing and/or displacement of the container 30.

[162] Descent of the containers 30 inside the tube 15 preferably occurs at a controlled speed. In fact, with reference to Figure 2, the tube 2 is at a pressure which is generally higher than 35 bar. Under these conditions, based on the principle of communicating vessels, the tube 14 may be full of pressurized air in order to compensate for the water pressure. The water level inside the tube 14 is indicated by the level 51 which generally does not coincide with the level 60. This means that the container 30 must descend over a vertical distance between the level 50 and the level 51, said distance being generally between 350 m and 3000 m, preferably between 750 ma and 2500 m, inside a tube full of air with the possibility of reaching high free-falling speeds.

[163] If not suitably braked during descent, the containers 30 could reach the level 51 at very high speeds.

[164] In the case where the containers 30 are made of fragile materials such as glass or ceramic material and should there be the danger of their breaking upon impact with the surface of the water at the level 51, the speed of descent of said containers 30 would have to be braked using suitable means described below.

[165] With reference to Figures 21. a and 21. b it is possible to define a particular form of the tube 14 aimed at controlling the speed of descent of the containers 30 along the tube 14. In accordance with this embodiment, the tube 14 comprises: a pressure-tight wall 141;

ribs 142 which allow the container 30 to be kept at a controlled distance from the wall 141 of the tube 14, thus creating slits 143.

[166] With reference to Figure 21. b it can be seen that the container 30 which descends along the tube 14 defines two portions of said tube: a top portion 146 situated between the container 30 and the loading device 12 and a bottom portion situated between the container 30 and the water level 51. The container 30 tends to descend along the tube 14 by means of the force of gravity. Since the air of the portion 145 underneath the container 30 is confined by the wall 141 of the tube 14 and by the surface of the water 51, it exerts a force which opposes the descent of the container 30. In fact, the container 39, in order to be able to descend along the tube 14, must allow the air contained in the underlying portion 145 to pass to the portion 146 situated above: this occurs via the slits 143 where only a controlled amount of air may pass. This allows the speed of descent of the container 30 to be controlled.

[167] In accordance with other possible embodiments, the same result may be obtained with different systems. For example, Figures 22. a and 22.b show a solution similar to that described above, where however the container 30 has a different (for example cylindrical) form designed to increase the aerodynamic resistance thereof and therefore influence further the speed of free descent along the tube 14. Furthermore, Figures 23. a and 23.b show a further solution similar to those described, where, however, the cross-section of the tube 141 is uniform and the ribs 142 are mounted on the external surface of the container 30.

[168] In accordance with other possible embodiments (see for example Figures 22), the tube 14 may be advantageously constructed using an outer tube 140 and an inner tube 144. The outer tube 140, which is preferably made of metallic material, is designed to withstand the high working pressures and may have a smooth inner wall. The inner tube 144, which is preferably made of plastic, defines the ribs 142. It can be noted that it is not necessary for the inner tube 144 to be suitable for withstanding high pressures, since the pressure is counteracted by the outer tube 140. With this configuration it is possible to use as an outer tube 140 tubes which are already commercially available with very high qualitative standards because they are used for gas pipelines. On the other hand, the inner tube 144 may be easily made, with the necessary ribs 142, by means of extrusion processes.

[169] In greater detail the embodiment of the plant 100, the overall form of which is shown in Figure l.b and some details of which are shown in Figures 28 and 30, will be described below in greater detail. In this embodiment the logistics base 200 is provided on the mainland or on the coast or in any case on structures which are connected to it in a stable and direct manner, such as piers, quays or the like. With this solution it is possible to avoid the use of off-shore platforms and therefore simplify the supply of materials to the apparatus 10. In this case, therefore, the tube 14 may not have generally an orientation close to the vertical as in the embodiment shown in Figures l.a and 2. The tube 14 of the embodiment shown in Figure l.b is generally inclined with the average slope of the seabed

which extends from the logistics base 200 to the bottom 60 where the design pressure is established. As the person skilled in the art may easily understand, the tube 14, following the profile of the seabed, will have in general a variable inclination along its path. It cannot be ruled out a priori that, along the path, there will sections with a zero inclination (i.e. horizontal sections) or even sections with a negative inclination (i.e. sections where the tube rises upwards briefly). This condition is shown schematically in Figure l.b.

[170] Unlike the situation which occurs in the embodiment of Figure l.a, in Figure l.b it is therefore not possible to allow the containers 30 to simply fall along the tube 14. In this embodiment it is required to provide a propulsive force which allows the containers 30 to be moved along the tube 14, if necessary even against the force of gravity.

[171] In this embodiment it is possible to use a technology similar to those used in pneumatic tube systems, transportation systems in which special capsules are moved along tubes by means of the application of pressure differences. The known systems are aimed at transporting capsules along a network of tubes which connects a plurality of stations. In the case of the present invention the transportation system is simplified because the tube 14 connects one or more dispatch stations (the loading device 12 at the logistics base 200) in one direction only towards the destination (the seawater 52).

[172] With particular reference to Figures l.b and 28, the operating principle of this specific embodiment will now be described in greater detail.

[173] In general the movement of the container 30 along the tube 14 is obtained by applying upstream a working pressure Pi greater than the design pressure Pp. In other words, the pressurization means 16 and the chamber 123 are designed to operate at a predefined level of high pressure greater than the design pressure Pp. In this way a single container 30 is exposed to a pressure difference between its upstream surface and its downstream surface. This pressure difference generates a force which pushes the container 30 along the tube 14 and is able to overcome the frictional forces which it encounters during its movement.

[174] This basic idea may be developed so as to allow the movement along the tube 14 of a plurality of containers 30 simultaneously. For this purpose it is

possible to provide a return tube 147 and a compressor 148. As may be seen in Figure l.b, the compressor 148 is located upstream, in the vicinity of the loading device 12. The return tube 147 connects the compressor 148 to the section of the tube 14 in the vicinity of its downstream end. In this way, the compressor 148 is able to cause circulation of the air, or other suitable fluid, recovering it at the downstream end of the tube 14, compressing it and re-introducing it upstream of the tube 14.

[175] As the person skilled in the art may easily understand, it is possible to consider that each container 30 along the tube 14 results in a localized pressure drop ΔΡ. In this way, knowing the number n of containers 30 which must be simultaneously moved and knowing the pressure drop ΔΡ for a single container 30, it is possible to calculate the working pressure Pi to be applied upstream by means of the compressor 148 so that the downstream end of the tube 14 is still at the design pressure Pp. The following is therefore obtained: Pi = Pp + n ΔΡ

[176] Along the end section of the tube 14, downstream of the connection of the return tube 147, there is no longer any pressure difference able to push the container 30 along the tube 14. It is therefore preferable that this tube section 14 should be relatively short and it is moreover preferable that it should have a suitable inclination so as to allow the container 30 to continue its movement by means of gravity to the downstream end of the tube 14.

[177] In accordance with these embodiments of the invention, where the containers 30 are pushed along the tube 14 by means of the pressure difference, it is preferably to define in a relatively precise manner the difference between the external diameter of the container 30 and the internal diameter of the tube 14. This difference must satisfy two requirements a priori of an opposing nature. A relatively high difference may be preferable because it allows the container 30 to travel along the tube 14 even when the latter has sections with a relatively small radius of curvature. On the other hand, a relatively small difference may be preferable because it allows the pressure drop defined by the container 30 to be minimized. The difference between the diameters must therefore be defined in each case so as to satisfy the specific requirements associated with each single plant 100.

[178] It is clear that the specific characteristic features are described in connection with various embodiments of the apparatus 10 by way of a non-limiting example.

Obviously a person skilled in the art, in order to satisfy any specific requirements which might arise, may make further modifications and variations to the apparatus 10 according to the present invention, all of which are contained moreover within the scope of protection of the invention, as defined by the following claims.