Plant and method for the generation of negative emissions of co 2 and decarbonised hydroxide

Abstract

The invention relates to a plant for the generation of negative emissions of CO2 and decarbonised hydroxide. The plant comprises a gasifier (1), a heat exchanger (3), an indirect calciner (10), a contactor (20), a pH corrector (30), a hydroxide production unit (60) and a hydroxide dosing unit (40). The gasifier (1) receives high-temperature fuel (12) and steam (32) and releases syngas (11). The exchanger (3) receives high-temperature flue gas (170) from the calciner (10) and low-temperature steam (612) from the hydroxide production unit (60) and releases low-temperature flue gas (171) containing CO2 and high-temperature steam (32). The calciner (10) receives carbonate (110), syngas (11) and oxygen (160) and releases oxide (130) and high-temperature flue gas (170). The contactor (20) reacts water with the CO2 of the low-temperature flue gas (171) and releases acidic water (230). The pH corrector (30) reacts the acidic water (230) with the hydroxide (640) and releases buffered acidic water (240). The hydroxide production unit (60) reacts the oxide (130) with water (610) and releases hydroxide (630) and low-temperature steam (612). The hydroxide dosing device (40) doses hydroxide (640) for pH correction and decarbonised hydroxide (450) for other uses. The invention also relates to a method for the generation of negative emissions of CO2 and decarbonised hydroxide emissions.

Description

PLANT AND METHOD FOR THE GENERATION OF NEGATIVE EMISSIONS OF CO2 AND DECARBONISED HYDROXIDEDESCRIPTION

[0001] The present invention relates to a plant and method for the generation of negative emissions and decarbonised hydroxide.

[0002] The effects of the so-called "greenhouse gases" on climate and especially the correlation between atmospheric concentrations of CO2 (carbon dioxide) and global warming have long been known.

[0003] The efforts of the scientific community and world politics in recent years have focused on trying to counteract the increase in greenhouse gas emissions into the atmosphere, in order to avoid the phenomenon of global warming, i.e. the rise in the average global temperature.

[0004] As is well known, many initiatives have been promoted at the international level aimed at limiting CO2 emissions into the atmosphere: the Kyoto Protocol in 1997 and the Paris Agreement in 2015, among others, are worth mentioning.

[0005] The ways identified by the scientific community to avoid global warming are numerous and basically involve reducing the use of fossil fuels such as coal, oil and natural gas by promoting the development of renewable energies such as hydropower, wind power, solar power, energy from biomass and zero-emission fuels such as hydrogen or ammonia.

[0006] In addition, many efforts of the international community focus on improving the efficiency of energy uses, such as in the case of lighting with energy-saving lamps, on transportation with new generations of high-efficiency engines, and, in the field of electricity generation, on replacing old and inefficient coal- or oil-fired power plants with new combined- cycle plants with gas and steam turbines, with energy efficiencies approaching 60%.

[0007] Despite the technological effort being made in the most advanced nations, forecasts by well-known international institutions on global energy needs in the coming years indicate a sharp increase in demand for electricity, thermal energy for industry and fuels for transportation.

[0008] Consequently, these forecasts indicate a steady increase in other uses of fossil fuels such as oil, coal and natural gas, especially by emerging, newly industrialised and developing countries. This consumption is in fact promoted by the wide availability of these resources andthe discovery of new deposits and techniques for their extraction, factors that on the whole make these energy sources economically advantageous.

[0009] Using the data predicted by these authoritative studies, not only is a global decrease in CO2 emissions not expected to contrast global warming, but a substantial increase in emissions is instead predicted over the next 50 years, mainly due to the increase in the world population and the new industrialisation of entire countries.

[0010] The catastrophic effects of this situation on the climate can be easily inferred and are difficult to avoid, mainly because developing countries consider the renewable energy option to be too sophisticated and expensive, and are more oriented towards short-term economic development programmes than towards reducing CO2 emissions and environmental issues.

[0011] One of the sectors that will be the object of future decarbonisation of the economy are the industrial sectors difficult to decarbonise and for which negative emissions must be generated by removing CO2 directly from the atmosphere.

[0012] It is estimated that the amount of CO2 to be subtracted directly from the atmosphere in 2050 should be between 1Gton / year and 5Gton / year (where Gton represents 109tons).

[0013] It is clear that, in order to generate negative emissions, there is a need to store the CO2 removed from the atmosphere in reservoirs where it can remain confined from the atmosphere for tens of thousands of years.

[0014] As is well known, CO2 capture and storage technologies are commonly referred to as CCS (Carbon Capture and Storage).

[0015] The main CCS (Carbon Capture and Sequestration) technologies proposed and known are:- the sequestration of CO2 in deep saline aquifers, a method recognised and promoted by the European Union through the 2009 directive;- the sequestration of CO2 directly on the ocean floor, in liquid form;- the sequestration of CO2 in calcium carbonates or calcium silicates, either directly or with other peptoid uses, known as Mineral Carbonation;- the sequestration of CO2 in oil wells where it is injected to increase the oil production of the well itself with a technology called EOR (enhanced oil recovery);- the sequestration of CO2 in the form of alkaline earth metal bicarbonates such as calcium and magnesium bicarbonate in seawater.

[0016] The main technologies to generate the proposed and known negative emissions are:- the capture of CO2 directly from the air by means of special contactors, either liquid or solid, which are periodically regenerated by releasing the captured CO2; these technologies are called DAC (Direct Air Capture) and require permanent storage of CO2 outside the capture plant- the capture of CO2 directly from the air through the carbonation of calcium hydroxide; these technologies generally require storage for the CO2 produced by the calcination process used in the preparation of calcium hydroxide outside the carbonation plant.- the capture of CO2 by spreading alkaline substances on the sea surface that induce CO2 absorption directly into the sea; such technologies are known by the acronym OAE (Ocean Alkalinity Enhancement) but require the generation of alkaline materials that generally generate gaseous CO2 that must be stored in a permanent CO2 storage.- the capture of CO2 from biomass combustion or gasification processes used for the production of energy and permanent storage of CO2 produced outside the plant; such technologies are commonly referred to as BECCS (Bio Energy Carbon Capture and Storage).

[0017] Although there are various technological alternatives available, one of the most important problems still to be solved is the prohibitive cost of capturing CO2 from the air and the limited availability of CO2 permanent storages especially in areas where the cost of decarbonised power is high, and therefore its use for the production of decarbonised calcium oxide or hydroxide in electric calciners for the permanent storage of CO2 in the form of calcium bicarbonates in the sea, as described in WO / 2022 / 137038 - "Plant and method for producing decarbonized oxide or hydroxide using carbonate and electric power", is expensive.

[0018] The technology described in WO / 2022 / 137038, proposed by the same inventor of the present invention, solves the problem of storing CO2 by reacting CO2, calcium hydroxide and seawater to form calcium bicarbonates Ca HCC h which are a stable form of storing CO2 in the sea, that is cost-effective and that can be developed in almost all coastal areas of the earth.

[0019] This technology is very effective if the objective is the production of decarbonised calcium hydroxide, but incomplete and inefficient if negative CO2 emissions are to be generated, as the electric calcination described in WO / 2022 / 137038 does not generate biogenic CO2 norcapture CO2 from the air, but only generates fossil CO2, derived from the limestone calcination process.

[0020] As is well known, in many geographical areas, there is an abundance of low-cost carbon fuels that can conveniently be used for the production of electric power, hydrogen or simply heat and biogenic CO2: carbon fuels comprise biomass and urban, agricultural and industrial waste.

[0021] The use of these carbon fuels is economically attractive in a context of high fossil fuel prices and decarbonization of energy sources.

[0022] As it can be immediately understood, there is a need to identify a technology that allows to carry out the capture and permanent storage of biogenic CO2 from carbon fuels at a reasonable cost.

[0023] As is well known, one of the most efficient systems for the use of carbon fuels, a system that also allows the production of chemicals such as hydrogen, is the gasification process.

[0024] The task of the present invention is to make available a system and method that can enable the efficient capture of biogenic CO2 , the permanent storage of biogenic CO2 and fossil CO2 produced by the process according to the invention while producing negative emissions using gasification of carbon fuels with lower costs than known technologies.

[0025] This aim and these tasks are achieved by means of a plant and a method for the generation of negative emissions of CO2 and decarbonised hydroxide according to claims 1 and 5, respectively. Other advantageous features are reported in the dependent claims.

[0026] The invention relates to a plant for the generation of negative emissions of CO2 and decarbonised hydroxide, comprising a gasifier, a high-temperature heat exchanger, an indirect calciner, a contactor, a pH correction apparatus, a hydroxide production unit and a hydroxide dosing device. In the plant of the invention:- the gasifier is adapted to receive, as input, a flow of fuel, a first flow of high-temperature steam and to release, as output, at least a flow of syngas;- the high-temperature heat exchanger is adapted to receive as input a first flow of high- temperature flue gas released from the indirect calciner and a second flow of low-temperature steam released from the hydroxide production unit and to release a second flow of low- temperature flue gas containing gaseous CO2 and the first flow of high-temperature steam;- the indirect calciner is adapted to receive as input a flow of carbonate, the flow of syngas, a flow of oxygen, and to release as output at least a flow of oxide and the first flow of high- temperature flue gas;- the contactor is adapted to receive as input the second flow of low-temperature flue gas, a first predetermined flow of water, is adapted to react water and the gaseous CO2 present in the second flow of low-temperature flue gas according to the known reaction CO2(g> + H2O H2CC>3(aq) H+(aq) + HCOs faq) and to release as output at least a flow of acidic water;- the pH correction apparatus is adapted to receive as input at least a predetermined flow of hydroxide and the flow of acidic water, it is adapted to react the acidic water with the predetermined flow of hydroxide according to the reaction Ca(OH)2(aq) + 2CO2(g> Ca HCOshtaqj (where Ca can be replaced with Mg if present in the carbonate) and to release as output a flow of buffered acidic water;- the hydroxide production unit is adapted to receive as input the flow of oxide released by the indirect calciner, a second predetermined flow of water, is adapted to react the oxide with water according to the reaction CaO(S> + H2O Ca(OH)2(s> (where Ca can be replaced with Mg if present in the carbonate) and to release as output a flow of hydroxide and the second flow of low-temperature steam;- the hydroxide dosing device is adapted to receive as input the flow of hydroxide released by the hydroxide production unit and to release as output at least the predetermined flow of hydroxide to supply the pH correction apparatus and an exceeding flow of decarbonised hydroxide for other uses.

[0027] Preferably, the contactor is adapted to receive as input a flow of fossil carbon dioxide, the second flow of low-temperature flue gas and the first predetermined flow of water; the contactor is also adapted to react the water and the gaseous CO2 present in the fossil carbon dioxide and in the second low-temperature flue gas according to the known reaction CO2(g> + H2O H2CC>3(aq) H+(aq) + HCOs taq) and to release as output at least the flow of acidic water.

[0028] In some embodiments, the plant further comprises an oxide dosing device installed between the indirect calciner and the hydroxide production unit, wherein the oxide dosing device is adapted to receive as input the flow of oxide released by the indirect calciner and to release as output a predetermined flow of oxide to supply the hydroxide production unit and possibly an exceeding flow of oxide available for other uses.

[0029] Preferably, the plant also comprises a14C meter capable of determining the percentage of biogenic carbon present in the second flow of low-temperature flue gas.

[0030] The invention also relates to a method for the generation of negative emissions of CO2 and decarbonised hydroxide, comprising the steps of:- providing a gasifier;- providing an indirect calciner;- providing a high-temperature heat exchanger;- providing a contactor;- providing a hydroxide production unit;- providing a hydroxide dosing device;- providing a pH correction apparatus;- supplying a flow of fuel and a first flow of high-temperature steam to the gasifier in order to obtain a flow of syngas;- releasing as output from the gasifier the flow of syngas;- supplying the flow of syngas, a flow of oxygen and a flow of carbonate to the indirect calciner in order to achieve calcination of the carbonate according to the reaction CaCOsts) CaO(S> + CC>2(g) (where Ca can be replaced with Mg if present in the carbonate);- releasing as output from the indirect calciner at least a flow of oxide and a first flow of high- temperature flue gas;- conveying the flow of oxide;- conveying the first flow of high-temperature flue gas;- supplying the first flow of high-temperature flue gas and a second flow of low-temperature steam to the heat exchanger;- releasing from the high-temperature heat exchanger the first flow of high-temperature steam and a second flow of low-temperature flue gas;- conveying the second flow of low-temperature flue gas;- supplying the second flow of low-temperature flue gas and a first predetermined flow of water to the contactor;- releasing as output from the contactor at least a flow of acidic water;- conveying acidic water;- supplying to the hydroxide production unit the flow of oxide and a second predetermined flow of water so that the reaction CaO(S> + H2O Ca(OH)2(s> (where Ca can be replaced with Mg if present in the carbonate) can take place;- releasing as output from the hydroxide production unit at least a flow of hydroxide and the second flow of low-temperature steam;- conveying the flow of hydroxide;- conveying the second flow of low-temperature steam;- supplying the flow of hydroxide to the dosing device;- releasing as output from the hydroxide dosing device at least a predetermined flow of hydroxide and an exceeding flow of decarbonised hydroxide for other uses;- conveying the predetermined flow of hydroxide;- supplying to the pH correction apparatus the flow of acidic water and the predetermined flow of hydroxide;- releasing as output a flow of buffered acidic water from the pH correction apparatus;- arranging the flow of buffered acidic water into the sea.

[0031] Preferably, the method further comprises a step of supplying to the contactor a flow of fossil carbon dioxide released by the indirect calciner.

[0032] In order to better understand the invention and appreciate its advantages, some illustrative and non-limiting embodiments are described below, with reference to the accompanying drawings:- Figure 1 is a schematic view of a plant for the generation of negative emissions and decarbonised hydroxide using syngas produced by gasifying fuels according to the invention;- Figure 2 is a schematic view of a plant for the generation of negative emissions and decarbonised hydroxide using syngas produced by gasifying fuels according to the invention;- Figure 3 is a schematic view of a plant for the generation of negative emissions and decarbonised hydroxide using syngas produced by gasifying fuels according to the invention;- Figure 4 is the chemical analysis of the carbonaceous fuel (RDF) used for the calculation of the mass and energy balance;- Figure 5 is a mass and energy balance related to the use of 1,000 kg of RDF as a carbonaceous fuel;- Figure 6 is a schematic view of a possible embodiment of an indirect calciner integrated with a hydroxide production unit;- Figure 7 is a schematic view of a possible embodiment of an indirect calciner integrated with a hydroxide production unit.

[0033] In the description, reference will also be made to a "gasifier" meaning any system, known in itself, capable of generating a syngas from a fuel. For example, gasifiers can be of different types: updraft, downdraft, crossdraft, fluidised bed, moving grate, rotary kiln, entrained, slagging type, pyrolysers or gasifiers that take advantage of solar energy. Gasifiers can be pressurised or atmospheric and can use oxygen and water vapour in various proportions as gasification agents.

[0034] In the description, reference will also be made to "synthesis gas" or "syngas", meaning a mixture of gases mainly containing CO2, CO, H2, CH4 in any proportion in the gaseous state, and other substances, including N2, Ar, O2, HC (hydrocarbons), HCO (oxygenated hydrocarbons), and H2O with an LHV (Low Heating Value) greater than 4Mj / Nm3.

[0035] In the description, reference will also be made to "oxygen", meaning a mixture of gases mainly containing oxygen and other substances, including N2 and H2O in any proportion, whereas when reference is only made to the chemical element O2, in the description O2 will be used. Atmospheric air falls under the definition of O2 as a special case.

[0036] In the description, reference will also be made to "CO2", meaning the chemical element CO2 (carbon dioxide).

[0037] In the description, reference will also be made to "fossil carbon dioxide" or "fossil CO2", meaning a gas mainly containing CO2, and possibly other substances, including N2, O2, H2O, Ar, produced by the calcination of carbonate according to the well-known chemical reactionCaCOs -> CaO + CO2.Fossil CO2 differs from biogenic CO2 by the absence of the carbon-14 isotope (14C).

[0038] In the description, reference will also be made to "biogenic carbon dioxide" or "biogenic CO2", meaning a gas containing mainly CO2, and possibly other substances, including N2, O2, H2O, Ar, produced by the combustion of biomass and characterised by the presence of the carbon-14 isotope (14C).

[0039] In the description, reference will be made to "flue gas", meaning the gas produced by the combustion of syngas mainly consisting of CO2, H2O, O2 and IXb and with an LHV (Low Heating Value) of 0 Mj / Nm3, possibly added with carbon dioxide from the carbonate calcination process.

[0040] The description will also refer to "high temperature", meaning temperatures between 500°C and 1500°C, preferably between 500°C and 1200°C.

[0041] The description will also refer to "low temperature", meaning temperatures between 0°C and 500°C, preferably between 80°C and 400°C.

[0042] The description will also refer to "fuel" as any liquid, solid or gaseous substance containing carbon, such as biomass, sewage sludge, MSW (Municipal Solid Waste), the organic fraction of municipal waste, RDF (Refused Derived Fuel), demolition wood, agricultural waste and algae, and also fossil fuels such as mineral coal or plastics.

[0043] The description will also refer to the "atmosphere", meaning any place in contact with atmospheric air.

[0044] In the description, reference will be made to "negative emissions", meaning the net subtraction of CO2 from the atmosphere. Biomass is considered as carbon captured directly from the atmosphere and CO2 that is produced by a process of gasification and / or combustion of biomass or syngas produced therefrom, it is considered biogenic CO2. For producing negative emissions with biogenic CO2, it is necessary to store this CO2 permanently.

[0045] In the description, reference will be made to the concept of "permanent storage", meaning the storage of CO2 in a form that allows it to be confined from the atmosphere for thousands of years. The storage duration of CO2 in the form of calcium bicarbonates Ca HCOsh in seawater is considered by the scientific world to be about 100,000 years.

[0046] In the description reference will be made to "inclined" as meaning an arrangement of the concerned apparatus in which its axis forms an angle between 0° and 90° relative to the horizontal.

[0047] Reference will also be made in the description to "water", meaning water in the liquid phase with the chemical and temperature characteristics necessary for use in the process according to the invention, whereas when reference is only made to the chemical element H2O , in the description, H2O will be used.

[0048] In the description, reference will also be made to the "sea", meaning the sea in its strict sense but also the ocean or any salty or brackish body of water.

[0049] In the description, reference will also be made to "carbonate" meaning any calcareous or dolomitic sedimentary rock such as calcite, aragonite, dolomite, siderite, magnesite, marble, but also any other carbonate material such as shells or corals with dimensions between 1 micron and 500 mm, preferably between 0.1 mm and 100 mm.

[0050] In the description reference will also be made to the "indirect calciner" meaning any known controlled atmosphere system capable of calcining carbonate according to the reactions CaCOs -> CaO + CO2 (+ 183 kj / mol) or MgCOs -> MgO + CO2 (+ 118 kj / mol). The calcination process, as known in itself, takes place at temperatures preferably between 500°C and 1300°C, depending on the composition of the atmosphere and the existing pressure, and is an endothermic process in which the energy required for calcination is provided by the combustion of the syngas in a combustion chamber separate from the calcination chamber. The controlled- atmosphere indirect calciner does not allow direct contact of the calcining zone with ambient air or flue gas while it allows the calcining zone to be possibly flushed with inert gases or water vapour or the unidirectional passage of fossil carbon dioxide to the combustion chamber where it mixes with the flue gases produced by the combustion of the syngas. Indirect calciners include fluidised-bed calciners flushed with water vapour or inert gases and molten-salt calciners where CaCOs is immersed in a molten salt at high temperature where it undergoes the calcination reaction CaCOs CaO + CO2: molten salts include sodium chloride NaCI and sea salt.

[0051] In the description, reference will also be made to "oxide", meaning the product of calcination mainly consisting of calcium oxide CaO or magnesium oxide MgO and to a lesser extent other materials (impurities) present in the carbonate rock with which the calciner is supplied.

[0052] In the description, reference will also be made to "hydroxide", by meaning the product of the hydration of calcium oxide Ca(OH)2 or magnesium oxide Mg(OH)2 with the following chemical reactions:CaO + H2O -> Ca(OH)2(-64.8 kj / mol)MgO + H2O -> Mg(OH)2(-37.0 kj / mol)

[0053] In the description, reference will be made to "bicarbonates" meaning the chemical compounds Ca HCOshtaq) and / or Mg HCOshtaq)

[0054] In the description, reference will be made to "impurities", meaning foreign substances present in the carbonate that do not take part in the chemical reactions according to the invention.

[0055] In the description, reference will be made to the "contactor", meaning a reactor in which gaseous CO2 and water are reacted according to the reaction CO2 + H2OH2CO3 -> H++ HCOs’ or where the flow of CO2 dissolved in water in the form of carbonic acid H2CO3 mixes with water and gaseous CO2 to form a flow of acidic water. Such a contactor may consist of a scrubber column, a bubbling column or simply a tube with possibly a static mixer to directly distribute the CO2 into the pressurised or atmospheric water flow, where the CO2 may remain in contact with water for longer than 0.5s, preferably between 10s and 1,000s and with pressures between 50 KPa and 10,000KPa;

[0056] In the description, reference will be made to "acidic water", meaning water in which CO2 has dissolved to form carbonic acid H2CO3 and whose pH has dropped from its initial pH to values typically below pH=8 preferably between 4.5 and 7.

[0057] In the description, reference will be made to "buffered acidic water", meaning an acidic water where the pH has been corrected to the desired value by adding a hydroxide.

[0058] In the description, reference will be made to "Ocai", meaning the calcite saturation state in seawater.

[0059] In this description, reference will be made to "pH", meaning the measurement scale indicating the acidity or basicity of a liquid, which is defined by the following formula: pH=-logio[H30+]

[0060] In the description, reference will be made to "alkalinity", meaning the amount of hydroxides OH; carbonates COs2-and bicarbonates HCOs2-present in seawater.

[0061] In the description, reference will also be made to the concept of "decarbonised", meaning a product or service with no CO2 emissions into the atmosphere, i.e. where the CO2 produced by the production process has been stored in a permanent form.

[0062] In the description, reference will be made to "low-temperature steam", meaning water vapour with an absolute pressure between 50KPa and 1,000 KPa and a temperature between 85°C and 500°C.

[0063] In the description, reference will be made to "high-temperature steam", meaning water vapour with an absolute pressure between 50KPa and 1,000 KPa and a temperature between 500°C and 1,200°C.

[0064] In the description, reference will be made to "enthalpy", meaning a state function defined as the sum of the internal energy U and the product of the pressure p for the volume V and is expressed in Jules in the international system:H = U + p*V

[0065] In the description, reference will be made to "14C" or carbon-14, meaning a radioactive isotope of carbon having 6 protons and 8 neutrons, which can be found in materials of biogenic origin and is generally integrated into every living organic system.

[0066] In the description, the dot will be used as a decimal separator and the comma as a thousand separator.

[0067] In the attached figures, reference 100 shows the overall plant according to the invention.

[0068] A first aspect of the invention relates to a plant 100 for the generation of negative emissions and decarbonised hydroxide according to the invention.

[0069] Referring to Figure 1, the plant 100 comprises a gasifier 1, a high-temperature heat exchanger 3, an indirect calciner 10, a contactor 20, a pH correction apparatus 30, a hydroxide production unit 60 and a hydroxide dosing device 40 wherein:- the gasifier 1 is adapted to receive as input a flow of fuel 12, a flow of high-temperature steam 32 and to release as output at least a flow of syngas 11;- the high-temperature exchanger 3 is adapted to receive as input a flow of high-temperature flue gas 170 released from the indirect calciner 10 and a flow of low-temperature steam 612 released from the hydroxide production unit 60 and to release a flow of low-temperature flue gas 171 and a flow of high-temperature steam 32;- the indirect calciner 10 is adapted to receive as input a flow of carbonate 110, the flow of syngas 11, a flow of oxygen 160 and to release as output at least a flow of oxide 130 and a flow of high-temperature flue gas 170;- the contactor 20 is adapted to receive as input the flow of low-temperature flue gas 171, a flow of water 210, is adapted to react the water 210 and the gaseous CO2 present in the flow of low-temperature flue gas 171 according to the known reaction CO2 +H++ HCOs’ and to release at least a flow of acidic water 230;- the pH correction apparatus 30 is adapted to receive as input at least a predetermined flow of hydroxide 640 and the flow of acidic water 230, it is adapted to react the acidic water 230 with the predetermined flow of hydroxide 640 according to the reaction Ca(OH)2(aq) + 2CO2(g>Ca HCCbhtaq) (where Ca can be replaced with Mg if present in the carbonate) and to release as output a flow of buffered acidic water 240;- the hydroxide production unit 60 is adapted to receive as input the flow of oxide 130 released by the indirect calciner 10, a predetermined flow of water 610, is adapted to react the oxide 130 with water 610 according to the reaction CaO(S> + H2OCa(OH)2(s> (where Ca can be replaced with Mg if present in the carbonate) and to release as output a flow of hydroxide 630;- the hydroxide dosing device 40 is adapted to receive as input the flow of hydroxide 630 released by the hydroxide production unit 60 and to release as output at least the predetermined flow of hydroxide 640 to supply the pH correction apparatus 30 and possibly a flow of decarbonised hydroxide for other uses 450.

[0070] In accordance with an embodiment and referring to Figure 2, the plant 100 comprises the contactor 20 wherein:- the contactor 20 is adapted to receive as input a flow of fossil carbon dioxide 140, the flow of low-temperature flue gas 171 and the flow of water 210, is adapted to react the water 210 and the gaseous CO2 present in the fossil carbon dioxide 140 and in the low-temperature flue gas 171 according to the known reaction CO2 + H2OH2CO3 -> H++ HCOs" and to release as output at least a flow of acidic water 230.

[0071] In accordance with an embodiment and referring to Figure 3, the plant 100 comprises an oxide dosing device 41 installed between the indirect calciner 10 and the hydroxide production unit 60 wherein:- the oxide dosing device 41 is adapted to receive as input the flow of oxide 130 released by the indirect calciner 10 and to release as output a flow of oxide 410 to supply a hydroxide production unit 60 and possibly an exceeding flow of oxide available for other uses 451.

[0072] In accordance with an embodiment and referring to Figures 1 and 2, the plant 100 further comprises:- a14C meter 55 capable of determining the percentage of biogenic carbon in the low- temperature flue gas 171.

[0073] A second aspect of the invention relates to a method for the generation of negative emissions and decarbonised hydroxide. The method according to the invention comprises the steps of:- providing a gasifier 1;- supplying a fuel 12 and a flow of high-temperature steam 32 to the gasifier 1 in order to obtain a flow of syngas 11;- releasing as output from the gasifier 1 the flow of syngas 11;- providing an indirect calciner 10;- supplying to the indirect calciner 10 the syngas 11, a flow of oxygen 160 and a flow of carbonate 110 in order to obtain calcination of the flow of carbonate 110 according to the reaction CaO + CO2 (where Ca can be replaced with Mg if present in the carbonate);- releasing as output of the indirect calciner 10 at least a flow of oxide 130 and a high- temperature flue gas 170;- conveying the flow of oxide 130;- conveying the high-temperature flue gas 170;- providing the high-temperature heat exchanger 3;- supplying to the high-temperature heat exchanger 3 a flow of high-temperature flue gas 170 and a flow of low-temperature steam 612;- releasing from the high-temperature heat exchanger 3, the flow of high-temperature steam 32 and a flow of low-temperature flue gas 171;- conveying the flow of low-temperature flue gas 171;- providing a contactor 20;- supplying the flow of low-temperature flue gas 171, and a predetermined flow of water 210 to the contactor 20;- releasing as output from the contactor 20 at least a flow of acidic water 230;- conveying the acidic water 230;- providing a hydroxide production unit 60;- supplying to the hydroxide production unit 60 the flow of oxide 130 and a predetermined flow of water 610 so that the reaction CaO + H2OCa(OH)2 can take place (where Ca can be replaced with Mg if present in the carbonate);- releasing as output from the hydroxide production unit 60 at least a flow of hydroxide 630 and the flow of low-temperature steam 612;- conveying the flow of hydroxide 630;- conveying the flow of low-temperature steam 612;- providing a dosing device 40;- supplying the flow of hydroxide 630 to the hydroxide dosing device 40;- releasing as output from the hydroxide dosing device 40 at least a predetermined flow of hydroxide 640 and possibly a flow of decarbonised hydroxide for other uses 450;- conveying the predetermined flow of hydroxide 640;- providing a pH correction apparatus 30;- supplying to the pH correction apparatus 30 the flow of acidic water 230 and the predetermined flow of hydroxide 640;- releasing as output a flow of buffered acidic water 240 from the pH correction apparatus 30;- arranging the flow of buffered acidic water 240 into the sea.

[0074] Referring to Figures 1, 2, 3 and 6, a skilled person will understand that the indirect calciner 10 is supplied with a flow of carbonate 110, syngas 11, oxygen 160 and separately releases at least a flow of oxide 130 and high-temperature flue gas 170.

[0075] As is well known, the calcination of the flow of carbonate 110 takes place according to the reaction CaCOsts) CaO(S> + CC>2(g), where Ca can be replaced by Mg if present in carbonate 110, at temperatures between about 500° (MgCOs) and 1300°C (CaCC ) and at intermediate values depending on the chemical composition of the carbonate which may also be a dolomite CaMg CCbh and the chemical composition and pressure of the atmosphere in the indirect calciner 10.

[0076] As is well known, the calcination reaction is an endothermic reaction requiring 118 KJ / mol of heat in the case of calcination of MgCOs and 183 KJ / mol in the case of CaCOs.

[0077] A skilled person can understand that the fossil carbon dioxide 140 produced by indirect carbonate calcination is a gas formed from CO2 and traces of gases such as N2 and such as O2 that may have entered with the flow of carbonate 110 into the indirect calciner 10 or gases intentionally supplied to the indirect calciner 10 to improve process conditions such as in the case of water vapour.

[0078] A skilled person can understand that the high-temperature flue gas 170 generated by the combustion of syngas 11 with oxygen 160 in the cavity 1012 used to supply the heat necessary for the indirect calciner 10 mainly consists of CO2, H2O, O2 and N2. The CO2 present in the flue gas is produced by the combustion of the CH4and CO present in the syngas and possibly from the CO2 generated by the calcination of the carbonate, while the N2 comes from the N2 possibly present in the oxygen 160. The presence of O2 in the flue gas is due to the excess oxygen that is generally used in the complete combustion of fuels. The presence of water vapour H2O in the flue gas is due both to the water vapour present in the syngas and resulting from the oxidation of H2, of CH4 and other hydrocarbons that may be present in the syngas.

[0079] A skilled person can understand that the high-temperature flue gas 170 released from the indirect calciner 10 is a high-enthalpy gas that can be conveniently used to improve the energy efficiency of the plant according to the invention

[0080] As is well known, the process of producing hydroxide 640 from oxide (130, 410) is an exothermic process that forms low-temperature water vapour due to the addition of excess water over stoichiometric water to maintain temperatures within the hydroxide production unit 60 at acceptable levels.

[0081] As is well known, water vapour at temperatures above 700°C is an agent for gasifying carbon-containing fuels by means of the well-known chemical reaction:H2O(g) + C(s) H2(g) + CO2(g)

[0082] A skilled person can understand that it is convenient to use the enthalpy of the high-temperature flue gas 170 to generate the high-temperature steam 32 by heating the low- temperature steam 612 released from the hydroxide production unit 60 by the high-temperature heat exchanger 3.

[0083] A skilled person can calculate that the energy that can be recovered from cooling the high-temperature flue gas 170 to generate high-temperature steam 32 in a plant 100 according to the invention represents about 20% of the energy contained in the fuel, with a clear energy and economic advantage.

[0084] A person skilled in gasification can calculate that, in the presence of high- temperature steam 32 at a temperature of about 950°C, the gasification of fuel 12 in the gasifier 1 can only take place by means of high-temperature steam 32 acting as gasification agent with an obvious plant advantage in that the use of O2 in the gasifier 1 is eliminated.

[0085] A skilled person can understand that if the carbon C contained in the syngas 11, mainly in the form of CO2, CH4 and CO were of biogenic origin, it would generate a high- temperature flue gas 170 consisting of biogenic CO2.

[0086] A skilled person can understand that if the low-temperature flue gas 171 were partly formed from carbon C of biogenic origin, the plant 100 according to the invention would generate negative emissions.

[0087] A skilled person can understand that, in order to generate negative emissions, it is sufficient to supply the gasifier 1 with a fuel 12 consisting, in whole or in part, of biogenic C- carbon.

[0088] A skilled person can understand that if the fuel 12 consisted of fossil carbon C, as in the case of mineral coal, the plant 100 according to the invention would not generate negative emissions but only decarbonised hydroxide for other uses 450 or decarbonised oxide for other uses 451.

[0089] Referring to the embodiments of Figures 1, 2, 3 and as described in WO / 2022 / 137038 the plant 100 according to the invention comprises the contactor 20 and the pH correction unit 30.

[0090] As is well known and referring to WO / 2022 / 137038, the contactor 20 uses water 210 as a medium to hydrate the CO2 contained in the flow of low-temperature flue gas 171 or in the fossil carbon dioxide flow 140 and form the acidic water 230 according to the reaction:

[0091] As is well known, there are different types of contactors for the absorption of CO2 present in a gas, which can be subdivided into scrubber columns, with or without bubbling column, or simply a tube, possibly provided with a static mixer in which the CO2 is injected directly into the flow of water.

[0092] As is well known, the permanent storage of CO2 in the sea in the form of calcium bicarbonates Ca HCCbh has been proposed in various scientific articles and is considered a form of permanent storage of CO2 also having a beneficial effect on ocean acidification as it increases its alkalinity.

[0093] A skilled person will understand that by neutralising the acidity present in acidic water 230 with the predetermined flow of hydroxide 640, it could be possible to discharge into the sea an effluent with the same natural pH as the seawater and store all the residual CO2 in the form of bicarbonates according to the reaction Ca(OH)2(aq> +Ca2++ (HCCbh’ , where the Ca2+ion can be replaced by the Mg2+ion, eliminating environmental issues and achieving a CO2 storage efficiency of approximately 100%.

[0094] As is well known, the reaction of Ca(OH)2 (where Ca can be replaced by Mg if present in the carbonate) with seawater is a complex reaction due to the presence of other chemical elements and thus it turns out that for each mole of Ca(OH)2 it is possible to neutralize from 1.9 to 1.98 moles of CO2 instead of the 2 moles in the equation Ca(OH)2(aq>+ 2CO2 Ca HCOshtaq). This variability depends on the chemical composition of the water, its temperature and is inversely proportional to the pressure.

[0095] As is well known, it is possible to carry out the process according to the invention using predominantly seawater since, while adding a predetermined flow of hydroxide 640 to acidic water 230, it is possible to reach Ocaiof 25 - 30 without the carbonate starting to precipitate. This would not be possible in river or lake fresh water where the pH of the water is higher than about 7 because carbonate precipitation would occur upon dilution of the buffered acidic water 240 with the surrounding water.

[0096] Referring to the embodiments of Figures 1, 2 and 3, the apparatus 100 according to the invention comprises the pH correction apparatus 30 wherein the acidic water 230 is buffered with a predetermined flow of hydroxide 640 sufficient to obtain the desired pH in the buffered acidic water 240.

[0097] Referring to Figures4 and 5, a skilled person can certainly understand the simplified mass and energy balance of a particular plant 100 for the generation of negative emissions of CO2 and decarbonised hydroxide from RDF according to the invention wherein:- the gasifier 1 is supplied with 1,000 kg of RDF, which represents an energy input to the plant 100 of 16,170Mj;- the indirect calciner 10 is supplied with 7,893 kg of carbonate 110, a flow of syngas 11, and 1,340 kg of O2 and releases as output 3,473 kg of carbon dioxide 140, 4,420 kg of oxide 130 and 1,412 kg of high-temperature flue gas 170;- the contactor is supplied with 14,655 tons of water 210, 3,473 kg of carbon dioxide present in the low-temperature flue gas 171 and 1,412 kg of carbon dioxide present in the flow of fossil carbon dioxide 140 and releases as output 14,660 tons of acidic water 230 with a pH of approximately 6.2;- the hydroxide production unit 60 is supplied with 4,420 kg of oxide 130 released from the indirect calciner 10, with 3,189 kg of water 610 and releases as output 5,841 kg of hydroxide 630 and 1,768 kg of low-temperature steam 612;- the hydroxide dosing device 40 receives as input 5,841 kg of hydroxide 630 released from the hydroxide production unit 60 and releases as output 4,564 kg of hydroxide 640 to the pH correction apparatus 30 and 1,277 kg of decarbonised hydroxide for other uses 450;- the pH correction apparatus 30 receives as input 14,660 tons of acidic water 230 released by the contactor 20 and 4,564 kg of the predetermined flow of hydroxide 640 released by the hydroxide dosing device 40 and releases 14,664 tons of buffered acidic water 240 with a pH of 8 by exploiting the reaction Ca(OH)2(aq>+2CO2 Ca HCC htaq) where Ca can be replaced byMg if present in the carbonate. In the case of seawater, depending on its chemical composition and depth, 1 mole of Ca(OH)2 neutralises 1.90 - 1.95 moles of CO2. In the present case, a ratio of 1.95 moles of CO2 per mole of Ca(OH)2 is considered, since a reaction pressure equal to atmospheric pressure is assumed to be used, so that the available moles of Ca(OH)2 of the predetermined flow of hydroxide 640 are perfectly balanced to buffer all the CO2 present in the acidic water 230.- the plant 100 according to the invention in the described configuration consumes approximately 1,000 kWh / tonRDF of electrical power for pumping water, producing oxygen and grinding carbonate.

[0098] As a skilled person can well understand from the above -re ported example, if RDF were composed of 50% biogenic carbon and 50% fossil carbon (plastics), from one ton of fuel 12 (RDF) it would be possible to generate 706 kg of negative emissions of CO2 and a flow of 1,277 kg of decarbonised hydroxide for other uses 450.

[0099] As the skilled person can calculate using market values, the cost of a ton of negative emission produced with RDF depends mainly on the cost of carbonate, the RDF contribution value, and the cost of electrical power, while plant and labour costs marginally affect the final result. Specifically, in order to produce 1 ton of negative emissions, about 1.41 tons of RDF and 11.18 tons of carbonate are needed. If the cost of carbonate were 5 € / ton, RDF were delivered to the plant at -100€ / ton, the market price of decarbonised hydroxide were 100€ / ton and the cost of electricity were 100€ / MWh, the variable cost of the negative emission ton would be about -75 € / ton.

[0100] A skilled person could therefore calculate that the installation costs of the gasifier, indirect calciner, contactor, dosing device, carbonate mill, civil works and services account for about 100 € / ton of negative emissions, while personnel costs are negligible. Considering therefore a final cost of 25 € / ton, the ton of negative emissions produced using a plant according to the invention is much more competitive in the market than the cost of producing negative emissions using any other known technology.

[0101] A skilled person will be able to understand the advantages of using a plant 100 according to the invention over the use of an electric calciner alone as described in WO / 2022 / 137038 because the gasification of the fuel 12 allows for having available, within the plant, both the energy necessary for calcination and the production of decarbonised hydroxide but above all the biogenic CO2 to be stored which, in the case of the electric calciner, would notbe available in the plant itself and would have to be sought outside the plant with an increase in costs.

[0102] A skilled person will certainly be able to understand that the plant 100 according to the invention, thanks to the recovery of the heat produced during the oxide hydration process, which takes place in the hydroxide production unit 60 to generate the low-temperature steam 612 necessary for the gasification process, and thanks to the high-temperature heat exchanger 3 which allows the recovery of the enthalpy of the high-temperature flue gas 170 to produce the high-temperature steam 32, has a higher energy efficiency than the electric calciner described in WO / 2022 / 137038, which cannot recover the thermal energy of the oxide hydration process taking place in the hydroxide production unit 60 to increase the efficiency of the process itself. This increase in efficiency of the energy required to carbonate calcination is calculated to be about 34.5%.

[0103] A skilled person will surely understand that the plant 100 according to the invention has, as a co-benefit of the production of negative emissions and decarbonised hydroxide / oxide, the possibility of using industrial, agricultural, MSW or RDF waste, which must necessarily be disposed of and is a major environmental problem in many countries; this possibility is not present in the electric calciner plant described in document WO / 2022 / 137038, which only uses electrical power, carbonate and seawater.

[0104] A skilled person will be able to understand the advantages of using a plant 100 according to the invention for the production of negative emissions compared to the use of a gasifier combined with a direct calciner for the production of negative emissions, as described in document WO / 2018 / 134775A1, proposed by the same inventor, since all the syngas produced by the gasification of the fuel 12 in the plant 100 according to the invention is used for generating the calcium hydroxide necessary for the storage of the CO2 produced by the plant in the form of bicarbonates and not for generating hydrogen with the need to have to store the CO2 produced in a storage outside the plant.

[0105] A skilled person will certainly be able to understand the advantage of the plant 100 according to the invention of being able to store the CO2 produced inside the plant itself and of not depending on external CO2 storage systems such as geological CCS.

[0106] A skilled person will also be able to verify that the amount of oxide or hydroxide produced in a plant according to the technology described in WO / 2018 / 134775 A 1 is farinsufficient to use the technology of storing in seawater all the CO2 produced in the process in the form of calcium bicarbonates, as proposed in the plant 100 according to the invention.

[0107] A skilled person will also be able to understand the advantages of the plant 100 according to the invention of producing flows of virtually pure CO2 (140 and 171) compared to the production of flows of CO2 mixed with syngas, as proposed by the process described by document WO / 2018 / 134775A1, which requires apparatuses for separating CO2 from syngas with significant plant complexities and increased costs.

[0108] As is well known, the14C (carbon-14) method, or radiocarbon method, is a radiometric dating method based on the measurement of the relative abundances of isotopes of carbon. Carbon is a chemical element essential for life and present in all organic substances. It is present on the earth in three isotopes: two of them are stable (12C and13C) and one is radioactive(14C). The latter transforms by beta decay into nitrogen (14N), with an average half-life of 5,730 years, so this isotope would disappear in the long run if not continually replenished. The production of new14C takes places regularly in nature in the upper layers of the troposphere and in the stratosphere, due to the capture of thermal neutrons secondary components of the cosmic rays by nitrogen atoms in the atmosphere. The dynamic equilibrium that is established between production and radioactive decay thus maintains a constant concentration of14C in the atmosphere, where it is present mainly bound to oxygen in the form of carbon dioxide.

[0109] All living organisms that are part of the carbon cycle continuously exchange carbon with the atmosphere through processes of respiration (animals) or photosynthesis (plants), or assimilate it by feeding on other living beings or organic substances. Consequently, as long as an organism is alive, the ratio of its14C concentration to that of the other two carbon isotopes remains constant and equal to the one found in the atmosphere.

[0110] A skilled person will understand that, by measuring the concentration of14C in the low-temperature flue gas 171 by means of a14C meter, it will be possible to determine with absolute certainty the amount of organic carbon in the total carbon even in fuels, such as RDF, wherein the biogenic fraction is unknown and above all variable over time and dependent on geographical origin. This measure of14C allows the sale of the negative emissions produced by the plant according to the invention.

[0111] Referring to the embodiments of Figures 6 and 7, the indirect calciner 10 according to the invention may comprise an inclined adiabatic tube 101, a calcination tube 102 positionedinternally to the adiabatic tube 101, a carbonate loading system 110 and a system 1330 for controlled discharge of the oxide 130 from the tube 102 to the hydroxide production unit 60.

[0112] The inclined adiabatic tube 101 and the calcination tube 102 can be static or rotating and preferably have an inclination between 0° and 90° relative to the vertical.

[0113] In accordance with a particular embodiment of the calciner 10, the inclined tube 102 can be made by one or more rotating tubes such as, for example, rotary kilns.

[0114] Referring to the embodiment of Figure 7, the inclined tube 102 may be permeable to the outflow of the flow of fossil carbon dioxide 140 generated therein by the calcination process towards the cavity 1012 where it mixes with the syngas combustion gases 11.

[0115] In accordance with a particular embodiment of the calciner 10 and referring again to Figures 6 and 7, the supply of syngas 11 and oxygen 160 are positioned so as to generate combustion in the cavity 1012 existing between the inclined adiabatic tube 101 and the calciner tube 102.

[0116] The combustion of syngas 11 with oxygen 160 generates the heat necessary for the calcination of carbonate particles 1101 and a flow of high-temperature flue gas 170 that is evacuated by the calciner 10.

[0117] The carbonate particles 1101 supplied to the calcination tube 102 by the flow of carbonate 110, during their stay inside the calcination tube 102 receive the energy required for calcination from the combustion of the syngas 11 with the oxygen 160, are transformed into oxide particles 1301 by the known chemical reaction CaCOsCaO + CO2.

[0118] The oxide particles 1301 are then discharged from the calcination tube 102 by means of a system for controlled discharge of oxide 1330 and conveyed into the hydroxide production unit 60 where they are reacted with water 610 according to the known reaction CaO + H2O Ca(OH)2 forming hydroxide particles 1030.

[0119] The hydroxide particles 1030 are supplied to the hydroxide 40 dosing device, forming the flow of hydroxide 630.

[0120] As a skilled person can surely understand, the process of permanent storage of CO2 coupled with the possibility of having available flows of biogenic CO2 according to the invention makes it possible to generate negative emissions and decarbonised hydroxide at a cost competitive over other technologies, and above all to install small-scale modular plants distributed along the coasts of many countries.

[0121] As a skilled person can surely understand, if the fuel 12 were of biogenic origin such as that contained in biomass, negative emissions could be generated with modular plants without requiring large amounts of energy and expensive nearby CCS geological storage systems which are currently required to generate negative emissions with DAC (Direct Air Capture) or BECCS (Bio Energy and Carbon Capture and Storage) plants.

[0122] As a skilled person can surely understand, the availability of carbonate, RDF or biomass and water are non-limiting factors for storing enough CO2 to meet the demand during the global energy transition period.

[0123] As the skilled person can well infer, the method and the plant according to the invention allow for the storage of biogenic CO2: it is thus possible to overcome one of the most important technical / economic obstacles due to the lack of permanent CO2 storage sites and the availability of substantial flows of biogenic CO2 for the production of negative emissions along coastlines worldwide and at competitive costs.

[0124] It is clear that the specific characteristics are described in relation to different embodiments of the plant and method for exemplary and non-limiting purposes. Obviously, a person skilled in the art may make further modifications and variations to the plant and method according to the present invention, in order to meet contingent and specific requirements, all of which fall within the scope of protection of the invention as defined by the following claims.

Claims

CLAIMS1. Plant (100) for the generation of negative emissions of CO2 and decarbonised hydroxide, comprising a gasifier (1), a high-temperature heat exchanger (3), an indirect calciner (10), a contactor (20), a pH correction apparatus (30), a hydroxide production unit (60) and a hydroxide dosing device (40), wherein:- the gasifier (1) is adapted to receive, as input, a flow of fuel (12), a first high- temperature flow of steam (32) and to release, as output, at least a flow of syngas (11);- the high-temperature heat exchanger (3) is adapted to receive as input a first flow of high-temperature flue gas (170) released from the indirect calciner (10) and a second flow of low-temperature steam (612) released from the hydroxide production unit (60) and to release a second flow of low-temperature flue gas (171) containing gaseous CO2 and the first flow of high-temperature steam (32);- the indirect calciner (10) is adapted to receive as input a flow of carbonate (110), a flow of syngas (11), a flow of oxygen (160) and to release as output at least a flow of oxide (130) and the first flow of high-temperature flue gas (170);- the contactor (20) is adapted to receive as input the second flow of low-temperature flue gas (171), a first predetermined flow of water (210), is adapted to react water (210) and the gaseous CO2 present in the second flow of low-temperature flue gas (171) according to the known reaction CO2 + H2OH2CO3 -> H++ HCOs" and to release as output at least a flow of acidic water (230);- the pH correction apparatus (30) is adapted to receive as input at least a predetermined flow of hydroxide (640) and the flow of acidic water (230), is adapted to react the acidic water (230) with the predetermined flow of hydroxide (640) according to the reaction Ca(OH)2(aq> + 2CO2(g>Ca(HCC>3)2(aq) (where Ca can be replaced with Mg if present in the carbonate) and to release as output a flow of buffered acidic water (240);- the hydroxide production unit (60) is adapted to receive as input the flow of oxide (130) released by the indirect calciner (10), a second predetermined flow of water (610), is adapted to react oxide (130) with the water (610) according to the reaction CaO(S> + Ca(OH)2(s> (where Ca can be replaced with Mg if present in the carbonate) and to release as output a flow of hydroxide (630) and the second flow of low-temperature steam (612);- the hydroxide dosing device (40) id adapted to receive as input the flow of hydroxide (630) released from the hydroxide production unit (60) and to release as output at least the predetermined flow of hydroxide (640) to supply the pH correction apparatus (30) and a flow of decarbonised hydroxide for other uses (450).

2. Plant (100) according to claim 1 comprising the contactor (20) wherein:- the contactor (20) is adapted to receive as input a flow of fossil carbon dioxide (140), the second flow of low-temperature flue gas (171) and the first predetermined flow of water (210), is adapted to react water (210) and the gaseous CO2 present in the fossil carbon dioxide (140) and in the second low-temperature flue gas (171) according to the known reaction CO2 + H2OH2CO3 -> H++ HCOs" and to release as output at least the flow of acidic water (230).

3. Plant (100) according to any one of the preceding claims, comprising an oxide dosing device (41) installed between the indirect calciner (10) and the hydroxide production unit (60), wherein:- the oxide dosing device (41) is adapted to receive as input the flow of oxide (130) released by the indirect calciner (10) and to release as output a flow of oxide (410) to supply the hydroxide production unit (60) and possibly a flow of oxide available for other uses (451).

4. Plant (100) according to any one of the preceding claims, further comprising:- a14C meter (55) capable of determining the percentage of biogenic carbon present in the second flow of low-temperature flue gas (171).

5. Method for the generation of negative emissions of CO2 and decarbonised hydroxide, comprising the steps of:- providing a gasifier (1);- providing an indirect calciner (10);- providing a high-temperature heat exchanger (3);- providing a contactor (20);- providing a hydroxide production unit (60);- providing a hydroxide dosing device (40);- providing a pH correction apparatus (30);- supplying a flow of fuel (12) and a first flow of high-temperature steam (32) to the gasifier (1) in order to obtain a flow of syngas (11);- releasing as output from the gasifier (1) the flow of syngas (11);- supplying to the indirect calciner (10) a flow of syngas (11), a flow of oxygen (160) and a flow of carbonate (110) in order to obtain calcination of the carbonate (110) according to the reaction CaCOsCaO + CO2 (where Ca can be replaced with Mg if present in the carbonate);- releasing as output from the indirect calciner (10) at least a flow of oxide (130) and a first flow of high-temperature flue gas (170);- conveying the flow of oxide (130);- conveying the first flow of high-temperature flue gas (170);- supplying the first flow of high-temperature flue gas (170) and a second flow of low- temperature steam (612) to the high-temperature heat exchanger (3);- releasing from the high-temperature heat exchanger (3) the first flow of high- temperature steam (32) and a second flow of low-temperature flue gas (171);- conveying the second flow of low-temperature flue gas (171);- supplying a second flow of low-temperature flue gas (171) and a first predetermined flow of water (210) to the contactor (20);- releasing as output from the contactor (20) at least a flow of acidic water (230);- conveying acidic water (230);- supplying to the hydroxide production unit (60) the flow of oxide (130) and a second predetermined flow of water (610) so that the reaction CaO + H2O Ca(OH)2 (where Ca can be replaced with Mg if present in the carbonate) can take place;- releasing as output from the hydroxide production unit (60) at least a flow of hydroxide (630) and the second flow of low-temperature steam (612);- conveying the flow of hydroxide (630);- conveying the second flow of low-temperature steam (612);- supplying the flow of hydroxide (630) to the hydroxide dosing device (40);- releasing as output from the hydroxide dosing device (40) at least a predetermined flow of hydroxide (640) and a flow of decarbonised hydroxide for other uses (450);- conveying the predetermined flow of hydroxide (640);- supplying to the pH correction apparatus (30) the flow of acidic water (230) and the predetermined flow of hydroxide (640);- releasing as output from the pH correction apparatus (30) a flow of buffered acidic water (240);- arranging the flow of buffered acidic water (240) into the sea.

6. Method according to claim 5, further comprising the step of: - supplying a flow of fossil carbon dioxide (140) released by the indirect calciner (10) to the contactor (20).

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