CARBON DIOXIDE RECYCLING DEVICE IN THE FRAMEWORK OF IMPROVED COGENERATION

Abstract

Autonomous device for producing thermal and electrical energy and for the simultaneous treatment of carbon dioxide from the combustion of fossil fuels. The energy produced, including that from exhaust stack gases, by an advanced cogeneration system, is recovered through a heat transfer system, steam turbines and carbon dioxide, then directed: - either to a heating system - or to the use of electrical appliances. The electrical energy is partially used in electrolyzers to generate sodium hydroxide, dihydrogen, dioxygen and sulfuric acid. The dihydrogen and dioxygen are reused in fuel cells, thus recycling electrical energy and thermal energy. When the cogeneration is stopped or idling, photovoltaic cells provide the electrical energy necessary for electrolysis.Carbon dioxide and sodium hydroxide produce sodium hydrogen carbonate which is consumed in many areas.

Description

Overall appearance (figure 1) The present invention relates to a device for the autonomous treatment of carbon dioxide emissions from the combustion of fossil fuels, by combining technologies such as cogeneration, electrolysis, fuel cells, photovoltaic cells and carbonation. - Cogeneration generates thermal energy for heating purposes and electrical energy. - By electrolysis of water, part of the electrical energy allows the production of sodium hydroxide, dihydrogen, dioxygen and sulfuric acid. - By chemical transformation, sodium hydroxide and carbon dioxide from combustion produce sodium hydrogen carbonate. - Dihydrogen and dioxygen are reused in fuel cells, either for general use in buildings or for electrolysis. When the cogeneration is stopped, the photovoltaic batteries provide electrical energy, either for domestic use or for electrolysis. This device therefore aims to produce thermal and electrical energy by burning fossil fuels and to block the release of CO2 into nature by transforming it into sodium hydrogen carbonate. The aim is to minimise energy losses as much as possible by recovering all combustion energy, including that of exhaust gases, and avoiding air pollution. This project is applicable to heating installations in SMEs or large residential buildings, but also to thermal power plants using fossil fuels, such as coal or natural gas. Advanced cogeneration (Figure 2) The combustion of fossil fuels or biomass in a boiler generates hot gases: - carbon dioxide CO2, 5 - water vapor, H2O - nitrogen oxides NOX sulfur oxides SOX depending on the purity of the fuel. - particles. Part of the heat captured by a heat transfer fluid such as water, 10 in an exchanger, contributes to heating the installations, by a routing system with insulated tubes and radiators. A second part of the released heat is captured in another exchanger, producing water vapor and then electrical energy in a water vapor turbine. 15 A third part of the heat, contained in the gases usually lost in the atmosphere, also produces electrical energy in a CO2 turbine, after filtering the particles and other gases. The fuel is burned in a condensing boiler, which allows significant energy recovery from the water vapor created by combustion. The heat of CO2 from the exhaust gas is always converted into a CO2 turbine. This process minimizes energy losses as much as possible. The energy from the exhaust gases is recovered. 25 Carbon dioxide generated by combustion contributes its own treatment. Electrolysis Electrolyte: Sodium sulfate (figure 3) Part of the electrical energy produced previously or by photovoltaic batteries, when the cogeneration is stopped or slowed down, is converted into chemical energy by electrolysis of water, in the presence of sodium sulfate in a suitable container. The products of electrolysis are dihydrogen, dioxygen, dilute sulfuric acid and sodium hydroxide (or soda). The electrolysis tank with anode and cathode compartments separated by a membrane, allows the collection of: - at the anode of dioxygen O2 and H+ ions, which gives diluted sulfuric acid with the sulfate ions present. 2 H2O(|) -> O2(g) + 4 H (aq) + 4 e - at the cathode of dihydrogen and OH ions which gives sodium hydroxide or soda, with the Na+ ions present. 2 H2O(|) + 2 e -► 2 OH (aqj + 2 H2(gj The hydrogen and oxygen are stored in suitable tanks awaiting use in fuel cells. The two compartments are under constant agitation around each electrode. Electrolysis is stopped when the cathodic pH is close to 14 and the anodic pH is close to 0. Acidic and basic solutions are isolated separately. Solid sodium hydroxide is obtained by evaporation, if the carbonation technique with alveolar supports is used. Sodium hydroxide is kept in solution if the carbonation technique in aqueous solution is used. Electrolyte: Sodium chloride (figure 4) Sodium sulfate can be replaced by sodium chloride, The electrolysis tank with anode and cathode compartments always separated by a membrane, allows the collection of: 5 - at the anode of dichlorine Cl2 2CI (aq) Cl2(g) + 2e at the cathode of dihydrogen and OH ions”, which gives sodium hydroxide with the Na+ ions present. 2 H2°(l) + 2 e 2 OH (aq) + 2 H2(g) 10 This procedure produces dihydrogen, which can be combined with air in the fuel cell. Chlorine and sodium hydroxide could generate bleach in a suitable reactor, corresponding to an aqueous solution of sodium hypochlorite and sodium chloride when the combustion chamber is stopped. 15 2 (Na (aq)+OH (aq)) + Cl2(g) —► (Na (aq)+CIO (aqp + (Na (aq)+CI (aq)) +^0(1) Fuel cell The previously produced hydrogen and oxygen are used in fuel cells. The hydrogen is the fuel and the oxygen is the oxidizer. The electrical energy produced with a set of batteries in series is either reinjected 5 in the building's usage circuit, or in the electrolysis circuit. The electrolyte of the battery is potassium or sodium or lithium hydroxide. The electrodes are made of porous platinum. The electrode equations are: - at the cathode, a reduction 10 °2(g) + 2 h2®(|) + 4 e -* 4 OH (aqj - at the anode, oxidation 4 0H (aq) + 2 H2(g) 4 H2°(g) + 4 e or the balance of water formation in the gaseous state. °2(g) + 2 H2(g) -* 2 H2°(g) 15 The heat released by the stack can be recovered by an exchanger and reused in the steam turbine. Carbonation of sodium hydroxide Carbonation with aqueous sodium hydroxide solution, (figure 5) Carbon dioxide from the exchange system dissolves in water according to the equation: 5 C02(g) * C02(aq) and reacts in a limited way with water to generate carbonic acid H2CO3 according to the equation: CO2(aq) + H2°(l) H2CO3(aq) Carbonic acid reacts with sodium hydroxide in a quasi-total acid-base reaction: H2CO3(aq) + 0H (aq) HCO3 (aq) + H2O(|) The reaction takes place in aqueous solution, in a suitable tank where the pH is constantly monitored, avoiding an excess of sodium hydroxide which could react with the ion - 2~ hydrogen carbonate HCO3 and generate the carbonate ion CO3 15 following the reaction: HCO3 (aq) + OH (aq) —» CO3 (aq) + H2O(|) Sodium hydrogen carbonate precipitates by evaporation. The final pH is slightly basic and does not exceed the value of 8 Carbonation with solid sodium hydroxide (Figure 6) The sodium hydroxide from electrolysis is precipitated in the form of solid flakes by evaporation. A gaseous stream of gaseous CO2 is directed into a reactor consisting 5 of a set of superimposed and alveolar supports, on which sodium hydroxide was deposited in the form of solid flakes. The reaction balance is then different, we obtain sodium carbonate which can also be recycled. CCfyg) + 2 NaOH -+ Na2CO3 (Sj + H2O(q 10 The hydrogen carbonate is purified by controlled action of the sulfuric acid solution obtained by electrolysis. + J— + — (2 H3O (aq)+SO4 (aq)) + 2 Na2CO3 -* 2 (Na (aq)HCO3 (aq)) + 2 H2O(|) + 9— + (2 Na (aq) + SO4 (aq)) Sodium sulfate and sodium bicarbonate are separated by solubility difference, with sodium sulfate precipitating first. -1 Solubility of sodium sulfate at 20°C = 20 gL -1 Solubility of sodium hydrogen carbonate at 20°C = 87 gL

Claims

Claims 1 Device for producing thermal and electrical energy by cogeneration and simultaneous treatment of carbon dioxide produced during the combustion of combustible derivatives from oil, natural gas or biomass, 5 characterized in that the device comprises: » a condensing boiler, receiving air, combustible derivatives from oil or natural gas or biomass and producing heat; ® a first exchanger recovering heat with a heat transfer fluid, for the purpose of heating a group of buildings; ® a second exchanger generating water vapor and producing energy 11 electric in a water steam turbine, for use, either in the installations of a group of buildings, or in an electrolysis circuit; ® a filter retaining particles, nitrogen oxides and sulfur oxides from the exhaust gas and releasing hot carbon dioxide; ® a CO2 turbine recovering hot carbon dioxide and producing 16 of electrical energy in for use purposes, either a group of buildings or in an electrolysis circuit. "an electrolysis circuit converting part of the electrical energy produced by cogeneration into chemical energy, i.e. into dihydrogen and dioxygen 20 gaseous, in solutions of sulfuric acid and sodium hydroxide during a first electrolysis and in dihydrogen and dichlorine gas and sodium hydroxide in aqueous solution during a second electrolysis. » means for carbonating sodium hydroxide into sodium hydrogen carbonate, by reaction of gaseous carbon dioxide from cogeneration and 25 sodium hydroxide from electrolysis means. 2 Device according to claim 1, characterized in that the electrolysis circuit comprises, in the context of the first electrolysis, an ion-permselective membrane electrolyzer containing an aqueous solution of sodium sulfate, allowing the production of gaseous dihydrogen and dioxygen, the production of an aqueous solution of sulfuric acid, the production of sodium hydroxide either in aqueous solution or in the form of solid flakes after evaporation. 3 Device according to claim 1, characterized in that the electrolysis circuit comprises, within the framework of the second electrolysis, an electrolyser with a permselective ion membrane containing an aqueous solution of sodium chloride allowing, the production of dihydrogen and dichlorine gas, the production of sodium hydroxide either in aqueous solution or in the form of solid flakes after evaporation. 4 Device according to claim 1, characterized in that it further comprises fuel cells in the electrolysis circuit or for use in buildings, using dihydrogen as fuel and dioxygen as oxidant, this dihydrogen and this dioxygen being produced in the electrolysis circuit. 5 Device according to claim 1, characterized in that it further comprises photovoltaic batteries in the electrolysis circuit or for domestic use, thus providing an additional source of energy when the cogeneration is stopped and thus allowing the storage of chemical energy. 6 Device according to claim 1, characterized in that the carbonation means comprise a first chemical reactor composed of a tank surmounted by a hood, containing an aqueous solution of sodium hydroxide, into which gaseous carbon dioxide is intended to be injected. The carbonation means are configured so that the final pH does not exceed the value of 8 and that the sodium hydrogen carbonate precipitates after evaporation. 7 Device according to claim 1, characterized in that the carbonation means comprise a second chemical reactor, composed of superimposed and alveolar supports, on which sodium hydroxide flakes are deposited and into which gaseous carbon dioxide 5 from the cogeneration is intended to be injected, the product generated being sodium carbonate in the solid state. 8 Device according to claim 1, characterized in that the carbonation means comprise a third chemical reactor composed of a tank, in which the sodium carbonate from the second chemical reactor and the sulfuric acid solution from the first electrolysis are intended to react in order to produce sodium hydrogen carbonate in aqueous solution. The third chemical reactor is configured so that sodium bicarbonate and sodium sulfate are separated by solubility difference, with sodium sulfate being less soluble in water, precipitating first.

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