Hydrogen production process powered by water from a CO2 capture unit
By recycling water from cement plant fumes in a CO2 capture unit to supply hydrogen production, the process addresses water consumption and discharge issues, achieving self-sufficiency and reducing environmental impact.
Patent Information
- Application Number
- FR2024012088
- Authority / Receiving Office
- FR · FR
- Patent Type
- Utility models
- Current Assignee / Owner
- Filing Date
- 2024-11-05
- Publication Date
- 2025-10-03
- Estimated Expiration
- 2034-11-05
AI Technical Summary
Hydrogen production processes consume significant amounts of water, and existing methods result in water loss and environmental discharge, despite the availability of water in cement plant fumes that could be utilized.
Utilize water condensed from cement plant fumes in a CO2 capture unit to supply hydrogen production units, integrating water treatment with CO2 capture to reduce external water consumption and discharge.
Achieves self-sufficiency in water for hydrogen production, minimizing external water use and environmental impact by recycling water from cement plant fumes through integrated CO2 capture and treatment.
Abstract
Description
Title of the invention: Process for producing hydrogen powered by water from a CO2 capture unit
[0001] The present invention relates to a process for producing hydrogen supplied by water from a CO2 capture unit.
[0002] The partial use of hydrogen to fuel the burners of a cement plant is known to those skilled in the art. The use of hydrogen in the burners makes it possible to increase the rate of substitute materials (biomass, plastics, etc.) as fuel and therefore to reduce the use of fossil fuels.
[0003] Hydrogen production consumes significant quantities of water. This is the case in production by steam reforming or by an electrolyzer.
[0004] The capture of CO2 from fumes from cement plants is also known to those skilled in the art. These fumes contain a significant amount of water. The treatment of the fumes (in particular their cooling) makes it possible to condense part of the water contained in these fumes. If the CO2 capture unit includes complete drying of the fumes, all of the water in the fumes is condensed. Typically, these condensates are also rich in derivatives of acid gases present in the fumes (NOX, SOX, HCl, HF, etc.).
[0005] In order to be discharged into the environment or used, these condensates require treatments to neutralize the acids and reduce the quantity of salts dissolved in the water.
[0006] The present invention makes it possible to reduce, or even eliminate, water consumption for the production of hydrogen. In fact, the electrolyser or steam reforming is supplied by water resulting from the condensation of the water contained in the fumes.
[0007] Burners are supplied with fuel (natural gas, coal, biomass, plastics, etc.) and oxidant (air, oxygen or a mixture of the two). In addition, they are also supplied with hydrogen.
[0008] This hydrogen is produced by a hydrogen production unit (typically either a steam reformer or an electrolyzer) from water. The water used is typically drinking water that is demineralized. The demineralization treatment (typically by reverse osmosis) does not have a 100% efficiency: water is therefore lost in this process.
[0009] From a molar point of view, the molar flow rate of hydrogen produced is equal to the molar flow rate of water used for the production of hydrogen (H2O = H2 + 0.5 O2). If the hydrogen is fully used in the burners, we therefore find in the fumes a quantity of water at least greater than that used to generate the hydrogen.
[0010] In the case of an electrolyser, there is a co-production of oxygen which makes it possible to enrich the oxidant with oxygen in the case of enriched air (oxygen content in the combustion air higher than the oxygen content in the air). The use of this oxygen has the advantage of enriching the fumes with CO2, which makes it possible to reduce the cost of capturing CO2.
[0011] The combustion reaction generates water: even without the addition of hydrogen, the fumes are therefore rich in water. Furthermore, water is also added to fuels that are not necessarily dry. In addition, hot fumes are sometimes used to heat and dry materials (for example, limestone in the cyclones of a cement plant).
[0012] The quantity of water present in the fumes is therefore much greater than the quantity of water used to produce the hydrogen. Indeed, the quantity of water in the fumes combines both the water produced by the combustion of hydrogen and by the combustion of other fuels (the quantity produced by the combustion of hydrogen is similar to that used to produce it). In the case where the fumes are used to preheat or dry materials (for example fuel or limestone in the case of a cement plant), the fumes are also enriched with the water coming from this raw material.
[0013] The CO2 capture process treats these fumes. This process may include a phase of condensation of part of the water in the fumes by cooling the fumes. It is also possible to condense all of the water in the fumes in the event of complete drying of the fumes. The CO2 capture unit will therefore generate condensates (mixture of water and other impurities present in the fumes).
[0014] These condensates are typically rich in nitrates and sulfites. They therefore require suitable treatment to be able to discharge the water into the environment. This treatment typically includes a pH neutralization step by adding a base (for example caustic soda). It also includes a reverse osmosis step to remove the salts dissolved in the water. Water treatment typically produces clean water (almost entirely demineralized) and liquid effluents rich in salts. The clean water is usually discharged into the environment and the liquid effluents are transformed or treated elsewhere.
[0015] The invention consists of using the water produced by the condensation of the flue gas water to supply the hydrogen production unit, after suitable treatment. The invention makes it possible to reduce the water taken from the environment but also the discharge of water into the environment. Depending on the efficiency of the water treatment plant, the amount of water used from outside to produce hydrogen can be reduced to zero.
[0016] The invention also makes it possible to combine the water treatment units into a single treatment unit, which makes it possible to reduce the capital invested.
[0017] In the case of burners powered solely by hydrogen, the system would not benefit from the water supplement provided by the other fuels. Nevertheless, the system as a whole would be almost self-sufficient in water, apart from losses at the water treatment plant and at the hydrogen production level.
[0018] The CO2 capture unit therefore provides a double benefit: capturing the CO2 from the combustion of carbon fuels and providing the water necessary for the production of hydrogen.
[0019] According to an object of the invention, there is provided a method for producing hydrogen supplied by water from a CO2 capture unit in which water contained in a flow containing at least 10 mol% CO2 is condensed, at least part of the water feeds an electrolyser or steam reforming to produce hydrogen and oxygen and the flow depleted in water following the condensation of the water is sent to a CO2 separation unit.
[0020] Preferably, the hydrogen produced by electrolysis feeds a unit which produces the flow containing at least 10 mol% of CO2.
[0021] In an example of a method according to the invention, water feeds an electrolyzer which produces hydrogen and oxygen. The hydrogen and possibly the oxygen feeds a unit which produces a flow containing at least 10% CO2, for example burners of a cement plant. The flow is compressed and / or cooled to condense water which contains and at least a portion of the water formed feeds the electrolyzer, which may constitute the sole source of water for the electrolyzer. The compressed and / or cooled flow with reduced water content is sent to a separation unit forming part of a CO2 capture unit. The separation unit may operate by partial condensation and / or distillation and / or solidification. Downstream or upstream of this separation, the flow to be separated or a separated flow may be separated by adsorption and / or permeation.
[0022] Alternatively, water feeds a steam reformer which produces hydrogen. The hydrogen feeds a unit which produces a flow containing at least 10% CO2, for example burners in a cement plant. The flow is compressed and / or cooled to condense water which contains and at least part of the water formed feeds the electrolyser, which may constitute the sole source of water for the electrolyser.
Claims
4 Claims
1. A method for producing hydrogen powered by water from a CO2 capture unit in which water contained in a flow containing at least 10 mol% CO2 is condensed, at least part of the water feeds an electrolyzer or steam reformer to produce hydrogen and oxygen and the water-depleted flow following the condensation of the water is sent to a CO2 separation unit.