Device for targeted hydrogen permeation

Abstract

Device for the efficient separation of hydrogen (H2) from biogas streams in biogas plants for the optimization of the liquefaction processes of methane (CH4) and carbon dioxide (CO2), comprising a special separation membrane based on the different permeances of H2, CO2 and CH4 to selectively remove H2 and subsequently maximize the purity of CH4 and CO2.

Description

[0001] Description: The invention relates to a device for the efficient separation of hydrogen (H2) from biogas streams in biogas plants. The main objective is to optimize the liquefaction processes of methane (CH4) and carbon dioxide (CO2) in order to improve their purity and marketability.

[0002] In biogas plants, small amounts of H2 are produced during the fermentation process, which predominantly converts into the CO2 fraction in the first stage of gas treatment (separation of the binary gas mixture CH4 / CO2). During the liquefaction of the CO2 stream, most of the H2 remains, which presents operational challenges. Non-condensable gases must be regularly removed from current liquefaction plants and often thermally recycled. This results in approximately 10% of the total mass flow to be liquefied being unmarketable. This flow typically consists of 70-80% CO2, 15-18% CH4, 7-10% O2, and 0.2-0.4% H2.

[0003] Conventional CO2 liquefaction plants use a stripper-reboiler stage to remove non-condensable gases. Part of the gas mixture can be recycled back into the fermentation, with CO2 and CH4 recirculating, and O2 consumed in the fermentation or adsorbed with H2S. However, H2 continues to accumulate, leading to increasing operating costs and losses.

[0004] This is where the invention comes in: By implementing an additional step, a special separation membrane is used, based on the different permeances of the molecules. This membrane enables efficient removal of H2 while largely retaining CO2 and CH4. Despite the membrane's natural affinity for rapidly permeating CO2, operation is optimized to selectively remove a relevant portion of the H2.

[0005] The device thus contributes significantly to improving the purity and marketability of CH4 and CO2 by reducing the amount of non-condensable gases and increasing the efficiency of the liquefaction process. This leads to a significant reduction in operating costs and improved profitability of these biogas plants.

Claims

[1] Device for the efficient separation of hydrogen (H2) from biogas streams in biogas plants to optimize the liquefaction processes of methane (CH4) and carbon dioxide (CO2), comprising a special separation membrane based on the different permeances of H2, CO2 and CH4 to selectively remove H2 and further maximize the purity of CH4 and CO2. [2] The device according to claim 1, wherein the separation membrane is configured to allow H2 to permeate significantly despite its affinity to permeate CO2 more rapidly, while retaining most of CO2 and CH4. [3] Device according to claim 1 or 2, wherein the separated gases (CH4 and CO2) are made available for marketing in marketable purity and the proportion of non-condensable gases is significantly reduced. [4] Device according to one of the preceding claims, wherein the separation membrane is integrated in an additional step after the stripper-reboiler stage of a CO2 liquefaction plant. [5] Device according to one of the preceding claims, wherein the biogas produced during the fermentation process and typically containing small amounts of H2 is first subjected to a first separation of the binary gas mixture CH4 / CO2 before passing through the separation membrane. [6] Device according to one of the preceding claims, wherein the total mass flow to be recycled typically consists of 70-80% CO2, 15-18% CH4, 7-10% O2 and 0.2-0.4% H2, and the H2 content is selectively separated by the separation membrane at the corresponding concentration. [7] Device according to one of the preceding claims, wherein the non-condensable gases, which usually have to be thermally utilized, are significantly reduced by the separation of the H2, which leads to an increase in efficiency and a significant reduction in operating costs of the entire plant network. [8] Device according to one of the preceding claims, wherein the gases remaining in the retentate can be fed back into the process after their separation, wherein CO2 and CH4 pass through the process again and O2 is consumed in the fermentation or adsorbed with H2S, while H2 does not accumulate adversely.