FACILITY FOR PRODUCING LIQUID CO2 AND BIOMETHANE WITH A MEANS FOR PREVENTING THE BUILD-UP OF HYDROGEN AND OXYGEN

Abstract

The invention relates to a facility for producing liquid CO.sub.2 and biomethane, comprising: a unit for producing biogas; at least one unit for the membrane separation of biogas to produce biomethane and a gaseous mixture M1 mainly comprising carbon dioxide; a unit for cryogenically distilling the gaseous mixture M1 to produce liquid CO.sub.2 and a gaseous mixture M2 comprising carbon dioxide, methane, oxygen and hydrogen; one or more membranes located in the flow of the gaseous mixture M2 to separate the methane from the oxygen-hydrogen mixture

Claims

1. A facility (1) for the production of liquid CO.sub.2 (6) and biomethane (4), from a biogas (2) production unit (3), the facility comprising: at least one biogas membrane separation unit (5) configured to produce biomethane (4) and a gas mixture M1 predominantly comprising carbon dioxide, a cryogenic distillation system (7) configured to cryogenically distill the gas mixture M1 to thereby produce a liquid CO.sub.2 (6) and a gas mixture M2 comprising carbon dioxide, methane, oxygen and hydrogen, one or more membranes (9) configured to receive a flow of the gas mixture M2 and separate the methane (8) from the oxygen and hydrogen (10) in the gas mixture M2, a conduit (11) configured to recycle the methane (8) resulting from the gas mixture M2 to the at least one biogas membrane separation unit (5), and a vent (13) configured to discharge of the oxygen and hydrogen (10) resulting from the gas mixture M2.

2. The facility as claimed in claim 1, further comprising, between the biogas production unit (3) and the at least one biogas membrane separation unit (5), a compressor configured to compress the biogas (2).

3. The facility as claimed in claim 2, characterized in that the compressor is a lubricated screw compressor.

4. The facility of claim 1, further comprising, between the biogas production unit (3) and the at least one biogas membrane separation unit (5), a purification system configured to remove, at least in part, hydrogen sulfide and volatile organic compounds from the biogas (2).

5. The facility as claimed in claim 4, characterized in that the purification system is a pressure swing adsorption unit.

6. The facility of claim 1, characterized in that the one or more membranes (9) are more permeable to oxygen and to hydrogen than to methane.

7. The facility of claim 1, characterized in that the at least one biogas membrane separation unit (5) comprises three or four membrane stages.

8. The facility as claimed in claim 7, characterized in that the at least one biogas membrane separation unit (5) comprises: a first membrane separation stage equipped with a first membrane capable of receiving the biogas (2) stream and of providing a first permeate and a first retentate, said first membrane being more permeable to carbon dioxide than to methane, a second membrane separation stage equipped with a second membrane capable of receiving a second feed gas and of providing a second permeate and a second retentate, said second membrane being more permeable to carbon dioxide than to methane, and said second membrane separation stage being connected in series with the first membrane separation stage so that the first retentate constitutes the second feed gas, a third membrane separation stage equipped with a third membrane capable of receiving a third feed gas and of providing a third permeate and a third retentate, said third membrane being more permeable to carbon dioxide than to methane, and said third membrane separation stage being connected in series with the first membrane separation stage so that the first permeate constitutes the third feed gas.

9. The facility as claimed in claim 8, characterized in that the at least one biogas membrane separation unit (5) further comprises a fourth membrane separation stage equipped with a fourth membrane capable of receiving a feed gas and of providing a permeate and a retentate, said fourth membrane being more permeable to carbon dioxide than to methane, and said fourth membrane separation stage being connected in series with the third membrane separation stage so that the third retentate constitutes the fourth feed gas.

10. A process for the production of liquid CO.sub.2 and methane comprising: a) a first step of membrane separation of biogas, to produce biomethane (4) and a gas mixture M1 predominantly comprising carbon dioxide, b) a step of cryogenic distillation of the gas mixture M1, to produce liquid CO.sub.2 (6) and a gas mixture M2 comprising carbon dioxide, methane, oxygen and hydrogen, c) a second step of membrane separation of the gas mixture M2, to separate the methane (8) from the oxygen and hydrogen (10) included in the gas mixture M2, d) a step of recycling the methane (8) resulting from the gas mixture M2 to the feed gas for the first step of membrane separation of biogas, and e) a step of discharging of the oxygen and hydrogen (10) resulting from the gas mixture M2.

11. The process as claimed in claim 10, further comprising a biogas compression step prior to the first step of membrane separation of biogas.

12. The process of claim 10 further comprising a prepurification step to remove, at least in part, hydrogen sulfide and volatile organic compounds from the biogas (2) prior to the first step of membrane separation of biogas.

13. The process as claimed in claim 12, characterized in that the prepurification step is a step of purification by adsorption.

14. The process of claim 10, characterized in that step e) is carried out continuously.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0051] For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawing in which like elements are given the same or analogous reference numbers and wherein:

[0052] FIG. 1 illustrates a block flow diagram of an exemplary biogas processing facility.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0053] The present invention will be described in greater detail with the help of the example below.

[0054] The biogas contains 100 ppm of hydrogen and 0.2% of oxygen. Hydrogen must be completely purged through the membrane.

[0055] This solution, which impacts the biomethane yield, is necessary to ensure the safety of the facility. It is illustrated in this table, which is given as an example. This table takes the example of treatment of a maximum biogas flow rate (1100 Nm.sup.3/h of wet crude biogas) having a nominal composition.

TABLE-US-00001 Biogas LCO.sub.2 Biomethane Purge Dry flow rate 1043 Nm.sup.3/h 374 Nm.sup.3/h 667 Nm.sup.3/h 1.7 Nm.sup.3/h N.sub.2 0.4% 0.0% 0.7% 0.6% O.sub.2 0.2% 0.0% 0.3% 8.3% Methane 62.4% 0.0% 97.5% 8.0% CO.sub.2 37.0% 100.0% 1.6% 76.7% H.sub.2 0.01% 0.0% 0.0% 6.4% BioCH.sub.4 yield 99.98%

[0056] In other words, the solution according to the invention makes it possible not only to ensure the safety of the operation, by removing the compounds responsible for risks of explosion, but also to increase the methane yield.

[0057] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0058] The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

[0059] Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of comprising). Comprising as used herein may be replaced by the more limited transitional terms consisting essentially of and consisting of unless otherwise indicated herein.

[0060] Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0061] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0062] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

[0063] All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.