PLANT AND PROCESS FOR OBTAINING BIOMETHANE IN ACCORDANCE WITH THE SPECIFICITIES OF A TRANSPORT NETWORK

Abstract

Methane and carbon dioxide-containing feed gas stream is compressed and cooled to condense and remove a portion of water therein, separated with a membrane separation unit into a permeate enriched in carbon dioxide and a biomethane stream scrubbed of CO.sub.2 that is subsequently scrubbed of water in an adsorption purification unit.

Claims

1. A process for producing biomethane that is scrubbed of CO.sub.2 and of water, from a feed gas stream comprising methane and carbon dioxide, comprising the steps of: compressing the feed gas stream with a compressor, thereby producing a compressed feed gas stream; cooling the compressed feed gas stream so as to condense at least one portion of water in the compressed feed gas stream; removing at least one portion of the condensed water in the feed gas stream, thereby producing a water-depleted compressed feed gas stream; separating the water-depleted compressed feed gas stream with a membrane separation unit into a permeate enriched in carbon dioxide and a biomethane stream scrubbed of carbon dioxide; recovering the biomethane stream scrubbed of carbon dioxide from the membrane separation unit; removing at least one portion of water remaining in the recovered biomethane stream scrubbed of carbon dioxide with an adsorption purification unit comprising an adsorber to produce biomethane scrubbed of carbon dioxide and water; and recovering the biomethane scrubbed of carbon dioxide and water from the adsorption purification unit.

2. The process of claim 1, further comprising regenerating the adsorber by using a portion of the water-depleted compressed feed gas stream as regeneration gas.

3. The process of claim 2, further comprising recovering the regeneration gas at an outlet of the adsorber and recycling the recovered regeneration gas in said process upstream of the compressor.

4. The process of claim 3, further comprising the steps of: cooling the recovered regeneration gas so as to condense at least one portion of water in the regeneration gas, said step of cooling the regeneration gas being performed between said step of recovering the regeneration gas and said step of recycling the recovered regeneration gas; and removing the at least one portion of condensed water from the regeneration gas.

5. The process of claim 1, further comprising heating the water-depleted compressed feed gas stream in a heat exchanger.

6. The process of claim 1, further comprising measuring a concentration of CO.sub.2 and/or of water in the recovered biomethane scrubbed of carbon dioxide and water.

7. The process of claim 1, wherein the feed gas stream is compressed to a pressure greater than 60 bar.

8. The process of claim 1, wherein the compressed feed gas stream is cooled to a temperature below 15° C.

9. The process of claim 1, wherein the feed gas stream is chosen from biogas or biomethane.

10. The process of claim 1, wherein the adsorber comprises an adsorbent chosen from alumina or molecular sieve.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0051] FIG. 1 illustrates an example of a plant according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0052] In the context of this example, the feed gas stream A is biomethane comprising 3.5% of CO.sub.2, 800 ppm of water and the remainder is methane; it has a flow rate of 760 Nm.sup.3/h and a pressure of 3.5 bar. The biomethane A is firstly compressed in a compressor 0 to a pressure of 62 bar before being cooled 1 to a temperature of 5° C. This cooling makes it possible to condense the water which is removed in a separator 2. 80% of the water initially included in the biomethane A is thus removed. The biogas is then heated to a temperature of 15° C. in an exchanger 3 before being introduced into the membrane separation unit 4. This membrane separation unit 4 comprises at least one membrane permeable to carbon dioxide and thus makes it possible to recover a permate 10 enriched in carbon dioxide and biomethane 11 scrubbed of carbon dioxide, that is to say comprising in the present case 2.5% carbon dioxide. The biomethane 11 scrubbed of carbon dioxide is analysed in the analyser 9 in order to control the concentration of CO2 and/or of water before being introduced into the adsorption purification unit 5 in order to remove at least one portion of the water remaining in the biomethane scrubbed of carbon dioxide. The adsorption purification unit 5 comprises two adsorbers which each follow, with an offset, a pressure cycle comprising an adsorption phase and a regeneration phase. These adsorbers each comprise an adsorbent for adsorbing water, chosen from alumina and molecular sieve. Biomethane scrubbed of carbon dioxide and of water is recovered at the outlet of the adsorption purification unit. It comprises precisely 2.5% of CO.sub.2, less than 40 ppm of water and the remainder is methane. This composition is verified in the analyser 12. The adsorbent of the adsorbers is regenerated using a portion R of the biogas exiting the exchanger 3. This portion R of the biomethane is heated in a heater 6 to a temperature of 150° C. before being introduced as regeneration gas into the adsorber in regeneration mode of the adsorption purification unit 5. Recovered at the outlet of the adsorption purification unit 5 is the regeneration gas which is cooled at 20° C. in a cooler 7, which makes it possible to condense at least one portion of the water included in the regeneration gas. This condensed water will be removed 8 before being recycled upstream of the compressor 0.

[0053] 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.

[0054] The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

[0055] “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” is defined herein as necessarily encompassing the more limited transitional terms “consisting essentially of” and “consisting of”; “comprising” may therefore be replaced by “consisting essentially of” or “consisting of” and remain within the expressly defined scope of “comprising”.

[0056] “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.

[0057] 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.

[0058] 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.

[0059] 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.