Patent Application
20220298443
This application claims the benefit of priority under 35 U.S.C. § 119 (a) and (b) to French patent application No. FR 2102829, filed Mar. 22, 2021, the entire contents of which are incorporated herein by reference.
The present invention relates to a plant and a process for producing biomethane, scrubbed of carbon dioxide and of water, from a feed gas stream comprising methane and carbon dioxide, preferably biogas or biomethane.
Biogas is the gas produced during the degradation of organic matter in the absence of oxygen (anaerobic fermentation), also known as methanization. This can be natural decomposition. It is thus observed in marshland or in household waste landfills. However, the production of biogas can also result from the methanization of waste in a dedicated reactor, known as methanizer or digester.
Owing to its main constituents, methane and carbon dioxide, biogas is a powerful greenhouse gas. At the same time, it also constitutes a source of renewable energy, which is appreciable in the context of the increasing scarcity of fossil energy sources.
Biogas predominantly contains methane (CH4) and carbon dioxide (CO2) in proportions which can vary according to the way in which it is obtained. It also contains, in smaller proportions, water, nitrogen, hydrogen sulfide, oxygen, as well as other organic compounds, in trace amounts.
Depending on the organic matter which has been degraded and on the techniques used, the proportions of the components differ. But on average, biogas comprises (on a dry gas basis) 30-75% methane, 15-60% CO2, 0-15% nitrogen, 0-5% oxygen and trace compounds.
Biogas is upgraded in various ways. It can, after minor treatment, be upgraded close to the production site to supply heat, electricity or a mixture of both in a process called cogeneration. The high carbon dioxide content reduces its calorific value, increases the costs of compression and transportation, and limits the economic advantage of upgrading it to this nearby use.
More intensive purification of biogas allows it to be more widely used. In particular, intensive purification of biogas makes it possible to obtain a biogas which has been purified to the specifications of natural gas and which can be substituted for the latter. Biogas thus purified is known as “biomethane”. Biomethane thus supplements natural gas resources with a renewable part produced within territories. It can be used for exactly the same uses as natural gas of fossil origin. It can supply a natural gas network or a vehicle filling station. It can also be liquefied to be stored in the form of liquefied natural gas (LNG).
The ways of upgrading biomethane are determined according to the local contexts, such as local energy requirements, the possibilities of upgrading as biomethane fuel, and the existence of nearby natural gas distribution or transportation networks. By creating synergies between the various parties operating in a given territory, such as farmers, manufacturers, and public authorities, the production of biomethane helps the territories to acquire greater energy self-sufficiency.
Several steps need to be completed between collecting the biogas and obtaining the biomethane which is the end product capable of being compressed or liquefied.
Carbon dioxide is a contaminant typically present in natural gas, from which it is common to have to strip it.
Water however is a contaminant which has rarely been removed to very low contents. Specifically, the water content to be achieved is generally of the order of 100 to 300 ppm, because such water levels are sufficient for the distribution network. For example, the distribution network may require a water dew point below −5° C. at the maximum operating pressure (4-8 barg) of the network.
In the context of the present invention, it is desired to be able to compress the biomethane to a level requiring a more thorough removal of water so as to be able to interconnect a distribution network operating at low pressure, typically between 4 and 8 bar, and a transport network operating between 40 and 70 bar.
This “reverse” operation aims to “decongest” the network to make sure that the number of forthcoming projects is not limited by the space in the distribution network.
Starting from that point, one problem that is faced is to provide a plant and a process for obtaining biomethane scrubbed of carbon dioxide and of water in order to be in accordance with the specificities of the transport network operating at higher pressure.
One solution of the present invention is a plant for producing biomethane B, scrubbed of CO2 and of water, from a feed gas stream A comprising methane and carbon dioxide comprising:
According to the case in hand, the plant according to the invention may have one or more of the characteristics below:
The plant may also comprise an analyser for measuring the concentration of CO2 and/or of water in the biomethane scrubbed of carbon dioxide at the outlet of the membrane separation unit.
Note that the adsorption purification unit will preferably be of PSA (pressure swing adsorption) type.
The purification unit will preferably comprise at least two adsorbers which follow, with an offset, a pressure cycle comprising an adsorption (purification) phase and a regeneration phase.
The membrane separation unit will preferably comprise only a single membrane stage. In other words, the retentate will not be sent to a second membrane stage.
Another subject of the present invention is a process for producing biomethane B, scrubbed of CO2 and of water, from a feed gas stream A comprising methane and carbon dioxide, using a plant according to the invention, and comprising:
Depending on the case, the process according to the invention may have one or more of the features below:
The present invention will now be described in more detail using
In the context of this example, the feed gas stream A is biomethane comprising 3.5% of CO2, 800 ppm of water and the remainder is methane; it has a flow rate of 760 Nm3/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 CO2, 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.
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.
The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.
“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”.
“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.
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR 2102829 | Mar 2021 | FR | national |
