Method and device for conditioning biogas in compact form

Abstract

The invention relates to a method (100) for conditioning biogas in compact form, the method comprising: - a step (105) of receiving a biogas stream comprising at least methane; - a step (110) of measuring a flowrate of biogas at the inlet; - a step (115) of injecting a carbon dioxide stream into the biogas stream according to the measured flowrate, configured so that the fraction of carbon dioxide represents between 40% and 56% of the molar mass of the mixture comprising at least carbon dioxide and methane; - a step (120) of compressing the mixture to a pressure higher than or equal to 80 bara; - a step (125) of cooling the compressed mixture to a temperature of between -50°C and 5°C to bring the mixture to a liquid or supercritical state; and - a step (130) of releasing the mixture.

Description

[0001] METHOD AND DEVICE FOR CONDITIONING BIOGAS IN THE FORM

[0002] COMPACT

[0003] Technical field of the invention

[0004] The present invention relates to a method for packaging biogas in compact form and a device for packaging biogas in compact form. It applies, in particular, to the field of treatment and packaging of biogas with a view to the recovery of said biogas.

[0005] State of the art

[0006] In the field of biogas (or biomethane), one difficulty is the collection of biogas produced on a small scale and in locations far from the gas transport network.

[0007] Indeed, to be able to collect this biogas, logistical and local processing costs must be minimized. These costs are induced by current collection and processing methods.

[0008] To solve this technical problem, four types of strategies are currently implemented:

[0009] - compress the biogas to transport it at high pressure (typically at a pressure above 200 bara) - the problem is that due to the high carbon dioxide content of the biogas (typically above 35% of the molar mass), the carbon dioxide can condense during compression and therefore this requires a specific expensive compressor capable of evacuating the carbon dioxide which condenses during treatment,

[0010] - cool and liquefy the biogas to condense it: the problem here is that, given once again the high carbon dioxide content of the biogas, there is a risk that part of the carbon dioxide crystallizes well before the methane-enriched mixture becomes liquid, and therefore that this blocks the process by progressively blocking the exchangers,

[0011] - at least partially purify the biogas into carbon dioxide and then condense it: this is the BioGNC technique (CNG being the acronym for “Compressed Natural Gas”) or BioGNL (LNG being the acronym for “Liquefied Natural Gas”) - the processes are expensive and therefore difficult to make profitable at low biogas production levels, which typically correspond to agricultural farms (less than 150 Nm 3 / h of biogas) and

[0012] - modify the composition of the biogas by adding a third component to block the crystallization of carbon dioxide and therefore condense the biogas into liquid form - the third component, typically a C3 to C7 hydrocarbon, always requires liquefaction at low temperatures (at least -50°C and more often below -80°C) if we want to limit the quantity of the third component so as not to overload the logistics chain, in addition to difficulties linked to the regeneration of this third component which often requires specific separation with a distillation column.

[0013] Thus, current methods present technical risks for compressors, linked to the risks of condensation of carbon dioxide, risks of clogging of heat exchangers or costs such that they do not allow them to be implemented for small-scale biogas sources.

[0014] Therefore, there is currently no solution for conditioning biogas that would allow the small-scale exploitation of the biogas produced.

[0015] Subject of the invention

[0016] The present invention aims to remedy all or part of these drawbacks.

[0017] To this end, according to a first aspect, the present invention aims at a method for conditioning biogas in compact form, which comprises:

[0018] - an input stage of a biogas flow comprising at least methane,

[0019] - a step of measuring a flow rate of biogas at the inlet,

[0020] - a step of injecting a flow of carbon dioxide into the biogas flow as a function of the measured flow rate, configured so that the carbon dioxide fraction represents between 40% and 56% of the molar mass of the mixture comprising at least carbon dioxide and methane,

[0021] - a step of compressing the mixture to a pressure greater than or equal to 80 bara,

[0022] - a step of cooling the compressed mixture to a temperature between -50°C and 5°C to bring the mixture to a liquid or supercritical state and - a step of removing the mixture from the cooling step.

[0023] Thanks to these provisions:

[0024] - condensation of carbon dioxide during compression is avoided,

[0025] - crystallization of carbon dioxide is also avoided,

[0026] - the pressure implemented makes it possible to limit the cost and energy spent to set up the device implementing the method which is the subject of the invention,

[0027] - the implementation of a low temperature but higher than -50°C makes it possible to reduce cooling costs and to implement non-cryogenic equipment,

[0028] - the injection of carbon dioxide into the flow allows condensation at relatively warm temperatures and allows simplified regeneration because it is shared with a final purification phase of the biogas.

[0029] In embodiments, the cooling step comprises a heat exchange step with at least partially liquid carbon dioxide, the carbon dioxide leaving the heat exchange step being used during the injection step.

[0030] In embodiments, the liquid carbon dioxide used during the heat exchange step has a pressure greater than or equal to 6 bara.

[0031] Thanks to these provisions, the cold of the vaporized liquid carbon dioxide allows the condensation of the mixture of biogas and carbon dioxide to be completed, making it possible to implement only one cooling cycle down to 0°C.

[0032] In embodiments, the method which is the subject of the present invention comprises a step of separating water contained in the biogas flow from the input step and / or in the mixture from the injection step.

[0033] These embodiments limit the risks of damage to equipment.

[0034] In embodiments, the process which is the subject of the present invention comprises a step of drying the biogas upstream of a step of the process using a temperature below 0°C.

[0035] These embodiments limit the risks of damage to the equipment. In embodiments, the method which is the subject of the present invention comprises an additional step of water purification of the biogas upstream of a step of the process using a temperature below 0°C.

[0036] These embodiments limit the risks of damage to equipment.

[0037] In embodiments, the method which is the subject of the present invention comprises a step of separating hydrogen sulfide contained in the biogas flow from the input step and / or in the mixture from the injection step.

[0038] These embodiments limit the risks of damage to equipment.

[0039] In embodiments, the method which is the subject of the present invention comprises a step of separating volatile organic compounds contained in the flow resulting from the input step and / or in the mixture resulting from the injection step.

[0040] These embodiments limit the risks of damage to equipment.

[0041] In embodiments, the method which is the subject of the present invention comprises, downstream of the compression step, a step of pre-cooling the mixture to a temperature less than or equal to 2°C.

[0042] In embodiments, the step of compressing the mixture is configured to compress the mixture to a pressure of between 80 bara and 120 bara.

[0043] These embodiments allow, in particular, the formation of a biogas in compact form under optimal operating conditions.

[0044] According to a second aspect, the present invention aims at a biogas conditioning device in compact form, which comprises:

[0045] - a means of entry of a biogas flow comprising at least methane,

[0046] - a means of measuring a flow rate of biogas at the inlet,

[0047] - a means for injecting a flow of carbon dioxide into the biogas flow as a function of the measured flow rate, configured so that the carbon dioxide fraction represents between 40% and 56% of the molar mass of the mixture comprising at least carbon dioxide and methane,

[0048] - a means of compressing the mixture to a pressure greater than or equal to 80 bara, - a means of cooling the compressed mixture to a temperature between -50°C and 5°C to bring the mixture to a liquid or supercritical state and

[0049] - a means of exiting the mixture from the cooling stage.

[0050] The advantages of the device which is the subject of the present invention are similar to the advantages of the method which is the subject of the present invention.

[0051] Brief description of the figures

[0052] Other advantages, aims and particular characteristics of the invention will emerge from the following non-limiting description of at least one particular embodiment of the method and device which are the subject of the present invention, with reference to the appended drawings, in which:

[0053] Figure 1 represents, schematically and in the form of a flowchart, a first particular succession of steps of the method which is the subject of the present invention,

[0054] Figure 2 schematically represents a first particular embodiment of the device which is the subject of the present invention,

[0055] Figure 3 represents, schematically and in the form of a flowchart, a second particular succession of steps of the method which is the subject of the present invention,

[0056] Figure 4 schematically represents a second particular embodiment of the device which is the subject of the present invention,

[0057] Figure 5 schematically represents a third particular embodiment of the device which is the subject of the present invention,

[0058] Figure 6 represents, schematically and in the form of a flowchart, a second particular embodiment of the device which is the subject of the present invention,

[0059] Figure 7 represents, schematically and in the form of a flowchart, a third particular embodiment of the device which is the subject of the present invention and

[0060] Figure 8 schematically represents a fourth particular embodiment of the device which is the subject of the present invention.

[0061] Description of the embodiments

[0062] This description is given without limitation, each feature of an embodiment being able to be combined with any other feature of any other embodiment in an advantageous manner. As understood from reading this description, various inventive concepts can be implemented by one or more methods or devices described below, several examples of which are provided herein. The actions or steps performed in carrying out the method or device can be ordered in any suitable manner. Accordingly, it is possible to construct embodiments in which the actions or steps are performed in a different order than that illustrated, which may include performing certain acts simultaneously, even if they are presented as sequential acts in the illustrated embodiments.

[0063] The expression "and / or", as used herein and in the claims, is to be understood to mean "either or both" of the elements so conjoined, i.e., elements which are present conjunctively in some cases and disjunctively in other cases. Multiple elements listed with "and / or" are to be interpreted in the same way, i.e., "one or more" of the elements so conjoined. Other elements may optionally be present, other than the elements specifically identified by the "and / or" clause, whether or not they are related to these specifically identified elements.Thus, by way of non-limiting example, a reference to "A and / or B", when used in conjunction with open language such as "comprising" may refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0064] As used herein in the description and claims, "or" is to be understood inclusively.

[0065] As used in this specification and in the claims, the expression "at least one", with reference to a list of one or more elements, is to be understood to mean at least one element selected from one or more elements in the list of elements, but not necessarily including at least one of each element specifically listed in the list of elements and not excluding every combination of elements in the list of elements. This definition also allows for the optional presence of elements other than the specifically identified elements in the list of elements to which the expression "at least one" refers, whether or not related to those specifically identified elements.Thus, by way of non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B", or, equivalently, "at least one of A and / or B") may refer, in one embodiment, to at least one, optionally including more than one, A, without B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, without A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0066] In the claims, as well as in the description below, all transitional expressions such as "comprising", "including", "carrying", "having", "containing", "involving", "holding", "consisting of", and the like, are to be understood as open, i.e., as meaning including but not limited to. Only the transitional expressions "consisting of" and "consisting essentially of" are to be understood as closed or semi-closed transitional expressions, respectively.

[0067] In this description, the term "biogas stream comprising at least methane" refers to a stream which may comprise, in addition to methane, at least one of the following elements:

[0068] - water,

[0069] - hydrogen sulfide

[0070] - volatile organic compounds and / or

[0071] - carbon dioxide.

[0072] Please note that the figures are not to scale.

[0073] Figure 1 shows a particular succession of steps of the method 100 which is the subject of the present invention. This method 100 for packaging biogas in compact form comprises:

[0074] - a step 105 of entry of a biogas flow comprising at least methane,

[0075] - a step 110 of measuring a flow rate of biogas at the inlet,

[0076] - a step 115 of injecting a flow of carbon dioxide into the flow of biogas as a function of the measured flow rate, configured so that the fraction of carbon dioxide represents between 40% and 56% of the molar mass of the mixture comprising at least the carbon dioxide and the methane,

[0077] - a step 120 of compression of the mixture to a pressure greater than or equal to 80 bara,

[0078] - a step 125 of cooling the compressed mixture to a temperature between -50°C and 5°C to bring the mixture to a liquid or supercritical state and

[0079] - a step 130 for the outlet of the mixture from the cooling step.

[0080] The input step 105 is carried out, for example, by an input means 205 as shown in FIG. 2. Such an input means 205 is, for example, a pipe configured to transport a biogas stream comprising at least methane. This pipe may be connected to a tank (not shown) or directly or indirectly connected to a port compatible with the pipe. Such a port is, for example, configured to be connected to a mobile tank, such as a tanker truck for example.

[0081] The exact nature of the input means 205 depends on the use case of the method 100 which is the subject of the present invention and its exact implementation is unimportant provided that the biogas comprising at least methane can be conveyed to a carbon dioxide injection means 215.

[0082] The measurement step 110 is carried out, for example, by implementing a means 210 for measuring the flow rate of the biogas flow as shown in FIG. 2. Such a measurement means 210 is, for example, a flow meter or any other sensor suitable for measuring a flow rate of fluid in a pipe.

[0083] In variants, the measuring step 110 is not present in the method 100, the device 200 carrying out the method 100 being adapted for a nominal and stable flow rate of biogas flow, the injection of gaseous carbon dioxide being adapted to this predetermined nominal flow rate to reach a determined proportion in the mixture resulting from the injection.

[0084] The injection step 115 is carried out, for example, by an injection means 215 as shown in FIG. 2. Such an injection means 215 is, for example, a pipe for injecting carbon dioxide into the biogas stream. In variants, the injection means 215 is a mixer with two inlets, one for the biogas stream and the other for carbon dioxide, and with an outlet for the mixture thus formed. For example, downstream of this injection step, the mixture stream has the following characteristics:

[0085] - a volume flow rate close to 108 Nm 3 / h,

[0086] - a mass flow rate close to 153 kg / h, formed for 119 kg / h of carbon dioxide and for 34 kg / h of methane,

[0087] - a pressure close to 1.05 bara,

[0088] - a temperature close to 30°C and

[0089] - a molar ratio close to 44% methane and 56% carbon dioxide.

[0090] In variants, the carbon dioxide injected into the biogas stream is injected in liquid form. In variants, the carbon dioxide injected into the biogas stream has a temperature lower than the temperature of the biogas. In variants, the device 200 carrying out the method 100 which is the subject of the present invention comprises a biogas temperature sensor (not shown), the flow rate of carbon dioxide injected into the biogas being controlled by the measured temperature.

[0091] In variants, the carbon dioxide used during the injection step 115 is initially stored in a reservoir (not shown), in liquid and / or gaseous form.

[0092] In variants, the method 100 which is the subject of the present invention comprises a step (not shown) of expanding the carbon dioxide upstream of the injection step 215. This expansion step is carried out, for example, by an expansion means 214 as shown in FIG. 2. This expansion means 214 is, for example, an expansion valve.

[0093] For example, upstream of this expansion stage, the carbon dioxide flow has the following characteristics:

[0094] - a pressure close to 6 bara and

[0095] - a temperature close to 0°C.

[0096] For example, at the outlet of this expansion stage, the carbon dioxide flow has the following characteristics:

[0097] - a pressure close to 1.05 bara and

[0098] - a temperature close to -7.2°C.

[0099] The compression step 120 is carried out, for example, by a compression means 220 as shown in FIG. 2. Such a compression means 220 is, for example, a turbine compressor or any other type of compressor adapted to the particular operating conditions of the mixture of biogas and carbon dioxide.

[0100] In embodiments, the compression step 120 is performed at a value between 80 bara and 120 bara.

[0101] The cooling step 125 is carried out, for example, by a cooling means 225 as shown in FIG. 2. Such a cooling means 225 is, for example, a heat exchanger of any type adapted to the particular operating conditions of the mixture of biogas and carbon dioxide. For example, the heat exchanger is a tubular or finned heat exchanger.

[0102] In particular embodiments, such as that shown in FIG. 3, the cooling step 125 comprises a step 305 of heat exchange with at least partially liquid carbon dioxide, the carbon dioxide at the outlet of the heat exchange step 305 being used during the injection step 115.

[0103] This heat exchange step 305 is carried out, for example, by the heat exchange means 225 implemented during the heat exchange step 125, in which the carbon dioxide acts as a cold fluid.

[0104] In variants, the method 300 which is the subject of the present invention comprises a step (not shown) of expanding the carbon dioxide upstream of the heat exchange step 305. This expansion step is carried out, for example, by an expansion means 224 as shown in FIG. 2. This expansion means 224 is, for example, an expansion valve.

[0105] For example, upstream of this expansion stage, the carbon dioxide flow has the following characteristics:

[0106] - a mass flow rate close to 80 kg / h,

[0107] - a pressure close to 19.5 bara and

[0108] - a temperature close to -20°C

[0109] For example, at the outlet of this expansion stage, the carbon dioxide flow has the following characteristics:

[0110] - a pressure close to 6 bara,

[0111] - a temperature close to -52.5°C and

[0112] - a vapor fraction close to 0.19. In variants, the carbon dioxide used during the heat exchange step 305 has a pressure greater than or equal to 6 bara.

[0113] The outlet step 130 is carried out, for example, by an outlet means 230 as shown in FIG. 2. Such an outlet means 230 is, for example, a pipe allowing the transfer of the cooled mixture during the cooling step 225.

[0114] For example, at the outlet of this output stage, the mixture flow has the following characteristics:

[0115] - a pressure close to 88 bara,

[0116] - a temperature close to -17°C and

[0117] - a vapor fraction close to 0.

[0118] In variants, the gaseous mixture cooled during the cooling step 225 is stored in a tank (not shown), in liquid and / or gaseous form.

[0119] In embodiments of the method 300 which is the subject of the present invention, such as that represented in FIG. 3, the method 300 comprises a step 315 of separating water contained in the biogas flow from the inlet step 105 and / or in the mixture from the injection step 115.

[0120] The separation step 315 can be carried out, for example, by a separation means 207, as shown in FIG. 2. Such a separation means 207 is, for example, a condensation water separator.

[0121] The separation step 315 may also be carried out, for example, by a separation means 209, as shown in FIG. 2. Such a separation means 209 is, for example, a condensation water separator. This separation means 209 is also called a “drying and polishing means” of the mixture.

[0122] For example, this drying and polishing means is configured to lower the dew point to 2°C / 88 bara.

[0123] In embodiments of the method 300 which is the subject of the present invention, such as that represented in FIG. 3, the method 300 comprises a step 320 of separating hydrogen sulfide contained in the biogas stream resulting from the inlet step 105 and / or in the mixture resulting from the injection step 115.

[0124] The step 320 of separating the hydrogen sulfide can be carried out, for example, by a separation means 208, as shown in FIG. 2. Such a separation means 208 is, for example, an active carbon filter positioned downstream of the mixer 215.

[0125] The step 320 of separating the hydrogen sulfide can be carried out, for example, by a separation means 208, as shown in FIG. 4. Such a separation means 208 is, for example, an active carbon filter positioned upstream of the mixer 215.

[0126] In embodiments of the method 300 which is the subject of the present invention, such as that shown in FIG. 3, the method 300 comprises a step 320 of separating volatile organic compounds contained in the flow resulting from the inlet step 105 and / or in the mixture resulting from the injection step 115. This step 320 of separating volatile organic compounds can be carried out jointly with the step 320 of separating hydrogen sulfide.

[0127] The hydrogen sulfide purification step 320 is carried out, for example, by a separation means 209, as shown in FIG. 2. Such a separation means 209 is, for example, an active carbon filter.

[0128] In embodiments of the method 600 which is the subject of the present invention, such as that shown in FIG. 6, the method 600 comprises a step 605 of drying the biogas upstream of a step of the method implementing a temperature below 0°C. This step implementing a temperature below 0°C corresponds, for example, to a step 305 of heat exchange or to a pre-cooling step 330 according to the implementation specifications of the method which is the subject of the present invention.

[0129] The drying step 605 is carried out, for example, by a drying means 405, as shown in FIG. 4. Such a drying means 405 is, for example, a heat exchanger combined with a phase separator container.

[0130] In embodiments of the method 600 which is the subject of the present invention, such as that shown in FIG. 6, the method 600 comprises an additional water purification step 610 of the biogas upstream of a step of the method implementing a temperature below 0°C. This additional purification can be carried out, for example, using an adsorption system to lower the dew point temperature of the biogas to a value below -50°C. The additional water purification step 610 is carried out, for example, by a water purification means 410, as shown in FIG. 4. Such a water purification means 410 is, for example, molecular sieves.

[0131] In embodiments of the method 700 which is the subject of the present invention, such as that represented in FIG. 7, the method 700 comprises a step 705 of desaturation of the biogas from the input step 105.

[0132] The desaturation step 705 is carried out, for example, by a desaturation means 505, as shown in FIG. 5. Such a desaturation means 505 is, for example, a heat exchanger combined with a phase separator container.

[0133] In embodiments of the method 700 which is the subject of the present invention, such as that represented in FIG. 7, the method 700 comprises a step 710 of purification of hydrogen sulfide and / or volatile organic compounds from the biogas resulting from the desaturation step 705.

[0134] The biogas purification step 710 is carried out, for example, by a biogas purification means 510, as shown in FIG. 5. Such a biogas purification means 510 is, for example, an activated carbon filter.

[0135] For example, at the outlet of purification stage 710, the biogas flow has the following characteristics:

[0136] - a volume flow rate close to 80 Nm 3 / h,

[0137] - a mass flow rate close to 97 kg / h, formed for 63 kg / h of carbon dioxide and for 34 kg / h of methane,

[0138] - a pressure close to 1.05 bara,

[0139] - a temperature close to 30°C and

[0140] - a molar ratio close to 60% methane and 40% carbon dioxide.

[0141] In particular embodiments, the method 300 which is the subject of the present invention comprises a step 330 of pre-cooling the mixture to a temperature less than or equal to 2°C.

[0142] This pre-cooling step 330 is carried out, for example, by a pre-cooling means 222, as shown in FIG. 2. Such a pre-cooling means 222 is, for example, a heat exchanger.

[0143] In variants, the pre-cooling step 330 is carried out in two pre-cooling sub-steps. Such a variant is shown in FIG. 2 and comprises an initial pre-cooling means 221 followed by a pre-cooling means 222.

[0144] For example, at the outlet of this initial pre-cooling stage, the mixture flow has the following characteristics:

[0145] - a pressure greater than 80 bara and

[0146] - a temperature close to 30°C.

[0147] For example, at the outlet of this pre-cooling stage, the mixture flow has the following characteristics:

[0148] - a pressure greater than 80 bara,

[0149] - a temperature close to 2°C and

[0150] - a vapor fraction close to 1.

[0151] Figure 3 shows a particular succession of steps of the method 300 which is the subject of the present invention. This method 300 for packaging biogas in compact form comprises, in addition to the steps described with reference to Figure 1, at least one of the steps mentioned below.

[0152] As can be understood from reading this description, in Figure 2, we observe schematically an embodiment of the device 200 which is the subject of the present invention. This device 200 for conditioning biogas in compact form, comprises:

[0153] - a means 205 for inputting a biogas flow comprising at least methane,

[0154] - a means 210 for measuring a flow rate of biogas at the inlet,

[0155] - a means 215 for injecting a flow of carbon dioxide into the flow of biogas as a function of the measured flow rate, configured so that the fraction of carbon dioxide represents between 40% and 56% of the molar mass of the mixture comprising at least the carbon dioxide and the methane,

[0156] - a means 220 of compressing the mixture to a pressure greater than or equal to 80 bara,

[0157] - a means 225 for cooling the compressed mixture to a temperature between -50°C and 5°C to bring the mixture to a liquid or supercritical state and

[0158] - a means 230 for outputting the mixture resulting from the cooling step. Examples of implementation of the characteristic means of the devices, 200 and 400, objects of the present invention are described with reference to figures 1 and 3 corresponding to the methods which are the subject of the present invention.

[0159] In Figure 8, we observe schematically a particular embodiment of the device 800 for conditioning biogas in compact form, which comprises:

[0160] - a means 205 for inputting a biogas flow comprising at least methane,

[0161] - a means 210 for measuring a flow rate of biogas at the inlet,

[0162] - a means 215 for injecting a flow of carbon dioxide into the flow of biogas as a function of the measured flow rate, configured so that the fraction of carbon dioxide represents between 40% and 56% of the molar mass of the mixture comprising at least the carbon dioxide and the methane,

[0163] - a means 220 of compressing the mixture to a pressure greater than or equal to 80 bara,

[0164] - a means 225 for cooling the compressed mixture to a temperature between -50°C and 5°C to bring the mixture to a liquid or supercritical state and

[0165] - a means 230 for exiting the mixture from the cooling stage.

[0166] This particular embodiment of the device 800 furthermore implements in particular:

[0167] - a means 805 for inlet of carbon dioxide, liquid or gaseous, configured to interact with the injection means 215 in order to form the mixture to be cooled and

[0168] - a cooling cycle 810 at a temperature between -50°C and 5°C, configured to act as a cold fluid in the cooling means 225.

[0169] In these embodiments, the cooling of the mixture and the supply of carbon dioxide are separate.

[0170] As understood, the method and device which are the subject of the present invention allow the condensation of biogas, that is to say on the one hand with a final mixing density greater than 380 kg / m 3and a specific density of methane (the most valuable compound) in the mixture greater than 90 kg / m 3 , at temperatures greater than or equal to -50°C (therefore a level which is not cryogenic) and even preferably greater than or equal to -20°C and at pressures less than or equal to 120 bara and preferably less than or equal to 100 bara.

Claims

DEMANDS 1. A process (100, 300, 600, 700) for conditioning biogas into a compact form, characterized in that it comprises: - an inlet step (105) of a biogas stream containing at least methane, - a step (110) for measuring the flow rate of the incoming biogas, - a step (115) of injecting a carbon dioxide stream into the biogas stream according to the measured flow rate, configured so that the carbon dioxide fraction represents between 40% and 56% of the molar mass of the mixture comprising at least carbon dioxide and methane, - a step (120) of compressing the mixture to a pressure greater than or equal to 80 bara, - a step (125) of cooling the compressed mixture to a temperature between -50°C and 5°C to bring the mixture to a liquid or supercritical state and - a step (130) for exiting the mixture from the cooling step.

2. Method (300, 600, 700) according to claim 1, wherein the cooling step (125) comprises a heat exchange step (305) with at least partially liquid carbon dioxide, the carbon dioxide exiting the heat exchange step being used during the injection step (115).

3. Method (300, 600, 700) according to claim 2, wherein the liquid carbon dioxide used in the heat exchange step (305) has a pressure greater than or equal to 6 bara.

4. A process (300, 600, 700) according to any one of claims 1 to 3, comprising a step (315) of separating water contained in the biogas stream from the inlet step (105) and / or in the mixture from the injection step (115).

5. A process (600) according to any one of claims 1 to 4, comprising a drying step (605) of the biogas upstream of a step in the process using a temperature below 0°C.

6. Process (600) according to claim 5, which includes an additional water purification step (610) of the biogas upstream of a process step involving a temperature below 0°C.

7. A process (300, 600, 700) according to any one of claims 1 to 6, comprising a step (320) of separating hydrogen sulfide contained in the biogas stream from the inlet step (105) and / or in the mixture from the injection step (115).

8. A process (300, 600, 700) according to any one of claims 1 to 7, comprising a step (325) of separating volatile organic compounds contained in the stream from the inlet step (105) and / or in the mixture from the injection step (115).

9. A method (300, 600, 700) according to any one of claims 1 to 8, comprising, downstream of the compression step (120), a pre-cooling step (330) of the mixture to a temperature less than or equal to 2°C.

10. Method (100, 300, 600, 700) according to any one of claims 1 to 9, wherein the mixing compression step (120) is configured to compress the mixture to a pressure between 80 bara and 120 bara.

11. Device (200, 400, 500, 800) for conditioning biogas in compact form, characterized in that it comprises: - an input means (205) for a biogas stream comprising at least methane, - a means (210) for measuring the flow rate of biogas inlet, - a means (215) for injecting a carbon dioxide stream into the biogas stream according to the measured flow rate, configured so that the carbon dioxide fraction represents between 40% and 56% of the molar mass of the mixture comprising at least carbon dioxide and methane, - a means (220) of compressing the mixture to a pressure greater than or equal to 80 bara, - a means (225) for cooling the compressed mixture to a temperature between -50°C and 5°C to bring the mixture to a liquid or supercritical state and - a means (230) of outlet of the mixture from the cooling step.

Images