FR3035598B1 - METHOD AND SYSTEM FOR DIRECT INJECTION OF BIOMETHANE FROM BIOGAS WITHIN A DISTRIBUTION NETWORK. - Google Patents

Abstract

Installation for injecting gas from a renewable source into an injection station in a natural gas distribution and / or transport network, comprising a main circuit including: a unit for continuously collecting the gas from the renewable source, - a gas purifier mounted downstream of the gas collection unit - a purified gas quality control instrument mounted at the outlet of the purifier to check its compliance with predetermined requirements, - an injection station within the distribution and / or transport network, the controlled gas, mounted downstream of the purifier and the control instrument, a solenoid valve controlled according to the measurements delivered by the instrument of control preventing the introduction of improper gas into the injection station, the plant comprising, upstream of the injection station, a primary deflection circuit of the non-compliant gas within the main circuit to store the gas coming continuously from the collection unit, within the main circuit or in order to reprocess this gas within the main circuit.

Description

METHOD AND SYSTEM FOR DIRECT INJECTION OF BIOMETHANE FROM BIOGAS WITHIN A DISTRIBUTION NETWORK

Technical field of the invention

The technical field of the invention is that of renewable energies, and more particularly, that of the injection of a purified gas from biogas produced by green waste, within a distribution network and / or transport of gas.

Biogas is a gas produced by the fermentation of animal or vegetable organic matter in the absence of oxygen (anaerobic fermentation). A biogas typically comprises from 45% to 70% by volume of methane (CH4), from 30% to 50% by volume of carbon dioxide (CO2), it may also contain nitrogen (N2) as well as traces of other components such as sulphide, siloxane, VOC (volatile organic compound) in particular. It can be collected in landfill sites or obtained through an anaerobic digestion unit.

Bio methane is a biogas that has undergone a thorough purification that gives it a composition comparable to that of natural gas, allowing it to be used instead of natural gas, and is also identified as a natural gas substitute. In other words, bio methane (bio methane) is a biogas purified to meet the specifications of the natural gas to which it will be substituted.

It is then essentially to have a calorific value sufficient to be at least equivalent to the marketable natural gas to which it is substitutable. The standards vary according to the distribution networks, so the specifications imposed on bio methane can also vary according to the distributed natural gas to which it can be substituted. The purification of biogas from bio-methane thus essentially consists in eliminating CO2, in order to increase the methane content, but it must be accompanied by the elimination of the harmful elements present in the biogas, among which at least the sulfur-containing compounds. , but also siloxanes and VOCs.

Used as a natural gas substitute in distribution networks, bio methane can also be used as a substitute for natural gas to produce hydrogen.

State of the art and its disadvantages

Nowadays, on a green waste recovery site, the biogas produced by this waste is converted into biomethane by facilities provided for this purpose.

A major part of the biomethane produced is used on the site itself to supply energy to the various units of the facility, or other facilities present on the site.

A minor or secondary part of this biomethane is, after purification, odorization, control, counting, and a regulation of its pressure, likely to supply the distribution network and / or natural gas transport.

Ideally, this part of biomethane could be introduced directly into the distribution and / or transport network.

However this part of biomethane should then continuously meet all the quality criteria allowing its introduction into the network while it comes from a biogas source whose quality fluctuates by definition.

And as soon as this is not the case, the injection should immediately be stopped in order to prevent its injection into the network. The immediate solution for treating this non-compliant biomethane would be to burn it with dry losses. If, on the contrary, the whole - and not a minor part - of the biogas production were to be devoted to the production of biomethane to be introduced directly into the distribution and / or transport network, these would be considerable quantities. of biomethane, which would then be totally lost.

These losses would also become colossal in the particular case of an injection in the transport network since it requires considerable flow rates and pressures.

Thus, it has been retained in the prior art the solution of an indirect introduction of this biomethane.

For example, in US Pat. No. 8,404,025, the solution adopted was to compress and store the biomethane produced in pressurized and transportable tanks, which are transported to the natural gas distribution sites, for example by truck, and inject it only afterwards.

This solution thus not only has an unsatisfactory carbon footprint and indirect injection into the distribution and / or transport network, the biomethane being stored in an intermediate reservoir.

Also, it is provided in the process for converting biogas into a renewable natural gas pipeline described in international application WO 2008097304 that the gas treated by the process is then dried and compressed to be introduced into storage tanks.

Thus, in this example also, the injection of biomethane into the distribution network and / or transport, is performed after having stored in the tank.

Presentation of the invention

The aim of the present invention is to propose an installation capable of injecting biomethane from a biogas source directly into the natural gas distribution and / or transport network even when this biomethane represents a major part, or even the biogas production, and is therefore produced in large quantities and with a high throughput.

In this context, precautions must also be taken, always because of the large quantities or volumes of biomethane produced, when the latter does not fulfill, even at the end of purifier, the specifications authorizing its injection into the network, to avoid that these quantities of purified but non-compliant biomethane are also not released into the ambient air. The invention aims to solve this problem by proposing a facility for injecting gas from a renewable source into an injection station in a natural gas distribution and / or transport network, comprising a main circuit including: - a unit for the continuous collection of gas from the renewable source, - a gas purifier mounted downstream of the gas collection unit - a purified gas quality control instrument mounted at the outlet of the purifier to check its compliance with predetermined requirements, - a purified gas compressor making it reach a pressure depending on that prevailing in the network into which this gas is injected - an injection station within the distribution network and / or transport, controlled and compressed gas, mounted downstream of the purifier and the control instrument, a solenoid valve controlled according to the measurements delivered by the instrument of co control preventing the introduction of nonconforming gas into the injection station, the plant comprising, upstream of the injection station, a primary deflection circuit of the non-compliant gas comprising a portion of the main circuit excluding the injection station , in order to store the gas coming continuously from the collection unit, and / or to reprocess this gas within said portion of the main circuit.

The device according to the invention may furthermore have one and / or the other of the following characteristics: the primary deflection circuit of the non-compliant gas comprises a non-compliant gas deflection duct opening into the unit of collection or in the purifier. - The non-compliant gas diversion line further comprises a bypass line to a torch for burning the non-compliant gas and / or to a hydraulic guard for storing this non-compliant gas. - The primary deflection circuit of the non-compliant gas comprises a pipe whose inlet is disposed between the scrubber and the injection station. - A compressor interposed between the scrubber and the injection station, the inlet of the primary deflection line being disposed between the scrubber and the compressor or between the compressor and the injection station. - The input of the primary deflection pipe comprises a solenoid valve controlled by the quality control instruments of the gas leaving the purifier. - upstream of the purifier, are disposed a second instrument for analyzing the homogeneity of the gas flow from the collection unit, and a secondary deflection circuit of the non-homogeneous controlled gas by the second instrument, of which the The inlet is interposed between the collection unit and the purifier of the main circuit and opening into the deflection circuit. the secondary deflection circuit comprises a secondary purifier. - At the input of the secondary deflection circuit, is disposed a secondary solenoid valve controlled by the second analysis instrument. the solenoid valve is controlled so as to distribute the gas between the main circuit and the secondary deflection circuit in predetermined proportions;

BRIEF DESCRIPTION OF THE DRAWINGS Other data, characteristics and advantages of the present invention will appear on reading the following unrestricted description, with reference to: FIG. 1, which diagrammatically represents a biogas treatment injection plant with a view to its introduction into an injection station of a natural gas distribution and / or transport network, according to a first embodiment, FIG. 2 which schematically represents a second embodiment of the installation according to FIG. The invention, and with reference to FIG. 3 illustrates by a graph, a principle of possible distribution of non-compliant gas between a main processing circuit and a secondary deflection circuit.

DETAILED DESCRIPTION OF AN EMBODIMENT The invention as represented in FIG. 1 relates to a biogas injection plant 1 originating from a renewable source, within an injection station 2 in a distribution network and / or transport of natural gas 3.

This installation comprises, in a conventional manner, a main circuit oc including: - a collecting unit 4 of gasometer type, continuously gas from the renewable source, - a gas purifier 5 mounted downstream of the collection unit gas 4 - a control instrument or analyzer 6 of the purified gas quality mounted at the outlet of the purifier 5 to verify compliance with predetermined requirements, - the injection station 2 of the distribution and / or transport network 3, which allows the introduction of the controlled gas within the network, the injection station 2 being mounted downstream of the purifier 5 and the analyzer 6, a solenoid valve 7 controlled by the analyzer 6 preventing the introduction of non-compliant gas into the injection station 2, - possibly, when the pressure prevailing in the distribution and / or gas transport network is greater than that admitted by the gasometer 4, the main circuit comprises a ompresseur 8 disposed between the purifier 5 and the injection station 2. - The various elements above the main circuit are successively connected in pairs by gas circulation pipes.

The quality of the biogas from the gas source does not allow its introduction into the network as such, this quality fluctuating further over time due to the inhomogeneity of the biogas produced by the source as a function of time.

By biogas quality is meant the conformity of its methane, CO2, N2, and traces of other components, with predefined specific reference levels for each of its elements (specific biomethane contents). A maximum quality "n" is obtained when the contents of these elements fall within the ranges of values of the specific reference levels or reach specific reference levels. A lower quality "n-2%", "n-10%" ... "ni%" ... representing a variation of the biogas contents considered of i% on average with respect to the ranges of values of the specific contents of reference.

The aim of the gasometer is to store, by mixing it and thus homogenizing it by volume, a large quantity of biogas, so that at the outlet of the gasometer 4, fluctuations in the quality and flow of the biogas are less than in out of the biogas source. The gas meter will for example be sized in volume according to the flow rate of the biogas source, in order to ensure a buffer role of the fluctuation of the quality of the biogas, in order to reduce the output of the gasometer, with respect to the inlet , the "i" differences between the biogas element contents with respect to the specific reference levels. Also, the gasometer will be dimensioned to reduce the fluctuation amplitude of these differences between the output and the gasometer inlet. Thus, the gas analyzer will be able to pass from a biogas quality fluctuating between n-30% and n-10% (in arbitrary units) in the biogas coming from the source, to a biogas quality fluctuating between n-15% and n-2% (in arbitrary units) in the biogas leaving the gasometer.

In an installation of this type, in which the biogas produced by a source is introduced continuously in a circuit connected to the injection station of a distribution and / or transport network, it is necessary to provide different levels of safety. to ensure that no molecule of gas that does not meet the requirements of the distribution and / or transport network is introduced.

A first essential level of security is to have before the entry of the injection station 2, a solenoid valve 7 whose closure will be controlled as soon as the analyzer 6 has detected that the purified gas is in fact not in conformity. Of course, the positioning of the analyzer 6 and the solenoid valve 7 along the main circuit oc will be studied (maximized taking into account the maximum flow rate of biogas for example), to ensure that no molecule of gas detected that does not conform to the level of the analyzer 6, does not reach the injection station.

According to a first possible option for treating the non-compliant gas, this solenoid valve 7 can then be controlled to direct the non-compliant gas to a torch which would burn as it is produced.

But this solution is not satisfactory since it leads to wastage at waste losses biogas continuously introduced into the main circuit, until the intervention of an operator who would put the circuit in operation.

The solution adopted by the invention is to recirculate this non-compliant gas, not to a unit that would waste it, but partly within the same main purification circuit, via a deflection circuit β.

According to FIG. 1, the input of this circuit β is disposed between the purifier 5 and the compressor 8 and a three-way solenoid valve VI is disposed at the inlet of this deflection circuit and on the main circuit oc. It is controlled by the analyzer 6 of the quality of the gas leaving the purifier, in "all or nothing" operation that allows the passage of gas to the valve 7 and the injection station via the main circuit when the gas is analyzed compliant (the valve 7 is then in the open position), and deflects the passage of the gas in the deflection circuit when it is no longer the case, while the valve 7 is in the closed position.

The deflection circuit β preferably opens in the gasometer 4 so that the non-compliant gas is diluted by the biogas entering the gasometer, and then purified with it in the purifier.

The volume represented by the gasometer, the portion of the main circuit extending to the inlet solenoid valve VI of the deflection circuit β and the deflection circuit β itself constitute a non-gas storage and recirculation volume. compliant, called "buffer volume".

It can be dimensioned according to the maximum flow rate of the biogas source in order to be able to store the equivalent of a biogas production over a certain period of time (a few hours, a few days, a week, etc.) allowing the treatment of this non-biogas gas. compliant and delay all (or make superfluous) possible on-site intervention of an operator.

An additional deflection pipe βΐ shown in dashed lines, makes it possible to recirculate the non-compliant gas directly within the scrubber 5. Only a redirection of the non-compliant gas within the gasometer or only within the scrubber can be provided. , or on the contrary a distribution of this gas between the gasometer 4 and the purifier 5 by means of a three-way solenoid valve (not shown) arranged at the crossing of the two recirculation lines β and βΐ.

In addition, still in this primary deflection circuit of the non-compliant gas, it is possible to direct part of this gas not only to the gasometer 4 and / or the purifier 5 but also to a torch to be burned, and / or to a hydraulic guard to be stored there. It may ideally be provided, upstream of the purifier 5, a second analysis instrument A2 which will study the homogeneity of the gas flow from the gasometer and the composition / quality fluctuations as a function of time, and a secondary circuit of deviation γ of the "nonhomogeneous" controlled gas by the second analyzer A2, the input of which is interposed between the gasometer 4 and the purifier 5 of the main circuit and opening into the deflection circuit downstream of the solenoid valve VI controlled by the analyzer 6.

This secondary deflection line may comprise a secondary purifier ensuring for example less thorough purification than the purifier 5 of the main circuit, such as an activated carbon membrane or other.

A three-way solenoid valve V2, driven as a function of the measurements delivered by the second analyzer A2, will then be arranged at the intersection of the main circuit oc and the secondary diversion line γ. This solenoid valve will not necessarily be "all or nothing" but instead able to distribute the gas between the main circuit (to the purifier 5) and the secondary deflection circuit (to possibly purifier 2 or directly to the gasometer) in predetermined proportions.

These proportions can be calculated in order to optimize the main circuit performance by maximizing the circulation time of the biogas within the main circuit and the secondary circuit treatment portion in the event of degradation of the biogas quality from the unit. storage.

This regulation process is illustrated in FIG. 3 in which: the curves in broken lines (quality of the biogas taken by the analyzer A2 between the gasometer and the scrubber E1, opening / closing of the valve VI) are curves obtained following a decrease in the quality of the biogas at the outlet of the gas meter due for example to a decrease in that of the biogas produced by the source, and when the secondary purification loop γ, β is not used (valve V2 closed). As soon as the quality of the biogas is less than n-10%, the valve VI is closed to prevent injection into the network. These curves will serve as a reference to illustrate the benefit of regulating the quality of biogas through the secondary purification loop. - The curves in solid line (scenario 1) are those obtained in the same context as the curve in broken lines (same profile of decrease of the quality of the biogas coming from the source) when however the secondary loop of purification γ, β is used, with, as explained hereinafter, an efficiency allowing the quality of the biogas at the exit of the gas meter to remain greater than n-10%. The operation of the installation is then not interrupted, the valve VI is kept open.

The dotted line curves (scenario 2) are those obtained in the same context as the curve in broken lines (same profile of decrease in the quality of the biogas coming from the source) when however the secondary purification loop is used, with this effectiveness does not prevent the quality of the biogas at the exit of the gasometer from falling to n-10%, this moment however being delayed by the duration "At l" thanks to the purification of the biogas within the secondary loop which This will have made it possible to increase the quantity of biogas injected into the network and to extend the operating time of the installation, as explained below.

Scenario 1:

In nominal operation, the main circuit injects on the network a biogas of quality n, corresponding to the highest specifications achievable by the biogas generation process.

When the gas quality at the outlet of the storage unit is greater than n-2%, the valve V2 is 100% open to the purifier and the valve VI is 100% open to the compressor.

When the gas quality decreases and falls below n-2%, the valve V2 will work to reduce the gas flow on the main line and thus redistribute part of the flow in the secondary line, to the storage unit via the E2 scrubber that will treat this biogas. The percentage of opening of VI and V2 towards the secondary network is inversely proportional to the quality of the gas. In other words, the lower the quality of the gas and the higher the flow to the secondary circuit (the opening percentage of VI and V2 is regulated for this purpose). The increase in flow to the secondary circuit via the valve V2 will allow the scrubber E2 to increase the average quality of the gas of the secondary line and thus the storage unit.

Reducing the gas flow will increase the scrubbing rate of the exhaust gas El and thus maintain the continuous operation of the installation by guaranteeing continuous quality for variable flow.

Reference A: Quality correction by "learning" or "step by step": the opening of the valve V2 is a function of the biogas quality measured by the analyzer A2 and is therefore higher when this quality is low

Low gain: "default" programming

Mark B: Quality correction by "anticipation": the opening of the V2 valve follows the guidelines provided by an abacus to achieve a given quality regardless of the quality measured.

The gains are associated with functions corresponding to scenarios of evolution of the quality of the biogas - this in order to correct as quickly / efficiently the quality before injection In scenario 1 illustrated, the action of the regulation of the opening of the V2 valve has allowed the biogas quality to remain above the "n-10%" value at which the VI valve is programmed to be closed. It will remain open throughout the process. The presence of the secondary circuit or purification loop has made it possible to avoid the closing of the valve VI and the stoppage of the injection which occurred in the abovementioned reference case (broken line curves). The intervention of an operator is useless.

Scenario 2:

In scenario 2 shown, the action of regulating the opening of the V2 valve did not allow the quality of the biogas to remain higher than "n-10%" value at which the valve VI is programmed to be closed (due for example to a high flow or other or a regulation too "cautious"). When the quality of the biogas becomes less than "n-10%", the valve VI is closed but thanks to the purification allowed by the secondary circuit, this moment is delayed by Atl which makes it possible to increase the quantity of quality biogas greater than "n-10%" injected into the network, and the operating time of the installation, and thus delaying the possible intervention of an operator.

The additional deflection circuits βΐ, γ, and / or the hydraulic guard can be taken into account for the calculation of the buffer volume and therefore for that of the on-site intervention time of an operator following the detection of an incident ( non-compliant gas).

FIG. 2 represents a variant embodiment in which the primary deflection circuit β originates on the main circuit oc between the compressor and the injection station. This secondary deflection circuit then comprises a gas regulator that is non-compliant and compressed before redirecting it towards the gasometer 4 and / or the scrubber E1. Another variant embodiment, not shown, is in accordance with that of FIG. 8 The installation as described above thus has the advantage of not leading to a waste of the biogas produced by the source as soon as the quality of the latter does not comply with requirements, as is the case when it is flared, but allows on the contrary: a recirculation of this gas in the main processing circuit and in a primary deflection pipe, thus forming a recirculation loop whose internal volume may allow storage of this gas before the intervention of an operator even if "fresh biogas" continues to be injected into the main circuit (creation of a volume ta mpon), while continuing to purify the gas mixture then formed between the non-compliant gas and the "fresh biogas" possibly until the mixture is again checked as compliant, and can be injected into the gas station. injection, without requiring any intervention, obtaining almost immediately after putting back into operation of the installation of a good quality of gas that can be injected due to the continuous treatment of the stored gas during the time of the stoppage of the injection a start and a restart following an interruption of the facility facilitated and made quicker because of the presence of the recirculation loops and purification of non-compliant gas which make it possible to advance in time the possibility of injection of the biomethane in the injection station compared to an installation without this type of recirculation loop and non-compliant detected gas treatment.

Claims (10)

1. Installation for injecting gas from a renewable source into an injection station in a natural gas distribution and / or transport network, comprising a main circuit including: a continuous storage unit gas from the renewable source, - a gas purifier mounted downstream of the gas collection unit - a purified gas quality control instrument mounted at the outlet of the purifier to check its compliance with predetermined requirements - a purified gas compressor making it reach a pressure depending on that prevailing in the network in which this gas is injected - an injection station within the distribution and / or transport network, the compressed and compliant controlled gas, mounted downstream of the purifier and the control instrument, a solenoid valve controlled according to the measurements delivered by the control instrument preventing the introduction of non-compliant gas s the injection station, the installation comprising, upstream of the injection station, a primary deflection circuit of the non-compliant gas comprising a portion of the main circuit excluding the injection station, in order to store the gas coming continuously; of the collection unit, and / or to reprocess this gas within said portion of the main circuit. 2. Installation according to claim 1, wherein the primary deflection circuit of the non-compliant gas comprises a deflection conduit of the non-compliant gas opening into the collection unit or within the purifier. The plant of claim 2, wherein the non-compliant gas bypass line further comprises a bypass line to a torch for burning off the non-compliant gas and / or to a hydraulic guard for storing this non-compliant gas. 4. Installation according to one of the preceding claims, wherein the primary deflection circuit of the non-compliant gas comprises a pipe whose inlet is disposed between the scrubber and the injection station. 5. Installation according to claim 4, comprising a compressor interposed between the scrubber and the injection station, the inlet of the primary deflection conduit being disposed between the scrubber and the compressor. 6. Installation according to claim 4 or 5, wherein the inlet of the primary deflection pipe comprises a solenoid valve controlled by the quality control instruments of the gas leaving the purifier. 7. Installation according to one of the preceding claims, comprising, upstream of the purifier, a second instrument for analyzing the homogeneity of the gas flow from the collection unit, and a secondary deflection circuit of the gas controlled non-homogeneous by the second instrument, whose input is interposed between the collection unit and the purifier of the main circuit and opening into the deflection circuit. 8. Installation according to claim 7, wherein the secondary deflection circuit comprises a secondary purifier. 9. Installation according to claim 7 or 8, comprising, at the input of the secondary deflection circuit, a solenoid valve controlled by the second analysis instrument. 10. Installation according to claim 9, wherein the solenoid valve is controlled to distribute the gas between the main circuit and the secondary deflection circuit in predetermined proportions.