“METHOD FOR REDUCING CONTINUOUS EMISSIONS IN A GAS CHROMATOGRAPHY ANALYSIS

PROCESS”

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The present invention relates to a method for reducing continuous emissions in a gas chromatography analysis process.

The present invention further relates to a gas chromatography analysis procedure, controlled by means of the aforesaid method of control.

In greater detail, the invention has application in the field of continuous grade sources of emissions deriving from intrinsic exhaust in systems for measuring the quality of natural gas.

As will be clearer below, the invention has the aim of reducing, in this context, the total emissions of CH4 and mixtures containing the latter and C02, which have a large environmental impact, in accordance with the proposal for a Regulation EU 2021/0423 (COD) issued by the European Commission.

The Applicant observes that the definition of an "emission source” is provided by standard CEI 31/87 as well as standard ISO EN 60079-10, and is introduced by the aforesaid standards substantially for the definition of potentially explosive areas:

"An emission source is a point or part of equipment, a container, an apparatus, a machine, a pipe, etc. from which a gas, vapour or mist, or an inflammable liquid may be released into the atmosphere so that an explosive atmosphere could be formed.”

The grade of an emission source may be one of three types:

Continuous grade: when the release is continuous or in any case occurs over a long time;

Primary grade: when the release occurs periodically or occasionally, but is in any case expected during normal operation;

Secondary grade: when the release occurs for short periods and is not expected during normal operation (faults, opening of safety valves, etc.).

From an environmental viewpoint, the invention relates to continuous grade emissions, as they prevail over others in the systems for measuring the quality of natural gas.

In addition to the above, the Applicant deems that the normative references relevant for the present context are the following:

ISO 60079: Electrical apparatus for explosive atmospheres

CEI 31/87: Guide to the application of Standard CEI EN 60079-10-1 a

ISO 6974: Natural gas — Determination of composition with defined uncertainty by gas chromatography

ISO 6976: Natural gas — Calculation of calorific values, density, relative density and Wobbe indices from composition

ISO 10715: Natural gas - Sampling guidelines

2014/34: ATEX Directive - harmonisation of the laws of the Member States relating to equipment and protective systems intended for use in potentially explosive atmospheres.

Generally, a system for measuring the quality of natural gas or biomethane is composed of a gas chromatographer (so-called "fiscal gas chromatographer”, which hereinafter will also be called "analyzer”) which determines the composition of the natural gas or biomethane by means of a standardised chromatography process (ISO 6974), based on which the physical properties of the sample are calculated according to standard ISO 6976.

In order to bring the gas to be measured to the gas chromatographer it is necessary to provide a transport line that brings the gas from the tap point to the instrument.

Also envisaged is a sample treatment system or sample conditioning system (SOS), composed at least of a pressure reducing station (PRS), a fast loop (conduit with a high flow rate and a filter, for example a self-cleaning membrane, a cyclone, coalescing filter or a combination thereof) which accelerates the velocity of the gas present in the tubing, reducing the transit time so that the gas chromatographer, at the time of injection thereof, can analyse a sample representative of what is present in the process pipeline, as indicated in standard ISO 10715. In this manner, the transit time of the sample from the tap point to the gas chromatographer is able to reach values meeting standard sampling requirements, typically comprised between 10 and 60 seconds, depending on the type of application.

In the specific case, the continuous grade emission sources present in the measurement system are substantially two:

Exhaust vent of the analyzer (gas chromatographer);

Exhaust vent of the fast loop.

The emission values vary depending on the type of analyzer, the type of filtration, the distance between the tap point and analyzer, the pressure of the sample, etc.; however, it is advisable to perform assessments to determine the actual quantity of methane released into the atmosphere, especially considering the current alarming climate situations, also in light of the fact that methane has a global warming potential at least 50 times greater than that of CO2.

Figures 1 a-1 b show a diagram of a measurement system in accordance with the prior art.

The term "Process” identifies a conduit in which the process gas, i.e. the natural gas or biomethane that needs to be analysed, flows.

The term "Flanged probe” identifies the flanged probe used to collect part of the process gas.

The acronym PRS indicates a pressure reducing station, comprising: a fine filter F-01, adapted to block particles larger than 7 pm; a pressure reducer / vaporiser PRV-01 , set at a pressure of 1.5 barg; a safety valve PSV-01, set at 3 barg and coupled to a "Vent” outlet (SE-03); a pressure indicator PI-01 , capable of detecting pressures of up to 2 barg; and a ball valve BV-01 , diameter 6mm.

The system further comprises a conduit for the natural gas or biomethane, with a diameter equal to 6mm ("sample line 6mm OD”), which connects the pressure reducing station with a sample conditioning and filtering system with a fast loop SCS.

Sometimes, where the process pressure conditions are not such as to require a separate PRS positioned in proximity to the tap point, the PRS is incorporated in the SCS itself; therefore, the sample transport line will be upstream of the latter.

The SCS system has, at the inlet thereof, a ball valve BV-01, diameter 6mm; there is also provided a pressure indicator PI-01, downstream of which there is a membrane filter S-01. Extending from the membrane filter S-01 there is a first branch R1 , comprising a flow meter Fl-01 , set at 50 cc/min, which then leads to the outside via the vent outlet (SE-02), and a second branch (R2), comprising a fine filter F-02 (2 m) followed by a flow meter Fl-02, set at 2.5 cc/min, which is connected to an inlet of the gas chromatographer GC.

The gas chromatographer GC also receives as input an eluent (via the "Carrier gas” inlet, through a ball valve BV- 01 , diameter 6mm), and has an exhaust opening/vent (SE-01).

In addition to the above, the gas chromatographer GC may be endowed with a "Cal gas” inlet to receive a calibration gas.

As mentioned, in a system of this type, therefore, there are substantially two emission sources:

Exhaust vent of the analyzer SE-01 ;

Exhaust vent of the fast loop SE-02.

In this context, the Applicant observes that, in a station for measuring natural gas or biomethane or hydrocarbons as described above, the gas consumption of the analyzer (gas then dispersed through the vent SE-01) is about 50 cc/minute.

As regards the fast loop system, it requires a flow rate ratio of about 1 to 5 between the filtered and non-filtered gas (as long as the filter remains clean).

However, the fast loop flow rate must also take into consideration the gas transport time so that it is reduced to a minimum to ensure the representativeness of the measurement.

There are various methods for reducing this time:

1) Reducing the pressure from the line value (75 barg) to the value required by the gas chromatographer (1 .5 barg) as close as possible to the tap point in order to reduce the amount of gas to be consumed;

2) Reducing the internal cross section size of the transport line (remaining within the requirements of ISO 10715, thus let us say an internal diameter of 4mm);

3) Reducing the fast loop flow rate, compatibly with the minimum required for the correct operation of the fast loop filter.

In this scenario, the following numerical example is considered:

Line pressure 75 barg

Pressure reduction to 1 .5 barg at a distance of 1 metre from the tap point with a 6mm OD line (4 mm inner diameter) 6mm OD transport line (4 mm inner diameter) with a length of about 10 metres

Gas chromatographer consumption 50 cc/min Measurement cycle of 7 minutes (420 seconds), typical for the measurement of natural gas to which H2 is added. Again by way of example, the transit time is set at 30 seconds (typical average for the various applications for fiscal and plant management applications), thus obtaining a fast loop flow rate value of 2,500 cc/min (2.5 Nlit/min).

The general operating parameters, corresponding to the operating condition in which this quantification was performed, are shown in the tables in figures 3a-3b.

Under these conditions it is possible to determine the emission flow rates of the two emission sources:

Table 1

Therefore, on average, each measurement system releases about 1 ,340 Nm3 of natural gas or biomethane into the atmosphere.

It should be noted that the “N” that precedes the unit of measurement indicates that the volume measurements (m3 or litres) are considered under the reference conditions (pressure and temperature) and not under the current conditions of the sample. The units of measurement, therefore, represent "normal cubic metres” and "normal litres”. This clarification is necessary since, as the quantities are expressed in volume and the gas is compressible, it is advisable to specify under what conditions this volume is defined (for example, a litre at 10 bar contains much more sample than a litre at 2 bar).

In consideration of the foregoing, the Applicant observes that, in order to be able to perform quality measurements where necessary, multiple measurement systems must be installed on the distribution network, each of which entails a consumption in the order of the one exemplified above.

Furthermore, it is necessary to carry out surveys and measurements with periodic frequency, since the characteristics of the gas are not always constant over time and, to enable the attribution of the correct commercial value to the gas itself (based on its heat capacity), frequent, accurate measurements must be performed.

In the light of the above, the Applicant set itself the objective of providing an innovative technique which enables natural gas or biomethane emissions to be reduced, with a consequent positive impact in terms of pollution and savings from an economic viewpoint.

In seeking a solution, the Applicant perceived that, as the measurement of a gas chromatographer is of a cyclical type, it is not always necessary for gas to flow through the sample transport line; it is rather sufficient that, at the time of injection, the sample that is introduced into the analyzer is "fresh” and representative of what is present in the process line.

The Applicant has thus found that a possible solution could provide for an interruption of the fast loop flow, and possibly of the analysis flow, when it is not necessary, i.e. for the period of time in which the gas chromatographer processes the measurement and does not require the injection of a sample.

In accordance with a first aspect, the invention relates to a method for reducing continuous emissions in a gas chromatography analysis process.

Preferably, the method comprises associating a first control valve with a filter element.

Preferably, the filter element is comprised in a sample conditioning station.

Preferably, the sample conditioning station is configured to separate a fraction of process gas.

Preferably, the fraction of process gas comes from a process conduit in which the process gas flows.

Preferably, said sample conditioning station is provided with an emission branch.

Preferably, said sample conditioning station is provided with an injection branch.

Preferably, the injection branch is located on the inlet side of a gas chromatographer for the performance of a gas chromatography analysis process on said gas.

Preferably, said first control valve is configured to selectively interrupt a flow of gas into said emission branch.

Preferably, the method comprises maintaining said first control valve in a normally closed condition.

Preferably, the method comprises determining an instant of time in which said gas chromatographer must perform a gas chromatography analysis.

Preferably, the method comprises performing a first opening operation to open the first control valve.

Preferably, the first opening operation is performed with a first timing advance relative to said instant of time.

Preferably, the method comprises sending to said gas chromatographer an enabling signal to enable the performance of the gas chromatography analysis.

Preferably, the method comprises bringing the first control valve back into the normally closed condition.

Preferably, the first control valve is brought back into the normally closed condition at the time of sending said enabling signal.

In accordance with a second aspect, the invention relates to a gas chromatography analysis process.

Preferably, the process comprises collecting, from a process conduit, a fraction of a process gas that flows in said process conduit.

Preferably, the process comprises feeding said fraction of process gas to a sample conditioning station.

Preferably, said sample conditioning station comprises a filter element.

Preferably, the filter element is configured to separate said fraction of process gas into an emission branch and an injection branch.

Preferably, the process comprises placing said injection branch on the inlet side of a gas chromatographer for the performance of a gas chromatography analysis process on the process gas that flows in said injection branch. Preferably, the process comprises carrying out the aforesaid method for reducing continuous emissions.

In one or more of the aforesaid aspects, the invention can comprise one or more of the following preferred features.

Preferably, the method comprises providing a second control valve on said injection branch.

Preferably, the method comprises maintaining said second control valve in a normally closed condition.

Preferably, the method comprises performing a second opening operation to open the second control valve. Preferably, the second opening operation is performed with a second timing advance relative to said instant of time. Preferably, said second timing advance is shorter than said first timing advance.

Preferably, the method comprises bringing the second control valve back into the normally closed condition.

Preferably, the second control valve is brought back into the normally closed condition at the time of sending said enabling signal.

Preferably, said first control valve remains continuously open between said first opening operation and the sending of said enabling signal.

Preferably, said second control valve remains continuously open between said second opening operation and the sending of said enabling signal.

Preferably, the method comprises a step of configuring said first timing advance as a function of a distance travelled by the process gas from a point of collection of said fraction of process gas from said process conduit to said first control valve.

Preferably, the method comprises a step of configuring said second timing advance as a function of a distance travelled by said fraction of process gas from said filter element to said gas chromatographer.

Preferably, the method comprises sending a sequence of enabling signals to said gas chromatographer.

Preferably, each enabling signal is separated from the previous and/or subsequent enabling signal by a given time interval.

Preferably, said given time interval is comprised between 1 and 60 minutes, in particular between 5 and 30 minutes.

Preferably, said first timing advance is comprised between 5% and 80% of said given time interval.

Preferably, said second timing advance is comprised between 1 % and 50% of said given time interval.

Preferably, said process gas is a mixture of hydrocarbons, in particular natural gas, and/or biomethane in the gaseous phase or regasified liquid, and/or GPL.

Preferably, said fraction of process gas is fed to a pressure reducing station for a reduction of the pressure of said fraction of process gas.

Preferably, said fraction of process gas is fed to the pressure reducing station before being fed to said sample conditioning station.

Additional features and advantages will become more apparent from the detailed description of example embodiments of the invention, provided below. The description will make reference to the appended figures, which likewise have a purely illustrative and thus non-limiting purpose, in which: figures 1 a-1 b, as mentioned, show a block diagram of a system in accordance with the prior art; figures 2a-2b show a block diagram of a system that operates according to the method of the present invention; figure 2b' shows a more general block diagram of the part of the system represented in figure 2b; figures 2c, 2c', 2c” show possible variants of the diagram in figure 2a-2b (or 2a-2b'); figures 2d, 2d' show possible variants of the diagram in figure 2b (or 2a-2b'); figure 2e shows a possible variant of the diagram in figure 2d; figures 3a-3b show operating parameters of the system in figure 1 a-1 b; figure 4 shows a time diagram representative of operations that are carried out by the system in figures 2a-2b.

With reference to the appended figures, 1 denotes in its entirety a system operating according to the method of the present invention.

At a general level, the system 1 (figures 2a-2b) can be substantially identical, from a functional viewpoint, to the system already illustrated with reference to figures 1 a-1 b, with the addition of a first control valve EV-02, a second control valve EV-01 and a control unit U, which will be described below.

As will be clearer hereafter, the system can also have the structure represented by figures 2a-2b', and thus be without the second control valve EV-01.

The system 1 comprises a flanged probe ("Flanged probe” in figure 2a) for collecting a fraction of a process gas from a conduit 10 (also identified with the word "Process” in figure 2a).

By way of example, the conduit 10 can be part of a gas supply network or plant.

The process gas can be, for example, a mixture of hydrocarbons, comprising preferably natural gas, and/or biomethane in the gaseous phase or regasified liquid, and/or LPG.

The system 1 further comprises a pressure reducing station PRS.

The pressure reducing station PRS is preferably located downstream of the flanged probe.

The pressure reducing station PRS is configured to reduce the pressure of the fraction of process gas collected from the conduit 10.

In one embodiment, the pressure reducing station PRS comprises, at an inlet thereof, a fine filter F-01 (for example, with a filter size of 7 pm). Downstream of the fine filter F-01 there is provided a pressure reducer I vaporiser PRV, set, for example, at 1.5 barg. Downstream of the pressure reducer I vaporiser PRV there is a safety valve PSV-01 , set, for example, at 3 barg and connected to an emission vent opening (SE-03). Downstream of the safety valve PSV-01 there is a pressure indicator PI-01 , capable of detecting pressures of up to 2 barg. Downstream of the pressure indicator PI-01 there is a ball valve BV-01 , for example with a diameter of 6mm, which leads to the outlet of the pressure reducing station PRS.

The system 1 further comprises a connecting conduit, or "sample line”.

The connecting conduit has, for example, a diameter comprised between 5 mm and 7 mm, in particular equal to 6 mm.

The connecting conduit extends from the outlet of the pressure reducing station PRS to the inlet of a sample conditioning station SCS (figure 2b).

If the process pressure conditions are such as not to require a separate pressure reducing station PRS positioned in proximity to the tap point, the pressure reducing station PRS is incorporated in the SCS itself; therefore, the sample transport line will be upstream of the pressure reducing station PRS. This embodiment is schematically illustrated in figure 2c: as may be noted, the sample conditioning station SCS, in this case, in addition to comprising the components described here below, is also provided with the components BV-01 , F-01 , PRV-01, PI-01 and PSV- 01 which, in the embodiment in figure 2a, are comprised in the separate pressure reducing station PRS.

The inlet of the sample conditioning station SCS provides a ball valve (e.g. diameter 6mm), downstream of which a first control valve EV-02 (which will be better described below) is mounted. Upstream of the first control valve EV- 02 there is a pressure indicator PI-01 (preferably capable of detecting pressures of up to 2 barg), followed by a filter element S-01 . The filter element S-01 can be positioned either before or after the first control valve EV-02, for example based on different application needs. Figure 2c shows the filter element S-01 positioned downstream of the first control valve EV-02. Figure 2d shows the filter element S-01 positioned upstream of the first control valve EV-02. Figure 2e shows the same embodiment as figure 2d, wherein downstream of the filter element S-01 , and in particular downstream of the fine filter F-02, there is a branch for a connection with one or more further analysis units - in this latter circumstance, the embodiment in figure 2d can have advantageous application.

The filter element S-01 can be constructed, for example, as a membrane filter, preferably of the self-cleaning type, a cyclone, or coalescing filter, or it can be obtained as a combination of these types of filters.

The filter element S-01 is configured to separate the fraction of process gas received as input into an emission branch R1 and an injection branch R2.

The emission branch R1 leads to an emission vent opening (SE-02).

The emission branch R1 comprises a first flow meter Fl-01 , preferably set at 50 cc/min.

The emission branch R1, together with the filter element S-01, constitutes a so-called fast loop, i.e. a branch with a high flow rate configured to accelerate the velocity of the gas present in the tubing, thus reducing the transit time thereof, so that the gas chromatographer GC, at the moment of injection thereof, can analyse a representative sample of what is present in the process conduit 10, as indicated in standard ISO 10715. In this manner, the transit time of the sample from the tap point at the process conduit 10 to the gas chromatographer GC is able to reach functionally suitable values, for example comprised between about 10 seconds and about 60 seconds, depending on the type of application.

The injection branch R2 connects the filter element S-01 with an inlet of a gas chromatographer GC.

The injection branch R2 comprises, for example, a fine filter F-02 (filter size preferably equal to about 2 pm) and a second flow meter Fl-02, preferably set at 2.5 l/min.

Downstream of the second flow meter Fl-02 there is preferably provided a second control valve EV-01 , positioned at the outlet of the sample conditioning station SCS, near the inlet of the gas chromatographer GC, or also inside the gas chromatographer GC itself where the chromatographer thus allows.

In a possible variant embodiment (figure 2c'), the first control valve EV-02 can be positioned downstream of the filter element S-01 , and in particular interposed between the filter element S-01 and the first flow meter Fl-01. In this variant embodiment the pressure regulator is incorporated in the sample conditioning station SCS.

In a possible variant embodiment (figure 2c”), the first control valve EV-02 can be positioned downstream of the first flow meter Fl-01 . In this variant embodiment the pressure regulator is incorporated in the sample conditioning station SCS. In a variant embodiment (figure 2d'), the first control valve EV-02 can be positioned downstream of the first flow meter Fl-01. In this variant embodiment, the pressure regulator is external to the sample conditioning station SCS and obtained by means of the separate pressure reducing station PRS (as, for example, in figures 2a-2b).

The first and second control valves EV-02, EV-01 (when provided for) are connected to a control unit U or LOGIC (also possibly incorporated in the chromatographer where the latter has the capacity); the first control valve EV-02, second control valve EV-01 (when provided for), and control unit U together form a control device of the gas chromatography analysis process carried out by the gas chromatographer GC.

The first and/or second control valves EV-02, EV-01 can be constructed as solenoid valves suitable for operating in an area classified in accordance with standard ISO 60079, as well as functioning at the pressure available in the sample conditioning station SCS.

The first and/or second control valves EV-02, EV-01 can be powered at 24Vdc, 120Vac or 230Vac depending on the type of command that is imparted by the control unit U.

The sample conditioning station SCS further has a Carrier Gas inlet for a carrier gas (also called eluent), and a Cal Gas inlet for a calibration gas. The latter, from a practical viewpoint, is an inlet through which a sample with known characteristics enters and is analysed and the results of the analysis are compared with the data related to the sample itself, previously uploaded to the system. This activity is carried out autonomously of the instrument at a settable frequency (for example once a week).

During the normal operation of the system, a fraction of the process gas is collected from the process conduit 10, is fed to the pressure reducing station PRS and, downstream thereof, is supplied to the sample conditioning station SCS. The process gas that flows in the injection branch R2 is fed to the gas chromatographer GC, in order for the appropriate analyses to be performed.

The control unit U is configured so as to control this process and obtain significant reductions of the gas dispersed into the atmosphere.

In greater detail, the first and second control valves EV-02, EV01 are normally closed.

The control unit U, autonomously or thanks to its connection with another management device/apparatus, determines an instant of time T in which the process gas must be analysed by the gas chromatographer GC.

As will be clearer below, the gas chromatographer GC performs multiple analyses over time, according to a substantially pre-established frequency; in order to better describe the invention, reference will now be made to a single analysis operation.

As mentioned, the gas chromatography analysis of the gas chromatographer GC is programmed to start at the instant of time T.

The control unit U, on which a first timing advance Tf relative to the instant of time T is set, activates the opening of the first control valve EV-02.

Advantageously, the first timing advance Tf is determined as a function of a distance travelled by the process gas from the point of collection of the fraction of process gas from the process conduit 10 to the first control valve EV- 02. In practical terms, the first timing advance Tf depends on the distance, measured along the pipes forming the system 1, between the point of collection of the fraction of process gas and the first control valve EV-02; in this manner, the first timing advance Tf takes into consideration the time it will take the fraction of process gas to transit from the process conduit 10 to the inlet of the sample conditioning station SCS.

The control unit U, on which a second timing advance Ta relative to the instant of time T is preferably set, can further activate the opening of the second control valve EV-01.

Advantageously, the second timing advance Ta is determined as a function of a distance travelled by the fraction of process gas from the filter element S-01 to the gas chromatographer GC.

In practical terms, the second timing advance Ta depends on the distance, measured along the pipes forming the system 1 , between the filter element S-01 and the inlet of the gas chromatographer GC; in this manner, the second timing advance Ta takes into consideration the time it will take the process gas to transit from the fast loop to the gas chromatographer GC.

The second timing advance Ta is shorter than the first timing advance Tf; this means that, on a time axis, the instant T-Ta falls after the instant T-Tf.

Figure 4 represents the instant of time T, the first and second timing advances Tf, Ta and the operation of the control unit U as described here below.

Given said instant of time T in which the analysis must be performed by the gas chromatographer GC, the control unit U will open the first control valve EV-02 (first opening operation) at the time T-Tf, i.e. with a timing advance of Tf relative to the instant of time T.

The first control valve EV-02 is then kept open until the instant of time T; at the instant of time T, the first control valve EV-02 is closed, i.e. brought back into the normally closed condition.

The control unit U will preferably further open the second control valve EV-01 (second opening operation) at the time T-Ta, i.e. with a timing advance of Ta relative to the instant of time T.

The second control valve EV-01 is then preferably kept open until the instant of time T; at the instant of time T, the second control valve EV-01 is preferably closed, i.e. brought back into the normally closed condition.

Therefore, before the instant T-Tf, both the first and second control valves EV-02, EV-01 are closed - consistently with the fact that, as mentioned, they are normally closed.

At the instant T-Tf, the first control valve EV-02 is opened, and the second control valve EV-01 still remains closed. In this manner, the process gas starts flowing in the fast loop and in the section that leads from the fast loop to the second control valve EV-01 , but does not reach the gas chromatographer GC.

At the instant T-Ta, the first control valve EV-02 is still open, and the second control valve EV-01 is open too, so the process gas can start flowing into the gas chromatographer GC.

The times are determined in such a way that at the instant T the gas chromatographer GC has received the quantity of gas necessary to carry out the analysis; at this point, the control unit U will send an enabling signal Inj to the gas chromatographer GC to start, precisely, the analysis and, simultaneously brings the first and second control valves EV-02, EV-01 into the closed condition. It should be noted that, as schematically shown in figure 4, the first control valve EV-02 remains continuously open between the first opening operation and the sending of the enabling signal Inj, i.e. between the instant T-Tf and the instant of time T; the second control valve EV-01 remains continuously open between the second opening operation and the sending of the enabling signal Inj, i.e. between the instant T-Ta and the instant of time T.

As mentioned above, from a practical viewpoint the gas chromatographer GC is configured to perform, in succession, a series of analyses on respective samples of process gas received as input.

For each analysis to be performed, the control unit U sends a respective enabling signal Inj to the gas chromatographer GC.

In figure 4, the distance in time between two consecutive analyses - and thus between two consecutive enabling signals Inj- is represented as AT and indicates, precisely, a given time interval that separates the beginning of two consecutive analyses.

The given time interval AT can be comprised between 1 minute and 60 minutes; more in particular, it can be comprised between 5 minutes and 30 minutes.

For example, the given time interval AT can be equal to about 5 minutes if the process gas is natural gas, and can be equal to about 7 minutes in the case of natural gas with added H2.

In one embodiment, the first timing advance Tf is comprised between 5% and 80% of the given time interval AT.

In one embodiment, the second timing advance Ta is comprised between 1 % and 50% of the given time interval AT.

The Applicant observes that, in some embodiments, the second control valve EV-01 might not be necessary.

For example, if the gas consumption of the gas chromatographer GC is less than 10%, in particular 5%, and even more particularly 1 %, compared to the consumption of the fast loop (i.e. of the emission branch R1 and the components associated therewith), it would be possible to obtain satisfactory results even with the first control valve EV-02 alone.

In this case, as schematically shown in figure 2b', the injection branch R2 has no interruptions/controls.

From a viewpoint of operation, managed by the control unit U, the first control valve EV-02 is kept in a normally closed condition.

Thus, the instant of time T in which the gas chromatographer GC must perform a gas chromatography analysis, and the first timing advance Tf are determined.

The first opening operation is carried out to open the first control valve EV-02 with the first timing advance Tf relative to the instant of time T.

In this manner, the process gas will start flowing both in the fast loop and in the injection branch R2.

The enabling signal Inj is then sent to the gas chromatographer GC and at the time of this sending, the first control valve EV-02 is brought back into the normally closed condition - preferably after having remained open continuously between the first opening operation and the sending of the enabling signal Inj.

The remaining structural/functional features of the invention preferably remain unchanged from what was described above with reference to figures 2a-2b and the respective variant embodiments, with the exception - as mentioned - of the absence of the second control valve EV-01.

From a practical viewpoint, the control unit U can be built with any device/module capable of implementing the logic described hereinabove. For example, the control unit U can be built with relay logic or an industrial PLC, or it can be incorporated in the programming of the chromatographer itself. Conveniently, the control unit U is built in accordance with ATEX Directive 2014/34, according to the requirements laid down by standard ISO 60079. In particular, the control unit U provides for normally open contacts that close when activated to switch the first and/or second control valves EV-02, EV-01. The communication and synchronisation with the gas chromatographer GO can be implemented both by means of serial communication and by means of a remote activation contact. In one embodiment, the control unit U can be directly incorporated in the gas chromatographer GC, if the latter is endowed with the logical capacities and programmability to configure the timing advances Ta, Tf.

In the light of the foregoing, the Applicant deems it useful to present here below a numerical example that provides an idea of the results that may be obtained through the present invention.

Going back to the scenario described in the introductory part of the description, according to which, on average, each measurement system releases about 1 .340 Nm3 of natural gas or biomethane into the atmosphere every year, and considering that by applying the teachings of the present invention it is possible to reduce the time of gas delivery over the fast loop and towards the analyzer from 420 seconds (continuous) between one cycle and the other to respectively 30 seconds for the fast loop and 5 seconds for the analytic loop, one obtains in this manner a drastic reduction in the quantity of gas emitted into the atmosphere, as shown in the following table:

Table 2

When comparing these data with the previously indicated values (emissions equal to 1 ,340.057 Nm3/year), one finds a 92.97% reduction.

The invention achieves important advantages.

First of all, the invention enables the emissions of natural gas and/or biomethane into the atmosphere to be considerably reduced.

This means a significant improvement from both an environmental viewpoint (less pollution), and an economic viewpoint (less waste of gas).

Furthermore, despite reducing, as mentioned, the emissions into the atmosphere, the invention nonetheless enables reliable, accurate and precise measurements of the process gas to be performed, with consequent positive repercussions from a technical standpoint, as regards the results of the analyses themselves, and from an economic standpoint, as regards the costs and transactions defined based on the detected characteristics of the process gas.