FR3096464A1 - Device for recycling carrier gas from a gas chromatograph - Google Patents

Abstract

The invention provides a method of operating an installation for gas analysis by gas chromatography, which installation comprises the following elements: a gas chromatograph (28); a detector (26), for example a thermally conductive detector; a source of carrier gas (16); of the type where the carrier gas continuously sweeps the separation column (20) of the chromatograph and the detector, a method organizing the recycling of the carrier gas. Abstract figure: Fig. 1

Description

Description Title of the invention: Device for recycling the carrier gas of a gas phase chromatograph

The present invention relates to the field of gas analysis and in particular chromatographs (gas chromatography analyzers).

[0002] Recall that chromatographs are analyzers which are permanently fed by a carrier gas.

This carrier gas sweeps the separation column and detector, this gas is then released into the air and therefore lost.

Putting this type of analyzer into operation requires a long period of purging and temperature stabilization under scanning, up to several hours.

Queuing these analyzers involves constantly scanning with a carrier gas.

The gas supply must be permanent even outside of the analysis, 24 hours a day. This type of device generally operates with helium resulting in a certain cost, even if the device is in the standby phase.

The quantity of gas coming from pressurized cylinders is a factor limiting the autonomy of the device.

[0003] It should also be noted that new generations of gas chromatography analyzers have appeared, with the aim of being able to enable field analyzes to be carried out.

These devices referred to as "Micro CC" or "portable chromatographs" are dc reduced in size and of a weight allowing easy transport and movement of the device.

[0004] Portability poses the problem of independence with respect to utilities such as energy and gas.

With regard to energy, dc battery systems make it possible to address this need, on the other hand for gas a problem arises for the autonomy of the device which requires large quantities of gas depending on the duration of autonomy required.

[0005] If the size of the packaging is reduced to meet the expected compactness, then the pressure must be increased to store the quantity of gas required in a smaller volume.

The packaging therefore then increases in mass and in volume since the thickness of the wall of the packaging must be sufficient to make it possible to withstand the pressure.

Thus a small bottle of one liter of water capacity at a pressure of 150 bar gives 66 times less gas than a bottle of water capacity of 50 liters at a pressure of 200 bar.

[0007] Consequently, if we consider small bottles with higher pressure, such as 600 bar, for example, the calculations carried out show that we reach more than 40 kg for a packaging with a water capacity of 1 liter at a pressure of 600 bar to finally have 590 liters of gas, that is to say 17 times less than a bottle of gas of 50 2 liters of water volume at 200 bar.

The present invention therefore aims in particular to provide a solution to the problems listed above, and in particular to the problems of danger linked to high pressures and mass of a packaging subjected to higher pressure, this by proposing a recycling device carrier gas used continuously by the analyzer.

A small bottle of make-up gas then becomes sufficient.

The present invention allows the analysis device to be easily transportable, it allows a gain in autonomy linked to a significant reduction in the consumption of carrier gas, it makes it possible to reduce the size of the bottle of carrier gas supply, resulting in a compact, transportable and functional analysis solution in environments where available space and gas consumption are limited.

This device can be adapted to a gas chromatograph ("GC") equipped with a thermal conductivity detector ("TCD"), but other types of detectors are possible, it makes it possible to recycle the carrier gas leaving the latter.

The improvement proposed according to the present invention therefore makes it possible to limit the gas consumption, to increase the autonomy of the apparatus, to regulate the pressure at the outlet of the detector (promoting the precision of the analysis), to improve the quality of the carrier gas and to reduce the volume of implantation of the device.

But it also makes it possible to consider the use of other much more expensive carrier gases.

[0011] [fig.1] attached provides a better understanding of the operation of the equipment proposed here, which is a partial schematic representation of a recycling device according to the invention.

Let us detail in what follows the constitution and the operation of the device of the invention, in connection with the appended figure 1:

[0012] a pump 3 associated with well-positioned pressure and flow regulations, and with a purification system, allows the recirculation of the gas from the analyzer.

This purified gas is reinjected into the chromatograph. there are 4 operating phases:

[0013] i.

Evacuation of the recycling system Filling of the system, start of recirculation and start-up of the analyzer, zero adjustment of the device on gas from a bottle (“clean” gas); Visualization of the "homogenization" of the recycle gas with the thermal conductivity detector; iv.

Feeding the analyzer with recycled gas.

In the operating phase, the pump 3 forces the circulation of the gas in the recycling part 6 which supplies the carrier circuit of the clu-omatograph and the collector 29 at the output of the thermal conductivity detector 26.

The gas passes through the scrubber 35.

3 The flow in the recycling loop 6 is regulated by the flow regulator 30.

The regulations made for the embodiment represented can be summarized as follows:

[0016] The pressure at the level of the buffer capacity 10 is regulated by the deverscur 39 up to the regulator 11.

The pressure at circuit 6 is regulated from regulator 11 to flow regulator 30.

The pressure at the analyzer 26 outlet manifold 29 is regulated from the flow regulator 30 to the spillway 39.

The pressure of the buffer capacity 2 is not regulated, it will be variable and will be balanced according to the capacity of the pump 3 and the quantity of gas available in the circuit.

The flow of the entire recycling loop 6 is regulated by the flow regulator 30.

The recycled carrier gas supplies the “analysis” 23 and “reference” 25 channels of the chromatograph at the pressure regulated by the regulator 11.

[0017] All the elements of the circuit are pressure-regulated by pressure regulators except buffer capacity 2.

As we said, at this level the pressure is variable, it depends on the quantity of gas in the circuit and the capacity of the pump.

In stabilized operation the gas circulates in the loop 6 without addition and without loss.

Valve 14, normally closed, controlled by Pressure switch 1 remains in the closed position.

In the event of a micro-leak, the pressure in the buffer capacity 10 will drop and the pressure switch 1 detecting this variation will control the opening of the valve 14 to reinject gas.

[0019] Conversely, as samples are injected, gas will be added to the circuit, the pressure of which will increase. In order to eliminate this excess material, a normally closed valve 9, controlled by the Ibis pressure switch will allow the opening of this one in order to evacuate the excess of gas.

A match between the two action pressure thresholds of the pressure switches (high threshold and low threshold) makes it possible to set one of the operating parameters and to regulate the pressure in the buffer tank 10.

[0020] In the following, we will detail the phases mentioned above.

[0021] a) phase 1: Evacuation of the recycling system The analyzer is supplied by the bottle (16), for this the valve 14 is closed, the valves (22) (24) are open, the valve (27 ) is closed.

[0022] The recycling circuit will be put under vacuum.

To do this: pump (37) is running, the purifier is isolated by closing valves (34) and (36) and opening valve (33), valve (30) is closed so that the vent the analyzer is not under vacuum, the valve (9) is closed, then the purge can begin by opening the valve (31) and by opening the flow limiter (32) as far as possible.

The gas evacuated by the analyzer can be eliminated by the discharge valve (39) without there being a pressure below atmospheric pressure at the analyzer outlet.

[0024] b) phase 2: filling When the system is started, the ambient air present in the circuit must be replaced by “clean” carrier gas.

For this the purifier 35 is isolated by the closed valves 34 and 36.

The pump in operation (3) makes it possible to ensure the circulation of the carrier gas in the recycling circuit to clean the line.

Carrier gas bottle 16 supplies circuit 6 via open valves 14 and 33.

After disconnecting the pump 37, the manual valve 31 open allows the evacuation of the gas to the vent to purge the circuits.

The gas during this phase therefore follows the path “17/18/14/12/2/3/10/11/33/31/32/30/29 towards the vent”.

But it can be noted that the gas also enters the circuit 19 i.e until the valve 27 is closed.

The valve 27 being closed in this phase, the gas does not enter the analyzer.

[0028] In fact, the gas "naturally" occupies the space it may have, which means that part of the gas flow will go naturally to the valve 27 and to the manifold, but of course depending on the state of the valve 30, it is possible to choose at the beginning of the filling of the recycling circuit to direct all the gas towards the purge.

[0029] During this time or subsequently, (clean) carrier gas (16) supplies the chromatograph via circuit 19, valves 22 and 24 are open, valve 27 is closed.

This starts the analyzer.

Valve 27 being closed, the gases from the recycle circuit ("dirty") and from the analysis circuit ("clean") only mix at the level of the collector 29.

[0030] c) phase 3: end of purge, commissioning and evaluation of the quality of the recycled gas.

After a determined purge time, the manual valve 31 is closed which causes a complete recirculation of the gas and a rise in pressure at the level of the buffer capacity 10 and therefore a closing of the valve 14 controlled by the Pressure switch 1.

From the moment the analyzer is in service, it is necessary to “balance” the thermal conductivity detector.

It is possible to assess the level of purity of the gas coming from the recycling circuit 6 by opening the valve 27 and closing the valve 24.

The “recirculated” gas then supplies the “reference” branch (25), the “clean” gas from bottle 16 supplies the “analysis” branch (23).

A comparison is then made between the conductivity results obtained for the two fluids.

A significant “imbalance” in the signal delivered by the detector indicates insufficient purity of the recycle gas.

To regain purity in the recycle gas, it is possible to repeat the purge phase as much as necessary.

Once the desired purity has been reached, in other words once a difference between the two analysis results has been observed that is less than a given set point, it is possible to decide to open the valves 24 and 27 and to close the valve 22.

Then, the opening of the valves 34 and 36 and the closing of the valve 33 allows the return to service of the purifier 35.

[0033] Nomenclature of the elements present in Figure 1:

[0034] 1: Pressure switch - low pressure, controls the addition valve 14 1a: Pressure switch - high pressure, controls the evacuation valve 9 2: Low pressure buffer volume upstream of the pump, pressure < atmospheric pressure 3 : circulation pump 4: Circulation pump overload relief valve 3 5: Pressure sensor - buffer capacity pressure display 10 6: Recirculation circuit 7: Expansion valve regulation pressure sensor 11 8: Manual valve for air gas exhaust flow adjustment - interface between buffer tank pressure 10 and atmospheric pressure 9: "Overflow" discharge valve, controlled by the ibis pressure switch 10: Downstream pressure buffer volume of the pump - circuit pressure tank 11: Pressure regulator - regulates the pressure in the recycling loop and the carrier gas supply to the analyzer i2: Flow adjustment valve for adding gas to the circuit - interface between the pressure of the buffer tank 2 and of the regulator 11 13: Circuit for adding "clean" gas i4: Valve for adding "clean" gas, controlled by the pressure switch 1 15: Safety valve downstream of the regulator 11 16: Cylinder 17: Carrier gas bottle regulator 18: Carrier gas regulator pressure gauge or sensor 19: Carrier gas chromatograph supply circuit during the start-up phase 20: Chromatograph analysis circuit - separation column 21 : Chromatograph injection valve 22: Shut-off valve 23: Chromatograph pressure/flow regulation - analysis channel 24: Shut-off valve 25: Chromatograph pressure/flow regulation - reference channel 6 26: TCD detector (katharometer ) 27: Shut-off valve 28: CC furnace 29: Detector outlet manifold 30: End-of-adjustment valve, regulation of the gas flow in the recycling loop 31: Manual shut-off valve - purge circuit at the vent 32: Manual flow adjustment valve - limits purge flow -- interface between pressure regulated by regulator 11 and atmospheric pressure 33: Manual shut-off valve - purifier bypass circuit 34: Air vent valve manual shut-off - purifier isolation 35 35: Recycle gas scrubber 36: Manual shut-off valve - purifier isolation 35 37: Purge pump 38: Backpressure regulator pressure sensor 39 39: Backpressure regulator - regulates pressure in manifold 29 40: Pressure sensor - display of pressure in buffer tank 2

The invention therefore relates to a method of operating a gas analysis installation by gas chromatography, an installation which comprises the following elements:

[0036] a gas chromatograph; a detector, for example a thermal conductivity detector; a source of carrier gas; of the type where the carrier gas continuously sweeps the separation column of the chromatograph and the detector, characterized by the implementation of the following measures:

a) there is a carrier gas recirculation circuit, provided with a purification system;

b) one proceeds to a purge phase of the recirculation circuit by filling the recirculation circuit with carrier gas from said source of carrier gas, bypassing the purification system;

c) concomitantly or subsequently, a commissioning phase of the analyzer is carried out during which the chromatograph is supplied with carrier gas from said source of carrier gas;

[0040] d) a phase of "balancing" of the detector is carried out as follows:

using carrier gas circulating in the recycling circuit, a "reference" branch of the chromatograph is fed to evaluate the thermal conductivity of this recycled gas; 7 the carrier gas coming from the carrier gas source is fed to an “analysis” branch of the chromatograph to evaluate the thermal conductivity of this source carrier gas; the two results thus obtained are compared, if the two results are far apart by more than a set value, a sign of insufficient purity of the recycled gas, one or more additional phases of purging the recirculation circuit are carried out until the obtaining a comparison below said set value, allowing the purifier to be put back into service;

e) the carrier gas passing through the analyzer is recycled and purified in the recirculation circuit, then the gas thus recycled and purified is supplied to the analyzer.

An example of a setpoint value for the difference between the two measurements of the source carrier gas and the purified gas is of the order of 10%.

As will clearly appear to those skilled in the art, depending on the compounds being analyzed, if these compounds are not present in the unpurified mixture, the set point value can be much higher without the analyzes being distorted since the carrier and reference matrix are the same. 8

Claims (1)

CLAIMS [Claim 1] Method of operating a gas analysis installation by gas phase chromatography, installation which comprises the following elements: a gas phase chromatograph (28); - a detector (26), for example a thermal conductivity detector; - a carrier gas source (16); of the type where the carrier gas continuously sweeps the separation column (20) of the chromatograph and the detector, characterized by the implementation of the following measures: a. there is a circuit (6) for recirculating the carrier gas, provided with a purification system (35); b. a phase of purging the recirculation circuit (6) is carried out pat- filling the recirculation circuit with the aid of the carrier gas coming from the said source of carrier gas, bypassing the purification system (35); vs. concomitantly or subsequently, a phase of commissioning of the analyzer is carried out during which the chromatograph is supplied with the aid of the carrier gas coming from the said source of carrier gas; d. a phase of "balancing" of the detector is carried out as follows: - using the carrier gas circulating in the recycling circuit, a "reference" branch (25) of the chromatograph is fed in order to evaluate the thermal conductivity of this recycled gas; - the carrier gas coming from the carrier gas source is fed to an “analysis” branch (20) of the chromatograph to evaluate the thermal conductivity of this source carrier gas; - the two results thus obtained are compared, if the two results are far apart by more than a set value, a sign of insufficient purity of the recycled gas, one or more additional phases of purging the recirculation circuit are carried out until obtaining a comparison below said set value, allowing the purifier (35) to be put back into service; e) the carrier gas passing through the analyzer is recycled and purified, in the recirculation circuit, then the gas thus recycled and purified is supplied to the analyzer.