CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. Â§119 (a) and (b) to French Application No. 1155038 filed Jun. 9, 2011, the entire contents of which are incorporated herein by reference.

BACKGROUND

The invention relates to a method for packaging a gaseous NO/N₂mixture into a container, particularly one or more gas cylinders, comprising various successive purging and gas rinsing steps.

Gaseous NO/N₂mixtures are commonly used to treat pulmonary vasoconstrictions in adults or children, particularly in new born infants suffering from primary pulmonary hypertension or in patients who have undergone cardiac surgery.

These NO/N₂mixtures are conventionally packaged into steel gas cylinders. Typically these cylinders contain, by volume, from 100 to 1000 ppm of NO, the remainder being nitrogen (N₂). These cylinders usually have a water capacity of 2 to 50 litres, which means that a total charge of as much as 15 m³of NO/N₂mixture can be admitted to them.

The packaging of these mixtures, which means the filling of cylinders with these mixtures, is done at gas filling centres.

However, given the low NO content in the mixture, which is typically of the order of a few hundred ppm by volume, it is not always easy to package these mixtures on an industrial scale. In particular, the gaseous NO/N₂mixture is sensitive to the presence of residual impurities of the oxygen type likely to be present in the cylinders at the time of their filling.

Indeed it is of the utmost importance to be able to ensure that the cylinders, prior to being filled, have been correctly rid of all the gaseous impurities they are likely to contain, particularly oxygen which can react with the NO to form toxic NO₂.

Stated differently, if the internal volume of the cylinders is not correctly purged and cleaned, the NO/N₂mixtures produced will not comply with the specifications and will have to be scrapped.

The problem is therefore that of providing an improved packaging method that makes it possible to eliminate all or almost all of the impurities, especially oxygen, likely to be found in one or more gas cylinders that are to receive a gaseous mixture of the NO/N₂type.

SUMMARY

The solution of the invention is therefore a method for packaging a gaseous NO/N₂mixture into at least one container, in particular one or more gas cylinders, characterized in that, prior to admitting said NO/N₂mixture, said at least one container, which means to say the container or containers, is subjected to at least:

- a) a purging step during which the internal volume of the container is placed in fluidic communication with the ambient atmosphere,
- b) an evacuating step during which the internal volume of the container is placed under depression, which means to say that the internal pressure of the container is reduced until it reaches a pressure lower than atmospheric pressure (<1 bar absolute), and
- c) a gas rinsing step during which an inert gas is admitted to said at least one container.

Depending on circumstance the method of the invention may have one or more of the following technical features:

- Evacuating step b) is performed by withdrawing gas using a vacuum pump.
- Said at least one container is subjected to steps a) and c) several times in succession prior to said NO/N₂mixture being admitted into the said at least one container.
- Two successive sequences of steps a) and c) are separated by a sequence of steps a), b) and c).
- A sequence of steps a), b) and c) is immediately followed by a sequence of steps a) and c) or by a sequence of steps a), c) and a).
- During steps c), the inert gas used to perform the gas rinsing is nitrogen.
- Several gas containers are subjected simultaneously to steps a) to c).
- After at least two sequences of steps a) and c) have been carried out, a gaseous mixture made of NO and N₂is admitted to the container or containers.
- After at least two sequences of steps a) and c) have been carried out, the following are admitted in succession to the container or containers:
  - i) a gaseous premix made of NO and N₂containing an NO content less than 10% by volume until a first pressure P1 is reached where P1>1 bar absolute;
  - ii) gaseous nitrogen until, through mixing of the nitrogen with the said NO/N₂premix, a final gaseous NO/N₂mixture containing an NO content less than or equal to 1200 ppm by volume and a second pressure P2 of between P1 and 800 bar are achieved.
- Gas rinsing step c) involves admitting gaseous nitrogen into the container or containers until a rinsing pressure of between 2 and 20 bar, preferably of between 2 and 12 bar, is reached within said container or containers.
- During the purging step a), the internal volume of the container is kept in fluidic communication with the atmosphere as long as the internal pressure inside the container is higher than a minimal purge pressure (Pmin) such that 3.5 bar>Pmin>1 bar, preferably between around 1.1 and 3 bar.
- During at least one evacuating step b), the internal volume of the container is placed under depression until a pressure level below 0.5 bar, preferably below 0.2 bar is reached.
- It comprises, prior to step a), a step d) of evacuating and a step e) of purging at least one flexible hose connecting the filling system to a gas container.
- During the gas rinsing step c), the admission of inert gas to the said at least one container is halted when the pressure in said at least one container reaches a value of between 2 and 20 bar, preferably of between 3 and 10 bar.
- Fluidic communication with the ambient atmosphere during purging step a) is halted when the pressure in the internal volume of the container reaches a value of between 1 and 1.5 bar.
- The first pressure P1 is between 2 and 10 bar, preferably less than or equal to 5 bar.
- The second pressure is between 100 and 700 bar, preferably at least 200 bar.
- The gaseous premix made of NO and N₂contains an NO content less than or equal to 8% by volume, preferably an NO content less than or equal to 5% by volume.
- The gaseous premix made up of NO and N₂contains an NO content of the order of 4% by volume and the first pressure P1 is of the order of 2 to 10 bar abs, for example of the order of 2 to 5 bar abs.
- The final gaseous NO/N₂mixture contains an NO content less than or equal to 1000 ppm by volume, preferably the final gaseous NO/N₂mixture contains an NO content of between 200 and 1000 ppm by volume and more preferably still, of between 200 and 800 ppm by volume.
- It is performed using a gas container filling system comprising means of connection allowing several containers to be filled at once.
- The container is a gas cylinder, preferably a gas cylinder with a body made of steel, of aluminium or an aluminium alloy.
- In the context of the present invention, the pressures quoted are absolute pressures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be better understood by virtue of the description given hereinafter with reference to the attached figures in which:

FIG. 1 schematically illustrates one embodiment of a packaging cycle according to the present invention, and

FIG. 2 is the diagram of an installation for implementing the method of the invention.

FIG. 1 schematically depicts one embodiment of a packaging cycle that can be applied in the context of the method of packaging the gaseous NO/N₂mixture of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

As can be seen, this packaging cycle comprises several successive steps, spaced out over time from T0 to T13, and which are applied to each cylinder and are detailed hereinbelow. Successive steps a) to c) of the method of the invention have been indicated in FIG. 1.

Between T0 and T1, the flexible hoses of the installation are vented to the open air, which means to say that the internal volume of the flexible filling hoses is placed in fluidic communication with the ambient atmosphere in order to remove any possible residual raised pressure. During this phase, the valve or valves of the gas containers connected to the hoses are closed, so that there is no exchange of gas with the container or containers. This corresponds to step d) of the method.

Between T1 and T2, a vacuum pump is used to place the inside of the flexible hoses under connected depression, i.e. under a pressure below atmospheric pressure, for example of the order of 0.15 bar, thus making it possible to remove any residual gas and/or air contained therein. This phase is therefore also performed with the cylinder valve closed. Placing the flexible hoses under vacuum is a safety measure which makes it possible to check that all the hoses are correctly connected and that there are no leaks. Specifically, if there was a leak or if a hose was incorrectly connected, it would not be possible to establish the stable vacuum. This corresponds to step e) of the method schematically illustrated in FIG. 1.

Between T2 and T3, the operator opens the valve on each cylinder and the residual pressure present in each cylinder then rises and reaches the pressure sensor, which detects the said rise in pressure. Typically the residual pressure in the cylinder is of the order of around 3 to 4 bar absolute. Before T2, no gas rinsing of the container with nitrogen took place. This corresponds to step f) of the method schematically illustrated in FIG. 1.

Between T3 and T4, the actual treatment of each cylinder begins. More specifically, each cylinder is vented to the atmosphere, i.e. the gas contained in the cylinder is allowed to escape to the external atmosphere under the simple effect of the difference in pressure between the inside and the outside of the cylinder, so as to decrease the internal pressure of the cylinder to atmospheric pressure. This corresponds to step a) of the method of the invention. At T4, the internal pressure of the gas cylinder is therefore more or less equal to atmospheric pressure (1 atm=around 1 bar absolute), i.e. of the order of 1 to 1.5 bar abs.

Between T4 and T5, the cylinder is rinsed with nitrogen while its internal pressure is raised to around 10 bar. The addition of nitrogen is performed via a gas line and/or a store of nitrogen under pressure so as to raise the internal pressure of the cylinder to the desired pressure. This corresponds to step c) of the method of the invention.

Between T5 and T6, the nitrogen contained in the cylinder is again allowed to escape to the atmosphere, which allows any impurities that might be present in the cylinder to be removed. This corresponds to a further step a) of the method of the invention.

Between T6 and T7, the cylinder is purged by placing its internal volume under depression by withdrawing the residual gas contained therein using a vacuum pump until an internal depression of below 0.2 bar abs, preferably of below 0.1 bar, for example of the order of 0.05 bar, is reached. This corresponds to a further step b) of the method of the invention.

Between T7 and T8, the cylinder undergoes a further rinsing with nitrogen to raise its internal pressure to around 10 bar as between T4 and T5. This corresponds to a further step c) of the method of the invention.

Between T8 and T9, the cylinder is once again discharged to the ambient atmosphere as during times T5 and T6. The residual gas pressure is then kept at around 1.35 bar in order to avoid unwanted ingress of atmospheric contaminants. This corresponds to a further step a) of the method of the invention.

Between T9 and T10, the cylinder once again undergoes additional rinsing with nitrogen to raise its internal pressure to around 10 bar, as before. This corresponds to a further step c) of the method of the invention.

Between T10 and T11, the nitrogen is discharged into the atmosphere, as between T8 and T9 and between T5 and T6, but this time maintaining a residual internal pressure of the order of 3 bar. This corresponds to a further step a) of the method of the invention.

Between T11 and T12, a gaseous premix formed of NO and N₂containing an NO content less than 10% by volume is admitted to the cylinder in order to reach a first filling pressure P1 where P1>1 bar, typically a pressure P1 of the order of 2 to 10 bar abs, preferably of around 3 to 5 bar abs. Advantageously, the gaseous premix formed of NO and N₂contains an NO content of the order of 4% by volume.

Between T12 and T13, gaseous nitrogen is then admitted to the container containing the NO/N₂premix at the first pressure P1 in order to obtain a final gaseous NO/N₂mixture containing an NO content less than or equal to 1200 ppm by volume, for example a final NO content of 200 to 800 ppm, and a second pressure P2 of between P1 and 800 bar, for example in this instance a pressure of 180 to 200 bar.

This method can be implemented via a packaging installation like the one depicted schematically in FIG. 2, fitted with a filling system 14 for filling gas containers, i.e. gas cylinders, comprising connecting means 15 allowing several containers 11 to 13 to be connected at once, typically that allow simultaneous connection of 2 to 20 cylinders.

The nitrogen is stored in the reservoir 1 in liquid form and then withdrawn in liquid form by a cryogenic pump 2 which compresses it to a pressure of the order of 100 to 300 bar, before sending it to an atmospheric heater 3 where it is vaporized to yield gaseous nitrogen. As may be seen, it comprises a main line or pipe 20 for carrying nitrogen from a reservoir 1 to the filling system 14. In fact, the pressure in the line varies between around 100 bar immediately downstream of the outflow from the buffer volume into the cylinders and around 260 bar which corresponds to the threshold at which the pump is stopped.

The nitrogen gas is then carried by the line 20 to a purification device 6 able to eliminate traces of O₂and H₂O, for example using a suitable molecular sieve, for example of the zeolite, silica gel, alumina or similar type, or mixtures thereof.

It should be noted that the line 20 is also fluidically connected to a buffer volume 4 capable of storing some of the gaseous nitrogen, and to backup racks 5, each comprising several nitrogen cylinders.

Moreover, the installation also comprises a cabinet 16 comprising several cylinders 9 of an NO/N₂premix, here containing 4% by volume of NO, which cylinders 9 are fluidically connected to the line 20 by an NO/N₂premix supply line 22. In fact, the NO/N₂line 22 and the nitrogen line 20 are not connected directly to one another but are connected to the valve unit 8 which is itself connected by the line 21 to the filling system or systems 14. The valves in the valve unit 8 make it possible to select the fluid with which the cylinders 11 to 13 of the system 14 are filled. The nitrogen line 20 and the NO/N₂premix line 22 are therefore fluidically connected firstly by the valve unit 8 then a common section 21 to the filling system 14. The valve unit 8 comprises valves, control elements controlled by the control device 10, etc.

Flow meters 7 make it possible to measure the quantity of N₂and NO flowing through the lines 20 and 22 and to transmit the measured information to a control device 10, such as a computer or the like. The installation also comprises a vent-to-atmosphere line 17 allowing the gases to be discharged to the ambient atmosphere, notably during the purge step or steps during which the internal volume of the container is placed in fluidic communication with the ambient atmosphere.

A vacuum pump (not shown) allows the container or containers to be evacuated, i.e. allows their internal pressure to be reduced down to a pressure below atmospheric pressure, i.e. <1 bar absolute.

It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.