On-board oxygen production system for aircraft, in particular long-range aircraft

Method and system on board an aircraft for the production of an oxygen-enriched gas stream from an oxygen/nitrogen gas mixture, particularly air, comprising at least one adsorber containing at least one adsorbent for adsorbing at least some of the nitrogen molecules contained in the oxygen/nitrogen feed mixture, characterized in that the adsorbent comprises a faujasite-type zeolite, having a Si/Al ratio of 1 to 1.50, exchanged to at least 80% with lithium cations. Aircraft equipped with such a system, in particular an airliner, especially an airliner of the long-range, large-capacity type.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an oxygen concentration system, especially of the OBOGS type, for aircraft, in particular for long-range, large-capacity airliners.

2. Related Art

At the present time, gaseous oxygen is used by the pilots and passengers of a civil commercial airliner in the event of cabin decompression (passengers and pilots), in the event of protection against smoke and toxic gases (pilots) and in the event of prior protection when cruising at high altitude (pilots).

Moreover, the pilots of military aircraft have need for a permanent oxygen supply, throughout their flight missions. In certain specific missions, the same applies to the crew of military tactical transport planes and helicopters.

The constraints imposed by the aeronautical environment mean equipment must be designed to be as light as possible and capable of providing the largest quantity of oxygen possible, with substantial self-sufficiency, and consequently the least possible logistics.

In modern fighter planes, the pilot or pilots are permanently supplied by an on-board oxygen generating system (commonly abbreviated to OBOGS), using the technology for separating gases from the air by a zeolite-type molecular sieve.

Document EP-A-391 607 thus discloses an OBOGS-type oxygen concentration system that can be used for supplying the crew members of an aircraft using an adsorbent of the molecular sieve type.

Furthermore, document U.S. Pat. No. 4,960,119 also teaches an OBOGS-type system using adsorbents that have a higher affinity for nitrogen than for oxygen.

On the other hand, in civil aircraft, the total supply of gaseous oxygen to the people on board is provided by pressurized oxygen cylinders or by chemical oxygen generators, for example on the AIRBUS A340 (tank of oxygen in gaseous form) and AIRBUS A320 (chemical generator). These civil oxygen production systems are currently designed and sized so as to deliver oxygen to the passengers for a period varying from 15 to 22 minutes, essentially following a loss of cabin pressure.

As in the case of military aircraft, it is now envisaged to also equip new airliners, especially long-range, large-capacity airliners, for example the AIRBUS A380-type planes, as well as business planes, with on-board systems of the OBOGS type based on an adsorbent molecular sieve.

This is because, compared with oxygen storage, molecular-sieve OBOGS-type systems have the advantages:of a weight saving when the time they are in use typically exceeds 30 min, as is the case with the planned diverting of aircraft to the new longer-haul air routes;of reduced logistics;of greater safety and availability; andof unlimited self-sufficiency.

These same advantages also exist when the OBOGS system is on board a military tactical transport plane or a helicopter, when these have to carry out missions requiring the use of oxygen.

However, one problem that arises is that the existing OBOGS-type systems are much heavier than conventional on-board oxygen storage systems, and this constitutes a serious impediment to their use in aircraft in which the reduction in on-board weight is a constant concern, as it has a not insignificant impact on fuel consumption.

In other words, the problem that arises is to be able to fit molecular-sieve OBOGS-type systems on board aircraft without this having a negative impact on the on-board weight, and to achieve this with substantially the same, or even greater, oxygen production compared with a conventional system.

SUMMARY OF THE INVENTION

The solution of the invention is therefore a system fitted on board an aircraft for the production of an oxygen-enriched gas stream from an oxygen/nitrogen gas mixture, particularly air, comprising at least one adsorber containing at least one adsorbent for adsorbing at least some of the nitrogen molecules contained in the oxygen/nitrogen feed mixture, characterized in that the adsorbent comprises a faujasite-type zeolite, having an Si/Al ratio of 1 to 1.50, exchanged to at least 80% with lithium cations.

EXAMPLES

Concentrator System for Pilots

The performance of an oxygen concentrator system having to supply the pilots of an aeroplane has been shown inFIG. 1, which gives the oxygen concentration (purity) curves obtained as a function of the production output for adsorbents according to the invention (ADS 2 and ADS 3) and, as a comparison, for an adsorbent according to the prior art (ADS 1), i.e.:
O2concentration=f(production output).

The operating conditions under which the measurements were carried out are the following:system based on 2 adsorbers operating alternately;adsorption pressure: 2 bar;desorption pressure: 0.43 bar;feed gas: air having an oxygen content of 21 vol %;temperature of the feed gas: 20° C.;cycle time: 2×2.9 s;ADS 1: a zeolite according to the prior art of the NaX type, containing essentially Na cations (and possibly K cations), having a mean particle size of about 0.7 mm;ADS 2: an Li-LSX-type zeolite exchanged to about 95% with Li cations (and having Na and possibly K cations for the remainder), having an Si/Al ratio of between 1 and 1.2 and a particle size of about 0.7 mm; andADS 3: an Li-LSX zeolite identical to that of ADS 2, but having a particle size of about 1.5 mm.

The oxygen concentrator used had two adsorption columns filled with particles of the adsorbent in question. Oxygen was produced continuously, one column regenerating (desorption phase) when the other was in production (adsorption phase). The desorption also included a step called elution, and this corresponded to sending a small flow of O2-enriched gas as a countercurrent into the column in regeneration phase so as to supplement the regeneration.

In this way, the concentrator operated cyclically (2 phases) and each column experiences 4 different steps, as shown inFIG. 3, namely:an adsorption phase, characterized by the half-cycle time T and comprising:a “pure” production step (Ref.1inFIG. 3)a production and elution phase for the other column (Ref.2in FIG.3); anda regeneration phase with:a desorption (purge) step (Ref.3inFIG. 3)an elution step (elution time te) (Ref.4in FIG.3).

The mean flow rate of gas in each adsorption column therefore changes as a function of time as represented inFIG. 3, which shows the average flow rate within each column as a function of time.

The elution step takes place at the end of the cycle, when the O2concentration of the gas output by the column is at a maximum. The elution period is typically between 10 and 50% of the half-cycle time, as may be seen in FIG.3.

The superiority of the type of adsorbent of the invention (ADS 2 and ADS 3) compared with a standard adsorbent (ADS 1) is apparent inFIG. 1, given that this shows that, for a given output oxygen concentration, the output of oxygen produced is markedly greater than for a conventional adsorbent (ADS 1) and that, furthermore, for a given production output, the oxygen concentration produced in the output gas is markedly higher than that of a conventional adsorbent.

Moreover, there may also be a benefit in using adsorbent particles according to the invention of smaller diameter, since the 0.7 mm beads (ADS 2) result in a better performance than 1.5 mm beads (ADS 3), all other things being equal.

The expected weight saving for such an OBOGS system according to the invention for pilots is around 1 kg (10%) compared with a conventional adsorbent, all other things being equal.

Concentrator System for Passengers

The performance of an oxygen concentrator system having to supply the passengers of an aeroplane has been represented diagrammatically inFIG. 2, which shows the oxygen concentration (% purity) curves obtained as a function of the production output (in l/min) for an adsorbent according to the invention (proposed sieve) and, as a comparison, for an adsorbent according to the prior art (standard sieve), i.e.:
O2concentration=f(production output)

The operating conditions under which the measurements were carried out are the following:system based on two adsorbers operating alternately;adsorption pressure: 3 bar;desorption pressure: 0.46 bar;feed gas: air having an oxygen content of 21%;temperature of the feed gas: 20° C.;cycle time: 2×5 s;adsorbent according to the invention: identical to ADS 2 of Example 1;adsorbent according to the prior art: identical to ADS 1 of Example 1;cycle: identical to that of Example 1 and FIG.3.

In this case, the expected weight saving for a concentrator system, especially an OBOGS, for passengers is 60 kg (30%) with the adsorbent of the invention compared with a conventional adsorbent, all other things being equal.