SYSTEM FOR PROVIDING A HYPOXIC AIR ATMOSPHERE IN AN ENCLOSED SPACE

Abstract

 The present invention relates to a system for providing a hypoxic air atmosphere in at least one protected zone P comprising at least one compressor (1) for providing compressed fresh air; at least one cabinet C arranged downstream of the at least one compressor (1), wherein the at least one cabinet C comprises at least one, preferably at least two pressure switches (6a) for continuously monitoring the air inlet pressure, wherein each pressure switch (6a) is monitored by a first functional safety related system, at least one air separation device (8) arranged downstream of the at least one pressure switch (6a) having one inlet for the compressed fresh air, one first outlet for the oxygen-depleted air and one second outlet for oxygen-enriched air; at least one protected zone control valve (13) arranged downstream of the at least one air separation device (8); and at least one, preferably at least three oxygen sensors (16) arranged in the protected zone P, wherein each of the oxygen sensors (16) is independently monitored by a second functional safety related system for oxygen control in the protected zone P, and wherein the oxygen sensors in the protected zone P interact with the at least one protected zone control valve (13) in the cabinet C.

Description

[0001] The present invention relates to a system for providing a hypoxic air atmosphere in an at least one enclosed space according to claim 1 and a method for providing a hypoxic air atmosphere using said system according to claim 12.

Description

[0002] In a hypoxic air atmosphere or environment the partial pressure of oxygen is lower than at sea level whereas the normal barometric pressure is equal to the barometric pressure at the sea level. This means that in a hypoxic air atmosphere the oxygen concentration is lower compared to normal air. Usually, about 5 to 10 % of oxygen contained in the normal air is replaced by the same amount of nitrogen and thus as a consequence a hypoxic atmosphere is created which contains between 10 and 18 %, typically 15 vol% of oxygen and 85 vol% of nitrogen. Under such conditions in a normobaric hypoxic environment common materials cannot ignite or burn. Thus, a fire cannot occur because of the lack of sufficient oxygen for starting a fire and keeping it alive.

[0003] This makes hypoxic air an ideal candidate for fire prevention systems, also known as oxygen reduction systems. Thus, the hypoxic air technology for fire prevention is an active fire prevention technique based on the permanent reduction of the oxygen concentration in the protected rooms. In contrast to traditional fire suppression systems that usually extinguish fire after it has been detected, i.e. after the fire has already been started, hypoxic air is able to prevent fire.

[0004] A technology based on hypoxic air was originally developed for athletic training but the application of the hypoxic air technology for fire prevention was only developed in the late 1990s.

[0005] The general concept of using the hypoxic air technology for fire prevention is that air with a reduced oxygen content (hypoxic air) is injected to the respective protected volumes or enclosed spaces to lower the oxygen concentration therein until the desired oxygen concentration is reached. The exact oxygen level to be retained in the protected volumes is determined beforehand after assessing the ignition thresholds of the material and hazards being present in the volume to be protected. The hypoxic air is produced by hypoxic air generators also known as air separation units which create an oxygen enriched volume and an oxygen reduced volume, the later one being used in a hypoxic air technology. At the moment, three different types of hypoxic air generators are known. These are membrane based, PSA-based and VSA-based hypoxic air generators.

[0006] The hypoxic air generators can be located inside or outside of the protected rooms. The hypoxic air is transported to the protected volumes or protected spaces through specific pipes or more simply via an existing ventilation system. Oxygen sensors are installed in the protected spaces to monitor continuously the oxygen concentration. Smoke detectors may be added to detect any possible smoldering and pyrolyzing processes, which are not prevented by hypoxic air.

[0007] The benefits of preventing a fire instead of suppressing an already open fire makes hypoxic air specifically suitable for applications where a conventional fire suppression (such as water or other chemical compositions) are unacceptable or unusable. Hypoxic air for fire prevention is in particular suitable for IT facilities such as data centers, storage of high value items, archives, large warehouses, telecom and other utilities. Furthermore, due to the reduced oxygen concentration other metabolic reactions such as food deterioration, is reduced in hypoxic air and thus the hypoxic air is very well suitable for food warehouses and similar storage facilities.

[0008] Even though the oxygen content in hypoxic air environment is less than 18 %, preferably about 16, and thus lower than the normal air it is still considered to be safe to breath for most people. Several studies have been conducted and it is concluded that working environments with low oxygen concentrations to a minimum of 13 % and normal barometric pressure do not impose a health hazard provided that precautions are observed comprising medical examinations and limitation of exposure time. It has also been stated that an oxygen concentration between 14.8 % and 17 % does not cause any risk for healthy people by hypoxia. For instance, the oxygen concentration in pressurized aircraft cabins is about 15 %, however, passengers are not active under such conditions and crewmembers have immediate access to additional oxygen sources (wikipedia online).

[0009] The hypoxic air fire prevention technology has been widely developed and implemented. For instance, US 6,334,315 B1 describes a hypoxic fire prevention and fire suppression system for computer cabinets and other fire hazardous industrial containers. Here, a system is described which comprises an air compressor, an air separation device using either molecular sieve material or a membrane system for separating the air into an oxygen depleted fraction and into an oxygen enriched fraction and a collecting tank which is operatively associated with the separation device into which the oxygen reduced gas is passed to. This allows for keeping a fire-retarding environment inside the tank. The technology described herein can be applied for ventilating underground communication tunnels, mining facilities, ammunitions and missile bunkers and other underground facilities in order to remove explosive gases and replace them with fire safe hypoxic air.

[0010] US 2001/0029750 A1 relates to fire prevention and suppression systems provided for human occupied environments such as rooms, houses and buildings, employing also an oxygen extraction apparatus supplying oxygen depleted air inside into the human occupied area or storing it in a high pressure container for use in case of fire. The fire suppression system is provided having an oxygen concentration under 16 % such when it released it creates a breathable fire suppressive atmosphere with an oxygen concentration from 10 to 16 %.

[0011] The presently known fire prevention systems based on hypoxic air are only to a limited extend applicable of creating and maintaining a hypoxic air environment in an enclosed space continuously over a longer period of time. In particular the present systems lack safety functions which are however required, in particular when a system is a computer managed system or programmable electronic system.

[0012] Thus, it is an object of the present invention to provide a computer-managed system which allows for an automatic and continuous maintenance of a hypoxic air environment which is easy to handle and to control and which fulfills the presently required safety standards.

[0013] This object is being solved by a system according to claim 1 and a method according to claim 12.

[0014] Thus, a system, in particular a computer-managed system, is provided which provides a hypoxic air atmosphere in an at least one protected zone P (enclosed space) comprising

• at least one compressor for providing compressed fresh air;
• at least one cabinet C arranged downstream of the at least one compressor wherein the at least one cabinet C comprises:
  • at least one pressure switch, preferably at least two pressure switches, for continuously monitoring the air inlet pressure, wherein each pressure switch is monitored by a first functional safety related system S1,
    • at least one air separation device arranged downstream of the at least one pressure switch having one inlet for the compressed fresh air, one first outlet for the oxygen-depleted air and one second outlet for oxygen-enriched air;
    • at least one protected zone control valve arranged downstream of the at least one air separation device; and
  • at least one, preferably at least three oxygen sensors arranged in the protected zone P, wherein each of the oxygen sensors is independently monitored by a second functional safety related system S2 for oxygen control in the protected zone, and wherein the oxygen sensors in the protected zone P interact with the at least one protected zone control valve in the cabinet C.

[0015] The first and second functional safety related systems are each implemented preferably in form of SIL (Safety Integrity Level) rated controller components, in particular in form of SIL cards.

[0016] Thus, there is a fire prevention system provided which generates hypoxic air and comprises at least two functional safety related systems monitored by SIL rated controller components (such as SIL cards).

[0017] The first of these systems monitors the compressed air transmission piping. For this reason, at least one, preferably at least two pressure switches are arranged in the cabinet downstream of the air inlet for continuously monitoring the air inlet pressure. A first pressure switch is preferably located upstream of a heater for heating the compressed fresh air; a second pressure switch is preferably located downstream of said heater but upstream of the separation device.

[0018] These switches preferably interact with a Safety Integrity Level control, such as SIL2/SIL3 using SIL rated cards. Such SIL rated cards are designed to create a user configurable SIL2/SIL3 rated output. If either switch is faulty, a SIL compliant alarm is given. Furthermore, should either of these switches detect a loss of pressure due to pipe breakage then an alarm is provided.

[0019] The second functional safety system monitored by SIL rated devices is connected to the redundant oxygen sensors located within the fire-protected spaces or protected zone. Each sensor is connected to independent SIL rated controllers. Should the sensor system detect an oxygen level below or above the prescribed minimum/maximum thresholds, the SIL rated system will create user configurable outputs.

[0020] For creating a hypoxic air atmosphere, the compressed fresh air may heated at first (see details below) in order to prevent any type of condensation inside the air separation device arranged downstream of the heater. By avoiding a water condensation in the air separation device, the separation quality and effectiveness is improved and the costs for running such an air separation device can be reduced. Once, the compressed fresh air is heated said air is fed into at least one air separation device through one inlet. In said device the normal air is separated into an oxygen depleted air (retentate) which leaves the air separation device through a first outlet and which is fed further down finally to the enclosed space. The second fraction obtained in the separation device is an oxygen enriched air fraction (permeate) which leaves the air separation device through a second outlet and is vented to the outside building atmosphere. The oxygen enriched air normally contains 30 to 35 % oxygen.

[0021] The oxygen depleted air or hypoxic air having for instance an oxygen content of approximately 10 % leaving the separator is subsequently fed through a piping system equipped with a pressure valve and protected zone control valves into the protected zone, which can be for instance in an enclosed space serving as a server room, storage room or even a normal office space.

[0022] Within the protected zone, at least one, preferably at least three oxygen sensors, more preferably multiple averaging oxygen sensors, are arranged, which interact with the protected zone control valve within the cabinet. Once, the protected zone reaches the preset low oxygen level, detected by the oxygen sensors, the protected zone valve will close and the compressor will be shut down thereby stopping the flow of hypoxic air to the protected zone. In contrast, when the oxygen level goes above the upper set point said protected zone valve will reopen, the compressor will be restarted and the flow of hypoxic air to the respective protective zone to be restored.

[0023] The oxygen sensors interact with or are connected to the protected zone control valve, in particular the main PLC via a satellite module. All oxygen sensors are connected to SIL (Safety Integrity Level) rated cards and controllers, which provide user configurable outputs for oxygen levels below 12% and above the upper protected room threshold.

[0024] In an embodiment of the present system there is at least one cyclone type water separation device to remove liquid water from the compressed air prior to and upstream of the cabinet. This device is arranged downstream from the at least one compressor for providing compressed fresh air. It is also optionally possible that at least one oil water separator is connected to the at least one cyclone.

[0025] In an embodiment of the present invention, the system comprises at least one buffer vessel which is arranged downstream from the at least one compressor outside of the cabinet. This vessel is sized based on the volume of the compressed air generated.

[0026] It is furthermore preferred that at least two filters, preferably three filters are arranged downstream from the compressor and the buffer vessel. In case three filters are installed, a first filter may have a filtering size of about 2 to 5, preferably 3 µm. This filter removes impurities, like dust or microorganisms from the compressed fresh air. The second filter is a carbon filter followed by a third filter of 0.01 microns to filter fine carbon particulate.

[0027] It is important to note that the compressor, the cyclone, the buffer vessel and the filter system are arranged outside of the cabinet comprising the actual air separation systems.

[0028] In an embodiment the cabinet is equipped with at least one inlet pipe for the compressed fresh air. The at least one inlet allows for feeding the compressed air into the cabinet. The maximum pressure of the compressed air is between 5 and 10 bar, preferably 6 and 8 bar.

[0029] In a further preferred embodiment of the present system the cabinet comprises at least one heater arranged upstream from the air separation device, different valve systems and a control system.

[0030] The at least one heater heats the compressed air to a temperature T1 which is 10 °C, preferably 6°C above the inlet temperature T2 of the compressed air. The heating of the compressed air to a temperature of being about 6°C or more higher than the inlet temperature prevents condensation inside the downstream air separation device. The heater further controls with the high temperature cutoff the maximum operating conditions of the air separation device. Said heater temperature control is preferably implemented by a two level power cut-off (fail safe). In a further variant, the present system comprises at least one device for monitoring the heater outlet temperature, which is arranged downstream of the at least one heater in the at least one cabinet. This allows for monitoring the heater outlet temperature as feedback for the air temperature control system. The heater outlet temperature has also to be monitored in order to prevent any damage to the air separation device due to a possible overheating.

[0031] In another preferred embodiment, the at least one air separation device is a membrane based separation device. Here, a membrane separator is used to separate the oxygen and nitrogen from the compressed air feed and creates an oxygen rich permeate and an oxygen depleted retentate (hypoxic air). The membranes are preferably made as elongated containers filled with synthetic hollow fibers that permit oxygen under pressure through their walls and allow nitrogen enriched fraction to pass through the hollow fibers. The compressed and heated fresh air enters the membrane based separation device through one inlet and the air is separated into the oxygen enriched permeate and oxygen depleted retentate (hypoxic air product). The hypoxic air product leaves the membrane based system through a first outlet and is further flushed through the piping system controlled by several valves into the protected zone for reducing the oxygen there inside. The retentate flow rate of at least one membrane is approximately 20m³ per hour at no less than 10% oxygen by volume.

[0032] The oxygen enriched air (oxygen enriched permeate) leaves the membrane based device through the second outlet and is vented to the outside of the building atmosphere.

[0033] The efficiency of the membrane separator depends strongly on the back pressure, which is regulated by the back pressure valve which is arranged downstream of the membrane separation device. A higher back pressure provides a higher purity of the retentate (hypoxic air), thus the oxygen content in the hypoxic air will be rather low. However, if the oxygen concentration in the hypoxic air is too low, this can be detrimental to any presence of humans within the protected zone and is thus not preferred. Therefore, the control of the oxygen concentration in the retentate flow is accomplished by regulating the back pressure valve in an appropriate manner.

[0034] In a further embodiment, the present system comprises at least one hypoxic air sampler arranged downstream of the at least one air separation device within the cabinet for analyzing the oxygen content in the oxygen depleted retentate. For this reason, a small amount of retentate is drawn by a SS tube to a sensor for oxygen analysis. This, in turn, provides a feedback to the control of the back pressure valve which in turn regulates the oxygen content in the retentate.

[0035] In another variant of the present system, there is provided at least one flowmeter arranged downstream of the at least one air separation device and the at least one hypoxic air sampler within the cabinet. The flowmeter enables a continuous monitoring of the retentate (hypoxic air) flow to the protected zone and provides furthermore the temperature and the pressure of the hypoxic air flow from the air separation device to the protected zone.

[0036] In a further variant of the present system there is at least one back pressure valve arranged downstream of the at least one air separation device, the at least one hypoxic air sampler and the at least one flowmeter.

[0037] In another embodiment, the present system comprises at least one restriction valve which is arranged downstream of the at least one back pressure valve within the cabinet. This is a manually operated mechanical valve, which limits the oxygen percentage in the hypoxic air from increasing oxygen percentage beyond a factory set value, which is the lower limit of the value set for the protected zone. Should the backpressure valve fail for any reason, the back pressure valve will be open fully. The factory set restriction valve will maintain the delivery of hypoxic air to the protected zone.

[0038] As mentioned above, there is at least one protected zone control valve which is arranged downstream of the air separation device, the back pressure valve and the restriction valve. There can be also more than one protected zone control valve depending on the number of protected zones, i.e. one control value for each protected zone.

[0039] In another variant, the present system comprises at least one bypass valve for each protected space for fresh air which is arranged in the cabinet and enables the control of a direct flow of compressed non-separated air (i.e. before the compressed air enters the air separation device) to the protected zone if required. Said one fresh air bypass valve for fresh air for the protected zone, is arranged downstream or upstream of the at least one heater. The fresh air may enter the flow of hypoxic air at a location in the piping system downstream of the at least one protected zone control valve. The bypass valve regulates a direct feeding of fresh air into the hypoxic air flow piping. This can be, for instance, necessary if the oxygen percentage in any of the protected zones falls below 12 %, then as a safety measure the fresh air bypass valve for the corresponding protected zones opens and fresh air with 20.9 % oxygen will be directly flushed to the protected zone until the oxygen level reaches the upper preset value for that zone.

[0040] The cabinet further comprises appropriate piping connecting the heater, air separation device and the protected zone for supplying the hypoxic air to said protected zone. The valves described above are arranged at their respective positions along the piping system. The valves are typically selected from a group consisting of electrical, mechanical or pressure valves of linear or rotary configuration with appropriate actuators.

[0041] In a further embodiment, the cabinet of the present system comprises at least one control panel, at least one electrically backup supply and at least one display. The control panel is mounted together with the electrical and control hardware on an appropriate assembly in the inside of the cabinet, whereby the said assembly is separately movable from the cabinet. The hardware includes MCBs, PLCs, SIL rated cards, relays, fuses, a power unit, UPS, further oxygen analyzer, contactor and SSR. It is important to point out that the SIL rated cards serve the oxygen control in the protected zone by interacting with the oxygen sensors and/or the air pressure within the piping system by interacting with the pressure switches monitoring the air inlet pressure.

[0042] The at least one electrical backup supply, in particular in form of batteries, is provided for the backup power to the control panel. In particular, batteries are designed for a continuous backup up to 5 hours, preferably up to 8 hours. The backup power is provided for all sensors and monitoring equipment.

[0043] The display, in particular in form a human machine interface (HMI), provides the interface for operation of the cabinet. Monitoring and limited control features like changing the set points for oxygen level in the protected zone, manual and automatic operation selection etc. are provided on the display. Furthermore, data logging and alarm monitoring features are also available.

[0044] It is furthermore of an advantage that at least three zirconium-based oxygen sensors are arranged in each protected zone. Said oxygen sensors shall continuously monitoring oxygen levels for each zone. Each sensor has user configurable upper and lower alarm limits. As described above, each oxygen sensor is connected to at least one Safety Integrity Level control or independent SIL rated controllers (SIL2/SIL3) that have user configurable outputs. A backup power supply for up 5 hours, preferably up to 8 hours, is provided to the sensors in case of a main power supply failure. Said SIL rated controller is arranged in form of a SIL rated card arranged as hardware on said assembly.

[0045] In another variant, there is furthermore at least one display outside of the protected room for controlling the conditions within the protected room. Said display can also be in form of a human machine interface and is in communication with the oxygen sensors located within the protected zone. This HMI displays the oxygen level within the protected zone so that any person entering the protected zone will be aware of the reduced oxygen level inside the room. It also provides a visual alarm if an oxygen sensor within the protected zone fails.

[0046] The object of the invention is also solved by a method for providing a hypoxic air atmosphere in at least one protected zone using a system as described above. The method comprises the steps of

• providing compressed fresh air using the at least one compressor;
• feeding the compressed fresh air to the at least one cabinet arranged downstream of the at least one compressor, wherein the air inlet pressure is monitored by at least one, preferably at least two pressure switches,
• separating the compressed fresh air into oxygen depleted air and oxygen enriched air in the at least one air separation device arranged in the cabinet having one inlet for the compressed fresh air, one first outlet for the oxygen depleted air and one second outlet for oxygen enriched air;
• feeding the oxygen-depleted air out of the cabinet into the at least one protected zone comprising at least one, preferably at least three oxygen sensors,
• wherein the at least one pressure switch is monitored by a first functional safety related system, and
• wherein each of the oxygen sensors in the protected zone is monitored by a second functional safety related system for oxygen control in the protected zone.

[0047] As described previously, the first and second functional safety related systems are implemented as SIL rated controller components, in particular in form of SIL cards.

[0048] As described above in the context of the system the oxygen depleted air after leaving the air separation device is fed through a piping system comprising at least one back pressure valve arranged downstream of the at least one air separation device and at least one protected zone control valve arranged downstream of the at least one back pressure valve out of the cabinet into the at least one protected zone.

[0049] The present method allows for the reduction of oxygen content of the air in at least one protected zone by the hypoxic air atmosphere created having an oxygen content between 10 and 18 %, preferably between 12 and 16 %. The nitrogen content of the hypoxic air created by the present method in the at least one protected zone is below 88 %, preferably below 85 %.

[0050] The present invention is explained further in more detail by the means of an example with reference to the Figures. It shows:

Figure 1 a schematic overview of the present system according to a first embodiment;

Figure 2 a more detailed schematic overview of the cabinet content of the system according to Figure 1.

[0051] Figure 1 provides another view of the components of the present system. As deducible from Figure 1, the system comprises one compressor 1 for providing compressed fresh air whereby the maximum working pressure is 8 bar. The compressed fresh air is passed to a hydrocyclone water separator 2 and subsequently to a buffer vessel 3. The hydrocyclone water separator 2, the buffer vessel 3 and each of the filters 4 may be connected to an oil-water separator 3a.

[0052] After passing the buffer vessel 3 the compressed fresh air is further fed through filter units comprising a first filter 4a, a second filter 4b and a third filter 4c. Said filter system removes any impurities from the fresh compressed air, whereby the first filter system 4a is comprised of a 3 micron filter, the second filter system 4b is comprised of a carbon filter, and the third filter 4c is comprised of a 0.01 micron filter. Such purified compressed fresh is then fed through a compressed air inlet into the cabinet C (CAP9 system).

[0053] Figure 2 shows the structure of cabinet C. After entering the cabinet C there are two pressure switches or pressure transmitters 6a provided which continuously monitor the air inlet pressure. One first pressure switch 6a is located upstream of the heater 6 and one second pressure switch 6a is located downstream of the heater system, but upstream of the membrane separator 8. Each of the pressure switches 6a is monitored by a SIL2/SIL3 rated controller component, which in turn is part of the system hardware. Should either of the two pressure switches downstream of the air inlet detect a pressure loss due to pipe breakage, a SIL2/SIL3 rated card will create a user configurable output. Should a pressure switch fail, a SIL compliant alarm will be produced.

[0054] The compressed fresh air enters then a heater system 6 arranged within the cabinet, wherein the compressed air is heated to approximately 6 degrees higher than the inlet temperature to prevent condensation inside the downstream located membrane-based air separation system. The heater 6 is further controlled with a high temperature cutoff set for the maximum operation conditions of the heater. Downstream of the heater 6 an appropriate temperature sensor 7 is arranged for monitoring the heater outlet temperature as feedback for the air temperature control system. Said temperature sensor 7 monitors the temperature for preventing damages to the membranes within the subsequently arranged membrane based air separation device 8 due to a possible overheating. Heater controls consist of a two-stage cut-off through a solid-state-relay (SSR) and a contactor for fail-safe temperature control.

[0055] Such heated compressed air is then passed into a membrane separator system 8 which is used for separating the oxygen (permeate), a nitrogen (retentate) from the compressed air feed. The oxygen percentage of the compressed fresh air of about 20.9 % is reduced to an approximately 10 % and the retentate (oxygen depleted air or hypoxic air) is flushed through the appropriate outlet through a piping system finally into the protected zone.

[0056] Permeate (oxygen rich fraction) from the membrane separator 8 is vented through a high oxygen outlet 15 to the outside building atmosphere and contains normally about 30 to 35 percent oxygen.

[0057] After the membrane separator 8 a small amount of the oxygen depleted fraction (retentate) is sampled by a hypoxic air sampler 9 for analyzing the oxygen content. The hypoxic air sampling can be done by a SS tube, which draws a small amount of retentate to a sensor for analysis. This provides a feedback to the control of the subsequently arranged back pressure valve 11 which in turn regulates the oxygen content in the retentate.

[0058] The retentate (hypoxic air) flowing to the protected zone is continuously monitored by a flowmeter 10 to analyze the proper functioning of the cabinet (CAP9 unit). This flowmeter also provides temperature and pressure of the retentate flow.

[0059] The efficiency of the membrane separator 8 depends on the back pressure. When the back pressure is high, the purity of the retentate will be high, thus, the retentate will contain less oxygen. Therefore, a control of the oxygen concentration and the retentate flow is necessary and is accomplished by regulating a back pressure valve 11, which is arranged downstream of the flowmeter 10.

[0060] Following the back pressure valve 11, there is a restriction valve 12 which is a manually operated mechanical valve for limiting the oxygen percentage in the hypoxic air from increasing beyond a factory set value. Should the back pressure valve 11 fail for any reason the back pressure valve 11 will be opened fully and the factory set restriction valve 12 will maintain the delivery of hypoxic air to the room.

[0061] Two protected zone control valves 13 are arranged downstream of the back pressure valve 11 and the restriction valve 12 which controls the flow of hypoxic air to the protected zone. Once, the protected zone reaches the preset lower oxygen level, said protected zone control valves will close and stop the flow of hypoxic air to that zone. When the oxygen level goes above the upper set point the protected zone control valve will be reopened and the hypoxic flow to the respective zone will restart. These protected zone control valves are in communication with oxygen sensors 16 arranged within the protected zone.

[0062] If the oxygen percentage in any of the protected zones falls below 12 % there is as a safety measure, a fresh air bypass valve 14 for each of the corresponding protected zones which can provide fresh air with 20.9 % oxygen to the protected zones until the oxygen level reaches the preset values. The fresh air bypass valve 14 is thereby constructed in such a manner that fresh air is directly fed to the hypoxic air flow piping.

[0063] The hypoxic air leaves the cabinet C after passing the protected zone control valves 13 through appropriate piping to the respective protected zones.

[0064] The cabinet C comprises furthermore a control panel 17 where all of the electrical and control hardware is mounted within the cabinet. The hardware includes MCBs, PLC, SIL cards, relays, fuses, power unit, UPS, oxygen analyzer, contactor and SSR. The cabinet also comprises in particular on its bottom backup batteries 18 which are provided for the backup power to the control panel. The batteries are designed for a continuous backup of 5 hours. Backup power is given for all sensors and monitoring equipment. A human machine interface display 19 provides the interface for operation of the CAP9 unit. Monitoring of limited control features like changing the set points for a room oxygen level, manual and automatic operation selection etc. provided on the HMI. Data logging and alarm monitoring features are also available.

[0065] A minimum of three oxygen sensors 16 are arranged in the protected zone P which are zirconium-based sensors. Each sensor is connected to the main controller and to SIL rated cards with user configurable outputs. A backup power supply for up 5 hours allows the sensors to function in case of a main power supply failure.

[0066] There is furthermore one display in form of a HMI 20 outside of the protected room for displaying the conditions within the protected room. Said display is in communication with the oxygen sensors located within the protected zone. This HMI displays the oxygen level within the protected zone so that any person entering the protected zone will be aware of the reduced oxygen level inside the room. It also provides a visual alarm if an oxygen sensor within the protected zone fails.

Claims

1. System for providing a hypoxic air atmosphere in at least one protected zone (P) comprising

- at least one compressor (1) for providing compressed fresh air;

- at least one cabinet (C) arranged downstream of the at least one compressor (1), wherein the at least one cabinet (C) comprises:

- at least one, preferably at least two pressure switches (6a) for continuously monitoring the air inlet pressure, wherein each pressure switch (6a) is monitored by a first functional safety related system (S1),

- at least one air separation device (8) arranged downstream of the at least one pressure switch (6a) having one inlet for the compressed fresh air, one first outlet for the oxygen-depleted air and one second outlet for oxygen-enriched air;

- at least one protected zone control valve (13) arranged downstream of the at least one air separation device (8); and

- at least one, preferably at least three oxygen sensors (16) arranged in the protected zone (P), wherein each of the oxygen sensors (16) is independently monitored by a second functional safety related system (S2) for oxygen control in the protected zone (P), and wherein the oxygen sensors in the protected zone (P) interact with the at least one protected zone control valve (13) in the cabinet (C).

2. System according to claim 1, characterized in that the first and second functional safety related systems (S1, S2) are each implemented in form of SIL rated controller components, in particular in form of SIL cards.

3. System according to claim 1 or 2, characterized in that at least one heater (6) for heating the compressed fresh air is arranged downstream of the at least one compressor in the cabinet (C).

4. System according to one of the preceding claims, characterized by at least one device for monitoring the heater outlet temperature (7) arranged downstream of the at least one heater (6) in the at least one cabinet (C).

5. System according to one of the preceding claims, characterized by at least one hypoxic air sampler (9) arranged downstream of the at least one air separation device (8) in the cabinet for analyzing the oxygen content in the oxygen depleted retentate.

6. System according to one of the preceding claims, characterized by at least one flow meter (10) arranged downstream of the at least one air separation device (8) and the at least one hypoxic air sampler (9) in the cabinet (C).

7. System according to one of the preceding claim, characterized by at least one back pressure valve (11) arranged downstream of the at least one air separation device (8).

8. System according to one of the preceding claims, characterized by at least one bypass valve for fresh air (14) arranged in the cabinet for controlling a direct flow of compressed non-separated air to the protected zone (P) if required.

9. System according to one of the preceding claims, characterized by at least one at least one control panel (17) arranged in the cabinet (C), at least one electrical back up supply (18) and at least one display (19).

10. System according to one of the preceding claims, characterized in that the at least three oxygen sensors (16) arranged in at least one protected zone (P) are Zirconium based sensors.

11. System according to one of the preceding claims, characterized by at least one display (20) outside of the protected zone (P).

12. Method for providing a hypoxic air atmosphere in at least one protected zone (P) in a system according to one of the preceding claims comprising the steps of:

- providing compressed fresh air using the at least one compressor (1);

- feeding the compressed fresh air to the least one cabinet (C) arranged downstream of the at least one compressor (1), wherein the air inlet pressure is monitored by at least one, preferably at least two pressure switches (6a),

- separating the compressed fresh air into oxygen-depleted air and oxygen-enriched air in the at least one air separation device (8) arranged downstream in the cabinet having one inlet for the compressed fresh air, one first outlet for the oxygen-depleted air and one second outlet for oxygen-enriched air;

- feeding the oxygen-depleted air out of the cabinet (C) into the at least one protected zone (P) comprising at least one, preferably at least three oxygen sensors,

- wherein the at least one pressure switch (6a) is monitored by a first functional safety related system (S1), and

- wherein each of the oxygen sensors in the protected zone is monitored by a second functional safety related system (S2) for oxygen control in the protected zone.

13. Method according to claim 12, characterized in that the first and second functional safety related systems (S1, S2) are implemented as SIL rated controller components, in particular in form of SIL cards.

14. Method according to claim 12 or 13, characterized in that the air in the at least one protected zone P is completely or partly replaced by the hypoxic air atmosphere having an oxygen content between 10 and 18%, preferably between 12 and 16%.

15. Method according to one of the claim 12 to 14, characterized in that the nitrogen content of the hypoxic air in the at least one protected zone is below 88%, preferably below 85%.

Drawing