FR2751894A1 - Dry compressed gas production, e.g. compressed air for medical use - Google Patents

Abstract

Humid gas or a gas mixture such as air is compressed and then passed along at least one open-ended tube (2), so that the water vapour content diffuses outwards through the permeable membrane forming the tube wall into an enclosing housing (1) while dry gas is extracted from the downstream end of the tube. Periodically accumulated water vapour is flushed from the housing by a flow of dry gas from inlet (7) to outlet (8). Also claimed are (i) air of a stated purity produced by the above process; and (ii) a housing (1) enclosing tubes (2) whose walls are permeable to water vapour, with a main inlet (3) and outlet (5) communicating with the respective ends of the tubes and an inlet (7) and outlet (8) for flushing the space outside the tubes with dry gas.

Description

PROCESS FOR PRODUCING DRY COMPRESSED GAS, IN PARTICULAR
DRY COMPRESSED AIR, DEVICE FOR ITS IMPLEMENTATION AND
ITS APPLICATION FOR MEDICAL USE.

 The present invention relates to a process for manufacturing dry compressed gas, in particular dry compressed air, and the device for implementing such a process. Dry compressed air can be used for human respiration.

 Devices are known for compressing air at pressures varying from 3 to 15 bar. This compressed air is then dried for industrial use.

In a known manner, a compressed gas or compressed air is dried by one of the following methods:
The refrigeration drying process involves cooling the gas or air containing water vapor to a temperature at which the water can condense. According to this continuous process, the condensed water is then removed from the system in liquid form. By this process, the dew point that can be obtained is 4 "C. The device necessary to carry out this process on an industrial scale is very bulky and consumes a lot of energy. In addition, this process does not allow obtain air with dew points below O "C.

 Another method used is the adsorption method. To do this, certain types of zeolites or other adsorbents are used, such as silica gel or activated alumina, which are materials in the form of fine particles and having a large active surface.

 According to this process, the gas, the gas mixture or the air which must be dried, is introduced into a first column or a tower containing the adsorbent material. The water in the air is adsorbed and the material becomes charged with water vapor. At the same time, a second column of the same type is regenerated. Pipes, valves and control systems make it possible to interrupt or restore the circulation between the two columns. Then, we repeat the process. Because two pressure columns, valves and control systems are used, adsorption dryers are complex and expensive.

 The regeneration of the adsorbent material can be done in several ways. A first method consists in increasing the temperature of the adsorbent bed, during the regeneration phase, so as to desorb the humidity. Another method for regenerating the adsorbent material is to subject it to an abrupt low pressure during the regeneration phase.

 Dew points can be obtained with these processes under pressure from -20 "C to -40" C, with zeolites or other adsorbents.

However, this results in energy losses.

 The air can also be dried by cooling it by circulation in a refrigeration circuit, for example using Freon or C.F.C.

 Thus, the methods of drying compressed gas, mixing compressed gases or compressed air, of the prior art, have many drawbacks.

 In addition, dry compressed air is commonly used in hospitals, clinics, laboratories, etc., in particular for human respiration.

This compressed air is obtained by mixing oxygen and liquid nitrogen under pressure, in proportions close to those of air 78.22. However, it is not a natural mixture and therefore the proportions of the various constituents of the air are not respected. In addition, to make the mixture, it is necessary to have special and expensive facilities.

 The invention aims to overcome these drawbacks.

 A first object of the invention is to provide a simple method for obtaining dry compressed air.

 A second object of the invention is to provide a device for drying compressed air which does not require periodic maintenance.

Another object of the invention is to provide a device for drying compressed air which does not require refrigerating gas such as Freon or
CFC

 A fourth object of the invention is to provide a device having no electrical connection, which makes it possible to use it in an explosion-proof zone.

 Another object of the invention is to provide a method of drying the compressed air which gives immediate obtaining of the dew point.

 A final object of the invention is to provide dry compressed air which can be used for human respiration.

To this end, the invention relates to a process for manufacturing a compressed compressed gas or mixture of gases, such as the following steps are carried out:
- the gas or mixture of wet gases is compressed,
the gas or mixture of gases, compressed and wet, is circulated from the inlet of at least one hollow tube, the wall of which is made of a membrane permeable to water vapor, towards the outlet of the tube, the hollow tube being placed in an enclosure, the water vapor passing through the membrane from the inside of the tube towards the outside of the tube, to accumulate in the enclosure,
- the gas or mixture of compressed and dry gas is recovered at the outlet of the tube,
- Periodically expels the water vapor accumulated in the enclosure by circulating part of the gas or mixture of dry gas from inside the enclosure to the outside, and outside the tube.

 Preferably, the compressed gas or mixture of gases is filtered, after drying, to remove carbon dioxide, sulfur and nitrogen monoxide and carbon.

 The method according to the invention is such that the gas or compressed gas mixture is filtered, before drying, to remove the dust.

 According to one embodiment of the invention, the compressed gas or mixture of gases is sent, after drying, to a pressure tank and the mixture is homogenized.

 Compressed gas is air.

The device according to the invention comprises a drying enclosure in which parallel hollow tubes are placed, the wall of the tubes consisting of a membrane permeable to water vapor, an inlet of moist compressed air at one end of the tubes , a dry compressed air outlet at the opposite end of the tubes, a dry air inlet into the enclosure,
Dry air circulating in the enclosure, outside the tubes, and a humid air outlet from the drying enclosure.

 The device according to the invention comprises dust filters, optionally an oil separator filter, placed upstream of the enclosure and traps of carbon and sulfur dioxides, nitrogen and carbon monoxides, downstream of the enclosure. drying.

 According to a second embodiment, the device according to the invention comprises a gas homogenizer placed downstream of the drying enclosure.

 According to a third embodiment of the invention, the device comprises an air compressor upstream of the dust filters operating without lubricant.

 The following description, with reference to the accompanying drawings by way of nonlimiting examples, will make it possible to understand how the invention can be put into practice.

 Figure 1 is a schematic view of the enclosure comprising the hollow tube or tubes.

 Figure 2 is a schematic view of a first embodiment of the device according to the invention.

 Figure 3 is a schematic view of a second embodiment of the device according to the invention.

 Figure 4 is a schematic view of a third embodiment of the invention.

 embodiment of the device according to the invention.

 Figure 5 is a front view of the device according to the invention, according to the second embodiment.

 Figure 6 is a top view of the device according to the invention, according to the second embodiment.

 Figure 7 is a sectional view of a filter.

 In Figure 1, there is shown an enclosure (1) in which is placed one or more hollow tubes (2). These hollow tubes (2) or hollow fibers have a wall which is a membrane permeable to water vapor. The tubes (2) are placed parallel to each other. The enclosure (1) comprises a supply line (3) which is connected to the ends (4) of the tubes (2) and an outlet line (5) which is connected to the opposite ends (6) of the tubes (2) . The outlet pipe (5) comprises a branch (7) of reduced size compared to the outlet pipe and which opens into the enclosure (1), outside the tubes or fibers (2). Finally, the enclosure (1) has a lateral outlet (8).

The enclosure (1) shown in Figure 1 is a membrane dryer, the operation of which is as follows:
The compressed gas, or the compressed gas mixture enters through the supply line (3), into the tubes (2). Preferably, the gas mixture is compressed air. This compressed air can, for example, be at a pressure of between approximately 8 and approximately 12 bar, preferably between 9 and bar.

 Compressed air enters the supply line (3) in a direction according to Arrow F1. Compressed air enters the tubes (2) through their ends (4) which are connected to the supply line (3). Compressed air moves from the ends (4) of the tubes (2) to the opposite ends (6) of the tubes (2). During the movement of the compressed air, the water molecules pass through the walls of the tubes (2), these walls being permeable to water vapor and impermeable to other gases.

Water vapor is therefore stored inside (9) of the enclosure (1).

 The dry compressed air exits through the outlet pipe (5), in the direction of Arrow F2.

 When the interior (9) of the enclosure (1) is saturated with water vapor, part of the dry air bypassed, through the outlet pipe (5), and the bypass (7), at the inside (9) of the enclosure (1), in the direction of the arrow F3 evacuates the water vapor.

 The dry air inside (9) of the enclosure (1), but outside the tubes (2), saturates with water vapor and exits through the lateral pipe (8). Because the walls of the tubes are permeable in one direction to water vapor, that is to say from the inside of the tubes (2), towards the outside of the tubes (2), but impermeable in the opposite direction, that is to say from the outside of the tubes (2), towards the inside, the passage of dry air in the enclosure (9), makes it possible to evacuate the water vapor or the water inside (9) of the enclosure.

 FIG. 2 shows an embodiment of the invention, this embodiment being the simplest. The device shown schematically in Figure 2 can be used, for example in a hospital or clinic which is already equipped with an air compressor. Two cases can arise: the compressor in the hospital or clinic is an oil compressor or else a compressor of another kind.

 When the compressor is an oil compressor, it supplies compressed air comprising oil. This is the reason why, before reaching the enclosure (1), the compressed air passes through an oil separator (10).

 When the compressor is of another kind than an oil compressor, the compressed air not comprising oil, the device according to the invention does not comprise an oil separator.

 The device according to the invention comprises one or more dust filters. For example, it includes a micron filter (11) of 1 micron and a submicron filter (12) of 0.01 micron, upstream of the drying chamber (1).

 At the outlet of the enclosure (1), the device according to the invention comprises a catalyst filter (13) making it possible to transform carbon monoxide into carbon dioxide, then downstream a retention filter (14) making it possible to retain the carbon dioxide and, still downstream, a deodorization filter (15) with activated carbon and an antibacterial filter (16) of 0.01 micron.

 The catalyst filter (13) is filled with black “HOPCALITE” granules of dimensions between 1 and 3.5 mm and the average composition of which is 57% manganese oxide, 13% copper oxide, 30% manganese carbonate. The apparent density of the mixture is 1 and this filter is regenerated during the periods when the compressor does not work. The granules are arranged in the body of the filter (13) which is identical in terms of constitution to that (140) shown in Figure 7. The cylindrical body (141) ends at one end by a shoulder (1410) against which comes to bear a perforated grid (145) and above this grid a plug (142) is crimped in the cylindrical body (141) by the upper ends of the cylindrical body folded over the plug (142).

This plug has holes (143, 144) and a threaded blind hole allowing it to be fixed on the associated filter caps (139, 149, 159, 169). The other end of the cylindrical body also has a shoulder (1411) against which abuts a perforated grid (146) held against the shoulder by a circlip (148) which is received in a groove in the body (141). The empty space of the filter (147) is filled with granules of either catalysts, molecular sieves or activated carbon depending on the type of filter. The carbon dioxide retention filter (14) is filled with Siliporite G5 molecular sieves which are synthetic zeolites, of crystal structure type X, in sodium form, which have a network of pores with an effective diameter of 10 angstroms. These marbles
Siliporite G5 have a particle size of 1.6 to 2.5 mm. Finally, the filter (15) is filled with granulated activated carbon, based on activated coconut shells, with steam and having a particle size at 90% of between 2 and 5 mm. The size of the filters is calculated according to the flow rate of the installation which can be 8 m3 / h, 1 9m3 / h, 30m3 / h, 50 m31h, for example. Depending on these flow rates, the catalysis filter, the retention filter or the deodorization filter, consists of a container whose volume is calculated so that it can contain the weights of granules corresponding to each of the properties of filtering according to the desired flow for the installation. The table below gives examples of calculations of weight of granules to be contained by the respective filters according to the flow rates of the installation.

DEODORIZATION RETENTION CATALYSIS
Q m3 / h Weight Kg Weight Kg Weight Kg
8 0.112 0.20 0.06
19 0.266 0.475 0.14
30 0.420 0.750 0.225
50 0.700 1.25 0.375
Average 0.014 0.025 0.0075
in grlm3
Thus for 8m3 / h we must have for the catalysis filter a volume allowing to contain a weight of "HOPCAL1TE" of 112 gr. Given this table, it is necessary to provide a filter element container allowing to contain between 0.010 to 0.017 gr of HOPCALITE constituting the catalyst per m3 / h of air treated by the installation, 0.02 to 0, 03 gr of molecular sieve per m3 / h of air treated by the retention filter and 0.005 to 0.010 gr of activated carbon per m3 / h of air treated by the deodorizing filter.

 In Figure 3, there is shown another embodiment of the device according to the invention. This device includes a homogenizer (17).

Indeed, the air which is compressed is atmospheric air, and depending on the quality of the ambient air, the components of the compressed air can vary.

Thus, thanks to the homogenizer (17), a dry compressed air is obtained which is of substantially constant composition.

 The homogenizer (17) includes a pressure switch (18). The device according to the invention is such that when the pressure of dry compressed air drops in the homogenizer (17), the pressure switch trips and starts the compressor. Thus, the device according to the invention operates only according to demand, namely, when no dry compressed air is pumped at the outlet (19), the compressor is stopped and it does not triggers only when dry compressed air is pumped. A non-return valve (20) closes the dry compressed air supply line to the homogenizer (17).

 The device shown in Figure 4 is a complete device that can be supplied to a hospital or clinic that is not already equipped with a compressor. This group is compact and autonomous. This device comprises, upstream of the enclosure (1), a micron filter (11), a submicron filter (12), and downstream of the drying enclosure (1), a catalyst filter (13), a retention (14), a deodorizing filter (15) and an antibacterial filter (16), a homogenizer (17), a non-return valve (20). The device further comprises a compressor (21) and possibly a second compressor (22), upstream of the filters (11) and (12). These compressors (21, 22) are preferably chosen without oil, which makes the oil separator unnecessary.

 In Figures 5 and 6, there is shown a device according to the invention, in front view and in top view. The homogenizer (17) has at its upper end a safety valve (23) and a pressure gauge (24) for pressure measurement. The drying enclosure (1) is placed so that its longitudinal axis is vertical. The wet compressed gas enters the filters (11, 12), via the pipe (25), according to the arrow F1 and leaves the homogenizer (17) by one or more outlet pipes (26, 27) according to the arrows F2 , F'2.

 The device according to the invention can be placed on a support (28) on which the various members are fixed.

 With this device, you obtain dry compressed air which meets AFNOR NFS 90140 and NFS 90155 standards and even which can be of superior quality.

 8 m3 / h to 400 m3 / h of dry compressed air can be produced at pressures from 10 to 12 bar.

If we compare the quality of the dry compressed air obtained with the device according to the invention, with the AFNOR NFS 90140 standard, we have the following results:
AFNOR NFS Standard Device according to
90140 I'invention Oil content in mglm3 0.1 <0.01
Water vapor in g / m3 0.09 0.09 = - 42 C
CO content in ppm <5 <2
CO2 content in ppm <350 <300 SO2 content in ppm 16.10 3 <16.10 3
25.5 content. 10-3 <25.5. 10-3 nitrogen oxide per ppm
The dry compressed air obtained with the device according to the invention therefore has a quality superior to the AFNOR standard since the contents of oil, water vapor, carbon monoxide, carbon dioxide, sulfur dioxide, monoxide and dioxide of nitrogen are lower.

Claims (10)

 1. Method for manufacturing a gas or mixture of gases, compressed, dry, characterized in that the following steps are carried out:  - the gas or mixture of wet gases is compressed,  the gas or mixture of gases, compressed and wet, is circulated from the inlet of at least one hollow tube, the wall of which is made of a membrane permeable to water vapor, towards the outlet of the tube, the hollow tube being placed in an enclosure, the water vapor passing through the membrane from the inside of the tube towards the outside of the tube, to accumulate in the enclosure,  - the gas or mixture of compressed and dry gas is recovered at the outlet of the tube,  - Periodically expels the water vapor accumulated in the enclosure by circulating part of the gas or mixture of dry gas from inside the enclosure to the outside, and outside the tube.  2. Method according to claim 1, characterized in that the gas or compressed gas mixture is filtered before drying, to remove dust.  3. Method according to claim 1 or 2, characterized in that the gas or compressed gas mixture is filtered, after drying, to remove the oxides of carbon and sulfur.  4. Method according to one of the preceding claims, characterized in that the gas or compressed gas mixture is sent, after drying, to a pressure tank and the mixture is homogenized.  5. Method according to one of the preceding claims, characterized in that the compressed gas is air.  6. Device for implementing the method according to one of the preceding claims, characterized in that it comprises a drying enclosure (1) in which are placed hollow tubes (2) parallel, the wall of the tubes being consisting of a membrane permeable to water vapor, an inlet (3) of wet compressed air at one end (4) of the tubes (2), an outlet (5) of dry compressed air at the opposite end (6) tubes (2), an inlet (7) of dry air into the enclosure (1), the dry air circulating in the enclosure (1), outside the tubes (2), and a humid air outlet (8) from the drying enclosure (1).  7. Device according to Claim 6, characterized in that it comprises dust filters (11, 12), possibly an oil filter (10), placed upstream of the enclosure (1), traps (13 , 14,15) carbon dioxide and sulfur, and an antibacterial filter (16) placed downstream of the drying chamber.  8. Device according to one of claims 6 and 7, characterized in that it comprises a homogenizer (17) of air, placed downstream of the enclosure (1) for drying.  9. Device according to one of claims 6 to 8, characterized in that comprises one or more air compressors (21, 22), upstream of the dust filters operating without lubricant.  10. Dry compressed air, obtained by the method according to one of claims 1 to 5, characterized in that its pressure is between 8 and 12 bar, its oil content is less than 0.01 mglm3, its content in water vapor is 0.09 gim3, = - 42 "C, its CO content is less than 2 ppm, its CO2 content is less than 300 ppm, its SO2 content is less than 16.10 3 ppm and its content in nitrogen monoxide / dioxide is less than 25.5.10-3ppm.