CH659698A5 - METHOD FOR PRE-COOLING A PLANT FOR GENERATING LOW TEMPERATURE GAS, AND DEVICE FOR IMPLEMENTING THE METHOD. - Google Patents

Description

The present invention relates to a method for pre-cooling a plant for the production of low-temperature gas, wherein in the normal process this first gas to be cooled is fed under pressure into a first gas path, which leads successively via a dehumidifier, a dryer and a heat exchanger, and in which a second Gas in the form of a cryogenic liquid gas is fed to a second gas path, which leads from the heat exchanger to the dehumidifier for the purpose of heat exchange between the first gas and the second gas, in order to cool the first gas to low temperature, and a device for carrying out the method.

Cryogenic gases, in particular cryogenic air, are used, for example, for medical treatments, the machining of metals and the like.

Recently, low temperature gas, specifically cryogenic gas, with temperatures no higher than -100 ° C has been used to cool workpiece surfaces and cutting tool edges during metal cutting, or to cool rheumatic parts of the body in medical cryogenic treatment exercises. As a cryogenic gas e.g. a cryogenic liquefied gas, e.g. liquid nitrogen can be used; however, it is not conducive to human health to let such a gas escape into its surroundings.

Therefore, a method has conventionally been adopted in which atmospheric air is taken and cooled using a cryogenic liquefied gas such as liquid nitrogen or the like, whereupon the air of predetermined low temperature is directed to where the cryogenic treatment is being carried out.

The present invention aims to remedy the disadvantages - condensation in the heat exchanger - in the pre-cooling of plants for the production of low-temperature air. It is also worth mentioning that the following objects of the invention are achieved.

Creation of a method and a device for the pre-cooling of a plant for the production of low-temperature air, by means of which a rapid and low-water pre-cooling of the dryer can be achieved, io creation of a method and a device for the pre-cooling of a plant for the production of low-temperature air, in which the System can be quickly and effectively cooled to a temperature that is necessary for normal operation or low-temperature air generation. 15 Creation of a method and a device for the pre-cooling of a plant for the generation of low-temperature air, in which the water absorption capacity of a dryer is improved, whereby the maximum amount of air which can be treated in normal operation is increased 20.

Creation of a method and a device for the pre-cooling of a plant for the generation of low-temperature air, the method preferably being applied to plants which air is led under low pressure, 25 and in which the dehumidifying effect on the dehumidifier is low.

Creation of a method and a device for pre-cooling a plant for the generation of low-temperature air, with the help of which the energy costs for the plant 3o can be reduced.

In this sense, a method for precooling a plant for generating low-temperature air is proposed, in which a first gas e.g. Air under pressure is successively fed to a dehumidifier, a dryer and a heat exchanger, and in which a cryogenic, second gas, a liquefied gas, is fed to a flow system which leads to the dehumidifier via the heat exchanger in order to exchange heat between air under pressure and liquefied petroleum gas while cooling the air under 40 pressure to obtain cryogenic air. This procedure includes the following steps:

- stopping the supply of the first gas.

- Feed the second gas into the second gas path and via the heat exchanger into the dehumidifier.

45 - Subsequently supplying the second gas from the outlet of the dehumidifier into the first gas path in order to pass the second gas in succession through the dehumidifier, the dryer and the heat exchanger.

According to a further aspect of the present invention, a device for the pre-cooling of a plant for the generation of low-temperature air is proposed, which is designed according to the aforementioned method, in which the outlet of the second gas path at the dehumidifier via a valve with the inlet of the first Gaswe-55 is connected to the dehumidifier.

The invention, defined in claim 1, is subsequently explained, for example, with the aid of a drawing which shows the flow diagram of a system according to the invention.

60 In the known method, a first gas, e.g. Air, through an air delivery arrangement 1, e.g. a blower, a compressor or the like is supplied. It passes through a valve 2 and a line 3 into a dehumidifier 4 which is cooled to a temperature close to zero degrees 65, for example +1 ° C., at which moisture contained in the air cannot freeze. Water falls below the dew point temperature of the air in the dehumidifier 4, and this falls out of the air. It will

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discharged via a line 5 and a valve 6. The dehumidified air is then fed to a heating element 8 which is activated exclusively when the system is regenerated. Then it flows through a line 9 into a dryer 10 which contains a drying substance such as alumina gel, silica gel or the like. In the dryer 10, the majority of the water vapor still present is removed from the air and the dried air is then fed via lines 11 and 12 to a heat exchanger 13, which is likewise mixed with a cryogenic, liquefied second gas, e.g. liquid nitrogen (boiling point - 196 ° C), is fed. The air and the second gas exchange heat in the heat exchanger 13. This is thereby cooled to a predetermined low temperature, then flows out through a line 14 and is supplied to the place of use via a valve 15. Lines 3, 7, 9, 11, 12 and 14 thus form the airway. The reference numerals 16 and 17 denote thermometers which are installed in the air path in the region of the outlet of the dehumidifier 4 and the outlet of the heat exchanger 13.

On the other hand, the coolant is in the form of the second gas for the air to be cooled, for example a cryogenic, liquid gas, e.g. liquid nitrogen, taken from a reservoir (not shown) and fed to the heat exchanger 13 via lines 18, 19, a valve 20 and a line 21. The amount of coolant supplied is determined by correspondingly controlling the passage of the valve 20 in accordance with the temperature in the thermometer 17 in order to keep the temperature of the air which is led to the destination via the line 14 and the valve 15 within certain temperature limits. After the liquid nitrogen has cooled the air in the heat exchanger 13 and thereby evaporates, it reaches the dehumidifier 4 via a line 22 and a line 23 for cooling the air. Thereupon the gaseous nitrogen is released into the atmosphere via a line 24 and a valve 25 emanate. The lines 19, 21, 22, 23, 24 thus form the path for the gas. It is necessary to keep the temperature of the dehumidifier 4 at approximately + 1 ° C as previously described. If the amount of gaseous nitrogen flowing through lines 22 and 23 becomes too large and there is a tendency for the dehumidifier 4 to be cooled to a temperature below + 1 ° C., excess nitrogen becomes available by opening a valve 27 of line 26 and a main line 35 is blown off into the atmosphere. If, however, the flow rate of the gaseous nitrogen flowing through line 23 is too low and the temperature at the dehumidifier 4 threatens to rise above the value of +1 ° C., liquid nitrogen is released by opening a valve 29, which on the one hand is connected to line 18 is connected from the reservoir (not shown) and, on the other hand, leads into line 22 via a bridging line with lines 28 and 30, into which dehumidifier 4 reaches. The temperature at the dehumidifier 4 is thus controlled in accordance with the temperature at the thermometer 16 by opening or closing the valves 27 and 29 accordingly. The thus prepared air of a predetermined low temperature, usually below −100 ° C., is removed via line 14 and valve 15.

During the generation of the low-temperature air, the dryer 10 absorbs water vapor from the air, the remaining water portion of which is essentially condensed and frozen when it flows through the heat exchanger 13. A regeneration cycle is therefore necessary in order to remove water and ice accumulated in the dryer 10 and in the heat exchanger 13 after a predetermined operating time of the system. In this regeneration step, the supply of liquid nitrogen is stopped by closing the valves 20 and possibly 29. The air, which by means of the blower 1 through the

Air flows, is heated by putting the heater 8 into operation, whereupon the air is supplied to the dryer 10 for heating it. The air then flows out via line 11, branches, and a part thereof flows into the atmosphere via line 31 and valve 32. The remaining air is fed via line 12 to the heat exchanger 13, where it heats it up and melts ice deposited therein. The water is discharged through the air and flows out into the atmosphere via lines 14 and 33, a valve 34 and line 35.

After the aforementioned regeneration has ended, the system can be started again. However, in order to generate air of a predetermined low temperature, it is necessary to pre-cool the system for a certain period of time. For this purpose, liquid nitrogen is fed through the lines 21 and 23 to the heat exchanger 13 and the dehumidifier 4, while the air, which is fed in with the aid of the blower 1 and flows through the airway, is cooled and by opening the valve 34 with the valve 15 closed in the Air is blown off. After the thermometer 17 shows that the temperature of the air flowing through the valve 34 has dropped to the predetermined temperature due to the precooling for a sufficiently long period of time, the removal of low-temperature air by closing the valve 34 and opening the valve 15 again started.

In the cryogenic air generation system described above, while the system is being pre-cooled, air at a temperature above normal temperature is fed directly into the dryer 10. Therefore, this large amount of moisture cannot be absorbed sufficiently in the supplied air, so that these known systems have the disadvantage during pre-cooling that a large part of the water condenses in the heat exchanger 13.

Accordingly, it is an object of the present invention to remedy the disadvantages mentioned in the pre-cooling of plants for the generation of low-temperature air.

The method according to the invention for precooling the system is subsequently explained, for example.

After the blower or the compressor 1 has stopped, liquid nitrogen is sent by opening the valve 20 via the line 21 into the heat exchanger 13, where it evaporates (at about -196 ° C.). The gaseous nitrogen is now fed through lines 22 and 23 to the dehumidifier 4 in order to cool the latter. Then the nitrogen gas from the dehumidifier 4 is blown off into the atmosphere via line 24 and not via valve 25. For this purpose, it is led into a second line 101 and then fed via a valve 102, the latter being opened only for this precooling operation, into line 3, which forms part of the airway, with valve 2 closed. The nitrogen then flows over the air, i.e. through the dehumidifier 4 and the dryer 10 into the heat exchanger 13. From there it is blown off from the line 14 via the lines 33 and 35 into the atmosphere by opening the valve 34 with the valve 15 closed. This operation continues until the temperature of the dehumidifier 4 has dropped to + 1 ° C. The nitrogen gas that is blown into the airway via line 101 is vaporized, formerly liquid nitrogen. It therefore contains little water vapor, since the dew point of this gas is not higher than -70 ° C (water content 2.5 PPM). Thus, the pre-cooling is carried out very gently in the sense that it only slightly loads the dryer 10 with regard to the amount of water. It also has no disadvantages, e.g. the condensation of water in the heat exchanger 13. Furthermore, the dryer 10 can be pre-cooled in a simple manner, since it generates little heat of absorption during such a pre-cooling process. As soon as the temperature in the dehumidifier 4 has dropped to + 1 ° C, the valve

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102 closed and the blower 1 started again to supply air in normal procedures.

During the aforementioned pre-cooling operation, part of the nitrogen gas which is conducted from the dryer 10 into the line 11 can be blown off into the atmosphere by opening the valve 32 via the lines 31 and 35, whereby the pre-cooling of the dryer 10 can be accelerated. As can be seen from the preceding description, the disadvantage of the prior art according to which water condenses in the heat exchanger 13 during the pre-cooling operation is eliminated according to the invention, and the dryer 10 can be gently pre-cooled due to the very small amount of water vapor in the nitrogen. The plant according to the present invention can be quickly and effectively cooled to the temperature necessary for normal operation. In particular, the present invention is suitable for use on a low-temperature system, which has an air supply element 1 with a deep

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Supply pressure, corresponding to a water column of some 10 mm, e.g. a blower, works. In such a system, the effect is particularly good in the precooling according to the invention, since in the known method when

5 blowers fail to produce more water than compressors. The dehumidification effect (loss of water) in the dehumidifier 4 for the method according to the invention is therefore still relatively less than with compressors. As can be seen from the Mollier i-x diagram for air / water vapor.

io, the dew point temperature rises with increasing pressure for a certain water content x. It is m.a.W. at higher pressure, the dew point temperature tends to reach during the cooling process and therefore more water vapor condenses when cooling to a predetermined temperature

15 than at lower total pressure. The present invention can also save energy costs because the air supply member does not run during the pre-cooling of the system.

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1 sheet of drawings

Claims (4)

659 698 1. Method for precooling a plant for the production of low-temperature gas, whereby in the normal process this first gas to be cooled is fed under pressure (1) into a first gas (3), which is successively used via a dehumidifier (4), a dryer (10) and a heat exchanger (13), and in which a second gas in the form of a cryogenic liquid gas is fed to a second gas path (18) which leads from the heat exchanger (13) to the dehumidifier (4) for the purpose of heat exchange between the first gas and the second gas in order to cool the first gas to low temperature, characterized in that the following process steps are provided for pre-cooling the system: - stopping the supply (1) of the first gas, - supplying the second gas into the second gas path (18) and via the heat exchanger (13) into the dehumidifier (4), - Subsequent supply of the second gas from the outlet of the dehumidifier (4) in the first gas path in order to pass the second gas in succession through the dehumidifier (4), the dryer (10) and the heat exchanger (13). 2. The method according to claim 1, characterized in that at least part of the second gas at the outlet of the dryer (10) is blown off directly into the atmosphere. 2nd PATENT CLAIMS 3. Device for carrying out the method according to claim 1, characterized in that the outlet (24) of the second gas path on the dehumidifier (4) is connected via a valve (102) to the inlet (3) of the first gas path on the dehumidifier (4) . 4. The device according to claim 3, characterized in that the output (11) of the first path on the dryer (10) via a valve member (32) is connected to the atmosphere.