GB2090160A

GB2090160A - Process and Apparatus for Separating a Mixed Gas Such as Air

Info

Publication number: GB2090160A
Application number: GB8137078A
Authority: GB
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Ltd
Priority date: 1980-12-25
Filing date: 1981-12-09
Publication date: 1982-07-07
Also published as: GB2090160B; DE3150624A1; FR2497119A1

Abstract

The process and apparatus is of the kind where the mixed gas is compressed (28) and subsequently cooled (60) and then fed into an adsorption tower (1, 2) to adsorb one constituent gas in said mixed gas, and extract the other constituent gas. An object of the invention is to provide such a process and apparatus in which energy is efficiently recovered from the unadsorbed constituent gas and in which the cooling requirement for the mixed gas to cool it down to adsorption temperature is significantly reduced. The invention is mainly characterised in that heat exchange is effected (61) between the unadsorbed constituent gas (58) extracted from said adsorption tower and incoming mixed gas, so that the unadsorbed constituent gas is heated thereby, whilst the raw mixed gas is cooled, and in that the unadsorbed constituent gas is fed for adiabatic expansion (67) to recover pressure energy therefrom. The heat exchange may be before and/or after the compression which may be aided by the energy recovered from the unadsorbed gas by using a turbine. <IMAGE>

Description

SPECIFICATION Process Land Apparatus for Separating Mixed Gas by Adsorption The present invention relates to a process and apparatus for separating mixed gas in which any one particular gas in the mixed gas such as, for example, air consisting of oxygen and nitrogen, or a mixture of air and moisture, is separated by causing it to be absorbed by an adsorbent.

Referring to Figure 1 of the accompanying drawings, in one conventional process for separation by adsorption of 02 from, N2, natural mordenite or synthetic zeolite 5A is used as an adsorbent and made to preferentially adsorb an N2 gas constituent. In this conventional process header pipes 3, 4, 5 and 6 are mounted on the opposite sides of two adsorption towers 1 and 2. The header pipe 3 is connected to an air feed pipe 8 having a valve 7, an air discharge pipe 10 having a valve 9, and an N2 gas delivery pipe 12 having a valve 11. Likewise the header pipe 5 is connected to an air feed pipe 14 having a valve 13, an air discharge pipe 16 having a valve 15, and an N2 gas delivery pipe 1 8 having a valve 17.The header pipe 4 is connected to an 02 gas delivery pipe 20 having a valve 19, and an 02 gas feed pipe 22 having a valve 21, and likewise, the header pipe 6 is connected to an 02 gas delivery pipe 24 having a valve 23, and an 02 gas feed pipe 26 having a valve 25. The air feed pipes 8 and 14 are connected to a main air feed pipe 29 which is in communication with a compressor 28 driven by a motor 27. The air discharge pipes 10 and 16 are connected to a main air discharge pipe 30, and the N2 gas delivery pipes 12 and 18 are connected to a main N2 gas delivery pipe 33 which is in communication with a vacuum pump 32 driven by a motor 31.The 02 gas delivery pipes 20 and 24 are connected to a main 02 gas delivery pipe 35 having a reducing valve 34, whilst the 02 gas feed pipes 22 and 26 are connected to a main 02 gas feed pipe 37 which is branched from the main 02 gas delivery pipe 35 on the upstream side of the reducing valve 34 and has its own valve 36.

The adsorption towers 1 and 2 are respectively filled with an adsorbent for adsorbing an N2 gas.

Air is pressurized by the compressor 28 driven by the motor 27 and thus flows through the main air feed pipe 29. It is now assumed that an adsorption step is effected in the adsorption tower 1 and a desorption step is effected in the adsorption tower 2.

The valves 7 and 19 on the opposite sides of the adsorption tower 1 are opened, whilst the valves 9, 11, and 21 are closed. The compressed air passed through the main air feed pipe 29 flows through the air feed pipe 8, enters into the header pipe 3 via the valve 7 and thence into the adsorption tower 1.

When the compressed air enters and passes through the adsorption tower 1, N2 gas in the air is preferentially absorbed by the absorbent, and residual 02 gas is concentrated and extracted through the header pipe 4. The 02 gas passes through the valve 19 into the main 02 gas delivery pipe 35, via the 02 gas delivery pipe 20, and passes through the reducing valve 34 to be delivered to other processing equipment, while maintaining the adsorption tower 1 at a predetermined absorption pressure. Meanwhile a desorption step is effected in the other adsorption tower 2. Thus, initially, the valve 1 5 is opened and the other valves 13, 1 7, 23, 25, and 36 are closed.By opening the valve 15, air containing predominantly an O, gas in the adsorption tower 2 is extracted, and is passed through the valve 15, air discharge pipe 16 and main air discharge pipe 30 and then discharged. When the pressure in the adsorption tower 2 has been reduced to a predetermined pressure by the discharge of air, the valve 1 5 is closed, then the valve 1 7 is opened and the motor 31 actuated to extract the air in the adsorption tower 2 through the main-N2 gas delivery pipe 35, N2 gas delivery pipe 18 and valve 17 for further reducing the pressure in the adsorption tower 2, thereby the N2 gas adsorbed by the adsorbent is desorbed.After the N2 gas has been desorbed and delivered from the adsorption tower 2, the valve 1 7 is closed, while the valves 36 and 25 are opened; thereby a part of the compressed 02 gas flowing through the main 02 gas delivery pipe 35 is made to pass through the main 02 gas feed pipe 37, 02 gas feed pipe 26 and header pipe 6 to be fed into the adsorption tower 2 to raise the pressure of the latter.

According to conventional processes such as described above, energy is required for compressing the air and for cooling the air when compressed, and no provision is made for effectively recovering such energy.

An object of the present invention is to provide process and apparatus for separating mixed gas by adsorption in which recovery of energy can be achieved effectively.

In accordance with the invention, such process and apparatus are characterised by having features as set out in the appended patent Claims.

In order that the present invention will be readily understood and the various features thereof made apparent a number of embodiments will now be described, with reference to the accompanying drawings in which:~ Figure 1 is a block diagram of one form of conventional apparatus for carrying out a process for separating air by adsorption, and Figures 2 to 9 are block diagrams of eight embodiments of process and apparatus in accordance with the invention for separating air by adsorption.

Referring to Figure 2 in a first embodiment, the apparatus is largely based on that used for the conventional process described above, and like parts have been given the same reference numerals.

Thus, the process uses adsorption towers 1 and 2 and headers 3 to 6 as described above. Also as described above the header 3 is connected to pipes 8 and 10 having respective valves 7 and 9.

However, in this embodiment the 02 gas delivery pipe having the valve 11 is referenced 51. Likewise the header 5 is connected to pipes 14 and 1 6 having respective valves 13 and 1 5, but the 02 gas delivery pipe having the valve 17 is referenced 52 and is branched into a main 02 gas delivery pipe 57, which latter connects to the vacuum pump 32. The header pipe 4 is connected to an N2 gas delivery pipe 53 having a valve 19 and an N2 gas feed pipe 54 having a valve 21, and likewise, the header pipe 6 is connected to an N2 gas delivery pipe 55 having a valve 23 and an N2 gas feed pipe 56 having a valve 25. The N2 gas delivery pipes 53 and 55 are connected to a main N2 gas delivery pipe 58, whilst the N2 gas feed pipes 54 and 56 are connected to a main N2 gas feed pipe 59 having a valve 36 branched from the N2 gas delivery main pipe 58.In the main air feed pipe 29 between the compressor 28 and the feed pipes 8 and 10 are disposed in sequence in the flow direction a heat-exchanger 61, a water-cooled after-cooler 60, a drain-separator 63, a dryer 64 and a refrigerator 42. The down-stream end of the N2 gas delivery main pipe 58 is connected to a refrigerant inlet of the heat-exchanger 61. A connecting pipe 66 is provided at the refrigerant outlet of the heat-exchanger 61 which communicates with the inlet of an expansion turbine 67 coupled to the motor 27, and an N2 gas delivery pipe 68 is provided at an outlet of the expansion turbine 67.

The adsorption towers 1 and 2 are filled with an adsorbent for adsorbing 02 such as, for example, zeolite in which iron having a valency of two or higher is resolved in pure Na-A type zeolite (hereinafter called Fe-Na-A type zeolite) in which iron having a valency of two or higher is resolved in pure Na-A type zeolite and a part of Na is replaced by K (hereinafter called Fe-K-Na-A type zeolite).

In use, air is compressed by the compressor 28 and flows through the air feed pipe 29. The compressed air which is at a high temperature, at first flows through the heat exchanger 61 where it is cooled, and it is then further cooled by the water-cooled after-cooler 60. It is then fed to the drain separator 63 where water condensed by cooling is removed, and thereafter it is fed to the dryer 64 where any moisture contained in the air is t loved. The air flowing out of the dryer 64 is then fed to the refrigerator 42, where the air is cooled LO an adsorption temperature.

Now it is assumed that an adsorption step is effected in the adsorption tower 1 and a desorption step is effected in the adsorption tower 2. The valves 7 and 19 of the adsorption tower 1 are opened, and the valves 9, 11 and 21 are closed. The compressed and subsequently cooled air from the main air feed pipe 29, flows through the air feed pipe 8, and the header pipe 3 via the valve 7, and enters the adsorption tower 1. 02 gas in the air is adsorbed by the adsorbent in the tower 1, and the residual N2 gas is concentrated and extracted through the header pipe 4, the N2 gas flowing via the valve 19 through the N2 gas delivery pipe 53 into the main N2 gas delivery main pipe 58. It is then fed as a refrigerant to the heat-exchanger 61.Heat exchange with air is effected in the heat-exchanger 61, so that the N2 gas is heated up and fed through the connecting pipe 66 to the expansion turbine 67, in which the N2 gas undergoes adiabatic expansion and actuates the expansion turbine 67. The N2 gas having had its pressure lowered by the adiabatic expansion in the expansion turbine 67 is delivered through the N2 gas delivery pipe 68 to further equipment. Meanwhile the other adsorption tower 2 effects a desorption step, and at first the valve 15 is opened, while the other valves 13, 1 7, 23, 25, and 36 are closed. By opening the valve 15, air containing predominantly an N2 gas in the tower 2 is extracted through the header pipe 5, and is passed via the valve 15 through the air discharge pipes 16 and 30, is then discharged.When the pressure in the tower 2 has been reduced to a predetermined pressure, for example, to about that of the atmosphere by the discharge of the air, the valve 1 5 is closed, and subsequently the valve 17 is opened. Simultaneously the motor 31 is actuated to extract the air in the tower 2 through the main 02 gas delivery pipe 57, 02 gas delivery pipe 52 and valve 17 by means of the vacuum pump 32; thus, the pressure in the adsorption tower 2 is further reduced, and thereby the 02 gas adsorbed by the adsorbent is caused to be desorbed.After the 02 gas has been desorbed and delivered from the tower 2, the valve 17 is closed, while the valves 36 and 25 are opened, so that a part of the compressed N2 gas flowing through the main N2 gas delivery pipe 58 is passed through the main N2 gas feed pipe 59, N2 gas feed pipe 56 and header pipe 6 and thence into the tower 2, thereby raising the pressure in the adsorption tower 2.

With this embodiment the amount of 02 adsorbed by the adsorbent, is about 1/5 of the total air; hence N2 and 02 can be separated from each other by adsorbing only a small amount of gas. In addition, since the amount of the N2 gas not adsorbed by the adsorbent is about 4/5 of the total air and the N2 gas occupying a major part of the air is delivered from the adsorption tower 1 to the heat exchanger 61 in which heat exchanger is effected between the N2 gas and air to heat up the N2 gas and simultaneously cool the air, the coldness possessed by the N2 gas can be effectively utilized and the recovery rate of the applied coldness is also high. In addition, since the heated N2 gas is fed to the expansion turbine 67 to drive the latter by undergoing an adiabatic expansion, and the output of the expansion turbine 67 drives the motor 27, the compression energy of the N2 gas can thereby be effectively recovered, and the recovery rate of the energy used for compression is also high.

Furthermore, owing to the fact that he N2 gas is heated up, an increase in the output of the expansion turbine 67 can be achieved.

A practical experiment for separating air into N2 and 02 through adsorption by making use of the above-described embodiment produced the following results: A separation test of air was conducted by employing apparatus in which a pressure regulating valve was provided in place of the expansion turbine 67 in the apparatus described above.

The adsorption towers 1 and 2 were filled with 300 kg of Fe-K-Na-A type zeolite having grain diameters of about 1 nim. Air having a relative humidity of 70% at 300C and at 1 ata, was compressed by the compressor 28 up to 6.5 ata. The temperature immediately after the compression was about 2400 C. The heated air at about 2400C was subjected to pretreatments such as cooling, drying, etc.

and the compressed air cooled down to 250C was fed to the adsorption tower 1 at a rate of 100 Nm3/H to cause an 02 gas to be adsorbed by the Fe-K-Na-A type zeolite. The pressure within the adsorption tower 1 at this moment was about 6 ata. From the adsorption tower 1 N2 gas was delivered having an 02 concentration of 1% or less at a rate of 57 Nm3/H.

From the adsorption tower 2 in which a desorption step was effected, O2 gas was delivered having an 02 concentration of 79% at a rate of 21 Nm3/H, and the final pressure in the adsorption tower 2 was reduced to 0.2 ata.

In this experiment, separation by adsorption of air was tested by making use of a small-scale apparatus in which compressed air was fed at a rate of 100 Nm3/H, and in this case, since the rate of gas delivery was small, actuation of the expansion turbine 67 was impossible. However, even when the apparatus is scaled up to such extent that the delivery rate of the compression air fed to the adsorption tower 1 may be increased to 1 0,000 Nm3/H so that actuation of the expansion turbine 67 becomes possible, N2 and 02 gases are obtained in the following manner, if operation is made in the same way as the above-described experiment.

That is, the gas delivered during the adsorption step is N2 gas having an 02 concentration of 1% or less and flowing at a rate of 5700 Nm3/H, and the gas delivered during the desorption step is an 02 gas having an 02 concentration of 79% and flowing at a rate of 2100 Nm3/H.

Now quantities of heat in the respective devices in the apparatus for processing compressed air at a rate of 10,000 Nm3/H will be calculated. In this instance, although the enthalpies of air, N2 gas and 02 gas are somewhat different from each other, calculation will be made assuming them to be equal to each other for the sake of simplicity.

An enthalpy difference when air at 300C and at 1 ata was subjected to adiabatic compression to 6.5 ata by means of the compressor 28 is 48 kcal/kg, and so, assuming that an efficiency of the compressor 28 is 80%, the power necessary for processing dry air at a rate of 10,000 Nm3/H (12.95x103 kg/H) is as follows: 48 kcal/kgxl2.95x103 kg/H+0.8=777x103 kcal/H.

An enthalpy difference in the case where an N2 gas at 250C and at 6 ata delivered from the adsorption tower 1 effecting an adsorption step was subjected to adiabatic expansion down to 1.2 ata in the expansion turbine 67, is 26 kcal/kg, and hence, assuming that an efficiency of the expansion turbine 67 is 80%, the power obtained by processing of an N2 gas at a rate of 5,700 Nm5H (7.1 x 103 kg/H) is as follows: 26 kcal/kgx7.1 x103 kg/Hx0.8-148x103 kcal/H.

Accordingly, about 19% of the power necessary for the compressor 28 can be recovered by the expansion turbine 67.

However, by feeding N2 gas at 250C delivered from the adsorption tower 1 to the heat-exchanger 61 as a refrigerant to effect heat exchange with the compressed air at 2400C for cooling the compressed air, the N2 gas is heated up to 2000 C. An enthalpy difference when the N2 gas heated up to 2000C is fed to the expansion turbine 67 and the N2 gas at 2000C and at 6 ata is subjected to adiabatic expansion until the pressure is lowered to 1.2 ata, is 41 kcal/kg, and hence, assuming that the efficiency of the expansion turbine 67 is 80%, the power recovered by the expansion turbine 67 is as follows: 41 kcal/kgx7.1 xl 03 x103 x0.8=233x 1 0# kcal/H.

Accordingly, owing to the provision of the heat-exchanger 61,30% of the power necessary for the compressor 28 can be saved by the expansion turbine 67. In addition, while the compressed air at 2400C was cooled to 400C by the after-cooler 60 in the case where the heat-exchanger 61 was not provided, when the heat-exchanger 61 is provided, the after-cooler 60 is only required to cool the compresed air from 1 700C to 400 C, and hence it is also possible to reduce the cooling load of the after-cooler 60.

Referring now to Figure 3, in a second embodiment of the invention, it is to be noted that component parts identical to those in the first preferred embodiments are given like reference numerals, and in the following description only those portions which are different from the first preferred embodiment will be explained.

In this embodiment, a vacuum pump 32 and motor 31 are omitted from the 02 main gas delivery pipe 57. A main N2 gas return pipe 69 is branched-off from the N2 gas delivery pipe 68 and is connected to the header pipe 4 through an N2 gas return pipe 71 having a valve 70. Also, the main N2 gas return pipe 69 is connected to the header pipe 6 through an N2 gas return pipe 73 having a valve 72.

This second embodiment is different from the first embodiment only in the desorption step within the adsorption tower 2, as follows Upon effecting the desorption step, delivery of the air within the adsorption tower 2 is achieved in the same manner as the first preferred embodiment, and by delivering the air within the adsorption tower 2 the pressure in this tower is reduced to about that of the atmosphere. After reducing the pressure, the valve 1 5 is closed and the valves 72 and 1 7 are opened to lead a part of the N2 gas flowing through the N2 gas delivery pipe 68 into the tower 2 through the main N2 gas return pipe 69 and the N2 gas return pipe 73.In the adsorption tower 2, since the N2 gas is introduced and the partial pressure of the O2 gas is lowered, the 02 gas is desorbed from the adsorbent and extracted through the O2 gas is delivery pipe 52 and main delivery pipe. After the O2 gas has been delivered, the valves 17 and 72 are closed and the valves 36 and 25 are opened to feed the compressed N2 gas into the tower for raising the pressure therein.

Modifications of the above described embodiments may be made within the scope of the invention. For example, in both embodiments the main N2 gas feed pipe 59, valve 36, N2 gas feed pipes 54 and 56 and valves 21 and 25 could be omitted and the increase in pressure in the adsorption tower 2 could be achieved by introducing a compressed N2 gas through the N2 gas delivery pipe 55 into the adsorption tower 2 by opening the valve 23. Moreover, the increase in pressure could be achieved by opening the valve 1 3 to feed the compressed air into the adsorption tower 2. If the moisture content is removed from the air before compression, the drain separator 63 and the dryer 64 could also be omitted.Furthermore, by cooling the compressed air by making use of the coldness of the lowtemperature N2 gas delivered from the expansion turbine 67, the refrigerator 42 can either be omitted, or can have a smaller capacity. Also, the heat-exchanger 61 and water-cooled after-cooler 60 could be disposed in reverse sequence. The number of the adsorption towers is not limited to two, but any number of adsorption towers could be provided, in which case the respective pipes could be directly connected to the adsorption towers with the header pipes omitted. In addition, the present invention could be applied not only to the separation of air, but also to the separation of other mixed gases where there is a requirement for adsorption of an N2 gas.

Referring now to Figure 4, in a third embodiment, two adsorption towers 1 and 2 are provided with are filled with an 02 adsorbent for example, Fe-Na-A type zeolite, or Fe-K-Na-A type zeolite. There is provided an air line 29 for feeding air to be used as a raw gas, in the adsorption towers 1 and 2, and also provided are air feed lines 8 and 14 branched from the air line 29 and having valves 7 and 13, respectively. A heat-exchanger 62, a compressor 28, a water-cooled after-cooler 60 and a refrigerator 42 are all disposed in the air line 29. The compressor 28 is coupled to a motor 27, which is in turn coupled to an expansion turbine 67 which operates as an adiabatic expansion device.On the same side of the respective adsorption towers 1 and 2 where the air feed lines 8 and 14 are provided air discharge lines 10 and 16 are also provided, respectively, having valves 9 and 15 and 02 delivery lines 51 and 52, respectively, having valves 11 and 17. The air discharge lines 10 and 16 join together to form a common air discharge line 30. The 02 delivery lines 51 and 52 also join together to form a common O2 delivery line 57, in which a vacuum pump 32 coupled to a motor 31 is disposed. Directly opposite the side where the air feed lines 9 and 14 join the respective adsorption towers 1 and 2, there are provided N2 delivery lines 13 and 55, respectively, having valves 19 and 23, and N2 feed lines 54 and 56, respectively, having valves 21 and 25.The N2 delivery lines 53 and 55 join together to form a common N2 delivery line 58. The N2 feed lines 54 and 56 communicate with an N2 line 59 branched from the N2 delivery line 58 and having a valve 36. An expansion turbine 67, is disposed in the N2 delivery line 58, and the downstream end of the N2 delivery line 58 communicates with the inlet of a refrigerant path in the heat-exchanger 62. An N2 discharge line 68 is provided at the outlet of the refrigerant path in the heat-exchanger 62.

Air as raw material having dust and moisture removed from it, is fed to the heat-exchanger 62, in which the air is cooled. The air flowing out of the heat-exchanger 62 is fed to the compressor 28 driven by the motor 21 where it is compressed and, the temperature of the air will rise accordingly. This air is fed from the compressor 28 through the air line 29 to the water-cooled after-cooler 60 where the temperature of the air is lowered again and then it is sent on to the refrigerator 42, where the temperature is further reduced. The case where an adsorption step is effected in the adsorption tower 1 and a desorption reproduction step is effected in the adsorption tower 2 will now be described. In this case, the valves 7 and 19 on the side of the adsorption tower 1 are opened, the valves 9, 11 and 21 are closed, and the valves 1 3 and 23 on the side of the other adsorption tower 2 are closed. The air flowing out of the refrigerator 42 passes through the air line 29, the air feed line 8 and the valve 7, and enters the adsorption tower.

Within the adsorption tower 1, the O2 gas in the air is adsorbed by an adsorbent. The residual N2 gas is delivered from the adsorption tower. The N2 gas delivered from the adsorption tower 1 is fed to the expansion turbine 67 through the valve 19, N2 delivery line 53 and N2 delivery line 58 to drive the expansion turbine 67 by the pressure of the N2 gas. The power of the expansion turbine 67 in turn drives the motor 27 and thereby the energy consumption of the motor 27 is reduced. In the expansion turbine 67, the N2 gas expands, so that the pressure is lowered and as a consequence the N2 gas temperature falls, and the N2 gas flowing out of the expansion turbine 67 enters the heat-exchanger 62.In the heat-exchanger 62, heat-exchange with the air is effected, so that the temperature of the N2 gas rises, and it is sent to a predetermined location or plant through the N2 discharge line 68. On the other hand, in the adsorption tower 2 where the valves 13 and 23 are c'osed, the valves 25 and 17 are also closed with only the valve 1 5 kept opened, thereby the air within the adsorption tower 1 is discharged through the valve 15, air discharge line 16 and air discharge line 30, and thus the pressure in the adsorption tower 2 is lowered. Initially, the air accumulated in the interstices between the adsorbent grains is discharged through the air discharge line 30, and thereafter a gas having a gradually increasing 02 concentration is discharged.When the O2 concentration in the gas discharged through the air discharge line 30 has reached a predetermined value, the valve 15 is closed and the valve 17 is opened. The vacuum pump 32 is actuated by the motor 31 to suck out the gas in the adsorption tower 2 through the valve 17 and O2 delivery lines 52 and 57, whereby the pressure within the adsorption tower 2 is reduced, and the O2 adsorbed by the adsorbent is desorbed. After the 02 has been desorbed by reducing the pressure to a predetermined level and the 02 has been delivered to a predetermined location or plant through the valve 17 and O2 delivery lines 52 and 57, the valve 17 is closed and the valves 25 and 36 are opened.By opening valves 36 and 25, a part of the N2 gas flowing through the N2 delivery line 58 is fed into the adsorption tower 2 through the N2 line 59 and N2 feed line 56, thereby raising the pressure in the adsorption tower 2. Alternatively, the pressure in the adsorption tower 2 could be raised by feeding compressed air, in place of the N2 gas, by opening the valve 13 with the valves 25 and 36 kept closed and leading the compressed air through the air line and air feed line 14.

According to the above-described embodiment, since O2 is adsorbed by the adsorbent and the O2 to be adsorbed represents about 1/5 of the total amount of air, N2 and O2 can be separated from each other by adsorbing only a small amount of gas. In addition, since the N2 gas not adsorbed by the adsorbent represents the other 4/5 of the air when it expands in the turbine 67 in which power is recovered, the recovering rate of the compression energy of the compressed air is very large. Moreover, since the temperature of the air before compression is lowered by means of the cooled N2 gas that has been expanded in the turbine 69, the compressor 28 can be driven with less energy needed to compress the air to a predetermined pressure, with a consequent increase of the efficiency of the compressor 28.Furthermore, since the temperature of the air is lowered before compression, the temperature is raised only slightly after compression and thus the air temperature rise after compression is made smaller, so reducing the amount of energy needed for cooling.

Now description will be made of practical examples of experiments for separating air into N2 and O2 through adsorption by making use of the above-described embodiment of the present invention.

Example 1 An air separation test was conducted by employing an apparatus in which a pressure regulating valve was provided in place of the expansion turbine 67 used in the apparatus illustrated in Figure 4.

The adsorption towers 1 and 2 were filled with 30 kg. of Fe-K-Na-A type zeolite having grain diameters of about 1 mm.

Dry air at 250C and at 1 ata was compressed by the compressor 28 up to 6.5 ata. The temperature immediately after the compression was about 2300 C. The compressed air at about 2300C was cooled to about 250C and then fed to the adsorption tower 1 at a rate of 10 Nm3/H to cause the 02 gas to be adsorbed by the Fe-K-Na-A type zeolite. The pressure within the adsorption tower 1 at this moment was about 6 ata. N2 gas having an O2 concentration of 1% or less was delivered from the adsorption tower at a rate of 5.6 Nm3/H.

O2 gas having an O2 concentration of 78% was delivered from the adsorption tower 2 in which a desorption step was being effected, at a rate of 2.0 Nm3/H, and the final pressure in the adsorption tower 2 was reduced to 0.2 ata.

In this experiment, separation by adsorption of air was tested by making use of a small-scale apparatus in which compressed air was fed at a rate of 10 Nm3/H, and in this case, since the rate of delivery of the gas was so small, operation of the expansion turbine 67 was impossible. However, even when the apparatus is scaled up to such extent that the delivery rate of the compressed air fed to the adsorption tower 1 may be increased to 10,000 Nm3/H so that operation of the expansion turbine 67 becomes possible, N2 and 02 gases are obtained in the following manner if operation is made in the same way as in the above-described example of experiment.

That is, the gas delivered during the adsorption step is an N2 gas having an O2 concentration of 1% or less and flowing at a rate of 5,600 Nm3/H, and the gas delivered during the desorption step is an O, gas having an 02 concentration of 78% and flowing at a rate of 2,000 Nm3/H.

Now quantities of heat in the respective devices in the apparatus for processing compressed air at a rate of 10,000 Nm3/H will be calculated. In this instance, although the enthalpies of air, N2 and 02 gases are somewhat different from each other, calculation will be made as if they are equal to each other for the sake of simplicity.

An enthalpy difference when dry air at 250C and at 1 ata has been subjected to adiabatic compression to 6.5 ata by means of the compressor 28 is 50 kcal/kg and so, assuming that an efficiency of the compressor 28 is 80%, the power necessary for processing dry air at a rate of 10,000 Nm3/H (12.95x103 kg/H) is as follows: 50 kcal/kgx 1 2.95x 103 kg/H+08=809x1 103 kcal/H.

The enthalpy difference in the case where N2 gas at 250C and at 6 ata delivered from the adsorption tower 1 effecting an adsorption step has been subjected to adiabatic expansion to 1.2 ata in the expansion turbine 67, is 26 kcal/kg, and hence, assuming that the efficiency of the expansion turbine 67 is 80%, the power obtained by processing N2 gas at a rate of 5,600 Nm3/H (7.0x 103 kg/H) is as follows: 26 kcal/kgx7.0x103 kg/Hx0.8=146x103 kcal/H Accordingly, about 18% of the power necessary to drive the compressor 28 can be recovered by the expansion turbine 69.

In addition, the N2 gas flowing out of the expansion turbine 67 has its temperature lowered from 250C to about --63 OC by adiabatic expansion, and so, assuming that this cold N2 gas is fed to the heatexchanger 62 as a refrigerant and is withdrawn at 200C from the heat-exchanger 62, then the dry air before compression entering the heat-exchanger 62 can be lowered in temperature by 450C,so that the dry air flowing out of the heat-exchanger 62 has a temperature of 200 C.

Therefore, the enthalpy difference when dry air at -200C and at 1 ata has been subjected to adiabatic compression up to 6.5 ata, is 42 kcal/kg, and hence assuming that the efficiency of the compressor 28 is 80%, the power necessary to drive the compressor 28 is as follows: 42 kcal/kgx 12.95 xl O# kg/H+0.8=680 xl 0# kcal/H.

Accordingly, owing to the provision of the heat-exchanger, only a power of 680x 103 kcal/H is required, in contrast to a power of 809x 103 kcal/H that was necessary in the prior art, and hence a power saving of 129 x 103 kcal/H results. Moreover, since a power of 146x103 kcal/H can be recovered by the expansion turbine 67, the corresponding amount of power for the compressor 28 can be saved, and a total power saving for the compressor 28 of (129 x 103+ 146 x 103) kcal/H can be achieved, which is equal to about 34% of the power needed to drive the compressor.

Example 2 An air separation test was conducted by employing an apparatus in which a pressure regulating valve was provided in place of the expansion turbine 67 used in the apparatus illustrated in Figure 2.

The adsorption towers 1 and 2 were filled with 20 kg of Fe-Na-A type zeolite having grain sizes of about 1 mm.

Dry air at 250C and at 1 ata was compressed by the compressor 28 up to 6.5 ata. The temperature immediately after the compression was about 2300 C. The compressed air at about: 2300C was cooled to about 00C and then fed to the adsorption tower 1 at a rate of 10 Nm3/H to cause O2 gas to be adsorbed by the Fe-Na-A type zeolite. The pressure within the adsorption tower 1 at this moment was about 6 ata. N2 gas having an O2 concentration of 1% or less was delivered from the adsorption tower 1 at a rate of 5.8 Nm3/H.

O2 gas having an O2 concentration of 81% was delivered from the adsorption tower at a rate of 2.0 Nm3/H, and the final pressure in the adsorption tower 2 was reduced to 0.2 ata.

In this experiment, separation by adsorption of air was tested by making use of a small-scale apparatus in which compressed air was fed at a rate of 10 Nm3/H, and in this case, since the rate of delivery of gas was so small, operation of the expansion turbine 67 was impossible. However, even when the apparatus is scaled up to such an extent that the delivery rate of the compressed air fed to the adsorption tower 1 may be increased to 10,000 Nm3/H so that operation of the expansion turbine 67 becomes possible, N2 and O2 gases are obtained in the following manner if operation is made in the same way as in the above-described example of experiment.

That is, the gas delivered during the adsorption step is N2 gas having an 02 concentration of 1% or less and flowing at a rate of 5,800 Nm3/H, and the gas delivered during the desorption step is 02 gas having an O2 concentration of 81% and flowing at a rate of 2,000 Nm3/H.

Now quantities of heat in the respective devices in the apparatus for processing compressed air at a rate of 10,000 Nm3/H will be calculated. In this instance, although the enthalpies of air, O2 and N2 gases are somewhat different from each other, calculation will be made as if they are equal to each other for the sake of simplicity.

The enthalpy difference when dry air at 250C and at 1 ata has been subjected to adiabatic compression to 6.5 ata by means of the compressor 28 is 50 kcal/kg, and so, assuming that the efficiency of the compressor 28 is 80%, the power necessary for processing dry air at a rate of 10,000 Nm3/H (12.95x103 kg/H) is as follows: 50 kcal/kg x 12.95 x 103 kg/H+0.8=809 x 103 kcal/H.

The enthalpy difference in the case where N2 gas at 00C and at 6 ata delivered from the adsorption tower 1 effecting an adsorption step has been subjected to adiabatic expansion to 1.2 ata in the expansion turbine 67, is 24 kcal/kg, and hence, assuming that the efficiency of the e expansion turbine 67 is 80%, the power obtained by processing N2 gas at a rate of 5,800 Nm3/H (7.3x103 kg/H) is as follows:: 24 kcal/kgx7.3x103 kg/Hx0.8=140x103 kwal/H In addition, the N2 gas flowing out of the expansion turbine 67 has its temperature !owered from 00C to about -850C by adiabatic expansion, and so, assuming that this cold N2 gas is fed to the heatexchanger 62 as a refrigerant, and is withdrawn at 00C from the heat-exchanger 62, then the dry air before compression entering the heat-exchanger 62 can be lowered in temperature by 480C, so that the dry air comes out of the heat-exchanger 62 with a temperature of-230C. Therefore, the enthalpy difference when dry air at -230C and at 1 ata has been subjected to adiabatic compression to 6.5 ata, is 43 kcal/kg, and hence, assuming that the efficiency of the compressor 28 is 80%, the necessary power to drive the compressor 28 is as follows: 43 kcal/kgxl2.95x103 kg/H+0.8=696 kcal/H.

Accordingly, owing to the provision of the heat-exchanger 62, only a power of 696x 103 kcal/H is required, instead of a power of 809 x 103 kcal/H that was necessary in the prior art, and hence a power saving of 1 113 x 103 kcal/H results. Moreover, since a power of 140x 103 koal/H can be recovered by the expansion turbine 67, the corresponding amount of power to drive the compressor 28 can be saved, and a total power saving for the compressor 28 of 11 3x 1 0#+ 1 40x 1 0# kcal/H can be achieved, which is equal to about 31% of the power required to drive the compressor.

Referring now to Figure 5, in a fourth embodiment, it is to be noted that component parts identical to those in the third embodiment are given like reference numerals, and in the following description only those portions which are different from the third embodiment will be explained.

The vacuum pump 32 driven by the motor 31 of the third embodiment is omitted from the 02 delivery line in this embodiment. An N2 return line 69 is branched from the N2 discharge line 68, and on the side of the respective adsorption towers 1 and 2 where the delivery lines 53 and 55, respectively, are provided, there are also provided N2 feed lines 71 and 73 which are branched from the N2 return line 69 and provided with valves 70 and 72, respectively.

The difference between this and the third embodiment is only in the reduced-pressure desorption step, and only that difference will be explained here. While an adsorption step is being effected in the adsorption tower 2, the valves 13 and 23 are closed, and also the valves 25, 17, 36 and 72 are closed with only the valve 15 kept opened to discharge the air in the adsorption tower 2 through the valve 15, air discharge line 16 and air discharge line 30, thereby lowering the pressure in the adsorption tower 2.

Initially the air accumulated in the interstices between the adsorbent grains is discharged through the air discharge line 30, and thereafter a gas having a gradually increasing O2 concentration is discharged.

When the 02 concentration in the gas discharged through the air discharge line 30 has reached a predetermined value, the valve 13 is closed and the valve 17 is opened. Furthermore, the gas in the adsorption tower 2 is discharged through the valve 17 and O2 delivery lines 52 and 30 to continue to lower the pressure in the adsorption tower 2, and when the pressure has been reduced to a predetermined pressure, the valve 72 is opened to feed a part of the N2 gas having a reduced pressure through the return line 69 and N2 feed line 73 into the adsorption tower 2, in which an 02 gas is desorbed from the adsorbent due to the difference between the partial pressure of the O2 gas corresponding to the adsorbed quantity of O2 gas in the adsorbent and the partial pressure of the O2 gas in the fed N2 gas, and the desorbed O2 gas is scavenged by the N2 gas and delivered from the adsorption tower 2 through the valve 17 and O2 delivery lines 52 and 57 to a predetermined location or plant. Thereafter, the valve 17 and valve 72 are closed and the valves 25 and 36 are opened. By opening the valves 36 and 25, a part of the N2 gas flowing through the N2 delivery line 58 is fed into the adsorption tower 2 through the N2 line 59 and N2 feed line 56 to thereby raise the pressure in the adsorption tower 2. Alternatively, the pressure in the adsorption tower 2 could be raised by feeding compressed air, in place of the N2 gas, through the air line 29 and air feed line 1 4 into the adsorption tower 2 by opening the valve 13 with the valves 25 and 36 kept closed.

In these third and further embodiments, modifications may be made, e.g. any number of adsorption towers could be used; the expansion turbine 67 could be coupled to the vacuum pump 32 instead of the motor 31. Moreover, depending upon the operating conditions, to achieve a better power balance instead of reducing the proportion of energy consumption of the compressor 28, the refrigerating load which is relatively expensive could be reduced by providing a further heat-exchanger either in place of the refrigerator 42, or downstream of the refrigerator, feeding a part of the N2 gas delivered from the expansion turbine 67 to the new heat-exchanger and cooling the air by the coldness of the N2 gas. Furthermore, the adsorbent could be changed so as to achieve separation by adsorption of N2 of separation by adsorption of moisture, or mixed gases other than air.

Referring now to Figure 6, in a fifth embodiment of the invention, it is to be noted that component parts identical to those of the first embodiment (Figure 2)are given like reference numerals. Also, in the following description, only those portions which are different from the first embodiment will be explained.

In this embodiment, a drain separator 63 and a dryer 64 are omitted from the main air feed pipe 29 but a heat-exchanger 62 is added to it upstream of the compressor 28. In use the process of this embodiment is identical to that of the first embodiment except that the cold N2 gas being exhausted from the expansion turbine 67 is directed into the heat-exchanger 62 via the pipe 65 where it cools down the incoming air and thereby raises its own temperature before passing into an external equipment.

Now description will be made of practical examples of experiments for separating air into N2 and 02 through adsorption by making use of this fifth embodiment of the present invention.

Example 1 A separation test of air was conducted by employing apparatus in which a pressure regulating valve was provided in place of the expansion turbine 67 and a refrigerator was provided in place of the heat-exchanger 61.

Dry air at 250C and at 1 ata was compressed by the compressor 28 up to 6.5 ata. The compressed air immediately after the compression was cooled to about 250C and then fed to the adsorption tower 1 at a rate of 10 Nm3/H to cause an 02 gas to be adsorbed by the Fe-K-Na-A type zeolite. The pressure within the adsorption tower 1 at this moment was about 6 ata. From the adsorption tower 1 was delivered an N2 gas having an O2 concentration of 1% or less at a rate of 5.6 Nm3/H.

From the adsorption tower 2 in which a desorption step was being effected, was delivered an O2 gas having an O2 concentration of 78% at a rate of 2.0 Nm3/H, and the final pressure in the adsorption tower 2 was reduced to 0.2 ata.

In this experiment, separation by adsorption of air was tested by making use of a small-scale apparatus in which compressed air was fed at a rate of 10 Nm3/H, and in this case, since the rates of delivery of gases were small, actuation of the expansion turbine 67 was impossible. However, even when the apparatus is scaled up to such extent that the delivery rate of the compressed air fed to the adsorption tower 1 may be increased to 10,000 Nm3/H so that actuation of the expansion turbine 67 becomes possible, if operation is made in the same way as the above-described example of experiment, an N2 gas and an O2 gas would be obtained in the following manner.

That is, the gas delivered during the adsorption step is an N2 gas having an 02 concentration of 1% or less and flowing at a rate of 5,600 Nm3/H, and the gas delivered during the desorption step is an 02 gas having an O2 concentration of 78% and flowing at a rate of 2,000 Nm3/H.

Now the quantities of heat in the respective devices in the apparatus for processing a compressed air at a rate of 10,000 Nm3/H, will be calculated. In this instance, although the enthalpies of air, an N2 gas and an O2 gas are somewhat different from each other, calculation will be made as if they are equal to each other for the sake of simplicity.

An enthalpy difference when dry air at 250C and at 1 ata has been subjected to adiabatic compression to 6.5 ata by means of the compressor 28 is 50 kcal/kg, and so, assuming that an efficiency of the compressor 28 is 80%, the power necessary for processing dry air at a rate of 1 0,000 Nm3/H (12.95x103 kg/H) is as follows: 50 kcal/kgx 1 2.9 5 103 kg/H+0.8=809 103 kcal/H.

An enthalpy difference in the case where an N2 gas at 250C and at 6 ata delivered from the adsorption tower 1 effecting an adsorption step has been subjected to adiabatic expansion to 1.2 ata in the expansion turbine 63, is 26 kcal/kg, and hence, assuming that an efficiency of the expansion turbine 63 is 80%, a power obtained by processing of an N2 gas at a rate of 5,600 Nm3/H (7.0x 103 kg/H) is as follows: 26 kcal/kgx7.0x103 kg/Hx0.8=146x102 kcal/H.

The N2 gas at 250C fed from the adsorption tower 1 enters as a refrigerant into the heatexchanger 61, in which the N2 gas is subjected to heat exchange with the compressed air and heated up to 350C, and then the N2 gas enters into the expansion turbine 67. An enthalpy difference when an N2 gas at 350C and at 6 ata has been subjected to adiabatic expansion to 1.2 ata in the expansion turbine 63, is 27 kcal/kg, and hence, assuming that an efficiency of the expansion turbine is 80%, a power recovered by the expansion turbine 63 is as follows:: 27 kcal/kgx7.0x 103 kg/hx0.8=1 51 103 kcal/H The N2 gas flowing out of the expansion turbine 67 has its temperature lowered from 350C to about -540C by adiabatic expansion, and so, assuming that this cold N2 gas is fed to the heatexchanger 62 as a refrigerant and is withdrawn at 1 50C from the heat-exchanger 62, then the dry air before compression entering into the heat-exchanger 62 can be lowered in temperature by 370C, so that the dry air before compression flowing out of the heat-exchanger 62 has a temperature of -1 20C.

An enthalpy difference when dry air at -1 20C and at 1 ata has been subjected to adiabatic expansion up to 6.5 ata, is 44 kcal/kg, and hence, assuming that an efficiency of the compressor 28 is 80%, a power required by the compressor 28 is as follows: 44kcal/kgxl2.95x103kg/H+0.8=712x103kcal/H.

Accordingly, owing to the provision of the heat-exchanger 62, only a power of 7l2x103 kcal/H is required in contrast to a power of 809 x 103 kcal/H that was necessary in the prior art, and hence, a power saving of 97 kcal/H results. Moreover, a power of 15 x 103 kcal/H can be recovered by the expansion turbine 67, hence the power of the compressor 28 can be reduced by a corresponding amount and a total power saving of 1 5x1 03+97 xl 103 kcal/H can be achieved, which is equivalent to about 31% of the power necessary to drive the compressor 28.

Since the dry air before compression is lowered in temperature by the low-temperature N2 gas discharged from the expansion turbine 67, and the compressed air is also lowered in temperature by the N2 gas discharged from the adsorption tower 1, it becomes possible to reduce the cooling load of the after-cooler 60, the refrigerator 42 and the like.

Example 2 A separation test of air was conducted by employing an apparatus in which a pressure regulating valve was provided in place of the expansion turbine 67 in the apparatus illustrated in Figure 6 and also a refrigerator was provided in place of the heat-exchanger 61.

^ Dry air at 250C and at 1 ata was compressed by the compressor 28 up to 6.5 ata. The compressed air immediately after the compression was cooled to about 00C and then fed to the adsorption tower 1 at a rate of 10 Nm2/H to cause an O2 gas to be adsorbed by the Fe-Na-A type zeolite. The pressure within the adsorption tower 1 at this moment was about 6 ata. From the adsorption tower 1 was delivered an N2 gas having an O2 concentration of 1% or less at a rate of 5.8 Nm3/H.

From the adsorption tower 2 in which a desorption step was being effected, was delivered an O2 gas having an O2 concentration of 81% at a rate of 2.0 Nm3/H, and the final pressure in the adsorption tower 2 was reduced to 0.2 ata.

In this experiment, separation of adsorption of air was tested by making use of a small-scale apparatus in which compressed air was fed at a rate of 10 Nm3/H, and in this case, since the rates of delivery of gases were small, actuation of the expansion turbine 67 was impossible. However, even when the apparatus is scaled up to such extent that the delivery rate of the compressed air fed to the adsorption tower 1 may be increased to 10,000 Nm3/H so that actuation of the expansion turbine 67 becomes possible, if operation is made in the same way as the above-described example of experiment, then an N2 gas and an O2 gas are obtained in the following manner.

That is, the gas delivered during the adsorption step is an N2 gas having an O2 concentration of 1% R6 or less and flowing at a rate of 5,800 Nm3/H, and the gas delivered during the desorption step is an O2 gas having an O2 concentration of 81% and flowing at a rate of 2,000 Nm3/H.

Now the quantities of heat in the respective devices in the apparatus for processing a compressed air at a rate of 10,000 Nm3/H, will be calculated. In this instance, although the enthalpies of air, an O2 gas and an N2 gas are somewhat different from each other, calculation will be made as if they are equal to each other for the sake of simplicity.

An enthalpy difference when dry air at 250C and at 1 ata-has been subjected to adiabatic compression to 6.5 ata by means of the compressor 28 is 50 kcal/kg, and so, assuming that an efficiency of the compressor 28 is 80%, the power necessary for processing the dry air at a rate of 10,000 Nm3/H is as follows: 50 kcal/kg xl 2.95 x 103 kg/H+O.8=809 103 kcal/H.

An enthalpy difference in the case where an N2 gas at 00C and at 6 ata delivered from the adsorption tower 1 effecting an adsorption step has been subjected to adiabatic expansion to 1.2 ata in the expansion turbine 67, is 24 kcal/kg, and hence assuming that an efficiency of the expansion turbine 67 is 80% a power obtained by processing of an N2 gas at a rate of 5,800 Nm3/H is as follows: 24 kcal/kgx7.3x103 kg/HxO.8=140x103 kcal/H.

The N2 gas at 00C delivered from the adsorption tower 1 enters as a refrigerant into the heatexchanger 61, in which the N2 gas is subjected to heat exchange with the compressed dry air and heated up to 250C, and then it enters into the expansion turbine 67.

An enthalpy difference when an N2 gas at 6 ata has been subjected to adiabatic expansion to 1.2 ata in the expansion turbine 67, is 26 kcal/kg, and hence assuming that an efficiency of the expansion turbine 63 is 80%, a power recovered by the expansion turbine 67 is as follows: 26 kcal/kgx7.3x 103 kg/HxO.8=i x 103 kcal/H The N2 gas flowing out of the expansion turbine 67 has its temperature lowered from 250 C- 630C by adiabatic expansion, and so, assuming that this cold N2 gas is fed to the heat exchanger 62 as a refrigerant and is withdrawn at 00C from the heat-exchanger 62, then the compressed air having entered into the heat-exchanger 62 can be lowered in temperature by 360C, so that the dry air before compression which comes out of the heat-exchanger 62 is at a temperature of~11 OC.

An enthalpy difference when dry air at~11 0C and at 1 ata has been subjected to adiabatic expansion to 6.5 ata, is 44 kcal/kg, and hence, assuming that an efficiency of the compressor 28 is 80%, the necessary power for the compressor 28 is as follows: 44 kcal/kgxl2.95x1010 kg/Hx0.8=712x103 kcal/H.

Accordingly owing to the provision of the heat-exchanger 62, the compressor only requires a power of 712 x 103 kcal/H, in contrast to a power of 809 x 1 03 kcal/H that was necessary in the prior art, and hence a power saving of 97 x 103 kcal/H results. Moreover, a power of 152x103 kcal/H can be recovered by the expansion turbine 67, hence the corresponding amount of power can be saved and a total power saving of 1 52 xl 103+97 x 103 kcal/H can be achieved, which is equivalent to about 31% of the power required by the compressor 28.

Since the dry air before compression is lowered in temperature by the low-temperature N2 gas discharged from the expansion turbine 63 and in addition the compressed air is also lowered in temperature by the N2 gas discharged from the adsorption tower 1, it also becomes possible to reduce the cooling load of the after-cooler 60, the refrigerator 42, and the like.

Referring now to Figure 7 in a sixth embodiment of the invention, like component parts to those of the second embodiment (Figure 3) are given the same reference numerals and in the following descriptions only those portions which are different from the second embodiment will be explained.

In this embodiment a drain separator 63 and a dryer 64 are omitted from the main air feed pipe 29 but a heat exchanger 62 is added to it upstream of the compressor 28. In use, the process of this embodiment is identical to that of the second embodiment, except that the cold N2 gas being exhausted from the expansion turbine 67 is directed into the heat exchanger 62 via the pipe 65 where it cools down the incoming air and thereby raises its own temperature before passing on to the external equipment.

Referring now to Figure 8 is a seventh embodiment of the invention like component parts to those of the first embodiment (Figure 2) are given like reference numerals and in the following description only those portions which are different from the first embodiment will be explained.

In this embodiment a drain separator 63 and a dryer 64 are omitted from the main air feed pipe 29 but a heat exchanger is added to it upstream of the compressor 28. Instead of the N2 delivery pipe 58 connecting with the downstream heat exchanger 61 it is here connected to the upstream heat exchanger 62. Also the pipe 65 now connects the outlet from the heat exchanger 62 to the inlet of the expansion turbine 67 whilst the outlet from this turbine passes to the downstream heat exchanger 61 via the pipe 66.

In use, the process of this embodiment is identical to that of the first embodiment, except that the cold N2 gas from the delivery pipe 58 is heated up by the incoming air in the upstream heat exchanger 62 before being expanded and cooled again in the turbine 67. It is then passed to the downstream heat exchanger 61 through the pipe 65 where it cools the incoming air still further meanwhile raising its own temperature again before passing on to otheiexternal equipment.

Example A separation test of air was conducted by employing an apparatus in which a pressure regulating valve was provided in place of the expansion turbine 67 and a refrigerator was provided in place of the heat-exchanger 61.

The adsorption towers 1 and 2 were filled with 20 kg of Fe-Na-A type zeolite having grain sizes of about 1 mm. Dry air at 250C and at 1 ata was compressed by the compressor 28 up to 6.5 ata. The temperature immediately after the compression was 2300 C. The compressed air at about 2300C was cooled to about 00C and then fed to the adsorption tower 1 at a rate of 10 Nm3/H to cause an O2 gas to be adsorbed by the Fe-Na-A type zeolite. The pressure within the adsorption tower 1 at this moment was about 6 ata. From the adsorption tower 1 was delivered an N2 gas having an O2 concentration of 81% at a rate of 2.0 Nm3/H, and the final pressure in the adsorption tower 2 was reduced to 0.2 ata.

In this experiment, separation by adsorption of air was tested by making use of a small-scale apparatus in which compressed air was fed at a rate of 10 Nm3/H, and in this case, since the rate of delivery of gas was small, actuation of the expansion turbine 67 was impossible. However, even when the apparatus is scaled up to such extent that the delivery rate of the compressed air fed to the adsorption tower 1 may be increased to 10,000 Nm3/H so that actuation of the expansion turbine 67 becomes possible, an N2 gas and an O2 gas are obtained in the following manner if operation is made in the same way as the above-described example of experiment.

That is, the gas delivered during the adsorption step is an N2 gas having an O2 concentration of 1% or less and flowing at a rate of 5,800 Nm3/H, and the gas delivered during the desorption step is an 02 gas having an 02 concentration of 81% and flowing at a rate of 2,000 Nm3/H.

Now quantities of heat in the respective devices in the apparatus for processing a compressed air at a rate of 10,000 Nm3/H will be calculated. In this instance, although the enthalpies of air, an O2 gas and an N2 gas are somewhat different from each other, calculation will be made as if they are equal to each other for the sake of simplicity.

An enthalpy difference when dry air at 250C and at 1 ata has been subjected to adiabatic compression to 6.5 ata by means of the compressor 28 is 50 kcal/kg, and so, assuming that an efficiency of the compressor 28 is 80%, a power required for processing dry air at a rate of 10,000 Nm3/H (12.95x10-3 kg/H) is as follows: 50 kcal/kg x 12.95 x 103 kg/H+0.8-809 x 103 kcal/H.

An enthalpy difference in the case where an N2 gas at 00C and at 6 ata delivered from the adsorption tower 1 effecting an adsorption step has been subjected to adiabatic expansion to 1.2 ata in the expansion turbine 67, is 24 kcal/kg, and hence, assuming that an efficiency of the expansion turbine 67. is 80%, a power obtained by processing of an N2 gas at a rate of 5,800 Nm3/H (7.3x103 kg/H) is as follows: 24 kcal/kgx7.3x 103 kg/Hx0.8=l 40x 103 kcal/h.

The N2 gas fed from the adsorption tower 1 enters as a refrigerant into the heat-exchanger 62, in which the N2 gas lowers the temperature of the dry air at 250C before compression to 1 OOC, and the N2 gas is heated up to 1 80C and enters into the expansion turbine 67.Then, an enthalpy difference when the dry air at 1 00C and at 1 ata has been subjected to adiabatic compression to 6.5 ata, is 48 kcal/kg, and hence, assuming that an efficiency of the compressor 28 is 80%, the necessary power to drive the compressor 28 is as follows: 48 kcal/kgx 1 2.95x 103 kg/K+0.8=777 x 103 kcal/H, and an enthalpy difference when the N2 gas at 1 80C and at 6 ata has been subjected to adiabatic expansion to 1.2 ata in the expansion turbine 67, is 26 kcal/kg, and hence, assuming that an efficiency of the expansion turbine 67 is 80%, a power recovered by the expansion turbine 67 is as follows:: 26 kcal/kgx7.0x 103 kg/Hx0.8=1 52x 103 kcal/H.

Accordingly, owing to the provision of the heat-exchanger 62, the necessary power for the compressor could be reduced by 4% and furthermore the power recovery by the expansion turbine 67 could also be increased by about 10%. In other words, with regard to the overall power saving, in contrast to a power of 809x 103 kcal/H that was required in the prior art, only a power of 777x103 kcal/H is required, resulting in power saving of 32 x 103 kcal/H, and further since a power of 152 x 103 kcal/H can be recovered, this amount of power can also be saved resulting in a total power saving of 1 52x 1 03+32x 103 koal/H which is equivalent to about 23% of the total power consumption.

In addition, assuming that the N2 gas discharged from the expansion turbine 67 has been lowered in temperature to -690C by adiabatic expansion, this N2 gas is fed to the heat-exchanger 61 as a refrigerant and it is withdrawn at 00C from the heat-exchanger 61, then the compressed air entering into the heat-exchanger 61 can be lowered in temperature by 390C, and thus the temperature of the compressed air entering into the heat exchanger 61 could be as high as 390C, so that it is only necessary to cool the compressed air after compression to 390C by means of the after-cooler 60 or the like. In addition, since the temperature of air is lowered before compression, it is possible to reduce the cooling load of the after-cooler 60 or the like corresponding to the above-mentioned cooling.

Referring now to Figure 9 in an eighth embodiment of the invention, again like component parts to those of the second embodiment (Figure 3) are given like reference numerals and, in the following description, only those portions which are different from the second embodiment will be explained.

In this embodiment, a drain separator 63 and a dryer 64 are omitted from the main air feed pipe 29; but a heat exchanger 62 is added to it, upstream of the compressor 28. Instead of the N2 delivery pipe 58 connecting with the downstream heat exchanger 61 it is here connected to the upstream heat exchanger 62. Also the pipe 65 now connects the outlet from the heat exchanger 62 to the inlet of the expansion turbine 67 whilst the outlet from this turbine passes to the downstream heat exchanger 61 via the pipe 66.

In use, the process of this embodiment is identical to that of the second embodiment, except that the cold N2 gas from the delivery pipe 58 is heated up by the incoming air in the upstream heat exchanger 62 before being expanded and cooled again in the turbine 67. It then passes to the downstream heat exchanger via the pipe 65 where it cools the incoming air still further and meanwhile raises its own temperature again before passing on to other external equipment.

Claims

1. A process for separating a raw mixed gas, of the kind in which the raw mixed gas is compressed and subsequently cooled and then fed into an adsorption tower filled with an adsorbent so as to adsorb an adsorbate constituent gas in said mixed gas, thereby enabling residual unadsorbed constituent gas or gases to be extracted from said adsorption tower, characterised in that heat exchange is effected between the unadsorbed constituent gas extracted from said adsorption tower and incoming raw mixed gas, said unadsorbed constitutent gas being heated thereby, whilst said raw mixed gas is cooled, and in that said unadsorbed constituent gas is fed for adiabatic expansion to recover pressure energy therefrom, the process thereby enabling energy to be recovered efficiently from the unadsorbed constituent gas, and a reduction in the amount of cooling required for the raw mixed gas to cool it down to adsorption temperature.

2. A process according to Claim 1, characterised in that said heat exchange is effected after compression of the incoming raw mixed gas, so that heat generated during compression at least assists in setting the temperature of said raw mixed gas, and in that the unadsorbed constituent gas is fed for adiabatic expansion after said heat exchange.

3. A process according to Claim 1 or 2, characterised in that, after heat exchange with the unadsorbed constituent gas, the raw mixed gas is further cooled to separate out moisture, dried, and thereafter refrigerated to adsorption temperatuare.

4. A process according to Claim 1, characterised in that said heat exchange is effected prior to compression of the incoming raw mixed gas and subsquent to adiabatic expansion of the unadsorbed constituent gas, thereby enabling compression of said raw mixed gas to take place with reduced energy.

5. A process according to Claim 1, characterised in that heat exchange is carried out both before and after compression of the incoming raw mixed gas, the unadsorbed constituent gas being fed for an initial heat exchange with said raw mixed gas, after compression of the latter, after which the heated unadsorbed constituent gas is fed for adiabatic expansion to produce energy recovery at an increased level, the now cooled unadsorbed constituent gas being fed to the second heat exchange step to reduce the cooling requirement for the raw mixed gas.

6. A process according to Claim 5, characterised in that, after compression, the raw mixed gas is cooled before being fed for said initial heat exchange with the unadsorbed constituent gas and, after said initial heat exchange, the raw gas is refrigerated to adsorption temperature.

7. A process according to Claim 1, where adsorption is effected at or below ambient temperature, characterised in that heat exchange is carried out both before and after compression of the incoming raw mixed gas, the unadsorbed constituent gas being fed for an initial heat exchange with said raw mixed gas before compression of the latter, to heat up the unadsorbed constituent gas, after which the heated unadsorbed constituent gas is fed for adiabatic expansion at an increased energy recovery level, the now cooled unadsorbed constituent gas then being fed to said second heat exchange step to assist in cooling said raw mixed gas.

8. A process according to Claim 7, characterised in that, after compression, the raw mixed gas is cooled before being fed for its second heat exchange with the unadsorbed constituent gas.

9. A process according to any one of the preceding claims, characterised in that adiabatic expansion is carried out in an expansion turbine, and in that said expansion turbine is used at least in part to drive a compressor for compressing said incoming raw mixed gas.

10. A process according to any one of the preceding claims, wherein the raw mixed gas is air, the adsorbed constituent gas is O2 and the unadsorbed constituent gas is N2.

11. A process according to any one of the preceding claims, characterised in that at least two adsorption towers are provided, and in that an adsorption step is carried out in one tower, whilst a desorption step is carried out in the other tower.

12. Apparatus for separating a raw mixed gas of the kind comprising at least one adsorption tower, a raw mixed gas feed line having a compressor therein, valved connections at each end of said tower for controlling the feed of said mixed gas into and through said tower so that an adsorbate constituent gas can be removed therefrom, and a delivery line for extracting and deliverying the residual unadsorbed constituent gas from the tower, characterised in that said delivery line is fed through one side of a heat exchanger, the other side of which is connected in the raw mixed gas feed line, and in that an adiabatic expansion device is included in said delivery line.

13. Apparatus according to Claim 12, characterised in that said heat exchanger is located downstream of the raw mixed gas compressor, and in that said adiabatic expansion device is located in said delivery line downstream of the heat exchanger.

14. Apparatus according to Claim 13, characterised in that an after cooler, drain separator, drier and refrigerator are included in sequence in the raw mixed gas feed line downstream of said heat exchanger.

15. Apparatus according to Claim 12, characterised in that the heat exchanger is connected into the raw mixed gas feed line upstream of the compressor, and into the unadsorbed constituent gas delivery line downstream of the adibatic expansion device.

1 6. Apparatus according to Claim 12, characterised in that two heat exchangers are connected into the raw mixed gas feed line, on either side of the compressor, and in that the unadsorbed constituent gas delivery line is connected in sequence into the heat exchanger downstream of the compressor, the adiabatic expansion device, and the other heat exchanger.

17. Apparatus according to Claim 12, characterised in that two heat exchangers are connected into the raw mixed gas feed line, on either side of the compressor, and in that the unadsorbed constituent gas delivery line is connected in sequence into the heat exchanger upstream of the compressor, the adiabatic expansion device and the other heat exchanger.

18. Apparatus according to any one of the Claims 12 to 17, characterised in that the adiabatic expansion device is an expansion turbine, and in that said turbine is coupled to the drive for the raw mixed gas compressor.

19. Apparatus as claimed in any one of Claims 12 to 18, characterised in that the or a heat exchanger for effecting heat exchange between the unadsorbed constituent gas and the raw mixed gas, either before or after compression, is provided with a by-pass line so that the temperature of the unadsorbed constituent gas can be adjusted for external delivery.

20. Apparatus as claimed in any one of Claims 1 2 to 1 9, characterised in that a part of the unadsorbed gas to be delivered externally is fed via a feed line to the adsorption tower, in which a pressure has been lowered, whereby the adsorbate constituent gas within said adsorption tower can be desorbed and scavenged.

21. Apparatus as claimed in any one of Claims 12 to 20, characterised in that at least two adsorption towers are provided filled with appropriate adsorbents, whereby one tower adsorbs one constituent gas and the other adsorbs another constituent gas, so that a selected constituent gas can be readily recovered.

22. A process for separating air by adsorption into its O2 and N2 constituents, substantially as hereinbefore described with reference to Figures 2, 3, 4, 5, 6, 7, 8 or 9 of the accompanying drawings.

23. Apparatus for separating air by adsorption into its O2 and N2 constituents, substantially as hereinbefore described with reference to and as shown in Figures 2, 3, 4, 5, 6, 7, 8 and 9 of the accompanying drawings.