JPH02962B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved pressure swing method for the continuous separation of gas mixtures by adsorption, which method can advantageously be used to enrich air with oxygen.

If the component to be removed from the crude product gas is present in a relatively high concentration, e.g. 1% by volume or more, or if it is insufficiently adsorbed by the adsorbent and as a result a large adsorption device for thermal regeneration is required. and when a large regeneration amount is required, a method using pressure swing adsorption (PCA) is used. Separation by adsorption is generally carried out at a higher pressure than the desorption of the adsorbed component after the adsorption step. The desorption process is most often assisted by washing the adsorbent with a portion of the product gas, for example during recovery of nitrogen from combustion gases or during gas drying. When enriching the air with oxygen by adsorption, this cleaning is
carried out at 1 bar (absolute) for an adsorption pressure of 4 bar (absolute) using the separated product gas (German Publication No. 1259844) or a part of the pressure relief gas (German Publication No. 2338964). It will be done.

Molecular sieve zeolites used as adsorbents adsorb not only nitrogen but also oxygen and argon from the air, so enriching the air with oxygen is a
It occupies a position of particular importance compared to the PCA method. It is therefore not possible to adsorb only nitrogen and obtain all the oxygen present in the crude product air. Since argon is adsorbed at the same slow rate as oxygen, the method of enriching air with oxygen provides only 95% oxygen product with a residual content of 5% argon and nitrogen. In the hitherto known methods, these high oxygen concentrations can only be achieved if the amount of nitrogen on the molecular sieve zeolite is kept as low as possible in the adsorption outlet zone at the end of the adsorption stage, or if this zone is filled with oxygen. It will be done.
This means that during the performance of the desorption stage a valuable high percentage of oxygen is lost in the adsorption outlet zone and therefore the recovery rate for oxygen (obtained in proportion to the amount of atmospheric oxygen added to the process) is amount of oxygen) and
This means that the yield of the PCA device is considerably reduced.

This also applies if the adsorption is carried out under a pressure of about 1 bar (absolute) and the desorption is carried out by pumping the molecular sieve countercurrently to the adsorption using a vacuum pump. German Publication Specifications 1265724 and 1817004]. When the desorption is carried out under reduced pressure to enrich the air with oxygen, the nitrogen desorption is improved by the scavenging effect of the oxygen in the adsorption outlet zone. The oxygen enrichment process is further improved considerably by filling the adsorber with oxygen product after depressurization to the adsorption pressure, since this gas pushes the amount of nitrogen from the adsorption outlet section to the inlet section. [German Publication Specification 1544152]. Attempts have also been made to improve the cleaning effect by adding a portion of the product stream into the molecular sieve bed that needs to be desorbed [German Published Specification 2707745]; Due to the losses involved, this did not result in a substantial improvement in the efficiency of the process. The experimental results obtained in Example 1 below show that the production of 100 Nm ³ /h of oxygen (90% concentration) requires an amount of molecular sieves of about 5 m ³ per adsorber. This means that if 10% of the product gas is divided as cleaning gas, it gives an individual amount of cleaning gas of only 0.033 Nm ³ per m ³ of zeolite, which produces a cleaning effect from the experiments. It is known that there are far too few.

The present invention relates to a method for separating gas mixtures which eliminates these drawbacks of vacuum cleaning with a proportion of product gas and substantially improves the efficiency of the separation method by pure vacuum desorption (without cleaning gas). be.

The percentage recovery of the product obtained is thereby increased, thereby increasing the specific output of the vacuum pump (kwh/
A method has been found which allows the amount of oxygen produced (Nm ³ ) to be improved and the amount of adsorbent and crude product gas used to be reduced.

The present invention provides at least 30% of the crude product, e.g.
Desorption of the adsorbed components is carried out using several adsorbent beds below 1 bar (absolute pressure) while removing the purified or separated product, e.g. oxygen-enriched air, at the adsorber outlet. pressure and use the cleaning gas obtained from the adsorber for improved desorption when the adsorber has completed its adsorption stage, i.e. product release, and this cleaning gas is used for the improved desorption of the charged adsorber. adsorption is removed from the adsorption in the same flow direction and at the same time the adsorber is kept at its adsorption pressure by continued connection to the crude product, or the pressure in the adsorber is reduced by closing the adsorption inlet end during the discharge of the wash gas. This cleaning gas is then passed through a bed of adsorbent (the one to be desorbed) countercurrently to the direction of adsorption to 1 bar (absolute pressure).
Remove at the following pressure.

The method according to the invention is preferably used to enrich air with oxygen. It is used for the separation of gases and vapors with components that differ in their ability to be adsorbed, e.g. CO ₂ or from N ₂ or CH ₄ .
Removal of CO or _N2 , CO or _CH4 from _H2
Suitable for removal.

We have found a method that differs from the methods used hitherto in its improved efficiency and reduced operating costs. The structural features of the method according to the invention will now be described with reference to the accompanying drawings: FIG. and FIG. 2 is a flowchart of the method according to the invention.

With more particular reference to the drawings, in FIG. 1 a valve 11 for the inlet of the crude gas and an outlet valve 12 for the desorbed gas are located at the bottom of the adsorber. The adsorbent bed comprises at its lower end a protective layer, e.g. silica gel, for the predrying of the incoming crude gas, and above this layer a main zone containing the adsorbent for the separation of the gas stream. There is. A valve 14 for the release of the gas being treated by adsorption and a valve 13 for refilling the adsorber to adsorption pressure are located at the upper end of the adsorber. The filling of the adsorber can be regulated by a valve 15 to provide a constant increase in pressure and thus a constant supply of fill gas.

The device in FIG. 2 is the same as that in FIG. 1 with an additional valve 25.
and a limiter 26. The dimensional proportions of the valve are approximately indicated in the drawing. The additional valve 25 is relatively small due to the low velocity of the cleaning gas flow.
The dimensions of the cleaning gas flow can be adjusted by restrictor 26.

An essential feature of the process according to the invention is that the desorption of the adsorbent carrying adsorbent material is carried out at a pressure of less than 1 bar (absolute) and that a separate cleaning gas stream is used. This cleaning gas is not part of the product gas, but is obtained from the adsorber in which its adsorption, i.e. the release of the product, has already been completed.
To obtain this gas, the adsorber removed from the adsorption stage is kept in association with the crude gas, and the gas stream is removed from the adsorption outlet at the adsorption pressure, and the gas stream is removed at low pressure in a countercurrent manner to the adsorption. It passes through the adsorption bed where it is to be desorbed.

In another embodiment of the process according to the invention, the adsorber which has completed the adsorption stage is closed with a crude gas inlet and the gas from this adsorber is attempted to be desorbed countercurrently to the adsorption direction at a pressure of less than 1 bar. A cleaning gas is obtained by passing it through the adsorber.

The examples and comparative examples below explain in detail the various steps of the process, and the experimentally obtained values regarding the amount of product gas demonstrate the important effects and advantages of the cleaning process according to the invention. There is.

Comparative Example A pressure swing adsorber as shown in FIG. 1 was used. The total height of the bed in the adsorber was 2500 mm. Each adsorber has a particle size of 2-5mm for 2.5Kg
It contained 3Kg of silica gel at the bottom covered by molecular sieve zeolite 5A. twenty five
An oil-operated rotary vacuum pump V with a nominal capacity of m ³ /h was used. Adsorber A absorbs oxygen-rich air.
Compressor R is used to remove from B and C and pressurize it to 1.1-1.5 bar (absolute).
was provided.

A continuous process involving continuous removal of gas by compressor R was obtained using these three adsorbers. The following time program was selected: Steps: 0-60 seconds Ambient air was transferred to blower G, pipe L12 and valve 1.
Approximately 1 bar (absolute pressure) into adsorber A through 1A
It was flowed in at a constant pressure of . Oxygen-enriched air was removed as product at blower R via valve 14A and pipe L13. Valves 12A and 13A were closed. At the same time, a portion of the oxygen-enriched air flows from pipe L13 through flow regulating valve 15, pipe L14 and valve 13B into adsorber B, while valve 1
4B, 11B and 12B were closed. The previously desorbed, ie depressurized, adsorber B was refilled with oxygen-enriched air. In order to prevent a pressure drop in adsorber A due to rapid removal of the product (filling gas) through pipe L13, for example,
Valve 15 was adjusted to ensure a constant rate of product flow (expressed in Nm ³ /h) into adsorber B via pipe L14 and valve 13B.

During the adsorption stage in adsorber A and the filling stage in adsorber B, adsorber C is depressurized by a vacuum pump using valve 12C and pipe L11, i.e. valves 11C, 13C and 14C of adsorber C are It was closed. After a 60 second desorption or pump suction time, a mercury pressure gauge placed between valve 12C and adsorber C indicated a final pressure of 200 bar.

Stage 2: 60-120 seconds While closing valves 11A, 13A and 14A, adsorber A was evacuated to a final pressure of 200 mbar by means of a vacuum pump using valve 12A and pipe L11. Air is supplied to adsorber B using blower G and pipe L1.
2 and valve 11B, and product gas was removed from adsorber B by compressor R using valve 14B and pipe L13. Valve 12B
and 13B were closed. Pipe L13, flow control valve 15, and pipe L1 supply oxygen-rich air to adsorber C.
4 and valve 13C, so that the pressure in adsorber C was increased from 200 mbar to an adsorption pressure of about 1 bar. At the same time, valve 11 of adsorber C
C, 12C and 14C were closed.

Stage 3: 120-180 seconds Adsorber A is filled with oxygen-enriched air from pipe L13 using valve 15, pipe L14 and valve 13A, so that the pressure in adsorber A reaches its minimum desorption pressure (200 The adsorption pressure was increased from 1 bar (mbar) to 1 bar and one-way valves 11A, 12A and 14A were closed.

Adsorber B was evacuated to a final pressure of 200 mbar by vacuum pump V using pipe L11 and valve 12B, while valves 11B, 13B and 14B were closed.

Adsorber C is supplied with oxygen-enriched air, i.e. ambient air is supplied to blower G, pipe L12 and valve 1.
1C into adsorber C, and the product gas is removed by compressor R using valve 14C and pipe L13, while one valve 12C and 13C
closed.

After a cycle of 180 seconds, the method repeats itself, i.e. adsorber A is adsorbing and adsorber B
was being filled and adsorber C was under vacuum.

A product stream with a constant oxygen concentration was obtained from Compressor R within 0.5 to 1 hour after the start of the experiment. To measure product rates at 90% and 80% oxygen content, the method was adjusted to various product rates by adjusting blower G to a bypass setting (not shown in Figure 1). . At 90% oxygen concentration, 0.675N based on 100% oxygen
Oxygen product rates in m ³ /h were obtained. At 80% oxygen concentration, the oxygen product based on 100% oxygen was 0.90 Nm ³ /hr.

EXAMPLE 1 FIG. 2 is a flow diagram of a method according to the invention for enriching air with oxygen by PCA technology using three adsorbers. Desorption was carried out by evacuation of the adsorbent bed in countercurrent to adsorption, and at the end of desorption a second portion of product was removed as a wash gas from the adsorber where product release was completed. This cleaning gas was passed in countercurrent to the adsorption through the bed to be desorbed. During this desorption step, the adsorber from which the second portion of product was taken was kept at its previous adsorption pressure with the air inlet end kept open by a valve. In the experiment of Example 2, the amount of the above cleaning gas was 1.98N
m ³ /h, ie 11 Nl per adsorption cycle. The adsorber dimensions, adsorbent temperature, adsorption pressure, quantity and type, and vacuum pump dimensions were the same as in Example 1. The following program was used in one experiment: Stage 1: 0-20 seconds Ambient air was added to adsorber A using blower G, pipe L22 and valve 21A at an adsorption pressure of 1 bar (absolute). Oxygen-enriched air leaves adsorber A using valve 24A and pipe L23 and is removed as product through compressor R. Adsorber B has reached the final phase of its regeneration stage, i.e. adsorber B is depressurized by vacuum pump V using valve 22B and pipe L21, and oxygen-enriched air is transferred to valve 25C, restrictor 26,
It was transferred from adsorber C to adsorber B using pipe L24 and valve 23B. During this time, valve 21C remained open, ie adsorber C was held at adsorption pressure and filled with air from blower G. Although the valve 26 used in the experiments was a simple restrictor valve, the valve 26 could also be designed to be adjusted to ensure a constant flow rate. valve 22
A, 23A, 25A, 21B, 24B, 25B,
22C, 23C, 24C and 25 were closed.

Stage 2: 20-60 seconds Discharge ambient air to blower G, pipe L22 and valve 2
1A into adsorber A and discharged oxygen-enriched air from adsorber A through valve 24A and pipe L23, which was removed as product by compressor R.

Adsorber B was filled with oxygen-enriched air from pipe L23 to adsorption pressure using valve 25, pipe L24 and valve 23B.

Adsorber C was depressurized by vacuum pump V using valve 22C and pipe L21. Valve 22A, 23
A, 25A, 21B, 22B, 24B, 25B,
21C, 23C, 24C and 25C were closed.

Stage 3: 60-80 seconds The process steps were similar to stages 0-20 seconds, ie adsorber C was under vacuum. Oxygen-enriched air was removed from adsorber A, which had completed its release of oxygen product, and entered adsorber C as a cleaning gas, while adsorber C was being evacuated by vacuum pump V. Blower G transports surrounding air into adsorber B.
and oxygen-enriched air was added as product, which was removed by blower R.

Step 4: 80-120 seconds The process steps were similar to steps 20-60 seconds, ie adsorber A was evacuated by vacuum pump V. Adsorber B has blower G and compressor R
was used to generate oxygen-enriched air. Adsorption device C
was charged with oxygen-enriched air from adsorber B until it reached adsorption pressure.

Step 5: 120-140 seconds The process steps are similar to steps 0-20 seconds, i.e. flush adsorber A with oxygen-enriched air from the adsorber after product release is complete; The pressure was reduced using a vacuum pump. Adsorber C was filled with ambient air using blower G at an adsorption pressure of 1 bar (absolute), and oxygen-enriched air was discharged from adsorber B, which was removed as product by compressor R. .

Step 6: 140-180 seconds The process step is similar to the time cycle 20-60 seconds, ie adsorber A is filled with oxygen-enriched air from adsorber C to adsorption pressure. Ambient air was sent to adsorber C using blower G, while oxygen-enriched air was discharged from adsorber C and removed as product by compressor R. Adsorber B was depressurized by vacuum pump V.

When the oxygen concentration was 90%, an oxygen product of 0.76 Nm ³ /hour was obtained based on 100% oxygen.
When the oxygen concentration was 80%, the oxygen product rate based on 100% oxygen was 1.02 Nm ³ /hr.

Compared to the comparative known method, the oxygen product rate could be increased by only 12.6% when the oxygen concentration was 90% and by 7% when the oxygen concentration was 80%.

Example 2 FIG. 2 is a flow diagram of a method according to the invention for enriching air with oxygen by PCA technology using three adsorbers. Desorption was performed by evacuation of the adsorbent bed in countercurrent to adsorption. At the end of the desorption, oxygen-enriched air or cleaning gas was removed from the adsorber in which the adsorption stage, ie the product release, had already been completed, in the same flow direction as the adsorption. This cleaning gas was passed by a vacuum pump in countercurrent to the adsorption into the adsorber to be desorbed. During this desorption stage, the adsorber from which the cleaning gas was removed had a closed adsorption inlet end, resulting in a pressure drop. received.

In example 2, this pressure is 1 bar (absolute)
to 770 mbar (absolute). the optimum removal rate of the cleaning gas, i.e. the optimum drop in pressure;
has to be determined experimentally, since it depends inter alia on the nature of the adsorbent used and on the nature of the vacuum pump.

A process program similar to that of Example 1 was used in the experiment of Example 3. Adsorber dimensions, adsorbent temperature,
Adsorption pressure, volume and type, and vacuum pump dimensions were the same as in the comparative experiment.

The various process steps of Example 2 will now be described in detail with respect to the first two cycles.

Stage 1: 0-20 seconds Ambient air was added to adsorber A using blower G, pipe L22 and valve 21A at an adsorption pressure of 1 bar (absolute). Oxygen-enriched air leaves adsorber A using valve 22A and pipe L23 and is removed as product through compressor R. Adsorber B has reached the final phase of its regeneration stage, i.e. adsorber B is depressurized by vacuum pump V using valve 22B and pipe L21, and oxygen-enriched air is transferred to valve 25C, restrictor 26,
It was transferred from adsorber C to adsorber B using pipe L24 and valve 23B. During this period, valve 21C is closed, so that the pressure in adsorber C is between 1 bar (absolute) and, for example, 770 mbar (absolute).
descended to The wash gas added into adsorber B did not lead to a final pressure of 200 mbar at the end of the vacuum cycle as in the comparative example, but the amount of wash gas led to a final pressure of 220-300 mbar. Valve 22A, 23A, 25A, 21B, 2
4B, 25B, 22C, 23C, 24C and 25
was closed.

Stage 2: 20-60 seconds Discharge ambient air to blower G, pipe L22 and valve 2
1A into adsorber A and discharged oxygen-enriched air from adsorber A through valve 24A and pipe L23, which was removed as product by compressor R.

Adsorber B was filled with oxygen-enriched air up to adsorption pressure, and gas from pipe L23 entered adsorber B through valve 25, pipe L24, and valve 23B.

Adsorber C was depressurized by vacuum pump V using valve 22C and pipe L21. Valve 22A, 23
A, 25A, 21B, 22B, 24B, 25B,
21C, 23C, 24C and 25C were closed.

Stage 3: 60-80 seconds The process steps are similar to stages 0-20 seconds, i.e. adsorber C is empty, adsorption inlet end of adsorber A is closed (valve 21A/22A), and Oxygen-rich gas was depressurized from adsorber A in the same flow direction as the adsorption, and it flowed into adsorber C as a wash gas. Adsorber B produced oxygen-enriched air as a product.

Stage 4: 80-120 seconds The process steps were similar to the time cycle 20-60 seconds, ie adsorber B distributed oxygen-enriched air, which was received by compressor R as product. Adsorber C was filled with oxygen-enriched air from adsorber B to adsorption pressure. Adsorber A was depressurized using a vacuum pump.

Step 5:: 120-140 s Similar to the 0-20 s time cycle, i.e. the adsorption inlet end of adsorber B is closed (valve 21B/22
B) continued to depressurize adsorber A and removed oxygen-enriched gas from adsorber B in the same flow direction as the adsorption, and it flowed through adsorber A as a wash gas. Adsorber C produced oxygen-enriched air as a product.

Step 6: 140-180 seconds The process steps were similar to the 20-60 second time cycle, ie adsorber C produced oxygen-enriched air which was distributed as product to compressor R. Adsorber A was filled with oxygen-enriched air from adsorber C to adsorption pressure. Adsorber B was depressurized by vacuum pump V.

In the experiment of Example 2, based on 100% oxygen
An oxygen product rate of 0.87 Nm ³ /h was obtained from Compressor R at an oxygen concentration of 90%. Oxygen concentration is 80
%, the oxygen product rate based on 100% oxygen was 1.02 Nm ³ /hr. Compared to the experiment from Comparative Example 2, the oxygen product rate is
When it is 90%, it is only 29% and the oxygen concentration is 80
%, it could only increase by 13.5%.

A further improvement was obtained in the process according to the invention by using four adsorbers. In the system using three adsorbers, the time required to fill the adsorbers to adsorption pressure was reduced by the final washing step, ie, it was not equal to the adsorption time. During the final cleaning period, blower G supplied air at a below average rate, while during the filling process it supplied air at an above average rate.

By providing four adsorbers, a constant distribution rate was obtained from blower G, and as Example 3 shows, a higher oxygen product rate was obtained compared to the method of Example 2, for example. . However, the equipment cost for the four adsorber system was higher than that for the three adsorber system. For the four adsorber system, a relatively high specific oxygen product rate (Nm ³ oxygen/hour x Kg of zeolite in the adsorber) results in a relatively low for the same oxygen product rate (Nm ³ /hour). Due to the possible energy consumption of the pumps, the overall equipment and operating costs for a four adsorber system have proven advantageous.

A program similar to the comparative example was used for the experiments in Example 3. The adsorber dimensions, adsorbent temperature, adsorption pressure, volume and type, and vacuum pump dimensions were the same as during the comparative experiment.

Example 3 Stage 1: 0-60 seconds Adsorber A supplies oxygen-enriched air, i.e. blower G directs the air to pipe L32 and valve 31A.
and oxygen-enriched air was discharged from adsorber A using valve 34A and pipe L33 and removed as product by compressor R. The oxygen-rich air from adsorber A is supplied to adsorber B through flow control valve 36 and pipe L3.
4 and valve 33B, so that the pressure in adsorber B rose from its lowest desorption pressure to an adsorption pressure of 1 bar (absolute). Adsorber B is connected to vacuum pump V using pipe L31 and valve 32B.
The cleaning gas was desorbed or depressurized by , and the cleaning gas was removed from adsorber D in countercurrent to the adsorption. Since valves 31D and 32D are closed, the pressure in adsorber D drops, for example from 1 bar (absolute) to 770 mbar (absolute), and the cleaning gas from adsorber D flows through valve 35D, pipe L35, Adsorber C was entered using restrictor 39 and valve 35C. valve 32
A, 33A, 35A, 31B, 32B, 34B,
35B, 31C, 33C, 34C, 31D, 32
D, 33D, and 34D were closed.

Stage 2: 60-120 s Similar to the 0-60 s time cycle, adsorber B distributes oxygen-enriched air and transfers a portion of this enriched air to adsorber C at 1 bar (absolute). It was used to fill up to the pressure. Adsorber D was evacuated and the wash gas was removed from adsorber A and added into adsorber D.

Stage 3: 120-180 seconds Similar to the 0-60 seconds time cycle, adsorber C produced oxygen-enriched air, part of which was used to fill adsorber D to adsorption pressure. .
Adsorber A was evacuated and the wash gas was removed from adsorber B and added into adsorber A.

Stage 4: 180-240 seconds Similar to the 0-60 seconds time cycle, adsorber D dispenses oxygen-enriched air and fills adsorber A with a portion of this enriched air to adsorption pressure. used for. Adsorber B was evacuated and the wash gas was removed from adsorber C and added into adsorber B.

In the experiments of Example 3, an oxygen product rate of 0.93 Nm ³ /hr based on 100% oxygen was obtained from Compressor R when the oxygen concentration was 90%. 80
% oxygen concentration, the oxygen product rate based on 100% oxygen was 1.05 Nm ³ /hr. In this way, the method of Example 3 is 90% more effective than the comparative example.
and a product increase of 38% at an oxygen concentration of 80
% oxygen concentration gave a 17% increase.

It will be recognized that the specification and examples are presented in an illustrative and not a restrictive sense, and that various modifications may be made without departing from the spirit and scope of the invention.

[Brief explanation of drawings]

FIG. 1 is a diagrammatic representation of the conventional method. 2 and 3 are process diagrams of the method according to the invention.

Claims (1)

[Claims] 1. Continuous operation adsorption for purifying gases and separating gas mixtures, in particular for increasing the oxygen content of air, by pressure swing adsorption using at least three adsorbers A, B, C. A method, comprising: (a) introducing an unpurified gas into an adsorber from the bottom end of the adsorber, and extracting a component of the gas that is difficult to adsorb as a product from the top of the adsorber A, thereby producing an unpurified gas mixture; Separate into easily adsorbable components and poorly adsorbable components by adsorption under adsorption pressure in adsorber A, and (b) While the step (a) above is being carried out, adsorber B is evacuated in the final stage of the regeneration process. , and then move adsorber B to adsorber C in the opposite direction to the adsorption direction.
c) On the other hand, in adsorber C, when the cleaning gas is discharged, the raw gas inlet end closing and reducing the pressure to approximately 770 mbar (absolute); during the same period of time, (b) filling adsorber B with product gas until adsorption pressure is reached, and (c) evacuating adsorber C starting from about 770 mbar. . 2. The method according to claim 1, wherein A-type and/or X-type molecular sieve zeolite is used. 3. A method according to claim 1 or 2, wherein an adsorption pressure of 1 to 4 bar (absolute) is used.