Note: Descriptions are shown in the official language in which they were submitted.
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Metha~d for the seParation of ~as mixtures by pressure-swin~ adsorption in a
two-bed adsorber s~vstem
5 The present invention relates to an improved and simplified method, which is also
favourable as regards energy, for the adsorptive separation of gas mixtures, in
particu.lar of air, by means of inorganic adsorbents, in particular by means of
molecular-sieve zeolites, by pressure-swing adsorption in a two-bed adsorber
system.
10 The adsorptive separation of gas mixtures with the aid of pressure-swing
adsorption has been known for over 20 years, in connection with which a variety
of teclmical separation processes have been developed. However, all methods are
based on the principle that the gas portion of the gas mixture (crude gas) that has
the higher affinity to the adsorbent is retained in a so-called adsorption step on the
15 surface of the adsorbent in an adsorber and the less strongly adsorbed component
can be withdrawn from the adsorber that is charged with adsorbent. Desorption ofthe adsorbed phase is then achieved by lowering the pressure after the adsorption
step and optionally in addition by flushing the adsorbent with a portion of the less
strongly adsorbed gas. If the pressure is lowered to approximately ambient
20 pressure or slightly above ambient pressure, one speaks of PSA systems (Pressure
Swing Adsorption). In the case where the pressure is lowered to a pressure belowambient pressure by means of a vacuum pump, one speaks of VSA systems
(_acuum Swing Adsorption). Also in this case the adsorbent is optionally flushedwith a portion of the less strongly adsorbed gas. But there are also cases in which
25 flushing is dispensed with, in particular for example in the case of oxygen
enrichment of air with molecular-sieve zeolites. The processes with excess-
pressu:re adsorption and vacuum desorption are designated as PVSA systems
(Pressure Vacuum Swing Adsorption).
In the following explanatory details the data in "bar" are to be understood as being
30 excess pressure in relation to the ambient pressure, the evacuation pressures"mbar" are to be understood as being absolute values and Nm3 is to be understoodas m3 at 0~C and 1.013 bar abs.
If the adsorption is effected at approximately ambient pressure - that is to say~ at
-0.05 to 0.1 bar for example, and the desorption is effected at a low pressure of,
for example, 100 to 400 mbar (abs), then one speaks of a VSA process. After the
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desorption step, charging of the adsorbent with gas is always effected to the
pressure of the adsorption step - in the cases of PSA adsorption, with the less
strongly adsorbed gas portion or crude gas or with both simultaneously. In the
case of the VSA technique, charging is effected with the less strongly adsorbed
gas portion.
The aforementioned separation processes are therefore divided up into three steps:
adsorption (separation), desorption (with lowering of pressure) and recharging
(with l)uild-up of pressure), on account of which three adsorbers are necessary for
a PSA or VSA process that operates in totally continuous manner.
With a view to reducing the investment costs, VSA systems with 2 adsorbers and
a product buffer have been customary for some time. Since also in this case the
adsorption process consists of 3 stages - adsorption, evacuation, charging to
adsorption pressure - but only two adsorbers are available, some stages flow
smoothly into one another or are kept very short. Adsorption is mostly effected at
0.1 to 1 bar, the desired product being produced already in the course of build-up
of pressure above ambient pressure with air.
The temporal processing sequence of two-bed adsorbers in the case of a PVSA
proces:s for the ~2 enrichment of air is frequently (see also Fig. 5 and Fig. 6) the
following:
20 a) end of the adsorption in adsorber A at, for example, 0.4 bar (pressure =
PAd max) excess pressure
b) decanting step (so-called BFP step; time tl) from adsorber A into the
second adsorber B down to approximately ambient pressure or somewhat
lower, for example to 700 mbar (pressure = PDeS O)7 whereby adsorber B is
simultaneously evacuated and the pressure in B rises from its lowest
pressure (pressure = PDes min) to a higher pressure, for example from 200 to
400 mbar (pressure = PBFP)
c) evacuation of adsorber A (times t2, t3 and t4; N2 desorption with or without
flush gas by means of vacuum pump "V" to between 600 and 200 mbar
(abs) (pressure = PDes,min)
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d) decanting step (see under b), as a result an increase in pressure in adsorber
A from, for example, 200 to 400 mbar (time t5)
e) residual charging step to approximately ambient pressure in adsorber A and
to adsorption pressure with air via blower "G", optionally in addition while
circumventing "G", partly in the first charging period also with ~2 product
from the buffer "R" (time t6); product gas is continll~lly withdrawn from
the reservoir "R" with the aid of compressor "K".
Since the ~2 yield - that is to say, the ratio of the quantity of ~2 in the product
gas to the quantity of ~2 in the air that is used - has a direct influence on the
energy that has to be provided for the air blower and for the vacuum pump,
attempts have been made by means of suitable measures to conclude the process
prior to the evacuation in such a way that the ~2 concentration in the adsorption
exit zone is virtually equal to the ~2 concentration in the entry zone. This is the
case with methods in which gas from the exit zone is recycled into the entry zone.
In GB-A 1,559,325 (in particular Figs. 7 and 8; 3-adsorber adsorption method) atthe end of the adsorption, for example by adsorber A, the gas at adsorption
pressu:re that is low in ~2 in comparison with the ~2 product gas is fed back into
the already charged adsorber B at adsorption pressure into the entry zone and the
product gas is withdrawn from the exit zone of adsorber B. The time for the
recirculation is relatively long, since the ~2 product rate determines the
recirculated quantity and the time. This method has the crucial disadvantage that
the tirne for product recirculation reduces either the time for pressurising theadsorbers or the pumping-out time. In addition, dry gas is conducted through thedrying zone upstream of the zeolite feedstock, as a result of which moisture gets
into the N2-O2 separation zone of the zeolite feedstock.
In GB-A 2,154,465 (in particular Fig. 3), in a 3-adsorber system at the end of the
adsorption, for example by adsorber A, a pressure compensation is carried out
across the exit zone of adsorber A into the entry zone of the evacuated adsorberB, whereby the pressure drops in adsorber A and increases in adsorber B. The
same Imethod is described in DE-A 30 30 081 (in particular Fig. 1 and column 4,
lines 18-47). A disadvantage of this method is that the quantity to be decanted is
predetermined and limited by the possible pressure difference of the pressure relief
-that is to say, it ceases to apply in the case of adsorption at ambient pressure.
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In EP-A 0 334 495 a pressure-compensation system in a 2-adsorber system is
likewise described. At the start of evacuation, evacuation is effected, for example,
from a~dsorber A in downward flow, at the exit end of adsorber A gas that is lowin ~2 iS simultaneously withdrawn in upward flow and charged into the already
5 evacua,ted adsorber B into the entry zone thereof in upward flow. The quantity of
recirculated gas is also limited in this case, namely within the pressure difference
in the course of pumping-out, which is a disadvantage.
The known methods described above have the disadvantage that the so-called "exitgas" is dry and in the course of recirculation is conducted through the drying zone
10 and that, as a result, the water front is displaced into the zeolite zone. In addition,
the quantity of gas involved in the recirculation is limited by the predetermined
pressure differences of the pressure relief in co-current flow or the recirculation
time is too long as a result of the predetermined parameters such as product
quantil~y, for example. As a result, in the case of ~2 enrichment of air the entire
possible quantity of the gas that is low in ~2 (21 to 90%) cannot be recycled.
The object was therefore to make available an improved method for the separationof gas mixtures, in particular air, by pressure-swing adsorption in a two-bed
adsorber system that makes it possible to carry out the adsorptive separation in a
manner that is simple and favourable as regards energy, to avoid conducting dry
20 gas through the so-called damp drying zone and to avoid the disadvantages of
recirculating the product gas that is low in ~2 (residual product gas), such as loss
of tim~e or limitation of the quantity of recirculated gas.
It has been possible to achieve this object with the method according to the
mvention.
25 The subject of the invention is a method for the separation of air by adsorption
with molecular-sieve zeolites in a two-bed adsorber system with product buffer for
the purpose of m~int:~ining a continuous, constant stream of oxygen product,
whereby the two adsorber beds with molecular-sieve zeolites are present in a
homogeneous feedstock or in several different feedstocks of various types of
30 zeolite and optionally a layer of an adsorbent that is selective with respect to
water is located upstream of the feedstocks, wherein, at approximately ambient
pressure or up to an excess pressure of 0.5 bar during the adsorption, air is
conducted through the first adsorber A and nitrogen is adsorbed on the molecular-
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sieve z:eolite preferentially in relation to oxygen, whereby product gas that is high
in oxygen having an ~2 concentration amounting to between 60 and 96 vol-% is
obtained at the exit end of adsorber A, after the adsorption the desorption of the
nitrogen and optionally of the moisture is carried out by evacuation in counterflow
to the adsorption at a lowest pressure of 100 mbar to 600 mbar (absolute),
characlerised in that
a) after the adsorption in adsorber A, the pressure of which drops from its
final value after the adsorption step to A) ambient pressure, to B) low
pressure down to 600 mbar or to C) excess pressure up to 0.2 bar, and the
inlet end of which in the process is a) closed, is b) open in relation to the
environment or c) an air compressor remains connected, residual product
gas flows out of the outlet end of adsorber A into the outlet end of
adsorber B, whereby at the start of this step adsorber B is at its lowest
pressure level of 100 to 600 mbar, and optionally adsorber B is
simultaneously evacuated via its inlet end, whereby the pressure in
adsorber B a) rises, b) remains constant or c) drops,
b) ambient air without additional compression is introduced into adsorber A
via the inlet end thereof, in the process the pressure in adsorber A remains
at approximately ambient pressure or adsorber A is charged up to ambient
pressure, gas that is rich in O2is taken off at the outlet end of adsorber A
and is introduced into adsorber B via the inlet end thereof until
approximately ambient pressure is reached and optionally additional
ambient air is introduced without additional compression directly into the
inlet end of adsorber B,
25 c) ambient air with compression is conducted into adsorber B via the inlet
end thereof and product gas is simultaneously supplied to the product
buffer, optionally product gas from the product buffer is supplied to the
outlet end of adsorber B and adsorber A is simultaneously evacuated via
the inlet end thereof,
d) adsorber A is evacuated to its lowest pressure of 100 to 600 mbar and is
simultaneously adsorbed in adsorber B, by ambient air with compression
being conducted via the entry end of adsorber B and product gas being
conducted via the outlet end of adsorber B into the product buffer and
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optionally adsorber A being simultaneously flushed via the exit end thereof
with product gas.
In particularly preferred manner the method according to the invention is carried
out in such a way that
5 a) after the adsorption in adsorber A residual product gas is conducted out of
the outlet end of adsorber A, the pressure of which drops in the process
from between 0.2 and O.S bar excess pressure to approximately ambient
pressure, into adsorber B, which is at its lowest pressure level of 100 to
600 mbar, via the outlet end thereof and optionally adsorber B is
simultaneously evacuated via the inlet end, whereby the pressure in
adsorber B rises to max. 90% of the ambient pressure or remains constant,
b) ambient air without additional compression is introduced into adsorber A
via the inlet end thereof, gas that is rich in O2is taken off at the outlet end
of adsorber A and is introduced into adsorber B via the inlet end thereof
until approximately ambient pressure is reached and optionally additional
ambient air without additional compression is introduced directly into
adsorber B,
c) ambient air with compression is conducted into adsorber B via the inlet
end thereof and optionally product gas is introduced simultaneously from
the product buffer into adsorber B via the outlet end thereof and adsorber
A is simultaneously evacu~tecl7
d) adsorber A is evacuated to its lowest pressure of 100 to 600 mbar and is
simultaneously adsorbed into adsorber B, by ambient air with compression
being conducted through via the entry end of adsorber B and product gas
being conducted via the exit end of adsorber B into the product buffer and
optionally adsorber A being flushed simultaneously via the exit end thereof
with product gas.
An adsorption method for ~2 enrichment of air in a two-bed adsorber system with
molecular-sieve zeolites has been discovered, with the aid of which the energy
demand for the purpose of generating the oxygen can be considerably reduced in
comparison with conventional methods, wherein after the adsorption step of air
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separation in particular at 0.05 to 0.5 bar (max. 1 bar, excess pressure) optionally
a lowering of pressure in the co-current flow direction in relation to the adsorption
to, for example, ambient pressure is effected, this pressure-relieved gas is passed
in known manner into an already evacuated adsorber, then ambient air is passed
5 through the relieved adsorber in the co-current flow direction in relation to the
adsorption, at the adsorber exit thereof gas containing ~2 iS withdrawn and thisexit gas is introduced into the entry zone of the evacuated and optionally partly
repressurised adsorber, and this charging is concluded at a charging pressure ofapprox.imately ambient pressure or with an ~2 concentration of the charge gas
10 amounting to between 15 and 90%, whereby optionally during the charging
ambient air flows simultaneously into the entry zone of the adsorber to be
pressurised, then this adsorber is charged further with ambient air and
simult;meously with ~2 from the buffer in counterflow to the adsorption to a final
presswre of 0.03 to 0.5 bar, max. 1 bar (excess pressure), prior to reaçhing its final
15 presswre ~2 product is emitted into a reservoir, namely at a time when the
reservoir pressure is slightly below the adsorber pressure, during this time thesecond adsorber is evacuated in counterflow and during the entire evacuation
period or at the end of the evacuation step is flushed with ~2 product gas in
counterflow to the separation of air.
20 The nnethod according to the invention avoids the disadvantages of the
recirculation and introduction of dry gas into the entry side of the drying zone.
No loss of time arises as a result of the recirculation, and no limitation of the
quantil:y of recirculated gas.
The recirculation of the product gas that is low in ~2 (residual product gas) at the
25 end of ~2 production (adsorption) and optionally the decanting step may be
.
carrlecl out In vanous ways.
In Figures 4a to 4d the individual process stages of one half-cycle are represented
schematically by way of example. In addition, the pressure profile has been
sketched in schematically in the adsorbers.
30 Embodiment of Figure 4a: at time tl adsorber "A" has concluded its ~2 production
step at approximately 1 atm, the air continues to pass at approximately 1 atm inco-current flow in relation to the adsorption by adsorber "A", gas cont~ining O2is
withdrawn at the adsorber exit, said gas being conducted in counterflow to the
23189-8208
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adsorption through adsorber "B", the vacuum pump at adsorber "B" is still
connected, the "quantity of decant gas" is such that a sufficient flushing action
arises, as a result of which the pressure in the adsorber may possibly not drop any
further but remains constant or rises. In the next step (time t2) air continues to be
5 conducted in co-current flow through, for example, adsorber "A", gas that is low
in ~2 iS withdrawn at the adsorber exit and this gas is sent in co-current flow in
relatio:n to the adsorption into adsorber "B" which is to be brought to adsorption
pressure, whereby simultaneously, as needed, ambient air is sent into adsorber "B"
in co-c,urrent flow in relation to the adsorption. The pressure in adsorber "A"
10 which emits gas that is low in ~2 amounts to approximately ambient pressure.
The amount of gas conducted away that is low in ~2 iS not limited in its total
quantily, since sufficient ambient air is available for the subsequent separation.
Since the gas that is low in O2is generated at ambient pressure, as a result of the
loss oi.' pressure of the system a low pressure in the adsorber emitting gas that is
15 low in ~2 may arise (see Fig. 4a, time t2). Then in time t3 adsorber "A" is
evacuated in counterflow to the adsorption, air at approximately ambient pressure
is passed through adsorber "B" and ~2 product is introduced into a product
reservoir. At the end of the adsorption step and the evacuation step, adsorber "A"
may optionally be flushed with a partial current of the product (time t4).
20 In another embodiment, according to Figure 4b the entire process proceeds
similarly to the process of Figure 4a, only the air separation is carried out at a
pressure above ambient pressure, for example 0.1 to 0.6 bar. Then, after the
adsorption step, adsorbers "A" and "B" are connected at the outlet end, a so-called
BFP step takes place - that is to say, adsorber "A" drops in pressure to ambient25 pressure in adsorber "B", whereby adsorber "B" is still connected to the vacuum
pump and the pressure in adsorber "B" can rise. The relief of adsorber "A" may
also be effected in two stages, firstly the BFP step from, for example, 0.5 bar to
0.2 bar and continuation of the pressure compensation (PB step) to ambient
pressu:re in "A", whereby the vacuum pump in "B" is not connected.
30 In another embodiment according to Figure 4c, the recirculation of gas that is low
in ~2 into adsorber A at time t2 proceeds at decreasing excess pressure from, for
example, 0.1 bar down to approximately ambient pressure, since the decanting
steps "BFP" and/or "PB" into adsorber "A" have been concluded at 0.1 bar.
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g
In another embodiment, according to Figure 4d the recirculation of gas that is low
in ~2 into adsorber A proceeds at time t2 at increasing pressure from, for example,
800 mbar (abs) - that is to say, beginning at low pressure, rising to approximately
ambient pressure - since the decanting steps "BFP" and/or "PB" into adsorber "A"5 have been concluded at 800 mbar (abs).
With reference to Figs. 1, 2a, 2b and 3 an implementation of the method
according to the invention will be elucidated in more detail.
In Fig. 3 the temporal pressure profile of adsorbers A and B and of the ~2 buffer
is shown, in Figs. 2a and 2b the process stages at the respective times are
1 0 represented.
Time tl: Via valve A4/B4 a partial pressure compensation is effected.
Valves A1/A21A31B l/B3/AB 1 are closed. The air blower "G"
operates in the circuit. Valve B2 can be closed, in this case a
"pure" pressure compensation (PB) arises, the vacuum pump "V"
lS then operates in the circuit. But it is also possible to accelerate the
charging in the PB step by valve B1 additionally being opened and,
as a result of this, air from blower "G" flowing in from the entry
side. In another variant, valve B2 is open (BFP process), as a result
of which adsorber B continues to be evacuated. During time tl the
pressure in the adsorber rises from PDes,min to PPB or PBFP
respectively.
A combination of the BFP and PB steps is also possible - that is to
say, firstly the BFP step is effected (ie, inclusive of evacuation),
lowering of the pressure of adsorber A to above ambient pressure,
then the PB step (ie, partial pressure compensation) with a relief of
adsorber A to approximately ambient pressure (or slightly lower).
The decanting step (PB) may also be effected via valve A4/B3 and
lines Lp and LR, whereby optionally adsorber B is also
simultaneously topped up with air via valve B1.
During time t1, product that is high in ~2 iS withdrawn from
reservoir "R" to the consumer.
Time ~2: Valves A4, B3 and A1, B1 are open, rem~ining valves are closed.
The air compressor is operated at about ambient pressure, air flows
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via valve A1 into adsorber A, gas that is low in ~2 leaves adsorber
A via valve A4, flows into a recirculation line LR and flows via
valve B3 into adsorber B, whereby optionally in addition air flows
via the air line LL into adsorber B (valve Bl) (= RBF step). In this
case the vacuum pump operates in the circuit. As a result of the
loss of pressure of the feedstock of the adsorber, at time t2 the
pressure in adsorber A can easily fall below ambient pressure. The
quantity of gas that is low in ~2 which reaches adsorber B via line
LR may be adjusted by regulation of the quantity of air at valve B1
- for example by delayed opening of B1. This quantity of air
depends on the minimum extraction pressure, the difference of the
relief pressure in adsorber "A" and the quantity of the recycled gas
that is high in ~2 The recirculation of the gas that is low in O2iS
concluded when the charging pressure amounts to approximately
ambient pressure or the ~2 concentration thereof reaches
approximately 15-90 vol-%. If the quantity of charge gas is limited
on account of too small a difference in the charging pressure
(between ambient pressure and evacuation pressure), the final ~2
concentration of the charge gas may also be far above 21%. In this
case an additional charging of "B" with air is unnecessary.
Time t3: Adsorber A is exhausted via valve A2. Adsorber B is pressurised
via valve B1 with the aid of the air compressor, whereby valves
B2/B3 are closed or in another embodiment is simultaneously
charged with ~2 product from the reservoir "R" via valves B4 and
AB1. During the evacuation of adsorber A, adsorber A can be
flushed with product via valve AB1/A4. The end of time t3 is
reached when the reservoir pressure has dropped from maximum
PAd maX to its lowest pressure PR m
Time t4: Adsorber A is exhausted via valve A2 to its lowest pressure PDeS min
and is simultaneously flushed with product gas from the product-gas
line LP via valve A4. The flush gas, which reaches adsorber A via
valve A4, must accordingly be optimised in quantity. In the case of
a BFP process (see time t1), this quantity of flush gas is very small
or can be omitted. Adsorber B continues to be brought to its final
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pressure via valve B1, the emission of ~2 product into the reservoir
"R" is effected within time t4.
The process is continued in a manner analogous to these process steps (times tl-t4)
by exch~ngin~ the adsorbers A and B.
5 Suitable by way of adsorbents for the method according to the invention for the
~2 enrichment of air are molecular-sieve zeolites exhibiting preferential adsorption
of N2 in relation to ~2~ such as zeolite A and zeolite X in the Na form or in the
form substituted with divalent alkaline(-earth metal) ions (such as Ca, Mg, Sr or
mixtures thereof) or in the form substituted with monovalent ions such as lithium
10 with substitution rates above 85%, or natural zeolites or their synthetically produced forms such as mordenite or chabazite.
The method according to the invention will be elucidated in more detail in the
following Examples.
Examl~les
15 For all the Examples the following data remain constant:
Reservoir volume 1.5 m3
Inside diameter of adsorber 550 mm
Packing height of adsorber 1,800 mm
Ambient pressure about 1045 mbar
20 Adsorbent charge per adsorber:
56 dm3 medium-pore silica gel at the lower end of the adsorber, residual feedstock
in each case 240 kg molecular-sieve Ca zeolite A, produced in accordance with
EP-A 0 170 026, Example 2. Calcination was effected in a stream of nitrogen at
500 to 600~C. The molar CaO/AI2O3 ratio amounted to 0.72. The granulation
25 amounted to 1 - 2.5 mm in diameter, spherical form.
The crude gas supplied had a temperature of +30~C and was always 75~/0 saturatedwith water at ambient pressure and 30~C. By way of vacuum pump, use was
made of a 2-stage rotary-piston blower ("Roots") that was capable of being
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adjusted via a mech~nism The crude gas was compressed with the aid of a
rotary-piston blower. The pressure was measured in each case at the lower end
(air-entry side) of the adsorber.
The energy demand of the vacuum pump was calculated from the pressure profile
5 durin~; pumping-out upstream of the feedstock, use being made of the
characteristic (= energy demand as a function of the extraction pressure) of a
known Roots blower having an extraction capacity of 20,000 m3/h at 1.03 bar,
abs..
The energy demand of the air blower was calculated in accordance with the
followïng formula:
Pm = 1045 mbar
(0.306 x Pm - 286) x Vo Vo = amount of air at 1.03 bar, abs. (m3/h)
10,306 x ~
,u = efficiency = 0.95
Example 1 (Comparison)
Use was made of an installation corresponding to Figure 5. The process sequence
and the pressure profile are reproduced in Figure 6.
15 Time tl: 0 to 4 seconds
An air compressor was located in the circuit. The pressure in adsorber B rose
from I'DeSmin = 250 mbar to PBFP = 450 mbar7 simultaneously in adsorber A the
maxim.um pressure PAd maX = 0 3 bar dropped, whereby at the upper end gas was
conducted out of adsorber A via valve A03 into adsorber B via valve B03, at the
20 lower end adsorber B was evacuated via valve B02 with a vacuum pump. The
pressure in adsorber A dropped to PDeS O = 990 mbar. Reservoir R supplied
produc;t gas at a pressure of about 0.3 bar; valve AB01 was closed.
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Time t2: 4 to 9 seconds
Adsorber A was evacuated via valve A02 to approximately 650 mbar, the upper
end of the adsorber was closed. Adsorber B was pressurised to 1 atm at the lowerend vi.a valve B01 with air from the air compressor "G", simultaneously a
5 charging with gas from the reservoir "R" was effected via a volume-controlled
valve AB01 and valve B03, whereby the pressure in the reservoir dropped from
about 0.3 bar to approximately 0.2 bar. Product gas continued to be withdrawn
from reservoir R.
Time t3: 9 to 13 seconds
10 Adsorber A was evacuated further, adsorber B was charged with air from air
compressor "G" and product from the reservoir "R" as in time t2. Reservoir
pressure and pressure in adsorber B reached 0.05 bar.
Time t4: 13 to 30 seconds
Adsorber A was evacuated further, whereby a final pressure of 250 mbar was
15 reached. Via the air compressor "G" and valve B01 air flowed into adsorber B,product gas was fed into reservoir R via valves B03 and AB01, the pressure in
adsorber A and in the reservoir R reached a final pressure of 0.3 bar.
The process proceeded further in a manner analogous to times t1/t2lt3/t4, only
adsorber A was exchanged for adsorber B.
20 A quantity of product gas from reservoir R of 19 Nm3/h with an ~2 concentration
of 93~/'o was obtained. The ~2 yield amounted to 46%, the specific energy value
of the vacuum pump was calculated as 0.378 kWh/Nm302, the total energy value
derived from pump and air compressor amounted to 0.472 kWh/Nm3O2.
Example 2 (Comparison)
25 Use was made of an installation corresponding to Figure 5. The process sequence
and the pressure profile are reproduced in Figure 6. During time tl, however, the
vacuum pump was disconnected from the adsorber with valves A02 and B02.
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Time tl: 0 to 4 seconds
Valve B01 was open. Ambient air flowed into the evacuated adsorber B. Valve
B02 was closed. The pressure in aclsorber B rose from PDeSmjn = 250 mbar to
PPB-I = 650 mbar, simultaneously the pressure in adsorber A dropped from its
5 maximum value PAd maX = 0 3 bar to PDeS o = 990 mbar, whereby at the upper endgas flowed out of adsorber A via valve A03 into adsorber B via valve B03.
Reservoir R supplied product gas at a pressure of about 0.3 bar; valve AB01 was
closed.
Time t2: 4 to 9 seconds
Adsorber A was evacuated via valve A02 to approximately 650 mbar, the upper
end of the adsorber was closed. Adsorber B was pressurised to ambient pressure
at the lower end via valve B01 with air from the air compressor, simultaneously a
charging with gas from the reservoir R was effected via a volume-controlled valve
AB01 and valve B03, whereby the pressure in the reservoir dropped from about
15 0.3 bar to approximately 0.2 bar. Product gas continued to be withdrawn from
reservoir R.
Time t3: 9 to 13 seconds
Adsorber A was evacuated further. Adsorber B was charged with air and product
gas from the reservoir, as in time t2. Reservoir pressure and pressure in adsorber
20 B reached approximately ambient pressure.
Time t4: 13 to 30 seconds
Adsorber A was evacuated further, whereby a final pressure of 250 mbar was
reached. Via valve B01 air flowed into adsorber B, product gas was fed into
reservoir R via valves B03 and ABOI, the pressure in adsorber A and in the
25 reservoir R reached a f1nal pressure of 0.3 bar. During this time adsorber A was
flushed with ~2 product gas, namely via the volume-controlled valve B03,
whereby the quantity of flush gas was adjusted on the basis of a maximum ~2
concentration of 18 vol-% in the residual gas downstream of the vacuum pump.
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The process proceeded further in a manner analogous to times tllt2lt31t4, only
adsorber A was exchanged for adsorber B.
A quantity of product gas from reservoir R of 17.68 Nm3/h with an ~2
concentration of 93% was obtained. The ~2 yield amounted to 44%, the specific
energy value of the vacuum pump W;1S calculated as 0.379 kWh/Nm302, the total
energy value derived from pump and air compressor amounted to
0.46~ kWh/Nm302.
Example 3 (Comparison; according to EP-A 0 334 495 (Figs. 3d/4d))
Use was made of an inst~ tion corresponding to Figure 1. The process sequence
and the pressure profile are evident from Figure 6.
Time tl: 0 to 4 seconds
An air compressor was located in the circuit. The pressure in adsorber B rose
from PDeS min = 250 mbar to PBF-I = 450 mbar, simultaneously in adsorber A the
pressure dropped from its maximum pressure PAd maX = 0 3 bar, whereby at the
upper end gas flowed out of adsorber A via valve A4 into adsorber B via valve
B4 and at the lower end adsorber B was evacuated via valve B3 with a vacuum
pump. The pressure in adsorber A dropped to PDeSo = 990 mbar. Reservoir R
supplied product gas at a pressure of about 0.3 bar; valve AB1 was closed.
Time t2: 4 to 6 seconds
Adsorber A was evacuated via valve A2 to approximately 650-700 mbar, the
upper end of adsorber A was opened via valve A4. Adsorber B was charged with
gas that was low in ~2 from adsorber A to approximately 650 mbar, namely via
valve A4, lines Lp and LR and inlet valve B3. Product gas was withdrawn from
reservoir R.
Time t2b: 6 to 9 seconds
Adsorber A was evacuated via valve A2 to approximately 450 mbar, the upper
end of adsorber A was closed. Adsorber B was pressurised to about ambient
pressure with air from the air compressor at the lower end via valve B1 and with
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gas from the reservoir R (valves A131 and B4). Product gas continued to be
withdrawn from reservoir R, the pressure of the reservoir R dropped to 0.15 bar.
Time t3: 9 to 13 seconds
Adsorber A was evacuated further, adsorber B was charged with air and product
S gas from the reservoir, as in time t2b; reservoir and pressure in adsorber B reached
0.05 bar.
Time t1: 13 to 30 seconds
Adsorber A continued to be evacuated, via valve A4 ~2 gas was admitted as flush
gas, whereby a final pressure of 250 rnbar was reached. Via valve B1 air flowed
10 into adsorber "B", product gas flowed via valves B4 and AB1 into the reservoir R;
the pressure in adsorber A and in the reservoir R reached a final pressure of
0.3 bar. The quantity ~f ~2 flush gas was adjusted with valve A4.
The process proceeded further in a manner analogous to times tllt2a/t2blt31t4, only
adsorber A was exchanged for adsorber B.
A quantity of product gas from reservoir R of 19.8 Nm3/h with an ~2
concentration of 93% was obtained. The ~2 yield amounted to 47.5%, the
specific energy value of the vacuum pump was calculated as 0.375 kWh/Nm3O2,
the total energy value derived from pump and air compressor amounted to
0.466 kWh/Nm3O2.
20 Example 4 (according to the invention)
Use was made of an installation corresponding to Figure 1. The process sequence
is reproduced in Figures 2a/2b and the pressure profile is reproduced in Figure 3.
During time t1 the vacuum pump was disconnected from the adsorber with valves
A2 and B2.
25 Time tl: 0 to 4 seconds
All valves of adsorbers A and B except A4 and B4 were closed. As a result, gas
that was high in ~2 flowed out of adsorber A into the previously evacuated
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adsorber B. The pressure in adsorber B rose from PDes min = 250 mbar to PPB1 =
650 mbar, simultaneously in adsorber A the pressure PAd maX = 0 3 bar (excess
pressure) dropped to PDeS O = ambient pressure. Reservoir R supplied product gasat a pressure of about 0.3 to 0.25 bar.
5 Time t2: 9 to 13 seconds
Adsorber B was charged to approxirxlately ambient pressure, by air flowing via
valve A1 into adsorber A, gas that was low in ~2 being withdrawn via valve A4
and flowing into adsorber B via lines Lp and LR and valve B3. Simultaneously
adsorber B was topped up with air via the volume-controlled valve B1. The
10 charging with gas that was low in ~2 via line LR was concluded at an ~2
concentration of 20-40 vol-%. Product gas continued to be withdrawn from
reservoir R.
Time t3: 9 to 13 seconds
Adsorber A was evacuated via valve A2 from ambient pressure to approximately
15 650 mbar, adsorber B was charged with air via valve B1 and with product gas via
valves AB1 and B4 from the reservoir until reservoir pressure and pressure in
adsorber B reached approximately the same level. Product gas continued to be
withdrawn from reservoir R.
Time t4: 13 to 30 seconds
20 Adsorber A continued to be ev~c~l~terl, whereby a final pressure of 250 mbar was
reached. In this connection, with a view to assisting the desorption of N2, gas that
was high in ~2 was introduced into adsorber A via valve A4, namely in such a
quantity that the ~2 concentration of the exhaust gas of the vacuum pump did notexceed a value of 18 vol-%. With the aid of the air blower adsorber B was
25 pressurised to its final pressure of 0.3 bar. Product gas flowed into reservoir R via
valves B4 and AB1.
The process proceeded further in a manner analogous to times tllt2lt3lt4, only
adsorber A was exchanged for adsorber B.
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A quantity of product gas from reservoir R of 22 Nm3/h with an ~2 concentration
of 93% was obtained. The ~2 yield amounted to 48%, the specific energy value
of the vacuum pump was calculated as 0.341 kWh/Nm302, the total energy value
derived from pump and air blower amounted to 0.437 kWh/Nm302.
S Example 5 (according to the invention)
Use was made of an installation corresponding to Figure 1. The pressure profile
has been reproduced in Figure 3. The process sequence can be seen from Figures
2a/2b.
Time tl: 0 to 4 seconds
10 Only valves B2, B4 and A4 were open; adsorber B was connected to the vacuum
pump. As a result, gas that was high in ~2 flowed out of adsorber A into the
previously evacuated adsorber B. The pressure in adsorber B rose from PDesmin =
250 mbar to PBFP ~ = 450 mbar, simultaneously in adsorber A the pressure PAd max= 0.3 bar dropped to PDeS O = ambienl pressure. Reservoir R supplied product gas at a pressure of about 0.3 to 0.25 bar.
Time t2: 4 to 9 seconds
Adsorber B was charged to approximately ambient pressure, by air flowing into
adsorber A via valve A1, gas that was low in ~2 being withdrawn via valve A4,
being pressurised into adsorber ]3 via lines Lp and LR and valve B3.
20 Simultaneously adsorber B was topped up with air via the volume-controlled valve
B1. The charging with gas that was low in ~2 via line LR was concluded at an
~2 concentration of 20-40 vol-%. Product gas continued to be withdrawn from
reservoir R.
Time t3: 9 to 13 seconds
25 Adsorber A was evacuated via valve A2 from ambient pressure to approximately
650 mbar, adsorber B was charged with air via valve B1 and with product gas
from the reservoir via valves AB1 and B4 until reservoir pressure and pressure in
adsorber B reached about the same level. Product gas continued to be withdrawn
from reservoir R.
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Time t4: 13 to 30 seconds
Adsorber A continued to be evacuated, whereby a final pressure of 250 mbar was
reached. With the aid of the air blower adsorber B was pressurised to a final
pressure of 0.3 bar. Product gas flowed into reservoir R via valves B4 and AB1.
5 Adsorber A was not flushed with ~2 product gas.
The process proceeded further in a manner analogous to times tllt2/t31t4, only
adsorber A was exchanged for adsorber B.
A quantity of product gas from reservoir R of 22 Nm3/h with an ~2 concentration
of 93% was obtained. The ~2 yield amounted to 51%, the specific energy value
of the vacuum pump was calculated as 0.342 kWh/Nm302, the total energy value
derived from pump and air blower amounted to 0.438 kWh/Nm302.
Example 6 (according to the invention)
Use was made of an installation corresponding to Figure 1. The process sequence
and the pressure profile are reproduced in Figure 3. Process sequence and
pressure profile over time can be seen from Figures 2al2b and 3.
Time tl: 0 to 4 seconds
Only valves B2, B4 and A4 were open; adsorber B was connected to the vacuum
pump. As a result, gas that was high in ~2 flowed out of adsorber A into the
previously evacuated adsorber B. The pressure in adsorber B rose from PDesmin =
250 mbar to PBFP-I = 450 mbar, simultaneously in adsorber A the pressure PAd maX= 0.3 bar dropped to PDeSo = 1 atrn. Reservoir R supplied product gas at a
pressure of about 0.3 to 0.25 bar.
Time t2: 4 to 9 seconds
Adsorber B was charged to approximately ambient pressure, by air flowing into
adsorber A via valve A1, gas that was low in ~2 being withdrawn via valve A4.
Via lines Lp and LR and valve :B3 adsorber B was thereby pressurised.
Simultaneously adsorber B was toppecl up with air via the volume-controlled valve
B1. The charging with gas that was low in ~2 via line LR was concluded at an
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~2 concentration of 20-40 vol-%. P:roduct gas continued to be withdrawn from
reservoir R.
Time t3: 9 to 13 seconds
Adsorber A was evacuated via valve A2 from ambient pressure to approximately
650 mbar, adsorber B was charged with air via valve Bl and with product gas
from the reservoir via valves AB1 and B4 until reservoir pressure and pressure in
adsorber B reached about the same level. Product gas continued to be withdrawn
from reservoir R.
Time t4: 13 to 30 seconds
Adsorber A continued to be evac l~terl, whereby a final pressure of 250 mbar wasreached. With the aid of the air blower adsorber B was pressurised to its final
pressure of 0.3 bar. Product gas flowed into reservoir R via valves B4 and AB l .
Adsorber A was flushed with ~2 product gas by product gas flowing out of line
Lp into adsorber A via valve A4. lhe quantity of flush gas was adjusted with
valve A4.
The process proceeded further in a manner analogous to times tllt21t3lt4, only
adsorber A was exchanged for adsorber B.
A quantity of product gas from :reservoir R of 22.5 Nm3/h with an ~2
concentration of 93% was obtained. The ~2 yield amounted to 52%, the specific
energy value of the vacuum pump was calculated as 0.339 kWhlNm3O2, the total
energy value derived from pump and air compressor amounted to
0.433 kWh/Nm3O2.
The comparison of Examples 3 and l shows that the recirculation of the product
gas that was low in ~2 of Example 3 produces an increase in the ~2 yield, but onaccount of a disadvantageous pressure profile in the course of pumping-out no
improvement in the current demand of the vacuum pump is achieved.
On the other hand, the emission of the product gas that is low in ~2 after the
adsorption step at approximately ambient pressure in Examples 4 to 6 according to
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the invention shows a clear improvement in the energy demand of the vacuum
pump in comparison with Comparative Examples 1 to 3.