Patent Description:
<FIG> is a system diagram illustrating the basic configuration not according to the current invention of a nitrogen generator that distills from air as a raw material through cryogenic separation. This nitrogen generator <NUM> includes a distillation column <NUM> in which an upper liquid distributor <NUM>, an upper gas-liquid contactor <NUM>, an intermediate liquid distributor <NUM>, and a lower gas-liquid contactor <NUM> are disposed in this order from the top. The upper gas-liquid contactor <NUM> and the lower gas-liquid contactor <NUM> are typically contactors using structured packing.

In a case of using this nitrogen generator <NUM> to distill nitrogen gas of <NUM> kPaG (gauge pressure; the same applies below) as a product, air as a raw material is compressed by an air compressor <NUM> to <NUM> kPaG. The heat of compression generated by the compression of the air is removed by an aftercooler <NUM>, so that the compressed air is cooled to <NUM>. Then, the carbon dioxide, water, and hydrocarbons contained in the air are removed through adsorption by a pre-treatment unit <NUM> that alternately uses two adsorbers, so that the air becomes purified air.

The purified air after exiting the pre-treatment unit <NUM> is introduced into a cold box <NUM> through a purified air stream <NUM> and cooled to -<NUM>, which is near the dew point, by a main heat exchanger <NUM>. The cooled purified air is then introduced into a lower portion of the distillation column <NUM> through a gas introduction stream <NUM> as ascending gas in the distillation column <NUM>. Nitrogen gas in an upper portion of the distillation column <NUM> separated by distillation operations inside the column is drawn to a gas discharge stream <NUM> at the top of the column. Part of the nitrogen gas branches off into a condensation stream <NUM> and is introduced into a condenser <NUM>.

Meanwhile, at the bottom of the distillation column <NUM>, oxygen-enriched liquid air is separated by the distillation, drawn into a liquid discharge stream <NUM>, and lowered in pressure to <NUM> kPaG by a liquid-air pressure reducing valve <NUM>, so that the temperature drops to -<NUM> due to the Joule-Thomson effect. This low-temperature liquid air is introduced into the condenser <NUM> and exchanges heat with the above-mentioned nitrogen gas. Consequently, the nitrogen gas is liquefied and the whole low-temperature liquid air is vaporized into low-temperature air. The liquid nitrogen liquefied at the condenser <NUM> is introduced into the upper portion of the distillation column <NUM> through a liquid introduction stream <NUM> as descending liquid in the distillation column <NUM>.

The low-temperature air vaporized at the condenser <NUM> is introduced into the main heat exchanger <NUM> through a low-temperature air stream <NUM>, exchanges heat with the purified air to be heated to -<NUM>, and is drawn in this intermediate temperature state into a turbine inlet stream <NUM> from an intermediate portion of the main heat exchanger <NUM>. The low-temperature air in the intermediate temperature state is introduced into an expansion turbine <NUM>, in which the low-temperature air is expanded to <NUM> kPaG and its temperature is lowered to -<NUM> by adiabatic expansion. The low-temperature air lowered in temperature by the expansion turbine <NUM> is introduced into the main heat exchanger <NUM> again through a turbine outlet stream <NUM> and exchanges heat with the purified air to cool the purified air. Consequently, the low-temperature air is sufficiently warmed to a temperature that is several °C lower than the purified air, and then discharged from the cold box <NUM> through a waste gas stream <NUM>.

Also, the remaining portion of the nitrogen gas discharged into the gas discharge stream <NUM> from the distillation column <NUM> is introduced into the main heat exchanger <NUM>. Then, as in the low-temperature air, the remaining portion of the nitrogen gas exchanges heat with the purified air to be sufficiently warmed to a temperature several °C lower than the purified air. Thereafter, the remaining portion of the nitrogen gas is discharged from the cold box <NUM> through a product nitrogen gas stream <NUM> and collected as a product nitrogen gas. In the case of distilling a product nitrogen gas at a pressure of <NUM> kPaG as described above, the distillation column <NUM> is operated at a high pressure of <NUM> kPaG.

In the distillation column <NUM>, the liquid nitrogen introduced into the distillation column <NUM> from the condenser <NUM> through the liquid introduction stream <NUM> is distributed uniformly in the cross-sectional direction of the packed column <NUM> by the upper liquid distributor <NUM> and then flows down toward the upper gas-liquid contactor <NUM>. The descending liquid flowing down from the lower end of the upper gas-liquid contactor <NUM> is distributed uniformly in the cross-sectional direction of the packed column <NUM> again by the intermediate liquid distributor <NUM> and then flows down toward the lower gas-liquid contactor <NUM>. This is done so that the flow rate and composition of the descending liquid flowing down inside the upper gas-liquid contactor <NUM> and the lower gas-liquid contactor <NUM> while being in gas-liquid contact with the ascending gas, can be uniform.

Meanwhile, a configuration like a distillation column <NUM> illustrated in <FIG> is sometimes adopted in which a single liquid distributor <NUM> is disposed above a single gas-liquid contactor <NUM>. However, widely used is a packed column <NUM> in which a gas-liquid contactor is divided vertically into a plurality of parts, for example, divided vertically into two gas-liquid contactors <NUM>, <NUM>, and an upper liquid distributor <NUM> and a intermediate liquid distributor <NUM> are provided respectively above the gas-liquid contactors <NUM>, <NUM>, as illustrated in <FIG> (see Patent Literature <NUM>, for example). <CIT> shows a gas-liquid contact device which brings liquid and gas into contact with each other while letting liquid flow down along the surface of a filler and besides raising gas, non-distribution-acceleration type of regular fillers and where thin plates or pipes in each shape to decide the direction of the stream of liquid or gas are stacked or disposed in vertical direction are used, and also this device is equipped with one piece each of liquid distributors and consisting of rough distribution parts and which roughly distribute liquid and fine distribution parts and which finely and equally distribute the liquid. <CIT> shows a a packed column according to the preamble of claim <NUM> into which lliquid is introduced through a liquid inlet nozzle at the top of the tower, then, is introduced into a gas/liquid contacting structural filler from a liquid dispersing device through liquid/gas dispersing structural filler. In this case, the liquid, dispersed uniformly by the filler, is brought into contact with gas phase, ascended from lower part, on the wall surface of the filler whereby the liquid is fractionated while accompanying material transfer. Biased flow of descending liquid is generated during passing layer divisions filled with the filler and the descending amount is reduced. Therefore, the descending liquid is introduced again into the liquid/gas dispersing structural filler. On the other hand, gas is introduced into the tower through gas inlet nozzle at the bottom of the tower, then, the gas is dispersed uniformly the filler and, thereafter, is contacted with the descending liquid by the filler.

In a packed column operated at relatively low pressure, such as a packed column operated at <NUM> to <NUM> kPaG like a crude argon column in a cryogenic air separation unit, the relative volatility is <NUM> to <NUM>, which is relative low, and the operating line and the equilibrium line in distillation is close to each other. It is therefore known that if small liquid maldistribution occurs, the operating line and the equilibrium line get closer to each other, thereby deteriorating the distillation performance (separation performance). To prevent maldistribution of the descending liquid, intermediate liquid distributors are placed at regular intervals, as illustrated in <FIG>.

On the other hand, in a packed column operated at relatively high pressure, such as the one in the above-described nitrogen generator, the operating line and the equilibrium line are relatively far from each other in distillation in which the relative volatility is <NUM> to <NUM>, that is, the operation pressure is <NUM> to <NUM> kPaG. Thus, the direct influence of liquid maldistribution on deterioration in distillation performance is small. Despite that, there are cases where the distillation performance is still deteriorated when the packed column is used, even with intermediate liquid distributors placed therein.

No adequate solution to this problem has been developed. Currently, the problem is handled by simply increasing the height of the gas-liquid contactors in the packed column or increasing the amount of feed air. However, increasing the amount of the feed air results in increased power consumption at the air compressor. Also, increasing the height of the gas-liquid contactors increases not only the size of the distillation column but also the size of the cold box, which leads to a problem of an increased apparatus cost.

These problems occur not only with nitrogen generator but also with the high-pressure column (lower column) of cryogenic air separation unit by a double column system, which additionally generate oxygen and argon.

In view of this, an object of the present invention is to provide a packed column that is operated at relatively high pressure and prevent deterioration in distillation performance without having to increase the height of its gas-liquid contactors or increase the amount of air.

The above object is achieved by the subject matter of the independent claim.

The packed column of the present invention is characterized in that a total height of the gas-liquid contactors above the highest gas disperser of the two or more gas dispersers is set such that a ratio of the total height to a height of all the gas-liquid contactors is <NUM> or greater.

Also, the packed column of the present invention may further comprise at least one intermediate liquid distributor that distributes the descending liquid again.

In addition, one of the gas dispersers may be formed integrally with the intermediate liquid distributor.

According to the packed column of the present invention, the ascending gas rising toward a gas-liquid contactor can be dispersed by the respective of the two or more gas dispersers. In this way, the composition of the ascending gas can be uniformed, and the flow rate of the ascending gas can be uniformed as well. Thus, decrease in distillation efficiency and gas-liquid contact efficiency can be suppressed. It is therefore possible to reduce the height of the gas-liquid contactors and reduce the amount of gas and liquid to be introduced.

<FIG> illustrates a first example of a packed column. This packed column <NUM> is a packed column with a gas-liquid contactor provided inside a tubular body <NUM> including a gas introduction portion <NUM> and a liquid discharge portion <NUM> at the bottom and including a gas discharge portion <NUM> and a liquid introduction portion <NUM> at the top. The gas-liquid contactor in the tubular body <NUM> is formed into vertically divided upper gas-liquid contactor <NUM> and lower gas-liquid contactor <NUM>. Above the upper gas-liquid contactor <NUM>, a liquid distributor <NUM> is provided which causes liquid introduced from the liquid introduction portion <NUM> to flow down uniformly toward the upper gas-liquid contactor <NUM>. Between the upper gas-liquid contactor <NUM> and the lower gas-liquid contactor <NUM>, a gas disperser <NUM> is provided which uniformly disperses the composition of ascending gas rising from the lower gas-liquid contactor <NUM> toward the upper gas-liquid contactor <NUM>.

The ascending gas introduced from the gas introduction portion <NUM> is subjected to a distillation operation in the lower gas-liquid contactor <NUM>, introduced into the gas disperser <NUM> to be dispersed, introduced into the upper gas-liquid contactor <NUM> to be subjected to a distillation operation, and then discharged from the gas discharge portion <NUM>. On the other hand, the descending liquid introduced from the liquid introduction portion <NUM> is distributed by the liquid distributor <NUM> and introduced into the upper gas-liquid contactor <NUM> and the lower gas-liquid contactor <NUM> in this order. The liquid thus introduced becomes maldistributed as it descends, and is discharged from the liquid discharge portion <NUM>.

<FIG> is a schematic cross-sectional view illustrating an example of the gas disperser <NUM>, and <FIG> is a schematic bottom view of the same. In this gas disperser <NUM>, the ascending gas rising from the lower gas-liquid contactor <NUM> passes through a plurality of paths <NUM> and resisted by turn back portions <NUM>, so that its composition becomes even horizontally. The ascending gas flowing from the gas disperser <NUM> into the upper gas-liquid contactor <NUM> is introduced thereinto such that its flow rate has a distribution dependant on the maldistribution of the descending liquid flowing down in the upper gas-liquid contactor <NUM>. Also, the descending liquid flowing down out of the upper gas-liquid contactor <NUM> flows down into liquid receiving portions <NUM> from the upper sides of the turn back portions <NUM> and then flows down through bottom holes <NUM> toward the lower gas-liquid contactor <NUM>.

<FIG> illustrates a second example of a packed column. Note that in the following description, identical constituent elements to the constituent elements of the packed column presented in the first example will be denoted by the identical reference signs, and detailed description thereof will be omitted.

In this packed column <NUM>, a gas-liquid contactor in a tubular body <NUM> is formed into three horizontally divided upper gas-liquid contactor 33a, intermediate gas-liquid contactor 33b, and lower gas-liquid contactor <NUM>. An upper liquid distributor 35a is provided above the upper gas-liquid contactor 33a, an intermediate liquid distributor 35b is provided between the upper gas-liquid contactor 33a and the intermediate gas-liquid contactor 33b, and a gas disperser <NUM> is provided between the intermediate gas-liquid contactor 33b and the lower gas-liquid contactor <NUM>.

Ascending gas introduced into a lower portion of the packed column <NUM> from the gas introduction portion <NUM> is subjected to a distillation operation in the lower gas-liquid contactor <NUM>, introduced into the gas disperser <NUM> to be dispersed, introduced into the intermediate gas-liquid contactor 33b and the upper gas-liquid contactor 33a in this order to be subjected to distillation operations, and then discharged from the gas discharge portion <NUM>. On the other hand, descending liquid introduced from the liquid introduction portion <NUM> is distributed in the upper liquid distributor 35a, introduced into the upper gas-liquid contactor 33a, and then distributed again in the intermediate liquid distributor 35b. Thereafter, the descending liquid is introduced into the intermediate gas-liquid contactor 33b and the lower gas-liquid contactor <NUM> in this order to be subjected to distillation operations.

The results of simulations performed to check the effect of placing a gas disperser between upper and lower gas-liquid contactors will be described below. Meanwhile, in each simulation model, descending liquid is indicated by solid lines while ascending gas is indicated by broken lines.

<FIG> is a simulation model of the case where the gas disperser <NUM> is provided between the upper gas-liquid contactor <NUM> and the lower gas-liquid contactor <NUM>, as illustrated in the first example. Descending liquid to be introduced into packed column models <NUM>, <NUM> is introduced at a given ratio from a liquid distributor model <NUM> into the uppermost portions of the packed columns, and then reaches the lowermost portions of the packed column models <NUM>, <NUM>. Also, assuming that the total amount of descending liquid to be introduced into the packed column models <NUM>, <NUM> is LF and the amount by which the amount of descending liquid is to be adjusted by the liquid distributor model <NUM> is δF, an amount LF1 of descending liquid to be introduced into the first packed column model <NUM> is LF/<NUM> + δF while an amount LF2 of descending liquid to be introduced into the second packed column model <NUM> is LF/<NUM> - δF, and δF/LF is the liquid maldistribution rate.

In this simulation model, a gas disperser model <NUM> corresponding to the gas disperser <NUM> is provided between upper gas-liquid contactor models <NUM> and lower gas-liquid contactor models <NUM>. <FIG> is a simulation model of a conventional example provided with no gas disperser or intermediate liquid distributor, as illustrated in <FIG>.

In the simulation model illustrated in <FIG>, feed air to be introduced from a gas introduction portion <NUM> is introduced into the packed column models <NUM>, <NUM> as ascending gases and subjected to distillation operations in the respective lower gas-liquid contactor models <NUM>. Thereafter, the ascending gases are introduced into the gas disperser model <NUM> to uniform the compositions of the ascending gases, introduced into the respective upper gas-liquid contactor models <NUM> to be subjected to distillation operations, and then rise to the uppermost portions of the respective packed column models <NUM>, <NUM>.

The descending liquid to be introduced from a liquid introduction portion <NUM> is introduced at a given ratio from the liquid distributor model <NUM>, and then descends to the lowermost portions of the respective packed column models without their flow rates or compositions corrected at the intermediate portions.

In the simulation model illustrated in <FIG>, feed air to be introduced from a gas introduction portion <NUM> is introduced into packed column models <NUM>, <NUM> as ascending gases and then introduced from lower gas-liquid contactor models <NUM> directly into upper gas-liquid contactor models <NUM>. These ascending gases rise to the uppermost portions of the respective packed column models <NUM>, <NUM> without their flow rates or compositions corrected. Descending liquid to be introduced from a liquid introduction portion <NUM> is introduced at a given ratio from a liquid distributor model <NUM> into the uppermost portions of the packed column models <NUM>, <NUM>, and then descend to the lowermost portions of the respective packed column models <NUM>, <NUM> without their flow rates or compositions corrected, as in the simulation model illustrated in <FIG>.

<FIG> illustrates the result of calculation of the performance deterioration rate versus the liquid maldistribution rate (δF/LF) using each of the simulation models illustrated in <FIG> and <FIG>. A performance deterioration rate 6A of the conventional example model illustrated in <FIG> sharply increases after a liquid maldistribution rate of <NUM>%. This is because the compositions of the ascending gases in the packed column model <NUM>, <NUM> become markedly different from each other. On the other hand, a performance deterioration rate 5A of the first example model illustrated in <FIG>, in which the gas disperser model <NUM> is placed to uniform the composition of the ascending gas, changes gently up to a liquid maldistribution rate of <NUM>%, and performance deterioration hardly occurs up to a liquid maldistribution rate of <NUM>%. This result indicates that placing a gas disperser to uniform the composition of the ascending gas can effectively suppress performance deterioration.

<FIG> is a simulation model of the case where a gas-liquid contactor is formed into the horizontally divided upper gas-liquid contactor 33a, intermediate gas-liquid contactor 33b, and lower gas-liquid contactor <NUM>, the upper liquid distributor 35a is provided above the upper gas-liquid contactor 33a, the intermediate liquid distributor 35b is provided between the upper gas-liquid contactor 33a and the intermediate gas-liquid contactor 33b, and the gas disperser <NUM> is provided between the intermediate gas-liquid contactor 33b and the lower gas-liquid contactor <NUM>, as illustrated in the second example.

In this simulation model, feed air to be introduced from a gas introduction portion <NUM> is introduced into lower portions of packed column models <NUM>, <NUM> as ascending gases and subjected to distillation operations in respective lower gas-liquid contactor models <NUM>. Thereafter, the ascending gases are introduced into a gas disperser model <NUM> to uniform the compositions of the ascending gases, and rise through intermediate gas-liquid contactor models 66b and upper gas-liquid contactor models 66a to the uppermost portions of the respective packed column models <NUM>, <NUM>.

On the other hand, descending liquid to be introduced from a liquid introduction portion <NUM> is introduced at a given ratio from an upper liquid distributor model 68a into upper portions of the packed column models <NUM>, <NUM>, subjected to distillation operations in upper gas-liquid contactor models 66a, and have their compositions uniformed in an intermediate liquid distributor model 68b. Thereafter, the resultant descending liquid is introduced at the same ratio as that by the upper liquid distributor model 68a into the intermediate gas-liquid contactor models 66b, introduced directly into the lower gas-liquid contactors <NUM>, and descend to the lowermost portions of the packed column models <NUM>, <NUM>.

<FIG> is a simulation model of the packed column <NUM>, in which the intermediate liquid distributor <NUM> is placed between the horizontally divided two upper gas-liquid contactor <NUM> and lower gas-liquid contactor <NUM>, as illustrated in the conventional example of <FIG>.

In this simulation model, feed air to be introduced from a gas introduction portion <NUM> is introduced into packed column models <NUM>, <NUM> as ascending gases and subjected to distillation operations in respective lower gas-liquid contactor models <NUM>. Then, the ascending gases rise directly through upper gas-liquid contactor models <NUM> to the uppermost portions of the respective packed column models <NUM>, <NUM> without their flow rates or compositions corrected.

On the other hand, descending liquid to be introduced from a liquid introduction portion <NUM> is introduced at a given ratio from an upper liquid distributor model <NUM> into the packed column models <NUM>, <NUM>, subjected to distillation operations in the upper gas-liquid contactor models <NUM>, and have their compositions uniformed in an intermediate liquid distributor model <NUM>. Then, the resultant descending liquid is introduced at the same ratio as that by the upper liquid distributor model <NUM> into the lower gas-liquid contactor models <NUM>, and descends to the lowermost portions of the packed column models <NUM>, <NUM>.

<FIG> illustrates the result of calculation of the performance deterioration rate versus the liquid maldistribution rate using each of the simulation models illustrated in <FIG> and <FIG>. A performance deterioration rate 9A of the simulation model illustrated in <FIG>, in which no gas disperser is placed but an intermediate liquid distributor is placed, changes gently with increase in liquid maldistribution rate. The performance deterioration rate 9A is effective to some extent in reducing the rate of deterioration in distillation performance as compared to the performance deterioration rate 6A of the conventional example model, illustrated in <FIG>. Nonetheless, a performance deterioration rate 8A of the simulation model illustrated in <FIG> indicates that a higher suppressing effect can be achieved by using both an intermediate liquid distributor and a gas disperser.

Further, <FIG> illustrates the result of calculation of the performance deterioration rate versus the operation pressure using each of the simulation models illustrated in <FIG> and <FIG> with the liquid maldistribution rate set to <NUM>%. As for a performance deterioration rate 9B of the simulation model illustrated in <FIG>, in which no gas disperser is placed, when the operation pressure is higher than or equal to <NUM> kPaG, the maldistribution of the ascending gases causes a great difference in composition between the ascending gases, and therefore the performance deterioration rate is markedly high. In contrast, a performance deterioration rate 8B of the simulation model illustrated in <FIG>, in which a gas disperser is placed, indicates that the simulation model can suppress deterioration in distillation performance in the operation pressure range of <NUM> to <NUM> kPaG, i.e., in the relative volatility range of <NUM> to <NUM>.

Furthermore, <FIG> illustrates the result of consideration of the relationship between the position of placement of a gas disperser and the performance deterioration rate using the simulation model illustrated in <FIG>. A performance deterioration rate 8C is calculated in a setting where in <FIG>, the height of each upper gas-liquid contactor model 66a is H1A, the height of each intermediate gas-liquid contactor model 66b is H1B, the height of each lower gas-liquid contactor model <NUM> is H2, and the height H2 of the lower gas-liquid contactor model <NUM> is reduced while the entire height of all gas-liquid contactor models (H1A + H1B + H2) and the height H1A of the upper gas-liquid contactor model 66a are fixed, that is, the gas disperser <NUM> is shifted downward without changing the entire height. <FIG> illustrates the result.

This result indicates that the effect of suppressing performance deterioration is high when the ratio of the total height of the upper gas-liquid contactor model 66a and the intermediate gas-liquid contactor model 66b to the entire height of all gas-liquid contactor models is set to <NUM> or greater and in particular to <NUM> or greater. Note that although the performance deterioration rate is calculated in the setting where the entire height of all gas-liquid contactor models (H1A + H1B + H2) and the height H1A of the upper gas-liquid contactor model 66a are fixed, the advantageous effect of the invention of the present application can be achieved regardless of which part is fixed in length. For example, the performance deterioration rate may be calculated with the entire height of all gas-liquid contactor models (H1A + H1B + H2) and the height H1B of the intermediate gas-liquid contactor model 66b fixed.

Further, using the simulation model illustrated in <FIG>, a performance deterioration rate 5A is calculated in a similar setting where the height of each upper gas-liquid contactor model <NUM> is H1, the height of each lower gas-liquid contactor model <NUM> is H2, and the height H2 of the lower gas-liquid contactor model <NUM> is reduced while the entire height of all gas-liquid contactor models (H1 + H2) is fixed, that is, the gas disperser <NUM> is shifted downward without changing the entire height of all gas-liquid contactor models. As illustrated in <FIG>, this result also indicates that the effect of suppressing performance deterioration is high when the ratio of the height H1 of the upper gas-liquid contactor model <NUM> to the entire height of all gas-liquid contactors is set to <NUM> or greater and preferably to <NUM> or greater. Note that although the performance deterioration rate is calculated in the setting where the entire height of all gas-liquid contactor models (H1 + H2) is fixed, the advantageous effect of the invention of the present application can be achieved regardless of which part is fixed in length.

<FIG> is a simulation model in which an intermediate liquid distributor <NUM> and a gas disperser <NUM> are provided between upper gas-liquid contactors <NUM> and lower gas-liquid contactors <NUM>. In the case of providing the intermediate liquid distributor <NUM> and the gas disperser <NUM> at the same position as above, a liquid distributor-gas disperser unit formed to integrate a liquid distributing function and a gas dispersing function can be provided. This result is illustrated by the black triangle in <FIG> (H1B is zero). The same result as the simulation model illustrated in <FIG> is obtained at the point where the ratio of (H1A + H1B) to (H1A + H1B + H2) is <NUM>.

Claim 1:
A packed column (<NUM>; <NUM>) which includes a gas-liquid contactor (<NUM>, <NUM>; 33a, 33b, <NUM>) inside a tubular body (<NUM>; <NUM>) and a liquid distributor (<NUM>; 35a) in an uppermost portion and causes descending liquid and ascending gas to contact each other in the gas-liquid contactor (<NUM>, <NUM>; 33a, 33b, <NUM>), wherein
operation pressure is in a range of <NUM> to <NUM> kPaG,
relative volatility is in a range of <NUM> to <NUM>,
the gas-liquid contactor is horizontally divided into at least two parts to thereby form a plurality of gas-liquid contactors (<NUM>, <NUM>; 33a, 33b, <NUM>),
wherein:
two or more gas dispersers (<NUM>; <NUM>) is-are each provided between a lower one (<NUM>; <NUM>) of the gas-liquid contactors and an upper one (<NUM>; 33a) of the gas-liquid contactors, the gas dispersers (<NUM>) uniformly dispersing composition of the ascending gas rising from the respective lower gas-liquid contactor (<NUM>) toward the respective upper gas-liquid contactor (<NUM>), characterised in that
a total height of the gas-liquid contactors (<NUM>; 33a, 33b) above the highest gas disperser (<NUM>; <NUM>) of the two or more gas dispersers is set such that a ratio of the total height to a height of all the gas-liquid contactors (<NUM>, <NUM>; 33a, 33b, <NUM>) is <NUM> or greater, in particular <NUM> or greater.