DE1814064A1 - Method and device for selective absorption - Google Patents

Description

■ Process and: ■ Device for selective atasorption

The invention relates to a method for removing at least a component of a gas mixture composed of this by selective absorption with a solvent. the heat of solution, except through the media involved, through the absorbed during the subsequent desorption Components released cold and discharged by an external cold source, as well as a device for Perform this procedure.

In the process of selective absorption, the washing temperature is established along the column by interaction

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of inlet temperature and heat capacity of the detergent » and the gas as well as the heat of solution of the dissolved gases, a «■ Is the heat of solution large compared to the heat capacity of the media involved, the washing temperature can be as high increase and thus the solubility decrease so much that it is no longer possible to absorb the constituent as far as necessary. to remove the gas mixture. In this case, the heat of solution by additional Cooling are dissipated «.

Part of the cold required for this is usually used. applied by relaxing the loaded detergent the absorbed constituents are largely released while the solution is cooled, lira die so 'to return recovered cold to the absorption process, becomes the solution partially regenerated by relaxation; either directly with the low temperature reached fed into the column or to be fed with one of these Wash liquid flow brought into heat exchange.

Since complete degassing of the solution is not possible when relaxing, - however, only part of the heat of the solution can be recovered as desorption cold. This is one of the reasons for the irreversible cold losses of such ^; ',

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Procedure. Other causes for this are inadequate insulation, non-ideal heat exchange and the heat equivalent the pump work. These cold losses must be covered by an external cold source.

In order to transfer both the cold from the external cold source and the cold recovered by expansion to the solvent with the difference between the top and bottom temperature of the ή washing column remaining the same, it is known to select the amount of detergent appropriately large and to pass it once through a cooling stage respectively. The term "cooling stage" describes the entirety of the cold-emitting devices such as refrigerant evaporators and heat exchangers through which the relaxation-cooled solution flows and which work at the same temperature level as the column bottom, from which the washing liquid to be cooled is drawn off. The refrigerant evaporator can get in the way of

loaded solution in front of the expansion vessel or within the column itself in a middle section or finally in the path of the regenerated solvent immediately before it enters the head of the column, i.e. at the point the lowest temperature. It is also known, the washing liquid a central portion of the To be removed from the column and

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stage to direct.

These processes, which work with a large amount of detergent, have the disadvantage that the amount of detergent when relaxing The constituents remaining in the solution are very large and the amount of cold that can be recovered during desorption is correspondingly large is low. This increases the need for external cooling. Due to the large amount of solvent " Furthermore, increased consumption of pump energy and steam for regeneration as well as increased losses during heat exchange.

If the pure solvent is cooled by the external cold source before it enters the column, it works so at the lowest temperature level., so is another The result is an increase in energy demand. If, on the other hand, an evaporator is built into the column, then this is required The heating surface is very large, the refrigerant evaporator is difficult to access and, in the event of leaks, the gas to be washed penetrates the refrigerant circuit a. When working with a cooling stage located outside the column, a cold pump is for large ones Quantities of saturated solution and a device for redistribution to provide the liquid in the column and in addition, the heat equivalent of the pump work by the external cold source can be compensated.

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The required cold can finally be transferred to the washing liquid in a known manner, that the amount of solvent is kept relatively low, but that the washing liquid several times of each is withdrawn from different column bottoms and passed over cooling stages arranged outside the column. The one in case a single cooling stage arranged outside the column, the disadvantages already described are multiplied: Several cold pumps are required, the number of connection points at the column and the number of individual devices will be increased.

The task of the invention is to develop a method create that avoids the disadvantages aer known method, so it allows the energy demand and the to reduce the expenditure on equipment when dissipating the heat of solution.

This object is achieved according to the invention in that the Gas mixture at least partially, preferably completely, taken from a central section of the scrubbing column, cooled and then fed back into the washing column. The gai to be washed; so will be on its way through the pillar withdrawn once from servant and the next higher

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The column bottom is fed back in via a cooling stage arranged outside the column.

With this-r method that is necessary to dissipate the heat of solution Transferring cold is primarily associated with the advantage that the amount of solvent can be reduced to the minimum amount required by temperature and pressure. This has the consequence that the amount of cold that cannot be recovered during relaxation is reduced and that the energy requirement is reduced for the pumps, the heat regeneration and the exchange losses. In addition, there is no need for equipment for one or more cold pumps and for the correspondingly high number of connection points in the case of repeated withdrawals from the column. Finally, less additional cooling is required to compensate for the heat equivalent of the pump work to become.

As the heat capacity of the gas mixture increases, the temperature level at which the external cold is transferred increases must become. If the heat capacity of the gas mixture is greater than that of the solvent, as may be the case, if the absorption is carried out under higher pressure or if the solubility of the gases to be washed out is very high large and the required amount of solvent accordingly

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is low, the external cold at a higher temperature are supplied than in the known cooling of the washing liquid. In this case, the method according to the invention is therefore used with particularly great advantage.

A very useful further development of the inventive concept is that the gas mixture into the condensation area of at least one component to be absorbed j is cooled. The advantage of this procedure is that the heat of solution is at least partially in the form of Heat of condensation is removed. This means that the temperature difference required to transmit a certain The amount of cold required is reduced, i.e. the cold at a higher temperature and therefore with less energy consumption can be generated.

If the gas mixture to be cooled removed from the washing column is in the unsaturated state ™ in the constituent to be condensed before, the condensate formation is expediently achieved in that the gas mixture is exposed to heat exchange brings the dew point temperature, then with condensation cools down further and the condensate-free gas mixture is finally warmed up again through heat exchange with itself that it can be returned to the washing column. This

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Procedure is advantageous if the condensed Component is to be dispensed in liquid form; because at this point in the process there are others in the raw gas The more soluble impurities contained in it have already been absorbed by the solvent Condensate in a very pure form.

A particularly advantageous embodiment of the method that works with condensation of a gas component consists in that the gas mixture is taken from the scrubbing column at a point at which the partial pressure of this component is so great is that when the amount of cold necessary to dissipate the heat of solution is transferred, condensation already occurs and that the gas mixture is then returned to the washing column in a saturated state with the condensed constituents is returned. The temperature level at which the heat of solution is to be dissipated is now above that for Process with pure gas cooling valid value. This is particularly important where the gas mixture has a Has a lower heat capacity than the solvent, because then there is also the possibility of the external cold source to operate at a higher temperature than in the 'working with cooling the washing liquid method.

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An expedient further development of the concept of the invention consists in that the liquid condensed out of the gas mixture is at least partially returned to the washing column is introduced. This embodiment is recommended when the washing stage operated according to the invention is a Upstream absorption step is carried out in which a more soluble component is previously mixed with the same solvent to be removed. In this way, the gas mixture that is largely saturated with the sparingly soluble constituent flows Solvent against, so that here only the heat of solution of the more soluble component to be dissipated needs. In the column section, in which the constituents to be absorbed are fed back in as condensate, is then only the heat of the mixture between solvent and condensate is released; the resulting warming can be neglected.

It is particularly advantageous if the constituents to be absorbed are in the liquid state together with the gas mixture to reinsert them into the washing column at their own expense. In these circumstances, a cold pump is complete dispensable. However, it can also be useful that the Collect condensate in a separator and at least partially pump it back into the column. In this case it is

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only one designed for a small amount of liquid Provide a cold pump.

The gas mixture is preferably cooled by heat exchange with a solution cooled by degassing. The irreversible Cold losses are expediently covered by the fact that an amount of liquid intended for heat exchange with the gas mixture is cooled by an external cold source before degassing.

The device for performing the method according to The invention is characterized by a column extending from the gas space above a column base at the middle height of the column Line that is routed through a cooling stage and is connected to the column again via the next higher floor. The cooling level is preferably attached at such a height that condensates can get back into the column under their own incline. However, it can also be advantageous to connect a separator downstream of the cooling stage and to use this apart from via the The supply line can also be connected to the column via a liquid line with a pump; it is then expedient to connect it to the column Separator branch off a line for liquid COg product.

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The raw gas to be processed has the following composition:

H ₂ 61 % -.

N ₂ , CO, Ar, CH ₄ 4 % HgS 0.5 %

CO ₂ 34.5 %

It is fed to the system through line .1 at a pressure of about 76 at. Water-containing condensate collects in separator 2. Methanol is injected into the gas mixture through line 3 in order to prevent the formation of ice in the downstream "apparatus parts. The raw gas now passes into the heat exchanger 4, in which it is protected against cold decomposition products, namely against the hydrogen-nitrogen gas arriving through line 5a. Mixture from the downstream, not shown liquid nitrogen scrubbing and against COp-rich gas mixture from line 5b is cooled. At a temperature of about -10 ⁰ C the raw gas is introduced into the HpS absorption stage 6a of the washing column and there in contact with COp-saturated methanol brought, which absorbs the hydrogen sulfide

HpS-free gas now enters the COp absorption stage 6b, in which part of the C0 ₂ content is initially taken up by the methanol. At the point 7, where the gas mixture has ata a temperature of -20 ⁰ C and a partial pressure of COP 25, it is withdrawn from the column and in the group consisting of the heat exchangers 8 and 9, cooling step to -45 ⁰ C. cooled down. Most of the CO _{2 condenses in the process}

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the end. Both heat exchangers are set so high that the condensate under its own gradient together with the Gas mixture flows back into the column. In the upper column section, the gas mixture is countered with pure solvent. The gas mixture leaves the top of the column 6 at a temperature of -6o ° C and a residual content of

1 ppm HS and 20 ppm CO ₂ .

The solution which runs out of the COo absorption stage 6b and is almost saturated in COp is divided. One part is returned through line 10 into the column section 6a. The remaining part is cooled in the heat exchanger 11 by an ammonia refrigerator to -30 ° C and initially expanded in the separator 12 to 25 ata and then in the separator 1J to about 2 ata. A hydrogen-rich gas mixture escapes from the separator 12 through line 14 and is returned to the raw gas via the compressor 15. In this way the hydrogen losses are reduced. The solution running out of the separator 1J and _{already largely freed of CO 2} now flows through the heat exchanger 9 and there releases the cold released during the desorption to the gas mixture. The heated solution is put on the head of at about

2 ata working degassing column 16 abandoned. Ones middle section of this pillar is also the one from the swamp

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the absorption column 6 with about -10 ⁰ C running, with H ₃ S loaded solution fed: This is first in the heat exchanger 17 by an external cold source to -30 C, then in the heat exchanger 18 by CCU-rich gas and finally by decompression to a pressure cooled by 25 ata and separated in the separator 19 from the hydrogen-rich gas set free. In order to increase the hydrogen yield, this gas is also added to the raw gas via the compressor I5. After further expansion to the pressure of the degassing column 16, the solution leaving the separator 19 has a temperature of approximately −60 ° C. and is fed into the column 16 in this state. Under the action of the nitrogen flowing in through line 20 and serving as stripping gas, a large part of the dissolved CO ₂ and some HgS is released from the solution. Due to the HpS-free solution which is applied to the top of the column 16 and originates from the CO _{2 absorption stage 6b, the H 2} S carried along by the ascending gas stream is retained, so that the column 16 has H ₂ S-free COp diluted with nitrogen as the top product can be taken. This cools the stripping gas in the heat exchanger 21 and is finally released together with the CO ₂ escaping from the separator 13 through the heat exchangers 4 and 4 from the system.

Due to the degassing of the washing liquid, this has become

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cooled about -65 ^{0 C.} The liquid is withdrawn from the column 16 by the pump 22, first cools the pure methanol from the heat regeneration in the heat exchanger 23 and then in the heat exchanger 8 the gas mixture removed from the column section 6b and is finally fed back into the column 16 at 24. _{A solution containing H 2} S, which has been largely freed _{of CO 2} , is drawn off from the bottom of the column 16 and fed to the heat regeneration.

In FIG. 2, only that section of the method is shown which differs from the method according to FIG. 1. The same parts are denoted by the same numbers. The gas mixture is removed from column 6 at 7, cooled in heat exchangers 8 and 9 to such an extent that the CO ₂ partially condenses and then returned to column 6 via the separator. The liquid CO ₂ collected in 30 is fed back into the column via the pump 31 at 32. The advantage of this process variant is that part of the C0 _g separated in 30 can be given off as product via line 33.

11 claims
2 sheets of drawings

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Claims (11)

-15- LINDE AKTIENGESELLSCHAFT (H 457) η 68/0 87 Str / kp December 4, 1968 Claims yProcedure for removing at least one component a gas mixture from this by selective absorption with a solvent in which the heat of solution except dissipated by the media involved, by the cold released during the subsequent desorption of the absorbed components and by an external cold source is, characterized in that the gas mixture at least partially from a central portion of the Wash column removed, cooled and then fed back into the wash column. ' 2. The method according to claim 1, characterized in that the gas mixture into the condensation region at least a component to be absorbed is cooled. 009826/1775 -16- LINDE AKTIENGESELLSCHAFT 3. The method according to claim 2, characterized in that the gas mixture is taken from the scrubbing column at a point at which the partial pressure of the to be condensed Component is so large that when transferring the ■ amount of cold necessary to dissipate the heat of solution condensation already occurs and that the gas mixture is then saturated in the condensed constituents State is fed back into the washing column. 4. The method according to claim J5, characterized in that the liquid which has condensed out of the gas mixture is at least partially fed back into the washing column will. 5. The method according to claim 4, characterized in that the condensate together with the gas mixture under the own gradient is introduced back into the washing column. 6. The method according to any one of claims 1 to 5 *, characterized in that that the gas mixture is cooled by heat exchange with a solution cooled by degassing. 009826/1775 -17- LINDE AKTIENGESELLSCHAFT 7. The method according to any one of claims 1 to 6, characterized in that that the amount of liquid determined for heat exchange with the gas mixture before degassing is cooled by an external cold source. 8. An apparatus for performing the method according to any one of claims 1 to 7 »characterized by a (at 7) of the washing column (6) from the gas volume at mid-height on g a column bottom outgoing line, which on a cooling stage (8; 9) guided and üher the next higher floor is connected to the column again. 9. Apparatus according to claim 8, characterized in that the cooling stage (8; 9) is attached at such a height that Condensates get back into the column (6) below their own slope. 10. Apparatus according to claim 8, characterized in that the cooling stage (8; 9) is followed by a separator (50; from which a liquid line is connected to the column (6) via a pump. 11. The device according to claim 10, characterized in that a line (j3j5) for liquid C0 _o product is branched off from the separator (j50). 009826/1775