DE1088991B - Process and device for the decomposition of gas mixtures by means of low-temperature rectification - Google Patents

Description

GERMAN

The invention relates to a method and a device for the decomposition of gas mixtures by means of low-temperature rectification in a main rectification column consisting of at least three consecutive decomposition stages and an auxiliary column, the gas mixture being fed to the first decomposition step under the highest pressure according to its composition and pre-decomposed therein, whereupon a Part of the constituent present in larger quantities in the gas mixture is withdrawn as a pure product and the impure product is fed to the next, lower-pressure decomposition stage at a corresponding point, in which the same constituent is again withdrawn as a pure product and the impure product to another, under still The lower pressure decomposition stage is fed and the heat released during the condensation of the gas flowing into the head of the w-th decomposition stage into the foot of the (ra-f-1) -th decomposition stage to the end test of the sump liquid boiling there, in particular for the decomposition of C ₂ mixtures with two or more constituents, in which at least one constituent is present in a smaller amount and which has a boiling graph approximately according to the curve "C ₂ H ₄ C ₂ H ₆ " which is shown in FIG.

In the case of these gas mixtures, the equilibrium curve for the dependence of the composition in the vapor on the composition in the liquid for the higher and lower boiling points does not lie on the thin, drawn-out curves that correspond to the equilibrium of ideal gas mixtures at a given vapor pressure ratio ε , but overlap them for small amounts Higher or lower boiling points in the liquid. Here, the parameter ε is equal to the ratio of the vapor pressure of _{the higher boiling Ji 1} to that of the lower boiling π ₂ . The equilibrium curve itself is represented by the function

y =. where χ is the mole fraction of the heavier constituent in the liquid and y is the mole fraction of the heavier constituent in the vapor at equilibrium.

Furthermore, the method according to the invention can be successfully applied to all gas mixtures where the vapor pressure ratio ε is greater than about 0.3. In addition, the method is advantageous used when a component is present in a low concentration in a gas mixture.

Gas mixtures that have a boiling diagram as described above are difficult to separate. To the The object of the invention is to achieve this separation with less effort than before, especially when it comes to procedures and setup

for the decomposition of gas mixtures

by means of low temperature rectification

Applicant:

ίο Society for Linde's ice machines

Corporation,

Branch office Höllriegelskreuth,
Höllriegelskreuth near Munich

Dipl.-Ing. Rudolf Becker, Munich-Solln,
has been named as the inventor

a component is only present in low concentration.

It is possible and also known to carry out the separation of such gas mixtures in a single rectification column with a large gas circuit. That is uneconomical. The gas circuit can be reduced in size in a multi-stage column order reach.

This procedure brings a substantial increase of the outlet pressure of the gas mixture to be broken down, since each previous decomposition stage has a must have higher pressure than the following. The energy savings due to the smaller circulation volume as the number of stages increases, this cannot have any effect due to the increase in the raw gas and circuit pressure.

These disadvantages are avoided according to the invention in that from the decomposition stage with the A gas mixture of both components is taken from the lowest pressure and in the auxiliary column at the same Pressure is rectified, with the constituent present in small quantities in the gas mixture being obtained in pure form and withdrawn from the auxiliary column while the impure gas mixture enters the one below the lowest Pressurized decomposition stage is returned. The advantage of the method according to the invention is there in that it takes advantage of the smaller circulation volume of a multi-stage column arrangement, but with the auxiliary column operated with the pressure of the last decomposition stage the output

009 607/85

and keeps circuit pressure lower than with the known Procedure and therefore more economical than this.

The process is carried out in a rectification arrangement, which consists of a main and a Auxiliary column exists. The main column is composed of at least three stages of decomposition. This individual Decomposition levels are connected with each other in such a way that only heat from the κ-th to the (w + l) -th Decomposition level is transferred. This is done by arranging the decomposition stages one above the other and connected by condenser evaporators. They can also be arranged next to each other, when the heat is transferred from one decomposition stage to another in a known manner.

The pressures in the individual decomposition stages are chosen so that at the head of a decomposition stage the gas condenses at the temperature at which the liquid in the sump of the following decomposition stage evaporates. The amount of mixture to be broken down decreases from step to step.

The auxiliary column consists of a single column that is not thermally connected to the main column is. In their arrangement, however, they can be combined with the main column to form a unit or but to be set up separately.

The mixture to be broken down is introduced in liquid form into the decomposition stage, which is under the highest pressure. For the sake of simplicity, it is assumed in the following that there is a gas mixture of two Components. Gas mixtures with several components can also be processed, but can in an arrangement of the type described, only the main component is pure, the others, on the other hand, only be taken as a mixture. The mixture can then be optionally followed by the same procedure further disassemble.

The constituent present in larger quantities in the raw gas is purely in the first decomposition stage Taken from liquid form, when the lower-boiling component is present in larger quantities was at the head, if this was the higher-boiling component, at the foot of the decomposition stage. The removed pure product is relaxed and with that from the further decomposition stages in corresponding Wise withdrawn products either as washing liquid or at least partially to the condenser evaporator at the head of the decomposition stage which is under the lowest pressure. The unclean The liquid mixture collects at the foot or at the head of the decomposition stage and is removed from there. After relaxation to the pressure of the next decomposition stage, it becomes liquid in one of its composition appropriate place in this next decomposition level introduced.

Here it is further broken down, the pure product is returned to the top or bottom of the cutting stage withdrawn and abandoned the last decomposition stage, while the impure liquid mixture in which the component initially present in a smaller amount has enriched, liquid one of its composition corresponding point of the next decomposition. stage is forwarded.

An impure gas mixture is removed from the last decomposition stage, while the one in the raw gas is less Amount of existing constituent is highly enriched, and at the same pressure of the auxiliary column for pure recovery this component supplied.

If the lower-boiling component was present in larger quantities in the raw gas, the base of the An impure liquid mixture was removed from the last decomposition stage and passed to the auxiliary column. In this is a large part of the higher boiling pure separated and can be taken from it while the remainder is returned in gaseous form to the last decomposition stage. The sump of the auxiliary column can be heated with raw gas.

If the higher-boiling component was present in the raw gas in large quantities, the

ίο last decomposition stage a gaseous gas mixture taken and fed to the auxiliary column, in which this higher boiling point is recovered and withdrawn can, while the rest of the liquid flows back to the last decomposition stage. The auxiliary column as well as the last Decomposition stage contain condenser evaporator in the head. This is done from the outside in all stages of decomposition withdrawn, liquid higher boiling ends at least partially fed in and at least in them partially evaporated. The bottom of the first decomposition stage can be condensed by higher boiling be heated, which is taken from the cutting plant.

In Fig. 2 and 3 embodiments of the object according to the invention are shown schematically.

It shows

2 shows an embodiment in which raw gases with a lower content of higher-boiling gas are broken down will,

Fig. 3 shows an embodiment for the decomposition of raw gas with a lower content of lower boiling Gas.

In Fig. 2, 1, 2, 3 are the three decomposition stages of the main column, 4 is the auxiliary column. Through the line 5 z. B. 1000 Nm ³ / h liquid (^ mixture that consists of

about 70 _{% C 2} H ₄ and 30% C ₂ H ₆ , taken from a methane column working under atmospheric pressure and conveyed by means of a pump 6 via line 7 to the first decomposition stage 1, which is under a pressure of about 4 ata. There, the C ₂ mixture is broken down into liquid, pure ethylene, which collects at the top of decomposition stage 1 at 14, and into a liquid enriched with ethane, which is obtained at the foot of decomposition stage 1. This liquid is withdrawn, expanded in valve 11 to the pressure of about 2.6 ata prevailing in decomposition stage 2 and introduced into decomposition stage 2 via line 17 at a point corresponding to its composition. Here the liquid is further broken down. At 18, liquid, pure ethylene is withdrawn again, released in valve 19 to the pressure of the decomposition stage 3 and given up at the head of the decomposition stage 3 via line 21 together with the portion withdrawn at 14 and relaxed in valve 15 as washing liquid. The impure bottom liquid from the decomposition stage 2 is expanded at 16 and fed to the decomposition stage 3 via line 20 at a point corresponding to its composition. At the head of the decomposition stage 3, pure, gaseous ethylene is taken off through line 22, while at the foot a liquid mixture enriched with ethane is taken through line 25 and fed to the auxiliary column 4. There pure ethane is deposited at the foot of the auxiliary column 4 and can be discharged via the valve 28 at 26, while gaseous, impure ethylene returns via the line 30 to the decomposition stage 3, which, like the auxiliary column 4, is operated a little above atmospheric pressure. The auxiliary column 4 is heated with raw gas flowing through the line 27. Pure ethylene is used to heat the decomposition stage 1;

Line 22 is branched off and fed to a compressor 9 via line 8. There it will be about 6 ata compressed and passed through the coil 10 in the foot of the decomposition stage 1. This condenses the ethylene, whereby it evaporates the bottom liquid in the decomposition stage 1. In valve 12 it becomes then relaxed, in order to also be passed into the decomposition stage 3 via line 21 as washing liquid to become. Pure ethylene is taken off at 24. The lines 13 are used to vent the condenser evaporator 29

In Fig. 3, 31, 32, 33 are the three decomposition stages ■ of the main column, 34 is the auxiliary column. That about Ethan rich raw gas flows at a pressure of about 6.6 ata through line 45 at one of its composition corresponding point in the decomposition stage 31 and is liquefied and rectified there, where pure ethane is obtained at the foot of the decomposition stage 31 and discharged via line 35. At the head of the decomposition stage 31, impure ethylene is withdrawn via line 46, in valve 47 relaxed to about 5 ata and introduced into the decomposition stage 32 at a point corresponding to its composition. There something pure falls again at the foot Ethane, which is withdrawn via line 36, while impure ethylene arises at the head, which withdrawn liquid via the line 48, relaxed in the valve 49 to about 2.4 ata and at the corresponding Place in the decomposition stage 33 is given. Here at the foot through the line 37 pure again, liquid ethane removed, while from the head of the decomposition stage 33 through the line 50 impure, with Ethylene-enriched gas is passed into the auxiliary column 34. At the head of the auxiliary column 34 is then at 51 obtained pure, gaseous ethylene at a pressure of about 2 ata. The one at the foot of the auxiliary column 34 Accumulating liquid ethane-ethylene mixture is passed via line 52 as scrubbing liquid into the decomposition stage 33. That through the lines 35, 36, 37 Pure, liquid ethane withdrawn at the foot of each decomposition stage is adjusted to about 1.2 ata relaxed and fed to a manifold 39. About half of the liquid goes from this via line 38 to the condenser evaporator at the head of the decomposition stage 33, the other half via Valve 40 and line 41 with a pressure of about 0.75 ata to the condenser evaporator at the top the auxiliary column 34 and evaporates there. The resulting gas is passed through line 57 to a heat exchanger 42 and divided after flowing through it at point 53. One part of the gas is compressed to about 6.6 ata with the compressor 43 and goes in countercurrent with itself through the heat exchanger 42 and the line 44 to the foot of the decomposition stage 31, while the other Part is compressed in the compressor 54 to about 1.2 ata and discharged via the line 55. At point 56 this gas stream combines with that through line 58 from the condenser evaporator at the top of the Decomposition level 33 coming pure, gaseous ethane.

When processing, for example, 1000 Nm ³ / h crude Cg gas mixture, which consists of 80% ethane and 20% ethylene, and is added to the system at 45, about 400 Nm ³ / h can, for example, through line 57, through line 58 about 490 Nm ³ / h and through line 44 about 90 Nm ³ / h ethane flow. At about 800 Nm ³ / h of pure ethane, at 51 about Nm ³ / h of pure ethylene can be withdrawn.

Claims (6)

Patent claims: 1. Process for the decomposition of gas mixtures by means of low-temperature rectification in a main rectification column and an auxiliary column consisting of at least three consecutive decomposition stages, the gas mixture being fed to the first decomposition step under the highest pressure according to its composition and pre-decomposed therein, whereupon part of the gas mixture in larger amount \ ^r orhan which component withdrawn as a pure product and the impure product to the next lower pressure decomposition stage is fed at a corresponding position, taken off as a pure product in the turn of the same element and the impure product to another, under still lower pressure Decomposition stage is fed and the heat released during the condensation of the gas flowing into the head of the rat-th decomposition stage in the foot of the (# + l) -th decomposition stage for evaporation of the sump liquid boiling there is transferred, characterized in that a gas mixture of the two components is removed from the decomposition stage with the lowest pressure and rectified in the auxiliary column at the same pressure, the component present in the gas mixture in small quantities being recovered and withdrawn from the auxiliary column, while the impure gas mixture is returned to the decomposition stage which is under the lowest pressure. 2. The method according to claim 1, characterized in that the liquid in the foot of the first The decomposition stage is heated with a gaseous product obtained during rectification, this is condensed and given as washing liquid in the last decomposition stage. 3. The method according to claim 1, characterized in that the bottom liquid of the auxiliary column is heated with raw gas. 4. Device for performing the method according to claim 1, characterized in that the decomposition stages (1, 2, 3) arranged one above the other and through the condenser evaporator (29) are thermally connected to each other. 5. Device for performing the method according to claim 1, characterized in that the head of the auxiliary column (4) through a line (30), which is above the liquid level, and a Line (25) which opens below the liquid level in the foot of the decomposition stage (3), is connected to this. 6. Device for performing the method according to claim 1, characterized in that the head of the multiple decomposition stages (31, 32, 33) connected in series Main column through a line (50), which is above, and a line (52), which is below the liquid level opens in the foot of the auxiliary column (34), is connected to this. Considered publications:
German patent specification No. 1 048 600. 1 sheet of drawings & 009 607/85 9.60