DE729475C - Process for gas separation using an auxiliary material cycle - Google Patents

Description

Process for gas separation using an auxiliary material cycle When breaking down gas mixtures, e.g. B. those with a high content of hydrogen on the order of. z. B. 50 ° (0, which can be obtained in great purity it is known, with the help of a substance, which is involved in the gas decomposition itself is not involved, the refrigeration required for the gas separation, or at least to cover a significant proportion of the same. As an adjuvant z. B. nitrogen in question. For this purpose, the nitrogen is at high pressure, e.g. B. -2oo at, compressed, cooled in countercurrents and relaxed in a throttle valve, the process is expediently conducted so that a liquefaction or at least a partial liquefaction of nitrogen occurs. The resulting in the relaxation steam is z. B. the High pressure nitrogen counteracted, whereby it its cold to the high pressure nitrogen gives away. The liquefied portion is z. B. transferred to an evaporation vessel, where it boils under atmospheric pressure and that for the separation of the remaining impurities provides condensation cooling required by the hydrogen. In addition, it is known the greater part of the high pressure nitrogen after going in countercurrent cooled to low temperature, to an intermediate pressure; z. B. 5o at to relax and the cold thus obtained in the same countercurrent again on the high pressure nitrogen transferred to. This method is particularly favorable because of the energy consumption significantly smaller for the compression of medium pressure nitrogen to high pressure is the refrigeration capacity than for the compression of relaxed nitrogen to high pressure but does not decrease to the same extent during relaxation, so that the ever kcal of cold compression work to be expended when relaxing from high to medium pressure is much smaller than with the relaxation to atmospheric pressure.

The invention consists in that only a small part of the medium pressure nitrogen in a manner known per se for cooling the high-pressure component serves, while the other part is directed towards the raw gas in the heat exchange and here its cold is used to condense the high-boiling components of the raw gas whereupon the evaporation coolness of these components in the heat exchange on the entering high pressure nitrogen is transferred. As with the known systems the medium-pressure nitrogen and the low-pressure nitrogen are then also used here after warming up, fed back to the corresponding stages of the compression system and compressed to high pressure.

According to the state of the art (see "Journal for the entire refrigeration industry" 1925, page 97) it would have to be assumed that an increase in the medium-pressure nitrogen quantity beyond the value determined by the heat capacity of the high-pressure quantity is not possible without cold losses. The fact that the particularly economical cold provided by the additional medium pressure nitrogen is used for the fractional condensation of the raw gas, the medium pressure nitrogen can surprisingly be increased by a considerable amount, for which a corresponding amount of high pressure nitrogen does not need to be expanded to atmospheric pressure. In this way, the condensation cooling is generated much cheaper than before. ° The invention is explained below with reference to the schematic drawing Fig. I. B. 17 at is in heat exchange with the decomposition products, which are z. B. hydrogen and residual gas, cooled to liquefaction of the ethylene fraction. In the same countercurrent, cold nitrogen from Soat flows against the raw gas, which transfers the cold required for the condensation of the ethylene fraction to the raw gas.

In the separator 3, the condensate is separated from the gas. In countercurrent 2 becomes high pressure nitrogen from Zoo at by counterflowing nitrogen from 5o at and cooled by nitrogen expanded to atmospheric pressure or negative pressure. In this countercurrent flow, the liquid ethylene fraction from the separator is also removed 3, which is downregulated by valve .1, evaporates and warms up, whereby the The ethylene fraction also transfers its cold to the high pressure nitrogen entering. The cold high-pressure nitrogen is in the throttle valve after leaving the counterflow 2 6 to 5o at relaxed. Part of this nitrogen, which is relaxed to medium pressure is, as already said, in the countercurrent # ', sent towards the high pressure nitrogen, a further part of the nitrogen expanded to medium pressure is known per se Way via the countercurrent g and after expansion to atmospheric pressure in the Venti17 the separator is supplied by a portion of the relaxed nitrogen in the spiral ii enters into heat exchange with the raw gas. A liquefied portion of the relaxed Nitrogen is fed into the evaporator 12 via the regulating valve 8, «-o er under reduced pressure of e.g. B. o, 1 ata boils and its coldness for the rest Separation of the residual gases from the hydrogen emitted. The relaxed nitrogen leaves the separator io through the lines 13 and 1.1 via the countercurrents g and 2. The the remaining medium-pressure nitrogen is fed through line 15 to the countercurrent flow device i, so where he brings about the condensation of the Äthvlenfraktion according to the invention. Of the The vaporous part of the raw gas emerges from the separator 3 via the countercurrent 5 through line 16 into the separator io, from which the hydrogen obtained through line 17 and the residual gas through line 18 via the countercurrents 5 and i exit in order to then be used for further purposes.

The one from the countercurrent? exiting nitrogen from o, i ata becomes compressed by a vacuum pump, not shown, to atmospheric pressure and combined with the nitrogen from i ata and also exiting from countercurrent -a is then fed to a compressor to be compressed again on Zoo at. The nitrogen of 50 atm exiting from the countercurrents i and 2 becomes a medium-pressure stage of the same compressor and also compressed at Zoo at. The nitrogen cycle is closed this way. The ethylene fraction leaving the countercurrent 2 is under a pressure of z. B. i, o to 1.5 ata, under which they another Can be fed to the decomposition process.

In the process according to the invention, the ethylene fraction is liquefied with particularly little energy in the countercurrent i, because this only the compression of the auxiliary material from medium pressure to high pressure is required is. Furthermore, when re-evaporation of the liquefied fraction is in countercurrent 2 released cold practically completely recovered, which is at. the earlier procedures encountered considerable difficulties, and that is achieved by the enlargement the amount of the particularly favorable medium-pressure nitrogen circuit (with the two Branches that are distributed on countercurrents i and 2) with simultaneous reduction the amount of nitrogen to be released to atmospheric pressure, its recompression at high pressure requires a greater expenditure of energy with the same cooling capacity. The inventive effect is based on the fact that the medium-pressure nitrogen to be heated its cold partly on that Raw gas to liquefy the ethylene fraction and only a small part of it transfers to the high pressure nitrogen. In this way. the condensation cooling, for the ethylene fraction on the raw gas, is not carried out relaxed nitrogen with low specific heat transferred, but through the high-pressure nitrogen with a high specific heat during the evaporation of the ethylene fraction initially recorded and then after the expansion to medium pressure on the raw gas transfer. This actually has the effect of reducing the amount of nitrogen that must be compressed from the relaxed state to high pressure, considerably smaller will. It is true that the amount of nitrogen that compresses from medium pressure to high pressure is, somewhat larger, but overall there is an energy saving of the order of magnitude of 10% of the total energy required for hydrogen production.

The invention can similarly be used in the decomposition of synthesis gases or other gas mixtures are used in which larger quantities are produced higher-boiling fractions are eliminated before the final gas separation should.

It is also possible to use the same procedure for multiple fractions to be separated out separately, e.g. B. by appropriate subdivision of the countercurrent i and activation of further separators. .

Another example of an application of the invention is shown in Fig. 2. Using a nitrogen cycle, the raw gas should be converted into a carbon-oxide-free gas Hydrogen-nitrogen mixture can be obtained. The heat exchange takes place again in countercurrents 1, 2, 5 and g. The ethylene fraction is also in the separator 3 obtained and through valve q. downregulated in order to keep their cold on it in countercurrent 2 to be transferred to the entering high pressure nitrogen. The remaining raw gas occurs through line 16 via the countercurrent 5 into the column ig, in which a CH4-containing Residual gas is excreted, which through line 18 via the countercurrent 5 and i is led. The further dismantling of the ig at the upper end of the column Gas mixture takes place in the column 2o, which is the carbon oxide-free at the upper end Hydrogen-nitrogen mixture is taken, while at the lower end a carbon dioxide-containing Nitrogen-residual gas mixture is withdrawn, which is passed over the countercurrent g and 2.

The high pressure nitrogen entering is in valve 6 to medium pressure relaxed. A part of the medium pressure nitrogen is the high pressure nitrogen in the Countercurrent flow 2 countered, another part of the medium pressure nitrogen is passed via line 15 to countercurrent i, where it is used to liquefy the ethylene fraction serves. The remaining part of the medium pressure nitrogen is after flowing through the Countercurrent g is again divided into branches 22 and 23. In branch 22 is in the valve 24 medium pressure nitrogen is expanded to atmospheric pressure and is used to cool the Column ig through the condenser 21. The still remaining medium pressure nitrogen of the branch 23, which would be liquefied in the countercurrent g, is in the valve 25 to the Decomposition pressure of column 2o, e.g. B. x2 atü, relaxed to carbon dioxide and others Wash residual gases in countercurrent from the hydrogen, with some of the nitrogen in the hydrogen, the remainder remains in the CO-containing residual gas.

In this process, part of the nitrogen cycle is constantly being used in the column "2o consumed. An equal amount must be constantly before the circuit The compressor that is not shown can be replaced again. The advantages of the medium pressure nitrogen cycle are not affected.

Claims (3)

PATENT CLAIMS: i. Process for the decomposition of gas mixtures by deep freezing, in particular of coke oven gas or synthesis gas, from which in addition to a main product with a low boiling point, e.g. B. hydrogen, one or more fractions with high boiling temperatures, e.g. B. hydrocarbons with two or more carbon atoms, are separated out, whereby a gaseous, low-boiling auxiliary substance, preferably nitrogen, is used to cover the cooling requirement and to transfer the cold that can be achieved by re-evaporation of liquefied gas components, which is operated at high pressure (e.g. Zoo at ) is compressed and of which then only a relatively small part is expanded in the separation plant to atmospheric pressure or negative pressure, while the greater part of the cold high-pressure nitrogen to medium pressure, z. B. io to 7o at, preferably to around 5o at is relaxed and partly used to cool the high-pressure nitrogen, characterized in that the other part of the medium-pressure nitrogen in the heat exchange against the raw gas and here its cold is used to condense the high-boiling components of the raw gas , whereupon the evaporation cold of these components is transferred in heat exchange to the incoming high pressure nitrogen; the medium-pressure nitrogen and the low-pressure nitrogen are compressed again to high pressure in a manner known per se after they have been heated. 2. Procedure according to claim Z, characterized in that part of the medium pressure nitrogen to about atmospheric pressure. relaxed and in heat exchange with the one to be dismantled Gas mixture is brought. 3. The method according to claim 2, characterized in that that the relaxation of part of the medium pressure nitrogen to about atmospheric pressure liquid portion obtained under reduced pressure to achieve very low decomposition temperatures is evaporated. Method according to claim z to 3, characterized in that a Part of the 'medium pressure nitrogen in a washing column on the pressure of this column relaxed, as''4aschiquid led towards the rising gas stream in the scrubbing column and then leaves the decomposition apparatus together with the decomposition products.