DE1145649B - Process for low-temperature gas separation with high cooling requirements - Google Patents

Description

Process for cryogenic gas separation with high refrigeration requirements The invention relates to a method for low-temperature gas separation with high refrigeration requirements, for example for the liquid production of gas separation products, in particular for Production of liquid oxygen and / or nitrogen from air separation.

It is known to use liquid gas separation products, in particular air separation products, to be obtained in high-pressure systems that operate at around 150 to 200 atmospheres pressure. For this it is necessary to bring the gases in oil-lubricated compressors to this pressure compress and then free from higher-boiling impurities. Water- and oil vapors are mostly separated in tubular heat exchangers, carbon dioxide by means of a lye wash or adsorber.

It is also known, low-pressure systems in general serve to generate gaseous separation products, smaller amounts of liquid gas separation products refer to. These low pressure systems, which operate at around 5 to 6 atmospheres, Although they have the advantage that regenerators are used to cool and purify the gases to be broken down can be used and the compression in oil-free turbo or screw compressors can take place, but the specific energy consumption in the generation is more liquid Gases high.

It is also already a method for gas, in particular air, separation known, in which the gas to be separated to a uniform pressure of 15 to 30 atmospheres condensed and through essentially work-performing, multi-level relaxation in the lowest temperature occurring in the system cold is generated to liquid or to win highly stressed decomposition products. This is where the cold is generated in. At least two expansion turbines connected in series or in one multi-stage turbine, if necessary with intermediate heating. Part of the in the the first stage of the gas, which has been expanded to intermediate pressure, is withdrawn, and only the rest is further relaxed in the next stage.

According to another known method for the partial liquefaction of gas tables liquefies the relaxed, work-performing part, which is combined with the non-liquefied part Amount of gas in countercurrent with that to be compressed, by the portion that is branched off reduced amount of gas cooled, diverted portion in the heat exchange before it discharged through the regenerator to be cold blown and before the diverted portion is relaxed in a throttle valve and passed into the separator, from where the non-liquefied portion combined with the work-producing relaxed amount of gas will.

Finally, it is also known to produce cold by labor-performing Relaxation of a frozen and cleaned one by means of a regenerator arrangement Gas or gas mixture, which is warmed up before the relaxation, which is used for the work Relaxation intended to preheat gas in a regenerator group, their individual Regenerators periodically first of raw gas, then of purge gas and finally of be flowed through to be expanded gas.

These known methods also require a considerable amount of energy still significant investment funds, especially for the necessary ones Heat exchange processes for the production of liquid gas separation products.

The invention has the task of creating a method that when using relatively low pressures and using as little equipment as possible Expenditure permits larger quantities of liquid gas separation products in an economical way Way to generate.

The low specific cooling capacity of low-pressure systems has to go through large air flow can be compensated. This results in great cold losses. This disadvantage can be reduced if the pressure of the gas mixture to be broken down is increased. This increases the cooling capacity per Nm3 at the same time, and the Losses decrease. The pressure However, it cannot be grasped at will increase if regenerators and oil-free compressors are required. The scope the regenerators and also the reversing exchanger is due to the so-called switching losses limited.

Increasing the pressure above about 12 to 14 ata results in only a moderate one Energy saving. However, since the apparatus difficulties in. The regenerators grow considerably and the efficiency of the turbo compressors falls, the actual increases The total of the energy requirements is rather something so that it is not worth it, higher pressures apply. So there is a relatively low pressure range in. which the production of liquid gases is possible under optimal conditions.

The invention therefore relates to a method for producing liquids Gas decomposition products by low-temperature rectification, in which the Gas mixture is cooled and cleaned in switchable regenerators and in which at least part of this gas mixture is then heated and then in at least, two stages with intermediate heating by means of the gas mixture under initial pressure is relaxed, the relaxation at least in the second relaxation stage work done. The invention is characterized in that the intermediate heating at least part of the gas mixture coming from the first expansion stage in the heat exchange with the condensing and / or condensed gas, mixture takes place, that comes from the regenerators and through a valve into the low pressure part of the rectification column is relaxed.

The advantage of this method is that the compression of the to be dismantled Gases oil-free compressors, such as turbo or screw compressors, and for cleaning of the gas and regenerators can be used for heat exchange. Farther the outlay on equipment for the necessary heat exchange processes is lower than with the known methods, the energy requirements being practically the same. This is possible by overcoming the prejudice that regenerators only go up to about 6 ata can be operated economically. The heat transfer conditions are particularly favorable in the arrangement according to the invention, which accordingly result in low costs for the heat exchangers.

In the method according to the invention, the gas mixture to be broken down is with a pressure between 10 and 18 ata, in the case of air separation preferably with 12 up to 15 ata, by one of the regenerators of the cryogenic gas separation plant guided. The gas is reduced to a temperature slightly above the liquefaction temperature, Temperature cooled and thereby of higher boiling impurities such as water and COz in the case of air separation. If the level of impurities, If the C02 content is still too high during the air separation process, the gas can be used if necessary wholly or partially still be passed through an adsorber.

By further cooling in indirect heat exchange with cold gas, at least part of the gas is liquefied and fed to the condenser evaporator at the top of this column together with at least part of the bottom product that collects in a preferably single-stage rectification column. The liquid part evaporates, and the gas flows, preferably indirectly Heat exchange with gas to be decomposed, to the "in Regenera loaded from a previous period; gates that it cleans and cools in the process, and leaves then the plant. A dead end branched off behind the regenerators flow of the gas to be decomposed is optionally cleaned in an adsorber and then again divided up. A preferably controllable first part sirom is fed directly to the relaxation machine, while a second partial flow through the colder one Part of a discharged regenerator flows, thereby heated and then before the relaxation machine mixed with the first partial flow ° ^ wirä, whose strength is regulated so that an optimal Sublimation ratio arises in the regenerator. Xach the work-performing relaxation, the Sme ' is shared again. A part goes into the rectification, ° pillar and is dismantled there, while the other Üil through indirect heat exchange with incoming the '04 going to the condenser evaporator is heated and then further relaxed, and together with that of the condenser evaporator coming gas the plant in the described Way leaves. To warm up the too enitspann Gas can also be gas or a gas separation product that comes from another part of the system, vetce be turned. It is also possible for strangers Heat sources, such as someone else's gas Cutting plant, to be used for heating ,,,, - The @ ",, d! '@ Gssige that arises in the rectification column Product becomes deeper in the production of liquid boiling nitrogen on the head during air separation the column, in the production of, liquid high-pressure boiling, in the air separation. Oxygen, from, that The bottom of the column is drawn off and a collecting vessel forwarded. "'y In the figures, systems for carrying out the Method according to the invention schematically and both for example shown. As an example, the. He- generation of liquid nitrogen during air separation chosen, but the invention is not Ixe- restricts. In a corresponding way also summarizes Obtain liquid oxygen from air separation or other decomposition products during your decomposition other gas mixtures. Fig. 1 shows a system in which four Regeneratobm 1, 2, 3, 4 can be used, the center tapping exhibit. The use of four regenerators has the advantage that for the removal of dr of loose gas, two regenerators are available and thus the cross-section is doubled and the flow ming resistance is only a quarter as great as with the arrangement with a rainbrator. Will be on if this advantage is waived, the system can be sewn on operate with three regenerators. Give the arrows determines the flow path of the gases in a Working period again. The valves that control this flow effect, are not shown. At 13, compressed air is about 14 ata fed to the system. It is initially rator 1 cooled down and largely cleaned, ansclei @ ßend in the carbon dioxide adsorber 72 even further cleans. Then part of the air is in each case in the heat Ausausehern 5 and 6 cooled further, liquefied and - supercooled and then reunited,. relaxed in the valve 14, then by a Acetylene adsorber 7 out, in valve 15 wide external tensioned and fed to the condenser evaporator 16 of the rectification column 10. In this, the liquid portion of the gas evaporates, the top product of the column 10 condensing. This is removed at 17, expanded in a valve 18 and passed into the separator 11. The liquid product can be withdrawn from this through line 19. Gaseous nitrogen is removed from separator 19 through line 20 and combined with the gas coming from condenser-evaporator 16 through line 21, fed to heat exchanger 5 and then passed through regenerators 2 and 3, which are cleaned and cooled in the process, and leaves the system at 22 .

Part of the air stream cleaned and cooled in the regenerator 1 is branched off and divided upstream of the heat exchangers 5 and 6. A partial flow is passed through the colder section .des regenerator 4, warmed there, removed at 25 and mixed with a cold air flow coming directly from adsorber 12 through line 24, the amount of which can be adjusted with the aid of valve 23 so that the sublimation ratios in Regenerator are optimal. The total flow is then expanded to perform work in the medium-pressure turbine 8 and divides at point 26 into a partial flow 27, which goes into the rectification column 10, and another partial flow, which is heated in the heat exchanger 6, preferably with the help of condensing medium-pressure air, and to the low-pressure expansion turbine 9 flows. There the air is further expanded and mixed with the gas withdrawn through line 28. The bottom liquid of the rectification column 10 is fed through line 29 to the liquid stream going to the evaporator. The pressure in the column 10 is preferably about 3 ata for the recovery of liquid nitrogen. The column shown is not suitable for obtaining liquid oxygen. In this case, a column should preferably be used, the bottom of which is heated by indirect heat exchange with condensing air and which works at approximately 1 ata pressure. In the case of a two-column apparatus, the pressure in the pressure stage is about 6 ata.

Fig. 2 shows a further installation for carrying out the method according to the invention. In this are in the cold parts of the regenerators pipe coils 33, 34 inserted. To simplify the system, there is only one system in this case provided by two regenerators 31 and 32. Otherwise the system largely corresponds that already shown in FIG.

At 13, compressed air of about 14 ata is fed into the system again. After cooling and cleaning in the regenerator 31, the gas flow is again divided into several Split partial flows.

One of the partial flows branched off behind the regenerator 31 is, unlike in FIG. 1, reheated in the coil 33 inserted in the regenerator 31 and then fed to the turbine 8 with a further partial flow, the amount of which can be regulated by the valve 38, where it performs work relaxed. The way in which the rest of the system works has already been described in the explanations relating to FIG. 1. Another difference is that the sump liquid withdrawn from the column 10 is passed through the heat exchanger 35 and the expansion valve 37 to the evaporator 16, while the expansion of the gas mixture takes place in the valve 36.

Instead of the single-column rectifier shown in the figures the process can also be carried out in a corresponding manner with a two-column rectifier carry out. In addition, combinations of corresponding parts of the two are described Attachments possible.

Claims (5)

PATENT CLAIMS: 1. Process for producing liquid gas separation products by low-temperature rectification, in which the gas mixture to be broken down into switchable Regenerators are cooled and cleaned and at least part of this Gas mixture is then heated and then in at least two stages with intermediate heating is expanded by means of the gas mixture under initial pressure, the Relaxation takes place at least in the second relaxation stage while doing work, characterized in that the intermediate heating of at least part of the the first expansion stage coming gas mixture in heat exchange with the condensing and / or condensed gas mixture that comes from the regenerators and is let down via a valve in the low-pressure part of the rectification column. 2. Process according to Claim 1, characterized in that the initial pressure of the gas mixture in a manner known per se between 10 and 18 ata, preferably between 12 and 15 ata, lies. 3. The method according to claim 1 or 2, characterized in that a partial flow of the purified gas mixture from the regenerators via a with partly from the rectification column and partly from the second expansion stage Purge gas acted upon regenerator out and with the more or less condensed Gas mixture is combined from the heat exchanger to heat the next comes to relaxing gas mixture proportion. 4. Procedure according to one or more of claims 1 to 3, characterized in that the to be relaxed in the first stage Gas mixture is heated in the regenerators in a manner known per se, wherein a bypass line provided with a valve is used for adjustment. 5. Procedure according to one or more of claims 1 to 3, characterized in that the gas mixture to be expanded in the first stage in a manner known per se pipe coils inserted into the regenerators is guided. Considered Publications: German Patent Specifications No. 830 805, 1019 664, 1046640.