DE1250848B - Method and device for the low-temperature decomposition of air with fluctuations in oxygen decrease - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

F25j

German class: 17g- 2/01

Number: 1250 848

File number: G 375081 a / 17 g

Filing date: April 11, 1963

Opening day: September 28, 1967

The invention relates to a method and an apparatus for the low-temperature decomposition of air by means of two-stage rectification, in which fluctuations in the withdrawal amount of gaseous oxygen can be balanced by with heavy withdrawal liquid stored oxygen is additionally evaporated, while at the same time gaseous nitrogen is evaporated the head of the pressure column of the work-performing relaxation is withdrawn, liquefied and stored, and in the case of a small withdrawal, the excess amount of oxygen is stored in liquid form, the liquefied Nitrogen is evaporated.

In connection with the so-called internal oxygen compressionj d. H. the evaporation of the previously liquid brought to the consumption pressure by pumping Oxygen in the decomposition apparatus, a way has already been shown to use in oxygen systems Regenerators as heat exchangers increase the oxygen yield from the decomposition air. oxygen or one in heat exchange with the evaporating one Oxygen liquefied gas, in particular nitrogen, is vaporized to liquefy rectification vapors, which the low pressure column roughly in the middle or, more precisely, between the feed point for the raw oxygen from the pressure column and taken from the bottom of the low pressure column.

The increase in the yield, or in other words the reduction in the air requirement for the oxygen obtained, is due to the fact that the large amount of return flow required for the rectification, which practically only takes place between argon and oxygen in the lower section of the low-pressure column, is partly formed from the vapors rising in this column section is, so only partially has to be removed from the pressure column. For the rectification between argon and oxygen taking place in the lower section of the low-pressure column, _{at least 400 parts of reflux are required for every 100 parts of oxygen product with 99.5% O 2} content, because the vapor pressure ratio of oxygen to argon is about 100: 130. With normal two-stage rectification, this return flow must be formed entirely by liquids removed from the pressure column. Taking into account the evaporation losses when the liquids are transferred and as a result of the different evaporation heats of oxygen and nitrogen, at least 440 parts of liquid must be transferred from the pressure column to the low pressure column. If to cover the cold losses of the separating apparatus 120 parts of the decomposition air relaxed to perform work, so not ver process and device

for the low-temperature decomposition of air

with fluctuations in oxygen consumption

Applicant:

Linde Aktiengesellschaft,

Wiesbaden, Hildastr. 2-10

Named as inventor: ^l

Max Seidel, Munich-Solln

are liquid, this results in an air requirement of 440 ■ + 120 = 560 parts of separation air for 100 parts Oxygen of 99.5% purity.

Assuming that the crude oxygen is taken from the pressure column with 39% O ₂ content, the equilibrium conditions at the point of introduction of the crude oxygen into the upper column show that for the recovery of 100 parts of pure oxygen from 500 parts of decomposition air in addition to about 255 Parts of raw oxygen with 39% O ₂ content still need about 125 parts of scrubbing nitrogen with about 3% O ₂ content. At the column head of the low-pressure column, 120 parts of washing nitrogen for 255 + 120-100 = 275 parts of rising vapors are then available at approximately 5% inlet evaporation of the washing nitrogen. This ratio of about 2.30 ensures that the oxygen is well removed from the rising vapors.

With a partial reflux formation from the column vapors of the lower section of the low-pressure column can therefore determine the amount of liquids to be transferred from the pressure column into the low-pressure column from 440 parts to about 360 parts per 100 parts of oxygen product.

The difference between 440 parts and 380 parts of liquid withdrawal from the pressure column is either available as an additional amount for work-performing relaxation, i.e. for additional cooling or can serve to reduce the air throughput per 100 parts of oxygen.

With only 500 parts of decomposition air per 100 parts of oxygen product of 99.5% purity, there are then 120 parts of nitrogen per 100 parts of oxygen product are still used for work-performing relaxation to disposal.

Since the cold losses in the air separation plant are roughly proportional to the amount of air converted,

709 649/124

with reduced air volume and the same amount of work relaxed amount in relation to the cooling requirement of the cutting unit generates more cold.

The present invention has set itself the task of further reducing the energy expenditure for the production of oxygen, in particular for the highest oxygen purities with over 99% O ₂ content, and furthermore for ancillary equipment, such as for the storage of liquid gases with fluctuations Oxygen demand (German Auslegeschrift 1105 897) - especially for the purpose of expanding the scope for consumption of the gaseous oxygen - to gain sufficient excess cold without any special effort.

This object is achieved according to the invention in that with normal removal of oxygen the evaporation of the same by heat exchange with from the middle part of the low pressure column removed vapors takes place, which after condensation are returned to this as return be, and that with a low withdrawal of oxygen additionally stored liquid nitrogen for Condensation of the vapors removed from the low pressure column is evaporated.

With the new method, with few and simple additional means, when applying the exchange storage kept the oxygen production unaffected by fluctuations in oxygen consumption will.

The lack of refrigeration requirement is advantageous in a manner known per se due to the work performing Relaxation of the increased amount of nitrogen from the during the times of low oxygen extraction Pressure column covered.

According to the invention, the evaporator side of the intermediate condenser is advantageously used as a circulation evaporator operated and the liquid not evaporated with each circulation is in a separator of the formed vapor is separated and together with the new one via a deeper adsorber Oxygen product taken from the bottom of the low-pressure column on the evaporator side of the intermediate condenser again "fed.

A level vessel with free overflow to the Säüer material storage tank, which can be combined into a structural unit around the separator and its vapor space is connected to the vapor space of the oxygen storage tank, maintains the liquid level in the Evaporation space of the intermediate condenser.

Operation is simplified by the automatic liquid level maintenance in the evaporation chamber of the intermediate condenser. ^:

Corresponding to the mode of operation of the oxygen evaporator for condensation of the low-pressure column vapors the additional storage nitrogen to be evaporated is expediently also evaporated in the circulation process and the amount not evaporated during each circulation is separated from the vapors and fed back to the nitrogen stream to be evaporated. The liquid level in the sump of the low pressure column is according to a further feature of the Invention by free overflow, preferably in a level vessel, kept constant so that the flooding the evaporator side of the nitrogen condenser for heating the low pressure column remains constant.

To achieve the necessary temperature gradient for the condensation of column vapors through the evaporating To create oxygen product, the pressure on the product evaporation side of the intermediate condenser compared to the pressure in the low-pressure column. The pressure at the lower end of the low pressure column is opposite to the usual Double rectification increased from 1.4 ata to 1.6 ata and the product at a reduced pressure of 1.2 ata evaporated to cool the intermediate condenser. The evaporation pressure of 1.2 ata is sufficient around the oxygen after heating in

ίο the usual regenerator coils available at a pressure not below atmospheric pressure. When the oxygen is consumed under pressure, the heated oxygen is compressed outside the decomposition apparatus (Outer compression of oxygen).

Because of the higher pressure in the low-pressure column, there is an air pressure of about 6.6 ata required instead of about 5.8 ata with the normal Linde-Fränkl method.

The switching loss of the regenerators increases the air requirement of 560 Nm ³ or 500 Nm ³ by about 20 Nm ³ per 100 Nm ^{3 of} oxygen product. The comparison shows that for the compression of 520 Nm ^{3 of} air to 6.6 ata pressure, which are required according to the method of the invention to obtain 100 Nm ^{3 of} oxygen to 99.5% O 2 content, about 48 kWh are required , while the normal Linde-Ffänkl process for 580 Nm ³ / h with 5.8 ata pressure ^{requires about 50 kWh / 100 Nm 3} oxygen.

Since the same gas quantities are available for the work-performing expansion in both cases, but according to the invention, on the one hand, because of the greater pressure drop, about 10% more cold is generated and on the other hand, because of the smaller amount of air, about 10% less cold losses have to be covered, results With the new process, there is a sufficient excess of cold in addition to the cold losses of the Air separator still cover evaporation losses from liquid storage, which is used to compensate between serve constant generation and fluctuating consumption of oxygen.

If less oxygen is withdrawn for consumption, the oxygen pressure in the evaporation space rises of the intermediate condenser, the temperature difference of the heating surface of the intermediate condenser decreases and the evaporation capacity decreases. Since from the bottom of the low pressure column one If a constant amount of liquid oxygen flows to the intermediate condenser, the liquid level rises the evaporation side of the intermediate condenser. .

As a consequence of the reduced intercondensation of rectification vapors, the amount of return flow in the lower column section of the low-pressure column initially decreases and, associated with this, the O, -content of the column vapors increases at the connection point of the intermediate condenser and in the column section above. The oxygen purity in the lower section and in the bottom of the low-pressure column changes much more slowly as a result of the storage effect of the column. The liquid nitrogen taken from the nitrogen reservoir, which evaporates under a pressure approximately equal to the pressure of the low-pressure column, now additionally condenses as much of the column vapors as has failed due to the lower oxygen evaporation in the intermediate condenser. The disturbed equilibrium of the low pressure _{column and thus the O. 7} content above the intermediate condensation point

the low-pressure column is thus restored. There is no noticeable change in the purity of the product oxygen. As a basis for the The analysis of the regulation of the amount of nitrogen evaporated in the additional intermediate condenser is used Rectification vapors at the connection point of the intermediate condensers or expediently at one point between the connection of the intermediate condensers and the introduction of raw oxygen into the low-pressure column. The regulation can be done manually or automatically. .

When the oxygen consumption exceeds the production, the oxygen storage system changes - expediently by means of a pump - oxygen to the level vessel on the oxygen evaporation side of the intermediate condenser promoted. A special quantity regulation is not necessary for this, as there is too much Pumped liquid quantities flow back through the overflow of the level vessel to the liquid oxygen storage.

To evaporate the excess amount of oxygen without affecting the low pressure column according to the invention an additional product evaporator to the level vessel on the evaporation side of the intermediate condenser connected, which is heated by condensing nitrogen from the pressure column. The amount of condensing nitrogen is controlled manually or automatically so that the composition the vapors at the connection point of the intermediate condenser to the low-pressure column or at a selected point between this point and the point where the raw oxygen is fed into the low-pressure column remains constant. This ensures that the amount of in the intermediate capacitor for the normal operation formed additional return for the lower section of the low-pressure column unchanged remain.

The one for the evaporation of the liquid oxygen taken from the oxygen storage tank condensed nitrogen is fed to the nitrogen exchange storage, so that a repercussion on the No separation column.

To get the required amount of nitrogen; To have the pressure column available for the evaporation of the _{oxygen added in liquid form from the O 2} swap storage unit without changing the heating of the low-pressure column, the pressure on the expansion turbine must be reduced to such an extent that the heating of the low-pressure column by condensing pressurized nitrogen and thus the purity of the oxygen in the The column bottom of the low pressure column remains unchanged. The temporary waiver of part of the possible cooling capacity can be replaced by the cold storage of the removable storage.

By switching on a rectification between the point of the low pressure column from which the column vapors removed for the intermediate condensation and returned to the intermediate condensate formed is, and the intermediate condensation itself can be enriched argon to the extent that it as relatively pure crude product can be discharged at the intermediate condenser. In the intermediate capacitor then practically only argon condenses. The extraction of argon through such an intermediate rectification between the low-pressure column and intermediate condensation requires an additional increase of the pressure of the low pressure column, since the pressure of the ini intermediate condenser condensing Argon has to be higher because of the lower boiling temperature than oxygen and the flow resistance the argon rectification leads to a further pressure increase in the bottom of the low-pressure column. In order to the nitrogen of the pressure column from the bottom liquid of the low pressure column the rectification vapors can evaporate for the low-pressure column, the decomposition air pressure must be selected 1 to 1.5 at higher are considered to be without argon extraction.

The figure shows, for example and schematically, a system for carrying out the method.

The air compressed to 6.6 ata, about 520 parts per 100 parts of product, is cooled and cleaned via line 1 in regenerators 2, 4 or 3, 5. The amount of air remaining after deduction of the switching losses, about 500 parts, is fed through the line 6 to the lower end of the pressure column 12 of the double rectifier, which is under a pressure of 6.5 ata. The liquid collecting in the sump of the pressure column 12, about 255 parts with about 39% oxygen content, is withdrawn via line 7 and passed through the alternately operated adsorbers 8 α and Sb and freed from traces of carbon dioxide and hydrocarbons there. The purified liquid is then expanded through the line 9 via the subcooling countercurrent 10 and the expansion valve 11 into the low-pressure column 13, in which there is a pressure of about 1.5 ata at this point.

The upper part of the pressure column 12 is about 125 parts of liquid nitrogen with about 3% oxygen content Taken via the control valve 14 and fed to the nitrogen reservoir 16 through the line 15. Liquid nitrogen is withdrawn from the nitrogen accumulator 16 through the line 17 in the heat exchanger 18 is supercooled, relaxed in the valve 19 and introduced into the head of the low-pressure column 13 as washing liquid. With normal oxygen consumption, deviating from the drawing, the Nitrogen reservoir 16, the line 15 with the line

17 are connected. Gaseous nitrogen, about 120 parts, is taken from the top of the pressure column 12 through line 20, passed through pipe coils in the lower part of the regenerators 2, 3, 4, 5, warmed up a little there and fed via line 21 into the turbine 22 or 23 and relaxed while doing work. This amount of nitrogen is then passed through line 24 via check valves 25 a and 25 c or 256 and 25 d into regenerators 2, 4 or 3, 5, where it is heated to ambient temperature and leaves the system through line 26, from the head the low pressure column 13, 280 parts of nitrogen with about 2.3% oxygen content are withdrawn through the line 27 to subcool the liquids transferred from the pressure column 12 to the low pressure column 13 by the heat exchanger

18 and 10 passed and through the throttle valve 28 of the supplied by the turbine 22 or 23 coming amount of nitrogen.

From the bottom of the low-pressure column 13, liquid oxygen is withdrawn via line 29 and fed into the Level vessel 30 passed, the upper end with the vapor space of the column sump of the low pressure column 13 is connected. The running liquid product, with normal consumption 100 parts of oxygen about 99.5% purity, is through line 31 Via the throttle valve 32 and the adsorber 33 with the line 34 in the under a pressure of about

1.2 ata standing intermediate condenser 35 passed, in which it is exchanged by heat with about 100 parts condensing rectification vapors, which the low-pressure column 13 between the feed point of the Raw oxygen taken from the pressure column and the bottom of the low pressure column via line 36 and returned as condensate through line 37, evaporated. By manual adjustment of the throttle valve 32 can increase the level in

evaporated from the pressure column 12 and evaporated in the level vessel 38 in the intermediate condenser 35 Product oxygen added. Of the nitrogen withdrawn from the top of the pressure column 12 for 5, part of the expansion turbine is branched off via the three-way regulating valve 54 and via the line 53 and condensed in the condensation space of the additional product evaporator 52. About 36 parts Pressure nitrogen condense in the heat exchange level vessel 30 easily within a relatively wide io with the evaporating excess product of 25 parts Range can be set without the liquid oxygen. In the separator 55 is the liquid part The level of liquidity in the column sump changes. The evaporator is separated and through line 56 to the nitrogen side the intermediate capacitor 35 is supplied as a circulating accumulator 16. A non-condensed residue vaporizer shown. In the subsequent level of nitrogen is from the separator 55 through the Vessel 38, which also serves as a separator, is taken from line 57 and that from the head of the pressure Circulation of the evaporating liquid column to the expansion turbines 22 or 23 remains separated the liquid part and fed through the nitrogen line 20. To the for device 39 via the adsorber 33 to the intermediate condenser - evaporation of the oxygen excess of 25% sator35 fed back. The gaseous end product required pressure nitrogen without any influence is available through line 40 to the head of the Ni- 20 solution for double rectification, veaugefäßes 38 removed, in the coils during the time of the oxygen extraction the regenerators to ambient temperature - the throughput rate of the nitrogen expansion tower warms up and reduced in the compressor 41 to, for example, bine 22 or 23. Serves as the rule basis 30 ata compressed. the deviation from the steady state of low

Operation with a below-average acid pressure column, preferably the oxygen content of the Material consumption: For example, with 25% less nitrogen being withdrawn from the top of this column.

Oxygen consumption than corresponds to generation will be 25%> of the liquid product coming from the low pressure column on the evaporator side of the Intermediate capacitor 35 not evaporated. The non-evaporated part, about 25 parts, is released through Overflow of the level vessel 38 by means of the line 42 to the oxygen storage 43, in which a pressure of about 1.2 ata prevails, supplied. The vapor space of the oxygen storage 43 is with the upper end of the Level vessel 38 connected, as indicated by dashed lines.

An additional 25 to 30 parts of liquid nitrogen are withdrawn from the nitrogen reservoir 16, passed through line 44 via expansion valve 45 into separator 46, from the base of the separator removed through line 47 and on the evaporator side of an additional intermediate condenser, which, according to the drawing, is combined with the intermediate capacitor 35 to form a structural unit, in the heat exchange with the condensing column vapors from the low pressure column 13 in constant circulation evaporates. This nitrogen also condenses about as much of the column vapors as is less condensed due to lower oxygen evaporation in the intermediate condenser. In the separator 46 is the liquid part of the circulated during the evaporation in the additional intermediate condenser Separated nitrogen and fed back to the evaporator side of the additional intermediate condenser. The gaseous part is withdrawn from the top of the separator 46 via line 48 and with the from At the top of the low-pressure column 13, incoming nitrogen is brought together in line 27.

Working method with above-average oxygen consumption; For example, 25% higher Oxygen consumption than corresponds to the generation, are from the oxygen storage 43 by means of a Pump 49 pumped 25 parts of oxygen with a purity of 99.5% through line 50 to level vessel 38. That Additional product is branched off from line 34 via line 51, in additional product evaporator 52 in heat exchange with condensing nitrogen

Claims (17)

Patent claims: 1. Process for low temperature reduction of air by means of two-stage rectification, in which Fluctuations in the withdrawal amount of gaseous oxygen can be compensated by in the case of large amounts of liquid stored oxygen is additionally evaporated, while at the same time gaseous nitrogen from the head of the pressure column of the work-performing relaxation is withdrawn, liquefied and stored, and with little withdrawal the excess amount Oxygen is stored in liquid form, whereby the liquefied nitrogen is evaporated, thereby characterized in that with normal removal of oxygen the evaporation of the same by heat exchange with vapors taken from the middle part of the low pressure column takes place, which are given up again after condensation as a return to this, and that at low extraction of oxygen additionally stored liquid nitrogen for condensation the vapors removed from the low pressure column is evaporated. 2. The method according to claim 1, characterized in that by the work-performing relaxation the increased amount of nitrogen from the Pressure column is covered in a manner known per se, the missing refrigeration requirement. 3. The method according to claim 1 or 2, characterized in that the evaporation of the oxygen takes place in the circulation process' and the amount of not evaporated with each circulation separated from the vapors and the oxygen stream to be evaporated again via an adsorber is fed. 4. The method according to any one of claims 1 to 3, characterized in that the liquid level in the oxygen separation room through free overflow to the storage tank for liquid oxygen is kept constant. 5. The method according to claim 1, characterized in that by the condensation Additional storage nitrogen to be evaporated from vapors from the low-pressure column in the circulation process evaporated and the amount not evaporated with each circulation is separated from the vapors and is fed back to the nitrogen stream to be evaporated. 6. The method according to claim 1, characterized in that the liquid level in the sump the low pressure column kept constant by free overflow, preferably into a level vessel will. 7. The method according to one or more of claims 1 to 6, characterized in that the pressure level of the rectifier is set so high that the heat exchange with the condensing vapors of the low pressure column evaporating oxygen to the compressor still flows in at about atmospheric pressure or slightly overpressure. 8. The method according to claim 1 or 5, characterized in that the amount of additionally to be evaporated liquid nitrogen from the nitrogen storage according to the composition of the Vapors from the low-pressure column at the extraction point for the return flow or at a between this point and the point of application of the oxygen-rich mixture from the pressure column is regulated manually or automatically. 9. The method according to any one of claims 1 to 3, characterized in that the amount of additionally Nitrogen to be condensed from the pressure column according to the composition of the vapors of the low pressure column at the extraction point for the return formation or at one between this point and the task point of the oxygen-rich mixture from the pressure column lying point manually or automatically will. 10. The method according to claim 1, characterized in that the heating of the low-pressure column by condensing nitrogen of the pressure column by regulating the work-performing the amount of nitrogen to be released, which is taken from the pressure column, manually or automatically according to the composition of the gaseous withdrawn from the top of the low pressure column Nitrogen is regulated. 11. The method according to one or more of claims 1 to 10, characterized in that the vapors of the low-pressure column condensing to form the return flow before their condensation in a secondary column through which these vapors condensed by evaporating decomposition products Liquid as reflux can be enriched with argon, with part of the enriched Argon is taken as vapor or as a liquid at the top of the secondary column and the reflux liquid from the bottom of the secondary column of the low-pressure column approximately at the level of the extraction point for the column vapors to be condensed is fed. 12. Device for performing the method according to claim 1, characterized in that that in addition to an intermediate condenser (35) cooled by evaporation of the oxygen for vapors removed from the middle part of the low-pressure column (13), the evaporation side of which is provided with an overflow line (42) for non-evaporated liquid oxygen to an oxygen storage (43) is provided, the vapor space with that of the evaporator is in connection, on the condensation side of the intermediate condenser (35) parallel-connected nitrogen additional evaporator is provided, the liquid supply line (44) with a nitrogen accumulator (16) via a control valve (45) and its vapor discharge (48) is connected to the nitrogen discharge line (27) from the top of the low pressure column (13), and that an additional oxygen evaporator (52) is also provided, the liquid supply line of which via a Control valve with the oxygen storage tank (43) and its vapor discharge with the oxygen discharge (40) is connected and its condensation side with a steam supply line (53) together with Control valve (54) from the head of the pressure column (12) and a liquid discharge line (56) to the nitrogen reservoir (16) is provided. 13. Device according to claim 12, characterized in that the evaporator for the Oxygen as a circulation evaporator with vapor separator and return line for liquid are formed from the separator via an adsorber (33) into the evaporation chambers. 14. Device according to claim 13, characterized by the design of the separator as Level vessel (38) with overflow (42) to the oxygen storage tank (43) and vapor return line from this Oxygen storage to the level vessel. 15. Device according to claim 12, characterized by the formation of the additional nitrogen evaporator as a circulation evaporator with vapor separator (46) and return line (47) of the liquid from the separator (46) into the evaporation chamber. 16. Device according to one or more of claims 12 to 15, characterized by a Overflow for the bottom of the low pressure column (13) with subsequent level vessel (30), with the upper connecting line of the level vessel (30) with the vapor space of the low-pressure column sump and with the lower discharge (31) Control valve (32) to the evaporation chamber of the oxygen evaporator. 17. Device according to one or more of claims 12 to 16, characterized by a Secondary column provided with an argon head discharge, connected to the vapor and liquid communication paths between the middle part of the low pressure column (13) and the intermediate condenser (35). Considered publications:
German Patent Nos. 1,012,939, 1,056,633; German interpretative document No. 1105 897. 1 sheet of drawings 709 649/124 9. 67 © Bundesdruckerei Berlin