EP1052465B1 - Process and device for cryogenic air separation - Google Patents

Description

The invention relates to a method for the cryogenic separation of air according to the The preamble of claim 1.

Relevant air separation processes and devices are, for example, in Hausen / Linde, Tiefftemperaturtechnik, 2nd edition 1985, chapter 4 (pages 281 to 337) described. The invention particularly relates to two-pillar systems with a Pressure column and with a arranged above the pressure column low pressure column and / or multi-column systems with further separation columns for nitrogen-oxygen separation. The pressure column in this case represents the "first rectification column" in the sense of Invention; the rectification in the low pressure column and / or the evaporation in the Top condenser of the crude argon column is the "further process step". The "Transfer fraction" is here by the bottoms liquid or a Intermediate liquid of the pressure column formed in the low pressure column or in the Evaporation space of the top condenser of the crude argon column is initiated.

The invention relates in particular to double-column methods, as shown in FIGS. 4.23, 4.26, 4.28 and 4.34 are presented in Chapter 4.5 of Hausen / Linde. Notwithstanding the examples in Hausen / Linde is in the invention of Mass transfer preferably in at least one separation column (e.g. Low pressure and / or crude argon column) at least partially by packing or ordered Pack causes.

The transfer fraction collects within the first rectification column in one Reservoir that through the bottom of this column or a cup located in the column is formed. The liquid level in this reservoir sets the "first level" h1 within the meaning of the invention. From this reservoir, the transfer fraction in directed a container in which a further process step is carried out, for example, the low-pressure column or the evaporation chamber of a condenser-evaporator (e.g., top condenser of the crude argon column). The place of supply to This further process step defines the "second, higher level" in the sense of Invention.

For some years, the use of low pressure loss internals in Air decomposition columns more and more, because they have a number of advantages. Air separation plants in which packages in the low-pressure part of a double column are used, for example, in EP 321163 A, WO 9319335, WO 9319336 or EP 628777A.

A disadvantage of the use of packages is that the height noticeably increased in comparison with tray columns. In this case, in the claim the inequality stated, that is, the pressure difference between pressure and pressure Low pressure column or between pressure column and evaporation chamber of the Top condenser of the crude argon column is no longer sufficient to the corresponding hydrostatic pressure of a liquid column of the transfer fraction to overcome. While this situation in some systems in normal operation under full load often appears particularly in special operating cases, especially when operating under load, so with a lower product and Amount used as at full load.

The problem has already been mentioned in EP 567360 A in principle and by the Supply of a "relief gas" downstream of the valve solved.

The invention is based on the object, the aforementioned method and the appropriate device to be further improved.

This object is achieved by the characterizing feature of patent claim 1 solved.

In the context of the invention it has been found that it is possible that "Lightening gas" in the sense of EP 567360 A directly from the To transfer the transition fraction itself. The disadvantages of EP 567360 A described method are avoided, in particular are in the Conversion of oxygen-enriched liquid from the pressure column neither a Consumption of compressed air as "relief gas" still consuming additional steps necessary to generate "facilitating gas" from the transfer fraction; also no additional regulation is required.

This requires an arrangement of the expansion valve at a suitable intermediate level between the first and the second level. The concrete determination of this intermediate level is different for each specific embodiment of the invention, but can be easily determined by means of the calculation tools available to the person skilled in the art, if one specifies the height of the intermediate level as a degree of freedom. In typical cases, the expansion valve will be at an intermediate level of hz = h1 + x · (h2-h1) where x is 30 to 80%, preferably 40 to 70%.

This interpretation must be made for a specific operating case, for Example for starting the system. In another example, the arrangement becomes of the expansion valve for under load in stationary operation of the plant designed; then you may need additional funds to transport the Transfer fluid to the "further process step" during the start of the Be provided plant; In doing so, conventional methods for the transport of Liquid (mechanical pump, injection of external gas, etc.) used be, alternatively or additionally, the pressure level in the first rectification column be increased when starting.

In the method according to the invention, it is advantageous if the transfer fraction is subcooled before relaxing by indirect heat exchange. This will the formation of a two-phase mixture upstream of the relaxation all or partially avoided, so that only when relaxing the inventive targeted Steam bubble formation takes place. The subcooling usually takes place near the first levels.

Preferably, it is just so much supercooled that the transfer fraction immediately upstream of the relaxation completely or substantially completely in liquid form is present, but not overcooled.

In the design of a plant, this is done practically so that the first Hypothermia is set. The degree of supercooling of the transfer fraction becomes usually determined independently of the liquid transport process and is of other criteria, such as the desire to have relatively little flash gas when feeding into the second container to produce. The relaxation process, in particular, the arrangement of the expansion valve, is then so determines that at the given supercooling the transfer fraction immediately before relaxing just in the single-phase liquid state and neither a significant hypothermia still steam bubbles in appreciable extent available.

The invention also relates to a device for the cryogenic separation of air according to claims 3 and 4.

The invention and further details of the invention are described below an embodiment schematically shown in the drawing explained. In the embodiment, both the transfer of pressure column bottom liquid and pressure column nitrogen into the low pressure column as well Argon recovery with transfer of the pressure column sump liquid in the Top condenser of a crude argon column shown.

In the process shown in the scheme purified air 1 is under a Pressure of 4 to 20 bar, preferably 5 to 12 bar in a heat exchanger 2 against Product streams cooled to about dew point and in the pressure column 3 a two-stage Rectifier fed. The pressure column 3 is connected via a common Condenser-evaporator 4 in heat exchange relationship with a low pressure column 5th

Bottom liquid 6 and nitrogen 7 are withdrawn from the pressure column 3, in one Countercurrent 8 undercooled and at least partially in the low pressure column. 5 throttled. From the low pressure column are oxygen 9, nitrogen 10 and impure nitrogen 11 removed in gaseous form. The products can also be at least are partially removed liquid (oxygen 9a, nitrogen 10a).

h1 = 3100 mm

hz = 22100 mm

h2 = 46100 mm

In the pressure column, the sump forms a reservoir 24 for the column liquid draining from the lowest mass transfer section. The bottom liquid which collects in this reservoir forms the transfer fraction in the sense of the invention. The "first level" h1 is determined by the liquid level in the bottom of the pressure column. The transfer fraction 6 is supercooled in the countercurrent 8. The supercooled transfer fraction flows to a first part 13 to an expansion valve 14, which is arranged at the level hz. When relaxing 14 so much vapor is generated that the remaining pressure difference is sufficient to push the transfer fraction as a two-phase mixture 15 in the low-pressure column, namely at the "second level" h2. In a concrete numerical example:

h1 = 3100 mm

hz = 22100 mm

h2 = 46100 mm

The inventive method of transferring a liquid may as well the liquid nitrogen 7 from the head of the pressure column as (further) "transfer fraction" be applied. The "first level" is thereby by the liquid level formed within the cup 16, in which coming from main capacitor 4 Liquid is collected. Undercooling is again in the counterstroller 8. The supercooled nitrogen 17 flows to a relief valve 18, which on a Intermediate level hz 'is arranged and finally on to the feed point 19 ("second level" h2 ') at the top of the low pressure column.

If additional argon is recovered, as shown in the drawing, the Invention also to the transport of a liquid transfer fraction in the Evaporation space of the top condenser of a crude argon column can be applied. The crude argon column is formed in the example by two sections 20a, 20b, their function in European patent EP 628777 B1 and in the corresponding US Patent US 5426946 is described in detail. The invention can be applied to anyone known type of Rohargongewinnung be used, in which an argon-containing Oxygen fraction 21 introduced from the low pressure column 5 in a crude argon column is, wherein in the upper part of the crude argon column depleted of oxygen Argon product 22a, 22b obtained in gaseous and / or liquid state.

The further transfer fraction is in the example shown in the drawing through a part 13a of the supercooled bottoms liquid 6 from the pressure column 5 educated. She is relaxed in a relaxation valve 14a, which on a Intermediate level is arranged. This intermediate level is in the example the same or about the same height as the intermediate level hz. The in 14a relaxed transfer fraction 15a of sump 12 of the pressure column 3 is on a "second level" h2 "in the evaporation space 23 of the top condenser Introduced crude argon column.

Claims (4)

1. Process for the cryogenic separation of air, in which feed air (1) is introduced into a first rectification column (3) and a transfer fraction (6, 7) of density ρ is removed in the liquid state from a reservoir (24, 16) inside the first rectification column (3), is supercooled by indirect heat exchange (8), expanded (14, 14a, 18) and fed to a further process step (5, 23), in which process

   the liquid level in the reservoir (24, 16) is at a first level h1 and is under a first pressure p1,

   the expanded transfer fraction is fed to the further process step (5, 23) at a second, higher level h2(h2 > h1) and under a second, lower pressure (p2 < p1),

   the difference between the two pressures Δp = p1 - p2 is lower than the hydrostatic pressure (p_hydr = ρ· g· [h2-h1]) generated by a liquid column of the transfer fraction between the first level and the second level

   Δp = p1 - p2 < ρ· g· [h2 - h1]   (g: gravitational acceleration), characterized in that the expansion (14, 14a, 18) is carried out in such a way that the gas bubbles which are formed during the expansion reduce the density of the transfer fraction to such an extent that the pressure difference Δp is sufficient to feed the transfer fraction to the further process step (5, 23), without a gaseous or liquid stream being fed to the. transfer fraction downstream of the expansion (14, 14a, 18) or a liquid stream being fed to the transfer fraction between supercooling (8) and expansion (14, 14a, 18).
2. Process according to Claim 1, characterized in that the supercooling (8) is carried out in such a way that the transfer fraction (13, 13a, 17) is completely or substantially completely in liquid form immediately upstream of the expansion (14, 14a, 18).
3. Apparatus for carrying out the process according to Claim 1, which is designed for at least one operating situation and has a first rectification column (3) with a reservoir (24, 16) for a liquid transfer fraction and a liquid line (6 - 13 - 15, 6 - 13a - 15a, 7 - 17 - 19), which is connected to the reservoir (24, 16) in the first rectification column (3) and to a further vessel (5, 23), has an expansion valve (14, 14a, 18) between these connections and upstream of the expansion valve (14, 14a, 18) leads through a heat exchanger (8) in order to cool the transfer fraction by indirect heat exchange, in which apparatus

   in the operating situation the liquid level in the reservoir (24, 16) is at a first level h1 and is under a first pressure p1,

   in the further vessel (5, 23) a second pressure (p2) prevails at the location of the connection between liquid line (15, 15a, 19) and further vessel (5, 23) in the operating situation,

   the location of the connection between liquid line (15, 15a, 19) and further vessel (5, 23) is arranged at a second, higher level h2 (h2 > h1),

   the difference between the two pressures Δp = p1 - p2 in the operating situation is lower than the hydrostatic pressure (p_hydr=ρ g[h2-h1]) generated by a liquid column of the transfer fraction between the first level and the second level:

   Δp = p1 - p2 < ρ g [h2 - h1]   g: gravitational acceleration. characterized in that the expansion valve (14, 14a, 18) is arranged in such a way that in the operating situation the gas bubbles which are formed during the expansion reduce the density of the transfer fraction during expansion to such an extent that the pressure difference Δp is sufficient to feed the transfer fraction into the further vessel (5, 23), without a gaseous or two-phase stream being fed to the transfer fraction downstream of the expansion valve (14, 14a, 18) or a liquid stream being fed to the transfer fraction between the heat exchanger (8) and the expansion valve (14, 14a, 18).
4. Apparatus according to Claim 3, characterized in that the heat exchanger (8) is arranged in such a way that in the operating situation the transfer fraction is completely or substantially completely in liquid form immediately upstream of the expansion valve (14, 14a, 18).

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