MXPA00010199A - Low temperature decomposition of air comprises using rectification system consisting of condenser-vaporizer system, pressure column and low pressure column - Google Patents

Abstract

A condenser-vaporizer system has second section (102,103). A oxygen-rich liquid (12,13) is fed partially by a conveyor (14) to the vaporization passages of the second section of the condenser-vaporizer system. Low temperature decomposition of air comprises introducing compressed and pre-purified air into a rectification system for the separation of nitrogen and oxygen. The rectifier system comprises a pressure column(2), a low pressure column (3) and a condenser-vaporizer system (101,102,103) for heating the low pressure column. The condenser-vaporizer system has a first section (101) formed as a falling film vaporizer. A first oxygen-rich liquid (6) is fed into the vaporization passages of the falling film vaporizer form the low pressure column and vaporized. An oxygen-rich vapor (11) and a second oxygen-rich liquid (12) are formed. The oxygen-rich vapor is partially recycled to the low pressure column. The condenser-vaporizer system has second section (102,103). A oxygen-rich liqui d (12, 13) is fed partially by a conveyor (14) to the vaporization passages of the second section of the condenser-vaporizer system.

Description

PROCEDURE AND DEVICE FOR DECOMPOSITION AT LOW AIR TEMPERATURES DESCRIPTION OF THE INVENTION The invention relates to a method for the decomposition at low temperature of the air with the characteristics of the main idea of claim 1. The bases of the decomposition at low temperature of the air in general, as well as the structure of the system of rectification for oxygen-nitrogen separation with two or more columns is especially known in Hausen Linde's "Low Temperature Technique" monograph (2nd edition 1985) or by an article by Latimer in Chemical Engineering Progress (volume 63, no. 2, 1967, page 35). The pressure column and the low pressure column of a two-column system are in regulation by means of an evaporator-condenser system (main condenser) in a heat exchange relationship in the gas at the top of the pressure column against the evaporated well liquid of the medium pressure column that liquefies. The rectification system of the invention can be constructed as a classic two-column system, but also with three or more columns. It can, in addition to the columns for nitrogen-oxygen separation, present other devices to gain other components of the air, especially noble gases, for example to gain argon.

Ref: 123873 A heat exchanger constructed as condensing vapor presents evaporation and liquefaction steps. In the evaporation steps, a liquid evaporates. These are in heat exchange contact with the liquefaction passages, in which a fraction in the form of gas condenses in the indirect heat exchange with the evaporated liquid. Particularities about the evaporation process are known from the monograph "Evaporation and its Technical Applications" by Billet (1981). An evaporator-condenser can be constructed from one or more heat exchanger blocks. A condensing evaporator system has one or more evaporators-condensers. During a space of ten years, in the decomposition of the air at low temperature, practically only cyclic evaporators were used as evaporator-condenser, in this type a heat exchanger block is placed in a liquid bath that is going to evaporate. The evaporation passages are open above and below. The liquid from the bath is dragged by the gas that is produced in the evaporation upwards (thermosiphon effect), and flows back to the liquid bath. With this, a circulation of natural liquid is produced only by the evaporation process and without mechanical power supply.

For some time, film evaporators have also been used as a condenser-evaporator in air decomposition apparatus, as represented, for example, in EP 681 153 A, or in EP 410 832 A. In this type of evaporator the liquid that is going to evaporate from the evaporator in the evaporation passages and flows as a relatively thin film in the walls separating the evaporation and liquefaction passages downwards. This type of evaporator has a particularly low pressure loss in the evaporation steps, and is therefore energetically generally better than a cyclic evaporator. In any case, in the evaporation of a liquid rich in oxygen, a total evaporation must be prevented, which would result in a dry run of the evaporation passages. For this, as a rule, the liquid that comes out of the evaporation passages is returned by means of a pump back to the entrance of the evaporation passages. This measure acts on the one hand against the energy-saving effect of the film evaporator, and on the other hand constituent parts of difficult fluidity in the liquid are produced. Therefore the invention proposes the task of presenting a method of the type mentioned and a corresponding device that economically and functionally, work especially well, and especially have a particularly low energy expenditure. This task is solved by the characteristics of the characteristic part of claim 1. The non-evaporated liquid in the brine evaporator (first section of the condenser-evaporator system), which is the second oxygen-rich liquid, is conducted precisely as in the usual evaporation of the dropping film from a driving device, for example a pump; but this does not transport liquid back to the entrance of the evaporation passages of the same falling film evaporator, but a second section of the evaporator-condenser system, for this it needs the first section, only relatively sparse, for example from 30 to 50 %, preferably from 38 to 42% of the total evaporative power of the condenser-evaporator system. Correspondingly large is the fraction of natural liquid at the outlet of the evaporation passages, of the falling film evaporator. Thus, a circulation of artificial fluid can be completely dispensed with, at least almost completely. The impulse installation lets the non-evaporated liquid circulate again to a second section of the condenser-evaporator system. This is transformed totally or partially as a circulating evaporator. Here the problem of the need for a circulation of artificial fluid does not exist or hardly exists. In the context of the invention, it has been shown that with the help of the measures according to the invention, the amount of pumping can be reduced by approximately 30%. The energetic effect of the reduction of pumping, is not limited to the saving of driving energy, the advantage is still based more on a decrease of the heat input that is produced by the low quantity of impulsion in the second liquid rich in oxygen, the Oxygen product is in the process according to the invention, preferably obtained from the second section of the condenser-evaporator system, either as a gas or as a liquid, in the latter case, it can be combined with a product, obtained as a gas when the liquid rich in oxygen in a liquid state, is brought to a high pressure and then evaporated against air or nitrogen (called internal compression). The first section of the condenser-evaporator system of the invention can be disposed within the low pressure column or in a separate container. The process according to the invention, and the corresponding device can be used for all kinds of nitrogen-oxygen separation, especially independently of the product units in the head and the wells of the columns. The steam that is generated in the evaporation passages of the second section of the evaporator condenser system, preferably not exclusively or principally, is removed as an oxygen product in the form of a gas, but at least one half is conducted in the column Low pressure and there is used as rising steam. In case all the oxygen product is gained as liquid and / or compressed internally, also all the gas generated in the second section of the evaporator-condenser system is returned to the low pressure column. A third oxygen-rich liquid remains in the second section of the condenser-evaporator system as a non-evaporated part of the second oxygen-rich liquid. It preferably accumulates in the liquid bath of one or more of the circulating evaporators. In the process according to the invention, partial return is preferably made to the low pressure column and / or to the evaporation passages of the first section of the evaporator condenser system in the form of a liquid. This feedback can be performed favorably together with the aforementioned return of the steam to the low pressure column, when a duct corresponding to the height of the liquid level of the bath is arranged. Here, the liquid state in the circulating evaporator is simultaneously regulated without the need for additional adjustment or adjustment facilities.

If the second section is partly constructed as a second falling film evaporator, the existing flow installation between the first and second and second sections can be used for the generation of a liquid circulation to the second film evaporator. fall. The liquefaction steps of the condenser-evaporator system are preferably connected with the two columns as described in claim 4. With this, it is possible to dispense with pumps in those places, and It is also precisely then whether the pressure column and the low pressure column are arranged one by one to the other. (In this case it is favorable that the first section of the condenser-evaporator system is below the bottom floor of the low pressure column and the second section of the system condenser-evaporator is above the supreme floor of the pressure column). The first section built as falling film evaporator, preferably has such dimensions that it produces a quantity of liquid rich in nitrogen by condensation of a fraction of gas - t - a ---- »- rich in nitrogen from the pressure column, which is needed as a return in the low pressure column (more possibly the quantity withdrawn as a liquid product without pressure). This represents, for example, a fraction of 30 to 50%, preferably 38 to 42% of the total heat transfer power of the condenser-evaporator system. The rest of the heat transmission (50 to 70%, preferably 58 to 62%) is conducted to the second section of the condenser-evaporator system, and precisely in such a way that at least the amount of liquid needed is generated as a return to the pressure column. Because of the spatial division of the heating surface, it may be favorable in many cases to condense in the first section a significant fraction of the nitrogen-rich fraction as described, for the corresponding hot surface of the second section (as a rule at the head of the pressure column), extend it to the first section (usually in the well of the low pressure column). In this case, a part of the first liquid rich in nitrogen, which is formed in the first section, is given as a return to the pressure column. Here, if necessary, the installation of a liquid pump. The gas fraction rich in nitrogen is generally formed by the nitrogen in the upper part of the pressure column. The first section of the condenser-evaporator system is preferably formed exclusively as a falling film evaporator. With the aid of the dimensions indicated above, it can be particularly advantageous to produce a relatively compact single block or in the form of several blocks, for example (4) which are particularly low, which are arranged next to one another. An arrangement directly in the well of the column of low pressure, is equally favorable for a low constructive height of the apparatus and its insulation (Cold Box). The second section of the condenser-evaporator system can be formed by at least two partial sections connected in series on the evaporation side, of which the first is constructed as a falling film evaporator and the second as a circulating evaporator. The liquid that runs through the evaporation passages of the partial section carried out as a falling film evaporator is, for example, conveyed to the liquid bath of the partial section developed as a circulating evaporator. The falling film evaporator-circulating evaporator combination can be equipped with liquefying passages, as is particularly described in EP 795 349 A. In this case, the liquid can be returned from the circulating evaporator bath to the low pressure column or the exit of the evaporation passages of the first section of the condenser-evaporator system, and to increase the amount of fluid in the partial section of the second section that is constructed as a falling film evaporator. The invention also relates to a device for the decomposition at low temperature of the air according to claim 9. Especially advantageous conformations of the device are described in claims 10 to 13. The invention as well as other features thereof are explained in more detail by means of of two embodiments for obtaining oxygen under pressure in gaseous form represented schematically in the drawings. According to Figure 1, the incoming air in gaseous form 1, which is previously compressed, is purified and cooled approximately to a sprinkling point (not shown) is conducted to the pressure column 2, directly above the well. The pressure column 2 is part of a rectification system which also has a low pressure column 3, and a main condenser in the form of a condenser-evaporator system 101, 102, 103. The air decomposes in the pressure column 2, in nitrogen in the upper part and in a liquid rich in oxygen. The last one in the special embodiment example is not carried as usual to the well, but is extracted from a higher theoretical or practical floor by means of conduit 5. (Particularities of this form of procedure that serve to return the difficult constituent parts of the structure. liquefying are indicated in German patent application 1 983 547 4, or can be taken from applications corresponding to that request made in other countries). The oxygen-rich liquid 5 is passed through a duct not shown to an intermediate position in the low-pressure column 3, where it is throttled. In the low pressure column 3, one or more nitrogen products (not shown) are removed in the upper region, below the lower rectification section, oxygen is obtained with the purity necessary for the product.

This flows as the first oxygen-rich liquid from the lowest floor or packing section of the low pressure column 3, and accumulates in an accumulation tank 7. The first oxygen-rich liquid also flows to the upper end of the column. first section 101, of the condenser-evaporator system, and is introduced into its evaporation passages. The first section 101 is constructed as a falling film evaporator. There, about 28 to 30% of the first liquid 7, rich in oxygen in an indirect heat exchange with a first part 8, of the gas fraction 4, rich in nitrogen from the head of the pressure column 2, condenses here the gas rich in nitrogen 8, to a liquid 9, first rich in nitrogen. This expands in a valve 10, and is completely returned to the head of the low pressure column 3. Since in the example no liquid nitrogen product is produced, the falling film evaporator 101, has a dimension such that he exactly condensed that amount of gas 8, rich in nitrogen that is needed as a feedback liquid for the low pressure column. The vapor 11, which is generated in the first section 101, of the condenser-evaporator system flows back to the lower rectification section of the low pressure column and takes part in the exchange of countercurrent substance within that column. The fraction that remains liquid 12, forms a second liquid rich in oxygen, this is removed by the conduit 13, and by means of a pump 14, is carried to the second section of the condenser-evaporator, which is formed by a combination of another falling film evaporator 102 and a circulating evaporator 103, as described in particular in EP 795 349 A. The second oxygen-rich liquid flows into the evaporation passages of the other falling film evaporator 102, downwards and it evaporates in about a 40% The produced steam 15 is completely returned via line 16 to the low pressure column 3, since in the example no oxygen as a gaseous product is removed directly from the rectification system. The conduit 16, simultaneously serves to maintain constant the level of liquid in the bath 18, where the excess liquid together with the steam generated in the second section 102, 103, is conducted to the low pressure column 3. (This function will be described in detail in relation to Figure 2). The remaining liquid 17 flows from the partial section 102 to the liquid bath 18, from the circulating evaporator 103, and forms together with the liquid 19, thrown into the circulating evaporator, a third liquid rich in oxygen. This is gained as an oxygen product when it is partly removed by line 20, by means of a pump 21, it is internally compressed in a known manner, it is evaporated at high pressure and finally it is removed as a gaseous pressure product. If a part of the introduced air is used for the evaporation of the product oxygen, the liquefied air stream 24 can be introduced into an intermediate position in the pressure column 2, alternatively or additionally a stream of nitrogen carried by the pressure column against the evaporated product oxygen to condense (nitrogen circulation is not shown). The liquefaction passages of the other falling film evaporator 102, and of the circulating evaporator 103 are carried out crosswise. They receive the action of a second part 22, of the fraction of gas 4, rich in nitrogen from the pressure column 2, the nitrogen flows first through the falling film evaporator 102, and then by the circulating evaporator 103, and at least partially, but preferably, in practice completely, the liquid 23, rich in second nitrogen that has been produced, is completely returned to the pressure column 2. Figure 2 shows in detail the connection between the duct 16 and the outer space around the two condenser-evaporator 102, 103, forming the second section of the condenser-evaporator system. The dimensions of the duct are established essentially according to the amount of gas that must be transported. It is arranged in such a way that the liquid from the liquid bath of the circulating evaporator 103 comes out and as a film 26, it can flow back into the lower side of the duct 16, into the low pressure column 3, or into the well of liquid under the first falling film evaporator 101, for this the liquid level of the liquid bath of the circulating evaporator 103, is maintained at a constant height without special regulation measures. Figure 3, differs from Fig. 1, by means of an additional conduit 301, by means of which a part of the first liquid 9, rich in nitrogen, can be given as a return to the pressure column 2, in the arrangement represented of the columns and the capacitors, a liquid pump 302, to overcome the static height between the first section 101, of the condenser-evaporator system and the upper region of the pressure column 2. With the aid of this liquid conduit in the pressure column, it is possible to variant of Fig. 3, compared to Fig. 1, use more heating surface in the first section 101, which here is built as a well evaporator of the low pressure column 3. Correspondingly, less heating surface (and with this less volume) is needed, for the second section 102, 103, in the example will be in the head of the pressure column 2. In this way the spatial division of the condenser-evaporator system is brought to an optimum state. The advantage of this optimum state is in many cases higher than the expense for the additional conduit 301 and the liquid pump 302.

In an extreme example (not shown in the drawing), the entire heating surface of the partial section 102 can be integrated into the first section 101, so that the second section of the condenser-evaporator system still only consists of a circulating evaporator 103. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention is that which is clear from the present description of the invention.

Claims (5)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property. 1.- Procedure for the decomposition at low temperature of the air in which air of pre-compressed and pre-purified application is introduced, in a rectifier system for nitrogen-oxygen separation, which has: a pressure column; a low pressure column; and a condenser-evaporator system for the heating of the low pressure column, where the condenser-evaporator system has a first section that is built as a falling film evaporator, a first oxygen-rich liquid from the low pressure column is conducted to the evaporation passages from the falling film evaporator and there it is partially evaporated where an oxygen-rich vapor and a second oxygen-rich liquid are formed, and where the oxygen-rich vapor is at least partially returned to the low column. pressure, a method characterized in that the condenser-evaporator system has a second section that is at least partly constructed as a circulating evaporator and the second oxygen-rich liquid at least partially by a driving installation is led to the evaporation passages of the second section of the condenser-evaporator system.
2. 2. Method according to claim 1, characterized in that the steam generated in the evaporation passages of the second section of the condenser-evaporator system is brought at least in half to the low pressure column.
3. 3. Method according to claim 1 or 2, characterized in that a third liquid rich in oxygen that has been formed from the non-evaporated part in the second section of the evaporator condenser system of the second oxygen-rich liquid, at least partially returns to the low pressure column and / or to the evaporation passages of the first section of the condenser-evaporator system.
4. 4. Method according to one of claims 1 to 3, characterized in that: - a gas fraction rich in nitrogen is generated in the upper zone of the pressure column; a first part of the gas fraction rich in nitrogen is conducted to the liquefaction passages of the first section of the condenser-evaporator system and there at least partially condenses where a first liquid rich in nitrogen is formed; a second part of the gas fraction rich in nitrogen is conducted to the liquefaction passages of the second section of the condenser-evaporator system and there at least partially condenses, where a second liquid rich in nitrogen is formed; - the first nitrogen-rich fluid, at least partially expands and is given to the low-pressure column as feedback; and - the second liquid rich in nitrogen at least partially is given as feedback to the pressure column.
5. 5. Process according to claim 4, characterized in that a part of the first liquid rich in nitrogen is given as feedback to the pressure column. Method according to one of claims 1 to 5, characterized in that the pressure column and the low pressure column are arranged next to each other, where the first section of the condenser-evaporator system is below the lowest floor or from the lower packing section of the low pressure column and / or the second section of the condenser-evaporator system is above the upper floor or the upper packing section of the pressure column. 1 . - Method according to one of claims 1 to 6, characterized in that the first section of the condenser-evaporator system is constructed exclusively as a falling film evaporator. 8. Method according to one of claims 1 to 7, characterized in that the second section of the condenser-evaporator system is formed by at least two partial sections joined in series on the evaporation side of which at least one is Built as falling film evaporator and at least one as a circulation evaporator. 9. Device for separating at low temperature 15 with a rectification system for nitrogen-oxygen separation, which has: - a pressure column; - a low pressure column; a condenser-evaporator system for the heating of the low pressure column, where the condenser-evaporator system has a first section that is constructed as a falling film evaporator, and with an air application conduit for conducting the introduced air that has been compressed and pre-p rified to the I ^ L ^ ¡& ^ á & • & & amp; & & amp; & amp; **, * É. ^ »¿- * • * & -. - "? ^ ~ & - J-tt-iMh -..- ataJ - ** to --------- * ^ * J _s_ _? ¿¿K pressure column; - means for supplying a first oxygen-rich liquid from the low pressure column to the evaporation passages of the falling film evaporator; and - means for the feedback of oxygen-rich vapor from the evaporation passages of the falling film evaporator to the low pressure column; device characterized in that the condenser-evaporator system has a second section which is at least partly constructed as a circulation evaporator and the device has means for conducting a second liquid rich in oxygen from the evaporation passages of the falling film evaporator to the passages of Evaporation of the second section of the evaporator-condenser system including a driving installation. 10. Device according to claim 9, characterized in that the pressure column and the low pressure column are arranged next to each other, where the first section of the evaporator condenser system is below the lowest floor or section of the evaporator. Lower packing of the low pressure column and / or the second section of the evaporator condenser system is above the upper floor or the uppermost packing section of the pressure column. ? it & b? * ± * * Mt * £ *? aF > ** ?? - - ** - > _ £ «* - ^ -. J ---- *. 4 »JÉJaiS a & fo» -. 11. - Device according to the claim 9 or 10, characterized in that the first section of the condenser-evaporator system is constructed exclusively as a falling film evaporator. 12.- Device according to the claim 9 to 11, characterized in that the second section of the condenser-evaporator system is formed by at least two partial sections connected in series on the evaporation side, of which the first is constructed as a falling film evaporator and the second as an evaporator. circulation. 13. Device according to one of claims 9 to 11, characterized in that the outlet of the liquefaction passages of the first section of the condenser-evaporator system is connected by a conduit for liquid and, if necessary, by means of a pump. of liquid with the pressure column.