FR3020866A1 - DISTILLATION COLUMN AND CRYOGENIC DISTILLATION AIR SEPARATION APPARATUS FOR THE POSSIBLE PRODUCTION OF A MIXTURE OF KRYPTON AND XENON - Google Patents

Abstract

Distillation column (3), operable at operating pressure, the column containing a plurality of mass exchange and heat exchange sections (25), an end of a first pipe (C1) and a pipe end (25). a second pipe (C2) being connected to the tank of the column, the first pipe being connected to a first valve capable of closing the first pipe, the other end of the first pipe being capable of being connected to a heat exchanger; heat (9) and the second pipe being connected to a second valve capable of closing the second pipe and a third pipe having an end connected to an intermediate level of the column and comprising the third pipe (C3) being connected to a third valve capable to close the third pipe.

Description

The present invention relates to a distillation column and to an apparatus for separating air by cryogenic distillation for the possible production of a mixture of krypton and xenon. On a so-called "pump" apparatus, the oxygen is drawn off. in liquid form of a low pressure column of a double column, pressurized, then vaporized to be produced as gaseous oxygen under pressure. When making a column, the question often arises of a (1) subsequent production of a krypton / xenon mixture which is not required in the immediate future. Conventional solutions, when one wants to produce Kr / Xe, are generally expensive in investment because one aims at maximizing the Kr / Xe yield. 15 For devices in which the Kr / Xe option is only an option for the future (custom-made devices), or on standardized (or partially standardized) devices for which the Kr / Xe is only an option, such an overinvestment can be problematic. The devices according to the invention require only a small over-investment and thus give the possibility of a Kr / Xe production at a lower cost. According to the prior art, for the apparatuses where the produced oxygen is withdrawn gaseous from the low pressure column (BP), and that it is desired to produce Kr / Xe, a few theoretical plates are added to the bottom of the low pressure column. just below the gaseous oxygen withdrawal, and just above the column vaporizer of the column, and draw a small flow of liquid oxygen at the vaporizer in which is concentrated all the Kr and the Xe of the air separation apparatus. This small flow rate of liquid oxygen, rich in Kr / Xe is then sent to a Kr / Xe purification unit to produce the purified Kr / Xe mixture. With such a scheme, the Kr / Xe yield is close to 100% when leaving the low pressure column. US-A-2004/0007016 discloses an air separation process in which liquid oxygen is withdrawn from the low pressure column at a position separated from the low pressure column vessel by a theoretical plateau section. The mixture rich in Kr / Xe is withdrawn in the bottom of the low pressure column. According to the invention, modification of the plant is allowed at a very late stage to allow Kr / Xe production or not. According to one object of the invention, there is provided a distillation column, capable of operating at an operating pressure, for a cryogenic distillation air separation apparatus comprising a double column, the double column comprising a first column capable of operating at a first pressure and the column capable of operating at the operating pressure which is lower than the first pressure, the head of the first column being adapted to be connected to the column vessel by means of a vaporizer-condenser the column containing a plurality of heat exchange and mass exchange sections, one end of a first pipe and one end of a second pipe being connected to the column vessel, the first pipe being connected to a pipe, first valve capable of closing the first pipe, the other end of the first pipe being capable of being connected to a heat exchanger and optionally to a pump and the second conduit being connected to a second valve capable of closing the second conduit and a third conduit having an end connected to an intermediate level of the column and comprising the third conduit being connected to a third valve capable of to close the third pipe. According to other optional objects: the intermediate level of the column is just below the lowest section of the column. the intermediate level of the column is separated from the column vessel by at least one theoretical plate and at most 10 theoretical plates. the other end of the third pipe is not connected to another element. The other end of the second pipe is not connected to another element. the first and second pipes are connected to the bottom of the column by a common pipe. According to another object of the invention, there is provided a cryogenic distillation air separation apparatus comprising a double column, the double column comprising a first column capable of operating at a first pressure and a second column according to one of the preceding claims operable at the operating pressure which is less than the first pressure, the head of the first column being connected to the vessel of the second column by means of a vaporizer-condenser, each column containing several sections of mass exchange and heat exchange elements and the second pipe is connected to a heat exchanger to allow vaporization of liquid oxygen. According to other optional aspects of the invention: To have an apparatus capable of producing a Kr / Xe mixture in which the other end of the first conduit is connected to a processing unit to produce the mixture and the first valve is opened. The other end of the third pipe can be connected to the heat exchanger. Otherwise, if production of a Kr / Xe mixture is not required, the first valve is closed and the first conduit is connected only to the vessel of the second column. The first drive will be relatively short so as not to unnecessarily increase the size of the cold box. The existence of these connections, which are the first, second and third conduits, makes it possible to postpone the decision to produce a Kr / Xe mixture or not. It is relatively simple to add a connection between the first conduit and the processing unit that produces the Kr / Xe mixture, if necessary. Similarly, either the second or the third pipe or both can be connected to the heat exchanger to ensure the vaporization of liquid oxygen and possibly the purge of deconcentration. The invention will be described in more detail with reference to Figs. 1-3. Fig. 1 shows a separation apparatus according to the invention in use. Figures 2 and 3 show the apparatus of Figure 1 during manufacturing steps. In FIG. 1, an air separation apparatus comprises a double column comprising a first column 1 operating at a first pressure and a second column 3 operating at a second pressure, lower than the first pressure. The head of the first column 1 is thermally connected to the tank of the second column 3 by means of a vaporizer-condenser 5. An oxygen-enriched liquid 15 is withdrawn in the tank from the first column 1, expanded and sent to the second column 3. A nitrogen-enriched liquid 17 is withdrawn at the top of the first column 1, expanded and sent to the head of the second column 3.

Compressed and purified air 7 cools in the heat exchanger 9 and returns to gaseous form in the first column 3. Liquid oxygen 13 enriched in Kr / Xe is withdrawn from the bottom of the second column and sent to a processing unit 21.

Liquid oxygen 19, which is less rich in Kr / Xe than the liquid 13, is withdrawn from a collector 23 just below the first section 25 of the second column 3, counting from the bottom. This liquid 19 is pressurized by a pump 11 and vaporizes in the heat exchanger 9.

Thus the method according to the invention operates when the decision has been made to produce oxygen enriched in Kr / Xe. By choosing the structure of the column in the ways illustrated in Figures 2 and 3, this production decision Kr / Xe can be made as late as possible and involving the least possible modifications.

In FIG. 2, it can be seen that a pipe CO connected to the tank of the second column 5 at one end is connected at the other end to one end of each of two pipes C1, C2, both of which can be closed by a respective valve. The other end of the second pipe C2 is connected to a pipe 19A connected to the heat exchanger 9, preferably via the pump 11. At the time of construction, the ends of the first and second conduits C1, C2 are not not connected to another pipe (apart from the first pipe C1 for the second pipe C2). If the decision is made to operate the column without producing 25 Kr / Xe, the valves of the first and third pipes will be closed or the first and third pipes will be condemned in another manner. As the valve of the second pipe C2 is open, the oxygen of the tank passes into the pipe 19A which has been added and supplies the customer with gaseous oxygen after vaporization in the exchanger 9. If, on the other hand the decision is made of operating the column with Kr / Xe production, the valve of the second line C2 is closed, the valves of the first and third lines are open. The first pipe C1 is connected to a pipe 13A bringing the liquid to the processing unit 21 to enrich the flow Kr / Xe. The third pipe C3 is connected, by the addition of a pipe 19B, to the pipe 19A and pours liquid oxygen to vaporize in the passages of the heat exchanger 9 via the pump 11. The interest of Figure 2 is that at the level of the safety of the apparatus, as long as the pipes 19B and 13A for the Kr / Xe concentration are not installed, there is a conventional "pump" apparatus, therefore not concentrated in hydrocarbons at the level of the bath of column 3. 15 In this option, therefore, for the future Kr / Xe / potential, only the waiting queues (lines C1, C3) and an additional distributor 23 designed to perform the future withdrawal of intermediate liquid oxygen for the production of pumped oxygen. Figure 3 shows another way of constructing the second column, pending the decision for Kr / Xe production. Here we find the pipes CO, Cl, C2, C3 of Figure 4. In this case, if we decide not to produce Kr / Xe, oxygen is produced from the third pipe C3, the latter being connected to the pipe 19B already installed as well as the pipe 19A. Here the second line C2 acts as a deconcentration line and is also connected to the lines 19A, 19B. The first pipe C1 is closed. When it is decided to produce Kr / Xe, the first pipe C1 is connected to the processing unit 21 by adding the pipe 13A, the second pipe C2 is closed and the liquid oxygen is withdrawn as for the previous case of the distributor 23 by the third pipe C3. In this variant, the yield Xe at the exit of the BP column is thus kept close to 70%, while the yield of Kr is decreased. In order to increase the yield Kr, one may decide to voluntarily increase the small flow of LOX to the Kr / Xe purification unit. The table below gives, as a rough guide, a few figures of Kr / Xe efficiency (at the end of the BP column) in the various options: Device "with pumps" With Without section Kr / Xe section Kr / Xe Q LOX to 1 % Qair 1% Qair 2% Qair Kr / Xe Yield Xe (column output 3) ',' 70% Yield Kr (column output 3) ',' 70% ',' 30% ',' 40% The advantage of such a variant is that the extra investment to make the Kr / Xe is less. Even if the section between the withdrawal of liquid oxygen and the tank withdrawal is very small, the presence of a section implies the presence of a dispenser, necessarily expensive, above the section for the distribution of the liquid. Thus the removal of the section allows significant savings. 15 This is interesting for example if the Kr / Xe option is only an assumption for the future, or on standardized (or partially standardized) devices with a Kr / Xe option (retained or not, as the case may be).

The partial withdrawal of LOX for the production of oxygen (above the vaporizer), will be done through a distributor designed for this purpose. Multiple options exist to achieve such a function. Note that it is possible to use the present invention in the case where the oxygen-rich liquid is withdrawn from the second column at a level of the second column at least one theoretical plate above the tank of the second column. or, as illustrated, without theoretical plate between the tank and the racking. In both cases of Figures 2 and 3, the first and second lines 1 () Cl, C2 can lead directly into the tank of the column 3, the CO pipe does not exist. It is obviously possible to manufacture the second column 3 at a first location and the first column at a second location and to assemble them later. 15

Claims (10)

REVENDICATIONS1. Distillation column (3), operable at operating pressure, for a cryogenic distillation air separation apparatus comprising a double column, the double column comprising a first column (1) capable of operating at a first pressure and the column capable of operating at the operating pressure which is lower than the first pressure, the head of the first column being adapted to be connected to the column vessel by means of a vaporizer-condenser (5), the column containing a plurality of mass exchange and heat exchange sections (25), one end of a first pipe (C1) and one end of a second pipe (C2) being connected to the bottom of the column, the first pipe being connected to a first valve capable of closing the first pipe, the other end of the first pipe being capable of being connected to a heat exchanger (9) and possibly to a pump (11) and the second pipe being connected to a second valve capable of closing the second pipe and a third pipe having an end connected to an intermediate level of the column and comprising the third pipe (C3) being connected to a third valve able to close the third pipe. The column of claim 1 wherein the intermediate level of the column (3) is just below the lowest section of the column. 3. Column according to claim 1 in the intermediate level of the column (3) is separated from the column vessel by at least one theoretical plate and at most 10 theoretical plates. 4. Column according to one of the preceding claims wherein the other end of the third pipe (C3) is not connected to another element. 5. Column according to one of the preceding claims wherein the other end of the second pipe (C2) is not connected to another element. 6. Column according to one of the preceding claims wherein the first and second ducts (C1, C2) are connected to the bottom of the column by a common pipe (CO). 7. Apparatus for separating air by cryogenic distillation comprising a double column, the double column comprising a first column (1) capable of operating at a first pressure and a second column (3) according to one of the preceding claims capable of operate at the operating pressure which is lower than the first pressure, the head of the first column being connected to the vessel of the second column by means of a vaporizer-condenser (5), each column containing several sections of elements mass exchange and heat and the second pipe (C2) is connected to a heat exchanger (9) to allow vaporization of liquid oxygen. The apparatus of claim 7 capable of producing a Kr / Xe mixture in which the other end of the first conduit (C1) is connected to a process unit (21) to produce the mixture and the first valve is opened. 9. Apparatus according to one of claims 7 and 8 capable of producing a Kr / Xe mixture in which the other end of the third pipe (C3) is connected to the heat exchanger (9). 10. Apparatus according to claim 7 wherein the first valve is closed and the first pipe (Cl) is connected to the tank of the second column.