DE19526226C2 - Device for the production of pure xenon - Google Patents

Description

The extraction of xenon from air separation plants keeps getting higher Purity requirements are placed on the end product. In contrast, are in the Intake air more and more impurities such. B. C₂F₆, N₂O, SF₆, CF₄ and / or R115, the accumulate primarily in raw xenon and are difficult to remove. The invention relates to the purest xenon production from a raw xenon stream, which is predominantly xenon and for example a few tenths of a percent of krypton and traces of contaminants, for example of the type mentioned above.

So far, it has been common to use batch distillation for this purpose. to use. Solid carbon dioxide is used to cool the head of the distillation column Carrier liquid used. The temperature of the melting carbon dioxide is sufficient for that Condensation of the top fraction of the column no longer occurs when the volatile Have enriched ingredients to a relatively high concentration. So that's the familiar Process not suitable for high xenon yields. To a satisfactory one Heat transfer between the condensing head gas and the carrier liquid To reach the carbon dioxide mixture, the liquid must also be kept in motion (e.g. by stirring). There are fluctuations in the Heat transfer performance and therefore fluctuating return quantities and pressures in the Pillar one. A head cooling of a xenon column known from DE 42 02 468 C2 of a nitrogen cycle is difficult to regulate.

The invention has for its object a device for the purest xenon production specify, largely avoided at the return fluctuations in the distillation column will.

This object is achieved by the features of patent claim 1.

In the device according to the invention, a boiling refrigerant can be used instead of one melting can be used. This ensures good and even heat transfer secured to the top condenser of the distillation column.

The device preferably comprises a second condenser-evaporator, the Liquefaction side on the one hand via a gas line and on the other hand via the Liquid line with the evaporation side of the first condenser-evaporator connected is. Especially when on the one hand in the second condenser-evaporator a flammable and, on the other hand, an oxygen-containing refrigerant can be used  (especially ethylene on the liquefaction side and oxygen on the evaporation side) it is favorable if evaporation and evaporation in the second condenser Liquefaction side are separated from each other by a single workpiece. This can be avoided that the two refrigerants through leaky seams (e.g. welds) between different workpieces to form an explosive Exchange mixture. This is best realized by evaporating and Liquefaction side are each enclosed by a separate container, which consists of a Shell and consists of the single workpiece, the shells of the two containers are not connected to each other; there is therefore no connection to be sealed between the liquefaction and evaporation sides of the second condenser-evaporator.

It is advantageous if the evaporation side of the first condenser evaporator is in There is a flow connection to a gas storage unit and in particular the liquefaction side of the second condenser-evaporator is designed so that when a determined value of the amount of in the evaporation side of the first condenser Ver steamer, condensing side of the second condenser-evaporator, gas line and Liquid line formed the primary circuit existing liquid Heat transfer performance is greatly reduced. This makes it possible to use a certain initial pressure in the primary circuit and by regulating the temperature in the Evaporation space of the second condenser-evaporator the entire process Taxes.

The device according to the invention can be used in a method for obtaining Ultrapure xenon can be used.

Especially in connection with air separation plants, it is advantageous if a fluid, which contains one or more air gases as the second refrigerant, the second condenser Ver evaporator is evaporated, is used. Evaporating oxygen is preferred or nitrogen is used.

The chemical composition of the first refrigerant should be chosen so that on the one hand its boiling temperature is low enough to also contribute to the top gas of the column to condense high concentrations of volatiles, and on the other hand it is ensured that the temperature at the top of the column does not fall below the melting point of Xenon is sinking.  

These conditions are met when ethylene is used as the first refrigerant. With "Ethylene" here is a mixture containing predominantly ethylene, especially technically pure ethylene (with, for example, about 1% by volume of impurities) is meant. The Boiling temperature of ethylene at a pressure of 2.0 bar is 182 K. At one Temperature difference of 8 K at the top capacitor can thus be pure xenon under one Pressure of 3.5 bar (corresponding to 190 K) can be condensed. The concentration of Contamination at the top of the distillation column can be done by lowering the pressure on the evaporation side of the top condenser.

For example, the raw xenon contains impurities of 5000 vppm krypton, which should be withdrawn with the residual gas at the top of the column, and you only want to If you lose about 0.5% xenon, the top gas must consist of 50% krypton and 50% xenon put together. Instead of simply increasing the column pressure (16.9 bar required) in the process according to the invention, the ethylene evaporation pressure 1.0 bar corresponding to an evaporation temperature of 169 K. In order to at a temperature difference of 8 K, a condensation temperature of 50% krypton-xenon mixture of 177 K and thus a column pressure of 11 bar to adjust.

When using ethylene as the first and oxygen or nitrogen as the second refrigerant it should be noted that ethylene solidifies at a temperature of 103.4 K, ie The boiling point of the liquid used to liquefy the ethylene is not lower than 104 K. This corresponds to liquid oxygen of 3.5 bar or liquid nitrogen of 10.2 bar. When operating with ethylene under 2 bar and liquid oxygen under 3.5 bar or liquid nitrogen below 10.2 bar results on the second condenser Ver steamer to re-liquefy the ethylene a temperature difference of 78 K. Aus this large temperature difference results in a relatively small heating surface. Even after Taking into account the Leidenfrost effect, this leads to the construction of a compact, self self-regulating facility.

The invention and further details of the invention are described below with reference to an in the drawing illustrated embodiment explained in more detail.

A raw xenon feed line 2 is used to introduce raw xenon, which contains a few tenths of a percent of krypton and traces of contaminants such as e.g. B. C₂F₆, N₂O, SF₆, CF₄ and / or R115 contains, in a distillation column 1 , of which only a section is shown in the drawing. At the bottom of column 1 , liquid ultrapure xenon can be removed continuously or discontinuously via a product line 3 . An electrically operated heater serves to supply heat to the column sump. (Alternatively, other types of heating are also possible, for example by burning gas.) The upper section of the distillation column 1 is connected to the liquefaction chamber 51 of a first condenser-evaporator 50 , which is operated as a top condenser. The liquefaction space 51 has an essentially cylindrical shape and is surrounded by the essentially cylindrical evaporation space 52 of the first condenser-evaporator 50 .

A residual gas line is connected to the upper end of the liquefaction space 51 . The valve 7 in the residual gas line 5 also serves to adjust the pressure in the liquefaction space 51 and thus in the distillation column 1 . For this purpose, it can be controlled via a pressure measuring and regulating device 6 (PIC: pressure indication and control). In addition or as an alternative to a liquid level control in the bottom of the column, the same control device 6 can also be used to adjust the heating power, as is shown by the corresponding dashed connection in the drawing.

The evaporation chamber 52 is connected to a gas line in its upper region and to a liquid line 9 in its lower region and communicates via both with the liquefaction chamber 61 of a second condenser-evaporator 60 . The gas line 8 is connected to the evaporation space 52 of the first condenser-evaporator 50 at a point which is geodetically higher than the point of connection of the gas line 8 to the liquefaction space 61 of the second condenser-evaporator 60 . The latter is preferably arranged at the upper end of the liquefaction space 61 of the second condenser-evaporator.

The evaporation chamber 62 of the second condenser-evaporator 60 each has a line for the supply of liquid ( 63 ) and for the removal of steam ( 64 ). The level in the evaporation chamber 62 is regulated via the liquid supply (liquid level regulator 65 , LIC: liquid indication and control), and the pressure is removed via the gas extraction (pressure regulator 66 ). A safety drain 72 is used for occasional liquid removal at the lower end of the evaporation space 62 . The evaporation space 62 is enclosed by a container which is formed by a casing 67 and a heat transfer plate 68 . The container of the liquefaction space 61 is formed by a further shell 69 and also by the heat transfer plate 68 . The heat transfer plate 68 is made from a single workpiece. The two sleeves 67 , 69 are each connected to the heat transfer plate by an annular weld seam 70 , 71 , but not to one another.

The distillation column 1 and the two condenser evaporators 50 , 60 are arranged within a cold box, which is used for thermal insulation.

The gas line 8 is connected via a compensating line 10 to a gas storage 11 , which has a relatively large filling volume, for example approximately 100 times the volume of the primary circuit (evaporation space 52 of the first condenser-evaporator 50 , liquefaction space 61 of the second condenser-evaporator 60 , Gas line 8 and liquid line 9 ) is. The pressure in the gas storage can be adjusted by supplying additional quantities of the first refrigerant circulating in the primary circuit via line 12 .

In the exemplary embodiment, ethylene with a purity of approximately 99% by volume is used as the first refrigerant. In the second condenser-evaporator 60 , oxygen is evaporated as the second refrigerant.

To understand the operation of the device for the purest xenon extraction is in the following their operation including starting from the warm state is described.

The amount of liquid ethylene in operation or the amount of gas of ethylene in the warm state are designed in the example so that in the warm state, that is to say at ambient temperature, the ethylene pressure is approximately 6.5 bar. When starting up, liquid oxygen is first filled into the evaporation space 62 of the second condenser-evaporator 60 ; the oxygen evaporates strongly. The pressure in the evaporation chamber 62 is kept constant at 3.5 bar. After the components have cooled accordingly, the liquefaction of the initially gaseous ethylene begins in the liquefaction chamber 61 of the second condenser evaporator. Since the volume of the liquefied gas is much smaller than the volume in the gaseous state, the pressure in the primary circuit, in the compensating line and in the gas storage device slowly drops. This continues until the liquid level in the liquefaction space 61 has reached the heat transfer plate 68 . An ethylene pressure (pressure of the gas in the primary circuit) of 2 bar is established. The liquid ethylene communicates via the liquid line 9 with the heating surface in the first condenser-evaporator 50 .

After raw xenon has been fed into the distillation column 1 (preferably via branch line 2 a at the top of the column), this is liquefied in the liquefaction space 51 of the first condenser-evaporator 50 , runs down the column and collects in its sump. When enough liquid has accumulated in the sump, it is heated with constant power and the feed is switched from a line 2 to line 2 b, which ends at an intermediate point in the distillation column. 1 A pressure is initially set in the column which is so high that the sum of the amount of crude xenon drawn in and the amount of xenon evaporated in the sump is condensed in the first condenser-evaporator 50 . After some time, when the trace impurities have accumulated at the top of the column, the pressure in the column begins to rise so that the lower-boiling constituents can also be liquefied. At a target pressure previously determined on the basis of the amount of impurities in the xenon and the desired yield of ultrapure xenon, these impurities are regulated as residual gas with a fine control valve 7 .

If the impurities in the raw xenon are large, for example up to 1 vol% krypton, and you want to achieve a high concentration of the impurity components in the residual gas in order to lose as little xenon as possible with the residual gas, the ethylene pressure can be released by blowing off the primary circuit or out the gas storage system can be reduced to, for example, 1.0 bar. The temperature difference at the first condenser-evaporator 50 is thus initially increased. Over time, with increasing pressure, more and more pure xenon accumulates in the bottom of the column, which is discharged as a product continuously or from time to time via line 3 .

The device described can be used with small quantities of Raw xenon can also be operated completely discontinuously (batch operation). Doing so the raw xenon quantity to be processed is first condensed and in the sump  collected. The procedure is then as described above, only none continuous supply of raw xenon. Residual gas must also be removed here to draw off a pure product in the sump at the end of batch distillation can. Part of this residual gas is initially discarded; the bulk of the Residual gas can, however, be collected for recycling.

Claims (7)

1. Device for the production of ultrapure xenon from a contaminated raw xenon stream with a distillation column ( 1 ) which is connected to a raw xenon feed line ( 2 ) and with a first condenser-evaporator ( 50 ) in flow connection , whose liquefaction side ( 51 ) is connected to the upper area of the distillation column ( 1 ) and whose evaporation side ( 52 ) is connected to a liquid line ( 9 ) for supplying a first refrigerant. 2. Device according to claim 1 with a second condenser-evaporator ( 60 ), the liquefaction side ( 61 ) on the one hand via a gas line ( 8 ) and on the other hand via the liquid line ( 9 ) with the evaporation side ( 52 ) of the first condenser-Ver evaporator ( 50 ) is connected, the evaporation and liquefaction side ( 62 , 61 ) in the second condenser-evaporator ( 60 ) being separated from one another by a single workpiece ( 68 ). 3. Apparatus according to claim 2, wherein the evaporation side ( 52 ) of the first condenser-evaporator ( 50 ) is in flow connection ( 10 ) with a gas reservoir ( 11 ). 4. Apparatus according to claim 2 or 3, wherein the liquefaction side ( 61 ) of the second condenser-evaporator ( 60 ) is designed such that when a certain value of the amount in the evaporation side ( 52 ) of the first condenser-evaporator ( 50 ), liquefaction side ( 61 ) of the second condenser-evaporator ( 60 ), gas line ( 8 ) and liquid line ( 9 ) formed primary circuit existing liquid, the heat transfer capacity is greatly reduced. 5. Application of the device according to one of claims 1 to 4 in a method for Obtaining pure xenon. 6. Application of the device according to one of claims 2 to 4, in which oxygen or nitrogen ( 63 ) in the evaporation side ( 62 ) of the second condenser-evaporator ( 60 ) are introduced. 7. Application according to claim 5 or 6, in which ethylene is used as the first refrigerant ( 9 ).