Method and apparatus for separating a liquefiable gas mixture

Abstract

The invention relates to a method for separating a liquefiable gas mixture consisting of a plurality of components, comprising at least one first component (K1) and one second component (K2), wherein, under an increased pressure p.sub.1, the first component (K1) has a melting point T*.sub.K1 that is higher than the melting point T*.sub.K2 of the second component (K2). In order to realise a configuration that is as compact as possible, it is provided in accordance with the invention that the method comprises the following steps: converting the gas mixture to a liquid state at a temperature T.sub.0 and a pressure p.sub.0, wherein T*.sub.K2<T.sub.0T*.sub.K1 and p.sub.0<p.sub.1 applies, and wherein the first component (K1) is present in an initial concentration (C0); producing a pressure gradient in the liquefied gas mixture, wherein the increased pressure p.sub.1 prevails at least in a limited spatial region (3) of the liquefied gas mixture, and freeze separation of the first component (K1) occurs.

Claims

1. A method for separating a liquefiable gas mixture comprising a plurality of components, the plurality of components comprising at least one first component and one second component, wherein, under an increased pressure, the first component has a first component melting point that is higher than a second component melting point of the second component, wherein the liquefiable gas mixture comprises air, the first component comprises nitrogen and the second component comprises oxygen; wherein the method comprises the following steps: converting the liquefiable gas mixture to a liquid state at a first temperature and a first pressure so that a liquefied gas mixture is formed, wherein the second component melting point <the first temperature the first component melting point and the first pressure <the increased pressure, in order to ensure the presence of the first component and the second component in liquid form at the first temperature and the first pressure, and wherein the first component is present in an initial concentration; and producing a pressure gradient in the liquefied gas mixture by rotating the liquefied gas mixture in a vessel about a rotational axis such that the pressure gradient is radially oriented, wherein the increased pressure prevails at least in a limited spatial region of the liquefied gas mixture and a pressure less than the increased pressure is present within a radial distance from the rotational axis, and freeze separation of the first component occurs due to the increased pressure; wherein the first component belongs to a first group of substances and the second component belongs to a second group of substances; wherein the substances of the first group freeze out at the first temperature and the increased pressure; wherein the substances of the second group remain liquid at the first temperature and the increased pressure; wherein the freeze-separated substances of the first group have a lower density than the substances of the second group that remain liquid; wherein the liquefied gas mixture is discharged along a region including the rotational axis; and wherein in the region the first component has an increased concentration as compared to the initial concentration.

2. The method according to claim 1, wherein the vessel is a tube.

3. The method according to claim 1, wherein the first component is separated from the second component by centrifuging.

4. The method according to claim 1, wherein the liquefied gas mixture flows through the vessel parallel to the rotational axis.

5. The method according to claim 1, wherein 65 K the first temperature 80 K applies.

6. The method according to claim 1, wherein 20 bars the increased pressure 2700 bars applies.

7. The method according to claim 1, wherein the liquefiable gas mixture is converted to the liquid state at the first temperature and the first pressure via liquefying and subsequently cooling the liquefiable gas mixture.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained below in closer detail by reference to the embodiments. The drawings are exemplary and, although they explain the concept of the invention, they shall not limit said concept in any way or finally represent the same, wherein:

(2) FIG. 1 shows a schematic axonometric sectional view of a rotating tube for producing a pressure gradient of a liquefied gas mixture situated in the tube;

(3) FIG. 2 shows a schematic sectional view of the tube of FIG. 1, but with an inner tube arranged in the tube;

(4) FIG. 3 shows a design variant similar to FIG. 2, but with a conical cross-section of the tube along the rotational axis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) FIG. 1 shows a schematic view of an apparatus in accordance with the invention, comprising a tube 1 with a clear radius R (see FIG. 2), in which tube 1 there is situated a liquefied gas mixture, preferably liquefied air. The liquefied gas mixture has a pressure p.sub.0 at first which preferably corresponds to the ambient pressure and is cooled to a temperature T.sub.0.

(6) The liquefied gas mixture comprises a first component K1 and a second component K2, which are both liquid at the pressure p.sub.0 and temperature T.sub.0. The first component K1 is present in the liquefied gas mixture with an initial concentration C0.

(7) The first component K1 has a melting point T*.sub.K1 at a pressure p.sub.1 which is increased over p.sub.0. The second component has a melting point T*.sub.K2 at the same pressure p.sub.1, wherein T*.sub.K2<T*.sub.K1.

(8) In the case of liquefied air, nitrogen forms the first component K1 and oxygen the second component K2. At a pressure p.sub.1=1000 bars, nitrogen has a melting point T*.sub.K1 of approximately 83 K and oxygen a melting point T*.sub.K2 of approximately 65 K.

(9) T.sub.0 lies between T*.sub.K2 and T*.sub.K1. In the case of liquefied air, T.sub.0 can be selected between 65 K and 80 K, preferably between 70 K and 75 K.

(10) Tube 1 now rotates about a centrally arranged rotational axis 2 with a direction of rotation 5, as a result of which the liquefied gas mixture situated in the tube 1 is rotated. A pressure gradient is thus produced in the liquefied gas mixture in tube 1, which pressure gradient faces radially away from the rotational axis 2, i.e. the pressure increases continuously to the outside starting from the rotational axis 2. As a result, a pressure rise to the pressure p.sub.1 at the temperature T.sub.0 occurs in a limited spatial area 3 of the liquefied gas mixture.

(11) Said limited spatial area 3 is shown in FIG. 2, which shows a schematic sectional view of the tube 1, in an interval of the radial distance of the rotational axis 2 from a to a+a. a is assumed to be so small that a constant pressure p.sub.1 is assumed substantially in the entire region 3. There is a pressure less than p.sub.1 in a region around the rotational axis 2 which has a radial distance of less than a.

(12) By selecting the rotational speed of the tube 1, the pressure gradient or the pressure can be set in a controlled manner in a specific spatial region of the liquefied gas mixture within the tube 1. The pressure p.sub.1 of a proximally 1000 bars is present for example in a tube 1, which rotates at a velocity of 18,000 rpm and is filled with liquid air, at a radial distance of a=24 cm from the rotational axis 2.

(13) This leads to freeze separation of the first component K1 or freeze separation/crystallisation of nitrogen in the region 3, but principally obviously also outside thereof, i.e. at a radial distance greater a.

(14) If the freeze-separated parts of the first component K1 have a density greater than that of the remaining liquefied gas mixture, said parts in the rotating tube 1 will travel to the outside because the rotating tube 1 acts as a centrifuge, i.e. these frozen parts of the first component K1 can be removed in the known manner by centrifuging.

(15) FIG. 1 shows the case however in which the freeze-separated parts of the first component K1 have a lower density than the remaining liquefied gas mixture. One example for this is frozen nitrogen in liquefied air. The lower density of the freeze-separated parts of the first component K1 or the nitrogen crystals leads to the consequence that a radial flow 6 of the freeze-separated parts of the first component K1 or nitrogen crystals is obtained in relation to the rotational axis 2.

(16) In order to structure the flow conditions in the tube 1 for avoiding imbalance, guide elements (not shown) can be provided within the tube 1. The flow channelled in this manner can lead to evening out of the process described below.

(17) Once the freeze-separated parts of the first component K1 have left the region 3 and have radial distances from the rotational axis 2 which are less than a, they are subjected to pressures which are lower than p.sub.1. At a sufficiently low pressure which is lower than p.sub.1, melting of the freeze-separated parts of the first component K1 occurs. A liquefied gas mixture with an increased concentration C1 of the first component K1 can consequently be found within a region around the rotational axis 2 with radial distances lower a.

(18) The unbroken serpentine lines in FIG. 1 indicate a transitional zone 7, in which the freeze-separated parts or nitrogen crystals are molten down and are mushy.

(19) For the purpose of separating the components K1, K2, the liquefied gas mixture with the increased concentration C1 of the first component K1 can be discharged from the region around the rotational axis 2 with radial distances smaller than a. As is schematically shown in FIG. 2, this can occur by means of an inner tube 4, which in the illustrated embodiment is arranged centrically within the tube 1. The inner tube 4 has a clear radius r and a respective circular clear cross-section. With its clear cross-section, the inner tube 4 therefore covers a region which includes the rotational axis 2.

(20) While the liquefied gas mixture flows through the tube 1 axially or parallel to the rotational axis 2, it is merely necessary for discharging the liquefied gas mixture with increased concentration C1 of the first component K1 to arrange the inner tube 4 in the tube 1 as described above.

(21) In order to ensure that no freeze-separated parts of the first component K1 or no nitrogen crystals need to be discharged by the inner tube 4, the clear radius r is chosen smaller than a in the embodiment of FIG. 2.

(22) FIG. 3 shows a schematic sectional view of a further embodiment of the apparatus in accordance with the invention for carrying out the separating method in accordance with the invention. In this case, the cross-section of the tube 1 along the rotational axis 2 has a conical shape. As already mentioned above, the crystals or freeze-separated parts of a component of the liquefied gas mixture with a density greater than that of the remaining liquefied gas mixture in the rotating tube moves in the rotating tube 1 radially to the outside, away from the rotational axis 2. The conical shape promotes the movement component of said crystals or freeze-separated parts parallel to the rotational axis 2 towards an outlet (not shown) in the jacket of the tube 1. One example for such crystals are argon crystals, which occur in the separation of liquefied air in accordance with the invention because argon has a higher melting point than nitrogen and oxygen.

LIST OF REFERENCE NUMERALS

(23) 1 Tube 2 Rotational axis 3 Limited spatial region 4 Inner tube 5 Direction of rotation 6 Radial flow 7 Transitional zone K1 First component of a gas mixture K2 Second component of the gas mixture C0 Initial concentration C1 Increased concentration R Clear radius of the tube r Clear radius of the inner tube