Method for obtaining an air product in an air separating system with temporary storage, and air separating system

Abstract

A method for obtaining an air product in an air separating system in which a liquid fraction is obtained from feed air and used to provide the air product and in which the liquid fraction is temporarily stored in a tank arrangement. A tank arrangement with at least two tanks is used, and the liquid fraction is fed to at least one of the tanks and/or is removed from at least one of the tanks in order to provide the air product. In the process, the liquid fraction is not fed to and removed from any one of the tanks at the same time, and the composition of the liquid fraction in a tank is ascertained prior to each removal of the liquid fraction from the tank. An air separating system is also described.

Claims

1. A method for obtaining an air product in an air separating plant, said method comprising: obtaining a liquid fraction from feed air and said liquid fraction is used at least in part for providing said air product, introducing said liquid fraction is into a tank arrangement having at least two tanks, wherein said liquid fraction is fed to one or more of said tanks of the tank arrangement and is withdrawn from one or more of said tanks of the tank arrangement to provide said air product and said liquid fraction is not simultaneously fed to and withdrawn from any of said tanks, and wherein, prior to withdrawing liquid fraction from said one of the tanks, the composition of the liquid fraction within said one of the tanks is determined.

2. The method as claimed in claim 1, further comprising pressurizing in the liquid state the liquid fraction used to provide said air product to a target pressure, and wherein the liquid fraction is subsequently vaporized against a heat transfer medium and then discharged from said plant in the gaseous state as said air product.

3. The method as claimed in claim 2, wherein said pressurizing of the liquid fraction is performed in the tank arrangement by pressurization vaporization.

4. The method as claimed in claim 3, wherein said liquid fraction is only withdrawn from a tank of the tank arrangement to provide air product only when said composition of the liquid fraction within said tank of the tank arrangement is determined to correspond to a setpoint value.

5. The method as claimed in claim 1, wherein said feed air is cooled in a main heat exchanger and then is injected into a first separation column of the air separating plant, wherein an oxygen-enriched flow from the first separation column is introduced into a second separation column of said plant and a pure oxygen is obtained from said second distillation column as said liquid fraction and the pure oxygen is stored in the tank arrangement, then pressurized and subsequently vaporized in the main heat exchanger against at least part of the feed air as heat transfer medium, and then discharged from the plant in gaseous form as the air product.

6. The method as claimed in claim 5, wherein a first fluid flow and a second fluid flow are is withdrawn from the first separation column and heated in a top condenser of the first separating column, and wherein said first fluid flow is further heated in the main heat exchanger and then expanded in an expansion machine, and said second fluid flow is compressed in a compressor coupled to said expansion machine, then cooled in the main heat exchanger and then injected into the first separation column.

7. An air separating plant comprising: a separation system for obtaining a liquid fraction from feed air, and said separation system having a discharge system wherein at least part of the liquid fraction is used to provide an air product, said discharge system comprising a tank arrangement with at least two tanks set up to store the liquid fraction, and means for feeding the liquid fraction to at least one of the tanks and means for withdrawing the liquid fraction from one or more of the tanks to provide the air product and said means for feeding and said means for withdrawing cannot simultaneously feed and withdraw the liquid fraction from any of the tanks of the tank arrangement, and, and a control device for determining the composition of the liquid fraction prior to the liquid fraction being withdrawn from a tank of the tank arrangement to provide the air product.

8. The air separating plant as claimed in claim 7, further comprising means for pressurizing the liquid fraction in the liquid state to a target pressure, means for vaporizing the liquid fraction against a heat transfer medium, and means for discharging the vaporized liquid fraction from the plant as the gaseous air product.

9. The air separating plant as claimed in claim 7, further comprising at least one main heat exchanger for cooling the feed air, a first separation column into which cooled feed air from the at least one main heat exchanger is injected, and a second separation column for obtaining, from an oxygen-enriched flow from the first separation column, pure oxygen as the liquid fraction, and means in said at least one main heat exchanger for vaporizing the pure oxygen, after storage of the pure oxygen in the tank arrangement and after pressurization of the pure oxygen, against at least part of the feed air as heat transfer medium.

10. The air separating plant as claimed in claim 9, further comprising means for withdrawing a first fluid flow and means for withdrawing a second fluid flow from the first separation column and introducing said first fluid flow and said second fluid flow into a top condenser of the first separation column to heat said first fluid flow and said second fluid flow, and means for further heating the first fluid flow in said main heat exchanger, an expansion machine for expanding the further heated first fluid flow, a compressor for compressing the second fluid flow, wherein said compressor is coupled to the expansion machine, means for cooling the expanded second fluid flow in said main heat exchanger, and means for introducing the cooled, expanded second fluid flow into the first separation column.

11. The air separating plant as claimed in claim 7, further comprising means for withdrawing the liquid fraction from the separation system at a withdrawal point which lies geodetically above an injection point for introducing the liquid fraction into the tank arrangement.

12. The method as claimed in claim 5, wherein a fluid flow is withdrawn from the first separation column and heated in a top condenser of the first separating column, and after being heated in said top condenser said fluid flow is divided into a first fluid flow and a second fluid flow, and wherein said first fluid flow is further heated in the main heat exchanger and then expanded in an expansion machine, and said second fluid flow is compressed in a compressor coupled to said expansion machine, then cooled in the main heat exchanger and then introduced into the first separation column.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an air separating plant according to the prior art,

(2) FIG. 2 shows an air separating plant according to one embodiment of the invention.

(3) In the figures, identical or mutually corresponding elements are indicated with identical reference signs. Explanations will not be repeated, for the sake of clarity.

EMBODIMENT(S) OF THE INVENTION

(4) FIG. 1 shows, schematically in the form of a plant diagram, an air separating plant with internal compression according to the prior art, as is known for example from EP 1 995 537 A2. The air separating plant set up for internal compression, as a whole, is given the label 110. As mentioned, however, the invention is also suited to use in air separating plants without internal compression.

(5) Atmospheric air 1 (AIR) is drawn in, via a filter 2, by an air compressor 3 where it is compressed to an absolute pressure of between 6 and 20 bar, preferably approximately 9 bar. After flowing through an after cooler 4 and a water separator 5 for separating off water (H.sub.2O), the compressed air 6 is purified in a purification apparatus 7 which has a pair of containers filled with adsorption material, preferably a molecular sieve. The purified air 8 is cooled to near dew point, and partially liquefied, in a main heat exchanger 9. A first part 11 of the cooled air 10 is introduced, via a throttle valve 51, into a single column 12. The injection preferably takes place several practical or theoretical trays above the sump.

(6) The operating pressure of the single column 12 (at the top) is between 6 and 20 bar, preferably approximately 9 bar. Its top condenser 13 is cooled with a first fluid flow 14 and a second fluid flow 18. The first fluid flow 14 is drawn off from the sump of the single column 12, the second fluid flow 18 is drawn off from an intermediate point which is several practical or theoretical trays above the air injection, or which is at the same height as the latter.

(7) Gaseous nitrogen 15, 16 is drawn off at the top of the single column 12 as the main product of the single column 12, is heated in the main heat exchanger 9 to approximately ambient temperature, and is finally drawn off via line 17 as a pressurized gas product (PGAN). Further gaseous nitrogen is fed through the top condenser 13. A part 53 of the condensate 52 obtained in the top condenser 13 can be obtained as liquid nitrogen product (PLIN); the remainder 54 is delivered to the top of the single column 12 as return flow.

(8) The first fluid flow 14 is vaporized in the top condenser 13 at a pressure of between 2 and 9 bar, preferably approximately 4 bar, and flows in gaseous form via line 19 to the cold end of the main heat exchanger 9. It is withdrawn from the latter (line 20) at an intermediate temperature and, in an expansion machine 21 which in the example takes the form of a turbo expander, is expanded, so as to perform work, to approximately 300 mbar above atmospheric pressure. The expansion machine 21 is mechanically coupled to a cold compressor 30 and to a brake device 22 which in the exemplary embodiment takes the form of an oil brake. The expanded fluid flow 23 is heated in the main heat exchanger 9 to approximately ambient temperature. The hot fluid flow 24 is vented (line 25) to the atmosphere (ATM) and/or is used as regeneration gas 26, 27 in the purification apparatus 7, possibly after heating in the heating device 28.

(9) The second fluid flow 18 is vaporized in the top condenser 13 at a pressure of between 2 and 9 bar, preferably approximately 4 bar, and flows in gaseous form via a line 29 to the cold compressor 30 where it is recompressed to approximately the operating pressure of the single column. The recompressed fluid flow 31 is cooled in the main heat exchanger 9 back down to the column temperature and is finally fed, via line 32, back to the sump of the single column 12.

(10) An oxygen-enriched flow 36, which is essentially free from heavy volatile contaminants, is drawn off in the liquid state from an intermediate point in the single column 12, which point is arranged 5 to 25 theoretical or practical trays above the air injection point. Where appropriate, the oxygen-enriched flow 36 is supercooled in a sump vaporizer 37 of a pure oxygen column 38 and is then delivered, via a line 39 and a throttle valve 40, to the top of the pure oxygen column 38. The operating pressure of the pure oxygen column 38 (at the top) is between 1.3 and 4 bar, preferably approximately 2.5 bar.

(11) The sump vaporizer 37 of the pure oxygen column 38 is also cooled by means of a second part 42 of the cooled feed air 10. The feed air flow 42 is then at least partially, for example entirely, condensed and flows via a line 43 to the single column 12 where it is introduced approximately at the height of the injection of the remaining feed air 11.

(12) A high-purity oxygen product is withdrawn as the liquid fraction 41 from the sump of the pure oxygen column 38, is raised by means of a pump 55 to an increased pressure of between 2 and 100 bar, preferably approximately 12 bar, is fed via a line 56 to the cold end of the main heat exchanger 9 where it is vaporized at the increased pressure and is heated to approximately ambient temperature, and is finally obtained via line 57 as a gaseous product (GOX-IC).

(13) A top gas 58 of the pure oxygen column 38 is mixed into the previously mentioned expanded second fluid flow 23 (cf. connection A). Where relevant, part of the feed air is guided via a bypass line 59 to the inlet of the cold compressor 30 for surge prevention of the latter (what is referred to as anti-surge control).

(14) When necessary, it is possible to withdraw from the plant, upstream and/or downstream of the pump 55, liquid oxygen as liquid fraction (labelled LOX in the drawing). In addition, an external liquid, for example liquid argon, liquid nitrogen or liquid oxygen, can be vaporized in the main heat exchanger 9 in indirect exchange of heat with the feed air (not shown in the drawing).

(15) FIG. 2 shows, schematically, an air separating plant according to a particularly preferred embodiment of the invention, which as a whole is provided with the label 100. The air separating plant 100 shown in FIG. 2 differs from the air separating plant 110 shown in FIG. 1 essentially by a tank arrangement 70 having multiple tanks 72, two in the example shown.

(16) The tank arrangement 70 comprises, in the example shown, two tanks 72 of identical construction, of which only the left-hand tank 72 will be explained here in further detail. As mentioned above, the air separating plant 100 according to the invention can also be designed with more than two tanks 72. The tanks 72 can be arranged upright or recumbent and for example can be filled from above or from below. The tank arrangement 70 further comprises in the example shown a valve pair 71 by means of which the tanks 72 can be filled in alternation or in parallel. It is to be understood that, if a greater number of tanks 72 is provided, there is accordingly provided a greater number of valves.

(17) The tank arrangement 70 can for example be arranged geodetically below a withdrawal point from the pure oxygen column 38, in this case therefore below the lowest point of the pure oxygen column 38, in order to support the transfer of the liquid fraction 41 into the tank arrangement 70. In general, however, the pure oxygen column 38 is operated at a pressure, for example 3 bar, which ensures the transfer of the liquid fraction 41 into the tank arrangement 70.

(18) In the example shown, each of the tanks 72 is assigned pressurization vaporizer 73. The pressurization vaporizers 73 operate in a manner which is known in principle. In each case, a small quantity of the oxygen product 41 present in the corresponding tank 72 is withdrawn from the bottom region of the tanks 72, is heated and is injected into the top of the tank via a valve which is not shown in more detail. The vaporization increases the pressure in the tanks 72. By virtue of the pressurization vaporization, the tank arrangement 70 can entirely replace the above-mentioned pump 55, as an alternative however can also be provided in addition to a corresponding pump 55 (not shown in FIG. 2).

(19) As already explained, the tanks 72 in the air separating plant 100 according to the invention are operated in alternation, wherein, as explained, the liquid fraction 41 is fed to at least one of the tanks 72 and/or is withdrawn from at least one of the tanks 72 but in that context is not simultaneously fed to one of the tanks 72 and withdrawn therefrom for providing the air product.

(20) For example, in this context only one of the valves of the valve pair 71 is open at any one time. Thus, the tank 72 associated with the corresponding valve is filled. A corresponding bottom-side valve 74 is closed. Simultaneously, or only after sufficient filling of the corresponding tank 72, the pressure in the respective tank 72 is raised by means of the pressurization vaporizer 73. Once the corresponding tank 72 is sufficiently full and is at the desired pressure, the corresponding valve of the valve pair 71 is closed (and the respective other is opened) and then a valve 74 on the bottom side of the tank 72 is opened (and the respective other is closed). The pure oxygen contained in the tank 72 can therefore, as explained above, flow via the line 56 to the cold end of the main heat exchanger 9, wherein it is vaporized at the increased pressure and heated to approximately ambient temperature, and finally withdrawn via line 57. At the same time, the other tank 72 is filled.

(21) The air separating plant 100 according to the invention, with the tank arrangement 70, proves to be particularly advantageous in that context because the liquid oxygen which is in each case present in the corresponding tanks 72 is not directly delivered at the plant boundary, i.e. in particular not without further monitoring. It is further provided to continuously or intermittently monitor the purity of the oxygen in the respective tank 72 by means of a control device 75 which, in the example represented, is visible only on the right-hand tank 72. The valve 74 arranged on the bottom side of the corresponding tank 72 is then opened only when the oxygen in the corresponding tank 72 is of sufficient purity. If this is not the case, the contents of the tank 72 can be discarded or recirculated, via a line which is not shown, for example into the pure oxygen column 38. This ensures that oxygen of high and in particular specifiable purity is always delivered at the plant boundary. This is not possible in conventional plants because, as explained, with a corresponding pump 55 oxygen is delivered continuously.

(22) Continuous provision of pressurized oxygen at the plant boundary via the line 57 is still ensured because, as explained, the tanks 72 can be operated in alternation. It is thus always possible for oxygen to be withdrawn from one of the two tanks 72 via the valve 74 arranged on the bottom side while the respective other tank 42 is filled and monitored by means of the control device 75.

(23) Any control device 75 known from the prior art can be used for monitoring purity. Purity monitoring is preferably carried out by means of gas chromatography.

(24) A further advantageous aspect of the air separating plant 100 according to the invention results from the fact that, as explained, the ingress of contamination into the tank arrangement 70 is markedly reduced in comparison to compression by means of a pump 55. Known sources of contamination in the context of pumps include the pump seals, which are entirely unnecessary in the tank arrangement 70.