APPARATUS AND METHOD FOR SEPARATING AIR

Abstract

Apparatus for separating air comprising a device for breaking up a jet of cryogenic liquid in a gas flow, comprising a supply pipeline for the cryogenic liquid having an inside diameter greater than or equal to 10 mm, and a gas pipe of circular section, with a diameter d, the gas pipe comprising a portion having a reduction in diameter by a ratio of 20 to 50% at the point of injection of liquid and over a distance y wherein:

y=nd

and wherein the supply pipeline penetrates the gas pipe such that its end is in the portion of the pipe having the reduction in diameter and n is between 7 and 9.

Claims

1. An apparatus for separating air by cryogenic distillation, the apparatus comprising: a heat exchanger configured to cool air by exchange of heat with a gas, a system of columns comprising at least one distillation column configured to separate air cooled in the exchanger, a pipeline configured to supply cryogenic liquid having an end, and a gas pipe, wherein the liquid supply pipeline has an inside diameter greater than or equal to 10 mm, and the gas pipe has a circular section, and a diameter d of less than 600 mm over more than 50% of its length, the gas pipe comprising a portion having a reduction in diameter by a ratio of 20 to 50% at the point of injection of liquid and over a distance y wherein:
y=nd and wherein the supply pipeline penetrates the gas pipe such that its end is in the portion of the gas pipe having the reduction in diameter and n is between 7 and 9 in order to break up a jet of cryogenic liquid in the gas flow, wherein the gas pipe is connected to the exchanger so as to be supplied with gas produced by the system of columns and the liquid pipeline being connected to the system of columns so as to be supplied with a liquid produced by the system of columns.

2. The apparatus according to claim 1, wherein a liquid injection nozzle is arranged at the end of the pipeline.

3. The apparatus according to claim 2, wherein the nozzle is of the flat jet type capable of producing a flat jet or a jet in sheet form.

4. The apparatus according to claim 1, wherein the end of the pipeline is within a radius of d/10 around the central axis of the gas pipe.

5. The apparatus according to claim 1, wherein the system of columns comprises a column having a bottom surrounded by a liquid which is rich in oxygen compared to air, the pipeline being connected to this bottom.

6. The apparatus according to claim 5, wherein the system of columns comprises a column having a top-end condenser containing a liquid which is rich in oxygen compared to air, the pipeline being connected to the condenser.

7. The apparatus according to claim 1, comprising a turbine, the gas pipe being connected to the system of columns so as to send to the portion of the pipe having a reduction in diameter a gas which is rich in nitrogen compared to air and the portion of the pipe having a reduction in diameter being connected to the turbine so as to send to it the gas rich in nitrogen in which the liquid has been broken up.

8. The apparatus according to claim 1, wherein the liquid pipeline is arranged such that the liquid is pressurized by hydrostatic pressure.

9. A method for separating air by cryogenic distillation, the method comprising the steps of: cooling air in a heat exchanger by exchange of heat with a gas, separating the air cooled in the exchanger in a system of columns comprising at least one distillation column, breaking up a jet of cryogenic liquid in a gas flow, circulating a cryogenic liquid at a temperature below 100 C. in a supply pipeline having an end, wherein the liquid supply pipeline has an inside diameter greater than or equal to 10 mm, and circulating a gas at a temperature of between 10 and 30 C. above its dew point in a gas pipe of circular section, having a diameter d over more than 50% of its length, the gas pipe comprising a portion having a reduction in diameter by a ratio of 20 to 50% at the point of injection of liquid over a distance y wherein:
y=nd transferring the liquid via the supply pipeline, which penetrates the gas pipe such that its end is in the portion of the gas pipe having the reduction in diameter, such that the liquid emerges in said portion of the gas pipe, and n is a number between 7 and 9, the gas pipe being connected to the exchanger and being supplied with gas produced by the system of columns and the liquid pipeline being connected to the system of columns and being supplied with a liquid produced by the system of columns.

10. The method according to claim 9, wherein the cryogenic liquid and the gas circulate from top to bottom.

11. The method according to claim 9, wherein the gas is residual nitrogen.

12. The method according to claim 9, wherein the gas contains between 45 and 95 mol % of oxygen.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Other features and advantages of the invention will be further disclosed in the description that follows, and in several embodiments provided as non-limiting examples in reference to the appended schematic drawings, in which:

[0039] FIG. 1 shows the sizes of drops calculated by various models as a function of the load of the apparatus.

[0040] FIG. 2 shows the evaporation time and the distance travelled before evaporation of a drop as a function of its initial size.

[0041] FIG. 3 shows models of maximum drop size as a function of the diameter of the gas pipe in a configuration with a liquid jet in a transverse gas flow. The reduction in diameter of the gas pipelines at the point of injection and over the distance for breaking up the liquid jet makes it possible to reduce the maximum size of the drops.

[0042] FIG. 4 shows a device for breaking up liquid in a gas pipe to be incorporated in an apparatus for separating air, with a configuration with central injection (left-hand side) and a configuration with central injection and reduction in diameter of the gas pipe according to the invention (right-hand side).

[0043] FIG. 5 shows an apparatus for separating air by cryogenic distillation according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0044] FIG. 4 shows the configuration with central injection (left-hand side) and with central injection and reduction in diameter of the gas pipe according to the invention (right-hand side). The right-hand figure shows liquid L being sent to the centre of the gas G pipe T. The right-hand figure shows the right-hand pipe T having a diameter d of less than 600 mm, preferably less than 450 mm over most of its length, in other words more than 50% of its length, and a portion of its length having a reduction in diameter by a ratio of 20 to 50% at the point of injection of liquid at a temperature below 100 C. over a distance y wherein:

y=nd

wherein n is between 7 and 9, preferably between 7.5 and 8.5, for example 8.

[0045] The gas G is preferably at a temperature between 10 and 30 C. above its dew point. The end of the liquid injection pipeline is within a radius of d/10 around the central axis of the gas pipe T; this reduction in diameter of the gas pipe over the distance y for breaking up the liquid jet makes it possible to reduce the maximum initial size of the drops.

[0046] The gas pipe T in the right-hand figure has a first section having a first diameter and a second section having a second diameter which is less than the first diameter by a ratio of 20 to 50%. The gas pipe T has an intermediate section between the first section and the second section. The end of the liquid L supply pipeline is in the intermediate section or the second section, since the reduction in diameter in the narrowest portion of the intermediate section is still between 20 and 50% of the diameter.

[0047] The supply of cryogenic liquid to the centre of the gas pipeline makes it possible to promote mixing between the gas and the liquid while limiting the risk of coalescence on the wall.

[0048] The use of a flat jet nozzle provides a first mechanism for atomization in film form, which limits the initial drop size while retaining a diameter for passage which is sufficient to prevent blockage. A flat jet nozzle is known from FR3113608 and FR3107659.

[0049] The device is incorporated in an apparatus for separating air by distillation shown in FIG. 5. An apparatus for separating air by cryogenic distillation A comprises a heat exchanger E for cooling air 1 by exchange of heat with the gas 1, and a system of columns C comprising at least one distillation column for separating air cooled in the exchanger.

[0050] The system of columns may comprise a single column or a first column operating at a first pressure and a second column operating at a second pressure, the top of the first column being thermally coupled to the bottom of the second column. The gas pipe T is connected to the exchanger E so as to be supplied with gas produced by a column of the system of columns C. The gas may be heated in the heat exchanger E before being sent to the device such that the gas arrives at the device at a temperature between 10 and 30 C. above its dew point. The liquid pipeline is connected to the system of columns so as to be supplied with a liquid produced by a column of the system of columns at a temperature below 100 C. The liquid preferably corresponds to a purge of the system of columns.

[0051] According to one variant, the system of columns comprises a column, for example the second column, having a bottom surrounded by a liquid which is rich in oxygen compared to air, the pipeline being connected to this bottom.

[0052] According to another variant, the system of columns comprises a column, for example a single column, having a top-end condenser containing a liquid which is rich in oxygen compared to air, the pipeline being connected to the condenser.

[0053] The apparatus may comprise a turbine D, the gas pipe T being connected to the system of columns so as to send to the device a gas which is rich in nitrogen compared to air and the device being connected to the turbine so as to send to it the gas rich in nitrogen in which the liquid has been broken up.

[0054] The liquid pipeline is arranged such that the liquid is pressurized by hydrostatic pressure. In this case, it is sometimes possible to dispense with a pump for sending the liquid to the device.

[0055] The gas in which the liquid is broken up may be residual nitrogen or may contain between 45 and 95 mol % of oxygen.

[0056] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0057] The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

[0058] Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of comprising). Comprising as used herein may be replaced by the more limited transitional terms consisting essentially of and consisting of unless otherwise indicated herein.

[0059] Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0060] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0061] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.