Apparatus for separating a gas mixture by cryogenic distillation

Abstract

Apparatus for separating a gas mixture by cryogenic distillation. An apparatus for separating a gas mixture by cryogenic distillation comprising a column system including at least one distillation column, a heat exchanger, at least one thermally insulated enclosure containing at least one distillation column and / or the heat exchanger, an expansion turbine outside any thermally insulated enclosure, means for supplying air or gas to the turbine consisting of a first cylindrical pipe (100) coated on the outside with an annular layer (104) of thermal insulation, and means for recovering the air or expanded gas consisting of a second cylindrical pipe (100) coated on the outside with an annular layer (104) of thermal insulation. Abstract figure: Figure 1

Description

Title of the invention: Apparatus for separating a gas mixture by cryogenic distillation

[0001] The present invention relates to an apparatus for separating a gas mixture by cryogenic distillation.

[0002] An apparatus for separating a gas mixture, for example air, often comprises a system of distillation columns comprising at least one column, the at least one column having to operate at a cryogenic temperature and being inside a thermally insulated enclosure.

[0003] To keep the distillation process cold, it is common to expand a fluid from the apparatus in a turbine, the fluid entering the turbine and the fluid leaving the turbine both being at cryogenic temperatures. The fluid may be at least part of an air flow or a gas flow produced by the distillation.

[0004] The turbine is often arranged in the same enclosure as at least one of the columns of the column system. Otherwise the turbine can be arranged in a dedicated module as illustrated in JP2006275462 A2 or EP 0 629 829 A1, this module being thermally insulated with, for example, rock wool.

[0005] Research Disclosure Vol. 51 no. 451060 XP007129240 describes that a turbine can be placed in a dedicated enclosure whose walls are covered with thermal insulation. Such an enclosure must be designed and manufactured: it takes up space and the insulation in the form of rock wool can only be installed on site

[0006] If it is necessary to intervene on the turbine, the presence of insulation, either particulate or rock wool, complicates the intervention task.

[0007] An object of the present invention is to reduce the time required to construct an air separation apparatus by cryogenic distillation involving an expansion turbine.

[0008] The present invention provides for a turbine of an air separation apparatus which expands a gas at cryogenic temperature and produces an expanded gas at cryogenic temperature, preferably without placing the connections between the expanded or to-be-expanded gas lines and the turbine in a thermally insulated enclosure. Surprisingly, the turbine itself does not need to be thermally insulated.

[0009] According to an object of the invention, there is provided an apparatus for separating a gaseous mixture by cryogenic distillation comprising a system of columns comprising at least one distillation column, a heat exchanger, at least one thermally insulated enclosure containing the at least one distillation column and / or the heat exchanger, means for sending cooled air into the heat exchanger heat to the column system, means for withdrawing at least one nitrogen- or oxygen-enriched gas from the column system, an expansion turbine, means for sending air cooled to a cryogenic temperature or a nitrogen- or oxygen-enriched gas at a cryogenic temperature to the turbine, means for recovering the expanded air or gas in the turbine at the outlet of the turbine, characterized in that the turbine is located outside any thermally insulated enclosure, the means for sending air or a gas to the turbine being constituted by a first cylindrical pipe coated on the outside with an annular layer of thermal insulation and the means for recovering the expanded air or gas being constituted by a second cylindrical pipe coated on the outside with an annular layer of thermal insulation.

[0010] According to other optional aspects: • the thermal insulation forming the annular layer is made of cellular glass. • the outer surface of the thermal insulation layer is water-repellent, even impermeable. • the conductivity of the thermal insulation layer is less than 0.03W / mK, or even 0.025 W / mK, at the turbine operating temperature. • the turbine is open air. • the gas mixture is air or a mixture having at least two of the following as principal components: carbon dioxide, carbon monoxide, hydrogen, methane, argon, oxygen, nitrogen, helium, krypton, xenon.

[0011] According to another object of the invention, there is provided an apparatus for liquefying a gas having a cryogenic condensation temperature by cryogenic distillation comprising at least one heat exchanger, means for sending the gas to be liquefied to the at least one exchanger, at least one refrigeration cycle comprising a cycle fluid compressor and at least one cycle fluid turbine, at least one thermally insulated enclosure in which the at least one heat exchanger to the column system is located, characterized in that the turbine is located outside any thermally insulated enclosure, the means for sending the cycle gas to the turbine being constituted by a first cylindrical pipe coated on the outside with an annular layer of thermal insulation and the means for recovering the expanded gas in the turbine being constituted by a second pipe coated on the outside with an annular layer of thermal insulation.

[0012] The invention will be described in more detail with reference to the figures:

[0013] [Fig-1] illustrates a section of a thermally insulated conduit for use in a air separation apparatus according to the invention.

[0014] [Fig.2] illustrates a support for thermally insulated pipes for use in an air separation apparatus according to the invention.

[0015] [Fig.3] illustrates an air separation apparatus according to the invention.

[0016] [Fig-1] illustrates means 100 for supplying a gas to be expanded to a turbine or to transporting an expanded gas leaving a turbine, the means comprising a cylindrical pipe 106 in which the gas to be expanded or expanded circulates and an annular layer of thermal insulation 104, allowing the gas to circulate while reducing heat losses as much as possible.

[0017] In the absence of an enclosure enclosing the turbine and the means 100 bringing the gas towards the turbine and removing the expanded gas, it is necessary, as illustrated in [Fig. 2], to provide a vertical support 300 carrying horizontal supports 400 on which the means 100 rest, at a distance from the ground, the means 100 being as illustrated in [Fig. 1]

[0018] According to the invention, in [Fig. 3], compressed air 7, purified of water and carbon dioxide, is cooled in a heat exchanger 1 and sent to a distillation column 2 operating at approximately 9 bars to be separated. The rich liquid (oxygen-enriched liquid) 10 is withdrawn from the bottom of column 2 and sent to a first nitrogen condenser 3 where nitrogen from the top of the column is condensed. The vaporized rich liquid 13 is compressed by a cold compressor 5 and is divided into two.

[0019] The liquid 11 which is not vaporized in the first condenser 3 is expanded in a valve and feeds a second nitrogen condenser 4. This second condenser 4 also serves to condense the top nitrogen from column 2. The vaporized liquid 21 is taken out of the second condenser 4 and heated in the heat exchanger 1 to an intermediate temperature thereof.

[0020] The purge liquid 23 from the condenser 4 is vaporized in a heat exchanger 6 by heat exchange with a portion 19 of the vaporized liquid compressed in the cold compressor 5. The vaporized liquid is thus reheated and is sent to the column 2 to be separated.

[0021] The remainder 17 of the vaporized liquid compressed in the cold compressor is cooled in the heat exchanger 2 and is sent to the column 2 to be separated.

[0022] The purge liquid vaporized in the exchanger 6 is mixed with the gas from the second condenser heated in the heat exchanger 1. The heat exchanger is arranged inside a thermally insulated enclosure. The column is arranged in the same enclosure as the exchanger or in a dedicated thermally insulated enclosure. The mixture 25 is expanded in the turbine 5A coupled to the cold compressor 5. The mixture arrives in the turbine at a cryogenic temperature via a first cylindrical pipe coated on the outside with an annular layer of thermal insulation. The turbine 5A is not inside a thermally insulated enclosure and is preferably located in the open air.

[0023] The gas expanded in the turbine 5A circulates in a second cylindrical pipe coated on the outside with an annular layer of thermal insulation, for example cellular glass such as FOAMGLAS ®.

[0024] The gas expanded in the turbine 5A is reheated in the heat exchanger 2 to form a residual gas 9.

[0025] The top nitrogen of the column is also reheated in the heat exchanger 2 to form a product 8.

[0026] The heat exchanger 6 may be a brazed aluminum plate heat exchanger maintaining a temperature difference of less than

[0027] 20-30 °C. The exchanger 6 can be placed at the bottom of the cold box and thus the effect of Distillation is avoided by using a high flow rate of rich liquid. This arrangement also increases the hydrostatic pressure of the purge liquid.

[0028] It is obvious that the separation apparatus can take any known form, comprising for example a double column, instead of the single column of [Fig. 3]. The turbine can be an air turbine, such as a Claude turbine or an insufflation turbine, a turbine powered by nitrogen gas or a turbine powered by oxygen gas.

[0029] It will be understood that the invention could be applied to other fields than the cryogenic separation of air, in particular to the liquefaction of a gas such as hydrogen, nitrogen, etc. at least one turbine of a refrigeration cycle being located outside any thermally insulated enclosure, the means for sending air or a gas to the turbine being constituted by a first cylindrical pipe coated on the outside with an annular layer of thermal insulation and the means for recovering the expanded air or gas being constituted by a second cylindrical pipe coated on the outside with an annular layer of thermal insulation.

Claims

Claims

1. Apparatus for separating a gas mixture by cryogenic distillation comprising a column system (2) comprising at least one distillation column, a heat exchanger (1), at least one thermally insulated enclosure containing the at least one distillation column and / or the heat exchanger, means for sending air (7) cooled in the heat exchanger to the column system, means for withdrawing at least one gas (13, 21, 23) enriched in nitrogen or oxygen from the column system, an expansion turbine (5A), means for sending air cooled to a cryogenic temperature or a gas enriched in nitrogen or oxygen at a cryogenic temperature to the turbine, means for recovering the air or the gas expanded in the turbine at the outlet of the turbine, characterized in that the turbine is located outside any thermally insulated enclosure,the means for sending air or a gas to the turbine being constituted by a first cylindrical pipe (100) coated on the outside with an annular layer (104) of thermal insulation and the means for recovering the expanded air or gas being constituted by a second cylindrical pipe (100) coated on the outside with an annular layer (104) of thermal insulation.,

2. Apparatus according to claim 1 wherein the thermal insulator forming the annular layer (104) is made of cellular glass.

3. Apparatus according to claim 1 or 2 wherein the outer surface of the layer (104) of thermal insulation is water-repellent, or even impermeable.

4. Apparatus according to claim 1 or 2 or 3 wherein the conductivity of the thermal insulation layer (104) is less than 0.03W / mK, or even 0.025 W / mK, at the operating temperature of the turbine.

5. Apparatus according to one of the preceding claims in which the turbine (5A) is in the open air.

6. Apparatus according to one of the preceding claims wherein the gas mixture (7) is air or a mixture having at least two of the following components as main components: carbon dioxide, carbon monoxide, hydrogen, methane, argon, oxygen, nitrogen, helium, krypton, xenon.

7. Apparatus for liquefying a gas having a cryogenic condensation temperature by cryogenic distillation comprising at least one heat exchanger, means for sending the gas to liquefy to the at least one exchanger, at least one refrigeration cycle comprising a cycle fluid compressor and at least one cycle fluid turbine, at least one thermally insulated enclosure in which the at least one heat exchanger is located to the column system, characterized in that the turbine is located outside any thermally insulated enclosure, the means for sending the cycle gas to the turbine being constituted by a first cylindrical pipe coated on the outside with an annular layer (104) of thermal insulation and the means for recovering the expanded gas in the turbine being constituted by a second pipe coated on the outside with an annular layer (104) of thermal insulation.

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