PURIFICATION OF CARBON MONOXIDE BY CRYOGENIC DISTILLATION

Abstract

In a process for the separation of a flow containing at least 97% mol of carbon monoxide containing at least one lighter compound and at least one heavier compound, the flow is separated in a column and a column, one of the columns being a denitrogenation column and the other a column for purification in argon, in order to form a flow very rich in carbon monoxide.

Claims

1. A process for the purification of a first feed flow comprising at least 97% mol of carbon monoxide, a lighter component, and a heavier component, the process comprising the steps of: a) cooling the first feed flow thereby producing a cooled feed flow, and then sending the cooled feed flow to a first column operating at less than 5 bar, wherein the cooled feed flow is separated by distillation to form a top gas, which is enriched in the lighter component, and a bottom liquid, which is enriched in the heavier component; b) at least partially vaporizing at least a part of the bottom liquid by (1) indirect heat exchange with the first feed flow thereby cooling the first feed flow according to step a) and (2) at least one electrical heater, and then sending at least a part of the at least partially vaporized liquid to the first column, c) sending a second feed flow from the first column to an intermediate level of a second column, wherein the second feed flow comprises: i. at least a part of the vaporized bottom liquid or ii. at least a part of a gas withdrawn at the top of the first column, d) separating the second feed flow in the second column to form a top gas of the second column and a bottom fluid of the second column; wherein: e(i) if the second feed flow comprises the at least a part of the vaporized bottom liquid, a liquid enriched in the heavier component is withdrawn at the bottom of the second column and a gaseous product is withdrawn at the top of the second column, or e(ii) if the second feed flow comprises the at least a part of a gas withdrawn at the top of the first column, a gaseous product is withdrawn at the bottom of the second column and a gaseous product enriched in the lighter component is withdrawn at the top of the second column; and wherein the gaseous product contains at least 99% mol of carbon monoxide and less nitrogen and argon than the first feed flow, and the ratio of the flow rate of gaseous product to the flow rate of vaporized bottom liquid of stage ii) being between 8 mol % and 25 mol %.

2. The process according to claim 1, wherein the gaseous product of the second column contains at least 99.99% mol of carbon monoxide.

3. The process according to claim 1, wherein the first feed flow contains at least 99% mol of carbon monoxide.

4. The process according to claim 1, wherein the gaseous product contains less than 2 ppm of nitrogen.

5. The process according to claim 1, wherein the gaseous product contains less than 2 ppm of argon.

6. The process according to claim 1, wherein the bottom liquid flow is withdrawn from the column and sent to a reboiler, where the bottom liquid flow is partially vaporized by the first feed flow and the at least one electrical heater.

6. cess according to claim 6, wherein a liquid flow is withdrawn from the reboiler.

8. The process according to claim 1, wherein the feed flow is reduced in pressure upstream of the first column.

9. The process according to claim 1, wherein the first feed flow is at least partially condensed by heat exchange with the bottom liquid.

10. The process according to claim 1, wherein the at least one electrical heater is used to contribute at least 55% of the heat necessary to vaporize the at least a part of the bottom liquid.

11. The process according to claim 1, wherein the pressure difference between the first and the second columns is less than 2 bar.

12. The process according to claim 1, wherein a top condenser of the second column is cooled by a refrigerant originating from an external source.

13. The process according to claim 1, wherein the feed flow is purified in water and/or in carbon dioxide upstream of the first column.

14. An apparatus for the purification of a first feed flow containing at least 97% mol of carbon monoxide containing at least one lighter component and at least one heavier component, the apparatus comprising: a first column and a second column; means for cooling the first feed flow in order to produce a cooled feed flow; means for sending the cooled feed flow to the first column in order to be separated by distillation to form the top gas enriched in the lighter component and a bottom liquid enriched in the heavier component; wherein the means for cooling the first feed flow is configured to provide an indirect heat exchange between the first feed flow and at least a part of the bottom liquid which is at least partially vaporized; at least one electrical heater configured to heat the at least a part of the bottom liquid; means for sending at least a part of the at least partially vaporized liquid to the first column; means for sending a second feed flow from the first column to an intermediate level of the second column; wherein the second feed flow consists of: at least a part of the vaporized bottom liquid, or at least a part of a gas withdrawn at the top of the first column, wherein the second column is configured to separate the second feed flow in order to form a top gas of the column and a bottom fluid of the second column; and wherein: a) if the second feed flow consists of the at least a part of the vaporized bottom liquid, the apparatus comprises means for withdrawing a liquid enriched in the heavier component at the bottom of the second column and means for withdrawing a gaseous product at the top of the second column; or b) if the second feed flow consists of the at least a part of a gas withdrawn at the top of the first column, the apparatus comprises means for withdrawing a gaseous product at the bottom of the second column and means for withdrawing a gaseous product enriched in the lighter component at the top of the second column, wherein the gaseous product contains at least 99% mol of carbon monoxide and reduced amounts of the lighter component and of the heavier component as compared to the first feed flow.

15. The apparatus according to claim 14, comprising a reboiler outside any column containing the means for cooling the first flow and the at least one electrical heater, and means for sending the bottom liquid to the reboiler.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0108] Further features and advantages of the invention will become apparent from the description hereinafter of embodiments, which are given by way of illustration but without any limitation, the description being given in relation with the following attached figures:

[0109] [FIG. 1] illustrates a process according to the invention.

[0110] [FIG. 2] illustrates a process according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0111] The apparatus of [FIG. 1] comprises a first distillation column K1 operating at a first pressure and a second column K2 operating at a second pressure lower than the first pressure. The first pressure is preferably less than 5 bar abs; for example, the first pressure can be 3.5 bar abs and the second pressure 1.8 bar abs. The first column is at a temperature between 92 and 93K and the second column between 87 and 88K.

[0112] The first and second columns K1, K2 comprise structured packings in order to promote the exchange of mass and of heat in the column, thus making possible the distillation.

[0113] The first column K1 is used to remove the nitrogen and the second K2 the argon in a flow 1 containing at least 97% mol of carbon monoxide.

[0114] The second column K2 comprises, at the bottom, a first reboiler C connected in order to condense a top gas of the first column K1 and in order to heat a bottom liquid of the second column and, at the top, a condenser E2. The condenser E2 is cooled by a flow of liquid nitrogen 11 originating from a storage tank S which transfers heat indirectly at the top of the column, thus vaporizing the liquid nitrogen.

[0115] The feed flow can be provided from a gas storage tank or a lorry transporting gas cylinders containing relatively impure carbon monoxide. This gas is reduced in pressure in order to arrive at a pressure of 7 bar abs and subsequently is sent as flow 1 to the heat exchanger E1 of a second reboiler R. This bottom reboiler R is used to feed the bottom of the first column K1 with vapour and to provide the feed gas to the second column K2. It is positioned beside the column K1 in order to reduce the total height of the combined columns K1, K2 but can be incorporated in the column K1.

[0116] The gas 1 can contain at least 97% of carbon monoxide (or at least 99% of carbon monoxide) and also argon and nitrogen. It can also contain oxygen and/or methane and/or hydrogen.

[0117] If it contains water and/or carbon dioxide, these impurities are removed by adsorption or by deposition as described in WO18111719 upstream of the reboiler R.

[0118] The gas 1 enters the heat exchanger El at a temperature close to ambient temperature and with a flow rate of approximately 50 Nm.sup.3/h. It is condensed in E1, reduced in pressure down to 3.8 bar in the valve 4 and sent to an intermediate level of the first column in a two-phase form. It is separated by distillation and, at the bottom of the column, there is found a bottom liquid depleted in nitrogen which is sent, at least in part, as flow 3 to the reboiler R, where it is vaporized. Since the feed gas 1 is not sufficient to vaporize the flow 3, at least one electrical heater 21 also provides heat. Generally, two thirds of the vaporization heat are provided in this way.

[0119] The vaporized gas is divided into two, one part 5 being sent into the bottom of the first column K1 and the other part 7 being sent to an intermediate level of the second column K2 as sole feed flow.

[0120] A part 2 of the bottom liquid can be bled off.

[0121] A gas enriched in nitrogen 13 is withdrawn at the top of the first column K1.

[0122] A gas 9 is withdrawn at the top of the second column K2 containing at least 99.99% mol or at least 99.999% mol, indeed even at least 99.9999% mol, of carbon monoxide and the fluid 15 enriched in argon, which can be gaseous or liquid, is withdrawn at the bottom of the second column K2.

[0123] The flows 2, 13, 15 are sent to a scrubbing tower or another conversion or inerting plant because of their high content of carbon monoxide.

[0124] The product 9 can be heated by a heater, if the client desires it, to a higher temperature than that of the second column K2.

[0125] Liquid is not sent from the top of the first column K1 to the top of the second column K2.

[0126] No part of the bottom liquid from the first column K1 is sent in the liquid form to the second column K2.

[0127] The ratio of the production flow rate 9 to the boiling flow rate 5 plus 7 is between 8% and 25%.

[0128] The production flow rate is the flow rate of carbon monoxide 9 purified in argon and in nitrogen and the boiling flow rate is the amount of gas 5 plus 7 produced by the bottom reboiler of the lowest column of the double column used.

[0129] [FIG. 2] shows the alternative where the argon is removed in the first column K1 and the nitrogen in the second K2.

[0130] The apparatus of [FIG. 2] comprises a first distillation column K1 operating at a first pressure and a second column K2 operating at a second pressure lower than the first pressure. The first pressure is preferably less than 5 bar abs; for example, the first pressure can be 3.5 bar abs and the second pressure 1.8 bar abs. The first column is at a temperature between 92 and 93K and the second column between 87 and 88K.

[0131] The first and second columns K1, K2 comprise structured packings in order to promote the exchange of mass and of heat in the column, thus making possible the distillation.

[0132] The first column K1 is used to remove the argon and the second the nitrogen.

[0133] The second column K2 comprises, at the bottom, a first reboiler C connected in order to condense a top gas of the first column K1 and to feed the bottom of the second column with vapour and, at the top, a condenser E2. The condenser E2 is cooled by a flow of liquid nitrogen 11 originating from a storage tank S which transfers heat indirectly at the top of the column, thus vaporizing the liquid nitrogen to form a gas 19.

[0134] The feed flow can be provided from a gas storage tank or a lorry transporting gas cylinders containing relatively impure carbon monoxide. This gas is reduced in pressure by Joule-Thomson pressure reduction in order to arrive at a pressure of 7 bar abs and subsequently is sent as flow 1 to the heat exchanger E1 of a second reboiler R. This bottom reboiler R is used to provide gas to the bottom of the first column. It is positioned beside the column K1 in order to reduce the total height of the combined columns K1, K2 but can be incorporated in the column K1 .

[0135] The gas 1 can contain at least 97% of carbon monoxide (or at least 99% of carbon monoxide) and also argon and nitrogen. It can also contain oxygen and/or methane and/or hydrogen.

[0136] If it contains water and/or carbon dioxide, these impurities are removed by adsorption or by deposition, as in WO18111719, upstream of the reboiler R.

[0137] The gas 1 enters the heat exchanger El at a temperature close to ambient temperature and with a flow rate of approximately 50 Nm.sup.3/h. It is condensed in E1, reduced in pressure down to 3.8 bar in the valve 4 and sent to an intermediate level of the first column in a two-phase form. It is separated by distillation and, at the bottom of the column K1, there is found a bottom liquid enriched in argon which is sent, at least in part, as flow 3 to the reboiler R, where it is vaporized. Since the feed gas 1 is not sufficient to vaporize the flow 3, at least one electrical heater 21 provides heat. Generally, two thirds of the vaporization heat are provided in this way. For example, the electrical heater 21 can contribute between at least 55% and 85%, indeed even between at least 65% and 72%, of the heat necessary to vaporize the at least a part of the bottom liquid.

[0138] The vaporized gas 5 enriched in argon is sent into the bottom of the first column K1.

[0139] A liquid 2 withdrawn from the second reboiler R is bled off.

[0140] A gas depleted in argon 13 is withdrawn at the top of the first column K1, reduced in pressure in a valve and sent to an intermediate level of the column K2 as sole feed flow.

[0141] A gas 9 enriched in nitrogen is withdrawn at the top of the second column K2 and the gaseous product 15 depleted in nitrogen is withdrawn at the bottom of the second column K2 containing at least 99.99% mol or at least 99.999% mol, indeed even at least 99.9999% mol, of carbon monoxide. A liquid 14 makes it possible to bleed the bottom of the second column K2 when necessary.

[0142] The flows 2, 9, 14 are sent to a scrubbing or inerting tower because of their high content of carbon monoxide.

[0143] The product 15 can be heated by a heater, if the client desires it, to a higher temperature than that of the second column K2.

[0144] No part of the bottom liquid 3 enriched in argon is sent to the second column K2.

[0145] The ratio of the production flow rate to the boiling flow rate is between 8% and 25%.

[0146] The production flow rate is the flow rate of carbon monoxide 15 purified in argon and in nitrogen and the boiling flow rate is the amount of gas 5 produced by the bottom reboiler of the lowest column of the double column used.

[0147] In the examples, the lighter component is nitrogen and the heavier component is argon but other compositions are possible.

[0148] 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.

[0149] The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

[0150] “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.

[0151] “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.

[0152] 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.

[0153] 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.