Method and unit for removing carbon monoxide from a gas flow comprising CO2 and recovering energy from a flow leaving said unit

Abstract

The invention relates to a unit for the purification of a gas flow comprising CO and at least 45% CO2 and a method of operating said unit. In one embodiment, said unit contains a first compressor, a heat exchanger configured to cool the compressed gas flow, a separation chamber configured to separate head gas produced in the heat exchanger, a heater disposed on the line of the head gas originating from the separation chamber, a catalytic oxidation unit for oxidizing the compressed CO in the gas flow originating from the heater, and turbines placed downstream of the catalytic oxidation unit.

Claims

1. A process for purifying a feed gas stream comprising CO and at least 45% CO.sub.2, the process comprising the steps of: a′) providing a purification plant comprising: (i) a first compressor configured to compress the gas stream; (ii) a heat exchanger configured to cool the compressed gas stream; (iii) a separator pot configured to separate an overhead gas produced in the heat exchanger; (iv) a heater placed in a line of the overhead gas resulting from the separator pot; (v) a catalytic oxidation unit configured to oxidize the compressed CO in the gas stream resulting from the heater; and (vi) turbines disposed downstream of the catalytic oxidation unit, wherein said plant further comprises a membrane separation unit configured to recover the CO.sub.2 produced by the catalytic oxidation unit and the separator pot, wherein the turbines are disposed in the line of a residual gas resulting from the membrane separation unit, wherein said plant further comprises a second heat exchanger configured to use the heat at the outlet of the catalytic oxidation unit to preheat the gas stream entering the catalytic oxidation unit, thereby cooling the gas stream leaving the catalytic oxidation unit, wherein said plant further comprises a second heater between the membrane and the turbines a) separating the feed gas stream in at least one separator pot; b) heating the overhead gas resulting from the separator pot within the heater to a temperature within the range of 90° C. to 140° C.; c) catalytically oxidizing the gas stream heated in step b) in the presence of oxygen at a temperature between 90° C. and 200° C.; d) recovering the energy linked to the pressure and to the temperature of the gas stream recovered downstream of the catalytic oxidation unit using the turbines, wherein the temperature of the gas stream recovered is between 50° C. to 200° C. prior to expansion in the turbines.

2. The purification process as claimed in claim 1, wherein said process further comprises, between the steps c) and d), a step of recovering the CO.sub.2 produced in the catalytic oxidation step c2) by means of the membrane separation unit at a temperature between 25° C. and −50° C.

3. The process as claimed in claim 1, wherein the feed gas stream comprises oxygen and this oxygen is used in the catalytic oxidation step c).

4. The process as claimed in claim 1, wherein the concentration of CO in said feed gas stream is less than 1%.

5. The process as claimed in claim 1, wherein the concentration of CO in said feed gas stream is less than 0.1%.

6. The process as claimed in claim 1, wherein the concentration of CO.sub.2 in said feed gas stream is greater than 70%.

7. The process as claimed in claim 1, wherein the catalytic oxidation step c) is carried out at a pressure of between 5 and 50 bar.

8. The process as claimed in claim 1, wherein the feed gas stream is a stream of oxy-fuel combustion flue gases.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.

(2) FIG. 1 shows an embodiment of the invention.

(3) FIG. 2 shows an embodiment of the invention.

(4) FIG. 3 shows an embodiment of the invention.

DETAILED DESCRIPTION

(5) The invention will now be described in detail with the aid of FIGS. 1 to 3.

(6) Let it be noted that in each the figures, the separator pot or pots are not represented. The gas stream 1 will be considered to be the stream leaving the separator pot or pots. FIG. 1 represents the simplest version of a plant according to the invention. Indeed, this plant comprises neither a membrane that makes it possible to recover the CO.sub.2 generated by the last catalytic oxidation, nor a heat exchanger. The gas stream 1 leaving the separator pot or pots is heated to a temperature of between 90° C. and 140° C. in a heater 2, then is introduced into the catalytic oxidation unit 3 between 5 and 50 bar. The oxidant used in this catalytic oxidation unit 3 is the oxygen initially included in the feed gas stream and/or oxygen originating from an outside source. This catalytic oxidation unit 3 makes it possible to obtain a CO concentration of the order of 100 ppm. Thus recovered at the outlet of the catalytic oxidation unit is a gas stream that is depleted in CO and slightly enriched in CO.sub.2, at a pressure between 5 and 50 bar. This CO.sub.2-enriched stream is then cooled in a coolant 4 to a temperature of between 50° C. and 200° C. before being sent to the turbines 5 in order to recover the pressure energy from the gas stream. The energy recovered will depend on the degree of expansion in the turbine(s), on the inlet temperature and on the efficiency of the turbines. The temperature at the outlet is between −60° C. and 100° C.

(7) FIG. 2 represents the version of a plant according to the invention comprising a heat exchanger 6 that makes it possible to use the heat at the outlet of the catalytic oxidation unit to preheat the gas stream entering the catalytic oxidation unit and thus to cool the gas stream leaving the catalytic oxidation unit. The gas stream 1 leaving the separator pot or pots is heated to a temperature of between 90° C. and 140° C. partly by means of the heat exchanger 6 and partly by means of a heater 2. Since the catalytic reaction is exothermic, a portion of the heat will be generated by the catalytic oxidation unit. If the CO content is high, this production of heat may be sufficient to be able to avoid the use of the heater 2. The gas stream is then introduced into the catalytic oxidation unit 3 between 5 and 50 bar. The oxidant used in this catalytic oxidation unit 3 is the oxygen initially included in the feed gas stream and/or oxygen originating from an outside source. This catalytic oxidation unit 3 makes it possible to obtain a CO concentration of the order of 100 ppm. Thus recovered at the outlet of the catalytic oxidation unit is a gas stream that is depleted in CO and slightly enriched in CO.sub.2, at a pressure between 5 and 50 bar. This CO.sub.2-enriched stream is then cooled by virtue of the heat exchanger 6 to a temperature of between −50° C. and 25° C. Indeed, a portion of the heat from the outgoing stream makes it possible to heat, by means of the heat exchanger 6, the stream entering the catalytic oxidation unit. This operation makes it possible in fact, by means of the heat exchanger 6, to simultaneously cool the gas stream leaving the catalytic oxidation unit. The stream thus cooled is brought into contact with the membrane 7 which will make it possible to recover the CO.sub.2 generated by the catalytic oxidation unit 3. Indeed, recovered at the outlet of the membrane 7 are a CO.sub.2-enriched gas stream 8 and a residual gas stream 9 at a pressure of between 5 and 50 bar. This residual stream 9 is then heated in a heater 10 to a temperature of between 50° C. and 200° C. before being sent to the turbines 5 in order to recover the pressure energy from the gas stream.

(8) FIG. 3 represents the version of a plant according to the invention comprising a heat exchanger 6 that makes it possible to use the heat at the outlet of the catalytic oxidation unit to heat the residual gas resulting from the membrane and thus to cool the gas stream leaving the catalytic oxidation unit. The gas stream 1 leaving the separator pot or pots is heated to a temperature of between 90° C. and 140° C. in a heater 2 then is introduced into the catalytic oxidation unit 3 between 5 and 50 bar. The oxidant used in this catalytic oxidation unit 3 is the oxygen initially included in the feed gas stream and/or oxygen originating from an outside source. This catalytic oxidation unit 3 makes it possible to obtain a CO concentration of the order of 100 ppm. Thus recovered at the outlet of the catalytic oxidation unit is a gas stream that is depleted in CO and slightly enriched in CO.sub.2, at a pressure between 5 and 50 bar. This CO.sub.2-enriched stream is then cooled to a temperature of between −40° C. and 25° C. partly by virtue of the heat exchanger 6 and of a coolant 4. The stream thus cooled is brought into contact with the membrane 7 which will make it possible to recover the CO.sub.2 generated by the catalytic oxidation unit 3. Indeed, recovered at the outlet of the membrane 7 are a CO.sub.2-enriched gas stream 8 and a residual gas stream 9 at a pressure of between 5 and 50 bar. This residual stream 9 is then heated to a temperature of between 90° C. and 200° C. by virtue of the heat exchanger 6. Indeed, a portion of the heat from the stream leaving the catalytic oxidation unit makes it possible to heat, by means of the heat exchanger, the residual stream 9. This operation makes it possible in fact, by means of the heat exchanger, to simultaneously cool the gas stream leaving the catalytic oxidation unit. In this configuration, the temperature of the gas at the outlet of the catalytic oxidation unit will be between 140° C. and 150° C. for CO contents of between 600 and 800 ppm at the inlet of the first separator pot and an inlet temperature of the catalytic oxidation unit of between 125° C. and 145° C. The residual stream 9 thus heated is sent to the turbines 5 in order to recover the pressure energy from the gas stream.

(9) 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.

(10) The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

(11) “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.

(12) “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.

(13) 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.

(14) 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.

(15) All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.