COMPRESSION METHOD AND APPARATUS FOR AN APPARATUS FOR CAPTURING CO2 BY LOW-TEMPERATURE SEPARATION

Abstract

In a method for compressing a gas that is to be separated in a low-temperature CO.sub.2 separation unit using at least one partial condensation step and/or at least one distillation step, the gas that is to be separated has a variable composition and/or variable flow rate, the gas that is to be separated is compressed in a compressor to produce a compressed gas and the inlet pressure of the gas that is to be separated, entering the compressor, is modified according to the CO.sub.2 content and/or the flow rate of the gas that is to be separated so as to reduce the variations in volumetric flow rate of the gas that is to be separated entering the compressor.

Claims

1. A method for compressing a gas that is to be separated in a low-temperature CO.sub.2 separation unit using at least one partial condensation step and/or at least one distillation step, in which the gas that is to be separated has a variable composition and/or variable flow rate, the method comprising the steps of: compressing the gas that is to be separated in a compressor to produce a compressed gas; modifying the inlet pressure of the gas that is to be separated, when entering the compressor, according to a measured value selected from the group consisting of the CO.sub.2 content of the gas that is to be separated, the flow rate of the gas that is to be separated, and combinations thereof, thereby reducing the variations in volumetric flow rate of the gas that is to be separated entering the compressor.

2. The method according to claim 1, wherein if the CO.sub.2 content of the gas that is to be separated drops and/or the flow rate of the gas that is to be separated increases, the pressure of the gas that is to be separated, at the inlet to the compressor, is increased.

3. The method according to claim 1, wherein the volumetric flow rate of the flow of gas that is to be separated entering the compressor is substantially constant.

4. The method according to claim 1, wherein the gas that is to be separated is pressurized upstream of the compressor by means of at least one fan which produces a variable-pressure flow rate.

5. The method according to claim 1, wherein the composition of the flow compressed in the fan is not modified between the fan and the compressor.

6. The method according to claim 1, wherein the flow compressed in the fan is separated between the fan and the compressor to clean it of NOx and/or of SOx and/or of dust.

7. The method according to claim 1, wherein the fan is made up of two fan blowers connected in parallel or of a single fan blower.

8. The method according to claim 1, wherein the fan has a compression ratio of less than 2.

9. The method according to claim 1, wherein the gas that is to be separated contains at least 35 dry mol % CO.sub.2.

10. The method according to claim 1, further comprising the steps of: cooling the compressed gas in a heat exchanger to form a cooled gas; separating the cooled gas by at least one partial condensation step and/or at least one distillation step to produce a CO.sub.2-rich flow; and heating a fluid resulting from the partial condensation and/or distillation in the heat exchanger.

11. The method according to claim 10, wherein the fluid is a liquid, rich in CO.sub.2, which vaporizes in the heat exchanger.

12. An apparatus for compressing a gas that is to be separated in a low-temperature CO.sub.2 separation unit using at least one partial condensation step and/or at least one distillation step, in which the gas that is to be separated has a variable composition and/or variable flow rate, comprising a compressor for compressing the gas that is to be separated to produce a compressed gas; and means for modifying the inlet pressure of the gas that is to be separated, entering the compressor, according to the CO.sub.2 content and/or the flow rate of the gas that is to be separated so as to reduce the variations in volumetric flow rate of the gas that is to be separated entering the compressor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawing(s). It is to be noted, however, that the drawing(s) 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.

[0040] The FIGURE shows an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0041] Certain embodiments of the invention will be described in greater detail with reference to the FIGURE.

[0042] The gas that is to be separated is generated by an energy generation unit (but could for example come from a cement works), which may for example comprise an oxycombustion unit followed by a series of units for scrubbing the CO.sub.2-rich gas of NOx and/or of SOx and/or of dust. The generation unit 1 produces a gas 3 containing at least 50 dry mol % carbon dioxide, as well as other gases that may be hydrogen, carbon monoxide, oxygen, nitrogen and argon. Depending on the fuel used for the oxycombustion, the composition and therefore in general the flow rate of this gas 3 may vary. This gas 3 is compressed by a fan 5 having a compression ratio of at most 2 to produce a gas 7 at a pressure slightly above atmospheric pressure. At least a proportion of the gas 7 is compressed by a compressor 9. The other proportion (gas 10) may be recirculated to the generation unit 1 when the fan is used for drawing the flue gases (ID fan). The gas 11 produced by the compressor 9 is cooled in a heat exchanger then sent to a separation unit using partial condensation and/or distillation to produce at least one CO.sub.2-rich fluid. At least one fluid produced by the partial condensation and/or distillation heats up or even vaporizes in the heat exchanger.

[0043] If the CO.sub.2 content of the gas 11 drops at the inlet to the separation unit 13, that means that the CO.sub.2 in the gas 3 is diluted with incondensable gases and therefore that the flow rate of the gas 11 entering the CPU increases. In that case, the pressure at the outlet of the fan 5 needs to be increased in order to decrease the volumetric flow rate at the inlet to the compressor 9.

[0044] Likewise, if the CO.sub.2 content of the gas 11 increases at the inlet to the separation unit 13, that means that the CO.sub.2 in the gas 3 is less diluted by incondensable gases and therefore that the flow rate of the gas 11 entering the CPU drops. In this case, the pressure at the outlet of the fan 5 needs to be reduced in order to increase the volumetric flow rate at the inlet to the compressor 9.

[0045] In the example, the pressure at the inlet to the compressor 9 is regulated according to the flow rate 11 measured by the flow meter 8 for the gas 7 and/or of the flow meter 15 for the gas 11 is used. This pressure is varied by modifying the compression ratio of the fan 5.

[0046] Thus, if the flow rate 7 is 110 000 m.sup.3/h, the pressure at the inlet to the compressor 9 will be 1.17 bar, whereas if the flow rate 7 increases to 136 000 m.sup.3/h, the pressure at the inlet to the compressor 9 will be just 1.01 bar. In the former instance, the flow rate 7 will be 127 000 m.sup.3/h and in the latter, 126 500 m.sup.3/h.

[0047] Thus, for a volumetric flow rate 7 that increases by 24%, the volumetric flow rate 7 drops by less than one percent and therefore remains substantially constant.

[0048] It will be appreciated that, between the point at which the flow 10 is bled off and the compressor 9, the gas coming from the fan 5 may be cleaned in different ways, for example to remove NOx and/or SOx.

[0049] Otherwise, the fan may be a fan 5 all of the compressed gas from which is sent to the compressor 9. In that case, the flow 10 does not exist and the flow 7 is not cleaned between the fan 5 and the compressor 9.

[0050] 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.

[0051] The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

[0052] “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.

[0053] “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.

[0054] 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.

[0055] 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.

[0056] 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.