Method and Device for Recovering Carbon Dioxide from Fumes

1 . A method of capturing the carbon dioxide present in flue-gas, the method comprising the following steps:

a) first cooling of the flue-gas in order to eliminate a fraction of the water present therein by condensation;

b) dehydrating the flue-gas in order to eliminate the residual water;

c) second cooling of the flue-gas by heat exchange so as to bring them to a temperature such that carbon dioxide passes directly from the gaseous state to the solid state by anti-sublimation;

d) after removing the flue-gas, heating the solidified carbon dioxide in a closed enclosure up to the triple point where a liquid phase appears; and

e) drawing off or pumping out the liquid and/or gaseous carbon dioxide to a thermally insulated tank;

the method being characterized in that a fraction of the recovered liquid carbon dioxide is recycled, and after expanding to atmospheric pressure, is reinjected during the second cooling step in continuous or intermittent manner in order to be mixed with the flue-gas previously delivered by the dehydration step.

2 . A method according to claim 1 , characterized in that the fraction of the recovered liquid carbon dioxide that is recycled is reinjected during the second cooling step in the form of fine solid particles.

3 . A method according to claim 1 , characterized in that the fraction of the recovered liquid carbon dioxide that is recycled is injected during the second cooling step into the inside of a heat exchanger.

4 . A method according to claim 1 , characterized in that it further comprises a step of pre-cooling the flue-gas prior to said first cooling step, the pre-cooling step being performed by exchanging heat with at least one of the fluids comprising the liquid water recovered during the first cooling step and the flue-gas dehydration step, and the non-condensable compounds from the flue-gas that are recovered after said second cooling step.

5 . A method according to claim 1 , characterized in that the first cooling of the flue-gas, the dehydration of the flue-gas, and the second cooling of the flue-gas make use of heat exchange with the flue-gas via cooling loops operating by heat exchange with the liquefied natural gas that is present in a methane terminal for regassification, and that is used as a cold source.

6 . A method according to claim 5 , characterized in that the first cooling of the flue-gas and the dehydration of the flue-gas are performed by exchanging heat with the flue-gas via at least one cooling loop making use of glycol-containing water.

7 . A method according to claim 5 , characterized in that the second cooling of flue-gas makes use of heat exchange with the flue-gas via at least one cooling loop making use of methane or of nitrogen.

8 . A method according to claim 7 , characterized in that the second cooling of flue-gas makes use of heat exchange with the flue-gas via at least one additional cooling loop making use of ethylene or ethane.

9 . A method according to claim 1 , characterized in that the dehydration of flue-gas includes a step of exchanging heat with the non-condensable compounds from the flue-gas recovered after the second cooling step.

10 . A method according to claim 1 , characterized in that the step of dehydrating the flue-gas is performed discontinuously with alternation between a step of cooling the flue-gas to solidify water on the walls of a heat exchanger and a step of heating the solidified water in order to enable it to be recovered in liquid form.

11 . A method according to claim 10 , characterized in that the solidified water is heated by exchanging heat with the flue-gas prior to the flue-gas being cooled during the step of cooling flue-gas with water being solidified.

12 . A method according to claim 1 , characterized in that the second flue-gas cooling step for causing anti-sublimation of the carbon dioxide, and the solidified carbon dioxide heating step are performed discontinuously and in alternation.

13 . A method according to claim 12 , characterized in that the step of heating the solidified carbon dioxide to the triple point at which a liquid phase appears is performed by heat exchange with the flue-gas prior to the flue-gas being cooled during the second cooling step.

14 . A method according to claim 1 , characterized in that it further includes a step of recovering sulfur oxides contained in the flue-gas by anti-sublimation and reheating to the triple point where a liquid phase of sulfur oxides appears.

15 . A system for capturing carbon dioxide present in flue-gas, the system comprising:

a) first cooler means for cooling flue-gas and comprising at least one heat exchanger for eliminating a fraction of the water present in the flue-gas by condensation;

b) flue-gas dehydration means;

c) second cooler means for cooling flue-gas and comprising at least one heat exchanger for bringing the flue-gas to a temperature that causes anti-sublimation of the carbon dioxide present in the flue-gas;

d) heater means for heating the solidified carbon dioxide in a closed enclosure in order to cause it to melt; and

e) means for drawing off or pumping the liquid and/or gaseous carbon dioxide to a thermally insulated tank;

the system being characterized in that it further comprises expander means for expanding a fraction of the recovered liquid carbon dioxide to atmospheric pressure and for reinjecting said fraction of the carbon dioxide into the flue-gas at said second flue-gas cooler means.

16 . A system according to claim 15 , characterized in that it includes means for reinjecting said recovered fraction of the liquid carbon dioxide in the form of fine solid particles into the flue-gas.

17 . A system according to claim 15 , characterized in that the first cooler means comprise a heat exchanger between the flue-gas and at least one of the fluids comprising the liquid water recovered in the first cooler means or in the flue-gas dehydration means, and the non-condensable compounds of the flue-gas recovered at the inlet to the second cooler means.

18 . A system according to claim 15 , characterized in that it includes cooling loops using heat-transferring fluids flowing firstly in heat exchangers present in a methane terminal for exchanging heat with the liquefied natural gas subjected to a regassification process, and secondly in heat exchangers placed in at least one of the first cooler means, the dehydration means, and the second cooler means in order to exchange heat with the flue-gas, giving rise to capture of carbon dioxide.

19 . A system according to claim 18 , characterized in that it includes at least one cooling loop using glycol-containing water as its heat-transferring fluid and including at least one heat exchanger disposed in the first cooler means to the dehydration means.

20 . A system according to claim 18 , characterized in that it includes at least one cooling loop using methane or nitrogen as its heat-transferring fluid and including at least one heat exchanger disposed in the second cooler means.

21 . A system according to claim 20 , characterized in that it further includes at least one cooling loop using ethylene or ethane as its heat-transferring fluid and including at least one heat exchanger disposed in the second cooler means.

22 . A system according to claim 15 , characterized in that it includes means for recovering non-condensable compounds from the flue-gas at the outlet from the second cooler means, and means for exchanging heat with at least one of the flue-gas dehydration means.

23 . A system according to claim 15 , characterized in that the flue-gas dehydration means comprise at least first and second enclosures provided with heat exchangers and capable of receiving flue-gas discontinuously so that each of them can act in turn to cool flue-gas and solidify the water contained therein on the walls of the corresponding enclosure, and to heat the solidified water in order to enable it to be recovered in liquid form.

24 . A system according to claim 15 , characterized in that the second flue-gas cooler means and said heater means comprise at least first and second enclosures provided with heat exchangers and capable of receiving flue-gas discontinuously in such a manner that each of them in turn cools flue-gas with anti-sublimation of the carbon dioxide that is deposited on the walls of the corresponding enclosure, and heats the solidified carbon dioxide in order to cause it to melt.

25 . A system according to claim 15 , characterized in that it further comprises means for recovering sulfur oxides from said heater means in a closed enclosure.

26 . A method according to claim 2 , characterized in that

the fraction of the recovered liquid carbon dioxide that is recycled is injected during the second cooling step into the inside of a heat exchanger;

it further comprises a step of pre-cooling the flue-gas prior to said first cooling step, the pre-cooling step being performed by exchanging heat with at least one of the fluids comprising the liquid water recovered during the first cooling step and the flue-gas dehydration step, and the non-condensable compounds from the flue-gas that are recovered after said second cooling step;

the first cooling of the flue-gas, the dehydration of the flue-gas, and the second cooling of the flue-gas make use of heat exchange with the flue-gas via cooling loops operating by heat exchange with the liquefied natural gas that is present in a methane terminal for regassification, and that is used as a cold source;

the first cooling of the flue-gas and the dehydration of the flue-gas are performed by exchanging heat with the flue-gas via at least one cooling loop making use of glycol-containing water;

the second cooling of flue-gas makes use of heat exchange with the flue-gas via at least one cooling loop making use of methane or of nitrogen;

the second cooling of flue-gas makes use of heat exchange with the flue-gas via at least one additional cooling loop making use of ethylene or ethane;

the dehydration of flue-gas includes a step of exchanging heat with the non-condensable compounds from the flue-gas recovered after the second cooling step;

the step of dehydrating the flue-gas is performed discontinuously with alternation between a step of cooling the flue-gas to solidify water on the walls of a heat exchanger and a step of heating the solidified water in order to enable it to be recovered in liquid form;

the solidified water is heated by exchanging heat with the flue-gas prior to the flue-gas being cooled during the step of cooling flue-gas with water being solidified;

the second flue-gas cooling step for causing anti-sublimation of the carbon dioxide, and the solidified carbon dioxide heating step are performed discontinuously and in alternation;

the step of heating the solidified carbon dioxide to the triple point at which a liquid phase appears is performed by heat exchange with the flue-gas prior to the flue-gas being cooled during the second cooling step; and

it further includes a step of recovering sulfur oxides contained in the flue-gas by anti-sublimation and reheating to the triple point where a liquid phase of sulfur oxides appears.

27 . A system according to claim 16 , characterized in that

the first cooler means comprise a heat exchanger between the flue-gas and at least one of the fluids comprising the liquid water recovered in the first cooler means or in the flue-gas dehydration means, and the non-condensable compounds of the flue-gas recovered at the inlet to the second cooler means;

it includes cooling loops using heat-transferring fluids flowing firstly in heat exchangers present in a methane terminal for exchanging heat with the liquefied natural gas subjected to a regassification process, and secondly in heat exchangers placed in at least one of the first cooler means, the dehydration means, and the second cooler means in order to exchange heat with the flue-gas, giving rise to capture of carbon dioxide;

it includes at least one cooling loop using glycol-containing water as its heat-transferring fluid and including at least one heat exchanger disposed in the first cooler means to the dehydration means;

it includes at least one cooling loop using methane or nitrogen as its heat-transferring fluid and including at least one heat exchanger disposed in the second cooler means;

it further includes at least one cooling loop using ethylene or ethane as its heat-transferring fluid and including at least one heat exchanger disposed in the second cooler means;

it includes means for recovering non-condensable compounds from the flue-gas at the outlet from the second cooler means, and means for exchanging heat with at least one of the flue-gas dehydration means;

the flue-gas dehydration means comprise at least first and second enclosures provided with heat exchangers and capable of receiving flue-gas discontinuously so that each of them can act in turn to cool flue-gas and solidify the water contained therein on the walls of the corresponding enclosure, and to heat the solidified water in order to enable it to be recovered in liquid form;

the second flue-gas cooler means and said heater means comprise at least first and second enclosures provided with heat exchangers and capable of receiving flue-gas discontinuously in such a manner that each of them in turn cools flue-gas with anti-sublimation of the carbon dioxide that is deposited on the walls of the corresponding enclosure, and heats the solidified carbon dioxide in order to cause it to melt; and

it further comprises means for recovering sulfur oxides from said heater means in a closed enclosure.