Method and system for extracting a substance by means of anti-sublimation and melting

Abstract

The invention provides a method and a system for extracting a substance comprised in a gaseous mixture, the extraction being carried out in a cyclic manner in 2N chambers (AA, BB, CC, DD), each provided with a heat-exchanger (A, B, C, D), N being an integer greater than or equal to 3. Each chamber carries out a cycle comprising the following four steps in succession: a frosting step, a defrosting step, a step of recovering the liquid phase and the residual gas phase, and a temperature-reduction step of reducing the temperature of the heat-exchanger. Further, sequencing the passage from one step to another in each of the chambers is such that the number of chambers carrying out the frosting step and also the total number of chambers carrying out the defrosting, recovery, and temperature-reduction steps are both equal to N.

1 . A method of extracting a substance comprised in a gaseous mixture, in an extraction system comprising:
 a first supply circuit for supplying a refrigerant fluid for frosting or a coolant fluid;   a second supply circuit for supplying a refrigerant fluid for defrosting or a heat-transfer fluid;   a third supply circuit for supplying a gaseous mixture; and   2N chambers, N being an integer greater than or equal to three;   each chamber comprising:   a heat-exchanger that can be alternately connected to said first supply circuit via a first pair of valves, and to said second supply circuit via a second pair of valves;   a third pair of valves connecting an inlet and an outlet of the chamber to the third supply circuit, the third pair of valves being capable of controlling movement of the gaseous mixture over the heat-exchanger inside the chamber; and   an evacuation valve to evacuate a residual gas phase or a liquid associated with its gas phase that might accumulate in said chamber;   the treatment of the gaseous mixture in each of the chambers comprising, in a cyclic manner, the following steps in succession:   a frosting step (FS), carried out at a first heat-exchanger temperature at a first chamber pressure, allowing the substance to pass directly from the gaseous state to the solid state, thereby forming a solid deposit of the substance on the heat-exchanger, said first and the third pairs of valves being closed at the end of said frosting step;   a defrosting step (DS), comprising closing the chamber and allowing the solid deposit to pass directly into the gaseous state then allowing the solid deposit to pass directly into the liquid state when the temperature of the heat-exchanger and the pressure in the chamber become respectively higher than the temperature and the pressure of the triple point of the substance, thereby accumulating the liquid phase of the substance in the chamber, the second pair of valves being closed at the end of the defrosting step;   a recovery step (RS), comprising opening said evacuation valve so as both to allow the liquid phase and the residual gas phase that have accumulated in the chamber to be extracted, and also, simultaneously to reduce the pressure in the chamber so that it returns to substantially said first pressure; and   a step (TS) for reducing the temperature of the heat-exchanger, comprising opening said first pair of valves so that the temperature of the heat-exchanger returns to substantially the first temperature;   the method further comprising a general sequencing step aimed at sequencing the passage from one step to another in each of the chambers such that the number of chambers undergoing the frosting step and also the total number of chambers undergoing the defrosting, recovery, and temperature-reduction steps are both equal to N, wherein, after a first cycle, the following two conditions are satisfied throughout said method;   each of said frosting, defrosting, recovery, and temperature-reduction steps is carried out in at least one of said chambers; and   each of the chambers carries out one of said steps as dictated by the sequencing step.   
     
     
         2 . The method as claimed in  claim 1 , wherein said frosting step comprises a sub-step (VSS) for placing the chamber under vacuum after closing said first and third pairs of valves. 
     
     
         3 . The method as claimed in  claim 1  wherein after a first cycle, the number of chambers carrying out the defrosting step is equal to N/2 if N is equal to a power of two. 
     
     
         4 . The method as claimed in  claim 1  wherein after a first cycle, the number of chambers carrying out the defrosting step is equal to (N/2)−1 if N is even and is not equal to a power of two. 
     
     
         5 . The method as claimed in  claim 1 , wherein after a first cycle, the number of chambers carrying out the defrosting step is equal to (N−1)/2 if N is odd. 
     
     
         6 . The method as claimed in  claim 1 , wherein the duration of said frosting step is substantially equal to the cumulative duration of said defrosting, recovery, and temperature-reduction steps. 
     
     
         7 . The method as claimed in  claim 6 , wherein the extraction method further comprises a preliminary step (EX) for determining the duration of the frosting step, the duration of the frosting step being determined from a measurement of the maximum pressure drop between the inlet and the outlet of the chamber during a frosting step. 
     
     
         8 . A computer program comprising instructions for executing the steps of an extraction method as claimed in  claim 1 , when said program is executed by a computer. 
     
     
         9 . A computer-readable recording support on which a computer program comprising instructions for executing the steps of the extraction method as claimed in  claim 1  is recorded. 
     
     
         10 . A system for extracting a substance comprised in a gaseous mixture, the extraction system comprising:
 a first supply circuit for supplying a refrigerant fluid for frosting or a coolant fluid;   a second supply circuit for supplying a refrigerant fluid for defrosting or a heat-transfer fluid;   a third supply circuit for supplying a gaseous mixture; and   2N chambers, N being an integer greater than or equal to three;   each chamber comprising:   a heat-exchanger that is capable of being connected both to said first supply circuit via a first pair of valves and also to said second supply circuit via a second pair of valves;   a third pair of valves connecting an inlet and an outlet of the chamber to said third supply circuit, said third pair of valves being capable of controlling movement of said gaseous mixture over the heat-exchanger inside the chamber; and   an evacuation valve to evacuate a residual gas phase or a liquid associated with its gas phase that might accumulate in the chamber;   the extraction system further comprising control means to control the opening and closing of each of said valves in order to carry out an extraction method comprising, in a cyclic manner, the following steps in succession:   a frosting step (FS), carried out at a first heat-exchanger temperature at a first chamber pressure, allowing the substance to pass directly from the gaseous state to the solid state, thereby forming a solid deposit of the substance on the heat-exchanger, said first and third pairs of valves being closed at the end of said frosting step;   a defrosting step (DS), comprising closing the chamber and allowing said solid deposit to pass directly into the gaseous state then allowing said solid deposit to pass directly into the liquid state when the temperature of the heat-exchanger and the pressure in the chamber become respectively higher than the temperature and the pressure of the triple point of the substance, thereby accumulating the liquid phase of the substance in the chamber, said second pair of valves being closed at the end of said defrosting step;   a recovery step (RS), comprising opening said evacuation valve so as both to allow said liquid phase and the residual gas phase that have accumulated in the chamber to be extracted, and also, simultaneously to reduce the pressure in the chamber so that it returns to substantially said first pressure; and   a temperature-reduction step of reducing the temperature of the heat-exchanger (TS), comprising opening said first pair of valves so that the temperature of the heat-exchanger returns to substantially said first temperature;   said control means being configured such that each heat-exchanger is alternately connected to said first and second supply circuits;   said control means also being configured to sequence passage from one step to another in each of the chambers such that the number of chambers carrying out the frosting step and also the total number of chambers carrying out the defrosting, recovery, and temperature-reduction steps are both equal to N; and   wherein which the control means are also configured such that, after a first cycle, the following two conditions are satisfied throughout said method:   each of said steps of frosting, defrosting, recovery and temperature reduction is carried out in at least one of said chambers; and   each of said chambers carries out one of said steps as dictated by said sequencing step.   
     
     
         11 . A method according to  claim 10 , wherein said control means are also configured such that said frosting step comprises a sub-step (VSS) for placing the chamber under vacuum after said closure of the first and third pairs of valves. 
     
     
         12 . An extraction system as claimed in  claim 10 , wherein, after a first cycle, the number of chambers carrying out the defrosting step is equal to N/2 if N is equal to a power of two. 
     
     
         13 . An extraction system as claimed in  claim 10 , wherein, after a first cycle, the number of chambers carrying out the defrosting step is equal to (N/2)−1 if N is even and is not equal to a power of two. 
     
     
         14 . An extraction system as claimed in  claim 10 , wherein, after a first cycle, the number of chambers carrying out the defrosting step is equal to (N−1)/2 if N is odd. 
     
     
         15 . An extraction system as claimed in  claim 10 , wherein the duration of said frosting step is substantially equal to the cumulative duration of said defrosting, recovery, and temperature-reduction steps. 
     
     
         16 . An extraction system as claimed in  claim 10 , the extraction method further comprising a preliminary step (EX) for determining the duration of the frosting step, the duration of the frosting step being determined from a measurement of a maximum pressure drop between the inlet and the outlet of the chamber during a frosting step.