Method and device for condensing a first fluid rich in carbon dioxide using a second fluid

Abstract

The present invention relates to a process and device for condensing a first fluid rich in carbon dioxide using a second fluid.

Claims

1. A process for condensing a first fluid using an ammonia refrigerant, wherein the first fluid is rich in carbon dioxide, the process comprising the steps of: expanding the ammonia refrigerant in an expander to form a two phase ammonia refrigerant; introducing the two phase ammonia refrigerant to a phase separator under conditions effective to separate the two phase ammonia refrigerant into a gaseous portion and a liquid portion; withdrawing the gaseous portion of the ammonia refrigerant from the phase separator; introducing the liquid portion of the ammonia refrigerant to a heat exchanger; exchanging heat between the liquid portion of the ammonia refrigerant and the first fluid in the heat exchanger under conditions effective to at least partially condense the first fluid and to fully vaporize the liquid portion of the ammonia refrigerant, thereby forming an at least partially condensed first fluid and a vaporized ammonia refrigerant, wherein the first fluid is rich in carbon dioxide; and mixing the vaporized ammonia refrigerant with the gaseous portion of the ammonia refrigerant outside of the phase separator to form a single phase mixture, wherein the first fluid originates at least partly from the top of a distillation column and the at least partially condensed first fluid is sent to the top of the distillation column, wherein the process further comprises an absence of a step selected from the group consisting of: cooling the vaporized ammonia refrigerant prior to the step of mixing the vaporized ammonia refrigerant with the gaseous portion of the ammonia refrigerant, compressing the vaporized ammonia refrigerant prior to the step of mixing the vaporized ammonia refrigerant with the gaseous portion of the ammonia refrigerant, and combinations thereof, wherein the phase separator is sized solely for separating the liquid portion of the ammonia refrigerant from the gaseous portion of the ammonia refrigerant, wherein the ratio between the total volume of the ammonia refrigerant in the phase separator and the flow rate of the ammonia refrigerant at the inlet to the phase separator is between 0.01 and 0.05 L.Math.h/Nm.sup.3, wherein the first fluid comprises a first gaseous fraction rich in carbon dioxide and a second gaseous fraction rich in carbon dioxide, wherein the first gaseous fraction rich in carbon dioxide originates from the top of the distillation column, wherein the second gaseous fraction rich in carbon dioxide does not originate from the distillation column, wherein the ratio between the capacity of the heat exchanger and the flow rate of the ammonia refrigerant at the inlet to the phase separator is between 0.13 and 0.55 kW.Math.h/Nm.sup.3, wherein the second gaseous fraction rich in carbon dioxide is at a superheated temperature in an amount effective to entirely superheat the resulting vaporized ammonia refrigerant prior to the vaporized ammonia refrigerant exiting an outlet of the heat exchanger.

2. The process of claim 1, wherein the ratio between the volume of the liquid portion of the ammonia refrigerant in the phase separator and the flow rate of the ammonia refrigerant at the inlet to the separator is between 0.005 and 0.03 L.Math.h/Nm.sup.3.

3. A process for condensing a first fluid using a refrigerant, wherein the first fluid is rich in carbon dioxide, and the refrigerant comprises a single refrigerant of ammonia, the process comprising the steps of: expanding the refrigerant in an expander to form a two phase refrigerant; introducing the two phase refrigerant to a phase separator under conditions effective to separate the two phase refrigerant into a gaseous portion and a liquid portion; introducing the gaseous portion of the refrigerant to a mixing zone; introducing the liquid portion of the refrigerant to a heat exchanger; introducing a first gaseous fraction rich in carbon dioxide into a first fluid mixing zone, wherein the first gaseous fraction originates from a top portion of a distillation column; introducing a second gaseous fraction into the first fluid mixing zone in the presence of the first gaseous fraction to form the first fluid, wherein the second gaseous fraction rich in carbon dioxide originates from a source not comprising the distillation column; introducing the first fluid from the first fluid mixing zone to the heat exchanger; exchanging heat between the liquid portion of the refrigerant and the first fluid in the heat exchanger under conditions effective to partially condense the first fluid and to fully vaporize the liquid portion of the refrigerant, thereby forming a partially condensed first fluid and a vaporized refrigerant; mixing the vaporized refrigerant with the gaseous portion of the refrigerant downstream of the phase separator to form a single phase mixture; separating the partially condensed first fluid into a liquid phase and a gaseous phase; introducing the liquid phase of the partially condensed first fluid from the heat exchanger into the top portion of the distillation column; and recovering the gaseous phase of the partially condensed first fluid, wherein the process further comprises an absence of a step selected from the group consisting of: cooling the vaporized refrigerant prior to the step of mixing the vaporized refrigerant with the gaseous portion of the refrigerant, compressing the vaporized refrigerant prior to the step of mixing the vaporized refrigerant with the gaseous portion of the refrigerant, and combinations thereof, wherein the ratio between the total volume of the liquid portion of the refrigerant in the phase separator and the flow rate of the liquid portion of the refrigerant at the inlet to the phase separator is between 0.005 and 0.03 L.Math.h/Nm.sup.3, wherein the phase separator is sized solely for separating the liquid portion of the two phase refrigerant from the gaseous portion of the two phase refrigerant generated by the expansion of the refrigerant, wherein the ratio between the capacity of the heat exchanger and the flow rate of the ammonia refrigerant at the inlet to the phase separator is between 0.13 and 0.55 kW.Math.h/Nm.sup.3, wherein the second gaseous fraction rich in carbon dioxide is at a superheated temperature in an amount effective to entirely superheat the resulting vaporized ammonia refrigerant prior to the vaporized ammonia refrigerant exiting an outlet of the heat exchanger.

4. The process of claim 3, wherein the first fluid mixing zone is disposed completely outside of the distillation column and the heat exchanger.

5. The process of claim 1, wherein the phase separator is configured to not receive the vaporized ammonia refrigerant directly from the outlet of the heat exchanger.

6. The process of claim 1, wherein the process comprises an absence of introducing any other fluid to the phase separator other than the ammonia refrigerant.

7. The process of claim 1, wherein the first gaseous fraction rich in carbon dioxide is at a first temperature that is colder than that of the second gaseous fraction rich in carbon dioxide, such that when the first gaseous fraction and the second gaseous fraction are mixed upstream of the heat exchanger, the first fluid has a temperature that is warmer than the first temperature.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Exemplary embodiments of the invention will now be described more precisely, but nonlimitingly, with regard to the appended drawings in which:

(2) FIG. 1 illustrates a process for condensing a fluid rich in carbon dioxide according to the invention;

(3) FIG. 2 illustrates the structure of a condensation device according to a first embodiment of the invention; and

(4) FIG. 3 illustrates the structure of a condensation device according to a second embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(5) In the remainder of the description, the first calorigenic fluid is carbon dioxide (CO.sub.2) and the second refrigerant fluid is assumed to be ammonia (NH.sub.3). The invention is not however limited to ammonia as the second fluid.

(6) FIG. 1 illustrates the structure and the operation of the device 2 using a thermosiphon.

(7) Ammonia is provided to the device 2 in liquid form, at a pressure above the pressure needed to condense carbon dioxide. Expansion means 4 are provided in order to expand the ammonia to the desired operating pressure. This gives rise to a partial vaporization of the ammonia.

(8) The two-phase ammonia thus obtained is supplied to the inlet of a separator pot 6. The separator pot 6 is configured in order to separate the ammonia phases and supplies, at a first outlet 8, liquid ammonia and, at a second outlet 10, gaseous ammonia.

(9) The gaseous ammonia obtained at the second outlet 10 is sent downstream to the remainder of the refrigerant loop, not represented.

(10) The liquid ammonia obtained at the outlet 8 is then supplied to a first inlet 12 of a heat exchanger 14.

(11) In the example from FIG. 1, the heat exchanger 14 is a dephlegmator used in combination with a carbon dioxide distillation column 16.

(12) The distillation column 16 supplies carbon dioxide in the vapor phase to a second inlet 18 of the heat exchanger 14.

(13) In the heat exchanger 14, the cooling of the carbon dioxide by the ammonia produces, at a first outlet 20, two-phase ammonia and, at a second outlet 22, carbon dioxide.

(14) The condensed, that is to say liquid, part of the carbon dioxide is supplied to the distillation column 16.

(15) The two-phase ammonia obtained at the outlet 20 is returned to the separator pot 6 in order to separate its liquid and vapor phases.

(16) The separator pot 6 of the prior art thus serves both as an inlet separator for separating the vapor generated by the expansion of the ammonia from the corresponding liquid phase and as an outlet separator for separating the vapor generated by the heat exchange in the exchanger 14 from the excess recirculating liquid ammonia.

(17) This dual role means using a separator pot of large size so that the amount of ammonia present in the device 2 is high, which is not desirable.

(18) FIG. 2 illustrates an improvement according to the invention of the device 2 from FIG. 1. For this purpose, FIG. 2 represents a device 200 for condensing carbon dioxide using ammonia.

(19) The ammonia is supplied to the device 200 in liquid form, at a pressure above the pressure needed to condense the carbon dioxide. Expansion means 204 are provided in order to expand the ammonia to the desired operating pressure. This gives rise to a partial vaporization of the ammonia. The flow rate of the resulting gaseous portion of ammonia constitutes a small fraction of the total flow rate of ammonia.

(20) The two-phase ammonia thus obtained is supplied to the inlet of a separator pot 206. The separator pot 206 is configured in order to separate the ammonia phases and supplies, at a first outlet 208, liquid ammonia and, at a second outlet 210, gaseous ammonia.

(21) According to one aspect of the invention, the separator pot 216 is sized solely in order to carry out the separation of the ammonia intended for the heat exchanger. The diameter of this pot 206 is greatly reduced with respect to the diameter of the pot 6 from FIG. 1, given that the flow rate of the resulting gaseous portion of ammonia constitutes a small fraction of the total flow rate of ammonia. Thus, the amount of ammonia stored in the pot 206 is very low with respect to the amount stored in the pot 6 from FIG. 1.

(22) The ratio between the total volume of ammonia in the separator pot 206 and the flow rate of ammonia at the inlet of the separator pot 206 is between 0.01 and 0.05 L.Math.h/Nm.sup.3, preferably between 0.012 and 0.047 L.Math.h/Nm.sup.3.

(23) The ratio between the volume of the liquid portion of ammonia in the separator pot 206 and the flow rate of ammonia at the inlet of the separator pot 206 is between 0.005 and 0.03 L.Math.h/Nm.sup.3, preferably between 0.006 and 0.0023 L.Math.h/Nm.sup.3.

(24) The liquid ammonia obtained at the outlet 208 is then supplied to a first inlet 212 of a heat exchanger 214.

(25) In the example from FIG. 2, the heat exchanger 214 is a dephlegmator used in combination with a carbon dioxide distillation column 216.

(26) The invention is not however limited to exchangers of this type, it being possible for the exchanger 214 to be, for example, a counter-current or cross-current cooler or condenser, etc.

(27) Owing to the sizing of the separator pot 206 according to the invention, the amount of liquid ammonia provided to the heat exchanger 214 is limited.

(28) The distillation column 216 provides carbon dioxide in the vapor phase to a second inlet 218 of the heat exchanger 14.

(29) In the heat exchanger 214, the cooling of the carbon dioxide by the ammonia, in a limited amount, produces, at a first outlet 220, entirely vaporized and exclusively superheated ammonia, at a second outlet 222 liquid carbon dioxide and at a third outlet 224 gaseous carbon dioxide.

(30) The condensed, that is to say liquid, part of the carbon dioxide is supplied to the distillation column 216.

(31) The superheated ammonia supplied at the outlet 220 is mixed with the gaseous ammonia produced at the outlet 210 of the separator pot 206 in mixing means 226 before being supplied, in overall superheated form, to the remainder of the refrigerant loop.

(32) Thus, the exchanger 214 has no outlet of the second fluid in liquid form.

(33) FIG. 3 illustrates an embodiment variant of the device 200 from FIG. 2 in the particular case where the heat exchanger 214 is a carbon dioxide liquefier.

(34) In the case of such a use, the ascending carbon dioxide vapor of the column 216 constitutes only one part of the carbon dioxide to be condensed, a significant fraction of this carbon dioxide originating from a purification part, not represented, at a temperature above the liquid/vapor equilibrium temperature of carbon dioxide.

(35) The latter superheated fraction of carbon dioxide is generally introduced at the top of the column (FIGS. 1 and 2). It then cools in contact with the reflux of liquid carbon dioxide originating from the condenser 214, to a temperature very close to the liquid-vapor equilibrium temperature. This desuperheating then generates, by evaporation of a part of the reflux, an additional flow of carbon dioxide vapor.

(36) In the device from FIG. 3, mixing means 230 are provided upstream of the exchanger 214 in order to mix the flow of carbon dioxide with the carbon dioxide vapor exiting the column 216, outside thereof and without contact with the liquid carbon dioxide condensed in the exchanger 214.

(37) The mixing of these two gaseous flows of carbon dioxide is again superheated at the inlet of the exchanger 214, which makes it possible to increase the superheating to vapor of the ammonia at the outlet of the exchanger 214.

(38) Thus, the exchanger 214 has no outlet of the second fluid in liquid form.

(39) It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.