COOLING METHOD USING A HEAT EXCHANGER AND SUCH A HEAT EXCHANGER

Description

Technical field of the invention

[0001] The invention belongs to the technical field of heat exchangers. The invention relates more specifically to a cooling method using a heat exchanger. In particular, the method uses carbon dioxide in the supercritical phase. The invention further relates to a heat exchanger. A method according to the preamble of claim 1 is known from document US 4,294,658 A. Technical background

[0002] Industrial heat exchangers are used in various industries.

[0003] In particular, the nuclear power generation industry uses heat exchangers. Heat exchangers used in nuclear power plants are subject to strict regulations specific to this sector of activity. These regulations are supplemented by specific technical requirements.

[0004] In the secondary circuit of a nuclear power plant, the water vapor, after passing through at least one turbine to produce electricity, is cooled in a condenser to obtain liquid water. The condenser uses an external cooling fluid, such as sea water or river water; this is the tertiary circuit.

[0005] In the event of a technical problem in the tertiary circuit, it is necessary to continue cooling the secondary circuit. Cooling of the secondary circuit is then handled by a backup circuit separate from the tertiary circuit.

[0006] This emergency circuit includes, among other things, a heat exchanger that must be able to be arranged in the reactor building. In other words, the exchanger must be able to be arranged in a confined space, and therefore have reduced dimensions, while still being able to cool the water vapor in the secondary circuit to reach an acceptable outlet setpoint temperature.

[0007] Reducing the dimensions of heat exchangers has an immediate impact on the performance of the heat exchanger. The applicant realized that by reducing the dimensions of the heat exchanger, the temperature difference between the cold fluid and the hot fluid was such that it induced mechanical stresses likely to damage the heat exchanger, rendering the emergency circuit inoperative and endangering the nuclear power plant.

[0008] The invention therefore aims to propose a method for implementing a heat exchanger with reduced dimensions, and which ensures the cooling of a hot fluid without risk of damaging said heat exchanger due to excessively large temperature differences. Summary of the invention

[0009] To this end, there is proposed firstly a cooling method using a heat exchanger, the method being intended to cool a first fluid by means of a second fluid, method in which the first fluid leaves and enters the heat exchanger several times so as to exchange with itself and with the second fluid, by indirect contact, method in which: the first fluid enters and exits a first time in the heat exchanger forming a first passage of said first fluid in the heat exchanger, the first fluid enters and exits a second time in the heat exchanger forming a second passage of said first fluid in the heat exchanger, the first fluid enters and exits a third time in the heat exchanger forming a third passage of said first fluid in the heat exchanger, the first fluid enters and exits a fourth time in the heat exchanger forming a fourth passage of said first fluid in the heat exchanger, process in which the first fluid during its first pass successively exchanges with the first fluid during its second pass then with the first fluid during its fourth pass while exchanging with the second fluid, process in which the first fluid is water vapor and the second fluid is carbon dioxide in supercritical phase.

[0010] Such a process has the advantage of using only two fluids, namely water vapor and supercritical carbon dioxide. If such recirculation were not implemented, at least one additional fluid would be required to achieve an equivalent result.

[0011] Various additional features may be provided alone or in combination: during its first passage, the first fluid undergoes a temperature drop substantially between 100°C and 110°C; during its second passage, the first fluid undergoes a temperature increase substantially between 47°C and 57°C; during its third passage, the first fluid undergoes a temperature drop substantially between 70°C and 80°C; during its fourth passage, the first fluid undergoes a temperature increase substantially between 37°C and 47°C; the first fluid enters and exits a fifth time in the heat exchanger forming a fifth passage and undergoes a temperature drop substantially between 65°C and 75°C; the second fluid enters and exits the heat exchanger once; the second fluid exchanges with the first fluid in its fifth passage in the heat exchanger and undergoes a temperature increase substantially between 15°C and 25°C;the second fluid exchanges with the first fluid in its third passage through the heat exchanger and undergoes a temperature increase substantially between 20°C and 30°C; the second fluid exchanges with the first fluid in its first passage through the heat exchanger and undergoes a temperature increase substantially between 159°C and 169°C; the first fluid during its second passage exchanges in parallel with the second fluid and with the first fluid during its first passage; the first fluid during its third passage exchanges with the second fluid; the first fluid during its fourth passage exchanges in parallel with the first fluid during its first passage and with the second fluid; the first fluid during its fifth passage exchanges with the second fluid; the method is used in an emergency circuit intended to cool a secondary circuit of a nuclear power plant. ;

[0012] Secondly, a heat exchanger is proposed which is capable of implementing a method as previously described, said heat exchanger comprising: a first inlet for a hot fluid, a first outlet for said hot fluid fluidically connected to the first inlet inside said heat exchanger by a first passage, a second inlet for said hot fluid, connected to the first outlet by a first pipe, a second outlet for said hot fluid fluidically connected to the second inlet inside said heat exchanger by a second passage, a third inlet for said hot fluid connected to the second outlet by a second pipe, a third outlet for said hot fluid fluidically connected to the third inlet inside said heat exchanger by a third passage, a fourth inlet for said hot fluid connected to the third outlet by a third pipe, a fourth outlet for said hot fluid fluidically connected to the fourth inlet inside said heat exchanger by a fourth passage,a fifth inlet of said hot fluid connected to the fourth outlet by a fourth pipe, a fifth outlet of said hot fluid fluidically connected to the fifth inlet inside said heat exchanger by a fifth passage.

[0013] Various additional features may be provided alone or in combination: the heat exchanger has a length less than or equal to 2000 millimeters; the heat exchanger has a height less than or equal to 600 millimeters. Brief description of the figures

[0014] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which one will refer to the attached drawing in which: There Figure 1 is a schematic view of a heat exchanger in which the method according to the invention is illustrated. Detailed description of the invention

[0015] On the Figure 1 a heat exchanger 1 according to the invention is shown.

[0016] The heat exchanger comprises heads 2, 3, 4, 5 intended to distribute or collect the fluid in the heat exchanger.

[0017] The heat exchanger comprises several inlet heads 2 for a hot fluid and several outlet heads 3 for this same hot fluid. The heat exchanger comprises an inlet head 4 for a cold fluid and two outlet heads 5 for this same cold fluid.

[0018] The heat exchanger 1 is compartmentalized. This means that inside the heat exchanger 1, sealed compartments make it possible to organize the passage of fluids in said heat exchanger 1 so that the heat exchanges take place according to a predetermined plan. These compartments are not shown in the drawing.

[0019] The cooling method according to the invention uses the heat exchanger shown in the Figure 1 .

[0020] As can be seen on the Figure 1 , the hot fluid repeatedly enters and exits the heat exchanger.

[0021] By repeatedly exchanging heat between the hot fluid and itself in the heat exchanger, as well as between the cold fluid, it is possible to successively lower and raise the temperature. This prevents excessive temperature fluctuations. The heat exchanger is then protected from possible damage.

[0022] Heat exchange between the first fluid on the one hand and between the first fluid and the second fluid on the other hand, occurs by indirect contact. In other words, the fluids are not in direct contact but are separated by a wall so that they do not mix.

[0023] According to the invention, the hot fluid enters the heat exchanger 1 through a first inlet 6 and leaves it through a first outlet 7. This is a first passage 8 of the hot fluid in the heat exchanger 1. The hot fluid undergoes a temperature reduction substantially between 100°C and 110°C, preferably substantially equal to 105°C.

[0024] According to the invention, the hot fluid enters the heat exchanger 1 through a second inlet 9 and leaves it through a second outlet 10. This is a second passage 11 of the hot fluid in the heat exchanger 1. The hot fluid undergoes a temperature increase substantially between 47°C and 57°C, preferably substantially equal to 52°C.

[0025] According to the invention, the hot fluid enters the heat exchanger 1 through a third inlet 12 and leaves through a third outlet 13. This is a third passage 14 of the hot fluid in the heat exchanger 1. The hot fluid undergoes a temperature reduction substantially between 70°C and 80°C, preferably substantially equal to 75°C.

[0026] According to the invention, the hot fluid enters the heat exchanger 1 through a fourth inlet 15 and leaves it through a fourth outlet 16. This is a fourth passage 17 of the hot fluid in the heat exchanger 1. The hot fluid undergoes a temperature increase substantially between 37°C and 47°C, preferably substantially equal to 42°C.

[0027] Advantageously, the hot fluid enters the heat exchanger 1 through a fifth inlet 18 and leaves through a fifth outlet 19. This is a fifth passage 20 of the hot fluid in the heat exchanger 1. The hot fluid undergoes a temperature reduction substantially between 65°C and 75°C, preferably substantially equal to 70°C.

[0028] Advantageously, the cold fluid enters the heat exchanger 1 through the cold inlet head 4 and leaves it through two cold outlet heads 5. The cold fluid only makes one pass through the heat exchanger 1.

[0029] Advantageously, the cold fluid exchanges with the hot fluid during its fifth passage 20 in the heat exchanger 1. The cold fluid undergoes a temperature increase substantially between 15°C and 25°C, preferably substantially equal to 20°C.

[0030] Advantageously, the cold fluid exchanges with the hot fluid during its third passage 14 in the heat exchanger 1. The cold fluid undergoes a temperature increase substantially between 20°C and 30°C, preferably substantially equal to 25°C.

[0031] Advantageously, the cold fluid exchanges with the hot fluid during its first passage 8 in the heat exchanger 1. The cold fluid undergoes a temperature increase substantially between 159°C and 169°C, preferably substantially equal to 164°C.

[0032] According to the invention, the hot fluid during its first passage 8 in the heat exchanger 1, exchanges successively with the hot fluid during its second passage 11 then with the hot fluid during its fourth passage 17. In parallel, the hot fluid exchanges with the cold fluid throughout its path in the heat exchanger 1.

[0033] Advantageously, the hot fluid during its second passage 11 in the heat exchanger 1, exchanges in parallel with the hot fluid during its first passage and with the cold fluid.

[0034] Advantageously, the hot fluid during its third passage 14 in the heat exchanger 1, exchanges with the cold fluid.

[0035] Advantageously, the hot fluid during its fourth passage 17 in the heat exchanger 1, exchanges in parallel with the hot fluid during its first passage 8 and with the cold fluid.

[0036] Advantageously, the hot fluid during its fifth passage 20 in the heat exchanger 1, exchanges with the cold fluid.

[0037] According to the invention, the hot fluid is water vapor and the cold fluid is carbon dioxide in supercritical phase. The properties of carbon dioxide in supercritical phase are advantageous due to its high density, its intermediate diffusivity coefficient between gas and liquid and a low viscosity close to that of gases, thus allowing a more efficient heat exchange in the heat exchanger 1.

[0038] Advantageously, the method is used in an emergency circuit intended to cool a secondary circuit of a nuclear power plant. A nuclear power plant has a primary circuit for cooling the nuclear fuel by direct contact, a secondary circuit for cooling the primary circuit and also used for electricity production.

[0039] As can be seen on the Figure 1, the heat exchanger 1 comprises several pipes connecting the heads together, in order to implement the method previously described. Thus the heat exchanger comprises: a first pipe 29 connecting the first outlet 7 to the second inlet 9; a second pipe 21 connecting the second outlet 10 to the third inlet 12; a third pipe 22 connecting the third outlet 13 to the fourth inlet 15; a fourth pipe 23 connecting the fourth outlet 16 to the fifth inlet 18.

[0040] Pipes 29, 21, 22, 23 allow the recirculation of the hot fluid in the heat exchanger and therefore avoid a sudden drop in the temperature of the hot fluid. The mechanical constraints applied to the heat exchanger are therefore controlled.

[0041] This heat exchanger, implementing the process described above, thus has a maximum length less than or equal to 2000 millimeters.

[0042] This heat exchanger, implementing the process described above, thus has a maximum height less than or equal to 600 millimeters.

Claims

1. Cooling method using a heat exchanger (1), the method being intended to cool a first fluid by means of a second fluid, method wherein the first fluid leaves and enters the heat exchanger (1) multiple times so as to exchange with itself and with the second fluid, by indirect contact, method wherein: - the first fluid enters and leaves the heat exchanger (1) a first time, forming a first passage (8) for said first fluid in the heat exchanger, - the first fluid enters and leaves the heat exchanger (1) a second time, forming a second passage (11) for said first fluid in the heat exchanger, characterized in that - the first fluid enters and leaves the heat exchanger (1) a third time, forming a third passage (14) for said first fluid in the heat exchanger, - the first fluid enters and leaves the heat exchanger (1) a fourth time, forming a fourth passage (17) for said first fluid in the heat exchanger, method wherein the first fluid, during its first passage (8), exchanges successively with the first fluid during its second passage (11) then with the first fluid during its fourth passage (17) while exchanging with the second fluid, method wherein the first fluid is steam and the second fluid is carbon dioxide in supercritical phase.

2. Method according to claim 1, wherein, during its first passage (8), the first fluid is subjected to a temperature reduction of substantially between 100°C and 110°C.

3. Method according to claim 2, wherein, during its second passage (11), the first fluid is subjected to a temperature increase of substantially between 47°C and 57°C.

4. Method according to claim 3, wherein, during its third passage (14), the first fluid is subjected to a temperature reduction of substantially between 70°C and 80°C.

5. Method according to claim 4, wherein, during its fourth passage (17), the first fluid is subjected to a temperature increase of substantially between 37°C and 47°C.

6. Method according to claim 5, wherein the first fluid enters and leaves the heat exchanger (1) a fifth time, forming a fifth passage (20), and is subjected to a temperature reduction of substantially between 65°C and 75°C.

7. Method according to claim 6, wherein the second fluid enters and leaves the heat exchanger (1) once.

8. Method according to claim 7, wherein the second fluid exchanges with the first fluid in its fifth passage (20) in the heat exchanger (1) and is subjected to a temperature increase of substantially between 15°C and 25°C.

9. Method according to claim 8, wherein the second fluid exchanges with the first fluid in its third passage (14) in the heat exchanger (1) and is subjected to a temperature increase of substantially between 20°C and 30°C.

10. Method according to claim 9, wherein the second fluid exchanges with the first fluid in its first passage (8) in the heat exchanger (1) and is subjected to a temperature increase of substantially between 159°C and 169°C.

11. Method according to claim 10, wherein the first fluid, during its second passage (11), exchanges in parallel with the second fluid and with the first fluid during its first passage (8).

12. Method according to claim 11, wherein the first fluid, during its third passage (14), exchanges with the second fluid.

13. Method according to claim 12, wherein the first fluid, during its fourth passage (17), exchanges in parallel with the first fluid during its first passage (8) and with the second fluid.

14. Method according to claim 13, wherein the first fluid, during its fifth passage (20), exchanges with the second fluid.

15. Method according to any one of the preceding claims, wherein said method is used in an emergency circuit designed to cool a secondary circuit of a nuclear power plant.

16. Heat exchanger (1) suitable for carrying out a method according to any one of the preceding claims, said heat exchanger (1) comprising: - a first inlet (6) for a hot fluid, - a first outlet (7) for said hot fluid, which is fluidically connected to the first inlet (6) inside said heat exchanger (1) by a first passage (8), - a second inlet (9) for said hot fluid, which is connected to the first outlet (7) by a first pipe (29), - a second outlet (10) for said hot fluid, which is fluidically connected to the second inlet (9) inside said heat exchanger (1) by a second passage (11), - a third inlet (12) for said hot fluid, which is connected to the second outlet (10) by a second pipe (21), - a third outlet (13) for said hot fluid, which is fluidically connected to the third inlet (12) inside said heat exchanger (1) by a third passage (14), - a fourth inlet (15) for said hot fluid, which is connected to the third outlet (13) by a third pipe (22), - a fourth outlet (16) for said hot fluid, which is fluidically connected to the fourth inlet (15) inside said heat exchanger (1) by a fourth passage (17), - a fifth inlet (18) for said hot fluid, which is connected to the fourth outlet (16) by a fourth pipe (23), - a fifth outlet (19) for said hot fluid, which is fluidically connected to the fifth inlet (18) inside said heat exchanger (1) by a fifth passage (20).

17. Heat exchanger (1) according to claim 16, wherein the exchanger has a length of less than or equal to 2000 millimeters.

18. Heat exchanger (1) according to any one of claims 16 or 17, wherein the exchanger has a height of less than or equal to 600 millimeters.