Reboiler/condenser heat exchanger of the bath type

The process for vaporizing a first fluid, which comprises:

• providing a reboiler/condenser bath heat exchanger, for heat exchange between the first fluid to be vaporized and a second fluid to be condensed, said heat exchanger having a minimum exit pressure Pm, ex of the first fluid in order to allow a plant in which the heat exchanger is mounted to operate, said heat exchanger including a number of vertical heat exchange passages;
• flowing the second fluid through the vertical heat exchange passages, the second fluid having an outlet temperature T2-2 at the outlet of the passages;
• flowing the first fluid by a thermosiphon effect between the heat exchange passages from the bottom upwards over a height h, the first fluid having an entry temperature T1-1 where T1-1 is less than T2-2, and the vaporized first fluid having an exit pressure P1-2;
• pressuring the first fluid having an entry pressure P1-1 to a value such that the exit pressure P1-2 of the first fluid is greater than the minimum pressure Pm, ex;
• and
• selecting the height of the heat exchange passages and the temperature T2-2 of the second fluid such that at least both of the two following conditions are fulfilled:
• the height h of the heat exchange passages is at least equal to 2.5 m;
• and
• the outlet temperature T2 of the second fluid is less than T1-1+1.2° C.