Which type of distilling plant uses lowering of pressure to function?

The correct answer relates to the concept of using reduced pressure to facilitate the distillation process. In a flash type distiller, seawater is heated and then rapidly depressurized, causing a portion of the water to vaporize almost instantaneously - or "flash" - into steam. This process takes advantage of the principle that lowering the pressure over a liquid decreases its boiling point, allowing water to convert to steam at lower temperatures.

This method is efficient and allows for the extraction of distilled water from seawater or brackish water while conserving energy. The lower boiling point achieved in the vacuum conditions means that less energy is required to evaporate the water compared to traditional distillation methods.

In contrast, reverse osmosis desalination relies on a membrane to separate salts from water rather than using a phase change mechanism like distillation. Vacuum desalination also involves lowering pressure, but it typically refers to a more complex system that combines stages of evaporative techniques. Multi-stage flash distillation is another distillation process that incorporates the flash concept but is not as direct as a flash type distiller. Thus, the focus here is on the unique function of the flash type distiller specifically utilizing the drop in pressure in its operational process.