To provide a method for solution separation by multiple heat exchange vacuum distillation, cooling and freezing, a method of desalting seawater, and equipment therefor.

Evaporators 21 and heat exchangers 4 are stacked in multiple stages. In each of the evaporators, a heat exchanger evaporation surface 211 is arranged in the vicinity of a liquid level. A heat circulating solution is circulated through ducts b and c, and a treatment liquid under a vacuum condition in the evaporator is heated at a set temperature and evaporated. The liquid is passed through a duct a, condensed by applying heat exchange with the heat circulating solution at the heat exchanger 4, and recovered at a vacuum container 9. The heat circulating solution and treatment liquid are passed through ducts c and j, and led to the evaporator in the next stage. As repeating the same processes, temperature is gradually decreased. At the final stage, the heat circulating solution is cooled. The solution is passed through the heat exchanger 4 reversely, thereby the temperature is gradually increased. The solution is heated at the set temperature again at the final stage, and the above processes are repeated. The treatment liquid is cooled at the final stage, and the processes to contribute to vacuum are repeated.