The four effect falling film evaporator is used in series with four falling film evaporators, each with different temperatures and pressures. The generated steam enters the first effect heating chamber as a heat source, and a portion of the secondary steam from the first effect separation chamber is drawn into the first effect through a steam injector (according to design requirements), while the rest enters the second effect heating chamber as a heating source. The secondary steam from the second effect separation chamber enters the third effect heating chamber as a heating source, and the fourth effect steam from the third effect separation chamber enters the third effect heating chamber as a heating source. The secondary steam from the fourth effect separation chamber enters the indirect condenser for condensation, and the condensed water from the secondary steam is recovered through a condensate tank.