The dual effect falling film evaporator is a system in which two falling film evaporators are first connected and operated in series. The first effect uses fresh steam, and then the secondary steam generated by the first effect due to heat evaporation enters the second effect as the heat source for the second effect evaporator. Equivalent to steam being utilized twice. To achieve the goal of energy conservation and consumption reduction. Reduced steam consumption and also reduced the condensation of secondary steam evaporated. Therefore, the dual effect steam consumption ratio is generally around 0.57-0.6.