Double-effect evaporator is an efficient and energy-saving evaporation equipment, which uses the principle of multistage separation to carry out two-way heat transfer inside the evaporator, so that the evaporation effect is better and the heat energy utilization rate is higher. The double-effect evaporator feeds the treated material liquid into the first stage heater of the evaporator, where the liquid is heated and begins to evaporate, the steam is condensed into a liquid, and then returns to the evaporator to continue the cycle. The steam generated in the first stage heater will enter the second stage heater, where the steam will heat the steam generated in the first stage, further increasing its steam pressure, thereby speeding up the evaporation efficiency. In the second heater, the steam condenses into a liquid, which is also recycled.