Used evaporators can be categorized into evaporating concentrators and evaporating crystallizers, depending on their applications, each utilizing different processes. Their primary purpose is to evaporate the non-volatile solutes contained in the solution, causing it to boil and vaporize, thereby increasing the concentration of the solutes in the solution.

Used evaporators require the innovative saturated steam from a source plant, which is known as feed steam. Steam evaporated from the solution is called secondary steam, used to distinguish it from feed steam. In the operation of a used evaporator, secondary steam is typically condensed directly through condensation. The operation that does not utilize the condensation heat is called single-effect evaporation, while introducing secondary steam into the next stage of a used evaporator as heating steam and using its condensation heat is called multi-effect evaporation. Equipment using this evaporation method is known as a multi-effect used evaporator.

Additionally, second-hand evaporators include MVR evaporators, a device that utilizes steam recompression to condense steam, requiring no condenser equipment or external steam input, only electric power, and depending on the work of the steam recompressor. It boasts a high heat transfer coefficient, is non-clogging, and features a smooth surface for easy cleaning and maintenance. This evaporator vaporizes materials at relatively low temperatures, between 35 to 100 degrees Celsius, without producing bubbles. The materials and liquids are very uniform, ensuring no material exhaustion or coking.

However, the limitations of the MVR evaporator are also quite apparent. Affected by the increased boiling point of the material, its adaptability is narrower than that of a multi-effect evaporator. The evaporation and concentration of certain high-concentration materials must be completed by a multi-effect evaporator, such as calcium chloride evaporation and concentration.

Second-hand evaporators are widely used in the evaporation and concentration of water or organic solvent solutions in industries such as food, chemical, and light industry, as well as in waste liquid treatment. They are particularly suitable for thermosensitive materials. A second-hand double-effect evaporator is a slurry circulation continuous crystallizer with high production capacity, but the particle size distribution of the product is relatively broad.

In summary, used evaporators are a crucial chemical equipment, which, through evaporation, removes non-volatile solutes from solutions, increasing their concentration. They are widely used across various industries. Different types of used evaporators have distinct features and applications, necessitating selection and usage based on specific requirements.