Distillation seawater desalting system using expander and compressor

The invention discloses a distillation seawater desalting system using an expander and a compressor. The distillation seawater desalting system comprises a condenser, an expander and a compressor, wherein the condenser is used for performing heat exchange to influent raw seawater and secondary vapour, and then respectively discharging the heat-exchanged pre-heated seawater and condensed water, and discharging the seawater; an evaporator is provided with a primary effect evaporator, a plurality of middle effect evaporators and tail effect evaporators, which are arranged in series in sequence, wherein the tail effect evaporators are connected with the condenser, and the primary effect evaporator is provided with an inlet of mixed vapour; the expander is connected with the primary effect evaporator of the evaporator; and the compressor is respectively connected with the middle effect evaporators or the tail effect evaporators of the evaporator and the expander, respectively. The distillation seawater desalting s