Make full use of the thermal energy in the liquefaction section and adopt a one-time injection liquefaction process. The heat released by flash evaporation of each cubic meter of liquefied liquid can evaporate more than 200 kilograms of water. The secondary injection liquefaction process is adopted. The heat released by flash evaporation of each cubic meter of liquefied liquid can evaporate more than 500 kilograms of water, and no cooling water is needed for the liquefied liquid to drop from the liquefaction temperature to the saccharification temperature.