Method and device for recovering light hydrocarbon through refrigeration using compound refrigerant and secondary dealkylation

The invention discloses a method and a device for recovering light hydrocarbons through refrigeration using a compound refrigerant and secondary dealkylation, wherein the advantages of the traditional natural gas-dealkylation direct heat exchange process are combined with the method of the invention; the precooling of the raw material natural gas, the condensation of a deethanizer top gas, and the cold quantity recovery of the product natural gas and the liquid-phase material of a low-temperature separator are all realized in a main heat exchanger; the cold quantity source of the dealkylation process is provided by a compound refrigerant refrigerating system. The composition, the component contents, the flow rate and the evaporation pressure of the compound refrigerant are adjusted and matched cold quantity and different refrigeration temperatures are provided for the light hydrocarbon condensation process, so that the flexibility of the method in operation and good adaptability of the method to the amount, the pressure and the composition change of the raw material gas; and the method has the characteristics of low energy consumption, high C3 yield and good adaptability to the change of working conditions.