Screw cascade waste heat energy generating device and generating method

The invention discloses a screw cascade waste heat energy generating device and a screw cascade waste heat energy generating method. The device comprises at least one stage of generator sets, and each stage of generator sets comprises a flooded evaporator, a shell and tube preheater, a reservoir, a condenser and a screw expansion machine, wherein a shell pass outlet of the shell and tube preheater is communicated with the tube pass of the flooded evaporator, and a tube pass outlet of the shell and tube preheater is communicated with the shell pass of the flooded evaporator; an opening at the bottom of the reservoir is communicated with a tube pass inlet of the shell and tube preheater through a circulating pipeline on which a working medium circulating pump and a check valve are arranged; the condenser is connected above the reservoir; and a rotating shaft of the screw expansion machine is connected with a rotating shaft of a synchronizing generator, a shell pass outlet of the flooded evaporator is connected with an inlet of the screw expansion machine through a pipeline on which a flow regulating valve is arranged, and an outlet of the screw expansion machine is communicated with the shell pass of the condenser. By using the device and the method, the heat power generation with large temperature drop at low temperature is realized, and the conversion efficiency of low-temperature heat energy is improved.