Rankine cycling and seawater freshening dual-efficiency waste heat recovery system

The invention discloses a Rankine cycling and seawater freshening dual-efficiency recovery system. The system adopts the technical scheme that an evaporator, a steam turbine, a condenser and a working medium pump are sequentially connected, and the steam turbine is connected with a generator shaft, so as to form a Rankine cycling heat power generation system; high-temperature waste gas exhausted by an engine is directly subjected to heat exchange with working medium at the gas side of the evaporator, and a water pump is sequentially and serially connected with the seawater pipe of a three-stage flash evaporating chamber; the seawater in a first-stage flash evaporating chamber is subjected to heat exchange by the condenser, and then is changed into high-temperature seawater to sequentially enter the three-stage flash evaporating chamber, and along with the continuous evaporation of the seawater, the seawater with relatively higher concentration is drained by the concentrate seawater passage of the three-stage flash evaporating chamber; and the interiors of the first-stage flash evaporating chamber, a second-stage flash evaporating chamber and a third-stage flash evaporating chamber are respectively provided with a steam and water separator, and outlets of the three steam and water separators are connected in parallel to form a freshwater delivery passage. When the residual heat of the exhausted gas of the engine is utilized to generate power, the freshwater supply requirements on ships are met by a multi-stage flash evaporating seawater freshening device, so the fuel economy of the ships is greatly improved.