Cryogenic Expander Application in Propane Liquefaction Process

The use of cryogenic liquid expanders in the propane liquefaction process can increase the amount of liquefied product by reducing the boil-off losses.  Current practice is to use a Joule-Thomson valve to reduce the high pressure condensate.  Losses associated by throttling across a J-T valve result in additional heat causing unwanted boil-off.  A cryogenic expander reduces the enthalpy of the liquid during expansion which sub-cools the liquid, significantly reducing the boil-off losses, and can export this extracted energy as electrical energy.

The thermodynamic properties of propane are well suited to exploit the benefits of a cryogenic expander.  The technology for propane cryogenic expanders exists and has been proven in LNG liquefaction, both in the LNG stream and the Mixed Refrigerant cycle.  Mixed Refrigerant is comprised of mostly propane, making the technological transition from MR expander to propane expander negligible and low risk.  The benefit of increased production already proven in LNG liquefaction can be applied to propane liquefaction resulting in overall process efficiency and reduced costs.