Systems and methods for hydrocarbon refrigeration with a mixed refrigerant cycle
Methods and systems for reducing the pressure of a hydrocarbon-containing stream so as to provide a cooled, reduced-pressure hydrocarbon-containing stream are provided. Facilities as described herein utilize a single closed-loop mixed refrigeration system in order to facilitate transportation, loading, and/or storage of a liquefied hydrocarbon-containing material at or near atmospheric pressure. In some aspects, the facilities can include at least one separation device for removing lighter components from the feed stream, which may separately be recovered as a vapor product for subsequent processing and/or use.
1. A method for providing a cooled, reduced-pressure hydrocarbon-containing stream, said method comprising:
(a) cooling a hydrocarbon-containing stream via indirect heat exchange with a mixed refrigerant in a closed-loop mixed refrigerant system to provide a warmed refrigerant and a cooled stream;
(b) flashing said cooled stream to provide a two-phase fluid stream, wherein said two-phase fluid stream includes the entire hydrocarbon-containing stream;
(c) introducing said two-phase fluid stream into a separator vessel;
(d) separating said two-phase fluid stream in said separator vessel to form a vapor fraction and a liquid fraction;
(e) introducing said liquid fraction into a holding vessel;
(f) compressing said vapor fraction to provide a compressed vapor stream;
(g) cooling at least a portion of said compressed vapor stream in a heat exchanger to provide a second cooled fluid stream;
(h) withdrawing said second cooled fluid stream from an outlet of said heat exchanger, wherein said second cooled fluid stream is a liquid stream; and
(i) introducing the entirety of said second cooled fluid stream into said separator vessel with said two-phase fluid stream,
wherein prior to said cooling of step (a) said hydrocarbon-containing stream has a vapor fraction of less than about 0.10, wherein said cooling of step (a) is performed in a first cooling pass of said heat exchanger and said cooling of step (g) is performed in a second cooling pass of said heat exchanger, and wherein said first and said second cooling passes are separate from one another; and
wherein prior to said cooling of step (g) at least a portion of said compressed vapor stream is separated into a light component-enriched overhead stream and a light component-depleted bottoms stream in a fractionation column, and wherein said cooling of step (g) comprises cooling said light component-depleted bottoms stream to form said second cooled fluid stream, withdrawing a liquid stream from said holding vessel, wherein said liquid stream comprises less than about 5 mole percent of C 1 and lighter components and has a pressure within about 10 psig of atmospheric pressure, and wherein said hydrocarbon-containing stream comprises at least about 50 volume percent of C 2 and heavier components.
2. The method of claim 1 , further comprising cooling at least a portion of said light component-enriched overhead stream to provide a cooled overhead stream; separating the cooled overhead stream into an overhead vapor fraction and a reflux liquid fraction; and introducing at least a portion of the reflux liquid fraction into an upper portion of said fractionation column, wherein at least a portion of said cooling of said light component-enriched overhead stream is carried out via indirect heat exchange with said mixed refrigerant in said closed-loop mixed refrigeration system.
3. The method of claim 1 , further comprising, prior to said introducing of step (e), flashing at least a portion of said liquid fraction to form a flashed liquid stream and introducing at least a portion of said flashed liquid stream into said holding vessel.
4. The method of claim 1 , further comprising, compressing a stream of boil-off vapor withdrawn from an upper portion of said holding vessel to provide a compressed boil-off stream, wherein said compressed vapor stream comprises at least a portion of said compressed boil-off stream.
5. The method of claim 1 , wherein at least a portion of said cooling of step (g) is carried out via indirect heat exchange between said at least a portion of said compressed vapor stream and said mixed refrigerant in said closed-loop mixed refrigeration system.
6. The method of claim 1 , wherein said holding vessel is selected from the group consisting of a storage tank, a barge, a truck, a rail car, a ship, and combinations thereof.
7. The method of claim 1 , wherein said hydrocarbon-containing stream is a supercritical fluid stream prior to said cooling of step (a).
8. The method of claim 1 , wherein said separator vessel comprises a single separation stage.
9. The method of claim 1 , wherein said cooling of step (g) is performed via indirect heat exchange with said mixed refrigerant used during said cooling of step (a).