Configurations and methods for retrofitting an NGL recovery plant
Devices and methods for retrofitting a natural gas liquids plant are contemplated to extend recovery of C3+ hydrocarbons from various feed gases to recovery of C2+ and C3+ hydrocarbons. In especially preferred aspects, dedicated C2+ exchangers are integrated to exclusively cool the feed gas to produce a cooled absorber feed and to produce two separate absorber reflux streams. During C2+ recovery, absorber reflux is provided by a portion of the residue gas and a portion of the feed gas, while during C3+ recovery absorber and distillation column reflux are provided by the distillation column overhead product.
1. A method of retrofitting a natural gas liquids plant for recovery of C2+ hydrocarbons, wherein the natural gas liquids plant has an absorber, a downstream distillation column, and a C3+ recovery exchanger that is configured to cool a feed gas and to cool an overhead product from the distillation column to thereby form a reflux stream for the absorber, and wherein a bottom product of the absorber is fed to the downstream distillation column, comprising:
installing a bypass circuit for the C3+ recovery exchanger that includes first and second dedicated C2+ recovery exchangers;
wherein the first C2+ recovery exchanger uses refrigeration content from an absorber overhead product to produce an ultra-lean reflux stream from a portion of compressed residue gas and a reflux stream from a portion of the feed gas;
wherein the second C2+ recovery exchanger uses refrigeration content from the absorber bottom product to produce a cooled feed gas from another portion of the feed gas; and
installing a bypass that routes the overhead product from the distillation column to the absorber as a stripping vapor.
2. The method of claim 1 further comprising a step of installing a conduit that provides a liquid portion of the cooled feed gas to the absorber.
3. The method of claim 1 further comprising a step of installing a control circuit that controls operation of switching valves to fluidly bypass the C3+ recovery exchanger when C2+ recovery is desired.
4. The method of claim 1 further comprising a step of using an overhead condenser of the distillation column to produce the cooled feed gas.
5. The method of claim 1 wherein a vapor portion of the cooled feed gas is expanded to absorber pressure prior to feeding the vapor portion into the absorber.
6. A method of retrofitting a natural gas liquids plant for recovery of C2+ hydrocarbons, wherein the natural gas liquids plant has an absorber, a downstream distillation column, and a C3+ recovery exchanger that is configured to cool a feed gas and to cool an overhead product from the distillation column to thereby form a reflux stream for the absorber, and wherein a bottom product of the absorber is fed to the downstream distillation column, comprising:
installing first and second dedicated C2+ recovery exchangers, piping, and a plurality of switching valves such that:
(a) flow of the feed gas is routable exclusively to the C3+ recovery exchanger or the first and second C2+ recovery exchangers;
wherein the C3+ recovery exchanger is configured to produce a cooled feed gas from the feed gas, wherein the first C2+ recovery exchanger is configured to produce a feed gas reflux stream from a first portion of the feed gas, and wherein the second C2+ recovery exchanger is configured to produce a cooled feed gas from a second portion of the feed gas;
(b) flow of the bottom product of the absorber is routable exclusively to the C3+ recovery exchanger or the second C2+ recovery exchanger to provide refrigeration content to the C3+ recovery exchanger or the second C2+ recovery exchanger;
(c) flow of an overhead product of the absorber is routable exclusively to the first C2+ recovery exchanger to provide refrigeration content to generate for the absorber an ultra-lean reflux stream from a portion of compressed residue gas; and
(d) flow of an overhead product of the distillation column is routable exclusively to the absorber as a stripping vapor, or to the absorber as the reflux stream for the absorber and the distillation column as a distillation column reflux.
7. The method of claim 1 wherein at least one of the switching valves is a three-way valve.
8. The method of claim 1 further comprising a step of installing a control circuit that controls operation of the switching valves to bypass the C3+ recovery exchanger when C2+ recovery is desired.
9. The method of claim 1 further comprising a step of fluidly coupling an overhead condenser of the distillation column with the second C2+ recovery exchanger to produce the cooled feed gas from the second portion of the feed gas.