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LSP PROCESS FOR HIGH ETHANE RECOVERY

IP.com Disclosure Number: IPCOM000028362D
Publication Date: 2004-May-12
Document File: 4 page(s) / 31K

Publishing Venue

The IP.com Prior Art Database

Abstract

The following article describes the LSP process (Lean-oil Subcooled Process) for recovering a purified ethane product from a high pressure, dense phase natural gas stream.

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LSP Process for High Ethane Recovery

Summary

The following article describes the LSP process (Lean-oil Subcooled Process) for recovering a purified ethane product from a high pressure, dense phase natural gas stream.

The LSP process is essentially a hybrid turbo-expander/absorption process which utilizes C3+ material as light lean oil to enhance ethane recovery at cryogenic temperatures.  It can achieve economic ethane recoveries as high as 97% and is particularly suited to applications where complete recovery and commercial disposal of C3+ material is not required.

Pressure reduction is achieved by the use of two turbo expanders in series.  This configuration allows for operation of the brazed aluminum heat exchangers at conventional pressures.

Process Description

High pressure feed gas at 10,000 kPa to 14,000 kPa is dehydrated using 3A molecular sieves.  The dried gas (1) is expanded through the inlet turbo expander (2) to an intermediate pressure between 5,000 and 10,000 kPa preferably from 6,000 to 8,000 kPa, at temperatures determined by the feed gas temperature and the expansion ratio, and split into two separate streams (3a and 3b).

The smaller of the two streams comprising of approximately 40% of the total is cooled in a demethanizer side reboiler (4) while the larger stream is cooled by heat exchange with cold residue gas in the inlet residue gas exchanger (5).  The streams are then recombined and any liquid formed is separated in a knock-out drum (6).  The separated liquid (7) is reduced in pressure through a valve and fed to the absorber section (8) of the demethanizer.  The vapor stream from the separator is again split.

Approximately 65% of the gas flow from the knock out drum (6) is expanded to the demethanizer operating pressure (typically 2,500 kPa to 4,000 kPa) through the second turbo expander (9) and fed to the absorber section (8) of the demethanizer.  A small portion of the vapor stream is reduced in pressure and fed to the demethanizer (10) where it is used to fine tune CO2 recovery and reboiler duty.  The remaining vapor is condensed in the absorber overhead exchanger (11), flashed across a valve and fed into the middle section of the absorber tower.  The cold side fluids in this heat exchanger are the overhead and bottoms streams leaving the absorber.

The demethanizer tower consists of two distinct sections, an absorption section (8) where chilled feed gases at a temperature from –60°C to –110°C, are contacted with the cold light lean oil, and a demethanization section (10) where methane and carbon dioxide are separated from the higher boiling gas liquids.  The two sections can be combined in one tower shell or installed as two separate shells.

The demethanizer operates below the cricondenbar at relatively high pressure.  The selected operating pressure is dictated by economic criteria, and is preferably   between 2,750 kPa and 3,380 kPa.  The feed streams to the absorber section are described above...