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Gas Processing Ideas: Front-End Light Petroleum Gas Extraction with Solvent and End Flash Recycle

IP.com Disclosure Number: IPCOM000245708D
Publication Date: 2016-Mar-31
Document File: 3 page(s) / 358K

Publishing Venue

The IP.com Prior Art Database

Abstract

Solvent is injected to improve heavy component removal in a FE-LPG extraction process. End flash and/or boiloff gas are recycled to the warm end of the natural gas liquefaction process.

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Gas Processing Ideas

Front-End Light Petroleum Gas Extraction with Solvent

Fig. 1

Fig. 1 shows a typical front-end light petroleum gas (FE LPG) extraction scheme, a variation of the process shown in US 4,157,904 patent. Feed, such as natural gas, is cooled and partially liquefied in feed economiser heat exchanger EC1 and introduced to the phase separator PS. Resulting vapour is at least partially liquefied in the overhead economiser heat exchanger EC2 to provide reflux for the distillation column DIST; another portion is turbo-expanded in expander EXP to provide refrigeration. Liquid portion is fed to DIST as a separate stream. Expander drives the compressor COMP installed on common shaft. EC1 and EC2 are balanced by the DIST’s lean overhead vapour product stream, which becomes residue gas (RG). Residue gas is typically further compressed and may be put in a pipeline or liquefied to produce liquefied natural gas (LNG). Heavier components are withdrawn from the bottom of the column as LPG or natural gas liquid (NGL) and may be further fractionated. Other heavy hydrocarbons, including aromatics such as benzene, toluene, and xylenes (BTX), may also be removed by DIST.

Fig. 2

For the distillation column to be effective in removing heavy hydrocarbons, a high ethane, propane, and butanes content may be needed.  Feed natural gas with a low ethane, propane, and butanes content is referred to as “lean” gas.  When the feed gas is lean, it may be beneficial to introduce a solvent (SOL) upstream of the columns to improve the removal of heavy hydrocarbons. The solvent can be introduced at any point within the process (SOL1, SOL2, and SOL3 are examples). It may also be added to the column itself (SOL4, SOL5).  Some examples of locations for introduction are shown in Fig. 2. The solvent may be a pure component or a mixture. It may comprise propane, and heavier hydrocarbons or hydrocarbon derivatives.

The solvent may be imported into the facility or obtained by fractionation of DIST’...