Recovery of hydrocarbons from a gaseous stream

Abstract

A process (10) for the recovery of hydrocarbons from a Fischer-Tropsch tail gas includes providing a hydrocarbon rich Fischer-Tropsch tail gas (30) which includes hydrocarbons and carbon dioxide, compressing (14) the hydrocarbon rich Fischer-Tropsch tail gas (30) to provide a compressed hydrocarbon rich Fischer-Tropsch tail gas (36, 54), and contacting the compressed hydrocarbon rich Fischer-Tropsch tail gas (36, 54) with a lean oil (64, 54) to recover the hydrocarbons from the compressed hydrocarbon rich Fischer-Tropsch tail gas (36, 54) and to produce a hydrocarbon rich oil (66). Carbon dioxide is stripped (20) from the hydrocarbon rich oil (66) at a pressure which is below the pressure at which the hydrocarbon rich Fischer-Tropsch tail gas (36, 54) is contacted with the lean oil (64, 54), to provide a stripped hydrocarbon oil product (86).

Description

FIELD OF THE INVENTION[0001]THIS INVENTION relates to the recovery of hydrocarbons from a gaseous stream. In particular, the invention relates to a process for the recovery of hydrocarbons from a Fischer-Tropsch tail gas.BACKGROUND OF THE INVENTION[0002]Commercial Fischer-Tropsch synthesis processes principally produce a hydrocarbon product comprising hydrocarbons over a wide range of molecular weights, e.g. from C1 to heavier, waxy hydrocarbon products which may be liquid or solid at ambient temperature and pressure, and an aqueous stream, commonly referred to as a reaction water stream. The reaction water stream is typically condensed from a gaseous overhead product from a Fischer-Tropsch synthesis reactor by cooling the gaseous overhead product to a temperature in the range of from about 30° C. to about 80° C. by air and / or water cooling. Cooling the gaseous overhead product from the Fischer-Tropsch synthesis reactor also condenses valuable condensable hydrocarbons from the gaseo...

AI Technical Summary

Benefits of technology

The patent describes compressing a gas that has a lot of hydrocarbons in it and then heating it up to very high temperatures (over 100°C). This causes the gas to change from a solid to a liquid, which can help to purify it.

Problems solved by technology

Certain organic acids and oxygenated species present in Fischer-Tropsch tail gas are harmful to downstream processing operations and must be removed.

Water is problematic in cryogenic processes (which operate well below the freezing point of water) and so the Fischer-Tropsch tail gas must be dried downstream of the washing step, prior to the cryogenic separation step.

Cryogenic processes are equipment and capital intensive.

They are also high energy consumers and expensive to operate due to the large refrigeration duties required to achieve the low temperatures required for the cryogenic separation of the hydrocarbon products from other gaseous components in the Fischer-Tropsch tail gas.

This is undesirable as carbon dioxide is an unwanted species in the downstream processing of the hydrocarbon rich sponge oil.

Some of the valuable hydrocarbons in the hydrocarbon rich sponge oil may be undesirably lost in the carbon dioxide stripping process.

However, they are not as effective in separating the valuable hydrocarbons from the Fischer-Tropsch tail gas.

Consequently, conventional hydrocarbon wash processes do not achieve as high hydrocarbon recoveries as cryogenic processes.

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