Process and apparatus for removal of sour species from a natural gas stream

Abstract

A process for removal of sour species from a dehydrated natural gas feed stream is provided. The dehydrated natural gas feed stream is cooled to conditions where a slurry of solid sour species and hydrocarbon liquids is formed together with a gaseous stream containing gaseous sour species. The gaseous stream containing gaseous sour species is then separated from the slurry and treated with a liquid solvent, thereby forming a liquid solution of the sour species and a dehydrated sweetened natural gas product stream. An apparatus for removing sour species from a dehydrated natural gas feed stream is also provided. The apparatus has a vessel with a solids formation zone in fluid communication with a gas solvation zone. The solids formation zone is configured to facilitate formation of a slurry of solid sour species and hydrocarbon liquids and a gaseous stream containing gaseous sour species. The gas solvation zone is configured to facilitate formation of a liquid solution of sour species. The apparatus has an inlet for introducing the dehydrated natural gas feed stream to the solids formation zone, a conduit configured to direct the gaseous stream from the solids formation zone to the gas solvation zone, and an inlet for introducing liquid solvent into the gas solvation zone.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a process and apparatus for removal of sour species from a natural gas stream. In particular, the present invention relates to a process for removal of sour species in a liquid phase from a dehydrated natural gas stream.[0002]The present invention also relates to a process for recovering liquid carbon dioxide from a natural gas stream.BACKGROUND OF THE INVENTION[0003]Natural gas from either production reservoirs or storage reservoirs typically contains water, as well as other species, which form solids in low temperature conditions under which some process operations are performed.[0004]The formation of solids in pipe work, on the surface of heat exchangers and / or liquefaction and storage vessels is undesirable, as the accumulation of such solids eventually results in decreased operating and storage efficiencies, damage, and increased plant down time for maintenance and repair.[0005]Furthermore, several species, in particu...

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Benefits of technology

[0014]It has been demonstrated that a dehydrated natural gas stream may be sweetened by solidifying sour species contained therein. However, at any fixed temperature, the solid sour species has a characteristic fixed vapour pressure, and thus sour species will also be present in the vapour phase. The present invention is based on the realisation that it is possible to sequentially and selectively separate solid, liquid and gaseous fractions of a contaminant sour species from a dehydrated natural gas feed stream, thereby enhancing the removal of sour species from the dehydrated natural gas product stream.

[0045]Location of the solids formation zone and the gas solvation zone in a single vessel is cost effective, as the footprint of the apparatus is smaller and only one pressure containing head is required. However, in alternative embodiments it may be more advantageous to locate the solids formation zone in a first vessel and to locate the gas solvation zone in a second vessel, having a fluid communication device disposed therebetween. In these alternative embodiments, the fluid communication device is disposed externally of the first and second vessels with one end of the fluid communication device in fluid communication with an upper portion of the solids formation zone of the first vessel and the opposing end of the fluid communication device is in fluid communication with a lower portion of the gas solvation zone of the second vessel. In this particular embodiment, the fluid communication device comprises a conduit.

Problems solved by technology

The formation of solids in pipe work, on the surface of heat exchangers and / or liquefaction and storage vessels is undesirable, as the accumulation of such solids eventually results in decreased operating and storage efficiencies, damage, and increased plant down time for maintenance and repair.

It is generally acknowledged that these methods, while effective, are complex and expensive to implement, particularly in respect to large volume plants, and operational problems are frequently encountered.

However, an unfortunate side effect of using said sub-cooled liquid is that the heavier hydrocarbons contained in the liquid are removed with the sour species making recovery of the hydrocarbons difficult or costly to achieve.

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