Gas separation: processes – Liquid contacting – And degasification of a liquid
Reexamination Certificate
2002-03-29
2004-07-27
Smith, Duane S. (Department: 1724)
Gas separation: processes
Liquid contacting
And degasification of a liquid
C095S163000, C095S166000, C095S174000, C095S180000, C095S193000, C095S209000, C095S231000
Reexamination Certificate
active
06767388
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for dehydrating and fractionating a low-pressure natural gas.
BACKGROUND OF THE INVENTION
French patent FR-B-2,605,241 describes a process for treating a natural gas or a refinery gas containing water so as to eliminate at least part of the water contained in said gas, wherein:
a) the gas is contacted with a recycled liquid phase containing water and a solvent (methanol for example); the resulting aqueous liquid phase is discharged and a gas containing, in the vapour state, water and the major part of the solvent is recovered,
b) said gas is cooled so as to condense a liquid phase essentially consisting of water and solvent, and
c) the non-condensed gas is separated from this liquid phase, which forms the phase recycled to stage (a).
French patent FR-B-2,787,870 notably describes a process for fractionating a high-pressure natural gas (pressure above about 5 MPa) wherein at least part of the gas is expanded so as to be used as a cooling agent, expansion being carried out before the fractionating operation, and for gas purification (scrubbing), this operation being carried out by means of a technique allowing simultaneously distillation and heat exchange (for example in an exchanger-dephlegmator). This prior document also describes integration of the fractionating process with a dehydration process using methanol.
Now, there are cases where the natural gas, after coming out of the well or passing through various installations or equipments, is at a pressure lower than about 5 MPa. To fractionate these gases (i.e. extract the condensates or NGL), a new process has been discovered which also uses a simultaneous heat exchange and distillation operation (for example in an exchanger-dephlegmator type device) which, integrated with a dehydration stage, affords the advantage of being very simple and of requiring reduced investment costs.
SUMMARY OF THE INVENTION
The invention thus proposes a new process allowing both dehydration and fractionation (stripping) of a low-pressure wet natural gas containing notably hydrocarbon constituents referred to as <<heavy>> constituents (C
3
+
), hydrocarbon constituents referred to as <<light >> constituents (C
1
and C
2
) and water.
The process of the invention, applied to a low-pressure (P
0
below about 5 MPa) we natural gas containing constituents referred to as <<heavy >> constituents and constituents referred to as <<light >> constituents, can generally be defined by the fact that it comprises in combination at least the following stages:
a) at least a fraction of the wet gas at a temperature T
0
is contacted with an aqueous liquid phase L'
1
containing methanol, said gas carrying along substantially all of the methanol contained in said aqueous phase L'
1
,
b) the gas from stage (a) is cooled to a temperature T
1
lower than temperature T
0
, which produces a gas phase G
1
at equilibrium with a hydrocarbon-containing liquid phase L
1
containing C
3
+
and an aqueous liquid phase L'
1
containing methanol,
c) aqueous liquid phase L'
1
is sent to stage (a), and
d) gas phase G
1
is fractionated by distillation carried out by continuous thermal exchange with a cooling fluid, which allows to extract, on the one hand, the <<light)>> constituents in the gas form (phase G
2
) and, on the other hand, the <<heavy>> constituents in the form of condensates (phase L
2
).
To carry out the thermal exchange in stage (d), it is possible to use an external cooling fluid such as a propane cycle. However, according to a preferred embodiment of the process of the invention, the cooling fluid consists of gas G
2
itself after expansion. In this case, the expanded gas is heated by the thermal exchange of stage (d); it can also be heated by thermal exchange with the gas entering stage (b). It is recompressed thereafter in order to be exported.
More particularly, refrigeration of the gas in stage (b) can be achieved successively with cooling water or an air-cooled exchanger, then by exchange with the cooling fluid of stage (d), and finally, if necessary, by means of an external coolant such as a propane cycle.
Preferred and advantageous embodiments of the process according to the invention are described hereafter.
The hydrocarbon liquid phase L
2
formed in stage (d) and comprising mainly C
3
+
condensates can also contain lighter hydrocarbons (C
1
and C
2
) and require stabilization. It can then be sent to a stabilization stage (e) in order to obtain stabilized condensates L
3
and a gas phase G
3
, to be fractionated, which is then sent back to fractionating stage (d).
Small amounts of methanol which it may be desirable to recover generally remain in the C
3
+
condensates from stage (d) (phase L
2
) or in the stabilized C
3
+
condensates from stabilization stage (e) (phase L
3
). A condensate washing stage (f) can therefore be carried out using an aqueous phase; the aqueous phase having thus extracted the methanol can then be partly regenerated, in a regeneration stage (g), for example by stripping with the remaining fraction of the initial wet natural gas that has not been contacted with the aqueous liquid phase L'
1
in stage (a). The aqueous phase thus partly regenerated in regeneration stage (g) is used again to extract the methanol from the C
3
+
condensates in washing stage (f).
In the latter case, after stripping of the methanol, the natural gas fraction considered is mixed with the fraction that has been contacted with the aqueous liquid phase L'
1
in stage (a).
During the fractionating stage of the process according to the invention, methanol losses can occur. To compensate for these losses, extra methanol can be added, for example in the gas upstream from cooling stage (b) and/or at the start of the distillation operation of stage (d) and/or during the stage of expansion of gas G
2
.
REFERENCES:
patent: 3633338 (1972-01-01), Zahn
patent: 4775395 (1988-10-01), Rojey et al.
patent: 4979966 (1990-12-01), Rojey et al.
patent: 4999031 (1991-03-01), Gerhardt et al.
patent: 5167675 (1992-12-01), Rhodes
patent: 5782958 (1998-07-01), Rojey et al.
patent: 5797981 (1998-08-01), Collin et al.
patent: 5907924 (1999-06-01), Collin et al.
patent: 6001153 (1999-12-01), Lebas et al.
patent: 6004380 (1999-12-01), Landreau et al.
patent: 6461413 (2002-10-01), Landreau et al.
patent: 2002/0059865 (2002-05-01), Lemaire et al.
patent: 2002/0062735 (2002-05-01), Lecomte et al.
patent: 2002/0178918 (2002-12-01), Lecomte et al.
patent: 2002/0185006 (2002-12-01), Lecomte et al.
patent: 0362023 (1990-04-01), None
patent: 2605241 (1988-04-01), None
patent: 2787870 (2000-06-01), None
Fischer Beatrice
Lecomte Fabrice
Viltard Jean-Charles
Antonelli Terry Stout & Kraus LLP
Institut Francais du Pe'trole
Smith Duane S.
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