Gas separation: processes – Liquid contacting – And degasification of a liquid
Reexamination Certificate
2000-05-10
2001-10-09
Smith, Duane (Department: 1724)
Gas separation: processes
Liquid contacting
And degasification of a liquid
C095S167000, C095S169000, C095S179000, C095S188000, C095S191000, C095S193000, C095S207000, C095S209000, C095S234000
Reexamination Certificate
active
06299671
ABSTRACT:
The present invention relates to an apparatus and a method for regeneration of a drying agent, particularly for regeneration of a drying agent used in a method for dehydrating produced natural gas at an oil or gas field.
During gas production at an oil and gas field, gas is produced which contains water vapor that it is desirable to remove prior to the further processing and transport of the gas. A typical dehydrator for such gas consists of a contactor, i.e., a column where the produced gas is introduced in countercurrent to a drying agent such as triethylene glycol (TEG) at low temperature and high pressure. The contactor is a packed column having a large surface where the drying agent, such as TEG, is introduced at the top of the column and trickles down over the column while gas is brought in at the bottom of the column and thus runs in countercurrent. At the bottom of the column, the drying agent plus H
2
O plus some of the gas is removed, while the dehydrated gas is taken out at the top of the column.
Traditionally the wet triethylene glycol is conducted to a regenerator which comprises a still, where the damp TEG is introduced at the top of the column while a purer TEG is removed from the bottom of the column, and water and any gas that is present is taken out at the top of the column. From the bottom of the regeneration column the enriched TEG is often fed through a stripping column where a stripping gas is optionally supplied in countercurrent. From the stripping column the purer TEG is often conducted down into a retention vessel, where in a preferred embodiment there is provided a so-called “cold finger”, a cooler intended to condense water vapor over the surface of the liquid in the retention vessel in order to recirculate the condensed liquid through the TEG regeneration unit, while the “dry” TEG is removed from the retention vessel and conducted back to the contactor. To improve the effect of the extra dehydration by means of the “cold finger”, there is also introduced to the retention vessel what is called a “blanket gas” or stripping gas to reduce the partial pressure of the water vapor. This “blanket gas” is then also conducted on to the stripping column and optionally also the regeneration column to function as a stripping gas in addition to equalizing the pressure in the system. This gas is a fuel gas which is burned off after use.
This traditional TEG regeneration, however, yields a TEG which could advantageously be dried more thoroughly in order to produce more effective dehydration in the contactor, in addition to the fact that the supplying of stripping gas, which is often a purified hydrocarbon gas, is an environmental problem that must be taken care of, normally by burning, a situation which in turn gives the basis for payment of a CO
2
fee. The wet TEG that is removed from the contactor contains approximately 96% by weight of TEG, whereas the regenerated TEG from this traditional dehydration is about 99.0-99.5% pure. A seemingly minor increase (e.g., 0.1% by weight) of the purity (reduced water quantity) would thus produce a considerable increase in the capacity of the dehydrated TEG to take up water, thus enabling a reduction of the recirculation rate.
The goal of the present invention is thus to reduce the amount of water in the regenerated TEG at the same time as the supplying of an extra stripping gas can be avoided.
This is solved according to the present invention by a method for regeneration of triethylene glycol (TEG) that has been used as a drying medium to remove water from a fluid such as natural gas, where a drier TEG is recovered as the bottom fraction in a regeneration column, where water vapor together with other gases is removed as the top fraction and where the partially dried TEG from the regeneration column optionally is also supplied to a stripping column for further dehydration where, in the optional stripping column and in the still column, there is supplied a stripping gas in countercurrent to the TEG stream, where as stripping gas there is mainly used gas which is recovered from the top fraction from the regeneration column.
According to the present invention there is also provided an apparatus for regeneration of triethylene glycol (TEG) that has been used as a drying medium to remove water from a fluid such as natural gas, where the wet TEG is fed into the top of a regeneration column where a drier TEG is recovered as the bottom fraction, where water vapor and other gases are taken out as a top fraction and where to the regeneration column there is optionally connected a stripping column for further dehydration of the partially dried TEG from the regeneration column, where to the optional stripping column and to the still there is supplied a stripping gas in countercurrent to the TEG stream, where a cooler is provided for cooling down the top fraction from the regeneration column to a temperature where water vapor is condensed and may be separated from the rest of the top fraction.
Closer examinations of the wet TEG from the contactor have shown that this mixture contains of the order of 3 mole-% C
1
-C
5
hydrocarbons and 1.5 mole-% CO
2
, together with about 22 mole-% water.
According to the present invention, the quantity of gas contained in the drying agent is utilized as a stripping gas by recirculating and feeding it back to the TEG regeneration unit as stripping gas. This produces substantial savings in that one avoids having to use fuel gas as a stripping agent, in addition to the fact that it is possible to reduce severely the quantity of gas that is released and must be burned.
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patent: 3837143 (1974-09-01), Sutherland et al.
patent: 3975172 (1976-08-01), Ranke
patent: 4010065 (1977-03-01), Alleman
patent: 4273620 (1981-06-01), Knobel
patent: 4280867 (1981-07-01), Hodgson
patent: 5490873 (1996-02-01), Behrens et al.
patent: 5520723 (1996-05-01), Jones, Jr.
patent: 5536303 (1996-07-01), Ebeling
Browdy and Neimark
Greene Jason M.
Read Process Engineering A/S
Smith Duane
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