Natural gas purification

A process and apparatus for removing an impurity from a gas by means of selective absorption of a gas impurity by a suitable absorbent. The absorbent and gas are contacted in a cocurrent flow contacter which is submerged in the absorbent. The flow of the absorbent in the absorber can be induced by means of the dispersion of the gas in the absorbent thereby avoiding the need for pumps or other means to induce circulation. The process and the apparatus can be used for the removal of carbon dioxide from natural gas with the use of salt water, e.g., sea water as the absorbent. The invention is specially useful for removing carbon dioxide from natural gas obtained from a natural gas well located in off shore waters that produces a gas with a high concentration of carbon dioxide as the apparatus can be erected on the ocean floor and use the surrounding sea water as absorbent.

BACKGROUND OF THE INVENTION 
This invention relates to a method and apparatus for treating a gaseous 
mixture in order to change the concentration of a component thereof. In 
another aspect, this invention relates to the selective absorption of an 
undesirable component of a gaseous mixture. In another aspect, this 
invention relates to an apparatus used for treating a gaseous mixture 
wherein said apparatus is submerged in the absorbent. Still another object 
of this invention relates to the contacting of an absorbent with a gas 
wherein the flow within the absorber is induced by means of the dispersion 
of the gas in the absorbent. In yet another aspect, this invention relates 
to the removal of carbon dioxide from a gas. Still another aspect of the 
present invention is the removal of carbon dioxide from a gas using salt 
water, e.g., sea water, as the absorbent. Another aspect of the present 
invention is the removal of carbon dioxide from carbon dioxide-containing 
natural gas. In yet another aspect, this invention relates to the removal 
of an impurity from a gas with the absorber being submerged in the 
absorbent and the impurity-rich absorbent is discharged at an absorbent 
depth such that the absorbent density at the level of discharge is very 
close to the density of the impurity-rich absorbent being discharged. 
Still another aspect of this invention relates to a method for removing 
impurities from a gas in which the absorbent flow rate is controlled by 
manipulating the liquid level in the top of the absorber. In still another 
aspect, this invention relates to the treatment of carbon dioxide 
containing natural gas obtained from an offshore well wherein the absorber 
is erected on the ocean floor and sea water is used to absorb the carbon 
dioxide. 
The volume of natural and industrial gases treated for various purposes is 
continually increasing. Efficient and effective methods of treating gases, 
therefore, are very important to industry. The need for efficient and 
economical methods of treatment is especially important in the natural gas 
industry where the percentage of gas produced which requires treating will 
continue to increase as uncontaminated gas reserves are depleted. 
One of the most common impurities found in natural gas is carbon dioxide. 
In many areas of the world, natural gas, predomonantly methane, is found 
associated with major amounts of carbon dioxide. When the carbon dioxide 
content exceeds about 10 volume percent, especially about 20 volume 
percent or greater, its removal by conventional means, such as amine 
absorption, becomes uneconomical due to the high energy consumption of the 
amine process required for regenerating the amine and due to the excessive 
size of the equipment necessary to remove such a large amount of CO.sub.2. 
The problem also exists in the handling of the large volume of removed 
CO.sub.2 unless a special situation exists where there is a worthwhile use 
for large amounts of carbon dioxide such as in flooding reservoirs for 
secondary or tertiary oil recovery. Also, it may be economical to use the 
gas as it is produced as a low heating value fuel if a suitably large 
demand for fuel gas for power generation or industrial purposes exists 
within a reasonable distance from the production site. Unfortunately, 
however, many of these gas reservoirs are in remote areas where no major 
demand for fuel exists, where carbon dioxide has no value and where 
construction of gas processing facilities is expensive. The cost of 
transporting the gas can be reduced, therefore, if the CO.sub.2 could be 
removed at the well, especially if the CO.sub.2 is present in a very high 
concentration. 
Accordingly, it is an object of this invention to provide a method which 
enables more economical and convenient treating of gaseous mixtures. 
Another object of the present invention is to provide an apparatus to be 
used in the treatment of gaseous mixtures. 
Another object is to provide a process for treating a gas with an absorbent 
which does not require mechanical pumping of the absorbent or a high 
pressure absorber vessel. 
Another object of the present invention is to provide a simple process for 
treating natural gas obtained from off shore wells. 
Another object of the present invention is to save on cost of transporting 
gas from a well in a remote area, e.g., such as an offshore well 200 miles 
from land. 
Another object is to provide a novel means for achieving a single stage of 
contacting of absorbent sea water with CO.sub.2 -rich natural gas in a 
cocurrent flow contactor. 
Other objects, aspects, and the several advantages of this invention will 
be apparent to those skilled in the art upon a study of this disclosure, 
the appended claims and the drawing. 
SUMMARY OF THE INVENTION 
The present invention is concerned with a process for treating a gaseous 
mixture in order to change the concentration, i.e., remove a component or 
impurity thereof. The impurity is removed through selective absorption. A 
gas and absorbent are contacted in a cocurrent contacting zone wherein the 
flow of the absorbent is induced by means of the dispersion of the gas and 
the absorbent. 
In one embodiment, this invention is concerned with a method for removing 
at least one impurity from a gas comprising introducing an absorbent 
having an absorbing capacity for an impurity and a gas into the lower 
portion of an absorber's contacting zone, wherein the absorber is 
submerged in the absorbent, to thereby allow contact between the gas and 
absorbent as the gas and absorbent flow cocurrently upward through the 
absorber. Unabsorbed gas is accumulated near the top of the absorber and 
recovered. Impurity-rich absorbent is then discharged into the surrounding 
absorbent via appropriate discharge means. 
Another embodiment of the invention concerns the discharge of the 
impurity-rich absorbent into the surrounding absorbent at an absorbent 
depth such that the absorbent density at the level of discharge is very 
close to, but preferably, less than the density of the impurity-rich 
absorbent being discharged. 
In another embodiment, the absorbent flow rate through the absorber is 
controlled by manipulating the liquid level in the top of the absorber, 
thereby changing the liquid heat against which the absorbent must flow. 
The invention is especially applicable to any carbon dioxide-containing 
gas, but is particularly useful when the carbon dioxide concentration is 
10 volume percent or more. When the system is used for the removal of 
carbon dioxide from a gas, salt water, e.g, sea water, can be used as an 
appropriate absorbent. 
Accordingly, the process and apparatus of the present invention find great 
applicability in the treatment of a gaseous mixture of carbon dioxide and 
natural gas where the natural gas well is in a remote area with sea water 
available. The invention would be of particular importance in treating 
natural gas having a high concentration of carbon dioxide obtained from an 
offshore well. 
The apparatus generally used in the process of the invention comprises a 
contacting zone with means for introducing feed gas and absorbent into the 
bottom portion of the contacting zone with means near the top of the zone 
for collecting and removing unabsorbed gas. 
In another embodiment, the absorber also comprises a plurality of discharge 
means located at various levels to thereby allow the discharge of the 
impurity-rich absorbent at a depth such that the absorbent density at that 
level is very close to but, preferably less than the density of the 
impurity-rich absorbent being discharged. The absorber also comprises 
means to transport impurity-rich absorbent from the upper portion of the 
contacting zone to the discharge means.

DETAILED DESCRIPTION OF THE INVENTION 
Treatment of a gaseous mixture by an absorbent in order to remove an 
undesirable component thereof is well known in the art. The present 
invention, however, provides a novel means for achieving contacting of an 
absorbent with a gas in a cocurrent flow contactor. 
The absorber of the present invention comprises a contacting zone with 
means for introducing feed gas and absorbent into the lower portion of the 
contacting zone and accumulating means near the top of the contacting zone 
for collecting and removing unabsorbed gas. Any suitable accumulating 
means for collecting and removing the unabsorbed gas that is known in the 
art can be used in the present invention, e.g., a vapor-liquid separator 
or even an inverted funnel type structure wherein the gas is collected in 
the cone and removed by means of a conduit to appropriate storage for 
further use. The absorber is generally submerged in the absorbent at a 
sufficient depth to obtain the hydraulic pressure desired in order to 
maintain sufficient absorber pressure to thereby avoid mechanical pumping 
of absorbent and the need for a high pressure absorber vessel since 
internal and external pressures would therefore nearly be the same. 
The lower portion of the contacting zone into which the absorbent and gas 
are introduced can also comprise the dispersion means. The dispersion 
means can be any conventional dispersion device, e.g., a bank or plurality 
of orifices, or, a plurality of Venturi tubes. The dispersion device aids 
in dispersing the gas as bubbles into the absorbent which thereby aids in 
the contacting between the gas and absorbent and in inducing the flow of 
the absorbent upwardly through the contacting zone. 
The absorber can also comprise a plurality of discharge means located at 
various levels of the absorbent to thereby allow the discharge of the 
impurity-rich absorbent at an absorbent depth such that the absorbent 
density at that level is very close to, but, preferably, less than the 
density of the impurity-rich absorbent being discharged. It is preferred, 
therefore, that the impurity-rich absorbent is discharged at an absorbent 
depth such that the absorbent density at that level is at least about 
0.0002 g/ml less than the density of the impurity-rich absorbent being 
discharged. This insures that the impurity-rich absorbent sinks and does 
not rise to the surface of the body of the absorbent. If the impurity-rich 
absorbent is discharged at an absorbent depth at which the absorbent 
density is greater than that of the impurity-rich absorbent, bubbles of 
impurity can form and pass from solution. This is particularly important 
when CO.sub.2 is being absorbed by sea water as it is not desirable to 
allow the CO.sub.2 to come out of solution and pass into the atmosphere. 
It is preferable to have the CO.sub.2 rich sea water sink and have the 
CO.sub.2 remain subsurface so that the CO.sub.2 is gradually dissipated, 
e.g., by ocean currents. The depth at which the impurity-rich absorbent is 
discharged, however, should not be at such a shallow depth as to allow 
mixing with fresh absorbent to be used in the separation process. 
Passage means allow the impurity rich absorbent to flow from the contacting 
zone to the appropriate level of discharge. The passage means can be 
nothing more than an annulus between the contacting zone and an extended 
portion of the collecting means as shown in the FIGURE at 25. The annulus 
is formed by the extension of the lower portion of the collecting means 
for the unabsorbed gas. The lower portion extends outside of the 
contacting zone and below the lowest level at which effluent absorbent is 
likely to be discharged. The plurality of discharge means can be located 
vertically on the extended lower portion of the collecting means, which 
can also be referred to as the outside shell of the absorber. 
In another embodiment, the absorber can have a plurality of inlet means of 
different absorbent depths to thereby allow taking of absorbent of various 
densities and conduit means for transporting the absorbent from the 
plurality inlet means to the bottom portion of the contacting zone. The 
plurality of inlet means provides for selecting the desired absorbent 
density, and, for example, allows for the inlet of the absorbent to be 
from a depth where the absorbent density is less than that of the 
impurity-rich absorber effluent and is still above the depth at which 
impurity-rich absorbent is discharged. This prevents the mixing of 
impurity-rich absorber effluent with absorbent to be used in the 
contacting zone. 
The process generally comprises introducing a gas and an absorbent having 
an absorbing capacity for an impurity contained in said gas into the lower 
portion of an absorber's contacting zone to thereby allow contacting 
between the gas and absorbent as the gas and absorbent flow cocurrently 
upward through the absorber. The absorber is generally submerged in the 
absorbent, e.g., sea water, at a sufficient depth to obtain the hydraulic 
pressure desired to maintain absorber pressure sufficient to thereby avoid 
mechanical pumping of the absorbent. The need for a high pressure absorber 
vessel is also avoided since internal and external pressures are nearly 
the same due to the submergence of the absorber in the absorbent. When the 
absorbent and gas reach the top of the contacting zone, unabsorbed gas is 
accumulated near the top of the absorber in an accumulating means and 
recovered therefrom. The impurity-rich absorbent that issues from the top 
of the contacting zone is then discharged from the absorber into the 
surrounding absorbent via discharge means. 
The flow of the absorbent in the absorber is induced by means of the 
dispersion of the gas in the absorbent when being introduced into the 
cocurrent contacting zone. The feed gas is injected into the lower portion 
of the contacting zone which can comprise a conventional dispersion device 
such as a bank or plurality of orifices or a plurality of venturi tubes. 
The orifices or other dispersion means can be positioned across the entire 
cross section of the lower portion of contacting zone to insure the 
uniform dispersion of gas bubbles in the absorbent. The dispersion of the 
gas into the lower portion of the contacting zone induces the absorbent 
flow through the contacting zone and the bouyancy resulting from the feed 
gas being dispersed in the liquid in the contacting zone provides for 
continued absorbent circulation. This portion of the system, basically, 
operates on the same principle as an airlift pump. 
The discharge means used to discharge the impurity rich absorbent into the 
surrounding absorbent can be any appropriate means for allowing the used 
absorbent to pass from the absorber. For example, the discharge means can 
merely be an opening in the absorber located near the upper portion of the 
absorber. Passage means can also be used to pass the impurity-rich 
absorbent to a desired depth of absorbent prior to being discharged into 
the surrounding absorbent. It is preferred that impurity-rich absorbent 
effluent from the absorber is discharged at a depth such that the 
absorbent density at that level is very close to, but, less than the 
density of the impurity-rich effluent which thereby minimizes the chance 
for impurity-rich absorbent to back mix with fresh absorbent entering at 
the base of the absorber. Preferably, the impurity-rich absorbent effluent 
from the absorber is discharged at a depth such that the absorbent density 
at that level is at least about 0.0002 g/ml less than the density of the 
impurity-rich absorbent being discharged. The discharge of the used or 
impurity-rich absorbent at a depth of surrounding absorbent that is of a 
lesser density also avoids the release of large volumes of absorbed 
impurities to the atmosphere in the vicinity of the operation. This is 
especially desirable when the absorbed impurity is carbon dioxide as it is 
undesirable to release large volumes of carbon dioxide to the atmosphere 
in a single location. Furthermore, the CO.sub.2 will not have a tendency 
to rise and contaminate fresh sea water to be used in the separation 
process, which sea water is taken at a lesser depth than that at which the 
CO.sub.2 -rich sea water is discharged. The CO.sub.2, rather, will remain 
in solution at a low depth and gradually be dispersed by ocean currents. 
The invention, therefore, has special applicability when sea water is 
being used to absorb the carbon dioxide from natural gas. 
When the impurity-rich absorbent passes through a passage means prior to 
being discharged into the surrounding absorbent, the absorbent flow rate 
can be controlled by manipulating the liquid level in the top of the 
absorber, thereby changing the liquid head (.DELTA.H, see FIGURE) against 
which the absorbent must flow. The difference in the levels between the 
impurity-rich absorbent in the passage mans and the absorbent in the 
contacting zone is controlled to thereby control the absorbent flow rate. 
A small .DELTA.H, indicating a high level of impurity rich absorbent in 
the passage means, encourages greater absorbent flow, whereas a high 
.DELTA.H, indicating a low level of impurity rich absorbent in the passage 
means, causes reduced absorbent flow. Besides the level control, the 
absorbent flow rate can be controlled by other conventional methods such 
as the use of a pressure controller to control the back pressure of the 
treated gas or by just monitoring and controlling the rate at which the 
treated gas is taken off. Generally, any conventional method of 
controlling the rate of absorbent flow can be used to obtain and maintain 
the desired rate. 
Although it is generally desired to have a high absorbent flow, the rate of 
flow of the absorbent must be balanced against the practical aspect that 
too high an absorbent flow can dissolve too much of the gas and thereby 
give a low measure of recovery, e.g., this is true when sea water is being 
used to absorb carbon dioxide or some other impurity from natural gas. A 
high absorbent flow also affects the density of the impurity-rich 
absorbent as the concentration of impurity, e.g., CO.sub.2, would be less. 
This would require discharging the CO.sub.2 -rich absorbent at a less 
dense or shallower level which can increase the chances of back-mixing 
with fresh absorbent to be used in the separation process. 
The process and apparatus can be employed for the treatment and removal of 
components or impurities from any gas that contains components which are 
to be removed and are more soluble in the solvent than the other 
components of the gas. Natural gas, nitrogen, hydrogen, and many other 
synthesis, refinery, and manufactured gases can be treated by the process 
in order to remove impurities such as carbon dioxide, hydrogen sulfide, 
carbon monoxide, sulfur dioxide, and ammonia, to name a few. The type of 
absorbent used and the conditions of the treatment will vary, however, 
with the particular gases treated and particular impurities one wishes to 
remove. For example, the invention can be used to remove water-soluble 
gases from gases insoluble in water by using water as the absorbent. When 
a particular component of the gas is chosen as the component to be 
removed, an appropriate absorbent is chosen which has an affinity for the 
component but in which the other components are insoluble. 
The process and apparatus are particularly useful for the treatment of a 
carbon dioxide-containing gas for the removal of carbon dioxide. The 
invention is applicable to any carbon dioxide-containing gas, but will be 
particularly economical when the CO.sub.2 concentration is about 10, and 
especially 20, volume percent or more. 
The use of salt water, e.g., sea water can be used most economically and 
efficiently as the absorbent for carbon dioxide from a carbon 
dioxide-containing gas. Although other appropriate absorbents can be used, 
the particular type of absorbent used will ultimately be determined by the 
gas, which must be less soluble than the CO.sub.2 in the absorbent, in 
admixture with the carbon dioxide. 
The invention has been found to be particularly useful in the removal of 
carbon dioxide from natural gas, especially when the natural gas field is 
in a remote area and the CO.sub.2 concentration is 10 volume percent or 
more of the gas mixture. The removal of the carbon dioxide, when it is in 
such high concentrations, at the well will help reduce the cost of 
transporting the gas from the remote area to a place of use or storage. 
The invention, therefore, finds great applicability to the treatment of 
natural gas obtained from the gas well located at sea, e.g., 200 miles 
from land, as the pumping of the gas to land for processing will be a 
great expense and the removal of carbon dioxide, which can be about 70 
mole percent of the gas mixture, will help to reduce the cost of 
transporting the gas to shore. 
The invention does not require that the apparatus be used at sea, but can 
be also used in fresh or brackish water areas as long as the apparatus can 
be completely submerged. In shallow water areas, a hole can be dug in the 
bottom of the reservoir in order to completely submerge the column to 
provide greater hydrostatic operating pressure for the apparatus. In 
general, the hydrostatic operating pressure can be increased to the 
desired level if the body of absorbent is of insufficient depth by digging 
a hole in the floor of absorbent body. 
The invention is also applicable for use in a large pool or tank of solvent 
or absorbent in which the contacting device is completely submerged. Once 
the absorbent is introduced into the device and gas is introduced into the 
bottom of the device, the hydraulic lift is sufficient so that no other 
pumps are needed to effect the cocurrent contacting. 
One preferred embodiment of this invention, however, is the use of the 
process and apparatus to treat natural gas obtained from an off shore well 
at sea for the removal of carbon dioxide using the sea water as an 
absorbent. The CO.sub.2 removal is accomplished by erecting the cocurrent 
absorption towers on the ocean floor and using the surrounding sea water 
as the absorbent. The location on the ocean floor is not essential. As 
long as the column is completely submerged, it can be suspended or 
supported or can even rest in a hole of sufficient size bored into the 
bottom of the water reservoir in order to provide sufficient hydrostatic 
operating pressure for the process. 
The invention, therefore, provides a novel means for achieving a single 
stage of contacting the absorbent sea water with CO.sub.2 -rich natural 
gas in a cocurrent flow contactor. If more than one stage of contacting is 
desired, multiple stage contacting can be obtained by introducing the 
treated gas removed from the top of one absorber into the bottom of 
another similar absorber. 
Better understanding of the invention will be obtained by reference to the 
drawing and the following illustrative example. The drawing and 
illustrative examples are used as a detailed description of one preferred 
embodiment of the invention but is not meant to be limited thereto. 
Although the process is described with respect to the removal of carbon 
dioxide from natural gas using sea water as the absorbent, it is to be 
noted that the invention is not meant to be limited to this one preferred 
embodiment. 
Referring now to the FIGURE, the absorber is submerged in the sea at any 
desired level, but could most conveniently be located on or near the sea 
floor. The outer shell of the absorber, which is an extension of the means 
for accumulating the treated gas, can be closed at the bottom as 
illustrated, e.g., sealed to the draft tube contacting zone 2. 
Alternatively, the bottom of the outer shell can be open. The extension or 
skirt, however, should extend well below the lowest level at which 
effluent sea water is likely to be discharged. Feed gas, at near 
absorption temperature and at slightly higher pressure than the base of 
the absorber to thereby provide the energy for dispersion, is injected 3 
into the contacting zone, inducing the flow of sea water into the bottom 
of the contacting zone 4 by virtue of the bouyancy created by the column 
of dispersed gas bubbles. A dispersion means can be used to aid in 
dispersing the feed gas into the liquid in the contacting zone e.g. by 
means of orifices or a plurality of venturi tubes. 
Inlet sea water to be used as absorbent is preferably taken at a depth 
where water density is less than the CO.sub.2 -saturated effluent to 
thereby avoid possible mixing of the effluent water with the fresh water. 
Thus, the inlet will generally be at a shallower depth than the depth at 
which the effluent is discharged; hence, several inlet valves 5 can be 
provided at different water depths to allow for taking inlet sea water of 
such a lesser density. Absorbent sea water can be taken from any depth, 
however, as long as one is careful to avoid the problem of mixing the 
discharge with the inlet sea water. 
As the mixed phases issue from the top of the draft tube contacting zone 6 
into the means for accumulating the treated gas 7, the unabsorbed gas is 
disengaged and accumulated in 7 and is then removed from the top of the 
absorber via conduit means 8. The CO.sub.2 -rich sea water flows into a 
passage means and is then discharged into the ocean via a discharge line 
located at appropriate depth. In the drawing, the passage means is an 
annular space 25 between the contacting zone and the outer shell or 
extension of the accumulating means. The CO.sub.2 rich sea water is then 
discharged via one of the plurality of discharge means 9. If desired, 
fresh sea water can be introduced into the discharge line by means not 
shown to lower the CO.sub.2 concentration of the effluent, thereby 
assuring that gas bubbles are not released from the effluent stream. If 
fresh sea water is used to lower the CO.sub.2 concentration of the 
effluent, the level of discharge should be such that the density of the 
effluent is greater than that of the surrounding sea water, even upon 
temperature equilibration with the surrounding sea water. 
The liquid level at the top of the absorber, or the .DELTA.H, can be 
controlled in order to obtain the desired sea water flow rate or any 
conventional method can be used to control the sea water flow rate. One 
manner in which this can be done is by manipulating a control valve 10 on 
the treated gas effluent, thereby changing the gas back pressure. If 
desired, a pressure controller, not shown, can be provided on the 
discharge gas line 8 or a level controller 11 and level transmitter 12 can 
be used to manipulate valve 10. The sea water flow rate can be measured by 
any conventional means or the flow can be estimated indirectly by 
monitoring the composition of the treated gas with a conventional onstream 
analyzer, e.g., a gas chromatograph. The liquid level in the absorber can 
be either above or below the top of the draft tube contacting zone 
depending on flow conditions and the particular equipment configuration. 
The desired level of discharge of the CO.sub.2 -rich sea water can be 
determined by comparing the density profile of the surrounding sea with 
the density of the CO.sub.2 -saturated effluent using conventional density 
measuring devices or simply by determining the temperature profile of the 
sea, the temperature and composition of the effluent water and comparing 
these with known density-temperature relationships. Dissolved CO.sub.2 
tends to increase the density of sea water. For example, at 80.degree. F., 
sea water densities are as follows: 
______________________________________ 
CO.sub.2 Partial 
d, gm/ml Pressure, psia 
______________________________________ 
1.010426 0 
1.010634 15 
1.010762 20 
1.010850 25 
1.010880 30 
______________________________________ 
The density of sea water also tends to increase with decreasing 
temperature, of course, and the temperature of sea water decreases with 
increasing water depths. Thus, other things being equal, the more CO.sub.2 
enriched the effluent sea water becomes the deeper the point of discharge 
would be. 
The level of CO.sub.2 -enriched sea water discharge can be controlled in a 
variety of ways. The preferred manner of control is that of using 
discharge lines at two or more levels from the absorber, as indicated at 9 
in the FIGURE. These would preferably be remotely operated. The operation 
can even be automated by using a differential density instrument which can 
compare the density of the effluent water with that of the surrounding sea 
at appropriate levels. The level of sea water discharge can also be varied 
by using a movable or telescoping discharge means, e.g., a pipe or some 
other conduit, which can be pneumatically manipulated. 
The following example illustrates the utility of the invention and 
exemplifies the type of conditions used in the process of the invention. 
The example, however, is not meant to be limiting in any way as the 
conditions under which the process can run can vary greatly and depend 
upon, among other things, the location of the apparatus, the particular 
absorbent used and the gaseous mixture to be treated. The particular 
example is concerned with the preferred embodiment of the invention 
wherein the single stage absorber is submerged in sea water for the 
purpose of removing the carbon dioxide from methane gas. 
Example 
Natural gas comprising 70 percent by volume CO.sub.2 and 30 percent 
CH.sub.4 is produced at a rate of 18,000,000 SCFD (standard cubic feet per 
day) from well heads as deep as 450 feet below mean sea level at a 
pressure of 3,000 psig and a temperature of 260.degree. F. (127.degree. 
C.). Sea floor temperature is about 60.degree. F. The gas is passed to a 
40-foot single stage absorber as shown in the FIGURE. The pressure at the 
bottom of the absorber is about 210 psia with the pressure at the top of 
the absorber about 198 psia. The gas is contacted with the absorbent sea 
water in a 30-foot draft tube-type contacting zone. 
The following table give information with respect to the amount of CO.sub.2 
absorbed. 
______________________________________ 
Case I Case II 
______________________________________ 
Sea water absorbent 
36,000 gpm 72,000 gpm 
circulation (80 ft.sup.3 /s) 
(160 ft.sup.3 /s) 
CO.sub.2 final concentration 
42% 25% 
(% volume) 
CO.sub.2 removed (% volume) 
73% 90% 
CH.sub.4 removed (% volume) 
11% 28% 
______________________________________ 
Certain modifications of the invention will become apparent to those 
skilled in the art, and the illustrative details enclosed are not to be 
construed as imposing unnecessary limitations on the invention.