Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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HYDROCARBON RECOVERY SYSTEM
This application corresponds to United States Patent 5,766,313
which application was a continuation-in-part application of United
States patent application serial no. 08/583,560 filed January 5, 1996
now abandoned, which application was a continuation application of
United States patent application serial no. 08/354,607 filed December
13, 1994, now abandoned.
Field of the Invention
This invention relates to a system for recovering all the
hydrocarbons emitted from the still column of a natural gas
dehydrating system of the type employed to remove water vapor from a
natural gas stream composed of a mixture of natural gas, liquid
hydrocarbons, water and water vapor, and is particularly directed to
field natural gas dehydrators.
Background & Summary of the Invention
Examples of such gas dehydrating systems are disclosed in U.S.
Pat. Nos. 3,094,574; 3,288,448; 3,541,763; 4,402,652 and 4,588,424 by
Charles Richard Gerlach and Rodney Thomas Heath. In general, such
systems comprise a separator means for receiving the oil and water
liquids from "wet" (water vapor laden) gas; and a water absorber
means, which employs a liquid dehydrating agent such as glycol, for
removing the water vapor from the wet gas and producing
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"dry" gas suitable for commercial usage. The glycol is
continuously supplied by a pump to the absorber means in
a "dry" low-water vapor- pressure condition and is
removed from the absorber means in a "wet" high-water
vapor-pressure condition. The wet glycol is continuously
removed from the absorber means and circulated through a
reboiler means, which includes a still column, for
removing the absorbed water from the glycol and heating
the glycol to provide a new supply of hot dry glycol.
Heating of the glycol in the reboiler means is generally
accomplished through use of a gas burner mounted in a
fire tube. The hot dry glycol from the reboiler means
passes through a heat exchanger, where the hot dry glycol
transfers some of its heat to incoming wet glycol going
to the still column. The dry glycol subsequently passes
to a dry glycol storage tank. A glycol passage means is
provided to enable passage of wet glycol from the
absorber means to the reboiler means and to pump dry
glycol from the storage tank to the absorber means.
Besides water, the wet glycol going to the still
column of the reboiler of the natural gas dehydrator will
contain natural gas and absorbed hydrocarbons. A large
part of the natural gas flowing with the wet glycol to
the still column is the natural gas required to power the
glycol pump. The balance of the natural gas and other
hydrocarbons are absorbed into the glycol during the
water-absorption step in the absorber means.
On many dehycirator.s, a volume of natural gas is
intentionally induced into the reboiler in order to dry
the wet glycol to a higher concentration than can be
accomplished by simply adding heat. The process of
intentionally inducing a volume of natural gas into the
reboiler is referred to as gas stripping.
In the still column of the reboiler of the natural
gas dehydrator, the water, natural gas, and other
hydrocarbons are separated from the glycol by the
pressure reduction from the absorber pressure to
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approximately atmospheric pressure in the still column and by the
application of heat from the burner in the fire tube of the reboiler.
The water, natural gas, and other hydrocarbons contained in the
wet glycol stream which are separated in the still column from the wet
glycol will be exhausted into the atmosphere through the atmospheric
vent on the still column. The hydrocarbon vapors released through the
still column of a natural gas dehydrator are air pollutants.
Specifically, certain hydrocarbons such as benzene, toluene,
ethylbenzene, and xylene, commonly referred to as BTEX have been
proven to be carcinogenic.
To eliminate the air pollution created by a natural gas
dehydrator, the hydrocarbons being exhausted from the still column
would have to be collected and disposed of in some manner. Since in
the present configuration of most natural gas dehydrators, the volume
of hydrocarbons being vented by the still column are considerably
greater than the burner on the reboiler can consume, reduction of the
volume of hydrocarbons being vented would need to be one of the goals
of a hydrocarbon free venting system. Also, a field natural gas
dehydrator has a gas burner that operates on an on/off cycle so that a
system to eliminate the vented hydrocarbons must be compatible with
such a field natural gas dehydrator. Another goal would be to collect
and route to the reboiler burner for combustion the balance of the
irreducible volume of hydrocarbons being vented from the still column
of a natural gas dehydrator.
Thus, a need exists for a system which would first reduce the
volume of hydrocarbons being vented by the still column of a natural
gas dehydrator and second, would safely collect and route the
remaining vented hydrocarbons to the reboiler burner for combustion.
According to one aspect of the invention, there is provided in a
glycol dehydrator apparatus for removing water from natural gas using
dry glycol in an absorber to produce water laden wet glycol and
recovering dry glycol from the water laden wet glycol using a still
having a reboiler fired by a burner so that gaseous hydrocarbons,
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vaporized water and vaporized hydrocarbons are produced in the still
as emissions and wherein the dry glycol is supplied under relatively
high pressure to a water absorber apparatus, the improvement
comprising: collecting apparatus for collecting the emissions from the
still; condenser apparatus for condensing said emissions into
hydrocarbon vapors, liquid water and liquid hydrocarbons; pressurizing
apparatus for raising said hydrocarbon vapors, liquid water and liquid
hydrocarbons to a predetermined pressure to produce pressurized
hydrocarbon vapors, liquid water and liquid hydrocarbons; separating
apparatus for separating and removing said pressurized liquid water
and said pressurized liquid hydrocarbons and leaving said pressurized
hydrocarbon vapors; a first conduit extending between said separating
apparatus and said burner for feeding pressurized hydrocarbon vapors
from said pressurizing apparatus to said burner; a supply of fuel gas
under pressure; a second conduit extending between said supply of fuel
gas under pressure and said first conduit; and control apparatus for
supplying fuel gas from said supply of fuel gas to said first conduit
through said second conduit as needed to be combined with said
hydrocarbon vapors from said pressurizing apparatus to supply all of
the fuel required to fire said burner.
According to a further aspect of the invention there is provided
in a method for removing water from natural gas using dry glycol and
recovering dry glycol from the water laden glycol using a still having
a reboiler fired by a burner so that gaseous hydrocarbons are produced
in the still as emissions and wherein the dry glycol is supplied under
relatively high pressure to a water absorbing apparatus: collecting
the emissions from the still; condensing said emissions into
hydrocarbon vapors, liquid water and liquid hydrocarbons; raising the
pressure of said hydrocarbon vapors, liquid water and liquid
hydrocarbons to produce pressurized hydrocarbon vapors, pressurized
liquid water and pressurized liquid hydrocarbons; separating and
removing said pressurized liquid water and said pressurized liquid
hydrocarbons in a separator apparatus; conducting said pressurized
hydrocarbon vapors from said separator apparatus to the burner;
providing a supply of fuel gas under pressure; mixing portions of said
supply of fuel gas with portions of said pressurized hydrocarbon
vapors to supply the fuel needed to fire said burner.
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Brief Description of the Drawing
Illustrative and presently preferred embodiments of
the invention are shown in the accompanying drawing in
which:
Fig. I is a schematic drawing of a hydrocarbon
emissions-free, natural-gas dehydration system that would
be mainly applicable to dehydrators presently in use;
Fig. II is a schematic drawing of another embodiment
of a hydrocarbon, emissions-free, natural-gas dehydration
system that would be mainly applicable for the
manufacture of new dehydration systems;
Fig. III is a schematic drawing of another
embodiment of a hydrocarbon, emissions-free, natural-gas
dehydration system that would be mainly applicable for
the manufacture of new dehydration systems;
Fig. IV is a schematic drawing of another embodiment
of a hydrocarbon, emissions-free, natural-gas dehydration
system that would be mainly applicable to dehydrators
already in use;
Fig. V is a schematic drawing of another embodiment
of a hydrocarbon emissions-free natural gas dehydration
system employing a jet pump means; and
Fig. VI is a schematic drawing of another embodiment
of a hydrocarbon emissions-free system for use with
natural gas dehydration systems.
Fig. VII is a schematic drawing of another
embodiment of a hydrocarbon emissions free system for use
with natural gas dehydration systems.
Detailed Description of the Invention
Referring to Fig. 1, a vacuum pump 2, an over-head
condenser 3, a still column 9, a three-phase emissions
separator 4, all with inner-connecting piping, are shown
in association with the major components of a two-phased
conventional natural gas dehydrating system comprising a
gas liquid separator means 5 for removing oil and water
liquids from water vapor laden natural gas; an absorber
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means 1 for removal of water vapor from the natural gas,
including internal bubble tray means 6 for providing a
downward flow of dry glycol with upward counterflow of
the natural gas therethrough; an external gas-glycol heat
exchanger means 7 for cooling the dry glycol prior to the
entry of the dry glycol into the absorber means; a glycol
reboiler means 8 for receiving wet glycol and discharging
hot dry glycol, including a still column means 9 for
separating the water, natural gas, and other hydrocarbons
from the glycol by vaporizing the various components from
the glycol; a reboiler tank means 11 for holding and
heating the partially dry glycol received from the still
column means 9, and a gas burner means 13 and fire tube
means 14 for heating the partially dry glycol; a dry
glycol storage tank means 15 for storing the dry glycol
prior to return to the absorber means 1; and a glycol-
glycol heat exchanger means 16 for cooling dry glycol
from the reboiler means 8 before entry into the storage
tank means 15 while pre-heating the wet glycol from.the
absorber means 1 before entry into the still column means
9.
In operation of the system in Fig. 1, natural gas
under pressure enters separator means 5 through an inlet
line 17. The natural gas system is separated into its
gaseous and liquid components. The liquid components are
removed from the separator through outlet line 18 and
motor valve 19 which is operated by liquid level
controller 20. Wet gaseous components of the natural gas
stream under pressure are transmitted through line 21 to
the lower end of the absorber means 1 and enter the
absorber mean 1 between the bottom bubble cap tray 6 and
wet glycol sump means 22. Wet gaseous components of the
natural gas stream flow upwardly through the bubble cap
means 6 which provide for intimate contact between the
downward flowing dry glycol which enters the absorber
means 1 through line 23. Line 23 receives dry high
pressure glycol from the discharge port 113 of glycol
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pump means 24. Dry cooled glycol is received from the
glycol side of the gas-glycol heat exchanger means 7 by
the suction port 112 of glycol pump means 24 through line
25. In this manner water vapor is removed from the
gaseous components of the natural gas stream as the
components flow upwardly through the bubble tray means 6
and through line 26 to the gas side of glycol-gas heat
exchanger means 7 and then to pipeline 27 which contains
dry salable natural gas at relatively high pressures, for
example 50 psig to 1500 psig.
The dry glycol is delivered from storage means 15
through line 28 to inlet of gas-glycol heat exchanger
means 7 and from the outlet of gas-glycol heat exchanger
means 7 through line 25 to suction port 112 of pump means
24. Dry glycol under pressure is delivered from
discharge port 113 of pump means 24 through line 23 to
absorber means 1. Wet glycol is exhausted from the
glycol sump 22 and delivered to still column means 9 of
reboiler 8 through line 29, filter means 30, line 31,
motor valve means 32, line 33, overhead condenser means
3, line 34, heating coil 35 in three-phase emissions
separator means 4, line 36, glycol-glycol heat exchanger
means 16 in storage means 15, and line 37. Motor valve
means 32 is operated by liquid level controller 38. Wet
glycol flows downwardly in the still column means 9
toward reboiler means 8. Hydrocarbons in the gaseous
phase are immediately released from the wet glycol as a
result of pressure reduction from the absorber means 1
line pressure to still column means 9 at approximately
atmospheric pressure. The water and absorbed
hydrocarbons contained in the wet glycol are vaporized by
heat obtained from gas burner means 13 through fire tube
means 14 which extends into the tank means 11. Gaseous
hydrocarbons, vaporized water, and vaporized hydrocarbons
are removed from the upper end of still column means 9
through vent connection 10. Hot dry glycol collected in
tank means 11 flows downward through stand-pipe 39 into
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the top of glycol-glycol heat exchanger and storage means 15.
The vapors exhausting from vent 10 of still column means 9 flow
through line 41 to the inlet of overhead condenser means 3. In
overhead condenser means 3 the hot vapors are cooled by coil means 42
which contains cool wet glycol from absorber means 1. Cooling of the
hot vapors causes most of the water and some of the hydrocarbons to
change from a vapor to a liquid state. The uncondensed vapors, liquid
water and liquid hydrocarbons flow under a slight vacuum from outlet
44 of overhead condenser means 3 through line 3a to inlet port 45 of
vacuum pump means 2. Vacuum pump means 2 can be either a
reciprocating, rotary or other type of vacuum pump that is capable of
handling both liquids and vapors. Vacuum pump means 2 is required to
pull only a slight vacuum of 1 to 2 psig and to develop a discharge
pressure of 7 to 10 psig. The vacuum pump means 2 may be
hydraulically, electrically or engine driven.
Vapors, liquid water and liquid hydrocarbons are discharged under
pressure from the discharge port 46 of vacuum pump means 2 through
line 40 to three-phased emissions separator means 4.
In emissions separator means 4, the vapors, liquid water and liquid
hydrocarbons are separated from each other. The liquid water is
discharged through line 47, motor valve means 48, and discharge line
53 to disposal. Motor valve means 48 is operated by liquid level
controller 49. The liquid hydrocarbons are discharged through line 50,
motor valve means 51 and discharge line 52 to storage. Motor valve
means 51 is operated by liquid level control means 54. Liquids
contained in emissions separator means 4 are heated by heating coil
means 35 located in the lower portion of emissions separator means 4.
Coil means 35 contains wet glycol which has previously gained heat
from overhead condenser means 3.
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Hydrocarbon vapors which have not been condensed
exit under 7 to 10 psig from emissions separator means 4
through line 55 to drip pot means 56. Any liquids which
might be carried by the hydrocarbon vapors exiting
emissions separator means 4 are collected in drip pot
means 56, and the liquids are subsequently manually sent
to disposal through valve 57 and line 58.
Drip pot means 56 has two ports. Port 59 is an exit
port where the non-condensed hydrocarbon vapors, which
have been collected from the exhaust port 10 of still
column means 9, enter the dehydrator fuel gas system.
The fuel gas system is constructed to allow the burner
fuel to perform the function of gas stripping prior to
being combusted by burner means 13. Gas stripping
increases the removal of the water contained in the
glycol being heated in the tank means 11 of reboiler
means 8.
Without being supplemented, the volume of
hydrocarbon vapors exiting port 59 of drip pot means 56
is not enough to supply all of the fuel required to fire
burner means 13. In order to properly fire burner means
13, it is necessary to supplement the volume of
hydrocarbon vapors exiting through port 59 of drip pot
means 56. Drip pot means 60 contains supplemental fuel
gas which is supplied to drip pot means 60 through line
61. Line 61 is connected to the inlet end of regulator
means 63 and to port 62 located on the outlet end of gas-
glycol heat exchanger means 7. The regulator means 63
reduces the salable line pressure to 15 - 20 psig in drip
pot means 60. Valve 64 on drip pot means 60 can be used
to manually send to disposal any liquids which might
collect in drip pot means 60. Fuel gas exits drip pot
means 60 through line 65. At point 66 line 65 is split
into two lines 67 and 68. The outlet of line 67
terminates in regulator means 69. The outlet of line 68
terminates in regulator means 70. Regulator means 69 and
70 control the direction of the flow of any fuel gas that
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is required to supplement the hydrocarbon vapors exiting
drip pot means 56 at exit port 59. Regulator means 69 is
set at approximately 1 to 2 psig higher pressure than
regulator means 70. For example, regulator means 69
could be set at 8 psig and regulator means 70 could be
set at 6 psig. Under these conditions, 8 psig would be
maintained on lines 71 and 72 downstream of regulator
means 69. Line 72 terminates at check valve means 73.
Check valve means 73 prevents any fuel gas contained in
line 72 from entering the fuel gas system supplying the
burner means 13. Line 71 terminates at regulator means
74. Regulator means 74 is set to control 3 to 7 psig
pressure on line 75 downstream of regulator means 74.
Line 75 terminates at port 76 on reboiler means 8. Port
76 contains a 3/64 inch or larger orifice. The orifice
size contained in port 76 will be increased as the
natural gas handling capacity of absorber means 1 is
increased. Gas handling capacity of absorber means 1 is
a function of the diameter, height and pressure at which
absorber means 1 will be operating.
From port 76 natural gas passing through the small
orifice enters a gas stripping system indicated by line
77 in tank means 11 of reboiler means 8. Natural gas
released from the gas stripping system in reboiler means
8 combines with the natural gas, water vapor and
hydrocarbon vapors which are released into still column
means 9 by the rich glycol entering from line 37.
Ultimately the stripping gas will flow through port 10,
line 38, vacuum pump means 2, line 40 emissions separator
means 4, line 55, drip pot means 56, and the rest of the
fuel system, to be described later, to become part of the
fuel gas consumed by burner means 13.
The fuel gas flowing to burner means 13 can be
derived from two sources. The first source is the
hydrocarbon vapors exiting from emissions separator 4
which flow through line 55 and inlet port 78 into drip
pot means 56. The second source is supplemental fuel gas
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which is controlled by regulator means 70. If the volume
of fuel gas entering drip pot means 56 through line 55
and port 78 is not sufficient to meet the fuel
requirements of burner means 13, the pressure in drip pot
means 56 will decrease. When the pressure in drip pot
means 56 reaches the set pressure of regulator means 70,
supplemental fuel gas would begin to flow through
regulator means 70 into line 79 and inlet port 80 on drip
pot means 56. Regulator means 70 then would maintain
enough pressure, approximately 6 - 7 psig in drip pot
means 56, to supply the fuel requirements of burner
means 13.
The fuel gas flowing to burner means 13 will exit
drip pot means 56 at port 59 and into line 81. Line 81
splits at point 82 into lines 83 and 84. If, because of
excess hydrocarbon vapors exiting emissions separator
means 4, the pressure in line 83 becomes higher than the
set pressure on regulator means 69, then no supplemental
stripping gas is required. The supplemental stripping
gas flow through regulator means 69 would cease, and the
gas required for gas stripping would flow through line
83, check valve means 73, and line 72 into line 71. Line
84 handles the fuel gas flowing to both the pilot light
and main burner of burner means 13. Line 84 splits at
point 85 into lines 86 and 87. Line 87 leads to the
inlet side of regulator means 88. Regulator means 88
controls the fuel gas pressure at 6 to 10 psig flowing to
the main burner of burner means 13. From regulztor means
88, the fuel gas flows through line 89 to motor valve
means 90. Motor valve means 90 is controlled by
thermostat means 92 mounted in tank means 11 of reboiler
means 8. Thermostat means 92 senses the temperature of
the glycol in tank means 11 and through line 91 sends a
signal to motor valve means 90 to increase or decrease
the fuel gas flow through line 95 to the main burner of
burner means 13. Line 86 leads from point 85 to the
inlet of regulator means 93. Regulator means 93 controls
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the fuel gas pressure at 3 to 5 psig required to fire the pilot light
of burner means 13. From the regulator means 93, the fuel gas at
reduced pressure of 3 to 5 psig flows through line 94 to the pilot
light of burner means 13.
As previously mentioned, the volume of hydrocarbon vapors which are
being vented by the present configuration of most dehydrators which
could be retrofitted with the present invention is more than the
burner means 13 can consume. New dehydrators could be configured
differently thereby insuring that the volume of hydrocarbon vapors
being vented can be consumed by the burner. Application of the present
invention on new dehydrators will be explained in detail later. To
reduce the amount of hydrocarbon vapors which must be consumed by
burner means 13 on presently installed dehydrators, one embodiment of
the present invention incorporates a hydraulic pump means 96 which is
driven by a small horsepowered natural gas powered engine. At the
discharge port 97 of hydraulic pump means 96, glycol is discharged at
high pressure into line 98. Line 98 splits at point 99 into lines 100
and 101. Line 100 carries high pressure glycol to the inlet port 102
of hydraulic motor means 103. High pressure glycol flows through
hydraulic motor means 103 to provide the energy to power vacuum pump
means 2. Glycol exits at exit port 104 of hydraulic motor means 103 at
a reduced pressure. The low pressure glycol continues to flow through
line 105 to glycol reservoir means 106. The glycol reservoir means 106
stores enough low pressure glycol to always maintain a positive
suction head on hydraulic pump means 96. Glycol flows through line 107
from reservoir means 106 to the suction port 108 of hydraulic pump
means 96.
From point 99 on the discharge side of hydraulic pump means 96, high
pressure glycol flows through line 101 to the power port 103a of
glycol balanced pump means 24. Prior to this invention, the power port
103a of glycol balanced pump means 24 was normally connected to
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discharge port 111; Fig. 1, of glycol filter means 30.
The wet glycol under pressure from glycol sump 22
together with some gas provided the energy to power
glycol balanced means 24. The wet glycol leaving exit
port 109 would be fed into the still column 9 and this
.wet glycol has an excess amount of natural gas contained
therein. To eliminate from still column means 9 the
natural gas required to drive glycol balanced pump means
24, the present invention uses hydraulic energy supplied
by hydraulic pump means 96 to drive glycol balanced pump
means 24. Eliminating the natural gas required to drive
glycol balanced pump means 24 reduces the volume of
hydrocarbons being vented from still column means 9 to
less than the fuel gas required to fire burner means 13.
High pressure glycol from hydraulic,pump means 96 enters
the power port 108 of glycol balanced pump means 24
providing the energy to drive glycol balanced pump means
24. The glycol at reduced pressure exits glycol balanced
pump means 24 at exit port 109 and flows through line 110
back to glycol reservoir means 106. Any additional
glycol necessary for the operation of the system can be
added into the dry glycol storage 15. This is also
appropriate for the systems described below.
As shown in Fig. 2, hydraulic pump means 96 as well
as glycol pump means 24 could both be powered by electric
motors. Hydraulic dry glycol pump 24 has been changed
from a glycol balanced pump to a mechanical pump means
1.14. In thi s embodiinent of the invention, hydraulic
energy would still power the hydraulic motor means 103
which in turn drives vacuum pump means 2. All other
components of the system will function as previously
described in Fig. 1.
As shown in Fig. 3, hydraulic pump means 96,
hydraulic motor means 103, and vacuum pump means 2 have
all been eliminated. Again, dry glycol pump 24 has been
changed to a mechanical pump means 114. Vacuum pump
means 2 has been changed to a Roots-type blower means
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115. Both the mechanical pump means 114 and the Roots-
type blower means 115 would be directly driven by either
an electric motor or small horsepower internal combustion
engine. All other components of the system will function
as previously described in Fig. 1.
As shown by Fig. 4, hydraulic motor means 103 and
vacuum pump 2 have been replaced by a Roots-type blower
means 115, direct driven by the small horsepower internal
combustion engine. All other components of the system
will function as previously described in Fig. 1.
Fig. 5 shows another version of the process. In
Fig. 5, a jet pump means 116, such as could be provided
by Penberthy Houdaille, is used to provide the vacuum
needed to collect the effluent from still column means 9.
Also in Fig. 5, two gear-type hydraulic pump means 117
and 118, such as could be provided by Rotor-Tech, Inc.,
are connected to either an electric motor or a natural
gas engine means 119. Gear-type hydraulic pump means 117
circulates the process glycol through the system. Gear-
type hydraulic pump means 118 circulates oil from
emissions separator means 4 through jet pump means 116
before returning the oil to emissions separator means 4.
The three-phase emissions separator means 4 would be
filled to an operating level with a low viscosity oil
before the unit is placed in service. The original
charge of oil would continually be supplemented by any
liquid hydrocarbons condensed from the effluent exiting
still column means 9 and collected by the vacuum created
by jet pump means 116.
Jet pump means 116 creates, at vacuum port means
120, a vacuum which draws into the body of jet pump means
116 the condensed liquids and non-condensed gases
contained in the still column effluent from still column
means 9. A stream of oil from emissions separator means
4 with the pressure increased by gear-type hydraulic pump
means 118 enters jet pump means 116 at inlet port means
121. The stream of oil together with the effluent from
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still column means 9 exists from jet pump means 116 at discharge port
means 122. The oil continues flowing through line means 123 back into
three-phased emissions separator means 4.
Three-phased emissions separator means 4 separates the free liquids,
both oil and water, from the non-condensed gases. The non-condensed
gases are handled as previously described. The free liquids are
separated into oil and water components and are handled as previously
described. The residual oil contained in emissions separator means 4
is continuously circulated through line means 124 to suction port
means 125 of gear-type hydraulic pump means 118. Energy provided by
power means 119 turns gear-type hydraulic pump means 118 raising the
pressure of the oil exiting gear-type hydraulic pump means 118 at
discharge port means 126 to approximately 150-200 psig. The high
pressure oil from discharge port means 126 flows through line means
127 to inlet port means 121 of jet pump means 116. The pressure of the
oil entering inlet port means 121 of jet pump means 116 is reduced to
approximately 15 to 30 psig by flowing through an orifice and then a
venturi in jet pump means 116 thereby creating a vacuum at vacuum port
means 120.
Again, referring to FIG. 5, gear-type hydraulic pump means 117
circulates the process glycol. The function of the circulating glycol
has already been described. A possible mechanical configuration of
gear-type pump means 117 and 118 would have both pumps being driven in
parallel from the main shaft of either an electric motor or a natural
gas engine.
Referring to FIG. 6, it is envisioned that the concept of an
emissions-free dehydrator could be used on new dehydrators as well as
retrofitting dehydrators already in use.
On new dehydrators, the reboiler means 8 and other vessels could be
designed to withstand any anticipated
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external pressure, and control of the vacuum created by jet pump means
116 would not be necessary. The result of the increased vacuum which
would be available on new dehydrators would be to significantly
enhance the reboiler means 8 ability to obtain high purity
concentrations of the lean glycol. The higher the concentration of the
lean glycol, the better the gas water dew-point that can be obtained
by a dehydrator.
On dehydrators that are already in use, the reboiler means 8 and other
vessels are not designed for a significant external pressure. To
prevent possible collapse of reboiler means 11 and other vessels on
dehydrators already in use, it would be necessary to control the
vacuum created by jet pump means 116. A vacuum in the range of 12 to
60 inches of water column would be adequate to collect all the
effluent from still column means 9.
There are several methods to control the vacuum created by jet pump
means 116. One method would be to use a vacuum sensing controller
means 128 such as supplied by Fisher controls to sense the vacuum at
vacuum port means 120 of jet pump means 116. The controller means 128
would operate a motor valve means 129 to feed gases contained in
emissions separator means.4 through line means 130 and 131 into line
means 119a which connects to vacuum port means 120. The controller
means 128 could be set to control the desired vacuum. Anytime the
vacuum in line means 119a exceeded the set pressure of the controller
means 128, the controller means 128 would open motor valve means 129
to feed additional gases into line means 119a.
There are two possible heat sinks which could be used for cooling the
vapors in overhead condenser means 3.
One heat sink, the rich glycol from absorber means 1, has been
previously described. The other heat sink, the salable gas exiting
heat exchanger means 7, is shown in
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FIG. VII. In FIG. VII wet glycol from absorber means 1 is exhausted
from glycol sump means 22 and delivered to still column means 9 of
reboiler means 8 through line 29, filter means 30, line 31, motor
valve means 32, line 132, glycol to glycol heat exchanger means 16 in
storage means 15, line 133, heating coil means 35 in three-phase
emissions separator means 4 and line 134.
To provide the heat sink required to cool overhead condensed means 3,
dry salable gas from absorber means 1 flows through line 134, the gas
side of glycol to gas heat exchanger means 7, line 135, overhead
condenser means 3, and line 136 to gas outlet means 27.
FIG. VII also shows a gear-type hydraulic pump means 117 being used to
power glycol balanced pump means 24. Glycol from glycol reservoir
means 106 flows through line 136 to the suction port means 137 of
gear-type hydraulic pump means 117. The glycol pressure is increased
by the pumping action of gear-type hydraulic pump means 117. The power
to turn gear-type hydraulic pump means 117 is supplied by either an
electric motor or an internal combustion engine. The glycol at an
elevated pressure exits gear-type hydraulic pump means 117 at
discharge port means 133. The glycol at elevated pressure flows
through line 139 to the power port 140 of glycol balanced pump means
24. The glycol entering the power port 140 provides the energy to
drive glycol balanced pump means 24. The glycol at reduced pressure
exits glycol balanced pump means 24 at exit port 141 and flows through
line 142 back to glycol reservoir means 106.
Thus, the present invention provides a gas dehydrating system for
removing water vapor from a natural gas stream composed of natural
gas, liquid hydrocarbons, water and water vapor. The system comprises
a separator for receiving the natural gas stream and removing oil and
water liquids and producing a water vapor laden gas stream; a water
absorber for receiving the water vapor laden gas stream and removing
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water vapor to produce a dry sales gas stream. The water
absorber has a glycol inlet for receiving dry low water
vapor pressure glycol and a glycol outlet for removing
wet high water vapor pressure glycol. The system further
comprises a pump means for continuously supplying dry
glycol to the water absorber; a flow control for
continuously removing wet glycol from the water absorber;
and a reboiler for continuously receiving the wet glycol,
heating the wet glycol, removing absorbed water from the
glycol and providing a supply of hot dry glycol liquid.
The reboiler includes a still column for receiving glycol
laden with water and natural gas and other hydrocarbon
by-products; a hot dry glycol storage tank for
receiving the hot dry glycol liquid from the reboiler; a
natural gas-operated burner associated with the reboiler
for heating the wet glycol; and a wet glycol-dry glycol
heat exchanger pre-heating the wet glycol before entering
the reboiler and for cooling the hot dry glycol received
from the reboiler. A glycol emission recycling means is
connected to the still column for receiving all of the
water hydrocarbon laden gas stream generated in the still
column means and removing water and removing and storing
liquid hydrocarbons and collecting natural gas and
delivering collected natural gas to the burner for
combustion therein.
The invention also provides a method of recycling
natural gas hydrocarbons generated by a natural gas
drying process at a natural gas dehydrator comprising the
steps of separating the wellhead natural gas into wet
sales gas and liquid by-products in a closed environment;
treating the wet sales gas with substantially water-free
(dry) glycol to remove water vapor and create dry sales
gas and wet glycol containing water and hydrocarbon
constituents; heat treating the wet glycol to remove the
water and hydrocarbon constituents and creating a supply
of dry glycol for treatment of the wet sales gas and
creating hot gaseous water and hydrocarbon by-products;
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CA 02224389 1998-03-13
treating the hot gaseous water and hydrocarbon by-
products to remove water and liquid hydrocarbon by-
products and create a dry fuel gas by-product; collecting
the liquid hydrocarbon by-products and the dry fuel gas
by-product in a sealed reservoir; and delivering the dry
fuel gas by-product to a combustion device and burning
the dry fuel gas by-product during heat treatment of the
wet cool glycol.
The method further includes the use of the dry fuel
gas by-product in a gas stripping system to further dry
the wet glycol by collecting together with other
hydrocarbons and water all gases used by the gas
stripping system into a sealed reservoir; recycling
through the gas stripping system all gases collected in
the sealed reservoir in excess of the gas required for
heat treating the wet glycol to remove the water and
hydrocarbon constituents; and providing a pressure
control system to supplement when and where necessary the
gases required by either the gas stripping system or the
wet glycol heating system.
It is contemplated that the inventive concepts
herein described may be variously otherwise embodied and
it is intended that the appended claims be construed to
include alternative embodiments of the invention except
insofar as limited by the prior art.
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