Note: Descriptions are shown in the official language in which they were submitted.
CA 02426071 2011-12-13
-1 -
NATURAL GAS DEHYDRATOR AND SYSTEM
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part application of U.S. Patent
Application Serial
No. 10/071,721, now issued as United States Patent 6,551,379 entitled
"Apparatus for Use
with a Natural Gas Dehydrator", to Heath, filed on February 8, 2002". This
application is
also related to U.S. Patent No. 5,766,313, entitled "Hydrocarbon Recovery
System," to
Heath; U.S. Patent No. 6,238,461, entitled "Natural Gas Dehydrator," to Heath;
and U.S.
Patent No. 6,364,933, entitled "Apparatus for Use with a Natural Gas
Dehydrator," to Heath.
BACKGROUND OF THE INVENTION
Field of the Invention (Technical Field):
The present invention relates generally to an apparatus and system for use
with
natural gas dehydrators of the type used to remove water and water vapor from
a natural
gas stream having a mixture of natural gas, liquid hydrocarbons, liquid
hydrocarbon vapors,
water and water vapors. The invention is particularly directed for use in the
regulation of the
glycol and the processing of all combustible gases with natural gas
dehydrators.
Description of Related Art:
Note that the following discussion refers to a number of publications by
author(s) and
year of publication, and that due to recent publication dates certain
publications are not to
be considered as prior art vis-a-vis the present invention. Discussion of such
publications
herein is given for more complete background and is not to be construed as an
admission
that such publications are prior art for patentability determination purposes.
An example of natural gas dehydrators is disclosed in U.S. Patent No.
6,238,461
issued May 29, 2001 and U.S. Patent No. 6,364,933 issued April 2, 2002 to
Heath. In
general, such systems comprise a separator for
-2-
receiving oil and water liquids from "wet" (water vapor laden) gas; and a
water absorber, which employs
a liquid dehydrating agent such as glycol, for removing the water vapor from
the wet gas and producing
"dry" gas suitable for commercial usage. The glycol is continuously supplied
by a pump to the absorber
in a "dry" low-water vapor-pressure condition and is removed from the absorber
in a "wet" high-water
vapor-pressure condition. The wet glycol is continuously removed from the
absorber and circulated
through a reboiler, 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 is
generally accomplished through use of a gas burner mounted in a fire tube. The
hot dry glycol from the
reboiler 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 is provided to enable passage of wet glycol
from the absorber to the
reboiler and to pump dry glycol from a storage tank to the absorber. 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, and other gaseous components.
On many dehydrators, 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
approximately atmospheric pressure in the still column and by the application
of heat to the reboiler.
The water, natural gas, other hydrocarbons and gases contained in the wet
glycol stream which
are separated in the still column from the wet glycol are exhausted as vapors
into the atmosphere
through the atmospheric vent on the still column unless facilities are
installed to collect and dispose of
the vented vapors. 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. Other
;0 gases such as hydrogen sulfide, when present, are toxic.
The gas dehydrator and systems for use with gas dehydrators disclosed in U.S.
Patent Nos.
6,238,461, 5,766,313, 6,364,933, and SN 10/071,721 offer solutions to at least
some of the problems
discussed above. The present invention provides improvements to such gas
dehydrators and systems.
CA 02426071 2004-07-21
CA 02426071 2011-12-13
-3-
BRIEF SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided a method of
dehydrating
natural gas, the method comprising the steps of: providing an absorber for
receiving the
natural gas; linking the absorber to a still column; transferring wet glycol
from the absorber
to the still column; linking a reboiler to the absorber; transferring dry
glycol from the reboiler
to the absorber to dehydrate the natural gas; linking a glycol-to-glycol heat
exchanger to and
between the reboiler and the absorber; linking at least one separator to the
still column to
receive effluent and remove liquid hydrocarbons and water from the effluent
for collection
and removal of gaseous hydrocarbons from the effluent; linking at least one
vacuum
generating component to the at least one separator to receive gaseous
hydrocarbons from
the separator; linking at least one emissions separator to the at least one
vacuum
generating component to receive the wet glycol from the at least one vacuum
generating
component and from the absorber and to transfer gaseous hydrocarbons to a
firing system
of the reboiler; and not releasing gaseous hydrocarbons to the atmosphere.
According to yet a further aspect of the invention there is provided an
apparatus for
dehydrating natural gas, said apparatus comprising: an absorber linked to a
still column,
said absorber receiving the natural gas; wet glycol flowing from said absorber
to said still
column; a reboiler linked to said absorber; dry glycol flowing from said
reboiler to said
absorber to dehydrate the natural gas, thus hydrating the glycol and producing
wet glycol; a
glycol-to-glycol heat exchanger linked to, and between, said reboiler and said
absorber;
at least one separator linked to said still column to receive effluent and
remove liquid
hydrocarbons and water from said effluent for collection and removal of
gaseous
hydrocarbons from said effluent; at least one vacuum generating component
linked to said
at least one separator to receive gaseous hydrocarbons from said separator;
at least one emissions separator linked to said at least one vacuum generating
component
to receive said wet glycol from said at least one vacuum generating component
and from
said absorber and to transfer gaseous hydrocarbons to a firing system of said
reboiler; and
an effluent condenser linked between, and to, said still column and said at
least one
separator; and wherein gaseous hydrocarbons are not released to the
atmosphere.
CA 02426071 2011-12-13
-3A-
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
The accompanying drawings, which are incorporated into and form a part of the
specification, illustrate one or more embodiments of the present invention
and, together with
the description, serve to explain the principles of the invention. The
drawings are only for the
purpose of illustrating one or more preferred embodiments of the invention and
are not to be
construed as limiting the invention. In the drawings:
Figure 1 is a flow diagram of one embodiment of the invention;
Figure 2 is a flow diagram of another embodiment of this invention;
Figure 3 is a flow diagram of another embodiment of this invention;
CA 02426071 2010-05-19
-4-
Figure 4 is a sketch of a water exhauster of this invention;
Figure 5 is a sketch of a blowcase of this invention;
Figure 6 is a flow diagram of another embodiment of this invention;
Figure 7 is a sketch of a hydrocarbon gas stripping system of this invention;
Figure 8 is a flow diagram of another embodiment of this invention;
Figure 9 is a sketch of a glycol storage and glycol reservoir of this
invention; and
Figure 10 is a flow diagram of another embodiment of this invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is an apparatus and system for use with a natural gas
dehydrator. The gas dehydrator and systems disclosed in U.S. Patent Nos.
5,766,313, 6,238,461, 6,364,933, and 6,551,379 are useful in understanding the
present invention.
The volume and pressure of the natural gas flowing through the system of
the present invention can vary in wide ranges. Each unit is designed by those
skilled
in the art to perform at wide ranges of volume and pressure of the natural gas
being
processed and various controls have been associated with the natural gas
dehydrators so that these dehydrators can be operated in a conventional manner
by those skilled in the art. The operation of the various components of this
invention
uses conventional apparatuses that are normally used in the operation of a
natural
gas dehydrator. Therefore, the specific parameters associated with the
operation of
the various components of this invention are parameters known by those skilled
in
the art.
As shown in the drawings, in accordance with the present invention, the
natural gas is first passed through conventional two or three-phase inlet
separator 24
to remove water and liquid hydrocarbons therefrom. The natural gas is then fed
into
absorber 2, through inlet 4, so that the natural gas can flow upwardly through
absorber 2. Dry glycol is introduced through inlet 6 and flows through spaced
apart
bubble trays or other contact medium (not shown) in absorber 2 and then
downwardly through absorber 2. The dry glycol functions primarily to remove
water
from the natural gas and
CA 02426071 2003-04-22
-5-
becomes wet glycol. The treated natural gas exits through outlet 8 in the top
portion of absorber 2 and
is passed through tube side 9 of glycol-gas heat exchanger 10 and passes out
as dry, saleable natural
gas through pipe 12 at relatively high pressures, for example 50 PSIG to 1500
PS1G depending on the
operating pressures of the pipeline system. It is understood that any type of
conventional heat
exchanger can be used in place of exchanger 10 illustrated in Fig. 1.
In one configuration of the invention (see Figure 1), the wet glycol is
collected in wet glycol
sump 14 in the bottom portion of absorber 2 and contains entrained and
absorbed gases, liquid
hydrocarbons, and water and exits absorber 2 at point 16, is discharged by
control valve 17 through
filter 19 in pipe 18 to inlet 20 of reflux coil 22 located in still column 24
(explained below). The flow of
the wet glycol is controlled by a throttling liquid level control (not shown)
located in absorber 2 and
operates motor valve 17 to maintain a constant level of wet glycol in the
bottom of absorber 2. The wet
glycol flows through reflux coil 22, cooling and condensing some of the hot
vapors in the top of still
column 24. The wet glycol at inlet 20 is between approximately 90 and 120 F.
and at exit 26 is
approximately 150 F. The wet glycol exits reflux coil 22 at exit 26 and flows
through pipe 28 where at
point 30 it is combined with other wet glycol (explained below) flowing
through pipe 32. A by-pass can
be provided to by-pass reflux coil 22 when desired. The combined wet glycol
flows through pipe 34 and
enters inlet 36 of wet glycol cooler 38. Glycol cooler 38 may be one of many
types of coolers. As
shown in the drawings, the combined wet glycol flows through a radiator and is
cooled by air pushed
through the radiator by a fan. Preferably, the fan is driven at a constant
speed and the amount of the
cooling air passing through the radiator is controlled by a plurality of
pivotally mounted shutters moved
by suitable means, such as an air cylinder or other devices such as a servo
motor which moves a rack
to rotate each of the shutters between opened and closed positions such as
that marketed by AIR-X-
CHANGERS as MODEL 48H. In the system illustrated in Figure 1, the combined wet
glycol exits the
wet glycol cooler at a temperature of between approximately 90 and 120 F.
The cooled combined wet glycol exits the glycol cooler 38 and flows through
pipe 40 into inlet
42 of a three-phase emissions separator apparatus 50. Free gaseous
hydrocarbons contained in the
wet glycol are released in the three-phase emissions separator apparatus 50 as
a result of the reduction
of pressure from the pressure of the absorber of between approximately 50 and
1500 PSIG to the
pressure in the three-phase emissions separator which is between approximately
10 and 30 PSIG and
preferably about 15 PSIG. Liquid hydrocarbons are separated from the combined
wet glycol in the
three-phase emissions separator apparatus 50 by a weir system or interface
liquid level controller (not
shown) and are withdrawn through outlet 52 and flow through control valve 54
and pipe 55 to storage
(not shown) or other apparatus. The amount of the wet glycol from the combined
wet glycol entering
CA 02426071 2003-04-22
-6-
the emissions separator 50, after the gases and liquid hydrocarbons have been
removed, is then
combined with a fixed volume of wet glycol contained in the emissions
separator 50. The fixed volume
of wet glycol is continuously recirculated. Therefore, the total volume of wet
glycol in the emissions
separator may be described as at least two portions of wet glycol. One portion
is that required to be
continuously circulated through one type of apparatus as explained below and
another portion to be
passed through glycol-to-glycol heat exchanger 64 for heat exchange with the
hot dry glycol exiting the
reboiler as explained below. From the glycol-to-glycol heat exchanger the
heated wet glycol flows to the
still column and into the reboiler. The volume of wet glycol exiting emissions
separator 50 to enter the
glycol-to-glycol heat exchanger 64 is about the same volume as the volume of
glycol being pumped into
absorber 2 by glycol pump 76 (see Figure 1). The volume of dry glycol pumped
is usually in the range
of 3 to 6 gallons of dry glycol for each pound of water removed from the gas
stream. The
amount of dry glycol pumped is determined in a conventional manner known to
those skilled in the art.
The volume of wet glycol flowing out of emissions separator 50 to the glycol-
to-glycol heat exchanger 64
is controlled-by control valve 53 which is controlled by a throttling liquid
level control (not shown) located
in emission separator 50.
The freed gaseous hydrocarbons exit through outlet 56 in the top portion of
the three-phase
emissions separator apparatus 50 and- flow through pipe 58 into a system, such
as that described in the
United States Patent No. 5,766,313, to be used as fuel in a reboiler as
described therein.
Another portion of wet glycol passes from three-phase emissions separator 50
through pipe 60
and enters tube side 62 of glycol-to-glycol heat exchanger 64. It is
understood that any type of heat
exchanger may be used in place of the heat exchanger 64 shown in Figure 1.
Another portion of wet
glycol in glycol-to-glycol heat exchanger 64 is heated by the hot dry glycol
therein and flows from glycol-
to-glycol heat exchanger 64 through pipe 66 and enters still column 24 of
conventional reboiler 68, such
as that illustrated in the `313 Patent. Another portion of wet glycol is
changed into hot 'dry glycol which
is then fed through pipe 70 into glycol-to-glycol heat exchanger 64 and is
cooled by the other portion of
wet glycol. The partially cooled dry glycol then passes through pipe 72 into
dry glycol storage tank 74
from which it is pumped by pump 76 through pipe 78 into the gas to glycol heat
exchanger 10 to be
further cooled by the natural gas flowing through heat exchanger 10 and into
pipe 12.
The one portion of the wet glycol in, emissions separator 50 exits through
pipe 86 and enters
pump 88. The one portion of wet glycol exiting from pump 88 separates at point
90 into the first stream
of wet glycol flowing through pipe 92 and a second stream of wet glycol
flowing through pipe 94. The
wet glycol in pipe 94 passes through filter 96 and then through pipe 98 into
effluent condenser 84. As
;~ y t,
CA 02426071 2003-04-22
-7-
described above, the second stream of wet glycol exits effluent condenser 84
through pipe 32 and is
combined at point 30 with the wet glycol in pipe 28.
In a second configuration of the invention, as shown in Figure 2, the wet
glycol is collected in
wet glycol sump 14 in the bottom portion of absorber.2 and contains entrained
and absorbed gases,
liquid hydrocarbons and water and exits absorber 2 at point 16. It is
discharged by control valve 17
through filter 19 in pipe 18 to point 30 where the wet glycol from absorber 2
combines with cooled wet
circulating glycol from glycol cooler 38 (explained below). The flow of the
wet glycol from absorber 2 is
controlled by .a throttling liquid level control (not shown) located in
absorber 2 and operates control valve
17 to maintain a constant level of wet glycol in the bottom of absorber 2. The
combined wet glycol flows
through pipe 41 into inlet 42 of three-phased emissions separator apparatus
50. Free gaseous
hydrocarbons contained in the wet glycol from absorber 2 are released in three-
phased emissions
separator 50 as a result of the reduction of pressure from the pressure of the
absorber of between 50
and 1500 PSIG to the pressure in three-phased emissions separator 50 which is
between 10 and 30
PSIG and preferably about 15 PSIG. Liquid hydrocarbons are separated from the
wet glycol in three-
phased emissions separator 50 by gravity and by a weir system or an
interfacing liquid level controller
(not shown) and are withdrawn through outlet 52, control valve 54, and pipe 55
to storage (not shown)
or other apparatus. The wet glycol entering emissions separator 50, after the
gases and liquid
hydrocarbons have been removed, is then combined with a fixed volume of wet
glycol contained in
emissions separator 50. The fixed volume of wet glycol is continuously
recirculated. Therefore, the
total volume of wet glycol in the emissions separator has at least two
portions of wet glycol. One portion
is that required to be continuously circulated (explained below) and another
portion is to be passed
through a glycol-to-glycol heat exchanger 64 for heat exchange with the hot
dry glycol exiting reboiler 68
(explained below). From glycol-to-glycol heat exchanger 64 the heated wet
glycol flows to still column
24 and into reboiler 68. The volume of wet glycol exiting emissions separator
50 through control valve
53 to enter the glycol-to-glycol heat exchanger 64 is about the same volume as
the volume of glycol
being pumped into absorber 2 by the glycol pump 76 (see Figure 2). The volume
of dry glycol pumped
is usually in the range of 3 to 6 gallons of dry glycol for each pound of
water removed from the gas
stream. The amount of dry glycol pumped is determined in a conventional manner
known to those
skilled in the art. The volume of wet glycol flowing out of emissions
separator 50 to the glycol-to-glycol
heat exchanger 64 is controlled by control valve 53 which is controlled by an
interfacing liquid level
control (not shown) located in emissions separator 50. To overcome any
potential pressure drop, in
excess of the gas pressure in emissions separator 50, which might occur below
control valve 53 as a
result of friction drop in the glycol piping, glycol-to-glycol heat exchanger,
or other apparatus, valve 53 is
CA 02426071 2003-04-22
-8-
located to receive glycol from the discharge of circulating pump 88 at
approximately 100 PSIG above
the pressure in emissions separator 50 (explained below).
The freed gaseous hydrocarbons exit through outlet 56 in the top portion of
three-phased
emissions separator apparatus 50 and flow through pipe 58 into a system such
as that described in the
United States Patent No. 5,766,313, to be used as fuel in a reboiler as
described therein.
The other portion of wet glycol passes from three-phased emissions separator
50 through pipe
86, circulating pump 88, and pipe 61 to point 65. At point 65, the other
portion of wet glycol is split into
two streams. As described below, one stream of wet glycol flows through pipe
92 to power eductor 112.
The second stream of wet glycol flows through pipe 94 to point 90 where the
second steam of wet glycol
splits into wet glycol stream 3 and wet glycol stream 4. Wet glycol stream 3
flows through pipe 67,
control valve 53, and pipe 57 and enters tube side 62 of glycol-to-glycol heat
exchanger 64. It is
understood that any type of heat exchanger may be used in place of heat
exchanger 64 (Shown in
Figure 2). Wet glycol stream 3 in glycol-to-glycol heat exchanger 64 is heated
by the hot dry glycol
therein and flows from glycol-to-glycol exchanger 64 through pipe 66 and
enters still column 24 of
conventional reboiler 68 such as that illustrated in the `313 Patent wherein
the other portion of wet glycol
is changed into hot dry glycol which is then fed through pipe 70 into the
shell side of glycol-to-glycol
heat exchanger 64 and is cooled by the other portion of wet glycol. The
partially cooled dry glycol than
passes through pipe 72 into a dry glycol storage tank 74 from which it is
pumped by pump 76 through
pipe 78 into the gas to glycol heat exchanger 10 to be further cooled by the
natural gas flowing through
heat exchanger 10 and into pipe 12. Dry glycol storage 74 has vent pipe 75
which vents dry glycol
storage 74 to the atmosphere. Pipe 75 is connected to dry glycol storage 74 at
point 77.
Wet glycol stream 4 flows at approximately 100 PSIG pressure created by
circulating pump 88,
through pipe 95, filter 96, pipe 97, fixed choke 101 and pipe 98 to enter the
shell side of overhead
condenser 84. Fixed or variable choke 101 or a control valve actuated by a
pressure control device can
control the volume of wet glycol flowing through pipe 98. The temperature of
the wet glycol entering the
shell side of overhead condenser 84 is substantially the same as the
temperature of the wet glycol
contained in emissions separator 50. The temperature of the wet glycol in
emissions separator 50 is
maintained by a thermostat, located in emissions separator 60,. which opens
and closes shutters on
glycol cooler 38 (explained below), and the.temperature of the glycol in
emissions separator 50 is
normally maintained at approximately 90 to 120 degrees Fahrenheit. Wet glycol
stream 4 flows through
the shell side of overhead condenser 84 where wet glycol stream 4 is in a heat
exchange relationship
with the hot effluent from still column 24 (explained below). Wet glycol
stream 4 passes from overhead
CA 02426071 2003-04-22
-9-
condenser 84 through pipe 33 to the inlet 20 of a reflux coil located in still
column 24.(explained below).
Wet glycol stream 4 flows through reflux coil 22 cooling and condensing some
of the hot vapors in the
top of still column 24. Wet glycol stream 4 exits reflux coil 22 at exit 26
and flows through pipe 29 to
inlet 36 of wet glycol cooler 38. If desired, a bypass line can be provided to
bypass reflux coil 22. Glycol
cooler 38 may be one of many types of coolers useful in accordance with the
present invention. The
drawings show the wet glycol flowing through a radiator and cooled by air
pushed through the radiator
by a fan. Preferably, the fan is driven at a constant speed and the amount of
the cooling air passing
through the radiator is controlled by a plurality of pivotally mounted
shutters moved by a suitable means,
such as an air cylinder or other devices such as a servo motor which moves a
rack to rotate each of the
shutters between opened and closed positions such as that marketed by AIR-X-
CHANGERS as model
48H. In the system illustrated in Figure 2, cooled wet glycol stream 4 exits
glycol cooler 38 at point 35
at a temperature of between approximately 90 and 120 degrees Fahrenheit. From
point 35 cooled wet
glycol stream 4 flows through pipe 37 to point 30 where it combines with the
wet process glycol from
absorber 2 and the combined wet glycol flows through pipe 40 to inlet 42 of
emissions separator 50.
During the standard glycol dehydration process, gases and liquid hydrocarbons
generated by
the process are routinely released to the atmosphere. The gases and liquid
hydrocarbons released to
the atmosphere are the result of gas being entrained or absorbed in the dry
glycol while it is contacting
the natural gas in the absorber. Additional gas is entrained in the wet glycol
when a pressure actuated
pump is used to pump the dry glycol into the absorber. The entrained and
absorbed gases and
hydrocarbons are released from the wet glycol at two points in the process.
First, most of the entrained
gases are released from the wet glycol in the emissions separator by a
reduction of pressure. Second,
the balance of gases, liquid hydrocarbons, and water are substantially
released from the wet glycol by
the application of heat in the reboiler as well as by stripping in the still
column.
One of the goals of the process of this invention is to eliminate the
atmospheric pollution and
the wasting of hydrocarbon energy that now occurs inmost glycol dehydration of
natural gas. To
accomplish this goal, the process collects all the combustible,gaseous vapors
and liquid hydrocarbons
generated by the glycol dehydration process. The collected combustible vapors
are sent to the burner
fuel system to be used as fuel gas in heating the reboiler. The collected
liquid hydrocarbons are routed
to a liquid storage and handling system.
As stated above, the other portion of wet glycol entering reboiler 68 is
subjected to the heat in
the reboiler and an effluent is formed in still column U. This effluent may
comprise liquid water, liquid
hydrocarbons, vaporized water, gases and vaporized hydrocarbons. These
effluents may be treated in
CA 02426071 2003-04-22
-10-
systems similar to those described in the'461 and '933 Patents or by a system
illustrated in Figure 1,
wherein the effluent in still column 24 exits into pipe 82 and passes through
the tube side of effluent
condenser 84 where it is cooled as described below. Effluent condenser 84 may
be of the type
illustrated in the '461 and '933 Patents. If desired, the effluent condenser
illustrated in Figures 6 and 7
of the '933 Patent may be modified so that fans 234 and 252 illustrated
therein may be continuously
operated and not intermittently by a thermostat as described therein. Instead,
the control of the
temperature in the effluent condenser may be controlled by pivotally mounted
shutters located in either
the exit portion or the entrance portion of the effluent condenser. These
pivotally mounted shutters may
be operated between opened and closed positions by a servo motor, air
cylinder, or other similar device
controlled by a thermostat. As shown in Figure 2, the effluent passes through
tube side 109 of effluent
condenser 84 where it is cooled to approximately 90 to 120 degrees Fahrenheit
by wet glycol entering
the shell side of effluent condenser 84 via pipe 98. The cooled effluent
includes both gaseous and
liquid components which are routed to separator 102 via pipe 100. The cooled
effluent exiting effluent
condenser 84 flows through pipe 100 and enters separator 102 which is similar
to the separator shown
in Figures 8 and 9 of the '933 Patent except that it is mounted in a vertical
position instead of the
horizontal position.
In separator 102, the gaseous- hydrocarbons are withdrawn from the upper
portion of separator
102 through pipe 104; the liquid hydrocarbons collected in separator 102 are
withdrawn through pipe
108 and control valve 110 to the hydrocarbon storage facilities, the . water.
is withdrawn through pipe 118
and control valve 121 to disposal. The first stream of wet glycol passing
through eductor 112 creates a
vacuum to draw the gaseous hydrocarbons through pipe 104 and entrains the
gaseous hydrocarbons in
the first stream of wet glycol. The first stream of wet glycol passing through
eductor 112 compresses
the gaseous hydrocarbons entrained therein to the pressure maintained in
emissions separator 50 and
then flows through pipe 114 into emissions separator 50 wherein the gaseous
hydrocarbons separate.
from the first stream of wet glycol and flow with the freed gaseous
hydrocarbons through pipe 58 to the
fuel system. Although other types of devices may be used to create the vacuum
and compress the
gases, an eductor is the preferred device to be-used in the present invention.
Figures 3 to 5 illustrate another embodiment of the present invention. These
Figures
incorporate a large part of Figure 2 wherein the same reference numerals have
been applied to
corresponding parts of Figure 2. In Figures 3 to 5, there is illustrated an
embodiment of the invention
wherein additional water is removed from the dry glycol in pipe 70 to make
super dry glycol.
-11-
As illustrated in Figure 3, the dry glycol in pipe 70 enters water exhauster
120 (explained
below), wherein additional water is removed from the dry glycol to make super
dry glycol which exits
water exhauster 120 and flows through pipe 122 into the shell side of glycol-
to-glycol heat exchanger 64
and then through pipe 72 into what is now super dry glycol storage 74. From
storage 74, the super dry
glycol is pumped to absorber 2 and then completes the above described closed
loop system by
returning to reboiler 68 via emissions separator 50, pipe 86, circulating pump
88, pipe 61, pipe 94, pipe
67, control valve 53, pipe 57, glycol-to-glycol heat exchanger 64, and pipe 66
to still column 24.
The cooled, wet glycol exits glycol cooler 38 at point 35 and flows through
pipe 44 to inlet 164 of
a condenser tube bundle 160 mounted in water exhauster 120, as described
below, to condense some
of the vapors in the vapor section of water exhauster 120. The condensate
(mainly water and some
hydrocarbons) is transmitted to blowcase 124 through pipe 126. Blowcase 124
has a weir system that
separates the condensate into its water and hydrocarbon components. Water from
blowcase 124 is
discharged by control valve 178 into pipe 128 to combine at point 59 with the
wet glycol flowing in pipe
57. Control valve 178 is controlled by a liquid level control (not shown)
mounted in water chamber 172
of blowcase 124. Hydrocarbons from blowcase 124 (see Fig. 5) are preferably
discharged by control
valve 188 through pipe 113 into hydrocarbon chamber 111 of vacuum separator
102. In some
applications, the hydrocarbons are dumped directly to the hydrocarbon storage.
Control valve 188 is
controlled by a liquid level control (not shown) mounted in hydrocarbon
chamber 184 of blowcase 124.
Except during the dumping cycle of blowcase 124, the pressure in blowcase 124,
water
exhauster 120 and reboiler 68 is the same. The equal pressure in blowcase 124,
water exhauster 120
and reboiler 68 is established and maintained by connecting equalizing pipes
130 and 134 to inlet 136
of still column 24.
?5
Water exhauster 120, blowcase 124 and the flow of fluids is preferably as
illustrated in Figures 4
and 5; however, other systems, such as those described in United States Patent
Nos. 3,589,984 and
4,332,643 and in the article Cotdfinger by L.S. Reid may also be used in
accordance with the present
invention. As illustrated in Figure 4, dry glycol at about 3901 F having a
glycol concentration of
3 approximately 98.6 percent weight concentration exits reboiler 68 through
pipe 70 to water exhauster
120. Dry glycol 143 in water exhauster 120 is retained for about thirty (30)
minutes and is changed, as
described below, into super dry glycol that flows over dam 145 into weir
system 147 which separates
any entrained oil and the super dry glycol. Super dry glycol 148, having a
glycol concentration of about
99.8 percent weight concentration, exits water exhauster 120 into pipe 122 and
flows through the shell
side of the glycol-to-glycol heat exchange 64 and thereafter flows as
described above. Free oil 173
CA 02426071 2004-07-21
CA 02426071646 2003-04
-12-
exits weir system 147 of water exhauster 120 through pipe 150 and pipe 149 and
enters through inlet
151, the weir section 190 of blowcase 124 (explained below).
Dry glycol 143 in water exhauster 120 is maintained at approximately 3900 F by
thermo jet coil
153 which is connected to reboiler 68 at point 154. Thermo jet coil 153
continuously circulates hot dry
glycol out of reboiler 68. The thermo jet utilizes a small volume of the
recovered gas from emissions
separator 50 flowing through a small orifice 155 to create a flow of hot dry
glycol through coil 153. The
hot dry glycol flows through thermo-iet'coil 153 and returns to reboiler 68
through pipe 157 and enters
reboiler 68 at point 159.
The cooled, wet glycol flows from outlet 35 of glycol cooler 38 through pipe
44 to inlet 164 of
water exhauster 120. The cooled, wet glycol, at a temperature of between
approximately 90 to 120
degrees Fahrenheit, enters condenser tube bundle 160 at point 164 and exits at
point 165. From point
165, the cooled wet glycol flows through pipe 163 to point 30. where it
combines with the process glycol
from absorber 2, and, as previously described, from point 30, the cooled wet
glycol flows through pipe
41 to inlet 42 of emissions separator 50. The relatively cool wet glycol
flowing through condenser tube
bundle 160 cools the vapors in vapor section 162. Cooling of the vapors in
vapor section 162 results in
the condensation of some of the vapors in vapor section 162 changing the
partial pressure equilibrium
of the various vapor components in vapor section 162. The vapors in vapor
section 162 generally
include four components comprising water, glycol and condensable and non-
condensable
hydrocarbons. Since water has a relatively low boiling temperature compared to
glycol, it has a greater
vapor pressure than glycol and is the. largest component of the vapors in
vapor section 162. Liquids
condensed from vapor section 162 are collected on collection tray 168 and
removed from water
exhauster 120 at point 169. Condensation of the vapors and the removal of the
condensed liquids from
water exhauster 120 continually changes the partial pressure equilibrium of
the vapors in vapor section
162 and causes the liquid components (glycol, water and hydrocarbons) in dry
glycol 143 in water
exhauster.120 to react to re-establish their percentage of the equilibrium
vapor pressure in vapor
section 162. Being the largest component of the vapors in vapor. section 162,
water is the largest
component condensed and is the primary component evolved from hot dry glycol
143 while re-
establishing the partial pressure equilibrium of the vapors in vapor section
162. Therefore, the body of
hot dry glycol 143 in water exhauster 120 becomes increasingly water dry so
that super dry glycol flows
from weir system 147 into pipe 122.
The condensed liquids collected on collection tray 168 of water exhauster 120,
removed via
point 169 and line 126, are routed to three-phasing weir chamber 190 of
blowcase 124. Three-phasing
CA 02426071646 2003-04
-13-
chamber 190 separates the condensates from water exhauster 120 into water and
hydrocarbon
components and, through a weir system, routes the water through valve 182 into
water chamber 172
and the hydrocarbons through valve 176 into hydrocarbon chamber 184 of
blowcase 1.24. Vent pipe
130, vent pipe 134, and vent pipe 250 equalize the pressure in water exhauster
120, blowcase 124, dry
glycol storage 74, and glycol reservoir vessel 244 with the pressure in
reboiler 68 by connecting into still
column 24 at point 136.
Referring to Figure 5, when the water level in chamber 172 of blowcase 124
reaches a level to
actuate liquid level controller 174, a pressure signal is sent to close
normally opened valve 182 and to
open normally closed valves 178 and 180. Closing valve 182 temporarily stops
the transfer of water
from three-phasing chamber 190 into water chamber 172. Opening valve 180
allows recovered gas
from emissions separator 50 to enter water chamber 172 to provide the pressure
energy to partially
evacuate water chamber 172 through water dump valve 178 and line 128. The
evacuated water is
mixed and entrained into the wet glycol in line 57 before the wet glycol
enters tube side 62 of glycol-to-
glycol heat exchanger 64. When the water level lowers to a preset level,
liquid level controller 174 vents
pressure signal and valves 182, 178, and 180 return to their normal positions.
The gas in water
chamber 172 flows through normally opened valve 182 into three-phasing chamber
190. Once the
pressure in water chamber 172 and three-phasing chamber 190 equalizes, water
again begins to flow
from three-phasing chamber 190 into water chamber 172. The power gas, which
was released into
three-phasing chamber 190, passes from outlet 175 through equalizing pipes
134, and 130 into an inlet
136 of still column 24.
The operation of hydrocarbon chamber 184 mirrors the operation of water
chamber 172. Liquid
level controller 181 operates the same as liquid level controller 174.
Normally opened valve 176
operates the same as normally opened valve 182. Normally closed valves 188 and
189 operate the
same as normally closed valves 178 and 180. The hydrocarbons dumped through
valve 188 are
preferably transferred through pipe 113 to hydrocarbon chamber 111 of vacuum
separator 102. In
some applications, the hydrocarbons dumped from hydrocarbon chamber will be
transferred directly to
the oil storage facilities.
Figure 6 discloses another embodiment of the invention. Figure 6 incorporates
a large part of
Figure 2 wherein the same reference numerals have been applied to
corresponding parts of Figure 2.
In Figure 6, there is illustrated another embodiment of the invention wherein
additional water is removed
from the hot, dry glycol as the hot, dry glycol is exiting reboiler 68 through
packed stripping column 237
CA 02426071646 2003-04
-14-
mounted in reboiler 68. As illustrated in Figure 6, hot, dry glycol at
approximately 98.6 percent weight
concentration exits reboiler 68 and flows downwardly through packed stripping
column 237. While
flowing downwardly through packed stripping column 237, the hot, dry glycol
comes into intimate
contact with heated and vaporized, liquid hydrocarbon gases that are flowing
up, counter flow to the hot
dry glycol. While flowing in intimate contact with the hot dry glycol, the
heated, liquid hydrocarbon
gases "gas strip" additional water from the hot dry glycol, and the hot dry
glycol exits, at approximately
99.8 weight concentration, from stripping column 237. The super dry glycol
enters pipe 70 and flows
through glycol-to-glycol heat exchanger 64 and pipe 72 into super dry glycol
storage 74. Super dry
glycol storage 74 may be vented to the atmosphere or operating under a vacuum
as shown in Figure 9.
From glycol storage 74, the super dry glycol is pumped to absorber 2 and
completes the above
described closed loop system by returning to reboiler 68 via emissions
separator 50, circulating pump
88, pipe 61, pipe 94, pipe 67, control valve 53, pipe 57, glycol-to-glycol
heat exchanger 64, and pipe 66
to still column 24.
The heated, liquid hydrocarbon gases, required to strip additional water from
the hot dry glycol
exiting reboiler 68 through packed stripping column 237, flow through pipe 233
to the gas inlet of
stripping column 237. The heated, liquid hydrocarbon gases enter stripping
column 237 and flow
upwardly through the hot dry glycol and exit from the top of stripping column
237 into reboiler 68. From
reboiler 68 the heated, liquid hydrocarbon gases flow into still column 24 to
mix with the other gases
and water vapor contained in still column 24. The total of gases contained in
still column 24 are
effluents. The effluents rise to the top and exit still column 24 at point 27.
As previously described, the
effluents flow, under a vacuum, through pipe 82, overhead condenser 84 and
pipe 100 into vacuum
separator 102.
Overhead condenser 84 cools the effluent and most of the water. Hot,
vaporized, liquid
hydrocarbons, contained in the effluent, are changed from a vapor to a liquid
phase. The effluent enters
vacuum separator 102 and, through the weir system of vacuum separator 102, are
transferred to
hydrocarbon chamber III of vacuum separator 102. Most of the liquid
hydrocarbons transferred to
hydrocarbon chamber 111 are again used in a closed loop system (described
below), to strip additional
water out of the hot glycol flowing out of reboiler 68 through stripping
column 237.
The heated, liquid hydrocarbon gases used in stripping column 237 to remove
additional water
from hot glycol exiting reboiler 68, are obtained by heating a portion of the
hydrocarbon liquids which
have been recovered as previously described, in hydrocarbon chamber 111 of
vacuum separator 102.
CA 02426071646 2003-04
-15-
Referring to Figure 7, when the level of hydrocarbons in hydrocarbon chamber
111 reach the high level
set point of snap acting liquid control 192, liquid level control 192 sends a
pressure signal to the
common port of three-way pressure switch 194 such as supplied by Wellmark,
Inc. Three-way pressure
switch 194 is actuated by an adjustable spring working against a pressure-
loaded diaphragm. The
pressure to load the diaphragm of pressure switch 194 is supplied by
throttling liquid level control 196
mounted in hydrocarbon reservoir vessel'198. The throttling liquid level
control 196 maintains a
relatively fixed level of hydrocarbons in reservoir vessel 198 by increasing
or decreasing the pressure
signal being sent to three-way pressure switch 194. As the liquid level
control 196 senses the level in
reservoir vessel 198 needs to be raised, it increases the pressure signal to
three-way pressure switch
194 shifting the three-way switch to open port 202 and close port 200. When
the level in reservoir
vessel 198 rises to the high level set point, the output of liquid level
control 196 decreases to where
three-way pressure switch 194 reverses and port 202 closes and port 200 opens.
When port 202 of three-way pressure switch 194 is opened and port 200 is
closed, any
hydrocarbons being dumped from hydrocarbon chamber 111 of vacuum vessel 102 by
liquid level
control 192 are routed to hydrocarbon reservoir vessel 198 through pipe 204,
pipe 206, control valve
208, and pipe 210. When port 200 of three-way pressure switch 194 is opened
and port 202 is closed,
any hydrocarbons being dumped from the hydrocarbon chamber 111 of vacuum
vessel 102 by liquid
level control 192 are routed to storage (not shown) through pipe 204, pipe
212, control valve 214, and
pipe 216. By only sending recovered liquid hydrocarbons to storage when
reservoir vessel 198 is
operationally full, the previously described system insures that there is
always enough liquid
hydrocarbons in reservoir vessel 198 to operate the hydrocarbon stripping
system.
Reservoir vessel 198 is maintained at a pressure of between approximately 5
and 10 pounds
lower than the pressure used to evacuate hydrocarbon chamber 111 of vacuum
vessel 102. Back-
pressure regulator 238, which is connected to reservoir vessel 198 by line
236, is set to relieve, through
pipe 240, any pressure in reservoir vessel 198 that is in excess of the high
pressure set point. The
gases that are released from reservoir vessel 198 flow through pipe 236, back-
pressure regulator 238
and pipe 130 to inlet 136 on still column 24. The vented gases flow into still
column 24 where they mix
with the effluents in still column 24. As previously described, the vented
gases along with the other
effluents are recovered in vacuum separator 102. Pressure regulator 230 is set
approximately 5 pounds
lower then the high pressure set point on back pressure regulator 238. When
the pressure in reservoir
vessel 198 drops approximately 5 pounds below the high pressure set point,
pressure regulator 230
begins to open and either recovered gas from emissions separator 50 or gas
from the supply gas
system flows through pipe 234, pressure regulator 230, and pipe 232 into
reservoir vessel 198.
CA 02426071646 2003-04
-16-
Preferably, the gas passing through pressure regulator 230 to maintain the low-
pressure set point in
reservoir 198 would, as shown, come from the recovered gas system.
The liquid hydrocarbons in reservoir vessel 198 are released into the
hydrocarbon stripping
system by control valve 218. Control valve 218 is operated by pressure-stat
220 such as supplied by
Kimray, Inc. Pressure-stat 220 has an adjustable spring that opposes a
pressure-loaded diaphragm.
The diaphragm of pressure-stat 220 is connected through line 226 to pipe 224.
As the pressure rises in
pipe 224, the increased pressure on the diaphragm of pressure-stat 220 causes
pressure-stat 220 to
react to decrease the pressure on the diaphragm of control valve 218.
Decreasing the pressure on the
diaphragm of control valve 218 causes control valve 218 to partially or
completely close, decreasing or
stopping the flow of hydrocarbons through pipe 222 and control valve 218. As
the pressure in pipe 224
decreases, the decreased pressure on the diaphragm of pressure-stat 220 causes
pressure-stat 220 to
react to increase the pressure on the diaphragm of control valve 218.
Increasing the pressure on the
diaphragm of control valve 218 causes control valve 218 to partially or
completely open increasing the
flow of hydrocarbons through pipe 222 and control valve 218.
From outlet 219 of control valve 218, the recovered, liquid hydrocarbons flow
through pipe 223
to the inlet of either heat exchange coil 221 mounted in reboiler 68 or a heat
exchange coil mounted in
an indirect heater (not shown). To heat the recovered, liquid hydrocarbons on
new dehydrators, it is
preferable to use heat exchange coil 221 mounted in reboiler 68. To heat the
recovered, liquid
hydrocarbons on retrofitted dehydrators, it is preferable to use a heat
exchange coil mounted in an
indirect heater (not shown). For this embodiment, the operation of a new
dehydrator with a heat
exchange coil mounted in the reboiler is described. The recovered, liquid
hydrocarbons flow though
heat exchanger coil 221 which is immersed in the hot glycol contained in
reboiler 68. While in heat
exchange relationship with the hot glycol in reboiler 68, the recovered,
liquid hydrocarbons gain heat
causing the recovered, liquid hydrocarbons to vaporize and increase in
pressure. The hot, vaporized,
liquid hydrocarbons exit heat exchanger coil 221 and flow through pipe 224 to
fixed choke 228. Fixed
choke 228 is sized to pass the volume of vaporized, liquid hydrocarbons
required to super dry hot glycol
exiting stripping column 237 at point 235. Pressure-stat 220 controls the
pressure in pipe 224 as well
as allowing (within limits) the pressure in pipe 224 to be raised or lowered
to either increase or decrease
the volume of vaporized, liquid hydrocarbons flowing through fixed choke 228.
Pressure-stat 220 must
be set to maintain the maximum pressure in pipe 224 to at least 5 psig below
the minimum set pressure
in hydrocarbon reservoir 198.
CA 02426071646 2003-04
-17-
The hot, vaporized, liquid hydrocarbons exit fixed choke 228 and flow through
pipe 233 to the
gas inlet of stripping column 237. As described above, the hot, vaporized,
liquid hydrocarbons flow
upwardly through the packing in stripping column 237 coming in intimate
contact with the hot glycol
which is flowing downwardly out of reboiler 68 through the packing in
stripping column 237. While in
intimate contact with the hot glycol in stripping column 237, the hot,
vaporized, liquid hydrocarbons
cause additional water to be removed from hot, dry glycol exiting reboiler 68
and super dry glycol exits
stripping column 237 at point 235 and flow into pipe 70.
To complete the closed loop stripping system, as previously described, the
hot, vaporized, liquid
hydrocarbons flow through stripping column 237, reboiler 68, still column 24,
pipe 82, overhead
condenser 84, and pipe 100 into the weir section of vacuum separator 102 where
the condensed liquid
hydrocarbons are transferred into hydrocarbon chamber 111. From hydrocarbon
chamber 111, liquid
hydrocarbons, enough to keep reservoir vessel 198 operationally full of liquid
hydrocarbons, are
transferred through pipe 204, pipe 206, control valve 208, and pipe 210 into
reservoir 198. From
reservoir 198, the liquid hydrocarbons flow through pipe 222, valve 218, heat
exchange coil 221, pipe
224, fixed coke 228, and pipe 233 into the hot, vaporized, liquid hydrocarbon
inlet of stripping column
237.
In some applications, where it is anticipated that high temperature gas (110
to 140 degrees
Fahrenheit) will be encountered, it may be desirable to eliminate the hot
glycol flow exiting the absorber
from the glycol flow to the glycol cooler. Eliminating hot glycol from the
absorber flowing through the
glycol cooler significantly decreases the cooling load on the glycol cooler.
Figure 8 discloses another embodiment of the invention which eliminates the
hot glycol flow
from the absorber combining with the glycol flow to the glycol cooler. Figure
8 incorporates a large part
of Figure 3 and Figure 6 wherein the same reference numerals have been applied
to corresponding
parts of Figure 3 and Figure 6. Either of the processes to obtain super dry
glycol as shown by Figure 3
or Figure 6 are applicable for use with the embodiment shown in Figure 8. To
simplify the description of
the embodiment shown by Figure 8, the process to obtain super dry glycol, as
shown in Figure 3, has
been selected for the description of the embodiment shown by Figure 8.
As illustrated in Figure 8, wet glycol is collected in wet glycol sump 14 in
the bottom portion of
absorber 2 and contains entrained and absorbed gases, liquid hydrocarbons, and
water and exits
absorber 2 at point 16. The flow of the wet glycol is controlled by a
throttling liquid level control (not
shown) located in absorber 2 which operates control valve 17 to maintain a
constant level of wet glycol
CA 02426071646 2003-04
-18-
in the bottom of absorber 2. The wet glycol is discharged by control valve 17
and flows through pipe 13
to inlet 11 of three-phased flash separator 49.
Free gaseous hydrocarbons contained in the wet glycol are released in three-
phased flash
separator 49 as a result of the reduction of pressure from the pressure of the
absorber of between
approximately 50 and 1500 PSIG to the pressure in the three-phased flash
separator which is generally
between approximately 75 and 125 PSTG. Liquid hydrocarbons are separated from
the wet glycol in
three-phased flash separator 49 by a weir system or interface liquid level
control (not shown) and are
withdrawn through pipe 51, control valve 59 and pipe 79 to storage (not shown)
or other apparatus.
Control valve 59 is operated by a liquid level control (not shown) mounted in
three-phase flash
separator 49.
The freed gaseous hydrocarbons exit three-phased flash separator 49 and flow
through pipe 81,
back-pressure regulator 85, pipe 87, pressure regulator 89, and pipe 91 to
point 47 where the freed
gaseous hydrocarbons combine with gaseous hydrocarbons from emissions
separator 50 which are
flowing to point 47 through pipe 45. The operation of emissions separator 50
is explained below. From
point 47, the combined gaseous hydrocarbons flow through pipe 58 into a system
such as that
described in U.S. Patent No. 5,766,313, to be used as a fuel in a reboiler as
described therein.
Backpressure regulator 85 maintains the minimum set pressure on three-phased
flash
separator 49. Pressure regulator 89 controls the maximum set pressure on
emissions separator 50.
Backpressure regulator 93 controls the maximum set pressure on three-phased
flash. separator 49. In
the event the pressure in three-phased flash separator 49 builds to a point
high enough to actuate back
pressure-regulator 93, the excess pressure is relieved through pipe 91, back-
pressure regulator 93 and
pipe 101.
Wet glycol exits three-phased flash separator 49 and flows through pipe 15,
particulate filter 19,
pipe 31, control valve 23 and pipe 39 to inlet 20 of reflux coil 22. Control
valve 23 is preferably operated
by an interfacing liquid level control (not shown) mounted in three-phased
flash separator 49. Wet
glycol flows through reflux coil 22 cooling and condensing some of the hot
vapors in the top of still
column 24. The wet glycol at inlet 20 is between approximately. 110 to 130
degrees Fahrenheit and at
the exits approximately 160 degrees Fahrenheit. The wet glycol exits reflux
coil 22 at exit 26 and flows
through pipe 103 to inlet 63 of tube side 62 of glycol heat exchanger 64. It
is understood that any type
of heat exchanger may be used in place of glycol-to-glycol heat exchanger 64.
The wet glycol flowing
through tube side 62 of glycol-to-glycol heat exchanger 64 is heated by the
hot glycol therein and flows
CA 02426071646 2003-04
-19-
from glycol-to-glycol heat exchanger 64 through pipe 66 and enters still
column 24 of conventional
reboiler 68, such as that illustrated in the '313 Patent wherein wet glycol is
changed into hot, dry glycol
which is then fed through pipe 70 into water exhauster 120. Water exhauster
120 and blowcase 124
operate as previously described so that hot, super dry glycol exits from water
exhauster 120 through
pipe 122, enters the shell side of heat exchanger 64 and is cooled by the cool
glycol flowing through
tube side 62 of glycol-to-glycol heat exchanger 64. The partially cooled super
dry glycol then passes
through pipe 72 into a super dry glycol storage 74 from which it is pumped by
pump 76 through pipe 78
into the gas to glycol exchanger 10 to be further cooled by natural gas
flowing through heat exchanger
and into pipe 12. The cooled super dry glycol exits gas to glycol heat
exchanger 10 through pipe 6
10 and enters absorber 2 where it comes into contact with wet natural gas
flowing through absorber 2.
After the super dry glycol has been contacted by wet natural gas, it collects
as wet glycol in sump 14 of
absorber 2 and the closed glycol loop has been completed.
A second closed loop system is shown by Figure 8. The second closed loop
system
incorporates all the components required to recover the effluents which exit
the still column of a
dehydrator. The major components in the second closed loop system are
emissions separator 50,
vacuum separator 102, glycol cooler 38, and overhead condenser 84.
At start up of the second closed loop system, all major components and
associated equipment
and piping composing the second closed loop system, which require a glycol
flow, are charged with
glycol, and, at the same time, a level of glycol is established in emissions
separator 50, unless some of
the original charge of glycol is lost through leakage or other mechanical
problems, the glycol level in
emissions separator 50 remains relatively constant. Pipe 119 facilitates
making the original charge of
glycol in the second closed loop glycol system as well as replacing any glycol
that might be lost from the
second closed loop glycol system. Pipe 119 is connected at point 122 to
discharge pipe 78 from glycol
pump 76 and at point 123 to emissions separator 50. By opening a manual valve
(not shown), any
glycol needed in the second closed loop glycol system can be pumped by pump 76
through pipe 78 and
pipe 119 into emissions separator 50.
The glycol charge in the second closed loop is continuously circulated from
emissions separator
50 by circulating pump 88. The glycol, at a pressure of approximately 100 PSIG
higher than the
pressure in emissions separator 50, flows through line 61 to point 65. At
point 65 the glycol stream
splits. The first glycol stream flows through pipe 92 and provides energy to
power eductor 112
(described below). The second glycol stream flows from point 65 through pipe
69, particulate filter 96,
pipe 97, fixed choke or other control 101, and pipe 98 to inlet 107 of the
shell side of overhead
CA 02426071646 2003-04
-20-
condenser 84. Fixed choke or other control 101 controls the volume of glycol
that is flowing through
pipe 98 into overhead condenser 84. The second stream of glycol flows through
the shell side of
overhead condenser 84 and cools hot effluent from still column 24. The second
stream of glycol exits
overhead condenser 84 at exit 117 and flows through pipe 43 to inlet 36 of
glycol cooler 38. The design
and function of glycol cooler 38 has been previously described. The cooled
second stream of glycol
exits glycol cooler 38 at point 35 and flows through pipe 44 to inlet 164 of
condenser tube bundle 160
mounted in water exhauster 120. Condenser tube bundle 160 functions as
previously described to cool
hot vapors in the vapor section of water exhauster 120. The second stream of
glycol exits condenser
tube bundle 160 and flows through pipe 177 where it enters emissions separator
50 at point 42 closing
the loop of the second stream of glycol circulating in the second closed loop.
As previously described, heat applied to the wet glycol in reboiler 68
releases effluents that exit
from still column 24 at point 27. From point 27, the effluents flow through
pipe 82, overhead condenser
84, and pipe 100 into vacuum separator 102. The function of vacuum separator
102 and eductor 112
has been previously described. Emissions separator 50 has the same function as
previously
described, but since no processed glycol is being received or discharged by
emissions separator 50, no
automatic control of the glycol level in emissions separator 50 is required
nor is there any need for
emissions separator 50 to be three-phased.
The glycol storage on most glycol dehydrators operates at atmospheric
pressure. A pipe 75, as
shown in Figure 2, is generally used to vent to the atmosphere the glycol
storage of a dehydrator. Pipe
75 is opened to the atmosphere and is connected to glycol storage 74 at point
77.
Two problems are created when the glycol storage of a dehydrator is vented to
the atmosphere.
The first problem is that any excess glycol (more than the capacity of the
storage to handle) that flows
into the storage as a result of overfilling of the dehydrator, upset of the
process, or malfunction of the
equipment will flow out of the glycol storage through a vent line such as pipe
75. Depending upon how
the installation of the dehydrator is designed to handle glycol storage
overfill conditions, any glycol
which overfills the storage and flows out a vent pipe such as pipe 75 could
contaminate the
environment. As a minimum, unless special accommodations have been made, any
glycol, which flows
out pipe 75, will be wasted. The second problem that occurs when the glycol
storage of a dehydrator is
vented to the atmosphere is that the hot glycol in the storage is allowed to
contact oxygen in the air.
Oxygen in contact with hot glycol will cause degradation of the glycol.
CA 02426071646 2003-04
-21-
Figure 9 shows another embodiment of the invention. Figure 9 incorporates a
large portion of
Figure 3 wherein the same reference numerals have been applied to
corresponding parts of Figure 3.
In Figure 3 there is illustrated an embodiment of the invention wherein the
glycol storage operates under
a vacuum to eliminate the problems of the glycol storage being vented to the
atmosphere.
As illustrated in Figure 3, glycol storage 74 is connected to point 136 of
still column 24 by vent
pipe 246, vent pipe 250, vent pipe 134, and vent pipe 130. Still column 24
operates under a vacuum.
Glycol storage 74 is also connected to glycol reservoir 244 by vent pipe 248.
Glycol storage 74 is also
connected to glycol reservoir 244 by glycol fill pipe 258, control valve 254
and pipe 260. Glycol
reservoir 244 is connected to high-pressure discharge pipe 78 by pipe 272,
fixed choke 268, pipe 274,
control valve 262, and pipe 264. Operating glycol storage 74 in a closed loop
glycol system under a
vacuum eliminates the problems of hot glycol coming into contact with air and
of glycol being wasted or
contaminating the environment.
As shown in Figure 9, glycol storage 74 provides the glycol to the suction of
glycol pump 76
(glycol pump 76 may be a stand alone pump or it may be a pump that is
internally mounted in the glycol
storage). It is necessary at all times to maintain, in glycol storage 74, a
glycol level adequate to provide
the suction head to pump 76. To maintain the glycol level in glycol storage
74, a reverse acting,
interface liquid level control 255 is. utilized. Liquid level control 255 puts
out a pressure signal that
increases as the glycol level in glycol storage 74 lowers and decreases as the
glycol level in glycol
storage 74 rises. The pressure signal from liquid level control 255 is
connected to a control valve 254
and to a reverse acting pressure switch 256 such as a Kimray 3 PGRA Throttle-
Reverse Pilot. Pipe 258
connects control valve 254 to reservoir vessel 244. Pipe 260 connects control
valve 254 to glycol
storage vessel 74. The lower opening diaphragm pressure (15 PSIG) of control
valve 254 is adjusted
by turning jackscrew 257 to compress the diaphragm spring. As the glycol level
in glycol storage vessel
74 lowers, the output pressure of liquid level control 255 increases. When the
output pressure of liquid
level control 255 reaches 15 PSIG, control valve 254 begins to open and
control valve 254 will remain
open until the output pressure of liquid level control 254 drops below 15
PSIG. While control valve 254
is open, glycol in reservoir vessel 244 flows through pipe 258, controll valve
254, and pipe 260 into
glycol storage 74 maintaining the lower level of glycol in storage vessel 74.
As previously described, the output from liquid interface level control 255 is
connected to
pressure switch 256 as well as control valve 254. The lower operating pressure
of pressure switch 256
is set at 5 PSIG by adjustment of jackscrew 259. When a condition exists where
more glycol from
glycol-to-glycol heat exchanger 64 enters through pipe 72 into glycol storage
74 than pump 76 is
pumping to absorber 2, the glycol level in glycol storage 74 will rise. As the
glycol level in glycol storage
CA 02426071646 2003-04
-22-
74 rises, the output pressure of liquid level control 255 decreases. When the
output pressure of liquid
level control 255 drops to 5 PSIG, pressure switch 256 outputs a throttling
pressure signal to control
valve 262 beginning the opening of control valve 262.
The downstream side of control valve 262 is connected by pipe 264 to reservoir
vessel 244 at
point 270. The upstream side of valve 262 is connected by pipe 266, fixed
choke 268, and pipe 272 to
pump 76 high pressure (50 to 1500 PSIG) discharge pipe 78 which supplies the
lean glycol to absorber
2. When control valve 262 is open, fixed choke 268 controls the volume of
glycol flowing to reservoir
vessel 244. Fixed choke 268 is preferably sized to allow no more the 25% of
the output volume of
pump 76 to flow from pipe 78 through valve 262 into reservoir vessel 244. As a
result of allowing some
of the glycol being pumped by pump 76 to be transferred to reservoir vessel
244 instead of entering
absorber 2, the glycol overfill level in glycol storage 74 lowers. Lowering
the glycol level in glycol
storage 74 causes the output pressure from liquid level control 255 to
increase. When the output
pressure from liquid level control 255 again reaches 5 PSIG, pressure switch
256 bleeds off the
pressure signal to control valve 262 and control valve 262 closes, stopping
the flow of glycol from pipe
78 into reservoir vessel 244.
Normal operation of glycol storage 74 is when the output of liquid level
control 255 is between 5
and 15 PSIG. Opening and closing control valves 254 and 262 maintains the
level in glycol storage 74
at the normal condition where adequate glycol is supplied to pump 76 and no
hot glycol contacts air,
contaminates the environment, or is wasted. By using interfacing liquid level
control 255, liquid
hydrocarbons that might enter glycol storage vessel 74, through contamination
of the process glycol, will
not materially change the glycol level in glycol storage 74. Liquid
hydrocarbons, which might enter
glycol storage 74, would separate and float on top of the glycol. Over time,
the liquid hydrocarbons can
build to a high level on top of the glycol in glycol storage 74, and any
additional liquid hydrocarbons will
need to be removed. As shown in Figure 3, the outlet of pipe 261 is located
close to the top of glycol
storage 74 and exits glycol storage 74 at point 263. The purpose of pipe 261
is to set the upper level of
any liquid hydrocarbons that might collect on top of the glycol in glycol
storage 74. Liquid hydrocarbons
that exit glycol storage 74 through outlet 263 flow through pipe 265 to point
267 where the liquid
hydrocarbons combine with the liquid hydrocarbons from water exhauster 120.
The combined stream of
liquid hydrocarbons flows through pipe 149 to enter at point 151 into blowcase
124. As previously
described, the weir system of blowcase 124 transfers the liquid hydrocarbons
into oil chamber 184.
From oil chamber 184 the liquid hydrocarbons are transferred to either the
hydrocarbon chamber 111 of
vacuum separator 102 or to storage (not shown).
CA 02426071646 2003-04
-23-
There are applications where the amount of gas, recovered by the previously
described
invention, can be more than the amount of gas required to fire the reboiler.
One example, of an
application where the amount of gas recovered by the invention might be more
than is required by the
reboiler to heat the dehydration process, is at compressor stations where
widely varying flow rates and
temperatures of the gas being processed by the absorber can create conditions
where excess gas can
be recovered. A second example, of an application where the amount of gas
recovered by the
invention might be more then is required by the reboiler to heat the
dehydration process, is where the
composition of the gas being processed by absorber 2 creates unusually high
BTU values for the
recovered gas.
In applications where the amount of gas recovered by the invention is more
than is required by
the reboiler to heat the dehydration process, the excess recovered gas can be
used for other purposes.
Some of the other possible uses of the excess recovered gas are in a plants
fuel system or the firing of
other production equipment on the gas well or plant location.
In applications where there is no other use for excess gas recovered by the
invention, the
excess gas can be consumed by increasing the heat load on the reboiler. Figure
10 discloses another
embodiment of the invention. Figure 10 incorporates a large portion of Figure
3 wherein the same
reference numerals have been applied to corresponding parts of Figure 3. In
Figure 10, there is
illustrated an embodiment of the invention whereby additional heat load, more
then the heat load
required by the dehydration process, can be applied to the reboiler.
To illustrate the present invention, the dehydration process utilizing the
invention's gas recovery
system and water exhauster system for obtaining super dry glycol has been
chosen. Any of the other
dehydration gas recovery processes previously described can be used to
illustrate the present
invention.
Referring to Figure 10, the components necessary to inject water into still
column 24 are added
to the flow diagram illustrated by Figure 3. Pipe 278 is connected to outlet
276 located close to the
bottom of the recovered water section created by the weir system in chamber
123 of vacuum separator
102. Water flows from outlet 276 through. pipe 278 to the suction inlet of
metering pump 282. Metering
pump 282 may be electrically or pneumatically powered and is designed to allow
the output volume to
be varied over a wide range. From the discharge of metering pump 282,
recovered water is pumped
through pipe 284 to point 286. At point 286 the water pumped by metering pump
282 mixes with hot
wet glycol flowing in pipe 66 from glycol-to-glycol heat exchanger 64. The
mixture of water and hot wet
CA 02426071 2010-05-19
-24-
glycol enters still column 24 at point 288. Considering the firing efficiency
of the fire tube in reboiler 68,
each pound of water injected into still column 24 causes approximately 2000
BTU of excess gas to be
consumed by reboiler 68. In applications where injecting the water into still
column 24 is not practical,
the water can be injected directly into reboiler 68.
The injected water at point 288 converts to steam and mixes with other
effluents in still column
24. As previously described, the effluents exit still column 24 at point 27
and flow through pipe 82,
overhead condenser 84, and pipe 100 into the weir section of vacuum separator
102.
The injected water flows in a closed loop system from vacuum separator 102 to
still column 24
and overhead condenser 84, then back to vacuum separator 102. While flowing
through the closed
loop system, the injected water changes phase twice. The water exits vacuum
separator 102 as a
liquid, reboiler 68 adds heat which converts the liquid to steam, and overhead
condenser 84 condenses
the steam back to a liquid before the water returns to vacuum separator 102.
The approximately 1200 BTU per pound of water that is removed from reboiler 68
by converting
the injected water to steam increases the heat load on overhead condenser 84
by an equal amount. By
heat exchange with the glycol flowing in the shell side of overhead condenser
84, heat from the steam is
transferred to the flowing glycol. The flowing glycol exits overhead condenser
84 and flows through
pipe 33, reflux coil 22, and pipe 329 to glycol cooler 38 where heat is
removed from the flowing glycol by
exhausting the heat into the atmosphere.
The preceding examples can be repeated with similar success by substituting
the generically or
specifically described components and/or operating conditions of this
invention for those used in the
preceding examples.
Although the invention has been described in detail with particular reference
to these preferred
embodiments, other embodiments can achieve the same results. Variations and
modifications of the
present invention will be obvious to those skilled in the art and it is
intended to cover in the appended
claims all such modifications and equivalents.
