U.S. patent application number 11/456001 was filed with the patent office on 2007-07-05 for vapor recovery process system.
Invention is credited to Forrest D. Heath, Gary Heath, Rodney T. Heath.
Application Number | 20070151292 11/456001 |
Document ID | / |
Family ID | 36638811 |
Filed Date | 2007-07-05 |
United States Patent
Application |
20070151292 |
Kind Code |
A1 |
Heath; Rodney T. ; et
al. |
July 5, 2007 |
Vapor Recovery Process System
Abstract
The present invention provides for a natural gas well vapor
recovery processing system and method comprising recovering gaseous
hydrocarbons to prevent their release into the atmosphere including
providing a method for preventing the gaseous hydrocarbons from
returning to a liquid state.
Inventors: |
Heath; Rodney T.;
(Farmington, NM) ; Heath; Forrest D.; (Katy,
TX) ; Heath; Gary; (Farmington, NM) |
Correspondence
Address: |
PEACOCK MYERS, P.C.
201 THIRD STREET, N.W.
SUITE 1340
ALBUQUERQUE
NM
87102
US
|
Family ID: |
36638811 |
Appl. No.: |
11/456001 |
Filed: |
July 6, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11234574 |
Sep 22, 2005 |
|
|
|
11456001 |
Jul 6, 2006 |
|
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60612278 |
Sep 22, 2004 |
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Current U.S.
Class: |
62/617 |
Current CPC
Class: |
C10G 5/06 20130101 |
Class at
Publication: |
062/617 |
International
Class: |
F25J 3/00 20060101
F25J003/00 |
Claims
1. A method for preventing the release of natural gas at a natural
gas well processing system from being released to the atmosphere,
the method comprising: collecting evolved gases from a storage
tank; entraining the evolved gases into a fluid stream; compressing
the evolved gases and fluid stream; sending the evolved gases and
fluid stream to an emissions separator; and separating the gases
from the fluid for further processing.
2. The method of claim 1 further comprising collecting the evolved
gases using a vacuum.
3. The method of claim 2 further comprising providing an eductor to
create the vacuum and to entrain the gasses into the liquid
stream.
4. The method of claim 1 further comprising mixing a first
compressed gas with a second compressed gas flowing in a pipeline,
the second compressed gas having a BTU lower relative to the BTU of
the first compressed gas to prevent gaseous hydrocarbons in a
natural gas well processing system from entering a liquid
state.
5. A method for preventing the release of gaseous hydrocarbons at a
natural gas well processing system from entering the atmosphere,
the method comprising: providing an emissions separator; sending to
the emissions separator the entrained gases that evolve form
hydrocarbon liquids when the liquids are separated from a flowing
gas stream at higher pressure and put in the lower pressure of an
intermediate separator; sending the gaseous hydrocarbons to a
compressor and compressing the gaseous hydrocarbons; and sending
the compressed gaseous hydrocarbons to a flowing gas stream for
further processing or point of sale, compressing the gaseous.
6. A natural gas well processing system comprising: a hydrocarbon
storage tank; an eductor linked to said storage tank to receive
gasses that evolve in the storage tank, entrain said gasses into a
fluid stream and compress said gasses and said fluid stream; and an
emissions separator linked to said eductor for receiving said
evolved gases and fluid stream for separation of said gasses from
the fluid stream and for sending said gasses out of said emissions
separator for further processing.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation-in-part application of U.S. patent
application Ser. No. 11/234,574, titled "Vapor Process System"
filed Sep. 22, 2005, which claims the benefit of the filing of U.S.
Provisional Patent Application Ser. No. 60/612,278, entitled "Vapor
Process System", filed on Sep. 22, 2004, and the specifications and
claims of those applications are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention (Technical Field)
[0003] The present invention relates to vapor recovery processing
systems for use with natural gas wells. The invention comprises a
pumping system used with an engine instead of plunger lifts and can
be used to remove evolved gases from hydrocarbon liquids to storage
at or near atmospheric pressure.
[0004] 2. Background Art
[0005] In addition to producing natural gas, many natural gas wells
produce hydrocarbon liquids and water. The liquids, hydrocarbons,
and water are separated from the flowing natural gas by a separator
installed in the line carrying the flowing gas stream. The inline
separator may operate at pressures as high as 1,500 psig or as low
as 30 psig. The inline separator may separate the separated liquids
into hydrocarbon and water components. The separated water is
dumped to disposal, and the separated hydrocarbons are dumped to
storage. The storage for the separated hydrocarbons is generally a
steel tank or tanks with each tank having a capacity of 200 to 500
barrels. The storage tanks may operate at pressures as high as 16
ounces to as low as atmospheric pressure.
[0006] An intermediate pressure separator is often used on natural
gas wells that are operating at elevated pressures (150 to 1,500
psig). The intermediate pressure separator may operate at pressures
of 125 to 25 psig. The intermediate pressure separator receives the
total separated liquid from the inline separator. The intermediate
pressure separator separates the liquid into its components,
hydrocarbons and water. As described above, the water is dumped to
disposal and the hydrocarbons are dumped to storage. As a result of
the reduction of pressure, the intermediate pressure separator also
releases most of the entrained natural gas from the separated
hydrocarbons. Without a means to recover the entrained natural gas
or a means designed to collect and burn the entrained natural gas,
the entrained natural gas released in the intermediate pressure
separator will be vented to the atmosphere and wasted. In most
systems designed to collect and burn the entrained natural gas, the
heat energy released by burning the natural gas is wasted to the
atmosphere. A means is needed to prevent entrained natural gas from
being released to the atmosphere.
[0007] Because of the reduction in pressure from the intermediate
pressure separator to the storage tank, the liquid hydrocarbons
dumped to the storage tanks will release additional entrained
natural gas, and any component of the natural gas liquids that is
not stable at the storage tank pressure and temperature will begin
to evolve from the hydrocarbon liquids and change from a liquid to
a gaseous state. The changing in the storage tank of hydrocarbon
liquids from a liquid to a gaseous state is commonly referred to as
"weathering". Again, without a system to either recover or burn the
gases released from the hydrocarbon liquids dumped to the storage
tank, the gases will vent to the atmosphere and be wasted. The
gases released from the storage tank are a high BTU value of
approximately 3,000 BTU per cubic foot compared to the standard of
1,000 BTU per cubic foot required for residential gas. A means is
needed to prevent gases released from liquid hydrocarbons from
being released to the atmosphere.
[0008] For many years, systems have been made available to collect
the gaseous hydrocarbons that are released from liquid hydrocarbons
separated at elevated pressures and then transferred to storage
tanks operating at near atmospheric pressure. In addition to
operating problems that can occur with the currently available
recovery systems, the biggest problem that has limited their
application has been capital cost, and the systems have generally
been applied to gas wells that have operated at pressures of 250
psig or less and that have produced volumes of hydrocarbon liquids
in the range of 100 barrels per day or more.
[0009] Natural gas wells that can produce 100 barrels per day or
more of hydrocarbon liquids do not generally require any type of
artificial lift to lift the liquid hydrocarbons to the surface. In
most cases, smaller volume natural gas wells do require artificial
lift to lift the liquid hydrocarbons to the surface. A widely used
artificial lift systems is called a "plunger lift". The plunger is
a metal device that falls to the bottom of the natural gas well
tubing while the gas flow is shut off at the surface. The plunger
remains at the bottom of the tubing for a period of time while the
gas well builds up enough pressure to provide enough gas flow to
bring to the surface the plunger and the load of liquid
hydrocarbons the plunger is lifting. When the gas well is again
opened, the plunger and liquid hydrocarbons rise to the surface.
Often, the liquid hydrocarbons arrive at the surface as a slug that
is much larger than the normal hydrocarbon liquid production of the
well. The liquid hydrocarbon slug can create a volume of flash and
evolved gases that will overload the vapor recovery system.
[0010] On natural gas wells where the plunger lift or other types
of artificial lift creates a slugging condition that overloads the
vapor recovery system, a pumping system developed by Unico, Inc.
("Unico") can be used to lift the produced liquid hydrocarbons to
the surface. Up until now, pumping of natural gas wells has been
avoided because of pumping problems. Some of the problems with
pumping gas wells have been gas locking (a condition where the
pumping barrel fills with gas and no fluid can be pumped), gas
interference (a condition where the pumping barrel only partially
fills with fluid each stroke of the pump), and fluid pounding (a
condition where the downward stroke of the pump contacts the fluid
in a less than fluid filled barrel). The Unico pumping system
presents a solution to the problems of pumping gas wells by only
pumping the amount of fluids the well is producing. Pumping only
the amount of fluids the well is producing prevents "pump-off" (a
condition where the well bore is pumped dry thereby allowing gas to
enter the pump barrel). A method is needed to eliminate gas
entering the pump barrel to eliminate the problems associated with
pumping natural gas wells.
BRIEF SUMMARY OF THE INVENTION
[0011] An embodiment of the present invention provides for a
natural gas well vapor recovery processing system (referred to
herein as "VRSA") and method comprising recovering gaseous
hydrocarbons to prevent their release into the atmosphere including
providing a method for preventing the gaseous hydrocarbons from
returning to a liquid state.
[0012] In one embodiment of the present invention, evolved gases
are entrained at the vacuum port of an eductor into a fluid stream
and compressed. The fluid flowing through the eductor discharges
into an emissions separator where the compressed gases separate
from the fluid, and the compressed gases flow to the outlet of the
emissions separator to be further processed while the fluid falls
to the bottom of the emissions separator. The fluid collects in the
bottom of the emissions separator to provide a continuous closed
circuit fluid feed to the suction of a circulating pump.
[0013] The emissions separator also receives entrained gas that
evolves from hydrocarbon liquids when the liquids are separated
from a flowing gas stream at higher pressure and dumped to the
lower pressure of an intermediate pressure separator. In the
emissions separator, the two gases mix to form a homogeneous
mixture. The homogeneous gas mixture flows from the outlet of the
emissions separator to the suction of a gas compressor where the
gases are compressed to the pressure of the flowing gas stream. The
compressed gases are discharged back into the flowing gas stream at
the inlet to the inline separator where the compressed gases mix
with the flowing gas stream to form, in the inline separator, a
second homogeneous gaseous mixture. The second homogeneous gas
mixture flows from the outlet of the inline separator to other
processing or to points of sale.
[0014] Another embodiment provides for mixing a high BTU and vapor
pressure gas with a lower BTU and vapor pressure gas flowing in the
pipeline to reduce the BTU and partial pressure of the compressed
gas while at the same time slightly raising the BTU and partial
pressure of the flowing gas stream. Lowering the BTU and partial
pressure of the compressed gases reduces the tendency of the gases
evolved and recovered from the tank to return to a liquid state.
Any of the compressed gases that return back to a liquid state
prior to passing out of the inline separator are again separated
and dumped back to the storage tank.
[0015] Thus, an embodiment of the present invention provides a
method for preventing the release of natural gas in a natural gas
well processing system from entering the atmosphere comprising,
collecting evolved gases from a storage tank, entraining the
evolved gases into a fluid stream, compressing the evolved gases
and fluid stream, sending the evolved gases and fluid stream to an
emissions separator, and separating the gases from the fluid for
further processing. Preferably, the evolved gases are collected
using a vacuum, and preferably, the method further comprises
providing an eductor to create the vacuum and to entrain the gasses
into the liquid stream. The method preferably further comprises
mixing a first compressed gas with a second compressed gas flowing
in a pipeline, the second compressed gas having a BTU lower
relative to the BTU of the first compressed gas to prevent gaseous
hydrocarbons in the natural gas well processing system from
entering a liquid state.
[0016] Another embodiment provides a method for preventing the
release of gaseous hydrocarbons at a natural gas well processing
system from entering the atmosphere, the method comprising
providing an emissions separator, sending to the emissions
separator the entrained gases that evolve form hydrocarbon liquids
when the liquids are separated from a flowing gas stream at higher
pressure and put in the lower pressure of an intermediate
separator, sending the gaseous hydrocarbons to a compressor and
compressing the gaseous hydrocarbons, and sending the compressed
gaseous hydrocarbons to a flowing gas stream for further processing
or point of sale.
[0017] Another embodiment provides a natural gas well processing
system comprising a hydrocarbon storage tank, an eductor linked to
the storage tank to receive gasses that evolve in the storage tank,
entrain said gasses into a fluid stream, and compress the gasses
and said fluid stream, and an emissions separator linked to the
eductor for receiving the evolved gases and fluid stream for
separation of the gasses from the fluid stream and for sending the
gasses out of the emissions separator for further processing.
[0018] Other objects, advantages and novel features, and further
scope of applicability of the present invention will be set forth
in part in the detailed description to follow, taken in conjunction
with the accompanying drawings, and in part will become apparent to
those skilled in the art upon examination of the following, or may
be learned by practice of the invention. The objects and advantages
of the invention may be realized and attained by means of the
instrumentalities and combinations pointed out in the appended
claims.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0019] 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:
[0020] FIG. 1 is a flow diagram of an embodiment of the
invention;
[0021] FIG. 2 is a flow diagram of a modification of the embodiment
of FIG. 1; and
[0022] FIG. 3 is a schematic of a natural gas dehydrator system
that may be combined with the embodiment of FIG. 1 or FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The present invention provides a vapor recovery processing
system (referred to herein as "VRSA") and method. An embodiment
comprises a pumping system to replace plunger lifts used on natural
wells. For example, the pumping system such as that disclosed and
marketed by Unico, Inc. ("Unico") (or other appropriate) pumping
system can be used with an engine such as that provided by Marathon
Engine Systems (or other appropriate engine) to replace plunger
lifts on natural gas wells. Replacing the plunger lift increases a
well's production time by eliminating the lost production time
associated with shutting down the well to allow the plunger to fall
to the bottom as well as eliminating the lost production time
required for the well to build up enough pressure to cause the
plunger to rise to the surface. Often, the lost production time is
greater than a well's production time. Besides increasing a well's
production time, the Unico pumping system further increases a
well's production by lowering the pressure the producing formation
is producing against. The fluids produced by the well are pumped up
through the tubing, and the gas is produced out the casing,
eliminating the pressure deferential between the casing and tubing
required to produce both the fluids and gas up through the
tubing.
[0024] An embodiment of the present invention provides an
economical system for use on natural gas wells that produce a small
volume of hydrocarbon liquids (5 to 50 barrels per day), although
the present invention can also be used for larger volumes. The
system collects and returns the gaseous hydrocarbons to a gas
stream flowing at 250 psig or less, the gaseous hydrocarbons
released as a result of separating liquid hydrocarbons from the
flowing gas stream and transferring to, and storing in, tanks, at
near or atmospheric pressure, the separated liquid
hydrocarbons.
[0025] In an embodiment of the present invention, an engine
generator set such as, for example, a 7.5 horsepower engine
generator set (e.g. a generator set such as supplied by Marathon
Engine Company), is used to provide the power to operate the gas
recovery system. The engine generator set powers electric motors
(for example, two electric motors). One electric motor powers a
circulating pump to provide fluid energy to power an eductor that
creates a vacuum to collect evolved gases from the storage tanks.
The evolved gases are entrained at the vacuum port of the eductor
into the fluid stream and compressed to a maximum of, for example,
30 psig. The fluid flowing through the eductor discharges into an
emissions separator where the compressed gases separate from the
fluid and the compressed gases flow to the outlet of the emissions
separator to be further processed while the fluid falls to the
bottom of the emissions separator. The fluid collects in the bottom
of the emissions separator to provide a continuous closed circuit
fluid feed to the suction of a circulating pump.
[0026] The emissions separator also receives entrained gas that
evolves from hydrocarbon liquids when the liquids are separated
from a flowing gas stream at higher pressure and dumped to the
lower pressure of an intermediate pressure separator. On most
installations, the intermediate pressure separator and the
emissions separator operate at the same pressure (e.g. 30 psig or
less), but on some installations it is desirable to use a back
pressure to hold the intermediate pressure separator at a higher
pressure than the operating pressure of the emissions separator. In
the emissions separator, the two gases (one at, for example,
approximately 3,000 BTU per cubic foot from the storage tanks and
the other at, for example, approximately 2,000 BTU per cubic foot
from the intermediate pressure separator) mix to form, for example,
an approximately 2,500 BTU per cubic foot homogeneous mixture. The
2,500 BTU homogeneous gas mixture flows from the outlet of the
emissions separator to the suction of a small capacity,
conventional, reciprocating, gas compressor where the gases are
compressed to the pressure of the flowing gas stream (e.g. 250 psig
or less). The compressed gases are discharged back into the flowing
gas stream at the inlet to the inline separator where the
compressed gases mix with the flowing gas stream to form, in the
inline separator, a second homogeneous gaseous mixture. The second
homogeneous gas mixture flows from the outlet of the inline
separator to other processing or to points of sale.
[0027] Mixing the relatively small volume of high BTU and vapor
pressure gas (e.g., approximately 2,500 BTU per cubic foot
compressed gas) with the larger volume of lower BTU and vapor
pressure gas (e.g., approximately 1,000 BTU per cubic foot gas)
flowing in the pipeline greatly reduces the BTU and partial
pressure of the compressed gas while at the same time slightly
raising the BTU and partial pressure of the flowing gas stream.
Lowering the BTU and partial pressure of the compressed gases
reduces the tendency of the gases evolved and recovered from the
tank to return to a liquid state. Any of the compressed gases that
return back to a liquid state prior to passing out of the inline
separator are again separated and dumped back to the storage tank.
The physical process of gases evolving from hydrocarbon liquids
stored at low pressure, the gases being compressed to a higher
pressure, then, after compression, the gases changing state from a
gas back to a liquid, and, again, the liquid being dumped back to
low pressure storage to begin evolving into a gas again, greatly
increases the compressor horsepower required to recover evolved
gases. The higher the flowing line pressure, the more gases that
will be evolved when hydrocarbon liquids are separated from a
flowing gas stream and then dumped from the higher pressure to a
lower pressure Also, the higher the flowing line pressure, the
greater is the tendency for the evolved gases from liquid
hydrocarbons, dumped from a higher pressure to a lower pressure, to
change from a gaseous state back to a liquid state when the gases
are collected and compressed back to the higher pressure.
[0028] The tendency of hydrocarbon liquids to change state from
liquids to gases and then back to liquid again can create what are
commonly called "recycle loops". At times, the recycle loops can
become large enough to force the required compressor horsepower
needed to recover the evolved gases to become infinite and a simple
vapor recovery system cannot be used. The "Hero" system described
in U.S. Pat. No. 4,579,565, was designed to address applications
where simple vapor recovery was not practical.
[0029] Another object of the present invention is to provide a
process that allows the use, with some modifications, of the
previously described components of the simple vapor recovery system
to collect the evolved gases from hydrocarbon liquids separated at
pressures as high as, for example, 500 to 1,000 psig and then
dumped to storage at, or near, atmospheric pressure. As previously
described, without modifications to the process, the simple vapor
recovery system can develop, at high flowing gas pressures, recycle
loops that could cause the horsepower required by the recovery
system to become infinite.
[0030] To decrease the tendency of gases evolved from hydrocarbon
liquids separated at high pressure, dumped to storage at low
pressure, collected at low pressure, and then, again, compressed
back to high pressure to change state from a gas to a liquid, the
previously described simple vapor recovery system is modified in
the embodiment of the present invention described below.
[0031] In one embodiment, the collected volume of high BTU gas
forming the suction volume of any stage of the reciprocating
compressor is increased by as much as 5% to 10% by introducing
lower BTU line gas from the inline separator into the volume of
collected suction gas. Changing the partial pressure of the
homogenous gas mixture, by introducing lower BTU line gas into the
higher BTU suction gas, decreases the tendency of the higher BTU
suction gas to change state from a gas to a liquid when the
homogenous gas mixture is compressed and cooled. In another
embodiment, the temperature between stages of compression of the
homogenous gas mixture is controlled to maintain the suction
temperature of each stage of compression at approximately 100 to
120 degrees Fahrenheit. Both embodiments can be combined in one
system.
[0032] Turning now to the figures, FIG. 1 is a flow diagram of the
vapor system which accomplishes decreasing the tendency of the
higher BTU suction gas to change state from a gas to a liquid.
Referring to FIG. 1, line 3 comprises a flowing natural gas stream.
The flowing natural gas stream in line 3 enters inline separator 1
at inlet 2. While flowing through inline separator 1, the free
fluids, liquid hydrocarbons and water, are separated from the
flowing natural gas. The flowing natural gas exits inline separator
1 at exit 5 and flows through line 4 to sales or other
processing.
[0033] The free fluids fall to the bottom of inline separator 1 and
are dumped through valve 6 (valve 6 is actuated by a liquid level
control (not shown)) and flow through line 8 to enter intermediate
pressure separator 10 at inlet 12. The free fluids fall to the
bottom of intermediate separator 10. In the bottom of intermediate
separator 10, the free fluids are separated by a conventional weir
system into the free fluids components, liquid hydrocarbons and
water. The water is dumped by valve 14 (valve 14 is actuated by a
liquid level control (not shown)) and flows through line 16 to
disposal. The liquid hydrocarbons are dumped through valve 18
(valve 18 is actuated by a liquid level control (not shown)) and
flow through line 20 to the inlet 22 of storage tank 24. The
changes to the liquids being dumped from intermediate separator 10
to storage tank 24 are described below.
[0034] The gas that flashes as a result of the liquid hydrocarbons
being dumped from the higher pressure of inline separator 1 to the
lower pressure of intermediate separator 10 form a first body of
homogeneous gas mixture which comprises water vapor, portions of
natural gas that were entrained in the liquid hydrocarbons, and
components of the liquid hydrocarbons which have flashed and have
changed state from a liquid to a gas. The first body of homogenous
gas mixture exits intermediate pressure 10 at exit 26 and flows
through line 28 to the inlet 30 of emissions separator 32. The
length of flow line 28 varies from location to location and in most
cases, but not always, it is installed above ground. During winter,
line 28 may be exposed to low ambient temperatures which could cool
the first body of homogenous gas mixture flowing in line 28 to a
temperature in which the gaseous liquid hydrocarbons and water
vapor contained in the first body of homogenous gas mixture could
begin to change state from a gas to a liquid. It is desirable that
none of the gases contained in the first body of homogeneous gas
mixture change state from a gas to a liquid. The presence of any
free water in flow line 28 as a result of water vapor condensing
from the first body of homogeneous gas mixture would pose a risk of
ice forming in flow line 28 thus blocking the flow in line 28 of
the first body of homogeneous gas mixture.
[0035] Several types of gas-to-gas heat exchangers can be used to
provide heat to the first body of homogenous gas mixture flowing in
line 28. The gas-to-gas heat exchangers exchange the heat (e.g.,
between 225 and 300 degrees Fahrenheit) contained in the hot
discharge gas flowing in line 36 with the first body of homogeneous
gas mixture flowing in line 28 thus raising the temperature of the
gas flowing in line 28.
[0036] Both flow lines 28 and 36 may be field installed and connect
the vapor processing system to the inlet of inline separator 1 and
the outlet of intermediate separator 10 which are in close
proximity to each other. One type of heat exchange that may be used
is to field lay lines 28 and 36 so that they touch each other, and
the two lines are may be insulated with heat resistant insulation.
The heat of compression (e.g., 250 to 300 degrees Fahrenheit) from
flow line 36 provides heat along the entire length of line 28 to
substantially prevent some of the gases contained in the first body
of homogenous gas mixture from changing state from a gas to a
liquid, and the heat from flow line 36 prevents freezing of any
water vapor that might condense in flow line 28.
[0037] The first body of homogenous gas mixture flowing in line 28
enters emissions separator 32 at inlet 30. Emissions separator 32
is approximately half full of ethylene glycol (other appropriate
liquids or mixture of liquids can also be used). The purpose of the
body of ethylene glycol contained in emissions separator 32 is
described below. The first body of homogeneous gas mixture entering
emissions separator 32 from intermediate pressure separator 10
mixes with the higher BTU fourth body of homogeneous gas mixture
collected from the tanks and forms a second body of homogenous gas
mixture (collection of the tank gases is described below). Any
liquids that might condense from the collected second body of
homogeneous gas mixture will separate from the gas and be dumped
through motor valve 46 (motor valve 46 is controlled by a liquid
level controller (not shown)) and flow line 48 into storage tank
24. The collected second body of homogeneous gas mixture exits
emissions separator 32 at outlet 38. The collected second body of
homogeneous gas mixture at approximately 27 psig flows through
lines 41 and 40 to the suction 42 of reciprocating compressor 34.
Reciprocating compressor 34 compresses the collected gases up to a
pressure range of, for example, approximately 125 to 250 psig. The
discharge pressure of reciprocating compressor 34 is determined by
the pressure of the flowing gas stream contained in inline
separator 1. From the discharge port 44 of reciprocating compressor
34, the collected second body of homogeneous gas mixture flows
through line 71 to point 72. At point 72, line 71 divides to form
lines 74 and 36. Line 74 terminates at pressure regulator 76.
Pressure regulator 76 is set at approximately 27 psig to maintain a
near-to-constant suction pressure at suction port 42 of
reciprocating compressor 34. Compressor 34 is sized to compress
more gas than the volume of gas entering line 40 from emissions
separator 32. Any time the suction pressure at suction port 42
drops below the set point of pressure regulator 76, gas flows from
pressure regulator 76 through line 78 to inlet 79 on emissions
separator 32 to maintain a near-to-constant pressure at suction
port 42. From point 72, the collected second body of homogeneous
gas mixture flows through line 36 to point 142. From point 142, the
second body of homogeneous gas mixture flows through line 3 to the
inlet 2 of inline separator 1. In inline separator 1, the collected
higher BTU second body of homogeneous gas mixture from line 36
mixes with the larger volume lower BTU gases flowing through inline
separator 1 and forms a third body of homogeneous gas mixture.
[0038] Referring again to FIG. 1, and as previously described
herein, the liquid hydrocarbons, from intermediate pressure
separator 10 flow through motor valve 88 and line 20 and enter
storage tank 24 at inlet 22. The liquids from separator 10 flash to
form a fourth body of homogenous gas mixture as a result of the
pressure change from the pressure in intermediate separator 10 to
the near or atmospheric pressure in storage tank 24. In addition to
the immediate flash, the liquid hydrocarbons contained in tank 24
continue to evolve gases as the liquid hydrocarbons attempt to
reach equilibrium with the gases contained in tank 24. The fourth
body of homogenous gas mixture of flash and evolved gases exit
storage tank 24 at outlet 50. The fourth body of homogeneous gas
mixture from storage tank 24 flows through lines 51, back pressure
regulator 53, line 52, line 55, and line 57 to the vacuum inlet 54
of eductor 56.
[0039] Eductor 56 is powered by ethylene glycol or other
appropriate fluid that is pumped from emissions separator 32 by
circulation pump 58. The ethylene glycol exits emissions separator
32 at fluid outlet 60. The ethylene glycol (at, for example,
approximately 27 psig) flows through line 64 to suction inlet 62 of
circulation pump 58. Circulation pump 58 increases the pressure of
the ethylene glycol to approximately 120 psig. The pressurized
ethylene glycol exits circulation pump 58 at discharge port 66 and
flows through line 68 to power port 61 of eductor 56. While flowing
through eductor 56, the pressurized ethylene glycol powers eductor
56 to create a vacuum at vacuum port 54. The vacuum generated by
eductor 56 is controlled to a few inches of water column (e.g., 3
to 12 inches) by a vacuum controller such as, for example, a model
12 PDSC supplied by Kimray, Inc. Vacuum controller 82 is connected
to line 52 at point 81. Vacuum controller 82 outputs a throttling
pressure signal to normally opened motor valve 88. Normally opened
motor valve 88 is installed at the termination of line 86. Line 86
begins at point 84 at the end of line 41 and terminates at the
inlet of normally opened motor valve 88. Normally opened motor
valve 88 is connected by line 90 to line 55 at point 92. When the
vacuum at point 81 exceeds the set point of vacuum controller 82,
vacuum controller 82 decreases the output pressure to normally open
motor valve 88. The decrease of output pressure to normally opened
motor valve 88 causes normally opened motor valve 88 to partially
open thereby increasing the flow of gas from emissions separator 32
through line 86, motor valve 88, and line 90 into line 55.
Increasing or decreasing the volume of gas flowing from emissions
separator 32 to vacuum port 54 of eductor 56 maintains the desired
vacuum in line 52.
[0040] The fourth body of homogeneous gas mixture from storage tank
24 is drawn into eductor 56 through line 51, back-pressure
regulator 53, line 52, line 55, and line 57 by the vacuum created
by eductor 56. To prevent air entering the system, back-pressure
regulator 53 holds a positive pressure of approximately 8 ounces on
tank 24. The collected fourth body of homogenous gas mixture is
drawn into eductor 56 through vacuum port 54 and is entrained into
the flowing ethylene glycol and compressed to a pressure of, for
example, approximately 27 psig contained in emissions separator 32.
The ethylene glycol and the entrained and compressed fourth body of
homogenous gas mixture exit eductor 56 at port 68 and flow through
line 70 to inlet 72 of emissions separator 32. In emissions
separator 32, as previously described, the collected fourth body of
homogenous gas mixture from storage tank 24 mixes with the first
body of homogenous gas mixture from intermediate pressure separator
10 and forms a second body of homogeneous gas mixture. The ethylene
glycol separates from the entrained gases and falls toward the
bottom of emissions separator 32. The ethylene glycol discharged by
eductor 56 joins the body of ethylene glycol contained in the
approximate bottom two-thirds of emissions separator 32. The
ethylene glycol is continuously circulated in a closed loop by
circulation pump 62 to provide power to eductor 56.
[0041] Heat is generated by the pumping of the ethylene glycol as
well as the compression of the collected gases. It is desirable to
control the temperature of the ethylene glycol to, for example,
between approximately 100 and 120 degrees Fahrenheit. Forced draft
cooler 101 provides cooling for the ethylene glycol. Forced draft
cooler 101 is connected to circulating pump 58 discharge line 68 at
point 94. Line 96, hand valve 98, line 97, thermostatically
controlled mixing valve 102, and line 100 connect inlet 99 of
forced draft cooler 101 to point 94. Outlet 103 of forced draft
cooler 101 is connected by line 105 and line 104 to emissions
separator 32 at point 106.
[0042] A side stream of ethylene glycol under pressure from
circulating pump 58 flows through forced draft cooler 101 and
returns to emissions separator 32 thus cooling the ethylene glycol.
The volume of ethylene glycol (e.g., 3 to 6 gallons per minute)
flowing in the side stream is controlled by adjusting hand valve
98. To maintain the desired temperature of the ethylene glycol of
between 100 and 120 degrees Fahrenheit, thermostatically controlled
mixing valve 102 can bypass through line 107 a part of, or the
entire side stream of, ethylene glycol. Whenever the ethylene
glycol becomes too cold, thermostatically controlled mixing valve
102 reduces the volume of the side stream flowing through forced
draft cooler 101.
[0043] FIG. 2 is a flow diagram of the embodiment wherein the
temperature between stages of compression of the homogenous gas
mixture is controlled to maintain the suction temperature of each
stage of compression. As noted above, the embodiment shown in FIG.
2 is intended for applications where the flowing gas pressure is
elevated to pressures above, for example, 250 psig and where the
changing of liquid hydrocarbon vapors back from a gas to a liquid
state creates recycle loops.
[0044] All of the components described in FIG. 1 are incorporated
into FIG. 2 and only the components of FIG. 1 required to explain
the modifications shown in FIG. 2 are described detail below.
[0045] As shown in FIG. 2, a third stage of compressor 110 is added
to receive the discharge gas from second stage compressor 34. The
hot (e.g., 225 to 300 degrees Fahrenheit), compressed, and
collected second body of homogeneous gas mixture exits compressor
34 at discharge port 44 and flows to point 72. From point 72, the
hot, compressed, and collected second body of homogeneous gas
mixture flows through line 36 to point 112 where a side stream of
sales gas from inline separator 1 enters line 36 and mixes with the
hot, compressed, collected second body of homogenous gas mixture
forming a fifth body of homogeneous gas mixture. The volume of gas
from inline separator 1 that enters line 36 at point 112 increases
the total volume of gas passing through point 112 by approximately
5% to 10%. The side stream of gas flows from inline separator 1
through line 4 to point 114. From point 114, the side stream of gas
flows through line 116, flow meter 118, line 120, flow control
valve 122, and line 124 to point 112. Flow control valve 122 is
controlled by a PLC or other flow control device (not shown) to
allow the required volume of side stream gas from inline separator
1 to increase the volume of gas flowing through point 112 by, for
example, approximately 5% to 10%.
[0046] As described above, mixing a lower BTU and vapor pressure
gas with a higher BTU and vapor pressure gas reduces the tendency
of some of the components of the higher BTU gas to change state
from a gas to a liquid thereby reducing the chance of recycle loops
forming.
[0047] From point 112, the fifth body of hot homogeneous gas
mixture flows through line 127 to inlet 128 of forced draft cooler
133. While flowing through forced draft cooler 133 the gases are
cooled to an approximately 20 degrees Fahrenheit approach to
ambient temperature. The cooled gases exit forced draft cooler 133
at outlet 130 and flow through line 132 to cool gas inlet port 125
of thermostatic bypass valve 126. Thermostatic bypass valve 126
monitors the temperature of the gas flowing out of outlet 129 into
line 134. When the gas temperature exiting outlet port 129 of
thermostatic bypass valve 126 drops to approximately 120 degrees
Fahrenheit, thermostatic bypass valve 126 begins to bypass some of
the hot gas around cooler 133. The hot gas flows from point 135
through bypass line 131 to hot gas inlet port 139 of thermostatic
bypass valve 126. The hot gas from hot gas inlet port 139 mixes in
thermostatic bypass valve 126 with the cooled gas from cool gas
inlet port 125 thereby maintaining the gas temperature in line 134
at approximately 120 degrees Fahrenheit. Keeping the gas in line
134 at approximately 120 degrees Fahrenheit prevents most of the
liquid hydrocarbon condensation that might occur at a cooler
temperature in line 134 or separator 146.
[0048] The approximately 120 degrees Fahrenheit temperature fifth
body of homogeneous gas mixture enters separator 146 at inlet 148.
Separator 146 removes any liquids that may have resulted from a
phase change from a gas to liquid after the fifth body of
homogenous gas mixture is compressed and cooled. The liquids
separated in separator 146 are dumped by motor valve 150 (motor
valve 150 is actuated by a liquid level controller not shown)
through lines 152 and 154 into intermediate pressure separator 10.
As described above, some of the gases and liquids contained in the
liquid from separator 146 will flash. The balance of the liquids
from separator 146 will drop to the bottom of intermediate pressure
separator 10 and mix with the liquids from inline separator 1. The
overall operation of intermediate separator 10 has been described
above.
[0049] The fifth body of homogenous gas mixture in separator 146
exits at outlet 156 of separator 146 and flows through line 158 to
enter third stage compressor 110 at suction port 136. Third stage
compressor 110 compresses the fifth body of homogenous gas mixture
to the pressure of the flowing gas stream. From discharge port 139
of third stage compressor 110, the gas flows through line 140 (as
previously described, line 140 is installed to be in heat exchange
relationship with line 28 from intermediate pressure separator 10)
to point 142. At point 142, the fifth body of homogenous gas
mixture enters line 3 and mixes with the flowing gas stream to
form, in inline separator 1, the previously described third body of
homogeneous gas mixture. The function of inline separator 1, as
well as the function of the rest of the process, has been described
above.
[0050] The embodiments described herein have been shown utilizing
only three stages of compression (the eductor and two stages of
compression). However, it should be understood that other
embodiments of the present invention can incorporate more than
three stages of compression. Also, it should be understood that
mixing gases of different BTU's in relation to each other (i.e., a
lower BTU gas with a higher BTU gas such as a lower molecular gas
such as methane with a higher molecular weight gas such as butane)
can be done between any stage of compression (or at any point in
the system). Thus, such a mixing of gases can be performed between
the first and second stages and/or between the second and third
stages of compression shown in FIG. 2.
[0051] There is the potential in cold climates of gas hydrates
forming in volume control valve 122 and motor valve 150 (hydrates
are an ice-like substance that can form from natural gas when the
proper temperature, pressure, and water content are present). Where
needed, the potential of hydrates forming in the system can be
eliminated by installing a gas-to-gas heat exchanger upstream of
volume control valve 122 and a gas-to-liquid heat exchanger
upstream of motor valve 150. The hot gas for both exchangers can be
the hot discharge gas from compressor 34.
[0052] In another embodiment of the present invention, the Vapor
Recovery Process System ("VRSA") described above is combined with
natural gas dehydrations systems and methods such as that described
in U.S. Pat. No. 6,984,257, titled "Natural Gas Dehydrator and
System" (to the inventor herein), the specification and claims of
which are incorporated herein by reference, and which are referred
to herein as "QLT",to provide a combination QLT/VRSA unit. FIG. 3
shows such a natural gas dehydration system ("QLT") that may be
combined with the VRSA. By combining the two technologies into a
common unit, many of the features, which have commonality in both
technologies, are used to reduce the manufacturing costs of a
combination QLT/VRSA unit as well as reducing installation and
operating costs. The combination QLT/VRSA unit further comprises
improvements that enhance the performance of both technologies.
Although the description that follows is illustrative of a retrofit
unit, the combination QLT/VRSA unit could also be provided in
combination with a natural gas dehydrator.
[0053] Preferably, most of the operating features/components of the
QLT and VRSA would be utilized in the combination QLT/VRSA unit.
Because the majority of applications for the combination QLT/VRSA
unit are at a non-electrified well sites, the following description
is of a well site application where commercial electricity is not
available, although the present invention is applicable to well
sites having electric service.
[0054] Non-electrified well sites require either an engine
generator to provide electric power to run the pumps and compressor
required to operate the QLT and VRSA or else the pumps and
compressor can be direct belt driven from a common shaft powered by
an engine. Because of the possible explosive factor present when
using electricity, direct driving the pumps and compressor is a
better choice for non-electrified well site applications of the QLT
and VRSA.
[0055] Some of the commonality that exists between the QLT and VRSA
are obvious. Both technologies use a natural gas fueled engine to
provide unit operating power. In the combination QLT/VRSA unit,
only one engine is required. Both technologies use eductors to
create a vacuum and compress collected vapors. Both technologies
utilize a high volume circulating pump to circulate glycol to
provide the energy to power the eductor. In the combination
QLT/VRSA unit, only one high volume circulating pump is required.
Both units require a house and skid. Both units require an
emissions separator. In the combination QLT/VRSA unit, only one
emissions separator is used to receive the rich glycol from the
dehydrator absorber. The rich glycol from the dehydrator absorber
is circulated by a high volume pump through two eductors, one for
the VRSA and one for the QLT. Using the rich glycol from the
dehydrator absorber to power the VRSA eductor eliminates the
necessity for providing glycol for the original glycol fill of the
VRSA emissions separator, eliminates the need for heating the
glycol in the VRSA emissions separator, eliminates the concern for
ever having to replenish the glycol in the VRSA emissions
separator, and eliminates any concern that the glycol in the VRSA
emissions separator would ever become saturated with water or
hydrocarbons. Other commonalities and improved process functions
will become apparent as the design and operation of the combination
QLTNRSA unit is further described below.
[0056] As noted above, an embodiment provides that two eductors be
used in the combination unit. One eductor is used to provide the
vacuum to collect and compress the vapors from the gas well's or
wells' fluid production, and the other eductor is used to provide
the vacuum to collect and compress the emissions from the
dehydrator or dehydrators located at the well site.
[0057] Two eductors allow both the VRSA and QLT to be operated at
the most desirable vacuum for the process. Because a back-pressure
regulator is used in the VRSA system to hold a minimum of 4 ounces
on the storage tank, the vacuum on the VRSA system is operated at a
higher level than the vacuum on the QLT system. On most dehydrators
that would be retrofitted with the QLT, the reboiler operates at
atmospheric pressure, and any vacuum applied to the reboiler raises
the glycol level in the reboiler. The specific gravity of glycol
compared to water is approximately 1.1; therefore, each one inch
water column vacuum raises the glycol level in the reboiler
approximately 0.9 inches. Reboilers are generally designed to
operate substantially full of glycol, and any excess or
uncontrolled vacuum can cause glycol overfill conditions in the
reboiler. The QLT is designed to operate at 2 to 3 inches water
column vacuum.
[0058] Using two eductors in the combination unit requires that two
vacuum separators be used --one for the VRSA and one for the QLT.
The vacuum separator for the VRSA is two-phased--the first phase is
uncondensed hydrocarbon vapors, and the second phase is condensed
hydrocarbon liquids. The uncondensed hydrocarbon vapors under a
vacuum in the VRSA vacuum separator are pulled into the VRSA
eductor and compressed into a common emissions separator. The
condensed hydrocarbon liquids under a vacuum are collected in the
bottom of the VRSA vacuum separator and dumped back to the storage
tanks. It should be again noted that the VRSA eductor is powered by
rich glycol generated by the dehydration process. The vacuum
separator for the QLT is a three-phased and operates the same as
the three-phased vacuum separator previously described in, for
example, U.S. Pat. No. 6,984,257, and the QLT eductor also operates
the same as described in, for example, U.S. Pat. No. 6,984,257. The
uncondensed hydrocarbon vapors from the QLT vacuum separator are
collected and compressed into the common emissions separator to
form a homogeneous mixture with the hydrocarbons collected from the
VRSA vacuum separator.
[0059] Sizing of the VRSA eductor is complicated by the fact that
hydrocarbon liquid production from gas wells is seldom constant.
Generally, the volume of liquid hydrocarbons flowing to the storage
tanks is erratic, and many times the volume of liquid hydrocarbons
flowing to the storage tanks is produced in slugs. Because the
production of liquid hydrocarbons from gas wells is seldom
constant, the hydrocarbon vapor load on the combination VRSA
eductor is constantly changing, and sometimes the hydrocarbon vapor
load can, and will, overload the capacity of the VRSA eductor.
[0060] Sizing of the QLT eductor is not as complicated as the
sizing for the VRSA eductor. On a dehydrator, the glycol
circulation rate is fairly constant, and other conditions, such as
gas temperature or changes in dehydrator operating pressure do not
generally occur rapidly or of a magnitude to significantly affect
the uncondensed vapor load on the QLT eductor. In all cases, the
QLT eductor is sized to have excess capacity to handle any expected
uncondensed vapor load that might occur from the dehydration
process. In the combination unit, any available excess capacity of
the QLT eductor can be utilized to increase the capacity of the
VRSA eductor. An overload condition of the VRSA eductor occurs when
the VRSA vacuum separator experiences a positive pressure condition
approaching the 4 ounce positive pressure setting of the tank vent
line back-pressure regulator. As the positive pressure in the VRSA
vacuum separator approaches 4 ounces, a valve in a line between the
VRSA and QLT vacuum separators opens thus allowing excess
uncondensed hydrocarbon vapors in the VRSA vacuum separator to
begin flowing into the QLT vacuum separator. The volume of
uncondensed hydrocarbon vapors flowing from the VRSA to the QLT
vacuum separator is controlled so that the total volume of
uncondensed hydrocarbon vapors entering the QLT vacuum separator
does not exceed the capacity of the QLT eductor.
[0061] Combining the VRSA technology into other production
equipment such as a production unit, a standard dehydrator, or a
QLT equipped dehydrator creates a potential well site installation
problem. Because of safety concerns, the liquid hydrocarbon storage
tanks are located on the well site at a considerable distance (100
to 200 ft) from any piece of well site production equipment that is
direct fired. Ordinarily, the VRSA is installed in close proximity
to the storage tanks. By installing the VRSA close to the storage
tanks, the tanks' vent line can be sloped from the top of the tank
to the inlet connection on the VRSA. Sloping the tanks' vent line
prevents any condensed hydrocarbon liquids from collecting in the
tanks' vent line and creating a liquid seal to block the flow of
the hydrocarbon vapors from the tanks to the VRSA.
[0062] Because the retrofit combination QLT/VRSA unit is installed
in close proximity to the well site direct fired dehydrator, the
VRSA portion of the combined unit is located a considerable
distance from the liquid hydrocarbon storage tanks. It would be
impractical and costly to suspend in the air the tanks' vent line
from the top of the tanks to the VRSA inlet of the combination
unit. Therefore, connecting the combination VRSA inlet to the top
of the storage tanks is preferably by going directly down from the
top of the tanks to below ground level and running the vent line
underground to connect from underground into the inlet of the
combination VRSA.
[0063] Running the storage tanks' vent line underground from the
tanks to the VRSA solves all the problems with the tank vent line
except for the problem of creating a condensed liquid trap which
would form a liquid seal to stop the flow of vapors from the
storage tanks to the VRSA. To eliminate the fluid trap, the
following is installed as part of the combination unit. A vertical
fluid collection pot, preferably approximately two feet long and
four inches in diameter, is installed underground where the tank
vent line ends and the bottom of a preferably vertical two inch
diameter riser pipe connected to the VRSA inlet begins. The VRSA
inlet includes the back-pressure regulator that maintains a
positive pressure (approximately 4 ounces) on the storage tanks.
The vertical riser pipe connects to the VRSA inlet upstream of the
back-pressure regulator. The tanks' vent line is installed so that
there is a gradual slope from the tanks to the VRSA unit. The tank
vent line, generally an approximately two inch diameter pipe,
connects to the side near the top of the vertical fluid collection
pot. The bottom of the vertical riser pipe connected to the VRSA
inlet connects to the top of the vertical fluid collection pot. A
1/2 inch diameter pipe is installed inside the two inch vertical
riser pipe which is connected between the top of the fluid
collection pot and the VRSA inlet. The bottom end of the 1/2 inch
diameter pipe terminates approximately 1 inch above the bottom of
the fluid collection pot. The top of the 1/2 pipe turns horizontal
and exits the vertical two inch riser pipe through the side
approximately one foot below where the vertical two inch riser pipe
connects to the VRSA inlet. The horizontal top outlet of the 1/2
inch pipe connects to the vacuum port of a 1/2 inch eductor such as
a Penberthy model 1/2 ALH. A side stream of rich glycol
(approximately 2 gallons/minute) from the common emissions
separator circulates under pressure from the circulation pump of
the combination unit to the power port of the 1/2 inch eductor. The
outlet of the 1/2 inch eductor connects to the common emissions
separator at approximately the same level as the connections for
the QLT and VRSA eductors.
[0064] In operation, hydrocarbon liquids condensed from the vapors
collect in the tanks' sloped vent line and flow along the bottom of
the sloped vent line into the vertical fluid collection pot. The
1/2 inch eductor continually lifts the condensed hydrocarbon
liquids through the 1/2 inch line inside the riser pipe and sends
the condensed hydrocarbon liquids under pressure into the common
emissions separator. The common emissions separator collects the
condensed hydrocarbon liquids and dumps them back to the storage
tanks. During those times when the capacity of the 1/2 inch eductor
is not being required to lift condensed hydrocarbon liquids, the
1/2 eductor slightly increases the vacuum capacity (approximately
16 cubic feet per hour) of the VRSA.
[0065] As noted above, the vertical riser pipe connected to the top
of the fluid collection pot is connected to the VRSA inlet upstream
of the tank vent line back-pressure valve. Because the 1/2 inch
eductor is lifting fluids and possibly pulling a vacuum on the
tanks vent line upstream of the vent line back-pressure valve,
under conditions of no or little fluid production to the tanks, the
1/2 eductor could lower the positive pressure on the tanks and
possibly create a vacuum on the tanks. To prevent any possibility
that the 1/2 inch eductor could create a vacuum condition on the
tanks an ounces regulator is installed in a line running between
the common emissions separator and the vertical riser pipe. The
inlet of the line containing the ounces regulator is connected to
the common emissions separator in the vapor chamber close to the
top. The outlet of the line containing the ounces regulator is
connected to the riser pipe upstream of the vent line back-pressure
regulator.
[0066] In operation, the ounces regulator is set to maintain a
pressure in the tanks' vent line slightly less then the pressure
setting of the vent line back-pressure regulator. As long as the
pressure on the vent line is above the setting of the ounces
regulator, no vapors feed from the emissions separator into the
tanks vent line; however, if conditions ever exist where a vacuum
induced by the 1/2 inch eductor lowers the pressure in the tanks
vent line enough to reach the set pressure of the ounces regulator,
the ounces regulator would feed hydrocarbon vapors from the common
emissions separator into the tanks' vent line to maintain a
positive vent line pressure equal to the ounces regulator setting.
By using collected vapors from the common emissions separator to
maintain the positive pressure on the tanks' vent line, no
additional hydrocarbon vapors are introduced into the system.
[0067] It should be noted that the fluid pumping system described
above may be used on any type of unit where the VRSA technology is
combined with a piece of equipment that requires the combined unit
to be installed a distance from the hydrocarbon storage tanks. On
stand alone VRSA units where the tank vent line can be installed
allowing the line to be sloped from the top of the tank to the VRSA
inlet, the fluid pumping system is not required.
[0068] The application of the stand alone VRSA as well as
combination units designed to utilize the VRSA technology will be
increased by the move, on shore, to directionally drill multiple
gas wells from a common well pad. Having multiple gas wells
producing from a common well pad increases the volume of recovered
hydrocarbon liquids at the well pad which, in turn, improves the
economics of installing a VRSA. The economics of installing a VRSA
on multiple gas wells are improved because one VRSA can be utilized
to recover the venting from all the hydrocarbon storage tanks
located on the well pad. It follows that the economics of
installing, on a multiple well pad, a QLT or a combination QLT/VRSA
unit would be improved by designing the QLT or combination QLT/VRSA
unit so that one QLT unit can be utilized to collect all the
venting that occurs from multiple dehydrators on the well pad.
[0069] Thus, in an embodiment, one combination QLT/VRSA unit is
used to collect all the hydrocarbons that are vented to the
atmosphere by multiple dehydrators and multiple hydrocarbon storage
tanks located on one well pad. The one combination QLTNRSA unit
turns the well pad into an emissions free location with all
recovered hydrocarbons either being used for fuel gas or sold to
produce increased revenues. As previously noted, no design change
or concept is required for one VRSA to collect the storage tank
vapors from multiple wells on a common well pad. The QLT requires
some minor design and conceptual changes for one QLT to recover the
hydrocarbon venting from multiple dehydrators on a well pad.
[0070] On a multiple well pad with no commercial electricity, "one"
dehydrator on the multiple well pad would operate with a natural
gas fueled engine direct driving the circulation pump and positive
displacement pump needed to power the VRSA and all other
dehydrators. The balance of the QLT system on the "one" dehydrator
would be larger. Each additional dehydrator on the well pad
operates as follows. To eliminate the gas which is normally vented
by, for example, a Kimray glycol pump, the Kimray glycol pump is
powered by rich glycol from the emissions separator which is part
of the QLT system for the "one" dehydrator. The rich glycol is
pressurized by a positive displacement pump to a pressure adequate
to power the Kimray pumps on the additional dehydrators. One or
more positive displacement pumps are used to provide the
pressurized rich glycol required to run the additional Kimray
glycol pumps. After providing power to run the additional Kimray
glycol pumps, the rich glycol is returned to the emissions
separator which is part of the "one" dehydrator QLT system. It
should be noted that on some applications of the combination
QLTNRSA unit, depending upon the absorbers operating pressure, it
is possible to operate the Kimray glycol pumps the way they are
designed to be used (using the rich glycol exiting the absorbers to
power the pumps). If the application should allow the Kimray glycol
pumps to be powered by the rich glycol exiting the absorber, the
excess gas generated by the Kimray glycol pumps would be routed to
the first stage of the VRSA gas compressor to be compressed to
sales pressure along with collected vapors.
[0071] On all additional dehydrators on a common well pad where the
Kimray pumps are being driven with rich glycol with the energy
being supplied by a direct driven positive displacement pump, a
dump pot must be installed, and, if a three-phased flash separator
is not already on the dehydrator skid, in the preferred design, a
three-phased flash separator must be installed. The dump pot is
necessary for the process to function. The three-phased flash
separator is preferably, but not absolutely necessary, for the
process to function. In the preferred design, the dump pot receives
the rich glycol from the absorber and dumps the rich glycol to a
flash separator. The flash separator operates at a pressure higher
then the first stage of the VRSA gas compressor. When the pressure
in the three-phased flash separator reaches the pressure set point,
uncondensed gases released from the rich glycol exiting the
absorber flow to the first stage of the VRSA gas compressor to be
compressed to sales pressure along with collected vapors. Any
liquid hydrocarbons in the rich glycol exiting the absorber are
collected in the three-phased flash separator and dumped to the
hydrocarbon storage tanks. As in the normal dehydration process and
before the dump pot is installed, the rich glycol entering the
three-phased flash separator from the absorber is dumped from the
three-phased flash separator to flow through the same glycol path
as taken by the rich glycol when the rich glycol exited the Kimray
glycol pump after being used to drive the pump.
[0072] The still column effluents from each additional dehydrator
on a well pad are collected by connecting the still columns of each
additional dehydrator to the effluent condenser inlet on the "one"
dehydrator QLT system. The vacuum being generated by the eductor on
the "one" dehydrator QLT system provides the energy to move the
additional still column effluents to the inlet of the condenser. On
some dehydrators, a still column effluent condenser is provided.
Where a usable still column effluent condenser is provided on a
dehydrator to be retrofitted, the uncondensed vapors from the
effluent condenser are collected by connecting the vacuum generated
by the "one" dehydrator eductor to the outlet of the retrofitted
dehydrators' effluent condenser.
[0073] In another embodiment, one eductor and one vacuum separator
is used in the combination QLT/VRSA unit. This embodiment comprises
a vacuum chamber in the top of the emissions separator. One eductor
is used to create the vacuum in the vacuum chamber. The VRSA flow
line from the outlet of the back-pressure regulator connects
directly to the vacuum chamber with all other components and
operation of the VRSA remaining the same. The vacuum in the vacuum
chamber is preferably maintained at 2 to 3 inches of water column
which is enough vacuum for both the QLT and VRSA processes.
[0074] A two or three phased liquid accumulation separator is
installed in the line connected to the outlet of the dehydrator
effluent condenser. The separator collects condensed liquids
created by cooling the effluents from the dehydrator still column.
The uncondensed gases from the dehydrator effluents flow from the
gas outlet of the liquid accumulation separator to the vacuum
chamber. The vacuum port of the eductor connects to the vacuum
chamber, and the collected uncondensed gases and any unseparated
hydrocarbon liquids from the QLT and VRSA processes flow through
the eductor and are compressed to approximately 20 to 25 psig in
the lower chamber of the emissions separator.
[0075] As previously noted, the liquid accumulation separator can
be two or three-phased. A three-phased liquid accumulation
separator separates the condensed liquids into its hydrocarbon and
water components. The hydrocarbons and water are then be dumped to
separate storages. A two-phased liquid accumulation separator also
separates the condensed liquids into hydrocarbon and water
components, but the condensed hydrocarbons are not be dumped
directly to storage. Instead, the condensed hydrocarbons flow with
the uncondensed gases from the outlet of the liquid accumulation
separator and enter into the vacuum chamber. In the vacuum chamber,
the condensed hydrocarbons mix with any liquid hydrocarbons from
the VRSA process and flow with the collected gases through the
vacuum port of the eductor to be compressed into the lower chamber
of the emissions separator. The emissions separator is three-phased
to separate liquid hydrocarbons from glycol. Any liquid
hydrocarbons collected in the emissions separator are dumped to
storage by the three-phasing system of the emissions separator.
[0076] In one embodiment, the compressor used on the VRSA has an
extended cross-head system that connects the crank-shaft to the
piston. The extended cross-head system creates a chamber where the
connecting rod runs through two sets of packing. The top set of
packing prevents the compressed gases from entering the cross-head
chamber, and the lower set of packing prevents the compressor oil
from entering the cross-head chamber. The cross-head chamber has a
tapped and threaded opening to the atmosphere. Any gases or oil
that might enter the cross-head chamber are ordinarily released to
the environment.
[0077] Because the VRSA creates a vacuum, the release of gases or
oil from the cross-head chamber to the environment can be prevented
by connecting the cross-head chamber to the VRSA vacuum chamber. A
simple flow meter is installed in the line connecting the
cross-head chamber to the vacuum chamber. Excess flow through the
simple flow meter would indicate a problem with either the upper or
lower cross-head packing
[0078] The preceding examples can be repeated with similar success
by substituting the generically or specifically described
compositions, biomaterials, devices and/or operating conditions of
this invention for those used in the preceding examples.
[0079] 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 all such
modifications and equivalents. The entire disclosures of all
references, applications, patents, and publications cited above,
and of the corresponding application(s), are hereby incorporated by
reference.
* * * * *