Note: Descriptions are shown in the official language in which they were submitted.
CA 02593104 2007-07-03
PATENT APPLICATION
NATURAL GAS WELL VAPOR RECOVERY PROCESS SYSTEM
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to U.S. Patent Application No. 11/677,985,
titled "Natural Gas
Well Vapor Recovery Process System" and filed February 22, 2007, which is a
continuation-in-
part application of U.S. Patent Application No. 11/456,001, titled "Vapor
Recovery Process
System" and filed July 6, 2006, which in turn is a continuation-in-part
application of U.S. Patent
Application No. 11/234,574, titled "Vapor Process System" and filed September
22, 2005, which
claims the benefit of the filing of U.S. Provisional Patent Application Serial
No. 60/612,278, titled
"Vapor Process System" and filed September 22, 2004, and the specifications
and claims of
those applications are incorporated herein by reference.
[0002] This application also is related to Canadian Application No. 2,523,110,
titled "Vapor
Process System" and filed October 12, 2005 (the specification and claims of
which are
incorporated herein by reference), which in turn is related to U.S. Patent
Application No.
11/234,574.
BACKGROUND OF THE INVENTION
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.
Background Art:
[0004] 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
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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.
[0005] 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.
[0006] 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
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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.
[0007] 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.
[0008] 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 system 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.
[0009] 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.
However, pumping
of natural gas wells has not been favored because of pumping problems. Some of
the problems
with pumping gas wells have been gas locking (a condition where the pumping
barrel fills with
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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
[0010] 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.
[0011] 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.
[0012] 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
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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.
[0013] 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.
[0014] 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 comprises powering the eductor
with a circulating
pump and powering the circulating pump with a motor. The motor may be an
electric motor, and
the motor may be an electric motor. The electric motor is preferably powered
with an engine
generator set. 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.
[0015] The method may comprise providing a continuous closed circuit fluid
feed to a suction of
the circulation pump using a fluid collected at the bottom of the emissions
separator. The method
may further comprise separating hydrocarbon liquids from a flowing gas stream
coming from the
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storage tank at high pressure, dumping the hydrocarbon liquids to a lower
pressure of an
intermediate pressure separator, and receiving into the emissions separator
entrained gas that
evolves from the hydrocarbon liquids.
[0016] The method may further comprise sending a first gas stream from the
storage tank to the
emissions separator, sending a second gas stream, having a BTU per cubic foot
lower than the
first gas stream, from the intermediate pressure separator to the emissions
separator, mixing the
first and second gas streams to form a homogenous gas mixture, sending the
homogenous gas
mixture from an outlet of the emissions separator to a gas compressor,
compressing the
homogenous gas mixture to a pressure equivalent to that of the flowing gas
stream, sending the
compressed homogenous gas mixture into the flowing gas stream at an inline
separator to form a
second homogenous gas mixture, and sending the second homogenous gas mixture
out from the
inline separator; and wherein mixing the first gas stream with the second gas
stream lowers the
BTU per square foot and partial pressure of the compressed homogenous gas
mixture reduces a
tendency of the evolved gases from the storage tank to return to a liquid
state.
[0017] The method of claim may comprise providing more than two stages of
compression
between the emissions separator and the inline separator.
[0018] The method may comprise collecting a suction gas forming a suction
volume at a stage
of a reciprocating compressor and combining the volume of collected suction
gas with a gas from
an inline separator having a BTU lower than that of the volume of collected
suction gas to form a
homogenous gas mixture so that the tendency of the collected suction gas to
change from a gas
to a liquid state when the homogenous gas mixture is compressed and cooled.
[0019] Another embodiment of the present invention 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
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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 such disposition as further processing or point of sale.
[0020] Another embodiment of the present invention 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 such disposition as further
processing.
[0021] Another embodiment of the present invention provides a natural gas well
system
comprising combining a vapor recovery process system with a natural gas
dehydration system to
form a combination system, the combination system comprising at least one
eductor to create a
vacuum and to compress collected vapors, a circulating pump to circulate a
dessicant such as
glycol to power said eductor, an engine to power the circulating pump, an
emissions separator to
receive the dessicant from a dehydrator absorber, and wherein the dessicant
from the dehydrator
absorber powers the eductor. The system may comprise one eductor in
communication with one
vacuum separator and with a vacuum chamber in the emissions separator. The
system may
comprise a first eductor in communication with a two-phased vacuum separator
and a second
eductor in combination with a three-phased vacuum separator.
[0022] Another embodiment provides a system for controlling engine speed of a
natural gas well
vapor recovery processing system to increase a vapor handling capacity of said
vapor recovery
system, said engine speed control system comprising an emissions separator
comprising a
pressure chamber and a vacuum chamber, a first pressure transducer in
communication with the
pressure chamber to sense a rise or fall of pressure in the pressure chamber,
a computer in
communication with the first pressure transducer and in communication with an
engine to vary
engine speed in response to a signal from the first pressure transducer, and a
second pressure
transducer located on a vapor collection line between a storage tank and the
vacuum chamber,
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the second pressure transducer for sensing a rise in pressure in said vapor
collection line, and
the second pressure transducer in communication with the computer so that the
computer varies
the engine speed in response to a signal from the second pressure transducer.
[0023] 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
[0024] 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:
[0025] Fig. 1 is a flow diagram of an embodiment of the invention;
[0026] Fig. 2 is a flow diagram of a modification of the embodiment of Fig. 1;
[0027] Fig. 3 is a schematic of a natural gas dehydrator system that may be
combined with the
embodiment of Fig. 1 or Fig. 2; and
[0028] Fig. 4 is a schematic of the present invention comprising engine speed
control
components.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The present invention provides a vapor recovery processing system
(referred to herein as
"VRSA") and method. As used in the specification and claims herein, the terms
"a" and "an"
mean one or more.
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[0030] An embodiment comprises a pumping system to replace plunger lifts used
on natural gas
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, Inc. (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.
[0031] 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.
[0032] 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 Systems, Inc.), 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
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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 (circulation) pump.
[0033] 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.
[0034] 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
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to a liquid state prior to passing out of the inline separator are again
separated and dumped back
to the storage tank.
[0035] 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.
[0036] The tendency of hydrocarbon liquids to change state from liquids to
gases and then back
to liquid 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. Patent No. 4,579,565 (to the present
inventor), was designed to
address applications where simple vapor recovery was not practical.
[0037] The present invention also provides 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.
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[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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
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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.
[0042] 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.
[0043] 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.
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[0044] 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.
[0045] 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
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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.
[0046] 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.
[0047] 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
CA 02593104 2007-07-03
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.
[0048] 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.
16
CA 02593104 2007-07-03
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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 in detail
below.
17
CA 02593104 2007-07-03
[0053] As shown in Fig. 2, a third stage 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%.
[0054] 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.
[0055] 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
18
CA 02593104 2007-07-03
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.
[0056] 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.
[0057] 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.
[0058] The embodiments described above 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
19
CA 02593104 2007-07-03
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.
[0059] 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.
[0060] In another embodiment of the present invention, the Vapor Recovery
Process System
("VRSA") described above is combined with natural gas dehydration systems and
methods such
as that described in U.S. Patent 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 the systems and methods of that patent referred to herein as "QLT", to
provide a combination
"QLTNRSA" unit. Fig. 3 shows such a natural gas dehydration system, QLT 200,
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 QLTNRSA unit as well as reducing installation and
operating costs. The
combination QLTNRSA unit further comprises improvements that enhance the
performance of
both technologies. Although the description that follows is illustrative of a
retrofit unit, the
combination QLTNRSA unit can also be provided in combination with a natural
gas dehydrator.
[0061] Preferably, most of the operating features/components of the QLT and
VRSA are utilized
in the combination QLTNRSA unit. Because the majority of applications for the
combination
QLTNRSA unit are at non-electrified well sites, the following illustrative
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.
CA 02593104 2007-07-03
[0062] Non-electrified well sites require either an engine generator to
provide electric power to
run the pumps and the compressor required to operate the QLT and the VRSA, or
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.
[0063] Again, some commonality exists between the QLT and VRSA are obvious.
Both
technologies use a natural gas-fueled engine to provide unit operating power.
In the combination
QLTNRSA unit, only one engine is required. Both technologies use eductors
(such as the VRSA
eductor described above and QLT eductor 256 in Fig. 3) to create a vacuum and
to compress
collected vapors. Both technologies utilize a high volume circulating pump
(such as the VRSA
circulating pump described above and QLT circulating pump 262 in Fig. 3) to
circulate glycol to
provide the energy to power the eductor. In the combination QLTNRSA unit, only
one high
volume circulating pump is required. Both units require a house and skid. Both
units require an
emissions separator (such as the VRSA emissions separator described above and
emissions
separator 232 in Fig. 3). In the combination QLTNRSA unit, only one emissions
separator is
used to receive the rich glycol from the dehydrator absorber (such as the VRSA
absorber
described above and absorber 210 in Fig. 3). 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.
21
CA 02593104 2007-07-03
[0064] 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(s') 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.
[0065] 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 (such as reboiler 270 with still column 272 in Fig.
3) 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.
[0066] Using two eductors in the combination unit requires that two vacuum
separators be used
- one separator for the VRSA and one separator (such as separator 290 in Fig.
3) 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. Patent No. 6,984,257 (to the inventor herein, the specification and
claims of that patent
incorporated herein by reference), and the QLT eductor also operates the same
as described in,
for example, U.S. Patent No. 6,984,257 (to the inventor herein, the
specification and claims of
22
CA 02593104 2007-07-03
that patent incorporated herein by reference). 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.
[0067] 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.
[0068] 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.
23
CA 02593104 2007-07-03
[0069] 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.
[0070] Because the retrofit combination QLTNRSA 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
done by running the vent line 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.
[0071] 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
24
CA 02593104 2007-07-03
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~h 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'/2
inch diameter pipe
terminates approximately 1 inch above the bottom of the fluid collection pot.
The top of the'/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'/2 inch pipe connects to the vacuum port of a'/2 inch eductor
such as a Penberthy
model 1/2ALH. 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'/2 inch eductor. The outlet of the'h inch eductor
connects to the common
emissions separator at approximately the same level as the connections for the
QLT and VRSA
eductors.
[0072] 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'/z inch eductor continually lifts the condensed hydrocarbon liquids
through the'h 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'/2 inch eductor is not being required to lift condensed
hydrocarbon liquids, the'/2
eductor slightly increases the vacuum capacity (approximately 16 cubic feet
per hour) of the
VRSA.
[0073] 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'/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'h inch eductor could create a
vacuum condition on the
CA 02593104 2007-07-03
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.
[0074] 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'h 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.
[0075] 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.
[0076] 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
26
CA 02593104 2007-07-03
well pad, a QLT or a combination QLTNRSA unit would be improved by designing
the QLT or
combination QLTNRSA unit so that one QLT unit can be utilized to collect all
the venting that
occurs from multiple dehydrators on the well pad.
[0077] Thus, in an embodiment, one combination QLTNRSA 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.
[0078] 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
27
CA 02593104 2007-07-03
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.
[0079] 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.
[0080] 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
(such as
condenser 220 in Fig. 3) 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.
28
CA 02593104 2007-07-03
[0081] In another embodiment, one eductor and one vacuum separator is used in
the
combination QLTNRSA 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.
[0082] 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.
[0083] 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.
29
CA 02593104 2007-07-03
[0084] 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.
[0085] 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.
[0086] Another embodiment of the present invention comprises an engine speed
control. At
times, it may be necessary or desirable to increase the hydrocarbon vapor
handling capacity of
the VRSA to prevent hydrocarbon vapors from escaping to the atmosphere when
large slugs of
hydrocarbon liquids are dumped to the storage tanks. The engine on the present
invention runs
at a constant speed of, for example, approximately 2600 RPM. The maximum speed
of the
engine may be 3600 RPM. Thus, for example, the hydrocarbon vapor handling
capacity of the
present invention could be increased by approximately 40 percent by simply
increasing the
engine speed when the system begins to experience an over-load condition.
[0087] It might also be desirable to slow the engine speed below, for example,
2600 RPM when
the VRSA begins to experience an under-load condition. When allowed, slowing
the engine
speed to approximately 1500 RPM (the engine idle speed) would save engine life
and operating
fuel and would decrease the possibility of pulling a vacuum on the storage
tanks.
CA 02593104 2007-07-03
[0088] Thus, the object of this embodiment comprising the engine speed control
is to provide an
operating system that can sense over or under operating load conditions and
can adjust the
engine speed between, for example, approximately 1500 and 3600 RPM to
accommodate the
system load requirements.
[0089] As in the other embodiments described above, the basic components of
the invention
such as the engine, belt-driven compressor and circulation pump, eductor, and
two-chambered
(vacuum and pressure) emissions separator would remain the same in this
embodiment. For this
embodiment, the invention comprises the changes described below to accomplish
engine speed
control.
[0090] A first 12 volt pressure transducer is installed in the pressure
chamber of the emissions
separator to sense a rise or fall of the gas pressure (preferably in pounds
per square inch) in the
pressure chamber. The desired gas pressure range in the pressure chamber of
the emissions
separator is preferably between approximately 20 and 25 psig. A small increase
of gas pressure
in the pressure chamber causes an increase in the electrical signal from the
first 12 volt pressure
transducer. A small decrease of gas pressure in the pressure chamber causes a
decrease of the
electrical signal from the first 12 volt pressure transducer.
[0091] A second 12 volt pressure transducer is installed upstream of the
ounces back-pressure
valve presently installed on the vapor collection line from the storage tank
or tanks. The second
12 volt pressure transducer senses a rise (preferably in ounces) of the gas
pressure in the
collection line. The ounces back-pressure regulator, installed in the vapor
collection line from the
storage tank or tanks is preferably set to hold from between approximately two
to four ounces of
gas pressure on the storage tanks. A small increase in the ounces gas pressure
above the set
point of the ounces back-pressure regulator increases the electrical signal
from the second 12
volt pressure transducer.
[0092] A programmed computer or "process logic controller" ("PLC") is
installed to receive the
electrical signals from both the first and second 12 volt pressure
transducers. The PLC is
31
CA 02593104 2007-07-03
programmed to increase the engine speed to a maximum of preferably
approximately 3600 RPM
on an increase in the electrical signal from the first 12 volt pressure
transducer; or, to decrease
the engine speed to a minimum of preferably approximately 1500 RPM on a
decrease in the
electrical signal from the first 12 volt pressure transducer. The PLC is also
programmed to
increase the engine speed on an increase in the electrical signal from the
second 12 volt
pressure transducer. The program logic of the PLC thus allows for the
electrical signal from
either the first or second 12 volt pressure transducers to control the engine
speed depending on
which electrical signal is greater. The PLC is also in communication with the
circulation pump.
[0093] Referring to Fig. 4, a flow diagram is shown illustrating the process
of the VRSA
incorporating the present embodiment. Emissions separator 301 comprises
pressure chamber
301A and vacuum chamber 301B. Pounds first pressure transducer 302 is in
communication
with pressure chamber 301A. Ounces second pressure transducer 303 is located
on storage
tank vapor collection line 306 which leads from storage tank 307. Ounces back-
pressure valve
304 is located on line 306 between second transducer 303 and vacuum chamber
301 B. PLC
305, which is programmed to control the speed of engine 330, is in
communication with first
transducer 302 via electric line 310, second transducer 303 via electric line
311, compressor 317
via electric line 334, and circulation pump 362 via electric line 335. Engine
330 is preferably in
communication with the aforementioned components via electronic governor 332.
Production line
separator 308 is in communication with storage tank 307 via line 315 on which
intermediate
pressure 309 is located. Pressure regulator 312 is located on line 313 which
brings make-up gas
to emissions separator pressure chamber 301A. The pressure of the gas entering
pressure
chamber 301A from line 313 is regulated by pressure regulator 312 to maintain,
at all times, a
minimum pressure of approximately 20 PSIG in pressure chamber 301A. Line 314
brings flashed
gases from intermediate separator 309 to pressure chamber 301A. Line 315
transfers
intermediate pressure hydrocarbon liquids from intermediate pressure separator
309 to storage
tank 307. Line 316 is a flow line that transfers all the gases collected in
pressure chamber 301A
to compressor 317. Flow line 318 transfers all the gases compressed by
compressor 317 to the
inlet of production line separator 308. Flow line 320 transfers collected tank
vapors to the
vacuum port of eductor 319.
32
CA 02593104 2007-07-03
[0094] In this embodiment, the natural gas production stream from the natural
gas well or wells
enters production line separator 308, and the gas production stream is
separated into its gaseous
and liquid components. The gaseous components of the natural gas production
stream pass out
of production line separator 308 for further processing and sale. The liquid
components of the
natural gas production stream are dumped from production line separator 308 to
intermediate
pressure separator 309. Separator 309 will generally operate at a pressure of
from between
approximately 50 and 100 PSIG. The reduction of pressure from separator 308 to
separator 309
cause gases to flash from the liquid hydrocarbon stream. The flashed gases
flow through line
314 to enter pressure chamber 301A. The flashed gases mix with the gases in
pressure
chamber 301A as well as mixing with any other gases entering pressure chamber
301A.
[0095] The hydrocarbon liquids collected in intermediate pressure separator
309 are dumped
from intermediate separator 309 to storage tank 307 via conduit 315 where the
pounds of gas
pressure reduction from the pressure of intermediate pressure separator 309 to
the ounces gas
pressure of storage tank 307 cause the hydrocarbon liquids to further flash.
The flashed gas from
storage tank 307 flows through line 306 and back pressure valve 304 to enter
vacuum chamber
301 B. From vacuum chamber 301 B the collected gas flows through flow line 320
to be
compressed by eductor 319 into pressure chamber 301 A.
[0096] As previously described, all the gases entering pressure chamber 301A
are compressed
to flowing line pressure by compressor 317 and injected into the natural gas
stream flowing from
the gas well or wells. As long as the compressor 317 and eductor 319 have the
capacity to
handle the volume of gases flowing from intermediate separator 309, storage
tank 30, and make-
up gas line 313, no gases are vented to the atmosphere from tank 307. However,
because the
volume of hydrocarbon liquids being produced by the gas well(s) can vary
several times during
the day from no hydrocarbon liquids to a volume of hydrocarbon liquids large
enough to generate
enough flashed gases to exceed the gas handling capacity of the VRSA
embodiments described
above, the design of this embodiment must allow for the capacities of
compressor 317 and
eductor 319 to increase or decrease to accommodate the volume of liquid
hydrocarbons being
33
CA 02593104 2007-07-03
produced by the well(s). As previously described, first and second pressure
transducers 302 and
303, while reacting to the gas pressure in pressure chamber 301A and the gas
pressure in vapor
collection line 306, provide electrical signals to PLC 305 causing PLC 305 to
change the speed of
engine 330. Changing the speed of engine 330 either increases or decreases the
gas handling
capacities of both compressor 317 and eductor 319.
[0097] 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.
[0098] 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.
34
