Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE
Method and apparatus for recovering vented volumes of gas into containment.
INTRODUCTION
The invention relates to a method and apparatus for eliminating or
significantly reducing
the volume of vented gas(es) released into the atmosphere.
BACKGROUND OF THE INVENTION
The invention relates to a method and apparatus for introducing a gathered low
pressure
volume of gas(es) into a pressure containment of higher pressure, thereby
eliminating or
significantly reduce the venting of these gases to atmosphere. Particularly
useful in the upstream
and midstream segments of oil and gas production ¨ where the activity of
natural gas production
at various pressure values is prevalent ¨ the invention makes use of available
high-pressure motive
gas to power a parallel, sequentially initiated train of ejectors to inlet a
volume of low pressure
vented gas(es) and discharge the combined volumes into a contained pressure
higher than the
suction gas but lower than the motive gas.
Various processes common to the production and transmission of natural gas and
associated hydrocarbons result in the venting or release of gas(es) into the
atmosphere. Typical
sources are compressor seals and packings, valve actuators and positioners,
pneumatic
instrumentation, liquid storage tanks and other hydrocarbon processes such as
dehydration.
Generally referred to as leaked or vented gases, these volumes are frequently
released into the
atmosphere or introduced into a flare system and combusted.
Natural gas consists largely of methane and other flammable hydrocarbon gases
deemed to
be greenhouse gases. Methane gas has been assigned a 100-year global warming
potential
(GWT)of 25 X, giving 1 kg methane an equivalence of 25 kg CO2 or 25 kg CO2e.
Continuing to allow
these vented gas emissions to be released directly into the atmosphere is
undesirable and may
have associated regulatory penalties; active flaring is a highly visible and
also a subjectively
objectional activity; directing into the combustion air intake of an engine or
burner may be cost
prohibative and due to the inconsistencies inherent with vented gas volumes
and pressures, create
complicated equipment performance instability issues.
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The embodied invention provides a new and innovative method and apparatus to
mitigate
routine vent gas releases to atmosphere by introducing it into or back into
pressure containment
such as a gas compressor inlet or an engine fuel gas supply.
The embodied invention provides an innovative method to economically recover
small
volumes of vented gases released in normal day to day hydrocarbon production
operations.
Use of multiple ejectors in a tandem, series configuration as described in
Canadian Patent
CA 2736412, Dresser-Rand Company, US, 2015/11/24, SUPERSONIC EJECTOR PACKAGE:
this
method consists of various series arrangements and constructs of gas to gas
ejectors perhaps
capable of higher ratios of compression than absolutely necessary. The lack of
a subsonic ejector
offering or a control and throughput capacity means or philosophy could also
limit the effective
performance of the prior disclosure.
The use of a high pressure liquid as a motive source for an ejector to inlet
gathered liquid
hydrocarbon storage tank vapors and discharge into a pressurized flare, sales
or inlet line is
described in United States Patent 5,195,587, Conoco Inc., 1993/03/23, VAPOR
RECOVERY SYSTEM.
In this instance the versatility of an ejector in a multi-phase application is
evident. No variable
capacity control is described. A high pressure liquid source compatible with
the process must be
available. The use of produced water as a motive fluid requires cold weather
considerations.
As detailed in United States Patent 5,533890, Thermatrix Inc., 1996/07/09,
METHOD AND
APPARATUS FOR CONTROL OF FUGITIVE VOC EMISSIONS: embodies an arrangement of
components suitable to collect and process a VOC emission stream into a
flameless combustor. A
gas to gas ejector is mentioned as an option to draw a slight vacuum on the
entire system post
combustor. Compressed air is to be considered as a motive source. The primary
attribute of this
method and apparatus appears to be the combustor.
In United States Patent, 8,113,181 B2, REM Technology Inc., 2012/02/14, METHOD
AND
APPARATUS FOR CAPTURING AND CONTROLLING FUGITIVE GASES: the method describes
one in
which emitted gases are captured and directed to the air intake of an engine
or, should the
pressure at the air intake system exceed a predetermined value, release the
gases to vent through
a check valve. Significant effort is made to manage the fluctuations in
volumes being introduced to
the intake air stream of the engine and the stability of the engine itself as
air/fuel control systems
react to varying air to fuel volumes and ratios. A sudden pressure and volume
fluctuation burst of
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vented gases may over-tax the control system and cause the vented gas to vent
to atmosphere or
to flare. The requirement of sophisticated engine air-fuel control systems,
site utility power
requirements and PLC instrumentation and controls may eliminate this approach
uneconomical.
See also: World Intellectual Property Organization, WO 2009/052622 Al, REM
Technology Inc.,
2009/04/30 and WO 2006/094391 Al, REM Technology Inc., 2006/09/14 and United
States Patent,
8,235,029 B2, REM Technology Inc., 2012/08/07, METHOD AND APPARATUS FOR
PROCESSING
DILUTED FUGITIVE GASES.
A similar system and method for capturing emitted vent gas(es) and directing,
as a diluted
stream, into the combustion air intake of an engine are described in United
States Patent,
9,046,062 B2, Dresser-Rand Company, 2015/06/02. Several sources from which
vent gas is sourced
are depicted in the drawings and description, the sources indicated are common
and not unique.
The foregoing vent gas release mitigation techniques are useful but there
still remains a
need to provide additional solutions to reduce the amount of greenhouse gases
normally emitted
to atmosphere as a byproduct of oil and gas production or other like
industries. Relative to existing
options the embodied new and innovative approach will provide users: 1) lower
capital outlay,
attractive ROI as savings in regulatory activities and emissions mitigation
credit programs are
realized. 2) simple and reliable arrangement of components common to industry.
3) a broad range
of operation. 4) directing vented gases into the fuel gas supply rather than
the air intake of an
engine will create no impact to engine stability or performance. 5) method and
apparatus is well-
suited to use at gas compression stations and other gas production facilities.
6) the ability of this
embodied apparatus to discharge into pressures higher than the vented gas
pressure without the
use of conventional pumps and compressors, is an innovative and desirable
feature.
The innovation in this invention lies with the multiple configuration and
application of one,
two or more gas to gas ejectors assembled into the apparatus with unique
internal geometries and
similar motive pressures, unique internal geometries and dissimilar motive
pressures, similar
internal geometries and similar motive pressures or similar internal
geometries and dissimilar
motive pressures and to discharge recovered vented gases at a useful pressure.
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SUMMARY OF THE INVENTION
The present invention is directed to a means and method to inlet zero to low
pressure
vented or exhausted gas volumes and discharge those volumes into the pressure
containment of a
higher pressure. To this end, greenhouse gases such as methane are recovered
and prevented
from escaping into the atmosphere.
The use of parts and components common to industry innovatively arranged and
configured to sequentially enable a parallel train of two or more gas to gas
ejectors of same or
differing flow volume capabilities will provide industry a vented gas
containment solution with a
large capacity variance that is readily retrofittable or will suitably
integrate with new equipment
packaging. This invention will prove the control and small quantity recovery
of vented gases where
the cost and configurability of a conventional vapor recovery compressor would
be considered
impractical due to high capital and operating costs.
A typical installation for this invention would be a gas compression unit or
station where
vented and fugitive gases are collected and accumulated by means current and
common to
industry such as seal pots, tanks and knock-out vessels and routed to the
suction port on two or
more gas to gas ejectors. Sources for vented gases could be reciprocating
compressor rod packings,
compressor cylinder distance pieces, actuators, valve positioners and other
instrumentation and
source components on and off the compressor skid.
High pressure motive gas would be supplied from an appropriate point in the
gas
compression or production process to ensure correct ratio of motive to suction
gas for effective
ejector operation. Motive gas pressure would be controlled by a pressure
regulating device and
connected to each individual ejector via an operated valve. These valves will
be opened
sequentially and corresponding ejectors activated as warranted by suction gas
pressure and system
design parameters. As the motive gas enters and passes through the ejector,
suction gas volumes
are drawn in, the ejector will then discharge the combined high pressure
motive gas and low
pressure suction gas into the desired point of containment such as natural gas
compressor inlet or
a utility fuel gas line. The innovative design of this invention will also
provide for use in applications
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where H2S or CO2 content in the vented gases may have previously made recovery
unpractical or
prohibitively expensive.
A method of sequentially activating and deactivating the ejectors allows for
variable flow
volumes. A flow control computer with programmable and configurable Al & DO
may be used to
manage control of motive gas activation solenoid valves, suction gas pressure
sensing and
metering, system alarms and communication. A simple control system might be
preferred; such as
an electric switch gage or electric pilot controller with milliamp input and
output triggering a
relayed actuator. Two or more ejectors would be sequentially activated as
initiated by suction
pressure ranges and required system throughput capacity. Ejectors will be of a
constant-area
subsonic configuration and engineered and arranged to function under variable
and unique design
conditions. Should unusual discharge conditions or hinderances occur, or a
sudden burst of suction
gas volumes larger that total system design capacity, the apparatus control
logic will detect a rise
in suction pressure and, at a specific value, open a valve and release suction
gas to atmosphere or
flare. Should vented gas volumes reduce to a point where negative gauge
pressure may be
realized, a recycle device is employed to provide a method of maintaining a
minimum suction
pressure by routing a portion of ejector discharge volumes back into device
suction port. A
pressure relief valve exhausting to atmosphere or flare is a last fail-safe
should suction pressures
reach a critical high value.
This invention would be more attractive than current market offerings of vent
gas
evacuation via electric drive vacuum pumps or compressors; lower operating
costs would be
expected as there are no rotating components such as electric motors or
positive displacement
compressors that require lubrication and life-cycle wear maintenance. Lower
capital costs would
be expected as there will be no requirement for A.C. motor electrical supply
to be installed.
Other attributes of this invention include provision for the safe operation
and control of
this apparatus in a multitude of gas compositions, site specific pressure and
volume conditions and
control scenarios. The ubiquitous limitation of variable volume capability
through a single ejector
will be eliminated by utilizing an arrangement of two or more ejectors
individually sized to
application and activated into duty as variable requirement demand and
programmed control
philosophies dictate. This innovative approach to capacity control allows
significant turn-up and
turn-down vent gas volume capture and throughput to containment recovery. By
activating
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additional ejectors in a parallel arrangement based on suction pressure value
measurement this
apparatus will successfully manage vent gas volume increases and decrease
while minimizing over-
pressure atmospheric releases and low volume recycle actions.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings:
FIG 1 is a representational schematic of the invention depicted in a
simplistic control
application where a single ejector is enabled and actuated by an external
means.
FIG 2 is a representational schematic of the invention depicted in a
simplistic control
application where two parallel ejectors are enabled by an external means and
actuated via an
analogue suction pressure input device that produces at least two discrete
output signals to
activate one or both injectors.
FIG 3 is a representational schematic of the invention depicted in a PLC
control application
where three parallel ejectors are enabled and actuated as programmed based on
suction pressure
input and designed activation of one, two or three ejectors.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIG: 1 a depiction of the method and apparatus
incorporating a single gas
to gas ejector is presented. A locally available motive gas is connected at
"Motive", motive gas first
flows through a downstream pressure sensing regulator where desired motive gas
pressure is
maintained. An optional flow measurement device 4a to measure motive gas flow
volumes for
calculation and reporting requirements. An actuated solenoid valve is
connected to a control
panel, an existing and expandable local control panel or one specific to
apparatus installation.
Control can be accomplished by PLC or process sensing switch gauges. Apparatus
is to be switched
on only when discharged gas volumes can be consumed at volume required to
enable gas to gas
ejector function; that is below ejector back pressure stall point. Apparatus
to be switched off by a
predetermined operations process value or at discharge pressure sensing point
10 high value.
When normally closed actuated valve 7a is opened motive gas is introduced into
gas to gas ejector.
As understood in conventional fixed-area gas to gas ejector operational
theory, motive (high
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pressure) gas flows into the ejector through the nozzle into the diffuser
creating an internal low
pressure are into witch inlet gas volumes, "Inlet" flow through a one-way low
pressure cracking
check valve into the ejector housing to combine with the motive gas and enter
the discharge
diffuser portion of the ejector. These combined gas volumes are now discharged
from the ejector
at an intermediate pressure determined by the downstream contained pressure
into which the
discharge volumes are introduced and the ejector geometry and backpressure
valve 6. Also install
at apparatus discharge is a check valve 1, an actuated normally closed
solenoid valve 7c which
serves the purpose of a redundant shut down, a pressure safety valve 11 and a
flow measurement
device 4b. Inlet gas flow volume would be calculated by the value at 4b and
subtracting the value
at measurement device 4a. A recycle valve 5 communicates discharge to inlet,
valve set point
would be application specific and prevent undesirable high vacuum at inlet
should inlet flows be
less than ejector design point(s). Pressure sensing devices, inlet 10b and
discharge 10a, can be
configured to provide additional apparatus control; connected in series with
solenoids 7a & 7b to
deactivate and isolate when abnormal operating points are determined. A
pressure cracking check
valve 2 will open inlet pressure volumes to safe low pressure disposal flare
or vent, a manual valve
9 allows bypass of entire apparatus.
Shown in FIG: 2 is the apparatus configured with to gas to gas ejectors in a
parallel
arrangement with the valves and regulators necessary to accomplish a
controlled variable flow
throughput by the activation of one or both of the ejectors. As depicted in
FIG: 2 motive gas
"Motive" flows into the apparatus when actuated normally closed valve 7a and
7c are opened. A
downstream pressure sensing regulator is used to set and maintain motive gas
pressure. A flow
measurement device is installed at 4a. Motive gas can now be lowered (if
desired) at regulator 3a
before entering ejector 8a. As motive gas flows through ejector 8a inlet gas
if flowed through a low
pressure cracking check valve 1, to the suction port of ejector 8a, combined
with the motive gas
volumes and discharged at an intermediate pressure through a flow measurement
device 4b, a one
way check valve 1, an solenoid actuated normally closed valve and a
backpressure regulating valve.
A pressure sensing point at inlet 10b and discharge 10a can be configured to
provide additional
apparatus control; connected in series with solenoids 7a & 7b to deactivate
and isolate when
abnormal operating points are determined. A pressure cracking check valve 2
will open inlet
pressure volumes to safe low pressure disposal flare or vent, a manual valve 9
allows bypass of
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entire apparatus. A recycle valve will add discharge gas into inlet and
maintain a minimum inlet
pressure avoiding undesirable high vacuum situations. A multi-point switch
gauge 12 provides a
discrete output to solenoid valve 7b and, based on a application specific
value at met pressure
sensing point 10b, will open valve 7b to activate ejector 8b. Depending on
design, ejector
geometry, motive pressure delta at ejectors 8a and 8b, additional throughput
capacity will be
added to the apparatus. This additional capacity will activate and deactivate
as determined by inlet
pressure, an increase in pressure may be caused by an expected venting event
or as vented gas
volumes increase when wear components such as rod packings and seal age. The
innovation in this
invention lies with the multiple configuration and application of one, two or
more gas to gas
ejectors assembled into the apparatus with unique internal geometries and
similar motive
pressures, unique internal geometries and dissimilar motive pressures, similar
internal geometries
and similar motive pressures or similar internal geometries and dissimilar
motive pressures.
Additionally, a pressure cracking check valve 2 will open inlet pressure
volumes to safe low
pressure disposal flare or vent, a manual valve 9 allows bypass of entire
apparatus. A pressure
safety valve 11 will protect the apparatus and associated process equipment
from over pressure.
Referring to FIG: 3, an arrangement of three gas to gas ejectors 8a, 8b and 8c
are
configured is a parallel arrangement. Vented gas volumes generated as a result
of a hydrocarbons
production process are inlet "Inlet" on a common header and individual low
pressure cracking
check valves 2 to the ejectors. Hi pressure motive "Motive" gas is admitted
through a flow
measurement device 4a, a downstream sensing pressure regulator 3 when, global
control,
normally closed, solenoid actuated valves 7a & 7d are opened. At
initialization, motive gas flows to
ejector 8a only, motive gas pressure to ejector 8a can be further regulated at
valve 3a. Inlet gas is
flowed into ejector 8a and discharged at an intermediate pressure combined
with motive gas
volumes through a check valve 2 the open control valve 7d and a flow
measurement device 4b.
Vent gas flow will be calculated by subtracting flow value at 4a from value at
4b. Pressure sensing
points at inlet 10a and discharge 10b are fed to a PLC 6, program will respond
to inlet pressure
increases by adding ejector throughput volume opening motive gas control valve
7b to enable
ejector 8b. should additional capacity be required to maintain inlet pressures
as vented gas
volumes increase, control valve 7c will be opened and ejector 8c enabled.
Should vented gas
volumes diminish and inlet pressure decline, valves will be closed and
ejectors 8c & 8b deactivated
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in sequence. Should vented gas volumes continue to diminish below the design
throughput
capacity of ejector 8a, recycle valve 5 will open and make up inlet volumes
with communicated
discharge gas. PLC will manage high discharge pressure by closing control
valves 7a & 7d and
opening control valve 9 to relieve system pressure; a pressure safety relief
valve 11 is also
incorporated to prevent over pressure occurrence. A pressure cracking check
valve 1 will open inlet
pressure volumes to safe low pressure disposal flare or vent, a manual valve
12 allows bypass of
entire apparatus. The innovation in this invention lies with the multiple
configuration and
application of one, two or more gas to gas ejectors assembled into the
apparatus with unique
internal geometries and similar motive pressures, unique internal geometries
and dissimilar motive
pressures, similar internal geometries and similar motive pressures or similar
internal geometries
and dissimilar motive pressures.
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