Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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COAL BED METHANE EXTRACTION AND CARBON CAPTURE
FIELD
[0001] This relates to a process that displaces and extracts methane
from a coal bed by
storing carbon dioxide delivered by compression such as from a pipeline such
as the Alberta
Carbon Trunk Line. The pipeline delivered carbon dioxide stream is injected
into coal beds for
sequestration and storage
BACKGROUND
[0002] The generation of electricity in North America and in most parts of
the world is
primarily provided by the combustion of coal, a cheap and abundant fossil
fuel. Coal is typically
mined and transported to a power plant where it is processed before
combustion. The coal is
combusted in a furnace to generate heat for the production of high pressure
dry steam. The
produced dry and superheated steam drives a steam turbine generator to produce
electricity.
Coal is a high carbon content fuel, therefore a large emitter of carbon
dioxide as well as NOx and
S0x, greenhouse gases (GHG). Rapidly increasing concentrations of GHG's in the
atmosphere
and emerging evidence of global warming is now triggering international action
to reduce
GHG's emissions into the atmosphere. The combustion of coal to generate
electricity is
identified as a main contributor of GHG emissions, resulting in industry
action being taken to
reduce GHG emissions from the use of coal combustion. Recently, the government
of Alberta
has mandated that coal usage for power generation be terminated by the year
2030.
[0003] Coal bed methane extraction provides an alternative method to
recover energy from
coal in a safe, efficient and environmentally acceptable manner. Coal bed
methane extraction is
typically employed in un-mineable coal beds. Conventional coal bed methane
recovery methods
are based on reservoir pressure reduction, where methane is desorbed from the
coal surface by
reducing the reservoir pressure.
[0004] In the current standard mode of coal bed methane extraction,
wells are drilled into a
coal bed. The methane is extracted by desorption from coal surfaces where the
reservoir
pressure is first decreased by dewatering. The decrease in pressure allows the
methane to desorb
from the coal and flow as a gas to the well. The gas is processed at surface
and compressed in a
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natural gas pipeline network for delivery to markets. More recently, to
enhance coal bed
methane extraction new methods have been developed. As described by U.S.
patent no.
5,085,274 (Puri et al.) entitled "Recovery of methane from solid carbonaceous
subterranean of
formations", U.S. patent no. 5,332,036 (Shirley et al.) entitled "Method of
recovery of natural
gases from underground coal formations" and U.S. patent no. 5,014,785 (Puri et
al.) entitled
"Methane production from carbonaceous subterranean formations", the use of
carbon dioxide
diluted with inert gases enhances coal bed methane recoveries by reducing the
partial pressure of
methane and injecting other gases such as nitrogen, resulted in a substantial
increment in
production.
SUMMARY
[0005]
There is provided a method and system for safely storing carbon dioxide, and
for
extracting stored methane and other volatile hydrocarbons in a coal bed. The
method injects
carbon dioxide into a coal bed in a condition to be sequestered and stored,
and to extract
stored methane in the coal bed. The conditions under which the carbon dioxide
is injected
will depend on one or more of: coal bed depth relative to pressure and methane
extraction
relative to temperature. The extracted methane and other volatile hydrocarbons
may then be
recovered, processed and routed to natural gas pipeline distribution systems.
[0006] As
coal has a stronger affinity for carbon dioxide, it establishes an
adsorption/desorption process where carbon dioxide displaces and frees the
methane from the
coal bed to be recovered, processed and distributed to natural gas pipeline
distribution systems.
The objective of the method and system is to permit carbon dioxide to be
sequestered and stored.
In one example, the proposed Alberta Carbon Trunk Pipeline may be used to
transport carbon
dioxide recovered due to local carbon-generating activities. The carbon
dioxide may then be
injected into coal beds to establish an adsorption/desorption process where
carbon dioxide is
stored in the coal bed by displacing methane and other volatile hydrocarbons,
which may then be
recovered and processed, such as for pipeline transport and distribution.
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[0007] In one example, carbon dioxide recovered and delivered by
pipeline is injected at
desired pressure and temperature conditions into a coal bed for carbon dioxide
adsorption and
methane desorption, such that carbon dioxide is stored, and methane is
extracted from the coal
bed.
[0008] In one aspect, the process comprises the following steps:
(a) injecting carbon dioxide at optimum pressure and temperature for
adsorption into a coal
bed;
(b) displacing and producing methane by desorption of stored methane and other
volatile
hydrocarbons at optimum pressure and temperature in the coal bed; and
(c) processing the coal bed extracted hydrocarbon gas.
[0009] The above described process may be used to store carbon dioxide
and extract stored
methane in a coal bed. The extracted methane is processed and distributed as a
fossil fuel
derived from coal. The process stores carbon dioxide and extracts stored
methane in coal beds,
thus contributing to the production of clean abundant energy from a very
concentrated carbon
fuel. The process is considered to be clean since coal can store two or more
moles of carbon
dioxide for every mole of methane displaced. Coal can store up to 10 moles of
carbon dioxide
per mole of methane stored in coal, thus making it a carbon negative process.
[0010] As will hereinafter be further described, carbon dioxide is first
delivered by a
pipeline, such as the Alberta Carbon Trunk Line, and injected for adsorption
into a coal bed for
storage and desorption of stored methane from the coal bed. The desorbed and
extracted coal
bed methane may then be processed for distribution. The process may be used to
safely store
carbon dioxide in a coal bed by adsorption and also, by desorption, extract
and process the coal
bed hydrocarbons for distribution as a result of the carbon dioxide being
injected.
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BRIEF DESCRIPTION OF THE DRAWING
[0011] These and other features will become more apparent from the
following description
in which reference is made to the appended drawing, the drawing is for the
purpose of illustration
only and is not intended to in any way limit the scope of the invention to the
particular
embodiment or embodiments shown, wherein:
FIG. 1 is a schematic diagram of a pipeline delivered carbon dioxide stream
injected into
a coal bed for storage by adsorption and methane extraction by desorption. It
includes a
gas processing unit to treat the extracted coal bed hydrocarbons for
distribution.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0012] The method described may be used to safely store carbon dioxide
that is produced,
recovered and transported by pipeline in such as may occur in a carbon capture
process by
adsorbing carbon dioxide into a coal bed. It will be understood that a coal
bed may also be
referred to as a coal seam, or other deposit of coal that is accessible from
surface, such as by a
well drilled from surface. Furthermore, the hydrocarbons that may be produced
form a coal bed
are referred to herein as methane or coal bed methane, although the methane
may also include a
relatively small proportion of other, heavier hydrocarbons or other gases as
is known in the art
with respect to coalbed methane gas. In addition, the source of carbon dioxide
is preferably a
source of captured carbon dioxide, such as may be obtained from a power plant
or other
industrial activity. As it is primarily carbon dioxide that adsorbs to the
coal and causes the
methane to desorb, the source of carbon dioxide is preferably at least 90%
carbon dioxide gas,
and preferably more, such as 95% or more. The actual composition of the source
of carbon
dioxide gas may vary depending on the source and any applicable regulations,
but may also
include other gases, such as oxygen, nitrogen, nitrogen-based gases, other
carbon-based gases,
etc.
[0013] Coal can store two or more moles of carbon dioxide per mole of
methane stored in
coal. When carbon dioxide is adsorbed in coal, the methane stored in coal is
desorbed and freed
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to be extracted and processed. The disclosed method provides an alternative
solution to safely
store carbon dioxide. For example, the Alberta Carbon Trunk Line to be
commissioned in 2017
was built to collect and transport carbon dioxide produced in Alberta at major
industrial sites for
storage in deep saline aquifers and/or for use in EOR (enhanced oil recovery)
operations. The
5 proposed method offers a different approach in a unique and innovative
variant to store carbon
dioxide that may become available from resources such as the Alberta Carbon
Trunk Line and
other sources of carbon dioxide. The system here described takes advantage of
safely storing
carbon dioxide in coal beds by an adsorption/desorption process that also
produces methane
stored in the same coal beds.
[0014] In 2016, Shell Canada commissioned Quest, a carbon capture and
storage process
where the carbon dioxide captured from its oil upgrading and refinery
processes is compressed
and stored in underground caverns. The Alberta Carbon Trunk Line is under
construction and
due to be commissioned in 2017. The objective of this line is to transport and
distribute
recovered carbon dioxide from Alberta facilities to store in deep saline
aquifers and/or EOR
(Enhanced Oil Recovery) at oil wells. The use of carbon dioxide to enhance oil
production is
well documented and in operation since 2000 with success at Estevan,
Saskatchewan. However,
the use of carbon dioxide in EOR results in the continuous recycling and
recompression of
carbon dioxide into the oil formation. Historical records at Estevan showed
that only 30 to 40%
of the carbon dioxide injected is stored under pressure in the oil reservoir,
requiring a continuous
recycling compression step.
[0015] Coal beds have an affinity to absorb carbon dioxide and hence are
an ideal storage
resource. Furthermore, the injection of carbon dioxide into a coal bed can be
used to establish an
adsorption/desorption process that frees the methane and other volatile
hydrocarbons stored in
coal to be recovered, processed and distributed.
[0016] The method described herein provides a process that uses carbon
dioxide that may
be produced, recovered and transported for storage in coal fields and to
extract stored methane
and other volatile hydrocarbons from the coal beds. Carbon dioxide recovered
from industrial
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activities and transported by, for example a pipeline such as the Alberta
Carbon Trunk Line, may
be injected into coal beds to enhance coal bed methane extraction while
storing the carbon
dioxide, unlike the pipeline proposed practice of compressing it into saline
aquifers or oil wells.
Coal bed methane extraction works by replacing sorbed methane molecules with
more
strongly sorbed carbon dioxide molecules. The process is beneficial as coal
selectivity of
carbon dioxide to methane is greater than 2 to 1, coal adsorbs and stores 2
molecules or more
of carbon dioxide for every molecule of methane displaced, and the carbon
dioxide remains
adsorbed in the coal and displaces the methane. The extracted methane may then
be captured,
processed and routed to natural gas pipeline distribution systems. The
proposed method meets
a need to first store carbon dioxide safely and secondly to recover coal
stored methane gas and
volatile hydrocarbons from a coal bed economically.
[0017] The present method provides an alternative to store large volumes
of recovered
carbon dioxide safely, such as may be delivered by Alberta Carbon Trunk Line
or other sources
of carbon dioxide, and simultaneously extract methane from the coal beds for
distribution. The
description of application of the method herein should, therefore, be
considered as an example.
[0018] FIG. 1 depicts a preferred method of storing carbon dioxide
produced, recovered
and transported by a resource such as the Alberta Carbon Trunk Line from
industrial plants in
Alberta.
[0019] Carbon dioxide is transported and distributed by Alberta Carbon
Trunk Line through
stream 1 into a coal bed site and further compressed by compressor 2 to meet
optimum pressure
conditions. The pressurized carbon dioxide stream 3 flows through a fin fan
heat exchanger 4 to
meet coal bed optimum temperature conditions for adsorption of carbon dioxide
and desorption
of methane stored in coal bed. The pressure and temperature controlled carbon
dioxide stream 5
is injected into well 6 and distributed through slots 7 into the coal bed 8.
The injected pressure
and temperature controlled carbon dioxide stream is adsorbed in coal bed 8 and
the &sorbed
methane and other volatile hydrocarbon gases are displaced across the coal bed
8 and through
slots 9 into production well 10. The extracted methane is routed through
production well 10 and
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through stream 11 into gas processing unit 12. The processed gas exits gas
processing unit 12
through stream 13 to gas pipeline for distribution.
[0020] As noted, prior to injecting the carbon dioxide into the coal bed
8, it is conditioned
through compression and temperature control. This is preferably done to
achieve an optimal
amount of carbon dioxide adsorption, which will in turn enhance methane
production. The
optimal temperature and pressure conditions may be selected by analysing the
coal formation, or
through experimentation. Optimization may also include an analysis of the
energy required to
condition the carbon dioxide and any effect the compression and temperature
control has on
downstream transport or processing.
[0021] In one example, the process may be implemented by: first, storing
carbon dioxide
delivered from the Alberta Carbon Trunk Line by adsorption in a coal bed;
second, desorbing
and extracting stored methane from the coal bed; and third, processing and
distributing the
extracted coal bed methane. This process allows an efficient use of an
abundant supply of
recovered carbon dioxide for safe storage and simultaneous extraction of
stored methane from
the coal bed by establishing an adsorption/desorption process where carbon
dioxide displaces
and frees methane stored in a coal bed to flow into a production well. This
process provides for
coal beds to be a safe storage resource for carbon dioxide and to recover a
clean source of energy
from coal in the form of methane.
[0022] In this patent document, the word "comprising" is used in its non-
limiting sense to
mean that items following the word are included, but items not specifically
mentioned are not
excluded. A reference to an element by the indefinite article "a" does not
exclude the possibility
that more than one of the element is present, unless the context clearly
requires that there be one
and only one of the elements.
[0023] The scope of the claims should not be limited by the preferred
embodiments set forth
in the examples, but should be given a broad purposive interpretation
consistent with the
description as a whole.
