Note: Descriptions are shown in the official language in which they were submitted.
CA 02325966 2000-11-14
1
Patent
Method for "I'reating Vented or Fugitive Methane Streams
Field of the Invention
A device for conversion of a vented, or fugitive, methane stream, to produce a
vent
stream with a lower greenhouse gas emission factor. The method is intended for
use in
oil and gas operations, as an alternative to raw gas venting , flaring or
incineration.
Streams treated would consist of methane or methane air mixtures from well
vents, field
battery facilities, compressor station vents or process buildings. The
invention allows the
conversion of highly variable, low volume, and/or dilute hydrocarbon
containing streams,
by converting the bulk of the methane or other hydrocarbons in the stream into
carbon
dioxide and water. These streams are often at very low pressure, approaching
atmospheric pressure, although some streams may be at higher pressures.
Background of the Invention
In almost all areas where hydrocarbons are produced or used, highly variable
and/or
dilute methane gas streams are often produced, along with natural ~,7as, oil,
or other
hydrocarbons, in volumes which are often too small to make economic
conservation or
use of the gas possible with current technology. In these situations the gas
is vented
contributing to the build-up of methane in the atmosphere. These vent
emissions alone
(according to Statistics Canada in 1997) contribute 7.8% (53 Mt/yr CO,(eq)) of
the total
greenhouse gas emissions in Canada, and 30-50% of Canadian oil and gas
industry
greenhouse gas emissions from production and transportation of hydrocarbons.
In some
cases these vent streams also carry trace aromatic hydrocarbon compounds that
lead to
odour and chronic health complaints from residents in the areas surrounding
production
facilities.
Converting the methane, and any co-produced aromatics or hydrocarbons, to
carbon
dioxide, and water vapour through combustion has the effect of eliminating
odours and
converting the methane to carbon dioxide, resulting in a seven-fold reduction
in tonnes of
C02(eq) emissions, based on:
CH4 + 20, ---> CO2 + 2H,0 + energy (stoichiometric basis)
16 tonnes + 64 tonnes ---> 44 tonnes + 36 tonnes (approximate mass basis)
336 tCOZeq ---> 44 tCO2 (greenhouse gas basis)
Greenhouse Gas Reduction Factor = 7.64 or 18 tonnes of C02(eq) reduction per
tonne of methane converted '
The problem to be solved is to safely, effectively and economically complete
this
conversion in any typical venting location and application. The preferred
solution should
be relatively low cost, reliable in operation, safe, efficient, effective by
not generating
significant amounts of other greenhouse gas species (such as NO or NOX), and
not cause
CA 02325966 2000-11-14
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concerns for residents neighbouring the producing lease. It must also be
technologically
simple, as many venting sites do not have much in the way of monitoring,
control or
utilities systems. From an operational/design point of view the major
challenges are:
I) Gas flow rates are highly variable and unpredictable over hourlv, daily,
monthly and
annual timeframes. Gas rates are generally proportional to facility through-
put, however,
there are many other factors which can impact the rate of venting from any
individual
source at any time, such as use of part of the vented stream to meet on site
fuel needs.
2) The vast majority of venting sites often have no outside power supply,
communications or control facilities and are only monitored on an as required
basis.
This in turn requires that any new on-site equipment be easy to operate
unattended and be
a technology with which the site operators are already more or less familiar.
3) The solution must not cause any, or very limited, potential impact on
people, crops,
animals or the local environment, so must operate without noise, odour,
potential to harm
people or animals, or visible emissions at night.
4) In temperate or arctic latitudes it must operate in winter conditions, with
temperatures occasionally lower than -40 degrees C, and in areas sometimes
exposed to
high winds, rain and snow.
5) Ideally the operation should be able to be monitored in a simple fashion to
ensure it
is operating and periodically checked to ensure proper operation.
6) The system should be modular to allow easy movement of smaller components
between sites so installed capacity can be matched to the volume of vent gas
available to
minimize capital investment, and should be easy for one or two people to move
between
sites with only a few hours of effort.
7) Wherever possible there should be some method of utilizing the energy
generated by
the conversion process to produce some tangible or intangible benefit, which
will help to
provide an economic incentive for installing environmental impact mitigation
equipment.
Current methods of converting vented hydrocarbons to COz are limited to flare
systems,
blast tube type burners or incinerators. As these systems all operate at high
temperatures,
with open flames, they cannot be located too close to facilities and,
therefore, require
larger facility leases and often have a negative environmental impact on a net
or life
cycle basis. Flare type systems are expensive to build, and difficult to
design to handle
highly variable gas flow rates, resulting in either incomplete combustion,
formation of
intermediate oxidation products, or nitrogen oxides which have higher CO,(eq)
values
than methane and may, even in low concentrations, lead to a significant loss
in
greenhouse gas Reduction Factor. Open flames pose a hazard for animals, if
they are
close to the ground, burners or fuel supply lines can be subject to freezing,
are difficult to
maintain in operation in high winds or low gas flows, and often are noisy and
produce
visible emissions (light and potentially smoke) which can disturb neighbours.
Finally,
flares and other combustion options cannot be used for dilute vent streams
where the
hydrocarbon is mixed with even moderate amounts of air which might move the
combustion out of it's flammability range.
CA 02325966 2000-11-14
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Summary of the Invention
The purpose of the invention is to provide an alternative to flaring or
venting of
concentrated or dilute methane streams. The invention utilizes multiple, low
cost or even
recycled, thennal catalytic units to convert varying amounts of inethane, or
other vented
hydrocarbons, into carbon dioxide with the result being to lower the net
greenhouse gas
emissions from a given site. The first unit at each location would have an
electric
preheat element, or an alternate heating source, such as waste heat from an
engine or
fired heater. This first section serves as the pilot for other, simpler units
that are catalytic
converter pads with simple gas distributors and controls. Simple spring loaded
ball-
check valves, arranged in a series configuration, would be used to
automatically turn
units on sequentially as vented gas volumes increase, and shut sections down
as volumes
decrease. Based on need, sections can be easily removed or added. The energy
generated would be transferred to air flowing through radiantly heated
conduits in each
converter section or, alternatively to various streams or devices that can
effectively
utilize the heat produced by the conversion for some further benefit.
A general diagram (Figure 1) is provided of the preferred lavout based on one
application, consisting of converting methane from a conventional heavy oil
well casing
gas vent, where there is no opportunity to recover the energy generated.
Supplemental
diagrams illustrate how the basic unit can be adapted to heat various streams
which
might be found in some typical oil and gas facilities and which would generate
additional
benefits.
The proposed invention uses thermal catalytic converters to transform the
vented
hydrocarbons into carbon dioxide, and at the same time will eliminate odour
causing
components. Catalytic converters are unique for this in that reaction
temperatures are too
low to produce nitrogen oxides, there is no open flame, no noise, or other
visible
emissions at anytime. The produced energy is dissipated by thermal infrared
radiation
with no open flame. The specific apparatus proposed overcomes the major
challenges
indicated in the description of the background, specifically:
1) Individual sections come into use automatically as fuel becomes available
and
shutdown when they are not required so that those in operation are operating
effectively.
Units can be stacked vertically or horizontally depending on the configuration
and the
numbers of units changed without changing the basic installation.
2) Units are easy to start and will maintain themselves in operation without
operator
intervention. They require no outside fuel, or power, except during a 15
minute warm-up
on initial start up, that can be provided from a 12 volt supply such as the
battery on an
operators vehicle, or other portable power source. Similar technology is in
use
extensively for providing building heat in oil and gas facilities so most
operators are
familiar with the basic operation of catalytic heaters. Where a high
temperature waste
heat source is available this can also serve as the source of the initial
energy required to
preheat, or maintain, the temperature of the catalytic converter pad to
sustain the
reaction.
3) The converters will be housed and only put out invisible infrared thermal
radiation or
hot air. The outside of the units will not be hot enough to harm animals. The
units
CA 02325966 2000-11-14
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operate silently and destroy odour-causing components in the gas. As thermal
catalytic
converters operate at temperatures below the ignition point of a methane/air
mixture they
can be located beside right beside wellheads or beside existing facilities
without
requiring any increase in lease size to accommodate them.
4) The units can be housed in simple insulated boxes, or similar housings, to
shelter
them from high winds and generate their own heat to protect against cold
temperatures.
5) Operation can be monitored with simple, bi-metallic or thermo-chemical,
temperature indicators or pressure gauges on each section. Which will allow
operators to
determine if there is an opportunity to relocate a section or if additional
converter
sections are needed. Periodic checks can be made of flue gas from the heaters
to ensure
that combustion is occurring in an efficient manner and, low cost, portable
data loggers
might be used to monitor changes in operation over time.
6) Individual converter sections will be small and light weight. They can be
designed as
independent units to allow ease of relocation between sites and could be small
enough to
fit in a truck or van.
7) In the device proposed the conversion units can be easily configured to
provide
energy for heating various streams at facilities to generate positive
economics and other
tangible or intangible benefits. Some of these uses might consist of: a)
heating well
production to assist in separation; b) provide heat to winterize lease piping;
c) provide a
heat source for a refridgeration unit to recover hydrocarbon or other liquids
which can be
condensed from a vapour stream; d) heat water or other materials being
injected into a
formation to increase oil or gas production; e) provide building heat; f)
provide power
for other devices through use of thermophotovoltaic systems or Sterling
engines which
convert radiant energy or heat into power; g) heat or other utilities for
nearby
agricultural or industrial operations; h) fuel conditioning to eliminate
liquids from rich
or wet fuel gas streams feeding engines or flare stacks; i) other applications
where there
is some benefit of utilizing locally generated heat without the cost of
purchasing fuel.
In summary the current invention will take advantage of the many positive
characteristics
of thermal catalytic systems and provide a flexible, reliable and advantageous
method of
reducing greenhouse gas emissions, from highly variable vent hydrocarbon
sources and
potentially providing additional benefits where there is opportunity to make
use of the
waste heat generated in the conversion process.
Description of the Drawings
Figure 1 shows the basic equipment configuration to turn a highly variable
methane
casing vent stream, from a conventional heavy oil well, into a product stream
consisting
of carbon dioxide, water and energy, resulting in a reduction of greenhouse
gas emissions
by 80-85%. The unit will produce hot air which could be utilized to provide
building
heat, keep wellhead components warm, or provide heat for some other purpose
near the
wellhead. The unit consists of a primary catalytic pad that is preheated by an
external
energy source until it reaches reaction temperature. The primary pad, which
may be
similar to a conventional catalytic heater pad, provides preheat energy to the
first
CA 02325966 2000-11-14
secondary pad and surplus energry is transferred to the intervening air
spaces. 'I'he first
secondary pad generates heat, which preheats the second secondary pad, etc.
until all
vented gas is being consumed.
Figure 2 shows details of converter control for a single secondary pad design.
Figure 3 shows details for preheat grid for secondary catalytic pads. Unlike
conventional
catalytic heater panels the fuel pan is designed, by varying the materials
selection and
energy absorption characteristics, to increase its ability to absorb the
infrared energry
emitted by the previous pad. This energy serves to continuously preheat the
vent gas, and
the secondary catalytic pad, to a temperature greater then the activation
temperature for
the catalytic oxidation reaction which takes place in the catalyst bed.
Figure 4 shows details for a tertiary converter on the outlet duct from the
converter
sections, which may be used to further reduce any hydrocarbons slippage from
the
primary and/or secondary catalytic pads. This pad is maintained above the
activation
temperature by the hot air and combustion gases flowing through it, as well as
any energy
released by oxidation of any methane which might have been left unreacted in
the main
pad.
Figure 5 shows detail of proposed method of modularizing the converter to
allow for
capacity adjustment over time to minimize capital investment. This diagram is
generic
for systems which may use either, an electric preheat element, or a waste heat
source to
start the primary unit.
Figure 6 shows detail of proposed method of installing modular units on a
waste heat
source, such as an exhaust stack from a compressor or fired heater. The
drawing shows
the secondary catalytic modules arranged so that waste heat from the stack
provides the
required activation energy which is normally provided by a primary catalytic
converter.
Detail "A" show details of a typical secondary converter module.
Figure 7 shows the equipment modified to utilize the energy generated to heat
another
process stream in the facility. This stream could be wet vent gas, produced
heavy oil,
produced water for reinjection, a refridgerant for use in a cooling system, a
wet
hydrocarbon stream going to a flare stack, engine or power generator, or an
evaporator to
vapourize liquids separated from a wet hydrocarbons stream.
Figure 8 shows the equipment modified to generate power by utilizing the
infrared energy
produced by the catalytic pads, or temperature differences, to provide energy
to a thenno-
photovoltaic power generator or some other system, which can generate
electrical or
mechanical energy.
Figure 9 shows a possible arrangement for recovery of hydrocarbon liquids from
a tank
vent, through use of a refridgeration system. The tank vapours are cooled in a
cold box,
with any condensed liquids returned to the tank or other storage. The
uncondensed
methane and other light hydrocarbons in the vent stream, provide fuel for the
catalytic
converters to drive the refridgeration system. Heating coils for the
refridgerant can be
arranged in the various units such that the cooling effect produced will
automatically
vary with the volume of gas being vented.
CA 02325966 2000-11-14
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Figure 10 shows a possible arrangement for evaporating liquids from a wet fuel
or flare
stream and preheating the remaining vapour stream. At low flare rates, where
flow is too
low for proper combustion in the flare stack, the catalytic converters
efficiently oxidize
the waste hydrocarbon stream, while keeping liquid from building up in the
separator
which might carry over to the flare stack. At high flare rates, little
condensation would
occur in the flare line, and the main waste gas stream will be converted at
the flare tip.
In the case of a fuel system for an engine or power generator utilizing waste
gas, the
heaters will ensure that the engine or generator does not see slugs of liquid
in the fuel,
while converting surplus waste gas that cannot be utilized in the engine or
generator.
Disposal of liquids from a fuel gas separator is very costly in cold or remote
areas, so
keeping the liquid in vapour form is preferred.
Figure 11 shows a possible arrangement for collecting and converting methane
released
from multiple fugitive sources in a building. Figure l la shows a method of
installing
baffles in a building containing fugitive methane gas leaks, such that the
leaking. lighter
than air, gases are preferentially directed to the very top of the building,
while the bulk
air movement is not hindered. The lighter, methane enriched, air stream is
then directed
to thermal catalytic converter units on compressor exhaust stacks or other
sources of
waste heat which are hot enough to achieve activation for the hydrocarbon gas
and
catalyst. Figure 11b shows detail of the catalytic unit arranged on the stack.
Air is drawn
into the unit from the top of the building by the chimney effect caused by the
air being
heated in the converter, either from the waste stack energy or by hydrocarbon
reacting in
the unit and giving off energy. The methane contaminated air moves through
sections of
the unit where the air is heated enough for the methane contained in it to
react. This
could be supplemented by feeding more concentrated waste gas vent streams into
the
bottom of the same unit to further enrich the stream and generate additional
energy.
Figure 12 shows a possible arrangement for converting hydrocarbons released
from a
tank vent. In this case the vent stream will be higher in hydrocarbon content
but too low
in pressure to feed a fuel supply system as proposed in Figure 1. In this case
the chimney
effect will draw both the vent gas from the tank and ambient air into the unit
where they
can both be heated and reacted to convert the hydrocarbon.
Description of the Preferred Embodiment
There are a number of prefer-red embodiments depending on the venting streams
and
waste heat sources available in a given installation. The Figures provided
highlight a
number of the key applications related to the upstream oil and gas industry.
The
preferred applications are those that tend to have the widest application to
venting
sources.
The embodiment shown in Figure 1 can be used to convert any concentrated
methane
vent stream to- reduce GHG emissions, without requiring installation of a
flare system.
The typical use shown is for convei-ting methane venting from conventional
heavy oil
well casings. Other streams could be leakage from compressor seals, gas
vented.from
gas operated pumps or control valves, or other sources which are too small to
collect and
flare. Some of these streams may be large enough that conventional means may
be used
to economically reduce their volume, however, any such system will have limits
on how
CA 02325966 2000-11-14
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much gas can be utilized, so there will almost always be a highly variable
surplus which
must be vented to allow continued oil production. Typically these gas streams
are 95-
98% methane but the gas is vented at a pressures often less than 1 psig
pressure and in
volumes that may range on an hourly, daily, weekly or monthly basis from 0 to
several
hundred cubic meters a day of gas. The well sites are usually only briefly
visited by
operators and are equipped with minimal facilities. In this situation the
converter shown
in Figure I can be installed to inexpensively convert the vented methane to
C02. As the
volume being vented changes individual sections of the converter will start up
and
shutdown with only the first unit requiring either an operator, a simple
automatic restart
control utilizing a small local power source, or a waste heat source to
restart if the vent
gas supply drops too low to sustain operation of the primary unit. The energy
produced is
vented as hot air. As vent gas volumes increase the simple spring loaded
valves will
open to feed gas into additional converter sections, which will be preheated
by units
closer to the primary converter. The invention is modular so that additional
converter
sections can be easily added if there is a long-term increase in vented gas
volumes and
removed if there is a long-term decrease. Reductions in GHG emissions achieved
can be
utilized for realizing GHG trading credits and produce an economic benefit.
This same
configuration can be applied to converting other concentrated vent gas streams
such as:
gas from hydrocarbon gas compressor seals, gas from instrumentation or
metering pumps
utilizing pressurized natural gas as the energy source, vents from liquid
hydrocarbon
storage tanks, or other possible sources. These systems could be located
inside buildings,
which require heating, and. reduce the need for use of other pressurized fuel
for heating.
A typical case would be vents from compressor seals where the compressors are
housed
and the seal normally vents small amounts of methane into the building, this
gas could be
fed to a converter near the compressor to provide building heat. Monitoring
temperatures
in various sections of a converter, or the pressure in the gas supply streams,
can be
utilized to calculate how much energy is being produced and, from this, how
much
hydrocarbon is being converted into less intensive GHGs.
The second preferred embodiment is shown in Figure 7. In this case the
invention makes
use of the energy produced by conversion, to heat some process stream for the
facility in
which the venting is occurring. All that is required is to add piping into the
spaces
between the converter sections so that some of the energy produced can be
transferred to
the process stream contained in t-he~ pipe or channel rather than to the air.
The converters
would be designed such that there would still be sufficient radiant energy
transferred to
subsequent converter panels to allow them to begin operating if vent volumes
increase.
As can be seen from other figures this energy might be used for small
refridgeration units
to help condense and recover heavier hydrocarbons from vent streams which are
rich in
more valuable components, or to condense water vapour in water rich streams
such as
those venting from glycol dehydration units; streams could be heated to
prevent freezing;
streams could be heated to avoid the formation of liquids which might hinder
operation
of combustion systems; or such other applications which are commonly found in
hydrocarbon processing operations. In all cases these applications would
displace other
fuels, or energy sources, which would otherwise have to be consumed to achieve
the
desired operation, thus generating energy savings and a significant increase
in the
economic return from a converter installation.
CA 02325966 2000-11-14
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"I'he third preferred embodiment is for the conversion of fugitive hydrocarbon
emission
streams that are not localized enough to be collected by normal ineans. These
sources
might be leaking flanges or fittings in gas piping, small vents from sampling
points or
pressure gauges, which are commonly found in oil and gas operations. In
situations
where this equipment is contained in a building, a configuration such as is
shown in
Figure 11 could be used to generally collect these small emissions into a
methane
enriched stream which can then be directed to converters mounted on waste heat
sources,
such as compressor engine/turbine exhaust stacks. The waste heat maintains the
catalyst
beds at a temperature sufficient for any methane present to be converted to
carbon
dioxide with the heat released by the reaction also assisting in maintaining
the bed
temperature. The air/methane flow to each converter section would be
maintained at a
rate such that the waste heat source can maintain the catalyst bed above the
minimum
reaction temperature, under normal operating conditions, so that any methane
or other
light hydrocarbons present can be converted. This process could be combined
with a
thermal catalytic converter utilizing a more concentrated stream, with the
building
exhaust stream simply serving as combustion air, with any methane in the
building
exhaust serving as a small increment of fuel. This might be a solution for a
typical
compressor site where the seal leakage methane can provide heat to maintain
the
temperature of a secondary bed used to reduce the methane emissions from
fugitive
sources in the compressor building, with the compressor exhaust heat used to
initiate the
catalytic reactions in the primary unit. Monitoring of the temperature
increase across a
bed treating a dilute methane/air stream may also provide an indication of the
concentration of hydrocarbon which can be used to initiate and direct
maintenance
activity to reduce the fugitive emission at it's source.
New or Unique Features Claimed
Main unique features claimed are:
1) An apparatus, which will convert a highly variable flow, but concentrated,
vented
hydrocarbon stream to products with lower GHG emissions at a low cost and
minimal control.
2) An apparatus, in which the catalytic reaction in a primary unit is
initiated by
energy from a waste heat source.
3) An apparatus, where the waste heat generated by an environmental catalytic
converter is utilized to heat another process stream or to provide heating for
a
building or enclosure.
4) An apparatus, which will convert fugitive emissions, with a highly variable
and
dilute concentration of hydrocarbon vapours, contained in a process or
building
air exhaust stream, to products with lower GHG emissions.
5) An apparatus, as described in 4) which utilizes waste heat from other
sources to
initiate and maintain the catalytic conversion reaction.
CA 02325966 2000-11-14
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6) A method utilizing changing of conditions across the apparatus claimed in
1), 2)
or 3) to provide an indication of the volume of vent hydrocarbon being emitted
and converted.
7) A method utilizing a change of conditions across the apparatus claimed in
4) or 5)
to provide an indication of the volume of fugitive hydrocarbon being emitted
and
providing an indication of the emission source.
Results of Testing
It is well known that catalytic heaters convert methane to carbon dioxide,
water and heat
energy. The primary focus of testing, to demonstrate this invention, is to
demonstrate
that units can be sequentially started so that they can operate with highly
variable source
streams, with individual converters starting and stopping sequentially as the
vent gas
supply varies. Tests are planned for late 2000 or early 2001 and one on a
prototype unit.
Prototypes for specific applications will then be constructed and tested in
the field in
various operating conditions.
