Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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IN-BOREHOLE GAS MONITOR APPARATUS AND METHOD
COMPRISING A VOC CONCENTRATION ANALYSER AND A VOC COLLECTOR
Field of the Invention
The present invention relates to in-borehole gas monitor
(IGM) apparatus and methods.
Background to the Invention
The monitoring of gas concentrations, and in particular
methane and carbon dioxide, generated by landfill and
associated sites is becoming a more common legislative
requirement due to the potential problems these gases
pose, such as the risk of explosion and impacts as
greenhouse gases. At present, the majority of landfill
gas analysis is achieved either through spot sampling or
through the use of large expensive fixed position
monitoring stations. More recently it has been recognised
that gas production and migration responds to
environmental factors such as barometric pressure and
groundwater movement, with the accompanying realisation
that spot sampling will often miss such changes.
It is known from WO 2007/141512 to provide a self-
contained IGM apparatus comprising a detector for
measuring a gas variable, and a controller configured to
automatically periodically use the detector to measure a
gas variable.
However, the apparatus and method disclosed in WO
2007/141512 do not deal with volatile organic compounds
(VOC5).
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It is an aim of preferred embodiments of the present
invention to address, overcome or obviate a disadvantage
of the prior art, whether such prior art or disadvantage
is referred to herein or otherwise.
Summary of the Invention
According to the present invention in a first aspect,
there is provided an in-borehole gas monitor (IGM)
apparatus comprising a VOC concentration analyser and a
VOC collector.
Suitably, the VOC concentration analyser is configured to
provide a non-specific real-time concentration of VOCs.
Suitably, the VOC concentration analyser comprises a
photo-ionisation detector.
Suitably, the VOC collector is configured to provide a
specific concentration by volume. Suitably, the VOC
collector comprises a sorbent material.
Suitably, the apparatus further comprises a pressure
sensor configured to measure atmospheric pressure.
Suitably, the apparatus further comprises a clock.
Suitably, the apparatus comprises a pump for pumping gas
past the VOC concentration analyser and the VOC collector
in a downstream direction and the apparatus is configured
whereby the VOC concentration analyser determines a VOC
concentration at a predetermined time by the pump pumping
borehole gas past the VOC concentration analyser and the
VOC collector for a pumping period. Suitably, the
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apparatus is configured whereby the pumping period, a time
of measurement and an atmospheric pressure at the time of
measurement are recorded.
Suitably, the apparatus comprises a pump for pumping gas
past the VOC concentration analyser and the VOC collector
in a downstream direction and a filter for removing any of
particulates or moisture from a gas input, wherein the VOC
concentration analyser and the VOC collector are upstream
of the filter.
Suitably, the apparatus comprises a pump for pumping gas
past the VOC concentration analyser and the VOC collector
in a downstream direction and there is a gas flow path
comprising a gas input, a first valve upstream of the pump
and a pressure sensor, wherein the apparatus is configured
whereby with the first valve closed the pump is activated
for a predetermined period and if within the predetermined
period a predetermined pressure is not exceeded, as
measured by the pressure sensor, a pump fail signal is
generated. Suitably, the predetermined period is between
8 and 12 seconds and the predetermined pressure is 100mb.
Suitably, the apparatus comprises a pump for pumping gas
past the VOC concentration analyser and the VOC collector
in a downstream direction and there is a gas flow path
comprising a gas input, a first valve upstream of the
pump, a pressure sensor and a filter, wherein the
apparatus is configured whereby with the first valve open
a first pressure sensor reading is taken, the pump is
activated for a predetermined period after which a second
pressure sensor reading is taken, and if the magnitude of
the difference between the first pressure sensor reading
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and the second pressure sensor reading is greater than a
predetermined value, a filter fail signal is generated.
Suitably, the predetermined period is between 2 seconds
and 6 seconds. Suitably, the predetermined value is
250mb.
Suitably, the time of sensing and the length of time for
which the pump operates are recorded
Suitably the apparatus comprises a second valve downstream
of the first valve and a gas outlet.
Suitably, the apparatus is configured to have a borehole
side and an atmospheric side, wherein there is a gas
outlet to the borehole side of the device and to the
atmospheric side of the device.
Suitably, the VOC concentration analyser and the VOC
collector are in series in a gas flow path with a gas
analyser. Suitably, the gas analyser analyses one or more
of hydrocarbons, carbon dioxide, oxygen and hydrogen
sulphide.
According to the present invention is a second aspect,
there is provided a method of operation of an in-borehole
gas monitor apparatus, which method comprises the use of
an in-borehole gas monitor apparatus according to the
first aspect of the invention in a borehole.
Suitably, the VOCs collected by the VOC collector are
quantified.
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Suitably, the apparatus comprises a pump for pumping gas
from the borehole past the VOC collector and the VOC
analyser, wherein the time of sensing and the length of
time for which the pump operates are recorded to determine
5 the volume of gas passing through the apparatus. This
enable the VOC concentration to be determined.
Brief Description of the Drawings
The present invention will now be described, by way of
example only, with reference to the drawings that follow;
in which:
Figure 1 is a schematic illustration of a borehole site
with an in-borehole gas monitor according to the present
invention.
Figure 2 is a schematic cross-sectional elevation of an
in-borehole gas monitor apparatus according to the present
invention.
Figure 3 is a schematic flow diagram illustrating a method
of operation of an in-borehole gas monitor apparatus
according to the present invention.
Description of the Preferred Embodiments
Referring to Figure 1 of the accompanying drawings, there
is shown a borehole 2 in ground consisting of a landfill
site. The borehole 2 is supported by a liner 4 in which a
plurality of side-holes 6 are located to allow for
sampling.
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Referring to Figure 2 of the accompanying drawings, there
is shown an in-borehole gas monitor (IGM) apparatus 8
including a cap 10. The cap 10 comprises an inner bore 12
for receiving the IGM apparatus 8. The cap 10 includes an
exterior screw thread 14 for engaging with a corresponding
interior screw thread (not shown) on liner 4.
Alternatively, the cap can be made as part of the housing.
A seal 16 is provided for fitting the IGM apparatus 8 in a
borehole when a suitable screw thread is not available for
the cap 10 to be used.
The IGM apparatus 8 consists of a body portion 17 which is
a self-contained unit meeting environmental rating IP-68,
i.e. essentially waterproof. The IGM apparatus 8 comprises
a top 30 and an external tube 32. The external diameter
of tube 32 in this embodiment is approximately 40mm
allowing for it to be inserted into a typical borehole
liner. In this embodiment of the invention, the length of
tube 32 is 800mm, but may be less.
The IGM apparatus 8 further comprises a gas inlet 36
connected to a first entry valve 38, which gas inlet leads
to a volatile organic compounds ("VOC") detector 40
connected to a VOC collector 42, connected to a water and
particulate filter 44 for removing any excess moisture
and/or particles from the ingressed gases. The filter 44
is connected to a first pressure sensor 46, connected to a
pump 48 connected to a gas detector 50 comprising a
plurality of gas analysers, in this case and H2S and CO
sensor 52, a C02 sensor 54, a CH4 sensor 56 and an 02
sensor 58. The detector is connected to a second valve 60
which is connected to a return line (a first outlet) 62
back to the borehole and a branched connection to a third
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valve 64 which is connected to a second pressure sensor 66
from which extends a second outlet 68, this time to
atmosphere.
A suitable filter 44 is an in-line particulate and
moisture filter such as that available from Geotechnical
Instruments of Sovereign House, Queensway, Leamington Spa,
United Kingdom.
The VOC detector 40 detects the presence and concentration
of a range of VOCs but does not distinguish between the
various VOCs. A suitable VOC sampler 40 is a photo-
ionisation detector. The VOC collector 42 is a sorbent
and sorbs (that is, adsorbs or absorbs) VOCs passing
therethrough. A suitable VOC sampler 40 would be a
GORESorb (trade mark) tube with a multiplicity of small
sorbent balls therein.
Any suitable gas variable can be measured in the detector
50, the analysers typically being used to monitor
hydrocarbons (especially methane), carbon dioxide, oxygen
carbon monoxide and hydrogen sulphide concentrations.
The IGM apparatus 8 further comprises a combined
controller and memory 70 for controlling operation of the
apparatus 8 and a power cell (battery) 72 making the
operation of the apparatus 8 self-contained, i.e. not
reliant on data communication with or power from an
external source. The controller 70 includes a clock.
A vent pipe 74 is provided running through the apparatus 8
from the bore-hole end to an outlet 76 through the top 30
to atmosphere (the atmospheric end of the apparatus) . A
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vent pipe valve 78 is provided for the vent pipe 64 to
control whether it is open to atmosphere.
Also shown is a water detector 80, which detects the
presence or proximity of liquid water in the apparatus and
upon such detection transmits a signal to the controller
70. A conductance sensor is used to determine a liquid
water presence.
Further, a water level detector (not shown) can be
connected to the bottom of the IGM apparatus and suspended
therebelow in use into the borehole. As wired pressure
transducer can be used.
The top 30 includes a connector 82 allowing data
communication with a remote device and unit activation.
Additionally, a pressure sensor can be attached here for
monitoring borehole water level.
The IGM apparatus 8 is mounted in a borehole 2, within a
borehole liner with the cap 10 providing a gas-tight seal.
Over time, gases will build up in the borehole 2. The IGM
apparatus 8 is configured, specifically by programming of
the controller 70, to automatically and periodically test
a gas sample from the borehole. The process by which this
is undertaken will now be described.
First (step 100) a pump test is carried out. With first
valve 38 shut, the pump 48 is started and first pressure
sensor 46 must read 100mb within 10 seconds otherwise a
FAIL warning is produced by controller 70 as the pump 48
may have failed.
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Next (step 102) a filter test is carried out. With first
valve 38 open after 4 seconds first pressure sensor 46
takes a pressure reading BH. The pump 48 then runs for a
predetermined period and first pressure sensor 46 takes
another pressure reading BHP. If BHP-BH>250mb a FAIL
warning is produced by controller 70 as the filter 44 is
likely to have become blocked.
Any FAIL warnings appear prominently as part of a data
download from the apparatus.
First and second valves 38 and 60 are opened (step 104)
and pump 48 is activated (step 106) to pump gas from the
borehole through the gas flow path described above to
ensure the sensors have an up to date gas sample from the
borehole. The VOC detector 40 and VOC collector 42
precede the filter 44 which would otherwise remove the
VOCs from the gas flow. VOC's collected by the VOC
collector can be quantified by removing the VOC collector
and eluting the VOC's into an instrument such as a gas
chromatograph. Measurements (step 108) of VOC
concentrations are made by the VOC detector 40. Moisture
and particulates are removed by the filter 44.
Borehole gas then passes through the detector 50 where it
is analysed by (step 110) by gas analysers 57, 54, 56 and
58.
A concurrent gas pressure measurement (step 112) is made
by first gas pressure sensor 38 and a reference
measurement of atmospheric pressure is made by second
pressure sensor 66. The time of the sensing and length of
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time for which the pump is operated and recorded (step
114) Based on an empirical measurement or by
calculation, the volume of gas passing through the
apparatus 8 per unit time when the pump 48 is running can
5 be determined. Accordingly, it can be determined what
volume of gas has passed through the apparatus in any
given testing period. This data is stored in the
controller/memory 70. The amount of VOC's collected by the
VOC collector can then be divided by the volume of gas
10 passed over the collector giving a measure of VOC
concentration.
First and second valves 38 and 60 are then closed (step
116). The gas from the borehole is circulated back to the
borehole through the borehole end of the apparatus.
Gas variable measurements are carried out by the gas
analysers 52, 54, 56 and 58. Any appropriate variable can
be monitored including one or more of the presence or
absence of a particular gas, a gas concentration level, a
gas pressure, moisture content in a gas, etc. The data
from the gas variable measurements is stored in the
controller/memory 70.
A timer in the controller 70 is re-set (step 116) so that
a subsequent periodic measurement can be made.
The data stored in controller/memory 70 can be downloaded
over a hard-wired connection via the connector 82 or by
wireless transmission. This connection can also be used
to program the controller 70 to operate the apparatus 8 as
desired. For instance, variables such as the frequency of
sampling, whether sampling is regular or irregular,
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whether there should be a periodic venting to atmosphere,
etc can be set.
On an ongoing basis if the water detector 80 detects the
presence of water in the apparatus, a water detection
signal is sent to the controller 70 which can take an
appropriate step, such as deactivating the apparatus 8,
transmitting an alert signal, illuminating a warning light
etc. This can both protect the apparatus 8 from damage
and avoid contaminated readings being made.
As gases build up in the borehole over time, it can be
useful to open the borehole to atmosphere to reduce the
pressure therein, but also to provide the opportunity to,
in effect, re-start the sampling operation by allowing the
borehole to equilibriate to atmosphere. Thus, the base
line for any monitoring can be re-set and an analysis of
the variation of gas variables over time can be
undertaken. The apparatus 8 can be configured to vent the
borehole to atmosphere periodically or on instruction.
Thus, there is provided a portable, self-contained IGM
apparatus that can be conveniently deployed in a borehole
to take periodic data readings of gas variables in the
borehole.
In particular, preferred embodiments of the present
invention enable VOCs to be monitored. The combination of
the VOC detector together with the VOC collector and the
determination of the volume of gas passing through the
apparatus enables a calculation to be made of the absolute
concentrations of specific VOCs in the borehole and also
how they vary over time. By time-stamping the results,
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the variation of VOCs over time can be monitored enabling,
for instance, comparisons with other time-variable
phenomena, such as atmospheric pressure or weather
conditions.
Attention is directed to all papers and documents which
are filed concurrently with or previous to this
specification in connection with this application and
which are open to public inspection with this
specification, and the contents of all such papers and
documents are incorporated herein by reference.
All of the features disclosed in this specification
(including any accompanying claims, abstract and
drawings), and/or all of the steps of any method or
process so disclosed, may be combined in any combination,
except combinations where at least some of such features
and/or steps are mutually exclusive.
Each feature disclosed in this specification (including
any accompanying claims, abstract and drawings) may be
replaced by alternative features serving the same,
equivalent or similar purpose, unless expressly stated
otherwise. Thus, unless expressly stated otherwise, each
feature disclosed is one example only of a generic series
of equivalent or similar features.
The invention is not restricted to the details of the
foregoing embodiment(s). The invention extends to any
novel one, or any novel combination, of the features
disclosed in this specification (including any
accompanying claims, abstract and drawings), or to any
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novel one, or any novel combination, of the steps of any
method or process so disclosed.
