Field of the Invention
This invention relates to a method and apparatus for fumigant gas capture.
In preferred embodiments the invention can be used to treat or neutralise
fumigant compounds.
Background of the Invention
Fumigant gases are used to kill unwanted organisms in a variety of
applications. For example, fumigant gases which act as pesticides herbicides
or insecticides can be circulated within an enclosed volume. Fumigant gases
can be used to kill pests in the interior of structures such as buildings, ship
holds or grain silos, as well as to sterilise goods present within shipping
containers. In other applications fumigant gases can be deployed into stacks
of logs wrapped in fabric covers to sterilise the wood prior to or after
shipping. The range of applications for fumigant gases requires these gases
to be pumped into and removed from both comparatively small and
relatively large enclosed volumes.
However a number of commonly used fumigation gas compounds pose
human health and safety risks. Furthermore, some of these compounds are
also a source of environmental pollution when vented directly to the
atmosphere. For example, methyl bromide is a widely used fumigant which
reacts with ozone. Various regulatory bodies around the world are now
beginning to restrict the venting of these types of gases directly to the
atmosphere.
A number of prior art technologies have been developed to capture, scrub or
process fumigant gases released into various enclosed environments.
For example, US patent application US2010/0172807 discloses a
representative example of a fumigation gas scrubber which bubbles fumigant
gas through a bath of reactive liquid. These bath based systems rely on
sufficient contact surface area of fumigate gas exposed to the treatment
solution to react the gas into a less problematic compound. Due to gas
bubble sizes these systems are only practical or effective when used to treat
small volumes or low flow rates of fumigant gas. As the gas flow rate applied
to the solution bath increases so does the volume of the gas bubbles
transiting the bath which limits the amount of fumigant gas exposed to and
treated by the bath solution.
One attempt to address the scale or usability issues present in the above
systems has been to initially capture the fumigant gas in a matrix of
activated carbon. US patent number 5904909 provides a representative
example of this form of technology. Gas flows containing fumigant gases are
delivered to a conduit containing arrays of activated carbon material which
capture and remove the fumigant gas compounds from the gas flow. The
activated carbon in these conduits will eventually become saturated with
these compounds. The carbon is then removed and exposed to a further
solvents or reactive solutions used to treat and neutralise the trapped
fumigant gas compounds.
These types of activated carbon gas scrubbers can function effectively to
capture and treat large volumes of fumigant gas delivered at comparatively
high flow rates. However they are material intensive systems to implement
and have high maintenance requirements. Furthermore the capture of some
types of fumigant gases by the activated carbon triggers an exothermic
reaction, which requires the heat generated to be carefully managed and
which poses a potential fire risk.
It would therefore be of advantage to have improvements over the prior art
which addressed the above problems or at least provided the public with an
alternative choice. An improved fumigation gas capture and treatment
technology which could be used practically with both small and large
volumes of fumigant gases and which was inexpensive to implement, run
and maintain would be of particular advantage. An improved fumigation gas
capture and treatment apparatus which could be transported from site to
site easily and which could be configured to fit within restricted spaces would
also be of advantage.
In this specification, where reference has been made to external sources of
information, including patent specifications and other documents, this is
generally for the purpose of providing a context for discussing the features
of the present invention. Unless stated otherwise, reference to such sources
of information is not to be construed, in any jurisdiction, as an admission
that such sources of information are prior art or form part of the common
general knowledge in the art.
Disclosure of the Invention
According to one aspect of the present invention there is provided a
fumigant gas capture apparatus which includes
at least one channel adapted for connection to a volume containing a
fumigant gas, the channel defining an inlet which receives gas and an outlet
which allows gas to exit the channel,
at least one drive structure arranged to drive fumigant gas through the
channel,
at least one spray nozzle adapted to deliver a treatment liquid into the
channel, and
at least one packing element positioned within the channel to allow a spray
nozzle or nozzle to spray treatment liquid on to the packing element.
According to a further aspect of the present invention there is provided a
fumigant gas capture apparatus substantially as described above which
includes a reservoir of treatment liquid adapted to deliver treatment liquid to
said at least one spray nozzle.
A method of fumigant gas capture characterised by the steps of:
• spraying a treatment liquid into a channel to intersect with at least one
packing element, and
· driving a fumigant gas through the channel and into contact with the
sprayed treatment liquid.
According to a further aspect of the present invention there is provided a
fumigant gas capture apparatus substantially as described above wherein
spraying treatment liquid on a packing element reduces the size of
treatment liquid droplets which the fumigant gases are exposed to when
driven through the channel. A packing element used with the invention also
increases turbulence of the air flow through the column, increasing the
interaction between fumigant gases and treatment liquid.
According to a further aspect of the present invention there is provided a
fumigant gas capture apparatus substantially as described above wherein
said at least one packing element is sprayed with treatment liquid by a spray
nozzle to coat at least a portion of the surface of the packing element with
treatment liquid to expose fumigant gases to the coated surface or surfaces
of the packing element when driven through the channel.
Preferably the treatment liquid is a basic or alkaline liquid having a pH value
of at least seven.
Preferably the treatment liquid is composed from or includes an organic
solvent.
According to a further aspect of the present invention there is provided a
fumigant gas capture apparatus substantially as described above wherein at
least one spray nozzle is located adjacent to the outlet of a channel.
Preferably a channel is provided with a substantially vertical orientation with
the outlet at the top of the channel and the inlet at the bottom of the
channel. In this arrangement a channel forms a substantially vertical hollow
column through which gas is forced upwards against a flow of the treatment
liquid.
According to a further aspect of the present invention there is provided a
fumigant gas capture apparatus substantially as described above which
includes a plurality of channels with the outlet of at least one channel being
connected to the inlet of a further channel.
According to another aspect of the present invention there is provided a
fumigant gas capture apparatus substantially as described above which
includes a heat transfer structure engaged with the inlet of at least one
channel.
The present invention is adapted to provide an apparatus and method for
the capture of fumigant gases. The invention employs the use of a treatment
liquid to capture and react with these fumigant gases delivered from a
volume being fumigated (referred to herein as 'the fumigation chamber').
Those skilled in the art will appreciate that this invention may be used to
capture and treat a range of fumigant gases which can be delivered from a
variety of environments. The present invention may - for example - be used
to capture and treat fumigant gases formed from methyl bromide, sulphuryl
fluoride, or phosphine in various applications. Furthermore the invention
may be used, for example, to receive fumigant gases extracted from within
the interior of buildings, grain silos, ship holds, shipping containers or
fumigant gases trapped under covered stacks of logs in various applications.
Reference in general throughout this specification will however be made
primarily to the invention being used to capture and treat methyl bromide as
a fumigant gas. Again those skilled in the art will appreciate that other types
of gas may also be captured and treated in conjunction with the present
invention.
The invention employs at least one channel to control the passage or motion
of the fumigant gas being treated. A channel used in conjunction with the
present invention may preferably be formed by any type of conduit, housing
or enclosure which defines a pathway from an inlet to an outlet. Preferably
the path defined by the channel may be substantially linear, although those
skilled in the art will appreciate that alternative shapes or forms of conduit
may also be employed in a variety of embodiments.
In a preferred embodiment a channel employed with the invention may form
or define a single inlet at one end and a single outlet at its opposite end.
Again however in other embodiments multiple outlets and/or multiple inlets
may be provided for a single channel.
In a preferred embodiment a channel may be provided with a substantially
vertical orientation which positions its outlet at the top of the channel and its
inlet at the bottom of the channel. Again however those skilled in the art will
appreciate that other channel orientations - be they horizontal or angled -
may also be employed in various embodiments.
In a preferred embodiment a capture apparatus provided by the invention
may incorporate a plurality of channels. Potentially each of these channels
may provide a conduit for a separate or independent fumigant gas flow.
However in a further preferred embodiment these channels may be arranged
for interconnection with one another with linkages being provided between
the outlet of one or more channels to the inlet of one or more further
channels. In such embodiments fumigant gas flows may be filtered through
a number of sequentially arrayed channels, potentially being returned again
to the first channel in the sequence to recirculate these gas flows if required.
This arrangement of the invention provides it with a high degree of flexibility
and variability in how gas flows are managed and treated. In some cases a
single channel only may be employed to treat a gas flow, while in other
applications a gas flow may be run through a sequential array of channels
depending on the volume of gas to be treated and the concentration of
fumigant gas compounds it contains.
In a preferred embodiment the present invention also includes a mobile
support platform. This platform may be used to mount and support the
various components of the invention and in particular preferred
embodiments may support a plurality of channels. In a further preferred
embodiment a mobile support platform may be supported by set of wheels
and preferably include a towing linkage to allow the apparatus to be towed
by a vehicle to a new location.
In these embodiments the vertical height of each of the invention's channels
may be restricted or controlled to provide a compact and manoeuvrable
mobile apparatus. A number of interconnected channels may be mounted on
this type of mobile platform to provide the processing capacity required in a
range of applications - without necessarily increasing the height of the
apparatus to an extent which would prevent it from accessing confined
locations.
The invention includes at least one drive structure formed from a fan or
pump arranged to drive gas flows through its channel or channels. Those
skilled in the art will appreciate that various arrangements and
configurations of such a drive structure or structures may be employed in a
range of embodiments. For example, in some instances the invention may
employ a pair of fans or pumps to both push and or pull gas flows through
conduits, whereas in other cases a fan or pump may be provided for each
and every channel integrated into the apparatus.
Preferably the invention incorporates at least one spray nozzle for every
channel it integrates. A spray nozzle is provided to deliver treatment liquid
into the interior of a channel, preferably in the form of a mist of small
droplets.
I n some embodiments the treatment apparatus integrates one spray nozzle
only in each of its channels. A single nozzle can be arranged or positioned
adjacent to the outlet of the channel in such embodiments.
However those skilled in the art will appreciate that other configurations and
arrangements of the invention are also within its scope. For example, in
other embodiments two or potentially more spray nozzles may be located
within a channel, be they at the outlet or adjacent to the outlet of the
channel, or deployed along the length of the channel.
The invention incorporates at least one packing element located within a
channel between the inlet and outlet of the channel. A packing element used
with the invention is exposed to the spray of treatment liquid provided by a
nozzle and promotes or assists in changing the phase of the fumigant gas
compounds into a liquid form.
Preferably a packing element used with the invention acts t o reduce the size
of treatment liquid droplets which impact with the element. Relatively large
drops of liquid sprayed on to a packing element are broken up and atomised
further to preferably create a fine mist of treatment liquid within the
channel.
Preferably a packing element used with the invention increases the contact
surface area of sprayed treatment liquid to the gas driven through a
channel. Treatment liquid sprayed on to a packing elements coats a surface
(and preferably all surfaces) of the element thereby increasing the surface
area contact between fumigant gas and treatment liquid.
Preferentially the packing material increases turbulence within the fumigant
gas flow to provide greater interaction with the sprayed treatment liquid to
increase the rate of transfer of fumigant molecules from the gas to liquid
phase.
In a further preferred embodiment a packing element may be formed from a
tellerette with an appropriate shape and dimensions arranged to optimise
the surface area contact between the gases and liquids within a channel.
In a preferred embodiment a channel employed with the invention may be
used to locate a large number of packing elements. These packing elements
can form a packed tower arrangement when a channel has a substantially
vertical orientation, substantially increasing the contact surface area
between treatment liquid sprayed into the top of the tower and fumigant
gases driven through the bottom of the tower.
The present invention may employ a range of different types of treatment
liquids depending on the fumigant gas it is used to capture and treat. In a
variety of embodiments the treatment liquid used is preferably a basic or
alkali solution with a pH value of at least seven.
In a preferred embodiment the treatment liquid employed by the invention
may be composed from or include an organic solvent. These compounds
perform efficiently in respect of both the capture of fumigant gas compounds
into a liquid form, in addition to reacting with the chemicals of the fumigant
to neutralise same. An organic solvent provides specific advantages to the
invention in terms of speed of operation and the volumes of fumigant gas
which can be treated in a reasonable length of time. As these compounds
readily captures fumigant gases and can then subsequently neutralise them
in one step large volumes of fumigants can be processed efficiently by the
invention.
In a preferred embodiment the invention may include a heat transfer
structure engaged with the inlet of at least one channel. A heat transfer
element can be used to increase the temperature of gas flowing entering the
inlet of a channel, potentially increasing the efficiency of the apparatus
provided.
In a further preferred embodiment a heat transfer structure may be formed
from a heat exchange coil which surrounds a section of conduit linked to a
channel inlet and transporting a flow of fumigant gas. Such a structure can
also incorporate a heat source - such as, for example, a hydrocarbon burner
- which is used to heat a warm a fluid circulated through the heat exchange
coil. For example, in one possible embodiment a diesel burner system may
be used to heat water which is circulated through the heat exchange coil to
pre-heat fumigant gas flows entering a channel inlet.
Those skilled in the art will appreciate that the invention may include a
single heat transfer structure linked to one or more channels, or a plurality
of heat exchange structures - with the potential for one being provided for
each channel of the invention.
The present invention provides many potential advantages over the prior
art.
In various embodiments the invention can be used to both capture and treat
fumigant gases supplied over a range of flow rates from a variety of
fumigated enclosures. The invention utilises a spray of treatment liquid to
capture and treat fumigant gases, with this liquid only needing to be drained
from the apparatus after the completion of one or more treatment cycles.
This may be contrasted with prior art activated carbon-based based gas
scrubbing systems which have significantly increased implementation and
maintenance requirements.
In embodiments where a plurality of channels are provided these channels
can be interconnected with one another in a modular fashion to suit the
requirements of a particular application or fumigation space. Furthermore in
some embodiments this staged or modular arrangement provides for a
portable character allowing the operative components of the invention to be
mounted to a mobile platform capable of being towed from site to site.
Brief description of the drawings
Additional and further aspects of the present invention will be apparent to
the reader from the following description of embodiments, given in by way of
example only, with reference to the accompanying drawings in which :
• Figure 1 shows a side view of a fumigant is gas capture and treatment
apparatus as provided in accordance with a preferred embodiment,
and:
• Figure 2 shows a plan view of the apparatus of figure 1, and
• Figure 3 shows a side cross-section view of one of the channels
integrated into the apparatus shown with respect to figures 1 and 2.
Further aspects of the invention will become apparent from the following
description of the invention which is given by way of example only of
particular embodiments.
Best modes for carrying out the invention
Figures 1 and 2 show side and plan views of a gas capture and treatment
apparatus 1 as provided in accordance with a preferred embodiment. Figure
3 provides a side cross section view of one of the channels 2 used in the
construction of the apparatus.
The capture apparatus 1 includes an array of four channels 2 which can be
connected to a volume containing a fumigant gas. In the embodiment shown
the apparatus 1 is arranged to receive methyl bromide gas extracted from a
pile of covered logs after the completion of a fumigation process. In various
embodiments methyl bromide gas extracted from the log pile may pass
through a heat treatment structure (not shown) before reaching the
channels 2. This heat treatment structure can be used to raise the
temperature of the methyl bromide gas prior to delivery to a channel.
Each channel 2 defines an inlet 3 which receives gas and an outlet 4 which
allows gas to exit the channel. As can be seen from figures 1 and 2 the
channels have a vertical orientation with the outlet 4 at the top of the
channel and the inlet 3 at the bottom of the channel.
Figure 2 shows how each of these four channels can be configured in a
modular fashion to vary the treatment applied to the gas supplied to the
apparatus. I n the particular embodiment shown the four channels are split
into two pairs of channels. The outlet of a first channel 2a is connected to
the inlet of a second channel 2b. The outlet of the second channel is then
connected to a centrifugal filter 5 which removes entrained treatment liquid
and allows the treated gas flow to be vented to atmosphere.
I n other configurations all four channels may be connected outlet to inlet to
maximise the treatment applied to a gas flow, and can potentially have the
outlet of the final channel connected to the inlet of the first channel to
recirculate the gas flow.
The capture apparatus 1 includes a pair of drive structures, formed in this
embodiment by an inlet fan 6 and outlet fan 7. These fans are arranged to
drive fumigant gas through each of the channels by either a blowing or
suction effect.
As shown with respect to figure 3 the apparatus 1 includes a reservoir of
treatment liquid 8 which is provided to deliver treatment liquid to a spray
nozzle 9 integrated into each channel. I n the embodiment shown this
treatment liquid is formed from an organic solvent, although other
compounds such as basic or alkaline liquids can be used in alternative
embodiments.
Each spray nozzle 9 is adapted to deliver a treatment liquid into the channel
2 and is provided adjacent to the outlet 4 of the channel.
Each channel also contains a large number of packing elements positioned
within the channel to allow the spray nozzle 9 to spray treatment liquid on to
the packing elements. In the embodiment shown these packing elements are
formed by a collection of tellerettes 10.
I n use treatment fluid is delivered from the reservoir to each spray nozzle 8
and sprayed on to the tellerettes 10 packed into the interior of each
vertically orientated channel 2. Fumigant gas is then driven through the
channels under the action of either or both of the inlet and outlet fans 6, 7.
The action of the fans drives the fumigant gas into contact with both a mist
of treatment liquid droplets in addition to the treatment liquid coating the
surfaces of the packing element tellerettes 10.
This used of vertically orientated channels filled with packing elements
maximised the contact surface area and interaction between the treatment
liquid and the gas flow, promoting a phase change to liquid for the fumigant
gas. The treatment liquid then reacts with the captured fumigation
compounds to neutralise same into a more benign form. Treated gas flows
can then be vented to atmosphere without the fumigant compounds they
once captured, and the treatment fluid used to neutralise these compounds
can simply be drained from each channel and pumped back to the reservoir
8.
As can be seen from figures 1 and 2 the apparatus also includes a mobile
support platform 11. This platform is used to mount and support the various
additional components of the invention through the provision of a deck 12
mounted to a set of wheels 13. A towing linkage 14 is also provided at one
end of the deck to allow the apparatus t o be towed by a vehicle from site to
site.
I n these embodiments the vertical height of each of the invention's channels
may be restricted or controlled to provide a compact and manoeuvrable
mobile apparatus 1. The interconnected channels mounted on the mobile
platform can provide all the processing capacity required by a range of
applications without necessarily increasing the height of the apparatus to
where it would be prevented from accessing confined locations.
These channels can also be interconnected with one another in a modular
fashion to suit the requirements of a particular application or fumigation
space. When combined with the mobile platform this staged or modular
arrangement provides for a portable character, allowing the operative
components of the invention to be towed to various locations through or into
restricted spaces.
In the preceding description and the following claims the word "comprise" or
equivalent variations thereof is used in an inclusive sense to specify the
presence of the stated feature or features. This term does not preclude the
presence or addition of further features in various embodiments.
It is to be understood that the present invention is not limited to the
embodiments described herein and further and additional embodiments
within the spirit and scope of the invention will be apparent to the skilled
reader from the examples illustrated with reference to the drawings. In
particular, the invention may reside in any combination of features described
herein, or may reside in alternative embodiments or combinations of these
features with known equivalents to given features. Modifications and
variations of the example embodiments of the invention discussed above will
be apparent to those skilled in the art and may be made without departure
of the scope of the invention as defined in the appended claims.

What we claim is:
1. A fumigant gas capture apparatus which includes
at least one channel adapted for connection to a volume containing a
fumigant gas, the channel defining an inlet which receives gas and an
outlet which allows gas to exit the channel,
at least one drive structure arranged to drive fumigant gas through the
channel,
at least one spray nozzle adapted to deliver a treatment liquid into the
channel, and
at least one packing element positioned within the channel to allow a
spray nozzle or nozzle to spray treatment liquid on to the packing
element.
2. A fumigant gas capture apparatus as claimed in claim 1 wherein said
at least one packing element is sprayed with treatment liquid by a
spray nozzle to coat at least a portion of the surface of said at least
one packing element with treatment liquid to expose fumigant gases to
the coated surface or surfaces of the packing element when driven
through the channel.
3. A fumigant gas capture apparatus as claimed in claim 1 which captures
and treats methyl bromide.
4. A fumigant gas capture apparatus as claimed in claim 1 which includes
a reservoir of treatment liquid adapted to deliver treatment liquid to
said at least one spray nozzle.
5. A fumigant gas capture apparatus as claimed in claim 4 wherein the
treatment liquid is a basic or alkaline liquid having a pH value of at
least seven.
6. A fumigant gas capture apparatus as claimed in claim 4 wherein the
treatment liquid is composed from or includes an organic solvent.
7. A fumigant gas capture apparatus as claimed in claim 1 wherein a
channel is formed by a linear conduit with a single inlet at one end and
a single outlet at its opposite end.
8. A fumigant gas capture apparatus as claimed in claim 7 wherein a
channel has a substantially vertical orientation which positions its
outlet at the top of the channel and its inlet at the bottom of the
channel.
9. A fumigant gas capture apparatus as claimed in claim 7 which
incorporates a plurality of channels arranged for interconnection with
one another with linkages being provided between the outlet of one or
more channels to the inlet of one or more further channels.
10. A fumigant gas capture apparatus as claimed in claim 9 wherein
fumigant gas flows are filtered through a plurality of sequentially
arrayed channels.
11. A fumigant gas capture apparatus as claimed in claim 1 which
integrates one spray nozzle only in each of its channels, each spray
nozzle being positioned adjacent to the outlet of the channel.
12. A fumigant gas capture apparatus as claimed in claim 1 wherein a
packing element reduces the size of treatment liquid droplets sprayed
on the packing element on which the fumigant gases are exposed to
when driven through the channel.
13. A fumigant gas capture apparatus as claimed in claim 1 wherein a
packing element promotes a phase of the fumigant gas compounds
into a liquid form.
14. A fumigant gas capture apparatus as claimed in claim 1 wherein a
packing element is formed from a tellerette arranged to induce
turbulence in the fumigant gases and optimise the surface area
contact between the gases and liquids within a channel.
15. A fumigant gas capture apparatus as claimed in claim 1 wherein a
channel employed with the invention locates a plurality of packing
elements.
16. A fumigant gas capture apparatus as claimed in claim 1 wherein
packing elements form a packed tower arrangement when a channel
has a substantially vertical orientation with treatment liquid sprayed
into the top of the tower and fumigant gases driven through the
bottom of the tower.
17. A fumigant gas capture apparatus as claimed in claim 1 which employ
one or more of fans or pumps to push and or pull gas flows through
conduits.
18. A fumigant gas capture apparatus as claimed in claim 1 wherein a fan
or pump is provided for each channel.
19. A fumigant gas capture apparatus as claimed in claim 1 which includes
a heat transfer structure engaged with the inlet of at least one
channel.
20. A fumigant gas capture apparatus as claimed in claim 1 which includes
a mobile support platform supported by set of wheels.
21. A fumigant gas capture apparatus as claimed in claim 20 wherein said
mobile support platform include a towing linkage configured to allow
the apparatus to be towed by a vehicle to a new location.
22. A method of fumigant gas capture characterised by the steps of:
spraying a treatment liquid into a channel to intersect with at least one
packing element, and
driving a fumigant gas through the channel and into contact with the
sprayed treatment liquid.