Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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GAS DISTRIBUTOR FOR A STACKED PARTICLE BIOREACTOR
FIELD OF THE INVENTION
This invention relates to a gas distributor for a stacked particle bioreactor
in which organic
carbonaceous material is biologically treated to produce fuel.
BACKGROUND TO THE INVENTION
The demand for naturally occurring fuels is likely to exceed the world supply
in the near
future. Additionally, the natural distribution of fuels throughout the world
is disproportionate.
The development and use of synthetic fuels (synfuels), those derived from non-
traditional
feed stocks, is increasing. The production of ethanol, methane and other
hydrocarbon
products from carbonaceous material is increasing.
One answer to the problem is the production of synfuels through stacked
particle (heap)
bioreactors. These bioreactors operate on the principle of stacking particles
of biodegradable
carbonaceous material and providing optimal living conditions for the
microorganisms, which
are either naturally present or specifically added microorganisms to
biologically treat the
stacked particles. The biologically treated carbonaceous material produces
synfuels which
may include synthetic petroleum, alcohol, and/or a gaseous fuel.
The synfuel is recovered from the stack and processed further depending on its
quality and
purity. The synfuels may be in liquid form, such as synthetic petroleum or
alcohol, or in gas
form such as a gas which includes methane or alcohol. The recovery of gaseous
synfuels is
done by means of a gas collector system which is placed proximate the top of
the stack. The
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recovery of liquid synfuels is done by means of a collection system located at
the bottom of
the stack.
The biological treatment of the carbonaceous material in such a stack may be
aerobic and/or
anaerobic. In the case of aerobic treatment the microorganisms utilize oxygen
and oxygen is
preferentially added to supplement depleted oxygen to optimize the performance
of the
microorganisms, at least to the extent that it is dependant on the presence of
oxygen.
In the case of anaerobic treatment the microorganisms operate in the absence
of oxygen,
and oxygen is preferentially removed to optimize the performance of the
microorganisms, at
least to the extent that it is dependant on the absence of oxygen. Inert gas
is circulated
through the stack via the gas distribution/collection system and is either a
recycle of the
process effluent gas such as carbon dioxide or an externally supplied inert
gas.
To add oxygen to an aerobically treated bioreactor, oxygen or air is purged
into a stack,
typically from the bottom of the stack. Depending on the gas permeability of
the stack,
additional purge lines may also be located on levels higher than the bottom,
to optimize the
distribution of the purged oxygen or air through the stack. This allows oxygen
and air to be
added to the stack as needed to optimize the performance of the
microorganisms. The need
for this may be verified by means of strategically placed sensors in the stack
or to the outputs
from the stack.
To remove oxygen from the stack, which is needed to optimize the performance
of anaerobic
treatment of the carbonaceous material in the stack, oxygen is purged from the
stack. The
purging is done by using, for example, argon, nitrogen, carbon dioxide,
ammonia, or
hydrogen gas. At the same time the stack is covered with a gas impermeable
barrier which
prevents oxygen from being taken up into the stack through its surface.
In some processes a stack is initially treated aerobically and then switched
to anaerobic
treatment after a while. To switch from aerobic to anaerobic treatment,
anaerobic
microorganisms have to be added to the stack. This is done by means of
inoculation.
Inoculation can take many forms. During the initial construction of the
bioreactor, inoculation
can take the form of spraying the particles which form the stack with a fluid
which contains
the microorganisms as they are laid down, or by preparing layer and then
spraying its
surface and repeating this process to build the bioreactor. These examples of
inoculation are
only effective when the bioreactor is constructed. Once the bioreactor has
been constructed
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inoculation is done by irrigation with fluid which contains the
microorganisms. The inoculation
fluid may also contain nutrients for the microorganisms.
The inoculation by emitters may be done on the surface of the stack, or from
below the
surface to optimize the spread of the inoculum.
From the forgoing it should be clear that there are several fluid inputs and
outputs to the
system which comprises a stacked particle bioreactor.
The fluid inputs include gas which is forced or allowed into the stack from
below. This
includes oxygen and air which are used during aerobic treatment and argon,
nitrogen, carbon
dioxide, ammonia, or hydrogen gas which are used during anaerobic treatment.
The gas is
pumped or allowed under atmospheric pressure into the stack through the gas
purge lines.
The fluid inputs also include liquid with which the stack is irrigated. This
typically comprises
water and stack products which also contains microorganisms and nutrients. The
liquid
irrigation takes place from above or from within the stack.
The fluid outputs include gas synfuels, for example those containing methane,
that rise
through the stack and are collected by the gas collector system located
proximate the top of
the stack. The reversing of the gas flow directions is also facilitated in the
bioreactor.
The fluid outputs also include the liquid synfuels which drain through the
stack and are
collected at the bottom.
It should therefore be clear that the system includes fluids that move either
up or down in the
stack. To optimize the performance of the process, the fluid flows must be
balanced based
on heat generation.
The design, operation, and advantages of one such system have been described
in detail in
published patent application US2006/0223154A1.
A problem with the purge pipes located at the bottom of the stack is that
random alignment of
the material used to stack the bioreactor may block a hole or restrict flow of
gas from the
hole. Also, liquid synfuels which drain through the stack flow over such purge
pipes near or
over the holes therein. Since the environment near each hole is evaporative
due the inflow of
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gas from the purge pipe, precipitates may form due to evaporation of liquid
and such
precipitates may block the hole.
Another problem is that if the gas flow through the purge pipe is stopped, as
may be the case
when aerobic treatment takes place and the stack has been initially purged of
oxygen and air
and covered, there is an increased chance of flooding of the pipes with liquid
synfuels
draining through the stack.
Once a purge pipe has been so blocked or flooded it is very difficult, if not
impossible, to
clear it without removing it from the stack. It is not possible to remove a
pipe without at least
disturbing or damaging the stack, and most likely not without destroying the
fine balance
within the bioreactor. Since these bioreactors are constructed to operate for
several years a
blocked or flooded pipe normally results in loss of fluid input at the
specific point so blocked
or flooded.
In this specification the term "dry-shadow" refers to the area underneath a
gas distributor in a
stacked particle bioreactor that remains substantially dry despite the flow of
liquid down
through the stack. The size of the dry shadow depends on a number of factors,
including the
diameter of the pipe which forms the gas distributor, the hydraulic
conductivity of the drain
material in the stack, and the amount of liquid that drain through the stack.
OBJECT OF THE INVENTION
It is an object of the invention to provide a gas distributor for a stacked
particle bioreactor
which at least partly overcomes the abovementioned problems.
SUMMARY OF THE INVENTION
In accordance with this invention there is provided a gas distributor for a
stacked particle
bioreactor which produces synfuels from biodegradable carbonaceous material
comprising a
pipe having a series of apertures through the wall of the pipe, and for at
least one aperture to
be located in an indentation in the outer wall of the pipe.
There is further provided for the pipe to include a continuous indentation,
preferably for all
the apertures to be located in the continuous indentation, and more preferably
for the
continuous indentation to extend longitudinally along the outer wall of the
pipe.
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According to a further feature of the invention there is provided for the pipe
to include an
endless circumferential indentation, preferably for a plurality of endless
circumferential
indentations to be spaced apart along the pipe, alternatively for the pipe to
include a helical
indentation, and for a plurality of apertures to be located in the
circumferential indentations.
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There is further provided for the gas distributor to include a perforated
cover over each
aperture, and preferably for a single cover over the continuous indentation
and
circumferential indentations respectively.
There is still further provided for the gas distributor to be configured for
the series of
apertures to operatively face downwards in a stacked particle, preferably in
the dry-shadow
of the pipe.
According to an alternative feature of the invention there is provided a gas
distributor for a
stacked particle bioreactor which produces synfuels from biodegradable
carbonaceous
material comprising a pipe having a series of apertures through the wall of
the pipe, and for
the series of apertures to be configured operatively to face downwards in a
stacked particle,
preferably in the dry-shadow of the pipe.
There is yet still further provided for the gas distributor to include a
series of apertures which
extend longitudinally along the pipe in a line which is orientated between
about 00 and 45
degrees from the vertical along the circumference of the pipe.
There is also provided for the gas distributor which includes the endless
circumferential
indentation to include two apertures spaced apart by between about 0 and 450
degrees from
the vertical along the circumference of the pipe, and for each of these
apertures to be part of
a series of apertures which extend longitudinally along the pipe in a line
which is orientated
between about 00 and 450 degrees from the vertical along the circumference of
the pipe.
There is still further provided for the invention to extend to a stacked
particle bioreactor which
produces synfuels from biodegradable carbonaceous material which includes a
gas
distributor as defined above, a method of forming a stacked particle
bioreactor which
produces synfuels from biodegradable carbonaceous material which includes
installing a gas
distributor as defined above in the stacked particle bioreactor, and a method
of producing
gaseous fuel from biodegradable carbonaceous material using a stacked particle
bioreactor
which includes the step of introducing gas into the stacked particle
bioreactor through a gas
distributor as defined above.
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BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the invention is described by way of example only
and with
reference to the accompanying drawings in which:
Figure 1 A is a perspective view of a first embodiment of a gas distributor
according to
the invention which comprises a pipe with a continuous longitudinal semi
circular indentation within which a plurality of apertures is located;
Figure 1 B is an end view of the pipe of Figure 1 A;
Figure 1C is a bottom plan view of the pipe of Figure 1 A;
Figure 2A is a perspective view of a second embodiment of a gas distributor
according to
the invention which comprises a pipe with a plurality of longitudinally
arranged
smooth indentations within each of which an aperture is located;
Figure 2B is an end view of the pipe of Figure 2A;
Figure 2C is a bottom plan view of the pipe of Figure 2A;
Figure 3A is a perspective view of a third embodiment of a gas distributor
according to
the invention which comprises a pipe with a continuous longitudinal
rectangular indentation within which a plurality of apertures is located;
Figure 3B is an end view of the pipe of Figure 3A;
Figure 3C is a bottom plan view of the pipe of Figure 3A;
Figure 4A is a perspective view of a fourth embodiment of a gas distributor
according to
the invention which comprises a pipe with a plurality of longitudinally
arranged
rectangular indentations within each of which an aperture is located;
Figure 4B is an end view of the pipe of Figure 4A;
Figure 4C is a bottom plan view of the pipe of Figure 4A;
Figure 5A is a perspective view of a fifth embodiment of a gas distributor
according to
the invention which comprises a pipe with a continuous longitudinal V-shaped
indentation within which a plurality of apertures is located;
Figure 5B is an end view of the pipe of Figure 5A;
Figure 5C is a bottom plan view of the pipe of Figure 5A;
Figure 6A is a perspective view of a sixth embodiment of a gas distributor
according to
the invention which comprises a pipe, shown upside down for the sake of
clarity, with a plurality of longitudinally arranged indentations of different
shapes within each of which an aperture is located;
Figure 6B is and end view of the pipe of Figure 6A, also shown upside down;
Figure 6C is a bottom plan view of the pipe of Figure 6A;
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Figure 7A is a perspective view of the gas distributor pipe of Figure 1A,
shown upside
down for the sake of clarity, with a cover over the continuous longitudinal
indentation;
Figure 7B is an end view of the pipe of Figure 7A, also shown upside down;
Figure 7C is a bottom plan view of the pipe of Figure 7A;
Figure 8 is a sectional end view of an eight embodiment of a gas distributor
according
to the invention which comprises a pipe with, the view taken through an
endless circumferential indentation in which the two apertures have been
placed in the dry shadow of the pipe;
Figure 9 is a side view of the pipe in Figure 8, showing one row of apertures
extending
along the length of the pipe; and
Figure 10 is a sectional side view of a stacked particle bioreactor which
includes a gas
distributor according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
The inventors have determined that there are three key requirements of an
improved gas
distributor, namely:
= Protection for the apertures from blocking by random alignment of
carbonaceous
material, which may occur during stacking of the bioreactor after placement of
the
pipe;
= Protection for the apertures from precipitates forming in them as a result
of
evaporation of liquid draining through the stack which runs over the apertures
or over
material proximate the apertures; and
= The gas distributor should preferably comprise a single piece.
These requirements are achieved at least partly in the invention of which
several
embodiments are described by way of example only.
Figures 1A to 1C presents a preferred embodiment of the invention. A pipe (1)
with a
continuous semi-circular indentation (2) formed along the length of the pipe
(1) is used for
the gas distributor. Apertures (3) are drilled through the pipe wall in the
indentation (2). The
pipe (1) is laid with the apertures (3) facing downwards in the stack.
The apertures (3) are protected from blockage by adjacent material since it is
placed onto the
material, and additional material stacked onto the pipe will not be located
adjacent the
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apertures (3). The apertures (3) are located inside the indentation (2) which
creates a space
between the apertures (3) and the material on which the pipe (1) is laid.
The apertures (3) are protected from liquid running over them by having them
located
underneath the pipe (1) and spaced from the bottom (4) of the pipe (1). The
indentation (2)
provides an exit path along the entire length of the pipe (1) for gas
introduced through it, as
opposed to only in the immediate vicinity of the apertures (3).
Since the pipe is of a single length it is simply laid with the apertures (3)
face down onto a
layer of material and can then be covered with more material, which is
simpler, quicker and
cheaper than prior art gas distributor systems.
Figures 2A to 2C show an alternative embodiment of the invention. In this
embodiment a
plurality of indentations (5) are formed in the pipe (6) and an aperture (7)
is drilled through
the pipe wall inside each indentation (5). The indentations (5) are spaced
apart by a
predetermined distance. Although the exit path for gas is less than for the
preferred
embodiment shown in Figures 1A to 1C, it is still greater than just the
immediate vicinity of
the aperture. The apertures (7) are also protected from blockage by material
and precipitates
and the pipe (6) is made from a single piece of material.
For pipes which have a relative thick wall the indentation may be cut from the
pipe wall itself.
Two embodiment of gas distributors which includes such indentations are shown
in Figures
3A to 3C and 4A to 4C. In the pipes shown in these Figures, a rectangular
indentation is cut
from the pipe wall. In Fig 3A to 3C a continuous indentation (8) is cut from
the pipe wall (9)
and in Fig 4A to 4C a series of rectangular indentations (10) are cut from the
pipe wall (11).
The indentation, whether continuous or periodic, may take any size and form
that adequately
protects the apertures from blockage by material and precipitates. Non-
exhaustive examples
include V-shaped (12) or U-shaped indentations as shown in Figures 5A to 5C.
Further
examples of periodic indentations include circular (13), star (14), triangular
(15), pentagonal
(16), and square (17) shapes, as shown in Figures 6A to 6C.
The indentation may be covered by a shield (18) to protect further the
apertures (19) against
blockage, especially when the pipe (20) is intended to be placed in a layer of
relatively fine
material. The shield (18), as shown in Figures 7A to 7C, comprise a perforated
mesh (21)
which is secured over the indentation (22), in this case, or in the case of a
series of
indentations as shown in Figure 2A to 2C a complimentary number of shields
would be
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secured over the indentations. The pipe (20) is shown with the apertures
facing upwards in
Figures 7A and 7B. This is for the sake of clarity only and this pipe (20)
will be installed with
the apertures (19) facing downwards in the stack, similar to the other
embodiments
described above.
Figure 8 shows an end view of a purge pipe (23) with apertures (24) located in
the dry
shadow (25) of the pipe (23). As mentioned above, the size of the dry shadow
(25) depends
amongst other things on the diameter of the pipe (23), the hydraulic
conductivity of the
material within which the pipe is located, and the amount of liquid (26)
passed through the
stack. For given conditions in a stack there is a dry shadow (25). The size of
the dry shadow
(25) may vary with variations in the conditions of the heap, which means there
may be areas
at the boundary (27) of the dry shadow that do see solution from time to time.
To keep the
purge pipe (23) from flooding with liquid (26) through the apertures (24), the
apertures (24)
are located in the actual dry shadow (25) and not, for example, in the
boundary zone (27).
Figure 9 shows a side view of the pipe of Figure 8, in which the spaced apart
circumferential
indentations (28) or grooves are also shown.
Figure 10 shows a stacked particle bioreactor (30). The stacked particle
bioreactor (30)
includes a stack (31) of carbonaceous material, which is biologically treated
to produce
synfuels. The stack (31) is, in this embodiment, covered by means of a sheet
(32) to ensure
anaerobic conditions in the stack (31). Proximate the top surface of the stack
(31) there is
buried a network of irrigation emitters (33) which deliver irrigation solution
to the stack (31)
when required.
Located underneath the emitters (33) is a network of gas collectors (34) which
collect the gas
which rise through the stack (31). The collected gas is piped from the stack
(31) for further
processing or recycling.
At the bottom of the stack (31), buried in the drainage layer (35), is a
series of perforated
pipes (36) which form a drain. Liquid synfuel, which is produced in the stack
(31), drains
through the stack (31) to the drainage layer (36) where it is collected by the
perforated pipes
(36) and piped from the stack (31) for processing or recycling.
The construction of the stack (31) so far is similar to the constructions of
stacked particle
bioreactor as described in patent application US2006/0223154A1.
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The stack (31) also includes a network of gas distributors (37) according to
the invention,
which is buried in the stack (31) underneath the gas collector (34) and above
the drainage
layer (35). Each gas distributor (38) comprises a perforated pipe (39) as
described above
which extends through the stack (31). Gas, which may take the form of purge
gas or air, is
5 pumped, or in the case of air may also be allowed under atmospheric
pressure, into the gas
distributors (38). The gas exits the pipes (39) at their spaced apart
perforations and is
thereby distributed throughout the stack (31). The perforations on each pipe
(39) are
preferably equidistantly spaced apart. Also, the individual pipes (39) in the
network of pipes
are also preferably equidistantly spaced apart in the network of pipes. This
ensures a matrix
10 of evenly spaced perforations which evenly spreads the gas delivery through
the stack (31).
The location of the apertures in the bottom of each pipe (39) and in
particular in the dry
shadow of each pipe (39) ensures that liquid such as liquid synfuel draining
through the stack
(31) does not come into contact with the apertures which minimizes
precipitation in or around
the apertures. This reduces or minimizes the problems identified above.
It will be appreciated that the embodiments described above have been include
by way of
example only, and are not intended to limit the scope of the invention. It is
possible to alter
certain aspects of the embodiments within the scope of the invention.
It is for example possible for an aperture to face downwards even when it is
angled at about
just less than 45 from the vertical. If it was at 45 or more it would be
angled sideways. It is
possible to use a pipe with a single row of apertures which face downwards at
an angle just
less than 45 0 from the vertical.
