Note: Descriptions are shown in the official language in which they were submitted.
1 ~'7~ 3
This invention relates to the transport of a
slurry through a pipeline, and more particularly to the
pumping of a slurry which, in the interests of efficiency,
is as close as possible to saturated concentration.
In presently known systems for the transport of
particulate materials, such as comminuted coal, various
- extensions of the well-known 'IBechtel'' technology are employed,
and for these systems to succeed it is essential that suff-
icient fines should be provided to support the movement of
larger particles along pipelines through which the coal is
pumped. Thus, for most export requirements, it is necessaxy
for such coals to undergo "manufacturing" to produce a
suitable product, and then further processing, usually to
reject the carrying medium, and/or dumping and re-processing
for use in either coke ovens or thermal power stations. In
this connection, existing pipelines usually require coal to
be ground to less than 14 mesh, and in most coals a suff-
icient quantity of fines of the order of -325 mesh in excess
of 20% is ensured to give a suitable slurry capable of being
handled by available pumps and technology.
It is an object of the present invention to
eliminate completely all such "manufacturing" or "processing"
of the starting material, which can therefore be delivered
ta a site for pipeline transport in the same condition in
which it happens to exist as a result of the mining and
wash-rig procedure to which it has already been subjected.
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It is a further object of the invention to permit the
handling of both steaming and coking coals, meeting t~e
requlrements o~current export standards, with a minimum
water content and power requirement for transport. That
is to say, it is desirable that the size distribution of
solids is controlled so that voids (and hence the water
content of a slurry~ are a minimum.
According to the invention therefore, in one of
its aspects, a material transport system comprises, in
lD ~mbination, means for effecting the controlled distribution
of a particulate solid-liquid matrix, and means for urging
said matrix by positive displacement through a constraining
conduit so that no degradation of the particles of said
matrix occurs during transit thereof.
Apparatus constructed in accordance with various
embodiments of the invention as defined in the preceding
paragraph is based upon the concept that the optimum flow
properties of the matrix can be attained by adjusting the
size distribution of the solids therein to give the greatest
packing density. This distribution can be controlled to
give a "fluidity" to the matrix which allows the transport
of minerals generally at the highest possible concentration.
Any such increase in concentration above the
loose packing state reduces the relative mobility of the
particles and results in a rapid rise in pressure drop,until
at close packing the solid particles move as a plug with a
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:
resulting final reduction in pressure drop. If it can
be ensured that adequate slip occurs at the wall of a
~ipe, then the material moving therein is flowing as a
~lug, with no shear within the slurry itself. In this
cas~the velocity defining the-shear rate at the wall is
- identical with the mean slurry velocity. Hence, provided
that a layer of liquid at the wall has a sufficient
thickness maintained by the material properties, then the
shear rate at the wall is dependent only upon the slurry
velocity itself and not upon the ratio of velocity to
density as it is for other non-Newtonian liquids.
In tests leading to the prese~t invention it has
been found that, ~f a pipeline pump handles the material
at a controll~d packing density whereby the sizing
distribution gives a dry weight of approximately 70% for
steaming or coking coal, the requirements for the most
economical means of slurry transport are met.
To ensure the necessary "wall slip" condition
throughout the pipeline, the fluid sealing means of the
pistons and valve plates of said pump provides the film for
both the pump cylinders and the pipe wall and this, coupied
~ith the application of pressure by the piston to the core
of the material, ~aintains the necessary wall slip condition.
In a modification of the invention, suitable for
slurry transport through pipelines for short distances such
as those likely to exist between a stock-pile and a pulveriser,
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~ 3
or for the hydraulic loading of vessels either at dockside
or off-shore, it is possible to handle the material with
less than the ~sual amount of moisture in the voids, and
to depend only on said wall slip fluid to maintain the
flow without shear within the material itself.
It will be seen that the invention ensures that,
because the slurry contains particles of normal size
without any attempt to manufacture special sizes, the usual
particle size versus settling velocity parameters do not
apply, and hence any sized particulate solids may be
;~ transported sa~isfactorily at low velocities because the
only force to be overcome to move the slurry in the pipeline
is the force necessary to shear the water film, once it is
ensured that the slurry is capable of moving as a unitary plug.
The pump is preferably of a positive displacement
kind which moves material smoothly and provides a pulse-
free discharge without the use of cushion chambers. The
concentration at which particulate solids can be handled
is thus limited only by the facilities available to feed
these solids to the pump. If desired, thelsolids may even
be fed dry into the pump, and discharged with only the
flushing fluid which has leaked past the pistons and valve
plate.
It is emphasised that a major advantage of the
invention resides in the fact that the plug of material
not only moves bodily to give an economical delivery rate
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while shearing only the wall slip fluid, but also the
absence of shearing forces within the plug itself obviates
any grinding action mutually between the paticles in the
plug. Hence any degradation of those particles during
transit is prevented, even throughout the distance from
entrance to exit in a pipeline of substantial length.
One particular embodiment of the invention will
now be described here~n with reference to the accompanying
drawings, in which:-
.
Figure l is an explanatory diagram showing the
force to be overcome before flow can commence in a pipe,
Figure 2 illustrates the so-called "Magnus Effect"
in a pipe as velocity increases,
Figure 3 is an explanatory diagram showing how
"wall slip" fluid affects energy requirements in a pipe,
Figure 4 is a schematic view of an arrangement
for using pump sealing fluid as "wall slip" fluid, and
- Figure S shows schematically the use of an auger
or screw on the suction side of a pump.
Upon referring now to the drawings it will be
appreciated that there are four distinct regimes of particle
~on~eyance within a structure such as the pipe 1.
The flow characteristics are:-
(1) Conveyance as a heterogeneous æuspension, which
is maintained by turbulence in a liquid such as water.
(2) Conveyance by saltation, the particles being
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11'7(~33
alternately picked up by a liquid and deposited further
along the pipe.
(3) Conveyance as a sliding bed.
(All the above systems are unsuitable for long
distance transportl;
(4) Homogenous suspension flow which has both
laminar and turbulent flow coexisting. (This system is used
in the present invention and is known as "plug" flow, the film
of liquid 2 near the pipe wall being in turbulent flow and
the laminar section forming the "plug" 3 in the middle of the
pipe).
This last-mentioned type of flow is more efficient
than water turbulent flow. The reduction of the pipe friction
loss of water suspensions in the plug, below that of clear
water, results from the elimination of the loss due to
turbulence within the plug.
When the force applied to a pipe cross-section is
lower than the yield point, the mixture is elastically compressed
and water is squeezed out to the periphery of the plug, in much
the same manner as would occur in a compressed wet sponge.
For this accepted concept it is essential that the
transported material has a fluidity insofar that it will be
oompressable as a "sponge" to provide fluid on the periphery.
This requires the application of an initial force to establish
this condition before flow takes place, as shown in Figure 1.
As the "Magnus Effect" manifests itself the particles
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move towards the centre of the pipe 1 as the velocity of
the transported material increases. The core is thus under
pressure and the fluid moves towards the periphery and is
maintained there by virtue of the flow velocity.
A further development of this concept is the
provision of a means for ensuring a tightly packed core 5
of material surrounded by a film of "wall slip" fluid 6
which ensures a minimum resistance to flow whilst conveying
the maximum quantity of material for a minimum expenditure
of energy, as shown in Figure 3.
An arrangement whereby pump sealing provides "wall
slip" fluid is shown in F~gure ~, where the piston 7 intro-
duces sealing fluid at 8, 9 and 14.
Where the transported material is such that it
requires considerable force to pack it into the form of
a tight core plug,such as 10, then an auger type press or
screw 11 may be used on the suction side of the pump, with
water entry injectors at 12, 13 to provide the lubrication
fluid in addition to the pump sealing fluid, as shown in
Figure 5.
When a pipe line has been stopped for any period'
of time, there will be a tendency for the core to settle to
the bottom^'segment of a pipe, in much the same manner as a
shaft in a bearing. Provided there is no relief of pressure
in the line, then, with the provision of a factor of 1.5
times the working pressure for start up pressure, flow will
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be re-established as the velocity increases, (with no
relative displacement of particles).
When pressure has been relieved, then it will be
re-started on the normal "plug" flow basis, utilising the
1.5 factor for pressure supply to establish flow.
The thickness of the "wall slip" fluid will be
a function of distance pumped. For short distances it will
be a minimum, and for long distances additional fluid may
be required.
Clearly, the invention lends itself to a humber
of different applications, for example:-
Coal Siz-ing
Characteristics of structure andhardnessinherent
in the coal beds are initially responsible for influencing
the percentages of sizes produced. Depending on the coal
str~ture and crushing or other degradation process or
processes during preparation, there will result a product
having a mixture of several slightly different size distrib-
ution patterns approaching the maximum packing density.
The breaking of coal is not a haphazard event in
the sense that the distribution of sizes produced is entirely
unpredictable.
If desired, the crush~ng of the coal may be controlled
so that the product offered for transport has a size distrib-
ution giving the maximum packing density consistent with the
topsize meeting the market restraints and a minimum generation
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of fines in the processing required to meet these
conditions. The fines referred to are sized above the
washery reject sizing and no other carrier is required.
It is desirable for the particle size distribution
to be such that the voidage of the resultant product is a
minimum, and should approach the theoretical minimum voidage
2 to 3% by volume.
Coal Conversion
Coal conversion is performed by injecting it with
hydrogen in a reactor, at temperatures ranging from 550 to
2,000F at pressures of 1 to 150 atmospheres.
Coal can be converted to oil or gas because these
substances all contain hydrocarbons, and this is done by
altering the hydrogen/carbon ratio of the coal, using one
of the following processes:-
(a) Hydrogen can be added to the coal.
~b) Carbon can be taken from the coal.
(c) Coal can be broken down into individual carbon
atoms and rebuilt.
Most of the presently known methods are based on the
addition of hydrogen - which is'the direct "liquefaction" '
process.
Typical resultant products are known as:-
(d) Solvent Refined Coal (SRC).
(e) Exxon Donor Solvent (EDS) (produced by solvent).
(f) H-Coal produced by adding hydrogen directly.
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In the EDS process, coal is liquefied in a
reactor at 850F and a pressure of 100 to 150 atmospheres.
The hydrogen is~supplied by both a donor solvent and in a
gaseous form. The donor solvent is a coal liquid derived
from the process, which is upgraded in hydrogen content in
a separate catalytic reactor. The yield is 2.5 barrels of
oil per ton of coal. The H-Coal process adds hydrogen to
a coal slurry. A catalyst is used to speed the chemical
xeaction of the gaseous hydrogen with coal in the liquefaction
vessel operating at 650F.
Oil shale is actually rock containing an organic
material called kerogen~ When heated at 900F the kerogen
vaporises and is liberated from the rock, and recombines
into liquids and some gas.
One problem with shale oil production is what to
do with the spent shale, which increases in size by about
20% after it goes through the retorting process. Thus, an
operation producing 100,000 barrels a day of oil would have
to dispose of 200,000 tonnes of shale rock daily!
As part of most coal conversion processes, for
example, coal must be pumped into the pressurised and heated
reactors. Special pumps are needed to do this injecting.
Aftex this mixture passes through the reactor, some
of it is recycled. Again pumps are required. The present
invention, used in conjunction with the pump which is the
subject of m~ Australian Patent No. 461,204, is particularly
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suitable for coal and shale conversions. The pump is also
suitable for all three gasification processes - fixed bed,
fluidised bed, and entrained bed gasification. The pump
can maintain pressure in the feed system while coal or shale
is fed steadily into thé reactors to form a "seal" against
gas back pressure. This eliminates the necessity to bleed
off the gases in the feed system with resulting loss of
energy, which is typical of the current lock-hopper feed
system.
The invention is also suitable for the feeding of
pressurised fluidised bed steam generators and reactors.
The above-mentioned pump is capable of handling any combination
of feedstock, either as a single product or in any combination
required for controi and operation of the bed.
It is also capable of-delivering the product at a
variable delivery rate from zero to full predetermined capacity
so that the bed is under automatic control by-thiæ single
unit, thus reducing the control costs and complexity in
comparison with existing PFBC units.
All the moisture in the fuel must be heated from
atmospheric temperature (or from the temperature of the fuel
if this is above that of the atmosphere) to the temperature
~t which steam is formed, depending on the working pressure
of the combustor. The steam so formed must be heated to the
temperature of the furnace gases.
Perfect regulation is seldom attained in practice,
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and in order to ensure that at least sufficient air is
everywhere present to ensure complete combustion, it is
desirable to provide an average excess over the quantity
theoretically necessary.
The excess mixes with and dilutes the products
of combustion, lowering their average temperature and thus
reducing the rate at which they will transmit heat. It is
thus advisable to reduce the quantity of excess air to the
lowest amount which will enable combustion to be just
lD completed.
