Note: Descriptions are shown in the official language in which they were submitted.
~2355~Z
Installation and process for separating the
constituents of a suspension
The present invention relates to installations
and processes for separating the constituents of a
suspension containing solids, some of which are denser
and others of which are less dense than one of the liquid
constituents of the suspension. The invention applies
very particularly to the recovery of the constituents of
sludges in vats, in particular sludges in hydrocarbon
storage tanks.
Centrifugal separators are known which are
capable of continuously separating one or two immiscible
liquid phases with continuous discharge of a solid phase.
These centrifugal separators, produced by the Applicant
Company under the name of DCS type bowls, essentially
comprise a rotating bowl and an internal conveyor
rotating at a differential speed relative to the bowl
of the machine. The conveyor makes it possible firstly
to raise the sediments continuously up to ejection
orifices while preventing any accumulation of solids
in the bowl, and secondly to unclog the ejection nozzles,
which limits the likelihood of a blockage.
It has been shown that suspensions which are
difficult to separate can be separated into their solid
and liquid constituents using these centrifugal separators.
These separators are based on the centrifugation principle,
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whereby the constituents are separated according to their
specific gravity or density. The design of these centric
frugal separators supposes that the solid constituents are
denser than the liquid constituents to be separated off.
S However, if the suspension contains solids which are less
dense than the liquid constituents, as is the case, in
particular, of sludges in storage -tanks for petroleum
products, the centrifugal separator cannot be used without
risking serious operating problems.
The invention overcomes this disadvantage by
associating with the centrifugal separator a filter of
the particular type which is capable not only of removing
a large part of the solids, irrespective of their specific
gravity, and hence of relieving the centrifugal separator
of a corresponding burden, but especially of separating
off the solids which are less dense than the liquid
constituents of the suspension, so that the filtrate from
the filter can safely be sent directly to the centrifugal
separator.
In accordance with an aspect of the invention
there is provided installation for separating the
constituents of a suspension, in particular sludges in
hydrocarbon storage tanks, comprising a centrifugal
separator and upstream of the centrifugal separator a
self-cleaning filter with an envelope having an inlet for
the suspension and an outlet for the sediments, a filtering
surface delimiting with the inner wall of the envelope a
chamber for the filtrate which is provided with an outlet
for the filtrate, and brush means which are caused to
rotate relative to the axis of the filtering surface,
wherein the installation is mounted on a vehicle and an
intermediate heater is inserted between the self-cleaning
filter and the centrifugal separator and there is provided
a boiler for feeding the heater with steam mounted on a
separate vehicle.
In this self-cleaning filter, the envelope of
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which is generally essentially a body of revolution having
a vertical axis, with an outlet for the sediments provided
at the bottom of the envelope, the very dense solids
present in the suspension brought to the top of the
envelope fall gradually into the envelope until they form
a solid plug in front of the outlet for the sediments. The
solids which are less dense than the liquid constituents
of the suspension tend to clog the filtering surface, but
are unclogged by the unclogging means, which include, in
particular, brushes which are caused to rotate relative to
the axis of the filtering surface, which is coaxial with
the envelope. These solid products which are less dense
than the liquid constituents of the suspension thus also
comes into the plug, which is discharged from time to time
through the outlet for the sediments.
An intermediate heater is inserted between the
self-cleaning filter and the centrifugal separator so as
to heat the products entering the centrifugal separator
and to assist the operation of the latter.
Preferably, the whole of this installation is
mounted on a vehicle which can therefore be brought in
front of each storage tank to be cleaned, it being possible
to reject the sediments and the water directly and to
recover the petroleum products, these being the only con-
stituents which will have to be transported. The boiler
for feeding the heater with steam is advantageously mounted
on a separate vehicle, it being possible for the boiler to
be used for feeding other installations as well, and, in
particular, a primary separator with a heater, also mounted
on a separate vehicle and connected directly to the storage
tank. To clean the storage tank, hot water is sent to
the bottom, it being possible for the hot water to come
from the boiler, so as to make the solid sludges present
at the bottom of the tank capable of being pumped. A pump
is then used to pump them into the separator, or they are
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heated with steam coming from the boiler so as to be able
to carry out a first separation of the organic products
and the water, and the organic products, still containing
large amounts of water and solid products, which may be
inorganic, are then sent to the self-cleaning filter via
pumps and, preferably, a buffer tank.
In the attached drawings, which are given solely
by way of example:
Figure 1 is a diagram of an installation according
to the invention,
Figure 2 is a diagram of the self-cleaning filter
of the installation, and
Figure 3 is a diagram of the centrifugal separator
of the installation according to the invention.
The installation shown in Figure 1 is connected
to a storage tank R for petroleum products. The install-
lion comprises a first vehicle 1 carrying a hot water and
steam generator, or boiler, 2 with an electricity generating
unit 3. This generator 2 can be connected by a line 4 to
an inlet of the storage tank R, which comes out at the
bottom of the latter into the sludges. A line 5, with a
valve 6 and a pump 7, leaves the bottom of the storage
tank R and comes out half-way up a preliminary separating
vat or tank 8 carried by a vehicle 9. The tank 8 is heated
by a steam circuit 10 coming from the generator 2. The
bottom of the tank 8 has an outlet 11 for water. A line
12, with a pump 13, leaves the tank 8 near the top and
comes out, via a flexible line 14, into a buffer tank 15
carried by a third vehicle 16. This vehicle also carries
the remainder of the installation. A line 17, with a
pump 18, leaves the bottom of the buffer tank 15 and
communicates with the inlet for the suspension of a self-
cleaning filter 19. The outlet for the sediments of the
self-cleaning filter 19 communicates, via a line 20, with
a line 21 for rejecting the sediments. The outlet for
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the filtrate of the self-cleaning filter 19 communicates
with a line 22, which feeds an intermediate heater 23
heated by a steam circuit aye coming from the generator 2.
The heater 23 communicates via a line 24 with a centrifugal
separator 25 having an outlet for the sediments, which
communicates with a line 26 joining the line 21, an outlet
for the densest liquid constituent, which communicates
with a line 27, and an outlet for the less dense liquid
constituent, which communicates with a line 29 provided
with a pump 30.
Figure 2 is a more detailed diagram of the self-
cleaning filter 19. In essence, this filter comprises
an envelope 31 which is substantially a body of revolution
about a vertical axis, and the bottom of which assumes the
shape of a funnel 32 with an outlet 33 for the sediments.
The envelope is provided at the top with an inlet 34 for
the suspension to be filtered. An annular filtering sun-
face 35 is fixed along the inner cylindrical wall of the
envelope 31, delimiting, with the latter, a closed annular
chamber 36 for the filtrate. The chamber 36 is provided
with an outlet 37 passing through the envelope 31. The
shaft 38 of a gear motor 39 runs along the vertical axis
of the filter and carries a set of brushes inclined to
the horizontal. These brushes are caused to rotate and
rub against the filtering surface 35 to unclog it.
This self-cleaning filter operates as follows:
The suspension enters through the inlet 34. The
densest solid constituents gradually fall of their own
accord, under gravity, to the bottom and collect in the
funnel 32 in front of the outlet 33, since they cannot
pass through the filtering surface 35. The least dense
solid constituents are carried towards the filtering
surface 35 and would tend to remain there and clog it if
they were not pushed downwards by the brushes 40, with the
result that they also agglomerate at the plug of solids
which gradually forms in front of the outlet 33. The
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liquid constituents, together with very fine solid con-
stituents, for example those having a particle size of
less than 400 microns, pass through the filtering surface
35, arrive in the chamber 36 for the filtrate and leave
through the outlet 37. From time to time, the outlet 33
is opened in order to release the agglomerate of solids
which accumulate in the funnel 32. This filter is thus
capable of operating continuously, since it is self-
cleaning and has the noteworthy characteristic that, desk
pile operating continuously, it also removes the solid constituents of the suspension which are less dens than
the liquid constituents thereof.
Figure 3 is a diagram of the centrifugal separator
25. This separator, which operates continuously, includes
a central inlet 41 for the suspension entering a bowl 42
rotating at a different speed from that of an internal
conveyor 43 located at the periphery of the bowl, near
the envelope 45 of the whole of the centrifugal separator.
Under the effect of the centrifugal force, the densest
solid fines are immediately thrown onto the conveyor 43
and leave through ejection orifices 46, while the two
liquid constituents to be separated separate in the stack
of inclined plates inside the bowl, according to their
specific gravity, an outlet 47 being provided for the
densest liquid phase, which is rejected at the periphery
and which pushes inwards the less dense liquid constituent,
for which an outlet 48 is provided.
The installation operates as follows:
Hot water is sent through the line 4 into the
bottom of the storage tanks for petroleum products. This
hot water brings the sludges into suspension so as to lower
the viscosity of the whole sufficiently for it to be pumped
by the pump 7 into the separating vat 8. In the vat, the
suspension of sludges and hot water is heated by steam
coming from the generator 2 and brought by the line 10,
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so as to assist the separation. Water is rejected through
the line 12 while the remainder of the suspension, which
still contains water, hydrocarbon products and solid semi-
mints, both those which are less dense and those which are
denser than the liquid constituents, is sent to the buffer
tank 15 via the pump 13 and the line 14. From the buffer
tank 15, the suspension is sent into the self-cleaning
filter 19 via the pump 18 and the line 17. The greater
part of the solid products, and especially those which are
less dense than the liquid constituents of the suspension,
are discharged to the outside via the line 20 and the line
21, while the liquid constituents and the very fine solid
products pass into the intermediate heater 23, which heats
them so as to assist the action of the centrifugal swooper-
ion 25, to which the suspension is brought via the line connected to the feed 41 of the separator. The solid con-
stituents are separated off in the separator and leave via
the orifices 46, which communicate with the line 26 leading
to the line 21. The water, which is denser than the
petroleum products, leaves through the outlet 41, which
communicates with the line 27, and, if appropriate, can be
returned to the hot water and steam generator 2. The out-
let 48 is connected to the line 29, through which valuable
petroleum products are recovered.
The installation can operate continuously, can be
mowed so as to be brought up to a vat to be cleaned, and
makes it possible to transport only the petroleum product
recovered, without having to wait for this product to be
separated from the water in separating vats.
