Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ a~s~ K 9300 CAN
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PROC~SS AND APPARATUS FOR TREATING LIQUID SULPHUR
The invention relates to a process for treating liquid
sulphur for removing solid contaminants, mainly in the form of
solids, from the liquid sulphur. The invention also relates to
an apparatus for use in such a process.
It is well known to produce sulphur in the solid state by
causing liquid sulphur to flow through small orifices or
nozzles to form drops of sulphur which are subsequently
cooled, for example by allowing the drops to fall down a
tower, to give solid spheres or prills of the sulphur. Solid
sulphur in the particulate form is used in large quantities in
a great variety of industries, such as the fertilizer-, the
insecticide- and fungicide-, the rubber- and the metallurgical
industry. Liquid sulphur is obtained in large quantities,
either directly from mining operations, or from other sources
such as sour natural gas, refinery gas and sulphide-
containing ores, such as pyrites.
Depending on the source for obtaining liquid sulphur,
minor or larger amounts of contaminants may be present in the
liquid sulphur. Such solid contaminants should be removed from
the liquid sulphur prior to converting the liquid sulphur into
solid sulphur in the above-described manner, in order to avoid
clogging of the orifices or nozzles used in the conversion
process and prevent contamination of the formed solid sulphur.
In French patent specification 1,183,691 a process and an
apparatus are described for removing solid contaminants from
liquid sulphur. In this kno~m process liquid sulphur is passed
through a layer of filter material held between two perforated
walls. After a certain period the solid contaminants in the
supplied liquid sulphur will have formed a layer on top of the
perforated wall through which the liquid sulphur is supplied
to the filter material. According to the above publication
these contaminants are subsequently removed by passing a
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vapour stream along said perforated wall. A disadvantage of
this cleaning method is that solid contaminants which have
entered the layer of filter material cannot be removed.
Further it will be difficult to remove solid contaminants
which have entered the openings in the perforated walls when
using the cleaning method proposed in the above publication.
The object of the present invention is to provide a
process and an apparatus for treating liquid sulphur to remove
contaminants therefrom, allowing a more intensive cleaning of
the apparatus, without the necessity of replacement and
dismantling of the applied apparatus.
The process for treating liquid sulphur thereto comprises
according to the invention introducing liquid sulphur into a
vessel interiorly provided with a filter element, causing the
liquid sulphur to flow in a first direction through the filter
element to remove contaminants from the liquid sulphur, and
separately withdrawing the filtered liquid sulphur and the
contaminants from the vessel, wherein the filter element is
intermittently cleaned by introducing a cleaning fluid into
the vessel and causing the cleaning fluid to flow through the
filter element in a second direction opposite to the first
direction, and withdrawing the cleaning fluid with
contaminants from the vessel.
The apparatus for use in the above process for treating
liquid sulphur, comprises, according to the invention, an
elongated vessel provided with a separating chamber, inlet
means for introducing liquid sulphur to be treated into the
separating chamber, outlet means for separately withdrawing
treated liquid sulphur and contaminants from the separating
chamber, the separating chamber being provided wlth a
substantially cylindrically shaped filter element, the vessel
being further provided with inlet means for introducing a
cleaning fluid into the separating space and outlet means for
withdrawing the cleaning fluid and contaminants from the
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separating space, the inlet means for the cleaning fluid being
formed of an elongated tubular elenlent provided with openings,
at least partly arranged within the filter element, the inlet
means for liquid sulphur and the inlet ~eans for cleaning
fluid being arranged at opposite sides of the filter element.
The invention will now be described in more detail by way
of example only with reference to the accompanying drawing
showing a vertical section of a liquid sulphur treating
apparatus according to the invention.
The drawing shows an elongated, vertically extending
cylindrically shaped vessel 1 closed at its upper end by a
cover plate 2. The vessel 1 is provided with an inner wall 3
and an outer wall 4 arranged at some distance from one another
to form an insulating space 5. For heating purposes a heating
fluid such as steam may be circulated through the space 5. For
circulating the heating fluid an inlet 6 and an outlet 7 are
arranged in the outer wall 4. The interior of the vessel 1 is
provided with an elongated, cylindrically shaped filter
element 8 arranged in a separating space 9 of the vessel 1. A
suitable embodiment of the filter element 8 is a wire wound
stainless steel cartridge. The lower end of the filter element
is closed by a closure plate 10 supported in radial outward
direction by a support ring 11. The upper end of the filter
element 8 is provided with a flange 12 bolted to a flange 13
attached to the inner wall 3. The above-mentioned separating
space 9 is bounded in upward direction by the flange
construction 12-13, in downward direction by the closure plate
10 and in lateral outward direction by part of the inner wall 3.
The vessel 1 is further provided w~th an inlet 14 for
introducing liquid sulphur 1nto the vessel and outlets 15 and
16 for separately withdrawing filtered liquid sulphur and
contaminants, respectively, from the vessel. For cleaning the
filter element 8, the vessel 1 is provided with an elongated
coaxially arranged tubular element 17, hereinafter also called
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steam lance, passing through an opening in the cover plate 2
and having its lower part extending within the filter element
8. The part of the steam lance 17 arranged within the filter
element 8 is formed from a plurality of wound wires defining
openings 18. The steam lance 17 is provided with an open upper
end and is mounted onto the vessel 1 by means of a flange l9
arranged on top of a flange 20, connected to the vessel l by
means of tubular elements 21 and 22. The space between the
tubular elements 21 and 22 is provided with an inlet 23 and an
outlet 24 for circulating a heating fluid therethrough.
The operation of the apparatus described in the above is
as follows. Liquid sulphur to be filtered is introduced into
the vessel l via inlet 14. The liquid level in the vessel l
rises, so that after a while liquid sulphur reaches the
IS separating space 9 via the passage between the inner wall 3
and the periphery of the closure plate 10. Once arrived in the
separating space 9 the liquid sulphur will pass through the
openings of the filter element 3. The dimensions of the
openings in the filter element 8 are so chosen that the major
20 part of the solid contaminants in the liquid sulphur cannot
enter the filter element. The level of the filtered liquid
sulphur collected in the filter element 8 rises upon further
introduction of liquid sulphur into the vessel l until the
filtered liquid sulphur reaches the outlet 15, where it is
25 withdrawn from the vessel.
To keep the sulphur in the vessel in the liquid state, the
temperature in the vessel is maintained above the solidifi-
cation point of sulphur by circulating steam introduced via
inlet 6 through the insulating space 5 between the inner wall 3
and the outer wall 4. The steam or formed condensate is
subsequently withdrawn from the insulating space 5 via the
outlet 7. During the filtration of liquid sulphur the steam
lance 17 is closed off by means of a not shown valve.
Part of the contaminants separated from the liquid
35 sulphur upon passing through the filter element 8 may remain
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in suspension in space 9 or may descend through the liquid
sulphur and be collected in the bottom part of the vessel 1.
The rest of the separated contaminants will be deposited on
the outer side of the filter element 8, thereby causing a
gradual increase of the pressure drop over the filter element
during the filtering operation~
When the pressure drop over the filter element has
reached a certain value, or in other words when the effectiv -
ness of the filter element has fallen to a certain value, the
I0 filter element 8 should be cleaned. The introduction of liquid
sulphur into the vessel 1 is subsequently stopped, for example
by bringing a not shown valve, in the inlet 14 into its closed
position. The outlet 16, remaining in a closed position during
the filtration, is opened and the liquid sulphur still in the
vessel ls withdrawn together with the contaminants accumulated
in separating space 9 and deposited Oll the bottom part of the
vessel. The outlet 15 for the filtered liquid sulphur is
closed off. Subsequently the steam lance/ 17 is connected to not
shown steam supply means and steam under pressure is passed
through the steam lance. Rapid expansion of the steam to the
actual pressure inside the vessel upon passing through the
openings 18 generate high velocity steam jets against the
inner surface of the filter element 8. Contaminants deposited
during the filtration onto the outer surface of the filter
element 8 are removed therefrom and entrained by the generated
steam jets passing through the filter element. Steam and
entrained contaminants are withdrawn from the vessel via the
outlet 16 in the bottom part of the vessel. After cleaning the
filter element 8, the outlet 16 is closed and the steam lance
17 is shut off, wherea~ter the filtration of liquid sulphur is
restarted by opening inlet 14 and outlet 15.
For replacement or maintenance, the filter element 8 can
be easily removed from the vessel 1 by removing the cover
plate 2, retracting the steam lance 17 and disconnecting the
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flange connection at the upper end of the filter element. The
filter element may be cleaned by high pressure water jets or
sandblasting to remove bituminous matter therefrom and
re-assembled in the vessel or may be replaced by a clean
filter element.
Liquid sulphur filtered in the vessel 1 may be passed
into a further vessel provided with a filter element with
smaller openings than filter element 8 to remove small solid
contaminants passed through said filter element ~. After the
liquid sulphur has been sufficiently freed from contaminants
the liquid sulphur may be subjected to a solid sulphur forming
process by introducing the liquid sulphur into a vessel
provided with known prilling means such as orifices, spray-
holes or nozzles to form solids of sulphur. To prevent blockage
of the prilling means due to deposition of bituminous matter
in the liquid sulphur, the prilling means may be suitably
provided with a coating of for example teflon, known per se.
It should be noted that the invention is not restricted
to the application of a steam lance formed from wound wires.
20 Alternatively, the steam lance may for example consist of a
tube with discrete openings in its wall. In this case it is
preferred to rotate the steam lance during cleaning~ to supply
a uniform spray onto the whole surface area of the filter
element 8.
