Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
11~7~3
The invention relates to a process for the preparation
of dry soot from a suspenslon of soot particles in water~ A
suspension of soot particles in water is obtained for example
when washing gases ori~inat;ng from a process ~or the preparation
of gas by partial combustion of a carbon-containing feed. A
carbon-containing feed may be a mineral oil or a fracti~on there-
of, varying from methane to a heavy asphalt. It also includes
coal or a suspension of coal fines in a liquid oil or oil
fraction.
lQ The crude product gas contains very fine soot, the
quantity of which is dependent on various- factors such as compo-
sition of t~e feed, the fuel-oxygen ratio during t~e com~ustion,
temperature, pressure. A frequently occurring soot content of
the gas is 2-4%w. The soot can be removed from the gas by wash-
~;~ ing with water, which yi~elds an aqueous suspension of soot part-
icles The soot content of this suspension is 0.5~1.5%w. It
is in general necessaxy to work up th~s suspensi~on to soot-free
water. A convent~onal and effectlve method of do~ng this is to
bring the suspension to turbulence in an agglomeration zone
with addition of a liquid light hydrocar~on or mixture of
hydrocarbons. The soot particles will then agglomerate to
form lumps some mi~llimetres in dLameter which can be separated
from the water. Conventional methods here are the use of a
settling vesselr a vibrating screen or a sieve plate~
It has now-been found that when applied on a large
scale it is precisely this separation of liquid and agglomerates
that causes dif~iculties arising mainly from transport problems
and the invention indicates ho~ this pro~lem can be solved.
According to the present inventi~on there is provided a
process for the preparation of dry soot from a suspension with a
soot content of from 0 5 to 1.5%w of soot particles in water as
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obtained when washing gases originating from a process for the
preparation of gas ~y partial combustion of a carbon-containing
feed, the suspension being hrought to turbulence in an agglomer-
ation zone with addition of a liquid light hydrocarbon or mix-
ture of hydrocarbons, characterized in that the mixture of
liquid and agglomerates leaving the agglomeration zone is passed
through the drum of a rotary sieve, in which sieve drum the
mixture is filtered, the agglomerates leaving the sieve drum
having a water content of from 4-5~w and a light hydrocarbon(s)
a content of from 3ao-800%w-, and the agglomerates are de-watered
~hile being transported to the outlet of the drum, after which
the light hydrocarbon(s~ ;~s (are) recovered by evaporation and
condensation.
According to the invention the mixture of liquid and
; agglomerates leaving the agglomeration zone is passed through
the drum of a rotary s~eve, in which sieve drum the mixture is
fi~ltered and the agglomerates are de-watered while being trans-
ported to the outlet of the drum, after which the light hydro-
- carbon(s~ is ~are) recovered from the agglomerates by evaporation 2Q and condensation.
The mixture of l~quid - as a rule water - and agglomer-
ates should be handled w~th particular care. Agglomerates of
soot particles with ligHt hydrocarbons as the binder, for in-
stance naphtha or gasoline, are not strong. If agglomerates
should already disintegrate during the separation of agglomer-
ates and liquid, no clean liquid
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i~ obtained. Agglomeration with a light hydrocarbon or a mixture
of light hydrocsrbons is attractive, because the relatively expensive
binder can ea~ily be recovered and recirculated. The a~glomerates
are passed through the drum by the rotation of the sieve. This
can be done with a helical ribbon that is perpendicular to the
sieve wall, A slight inclination of the drum, combined with the
rotation, may likewise effect transportation of the agglomerates
through the drum. It has been found that no trsnsport difficultics
occur in the sieve drum, irrespective of the residence time of
the agglomerates~ There is no attrition and no agglomeration.
It has further been found that the water content of the agglomerates
leaving the sieve drum is very low, viz. 4-5 %w. Sur~risingly,
this water content even proves to be the theoreticsl minimum. The
a~glomerates in question have dimensions Or a few millimetresO
They come from an aqueous medium and because of their small d;mensions
much water adheres to the surface snd i5 present in the voids between
the agglomeratesO Filtration, also in this rotary sieve, occurs
as a result of gravity. For, the rotational speed Or the sieve
i~ very low~ 5-10 rev/min, With conventional separation methods
much water still adheres to and is held between the agglomerates.
In the rotary sieve the agglomerates are constantly tumbling one
over another. Every droplet of water gets a chsnce of contacting
the sie~e surface and thus being removedO This means that all the
adhering and enclosed water is removedO Only the water trapped
within the agglomerste~ fails to be removed in the rotary sieve.
Another important advantage of the process according to the
invention is thst it is technically no problem to enclose the rotary
sieve drum ~ithin an impervious, stationary wall, permitting operat;on
under pressure. This is important because sgglomeration is usually
carried out under pressure. As a rule, the soot suspension introduced
has a temperature upwards Or 10GCo There can then be sn open connection
from the scrubbine tower ~or the crude product gas to the agglomeration
zone and to the sieve drum, ~hich is a great advantage. For, it
is technically a complicated matter to pass dispersions with larger
particles through locks.
Finally, it has been found that the process according to the
invention can be carried out in continuous operation on any scale.
Apart from the aforementioned small quantity of water, the soot
agglomerates obtained in this way still contain the light hydrocarbon(s).
This quantity may be 300-~00 %w calculated on soot. It can be expelled
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by hc;ltillg alld be recoverecl by condellsation. This is preferably done by
bringing the agglomerates leaving tlle sieve drum to a fluidized state with
superlleated vapour o~ hydrocarbon~s) as used for the agglomeration as the
fluidizillg gas, after which the vapour rising from the fluidized bed is con-
densed. This process can be carried out in a vessel in which the same pres-
sure prevails as in the sieve drum. The use of vapour of ligllt hydrocarbon-
(s), for instance naphtha vapour, has the great advantage that the liquid or-
ganic product obtained by condensation can be used again for the agglomeration
and fluidization without any intermediate step. During the fluidization water
that was trapped in the agglomerates will also be removed, which water will
segregate from the hydrocarbon(s) after condensation. Obviously, also another
gas such as nitrogen may be used as the fluidizing gas. The agglomerates re-
main intact.
The agglomerates obtained in this way consist almost entirely of
soot and can be used for many purposes. As an example its use as an absorbent
may be mentioned here.
Theprocess according to the invention further creates the possibil-
ity of introducing the agglomerates leaving the sieve drum by means of a pump
into the feed for the process for the preparation of gas by partial combustion.
As a rule, this feed has a temperature upwards of 100C to have a viscosity
low enough to permit pumping and atomization in the burner. When under these
conditions water-containing soot is added, foaming will occur due to escaping
water vapour. It has now been found that the soot as obtained from the sieve
drum has already such a low water content that no foaming occurs. The binder
~ - light hydrocarbon(s) - can be removed from the fuel by flash evaporation and
; be recovered by condensation. A suitable pump for the introduction into the
fuel is an extrusion pump. This pump can introduce the agglomerates straight-
away into the hot and pressurized fuel, while at the same time the agglomer-
ates are ground. If desired, the agglomerates leaving the sieve drum can
first be incorporated into hydrocarbon(s) as used for the agglomeration, and
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tl~cn be pullll)ed illtO tlle fuel. It w:ill then be possib:le to use, for instance,
a sliding vanc pu~p. A disudvalltage is that more hydrocarbon(s) has(have)
to be recovered.
As a rule, the agglomerates will be transported from the agglomer-
ation zone to the sieve drum by a stream of water. However, it is also pos-
sible to pass the mixture of water and agglomerates after leaving the
agglomeration zone to a separator containing a bottom layer
,
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Or water and a top layer Or liquid light hydrocarbon(s) as used
for the agglomeration, from which unit ~urplus water is discharged
and the top lqyer with the agglomerates in it i~ pa~sed to the
sieve drum. The aeglomerates ~re thus taken up in the light hydro-
carbon(s) before they are filtered. The advantage is that practically
no adhering water enters the sieve drum with the agglomerates,
~o that further de-watering is accelerated.
The invention will now be elucidated Wittl reference to some
figures and examples.
Fig. 1 shows a scheme of the process for the preparation of
dry soot according to the invention.
Fig. 2 shows a scheme of the integrntion of the process according
to the invention for the preparation of dry soot with a gas preparation
process 0
In Fie. 1 10 is the stream of aqueous soot suspension entering
~he agglomeration apparatus 11. This apparatus is provided with
a stirrer 12 with motor 13. A stream of binder 14, for instance
naphtha or gasoline, is also passed into apparatus 11~ The turbulence
gives rise to the formation of soot agglomerates, which leave the
apparatus together with water as stream 15 and are introduced into
sieve drum 16. Drum 16 is slowly rotated by A motor 170 The cylindrical
wall of the drum has holes of about 200 ~m. The drum is internally
provided with a ver~ical helical ribbon. The rotation, e.g. 6-10
rev/min, and the pitch Or the ribbon cause the agglomerates to
move towards outlet 18. Water is discharged at 19. A housing 20
encloses drum 16. A sprinkler 21 may be present to deal with possible
blockage~ in the sieve wall of the drum, which may occur for instance
a~ a result of a maloperation.
The agglomerates freed from adhering water go to a drier
22~ In this drier they are brought to a M uidized stQte by means
of a hot gas issuine from nozzles 23. The binder, e.g. naphtha,
evaporates in this process and is dischar6ed, together with the
fluidizing gas~ at 24. The fluidizing gas is here superheated vspour
o~ the hydrocarbons that have been used as the binder. Vapour 24
passes through a conden~er 250 Thus a liquid binder is formed,
indicated earlier as stream 14, A side stream is evaporated in
heat exchanger 26 and supplies the fluidizing gas. Possible binder
losses are compensated for by stream 27. The dry agglomerates are
discharged as stream 280
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In Fig. 2 30 i9 a reactor for the incomplete combustion Or
a carbon-containing feed 31 by reaction with oxygen or an o~ygerl~con-
taining gas 32 with addition of steam 330 The gas is cooled in
cooler 35. In scrubber 37 the gas is treated with WQter 38 BS a
result of which gas 39, which contains no 900t anymore, und an
aqueous soot suspension 40 are obtained. This soot suspension is
brought to turbulence in an agglomeration spparatus 41 provided
with stirrer and motor 42, together with a liquid light hydrocarbon
43, eOg. naphth~. The agglomerates formed go with water as stream
44 to the rotary sieve apparatus 45 designated by numerals 45,
46, 47, 48 and 49, which numerals have the same meaning as 16,
17, 18, 19 and 20, respectively, in Fig. 1.
The dried agglomerates are taken up here into feed stream
51 with an extrusion pump. The agglomerates still contain the binder,
which is removed in flash evaporator 52. In condenser 53 the vapour
is condensed and used again as binder 43, replenished, if required,
with fresh material 54 to compensate for losses. the soot-enriched
feed stream, which is freed from binder, goes as feed 31 to reactor
30.
Several variations on this scheme are possible. ~o foaming
occurs in evaporator 52.
EXAMPLES
The suspension of soot particles in water contained 1.14 %w
sootO This suspension originated from a process for the preparation
of ~as by partial combustion Or a residual mineral oil. A stream
of this suspension was pas~ed through an agglomeration apparatus
at a rate of 1.12 m3/h. The stirrer rotated Qt a rate of 1000 rev/min.
A stream of naphtha of 58.8 kg/h was added aimultaneously. A quantity
of 12.77 kg/h of dry soot was thus introduced and the naphtha/soot
ratio was 406.
The stream leaving the agglomeration apparatus was passed
to a rota~y ~ieve~ The drum was 30 cm in diameter and 150 cm long.
helical, vertical ribbon against the inner wall of the sieve
wall (hole~ of 200 um) had a height of 2.5 cm and a pitch of 3
cm. The drum rotated at a rate of 6 rev/min.
The agglomerates leavine the drum were passed to a fluidized
bed. The fluidizing gas was naphtha vapour having a temperature
of 180C. This vapour was introduced at the rate of 340 kg/h. The
superficial gas rate was 0.16 m/~.
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From this drier emerged a stream Or dry soot of 12.04 ke~h
in the form of agglomerates. A further quantity of O.29 kg/h dry
soot WBS separated ~rom the stream of naphtha vapour by means of
Q cyclone.
The experiment lasted 8 hours and no bre~kdowns or blockages
were obser~ed. The agglomerates were externally completely dryo
They contained about 3 %w water1
The following table gives conditions and results of a series
of experiments with aeglomerates obtained as described hereinbefore
without application of a fluidized bed. The a~glomeration and sieve
conditions were vsried.
_______~_________________~_______________________________________________________
Supply rate
of soot suspension, l/h 810 810 olO 810 8101200 olO 860 1200
Soot content
in suspension, ~w 1.16 1.00 t.O2 o.98 o.87 o.89 0.94 0.85 o~88
Naphtha/soot ratio 4.1 5,1 5.2 5.0 5.6 6.o 9.7 4.7 4.B
Stirrer speed,
rev/min 900 900 900 800 900 900 900 900 900
____________________________________________ _______________________. ___________
Sieve drum speed,
re~/~ni~ 6 6 6 6 10 10 10 10 10
Inclination
of sieve drum, degrees 0 0 O O O O 0 10 10
____________________________~_______________---___________________________________
Water content
of ~gglomerates, %w 19.9 5.2 5.2 7.2 4,1 4.7 202 5.7 2.3
Water/soot ratio 1.27 0.34 0.34 o.46 0.28 0.34 0.24 0.36 0.13
At the optimum naphtha/soot wei~lt ratio for agglomeration
of 5.6_6.o, the uater content of the agglomerates was 4-5 %w. At
the very hig~l naphtha/soot ratia Or 9.7, the water conteat was
lower. At a low naphtha/soot ratio smaller pellets are obtaiaed.
These pellets bind more water to their surfaces, becsuse Or the
larger surface area per unit weight. It has beea found that by
increasing the residence time in the rotary sieve, by giving it
an upward inclination, better dry;ng is achieved again.
