Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The invention relates to an apparatus for separating gas and
liquid, comprising a central upflow tube which at the top opens, via an
overflow edge, into a separator hood fitted over and around the top of the
upflow tube and having a gas outlet above the overflow edge and a liquid out-
let below the overflow edge, but outside the upflow tube.
The simplest embodiment of such an apparatus is the one in which
the upflow tube is cylindrical and the overflow edge is formed by the upper
edge of the upflow tube. Such an embodiment has been described for instance
in French Patent 7,437,051.
Now, it has been found that the degree to which a separation
between gas and liquid is effected by means of the above-mentioned apparatus
depends on the combined effect of a residence of the phases to be separated
in the separator hood and of the movement of the phases over the overflow
edge. In certain applications - for instance in the synthesis of hydro-
carbons from synthesis gas in a slurry-type reactor in which the catalyst is
suspended in recycled liquid product or in a circulating auxiliary liquid and
in which liquid and catalyst, after having been separated from unconverted
gas and gaseous by-products at the top of the upflow reactor, are cooled
outside the reactor and recycled to the bottom of the reactor - it has been
found, when using the above-mentioned simplest embodiment of the separating
device, that the effect of the circular overflow edge alone does not bring
about an adequate separation. The separation then has to be completed in the
space of the separator hood outside the upflow tube where below the overflow
edge a liquid level must be maintained with a very large surface area. This
calls for an outer diameter of the separator hood many times larger than that
of the upflow tube - in this case the reactor - which is found to be
unacceptable in practice.
The present invention aims at solving this problem and therefore
proposes, instead of enlarging the liquid surface area in the separator hood,
to lengthen the overflow edge.
Thus, according to the invention there is provided an apparatus
for separating gas and liquid, comprising a central upflow tube which at the
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top opens, via an overflow edge, into a separator hood fitted over and around
the top of the upflow tube and containing a wall and having a gas outlet
above the overflow edge and a liquid outlet below the overflow edge, but out-
side the upflow tube, characterized in that the overflow edge is formed by a
system of partitions which traverse the space directly above the upflow tube
and continue in the radially adjacent space and which define two kinds of
compartment - open at the top - each compartment extending in the space over
the upflow tube and in said radially adjacent space, one kind of compartment
consisting of risers which have no bottoms in the space over the upflow tube
and which do have bottoms in said radially adjacent space, whereas the other
kind of compartment consists of downcomers which do have bottoms in the space
over the upflow tube and have no bottoms in said radially adjacent space, the
design being such that a riser and a downcomer are always side by side and
have one partition in common.
Thus, essentially the top edges of all the partitions together
function as the overf~ow edge. The liquid ascends from the upflow tube into
a riser compartment between the two partitions forming the riser. The liquid
is then present not only in the part of the riser that is located in the
space over the upflow tube - and has no bottom - but also in the other part
of the riser which is located in the radially adjacent space in areas where
there is a bottom.
The liquid may flow over the edge of one of the two partitions that
form the riser into a neighbouring downcomer compartment. There are two
possibilities here, namely:
a) the liquid flows over the partition directly above the upflow tube
and then plunges from the part of the riser over the upflow tube into that
part of a downcomer which is likewise located over the upflow tube, and
which at that location has a bottom, whereupon the liquid flows along this
bottom in the downcomer concerned to that part of the downcomer which is
located next to the space over the upflow
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tubc, wl~icl~ r~ h~ no bottom, wl~crcupon Lhe liquid ~lo~s iuto tlle
part of thc separator hood ne~l t~ ~he llpflow tube (;.e. ~clow tlle
partition), subsequently leaving the separator l)ood via the liquid
outlet;
b) the liquid f10ws over thc parcition ncxt to ~he space over
the upflow tube and thcn plunges from the part of the riser next to
the space over the upflow tube into the part of a downcomer which is
located next to the space ovcr the up~low tube, which downcomer has no
bottom at that location, so that the liquid can flow directly into the
space of the separator hood next to the upflow tube (i.e. below the
partitions), subsequently leaving the separator hood via the liquid
outlet.
With the apparatus according to the invention thc liquid at the
top of the upflow tube and in the risers will generally show some
foam formation and have a lower specific gravity than that in the
downcomer. The liquid level in the riser will almost come to the
upper edges of the partitions, whereas the liquid level in that part
of the downcomer which i9 located next to the space over the upflow
tube will in most cases have fallen to below the partitions, i.e.
remain below the top edge of the upflow tube. It will, however, be
clear that the whole situation will also depend on the surface area of
the passages in riser and downcomer and on the rate of discharge via
the liquid outlet, as well as on the level control, if any.
According to the invention the partitions traverse the space
directly above the upflow tube and the space next to it. The risers have
bottoms in the space next to the space over the upflow tube and the
downcomers have bottoms in the space over the upflow tube. The bottoms will
therefore be fitted both to the partitions and to the upflow tube. This
construction will prevent any liquid flowing from the upflow tube direct
into a downcomèr and from a riser direct into the space next to the
upflow tube. Thus the liquid i8 invariably forced to flow over the edge
of a partition, which edge thus actually acquires the function of an overflow
etge.
By installing a greater number of partitions, which also increases the
nuober of risers and downcomers, the overall length of the overflow edge
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is incrcased. It will be cle~r t11;~L tbe ov~rflow e(~e ccln be ml~dc
many timc~ longer th~n it i9 Wllf`ll tllC ~Op of thc u~flow tube itsclf
is uscd as (circula~) ovcrrlow edge. T11e numbcr of partitions is
limited by the consideration that, to hnve ~ome effcct in the sep~ration
of gas and li4tlid, the comp~rtments must have a certain minimum width.
According to 8 preferred embodimcnt of the invention all the
partitions have hori~ontal top edges ~nd all these top edges ]ie in
one plane. This embodimen~ will usually be chosen because it i~ the
simplest one to fabricate and has the advantage that all parts of the
overflow edge are equally functional. However, it is po~sible to depart
from this embodiment and yet to retain at least part of the advantages
of the invention.
According to the invention the partitions are preferably placed
in a radial position. This construction is preferred especially when
upflow tube and separator hood have a circular cross-section, which
will certainly be the case when an elevated pressure is used in the
upflow tube. A radial position of the partitions has the advantage that
all the risers and/or downcomers can be identical and can be equally
bpaced around the circumference of the upflow tube, so that the risers
and the downcomers, respectively, are all equally loaded.
A disadvantage of the radial position of the partitions is thae
the compartment~ will not be equally wide everywhere. It i8 also
possible for instance to place the partitions parallel, but then special
measures have to be taken on two sides of the separator hood, where the
partitions cannot traverse both the space over the upflow tube and the
space next to it.
When the partitions are placed radially it may be preferable not
to have them extend over the upflow tube as far as the produced
centre line of the upflow tube. If they do, the compartments narrow
down to a wedge shape. There i~ not much space there for the partitions
and, moreover, the top of each compartment near this point will contr;bute
only little to the separation of gas and liquid: the two p~rtitions of
a compartment come too close together there, 50 that the width of
the compartment becomes too small there.
When, as indicated hereinabove, the partition~ to not extend as far
as ~he prod~ced ccn~rc lin~ of Lh~ low tube, ~I-cn, accordinE to tlle
invention, cacl~ partition ;5 prefcr.lbly conn~ct~d, over the upflow
~ube, with the ends of tl~e two n~;g11~o~lring partitions by a lateral
partition. Thus, there will be some measure of structural rigidity
S in the compartm~nts and, in the case of the downcomers, th~ lateral
partition may function as overflow edge for the liquid coming up
cen~rally through the upflow tube. The latera] partitions of the down-
comers will be attached with their lower edges to the bottoms of the
downcomers; whilst the upper edges of these lateral partitions may be lev~l
wi~h the upp~r ed~es of the radial partitions. Unless this is undesirable
for structural reasons, the lateral partitions of the risers may be
omitted; they do not contribute to the overall length of the overflow
edge.
In particular when the phases to be separated also contain solids.
for instance in the case of a slurry reactor for hydrocarbons, where the
phase to be separated from the gas phase comprises the bydrocarbons
themselves or an auxiliary liquid with solid catalyst particles, but
also in other cases where no dead corners can be allowed in the
separator hood (in which corners the residence time of a phsse may
for instance become unacceptably long), each bottom, according to the
invention, preferably slopes downwards in the direction of that part
of the upflow tube wall which is located under the compartment belonging
to that bottom. For tbe bottom of tlle riser, which is located in the
space next to the space over the upflow tube, this means that it slopes
down inwards, and for the bottom of the downcomer, which is located in
the space over the upflow tube, that it slopes down outwards. Obviously,
to save material, the lower edge~ of the partitions may, if desired, be
sdapted to thi~ particular construction of the bottoms.
Preferably - in particular when a relatively large quantity of
liquit has to be separated from the gas - in the case of a radial position,
the two partitions forming a riser include an angle of less than 15
and the two partitions forming a downcomer include an angle of more than
15
According to another embodiment of the invention, which has
advantages for instance when a relatively small quantity of liquid has to
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be separated from a ~a.~. ~t~a~e, the ~-~v ~artition~ ~or~ing n riser include
an angle of more than 1~ and tllc two partit;on~s form;ns a downcomer
inclu~c an ang]e of less l-han 15 .
It will bc clear that, when the partitions are placed radially
and riser alnd downcomer have equal anglcs, the surface areas of the
passages in riser und downcomer are determined by the diameters of the
upflow tube and the separator hood (provided that the partitions tra~erse
both the space over the upflow tube and the space next to it). Now, in order
to keep the diameter of the scparator hood as small as possible, it is
advisable to make the angle included by the partitions forming a down-
comer compartment large with respect to the angle included by the
partitions forming a riser compartment. On the other hand, the overall
length of the overflow edge decreases when the total number of com-
partments decreases. In addition, the ratio between the passage of the
r;ser and that of the downcomer must not deviate too much from the value
dictated by the ratio between the quant;ties of gas and liquid to be
separated, because if it does, space will be lost. A total number of
twelve risers and twelve downcomers has been found to be a good compromi~e;
a riser and a neighbouring downcomer will then together occupy an
angle of 30.
According to an embodiment of the invention the partitions extend
as far as the wall of the separstor hood. In this way a simple construction
i~ obtained. The separator hood then forms the required back wall of
the r;ser compartments; whilst the partitions and the bottoms can be attached
to the separator hood. However, it is pointed out that more complicated
embodiments are possible. Thus, in each riser according to the above
embodiment 8 strip of the bottom adjacent to the separator hood may be
omitted, whilst at the location where the bottoms do begin the partitions
of each riser are connected by a lateral partition. In this way additional
downcomers sre formed which are entirely located next to the space over
the upflow tube, the overflow edge being formed by these lateral
partition~.
According to a particular embodiment of the invention, which i9
pre--eminently suitable for use in slurry reactors, the bottoms make an
sngle with the horizontal plane. This embodiment has special advantages
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whcn the liquid conta;ns ;oli~ p~rtic]cR, sucl~ as a cat~llyst
The invcDtion also relntcs to a s1urry reactor comprising ~ reactor
ve~sel c~nstructe(l a~ An upflow tu~ ~8 ~1] AS n scp~r~tor hood on thc
reactor vessel into wllicl1 the re.~ctor vessel opens via ~ln over~lo~ edge,
which separator hood has a ga~ outlet abovc the overflow edge and a liquid
outlet below the overflow edge, but outside the reactor vessel,
which liquid outlet is connected via a cooling dcvice placed outside
the reactor vessel to the bottom of the reactor vessel, which bottom
i8 also Eitted with a gas inlet. The constr~lct;on of thc separator hood
with overflow edge is in accordance with one of the above-mentioned
embodiments of the invention. Such a slurry reactor is ~uitable for
synthesizing a product that is liquid under the synthesis conditions
by catalytic conversion of a gas in the presence of a recycled
product containing a catalyst. The recycled liquid with the catalyst,
together with the gas, is passed upwards through the reactor; in the
separator hood the unconverted gas, together with gaseous reaction
products is separated from the liquid containing the catalyst, which
liquid i8 cooled outside the reactor and subsequently recycled to the
bottom of the reactor. Part of the liquid is carried off as product.
Another application of the slurry reactor is the one in which
from a gas a gaseous product is synthesized with the aid of a catalyst
suspended in a recirculating auxiliary liquid. The gases are then
separated from the auxiliary liquid. ~lternatives to the two above-
mentioned applications of the slurry reactor are, for instance, those
in which the external cooling of the liquid separated from the gas is
omitted, in which the separated liquid is not recycled or in which
during the separation the catalyst is left in the reactor.
The liquid discharge facilities in the separator hood preferably
comprise at least four discharge lines equally spaced around the circum-
ference of the separstor hood, each connected to the bottom of the
reactor via a separste heat exchanger. This embodiment is pre--eminently
suitable for use in the synthesis of one or more hydrocarbons from a
gas containing hydrogen and carbon monoxide. In this "Fiscber-Tropsch"
synthesis a considerable amount of heat is generated in the reactor,
which heat can be efficiently removed in the way indicated above.
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The invention wi]l now be f~lrther e]ucicla~ed witll re~erence to
the accompanying drawing.
In the drawing, Fig. 1 is a ~che~a~ic longitudinal section through
a slùrry rcactor with ~eparator hood in accordance with an embodiment of
the invention.
Fig. 2 is a cross-section, on a lsrger scale, according to
line I-I in Fig. 1.
Fig. 3 show~ a schematic perspective of part of the interior of
the sep~rator hood according to Figs. l and 2.
Fig. 4 shows a schematic pe~spective of the part of the interior
of a separator hood corresponding to that of Fig. 3 according to
ano~her embodiment of the invention.
With reference to Fig. 1~ first a short description will be given
of the principle of the slurry reactor according to an embodiment of
the invention.
The slurry reactor, l, is constructed as an upflow tube, i.e.
in the vertical reactor vessel l a liquid phase - containing catalyst
psrticles - and a gaseous phase flow upwards. The upper edge, 2, of
the reactor vessel 1 has becn cut off straight, so the upper edge~ 2, is
circular and lies in a horizon~al plane.
On top of and around the upper part of reactor vessel 1 a separator
hoot has been fitted, the dia~eter of the separator hood being larger
than that of reactor vessel l. The top of hood 3 i8 closed by a cover, 4,
with a central gas outlet 5. The underside of hood 3 is located beside
upper edge 2 of vessel 1 and is constructed as a bottom, 6, sloping down
inwards. This bottom 6 has outlets to four liquid discharge pipes 7,
two of which are visible in the drawing.
In the space directly above upflow tube l and in the space next
to it, hood 3 has a system of partitions - to be further described
hereinafter with reference to Figs. 2 and 3 - which together generate
a system of overflow edges lying in the horizontal plane 8 through
the upper edgeR of the vertical partitions 9, which upper edges them-
selves are also overflow edges. The liquid and the gas flow from
vessel 1 between certain pairs of vertical partitions 9 upwards to
- 35 plane 8, where the liquid plunges over the overflow edges and flows
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bctween other pair~ of vertic~l psrtit;~ns downw~rds into annular
~pace lQ under pl~ne 8 next to the sp;~ce d;rectly above reactor 1.
~ro~ annular sp~ce 10 the liquid flows dowo through d;scharge pipes 7
to heat exchangers 11 and from t~lere to the bottom 12 of rcactor 1 via
pipes 13.
The gas phase which i8 separated from the liquid during over-
flow of the liquid in hood 3 collects in space 14 above plane 8
and is removed from it via outlet S. At the bottom 12 of reactor 1
fresh gas is supplied via inle~ tube 15.
With this slurry reacto~ it is possible to synthesize, for inst~nce,
a hydrocarbon from sgnthesis gas containing H2 and CO supplied via
tube 15, by passing liquid product in which the catalyst required for the
synthesis is suspended, together with the gas, upwards through reactor 1,
by separating the unconverted gas and the gaseous reaction products in
hood 3 from the liquid containing catalyst and discharging it via
t~ e S, by recycling product and catalyst via tube 7, heat exchanger 11
and tube 13 to the bottom 12 of the reactor - meanwhile cooling product
and cAtalyst in exchanger 11 - and by discharging excess product and
any catalyst to be regenerated via discharge nozzle 16 from hood 3. In
the synthesis of hydrocarbons external cooling is often desirable
because of the highly exothermic character of the reactions.
With reference to Figs. 2 and 3 a further description will now
be given of the construction of the system of partitions in hood 3
of the apparatus according to Fig. 1.
As is seen from the top view of Fig. 2, the vertical partitions 9
have been placed radially in hood 3 in a particular manner. They extend
in plane 8 from the wall of hood 3 to a cylindrical opening 17 which
is in the centre of hood 3. Partitions 9 form neighbouring pairs including
a smaller and a larger angle, respectively (10 and 20, respectively).
Upper edges 18 of partitions 9 in plane 8 form overflow edges
(~ee Fig. 3). Between two neighbouring partitions 9 ma~ing an angle
of 10 a bottom 19 is present between the wall of hood 3 and upper
etge 2 of upflow tube 1~ which bottom slopes down inwards because
it adjoins the wall of hood 3 at the level of plane 8, i.e. at the
level of upper edges 18 of vertical partitions 9, whereas it adjoins
uppcr edgc 2 o~ upflo~ ~uhc 1 son~ ce bclow thi~s ylanc 8. Bottom 19
ends at edge 2, i.e. betwcen the verticnl part;tion~ referred to there
is no bottom in the sp~c~ over tu~
Between two neighbouring partition~ 9 making an angle of 20 a
bottom 20 is prcsent in the space over ~ube 1, which bottom cxtends
upwards from upper edge 2 of tube 1 ~o cylinder 17. The bottom begins
at the level of upper edge 2 and ends ~t cylinder 17, some distance below
plane 8, in an edge 21. From edge 21 a ]ateral partition 22 rises
vertically to plane 8, i.e. to the level of the upper edgeæ 18 of
partitioas 9. Bottoms 20 are located in the space over upflow tube 1,
so they do not extend into the spacc next to it. Bottoms 19 and 20
as well as partitions 22 have been welded in place between partitions 9.
This means that two kir1ds of compartment have been formed betwecn
partitions 9, vi~.:
lS - riser compartments between partitions 9 which include an angle of 10,
which riser compartment~ are open at the bottom in the space over
upflow tube 1 and closed at the bottom in the space next to it (bottoms 19).
- downcomer compartments between partitions 9 which include an angle
of 20, which downcomer compartments are closed at the bottom in
the space over upflow tube 1 (bottoms 20~ and open at the bottGm in the
space next to it. Moreover, in the space over upflow tube 1 the down-
comer compartments, when viewed in a radial direction, are closed at
the inside (làteral partitions 22).
The operation of the system of partitions and bottoms tescribed
and depicted is as follows:
In Fig. 3 three compartments are shown in perspective, of which
the foremost is a riser compartment, the middle one a downcomer com-
partment and the hind~ost a riser compartment again.
The liquid phase and the gas phase flow from reactor 1 between
partition~ 9 of the riser compartments and in the space inside the
circle of lateral partitions 22 upwards to overflow edges 18 and 23. As
the phases flow over these edges a separation takes place, the gas
being removed in an upward direction while the liquid flows down in the
downcomer compartments between partitions 9 and 22, eventually arriving
in fipace 10 beside reactor 1 and flowing downwards from there.
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~ing to the sp~cial :h;ll)c of Llle liser comp.~lLments -- wllich
widcn upw~rd~ - al~ ~pan~ 111;1*1; of fo;lm in hood 3 c~n ~c cope~l with:
whi]st owing to thc s]opinr, po:;;tion of bottoms 19 clnd 20 there are no
dcad corners in ~lhich cata~yst p.Jrticles can stay behind.
Fig. 4 shows a great~y simplificd embodiment of the construction
according to Fig. 3. TWO riser compartmcnts are visiblè, which are
bounded by radial partitions 24 and 25 and by radial partitions 26
flnd 27, respectively. Between partitions 25 and 26 there is a downcomer
compartment.
Wall 28 of the reactor ends at the top in a horizontal circular
edge 29 to which bottoms 30, 31 and 32, of a riser, A downcomer and
a riser, respectively, have been comlected by welding. The bottoms are
all in one plane, the plane through edge 29 and through the lower
edges of partitions 24 up to and including 27.
Bottoms 31 tapers off to a point in the centre where the
partitions meet. Bottoms 30 and 32 extend from edge 29 to wall 33 of
the separstor hood.
The top edges of partitions 24 up to and including 27 lie in one
horizontal plane and form overflow edges. Above this plane, inside wall 33,
i8 the gas-collecting space, below the plane between ~alls 28 and 33
i8 the liquid discharge space.
