Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2 2C9~9~ ~33
This invention relates to a method of removing,
possibly by chemical binding, contaminants in a fluid,
such as a gas or liquid stream, in which the fluid is
contacted with neutralizing and/or absorbing su-bstances
and the resulting mixing or reaction products are separated.
One example of an appliance wherein this method
is performed is the cyclone-shaped reaction chamber(s)
wherein absorption/neutralizing substances are contacted
with contaminated flue gases of refuse incinerators.
In these, the cyclones' first function is the
capture of sparks entrained from the incinerators in
those cases wherein cloth filters are used to remove
fly ash and reaction products from the 1ue gases, before
said flue gases are discharged into the atmosphere through
a chimney stack. The contact between the flue gases
and the absorption/neutralizing su~stances added thereto
in the cyclones is such that a part of the acid components
from the flue gases are bonded and neutralized. Tests
have shown that the neutralizing effect inside the cyclones
is higher than that of the neutralizing layer formed
on the downstream filter cloths. Yet there is evidence
that, in the case of heavy loads with acid components
as regularly occurring in practice in flue gases, the
total efficiency of upstream cyclones and downstream
cloth filters, is insufficient to meet the emission
standards recently laid down in national and international
regulations.
3 ~9~33
The alternative option would be for wet flue
gas cleaning, with which these standards can be met.
The consequence of that, however, is that it will increase
investments by a factor of 2 or 3 as a result of the
elaborate processing involved in this methocl, on top
of which, in most cases, additional waste water purification
is required.
It is an object of the present invention to
improve the dry flue gas purification with cyclones
in such a manner that emission standards are met and
expected by even lower valuas will result, thus achieving
a particular improvement in the solution of environmental
problems in respect of, for example, refuse incinerators.
This can be realized at quite acceptable prices at that.
To that effect, according to the present invention,
by application of the features reclted in the characterizing
clause of claim 1, the components entering the cyclone
are not only centrifugad but the light fractions in
the flue gases, including the major part of the gaseous
acid components, are prevented from diffusing directly
through the flue gas stream to the cyclone exit, so
that the contact with the neutralizing heavier components
is too short.
According to the present invention, the light
fractions in the flue gases, together with the heavier
fractions are jointly centrifuged after entering the
cyclones, while in contrast to the situation in the
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present design within cyclones, increasingly intensive
contact is enforced by increased concentration and at
the same time strongly increased velocity by means of
an inverted cone provided preferably in the centre of
the cyclone. This forces the light (i.e. the acid) com-
ponents in the flue gases to react with the neutralizing
substances immediately, intensively and for a prolonged
period of time.
By repeating the inverted cone construction,
as indicated above, at a lower level, there is obtained
a reversal of the flue gas motion, whereby the descending
high-velocity whirl is converted into a rising initially
expanding whirl of relatively low velocity. According
as the whirl thereafter at higher level again approaches
the centre of the cyclone, the acceleration and the
concentration are considerably increased. The heavier
fractions in the strongly accelerated rising whirl are
again mixed intensively with the light fractions (including
those to be neutralized) in the gas stream. Repetition
of the above inverted cone constructions in the interior
of the cyclone will increase the effect of mixing and
neutralizing acid components in the flue gases. Moreover,
the effect of mixing and chemical reaction can be increased
per "floor" by rendering the distance between the internal
cones adjustable. In this manner, substantially higher
vortex speeds (and hence higher mixing efficiency) can
be achieved than provided initially (i.e. upon entry
2Q~9~83
into the cyclone). The variation of the distance between
the internal cones can be controlled by coupling the
adjustment to e.g. the measured acidity of the flue
gases prior to their discharge to the chimney stack.
The last fixed cone can be extended to a cylindrical
bin where the vortex can be reduced to such a low velocity
- by properly dimensioning the cylinder - that solid
components (fly ash, chemical reaction products and
possible excess of neutralizing substances) are separated.
The purified gas stream is removed through a central
exhaust within the lowest cylinder. Naturally, exhaust
from the installation need not necessarily take place
in the above manner. It is also possible for instance
to select tangential exhaust from the circumference~
Another possibility could be: exhaust from the top of
the device in the case where one "floor" would be sufficient
to attain the required efficiency. IE an enlargement
of the lowest cone is selected, as mentioned abo~e,
there is automatically produced a collectin~ bin which
can selectively perform a number of useful functions:
a) temporary storage of separated and/or reacted products
prior to discharge into a container;
b) return of the separated products to the inlet of
the cyclone or one of the floors, to thereby allow
any neutralizing material not yet entirely reacted
to participated again in the process.
6 Z~)9~L133
Some embodiments of apparatus according to
the present invention will now be described, by way
of example, with reference to the accompanying drawings,
in which:
Fig. 1 diagrammatically shows the ope~ation
of a conventional cyclone;
Fig. lA is a cross-sectional view according
to the arrow A in Fig. l;
Fig. 2 shows in top plan view the operation
of a cyclone according to the present invention;
Fig. 3 is a diagrammatic cross-sectional view
of the cyclone shown in Fig. 2;
Fig. 4 is a view similar to E'ig. 3 but showing
the top of the cyclone illustrated in Fig. 3 and its
operation in more detail;
Fig. 5 is a view similar to Fig. 4, but in
a further stage of the fluid motion;
Fig. 6 is a similar view showing fluid motion
subsequent to the situation shown in Fig. 5; and
Fig. 7 shows the completion of the process
by collecting reaction products.
Fig. 1 is a cross-sectional view of a conventional
cyclone construction, showing the centrifugal separation
of heavier fly ash, neutralizing substances and reaction
products via the descending vortex (a) and the rapid
diffusion of the light (e.g. acid) components (b), including
light solid components of the flue gases, which are
7 Z~ 83
subsequently discharged to filters upstream of the chimney
stack. The flue gases mixed with absorbing and/or neutralizing
substances are introduced tangentially through 1 into
the cylindrical portion 2 where they are contacted with
each other. The heavier components, such as fly ash
and a part of the reaction material, descend via vortex
(a) into the discharge or collecting hopper 8. The lighter
fractions, such as acid gases, light fly ash particles
and residual reaction material, are separated from vortex
(a) directly at the open bottom of exhaust pipe 11 and
disappear through vortex (b) in fractions of seconds
through pipe 11. The reaction time available for neutralizing
undes:irable components is therefore very short. In those
cases where the percentage of undesirable chPmical components
in the gas stream is high, the added neutralizing and/or
absorption agent will react insufficiently. Thus the
composition of the flue gases discharged via 11 will
fail to meet the recently raised emission standards.
A substantial excess of neutralizing agent
has proved unable to solve the problem and moreover
creates two additional problems:
- the extra cost connected with the discharge
of substantial amounts of residues to dumping sites
which
- can accept these materials only at increase
rates.
8 2Q~ 8~
The residues, in fact, require additional provisions
at the dumping sites to control the water economy and
quality.
It is an object of the present invention to
avoid these drawbacks and to positively improve the
result in a manner as shown in principle in Figs. 2-7.
As shown in Figs. 2 and 3, flue gases are introduced
tangentially through 1 into the cylinder 2 - the cyclone -
possibly with added neutralizing substances. The additions
of these and/or other substances, naturally, can also
take place after the entry, e.g. through the apex of
cone 4 or the base of cone 5.
Undesirable components, together with the heavier
components (fly ash and neutralizing substances) are
centrifuged in cylinder ~, while in contrast to the
situation described for the cyclones of the prior art,
increasingl~ intensive contact is promoted by increased
concentration and at the same time strongly increase
velocity of vortex (a) by means of an inverted cone
4 provided (preferably) in the centre of the cyclone.
As appears from the detail shown in Fig. 4,
the centrality suspended inverted cone 4 products intially
the accelerated descending vortex (a) shown in Fig. 3.
This vortex is deflected 180 from its original direction
by the bottom of cone 5 and has as the only way out
the cylindrical cross-section II, being substantially
larger than cross-section I, in other words, besides
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a reversal through an angle of 180, a sudden expansion
takes place. This is highly favourable to additional
vortex effects/ resulting in additional mixing and enchanced
chemical reactions. The cyclonic gas motion cannot become
suddenly rectilinear, for a new vortex (b) is formed,
as model tests have shown, ~hich ascends according to
the dotted lines shown in the drawings between the two
cones at in'creasingly higher vertical and tangential
speed = mixing speed = chemical reaction speed. The
absorption/neutralizing agent is enforced to react for
the second time.
Fig. 5 shows the same cyclone detail as Fig. ~
with a representation o the gas motions which are deve~
loping in a stage further than that shown in Fig. 4.
From cross-section III, a substantially 180 reversal
of gas motions takes place again. It should be noted
that a 180 reversal, as used herein, should be construed
to mean the eventual effect in a vertical sense. The
actual gas motion remains tangential, resulting a vortex
ascending or descending, as a whirl, perpendicularly.
In cross-section III, such a 180 reversal takes place
again. Vortex (c) is formed, resulting-in very high
speeds, in other'words, a very high mixing effect and
very high chemical reaction speeds. The absorption/neutralizing
agent is enforced to react for the third time, now in
the second "floor".
Fig. 6 shows the possible sequel to the situation
shown in Figr 5. By repeating this construction over
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various "floors", the reaction eEficiency can, in fact,
be increased to an unlimited extent.
- Fig. 7 shows one of the possibilities to complete
the reaction process, using the same principle according
to the present invention, with the capture of reaction
products. When the wall of cone 7 is extended, the speed
of vortex (d) can be reduced by dimensioning of diameters
so that the solid components: fly ash, chemical reaction
products and any excess of neutralizing substances are
deposited within cylinder 8. The vortex (d) will automatic:ally
produce vortex (e), which now ascends according to the
dotted lines and the~eafter discharges through the central
exhaust the now strongly chemically purified gases through
11 .
The increase in efficiency of the deposition
of solids results in a lower load of the filters, which
reduces the cost of energy and maintenance. The increase
in efficiency of the chemical reactions means a saving
in chemicals and residual materials, hence lower exploitation
cost which, by means of the method and device according
to the present invention, can even be lower than those
of known installations.
It will be clear that where reference is made
to flue gases and acid components, the principle of
the present invention also applies to other fluids,
e.g. industrail exhaust gases or liquids and basic components
in which case naturally other absorption/neutralizing
33
agents can play a role. Where the term "absorption"
is used in the specification, the term "adsorption"
or a similar term may be used instead.
