Note: Descriptions are shown in the official language in which they were submitted.
CA 02648806 2015-10-08
SCRUBBER WITH MULTIPLE VENTURIS
BACKGROUND OF THE INVENTION
[0002] In some aspects, this invention generally relates to
scrubbers used to remove matter (e.g., particulate,
gaseous, or liquid) from a gas stream in order to recover
the matter and/or to clean the gas. In particular aspects,
this invention relates to a positioning of multiple
venturis that may provide additional flexibility and
increased efficiency. The invention also pertains to
related methods.
[0003] Scrubbers - such as those described in U.S. Patent
Nos. 5,279,646; 5,484,471; 5,512,085; and 5,759,233- are
known. Figure 1 of U.S. Patent No. 5,512,085, for example,
shows an example of extant technology.
[0004]This system of the '085 patent is quite simple. Gas
enters the venturi portion of the scrubber (on the left)
where a liquid is sprayed in to the throat of the venturi.
In many instances, the diameter of the venturi throat can
be approximately 12" to 48".
[0005] The purpose of the venturi is to impact the liquid
with the matter to be removed. The liquid is then separated
from the gas through impact with a liquid level at the
bottom of the venturi, and through centrifugal
1
CA 02648806 2009-01-08
forces in the separator vessel (on the right). There can
be a demister at the top of the separator vessel, or
external to the separator vessel, to remove any residual
liquid droplets.
[0006]An advantage of this technology is that it can be
very inexpensive. A disadvantage is that it may not be
efficient enough to meet gas cleanliness standards set by
regulatory agencies. Another disadvantage is that a high
pressure drop across the venturi may be required to
achieve high efficiency, which costs the mill energy and
possibly equipment upgrades.
[0007] Other scrubbers are also known. For example, Figure
1 shows a scrubber that is quite different than the =ones
mentioned above.
[0008] In Figure 1, the inlet 10 is not a venturi, but
rather a duct with spray nozzle(s) 12 used to quench the
gases to saturation. In this
illustrated device, there
are multiple venturis 30 positioned within the separator
vessel 20, each with its own spray nozzle 32. These
venturis may have throats with a diameter of between 6"
and 12". In a preferred embodiment, the venturi may have
a throat of approximately 8". There may be a preliminary
cleaning step (shown by sprayer 42) and demister(s) 40,
as shown in this figure.
[0009]An advantage of this system is that it may be highly
efficient at a low pressure drop. A disadvantage is that
it may be very expensive relative to a system with an
external venturi. Another disadvantage is that it may
2
CA 02648806 2009-01-08
require modification to an existing (e.g., older) vessel
in the case of a retrofit project.
[0010] In light of the above-identified deficiencies of the
prior art, there exists a need for an improved scrubber,
particularly a scrubber that enables a good efficiency
and reasonable pressure drop.
[0011] In certain embodiments, the multiple venturis of the
present invention may provide flexibility in scaling up
and scaling down the separation process, thus enabling a
wider range of operating parameters, process conditions,
and loading. The multiple venturis may also facilitate
repairs, as each venturi unit may be replaced, repaired,
or reconstructed individually. This flexibility may not
only reduce downtime, but may also provide flexibility in
designing, testing, and evaluating new configurations and
devices.
Furthermore, at least certain embodiments of
the present invention are particularly suitable for
relatively inexpensive retrofits to existing equipment.
BRIEF DESCRIPTION OF THE INVENTION
In an embodiment, the present invention generally
relates to a system for removing matter from a gaseous
stream. The
matter may comprise solids, liquids, or
gasses. The system for the separation of matter from a
gaseous stream may include: a cyclonic separator vessel
adapted to receive a first outlet stream and a second
outlet stream; and a first venturi external to the
cyclonic separator vessel and a second venturi external
to the cyclonic separator vessel. The first and second
3
CA 02648806 2009-01-08
venturis may be arranged in parallel and each adapted to
receive a portion of an inlet stream comprising gas and
matter to be separated from the gas. The first
and
second venturis may further be each adapted to receive
and distribute a solvent to entrain the matter to be
separated from the gas. The first venturi may be adapted
to discharge the first outlet stream, and the second
venturi may be adapted to discharge the second outlet
stream. The first and second outlet steams each include
gas and entrained matter to be separated from the gas.
The cyclonic. separator vessel may be adapted to separate
the entrained matter from the gas.
In another embodiment, the present invention relates
to a method of separating matter from a gaseous stream.
The method may comprise: providing a gaseous stream
comprising solid, liquid, or gaseous matter to be removed
from the stream; dividing the gaseous stream into two or
more gaseous streams; providing at least two venturis,
wherein the at least two venturis each comprise a nozzle,
an inlet cone, a throat, and an outlet cone; feeding each
of the divided streams into one of the at least two
venturis; mixing a solvent from the nozzle in at least
one of the at least two venturis with the divided stream
so as to entrain the matter and facilitate separation in
a separator; providing the separator downstream of the at
least two venturis; connecting the separator to the at
least two venturis; and separating the entrained matter
from the gaseous stream in the separator.
[0012] In some embodiments, the venturis are identical or
may be of different sizes.
4
CA 02648806 2009-01-08
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIGURE 1 is a prior art scrubber.
[0014] FIGURE 2 illustrates a scrubber in accordance with
an exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0015]There are three main scrubber applications used in
the processing of pulp and paper: kiln, power boiler, and
dissolving tank scrubbers. Aside
from those primary
uses, there are secondary, more minor applications for
scrubbers. In
various embodiments, this invention
relates to primary and secondary scrubber applications.
More specifically, this invention may be used in
connection with scrubbers intended to remove matter
(e.g., particulate, gaseous, or liquid) from a gas stream
in order to recover the matter and/or to clean the gas.
In one aspect, the scrubber described herein may have
particular utility in remediating a gaseous stream
containing pollution prior to exhausting to the
atmosphere.
[0016] In one embodiment, there is a system including
multiple venturis (e.g., four venturis) external to the
separator vessel. The
gaseous stream containing the
matter to be separated (e.g., particulate, gaseous, or
liquid matter) may be split across the multiple venturis.
As is well understood in the art, a venturi generally
includes a gaseous stream being contacted with a liquid
emitted from a high pressure spray nozzle. The injected
liquid may form droplets that scrub the to-be-separated
CA 02648806 2009-01-08
matter in the gaseous stream. That is, a high pressure
spray passing through the venturi throat may form
numerous fine liquid droplets that provide turbulent
mixing between the gas and liquid phases. A venturi
generally has a changing cross-sectional area, which
generally decreases then increases. These and
other
configurations are contemplated within various
embodiments of the present invention.
[0017]In a preferred embodiment, these venturis would be
arranged in parallel, although a series of multiple
venturis are also contemplated in other embodiments.
Indeed, the multiple venturis may be combined a virtually
limitless number of permutations involving venturis in
parallel and series.
[0018]The multiple venturis thus may provide flexibility
in scaling up and scaling down the separation process,
thus enabling a wider range of operating parameters,
process conditions, and loading. The multiple venturis
may also facilitate repairs, as each venturi unit may be
replaced, repaired, or reconstructed individually. This
flexibility may not only reduce downtime, but may also
provide flexibility in designing, testing, and evaluating
new configurations and devices.
Furthermore, at least
certain embodiments of the present invention are
particularly suitable for relatively inexpensive
retrofits to existing equipment.
[0019]In a preferred embodiment involving multiple
venturis solely in parallel, each venturi would be
responsible for handling a fraction of the incoming
6
CA 02648806 2009-01-08
gaseous stream containing the matter to be separated. In
such an arrangement, the diameter of each venturi may be,
for example, approximately 12". In
comparison to a
single venturi, there may not be a direct correlation
between the fraction of incoming gaseous stream and
diameter. That is, the diameter or cross-sectional area
of each venturi may depend on a number of different
factors, including, for example, angles of the venturi's
inlet and outlet cones, length of the venturi's throat,
pressure drop, etc.
[0020]A preferred embodiment is schematically illustrated
in Figure 2. This embodiment illustrates four venturis
in parallel, though other permutations involving greater
and fewer venturis as well as venturi(s) in series are
also contemplated. For
example, certain embodiments of
the present invention may include two, three, four, five,
six, seven, eight, nine, ten, or more venturis, solely in
parallel or in parallel and in series.
[0021] Figure 2 illustrates an overall air pollution
control system including multiple venturis and a
separator. A
contaminant-laden gaseous stream is
generated by a source (not shown). This source may be
involved in pulp and paper-making, such as, for example,
a kiln. The gaseous stream may have liquid, solid, or
gaseous matter entrained therein, including gaseous
contaminants that may condense as the gaseous stream is
cooled (if heated).
[0022] The gaseous stream enters via conduit 202, which is
split (either evenly or unevenly) among four streams into
7
CA 02648806 2009-01-08
=
conduits 204. Although
the division is depicted as a
series (i.e., with a fraction of conduit 202 being
sectioned off at each conduit 204), it is possible to use
other arrangements, such as a parallel division into four
streams at a singular node. If
heated, the gaseous
stream may be cooled to a lower temperature in
forechambers 214 prior to entering venturis 210. This
cooling may occur with water or other liquid(s) emitted
from nozzles 206. This cooling may lower the temperature
of the gaseous stream to approximately the saturation
temperature.
[0023] The nozzles 206 may be positioned remotely from the
entrance to the throats 212 of the venturis. After
flowing through forechambers 214, the effluent enters the
venturi scrubbers 210 comprising entrance cones 216,
throats 212 and an exit cone 218. The scrubbing liquid
for the venturi is provided by the spray from nozzles
208. In some
instances, nozzles 208 may be two-fluid
nozzles which form a spray of scrubbing liquid having
droplets which are optimized for maximum collection of
optically active particles. In some embodiments, nozzles
208 may be connected to a source of water or other
solvent and a source of compressed air.
[0024] The entrance or inlet cones 216 may have a wide
range of angles. In some embodiments, the angle of the
inlet cone may be between 60 and 90 , and in other
embodiments, the angle of the inlet cone may be between
30 and 45 or between 450 and 60 . A relatively larger
angle may require an increase in energy required to move
gas through the venturi, though it may also improve
8
CA 02648806 2009-01-08
scrubbing efficiency by maximizing the differential
velocity between the contaminant particles and the
scrubbing droplets.
[0025] The outlet cones 218 may be relatively long, which
may maximize the recovery of energy from both the gas
flow and from the droplets. Scrubbing may also occur in
the outlet cone as the scrubbing droplets and any
remaining contaminant particles decelerate at different
rates. The
precise configuration of the venturis,
including the angles of the inlet cones and outlet cones,
and the cross-sectional area may vary according to
different embodiments of the present invention. Any
suitable configuration of venturi(s) may be used.
[0026]The spray from nozzles 206 may introduce the
scrubbing liquid relatively uniformly into the gaseous
stream, such that cooling is uniformly achieved and the
gas flow and the scrubbing liquid form an homogenous
mixture when they enter the venturis 210. In some
embodiments, the differential velocity between the spray
droplets and the gas flow at the point of introduction is
low. Depending on the embodiments, the spray may or may
not assist the flow of gases through the venturis.
[0027]It should be appreciated that the venturis 210 need
not be identical, and that different sized venturis may
be used. In such an
embodiment, each venturi may be
designed to handle a different flowrate and/or
composition of the gaseous stream. In this
respect,
furthermore, individual venturis may be brought online as
necessary according to varying process conditions and/or
9
CA 02648806 2015-10-08
loading. In yet further embodiments, there may be greater
than or less than four venturis in series and/or parallel.
[0028] After leaving the exit cones 218 of the venturis
210, the contaminant laden spray droplets are removed from
the effluent stream. In the exemplary system depicted in
Figure 2, a cyclonic separator 220 and a mist eliminator
234 and nozzles 222 may be used to remove the contaminated
spray droplets from the effluent gas flow. Sprays from a
plurality of nozzles 222 may be introduced into the gas
flow just upstream of the mist eliminator 234 to keep the
surface of the mist eliminator wet and clean. The operation
of cyclonic separators and of mist eliminators are well
known to those skilled in the art and any suitable
configuration may be used in connection with the invention
described herein. Because the mixture of the gaseous stream
and spray droplets may have been reduced to substantially
saturation temperature, there may be little or no
evaporation of the scrubbing droplets after they exit the
venturis.
[0029] As depicted in Figure 2, streams exit from each
venturi 210 and connect to cyclonic separator 220 via
conduit 230. Stream 232 exits from separator 220 and may be
further cleaned and/or recycled to various processes, in
accordance with various embodiments.
[0030] Thus, a number of preferred embodiments have been
fully described above with reference to the drawing
CA 02648806 2015-10-08
figures. The scope of the claims should not be limited by
the preferred embodiments and examples, but should be given
the broadest interpretation consistent with the description
as a whole.
11
