Note: Descriptions are shown in the official language in which they were submitted.
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Chevron Mist Eliminator Wash Apparatus, and
Method and Sy~tem Employing th~ Apparatus
De3cription
Reference to Prior Applications
6 This application is based on and claims the benefit of the
filing dates of provisional patent applications U.S. S.N.
60/003,192, filed September 5, 1995, and U.S. S.N. 60/003,681,
filed September 11, 1995, both hereby incorporated by reference.
Background of the Invention
Chevron-type mist eliminators comprise a plurality of
generally spaced-apart, usually uniformly arranged chevron blades,
and are employed to remove entrained liquid and mist from a gas
stream. Such mist eliminator6 may be employed with vertical flow
gas streams or with horizontal flow gas streams. Quite often, with
~5 chevron-type mist eliminators, horizontal flow is preferred, since
there is less likelihood that the liquid in the gas streams would
be re-entrained when the collected liquid falls from the chevron-
type mist eliminator, while in the vertical flow mist eliminators,
the collected liquid flows downwardly into the upwardly flowing gas
stream. While some of the following comments may also apply to
vertical flow arrangements, this application is specific to
horizontal f low arrangements where the long dimension of the
chevron blades is vertical.
Mist eliminators are often employed with horizontally flowing
acid-c~nt~nin~ gases, particularly acid-containing gases derived
from a furnace or other type chemical operation, wherein the
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emitted gas would contain, in particular, oxides of sulfur, sueh as
sulfur dioxide. Acid-containing gas streams usually must have the
acid gases removed, and such gases are typically removed by
treating, e.g. spraying, or otherwise eontaeting, the aeid-
S r~lnte~in;n~ gas stream with a reactant liquid or slurry, sueh as analkaline earth salt-water slurry, which is used to eontaet the
aeid-containing gas stream, and to cause the reaction of the
reaetant with the acid gases, thereby reducing substantially the
amount of acid gas in the gas stream and providing an aeid-alkali
lO reaction product. The reactant slurry, sueh as a ealeium-salt
water slurry, is then, after the reaetion, removed, while a gas
stream, with the reduced acid gas content, and containing some
entrained water, and often minor amounts of solid slurry-reaetion
partieles, e.g. calcium sulfate, is then sent to a chevron-type
l5 horizontal mist eliminator, to remove the entrained slurry liquid
and the solid particles entrained with the liquid.
Solid particles from the slurry in the gas stream tend to
build up on the blades of the chevron-type mist eliminator. Wash
systems located upstream and/or downstream of the mist eliminator
2C have been devised to wash with water the chevron-type blade
surfaces, to remove the buildup of solid slurry particles thereon,
and to remove the particles, with the wash liquid, to a sump. The
liquid from the wash stream then drains downwardly from the
sùrfaces of the chevron blades into the sump. The horizontal flow-
25 type mist eliminator reduces the problems concerning re-entrainment
of the liquid wash water into the gas stream in comparison to a
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vertical mist eliminator, however 60me liquid wash water is i.n fact
entrained in the horizontally flowing gas stream. Despite the
washing process, however, often some solids build up on the chevron
blades, and periodic mechanical or chemical cléaning is still
6 re~uired. Periodically, the operation must be stopped and the
chevron blades physically or chemically cleaned to remove the solid
particles .
Generally, the wash nozzles used are a plurality of wash
nozzles, in which the wash nozzles are disposed to spray generally
between, e.g., intermediate the chevron-type blades, and to spray
each opposing surface of the blades. The wash nozzles are arranged
to be operated intermittently in a desired sequence during the
- washing process. At any one time only a small portion of the mist
eliminator is being washed. The wash nozzles are generally
~5 disposed toward the upstream end of the mist eliminator and toward
the downstream end of the mist eliminator. The upstream end wash
nozzles spray a wash liquor between the blades co-current with the
horizontal flow of the gas stream. The downstream end wash nozzles
spray wash water at the downstream end of the mist eliminator,
i.e., spray the wash water countercurrent to, or into the generally
horizontally flowing gas stream. The wash nozzles generally are
placed 80 that the wash water will spray against all surfaces of
the chevron blades, and the accumulated liquid with the collected
solid reactant particles i8 directed into the sump.
26 In current practice, the spray nozzles are arranged both on
the upstream end and downstream end, and are employed so as to
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cover and overlap the entire exposed surface area of the upstream
end and downstream end surfaces of the mist elimlnator. The
nozzles generally comprise what is known as a full cone nozzle,
i.e., provide a full conical spray pattern. The full cone nozzles
6 are 80 spaced as to cover all or substantially all of the entire
area of that part of the chevron mist eliminator at which they are
directed, and generally provide overlapping coverage, and generally
are operated intermittently in a timed, controlled manner, 80 that
a fraction of the spray nozzles are in operation at any one time.
Horizontal flow mi6t eliminators, because the captured liquid
falls away from the gas stream rather than back through it, as in
a vertical flow mist eliminator, can be operated at substantially
higher velocities than vertical flow units, for example, velocities
up to and exceeding 18-20 ft/sec. New high performance chevron
~5 mist eliminators will be permitting even higher velocities. This
has created a problem with the use of traditional wash systems.
The high horizontal velocity makes the downstream wash difficult
because the wash water must flow against the gas stream.
Increa~ingly, users are finding that the need to shut down to clean
20 mechanically the downstream portions of chevron bladeg ig bec 'n~
an operational and economic burden. Traditional systems employing
full cone sprays are not proving totally adequate to meet the needs
of horizontal flow chevron mist eliminators, more 80 than ever
~ecause of the willingness of operators to push all equipment to
qS their limits. New high performance mist ~1 ~m~n~tors will
exacerbate the situation.
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It is desirable to provide for a new and improved mist
eliminator-wash apparatus, and for a method and system employing
the wash apparatus, which apparatu6, method and system provides
improved wash efficiency and efficient removal of solid particles
5 from the blade surfaces.
Su~ary of the Invention
The invention relates to a mist eliminator wash system,
typically including a mist eliminator with chevron-type blades
employed with a horizontally flowing gas stream, and to an improved
lO method of washing the mist eliminator, and to a mist ~1 ~m~n~tor
system employing the mist eliminator and the washing method.
The invention comprises a bladed, generally a chevron-type
mist eliminator and associated wash apparatus, for use with
horizontal flow gas streams, and which apparatus comprises a
5 plurality of spaced-apart blades, e.g. chevron-type blades, having
an upstream end and a downstream end, the blades arranged to be
placed in the horizontal flow path of a gas stream, having
entrained liquid and solid particles therein and arranged and
constructed to remove or reduce said entrained liquid and particles
20 from the gas stream. An upstream wash means upstream of the blades
is arranged and constructed to direct wash water to remove solids,
against the upstream end of the mist eliminator, and directs the
wash water generally co-current with the horizontal flow path of
the gas stream. ~ downstream wash means at the down~tream end of
25 the mist eliminator is arranged and constructed to direct wash
water countercurrent to the gas stream flow, and to remove or
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reduce 801 ids .
The downstream wash means employs a plurality of nozzles, each
of which emits a concentrated non-spray, generally flat, wash
stream to provide a forceful wash stream against the downstream end
S of the mist eliminator, generally in a non-overlapping aLLa~ly --t
and countercurrent to the horizontal flow path of the gas stream,
thereby removing solids accumulated on the downstream portions of
chevron blades and reducing the entrainment of wash water into the
gas stream from the mist eliminator. The downstream wash means has
lO nozzles to provide a non-conical, fan-like horizontal line of wash
li~uid, rather than a cone spray pattern against the downstream end
of the mist eliminator.
- The method of the invention comprises directing, in place of
the downstream prior art conical spray nozzles, a plurality of
l6 concentrated wash streams from concentrated wash nozzles to provide
f lat wash streams against the downstream end of the mist
eliminator, the streams in a non-overlapping arrangement to remove
solid particles from the downstream portion of the chevron blades
and reducing the entrainment of such concentrated wash li~uid in
20 the clean gas.
The method of the invention comprises a combination of wash
3treams, conical and non-conical, for the feed gas stream. The
method of the invention further includes directing the wash water
from the upstream end in a conical spray, generally between
25 opposing, spaced-apart surfaces of the mist eliminator blades, and
also directing a concentrated flat, non-conical wash stream onto
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the opposing surfaces at the downstream end. The method
additionally includes controlling the sequence and timing of the
conical and flat wash water injections.
The invention comprises a replacement of all or most of the
5 full cone spray nozzles of the downstream part of the wash system,
and employing flat or concentrated, defined, stream nozzles, which
generate a thin, concentrated, water wash stream, rather than a
conical spray wash stream, which flat stream is directed in a
stream countercurrent to the gas flow, and directed to the selected
lO areas of the exposed surfaces of the chevron blades to ef fect
washing. The liquid stream does not have to cover the entire
surface of the blade surface to be washed, rather the concentrated
- stream is relied on to dislodge particles from the surface and to
form a concentrated, downwardly flowing wash stream on the blade
l5 surface, which concentrated descending liquid wash stream dislodges
solid particles on the blade surface and cleans the surface, and
this increases the ef f iciency of the wash method and extends the
time between shutdown for cleaning of the blade surfaces.
It has been found that the employment of concentrated stream
20 noz21es, and the use of a concentrated flat non-droplet liquid
stream of the wash water provides, surprisingly and unexpectedly,
for an efficient removal of particle buildup and has other
advantages; for example, the concentrated stream does not encourage
the pickup or entrainment of the wash water in the horizontal flow
25 gas stream, as would the use of a full conical spray made up of
spray droplets, where much of the downstream wash liquid would be
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picked up and re-entrained in the horizontal gas stream before it
went into the mi6t eliminator to be washed, which, in addition to
reducing washing capability, may also necessitate the use of an
additional mist eliminator. Further, the use of a concentrated
6 stream provides more direct power in the selected area for the
dislodgement of adhering solid particles, with the liquid striking
a solid blade surface area, and a lot more liquid wash water is
provided to a smaller blade surface area. Also, the concentrated
wash water stream more easily penetrates the counteL~uLL~ntly
lO flowing horizontal gas stream.
A wide variety of chevron-type or bladed mist eliminators may
be used, wherein the blades become encrusted with particles of
debris from a gas stream, and may be employed in conjunction with
the wash system of the invention. One type of a prior art
15 vertical-flow chevron-type mist eliminator is shown, for example,
in USP4,601,731, issued July 22, 1986. For example, a mist
eliminator may have a plurality of uniformly spaced-apart chevron
blade about 12" deep and about 6 to 8 feet in length. While a
concentrated stream may also be employed on the upstream end of the
20 chevron miat eliminator, this is not required and not necessarily
preferred, thus it i8 desirable, where both upstream and downstream
wash water is used, to maintain the present operation of using full
cone, overlapping spray nozzles on the upstream chevron blade
surfaces, while employing the concentrated stream nozzles with the
25 concentrated liquid stream in a non-overlapping aLLal~y~ - t against
the downstream chevron blades.
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The prior art method comprises directing such water in conical
sprays from full cone wash nozzles against the surfaces of the
upstream ends of the chevron blades and the downstream ends, to
provide the washing of 6ubstantially all of the surface~ of the
6 chevron blades to remove solid particles adhering to the chevron
- blades, and directing entrained liquid, wash water and washed off
solid particles to a sump; and removing from the mist eliminator
and di6charging a clean gas.
One key to successful washing of a horizontal flow chevron
lO mist eliminator is getting wash water to all parts of the chevron,
that is, to all or substantially all surfaces of each blade. Water
enters from the front, or upstream end, and from the back, or
- downstream end. Recent work has shown that an important action is
the flushing action; there is value to impingement, but it is not
l6 the only action. The full cone spray is effective when it does not
have to move against an opposing gas stream; it provide6 relatively
uniform coverage, and flushes well with some impingement. To date,
this method has been considered the best for all washing
applications of this type. The flat spray of this invention does
20 not provide a uniform initial distribution, and it was previously
held that such poor initial distribution would result in poor
washing. This, however, has not proven to true.
In the high velocity environments of today' 8 horizontal flow
chevron mist eliminators, ~or downstream washing the high
26 penetration of the flat spray is proving to be more important and
efficient than the uniform initial coverage provided by the full
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cone spray. For downstream washing, the flushing action of the
descending water, if provided with adequate penetration into the
body of the mist eliminator against the gas flow, approaches the
cleaning efficiency of upstream washing. For most current needs,
5 downstream washing with appropriate fixed position flat sprays
should prove very satisfactory, particularly in high wash liquor
velocity wash systems. For~ especially difficult services, some
washing enhancement can be provided by providing moveable f lat
spray nozzles. This will permit greater uniformity of delivery of
~0 wash water to the chevron blade surfaces. The need for moveability
must be balanced against its initial cost and the increased
maintenance required.
In another embodiment of the invention, the flat concentrated
downstream nozzles are made moveable to deliver wash water against
15 a greater selected area of the downstream end of the mist
eliminator and against the high velocity gas stream. In one
embodiment, the flat stream nozzles, in groups, may be vertically
moved, i.e., up and down adjacent the downstream end of the mist
eliminator to deliver the wash stream to a grèater selected blade
20 surface area to promote washing efficiency. For example, the flat
spray nozzles may be positioned on an H-type ladder, with the spray
nozzles on the cross bars, and the legs moveable vertically to
deliver the wash stream up and down the downstream blade surfaces.
In another embodiment, the f lat spray nozzles may be rotated a
25 selected angle ; e . g ., 3 0 to 6 0 degrees , to provide the f lat wash
spray against the downstream end of the mist eliminator.
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In a further embodiment, the flat spray nozzle may rotate in
a selected arc, and, in addition or separately, also move
vertically to provide a vertically and rotatably moveable
multiplicity of flat concentrated sprays of wash water against the
5 entire or substantially entire surface area of the downstream end
of the mist eliminator.
Thus, the movement of one or more of the flat spray nozzles in
various directions provides concentrated wash water over a greater
selected spray surface area of the downstream end of the blades to
~0 improve wash efficiency.
After the processing of the gas stream through the wash system
and the horizontal flow mist eliminator, the gas stream,
representing a clean gas stream, is then directed to a stack and
discharged, or if desired, may be subjected to other processing or
16 treatment, for example, the use of another mist eliminator to
remove any additional water as required.
The invention will be described for the purposes of
illustration only in connection with a preferred embodiment;
however, it is recognized that various changes, corrections,
20 additions, modifications and i ~ c,v~ -nts may be made to the
illustrated embodiments by persons 3killed in the art, all falling
within the spirit and ~cope of the invention.
Brief Description of the Dr~wings
Fig. l is a schematic illustration of the mist eliminator
25 system of the invention in a side elevational view.
Fig. 2 is a schematic illustration of the mist eliminator
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system shown in Fig. 1 in a top plan view.
Fig. 3 is a schematic illustration of another . ' -';.~nt of
the mist eliminator system of the invention in a side elevational
view .
s Flg. 4 is a schematic perspective illustration of the
embodiment of Fig. 3 illustrating vertically moving wash nozzles.
Flg. 5 is a schematic perspective illustration of another
embodiment of the mist eliminator illustrating a rotatable wash
nozzle .
I0 Flg. 6 is a schematic perspective illustration of the
embodiment of the mist eliminator of Fig. 5 illustrating a
rotatable wash nozzle in a multiple, H-type ladder configuration.
Description of the r o~- t~
Flg. 1 is a schematic illustration of the mist eliminator
S system including the invention 10 in a side elevational view. As
shown, fuel 12, e.g. coal or a fluid hydrocarbon, enters a furnace
14, which produces an acid-containing exhaust gas 16 to be
processed, e.g., a gas containing oxides of sulfur. The acid-
containing gas 16 is reacted with an alkalinè salt-water slurry
liquid 18, such as a limestone water slurry, and the reacted liquid
slurry 20 is removed. The reacted gas with entrained liquid 22,
said liquid having solids dissolved therein and/or carrying
particulate solids, then passes to the chevron-type mist eliminator
26. The chevron-type mist eliminator 26 is shown having full cone
2s wash nozzles 24 upstream of the inlet end 27 and the flat
c~nc-~n~rated stream wash nozzles 30 at the downstream of the outlet
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end 29 of the mist eliminator. A wash control means 28, to control
the timing and sequence of the spray nozzles 24 and 30, i8 6hown
above the mist eliminator 26, and a sump 32 for collected liquid
and particles is shown below. The clean gas 34 is then removed
S from the chevron-type mist eliminator 26 and directed to a stack
36 for discharge.
F$g. 2 illustrates schematically a portion of the system of
Fig. 1, that is, the mist eliminator wash apparatus of the
invention, in a top plan view 40. As seen from above, the full
10 cone wash nozzles 24 provide a wash water on the upstream end 27 of
the blades in a conical spray 44, while the flat stream wash
nozzles 30 provide a flat, concentrated spray arc 42 directed
toward the downstream end 29 of the blades.
Fig~. 3 and 4 illustrate another embodiment of the invention
15 50, wherein the flat concentrated downstream nozzles 58 are made
moveable to deliver wash water 56 against a greater selected area
of the downstream blade surface 29. Fig. 3 shows a side
elevational view of a single wash nozzle pipe configuration 57, and
as shown by arrows, the flat stream nozzles 5B may be vertically
20 moved, i.e., up and down, adjacent the downstream ends of the
blades 29 to deliver the wash stream 56 to a greater selected blade
surface area to promote washing efficiency. Fig. 4 shows the flat
spray nozzles 58 positioned on an H-type ladder 48, with the spray
nozzles 58 on the cross bars 46, and the legs 45 moveable
25 vertically to deliver the wash stream 56 up and down the downstream
end of the mist eliminator 29. Other structural c~ ents are
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numbered and unction as described in Fig. 1.
In another embodiment of the mist eliminator of the invention
60 shown in Figs. 5 and 6, the flat spray nozzle 62 may be rotated
a selected angle, e.g., 30 to 60 degrees, to provide the flat wash
5 apray 64 against the downstream end of the blades 29. Fig. 5 shows
one pipe 68 with the wash water 65 entering the pipe at one end,
and the pipe rotating i 30 to rotat~e the flat spray nozzles 62 to
provide wash water 64 to directly wash a wider area of the
downstream blades 29. In Fig. 6, multiple flat spray nozzles 62,
~0 positioned on a series of pipes 68 in the H-type ladder of Flg. 4,
rotate in a selected arc of i30. In addition or separately, the
pipes 68 also may move vertically, to provide a vertically and
rotatably moveable multiplicity of flat spray nozzlea 62 to provide
flat concentrated sprays of wash water 64 against the entire or
15 substantially entire surface area of the downstream end of the mist
el iminator 2 9 .
The invention thus comprises an improvement in the removal of
acid gases from an acid gas-containing feed gas stream, and also
has advantages for use with other mist eliminators, where gas
20 streams tend to build up particles on the blades of the mist
eliminator. The invention also is directed to a chevron mist
eliminator and wash apparatus for use with the horizontal f low gas
stream, particularly an acid gas-containing stream which haa been
treated prior to introduction into the mist eliminator, with a
26 reactant slurry, such as, for example, an alkaline slurry like a
lime or limestone, to react with the acid gases.
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The method of the invention provides for removal of acid gases
from an acid gas-containing feed gas stream, which method comprises
treating the feed gas stream with an alkaline reactant containing
liquid slurry to provide a gas stream with reduced amounts of acid
5 gases and entrained liquid and solid particles, and passing the
gas stream, with generally horizontal flow, through a blade-type
mi8t eliminator comprising a plurality of spaced-apart, generally
vertically arranged blades having a front and back end, to provide
a clean gas.
~0 The method comprises directing wash water in a conical spray
from full cone wash nozzles against the upstream end of the mist
eliminator and directing wash water in a flat stream spray from
flat wash nozzles against the downstream end, to provide the
washing of substantially all of the surfaces of the chevron blades
l6 to remove solid particles adhering to the chevron blades, and
directing entrained liquid, wash water and washed off solid
particles to a sump; and removing from the mist eliminator and
discharging a clean gas.
The composition o~ the wash water sprayed from the nozzles may
20 vary as required for the specific cleaning process; however, ~t may
be comprised of detergents, surfactants, chelating agents, or acid-
alkaline slurries or other combinations thereof. The temperature
of the wash water may also vary, for example, from between 500C and
100C, and the pressure of the wash water to the nozzles may be in
26 the range of 15 to 60 psig.
In another embodiment of the invention, the flat concentrated
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downstream nozzles are made moveable to deliver wash water against
a greater selected area of the down6tream surface of the mist
eliminator and against the high velocity gas stream. In one
t, the flat stream nozzle may be vertically moved, i.e.,
S up and down adj acent the downstream ends of the blades to deliver
the wash stream to a greater and selected blade surface area to
promote washing efficiency. For example, the flat spray nozzle may
be positioned on an H-type ladder, with the apray nozzle on the
cross bars, and the legs moveable vertically to deliver the wash
~0 atream up and down the downstream end of the mist eliminator. In
another embodiment, the flat spray nozzle may be rotated a selected
angle; e.g., 30 to 60 degrees, to provide the flat wash spray
against the downstream ends of the blades.
Thus, the ~ ,v~ - t of one or more of the flat spray nozzles in
~s various directions provides greater concentrated wash water over a
selected spray surface area of the downstream end of the blades to
improve wash efficiency.
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