Note: Descriptions are shown in the official language in which they were submitted.
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Th~s ~nyent~on ~el~tes gene~all~ t~ gas separation by
electxo~t~tic precipitato~s and more particularly to an improved drag
scraper assembly in electrostatic precipitators for removlng particles
from a collection sur~ace on the bottom of the precipitator.
; The removal of particles from a gas stream by an electro-
static precipitator is well known in the art. A typical electrostatic
precipitator of the plate type which removes part:Lcles from the gas flow~ ~
ing therethrough is illustrated in Ragland U.S. Patent No. 3,425,190. ~ ;
In such precipitators, gas ~lows through an inlet port into the precipi-
tator and through gas passages for~ed between rows of vertical co:Llecting
electrodes, Suspended within each of these gas passages are a plurality
of discharge electrode wires which are electr:Lcally insula~ed from the
shell. As the gas passes through the gas passages between the collector
electrodes, the dlscharge electrodes ionize the particles in the gas and
the particles are attracted to and collected on the collector electrodes.
The particles which collect on the collector electrodes are then removed
in any conventional manner such as by rapping the collec*or electrodes
causing the particles to be dislodged from the plates and fall to the
bottom of the precipitator. As shown in the Ragland Patent the bottom
o~ the precipitator contains a number of hopper bins into whlch the dust
particles fall and are collected and then removed through the bottom of
the hopper to the outside of the precipitator.
In many situations, it is undesirable to use hoppers at
the bottom of the precipitator ~or removal of dust particles. In many
industrial areas, the space in which a precipitator can be constructed
is limited and the hopper concept for removal of the particles may not
be practical. In such situations, the hoppers are replaced by a hori-
zontal floor or collection surface in the botto~ of the precipitator.
The particles from the collecting plates ~all to the floor and are
collected thereon. The preferred manner of removing the particles ~rom
the collec~ing surface on the bottom oE the precipitator is to ~1nploy an
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endless chain and scraper system ~ust above the collection surface. The
endless chain has a plurallty of spaced scrapers secured ~hereon which
run trans~erse to the ~low of gas through the precipitator. As the end~
less chain belt xevolves, the scraper blades contact the dust in the
bottom of the precipitator and push the dust particles to one end of the
precipitator where the dust can be collected in a single short hopper or
pushed onto a removal con~eyor means, or removed in any other convenient
~anner.
The removal of the particles by the use of an endless chain
and scraper system does have a number of disadvantages. ~or an electro-
static precipitator to properly remove particles suspended within the gas,
the gas must remain in the gas passages between the collector electrodes.
Since the collection surface of the precipitator is below the bottom of
the collector electrodes, there is a space between the collection sur~ace
and the collector electrodes where gas coming into the precipitator may
flow to the opposite side of the precipitator; thus, this gas is not
cleaned because it never passes between the collector electrodes. Since
it is desirable to ha~e a high degsee o~ efficiency in a~ electrostatlc
precipitator, this gas flowing along the bottom of the precipitator is
extremely undesirable as it reduces the efficiency of the precipitator.
In addition, the gas ~lowing along the bottom of the precipitator will
tend to re-entrain those particles which have been precipitated out of
the gas and have fallen to the collection surface of the precipitator.
To obstruct the flow of the gas below the collector elec~
t~odes and to ~orce the gas back up into the gas passages between the
- collector electrodes, a plurallty of baffle systems are suspended between
the ad~acent collector electrodes and collection surface o~ the precipi-
tator. These baffle systems have a plurality of pivotable or flexible ~ -
baffles so that when the endless chain revolves and the scrapers contact
the pivotable baffles, the baf~les will flex or pi~ot and allow the scraper
to pass thereunder. However, it has been found that when the scraper on
the top flight of the endless chain contacts and rotates the pivotable
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baffle, gas will flow th~ough 2 la~ge gap underneath the scraper lnto the
next sectlon between the ba~fles without being forced back up into the gas
passages or will flow upward over the ne~t baffle and back down into the
next section without being cleaned. In addition, as the gas flows around
the scraper blade when it is pivoting the baffle out of the way, the gas
will tend to re-entrain the particles that ha~e been collected on the
collection surface thus decreasing the efficiency of the precipitator
system.
It is not now dlfficult to make an elec-trostatic precipitator
1~ having a collection efficiency of 90%. However, it is much more difficult
and highly expensive to increase the efficiency from 90% to 100%. In an
electrostatic precipitator having the drag scraper and baffle system pre-
viously described, the efficiency of the precipi~ator is approximately
97.6%. Although this seems to be extremely efficient, it ls desirable to
reach as high an efficiency as possible in order to insure the least
amount of air pollution. Therefore, a means is desired wherein the
collection efPiciency of the precipitator can be increased even higher.
Accordingly, it is desirable to provide an electrostatic
precipitator with a particle removal system that will overcome the afore-
mentioned disadvantages and others; thus, this teaching enables the pro-
vision of an electrostatic precipitator with an improved drag scraper
assembly which includes an lmproved baffle system or increasing the
i collection efficiency of an electrostatic precipitator to substantially
98.8%.
More particularly in accordance with the invention there
is provided, an improved drag scraper assembly/or electrostatic precipi-
tators which include an endless chain means above a particle collection
surface of the precipitator having a top flight advancing in -the dlrection
of gas flow th~ough the precipitator and a bottom flight advancing in a
dlrection opposite to the gas flow; scraper means secured to the chain
- ~eans traverse to the flow o~ the gas for pushing articles collected on ~ ~
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the surface toward a collection hoppex ~o~ the pa~tLcles.; ~Lnd bAffle means
e~tending between lower portions of adJeLcent collector electrodes o~ the
precipitator and the particle collection surface ~or obstructing the flow
o~ gas between the lower portions and the collection surface, a first
portion of the baffle means being pivotable by the scraper means advancing
with the top flight to permit passage of the scraper means through the
baffle means, and a second portLon of the baffle means being pivotable by ~.
the scraper means advancing with the lower flight to permit passage of the
scraper means and the particles through the baffle means, the improvement
comprising: a plate means beneath the first portion oE each baffle means
for preventing the flow of gas between the first portions and fixed portions
o~ the ba~fle means dur;Lng pivotable movement of the first portion as the
8craper means passes through the baffle means.
The above and Purther objects and novel features of the
invention will appear more fully from the following detailed description
when the same is read in connection with the accompanying drawings. It
is to be expressly understood however, that the drawlngs are not intended
as a definition of the invention but are for the purpose of illustration
only.
In the accompanying drawings of a specific embodiment of
the invention, wherein like parts are marked allke~
~igure 1 is a schematic illustration in side elevation of : :
an electrostatic precipitator generally showing the improved drag scraper ~:
assembly of the present invention; ~ -
Figure 2 is a schematic end view of the improved drag
scraper assembly of Figure 1 taken along the lines II-II showing the endless
chains, scraper, and fixed and pivotable baffles; and
Figure 3 is an enlarged view of the drag scraper assembly
of ~igure l showing the endless chain and scraper assembly and the baffle
3~ assembly.
~eferring to Fi~ure l, an improved drag scraper assembly, ..
denoted generally by numeral 12, for use in electrostatic prec:Lpitators,
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denoted generall~ b~ nu~er~l 10, haying an endless chain 14 aboYe a
particl~ collectlon surface 16 of precip~tator 10 and ha~ing a top flight
18 advancing in the direction of gas flow, as shown by the arrow in
Figure 1, through precipitator lQ and having a bottom flig~t 20 advanclng
; in the direction opposite to the gas flow, as shown by the arrow in Figure
l. A scraper 22 is secured to endless chain 14 traverse to the flow of
the gas for pushing particles 24 collected on col:Lection surface 16 toward
a collection hopper 26 for disposal of particles 24. A baffle assembly,
denoted generally as numeral 28, extends between lower portions 29 of
adjacent collector electrodes 30 of precipitator 10 and the particles
collection surface 16 for obstructing the flow of gas between the lower
portions 29 of collector electrodes 30 and the collectlng surface 16. The
baffle assembly 28 includes a first portion, denoted generally by numeral
32, which is pivo~able by scraper 22 which advances with top fllght 18 to
permlt passage of scraper 22 through ba~fle assembly 28. Baffle assembly
28 ~urther includes a second portion denoted generally by numeral 34 which .
is pivotable by scraper 22 which advances with lower flight 20 to permit
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passage of scraper 22 and particles 24 through b~ffle assembly 28. The
improvement comprises a plate assembly, denoted generally by numeral 36, -.
beneath first portion 32 of each of the baffle assemblies 28 for preventing
the flow of gas between first portion 32 and a first fixed por-tion 38 and
a second fixed portion 40 of baffle assembly 28 during pivotable movement ~ :
of first portion 32. -~.
More specifically, and referring again to ~igure 1, elec~
trostatic precipitator 10 includes a plurality of collector electrodes ~0
. . . . ...
which are spaced apart and are suspended within electrical precipitator 10 :
in the conventional manner. Collector electrodes 30 are spaced within
precipitator 10 to for~ gas passages (not shown) therebetween for directing ~ -
the particle laden gas through precipitator lO between collector electrodes :
30. Suspended between the spaced collector electrodes 30 and in the gas '~
passages are a plurality of discharge wire electrodes ~8. The dlscharge :
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elect~odes 48 a~e suspended w~thin elect~ostat~c precipitator 10 ln any
conventional m~nner so that they are insulated fro~ the shell of precipi
tator 10. ~eights 50 are attached to the bottom of each of the discharge
electrodes 48 to keep the wires straight and to keep them from oscillat-
ing due to the electrical field around each discharge wire 4~. ~s the
particle laden gas flows between spaced collector electrodes 30 in the
gas passages, discharge electrodes 48 are energi~ed which cause particles
24 in the particle laden gas to be ioni~ed. These ionized particles 24
are then attracted to and collect on the surface of collector electrodes
30. ~fter a predetermined length of time a certain amount of particles
24 from the particle laden gas are collected on collector electrodes 30.
The collector electrodes 30 are then rapped in the conventional manner to
dislodge particles 24 from the collector electrodes. The partlcles 24
fall to the bottom of precipitator 10 where they are collected on collec-
tion surface 16.
Referring now to ~igures 1, 2, and 3~ once particles 24 are
collected on collection surface 16, a ~eans must be employed to remove
particles 24 from collection sur~ace 16 of preclpitator 10 for disposal
outside the precipitator system. To accomplish the removal o particles
24, a drag scraper assembly 12 is utili~ed. Drag scraper assembly 12
consists o~ a plurality of endless chain systems 14 (see Figure 2) spaced
traversely to the gas flow; each endless chain system 14 is spaced be-
tween lower portion 29 of collector electrodes 30 and collection surface
16. Each endless chain system 14 includes a pair of aligned sprockets
52 (Figure l) positioned at each end of precipitator 10. The traversely
spaced sprockets 52 of each endless chain system 14 are connected by a
shat 54 which extends the width of precipitator 10 traverse to the gas
flow. The ends of sha~ts 54 are supported in conventional bear~ng
mounted supports tnot shown) secured to the shell o precipitator 10.
Shats 54 are ~ree to rotate ~ithin the bearing mounted supports.
Surrounding and connecting each o~ the aligned sprockets 52 is an endless
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chain 17 as shown in ~iguxes 1 and 3. ~ndless chain 17 has a top flight
1~ ~hich t~als in the same direction as the gas flow and a bottom ~light !i
20 which tra~els counter to the direction of gas ~low. An end of one of
the shafts 54 is connected to an electric motor (not shown) Eor rotating
shaft 54 and consequently æprockets 52 and endless chain 17, in the direc-
tion and at the speed desired.
Endless chain 17 has a plurality of circumferentially spaced
scrapers 22, as shown in Figures 1, 2 and 3, which are attached to the
endless chain 17 in any conventional manner and extend traversely to the
gas flow as shown in ~igure 2. Scrapers 22 may be a single scraper extend-
ing the entire width of precipitator 10 but preferably comprises a plurality
of scraper segments 22 traversely aligned as shown ln ~igure 2. As shaft
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54 is rotated by the motor in the direction shown by the arrows in Figures
l and 3, scrapers 22 are also rotated by enclless chain 17. As scrapers
22 on bottom flight 20 traverse the length of precipitator 10 counter to
the direction of the gas flow, scrapers 22 push particles 24 along surface
16 of the bottom of precipitator 10 towards hopper 26. Scrapers 22 con- ~ ;
tinue to push particles 24 until they fall into hopper 26 where they are !`
disposed of in the conventional manner outside the precipi-tator system.
Referring to ~igure 1, between adjacent collector electrodes
30 and collection surface 16 is a plurality of baffle assemblies 28 which
run transversely to the gas flow and obstruct the gas from flowing along ,
; collection surface 16 of precipitator 10 to prevent the particle laden
gas from flowing out of precipitator 10 without being cleaned by discharge ' '`
electrodes 48 and collector electrodes 30. The baffle assemblies 28 are
designed to force the particle laden gas upward and into the gas passages
between collector electrodes 30 so that the particle laden gas can be
cleaned prior to exiting from precipitator lO.
Referring now to ~igures 2 and 3, which show the preferred r
con~truction of baffle assemblies 28, a support beam 56 is spaced between
lower portion 29 o~ collector electrodes 30 and top flight 18 of endless
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cha~n 17. Support bea~ 56 is po~itlone~ so it is in alignment ~lth the
s~ace between ad~acent electrodes 30. Suppor~ beam 56 is secured to side
walls 42 and 44 of precipitator 10 such as by welding. A first fixed
portion 38, which is preferably a solid plate, is secured to support beam
- 56 such as by welding and extends substantially the width of precipitator
10 and extends upward between ad~acent collector electrodes 30. First
fixed portion 38 deflects the particle laden gas which flows below the
bottom of col~ector plates 30 upward and into the gas passages between
collector electrodes 30 to insure proper cleaning of the gas. A plurality
o~ plates 58 are secured to a side of support beam 56 such as by welding
as shown in Figure 3. A chain link 60 is preferably used as a hinge for
allowing first portion 32 to pivot. Chain link 60 ls prefe~red as the
hinge beGause it provides a pivot and ls not adversely affected by the
hot, corrosive, and dusty atmosphere within precipitator 10~ conventional -
hinges tend to bind up within a short time a~er being exposed to such -
atmosphere. Chain link 60 is hung from plate 58 through a hole 59 and
supports pivotable baffle 64 through hole 61 in the baffle. Upper baffle
plate 64 spans the width of precipitator 10 transverse to the direction of
gas flow. Preferably, upper baffle plate 64 is made in sections as shown
in Figure 2. However, upper baffle plate 64 may be made as one piece and
extend the entire width of precipitator 10. Preferably upper baffle
plate 64 should extend downward to a point ~ust above endless chain 17 to
make as small a gap as possible between them to restrict the flow of gas
therethrough. In addition, this will allow upper baffle plate 64 to
freely pivot without contacting endless chain 17.
Plate assembly 36 includes a second fixed portion 40,
preferably an I-beam as shown in Figure 3, and is spaced between top
flight 18 and bottom flight 20 of endless chain 17. Second fixed portion
40 is secured at each end of sides 42 and 44 (Figure 2) of precipi-tator
10 such as by welding. A chain guide channel 68 (Figure 3) is posi-tioned
on top o~ fixed portions 40 and extends substantially between aligned -~
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sprockets 52 in vertical alignment-~ith top Plight 18, Chain guide channel
68 slidably supports top Plight 18 oP endless chain 17 as it traverses the
length oP precipitator 10 in the direction o~ gas Plow. Chain guide
channel 68 prevents top Plight 18 of endless chain 17 from flexing up and :
down as it travels the length oP preclpitator 10.
Plate assembly 36 Pu~ther includes Ll platform plate 66 which
substantially extends across the width of precipitator 10 transverse to the
direction oP gas flow. Platform 66 is secured to the top of second fixed
portion 40 such as by welding. Platform 66 extends in height substantially
the same as the top of top Plight 18 oP endless chain 17, and is notched
to receive chain guide channel 68 through which endless chain 17 passes. ~;
The top of platform 66 is in lateral alignment with the top of top flight
18 to provide a smooth slid-lng surface Por scraper 22 to sllde against
when it travels the length o~ precipitator 10 in the direction of gas flow.
Platform 66 extends downstream Prom second Pixed portion 40 a distance
needed so that the downstream edge 46 of platPorm 66 is beyond the dis~
engagement point where scraper 22 no longer contacts upper baffle plate 64
when it passes thereunder. That is, as endless chain 17 moves scraper 22
in the direction oP the gas flow, scraper 22 will contact and pivot baffle
64 upward. As scraper 22 pivots baf;Ele plate 64 upward, scraper 22 will
be -ln sllding engagement with the ~op oP platPorm 66. When scraper 22
travels do~mstream and passes beyond the upper baffle plate 64, it will
still be in sliding engagement with platform 66. As scraper 22 clears
upper baffle plate 64, and baffle plate 64 pivots downward, scraper 22
passes the downstream edge of platform 66 and is disengaged Prom platform
66.
The lower second baffle portion 34 includes an angle bracket
70 which is secured to the lower edge of second fixed portion 40 such as
by welding. A second chain link 60 supports baPfle pla-te 72 from bracket
70 in the same manner as described for baPPle plate 64. A plura;Lit:y oP ''.
traversely spaced lower bafPle segments 72 must be used rather than a
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single baffle t~aye~sing the Width of P;recipitator lO since baffles 72 must
extend below lower flight 20 of endless chain 17. Thus there will be a
slight gap between lower baffles 72 to allow lower flight 20 of endless
chain 17 to pass therethrough. This allows baf~les 72 to hand down below
bottom flight 20 of endless chain 17 so that the lower end of lower baf;fles
72 extend to a point just above collecting surface 16 as shown in Figure 1.
In operation, a particle laden gas enters precipitator 10
through an inlet port (not shown). The particle laden gas flows through
the gas passages (not shown) between collector electrodes 30. The dis-
charge electrodes 48 are energized causing particles 24 within the gas to
be ionized. Particles 24 are attracted to and collect on collecto~ elec-
trodes 30. Collector electrodes 30 are rapped in the conventional manner
to dislodge particles 2~ therefrom which fall to collection surface 16
at the bottom of precipitator 10. The particle laden gas which is flowing
through precipitator lO will also flow along the bottom of precipitator 10
below lower portion 29 of collector electrodes 30. When -the particle
laden gas contacts baffle- assembly 28, it is deflected upward so that it
re-enters the gas passages between collector electrodes 30 to be properly
cleaned.
To remove particles 24 from collection surface 16 of pre-
cipitator lO, shafts 54 and consequently sprockets 52 are rotated so that
the top fllght 18 of endless chain 17 moves in the direction of the arrows
shown in Figure l, that is, in the direction of gas flow. The bottom
flight 20 of endless chain 17 moves in the direction counter to the direc-
tion of gas flow as shown by the arrow in Figure l. As endless chain 17
moves, so does scraper 22. When scraper 22 is on top flight 18 of endless
chain 17, it will move in the direction of the gas flow. As shown in
Figure 39 top flight 18 of endless chain 17 moves within chain guide
channel 68. As scraper 22 approaches baffle assembly 2~, scraper 22 will
contact the top part of platform 66 and slide there along. As scraper 22
contacts platform 66, it also contacts upper baffle plate 64. Since upper
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31~045S63
baffle plate 64 is connected to cha~n link 60, scraper 22 will plyot upper
baffle plate 64 upward as scraper 22 continues t~ move ln the direction of
the gas ~low. ~s long as scraper 22 is in contact with upper ba~fle plate
64, it remains in sliding engagement with platform 66 thereby preventing
any particle laden gas from escaping between scraper 22 and platform 66
thus maintaining a gas seal while upper baffle plate 64 is pivoted. As
scraper 22 continues to travel in the direction of the gas flow, it will
release upper baffle plate 64 and allow it to pivot downward so that it is
again slightly above platform 66. Scraper 22 then passes beyond the down- ~
stream edge 46 of platform 66 and continues to travel in the direction of ~-
the gas flow.
As scraper 22 passes around sprocket 52, it will continue
its travel along bottom ~light 20 of endless chain 17 counter to the
direction of gas flow. As scraper 22 travels counter to the direction of
gas flow, it contacts and pushes particles 24 in the direction of hopper
26 as shown in Figures 1 and 3. As scraper 22 continues to travel along
bottom flight 20, it will also contact lower baffle plate 72 and pivot it
upward so that scraper 22 may pass thereunder. Since scraper 22 is travel-
ing counte~ to the direction o~ gas ~low, a good gas seal will be main- ~;
tained between the second fixed portion 40 and the bottom surface 16. ~s
scraper 22 continues to travel, it w:Lll pass from under lower baffle plate
72 and allow lower bafEle plate 72 to pivot downward so that it returns
to a posi~ion slightly above collection surface 16. Scraper 22 continues "
to push particles 24 counter to the diraction of gas flow until the
particles 24 fall into hopper 26 where they are disposed of outside the
precipitator system. Scraper 22 then passes upward around sprocket 52 and
starts its travel over again on top flight 18 of endless chain 17.
The foregoing has presented a novel drag scraper assembly
for use in electrostatic precipitators. The problem of a particle laden
gas passing beneath the collector electrodes along the length of the
precipi~ator and out to a gas stack without being sufficiently cleaned has
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been substantially eliminated by pr~Y~iding a baff]e system which will sub~
stantially prevent the particle laden gas ~rom flc~ing the length of the
precipitator outside the ln~luence o~ the collector electrodes by deflecting
the particle laden gas upward and into the gas passages between the collec-
tor electrodes where the cleaning process takes place. The problem o~
having a substantial air gap through the baffle system when the scraper
on the drag scraper assembly pivots the upper baffle out of the way has
been substantially eliminated by providing a platfor~ plate having a
downstream length sufficient to assure that the scraper is always in
contact with the platform while it ls pivoting the ba~Efle thereby main-
taining a gas seal between the platform and scraper.
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