Note: Descriptions are shown in the official language in which they were submitted.
4746 ~2 ~ 529
APPARATUS FOR THE REMOVAL OF PARTICULATES
FROM INDUSTRIAL GAS~S
SPECIFICATION
Field of the Invention
our present invention relates to an apparatus ~or the
removal of dust from indu~trial gases and, more particularly,
to a ~crubber operating with an aqueous scrubbing liquid, l.e.
a scrubber in which the ~crubbing solu~ion 1~ predominantly
water, and which can be u~ed for the scrubbing o~ du~t and
other particles fro~ industrlal gases and especlally
industrial wa~te qa~es such as flue ga~e~ (e.g. gases from
combustion cha~ber~ of boilers or the llke), metallurglcal
plant gases, che~ical plant g~se~, incinerators and the like.
Background _ the Invantion
Applicants and their assignee have fil0d numerou3
U.S. patent applications and obtain~d va~ious Letters Patent~
ln the United States inventing scrubbers ~or, inter aiia,
cleaning industrlal ga-~e~ and removlng particulates therefeom
and the following li~t of repre~entative
patent~ is con~idered to be of ~i~nificance for information
purpo~e~ 801ely and as r2presentative of the earl~er work in
this fiQlB by appli~ant~ and/or their assignee:
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14746
U.S. Patent 4,503,020 and u.S. patent
4,093,434.
Karl-Rudolf HEGEMANN: ~.S. patent~ 3,631,656,
3,726,065, 3,799,520 3,820,307, 3,844,744,- 3,844,745,
3,854,968, 3,976,454, ~,007,02~, ~,052,042, ~,055,331,
4,081,914, 4,145~193, 4,218,241, 4,23~,335, 4,316,727,
4,375,439, 4,427,183, 4,415l142.
From the above-mentioned
will be apparent that it 18 known to provide a ~crubbing
column for the scrubblng of an industrial ga~ with water
wherein at least one atomlzing nozzle is provlded for spraying
the scrubbing liquid and a sump or collectlon facility is
provided at the ba~e of the column for collectlng the
scrubbing liquid which may entrain lnto this ~ump or b~sin the
particulates which are washed from the gas,
It is also known in the scrubbing of indu~trlal gases
to provlde such a column ln conjunction with an electro~tatic
separator havlng a corona-discharge electrode assembly which
is maintained at an electrlcal potential ~uch that a corona or
glow discharge is generated at surfaces of the electrode3 for
charging the particle~.
14746
The term ~scrubbing column~ i8 u~ed herein to refer
to a predominantly upright flow pas~a~e for the gas and the
scrubbing liquid and along the axis of which column a
plurality of individual atomizlng nozzles can be d~sposed
along the axis of th~s tower or column; al~srnatlvely the
nozzle assemblle6 can be spaced along the axis of the flow
passage, each compris$ng a multipllcity of nozzles.
The wet scrubblng which 1B e~fa~tlYe in the nozzle
. region is a wet ~eparation of dust which 18 e~ected by
adhes~on of du3t partlcles to water dropl~ts; collection o~
water droplet~ or du~t particles, adhesion o~ multlple du~t
partlcles to a water droplet, etc., whereby ~h~ partlcles are
removed from the ga~ stream to collect in the step o~ the
scrubbing column.
It is ~el~-evldent that the ~crubbing water will al~o
remove soluble (absorpt~vely removed) and ~d~orbtively
collected gase3 and al90 thu8 ~ay ~crub one or more gaseous
components from the raw ga3,
The scrubblng column can also lnclude one vr more
annular gap or venturi wash~r3 (see the earlier patents
mentioned)~
The corona electrodes which are ut~llzed can operate
under the electrofilter principles described ln Lueger_Lexikon
der Verfahren6technik~ Vol. 16, 1970, p. 119.
. . , _
i;2~
14746
The principle of the electrofilter is similar to that of
a cylinder or plate condensor in which between the field
electrodes a direct potential i~ appl~ed of 20,000 - 70,000 V and
more, l.e. the potential across the gap is closed at the breakdown
S voltage, Thi~ potential i5 derived from an alternating or three-
phaRe network, a high voltage transformer connected to the supply
network and a rectifier connected to the ~ransformer. The
negative side of the rectifier output is connected to the corona-
-discharge electrodes wh~ch pr~ferably have a minimum radius of
curvature and can even be relatively thln wir~s of a rectangular
cro~s section and in many ca6e~ can be provided wlth barb~ or
points. The positive pole of the direct current source is
generally grounded a~ are the dust-collecting electrodes,
~owever, the reverRe polarization of the two sets of electrodes is
15 al30 pos~ible. Within ~he present inventlon as well, the corona-
-di~charge ~lectrodes will be negative and thu~ generally be
connected to the ne~ative side of the rectlfier output while the
electrode~ flanking the corona electrodes will generally be
grounded together with the positive terminal o~ the rectifier.
Within the pre~ent invention as well, the reverse polar$zation of
the electrode~ is pos~ible.
The raw gas ~tream carryiny partlculates i~ conducted
between the electrodes, the du~t particles and/or fine dropletq of
a liquid entrained in the gas stream, being charged by the corona-
-di~charge electrode~ predominantly negatively are attracted
to the du6t-collectlng electrodes. From the latter the
agglomerates of du~t are readily swept into a collecting bin.
~2~
14746
In prlor art sy~tems such an electrofilter can be
follow~d by the qcrubber and ba~ically the appara~us represents an
aggrega~e o~ two du~t-removal device~, namely, the electrofllter
and a scrubber. In such 6ystems the path of the gas through the
aggrega~e i8 relatively long~ e~peci311y since the sy~tem
endeavors to allow sufficient time for the particle~ to charge
be~ore the dust is collected or the collecting electroder4
surrounding the ~orona electrodes. Compact assemblies utillzing
wet Rcrubbing and electro~tatic principle~ have not, there~or~,
been used in pra~tice.
Ob~_cts of _ Invention
It ~, therefore, the prlncipal object of the present
invention to provide an improved du t-removal apparatus for
1ndustrial ga~es which merges an electrostatie and wet-scrubbing
op~ration in such clo~e symbiotic relationship a~ to allow the
entire system to be mo~e compact.
Another ob~ect of the invention is to provide an
apparatus with improved dust-removal capabilities, both with
respect to the dust-removal efficiency (i,e, the degree of removal
of the dust) as well as wlth respect to the li~iting particle
size, i.e. ~he particle size above which all du~t i3 collected
from an en~raine~ qas.
14746
~b~
We have now di~covered/ guite surpri~ingly, ~hat it is
possible to provide a ~elatively compact ~crubbing column which 18
~raversed by a gas and which includeR at least one atomizing
nozzle for spraying the ~crubbing liquid, generally water or a
water-ba~ed scrubbing solution into the ga~ passing vertically
through the column, and an electrosta~ic charging ~ystem so that
the electrostatic charge imparted to ~he particles is greatly
improves the wet scrbbing ~o that both the particle size and the
degree of particle removal will be greatly lmproved over earlier
scrubbing ~ystem~ and aggre~ate~. The invention is ba~ed upon our
discovery of an essential rel~tlonship between the charging system
and the noz~le arrangement and the con~truction of the column
which bring about this unique result and appe~rs to be due to the
fact that the electrostatic action no longer need depend upon
sufficlent time for the partlcles to collect on a dust-collecting
electrode. Indeed, lt appear~ that ~he water dropl~t~ function as
discrete electrostatic dust-collecting surfaces even though they
may not be independently charg~d under the conditions which will
be described,
Speci~ically we have found that it i8 e~ential ~or the
column cross section to be dimensioned so that the gas ~low
velocity i8 5 to 30 m/~ec., preferably 5 to 15 m/~ec. (the cross
section taking into con~lderation any objects within the pa~h of
the flow) while the corona-di~charge electrode assembly in the
flow dlrec~ion of th~ raw ga~ manife^qt~ a corona-discharge
electrode length o~ 15 to 40 cm, preferably 15 to ~0 cm and the
..... . _ . . , . . . . -
1 476 ~2~ 9
corona di~charge el~ctrod~3 are surrounded by polarlzaklon
~lectrode~, and th~ column in the region of the atomizing nozzle
or nozzles and the region lmmediately the~ebelow 1~ free from
p~cking or baf~le~, i.e. ~orms ~ ~ree space in which the
S ~paratlon o~ the du~t from the gas i8 effected.
In a pr~ferred embodiment of the inventlon, ~he flow
cros~ section of ~he column and, of cour3e, the meanR for inducing
the flow of the raw gas ~o and the di~charge o~ the ~crubbed gas
from the column ar~ con~tructed and arranged ~o that the gas
velocity i8 about 10 m/sec. while th~ length of the
corona-discharge electrod~ i~ about 15 cm and the and the corona
digcharge i8 effected with a potential of 20,000 to 70,000 V and
preferably 45,000 V.
~e have found that, under ~hese conditions, the
lS polarization electrode~ surroundlng th~ corona~dl~charge
electrodes do not collect ~ignificant quantitie~ of dust and they
readily release the dust thu3 co~lected in the ~luid traversing
the polarization el~ctrode a~Yembliy, while the agglomeriza~lon o~
dust or li~uid partlcle~ below the ~praying head or head~ is
slgnl~lcantly grea~er than that of other wet-~cxubbing By~ems 80
that th~ degree of 3eparation o~ the d~st i3 greatly ~mproved over
earller scrubblng aggregate~.
Th~ polarization a~embly can c0n8t8t 0~ a multipl$city
of tube sections ~oin~d together in lateral contact with one
another, the tub~ sectlons being, ~or example, hexagonal cross
section tube sections to form a honeyco~b construction through
which th~ corona discharge electrode~ pa88, baing locat~d along
14746 :~Z~Z9
the axes of these tub~ ~ectlons. The tu~e section~ can be
composed of metal and can also serve as dust-collecting electrode~
i de~ired, althou~h it should be noted that the eP~iciency of the
present inventlon does not require the tube ~ection~ to act as
du~t-collecting electrode~. .
The atomizing nozzle may be provided as a pre~Mure
atomizer, i,e. a nozzle which di~per~e~ the droplet~ in the mic~on
particle slze range 801ely by forcing the liquid at high ~elocity
through ~mall orifices, or a 3pin atomizer which impart~ a twist
to the spray. Best r~sults are obtained when each atomizing head
include~ a ~o-called twi~t-cup nozzle from which the spray i~
discharged tangentially from a cylindrical bed through appropriate
Or11Ce8 30 that the atomlzation 18 generated by the twist e~fect.
The washing column of the lnvention can al80 be provid~d
. 15 with an annular gap ~crubber and in thi~ cdse ~he corona electrode
assembly is provlded upstr~am o~ the annular gap scrubber in the
directlon of flow o the gas.
According to a preferred embodiment o ~he lnvention the
corona-di~charge ~lectrode a~sembly i8 provided down~tream of at
least one atomizing no~zle arrangement 80 that the gas reaching
the electrode a~sembly i3 saturated with water ~apor as i3 the gas
reaching the annular gap wa~her. The corona-discharge electrode
as~embly can be ad~u~table with respRct to the annular gap washerO
Summarizing the unique char~cteristics of the instant
invention, we can observe that while the invention utllize~
corona-disch~rge electrod~s to charg~ the dust particles, th~
~tatic collection of these dust par~icle~ on fixed-surface
" .
14746 ~f~
precipi~at~on electrode~ is not neces~ary and i~ replaced by the
collection of the du~t partlcles or droplets which function as
collection surfaces. ~he pola~ization electrodes indeed can
func~ion as du t collection or pre~ipitation electrode~ although
their main purpo~e is to enable a high potential gradient to be
established to facilitate charging of the dust particles.
rief_Description of the Drawing
The above and other objects, features and advantages o~
the pre~ent inventlon will be more readily apparent from the
following de~cription, reference being made to the accompanying
drawing in which:
FIG. 1 is an axial section through a scrubber according
to a first embodiment of the ~nvention~
~ G. 2 ls a detall view drawn to a larger scale of the
region of FIG. ls
FIG, 3 i~ a ~ection taken along the llnes III - III of
FIG. 27 and
FIG. 4 is an el~vational vlew, partly broken away, of a
~crubber according to another embodiment o the inventlon.
Specific De~crl tion
In FIG. 1 we have Rhown a scrubbing column 1 having a gas
inlet 5 at its upper end, a gas outlet 6 a~ its lower end and,
below ~his gas outlet, a sump 20 in which the scrubbing llquid can
collect, the ~crubbing liquid being di~charged via a line 21 along
with partlculates which have been R~parated from the ~ndu~rial
waste gas and which orm a suspens~on or a ~lurry in the liquld~
_g_
, . .
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~Z~Z9
14746
A manifold 22 i8 connected to a reclrculatlng pump or
other source of scrubblng liquid and communicates with a Rcrubber
of vertically ~paced atomizlng nozzle heads 2 which spray dropletY
whlch can be in the micron particle size range, into the ga~
stream passing through the column. According to ~he invention,
upQtream of the atomlzing nozzle arrangement gQnerally represented
at 23, 1~ a corona-di~charge electrode ass~mbly which ha been
represented at 4. The ax~s of the column haR been represented at
3. The column and any ob~truction~ along the path of the ga3 i
dimen~ioned 50 that the gas ~low velocity i8 a preferred value of
S to 15 m/sec. and most advantageou~ly is abou~ 10 m/sec.
A~ can be 3een ~rom FIG. 2, the corona dl~charge
electrode arrangement 4 can compri$e a plurality of vertical
di~charge electrQdes 7 which can depend from a bu~ bax 24
lS supported in t~e housing of the ~crubber by suitable insulators
which have been represented diagrammatically at 25 and 26 and
which are surrounded by polarizing electrodes 8, The polarization
electrode~ 8 are ha%agonal tube ~ection~ as ~hown ln PIG. 3 with
theie walls 8a and 8b, for example, abu~ting one another to ~orm a
honeycomb. A high voltage direct cur~ent ~ource 27 has it8
negatlve terminal connected at 9 to the electrode 7 while iS~
po itive terminal 1~ groundad. The honey comb i~ l~kewise
grounded as repre~ented at 10. The corona di~charge elec~rodes 7
are energized with 20,000 to 70,000 V, preerably 45,000 V a~
mea~ured across the gap beSween ~h~se electrode~ and the
con~ronting sur~aces o ~he hon~ycomb.
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. _ ..... .. . . . .. ... . ... .
147~6
~he tube ~e~tlons 8 are oriented in the flow direction of
the ga~ and the electrode 7 can be barbed electrode~ which lle
along the axes of the respective tube sections 8. The tube
~ections 8 can be compri~ed of metal or a metallic material and
can act as dust-collecting electrode~. The effective length of
the corona-dlscharge electrode has been repre~ented at L and
corresponds of cour~e to ~he length o the polarlzation electrode
tubes 8 and is pre~er~bly 15 to 20 cm.
In this embodiment, the solld part~cle~ or droplets in
lU the raw ga~ stream are negatively charg~d and are, as a result,
attracted to the more positively charged water droplet~ from the
twi~t spray ~rom the atomizing nozzles 2 and thus collect on the~e
water dropl~t~ particularly e~ficiently. The du~t-laden gas
encountering the corona discharge as~embly 7 can have previou~ly
been saturated wlth wat~r.
In the embodiment of PIG. 4 the sa~ura~ion o~ the du~t
with water is ensur~d by a palr o~ atomizlng nozzles 102 wh~ch
spray the scrubbing liquld into the ga~ stream admitted via an
inlet 105 to a scrubb~ng column 101. The latter ha~ a pair o~
housings 130 and 131 recelving the insulators 125 which Yupport~
the bus bar 127, the latter being connected to the direct current
source 1~7. The corona electrodes io7 are su~pended from the t)ar
124 and are disposed within a honeycomb of hexagonal tube sections
108 ~or the ~lectrode assembly 104 as previously de~cribed.
Ano~her at~mizing nozzle arrangement represented at 113
i~ provided below the corona dlscharge assembly and generates the
droplets at which the charged dust part1cles are attracted, the
,.~, . .
.
14746 ~Z~ 9
qeparation being intensiied by an annular gap or venturi scrubber
111 disposed downstream of the no2zle arrangemen~ 113. ~he
annular gap scrubber 111 comprises a vertically displaceable
fru~toconical body 112 dl~po~ed with a shell 132 forming a venturi
throat 133. The vertical adjustability of thi~ body, e.g, via a
~notor o~ other drive as~embly repre~ented at 134, allows the gap
width to be ad~u~ted in ~he annular gap wa~her and hence permits
the pressure drop across ~he annul~r gap washer to be varied.
This allows the control of the back pressure at the
~ource of the ga~, e.g, a press~riæed blas~ furnace. ~ blower 135
or an expansion ~urbine for release of ~he gas energy can be
prvvi~ed downstream o~ the venturi ~crubber and can op~n into a
stack 136 di~charging th~ ~crubbed gas into ~he atmosph~re. It
will be appreciated that the embodiment of FIG. 4, apart ~rom
differences already de~cribed, operates slmilarly to the
embodimen~ of FIG. 1 with re3pect to the collection o~ the charged
particle~. The as~embly 104 can be ral~ed and lowered rela~ive to
the annular gap washer 111 by hand wheel3 140 rota~ing insulating
tubes threaded over spindles 141 by which the as~embly is
su~pended in the insulator 125.
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