ACOUSTIC CHAMBER FOR THE AEROSOL TREATMENT OF EXHAUST GASES

CHAMBRE ACOUSTIQUE POUR AEROSOLISATION DE GAZ D'ECHAPPEMENT

English Abstract

2097070 9209354 PCTABS00013
The invention relates to an acoustic chamber (3, 6, 7) for the
aerosol treatment of exhaust gases, which are to flow through the
chamber and which are exposed therein to an acoustic field.
According to the invention, the chamber has a regular polygonal
cross-section and the sound sources (4, 5) transmit sound waves into
thechamber under such an angle that the sound is repeatedly
reflected from the walls of the chamber before it hits on the other end
of the chamber a sound reflector (8, 9). Due to the intensive
irradiation, fine dust particles are put into vibration and coagulate
to larger grains, which can then be filtered away.

Claims

WO 92/09354 PCT/EP91/02214
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CLAIMS
1. An acoustic chamber for the aerosol treatment of exhaust
gases, which are to flow through the chamber and which are
exposed therein to an acoustic field, wherein the chamber has
a regular polygonal cross-section with 2k sides and wherein k
sound sources are provided, the axes of which, projected on a
cross-section plane of the chamber, include an angle of 180/k
degree and who are each associated to a respective side wall
of the chamber, and that k reflectors are likewise disposed,
the sound sources transmitting sound waves into the chamber
under such an angle with the chamber axis that the sound is
repeatedly reflected from the walls of the chamber before it
hits on the other end of the chamber a sound reflector, which
is likewise disposed in an inclined position, so that a
stationary wave is formed and that the exhaust gases flow
through the chamber linearly and along the chamber axis.
2. An acoustic chamber according to claim 1, wherein k is two
or three.
3. An acoustic chamber according to claim 1, wherein means are
provided allowing to change the length of the chamber between
the sound sources and the reflectors.
4. An acoustic chamber according to claim 1, wherein the sound
sources are capable to excite a sound field at a frequency of
below 25 kHz.

Description

WS> 92i093~;4 2 0 9 7 0 7 0 PCI/EP91/0~711
-- 1 --
TITLE OF THE INVENTION
An acoustic chamber for the aerosol
treatment of exhaust gases
.
The invention relates to an acoustic chamber for the aerosol
treatment of exhaust gases, which are to flow through the
chamber and which are exposed therein to an acoustic field.
FIELD OF THE INVENTION
Exhaust gases often contain very fine solid particles, the
rate of which is to be reduced as much as possible before the
exhaust gases are freed into the environment. Up to now! such
- dust filters use either electrostatic fields or mechanical
processes (cyclone or venturi separators) which are very ex-
pensive and the filter effectiveness of which remains limited.
BACKGROVND OF THE INVENTION
,
From Spanish patent 459 523 a proposal is known to use an
ultrasound chamber for the cleaning of fumes. In this patent,
a sound field is produced in a tuke axially to its axis and
the gases to be cleaned are heli~ally led through the tube,
the particles being put into vibration and interaction by the
sound field, so that they agglomerate. Then, the larger par-
ticles can be evacuated from the exhaust gases by simple me- ;~
chanical filters.
.
The acoustic ch~nber according to this document is only suited
for small fume flow rates, since with greater fl~w rates, the
; helical laminar ]path of the fume-flow chan~es into a turbulent
~ 35 flow. Further, the pressure losses at passing through the
-.. .
:::. . . : . . ., ... ::.. . -- , - ,., , . ,,,,. ,.,:
., .. . . .,- . ... . . . . ... .

WO 92J?D93~4 ,, i l; p??CT/EP91/02214 ~g .
~9~ 0~ ~ - 2 - '-_)
chamber are important and may rlequire an additional ~fan to
finally expulse the exhaust gasles into th~e chlmney.
- ~ ` SUMMARY OF 5'HE INVENTION
The ob~ect of the'~nvention ls to adapt such a chanber,to the
use in ~he industrial field, i.ls. with greater flow rates, and
at th~e same-time to reduc~e'the pressureilosses in'the.chamber.
~ " .J.~ ! ;f . s, ,~ r ~ 3 ~,
This ob~ect'is~achisved'accordin~ to'the''~invention~by;the .
ac?ioustic chamber which comprises the features of l, the-charac-
teristic part of claim ~.iContrary.to the known aerosol-cham-
ber, the exhauts gases flow through the chamber along itsiaxis
in a-straight line, while the'sound''field fills'~the'chamber in
a multiply broken way.~Simultaneously,'-~'by`using~`several~.sound'`r
sources,'an optimal sonorisation of'^the'chamber~'is achi'eved
without the differènt c?ound waves?InfluencIng:each?other'. For
' con~tructional''reasons~'it is u33ful .to~give'the chamber-~a
square~or~hexagonal`constant crosis-section~ ?, ~ ,?.~f~
" , ~ Y ~ J~;'
By the maasure according to claim'~.3,~`it?becomes possible,~to
direct-this-sound sources preciis~ely:to the associated~re1ec-
tors,"which laads'to'an'?op~imaI~en~ergy efficiencyO'ip~..?~r??;~ ` ?~ r?.~.
~ ? ~it?~ r ~ c~?~ ~*~ ?~ ?r;l?t~ ~ f~ ~? r7t~-~
. ~ DETAILED DESCRIPTION~'THErINVENTION!~7~lr.
" ) ~ t ~, ;, r ~ f ~ h .f, r7~ ,r.?~ .?i~ .,t r ., ? S¢~??.~?~?,~JI~ ~I
The-lnvention will~now'be described'?'by~means'of-'?a pref2rred
~smbodiment and with~reference:to~~rthe~`~raw$ngs.r~ '; ~ ui-
-; c~ r ~ s m ~ ? ' ?~ I ~ F ~i~??S~:~ f; r-: ~ r,~ ~ ~ ,?~ I r~, ~?, ~ ~ ? ? ~ t? S ?~?~i ~ 3 i~ f`? ~
-Figure.1 show!3 in per-~p~ctive an outside`visw`of a~'chamber ~?`
according to the inv?antion . ~ ?
.? ( .? ~ ? ~ ? ,~ t~ r.~.?i ? S.? ~ r;
Flgure'2 shows'an axial cross-sacti'on~:*hrough'this:3~chamber.
Figure;3lshows'means'that Gan be used for varying'~the~''length~
: , ' ` ,; , ~ " -

~W~2/093~ 2 0 9 7 0 7 0 PCT/EP91/02214~
- 3 - i ) jl
of tha chamber between the sound sources and the reflectors.
Figure 1 shows an acoustic chamber according to the..invention
for the aerosol treatment of sxhaust gases.~It-is.~integrated
into an'lnstallation for cleanin~ fumes and has, in~his~envi-
ronment, the task to coagulate t:he fine particles~ito.ilarger
dust particles, which can then be separated by a mechanical
filter''~not shown). The exhaust gases are supplied~.to the`'
chamber Yia an inlet duct 1 in the direction of arrow;2,~ithe
~hamber consisting of three duct portions disposed`,in ali~n-~:
ment, i.e. a'fir~t duct portion 3, on which-'are mounted sound
transmitters 4 and 5, a duct portion 6,:in~whichithe inter-
action between the sound field and~the'fume particles.is ln-
tended to take essentially place, and a duct portion 7,ito
which are mounted:sound reflectors 8~and~9.~The~.ducts~ha~e ai
~quare'cross-section!and are traversed'`~linearly3lby~:the;~.f.umes
-~without any-en!cumbrance.`~iThe`sound~sources~4~and.'i;5~are'~axso~
- ' ciatad'to and respectively of two adjacent~iisides~of-'~$he~duct
portlon 3 and''are-'disposed'in-such-a.way~that thei~iaxis~hits
the respective'opposite wall under an'angle of;..for--.example 'Ci.
60.~In`the same'way,'~the re~lectors~8"and;9 are~mounted:``on`
the'duct`portionl-7;'`In-~the cross-section vlew according~.~to;LI'-
figure 2, the sound source 4 and the a~sociated reflector 9 as
`' well as the'sound field resulting:-tharefrom~in the duct(.1por-
25 ' ~';tion`'6`'are represented-~'If the~length of the central-~.duct t,~
portion'6 is-'chosen'appropriately, and if the-~oundssource 4
and the're~lector;are precisely aligned~~to'each'~other,~ his'
results-in a'stationary sound field as''indicated.
3 ' - ~ ~ ,? f~ ' Q.; . . i ~ ` ` T `~ } /?' I ~
Figure 2 might~also be~regarded as~an orthogonal'.cross-sec~
' tion, which runs-through'~the sound source~.?5~and'the~reflector
' 8.' The sound'source operates for example.~at~:a:.requency of 20
kHz~and the length;of~the chamber between~the~sound sources
and the~`reflectors lies between l andi3 r meters.~ If lower fre-
quanciesiareiused, for example lO kHz, a~tationaryr~soundl~'

W092/09354 ~CT/~P91/0221~ ~
.~grlQ~ - 4 -
field could be produced in a substantially longer chamber of
up to 6 meters, which means that the fumes stay longer in the
chamber and thus the coagulat.ion effect is increased. The
total acoustic power invested is for example 300 Watt, a high-
er eff~iciency being possible also in this case with lowerfrequencies.
In order to be able to precisely ætabilize the acoustic length
betwQen the sound sources and the reflectors, it is suggested
to render the length of the central duct portion 6 slightly
variable and to allow this length to be precisely varied. To
~ this end, for example, a double flange, as it is shown in
detail in figure 3, is used at one end of the central duct
portion. At this point, this duct portion is not directly
screwed to thè reflectors or sound sources, but via an inter-
- mediary member lO, the length ll of which can be varied in
axial direction of the duct by screw bolts 12, the wall conti-
nuity being ensured by two wall portions 13 and 14 sliding one
on the othsr. The pluraiity of bolts 12 distributed over the
duct periphery can be coupled to a common drive motor (not
shown) by a chain 15, so that the length variation can be
obtained by the operator at any time and in a precise manner.
In order to Xeep the reflection at the duct walls as lossfree
as posslble, it is advisable to keep the surface roughness of
the inner side of the ducts as low as possible, such that, if
poss~ble, there are no protuberances exceeding 1 mm.
The invention is not restricted to the embodiment described by
means of the drawings. Thus, ducts wlth hexagonal or even
octogonal cross-section can be used and then three or four
sound sources can be associated to the three or four facing
wall pairs~ It is also possible to invert the direction of
sound propagation for all or only for single ones of the
acoustic systems consisting of sound transmitter and reflector
.~ ~
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W'`~2/093~4 2 ~ 9 7 0 7 ~ PCT/~P91/0~211
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and to dispose the sound transmitters on the side of the duct
portion 7 for gas evacuation.
Due to the linear and practically undisturbed flow cross-sec-
tion of the chamber for the fume to be filtered, the pressure
losses can be kept small, so that there is no need for an
additional fan. The chamber can be mounted, as desired, with
horizontal, inclined or vertical axis.

Representative Drawing