Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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APPARATUS AND METHOD FOR FE'EDING COMBUSTIBLE
DUST M~TERIAL TO A DUST BU~NER
This invention relates to an appara~us and method for
feeding combustible dust material to a dust burner.
Heretofore, varioUs types of systems ha~e been known
for feeding ~ossile fuel powders, such as lîgnite and bituminous
coal dust and mixtures thereof to a dust burner. In many cases,
the dust material is conveyed pneumatically from a storage point
~o the burner. For this purpose 9 various ~ypes of devices have
been used. For example, ~s described in German 0.5~ 27 28 386,
one known device employs a ro~atable disc which is provided with
a plurality of passage holes for receiving charges of the
fluidized fuel. During rotation of ~he disc~ the ~assage hol~s
into which the fluidized mixture is charged are brought into
coaxial position with ~ pneumatic transport stream. In ~his
process, the mixture within the passage holes is taken along
by the transport stream and fed to the burner. It has also
been known to arrange ~uch a device downstream of a supply
tank in which ~he ~u~l is irst fluidized and then fed to the
devic~ for dosed transfer into th~ transport ~tream to the
burner.
~owever, it has been ~ound tha~ ~here are certain
risks involved in stoxing lignite and bituminous cs 1 powder
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or dust and mixtures thereo~ in a supply tank wherein there
is a substantially c~n~i.nuous feeding in of a considerable
amount of fresh air, especially of the fluidizing air, in ~he
supply tank and ~he device for transferring the powder into
the pne~matic transport stream. That is, there is a considerable
risk that the powdered or dust ma~erial m~y self-ignite.
It has also been known, as describe~ in French Patent
365jO9~ to feed fluidized vegatable fuels, especially moist
~aw dust, to a burner from a supply tank vi~ a worm. HPWeVer,
self-ignition of the moist saw dust is not pr~cluded. Furthex,
the fluidizing air which is a~ a slight overpre6sure is not
prevented from passing to~the supply of fuel.
While it is known to inhibite self-ignition of many
materials by feeding an inert gas to the supply tank or to khe
transport lines of the materials, such techni~ues not only
necessitate constant availability of the inert gas itself but
also feed lines for the gas and, in particular, sealing means
to prevent access of foreign gases to the inert gas.
Accordingly, it i~ an object of the invention to
reduce the risk o~ sel~-ignition in combustible dust materials
supplied to a dust burner from a storage tank.
It is another ob~ect of the invention to increase the
s~orage safety of a coal powder and its mixture in a suppl~
tank in a simple manner.
It is another object of the inventlon to increase
the s~orage safe~y of a co~bus~ible dust material wi~hout
adversely influencing the ~eeding ~f ~h~ material ~ a burner.
I~ is an~ther ob~ect o the lnvention to eliminate
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the need to provide a means for suppl~ing inert air or gas to
a ~ystem for ~eediny combustible ~ust matexials to a burner.
Briefly, khe in~ention provides an apparatus for
feeding combust~ble dust material to a dus~ burner which is
compxised of a supply tank, an air se~tling ~nd discharge chamber
an air di~chaxge line and means for E~neumatically transpsrting
chaxges o~ ~he dust material ~o the dust burner. The supply
tank serves to store the combustible material and is pro~vided
with a filling opening for charging of the tank and a discharge
1~ openin~ for discharging the material. The settling and discharge
chamber receives the dust material from the discharge opening
while the air discharge line communicates with *he discharge
chamber to exhaust air therefrom. The pneumatic means i~
situated below the settling and dischar~e chamber in ordex to
pneumatically transpor~ charge~ of the dust material to the dust
burner.
The tank may also be provided with a vibrator di~charge
means at the discharge opening for discharging dust material
unifoxmly through the discharge opening. In additivn, a
fluidizing chamber is positioned ~elvw the settling and discharge
chamber for receiving and fluidizing ~he dust material~
The invention also provides a method of feeding
combustible dust material to a ~urner. This me~hod includes
the StQps of storing a supply of combustible dust material in a
5uppl~ tank and o~ di~harging the material ~rom the tank into
and ~hrough an air sektling and discharge chamber main~ained a~
a pressure ~ubstantially e~ual to the air pressure in the supply
tank, Therea~kex, ~he dus~ ma~er~al is ~luidized ~ownstxeam o~
the set~ling and discharye chamber and charges of the fluidized
material are ~ransporte~ into a pneumatic ~ranspor~ ~tream for
delivery t~ the dust burner.
In acoordance with the invention it is considered
5 that atmospheric air which has penetra~ed from absve into the
supply tank durin~ filling of ~he tank ~ecomes inert in a
short time if the air col~mn above the fuel column is sta~nant
and no additional quantity of new air (oxygen) is fed there-
from to the powdered fuel in the supply tank~ This holds true
even if ~he ~upply tank is open a~ ~he filling opening or is
povided with a valve which only takes caxe that, while the supply
tank is ~eing emptied, no underpre~ure is generated therein.
The air settling and discharge chamber which is provided
serves to stop a continuous feeding in of fresh fluidizing ~ir
15 from ~he pneumatic transporting means. Thus, air (oxygen~ is
prevented frompassing from the pneumatic transporting means into
an adjacent section of ~he supply tank. In ~his way, th~ air
~oxygen~ is prevented from penetratiny into the uel colu~
so that the danyer of smolderin~ and burning is reduced.
Of note, there is a slight overpressure in the air
which passes ~rc: m the pneumatic transpor~ing means ~ However,
this sïi~3ht overpressure i5 led off via the air discharye line.
E'urther, by ha~ing the air discharge lisle directed upwardl~
at an inclined ~ngle ~ the dust thak snay b~ taken along with the
air i5 separa~ed in ~e manner e~f an air elutriator.
These and o~cher objec~s and advan~a~e~ o ~e inventiorl
will becc~me m~r~3 apparent ~rom the ollowing detailed descrip~ion
tak n ~n s:~on~un~tiorl wi~h ~he ac:compar~yi:ng ~rawings wherein:
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Fig. 1 illustrates a ~chematic ~iew of an apparakus
constructed in ac~Qrdance with the invention;
Fig. 2 illustrates an enlarged view of the apparatus
in paxt of Fig. l;
Fig. 3 illustrates a modified apparatus construc*ed
in aceordance with ~he in~ention: ~nd
Fig. 4 illustrates a further modified apparatus
sonstruGted in a~cordance with the invention.
Re~erri.ng to ~ig. 1, the apparatus f~r feeding a
combu~tible dust m~terial includes a supply tank 1 in which
a combustible dust m~terial such as a powdered coal is stored.
A means 2 is pr~vided below ~he supply tank 1 for pneumaticall~
transporting ehaxges of the dust material, for example to a
pneumatic eed line.
Referring to Fig. 2, the supply tank 1 has a filling
openin~ 3 at the upper end through which the dust material is
charged into the tank 1. This filling openin~ 3 may be provided
with a closure or may be left wi~h~ut such a closure~ I~ a
closure is used, a ~alve 4 is provided next to the opening 3
to admit only s~ much air to the supply tank 1 as fuel dust is
delivered therefrom withc:ut generating an underpres~ure in the
space 5 above the c~lumn St of fuel. In an~ case, the atmosphere
in the space 5 above the fuel dus~ column St i5 se~tled and
no 10w is generateh b tween the outside air above ~he ~ank 1
25 and the spac~ 5 ~n ~e tank 1. The air in the ~pace 5 can thus
be called ~tagnan~
The supply tanlc 1 is also provided Wi~}l a ~unnel shaped
lower sec~ion ïa whic}l terminates ~n a dischar~e opening. In
3 ~, ~ 'a
additiorl, a vibra~or discharge means 6 is provided at ~he lower
end of the tank 1~ This vibrator discharge means 6 is pro~ided
wi~h a suitable mo~r 7 and serves ~o discharge the dust material
uniformly downwardly fxom the tank 1.
An air settling and di$char~e chamber 8 is disposed
below ~le vibratGr discharge means 6 in order to receive dust
~aterial from the discharge opening o~ the tank lo This settling
and discharge chamber 8 may be o~ funnel-shape as indicated
and is disposed direc~ly below the discharge opening of ~he
tank 1- As indicated in Fig. 2, the funnel-shaped chamber 8
has a conical wall 9 o~er which the fuel dust may pass via a
neck 10 lnto a worm conveyor 11. As indicated, the worm conveyor
~1 has a ~ro~t end 12 which extends into a section 13 of the
pneumatic transporting means 2 in order to deliver dust material.
The pneumatic transportin~ means also has a fluidizing
chamber 15 below the section 13 in order to fluidize the dust
material delivered from the worm 11. As indicated in Fig~ 1,
a ~luidizin~ line 14 opens into the cham~er 15 in order to
~eliver air thereto ~o fluidize the dust material delivered via
the conveyor 11. In addition, a rotatabl~ disc 16 provided
with passaye holes is disposed within the chamber 15 for dîspen-
sing dosed charges of the dust material ~rom the chamber 15.
This di~c 16 is cons~ructed, for example, as descxibed in Germ~n
O.S. 27 2~ 386. During rotation, ~he hole~ o the di~c move
into a position which is axial with respect ~o a pair of
~ranspor~ s~ream lines 17, 17a ~hrough which a pneuma~ic txansport
stream passes. The pneum~tic transp~rt stream causes the dust
materlal to be b~own out o~ ~he respective holes o~ the disc 16
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~ s ~hown in Fig. 1, the fluidiæing line 14 and the
transpor stream line 17 axe connected to a common air line
18. In add~tion, an intermediate blower 19 may optionally
~e provided in the line 17~ The transport stream line 17a
leads, along with an air line 20, in~o a burner 21 of a heatin~
boiler 22 of a hot water heating plant 23.
Re~erring to ~igs~ 1 and 2~ an air dischargP li~e
24 communicates with the air settling and discha~ge.chamber 8
~o e~haust air ~here~rom. ~s shown in ~ig. 8, the discharge
line 24 leads to a filter 25, the lower section of which leads
via a line 26 directly or indirectly into the ~illing opening
3 of the tanX 1~ In addition, a ~lower 27 is disposed upstream
of the ilter 25 in ~he line 24 in order to create a slight
suction for drawing off air from the settling an~l discharge
chamber 8. In this way, a pressure can be maintained in the
chamber ~ which is no ~reater than the air pressure in the tank
1.
Sometime after the coal dust is filled into the tank
1, the air in the space 5 is made inert. Likewise, the air
which slowly follows a~ter ~ia the opening 3 or the valve 4 due
to the removal o:E the dust from the ~ank 1 becomes inert in a
short time~ The fluidizing air which emmenates ~xom the pneumatic
~ransporting means 2 is a~ a slight oYerpressure ts:~ which, in
part, ~e pressure ~rom the ~ransport line 17 is added i:~ the
dlsc 16 rotates in ~ront o~ tha lines 17,, 17a. ~lowever, this
slight overprPssUre is xeduced by the air discharge line 24 and
does not extend into the pile o~ coal dus~ in the tank 1. Further,
~he pressure wi~hin ~he air ~et~lin~ and di~char~e chamber 8
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can l~e controlled and reduced by means o:E the blower 27 BO that
no ~resh air can get in~o the pile of coal dust ~rom bel~w.
Referring to Fig. 3; wherein like reference chaxacters
indicate like par~s as above, a plurality of baffle~ e
5 compt:?nents 28 may be provided in and under the settling and
discharge chamber 8 in place of ~he wc)rm conveyor 11. These
baffl e-like component~ 28 serve to settlP the fluidizing air
which emerges upwardly xom the transporting means 2.and prevents
the fluidizing air from the transporting means 2 fxom passing
~ia the vibrator means 6 into ~he dust column St of the supply
tank. As i~dicated, the upper section ~f the fluidizing chamber
has a conical part 29 wi~h~ a downwardly directed opening 30 while
an upwardly directed mounting cone 31 is provîded above the p~rt
~9. The emerging flui.dizing air thus strikes the inside 32
of the coT71e 31 in the direction indicated by the arrows 33,
i5 deflected downwardly in the direction indicated by the arxsws
34 and, in the process, takes along the dust sliding down on the
conical part 29 without penetrating into the chamber ~ in larger
amounts.
ZO As indicated in Fig. 3, the tank 1 may be closed off
by means o~ a closure 35~ In additi~n, as an option, inert gas
can be admitted vîa a line 36 into the supply tank 1 above the
dust material column S~. This inert gas may be burnex gas
which is cooled down in a heat exchanger or another waste gasO
To avoid clogging with coal dust~ the e~haus~ line
24 can be replaced by a dischaxge line 44 whi~h is directed
upwardly at an inclined angle. The angle o inclinatic)n may
be near or ~3:o~re ~he an5~1e of repo~e or slide s~f the coal dust. .
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Re~erring to Fig. 4, wherein like refererlce chara~ters
indicate ~ ike par~.~ as above ~ ~e se~:~ling and discharge
chamber 4 O may have an upper inle~ ! opening ~o the discharge
opening of ~che supply tank 1 and a lower ou~le~ 41 opening
the fluidizing cha~er via the con~reyor 11 as well as a c:entral
portion which is of larger cross-sec~ion ~han the inlet 42
and outlet ~l. In this manner, ~e ~ettling of the air which
is introduced intc) the chamber 40 c::an be further ~romoted.
The ~arious apparatus described above may be operated
10 on a continuous basis or an intermittent basis ~cs as to ~eed
dust material to a burner.
