Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVE~TION
The present invention relates to treating material
and more specifically to a method and apparatus for process-
ing high sulfur and high alkali kiln dust.
Material treating systems such as a cement material
treating system results in tremendous amounts of dust particles
which must be controlled in some manner. This dust cannot be
allowed to escape to the atmosphere as it creates an environ-
mental problem which is not tolerable in our present society.
The physical operation of collecting the relative fine dust
also presents problems. Also, once the dust is collected,
disposal of the collected dust presents the additional problem
of disposal. A solution for the dust problem is to cycle the
dust back through an improved grate kiln system to utilize the
dust for improving the abrasion resistance of the pellets.
This is feasible hy collecting the dust carried by the off-gas
from a kiln system and dusting the pellets forming in the
pelletizer or blending the dust with the raw material.
A general object of the present invention is to
provide a method and apparatus to process high sulfur and
high alkali kiln dust.
Still another object of the invention is to provide
a method and apparatus wherein waste kiln dust may be utilized
to increase the abrasive resistance of pellets processed
through the treating system.
Yet another object of the present invention is to
provide a method and apparatus for utili2ing kiln dust as an
additive to or during the agglomeration without adding ingred-
ients to the dust to produce a more highly abrasion resistant
pellet.
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A further object of the present invention is to
provide a method for reacting high sulfur content off-gases
with lime to form gypsum anhvdrite which is readily collected
and has the potential to be utilized as a commercial by-product.
DESCRIPTION OF THE DRAWINGS
Fig. 1 is a diagrammatical view in side elevation
and partly in section of a material treating apparatus for
performing the process according to the present invention;
Fig. 2 is a fragmentary view of the material treat-
10 ing apparatus of Fig. 1 showing a modification thereof; !
Fig. 3 is a fragmentary plan view of the mixing boxshown in Fig. 1 showing a modification for supplying dust
to the kiln off-gases in the preheat zone;
Fig. 4 is a fragmentary plan view of the mixing box
of Fig. 3 showing still another modification for supplying
dust to the kiln off-gases in the preheat zone;
Fig. 5 is a diagrammatical view showing a source of
waste dust that is usable in the apparatus shown;
Fig. 6 is a diagrammatical showing of another source
Of waste dust usable in the apparatus; and
Fig: 7 is a diagrammatical showing of still another
source of waste dust usable in the apparatus.
Description of the Apparatus
Referring to the figure of the drawing, raw material
for the apparatus to be described is supplied by a suitable
agglomerating device such as a balling or pelletizing pan 10
or a dru~ that is fed from a hopper 11. The raw green pellets
are deposited on a feeder 12 which feeds the green pellets to
a gas pervious traveling grate 14. A housing structure 16 is
arranged to enclose a space over the grate 14 and define a
material inlet opening 17. A baf~le wall 18 is suspended from
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the roof of housing 16 to a predetermined distance above grate
14 and operates to divide a space enclosed by housing 16 into
a preconditioning or drying zone or chamber 21. Another baffle
wall 22, suspended from the ceiling of enclosure 16 to a pre-
determined distance above grate 14, serves to define a first
preheat or preburn zone 23 and a second preburn or preheat
zone 24. A negative pressure wind box 30 below the precondi-
tioning or dry zone 21 is provided. Green pellets on grate 14
will be transported through the drying zone 21, then through
the preburn zones 23 and 24, and then discharged down a chute
26 into an inlet opening 27 of a refractory lined rotary kiln
28.
Rotary kiln 28 slopes downwardly from chute 26 toward
a hood 29 that encloses the discharge end of the kiln 28 and
defines a passage 31 from kiln 28 to a cooler 32. The downward
slope of the rotary kiln 28 causes material received from chute
26 to pass through kiln 28, then into hood 29 and through pass-
age 31 to the cooler 32, which may be a device as shown in V.S.
patent No. 2,256,017 divided into stages.
The cooler 32 is provided with blowers (not shown)
that blow controlled quantities of air, through suitably
connected ducts 34 upwardly through wind boxes 37, 38 and then
through material on an air pervious grate 39. A baf~le 41 may
be provided to divide cooler 32 into a first stage or primary
cooling zone 42 and a second stage or final cooling zone 43
over grate 39. The cool air supplied is blown upwardly through
wind box 37, grate 39, chamber 42, and passage 31 into the
firing hood 29. A burner 44 is mounted on and projects into
the interior of hood 29 to deliver and burn fuel that raises
the temperature of gases passing into kiln 28 to the desired
high temperature level required for the difficult high sulfur
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and high alkali content materials receiving heat treatment in
the kiln. Gas flow input from the discharge end of kiln 28
and up chute 26 and into the mat~rial preheat zone 24 will be
in a temperature range of 1600-2400 Fahrenheit.
The waste off-gases from the cooler 32 are recouped
and utilized in the drying zone 21 and in both of the preheat
zones 23 and 24. To this end, the cooler off-gases from the
final zone 43 of the cooler 32 are drawn into an exhaust duct
46 which is connected to a mechanical cyclone dust collector
47. A fan 48 connected between the dust collector 47 and a
supply duct 49 operates to pass the gases into the supply duct
for subsequent utilization.
The kiln off-gases to preheat zone 24 can be very
high in sulfur and alkalies with gaseous sulfur exceeding the
level that can react with or tie-up with alkalies. Thus an
excess of gaseous sulfur in the gas from preheat zone 24 con-
ventionally bypassed to the drying chamber 21 or to the waste
gas exists and presents a problem since present environmental
standards prescribe maximum sulfur in waste or stack gases.
Thus, an efficient means must be provided to reduce the sulfur
in the waste gas to stack. With the conventional bypass, the
potential of the sulfur going through the drying bed in the
drying zone 21 and through a waste dust collector is great.
Also, when the preheat on-gas contains large amounts of sulfur,
a substantial internal sulfur cycle develops which will pre-
vent the desired reduction of sulfur in the ~iln product.
To alleviate the sulfur problems, the high sulfur
gases to the preheat zone 24 are treated with a material which
is chemically reactive with sulfur, such as lime bearing dust.
The lime bearing dust can be material collected from wind
boxes 30 and 62 under the drying zone 21 and the preheat
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zones 23 and 24. Included in these collected materials are
the pellets and fines which back-spill from chute 26.
Sulfur oxides (SO2 and SO3) have a strong affinity
for free lime at temperatures generally above 500 and up to
22~0 ~ahrenheit and readi1y form qypsum anhydrite (Ca 5O4).
The gyps~ anhydrite that is forme~ in the calcined material
bed is processed through the kiln 28. The high lime bearing
material from the wind boxes 30 and 62 is recycled and blown
into the kiln off-gas stream to add lime bearing fines with
lo which the sulfur in the kiln off-gas will combine and can be
removed.
To this end, the lime bearing material from the pre-
heat zone 24 and also from the preheat zone 23 and the drying
zone 21 which pass through the traveling grate 14 are collected
on a lower conveyor 63 and the pellets and fines are passed to
a pulverizer 65 and thence to an elevating device, such as a
pneumatic pump 66. The collected and pulverated dust from the
pump 66 is directed back to the preheat zone 24 via a duct 67
and is dropped in a substantially transverse vertical path into
the up-sweeping kiln off-gas stream flowing into a bypass
mixing box 81: Thus, the recycled dust from the pump 66 has a
better potential for being more completely calcined and thus
be reactive with the sulfur in the kiln off-gases. A portion
of this calcined dust will pass through a material bed on the
grate 14 and will be pulled out by the cyclone separator 73 in
the form of gypsum anhydrite.
Gas which is relatively free of sulfur is obtained
from the cooler 32 via the connected duct 46. As previously
mentioned, this gas is passed through a mechanical dust collec-
tor 47 wherein the larger dust particles are removed from thegas. The fan 48 draws the gas from the collector 47 and forces
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the gas through the duct 49. This relatively sulfur-free gas
is passed via duct 71 to burner 60 connected to preburn zone
24 to supply the necessary combustion air to burner 60 which
controls preheating and calcining of the bed material as well
- as for effecting the forming of gypsum anhydrite.
Another duct 72 connected between supply duct 49 and
burner 61 is connected to preburn zone 23 to supply the
necessary combustion air to burner 61 which initiates pre-
heating and calcining of the bed material as well as for
effecting the forming of gypsum anhydrite. Still another
portion of the sulfur-free gas is utilized in the drying
zone 21.
The preheat off-gas that is also delivered to the -
drying zone 21 might be too hot for the drying zone and thus
must be cooled. To this end, bleed-in air from a duct 70 is
utilized as tempering air for the relatively hot preheat off-
gases. Duct 70 also includes a damper 75 which is operative
to permit a controlled flow of te~pering air. The wind box
off-gases are passed through a cyclone dust collector 73 and
thence are passed via a fan 74 and a duct 76 to the drying
zone 21. A regulating damper 77 is operable to control the
volume of the wind box off-gases entering the drying zone 21.
Thus, the off-gas from preheat zones 23 and 24 entering the
drying zone 21 is tempered by ambient air to establish a
drying atmosphere of 700 ~ahrenheit or below.
A duct 7B connected to the supply duct 49 communicates
with the drying wind box 30 under drying zone 21. A damper 79
operates to control the pressure in the supply duct 49 dumping
excess gases into the drying wind box 30. This stabilizes the
flow of gases through the supply duct 49 and thereby stabilizes
the operation of the cooler recoup fan 48. With this arrange- -;^
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ment, only the single fan 48 is required to recoup the gases
from the cooler 32.
A portion of the kiln off-gas in the preheat zone
24 which contains a substantial amount of reacted and calcined
dust from duct 67 is drawn into a ported cage mixing box 81
and mixed with a controlled volume of cooler off-gases from
duct 82 or ambient tempering air from duct 80 that are directed
into the mixing box. To control the quantity of the cooler
off-gases that are directed to the mixing box 81, a damper 86
is operatively disposed within the duct 82. Duct 80 also
includes a damper 87 which is operative to admit a flow of
tempering air into the mixing box 81 as required. The mixed
gases in the mixing box 81 are moisturized as required by
means of sprays 83 which are a part of a water system 84.
The tempered and moisturized mixed gases in the mix-
ing box 81 carry some of the now reacted calcined dust, added
via the duct 67, and are mixed in the mixing box 81. This dust
is substantially free lime. Since sulfur oxides (S02 and SO3)
have a strong affinity for free lime at temperatures between
500~ and 2200 Fahrenheit, they react with the dust in the
mixed gases in the mixing box 81 and form gypsum anhydrite
which is a potential usable by-product. Thus, the gases from
the mixing box 81 are passed through a mechanical cyclone dust
collector 90 where the coarser gypsum anhydrite dust particles
are collected and thence through an el~ctrostatic or permeable
bag precipitator 91 wherein the finer dust particles are collec-
ted from the gas.
The relatively clean gases are drawn from the electro-
static precipitator 91 by a fan 92 and directed into an air
heater 94 via an interconnecting duct 93. Within the air
heater 94 the gases from the mixing box 81 are reheated. A
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controlled quantity of cooler off-gases obtained from the
supply duct 49 via an interconnecting duct 96 are supplied as
relatively sulfur-free combustion air to the air heater burner
95. The quantity of the cooler off-gases that are supplied to
the air heater 94 is controlled by a damper 97. The volume of
the bypass gases to the air heater 94 is controlled by a damper
98. Thus, the temperature of the mixture of bypass mixing box
gases is raised to a suitable level before it is passed via a
duct 99 to the preheat zone 23.
~he bypass gases, when not utilized in the preheat
zone 23, is directed to the stack 101. This is accomplished
by opening damper 100 and closing damper 98. On the other
hand, the gases in the negative pressure wind box side 30 of
the drying zone 21 are waste gases which are disposed of
through a stack 102. A fan 103 draws these waste gases through
a duct 104 and an electrostatic precipitator 106
Fig. 2 illustrates a modification of apparatus for
practicing the process herein disclosed. The apparatus dis-
closed is generally similar to that of Fig. 1 and includes the
feeder 12 which deposits the green pellets on the gas pervious
traveling grate 14. The housing structure 16 encloses a space
over the grate 14 and defines the material inlet opening 17.
The baffle wall 18 operates to divide the space enclosed by the
housing 16 into a preconditioning or drying zone 21 and a dual
preheat zone 23 and 24. The preheat zones 23 and 24 are
separated from each other by the baffle wall 22. As in the
case of the apparatus of Fig. 1, the baffle wall 22 extends
downwardly a distance just sufficient to allow the bed of
material moving with the grate 14 to clear the lower end of the
wall 22. The baffle wall 22 serves to maintain a separation of
the gases in the zones 23 and 24. That is, the high sulfur
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gases flowing from the kiln into preheat zone 24 are maintainedseparated from the relatively low sulfur gases in preheat zone
23. The cooler recoup gases to the supply duct 49 are utilized
in the drying zone 21 and preheat zones 23 and 24 in the manner
previously described for the system 9.
The system 110 varies from the system 9 in that the
wind box 162 is constructed and arranged to extend rightwardly,
as viewed in Fig. 2, to include a portion of the drying zone
21. Thus, the waste gases drawn out of the wind box 162 will
lo also include a portion of the relatively sulfur-free waste
gases from the drying zone 21. In addition, the portion of
the waste gases from the drying zone 21 will be at a tempera-
ture which is substantially lower than the temperature of the
drying gases. Thus, this relatively low temperature substan-
tially sulfur-free gas will serve to temper the off-gases from
the preheat zones 23 and 24. This blend of off-gas at a suit-
able temperature is directed back through duct 76 to the drying
zone 21 and reused. -~
A further modification which can be usefully employed
with either the system of Fig. 1 or the system of Fig. 2 re-
lates to the manner in which the reclaimed dust from the pneu-
matic pump 66 can be introduced into the kiln off-gases. As
shown in Fig. 2, a duct 167, in lieu of duct 67, is connected
to direct dust from the elevating pump 66 into the preheat zone
24. The duct 167 is connected to the housing 16 and communi-
cates with the interior of the preheat zone 24 from the end of
the housing 16. In this manner, the dust is introduced into
kiln off-gas in a direction with the stream flow.
Fig. 3 depicts still another modification of intro-
ducing the dust from the pneumatic elevating pump 66 into thekiln off-gases. In this case, a duct 267 is connected to the
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pump 66 and the side of the housing 16 to thereby effect the
introduction of the reclaimed dust into the kiln off-gas
stream at an angle to gas stream flow. This has an advantage
of exposing additional kiln off-gases not bypassed to the
treatment dust.
Fig. 4 depicts a further modification of introducing
the dust from the pneumatic pump 66 into the kiln off-gas
stream. As shown in Fig. 4, a duct 367 connects the pump 66
to the side of the mixing box 81. Thus, the waste dust is
introduced into the kiln off-gas as it mixes with recouped
gases from the cooler 32. This arrangement provides the advan-
tage of exposing only the bypassed kiln off-gases to the treat-
ment dust.
The systems set forth in detail above are well adap-
ted to utilizing nonmarketable waste dust which has a rela-
tively high sulfur content as an additive to the raw material
being fed to the balling device such as a pelletizer pan. The
addition of the high alkali waste dust increases the abrasion
resistivity of the wet pellets. This substantially reduces
the breakage or shattering of the pellets, reduces dusting and
generally increases the overall pellet quantity.
In Fig. 5, waste gas from a source such as a rotary
kiln 111 is passed to a mechanical separator 112. The separa-
tor 112 separates the larger dust particles from the gas with
the larger dust particles being deposited in an elevating and
feeding device. The cleaned waste gas passes from the mechani-
cal separator 112 to an electrostatic precipitator or bag house
116. The fine dust particles removed from the waste gas are
fed to the conveyor device 114 where it mixes with the coarser
dust particles from the mechanical separator 112. The cleansed
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waste gases are drawn from the precipitator 116 by a fan 117
and passed to a waste stack 118.
The combined waste dust particles are fed to a hopper
119 and thence to a balling device such as a pelletizer pan 121
which is similar to the pans associated with the systems
depicted in Figs. 1 and 2. The waste dust is moisturized in
the pan and formed into green pellets which are processed
through the systems of either Fig. 1 or Fig. 2.
In Fig. 6, another method of utilizing waste gas dust
as system material is shown. Waste dust from an electrostatic
p~ecipitator or bag house 116 is fed to a blender 127 and mixed
with new raw material to be processed. The blend of waste dust
and new raw material is delivered to a hopper 128 and thence
- fed to the pelletizer pan 129 and formed into raw green pellets
for processing through the systems. The cleansed waste gases
are drawn fr~m the precipitator 126 by operation of a fan 131
and passed to a stack 132.
~; Fig. 7 illustrates still another method of utilizing
waste dust having a relatively high alkali and sulfur content.
As shown, the waste dust is obtained from a source, either a
storage pile or a kiln 136. The waste gas and dust is drawn
;; into a mechanical separator 137 where the coarse dust particles
~ are separated out. These coarse dust particles are funneled to
-~ a conveyor 138. The waste gases are passed from the mechanical
separator 137 to an electrostatic precipitator 141 wherein the
, waste gases are cleansed of fine dust particles. The fine dust
particles are passed to the conveyor 138 combining with the
larger dust particles from the mechanical separator.` The con-
veyor 138 operates to deliver the collected dust to a hopper
30 144. The collected waste dust from the hopper 144 is fed
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to the outer stage of a two stage pelletizer 146 where it
is utilized to coat the green raw pellets formed in the inner
stage of the pelletizer 146. Waste gases are passed to the
waste stack 143 by operation of a fan 142.
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