Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF TEIE INVF,NTIO~I
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In -the operation of skeel mill and similar pro-
duction facilities large tonnages of rejected screenings
and waste are produced in the form of ore fines, furnace
dusts, water treatment plant sludges, grindings, borings,
scarfings, coke fines, mill scale, slags, and other materials
containing valuable constituents, such as iron oxide and
combustible elements, which range in size from sub-micron
to as læge as three-eighths inch but which are too finely
divided to feed into a melting furnace. The feeding of
such fine materials causes them to be blown out of the
combustion zone beore melting or chemical conversion can
take place.
Thus it has been recognized for many years that
if such screenings and wastes are to be utilized to recover
their constituents including any fuel value which they
contain, it is necessary to form the materials into
agglomerated form.
In the past agglomeration of ores~ concentrates,
screenings and wastes has been accomplished by one or more
of three procedures: pelletizing, sintering and briquetting.
Both pelle~izing and sintering require a high
; plant investment and have high operating costs. Because of
the lar~e scale on which such processes must be carried out
and the large quantities of air and other gases which must
` ~ be handled, pelletizing and sintering are not well suited to
`~ utilization of the more limited quantities of waste and
rejected screenings available at many plant locations. The
pelletiæing and sintering plants now in use require large
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amounts o~ ~uel, sin-teriny plants being particularly
inefficient in the use of fuel. Also, both processes require
complete combustion of non volatile combustible matter in the
material being processed. Objectionable volatile matter,
such as the oil frequently present in mill scale and water
plant sludges, can present serious pollution problems due
to its presence in the gases evolved from pelletizing and
sintering plants.
With respect to briquetting, the proces 6 has
received only limited acceptance. Agglomeration at low
temperature by compaction without binders produces a
fragile briquette and the use of binders is too expensive
~or most applications. Cold~bonded briquettes usually are
not acceptable as a furnace feed material because they tend
to disintegrate within the furnace prior to melting. Hot
briquetting, on the other hand, has not reached a mature
state of development or gained acceptance because large
quantities of ore fines have been generally available at
the steel mills for mixing with ~he wastes, so that large
sintering plan~s using well-known processing techniques
could be built and operated economically. With the advent
; of pelletizing plants located at the mine sites to process
the ore fines and concentrates, and with the increased cost
o~ energy and pollution controls for sintering plants, it
is no longer economical to construct sintering plants at
most mill sites, and many existing sintering plants have
been shut down for these reasons.
It is, accordingly, an object of the present
invention to prov;.de a plant, or system, capable of accepting
a wide variety of feed materials, such as rejected screenings,
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.nill wa~tes, ore f:ines~ ore concentrates alld other materials
having heat-softerlahle const-ltuents, and capable oE reliably
forming such materials into highly durable briquettes, by
hot briquettes which will hold together during the handling,
feeding and smelting process as, for examp:Le, in a blast
furnace, for melting and chemical conversion and without
reverting to fines or flue dust.
In one particular aspect the present application, a
division of copending Canadian Appl.ication No. 301,3~7, filed
April 18, 1978, is concerned with the provision of a system
for hot briquetting particulate feed material containing
heat-softenable matter and for cooling the resultl.ng briquettes
which comprises a fluid bed furnace having an inlet at the
top and an outlet at the bottom for utilizing the heat of
combustion to raise the temperature of the residue to the
point of incipient fusion, a compactor coupled to the outlet
of the furnace for compacting the residue into briquettes,
an enclosed cone type tumbler-heat exchanger having an
inclined axis and with an axial inlet at the top and an
axial outlet at the bottom together with means for slowly
rotating the same, the inlet being coupled to the compactor
for receiving hot briquettes therefrom, means for conveying
feed material to the inlet of the heat exchanger for mixing
~ith the briquettes so that the briquettes are cooled and
:: the feed material is heated, a screen assembly for separating
;~ the cooled briquettes from the heated feed material, a
~ conveyor for coupling the outlet of the heat exchanger to
: the screen for conveying briquettes and feed material
thereto, means for cDnveying the briquettes from the top of
the screen and means for conveying the heated feed material
from the bottom of the screen to the inlet of the furnace.
In anotheF particular aspect the present application,
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- division of copend-lng (`anadain Appl:ication No. 301~3~79
filed April 18, 1978, i6 concerned with the provis:ion of
a system for ~ot briquetting of particulate feed material
containing heat-softenable matter which comprises a vertical
frame, a furnace in the central region of the vertical
frame, the furnace being of the Eluid bed type having an
inlet at the top and an outlet at the bottom for heatin8 the
feed material to form a residue raised to a temperature of
incipient fusion, a roll type compactor arranged below the
outlet of the furnace for receiving the resldue and for
compacting it under high pressure to form brlquettes, a cone
type heat exchanger-tumbler located below the outlet of the
compactor for receiving the briquettes, the heat exchanger-
tumbler having an inclined axis with an axia]. inlet at the
top and an axial outlet at the bottom as well as drive means
for slowly rotating the same, means for conveying feed
material to the inlet of the heat exchanger-tumbler so that
the feed material is heated and so that the briquettes are
cooled, a vertically arranged bucket elevator extending
substantially f~om the bottom to the top of the frame, the
elevator being coupled at its lower end to the outlet of the
: heat exchanger-tumbler so that each bucket receives a uniform
mixture of briquettes and feed material, means for driving
the elevator so that the process of heat exchange continues
in the buckets as the buckets are elevated to the top of the
frame, a screen assembly at the top of the frame for separating
the briquettes Erom the heated feed material, means for
:~ dumping the buckets into the screen assembly so that the :.s .
-~ briquettes are discharged in a relatively cooled state and
so that the heated feed material falls through the screen,
means for feeding the material from the underside of the
~ screen to the inlet of the furnace, ancl a feed/gas heat
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dxchanger interposed at the inlet of the Eurnace for bringing
the off gas Erom the Eurnace into contact with the heated
feed material for further heating of the Eeed material to a
temperature more nearly approaching the temperature of the
Eurnace, and for cooling the oEE gas to a temperature more
nearly approaching the temperature of the feed material, and
means for subsequently purifying the off gases from the
furnace and the heat exchanger-tumbler for discharge into
the atmosphere.
10Other objects and advantages of the invention will
become apparent upon reading the attached detailed description
and upon reference to the drawings in which:
Figures la and lb comprise an elevational view, in
partial section, of a briquetting plant construction in
accordance with the present invention.
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Fig. 2 is a view simllar -to Fig. 1 but with super-
imposi-tion of flow lines indicating ~he paths taken by the
materials flowing within the plant.
Fig. 3 is a block type flow diagram correspondiny
to Figs. 1 and 2.
Fig. 4 is an elevational view of a simplified
installation employing elements of the present invention.
Fig. 5 is a flow diagram corresponding to Fig. 4.
Fig. 6 is a view similar to Fig. 4 but with
~;10 modified features.
Fig. 7 is a view similar to Fig. 6 but with still
further modifications.
While the invention has been described in connection
with certain preferred embodiments, it will be understood that
I do no~ intend to be limited by the disclosed embodiments but
intend to cover, on the contrary, the various alternative
and equivalent constructions included within the spirit and
scope of the appended claims.
Turning now to Figure 1 a preferred form of briquetting
plant designed to process a variety of steel mill was~es and
screenings is shown, of which the components will be understood
to be mounted upon a supporting framework which, for the sake
of simplicity, has been omltted from the drawings. At the
right-hand side of the plant is a wet feed conveyor belt 10
having a drive 11 for bringing into the,plant feed material
containing iron, primarily in the form o iron oxide, and
combustible elements, the latter predominantly car~on. The
materials are referred to as "wet" since they contain filter
; ~ cake or mill scale or have been taken from outside storage
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~ where large amounts of water, resulting from preclpi-
tation, are normally absorbed. ~eans are provided, also, for
bringing "dry" waste into the plant, such as dust which has
not been stored out of doors but which arrives directly from
current steel mill operations. For transporting this material
into the plant a dry feed conveyor 15 is used having a drive
16. Discussion of the flow of the dry feed component will
be reserved to a later point.
The discharge from the wet feed conveyor belt 10 is
conducted by an inlet chute 17 into a first, or low temperature,
heat exchanger 20 which is of the constantly rotating tumbler
type. The heat exchanger has an axial inlet 21 at the top
and an axial outlet 22 at the bottom, the inlet and outlet
being provided with seals to make the unit as nearly as
possible gas tight. The heat exchanger in its preferred
form is of double conical shape having a lower hollow conical
container 23 and which is enclosed by a cover 24 which may
also be of conical shape. For the details of such a conical
heat exchanger-tumbler reference may be made to my U.S. Patent
No. 4,106~114, issued August 8, 1978. It will suffice, for
the present, to say that the heat exchanger has a refractory
lining 24 and is supported for rotation about its axis by a
single large annular bearing 30 wi~hin which the lower cone
section is mounted, the axis defined by the bearing being
inclined at an angle of approximately 45 bot which may vary
between about 35 and 55. As a result of rotation and
inclination materials entering at the inlet are constantly
cascaded, and thus evenly distrlbuted, over the surface 26
of the
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contained load. A further advantage of the lnclination
is that mater:ials are drawn from the outlet 22 from over a
wide range of positions within the exchanger. The operation
may be contrasted with that of an hour glass in which the
grains are fed primarily along a fixed line which extends
vertically upwardly from the constriction. In the present
heat exchanger-tumbler the vertical line extending through
the mass of material within the device constantly orbits so
that the material drawn from the exit is not drawn from any
one particular location so that a mixing occurs which not
only equalizes the composition flowing through the outlet
but in addition greatly impxoves the efficiency of the heat
exchange. The unit is preferably driven by means of teeth
formed into the outer ring of the bearing 33 which are
engaged by the teeth of a pinion 34 connected to a drive 35
having a control 36 which is capable of adjusting the speed
from a portion of a r~volution to several revolutions per
minute, for example, from 0.2 to 2.0 rpm. In carrying out
the invention the heat exchanger 20, in addition to receiving
flow of feed material also receives a flow of hot, freshly
made briquettes, the purpose of the heat exchanger being to
pre-hjeat the feed material and, at the same time, to cool
the briquettes to a safe discharge t~mperature. However, a
discussion of briquette production and path of flow will
be temporarily deferred.
The mixture of briquettes and feed which is fed
;; ~ from the outlet 22 of the heat exchanger 20 passes in~o a
screw type feeder 40 having a drive 41, the feeder serving
`~ ~ to load an elevator 50 having chain supported buckets 51
driven by a drive 52. While the drive is shown for convenience
at the lower end, it is desirable, in fact, to have the drive
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at the upper end. At the upper end of the elevator the
buckets are emptied into a to-tally~enclosed screen assembly
60, which is preferably of the vibratory type having a frame
61 mounting a screen 62 and supported on resilient mounts 63. An
electric motor- driven vibrator 64~ which is preferably of
the eccentric type, causes the frame, and the screen 62
which it contains, to vibrate resulting in efficient separation
of the briquettes which flow along a path 65 on the upper side
of the screen, from which they are discharged from the plant,
and the heated feed material which flows through the screen
along a path 66.
The heated feed material is conducted downwardly
through a first feed tube 70 having an upper end 71 and a
lower end 72 which feeds into the second, or lntermediate
: . temperature, heat exchanger 80 to be discussed.
The heat exchanger-tumbler 80 is similar to the
heat exchanger 20 previously described having a sealed inlet
81 and a sealed outlet 82, with the vessel being formed by
a hollow conical receptacle 83 enclosed by a cover 84.
The receptacle has a refractory lining 85. The heat exchanger
is supported upon a bearing 93 having teeth driven by a
pini~h 94 which has a drive connection with the heat exchanger
drive 95 having a controller 96.
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At the outlet of the heat exchanger 80 is a screw
feeding device 100 powered by a drive 101 for the feeaing
~ of material at a controlled ra~e into an elevator 110 having
: a series of chain supported buckets 112 driven by a dxive 113.
; The elevator buckets are dumped into a screen assembly 120
having a gas-tight housing 121 and a stationary screen 122 of
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the inclined "grizzly" type, with the briquettes flowing
over the top oE the screen along path 125 and the heated
Eeed materials falling to a position 126 below the screen
which feeds a hopper 130. At -the hottom of the hopper is
a screw type feeding device 131 having a drive 132.
From the hopper 130 the heated feed material
is discharged into a furnace 140 of the ~luid bed type,
the furnace having an inlet 141 at its upper end and outlet
142 at its lower end. The furnace, in its preferred form,
10 has an upper cylindrical portion 143 and a lower conical
portion 144 lined wi~h a layer 145 of refractory material (Fig. la~.
The bottom of the fuxnace has multiple air inlets 146 and
an air plenum 147 underlying the inlets. The plenum receives
pressurized air through a line l48 leading from a blower 149
driven by a motor M~ The bed of material, indicated at 151,
at the bottom of the furnace is fluidized by the air which
flows upwardly through the inlets, as is characteristic of
a fluid bed, resulting in efficient burning of combustible
elements in the feed.
In accordance wi-th one of the more detailed aspects
of the present invention the off gases resulting from the
combustion are conducted upwardly through the inlet opening
141 and past the point of discharge of the feeder 131 which
feeds material into the furnace to provide a feed/gas heat
exchanger 150. Moreovery the inlet 141 is sufficiently
restricted so that the of gases have a sufficient velocity
as they pass the point of feeder discharge so a substantial
portion of the discharged material is conducted upwardly and
maintained in contact with the high kemperature off gases
thereby recover mg wast~ heat, which raises the temperature
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of ~he waste to more nearly that of the furnace. The
remaining coarser and more abrasive material discharged
by feeder 131 falls into -the furnace, counter current to
the gas, also aiding in heat recovery ~rom the gas. The
off gases and the entrained particles are conducted into
a vertical stack 152 and into a known cyclone type separator
153 having an upper discharge 154 i-or the gases and a down-
wardly extending convergent discharge 155 containing a
trickle valve (not shown) for returning the entrained
particles o waste back into the furnace. In addition to
recovering heat, the feed/gas heat exchanger causes a
reduction in the internal temperature of the cyclone separator
which tends to become plugged when operated at furnace bed
temperature. If desired, air may be injected into the upper
outlet port of the separator, as indicated at 156 for the
purpose of completing the oxidation of carbon monoxide and
any unburned hydrocarbons. The off gas then flows through
a duct 157 downwardly into a scrubber assembly 160 having an
upper, or manifold, section 161 and a lower section 162.
The manifold is positioned over the inlet opening 21 of the
- first heat exchanger 20 so as to receive, also, the off gases
from the heat exchanger. Water is sprayed into the gaseous
stream as indicated at 163 to purify the gases and to remove
any entrained particles, following which the stream of gas
is sucked into a blower 164 which discharges into an upstanding
flue or stack 165~ The solid particles, in ~he form of a slurry,
are drawn from a dLischarge port 166 at the lower end of the
scrubber assembly.
With regard to the off gases from the second, or
intermediate temperature, heat exchanger 80, these pass through
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a manifold 170 and a small scrubber 171, supplied with water
172. The effluent yases, oil, water and solids are conducted
by means of a duct 173 for injection, at 174, in the lower
portion 162 of the aforementioned scrubber. Scrubber 171
may be in the form of a jet-type venturi eductor, using
water 172 at high pressure to provide the efficiency necessary
to remove the oil vapors ~rom the gas. Preferably interposed
in the duct 173 is an oil separator 175 which removes the
oil condensed from the off gas and which is desirable in
the case of particularly oily feed materials. The duct 173
also includes a divertor 176 so that the off gas from the
second heat exchanger, instead of being sent to the scrubber,
may be directed back into the furnace via a line 177.
Turning attention to the furnace, the combustible
elements in the material 151 at the bottom of the furnace
are largely burned away to leave a residue o~ iron oxide-
containing material at a temperature of incipient ~usion
which may be on ~he order o~ 1800 F., such materials passing
through the outlet 142 of the furnace to engage a feeder 180
having a drive 181 which controls the rate of flow into a roll
type compactor 190. The latter has a pair of pocketed rolls
191, 192 rotating in opposition to one another and driven
by a drive motor 193. The compactor has an inner housing 194
enclosing the high temperature zone between the feed inlet
1~7 and the product outlet 199 and an outer housing 195 with
a source of water 196 which is sprayed onto the rolls,
between the housings, and at other strategic points, to
maintain the temperature at a safe level for the machine.
The exiting briquettes, interconnected by "flash", are broken
apart by a breaker 138 located at the output nip.
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A second compactor is employed in parallel with
the first and carries the same reference numerals followed
by suffix a. The two compactors discharge through outlets
199 and l99a into the manifold 170 ~rom which the briquettes
flow into the inlet opening 81 of t:he second heat exchanger
80.
In this second heat exchcLnger the briquettes mix
with the partially pre~heated feed material flowing thr~ugh
the feed tube 70 from the underside of the first screen
assembly 60.
Thus the bxiquettes, in the second heat exchanger,
lose a portion of their high furnace heat to the eed
material. The heat exchange is continued to the point of
near-equalization as the mix is transported upwardly in the
; buckets of the second elevator 110.
Following separation in the second screen assembly
120, the briquettes, flowing along the upper side o~ the
screen, pass into a downwardly angled feed tube 200 having
a feed gate 201 at the lower end thereof which is driven by
a drive motor 202. In accordance with one of the more detailed
aspects of the invention the feed tube 200 is kept substantially
full ~f briquet~es so that they are lowered gently to the
point of discharge rather than falling freely through the
tube. This is accomplished by providing a level detector
202 at the upper end of the tube which produces an output
~ignal feeding a controller 203 so that the drive 202 is
actuated, causing discharge at the gate 201, only when the
level of the briquettes in the tube is above the level of
the detector. As will appear, level detectors, and associated
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controllers are utilized for control purposes at a numbe~
of points in the plant and it will suffice to say that
while the invention is not limited to use of any particular
type of detector, it is preferred to employ a detector which
utilizes gamma rays and which may thus be mounted externally
of the device with which it is used. Such level detectors
and associated control equipmen-t are commonly used and are
available as standard equipment from a number of suppliers.
The gamma ray source,level detector and associa-ted electronic
equipment may, for example, be of catalog types 7063, 7002
and 7311, respectively, manufactured by Kay Ray, Inc. o~
Arlington ~Ieights, Illinois and the controller may be of
catalog type GS 2A4A manufactured by The Foxboro Company
of Foxboro, ~assachusetts.
The partially cooled briquettes are fed from the
lower end of the feed tube 200 into the inlet 21 of the
first heat exchanger 20 where they are mixed with the incoming
wet feed material which is fed into the plant on conveyor lO.
In the firs~ heat exchanger 20 the intimate mixing which
occurs as the heat exchanger revolves, and as the material
cascades upon the surface of the charge, brings about an
apprdximate equalization of temperature, which is continued
as the mix of briquettes and feed material is fed, by feeder
40, into the buckets of the first elevator 50. Separation
and discharge of the briquettes occurs in the screen assembly
60, with the briquettes passing along the top of the screen
and with the now pre-heated feed material being discharged
into the first feed tube 70 which leads to the second, or
intermediate temperature, heat exchanger as previously discussed.
In orde:r to insure that the temperature in the
first heat exchanger is kept below the temperature at which
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any oil containecl in the feed will vaporize, a ~ater spray
head 210 is provided in the first heat exchanger coupled to
a source oE water 211 which is under the control of a
temperature detector 212. In short, whenever the detector
reaches a temperature greater than a set value, water is
sprayed in automatically to reduce the temperature to a
safe level. Thus most of the oil contained in the feed
remains in the feed until vaporized at the higher temperature
existing in the second heat exchanger 80 and following
which the oil is preferably removed from the system by the
oil separator 175.
The above discussion has traced a charge of wet
feed material through the plant. I desired, all of the
feed, either wet or dry, may be caused to follow -~he same
paths but, in accordance with one of the aspects of the
present invention, the dry feed material entering on
collveyor 15 powered by drive 16, is fed directly to the second
heat exchanger 800 Preferably there is provided at the
output of the drive feed conveyor a shiftable director 220
having a normal position 221, an alternate position 222 and
a third position 223 which may, or example, be used on
start-up. In the normal position the dry f~ed material
passes through a conduit 225 which leads to the second heat
exchanger. In the alternate position 222, in which the dry
feed i5 combined with the wet, the dry feed is led through
a conduit 226 to the first heat exchanger. In the third
position 223 the director directs the dry feed intake directly
to the furnace by means of a conduit (not shown).
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Under conditions of star-t-up an auxiliary burner
230 for the furnace 140 is used which may, for example,
receive gas or oil ~rom an auxiliary source 231 and air
from a line 232 leading from the b]ower 149. In addition,
an inlet tube 233 having a three-way valve 284 is provided
for injecting fuel, water or purge air directly into the
fluidized bed when needed to control the bed temperature,
automatically, by temperature sensor 235 and controller 236.
In a plant having little or no fuel in its feed supply, coke
fines may be added to the feed, powdered coal may be fed
into the bed by a screw conveyor (not shown) or oil or gas
may be injected directly into the bed through one or more
fuel inlet tubes, of the type shown, in accordance with
standard techniques.
With the construction of the plant in mind,
reference may be made to Figs. 2 and 3 for a more detailed
understanding of the operation. In Fig. ~ the paths of
flow of the feed materials, the hot briqu~ttes, the recycled
fines and the off gases have been superimposed, in coded form,
upon the drawing, whereas in Fig. 3 the flow of such materials
has been set forth in a flow diagram. The flow of the wet
feed material 12 takes place vertically down the center of
the sheet to the compactor at the bottom. Thus the material
rom the wet feed conve~or 10 flows successively through the
low temperature heat exchanger 20, the feeder 40, the shaker
screen 60 into the intermediate temperature heat exchange~ 80.
From the latter, flow continues through the feeder 100, screen -
120, hopper 130, feeder 131, the heat exchanger 150 into the
furnace 140. From the furnace the residue, heated to incipient ~ -
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fusion, is fed via feeder 180 lnto the compactor 190 where
the briquettes are formed.
The hot briquettes, after compaction, are caused
to ~low in a hea~ exchange path which ls counter to the f]ow
of the waste material. That is to say the briquettes are
conducted from the compactor 190 along path 170 into the
intermediate heat exchanger. In this heat exchanger the
briquettes, at an entering temperature of approximately
1800 F., encounter the feed which has been pre-heated, in
the first heat exchanger, to a temperature of approximately
300 F. The resulting mix, which is conveyed through feeder
100 anA up elevator 110 to ~he screen 120 achieves a near-
equilibrium temperature which is on the order of 1000 F.
The briquettes flowing along the top of the screen in the
screen assembly 120 are lowered through the feed tu~e 200
to enter the low temperature heat exchanger at a temperature
of 1000F. Here the briquettes are joined by the wet feed
from conveyor 10 which is at an assumed temperature of 0 F.
The mix exiting from the low temperatu~e heat exchanger 20
and elevated by the elevator 50 reaches an equilibrium
temperature of approximately 300 F. which is then the
temperature of the briquettes at the point of discharge 65v
- The out gas from the low temperature heat exchanger, because
of the spraying of water from the spray head 210, is at a
somewhat lower temperature, namely,212 F.as it is fed into
scrubber 160. Furnace off gas passes through feed/sas heat
exchanger 150, cyclone 153 to scrubber 160 by way of conduits
152 and 157. Fines from the cyclone flow through tube 155 to
the furnace . Gas rom the intermediate temperature heat
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e~changer 80 ~lows into scrubber 171 and then into scrubher
160 dir~ctly or by way of oil separa-tor 175. Alternatively,
the gases from scrubber 171 may be piped into the furnace
for combustion of any fuel content.
AUTOMATIC FLOW CONTROL
.
In the above description it has been assumed that
the various feeding devices have each been adjusted to
produce equalized rates of feed so that there will be no
tendency toward material accumulation at any point in the
system. However, it is one of the features of the present
invention that manual intervention is not required to equalize
flow rates under changing conditions. Briefly stated, the
output rate of the plant is determined by the speed of
rotation of the compactor rollers and the degree of
compaction which is maintained. Working upwardly through
the syste~, back to the point of feed of the wet raw material,
each vessel is provided with a level detector which actuates
a controller which correctively controls a feeder located
upstream in the path of material flow to keep the level in
the vessel automatically at its working level. In other
words, each vessel has a level detector which "calls" for
material from an upstream point in the flow as needed to
keep the material in the vessel at its desired, and most
efficient, working level.
Attention will first be gi~en to the means for
controlling flow of the material, heated to incipient fusion,
to the compactor. For this purpose the compactor 190 has a
pressure sensor 240 which determines the force applied between
the two rolls and produces a signal to activate a controller 241.
The controller tends to maintain constant brique~te density by
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b~inging a~out a correctlve increase or decrease in the
speed of the drive ]81 for the feeder 180. A sui-table
pressure sensing cell 240 and controller 241, which completes
a servo loop, are available commercially from several suppliers.
When the pressure between the rolls drops, indicating that
insufficient material is being fed, a signal is produced
which actuates the controller in a direction to speed up the
drive 181, and vice versa.
Assuming that the rate of feed at the feeder 180
increases, this will tend to produce a drop in the body of
material contained in the furnace. In carrying ouk the
invention such drop in level is sensed by a level detector
242 which actuates a controller 243, causing a speed-up in
the drive 101 which drives the feeder 100 at the outlet of
the second heat exchanger 80. This causes loadiny of
material onto the second elevator 110 at a higher rate
thereby increasing the xate of replenishment of the furnace
140. Feeder controller 243 also controls the speed of
elevator 110 by changing the speed of its motor 133 in
proportion to the rate of feed.
; The hopper 130 which is positioned between the
elevator 110 and the furnace has its own control loop
including a level detector 244 which actuates a controllex
245 to correctively adjust the drive 132 associated with
the feeder 131. This sexvo loop tends to maintain a
constant leveI of material in the hopper so that when
additional material is deposited by the elevator 110,
raising the hopper level, this is immediately sensed by the
level detector 244 so that material is immediately fed from
the hopper to the furnace at a greater rate.
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The above mentioned increase in feed from the
second heat e~chanyer to satisfy -the requirements oE the
furnace, results in a drop in level of the material i.n
the second heat exchanger 80 which is sensed by the level
detector 246, producing an output signal which activa-tes
an associated controller 247 to increase the rate of feed
of the feeder 40, at the lower end oE the elevator 50
and the speed of the elevator. This produces a higher
rate of feed from th.e elevator so that feed material passes
at a greater rate through the screen 60 fox replenishment
of the second heat exchanger via the feed tube 70.
The greater rate of withdrawal from the first
heat exchanger 20, in turn, tends to cause a drop in level
in that heat exchanger which is sensed by a level detector
248 which transmits a signal to controller 249 which produces
a corrective adjustment in ~he speed of the drive 11 which
drives the wet feed conveyor 10, with the result that the
wet feed material is fed at a greater rate for immediate
replenishment of the first heat exchanger.
In the above discussion of the progressive
: automatic control by a series of servo loops, it has been
assumed that an increased rate of feed at the compactor
has occurred calling for replenishment at successive points
in the upstream path of flow. It will, however, be under~
stood by one skllled in the art that the reverse will take
place when the needs of the compa~tor tend to decrease~
with an over-pressure condition at the compactor resulting
in a cutting down of the flow successively in the upstream
position. In a practical case this replenishment, or cutting
down, does not take place in a step-by-step fashion as
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described but, instead, each ser~o loop tends to establish
and maintain an equilibrium condition until the equilibrium
tends to be upset in one direction or the other, whereupon
corrective action automatically occurs.
While no servo control has been shown for the
drive 16 for the dry feed conveyor 15, it will be understood
that where a dry feed is fed simultaneously, as will normally
be the case, the dry feed conveyor may be equipped with a
servo loop under the control of the level detector 246
10 in the second heat exchanger, so that a drop in the level
; of such heat exchanger simultaneously increases the rate of
feed from the first heat exchanger and the rate of input of
the dry feed from outside of the system. Alternatively,
where the director 220 is in its position 222, in which the
dry and wet feeds are combinedr the dry feed drive 16 may
be coupled to the wet feed drive 11 for simultaneous control~
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PHYSICA~ LAYOUT OF _LANT
While the invention as described by a ~low diagram
in Fig. 3 is not limited to any par~icular physical arrange-
ment, it is nevertheless one of the important features ofthe invention that the plant is constructed in a framework
in which the two heat exchangers 20, 80 occupy the lowermost
positions and the two screens, which are fed by respective
elevators from the heat exchangers, occupy the topmost positions,
with the furnace occupying an intermediate position, and with
the compactors interposed between the furnace and the inter-
mediate temperature heat exchanger. The wet ~eed conveyor 10
is preferably located at a level above the first heat exchanger
and the dry feed conveyor is preferably located at a level
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above the bot-tom o~ the furnace. In this way all of the
transport, except that which occurs in the two elevators,
is vertically downward under the action of gravity. This
greatly simplifies the system since the only -transport drives
which are required, aside from the input conveyors, are those
which are used to drive the elevators.
Preferably the openings in the intermediate
temperature screen assembly 120, which is just ahead of the
furnace, are larger than the openings in the screen assembly
60, thereby insuring that any materials which pass the low
temperature screen 60, and which are smaller than briquette
size, are certain to be passed by the intermediate temperature
screen for treatment in the furnace, including undersized
portions of the briquet~es which may break off as a result
of physical handling.
While it is one of the features of the present
invention that the materials fed into the plant on the inlet
conveyors 10, 15, are well mixed within the plant as a result
of the mixing actions, of the tumbler type heat exchangers,
the furnace, screens and conveying devices, the invention,
in one of its aspects, extends beyond the physical plant to
encom~ass the manner in which the raw materials are stored.
~s stated above, the waste materials from a steel making operation
vary widely in type, source, size and composition including
metallic iron, oxides of iron, other compounds of iron, coke
and other carbonaceous materials. In accordance with one
aspect o~ the present process, these raw materials are not
necessarily stored in separate piles but are, instead,
deposited on a sin~le pile or reservoir in relatively thin
layers. When the materials are scoop~d for the loading of
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the input conveyors 10, 15 it is contemplated that the
scooping, ~y a power shovel, front end loader, or the like~
will ta~e place in passes acxoss the layers so that each
scoop contains a por-tion of many layers from the pile. This
produces an automatic mixing of the available iron and carbon
containing components to bring them within the range of
tolerance of the present plant and without requiring the
provision of a separate, costly, or cumbersome pre-mi~ing
plant. This further adds to the economy of the present system.
A.LTERNATE EMBODIMENT
While the present invention has been described
in connection with Figs. 1-3 which show a preferred embodiment
employing a two-stage heat exchange cycle in which the
briquettes flow counter to the raw material, the invention
in its broader aspects is not limited to use of two heat
exchangers and a plant may be constructed in simplified
form as set forth in Figs. 4 and 5 without departing from
the invention. In this plant, in which similar elements
are denoted by similar reference numerals with addition of
subscript a, it will be noted that the intermediate
temperature heat exchanger 80, with its associated feeder
100, elevator 110 and screen 120, has been omitted. Instead,
only one heat exchanger 20a of the tumbling type is employed
wh~ch takes raw material directly from the wet feed conveyor --
lOa and which takes the briquettes direc~ly from the compactor
l90a. It will be understood that the features of automatic
control are the same. This plant design may be preferable to
that of the more complex plant in the following cases~
when the material fed contains so much water that the briquettes
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are su~ficiently coolecl in one heat ex.changer, (2) when -the
feed material softens and is briquetted at such a low
temperature that 2-stage heat exchange is not ~ustified
and (3) when the tonnage to be processed is too low to
justify the more expensive plant, even though the fuel
consumption might be greater.
While the embodiments of the present invention
illustrated were designed primarily to operate using as
raw material the waste and screenings in the form of iron
oxide together with combustible elements in the form of
carbon and hydrocarbons produced in the normal operation
of a steel plant, the invention may be employed in the
briquetting of particulate materials from a number of
different sources. Indeed, the present invention may be
utilized in hot briquetting many materials, including
iron ore fines and concentrates,chrome ore fines, ferro- ~.
manganese screenings, metal chips, phosphate rock, mixtures
of raw materials for glass and portland cement manufacture,
and other materials and mixtures that soften at temperatures
at least as high as 2000 F. In many such applications,
the plants illustrated in Figures 1-5 could be used with
~: little or no alteration. Also while the texm "briquette"
has been used to designate the end product, and while such
term is intended primarily to describe dense, pillow shaped
pellets of consistent size, it will be.understood that the
term "briquette" is by no means limited to production of
pellets of equal size and consequently it shall be interpreted
~ to cover irregular of broken pieces or granules of material
: produced by compaction in continuous strip form and then
broken or crushed and screened to the desired size.
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ALTERNATE ANTI-POI,LUTION EMBODIMENTS
While khe anti-pollution means described in connection
with the embodiments set forth in Figures :L-5 are adequate for
many materials and will meet ~he pollution standards for a
number of plant locations, even more elaborate anti-pollution
equipment may be required for processing some materials and
for locations having unusually stringent pollution limitations.
Two equipment arrangements involving more extensi-ve means for
pollution control are shown in Figures 6 and 7, which are
modifications of the arrangement set forth in Figure 4~
In both arrangements, all off gases are passed through a
combustion zone for removal of combustible contaminants,
such as oil vapors and carbon monoxide, prior to being
scrubbed and discharged to atmosphere. ~oth arrangements
include optional condensers for removing moist~re from the
gases prior to entering the combustion chamber, so as to
reduce the consumptionO~ fuel and the size of combustion and
scrubbing equipment when economically justified.
The arrangement illustrated in Fig. 6 is intended
for applicatlons in which ~he feed to the plant contains a
relatively low percentage of objectionable hydrocarbons
having a low boiling point or in which the feed contains an
- excess oE solid fuels that would provide a low-cost source
of the additional heat required. In the arrangement of
Figure 6 (in which corresponding reference numerals are
employed with addition of subscript b) the scrubber 160b
has been mo~red from its previous location (Fig. 4) a~ the
gas outlet of the heat exchange tumbler 80b to a pssition
near the outlet oE the cyclone separator 153b, and a condenser
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~ ' ' ', ' : : . '
253 has been added at the outlet o~ the tumbler 80b. In
this arrangemen-t, the off gases from the tumbler 80b,
compactor 190b and miscellaneous sources (no-t shown) are
collected by hood 250 into which water 251 is optionally
sprayed to minimize dust entering t:he condenser 253 by way
of inlet header 252. The condenser may be cooled with air
or water, as desired. The ~ases exit the condenser by way
of outlet header 254 and duct 255 and are injected into
the bottom of the fluid bed reactor 140b, by means of a
blower 256 and duct 257~ together with fluidizing air from
blower 149b and duct 148b. The gases from the furnace 140b
flow through optional gas/feed heat exchanger 150b, then duct
l51b and cyclone separator 153b. ~ir 156b is optionally
introduced into the off-gases at the gas outlet 154b of
the cyclone to burn any small amounts of carbon monaxide
or hydrocarbons in the gas, which flow through duct 157b
into scrubber 160b, which is supplied with water 163b.
The effluent gases are then exhausted to atmosphere by
blower 164b through stack 165b. Slurry and condensate
are drained from ~he scrubber 160b and condenser 253
through connections 166b and 258.
; The arrangement shown in Figure 7 is applicable
to feed materials having a relatively large amount of volatile
fuel difficult to remove by scrubbing in standard equipment.
In this arrangement, ~he gases from the tumbler 80c,
~compactor l90c and miscellaneous sources are processed in
an optional condenser 253c having features similar to those
described for the condenser 253 of Fig. 6. The gases from
condenser 235c pass through a head 254c which discharges
into the top of an afterburner 270. The off gases from
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~::
the furnace 140c also enter the top of the afterburner,
after passing throuyh the feed/gas heat exchanyer 150c,
cyclone separator 153c and duct 157c. The afterburner
is equipped with a burner 271 at the top to preheat the
unit and to supply heat as required to cause complete
combustion of all combustible matter in the gases. The
burner has suitable sources of fuel 272 and air 273, and
secondary air is supplled to the afterburner at inlet 274.
The burner and secondary air supply are conkrolled by
standard regulating devices to maintain the afterburner
; at the proper temperature. The afterburner is refractory
lined and insulated. The effluent gases pass from the
afterburner to the scrubber 160c, which is supplied with
water 163c for removing entrained par~iculate matter, and
then through exhauster 164c and stack 165c to the atmosphere.
Although the simplified plant design of Fig. 4 has been
used to illustrate these anti-pollution means, such means
are equally applicable to other plant designs that employ
the present invention, including the design shown in Fig. 1.
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