Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF T~IE INVENTION
The present invention relates to pneumatic trans-
port systems and more particularly to conduits for conveying
pressurized streams of gas entrained matter.
In the optimum operation of pneumatic transport
systems, gas velocities must be maintained above the level
which produces settling of the entrained matter and below
the level which results in excessive frictional pressure
loss and extensive wear of the conduit; and these limits must
be reconciled with the higher velocities resulting from the
increase in volume due to frictional pressure loss in the gas
as it moves through the conduits. A problem arises, however,
in the case of long distance conduits where, due to the length
of the conduit, a gas moving at minimum required velocities
at the inlet end of the conduit may reach velocities at the
outlet end which are in excess of the level set for acceptable
frictional pressure lossandnormalwearOfthe conduit.
SUMMARY OF THE INVENTION
; The present invention discloses a conduit structured
for maintaining gas velocities well within the limits pres-
cribed for optimum operation.
; Accordingly, there is provided a conduit which is
subdivided into a plurality of sections consecutively dis-
posed in the direction of transport and wherein the cross-
sectional flow area of each succeeding section is greater
than that of the preceding section. The increase in conduit
croæs-sectional flow area, in the direction of transport,
accommodates the increases in gas volume due to frictional
pressure losses thereby maintaining gas velocities and
frictional pressure losses within prescribed limits.
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BRIEF nESCRIPTIOM OF T~ DRAWINGS
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Figure 1 is a schematic diagram of a blast furnace
pulverized fuel preparation and transport system including
a conduit embodying the invention;
Figure 2 is a fragmented sectional view of the
conduit depicted in Figure 1.
DESCRIPTION OF THE PRE~'ERRED EMBODIMENT
The conduit is herein described in conjunction
with the preparation and conveying of air borne pulverized
coal to a blast furnace. It should be recognized, however,
that the disclosed conduit may also be used in conjunction
with other systems for the distribution of any pneumatically
transported particle-form material.
Figure 1 illustrates a coal preparation and trans-
port system of the character generally disclosed in U.S.
Patent No. 3,689,o45 and includes a raw coal bunker 10 which
discharges through an outlet conduit 12. A gate valve 1~ is
installed in the conduit 12 and, when open, allows coal to
gravitate to a feeder 16, the latter regulates the flow of
coal to a mill 18 in response to system demand. The mill 18
grinds the coal to a consistency suitable for pneumatic trans-
port to a blast ~urnace 20. Air is supplied to the mill 18
by a primary air fan 22. The air is passed through a heater
24 and is preheated prior to its entry into the mill 18. The
heated air,passing through the mill 18, dries the pulverized
coal and conveys it through an outlet conduit 26 to a cyclone
type separator 28. The coal-air mixture enterlng the
separator 28 is centrifugally separated and the coal gravitates
to a storage tank 30 via a discharge conduit 32, the latter
being provided with a rotary valve 34. The minute coal fines
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which rernain entraincd in the primary air are carried along
with the air, through a vent conduit 36 to a bag-filter house
38, or other functionally similar apparatus, and collected
therein. The cleaned primary air leaving the bag-house 38
is vented to atmosphere while the collected fines gravitate
to the storage tank 30 via a discharge conduit 40, the latter
being provided with a rotary valve 39.
If desired, a plurality of pulverized coal pre-
paration units can be operated in parallel to supply coal to
the storage tank 30 since with multiple units, intermittent
operation, maintenance, or emergency servicing of any single
unit can be accommodated without necessitating a shutdown of
the delivery system. In lieu of spare pulverizing capacity
afforded by multiple coal preparation units, an auxiliary
storage tank, not shown, can be provided. The auxiliary tank
could be suitably connected to the conduits 32 and 40 to re-
ceive some or all of the pulverized coal output in excess of
the then current needs of the blast furnace 20. The tank 30
is suitably vented through conduit 42 so as to operate at
atmospheric pressure and serves to provide sufficient storage
of pulverized coal to supply a plurality of feed tanks 44A,
44B and 44C through corresponding distribution conduits 116A,
46B and 46C. The conduits 46 A-C are provided with shutoff
valves 48A, 48B and 48C, respectively, which, when open,
allow the individual tanks 44 A-C to be filled with pulverized
coal.
The feed tanks 44 A-C communicate with the lower
segment 50A of a pneumatic transport conduit 50 through
corresponding outlet conduits 52A, 52B and 52C provided with
respectively shutoff valves 54A, 54B and 54C which can be
selectively opened to permit coal in dense phase fluidized
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form to flow from sel.ected tanks 44 A-C, one at a time, to
the segment 50A and closed to isolate, from segment 50A, those
tanks 44 A-C other than the one currently selected to supply
pulverized coal to the blast furnace 20.
Inert gas is used for pressurizing and aerating
the feed tanks 44 A-C and also for aerating the storage tank
30. The choice of an inert gas is favored since it precludes
the possibility of coal ignition within the storage and feed
tanks. The inert gas is delivered by a compressed gas source
78 through a supply conduit 80 at a pressure sufficient to
maintain coal flow from any given feed tank 44 A-C into and
through the segment 50A at maximum anticipated blast furnace
demand rate and against the combined transport system pressure
drop and the pressure within the hearth 76. The gas supply
conduit 80 includes a control valve 81 and a check valve 83. ..
The aeration of the storage tank 30 is accomplished through
conduit 82 which connects the tank 30 with the gas supply con-
duit 80 and includes a control valve 84. The venting of the
storage tank 30 is accomplished through conduit 42 which con-
nects the tank 30 with vent conduit 36 and includes a control
valve 88. The pressurization of the feed tanks 44 A-C is .
accomplished through corresponding conduits 90A, 90B and 90C
which connect the tanks 44 A-C with the gas supply conduit 80,
respectively, and include control valves 92A, 92B and 92C. The
aeration of the feed tanks 44 A-C is accomplished through
corresponding conduits 94A, 94B and 94C which connect the tanks
44 A-C with the gas supply conduit 80 and, respectively, include
control valves 96A, 96B and 96C. The venting of the feed tanks
44 A-C is accomplished through corresponding lines 98A, 98B and
98C which connect the tanks 44 A-C with a main vent condult
100 and, respectively, include control valves 102A, 102B and
102C. The conduit 100 vents into the storage tank 30.
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In accordance with the invention, the pneumatic
transport conduit 50 includes an upper segment 50B having an
increasing cross-sectional flow area in the direction of
transport.
A disperser 55 is fixe~ly interposed between the
conduit segments 50 A-B to effectuate a smooth transition of
the coal from dense to dilute phase fluidized form. The
pressurized air required for transition of the coal from
dense to dilute phase and for conveyance to the blast furnace
20 is supplied to the disperser 55 through a conduit 58
which is connected to a compressed air source 56 and includes
a control valve 60 and a check valve 62. The disperser 55
discharges into the segment 50B of the transport conduit 50.
The segment 50B is, in turn, connected for discharge into
one or more distributors 64 from which a plurality of feed
conduits 66 lead to individual tuyeres 7Q of blast furnace
20 in a manner similar to that described in U.S. Patent No.
3,204,942. The number of distributors 64 as well as the
number of tuyeres 70 served by each distributor 64 can be
varied according to the requirements of the blast furnace 20.
The blast air supplied through the tuyeres 70 is heated in
regenerative type stoves, not shown, to a temperature of
about 1800F and passes via a conduit, not shown, to a torus
shaped bustle 72 and thence to the individual tuyeres 70 by
way of gooseneck conduits 74. The coal-air stream from each
feed conduit 66 is directed by corresponding nozzles 68 into
the he~th 76 of the blast furnace 20 so that each stream is
projected into the high temperature blast air being injected
through the corresponding tuyere 70.
In the operation of the system, each of the feed
tanks 44 A C is alternately filled, pressurized, and emptied
to feed the blast furnace 20 in a predetermined c~clical
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sequence. For example, when tank 44A is feeding the blast
furnace 20, tank 44B is on standby status, filled with coal
and pressurized with inert gas, while tank 44C is being filled
with coal from storage tan~ 30.
The aeration valves 96 A-C are preferably left
open during operation of the system to assure satisfactory
fluidization of the coal within the respective tanks 44 A-C.
The quantity of pulverized coal being delivered to
the blast furnace 20 is regulated through the pressurization
valves 92 A-C and the vent valves 102 A-C associated with
whichever tank is feeding coal. In the event that the actual
coal flow rate is less than the demand rate, the pressurization
valve will open thereby raising the feed tank pressure to in-
crease the coal flow rate. Conversely, should the coal flow
rate be greater than the demand rate, the vent valve will open
thereby reducing the feed tank pressure to decrease the coal
flow rate.
The pressurized air delivered to the disperser 55,
to effectuate the transition of the coal from dense to dilute
phase fluidized form and to convey the coal from the disperser
55 to the blast furnace 20, is regulated thrcugh valve 60 to
provide the acceleration and uniformity of particle dispersion
required frorn a smooth transition from dense to dilute phase
and to maintain conduit velocities which will assure steady
flow and prevent the settling of coal while minimizing the
quantity of relatively cold air being thus introduced into
the blast furnace 20. The coal in dilute phase fluidized
form is conveyed through the transport conduit segment 50
to ~e distributor 64 which divides it into a plurality of
dilute phase effluent streams of substantially equal coal-air
density and coal quantity. The coal-air streams leaving the
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distributor 64 are conveyed thro-ugh respective conduits 66
to corresponding nozzles 68 for injection into the hearth 76
of blast furnace 20. The hot blast air, which is introduced
through the gooseneck conduits 74 into the tuyeres 70, mixes
with the dilute phase coal streams to promote rapid combustion
of the coal.
Referring to Figure 2, the present invention is
embodied in the upper segment 50B which represents a long
distance conduit that is subdivided into consecutively disposed
sections I, II,III, IV and V, with each section being pre-
ferably of uniform circular cross-section throughout its length.
In accordance with the invention, the cross-sectional flow
area of each succeeding section in the direction of transport
is greater than that of the preceding section. A relatively
short transition member 51 is appropriately sized to fixedly
interconnect ad~oining conduit sections and is suitably flared
to provide a smooth transition therethrough. It should be
recognized that a conduit embodying the invention may be sub-
divided into a greater or lesser number of sections than
that of the conduit herein described.
In the operation of the invention, a coal stream
in dense phase fluidized form, i.e., an approximate density
greater than 20 lb./cu. ft., flows from the conduit segment
50A to the disperser 55 wherein it is intercepted by pres-
surized air supplied from conduit 58 and is thereby converted
to light phase fluidized form, i.e., an appro~imate density
of less than 4 lb./cu. ft., and is discharged into the seg-
ment 50B of transport conduit 50. The light phase fluidized
coal stream experiences frictional pressure losses and
corresponding increases in volume as it moves through the
conduit segment 50B. In accordance with the invention, the
increasing cross-sectional flow area of conduit segment 50B
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accommoda~es th~ increases in gas volume thereby maintaiJIing
conduit velocities and frictional pressure losses within the
llmits consistent with economically acceptable compressor
pressures and normal conduit wear. The coal stream discharging
from conduit segment 50B flows into the distributor 64 and
thence to the feed conduits 66 for injection into the blast
furnace.
In fabricating the multi-scctioned conduit of the
present invention, the length of each section of conduit is
calculated to give the desired frictional pressure loss which
would result in an increase in volume that would produce the
desired minimum velocity in the next succeeding section. The
exit velocities for each section are the result of the gas
volume at the end of that section. The conduit will generally
comprise sections of standard pipe of required dimension with
the sections being seal-weldably united through suitably sized
transition members.
Tables A and B contain calculated data based on the
movement of 24 tons per hour of coal in light phase fluidized
form through a distance of approximately 310 feet and are
illustrative of the advantages of a conduit embodying the
present invention. Table A contains data relating to different
size conduits structured in terms of the prior art and Table B
contains data relating to the conduit of the present invention.
TABLE A
Conduit length, ft 310 310
Conduit internal diameter, in. 3.o68 3.626
Feed tank pressure, psi. 102.8 91.6
Coal rate, t/hr. 24 24
Transport gas flow, std. cu.ft./min. 950 1389.1
Velocity entering conduit, ft./min. 2580 3000
Velocity leaving conduit ft./min. 5452 5363.8
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Feed tank pressure,
psi. 80
Coal rate, t/hr. 24
Transport~as~ow std.
cu. ft./min. 760
Sections I II III IV V
Conduit length, ft. 138.8 41.7 39.6 33.3 58.7
Conduit I.D., in. 3.o68 3.364 3.438 3.548 3.626
Vel. ent. conduit,
ft./min. 2580 2820 2900 2950 3000
Vel. lvg. conduit,
ft./min. 3391 3031 3142 3127 3500
A comparison of the data set forth in ~ables A and
B shows that the conduit embodying the present invention re-
quires only 80 psi . feed tank pressure and 760 std. cu. ft./min.
to transport 24 t/hr. of light phase fluidized coal across a
distance of 312.1 feet while maintaining velocities within the
range of 2580 to 3500 ft./min. In contrast, the prior art
conduits of Table B show that transporting light phase
fluidized coal at the same rate and across a like distance
requires, through the conduit at column 1, 102.8 psi. feed
tank pressure and 950 std. cu. ft./min~ at velocities ranging
from 2580 to 5452 ft./min. and, through the conduit of
column 2, 91.6 psi. feed tank pressure and 1389.1 std. cu.
ft./min. at velocities ranging from 3000 to 5363.8 ft./min.
While in accordance with the provisions of the
statutes there is illustrated and described herein a specific
embodiment of the invention, those skilled in the art will
understand that changes may be made in the form of the in-
vention covered by the claims and that certain features of
the invention may sometimes be used to advantage without a ~-
corresponding use of the other features.
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