U.S. patent number 3,720,351 [Application Number 05/140,905] was granted by the patent office on 1973-03-13 for pulverized fuel delivery system for a blast furnace.
This patent grant is currently assigned to The Babcock & Wilcox Company. Invention is credited to Earl E. Coulter, Fritz L. Hemker, Elias A. Kazmierski.
United States Patent |
3,720,351 |
Coulter , et al. |
March 13, 1973 |
PULVERIZED FUEL DELIVERY SYSTEM FOR A BLAST FURNACE
Abstract
A pulverized fuel delivery system for a blast furnace in which
pulverized coal is delivered in dense phase fluidized form into the
blast furnace from gas pressurized tanks that are placed in
communication, one at a time, in cyclical sequence with a pneumatic
transport means. The tank gas pressure is regulated in accordance
with the blast furnace wind rate to control the weight flow rate of
pulverized coal into the furnace and the transport gas flow rate is
regulated in accordance with the fuel weight flow rate to maintain
a prescribed transport gas flow rate per pound of coal delivered to
the furnace.
Inventors: |
Coulter; Earl E. (Akron,
OH), Hemker; Fritz L. (Wadsworth, OH), Kazmierski; Elias
A. (Akron, OH) |
Assignee: |
The Babcock & Wilcox
Company (New York, NY)
|
Family
ID: |
22493308 |
Appl.
No.: |
05/140,905 |
Filed: |
May 6, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
799773 |
Feb 17, 1969 |
|
|
|
|
Current U.S.
Class: |
222/1; 75/460;
75/387 |
Current CPC
Class: |
F24F
13/00 (20130101); C21B 5/003 (20130101); F23K
3/00 (20130101); F23K 2203/006 (20130101) |
Current International
Class: |
C21B
5/00 (20060101); F24F 13/00 (20060101); F23K
3/00 (20060101); B67b 007/00 () |
Field of
Search: |
;222/1,4,57 ;75/42 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Coleman; Samuel F.
Parent Case Text
This application is a division of our co-pending application Ser.
No. 799,773 filed Feb. 17, 1969, now abandoned.
Claims
What is claimed is:
1. A method of supplying pulverized fuel to a blast furnace which
comprises introducing a quantity of pulverized fuel into a tank,
pressurizing the tank with a gas, communicating the tank with the
furnace to allow flow of pulverized fuel thereto under the
influence of the gas pressure in the tank, and adjusting said gas
pressure in accordance with a condition of the furnace to
correspondingly regulate the flow rate or pulverized fuel
thereto.
2. A method according to claim 1 wherein said tank gas pressure is
adjusted in accordance with the flow rate of combustion air to the
blast furnace.
3. A method according to claim 2 wherein said tank is communicated
with the furnace through a conduit and including the step of
introducing a carrier gas under pressure into said conduit to
pneumatically convey said pulverized fuel therethrough into the
furnace.
4. A method according to claim 3 including the step of adjusting
the flow rate of said carrier gas into the conduit in accordance
with flow rate of pulverized fuel out of said tank to maintain a
given carrier gas flow rate per weight unit of pulverized fuel
delivered into the blast furnace.
5. A method according to claim 1 including the steps of sensing the
weight of said tank to determine the delivery rate of pulverized
fuel into the furnace, converting raw fuel into pulverized fuel at
a rate equal to said delivery rate, and storing the pulverized fuel
resulting from such conversion for subsequent transfer into said
tank to replenish the pulverized fuel supply thereof.
6. In a method of supplying pulverized coal to a blast furnace
having a plurality of pressurizable tanks for holding pulverized
fuel, a conduit communicating with the blast furnace, and means for
selectively communicating each of said tanks with said conduit, a
method of supplying pulverized fuel to the blast furnace which
comprises the steps of communicating said tanks, one at a time in a
predetermined sequence, with said conduit, pressurizing with a gas
the tank currently communicated with the conduit to effect flow of
pulverized fuel from that tank into the conduit, introducing a
carrier gas under pressure into said conduit to pneumatically
convey said pulverized fuel therethrough into the blast furnace,
and adjusting the gas pressure in said communicated tank in
accordance with a condition of the furnace to correspondingly
regulate the flow of pulverized fuel thereto.
7. A method according to claim 6 including the steps of
pressurizing with a gas the next tank in said sequence to be
communicated with said conduit and adjusting the gas pressure in
said next tank to maintain such gas pressure equal to that in the
tank currently communicated with the conduit.
8. A method according to claim 6 including the step of adjusting
the flow rate of said carrier gas into the conduit in accordance
with the flow rate of pulverized fuel out of said communicated tank
to maintain a given carrier gas flow rate per weight unit of
pulverized fuel delivered into the blast furnace.
9. A method according to claim 6 including the steps of sensing the
weight of said communicated tank to determine the delivery rate of
pulverized fuel into the blast furnace, converting raw fuel into
pulverized fuel at a rate equal to said delivery rate, accumulating
the pulverized fuel resulting from such conversion, and introducing
such accumulated pulverized fuel into one of said tanks other than
the tank communicated with the conduit to continuously maintain
within said tanks a supply of pulverized fuel available for
delivery to the blast furnace.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
This invention relates in general to pulverized fuel handling
equipment and more particularly to a pulverized fuel delivery
method and a system which is capable of injecting pulverized coal
into a blast furnace to replace a portion of the coke normally
consumed thereby.
In the smelting of iron ore in a blast furnace, coke has been
traditionally the material used to provide the carbon and heat
necessary for the smelting process. Coke, which normally
constitutes about one-third of the furnace charge, is about the
most expensive commodity in the production of iron. Consequently,
replacement of a portion of the coke used with cheaper coal is of
economic importance.
Various prior art systems are available for injecting pulverized
coal into a blast furnace to replace part of the coke otherwise
consumed, as for example the pulverized coal firing system
described by U.S. Pat. No. 3,150,962 issued to L. Pearson, and that
described by U.S. Pat. No. 3,301,544 issued to N.W. Eft et al.
The present invention provides a somewhat more sophisticated
pulverized coal delivery system for a blast furnace which is
capable of automatic operation to meet the varying coal
requirements of the blast furnace. In the system of the invention,
pulverized coal is delivered in dense phase fluidized form into the
blast furnace from gas pressurized tanks that are placed in
communication one at a time, in cyclical sequence with a pneumatic
transport means. The tank gas pressure is regulated in accordance
with the blast furnace wind rate to control the weight flow rate of
pulverized coal into the furnace. The transport gas flow rate is
regulated in accordance with the pulverized coal weight flow rate
so as to maintain a prescribed transport gas flow rate per pound of
coal delivered into the furnace.
Within the system, means are provided for sensing the rate at which
pulverized coal is withdrawn from the tanks and for regulating, in
accordance with the coal withdrawal rate, the output of the
pulverized coal supply means that replenishes the tanks so as to
maintain a predetermined total quantity of pulverized coal stored
in the system. This assures that there will be an adequate reserve
of pulverized coal always available for delivery to the furnace
even though the coal consumption rate may fluctuate over a wide
range.
The pulverized coal delivery system includes a coal pulverizer
which operates to convert the coal as delivered into a dried,
pulverized product, a reservoir which receives and stores the
pulverized coal output of the pulverizer system and distributor
means connected to the reservoir and to feed tanks associated
therewith whereby the furnace is supplied from a feed tank through
pneumatic transport means. This distributor means also includes
multiple valved coal lines for controlling coal flow from the
reservoir to the individual feed tanks to replenish them one at a
time in a cyclical sequence that is in staggered relation with
respect to the coal delivery sequence from the feed tanks to the
furnace. Three or more feed tanks are provided so that while one
tank is feeding coal to the furnace, the second tank in the
sequence is in reserve, filled with coal and pressurized, and thus
is instantly available for feeding the furnace as soon as the first
tank approaches the empty condition, while the third tank in the
sequence is being refilled from the reservoir. With this
arrangement uninterrupted coal feed to the furnace is assured,
since regardless of which particular tank is feeding the furnace,
there will always be a pressurized full tank of pulverized fuel
available in reserve.
The various features of novelty which characterize the invention
are pointed out with particularity in the claims annexed to and
forming a part of this specification. For a better understanding of
the invention, its operating advantages and specific objects
obtained by its use, reference should be had to the accompanying
drawings and descriptive matter in which there is illustrated and
described a preferred embodiment of the invention .
BRIEF DESCRIPTION OF THE DRAWING
In the drawing:
FIG. 1 is a schematic diagram of a pulverized coal delivery system
according to a preferred embodiment of the invention.
FIG. 2 is a schematic diagram illustrating in greater detail the
controls associated with the system of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
In the pulverized coal delivery system 10 illustrated by way of
example in FIG. 1, raw coal is withdrawn from a storage bunker 11
and flows by gravity through a shut-off valve 13, which is open
when system 10 is in operation, to feeder 12. Feeder 12 supplies
coal to a pulverized 14 at a rate which can be adjusted by
regulating the setting of a variable speed drive means 12A
associated with feeder 12 to correspondingly regulate the
pulverized coal output rate of pulverizer 14.
The pulverizer 14 operates to convert the raw coal into pulverized
coal of a consistancy suitable for conveyance in dense phase
fluidized form into a blast furnace 15.
As shown, a separately fired air heater 16 connected to pulverizer
14 by a duct 22 supplies hot primary air to pulverizer 14 to dry
the coal and to subsequently convey coal product output through a
pipe 18 to the inlet of a cyclone separator 17. The hot primary air
is produced by burning natural gas, admitted to heater 16 through a
pipe 19, with air being supplied by a primary air fan 20 connected
to heater 16 by a duct 21. To allow proportioning of the primary
air flow rate according to the coal rate through pulverizer 14, the
fan 20 is provided with an adjustable damper 20A.
The air-coal mixture that enters the cyclone separator 17 is
centrifugally separated, with the coal passing to a storage
reservoir 23 by gravity flow by way of a coal line 24 which is
provided with a normally open shut-off valve 25. The extremely fine
coal particles entrained in the primary air as it leaves separator
17 are carried along with the air through a pipe 26 to a bag
filterhouse 27 or other functionally similar medium and collected
therein. The primary air stream is then vented to a low pressure
receiver (not shown) and the collected, coal fines are fed to a
storage reservoir 23 through a coal line 28 provided with a
normally open shut-off valve 29. Surface moisture evaporated from
the coal during the pulverizing and storage phases is vented with
the primary air.
If desired a plurality of pulverized coal preparation units can be
operated in parallel to supply coal to storage reservoir 23, since
with multiple units, intermittent operation, maintenance, or
emergency servicing of any single unit can be accommodated without
necessitating a shut-down of the delivery system 10. In lieu of
spare pulverizing capacity afforded by multiple coal preparation
units, an auxiliary storage reservoir (not shown) can be provided.
The auxiliary tank could be suitably connected to the coal lines 24
and 28 to receive some or all of the pulverizer output in excess of
the then current needs of the furnace 15.
The storage reservoir tank 23 is suitably vented so as to operate
at atmospheric pressure and serves to provide sufficient storage of
pulverized coal to supply a plurality of batch tanks 31A, 31B and
31C which feed the furnace 15. Tanks 31A-C are located at a lower
elevation than reservoir tank 23 and are connected thereto by a
plurality of corresponding coal distributor lines 30A, 30B, 30C,
respectively.
Coal distributor lines 30A-C are provided with remotely operable
shut-off valves 32A, 32B, 32C respectively that serve to control
the flow of pulverized coal from reservoir tank 23 to the
individual batch tanks 31A-C. The tanks 31A-C are placed in
communication with a pneumatic transport line 33 by means of
corresponding coal outlet lines 34A-C provided with respective coal
outflow control valves 35A-C that can be selectively opened to
permit coal flow from selected tanks 31A-C, one at a time, to
furnace 15 through line 33, and closed to isolate from line 33
those tanks 31A-C other than the one currently selected to supply
coal to furnace 15.
Transport line 33 is supplied with the compressed air needed for
pneumatic conveyance of the coal by a compressed air source 36, the
outlet of which is connected to line 33 through a control valve 37
and a check valve 38.
At the blast furnace 15, line 33 communicates with one or more
distributors 39 from which a multiplicity of coal pipes 40 lead to
the individual tuyeres 41 of furnace 15, in a manner similar to
that described in U. S. Pat. No. 3,150,962 to L. Pearson, and in U.
S. Pat. No. 3,204,942 to W. J. Matthys et al. The number of
distributors 39 as well as the number of tuyeres 41 served by each
distributor 39 can be varied according to the requirements of the
blast furnace 15. Each of the pipe 40 is provided with a nozzle 42
which extends through the tuyere 41, opening directly into the
furnace 15 directly into the blast air stream introduced through
the tuyeres 41 to quickly mix the coal with the blast air within
the furnace 15 and thereby promote rapid, complete combustion.
Inert gas is used for pressurizing the tanks 31A-C and also to
aerate the coal contents of the tanks and storage reservoir 23. For
such purposes, a compressed gas source 50 is provided with a
delivery pressure sufficient to maintain dense phase coal flow from
any given tank 31A-C into transport line 33 at the maximum
anticipated furnace 15 demand rate and against the maximum expected
back pressure of the furnace tuyeres 41. The tuyere back pressure
can run as high as about 50 psi and is caused by the high static
pressure at the bustle pipe 51 which supplies through tuyeres 41
the necessary process air to furnace 15. The choice of an inert gas
for pressurizing and aerating is favored because it prevents
ignition of the coal within the reservoir 23 and in tanks
31A-C.
In addition to the coal inert valves 32A-C and the coal outlet
valves 35A-C, the tanks 31A-C are provided with valves 52A-C,
53A-C, and 54A-C and 55A-C respectively to accomplish the
pressurization, aerating, and venting functions required in the
operation of the system 10. The pressurizing valves 52A-C are
connected by suitably arranged piping to the compressed inert gas
source 50 through a check valve 56 and control valve 57, and to the
upper portions of their respective tanks 31A-C and when open serve
to pressurize the coal contents of the tank. Aeration valves 53A-C
are connected to their respective tanks 31A-C and to source 50 by
suitably arranged piping in parallel with corresponding valves
52A-C and serve, when open, to introduce inert gas into the lower
portion of tanks 31A-C for aerating the coal therein. Valves 54A-C
serve, when open, to vent their respective tanks 31A-C to a
suitable receiver (not shown).
Valves 55A-C are connected via suitable piping to the storage
reservoir 23 and to their respective tanks 31A-C and serve, when
open, to equalize the pressures between tanks 31A-C and the
reservoir 23. Reservoir 23 is aerated with inert gas passed through
a conduit connecting the reservoir and the source 50, and having
suitably positioned control valve 60 and check valve 61.
In the operation of system 10, each of the tanks 31A-C is
alternately filled, pressurized, and emptied to feed the furnace 15
in a predetermined cyclical sequence. For example, while tank 31A
is feeding the furnace 15, tank 31B is in standby status, filled
with coal and pressurized with inert gas, while tank 31C is being
filled with coal from reservoir 23.
Accordingly, it can be stated that each tank 31A, 31B, 31C must
necessarily be in one of three operative states, namely:
1. The active mode, characterized by the tank being isolated from
the reservoir 23, in communication with the transport line 33, and
pressurized to deliver coal to the furnace 15;
2. The standby mode, characterized by the tank being isolated from
both the reservoir 23 and the transport line 33, filled with coal
and pressurized;
3. The refill mode, characterized by the tank being isolated from
the transport line 33, in gas pressure equalizing communication
with the reservoir 23, and in coal-flow communication with the
reservoir 23, to receive coal therefrom.
After a tank (31A, 31B, 31C) which has been in the active mode
becomes empty, that tank is switched to the refill mode, the tank
which was in the standby mode is concurrently switched to the
active mode so that the furnace 15 may be continuously supplied
with coal without interruption or overlap, and the most recently
filled tank i7 switched to the standby mode. The tanks 31A-C and
the coal lines 30A-C from reservoir 23 are proportioned so that the
tank in the refill mode will be filled with coal to its intended
capacity before the then currently active tank becomes empty. Thus
when switching tanks, that tank which was in the refill mode is
switched to the standby mode so that there is always one tank
filled and pressurized and therefore ready to immediately replace
the active tank.
One of the advantages of providing three tanks 31A-C is that should
it be necessary to remove one tank and its associated control
system from service, for maintenance and for repair, it is still
possible to continuously supply the furnace 15 using only the two
remaining tanks. In such case, the two tanks would alternate
between the active and refill modes.
If desired to provide additional batch tank storage capacity, this
can be done simply by adding to the system 10 extra tanks equipped
with valves and connected in a manner similar to the tanks 31A-C.
With more than three tanks 31A-C, there will be available two or
more standby tanks.
Preferably, the valves 53A-C are left open during all operating
modes to assure satisfactory fluidization of the coal contents of
the respective tanks 31A-C.
To place the individual tanks 31A-C in the active, standby and
refill modes of operation, their respectively associated coal inlet
valves 32A-C, coal outlet valves 35A-C and pressure equalization
valves 55A-C are set in the states indicated by the following Table
I:
table I
Required Valve States
Valve Active Standby Refill Mode Mode Mode Coal Inlet Closed Closed
Open (32A-C) Coal Outlet Open Closed Closed (35A-C) Equalization
Closed Closed Open (55A-C)
the states of the pressurization and vent valves 52A-C and 54A-C
associated with whichever tank is in the active mode are set by
control signals derived on the basis of the difference between the
actual coal flow rate to furnace 15 and the required or demand coal
flow rate thereto. Should the actual coal flow rate be less than
the demand rate, a control signal is applied to open the
pressurization valve 52A-C thus increasing the tank gas pressure to
raise the actual coal flow rate. Conversely, should the actual coal
flow rate be greater than the demand rate, a control signal is
applied to open the vent valve 54A-C thereby reducing the tank gas
pressure to correspondingly reduce the actual coal flow rate.
To prevent abrupt changes in the coal flow rate to furnace 15 when
a standby tank is about to be switched to the active mode, the
states of the pressurization and vent valves 52A-C and 54A-C
associated with the tank in the standby mode is set by control
signals so as to maintain the gas pressure in the standby tank the
same as that within the active tank.
The vent valve 54A-C for the tank in the refill mode is kept open
and the pressurization valve 52A-C for such refill mode tank is
kept closed.
It should be noted that in order to minimize the loading of the gas
source 50, the pressurization and vent valves 52A-C and 54A-C for
any given tank are never opened simultaneously.
FIG. 2 illustrates by way of example a typical control system 100
which can be used to regulate the operation of the valves 32A-C,
35A-C, 52A-C, 54A-C and 55A-C as to place the tanks 31A-C in their
active, standby, and refill modes according to a predetermined
sequence, and to regulate the coal output of the pulverizing unit
such that a predetermined total weight of coal is maintained within
storage reservoir 23 and tanks 31A-C regardless of changes in the
coal delivery rate to furnace 15.
Associated with control system 100 are a set of weight measuring
transducers 101A-D which are arranged to sense the weight of tanks
31A-C and reservoir 23 respectively, and to establish signals W1,
W2, W3, and W23 corresponding to the weight of the coal in the
tanks 31A, 31B, 31C and reservoir 23 respectively. These weight
signals are applied to a signal summing means 102 which provides an
output signal W.sub.T representing the total weight of all the coal
currently stored in the system 10 and available for delivery to
furnace 15. The weight signals W1, W2, W3, are also applied to
respective differentiators 103A, 103B, and 103C which derive
therefrom corresponding output signals Q.sub.1, Q.sub.2 and Q.sub.3
representing the rates at which the coal content weights of tanks
31A, 31B and 31C are changing. From the signals Q.sub.1, Q.sub.2,
and Q.sub.3, it is possible to determine at any time which of the
tanks 31A-C is in the active mode, which tank or tanks are on
standby, and which tank is being refilled. For such purpose, the
signals Q.sub.1, Q.sub.2, Q.sub.3, are applied to a polarity
discriminator 104 which produces an output signal, Q.sub.C,
equivalent in magnitude to the one of the signals Q.sub.1, Q.sub.2,
Q.sub.3 that represents a negative rate of weight change.
For example, when tank 31A is in the active mode, tank 31B on
standby and tank 31C is being refilled, signal Q.sub.1 will be
negative and its magnitude will represent the coal flow rate to
furnace 15, signal Q.sub.2 will be positive with its magnitude
representing the rate at which coal is being transferred from
storage reservoir 23 to the tank 31C.
The total stored coal weighed signal W.sub.T is applied to an error
detector 105 along with a reference signal W.sub.R established by
an adjustable selector 205 and representing the total stored coal
weight that is to be maintained. Error detector 105 provides an
output signal E.sub.W representing the difference, or error between
the signals W.sub.T and W.sub.R. Error signal E.sub.W is applied to
a feeder speed controller 106 that regulates the output speed of
the drive means 12A for feeder 12 (see FIG. 1) to correspondingly
regulate the coal output of pulverizer 14 in accordance with the
value of signal E.sub.W so as to null the error between W.sub.T and
W.sub.R. Thus, the operation of pulverizer 14 is controlled to
continuously introduce pulverized coal into the system 10 at the
same rate at which pulverized coal leaves the system 10, and
therefore, on a steady state basis the coal inflow rate to storage
reservoir 23 will be equal to the actual delivery rate Q.sub.C to
furnace 15.
The feeder speed controller 106 is connected to another controller,
107 which regulates the operation of the primary air fan damper 20A
in accordance with the feeder 12 speed to maintain a given weight
proportion between the primary air flow through pulverizer 14 and
the coal flow therethrough.
To determine the pulverized coal requirements of furnace 15, flow
transducer 207 is connected to the inlet of bustle pipe 51 (see
FIG. 1) to sense the combustion air flow rate, or wind rate, into
furnace 15, and to provide an output signal Q.sub.W representative
thereof. The wind rate signal Q.sub.W is applied to an adjustable
signal translator 108, which establishes an output signal Q.sub.CR
representing the coal demand rate of furnace 15. The signal ratio
[Q.sub.CR /Q.sub.W ] represents the number of pounds of pulverized
coal to be injected into furnace 15 per 1,000 CFM of combustion air
and can be adjusted to vary the percentage of coke replacement by
pulverized coal in furnace 15 operation.
The coal demand rate signal Q.sub.CR is applied to signal converter
109, along with the coal changes in weight rate signal Q.sub.C
obtained from discriminator 104. On the basis of the two input
signals Q.sub.CR and Q.sub.C, signal convertor 109 establishes an
output signal P.sub.R representing the value of the gas pressure
required in the tank 31A-C which then is feeding furnace 15 in
order to null the difference between the actual coal delivery rate
and the demand rate as indicated by signals Q.sub.C and Q.sub.CR,
and thereby maintain a steady state delivery rate equal to the
demand rate.
Each of the tanks 31A-C are provided with individual transducers
110A, 110B, 110C respectively, which sense the gas pressure in
associated tanks 31A-C and provide output signals P.sub.1, P.sub.2,
P.sub.3, indicative of the values of the pressurizing gas pressure
then prevailing in tanks 31A, 31B, and 31C respectively.
For the purpose of controlling the gas pressure in each of the
tanks 31A-C, the signals P.sub.1, P.sub.2, and P.sub.3 are applied
to corresponding error detectors 111A, 111B and 111C respectively,
the output signal P.sub.R is also applied to each of the error
detectors 111A-C. Error detector 111A establishes an error signal
E.sub.P1 corresponding to the difference between the gas pressure
in tank 31A and the required gas pressure indicated by signal
P.sub.R. Similarly, error detectors 111B and 111C establish error
signals E.sub.P2 and E.sub.P3 corresponding to the differences
between the required gas pressure and that existing in tanks 31B
and 31C respectively.
The tank pressure error signals E.sub.P1, E.sub.P2, and E.sub.P3
are individually applied to corresponding valve controllers 112A,
112B, 112C that regulate the operation of the associated pressuring
valves 52A-C and vent valves 54A-C in accordance with the
information presented by signals E.sub.P1, E.sub.P2, E.sub.P3 and
with mode indicator signals that are also applied to controllers
112A-C via respective input lines 113A, 113B, 113C as will be more
fully described later.
The operation of the controllers 112A-C is best explained by
considering a typical example in which tank 31A is active, tank 31B
is on standby, and tank 31C is being refilled. Under such
conditions, controller 112A, which has signal output lines
connected to the operating solenoids of the valves 52A and 54A
associated with tank 31A will regulate the opening and closing of
the valves 52A, 54A in accordance with the signal E.sub.P1, so as
to null the pressure error represented thereby. If signal E.sub.P1
indicates that the tank 31A pressure is greater, by a predetermined
threshold value, than the required value, controller 112A will
cause the pressurizing valve 52A to be held closed and the vent
valve 54A to be opened until the tank 31A pressure decreases to the
required value, upon which occurrence, vent valve 54A will be
closed by controller 112A. Conversely, should signal E.sub.P1
indicate that the tank 31A pressure is lower, by a predetermined
threshold value, than the required pressure, controller 112A will
cause the vent valve 54A to be held closed and the pressurizing
valve 52A to be opened until the tank 31A pressure increases to the
required value, upon which occurrence, valve 52A will be closed by
controller 112A.
Controller 112B has signal output lines connected to the operating
solenoids of the valves 52B and 54B associated with tank 31B, and
when tank 31B is either active or on standby, controller 112B
regulates the opening and closing of valves 52B and 54B to maintain
the tank 31B gas pressure equal to the required value set by signal
P.sub.R, in the same manner as previously described in connection
with controller 112A.
With regard to controller 112C and the valves 52C and 54C
associated with the tank 31C that is in the refill mode, it should
be noted that such mode requires that the tank be vented to a low
pressure receiver (not shown). Accordingly, where tank 31C is being
refilled, the mode indicator signal applied to controller 112C via
line 113C and identifying tank 31C as being in the refill mode
causes said controller 112C to hold the pressurizing valve 52C
closed, and the vent valve 54C open regardless of the value of the
signal E.sub.P3.
Although in the example given, individual tanks 31A-C were
identified as being in specific operating modes, it will be
understood that during the normal operating cycle of the system 10,
the tanks 31A-C will be placed in their other modes in accordance
with a set sequential pattern, and the controllers 112A-C will
function (1) to maintain the active tank at the pressure required
to satisfy the coal demand rate, (2) to maintain the standby tank
at the same pressure as the active tank, and (3) to maintain
venting of the refill tank during the filling operation regardless
of which of the tanks 31A-C are in a particular mode.
A typical mode sequencing program for the tanks 31A-C is given by
the following Table II:
table ii
sequence Active Standby Refill Period Tank Tank Tank 1 31A 31B 31C
2 31B 31C 31A 3 31C 31A 31B 4 31A 31B 31C
from Table II it can be noted that the tank mode pattern is
repeated after every third period in the sequence because there are
three tanks 31A-C and each is capable of assuming the three
different modes.
The setting of the tanks 31A-C in the sequence of modes prescribed
by Table II is accomplished by means of a sequential controller 114
having input lines 115A-C which receive the tank weight signals W1,
W2, and W3 provided by transducers 101A-C, and which has three sets
of output lines 116A-C, one set for each corresponding tank 31A-C.
Each output line set 116A-C includes three output lines A, S, R
that carry mode command signals for establishing the corresponding
tank 31A-C in the active, standby, and refill modes
respectively.
The sequential controller 114 output line groups 116A-C are
connected to corresponding valve controllers 117A-C to regulate the
operate thereof.
The valve controllers 117A-C have output lines connected to the
operating solenoids of the coal inlet, coal outlet and pressure
equalizing vents valves 32A-C, 35A-C and 55A-C. The refill R lines
of line groups 116A-C are connected to the mode indicator input
lines 113A-C of respective valve controllers 112A-C.
The valve controllers 117A-C themselves are so constructed and
arranged that a mode command signal applied to the active A line of
any controller 117A-C causes that controller to set the three valve
groups, (32A, 35A, 55A), (32B, 35B, 55B), (32 C, 35C, 55C)
associated with the controller in the states required to place the
corresponding tank 31A-C in the active mode. Similarly, a mode
command signal applied to the standby S line of a particular
controller 117A-C causes it to set its three valve group in the
states required to place the corresponding tank 31A-C in the
standby mode. Likewise, a mode command signal applied to the refill
R line of a controller 117A-C causes it to set its three valve
group in the states required to place the corresponding tank 31A-C
in the refill mode. In addition, a mode control signal on the R
line of a controller 117A-C is carried via the connected line
113A-C to the corresponding controller 112A-C to set the valves
(52A and 54A), (52B and 54B) or (52C and 54C) associated therewith
in the states required when the corresponding tank 31A-C is the
refill mode.
At any given time, the controller 114 applies only one mode command
signal per output line set. For example, in the first period of the
sequence defined by Table II, controller 114 applies a mode command
signal to the A line of the set 116A to put tank 31A in the active
mode, applies a second mode command signal to the S line of the set
116B to put tank 31B in standby mode, and applies a third mode
command signal to the R line of set 116C to put tank 31C in the
refill mode. During the course of such first period, the coal
weight in tank 31A will decrease and the coal weight in tank 31C
will increase. Should the coal weight in tank 31C reach a
predetermined maximum value as indicated by the W3 signal before
the coal weight in tank 31A reaches a predetermined minimum value
as indicated by the W1 signal, controller 114 will switch the third
mode command signal from the R line of set 116C to the S line to
put tank 31C into the standby mode, thereby eliminating any
possibility of overfilling tank 31C.
For sustained pulverized coal delivery to furnace 15 without
interruptions, it is necessary that the coal transfer rates from
storage reservoir 23 to the individual tanks 31A-C during their
refill modes be at least equal to, and preferably somewhat greater
than the maximum anticipated coal outflow rate of any tank 31A-C
during its active mode. Consequently, it is to be expected during
any typical period of operation that the tank which at the
beginning of the period was in the refill mode will become filled
with coal up to its maximum coal weight before the active tank is
emptied to its minimum coal weight, which of course, need not be a
completely empty condition.
In such case, during the latter part of the first period of
operation, there will be two tanks, 31B and 31C on standby, and the
one tank 31A active.
When the coal weight in the active tank 31A reaches the
predetermined minimum value, controller 114 terminates the first
period of operation and initiates the second by applying mode
command signals to the R line of set 116A, the A line of set 116B,
and the S line of set 116C. Here again, should the coal weight in
the refill tank 31A reach the maximum value before the end of the
second period, controller 114 will switch the command signal from
the R line of set 116A to the S line to place tank 31A on standby.
The second period of operation ends and the third period commences
when the coal weight in tank 31B reaches the minimum value.
At the end of the third period, which occurs when the coal weight
in tank 31C reaches the minimum value, controller 114 sets the
tanks 31A-C in the same modes as in the first period, and the tank
mode program cycle is repeated.
In the operation of the blast furnace 15, the combustion air is
supplied at a temperature normally 1,000.degree. F or greater above
the temperature of the carrier gas, which is preferably air,
introduced into line 33 (see FIG. 1) for transporting coal into
furnace 15. For efficient furnace 15 operation, it is important to
minimize the amount of cold air injected into the furnace 15 along
with the coal, since whatever cold air goes into the furnace 15
necessitates using a portion of the fuel to supply the heat
necessary to raise the temperature of the coal-air mixture to
furnace 15 operating temperature. On the other hand, if the flow of
carrier air in the transport line 33 is too low for the coal flow
rate, there is the danger of compacting and plugging the line.
Accordingly, there are optimal carrier air flow to coal flow rates
which are conducive to efficient operation of blast furnace 15.
The invention provides means for automatically regulating the flow
of carrier air into transport line 33 in accordance with the coal
flow rate, or more precisely in accordance with the coal demand
rate of furnace 15.
For such purpose, the coal demand rate signal Q.sub.CR from signal
translator 108 is applied to another signal translator 120 that
provides an output signal Q.sub.AR representing the required flow
rate of carrier air to be supplied to transport line 33 for the
coal flow rate represented by signal Q.sub.CR.
The signal Q.sub.AR is applied to an error detector 121 along with
a signal Q.sub.A derived from a flow transducer 122 connected to
the carrier gas source 36 to sense the flow rate of carrier air
into line 33. Signal Q.sub.A represents the actual flow rate of
carrier air. Error detector 121 supplies to the input of a valve
controller 123 an error signal E.sub.A representing the difference
between the actual and the required carrier air flow rates.
Controller 123 has an output connected to the operating solenoid of
valve 37 and serves to vary the effective opening of valve 37 in
accordance with signal E.sub.A so as to null the carrier air flow
rate error represented thereby and thus maintain on a steady state
basis a carrier air flow rate equal to that prescribed for the coal
demand rate.
It should be noted that while the carrier air flow rate could be
regulated on the basis of the actually existing coal flow rate,
regulation on the basis of the coal demand rate is preferable since
it tends to minimize the effects of system time constant lags.
As can be appreciated by the artisan, the pulverized coal delivery
system 10 can be operated manually instead of automatically as
provided by the control system 100, in which case the operation of
the various valves associated with the tanks 23 and 31A-C, and the
pulverization unit would be operated by personnel monitoring the
various weight, pressure and flow transducers provided in the
system.
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 invention 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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