Note: Descriptions are shown in the official language in which they were submitted.
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S P E C I F I C A T I O N
The present invention relates to control
systems for charging a steam boiler, and in particular
to control systems for charging a wood-waste burning
steam boiler in response to steam demand and pollution
output.
Large quantities of wood-waste particulate
materials, such as saw dust, wood chips, hogged bark,
tan bark, and the like are produced in many industries.
Disposal of such particulate material in a safe,
efficient and pollution-free manner is a problem faced
by all such industries. Waste material of this type
is generally stored in large containers equipped to
discharge the waste material utilizing various un-
loading mechanisms. Some known bottom unloadersare comprised of a rotating screw-type conveyor having
means for driving the conveyor screw around the bottom
of the container in a radially sweeping motion.
Driving the conveyor screw in this manner forces the
conveyor screw through the particulate ma.erial re-
gardless of whether the conveyor is moving material
at its maximum capacity, thus resulting in less than
maximally efficient operation. Such prior art con-
veyor devices also tend to arch upwardly into the
particulate material in the container as a result of
the natural tendency of the rotating screw to "climb,"
ultimately resulting in be~ing or breaking of the
conveyor screw.
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A particularly suita~le apparatus for unloading
particul~te material from the bottom of such containers is
disclosed and claimed in U.S. Patent No. 3,414,142 granted
to M.W~ Kolze, The system disclosed and claimed in U.S.
Patent No, 3,414,142 generally comprises a non-arching
radially sweep~ng conveyor screw for bottom unloading
Qf particulate material from a storage container into
a preparatory means which includes a sonic sensor
for maintaining an optimum amount of particulate
material in the preparatory means. A control system
integrated with the charging apparatus controls
mixing of the compacted particulate material with a
controllable volume of air provided by a blower and
also controls damper valves to feed an optimum amount
of particulate material-air mixture into a combustion
chamber, such as a boiler, for burning therein. The
integrated control system receives feedback information
rela~ing to critical parameters within the boiler, such
as boiler temperature, water supply, and smoke and
pollution level and varies the operation of the
charging system in accordance with the received feed-
~ack ~nformation so that an optimum amount of particulate
material is fed into the combustion chamber for
substantially complete combustion of the material and
minim~zation of pollutants,
~ problem in the art is that operation of a
conveyor screw below a discharge bin with an overloading
of saw dust ab~ve such a screw will, because of the
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tendency of saw dust to compact due to its own weight,
result in a sel~-supporting mass of material
which can be tunnelled through by the conveyor screw
thus leaving a support~ng arch of saw dust above the
screw. ~fter the conveyor screw tunnels out the saw
dust beneath the support~ng arch, no further saw dust
will be transported even though a measurement of saw
dust levels ~ould indicate that sufficient saw dust
is present in the bin. In fact, detection of the problem
is possible only after, for example, a saw dust burning
machine fed by the empty conveyor screw cycles down for lack
of saw dust input. The manual intervention of an operator
is then required to dislodge the compacted saw dust.
If too much saw dust or other wood-waste
material is supplied into a combustion chamber, incomplete
combustion will result and cause extensive and unaccept-
able smoke, ash and other pollution. If insufficient
- saw dust is fed into a combustion chamber, however, an
inefficient combustion and/or disposal of material occurs.
The same problems are present to a greater
or lesser deyree with the use of other types of wood-
~aste materials as fuel,
An apparatus for overcoming some of the
above pxQblems is claimed and disclosed in U~S. Patent
3,865,053 granted to B.A. Kolze and M.W. Kolze. That
apparatus utilizes the unloader of U.S. Patent No. 3,414,142 to
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adjustably control the input of wood-waste material
to a conveyor screw which feeds the material to a
choke screw which transports a selected amount of
material to a selected volume of air from a rotating
blade which pulls the material from the choke screw
and feeds the mixture into a combustion chamber of
a boiler for burning. The system includes control
circuitry for integrating the functions of the entire
system so that an optimum amount of particulate matter
is fed to the cumbustion chamber.
The present invention provides an integrated
control system for charging a boiler or other fuel-
burning system with particulate wood-waste material.
An object of the present invention is to pro-
vide an improved combustionable particulate wasteproduct burning system having a fully integrated
control system controlling the entire material feed
and burning process from a storage container to a
combustion chamber. Another object of the present
invention is to provide a wood-waste particulate
material burning system which includes a sonically
controlled material feed meter, a metered feed having
a rotary air lock for depositing particulate material
into a controllable air stream of a fuel injection
fan, which has a vortex controller on its inlet side
to modulate and maintain a proper fuel-air ratio,
a controlled proportioning valve for monitoring flow
of the f~el-air stream into the combustion chamber of
a boiler, and sensors for monitoring the steam demand
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and combustion efficiency of the boiler and the
pollutant level of exhaust gases, and controlling
operation of the various system elements in accordance
with a predetermined program to ensure substantially
complete combustion and pollutant minimization.
On the Drawing:
The drawing is a schematic diagram illustrating
a system flow and working relationship between various
elements of a particulate waste products firing system
constructed in accordance with the principles of the
present invention.
An improved particulate wood-waste material
burning system is shown in the drawing having a frame
10 which supports a container 11 having a base 13 and
a vertical wall 12. The base 13 has an opening 14
therein through which wood-waste material 15 such as
saw dust, wood chips, hogged bark, tan bark, and the
like can be deposited into a hopper 16.
Controlled transfer of material 15 from the
bin 11 to the hopper 16 is achieved by a rotating
conveyor screw 17 operated by a motor 18 through a
right angle linkage 19 and a rotational linkage 20.
The conveyor screw 17 terminates in a wheel 21 having
an outer diameter which is larger than the individual
flights of the conveyor screw 17, so that the flights
remain a distance above the base 13 as the wheel 21
rotates thereon. An annular retaining rim 22, ex-
tending perpendicular from the wall 12, restricts the .
natural tendency of the conveyor screw 17 to rise as
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it moves through the material 15.
The hopper 16 has an opening 23 in the bottom
thereof allowing flow of the material 15 into a
generally cylindrical housing 24a having a choke screw
70 therein, along with a shroud-like covering 24c
which compacts and regulates the amount of material
carried by screw 70. The choke screw 70 is rotated by
a motor (not shown). A limited amount of material 15
is carried by the choke screw 70 to a circular housing
24, insuring that the material is of optimum density
for combusti~n. A controlled volume of material 15
is thereby fed into the path of a plurality of blades
25 preferably terminate in a knife edge 25a to cut
any larger waste wood pieces into smaller pieces
during operation so as to insure that a complete air
seal between the blades 25 and the housing 24 is
maintained.
Rotation of the blades 25 deposits a pre-
determined constant volume of particular material 15
into a duct 28, which is connected to a housing 29
containing a blower 30. The material 15 is thus
deposited in the air flow of the blower 30, and the
blades 25 and housing 24 are constructed in sealed
relation forming an air-lock preventing air flow into
the housing 24. With the motor 26 providing a selected
constant rotational output, the volume of particulate
material 15 is deposited into the duct 28 is a known
value and the fuel-air mixture can be varied by con-
trolling the operation of the blower 30.
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The blower 30 has a vortex input 31 which
is adjustable by a motor 32 and a linkage 33 as is
known in the art to selectively vary the amount of
air intake to the blower 30. Interrelated control
of the motors respectively operating the choke
screw 70, the rotary feeder ~24, 25) and the blower
30, is undertaken to as to achieve an optimum fuel-to-
air ratio for the material 15 which is mixed with air
in the duct 28.
A further control for monitoring the amount
of the particulate material 15 in the hopper 16 is
provided in the form of a sonic monitor consisting
of a sonic transmitter 33 and a sonic receiver 34.
The transmitter 33 and the receiver 34 are positioned
in the hopper 16 so that a straight-line transmission
therebetween defines a maximum level of material 15
in the hopper 16. The intensity of the sonic energy
leaving the sonic transmitter 33 may be adjusted such
that when the feed of material 15 from the bin 11
exceeds the level defined by a line between the trans-
mitter 33 and the receiver 34, the material 15 will
block transmission of the sonic signal. Alternatively,
the intensity of the sonic signal may be increased
so that the signal will penetrate the material 15 as
long as a selected material density is not present.
For example, the signal intensity may be adjusted so
that transmission of the signal is not interrupted
until substantially the entire area between the
transmitter 33 and the receiver 34 is filled with
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material 15, i.e., the hopper 16 is essentially filled
to its outer edges. Such adjustment would prevent the
situation where a pile of material 15 exists in the
central portion of the hopper 16, yet does not reach
the sides of the hopper 16, so that even though the
pile would block sonic transmission, there would still
be insufficient material 15 in the hopper 16 to facili-
tate optimum boiler operation.
When the sonic signal transmission is inter-
rupted, a sensor analyzer 35, constructed as is knownin the art, will provide a signal to a control unit 36
which will in turn provide a signal to stop the motor
18 and thereby stop the flow of material 15, as more
fully explained below.
The duct 28 continues to a boiler 41 where
it is divided into two smaller ducts 37 and 38 con-
nected to dual inputs of the boiler 41. Air and
material flow through the ducts 37 and 38 occurs through
blow-back dampers, schematically shown at 39 and 40,
both of which are operated solely by air pressure.
The boiler 41 may comprise any fire tube or
water tube boiler or industrial hot air furnace, in-
dustrial incinerator or heat-exchanger (heating thermal
oil or water or other suitable medium) and can be
primarily or supplementarly fired by coal, gas, oil
or other available fuel. The firing system for such
devices and fuels are known so that further details
thereof are unnecessary. In the embodiment shown, the
; boiler 41 is mounted on a fire brick and steel base 44
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and may be equipped with an over-fire manifold 45 or
an under-fire manifold (not shown). The boiler 41
has a combustion area 46 and an upper heat-extraction
area 47 whereat steam lines or other like may be dis-
posed. Preferably suspension burning is utilizedwhereby an admixture of air and wood waste material
is blown into the boiler and burned at a proper fuel-
air ratio, resulting in substantially complete com-
bustion, with virtually no smoke or ash. The boiler
41 has an exhaust duct 48 connected to a stack 49
which may be provided with pollution controls (not
shown), such as a fly ash arrester, a scrubber (dry
or wet) or other equipment required by local air pollu-
tion governing agencies. An additional gas outlet
damper 48a may also be provided in the exhaust duct
48 as an aid in heat retention.
The blow-back dampers 39 and 40 also act as
a safety device to prevent gases and heat from
travelling through the duct 28, should an explosion or
other malfunction occur in the boiler 41, because the
blow-back dampers 39 and 40 allow air flow only in a
direction toward the boiler 41. The rotary air seal
between the blades 25 and the housing 24 also acts as
a safety feature to further prevent back flow of gases
and heat through the duct 28.
A sensor 50 disposed in the area 47 of the
boiler 41 monitors steam demand, and a second sensor
51, disposed in the exhaust duct 48, measures combus-
tion efficiency, such as by an O2-analyzer or other
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combustion analyzer. Both of the sensors 50 and 51
are connected to a boiler sensor analyzer 52 which
is connected to the control unit 36 for providing a
feedback signal thereto so that various system para-
meters may be adjusted in accordance with the signalsreceived from the sensors 50 and 51.
The system is connected to a power source at
terminals 53 and 54, such as a 60 cycle, 110-120 volt
single-phase supply line.
The control unit 36 is activated to initiate
the material burning process. The main power supply
switch 55 is closed, and a sensor 56 contained in the
bin 11 determines whether sufficient material 15 is
present to charge the system. As shown in the
drawing, the sensor 56 is disposed at a side of the
bin 12 to insure that material is present all the
way to the edges of the bin 12 by measuring the height
or weight of the materials. The control unit 36 will,
depending upon the signal received from the sensor 56,
either refuse to start the burning process, or activate
the process. The control unit 36 may also deactivate
the process should the availability of material 15
within the bin 11 become low at any time.
- The gear boxes associated with the auger 17
may be covered by a deflector 57.
Once power is provided to the system and the
presence of material 15 is detected within the storage
bin 11 by the weight sensor 56, the ultrasonic analyzer
35 begins monitoring an ultrasonic signal between the
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transmitter 33 and the receiver 34. The signal re-
ceived by the analyzer 35 is analy2ed to determine
if the desired level of accumulated material 15 is
present within hopper 16, as shown in the drawing.
If an insufficient level of material 15 is detected,
a signal is sent to the control unit 36 which in
turn closes a switch 58 which activates the bin un-
loader motor 18. The ultrasonic sensor analyzer 35
continually monitors the level of accumulated material
15 within the hopper 16 and provides a signal so that
the control unit 36 can control the operation of the
screw conveyor 17 and maintain a desired level of
accumulated discharge.
- After receiving the required signal from the
sensor analyzer 35 the control unit 36 actuates
; operation of the blower 30. The vortex intake 31
of the blower 30 can be selectively opened and closed
; by operation of a double pole switch 59 connected to
an induction coil 60, which controls the motor 32.
Connection of the switch 59 across a first pair of
terminals 61 operates the motor 32 in a first direc-
tion, and connection of the switch 59 across a second
pair of terminals 62 operates the motor 32 in a
second, opposite direction. Other suitable control
means may be utilized as are known to those skilled
in the art.
The control unit 36 also controls a switch
65 for selectively operating the motor 71 which con-
trols the flow of material 15 from the hopper 16 to
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the duct 28 through rotary feeder 24.
The entire system is thus operated in
response to feedback signals received from the
weight sensor 56, the sonic sensor analyzer 35 and
the boiler sensor analyzer 52, all connected to the
control unit 3~ and which may all be contained in a
control panel 66.
An example of a system utilizing the inven-
tive concept herein is as follows. It should be
understood that the following description is for
exemplary purposes only, and is not intended to
represent the only manner in which the concept dis-
closed herein may be utilized.
In an exemplary burning system which includes
a 25,000 pound high pressure boiler operating at
about 200 psig the above-described particulate wood-
waste storage and feed system may comprise a suitable
container 11 which may be a 200 ton metal storage
facility resting on a 10 foot high steel frame in
the boiler room location. The nonarching, radially
sweeping unloader may be of the type disclosed and
claimed in U.S. Patent Nos. 3,338,434 and 3,414,142
and sold under the registered trademark "SHUROUT."
The motor 18 may be a 10 horsepower totally enclosed
fan cooled (TEFC) unit. The blower 30 will have a
vortex controller on the inlet side and modulate to
maintain a proper fuel-air ratio for wood firing.
A nine inch diameter schedule 40 pipe with long
curved 90 radius elbows with removable backs of
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XAR material may be installed and connected to the
boiler 41 by two 7 inch diameters schedule 40 pipes
and elbows. The wood firing system may have its own
set of combustion controls and recorders as described
S above and will be pre-wired and mounted on the
standing electric control panel 66 with required
interlocks. A Breslove type fly ash arrester may
be utilized having an induced draft fan with an
Eddy drive motor to modulate according to fuel con-
sumption. Cinder re-injection may be installed and
connected to the stack 49. The stack 49 may be
approximately 36 inches in diameter and 40 feet high.
Properly adjusted operation of this system will
handle about 200 tons of waste material in a sub-
stantially smokeless manner with about 0.15 grains
of particulate fallout per cubic foot of flue gas or
0.20 pounds of fallout per million BTU of heat
input, producing from about 3,000 to 25,000 pounds
of steam per hour.
A second conveyor screw may be installed
parallel to the metered feed 70 to remove excess
material 15 to a truck or other overflow container
to accommodate excess material 15 if for some reason
material feed into the housing 24 exceeds the system
limits.
Although modifications and changes may besuggested by those skilled in the art it is the
intention of the inventors to embody within the
patent warranted hereon all such changes and
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modifications as reasonably and properly come within
the scope of their contribution to the art.
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