Note: Descriptions are shown in the official language in which they were submitted.
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~3134
SOLID FUEL CONVERSION SYSTEM
This invention relates to fuel conversion and,
more particularly, to burners capable of converting a wide
variety of solid fuels into energy with a minimum of
particulate emission.
With the growing shortage of energy sources, it
is desirable to extract energy from any available source.
Usually, this means that a fuel is burned in a furnace to
generate heat which is converted into steam or some other
usable form. At one time, these furnaces were
specifically designed to burn a particular solid fuelt
such as powdered coal, for example. The furnace could not
easily burn any other fuel.
Also, the known solid fuel furnaces are
labor-intensive since someone has to remove clinkers,
ashes, and the like. If the fuel includes oreign matter,
such as rocks or steel bolts, for example, the
fuel feeding mechanism may jam and a shear pin breaks~
Thenl it sometimes becomes necessary to unload the entire
coal bin to back the drive mechanism and remove the
foreign matter.
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For these and other reasons, solid fuel stokers
fell out of favor and have been largely replaced by yas
and oil-fired furnaces. Todayl however, gas and oil have
come into scarce supply and their costs have increased
sharply.
Along with these fuel requirements, modern
life-style has generated vast amounts of trash and other
waste material which must be eliminated. ~owever,
indiscriminate burning led to air pollution. As a result,
incinerators have been forbidden to burn much of this
trash and waste material.
As a result of these and other considerations9
there is now a need for a system which can burn almost any
combustible material for the purposes of energy
extraction, without pollution, and with little or no need
for manual labor.
Accordingly~ an object of the invention is to
provide equipment for converting a wide variety of solid
fuels into efficient eneryy, with a minimum of particulate
emission. ~ere, an object is to provide flexible and
versatile energy conversion systems. In this connectionl
an object is to provide a completely or nearly completely
automatic system which minimizes the need for human
supervision and servicing.
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Another object of the invention is to provide a
sulphur-absorbing material in a system for converting
high-sulphur coal to energy, without causing air pollution.
Yet another object of the invention is to provide
a system for converting at least some of the burnable
portions of urban trash into energy, without causing air
pollution.
Still another object of the invention is to
provide a system for burning the waste of forest products,
such as bark, chips, sawdust, and the like.
Yet a further object is to provide for automatic
ash disposal.
A still further object is to provide a modular,
skid mounted system which may be installed, moved or
removed quickly and easily.
In keeping with an aspec~ of the invention, these
and other objects are accomplished by a furnace having an
automatic feed system which is capable of delivering to a
burner almost any relatively solid fuel which can burn on
a grate. The grate has four cascaded sections which are
positioned to advance the solid fuel, as it burns~ The
speed and distance of the advance is controlled so that
the fuel is reduced to an ash by the time that it reaches
the end of the cascade of grates. Air is introduced into,
around and under the 9rate area in a manner which insures
~g83~
01 full and complete combus-tion, regardless of the type
02 and style of fuel tha~ is used. When a high-sulphur
03 fuel is burned, limestone, lime, or other
0~ sulphur-absorbing materials may be introduced in a
05 manner which completely covers the burni.ng bed to
06 absorb and reduce S~2 from the smoke and gas which is
07 released into the atmosphere. (For convenience of
08 expression, all of these and other suitable sulphur
09 materials will hereinafter be called "limestone."~
The system is modular so that a plurality
11 of systems may be operated in series or in parallel
12 depending upon instantaneous changes in demand ~or
13 heat.
14 In general, the invention is a solid fuel
conversion system comprising apparatus for introducing
16 fuel into the system responsive to a demand for heat,
17 apparatus for moving the introduced fuel into and
18 through a burning area at a controlled rate which
19 establishes a bed depth ~hat controls a stratification
of the fuel in the burning area, the stratifica-tion
21 maintaining the heat in the burning area at a
22 temperature which gasifies the uel in one
23 ~tratification without complete combustion in that
24 layer, and apparatus for removing ash af-ter the fuel
passes through the bed, whereby the depth of a
26 resulting bed of fuel in the burning area is
27 automatically controlled to a relatively thin depth in
2~ order to regulate the gasification of the fuel as a
29 function of energy demand.
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01 The invention is also a method of
02 converting solid fuel into energy comprising the s-teps
03 of feeding solid fuel into a burning area at a
04 con-trolled rate, drying the solid fuel in ~he burning
05 area before it reaches a bed of coals, advancing the
06 solid fuel at a controlled rate through an area of a
07 bed of coals to an ash area, the solid fuel burning at
08 a rate which establishes a plura~ity of successive
09 layers from the bottom to top, beginning with -the
burning bed oE coals, covered by a gasifying layer of
11 solid fuel, and topped b~ a layer of green fuel, the
12 successive layers together forming a relatively thin
13 bed for controlling a flow of air. The method further
1~ comprises the steps of delivering con~rolled amounts
of combustion air in a plurality of different
16 locations and levels for enabling the successive
17 layers to control the flow of gasified solid fuel -to a
18 gaseous burning area, delivering the solid fuel to the
19 burning area at a timed rate, and introducing
combustion air through uniformly distributed air holes
21 in a grate supporting the bed of coals, the air
22 distribution being controlled at least in part by the
23 thin depth o~ the fuel bed in the burning area for
24 providing a substantiall~ uniform distribution of air
to support combustion of the fuel in the burning area.
26 The nature of the invention will be
27 understood best from the following description of the
28 drawings in which:
29 Fig. 1 is a side elevation schematic of
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01 the inventive furnace system for converting solid
02 fuels to energy'
03 Fig. 2 is a top plan view of the furnace
04 of Fig. l;
05 Fig. 3A is a side elevation of four
06 cascaded grates using a reciproca~ing plate feeder
07 design, with provisions for an additional series or
08 cascade of four more grates for large-scale burning;
09 Fig. 3B is a plan view showing two of the
systems used in parallel;
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Fig. 3C is an enlarged view of the tip of the
grate sections;
Fig. 4A is a perspective view of a rotary feeder
for delivering a curtain of almost any burnable solid fuel
into a burner;
Fig. 4B is a plan view showing two of the systems
used in parallel;
FigO 4C shows a second alternative feeder which
uses the fuel conveyor to meter the incoming green fuel;
Fig. 5 is an elevation view ~taken along line 5~5
of Fig. 4A~ showing a rotarY feeder in cross section;
Fig, 6 is a stylized cross-sectional view of the
burner area of the inventive system;
Fig. 7 is a cross-sectional, schematic, elevation
view (taken along line 7-7 of Fig. 1) of the burning bed
and air delivery arch of the inventive furnace;
Yig. 8 is a top plan view of a portion of a
system using a sulphur-absorbing ~ such as limestone)
eeder; and
Fig. 9 is a schematic elevation view of the
burning bed of the inventive furnace with limestone added
thereto.
The principal subsystems of the inventive furnace
~Figs. 1 and 2~ are a fuel storage bin 20, a fuel conveyor
2.2, a fuel feeder 24, a burner 26, firebox 27, an ash
removal syst.em 28, a boiler 30, and a pair of blowers 32,
33. The entire assembly is a series of modules built on
one or more skids 34 ~here in the form of massive I-beams
-- see Fig. 7) for easy installation and moving.
The fuel bin 20 may take any suitable form.
Preferably, it is a "live bottom~ type of bin which means
that it contains any suitable mechanical means for
insuring that the fuel falls through a funnel-shaped area
36 in the bottom of the bin. From there, a fuel conveyor
22 transports the fuel to a gravity feed hopper 40.
Preferably, a screw-type conveyor is used at 22.
Beneath hopper 40 is a feeder 24 which is seen in
detail in Figs. 4, 5. This feeder includes a generally
cylindrical sheet metal or metal plate housing 42 having
an open top leading to hopper 40 and an open bottom
leading to burner 26. All of the housings 42 have the
same flange and bolt hole patterns so that they may be
substituted for each other. The feeder design depends
upon the fuel which is used.
In Figs. 4A, 5, a star wheel rotor 44 is mounted
along the longitudinal axis or the center of the
cylindrical section 42. This star wheel rotor 44 has a
plurality of flat blades, vanes or paddles extending
outwardly from a central axis 48. Thus, as the rotor 44
turns in direction A, fuel falls under gravity from hopper
40 and onto the pockets between blades 46. The turning of
the rotor 44 deposits metered amounts of this fuel into
the burner 26. Unlike most rotor feeders, there is a
substantial clearance B (Fig. 5) between the outer edge of
the blade and the inside surface o the cylindrical
housing 42. Thus/ a solid fuel material such as bark, or
the like, may tend to overflow and wrap around the edges
of the blades and still feed through housing 42.
The rotary feeder is thus different from other
feeders in that the fuel -- not the blades -- forms an air
lock for containing most of the air which is pumped into
the firebox to support combustion. The exact amount of
clearance B may vary with the fuel being used. Therefore,
the invention contemplates a provision of a plurality of
different size rotors 44 which may be substituted for each
other. If the fuel is changed from, sayp a shaqgy bark to
a powdered coal9 the rotors are switched so that the
clearance B is appropriate to the fuel which is being
burned.
As the rotary feeder 24 deposits the fuel 49, it
falls as a curtain into ~urner 26. The rotary feeder 24
spreads the fuel 49 fairly uniormly across the width of
the curtain. Therefore, the fire bed is spread fairly
uniformly across the width of the burning area 50 in
burner 26 tFigs. 6, 7)~
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In Fig. 4B, the feeder 42 is merely an inverted,
somewhat funnel-like housing which is, preferably, lined
with a refractory material 41 to block the outward flow of
heat, if live coals fall therethrough. Inside the
housing, a damper 43 is arranged to block the backward
flow of air or combustible gas into hopper 40.
This embodiment of the feeder may be placed at
the output or ash disposal end of some other solid
fuel-burning system. For example, an analysis of live
coals or ash taken from many older systems, which were
designed before the energy crisis developed, shows an
extremely high carbon content. This carbon can be
deposited as live coals into the burner of the inventive
system where it is converted into energy since this system
has an energy conversion efficiency which is much greater
than older systems.
Thus, the live coals, ash and carbon output from
the firebox of some other system is dumped directly into
the refractory-lined feeder 42 of Fig. 4B, when it
depresses da~per 43 during the time required for fuel to
enter the burner 260 As soon as the ash and carbon pass,
the damper 43 automatically closes again.
Fig. 4C shows a similar system for use with solid
fuels which do not require either the rotary feeder of
Fi~. 4A or the refractory feeder of Fig. 4B. Here, the
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solid fuel is dumped from the hopper 40 directly through
an intake chute 45 to the feeder.
The dampers 43 (Fig. 4B) and 47 tFig~ 4C) perform
the same function. However, damper 43 pivots about one
edge and damper 47 pivots around its center. Either style
may be selected depending upon the characteristics of the
incoming solid fuel. For example, shaggy bark might drape
over damper 47 and make it inoperative. On the other
hand, some granular fuels spread themselves better if the
stream is divided into two parts by the damper 47.
If the feeders of Figs. 4B, 4C are used, the
conveyor 22 is run intermittently to meter the flow of
fuels into the burner 26u The reciprocal motion of the
grates spreads the fuel uniformly throughout the fuel bid.
The burner 26 contains a system of cascaded
grates that is best seen in Fig. 3A~ As here shown, the
grate system includes five sections 54-60. The first
grate section 52 sits at a preferred angle of
approximately 60 with respect to the horizontal, which is
an ideal free-fall an~le in a usage such as this.
Therefore, fuel falls, without avalanching, from grate
section 52 to grate section 54. Each of the sections
54-60 sits at about 15 with respect to the hori20ntal.
In effect, the grate 52 breaks the free fall of the
incoming fuel deposited b~ rotary feeder 24 ~nd then acts
_g_
as a drying rack for the fuel. This is not to say that
the actual burning is necessarily restricted to any
specific area of the grate system.
The tip ends of each grate section are formed as
shown in Fig. 3C. The upper surface is the ideal 60
free-fall angle for the fuel and structure used in the
invention. The lower angle 30 is complementary to the~
60 angle at the point where the free-fall fuel-drying
grate 52 rests upon the inclined burn;ng grate 54.
When the burning area must be lengthened to add
to the burnin~ time for any particular fuel or for greater
heating demands, a second series of grates 52a,
54a,.~.(Fig. 3A~ are added at the ash output end. Here
again, the lower 30 angle at the tip end of the grate 52a
rests firmly upon the upper surface of the burning grate
54a.
Sometimes, the heating demands fluctuate
greatly. Therefore, two or more of the de~cribed modular
systems may be placed side by side, as FigO 3 shows
modules I and II placed side by side. Each module has its
own feeder system 24 and shares an input fuel conveyor 22
and output ash conveyor 28 with the other modules. When
the demand for heat is low, only one of the modules is
used. When the demand is high! both moduies come into
operation.
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Thus, the system may be enlarged either by
placing a plurality of modules side by side, as in Fig.
3B, or by adding new cascaded grate sections, as shown at
52a, 54a.
The (60) incline on the first grate 52 provides
a gravity free-flow angle for even the most difficult
solid fuel materials. The second and subsequent grates
54-60 are at an (15) angle which provides for flow
controllability for most materials. The angle of 15
provides some impetus to fuel flow and angular resistance
to gravity flow of siftings through the grate sections~ A
mechanical action of the grate system may be varied hy
adjusting the length of a mechanical stroke and the timing
of the strokes. These variations provide the equivalent
of a mechanical adjustment of the angle of the grates
54-60. This way~ the ash may be analyzed to determine
whether the fuel remains in the burning region long enough
for full and complete combustion.
Each of the cascaded grate sections 54-60 is
mounted for a reciprocatin~ plate eed, somewhat as taught
on page 10-78 of the Marks ~Standard Handbook for
Mechanical Engineers~ (Seventh Edition), McGraw-Hill Book
Company. More particularly, a number of arms 62, 64
periodically move the grates $4-60 back and forth
(directions C, D), with a maximum travel on the order of
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~ 98~3~'~
two to eight inches, for example. Adjustable collars 63,
65 may be moved up or down the arms 62, 64 to adjust the
length of the grate travel stroke. For example, arm 62
and collar 63 will reach a stop 67 after a short travel
~1, while arm 64 and collar 65 will reach stop 67 after a
long travel T2. If collars 63, 65 are moved back or
forward on arms 62, 64, the stroke is lengthened or
shortened.
When the grates 54-60 move forward (direction C),
the fuel material resting on them also moves forward.
When the grates move back (direction D), the fuel is
restrained from moving by the following fuel which fell
from grate 52, as the grates 54-60 moved forward~ and now
blocks the backward travel.
In greater detail, the back end of grate 54 is
supported by a wheel 66 which rides on a rail 68. The
front end of grate 54 rests directly on and slides over
the upper surface of grate S6. The lower end of grate 52
rests on and slides over the surface of grate 54.
Therefore, as arm 62 moves back and forth, grate 54 also
moves back and forth, rolling on wheel 66 and sliding over
the surface of grate 56. The end of grate 52 slides over
grate 54, and acts as a scraper. The remainder of the
cascaded grates 56-60 are mounted in a similar manner,
which is apparent from a study of Fig. 3.
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The curtain 49 (Fig. 6) of solid fuel free-falls
from hopper 40 ~Fig. 1) t through rotary feeder 24 (Fig.
4), and onto grate 52. As the curtain of material 49 so
falls, it passes a level sensor 70 ~Fig. 6), if provided.
This sensor includes a probe which is put into mechanical
oscillation and, thereafter, the oscillations are
detected. When the fuel reaches the level of the sensor,
the oscillations are damped, and that damping is
detected. The sensor is a commercially available product
of Automation Products, Inc., 3030 Max Roy Street,
Houston, Texas 77008. When the sensor 70 detects a low
level of fuel 49, the rotary feeder 24 is driven to
deliver metered amounts of fuel until the fuel level,
within the burner 26, is restored, which damps motion of
the probe of sensor 70.
Thus, ~he rotary feeder 24 introduces a curtain
of solid fuel which falls more or less uniformly over the
width of the burner inlet. This curtain effect
distributes a substantially uniform amount of material
over the width of the grate section and aids in producing
a uniform fuel bed which enhances burner performance. The
rotary feeder 24 also provides an assured positive fuel
flow and insurance against fuel avalanching, as is typical
with many gravity-fed burners. The rotary feeder may have
an adjustable timer control to drop the fuel periodically~
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as may be selected according to the weather. The timer
may have a self-adjusting feature to reduce feed if an
over-feed of fuel should build up.
In the feeders of Figs. 4B and 4C, the fuel is
such that the normal grate motion distributes the fuel
more or less uniformly across the width of the burning
bed. The dampers 43, 47 block the back flow Gf air and
the conveyor 22 meters the inflow o solid fuels.
If desired, the fuel level may be electronically
controlled to adjust the thickness of the fuel bed by
providing a high-limit shutoff at ad~ustable bed depths.
So~etimes, it is desirable to provide a level
sensor plus a variable time delay control. Thus, if there
is a demand for fuel, there may be a delay during which
the grates may be actuated in order to clear space for
green fuel to be deposited on the burner.
The cascaded grates are designed to deliver air
across approximately 4-1/2~ of the entire burning area
through quarter~inch holes more or less uniformly
distributed throughout. These air holes provide uniform
air distribution beneath the cascade o~ grates 52-60 and a
minimum of sifting of combustibles through the grates, due
to the relatively small air openin~s. The inclined angle
of all grate section~ also has a strong effect on reducing
siftings by providing an angular resistance to gravity
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flow of fuel. The first inclined grate 52 (60~) meets the
second inclined grate (15) and acts as a scraper which
minimizes the transfer of combustible directly into the
ash pit.
A distinction is made within the burner unit
between the gasification grates 52-56 and the ash
discharge grates 58-60. The gasification section enables
fuel pre-drying and gasification. The ash discharge
section provides additional time for combustion of
material that is not completely consumed on the
gasification grate sectlon. The completely combusted
material is automatically discharged from the ash
discharge grate 60 into an ash pit.
The unit is designed for continuous ash discharge
and can handle a wide variety of higher ash fuels and
inert materials ~e.g., lime and limestone)~ More
particularly, the ash falling off the end of the grate 60
is conveyed by a screw conveyor 72 (Fig. 1) to a conveyor
belt 74, from which it is deposited in an ash pot. The
rate at which fuel and air are fed into the burning area
controls the completeness of the combustion and,
therefore, the ash formation.
The air delivery is controlled by a fan 33 which
blows the combustion air into the burner 26 ~Fig. 2). The
fan 32 draws the air, smoke; etc. from the firebox 27 and
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on up the chimney. When the automatic controls of the
system call for more or less furnace draft, thi~ fan 32,
through an inlet damper control 35, responds to create a
negative back pressure in the firebox.
Fig. 7 schematically shows the air delivery
system and burning area of the furnace in cross section.
The outside walls 78 of the furnace surround an
arch-shaped air duct 80 which delivers a curtain of
incoming air around the periphery of the firebox. The
walls 78 are preferably steel and they rest on two I-beams
34, 34 which form skids for enabling an easy transportaion
of the furnace~ Inside the air duct arch 8D, there is a
lining of refractory material 86, which may be firebrick,
for example. The cold air in the duct 80 maintains a
curtain 88, 90 of relatively less hot air near the
firebricks 86 inside the burner 26. Therefore, the burner
tends to be much cooler alon~ its sidewallsl which
minimizes or avoids a formation of clinkers which may
adhere to the sidewalls. This minimization eliminates one
of the greatest single requirements for manual labor on
solid fuel furnaces o this type.
Air control is emphasi~ed in the burner design.
Damper controls are positioned within the air delivery
system to divide the incoming air into primaryl secondary
and tertiary air which is introduced throughout the burner
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unit. The primary air is introduced at three points 92,
94, 96 (Fig. 6) to provide a ~irectional adjustment of air
flow through the upper gasification, lower gasification
and ash discharge grate sections 52-60. Initially, the
air flow is adjusted by manual dampers. Thereafter, the
air flow may be modulated responsive to an automatic air
control. The quantity of introduced air can be modulated
over a wide range and this modulation is the primary
method for controlling energy output.
In greater detail, the flow of air is shown in
Fig. 6 by arrows rising through the grates 52-5a to
support combustion. The fire is initially started by a
pipe burner 98, which is a simple pipe that extends across
the full width of the burner. This pipe delivers a fuel,
such as propane gas through a series of perforations 98,
which ignites the fuel to start the solid fuel to
burning. As soon as the solid fuel ignitest and a
suitable bed of coals exists, the pipe burner is turned
Off. Thereafter~ the burning process is self-perpetuatingO
As the solid fuel burns, the air is adjusted so
that there is a burning bed 100 of coals topped by a layer
102 where the solid fuel is gasified or, in effect,
vaporized without complete burning at this point. A
gasification layer 104 of solid fuel also exists at or
near the junction between the free-falling fuel on grate
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52 and the reciprocally fed fuel on grates 54-60. The
gasification layer 102 is covereA by a layer 106 of ~reen
fuel. This gasification produces a draft of burnable gas
which is directed by secondary air 108 and tertiary air
110 into an area 112 within the firebox 279 where the
gasified fuel burns with intense heat. The tertiary air
causes additional turbulence and assures complete
combustion. By the time that the solid fuel reaches grate
60, it is completely reduced to an ash that falls off the
edge and into the ash delivery system. The gasificaticn
process is such that the fuel bed itself acts as the
particulate control device.
The rate of air flow is adjusted until this form
of burniny is establishedn Then, the process continues
substantially without change, as long as the solid fuel is
fed into the burner 26.
Figs. 8, 9 show how the system is modified to
burn high-sulphur coal with sharply reduced air
pollution. More specifically, the unit of Fig. 1 is
coupled to an additional bin 20a, conveyor 22a, hopper 40a
and rotary feeder 24a to provide for S0 control by an
introduction of a curtain of lime or limestone over the
fuel bed. These additional units (identified by reference
numerals with the suffix ~a"~ are essentially the same as
other previously described units bearing the same
reference numerals without the suffix ~a.
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Lime or limestone is fed from bin 20a through
conveyor 22a to hopper 40a and rotary feeder 24a. The
rotary feeder 24a deposits a curtain of limestone which
forms another layer 114 over the green fuel 106a (Fig. 9)
in the burner 26. Therefore, as the air (depicted by
arrows in Fig. 6) rises from the vents 92-96, the gasified
solid fuel material must pass through the limestone which
filters out the so2. The spent limestone in layer 114
falls off the end of grate 60 and is conveyed away in the
same manner that the ash falls off.
The advantages of the invention should now be
clear. The low-emission burners rely upon gasification of
solid fuel which, in turn, depends upon the flow
controllability of solid fuels coupled with a control over
the amount and location of combustion air flow. The solid
fuel flow control results from the angular positions and
movement of'the grates, wherein grate 52 breaks the
free-fall and dries the incoming fuel, while ~rates S4-60
advance and gasify the fuel at a controlled rate~ The
rate at which fuel is introduced through the rotary
feeder, the rate at which the grate movement feeds fuel,
and the rate at which ash is removed from grate 60 all
determine the depth of the bed of fuel. While combustion
air control is the primary method of varying energy
output, bed depth also controls the rate at which the heat
is produced.
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Those who are skilled in the art will readily
perceive how to modify the system. Therefore, the
appended claims are to be construed to cover all
equiYalent structures which fall within the true scope and
spirit of the invention.
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