Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to improvements in the controlled
incineration of agricultural waste products for utilization
of the ash residue and gaseous exhaust.
The disposal of waste or by-products from the processing of
agricultural food crops by incineration create many problems, particularly
the incineration of by-products such as rice and peanut hulls, wood
chips, cottonseed, etc., which are tough, woody and abrasive. Further,
such by-products are variable in density and have a high silica content.
Incineration of such by-products is not only expensive but consumes large
quantities of energy and creates air pollution problems.
The controlled combustion of the foregoing type of waste or
by-products has heretofore been attempted to deal with the problem of
abrasive fly ash and combustion efficiency. Because of feed density
variation, over~iring or underfiring o~ten occur~3 dur;ng comhustion
resulting in unstable heat generation and exhaust ~as quality that is not
satisfactory for heat recovery purposes. Prior burners are also
unable to control the degree of burn and therefore lack flexibility for
control of the ash content of the combustion residue as a marketable
product.
It is therefore an important object to provide an economical
combustion system for a variety of feeds without requiring pretreatment or
prior expensive processing and to accommodate a wide variation in feed bulk
density.
Another obJect is to provide a combustion system for such wa-3te
products whereby the ash content of the combustion residue may be controlled
and the fly ash content of its gaseous exhaust minimized.
In accordance with the present invention, a particulate feed is
fed into a combustion chamber and mixed with air at an infeed location
within the combustion chamber above a bed into which the particulate feed
drops. Combustion supporting air is supplied to the combustion chamber
from an underfire location below the bed. Underfire air enters the
combustion chamber through grate openings in a plurality of flow streams
at velocities insufficient to fluidize the particuLate material while
undergoing combustion. A sweep arm is rotated an adjustable distance
above the bed support to rake and agitate the particulate solids through
the fluidizing zone of the combustion chamber at a speed sufficient to
mechanically fluidize the solids during combustion. The raking action of
the sweep arm also induces radially outward movement of burning matter
under centrifugal force toward a non-fluidized collection zone above an
imperforate peripheral portion of the bed support from which the residue
agh i9 withdrawn.
Operation of the foregoing apparatus evolves a ~ascous e~chaust that
Elows past the ineecl location to an upper exhaust duct which delivers an
exhaust useful as a heating medium for boilers or the like. By control of the
feed rate of the particulate feed and adjustment of the vertical spacing of
the sweep arm above the bed support, the heat energy content of the e~haust
may be varied to meet different requirements. Further, the carbon content
of the ash residue may be varied by adjustment of underfire air inflow rates
between limits, in order to meet different market requirements for disposal
of the ash residue.
~ ccording to certain embodiments the flow streams of inflowing air
are separated by circular partitions within an inflow compartment underlying
the bed support. The inflow velocities of the flow streams are selected at
different values by use of separate air valves. The radially inner air inflow
zone aligned below the infeed location conducts its upward inflow stream at the
highest velocity.
Figure 1 is a simplified side elevational view of the apparatus
associated with the system of the present invention.
Figure 2 is an enlarged partial side sectional view of the apparatus
shown in Figure 1.
Figure 3 is a partial section view taken suhstantially through a
plane indicated by section line 3--3 in Figure 2.
Figure 4 is an enLarged partial section view taken substantially
through a plane indicated by section line 4--4 in ~igure 3.
Figure 5 is a partial transverse section view taken substantially
through a plane indicated by section line 5--5 in Figure 2.
Figure 6 is a block diagram schematically illustrating the system
of the present invention in association with its controls.
Referring now to the drawings in detail, Figure 1 illustrates
typical apparatus or practicing the system of the present invention,
generally referred to by reference numeral 10. ~ solid waste product is
stored in a stock hopper 12 having a lower unloading end portion 14 from
which particulate feed material enters an auger conveyor 16 at~ached to
the hopper. The conveyor 16 ia driven hy a varinble speed motor 18 to
deliver the Eeed to the upper inlet end of a gravity duct 20 oE generally
rectangular cross-section. The lower delivery end of the duct 20 is con-
nected to the housing of a flow meter 22 through which the feed passes into
a rotary type of metering device 24. The flow meter 22 may be of a commer-
cially available impact line type designed to measure the weight flow rate
of the feed and generate an electrical signal reflecting such measurement.
The signal output of the flow meter 22 is accordingly used ta control drive
of the variable speed motor 18 in order to maintain a substantially constant
weight flow feed rate for the infeed mechanism generally ref0rred to by
reference numeral 26. The rotary metering device 24 is well known in the
art and is utilized herein to prevent gas back-up.
The infeed mechanism 26 is driven by a variable speed motor 27 and
extends into combustion chamber device, generally referred to by reference
numeral 28. The products of combustion include a gaseous exhaust discharged
through an e~haust duct 30 from the upper end of the combustion chamber device,
and an ash residue withdrawn through a duct 32 from the lower end. Combustion
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supporting air i9 supplied through an overfire inflow duct 34 at the upper end
and an underEire inflow duct 36 at the lower end. The underfire inflow is
split between two inflow paths by inflow controlling air valves 37 and 39
through which air enters device 2~ at two different velocities. A feed raking
mechanism 38 is associated with the device 28 and extends from its lower end
for drive by a variable speed motor 40. The mechanism is vertically adjustable
through any suitable power operated adjusting device 41 from which a piston
adJustment rod 43 extends.
The system with which apparatus lO is associated, is diagrammed
in Figure 6 ~howing the flow of the particulate feed from storage 12 to the
combustion chamber device 28 with which some form of igniting device 42 is
associated. Also associated with combustion chamber device 28 are the rake
drive motor 40 afore-nentioned, and blowers 44 and 46 for respectively
~upplying air through the overfire and ~lnderf;re inflow ducts 34 and 36.
The flignal output of the flow meter 22 is fed to a visual display 48 and
as an input to a computer 50 to which adjustment input data is also fed
from 52. The computer produces outputs for control of the feed drives
18-26 in order to maintain an adjusted uniform weight flow rate for the
feed into the combustion chamber. IJnderfire inflow velocities from blower
46, the vertical spacing of the sweep arm and its rotational speed may also
be controlled by the co~lputer thrGugh valve control 53, motor 40 and rake
height adjustment control 55. The computer if utilized is thus programmed
to control the feed rate, inflow velocitie~ of the underfire air, and the
height and speed of the rake in accordance with the present invention.
Referring now to Figures 1 and 2, the infeed mechanism 26, includes
an auger type conveyor 54 driven by the motor 27 externally of the housing 56
of the combustion chamber device 28. The conveyor 54 is enclosed by air pas-
sages 58 and an outer water jacket 60 that extend into the housing 56 with the
conveyor 54 to cool the conveyor within the high temperature environment of
the combustion chamber 62 enclosed by housing 56 above a fixed, horizontal
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bed support generally referred to by reference numeral 64. An insulating
coating 61 i8 formed on the outer water cooling jacket 60 which extends
axially beyond the discharge end 66 of the auger conveyor 54 to form a
mixing space 68 at a central infeed location within the combustion chamber
substantially aligned with the vertical longitudinal axis of the housing 56.
The cooling air passages 58 open into the mixing space 68 so that air supplied
thereto externally of the housing by conduit 70 will discharge into space 68
for mixing with the particulate feed being di~charged from the delivery end
66 of the conveyor 54. The annular water space of jacket 60 is closed at its
inner end for circulation of water between inlet and outlet conduits 72 and 74.
Thus, air and water cooling of the conveyor 54 enables it to function continu-
ously in discharging a mixture of air and particulate solids at a relatively
hot central location in a thermal upflow of gaseous combustion products for
decelerated gravitational descent toward the bed support 64. The space fi8
not only provides for mixing of the particles with air before drop onto the
bed, but also prevents back firing into the auger conveyor 54 and clears the
discharge end thereof by the continued outflow of air from passages 58 when
feed from the conveyor 54 is interrupted.
The bed support 64 as shown in Figure 2 includes a steel gas dis-
20 tributor plate 76 spaced above the bottom wall 78 of the housing 56 and a
refractory plate 80 fixed to the steel plate. A major radially inner porous
portion of the plate 76 has closely spaced openings 82 to form a burner grate
above an underfire compartment divided into two radially spaced inflow zones
84a and 84b to which the underfire air is conducted through the air valves 37
and 39 as aforementioned. Accordingly, the blower pressurized underfire air
will be directed upwardly through the gra~e openings 82 under different
J velocities from two :Elow streams separated by a circular partition 85.
The particulates which form the bed as shown by dotted line 87 in
Figure 2, are mechanically fluidized, during combustion, by the rake mechanism
38 which includes a radial sweep arm 86 extending through the fluidized zone
~.2~i3161~3~
from a rotor portion 88 supported by a sealed bearing assembly 90 for
rotation about the vertical axis of the housing. The sweep arm will be
adjustably spaced above the plate 76. The rotor 88 has a gear 92 splined
thereto externally of the housing for driving connection to the motor 40.
A conduit 94 extends concentrically through the rotor 88 and sweep arm 86
to form an inner return flow passage 96 and an annular inflow passage 98,
respectively, connected through fixed manifolds 100 and 102 to coolant
outlet and inlet conduits 104 and 106. The end 108 of inner conduit 94
opens into a hollow paddle formation 110 connected to the radially outer
end of the sweep arm 86. The interior of the paddle is in communication
with the annular passage 98 so that water will circulate through the
flweep arm and paddle for cooling thereof.
The paddle llO i~ vertic~lly ~pflced above ~ radi~lly o~lter,
imperforate portion 112 of the be~ support 6~ over which a non-Eluidized
collection zone is established. It will be apparent that rotation of the
sweep arm through the rotor portion 88 of the mechanism 38 not only
fluidizes material during combustion, but also induces radially outward
movement thereof under centrifugal forces toward the non-fluidized
collection zone above the annular imperforate portion 112 of the bed
support. Thus, an ash residue is collected on portion 112 of the bed
support and is displaced by the paddle 110 each revolution to the upper
inlet end 114 of the residue discharge duct 32 as more clearly seen in
Figures 3 and 4. As shown in Figure 4, a water cooling jacket 116 is
mounted about the duct 32, which is connected at its upper inlet end to
the imperforate portion 112 of the bed support 64. The inlet end 114
is furthermore aligned with the paddle which cyclically passes thereabove
to effect withdrawal of the ash residue collected on the portion 112 of
the bed support.
As a result of the arrangemen~ of the apparatus hereinbefore
described, the 1y ash content and abrasiveness of the exhaust gas is minimal
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despite the use of a feed having a high silica content. The fly ash content
of the exhaust gas is furthermore reduced by a lower velocity of the underfire
inflow through the radially outer ~one 84b aligned below the radially outer
portion of the bed ~7 which is thinned out by the raking action. The central
portion of the bed 87, of maximum height because of its alignment with the
central infeed location, is aligned with the radially inner inflow zone 84a
through which inflow air enters at a higher velocity. Because of the foregoing
zoning of the underfire air, a fly ash reducing affect is realized which is
particularly critical in accommodating the combustion of lightweight feeds
such as cottonseed.
To accommodate heavier feeds such as rice hulls, the rake speed
of the sweep arm and the height of the sweep arm above the plate 76 must
be increased toward upper operational limits oE 7.5 RPM and 13-l/2 inches,
respectively, for efEicient combustion. For the lighter feeds, such as
cottonseed, sweep nrm hei~ht is lowered toward a lower limit oE 5-l/2
inches according to actual embodiments of the invention. Also, for lighter
feeds dimensional increases in width and height of the sweep arm paddle 110
was found to be beneficial in enhancing the recovery of the ash residue.
Variations in the aforementioned parameters, including sweep arm height and
speed, paddle size and underfire inflow zone velocities also affect the carbon
content of the ash residue in different ways which may thereby be tailored to
meet different combinations of product requirements and feed characteristics.
