Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates generally to incinerators and
more particularly concerns a fluidized bed type of combustor.
The theoretical advantages of pyrolysis "burning" for
waste disposal have long been recognized. A fluidized bed
incinerator, charged with sand kept in a fluidized state by the
flow of air or oxygen and a combustible gas, will completely
consume most burnable materials at a temperature of about 1700 F.,
thereby generating little noxious gas or other pollutants in the
discharged stack gas. Such incinerators are, however, expensive
since typically they use special heat resistant chambers that
must be sealed against inside pressure, require a constant flow
of gas, and embody mechanical, positive feed devices for the waste.
Moreover, such incinerators normally do not efficiently recover the
heat energy generated and require expensive maintenance to restore
the heating chamber and clean it of scrap metal and other
non-reduceable waste.
It is the primary aim of the invention to provide a
combustor that will consume materials by pyrolysis in a kind of
fluidized bed, but which is substantially less expensive to build
and operate than a conventional fluidized bed incinerator. In
more detail, the combustor of the invention requires no fluidizing
;gas flow, no special waste feed arrangement, no gas-tight sealing
and, moreover, efficiently recovers the energy of combustion in
the form of steam.
; Another object of the invention is to provide a combustor
of the above character that does not utilize refractory materials,
thereby reducing both the initial cost of the unit and the expenses
- of maintenance.
- A further object is to provide a combustor of the kind
characterized above whose design is quite flexible in the sense
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that the size of the unit can be readily proportioned to the
intended use; it being equally feasible to design such a
combustor to accept entire tree stumps as to design a small
unit for shipboard or small hospital useO
A resulting object is to provide a fluidized bed
combustor that can economically accomplish pollution-free
disposal of such things as lumbering waste products, shipboard
oil sludges, contaminated hospital paper waste, and similar
hard-to-dispose-of waste products.
Broadly speaking, therefore, the present invention
provides the method of creating a heated fluidized bed for
consuming burnable waste material by pyrolysis comprising
the steps of rotating a bed of sand in a partially filled
horizontal cylindrical drum, lifting and dropping sand from
the bed through the non-sand filled portion of the drum, and
heating the region through which the sand is dropped.
The above method may be carried out in a rotary
fluidized bed combustor comprising, in combination, a
cylindrical drum mounted for rotation about its axis with the
axis being substantially horizontal, the drum having annular
end plates defining inlet and outlet openings, a charge of sand
in the drum defining a bed extending between the openings, means
for slowly rotating the drum so as to tumble and thus fluidize
the sand, means for feeding waste material through the inlet
opening and into the fluidized sand bed, means for igniting the
- waste material and the gas generated by pyrolysis of the waste
material, and means for re~eiving ash and stack gas fro~ the
outlet opening.
Other objects, features, and advantages of the
invention will become apparent upon reading the following
detailed description and upon reference to the drawings, in which:
Figure 1 is a longitudinal vertical section, partially
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schematic, of a system using a combustor of the present
invention;
- Fig 2 is an end elevation of the combustor shown
in Fig.; and -
- Figs. 3, 4 and 5 are slightly enlarged sections
taken approximately along the lines 3, 4 and 5 in Fig. 1.
While the invention will be described in connection
with a preferred embodiment, it will be understood that I do
not intend to limit the invention to that embodiment. On the ~
contrary, I intend to cover all alternatives, modifications ~-
and equivalents as may be included within the spirit and scope
of the invention as defined by the appended claims.~ ;~
Turning to the drawings, there is shown a combustor
10 embodying the invention and including a drum 11, a waste
input chute 12, an ash and stack gas chamber 13, and steam ~ ;
and water connections 14 illustrated schematically. In
operation, burnable waste material is simply dropped through
the chute 12, becomes embedded in a fluidized bed of heated
sand 15 in the drum 11, is
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gradually forced from left to right as seen in Fig. 1 while being
consumed by pyrolysis, and the resulting ash is received in a
pit 16 and stack gas is discharged through a stack 17.
In accordance with one aspect of the invention, the
fluidized heated sand bed 15 is created by rotating a charge of
sand in the substantially horizontally disposed cylindrical
drum 11, and by lifting and dropping sand from the bed through the
open portion of the drum which is heated. The sand thus tends to
be carried up one side of the drum to an approximate surface angle
of 30 (see Figs. 3-5), whereupon the sand tumbles back "downhill"
producing a continuous rolling motion of the bed 15 not unlike the
fluidizing effect achieved by forcing air or other gas up through ;
a sand bed. A drum rotational speed on the order of 3 rpm is
satisfactory to produce the desired effect.
The sand is lifted and dropped by baffles 21 running
longitudinally on the inside of the drum 11 which, in effect,
sweep through the sand bed as the drum rotates, lift the sand
- from the bed, and then drop the sand through the open region of
the drum as the baffles rotate over the bed. The sand is initially
heated by the flame from a gas fired burner 22, but once pyrolysis
starts, gases from the waste material being consumed will be burned ~;
off just above the surface of the bed 15 so that the bed will be
~- self-heating with the burner 22 serving as a kind of pilot light.
In accordance with another aspect of the invention, the
drum is formed by a cylindrical water wall of adjacent pipes 23
: communicating with a source of water 24 and an outlet for steam
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shown here as a steam chest 25. The drum 11 has annular end
- plates 26 and 27 holding the ends of the sand bed 15 and defining
- inlet and outlet openings 28 and 29, respectively. The chute 12
and the burner 22 pass through the inlet opening 28 which is
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otherwise closed by a cover 31 to minimize heat loss although
there is no need for sealing the openings 28, 29.
The water wall is preferably formed by the pipes 23 being
accordion bent with adjacent runs being connected by joining
ribs 32, as in a conventional boiler water wall, although the
drum 11 wall is curved into a cylinder and held by a plurality
of circular I-beam bands 33 fitted on supporting rollers 34 much
like the water cooled kiln shown in U. S. patent No. 3,822,651,
issued July 9, 1974. However, an important distinction of the
water wall of the drum 11 over the kiln shown in the patent
referred to is that the drum 11 is imperforate.
In the illustrated drum, three accordion folded sections .;
of pipe are provided, each spanning 120 of the cylinder's
periphery, and each section ends in lengths of feeder pipes 35
leading to a manifold fitting 36 and a concentric, inner and outer
path, conduit 37 leading to a joint 38 allowing relative rotation
between the drum 11, feeder pipe 35 and conduit 37, and pipes 39
connecting the joint 38 to the water source 24 and the steam
chest 25. The joint 38 is a conventional subassembly, and one form of
double path conduit and rotating joint is disclosed in some detail
in patent No. 3,822,651 previously referred to.
For rotating the drum 11, a ring gear 41 fixed to the
periphery of the drum is driven by a pinion 42 powered through a
chain 43 from any suitable source of power. If desired, a separate
sand pit 44 can be opened by a positionable cover 45 to separate,
for reuse, from the ash discharge what little sand spills through
the outlet opening 29. Although the water wall will recover most
of the heat of combustion in the form of steam, while keeping the
drum well below destructive temperatures without the need for
refractories, it is also possible to use a simple waste heat boiler,
not shown, in the stack 17.
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As a feature of the invention, the baffle 21 has small,
arcuate cross sections defining elongated scoops that scoop out
the sand from the bottom of the bed, which sand will be the
coolest, for lifting and reheating. The small scoop sections,
being quickly filled with sand, do not lift appreciable amounts
of the waste materials being consumed so that the waste is left
embedded for pyrolysis consumption.
Another feature of the invention is the provision of
pipes 47 and a manifold 48 for introducing air up through the
bed 15 to help reduce especially difficult-to-burn waste. The
pipes 47 are perforated and fixed behind the baffles 21 with the
pipe ends opening through the inlet end plate 26. The manifold 48
is arcuate and approximates the expected cross section of the bed
when the combustor is in operation, so that air from a source 49
is distributed by the manifold 48 to those pipes then within the
bed 15. When such air is introduced, the effect is virtually
identical to a conventional fluidized bed incinerator although the
air flow, not being needed for the fluidizing action, may be
substantially less. Another blower 51 for introducing, still
additional air is fitted through the inlet opening cover 31.
The advantages of the combustor 10 can be quickly ~`
appreciated by those skilled in the art. Pyrolysis consumption
of waste material is achieved in a kind of fluidized bed with no
- need for the generation and introduction of a fluidizing gas flow
or the maintenance of a sealed burning chamber. The waste material
is simply dumped in with no need for a complicated feed arrangement,
and the resulting ash, being lighter than the sand bed, inherently
floats out of the outlet opening 29. The combustor itself is
-essentially a pipe-formed drum which can be economically made and
which does not require refractory materials that are particularly
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expensive to both assemble and maintain. The heat of combustion
is efficiently recovered in the form of steam and it has been
noted that in many possible applications for the combustor lO,
such as in the lumber industry, on shipboard, or in hospitals,
there is a direct need for steam by adjacent equipment. It can
also be appreciated that the combustor 10 can vary widely in size
and hence capacity, and thus it is quite feasible to design a small
compact unit for efficiently disposing of contaminated waste in a
small hospital, or to build a much larger unit intended to dispose
of forest waste in a large-scale lumbering operation.
The burner 22, auxiliary air blower 51, and pipes 47 and
manifold 48, give considerable flexibility to operation of the
combustor.
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