Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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APPARATUS AND METHOD FOR CONVERSION OF ANIMAL LITTER
BIOMASS INTO USEFUL ENERGY
FIELD OF THE INVENTION
The present invention relates to the conversion of animal litter biomass into
useful energy.
More specifically, the invention has particular, but not exclusive, reference
to
such conversion of poultry litter that essentially consists of a mixture of
wood
shavings, straw and fecal matter. The expression 'poultry' as used herein
means domestic foul of various kinds, inter alia chickens, turkeys, ducks and
geese. The invention may advantageously be used for the conversion of
biomass derived from the keeping of other farm animals, such as pigs and
bovines.
BACKGROUND OF THE INVENTION
Great emphasis is now placed by both government and the general public upon
the need to reduce the disposal of waste that might otherwise provide useful
feedstock for varied processes in industry and generally. Recycling of metals,
plastics and paper is now mandatory in many countries to ensure that the
optimum utilization of waste materials may be achieved by reuse in appropriate
processes. Equally, attention has been focused upon so called renewable
energy resources to provide 'green power' and among such resources biomass
constitutes a major element since agricultural waste is a continuous and
renewable source of fuel in the right process. Many and varied techniques have
been proposed and indeed adopted on a commercial basis for the destruction of
poultry litter biomass to produce energy by heat generation and/or
gasification
for use on site or for distribution to appropriate facilities for use.
Generally, techniques of this kind involve relatively complex plant, for
example
fluidized bed combustors using bubbling bed technology, or gasifiers, and
necessarily incur high capital and running costs.
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Accordingly, there is a need for a simpler and therefore cheaper approach to
the
conversion of animal litter biomass into useful energy.
SUMMARY OF THE INVENTION
It is therefore a general object of the present invention to provide a method
of
and apparatus for the conversion of animal litter biomass into useful energy.
A further object of the present invention is to provide such a method and
apparatus that employ relatively simple process steps and equipment of
comparatively simple construction with concomitant cost benefits.
According to a first aspect of the present invention there is provided a
method of
converting animal litter biomass into useful energy comprising the steps of
feeding said biomass in comminuted form into a primary combustion zone
comprising an upper region and a lower region, partially combusting the
biomass at the lower region thereof at an elevated temperature in the presence
of a combustion-sustaining medium thereby to provide heat into the upper
region thereof for pyrolysis to generate combustible gases, of subjecting the
lower partially combusted incandescent biomass to air flow to generate
combustion gases, of mixing the combustion gases and the combustible gases,
of igniting the resultant mixture of gases thereof to produce a hot gaseous
product, and of passing the hot gaseous product to a thermal recuperator for
expending and exploiting the heat energy thus produced.
The solid residue arising from combustion and pyrolisation is discharged and
may be employed further, for example for collection for use in horticultural
or
agricultural applications.
The mixing of the gaseous products before their egress from the process seeks
to secure the suppression of pollutants by heat destruction and enhanced rate
of combustion.
According to a second aspect of the present invention there is provided an
apparatus for the conversion of animal litter biomass into useful energy, the
apparatus comprising a primary combustion zone incorporating a chamber of
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frusto-conical form, a feed entry to the primary combustion zone, a feed
conduit
contiguous with said zone and connected to the feed entry at a relatively
upper
part of the zone, a combustible gas outlet for the primary pyrolysis
combustion
zone, a rotatable grate situated at the base of the primary combustion zone, a
means for rotating the grate, a combustion-sustaining fluid distributor
located at
said base, a secondary normal combustion zone on the grate circumscribing the
base of the primary pyrolysis combustion zone, a combustion exhaust gas outlet
from the secondary combustion zone, a gas mixing zone downstream of the
combustible gas outlet and the combustion exhaust gas outlet wherein in use
the respective combustion gases and the combustible gas mix, an ignition
station for the resultant mixture of gases, the gas mixing zone comprising at
least a partial tube bank for reheating and suppression of pollutant
emissions,
and a final gas discharge flue for the resultant gases.
Conveniently, the gas mixing zone includes a heat exchange zone for
expending and exploiting the heat energy of the hot mixture thus produced.
The apparatus may be of generally cylindrical form.
Conveniently, there is also provided a means of comminuting the feedstock
which may include a hopper with a rotating armature provided with blades
suitable for effecting the break up of the animal litter biomass introduced
thereto. A rotatable disc may be disposed beneath the hopper outlet for
feeding
the comminuted feedstock into the feed conduit.
The combustion-sustaining medium distributor may be of foraminous conical
form enclosing a plenum chamber therebeneath to which a suitable conduit for
the medium, e.g. air, is connected.
The gas mixing zone may be provided with a full tube bank of coiled tubes or
may in the alternative have a demi-bank of coiled tubes extending
substantially
half way around the zone.
Other objects and advantages of the present invention will become apparent
from a careful reading of the detailed description provided herein, with
appropriate reference to the accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
Further aspects and advantages of the present invention will become better
understood with reference to the description in association with the following
Figures, in which similar references used in different Figures denote similar
components, wherein:
Figure 1 is a diagrammatic vertical cross section of an apparatus for the
conversion of animal litter biomass in accordance with the present invention;
Figure 2 is a horizontal section taken through one embodiment of the apparatus
shown in Figure 1;
Figure 3 is a horizontal section taken through an alternative embodiment of
the
apparatus shown in Figure 1; and
Figure 4 is a fragmented view on the line 4-4 in Figure 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to the annexed drawings the preferred embodiment of the
present invention will be herein described for indicative purpose and by no
means as of limitation.
Referring first to Figure 1 there is shown diagrammatically an apparatus 1 for
the conversion of animal litter biomass into useful energy, the apparatus
including a generally hollow cylindrical body 2 enclosing a primary combustion
zone 4 of frusto-conical form vertically oriented centrally within the body 2,
the
zone 4 having an upper region 5a and a lower region 5b. The zone 4 has
connected at its top part a feed tube 6 which registers with an opening 7 in
the
top 8 of the body 2.
A feed hopper 10 is disposed vertically above the opening 7 and has a
rotatable
drive spindle 9 carrying a plurality of comminuting paddles 11; the hopper 10
has an outlet 13 feeding onto a rotating feed table 14 provided with a
discharge
station 15 selectively aligned with the opening 7 and the outlet 13. In use
feedstock, namely the biomass, is fed into the hopper 10 wherein it is
comminuted prior to delivery to the combustion zone 4.
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Alternatively, as it would be obvious to one skilled in the art, the
feedstock,
typically fed from a conveyor (not shown), can be directed into the hopper 10
free of any spindle 9 and paddles 11, or even directly fed into the feed tube
6
through opening 7, without deviating from the scope of the present invention.
5 At the base of the combustion zone 4 there is provided a circular rotatable
grate
20 the diameter of which is greater than the base dimension of the zone 4
which
is spaced therefrom to provide a path in use for the centrifugal conveyance of
incandescent biomass. The biomass located in the upper region of the
combustion zone 4 is heated and dried by the heat generated by the
incandescent biomass to form a pyrolysis zone. At the center of the grate 20
is
a foraminous conical plenum chamber 22 for the introduction of air into the
combustion zone 4, an air inlet pipe 24 being connected thereto and extending
therefrom the exterior of the body 2. A drive shaft 26 for the grate 20
extends
through the pipe 24 for rotating the grate. A solid waste collection area 30
is
defined beneath the rotatable grate 20 and a discharge outlet 32 is provided
for
that area and leads to a removal station 34.
A secondary, normal combustion zone 40 is defined externally of the primary
zone 4 and is provided with perforated air distributor tubes or sparge pipes
42 to
provide air for the combustion.
Both the zones 4 and 40 are contained within a central cylindrical core 50,
which is provided with suitable outlets 52 and 54 respectively for said zones,
a
gas discharge conduit 53 connecting the zone 4 to the outlet 52.
A gas mixing chamber 60 is defined between the core 50 and the wall of the
body 2 at the exit from the zones 4 and 40 and in this chamber the gases
arising from pyrolysis and the combustion zones are mixed. Thence the mixture
of gases flows through into a heat exchange zone 59 including a tube bank 61
formed in the annular space between the core 50 and the wall of the body 2. In
Figure 2 the post-combustion zone tube bank 61 extends substantially
throughout the whole of the annular space, the tubes 61' being held in tube
plates 63 and being disposed in spaced relation one to the other with baffles
62'
accommodated within the interstices between the tubes. The successive
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baffles 62' are alternately raised and lowered along the tubes 61' to force
the
hot gaseous product to vertically flow through the tubes 61', as illustrated
by the
alternating orientations of arrows around the baffles 62' in Figure 2. In
Figure 3
the annular space is only partially, e.g. half, filled with a demi-tube bank
61 with
tubes 61", the remainder of the space being provided with offset baffles 62".
Baffles 62' and 62", essentially vertically oriented, are provided as shown to
enhance in practice the turbulence of gases and to lengthen residence to time
thereby to optimize the various steps of mixing and suppression of noxious
emissions and heat transfer efficiency.
In use comminuted poultry litter biomass is fed from the hopper 10 into the
feed
tube 6 of the combustion zone 4 and descends onto the grate 20 and forms a
bed of biomass typically extending up into the tube as shown in order to
prevent
heat losses there through. The temperature of the zone 4 is initially raised
to a
level appropriate for the ignition of the biomass and air is provided through
the
plenum 22. The biomass is burned only at the bottom (lower region 5b) of the
zone (smothered combustion) and that combustion energy allows the pyrolysis
phenomenon in the biomass column thereabove (upper region 5a), and the hot
gases of pyrolysis exit therefrom through the conduit 53 and the outlet 52
into
the mixing chamber 60.
An incandescent layer or cake of biomass gradually radiates on the rotating
grate 20 to pass from the pyrolysis zone 4 into the normal combustion zone 40
supplied with air through sparge pipes 42, the gas being generated passing
through the outlet 54 into the mixing chamber 60 after providing more energy
to
the biomass in zone 4 for pyrolysis.
In the embodiment of Figure 2 the gas from zone 4 and the combustion gases
emanating from zone 40 are mixed in the chamber 60 and pass through the
tubes 61' of the substantially full tube bank 61. The gases after their
passage
through the tubes 61' enter into a further, ignition chamber 68, separated
from
the mixing chamber 60 by separation wall 67, provided with a pilot flame
igniter
69 and any remaining unburnt gas is combusted and all the gases from the
chamber 68 pass over the tubes 61', thereby effectively reheating the mixture
of
gases from pyrolysis zone 4 and those from combustion zone 40 passing
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through the tubes, thus improving efficiency and contributing to the
destruction
of any harmful elements that might give rise to atmospheric pollution. All
gaseous products of combustion exhaust through a common outlet 70 of the
body 2 whence they pass to a thermal recuperator (not shown) for appropriate
usage.
In the embodiment of Figure 3 the tube bank 61 is not so long but the gases
from zones 4 and 40 are again mixed in chamber 60 and pass through the
tubes 61 ". The mixture of gases then flow through a zone in which turbulence
is promoted by the baffles 62" and eventually enter an ignition chamber 68
wherein any remaining unburnt gas is ignited by the igniter 69. The resulting
gas exhausts from the chamber 68 into a space 71 (Figure 4) defined over the
offset baffles 62" before flowing around the tubes 61" of the tube bank 61 to
provide reheat for the gases passing therethrough for the same purpose as
described above in relation to Figure 2, the final mixture of gases then
exhausting through outlet 70 for passage to a thermal recuperator.
The baffles are provided to improve turbulence and simultaneously increase
residence time of the gases to enhance heat transfer and the consumption of
potentially noxious elements in the gases.
The present invention thus provides a relatively simple and yet effective
means
of disposing of a waste biomass product in a useful 'green' energy way, thus
reducing the time and cost of conventional disposal.
Although the present invention has been described with a certain degree of
particularity, it is to be understood that the disclosure has been made by way
of
example only and that the present invention is not limited to the features of
the
embodiments described and illustrated herein, but includes all variations and
modifications within the scope and spirit of the invention as hereinafter
claimed.
