[0001] This invention relates to solid fuel burners and has particular, though not exclusive
application to burners utilising low grade fuels such as unprocessed peat and pelleted
municipal waste.
[0002] There are a number of burners currently available that are capable of burning certain
low grade fuels, such burners commonly being of the flat bed type and incorporating
moving grates to attempt to avoid the build-up of clinker which inevitably forms an
combustion of such fuels. Thus it will be appreciated that such burners are of relatively
complex and therefore expensive construction.
[0003] These conventional burners, including chain grate stokers and fluidised bed combustors
are, however, still unable to burn satisfactorily sub-quality fuels such as unprocessed
peat, coal wash slurry, pelleted municipal waste material and the like because of
the problems of clinker.
[0004] In view of the ready availablity of such sub-quality fuels, it would be desirable
to be able to provide a burner capable of burning these fuels efficiently and without
any significant build-up of clinker or the like.
[0005] According to the present invention there is provided a solid fuel burner comprising
a substantially tubular housing mounted for rotation about a substantially horizontal
axis, a source of fuel adapted to supply fuel at a controlled rate to a region substantially
centrally of, at or adjacent one end of, the tubular housing, a source of air under
pressure adapted to be fed to the interior of the tubular housing, and means within
the housing which, on rotation of the housing, feed the fuel and products of combustion
thereof from the one end of the housing towards the other end thereof.
[0006] With such an arrangement, the fuel supplied to the burner housing is first of all
ignited and combustion air is then fed to the housing to maintain the flame. The rotation
of the housing together with the action of the feed means within the housing ensure
continuous movement and agitation of the fuel and combustion products thereof within
the burner in such a manner as to prevent any clogging of the bed whilst at the same
time providing an efficient output therefrom.
[0007] Such a burner is particularly suited to the burning of unprocessed peat which has
a high moisture content of up to 60%, sawdust, coal slurry from colliery washing plants
and pelleted municipal waste material even with high plastic content, none of which
can be burned satisfactorily in convention burners.
[0008] The housing may comprise a continuous tubular member the defining walls of which
are provided with a plurality of apertures therethrough, the burner further comprising
an outer sleeve surrounding said tubular member to define an annular chamber between
the sleeve and the tubular member, air under pressure being supplied to said chamber
and entering the interior of the housing, substantially radially thereof, through
the apertures in the tubular member.
[0009] Conveniently air under pressure is also supplied through the one end of the housing
in a direction substantially axially thereof.
[0010] In an alternative embodiment of the invention, the housing comprises a plurality
of axially aligned, tubular portions of increasing diameters, adjacent ends of which
are located one within the other to provide a substantially continuous housing with
annular gaps between said adjacent ends through which air under pressure can be supplied
to the interior of the housing.
[0011] In a still further embodiment, the housing may comprise a spirally wound strip of
material with the edge regions of adjacent windings overlapping one another but being
slightly spaced from one another in a substantially radial direction, air under pressure
being supplied to the interior of the housing through said radial spacings between
adjacent windings.
[0012] The feed means within the tubular housing may comprise one or more helical bars secured
to the inner wall of the housing.
[0013] Alternatively said feed means may comprise a plurality of fins secured to the inner
wall of the housing and spaced substantially helically therearound.
[0014] Preferably the source of fuel comprises a hopper supplying fuel to a rotary screw
feeder, the output end of said feeder being positioned at said region substantially
centrally of, at or adjacent the one end of, the tubular housing.
[0015] Conveniently the rotary screw feeder and the tubular housing are movable relative
to one another in a direction substantially axially of the housing whereby the position
of the output end of the feeder can be varied axially within the housing.
[0016] The solid fuel burner comprises drive means for rotating the tubular housing, which
drive means conveniently comprises a D.C. motor which may rotate the housing continuously
or periodically through predetermined angular steps.
[0017] Preferably said drive means for the tubular housing also drives the rotary screw
feeder, control means being provided whereby the drive to the housing and the drive
to the feeder can be varied independently of one another.
[0018] By way of example only, an embodiment of the invention will now be described in greater
detail with reference to the accompanying drawing which is a side view, partly in
vertical section, of a burner according to the invention.
[0019] Referring to the drawing, the illustrated burner comprises a fuel hopper 2 provided
in its lower regions with a rotary screw feeder 4 having an output end 6 projecting
from the hopper 2. The feeder 4 is driven by a D.C. motor 8 as will be described in
more detail below whereby fuel in the hopper 2 can be fed along the feeder 4 to the
output end 6 thereof in a controlled manner.
[0020] The burner further comprises a burner assembly indicated generally at 10 and including
a tubular housing 12 or combustion chamber mounted for rotation about a horizontal
axis. More particularly, the one end of the housing 12 comprises a gearwheel 14 inwardly
of which is provided a plate 16 whereby a chamber 18 is defined between said plate
16 and the gearwheel 14. A plurality of axial apertures 20 are formed through the
plate 16 to interconnect the chamber 18 with the interior of the housing 12.
[0021] A tubular sleeve 22 surrounds the housing 12 to define an annular chamber 24 between
said sleeve 22 and the housing 12, the housing 12 being rotatable in substantially
sealing relationship within the fixed sleeve 22. A plurality of radial apertures 26
are formed in the wall of the housing 12 to interconnect the chamber 24 with the interior
of the housing 12 and with the chamber 18.
[0022] A fan 28 is connected to an inlet 30 in the sleeve 22 feeding into the chamber 24
whereby air under pressure can be supplied by said fan 28 through said inlet 30 into
the chamber 24. Said air under pressure then flows through the radial apertures 26
into the interior of the housing 12 as well as into the chamber 18 and through the
axial apertures 20 into the interior of the housing 12 as will be described in more
detail below.
[0023] A pair of helical bars 32 are welded to the interior wall of the housing 12 in the
form of an Archimedean screw again for reasons which will become apparent.
[0024] A horizontal drive shaft 34 extends through the hopper as shown, one end of said
shaft carrying a gearwheel 36. A chain 38 interconnects said gearwheel 36 with the
output from the variable speed D.C. motor 8 whereby said shaft 34 is driven by said
motor 8.
[0025] An adjustable, eccentric indexing pawl 40 is mounted on the other end of, to be rotatable
with, the shaft 34, said pawl 40 co-operating with the teeth of the gearwheel 14 integral
with the housing 12. Thus, on each rotation of the shaft 34, the pawl 40 engages with
the gearwheel 14 to effect a predetermined degree of rotation of the housing 12 dependent
upon the precise setting of the pawl 40.
[0026] A further gearwheel 42 is mounted on the one end of the shaft 34 adjacent said gearwheel
36, a chain 44 interconnecting said gearwheel 42 with a gearwheel 46 mounted on the
end of, to be rotatable with, the feeder 4 whereby said feeder 4 is driven by the
motor 8.
[0027] A plurality of removable flails or agitators 48 are axially spaced along the shaft
34 to be rotatable with the shaft 34 to agitate the fuel in the hopper 2 as and when
necessary.
[0028] The described burner is conveniently mounted on wheels such as 50 so that the overall
apparatus can be mounted on rails and be readily presented to an aperture in the door
52 of a furnace or boiler to which the burner is to be applied.
[0029] The burner assembly 10 and associated equipment is movable axially relative to the
hopper 2 and feeder 4 so that the axial position of the output end 6 of the feeder
within the housing 12 can be varied.
[0030] The described apparatus operates as follows. With fuel in the hopper 2 and with the
motor 8 actuated, the feeder 4 delivers fuel from its output end 6 into the interior
of the housing 12. This fuel is ignited by applying a flame thereto, and, once established,
the fan 28 is actuated to deliver air to the housing 12 to maintain the combustion
in the housing. The flame so formed extends from the open end of the housing 12, the
air under pressure entering said housing 12 axially thereof through the apertures
20 serving to direct the flame in blow-torch manner from said open end of the housing
12.
[0031] The rotation of the housing effected by the drive pawl 40, typically one to three
revolutions per hour, together with the provision of the feed bars 32, serve to agitate
the fuel and products of combustion thereof within the housing 12 thus exposing any
unburnt fuel to the incoming combustion air which totally envelopes the fuel and ensures
complete combustion thereof. Furthermore, the configuration of the bars 32 is such
that the fuel and products of combustion thereof are continuously moved forwards within
the housing 12 towards the open end thereof, an ash disposal unit (not shown) being
provided below said open end of the housing to collect and dispose of the ash so formed.
[0032] Clearly the type of fuel being used determines the settings of the variable features
of the apparatus. If the fuel is very moist, such as unprocessed peat which may have
up to 60% moisture content, the output end of the feeder 4 is positioned as shown
in the drawing - i.e. as far into the combustion chamber as possible - so that the
fuel can be preheated and dried prior to ignition.
[0033] The speed of rotation of the housing 12 is chosen dependent upon the combustion time
of the fuel being supplied thereto. Peat, for example, needs time to burn and the
housing is therefore rotated relatively slowly, typically one revolution per hour,
while coal, being more volatile, needs more agitation and the housing is therefore
rotated faster, typically three revolutions per hour.
[0034] Conversely, the rotational speed of the feeder 4 supplying the fuel to the housing
12, for a given output from the burner, is substantially inversely proportional to
the rate of combustion, being slower for volatile fuels such as coal and faster for
less-combustible fuels such as peat.
[0035] The agitators 48 are particularly useful when dust-type fuels such as sawdust and
the like are used, the agitators serving to prevent caking of the fuel and bridging
of the feeder 4 by the fuel.
[0036] A burner according to the invention, the diameter of the housing 12 of which may
typically be up to 30 cms, may provide a thermal output equivalent to between 50 and
300 kilowatts.
[0037] As mentioned above, burners according to the invention are particularly suited to
low grade fuels that, in conventional flat-bed burners, would produce substantial
clinker and clog the grates. Such fuels include unprocessed peat, rice husks, pelleted
municipal waste, lignite, coal washery slurry, straw, wood chips and sawdust.
[0038] The burner may include an automatic control system to provide optimum operating conditions
for the various fuels at the required heat loads, said control system governing the
rate of feed of fuel to the burner assembly, the rate of rotation of the housing 12
and the flow of combustion air from the fan 28.
[0039] It will be appreciated that the precise construction of the burner can vary from
that detailed above without departing from the scope of the basic invention.
[0040] For example, the housing 12 may be other than a continuous tubular member and may
comprise a plurality of axially aligned, tubular portions of increasing diameters
the adjacent ends of which are located one within the other to provide a substantially
continuous housing with annular gaps between the adjacent ends of the tubular portions
permitting air under pressure to be supplied therethrough to the interior of the housing.
[0041] Alternatively, the housing may comprise a spirally wound strip of material with the
edge regions of adjacent windings overlapping one another but being slightly spaced
from one another to enable air under pressure to be supplied to the interior of the
housing through the radial spacings between adjacent windings.
[0042] The feed means within the housing 12 may be other than helical bars and may comprise,
for example, a plurality of fins secured to the inner wall of the housing and spaced
substantially helically therearound. Alternatively, the helical bars or fins may be
replaced by a pair of continuous hollow helical tubes within the housing 12 or by
a plurality of hollow tubes spaced substantially helically around the inner wall of
the housing, these tubes being provided with a plurality of holes therein. Thus, on
supplying air under pressure to these tubes, said air is emitted through the holes
in the tubes, substantially radially of the housing 12 to improve combustion within
said housing, such an arrangement being particularly useful in larger burners with
deeper beds therein.
[0043] The sleeve 22 may be arranged to rotate with the housing 12, while, instead of being
index driven in step-like manner by the eccentric pawl 40, the housing 12 may be continuously
rotated by a variable speed motor such as 8.
[0044] Other modifications and variations from the described arrangement will be apparent
to those skilled in the art.
1. A solid fuel burner characterised by a substantially tubular housing (12) mounted
for rotation about a substantially horizontal axis, a source of fuel (2,4,6) adapted
to supply fuel at a controlled rate to a region substantially centrally of, at or
adjacent one end of, the tubular housing (12), a source of air under pressure (28)
adapted to be fed to the interior of the tubular housing (12), and means (32) within
the housing (12) which, on rotation of the housing (12), feed the fuel and products
of combustion thereof from the one end of the housing towards the other end thereof.
2. A burner as claimed in claim 1 in which the housing comprises a continuous tubular
member (12) the defining walls of which are provided with a plurality of apertures
(26) therethrough, the burner further comprising an outer sleeve (22) surrounding
said tubular member (12) to define an annular chamber (24) between the sleeve (22)
and the tubular member (12), air under pressure being supplied to said chamber (24)
and entering the interior of the housing (12), substantially radially thereof, through
the apertures (26) in the tubular member (12).
3. A burner as claimed in claim 2 in which air under pressure is also supplied through
the one end of the housing (12) in a direction substantially axially thereof.
4. A burner as claimed in claim 1 in which the housing comprises a plurality of axially
aligned, tubular portions of increasing diameters, adjacent ends of which are located
one within the other to provide a substantially continuous housing with annular gaps
between said adjacent ends through which air under pressure can be supplied to the
interior of the housing.
5. A burner as claimed in claim 1 in which the housing comprises a spirally wound
strip of material with the edge regions of adjacent windings overlapping one another
but being slightly spaced from one another in a substantially radial direction, air
under pressure being supplied to the interior of the housing through said radial spacings
between adjacent windings.
6. A burner as claimed in any one of claims 1 to 5 in which the feed means within
the tubular housing comprise one or more helical members (32) secured to the inner
wall of the housing.
7. A burner as claimed in claim 6 in which the or each helical member comprises a
hollow tube, said tube or tubes being provided with a plurality of holes therein whereby,
on supply of air under pressure to the interior of said tube or tubes, air is emitted
through said holes into the interior of the housing (12).
8. A burner as claimed in any one of claims 1 to 5 in which the feed means within
the tubular housing comprise a plurality of fins secured to the inner wall of the
housing (12) and spaced substantially helically therearound.
9. A burner as claimed in claim 8 in which each fin is hollow and is provided with
a plurality of holes therein whereby, on supply of air under pressure to the interior
of said fins, air is emitted through said holes into the interior of the housing (12).
10. A burner as claimed in any one of claims 1 to 9 in which the source of fuel comprises
a hopper (2) supplying fuel to a rotary screw feeder (4), the output end (6) of said
feeder (4) being positioned at said region substantially centrally of, at or adjacent
the one end of, the tubular housing (12).
11. A burner as claimed in claim 10 in which the rotary screw feeder (4) and the tubular
housing (12) are movable relative to one another in a direction substantially axially
of the housing (12) whereby the position of the output end (16) of the feeder (4)
can be varied axially within the housing (12).
12. A burner as claimed in any one of claims 1 to 11 and including drive means for
rotating the tubular housing (12) said drive means comprising a D.C. motor (8).
13. A burner as claimed in claim 12 in which the D.C. motor (8) is of variable speed
and drives the tubular housing (12) continuously.
14. A burner as claimed in claim 12 in which the D.C. motor (8) is of variable speed,
the drive means further comprising an indexing mechanism (34,40,14) driven continuously
by said motor (8) and co-operating with the tubular housing (12) to rotate the housing
(12) through predetermined angles in step-like manner.
15. A burner as claimed in any one of claims 12 to 14 together with claim 10 or claim
11 in which the drive means (8) for the tubular housing (12) also drives the rotary
screw feeder (4), control means being provided whereby the drive to the housing (12)
and the drive to the feeder (4) can be varied independently of one another.