Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1 1'7~
The present invention relates to a~ improved solid
fuel burner.
Burners for burning solid fuel such as wood chips
or sawdust are well known. The known burners usually comprise
a cylindrical burning chamber having a longitudinal axis
generally horizontal. Fuel material to be burnt is introduced
tangentially into the chamber adjacent one end. Means are
provided at the one end for igniting the fuel material, and
the material burns as it moves in spiral fashion, toward outlet
means at the other end of the burner. Air can be introduced
at spaced locations along the length of the chamber to aid
combustion and also to aid in moving the material. U. S.
Patent 3,777,678 shows such a burner.
The known burners have disadvantages however.
Material in the formof unburnt fuel particles and ash,
accumulates in the bottom of the burner thus necessitating
frequent cleaning of the burner. In addition, wet and/or coarse
fuel material requires more igniting fuel and combustion
supporting gas to maintain the combustion process.
To overcome, or at least minimize the above disad-
vantages, the present invention proposes a burner having a
bottom portion in the burning chamber through which a
combustion-supporting gas can be introduced to both support
combustion more evenly and to fluidize the material being
transported through the chamber, thus allowing more complete
combustion, and removal of residue from the bottom of the
chamber.
It is well known to provide burners in which combustion
gas is introduced into the bottom of the burning chamber to
provide a fluidized bed. U.S. Patents 3,924,548 and 3,941,065
are representative of such burners. The present invention
however employs a novel structure in the burner for introducing
'~
- 1 - ~'
` 1178848
combustion gases from the bottom of the chamber. To provide
burners which last for a long time with a minimum of maintai-
nance, many burners are provided with burning chambers lined -
with heat resistant material such as firebricks, refractory
material or heat resistant grating. The present invention
proposes an improved solid fuel burner, having a combustion
chamber lined with a layer of heat resistant material, and
having means for introducing the combustion supporting gas
into the bottom of the chamber through the heat resistant layer.
The burner of the present invention has a bottom
section in the combustion chamber, which section is made of
pieces of heat resistant material. The heat resistant pieces
are mounted on support means in spaced-apart relation and a
combustion-supporting gas is blown through the spaces between
the heat resistant pieces into the burning chamber to support
combustion and to fluidize fuel material within the chamber.
More particularly, the burner according to the
invention comprises a burning chamber defined by a cylindrical
or pseudo-cylindrical wall whose longitudinal axis is generally
horizontal. One end of the wall is closed and~means are provi-
ded adjacent this one end for introducing the material to be
burnt tangentially into the chamber. Means at thë one end lgni-
te the material to have it burn as it moves spirally through the
chamber away from the one end. The interior of the burning
chamber is lined with a heat resistant material and means are
provided for supplying air under pressure into the chamber to
support the combustion.`A set of air inlets are provided in
the bottom portion of the chamber. mese air inlets are connected
to the air supplying means to introduce air into the chamber.
This introduction of pressurized air advantageously supports
combustion of the material to be burnt in the chamber and
simultaneously fluidizes the material being burnt.
-- 2
` 1 1'7~848
A preferred embodiment of the invention will now be .
described in detail having reference to the accompanying
_ . _ . . , _ . . .
. j4,j~
~788~8
drawings in which:
Fig. 1 is a partial longitudinal cross-section view
of a fuel burning system incroporating a burner according to
the invention;
Fig. 2 is a transverse cross-section view of the
burner; and
Fig. 3 is a detailed, longitudinal cross-section view
of the burner.
The fuel burner 1 as shown in Figs. 1 to 3, is
incorporated in a fuel burning system 3. Means are provided
for feeding solid fuel, such as sawdust, to the burner 1.
These means include a source of fuel, such as a hopper 5,
at least one duct 7 leading from the hopper 5 to burner 3,
and a blower or impeller 9 in the duct 7 for feeding the fuel
from the hopper 5 to the burner 1. The system 3 also includes
means for supplying a combustion supporting gas, such as air,
to the burner 1. These means comprise a blower 11 and a duct
13 leading from the blower 11 to the burner 1. The system 3
includes an exhaust duct 15 leading away from the burner 1.
The exhaust duct 15 carries away the combustion products from
the burner. The portion 17 o the exhaust duct 15 adjacent the
burner can be enlarged, as shown in Fig. 1, to accomodate a heat
exchanger 19.
The burner 1 of the present invention, as shown more
clearly in Figs. 2 and 3 has a cylindrical wall 21 defining
a cylindrical burning chamber 23. It should be noted that the
chamber 23 may also have a pseudo-cylindrical wall, i.e.
ellipsoidal or cylindrical with flat portions. The longitudinal
axis 25 of the cylindrical chamber 23 is generally horizontal.
One end of the wall 21 is closed with a circular end wall 27.
The innex surfaces of the walls 21 and 27 are covered with layers
! !_ 1178848
29 and 31 respectively of suitable heat resistant material.
An outer cylindrical wall 33 surrounds, and is concentric ~o,
the inner chamber wall 21. Ring-like end walls 35 and 37
.......
l-lt~8~ ~
join the ends of the concentric cylindrical walls 21 and 23
together to form a tubular distributing chamker 39 about the
burning chamber 23. The ring-like end wall 35 at the inlet
end of chamber 23 preferably lies in the same plane as the
circular end wall 27. The exhaust duct 15 can be attached to
the outer wall 33 at the open outlet end of the cha~ber 23,
adjacent the outlet end wall 37.
A set of air inlets are provided in the bottom portion
of the burning chamber 23. The inlets comprise a plurality of
narrow slots 41 arranged in columns and rows to provide a regular
array. The array of slots 41 extends over most of the length
of the burner chamber 23 and generally over the bottom third of
the chamber 23. The slots 41 are preferably formed by gaps left
between a regular array of fibrebricks 43 mounted in an opening
45 formed in both the firebrick layer 29 and the inner cylindrical
wall 21. The opening 45 has a pair of parallel straight sides
47 and 49, extending parallel to the longitudinal axis 25 of
chamber 23 and a pair of parallel, curved sides 51 and 53
extending transverse to the sides 47 and 49.
Means are provided for supporting the array the
fibrebricks 43 in the opening 45 with their inner surfaces 55
generally flush with the inner surface of the firebrick layer
29. The support means preferably comprises a grid 57, fixed
to the chamber wall 21, as will be described later.
A second set of air inlets are provided adjacent the
open outlet end of the chamber 23. This second set of air
inlets comprises a circle of radially-extending ports 61 of
large diameter joining the distributing chamber 39 to the
burning chamber 23. The ports 61 extend through the wall 21
and firebrick layer 29.
A third set of air inlets may be provided between the
inlet end and outlet end of the chamber 23, if desired. This
--4--
11'78~
third set of air inlets comprises a plurality of circles of
radially extending ports 62 of small diameter joining the
distributing chamber 39 to the burning chamber 23 at given
intervals at its length. The ports 62 also extend through the
wall 21 and firebrick layer 29.
The air duct 13 is connected to the distributing
chamber 39 via an air inlet 63 located close to the end wall
27. The fuel duct 7 is connected to the burning chamber 23
by at least one inlet tube 65 passing through the walls 21 and
33 and firebrick layer 29. The inlet tube 65 opens tangentially
into the chamber 23 adjacent the firebrick layer 31. If~
desired, a second inlet tube 67, spaced ninety degrees from the
first inlet tube 65, can'lead tangentially'into the chamber 23
adjacent the layer 31, from the fuel duct 7. A burning device
71 is mounted centrally in the end wall 27 of the chamber 23.
The nozzle 73 of the burning device 71 is located in a central
opening 75 in the firebrick layer 31, aligned with the longitu-
dinal axis 25 of the chamber 23, and pointing into the chamber.
In operation, the fuel to be burned is transported
from the hopper through the duct 7 and into the chamber 23
via the inlet 65, and inlet 67 if provided. The burning device
71 projects a flame axially into the chamber 23 to ignite
the fuel as it moves spirally through the chamber away from the,
; end wall 27. Simultaneously, air is introduced into the
distributing chamber 39 from the duct 13 via the inlet 63. The
air flows about the chamber 23, being pre-heated and simul-
taneously cooling the burner, and enters the chamber 23 through
slots 41 to both fluidize the fuel in the chamber to assist
its movement through the chamber, and to enhance combustion
of the fuel substantially throughout the length of the chamber.
Air also enters the chamber 23 through the circles of ports 62
to support combustion throughout the length of the chamber while
simultaneously cooling the wall of the burner. Last of all, air
enters the chamber 23 through the circle of ports 61 at the
end of the chamber to ensure complete combustion of the fuel
being burnt before it leaves the burner.
The grid 57 for supporting the array of firebricks
43 in the opening 45 comprises a number of curved, spaced-
apart main supports 79 and a plurality of pairs 81 of straight
secondary supports 83 extending transversely between the adjacent
main supports 79 to hold them together. The main supports 79
extends across the opening 45, transversely between the straight
sides 47 and 49 and project past the sides 47 and 49 to overlie
the chamber wall 21. Each main support 79 has a web 85 which
extends transverse to the longitudinal axis 25 of the chamber
23. The inner edge 87 of web 85 has a radius of curvature equal
to the radius of curvature of the outer surface of wall 21.
The main supports 79 are equally spaced-apart across the opening
45 with one support 79a adjacent one curved side 51 of opening
45 and with a second support 79b adjacent the other curved side
53 of opening 45. Each support 79 has a pair of flanges 89, 91
extending in opposite directions transverse to the web and
adjacent the outer edge 93 of the web. If desired, the flanges
89, 91 on the outer supports 79a, 79b respectively, which
flanges extend outwardly, could be omitted slnce they are not
needed. The main supports 79 are spaced apart a distance,
between the adjacent webs 85, sllghtly greater than the length
of a firebrick 43. The supports 79 are fastened to the chamber
wall 21, where they overlie it, by welding. In addition, the
outer supports 79a and 79b are fastened to the wall 21 along
the sides 51 and 53 of the opening 45 by welding. If necessary,
the inner supports 79c and 79d can be supported at spaced
locations along their length within opening 45 by pins 95 which
pins 95 extend radially between the supports 79c and 79d and
~1788~3
wall 33.
A plurality of pairs 81 of straight secondary supports
83 extend between adjacent maln supports 79. The secondary
supports 83 in each pair 81 are spaced apart a distallce slightly
greater than the width of a firebrick 33. The secondary supports
83 rest on the flanges of the main supports 79 and are fastened
in place by welding. Each pair 81 of supports 83 is spaced from
the adjacent pair 81 by a distance sufficient to leave a narrow
gap or slot 41 between the top surface 55 of adjacent firebricks
43 when the bricks are mounted on adjacent main supports 79
between adjacent pairs 81 of secondary supports 83.
The grid 57 supports the firebricks 43 in such a manner
that an array of slots 41 are provided between the bricks to
direct air from the distributing chamber to the burning chamber
23 in quantities sufficient to support combustion, and to fluidize
the fuel passing over the firebricks. The grid 57 also supports
the firebricks 43 in such a manner that they can be easily
replaced.
If desired, use can be made of at least one firebrick
44 higher than the others in the group of firebricks 43 supported
by the grid 57, as shown in Fig. 2. The higher firebrick 44 is
mounted onto the grid so as to extend inwardly into the burning
chamber 23. This arrangement advantageously permlts to disturb
at least partially the spiral movement of the material belng
burnt inside the burning chamber when this movement is too fast.
