Stoves and furnaces – Stoves – Heating
Reexamination Certificate
1999-10-01
2001-04-10
Lazarus, Ira S. (Department: 3743)
Stoves and furnaces
Stoves
Heating
C126S103000
Reexamination Certificate
active
06213116
ABSTRACT:
TECHNICAL FIELD
This invention relates to a wood and multi-fuel burning stove which will burn smoke.
BACKGROUND ART
Burning wood and related fuels efficiently in a domestic stove poses the dilemma of trying, on the one hand, to keep the burning temperature of the fire in the stove as high as possible to maximise the combustion efficiency, whilst upon the other hand, trying to get as much heat as possible from the stove into the room. A further challenge for a stove designer has been to provide for a practical and controllable method of burning combustible components carried in the smoke. Such a process is referred to as ‘burning its own smoke’ and such components in some fuels can constitute up to fifty percent of the calorific value energy value of fuel burnt in the stove.
In a traditional burning arrangement, with smoke rising from the embers (wood or coal), the temperature of the smoke is not raised sufficiently high to reach the combustion temperature of at least some of the combustible components without the help of a catalyst in the smoke flow path. Such a catalyst is easily damaged irrevocably by components in the smoke arising from burning an unsuitable fuel such as, for example, painted wood.
Stoves have been produced and designed using what is termed a ‘down draughter’ arrangement, whereby smoke is made to pass downwards, through glowing embers (such as of wood or coal) in a fire bed in the stove, before passing back to the flue. In this way the temperature of the glowing embers is sufficiently high for combustible components of the smoke to be burned. Few, if any, of these down draughter designs have proved both practicable and controllable and as a consequence such stoves have not been popular in the market place. This is despite their promise of much greater burning efficiency, with combustible elements in the smoke energy being converted to heat, and the concomitant benefit of the chimney not becoming coated with condensation products such as soot or tar.
U.S. Pat. No. 4,677,965 (Duerichen) shows a wood and coal burning heater which includes a primary combustion chamber for the controlled burning of a solid fuel positioned above a secondary combustion chamber for the subsequent combustion of combustible gases and pollutants which pass downwardly from the primary combustion chamber. An independent air supply is provided for each of the combustion chambers and air flowing to the primary combustion chamber is controlled to govern the rate of burn. A separate air supply is provided in the secondary combustion chamber and this air upon contact with the combustible gases and pollutants passing downwardly from the primary combustion chamber to cause further or secondary combustion to cleanse the smoke and gas of pollutants prior to discharge. Smoke and exhaust gases leaving the secondary combustion chamber pass first rearwardly and then upwardly along the back of the heater and then forwardly beneath the top surface of the heater prior to discharge to provide increased heat exchange contact between surfaces of the heater and exhaust smoke and gases.
The heater proposed and described by Duerichen is a complicated structure and does not make full use of air flows to promote effective operation of the stove when in use. In addition the flow passages described by Duerichen for the mixed exhaust gasses and what are referred to as ‘pollutants’ would tend to be readily blocked so serving to adversely affect efficient operation of the stove.
DISCLOSURE OF INVENTION
According to the present invention there is provided a wood or multi fuel stove comprising a primary combustion chamber, a flue duct extending from an upper part of the primary combustion chamber; a grate defining a lower boundary for the primary combustion chamber, the grate extending from the front towards the back of the stove interior and having a front edge juxtaposed with the front of the stove; a secondary combustion chamber located beneath the grate linked to the primary combustion chamber; an inlet path for supplying fresh air to the secondary combustion chamber, the inlet path by-passing the primary combustion chamber; and an outlet path for conveying combustion products from the secondary combustion chamber to the flue, the outlet channel by-passing the primary chamber; the stove being characterised in that:
the primary combustion chamber (X) is defined for the major part of its perimeter (grate
1
, its rear side and sides (
5
) and top (
12
)) by insulated members;
the grate (
1
) having:
i a rear edge off set from the insulated rear side (
5
) to leave a gap (G) extending over all, or part of, the width of the grate (
1
),
ii a front edge set higher than the rear edge (A) so that the grate (
1
) slopes down from the front towards the gap (G); and
a secondary combustion chamber C) located beneath the grate (
1
) and linked to the primary combustion chamber (X) solely by way of the gap (G).
According to a first preferred version of the present invention the stove is characterised in that the gap (G) is of a size sufficient to allow for ashes and some solids during combustion to fall from the primary combustion chamber(X) downwards through the gap (G), and smoke to pass through gap (G).
According to a second preferred version of the present invention or of the first preferred version thereof is characterised in that the grate (
1
) provides for extra air for burning to be channelled by the grate configuration to pass into the gap (G) so as to mix with the descending smoke, and so enhance the combustion of the smoke.
According to a third preferred version of the present invention or any preceding preferred version thereof the stove is characterised in that the stove (
10
) provides for smoke to pass downwards into the secondary combustion chamber (C) and subsequently back to the flue duct (
11
) by way of a route up either side of the stove (
10
) through a passage (
6
) defined between an inner fire box (
5
) and an outside casing (M) of the stove (
10
).
According to a fourth preferred version of the present invention or any preceding preferred version thereof the stove is characterised by means (
3
) provided to enable a primary flow of air to enter the stove-box and pass through a hollow top (
7
), to pass, or wash, down the inside of a glass panel (
4
) incorporated in an access door to the interior of the stove (
10
).
According to a fifth preferred version of the present invention or any preceding preferred versions thereof the stove is characterised by means providing for an additional flow of air to enter the stove (
10
) and follow a route (
1
A) under the grate (
1
), to pass into the gap (G).
According to a sixth preferred version of the present invention or of any preceding preferred version thereof the stove is characterised by a grate (G) of a hollow sandwich type construction.
According to a seventh preferred version of the present invention the stove is characterised in that the primary combustion chamber (X) is bounded by insulation material (
5
,
12
), apart from the front (
4
), where a glazed panel or access door (
4
) is located.
According to an eighth preferred version of the present invention or any preceding preferred version thereof the stove is characterised by a window (
2
) positioned so as to offer a view of burning smoke beneath the grate in the secondary combustion chamber (C). Typically the window (
2
) is double glazed. Additionally the window (
2
) can lie in an air flow path enabling an air wash to be directed past the window (
2
) on its inner side.
REFERENCES:
patent: 3952721 (1976-04-01), Patterson
patent: 4052608 (1977-10-01), Papenmeier
patent: 4102318 (1978-07-01), Runquist
patent: 4258692 (1981-03-01), Mackey
patent: 4572155 (1986-02-01), Engblom
patent: 4677965 (1987-07-01), Duerichen
patent: 4856491 (1989-08-01), Ferguson et al.
patent: 4883044 (1989-11-01), Levesque
patent: 880846 (1943-04-01), None
patent: 2 512 176 (1983-03-01), None
patent: 280 035 (1927-11-01), None
patent: 92 19916 (1992-11-01), None
Davis & Bujold P.L.L.C.
Lazarus Ira S.
Lee David
LandOfFree
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