US4646712A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Solid fuel heating appliances
Assignee: Vermont Castings Inc
•
Filing: 1984-11-21
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Granted: 1987-03-03
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Expires: 2004-11-21
Abstract
Abstract Solid fuel heating appliance having high thermal efficiency and low levels of polluting emissions. The heating appliance includes an insulated secondary combustion chamber where a mixture of exhaust gases from the primary combustion chamber and secondary air is burned. A catalytic igniter is provided in the secondary combustion chamber to lower the ignition temperature of the unburned volatile gases from the primary combustion chamber. Regenerative feedback structure is provided in heat exchange relationship with the exhaust from the secondary combustion chamber to preheat the mixture entering the secondary combustion chamber, catalytic igniter, and the regenerative heat transfer assure substantially continuous combustion within the secondary combustion chamber even when conditions in the primary combustion chamber change. In a retrofit embodiment for existing stoves, a sheet metal partition in the secondary combustion chamber allows heat transfer from spent gases to the entering mixture of exhaust and secondary air. In a unitary stove embodiment, secondary air is heated by the spent gases which proceed to remote heat exchangers separated from the primary firebox by ventilated air spaces. To prevent room emissions, the stove door is sealed by a vented double gasket system.
Inventors
- 👤 Robert W. Ferguson
- 👤 Derik K. Andors
- 👤 William W. Crossman, Jr.
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-05 19:39
CPC Classifications
F; F24; F24B; F24B1/00; F24B1/006; B; B67; B67B; B67B7/00; F23; F23B; F23B5/00; F23B5/04; F24B1/02; F24B1/026
Claims Analysis
Total Claims: 31
Claim 1
Independent Claim
217 words
A solid fuel burning heating stove with enhanced secondary combustion comprising: a primary combustion chamber for burning a load of fuel contained therein with a primary outlet for primary exhaust laden with unburned volatiles; an insulated secondary combustion chamber having an entrance followed by a combustion region where secondary combustion predominates and a final exhaust region of spent gases; a passageway leading from said primary outlet to said entrance; means for admitting secondary air to said passageway and for producing a mixture of secondary air and primary exhaust before said entrance; igniter means spanning said entrance for encouraging ignition of said secondary air/primary exhaust mixture by lowering the temperature of the mixture required to achieve ignition; means for admitting additional secondary air to said secondary combustion region after said igniter means; and regenerative feedback means in heat exchange relationship with said final exhaust for preheating said mixture before encountering said igniter means using the sensible heat of said spent gases; whereby secondary combustion is sustanied by the availability of the igniter means to overcome fluctuations in the temperature and composition of the primary exhaust which might otherwise foil ignition, and by using the heat of spent gases rather than primary combustion to maintain the temperature of the mixture entering the secondary combustion chamber at an elevated level.
Claim 2
Dependent Claim
217 words
A solid fuel burning heating stove with enhanced secondary combustion comprising: a primary combustion chamber for burning a load of fuel contained therein with a primary outlet for primary exhaust laden with unburned volatiles; an insulated secondary combustion chamber having an entrance followed by a combustion region where secondary combustion predominates and a final exhaust region of spent gases; a passageway leading from said primary outlet to said entrance; means for admitting secondary air to said passageway and for producing a mixture of secondary air and primary exhaust before said entrance; igniter means spanning said entrance for encouraging ignition of said secondary air/primary exhaust mixture by lowering the temperature of the mixture required to achieve ignition; means for admitting additional secondary air to said secondary combustion region after said igniter means; and regenerative feedback means in heat exchange relationship with said final exhaust for preheating said mixture before encountering said igniter means using the sensible heat of said spent gases; whereby secondary combustion is sustanied by the availability of the igniter means to overcome fluctuations in the temperature and composition of the primary exhaust which might otherwise foil ignition, and by using the heat of spent gases rather than primary combustion to maintain the temperature of the mixture entering the secondary combustion chamber at an elevated level.
Claim 3
Dependent Claim
29 words
The apparatus of claim 1, wherein said regenerative feedback means is formed by a common wall between said final exhaust region and said passageway acting as a heat exchanger.
Claim 4
Dependent Claim
15 words
The apparatus of claim 2, wherein said common wall is made of thermally conductive material.
Claim 5
Dependent Claim
12 words
The apparatus of claim 2, wherein said common wall is stainless steel.
Claim 6
Dependent Claim
23 words
The apparatus of claim 2, wherein said common wall has a convoluted configuration to present a large surface area to promote heat transfer.
Claim 7
Dependent Claim
33 words
The apparatus of claim 1, wherein said regenerative feedback means includes means for preheating the secondary air admitted to said passageway with the heat of said spent gases to thereby preheat said mixture.
Claim 8
Dependent Claim
26 words
The apparatus of claim 6, further comprising means for preheating the secondary air admitted to said secondary combustion region with the heat of said spent gases.
Claim 9
Dependent Claim
52 words
The apparatus of claim 1, further comprising heat exchanger means communicating with said secondary combustion chamber separated from said primary combustion chamber by a room air space for transferring the heat of the spent gases to the room air, whereby heat transfer to room air is accomplished without interfering with primary combustion.
Claim 10
Dependent Claim
54 words
The apparatus of claim 1 wherein said primary combustion chamber includes means for supporting a bed of coals, and means for forcing the primary exhaust through said bed of coals just before exiting to said passageway to enhance oxygen depletion of said primary exhaust to maintain a consistent level of oxygen in said mixture.
Claim 11
Dependent Claim
59 words
The apparatus of claim 9 wherein said means for admitting additional secondary air includes secondary air control means for controlling the amount of secondary air added to said secondary combustion region as a function of temperature inside said region such that the secondary air volume is adjusted from a minimum to a maximum level over a predetermined temperature range.
Claim 12
Dependent Claim
14 words
The apparatus of claim 10 wherein said minimum level has no additional secondary air.
Claim 13
Dependent Claim
17 words
The apparatus of claim 10 wherein said range is from about 1300° F. to about 1700° F.
Claim 14
Dependent Claim
13 words
The apparatus of claim 1 wherein said igniter means is a catalytic igniter.
Claim 15
Dependent Claim
27 words
The apparatus of claim 13 wherein said catalytic igniter has a thickness and perforate open area to reduce the pressure drop across the igniter for improved draft.
Claim 16
Dependent Claim
17 words
The apparatus of claim 13 wherein said catalytic igniter includes a ceramic substrate coated with a catalyst.
Claim 17
Dependent Claim
17 words
The apparatus of claim 13 wherein said catalytic igniter includes a metal substrate coated with a catalyst.
Claim 18
Dependent Claim
15 words
The apparatus of claim 1 wherein said secondary combustion chamber is insulated with refractory material.
Claim 19
Dependent Claim
23 words
The apparatus of claim 1 wherein said regenerative feedback means comprises secondary combustion air manifolds in heat exchange relation with said final exhaust.
Claim 20
Dependent Claim
34 words
The apparatus of claim 1 wherein said stove includes side heat exchangers separated from the primary and secondary combustion chambers by convective air spaces for enhanced heat transfer into a room to be heated.
Claim 21
Dependent Claim
19 words
The apparatus of claim 19 wherein said side heat exchangers include circuitous pathways to enhance heat exchange surface area.
Claim 22
Dependent Claim
33 words
The apparatus of claim 1 wherein the entrance to said secondary combustion chamber includes a lower ramp portion for guiding combustion gases and for substantially preventing ash build-up in said secondary combustion chamber.
Claim 23
Dependent Claim
29 words
The apparatus of claim 1 wherein said secondary combustion chamber includes refractory baffles arranged to enhance mixing of the combustion gases and to re-radiate heat onto the catalytic igniter.
Claim 24
Dependent Claim
22 words
The apparatus of claim 1 wherein said secondary combustion chamber is lined with insulating material having an undulating surface to enhance mixing.
Claim 25
Dependent Claim
55 words
The apparatus of claim 1 wherein said secondary combustion chamber includes a heat transferring barrier creating first and second passageways, the first passageway adapted for conveying primary exhaust through said catalytic igniter whereby secondary combustion heat in said second passageway is transferred to the exhaust gases in the first passageway through the heat transfer barrier.
Claim 26
Dependent Claim
59 words
The apparatus of claim 1 wherein said means for admitting additional secondary air includes secondary air control means for controlling the amount of secondary air added to said secondary combustion region as a function of temperature inside said region such that the secondary air volume is adjusted from a minimum to a maximum level over a predetermined temperature range.
Claim 27
Dependent Claim
14 words
The apparatus of claim 25 wherein said minimum level has no additional secondary air.
Claim 28
Dependent Claim
17 words
The apparatus of claim 25 wherein said range is from about 1300° F. to about 1700° F.
Claim 29
Dependent Claim
216 words
A solid fuel burning heating stove with enhanced secondary combustion, comprising: a primary combustion chamber for burning a load of fuel contained therein with a primary outlet for primary exhaust laden with unburned volatiles; a refractory lined secondary combustion chamber having as entrance followed by a combustion region where secondary combustion predominates in a final exhaust region of spent gases; a passageway leading from said primary outlet to said entrance; means for admitting secondary air to said passageway and for producing a mixture of secondary air and primary exhaust before said entrance; catalytic igniter means spanning said entrance for encouraging ignition of said secondary air/primary exhaust mixture by lowering the ignition temperature of the mixture; means for admitting additional secondary air to said secondary combustion region after said igniter means; and regenerative feedback means in heat exchange relationship with said final exhaust for preheating said mixture before encountering said catalytic igniter using the sensible heat of said spent gases, whereby secondary combustion is sustained by the availability of the igniter means to overcome fluctuations in the temperature and composition of the primary exhaust which might otherwise foil ignition, and by using the heat of spent gases rather than primary combustion to maintain the temperature of the mixture entering the secondary combustion chamber at an elevated level.
Claim 30
Dependent Claim
216 words
A solid fuel burning heating stove with enhanced secondary combustion, comprising: a primary combustion chamber for burning a load of fuel contained therein with a primary outlet for primary exhaust laden with unburned volatiles; a refractory lined secondary combustion chamber having as entrance followed by a combustion region where secondary combustion predominates in a final exhaust region of spent gases; a passageway leading from said primary outlet to said entrance; means for admitting secondary air to said passageway and for producing a mixture of secondary air and primary exhaust before said entrance; catalytic igniter means spanning said entrance for encouraging ignition of said secondary air/primary exhaust mixture by lowering the ignition temperature of the mixture; means for admitting additional secondary air to said secondary combustion region after said igniter means; and regenerative feedback means in heat exchange relationship with said final exhaust for preheating said mixture before encountering said catalytic igniter using the sensible heat of said spent gases, whereby secondary combustion is sustained by the availability of the igniter means to overcome fluctuations in the temperature and composition of the primary exhaust which might otherwise foil ignition, and by using the heat of spent gases rather than primary combustion to maintain the temperature of the mixture entering the secondary combustion chamber at an elevated level.
Claim 31
Dependent Claim
44 words
The apparatus of claim 28 wherein said primary outlet for primary exhaust is located to force the primary exhaust through a charcoal bed within the stove resulting from primary combustion to heat the primary exhaust and to substantially deplete the primary exhaust of oxygen.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1990-03-02 | 1990-09-01 | 1991-03-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1994-03-02 | 1994-09-01 | 1995-03-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1998-03-02 | 1998-09-01 | 1999-03-03 | $7700.00 | Window Closed / Lapsed |