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1. WO1985002455 - SOLID FUEL HEATING APPLIANCES

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[ EN ]

CLAIMS
-21- 1. 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
cαnbustion 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 secondar • air/primary exhaust mixture by
lowering the temperature of the mixture required to achieve
ignition;
means for admitting additional secondary air to said secondary cαnbustion 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 cαnbustion is sustained by the
availability of the igniter means to overcαne fluctuations in the temperature and composition of the primary exhaust which might otherwise foil ignition, and by using the heat of spent gases
ratlier than primary cαnbustion to maintain the temperature of the mixture entering the secondary combustion chamber at an elevated level.

2. The apparatus of claim 1, wherein said regenerative feedback means is formed by a cαnmon wall between said final exhaust region and said passageway acting as a heat exchanger.

3. The apparatus of claim 2 , wherein said common wall is made of thermally conductive material.

4. The apparatus of claim 2, wherein said common wall is stainless steel.

5. The apparatus of claim 2, wherein said common wall has a convoluted configuration to present a large surface area to promote heat transfer.

6. 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.

7. The apparatus of claim 6, further comprising means for preheating the secondary air admitted to said secondary cαnbustion region with the heat of said spent gases.

8. 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.

9. 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.

10. The apparatus of claim 1 wherein said igniter means is a catalytic igniter.

11. The apparatus of claim 1 wherein said secondary combustion chamber is insulated with refractory material.

12. The apparatus of claim 1 wherein said regenerative feedback means comprises secondary combustion air manifolds in heat exchange relation with said final exhaust.

13. The apparatus of claim 10 wherein said catalytic igniter has a thickness and perforate open area to reduce the pressure drop across the igniter for improved draft.

14. The apparatus of claim 1 wherein said stove includes side heat exchangers separated frαn the primary and secondary combustion chambers by convective air spaces for enhanced heat transfer into a room to bo heated.

15. The apparatus of claim 14 wherein said side heat exchangers include circuitous pathways to enhance heat exchange surface area.

16. The apparatus of claim 1 wherein the entrance to said secondary cαnbustion chamber includes a lower ramp portion for guiding combustion gases and for substantially preventing ash build-up in said secondary cαnbustion chamber.

17. The apparatus of claim 10 wherein said catalytic igniter includes a ceramic substrate coated with a catalyst.

18. The apparatus of claim 10 wherein said catalytic igniter includes a metal substrate coated with a catalyst.

19. 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.

20. The apparatus of claim 1 wherein said secondary cαnbustion chamber is lined with insulating material having an undulating surface to enhance mixing.

21. The apparatus of claim 1 wherein said secondary cαnbustion 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 cαnbustion heat in said second passageway is
transferred to the exhaust gases in the first passageway through the heat transfer barrier.

22. 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 an entrance followed by a combustion region where secondary cαnbustion 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 cαnbustion 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.

23. The apparatus of claim 22 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.

24. An external combustion system for attachment to a solid fuel heating apparatus comprising:
a firebox attached to said solid fuel heating apparatus in communication with flue gases frαn said heating apparatus, said firebox cαnprising refractory-lined walls including openings to allow secondary air to enter said firebox and separated by a heat exchange barrier creating first and second passageways; and a perforate catalytic igniter providing communication between said first and second passageways.

25. The apparatus of claim 24 wherein said heat exchange barrier is stainless steel.

26. The apparatus of claim 24 wherein said heat exchange barrier has a convoluted configuration to present a large surface area.

27. The apparatus of claim 24 wherein said
refractory-lined walls have an undulating configuration.

28. The apparatus of claim 24 wherein refractory-lined walls are made of low density formed refractory material.

29. The apparatus of claim 24 wherein said catalytic igniter is approximately one inch thick.

30. The apparatus of claim 24 wherein secondary air is caused to enter said refractory-lined combustion firebox chamber both before and after said catalytic igniter.

31. Woodburning heating apparatus comprising:
a primary cαnbustion chamber for burning a supply of wood contained therein;
a secondary cαnbustion chamber in gaseous communication with said primary combustion chamber;
said secondary cαnbustion chamber being lined with a refractory material and including a perforate catalytic igniter therein through which combustion gases from said primary
combustion chamber flow;
said secondary combustion chamber further including refractory baffles arranged to enhance mixing of said combustion gases and located to re-radiate heat onto said catalytic igniter; and
means for introducing secondary combustion air into said secondary combustion chamber;
whereby said combustion gases are more completely burned to improve heating efficiency and reduce emissions.

32. The apparatus of claim 31 including means for preheating said secondary combustion air before introduction into said secondary combustion chamber.

33. The apparatus of claim 32 wherein said means for preheating said secondary combustion air cαnprises secondary combustion air manifolds in heat exchange relation with said combustion gases after said gases have passed through said catalytic igniter and a subsequent refractory-lined chamber.

34. The apparatus of claim 31 wherein said catalytic igniter has a thickness and perforate open area to minimize the pressure drop across said igniter for improved draft.

35. The apparatus of claim 31 wherein said combustion gases pass through side heat exchangers separated from said primary and secondary combustion chambers by convective air spaces for enhanced heat transfer into a room to be heated.

36. The apparatus of claim 35 wherein said side heat exchangers include circuitous passageways to enhance heat exchange surface area.

37. The apparatus of claim 31 wherein the entrance to said secondary combustion chamber includes a lower ramp portion for guiding the combustion gases and for substantially preventing ash build-up in said secondary combustion chamber.

38. The apparatus of claim 31 wherein said catalytic igniter includes a ceramic substrate coated with a catalyst.

39. The apparatus of claim 31 wherein said catalytic igniter includes a metal substrate coated with a catalyst.

40. In a solid fuel heating appliance including a removable section, apparatus for sealing the removable section to prevent noxious gases frαn entering a om comprising:
an inner gasket between the stove and the removable portion;
an outer gasket between the stove and the removable section surrounding said inner gasket;
said inner and outer gaskets creating a space
therebetween; and
means for connecting said space for gaseous
communication with the exit flue of the stove.

41. The apparatus of claim 40, further cαnprising means for admitting roαn air to said space.

42. 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 cαnbustion 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.

43. The apparatus of claim 42 wherein said minimum level has no additional secondary air.

44. The apparatus of claim 42 wherein said range is from about 1300°F to about 1700°F.

45. 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.

46.. The apparatus of claim 45 wherein said minimum level has no additional secondary air.

47. The apparatus of claim 45 wherein said range is from about 1300°F to about 1700°F.