High efficiency wood or biomass boiler

1. A boiler comprising an inner casing, an outer casing defining with said inner casing a space in which fluid can be received for heating thereof, a fluid inlet to the space, a fluid outlet from the space, a refractory structure in said inner casing and defining an upper combustion chamber and a lower combustion chamber in said inner casing, at least one vertical passage through said refractory structure for flowing combustion gases from said upper combustion chamber to said lower combustion chamber, at least one first forced air inlet to said upper combustion chamber for providing oxygen for burning of material in said upper combustion chamber, at least one forced air passage in said refractory structure and opening into said vertical passage thereby providing at least one second forced air inlet to said vertical passage for providing oxygen in said vertical passage for burning of the combustion gases and particulates passing therethrough from said upper combustion chamber, wherein said refractory structure extends entirely across and sealingly engages said inner casing in a manner to seal said upper combustion chamber from said lower combustion chamber so that said upper combustion chamber can be made substantially air tight whereby said upper combustion chamber can be pressurized by forced air thereto to effect expulsion of combustion gases and particulates from said upper combustion chamber through said at least one vertical passage for burning thereof, and refractory material disposed in said lower combustion chamber and having an upper surface positioned so that the burning combustion gases and particulates expelled through said at least one vertical passage impinge on said upper surface.

2. A boiler according to claim 1 further comprising an exhaust passage including at least one flow restricting tube.

3. A boiler according to claim 1 further comprising a pump connected for pumping the fluid from the fluid outlet directly to the fluid inlet.

4. A boiler according to claim 1 wherein both of said inner and outer casing are composed of the same material.

5. A boiler according to claim 1 wherein both of said inner and outer casing are composed of boiler plate having a thickness of at least about ¼ inch.

6. A boiler according to claim 1 further comprising doors hingedly attached to the boiler to open and close said upper and lower combustion chambers respectively, wherein at least one of said doors comprises a first plate having an outer surface which defines an exterior of the door and having an inner surface, a second plate spaced inwardly from said first plate and having inner and outer surfaces, a block of refractory material attached to said inner surface of said second plate, and insulation material disposed between said first and second plates.

7. A boiler according to claim 1 further comprising a damper which is closable to thereby seal said upper combustion chamber and which is openable to relieve pressure in said upper combustion chamber, a rod connected to said damper and having a handle for pushing and pulling said rod for opening and closing said damper, a door to said upper combustion chamber, a handle pivotally attached to said door for opening and closing said door, and members on said rod and said door handle respectively which are engageable when said door is closed to prevent movement of said door handle to open said door when said rod is in a position such that said damper is closed and which are disengagable to allow movement of said rod to a position opening said damper.

8. A boiler according to claim 1 further comprising at least one forced draft fan for supplying air to said first and second forced air inlets, at least one electric motor for operating said at least one forced draft fan, and means for operating said electric motor between a first speed for increasing the liquid temperature to a set point temperature and a second speed which is a reduced speed for maintaining combustion without the liquid temperature being increased above the set point temperature.

9. A boiler according to claim 1 wherein said refractory structure includes at least one layer of laid refractory material containing said at least one forced air passage, a block of refractory material set into said laid refractory material and containing said vertical passage, and a plurality of blocks of refractory material set into said laid refractory material and defining an upper refractory structure surface for receiving wood or biomass.

10. A boiler according to claim 1 wherein said refractory structure includes at least one layer of laid refractory material containing said at least one forced air passage, a first block of refractory material set into said laid refractory material and containing said vertical passage, and a plurality of second blocks of refractory material set into said laid refractory material and defining an upper refractory structure floor for receiving wood or biomass and which slopes upwardly from said first block toward said inner casing in a manner to prevent bridging of the wood or biomass.

11. A boiler according to claim 10 wherein said floor extends upwardly over a distance of less than about 2¼ inches.

12. A boiler according to claim 1 wherein said refractory material upper surface is inclined downwardly form rear to front of the boiler.

13. A method of heating a fluid comprising the steps of:

(a) providing a fuel in an upper combustion chamber which is within an inner casing, wherein the upper combustion chamber is sealingly separated from a lower combustion chamber within the inner casing by a refractory structure which has at least one vertical passage which allows flow of combustion gases and particulates from the upper combustion chamber to the lower combustion chamber;

(b) flowing a fluid to be heated through a space between the inner casing and an outer casing to thereby receive heat through the inner casing;

(c) initiating burning of the fuel;

(d) effecting sealing of the upper combustion chamber;

(e) providing a forced air flow to the upper combustion chamber thereby providing oxygen for burning the fuel and thereby expelling combustion gases and particulates from the sealed upper combustion chamber downwardly through the at least one vertical passage;

(f) providing a forced air flow through at least one passage in the refractory structure to the at least one vertical passage to effect burning of the combustion gases and particulates being expelled therethrough; and

(g) effecting impinging of the burning combustion gases and particulates on refractory material in the lower combustion chamber.