Wood pellet burner for existing boilers and furnaces

Abstract

A pellet burner has inner and outer housings for defining a high pressure air plenum between. Angled perforations at strategic locations in the inner housing supplied pressurized primary and secondary combustion air so that, with pellets supplied to a burn pot of the inner housing and activation of a blower and an ignitor cartridge, the pellets auto-ignite and the air flow establishes a swirling flame in the burn pot that travels to a flame conduit of the inner housing where further swirling occurs in a venture section for shaping the flame into a clean, hot, symmetrical form.

1 . An arrangement for burning pellets to fire a combustion chamber of a boiler or furnace, the arrangement comprising:
 an outer housing ( 10 ) defining a first air space with an air inlet ( 14 ) for air and an outer housing outlet ( 16 );   an air blower ( 20 ) connected to the housing ( 10 ) for supplying air to the air inlet ( 14 ) and into the first air space for pressurizing the first space;   an inner housing ( 30 ) mounted in the outer housing ( 10 ) with the first air space surrounding at least some of the inner housing for defining an air plenum ( 12 ) between the inner and outer housings, said inner housing ( 30 ) defining a vertically extending burn pot ( 32 ) having an upper end and a lower base ( 34 ) with a side wall ( 36 ) extending around and vertically from the base ( 34 ), the side wall ( 36 ) including a plurality of first combustion air perforations ( 38 ) spaced around the side wall ( 36 ) and near the base ( 34 ) for supplying combustion air to the burn pot ( 32 ), the inner housing ( 30 ) defining a substantially horizontal flame conduit ( 50 ) connected to and communication with the upper end of the burn pot ( 32 ), the flame conduit ( 50 ) including an substantially horizontally extending frustoconical venture tube ( 52 ) that decreases in diameter in a direction away from the burn pot for creating an constricted venture flow alone the flame conduit ( 50 ), the venture tube ( 52 ) having a plurality of circumferentially and axially spaced secondary air perforations ( 54 ) each at a first acute angle (A) to an axis of the flame conduit and at a second acute angle (B) to a circumferential direction around the venture tube ( 52 ), the secondary air perforations communication with the plenum ( 12 ) for supplying swirling secondary combustion air to the venture flow that rotates in a selected direction, the flame conduit ( 50 ) having a flame outlet ( 56 ) extending out through the outer housing outlet ( 16 );   an ignition tube ( 40 ) connected to the inner housing side wall ( 36 ) at an off-center location and defining an off-center ignition passage communicating with the burn pot ( 32 ), the ignition tube containing at least one second combustion air perforation ( 42 ) communicating the plenum ( 12 ) with the ignition passage for supplying additional combustion air to the burn pot in an off-center direction into the burn pot for swirling second combustion air from the ignition tube ( 40 ) in the burn pot that rotates in the same selected direction as the swirling secondary combustion air in the venture flow;   ignitor means ( 44 ) in the ignition passage for raising the temperature of air in the burn pot to an auto-ignition temperature of fuel pellets in the burn pot; and   pellet supply means ( 60 ) connected to at least one of the inner and outer housings ( 10 ,  30 ) for supplying fuel pellets to the burn pot, so that, with activation of the blower ( 20 ) and the ignition means ( 44 ) and upon auto-ignition of fuel pellets in the burn pot, first and second combustion air from the first and second combustion air perforation ( 38 ,  42 ) establishes a swirling flame in the burn pot that travels to the flame conduit ( 50 ) and is further swirled by the swirling secondary combustion air from the secondary air perforations ( 54 ), the venture flow shaping the flame into a clean, hot, symmetrical flame that exits from the flame outlet ( 56 ).   
     
     
         2 . The arrangement according to  claim 1 , wherein the burn pot has a substantially circular horizontal cross section, the first combustion air perforations ( 38 ) being at an acute angle to a radial direction of the cross section for further enhancing the swirling of the combustion air in the burn pot, the arrangement including a flow directing cone ( 70 ) on the base ( 34 ) for channeling and further swirling combustion air in the burn pot around the cone ( 70 ). 
     
     
         3 . The arrangement according to  claim 1 , wherein the burn pot has a substantially circular horizontal cross section, the first combustion air perforations ( 38 ) being at an acute angle to a radial direction of the cross section for further enhancing the swirling of the combustion air in the burn pot, the arrangement including a flow directing cone assemble ( 70 ) on the base ( 34 ) for channeling and further swirling combustion air in the burn pot around the cone assembly ( 70 ), the cone assembly having a lower cylindrical platform ( 72 ) fixed to the base ( 34 ) and a conical top ( 74 ) tapering upwardly from the platform. 
     
     
         4 . The arrangement according to  claim 1 , wherein the burn pot has a substantially cylindrical side wall ( 36 ) with a circular horizontal cross section, the first combustion air perforations ( 38 ) being at an acute angle to a radial direction of the cross section for further enhancing the swirling of the combustion air in the burn pot, the arrangement including a flow directing cone ( 70 ) on the base ( 34 ) for channeling and further swirling combustion air in the burn pot around the cone ( 70 ). 
     
     
         5 . The arrangement according to  claim 1 , wherein the burn pot has a frustoconical side wall ( 36 ) with broader lower end at the base ( 34 ) and a circular horizontal cross section, the first combustion air perforations ( 38 ) being at an acute angle to a radial direction of the cross section for further enhancing the swirling of the combustion air in the burn pot, the arrangement including a flow directing cone ( 70 ) on the base ( 34 ) for channeling and further swirling combustion air in the burn pot around the cone ( 70 ). 
     
     
         6 . The arrangement according to  claim 1 , wherein the burn pot has a substantially rectangular side wall ( 36 ), the first combustion air perforations ( 38 ) being at an acute angle to sides of the rectangular side wall for further enhancing the swirling of the combustion air in the burn pot. 
     
     
         7 . The arrangement according to  claim 1 , including a burner adaptor ( 80 ) for firing a boiler or furnace ( 100 ) with pellets or at least one other fuel, the burner adaptor having two input walls ( 82 ,  84 ) that are at an obtuse angle to each other, each wall having a flame receiving opening ( 86 ), the flame outlet ( 56 ) of the flame conduit ( 50 ) being fixed to one of the input walls around the flame receiving opening of the one input wall, another burner ( 120 ) of at least one other fuel having a flame conduit fixed to the other input wall around the flame receiving opening of the other input wall, an adaptor enclosure ( 88 ) connecting the two input walls ( 82 ,  84 ) to a boiler or furnace ( 100 ), for communicating the flame receiving openings ( 86 ) the two input walls ( 82 ,  84 ) with a combustion chamber ( 110 ) of the boiler or furnace ( 100 ), and a closure plate ( 90 ) pivotally mounted to the adaptor enclosure ( 88 ) for pivoting between a first and second positions for alternatively closing the flame receiving opening ( 86 ) one input wall at a time while being spaced from the flame receiving opening ( 86 ) of the other input wall so that only flame of one of the flame receiving opening ( 86 ) will enter the combustion chamber ( 110 ). 
     
     
         8 . The arrangement according to  claim 1 , wherein the pellet supply means ( 60 ) includes a down pipe ( 62 ) connected at an acute angle to the burn pot side wall ( 36 ). 
     
     
         9 . The arrangement according to  claim 1 , wherein the pellet supply means ( 60 ) includes a substantially vertical down pipe ( 62 ) connected to a top of the flame conduit ( 50 ) at a location that is vertically aligned with the burn pot ( 32 ). 
     
     
         10 . The arrangement according to  claim 1 , wherein the pellet supply means ( 60 ) includes a substantially vertical down pipe ( 62 ) connected to the inner housing for supplying pellets to the burn pot ( 32 ), an auger pipe ( 64 ) containing an auger ( 66 ) for conveying pellets and connected to the down pipe ( 62 ), a hopper ( 68 ) connected to the auger pipe ( 64 ) for storing a supply of pellets and an auger motor ( 69 ) connected to the auger for rotating the auger to supply pellets from the hopper to the down pipe.