Wood pellet burner for existing boilers and furnaces

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).