Patent Application
20110297110
The present invention relates generally to the field of heating and, in particular, to a new and useful pellet burner for replacing the burner of an oil, propane, natural gas or other fueled boiler or furnace.
U.S. Pat. No. 4,312,278 discloses a chip wood furnace retrofitting system that seeks to replace the burner of an oil fired furnace and to solve the problem of ash buildup by establishing a combustion region above a grate through which the ash falls.
Also see U.S. Pat. No. 5,893,358 for a Pellet Fuel Burner for Heating and Drying Systems; U.S. Pat. No. 5,873,356 for a High Efficiency Wood Pellet Stove; and U.S. Pat. No. 5,183,028 for a Burning Apparatus with Pellet Fuel Burner.
A need remains, however, for an efficient replacement fuel burner that can use non-petroleum fuels such as wood pellets to fire an oil or other fueled furnace or boiler, and that can provide a flame that is as clean and hot as a gas or oil flame, with virtually no ash rising with the exhaust gases from the combustion chamber of the boiler or furnace.
The invention is a burner that burns wood pellets supplied from a source of wood pellets, the burner comprising an inner housing containing a lower burn pot which receives ignition heat and primary air through an ignition tube and lower perforation around the base of burn pot, to ignite pellets supplied to the burn pot from above, for producing a flame that is then steered horizontally through a conduit that includes a step down in diameter forming a venture space, the conduit containing a plurality of circumferentially spaced and axially spaced perforations that are each angled by a compound acute angle to the conduit axis and to the circumferential direction around the conduit, into the interior venture space, the compound angle being ideally 30 degrees, plus or minus 20 degrees, to the axial direction and 30 degrees, plus or minus 20 degrees, to the circumferential direction, and inclined toward an outlet of the venture space. The perforations provide secondary air into the venture space at a location that is spaced from the burn pot to swirl and feed the flame from the burn pot into a long, clean, hot, cylindrical, symmetrical and light ash containing flame that is well suited to file the boiler or furnace designed to be fueled by an oil or gas burner.
A directing cone in the base of the burn pot as well and circumferentially aimed primary air through the ignition tube and the perforations creates a cyclone of flame in the burn pot that rises and rotated from the burn pot, entraining all the ash and entered the horizontal venture space where the rotation is further enhanced by the swirling secondary air to fully oxygenate and shape the flame.
The inventors have found that the burner of the invention creates a closely controllable, clean flame which includes all the ash from the burning process that is advantageously and neatly deposited at the bottom of the boiler or furnace combustion chamber that has been retrofit to include the wood pellet burner of the invention, so that no ash leaves with the exhaust gases but all ash leaves the burner.
The pellets are supplied continuously from above the burner pot. When a thermostat calls for heat for example, because of a reduced temperature of water in the boiler, controls are activated to initiate an ignition temperature from the ignition tube as well as the feeding of some pellets to the burn pot. Primary and secondary air is also begun by activating a fan connected to an outer housing around the inner housing. Once a thermostat or other temperature sensor in the burner establishes that ignition has been achieved, the heating source in the ignition tube is switched off. The primary air flow and secondary air flow continue, however, and a regular continuous supply of pellet is initiated for maintaining the flame in the burn pot until the boiler or furnace thermostat determines that the temperature of water in the boiler or air in the furnace has reached the desired level. At that point a controlled shutdown of the burner is initiated until the next time heat is called for.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.
In the drawings:
The invention is a northern, green, environmentally friendly, climate-neutral, automatic, advanced, self-feeding and efficient wood pellet burner. A fuel pellet burning heating unit is a replacement for oil burners on existing boilers and furnaces or a stand alone system. The pellet burner is fed by means of an auger device from a main storage bin or hopper. Pellets enter through the top of the burner and fall by gravity, landing in a combustion chamber of the burner that is here called a burn pot.
The burn pot or combustion chamber is in an inner housing that is inside a pressurized outer housing that is continually fed air by means of a blower. Pellets are initially ignited by means of a known cartridge heater inside the ignition tube, that heats air to above the ignition temperature of the pellets. This ignition temperature is also call an auto-ignition temperature and is the temperature at which a material spontaneously ignites in the atmosphere it finds itself in, e.g. above about 500 degrees F. for wood pellets. One or more primary air perforations in the ignition tube receive pressurized air from the outer housing and this hot ignition air is directed into the burn pot in an off-center manner to swirl the air at the pellets in the burn pot. Once a flame is established, pellets are fed continuously into the burn pot or combustion chamber until the heating system is satisfied.
Combustion zone air is also introduced at the bottom of the burn pot through additional perforation in the side wall or walls of the burn pot. Combustion gases rise and enter a substantially horizontal flame conduit and are then drawn out of the inner housing by means of a venture shaped pipe or tube at the output end of the flame conduit. The venture tube has holes that are angled and through which secondary combustion air enters. These holes or secondary air perforations are angled in such a way that they not only inject secondary air into the combustion stream but also causes the gasses to be retained for cleaner burning and swirls the gas stream, increasing its velocity and its efficiency while also forming the flame into a symmetrical and substantially cylindrical shape.
Referring now to the drawings, in which like reference numerals are used to refer to the same or similar elements,
An inner housing 30 is 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, the 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 includes a plurality of, e.g. 3 to 12, preferably acutely angled 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 also defines a substantially horizontal flame conduit 50 connected to and communication with the upper end of the burn pot 32, the flame conduit 50 including a 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 inner and outer housings 10, 30 are preferably make of steel of sufficient thickness, e.g. ¼ to ½ inches, to withstand the heat and gases of the burning process. The inside diameter of the flame conduit 50 and the contiguous inlet end of the venture tube 52 is about 4 inches, plus or minus 1 inch, and the inside diameter of the outlet end of the venture tube 52 as will as a flame outlet 56 extending horizontally from the flame conduit, is about 1 inch less, or about 3 inches, plus or minus 1 inch. This dimensions, as well as the lengths and diameters of the other parts of the inner and outer housing can be changed and selected for the desired size and heat capacity of the pellet burner, however.
The venture tube 52 has a plurality, e.g. 20 to 40, circumferentially and axially spaced secondary air perforations 54 each, as shown in
An ignition tube 40 is connected to the inner housing side wall 36 at an off-center location, that is, in axial mis-alignment with the geometric center of the burn pot 32, to define 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 (i.e. clock wise but this time in an upward flow direction) as the swirling secondary combustion air in the venture flow in venture tube 52.
Ignitor means 44, for example a heating cartridge of known design, in the ignition passage 40 raises the temperature of air in the burn pot to the auto-ignition temperature of fuel pellets in the burn pot, e.g. 500 to 900 degrees F., and the arrangements is supplied with fuel by pellet supply means 60 connected to at least one of the inner and outer housings 10 and/or 30, for supplying fuel pellets, e.g. standard wood pellets, to the burn pot 32. With activation of the blower 20 and the ignition means 44, and upon reaching the auto-ignition temperature of fuel pellets in the burn pot 32, and further with first and second combustion air from the first and second combustion air perforation 38 and 42 establishing 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, a clean, hot, symmetrical flame 300 exits from the flame outlet 56 as shown in
As illustrated in
The arrangement also advantageously includes a central flow directing cone 70 on the base 34 and in the burn pot, for channeling and further swirling combustion air in the burn pot around the cone 70. Rather than a simple cone in the burn pot with its substantially circular horizontal cross section and its angled first combustion air perforations 38, the cone advantageously comprises 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 72.
The burn pot 32 preferably has a substantially cylindrical side wall 36 with a circular horizontal cross section, but as shown in
In
The pellet supply means 60 is of known design but must include a down pipe 62 connected either at an acute angle to the burn pot side wall 36 as shown in
While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
