NON-CATALYTIC BIOMASS FUEL BURNER AND METHOD
The present invention relates to a non-catalytic biomass burner that may be used to burn a variety of fuel types at high efficiencies. The burner may include a cylindrical combustion chamber with an auxiliary igniter to heat the fuel in the combustion chamber until desirable combustion temperatures are reached. Fuel may be added to the chamber via a fuel feed assembly, and the rate of fuel addition to the chamber by the fuel feed assembly may be controlled by a computer. A fan located on the distal side of a flue pipe from the chamber may also be provided that pulls air into the chamber through one or more air inlets that are designed to encourage cyclonic air and exhaust flow in the chamber. Methods are further provided for controlling the manner of operation of the burner by a computer that may be instructed by a computer program code.
This application claims benefit of priority to U.S. Provisional Patent Application No. 61/563,921 filed on Nov. 28, 2011, the entire contents and disclosure of which are incorporated herein by reference.
BACKGROUND1. Field of the Invention
The present invention relates to biomass burners and more particularly to an apparatus and method for non-catalytic biomass burning.
2. Related Art
In the United States, the Environmental Protection Agency classifies bio-mass burners into two categories: catalytic burners and non-catalytic burners. The two different types of stoves (or burners) are regulated differently and have different operating requirements. A catalytic wood stove uses a catalytic combustion device to heat, ignite and burn off the smoke generated by the fire. In general, this results in maximum “use” of the fuel (e.g., wood), even and steady production of heat, and very minimal output of smoke and pollutants. The principles of catalytic wood stoves apply to other catalytic stoves that burn fuels other than wood. The catalyst itself is usually a ceramic honeycomb or waffle shaped plate coated with a metal (e.g., platinum, palladium). The catalyst is heated to very high temperatures so that when the smoke and ash pass over it, they are also heated and ignited, causing more of this byproduct to be burned off, which generates more heat and less creosote and vents less smoke to the outside. The belief is that high efficiency is achieved by minimizing waste and maximizing heat (energy) output.
Another type of stove is a non-catalytic wood stove or a non-catalytic stove that burns other types of biomass. While the catalytic stoves have a special combustor to increase their efficiency by burning off the smoke and ash and “cooking” the wood to produce heat, non-catalytics do not have this modification and are thus structurally and functionally different. Even though generally viewed as less efficient than catalytic stoves, a non-catalytic stove avoids many of the complaints typically expressed about catalytic stoves. Most complaints about catalytic stoves relate to maintaining or replacing the catalytic combustor plate. Catalytic stoves are generally thought to be harder to maintain as the catalytic plate requires some amount of care with cleaning and replacing. In most household-type stoves, users get about five seasons on average before needing to replace the catalytic plate. Improper use or burning can reduce this expected lifetime to two years. As for expense, such replacement plates can cost hundreds of dollars to purchase today. There is also a learning curve to operating a catalytic stove. The catalyst must be preheated to a certain temperature before the damper is closed, and learning just the right timing may take a season or two. No such requirement exists for non-catalytic stoves.
In either a catalytic stove or non-catalytic stove or burner, providing biomass fuel in a form and condition to be burned efficiently is presently difficult to accomplish. In particular, most stoves or burners require the fuel to have a particular size, uniformity, and predetermined moisture content. If all of those conditions are met, then the fuel can be used efficiently in the stove, such that the fuel is burned almost entirely with little or no smoke or pollutants exhausted into the atmosphere. One way to completely burn the fuel and produce little exhaust is to use large commercial burn chambers that can operate in a range of about 1 million BTU/hour or greater. However, this type of burner is not practical for residential use where stoves may operate in the 100,000 BTU/hr to 500,000/hr BTU range.
Thus, there remains a need in the art for an improved non-catalytic biomass stove or burner and method of its operation that can burn a wide range of fuel types and generate from about 100,000 to about 500,000 BTU/hr or higher while maintaining a high efficiency that may be near or equivalent to a catalytic stove.
SUMMARYAccording to a broad aspect of the present invention, a non-catalytic biomass burner is provided comprising: a combustion chamber for burning a fuel to produce an exhaust gas, wherein the combustion chamber has a cylindrical interior shape with the sides of the combustion chamber enclosed by a side wall; one or more air inlets spanning the side wall of the combustion chamber to allow air to enter the combustion chamber from the outside of the combustion chamber through the one or more air inlets; a flue pipe connected at its proximal end to the top of the combustion chamber, the flue pipe being configured to receive the exhaust gas from the combustion chamber through a flue opening, a heat exchanger for transferring heat from the exhaust gas to a circulating fluid of the heat exchanger, wherein the heat exchanger is positioned in the path of the exhaust gas between the flue pipe and an exit opening of the burner, and wherein the flue pipe delivers the exhaust gas to the heat exchanger; a fuel inlet tube having an upper portion and a lower portion, wherein a fuel opening in the side wall of the combustion chamber allows fuel to enter the combustion chamber from the lower portion of the fuel inlet tube; and an auxiliary igniter pointed toward the combustion chamber through an igniter opening in the side wall of the combustion chamber, the auxiliary igniter configured to direct heat into a lower portion the combustion chamber.
According to a second broad aspect of the present invention, a non-catalytic biomass burner is provided comprising: a combustion chamber for burning a fuel to produce a hot exhaust gas, wherein the combustion chamber has a cylindrical interior shape with the sides of the combustion chamber enclosed by a side wall; one or more air inlets spanning the side wall of the combustion chamber to allow air to enter the combustion chamber from the outside of the combustion chamber through the one or more air inlets; a plurality of vertical side panels positioned above a floor of the burner, the plurality of vertical side panels surrounding the side wall of the combustion chamber to define a plenum space between the side wall and the plurality of vertical side panels; one or more air intake holes near the bottom of the plenum space to allow air to enter the plenum space; a flue pipe connected at its proximal end to the top of the combustion chamber, the flue pipe being configured to receive the exhaust gas from the combustion chamber through a flue opening and deliver the exhaust gas to a heat exchanger, a fuel inlet tube having an upper portion and a lower portion, wherein a fuel opening in the side wall of the combustion chamber allows fuel to enter the combustion chamber from the lower portion of the fuel inlet tube; and an auxiliary igniter pointed toward the combustion chamber through an igniter opening in the side wall of the combustion chamber, the auxiliary igniter configured to direct heat into a lower portion the combustion chamber.
According to a third broad aspect of the present invention, a non-catalytic biomass burner is provided comprising: a combustion chamber for burning a fuel to produce an exhaust gas, wherein the sides of the combustion chamber are enclosed by a side wall; one or more air inlets spanning the side wall of the combustion chamber to allow air to enter the combustion chamber from the outside of the combustion chamber through the one or more air inlets; a flue pipe connected at its proximal end to the top of the combustion chamber, the flue pipe being configured to receive the exhaust gas from the combustion chamber through a flue opening, a fuel inlet tube having an upper portion and a lower portion, wherein a fuel opening in the side wall of the combustion chamber allows fuel to enter the combustion chamber from the lower portion of the fuel inlet tube; and an auxiliary igniter pointed toward the combustion chamber through an igniter opening in the side wall of the combustion chamber, the auxiliary igniter configured to direct heat into a lower portion the combustion chamber; a first temperature sensor positioned near the top of the combustion chamber to measure a combustion temperature of the exhaust gas exiting the combustion chamber; and a computer in communication with the first temperature sensor, the computer receiving the combustion temperature from the first temperature sensor.
According to a fourth broad aspect of the present invention, a method of operating a non-catalytic biomass burner is provided comprising: (a) turning on an auxiliary igniter, the igniter pointed toward a combustion chamber of the burner through an igniter opening in a side wall of the combustion chamber, the auxiliary igniter configured to direct heat into a lower portion the combustion chamber; (b) monitoring by a computer a combustion temperature of an exhaust gas exiting the combustion chamber, the combustion temperature of the exhaust gas measured by a first temperature sensor positioned near the top of the combustion chamber, the exhaust gas being produced by the burning of a fuel in the combustion chamber, and the computer receiving the combustion temperature from the first temperature sensor; (c) adding fuel to the combustion chamber at a first predetermined fuel rate when the combustion temperature reaches a first fuel temperature, wherein the rate of fuel addition to the combustion chamber is controlled by the computer controlling a fuel feed assembly that delivers fuel to a fuel inlet tube of the burner; (d) adding fuel to the combustion chamber at a second predetermined fuel rate by controlling the fuel feed assembly when the combustion temperature reaches a second fuel temperature, the second fuel temperature being higher than the first fuel temperature; and (e) turning off the auxiliary igniter when the combustion chamber temperature reaches an igniter off temperature.
According to a fifth broad aspect of the present invention, a method of operating a non-catalytic biomass burner is provided comprising: (a) measuring by a first temperature sensor a combustion temperature of an exhaust gas exiting a combustion chamber of the burner, the exhaust gas being produced by the burning of a fuel in the combustion chamber; (b) monitoring by a computer the combustion temperature of the exhaust gas exiting the combustion chamber, the computer receiving the combustion temperature from the first temperature sensor; (c) determining a fuel rate for adding fuel to the combustion chamber, wherein the fuel rate is determined by the computer based on the combustion temperature; and (d) adding fuel to the combustion chamber at the fuel rate determined in step (c), wherein the rate at which the fuel is added to the combustion chamber is controlled by the computer controlling a fuel feed assembly that delivers fuel to a fuel inlet tube of the burner.
According to a sixth broad aspect of the present invention, a computer program product for controlling the operation of a non-catalytic biomass burner is provided comprising: a computer readable storage medium having computer readable program code embodied therewith, the computer readable program code comprising: computer readable program code configured to receive from a first temperature sensor a combustion temperature of an exhaust gas exiting a combustion chamber of the burner, the exhaust gas being produced by the burning of a fuel in the combustion chamber; computer readable program code configured to monitor by a computer the combustion temperature of the exhaust gas exiting the combustion chamber; computer readable program code configured to determine by the computer based on the combustion temperature a fuel rate for adding fuel to the combustion chamber; and computer readable program code configured to control by the computer the addition of fuel to the combustion chamber a fuel feed assembly at the determined fuel rate, wherein the fuel rate is controlled by the computer controlling a fuel feed assembly that delivers fuel to a fuel inlet tube of the burner.
It is understood that other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein it is shown and described only various embodiments of the invention by way of illustration. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modification in various other respects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.
The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the invention and is not intended to represent the only embodiments of the invention or the only manner in which the invention may be practiced. The detailed description includes some specific details for the purpose of providing an understanding of the invention. However, it will be apparent to those skilled in the art that these details may be provided as merely illustrative examples and/or optional features of the present invention. Some well-known structures and components may also be depicted in block diagram form to avoid obscuring concepts of the present invention.
The present invention relates generally to a non-catalytic multi-fuel burner (or stove) having improved efficiencies and methods of operation. Heat energy is created by burning either traditional or non-traditional biofuels inside a combustion chamber of the burner. Traditional fuels may include corn, wood chips, pellets, and the like. However, the present invention may also efficiently burn non-traditional fuels, such as crop stover, fine dust particles, animal feed, and other types of bio-waste mass. As described more fully below, a computer may monitor and control operation of a bio-mass burner of the present invention to provide efficient burning of a wide range of fuels. In general, the computer may control and coordinate multiple functions of the burner unit. For example, the computer may control the fuel to air ratio within the combustion chamber, such as to minimize the time that unburned fuel remains in the chamber, by controlling a fan, a gas igniter and/or the feed rate of fuel into the combustion chamber. The computer may control the gas igniter (or some other secondary igniter) to start up the burning and to eliminate or minimize smoke during certain periods of operation when the temperature gets too low. To ensure that there is an efficient burn with minimal output of smoke, temperatures within the combustion chamber and/or the exhaust stack may be monitored for adjusting operational parameters of the burner.
As a result of its design and control, a non-catalytic burner of the present invention can operate at about 100,000 to 500,000 BTU/hr output or more while still achieving high efficiency heat production. Such a non-catalytic burner of the present invention may be effective at burning fuel having a diameter as small as from about 20 mm (e.g., dust) up to about 2 inches or more and having a moisture content of about 40% or below, with greater than about 80% efficiency. These results may be achieved, in part, by operating the combustion chamber at a target combustion temperature within a range from about 1100 to about 1800° F. (e.g., 1600° F.).
Several design features come together to achieve a non-catalytic burner of the present invention with high efficiencies. First, the combustion chamber may be generally cylindrical in shape with air inlet(s) near the bottom of the combustion chamber that span the side wall of the chamber to allow air from the outside to enter the chamber. These air inlet(s) may also be positioned and angled to encourage a cyclonic air flow within the chamber during burning. A fan, such as a controllable variable speed fan, may be positioned distally to pull air into the chamber, and an igniter may be positioned and oriented to point or project into the interior of the chamber as an auxiliary energy source. Fuel may be generally metered or fed into the chamber continuously or in small incremental amounts over time (instead of being supplied in bulk or larger batches). Importantly, the rate at which fuel is fed into the chamber may be controlled in response to monitoring feedback information regarding the temperature of the combustion chamber. As a result, all burning may occur in a single chamber instead of having two or more burns in separate compartments or chambers as with catalytic burners or gasifiers. In addition, both the igniter and the fan of the present invention may be controlled as well in response to chamber temperature feedback information. Thus, each of these features of the burner, including temperature-dependent control of the various inputs into the combustion chamber, may be combined to allow for regulation of fuel burning, such that the combustion temperature inside the chamber may be maintained within a desired range.
The construction and material used to enclose the combustion chamber of the burner of the present invention are unlike prior combustion chambers that are surrounded by water jackets. The water jackets of these combustion chambers transfer heat from the chamber and thus prevent hot temperatures from being attained quickly. In contrast to these prior chambers, the combustion chamber 102 of the present invention may be designed to avoid absorption of heat as much as possible so that the heat remains in the chamber.
A first temperature sensor 104 may be present near the top of the combustion chamber 102 (e.g., near the top of the combustion chamber 102 or in a proximal portion of a flue pipe or flue 116 near the combustion chamber 102) such that the temperature of the exhaust gas 114 exiting the combustion chamber 102 may be monitored and maintained within a desired range (e.g., at a temperature between about 1100° F. to about 1600° F.). Such a first temperature sensor 104 may be positioned in the flue anywhere between the combustion chamber 102 and the heat exchanger 118. There may also be a fuel stirrer 106 located within the chamber 102, typically at or near the bottom of the chamber 102. The stirrer 106 may be of a variety of different designs, shapes, etc., but is configured to agitate the burning fuel within the chamber 102 so that different surface area portions of the burning fuel are exposed to the combustion temperatures and the air within the chamber 102. For example, the stirrer 106 may be a rod with a length about equal to, or less than, an inside diameter or radius of the combustion chamber 102 that spins about a central point near the floor of the combustion chamber 102.
The exhaust 114 from the combustion chamber 102 exits into the flue 116, which directs the exhaust 114 to a heat exchanger 118. A second temperature sensor 112 may be provided that monitors the temperature of the exhaust gases near a fan 122. Such a second temperature sensor 112 may be located on the distal side of the heat exchanger 118 or on the distal side of the partition 212 of the heat exchanger 118. The second temperature sensor 112 may also be located on the proximal side of the fan 122. The term “proximal” in reference to the flue 116 and the path of exhaust flow 114 refers to a position closer to the combustion chamber 102 (and further away from a distal exit opening where the exhaust gases exit the burner into the surroundings) in the path of the exhaust, whereas term “distal” refers to a position further away from the combustion chamber 102 (and closer to such a distal exit opening) in the path of the exhaust. Much like the first temperature sensor measurements, the temperatures measured by the second temperature sensor 112 may also be used to control the operation of the burner including possibly controlling the delivery rate of fuel 108 and/or the flow of air 110 into the chamber 102.
The temperatures of the exhaust within the combustion chamber and at a more distal location near an exit opening of the burner unit may generally vary hand-in-hand, but the distal temperature reading may depend on the size of the flue and the exact location of the second temperature sensor. High exhaust temperature readings in the flue and/or heat exchanger detected by the second temperature sensor (e.g., distal exhaust temperatures higher than a desired 250° F. to 450° F. range) may indicate a dirty flue, clogged fan, or dirty heat exchanger surfaces that need to be cleaned. For example, as a safety precaution, if the second temperature sensor 112 detects a flue temperature of about 450° F. or greater (or at or above some other predetermined temperature), then feeding of the fuel 108 to the combustion chamber 102 could be stopped. The fuel 108 may be later restarted when the second temperature sensor 112 detects a lower temperature (e.g., about 425° F. or less).
The exhaust gases produced by a bio-mass burner of the present invention may generally be provided to, and used by, a heat exchanger, to heat or increase the temperature of a circulating fluid (or gas) 120 in a separate compartment, which may then be utilized as an energy input for another process (e.g., a water heater, etc.). Embodiments of the present invention contemplate using any of a variety of different heat exchangers and peripheral equipment in the art that are suitable for use in conjunction with the burner of the present invention. A fan 122, such as an induced draft (ID) fan, may be located at a distal location within the exhaust flow, such as toward an end of the flue 116 or in a distal cavity on the distal side of the heat exchanger 118, near where the exhaust 114 exits into the surroundings through an exit opening. The fan may pull the exhaust gases 114 at a desired flow rate and thus control the amount of air 110 being drawn into the combustion chamber 102. The fan 122 creates a negative pressure within the combustion chamber 102 that causes air 110 to be drawn into the combustion chamber 102, which then flows into the flue 116 as an exhaust 114 and exits the apparatus through a distal exit opening after flowing through the fan 122.
A computer 124 may be provided as shown in
As shown in
An example of a heat exchanger 118 is shown in
Exchange of heat with the circulating fluid 120 inside the heat exchanger 118 may occur with the tubes heated by the exhaust gases near the bottom portion of the exchanger 118. The fluid 120 may enter a distal compartment of the heat exchanger 118 surrounding the distal vertical tubes 216 and enter a proximal compartment of the exchanger 118 surrounding the proximal vertical tubes 215 through a lower opening (not shown) before exiting the heat exchanger 118. Thus, the fluid 120 may be described as being in counter flow relative to the flow of exhaust gases 114 traveling through the exchanger 118. However, as stated above,
To encourage greater circulation of air within the plenum and contact of the air with the outside of the chamber 102, and thus greater preheating of the air entering the chamber 102, one or more channel(s) 303a, 303b may be further provided inside the plenum space. The channels 303a, 303b may be juxtaposed with the outside of the chamber and may reach or span from near or at the floor 205 of the unit to near the top of the plenum space. However, the channels 303a, 303b may generally not reach the top of the plenum space, the top panel 328 and/or the top of the chamber 102 such that there is a gap 310 near the top of the plenum where air inside the plenum may flow into the top of these channels 303a, 303b. Air entering the plenum through the air intake hole(s) 301a, 301b during operation near the bottom of the unit would then flow upward within the plenum where it would enter the channel(s) 303a, 303b through the gap 310. The air would then flow downward through these channel(s) 303a, 303b before entering the chamber 102 through an air inlet(s), which may be an air inlet tube, bore, etc., near or toward the bottom of the plenum (see below). Thus, the air entering the plenum 208 due to the negative pressure generated by the fan 122 is forced to flow over the outside combustion chamber 102 before descending through the channel(s) 303a, 303b and entering the chamber 102 through the chamber air inlet(s). In this way, the outside of the combustion chamber 102 is cooled while air entering the combustion chamber 102 is warmed or preheated. Although the channels 303a, 303b are shown as being vertically oriented, they need not be perfectly vertical or linear. Once the air is heated inside the chamber in and above the combustion zone to form an exhaust 114, the heated exhaust 114 then travels through a flue opening 330 in the top of the chamber.
A fuel inlet tube 502 is also shown in
As explained further below, the location, size and orientation of each air inlet tube 402 (along with the cylindrical shape of the chamber 102) is that air flow near the fuel in the bottom or lower portion of the chamber 102 is cyclonic in nature, which helps to burn the fuel more evenly and quickly and maintain a relatively uniform temperature within the lower fuel burning portion of the chamber 102. This design also helps to prevent or minimize sparks and unburned particles from escaping with the exhaust gases. In addition to being angled downward toward the combustion chamber 102, the air inlet tube 402 will also be angled off to one side such that it is tangential to the inner wall face of the combustion chamber. This combination of being angled downward and angled off to one side encourages the air flow to enter the bottom of the chamber 102 in an orderly fashion such that the air flows in a circular or spiral direction around the interior of the chamber to create a cyclonic flow of the heated air as it flows upward to the top of the chamber, which is further encouraged by the cylindrical shape of the chamber. This cyclonic flow of air and exhaust from the burn leads to a more complete and efficient burn of the fuel.
The figures described above illustrate an embodiment of a bio-mass burner in accordance with the principles of the present invention. The specific sizes, shapes and angles of the various components and features of the burner may vary without departing from the scope of the present invention. However, by way of example, specific sizes, shapes, angles, etc., of the components are provided below to illustrate configurations or embodiments of a non-catalytic bio-mass burner of the present invention that may be operable in the 100,000 to 500,000 BTU/hr range or higher. The non-catalytic bio-mass burner of the present invention may also operate at efficiencies of about 70-80% or higher, which may be at or near operating efficiencies of catalytic burners, although other efficiency ranges are also possible. According to some embodiments, there may be four cold air inlets with two of those inlets having a diameter of about two inches and the other two having a diameter of about 1 inch. The inside diameter of the combustion chamber may be about 10 or more inches, and the height of the combustion chamber may be between about 32 to 34 inches for a 100,000 BTU unit. But the height and diameter of the combustions chamber may be greater for units having higher BTU output. For example, the diameter of the chamber for a 500,000 BTU unit may be up to about 30 inches or higher, and the height of such a chamber may be up to 50 inches or higher. To maintain a cylindrical shape, the height of the chamber may generally increase as the diameter increases, and vice versa. The diameter of the flue from the combustion chamber to the heat exchanger may range from about 4 inches to about 8 inches. The fuel stirrer, if present, may have a length of about 9 inches or greater depending on the diameter of the chamber to allow for coverage and easy rotation within the chamber.
According to these embodiments, the fuel inlet tube may have a diameter of about 4 inches to 6 inches and have an opening in its lower portion nearest the combustion chamber that is between about 9 inches and 15 inches above the bottom of the combustion chamber. The fuel inlet tube may have a central or longitudinal axis that may be inclined more than 45° but less than or equal to 90° from horizontal (i.e., relative to the ground or the floor of the unit), such as approximately 55° from horizontal, so that the fuel may freely fall down the shaft of the fuel inlet tube. Each air inlet tube may have a diameter of about 1 or 2 inches and a central or longitudinal axis that is inclined or angled downward toward the combustion chamber at an angle in a range between about 15° and 40° from horizontal, such as about 25°, in addition to being angled off tangentially to one side as described above. The air inlet tube may enter the combustion chamber at a position that is in a range from about 2 inches to about 4 inches above the bottom of the combustion chamber.
There has been difficulty in providing a fuel feed assembly or mechanism that can deliver a wide range of fuels to the combustion chamber of a burner. In many fuel hopper designs, a phenomenon called “bridging” occurs that clogs the feed mechanism and requires frequent stoppage and cleaning of the feed mechanism. Thus, there is a need for a fuel hopper delivery system that can effectively provide a wide range of fuels to a burner or stove and avoid the consequence of bridging. Thus, according to another aspect of the present invention, a universal feed system is provided that can deliver a variety of fuel types to a burner. Although the burner itself of the present invention is described as being non-catalytic, such universal feed system could potentially be used to provide fuel to different types of stoves, burners, or boilers. The feed hopper may be sized to hold a multi-day supply of fuel that may be automatically fed to the burner at various controlled rates to maintain desired operating characteristics of the burner.
The hopper 602 may also include a floor 606 having an outside edge that is adjacent to the bottom of the sidewall(s) 604. The floor 606 may be “live” in that it can rotate relative to the sidewall(s) 604. Thus, the floor 606 may not be rigidly connected to the sidewall(s) 604 to allow for rotation. One of ordinary skill will recognize that there are functionally equivalent ways to create a live rotating floor 606. A motor 607 may be included and located beneath the floor 606 to provide the drive power to rotate the hopper floor 606. A variety of designs may be used to maintain a seal or barrier where the sidewall(s) and floor meet while allowing for free relative movement. For example, the outside edge of the floor 606 may travel in a groove within the sidewall 604 or the floor 606 may include a lip or groove that engages the bottom of the sidewall 604. The result in either case is that the sidewall 604 and floor 606 join in such a way that the floor 606 can rotate relative to the sidewall 604 but the fuel within the hopper 602 is prevented from inadvertently leaking from the hopper 602.
A generally horizontal rod 608 may be affixed to a center support 609 that is connected to the floor 606 such that rotation of the floor 606 causes the rod 608 to push the fuel that is within the hopper 602 against a feed auger 610 that pulls the fuel out of the hopper 602. Particularly with light fuels, rotation of the floor 606 can push the fuel up over the feed auger 610 if the rod 608 is not present. When the rod 608 is positioned in close proximity to the feed auger 610, the rod 608 acts to press, or hold, fuel near the feed auger 610 so that feed auger 610 may engage the fuel more effectively to pull it out of the hopper 602 instead of allowing a majority of the fuel to simply pass over the feed auger 610. The rod 608 may extend out lengthwise in one or both direction(s) from the center support 609 to a position near the sidewall(s) 604. If the rod extends out in one direction, it may generally be on the side where the fuel meets the feed auger 610. To be effective, however, it is not necessary that the rod 608 get very close or touch the sidewall 604. In general, the rod 608 will be positioned high enough off the floor to be above the fighting of the feed auger so that the rod 608 does not interfere with the fuel reaching the feed auger 610. The rod 608 may be positioned in a generally horizontal line or plane that is about 2 inches or less, or about 1 inch or less, above the floor of the hopper.
To pull and remove the fuel from the hopper 602, there is the feed auger 610 just above the floor 606 that rotates to move the fuel from inside the hopper 602 to an elevator screw 614 on the outside of the hopper 602. The elevator screw 614 then transports the fuel upwards to an exit opening 618 where it drops into a fuel inlet tube of a burner. The feed auger 610 and the elevator screw 614 may be driven separately by a first motor 612 and a second motor 616, respectively. As explained further below, the feed auger 610 along the bottom of the hopper 602 is positioned to span almost half the diameter of the inside of the hopper 602 from the sidewall 604 toward the center 609 of the hopper 602. Accordingly, the fuel inside the hopper 602 is moved by rotation of the floor 606 of the hopper 602 (see rotational arrow 620) to cause the fuel to engage the feed auger 610. The fuel is encouraged to meet the feed auger 610 in a uniform manner due to the action of the rod 608. The feed auger 610 rotates to pull the fuel out of the hopper through a side opening of the hopper 602 and into an elevator screw 614.
The rate at which the fuel moves out of the hopper 602, into the elevator screw 614 and ultimately into the fuel inlet tube of the burner may be controlled at least in part by coordinating the operation of the first and second motors 612, 616. The rate of fuel flow into the burner will also depend on the pitch and diameter of the fighting of both the feed auger 610 and elevator screw 614 in addition to their rate of rotation. By coordinating the operation and speed of the motors 612, 616 (including turning them on or off), the rate of fuel addition to the combustion chamber of a burner may be controlled such that a desired operating temperature and BTU output may be attained. All augers and screw conveyors, such as the elevator screw and the feed auger, that may be used as part of a fuel feed assembly of the present invention may be referred to jointly and collectively as screw augers.
In conjunction with the control of the motors 612, 616, a drive motor 607 that causes rotation of the floor 606 of the hopper 602 may also be variably controlled as an additional way to further control the rate at which fuel is fed out of the hopper 602. Indeed, each of these motors (particularly the drive motor 607 and the first motor 612) may be controlled by a computer, such as computer 124 in
The size or diameter of the fighting of the feed auger 610 and its length may be chosen to assist in keeping the fuel within the hopper from “bridging,” which refers to the fuel clumping together in such a way that it stops the flow of fuel from within the hopper 602 to outside the hopper 602. The feed auger 610 may generally extend toward the center 609 of the floor 606 of the hopper 602. A feed auger 610 that extends into the hopper 602 by about 90% of the hopper's radius or greater may be sufficient to avoid bridging. The feed auger 610 may extend into the hopper 602 by about 98% of the hopper's radius according to some embodiments. The size or diameter of the fighting of the feed auger may also depend on the size of the fuel. For example, a feed auger flighting that is approximately 2-by-2 (i.e., a two inch outer diameter with a two inch pitch) may be effective and beneficial for use with fuel that has a particulate size that ranges from about dust to about 2 inch or larger chips (e.g., G50 chip size).
The directions and speeds of rotation of the hopper floor 608, the feed auger 610 and the elevator screw 614, and thus motors 607, 612, 616, must be coordinated with each other for orderly flow of fuel out of the hopper and into the burner. According to the configuration shown in
According to another set of alternative embodiments, the floor of the hopper may not rotate, and instead a rod or some other functional equivalent, such as a plow, arm, etc., may be rotated around a center support to push the fuel to engage the feed auger. According to some embodiments, the feed auger may be recessed beneath the floor of the hopper in a cavity, and the fuel may be pushed into the cavity by the rotating rod, plow, arm, etc.
Generally speaking, the burner of the present invention may regulate the rate at which fuel is added to the combustion chamber by controlling the rate at which the fuel is delivered to a fuel inlet tube or opening of the burner that feeds, guides or drops the fuel into the combustion chamber of the burner. According to embodiments of the present invention, a fuel feed assembly that controls the rate at which the fuel is added to the burner (e.g., to the fuel inlet tube of the burner) may be any mechanized metering system known in the art, which may have one or more augers that have a rotational rate that is controlled by one or more motor(s). The auger system shown in
In accordance with the principles of the present invention, many different types of fuel can be efficiently burned regardless of the particulate size of the fuel, its uniformity, or its moisture content. Thus, it would be beneficial for a fuel feeding hopper of the present invention to be able to effectively delivery such varying types of fuel to the combustion chamber 102 of a burner to be burned. Accordingly, a restrictor plate is proposed for use in conjunction with a feed assembly and hopper to assist with controlled delivery of fuel to the elevator screw 614, and thus to the combustion chamber 102 of the burner.
As mentioned before, the computer 124 (of
As explained in the control algorithms below, the temperature inside the combustion chamber may be monitored and controlled to be at or near a desired temperature or within a desired range of temperatures by controlling the fuel flow rate, the air flow rate and operation of the auxiliary burner or igniter. Indeed, primary control of the combustion chamber temperature may be achieved by controlling the rate of fuel addition to the chamber with control of the fan/air flow and the igniter providing additional control or fine tuning of the combustion chamber temperature. In general, use of the igniter and addition of more fuel may each lead to higher combustion temperatures, whereas faster operation of the fan may cool the temperature. Generally, the fuel delivery rate may be increased to increase operating temperatures and slowed down to decrease operating temperatures. However, addition of fuel above a certain rate may cool the chamber at least temporarily (especially if the fuel has a high moisture content) if the fuel rate oversaturates or exceeds the amount of fuel that can be quickly combusted or burned. Based on the size of the fuel, its moisture content, and fuel type, different fuel delivery rates may be used to achieve a desired operating temperature. Since operation of the burner may be based on feedback information regarding the chamber temperature, the burner may self-regulate the rate of fuel addition and other parameters to control the temperature to keep it within a desired range.
As in any control system, there is a hysteresis curve that describes how a maximum temperature may be overshot and a minimum temperature may be undershot before equilibrium is reached. In certain embodiments, different types of fuel may be associated with different respective hysteresis curves. By operating based on feedback information, the general control algorithms for the burner of the present invention may be customized and used to automatically control the temperature regardless of the fuel type. In this way, the same general control algorithm applies for any type of fuel with different customized values that may depend on the physical qualities of the fuel.
Starting with a cold burner in step 901 with no fuel being present nor any auxiliary burner or igniter providing heat, an auxiliary heat source or igniter is turned ON in step 903 to begin warming and heating the combustion chamber. If fuel were simply added to the combustion chamber and ignited at this time, the burner would produce smoke and pollutants until the combustion chamber temperature became high enough to cleanly burn the fuel.
While the igniter is still running, the combustion chamber temperature is monitored and the fuel rate is controlled in step 905 to determine when and how much fuel is added to the chamber. The combustion chamber temperature may be measured by a temperature sensor, such as the first temperature sensor 104 in
Once the algorithm in
In addition to the general control steps depicted in
According to embodiments of the present invention,
At the beginning of the fuel control method shown in
After resetting the System Stable status, a decision step 1007 is reached in which it is determined whether the igniter delay timer (started at a previous step 1003) has expired (e.g., after 35 seconds). Obviously, if the timer had just started, it may not yet have expired. But, the timer would eventually expire after several passes or cycles through the algorithm. If it is determined at step 1007 that the igniter delay timer has not yet expired, then the fuel is turned (or remains) OFF at step 1011, which means that no fuel is added to the combustion chamber. The algorithm then proceeds to the “end,” at which point the fuel control algorithm is exited until the next pass through it according to a higher level control algorithm, such as the one in
After the igniter safety check step(s), the fuel control algorithm continues with the fuel rate being determined according to the following steps. At step 1009, a decision is made whether the combustion chamber temperature has reached a minimum fuel run temperature. The minimum fuel run temperature (e.g., a temperature in a range from 250° F. to 999° F., or from 400° F. to 700° F.) may be preset or set by the user (within limits) depending on a tolerable amount of smoke that may be produced during an initial period of time while the chamber is warming up to a more desirable operating temperature. Thus, even though very little smoke, if any, may be generated at a lower setting (i.e., a lower minimum fuel run temperature), a higher minimum fuel run temperature may ensure less smoke production when the fuel is first added. According to some embodiments, the minimum fuel run temperature may depend on a smoke guard setting or may be held constant regardless of smoke guard setting (see below). If it is determined at step 1009 that the combustion chamber temperature is not greater than the minimum fuel run temperature (e.g., 600° F.), then the fuel is turned (or remains) OFF at step 1011, and the algorithm proceeds to “End.” If, on the other hand, the combustion chamber temperature is greater than the minimum fuel run temperature, then the fuel control algorithm proceeds on to decision step 1013 to determine if a higher temperature threshold is reached, which affects the fuel rate. At step 1013, it is determined whether the combustion chamber temperature is greater than or equal to a full fuel run temperature, which may be any temperature in a range from about 600° F. to 1600° F., or any temperature from about 900° F. to 1100° F. (e.g., 999° F.). According to some embodiments, the full fuel run temperature may depend on a smoke guard setting (see below). If it is determined that the combustion chamber temperature is greater than or equal to a full fuel run temperature, then the method proceeds to step 1015 to run the fuel at a user selected fuel rate/speed. However, if it is determined instead that the combustion chamber temperature is less than the full fuel run temperature (or less than the full fuel run temperature minus 1° F.), then the method proceeds to step 1017 to run the fuel at slower rate that is a predetermined fraction (e.g., about half or 50%) of the user selected fuel rate. The user selected fuel rate may be set by the user before and/or during operation of the burner, but the user selected fuel rate may be limited to being within a preset range.
According to some embodiments, the user selected fuel rate may range about 20% and about 100% of the motor capacity causing rotation of one or more augers of a fuel feed assembly. It may be selected numerically by the user or according to a preset recipe (that may depend on the fuel type). The selected rate may be higher for lighter and/or wetter fuels (e.g., dust) and lower for denser fuels (e.g., pellets). Any preset or selected levels or ranges of fuel rate or speed for a particular type of fuel may vary according to empirical evidence. Indeed, the fuel rate may vary substantially depending on fuel type and density. For example, a denser fuel may be fed at a user selected rate of about 40% of the capacity of the fuel feed assembly motor, whereas a lighter or wetter fuel may be fed at a user selected rate of about 60% of the capacity of the fuel feed assembly motor. The feeding of fuel into the combustion chamber at a given rate (when running) may also be pulsed on/off for alternating time periods, such as for alternating 5-10 second (or longer) ON and OFF periods.
Continuing from step 1015 after it is determined at step 1013 that the chamber temperature is less than the full fuel run temperature, the algorithm proceeds to step 1023 in which a fuel prime timer is “reset.” The fuel prime timer is described further below, but resetting the fuel prime timer means that the timer is reset to a full amount of time for use later if the temperature falls below the full fuel run temperature. After resetting the fuel prime timer at step 1023, the fuel control algorithm proceeds to step 1025 discussed below.
Continuing instead from step 1017 (after it is determined at step 1013 that the chamber temperature is less than the full fuel run temperature), the algorithm proceeds to step 1019 in which a fuel prime timer is enabled or started to run for a period of time if it is not already started and running. After step 1019, a decision step 1021 is reached in which it is determined whether the fuel prime timer (started at a previous step 1019) has expired (e.g., after a period of time between about 30 seconds and about 10 minutes, such as after 120 seconds). Obviously, if this timer had just started, it may not have expired yet. But, decision step 1021 may eventually be reached with the fuel prime timer having expired after several passes or cycles through the algorithm. If it is determined at step 1021 that the fuel prime timer has not expired, then the fuel control algorithm proceeds to step 1025 discussed below. However, if it is determined at step 1021 that the fuel prime timer has expired, then the fuel control algorithm proceeds to step 1011 and the fuel is shut off. Basically, the fuel prime timer allows for a period of time to pass during which the fuel is allowed to run at a fraction or half the user selected fuel rate, but if the chamber temperature cannot reach the full fuel run temperature during this time, then the fuel is shut off and remains off until the chamber temperature reaches the full fuel run temperature, after which the fuel prime timer is reset. Importantly, the fuel prime timer is not reset when it expires unless step 1023 is reached.
At decision step 1025 with the fuel running at the user selected fuel rate or at a fraction or half of the user selected fuel rate depending on the combustion chamber temperature, the algorithm determines whether Auto Combustion is enabled. Auto Combustion is a state or manner of operation that may be selected by a user input (i.e., enabled or disabled by the user). If Auto Combustion is enabled, then a more elaborate set of controls are implemented to automatically control the fuel rate and thus the combustion chamber temperature. However, if Auto Combustion is not enabled, then a more simple routine is employed to control the fuel rate and chamber temperature.
If it is determined that Auto Combustion is not enabled at step 1025, then the fuel control algorithm proceeds to decision step 1027. At step 1027, it is determined whether the combustion chamber temperature is greater than a user combustion temperature. The user combustion temperature may vary (within limits) and may be selected by the user (e.g., a temperature in a range from about 1100° F. to 1800° F., or about 1500° F. to 1700° F., such as 1600° F.). It is basically the target or desired combustion chamber temperature for operating the burner. If it is determined at step 1027 that the combustion chamber temperature is greater than the user combustion temperature (e.g., 1600° F.), then the fuel is turned OFF at step 1029, and the method proceeds to step 1031. If the combustion chamber temperature is not determined to be greater than the user combustion temperature at step 1027, then the method proceeds to step 1031 without turning the fuel OFF (i.e., step 1029 is bypassed). Step 1031 determines instead if the combustion chamber temperature is less than the user combustion temperature or less than the user combustion temperature minus one or more degrees (e.g., 1599° F.). If the combustion chamber temperature is less than the user combustion temperature (or less than the user combustion temperature minus one or more degrees), then the method proceeds to step 1033 and the fuel is turned ON (if not already running) at the user selected fuel rate or at the slower fraction (e.g., half) of the user selected fuel rate depending on the determination at decision step 1013. After step 1031, the fuel control algorithm (without Auto Combustion enabled) then proceeds to “End.” If the combustion temperature is oscillating around the user combustion temperature, the fuel will not quickly and repeatedly switch back and forth between ON and OFF because the combustion chamber temperature reading received from the thermocouple of the temperature sensor is actually an integration (like a running average) over a period of time (e.g., 20 seconds). Therefore, the decisions at steps 1027 and 1031 will not result in the fuel being turned on and off too quickly due to short term temperature fluctuations around the user combustion temperature.
Returning to step 1025, if it is determined instead that Auto Combustion is enabled, the fuel control algorithm then proceeds to decision step 1035, which asks whether the combustion chamber temperature is greater than a user stable temperature (e.g., a temperature in a range from about 1100° F. to 1500° F., or from about 1200° F. to 1400° F.), which may be preset or selected by the user (within limits). The user stable temperature (e.g., 1350° F.) will generally be lower than the user combustion temperature and may function like a minimum chamber temperature for running the Auto Combustion algorithm. The user stable temperature and the user combustion temperature may vary together and may be separated by about 250° F. If it is determined that the chamber temperature is not greater than the user stable temperature, then the System Stable status (discussed above; see also step 1005) is reset at step 1037 (i.e., the system is set as unstable or not stable), and the method proceeds to the “End.” The System Stable status will become relevant in the subsequent step 1039 of the Auto Combustion algorithm.
If it is determined instead that the chamber temperature is greater than the user stable temperature, then the fuel control algorithm proceeds to step 1039 to determine whether the system is set to Stable. Whether or not the system is set to System Stable depends on (1) steps 1005 and 1037 discussed above, which reset the System Stable to being unstable or not stable (if not already set as unstable) due to upstream decision steps that are based on operating conditions, and (2) step 1049 discussed below which sets the system to Stable as a result of upstream decision steps based on operating conditions. If it is determined at step 1039 that the system is Stable, then the Auto Combustion algorithm proceeds to step 1041 to calculate an auto fuel rate (discussed below in reference to
With Auto Combustion enabled, if it is found that (1) the chamber temperature is greater than the user stable temperature at step 1035 and (2) the system is set to System Stable at step 1039, then the Auto Combustion control of the fuel rate is implemented first by calculating an auto fuel rate at step 1041 followed by additional steps depicted in
The PID function is a combination of a proportional term, an integral term, and a derivative term that works to keep a measured process variable (e.g., the combustion chamber temperature) at or near a set point or target value (e.g., the user combustion temperature) by affecting a manipulated variable (e.g., the fuel flow rate into the chamber). Each of the terms of the PID function inputs a measure of error (i.e., based on the departure of the process variable from the set point or target value) to affect the level or rate of operation of the manipulated variable (e.g., fuel rate). Each of the terms of the PID function has a separate constant that gives them relative weight, and the values for these constants may be determined empirically. The proportional (P) term is computed based on current error or deviation (e.g., difference between the combustion chamber temperature and user combustion temperature), the integral (I) term is based on the past error over a period (e.g., “area under the curve” over a period of time for chamber temperatures relative to the user combustion temperature), and the derivative (D) term is a measure of anticipated future error (e.g., current rate of change of combustion chamber temperature). A PID function has all three terms, whereas a PI function has only the P and I terms. Based on the combustion chamber temperature, the fuel rate may be modified according to a summation of these terms, which depend on the process variable (i.e., combustion chamber temperature readings) and the target value (i.e., a user combustion temperature). Again, the thermocouple of the temperature sensor integrates the temperature readings that are sent to the computer, and the PID function itself may integrate over a period of time interval or scan time (e.g., about 10-12 seconds). Thus, these integrations help to avoid rapid fluctuations in the fuel rate (discussed here and below) during Auto Combustion cycles. The variables of the PID including the integration time may also be chosen by the user directly or indirectly according to a preset recipe that is selected by the user (perhaps according to fuel type).
The output of the PID (or PI) function calculated in step 1041 provides an absolute value or a positive or negative value by which to change or alter the manipulated variable (i.e., the auto fuel rate). Continuing with
As described above, the user selected fuel rate may vary, such as from about 20% to about 100% of capacity of fuel feed assembly motor capacity). According to these embodiments, the maximum fuel offset and the minimum fuel offset may each be about 10-40% above or below the user selected fuel rate. A larger fuel offset(s) may be permitted for lighter and/or wetter fuels, whereas a smaller fuel offset(s) may be tolerated for denser fuels. For example, a denser fuel type (e.g., pellets) may be fed into the chamber at a user selected rate of about 40% of motor capacity with a maximum fuel offset of about 10% and a minimum fuel offset of about 20%, whereas a lighter fuel (e.g., wood dust) may be fed into the chamber at a user selected rate of about 60% of motor capacity with a maximum fuel offset and a minimum fuel offset of each about 40%. Feeding of any fuel type may be pulsed on/off, especially denser fuel types.
After the fuel rate is set to the auto fuel rate within the maximum and minimum fuel offset limits relative to the user selected fuel rate, then that Auto Combustion algorithm continues with a set of temperature and safety control steps based on the combustion chamber temperature. At decision step 1053, if it determined that the combustion chamber temperature is greater than the user combustion temperature (discussed above) plus a temperature offset, which may be from about 20 to about 100° F. or more, then the fuel rate is set to a low factory preset level at step 1055, which may be a minimum fuel rate needed to maintain combustion, and the method may then proceed to step 1057. If the combustion chamber temperature is greater than the temperature offset, then the fuel rate will remain at the low factory preset level until this condition is no longer met, which may be achieved by ignoring the output of the PID (even though it may continue to calculate auto fuel rates) and maintaining the rate at the factory preset level. If the combustion chamber temperature is not greater than the user combustion temperature plus the temperature offset, then the method proceeds to step 1057 and bypasses step 1055. At decision step 1057, if it is determined that the combustion chamber temperature is greater than a combustion warning off temperature (e.g., any temperature between about 1800 and 2100° F., such as 1900° F.), then the fuel system is disabled (i.e., turned OFF) in step 1059 for safety and temperature control, and a combustion warning flag is set in step 1061 before the method proceeds to step 1063. If it determined instead that the combustion chamber temperature is not greater than the combustion warning off temperature, then steps 1059, 1061 are bypassed, and the method proceeds directly to step 1063.
Continuing with the method in
Returning to
According to step 913 of
With the igniter ON in step 913, the combustion chamber temperature should begin to recover and rise until a second igniter off temperature is reached (e.g., potentially any temperature within a wide range from 900° F. and about 1700° F., such as between about 1100° F. and about 1700° F., or between about 900° F. and about 1400° F., or between about 1200° F. and about 1400° F.), at which point the igniter may be turned back OFF. The second igniter off temperature may depend on a smoke guard setting and/or whether an R1 or R2 state is determined or set (see below). Thus, the igniter step 913 may function to maintain minimum chamber temperatures by turning ON when the igniter on temperature is reached until the combustion chamber temperature rises to the second igniter off temperature. The second igniter off temperature is distinguished from the first igniter off temperature discussed above in 907, 909 for turning off the igniter during initial startup, although the second igniter off temperature may be the same temperature as the first igniter off temperature. The igniter on temperature and/or the second igniter off temperature may be varied or adjusted within a range of temperatures depending on user selection(s), such as the smoke guard setting. Generally speaking, the igniter on temperature will always be lower than the second igniter off temperature, and the temperature gap between the lower igniter on temperature and the higher second igniter off temperature may vary but may typically be about 200-250° F. or more. Indeed, the igniter on temperature and the second igniter off temperature may vary in tandem for different smoke guard settings with the temperature gap between them remaining constant or varying only slightly.
A user selected “smoke guard” setting may also be provided and selected for determining in step 913 when the igniter runs. The smoke guard setting may be selected by a user depending on the user's tolerance for lower temperatures and/or smoke during operation of the burner. The smoke guard setting may also depend on the type and moisture content of the fuel. Basically, a higher smoke guard setting would translate into a higher igniter on temperature and/or second igniter off temperature, whereas a lower smoke guard setting would mean a lower igniter on temperature and/or second igniter off temperature. A higher smoke guard setting may ensure higher operating temperatures and less smoke being produced (but may also consume more gas/energy over time to run the auxiliary igniter), whereas a lower smoke guard setting may conserve energy consumed by the igniter but may permit lower operating temperatures and increased exhaust smoke to occur. A higher or lower smoke guard setting will generally correspond respectively to a higher or lower igniter on temperature and/or second igniter off temperature. According to some embodiments, both the igniter on temperature and the second igniter off temperature may be raised or lowered depending on the smoke guard setting (i.e., raised for a higher setting; lowered for a lower setting). According to some alternative embodiments, only one of the igniter on temperature and the second igniter off temperature may be raised or lowered depending on the smoke guard setting with the other remaining fixed.
The smoke guard setting may be on a scale of 0 to 10 (or some other value) with this scale corresponding to temperature increments for the igniter on temperature and/or second igniter off temperature ranging from a lowest igniter on temperature and/or second igniter off temperature (i.e., lowest smoke guard setting) to a highest igniter on temperature and/or second igniter off temperature (i.e., highest smoke guard setting). Therefore, a lower smoke guard setting (e.g., “1”) would set the igniter on temperature and/or second igniter off temperature to lower temperature(s) within their respective temperature range(s), whereas a higher smoke guard setting (e.g., “10”) would set the igniter on temperature and/or second igniter off temperature to a higher temperature within their respective temperature range(s). According to some embodiments, the available smoke guard temperature ranges of the igniter on temperature and/or second igniter off temperature for a set of smoke guard settings may also be set by the user (perhaps within limits). According to some embodiments, there may also be additional ‘smart’ variables that are used by the computer to control or adjust these smoke guard temperature thresholds relative to those determined directly by the user-selected smoke guard setting (see, e.g., discussion below). For example, if the combustion temperature is determined to be falling rapidly (instead of slowly) toward the igniter on temperature, then the relevant temperature thresholds of the smoke guard feature (e.g., the igniter on temperature) may be set a little higher (relative to such temperature based only on the smoke guard setting) to anticipate and curtail the falling temperatures sooner.
As an example of the foregoing (without additional variable controls), if the smoke guard temperature range for the igniter on temperature was from 600° F. to 1200° F., the smoke guard temperature range for the second igniter off temperature was from 800° F. to 1400° F., and the smoke guard setting is at “8,” then the igniter would turn ON when the combustion chamber temperature fell below the igniter on temperature of 1080° F. but would later turn OFF when the chamber temperature reached 1280° F. As another example, if the igniter on temperature is fixed at 900° F. and the smoke guard temperature range for the second igniter off temperature was from 1000° F. to 1600° F., and the smoke guard setting is at “4,” then the igniter would turn ON when the combustion chamber temperature fell below the igniter on temperature of 900° F. but would later turn OFF when the chamber temperature reached the second igniter off temperature of 1240° F. In this latter example, if the smoke guard setting is instead set at “7,” then the igniter would turn ON when the combustion chamber temperature fell below 900° F. but would later turn OFF when the chamber temperature reached the second igniter off temperature of 1420° F.
In addition to controlling the combustion chamber temperature by controlling the fuel rate in step 911 and the igniter in step 913, operation of the fan may also be controlled in step 915 to help control the combustion chamber temperature before the high level algorithm in
Generally, the fan may operate at a range of speeds, which may be expressed as a percentage of fan's full speed capacity. The fan may be set at a highest predetermined fan speed (e.g., between about 60% and about 100%, such as about 100%) when the combustion chamber temperature rises to or above a maximum fan temperature (e.g., any temperature between 1500° F. and 2100° F., such as 1800° F.), and the fan may be set at a lowest predetermined fan speed (e.g., greater than 0% but less than about 50%, such as about 15%) when the combustion chamber temperature falls to or below a minimum fan temperature (e.g., any temperature between 800° F. and 1200° F., such as 1000° F.). According to some embodiments, the maximum fan temperature may be set to the user combustion temperature. When the chamber temperature rises above the maximum fan temperature and the fan is operating at its highest predetermined speed, then the fuel may also be optionally shut off or set to preset factory minimum rate (see, e.g., steps 1053 to 1061 in
Generally, the fan will usually be operating at least at a lowest or minimum predetermined fan speed even when the chamber temperature is low so that orderly air flow is maintained through the burner at all times. However, the fan may be turned OFF below a predetermined fan off temperature (e.g., a temperature between about 400° F. and 1200° F., such as 600° F.). Turning off the fan may also be tied to a shut off cycle for the burner unit or if a thermostat is no longer calling for heat. Likewise, the fan may be turned off if an excessively hot combustion temperature, such as 2100° F., is reached or surpassed.
When the fan speed increases in response to temperature, the chamber temperature may continue to rise slightly until enough cool air is infused into the chamber by operation of the fan for the chamber temperature to begin to fall. To respond to temperature changes and fluctuations over the range of temperatures between the minimum fan temperature and the maximum fan temperature, the fan speed may be adjusted over this temperature range between the lowest predetermined fan speed and the highest predetermined fan speed. More particularly, the fan speed or rate within this range of temperatures (i.e., the intermediate fan speed) may simply be a linear interpolation between the minimum and maximum predetermined fan speeds with the number of fan speeds between them corresponding to the number of equal temperature intervals (e.g., 100° F.) between the minimum and maximum fan temperatures. For example, if the maximum or highest predetermined fan speed is set to 80% of the fan capacity at a maximum fan temperature of 1800° F. and the minimum or lowest predetermined fan speed is set to 40% of the capacity of the fan at a minimum fan temperature of 1000° F. (with eight 100° F. intervals between them), then the (intermediate) fan speed or rate at 1300° F. would be set at 55% of the capacity of the fan. The number of temperature intervals between the minimum and maximum fan temperatures will determine the size of each fan speed increment, which may be about 1% to about 5% increments.
Continuing with
As further depicted in
There may be instances in which the combustion chamber temperature falls below a predetermined low threshold temperature such that additional measures are needed to raise the chamber temperature. For example, if the combustion chamber temperature falls below a predetermined low threshold temperature while the igniter is ON and the fuel is ON, then the following procedure may be used: First, the fuel and the auxiliary igniter may be turned off; the fan may be kept running so that the any combustible gasses may be purged from the combustion chamber; the igniter may then be turned back ON; the fuel may be turned back ON after that at a user selected fuel rate; and finally, the igniter may be turned OFF once a higher predetermined chamber temperature is reached.
In addition to the foregoing, there may also be additional control mechanisms including an overarching system on/off control. Such on/off control may be tied to a thermostat that relates to the function of the unit involving the heat exchanger (e.g., use of the circulating fluid to heat air in a house, water in a water heater, etc.). An internal thermostat may also be tied to the temperature of a circulating fluid in the heat exchanger to make sure it does not get too hot or boil. If the unit does not receive a call for heat from a control thermostat, then the unit may be shut down, which may cause the fuel and/or fan to be turned off, the timing of which may depend on various settings. Operation of the unit may be tied to other variables as well, such as the level of circulating fluid in the heat exchanger, etc.
The method described above in reference to
In such cases where action does not occur until the end of the algorithm, the last value assigned for a given operational parameter will determine the relevant action taken upon completion of the algorithm. For example, in reference to
Methods of the present invention may be implemented via hardware, software or a combination of hardware and software (including firmware, resident software, micro-code, etc.). Aspects of the present invention may be implemented by a computer according to a computer readable program code present on a computer readable medium. Indeed, some aspects of the present invention may take the form of a computer readable program product embodied in one or more computer readable media having the computer readable program code present thereon. The above-identified algorithms may be performed automatically by a programmable computer, such as a microcontroller or microprocessor, that executes software residing in an accessible non-transitory computer-readable media. The computer may include a programmable logic controller (PLC) or microcontroller for receiving inputs and sending outputs to control the burner on the basis of feedback information. The computer may further include a user interface that allows a user to enter values and operating parameters, such as various settings, fan speeds and temperatures, as discussed above.
As stated above, the computer of the present invention for controlling operation of the burner may comprise a processor and one or more computer readable media that may be part of, in communication with, and/or utilized by the computer. The computer may comprise a programmable logic controller (PLC), a microcontroller, or other programmable data processing apparatus. The computer may also comprise one or more computers, processors, servers, etc., jointly functioning to control the operation of the burner. The computer may be part of the burner unit and/or a separate or remote computer in communication with the burner. Any combination of one or more computer readable media may be utilized. The computer readable media may be a computer readable signal medium or a computer readable storage medium.
A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an appropriate optical fiber with a repeater, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.
A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. Program code embodied on a computer readable signal medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.
Computer program code for carrying out operations for aspects of the present disclosure may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Scala, Smalltalk, Eiffel, JADE, Emerald, C++, CII, VB.NET, Python or the like, conventional procedural programming languages, such as the “c” programming language, Visual Basic, Fortran 2003, Perl, COBOL 2002, PHP, ABAP, dynamic programming languages such as Python, Ruby and Groovy, or other programming languages. The program code may executed on a computer that is part of the burner unit and/or a remote computer or server. If used, the remote computer may be connected to the burner unit through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider) or in a cloud computing environment or offered as a service.
Aspects of the present disclosure are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatuses (systems) and computer program products according to embodiments of the disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of the computer to implement the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer program instructions may be stored in a computer readable medium as stated above that when executed can direct the computer to function in a particular manner, such as to control the operation of the burner. The computer program instructions may also be loaded onto the computer to cause a series of operational steps to be performed on the computer to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. It will be further understood that the method of the present invention may comprise all or a portion of the method steps described herein, and such steps may be performed in different orders as long as the sequence of steps maintains necessary logic flow and groupings.
While the present invention may have been disclosed with reference to certain embodiments to enable one skilled in the art to practice the invention, it will be apparent that modifications and variations are possible without departing from the spirit and scope of the invention as defined herein. Furthermore, it should be appreciated that any and all examples in the present disclosure, while illustrating embodiments of the invention, are provided as non-limiting examples and are, therefore, not to be taken as limiting the various aspects so illustrated. The present invention is intended to have its full scope consistent with the language of the claims and equivalents thereof. Accordingly, the drawings and detailed description are to be regarded as illustrative and not as restrictive.
Various modifications to the embodiments presented herein will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments. Reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” (or “step for” in the case of a method claim).
Claims
1. A non-catalytic biomass burner comprising:
- a combustion chamber for burning a fuel to produce an exhaust gas, wherein the combustion chamber has a cylindrical interior shape with the sides of the combustion chamber enclosed by a side wall;
- one or more air inlets spanning the side wall of the combustion chamber to allow air to enter the combustion chamber from the outside of the combustion chamber through the one or more air inlets;
- a flue pipe connected at its proximal end to the top of the combustion chamber, the flue pipe being configured to receive the exhaust gas from the combustion chamber through a flue opening,
- a heat exchanger for transferring heat from the exhaust gas to a circulating fluid of the heat exchanger, wherein the heat exchanger is positioned in the path of the exhaust gas between the flue pipe and an exit opening of the burner, and wherein the flue pipe delivers the exhaust gas to the heat exchanger;
- a fuel inlet tube having an upper portion and a lower portion, wherein a fuel opening in the side wall of the combustion chamber allows fuel to enter the combustion chamber from the lower portion of the fuel inlet tube; and
- an auxiliary igniter pointed toward the combustion chamber through an igniter opening in the side wall of the combustion chamber, the auxiliary igniter configured to direct heat into a lower portion the combustion chamber.
2. The biomass burner of claim 1, further comprising:
- a first temperature sensor positioned near the top of the combustion chamber to measure a combustion temperature of the exhaust gas exiting the combustion chamber.
3. The biomass burner of claim 2, wherein the first temperature sensor is positioned in a proximal portion of the flue pipe.
4. The biomass burner of claim 2, further comprising:
- a computer; and
- a fuel feed assembly,
- wherein the computer is in communication with the fuel feed assembly and the first temperature sensor, and
- wherein the computer controls the rate at which the fuel is added to the combustion chamber through the fuel inlet tube based on the combustion temperature from the first temperature sensor by controlling the speed of operation of the fuel feed assembly.
5. The biomass burner of claim 4, wherein the fuel feed assembly comprises one or more auger screws and one or more motors, the auger screws being rotated by the one or more motors to deliver fuel to the upper portion of the fuel inlet tube, and
- wherein the computer controls the rate at which fuel is added to the fuel inlet tube by controlling the speed of rotation of at least one of the auger screws.
6. The biomass burner of claim 4, wherein the fuel feed assembly further comprises a hopper for holding the fuel,
- wherein the auger screws comprise a feed auger and an elevator screw,
- wherein the feed auger directs the fuel from the hopper through an opening in the side of the hopper and into the elevator screw, and
- wherein the elevator screw transports the fuel into the upper portion of the fuel inlet tube of the burner.
7. The biomass burner of claim 1, wherein the longitudinal axis of the fuel inlet tube is angled greater than 45° and less than 90° relative to the ground.
8. The biomass burner of claim 1, further comprising:
- a computer, and
- a first temperature sensor positioned near the top of the combustion chamber to measure a combustion temperature of the exhaust gas exiting the combustion chamber,
- wherein the computer controls when the auxiliary igniter is turned on or off based on the combustion temperature from the first temperature sensor.
9. The biomass burner of claim 1, wherein the combustion chamber comprises an upper portion and a lower portion separated by a boundary, and
- wherein an inner part of the side wall facing the upper portion of the combustion chamber comprises a material that is different than the material of an inner part of the side wall facing the lower portion of the combustion chamber.
10. The biomass burner of claim 9, wherein the inner part of the side wall facing the upper portion of the combustion chamber comprises a ceramic fiber composite, and the inner part of the side wall facing the lower portion of the combustion chamber comprises a refractory brick or castable.
11. The biomass burner of claim 9, wherein the fuel opening in the side wall where the lower portion of the fuel inlet tube meets the combustion chamber intersects the boundary between the upper and lower portions of the combustion chamber.
12. The biomass burner of claim 9, wherein the igniter opening in the side wall of the combustion chamber intersects the boundary between the upper and lower portions of the combustion chamber.
13. The biomass burner of claim 1, further comprising:
- a variable speed fan positioned on the distal side of the heat exchanger that is configured to pull air into the combustion chamber.
14. The biomass burner of claim 13, further comprising:
- a computer; and
- a first temperature sensor positioned near the top of the combustion chamber to measure a combustion temperature of the exhaust gas exiting the combustion chamber,
- wherein the computer is in communication with the variable speed fan and the first temperature sensor, and wherein the computer controls the fan speed of the variable speed fan based on the combustion temperature from the first temperature sensor.
15. The biomass burner of claim 1, wherein each air inlet is angled downward toward the combustion chamber and has a longitudinal axis that is tangential to the inner surface of the side wall of the combustion chamber.
16. The biomass burner of claim 15, wherein the one or more air inlets are configured to produce cyclonic air flow within the combustion chamber.
17. The biomass burner of claim 15, further comprising:
- a plurality of vertical side panels positioned above a floor of the burner, the plurality of vertical side panels surrounding the side wall of the combustion chamber to define a plenum space between the side wall and the plurality of vertical side panels; and
- one or more air intake holes in the floor of the burner between the outside of the combustion chamber and the plurality of vertical side panels.
18. The biomass burner of claim 17, further comprising:
- one or more channels within the plenum space adjacent to the outside of the side wall of the combustion chamber,
- wherein the one or more channels span from near the floor of the burner to a location near the top of the plenum space, and wherein a gap is present between the top of the one or more channels and the top of the plenum space to allow air to enter the top of the one or more channels from the plenum space, and
- wherein the air inlets span from a lower portion of the one or more channels to the interior of the combustion chamber.
19. The biomass burner of claim 18, wherein the top of the plenum space is enclosed by a top panel and the bottom of the plenum space is enclosed by the floor of the burner, and
- wherein the gap is present between the top of the one or more channels and the top panel of the plenum.
20. The biomass burner of claim 1, further comprising:
- a computer; and
- a second temperature sensor that measures a distal exhaust gas temperature on the distal side of the heat exchanger,
- wherein the computer controls the operation of a fuel feed assembly of the burner based on the distal exhaust gas temperature from the second temperature sensor.
21. The biomass burner of claim 1, wherein the burner burns a biomass fuel at an efficiency of 80% or greater.
22. The biomass burner of claim 1, wherein the burner has a predetermined output in a range of about 100,000 to about 500,000 BTU/hr.
23. The biomass burner of claim 1, further comprising:
- a fuel stirrer located at the bottom of the combustion chamber for stirring the fuel.
24. A non-catalytic biomass burner comprising:
- a combustion chamber for burning a fuel to produce a hot exhaust gas, wherein the combustion chamber has a cylindrical interior shape with the sides of the combustion chamber enclosed by a side wall;
- one or more air inlets spanning the side wall of the combustion chamber to allow air to enter the combustion chamber from the outside of the combustion chamber through the one or more air inlets;
- a plurality of vertical side panels positioned above a floor of the burner, the plurality of vertical side panels surrounding the side wall of the combustion chamber to define a plenum space between the side wall and the plurality of vertical side panels;
- one or more air intake holes near the bottom of the plenum space to allow air to enter the plenum space;
- a flue pipe connected at its proximal end to the top of the combustion chamber, the flue pipe being configured to receive the exhaust gas from the combustion chamber through a flue opening and deliver the exhaust gas to a heat exchanger,
- a fuel inlet tube having an upper portion and a lower portion, wherein a fuel opening in the side wall of the combustion chamber allows fuel to enter the combustion chamber from the lower portion of the fuel inlet tube; and
- an auxiliary igniter pointed toward the combustion chamber through an igniter opening in the side wall of the combustion chamber, the auxiliary igniter configured to direct heat into a lower portion the combustion chamber.
25. The biomass burner of claim 24, further comprising:
- one or more channels within the plenum space adjacent to the outside of the side wall of the combustion chamber,
- wherein the one or more channels span from near the floor of the burner to a location near the top of the plenum space, and wherein a gap is present between the top of the one or more channels and the top of the plenum space to allow air to enter the top of the one or more channels from the plenum space, and
- wherein the air inlets span from a lower portion of the one or more channels to the interior of the combustion chamber.
26. The biomass burner of claim 24, wherein the one or more air intake holes are in the floor of the burner between the outside of the combustion chamber and the plurality of vertical side panels.
27. The biomass burner of claim 24, wherein the air inlet is angled downward toward the combustion chamber and has a longitudinal axis that is tangential to the inner surface of the side wall of the combustion chamber.
28. A non-catalytic biomass burner comprising:
- a combustion chamber for burning a fuel to produce an exhaust gas, wherein the sides of the combustion chamber are enclosed by a side wall;
- one or more air inlets spanning the side wall of the combustion chamber to allow air to enter the combustion chamber from the outside of the combustion chamber through the one or more air inlets;
- a flue pipe connected at its proximal end to the top of the combustion chamber, the flue pipe being configured to receive the exhaust gas from the combustion chamber through a flue opening,
- a fuel inlet tube having an upper portion and a lower portion, wherein a fuel opening in the side wall of the combustion chamber allows fuel to enter the combustion chamber from the lower portion of the fuel inlet tube; and
- an auxiliary igniter pointed toward the combustion chamber through an igniter opening in the side wall of the combustion chamber, the auxiliary igniter configured to direct heat into a lower portion the combustion chamber;
- a first temperature sensor positioned near the top of the combustion chamber to measure a combustion temperature of the exhaust gas exiting the combustion chamber; and
- a computer in communication with the first temperature sensor, the computer receiving the combustion temperature from the first temperature sensor.
29. The non-catalytic biomass burner of claim 28, wherein the computer controls when the auxiliary igniter is turned on or off based on the combustion temperature from the first temperature sensor.
30. The non-catalytic biomass burner of claim 28, further comprising:
- a fuel feed assembly,
- wherein the computer is in further communication with the fuel feed assembly, and
- wherein the computer controls the rate at which the fuel is added to the combustion chamber through the fuel inlet tube based on the combustion temperature from the first temperature sensor by controlling the speed of operation of the fuel feed assembly.
31. The non-catalytic biomass burner of claim 28, further comprising:
- a variable speed fan positioned on the distal side of the flue pipe that is configured to pull air into the combustion chamber.
- wherein the computer is in further communication with the variable speed fan, and wherein the computer controls the fan speed of the variable speed fan based on the combustion temperature from the first temperature sensor.
Type: Application
Filed: Nov 28, 2012
Publication Date: May 30, 2013
Inventors: Scott Laskowski (Madisonville, KY), Timothy Baughman (Madisonville, KY), Johann Duerichen (Smithers), Donald Laskowski (Indianapolis, IN)
Application Number: 13/687,736
International Classification: F23N 1/02 (20060101); F23L 5/02 (20060101); F23H 9/00 (20060101); F23K 3/14 (20060101);
