Patent Application
20160138810
The present invention generally relates to a heater system, and more particularly, to a heater system having improved fuel delivery and heat extraction systems.
Conventional heaters burn fuel to produce thermal energy or heat, which is usually used for heating air and/or water. Various fuels are burned, but biofuels have become increasingly popular. Solid biofuels include organic materials such as sawdust, wood chips, and other plant materials (e.g., corn husks). These biofuels are desirable because they are byproducts of industry. For example, sawdust and wood chips are readily available at sawmills and furniture manufacturers and provide a low-cost heating source. Plant materials are readily available at farms and nurseries and also may be used for heating. Other solid biofuels such as dried animal waste may also be available as fuel to provide heat.
Conventional heaters often include a stoker or fuel delivery system for delivering the selected fuel to a combustion chamber or combustor where the fuel is burned to produce heat. Fuel delivery mechanisms include conveyor belts, chutes, and augers. The burning fuel is supplied with air to provide oxygen needed to burn the fuel. In some cases, a blower forces air past the burning fuel to feed the fire. The resulting gases are vented through a vent pipe or exhaust vent extending from the combustor. Ash and residual solid materials are also removed, e.g., by gravity, to clear the combustor for further biofuel delivery.
Although these systems provide inexpensive heat, there are issues which limit their effectiveness. For example, the fuel delivery mechanisms may not be dependable. The fuels may stop flowing (e.g., due to rat holing or arching as will be explained below), thereby starving the fire. In other instances, the fuel delivery mechanism continues to feed fuel to the combustor after the fire goes out. Before the fire can be relit, the excess fuel must frequently be removed from the combustor.
Many heaters incorporate heat exchangers to capture heat from the system for heating air, water, or other fluids. Some prior heaters have heat exchangers that cause inefficient fuel burning, which results in excessive smoking and soot build up. In some heaters, heat fluctuates significantly with changing conditions, providing an undependable heat source and operating temperatures outside desirable working ranges. Thus, there remains a need for heater improvements that capture heat for warming air, water, and other fluids.
In one aspect, the present invention includes a heater having a combustion chamber for burning fuel. The combustion chamber has an interior defined by side walls and a top. The combustion chamber includes an air inlet at a bottom of the combustion chamber and an exhaust vent at the top of the combustion chamber. In addition, the heater includes a hopper mounted above the combustion chamber. The hopper is sized for holding a preselected amount of fuel and has an outlet at a lower end. The heater also has a chute extending from the outlet of the hopper to the combustion chamber. Still further, the heater includes a chute extending from the outlet of the hopper to the combustion chamber, a screw having a helical flight extending through the chute and into the hopper, and a drive operatively connected to the screw for turning the screw in a direction in which the flight would, but for downward forces, lift the fuel. The heater also has a vane rotatably attached to the screw. The vane rotates downward along the screw in absence of upward forces counteracting gravity. The vane is cambered to produce upward forces when turning with the screw beneath an upper surface of the fuel. The vane is biased toward the upper surface of the fuel by the upward forces and gravity to level the upper surface of the fuel and prevent the fuel from rat holing and arching.
In another aspect, the present invention includes a flowable material delivery system, comprising a hopper sized for holding a preselected amount of material and having an outlet at a lower end. Further, the heater includes a screw having a helical flight extending through the hopper, a drive operatively connected to the screw for turning the screw in a direction in which the flight would, but for downward forces, lift the material, and a vane rotatably attached to the screw. The vane rotates downward along the screw in absence of upward forces counteracting gravity. The vane is cambered to produce upward forces when turning with the screw beneath an upper surface of the material. The vane is biased toward the upper surface of the material by the upward forces and gravity to level the upper surface of the material and prevent the material from rat holing and arching in the hopper.
In still another aspect, the present invention includes a heater, comprising a combustion chamber for burning fuel. The combustion chamber has an interior defined by side walls and a top. The combustion chamber includes an air inlet at a bottom of the combustion chamber and an exhaust vent at the top of the combustion chamber. The heater includes a fuel delivery system mounted above the combustion chamber for delivering fuel to the combustion chamber, a primary heat exchanger surrounding the combustion chamber for heating fluid passing through the primary heat exchanger, and a secondary heat exchanger surrounding a vent passage extending from the exhaust vent for heating fluid passing through the secondary heat exchanger. At least one of the primary and secondary heat exchangers is packed in sand to moderate heat passing to the exchanger.
Other aspects of the present invention will be apparent in view of the following description and claims.
Corresponding reference characters indicate corresponding parts throughout the drawings.
Referring to
As illustrated in
A rake element, generally designated by 70, is mounted on the screw 36 in the hopper 34 for leveling fuel in the hopper to prevent rat holing and arching. Rat holing is a condition common in hoppers holding flowable solid materials in which a hole forms in the material above the hopper outlet but material clings to the hopper around the hole and does not fall through the outlet. Arching is another common condition similar to rat holing but where the hole formed in the material does not extend entirely upward through the material. Rather material bridges the hole over the hopper outlet. The rake element 70 includes a female-threaded connector 72 rotatably mounted on the screw 36 having a cambered vane 74 (
The fuel delivery system 40 maintains a controlled and constant fuel flow through the chute 32 to the combustion chamber 22 during operation. It is believed that maintaining optimal fuel flow improves fuel burn and induces an appropriate draft in the combustion chamber 22, reducing heater smoking and soot buildup. Toward this end, the damper 54 position can be controlled during heater idling so the heater maintains a minimal burn so the fuel remains burning for an extended duration without adding more fuel. In one embodiment, the damper position can be controlled by a solenoid (not shown).
As will be appreciated by those skilled in the art, the fuel delivery system 40 operates to deliver fuel to the combustion chamber 22 from the hopper 36. The drive motor 60 rotates the auger 36 at a constant speed (e.g., about ten rpm), causing the rake element 70 to rotate around the auger and seek the top of the fuel in the hopper 36. The rake element 70 levels fuel in the hopper 36 and prevents rat holing and arching. The fuel falls through the chute 32, spiraling along the flight around the central shaft of the auger 36 under the influence of gravity. The fuel falls into the combustion chamber 22 and feeds the burning fuel in the vicinity of the deflector 28. Air blown through the air inlet 30 into combustor 22 passes around the deflector to feed air to the fire and improve fuel burn. Other aspects of the fuel delivery system will be apparent to those skilled in the art.
In addition to heating surrounding air by radiation, the heater 20 may include a heat extraction system, generally designated by 78, having one or more heat exchangers such as shown in
In the illustrated case, an accumulator or hot water tank 94 is positioned along the water line 90. The accumulator 94 stores heated water ensuring water continuously flows through the water line 90. Ensuring continuous flow provides a constant supply to the remote heat exchanger 92 and prevents the coiled tubes 80, 82 from overheating. As will be appreciated by those skilled in the art, the accumulator 94 is positioned higher than the rest of the water loop and is vented to eliminate gas from the loop.
In an alternative embodiment of the heat extraction system (not shown), the water loop may be replaced with a forced air system by blowing air through the housings 86, 88 to heat the air directly. The sand is removed from the housings 86, 88 in this alternative forced air embodiment. Duct work (not shown) is used to transport the heated air to the locale where it is needed.
In one case, a pyrometer 96 is provided in the combustion chamber 22 for measuring temperature of the fire in the combustion chamber. The pyrometer 96 confirms that the fuel is burning and can be operatively connected to a control for controlling operation of the heater. For example, if the pyrometer 94 determines the flame has gone out, the motor can be stopped to reduce an amount of fuel entering the combustion chamber 22.
Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.
When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
As various changes could be made in the above constructions, products, and methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
