Ignition Element and Method for Kindling Solid Fuel

Abstract

An igniter element for igniting solid fuel particles in a retort furnace is disclosed. The igniter element is a substantially planar shaped element that is in direct contact with the fuel to be ignited. A configuration of various sections is formed into the planar igniter element in order to facilitate the conversion of electrical energy into thermal energy. The igniter element uses a control system to reliably facilitate the ignition of all solid fuels including difficult to start fuels, such as anthracite coal. The service life of the heat igniter is extended by its planar shape in contact with the surface of the retort and its ability to dissipate the thermal energy produced within the retort region.

Description

FIELD OF THE INVENTION

The present device and method pertains to the field of solid fuel burning stoves and furnaces. More particularly, what is discloses are a device and method for the ignition of the solid fuel by using electricity applied to a planar shaped ignition device.

DESCRIPTION OF RELATED ART

A conventional type of solid fuel burning stove or furnace contains a retort, or combustion region. The scale of the furnace can vary considerably, depending upon its intended use. The furnace should be capable of continuously and efficiently oxidizing pelletized or particulate fuel, including its gaseous by-products, collecting the produced heat, and then distributing the heat through conventional heat distribution systems to the targeted spatial heat zones, such as rooms in houses, office spaces, garages or small manufacturing facilities. It is necessary to produce high combustion temperatures in order to ensure that all solid fuel particles are consumed within the burner region of the furnace.

Problems that have been encountered with such furnaces relate to devices and methods for igniting the various types of fuels that may be used as the heat source. There are different combustion temperatures for different solid fuels such as wood, coal and wood pellets. Even between different types of wood or coal, there can be varying degrees of difficulty with igniting the fuel source and for maintaining a combustion temperature within a range sufficient to generate proper combustion. Especially difficult to ignite is anthracite coal. As a fuel source, though, it is highly desirable due to its density and ability to remain hot for an extended period of time. Conventional igniters include either coil or rod shapes that extend into the combustion region, severely limiting their serviceable life. Another method of heating such stoves and furnaces is to use distinct ignition materials or “mice”, as they are referred to in the industry. However, these are one time products and often produce unwanted smoke.

Certain fuels are extremely difficult to ignite and retain a hot enough flame to maintain low carbon monoxide by-product levels while still burning at a relatively low fuel consumption rate. This would require a system that had a means to control even the smallest combustion flame to maintain a precise temperature in addition to extracting the greatest ratio possible from the heat generated in order to be called a high efficiency system. They are set to a “level” of operation by the user and the furnace functions to that preset level regardless of changing ambient conditions, such as changing wind pressures on air inlet and exhaust outlets, fluctuating room temperatures and varying exhaust gas temperatures, etc. These systems do not continuously adjust for such varying conditions and the result is an efficient system. It is not possible for these systems to achieve a continuously clean burning operation.

Many attempts at solving these problems have been tried. For example, older solutions, such as those exemplified in U.S. Pat. Nos. 1,719,114 and 2,385,811 combined the elements of a stoker, a heater and a blower to provide a source of oxygen. Certain other inventions focused on the ignition source. Other attempted solutions include U.S. Pat. No. 2,549,806, which discloses either a heating coil or arc generating source to ignite a coal stove/furnace. Heating coils in proximity to the walls of the retort region are also disclosed in U.S. Pat. Nos. 3,060,868 and 4,454,827.

SUMMARY OF THE INVENTION

The present device uses electrical resistance as the heat generating source which is transmitted to an igniter element, where the igniter element is substantially planar shaped and is in direct contact with the fuel to be ignited. A pattern is formed into the planar igniter in order to efficiently facilitate the conversion of electrical energy into thermal energy. A second or bottom surface conducts the thermal energy from the burning fuel to the retort surface by direct contact. This design uses a control system to reliably facilitate the ignition of not only all solid fuels but also difficult to start fuels, such as anthracite coal. The service life of the heat igniter is extended by its planar shape and its ability to manage the thermal energy within the retort.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a plan view of the igniter element.

FIG. 2 shows a side elevation view along line 2-2 of FIG. 1 of the igniter element.

FIG. 3 shows an electrical schematic of the igniter element and its associated circuitry.

FIG. 4 shows an isometric view of the igniter element assembly.

FIG. 5 shows an isometric view of a conventional solid fuel burning grate employing the present igniter element.

FIG. 6 shows a diagrammatic depiction of an ignition process as exemplified by the device of FIG. 5.

FIG. 7 shows a diagrammatic depiction of the device of FIG. 5 except that the combustion air supply either substantially impinges the igniter element and/or combustion could occur near or on top of the igniter element itself.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a planar igniter element 100 is shown. It consists of any material that conducts electricity while being able to withstand extreme temperatures for long periods of time. A preferred material is a nickel-chromium alloy. The igniter element 100 is connected to an electric current source (not shown) by first electrical contact location 125 and second electrical contact location 130. As shown in FIG. 4 electric current flows from the electric current source via conductors 200 and 201 which are each attached to igniter element 100 at first and second electrical contact locations 125 and 130, respectively. Heating element sections 127 and 132 receives electric current through electrical contact locations 125 and 130, respectively. Heating element sections 127 and 130 are capable of generating up to 1800° F. when operated in free air. Free air is ambient air and is to distinguished from combustion air. This distinction will become clearer hereinbelow. Interface location 105 connects heating element section 127 to protection ring section 120. Correspondingly, interface location 110 connects heating element section 132 to protection ring section 121. Protection ring sections 120 and 121 conduct electrically parallel current and when connected form a complete electrical circuit. Either protection ring section 120 or 121 may be omitted from the igniter element 100 without loss of function. However, both sections are preferred in order to provide a 360° presence around the heating element sections 127 and 132 for protection from the force of the physical weight of solid fuel particles. Also, protection ring sections 120 and 121 facilitate the transition of the thermal gradient between heating element sections 127 and 132 and the external environment. The overall mechanical rigidity provided by the combined protection ring sections 120 and 121 insure reliable and continuous contact between the igniter element 100 and the retort surface (not shown) via the use of attachment devices, such as heat resilient screws, bolts, rivets or welds at the position of fastening notches 135 and 136.

FIG. 2 shows a cross section of the planar igniter element 100. The igniter element may range from 0.025 to 0.10 inch. Preferably, the thickness is approximately 0.05 inch. The surface area of the igniter element 100 may range from 1 to 4 inches in the X plane and from 2 to 5 inches in the Y plane, depending on size of the furnace. For most retort furnaces, a surface area of about 2 inches by 3 inches is adequate and is preferred.

FIG. 3 shows an electrical schematic of the igniter element 100. Power source 202 supplies electrical energy through conductors 200 and 201 to attachment locations 125 and 130, respectively, on igniter element 100. Heating element sections 127 and 132 together provide the active heating area of igniter element 100. Since protection ring sections 120 and 121 define a parallel current path, the combined electrical resistance is designed to be substantially lower than the heat generated by heating element sections 127 and 132. It is as a result of this parallel current design path that the igniter element 100 will still operate if either of the protection ring sections 120 or 121 are omitted or damaged and thus made ineffective during use.

It should be noted at this point that the design configuration of the surface of igniter element 100 shown in the appended Figures is not intended to be limiting. Other configurations are acceptable so long as they achieve the intended results. What is essential to the optimum operation of this invention is that the appropriate sections are present, those being heating element sections and at least one protective ring section surrounding the heating element sections. It is necessary, though, that there is a parallel electric circuit path to energize the heating element sections.

It has been determined that the design configuration of igniter element 100 results in the following power consumption. Heating element sections 127 and 132 together dissipate approximately 94% of the supplied electrical energy as heat while electrodes 125 and 130 and protection ring sections 120 and 121 dissipate the remainder. Power source 202 may put out either alternating or direct current at any practical voltage. Preferably, the voltage is reduced to approximately 6 V AC.

FIG. 4 is an isometric view of igniter element 100 showing some of the circuitry outlined in FIG. 3. Igniter element assembly 400 shows attachment means 404 joining conductor 200 to igniter element 100 at electrical contact location 125. Attachment means 405 joins conductor 201 to igniter element 100 at electrical contact location 130. The attachment means 404 and 405 may be electrically conductive weldments. Preferably, the weldments are formed from chrome-steel alloy pins. The method of making this connection may be achieved by combining the pins with chrome-steel alloy tubes and then compressing the tube around the pin. The location of the pin-tube-conductor compression point (not shown) is substantially within insulation sleeve 402. Insulation sleeve 402 insulates conductors 200 and 201 both thermally and electrically from the retort. Insulation sleeve 402 may be made out of any material suitable for this purpose. Preferably, it is made from ceramic or a ceramic alloy. Conductors 200 and 201 extend to the power source 202 (not shown in FIG. 4) in order to provide the electrical power necessary to run the igniter element 100.

FIG. 5 is a combustion assembly 500 is located underneath a conventional retort. Solid fuel particles 508 are transported along the planar grate by a fuel transporter means 504 toward the combustion region 512. The igniter assembly 400 is energized so that the solid fuel particles 508 are brought to their combustion temperature. The time required to achieve this is approximately from 2 to 20 minutes, depending on the type of solid fuel used. For anthracite coal as the solid fuel source, this time is preferably from about 4 to about 8 minutes. Most preferably, this time is approximately 6 minutes. The fuel transporter 504 then moves the heated fuel particles 508 into the combustion region 512 where combustion air 506 is introduced to the now heated fuel particles through combustion holes 510, thus igniting the fuel particles 508. During the time that the heated fuel particles are being moved to the combustion region 512, the igniter element 100 remains energized for approximately another 2 minutes, before current to it is stopped.

Igniter assembly 400 is attached to the bottom surface of the retort 502 and is located “upstream” of the combustion holes 510 within combustion region 512, as shown in FIGS. 5 and 6. The distance between the first row of combustion holes 510 and the igniter element 100 is approximately from 0.01 to 10 inches. Preferably the range is from about 0.1 to 1.0 inch. Most preferably, the distance is approximately 0.125 inch. Other retort configurations can place the igniter element very near to or underneath an active combustion zone (see FIG. 7).

The igniter element 100 is capable of receiving up to 500 watts of power and dissipating it over an area of from 1 to 10 square inches. In most cases, less power is needed. For example, with an igniter surface area of approximately 1 square inch, approximately 200 watts of power will reliably and repeatedly ignite rice anthracite coal, which is very difficult to ignite with conventional fuel ignition systems and materials.

Conventional retorts are constructed of electrically conductive iron or other metal materials as a barrier between the fuel and the ignition device. In igniter assembly 400, the igniter element 100 requires electrical insulation between the contact surface of heating element sections 127 and 132 and the retort. Operating the igniter assembly 400 at its optimum temperature for the type of fuel that it must ignite for only a few minutes, perhaps as little as 5 minutes in ambient air forms a metal-oxide insulating layer on the surface of igniter element 100, especially on heating element sections 127 and 132.

FIG. 6 is a side view schematic of an entire combustion assembly 600 where combustion is occurring in combustion region 612, which is not in contact, although being in close proximity, with igniter element 100. FIG. 7 is a side view schematic of an entire combustion assembly 700 where combustion 712 is occurring directly over the igniter element 100.

Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.

Claims

1. A device for igniting solid fuel in a solid particle fuel burning furnace comprising an electrically conductive igniter element connected to a retort of the furnace, wherein the igniter element has a configuration consisting of a plurality of sections.

2. The device of claim 1 wherein the igniter element is planar and lies horizontally on the surface of the retort of the furnace.

3. The device of claim 1 wherein the thickness of the igniter element ranges from about 0.025 to about 0.10 inch.

4. The device of claim 3 wherein the thickness of the igniter element is approximately 0.05 inch.

5. The device of claim 1 wherein the igniter element is divided into sections, said sections being physically connected to form interconnecting sections.

6. The device of claim 5 wherein the interconnecting sections consist of two heating element sections, two electrical contact sections, each electrical contact section being connected to one of the two heating element sections and at least one protection ring section.

7. The device of claim 1 wherein the igniter element is connected to an electrical power source.

8. The device of claim 7 wherein the electrical power source provides parallel current to the igniter element.

9. The device of claim 7 wherein the electrical power source provides either alternating or direct current.

10. The device of claim 1 wherein the igniter element is made from an electrically conductive material.

11. The device of claim 10 wherein the electrically conductive material is a nickel chromium alloy.

12. The device of claim 1 wherein the igniter element is in direct contact with the solid fuel particles are selected from the group consisting of wood, wood pellets and coal.

13. The device of claim 1 wherein the igniter element is capable of heating up to approximately 1800° F. when a sufficient amount of electricity is provided to the igniter element for a sufficient amount of time.

14. The device of claim 7 wherein the igniter element is capable of receiving up to approximately 500 watts of electrical power from the electrical power source.

15. The device of claim 14 wherein the igniter element preferably receives approximately 200 watts of power from the electrical power source.

16. The device of claim 7 wherein the power source delivers approximately 6 volts to the igniter element.

17. The device of claim 1 wherein the surface dimensions of the igniter element are approximately 1 to 4 inches in an X plane to approximately 2 to 5 inches in a Y plane.

18. The device of claim 17 wherein the surface dimensions of the igniter element are approximately 2 inches in the X plane and approximately 3 inches in the Y plane.

19. A method for igniting solid fuel particles in a retort furnace comprising the steps of: a) providing solid fuel particles from a hopper to a horizontal fuel transporter;b) urging the solid fuel particles down the horizontal fuel transporter into direct contact with an igniter element;c) providing sufficient electricity to the igniter element to heat the solid fuel particles to at least their ignition temperature; andd) introducing combustion air to the heated solid fuel particles to begin combustion of the solid fuel particles.

20. The method of claim 19 wherein the combustion of the solid fuel particles occurs directly over the igniter element.

21. The method of claim 19 wherein the fuel transporter continues to move the combusting solid fuel particles to a combustion region adjacent the igniter element.