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:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims one or more inventions which were disclosed in Provisional Application No. 61/104,880, filed Oct. 13, 2008, entitled “IGNITION ELEMENT AND METHOD FOR KINDLING SOLID FUEL ”. The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    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 
       [0003]    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. 
         [0004]    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. 
         [0005]    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. 
         [0006]    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 
       [0007]    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 
         [0008]      FIG. 1  shows a plan view of the igniter element. 
           [0009]      FIG. 2  shows a side elevation view along line  2 - 2  of  FIG. 1  of the igniter element. 
           [0010]      FIG. 3  shows an electrical schematic of the igniter element and its associated circuitry. 
           [0011]      FIG. 4  shows an isometric view of the igniter element assembly. 
           [0012]      FIG. 5  shows an isometric view of a conventional solid fuel burning grate employing the present igniter element. 
           [0013]      FIG. 6  shows a diagrammatic depiction of an ignition process as exemplified by the device of  FIG. 5 . 
           [0014]      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 
       [0015]    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 . 
         [0016]      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. 
         [0017]      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. 
         [0018]    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. 
         [0019]    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. 
         [0020]      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 . 
         [0021]      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. 
         [0022]    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 ). 
         [0023]    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. 
         [0024]    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 . 
         [0025]      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 . 
         [0026]    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.