Patent Publication Number: US-2006016446-A1

Title: Gas stove with thermoelectric generator

Description:
BACKGROUND OF INVENTION  
      Gas stoves have been used extensively around the world for indoor and outdoor cooking. However, there are many places, where gas cooking is common, without convenient sources of electricity. Gas stoves convert gaseous fuels into thermal energy through gas burners. To utilize waste thermal energy of the gas burners for electricity generation will provide convenience for people&#39;s daily life as well as energy savings. Electricity generated by the gas burner can be used to power electric fans, lights, televisions, battery chargers etc.  
      Major components of a typical gas burner include a gas supply head, a burner base, and a burner cap. The gas supply head provides gaseous fuel, such as natural gas or propane to the burner base. The top surface of the burner base and the bottom surface of the burner cap form a mixing chamber for proper fuel/air mixing. There are slots or holes around the burner head for the formation of flame jets.  
      Thermoelectric modules have been commercially available for about 30 years. One of such modules is described in U.S. Pat. No. 5,892,656. It has dimensions of 75 mm×75 mm×5 mm and produces 14 Watts at operating temperature difference of 185 C.  
      U.S. Pat. No. 6,588,419 describes a fireplace appliance with two thermoelectric modules. The thermoelectric modules receive heat energy from the fireplace. An electric fan, powered by the thermoelectric modules, is used to cool heat sink. U.S. Pat. No. 6,053,165 describes a stovepipe thermoelectric generator. Two thermoelectric modules are sandwiched between the stove exhaust pipe and the heat sink.  
      Both systems mentioned above consume up to 50% of power generated by the thermoelectric modules to cool the heat sink. Therefore, there is a need for a more efficient thermoelectric generator system. The present invention provides a gas burner thermoelectric generator with an internal gas cooling mechanism. This internal gas cooling mechanism eliminates the cooling fans and the heat sink units. Therefore, it significantly improves the overall system efficiency of the thermoelectric generator.  
     SUMMARY OF INVENTION  
      The present invention enables a gas burner to generate electricity with waste thermal energy. The invented gas burner can be installed on gas stoves, such as indoor cooking appliances or outdoor gas grills. At least one thermoelectric unit is installed underneath the burner cap of the gas burner. Gas flame at the edge of the burner cap creates heat source (hot side) for the thermoelectric unit. A gas-mixing chamber underneath the thermoelectric unit functions as heat sink (cold side) for the thermoelectric unit. An insulation plate is inserted in between the thermoelectric unit and the burner cap to control the hot side temperature. The thermoelectric unit generates electricity while the gas burner is in use and the flame heats up the burner cap. The thermoelectric unit connects to an electric circuit and provides electricity to power devices such as electric fans, lights, TVs, battery chargers etc. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  shows operating principle of the thermoelectric modules.  
       FIG. 2A and 2B  show a gas burner with preferred embodiments of the present invention for indoor gas stoves.  
       FIG. 3A and 3B  show other embodiments of the present invention for outdoor gas grills.  
       FIG. 4A and 4B  show a gas burner with preferred embodiments of the present invention for portable gas stoves.  
       FIG. 5A, 5B , and  5 C are cross-section views of thermoelectric modules.  
       FIG. 6  shows electric power output of gas stoves with thermoelectric generators. 
    
    
     DETAILED DESCRIPTION  
       FIG. 1  is a schematic representation of operating principle associated with thermoelectric module  10  in accordance with the present invention. Electrical circuit  13  is a typical circuit associated with thermoelectric elements or thermocouples to convert heat energy into electrical energy. Electrical circuit  13  generally includes two dissimilar or similar materials differing in the type of majority current carrier such as n-type thermoelectric element  21  and p-type thermoelectric element  18 . Thermoelectric elements  21  and  18  are typically arranged in an alternating n-type element to p-type element serpentine configuration. In almost all thermoelectric devices, semiconductor materials with these characteristics are connected electrically in series and thermally in parallel. N-type semiconductor materials have more electrons than necessary to complete a perfect molecular lattice structure. P-type semiconductor materials have fewer electrons than necessary to complete a lattice structure. The unbalance of electrons between the n-type semiconductor material and the p-type semiconductor material, coupled with lattice vibrations, transports thermal energy. Bonding joints  11 ,  16 ,  20  are attached to electrical interconnects  12  and  17  and to fix thermoelectric elements  18  and  21  between heat source  19  and heat sink  15 . Electrical power will be generated if there are temperature differences between heat source  19  and heat sink  15 .  
       FIG. 2A and 2B  disclose a gas stove with thermoelectric power generator  130  according to present invention. The power generation gas stove  130  includes a gas burner  100  with thermoelectric power generation module  109  installed underneath burner cap  108 . Fuel gas enters the gas burner through supply connection  120  and orifice  101  to mix with air through ports  119 . The orifice  101  is properly designed according to thermal content of the fuel. Burner cap  108  and burner base  106  form a mixing chamber  112 . The mixing chamber  112  allows further mixing of fuel and air. Thermoelectric module  109  is mounted underneath the burner cap  108  with thermal insulator  111 . Thermal insulator  111  should be properly designed according to the operating temperature range of thermal electric module  109 . The burner base  106  was designed to have outward slots or holes  113 . Igniter  107  can be used to ignite the fuel/air mixture to form sustainable flame jets  114 . The burner cap, heated up by flame jets  114 , will function as heat sources for thermoelectric modules  109 . Another side of the thermoelectric modules  109  faces the fuel/air mixtures of the mixing chamber  112 . The fuel/air mixture, which maintains almost constant temperature, functions as heat sinks for thermoelectric module  109  to create temperature difference across the thermoelectric modules for electricity generation. Thermoelectric module  109  can be the conventional Bismuth Telluride based thermoelectric module or nano-composite semiconductors, such as, SiGe/Si composite, with higher thermal conversion efficiency. Typically, the output voltage of thermoelectric modules is less than 12V, and a DC/DC voltage converter is needed to increase the output voltage to a proper range. Thermoelectric module  109  connects to a DC/DC converter  117  through electric outlets  118  and connecting wires  104 . Electricity generated by thermoelectric modules  109  will power electric devices  115 ,  131 ,  136 , battery charger  116  etc.  
      A thermoelectric gas burner for portable grills is shown in  FIG. 3A  and  FIG. 3B .  FIG. 3A  shows gas burner  200  with thermoelectric modules  211  installed inside burner head  210 . The burner head  210  is installed on top of burner base  213  with igniter  206 . A conical shaped windshield  204  supports the burner base  213  for outdoor usages. Fuel inlet  219  connects to gas tank  223  as illustrated in  FIG. 3B . An orifice  201  is designed according to heating content of the fuels.  
      The mixture supply tube  203  has air inlet holes  202  to allow proper fuel/air mixing. The burner head  210  has a mixture chamber  207  and fuel/air discharge holes for proper flame jet  212  distributions. While the grill is in use, the top surface  208  of the burner head  210  will be heated by the flame jets  212  and functions as heat source for the thermoelectric modules  211 . The fuel/air mixture in the mixing chamber  207  functions as heat sink to carry the heat away. The thermoelectric modules  211  have two outlets  209  and connecting wires  217  connected to a DC/DC converter  214 . Electric power generated by thermoelectric modules  211  can be used for to power electric devices  215 , such as lights  221  or battery charger  222 .  
       FIG. 4A and 4B  show a gas stove with thermoelectric generators for camping and other outdoor usages. Gas burner  300  has burner head  306 , in which, thermoelectric modules  308  are installed underneath the top surface of the burner head  306 . The enclosed burner head  306  forms a fuel/air mixture chamber  305 , which functions as a heat sink for thermoelectric modules  308 . Fuel, from fuel tank  320 , through inlet port  316 , orifice  315 , and valve  314 , flows to mixing chamber  305 . Windshield  303  is designed for outdoor cooking. Two electric outlets  309  connect the thermoelectric modules  308  to DC/DC converter  311  through wires  310 . DC/DC converter  311  converts the power generated by the thermoelectric modules to proper voltage for powering electric devices  312  and  313 .  
      The thermoelectric module should be designed for maximizing the electric power generation. Examples of thermoelectric module layout are shown in  FIG. 5A, 5B , and  5 C.  FIG. 5A  shows a square thermoelectric module  403  mounted on a round burner cap  404 .  FIG. 5B  shows an alternate layout of thermoelectric modules  402  mounted on a round burner cap  401 . An oval shaped burner cap with square shaped thermoelectric modules is shown in  FIG. 5C .  
      Power outputs of typical gas burner thermoelectric generators are shown in  FIG. 6 . Line  601  shows electrical power output by a commercially available thermoelectric module mounted on a gas burner with a diameter of 100 mm. Line  602  shows a simulated power output of the same size gas burner with nano composite thermoelectric modules.  
      Although particular systems are disclosed, it will be apparent to persons skilled in the art that modifications may be made without departing from the scope of the invention. All such modifications as well as equivalents are thereof to be included within the scope of the following claims.