Auto-igniter for biomass furnace

Abstract

A biomass furnace ( 12 ) includes an auto-ignition system ( 28 ) for automatically resuming combustion of a biomass fuel ( 16 ) in response to sensed conditions. The auto-ignition system ( 28 ) raises the temperature of biomass fuel ( 16 ) in the combustion chamber ( 14 ), in the absence of flame or spark, by pumping superheated air into the combustion chamber ( 14 ) causing the fuel ( 16 ) to spontaneously combust. An auxiliary heat source ( 34 ) is located in a plenum ( 30 ) leading to the combustion chamber ( 14 ). A fan ( 32 ) forcibly moves air through the plenum ( 30 ), around the auxiliary heat source ( 34 ) and then into the combustion chamber ( 14 ) to initiate combustion in the absence of flame.

1 . An automatic ignition system for a biomass-fueled furnace, said system comprising:
 a plenum;   a fan operatively associated with said plenum for forcibly moving air through said plenum toward a biomass fuel combustion chamber;   an auxiliary heat source configured to heat the air moved through said plenum to an elevated auto-ignition temperature;   at least one temperature sensor; and   a control module operatively connected to said fan, temperature sensor and auxiliary heat source, said control module configured to automatically activate said auxiliary heat source in response to the temperature at said temperature sensor falling below a preset limit.   
   
   
       2 . The ignition system of  claim 1  wherein said auxiliary heat source includes a heating element disposed within said plenum. 
   
   
       3 . The ignition system of  claim 1  wherein said auxiliary heat source includes an electric resistance heating element disposed within said plenum. 
   
   
       4 . The ignition system of  claim 1  wherein said at least one temperature sensor comprises a thermal fluid sensor, and further including a combustion temperature sensor associated with the biomass fuel combustion chamber and said control module whereby said control module automatically de-activates said auxiliary heat source in response to the temperature at said combustion temperature sensor rising above a preset limit. 
   
   
       5 . A biomass furnace of the type for heating a thermal fluid in response to the combustion of a biomass fuel, said furnace comprising:
 a combustion chamber configured to receive biomass fuel in incremental quantities and combust the biomass fuel therein to produce hot combustion gases;   an exhaust flue for conducting the hot combustion gases away from said combustion chamber;   a heat exchanger proximate at least one of said combustion chamber and said flue for channeling a thermal fluid to absorb heat energy from the combustion gases;   a plenum leading to said combustion chamber;   a fan operatively associated with said plenum for forcibly moving air through said plenum toward the biomass fuel contained in said combustion chamber;   an auxiliary heat source configured to heat the air moved through said plenum to an elevated auto-ignition temperature;   at least one temperature sensor; and   a control module operatively connected to said fan, temperature sensor and auxiliary heat source, said control module configured to automatically activate said auxiliary heat source in response to the temperature at said temperature sensor falling below a preset limit.   
   
   
       6 . The furnace of  claim 5  wherein said auxiliary heat source includes a heating element disposed within said plenum. 
   
   
       7 . The furnace of  claim 5  wherein said auxiliary heat source includes an electric resistance heating element disposed within said plenum. 
   
   
       8 . The furnace of  claim 5  wherein said at least one temperature sensor comprises a thermal fluid sensor, and further including a combustion temperature sensor associated with said combustion chamber and said control module whereby said control module automatically de-activates said auxiliary heat source in response to the temperature at said combustion temperature sensor rising above a preset limit. 
   
   
       9 . The furnace of  claim 5  wherein said heat exchanger comprises a water transmitting pipe. 
   
   
       10 . The furnace of  claim 5  wherein said heat exchanger comprises an air transmitting duct. 
   
   
       11 . A method for igniting a solid biomass fuel in a furnace of the type for heating an intermediate thermal fluid in response to combustion of the biomass fuel, said method comprising the steps of:
 providing a combustion chamber;   holding a quantity of solid biomass fuel in the combustion chamber in the absence of flame, the solid biomass fuel having a characteristic auto-ignition temperature;   heating air to a temperature above the auto-ignition temperature of the biomass fuel in the combustion chamber; and   injecting the heated air into the combustion chamber so that at least a portion of the solid biomass fuel in the combustion chamber spontaneously combusts.   
   
   
       12 . The method of  claim 11 , wherein said step of heating air includes passing air through an electric resistance heating element. 
   
   
       13 . The method of  claim 11 , wherein said step of injecting the heated includes conducting air through a plenum to the combustion chamber. 
   
   
       14 . A method for controlling the ignition of a solid biomass fuel in a biomass furnace, said method comprising the steps of:
 providing a furnace having a combustion chamber configured to receive biomass fuel in incremental quantities, the solid biomass fuel having a characteristic auto-ignition temperature;   combusting a quantity of the solid biomass fuel in the combustion chamber to produce hot combustion gases;   channeling a thermal fluid through the hot combustion gases to absorb heat energy therefrom and transport the heat energy to a remote space to be heated;   monitoring the temperature of the thermal fluid or the space to be heated to determine a control temperature;   terminating said combusting step when the control temperature reaches a predefined upper limit;   automatically resuming said combusting step when the control temperature reaches a predefined lower limit;   said automatically resuming step including raising the temperature of the solid biomass fuel above its auto-ignition temperature in the absence of flame.   
   
   
       15 . The method of  claim 14 , wherein said terminating step includes measuring the temperature of combustion gases at a point downstream of the combustion chamber and automatically initiating said terminating step in response to the combustion gas temperature reaching a pre-set limit. 
   
   
       16 . The method of  claim 14 , wherein said step of raising the temperature includes heating air to a temperature above the auto-ignition temperature of the biomass fuel and injecting the heated air into the combustion chamber so that at least a portion of the solid biomass fuel in the combustion chamber spontaneously combusts. 
   
   
       17 . The method of  claim 16 , wherein said step of heating air includes passing air around an electric resistance heating element. 
   
   
       18 . The method of  claim 17  wherein said step of injecting heated air into the combustion chamber includes routing air through a plenum surrounding the heating element. 
   
   
       19 . The method of  claim 14  wherein said step of channeling a thermal fluid includes transmitting liquid water through a pipe. 
   
   
       20 . The method of  claim 14  wherein said step of channeling a thermal fluid includes transmitting air through a duct.