Condensing furnace with submerged combustion

A recuperative furnace comprising:

• means for providing combustion products;
• means for holding a liquid and for directing said combustion products into said liquid wherein said combustion products bubble up through said liquid thereby raising the dew point of said combustion products;
• a metal fin and tube heat exchanger comprising means for extracting sensible heat and heat of condensation from said dew point elevated combustion products, said heat exchanger having an upwardly directed flow path for said dew point elevated combustion products wherein condensate from said condensation flows downwardly counter to the flow of said dew point elevated combustion products in said heat exchanger and into said holding means, said extracting means comprising water passing through said tube and being heated by said combustion products passing over fins of said heat exchanger;
• and
• a controller for activating said combustion products providing means and said combustion products directing means, said controller comprising means for continuing to activate said combustion products directing means for a predetermined time period after said combustion products providing means is deactivated.

A recuperative furnace comprising:

• a burner for providing combustion products;
• a fuel valve for providing a gaseous fuel to said burner;
• a metal fin and tube recuperative heat exchanger having an upward flow path for combustion products across metal fins of said heat exchanger;
• means for circulating water through the tube of said recuperative heat exchanger to extract sensible heat and heat of condensation from combustion products;
• means for raising the dew point of combustion products from said burner before introduction into said heat exchanger, said dew point raising means comprising a reservoir for holding a liquid and for receiving condensate dripping from said heat exchanger;
• said dew point raising means further comprising a partition having a lower portion submerged in said liquid wherein said reservoir is divided into first and second chambers;
• said dew point raising means further comprising means for providing a positive pressure differential between said first and second chambers wherein said combustion products from said burner pass under said partition and bubble up through said liquid in said second chamber;
• and
• a controller for activating said fuel valve and said pressure differential providing means, said controller comprising means for continuing to activate said pressure differential providing means for a predetermined time period after said fuel valve is deactivated wherein air is directed through said liquid and into said heat exchanger during said predetermined time period.

A method of heating water passing through tubes of a metal fin and tube heat exchanger, comprising the steps of:

• burning a gaseous fuel to provide combustion products;
• providing a reservoir holding a liquid
• providing a partition having a lower portion submerged in said liquid to separate said reservoir into first and second chambers;
• introducing said combustion products into said first chamber;
• providing a pressure differential between said first and second chambers thereby lowering the level of said liquid in said first chamber so that said combustion products flow underneath a portion of said partition and bubble up through said liquid in said second chamber to raise the dew point of said combustion products;
• directing said dew point elevated combustion products upwardly across the fins of said fin and tube heat exchanger to transfer sensible heat and heat of condensation from said dew point elevated combustion products to said water in a tube of said heat exchanger so that condensate flows downwardly in counter flow to said dew point elevated combustion products and maintains said fins in a substantially continuous wet state, said condensate dripping from said heat exchanger into said reservoir;
• and
• continuing to provide said pressure differential subsequent to terminating burning of gaseous fuel.