Black liquor chemical recovery unit utilizing gas recirculation

Claim 1

IN A SYSTEM FOR RECOVERING CHEMICALS AND GENERATING AND SUPERHEATING STEAM FROM THE COMBUSTION OF BLACK LIQUOR, THE COMBINATION OF A SMELTER FURNACE DEFINED BY GENERALLY VERTICAL WALLS, MEANS FOR SUPLYING BLACK LIQUOR INTO THE FURNACE INTERIOR AND FOR BURNING THE SAME IN THE LOWER PORTION THEREOF FOR PRODUCING COMBUSTION GASES LADEN WITH CHEMICAL ASH PARTICLES, A SUPER HEATER HEAT EXCHANGER POSITIONED WITHIN THE UPPER PORTION OF THE FURNACE, A GAS PASS CONNECTED TO THE UPPER PORTION OF THE FURNACE, SAID GAS PASS COMPRISED OF WALLS FORMING A TORTUOUS GAS PASSAGE MADE UP OF A PLURALITY OF UPWARDLY AND DOWNWARDLY EXTENDING INTERCONNECTED PASSAGES, THE WALLS OF THE GAS PASSAGE BEING LINED WITH FLUID COOLED TUBES, A FIRST PORTION OF THE GAS PASSAGE BEING CONNECTED TO THE UPPER PORTION OF THE FURNACE, SAID FIRST PORTION BEING AN OPEN GAS PASS FREE OF ANY HEAT EXCHANGE MEMBERS OTHER THAN THE FLUID COOLED TUBES LINING THE WALLS THEREOF, A SECOND PORTION OF THE GAS PASSAGE BEING DOWNSTREAM OF THE FIRST PORTION AND IN SERIES FLOW RELATIONSHIP THEREWITH, A PLURALITY OF STEAM GENERATING TUBES POSITIONED WITHIN THE SECOND PORTION OF THE GAS PASSAGE, A STACK OPEN TO ATMOSPHERE AT ONE END AND CONNECTED TO THE SECOND PORTION OF THE GAS PASSAGE AT THE OTHER END, A FAN POSITIONED WITHIN THE STACK, FIRST DAMPER MEANS POSITIONED WITHIN THE STACK DOWNSTREAM OF THE FAN, A DUCT HAVING AN INLET END AND AN OUTLET END, THE INLET END BEING CONNECTED TO THE STACK UPSTREAM OF THE FIRST DAMPER MEANS BUT DOWNSTREAM OF THE FAN, WITH THE OUTLET END OF THE DUCT CONNECTED TO THE FIRST PORTION OF THE GAS PASSAGE, SECOND DAMPER MEANS POSITIONED IN SAID DUCT, TEMPERATURE SENSING MEANS POSITIONED IN SAID FIRST PORTION OF THE GAS PASSAGE, SAID TEMPERATURE SENSING MEANS BEING OPERATIVELY CONNECTED TO THE FIRST AND SECOND DAMPER MEANS SO AS TO MOVE THE FIRST DAMPER MEANS IN A CLOSING DIRECTION WHEN AN INCREASE IN TEMPERATURE IS SENSED WHILE MOVING THE SECOND DAMPER MEANS IN AN OPENING DIRECTION, AND MOVING THE FIRST DAMPER MEANS IN AN OPENING DIRECTIONWHEN A DECREASE INTEMPERATURE IS SENSED WHILE MOVING THE SECOND DAMPER MEANS IN A CLOSING DIRECTION, TO THEREBY ALLOW THE ATTAINEMNT OF HIGHER SUPERHEAT TEMPERATURE WHILE STILL PREVENTING UNDUE SLAGGING OF THE STEAM GENERATING TUBES POSITIONED WITHIN THE SECOND PORTION OF THE GAS PASSAGE.