Vapor generator

Claim 1

A STEAM GENERATOR COMPRISING A FRONT WALL, A REAR WALL, AND A PAIR OF OPPOSITELY DISPOSED SIDE WALLS ARRANGED TO FORM A SUBSTANTIALLY RECTANGULAR SETTING, AN UPRIGHT PARTITION WALL EXTENDING TRANSVERSELY OF SAID SETTING AND DIVIDING SAID SETTING INTO A FURNACE AND A VAPOR GENERATING SECTION EXTENDING ACROSS THE ENTIRE WIDTH OF SAID SETTING, MEANS DIVIDING SAID SECTION INTO A PAIR OF PARALLEL FLOW GAS PASSES ARRANGED ON OPPOSITE SIDES OF SAID SECTION AND A COMMON GAS PASS DISPOSED INTERMEDIATE AND OPENING TO SAID PARALLEL GAS PASSES, THE OPPOSITE LATERAL ENDS OF SAID PARTITION WALL BEING SPACED FROM THEIR RESPECTIVE ADJACENT SIDE WALLS TO FORM THEREBETWEEN A PAIR OF HEATING GAS INLETS LEADING FROM SAID FURNACE TO SAID PAIR OF PARALLEL GAS PASSES, AN UPPER HORIZONTAL STEAM AND WATER DRUM EXTENDING ACROSS THE ENTIRE WIDTH OF SAID SETTING AND OVERLYING SAID VAPOR GENERATING SECTION AND HAVING OPPOSITE END PORTIONS AND A CENTRAL PORTION INTERMEDIATE SAID END PORTIONS, A LOWER HORIZONTAL WATER DRUM EXTENDING TRANSVERSELY OF SAID SETTING AND UNDERLYING SAID VAPOR GENERATING SECTION, A BANK OF STEAM GENERATING TUBES DISPOSED IN EACH OF SAID PARALLEL GAS PASSES AND AT LEAST A MAJOR PORTION OF WHICH EXTEND BETWEEN AND CONNECT INTO SAID UPPER AND LOWER DRUMS ALONG THE END PORTIONS THEREOF, AND A BANK OF DOWNCOMER TUBES DISPOSED IN SAID COMMON GAS PASS AND EXTENDING BETWEEN AND CONNECTED SUBSTANTIALLY ONLY INTO THE LONGITUDINALLY CENTRAL PORTIONS OF SAID UPPER AND LOWER DRUMS, SAID UPPER DRUM COOPERATING WITH SAID STEAM GENERATING TUBES AND SAID DOWNCOMER TUBES TO EFFECT THE FLOW OF WATER FROM THE END PORTIONS TO THE CENTRAL PORTION OF SAID UPPER DRUM TO MINIMIZE WATER LEVEL GRADIENT THEREIN.