Multi-pressure waste heat boiler

Claim 1

A BOILER FOR GENERATING STEAM AT A PLURALITY OF PRESSURE LEVELS COMPRISING: A PLURALITY OF SUBSTANTIALLY RECTANGULAR DUCT SECTIONS VERTICALLY STACKED ON TOP OF ONE ANOTHER, EACH OF SAID DUCT SECTION HAVING SPACED PARALLEL END WALLS AND SPACED PARALLEL SIDE WALLS AND HAVING A PLURALITY OF HORIZONTAL, VERTICALLY SPACED ROWS OF FINNED TUBES, ALL OF SUBSTANTIALLY THE SAME SIZE AND CHARACTERISTICS SUPPORTED BY AND EXTENDING PARALLEL TO SAID SIDE WALLS, EACH OF SAID DUCT SECTIONS HAVING INLET AND OUTLET HEADERS DISPOSED ON THE END WALLS AND CONNECTED TO ALL OF THE FINNED TUBES IN AT LEAST ONE OF SAID ROWS WITHIN THE DUCT SECTION, AT LEAST TWO OF SAID DUCT SECTIONS COMPRISING EVAPORATING HEAT EXCHANGERS WITH THE TUBE ROWS CONNECTED IN PARALLEL BETWEEN INLET AND OUTLET HEADERS DISPOSED ON OPPOSITE END WALLS, OTHER OF SAID DUCT SECTIONS COMPRISING ECONOMIZER HEAT EXCHANGERS WITH THE TUBE ROWS CONNECTED IN SERIES FLOW RELATION, AT LEAST ONE STEAM DRUM DISPOSED ADJACENT THE OUTLET HEADER OF EACH OF THE EVAPORATING HEAT EXCHANGERS, AND AT LEAST ONE RECIRCULATING PUMP FOR EACH EVAPORATOR AND ASSOCIATED STEAM DRUM ARRANGED TO RECIRCULATE LIQUID THERETHROUGH IN A CLOSED STEAM GENERATION LOOP AT A RATE SUBSTANTIALLY IN EXCESS OF THE EVAPORATION RATE WITHIN THE EVAPORATOR TUBES, EACH OF SAID EVAPORATING HEAT EXCHANGER SECTIONS OPERATING AT A DIFFERENT PRESSURE LEVEL.