Control system for steam generators

Claim 1

APPARATUS ARRANGED TO AUTOMATICALLY CONTROL THE HEATING OF VAPOR IN A GENERATING UNIT HAVING A CONVECTION HEATED TUBULAR VAPOR PATH AND CONVECTION HEATED TUBULAR REHEAT VAPOR PATH DISPOSED RESPECTIVELY IN DIVIDED AND SEPARATE MATERIALLY CONFINED PARALLEL GAS FLOW PATHS FROM A COMMON STRUCTURALLY DEFINED COMBUSTION ZONE, THE SUPERHEATER AND REHEATER HAVING GENERALLY SIMILAR UNCONTROLLED LOAD-TEMPERATURE CHARCTERISTIC CURVES WITH DIFFERENT DEGREES OF SLOPE, INCLUDING IN COMBINATION, APPARATUS ADAPTED TO AUTOMATICALLY REGULATE THE HEAT AVAILABILITY OF THE TOTAL HEATING GASES PASSING OVER THE SUPERHEATER AND REHEATER TO MAINTAIN SUPERHEAT AND REHEAT OUTLET TEMPERATURES AT PREDETERMINED VALUES THROUGH A LOAD RANGE BELOW A PREDETERMINED CONTROL POINT LOAD, OTHER APPARATUS ADAPTED TO AUTOMATICALLY LIMIT SUPERHEAT AND REHEAT TEMPERATURES THROUGH A LOAD RANGE ABOVE THE CONTROL POINT LOAD, SEPARATE DAMPER MEANS FOR THE PARALLEL GAS FLOW PATHS, AND CONTROL DEVICES ARRANGED TO POSITION SAID DAMPERS THUS PROPORTIONING THE TOTAL HEATING GAS FLOW BETWEEN THE PARALLEL PATHS THROUGH AN INCREASING LOAD OVER THE CONTROLLABLE LOAD RANGE BY MOVING ONE OF SAID DAMPERS ONLY THUS VARIABLY RESTRICTING GAS FLOW OVER ONE PATH WHILE ALLOWING UNRESTRICTED GAS FLOW OVER THE OTHER PATH THROUGH A LOWER PORTION OF THE CONTROLLABLE LOAD RANGE AND THEN MOVING THE OTHR DAMPER ONLY THUS VARIABLY RESTRICTING GAS FLOW OVER SAID OTHER PATH WHILE ALLOWING UNRESTRICTED GAS FLOW OVER THER SAID ONE PATH THROUGH THE REMAINING UPPER PORTION OF THE CONTROLLABLE LOAD RANGE, THE CONTROL DEVICES SEQUENTIALLY RESPONSIVE TO LOAD DETERMINATION.