Device for low load operation of once-through boilers

Claim 1

IN A FORCED FLOW ONCE-THROUGH TYPE STEAM BOILER HAVING SERIALLY CONNECTED STEAM GENERATING AND SUPERHEATING SECTIONS WITH THE TRANSITION ZONE BEING LOCATED BETWEEN SAID SECTIONS AT NORMAL OPERATING LOADS, MEANS FOR SUPPLYING FEED WATER TO SAID STEAM BOILER, MEANS FOR ADJUSTING THE LOCATION OF SAID TRANSITION ZONE TO ALTER THE EFFECTIVE SUPERHEATING SURFACE IN CORRESPONDENCE WITH A SELECTED LOAD ON SAID BOILER COMPRISING AT LEAST TWO CUTOFF VALVES, ONE OF SAID VALVES BEING POSITIONED IN SAID STEAM GENERATING SECTION AND THE OTHER BEING POSITIONED IN SAID STEAM SUPERHEATING SECTION, A FLASH DRUM HAVING A STEAM SPACE AND A WATER SPACE AND BEING MAINTAINED AT A PRESSURE SUBSTANTIALLY BELOW THE PRESSURE IN SAID STEAM GENERATING SECTION, CONDUITS ASSOCIATED WITH EACH OF SAID CUT-OFF VALVES WITH A FIRST CONDUIT CONNECTING THE SECTION IMMEDIATELY UPSTREAM OF EACH OF SAID CUT-OFF VALVES TO SAID FLASH DRUM AND EACH ARRANGED TO CONVEY THE ENTIRE DISCHARGE FROM SAID SECTION TO SAID FLASH DRUM WHEN THE CORRESPONDING CUT-OFF VALVE IS CLOSED, A PRESSURE REDUCING VALVE IN EACH OF SAID FIRST CONDUITS ARRANGED TO CAUSE WATER DISCHARGED FROM THE CORRESPONDING SECTION TO FLASH INTO STEAM, AND VALVE CONTROLLED SECOND CONDUITS ASSOCIATED WITH EACH OF SAID CUT-OFF VALVES AND CONNECTING THE STEAM SPACE OF SAID FLASH DRUM TO SAID SECTIONS IMMEDIATELY DOWNSTREAM OF THE CORRESPONDING CUT-OFF VALVE FOR SUPPLYING THE FLASHED STEAM TO SAID SECTION TO SUPERHEAT SAID FLASHED STEAM.