Patent GB-857637-A (GB)
Title: Improvements in means for the protection of tubulous vapour superheaters from overheating
IPC: F22G5/00
Filed: 1959-04-21
Abstract: 857,637. Steam superheaters; raising steam in boilers. BABCOCK & WILCOX Ltd. April 21, 1959 [April 26, 1958], No. 13533/59. Classes 123(2) and 123(3) In a return tube steam boiler 1 having a superheater 6 located in the rear gas turning space in a position which is below the water level of the boiler, the superheater tubes are flooded to protect them whilst the boiler is warmed up, during which period the boiler is fired uninterruptedly and automatic provision is made for the cessation of firing once normal working has commenced if the steam flow through the superheater falls below a safe value. The steam space 13 and water space 25 of the boiler are respectively connected to the inlet header 7 of the superheater by a pipe 12 containing a attemperating spray nozzle 32 and by a pipe 24 provided with a valve 26 and a valved drain 27. The superheater outlet header 8 is connected to the boiler stop valve 20 by a pipe 18 containing a flow measuring device 19 and from which branches a steam blow-off pipe 42 controlled by a valve 41. The outlet header is also connected to the steam space 13 by a pipe 15 containing a flow measuring device 17 and a stop valve 16 controlled by the two flow measuring devices. The boiler is fired by a burner 3 having a valve 45 automatically controlled by the devices 17, 19 so that if the respective flows in the pipes 15, 18 are at the same time less than predetermined values the burner is shut off. The fuel supply to the burner is controlled by a valve 40 which is adjusted by a motor 39 in response to signals from a temperature sensing device 37 in the outlet header 8, the signals from the device 37 also controlling a valve 34 in the supply pipe 33 to the attemperator spray nozzle 32. A second temperature sensing device 44 in the outlet header controls the valve 41 in the steam blow-off pipe 42. During normal operation the steam flow through the device 19 maintains the valve 16 shut. If the steam temperature in the header 8 falls to too low a value the device 37 opens the fuel valve 40 further. If the steam temperature rises above the desired value the device 37 is effective first further to close the valve 40 and then to open the spray attemperator valve. If the high temperature persists the device 44 opens the valve 41 allowing steam to blow-off until the increased flow in the superheater reduces the temperature to the desired value. During starting up the superheater is flooded by opening the valve 26, the superheater being vented through a valve 31. Since there is no flow through the device 19 the valve 16 is open and steam generated in the superheater escapes along the pipe 15. A time delay switch renders the device 17 ineffective for the first ten minutes of firing when there is no steam flow in the pipe 15 so that it will not shut off the valve 45. When the boiler reaches working temperature the superheater is drained by opening the valve 27 and closing the valve 26, the device 17 again being rendered inoperative during this period. Simultaneously the stop valve 20 is opened the flew through. the device 19 effecting closure of the valve 16 and normal operation commences.