GB760847A - Improvements in or relating to once-through vapour generating and superheating units - Google Patents

Abstract

760,847. Forced-flow steam boilers. DURRWERKE AKT.-GES. June 3, 1955 [June 3, 1954], No. 16482/54. Class 123(2) A forced-flow; once-through steam boiler has a preheater 5, a vaporizer 6, and primary and secondary superheaters 7, 8 serially connected between an inlet header 4 supplied with water from a pump 1 and an outlet header 9 from which a line 10 having a stop valve 11 conveys superheated steam to a main 12. A starting pipe 13 branches from pipe 10 between header 9 and valve 11, the pipe having a valve 14 which is opened when starting up, valve 11 being closed, so that the steam generated escapes through pipe 13 until the required degree of superheat is reached, when valve 14 is closed and valve 11 opened. Pipe 13 is of large diameter to prevent pressure build-up during the starting period. A blowing-off pipe 15, of smaller diameter than pipe 13 and provided with a valve 16, is connected to header 9, alternatively, to a header 17 disposed between superheaters 7 and 8. During shutting-down, the boiler heating surfaces, which might otherwise become overheated due to radiation from the hot brickwork, are cooled by feeding water slowly into the unit until eventually it flows from pipe 15, the flow rate being determined by the setting of valve 16 which, being of small diameter, gives a sensitive control so that pressure build-up due to steam generation can be relieved whilst preventing contact between highly heated tubes and the water.