Patent GB-987365-A (GB)
Title: Improvements in and relating to forced flow steam generators
IPC: F01K3/22
Filed: 1963-08-12
Abstract: 987,365. Forced flow steam boilers. SULZER BRO. Ltd. Aug. 12, 1963 [Aug. 22, 1962], No. 31790/63. Heading F4A. In a method of starting a forced flow, once through boiler having a radiantly heated evaporator section and a superheater section subjected to relatively intense heating, steam is made available very quickly for cooling the superheater by filling the evaporator and shutting off the superheater therefrom by a valve, circulating the water around the evaporator with a low rate of firing until a preset pressure is reached therein, then withdrawing and partially expanding working medium from the evaporator, passing the steam to the superheater, starting the feed supply and increasing the firing rate and, when the evaporator and superheater pressures are equal, opening the valve to allow the working medium to flow directly to the superheater. In the form shown, the generator has an economizer 11, a radiantly-heated evaporator 2, convection superheaters 8, 11, the former being heated partly by radiation, and a reheater 9. The evaporator is connected to the superheater 8 by a pipe 13 in which is a shut-off valve 14 and is supplied with water from the economizer 11 through a pipe 12 containing a shut-off valve 18, a circulating pump 16 and non-return valve 17, the pipes 12, 13 being connected by a pipe 15. A pipe 19 by-passes the valve 14 and contains a pressure-actuated throttle valve 20 and separator 21. The generator supplies steam to a turbine 36, 39 through a main 35 containing a speed-regulated throttle 38, a turbine by-pass pipe 47 containing a pressure-responsive valve 48 branching off before the valve 38 to convey start-up steam to the turbine condenser 28. In starting-up, the valve 14 is closed and the valve 48 opened and the economizer and evaporator are filled with water by running the main feed pump 44 to pump water through the system and the separator and back to the feed tank 32. The valve 20 is closed and the pump 16 started, the firing being started at the lowest possible rate. The circulating water is heated and when its pressure reaches a preset value the valve 20 opens. The working medium expands through the valve and into the separator where steam is separated and flows to the superheaters 8, 10 to cool them. Steam flow through the superheaters is controlled by the setting of a valve 34 in a pipe 23 connecting the pipes 19, 47, the valve being adjusted according to temperature in the steam main 35. Steam is dumped through the line 47 whilst the water accumulating in the separator flows through pipes 22, 22<SP>1</SP> containing a level controlling valve 24 to the feed tank 32. When the steam in the main 35 has sufficient temperature and pressure, the valve 38 is opened to warm the turbines. The feed pump 44 is then started and the firing rate increased and when the pressures at each side of the valve 14 are equal, this valve is opened, the boiler then being brought up to operating values. In a modification the steam branch pipe 23 is omitted and steam main temperature signals exert an overriding control on the valve 24 to control superheater start-up steam flow. In a further modification, the circulating pump suction is connected to the evaporator outlet whilst the setting of valve 14 is controlled in response to the pressure difference thereacross.