GB1029695A - A once-through steam generating unit - Google Patents

Abstract

1,029,695. Raising steam in once-through boilers. A. S. GRIMES, R. S. HUNTER, and J. A. TILLINGHAST. March 6, 1964 [March 7, 1963], No. 9611/64. Heading F4A. In a forced flow, once through boiler means are provided for use during the starting operation for reducing the pressure of the working fluid to a value such that it may be discharged into the condenser of the turbine supplied by the boiler, the means consisting of at least one elongated tube wherein the pressure reduction is effected by friction of the fluid in the course of its flow therethrough. In the apparatus shown, a feed pump drawing water from a condenser 10 forces the water through an evaporating section 2, the steam flowing through a shut-off valve 4 to and through a superheater 3 whence it passes to a turbine 8 through a stop valve 7, the turbine exhausting on to the condenser. A pipe branches from the tube system between the evaporator outlet and the valve 4 and leads to a header 14 through a valve 15. From the header 14 a number of small bore tubes 20 each with a control valve 4 and a pipe 22 with a reducing valve 23 lead to a header 17 connected by a pipe having a valve 18 to a separator 19. Steam and water flow from the separator to the condenser through liner 24, 26 respectively. A similar pressure reduction apparatus 28 is provided branching from the tube system between the superheater outlet and the valve 7. At the initial phase of the start-up operation the valve 4 is closed and water pumped through the evaporator flows through one or more of the tubes 20 entering the separator at reduced pressure. The boiler is fired and when the flow at the branch point 16 consists essentially of steam the pressure reducing valve 23 is opened and one or more shut-off valves 20 closed. As the steam reaches its desired operating pressure valve 4 is opened and steam flows through the superheater and is reduced in pressure in the apparatus 28 which at this stage may be used alone or with the first pressure reducing apparatus. Finally, the valve 7 is opened and the valves 15, 15<SP>1</SP> closed and steam at working pressure and temperature passes to the turbine.