Patent GB-952398-A (GB)
Title: Forced-flow once-through steam generators with intermediate reheating
IPC: F01K3/04
Filed: 1961-12-20
Abstract: 952,398. Forced flow steam boilers. SULZER FRERES S.A. Dec. 20, 1961 [Dee. 28, 1960], No. 45695/61. Heading F4A. In a forced-flow once-through steam generator with intermediate re-heating of the steam which has been partly expanded in the high pressure part of a prime mover, a liquid separator is disposed in a by-pass connecting the high pressure steam main and the steam line leading to the intermediate re-heater, the liquid separator constituting a starting vessel and heat store and being connected to the feed water circuit. A flow regulating element is fitted in the part of the by-pass between the separator and the reheater. The forced-flow once-through stream generator 1 having a superheater 2 is connected by a high pressure steam main 32 through a valve 25 to the H.P. part 3 of a turbine. From here an intermediate pressure steam line 33 fitted with a valve 15 leads to an intermediate re-heater 4, thence through a line 34 to the medium and low-pressure parts 5 of the turbine. A liquid separator 13 is situated in a by-pass line 42 and a valve 20 is provided before the separator, a further valve 21 for regulating the flow of saturated steam from the separator being placed in the line after the separator. A pipe 44 connects the separator to the intermediate pressure steam line 33 upstream of the point where the by-pass 42 joins the said line. Valves 26, 27 control the proportions of intermediate steam flowing to the separator and directly to the re-heater. A condenser 6 is connected to the medium and low pressure parts 5 of the turbine and a pipe line 35 leads from the condenser to a feed tank 10 via a pump 7 and preheaters 8 and 9. From the feed tank a line 38 leads to the liquid separator via a low pressure feed pump 11 and a pre-heater 12 which may be by-passed by the use of the line 46 in conjunction with valves 30 and 41, if so desired. From the water chamber of the liquid separator 13 a pipe 39 fitted with a high pressure feed pump 14 leads to the steam generator 1. For starting purposes by-pass lines 43 and 45 are provided, each having a control valve, and arranged so that they connect the steam line 34 with the feed tank 10, and the condenser 6 via an injection cooler 24, respectively. On starting up the plant the valves 25, 50 and 15 are closed while the by-pass valves 20, 22 or 23 and 21 are open. Water is then drawn from the water chamber of the liquid separator 13 by the pump 14 and circulated through the steam generator 1, the superheater 2 and the by-pass 42 to the liquid separator again. As the water heats up resultant steam passes through the valve 21 to the intermediate re-heater 4 then through one of the by-passes to either the feed tank 10 or to the condenser 26 according to which by-pass valve is open. During normal operation of the plant the by-pass valves 20, 22 and 23 are closed and the valves 15, 25, 50 and 27 are open. Steam from the turbine part 3 flows largely through the intermediate pressure line 33 to the re-heater 4 and from there to the medium and low pressure ports 5 of the turbine. The remainder of steam flows through a pipe 44 to the water chamber of the liquid separator 13 where it gives up some of its heat and then flows through the valve 21 as saturated steam to rejoin the remainder of steam entering the reheater. If the valve 21 is closed the steam condenses and flows with the feed water to the steam generator 1. In a modification the liquid separator is fed with a controllable amount of steam tapped from the high pressure stage of the turbine at a higher pressure than that in the steam line to the intermediate re-heater, the amount being controlled by a regulator in dependence on the turbine inlet pressure, and the separator is arranged in parallel with a controllable shunt in the boiler feed line.