GB1425058A - Forced through-flow steam generators with superimposed forced citculation - Google Patents

Abstract

1425058 Steam generation SULZER BROS Ltd 8 June 1973 [12 June 1972] 27408/73 Heading F4A In a forced through-flow steam generator with superimposed circulation, a main working fluid path comprises in series, a feed pump 1, a circulating pump 5, an evaporator 6, a water separator 7, and at-least two superheaters 8, 10, 12, a circulating path is also provided comprising a line 20 leading from the water separator 7 to the main working fluid path upstream of the circulating pump through a non-return valve 21. A water injection line 50 leads from the main working fluid path between the circulating pump 5 and the evaporator 6 to an injection point 9 in the main working fluid path between two of the superheaters 8 and 10 and contains the injection valve 51 controlled in dependence on the temperature of the superheated steam measured by a device 52. A first device 38 measures the flow delivered by the feed pump and a second device f measures the flow in the water injection line. A controller 37 adjusts the feed water delivered by the feed pump in dependence upon the flow rate measured by the second device f so as to tend to increase the feed water flow as the flow rate increases. As shown in Fig. 1, a second water injection line 26 branches off from a point 25 and its output is controlled by an injection valve 27 through a temperature controller 29 connected to the live steam line 13. The water separator 7 is provided with a level measuring element 30 the output of which is connected to a change-over switch the output of which acts via a controller 36 on the feed controller 37. A load signal generator 41 supplies a load-dependent set value signal to a P.I. controller 36 and acts on a servomotor 34 which operates a change-over switch 31 so that at low loads the switch transmits the signal formed by the level measuring element 30 to the controller 36 but at high loads the switch transmits the signal from the temperature sensor 32 to the comptroller 36. In an alternative embodiment (Fig. 2, not shown) both injection points 9, 11 are connected to the same injection line and an integral-action controller is arranged to regulate the temperature difference measured by thermocouples disposed upstream and downstream of the injection point 11.