Patent GB-821700-A (GB)
Title: Steam power plants employing a plurality of steam generators connected in parallel and provided with intermediate reheaters
IPC: F22B35/00
Filed: 1956-06-12
Abstract: 821,700. Steam turbine plant. SULZER FRERES S.A. June 12, 1956 [June 23, 1955], No. 18174/56. Class 110 (3). [Also in Group XXIX] In a steam power plant having a number of steam generators A, B, C connected in parallel and provided with intermediate reheaters 4, 5, 6, the proportion of steam for reheating that is passed through the reheater of the most heavily loaded steam generator is regulated by throttling the steam flowing through the heater of a less heavily loaded steam generator. The regulation is such that the ratio of the steam flow through one reheater to the total steam flow through all the reheaters is approximately equal to the ratio of the load on the corresponding steam generator to the sum of the loads on all the generators. Such regulation is achieved by an arrangement of steam apportioning devices 10, 11, 12 one for each reheater, these being controlled so that the steam-controlling valve 93, 94 or 95, Fig. 2, of the device 10, 11 or 12 corresponding to the most heavily loaded steam generator is fully open regardless of the load or this steam generator or of the loads on the other steam generators. The steam generators A, B, C are supplied from a hot well 17 by pumps 19, 20, 21. Each feed pipe contains a feed water regulating valve such as 22 the pressure drop across which is regulated by a valve such as 25 through a control instrument such as 28. The feedwater regulating valves 22, 23, 24 themselves are regulated by isothermal load responsive regulators 45, 46, 47, respectively. Steam from the superheaters a, b, c passes to a highpressure turbine 2 through a common main 1 and returns via a main 3 to the reheaters 7, 8, 9, the outlets (or in some cases the inlets) of which are controlled by the apportioning devices 10, 11, 12. The reheated steam passes via a main 13 to a medium pressure turbine 14 the outlet of which leads to a condenser 15 and to the hot well 17. The devices 10, 11, 12 are controlled by the respective steam-apportioning control valves 31, 32, 33 and are subject to overriding control by steam temperature and pressure-responsive devices such as 57 and 62 operative through a control valve device such as 60. The steam-apportioning control valves such as 31 each comprises a piston having on one side a series of equal area steps or other surfaces 82, 83 subject to the regulating pressures developed by the load-responsive regulators 46, 47 corresponding to the other apportioning control valves 32 and 33. The other side 81 of the piston is subject to a reaction pressure common to all the valves 31, 32, 33 and is developed by a series of reaction devices 37, 38, 39, each of which has a piston valve such as 84 responsive to the output pressure of the corresponding steam-apportioning control valve 31 or 32 or 33. The piston valve 84 is movable from a central position to connect it to a pressure supply network or to a drain network. The valve 84 and similar valves 85, 86 are connected in series to a pipe 42 with branches to the upper sides of each of the steam-apportioning control valves 31, 32, 33. Each of the latter valves has a piston portion movable away from a central position to connect its output pipe 34, 35 or 36 to the pressure network or to drain. The valve 84, 85 or 86 is in its central position when the regulating pressure in the corresponding output pipe 34, 35 or 36 has a certain maximum value at which the corresponding steam-controlling valve 93, 94 or 95 is fully open. Each steam-controlling valve such as 93 is operated by a servomotor such as 96 under the control of a valve such as 102 responsive to the pressure in the corresponding output pipe 34 and returnable to its central position by a spring force varied by a cam 105 through a feed-back lever 111 with a fixed fulcrum 108. Each valve such as 93 may be closed to shut down the corresponding steam generator by a change-over cock 132. Under certain conditions, each valve such as 93 may be fully opened by a change-over cock 135 regardless of the load on the generator concerned. Each valve 93 &c. is shut down automatically if the temperature or pressure of the steam flowing through it is below predetermined valves determined by the temperature and pressure-responsive devices 57 and 62 respectively. The latter include valves 123, 117 normally balanced in a central position in which their respective output pipes 59, 61 are cut off from the pressure network and from drain. The regulating pressures in the pipes 59, 61 normally maintain two valves 120, 126 in the pressure supply connection 64 to the valve 102 raised so that a pressure supply is available. If either valve 120, 126 descends due to temperature or pressure of the steam falling below the minimum value the connection 64 is connected to drain and the corresponding steam-controlling valve 93 closes. If the steam generator A, say, has the greatest load, its load-responsive regulator 45 produces the highest regulating pressure and correspondingly the steam-apportioning control valve 31 produces the highest pressure in the pipe 34 so that the valve 84 is in its central position and the steam controlling valve 93 fully open whilst the valves 85, 86 are below their central positions and the valves 94, 96 are only partly open. The regulators 45, 46, 47 may be replaced by others responsive to the amount of live steam or to the firing intensity as represented by the consumption of air or fuel.