GB879032A - A method of starting-up and closing-down a once-through forced-flow, vapour generating and superheating unit, and such a unit - Google Patents

Abstract

879,032. Forced-flow steam boilers. DURRWERKE A. G. Dec. 9, 1957 [Dec. 8, 1956], No. 38279/57. Class 123(2) To enable a forced-flow, once-through steam boiler comprising preheating and evaporating sections 22, 23, 24 and an austenitic steel superheater 25 to be started up and closed down without thermal shock damage to the superheater, the boiler has means whereby only superheated steam is admitted to the superheater during these periods. The boiler which is heated by a main burner 27, has additional burners 6, 12 for heating the sections 23, 24 respectively when starting up or shutting down and is provided with three starting lines 4, 10, 17 respectively branching from the tube system at the outlets of the preheater 22, evaporator 23 and superheater 25 and leading to a pressure relieving vessel 19. To start the boiler the feedpump 20 is started and supplies water at minimum load rate and, after a predetermined volume has been supplied, regulators 8, 14 start the burners 27, 6, 12 at minimum load rate. Simultaneously the regulators open the valves 5, 11, 18 respectively controlling the flows in branch lines 4, 10, 17 to settings whereby a major part of the fluid flow is diverted through the branch 4 and a major part of the flow through section 23 is diverted through the branch 10, the remaining part of the flow entering the superheater 25 as superheated steam. When the steam temperature at the superheater inlet 15 reaches the pre-set value the regulator 14 closes the valve 18 sufficiently to pressurize the unit to the desired value. The reduced flow resulting in the sections 23, 24 causes a temperature rise at points 9, 15 to which the regulators respond by gradually closing the valves 5, 11 and the burner valves 7, 13 meanwhile opening the valve 18 at a rate which maintains the pressure at 16 at the superheater inlet constant. The rate at which the valve 18 is opened is reduced if steam is diverted to the turbine for preheating thereof. The reverse procedure is adopted to close down the boiler.