Abstract
In a semi technical test rig experiments were accomplished to test the dyamic behaviour of an once through heat recovery steam generator. The digital control system allowed to run experiment with predefined transients using different control schemes. The results may be summed up as follows : Load changes of the gas turbine achieved by varying the flue gas flow while maintaining the flue gas temperature are transmitted with only short delay to the water steam cycle as the heat transfer condition varies simultaneously throughout the heat recovery steam generator. Movements of the evaporation end point happen only slowly. Load changes of the gas turbine where the exhaust flue gas temperature of the gas turbine varies cause large storage or release of stored heat in the tube sheets and steam generator structure. This phenomena delays substantially the load following ability of the steam generator. A relatively long time is needed until new optimal energetic conditions are reached. Flue gas temperature changes of the gas turbine cause an important displacement of the zones of super heating, evaporation and to a lesser extent preheating in the steam generator. Conventional feed water control schemes are not perfectly apt to restrict those displacements, thus large amounts of heat are unnecessarily stored in or released from the system. This deficiency may be mended by using a feed water control concept which takes into consideration the actual need or overcapacity of heat in the tubing and structure of the steam generator. This approach permits a rapid and straight forward load change of the steam generator, with stationary conditions being quickly reached after a transient.
