International Journal of Energy Research, Vol.43, No.6, 2296-2311, 2019
One feedwater heater taken out of service as a strategy to maintain full load and its effect on steam power cycle parameters and performance
The aim of this study is to analyze the suitability of one heater removal as a strategy for maintaining full load operation of steam power cycles when superheated and/or reheated temperatures (T-SS, T-RS) decrease and the effect on the net heat rate (HRNet). For this purpose, three regenerative cycles with different numbers of closed feedwater heaters were chosen. The cycles were analyzed at different steady states with Thermoflex software. Removing a heater has an important influence on the cycle operation and performance, leading to the redistribution of extraction mass flows, with the heater immediately downstream being the most affected. This may make it necessary to reduce the load of the cycle. However, when the highest pressure heater (highest PH) is removed from service, the changes are not so significant. When T-SS and/or T-RS decrease, the plant may not achieve full load operation. Nevertheless, if the highest PH is removed from service, it can help to recover full load. This is due to the decrease in the water/steam mass flow through the steam generator, which produces an increase in T-SS and/or T-RS. On the one hand, this measure leads to higher HRNet in comparison to that of the nominal conditions. On the other hand, there are certain conditions at which HRNet is lower than when all the heaters are in service and the values of T-SS and/or T-RS are low. Thus, for maintaining full load, the highest PH removal can be applied and cycle parameters optimized in order to reach a HRNet closer to its nominal value. The higher the number of closed feedwater heaters, the more adequate is the application of this strategy.