Fig. 1. Schematic temperature-enthalpy diagrams for the charging and discharging processes with water/steam as heat transfer fluid – (a) using a
sensible storage medium, (b) using a sensible storage medium with different mass flows and (c) using a sensible storage medium for pre- and
superheating and a latent storage medium for evaporation.
One possibility to reduce this problem would be to use a three-part storage system for preheating, evaporation and
superheating like proposed in [2]. To store the sensible heat, a molten salt storage system with a cold tank, a hot tank
and an intermediate tank is used. This approach would allow two different mass flows. A higher mass flow in the
lower temperature range and a smaller mass flow in the higher temperature range. According to figure 1 (b), the live
steam temperature and pressure reduction is not as large as in the previous case leading to a more moderate reduction
of the power block efficiency during discharging.
If a latent heat storage system is used to store the evaporation enthalpy of water/steam, the temperature profile in
the storage system is matched to the temperature profile of the heat transfer fluid during charging and discharging.
This approach leads to the highest live steam parameters and thus power block efficiency during discharging at the
expenses of an increased system complexity. Since the specific heat capacity of water is much higher than that the
one of steam, the gradient of the steam curves is steeper when compared to the water curves in figure 1. To
compensate the different slopes, different molten salt mass flows are utilized in the preheating and in the
Fig. 1. Schematic temperature-enthalpy diagrams for the charging and discharging processes with water/steam as heat transfer fluid – (a) using asensible storage medium, (b) using a sensible storage medium with different mass flows and (c) using a sensible storage medium for pre- andsuperheating and a latent storage medium for evaporation.One possibility to reduce this problem would be to use a three-part storage system for preheating, evaporation andsuperheating like proposed in [2]. To store the sensible heat, a molten salt storage system with a cold tank, a hot tankand an intermediate tank is used. This approach would allow two different mass flows. A higher mass flow in thelower temperature range and a smaller mass flow in the higher temperature range. According to figure 1 (b), the livesteam temperature and pressure reduction is not as large as in the previous case leading to a more moderate reductionof the power block efficiency during discharging.If a latent heat storage system is used to store the evaporation enthalpy of water/steam, the temperature profile inthe storage system is matched to the temperature profile of the heat transfer fluid during charging and discharging.This approach leads to the highest live steam parameters and thus power block efficiency during discharging at theexpenses of an increased system complexity. Since the specific heat capacity of water is much higher than that theone of steam, the gradient of the steam curves is steeper when compared to the water curves in figure 1. Tocompensate the different slopes, different molten salt mass flows are utilized in the preheating and in the
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