The third storage configuration is designed with two tanks for the pre- and superheating of steam aiming at the
reduction of the investment cost of the storage system on the one hand and attaining the highest possible discharging
steam parameters on the other hand. If the intermediate Tank can be avoided, only two tanks would have to be built.
Furthermore, all of the molten salt could be used all over the temperature range, and thus more heat is stored per kg
salt. The both three tank solutions as discussed in sections 2.1 and 2.2 have a large amount of salt that is stored in
the intermediate tank and is not further heated to the higher temperatures of the hot tank. It is only used for the
sensible temperature difference between the cold and intermediate tank. The two tank solution that is shown infigure 9 only needs a mass of 3,000 t salt, what can also be seen in table 2. For the PCM module approx. 13,300 t of
sodium nitrate is used to store the latent heat of the condensing steam.
A two tank system may not be ideal to deal with the change of the specific heat capacity, since there is no change
of the salt mass flow inside the sensible storage part. For this reason, it is necessary to introduce a bypass at the
steam side during charging operation (see figure 9 (a)). Steam from the SF is entering the superheater (stream 1) and
is de-superheated down to 350 °C (stream 2). There, a small mass flow of about 6 kg/s of the still superheated steam
is passed around the PCM-storage to stream 3. Additionally, there is again a recirculation of saturated water to
control the temperature of the remaining superheated steam at the entry of the PCM-storage. This recirculation is
similar to the reference system explained in section 2.1.