Molten Salt Container
The use of molten salt for energy storage is not new. It has been used in similar concentrated solar power applications, like parabolic through and heliostat. Molten salt is also been used in nuclear reactors and for hardening metals. It has a long track record on how it can be used in a save way. One of the main problems of molten salt is it’s high corrosiveness, which makes the choice of materials to be used limited. An other problem is that molten salt freezes when the temperature drop below it’s freezing point. This point depends on the chemistry of the used salt. For the Archimedes project a mixture of sodium nitrate, potassium-nitrate and Calcium Nitrate, with a freezing temperature between 120°C and 230°C is used. The Maximum stable temperature of the salt is about 700°C, which gives it a very high range of usable temperatures. The tank is a 2 meters high, 90 centimetre wide themocline cylinder, with a storage capacity of about 300KwTh. The container will be filled with filler materials like quarts rock and sand, which will give the container an extra 5% storage capacity.
300 KwTh salt container
The container itself can be constructed using mellow steel coated with a special heat resistant coating (SEALMET or NDBSTOPOFF) from www.zypcoatings.com that will allow temperatures up to 1100°C. When the container is surrounded by a concrete surrounding the steel gauge can remain at a minimum like 3- 4 mm. The concrete material needs to be mixed with aluminium oxide to withstand the high temperatures. The concrete layer needs to be reinforced with iron. The next layer will be a heat shield, preventing radiated heat to leave the container. Finally there is a rock wool layer and the (aluminium plate) cover. Leak detectors in the isolation layer are used to shut down the system in case of salt leakage.
A high temperature pump transports the salt from a separated reservoir outside the container to the receiver. If The system is starting up or if for some other reason the salt is in frozen condition, the backup burner is used to bring the salt mixture at the right temperature. After the salt is pumped up through the (stainless steel 316I) supply pipe and passes the receiver it falls back under atmospheric pressure through a second pipe into the upper side of the thermocline tank. When the salt in the tank is solid, the molten salt loses some of it’s temperature on the solid salt and falls back into the reservoir, where the cycle is repeated. When all the salt in the tank is molten, the salt is pumped up from the lower (cold) part of the tank.
Last Modified September 13, 2007