In case of the conditioned dry sorption, the Ca-based additive powder is injected into the reactor in the form of Ca(OH)2.
Compared to the use of CaO, e.g. for the spray sorption, this results in a disadvantage due to the higher purchase costs for Ca(OH)2. In order to offset this cost disadvantage, plants with higher additive powder consumption are often provided with an additional dry hydrator for CaO. In this case, the additive powder is supplied in the form of CaO.
It is converted into Ca(OH)2 by means of H2O injection in a dry hydrator, it is stored in an intermediate silo, and provided as dry additive powder for the injection into the reactor and / or upstream evaporative cooler.
The intermediate silo is adequately dimensioned to allow a direct filling of the silo with Ca(OH)2 in case of maintenance and repair works near the dry hydrator. A corresponding scheme is shown in the illustration below. Several plants in Europe have been provided with this technology.
The illustration shows a plant, realised with a dry hydrator for a Ca(OH)2 production capacity of approx. 3.5 t / h. As an alternative, there is also the possibility to install the dry hydrator close to the additive powder injection point near the reactor.
The produced Ca(OH)2 can now be injected directly into the reactor without temporary storage in a silo. This variant will not be possible in the case of a graded additive powder injection.