Analysis of steel making slag pebbles as filler material for thermocline tanks in a hybrid thermal energy storage system

This work focuses on the reliable use of the steel making slag pebble as filler material of thermocline tanks which are combined with conventional molten salt tanks in a hybrid thermal storage configuration. The use of this hybrid configuration not only improves the efficiency and operation of the plant when there is solar radiation fluctuation but also includes pumps in separate molten salt tanks in order to increase the maximum height of the thermocline tanks and its useful storage volume, i.e. its storage capacity. A packed-bed numerical model has been used to study the potential of the slag pebbles in this hybrid storage configuration, comparing it against other well-known potential filler materials for thermocline tanks as the taconite and quartzite rock. The study carried out considers a storage capacity of 9 full load hours for a central receiver system of 110 MWe gross power. The results show that two thermocline tanks of 20 × 20 m, filled with steel making slag pebbles, reaches a capacity of 6.61 full load hours. An economic analysis is included which shows that the hybrid storage solution using slag pebbles represents a cost reduction of 13.7% against the state of the art solution. Additionally, comparing it against other filler materials, the slag hybrid storage solution has a cost reduction of 3.8% and 13% against the quartzite and taconite hybrid storage solution, respectively.