S. Warerkar[10]*, S. Schmitz1, J. Gottsche1, B. Hoffschmidt1, R. Tamme[11]

1 Fachhochschule Aachen, Solar-Institut Julich, Heinrich-Muflmann-Str. 5, 52428 Julich, Germany
2 DLR, Institute of Technical Thermodynamics, Pfaffenwaldring 38-40, 70569 Stuttgart
* Corresponding Author, warerkar@sij. fh-aachen. de

Abstract

In view of rising energy prices and an increasing share of power generated by renewable energy sources, the importance of energy storage is growing. In the framework of this project a thermal energy storage concept for solar power towers is being developed, in which quartz sand serves as storage medium. Sand is suited due to its properties of high thermal stability, specific heat capacity and low-cost availability. Compared to storages based on ceramic bodies the usage of sand promises to reduce costs of energy storage and thus to reduce the costs of electricity generation. Beside solar thermal power plants the storage concept could be applicable in steel industry.

A central element of the storage concept is an air-sand heat exchanger, which is presently under development. This paper describes simulation results and measurements of the heat exchanger prototype. It includes sand flow behaviour and experience with different porous walls as well as up-scaling options.

Keywords: energy storage, thermal storage, heat exchanger, sand

The sand which is heated up in the air-sand heat exchanger to approx. 800 °C flows to the hot storage through a down pipe and further to the fluid bed cooler. The fluid bed cooler, a unit which is a standard component of fluidized bed combustion units, is the driving element of the steam cycle. The generated steam is finally fed to the steam turbine for power generation. The cooled sand exits from the fluid bed cooler at a temperature of approximately 150 °C and returns to either the air-sand heat exchanger or is stored in the cold storage tank.

The main advantages of the storage concept are:

• Low-cost storage medium

• Storage at ambient pressure

• Almost 100 % of the hot storage volume can be used

• The heat exchanger pressure losses are independent of the storage capacity

For implementation of the concept a suitable heat exchanger is required, which was developed and analysed at SIJ and is described in the following.