06.10.21 Developing pumps for higher temperature systems

Raising the bar

In large-scale solar plants, mirrors focus the sun's energy to a central tower where it is used to increase the temperature of the molten salts. Pumps are used to transfer molten salts from the 'cold' tank through the pipes to a hot salt tank and on to a steam generator. The steam powers a turbine, which turns a generator and produces electricity for the local grid.

For renewable solar energy plants, efficiency can be improved by increasing the temperature of the salt used to store the sun's energy. Until recently, various salts have been used at temperatures around 600°C (1'100°F) and the pumping technology for this application is well-established. In order to improve efficiency, operators and manufacturers intend to increase the working temperature for new systems beyond 700°C (1'300°F).

At these temperatures, molten chloride salt has to be used. The use of this type of salt presents additional issues, such as its corrosive properties, that are not a problem with 600 °C pumps, which operate with more benign salts. To address this, the existing second-generation pumps have many proven design characteristics that now need to be extended.

The next generation

For the next phase of more advanced solar plants, third generation pumps are in development, with projects being funded by the Department of Energy (DoE) in the United States and other organizations in Europe. Work is underway to establish the materials and components that need to be upgraded for this project to be successful.

Both designers and product developers are working together to develop new materials for wear components that will be used in this arduous environment. One group of high-toughness, ceramic-metal composite materials, known as cermets, will be used to manufacture strong, long-lasting components, such as bearings and sealing elements.