Development and test of a direct contact heat exchanger (particle – air) for industrial process heat applications

A direct absorption receiver using ceramic particles (CentRec) has been successfully developed by DLR and tested under solar conditions at the Juelich Solar Power Tower, demonstrating receiver outlet temperatures of more than 900 °C. The next step towards commercial application of the technology is to demonstrate a cost-effective, high temperature heat extraction and transfer to a process medium. Besides e.g. steam for electricity generation in a steam turbine, hot air can be used to supply heat to industrial processes with energy demand at high temperature level. A great potential for higher efficiencies and lower costs has been identified for a moving bed heat exchanger. Several concepts of direct contact heat exchangers have been analyzed and evaluated. The selected concept is a combination of several crossflow-sections that are arranged in series with fluid-mixing-chambers between each crossflow-section. Based on the selected design a heat exchanger prototype with 10 kW thermal power and a design air outlet temperature of 750 °C has been built and integrated into a test setup. The test setup provides particles at 900 °C that are heated up electrically inside a hopper on top of the heat exchanger. Hot particles are then moving downwards (moving bed) from the hopper through the direct contact heat exchanger driven by gravity. Cold air supplied by a compressor flows through the particle bed in cross-flow and is heated up. The hot air flow leaves the heat exchanger with a temperature of 750 °C. The particle mass flow is controlled by an oscillating mass flow controller, positioned under the heat exchanger. The cold particles are collected in a container on the bottom. The particle cycle is closed by transporting them back to the hopper. A measurement and control system is implemented to carry out the tests. The test setup has undergone successful commissioning in October and an extensive testing phase started in January 2019. This paper presents the development and manufacturing as well as the successful commissioning of the heat exchanger prototype