AMTEC-D – Alkali-Metal-Thermo-Electric-Converter - Type Dresden
The direct conversion of heat to electric power is a promising contribution to accomplish the energy transition towards sustainable energy and to increase resource efficiency. Alkali-Metall-Thermo-Electric-Converters (AMTEC) appear to be especially suitable, because they operate without moving parts and are practically maintenance free. The superior power adjustment to fluctuating loads opens very flexible stationary and mobile applications, e.g. the use of waste heat from industrial processes, heat from solar receivers, waste heat from motor vehicles or heat, which is generated during hydrogen production.
Challenges are the high requirements on used materials and the cell fabrication. Of special importance are the robustness and the resistance to the high reactivity of alkali metals as well as the high pressure and temperature differences.
The aim of this joint project is, while utilising new ceramic materials and innovative laser procedures, to develop a highly efficient, ecologically friendly and economically competitive AMTEC, to build a prototype (AMTEC-D) and to study it in practice for various applications. Furthermore, at HZDR, we investigate the potential of an alternative AMTEC-concept based on two liquid metal electrodes and analyse its thermochemical design. The usage of liquid metal electrodes appears to be attractive, because of their lower contact resistances and no requirement to apply the failure-prone electric contact to the solid electrolyte.
A converter consists of two electrode compartments, which are separated by a ceramic membrane (Beta''‐Alumina Solid Electrolyte, BASE). This membrane conducts only alkali ions and is insulating for electrons. In a conventional AMTEC the alkali metal exists in its gaseous state at the cathode side at low pressures (120 °C bis 450 °C, < 100 Pa). Heat is supplied at the anode side (typically 600 °C to 1100 °C, 20 to 100 kPa), which creates a pressure difference that drives alkali metal from the anode through the BASE to the cathode. Only alkali metal ions can diffuse through the membrane, hence each atom releases one electron at the anode side and accepts another electron at the cathode side. Additionally applied electrodes on the membrane provide the electronic conductivity. Thus, the charge transfer reaction can only occur at a three-phase-boundary. The electrons flow through an external circuit where they are used as electric power.
In an alternative AMTEC-concept, two liquid metal electrodes are used on both sides and thus charge transfer is improved as is cell fabrication, performance and life time. The driving force for the electric current is the different activity of the alkali metals on each electrode side, while it has been the pressure difference for conventional AMTEC. Such cells could operate at lower temperatures, with our without a temperature gradient. The liquid metal alloy from the cathode side is thermally separated and recycled.
The project "AMTEC-D - Entwicklung eines Alkalimetall-Konverters
zur hoch effizienten Direktumwandlung von Wärme in elektrischen Strom" was supported by the European Regional Development Fund.