The DLR High Temperature Heat Pump Pilot Plants

Abstract

The new German Aerospace Center’s (DLR) Institute of Low-Carbon Industrial Processes is currently developing new prototypes of high temperature heat pumps (HTHP). Those are needed to process streams in industrially relevant high temperature ranges that cannot be achieved with state-of-the-art heat pumps. This novel technology will deliver process heat and, if required, additional cooling for industrial applications, which currently utilize fossil fuels. Furthermore, the valorization of industrial exhaust heat can result in considerable primary energy savings for the same amount of process heat delivered. The new DLR institute is based in two locations in Germany, Cottbus and Zittau. Currently, two heat pump concepts are being developed. The first one is a HTHP based on the Brayton cycle with air as the working fluid and will be placed in Cottbus (CoBra). The second one is based on the Rankine cycle using water as the working fluid and will be placed at the second location Zittau (ZiRa). The general technical scope for the heat pumps will be to achieve a heat delivery of at least 500 °C and at the same time demonstrate an industrial scale HTHP providing power in the MegaWatt-range. Along this way, smaller pilot plants were designed. These are currently under construction (Pilot CoBra) or in the detailed planning and procurement phase (Pilot ZiRa). The pilot plants of smaller size / performance and sink temperature (~200 – 300°C) will be on one hand side perfect as learning and innovation platforms but on the other side many industrial processes need heat in this temperature range and also in that size. At the moment, extensive research is taking place on developing and enhancing the performance of various components of the heat pump. For example, two compressor stages will be used in Pilot ZiRa to raise the pressure of steam to the required level without compromising the efficiency of the cycle. This is done by inter-stage cooling between the compressors in order to avoid very high temperature at the outlet and consequently increasing the density of steam. Another research project deals with an innovative concept of a supersonic two- phase steam ejector to be integrated in ZiRa. Research is taken place at the moment to investigate new ejector designs and to test it experimentally in our ZiRa pilot plant. On the other hand, the complete cycle is currently being optimized to reduce energy losses in cycle components.