Christoph Zauner

Durability of a fin-tube latent heat storage using high density polyethylene as PCM

Polymers have rarely been used as storage materials in latent heat storages up to now. Thus, we systematically screened all polymers available on a large-scale, selected promising ones based on their theoretical properties and experimentally tested more than 50 candidates. We found that polyethylene, polyoxymethylene and polyamides are promising even as recycled material. Especially high density polyethylene (HDPE) turned out to be suitable as was shown by detailed thermophysical characterization including more than 1000 heating and cooling cycles for INEOS Rigidex HD6070EA. We built a storage with 170 kg HDPE and a total mass of 600 kg based on a fin-tube heat exchanger and characterized its energy capacity, power characteristics and temperature profiles using a thermal oil test rig. In total we performed 30 melting and crystallization cycles where the whole storage was above 100 °C for more than 140 hours. After usage we examined the interior of the storage by cutting it into various pieces. A thin layer of degradation was observed on the surfaces of the PCM which is most likely related to thermo-oxidative degeneration of HDPE. However, the bulk of the PCM is still intact as well as the heat exchanger itself.

Increasing Energy Efficiency in Pulp and Paper Production by Employing a New Type of Latent Heat Storage

Abstract In pulp and paper production black liquor is burnt to recover base chemicals and to generate electricity and steam which is e.g. used in papermaking machines. In the event of paper tearing excess steam has to be condensed usually. We propose a latent thermal energy system to recover that energy and re-use it in the papermaking machines. A storage model was developed and experimentally verified by a lab-scale prototype. For the specific process, we designed a tube-bundle storage using thermally conductive HDPE as PCM and show that up to 30 MWh can be recovered per day. Finally, we describe the potential of storages to improve energy generation and efficiency in plants.