EnCN – project part Peak-Load High Temperature Heat Storage
EnCN²: Peak-Load High Temperature Heat Storage with Calciumcarbonat
Isothermal high temperature carbonate storage above 800 °C offers enormous storage densities and can be applied in highly flexible conditions for dynamic steam generation. Thus, the existing conventional power plant infrastructure can be flexibilised to cope with fluctuating load curves caused by large shares of renewables in power generation. As part of the Energie Campus Nürnberg, this innovative storage system with high temperature heat pipes is investigated in lab and pilot scale to achieve a Proof-of-Concept and evaluate the technical potential of possible applications within a local power plant.
Laufzeit: 01.01.2017 – 31.12.2021
Bayerisches Staatsministerium für Wirtschaft und Medien, Energie und Technologie
Technische Hochschule Nürnberg
Prof. Dr. Ing. Wolfgang Krcmar: Professor für Grobkeramik, Fakultät Werkstofftechnik
I-MEET (Institut für Materialien der Energie- und Elektrotechnik)/ZAE Bayern
Peak-Load High Temperature Heat Storage with Calciumcarbonat
Fossil power plants in Germany, especially hard coal plants, need to supply large power output and high load gradients especially during morning and evening hours. The coverage of these load gradients with renewable power generation from wind and photovoltaic during transition and winter periods is not possible since sufficiently high power output from these sources is not achieved before midday.
Because of the complex control mechanisms for the electricity grid these load peaks need to be continually supplied with existing conventional power plants. Existing steam turbines are ideally suited for these load gradients, however large steam generators are too slow to follow the demand curve (± 10-15 GW within 2 hours) because of their high thermal masses and material considerations. Accordingly, electricity prices rise considerably during of times of high load gradients.
High temperature heat storage could present a solution to this challenge because of their ability to supply high pressure steam dynamically to steam lines of existing thermal power plants. Therefore, only the steam turbine receives additional steam and can achieve large load gradients within minutes. Heat and Power Plant Sandreuth (Nürnberg) is taken as example for the technical investigation and evaluation of steam injection at different temperature and pressure levels to achieve significant load increase in short time.
For this dynamic application mostly thermochemical heat storage, especially carbonate storage is suited. Magnesia- and Calcium carbonate storage was so far mainly discussed for solar thermal power plants. Recarbonation of previously calcined calcium carbonate (burnt lime) generates large quantities of heat above 800 °C. However, dynamic loading and unloading is only possible if the storage is operated isothermally, i.e. with the same temperature in the whole reactor. Conventionally operated storage systems with varying temperature levels throughout the reactor achieve smaller heat transfer coefficients. The resulting smaller heat flux densities do not allow operation with sufficiently high load gradients. Therefore, conventional carbonate storage systems are not really superior to sensible heat storage systems without chemical reaction such as pebble bed storage or ceramic brick storage.
The integration of high temperature heat pipes is an innovation to achieve an isothermal temperature profile in the reactor. Because of its ideal heat transfer properties heat pipes can achieve significantly higher heat flux densities in a carbonate reactor than with conventional storage. They have been tested extensively with the Carbonate-Looping-Process during the CARINA project and will be applied for the first time in a high temperature storage setting at the Chair of Energy Process Engineering.