Demand-based process steam from renewable energy: Implementation and sizing of a latent heat thermal energy storage system based on the Rotating Drum Heat Exchanger

Today's heat demand of industrial processes is mainly supplied by the combustion of fossil fuels. Within this paper, a thermal energy storage system using the Rotating Drum Heat Exchanger is proposed for a carbon-neutral steam generation and additional co-generation of electricity. At the Rotating Drum Heat Exchanger, a phase change material (PCM) solidifies on the outer surface of a drum, which is partially immersed into liquid PCM, while water evaporates on the inner surface of the drum. With this design, the storage density of the proposed nitrate salts as storage material can be increased up to 330 kW.m(-3) by utilizing the energy stored within the phase change and the energy stored due to the temperature change of the liquid and solid storage material. The storage system is sized for the generation of 20 000 kg.h(-1) of saturated steam at 2.5 bar, 8 bar, 20 bars and 75 bar of steam pressure. During the discharge process, a surface-specific heat transfer of above 300 kW.m(-2) and a share of electricity generation of up to 24 % can be achieved, which shows the high potential of the Rotating Drum Heat Exchanger. The thermal energy storage system can either be charged by fluctuating renewable energy or can be used to decouple the steam and electricity production of today's cogeneration plants. The presented storage system can thus make a decisive contribution to decarbonization and flexibilization of the industrial process steam supply.