There are lots of types of TES, which can be divided by the heat storage material (e.g., steel, concrete, water), by the physical behavior of the heat storage material (sensible, latent) or by other criteria. Due to the variety of TES, there is a fitting solution for almost every customer’s process. But it is essential to consider all operational states (charging, storing, discharging) to match the TES with the energy source and the consumer.
Besides the TES itself, one also must take care of the heat transfer between the heat source, the storage material, and the consumer. This is done by the Balance of Plant (BoP), which especially includes the necessary heat exchangers, pumps, control devices and other components.
A typical use case of a TES can be found in hydraulic press applications, which usually have a cyclic load profile with heating and cooling phases. For these applications, we realized systems with a direct hot oil buffer storage, which is charged during cooling phase and can be discharged for heating. Another option would be a two-tank solution, storing hot and cold oil in different vessels whereas one of the vessels can be empty. For CST systems, we were involved in projects with different approaches, such as a solid-state TES for a thermal oil system up to 400 °C or a liquid-state TES for a pressurized water system with a design temperature of 240 °C.
The heat transition in the industry requires the implementation of thermal energy storage (TES) systems, which will play a crucial role in the coming years. TES can utilize various principles and storage materials.
Here a use case for large pressure vessels to store hot water.
A particularly challenging type of water storage is the single-tank solution, where a single tank is responsible for storing both the hot and cold mediums. In this system, when the tank is loaded, the hot medium from the heat source enters the tank from the top and displaces the cold medium. Conversely, during the unloading process, the cold medium from the consumer enters the tank from the bottom and displaces the hot medium. Implementing a one-tank solution instead of a two-tank solution can lead to significant cost savings, especially in high-temperature water storage systems where the tank’s wall thickness can be substantial, reaching around 10 mm.
To achieve the maximum energy unloading at the highest temperature level, it is essential to avoid mixing of the medium within the tank and establish a distinct thermocline. To address this, computational fluid dynamics (CFD) is utilized to optimize the flow distribution within the tanks, aiming to minimize the mixing of hot and cold fluids. The results obtained through CFD analysis provide specific inlet geometries for the respective temperature, medium, pressure, and installed volume.
The attached pictures depict the calculated temperature distribution within a single tank during a typical unloading process, showcasing the temperature distribution after 10 minutes, 1 hour, and 3 hours. These visual representations help to understand the effectiveness of the system and the behavior of the temperature profile over time.