Segmental design reduces costs of storage tanks
Large-scale hot water storage tanks have proved to be reliable and efficient heat storage for cogeneration as well as for solar thermal plants and industrial processes. As part of the research project OBSERW, scientists try to reduce the construction costs of such storage tanks. To accomplish this goal they develop a segmental design for aboveground storage tanks from 500 to 8.000 m³ volumetric capacity.
|Storage effect||Temperature change (sensible heat)|
|Storage construction||Steel, segmental design, aboveground, 500 to 8,000 m³|
|Storage / Charge||Direct|
|Number of cycles||1/d|
|Charging temperature range||98 to 40 °C|
|Discharging temperature range||98 to 40 °C|
|Storage capacity||1,792 GJ (8,000 m³; 95/40 °C)|
|Energy storage density||4.1 MJ/m³K|
|Project duration||November 2014 until February 2018|
In many applications large storage tanks secure an efficient heat supply. Their economic viability is substantially influenced by the construction costs. With use of segmental design it should be possible to reduce these costs significantly.
Segmental design has already been proven successful at cold water storage tanks. “eins energie in sachsen“, for instance, is operating an aboveground storage tank of 3.500 m³ cold water with direct charge and discharge since 2007. Inside the tank a thermal stratification is being generated and kept. At the bottom there is a zone with cold water (approx. 5 °C) while there is a zone with warm water (approx. 13 °C) at the top. These layers or zones move according to the state of charge. The tank is fully heat insulated to avoid losses over the surface.
Benefits of cold water storages
The projects with large cold water storages showed the practical benefits of this technology:
- Flexible adjustment of storage size and shape,
- High dynamics of loading and unloading,
- Effective use of the storage volume with an operation mode using stratification and fulfillment of planned discharging temperature,
- Good adaptation to the respective application (public utilities, local supply systems, industrial networks),
- Quick and rational construction with minimal material usage,
- Lower cost of ownership (simple authorization, operation, monitoring, etc.),
- Ability to repair (compared to underground thermal energy storages),
- Very good control of quality in the pre-fabrication and on site.
New solutions for hot water storages
The know-how from cold water storages cannot be completely transferred to hot water storage technology, since the water temperature can reach up to 95 °C. For example, temperature-resistant sealing of the segments and new constructive solutions must be developed.
This is the objective of the joint project „Oberirdische Speicher in Segmentbauweise für Wärmeversorgungssysteme“ (OBSERW). By investigating and testing of suitable materials, the complete revision of the storage structure and construction technique and the further development of charging and discharging facilities, the researchers want to develop efficient storages with low investment costs. In addition to the energy requirements such storage systems can provide useful system services such as maintenance of pressure, stabilizing the system or emergency operation.
Researchers are aiming for a construction concept which is suitable for many applications and is cost effective to implement in different locations. With slight adjustments, it will be suitable for both short-term and long-term storage. The heat storages shall be characterized by low heat losses and should allow high loading capacities. Permanent tightness and preservation of water quality are other criteria for a high level of functionality. The researchers minimize the use of materials and develop rational implementation processes to allow relatively low storage construction costs.
- Testing of sealant and heat insulation materials as well as different constructional systems of walls,
- further development of charging and discharging systems including hydraulic interface,
- complete revision of storage tank design and construction technology,
- development of a demonstrator and practical test of all components,
- improvement of the planning and calculation as well as the simulation.