The New Thermal Storage Technology is the most versatile and efficient way of storing heat for reconversion. In the field of thermal energy storage, there have so far been some basic requirements that are not relevant here and have been rethought:
The decoupling of heat should be secondary at this point, but still possible. The priority with the New Thermal Storage Technology is the generation and smoothing of electricity. Heat to Power !
Previous heat accumulators clearly differentiate between charging and discharging cycles. The New Thermal Storage Technology should function as a system in which this is possible simultaneously through separate media circuits. What is the benefit?
Several heat sources supply their energy to the storage tank at irregular intervals. However, the the subsequent heat engine should run continuously.
Charging and discharging curcuits can use different fluids. External heat transfer or decoupling of heat to a secondary circuit is therefore not required.
The heat input occasionally falls below the minimum temperature required by a subsequent heat engine. However, it can still generate electricity continuously. Overall, constant operation for subsequent power generation without frequent starting and stopping of the heat engine is assured.
It should also be possible to extract heat for heating purposes in parallel with generating electricity. This makes sense only at certain times of the year if the heat is continuously and consistently available. The required temperature level for this heat is significantly lower than that required for power generation. The New Thermal Storage Technology can easily be configured in a manner that two gas streams of different temperatures are drawn off simultaneously.
If a subsequent heat engine is installed in the air circuit with a New Thermal Storage, the returning gas flow first returns its residual heat to the storage tank by using a counterflow configuration. In this way, a temperature gradient in the New Thermal Storage is maintained and the temperature level of the hottest modules remains spared.
The New Thermal Storage Technology is ahead of other thermal storage systems with a combination of advantages based on the following points:
Optimum combination of the materials used in the heat storage mass. A high proportion of steel ensures short response times.
Charging and discharging takes place in different pipeline systems. So it is not necessary to stop charging to extract heat.
The storage consists of a package of individual modules that can be controlled independently of one another and in which different temperature levels can also prevail independently of one another.
The individual modules can be connected in series, in series or in parallel, thus meeting any requirement (charging speed and efficiency, low temperature use, etc.).
Connecting the modules in series leads to gradual charging or discharging, so that residual heat at a low temperature level can also be used.
In this way, a countercurrent heat exchange can be implemented, which also enables the use of heat at temperatures that are actually too low for heat engines. Heat at a lower temperature must not be used for heating purposes only, but can participate in the generation of electricity: "Power To Heat To Power".
Despite its high performance, the system is based on an impressively simple design.
Components of the New Thermal Storage
One or more heat-insulated casings house a heat-storage mass made of fine bulk material, such as quartz sand. The heat storage mass is divided into spatially separated units ("modules").
Example arrangement of the modules
Each module is traversed by at least two piping systems: The charging piping system (or systems) and the discharging piping system (or systems). The heat transfer media, mostly air, flow through these in separate circuits. The heat storage mass is heated or cooled by the flow. The fine-grained bulk material and the steel pipes conduct the heat nearly like a compact solid material.
Example of a simple loading and unloading pipework system of a module.
The line systems penetrate each other, they occupy the same place
Outside the thermally insulated housing there are manifolds for distributing the incoming flow to the modules and for collecting the outgoing flows from the modules, respectively.
The modules are also connected each other by bypass and return flow lines. This allows the fluid to further heat exchange in other modules. This applies to both the charging pipe system and the discharging pipe system.
Structure of the New Thermal Storage Technology
Example configuration: Serial loading of the modules of the HT thermal storage
BExample configuration: Serial discharge of the modules of the HT thermal storage
Types of construction
The system basically consists of individual but interconnected heat storage units (“modules”). In the following figures - as above - six cuboid modules are provided as examples for the sake of simple illustration. The representation of the modules in cuboid form is only intended to illustrate the functionality. On the contrary, an optimal configuration with regard to reducing the heat losses and minimizing the material expenditure could also provide a cylindrical shape. In this case, the Storage can consist of concentric or layered modules or modules arranged in sectors or a combination thereof. Cuboid modules, on the other hand, can be expanded more easily with additional modules.
Examples of possible Geometries:
Examples of possible geometries: stacked-cylindrical and stacked-rectangular
The Heat Storage Mass
The heat is stored in different materials at the same time:
Charging piping system and discharging piping system preferably are made of steel. In order to allow the flow through several modules one after the other and to keep the flow resistance low, they have a generous inside diameter. This results in a high proportion by weight of steel in the total heat storage mass.
A fine bulk material, for example quartz sand. Typical properties: grain size from 0.06 mm, no formation of cavity bridges, melting point approx. 1500°C
Optionally, molded bricks, for example fireclay, can be stored in the gaps.
Melting cores: These are hermetically sealed, horizontally arranged tubes filled with a latent heat storage mass such as aluminum and a small amount of compressible filling gas to compensate for volume changes during phase change. Due to the phase change during the melting/solidification of the latent heat storage mass, considerable heat is absorbed/released.
Example of the structure of a module with built-in components
How the New Thermal Storage Technology works
Charging: A first flow of medium circulates between the heat source and the Thermal Storage Device, which is initially cold. It is fed to one or more modules through the external distribution piping system. The charging piping system heats the sand bed in which it is embedded by direct contact. The sand heats itself, the unloading piping system and the melting cores.
After the heat has been released to the storage tank, the medium returns cooled through the external collection line to the heat source, where it is heated up again and then returns to the storage modules.
Discharging: Unloading takes place independently and, if necessary, at the same time as the loading process. A second flow of medium circulates between the hot heat storage and the heat engine. Here, the heat extracted from the storage tank is converted into electricity.
During the discharge process, the discharge pipe system transfers heat to the heat transfer fluid, which it previously absorbed from the sand and the melting cores. Completely different pipelines are used here than for loading.
Temperature distribution: Heat is stored collectively in the charging piping system, the sand, the melting cores and the discharging piping system and is transferred from one material to the other through direct contact.
The mutual penetration of the piping systems ensures a homogeneous distribution of the heat in the module. There is no "heat front" propagating inside.
Most mineral bulk materials are poor conductors of heat. However, the special arrangement of the internals ensures that every point inside the module is close to a metallic element and the heat only has to travel very short distances everywhere.
In the example shown, the pipes are designed in such a way that the innermost area is heated first during loading. When discharging, the heat is first absorbed from the outer areas of the heat storage mass and finally flows through the hot, inner area. In this way, the heat dissipation to the outer wall is reduced.
Loading dynamics: The modules are connected in series and can be charged and discharged in a highly dynamic manner. Hot air flows into the first module and heats the internal pipes. The pipes heat the sand. Since the sand conducts heat more slowly than the metallic components, it heats up with a delay. As the storage mass heats up, the temperature of the escaping air also increases. This heat is used to (pre)heat the subsequent modules.
Example of the filling level of serially connected 2000 kWh modules with 600 kW feed-in into the first modulel
The heating of the storage mass occurs exponentially, with the temperature asymptotically approaching that of the supplied air. As soon as one module is sufficiently charged, the hot air is fed directly into the next (already preheated) module.
Example of the temperature profile of serially connected 2000 kWh modules with 600 kW feed-in into the first module
Heat exchange is most efficient at the beginning of the charging process. As the storage mass heats up, the temperature of the escaping air increases (other heat storage manufacturers keep this quiet). Therefore, this heat is used to preheat the subsequent modules.
Control: Temperature measuring devices are linked to a central control unit that activates valves and thus controls the flow paths.
As a result, the modules are flown through during charging and discharging, depending on the situation and requirements, individually (alternating to one another), one after the other (serial), simultaneously (parallel) or a combination of these.
The heat transfer when flowing through a module results in the gas leaving a module with a temperature change compared to entering. If modules are connected in series, a cascade-like temperature change can be implemented across all modules involved. Mixed temperatures can also be achieved by parallel connection.
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