R. Eisl’s research while affiliated with Institute of Science and Technology Austria and other places

Adiabatic compressed air energy storage systems offer large energy storage capacities and power outputs beyond 100 MWel. Salt production in Austria produces large caverns which are able to hold pressure up to 100 bar, thus providing low cost pressurized air storage reservoirs for adiabatic compressed air energy storage plants. In this paper the results of a feasibility study is presented, which was financed by the Austrian Research Promotion Agency, with the objective to determine the adiabatic compressed air energy storage potential of Austria’s salt caverns. The study contains designs of realisable plants with capacities between 10 and 50 MWel, applying a high temperature energy storage system currently developed at the Institute for Energy Systems and Thermodynamics in Vienna. It could be shown that the overall storage potential of Austria’s salt caverns exceeds a total of 4 GWhel in the year 2030 and, assuming an adequate performance of the heat exchanger, that a 10 MWel adiabatic compressed air energy storage plant in Upper Austria is currently feasible using state of the art thermal turbomachinery which is able to provide a compressor discharge temperature of 400 °C. © 2017, International Centre for Sustainable Development of Energy, Water and Environment Systems SDEWES. All rights reserved.

An active fluidization thermal energy storage (TES) called “sandTES” is presented. System design, the fundamental features and challenges of fluidization stability such as mass flux uniformity, powder transport and heat transfer, as well as auxiliary power minimization are thoroughly discussed. The tools and methods for evaluating or simulating the behavior of the fluidized bed heat exchanger (HEX) and the dense particle flow within it are explained along with criteria for the selection of storage powders.

Active Fluidized Bed Thermal Energy Storage (sandTES) offers a promising alternative to the current state of the art thermal energy storages (TES), such as active TES based on molten salt or passive TES (Regenerators) realised as a porous packing of ceramics. The characteristic of a sandTES system applying sand in an active TES using a fluidized bed heat exchanger (HEX) is explained. The exergetic performance of a sandTES is compared to a passive Regenerator.

Good gas-solid contact is essential in a coal bed gasifier such as in a COREX® melter gasifier. The charged particle size distribution and the particle fragmentation behavior inside the slowly moving fixed bed strongly influence the local counter current gas flow and therefore also the rate of heat transfer between gas and coal, the rate of drying, devolatilisation and gasification. COREX® is the first commercially operating smelting reduction process, based on coal instead of coke, as alternative for industrial ironmaking route via the blast furnace. Besides coal the melter gasifier also contains reduced iron ore and additives, which are not subject of this paper. General multiphase models in commercial CFD codes are not directly applicable to the simulation of moving reactive beds considering changes in particle size distribution. A customized approach based on a combination of Eulerian and Lagrangian formulation is used to describe the flow of gas and solids as well as the physical and chemical processes across the moving bed reactor. The solids flow and the gas flow are represented by a set of Eulerian equations. So the flow of solids respectively the flow of a granular material is treated as a continuum with appropriate material properties. The balances for solids and gas flow are interconnected via source terms. The energy balance of the solids flow and the models for fragmentation and devolatilization are implemented by means of a Lagrangian formulation. The solids flow consists of a set of particle sizes including dust. This set of particle sizes changes according to local process parameters which are: solids pressure, shear stress, rate of water evaporation (coal drying), rate of devolatilization, rate of gasification and rate of temperature change. To take this into account a fragmentation model has been developed which solves a conservation equation for each particle size. The local source terms within these equations are connected to the above mentioned local process parameters. Due to the fact that the considered moving bed consists of nonuniformly sized particles the temperature of small particles will be different from the temperature of larger particles. However, the temperature of the particles is important for the rate of drying, devolatilization and gasification. Therefore an energy balance for each particle size is implemented within the presented model. In a first step the model has been used to study the impact of a changing particle size distribution on the gas flow and heat transfer between gas und solids. The effect of fragmentation on the devolatilization process has been simulated too. Next development steps are the integration of models for coal drying and gasification as well as a gas phase reaction model.