Antje Wörner

High Temperature Thermochemical Heat Storage for Concentrated Solar Power Using Gas–Solid Reactions

High temperature thermal storage technologies that can be easily integrated into future concentrated solar power plants are a key factor for increasing the market potential of solar power production. Storing thermal energy by reversible gas-solid reactions has the potential of achieving high storage densities while being adjustable to various plant configurations. In this paper the Ca(OH) 2 /CaO reaction system is investigated theoretically. It can achieve storage densities above 300 kWh/m 3 while operating in a temperature range between 400 and 600°C. Reactor concepts with indirect and direct heat transfer are being evaluated. The low thermal conductivity of the fixed bed of solid reactants turned out to considerably limit the performance of a storage tank with indirect heat input through the reactor walls. A one-dimensional model for the storage reactor is established and solved with the Finite Element Method. The reactor concept with direct heat transfer by flowing the gaseous reactant plus additional inert gas through the solid reactants did not show any limitation due to heat transfer. If reaction kinetics are fast enough, the reactor performance in case of the Ca(OH) 2 /CaO reaction system is limited by the thermal capacity of the gaseous stream to take-up heat of reaction. However, to limit pressure drop and the according losses for compression of the gas stream, the size of the storage system is restricted in a fixed bed configuration.

Power generation based on biomass by combined fermentation and gasification – A new concept derived from experiments and modelling

A new concept is proposed for combined fermentation (two-stage high-load fermenter) and gasification (two-stage fluidised bed gasifier with CO2 separation) of sewage sludge and wood, and the subsequent utilisation of the biogenic gases in a hybrid power plant, consisting of a solid oxide fuel cell and a gas turbine. The development and optimisation of the important processes of the new concept (fermentation, gasification, utilisation) are reported in detail. For the gas production, process parameters were experimentally and numerically investigated to achieve high conversion rates of biomass. For the product gas utilisation, important combustion properties (laminar flame speed, ignition delay time) were analysed numerically to evaluate machinery operation (reliability, emissions). Furthermore, the coupling of the processes was numerically analysed and optimised by means of integration of heat and mass flows. The high, simulated electrical efficiency of 42% including the conversion of raw biomass is promising for future power generation by biomass.

Power-to-liquids: Synthetic fuels from a sustainable pathway

Introduction Liquid fuels will be the fuel of choice for air and cargo transport for the coming decades. Synthetic fuels produced by the power-to-liquid route together with CO2 from industrial processes are a promising alternative to biofuels and can contribute significantly to the production of sustainable liquid fuels. Different process routes using hydrogen obtained by electrolysis from renewable power sources combined with Fischer-Tropsch process are analyzed by process simulation. Results Integration of SOEC with the FTS is highly advantageous in terms of process efficiency. The high pressure steam that is obtained by cooling of the FTS can be used as input for the SOEC that can in this way attain an electrolyser efficiency (electrical) of >95%. The total system efficiency calculated for Power-to-Liquid can be more than 60% for optimal conditions and unit operations. Discussion and Conclusion A sustainable pathway for the production of synthetic liquid fuels is technically feasible. The fluctuating power supply from renewable sources poses questions with regard to system design, operational characteristics and economic viability that will be discussed.