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This work describes the one-dimensional, thermo-hydraulic model of the sCO 2 cycle Sofia developed to investigate optimal control methods and the behaviour of the cycle during operation. This dynamic model includes all devices such as turbomachinery, heat exchangers, valves, and piping including heat loss, in line with concept of the 1 MWe sCO 2 cycle, to be realised in the site of a fossil power plant in the Czech Republic. The model assembly and calculations were conducted using the commercial Modelica-based library ClaRa + using the simulation environment Dymola and in combination with another Modelica-based library, UserInteraction; the real-time simulations, with some parameter changes during the calculation, are made and described in this paper. Nominal parameters were achieved during the steady-state simulation, except for the lower mass flow of sCO 2. Transient simulation of power turbine start-up from standby state and results are also presented in this paper. The nominal state is achieved with the semi-automatic procedure in approx. 3 h. The simulation results allow more detailed analyses of control methods and a better understanding of real device control and behaviour during start-up, shutdown, or other transients. Careful manipulation of turbine valves in coordination with the pressuriser operation was identified as crucial for optimal control of the system. Also, the initial amount of CO 2 in the pressuriser affects its behaviour during transients. • Models of the PCHE and BPHE heat exchangers were prepared, and turbomachines models determined by CFD simulations were used. • Control system of the electric heater, which is the largest facility in the Sofia cycle, was designed. • Real-time simulations were performed using ClaRa+ and UserInteraction Dymola libraries. • Careful trubine valves manipulation and corresponding pressuriser control were identified as key control interventions. • Initial amount of CO 2 in the pressuriser affects its behaviour during transients. [ABSTRACT FROM AUTHOR]

External energy security has gained importance within the EU due to the current Russian-Ukrainian natural gas dispute, but also because of mid- and long-term issues connected to the availability of energy supply in Europe. The Energy Union proposal is supposed to increase the coherence of the EU in external energy, thus contributing to the energy security of the Community. However, various member states have already expressed different (not always positive) views, concerning this project. In order to shed light on the further development of the Energy Union, the present paper – based on 52 semi-structured interviews – examines members states' support for and opposition to the further deepening of integration in external energy security. By analysing Austria, the Czech Republic and Slovakia, this paper argues that member states' preferences depend at least partly on the decision-makers' perceptions of their state's ability to cope with three energy security challenges (external, internal and business). States whose decision-makers believe that their countries are able to successfully cope with these challenges are more likely to oppose further integration in energy security area, while member states whose decision-makers view these tasks as challenging are more likely to support the transfer of competences to the EU. [ABSTRACT FROM AUTHOR]

The data regarding the current potential of unrecyclable waste and its spatial distribution play an essential role in the planning process. As per the circular economy strategies, especially the bulky waste streams suitable for energy recovery are to be identified. The public databases, however, collect data from a variety of sources (production and handling reports), which implies the presence of errors. This paper therefore proposes a multi-objective approach to identification and elimination of such errors to improve the accuracy of the assessment of potential energy recovery. The discussed model tracks the flow of waste from producers to processing nodes and minimises the deviation from the original data. Economic aspects are considered as well by preferring the shortest transport distance. The combination of data reconciliation and network flow enhances performance, as objective functions are solved separately, and only then the normalised individual optima are used in the multi-objective function. The model was tested using a Czech Republic regional-level dataset from 2015. A new perspective on the current state of waste management was provided, and valuable information for future planning was revealed, which can be useful for modelling of flows of other commodities. Image 1 • Novel supply chain model for transportation and treatment reconciliation is presented. • Large amount of bulky waste is identified as suitable for energy recovery. • Region-specific waste potential for an environmental treatment option is analysed. [ABSTRACT FROM AUTHOR]