• Energy Research

Exergy-based methods support the identification of thermodynamic inefficiencies and the discovery of optimization potentials in thermal engineering applications. Although a large variety of simulation software is available in this field, most do not offer an integrated solution for exergy analysis. While there are commercial products on the market with such capabilities, their access for research and educational purposes is limited. The presented open-source software offers an integrated and fully automated exergy analysis tool for thermal conversion processes. In a first step, physical exergy is implemented, and the tool is then applied to three different example plants to highlight its capabilities and validate the implementation: A solar thermal power plant, a supercritical CO2 power cycle, and an air refrigeration cycle. The respective models and the results of the analyses are presented briefly. By providing the results in modern data structures, they are easily accessible and postprocessible. Future work will include chemical exergy to enable analyses of applications with conversion of matter. Additionally, the implementation of the exergoeconomic analysis and optimization is envisaged.

Renewable sources of energy supply an increasing share to the electricity mix although they show much more fluctuations than conventional energy sources. Hence, net stability and availability represent very large challenges. Demand response can positively contribute to the solution of this issue as large electricity consumers adapt their consumption to the available electricity. In the past, chloralkali electrolysis has been suggested as such a large consumer. Unfortunately, its main product, chlorine, cannot be easily stored in large amounts, so that downstream processes have to operate based on a fluctuating feed. This work reviews the processes within the chlorine value chain, determines the most promising ones for flexibilisation based on their chlorine consumption, and analyses these processes in more detail to assign them to one of four flexibility categories. It is shown that 45% of the theoretical potential could be used for demand response right away.

The increasing share of variable renewable energies in the power grid is an incentive to explore demand response strategies. Chlor-alkali processes are high potential candidates, according to previous publications. Within Germany’s chemical industry, chlorine production accounts for approximately 20% of electricity use and could play a significant role in power grid stabilisation on the consumer end. This study focuses on the feasibility of load flexibilisation in epichlorohydrin plants, with the second biggest estimated demand response potential for chlorine-based products in Germany. A plant model with allyl chloride storage was created based on real data and literature values. Results from this model, spot market and balancing power prices, and future electricity market scenarios were used in a mixed-integer linear optimisation. We find that benefits from demand response can be generated as soon as additional power and storage volume is provided. The composition of provided types of balancing power bids follows the price trend on the market. Additionally, the computation time could be lowered significantly by running the scenarios in parallel. The results encourage a practical validation of the flexibility of epichlorohydrin production.

State-of-the-art thermodynamic simulation of energy conversion processes requires proprietary software. This article is an attempt to refute this statement. Based on object-oriented programming a simulation and exergy analysis of a combined cycle gas turbine is carried out in a free and open-source framework. Relevant basics of a thermodynamic analysis with exergy-based methods and necessary fluid property models are explained. Thermodynamic models describe the component groups of a combined heat and power system. The procedure to transform a physical model into a Python-based simulation program is shown. The article contains a solving algorithm for a precise gas turbine model with sophisticated equations of state. As an example, a system analysis of a combined cycle gas turbine with district heating is presented. Herein, the gas turbine model is validated based on literature data. The exergy analysis identifies the thermodynamic inefficiencies. The results are graphically presented in a Grassmann chart. With a sensitivity analysis a thermodynamic optimization of the district heating system is discussed. Using the exergy destruction rate in heating condensers or the overall efficiency as the objective function yields to different results.

Demand response is a viable concept to deal with and benefit from fluctuating electricity prices and is of growing interest to the electrochemical industry. To assess the flexibility potential of such processes, a generic, interdisciplinary methodology is required. We propose such a methodology, in which the electrochemical fundamentals and the theoretical potential are determined first by analyzing strengths, weaknesses, opportunities, and threats. Afterward, experiments are conducted to determine selectivity and yield under varying loads and to assess the additional long-term costs associated with flexible operation. An industrial-scale electrochemical process is assessed regarding its technical, economic, and practical potential. The required steps include a flow sheet analysis, the formulation and solution of a simplified model for operation scheduling under various business options, and a dynamic optimization based on rigorous, dynamic process models. We apply the methodology to three electrochemical processes of different technology readiness levels—the syntheses of hydrogen peroxide, adiponitrile, and 1,2-dichloroethane via chloralkali electrolysis—to illustrate the individual steps of the proposed methodology.

The aim of this work is to study a binary Rankine process with a significantly higher efficiency compared to a conventional coal-fired power plant. This paper focuses on the design of the process and especially on an efficient combination of flue gas, potassium, and water streams in the components of the steam generator, such as economizers, evaporators, and superheaters, to decrease the overall exergy destruction. Based on a literature review, a base case for a coal-fired binary Rankine cycle with potassium and water as working fluids was developed and, in order to evaluate the thermodynamic quality of several variants, comparative exergy analyses were conducted. A simulation of the process and calculation of the values for the streams were carried out by using the flow-sheeting program CycleTempo, which simultaneously solves the mass and energy balances and contains property functions for the specific enthalpy and entropy of all the substances used. Necessary assumptions are predominantly based on literature data or they are discussed in the paper. We present the exergy analysis of the overall process that includes the flue gas streams as well as the potassium and water cycles. A design analysis and sensitivity studies show the effects of stream combinations and key parameters on the net efficiency, which is higher than 50%.