Renewable hydrogen from water electrolysis could contribute to the defossilization of various energy intensive sectors but continues to suffer from unfavorable economics. Attention is being paid to ...the direct supply of renewable electricity to electrolyzers; in particular from photovoltaic (PV) and wind units, whose fixed remuneration period has expired. However, detailed analysis of such operating strategies via modeling and simulation of the dynamic behavior of alkaline electrolysis (AEL) and polymer electrolyte membrane electrolysis (PEMEL) is lacking. In this work, an electrolyzer model is developed for both AEL and PEMEL and analyzed for PV and wind power input data sets from the region of northwest Germany. It is shown that key performance indicators (KPI) such as hydrogen production efficiency, electricity utilization rate, product output and net production costs are highly reliant on the shape of transient power input signals as well as the electrolyzers ability to cope with them. PEMEL technology generally has higher electricity utilization rates than AEL, while AEL still achieves relatively large hydrogen production quantities due to its higher efficiency. Thus, the better operational flexibility of PEMEL cannot generally be considered advantageous in terms of hydrogen production quantities – the same applies for economics. The most competitive hydrogen production costs were 4.33 € per kg for the AEL technology with direct electricity supply from old wind farms, which no longer receive fixed remuneration.
•Modeling and simulation of dynamic electrolyzer operation over a period of one year.•KPI's are reliant on transient power profile and electrolyzer operating flexibility.•Cheapest hydrogen production costs are 4.33 €/kg for AEL with onshore wind.
Methanol is a very valuable chemical with a variety of uses, either as a fuel or as building block for the synthesis of other chemicals. In the last years, interest was growing in the production of ...methanol from CO2, based on the so called “Power-to-Fuel” concept. In this research, an equilibrium analysis of a methanol reactor with pure CO2 and H2 in the feeding stream was developed. Three novel reactor configurations at equilibrium conditions were considered: once-through reactor, reactor with recycle of unconverted gases after separation of methanol and water by condensation; reactor equipped with membrane permeable to water. An additional important feature of this work was the development of a methodology that assists in comparison of different process schemes by simulation of two different methanol plants configurations in ChemCad®. An adiabatic kinetic reactor with recycle of unconverted gases was considered and simulated in Aspen Plus®, while the performance of a methanol reactor with heat exchange at the pipe wall was simulated in MATLAB. Results show that at equilibrium conditions a reactor with the recycle of unconverted gases ensures the highest CO2 conversion: 69% at 473 K and 55 bar. In addition, the use of pure CO2 and H2 in the feeding stream allows an overall reaction enthalpy change lower than that obtained by the use of syngas in the feed. The kinetic simulation of the methanol reactor in MATLAB showed that axial dispersion phenomena are negligible and the effect of the global heat exchange coefficient on reactor performance is less important than the effect of isothermal heat exchange fluid temperature.
•An equilibrium analysis of three methanol reactor configurations by CO2 and H2.•A modeling of real methanol plants and methanol reactor from CO2 an H2.•Reactor with the recycle of unconverted gases reaches the highest CO2 conversion.•Phenomena of axial dispersion can be neglected in the packed bed methanol reactor.•Operating ranges for the feasibility of methanol production by pure CO2 and H2.
•A model for the design and operation of novel hydrogen supply chain networks for Germany.•A novel hydrogen based economy from conventional towards renewable technologies.•A valuable and up-to-date ...dataset of economic, geographic and production data for Germany.
This work provides a comprehensive investigation of the feasibility of hydrogen as transportation fuel from a supply chain point of view. It introduces an approach for the identification the best hydrogen infrastructure pathways making decision of primary energy source, production, storage and distribution networks to aid the target of greenhouse gas emissions reduction in Germany. The minimization of the total hydrogen supply chain (HSC) network cost for Germany in 2030 and 2050 years is the objective of this study. The model presented in this paper is expanded to take into account water electrolysis technology driven by solar and wind energy. Two scenarios are evaluated, including a full range of technologies and “green” technologies using only renewable resources. The resulting model is a mixed integer linear program (MILP) that is solved with the Advanced Integrated Multidimensional Modeling System (AIMMS). The results show that renewable energy as a power source has the potential to replace common used fossil fuel in the near future even though currently coal gasification technology is the still the dominant technology.
Two of the most commonly used solid biomass sources for fuel are wood chips and wood pellets. The calorific value and the moisture content of those biofuels determine the efficiency of the CHP and ...the biorefinery plants. Therefore, with the increased shift towards a biobased economy, the biomass cost and its physical properties must be precisely determined. Most of the current standards are lacking and provide neither enough details about the issues caused by the biomass heterogeneity nor with the variation in experimental practice. Phenomena such as data scattering, poor repeatability and wide uncertainty, are mostly observed during the measurements of the calorific value and the moisture content. To overcome such issues, an interlaboratory comparison between three national metrology institutes using bomb calorimetry has taken place. The comparison helped to identify the root causes behind the poor reproducibility of the wood samples. Factors such as the equilibrium moisture content of the biomass, the pellet mass, the applied pressure to form the pellet, the handling techniques and the determination errors are highlighted and analyzed. The final results paved the way to provide an enhanced detailed experimental practice where the repeatability and reproducibility have been strongly improved. Moreover, the detailed uncertainty sources and calculations are presented. It has been found that by fulfilling the recommended approach the measurement repeatability improved by up to 50–80%, while the final uncertainty improved by 10–30%. This enhancement leads to a maximum relative expanded uncertainty of around ±1% (coverage factor of k = 2 and a confidence level of 95%).
Direct air carbon capture (DAC) technologies can substantially lower the CO2 concentrations in the atmosphere by enabling negative emissions. This study shows in detail the design of the DAC plant at ...industrial scale and provides insights on its performance in terms of process economic and CO2 emissions count. The proposed DAC plant is optimized to capture CO2 directly from the atmospheric air, employing a sensitivity analysis to find the influence of operation and design parameters on the total cost. Absorption using sodium hydroxide as chemisorbent is utilized with a capture rate of 0.7. Industrially mature common process units are considered to achieve a design that is relevant in the near future. An initial base case design indicates a carbon cost of 244 $/ton-CO2 with the operating expenses comprising 84% of the total cost. Then, two scenarios are proposed to enhance the process performance: heat integration and use of renewable energy. Through the heat integration, the carbon ratio (CO2 captured / CO2 emitted) improves from a value of 2.7 for the base case to 3.73, meaning less CO2 is emitted per captured amount due to lower fuel consumption. The resulting cost goes down to 125 $/ton-CO2, with two additional heat exchangers added to the network. Furthermore, renewable scenario is considered where a parallel electrolysis stage feeds the process hydrogen fuel and oxygen required for combustion in the calciner. This scenario indicates that higher operating costs are incurred due to the expensive green fuel. Finally, a profitability analysis is performed to establish the feasibility for further processing to methanol in a Power-to-X facility. The estimations indicate that the hydrogen price has to go down by 46.3% in order to break-even.
In future energy scenarios with a high share of renewable energies within the electricity system, power-to-heat technologies could play a crucial role for achieving the climate goals in the heating ...sector. District heating systems can integrate volatile wind and photovoltaic energy sources and resolve congestions within the electricity grid, leading to curtailment of renewable electricity generation. This paper presents a design approach for setting up system-beneficial power-to-heat-based district energy systems. Within the scope of the project QUARREE100 an existing district in the provincial town Heide in Northern Germany is examined. A linear investment and unit commitment optimization model is applied. By considering local dynamic emission factors for grid-sourced electricity, which contain information on local wind energy curtailment as well as the emission intensity of the overall electricity generation, a renewable and system-beneficial design can be derived. With this method, the minimal rated power and capacity of energy converter and storage units can be determined to achieve emission reductions with respect to minimum costs. The approach of using different methods for the consideration of the emissions of grid-sourced electricity is analyzed based on different scenarios. By using a dynamic emission factor for grid-sourced electricity, lower emissions with fewer costs can be achieved. It is shown that a dynamic assessment leads to different design decisions and far-reaching deviations in the unit commitment. The results clearly show that a constant emission factor is no longer an option for grid-sourced electricity in urban energy system models.
District heating systems have a great potential for supporting the energy transition towards a renewa-ble energy system, and could also be an option in less dense populated urban districts and rural ...communities with a medium heat density. In these cases, distributed thermal energy storages at each building could improve the overall system performance by enabling a leaner sizing of the piping sys-tems due to peak-shaving and reducing the heat losses of the distribution grid. But how can distribut-ed storages already be considered within the design of the district heating network itself? And what are the quantitative benefits with respect to the district heating piping system? This paper answers these questions and presents an open-source optimisation approach for designing the piping network of a district heating system. This includes the optimisation of the network topology, the dimensioning of the pipes, and the consideration of distributed storage options. A linear mixed-integer program-ming model with a high spatial resolution including heat storages at each customer has been imple-mented. Within the QUARREE100 project, the approach is demonstrated on a real world case of an existing district with 129 houses in the provincial town Heide in Northern Germany. In the scenario with 1 m³ heat storages, the thermal losses of the district heating network can be reduced by 10.2 % and the total costs by 13.1 %.
The flexible operation of alkaline water electrolyzers enables power-to-x plants to react efficiently to different energy scenarios. In this work, a novel scheduling model for alkaline water ...electrolysis is formulated as a mixed-integer linear program. The model is constructed by implementing operational states (production, standby, idle) and transitions (cold/full startup, shutdown) as integer variables, while the power loading and hydrogen flowrate are set as continuous variables. The operational characteristics (load range, startup time, ramp rates) are included as model constraints. The proposed model allows finding optimal number of electrolyzers and production schedules when dealing with large data sets of intermittent energy and electricity price. The optimal solution of the case study shows a balance between hydrogen production, energy absorption, and operation and investment costs. The optimal number of electrolyzers to be installed corresponds to 54% of the ones required to absorb the highest energy peak, being capable of loading 89.7% of the available energy during the year of operation, with an overall plant utilization of 93.7% and 764 startup/shutdown cycles evenly distributed among the units.
•A novel scheduling model for alkaline water electrolysis (AEL) has been developed.•The model introduces AEL states, transitions, and operational characteristics.•The model allows to find optimal number of electrolyzers and production schedules.•The model is suitable to handle large data sets of fluctuating energy and prices.•The MILP solution provides a balance between production, energy absorption and costs.
•Power grid and alkaline water electrolysis models have been coupled through data exchange.•Average power line utilization as indicator of grid impacts.•Daily-constrained hydrogen production yields ...low production costs and minimum grid congestion.
This work presents a study of the effects that integration of electrolysis facilities for Power-to-X processes have on the power grid. The novel simulation setup combines a high-resolution grid optimization model and a detailed scheduling model for alkaline water electrolysis. The utilization and congestion of power lines in northern Germany is investigated by setting different installed capacities and production strategies of the electrolysis facility. For electrolysis capacities up to 300 MW (∼50 ktH2/a), local impacts on the grid are observed, while higher capacities cause supra-regional impacts. Thereby, impacts are defined as deviations from the average line utilization greater than 5%. In addition, the minimum line congestion is determined to coincide with the daily-constrained production strategy of the electrolysis facility. Our result show a good compromise for the integrated grid-facility operation with minimum production cost and reduced impact on the grid.
The goal of this study is to develop a dynamic model for a Carbon Capture (CC) process that can be integrated with a water electrolysis facility. The possibility of operating the post-combustion CC ...plant dynamically is investigated. The final model successfully tracks the parallel hydrogen production, providing the stoichiometric required CO2 stream for the subsequent methanol reactor. A dynamic model is used to configure controllers and to test the unit performance and stream conditions for various set points. Through the transient operation, the required feed gas is provided while optimizing the solvent and energy requirements. It is found that the slowest acting stage is the reboiler with a time constant of 3.8 h. Other process variables stabilize much quicker, requiring only a few minutes to reach steady-state conditions. The hydrogen-tracking scenario shows that the carbon capture plant can successfully operate under varying conditions with a maximum CO2 output increase of 7% of the minimum flowrate in the representative 24 h simulation time. The output CO2 stream is maintained at the desired >98% purity, 25 °C temperature, and 1.85 bar pressure, which allows to successfully perform hydrogen tracking operations.
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