• Energy Research

Abstract In this paper, a thermo-economic analysis concerning a methanol production plant is performed. In particular, this study was developed with the aim of evaluating the opportunity and viability of obtaining methanol from the chemical reaction between recycled CO2, emitted from a fossil-fuel power station, and hydrogen produced by water electrolysis. This solution can represent an interesting carbon dioxide reduction method and methanol as a product can be considered an energy storage means. As a first step, a thermodynamic analysis is performed in order to determine the mass and energy flows of the plant; then, a feasibility analysis concerning a large size methanol production plant is performed taking into account three different economic scenarios (Germany, Italy, and China). In order to evaluate the economic viability, the total investment cost and payback period are calculated in all the scenarios. Different methanol and electrical energy prices are considered, to take into proper account the influence of these parameters on mid-term future scenarios. Moreover, a sensitivity analysis, considering different oxygen selling prices and PEM electrolyzer capital costs, were performed.

This paper presents a techno-economic feasibility analysis related to a heat pump installation in a poly-generative energy district to convert the overproduction of electricity into thermal power, easy to be stored in thermal storage tanks. The heat pump technology is already used for thermal/cooling energy production in different areas although application in energy districts in a power-to-heat modality to improve management of electrical/thermal energy demands is still limited.In this research, the installation of a heat pump in the poly-generative smart grid located at the University of Genoa Campus is presented. A time dependent one-year techno-economic analysis of the energy district is performed, throughout a model built with a software developed by the authors. The integration of the heat pump in the energy district is analysed, comparing the energetic, environmental and economic performance to the present configuration of the poly-generative energy district. The results show that the heat pump introduction grants several advantages, such as a reduction in gas consumption (24 ton/year, −15%) and an increase in the annual energy efficiency of cogenerative prime movers which can work for a higher number of hours (+23%) close to the design point.

Abstract In this paper, the authors present an innovative approach to compare the most promising innovative technologies for energy production and storage for maritime applications. The developed algorithm, which include a large database built with market and literature data, compares several possible solutions, including innovative ones, from the environmental, economic and energetic standpoints. A detailed decription of the functions implemented in the database is reported, explaining also in detail the algorithm developed to evaluate and compare the technologies. Then, the methodology is applied to two case studies to demonstrate the algorithm’s potential, the reliability of the wide range of data included in the database and the impact of the scenario on the final results. The investigated case studies are: (i) a small size passenger ship operating in urban areas (ii) a large size cruise ship. Analyzing the first case study, a focus on the impact of generation unit and fuel storage systems is developed for the most promising solutions, represented by fuel cells in comparison to standard solutions. The second case study shows that, as could be expected, the most promising solutions in this range of application is the use of MDO or LNG in Internal Combustion Engines. In order to evaluate the future potential of the different alternative fuels, a sensitivity analysis is performed to evaluate the impact of the increasing emissions' importance: methanol, LNG, and ammonia are indicated as the most futurible fuels. It is worth noting that the presented approach has a general validity, thus it can be applied to other ships' typologies; the modular structure also allows for including further emerging technologies.

In this paper the design point definition of a pressurised hybrid system based on the Rolls-Royce Integrated Planar-Solid Oxide Fuel Cells (IP-SOFCs) is presented and discussed. The hybrid system size is about 2 MWe and the design point analysis has been carried out using two different IP-SOFC models developed by Thermochemical Power Group (TPG) at the University of Genoa: (i) a generic one, where the transport and balance equations of the mass, energy and electrical charges are solved in a lumped volume at constant temperature; (ii) a detailed model where all the equations are solved in a finite difference approach inside the single cell. The first model has been used to define the hybrid system lay out and the characteristics of the main devices of the plant such as the recuperator, the compressor, the expander, etc. The second model has been used to verify the design point defined in the previous step, taking into account that the stack internal temperature behavior are now available and must be carefully considered. Apt modifications of the preliminary design point have been suggested using the detailed IP-SOFC system to obtain a feasible solution. In the second part of the paper some off-design performance of the Hybrid System carried out using detailed SOFC model are presented and discussed. In particular the influence of ambient conditions is shown, together with the possible part load operations at fixed and variable gas turbine speed. Some considerations on the compressor surge margin modification are reported.

Abstract The aim of this paper is the analysis of a turbocharged Solid Oxide Fuel Cell (SOFC) system considering the influence of fuel composition variation. This is an innovative system layout based on the coupling of an SOFC stack with a turbocharger. The SOFC pressurization carried out with a turbocharger instead of a microturbine is a solution to combine high efficiency with reduced-cost plant layout. Moreover, the fuel flexibility is an essential issue to operate the system with different fuel compositions ranging from natural gas to biogas (considering also the CO2 removal option). This research activity started from the development of a steady-state system model using previously validated tools. The software was implemented in Matlab®-Simulink® environment considering the coupling of the different plant components. The analysis was started considering design conditions for a system fed by biogas (50% CH4 and 50% CO2 molar composition). Then, to reach fuel flexibility performance (as required for applications with renewable sources), the anodic ejector was re-designed to satisfy the related constraint for the Steam-to-Carbon ratio. The mentioned change in fuel composition involved also the control valves (bypass and/or bleed) to maintain the SOFC temperature at its set-point value, taking into account all the system constraints.

Abstract The aim of this study is to analyse the off-design performance of an innovative turbocharged solid oxide fuel cell system, fed by biogas and designed to generate 30 kW during nominal operating conditions. The layout of such a plant combines the high efficiencies of the solid oxide fuel cell with a reduced-cost option for fuel cell pressurization: fuel cells are usually pressurized by a micro gas turbine, but the alternative use of a turbocharger, a mass-produced component widely used in the automotive field, could reduce significantly the capital cost of the system. This kind of layout has been rarely investigated in literature, and a detailed performance analysis of a turbocharged SOFC system would be a valuable source of information for both academia and industry. To perform this analysis, a steady-state model has been created using a modular tool developed in Matlab®-Simulink® that includes off-design models of the system components. The model has been used to compare different control strategies. The most suitable control strategy, based on wastegate and cold bypass valves, was adopted, obtaining compliance with the operative constraints and high system efficiency. Afterward, the system steady-state operation was simulated for various electric power loads and ambient temperatures. The performance analysis focused on the effect of these two variables on the system behaviour and has provided insight on the influence on the most significant system outputs, including global efficiency, temperatures and pressures. A system efficiency increase was observed at part load, with values growing from 50.8% to 57.3%. Higher values of ambient temperature resulted in a more significant pressurization of the fuel cell, affecting positively the system efficiency: from 50.5% at 0 °C to 51.0% at 30 °C. Great attention was paid to the system constraints, to verify that the plant could operate properly in all the considered conditions. The proposed control strategy was tested and proved to be effective at achieving this objective.

Abstract This work deals with the design and off-design performance evaluation of an anodic recirculation system based on ejector technology for solid oxide fuel cell hybrid applications. The analysis presented here has been divided into three parts: (i) ejector design taking into account all the thermodynamic, fluid dynamic and chemical constraints, such as steam to carbon ratio (two ejector geometries have been considered: constant area mixing section, constant pressure mixing section); (ii) stand-alone ejector design and off-design performance analysis; (iii) influence on the whole hybrid system—SOFC, reformer, anode recirculation-design and off-design performance of the ejector primary flow conditions (hybrid system part-load conditions).

We present here a model we have established for a laboratory-size SOFC system. Model equations are presented and discussed, together with an extensive model validation, carried out in both steady state and transient operating conditions. The validated model is then used to simulate four classes of system faults, i.e. air leakage, fuel leakage, SOFC degradation and reformer degradation. When the different faults occur, the physico-chemical operating parameters of the system vary in a different manner, and our main objective is to understand their behavior. For example, for the system under analysis, SOFC degradation and fuel leakage cause a decrease of the gas discharge temperature, while reformer degradation causes an increase of the same parameter. The results of the fault analysis are described and discussed, and are reported in such a way to provide a basis for the development of an FDI tool based on pattern recognition techniques.