CET vol 99 DOI: 10.3303/CET2399097 Paper Received: 15 January 2023; Revised: 6 March 2023; Accepted: 20 April 2023 Please cite this article as: Russo R., Coppola T., Micoli L., Pietra A., 2023, Preliminary Investigation of a Multi-MW Solid Oxide Fuel Cell Power Plant to be Installed on Board a Cruise Ship, Chemical Engineering Transactions, 99, 577-582 DOI:10.3303/CET2399097 CHEMICAL ENGINEERING TRANSACTIONS VOL. 99, 2023 A publication of The Italian Association of Chemical Engineering Online at www.cetjournal.it Guest Editors: Sauro Pierucci, Flavio Manenti Copyright © 2023, AIDIC Servizi S.r.l. ISBN 978-88-95608-98-3; ISSN 2283-9216 Preliminary Investigation of a Multi-MW Solid Oxide Fuel Cell Power Plant to be Installed on Board a Cruise Ship Roberta Russoa*, Tommaso Coppolaa, Luca Micolia, Andrea Pietrab aUniversity of Naples Federico II, Department of Industrial Engineering bFincantieri group S.p.a roberta.russo5@unina.it As the use of both clean energy technologies and alternative fuels in the maritime sector is spreading, studies dealing with the installation of multi-MW power generation plants on board ships have been increasing. Considering this, the present work proposes a 12 MW Solid Oxide Fuel Cell (SOFC) to be installed on board a cruise ship of about 175000 gross tonnes, 345 m length, and powered by Liquefied Natural Gas (LNG). It is supposed that the SOFC generates electrical energy and provides part of the thermal power demand by integrating a heat recovery system. A zero-dimensional (0D) Aspen Plus model has been developed to optimize the onboard layout and to predict the performance of the integrated power plant. Specific parameters, such as the fuel utilisation factor, the pre-heated air temperature, the anodic recycle flow rate, and the exhaust gas temperature, have been manipulated to evaluate the overall efficiency of the integrated power plant under different operating conditions. The model has been validated by comparing the results obtained with data from literature and commercial SOFC modules. A layout configuration of the SOFC plant is suggested and the performances are investigated by varying the efficiency in the range of 60-40%. 1. Introduction With ever-increasing attention to the issue of sustainability in the maritime shipping sector, it is increasingly necessary to introduce important technological changes to reduce emissions and the impact they generate on the environment (Ampah et al., 2021). Starting from 1st January 2023, new and supplementary regulations became effective to optimize the efficiency of ships and encourage the introduction of alternative fuels to reduce the carbon footprint and the overall impact of the sector (Joung et al., 2020). Favouring compliance with environmental regulations, in line with more sustainable development in the shipping industry, Fuel Cell (FC) power generation is a technology that shows great potential in eliminating harmful emissions (e.g. NOX, SOX, and particulate matter), and in the reduction of CO2 emissions, especially when compared with emissions from diesel engines (Altosole et al., 2022). A FC power pack consists of a fuel and oxidant processing system and a stack of single FCs that convert the chemical energy of the fuel to electric power through electrochemical reaction (Abdelkareem et al., 2021). There are different types of FC technology, mainly classified according to their operating temperature and electrolyte materials (Sazali et al., 2020). Smaller and medium power applications may favor low and medium temperature FC technologies, such as Proton Exchange Membrane FC (PEM) and high-temperature PEM FC. Larger application which can more easily accommodate waste heat solutions, such as industrial and large maritime, are more suitable for the high temperature technologies such as Solid Oxide FCs. The deployment of FCs fueled with low-carbon fuels (e.g. Natural Gas, NG) or green fuels will also bring local and regional benefits as both emissions and noise are drastically reduced (Kumar Singla et al., n.d.). A SOFC operates at temperatures between 500-1000°C having an electrolyte based on porous ceramic material, the most commonly used being yttrium-stabilized zirconia. The anode is generally made of a nickel alloy, while the cathode is normally made of lanthanum strontium manganite. 577 mailto:roberta.russo5@unina.it The feature that makes the SOFC a very attractive technology for the maritime sector, where the introduction of different alternative fuels represents a challenge, is the flexibility of fuel supply. In fact, SOFCs are independent of the hydrogen supply chain and related challenges, and can be fed with NG, light hydrocarbon mixtures, alcohols, and biogas. Fuels are converted into a hydrogen-rich stream through external or internal reforming and CO2-shift reactions, favoured by the internal thermodynamic condition (IMO’s Work to Cut GHG Emissions from Ships, n.d.). The resulting process gas is a stream of H2, CO, CO2, H2O, N2 and CH4 in different proportions depending on the primary mixture treated and the operating conditions. SOFCs also electrochemically convert carbon monoxide (CO), thus contributing to energy production (Baldi et al., 2020). SOFCs generally have energy efficiencies of up to 60% which can be further increased when combined with Heat Recovery Systems (HRS), thus saving additional fuel (Al-Hamed & Dincer, 2021). Considering the overall benefits that could derive from a SOFC power plant on board a ship, this study considers a multi-MW power plant based on this technology to be installed on board a cruise ship to supply the hotel loads and part of the thermal loads by integrating an HRS. As a case of study, a large cruise ship of the latest generation powered by LNG of about 175000 gross tonnes and 345 m length was considered. The study aims to optimize the onboard integrated system layout and evaluate its performance by using a 0D Aspen Plus model. A preliminary investigation on the impact of such a system on the global footprint of the ship is also conducted. 2. SOFC model There are different SOFC stack technologies and plant designs depending on materials' components, power size, specific application, and SOFC producer (Ellamla et al., 2015). In this work, it has been assumed to model a planar SOFC operating at about 900 °C with an anode gas recirculation, which is one of the most used technologies for nominal power of the order of hundreds of kW (Cigolotti et al., 2021). Since in Aspen Plus there is no built-in model that can represent the SOFC stack, each of its components has been considered as a separate unit and modelled using the unit operation blocks provided with the software. The thermodynamics and reaction kinetics of each block has been implemented according to the literature data. Each block incorporates complex phenomena like chemical, equilibrium, and electrochemical reactions, and heat and mass transfers, which allow the investigation of single SOFC cell performances, losses, etc. Models of this type are still generally difficult and time-consuming to develop and use as they require the definition of several parameters related to both the materials used and the stack geometry, which are often not declared by SOFC manufacturers. However, this investigation does not achieve the objectives of the present work, which instead focuses on optimizing the layout of the multi-MW SOFC power plant on board the cruise ship to be integrated with an HRS (Rokni, 2010); therefore, the 0D model has been developed for the preliminary calculation of mass and heat flows (Martins, 2022). The flowsheet of the SOFC plant is shown in Figure 1 while Table 1 lists the acronyms and the Aspen Plus unit operation blocks used with a brief description. Figure 1: SOFC power generator system flowsheet built-in in Aspen Plus. 578 Table 1: Description of Aspen Plus unit operation blocks of the flowsheet presented in Figure 1. Block ID Aspen Plus unit block Description NG-TCON Heater Sets the fuel inlet temperature MIXER Mixer Mixes of the recycled unconverted fuel with fresh fuel T-CON Heater Preheats the inlet stream to the reformer reactor up to 850 °C PREREFOR RGibbs (Gibbs free energy reactor) Simulates steam reforming of CH4 of lighter hydrocarbons and the shifting of CO to H2 (Water Gas Shift reaction) ANODE RGibbs (Gibbs free energy reactor) Simulates the reforming and electrochemical reactions occurring at the anode ANSEP FSplit (Splitter) Splits the anode outlet into a recycle stream and a stream sent to the afterburner AFTERBUR RStoic (Stoichiometric reactor) Simulates the complete combustion of the remaining fuel with the depleted oxidant AFT-TCON Heater Manages the overall heat balance HEATER Heater Sets the cathode temperature at 900 °C CATHODE Sep (Separator) Simulates the cathode and the electrolyte ion flow separating the O2 required by the electrochemical reactions from the air inlet stream HEATEX HeatX (Heat exchanger) Preheats the inlet air using the hot gases from the afterburner AIR-TCON Heater Sets the air inlet temperature The evaporated LNG (CH4: 90 % vol; C2H6: 8% vol; C3H8: 2% vol) is fed to the plant at the constant temperature of 20°C and then mixed with the hot unconverted products coming from the anode section. The mixture is sent to an external reforming reactor (pre-reformer) operating at about 850 °C which partially converts methane, light hydrocarbons contained in the LNG, and steam mainly into hydrogen, carbon monoxide, and carbon dioxide. Products from the pre-reformer are fuelled to the anode section where the electrochemical oxidation and the reforming reactions take place, assuming that all the reactions reach the chemical equilibrium. The anode outlet is split into a recycle stream and a stream sent to the afterburner. The anode recycle is at about 900 °C and provides the steam and heat required for the endothermic reforming reactions occurring in the pre-reformer. The recycle flow rate depends on the steam-to-carbon ratio to avoid carbon deposition on the catalyst surface (Doherty et al., 2015). The presence of the afterburner allows the complete combustion of the remaining fuel from the anode with the depleted oxidant and provides the heat required to maintain the stack components at 900 °C. A heat exchanger is used to pre-heat the air inlet using hot exhaust gases from the afterburner. The generated power and voltage depend on the fuel consumption, SOFC efficiency, etc. which are calculated by applying the widely known equations taken from the literature (Winkler, 2016). This model can be adapted to different SOFC power sizes. In the present work, to better manage the load variations, a plant composed of multiple 300 kW modules (each made up of 4 x 75 kW SOFC stacks) was considered. Each basic module has a footprint of about 1.1 x 1.3 x 2.1 m (D x W x H), a weight of about 1.8 t, and integrates all the required auxiliaries (BoP – Balance of Plant) (McPhail et al., 2022). 3. Results 3.1 Model validation The model was validated using data from literature and those available from some commercial products based on 20 - 100 kW SOFC stacks and plants powered by natural gas. Specifically, the calculated exhaust temperature (TEX) and available thermal power were compared with literature data. It was considered that TEX is affected by the air flow rate, which varies considering an O2 inlet / O2 stoichiometric ratio in the range of 3.5 - 5.5 depending on the considered SOFC technology and the overall heat balance. It resulted that the calculated TEX varies in the range of about 280 – 350 °C and decreases as the air flow increases; this temperature range is in agreement with literature data (Doherty et al., 2010, 2015). To simplify the calculation, steady-state and isothermal conditions have been considered and all the pressure drops have been neglected. 3.2 Simulation results Multiple sensitivity analyses were conducted to evaluate the optimal values of some SOFC stack’s parameters; due to the limited space available for the text, it is preferred to report only the optimal calculated values, which are shown in Table 2. These values are similar to those presented in other works (Pourrahmani et al., 2022). Then, assuming 60% electric efficiency and steady-state condition, the specifications of each stream of the SOFC model (refer to 579 Figure 1) can be calculated and reported in Table 3. It should be noted that the fuel utilization factor refers to hydrogen electrochemically reacting to produce the electric power compared to the stoichiometric one that could be obtained from the LNG through the reforming reactions. It is assumed that CO is shifted to H2 and only H2 reacts electrochemically. Table 2: SOFC stack parameters. Parameters Value Anodic recycle ratio (%) 85 Fuel utilization factor (%) 67 Molar feed ratio (molAIR/molLNG) 23 Pre-heated air temperature (°C) 650 Table 3: Main specifications of each stream of the proposed SOFC model. Stream Mass Flow [kg/h] T [°C] Composition [mol fraction] H2 O2 CH4 CO N2 H2O C2H6 C3H8 CO2 AFT-PR 338.9 1183 0 0.10 0 0 0.75 0.10 0 0 0.05 AFTB-IN 300.6 850 0 0.13 0 0 0.85 0.02 0 0 0 AFTB-OUT 339.0 850 0 0.10 0 0 0.75 0.10 0 0 0.05 AIR 330.2 20 0 0.20 0 0 0.80 0.02 0 0 0 AIR-CAT 330.2 650 0 0.20 0 0 0.80 0.02 0 0 0 AIR-IN 330.2 25 0 0.20 0 0 0.80 0.02 0 0 0 AIRC-OUT 330.6 650 0 0.13 0 0 0.85 0.02 0 0 0 AN-OUT 255.7 850 0.13 0.08 0 0.21 0 0.48 0 0 0.10 EXHAUST 399.0 303 0 0.10 0 0 0.75 0.10 0 0 0.05 NG 8.8 20 0 0 0.90 0 0 0 0.08 0.02 0 NG+R 226.2 791 0.12 0.07 0.04 0.20 0 0.45 0 0 0.10 NG-IN 8.8 25 0 0 0.90 0 0 0 0.08 0.02 0 O2-IN 29.5 650 0 1.00 0 0 0 0 0 0 0 RECYCLE 217.4 850 0.13 0.08 0 0.21 0 0.48 0 0 0.11 REF-IN 226.2 850 0.12 0.07 0.04 0.20 0 0.45 0 0 0.10 REF-OUT 226.2 850 0.16 0 0 0.21 0 0.50 0 0 0.14 UN-PROD 38.4 850 0.13 0.08 0 0.21 0 0.48 0 0 0.11 3.3 Plant performance The performance of a 12 MW SOFC power plant was investigated by considering the stack efficiency value at 60, 50 and 40%. An efficiency reduction is expected due to ageing. Most relevant results are reported in Table 4. Table 4: Specifics of the main streams. Stream Temperature [°C] Mass Flow [t/h] η 0.60 0.50 0.40 0.60 0.50 0.40 NG 20 20 20 1.4 1.8 1.6 AIR 20 20 20 52.8 108.6 45.9 EXHAUST 303 284 316 54.2 110.4 47.5 As expected, the reduction in efficiency affects the TEX, fuel consumption, airflow, and produced power. The highest efficiency value (60 %) results in the lowest fuel consumption (1.4 t/h) producing exhaust at about 303 °C. If the efficiency is at 50 %, as the fuel consumption increases (1.8 t/h), the generated heat increases, and the airflow increases accordingly (almost doubled), thus resulting in a higher thermal power available in the exhaust for heat recovery, even though TEX is slightly lower (284 °C). In this condition, the nominal power is still guaranteed (12 MW). In the case the efficiency is 40%, the resulting power that can be produced by the SOFC plant is about 10.1 MW as part of the fuel is not converted electrochemically but burns catalytically producing overheating; as a result, an increase in the airflow is required to control the overall heat balance, and the fuel flow is reduced as well. 580 3.4 Onboard layout Three rooms were identified on board the cruise ship (named FC Room 1, 2 and 3) intended to contain the SOFC modules, with volume and surface area as per Table 5. According to this, to generate 12 MW of electric power, the arrangement of 40 SOFC modules is proposed as shown in Figure 2. The weights and footprints of the SOFC modules in each room are shown in Table 5. Table 5: Main specifics of the FC rooms on board the cruise ship. SOFC ROOM Module [num] Power [kW] Volume [m3] Area [m2] Weight [t] Volume [m3] Area [m2] Room 1 14 4200 270.2 126.3 62.6 1290 300 Room 2 14 4200 270.2 126.3 62.6 1290 300 Room 3 12 3600 231.6 108.2 53.6 780 280 Figure 2 : 12 MW SOFC layout flowsheet built-in in Aspen Plus. The fuel distribution scheme includes an evaporator for LNG and a separator of the main NG flow into three main streams, which are connected to secondary separators which feed the SOFC modules of the three rooms (in Figure 2). A vent line was also considered to manage overpressures and overloads. Each separator feeds two separate groups of SOFCs composed of 7 or 6 modules connected in series, where the first module’s overload fuel of constitutes the inlet stream of the second one, and so on. The last module of the series has no residual NG. It was verified that this configuration ensures that most of the SOFC modules operate in the optimal supply condition in case of load variations, allowing the lowest LNG consumption (highest efficiency). A similar configuration is also adopted for the distribution of the air streams to the cathodic sections. The exhausts from each module are collected by a mixer and then directed to an HRS, which can both generate steam flows and recover condensed water to be used on board, thus saving further fuel. 4. Conclusions The installation of a 12 MW SOFC power plant on board an LNG-fuelled cruise ship was considered in order to reduce its global emissions, especially while moored in ports, where it would be beneficial to turn off the dual- fuel engines. The SOFC plant is meant to supply the hotel loads and a part of the thermal loads by integrating a heat recovery system. A zero-dimensional Aspen Plus model was developed to optimize the most relevant SOFC working parameters and predict the SOFC plant performance mainly as a function of the efficiency reduction. The model was also used to suggest a preliminary layout configuration on board the cruise ship. The 12 MW SOFC plant is made of stacks that are grouped in 300 kW modules, located in three different rooms, and integrated with three independent HRSs. Although the 12 MW SOFC plant requires considerably more space than an ICE of the same power, on the other hand, it allows to save fuel and reduces the ship’s overall emissions. 581 References Abdelkareem, M. A., Elsaid, K., Wilberforce, T., Kamil, M., Sayed, E. T., & Olabi, A. ,2021, Environmental aspects of fuel cells: A review. Science of the Total Environment, 752. Al-Hamed, K. H. M., & Dincer, I., 2021, Development and optimization of a novel solid oxide fuel cell-engine powering system for cleaner locomotives. Applied Thermal Engineering, Vol 183.part I. Altosole, M., Campora, U., Mocerino, L., & Zaccone, R., 2022, An Innovative variable layout steam plant for waste heat recovery from marine dual-fuel engines Ampah, J. D., Yusuf, A. A., Afrane, S., Jin, C., & Liu, H., 2021, Reviewing two decades of cleaner alternative marine fuels: Towards IMO’s decarbonization of the maritime transport sector. Journal of Cleaner Production, 320 Vol 338. Baldi, F., Moret, S., Tammi, K., & Maréchal, F., 2020, The role of solid oxide fuel cells in future ship energy systems. Energy, 194 Cigolotti, V., Genovese, M., & Fragiacomo, P., 2021, Comprehensive review on fuel cell technology for stationary applications as sustainable and efficient poly-generation energy systems. In Energies (Vol. 14, Issue 16). MDPI AG Doherty, W., Reynolds, A., & Kennedy, D., 2010, Computer simulation of a biomass gasification-solid oxide fuel cell power system using Aspen Plus. Energy, 35(12), 4545–4555. Doherty, W., Reynolds, A., & Kennedy, D., 2015, Process simulation of biomass gasification integrated with a solid oxide fuel cell stack. Journal of Power Sources, 277, 292–303. Ellamla, H. R., Staffell, I., Bujlo, P., Pollet, B. G., & Pasupathi, S., 2015, Current status of fuel cell based combined heat and power systems for residential sector. In Journal of Power Sources (Vol. 293, pp. 312– 328). Elsevier B.V. IMO’s work to cut GHG emissions from ships., n.d., Retrieved 14 February 2023, from https://www.imo.org/en/MediaCentre/HotTopics/Pages/Cutting-GHG-emissions.aspx. Joung, T. H., Kang, S. G., Lee, J. K., & Ahn, J., 2020, The IMO initial strategy for reducing Greenhouse Gas(GHG) emissions, and its follow-up actions towards 2050. In Journal of International Maritime Safety, Environmental Affairs, and Shipping (Vol. 4, Issue 1, pp. 1–7). Informa UK Ltd. Kumar Singla, M., Nijhawan, P., & Singh Oberoi, A., n.d., Hydrogen fuel and fuel cell technology for cleaner future: a review Martins, A. H., 2022, Biomass gasification as a way of producing green hydrogen: modelling and simulation in Aspen Plus®., master’s dissertation, Faculdade de Engenharia, Universidade Do Porto, Porto, Portugal McPhail, S. J., Kiviaho, J., & Conti, B., 2022, The yellow pages of SOFC technology. International Status of SOFC deployment 2017. 1–50. Pourrahmani, H., Xu, C., & van herle, J., 2022, Two novel cogeneration charging stations for electric vehicles: Energy, exergy, economic, environment, and dynamic characterizations. Energy Conversion and Management, 271. Rokni, M., 2010, Plant characteristics of an integrated solid oxide fuel cell cycle and a steam cycle. Energy, 35(12), 4691–4699. Sazali, N., Salleh, W. N. W., Jamaludin, A. S., & Razali, M. N. M., 2020, New perspectives on fuel cell technology: A brief review. In Membranes (Vol. 10, Issue 5). MDPI AG. Winkler, W., 2016, Thermodynamics. In High-Temperature Solid Oxide Fuel Cells for the 21st Century: Fundamentals, Design and Applications: Second Edition (pp. 51–83). Elsevier Inc. 582 84russo.pdf Preliminary Investigation of a Multi-MW Solid Oxide Fuel Cell Power Plant to be Installed on Board a Cruise Ship