Oxide Fuel Cell Combined Heat Research Articles

Comparative study on thermodynamic analysis of solid oxide fuel cells supplied with methanol or ammonia

The increasing demand for green hydrogen and power production necessitates the development of novel and upgraded power generation technologies. The solid oxide fuel cell combined heat and power (SOFC–CHP) system is a promising solution due to its high efficiency, clean operation, and fuel flexibility. In practical terms, SOFCs can operate using a variety of fuels such as alcoholic fuel, hydrogen, ammonia, etc. Recently, methanol and ammonia have become noteworthy alternative fuel options as it possesses advantages such as low transportation cost and high hydrogen storage capacity. In this paper, we have established two SOFC–CHP models fueled by methanol or ammonia integrated with the steam Rankine cycle. A comprehensive thermodynamic model is proposed for energy and exergy analyses. Sensitivity analysis is performed to study the system's characteristics. The results show that the SOFC–CHP system fueled by ammonia exhibits superior performance, the maximum electrical power, efficiency, and exergy efficiency is 430W, 7% and 10% greater than the methanol fueled system. The operating temperature is about 30K higher in methanol supplied system. The largest thermal power difference can reach 0.65 kW. Overall, the ammonia fueled SOFC–CHP system shows greater potential than that fueled by methanol.

Dual-adaptive energy management strategy design for fast start-up and thermal balance control of multi-stack solid oxide fuel cell combined heat and power system

Solid oxide fuel cell (SOFC) hybrid system offers several advantages, including rapid start-up, effectively mitigating thermal stress and system stability. In this study, a multi-stack SOFC battery hybrid (SBH) Combined Heat and Power (CHP) system is designed. A dual-adaptive control strategy for this multi-stack system is proposed. The assembly of each power generation module (PGM) in parallel is implemented and the reliability of the system is verified. The dynamic characteristics of the multi-stack SBH-CHP system and the effect of temperature on the system are investigated. The results show that the multi-stack system can achieve stability within 80 s. The transient current observed in the system reaches up to 40 A, which accounts for at least 25% of the current generated by the SOFC. The system exhibits robust and prompt dynamic response characteristics, which ultimately contribute to an extended operational lifespan. The proposed adaptive control method and adaptive energy management strategy have been proven to be effective approaches for addressing the issues associated with rapid start-up and over-temperature within the multi-stack SBH-CHP system.

Multi-criteria assessment and optimization of a natural gas-fed solid oxide fuel cell combined heat and power system

Solid oxide fuel cell (SOFC) combined heat and power (CHP) system is a promising candidate for efficient power generation. Due to its complex dynamic characteristics, system performance is still unsatisfied when it operates in variable load conditions. In this study, five improved layouts of a natural gas-fed SOFC-CHP system are proposed using three-fluid heat exchangers innovatively. Performance of the system under different layouts is compared from both energy and exergy perspective and their feasibility in multi-load conditions is evaluated. Sensitivity analysis of four key parameters is conducted to clarify their influences and potential ways for efficiency improvements from both system and component level are explored under different load conditions. Results show that the system with direct combustion of anode off-gas has better adaptability to multi-load conditions. Exergy loss of the combustor always occupies the highest proposition among all the components, at least 30%. Because of the large thermal load and high outlet temperature of the cold fluid, thermal management of the reformer is crucial for the system operation. Changes of the reforming temperature and fuel utilization ratio significantly affect the system performance. As the load increasing, the electric efficiency decreases and the thermal efficiency increases, the total efficiency can always be more than 85% for the SOFC-CHP system.

Energy Transition Scenarios in Off-grid Communities using SOFC-CHP/Battery Hybrid Systems

Today, off-grid communities rely mainly on diesel gensets with limited electrical efficiency and diesel furnaces for electricity and heat generation, respectively. The CO2 emissions associated with this electricity production can be reduced by improving the electrical efficiency of the system thus reducing the fuel consumption. Additionally, waste heat from the electricity production can be recovered for heating thus creating a combined heat and power system. In this work, a solid oxide fuel cell combined heat and power system hybridized to a battery was proposed for this purpose. Simulation of the annual electricity and heat production were performed using real temporal electrical demand data. Results showed that a reduction of up to 36 % in primary energy consumption can be reached compared with the current situation.

Techno-economic and thermodynamic analysis of solid oxide fuel cell combined heat and power integrated with biomass gasification and solar assisted carbon capture and energy utilization system

A new system involving biomass gasification (BioG) with solid oxide fuel cell (SOFC) in combined heat and power (CHP) manner is evaluated. The aim of this system is to efficiently utilize biomass, while solar-assisted solid oxide electrolyzer cell (SOEC) methanation exploits CO2 from the system exhaust. CO2 and H2O are co-electrolyzed to form syngas, followed by four step methanation to produce synthetic natural gas. The energy system is thoroughly assessed using energy, exergy, exergoeconomic, and environmental assessments. The BioG-SOFC-CHP overall energy and exergy efficiencies reach up to 59 % and 44.7 %, respectively. Additionally, the SOEC-methanation subsystem achieved overall energy and exergy efficiencies of 78.5 % and 73.8 %, respectively. BioG showed the largest exergy destruction of 78.34 kW compared to 12.3 kW for SOFC. In SOEC-methanation subsystem, heater 2 has the largest exergy destruction of 98.93 kW. The economic analysis showed that the methane selling price of 18 $/GJ and the electricity tariff of 0.13 $/kW, which are nearly identical to the market price, resulting in a payback period of 10 years. Exergoeconomic analysis showed cost rate of SOFC power generation and methane production of 0.05225$/kWh and 29.5$/GJ, respectively. The BioG-SOFC-CHP provided low CO2 emission of about 0.13–0.166 t/GJ, which indicates its low environmental impact.

Evaluation of SOFC-CHP’s ability to integrate thermal and electrical energy system decentrally in a single-family house with model predictive controller

The integration of natural gas powered solid oxide fuel cell combined heat and power (SOFC-CHP) unit into a decentral residential energy system consisting of solar thermal collectors, photovoltaic with both thermal sensible heat storage and lithium-ion battery is simulatively evaluated. The system also includes gas boiler and electrical grid as back up. The system is investigated along with status quo controllers and how an implementation of a model predictive controller (MPC) and seasonal shutdown of the FC-CHP influences the performances of the SOFC-CHP. The performance is also analysed with two different single-family house German energy standards: Sonnenhaus (relatively new high renewable fraction house) and WSchVO95 (old house as per the year 1995′s standard). The results show that via SOFC-CHP 100% self-supply of the electrical loads is possible and a 10% increase in decentral system self-consumption fraction by introducing MPC control. Also, it could be seen here that the MPC control for FC-CHP and the use of FC-CHP for the old WSchVO95 building has more advantages than anticipated. SOFC-CHP seasonal shutdown along with +12% & +7% self-consumption fraction at the expense of +5% & +2% electricity import in Sonnenhaus and WSchVO95 buildings respectively also increases photovoltaic, solar thermal and battery use.

Operating limitation and degradation modeling of micro solid oxide fuel cell-combined heat and power system

The micro Solid Oxide Fuel Cell-Combined Heat and Power (SOFC-CHP) System is one of the most promising technologies of distributed generation and has been commercialized in Japan and Europe. However, the performance degradation of an SOFC stack still exists, causing the ratio of power and heat to change and the Joule heat to increase in the stack. This phenomenon should not have been neglected. A zero-dimension SOFC model including basic Nernst, ohmic, activation and concentration voltage loss was used to simulate the micro SOFC-CHP system, and a degradation model was also applied to modeling the power change with respect to operating time in different situations. Both of the models were verified by real stacks experiment data and the effectiveness was proved in system-level modeling. Three key operating parameters of the system were promoted: stack current I, excess air factor α and fuel utilization Uf. Given the safe temperature ranges of an SOFC stack, combustor and reformer, the most appropriate parameter range was illustrated to be limited in a shape of a small triangle. Within the safe parameter range, while the excess air factor α was fixed at 2.64, the electrical efficiency reached a maximum 44.9% (HHV) at 120 A, while the electric power output of SOFC and hot water were both 5.58 kW. As for the dynamic modeling, by comparing constant current, constant voltage and constant power three operating patterns, results showed that the constant current pattern had the longest lifetime and the constant power pattern followed.

Techno-economic assessment of biogas-fed solid oxide fuel cell combined heat and power system at industrial scale

Wastewater treatment plants (WWTP) are currently very energy and greenhouse gas intensive processes. An important opportunity to reduce both of these quantities is via the use of biogas produced within the treatment process to generate energy. This paper studies the optimal energy and economic performance of a wastewater treatment facility fitted with a solid oxide fuel cell (SOFC) based combined heat and power (CHP) plant. An optimisation framework is formulated and then applied to determine cost, energy and emissions performance of the retrofitted system when compared with conventional alternatives.Results show that present-day capital costs of SOFC technology mean that it does not quite compete with the conventional alternatives. But, it could become interesting if implemented in thermally-optimised WWTP systems. This would increase the SOFC manufacturing volumes and drive a reduction of capital and fixed operating costs.

Comparative study of solid oxide fuel cell combined heat and power system with Multi-Stage Exhaust Chemical Energy Recycling: Modeling, experiment and optimization

In this paper, a novel Multi-Stage Exhaust Energy Recycling strategy was proposed and optimized to maximize the system efficiency and performance of solid oxide fuel cell-combined heating and power (SOFC-CHP). Both process modeling and experiment work based on 1kW SOFC-CHP systems were carried out to prove the concept and optimize the system. It is found that the system with multi-stage exhaust gas combustion (MS-EGC) will reduce the system operating temperature from 1149°C to 830°C, which significantly increases the safety of system operation and reduces the material requirement. The system combining MS-EGC with anode off gas recovery (MS-AOGR & EGC) leads to highest overall co-generation efficiency up to 92%. A coupled reactor integrating MS-EGC modules was developed and tested for a 1kW SOFC system to realize the proposed strategy. The results showed that in MS-EGC, recycling of thermal energy at first stage rarely affects the chemical energy utilization in subsequent stages and the overall system performance, further confirming the advantages of the innovative multi-stage energy recycling strategy.

Model-based evaluation of an integrated autothermal biomass gasification and solid oxide fuel cell combined heat and power system

Numerical analysis of combined heat and power plant consisting of a solid oxide fuel cell and autothermal gasification system has been made for several cases of different composition of fuel relevant to air and steam blown biomass gasification process. Wet wood is fed to the fixed-bed downdraft gasifier and gaseous fuel is produced then after gas cleaning and conditioning can be used in solid oxide fuel cells. The integrated plant is investigated by thermodynamic modeling combining a one-dimensional model of direct internal intermediate planar type solid oxide fuel cell which allows monitoring the temperature gradients along the cell length in different operating conditions and a zero-dimensional autothermal gasifier. The solid oxide fuel cell mathematical model is developed based on gas species mass balances, energy balance, and an electrochemical model beside the kinetics describing internal reforming and water-gas shift reactions. Such a model can be integrated with adiabatic gasification modeling which includes atom balance conservation for assumed gas species and a modified thermodynamic equilibrium analysis. Both gasifier and solid oxide fuel cell models are verified against experimental and previous numerical data available in the literature. Two main parameters, namely modified equivalence ratio and air-to-steam ratio are investigated and the most important cycle parameters such as power, electric and combined heat and power efficiencies, temperature gradients along the cell length, and mole fractions of gaseous species of the produced fuel are analyzed. It has been revealed that any increase in air-to-steam ratio at fixed modified equivalence ratio leads to penalty on cold gas efficiency of the gasifier and both solid oxide fuel cell and combined heat and power plant electric efficiencies. Increased air-to-steam ratio at constant modified equivalence ratio produces a mixture with lower low heating value, higher steam-to-carbon ratio, rich in CO and lower in CH4 content. Under this condition the operating temperature of the cycle and solid oxide fuel cell increases and consequently improves the operating voltage of the cell and combined heat and power efficiency of the plant. On the other hand, results show that gasification with increased modified equivalence ratio at constant air-to-steam ratio produces mixtures richer in CH4 and CO, poorer in H2 with higher low heating value and cold gas efficiency, and lower steam-to-carbon ratio. Such condition improves the electric efficiency of the solid oxide fuel cell and the integrated plant, but the combined heat and power efficiency of the cycle decreases due to decreased operating temperature of the solid oxide fuel cell and the cycle.

Competitiveness of CO2 capture from an industrial solid oxide fuel cell combined heat and power system in the early stage of market introduction

In this article, it was investigated whether potentially low-cost CO2 capture from SOFC systems could enhance the penetration of SOFC in the energy market in a highly carbon-constrained society in the mid-term future (up to year 2025). The application of 5MWe SOFC systems for industrial combined heat and power (CHP) generation was considered. For CO2 capture, oxyfuel combustion of anode off-gas using commercially available technologies was selected. Gas turbine (GT-) CHP plant was considered to be the reference case.Technical results showed that despite the energy penalties due to CO2 capture and compression, net electrical and heat efficiencies were nearly identical with or without CO2 capture. This was due to higher heat recovery efficiency by separating SOFC off-gas streams for CO2 capture. However, CO2 capture significantly increased the required SOFC and heat exchanger areas.Economic results showed that for above 40–50$t−1 CO2 price, SOFC-CHP systems were more economical when equipped with CO2 capture. CO2 capture also enabled SOFC-CHP to compete with GT-CHP at higher cell stack production costs. At zero CO2 price, cell stack production cost had to be as low as 140kW−1 for SOFC-CHP to outperform GT-CHP. At 100$t−1 CO2 price, the cell stack production cost requirement raised to 350$kW−1. With CO2 capture, SOFC-CHP still outperformed GT-CHP at a significantly higher cell stack production cost above 900$kW−1.

Techno-economic modelling of a solid oxide fuel cell stack for micro combined heat and power

Solid oxide fuel cell combined heat and power (CHP) is a promising technology to serve electricity and heat demands. In order to analyse the potential of the technology, a detailed techno-economic energy-cost minimisation model of a micro-CHP system is developed drawing on steady-state and dynamic SOFC stack models and power converter design. This model is applied it to identify minimum costs and optimum stack capacities under various current density change constraints. Firstly, a characterisation of the system electrical efficiency is developed through the combination of stack efficiency profiles and power converter efficiency profiles. Optimisation model constraints are then developed, including a limitation in the change of current density (A cm −2) per minute in the stack. The optimisation model is then presented and further expanded to account for the inability of a stack to respond instantaneously to load changes, resulting in a penalty function being applied to the objective function proportional to the size of load changes being serviced by the stack. Finally, the optimisation model is applied to examine the relative importance, in terms of minimum cost and optimum stack maximum electrical power output capacity, of the limitation on rate of current density change for a UK residential micro-CHP application. It is found that constraints on the rate of change in current density are not an important design parameter from an economic perspective.