SOFC CHP System Research Articles

System simulation and parametric analysis of low-concentration coal mine gas fed SOFC-CHP with deoxygenation and enrichment pretreatment

Solid oxide fuel cell (SOFC) combined heat and power (CHP) can efficiently convert low-concentration coal mine gas (LC-CMG) into clean energy, avoiding the greenhouse effect of LC-CMG. Deoxygenation and methane enrichment pretreatment of LC-CMG can prevent explosion and anode oxidation risk. Herein, a chemical process model of LC-CMG fed SOFC-CHP system with the pretreatment was established to predict the performances under different operating conditions. Performance evaluation and exergy analysis were performed considering the use of oxygen-rich gas from the pretreatment at SOFC cathode. The effects of key operation parameters on system performances were investigated in terms of residual oxygen concentration, inlet methane concentration, fuel flow and fuel utilization. The results indicated that net electrical efficiency and heat supply efficiency can respectively reach 49.13 % and 23.90 % using LC-CMG of 15 % CH4 with enhancing effect of oxygen-rich gas at cathode. The decrease of methane concentration and the increase of residual oxygen concentration and flow rate caused the decreased electrical efficiency but the increased heat supply efficiency due to the enlargement of concentration polarization and heat supply. The optimal operation parameters were recognized by comprehensively considering diverse performance indicators. This work can guide system integration and operation optimization of LC-CMG fed SOFC-CHP.

Recovery of Flared Natural Gas with High CO<sub>2</sub> Content Using SOFC CHP System: Feasibility Study for Neem-Field, Sudan

Flared natural gas emissions are one of the main sources of environmental pollution and global warming. To recover this gas, the presence of impurities like CO2 in high concentrations forces oil producers to escape from investing in such intensive processing. Several implementations of no flaring methods have been reported in the literature, however, there have been limited concerning the bulk-CO2 natural gases. This research developed an innovative idea for the use of the SOFC CHP system to recover flared bulk-CO2 associated gas of Neem-Field in Western Sudan. The exergy of the system and the performance of the SOFCs are investigated in this paper, in addition to environmental and economic analysis. The simulation (Cycle-Tempo©) results demonstrate that the proposed system can generate 1 MW electrical power and 0.068 MW thermal energy with efficiency approached 43.3% (based on LHV). The exergy analysis showed that 38% of system losses occurred in the air preheaters. Instead of conventional gas-burning, recovering the flared gas reduced the equivalent CO2 GHGs emissions by 80%. Overall, the novel solution found to be environmentally friendly, and economically appealing with a total capital investment estimated to be US$1.175 million and a cost of electricity (COE) of 4.07 cents per kWh.

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.

Status of SOC Development at Chaozhou Three-Circle

Chaozhou Three-Circle (Group) Co., Ltd. (CCTC) is a leading company in developing and manufacturing of electronic and ceramic components. Since more than 19 years ago, CCTC has been focusing on SOFC R&D and manufacturing, covering the complete value chain from powder to power. Based on anode-supported cell technology (ASC in fuel cell mode), the latest C2-stack in planar design using metallic interconnect exhibits a high efficiency of more than 69% (DC, LHV) at 1.5 kW. Long-term stack tests using pipeline natural gas have been conducted for 20,000 hours, with low degradation rates of below 0.4%/kh. In 2022, several 35 kW SOFC CHP systems were demonstrated with C2 stacks, which showed stable performance over 3,000 hours of operation. According to the verification test by Societe Generale de Surveillance S.A., the net AC efficiency of the system reached 64.1%, and the total efficiency was up to 91.2% after 1,000 hours of continuous operation. In parallel to the continuous progressing in SOFC, optimization in cells and stack designs dedicated for SOEC applications were also conducted in recent years. The status of both SOFC and SOEC development at CCTC will be presented.

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.

Effects of Synthesis Gas Concentration, Composition, and Operational Time on Tubular Solid Oxide Fuel Cell Performance

There is tremendous potential to utilize the exhaust gases and heat already present within combustion chambers to generate electrical power via solid oxide fuel cells (SOFCs). Variations in system design have been investigated as well as thorough examinations into the impacts of environmental conditions and fuel composition/concentration on SOFC performance. In an attempt to isolate the impacts of carbon monoxide and hydrogen concentration ratios within the exhaust stream, this work utilizes multi-temperature performance analyses with simulated methane combustion exhaust as fuel combined with dilute hydrogen baseline tests. These comparisons reveal the impacts of the complex reaction pathways carbon monoxide participates in when used as an SOFC fuel. Despite these complexities, performance reductions as a result of the presence of carbon monoxide are low when compared to similarly dilute hydrogen as a fuel. This provides further motivation for the continued development of SOFC-CHP systems. Stability testing performed over 80 h reveals the need for careful control of the operating environment as well as signs of carbon deposition. As a result of gas flow disruption, impacts of anode oxidation that may normally not hinder power production become significant factors in addition to coarsening of the anode material. Thermal management and strategies to minimize these impacts are a topic of future research.

Performance evaluation of a solid oxide fuel cell multi-stack combined heat and power system with two power distribution strategies

Solid oxide fuel cell (SOFC) combined heat and power (CHP) system is a promising candidate for future energy conversion systems. Large power SOFC-CHP system needs multi-stack fuel cell (MFC) to solve the problems of thermal stress and system stability because MFC systems can achieve better performances for maximum power output and average efficiency than single stack fuel cell systems. This study develops an energy management strategy (EMS) for a SOFC multi-stack CHP system coupled with a methane reformer. SOFC multi-stacks are connected in parallel and verified by the published results. The effect of pressure and temperature on the overall multi-stack CHP system electrical efficiency and heat power is investigated with chain and adaptive EMS. The results show that as temperature and pressure increase, the system power increases. The temperature is more effective for the multi-stack system peak efficiency. Up to 11% of electrical system efficiency can be improved when the temperature rises from 700 °C (973 K) to 900 °C (1173 K). However, higher pressure reduces the peak efficiency by 1.5%. Both temperature and pressure can enlarge the output power range. The proposed model can serve as an effective solution for optimizing the SOFC multi-stack CHP system running on methane.

Combined heat and power system based on Solid Oxide Fuel Cells for low energy commercial buildings in Qatar

Commercial buildings in Qatar account for 19% of the total energy consumption in the country. To reduce this significant amount of energy, a Solid Oxide Fuel Cell Combined Heat and Power (SOFC CHP) system with natural gas as fuel is studied. An office building model is created in eQuest energy modeling package. Several baseline cases were considered to optimize the HVAC system and loading profile to utilize the SOFC to its full extent. These baselines are: electric chiller, absorption chiller, and combined electric-absorption chiller systems. Performance curves were analyzed for a range of SOFC CHP system capacities (25–250 kW) in terms of energy produced, utilized thermal energy, overall efficiency and annual energy costs to assess potential cost savings. Results showed that using SOFC CHP with combined electric-absorption chiller system can reduce the annual energy cost by 67% compared to the baseline case with electric chiller. Moreover, optimum overall efficiency of the system can reach 73%. Finally, an environmental impact assessment was evaluated in terms of CO2, NOx, and SO2 emissions. It was found that application of SOFC CHP system resulted in reductions in CO2 emissions of 30%, NOx of 90%, and SO2 of 90%.

Field Test Result of Residential SOFC CHP System Over 10 Years, 89000 Hours

The maximum operating time, without stack replacement, residential SOFC power generation unit (manufactured by Kyocera in 2009), which was installed by Osaka Gas in a house in 2009, has exceeded over 10 years, 89,000 power generating hours. It may be the first data as a SOFC system to succeed in operating in the actual field for 10 years. We will report performance results for 10 years. In 2004, Osaka Gas and Kyocera started joint development of residential SOFC CHP system and from 2007, we conducted series of field test in the SOFC demonstration project operated by NEDO and NEF. At that time, various technical issues still remained, and after joint development with Aisin and Toyota Motor, it was mass-produced and commercialized in 2012. We also mention current status of residential SOFC (Manufactured by Aisin, Stack supplied by Kyocera), which have sold more than total 80,000 units at Osaka Gas.

Field Test Result of Residential SOFC CHP System Over 10 Years, 89000 Hours

The maxmum operating time without stack replacement, residential SOFC power generation unit (manufactured by Kyocera in 2009), which was installed by Osaka Gas in a house in 2009, has exceeded over 10 years, 89000 power generating hours. In 2004, Osaka Gas and Kyocera started joint development of residential SOFC CHP system and from 2007, we conducted series of field tests in the SOFC demonstration project operated by NEDO and NEF. At that time, various technical issues remained, and after joint development with Aisin and Toyota Motor, it was mass-produced and commercialized in 2012. We also mention the current status of residential SOFC (Manufactured by Aisin, SOFC stack supplied by Kyocera). Osaka Gas has sold more than a total of 88,000 residential SOFC CHP systems as of October 2020.

Thermodynamic Optimization of a SOFC-CHP System with Exhaust Gas Recirculation Employing an In-House Numerical Simulator

Thermodynamic optimization of a solid oxide fuel cell-combined heat and power system is the first step for its commercialization. This study suggests a thermodynamically optimized SOFC-CHP system through numerical modeling and simulation. An in-house numerical simulator is developed, which utilizes design variables of system components and their empirical correlations to enhance the accuracy of simulation. It is developed with C# language, equipped with graphical user interface by making use of Windows Presentation Foundation. Two system layout designs are comparatively analyzed: Direct Combustion Branching (DC Branching) and Direct Combustion Branching equipped with Anode exhaust gas Recirculation (DC Branching AR). The thermodynamic performance of two system layouts are compared in the aspects of efficiency and power. It is found that employing anode exhaust gas recirculation enhances thermodynamic efficiencies but reduces net electrical power.

Operation of an SOFC CHP System with Wood Gas from a Fixed-Bed Updraft Gasifier

This paper will show the results of operating an SOFC system with the product gas from a biomass gasifier for more than 200 hours under constant and dynamic operation. The SOFC system was operated at different load cases, 50 % and 100 % load, and achieved a gross electrical efficiency of 42 %. It shows a high dynamic behavior, so that electric load changes could be performed within a few seconds from full load to part load. Furthermore, AVL developed a simulation software by which a SOFC stack model can be simulated dynamically. A comparison of the measured and simulated values of the stack module will be presented. By using the results of the test runs the software could be validated successfully.

Research of SOFC Combined Heat and Power Systems with Natural Gas

In this study, three types of SOFC-CHP systems with natural gas were compared and analyzed, including basic type with external reforming, partial off-gas reflux type and reforming gas separation type. The effects of some parameters such as fuel flow rate, reformer temperature, stack temperature, and air inlet temperature on the energy efficiency of the system are analyzed. As results, increasing the fuel flow rate will reduce the electrical efficiency of the system. Increase of temperature in reformer and the stack temperature is always beneficial to the system electrical efficiency. Increasing the air inlet temperature will lead to lower electrical efficiency. For any fuel flow rate, there always exists an optimal operating current to maximize electrical efficiency. In addition, this study analyzed the operating costs of three types of systems, among which reforming gas separation type has the highest electrical efficiency and the lowest operating cost.

Performance of residential fuel-cell-combined heat and power systems for various household types in Japan

A residential fuel-cell-combined heat and power (FC-CHP) system is considered a promising low-carbon technology that can reduce residential energy consumption and thus, achieve Japan's greenhouse gas (GHG) emissions reduction targets. However, to consider future directions for the systems' research and development, it is critical to understand the relationships between the performances of FC-CHP systems and residential energy demand profiles, which vary by household characteristic. This study evaluates the effects of applying city gas-fueled FC-CHP systems to Japanese households with different attributes. We compare total costs and GHG emissions for residential energy use between the FC-CHP systems and a conventional system. The economic performance results suggest that the basic PEMFC-CHP systems have an economic advantage only for four-person families with teenage children and further development efforts for low-output FC-CHP systems are required to enable various households save energy costs. The environmental evaluation results show that SOFC-CHP systems can drastically reduce GHG emissions from particularly small-sized households.

Experimental and numerical analysis of a SOFC-CHP system with adsorption and hybrid chillers for telecommunication applications

This paper reports about the combined experimental and numerical investigation of a novel small size multi-generation system, for electric (i.e. <10 kW) and cooling (i.e. <20 kW) energy provision to Base Transceiver Stations and small data centers. The proposed concept is based on a high-efficiency natural gas driven SOFC-CHP coupled to commercially available thermally driven adsorption chillers. The main components of the system were experimentally characterized under relevant boundaries and the obtained performance maps were used to implement a TRNSYS model of the whole multi-generation system. The developed model was used to investigate the effect of the sizing of each component as well as the integration of two different commercial thermally driven chillers on the achievable global efficiency. This analysis demonstrated the possibility of getting global energy efficiency up to 0.63 and yearly primary energy savings up to 110 MWh. CO2 emissions avoided are up to 43 t/y.

Development of a Highly Flexible SOFC CCHP System Towards Demand-Oriented Power Generation from Renewable Fuels

This paper presents the current development status of AVLs stationary SOFC CCHP (combined cooling, heat and power) platform with special focus on the coupling of an SOFC with an absorption heat pump. Furthermore, the SOFCs fuel capability was extended towards the utilization of multiple renewable fuels such as biogas, biomass product gas and synthetic diesel. In the past AVL developed a natural gas operated SOFC CHP platform in the power range of 5 – 10 kWel with an electrical efficiency of >55 % using the Plansee/IKTS stack technology. For certain applications such as buildings, a heat driven operation mode leads to low operating hours per year for conventional CHP systems due to the low heat demand during summer season. The option to generate cooling power in addition to heat will increase the annual operating hours per year and thus economic efficiency significantly. This work will show the coupling of a stationary 6 kWel SOFC CHP system developed by AVL using an IKTS stack module with a 5 kWcooling absorption heat pump developed by TU Graz, Institute of Thermal Engineering. The exhaust gas heat from the SOFC which is available at >200 °C will be used to operate the thermally driven heat pump. The SOFC exhaust gas heat is transferred in the generator of the absorption heat pump to be converted to cooling power. To maximize the cooling power output of the SOFC CCHP system it is important to utilize as much SOFC exhaust gas heat as possible in the absorption heat pumping process. Furthermore, it is important to optimize the energy efficiency ratio of the absorption heat pump. In this context the influence of the cold and cooling water temperatures of the absorption heat pumping process on the system size and system total efficiency were investigated. It can be shown that for cold and cooling water temperatures as required in office buildings and hospitals a ratio between electrical power and cooling power of 4 - 6 can be achieved by the SOFC CCHP system. This analysis presents the capability of the SOFC CCHP system for a flexible and demand-oriented generation of electricity, heat and cooling power. As the electrical efficiency of the SOFC determines the exhaust gas heat output the system performance was further investigated towards the operation of renewable fuels. Biogas or synthetic diesel for instance may lead to lower electrical efficiencies compared to natural gas. Therefore, the type of fuel also influences the SOFC exhaust mass flow and temperature which is the main driving power for the absorption heat pump. In this work the fuel capability of the platform was extended from natural gas to renewable fuels. From economic point of view it is desired to benefit from volume effects for stacks and balance of plant components which is why AVLs system development approach is oriented towards a multi-fuel platform which requires only minor design adaptions when it comes to the utilization of different fuels including renewables. As a technology provider this approach is certainly a major advantage for customers who are used to a power generation technology that can be easily applied in various regions all over the world while facing varying fuel specifications. Therefore, this work will provide an overview of the most relevant renewable fuels and its composition for stationary SOFC CHP applications. Consequently, design synergies regarding the process design of the hot anode gas recirculation loop in terms of the recirculation ratio and reforming temperature which are influenced by the specific fuel, are shown. A comparison of system performance results based on process simulations will be discussed. The process simulation uses results from specific reforming tests for e.g. biogas and diesel which will be shown. Furthermore, compared to natural gas based systems a considerably higher effort has to be done in terms of the gas cleaning for biogas and biomass product gas. In case of biogas the main impurities are S, Cl, NH3 which need to be eliminated before sending the fuel to the steam reformer and stack respectively. A low cost gas cleaning concept for biogas based on several low temperature adsorption steps was developed by TU Graz. It can be shown that the absorption efficiency is highly depending on the fuel mixture. The influence of CH4, CO2 and H2O was identified to allow a proper design of the gas cleaning unit. Finally, the build-up of the prototype including first test results will be shown in this work.

Development and Commercialization of New Residential SOFC CHP System

Osaka Gas began selling the new version residential SOFC CHP system “ENE-FARM type S” in April 2016, which is developed in collaboration with Osaka Gas, Aisin Seiki, Kyocera and Noritz. Kyocera manufactures SOFC stacks, Aisin Seiki manufactures power generation units, and Noritz manufactures boiler and remote-control units. The electrical efficiency is 52% (net AC, LHV), whereas that of the previous model was 46.5%.The previous system comprised two units: a power generation unit and a heat recovery unit. The latter unit contained the hot-water storage tank and the boiler. The new power generation unit contains the hot-water storage tank. This tank is configured for connection to a normal household boiler. The system size is minimized to facilitate its use as a residential CHP system. Moreover, it is possible to install the new system in a housing complex, where the available space is limited. This feature expands the market for this system because the previous model could only be installed in a single-family house. To achieve the high electrical efficiency of 52% (net AC, LHV) and the cost reduction, three technical issues were addressed. The first was the improvement of the fuel cell performance, the second was the optimization of the fuel utilization rate, and the third was the improvement in durability. Kyocera reduced the internal electrical resistance of the fuel cell stack. In addition, a new coating technology, i.e., electropainting, which is developed by Osaka Gas and Kyocera, was used for current collectors. Consequently, both an increase in power density (reducing the number of cells) and an improvement in the electrical efficiency have been achieved. Current collectors are oxidized at a high temperature because they comprise stainless steel. Their durability has been considerably improved by the electropainting coating technology. Aisin Seiki optimized the system controls, resulting in enhanced electrical efficiency. Osaka Gas conducted field tests in the Kansai area in Japan. We installed the systems in the houses of several employees for evaluating the system behavior. The results made it possible to accelerate product development. In accordance with the liberalization of the power market in Japan in April 2016, if customers use natural gas provided by Osaka Gas, the electrical power from the unit can be sold back to Osaka Gas. We consider that 2016 is a transition period for residential CHP from the market introduction stage to the autonomous market spread stage. We are currently focusing on achieving further developments in the technology, which will enable cost reduction and higher power generation efficiency in order to maximize the target market.

Development and Commercialization of New Residential SOFC CHP System

In April 2016, Osaka Gas began the marketing of “ENE-FARM type S,” which was an advanced version of the residential SOFC CHP system. Osaka Gas developed this system in collaboration with Aisin Seiki, Kyocera, and Noritz. The electrical efficiency of the new model was 52 % (net AC, LHV), whereas that of the previous model was 46.5 %. The system size was minimized to facilitate its use as a residential CHP system. We reduced the maintenance, stack, and system costs. In this paper, we describe the developments and features of new residential SOFC CHP system.

Development of a Highly Flexible SOFC CCHP System Towards Demand-Oriented Power Generation from Renewable Fuels

The coupling of AVLs 6 kWEL SOFC CHP system using an IKTS stack module with a 5 kWCOLD absorption heat pump developed by TU Graz will be presented. The exhaust gas heat from the SOFC which is available at >200 °C will be used to operate the thermally driven heat pump. The SOFCs fuel capability was extended towards renewable fuels such as biogas, and synthetic diesel using a novel gas cleaning concept. For buildings, a heat driven operation mode leads to low operating hours per year for conventional CHP systems during summer season. Generating cooling power in addition to heat will increase the annual operating hours per year and thus economic efficiency significantly. This analysis presents the capability of the SOFC CCHP system for a flexible and demand-oriented generation of electricity, heat and cooling power and shows how cold and cooling water temperatures influence the overall system size

AVL SOFC Systems on the Way of Industrialization

The AVL SOFC Auxiliary Power Unit development program has reached significant milestones within the last year. The performance of the system has been significantly increased to 30% electrical efficiency and up to 4kW net electrical power. The first successful vehicle demonstration has been performed. Operation on sulfur containing fuels is possible. A commercial product launch is planned for 2016. In parallel also the AVL SOFC CHP system showed significant progress. The system is designed for 5-10kW electrical power based on electrolyte supported stacks from Plansee/IKTS and a hot gas anode recirculation process. The system is since early 2013 continuously in operation and shows very promising results like an electrical efficiency around 50%.