Optimization and efficiency analysis of methanol SOFC-PEMFC hybrid system

In order to improve the power generation efficiency of fuel cell systems employing liquid fuels, a hybrid system consisting of solid oxide fuel cell (SOFC) and proton exchange membrane fuel cell (PEMFC) is proposed. Utilize the high temperature heat generated by SOFC to reform as much methanol as possible to improve the overall energy efficiency of the system. When SOFC has a stable output of 100 kW, the amount of hydrogen after reforming is changed by changing the methanol flow rate. Three hybrid systems are proposed to compare and select the best system process suitable for different situations. The results show that the combined combustion system has the highest power generation, which can reach 350 kW and the total electrical efficiency is 57%. When the power of the tail gas preheating system is 160 kW, the electrical efficiency can reach 75%. The PEM water preheating system has the most balanced performance, with the electric power of 300 kW and the efficiency of 66%.     

Performance of hybrid refrigeration system using ammonia

This paper investigates the performance of a hybrid refrigeration system that combines sorption–conventional vapour compression refrigeration machine driven by dual source (heat and/or electricity). The dual source makes the system highly flexible and energy efficient. The ammonia refrigerant (R717) is used in both adsorption and associated conventional refrigeration cycles. The model of thermal compressor corresponds to a multiple pair of compact adsorption generators operating out of phase with both heat and mass recovery for continuous cooling production and better efficiency. Each generator is based on a plate heat exchanger concept using the activated carbon–ammonia pair. The model of conventional vapour compressor is a reciprocating compressor from Frigopol. The hybrid refrigeration performances are presented mainly for ice making and air conditioning applications (T_C = 40 °C, −5 °C < T_E < 20 °C). The exhaust temperature of the compressor (driving temperature for thermal compressor) varies from 90 °C to 250 °C. The results show a cooling production ranging from 4 kW to 12 kW with back-up mode (both cycles not operating simultaneously) and from 8 kW to 24 kW with complementary mode (both cycles operating simultaneously). The effective overall COP based on the total equivalent heat rate input varies from 0.24 to 0.76.     

Performance investigation of hydrogen production from a hybrid wind-PV system

In this study, a hybrid system consisted of 10 kW wind and 1 kWp PV array is built to meet the load demand of a raise chucker partridge raising facility by renewable energy sources. The facility has an average energy consumption of about 20.33 kWh/day, with a peak demand of 2.4 kW. The solar radiation data and wind data of the region are analyzed for sizing of the renewable energy system. The performance of each alternative system is examined in terms of energy efficiency, and H₂ production capacity of the hybrid system from due to excessive electrical energy is studied. A Matlab-Simulink Software is used for analyzing the system performance. The average range of state of charge varies between 56.6% and 88.3% monthly from April to July. The amount of hydrogen production by excess electricity is 14.4 kg in the month of July, due to the high wind speed and solar radiation. Energy efficiency of the electrolyser is found to be varying between 64% and 70% percent. Energy efficiency of each hybrid system is calculated. The overall energy efficiency of wind-electrolyser system varies between 5% and 14% while the energy efficiency of PV-electrolyser system changes within a narrower range, as between 7.9% to and 8.5%, respectively.     

Off-design analysis of SOFC hybrid system

This paper sets out the results of mathematical modeling and numerical simulations of the off-design (part-load) operation of the solid oxide fuel cell hybrid system (SOFC-HS).     

In-line adsorption system for reducing cold-start ammonia emissions from engines fueled with ammonia and hydrogen

Ammonia-free emissions from an engine system fueled with ammonia and hydrogen during cold-start and warm-up periods are demonstrated. The fuels are supplied into a single-cylinder test engine under constant-speed conditions. The exhaust system consists of a redox catalyst followed by an in-line adsorber, the latter of which stores the ammonia that flows through the former. The results show that all adsorbers, H-ZSM-5, Cu-ZSM-5, and Pt-ZSM-5, can adsorb ammonia during cold-start conditions although the engine should be operated with retarded spark timing and a high hydrogen ratio because of low combustion efficiency at low coolant temperatures. Cu-ZSM-5 and Pt-ZSM-5 are regenerated after adsorption through their catalytic reactions without ammonia slip. Cu-ZSM-5, which has the largest adsorption capacity among the tested adsorbers, favors lean burn operation for regeneration. Pt-ZSM-5 has the advantage of simple regeneration control.     

Grid connected fuel cell and PV hybrid power generating system design with Matlab Simulink

Renewable energy sources have been taken the place of the traditional energy sources and especially rapidly developments of photovoltaic (PV) technology and fuel cell (FC) technology have been put forward these renewable energy sources (RES) in all other RES. PV systems have been started to be used widely in domestic applications connected to electrical grid and grid connected PV power generating systems have become widespread all around the world. On the other hand, fuel cell power generating systems have been used to support the PV generating so hybrid generation systems consist of PV and fuel cell technology are investigated for power generating. In this study, a grid connected fuel cell and PV hybrid power generating system was developed with Matlab Simulink. 160 Wp solar module was developed based on solar module temperature and solar irradiation by using real data sheet of a commercial PV module and then by using these modules 800 Wp PV generator was obtained. Output current and voltage of PV system was used for input of DC/DC boost converter and its output was used for the input of the inverter. PV system was connected to the grid and designed 5 kW solid oxide fuel cell (SOFC) system was used for supporting the DC bus of the hybrid power generating system. All results obtained from the simulated hybrid power system were explained in the paper. Proposed model was designed as modular so designing and simulating grid connected SOFC and PV systems can be developed easily thanks to flexible design.     

Performance evaluation of an alkaline fuel cell/thermoelectric generator hybrid system

A hybrid system consisting of an AFC (Alkaline Fuel Cell), a TEG (Thermoelectric Generator) and a regenerator is put forward, where the AFC converts the chemical energy in the hydrogen into electrical energy and thermal energy, and the released thermal energy is subsequently converted into electrical energy through the bottoming TEG. The main irreversible losses in each element of the hybrid system are characterized, and numerical expressions for the efficiency and power output of the AFC, TEG and hybrid system are respectively derived. The fundamental relation between the operating current density of the AFC and the dimensionless current of the TEG is obtained, from which the region of the operating current density of the AFC that the TEG exerts its function is determined. By employing such a hybrid system, the equivalent maximum power density of the AFC can be increased by up to 23%. The effects of the operating current density, operating temperature, heat conductivity, and integrated parameter on the performance of the hybrid system are revealed. The results obtained in the present paper will provide some theoretical guidance for the performance improvement of the AFC.     

The characteristics of regenerative energy for PEMFC hybrid system with additional generator

This study focuses on the use of the Polymer Electrolyte Membrane Fuel Cell (PEMFC) hybrid system, which consists of a generator, a supercapacitor, and a battery, to obtain regenerative energy. The fuel cell is a Nexa™ Power Module of Ballard Power Systems Inc., and the battery is a Ni-MH battery of Global Battery Co., Ltd. The supercapacitor, which features an excellent power density and capacity of 30 V and 100F, can minimize its power consumption via a cell balancing circuit. This study aimed to evaluate the characteristics of regenerative energy and suggest solutions to increase regenerative energy using a vehicle simulation.     

Concept of twining injector system for spark-ignition engine fueled with syngas-biogas-hydrogen operating in solar-biomass hybrid energy system

This paper presents the research results on an innovative concept of a twining injector system to supply a flexible syngas-biogas-hydrogen blend for engines working in a hybrid solar-biomass renewable energy system. The effects of nozzle diameter, injection pressure and nozzle location were considered. Simulation results showed that the twining injector system, including 2 injectors with a nozzle diameter of 5 mm located close to the inlet port and 1-bar injection pressure is suitable for Honda GX200 engine fueled with syngas-biogas-hydrogen. At engine speed of 3000 rpm, for syngas-biogas blend, the injection duration of the first injector is reduced from 120 CA to 23 CA while the second injector keeps the injection duration stable at 120 CA to 50% biogas, then reduced to 74 CA for full biogas injection. For syngas-hydrogen blend, the first injector keeps the stable injection duration of 120 CA to 50% hydrogen, then gradually decreases to 44 CA, corresponding to 100% hydrogen; the injection duration of the second injector decreases from 120 CA to 24 CA and then keeps constant until hydrogen content reaches 70%. The injection duration of each injector for syngas-biogas-hydrogen blend is within the limits between the injection duration of the syngas-biogas and that of the syngas-hydrogen blends. The mixture of syngas-biogas-hydrogen blend and air in the combustion chamber created by twining injector system was more homogeneous than that created by traditional port fuel injection system.     

A hybrid fuel cell system integrated with methanol steam reformer and methanation reactor

In this paper, a hybrid fuel cell system integrated with methanol steam reformer and methanation reactor is demonstrated. Methanol steam reformer employed in this system is to produce hydrogen-rich reformate in connection with a methanation reactor to reduce the carbon monoxide content effectively, and the reformate gas is sent into a low-temperature polymer electrolyte fuel cell for direct electric power generation. The optimum conditions (temperature, water to methanol ratio, and space velocity) for methanol steam reforming (MSR) reaction and methanation (MET) reaction are verified by experiments. A comparison between pure hydrogen, reformate surrogate, and actual reformate is performed. The results show that the power density of this hybrid system achieves 245.2 mW/cm² while it achieves 268.8 mW/cm² when employing pure hydrogen as the fuel. An alternative novel method to solve the problem of hydrogen storage and transportation is provided and the in-situ hydrogen production and utilizing through low-temperature fuel cell system is realized, which is helpful to accelerate the commercialization process of the fuel cell.     

Performance characterisation of liquid desiccant columns for a hybrid air-conditioner

Use of liquid desiccant-vapor compression hybrid system is encouraged for low humidity applications. The liquid desiccant is primarily used to further dehumidify the supply air. In the present study, by using psychrometric equations and liquid desiccant property data, heat and mass transfer analysis for the dehumidifier and regenerator columns in counter flow configuration has been carried out. The simulation of the columns corresponds to low solution to air (S/A) flow ratio where precooled air gets dehumidified in the absorber while preheated air is used for regeneration of the solution. A detailed study of the performance characteristics for the absorber and regenerator columns confirms the requirement of the desiccant loop for additional dehumidification of the conditioned air. This need develops the main motive towards the concept of hybrid air conditioning.     

Performance characteristics of a solid oxide fuel cell/gas turbine hybrid system with various part-load control modes

The purpose of this study is to compare the part-load performance of a solid oxide fuel cell/gas turbine (SOFC/GT) hybrid system in three different control modes: fuel-only control, rotational speed control, and variable inlet guide vane (VIGV) control. While the first mode maintains a constant air supply and reduces the supplied fuel to achieve part-load operation, the other modes are distinguished by the simultaneous controls of the air and fuel supplied to the system. After the performance analysis of a SOFC/GT hybrid system under part-load operating conditions, it was concluded that the rotational speed control mode provided the best performance characteristics for part-load operations. In spite of worse performance than the rotational speed control mode, the VIGV control mode can be a good candidate for part-load operation in a large-scale hybrid system in which the rotational speed control is not applicable. It was also found that, in spite of a relatively small contribution to the total system power generation, the gas turbine plays an important role in part-load operation of a SOFC/GT hybrid system.     

Performance analysis of an SOFC/HCCI engine hybrid system: System simulation and thermo-economic comparison

A novel SOFC hybrid system is proposed and evaluated relative to its thermodynamic efficiency and economy. The proposed system combines an SOFC stack with an HCCI-type internal combustion engine; the HCCI engine replaces a conventional combustor, simultaneously burns the anode off-gas, and produces additional power. To calculate the efficiency of the suggested system, each component and the overall system have been thermodynamically modeled. The levelized cost of electricity (LCOE) has been calculated and economically assessed. For quantitative comparison and evaluation, a simple SOFC system and an SOFC/GT hybrid system are designed. Consequently, the proposed hybrid system shows the efficiency 59.5%, which is 7.8% and 0.9% higher efficiency than those of the SOFC simple system and the SOFC/GT hybrid system, respectively. And the system exhibits the LCOE $0.23/kWh, that is 12.9% and 7.6% reduced LCOE compared with the other two reference cases.     

Assessment of an integrated solar hydrogen system for electrochemical synthesis of ammonia

In this paper, a solar based electrochemical system is designed, built and tested to synthesize ammonia and hydrogen from nitrogen and saturated steam. Ammonia can serve as a sustainable fuel and is in heavy demand by the fertilizer industry. However, the conventional methods rely on hydrogen produced from fossil fuels. Hydrogen can be supplied back by implementing fuel cells and feeding electricity back to the system, directed to the conventional ammonia production methods as a reactant, or sold as a fuel. A simple and direct system is studied to pose a sustainable option for ammonia and hydrogen production. Very high concentrations of Nano iron catalyst are used to promote the concentration of ammonia at the output. The reactor is designed for continuous flow and can be disassembled for varying tests and scenarios. The maximum concentration of ammonia is found to be 950 ppm measured with excess reactant supply. Increasing nitrogen flow rates along with decreasing steam flow rates render increasing concentration results. The system at optimum conditions consumes 650 mA at 1.7 V. The low power requirements and valuable products of the system encourage further studies. Additionally, a solar energy based system is proposed as a renewable approach to ammonia synthesis with a fuel cell component to increase the efficiency by reducing the power consumption to 60% of its original value.     

An integrated system for ammonia production from renewable hydrogen: A case study

This study presents an analysis and assessment study of an integrated system which consists of cryogenic air separation unit, polymer electrolyte membrane electrolyzer and reactor to produce ammonia for a selected case study application in Istanbul, Turkey. A thermodynamic analysis of the proposed system illustrates that electricity consumption of PEM electrolyzer is 3410 kW while 585.4 kW heat is released from ammonia reactor. The maximum energy and exergy efficiencies of the ammonia production system which are observed at daily average irradiance of 200 W/m² are found as 26.08% and 30.17%, respectively. The parametric works are utilized to find out the impacts of inlet air conditions and solar radiation intensity on system performance. An increase in the solar radiation intensity results in a decrease of the efficiencies due to higher potential of solar influx. Moreover, the mass flow rate of inlet air has a substantial effect on ammonia production concerning the variation of generated nitrogen. The system has a capacity of 0.22 kg/s ammonia production which is synthesized by 0.04 kg/s H₂ from PEM electrolyzer and 0.18 kg/s N₂ from a cryogenic air separation unit. The highest exergy destruction rate belongs to PEM electrolyzer as 736.2 kW while the lowest destruction rate is calculated as 3.4 kW for the separation column.     

Design optimization for the hybrid power system of a green building

This paper proposes an optimal design procedure for a green building equipped with renewable energy, energy storages, and proton exchange membrane fuel cells (PEMFCs). First, we introduce the hybrid power system of the green building and construct a simulation model using Matlab/SimPowerSystem?. The model parameters are tuned so that the system responses can be estimated without extensive experiments in the optimization processes. Second, we define the cost and reliability indexes to optimize the system design using three steps: component selection, component sizing, and power management (PM) adjustment. We further define the safety index to evaluate the system's sustainability under extreme conditions when no renewable energy is available. Last, we apply the proposed procedures to the green building and demonstrate the benefits of the optimal design. The proposed method can be directly applied to develop customized hybrid power systems in the future.     

Operation of solid oxide fuel cells with alternative hydrogen carriers

Future electricity production will use fossil-free sources with zero CO₂ emission or closed carbon cycle technologies based on renewable sources. While hydrogen is considered a key energy source, its production at present time relies heavily on fossil fuels. Furthermore, distribution and storage are not well established and require substantial investments. This is a strong motivation to identify alternative, safe, high power density hydrogen carriers, where existing logistics and infrastructure can be utilized. In this contribution, ammonia and biogas are considered for high-efficient electricity production in solid oxide fuel cells (SOFCs). It is demonstrated that the properties and operating conditions of SOFC allow for direct use of these fuels, with fuel pretreatment inside the SOFC anode. The high efficient electricity production using pure ammonia or real biogas was successfully proven on state-of-the-art SOFCs. Even without optimization of operating parameters, electrical efficiencies of 40–50% and high and stable power output were demonstrated.     

Solid oxide fuel cell-lithium battery hybrid power generation system energy management: A review

The solid oxide fuel cell (SOFC)/lithium battery hybrid energy structure uses lithium batteries as the energy buffer unit to ensure that the SOFC can operate safely and stably when the load power increases suddenly. For the SOFC/lithium battery hybrid power generation system, a real-time energy management strategy based on power prediction is discussed, and an in-depth summary is made from system construction, power prediction, energy distribution, and power tracking. In the hybrid power generation system, the SOFC system and the lithium battery influence each other. Research the appropriate energy management strategies and realize real-time energy distribution and tracking of hybrid power generation systems in order to improve system performance and economy. This has become a key issue in the current SOFC hybrid power generation system research field.     

Transient thermodynamic analysis of a novel integrated ammonia production,storage and hydrogen production system

A transient thermodynamic analysis is reported of a novel chemical hydrogen storage system using energy and exergy approaches. The hydrogen is stored chemically in ammonia using the proposed hydrogen storage system and recovered via the electrochemical decomposition of ammonia through an ammonia electrolyzer. The proposed hydrogen storage system is based on a novel subzero ammonia production reactor. A single stage refrigeration system maintains the ammonia production reactor at a temperature of −10 °C. The energy and exergy efficiencies of the proposed system are 85.6% and 85.3% respectively. The proposed system consumes 34.0 kJ of work through the process of storing 1 mol of hydrogen and recovering it using the ammonia electrolyzer. The system is simulated for filling 30,000 L of ammonia at a pressure of 5 bar, and the system was able to store 7500 kg of ammonia in a liquid state (1% vapor) in 1500 s. The system consumes nearly 45.3 GJ of energy to store the 7500 kg of ammonia and to decompose it to reproduce the stored hydrogen during the discharge phase.     

SOFC and MCFC system level modeling for hybrid plants performance prediction

In this paper a generalized model, based on system-level approach, for predicting the High Temperature Fuel Cells (HTFCs) behavior and performance is presented.The system-level model allows to forecast the HTFC performance under different operating conditions (cell temperature, anode off-gas recirculation, reactants temperatures, fuel and oxidant utilization factors, etc.) and cell design (tubular and planar configurations and with co-flow, counter-flow and cross-flow arrangements).Mass and energy balances are solved by considering both the electrochemical (i.e. electro-oxidation of hydrogen) and thermochemical reactions (i.e. reforming and shifting reactions) which occur in the anode and cathode sides and by applying different equations systems to take into account the type of fuel cell (MCFC or SOFC).The ability of the proposed model in the HTFCs performance prediction is pointed out by the model validation carried out by using experimental data and by analyzing the impact of the model calibration parameters on the cell voltage calculation carried out by means of a sensitivity analysis.Numerical results show that the model allows to characterize the behavior of the HTFCs with a good approximation so, thanks to the simplicity of the simulation procedure and to the small computational time efforts, it can be a useful tool for predicting the performance of hybrid power plants or more complex systems in which the fuel cell is one of the main components.