Turbine Hybrid Power System Research Articles

Thermodynamic performance analysis of direct methanol solid oxide fuel cell hybrid power system for ship application

Methanol is a fuel that can be directly supplied to solid oxide fuel cell (SOFC) without carbon deposition. This paper introduces the direct methanol SOFC-Internal combustion engine (ICE) hybrid power and SOFC-Gas turbine (GT) hybrid power systems. Thermodynamic performance analysis of the hybrid power systems and an investigation into the impact of various parameters were conducted. The results indicate that the electric efficiency of the SOFC-ICE system is 56.07 %, which is 3 percentage points higher than the SOFC-GT system but 3–4 percentage points lower than the SOFC-ICE system with pre-reforming. Increasing fuel utilization rate, operation temperature, and excess air ratio is beneficial to the performance of the SOFC, and raising current density helps improve the system's power density. Load-sharing strategy research demonstrates that in a scenario where the power ratio between SOFC and the ICE is 35:65, compared to a methanol engine, the efficiency of the SOFC-ICE hybrid power system increases by 4.3 %. Despite a 1.4-fold increase in weight and a 1.66-fold increase in cost, the fuel consumption rate and carbon emissions decrease by 8.8 %. Therefore, the strategy of combining a high-power engine with a low-power SOFC is currently a suitable load-sharing strategy for ship applications.

Techno-Economic and Environmental Analysis of a Hybrid Power System Formed From Solid Oxide Fuel Cell, Gas Turbine, and Organic Rankine Cycle

Abstract Distributed energy technology is an essential pathway for future advancements in the field of energy technology. In the present study, organic Rankine cycle (ORC) is integrated with solid oxide fuel cell (SOFC)-gas turbine (GT) hybrid power system. The conventional metrics employed for assessing the performance of SOFCs, gas turbines, and organic Rankine cycles, such as voltage and gross real efficiencies, have some limitations as indices of merit. Contemporary second law concepts and economic and environmental analysis have been used to enhance hybrid power system evaluation. R1233zd(E) has been selected as the ORC working fluid. The outcomes reveal that, under certain conditions, the present configuration may reach 55.67% energy efficiency and 53.55% exergy efficiency. Economic and environmental analysis shows that the hybrid system's total cost rate and Emissions of CO2 gas (EMI) under design conditions are 36.09 $/h and 355.8 kg/MWh, respectively. Thermodynamic evaluation of present SOFC-GT-ORC configuration shows 11.72% improvement in exergy efficiency compared to hybrid SOFC-GT cycle. Consequently, the hybrid SOFC-GT-ORC system is far better than the hybrid SOFC-GT system. In the future, other ORC fluids like R123, R601a, and R245fa can be used as ORC fluids.

Model Development and Optimization of a Solid Oxide Fuel Cell/Gas Turbine Hybrid Power System for Electric Aviation

With countless global industries pledging and pursuing decarbonization targets set for the 2030 – 2050 timeframe, the aerospace industry faces many key challenges including reduction of greenhouse gas emissions, contrail abatement, and development/adoption of technologies with higher Fuel-to-Electricity (FTE) conversion efficiencies. One such technology identified as a potential fit for commercial aircraft is the solid oxide fuel cell and gas turbine (SOFC-GT) hybrid power system. Progress in system-level SOFC-GT modeling is critical to produce higher fidelity feasibility studies used to influence SOFC design and performance targets of the future. In this study, the first ProMax 5.0-based SOFC-GT model was developed, validated, and optimized. The impact of process configuration, balance-of-plant, and operating conditions were investigated. An optimal process design comprising 8 SOFC stacks and 7 Energy Storage and Power Generation (ESPG) modules with a total power output of > 7.0-MW and FTE conversion efficiencies of 73 – 76% is reported. Additionally, preliminary airplane architecture with the 7 onboard ESPG modules is presented to show the feasibility of future, hybrid electric airplane design.

Hybrid Solid Oxide Fuel Cell/Gas Turbine Model Development for Electric Aviation

A thermodynamic model was developed and validated to analyze a high-performance solid oxide fuel cell and gas turbine (SOFC-GT) hybrid power system for electric aviation. This study used a process simulation software package (ProMax) to study the role of SOFC design and operation on the feasibility and performance of the hybrid system. Standard modules, including compressor, turbine, heat exchanger, reforming reactor, and combustor were used from the ProMax tool suite while a custom module was created to simulate the SOFC stack. The model used an SOFC test data set as an input. Additional SOFC stack performance effects, such as pressure, temperature, and utilization of air and fuel, were added from open source data. System performance predictors were SOFC specific power, fuel-to-electricity conversion efficiency, and hybrid system efficiency. Using these input data and predictors, a static thermodynamic performance model was created that can be modified for different system configurations and operating conditions. Prior to creating the final aircraft performance model, initial demonstration models were developed to validate output results. We used the NASA SOFC model as a benchmark, which was created with their Numerical Propulsion System Simulator (NPSS) software framework. Our output results matched within 1% of both the NASA model and open source SOFC performance data. With confidence gained in the accuracy of this model, a 1-MW SOFC-GT hybrid power system was constructed for an aircraft propulsion concept. Overall hybrid system efficiencies of > 75% FTE were observed during standard 36,000 feet cruise flight conditions.

Numerical investigation of a dual-stage off-gas burner to support high pressure and high temperature solid oxide fuel cell/gas turbine (SOFC/GT) hybrid systems

The objective of this study is to investigate the challenges associated with burning these off-gases and to develop a simple yet efficient combustor to support solid oxide fuel cell/gas turbine hybrid power systems. As a result of operating of the fuel cell under conditions of high fuel utilization, a solid oxide fuel cell produces high temperature exhaust gases on the anode side that are of low heating value, and depleted air with low oxygen content on the cathode side. Anode off-gases characterized by heating values less than 2 MJ/m3 and cathode off-gases with as little as 9 vol % oxygen concentration present a challenge for achieving stable combustion. In this study, the focus is on the development of a dual-stage combustor for low-calorific solid oxide fuel cell off-gases at combustor inlet temperatures up to 1100 K. In addition to taking advantage of high temperature off-gases to support the stable combustion of these low heating value off-gases, the influence of elevated-pressure combustor operation (set by the solid oxide fuel cell operating pressure) is investigated. Initially, a chemical reactor network is developed and used to simulate mixing and flow characteristics of a typical gas turbine combustor operating on the aforementioned fuel/air mixtures at the elevated operating conditions. These results are then used to inform a dual-stage burner design in the form of a computational fluid dynamics model for simulations incorporating both flow and combustion dynamics. The final parameters that are used to evaluate the final design are criteria pollutant emissions such as carbon monoxide and oxides of nitrogen, as well as suitable temperature profiles across the burner.

Performance evaluation of intermediate temperature solid oxide fuel cell-gas turbine hybrid power system

PurposeThe purpose of this paper is to analyze the performance of the gas turbine cycle integrated with solid oxide fuel cell technology. In the present work, intermediate temperature solid oxide fuel cell has been considered, as it is economical, can attain an activation temperature in a quick time, and also have a longer life compared to a high-temperature solid oxide fuel cell, which helps in the commercialization and can generate two ways of electricity as a hybrid configuration.Design/methodology/approachThe conceptualized cycle has been analyzed with the help of computer code developed in MATLAB with the help of governing equations. In this work, the focus is on the performance investigation of a Gas turbine intermediate temperature solid oxide fuel cell hybrid cycle. The work also analyzes the performance behavior of the proposed cycle with various design and operating parameters.FindingsIt is found that the power generation efficiency of the IT-SOFC-GT hybrid system reaches up to 60% (LHV) for specific design and operating conditions. The cycle calculations of an IT-SOFC-GT hybrid system and its conceptual design have been presented in this work.Originality/valueThe unique feature of this work is that IT-SOFC has been adopted for integration instead of HT-SOFC, and this work also provides the performance behavior of the hybrid system with varying design and operating parameters, which is the novelty of this work. This work has significant scientific merit, as the cost involved for the commercialization of IT-SOFC is comparatively lower than HT-SOFC and provides a good option to energy manufacturers for generating clean energy at a low cost.

A Novel Multiagent Resource Sharing Algorithm for Control of Advanced Energy Systems

This paper implements a novel resource sharing control strategy on a fuel cell–gas turbine hybrid power system at the National Energy Technology Laboratory’s Hybrid Performance Facility (Hyper). In a fuel cell–gas turbine hybrid power system, the simultaneous interaction of the gas turbine and the fuel cell creates a tightly coupled environment characterized by conflicting dynamics. In this paper, a model-free control approach is applied to solve the tightly coupled control problem posed by this challenging environment. Specifically, this control problem is presented as a resource sharing problem that can be solved using a resource sharing algorithm that is defined based on the distribution construction concept. This algorithm creates computational agents and solves the problem through the distribution and redistribution of shared resources defined as blocks. Two agents were created; the first agent (agent 1) controls the gas turbine speed by adjusting the electric load, and the second agent (agent 2) controls the cathode mass flow through the fuel cell using the cold-air bypass valve. A parametric study was performed over the course of 15 experimental tests for both agents 1 and 2 through an evaluation of the responses based on setpoint changes. The algorithm was shown to have behavior comparable to a previously implemented multi-input multioutput state-space controller, which was designed through a model-based control approach. The resource sharing algorithm was able to find stable performance during run-time operations without any prior system knowledge identification on the power plant and without creating models used in traditional control strategies.

Real-Time Interface Model Investigation for MCFC-MGT HILS Hybrid Power System

The research on the control strategy and dynamic characteristics of the Molten Carbonate Fuel Cell-Micro Gas Turbine (MCFC-MGT) hybrid power system has received much attention. The use of the Hardware-In-the-Loop Simulation (HILS) method to study the MCFC-MGT hybrid power system, where the MCFC is the model subsystem and the MGT is the physical subsystem, is an effective means to save development cost and time. The difficulty with developing the MCFC-MGT HILS system is the transfer of the mass, energy, and momentum between the physical subsystem and the model subsystem. Hence, a new Simulation–Stimulation (Sim–Stim) interface model of the MCFC-MGT HILS hybrid power system to achieve a consistent mass, energy, and momentum with the prototype system of the MCFC-MGT hybrid power system is proposed. In order to validate the Sim–Stim interface model before application in an actual system, both a real-time model of the MCFC-MGT hybrid power system and the MCFC-MGT HILS hybrid power system based on the Sim–Stim interface model were developed in the Advanced PROcess Simulation (APROS) platform. The step-up and step-down of the current density, which were strict for the Sim–Stim interface model, were studied in these two models. The results demonstrated that the Sim–Stim interface model developed for the MCFC-MGT HILS hybrid power system is rapid and reasonable.

Carbon monoxide reduction in solid oxide fuel cell–mini gas turbine hybrid power system

In this paper, combined heat and power frameworks employing solid oxide fuel cell power module and a small-scale gas turbine are presented. The offered system is utilized as heat and power supply for residential consumers with a carbon dioxide sorption circulating fluidized bed. As well a favorable solution for the high penalties associated with CO2 capture and reuse of the CO contents is offered. The combined heat and power system considered by a different arrangement in order to high proficiency, controllability, heat recovery and high capacity of energy. In the proposed system, the unburned product from the solid oxide fuel cell is re-extracted and utilized as a fuel source. The suggested system is analyzed by the first and second law of thermodynamics. During this study, comprehensive calculations of chemistry and thermal within the fuel cell are performed to get accurate results. The impact of various parameters, for example fuel and oxidant rate, carbon dioxide removal, operating pressure, compressor parameter on work and heat output of the cycle as well as the discharge of carbon dioxide contamination, is investigated. The optimal pressure ratio of the compressor to minimize the carbon dioxide production is found.

Optimal operation of fuel cell/wind turbine hybrid power system under turbulent wind and variable load

In this paper is proposed a new Extremum Seeking Control (ESC) algorithm for optimal operation of Wind Turbine (WT) under turbulent wind. In this proposal the dithers’ amplitude is WT system dependent, not constant or decreasing exponentially as in the classic ESC schemes. So, instead of one, the proposed ESC scheme has two loops: (1) the classic ESC loop controlled by the loop gain (k1) to accurately find the Maximum Power Point (MPP); (2) the anticipative ESC loop controlled by the dither gain (k2) to speed-up the localization of the current MPP under turbulent wind. The obtained results for a 100 Hz dither highlight the performance of the ESC-based MPP tracking algorithm proposed: about 99.9% tracking accuracy and a searching time less than 120 ms. This performance assures a tracking efficiency higher than 99% even for gusts of wind that may occur. The Fuel Cell is proposed as backup energy source for WT Hybrid Power System to sustain the load demand and reduce the size of the Energy Storage System (ESS), even for a high variability of the WT power. In comparison with Static Feed-Forward (sFF) strategy, a fuel economy of 5 lpm can be obtained using the ESC-based Real-Time Optimization (RTO) strategies proposed here, which means about 10% from the nominal fuel consumption.

Technical challenges in operating an SOFC in fuel flexible gas turbine hybrid systems: Coupling effects of cathode air mass flow

Considering the limited turndown potential of gasification technologies, supplementing a fuel cell turbine hybrid power system with natural gas provides flexibility that could improve economic viability. The dynamic characterization of fuel composition transients is an essential first step in completing the system identification required for controls development. In this work, both open loop and closed loop transient responses of the fuel cell in a solid oxide fuel cell (SOFC) gas turbine (GT) hybrid system to fuel composition changes were experimentally investigated using a cyber-physical fuel cell system. A transition from methane lean syngas to methane rich gases with no turbine speed control was studied. The distributed performance of the fuel cell was analyzed in detail with temporal and spatial resolution across the cell.Dramatic changes in fuel cell system post combustor thermal output or “thermal effluent” resulting from anode composition changes drove turbine transients that caused significant cathode airflow fluctuations, by as much as 8% in less than a minute. In comparing the open loop responses to identical tests conducted under closed loop conditions without significant airflow changes, it was discovered that the cathode airflow change was a major linking event in short-term system transient response. The results suggested that modulating cathode air flow in response to fuel composition changes offers promise for the dynamic control of SOFC/GT hybrid systems with fuel flexibility.

Effect of anode–cathode exhaust gas recirculation on energy recuperation in a solid oxide fuel cell-gas turbine hybrid power system

A solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system supplying liquid fuel as ethanol exhibits promise as an auxiliary power unit. In this study, the recirculation of anode and cathode exhaust gas in the SOFC-GT system is proposed to improve the efficiency of heat management in the SOFC-GT hybrid system. The key operating parameters, such as fuel utilization factor and the cell and GT temperatures, are analyzed in terms of the performance of the SOFC-GT hybrid systems. The simulation results show that the recirculation of anode and cathode exhaust gas has a direct impact on the turbine performance. To maintain the inlet temperature of the small turbine in the range of 873–1223 K, the amount of fuel and air added to the combustor to control the turbine inlet temperature on the system performance is also investigated. A SOFC-GT hybrid system with both anode and cathode exhaust gas recirculation achieves the highest system and thermal efficiency.

Flexible photovoltaics/fuel cell/wind turbine (PVFCWT) hybrid power system designs

Flexible photovoltaics/fuel cell/wind turbine (PVFCWT) hybrid power system designs

Performance Analysis of a MCFC/MGT Hybrid Power System Bi-Fueled by City Gas and Biogas

This study evaluates the performance of a molten carbonate fuel cell and micro gas turbine (MCFC/MGT) hybrid power system bi-fueled by city gas and biogas. The performance of the MCFC/MGT hybrid power system and MFCF/MGT hybrid power system response have been investigated experimentally and numerically. Results show that the MCFC, steam reformer, and catalytic combustor models are in agreement with the experimental results of the system fueled by city gas only and the system bi-fueled by city gas and biogas. The MFCF/MGT hybrid power system can have manifest operation with the addition of biogas at a flow rate of up to 150.0 Nm3·h−1, which is about 50% of the overall input heat value. In addition, the MCFC and MGT outputs decrease with the increase in the flow rate of added biogas, with an overall power generation efficiency ranging from 39.0% to 42.0%. Furthermore, the MCFC/MGT hybrid power system can be operated stably both at low amplitude with slow current change and large amplitude with rapid power conditions. Finally, the MCFC/MGT hybrid system bi-fueled by city gas and biogas may be applicable to the energy supply of the micro–grid network.

Transfer function development for control of cathode airflow transients in fuel cell gas turbine hybrid systems

Direct-fired fuel cell gas turbine hybrid power system responses to open-loop transients were evaluated using a hardware-based simulation of an integrated solid oxide fuel cell gas turbine (SOFC/GT) hybrid system, implemented through the Hybrid Performance (Hyper) facility at the U.S. Department of Energy, National Energy Technology Laboratory (NETL). A disturbance in the cathode inlet air mass flow was performed by manipulating a hot-air bypass valve implemented in the hardware component. Two tests were performed; the fuel cell stack subsystem numerical simulation model was both decoupled and fully coupled with the gas turbine hardware component. The dynamic responses of the entire SOFC/GT hybrid system were studied in this paper. The reduction of cathode airflow resulted in a sharp decrease and partial recovery of the fuel cell thermal effluent in 10 s. In contrast, the turbine rotational speed did not exhibit a similar trend. The transfer functions of several important variables in the fuel cell stack subsystem and gas turbine subsystem were developed to be used in the future control method development. The importance of the cathode airflow regulation was quantified through transfer functions. The management of cathode airflow was also suggested to be a potential strategy to increase the life of fuel cells by reducing the thermal impact of operational transients on the fuel cell subsystem.

The development of control strategy for solid oxide fuel cell and micro gas turbine hybrid power system in ship application

A solid oxide fuel cell (SOFC) and micro gas turbine (MGT) hybrid power system is a newly developed and promising power technology for ship power systems. Compared to conventional power plants on commercial ship, the technology can achieve a high efficiency (up to 80 %) and very low emission (up to zero) [1]. However, working as a marine power provider onboard ship, the control strategy of the hybrid system is one of the key challenges due to the requirement of balance between power generation from the SOFC’s chemical reaction and the MGT’s rotation mechanical power generation. In this paper, based on a system model, the control strategy for the hybrid power systems is presented. To get the maximum efficiency, the control of key parameters of the SOFC, such as stack temperature, fuel flow rate, fuel utilization and related power have been investigated and the control of power sharing between the two power sources of SOFC and MGT is proposed. The simulation results demonstrate that the control system can effectively control the SOFC and MGT subsystem and make them undertake their appropriate load separately with the forthcoming load.

Evaluation of Cathode Air Flow Transients in a SOFC/GT Hybrid System Using Hardware in the Loop Simulation.

Thermal management in the fuel cell component of a direct fired solid oxide fuel cell gas turbine (SOFC/GT) hybrid power system can be improved by effective management and control of the cathode airflow. The disturbances of the cathode airflow were accomplished by diverting air around the fuel cell system through the manipulation of a hot-air bypass valve in open loop experiments, using a hardware-based simulation facility designed and built by the U.S. Department of Energy, National Energy Technology Laboratory (NETL). The dynamic responses of the fuel cell component and hardware component of the hybrid system were studied in this paper.

Control Impacts of Cold-Air Bypass on Pressurized Fuel Cell Turbine Hybrids

A pressure drop analysis for a direct-fired fuel cell turbine hybrid power system was evaluated using a hardware-based simulation of an integrated gasifier/fuel cell/turbine hybrid cycle, implemented through the hybrid performance (Hyper) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL). The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transient behavior. It is possible to model, test, and evaluate the effects of different parameters on the design and operation of a gasifier/fuel cell/gas turbine hybrid system and provide means of evaluating risk mitigation strategies. The cold-air bypass in the Hyper facility directs compressor discharge flow to the turbine inlet duct, bypassing the fuel cell, and exhaust gas recuperators in the system. This valve reduces turbine inlet temperature while reducing cathode airflow, but significantly improves compressor surge margin. Regardless of the reduced turbine inlet temperature as the valve opens, a peak in turbine efficiency is observed during characterization of the valve at the middle of the operating range. A detailed experimental analysis shows the unusual behavior during steady state and transient operation, which is considered a key point for future control strategies in terms of turbine efficiency optimization and cathode airflow control.

Research of the Power Control for a MCFC/GT Hybrid System

Molten carbonate fuel cell/ gas turbine hybrid power system (MCFC/GT) output power should real-time response the demand of load. The auto-tuning ZieglerNichols tuned PI controller (AZNPIC) as a feedback controller for power corrective action is added to the hybrid power system. The optimal setpoints and feed forward control inputs of the controller are given by Multi-output Support Vector Machine Regression (MSVR) predictor for the hybrid system. Simulation results show that the power of hybrid system can be effectively close to the desired setpoints based on the control method.

Avoiding Compressor Surge During Emergency Shutdown Hybrid Turbine Systems

A new emergency shutdown procedure for a direct-fired fuel cell turbine hybrid power system was evaluated using a hardware-based simulation of an integrated gasifier/fuel cell/turbine hybrid cycle (IGFC), implemented through the Hybrid Performance (Hyper) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL). The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transient behavior. It is possible to model, test, and evaluate the effects of different parameters on the design and operation of a gasifier/fuel cell/gas turbine hybrid system and provide a means of quantifying risk mitigation strategies. An open-loop system analysis regarding the dynamic effect of bleed air, cold air bypass, and load bank is presented in order to evaluate the combination of these three main actuators during emergency shutdown. In the previous Hybrid control system architecture, catastrophic compressor failures were observed when the fuel and load bank were cut off during emergency shutdown strategy. Improvements were achieved using a nonlinear fuel valve ramp down when the load bank was not operating. Experiments in load bank operation show compressor surge and stall after emergency shutdown activation. The difficulties in finding an optimal compressor and cathode mass flow for mitigation of surge and stall using these actuators are illustrated.