Loredana Magistri

A Hybrid System Based on a Personal Turbine (5 kW) and a Solid Oxide Fuel Cell Stack: A Flexible and High Efficiency Energy Concept for the Distributed Power Market

In this paper a high efficiency and flexible hybrid system representing a new total energy concept for the distributed power market is presented. The hybrid system is composed of a very small size (5 kW) micro gas turbine (named personal turbine-PT) presented in a companion paper by the authors coupled to a small size solid oxide fuel cell (SOFC) stack. The power of the whole system is 36 kW depending on the design parameters assumed for the stack. The design and off-design performance of the hybrid system have been obtained through the use of an appropriate modular code named HS-SOFC developed at the University of Genoa and described in detail in this paper. The results of the simulation are presented and discussed with particular regards to: choice of the hybrid system (HS) design point data, HS design point performance, off-design performance of PT and SOFC stack, and off-design performance of the whole HS. Some preliminary economic results are also included based on different fuel and capital cost scenarios and using the cost of electricity as the parameter for comparison between PT and HS.

Heat Exchangers for Fuel Cell and Hybrid System Applications

The fuel cell system and fuel cell gas turbine hybrid system represent an emerging technology for power generation because of its higher energy conversion efficiency, extremely low environmental pollution, and potential use of some renewable energy sources as fuels. Depending upon the type and size of applications, from domestic heating to industrial cogeneration, there are different types of fuel cell technologies to be employed. The fuel cells considered in this paper are mainly the molten carbonate (MCFC) and the solid oxide (SOFC) fuel cells, while a brief overview is provided about the proton exchange membrane (PEMFC). In all these systems, heat exchangers play an important and critical role in the thermal management of the fuel cell itself and the boundary components, such as the fuel reformer (when methane or natural gas is used), the air preheating, and the fuel cell cooling. In this paper, the impact of heat exchangers on the performance of SOFC, MCFC gas turbine hybrid systems and PEMFC systems is investigated. Several options in terms of cycle layout and heat exchanger technology are discussed from the on-design, off-design and control perspectives. A general overview of the main issues related to heat exchangers performance, cost and durability is presented and the most promising configurations identified.

Hybrid Simulation Facility Based on Commercial 100 kWe Micro Gas Turbine

A new high temperature fuel cell-micro gas turbine physical emulator has been designed and installed in the framework of the European Integrated Project “FELICITAS” at the Thermochemical Power Group (TPG) laboratory located at Savona. The test rig is based on a commercial 100 kWe recuperated micro gas turbine (mGT) (Turbec T100) modified to be connected to a modular volume designed for physical emulation of fuel cell stack influence. The test rig has been developed starting with a complete theoretical analysis of the micro gas turbine design and off-design performance and with the definition of the more flexible layout to be used for different hybrid system (molten carbonate fuel cell or solid oxide fuel cell) emulation. The layout of the system (connecting pipes, valves, and instrumentation, in particular mass flow meter locations) has been carefully designed, and is presented in detail in this paper. Particular attention has been focused on the viscous pressure loss minimization: (i) to reduce the unbalance between compressor and expander, (ii) to maintain a high measurement precision, and (iii) to have an effective plant flexibility. Moreover, the volume used to emulate the cell stack has been designed to be strongly modular (different from a similar system developed by U.S. Department Of Energy-National Energy Technology Laboratory) to allow different volume size influence on the mGT rig to be easily tested. The modular high temperature volume has been designed using a computational fluid dynamics (CFD) commercial tool (FLUENT ). The CFD analysis was used (i) to reach a high level of uniformity in the flow distribution inside the volume, (ii) to have a velocity field (m/s) similar to the one existing inside the emulated cell stack, and (iii) to minimize (as possible) the pressure losses. The volume insulation will also allow to consider a strong thermal capacity effect during the tests. This paper reports the experimental results of several tests carried out on the rig (using the mGT at electrical stand-alone conditions with the machine control system operating at constant rotational speed) at different load values and at both steady-state and transient conditions.

Simplified versus detailed solid oxide fuel cell reactor models and influence on the simulation of the design point performance of hybrid systems

High-efficiency hybrid systems (HS) based on the coupling of solid oxide fuel cells (SOFCs) and gas turbines (GT) are analyzed in this paper through the use of two different approaches: simplified and detailed SOFC models. The simplified model, already presented by the authors, is very useful for HS design and off-design analysis. The detailed model, developed by the authors and verified through the use of available experimental data, allows the complete description of the SOFC reactors internal behavior to be obtained. The detailed model can also be utilized for HS modeling. Both models are presented and discussed in this paper, and they are compared to each other. The results obtained for the stand-alone SOFC reactor, and the HS design point configuration are presented and carefully discussed, also taking into account the nonlinear SOFC response.

Micro Gas Turbine Recuperator: Steady-State and Transient Experimental Investigation

The aim of this work is the experimental analysis of a primary-surface recuperator, operating in a 100 kW micro gas turbine, as in a standard recuperated cycle. These tests, performed in both steady-state and transient conditions, have been carried out using the micro gas turbine test rig, developed by the Thermochemical Power Group at the University of Genova, Italy. Even if this facility has mainly been designed for hybrid system emulations, it is possible to exploit the plant for component tests, such as experimental studies on recuperators. The valves installed in the rig make it possible to operate the plant in the standard recuperated configuration, and the facility has been equipped with new probes essential for this kind of tests. A wide-ranging analysis of the recuperator performance has been carried out with the machine, operating in stand-alone configuration, or connected to the electrical grid, to test different control strategy influences. Particular attention has been given to tests performed at different electrical load values and with different mass flow rates through the recuperator ducts. The final section of this paper reports the transient analysis carried out on this recuperator. The attention is mainly focused on thermal transient performance of the component, showing the effects of both temperature and flow steps. [DOI: 10.1115/1.3156822].

Modeling and Performance Analysis of the Rolls-Royce Fuel Cell Systems Limited: 1 MW Plant

This paper is focused on the performance of the 1 MW plant designed and developed by Rolls-Royce Fuel Cell Systems Limited. The system consists of a two stage turbogenerator coupled with pressure vessels containing the fuel cell stack, internal reformer, cathode ejector, anode ejector, and off-gas burner. While the overall scheme is relatively simple, due to the limited number of components, the interaction between the components is complex and the system behavior is determined by many parameters. In particular, two important subsystems such as the cathode and the anode recycle loops must be carefully analyzed also considering their interaction with and influence on the turbogenerator performance. The system performance model represents the whole, and each physical component is modeled in detail as a subsystem. The component models have been validated or are under verification. The model provides all the operating parameters in each characteristic point of the plant and a complete distribution of thermodynamics and chemical parameters inside the solid oxide fuel cell (SOFC) stack and reformer. In order to characterize the system behavior, its operating envelope has been calculated taking into account the effect of ambient temperature and pressure, as described in the paper. Given the complexity of the system, various constraints have to be considered in order to obtain a safe operating condition not only for the system as a whole but also for each of its parts. In particular each point calculated has to comply with several constraints such as stack temperature distribution, maximum and minimum temperatures, and high and low pressure spool maximum rotational speeds. The model developed and the results presented in the paper provide important information for the definition of an appropriate control strategy and a first step in the development of a robust and optimized control system.

Design and Off-Design Analysis of a MW Hybrid System Based on Rolls-Royce Integrated Planar Solid Oxide Fuel Cells

In this paper the design point definition of a pressurised hybrid system based on the Rolls-Royce Integrated Planar-Solid Oxide Fuel Cells (IP-SOFCs) is presented and discussed. The hybrid system size is about 2 MWe and the design point analysis has been carried out using two different IP-SOFC models developed by Thermochemical Power Group (TPG) at the University of Genoa: (i) a generic one, where the transport and balance equations of the mass, energy and electrical charges are solved in a lumped volume at constant temperature; (ii) a detailed model where all the equations are solved in a finite difference approach inside the single cell. The first model has been used to define the hybrid system lay out and the characteristics of the main devices of the plant such as the recuperator, the compressor, the expander, etc. The second model has been used to verify the design point defined in the previous step, taking into account that the stack internal temperature behavior are now available and must be carefully considered. Apt modifications of the preliminary design point have been suggested using the detailed IP-SOFC system to obtain a feasible solution. In the second part of the paper some off-design performance of the Hybrid System carried out using detailed SOFC model are presented and discussed. In particular the influence of ambient conditions is shown, together with the possible part load operations at fixed and variable gas turbine speed. Some considerations on the compressor surge margin modification are reported.

Transient Analysis of Solid Oxide Fuel Cell Hybrids: Part C — Whole-Cycle Model

A Solid Oxide Fuel Cell-Hybrid System is mainly composed of three parts: the stack, the anodic recirculation system with fuel feeding, and the cathodic side (air side) where turbomachinery and heat exchangers are installed. In Part A of this work the transient models of the fuel cell are described, while in Part B the anodic side is investigated. Many previous studies have been carried out on the cathodic side at the Thermochemical Power Group facility to simulate the transient behavior of the main components such as compressors, expanders and heat exchangers. In this paper attention is focused on the integration of the transient models of the hybrid system components. Following the on and off-design analysis of the SOFC-HS the transient response of the system from an electrochemical, fluid dynamic and thermal point of view has been studied at several operating conditions.Copyright

Transient Analysis of Solid Oxide Fuel Cell Hybrids—Part I: Fuel Cell Models

The main goal of this work is the transient analysis of hybrid systems based on solid oxide fuel cells (SOFC). The work is divided into three parts: in the first, the fuel cell transient models are presented and discussed, whereas in the subsequent parts of the paper the anodic recirculation system (Part B: Ferrari, M.L., Traverse, A., Massardo, A.F, 2004, ASME Paper No. 2004-GT-53716) and the entire hybrid transient performance (Part C: Magistri. L., Ferrari, M.L., Traverse, A., Costamagna, P, Massardo, A.E, 2004, ASME Paper No. 2004-GT-53845) are investigated. In this paper the transient behavior of a solid oxide fuel cell is analyzed through the use of two different approaches: macroscopic and detailed SOFC models. Both models are presented in this paper and their simulation results are compared to each other and to available experimental data. As a first step the transient response of the fuel cell was studied using a very detailed model in order to completely describe this phenomenon and to highlight the critical aspects. Subsequently some modifications were made to this model to create an apt simulation tool (macroscopic fuel cell model) for the whole plant analysis. The reliability of this model was verified by comparing several transient responses to the results obtained with the detailed model. In the subsequent papers (Parts B and C), the integration of the macroscopic fuel cell model into the whole plant model will be described and the transient study of the hybrid plant will be presented.

Demonstration Plant and Expected Performance of an Externally Fired Micro Gas Turbine for Distributed Power Generation

The paper presents the design and development of the first world-wide Externally Fired micro Gas Turbine (EFmGT) demonstration plant based on micro gas turbine technology. The system is particularly useful for exploitation of renewable resources for distributed power and heat generation. The plant has been designed by Ansaldo Ricerche (ARI) s.r.l. and Thermochemical Power Group (TPG) of University of Genoa using TPG in house codes such as TEMP (Thermoeconomic Modular Program) and TRANSEO (TRANSient analysis of energy systems). The plant is based on a recuperated 80 kW micro gas turbine (Elliott TA-80R), and it is under construction at ARI laboratory. The first goal of this plant is the demonstration of the EFmGT system at full and part load operations, mainly from the control point of view. The expected performance (50kW at 16% LHV efficiency) can be improved in the near future using high temperature heat exchangers (a field where ARI has a very long expertise), which should allow the system to operate at the actual micro gas turbine inlet temperature (900–950 °C). In the present paper the design point, off design performance, and part load control system are presented and analysed in depth: it is shown that there are no “forbidden” part load steady state operating points. In a companion paper, where transients of advanced cycles based on mGT technology are discussed, TPG presents the fast and slow transient operation of the EFmGT system.Copyright