lean H2 and NH3 large production in Paraguay by the 14 GW Itaipu hydroelectric facility

This paper aims to present a feasibility study for clean production, storage and distribution of large amounts of hydrogen, starting from low-cost available renewable electrical energy. Paraguay and Brazil own equally the binational company ITAIPU Hydroelectric Plant (14 GW, about 96,000 GWh/year of production). 50% of this energy corresponds to Paraguay: however, since its energy demand is quite low, a large amount of this energy is sold to Brazil, receiving a compensation of 10 $/MWh. In this context, seeking for ways of adding value to generated electricity, this paper assesses the potential of clean H2 production by water electrolysis, simulating the use of one generator unit of the mentioned company (700 MW) and discussing two alternatives for the produced hydrogen: a) using it for ammonia production as base for fertilizers; b) using it for passenger cars. A detailed thermo-economic analysis is performed using a dedicated software developed by the authors. The results show that production is economically feasible for both cases, moreover the process is completely clean and significant amounts of oxygen are produced, potentially representing an additional revenue for the process

Cathode\u2013anode side interaction in SOFC hybrid systems

Cathode-anode interaction, mainly based on cathode versus anode volume influence, recirculation performance, and turbomachinery integration, is an important issue for pressurised SOFC hybrid systems, and this aspect must be carefully considered to prevent fuel cell ceramic material failures through a reliable control system. Over the last 10 years, several theoretical analyses of this issue have been carried out at the University of Genoa. These interaction studies have been analysed and an experimental approach (for model validation, system development and prototype design activities) has been applied using emulator facilities or real plants. In particular, general hybrid system layouts based on the coupling of pressurized SOFC stacks of different geometries (planar, tubular, etc.) with a gas turbine bottoming cycle have been investigated using the hybrid system emulator facility of the University of Genoa. The experimental results are focused on the interaction between gas turbine and anodic circuit and on cathode-anode differential pressure behaviour for design, off-design and transient hybrid system operative conditions. The information obtained in these tests is essential to understand the main features of the variables that drive the phenomena and to design a suitable control system that can mitigate the differential pressure values during all plant operating conditions

Comparison Between Uncontrolled and Controlled Solid Oxide Fuel Cell Hybrid Systems

Because of the high complexity of Solid Oxide Fuel Cell hybrid systems, a transient analysis is mandatory to implement a control system able to maintain safe operation during disturbances or regular operational load variations. In fact, several parameters, such as the turbine rotational speed, the surge margin, the temperatures within the fuel cell, the turbine inlet temperature, the differential pressure between the anodic and the cathodic side and the Steam-To-Carbon Ratio need to be monitored and kept within safe limits. On the other hand, the system response to load variations is required to be as quick as possible in order to meet the energy demand. To develop a control strategy for these cycles, the work starts from the implementation of a transient model necessary to simulate a hybrid system based on the tubular SOFC technology. In fact, the first goal of this work is the analysis of the response to a step decrease in the fuel mass flow rate of the uncontrolled system, focusing the attention on the time scales of the transient phenomena and discussing the results from electrochemical, fluid dynamic and thermal point of view. The simulation shows that while the cathodic side is driven only by the temperature variation, because of the rotational speed is assumed to be constant, the anodic side is characterized by three different time-scale phenomena. In fact, all the plant properties show a negligible fluid dynamic delay, a depressurization time delay and a thermal long time-scale effect mainly due to the high thermal inertia of the cell. The considerations, carried out with the uncontrolled system, are used in the second part of the work to develop a control strategy to follow the power demand over time avoiding malfunctions or risk situations. The paper focuses the attention on a detailed presentation of the control system layout based on the by-pass valve between the compressor outlet and the turbine inlet, necessary to overcome the difficulty due to the difference between the small mechanical inertia of the microturbine shaft and the very high thermal inertia of the fuel cell stack. The simulations, carried out with a load step decrease, show the transient behaviour of the controlled SOFC hybrid system, presenting, over time, the values of the main critical parameters. Finally, the paper presents the results obtained with a power step increase to investigate the limitations of this control strategy focusing the attention on the fuel cell average temperature and the fuel utilization factor

Ejector performance influence on a solid oxide fuel cell anodic recirculation system

This work deals with the design and off-design performance evaluation of an anodic recirculation system based on ejector technology for solid oxide fuel cell hybrid applications. The analysis presented here has been divided into three parts: (i) ejector design taking into account all the thermodynamic, fluid dynamic and chemical constraints, such as steam to carbon ratio (two ejector geometries have been considered: constant area mixing section, constant pressure mixing section); (ii) stand-alone ejector design and off-design performance analysis; (iii) influence on the whole hybrid system\u2014SOFC, reformer, anode recirculation-design and off-design performance of the ejector primary flow conditions (hybrid system part-load conditions)

Design and Testing of Ejectors for High Temperature Fuel Cell Hybrid Systems

Our goal in this work is the improvement of the ejector performance inside hybrid systems supporting the theoretical activity with experimental tests. In fact, after a preliminary ejector design, an experimental rig has been developed to test single stage ejectors for hybrid systems at different operative conditions of mass flow rates, pressures, and temperatures. At first, an open circuit has been built to perform tests at atmospheric conditions in the secondary duct. Then, to emulate a SOFC anodic recirculation device, the circuit has been closed, introducing a fuel cell volume in a reduced scale. This configuration is important to test ejectors at pressurized conditions, both in primary and secondary ducts. Finally, the volume has been equipped with an electrical heater and the rig has been thermally insulated to test ejectors with secondary flows at high temperature, necessary to obtain values in similitude conditions with the real ones. This test rig has been used to validate simplified and CFD models necessary to design the ejectors and investigate the internal fluid dynamic phenomena. In fact, the application of CFD validated models has allowed us to improve the performance of ejectors for hybrid systems optimizing the geometry in terms of primary and secondary ducts, mixing chamber length, and diffuser. However, the simplified approach is essential to start the analysis with an effective preliminary geometry

An Analytical Procedure for the Carbon Tax Evaluation

In this paper, an analytical procedure for carbon tax evaluation is presented. The aim is the assignment to energy plants of a charge linked to their CO 2 emissions. The problem is faced through the use of an environomic approach, including evaluation of the cost of the exergy destroyed inside the system and the cost of exergy rejected to the biosphere with the plant wastes ( EÅciency penalty ) coupled with evaluation of the Index of CO 2 emission herein deÆned. In this way, the procedure allows a cost of the emitted CO 2 to be obtained based not on political considerations but only on eÅciency and exergy analysis. The aim is to reward the eÅcient use of energy resources and to penalize the ineÅcient plants. The procedure is applied for the analysis of three typical Italian energy plants burning fossil fuels: a 320 MW coal steam plant; a 700 MW natural gas combined plant; and a 30 MW gas turbine cogeneration plant. The plants are analysed using an environomic optimization and taking into account all their pollutant emissions (CO, NO x ,SO x and CO 2 ). The values of the CO 2 emissions charges obtained with the proposed procedure are presented and discussed in depth and a comparison with the possible costs of CO 2 sequestration activities is presented to