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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.

A dynamic solid oxide fuel cell (SOFC) model was integrated with other system components (i.e., reformer, anodic off-gas burner, anodic ejector) to build a system model that can simulate the time response of the anode side of an integrated 250 kW pressurized SOFC hybrid system. After model description and data on previous validation work, this paper describes the results obtained for the dynamic analysis of the anodic loop, taking into account two different conditions for the fuel flow input: in the first case (I), the fuel flow follows with no delay the value provided by the control system, while in the second case (11), the flow is delayed by a volume between the regulating valve and the anode ejector, this being a more realistic case. The step analysis was used to obtain information about the time scales of the investigated phenomena: such characteristic times were successfully correlated to the results of the subsequent frequency analysis. This is expected to provide useful indications for designing robust anodic loop controllers. In the frequency analysis, most phase values remained in the 0-180 deg range, thus showing the expected delay-dominated behavior in the anodic loop response to the input variations in the fuel and current. In Case I, a threshold frequency of 5 Hz for the pressure and steam to carbon ratio and a threshold frequency of 31 Hz for the anodic flow were obtained. In the more realistic Case 11, natural gas pipe delay dominates, and a threshold frequency of 1.2 Hz was identified, after which property oscillations start to decrease toward null values. [DOI: 10.1115/1.2772638]

An instrument for promoting C[O.sub.2] emission reductions, taking the Kyoto Protocol goal into account, could be the assignment to energy conversion plants of a monetary charge linked to their specific emission intensity, usually called carbon tax. There are two main problems closely connected with this approach: the estimation of the charge (that must be related to the 'external' cost associated with C[O.sub.2] emission) and the choice of the strategy to determine the amount of the imposed charge. In this paper an analytical procedure proposed by the authors and called carbon exergy tax (CET) for the evaluation of C[O.sub.2] emission externalities is presented. It is based on the thermoeconomic analysis of energy systems, which allows second law losses to be quantified in monetary terms: the resulting cost represents the taxation that is to be applied to the energy system under examination, calculated without any arbitrary assumption. Since the complete procedure of the CET evaluation is too complex to become a feasible instrument of energy policy, hereby, after applying the procedure to some conventional and advanced power plants, gas, oil, and coal-fueled, a new generalized approach, based on the results of the complete CET procedure, is proposed. The generalized CET evaluation requires much less information about the energy system and thus a simple and effective energy policy rule to manage global warming is obtained and available. [DOI: 10.1115/1.1610013

This paper addresses the off-design analysis of a hybrid system (HS) based on the coupling of an existing Ansaldo Fuel Cells (formerly Ansaldo Ricerche) molten carbonate fuel cell (MCFC) stack (100 kW) and a micro gas turbine. The MCFC stack model at fixed design conditions has previously been presented by the authors. The present work refers to an off-design stack model, taking into account the influence of the reactor layout, current density, air and fuel utilization factor, C[O.sub.2] recycle loop, cell operating temperature, etc. Finally, the design and off-design model of the whole hybrid system is presented. Efficiency at part load condition is presented and discussed, taking into account all the constraints for the stack and the micro gas turbine, with particular emphasis on C[O.sub.2] recycle control. [DOI: 10.1115/1.1587742]

In this paper the thermoeconomic analysis of gas turbine plants with fuel decarbonization and carbon dioxide sequestration is presented. The study focuses on the amine (MEA) decarbonization plant layout and design, also providing economic data about the total capital investment costs of the plant. The system is fuelled with methane that is chemically treated through a partial oxidation and a water-gas shift reactor. C[O.sub.2] is captured from the resulting gas mixture, using an absorbing solution of water and MEA that is continuously recirculated through an absorption tower and a regeneration tower: the decarbonized fuel gas is afterwards burned in the gas turbine. The heat required by C[O.sub.2] sequestration is mainly recovered from the gas turbine exhausts and partially from the fuel treatment section. The reduction in efficiency and the increase in energy production costs due to fuel amine decarbonization is evaluated and discussed for different gas turbine sizes and technologies (microturbine, small size regenerated, aeroderivative, heavy duty). The necessary level of carbon tax for a conventional plant without a fuel decarbonization section is calculated and a comparison with the carbon exergy tax procedure is carried out, showing the good agreement of the results. [DOI: 10.1115/1.1587744]

The aim of this work is to investigate the performance of internal reforming solid oxide fuel cell (IRSOFC) and gas turbine (GT) combined cycles. A mathematical model of the IRSOFC steady-state operation was presented in Part I of this work coupled to the thermodynamic analysis of a number of proposed IRSOFC-GT combined cycles, taking into account the influence of several technological constraints. In the second part of this work, both an exergy and a thermoeconomic analysis of the proposed cycles have been carried out using the TEMP code developed by the author. A suitable equation for IRSOFC cost evaluation based on cell geometry and performance has been proposed and employed to evaluate the electricity generation cost of the proposed combined systems. The results are presented and the influence of several parameters is discussed: external reformer operating conditions, fuel-to-air ratio, cell current density, compressor pressure ratio, etc. Diagrams proposed by the author for cost versus efficiency, cost versus specific work, and cost versus system pressure are also presented and discussed. [DOI: 10.1115/1.1492837]

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. [DOI: 10.1115/1.1473825]

Microturbines and fuel cells are currently attracting a lot of attention to meet future users needs in the distributed generation market. This paper addresses a preliminary analysis of a representative state-of-the-art 50-kW microturbine coupled with a high-temperature solid-oxide fuel cell (SOFC). The technologies of the two elements of such a hybrid-power plant are in a different state of readiness. The microturbine is in an early stage of pre-production and the SOFC is still in the development phase. It is premature to propose an optimum solution. Based on today g technology the hybrid plant, using natural gas fuel, would have a power output of about 389 kW, and an efficiency of 60 percent. If the waste heat is used the overall fuel utilization efficiency would be about 80 percent. Major features, parameters, and performance of the microturbine and the SOFC are discussed. The compatibility of the two systems is addressed, and the areas of technical concern, and mismatching issues are identified and discussed. Fully understanding these, and identifying solutions, is the key to the future establishing of an optimum overall system. This approach is viewed as being in concert with evolving technological changes. In the case of the microturbine changes will be fairly minor as they enter production on a large scale within the next year or so, but are likely to be significant for the SOFC in the next few years, as extensive efforts are expended to reduce unit cost. It is reasonable to project that a high performance and cost-effective hybrid plant, with high reliability, will be ready for commercial service in the middle of the first decade of the 21st century. While several microturbines can be packaged to give an increased level of power, this can perhaps be more effectively accomplished by coupling just a single gas turbine module with a SOFC. The resultant larger power output unit opens up new market possibilities in both the industrial nations and developing countries. [DOI: 10.1115/1.1398552]

The aim of this work is to investigate the performance of molten carbonate fuel cells (MCFCs), with external sensible heat reformer and gas turbine/steam turbine (GT/ST) combined cycles. The analysis of these MCFC-GT/ST combined cycles has been carried out using the thermo economic modular program (TEMP) modified to allow MCFC, external sensible heat reformer, and catalytic burner performance to be carefully taken into account. The code has been verified through the use of a detailed MCFC model and of the data available for an existing MCFC unit. The thermodynamic and exergy analysis of a number of MCFC combined cycles is presented and discussed, taking into account the influence of technological constraints, also evaluated with the sophisticated model, and the influence of the post-combustion of the fuel directly in the external catalytic burner. The results are presented and discussed in depth. [DOI: 10.1115/1.1398551]

This paper presents optimized cycle performance that can be obtained with systems including a closed cycle gas turbine (CCGT). The influence of maximum temperature, minimum temperature, and recuperator effectiveness on cycle performance is illustrated. Several power-plant arrangements are analyzed and compared based on thermodynamic performance (thermal efficiency and specific work); enabling technologies (available at present); and developing technologies (available in the near term or future). The work includes the effects of utilization of high temperature ceramic heat exchangers and of coupling of CCGT systems with plants vaporizing liquid hydrogen (L[H.sub.2]) or liquefied natural gas (LNG). Given the versatility of energy addition and rejection sources that can be utilized in closed gas-cycle systems, the thermodynamic performance of power plants shown in this paper indicate the remarkable capabilities and possibilities for closed gas-cycle systems.

This paper reports an experimental investigation on centrifugal compressor surge. The compression system consists of a four-stage blower with vaned diffusers and a large plenum discharging into the atmosphere through a throttle valve. Measurements of unsteady pressure and flow rate in the plant, and of instantaneous velocity in the diffusers of the first and fourth compressor stage, are performed during deep surge, at several valve settings and three different rotation speeds. Additional tests have been carried out on a different system configuration, i.e., without plenum, in order to obtain the steady-state compressor characteristics and to collect reference data on stall in surge-free conditions. In this configuration, a fully developed rotating stall was detected in the compressor diffusers, while during surge it affects only a limited part of the surge cycle. The goal of the present experimental work was to get a deeper insight into unstable operating conditions of multistage centrifugal compressors and to validate a theoretical model of the system instability to be used for the design of dynamic control systems.

This paper describes, from a theoretical point of view, the behavior of compression systems during surge and the effect of passive and active control devices on the instability limit of the system. A lumped parameter model is used to simulate the compression system described in Part I of this work (Arnulfi et al., 1999), based on an industrial multistage centrifugal compressor. A comparison with experimental results shows that the model is accurate enough to describe quantitatively all the features of the phenomenon. A movable wall control system is studied in order to suppress surge in the compressor. Passive and active control schemes are analyzed; they both address directly the dynamic behavior of the compression system to displace the surge line to lower flow rates. The influence of system geometry and compressor speed is investigated; the optimum values of the control parameters and the corresponding increase in the extent of the stable operating range are presented in the paper.

Methods to analyze, improve, and optimize thermal energy systems have to take into account not only energy (exergy) consumption and economic resources, but also pollution and degradation of the environment. The term 'environomics' implies a method that takes thermodynamic, economic, and environmental aspects systematically into consideration for the analysis and optimization of energy systems. For optimization of energy systems, the environmental aspects are quantified and introduced into the objective function. In this particular work, the environomic approach is followed for the analysis and optimal design of a combined-cycle plant. In addition to the basic configuration, two alternatives for N[O.sub.x] abatement are studied: Selective Catalytic Reduction (SCR) and steam injection. The optimization problem is solved for each configuration, and the results are compared with each other. The effect of the unit pollution penalties and of the limits imposed by regulations is studied. Some general conclusions are drawn.

The aim of this work is to demonstrate the capability of an original 'modular' simulator tool for the thermoeconomic analysis of thermal-energy systems. The approach employed is based on the Thermoeconomic Functional Analysis (T.F.A.), which, through definition of the 'functional productive diagram' and the establishment of the capital cost function of each component, allows the marginal costs and the unit product costs, i.e., the 'internal economy,' of the functional exergy flows to be obtained in correspondence to the optimum point. The optimum design of the system is obtained utilizing a traditional optimization technique, which includes both physical structure of the energy system described in terms of thermodynamic variables and cost model (capital cost of the components, maintenance and amortization factors, unit fuel cost, unit electricity cost, etc.). As an application example to show the practicability of the tool, the thermoeconomic analysis of various complex multipressure combined cycles (with or without steam reheating) is carried out. The results are analyzed and discussed in depth.

A two-step experimental investigation of an energy-saving nacelle anti-ice system, named hot-film, demonstrates its superiority over the conventional spray-bar anti-ice system. The hot-film system allows a more uniform distribution of the internal heat transfer coefficient, and a reduction in the hot-air mass flow rate and weight of the system. Design optimization aims at achieving sufficient anti-ice capability with minimal use of engine bleed air. The efficiency of the aircraft protection system is analyzed with respect to engine integration problems.

The thermoeconomic analysis of gas turbine based cycles is presented and discussed in this paper. The thermoeconomic analysis has been performed using the ThermoEconomic Modular Program (TEMP V. 5.0) developed by Agazzani and Massardo (1997). The modular structure of the code allows the thermoeconomic analysis for different scenarios (turbine inlet temperature, pressure ratio, fuel cost, installation costs, operating hours per year, etc.) of a large number of advanced gas turbine cycles to be obtained in a fast and reliable way. The simple cycle configuration results have been used to assess the cost functions and coefficient values. The results obtained for advanced gas turbine based cycles (inter-cooled, re-heated, regenerated and their combinations) are presented using new and useful representations: cost versus efficiency, cost versus specific work, and cost versus pressure ratio. The results, including productive diagram configurations, are discussed in detail and compared to one another. [S0742-4795(00)01903-7]

Focuses on a study which investigated the performance of internal reforming solid oxide fuel cell (IRSOFC) and gas turbine (GT) combined cycles. Parametric analysis of IRSOFC; Integration analysis of solid oxide fuel cell and GT; IRSOFC-GT power system analysis.

Abstract: In this paper, the results of the thermodynamic and economic analyses of distributed power generation plants (1.5MWe) are described and compared. The results of an exergetic analysis are also reported, as well as the thermodynamic details of the most significant streams of the plants. The integration of different hybrid solid oxide fuel cell (SOFC) system CO2 separation technologies characterizes the power plants proposed. A hybrid system with a tubular SOFC fed with natural gas with internal reforming has been taken as reference plant. Two different technologies have been considered for the same base system to obtain a low CO2 emission plant. The first technology involved a fuel decarbonization and CO2 separation process placed before the system feed, while the second integrated the CO2 separation and the energy cycle. The first option employed fuel processing, a technology (amine chemical absorption) viable for short-term implementation in real installations while the second option provided the CO2 separation by condensing the steam from the system exhaust. The results obtained, using a Web-based Thermo Economic Modular Program software, developed by the Thermochemical Power Group of the University of Genoa, showed that the thermodynamic and economic impact of the adoption of zero emission cycle layouts based on hybrid systems was relevant. [Copyright &y& Elsevier]