Francesco Calise

Thermoeconomic Modeling and Parametric Study of Hybrid Solid Oxide Fuel Cell-Gas Turbine-Steam Turbine Power Plants Ranging From 1.5MWeto10MWe

Detailed thermodynamic, kinetic, geometric, and cost models are developed, implemented, and validated for the synthesis/design and operational analysis of hybrid solid oxide fuel cell (SOFC)-gas turbine-steam turbine systems ranging in size from 1.5 MWe to 10 MWe. The fuel cell model used in this research work is based on a tubular Siemens-Westinghouse-type SOFC, which is integrated with a gas turbine and a heat recovery steam generator (HRSG) integrated in turn with a steam turbine cycle. The current work considers the possible benefits of using the exhaust gases in a HRSG in order to produce steam, which drives a steam turbine for additional power output. Four different steam turbine cycles are considered in this research work: a single-pressure, a dual-pressure, a triple-pressure, and a triple-pressure with reheat. The models have been developed to function both at design (full load) and off-design (partial load) conditions. In addition, different solid oxide fuel cell sizes are examined to assure a proper selection of SOFC size based on efficiency or cost. The thermoeconomic analysis includes cost functions developed specifically for the different system and component sizes (capacities) analyzed. A parametric study is used to determine the most viable system/component syntheses/designs based on maximizing the total system efficiency or minimizing the total system life cycle cost.

One-Dimensional Model of a Tubular Solid Oxide Fuel Cell

In this paper, a detailed model of a solid oxide fuel cell (SOFC) tube is presented. The SOFC tube is discretized along its longitudinal axis. Detailed models of the kinetics of the shift and reforming reactions are introduced in order to evaluate their rates along the SOFC axis. Energy, moles, and mass balances are performed for each slice of the components under investigation, allowing the calculation of temperature profiles. Friction factors and heat-exchange coefficients are calculated by means of experimental correlations. As for the SOFC overvoltages, the activation overvoltage is calculated using the Butler‐Volmer equation and semiempirical correlations for the exchange current density, Ohmic losses are evaluated introducing an appropriate electrical scheme and material resistivities, and concentration overvoltage is calculated by means of both binary and Knudsen diffusion coefficients. On the basis of this model, a case study is presented and discussed, in which temperatures, pressures, chemical compositions, and electrical parameters are evaluated for each slice of the SOFC tube under investigation. Finally, a sensitivity analysis is performed, in order to investigate the influence of the design parameters on the performance of the system. DOI: 10.1115/1.2784296

Dynamic simulation and parametric optimisation of a solar-assisted heating and cooling system

SYNOPSIS In this paper, a complete transient simulation model of a solar heating and cooling plant is presented. The system under analysis is based on the coupling of evacuated solar collectors with a single-stage LiBr-H2O absorption chiller. An auxiliary heater, circulation pumps, storage tanks, feedback controller, mixers, diverters, ON/OFF hysteresis controller, single lumped capacitance building and controllers are also included. The simulation was performed using the TRNSYS environment. This software also includes a detailed database with weather parameters for several cities all over the world. The system was simulated using specially designed control strategies and varying the main design variables. In particular, a variable speed pump on the solar collector was implemented, in order to maximise the tank temperature and minimise heat losses. A cost model was also developed in order to calculate operating and capital costs. A case study is presented and discussed, aiming at determining the performance of the system, from both energetic and economic viewpoints, in a specific application. A thermoeconomic objective function was also introduced, and finally a sensitivity analysis was performed, in order to calculate the set of synthesis/design parameters that maximise the global efficiency of the system or the above-mentioned objective function, for the case under analysis. The results of the case study showed that a good selection of the solar collector (SC) area and of the volume of the storage tank (TK1) are mandatory. The Primary Energy Saving (PES) is positive in the case of high solar field area, while the optimal thermo-economic volume of the storage tank was found to be 75 l/m2. The parametric optimisation also showed that it is important to lower the SC and auxiliary heater (AH) set-point temperatures, as much as possible.

Solar heating and cooling systems by absorption and adsorption chillers driven by stationary and concentrating photovoltaic/thermal solar collectors: Modelling and simulation

Solar heating and cooling systems are a promising technology which may significantly contribute to the reduction of greenhouse gas emissions, the enhancement of energy efficiency, and the increase of renewables share in the building sector. The available literature show a high number of papers aiming at investigating solar heating and cooling systems based on heat driven and solar technologies, configurations, operating strategies, and financing issues. Nevertheless, none of the papers available in literature investigates the possibility to replace conventional solar thermal collectors by flat plat and concentrating photovoltaic/thermal systems, also producing renewable electricity. To cover this lack of knowledge, in this paper a dynamic simulation model of novel solar polygeneration heating and cooling systems is presented. Such dynamic simulation model is developed and implemented in a computer code, written in MatLab, and allows investigating the energy, economic and environmental performance of such novel solar polygeneration systems, based on both adsorption and absorption chiller technologies fed by dish-shaped concentrating and flat photovoltaic/thermal collectors. In order to show the potentiality of the presented tool, a comprehensive parametric case study is carried out to find out the optimal system configurations, as a function of crucial design and operating parameters and of weather conditions. The presented case study analysis refers to a small cluster of four buildings, including office and residential spaces, located in different European weather zones. The modelled solar polygeneration systems simultaneously produce electricity, space heating and cooling, and domestic hot water; electricity is self-consumed or delivered to the electrical grid. For comparative purposes, two different back-up system configurations, based on an electric chiller and a condensing gas-fired heater are also taken into account as conventional reference building-plant systems. By means of this systematic parametric analysis, comprehensive guidelines for system designers, practitioners and/or researchers focused on the development and use of solar heating and cooling systems are provided.

Simulation Model and Analysis of a Small Solar-Assisted Refrigeration System: Dynamic Simulation and Optimization

In this paper, a complete zero-dimensional transient simulation model of a solar-assisted refrigeration plant is presented. In addition, a case study is discussed, aiming at determining the optimal configuration of the system, from the energetic point of view, in a specific application. The system under analysis consisted of several components: evacuated solar collectors, circulation pumps, variable speed pump, water storage tanks, auxiliary heater, single-stage H2 O-LiBr absorption chiller, cooling tower, feedback controller, on/off hysteresis controller, single lumped capacitance building and controllers. The simulation was performed using the TRNSYS environment which is provided by a large component library. This software also includes a detailed database with weather parameters for several European cities. The system and the building were simulated using TRNSYS built in models. The system was simulated using specially designed control strategies and varying the main design variables. In particular, a variable speed pump on the solar collector was implemented in order to maximize the tank temperature and minimizing the heat losses. Finally a sensitivity analysis was also performed in order to calculate the set of synthesis/design parameters that maximize the total system efficiency.Copyright

Exergetic Analysis of a Novel Solar Cooling System for Combined Cycle Power Plants

This paper presents a detailed exergetic analysis of a novel high-temperature Solar Assisted Combined Cycle (SACC) power plant. The system includes a solar field consisting of innovative high-temperature flat plate evacuated solar thermal collectors, a double stage LiBr-H2O absorption chiller, pumps, heat exchangers, storage tanks, mixers, diverters, controllers and a simple single-pressure Combined Cycle (CC) power plant. Here, a high temperature solar cooling system is coupled with a conventional combined cycle, in order to pre-cool gas turbine inlet air in order to enhance system efficiency and electrical capacity. In this paper, the system is analyzed from an exergetic point of view, on the basis of an energy-economic model presented in a recent work, where the obtained main results show that SACC exhibits a higher electrical production and efficiency with respect to the conventional CC. The system performance is evaluated by a dynamic simulation, where detailed simulation models are implemented for all the components included in the system. In addition, for all the components and for the system as whole, energy and exergy balances are implemented in order to calculate the magnitude of the irreversibilities within the system. In fact, exergy analysis is used in order to assess: exergy destructions and exergetic efficiencies. Such parameters are used in order to evaluate the magnitude of the irreversibilities in the system and to identify the sources of such irreversibilities. Exergetic efficiencies and exergy destructions are dynamically calculated for the 1-year operation of the system. Similarly, exergetic results are also integrated on weekly and yearly bases in order to evaluate the corresponding irreversibilities. The results showed that the components of the Joule cycle (combustor, turbine and compressor) are the major sources of irreversibilities. System overall exergetic efficiency was around 48%. Average weekly solar collector exergetic efficiency ranged from 6.5% to 14.5%, significantly increasing during the summer season. Conversely, absorption chiller exergy efficiency varies from 7.7% to 20.2%, being higher during the winter season. Combustor exergy efficiency is stably close to 68%, whereas the exergy efficiencies of the remaining components are higher than 80%.

Multi-Point Energy and Exergy Analysis of a 1.5 MWe Hybrid SOFC-GT Power Plant

This paper presents a multi-point energy and exergy analysis of a hybrid SOFC–GT power plant. The plant layout consists of the following principal components: an internal reforming SOFC, a steam-methane pre-reformer, a catalytic burner, a radial gas turbine, a centrifugal air compressor, a centrifugal fuel compressor, plate-fin heat exchangers, counter-flow shell and tube heat exchangers, and mixers. The partial load performance of the centrifugal compressors and radial turbine is determined using maps, properly scaled in order to match required mass flow rate and pressure ratio values. The plant is simulated on the basis of a zero-dimensional model discussed in previous papers. Two different partialization strategies are introduced in order to assess the partial load behavior of the plant. Results show that the plant achieves the best partial load performance for the case when both air and fuel mass flow rates are simultaneously reduced.Copyright

Trigeneration and Polygeneration Configurations for Desalination and Other Beneficial Processes

Abstract The integration of renewable energy sources (geothermal, biomass, and solar) and desalination systems into novel polygeneration plants is investigated. Two main arrangements are considered: geothermal (GP) and biomass (BP) polygeneration. Both systems include concentrating photovoltaic/thermal solar collectors, a multieffect distillation system for seawater desalination, a single-effect LiBr-H2O absorption chiller, storage tanks, heat exchangers, balance-of-plant devices; a biomass auxiliary heater and geothermal wells are also included, in BP and GP, respectively. The systems can provide electricity and hot water, used for space heating, cooling, domestic hot water production, and drinkable desalted water. Both systems are simulated by means of a zero-dimensional dynamical simulation model. Thermoeconomic, exergy, and exergoeconomic analyses are also presented, aiming at defining the best values of the main design variables. Two case studies are discussed: city of Naples (BP) and Pantelleria island (GP), both characterized by solar and geothermal resources and scarcity of fossil fuels and freshwater.

CHAPTER 13:Integrated SOFC and Gas Turbine Systems

Solid Oxide Fuel Cells (SOFC) are particularly promising for their capability to be integrated in complex power plants, showing ultra-high conversion efficiencies. This chapter investigates some possible layout configurations of hybrid power plants including both SOFC and Gas Turbine (GT) technologies. SOFC/GT power plants have been diffusely investigated in literature, from both numerical and experimental viewpoints. Such systems are mainly fed by methane which can be reformed into hydrogen inside (internal reforming) or outside (external reforming) the stack. The majority of SOFC/GT hybrid systems use the internal reforming arrangement which allows one to minimize system capital cost. The steam required to drive the reforming reaction can be supplied by the anode recirculated stream. Alternatively, such steam can be produced externally, using the heat of the exhaust gases. SOFC/GT power plants can operate both in atmospheric and pressurized modes. The atmospheric plants are easier to manage due to the possibility to decouple SOFC and GT operations. On the other hand, pressurized SOFC/GT power plants show higher efficiencies. More complex SOFC/GT configurations are also analyzed, such as: SOFC/HAT turbines, IGCC SOFC/GT power plants, SOFC/GT Cheng cycles, etc. Finally, the chapter also presents the control strategies to be used in the managements of hybrid SOFC/GT power plants, also showing some results of the transient operation of these systems.