Claudia Toro

Modeling Carbon Monoxide Direct Oxidation in Solid Oxide Fuel Cells

In the present study, the results of the numerical implementation of a mathematical model of a planar anode-supported SOFC are reported. In particular, model results are validated and discussed when the fuel is a mixture of hydrogen and carbon monoxide, focusing on the importance of simulating direct oxidation of carbon monoxide. The mathematical model is solved in a 3D environment and the key issue is the validation comparing with experimental data, which is made in different operating conditions to establish the reliability of the presented model. The results show the importance of simulating direct oxidation of carbon monoxide and its effect on the fuel cell performance.

The Gas Turbine Hybrid Vehicle LETHE™ at UDR1: The On-Board Innovative ORC Energy Recovery System — Feasibility Analysis

A GTHV (gas turbine hybrid vehicle) is an electric vehicle with traction entirely electric on 1 or 2 axles, equipped with a small turbogas whose only function is that of recharging the battery pack and possibly other energy storage devices present on board. After a brief review of the history of the GTHV technology, a complete feasibility assessment of a prototype configuration of a GTHV designed by the University of Roma 1 is presented. All issues related to the system and component design, packaging, identification of the “optimal” hybridization ratio, performance of the (gas turbine + batteries + electrical motor) conversion system, braking energy recovery systems (KERS), mechanical and electric storage devices (flywheels, capacitors, advanced batteries), monitoring and control logic, compliance with the European vehicular ECE emission regulations, have been already discussed in previous papers. The present study analyzes the feasibility to insert “on-board” an innovative and patented ORC (Organic Rankine Cycle) recovery system. In fact, the thermal source on the LETHE© vehicle is a turbogas of suitable power (10 to 30 kW depending on the vehicle class). The sensible heat of the exhaust gases is an ideal thermal source for an ORC system that can feed the car conditioning system and other auxiliaries.Copyright

Exergy analysis of a solid oxide fuel cell-gas turbine hybrid power plant

The paper presents the exergy analysis of a natural gas fuelled energy conversion process consisting of a hybrid solid oxide fuel cell coupled with a gas turbine. The fuel is partly processed in a reformer and then undergoes complete reforming in an internal reforming planar SOFC stack (IRSOFC). The syngas fuels in turn a standard gas turbine cycle that drives the fuel compressor and generates excess shaft power. Extensive heat recovery is enforced both in the Gas Turbine and between the topping SOFC and the bottoming GT. Two different configurations have been simulated and compared on an exergy basis: in the first one, the steam needed to support the external and the internal reforming reactions is completely supplied by an external Heat Recovery Steam Generator (HRSG), while in the second one that steam is mainly obtained by recirculating part of the steam-rich anode outlet stream. The thermodynamic model of the fuel cell system has been developed and implemented into the library of a modular object-oriented Process Simulator, Camel-Pro® ; then, by means of this simulator, the exergetic performance of the two alternative configurations has been analyzed. A detailed analysis of the exergy destruction at component level is presented, to better assess the distribution of irreversibilities along the process and to gain useful design insight.Copyright

Process Simulation and Exergy Analysis of a Reverse Osmosis Desalination Plant Powered by Photovoltaic Panels in Basra (Iraq)

The paper presents the simulation and the exergy analysis of a solar-powered reverse osmosis plant (PV-RO) located in Basra (Iraq) characterized by an average production of 5 m3 of fresh water per hour. The system layout includes the PV system powering the reverse osmosis unit. Since the purpose of the plant is to supply freshwater to a rural village, the installation of a battery pack as an energy storage is not foreseen. The influence of some relevant process parameters like ambient temperature, global radiation and salinity of the raw water are studied by means of numerical process simulations of the plant. A suitable thermodynamic model of the PV-RO has been developed and implemented into the library of a modular object-oriented Process Simulator, CAMEL-Pro™ and the code has been then used to study the exergetic performance of the plant, to help identify and quantify irreversibilities and losses in energy quality. In CAMEL, the exergy flow associated with each energy and material stream in the plant is calculated on the basis of mass- and energy balances and of a proper set of libraries of material properties, so that the values of the exergy destruction, ExD and of the exergy efficiency, ExEff, of each component can be evaluated.Copyright

Optimal operation and sensitivity analysis of a large district heating network through pod modeling

District heating networks (DHNs) are crucial infrastructures for the implementation of energy efficiency and CO2 reduction plans, especially in countries with continental climate. DHNs are often complex systems and their energy performance may be largely affected by the operating conditions.Optimal operation of DHNs involves the optimization of the pumping system. This is particularly important for large networks and for low temperature networks. A common practice to perform optimization consists in using a phyical model. Nevertheless, simulation and optimization of DHNs may involve large computational resources, because of thire possible large extension and the number of scenarios to be examined. A reduced model, obtained from the physical model, can be effectively applied to multiple simulations of a network, with significant reduction of the computational time and resources.In this paper, a large district heating system, which supplies heating to a total volume of buildings of about 50 million of cubic meters, is considered. The use of a reduced model based on proper orthogonal decomposition (POD) is investigated. Various operating conditions corresponding to partial load operation are analyzed using a fluid-dynamic model of the network. Results show that optimal settings are not particularly regular with respect to load variation. This means that any variation in the thermal load generally involves changes in the set points of all groups. For this reason, a sensitivity analysis is performed using the POD model in order to check the opportunities to limit the number of variations in the pumping settings without significant penalization of the total pumping power.The proposed approach is shown to be very effective for the optimal management of complex district heating systems.Copyright

An Example of Thermo-Economic Optimization of a CCGT by Means of the Proper Orthogonal Decomposition Method

This paper presents an application of the Proper Orthogonal Decomposition (POD) technique (also called Karhunen-Loeve Decomposition, Principal Component Analysis, or Singular Value Decomposition) to the thermo-economic optimization of a realistic Combined-Cycle Gas Turbine (CCGT) process. The novel inverse-design approach proposed here employs the thermo-economic cost of the two products as objective function.The proposed procedure does not require the generation of a complete simulated set of results at each iteration step of the optimization, because POD constructs a very accurate approximation to the function described by a certain number of initial simulations, and thus “new” points in design space can be extrapolated without recurring to repeated process simulations. Thus, the often taxing computational effort needed to iteratively generate numerical process simulations of incrementally different configurations is substantially reduced by replacing much of it by easy-to-perform matrix operations: a non-negligible but quite small number N of initial process simulations is used to calculate the basis of the POD interpolation and to validate (i.e., extend) the results.Since the accuracy of a POD expansion depends of course on the number N of initial simulations (the “snapshots”), the computational intensity of the method is certainly not negligible: but, as successfully demonstrated in the paper for a realistic CCGT inverse process design problem, the idea that additional full simulations are performed only in the “right direction” indicated by the gradient of the objective function in the solution space leads to a successful strategy at a substantially reduced computational intensity. This “economy” with respect to other classical “optimization” methods is basically due to the capability of the POD procedure to identify the most important “modes” in the functional expansion of the vector basis consisting of a subset of the design parameters used in the evaluation of the objective function.Copyright

EXERGY ANALYSIS AND OPTIMIZATION OF A BUILDING AIR CONDITIONING SYSTEM IN TROPICAL CLIMATE

The space conditioning sector is one of the highest exergy consumers and least efficient from the point of view of primary-to-end-use matching. Exergy analysis can be considered as a reliable tool for analyzing and optimizing energy consumption related to building conditioning systems.The present study presents a comparative exergy analysis of the air conditioning system of the TOTAL S.A. offices located in Caracas, Venezuela to finally achieve a reduction of the global electric energy use of the considered building. Starting from the provided thermal cooling load, different possible cooling chains (primary-to-final energy conversion chain) are considered in order to locate the thermodynamically more efficient one from an exergetic point of view. The internal air handler unit, which provides for the cooled and dehumidified air to the building, is fed by the energy obtained from different possible converters of renewable energy primary sources. Specifically, solar and hybrid photovoltaic-thermal (PV/T) panels coupled with an absorption refrigeration machine and with an ejector refrigeration cycle are analyzed.The study that has been carried on leads to identify the most convenient matching between final use and primary sources allowing to substantially reduce the global non-renewable energy consumption of the considered building.Copyright

Design and thermoeconomic evaluation of a waste plant with an integrated CO2 chemical sequestration system for CH4 production

Object of this paper is the modelling, process design and simulation of a waste incineration plant integrated with a novel CO2 chemical sequestration system for CH4 production.The main components of the proposed system are: the incineration plant (whose operational data are considered known here), a Sabatier reactor for CH4 production, a post-combustion monoethanolamine (MEA) chemical absorption unit and a H2O electrolyser.Carbon dioxide captured from the waste plant stack gases and hydrogen from water electrolysis feed the Sabatier chemical reactor in a temperature range of 250–450°C. Through the exothermic methanation reaction (CO2 + 4H2 = CH4 + 2H2O + Heat), methane is produced with a conversion yield of 90–95%. Through a perm-selective membrane, hot steam can be extracted from the reactor and recycled to cover about 40% of the MEA regenerating re-boiler duty.The methanation of CO2 is an established carbon capture technique, profitably suitable for waste plants. When the produced methane is burned, the CO2 absorbed in the process returns to the environment, enacting in a global sense a quasi-zero-emissions cycle.The possible integration of the electrolyser with renewable-generated electricity has been investigated to evaluate the storage capacity of electrical energy as “renewable methane”, which from a technical point of view is more suitable than hydrogen to be stored, burned or sent into natural gas pipelines. A thermo-economic analysis is presented to evaluate the exergetic performance of the proposed system and the final cost of products.Copyright

Integrated Study of a Minimum Exergy Destruction Building Conditioning System

The relatively low average conversion efficiency of air-conditioning systems and the recently imposed upper bounds to the final energy use in the heating and cooling of residential buildings suggest to consider new approaches to design less energy intensive systems.An integrated, exergy-based approach for the optimal matching of internal and external heating plants in building conditioning systems has been proposed — and its theoretical basis discussed — in a previous paper. The procedure allows the designer to obtain a pseudo-optimal integration of the building and its heating plant (heating element + primary energy supply system) and to identify, among a set of alternative solutions for the building under examination, the thermodynamically most efficient plant.The objective of this paper is to validate the method on a real building in order to demonstrate its practical applicability. The large “Chiostro Hall” (220 square meters, 1245 cubic meters) of the Engineering School of the University “Sapienza” of Roma has been employed as the benchmark. This is the main hall of the building, reconverted from a previously existing Renaissance structure, the old convent of San Lorenzo in Panisperna, which was in turn built on the ruins of a pre-christian roman basilica and of a portion of emperor Nero’s Domus Aurea.The hall consists of two semi-connected rooms, originally the Refectory of the old Convent, that are now used for public events, conferences and graduation ceremonies.This structure can be considered as a model case for similar halls in historical buildings, so that the guidelines deriving from the present study can be extended to other similar environments.The current heating elements are traditional radiators: in our simulations, they have been successively replaced by other elements such as floor and ceiling heating panels and fan coils. Each one of these configurations (the hall and its heating elements) has been modeled and simulated via a commercial CFD code to generate detailed thermal maps and to compute the actual thermal load. Different global “heating chains” were then modeled by coupling solar and hybrid photovoltaic-thermal (PV/T) panels with radiant panels and ground-source heat pumps with fan coils and radiant heating panels. Finally by means of a process simulator software each one of these configurations was analyzed to identify the one that provides the same comfort level with the least exergy use. The procedure also allows to calculate the savings obtained in terms of primary resources.Copyright