Piero Lunghi

Analysis and optimization of hybrid MCFC gas turbines plants

Abstract High temperature fuel cells are electricity producers that guarantee relevant energetic and environmental performances. They feature high electricity to input chemical energy ratios and availability of high temperature heat. Notwithstanding, the search for a further increase in electric efficiency, especially when applying a CHP solution is not feasible, has brought to plant integration with gas turbines (GTs) in several studies and some pilot installations. While for pressurized fuel cells the choice of internal combustion gas turbines seem to be the only one feasible, in ambient pressure fuel cells it seems useful to analyze the combination with indirect heated GT. This choice allows to optimize turbine pressure ratio and cell size. In this work, a parametric performance evaluation of a hybrid molten carbonate fuel cell (MCFC) indirect heated gas turbine has been performed by varying the fuel cell section size and the fuel utilization coefficient. The analysis of performance variation with the latter parameter shows how a cell that is optimized for stand alone operation is not necessarily optimized for the integration in a hybrid cycle. Working with reduced utilization factors, in fact can reduce irreversible losses and does not necessarily yield to less electricity production since the heat produced in the post combustor is recovered by the gas turbine section. This aspect has not been taken into sufficient consideration in literature. The analysis illustrates the methodology to define new operating conditions so to allow global output and global efficiency maximization.

Highly efficient electricity generation through a hybrid molten carbonate fuel cell-closed loop gas turbine plant

Abstract Fuel cells have been revealed to be very attractive power generation systems, promising highly efficient electricity generation and very low environmental impact. With the high-temperature fuel cells still in embryonic infancy, the very high energetic efficiency can be further increased by their integration into hybrid cycles. While a wide variety of potential bottoming technologies for the exploitation of the high temperature exhaust gases waste heat is available, a lot of research effort is needed to determine the optimal integration of well established technologies with these very novel conversion devices. The aim of this work is to provide a contribution to selecting promising plants for the electricity generation of the future, and it constitutes an attempt to optimize the working parameters and estimation of the performances. A basic plant configuration and its main working parameters have been determined, including the plant performance, the stream thermodynamic and chemical properties and the component temperatures. A modified plant configuration has been found, allowing the optimal exploitation of the waste heat streams for internal heat regeneration. Different bottoming cycles have been considered, and a parametric analysis has been performed with the aim of performance comparisons. The most promising solution has been determined, and its performance evaluated.

Efficiency upgrading of an ambient pressure molten carbonate fuel cell plant through the introduction of an indirect heated gas turbine

The efficient end environmentally friendly production of electricity is undoubtedly one of the 21st century priorities. Since renewable sources will be able to guarantee only a share of the future demand, the present research activity must focus on innovative energy devices and improved conversion systems and cycles. Great expectations are reserved to fuel cell systems. The direct conversion from chemical to electrical energy eliminates environmental problems connected with combustion and bypass the stringent efficiency limit due to Carnots principle. Still in infancy, high-temperature fuel cells present the further advantage of feasible cycle integration with steam or gas turbines. In this paper, a molten carbonate fuel cell plant is simulated in a cycle for power generation. The introduction of an external combustion gas turbine is evaluated with the aim of efficiency and net power output increase. The results show that the proposed cycle can be conveniently used as a source of power generation. As compared to internal combustion gas turbine hybrid cycles found in the literature the plant is characterized by fuel cell greater simplicity, due to the absence of pressurization, and gas turbine increased complexity, due to the presence of the heat exchange system.

Assessment of an Ambient Pressure MCFC: External Heated GT Hybrid Plant with Steam Injection and Post-Combustion

The constant growth in demand for energy and the awareness of environmental problems requires the development of technologies which lead to significant increases in both energy efficiency and environmental protection. Great expectations have been placed on both simple and hybrid fuel cell plants, thus making necessary the evolution of analysis strategies to evaluate thermodynamic performances, design improvements and acceleration of new developments. This paper investigates the thermodynamic potential of combining a Steam Injected Gas Turbine (STIG) with a Molten Carbonate Fuel Cell (MCFC) for medium and large-scale electrical power production. The MCFC electrochemical core consists of 32 stacks for a total nominal power of 16 MW. The indirect heat transfer to the bottoming cycle allows the GT pressure ratio to be fixed independently from the fuel cell, yielding optimization of the power plant performances in a GT pressure ratios range from 2 to 22. Since the fuel cell exhaust does not have a very high temperature level, the effect of introducing a combustion chamber before the gas turbine is analyzed. The performances of simple and fired bottoming cycles are evaluated and compared as a function of the different parameters in order to identify optimal solutions.

State of the Art About the Effects of Impurities on MCFCs and Pointing Out of Additional Research for Alternative Fuel Utilization

Fuel cells are very flexible energy conversion devices and in particular MCFC power generating system are among the most promising for stationary power generation. Potentially, MCFCs can be fed by a great variety of gaseous fuels comprising low calorific values gases like landfill gas. Thanks to fuel processing technologies, like gasification, suitable anode input gases can also be obtained from solid matters. Coal, but also RDF (Refuse Derived Fuel), industrial waste and biomasses are potential fuels for the fuel cell technology after a specific treatment aimed to yield a proper gas for the cell requirements. The gases mentioned above are characterized by low calorific values, presence of inert gases, presence of carbon monoxide and dioxide, presence of various contaminants such as chlorine, sulphur and nitrogen compounds or metals and they can be utilized for power production in high temperature fuel cell units only after a proper clean-up treatment (tars, particulate and sulphur removal). Although interest in alternative fuels for fuel cells has spread in the recent years, most research activity related to fuel treatment has been performed on methane. The biggest drawback deriving from this situation is a general lack of information. When present, moreover, the information is often contradictory. An example of this is given by the acceptable contaminants levels for molten carbonate fuel cells about which there are not values that are based on sufficient experimental evidence. Unfortunately the design of a clean-up system, the choice of the best technology, the optimization of the BOP relies just on these values. In this work a literature research and an analysis of the present knowledge about the effect of impurities in fuel for fuel cells has been preformed. The goal is the definition of concentration levels that can be tolerated by MCFCs and the degradation in performance or the reduction of cell life related to the presence of different pollutants. A second step of the work is the comparison of the levels of impurities tolerated by the cells with those present in the different low calorific value gases in order to define the clean-up requirements. The research priorities in this field have been pointed out. Finally, the project of the fuel cell team of University of Perugia about this topic is briefly described.Copyright

Energy saving strategies in an actual confectionery plant

The achievement of a more rational use of energy can be difficult when large and complex industrial plants are considered. In the present work, an example is given of how a well-focused energy analysis, based on experimental data, can help to point out possible relevant energy savings. In particular, two different refrigeration systems have been examined for a confectionery plant in different seasons, atmospheric and production conditions, allowing us to understand the actual operation. Based on the analysis of the results, energy saving strategies have been proposed and discussed. Copyright

Feasibility and Performance of an Ambient Pressure MCFC Combined With a Commercial Gas Turbine

Fuel cells have resulted to be very attractive power generation systems, promising highly efficient electricity generation with very low environmental impact. Although still in embryonic infancy high-temperature fuel cells, the very high energetic efficiency can be further increased by their integration in hybrid cycles. While a wide variety of potential bottoming technologies for exploiting the high temperature exhaust gases waste heat is available, a lot of research effort is needed to determine the optimal integration of well established technologies with these very novel conversion devices. This work, using results from previous works, in which a MCFC/Gas Turbine hybrid plant was defined and the working parameters optimised both with a GT simple cycle and with steam injection and post combustion, starts from choosing an existing gas turbine technology with suitable working parameters to perform a system evaluation and integration. Since the gas turbine nominal maximum temperature cannot be reached by the only means of heat exchange from the MCFC plant section, post combustion has been considered and the turbine has been simulated both in nominal and in off design conditions in order to find an optimal solution. The work takes into consideration not only the main plants modifications of the existing components to allow for system integration but also the most relevant issues connected with altered working conditions.Copyright

Performance Enhancement of Fuel Cells Systems Through Series and Parallel Connections of Multi Stack Arrays

Fuel cells have been known theoretically for more than a century. Recently conceived high temperature fuel cells, by guaranteeing higher degrees of efficiencies and greater fuel flexibility, have the potential to yield a radical change in the future of distributed electricity market promising high efficient and ultra-clean power generation. In the last years progress has been so relevant that they seem to be on the verge of commercialization. All plants commissioned seem to consider the parallel flow solution i.e. in which primary fuel flow splits to enter all the stacks that works with nominally equal operational parameters. The present work analysed the possibility of disposing stacks in an array, thus leading to a combination of series and parallel fluid dynamic connection so that one cell anode may have as input the exhaust of another cell anode. The aim is to allow some cells to work with low utilization factors and therefore at greater voltages. Different solutions have been analysed with a tool obtained from the integration of a proprietary code for cells simulation, with Aspen+ flowsheet. Code predictions of cells performances have been validated by experimental campaigns [Lunghi and Burzacca 2002]. The results showed that a noticeable performance increase can be obtained with the proposed configuration without any significant complication in the process. The authors believe that this should be considered as a very interesting research field and strongly encourage participation of the scientific community.Copyright

A Methodology for Assessing Fuel Cell Performance Under a Wide Range of Operational Conditions: Results for Single Cells

Testing the performance of fuel cells is an important key for verifying technology improvements and for demonstrating their potential. However, due to the novelty of this technology, there is not a standardized procedure for testing fuel cell performance. In order to fully investigate fuel cell performance, the behavior must be known under a wide range of operational conditions. Furthermore, in order to compare results coming from different test teams, a set of procedures and parameters to evaluate single cell performance should be defined. The research group of the Fuel Cell Laboratory of the University of Perugia is conducting performance tests on single cells, focusing on defining test procedures to find effective parameters to be used to compare tests performed by different teams. This work demonstrates how the testing parameters developed by the team allow one to perform advanced control on test procedures, to understand test results, and to compare them with tests carried out under different operational conditions. The entire analysis is easily conducted by using a single parameter variation hyperspace approach. The experimental results obtained on single fuel cells are reported.

A Comparison Between Life Cycle Assessment Of An MCFC System, An LFG – MCFC System, And Traditional Energy Conversion Systems

The present work aims at evaluating the environmental impact caused by fuel cell systems in the production of electric energy. The very low pollutant emission levels in fuel cells makes them an attractive alternative in ultra clean energy conversion systems. Actually, to truly understand the environmental impact related to fuel cells, it is necessary to study their “cradle-to-grave” life, from the construction phase, during the conversion of primary fuel into hydrogen, to its disposal. The tool used in this analysis is the Life Cycle Assessment approach; in particular the environmental impact of a fuel cell system has been simulated through the software SimaPro 5.0. Thanks to this approach, once the critical process regarding the production of energy by fuel cell system, (i.e. the production of hydrogen by natural gas steam reforming), has been determined, an analysis of the use of landfill gas as a renewable source to produce hydrogen was done. Finally, the production of electric energy by fuel cell systems was compared to that by some conventional energy conversion systems. A second comparison was done between the Molten Carbonate Fuel Cell (MCFC) fuelled by landfill gas and natural gas.Copyright