Vincenzo Spallina

SOFC-Based Hybrid Cycle Integrated With a Coal Gasification Plant

Application of large scale high temperature fuel cells on syngas fuel produced from coal would be a turning point in the power generation sector, dramatically improving the efficiency and the environmental performance of coal-fired power plants. The purpose of this study is the assessment of a system constituted by a SOFC-based hybrid cycle integrated with a coal gasification process. In this system, syngas produced in a high efficiency, dry feed, oxygen blown, entrained flow Shell gasifier is cooled, depurated from particulate and sulfur compounds and reheated; the clean syngas feeds a pressurized SOFC together with high pressure air generated by the compressor of a gas turbine. After combustion of unconverted syngas, fuel cell exhausts are expanded and cooled, providing heat to a bottoming steam cycle for an efficient energy recovery. A high integration between gasification and power islands is necessary in order to obtain an elevated efficiency: the heat recovery system from syngas cooling is carefully arranged to provide thermal power for clean syngas reheating, air preheating and steam generation. The paper presents a preliminary analysis of literature results and a discussion of the thermodynamic implications arising from the use of different primary fuels in a fuel cell-gas turbine cycle. Then the work presents a detailed thermodynamic analysis of the proposed IGFC layout, assessing the effect of SOFC operating pressure on power balance and net plant efficiency. A sensitivity analysis on the variation of fuel and air utilization in the fuel cell is also performed. Results show that the present innovative SOFC-based power system may achieve an efficiency gain of 7–11 percentage points, with respect to an advanced IGCC based on state of the art technology.Copyright

CHAPTER 2:Chemical Looping for Hydrogen Production and Purification

Chemical Looping is an interesting technology that allows (partial) oxidation of a fuel without direct contact between the fuel and air. Instead, a solid material, referred to as oxygen carrier, is used to transport the oxygen from the air to the fuel by solid circulation between two reactors operated under different conditions. As such, the products of the fuel oxidation are nitrogen free. In the case of combustion (full oxidation), this means that the CO2 is not diluted with nitrogen. In the case of reforming/partial oxidation, the syngas is nitrogen free and thus easier to purify. In the presence of an H2 permselective membrane, the syngas production (through chemical looping) and pure H2 separation are combined in the same unit. This chapter introduces the chemical looping principle and describes a new reactor concept that combines the advantages of chemical looping technology and membrane reactors. This concept is referred to as Membrane-Assisted Chemical Looping Reforming (MA-CLR), which allows high hydrogen purity with integrated CO2 capture and high energy efficiency.

Application of MCFC in Coal Gasification Plants for High Efficiency CO

Integrated gasification combined cycles (IGCCs) are considered the reference technology for high efficiency and low emission power generation from coal. In recent years, several theoretical and experimental studies in this field have been oriented towards capturing CO2 from IGCCs through the integration of Solid Oxide Fuel Cells (SOFC) for coal-syngas oxidation, investigating the so-called Integrated Gasification Fuel Cell cycles (IGFC). However, Molten Carbonate Fuel Cells (MCFC) can also be a promising technology in IGFCs. After a rather comprehensive research carried out by the authors on modeling and simulation of SOFC-based IGFC plants, an interesting IGFC cycle based on MCFC is assessed in this work, where plant layout is designed to exploit the capability of MCFCs of transferring CO2 and O2 from the oxidant side to the fuel side. Syngas produced in a high efficiency Shell gasifier is cleaned and mainly burned in a combustion turbine as in conventional IGCCs. Turbine flue gas, rich of oxygen and carbon dioxide, are then used as oxidant stream for the fuel cell at the cathode side, while the remaining clean syngas is oxidized at the anode side. In this way the MCFC, while efficiently producing electricity, separates CO2 from the gas turbine flue gas as in a post-combustion configuration; oxygen is also transported towards the anode side, oxidizing the remaining syngas as in an oxy-combustion mode. A CO2 -rich stream is hence obtained at anode outlet, which can be cooled and compressed for long term storage. This configuration allows to produce power from coal with high efficiency and low emission. In addition, as already highlighted in a previous study where a similar concept has been applied to natural gas-fired combined cycles, a limited fraction of the power output is generated by the fuel cell (the most expensive component), highlighting its potential also from an economic point of view. Detailed results are presented in terms of energy and material balances of the proposed cycle.Copyright

A SOFC-Based Integrated Gasification Fuel Cell Cycle With CO2 Capture

Application of Solid Oxide Fuel Cells (SOFC) in gasification-based power plants would represent a turning point in the power generation sector, allowing to considerably increase the electric efficiency of coal-fired power stations. Pollutant emissions would also be significantly reduced in Integrated Gasification Fuel Cell cycles (IGFC) considering the much lower emissions of conventional pollutants (NOx , CO, SOx , particulate matter) typical of fuel cell-based systems. In addition, SOFC-based IGFCs appear particularly suited to applications in power plants with CO2 capture. This is evident by considering that SOFCs operate as air separators and partly oxidized fuel exiting the fuel cell does not contain nitrogen from air, like in conventional oxy-fuel processes. The aim of the present paper is the thermodynamic analysis of a SOFC-based IGFC with CO2 capture. In the assessed plant, syngas produced in a high efficiency Shell gasifier is used in SOFC modules after heat recovery and cleaning. Anode exhausts, still containing combustible species, are burned with oxygen produced in the air separation unit, also used to generate the oxygen needed in the gasifier; the product gas is cooled down in a heat recovery steam generator before water condensation and CO2 compression. The plant layout is carefully designed to best exploit heat generated in all the processes and, apart from the fuel cell, exotic components, far from industrial state-of-the-art, are not included. Detailed energy and mass balances are presented for a better comprehension of the obtained results.Copyright