1,720,988 research outputs found
Integration of oxygen transport membranes in glass melting furnaces
Full text linkGlass manufacturing is an energy-intensive process where the bulk of energy, necessary to maintain high temperatures for glass melting, usually comes from natural gas combustion. A solution for energy saving is an oxy-fuel glass furnace. This paper investigates the possible application of a membrane based oxygen separation module in glass melting furnaces. The mass and energy balances of two oxy-fuel glass furnaces have been reproduced and compared to an air-blown unit assumed as benchmark. The two oxy-fuel cases differ for the technology adopted to supply oxygen: in the first case, it is delivered by a PSA/VSA unit, whereas in the second case, oxygen is separated from a hot air stream in a membrane module integrated in a micro-gas turbine system. The assessment of the primary fuel demand of the three options highlights the superiority of the oxy-fuel glass furnace with the advanced membrane-based technology. The economic assessment, included to highlight the potential of the proposed application, outlines further advantages
Numerical analysis of NOx production within a hydrogen catalytic combustor
Full text linkHydrogen combustion reactions produce nitrogen oxides as a byproduct. They can be reduced by exploiting the catalytic combustion of hydrogen in a monolith. However, some nitrogen oxides can still be produced in the gas-phase of the catalytic combustor. The present work numerically investigates the production of nitrogen oxides as a by-product of the combustion of a lean air-hydrogen mixture in a catalytic monolith with an equivalence ratio lower than 0.3. The analysis is carried out with a 2D dynamic numerical model implemented in MATLAB. The model solves mass and energy balances in a domain describing a single channel of the monolith. The model involves a detailed reaction mechanism for the gas-phase combustion, including the subsets that model the production of nitrogen oxides. As a result, the model indicates that the catalytic combustor does not produce nitrogen oxides with an inlet hydrogen fraction lower than 9%vol. Furthermore, the maximum value of nitrogen oxide at the outlet of the channel is lower than 0.4 ppm, obtained with the highest hydrogen fraction simulated in this work (12%vol inlet hydrogen fraction)
Electrochemical Carbon Separation in a SOFC-MCFC Polygeneration Plant With Near-Zero Emissions
No full textThe modularity and high efficiency at small-scale make high temperature (HT) fuel cells an interesting solution for carbon capture and utilization at the distributed generation (DG) scale when coupled to appropriate use of CO2 (i.e., for industrial uses, local production of chemicals, etc.). The present work explores fully electrochemical power systems capable of producing a highly pure CO2 stream and hydrogen. In particular, the proposed system is based upon integrating a solid oxide fuel cell (SOFC) with a molten carbonate fuel cell (MCFC). The use of these HT fuel cells has already been separately applied in the past for carbon capture and storage (CCS) applications. However, their combined use is yet unexplored. The reference configuration proposed envisions the direct supply of the SOFC anode outlet to a burner which, using the cathode depleted air outlet, completes the oxidation of the unconverted species. The outlet of the burner is then fed to the MCFC cathode inlet, which separates the CO2 from the stream. This layout has the significant advantage of achieving the required CO2 purity for liquefaction and long-range transportation without requiring the need of cryogenic or distillation plants. Furthermore, different configurations are considered with the final aim of increasing the carbon capture ratio (CCR) and maximizing the electrical efficiency. Moreover, the optimal power ratio between SOFC and MCFC stacks is also explored. Complete simulation results are presented, discussing the proposed plant mass and energy balances and showing the most attractive configurations from the point of view of total efficiency and CCR
Simulation of Oxygen Transport Membranes for CPO Reactors in Small-scale Hydrogen or Syngas Production Applications
Full text linkThe proposed work aims at presenting a 1D finite volume steady state simulation model of an Oxygen Transport Membrane for Catalytic Partial Oxidation (OTM-CPO) reactor developed at the Group of Energy COnversion Systems (GECOS) at Politecnico di Milano. The model is able to simulate supported and unsupported perovskite-based reactive membranes by means of a lumped mass and energy transport method; the active ceramic layer is modelled throughout a generalised O2permeation equation, which depends on the micro-structure characteristics and mixed-ion conduction properties of the material. The supporting porous structure is represented by a mass diffusion model dominated by gas-gas, porous and surface exchange transport processes. The model also includes a global chemical reaction kinetic mechanism of CPO on Rh-based catalysts. The model is applied to simulate the behaviour of a membrane reactor operated upstream the Hydrogen Transport Membrane for Methane Steam Reforming (HTM-MSR) installed at the Laboratory of Micro-Cogeneration (LMC) at Politecnico di Milano. The test bench is focused on testing fuel pre-processing systems for low temperature fuel cells (PEM) applications. The simulation object of this work would allow obtaining a feasibility assessment of the system and a preliminary design of the OTM-CPO reactor
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Multilevel modeling of solid oxide electrolysis
No full textThis chapter discusses the methods of numerical modeling of solid oxide electrochemical cells operated in electrolysis mode. Techniques related to computer simulations of processes taking place in a high-temperature electrolyzer at the level of microstructure, cells, stack, and power systems with solid oxide electrolyzers (SOEs) are presented. A brief introduction to the key electrochemical and mass and energy transfer processes is followed by a discussion of numerical approaches, with particular focus on reduced order and lumped volume models. Numerical methodologies related to system-level studies, including both steady state (i.e., nominal and off-design) and dynamic operation, are presented for the purpose of characterizing the thermodynamic performances. This chapter presents recent advances in the numerical modeling of SOEs and provides a review of recent literature in the field
Predicting the ultimate potential of natural gas SOFC power cycles with CO2 capture – Part A: Methodology and reference cases
Full text linkDriven by the search for the highest theoretical efficiency, in the latest years several studies investigated the integration of high temperature fuel cells in natural gas fired power plants, where fuel cells are integrated with simple or modified Brayton cycles and/or with additional bottoming cycles, and CO2 can be separated via chemical or physical separation, oxy-combustion and cryogenic methods. Focusing on Solid Oxide Fuel Cells (SOFC) and following a comprehensive review and analysis of possible plant configurations, this work investigates their theoretical potential efficiency and proposes two ultra-high efficiency plant configurations based on advanced intermediate-temperature SOFCs integrated with a steam turbine or gas turbine cycle. The SOFC works at atmospheric or pressurized conditions and the resulting power plant exceeds 78% LHV efficiency without CO2 capture (as discussed in part A of the work) and 70% LHV efficiency with substantial CO2 capture (part B). The power plants are simulated at the 100 MW scale with a complete set of realistic assumptions about fuel cell (FC) performance, plant components and auxiliaries, presenting detailed energy and material balances together with a second law analysis
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
