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Languages : en
Pages : 23
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Hydrogen production by the water gas shift reaction (WGSR) is equilibrium limited due to thermodynamic constrains. However, this can be overcome by continuously removing the product CO2, thereby driving the WGSR in the forward direction to enhance hydrogen production. This project aims at using a high reactivity, mesoporous calcium based sorbent (PCC-CaO) for removing CO2 using reactive separation scheme. Preliminary results have shown that PCC-CaO dominates in its performance over naturally occurring limestone towards enhanced hydrogen production. However, maintenance of high reactivity of the sorbent over several reaction-regeneration cycles warrants effective regeneration methods. We have identified sub-atmospheric calcination (vacuum) as vital regeneration technique that helps preserve the sorbent morphology. Sub-atmospheric calcination studies reveal the significance of vacuum level, diluent gas flow rate, thermal properties of diluent gas, and sorbent loading on the kinetics of calcination and the morphology of the resultant CaO sorbent. Steam, which can be easily separated from CO2, has been envisioned as a potential diluent gas due to its better thermal properties resulting in effective heat transfer. A novel multi-fixed bed reactor was designed which isolates the catalyst bed from the sorbent bed during the calcination step. This should prevent any potential catalyst deactivation due to oxidation by CO2 during the regeneration phase.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 23
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Book Description
Hydrogen production by the water gas shift reaction (WGSR) is equilibrium limited due to thermodynamic constrains. However, this can be overcome by continuously removing the product CO2, thereby driving the WGSR in the forward direction to enhance hydrogen production. This project aims at using a high reactivity, mesoporous calcium based sorbent (PCC-CaO) for removing CO2 using reactive separation scheme. Preliminary results have shown that PCC-CaO dominates in its performance over naturally occurring limestone towards enhanced hydrogen production. However, maintenance of high reactivity of the sorbent over several reaction-regeneration cycles warrants effective regeneration methods. We have identified sub-atmospheric calcination (vacuum) as vital regeneration technique that helps preserve the sorbent morphology. Sub-atmospheric calcination studies reveal the significance of vacuum level, diluent gas flow rate, thermal properties of diluent gas, and sorbent loading on the kinetics of calcination and the morphology of the resultant CaO sorbent. Steam, which can be easily separated from CO2, has been envisioned as a potential diluent gas due to its better thermal properties resulting in effective heat transfer. A novel multi-fixed bed reactor was designed which isolates the catalyst bed from the sorbent bed during the calcination step. This should prevent any potential catalyst deactivation due to oxidation by CO2 during the regeneration phase.
Author: Liang-Shih Fan
Publisher:
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Category :
Languages : en
Pages :
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Book Description
Hydrogen production from coal gasification can be enhanced by driving the equilibrium limited Water Gas Shift reaction forward by incessantly removing the CO{sub 2} by-product via the carbonation of calcium oxide. This project uses the high-reactivity mesoporous precipitated calcium carbonate sorbent for removing the CO{sub 2} product to enhance H{sub 2} production. Preliminary experiments demonstrate the show the superior performance of the PCC sorbent over other naturally occurring calcium sorbents. It was observed that the CO{sub 2} released during the in-situ calcination causes the deactivation of the iron oxide WGS catalyst by changing the active phase of the catalyst from magnetite (F{sub 3}O{sub 4}). Detailed understanding of the iron oxide phase diagram helped in developing a catalyst pretreatment procedure using a H{sub 2}/H{sub 2}O system. Intermediate catalyst pretreatment helps prevent its deactivation by reducing the catalyst back to its active magnetite (Fe{sub 3}O{sub 4}) form. Multicyclic runs which consist of combined WGS/carbonation reaction followed by in-situ calcination with a subsequent catalyst pretreatment procedure sustains the catalytic activity and prevents deactivation. The water gas shift reaction was studied at different temperatures, different steam to carbon monoxide ratios (S/C) 3:1, 2:1, 1:1 and different total pressures ranging from 0-300 psig. The CO conversion was found to have an optimal value with increasing pressure, S/C ratio and temperatures. The combined water gas shift and carbonation reaction was investigated at 650 C, S/C ratio of 3:1and at different pressures of 0-300 psig.
Author: Liang-Shih Fan
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Enhancement in the production of high purity hydrogen from fuel gas, obtained from coal gasification, is limited by thermodynamics of the Water Gas Shift Reaction. However, this constraint can be overcome by concurrent water-gas shift (WGS) and carbonation reactions to enhance H{sub 2} production by incessantly driving the equilibrium-limited WGS reaction forward and in-situ removing the CO2 product from the gas mixture. The spent sorbent is then regenerated by calcining it to produce a pure stream of CO{sub 2} and CaO which can be reused. However while performing the cyclic carbonation and calcination it was observed that the CO{sub 2} released during the in-situ calcination causes the deactivation of the iron oxide WGS catalyst. Detailed understanding of the iron oxide phase diagram helped in developing a catalyst pretreatment procedure using a H{sub 2}/H{sub 2}O system to convert the deactivated catalyst back to its active magnetite (Fe{sub 3}O{sub 4}) form. The water gas shift reaction was studied at different temperatures, different steam to carbon monoxide ratios (S/C) 3:1, 2:1, 1:1 and different total pressures ranging from 0-300 psig. The combined water gas shift and carbonation reaction was investigated at temperatures ranging from 600-700C, S/C ratio of 3:1 to 1:1 and at different pressures of 0-300 psig and the calcium looping process was found to produce high purity hydrogen with in-situ CO{sub 2} capture.
Author: Sushant Kumar
Publisher: Springer
ISBN: 3319140876
Category : Science
Languages : en
Pages : 75
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Book Description
This brief covers novel techniques for clean hydrogen production which primarily involve sodium hydroxide as an essential ingredient to the existing major hydrogen production technologies. Interestingly, sodium hydroxide plays different roles and can act as a catalyst, reactant, promoter or even a precursor. The inclusion of sodium hydroxide makes these processes both kinetically and thermodynamically favorable. In addition possibilities to produce cleaner hydrogen, in terms of carbon emissions, are described. Through modifications of steam methane reformation methods and coal-gasification processes, from fossil as well as non-fossil energy sources, the carbon dioxide emissions of these established ways to produce hydrogen can significantly be reduced. This brief is aimed at those who are interested in expanding their knowledge on novel techniques and materials to produce clean hydrogen and capture carbon dioxide at a large-scale. The detailed thermodynamic analysis, experimental findings and critical analysis of such techniques are well discussed in this brief. Therefore, this book will be of great interest and use to students, engineers and researchers involved in developing the hydrogen economy as well as mitigating carbon dioxide emissions at a large-scale.
Author: Ram B. Gupta
Publisher: CRC Press
ISBN: 1420045776
Category : Science
Languages : en
Pages : 626
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Book Description
From Methane to Hydrogen-Making the Switch to a Cleaner Fuel Source The world's overdependence on fossil fuels has created environmental problems, such as air pollution and global warming, as well as political and economic unrest. With water as its only by-product and its availability in all parts of the world, hydrogen promises to be the next grea
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Category :
Languages : en
Pages :
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Book Description
Enhancement in the production of high purity hydrogen (H2) from fuel gas, obtained from coal gasification, is limited by thermodynamics of the water gas shift (WGS) reaction. However, this constraint can be overcome by conducting the WGS in the presence of a CO2-acceptor. The continuous removal of CO2 from the reaction mixture helps to drive the equilibrium-limited WGS reaction forward. Since calcium oxide (CaO) exhibits high CO2 capture capacity as compared to other sorbents, it is an ideal candidate for such a technique. The Calcium Looping Process (CLP) developed at The Ohio State University (OSU) utilizes the above concept to enable high purity H2 production from synthesis gas (syngas) derived from coal gasification. The CLP integrates the WGS reaction with insitu CO2, sulfur and halide removal at high temperatures while eliminating the need for a WGS catalyst, thus reducing the overall footprint of the hydrogen production process. The CLP comprises three reactors - the carbonator, where the thermodynamic constraint of the WGS reaction is overcome by the constant removal of CO2 product and high purity H2 is produced with contaminant removal; the calciner, where the calcium sorbent is regenerated and a sequestration-ready CO2 stream is produced; and the hydrator, where the calcined sorbent is reactivated to improve its recyclability. As a part of this project, the CLP was extensively investigated by performing experiments at lab-, bench- and subpilot-scale setups. A comprehensive techno-economic analysis was also conducted to determine the feasibility of the CLP at commercial scale. This report provides a detailed account of all the results obtained during the project period.
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Category :
Languages : en
Pages :
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The objective of the project was to develop a novel complementary membrane reactor process that can consolidate two or more downstream unit operations of a coal gasification system into a single module for production of a pure stream of hydrogen and a pure stream of carbon dioxide. The overall goals were to achieve higher hydrogen production efficiencies, lower capital costs and a smaller overall footprint than what could be achieved by utilizing separate components for each required unit process/operation in conventional coal-to-hydrogen systems. Specifically, this project was to develop a novel membrane reactor process that combines hydrogen sulfide removal, hydrogen separation, carbon dioxide separation and water-gas shift reaction into a single membrane configuration. The carbon monoxide conversion of the water-gas-shift reaction from the coal-derived syngas stream is enhanced by the complementary use of two membranes within a single reactor to separate hydrogen and carbon dioxide. Consequently, hydrogen production efficiency is increased. The single membrane reactor configuration produces a pure H2 product and a pure CO2 permeate stream that is ready for sequestration. This project focused on developing a new class of CO2-selective membranes for this new process concept. Several approaches to make CO2-selective membranes for high-temperature applications have been tested. Membrane disks using the technique of powder pressing and high temperature sintering were successfully fabricated. The powders were either metal oxide or metal carbonate materials. Experiments on CO2 permeation testing were also performed in the temperature range of 790 to 940 C for the metal carbonate membrane disks. However, no CO2 permeation rate could be measured, probably due to very slow CO2 diffusion in the solid state carbonates. To improve the permeation of CO2, one approach is to make membranes containing liquid or molten carbonates. Several different types of dual-phase membranes were fabricated and tested for their CO2 permeation in reducing conditions without the presence of oxygen. Although the flux was quite low, on the order of 0.01-0.001 cc STP/cm2/min, the selectivity of CO2/He was almost infinite at temperatures of about 800 C.A different type of dual-phase membrane prepared by Arizona State University (ASU) was also tested at GTI for CO2 permeation. The measured CO2 fluxes were 0.015 and 0.02 cc STP/cm2/min at 750 and 830 C, respectively. These fluxes were higher than the previous flux obtained ((almost equal to)0.01 cc STP/cm2/min) using the dual-phase membranes prepared by GTI. Further development in membrane development should be conducted to improve the CO2 flux. ASU has also focused on high temperature permeation/separation experiments to confirm the carbon dioxide separation capabilities of the dual-phase membranes with La{sup 0.6}Sr{sub 0.4}Co{sub 0.8}Fe{sub 0.2}O{sub 3-{delta}} (LSCF6482) supports infiltrated with a Li/Na/K molten carbonate mixture (42.5/32.5/25.0 mole %). The permeation experiments indicated that the addition of O2 does improve the permeance of CO2 through the membrane. A simplified membrane reactor model was developed to evaluate the performance of the process. However, the simplified model did not allow the estimation of membrane transport area, an important parameter for evaluating the feasibility of the proposed membrane reactor technology. As a result, an improved model was developed. Results of the improved membrane reactor model show that the membrane shift reaction has promise as a means to simplify the production of a clean stream of hydrogen and a clean stream of carbon dioxide. The focus of additional development work should address the large area required for the CO2 membrane as identified in the modeling calculations. Also, a more detailed process flow diagram should be developed that includes integration of cooling and preheating feed streams as well as particulate removal so that steam and power generation could be optimized. For the tubular membranes that were fabricated by solution impregnation with metal carbonates, difficulties were encountered in removing the impurity salts that were trapped inside the porous support tube. The membrane tube would continue losing weight even after being heated up to 500 C in air and could not maintain its nonporous characteristics. This approach was therefore abandoned. Dual-phase membranes with molten carbonates were subsequently shown to have CO2 permeability in reducing conditions without the presence of oxygen; they were also tested for H2S permeation. Permeation tests were conducted with a gas feed composition consisting of 33.6% CO2, 8.4% He, 57.6% H2 and 0.4% H2S at temperatures between 820 and 850 C and a pressure of 1 bar.
Author: Secgin Karagoz
Publisher:
ISBN:
Category :
Languages : en
Pages : 190
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Book Description
As a result of fossil fuels-based energy production, reducing atmospheric carbon dioxide emissions has become an urgent issue. Especially, carbon capture and storage (CCS) technology, being one of the leading processes to reduce total carbon emissions, has become increasingly important. Hydrogen is an important energy carrier, and hydrogen-based technologies have increased in importance recently due to the worldwide focus on green processes. The Integrated Gasification Combined Cycle (IGCC) is a promising technology supplying clean energy at affordable prices. The IGCC process is currently being coupled with CCS technologies. However, using CCS technologies in power generation processes is a great challenge, necessitating the intensification of the coupled IGCC-CCS process. Process intensification (PI), leads to substantially smaller, cleaner, and more energy efficient processes, and is a prominent topic, receiving significant attention in recent years. As part of intensifying a process, integration of multiple operations (e.g., reaction and separation) in a single unit is often carried out, to improve the existing process efficiency, and to reduce energy consumption, and unwanted output/by-product generation. The objective of this work is to demonstrate the process intensification potential of a technology, containing one or more water gas shift (WGS) reactor components seamlessly integrated with other plant components. We investigate the applicability of various (alternative to the conventional process) novel and efficient reactor configurations that include self-standing adsorptive reactor (AR)/membrane reactor (MR), and the combination of a MR-LTSR-AR-adsorptive separator (AS)-membrane separation (MS) units (herein after referred to as the LTSR-MS/LTSR-AS/AS-LTSR-AS/MR-AS/AS-MR-AS/MR-AR systems). The proposed WGS reactor technologies have the potential to generate highly efficient and ultra-compact processes, by producing H2 for use in IGCC with simultaneous CO2 capture. Innovative designs of the proposed processes are determined based on the comprehensive modeling and design of the selected IGCC plant's section. Comprehensive, multi-scale, multi-phase, computational fluid dynamics (CFD) models are developed for reaction/separation processes. Developed models quantify the many complex physicochemical phenomena occurring within the process, thus providing the basis to better understand, and intensify the overall system. Model predictions are generated for a broad range of operating conditions and design parameters, thus enabling a comparative performance assessment of the proposed process versus a conventional process for the proposed IGCC application.
Author: Mehmet Sankir
Publisher: John Wiley & Sons
ISBN: 1119283655
Category : Science
Languages : en
Pages : 653
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Book Description
Provides a comprehensive practical review of the new technologies used to obtain hydrogen more efficiently via catalytic, electrochemical, bio- and photohydrogen production. Hydrogen has been gaining more attention in both transportation and stationary power applications. Fuel cell-powered cars are on the roads and the automotive industry is demanding feasible and efficient technologies to produce hydrogen. The principles and methods described herein lead to reasonable mitigation of the great majority of problems associated with hydrogen production technologies. The chapters in this book are written by distinguished authors who have extensive experience in their fields, and readers will have a chance to compare the fundamental production techniques and learn about the pros and cons of these technologies. The book is organized into three parts. Part I shows the catalytic and electrochemical principles involved in hydrogen production technologies. Part II addresses hydrogen production from electrochemically active bacteria (EAB) by decomposing organic compound into hydrogen in microbial electrolysis cells (MECs). The final part of the book is concerned with photohydrogen generation. Recent developments in the area of semiconductor-based nanomaterials, specifically semiconductor oxides, nitrides and metal free semiconductor-based nanomaterials for photocatalytic hydrogen production are extensively discussed.
Author: Korneel Rabaey
Publisher: IWA Publishing
ISBN: 184339233X
Category : Science
Languages : en
Pages : 525
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Book Description
In the context of wastewater treatment, Bioelectrochemical Systems (BESs) have gained considerable interest in the past few years, and several BES processes are on the brink of application to this area. This book, written by a large number of world experts in the different sub-topics, describes the different aspects and processes relevant to their development. Bioelectrochemical Systems (BESs) use micro-organisms to catalyze an oxidation and/or reduction reaction at an anodic and cathodic electrode respectively. Briefly, at an anode oxidation of organic and inorganic electron donors can occur. Prime examples of such electron donors are waste organics and sulfides. At the cathode, an electron acceptor such as oxygen or nitrate can be reduced. The anode and the cathode are connected through an electrical circuit. If electrical power is harvested from this circuit, the system is called a Microbial Fuel Cell; if electrical power is invested, the system is called a Microbial Electrolysis Cell. The overall framework of bio-energy and bio-fuels is discussed. A number of chapters discuss the basics – microbiology, microbial ecology, electrochemistry, technology and materials development. The book continues by highlighting the plurality of processes based on BES technology already in existence, going from wastewater based reactors to sediment based bio-batteries. The integration of BESs into existing water or process lines is discussed. Finally, an outlook is provided of how BES will fit within the emerging biorefinery area.
