1,720,965 research outputs found
Techn-economic assessment of power-to-methane and power-to-syngas business models for sustainable carbon dioxide utilization in coal-to-liquid facilities
No full textThe work reported in this paper aimed to evaluate and assess the technical and economic prospects of implementing a renewable-energy-based technology namely power-to-gas (PtG) for sustainable utilization of CO2 emissions from syngas islands within coal-to-liquid facilities. Two possible PtG technology vectors (business models) namely power-to-methane (PtM) and power-to-syngas (PtS) were investigated. Three cases for each business model were developed namely PtM-Scenarios 1–3 and PtS-Scenarios 1–3 corresponding to CO2 feed-in scales 10%, 20%, and 50% of the total CO2 emission throughput, respectively. The mass flows generated for each case were used to develop a cost model, which evaluated and compared the economic merits of the various scenarios of the PtM and PtS value propositions based on an economic indicator vis-à-vis levelized cost of syngas production (LCOS). This study indicated that at present market conditions, only PtS-Scenarios 1–2 demonstrated cost competitiveness against the reference syngas plant. In addition, we concluded that PtM is not a viable proposition for sustainable CO2 utilization in coal-to-liquid facilities at least for the near-to-medium term. However, a sensitivity analysis indicated that viability for PtM Scenarios 1–2 and all PtS business model scenarios is possible under future market conditions particularly when the CAPEX and OPEX relating to methanation and electrolyzers decrease, low electricity price, as well as when a CO2 emission credit/tax scheme (>30 $/ton) is instigated for the reference syngas plant. Even so, it will not be possible to completely decarbonise a syngas plant within a coal-to-liquid facility using power-to-gas at competitive cost
Hydrogen production from ammonia decomposition over a commercial Ru/Al2O3 catalyst in a microchannel reactor: experimental validation and CFD simulation
No full textIn this work, an integrated experimental and CFD modelling technique was used to evaluate a microchannel reactor producing hydrogen from ammonia decomposition using a commercial Ru/Al2O3 catalyst. The microchannel reactor performance was first assessed in a series of experiments varying the reaction temperature (723–873 K) and ammonia flow rates (100–500 Nml min−1) at atmospheric pressure. A global rate expression based on Temkin-Pyzhev kinetics that accurately predicts the entire experimental operating space was established using a model-based technique with parameter refinement and estimation. The kinetic model provided the reaction source term for subsequent CFD simulations aiming to obtain a more fundamental understanding of the reaction-coupled transport phenomena within the microchannel reactor. The transport processes and reactor performance were discussed in detail using velocity, temperature, and species concentration profiles. Finally, the influence of mass transport limitations within the various regions of the microchannel reactor was evaluated and discussed by means of dimensionless numbers vis-à-vis Damköhler and Fourier numbers. Overall, results presented in this paper provide valuable data for the efficient design of ammonia-fuelled microchannel reactors for hydrogen generation aimed at portable and distributed fuel cell application
Experimentation and CFD modelling of a microchannel reactor for carbon dioxide methanation
Full text linkThe methanation of carbon dioxide (CO2) via the Sabatier process is increasingly gaining interest for power-to-gas application. In this investigation, a microchannel reactor was evaluated for CO2 methanation at different operational pressures (atmospheric, 5 bar, and 10 bar), reaction temperatures (250–400 °C) and space velocities (32.6–97.8 L.gcat−1.h−1). The recommended operation point was identified at reactor conditions corresponding to 5 bar, 400 °C, and 97.8 L.gcat−1.h−1. At this condition, the microchannel reactor yielded good CO2 conversion (83.4%) and high methane (CH4) productivity (16.9 L.gcat−1.h−1). The microchannel reactor also demonstrated good long-term performance at demanding operation conditions relating to high space velocity and high temperature. Subsequently, a CFD model was developed to describe the reaction-coupled transport phenomena within the microchannel reactor. Kinetic rate expressions were developed and validated for all reaction conditions to provide reaction source terms for the CFD modelling. Velocity and concentration profiles were discussed at different reaction conditions to interpret experimental results and provide insight into reactor operation. Overall, the results reported in this paper could give fundamental design and operational insight to the further development of microchannel reactors for CO2 methanation in power-to-gas application
A performance evaluation of a microchannel reactor for the production of hydrogen from formic acid for electrochemical energy applications
Full text linkAn experimen
tal evaluation of a microchannel reactor was completed to assess the reactor performance
for the catalytic decomposition of vaporised formic acid
(FA) for H2
production. Initially,
X-ray
powder diffraction (XRD),
elemental mapping using SEM
-
EDS and BET sur
face area measurements
were done to characterise
the commercial Au/Al2O3 catalyst
.
The reactor was evaluated using pure
(99.99%) and diluted (50/50 vol.%) FA at reactor temperatures of 250
–
350°C and inlet vapour flow
rates of 12
–
48
mL.min
-
1
.
Satisfactory r
eactor performance was demonstrated at 350°C as near
-
equilibrium FA conversion (>98%) was obtained for all flow rates investigated. The best operating
point was identified as 350°C and 48 mL.min-1
(pure FA feed) with a H2
yield of 68.7%.
At these
condition
s
the reactor performed well in comparison to conventional systems, achieving a H2
production rate of
11.8 NL.gcat -1.h-1. This paper therefore highlights important considerations for
ongoing design and development of microchannel reactors for the decomposition of FA for H2
productio
Performance evaluation of a high-throughput microchannel reactor for ammonia decomposition over a commercial Ru-based catalyst
No full textIn this work, the prospect of producing hydrogen (H2) via ammonia (NH3) decomposition was evaluated in an experimental stand-alone microchannel reactor wash-coated with a commercial Ruthenium-based catalyst. The reactor performance was investigated under atmospheric pressure as a function of reaction temperature (723–873 K) and gas-hourly-space-velocity (65.2–326.1 Nl gcat−1 h−1). Ammonia conversion of 99.8% was demonstrated at 326.1 Nl gcat−1 h−1 and 873 K. The H2 produced at this operating condition was sufficient to yield an estimated fuel cell power output of 60 We and power density of 164 kWe L−1. Overall, the microchannel reactor considered here outperformed the Ni-based microstructured system used in our previous workDST Hydrogen Infrastructure
Centre of Competence, and the North-West University (under
the following Grant numbers: KP5-I05-Chemical Hydrogen
Production Technologies; KP4-Hydrogen Fuelling Options;
NRF grant 85309
Experimental performance evaluation of an ammonia-fuelled microchannel reformer for hydrogen generation
No full textMicrochannel reactors appear attractive as integral parts of fuel processors to generate hydrogen (H2) for portable and distributed fuel cell applications. The work described in this paper evaluates, characterizes, and demonstrates miniaturized H2 production in a stand-alone ammonia-fuelled microchannel reformer. The performance of the microchannel reformer is investigated as a function of reaction temperature (450–700 °C) and gas-hourly-space-velocity (6520–32,600 Nml gcat−1 h−1). The reformer operated in a daily start-up and shut-down (DSS)-like mode for a total 750 h comprising of 125 cycles, all to mimic frequent intermittent operation envisaged for fuel cell systems. The reformer exhibited remarkable operation demonstrating 98.7% NH3 conversion at 32,600 Nml gcat−1 h−1 and 700 °C to generate an estimated fuel cell power output of 5.7 We and power density of 16 kWe L−1 (based on effective reactor volume). At the same time, reformer operation yielded low pressure drop (<10 Pa mm−1) for all conditions considered. Overall, the microchannel reformer performed sufficiently exceptional to warrant serious consideration in supplying H2 to fuel cell systemsHydrogen Infrastructure Centre of Competence, Department
of Science and Technology of the Republic of South Africa
(under the following Grant numbers: KP5-I05-Chemical
Hydrogen Production Technologies; KP4-Hydrogen Fuelling
Options; NRF grant IFR13022017531), and the North-West
Universit
A modelling evaluation of an ammonia-fuelled microchannel reformer for hydrogen generation
No full textHydrogen production from an ammonia-fuelled microchannel reactor is simulated in a three-dimensional (3D) model implemented via Comsol Multiphysics™. The work described in this paper endeavours to obtain a mathematical framework that provides an understanding of reaction-coupled transport phenomena within the microchannel reactor. The transport processes and reactor performance are elucidated in terms of velocity, temperature, and species concentration distributions, as well as local reaction rate and NH3 conversion profiles. The baseline case is first investigated to comprehend the behaviour of the microchannel reactor, then microstructural design and operating parameters are methodically altered around the baseline conditions to explore the optimum values. The simulation results show that an optimum NH3 space velocity (GHSV) of 65,000 Nml gcat−1 h−1 yields 99.1% NH3 conversion and a power density of 32 kWe L−1 at the highest operating temperature of 973 K. It is also shown that a 40-μm-thick porous washcoat is most desirable at these optimum conditions. Finally, a low channel hydraulic diameter (225 μm) is observed to contribute to high NH3 conversion. Mass transport limitations in the porous-washcoat and gas-phase are negligible as depicted by the Damköhler and Fourier numbers, respectively. The experimental microchannel reactor yields 98.2% NH3 conversion and a power density of 30.8 kWe L−1 when tested at the optimum operating conditions established by the model. Good agreement with experimental data is observed, so the integrated experimental-modelling approach developed in this paper may well provide an incisive step toward the efficient design of ammonia-fuelled microchannel reformer
HySA infrastructure center of competence: a strategic collaboration platform for renewable hydrogen production and storage for fuel cell telecom applications
No full textThe Department of Science and Technology of South Africa developed the National Hydrogen and Fuel Cells Technologies (HFCT) Research, Development and Innovation Strategy. The National Strategy was branded Hydrogen South Africa (HySA). HySA has been established consisting of three Competency Centres - HySA Infrastructure, HySA Catalyst and HySA Systems. The scope of the Hydrogen Infrastructure Competency Centre (HySA Infrastructure CoC, [1]) is to develop applications and solutions for small- and medium-scale hydrogen production and storage through innovative research and development. The aim of this paper is to present an overview of the HySA Infrastructure CoC projects related to renewable hydrogen and fuel cell applications. The presentation will discuss how the HySA Infrastructure could assist telecommunication industry with providing a potential strategic platform for developing and testing various hydrogen generating solutions for fuel cell applications specific to African conditions. More specifically, the following enablers will be discussed: existing active projects for hydrogen production: solar-to-hydrogen demonstrations based on PEM electrolysis, ammonia-to-hydrogen projects for telecom, advanced PEM electrolysis concepts (high-current density operation), hydrogen storage, safety and codes, as well as close proximity of HySA Infrastructure to Gauteng, an economical hub of South Africa, commercialization road map, activities towards establishing “Platinum Valley” SEZ (special economic zone for Pt-related activities
Reactor technology options for distributed hydrogen generation via ammonia decomposition: a review
No full textHydrogen (H2) fuel obtained via thermo-catalytic ammonia (NH3) decomposition is rapidly
attracting considerable interest for portable and distributed power generation systems.
Consequently, a variety of reactor technologies are being developed in view of the current
lack of infrastructure to generate H2 for proton exchange membrane (PEM) fuel cells. This
paper provides an extensive review of the state-of-the-art reactor technology (also referred
to as reactor infrastructure) for pure NH3 decomposition. The review strategy is to survey
the open literature and present reactor technology developments in a chronological order.
The primary objective of this paper is to provide a condensed viewpoint and basis for
future advances in reactor technology for generating H2 via NH3 decomposition. Also, this
review highlights the prominent issues and prevailing challenges that are yet to be overcome
for possible market entry and subsequent commercialization of various reactor
technologies. To our knowledge, this work presents for the first time a review of reactor
infrastructure for distributed H2 generation via NH3 decomposition. Despite commendable
research and development progress, substantial effort is still required if commercialization
of NH3 decomposition reactor infrastructure is to be realized
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