Papers by Tigabwa Y . Ahmed, PhD
Renewable Energy , 2019
Tar formation during biomass gasification has remained a major challenge. Using acetol and guaiac... more Tar formation during biomass gasification has remained a major challenge. Using acetol and guaiacol as model tar compounds from cellulose and lignin, respectively, in-situ tar conversion into synthesis gas (H2 and CO) was studied using a Rh–Ni/Al2O3 catalyst under reactive flash volatilization conditions. The influence of operating conditions, including temperature, steam-to-carbon molar ratio (S/C), carbon-to-oxygen molar ratio (C/O), gas hourly space velocity (GHSV), and catalyst weight, on the H2/CO molar ratio in the product gas were experimentally examined. The contribution of non-catalytic thermal oxidation on overall conversion was also measured by varying the distance between the catalyst bed and the feeding point position. In the case of acetol reforming at 650 °C, more than 60% of the carbon in the feed was converted via thermal oxidation into permanent gases before reaching the catalytic bed. Moreover, a minimum reaction temperature of 500 °C was necessary to avoid coke formation and the optimal operating conditions for reforming of acetol were 650 °C, C/O = 1.7, S/C = 1.2, and atmospheric pressure. Likewise, for guaiacol, the minimum operating temperature of 600 °C was required. By using two pure components, this study has provided insight into how reactive flash volatilization generates tar-free synthesis gas.
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… and Sustainable Energy …, 2012
The ever growing environmental concern caused by excessive use of fossil fuels in energy and tran... more The ever growing environmental concern caused by excessive use of fossil fuels in energy and transportation systems triggered considerable investigations on alternative energy sources such as biomass. Furthermore, the availability and security of fossil fuels to meet future global energy need are also subjected to uncertainty. For these reasons, the world's current focus is shifted towards hydrogen-based future economy. Gasification is a proven technology to produce satisfactory yield of hydrogen. Many studies have been performed to increase the production yield. Due to the extensive range of investigations, mathematical and computational approaches have been applied to conduct these studies. Thus, this paper aims to update and broaden the review coverage by incorporating works done to materialize the investigations on the potential of producing hydrogen from biomass via gasification encompassing mathematical modeling, simulation, optimization, process heat integration and cogeneration. Each of these subjects is reviewed and analyzed which helped to identify their respective strength and areas which require further research effort.
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Reactive flash volatilization (RFV) integrates flash pyrolysis with catalytic gasification in a ... more Reactive flash volatilization (RFV) integrates flash pyrolysis with catalytic gasification in a single millisecond residence reactor (RFV gasifier) for producing clean syngas from biomass. The RFV gasifier is a down flow reactor with a preheated fixed-bed of catalyst with cocurrent flow of the biomass and air-steam feed streams. This process is complex and difficult to understand as it involves the biomass particle, the surrounding gas and the surface chemistry. In this work, an equilibrium ASPEN PLUS model was developed to provide a preliminary understanding of the complex integrated process that represents RFV of cellulose, a major component of lignocellulosic biomass. The most probable cellulose pyrolysis oil compounds, hydroxyacetaldehyde and levoglucosan, were identified with a novel devolatilization submodel. The model was then applied to predict thermodynamic equilibrium compositions of the product gas with varying steam-to-carbon ratios (S/C) of 0.09-2.4, carbon-to-oxygen ratios (C/O) of 0.6-0.9 and temperatures of 400-1000 degreesC. Over the investigated ranges of operating conditions, 85% of selectivity to H2 was predicted at C/O of 0.8, S/C of 2.4 and a temperature of around 550 degreesC. The selectivity to CO declined with the increase in S/C unlike the selectivity to H2 due to the effect of the water-gas shift reaction equilibrium. In contrast, increasing the C/O led to the production of more of the oxygen deficient species (CO) and hydrogen attributable to partial oxidation. The predicted model results agreed well with experimental data from the literature. The findings from this study help to direct the technology development based on better understanding of the process.
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Clean Technologies and Environmental Policy June 2013, Volume 15, Issue 3, pp 513-523
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Hydrogen is a potential alternative energy source over fossil fuels when produced from biomass vi... more Hydrogen is a potential alternative energy source over fossil fuels when produced from biomass via thermal conversion process. This is indeed attractive as Malaysia is having abundant biomass resources. In this paper, a mathematical model is developed to predict ...
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CHEMICAL ENGINEERING, 2012
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International Journal, 2011
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… Conference (NPC), 2011, 2011
Hydrogen is a potential alternative energy source over fossil fuels when produced from biomass vi... more Hydrogen is a potential alternative energy source over fossil fuels when produced from biomass via thermal conversion process. This is indeed very attractive as Malaysia is having abundant biomass resources. In this paper, a mathematical model is developed to predict the maximum possible attainable composition of the product gas from a thermal conversion process, i.e. gasification, of palm kernel shell for hydrogen production. The work is motivated by the need to study the technical feasibility of the process under different operating conditions, i.e., temperature and Steam/Biomass ratio. The model predicts a maximum hydrogen production of approximately 50 mol% at system pressure and temperature of 1 atm and 1200 K and steam/biomass ratio of 1. Generally, the model is capable to capture the thermodynamic limit of the process, which is an essential knowledge on accessing the feasibility of the process. In addition, such information is also vital in designing the gasifier and for selection of materials for construction as well.
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Papers by Tigabwa Y . Ahmed, PhD