In this context, palm waste mixtures were collected and characterised. The characterisation encompassed proximate and ultimate analyses, inorganic content, chemical composition, and their potential for hydrogen generation. Subsequently, a comprehensive chemical kinetic investigation was conducted using thermogravimetric analysis (TGA) coupled with master plot techniques to determine the kinetic triplets during the devolatilisation [3]. These included calculations of the activation energy (Ea), pre-exponential factor (A), and reaction order (n). In parallel, pyrolysis experiments were carried out to assess product yields (char, gas, and bio-oil) – as well as to quantify the composition of the produced gases.
The collected information was subsequently utilised to develop a Computational Fluid Dynamics (CFD) model for the pyrolysis of palm waste. The model was implemented in ANSYS Fluent, employing the Two-Fluid Model (TFM) theory under transient simulation conditions [4]. Model predictions were validated against experimental data, demonstrating good agreement. The results indicated that elevated temperatures (above 900 °C), moderate residence times (less than 6 seconds), and slow heating rates (below 10 K/min) significantly enhance hydrogen production.
Furthermore, a CFD model was developed to simulate the gasification of the same feedstock using steam as the gasifying agent. Steam gasification offers several key advantages over other gasifying mediums, notably a higher hydrogen yields due to the contribution of water-gas shift reactions. It also leads to an improved heating value of the produced gas and significantly reduces tar formation. Steam gasification is particularly compatible with biomass feedstocks, as it efficiently accommodates the inherent moisture content in such materials. Consequently, steam gasification holds great potential for sustainable hydrogen production, serving as a cleaner and more environmentally friendly alternative to conventional fossil-fuel-based hydrogen generation technologies [5], [6].
The CFD gasification model was validated across four primary types of gasifier reactors under various operating conditions (updraft, downdraft, moving bed, and fluidised bed). Following this, the different reactor configurations were evaluated under identical working conditions to enable a direct performance comparison. The results from the extensive validation programme are presented and discussed.
References
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[2] M.F. Awalludin, O. Sulaiman, R. Hashim, W.N.A.W. Nadhari, “An overview of the oil palm industry in Malaysia and its waste utilization through thermochemical conversion, specifically via liquefaction,” Renew. Sustain. Energy Rev.,, vol. 50, pp. 1469-1484, 2015
[3] F. Dessi, M. Mureddu, F. Ferrara, J. Fermoso, A. Orsini, A. Sanna, A. Pettinau, “Thermogravimetric characterisation and kinetic analysis of Nannochloropsis sp. and Tetraselmis sp. microalgae for pyrolysis, combustion and oxy-combustion,” Energy, vol. 217, p. 119394, 2021
[4] Y. Makkawi, X. Yu, R. Ocone, “Parametric analysis of biomass fast pyrolysis in a downer fluidized bed reactor,” Renewable Energy, vol. 143, pp. 1225-1234, 2019
[5] B. Hejazi, J.R. Grace, X. Bi, A.S. Mahecha-Botero, “Kinetic Model of Steam Gasification of Biomass in a Bubbling Fluidized Bed Reactor,” Energy & Fuels, vol. 31, no. 2, pp. 1702-1711, 2017
[6] N. Gao, A. Li, C. Quan, F. Gao, “Hydrogen-rich gas production from biomass steam gasification in an updraft fixed-bed gasifier combined with a porous ceramic reformer,” International Journal of Hydrogen Energy, vol. 33, no. 20, pp. 5430-5438, 2008