Abstract
To help meet the global demand for energy and reduce the use of fossil fuels, alternatives such as the production of syngas from renewable biomass can be considered. This conversion of biomass to syngas is possible through a thermochemical gasification process. To design such gasification systems, model equations can be formulated and solved to predict the quantity and quality of the syngas produced with different operating conditions (temperature, the flow rate of an oxidizing agent, etc.) and with different types of biomass (wood, grass, seeds, food waste, etc.). For the comparison of multiple different types of biomass and optimization to find optimal conditions, simpler models are preferred which can be solved very quickly using modern desktop computers. In this study, a number of different stoichiometric thermodynamic models are compared to determine which are the most appropriate. To correct some of the errors associated with thermodynamic models, correction factors are utilized to modify the equilibrium constants of the methanation and water gas shift reactions, which allows them to better predict the real output composition of the gasification reactors. A number of different models can be obtained using different correction factors, model parameters, and assumptions, and these models are compared and validated against experimental data and modelling studies from the literature.
Highlights
To meet the growing global demand for energy, various sources of energy are being considered and utilized
The biomass feedstock consists of carbon, hydrogen, oxygen, and nitrogen; Alkalis and metal contents in the biomass are neglected; Ash is considered as inert; The syngas consists of H2, carbon monoxide (CO), CO2, CH4, H2 O, and N2 ; The negligible amount of tar is produced from the downdraft gasifier; The feedstock of biomass and the air enters the gasifier at the temperature of 25 ◦ C, and the gasifier pressure is 101.13 kPa; The system is considered as adiabatic and there is not any heat loss from the system; All the reactions inside the gasifier achieved the equilibrium; All the gases of the developed system are considered as ideal gases; N2 is not participating in any chemical reaction
Stoichiometric thermodynamic equilibrium models were optimized on the basis of an overall objective function
Summary
To meet the growing global demand for energy, various sources of energy are being considered and utilized. The modelling of biomass gasification generally involves the formulation and solving of sets of equations, including mass and energy balances, in addition to either rate-based or equilibrium-based expressions to determine the effect of the reactions occurring To simplify this approach, various assumptions can be made and correlations can be utilized relating to experimentally measured properties (e.g., feed composition and operating conditions). Zainal et al [27] constructed a thermodynamic equilibrium model based on the equilibrium constant of the methane formation reaction and water gas shift reaction to predict the syngas composition They analysed the effect of parameters such as the initial water content and the gasification temperature at a fixed equivalence ratio. The different models are validated with different experimental results and compared with some other stoichiometric thermodynamic models from the literature
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