Enhancing small-scale biomass gasification through steam and oxygen injection : experimental and numerical analysis
(2024)
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Rouanet_2024_Enhancingsmall-scalebiomassgasificationthroughsteamandoxygeninjection_Experimentalandnumericalanalysis.pdf
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- Authors
- Supervisors
- Jeanmart, Hervé
- Abstract
- Lignocellulosic biomass gasification converts solid biomass resources such as forest residues or wood waste into a more versatile, CO2-neutral gaseous fuel called syngas. Syngas is a sustainable and promising alternative to fossil fuels in a number of applications, such as high-temperature industrial heat production or decentralized, flexible Combined Heat and Power (CHP). Syngas produced by small-scale downdraft gasification faces two problems: it has a low energy density and contains residual tars that can harmfully condense in downstream processes. Steam and oxygen injection is seen as a way to overcome these challenges and improve syngas quality. This thesis combines numerical models and experimental campaigns to study their effects on two-stage downdraft gasification. Experiments performed on a pilot gasifier show that replacing secondary air with oxygen and steam improves the lower heating value (LHV) of syngas by 55%, from 4.4 to 6.8 MJ/Nm3. Compared to using only oxygen, steam adversely affects the LHV but is required for its role of thermal damper against excessive process temperatures. The increase in syngas LHV translates into higher engine volumetric efficiency in CHP applications, and higher flame temperatures for industrial burners. Although the combined use of steam and oxygen produces higher concentrations of Class III and IV tars in the syngas, the total amount of tar remains very low compared to most other gasification technologies. Extending the replacement of air by oxygen and steam to the primary stage of the gasifier first requires a better understanding of the propagation dynamics of the “smoldering" front through the biomass bed. A numerical model of the pyrolysis zone is built by coupling a CFD model of biomass combustion with a single-particle pyrolysis model, to account for the effect of particle thermal thickness. Preliminary results of the model are promising, with the aim of predicting the dynamics of the pyrolysis front under variable operating conditions.
- Affiliations
Citations
Rouanet, A. (2024). Enhancing small-scale biomass gasification through steam and oxygen injection : experimental and numerical analysis. https://hdl.handle.net/2078.5/29818