Study of peak Laminar Burning Velocity of several syngas compositions at different temperatures

Abstract

In the context of the current energy transition, the use of biomass-derived syngas (BDS) is often recognized as a fundamental path towards decreasing fossil fuel dependency and greenhouse gas emissions. However, hydrogen-containing BDS are prone to flame instability problems. More efforts are being carried out aiming at efficiently adopting BDS in industrial combustors with CH₄ co-firing or inert gas dilutions by exploring accurate knowledge of burning velocity. To do so, a deeper knowledge of the syngas combustion behaviour is strictly necessary. The objective of this study fits in this framework: in particular, a computational study has been carried out to evaluate kinetic models and present fresh insights on the effects of varying syngas mixtures such as CO/H₂, CO/H₂/CO₂ and CO/H₂/CH₄ on Laminar Burning Velocity (LBV) and peak LBV location $\left({\Phi }_{LBV=\max }\right)$. In-detail chemical kinetic simulations of equimolar (CO: H₂ = 1:1) forestry waste syngas were systematically carried out taking advantage of the open-source CANTERA solver. Three detailed kinetic models i.e., newly released FFCM-2, USC mech II, and modified GRI mech III were implemented to report accurate flame parameters at 1 bar and different temperature levels (from 300 K up to 450 K). On comparing the results with experiments, FFCM-2 proved to be a good kinetic model for the considered syngas mixtures CO/H₂, CO/H₂/CO₂ and especially for CO/H₂/CH₄ for mixtures containing a limited share of 30 % methane at normal and moderately elevated temperature at 0.4 ≤ Φ ≤ 2.1. The USC mech II performed very well for CO/H₂, and CO/H₂/CO₂, while the modified GRI mech III model also gave agreeable predictions for CO/H₂/CH₄ mixture having rich methane content. Additionally, when varying syngas composition analysis was conducted at different temperatures, the progressive CO₂ dilution and CH₄ addition of up to 30 % reduced the peak LBV and moved the peak LBV locations $\left({\Phi }_{LBV=\max }\right)$ towards lean ER conditions with 9 % and 40 % reductions, respectively; however, only the latter effect was enhanced at the elevated initial temperature. Furthermore, sensitivity analysis of respective syngas mixtures is reported at normal and elevated temperatures to explore the most sensitive intermediate reactions relative to LBV. The shift of peak LBV locations and their enhancement at elevated temperatures also open the research path to study the underlying impacts on the flame modes/regimes and structure, especially CO emissions pathways in syngas with 30 % of CH₄ and CO₂ additions.