Laminar Burning Velocity and Markstein Length Characterisation of Compositionally Dynamic Blast Furnace Gas

Abstract

Blast Furnace Gas is a poor quality process gas comprising proportions of CO, H2, CO2, and N2, with a low energy density typically in the order of 3 MJ·kg−1. Produced in large quantities as a by-product of blast furnace iron making, it is one of the process gases indigenous to integrated steelworks worldwide. The inherently dynamic nature of furnace operation causes compositional variation and therefore leads to fluctuation in the fuel characteristics, often dissuading engineers from fully utilising the gas in increasingly complex and efficient technologies such as gas turbines. Characterisation studies were undertaken in a new constant volume bomb to determine the sensitivity to change in laminar burning velocity and Markstein length experienced as a result of increasing the volumetric H2 fraction in the range of 1–7%. Experiments were performed by measuring outwardly propagating spherical flame evolution, recorded using a Schlieren flame visualisation technique for a range of equivalence ratios, and processed using nonlinear data analysis. The relative performance of the experimental technique was benchmarked against other works using well-investigated CH4 and yielded results in good agreement with published values. Peak laminar burning velocity was shown to increase by a factor of approximately 3.5 over the tested range, with H2 concentration and equivalence ratio shown to greatly influence the effect of flame stretch. Comparisons of results were also made with values obtained from different reaction mechanisms employed using the PREMIX code developed by Sandia National Laboratories.

Laminar flame speed and markstein length characterisation of steelworks gas blends

“…When these properties are equal, the mixture can be defined as equidiffusive and the influence of flame stretch minimised, occurring under leaner conditions for the combustion of COG. The observations are interesting as the most significant fuel fraction is H 2 , which is more than double the nearest constituent CH 4 fraction; and an increase in H 2 tends to provide a decrease in the measured L b , as was seen with BFG results and data from other institutions [10][11][12][13]. However, the negative offset in L b resulting from H 2 addition is increased by the presence of heavier inert diluents in the fuel [11][12][13], which is minimal for COG (respective molar CO 2 and N 2 fractions of 1.5 and 4 %), with heat release from combustible constituents increasing the relative influence of thermal diffusivity.…”

“…[32] reaction mechanism with C1 species (21 in total, in 93 reactions), which compares poorly to the GRI-Mech model and experimental data. However, this mechanism is designed primarily for the combustion of CO, and consequently has been shown to perform well for modelling BFG [10]. The highest value of u L is appears under marginally rich conditions at the hottest flame temperature [29,9].…”

“…A fundamental physiochemical property of a fuel often used to characterise combustion performance is the Laminar burning velocity (u L ), and is directly related to operational instabilities such as blow-off and flashback [9,29]. Previous work undertaken by the authors quantified the significant changes in u L possible with small variation of H 2 fraction within BFG composition, inherent from operational changes made to the blast furnace [10]. Figure 1.1 presents the fluctuation in u L for BFG comprising molar fractions of 23% CO and CO 2 , 54% N 2 , with displacing H 2 added in the range of 1-7%, for atmospheric conditions.…”

“…Different chemical reaction mechanisms were used by the software for this part of the study, and the employed model specifications and selection of each mechanism are discussed further in section 4. The performance of the described experimental system and methodology has been benchmarked against analogous literature, with results highlighted by Pugh et al [10].…”

Integrating Hypersonics into a Combustion Test Facility with 3D Viewing Capability

“…Cardiff University has been developing optical, non-intrusive laser-diagnostic techniques for use in combustion applications for almost 30 years, having a successful ongoing partnership with the Danish advanced diagnostics developers and manufacturers, DANTEC Dynamics Ltd. (Bristol), leading to successful engagement with a range of industrial companies on collaborative R&D programmes utilising these skills, hardware and expertise (LDA, PDA, LIF, PIV and Schlieren). [2][3][4][5][6][7] Recently, for example, Cardiff University proposed a new Laser Induced Fluorescent (LIF) technique for quantifying the transient development of liquid fuel films within combustors. 2 In terms of combustion expertise, the Cardiff University group is known for characterising and developing understanding of combustion instabilities, combustion of difficult 'alternative fuel' gaseous fuel mixtures, swirl flows and combustion, large-scale combustion hazards (e.g.…”