Effect of Natural Gas Composition on Thermal Performance and NOx Emission Characteristics in Boiler Combustion Systems

Alrafly Rizky Putra Henryansyah (State University of Surabaya)
A. Grummy Wailanduw (State University of Surabaya)
Mohammad Effendy (State University of Surabaya)

International Journal of Innovation in Mechanical Engineering and Advanced Materials
Vol. 8 No. 2 (2026)

The composition of natural gas supplied to industrial boilers varies significantly depending on source origin and upstream processing, particularly in the proportions of heavier alkane fractions (C₂–C₆), nitrogen (N₂), and carbon dioxide (CO₂). While prior studies have predominantly treated fuel composition as a fixed parameter or post-combustion control technologies, the systematic influence of multi-component natural gas composition specifically the C₂+alkane fraction distribution on combustion thermal performance and NOx formation in medium-capacity industrial boilers remains insufficiently characterized. This study addresses this gap through computational fluid dynamics (CFD) simulations of a 17 ton/hour steam boiler under fifteen systematically designed fuel composition scenarios, maintaining a constant heat input of 11,704 kW and an excess air ratio of 16% across all cases. Simulations were performed using Ansys Fluent 2022 with the shear stress transport k-ω turbulence model, Eddy Dissipation combustion model, and Discrete Ordinates radiation model. The analyzed parameters include furnace temperature distribution, CO₂ mole fraction in flue gas, and thermal NOx concentration. Results reveal that fuel composition exerts a near-twofold variation in NOx emissions, from a minimum of 25.88 ppm (Set 14: 88% CH₄ + 12% C₂–C₅ N2+CO2 blend) to a maximum of 51.05 ppm (Set 9: CH₄ + C₂–C₅ blend), representing a 97.3% difference attributable solely to compositional variation under identical thermal load conditions. Field-realistic multi-component compositions (Sets 12–15) consistently yield the lowest NOx emissions (25.88–28.01 ppm), approximately 30–49% lower than simplified laboratory compositions (Sets 1–11: 31.93–51.05 ppm), demonstrating that fuel composition management alone without any hardware modification or flue gas treatment can achieve NOx reductions comparable to conventional emission control strategies. These findings provide quantitative evidence that natural gas composition is a viable and underutilized primary variable for emission control in industrial boiler operations, with direct implications for fuel procurement specifications and supply chain quality management in manufacturing sectors.