Investigation on the altitude dependence of boiler combustion

As a core energy conversion device, boilers have combustion performance closely linked to the development of industrialization and urbanization. Against the backdrop of global warming, improving boiler thermal efficiency and reducing pollutant emissions have become urgent issues to address. Altitude, as a key environmental factor, significantly affects the combustion process by altering atmospheric pressure and oxygen density. However, existing studies are mostly confined to simplified laboratory scenarios, lacking systematic analysis under actual operating conditions. In this study, a WNS0.35–0.7/90/30-Q gas-fired boiler was selected, and on-site operational tests were conducted in 6 regions with different altitudes (45 m in Beijing, 470 m in Xi'an, 1800 m in Haidong, 2200 m in Xining, 3000 m in Golmud, and 4700 m in the Kunlun Mountains) in accordance with standards such as TSG 91–2021 and NB/T 47066–2018. The coefficient of determination (R²) was used to quantify the correlation between parameters (e.g., load rate, excess air coefficient) and indicators (e.g., flue gas temperature, CO/CO₂/NOₓ emissions, condensing/non-condensing thermal efficiency), aiming to explore the influence mechanism of altitude (atmospheric pressure) on boiler combustion. The results show that: load rate and excess air coefficient exert significant regulatory effects on boiler combustion, among which the regulatory effect of excess air coefficient is more direct (R² > 0.90); load rate has a stable positive impact on combustion efficiency, and the regulatory effects of both are not affected by altitude. Altitude (atmospheric pressure) has a strong influence on boiler combustion characteristics (R² > 0.50): with the increase of atmospheric pressure (i.e., decrease of altitude), flue gas temperature decreases (by up to 2.2 °C), non-condensing thermal efficiency increases (by up to 0.55%), CO emissions decrease while CO₂ emissions increase (CO achieves zero emission below 2200 m), and NOₓ emissions increase (by up to 14.34 mg/m³). This study reveals the altitude-dependent law of boiler combustion, providing data support and technical reference for the optimal design and efficient, low-emission operation of boilers in regions with different altitudes.