EFFECT OF COMBUSTION CHAMBER DIAMETER ON NOX EMISSIONS IN A LIQUID FUEL COMBUSTION STEAM BOILER

Abstract

Introduction: Industrial boilers are significant stationary sources of nitrogen oxides (NOx). Reducing the volumetric load rate of the combustion chamber through geometric changes can reduce the maximum flame temperature and NOx formation, but limited field data exists under fixed operating conditions

Methods: An A/B comparison was performed on a 495 kW combustion chamber boiler configured with two combustion chamber diameters, keeping the rated output and heating surface constant: Ø 550 mm (boiler I) and Ø 650 mm (boiler II). At half load (Q = 272 kW) and full load (Q = 495 kW), the NOx concentration (mg/m³), thermal efficiency (η), and combustion chamber outlet temperature (°C) were measured. The volumetric load rate of the combustion chamber Qvf (kW/m³) was calculated for each configuration. The mass emission rates were estimated based on a measured flue gas flow rate of ≈770 m³/h per boiler.

Results: Increasing the combustion chamber diameter from 550 mm to 650 mm reduced Qvf by 29% (1358 → 963 kW/m³) and lowered the NOx concentration at both loads: from 111 → 101 mg/m³ (half load) and 124 → 113 mg/m³ (full load).At full load, the outlet temperature dropped from 920 °C (Ø550) to 903 °C (Ø650). Thermal efficiency remained almost unchanged (92.3% compared to 92.1% at full load; 93.2% compared to 92.8% at half load; ≤0.4 percentage points difference). The reduction of 11 mg/m³ at full load corresponds to an emission reduction of ≈8.5 g NOx/h (≈85 g over 10 h).

Discussion: Reducing the volumetric load rate of the combustion chamber by slightly increasing the combustion chamber diameter leads to a consistent reduction in NOx without any loss of performance or significant loss of efficiency under real operating conditions. Optimizing the combustion chamber geometry is a practical, cost-effective way to control NOx in industrial liquid fuel boilers.