Renewable heat generation from waste gasification: Infrared thermal imaging and flue gas emissions monitoring of producer gas flame

• Experimental combustion investigation of Producer Gas (PG) obtained from waste gasification. • Infrared (IR) thermal imaging of PG flame temperature field and flame control strategies at ultra-lean Equivalence Ratios (ERs) conditions. • Identification of PG flame shape topology and stabilization behaviour at various Thermal Loads (TLs) at ultra-lean ERs. • Effect of the introducing small share (5 percent) of methane on PG flame stabilization at ultra-lean ERs. • The quantitative CO and NO x emissions analysis as a function of ERs and TLs. This work investigates the combustion of Producer Gas (PG), composed of 1.90 % CH 4 , 18.50 % H 2 , 8.85 % CO 2 , 22.20 % CO, 7.40 % H 2 O, and 41.15 % N 2 , obtained from wood packaging waste gasification. Experiments were conducted using a rising co-current stationary fluidized-bed gasifier coupled with a purpose-built combustion test rig. Flame stability and temperature distribution were analysed through thermal imaging in the 7.5–14 μm spectral range, using a pixel-based correlation method. The flame emissivity was calibrated in multiple points using N-type thin-wire thermocouples and adjusted on the Infrared (IR) thermal camera allowing a simplified dynamic analysis of the flame. Results demonstrate that at an ER (Φ) of 0.85, the PG flame remained stable and uniformly distributed within the combustion chamber. However, at a lower Φ of 0.43, the flame exhibited instability, likely due to reduced flame temperatures, which lower reaction rates and weaken the chemical kinetics governing PG combustion. Additionally, high air-flow rates at this condition contributed to flame perturbation, detachment, and quenching. At ultra-lean conditions (Φ = 0.43 and TL ∼ 10 kW), significant flame instability and “neck thinning” were observed. Introducing a small amount of methane (up to 5 %) helped stabilize the flame under these conditions, suggesting a potential strategy for maintaining flame stability during ultra-lean PG combustion. Flue gas emissions were monitored for 0.45 ≤ Φ ≤ 0.70 and varied from 53 ppm CO, 10 % CO 2 and 55 ppm NO x to 550 ppm CO, 15 % CO 2 and 275 ppm NO x . Data analysis highlighted the fuel-prompt NOx production mechanism at lower flame temperatures where thermal NO x formation is unlikely to occur. The NO x emissions increased from 200 ppm to 275 ppm as the TL rose from 20 kW to 25 kW but remained nearly constant under increasing lean Φ conditions. This trend revealed the further evidence supporting the predominance of fuel-promt NOx formation