PTQ Q1 2026 Issue

Figure 4 Multi-burner test- ing of new burner design

Figure 3 Single burner testing showing various levels of hydrogen in natural gas

This design does not use traditional lean-pre-mix meth- odology, eliminating burner flashback concerns. No exter - nal flue gas recirculation is required. Additionally, the burner can operate in either forced or natural draft modes and with ambient or preheated combustion air. Regarding NOx emission performance, this new burner design achieves about a 50% reduction in NOx emissions compared to the current generation of ULNBs, while still enabling firing up to 100% hydrogen without sacrificing flame stability. Figure 2 shows the NOx emission perfor - mance compared to current-generation ULNBs. Performance test results The new burner design was rigorously tested in various operating conditions to verify its performance and evolve its design. The companies’ extensive development pro - gramme included single-burner testing, multi-burner test - ing, ambient and preheated air, forced draft and natural draft applications, and firing of natural gas, typical blends of refinery/petrochemical fuel gas, 100% hydrogen, and LBG waste gases. Testing of the final design showed excep - tional performance and flame stability over a wide range of fuel gas compositions. Table 1 summarises the burner test results for various conditions (single burner/multiple burn - ers, ambient air/preheated air, natural draft/forced draft). Figure 3 shows single-burner testing across a range of hydrogen concentrations in the fuel blends. As can be seen from the images, the burner tested included a nozzle for LBG fuel firing (a large circular nozzle in the centre of the burner), but LBG was not in service when the photographs were taken. Test results show the burner is fully capable of firing 100% hydrogen and provides about a 50% reduction in NOx emissions versus current-generation UNLBs, with sin - gle-digit NOx emission performance on natural gas firing. Even at 100% hydrogen firing, NOx emissions were close to single digits at approximately 10 ppm(v) in natural draft application and 9 ppm(v) in forced draft application, values corrected to 3% O₂ dry. It was observed that NOx emis - sions increase as hydrogen content increases in fuel gas, but peak at about 80% hydrogen and then drop beyond that until 100% hydrogen firing, as evident in the Fuel C data (Table 1). CO probing and O₂ profiling verified that the flame length and width are comparable to current-genera - tion ULNBs. CO breakthrough tests verified the stability of the burners irrespective of fuel composition.

Multi-burner tests were conducted to assess potential adverse effects of flame-to- flame interactions on NOx emissions (see Figure 4 ), and the effects were found to be negligible. Since many older fired heaters have burners spaced closer than API 560 rec - ommendations, additional tests were carried out at burner spacings tighter than those guidelines. The NOx emissions increase was less than 20% when burner spacing was reduced to 75% of the recommended spacing in API 560, across a wide range of fuel firing, including 100% hydrogen. Field test results ExxonMobil installed 12 of Zeeco’s Free Jet Gen 3 burn - ers in one of the vertical cylindrical heaters at its Baytown facility for field application in early 2024. The burners are forced draft, preheated air, suitable for both natural draft and ambient air operation, and have a design heat release of 9.8 MMBTU/hr (LHV basis) each. The CO emissions remained compliant even during commissioning without the need to adopt additional mitigation measures. Performance was noted as a significant improvement over the previous burners. The CO emissions stayed below a 50 ppm hourly rolling average even during start-up operations. Field reports confirmed that all burners remained stable even at low firing rates and with excess oxygen as high as 10 vol% (wet). Preliminary emission testing was done with the burners firing at 60-75% of the designed heat release, a hydrogen concentration in the fuel gas ranging from 45% to 60%, and a combustion air temperature between 135°F and 230°F. Measured NOx emissions, when corrected to 3% O₂ (dry) and 1,600°F bridgewall temperature, remained at or below 12 ppm. This matched the performance testing results. Conclusion In the coming years, there will be increased demand for next-generation ULNBs designed for 100% hydrogen fir - ing, while still producing much lower NOx emissions. These advanced burners must be easy to retrofit into existing fired heaters, simple to install on new units, and require minimal hardware and control systems. Current ULNBs are unable to meet these needs. The alternative is to install SCR systems on fired equipment, which significantly raises the transition cost. Therefore, complex burner designs or SCR installations are unlikely to be practical solutions for large-scale fuel switching to high-hydrogen fuels.

PTQ Q1 2026