Raw NO da x ta of modern ULNBs vs. FREE JET Gen 3
20
Current generation of ULNBs
12 MMBTU/hr FREE JET Gen3 data
10
0
NG
30% H
80% H
100% H
Figure 1 New burners installed in an operating unit
requirement of an SCR can be challenging, especially when retrofitting existing equipment. Lastly, SCRs must be oper - ated within the specified flue gas temperature and ammo - nia/urea injection rates to avoid deterioration of the catalyst bed and/or ammonia slippage to the atmosphere. Advanced ULNB technology Addressing these industry challenges requires a 100% hydrogen-capable process burner without complicated controls, extra systems, or unique space and shape require- ments. ExxonMobil and Zeeco collaborated on a new burner design capable of meeting the previously mentioned requirements and seamlessly transitioning from a vari- ety of fuel blends to 100% hydrogen and vice versa. The resulting burner is a patent-pending design incorporating a new square burner tile configuration and an adaptation of proven ULNB technology to reduce NOx emissions sig- nificantly. The two companies worked together to design, performance test, and field test the burner to verify that it would safely, reliably, and cost-effectively achieve perfor- mance and emission objectives. Previous generations of the process burners using free- jet theory had individual burner staged fuel tips with a sin- gle fuel port. This optimised the benefit of IFGR to lean the fuel mixture, and when combined with the round tile shape, produced a nearly universal lean fuel mixture composition along the burner firing ledge. Primary firing tips located along the inner diameter of the burner throat ensured burner stability, and the uniform flame temperature result - ing from the fuel mixture generated excellent NOx perfor- mance for more than two decades. The new square-tile burner design builds upon the well-established free-jet concepts and also introduces a new way of staging fuel and air to reduce thermal NOx generation further. The new burner reduces the number of staged fuel tips but adds multiple ports to each tip that deliver a fuel mixture along the tile surface. Fewer points of fuel introduction and the new square tile shape create non-uniform areas of rich and lean fuel mixtures. These non-uniform areas mean the primary tips that generate higher levels of thermal NOx can be located in a lean fuel Figure 2 Burner test results of Free Jet Gen 3 NOx perfor - mance across a range of hydrogen fuel blends vs measured NOx of various current-generation ULNBs
(1,370°F) is conducive to the formation of small amounts of NOx, and at temperatures above 1,100°C (2,000°F), NOx increases exponentially. 3 Current ULNBs often produce 50% more NOx emissions when switching fuels from low to high hydrogen content. Local regulatory limits for NOx emissions are expected to keep increasing, regardless of hydrogen firing. Therefore, the next-generation ULNB designs capable of firing 100% hydrogen must also reduce NOx emissions even more than the current ULNBs. Current ULNB technologies Process burner designs have improved over the decades, and various technologies have been deployed to lower NOx emissions with a primary focus on manipulating localised areas of the air/fuel mixture to create either fuel-rich or fuel- lean combustion zones to lower the peak flame tempera - ture and reduce NOx formation. Air staging, fuel staging, internal flue gas recirculation (IFGR), and lean pre-mix have been the primary techniques for reducing NOx with cur- rently available ULNBs. However, these techniques cannot meet the demands of high hydrogen firing while keeping NOx emissions within limits. Emerging technologies have attempted to use combina- tions of these methods, and concepts such as ‘flameless combustion’ have shown some promise. However, these burner designs require complicated hardware, sophisti- cated controls, and protective systems to be added to the existing equipment. Additionally, these burners are typically limited to forced draft installations, making them unsuitable for most retrofits without significant investment because most fired heaters are natural draft. Some of these designs also use lean-pre-mix technologies, which can have poten- tial flashback limitations when firing high hydrogen fuels, especially at the lower end of the burner heat release (i.e., at higher burner turndowns). Installation of an SCR unit is an alternative means of addressing higher NOx emissions due to high hydrogen firing. An SCR is a post-combustion system installed in the flue gas duct downstream of the convection section. SCRs can reduce NOx emissions by up to 95%, but install - ing one is a significant capital expenditure with long-term operational challenges. Furthermore, the additional space
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PTQ Q1 2026
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