Decarbonisation Technology - November 2021

Figure 3 Left: burner starting up on natural gas with base fuel injectors. Right: normal operation on high H 2 fuel gas with added staged fuel injectors

is approximately constant. Since radiation is dependent on the fourth power of the absolute temperature, radiation would be increased. Also, gaseous radiation may be increased due to the higher water content in the flue gases. However, since there is no carbon in hydrogen, there would be no soot formation. That means a hydrogen flame would not have any soot (luminous) radiation, which can be significant for hydrocarbon fuels. Some studies have shown a relatively minimal impact on heat flux when switching from hydrocarbon fuels to hydrogen. 5 Conclusions Using high hydrogen fuels has the potential to dramatically reduce or eliminate CO 2 emissions compared to conventional hydrocarbon fuels, depending on how the hydrogen is produced. Hydrogen has many unique characteristics, such as a higher flame speed and adiabatic flame temperature, compared to conventional fuels. There are many challenges and design issues that need to be considered when using high hydrogen fuels. In general, depending on the specific application, the transition from typical hydrocarbon fuels to hydrogen may be possible with relatively little change in performance. A thorough analysis is recommended before making such a change.

burner design and operation. This is handled through proper burner design. Hydrogen produces a weaker flame rectification signal in flame rods commonly used in pilots. Also, higher flame temperatures with hydrogen may shorten a flame rod’s life. Conversely, hydrogen produces a very strong ultraviolet signal easily detected by ultraviolet flame scanners. The benefit is that flame sighting of UV scanners is less challenging and hydrogen flames may be able to be seen through more dust on a scanner lens before needing to be cleaned compared to conventional fuels. Flame scanners can be mounted on pilots to replace flame rods. Fuel injectors may need to be changed if retrofitting existing burners designed for another fuel like natural gas. Fuel injection holes (ports) may need to be significantly larger when using high hydrogen fuels, to reduce the fuel pressure when using hydrogen. Larger holes reduce the likelihood of tip plugging. The actual impact on retrofitting existing burners is very dependent on the burner design. For example, previous experience with boiler burners has shown that traditional staged combustion technology may be compatible with switching to hydrogen, but vibration could be an issue if the burners are not properly designed. Because of hydrogen’s shorter flames, overheating the burner front could be an issue. Therefore, burner parts may need to be made of high grade stainless steel. Radiation heat transfer is another factor to consider. The flame temperature is likely to increase significantly, assuming everything else

Chuck Baukal charles.baukal@kes.global VIEW REFERENCES