(42e) Effect of Blending Hydrogen into Natural Gas on Selective Catalytic Reduction of NOx for Stationary Power Applications

Introducing carbon-free fuels, such as renewable hydrogen, into the natural gas pipeline has the potential to decrease the amount of fossil fuel use and reduce greenhouse gas emissions. Previous studies in the literature mainly focused on how the addition of hydrogen would influence the combustion process in terms of flashback, ignition delay, flame structure, and emission of pollutants; however, research to date has not yet determined the effect of hydrogen blending on post-combustion pollution control units such as the selective catalytic reduction (SCR) for reducing nitrogen oxides (NO_x). Selective catalytic reduction of NO_x is used in several applications such as gas-fired utility boilers, coal-fired boilers, oil-fired boilers, process heaters, gas turbines and stationary engines. The objective of this study is to investigate the performance of the SCR unit and how it is influenced by hydrogen addition for several stationary power applications.

A simulated flue gas environment was created through the combustion of CH₄ and H₂ blends in a quartz burner followed by a packed-bed reactor housing the SCR catalyst where NO and NH₃ were injected. Performance of a commercial SCR catalyst was examined in a parametric study with various methane to hydrogen (CH₄/H₂) ratios and NO concentrations (300, 500 and 1000 ppm). Different equivalence ratios were tested to simulate different applications such as gas-fired utility boilers, gas turbines, gas-fired reciprocating engines and process heaters. Finally, the temperature effect was studied by varying the temperature between 300-400°C, representative of standard operating temperatures in SCR units. At constant temperature, NO_x conversion decreases slightly when going from lean to stoichiometric conditions due to the lack of excess oxygen which is a role player for the NH₃-SCR reaction. Increasing the amount of hydrogen up to 20% does not significantly change the performance of the catalyst. Higher hydrogen amounts will be tested in the future.