Hydrogen Impurities and Their Potential Impact on Retrofitting Plans When Transitioning to Hydrogen – Natural Gas Blends

Abstract Hydrogen is being considered as one of the key options toward decarbonizing the existing energy system, however, hydrogen production, which is a key part of hydrogen value chain, has remained a challenge as producing enough hydrogen for an impactful decarbonization plan is an energy and resource intense process. There are several pathways to produce hydrogen, with different colors such as grey, brown, blue, turquoise, and green have been designated to different hydrogens based on their production methods. For example, blue hydrogen is produced from steam methane reforming (SMR) process that includes carbon capture and storage (CCS) technology, whereas green hydrogen is produced via water (H2O) electrolysis using renewable energy sources. While green hydrogen does not contain many impurities, hydrogen produced from fossil fuels may contain impurities such as carbon monoxide (CO), H2O, hydrogen sulfide (H2S), etc., that could jeopardize the integrity of the gas grid upon blending. Additionally, stored hydrogen including green hydrogen could get contaminated while being stored, e.g., stored hydrogen in depleted gas reservoirs could be contaminated with biological contaminants, which could lead to microbiological corrosion (MIC). The current paper examines different hydrogen impurities based on their production or storage paths and their potential adverse impact on the existing natural gas grid. Additionally, potential approaches are discussed to mitigate the negative impact of impurities on the overall grid’s integrity and continuity of operation.