(162c) Ammonia As a Safe Alternative for Transporting Hydrogen

Hydrogen plays an important role in the next energy transition where the world transitions from fossil fuels to energy sources with lower carbon content. Ammonia is proposed as a possible hydrogen energy carrier when studying the transportation mechanisms for hydrogen. Moving hydrogen molecules using ammonia though a pipeline poses unique challenges. The purpose of this presentation is to compare possible safety consequences of transporting hydrogen molecules through an ammonia pipeline, through a hydrogen-injected (15% by volume) natural gas, and through a pure hydrogen pipeline. This comparison is performed assuming somewhat realistic pipeline operations. The risk of transporting the same amount of hydrogen per unit time is calculated to understand whether ammonia is a safer alternative for transporting hydrogen in a pipeline.

First, a fixed rate of hydrogen demand is assumed at the delivery point of the pipeline. Based on the hydrogen delivery rate, three imaginary pipelines have been modeled using DNV PHAST® Software. Operating pressure and temperature for these pipelines (ammonia, natural gas and hydrogen) were selected based on existing pipelines making the comparison realistic. Two leak scenarios have been selected. The small leak size is set as 25 mm, and a large leak size is set as 100 mm. When simulating ammonia leaks, only toxic impact has been analyzed although flammable/explosive impacts of ammonia releases are theoretically possible. The potential releases of hydrogen or hydrogen mixed in natural gas are analyzed as jet fire. The release modeling included additional factors such as weather conditions, release direction, and duration of interest. Based on release modeling, the probability of fatality has been calculated using the International Association of Oil and Gas Producers’ (IOGP) Vulnerability of Humans data from the Risk Assessment Data Directory series.

Upon review of the simulation results, the ammonia impact area from a small leak (25 mm) is about 100 times larger than either pure hydrogen or hydrogen-injected natural gas pipeline. When the leak size increases to 100 mm, the impact area for ammonia increases roughly three times whereas the impact area for the other pipelines increases up to 10 times. In either case, the conclusion is that the ammonia pipeline that carries hydrogen molecules is posing a higher risk than pure hydrogen or hydrogen-injected natural gas pipeline. In general, the impact area of a hydrogen-injected natural gas pipeline is about half of a pure hydrogen pipeline.

It should be noted that this analysis does not take into account the mechanical integrity challenges associated with a pure hydrogen pipeline or other operational factors that might change the risk in operating any of these pipelines.