Analysis of nitrogen oxide emissions produced during combustion of cracked-ammonia fuels

Ammonia has emerged as a chemical with the potential to bridge the gap in the global initiative to replace organic fuels with hydrogen. While hydrogen boasts high energy density and zero carbon emissions, it is difficult to store, transport, and utilize directly. Ammonia is a hydrogen-dense chemical that is an excellent hydrogen carrier, thus presenting a means to overcome the storage and transportation challenges associated with hydrogen. Ammonia also provides a means for safe and timely utilization of hydrogen through ammonia-hydrogen combustion. Pure ammonia is difficult to ignite and burn. In contrast, pure hydrogen is extremely flammable and difficult to control. However, ammonia-hydrogen blends have proven to burn efficiently in a myriad of combustion-based power generation systems including gas turbines, compression engines, and spark ignition engines. An advantage of ammonia is that it can produce ammonia/hydrogen blends directly through cracking, which is the decomposition of ammonia to produce hydrogen and nitrogen. Conventional ammonia cracking produces NH3/H2/N2 fuel mixtures. Our research group has developed a catalytic membrane reformer that rejects nitrogen, and produces NH3/H2 blends. To date, little attention has been paid to the potential differences of the two blends in terms of combustion. This work compares the flame stability and NOx production of the two mixtures (with and without additional nitrogen). The range of operating conditions (equivalence ratio, fuel-hydrogen mole fraction, axial velocity) at which laminar burner-stabilized flames exist is defined. Experimental NOx measurements are compared to Chemkin simulated NOx concentrations, revealing the potential occurrence of selective catalytic reduction. In this work we built a laminar, 1-dimensional flat flame apparatus to study NOx emissions produced from the two mixtures. It was found that rejection of nitrogen improved flame stability, particularly at low fuel-hydrogen mole fractions. However, rejection of nitrogen has negligible effect on the production of NOx. Initial experiments contradicted expectations based on theoretical modeling in terms of NOx production. It was determined that the NOx analyzers used do not function properly in the high humidity environments resulting from ammonia combustion. This issue was partially resolved by providing additional dilution to the post flame sampling region. Under these conditions, very good qualitative agreement between data and model expectations were observed. However, the experimental NOx concentrations remained below model expectations, which was attributed in part to catalytic reduction of NOx in the sampling line. This might be a promising avenue for NOx reduction in the future.

Name thesis:degree_name

Master of Science (M.S.)

Level thesis:degree_level

Masters

Discipline thesis:degree_discipline

Chemical and Biological Engineering

Grantor dc:publisher

Colorado School of Mines. Arthur Lakes Library

Year dc:date.issued

2024

Author dc:creator

• Golonski, Elizabeth

Advisors dc:contributor.advisor

• Wolden, Colin Andrew
• Way, J. Douglas

Committee members dc:contributor.committeemember

• Agarwal, Sumit
• Kwon, Stephanie

• ammonia
• combustion
• flame stability
• fuels
• NOx emissions

Statement dc:rights

• Copyright of the original work is retained by the author.

Language dc:language.iso

eng, English

Dc Identifier Other

T 9750

OAI identifier oai:identifier

oai:repository.mines.edu:11124/179276