Ph.D Thesis
Ph.D Student Alon Grinberg Dana Reactions of a Nitrogen-Based Alternative Fuel Department of Energy Dr. Shter Gennady Full Professor Grader Gideon

Abstract

Achieving a sustainable climate-neutral and environmentally friendly global energy system is among the most significant challenges our society must address. Incorporating renewable energy into our energy mix is advantageous and desired, yet these energies are intermittent and not readily distributed. Large-scale energy storage technologies are essential to provide energy on demand. Alternative fuels that could be synthesized from abundant elements using excess of renewable energy or off-peak conventional power are perhaps the preferred route for large-scale storage due to their transportability and relatively high energy density. Nitrogen-based alternative fuels in particular are an attractive branch due to the abundance of molecular atmospheric nitrogen as feedstock. Nevertheless, the missing link to the utilization of nitrogen-based fuels is an establishment of a knowledge base of their reactions and developing respective combustion technologies.

The current dissertation is focused on a model nitrogen-based fuel in the form of aqueous urea and ammonium nitrate (UAN). The principal examined hypothesis is that the aqueous UAN fuel will produce lower pollutant levels when combusted at relatively high pressures. Two principal approaches were implemented in the research: a continuous high pressure combustion system and thermal analysis using three distinct setups (ambient pressure under flow, isobaric high pressure, isochoric high pressure). In addition, an energy analysis study of carbon- vs. nitrogen-based fuels was conducted by carefully defining an evaluation index. This study was performed to provide the justification for pursuing the nitrogen-based fuel research branch.

The continuous combustion of aqueous UAN was shown to be feasible. An increase of pressure was found to have a positive effect on pollution reduction. As the pressure increased more moles of products were produced from a given fuel volume at a higher rate, more energy was released, the pollutants decreased (nitrogen oxides decreased to below US regulation at 25 MPa), and the yield of the desired product (N2) increased and approached 99.9%. The chemical processes that occur during the decomposition of the aqueous UAN fuel were characterized at both ambient and high pressures, and the combustion activation energy was found to increase at a pressure range higher than 5 MPa. Nitrogen-based alternative fuels were found to be competitive with carbon-based fuels on an energy basis.

The work suggests a new paradigm for large-scale energy storage in the form of nitrogen-based alternative fuels, and unveils the combustion pressure dependency of a model nitrogen-based fuel.