M.Sc Thesis

M.Sc StudentTvil Gal
SubjectCatalytic Pollution Reduction for the Combustionn of a
Nitrogen-Based Alternative Fuel
DepartmentDepartment of Chemical Engineering
Supervisors PROF. Gideon Grader
DR. Gennady Shter


Renewable energy sources are expected to provide an increasing portion of our global energy demand. On a large-scale, however, these ultimately clean sources suffer from fundamental drawbacks such as intermittency and deliverability. These issues can be resolved by converting them into storable and transportable fuels. Commercial, economically viable production of renewable hydrogen may have an important role in the long term transition between renewable and non-renewable energy production economies. This technology is expected to become a key element in sustainable and practical renewable energy utilization in the future. Storing that hydrogen as transportable liquid fuels would be beneficial and even required in order to increase the volumetric energy density and to overcome the safety and logistic issues associated with a pure hydrogen economy. Two routes may be considered: the carbon route, by fixating CO2 and the nitrogen route, by fixating atmospheric N2. Conceptually, the thought of a future where atmospheric N2 becomes a source for synthetic fuels by storing renewable hydrogen is intriguing.

The current thesis focuses on a model Nitrogen-based fuel in the form of an aqueous solution of Urea and Ammonium nitrate (UAN). Various aspects of this fuel have previously been studied, including computational simulations, continuous combustion, corrosion, safety and stability and thermal analysis at ambient and high pressures. In this work, the demonstration of a catalytic abatement treatment for a continuous combustion process of aqueous UAN was attempted for the first time. The catalytic pollution reduction for the combustion process of aqueous UAN was investigated in two stages. The first stage was a catalyst screening study, intended to map potential catalyst for the abatement process. The second stage was scaling up the abatement process using the data obtained, and integrating a catalyst in a continuous combustion system.

Noble metals were found to be very effective in reducing the main pollutants present in the effluent gas. A proposed mechanism for the pollution reduction observed over the noble metals tested was suggested. High N2 and CO2 yields of 99.99% and 99.98%, respectively, were obtained at working pressure of 20 MPa. A kinetic limiting regime was pointed out by the experimental results. A detailed evaluation of the experimental results was conducted with regard to emission standards set by both the EU and EPA. Reaching regulatory concentrations was shown to be possible. When compared to non-catalytic results, it was shown that lower working pressures were required in order to decrease pollutants in the effluent gas below regulation levels. In general, the feasibility of the catalytic pollutant reduction in a combustion process of a novel nitrogen-based alternative fuel was shown. A substantial reduction in pollutant emission was achieved by the implementation of a Ru/Al2O3 catalyst during high pressure continuous combustion of aqueous UAN.