(286e) Techno-Economical Analysis of Solar Thermochemical Ammonia Production At near Atmospheric Pressure

Techno-economical analysis of solar thermochemical
ammonia production at near atmospheric pressure

Ronald
Michalsky ¹, Peter H. Pfromm ¹, Bryon Parman
², Vincent Amanor-Boadu ²

¹ Department of Chemical Engineering, ²
Department of Agricultural Economics,

Kansas
State University, Manhattan, Kansas, USA

Ammonia is the
basis for modern agriculture and ensures the food supply for a growing world
population. It is used widely as base chemical for the chemical industry. Over
100 million metric tons NH₃ are produced world wide per year. NH₃
has been proposed recently as sustainable transportation fuel and may enable
efficient H₂ storage.

At industrial
scale the Haber-Bosch process synthesizes NH₃ catalytically at high pressure and elevated temperature with natural
gas and nitrogen as main inputs. Globally this process consumes up to 5%
of all natural gas produced and 2% of the total world energy production, with
significant fossil-based CO₂ emissions. Aiming at reactive NH₃
synthesis without natural gas from air and steam at ambient pressure, this work
studies a solar thermochemical cycle employing a molybdenum-based reactant.

Based on Gibbs
free energy computations, a process sequence of Mo₂N formation from
its elements, nitride hydrolysis forming NH₃ and MoO₂ at
ambient pressure, and metal oxide reduction using solar heat and H₂
as chemical reducing agent below 1200 °C, is proposed. Experimental data on a
Mo-based transition element reactant utilized for the fixation of N₂
and formation of NH₃ from the solid nitride hydrolyzed with steam
will point out process limiting steps such as diffusion in the solid state and
ionicity of an interstitial nitride reactant. To assess sustainability and
economic competitiveness compared to the state of the art Haber-Bosch
process, the mass and energy balance for Mo-based solar thermochemical NH₃
synthesis including on-site production of H₂ used as reducing agent
will be presented along with an economic analysis determining the price of NH₃
required for breaking even with plant investment and operational costs.